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#2201 2024-07-04 14:02:42

Jai Ganesh
Administrator
Registered: 2005-06-28
Posts: 47,007

Re: Miscellany

2203) LDL

Gist

LDL , the "bad" cholesterol, transports cholesterol particles throughout your body. LDL cholesterol builds up in the walls of your arteries, making them hard and narrow. High-density lipoprotein (HDL). HDL , the "good" cholesterol, picks up excess cholesterol and takes it back to your liver.

Summary

Low-density lipoprotein (LDL) is one of the five major groups of lipoprotein that transport all fat molecules around the body in extracellular water. These groups, from least dense to most dense, are chylomicrons (aka ULDL by the overall density naming convention), very low-density lipoprotein (VLDL), intermediate-density lipoprotein (IDL), low-density lipoprotein (LDL) and high-density lipoprotein (HDL). LDL delivers fat molecules to cells. LDL has been associated with the progression of atherosclerosis.

Overview

Lipoproteins transfer lipids (fats) around the body in the extracellular fluid, making fats available to body cells for receptor-mediated endocytosis. Lipoproteins are complex particles composed of multiple proteins, typically 80–100 proteins per particle (organized by a single apolipoprotein B for LDL and the larger particles). A single LDL particle is about 220–275 angstroms in diameter, typically transporting 3,000 to 6,000 fat molecules per particle, and varying in size according to the number and mix of fat molecules contained within. The lipids carried include all fat molecules with cholesterol, phospholipids, and triglycerides dominant; amounts of each vary considerably.

A good clinical interpretation of blood lipid levels is that high LDL, in combination with a high amount of triglycerides, which indicates a high likelihood of the LDL being oxidised, is associated with increased risk of cardiovascular diseases.

Biochemistry

Structure

Each native LDL particle enables emulsification, i.e. surrounding the fatty acids being carried, enabling these fats to move around the body within the water outside cells. Each particle contains a single apolipoprotein B-100 molecule (Apo B-100, a protein that has 4536 amino acid residues and a mass of 514 kDa), along with 80 to 100 additional ancillary proteins. Each LDL has a highly hydrophobic core consisting of polyunsaturated fatty acid known as linoleate and hundreds to thousands (about 1500 commonly cited as an average) of esterified and unesterified cholesterol molecules. This core also carries varying numbers of triglycerides and other fats and is surrounded by a shell of phospholipids and unesterified cholesterol, as well as the single copy of Apo B-100. LDL particles are approximately 22 nm (0.00000087 in.) to 27.5 nm in diameter and have a mass of about 3 million daltons. Since LDL particles contain a variable and changing number of fatty acid molecules, there is a distribution of LDL particle mass and size. Determining the structure of LDL has been a tough task because of its heterogeneous structure. However, the structure of LDL at human body temperature in native condition, with a resolution of about 16 Angstroms using cryogenic electron microscopy, has been described in 2011.

Details

Cholesterol travels in the blood via “bad” LDL (low-density lipoprotein) and “good” HDL (high-density lipoprotein). Excess LDL cholesterol can form plaque on blood vessels, narrowing them and making it hard for blood to reach organs like the heart.

Blood cholesterol, a waxy, fat-like substance, is made by your liver. Cholesterol is essential for full-body health. It’s needed for actions such as hormone creation and digesting fatty foods.

While our bodies make all the cholesterol we need, dietary cholesterol is found in most animal foods: meat, poultry, eggs, seafood, and dairy products.

What is LDL cholesterol?

Cholesterol is carried through the blood on two types of proteins called lipoproteins. These lipoproteins include LDL (low-density lipoprotein), which is sometimes referred to as “bad” cholesterol, and HDL (high-density lipoprotein), or what is typically referred to as “good” cholesterol.

The science over “good” and “bad” cholesterol has shifted quite a bit recently, so how can you be sure that you’re not putting your health in danger? Read on for everything you need to know about LDL — backed by the most recent science.

LDL vs. HDL, good vs. bad

If cholesterol is essential for overall health, why would one type be bad?

In simple terms, if there is too much LDL cholesterol running through your blood vessels, it can, over time, start to build up on the sides of those blood vessels. This buildup is typically referred to as “plaque.”

Plaque buildup in your blood vessels can eventually cause those vessels to become narrower. The more narrow your blood vessels are, the harder it is for blood to reach your heart and other organs.

When blood flow becomes very blocked, it can cause chest pain (angina) and even a heart attack.

HDL cholesterol, on the other hand, returns cholesterol to the liver so it can be flushed from the body.

What should your LDL level be?

In general, most adults want to keep their LDL cholesterol levels in a certain rangeTrusted Source. Because a lot of other personal factors play into these numbers, it’s important to have a healthcare professional check your levels to help them create specific recommendations for you to go by.

LDL Cholesterol Level  :  Category
Less than 100mg/dL  :  Recommended
100-129mg/dL  :  Slightly above recommended
130-159 mg/dL  :  Borderline high
160-189 mg/dL  :  High
190 mg/dL and above    Very high

Dangers of high cholesterol

If you have high LDL (bad) cholesterol, you may not even know it, because there are typically no symptoms associated with this issue. This is why routine blood work is so important.

