Miscellany

Jai Ganesh · 2020-03-28 01:20:04

506) Ventilator

A ventilator is a machine designed to provide mechanical ventilation by moving breathable air into and out of the lungs, to deliver breaths to a patient who is physically unable to breathe, or breathing insufficiently. While modern ventilators are computerized microprocessor controlled machines, patients can also be ventilated with a simple, hand-operated bag valve mask. Ventilators are chiefly used in intensive care medicine, home care, and emergency medicine (as standalone units) and in anesthesiology (as a component of an anesthesia machine).

Ventilators are sometimes colloquially called "respirators", a term stemming from commonly used devices in the 1950s (particularly the "Bird respirator"). However, in modern hospital and medical terminology, a respirator is a protective face mask.

Function

In its simplest form, a modern positive pressure ventilator consists of a compressible air reservoir or turbine, air and oxygen supplies, a set of valves and tubes, and a disposable or reusable "patient circuit". The air reservoir is pneumatically compressed several times a minute to deliver room-air, or in most cases, an air/oxygen mixture to the patient. If a turbine is used, the turbine pushes air through the ventilator, with a flow valve adjusting pressure to meet patient-specific parameters. When over pressure is released, the patient will exhale passively due to the lungs' elasticity, the exhaled air being released usually through a one-way valve within the patient circuit called the patient manifold.

Ventilators may also be equipped with monitoring and alarm systems for patient-related parameters (e.g. pressure, volume, and flow) and ventilator function (e.g. air leakage, power failure, mechanical failure), backup batteries, oxygen tanks, and remote control. The pneumatic system is nowadays often replaced by a computer-controlled turbopump.

Modern ventilators are electronically controlled by a small embedded system to allow exact adaptation of pressure and flow characteristics to an individual patient's needs. Fine-tuned ventilator settings also serve to make ventilation more tolerable and comfortable for the patient. In Canada and the United States, respiratory therapists are responsible for tuning these settings, while biomedical technologists are responsible for the maintenance. In the United Kingdom and Europe the management of the patient's interaction with the ventilator is done by critical care nurses.

The patient circuit usually consists of a set of three durable, yet lightweight plastic tubes, separated by function (e.g. inhaled air, patient pressure, exhaled air).
Determined by the type of ventilation needed, the patient-end of the circuit may be either noninvasive or invasive.

Noninvasive methods, such as continuous positive airway pressure (CPAP) and non-invasive ventilation, which are adequate for patients who require a ventilator only while sleeping and resting, mainly employ a nasal mask. Invasive methods require intubation, which for long-term ventilator dependence will normally be a tracheotomy cannula, as this is much more comfortable and practical for long-term care than is larynx or nasal intubation.

Life-critical system

Because failure may result in death, mechanical ventilation systems are classified as life-critical systems, and precautions must be taken to ensure that they are highly reliable, including their power-supply.

Mechanical ventilators are therefore carefully designed so that no single point of failure can endanger the patient. They may have manual backup mechanisms to enable hand-driven respiration in the absence of power (such as the mechanical ventilator integrated into an anaesthetic machine). They may also have safety valves, which open to atmosphere in the absence of power to act as an anti-suffocation valve for spontaneous breathing of the patient. Some systems are also equipped with compressed-gas tanks, air compressors or backup batteries to provide ventilation in case of power failure or defective gas supplies, and methods to operate or call for help if their mechanisms or software fail.

History

The history of mechanical ventilation begins with various versions of what was eventually called the iron lung, a form of noninvasive negative pressure ventilator widely used during the polio epidemics of the twentieth century after the introduction of the "Drinker respirator" in 1928, improvements introduced by John Haven Emerson in 1931, and the Both respirator in 1937. Other forms of noninvasive ventilators, also used widely for polio patients, include Biphasic Cuirass Ventilation, the rocking bed, and rather primitive positive pressure machines.

In 1949, John Haven Emerson developed a mechanical assister for anaesthesia with the cooperation of the anaesthesia department at Harvard University. Mechanical ventilators began to be used increasingly in anaesthesia and intensive care during the 1950s. Their development was stimulated both by the need to treat polio patients and the increasing use of muscle relaxants during anaesthesia. Relaxant drugs paralyse the patient and improve operating conditions for the surgeon but also paralyse the respiratory muscles.

In the United Kingdom, the East Radcliffe and Beaver models were early examples. The former used a Sturmey-Archer bicycle hub gear to provide a range of speeds, and the latter an automotive windscreen wiper motor to drive the bellows used to inflate the lungs. Electric motors were, however, a problem in the operating theatres of that time, as their use caused an explosion hazard in the presence of flammable anaesthetics such as ether and cyclopropane. In 1952, Roger Manley of the Westminster Hospital, London, developed a ventilator which was entirely gas-driven and became the most popular model used in Europe. It was an elegant design, and became a great favourite with European anaesthetists for four decades, prior to the introduction of models controlled by electronics. It was independent of electrical power and caused no explosion hazard. The original Mark I unit was developed to become the Manley Mark II in collaboration with the Blease company, which manufactured many thousands of these units. Its principle of operation was very simple, an incoming gas flow was used to lift a weighted bellows unit, which fell intermittently under gravity, forcing breathing gases into the patient's lungs. The inflation pressure could be varied by sliding the movable weight on top of the bellows. The volume of gas delivered was adjustable using a curved slider, which restricted bellows excursion. Residual pressure after the completion of expiration was also configurable, using a small weighted arm visible to the lower right of the front panel. This was a robust unit and its availability encouraged the introduction of positive pressure ventilation techniques into mainstream European anesthetic practice.

The 1955 release of Forrest Bird's "Bird Universal Medical Respirator" in the United States changed the way mechanical ventilation was performed, with the small green box becoming a familiar piece of medical equipment. The unit was sold as the Bird Mark 7 Respirator and informally called the "Bird". It was a pneumatic device and therefore required no electrical power source to operate.

In 1965, the Army Emergency Respirator was developed in collaboration with the Harry Diamond Laboratories (now part of the U.S. Army Research Laboratory) and Walter Reed Army Institute of Research. Its design incorporated the principle of fluid amplification in order to govern pneumatic functions. Fluid amplification allowed the respirator to be manufactured entirely without moving parts, yet capable of complex resuscitative functions. Elimination of moving parts increased performance reliability and minimized maintenance. The mask is composed of a poly(methyl methacrylate) (commercially known as Lucite) block, about the size of a pack of cards, with machined channels and a cemented or screwed-in cover plate. The reduction of moving parts cut manufacturing costs and increased durability.

The bistable fluid amplifier design allowed the respirator to function as both a respiratory assistor and controller. It could functionally transition between assistor and controller automatically, based on the patient's needs. The dynamic pressure and turbulent jet flow of gas from inhalation to exhalation allowed the respirator to synchronize with the breathing of the patient.

Intensive care environments around the world revolutionized in 1971 by the introduction of the first SERVO 900 ventilator (Elema-Schönander). It was a small, silent and effective electronic ventilator, with the famous SERVO feedback system controlling what had been set and regulating delivery. For the first time, the machine could deliver the set volume in volume control ventilation.

Ventilators used under increased pressure (hyperbaric) require special precautions and few ventilators can operate under these conditions. In 1979, Sechrist Industries introduced their Model 500A ventilator which was specifically designed for use with hyperbaric chambers.

Microprocessor ventilators

A major event in the development of mechanical ventilators was the introduction of microprocessor control, which led to the third generation of intensive care unit (ICU) ventilators, starting with the Dräger EV-A in 1982 in Germany which allowed monitoring the patients breathing curve on an LCD monitor. One year later followed Puritan Bennett 7200 and Bear 1000, SERVO 300 and Hamilton Veolar over the next decade. The use of microprocessors enabled almost any approach to gas delivery and monitoring to be possible, vastly enhanced mechanisms for gas delivery, and ventilators much more responsive to patient demand than previous generations of mechanical ventilators.

In 1991, the SERVO 300 ventilator series was introduced. The platform of the SERVO 300 series enabled treatment of all patient categories, from adult to neonate, with one single ventilator. The SERVO 300 series provided a completely new and unique gas delivery system, with rapid flow-triggering response.

In 1999, the LTV (Laptop Ventilator) Series was introduced into the market. The new ventilator was significantly smaller than the ventilators of that time, weighing approximately 6.4 kg (14 lb) and around the size of a laptop computer. This new design kept the same functionality of the in-hospital ventilators while opening up a world of opportunity of mobility for the patients.

A modular concept, meaning that the hospital has one ventilator model throughout the ICU department, instead of a fleet with different models and brands for the different user needs, was introduced with SERVO-i in 2001. With this modular concept, the ICU departments could choose the modes and options, software and hardware needed for a particular patient category.

In the twenty-first century small portable ventilators, for example the SAVe II, have been manufactured for forward combat use.

Open-source ventilator

An open-source ventilator is a disaster-situation ventilator made using a freely-licensed design, and ideally, freely-available components and parts. Designs, components, and parts may be anywhere from completely reverse-engineered to completely new creations, components may be adaptations of various inexpensive existing products, and special hard-to-find and/or expensive parts may be 3-D-printed instead of sourced.

One small, early prototype effort was the Pandemic Ventilator created somewhere back in 2008 (per oldest comments) during the resurgence of H5N1 Avian Influenza that began in 2003, and so named "because it is meant to be used as a ventilator of last resort during a possible avian (bird) flu pandemic."

A major worldwide design effort began during the 2019-2020 coronavirus pandemic after a Hackaday project was started, in order to respond to expected ventilator shortages causing higher mortality rate among severe patients.
On March 20, 2020 Irish Health Services began reviewing designs. A prototype is being designed and tested in Colombia.

The Polish company Urbicum reports successful testing of a 3D-printed open-source prototype device called VentilAid. The makers describe it as a last resort device when professional equipment is missing. The design is publicly available. The first Ventilaid prototype requires compressed air to run.

On March 21, 2020 the New England Complex Systems Institute (NECSI) began maintaining a strategic list of open source designs being worked on. The NECSI project considers manufacturing capability, medical safety and need for treating patients in various conditions, speed dealing with legal and political issues, logistics and supply. NECSI is staffed with scientists from Harvard and MIT and others who have an understanding of pandemics, medicine, systems, risk, and data collection.

Jai Ganesh · 2020-03-30 02:17:34

507) Dialysis

Dialysis, also called hemodialysis, renal dialysis, or kidney dialysis, in medicine, the process of removing blood from a patient whose kidney functioning is faulty, purifying that blood by dialysis, and returning it to the patient’s bloodstream. The artificial kidney, or hemodialyzer, is a machine that provides a means for removing certain undesirable substances from the blood or of adding needed components to it. By these processes the apparatus can control the acid–base balance of the blood and its content of water and dissolved materials. Another known function of the natural kidney—secretion of hormones that influence the blood pressure—cannot be duplicated. Modern dialyzers rely on two physicochemical principles, dialysis and ultrafiltration.

In dialysis two liquids separated by a porous membrane exchange those components that exist as particles small enough to diffuse through the pores. When the blood is brought into contact with one side of such a membrane, dissolved substances (including urea and inorganic salts) pass through into a sterile solution placed on the other side of the membrane. The red and white cells, platelets, and proteins cannot penetrate the membrane because the particles are too large. To prevent or limit the loss of diffusible substances required by the body, such as sugars, amino acids, and necessary amounts of salts, those compounds are added to the sterile solution; thus their diffusion from the blood is offset by equal movement in the opposite direction. The lack of diffusible materials in the blood can be corrected by incorporating them in the solution, from which they enter the circulation.

Although water passes easily through the membrane, it is not removed by dialysis because its concentration in the blood is lower than in the solution; indeed, water tends to pass from the solution into the blood. The dilution of the blood that would result from this process is prevented by ultrafiltration, by which some of the water, along with some dissolved materials, is forced through the membrane by maintaining the blood at a higher pressure than the solution.

The membranes first used in dialysis were obtained from animals or prepared from collodion; cellophane has been found to be more suitable, and tubes or sheets of it are used in many dialyzers. In the late 1960s hollow filaments of cellulosic or synthetic materials were introduced for dialysis; bundles of such filaments provide a large membrane surface in a small volume, a combination advantageous in devising compact dialyzers.

Dialysis—which was first used to treat human patients in 1945—replaces or supplements the action of the kidneys in a person suffering from acute or chronic renal failure or from poisoning by diffusible substances, such as aspirin, bromides, or barbiturates. Blood is diverted from an artery, usually one in the wrist, into the dialyzer, where it flows—either by its own impetus or with the aid of a mechanical pump—along one surface of the membrane. Finally the blood passes through a trap that removes clots and bubbles and returns to a vein in the patient’s forearm. In persons with chronic kidney failure, who require frequent dialysis, repeated surgical access to the blood vessels used in the treatments is obviated by provision of an external plastic shunt between them.

What is dialysis?

Dialysis is a treatment for kidney failure. Kidney failure, also called renal failure, is a life-threatening condition. Healthy kidneys produce urine by filtering waste from your blood and controlling water levels in the body. Diseases or injury can damage your kidneys so they no longer perform these critical functions.

Kidney failure leads to a buildup of waste and fluid in the body. Dialysis substitutes for damaged kidneys by filtering waste products from the blood and regulating the amount of fluid in the body.

Chronic kidney failure occurs over a long period of time and can lead to permanent kidney damage and end-stage kidney failure. Treatment for end-stage kidney failure is life-long dialysis or a kidney transplant.

Acute kidney failure occurs suddenly. Acute kidney failure may go away after treating the cause. In this case, dialysis is a temporary treatment used until the kidneys heal.

Types of dialysis

There are two general types of dialysis. Discuss all of your dialysis options with your doctor to understand which option is right for you. The types of dialysis include:

* Hemodialysis is a procedure in which your blood flows from your body to a machine called a hemodialyzer. The hemodialyzer removes wastes, extra fluid, and other harmful substances from your blood. It then returns the blood to your body. A specialized hemodialysis team often performs hemodialysis in a hospital or outpatient dialysis center. Some patients are trained to perform hemodialysis in the home.

* Peritoneal dialysis is a procedure that you perform at home. It involves filling the space in your abdomen with a dialyzing solution through a small tube called a catheter. The catheter is surgically implanted in your abdomen and comes out below your belly button. The dialyzing solution draws wastes and extra water out of your blood through the small blood vessels in your abdomen. The solution, wastes, and extra body water then drain out of your abdomen through the catheter into a bag. There are two types of peritoneal dialysis. Continuous ambulatory peritoneal dialysis (CAPD) is a treatment you perform several times throughout the day without a machine. Ambulatory means that CAPD is adapted for staying mobile. You can take part in various activities with the solution in your abdomen. Continuous cycling peritoneal dialysis (CCPD) is a treatment in which a machine performs multiple cycles of dialysis during the night while you sleep.

Why is dialysis performed?

Your doctor may recommend dialysis to treat kidney failure. Kidney diseases, injury and other conditions can lead to kidney damage, poor kidney function, and possibly kidney failure. Doctors generally recommend dialysis when 85% to 90% of kidney function is lost.

Conditions that can lead to kidney failure include:

* Autoimmune diseases that attack the kidneys, such as lupus (systemic lupus erythematosus, or SLE). Autoimmune diseases occur when the body’s immune system attacks its own healthy cells and tissues.

* Diabetes, which can damage the kidneys over time if blood sugar is not properly controlled

* High blood pressure, which can damage the kidneys over time when not properly controlled

* Infections, such as repeated bladder, kidney or blood infections

* Kidney cancer, which can damage the kidneys

* Medications, such as intravenous (IV) drug abuse, overdose of certain drugs, or long term-use of certain medications, such as nonsteroidal anti-inflammatory drugs

* Nephritis and glomerulonephritis and other diseases that cause kidney inflammation and damage

* Polycystic kidney disease, an inherited disease that causes formation of large cysts in the kidneys

* Reduced blood flow to the kidneys due to shock or renal artery stenosis, which is a narrowing of the renal arteries

* Trauma or injury that affects the kidneys or the arteries that supply blood to the kidneys

* Urinary tract obstruction due to a kidney stone, tumor, congenital deformity, or enlarged prostate gland

Who performs dialysis?

A specialized dialysis team performs dialysis. A nephrologist leads the dialysis team. A nephrologist is a doctor who specializes in kidney diseases. Critical care medicine doctors (intensivists) also prescribe dialysis. These doctors specialize in caring for acute, life-threatening illnesses or injuries.

Dialysis teams also include specialized nurses and certified hemodialysis technologists. Some patients may be trained to perform their own hemodialysis at home with the support of a trained partner and a home care dialysis team.

How is dialysis performed?

Dialysis procedures vary depending on the type of dialysis.

The frequency and length of hemodialysis sessions vary depending on your condition. Hemodialysis often takes three to five hours, three times a week. Some people may have hemodialysis for a shorter period every day.

Weeks to months before starting hemodialysis, your surgeon will create a vascular access. This is a minor surgical procedure. A vascular access is the place where your dialysis team will insert the dialysis needles. Dialysis needles allow blood to flow out to the hemodialyzer machine and return back to your body after filtering.

The best long-term vascular access is an arteriovenous (AV) fistula. Your surgeon makes an AV fistula by connecting an artery to a vein, usually in the forearm. Sometimes, a piece of synthetic material called a graft is needed to construct the connection between the artery and vein.

Another type of vascular access is a tube (catheter) inserted into a large neck vein, called a vasc-cath or perma-cath. This type of access is often temporary. The dialysis team uses it only until an AV fistula or other permanent access is ready.

Your hemodialysis will be performed in a hospital or outpatient dialysis center. The procedure generally includes these steps:

(1) The dialysis team checks your vital signs and weight.

(2) The dialysis team cleans your vascular access site and may apply an anesthetic cream or spray to numb your skin.

(3) The dialysis team inserts one or two needles through the skin into your vascular access point. The needles are attached to tubes that carry your blood to the dialyzer machine and back to your body.

(4) You can relax, read, watch TV, text, use your laptop, or nap during the treatment.

(5) Your dialysis team will check your vital signs throughout the procedure.

(6) Your dialysis team removes the needles, applies a dressing, and rechecks your weight.

How peritoneal dialysis is performed

A surgeon will perform a surgery to insert a small soft tube (catheter) into the abdomen before your first peritoneal dialysis treatment. The tube has a port outside your body located near the belly button. The catheter stays in your abdomen between dialysis sessions. Peritoneal dialysis can begin as soon as the catheter is in place. You may begin with a partial schedule of sessions until the site is fully healed.

Continuous ambulatory peritoneal dialysis (CAPD) generally involves these steps:

(1) You wear a surgical mask and wash your hands, catheter site, and other equipment as directed to prevent infection. You should perform the procedure in a clean, dry place.

(2) You connect your catheter to a tube and bag containing dialysis fluid.

(3) You fill your abdomen with the dialysis fluid. The fluid flows into your abdomen by gravity.

(4) You disconnect the tube and allow the fluid to stay (dwell) in your abdomen for a certain period of time, generally four to six hours. Your doctor will tell you what dwell time period is appropriate for you. You can perform certain activities with the solution in your abdomen.

(5) You connect a tube to your abdominal catheter and allow the fluid to drain out by gravity. The fluid now contains wastes and extra water that your body doesn’t need.

(6) You repeat this procedure, usually several times a day. Your doctor will tell you how many times a day to do this.

Continuous cycling-assisted peritoneal dialysis (CCPD) generally involves these steps:

(1) You wear a surgical mask and wash your hands, catheter site, and other equipment as directed to prevent infection. You should perform the procedure in a clean, dry place.

(2) At bedtime, you connect your catheter to a tube attached to your automated cycler machine.

(3) As you sleep, the automated cycler fills your abdomen with dialysis fluid and allows it to dwell. It then drains the fluid at the right time. The automated cycler will generally perform this about three to five times a night for a total of 10 to 12 hours. Your doctor will tell you how many cycles you need each night and the best dwell time for you.

(4) In the morning, your automated cycler fills your abdomen with dialysis fluid, but you disconnect your catheter from the machine before draining the fluid.

(5) You allow this cycle of fluid to dwell in your abdomen for a prescribed amount of time during the day. Your doctor will tell you how long your daytime dwelling should last. After the dwell time, you reconnect your catheter to the machine to drain the used fluid.

(6) You repeat this procedure every night.

Your doctor will customize your dialysis time based on how you feel, your activity and lifestyle, and other factors. Some people find that they feel best with a combination of cycler-assisted and ambulatory peritoneal dialysis.

Will I feel pain?

Your comfort and relaxation is important to you and your care team. Dialysis itself is not painful. You may feel a pinch or pin prick pain during the placement of the dialysis needles for hemodialysis. Many people say that they quickly become accustomed to this. Your care team can also use an anesthetic spray or cream to numb your skin before inserting the dialysis needle.

You may feel a bit bloated when the dialysis solution is in your abdomen during peritoneal dialysis. You should not feel pain. Tell your dialysis team if you are uncomfortable in any way.

What are the risks and potential complications of dialysis?

Dialysis involves risks and potential complications. Complications may become serious in some cases. In addition, dialysis does not replace all the functions of healthy kidneys. Some complications of kidney failure will need ongoing monitoring and treatment.

Complications of dialysis and kidney failure include:

* Anemia, a low number of red blood cells. Healthy kidneys produce the hormone erythropoietin, (EPO). EPO stimulates your body to make red blood cells. Diseased kidneys often don't make enough EPO. Dialysis patients may need to take synthetic EPO.

* Blood clot that develops in the vascular access, requiring surgical revision.

* Dialysis-related amyloidosis (DRA), a complication where proteins in the blood build up on joints and tendons. This causes pain, stiffness, and fluid in the joints. Dialysis is less effective in filtering out these harmful proteins than healthy kidneys. It is common in people who need dialysis for more than five years.

* Infection, including peritonitis (an infection of the abdomen). Peritonitis is a risk of peritoneal dialysis.

* Low blood pressure, which generally goes away after you get used to dialysis treatments

* Renal osteodystrophy, which causes bones to become thin and weak or form incorrectly

Reducing your risk of complications

You can reduce the risk of certain complications by following your treatment plan and:

(1) Following activity, dietary and lifestyle restrictions and recommendations before your procedure and during recovery

(2) Notifying your doctor or care team immediately of any concerns, such as fever, pain, weakness, dizziness, or changes in the way you feel

(3) Performing or going to your dialysis treatments as often and as long as recommended

(4) Taking your medications exactly as directed

(5) Using proper clean technique when performing peritoneal dialysis

How do I prepare for dialysis?

You are an important member of your own healthcare team. The steps you take before beginning dialysis can improve your comfort and overall health. This includes answering all questions about your medical history and medications you take. Medications include prescriptions and over-the-counter drugs, herbal treatments, and vitamins. It is a good idea to carry a current list of your medical conditions, medications, and allergies at all times.

Questions to ask your doctor

Facing dialysis is stressful. Dialysis requires a big change in your lifestyle. It requires a large time commitment and you will also have dietary restrictions. However, many people who need dialysis live active lives and continue to work and participate in many favorite activities.

You will likely have many questions about living with dialysis. It is common for patients to forget some of their concerns during a brief doctor’s office visit. You may also think of other questions after your appointment. Contact your doctor with concerns and questions before dialysis and between appointments.

It is also a good idea to bring a list of questions to your appointment. Questions can include:

(1) Why do I need dialysis? Are there any other options for diagnosing or treating my condition, such as a kidney transplant?

(2) How long will dialysis take? How often will I need to go to dialysis or perform it myself?

(3) What restrictions will I have with dialysis? What can I eat and drink?

(4) Can I return to work and other activities?

(5) What kind of assistance will I need at home?

(6) How should I take my medications?

(7) What other tests, procedures or surgeries might I need?

(8) When should I follow up with you?

(9) How should I contact you and my dialysis team? Ask for numbers to call during and after regular hours.

What can I expect after dialysis?

Dialysis is a life-saving treatment for severe chronic kidney failure, but it is not a cure. The only cure for end-stage chronic kidney failure is a kidney transplant. You will need life-long, regular medical care and dialysis treatments for chronic kidney failure. With good care, many people on dialysis live full, active lives. This includes doing many types of work, travel and other activities.

You will have dietary restrictions and recommendations to keep you as healthy as possible. Your doctor will tell you what diet is best for you. A registered dietician will help you understand and stick to your diet while enjoying a wide variety of foods. Common dietary recommendations include:

(1) Avoiding foods that are high in phosphorus, which can be harmful to the bones of a person on dialysis. Foods high in phosphorus include dairy products, legumes (such as soybeans), and nuts.

(2) Avoiding foods that are high in potassium, such as oranges, bananas, tomatoes, potatoes, and dried fruits. Too much potassium can be harmful to the heart of a person on dialysis.

(3) Eating a low salt diet. Salt (sodium) causes increased fluid retention and can lead to high blood pressure and heart failure.

(4) Monitoring and possibly restricting fluids

(5) You may need to adjust the amount of protein in your diet.

(6) You may need to eat a healthy diet with extra calories if you are underweight.

How will I feel after dialysis?

Your blood pressure may get lower after dialysis. This can lead to nausea, vomiting, and headache. This problem generally goes away after you get used to your dialysis treatments. You may also feel tired after your dialysis session.

People on dialysis may also experience itchy skin, restless legs, or problems sleeping. Tell your doctor or dialysis team if you have any of these problems. Treatments are available to help you live and sleep comfortably.

When can I go home?

Patients generally go home right after dialysis treatments, as long as heart rate, blood pressure, and other vital signs are stable.

When should I call my doctor?

It is important to keep your follow-up appointments. Contact your doctor for questions and concerns between appointments.

Call your doctor right away or seek immediate medical care if you have:

(1) Catheter that is dislodged

(2) Fever

(3) Nausea or vomiting

(4) Redness, swelling or pain around your catheter or vascular access

(5) Unusual bloating or swelling

(6) Unusual color or cloudiness in the used peritoneal dialysis solution

(7) Vision problems.

Jai Ganesh · 2020-04-01 00:47:45

508) Cow

Cow, in common parlance, a domestic bovine, regardless of gender and age, usually of the species ‘Bos taurus’. In precise usage, the name is given to mature females of several large mammals, including cattle (bovines), moose, elephants, sea lions, and whales.

Domestic cows are one of the most common farm animals around the world, and the English language has several words to describe these animals at various ages. A baby cow is called a calf. A female calf is sometimes called a heifer calf and a male a bull calf. A heifer is a female that has not had any offspring. The term usually refers to immature females; after giving birth to her first calf, however, a heifer becomes a cow. An adult male is known as a bull. Many male cattle are castrated to reduce their aggressive tendencies and make them more tractable. Young neutered males, which are primarily raised for beef, are called steers or bullocks, whereas adult neutered males, which are usually used for draft purposes, are known as oxen. A group of cows, cattle, or kine (an archaic term for more than one cow) constitutes a herd. English lacks a gender-neutral singular form, and so “cow” is used for both female individuals and all domestic bovines.

Domestic Cattle

Cows are members of the order Artiodactyla. The order contains even-toed hoofed mammals, and cows have distinctive cloven hooves (derived from the toenails from the middle two digits of each foot). Cows belong to the family Bovidae (hollow-horned ruminants, which also includes antelope, sheep, and goats), subfamily Bovinae (which includes buffaloes and spiral-horned antelope), tribe Bovini (which includes cattle, bison, and yak), and genus Bos—the names of which are all derived from bos, the Latin word for cow.

Natural history

The size and weight of a cow is highly dependent on the breed. Mature males weigh 450–1,800 kg (1,000–4,000 pounds) and females weigh 360–1,100 kg (800–2,400 pounds). Both males and females have horns, and although these may be short in many breeds, they can grow to be spectacularly large, such as in Texas longhorns and African Ankole-Watusi cows. Some breeds are genetically polled (hornless), and many other cows may be dehorned (that is, have their horn buds destroyed) at young age to make them easier to transport and safer to work around. Cows are renowned for their large milk-producing (mammary) glands known as udders.

Cows are well adapted for grazing (feeding on grass), with a wide mouth and specialized teeth for eating tough vegetation. Adults have 32 teeth but lack upper incisors and canines—they have a gummy pad instead that is used to help rip up grass. The molars have moon-shaped ridges that run parallel to the tongue, and thus chewing must be done with a circular motion to be effective.

The most specialized adaptation that cows (and other ruminants) have is their massive four-chambered stomach, which acts as a fermentation vat. Inside the rumen, the largest chamber of the stomach, bacteria and other microorganisms digest tough plant fibres (cellulose). To aid in this process, cows regurgitate and re-chew food multiple times before it passes on to the rest of the digestive system via the other stomach chambers. This process, called “chewing the cud,” helps sort the digesta (the material being digested) and absorb nutrients. By taking time to re-chew their food later, cows avoid the need to chew well when they eat. This enables them to quickly ingest large quantities of grass while in the vulnerable head-down position required for grazing.

Domestication and economic production

Cows are currently the most common domesticated ungulate (hoofed mammal), and they are found wherever humans live. Global stocks of cows were estimated at nearly one billion animals in 2016, with India, Brazil, and China having the largest populations (together maintaining approximately one-third of all cows).

Cows were first domesticated between 8,000 and 10,000 years ago from the aurochs (B. taurus primigenius), a wild species of cattle that once ranged across Eurasia. The wild aurochs became extinct in the early 1600s, the result of overhunting and loss of habitat due to the spread of agriculture (and domestic herds). Today, there are two broadly recognized forms of cow: the zebu or humped cattle from eastern Asia (B. taurus indicus) and cattle without humps (B. taurus taurus) from western Eurasia, although the two forms readily interbreed. Genetic studies suggest that both forms descend from the aurochs, but they are the products of independent domestication events.

Cows were first domesticated as “all-purpose” animals, used as draft animals and also for their milk and meat products. Regional specializations led to the formation of a range of varieties, or breeds, that were adapted to different climates or that were selectively bred to emphasize valuable characteristics, such as milk or meat production. Cows are used by humans in many other ways, such as a source of leather for clothing and other products and, albeit controversially, as participants in sporting events (e.g., bullfighting, bull riding, and rodeo events). Cows may also serve as a measure of wealth, and they are even worshipped as sacred animals in some religions. Historically, northern Europeans constructed their dwellings alongside or on top of cow stables, creating “housebarns” warmed by the body heat of cows.

All mammals produce milk to feed their young, but dairy cattle, such as the well-known Holstein-Friesian cow, have been specially bred to produce very large quantities of milk. Since only females produce milk, they are far more common in the dairy industry. Dairy bulls are often large, powerful, and aggressive and are more challenging to keep. As a result, most breeding in modern dairy operations occurs through artificial insemination, with bulls living at just a few specialized facilities. Different breeds of dairy cows have been bred for specific milk characteristics, such as to maximize yield or to produce a desired level of fat in the milk. Milk from cows is a significant part of many food items; in addition to its direct consumption as a beverage, it is used to make a wide range of products including butter, yogurt, cheese, and ice cream.

Dairy cows produce milk for around 10 months following the birth of the calf. A typical western dairy cow is usually milked twice per day and produces on average 30 litres (8 gallons) of milk daily; however, the actual amount produced depends upon the age and breed of the cow. Most modern milking is not done by hand but by machines.

Cows usually have their first calf when they are just under two years old—with single calves being typical, although twins sometimes occur—and each cow may have ten or more calves over the course of her life. Even though cows can live for 20 years or more, older dairy cows are often culled from commercial herds and used for meat when their milk yield begins to decline.

Sanctity of the cow

Sanctity of the cow, in Hinduism, the belief that the cow is representative of divine and natural beneficence and should therefore be protected and venerated. The cow has also been associated with various deities, notably Shiva (whose steed is Nandi, a bull), Indra (closely associated with Kamadhenu, the wish-granting cow), Krishna (a cowherd in his youth), and goddesses in general (because of the maternal attributes of many of them).

Jai Ganesh · 2020-04-02 22:10:23

509) Some breeds of dogs

(1) German shepherd

German shepherd (Alternative Title: Alsatian), breed of working dog developed in Germany from traditional herding and farm dogs. Until the 1970s the breed was known as the Alsatian in the United Kingdom. A strongly built, relatively long-bodied dog, the German shepherd stands 22 to 26 inches (56 to 66 cm) and weighs 75 to 95 pounds (34 to 43 kg). Its coat is of coarse, medium-long outer hair and shorter, dense inner hair and ranges from white or pale gray to black and is often gray and black or black and tan. Noted for intelligence, alertness, and loyalty, the German shepherd is used as a guide for the blind and as a watchdog and also serves in police and military work.

(2) Dalmatian

Dalmatian, dog breed named after the Adriatic coastal region of Dalmatia, Croatia, its first definite home. The origins of the breed are unknown. The Dalmatian has served as a sentinel, war dog, fire department mascot, hunter, shepherd, and performer. It is best known, however, as a coach or carriage dog, functioning as an escort and guard for horse-drawn vehicles. A sleek, symmetrically built, short-haired dog, the Dalmatian is characterized by its dark-spotted white coat. The pups are born white, and the spots develop a few weeks after birth. The Dalmatian stands 19 to 23 inches (48 to 58 cm) and weighs 50 to 55 pounds (23 to 25 kg). In general, it is even-tempered and friendly. Among its nicknames are English coach dog, firehouse dog, and plum-pudding dog.

(3) Dachshund

Dachshund, (German: “badger dog”) dog breed of hound and terrier ancestry developed in Germany to pursue badgers into their burrows. The dachshund is a long-bodied, characteristically lively dog with a deep chest, short legs, tapering muzzle, and long ears. Usually reddish brown or black-and-tan, it is bred in two sizes—standard and miniature—and in three coat types—smooth, longhaired, and wirehaired. The standard dachshund stands about 7 to 10 inches (18 to 25 cm) and weighs 16 to 32 pounds (7 to 14.5 kg); the miniature is shorter and weighs no more than 11 pounds (5 kg).

(4) Labrador retriever

Labrador retriever, breed of sporting dog that originated in Newfoundland and was brought to England by fishermen about 1800. It is an outstanding gun dog, consistently dominating field trials. Standing 21.5 to 24.5 inches (55 to 62 cm) and weighing 55 to 80 pounds (25 to 36 kg), it is more solidly built than other retrievers and has shorter legs. Distinctive features include its otterlike tail, thick at the base and tapered toward the end, and its short, dense coat of black, brown (“chocolate”), or yellow. The Labrador retriever is characteristically rugged, even-tempered, and gentle. In England it has been used in military and police work, as a rescue dog, and as a guide dog for the blind. An ideal family pet, the Labrador retriever became in the 1990s the most popular dog breed in the United States.

(5) Poodle

Poodle, breed of dog thought to have originated in Germany but widely associated with France, where it is hugely popular. The poodle was developed as a water retriever, and the distinctive clipping of its heavy coat was initiated to increase the animal’s efficiency in the water. The breed has been used for such diverse undertakings as performing in circuses and hunting for truffles (scenting and digging up the edible fungus).

An elegant-looking dog, often ranked as one of the most intelligent of all breeds, the poodle has been bred in three size varieties—standard, miniature, and toy. All three are judged by the same standard of appearance, which calls for a well-proportioned dog with a long, straight muzzle, heavily haired, hanging ears, a docked pompom tail, and a characteristic springy gait and proud manner of carrying itself. The coat consists of a woolly undercoat and a dense wiry topcoat; if allowed to grow, the hair forms ropelike cords, and the dog is called a corded poodle. The coat should be solid, not variegated, and may be any of a number of colours, among them gray, white, black, brown, apricot, and cream. The standard poodle stands more than 15 inches (38 cm); the miniature is in excess of 10 inches (25 cm) and no more than 15 inches (38 cm); the toy is 10 inches (25 cm) or under. Weight variations range from as much as 70 pounds (32 kg) to as little as 7 pounds (3 kg). The standard and miniature poodles are classed by the American Kennel Club as Non-Sporting dogs, the toy as a Toy dog.

In the late 20th century, breeders began to cross poodles with other purebred dogs in what was called the “designer dog” fad; the goal was the incorporation into the offspring of the poodle’s intelligence and non-shedding coat. All sizes of poodles were crossed with other breeds, resulting in such mixed breeds as the Labradoodle (Labrador retriever + poodle), schnoodle (schnauzer + poodle), and Pekepoo (Pekingese + poodle). However, many poodle breeders deplored the trend and regretted the dilution of carefully managed bloodlines.

(6) Pomeranian

Pomeranian, breed of toy dog that can be traced back, like the related Keeshond, Samoyed, and Norwegian elkhound, to early sled-dog ancestors. The breed is named for the duchy of Pomerania, where, in the early 19th century, it is said to have been bred down in size from a 30-pound (13.5-kg) sheepdog. Characteristically spirited but docile, the Pomeranian is a compactly built dog with a foxlike head and small, erect ears. Its long coat, especially full on the neck and chest, may be any of a variety of colours, including white, black, brown, and reddish brown. The Pomeranian stands about 6 to 7 inches (15 to 18 cm) high and weighs about 3 to 7 pounds (1.5 to 3 kg).

(7) Golden retriever

Golden retriever, breed of sporting dog developed in Scotland in the 19th century as a water retriever. Typically a strong and hardy all-around dog and an excellent swimmer, it stands 21.5 to 24 inches (55 to 61 cm) and weighs 55 to 75 pounds (25 to 34 kg). Its thick coat is long on the neck, thighs, tail, and back of the legs and may be any shade of golden brown. The golden retriever was first shown in England in 1908 and was registered with the American Kennel Club in 1925. In 2002 it was the second most-popular dog breed in the United States, after the Labrador retriever. The golden retriever is noted for its friendly, gentle temperament and willingness to work. It has been trained as a guide dog for the blind and makes an excellent family pet.

(8) Rottweiler

Rottweiler, a breed of working dog which is thought to be descended from drover dogs (cattle-driving dogs) left by the Roman legions in Rottweil, Germany, after the Romans abandoned the region during the 2nd century CE. The Rottweiler accompanied local butchers on buying expeditions from the Middle Ages to about 1900, carrying money in a neck pouch to market. It has also served as a guard dog, a drover’s dog, a draft dog, a rescue dog, and a police dog.

Characteristically stocky and strongly built, the Rottweiler stands approximately 22 to 27 inches (56 to 68.5 cm) tall and weighs between 90 and 110 pounds (41 and 50 kg). It has a short, coarse, black coat with tan markings on its head, chest, and legs. The Rottweiler’s historic role as a guardian and herder has honed the breed’s instinct for wariness and protectiveness when encountering strangers. Rottweilers are known for their confidence and intelligence; however, they also require a steady training regimen to learn social skills.

The formal history of the breed dates back to 1901, with the production of the first standard Rottweiler by the International Club for Leonbergers and Rottweiler Dogs in Germany. The breed was officially recognized by the American Kennel Club in 1931.

(9) Bulldog

Bulldog, also called English bulldog, breed of dog developed centuries ago in Great Britain for use in fighting bulls (bullbaiting). Characteristically powerful and courageous, often vicious, and to a great extent unaware of pain, the bulldog nearly disappeared when dogfighting was outlawed in 1835. Fanciers of the breed, however, saved it and bred out its ferocity. Nicknamed the “sourmug,” the bulldog is a stocky dog that moves with a rolling gait. It has a large head, folded ears, a short muzzle, a protruding lower jaw, and loose skin that forms wrinkles on the head and face. Its short, fine coat is tan, white, reddish brown, brindle, or piebald. The bulldog stands 13 to 15 inches (33 to 38 cm) and weighs 40 to 50 pounds (18 to 23 kg). Typically gentle and reliable, it is placed in the Non-Sporting Dog group of the American Kennel Club.

(10) Pug

Pug, breed of toy dog that probably originated in China and was introduced to England near the end of the 17th century by Dutch traders. The pug has a short muzzle and a tightly curled tail. It is a squarely built, muscular dog, with a large head, prominent, dark eyes, and small, drooping ears. At maturity it stands 10 to 11 inches (25.5 to 28 cm) and weighs about 14 to 18 pounds (6 to 8 kg). Its coat is short and glossy; colour is given in the breed standard as black or as silver or apricot fawn with a black line on the back and a black mask on the face. Typically loyal and alert, the pug is a valued companion dog.

(11) Doberman Pinscher

Doberman Pinscher, also called Doberman or Dobe, breed of working dog developed in Apolda, Germany, by Karl Friedrich Louis Dobermann, a tax collector, night watchman, dogcatcher, and keeper of a dog pound, about 1890. The Doberman Pinscher is a sleek, agile, and powerful dog standing 24 to 28 inches (61 to 71 cm) and weighing 60 to 88 pounds (27 to 40 kg). It has a short smooth coat, black, blue, fawn, or red in colour, with rust markings on the head, throat, chest, base of the tail, and feet. The breed has a reputation for fearlessness, alertness, loyalty, and intelligence.

During his time as a dogcatcher and pound keeper, Dobermann was thought to have crossed several breeds—including the Rottweiler, German Pinscher, Black and Tan Terriers, Weimaraner, and short-haired shepherds—to develop the breed, which was first registered with the American Kennel Club (AKC) in 1908. The Doberman Pinscher Club of America, an organization devoted to promoting the purity of the breed, was founded in Michigan in 1921, by George Earle III, an American diplomat who also served as governor of Pennsylvania from 1935 to 1939. Doberman Pinschers have been used in police and military work (such as in message delivery, scouting, and guarding) and as a watchdog and as a guide dog for the blind.

(12) Boxer

Boxer, smooth-haired working dog breed named for its manner of “boxing” with its sturdy front paws when fighting. The boxer, developed in Germany, includes strains of bulldog and Great Dane in its heritage. Because of its reputation for courage, aggressiveness, and intelligence, it has been used in police work but is also valued as a watchdog and companion. It is a trim, squarely built dog with a short, square-shaped muzzle, a black mask on its face, and a shiny shorthaired coat of fawn (reddish brown) or brindle. It stands 21 to 25 inches (53 to 63.5 cm) and weighs 60 to 70 pounds (27 to 32 kg).

(13) Chihuahua

Chihuahua, smallest recognized dog breed, named for the Mexican state of Chihuahua, where it was first noted in the mid-19th century. The Chihuahua is thought to have been derived from the Techichi, a small, mute dog kept by the Toltec people of Mexico as long ago as the 9th century AD. Typically a saucy-looking, alert dog that is sturdier than its small build would suggest, the Chihuahua stands about 5 inches (13 cm) and weighs 1 to 6 pounds (0.5 to 3 kg). It has a rounded head, large, erect ears, prominent eyes, and a compact body. The coat is variable in colour and may be either smooth and glossy or long and soft. It is valued as a spirited companion especially suited to apartment living.

(14) Mastiff

Mastiff, breed of large working dog used as a guard and fighting dog in England for more than 2,000 years. Dogs of this type are found in European and Asian records dating back to 3000 BC. Sometimes called the Molossian breeds for a common ancestor, numerous large, heavily built dog breeds incorporate the name mastiff. They often function as war dogs or guardians. The Roman invaders of England sent the English mastiff to compete in the arenas of ancient Rome, where the dog was pitted against bears, lions, tigers, bulls, other dogs, and human gladiators. The breed also fought in the later bullbaiting and bearbaiting rings of England.

A powerful but characteristically gentle dog, the mastiff has a broad head, drooping ears, a broad, short muzzle, and a short, coarse coat. Colour, as specified by the breed standard, is apricot, silver fawn, or brindled fawn and black. Ears and muzzle are dark. According to the American Kennel Club, male mastiffs must stand at least 30 inches (76 cm) and females at least 27.5 inches (70 cm). The breed weighs 165 to 185 pounds (75 to 84 kg).

The bullmastiff, a cross between the mastiff and the bulldog, was developed in 19th-century England; it was used chiefly to discourage poaching on estates and game preserves and was known as the “gamekeeper’s night-dog.” The bullmastiff is a tan, reddish brown, or brindled dog, with black on the face and ears. It stands 24 to 27 inches (61 to 69 cm) and weighs 100 to 130 pounds (45 to 59 kg). It is frequently used as a police and guard dog.

Jai Ganesh · 2020-04-04 01:00:50

510) Halley's Comet

Halley’s Comet, also called Comet Halley, the first comet whose return was predicted and, almost three centuries later, the first to be imaged up close by interplanetary spacecraft.

In 1705 English astronomer Edmond Halley published the first catalog of the orbits of 24 comets. His calculations showed that comets observed in 1531, 1607, and 1682 had very similar orbits. Halley suggested that they were really one comet that returned approximately every 76 years, and he predicted that comet’s return in 1758. Halley did not live to see his prediction come true (he died in 1742), but the comet was sighted late in 1758, passed perihelion (closest distance to the Sun) in March 1759, and was named in Halley’s honour. Its periodic returns demonstrated that it was in orbit around the Sun and, thus, that at least some comets were members of the solar system.

Earlier passages of Halley’s Comet were later calculated and checked against historical records of comet sightings. Some have speculated that a comet observed in Greece between 467 and 466 BCE may have been Halley. However, the generally accepted date for its earliest recorded appearance, which was witnessed by Chinese astronomers, was in 240 BCE. Halley’s closest approach to Earth took place on April 10, 837, at a distance of only 0.04 astronomical units (AU; 6 million km [3.7 million miles]). It was the large bright comet seen six months before the Norman Conquest of England in 1066 and depicted in the Bayeux Tapestry from that time. Its passage in 1301 may have inspired the form of the Star of Bethlehem that the Italian painter Giotto used in his ‘The Adoration of the Magi’, painted around 1305. Its passages have taken place every 76 years on average, but the gravitational influence of the planets on the comet’s orbit has caused the orbital period to vary from 74.5 to slightly more than 79 years over time. During the comet’s return in 1910, Earth passed through Halley’s dust tail, which was millions of kilometres in length, with no apparent effect.

The most-recent appearance of Halley’s Comet in 1986 was greatly anticipated. Astronomers first imaged the comet with the 200-inch Hale Telescope at Palomar Observatory in California on October 16, 1982, when it was still beyond the orbit of Saturn at 11.0 AU (1.65 billion km [1 billion miles]) from the Sun. It reached perihelion at 0.587 AU (88 million km [55 million miles]) from the Sun on February 9, 1986, and came closest to Earth on April 10 at a distance of 0.417 AU (62 million km [39 million miles]).

Five interplanetary spacecraft flew past the comet in March 1986: two Japanese spacecraft (Sakigake and Suisei), two Soviet spacecraft (Vega 1 and Vega 2), and a European Space Agency spacecraft (Giotto) that passed only 596 km [370 miles] from the comet’s nucleus. Close-up images of the nucleus obtained by Giotto showed a dark potato-shaped object with dimensions of about 15 × 8 km (9 × 5 miles). As expected, the nucleus proved to be a mixture of water and other volatile ices and rocky (silicate) and carbon-rich (organic) dust. About 70 percent of the nucleus surface was covered by a dark insulating “crust” that prevented water ice below it from sublimating, but the other 30 percent was active and produced huge bright jets of gas and dust. The crust turned out to be very black (blacker than coal), reflecting only about 4 percent of the sunlight it received back into space, and it was apparently a surface coating of less-volatile organic compounds and silicates. The dark surface helped explain the high temperature of about 360 kelvins (87 °C [188 °F]) as measured by Vega 1 when the comet was 0.79 AU (118 million km [73 million miles]) from the Sun. As the comet rotated on its axis, the rate of dust and gas emission varied as different active areas on the surface came into sunlight.

The spacecraft encounters proved that the comet nucleus was a solid body, in effect a “dirty snowball,” as proposed by American astronomer Fred Whipple in 1950. This discovery put to rest an alternate explanation known as the sandbank model, promoted by English astronomer R.A. Lyttleton from the 1930s to the 1980s, that the nucleus was not a solid body but rather a cloud of dust with adsorbed gases.

Dust particles shed during the comet’s slow disintegration over the millennia are distributed along its orbit. The passage of Earth through this debris stream every year is responsible for the Orionid and Eta Aquarid meteor showers in October and May, respectively.

Halley’s Comet is next expected to return to the inner solar system in 2061.

Jai Ganesh · 2020-04-05 00:48:07

511) Heart

Heart, organ that serves as a pump to circulate the blood. It may be a straight tube, as in spiders and annelid worms, or a somewhat more elaborate structure with one or more receiving chambers (atria) and a main pumping chamber (ventricle), as in mollusks. In fishes the heart is a folded tube, with three or four enlarged areas that correspond to the chambers in the mammalian heart. In animals with lungs—amphibians, reptiles, birds, and mammals—the heart shows various stages of evolution from a single to a double pump that circulates blood (1) to the lungs and (2) to the body as a whole.

In humans and other mammals and in birds, the heart is a four-chambered double pump that is the centre of the circulatory system. In humans it is situated between the two lungs and slightly to the left of centre, behind the breastbone; it rests on the diaphragm, the muscular partition between the chest and the abdominal cavity.

The heart consists of several layers of a tough muscular wall, the myocardium. A thin layer of tissue, the pericardium, covers the outside, and another layer, the endocardium, lines the inside. The heart cavity is divided down the middle into a right and a left heart, which in turn are subdivided into two chambers. The upper chamber is called an atrium (or auricle), and the lower chamber is called a ventricle. The two atria act as receiving chambers for blood entering the heart; the more muscular ventricles pump the blood out of the heart.

The heart, although a single organ, can be considered as two pumps that propel blood through two different circuits. The right atrium receives venous blood from the head, chest, and arms via the large vein called the superior vena cava and receives blood from the abdomen, pelvic region, and legs via the inferior vena cava. Blood then passes through the tricuspid valve to the right ventricle, which propels it through the pulmonary artery to the lungs. In the lungs venous blood comes in contact with inhaled air, picks up oxygen, and loses carbon dioxide. Oxygenated blood is returned to the left atrium through the pulmonary veins. Valves in the heart allow blood to flow in one direction only and help maintain the pressure required to pump the blood.

The low-pressure circuit from the heart (right atrium and right ventricle), through the lungs, and back to the heart (left atrium) constitutes the pulmonary circulation. Passage of blood through the left atrium, bicuspid valve, left ventricle, aorta, tissues of the body, and back to the right atrium constitutes the systemic circulation. Blood pressure is greatest in the left ventricle and in the aorta and its arterial branches. Pressure is reduced in the capillaries (vessels of minute diameter) and is reduced further in the veins returning blood to the right atrium.

The pumping of the heart, or the heartbeat, is caused by alternating contractions and relaxations of the myocardium. These contractions are stimulated by electrical impulses from a natural pacemaker, the sinoatrial, or S-A, node located in the muscle of the right atrium. An impulse from the S-A node causes the two atria to contract, forcing blood into the ventricles. Contraction of the ventricles is controlled by impulses from the atrioventricular, or A-V, node located at the junction of the two atria. Following contraction, the ventricles relax, and pressure within them falls. Blood again flows into the atria, and an impulse from the S-A starts the cycle over again. This process is called the cardiac cycle. The period of relaxation is called diastole. The period of contraction is called systole. Diastole is the longer of the two phases so that the heart can rest between contractions. In general, the rate of heartbeat varies inversely with the size of the animal. In elephants it averages 25 beats per minute, in canaries about 1,000. In humans the rate diminishes progressively from birth (when it averages 130) to adolescence but increases slightly in old age; the average adult rate is 70 beats at rest. The rate increases temporarily during exercise, emotional excitement, and fever and decreases during sleep. Rhythmic pulsation felt on the chest, coinciding with heartbeat, is called the apex beat. It is caused by pressure exerted on the chest wall at the outset of systole by the rounded and hardened ventricular wall.

The rhythmic noises accompanying heartbeat are called heart sounds. Normally, two distinct sounds are heard through the stethoscope: a low, slightly prolonged “lub” (first sound) occurring at the beginning of ventricular contraction, or systole, and produced by closure of the mitral and tricuspid valves, and a sharper, higher-pitched “dup” (second sound), caused by closure of aortic and pulmonary valves at the end of systole. Occasionally audible in normal hearts is a third soft, low-pitched sound coinciding with early diastole and thought to be produced by vibrations of the ventricular wall. A fourth sound, also occurring during diastole, is revealed by graphic methods but is usually inaudible in normal subjects; it is believed to be the result of atrial contraction and the impact of blood, expelled from the atria, against the ventricular wall.

Heart “murmurs” may be readily heard by a physician as soft swishing or hissing sounds that follow the normal sounds of heart action. Murmurs may indicate that blood is leaking through an imperfectly closed valve and may signal the presence of a serious heart problem.

Jai Ganesh · 2020-04-06 01:37:59

512) Lens

Lens, in optics, piece of glass or other transparent substance that is used to form an image of an object by focusing rays of light from the object. A lens is a piece of transparent material, usually circular in shape, with two polished surfaces, either or both of which is curved and may be either convex (bulging) or concave (depressed). The curves are almost always spherical; i.e., the radius of curvature is constant. A lens has the valuable property of forming images of objects situated in front of it. Single lenses are used in eyeglasses, contact lenses, pocket magnifiers, projection condensers, signal lights, viewfinders, and on simple box cameras. More often a number of lenses made of different materials are combined together as a compound lens in a tube to permit the correction of aberrations. Compound lenses are used in such instruments as cameras, microscopes, and telescopes.

Optical Principles For Lenses

A lens produces its focusing effect because light travels more slowly in the lens than in the surrounding air, so that refraction, an abrupt bending, of a light beam occurs both where the beam enters the lens and where it emerges from the lens into the air.

A single lens has two precisely regular opposite surfaces; either both surfaces are curved or one is curved and one is plane. Lenses may be classified according to their two surfaces as biconvex, plano-convex, concavo-convex (converging meniscus), biconcave, plano-concave, and convexo-concave (diverging meniscus). Because of the curvature of the lens surfaces, different rays of an incident light beam are refracted through different angles, so that an entire beam of parallel rays can be caused to converge on, or to appear to diverge from, a single point. This point is called the focal point, or principal focus, of the lens. Refraction of the rays of light reflected from or emitted by an object causes the rays to form a visual image of the object. This image may be either real—photographable or visible on a screen—or virtual—visible only upon looking into the lens, as in a microscope. The image may be much larger or smaller than the object, depending on the focal length of the lens and on the distance between the lens and the object. The focal length of a lens is the distance from the centre of the lens to the point at which the image of a distant object is formed. A long-focus lens forms a larger image of a distant object, while a short-focus lens forms a small image.

Usually the image formed by a single lens is not good enough for precise work in such fields as astronomy, microscopy, and photography; this is because the cone of rays emitted by a single point in a distant object is not united in a perfect point by the lens but instead forms a small patch of light. This and other innate imperfections in a lens’s image of a single object point are known as aberrations. To correct such aberrations, it is often necessary to combine in one mount several lens elements (single lenses), some of which may be convex and some concave, some made of dense high-refractive or high-dispersive glass, and others made of low-refractive or low-dispersive glass. The lens elements may be cemented together or mounted at carefully calculated separations to correct the aberrations of the individual elements and obtain an image of acceptable sharpness. The precise mounting also ensures that all lenses are properly centred; that is, the centres of curvature of all the lens surfaces lie on a single straight line called the principal axis of the lens. A frequently used measure of the quality of any lens system is its ability to form an image that is sharp enough to separate, or resolve, two very close dots or lines in an object. Resolving power depends on how well the various aberrations in a lens system are corrected.

The simplest compound lens is a thin cemented combination of two single lenses, such as that used in the objective (the lens nearest the object) of a small refracting telescope. Microscope objectives may contain as many as eight or nine elements, some of which may be made of different materials in order to bring all colours of light to a common focus, and thus prevent chromatic aberration. The objective lenses used in cameras may contain from two to 10 elements, while a so-called zoom or variable-focal length lens may have as many as 18 or 20 elements in several groups, the different groups being movable along the axis by levers or cams in order to produce the desired change in focal length without a shift of the focal plane. Lenses also vary greatly in diameter, from as small as 0.16 cm (1/16 inch) for an element in a microscope objective to as large as 100 cm (40 inches) for an astronomical telescope objective. In reflectors and several other types of astronomical telescopes, concave mirrors are used for the objective instead of lenses.

Manufacturing Optical Lenses

In the manufacture of lenses, slabs of glass are cut with a glass saw or slitting disk; a piece of the desired type and shape is chipped to a rough, round blank, or the pieces may be heated to softness, rolled to a round shape, and pressed in a mold to the desired size and to approximately the desired curvature of the surfaces. The surfaces are then ground, or lapped, to the final form, using coarse emery, carborundum, or diamond as an abrasive. Lens surfaces are ground on an iron tool, either flat or suitably curved, using progressively finer grades of one of the abrasives mentioned above. In the grinding process, a rotating cup-shaped tool is mounted so that its axis of rotation intersects the axis of the lens at the centre of curvature of the desired spherical surface. The obliquity of the tool axis must be adjusted so that the rim of the tool cuts across the centre of the (concave) lens being generated. For convex lenses, the centre of the rotating tool face cuts the rim of the lens blank. As both tool and lens rotate about their respective axes, a spherical surface of the desired radius of curvature is generated on the lens.

Fine grinding, or smoothing, is done using carefully graded emery flour as an abrasive. A number of fine-ground lens blanks are then mounted with pitch on a block so that they can be polished together. The polishing tool is covered with a thin layer of pitch, wax, or even coarse cloth, and wet rouge or certain other mineral oxides are also used as polishing agents. The polishing of glass is a slow process, requiring lenses to be oscillated back and forth, sometimes for hours, against the rotating polisher. After both sides have been polished, the lens is ground around the edge to centre it and give it the correct diameter. If a compound objective is being made, several single lenses must be mounted together in a precise coaxial arrangement, and their thicknesses, separations, and centring must be kept very close to the prescribed values, or the aberration corrections laboriously determined by the lens designer will not be realized. The finished lens’s resolving power is then tested by using the lens to form an image of a point source or other suitable test object. Sophisticated variants of this basic testing procedure have been developed using photoelectric cells or interferometers to obtain greater measuring accuracy.

Jai Ganesh · 2020-04-07 00:35:43

513) Thyroid gland

Thyroid gland, endocrine gland that is located in the anterior part of the lower neck, below the larynx (voice box). The thyroid secretes hormones vital to metabolism and growth. Any enlargement of the thyroid, regardless of cause, is called a goitre.

Anatomy Of The Thyroid Gland

The thyroid arises from a downward outpouching of the floor of the pharynx, and a persisting remnant of this migration is known as a thyroglossal duct. The gland itself consists of two oblong lobes lying on either side of the trachea (windpipe) and connected by a narrow band of tissue called the isthmus. In normal adults the thyroid gland weighs 10 to 15 grams (0.4 to 0.5 ounce), though it has the capacity to grow much larger.

The lobes of the gland, as well as the isthmus, contain many small globular sacs called follicles. The follicles are lined with follicular cells and are filled with a fluid known as colloid that contains the prohormone thyroglobulin. The follicular cells contain the enzymes needed to synthesize thyroglobulin, as well as the enzymes needed to release thyroid hormone from thyroglobulin. When thyroid hormones are needed, thyroglobulin is reabsorbed from the colloid in the follicular lumen into the cells, where it is split into its component parts, including the two thyroid hormones thyroxine (T4) and triiodothyronine (T3). The hormones are then released, passing from the cells into the circulation.

Biochemistry Of Thyroid Hormone

Thyroxine and triiodothyronine contain iodine and are formed from thyronines, which are composed of two molecules of the amino acid tyrosine. (Both iodine and tyrosine are acquired in the diet.) Thyroxine contains four iodine atoms, and triiodothyronine contains three iodine atoms. Because each molecule of tyrosine binds one or two iodine atoms, two tyrosines are used to synthesize both thyroxine and triiodothyronine. These two hormones are the only biologically active substances that contain iodine, and they cannot be produced in the absence of iodine. The process leading to the eventual synthesis of thyroxine and triiodothyronine begins in the thyroid follicular cells, which concentrate iodine from the serum. The iodine is then oxidized and attached to tyrosine residues (forming compounds called iodotyrosines) within thyroglobulin molecules. The iodinated tyrosine residues are then rearranged to form thyroxine and triiodothyronine. Therefore, thyroglobulin serves not only as the structure within which thyroxine and triiodothyronine are synthesized but also as the storage form of the two hormones.

Considerably more thyroxine is produced and secreted by the thyroid gland than is triiodothyronine. However, thyroxine is converted to triiodothyronine in many tissues by the action of enzymes called deiodinases. After thyroxine enters a cell, deiodinases located in the cytoplasm remove one of its four iodine atoms, converting it into triiodothyronine. The triiodothyronine either enters the nucleus of the cell or is returned to the circulation. As a result, all of the thyroxine and about 20 percent of the triiodothyronine produced each day come from the thyroid gland. The remaining 80 percent of triiodothyronine comes from deiodination of thyroxine outside of the thyroid. Most if not all of the action of thyroid hormone in its target tissues is exerted by triiodothyronine. Therefore, thyroxine may be considered a circulating precursor of triiodothyronine.

In serum more than 99 percent of the thyroxine and triiodothyronine is bound to one of three proteins. These binding proteins are known as thyroxine-binding globulin, transthyretin (thyroxine-binding prealbumin), and albumin. The remaining thyroxine and triiodothyronine (less than 1 percent) is free, or unbound. When free hormone enters a cell, it is replenished immediately by hormone attached to the binding proteins. The binding proteins serve as reservoirs of the two hormones to protect the tissues from sudden surges of thyroid hormone production and probably also to facilitate delivery of the hormones to the cells of large, solid organs such as the liver.

Essentially all cells in the body are target cells of triiodothyronine. Once triiodothyronine is inside a cell, it enters the nucleus, where it binds to proteins known as nuclear receptors. The triiodothyronine-receptor complexes then bind to deoxyribonucleic acid (DNA) molecules. This results in an increase in the rate at which the affected DNA molecules are transcribed to produce messenger ribonucleic acid (mRNA) molecules and an increase in the rate of synthesis of the protein (translation) coded for by the DNA (by way of the mRNA). Triiodothyronine increases the transcription of DNA molecules that code for many different proteins; however, it also inhibits the transcription of DNA that codes for certain other proteins. The patterns of activation and inhibition differ in different tissue and cell types.

Actions Of Thyroid Hormone

The substances produced in increased quantities in response to triiodothyronine secretion include many enzymes, cell constituents, and hormones. Key among them are proteins that regulate the utilization of nutrients and the consumption of oxygen by the mitochondria of cells. Mitochondria are the sites at which energy is produced in the form of adenosine triphosphate (ATP) or is dissipated in the form of heat. Triiodothyronine activates substances that increase the proportion of energy that is dissipated as heat. It also stimulates carbohydrate utilization, lipid production and metabolism (thereby increasing cholesterol utilization), and central and autonomic nervous system activation, resulting in increased contraction of cardiac muscle and increased heart rate. During fetal life and in infancy this stimulatory activity of triiodothyronine is critically important for normal neural and skeletal growth and development; in both the unborn and the newborn, thyroid deficiency is associated with dwarfism and intellectual disability.

Regulation Of Thyroid Hormone Secretion

The thyroid gland is one component of the hypothalamic-pituitary-thyroid axis, which is a prime example of a negative feedback control system. The production and secretion of thyroxine and triiodothyronine by the thyroid gland are stimulated by the hypothalamic hormone thyrotropin-releasing hormone and the anterior pituitary hormone thyrotropin. In turn, the thyroid hormones inhibit the production and secretion of both thyrotropin-releasing hormone and thyrotropin. Decreased production of thyroid hormone results in increased thyrotropin secretion and thus increased thyroid hormone secretion. This restores serum thyroid hormone concentrations to normal levels (if the thyroid gland is not severely damaged). Conversely, increased production of thyroid hormone or administration of high doses of thyroid hormone inhibit the secretion of thyrotropin. As a result of this inhibition, serum thyroid hormone concentrations are able to fall toward normal levels. The complex interactions between thyroid hormone and thyrotropin maintain serum thyroid hormone concentrations within narrow limits. However, if the thyroid gland is severely damaged or if there is excessive thyroid hormone production independent of thyrotropin stimulation, hypothyroidism (thyroid deficiency) or hyperthyroidism (thyroid excess) ensues.

As noted above, much of the triiodothyronine produced each day is produced by deiodination of thyroxine in extrathyroidal tissues. The conversion of thyroxine to triiodothyronine significantly decreases in response to many adverse conditions, such as malnutrition, injury, or illness (including infections, cancer, and liver, heart, and kidney diseases). The production of triiodothyronine is also inhibited by starvation and by several drugs, notably amiodarone, a drug used to treat patients with cardiac rhythm disorders. In each of these situations, serum and tissue triiodothyronine concentrations decrease. This decrease in triiodothyronine production may be a beneficial adaptation to starvation and illness because it reduces the breakdown of protein and slows the use of nutrients for generating heat, thereby maintaining tissue integrity and conserving energy resources.

The fetal thyroid gland begins to function at about 12 weeks of gestation, and its function increases progressively thereafter. Within minutes after birth there is a sudden surge in thyrotropin secretion, followed by a marked increase in serum thyroxine and triiodothyronine concentrations. The concentrations of thyroid hormones then gradually decline, reaching adult values at the time of puberty. Thyroid hormone secretion increases in pregnant women. Therefore, women with thyroid deficiency who become pregnant usually need higher doses of thyroid hormone than when they are not pregnant. There is little change in thyroid secretion in older adults as compared with younger adults.

The Thyroid Gland And Calcitonin

The thyroid gland is also the site of the production of calcitonin, a hormone that can lower serum calcium concentrations. The cells that produce calcitonin, which are called C cells, or parafollicular cells arise, separately from the thyroid and migrate into it during development of the embryo. The C cells end up nestled in the spaces between the follicles. Because these cells have a separate embryological origin from the thyroid follicular cells,and because they secrete calcitonin, they in essence form a separate endocrine organ. (In some animals the C cells remain separate from the thyroid.)

Calcitonin is secreted in response to high serum calcium concentrations, and it lowers the concentrations acutely by inhibiting the resorption of bone. However, its action wanes within days, so calcitonin therapy is not an effective treatment for high calcium levels.

Diseases Of The Thyroid Gland

The most common thyroid disease is thyroid nodular disease (the appearance of small, usually benign lumps within an otherwise healthy gland), followed by hypothyroidism, hyperthyroidism, and thyroid cancer.

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Jai Ganesh · 2020-04-08 01:07:58

514) Shinkansen

Shinkansen, (Japanese: “New Trunk Line”) by name bullet train, pioneer high-speed passenger rail system of Japan, with lines on the islands of Honshu, Kyushu, and Hokkaido. It was originally built and operated by the government-owned Japanese National Railways and has been part of the private Japan Railways Group since 1987.

The first section of the original line, a 320-mile (515-km) stretch between Tokyo and Ōsaka, was opened in 1964. Known as the New Tōkaidō Line, it generally follows and is named for the historic and celebrated Tōkaidō (“Eastern Sea Road”) highway that was used especially during the Edo (Tokugawa) period (1603–1867). Inauguration of the line, just before the start of the Tokyo 1964 Olympic Games, was greeted by widespread international acclaim, and the Shinkansen was quickly dubbed the “bullet train” for the great speed the trains obtained and for the aerodynamic bullet shape of their noses. Many innovations, such as the use of prestressed concrete ties and mile-long welded sections of track, were introduced in the line’s construction. A 100-mile (160-km) extension of that line westward from Ōsaka to Okayama was completed in 1972, and its final segment, a 244-mile (393-km) stretch between Okayama and the Hakata station in Fukuoka, northern Kyushu, opened in 1975.

Other lines radiating northward from Tokyo were completed in 1982 to the cities of Niigata (the Jōetsu line) and Morioka (the Tōhoku line), the Tōhoku line subsequently being extended northward to Hachinohe in 2002. Work to build a link to Aomori, northwest of Hachinohe, began in the late 1990s. When that segment opened in 2010, the Shinkansen was essentially complete for the entire length of Honshu. However, plans had long been in place to connect all three main Japanese islands by Shinkansen with a line northward into Hokkaido (via the Seikan Tunnel under Tsugaru Strait). Construction on the Hokkaido line began in 2005 on the segment between Aomori and Hakodate in southern Hokkaido, the ultimate goal being to extend the line to Sapporo. The line between Aomori and Hakodate opened in 2016. Construction on the section from Hakodate to Sapporo was begun in 2012 and expected to be completed in 2031.

Branches from the Tōhoku line to Yamagata opened in 1992 (extended north to Shinjo in 1999) and to Akita in 1997; a branch from the Jōetsu line to Nagano also opened in 1997. Segments of a further extension of the Nagano branch westward to Toyama and Kanazawa opened in 2015. In addition, a line was completed between Yatsushiro and Kagoshima in southwestern Kyushu in 2004. In the late 1990s work commenced to extend that line northward from Yatsushiro to Hakata, and the opening of the segment in 2011 completed the full north-south route of the Shinkansen on Kyushu. Work began in 2008 on a branch from the Kyushu line southwestward to Nagasaki.

Much of the system’s track runs through tunnels, including one under Shimonoseki Strait between Honshu and Kyushu, another on the Tokyo-Niigata line that is 14 miles (23 km) long, and another near Aomori with a record length (for a double-tracked inland tunnel) of 16.5 miles (26.5 km) when the bore was finished in 2005. Several hundred trains operate daily on the Shinkansen system. The most-frequent service is between Tokyo and Ōsaka, especially during the morning and evening rush hours, when trains depart at intervals of 10 minutes or less. The fastest trains can make the trip from Tokyo to Hakata in about five hours, and the quickest from Tokyo to Aomori take about three hours.

The electric multiple-unit trains, which can seat 1,000 passengers or more, derive their power from an overhead wire system. Trains originally reached top speeds of 130 miles (210 km) per hour, but improvements in track, train cars, and other components have made possible maximum speeds of between 150 and 185 miles (240 and 300 km) per hour. In early 2013 some trains began operating at up to 200 miles (320 km) per hour. Such high speeds made it necessary to develop elaborate safety features. Each car, for example, is equipped with brakes consisting of cast-iron discs and metallic pad linings specially designed not to distort under emergency braking. Moreover, all movements of the trains are monitored and controlled by a central computerized facility in Tokyo.

Jai Ganesh · 2020-04-09 02:27:01

515) Cullinan diamond

Cullinan diamond, world’s largest gem diamond, which weighed about 3,106 carats in rough form when found in 1905 at the Premier mine in Transvaal, S.Af. Named for Sir Thomas Cullinan, who had discovered the mine three years earlier, the colourless stone was purchased by the Transvaal government and was presented (1907) to the reigning British monarch, King Edward VII. It was cut into 9 large stones and about 100 smaller ones by I.J. Asscher and Company of Amsterdam, famed for their cutting of the Excelsior diamond, which until the discovery of the Cullinan had been the largest known diamond. The stones cut from the Cullinan diamond, all flawless, are now part of the British regalia. The largest of these is the second largest cut diamond known and is called the Great Star of Africa, or Cullinan I, a 530.2-carat, pear-shaped gem set in the English sceptre. Another is the most valuable stone in the imperial state crown, the 317-carat Cullinan II, sometimes called the Second Star of Africa.

The Cullinan Diamond was the largest gem-quality rough diamond ever found, weighing 3,106.75 carats (621.35 g), discovered at the Premier No.2 mine in Cullinan, South Africa, on 26 January 1905. It was named after Thomas Cullinan, the mine's chairman. In April 1905, it was put on sale in London, but despite considerable interest, it was still unsold after two years. In 1907, the Transvaal Colony government bought the Cullinan and then presented it to Edward VII, King of the United Kingdom, who had it cut by Asscher Brothers in Amsterdam.

Cullinan produced stones of various cuts and sizes, the largest of which is named Cullinan I or the Great Star of Africa, and at 530.4 carats (106.08 g) it is the largest clear cut diamond in the world. The stone is mounted in the head of the Sovereign's Sceptre with Cross. The second-largest is Cullinan II or the Second Star of Africa, weighing 317.4 carats (63.48 g), mounted in the Imperial State Crown. Both are part of the Crown Jewels. Seven other major diamonds, weighing a total of 208.29 carats (41.66 g), are privately owned by Elizabeth II, who inherited them from her grandmother, Queen Mary, in 1953. The Queen also owns minor brilliants and a set of unpolished fragments.

Discovery and early history

The Cullinan is estimated to have formed in Earth's mantle transition zone at a depth of 410–660 km (255–410 miles) and reached the surface 1.18 billion years ago. It was found 18 feet (5.5 m) below the surface at Premier Mine in Cullinan, Transvaal Colony, by Frederick Wells, surface manager at the mine, on 26 January 1905. It was approximately 10.1 centimetres (4.0 in) long, 6.35 centimetres (2.50 in) wide, 5.9 centimetres (2.3 in) deep, and weighed 3,106 carats (621.2 grams). Newspapers called it the "Cullinan Diamond", a reference to Sir Thomas Cullinan, who opened the mine in 1902. It was three times the size of the Excelsior Diamond, found in 1893 at Jagersfontein Mine, weighing 972 carats (194.4 g). Four of its eight surfaces were smooth, indicating that it once had been part of a much larger stone broken up by natural forces. It had a blue-white hue and contained a small pocket of air, which at certain angles produced a rainbow, or Newton's rings.

Shortly after its discovery, Cullinan went on public display at the Standard Bank in Johannesburg, where it was seen by an estimated 8,000–9,000 visitors. In April 1905, the rough gem was deposited with Premier Mining Co.'s London sales agent, S. Neumann & Co. Due to its immense value, detectives were assigned to a steamboat that was rumoured to be carrying the stone, and a parcel was ceremoniously locked in the captain's safe and guarded on the entire journey. It was a diversionary tactic – the stone on that ship was fake, meant to attract those who would be interested in stealing it. Cullinan was sent to the United Kingdom in a plain box via registered post. On arriving in London, it was conveyed to Buckingham Palace for inspection by King Edward VII. Although it drew considerable interest from potential buyers, Cullinan went unsold for two years.

Presentation to Edward VII

Transvaal Prime Minister, Louis Botha, suggested buying the diamond for Edward VII as "a token of the loyalty and attachment of the people of the Transvaal to His Majesty's throne and person". In August 1907, a vote was held in Parliament on the Cullinan's fate, and a motion authorising the purchase was carried by 42 votes in favour to 19 against. Initially, Henry Campbell-Bannerman, then British Prime Minister, advised the king to decline the offer, but he later decided to let Edward VII choose whether or not to accept the gift. Eventually, he was persuaded by Winston Churchill, then Colonial Under-Secretary. For his trouble, Churchill was sent a replica, which he enjoyed showing off to guests on a silver plate. The Transvaal Colony government bought the diamond on 17 October 1907 for £150,000 at the time, which adjusted for pound-sterling inflation is equivalent to £15 million in 2016. Due to a 60% tax on mining profits, the Treasury received some of its money back from the Premier Diamond Mining Company.

The diamond was presented to the king at Sandringham House on 9 November 1907 – his sixty-sixth birthday – in the presence of a large party of guests, including the Queen of Norway, the Queen of Spain, the Duke of Westminster and Lord Revelstoke. The king asked his colonial secretary, Lord Elgin, to announce that he accepted the gift "for myself and my successors" and that he would ensure "this great and unique diamond be kept and preserved among the historic jewels which form the heirlooms of the Crown".

Cutting process

The king chose Asscher Brothers of Amsterdam to cleave and polish the rough stone into brilliant gems of various cuts and sizes. Abraham Asscher collected it from the Colonial Office in London on 23 January 1908. He returned to the Netherlands by train and ferry with the diamond in his coat pocket. Meanwhile, to much fanfare, a Royal Navy ship carried an empty box across the North Sea, again throwing off potential thieves. Even the captain had no idea that his "precious" cargo was a decoy.

On 10 February 1908, the rough stone was split in half by Joseph Asscher at his diamond-cutting factory in Amsterdam. At the time, technology had not yet evolved to guarantee the quality of modern standards, and cutting the diamond was difficult and risky. After weeks of planning, an incision 0.5 inches (1.3 cm) deep was made to enable Asscher to cleave the diamond in one blow. Making the incision alone took four days, and a steel knife broke on the first attempt, but a second knife was fitted into the groove and split it clean in two along one of four possible cleavage planes. In all, splitting and cutting the diamond took eight months, with three people working 14 hours per day to complete the task.

"The tale is told of Joseph Asscher, the greatest cleaver of the day," wrote Matthew Hart in his book ‘Diamond: A Journey to the Heart of an Obsession’ (2002), "that when he prepared to cleave the largest diamond ever known … he had a doctor and nurse standing by and when he finally struck the diamond … he fainted dead away". Lord Ian Balfour, in his book ‘Famous Diamonds’ (2009), dispels the fainting story, suggesting it was more likely Joseph would have celebrated, opening a bottle of champagne. When Joseph's nephew Louis heard the story, he exclaimed "No Asscher would ever faint over any operation on any diamond".

Diamonds cut from the Cullinan

Cullinan produced 9 major stones of 1,055.89 carats (211.178 g) in total, and 96 minor brilliants weighing 7.55 carats (1.510 g) (on average, 0.079 carats each) – a yield from the rough stone of 34.25 per cent. There are also 9.5 carats (1.90 g) of unpolished fragments. All but the two largest stones – Cullinans I and II – remained in Amsterdam by arrangement as the fee for Asscher's services, until the South African government bought them (except Cullinan VI, which Edward VII had purchased and given to his wife Queen Alexandra in 1907), and the High Commissioner for Southern Africa presented them to Queen Mary on 28 June 1910. Mary also inherited Cullinan VI from Alexandra, and she left all of her Cullinan diamonds to her granddaughter Queen Elizabeth II in 1953.

Cullinans I and II are part of the Crown Jewels, which belong to the Queen in right of the Crown. Asscher sold the minor stones to the South African government, which distributed them to Queen Mary; Louis Botha, then prime minister of South Africa; and the diamond merchants Arthur and Alexander Levy, who supervised the cutting of Cullinan. Some were set by Mary into a long platinum chain, which Elizabeth has never worn in public, saying that "it gets in the soup". In the 1970s, two minor Cullinan diamonds owned by Louis Botha's heirs were analysed by De Beers at their laboratory in Johannesburg and found to be completely free of nitrogen or any other impurities. Cullinans I and II were examined in the 1980s by gemologists at the Tower of London and both graded as colourless type IIa.

Cullinan I

Cullinan I, or the Great Star of Africa, is a pendeloque-cut brilliant weighing 530.2 carats (106.04 g) and has 74 facets. It is set at the top of the Sovereign's Sceptre with Cross which had to be redesigned in 1910 to accommodate it. Cullinan I was surpassed as the world's largest cut diamond of any colour by the 545.67-carat (109.134 g) brown Golden Jubilee Diamond in 1992, but is still the largest clear cut diamond in the world. In terms of clarity, it has a few tiny cleavages and a small patch of graining. The 5.89 cm × 4.54 cm × 2.77 cm (2.32 in × 1.79 in × 1.09 in) diamond is fitted with loops and can be taken out of its setting to be worn as a pendant suspended from Cullinan II to make a brooch. Queen Mary, wife of George V, often wore it like this.[34] In 1908, the stone was valued at US$2.5 million (equivalent to US$51 million in 2018) – two and a half times the rough Cullinan's estimated value.

Cullinan II

Cullinan II, or the Second Star of Africa, is a cushion-cut brilliant with 66 facets weighing 317.4 carats (63.48 g) set in the front of the Imperial State Crown below the Black Prince's Ruby (a large spinel). It measures 4.54 cm × 4.08 cm × 2.42 cm (1.79 in × 1.61 in × 0.95 in). The diamond has a number of tiny flaws, scratches on the table facet, and a small chip at the girdle. Like Cullinan I, it is held in place by a yellow gold enclosure, which is screwed onto the crown.

Cullinan III

Cullinan III, or the Lesser Star of Africa, is pear-cut and weighs 94.4 carats (18.88 g). In 1911, Queen Mary, wife and queen consort of George V, had it set in the top cross pattée of a crown that she personally bought for her coronation. In 1912, the Delhi Durbar Tiara, worn the previous year by Mary instead of a crown at the Delhi Durbar, where her husband wore the Imperial Crown of India, was also adapted to take Cullinans III and IV. In 1914, Cullinan III was permanently replaced on the crown by a crystal model. Today, it is most frequently worn in combination with Cullinan IV by Elizabeth II as a brooch. In total, the brooch is 6.5 cm (2.6 in) long and 2.4 cm (0.94 in) wide. Cullinan III has also been used as a pendant on the Coronation Necklace, where it occasionally replaced the 22.4-carat (4.48 g) Lahore Diamond.

Cullinan IV

Cullinan IV, also referred to as a Lesser Star of Africa, is square-cut and weighs 63.6 carats (12.72 g). It was also set in the base of Queen Mary's Crown but was removed in 1914. On 25 March 1958, while she and Prince Philip were on a state visit to the Netherlands, Queen Elizabeth II revealed that Cullinan III and IV are known in her family as "Granny's Chips". They visited the Asscher Diamond Company, where Cullinan had been cut 50 years earlier. It was the first time the Queen had worn the brooch publicly. During her visit, she unpinned the brooch and offered it for examination to Louis Asscher, nephew of Joseph Asscher, who split the rough diamond. Aged 84, he was deeply moved that the Queen had brought the diamonds with her, knowing how much it would mean to him seeing them again after so many years.

Cullinan V

Cullinan V is an 18.8-carat (3.76 g) heart-shaped diamond set in the centre of a platinum brooch that formed a part of the stomacher made for Queen Mary to wear at the Delhi Durbar in 1911. The brooch was designed to show off Cullinan V and is pavé-set with a border of smaller diamonds. It can be suspended from the VIII brooch and can be used to suspend the VII pendant. It was often worn like this by Mary.

Cullinan VI

Cullinan VI is marquise-cut and weighs 11.5 carats (2.30 g). It hangs from the brooch containing Cullinan VIII and forming part of the stomacher of the Delhi Durbar parure. Cullinan VI along with VIII can also be fitted together to make yet another brooch, surrounded by some 96 smaller diamonds. The design was created around the same time that the Cullinan V heart-shaped brooch was designed, both having a similar shape.

Cullinan VII

Cullinan VII is also marquise-cut and weighs 8.8 carats (1.76 g). It was originally given by Edward VII to his wife and consort Queen Alexandra. After his death she gave the jewel to Queen Mary, who had it set as a pendant hanging from the diamond-and-emerald Delhi Durbar necklace, part of the parure.

Cullinan VIII

Cullinan VIII is an oblong-cut diamond weighing 6.8 carats (1.36 g). It is set in the centre of a brooch forming part of the stomacher of the Delhi Durbar parure. Together with Cullinan VI it forms a brooch.

Cullinan IX

Cullinan IX is smallest of the principal diamonds to be obtained from the rough Cullinan. It is a pendeloque or stepped pear-cut stone, weighs 4.39 carats (0.878 g), and is set in a platinum ring known as the Cullinan IX Ring.

Jai Ganesh · 2020-04-10 01:12:35

516) Khone Falls

Khone Falls, French Chutes De Khone, series of cataracts on the Mekong River, extreme southern Laos, on the Cambodian border. The falls are the principal impediment to navigation of the river and have impeded economic use of the Mekong by the peoples of the Cambodian plain to the south and those of Laos to the north; a narrow-gauge railway was once built for transport around the falls. The double series of cataracts is caused by a resistant bed of basalt over which the river tumbles 45 feet (14 m) to a pool 269 feet (82 m) above sea level. The strata causing the falls are also responsible for several islands, the largest of which, Không, has a small port based on the portaging of goods around the falls. The Khone has the greatest volume of the world’s waterfalls, its 2,500,000 gallons (9,500,000 litres) per second being nearly double that of Niagara Falls.

Series of cascading waterfalls and rapids in the Mekong river

The Khone falls, a series of cascading waterfalls in the Mekong river is one of Laos’ most beautiful natural attractions. The impressive falls in Champasak province near the Cambodian border are the largest in volume in South East Asia.

The falls, also known as Khone Phapheng, are located in an area called Si Phan Don, which literally translates to “Four thousand islands”. At this point the Mekong river broadens out; during the rainy season the river and series of cascades is kilometers wide and extend over a length of almost 10 kilometers downstream.

The falls are most impressive during the dry season. In the rainy season much of the rapids and falls disappear as a result of the raised water level in the river.
The Khone falls are located South of Don Khon island, the area which is the home of a small group of rare Irrawaddy dolphins. At the highest point the waterfall is 21 meters high. Just above the Khone falls is a viewpoint with a pavilion providing great views over the waterfalls and numerous islands. Several food stalls and stalls selling handicrafts are found nearby.

Colonial era railway and bridge

The Khone Phapheng falls are the main reason why the over 4,000 kilometer long Mekong river is not navigable by ship from China downstream into the South China sea. In the 19th century, when Laos was part of French Indochina, the French tried to establish a shipping route in an attempt to connect the countries of French Indochina to the sea. After several attempts to navigate the falls by ship had failed, they decided to go around the falls by building a railway and a railway bridge between Don Det and Don Khon islands.

Khone Phapheng Falls

The Khone Falls and Pha Pheng Falls together form a waterfall located in Champasak Province on the Mekong River in southern Laos, near the border with Cambodia. At 35,376 feet (10,783 m) wide, it is the widest waterfall in the world.

The Khone Falls are the largest in southeast Asia, and are the main reason that the Mekong is not fully navigable into China. The falls are characterised by thousands of islands and countless waterways, giving the area its name Si Phan Don or 'the 4,000 islands'.

The highest falls reach to 21 metres (69 ft); the succession of rapids stretch 9.7 km (6.0 mi) of the river's length. The average discharge of the cataract is nearly 11,000 cubic meters per second (390,000 cu ft/s), with the highest flow on record at over 49,000 cubic meters per second (1,700,000 cu ft/s).

Navigable efforts

The Khone Falls is the prime reason why the Mekong river is not fully navigable into China. In the late 19th century French colonialists made repeated attempts to navigate the falls but their efforts failed. This difficulty led to the construction of the Don Det – Don Khon narrow gauge railway on Don Det and Don Khon islands.

Wildlife

Hillstream loach ‘Hemimyzon khonensis’ is known from a single specimen collected in the Mekong at the Khone Falls. The falls are home to the plabuck, an endangered species of catfish said to be the largest freshwater fish in the world. The plabuck is alleged to reach lengths of 3 m (10 ft) and weights of up to 646 pounds (293 kilograms).

Jai Ganesh · 2020-04-11 01:02:25

517) Tristan da Cunha

Tristan da Cunha, colloquially Tristan, is a remote group of volcanic islands in the south Atlantic Ocean which includes Gough Island. It is the most remote inhabited archipelago in the world, lying approximately 1,511 miles (2,432 km) off the coast of Cape Town in South Africa, 1,343 miles (2,161 km) from Saint Helena and 2,166 miles (3,486 km) off the coast of the Falkland Islands.

The territory consists of the inhabited island, Tristan da Cunha, which has a diameter of roughly 11 kilometres (6.8 mi) and an area of 98 square kilometres (38 sq mi), and the wildlife reserves of Gough Island and Inaccessible Island and the smaller, uninhabited Nightingale Islands. As of October 2018, the main island has 250 permanent inhabitants who all carry British Overseas Territories citizenship. The other islands are uninhabited, except for the personnel of a weather station on Gough Island.

Tristan da Cunha is a British Overseas Territory with its own constitution. There is no airstrip of any kind on the main island, meaning that the only way of travelling in and out of Tristan is by boat, a six-day trip from South Africa.

Tristan da Cunha, island and group of islands in the South Atlantic Ocean, about midway between southern Africa and South America. The island group is a constituent part of the British overseas territory of St. Helena, Ascension and Tristan da Cunha. The six small islands of the Tristan da Cunha group are administered collectively. Five of them—Tristan da Cunha, Inaccessible, Nightingale, Middle, and Stoltenhoff—are located within 25 miles (40 km) of one another, and the sixth, Gough, lies about 200 miles (320 km) south-southeast of the group. The territory is located approximately 1,300 miles (2,100 km) to the south of St. Helena. Inaccessible, Nightingale, Middle, and Stoltenhoff are uninhabited, while a weather station is manned on Gough Island.

Tristan da Cunha island, the largest and northernmost of the group, is roughly circular, with a coastline of 21 miles (34 km) and a central volcanic cone (6,760 feet [2,060 metres]) that is usually cloud-covered. The climate is wet, windy, and mild. About 66 inches (1,675 mm) of rain falls annually on the north coast at Edinburgh of the Seven Seas (frequently shortened to Edinburgh), the only permanent settlement. Plant and animal life includes elephant seals and other species not found elsewhere in the world.

Gough and Inaccessible islands together constitute a wildlife reserve, designated a UNESCO World Heritage site in 1995. Inaccessible is about 20 miles (32 km) west-southwest of Tristan da Cunha. It is ringed by cliffs some 1,000 feet (300 metres) high, and beneath the cliffs are occasional narrow beaches. A bird endemic to Inaccessible is the small, flightless land rail. Nightingale Island, the southernmost of the group, is 12 miles (19 km) southeast of Inaccessible and 20 miles (32 km) south-southwest of Tristan da Cunha. Its coasts have low cliffs where millions of seabirds nest. The tiny islands of Middle and Stoltenhoff abut the north coast of Nightingale. Gough Island is about 8 miles (13 km) long and 4 miles (6 km) wide and is of volcanic origin.

Executive authority is vested in a governor, who is also the governor of St. Helena and resides on that island. The governor appoints an administrator to represent him or her in Tristan da Cunha. An Island Council advises the administrator; it has three ex officio members and eight elected members. The administrator serves as president of the Island Council.

The island group was discovered in 1506 by a Portuguese admiral, Tristão da Cunha. Two unsuccessful attempts to settle the islands during the 17th century and one in 1810 preceded the stationing of a British garrison on Tristan da Cunha in 1816, when the island group was formally annexed by the United Kingdom. When the garrison was withdrawn in 1817, three of its members chose to stay, and over the years they were joined by shipwrecked sailors, settlers of European extraction, and women from St. Helena. By 1886 there were 97 inhabitants. The settlement, named Edinburgh of the Seven Seas, was located on the largest lowland strip, about 0.5 mile (0.8 km) wide and 5 miles (8 km) long. In 1938 the six islands were made dependencies of St. Helena. During World War II a naval meteorological and radio station was set up on Tristan da Cunha; afterward a South African weather station was also established there.

A volcanic eruption on the island in October 1961 directly threatened the settlement, and the inhabitants were evacuated to England via Nightingale Island. The main body of 198 islanders returned to the island in November 1963. A new harbour was built in 1965–67. Roads and a hospital, as well as electric, water, and sewerage facilities, were later constructed. After a hurricane severely damaged Edinburgh in May 2001, aid flowed in from abroad to pay for rebuilding. According to the terms of the 2009 constitution drawn up for the islands, Tristan da Cunha was no longer a dependency of St. Helena but an equal part of the territory of St. Helena, Ascension and Tristan da Cunha.

Potatoes are the main crop and shore-based shellfish fishing the main industry; lobster and crawfish are exported. Livestock is raised for domestic consumption. Sales of the island’s postage stamps and coins also contribute to revenue. Area Tristan da Cunha island, 38 square miles (98 square km). Pop. (2014 est.) Tristan da Cunha island, 269.

Jai Ganesh · 2020-04-11 14:39:47

518) Eiffel Tower

Eiffel Tower, French Tour Eiffel, Parisian landmark that is also a technological masterpiece in building-construction history. When the French government was organizing the International Exposition of 1889 to celebrate the centenary of the French Revolution, a competition was held for designs for a suitable monument. More than 100 plans were submitted, and the Centennial Committee accepted that of the noted bridge engineer Gustave Eiffel. Eiffel’s concept of a 300-metre (984-foot) tower built almost entirely of open-lattice wrought iron aroused amazement, skepticism, and no little opposition on aesthetic grounds. When completed, the tower served as the entrance gateway to the exposition.

Nothing remotely like the Eiffel Tower had ever been built; it was twice as high as the dome of St. Peter’s in Rome or the Great Pyramid of Giza. In contrast to such older monuments, the tower was erected in only about two years (1887–89), with a small labour force, at slight cost. Making use of his advanced knowledge of the behaviour of metal arch and metal truss forms under loading, Eiffel designed a light, airy, but strong structure that presaged a revolution in civil engineering and architectural design. And, after it opened to the public on May 15, 1889, it ultimately vindicated itself aesthetically.

The Eiffel Tower stands on four lattice-girder piers that taper inward and join to form a single large vertical tower. As they curve inward, the piers are connected to each other by networks of girders at two levels that afford viewing platforms for tourists. By contrast, the four semicircular arches at the tower’s base are purely aesthetic elements that serve no structural function. Because of their unique shape, which was dictated partly by engineering considerations but also partly by Eiffel’s artistic sense, the piers required elevators to ascend on a curve; the glass-cage machines designed by the Otis Elevator Company of the United States became one of the principal features of the building, helping establish it as one of the world’s premier tourist attractions.

The tower itself is 300 metres (984 feet) high. It rests on a base that is 5 metres (17 feet) high, and a television antenna atop the tower gives it a total elevation of 324 metres (1,063 feet). The Eiffel Tower was the tallest structure in the world until the topping off of the Chrysler Building in New York City in 1929.

Jai Ganesh · 2020-04-12 01:06:18

519) Taj Mahal

The Taj Mahal ( lit. Crown of the Palace) is an ivory-white marble mausoleum on the south bank of the Yamuna river in the Indian city of Agra. It was commissioned in 1632 by the Mughal emperor Shah Jahan (reigned from 1628 to 1658) to house the tomb of his favourite wife, Mumtaz Mahal; it also houses the tomb of Shah Jahan himself. The tomb is the centrepiece of a 17-hectare (42-acre) complex, which includes a mosque and a guest house, and is set in formal gardens bounded on three sides by a crenellated wall.

Construction of the mausoleum was essentially completed in 1643, but work continued on other phases of the project for another 10 years. The Taj Mahal complex is believed to have been completed in its entirety in 1653 at a cost estimated at the time to be around 32 million rupees, which in 2020 would be approximately 70 billion rupees (about U.S. $916 million). The construction project employed some 20,000 artisans under the guidance of a board of architects led by the court architect to the emperor, Ustad Ahmad Lahauri.

The Taj Mahal was designated as a UNESCO World Heritage Site in 1983 for being "the jewel of Muslim art in India and one of the universally admired masterpieces of the world's heritage". It is regarded by many as the best example of Mughal architecture and a symbol of India's rich history. The Taj Mahal attracts 7–8 million visitors a year and in 2007, it was declared a winner of the New7Wonders of the World (2000–2007) initiative.

Inspiration

The Taj Mahal was commissioned by Shah Jahan in 1631, to be built in the memory of his wife Mumtaz Mahal, who died on 17 June that year, giving birth to their 14th child, Gauhara Begum. Construction started in 1632, and the mausoleum was completed in 1643, while the surrounding buildings and garden were finished five years later. The imperial court documenting Shah Jahan's grief after the death of Mumtaz Mahal illustrates the love story held as the inspiration for the Taj Mahal.

Architecture and design

The Taj Mahal incorporates and expands on design traditions of Persian and earlier Mughal architecture. Specific inspiration came from successful Timurid and Mughal buildings including the Gur-e Amir (the tomb of Timur, progenitor of the Mughal dynasty, in Samarkand), Humayun's Tomb which inspired the Charbagh gardens and hasht-behesht (architecture) plan of the site, Itmad-Ud-Daulah's Tomb (sometimes called the Baby Taj), and Shah Jahan's own Jama Masjid in Delhi. While earlier Mughal buildings were primarily constructed of red sandstone, Shah Jahan promoted the use of white marble inlaid with semi-precious stones. Buildings under his patronage reached new levels of refinement.

Tomb

The tomb is the central focus of the entire complex of the Taj Mahal. It is a large, white marble structure standing on a square plinth and consists of a symmetrical building with an iwan (an arch-shaped doorway) topped by a large dome and finial. Like most Mughal tombs, the basic elements are Persian in origin.

The base structure is a large multi-chambered cube with chamfered corners forming an unequal eight-sided structure that is approximately 55 metres (180 ft) on each of the four long sides. Each side of the iwan is framed with a huge pishtaq or vaulted archway with two similarly shaped arched balconies stacked on either side. This motif of stacked pishtaqs is replicated on the chamfered corner areas, making the design completely symmetrical on all sides of the building. Four minarets frame the tomb, one at each corner of the plinth facing the chamfered corners. The main chamber houses the false sarcophagi of Mumtaz Mahal and Shah Jahan; the actual graves are at a lower level.

The most spectacular feature is the marble dome that surmounts the tomb. The dome is nearly 35 metres (115 ft) high which is close in measurement to the length of the base, and accentuated by the cylindrical "drum" it sits on which is approximately 7 metres (23 ft) high. Because of its shape, the dome is often called an onion dome or amrud (guava dome). The top is decorated with a lotus design which also serves to accentuate its height. The shape of the dome is emphasised by four smaller domed chattris (kiosks) placed at its corners, which replicate the onion shape of the main dome. The dome is slightly asymmetrical. Their columned bases open through the roof of the tomb and provide light to the interior. Tall decorative spires (guldastas) extend from edges of base walls, and provide visual emphasis to the height of the dome. The lotus motif is repeated on both the chattris and guldastas. The dome and chattris are topped by a gilded finial which mixes traditional Persian and Hindustani decorative elements.

The main finial was originally made of gold but was replaced by a copy made of gilded bronze in the early 19th century. This feature provides a clear example of integration of traditional Persian and Hindu decorative elements. The finial is topped by a moon, a typical Islamic motif whose horns point heavenward.

The minarets, which are each more than 40 metres (130 ft) tall, display the designer's penchant for symmetry. They were designed as working minarets— a traditional element of mosques, used by the muezzin to call the Islamic faithful to prayer. Each minaret is effectively divided into three equal parts by two working balconies that ring the tower. At the top of the tower is a final balcony surmounted by a chattri that mirrors the design of those on the tomb.

Jai Ganesh · 2020-04-13 02:59:20

520) Zürich

Zürich, largest city of Switzerland and capital of the canton of Zürich. Located in an Alpine setting at the northwestern end of Lake Zürich, this financial, cultural, and industrial centre stretches out between two forested chains of hills, about 40 miles (60 km) from the northern foothills of the Alps. Two rivers, the Limmat and Sihl, run through the city. Zürich’s western and northeastern limitations are formed by the Albis mountains (which include the 2,850-foot [870-metre] Üetliberg, considered the “top” of Zürich, with an idyllic view of the lake, mountains, and city) and by Zürichberg, a wooded hilly area. Area city, 34 square miles (88 square km). Pop. (2010) 372,857.

History

The first inhabitants of the region were the prehistoric peoples whose hut dwellings rose from pile foundations driven into the shores of the lake. The Celtic Helvetii founded a community on the right bank of the Limmat River; when the Romans conquered this area about 58 BCE, they made the settlement, which they called Turicum, a customs post. Under Roman rule, Zürich grew into a small army stronghold with an adjacent vicus, or Roman village. After the collapse of Rome, the community fell first to the Alemanni, a Germanic people from the north, and later to the Franks, who made it a royal residence.

The community began to flourish as traders settled in the town and took advantage of its position straddling European trade routes. In 1218 Zürich became an imperial free city, and in 1351 it joined the Swiss Confederation, a coalition of cantons that were opposed to the Austrian Habsburgs. In 1336 the citizens accepted a constitution that, based democratically on the guild system, balanced the power of the various crafts, the trades, and the nobility. As the guilds became more powerful, the city was able to purchase its freedom from the emperor in 1400, and tax obligations were lifted. Zürich became embroiled in conflicts with neighbouring territories, but economic growth continued relatively unimpeded. Staging repeated successful forays into the surrounding countryside, the city began controlling an even larger part of it; moreover, Zürich profited from being conveniently located on both the southbound trade route, centred on the St. Gotthard Pass, and the east-west route from the Rhône River to the Danube.

In 1519 Huldrych Zwingli, a priest at the Grossmünster (“Great Minster”), began to preach a series of sermons that initiated the Swiss Protestant Reformation and transformed the character of Zürich itself. It turned into an industrious puritanical city maintaining lively business relations and an exchange of ideas with other Protestant cities, notably Bern and Geneva. During the Counter-Reformation, the city offered asylum to many refugees from northern Italy and France, and the new residents further stimulated cultural and economic growth.

Napoleon’s occupation of Switzerland in 1798 ended the old political order, and Zürich was reorganized under the Helvetic Republic, which tried to form a unitary Swiss state. Zürich residents did not like the centralized control imposed by the new republic, and years of conflict between the city, the surrounding countryside, and the other cantons ensued. The disputes ended in 1803 when Napoleon mediated, and the canton of Zürich, dominated by the city, became a sovereign member of a new Swiss Confederation. The political rule exerted by the aristocratic ancien régime was replaced by a liberal democratic order by 1816.

The 1830 July Revolution in Paris sparked similar revolutions in Swiss cantons, including Zürich canton, which gave way to liberal reform. The cantons’ citizenry was able to elect and exercise strong control over the legislature (Gemeinderat) as well as the executive branch of government (Stadtrat). A new canton constitution was drafted in 1831. Under the Swiss constitution of 1848, the autonomous cantons became federal states, each with its own constitution. The people of Zürich adopted a new constitution in 1869, which included mandatory referendums, direct election of cantonal government by the citizens, and limits on presidential terms. This democratic constitution served as a model for other Swiss cities and influenced the revision of Switzerland’s national constitution in 1874.

Zürich thus became well equipped to enter the modern industrial era. As early as 1787, about one-fourth of the population was engaged in textile manufacturing (a successor to the medieval silk industry, which lost its importance after French occupation). Agriculture and textile production were gradually replaced with small-scale industry, and local factories focused on producing specialized goods. All of these changes helped aid an economic expansion centred on manufacturing and service industries. Zürich’s historical international links also placed it in the forefront of modern world finance.

Improved transport played an important role in the 19th century. Among Switzerland’s first railway lines was the one linking Zürich with the neighbouring city of Baden; opened in 1847, it was nicknamed the “Spanish Roll Railway” because the bread rolls it brought from Baden were reputedly still warm on arrival. In 1882 the Zürich-Milan trans-Alpine railway line opened, its existence made possible by the construction of the 10-mile (16.3-km) Gotthard Tunnel, designed by industrial and railway pioneer Alfred Escher.

In the mid-19th century the University of Zürich (1833), maintained by the canton, and the Swiss Federal Institute of Technology (1855) were founded. The University of Zürich was the first university in Europe to accept female students. Zürich also boasts a long line of Nobel Prize winners among its citizenry, particularly in the fields of physics (Wilhelm Conrad Röntgen, 1901; Albert Einstein, 1921; and Wolfgang Pauli, 1945), chemistry (Richard Ernst, 1991), and medicine (Rolf Zinkernagel, 1996). Noted Zürich-born authors include Gottfried Keller, Conrad Ferdinand Meyer, and Max Frisch.

The financial services sector developed in response to the growing demand for capital by the evolving industries and the railways. In 1856 Escher founded the Schweizerische Kreditanstalt, a banking institute wholly geared to financing industrial and commercial projects. By the end of the 19th century, Zürich had become Switzerland’s financial and economic centre. Before that time, Zürich’s banks had been in the shadow of those of Basel and Geneva.

Switzerland was neutral during World War I, and Zürich gave asylum to intellectuals including James Joyce and Vladimir Ilich Lenin. In reaction to the horrors of the war, the Dada art movement emerged in Zürich at the Cabaret Voltaire, a small tavern established in 1916 by Hugo Ball on Spiegelgasse.

During World War II, Zürich banks took advantage of banking secrecy laws to help the Nazi Party launder gold and stolen valuables. It was not until the 1990s that the banks’ role during the war was made public. In 1998 the two largest Swiss banks, Credit Suisse Group and UBS AG, agreed to pay two billion Swiss francs to international Jewish organizations.

After World War II, Zürich’s airport became the primary international airport of Switzerland. This helped the city to further strengthen its economic position in the country. By the second half of the 20th century, the textile industry had completely lost its importance, and the production of machines had become dominant. At the same time, the service sector, notably banks and insurance companies, gained in importance. Further developments that bolstered the financial sector in Zürich were the decision of the National Bank of Switzerland, which has headquarters in Zürich and Bern, to install its board of directors in Zürich, the introduction of absolute confidentiality in banking, and the temporary closure of the London Gold Exchange in 1968. The Zürich banks reacted at once and founded the Zürich Gold Pool, a gold trading organization set up by Switzerland’s largest banks, which helped establish Zürich as one of the most important trading places for gold worldwide.

The postwar period brought an influx of immigrants both from rural Switzerland and from abroad, pushing the population past the city’s administrative boundaries and into the hinterland. For the first time, the city and surrounding area reached a population of one million.

The beginning of the 21st century was a difficult time for the city, whose finance-oriented economy was shaken by crises in the world financial markets in the wake of corporate collapses and the spiraling stock market in the United States. In 2001 Zürich-based Swiss Air Transport Company Ltd. (Swissair) collapsed as a result of both an aggressive business expansion strategy and the airline crisis following the September 11 attacks in the United States. In 2002, however, elements of the former airline reemerged as Swiss International Air Lines (SWISS), which, after a difficult start, grew rapidly. Similarly, the recovery of the financial markets in the following years brought a period of prosperity to the city in general, securing Zürich’s position as the uncontested economic capital of Switzerland. Moreover, Switzerland’s resistance to joining the European Union (EU) had not hindered Zürich’s economic development, as bilateral agreements with the EU gave Switzerland full access to EU markets.

Since the 1990s Zürich has been governed by a centre-left coalition of parties, which has undertaken efforts to create sustainable development even as it continued to position the city as the economic centre of Switzerland. Together with the Swiss Federal Institute of Technology and the University of Zürich—both leading universities in environmental sciences—the city pursues ambitious energy, environmental, and spatial development policies.

The Contemporary City

Zürich is at the core of a constantly expanding metropolitan area that encompasses parts of central, northern, and eastern Switzerland. It is the industrial, financial, and cultural centre of the country and one of the most cosmopolitan and dynamic Swiss cities. Throughout the city centre, green space extends to the shores of Lake Zürich, which are lined by attractive public parks, and up to the slopes of Zürichberg.

The city has a diverse ethnic composition; more than one-third of its population is made up of immigrants. The largest immigrant groups are from Italy, the Balkans, Portugal, and Germany. There is also a small population of non-European immigrants. The integration of immigrants, particularly those displaced by conflict in the Balkans and those from non-European countries, posed a series of problems, especially for schools, at the end of the 20th century and beginning of the 21st. The resulting ethnic tensions eased, however, with the city’s introduction of social programs targeted at immigrants and as tighter restrictions were instituted for immigration from outside the EU. Switzerland and Zürich were not inundated with as many migrants as other western European countries were during the migrant crisis of 2015–16, partly because the Muslim diaspora in Switzerland was small, making it a less attractive destination for those fleeing the Syrian Civil War and other turbulent events in the Middle East and Africa.

Zürich was once a Protestant stronghold, but by the early 21st century only about one-third of Zürich’s inhabitants were Protestant. Roman Catholicism became the dominant religion, mainly due to immigration. Immigrants from the Balkans and Turkey have contributed to a growing Muslim community. There is also a small Jewish community in Zürich.

Zürich’s city centre and most of the city’s architectural features extend along both shores of the Limmat River, which runs from the north side of Lake Zürich through the city centre and out to the west. Zürich’s lively and well-preserved Altstadt (Old Town), part of the city centre, boasts an architectural legacy including the Romanesque Grossmünster, built by Charlemagne in the 700s; the 13th-century St. Peter’s Church; and elegant guild houses and patrician residences, some of which are used as restaurants or for civic functions. The Fraumünster (Minster of Our Lady) is noted for its stained glass windows designed by Marc Chagall.

Adjacent to the historic Altstadt is the Bahnhofstrasse shopping district, whose distinguished architecture dates back to 1870. Centred on Paradeplatz, Bahnhofstrasse is home to luxury shops, including those of the country’s renowned jewelers and watchmakers. Cafés, department stores, and shops selling local handicrafts and books also line the boulevard. Just across the Limmat River from the Bahnhofstrasse lies Zürich’s youth-oriented Niederdorfstrasse, which features bistros, shops, and ethnic restaurants.

Zürich’s middle- and lower-class neighbourhoods are in the western and northern parts of the city. To the north of Zürichberg, between the airport and the city, is the Glattal, one of the most rapidly growing areas in Switzerland. In Zürich Nord, a district in the north of the city near the airport, a minor downtown area has gradually formed. A large number of firms, particularly the headquarters of international companies, have located there. Zürich West, a former industrial and red-light district, has been transformed into a popular area with ambitious contemporary architecture, theatres, shops, art galleries, residential living spaces, and lots of nightlife.
Zürich has nurtured a rich cultural life, and its theatres and opera have often been characterized by innovation and experiment. The Zürich Opera House (1891), the Schauspielhaus (Theatre; 1901), and the Schiffbau (Shipping Hall; 2001) have international prominence. Zürich has its own orchestra, the Tonhalle, which has its own hall, where the Zürich Chamber Orchestra also plays. Cabaret Voltaire reopened in 2004 in the Altstadt, reviving Zürich’s tradition of avant-garde performance.

In the early 2000s more art galleries opened throughout Zürich, and Raemistrasse, just east of the city centre, became known as the city’s “art mile.” Notable museums include the Swiss National Museum (1898), which has a treasure trove of historical, artistic, and scientific collections, and Kunsthaus Zürich, whose broad collection includes Swiss and modern paintings.

The city has traditional annual festivals: the Sechseläuten in April, with a guild procession and the ceremonial burning of a snowman, and the Knabenschiessen in September, a sharpshooting contest for young people. Along with these traditional festivals, there is the Zürich Carnival (Fasnacht) in late winter and the Street Parade in August, which began in the 1990s and draws thousands of people to dance to techno music.

The city also has two top-division football (soccer) teams, Grasshoper-Club Zürich and Zürich F.C. A new football stadium, Letzigrund, was constructed in 2007. Mountain climbing is also a popular sport for the people of Zürich.

The city has built new hotels, renovated museums and theatres, and illuminated landmarks in its attempt to become a premier tourist destination. At the same time, “Science City,” an international think-tank campus constructed by the Swiss Federal Institute of Technology, has contributed to Zürich’s stature as an important centre for innovative research and education. Long prominent in banking and business, Zürich has been energized by its emerging art scene, newly popular neighbourhoods, and an influx of immigrants that have contributed to its revived youthfulness and diversity. Zürich has become one of the most vibrant cities in 21st-century Europe.

Jai Ganesh · 2020-04-14 03:17:50

521) Zulu

Zulu, a nation of Nguni-speaking people in KwaZulu-Natal province, South Africa. They are a branch of the southern Bantu and have close ethnic, linguistic, and cultural ties with the Swazi and Xhosa. The Zulu are the single largest ethnic group in South Africa and numbered about nine million in the late 20th century.

Traditionally grain farmers, they also kept large herds of cattle on the lightly wooded grasslands, replenishing their herds mainly by raiding their neighbours. European settlers wrested grazing and water resources from the Zulu in prolonged warfare during the 19th century, and, with much of their wealth lost, modern Zulu depend largely on wage labour on farms owned by individuals of European descent or work in the cities of South Africa.

Before they joined with the neighbouring Natal Nguni under their leader Shaka in the early 19th century to form a Zulu empire, the Zulu were only one of many Nguni clans; Shaka gave the clan name to the new nation. Such clans continue to be a basic unit of Zulu social organization; they comprise several patrilineal households, each with rights in its own fields and herds and under the domestic authority of its senior man. Paternal authority is so strong that the Zulu may be called patriarchal. Polygyny is practiced; a man’s wives are ranked by strict seniority under the “great wife,” the mother of his heir. The levirate, in which a widow goes to live with a deceased husband’s brother and continues to bear children in the name of the dead husband, is also practiced.

The genealogically senior man of each clan is its chief, traditionally its leader in war and its judge in peace. Headmen (induna), usually close kin of the chief, continue to have charge of sections of the clan. This clan system was adopted nationwide under the Zulu king, to whom most clan chiefs are related in one way or another. When the Zulu nation was formed, many chiefs were married to women of royal clan or were royal kinsmen installed to replace dissident clan heads. The king relied on confidential advisers, and chiefs and subchiefs formed a council to advise him on administrative and judicial matters.

Boys in this highly organized military society were initiated at adolescence in groups called age sets. Each age set constituted a unit of the Zulu army and was stationed away from home at royal barracks under direct control of the king. Formed into regiments (impi), these men could marry only when the king gave permission to the age set as a whole.

Traditional Zulu religion was based on ancestor worship and on beliefs in a creator god, witches, and sorcerers. The king was responsible for all national magic and rainmaking; rites performed by the king on behalf of the entire nation (at planting season, in war, drought, or famine) centred on the ancestors of the royal line. Modern Zulu Christianity has been marked by the growth of independent or separatist churches under prophets, some of great wealth and influence.

The power and importance of the king, chiefs, and military system have declined substantially, and many of the young men leave KwaZulu-Natal to seek work elsewhere in South Africa. Knowledge of and strong pride in traditional culture and history are, however, almost universal among contemporary Zulu.

Jai Ganesh · 2020-04-15 00:54:12

522) Mount Fuji

Mount Fuji, Japanese Fuji-san, also spelled Fujisan, also called Fujiyama or Fuji no Yama, highest mountain in Japan. It rises to 12,388 feet (3,776 metres) near the Pacific Ocean coast in Yamanashi and Shizuoka ken (prefectures) of central Honshu, about 60 miles (100 km) west of the Tokyo-Yokohama metropolitan area. It is a volcano that has been dormant since its last eruption, in 1707, but is still generally classified as active by geologists. The mountain is the major feature of Fuji-Hakone-Izu National Park (1936), and it is at the centre of a UNESCO World Heritage site designated in 2013.

The origin of the mountain’s name is uncertain. It first appears as Fuji no Yama in Hitachi no kuni fudoki (713 CE), an early government record. Among the several theories about the source of the name is that it is derived from an Ainu term meaning “fire,” coupled with san, the Japanese word for “mountain.” The Chinese ideograms (kanji) now used to write Fuji connote more of a sense of good fortune or well being.

Mount Fuji, with its graceful conical form, has become famous throughout the world and is considered the sacred symbol of Japan. Among Japanese there is a sense of personal identification with the mountain, and each summer thousands of Japanese climb to the shrine on its peak. Its image has been reproduced countless times in Japanese art, perhaps no more famously than in the series of woodblock prints ‘Thirty-six Views of Mount Fuji’ by Hokusai, which were originally published between 1826 and 1833.

According to tradition, the volcano was formed in 286 BCE by an earthquake. The truth is somewhat more complex. The age of Fuji is disputed, but it seems to have formed during the past 2.6 million years on a base dating from up to 65 million years ago; the first eruptions and the first peaks probably occurred some 600,000 years ago. The present-day mountain is a composite of three successive volcanoes: at the bottom is Komitake, which was surmounted by Ko Fuji (“Old Fuji”) and, finally, by the most recent, Shin Fuji (“New Fuji”). Over the millennia, the lava and other ejecta from Ko Fuji covered most of Komitake, although the top of the latter’s cone continued to protrude from the slope of Ko Fuji. Shin Fuji probably first became active about 10,000 years ago and has continued ever since to smolder or erupt occasionally. In the process it has filled in the slopes of its two predecessors and added the summit zone, producing the mountain’s now nearly perfect tapered form. The mountain is part of the Fuji Volcanic Zone, a volcanic chain that extends northward from the Mariana Islands and the Izu Islands through Izu Peninsula to northern Honshu.

The base of the volcano is about 78 miles (125 km) in circumference and has a diameter of some 25 to 30 miles (40 to 50 km). At the summit of Mount Fuji the crater spans about 1,600 feet (500 metres) in surface diameter and sinks to a depth of about 820 feet (250 metres). Around the jagged edges of the crater are eight peaks—Oshaidake, Izudake, Jojudake, Komagatake, Mushimatake, Kengamine, Hukusandake, and Kusushidake.

On the northern slopes of Mount Fuji lie the Fuji Five Lakes (Fuji Goko), comprising, east to west, Lake Yamanaka, Lake Kawaguchi, Lake Sai, Lake Shōji, and Lake Motosu, all formed by the damming effects of lava flows. The lowest, Lake Kawaguchi, at 2,726 feet (831 metres), is noted for the inverted reflection of Mount Fuji on its still waters. Tourism in the area is highly developed, with Lake Yamanaka, the largest of the lakes (at 2.5 square miles [6.4 square km]), being the focus of the most popular resort area. Southeast of Mount Fuji is the wooded volcanic Hakone region, well known for its hot-springs resorts at Yumoto and Gōra.

The area’s abundant groundwater and streams facilitate the operation of paper and chemical industries and farming. Cultivation of rainbow trout and dairy farming are other activities.

A sacred mountain (one sect, the Fujikō, accords it virtually a soul), Mount Fuji is surrounded by temples and shrines, there being shrines even at the edge and the bottom of the crater. Climbing the mountain has long been a religious practice, though until the Meiji Restoration (1868) women were not allowed to climb it. The ascent in early times was usually made in the white robes of a pilgrim. Today great crowds flock there, mostly during the climbing season from July 1 to August 26. Typically, climbers set out at night in order to reach the summit by dawn.

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Jai Ganesh · 2020-04-16 00:59:28

523) CN Tower

CN Tower, also called Canadian National Tower, broadcast and telecommunications tower in Toronto. Standing at a height of 1,815 feet (553 metres), it was the world’s tallest freestanding structure until 2007, when it was surpassed by the Burj Dubai building in Dubayy (Dubai), U.A.E. Construction of CN Tower began in February 1973 and involved more than 1,500 workers; the tower was completed in February 1974, and the attachment of its antenna was finished in April 1975. First opened to the public on June 26, 1976, CN Tower was built by Canadian National Railway Company and was initially privately owned, but ownership of the tower was transferred to the Canadian government in 1995; it is now managed by a public corporation. CN Tower, whose designers included John Andrews, Webb Zerafa, Menkes Housden, and E.R. Baldwin, is by far Toronto’s most distinctive landmark. It is a major tourist attraction that includes observation decks, a revolving restaurant at some 1,151 feet (351 metres), and an entertainment complex. It is also a centre for telecommunications in Toronto.

The CN Tower is a 553.3 m-high (1,815.3 ft) concrete communications and observation tower located in Downtown Toronto, Ontario, Canada. Built on the former Railway Lands, it was completed in 1976. Its name "CN" originally referred to Canadian National, the railway company that built the tower. Following the railway's decision to divest non-core freight railway assets prior to the company's privatization in 1995, it transferred the tower to the Canada Lands Company, a federal Crown corporation responsible for real estate development.

The CN Tower held the record for the world's tallest free-standing structure for 32 years until 2007 when it was surpassed by the Burj Khalifa and was the world's tallest tower until 2009 when it was surpassed by the Canton Tower. It is now the ninth tallest free-standing structure in the world and remains the tallest free-standing structure on land in the Western Hemisphere. In 1995, the CN Tower was declared one of the modern Seven Wonders of the World by the American Society of Civil Engineers. It also belongs to the World Federation of Great Towers.

It is a signature icon of Toronto's skyline and attracts more than two million international visitors annually.

Jai Ganesh · 2020-04-17 01:18:53

524) Kilimanjaro

Kilimanjaro, volcanic massif in northeastern Tanzania, near the Kenya border. Its central cone, Kibo, rises to 19,340 feet (5,895 metres) and is the highest point in Africa. Kilimanjaro lies about 100 miles (160 km) east of the East African Rift System and about 140 miles (225 km) south of Nairobi, Kenya. The massif extends approximately east-west for 50 miles (80 km) and consists of three principal extinct volcanoes: Kibo (centre), Mawensi (east), and Shira (west). Kibo, the youngest and highest, retains the form of a typical volcanic cone and crater and is linked by a 7-mile (11-km) saddle at about 15,000 feet (4,500 metres) with Mawensi (16,893 feet [5,149 metres]), which is the older core of a former summit. Shira ridge (13,000 feet [3,962 metres]) is a remnant of an earlier crater. Below the saddle, Kilimanjaro slopes in a typical volcanic curve to the plains below, which lie at an elevation of about 3,300 feet (1,000 metres). The breathtaking snow-clad dome of Kibo contains a caldera (crater) on its southern side that is 1.2 miles (2 km) across and some 980 feet (300 metres) deep, with an inner cone that displays residual volcanic activity. Mawensi’s cone is highly eroded, jagged, and precipitous and is cleft east and west by gorges. Only Kibo retains a permanent ice cap. Mawensi has semipermanent ice patches and substantial seasonal snow.

The mountain and its surrounding forests were designated a game reserve in the early part of the 20th century. In 1973 Mount Kilimanjaro National Park was established to protect the mountain above the tree line as well as the six forest corridors that extend downslope through the montane forest belt. The park was designated a UNESCO World Heritage site in 1987.

Kilimanjaro has a succession of vegetation zones consisting of (from base to summit) the semiarid scrub of the surrounding plateau; the massif’s cultivated, well-watered southern slopes; dense cloud forest; open moorland; alpine desert; and moss and lichen communities. Two notable species that grow in the moorlands are the giant lobelia (Lobelia deckenii) and the giant groundsel (Senecio johnstonii cottonii). The forests of the southern slopes and surrounding areas are home to elephants, buffalo, and eland (oxlike antelopes). Smaller mammals inhabiting the forests include black and white colobus monkeys, blue monkeys, and bushbuck and duikers (small African antelopes). The forests also host a rich variety of birdlife, including the rare Abbot’s starling.

The Kilimanjaro formations became known to Europeans when they were reached in 1848 by the German missionaries Johannes Rebmann and Johann Ludwig Krapf, although the news that there were snow-capped mountains so close to the Equator was not believed until more than a decade later. The Kibo summit was first reached in 1889 by the German geographer Hans Meyer and the Austrian mountaineer Ludwig Purtscheller. The Kilimanjaro region is one of Tanzania’s leading producers of mild coffee, barley, wheat, and sugar; other crops include sisal, corn (maize), beans, bananas, wattle bark (Acacia), cotton, pyrethrum, and potatoes. The region is populated by the Chaga (Chagga), Pare, Kahe, and Mbugu peoples. The town of Moshi, at the southern foot of Kilimanjaro, is the chief trading centre and base for ascent. As Kibo’s peak can be reached without the aid of mountaineering equipment, thousands of hikers attempt the ascent each year.

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Jai Ganesh · 2020-04-18 00:57:04

525) Conveyor

Conveyor, any of various devices that provide mechanized movement of material, as in a factory; they are used principally in industrial applications but also on large farms, in warehousing and freight-handling, and in movement of raw materials. Conveyors may be only a few inches in length, or they may be integrated systems several miles long.

Gravity-roller conveyors consist of a series of parallel rollers fastened to a metal frame supported at intervals. The frame can be inclined slightly for gravity flow, but objects and packages may also be rolled along manually. Gravity-wheel conveyors are similar but consist of skate wheels instead of rollers and are usually used for lighter loads. Live-roller conveyors are gravity-roller conveyors that are power driven by means of a belt snubbed against the underpart of the rolls or by a chain driving sprockets attached to the rolls.

Belt conveyors of fabric, rubber, plastic, leather, or metal are driven by a power-operated roll mounted underneath or at one end of the conveyor. The belt forms a continuous loop and is supported either on rollers, for heavy loads, or on a metal slider pan when the load is light enough to prevent frictional drag on the belt. Electric motors operating through constant- or variable-speed reduction gears usually provide the power.

Floor conveyors use chain, cable, or other linkage mounted in or close to the floor in an endless track. They are usually designed to drag a train of four-wheeled carts around in a loop to carry large products or materials for assembly on the conveying system. Power is furnished to the chain by guiding rollers.

Slat conveyors consist of endless chains, driven by electric motors operating through reduction gears and sprockets, with attached spaced slats to carry objects that would damage a belt because of sharp edges or heavy weights.

Flight conveyors have scrapers, or flights, mounted at intervals perpendicular to the direction of travel on endless power-driven chains operating within a trough. Bulk materials such as sawdust, sand, gravel, coal, and chemicals may be pushed along the trough.

Apron conveyors consist of endless chains with attached overlapping and interlocking plates to provide a continuous-carrying surface that forms a leakproof bed suitable for bulk materials without containers.

Vibrating conveyors consist of troughs or tubes flexibly supported and vibrated by mechanical or electrical means to convey objects or bulk materials; vibration takes place in an inclined, elliptical pattern to cause directional as well as upward movement of the material.

In trolley conveyors an overhead rail carries a series of load-bearing containers (trolleys) that are coupled together on an endless propelling medium such as cable, chain, or other linkage. The trolleys may be hooks, magnets, or various carriers designed for the particular load to be handled. The rails are usually supported by the framework of the plant building.

En masse conveyors use skeletal or solid flights mounted at intervals on a cable or chain power driven within a closely fitting casing. Designed for bulk materials that must be enclosed to prevent leakage or explosion, the conveyors can operate in horizontal, vertical, or inclined positions.

Bucket conveyors consist of endless chains or belts to which are attached buckets to convey bulk material in horizontal, inclined, and vertical paths. The buckets remain in carrying position until they are tipped to discharge the material. Various discharging mechanisms are available.

Screw conveyors consist of revolving shafts with continuous or broken spiral flighting that operates inside a casing. Powered by an electric motor and suitable gearing, the screw conveyor usually operates in one direction only to move fine bulk material such as meal, seed, and coal.

Pneumatic conveyors use air pressure or vacuum to move bulk material in tubes or ducts.

Tow conveyors may be overhead trolley cars or floor conveyors adapted for handling dollies, trucks, and cars, which are locked into the towing chain to be moved from any point in the system to any other point.

Various conveyors may be mounted on mobile supports, particularly gravity roller and wheel conveyors and short belt conveyors, for adaptation to portable use.

During the 1960s, air-float conveyors were introduced consisting of a platform, or pallet, equipped with air jets underneath to provide levitation. Thus supported, the platform can be easily moved in any direction over a flat surface.

Jai Ganesh · 2020-04-19 00:30:28

526) Zebra

Zebra, any of three species of strikingly black-and-white striped mammals of the horse family Equidae (genus Equus): the plains zebra (E. quagga), which is found in rich grasslands over much of eastern and southern Africa; Grevy’s zebra (E. grevyi), which lives in arid, sparsely wooded areas in Kenya and a few small areas in Ethiopia; and the mountain zebra (E. zebra), which inhabits dry upland plains in Namibia and a few scattered areas in western South Africa. The plains zebra is made up of six subspecies: E. quagga crawshaii (Crawshay’s zebra), E. quagga borensis (half-maned zebra), E. quagga boehmi (Grant’s zebra), E. quagga chapmani (Chapman’s zebra), E. quagga burchellii (Burchell’s zebra), and E. quagga quagga (quagga, which is extinct). The mountain zebra is made up of two subspecies: E. zebra hartmannae (Hartmann’s mountain zebra) and E. zebra zebra (Cape Mountain zebra).

Zebras are closely related to domestic horses. They are large single-hoofed ungulates built for speed and long-distance migrations. Zebras typically stand about 120–140 cm (47–55 inches) at the shoulder. Male Grevy’s zebras are larger than females; in the plains zebra and the mountain zebra, the males and females are nearly the same size. Zebras exhibit no other male/female dimorphism except for males having spade-shaped canines used in fighting. The teeth of all three species are adapted for grazing. Zebras possess strong upper and lower incisors for cropping grasses and large high-crowned teeth for processing silicate-rich grasses that wear down molars.

All zebras are dark-skinned animals. The zebra’s stripes arise from melanocytes (specialized skin cells) that selectively determine the pigmentation of the animal’s fur. These cells transfer melanin (a skin-darkening pigment produced by melanocytes) into some of the animal’s growing hairs. Hairs that contain melanin appear black, whereas those without melanin appear white.

The three species are easily distinguished by the pattern of their stripes. In the plains zebra the stripes are wide and widely spaced; some subspecies have lighter “shadow stripes” between the main stripes. The northern subspecies of the plains zebra are more fully striped than the southern ones, in which the striping of the lower legs tends to give way to white. The mountain zebra has smaller stripes than the plains zebra; its stripes are closely spaced on its head and shoulders but widely spaced on its haunches. The mountain zebra also has a peculiar gridlike pattern of stripes on the rump. The stripes of Grevy’s zebra are the narrowest and most closely spaced of the three species; its belly is white. Where stripes converge on the shoulders, all zebras have triangular chevrons. Grevy’s zebra is the only species with a second chevron on the rump where the stripes converge. In all zebra species, the stripes are like fingerprints, allowing scientists to easily identify individuals.

Many scientists maintain that the zebra’s stripes evolved to thwart horse fly infestation, which would have reduced the chance for disease. Indeed, there is evidence that the zebra’s stripes disrupt the horizontal pattern of polarized light reflected from dark surfaces that normally attracts horse flies. This would make the zebra’s striped fur less attractive to horse flies than the solid-coloured fur common among horses. A 2019 study of horses and captive zebras in Britain appears to support this notion; the study showed that the zebra’s black-and-white striped pattern appeared to confuse biting horse flies, which landed upon and bit zebras less frequently than they did horses.

Two types of mating systems are observed in zebras. Like the horse, the mountain and the plains zebras live in small family groups consisting of a stallion and several mares with their foals. The females that form the harem are unrelated. The harem remains intact even when the stallion leading the harem is replaced by another male. When moving, stallions usually remain in the rear but still maintain control over the movement of the herd.

In Grevy’s zebra, males are territorial. Males create dung piles, or middens, to mark territorial boundaries that typically follow physical features such as streambeds. Increased reproductive success is enjoyed by males that occupy territories through which females must pass in order to gain access to safe drinking areas or prime grazing sites. Females and bachelor males form unstable groups without any clear dominance hierarchy. Adult males and females do not form lasting bonds, but related females may occupy the same grazing areas. Grevy’s stallions maintain territories as large as 10–15 square km (4–6 square miles). However, females and bachelor male groups use annual home ranges of several thousand square kilometres. Territoriality has evolved because resources are widely scattered and easily defendable.

With plentiful food, small groups may coalesce into large herds, but the smaller groups still retain their identities. Zebras often form mixed herds with other mammals such as wildebeests and giraffes, which gain protection from predators by the alertness of the zebras. Zebras with young colts avoid predators such as hyenas by forming a cluster around the mother and young rather than bolting. A stallion will attack hyenas and wild dogs if his harem is threatened. Unless hyenas hunt in large groups, their attacks on zebras are often unsuccessful.

Available surface water is a critical need of zebras during the hot dry season. Both Grevy’s and mountain zebras excavate pits in dry streambeds to obtain subsurface water, and they defend these waterholes against strangers. After these species have moved on, the drinking holes are used by other animals such as oryxes, springboks, plains zebras, kudus, giraffes, hyenas, and lions.

Like other perissodactyls, zebras digest their food in the cecum, a blind sac at the far end of the small intestine where complex compounds such as cellulose are acted upon by symbiotic bacteria. Cecal digestion is less efficient for digesting grasses than ruminant digestion, but zebras compensate by ingesting more forage than do ruminants. This forage often includes grass stems and leaves too high in fibre or low in protein for ruminants to digest effectively and meet metabolic needs. Food travels rapidly through the cecum, and forage passes faster through a zebra than, for example, a wildebeest. Thus, even though zebras are less efficient than wildebeests in extracting protein from their food, they can extract more protein from low-quality grasses because of their faster rate of digestion and assimilation. The selective advantage of this approach is that zebras can subsist on range grasses unsuitable for antelope, an especially important adaptation during periods of drought or seasonal declines in forage quality. The disadvantage is that zebras must spend a considerable part of their day feeding to maintain the high rate of intake. The increased time spent foraging exposes them to greater risks of predation.

All three zebra species have decreased in abundance through human activities, and Grevy’s zebra is listed as an endangered species by the International Union for Conservation of Nature (IUCN). IUCN listed the mountain zebra as an endangered species during the 1990s and early 2000s; however, after subsequent population increases, IUCN reclassified the species as vulnerable in 2008. The plains zebra, although relatively abundant, engages in an outstanding example of an endangered behaviour pattern—large-scale migration. Protecting migration corridors of plains zebras in East Africa is therefore as much a conservation priority as efforts conducted on behalf of Grevy’s zebra.

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Jai Ganesh · 2020-04-20 00:56:43

527) Turmeric

Turmeric, (Curcuma longa), perennial herbaceous plant of the ginger family (Zingiberaceae), the tuberous rhizomes, or underground stems, of which have been used from antiquity as a condiment, a textile dye, and medically as an aromatic stimulant. Native to southern India and Indonesia, turmeric is widely cultivated on the mainland and in the islands of the Indian Ocean. In ancient times it was used as a perfume as well as a spice. The rhizome has a pepperlike aroma and a somewhat bitter warm taste and has a strong staining orange-yellow colour. It is the ingredient that colours and flavours prepared mustard and is used in curry powder, relishes, pickles, and spiced butters for vegetables, in fish and egg dishes, and with poultry, rice, and pork. In parts of Asia turmeric water is applied as a cosmetic to lend a golden glow to the complexion. Reputed to have anti-inflammatory properties, turmeric is sometimes consumed as a tea or in pill form for a variety of ailments, including arthritis and intestinal problems.

Turmeric plants reach about 1 metre (3.3 feet) in height and bear long simple leaves with long petioles (leaf stems). The leaves emerge from the branching rhizomes that lie just below the soil surface. Older rhizomes are somewhat scaly and brown in colour, while young rhizomes are pale yellow to brown-orange. The small yellow-orange flowers are borne in the axils of waxy bracts that are usually pale green or tinged with purple.

Production involves a boiling process, which is followed by exposure of the rhizomes to sunlight for five to seven days to dry. Then they are polished by hand rubbing or by rotation in a mounted drum. Dried rhizomes vary from about 2.5 to 7.5 cm (1 to 3 inches) in length. The spice is usually sold in ground form. Distillation yields 1.3 to 5.5 percent essential oil, the main components of which are turmerone and ar-turmerone. The colouring matter is curcumin, which is also an antioxidant.

Paper tinged with a tincture of turmeric, on addition of alkali, turns from yellow to reddish brown, becoming violet on drying, thus providing a test for alkalinity.

Jai Ganesh · 2020-04-21 01:04:24

528) Pearl

Pearl, concretion formed by a mollusk consisting of the same material (called nacre or mother-of-pearl) as the mollusk’s shell. It is a highly valued gemstone. Pearls are often strung into a necklace after a small hole is drilled by hand-driven or electric tools through the centre of each pearl.

Pearls are characterized by their translucence and lustre and by a delicate play of surface colour called orient. The more perfect a pearl’s shape (spherical or droplike) and the deeper its lustre, the greater its value. Only those pearls produced by mollusks whose shells are lined with mother-of-pearl (e.g., certain species of both saltwater oysters and freshwater clams) are really fine pearls; pearls from other mollusks are reddish or whitish, like porcelain, or lacking in pearly lustre. Jewelers commonly refer to saltwater pearls as Oriental pearls and to those produced by freshwater mollusks as freshwater pearls.

The chief component of the nacre that constitutes the pearl is aragonite (CaCO3). Nacre also contains a small amount of conchiolin, a hornlike organic substance (albuminoid) that is the main constituent of the mollusk’s outer shell. The shell-secreting cells of the mollusk are located in the mantle, or epithelium, of its body. When a foreign particle penetrates the mantle, the cells attach to the particle and build up more or less concentric layers of pearl around it. Irregularly shaped pearls are called baroque pearls. Pearls that grow attached to the shell are often flat on one side and are called blister pearls.

The colour of pearls varies with the mollusk and its environment. It ranges from black to white, with the rose of Indian pearls esteemed most. Other colours are cream, gray, blue, yellow, lavender, green, and mauve. All occur in delicate shades. The surface of a pearl is rough to the touch. Pearls come in a wide range of sizes. Those weighing less than 1/4 grain (1 pearl grain = 50 mg = 1/4 carat) are called seed pearls. The largest naturally occurring pearls are the baroque pearls; one such pearl is known to have weighed 1,860 grains (121 grams [about 4.3 ounces]).

The finest Oriental pearls are produced by the mohar, the Atlantic pearl oyster (Pinctada imbricata). Found in the Persian Gulf, with the richest harvest taken from the waters off the great bight that curves from the peninsula of Oman to that of Qatar, the pearls come from depths of 8 to 20 fathoms (14.6 to 36.6 metres [48 to 120 feet]). Other notable sources of fine-quality pearls include the Gulf of Mannar between India and Sri Lanka; the waters off Celebes, Indonesia; and the islands of the South Pacific. In the Americas the Gulf of California, the Gulf of Mexico, and the Pacific coast of Mexico have yielded dark-hued pearls with a metallic sheen as well as white pearls of good quality.

Freshwater mussels in the temperate zone of the Northern Hemisphere have produced pearls of great value—for example, those from the Mississippi River. Pearling is a carefully fostered industry in central Europe, and the forest streams of Bavaria, in particular, are the source of choice pearls. Freshwater pearling in China has been known from before 1000 BCE. In all pearl fisheries, however, production has declined significantly since the widespread introduction of cultured pearls.

Cultured pearl

Cultured pearl, natural but cultivated pearl produced by a mollusk after the intentional introduction of a foreign object inside the creature’s shell. The discovery that such pearls could be cultivated in freshwater mussels is said to have been made in 13th-century China, and the Chinese have been adept for hundreds of years at cultivating pearls by opening the mussel’s shell and inserting into it small pellets of mud or tiny bosses of wood, bone, or metal and returning the mussel to its bed for about three years to await the maturation of a pearl formation. Cultured pearls of China have been almost exclusively blister pearls (hemispherical pearls formed attached to the mussel’s shell), which are filled with resin and capped with a flat piece of nacre (mother-of-pearl) to become a mabe pearl or pearl doublet.

The production of whole cultured pearls was perfected by the Japanese. The research that led to the establishment of the industry was started in the 1890s by Mikimoto Kōkichi, who, after long experimentation, concluded that a very small mother-of-pearl bead introduced into the mollusk’s tissue was the most successful stimulant to pearl production. It possesses the added virtue of providing a pearl entirely of nacreous content. Cultured pearls closely approximate natural pearls. If the covering of nacre is too thin, however, it will deteriorate upon prolonged contact with the acids of the human body and eventually will reveal the mother-of-pearl matrix.

Once a shore-based activity, pearl farms now generally use a vessel as an operating platform. Immature pearl oyster shells (usually Pinctada fucata or Pteria penguin in Japan and Pinctada maxima in Australia) are reserved in barrels until maturation (2 to 3 years) and, when the shells reach certain size, are implanted with a tiny polished sphere of mother-of-pearl. The implanted oysters are suspended in wire nets from floating rafts or contained in some other way and are tended by divers until they are ready for harvesting; readiness is often determined by X-ray.

Northern Australia established its first pearl farms in the 1960s, principally with Japanese collaboration, and by the mid-1970s they were an established industry, producing pearl shell as well as pearls. Japan and Australia are the largest producers of cultured pearls, though Fiji also produces some.

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Jai Ganesh · 2020-04-22 00:53:06

529) Amber

Amber, fossil tree resin that has achieved a stable state through loss of volatile constituents and chemical change after burial in the ground. Amber has been found throughout the world, but the largest and most significant deposits occur along the shores of the Baltic Sea in sands 40,000,000 to 60,000,000 years old.

Amber occurs as irregular nodules, rods, or droplike shapes in all shades of yellow with nuances of orange, brown, and, rarely, red. Milky-white opaque varieties are called bone amber. The turbidity of some amber is caused by inclusions of many minute air bubbles. Many hundreds of species of fossil insects and plants are found as inclusions. Deeply coloured translucent to transparent amber is prized as gem material.

Modern investigative techniques are directed toward isolating and identifying as many as possible of the individual resin components and, ultimately, to establishing a genetic relationship between fossil resins and modern resin-producing trees. By means of infrared spectroscopy, Mexican (Chiapas) amber has been shown to be related to a modern leguminous tree, Hymenaea. Though in the past amber was believed to be completely amorphous, subsequent X-ray diffraction studies have revealed crystalline components in some fossil resins.

Ornamental carved objects, beads, rosaries, cigarette holders, and pipe mouthpieces are made from amber. Amberoid, or “pressed amber,” is produced by fusing together small pieces of amber under pressure. Parallel bands, or flow structure, in amberoid help to distinguish it from natural amber. Despite the introduction of numerous synthetic substitutes, the beauty of the real material has remained unexcelled.

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Jai Ganesh · 2020-04-23 00:32:02

530) Endoscopy

Endoscopy, medical examination of the interior of the body, usually through a natural body opening, by the insertion of a flexible, lighted optical shaft or open tube. Instruments used include the endoscope, a flexible tube for examination of the esophagus, stomach, and duodenum, and the bronchoscope, a flexible tube for examination of the bronchial tubes. These are passed through the mouth into the respective organs. The examinations are usually performed in a hospital or a physician’s office with local anesthesia. The colonoscope, a flexible tube used for examination of the colon, and the proctosigmoidoscope, a similar instrument used for examination of the rectum and lower colon, are passed through the anal orifice; mild sedation and pain medication are typically administered during these procedures. The cystoscope, a lighted rod, is passed through the urethra for examination of the bladder with local, spinal, or general anesthesia. Today these procedures are generally accompanied by the use of camera or video technology in order to collect images of the tissues being examined. In addition, endoscopes may be designed with digital modifications that facilitate the visualization of tissues.

Three endoscopic procedures require incisions for the introduction of the lighted shaft. The thoracoscope permits examination of the chest cavity and surface of the lungs through a small incision between the ribs. The peritoneoscope allows examination of the abdominal cavity and lower surfaces of the liver and gallbladder through a small incision in the abdominal wall. The culdoscope permits examination of the female pelvic organs through a small vaginal incision.

Fibre-optic endoscopes are pliable, highly maneuverable instruments that allow access to channels in the body that older, semirigid instruments cannot access at all or can access only at great discomfort to the patient. Composed of multiple hairlike glass rods bundled together, these instruments can be more easily bent and twisted, and the intense light enables the endoscopist to see around corners as well as forward and backward. Accessories can be added to the instrument that make it possible to obtain cell and tissue samples, excise polyps and small tumours, and remove foreign objects.

Although fibre-optic endoscopes can be used to visualize the stomach and duodenum, they are unable to reach farther into the small intestine. As a result, examination of the small intestine may require the use of wireless capsule endoscopy (video capsule endoscopy), which consists of a pill-sized camera that is swallowed. The camera transmits data to sensors that are attached to the abdomen with adhesive, and a data recorder that stores image information collected by the camera is attached to a belt worn around the waist. In most cases, the sensors and belt are worn for a period of eight hours, during which time the camera capsule obtains images of nearly the entire length of the small intestine. The images stored in the data recorder are downloaded onto a computer for analysis. The capsule eventually travels the length of the gastrointestinal tract and is excreted in a bowel movement.

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