If you have extremely high LDL levels, you may notice little bumps on your skin called xanthomas or gray-white rings around the corneas of your eye called corneal arcus.

High LDL complications

Besides heart attack, there are other serious complications of not treating “bad” cholesterol.

* atherosclerosis, which is plaque buildup throughout the body
* carotid artery disease
* coronary heart disease
* peripheral artery disease
* stroke
* sudden cardiac arrest

Certain individuals may need medication or surgery due to complications of long-term high cholesterol.

LDL diagnosis

The best way to find out if you have too much LDL cholesterol is having your doctor order a blood test that checks your levels. Your doctor will also request and review your family history, as high cholesterol can sometimes be hereditary.

The test your doctor will likely order is called a lipid panel. This panel shows your LDL, HDL, and other types of non-HDL cholesterol that can raise your risk of complications.

You will be diagnosed with “high cholesterol” if your non-HDL cholesterol level is higher than what your doctor thinks is ideal for you. Your doctor will also review your lab tests to see if your HDL, the healthy cholesterol, is too low.

There may be follow-up tests and visits if your doctor is concerned that you may need medication or further intervention.

How common is high cholesterol?

According to the Centers for Disease Control and Prevention (CDC), between 2015 and 2016, more than 12 percent of adults ages 20 and older had total cholesterol levels higher than 240 mg/dL, which is quite high. About 7 percent of U.S. children and adolescents ages 6 to 19 were also found to have high cholesterol.

While it’s known that individuals living with high cholesterol are at an elevated risk of developing heart disease, new research suggests that individuals living with moderately high cholesterol for a long time, who also have higher blood pressure, may have the same risk of heart disease as those who have high cholesterol for only a short period of time.

Who needs to get checked?

Everyone should get their cholesterol checked, starting at age 20 and then every 4 to 6 years after that if their risk remains low.

After age 40, your doctor may want to check your levels more often. Typically, people assigned male at birth who are ages 45 to 65, along with people assigned female at birth who are ages 55 to 65, should have their cholesterol checked every 1 to 2 years.

Risk factors for high cholesterol

Everyone’s risk for high cholesterol goes up with age. This is because the older we get, the harder it becomes for our bodies to filter out cholesterol.

A family history of high cholesterol can also increase risk.

While it’s impossible to control aging and family history, there are some behaviors that increase the risk of developing high cholesterol that can be changed

Individuals living with obesity and type 2 diabetes are more at risk for an increase in bad cholesterol and a dip in good cholesterol.

It’s important to work with your doctor, who can provide support and resources, to help you adhere to their recommendations on how to lower your risk. Recommendations may include losing excess weight and focusing on finding what works best for you in managing your diabetes.

Other behaviors that may put you at a higher risk include:

* smoking, which can damage blood vessels and may lower good cholesterol
* eating a diet high in saturated and trans fat, which includes foods like fatty meats and dairy-based desserts
* not getting enough physical movement throughout the week (2 hours and 30 minutes of moderate-intensity exercise per week is recommended)
* drinking an excess of alcohol

The composition of LDL cholesterol: Why it matters

While it was traditionally thought that high LDL cholesterol as a whole was “bad” and a predictor of heart disease complications, new research, including a 2019 study from Ohio University, suggests that the real predictor of complications may be a particular subclass of LDL.

LDL is comprised of three subclasses of low-density lipoproteins, A, B, and I. According to researchers, one subclass — subclass B — was found to be the most damaging and a much better predictor of potential heart attacks than the total measurement of LDL.

While this type of research is new and evolving, if you are concerned about your LDL numbers and the possibility of complications, talk with your doctor.

How to lower LDL cholesterol

If you’ve been diagnosed with high LDL, the good news is that there are ways to lower it to a healthier range.

If your doctor is concerned about your LDL levels, they may prescribe medication, such as:

* Statins. Statins are the most commonly prescribed medication for high cholesterol. They have been shown to lower the risk of heart attack and stroke in individuals with high LDL
* Ezetimibe. These medications are sometimes prescribed if statins are not effective.
* Bile acid sequestrants. These medications are prescribed if an individual cannot take statins, or if their cholesterol levels need to be lowered more than statins alone can do.
* PCSK9 inhibitors. PCSK9 inhibitors are injected into the skin every couple of weeks and are prescribed when someone is at an unusually high risk for complications
* Lomitapide and Mipomersen. These drugs are typically prescribed for individuals who have a family history of high cholesterol.

Each drug has its own side effects, so it’s important to talk with your doctor about why they’re prescribing a specific medication and what the possible side effects might be.

Your doctor will also likely recommend specific lifestyle changes regardless of whether you’re prescribed medication.

Lifestyle changes

If your lipid test shows high or borderline-high LDL levels, your doctor will most likely recommend some lifestyle changes that can make a positive impact on your cholesterol as a whole based on your specific situation.

Increase physical activity

Regular physical activity can help lower both your cholesterol and blood pressure levels, and may even help you lose excess weight (if that’s something your doctor has advised or it’s simply a personal goal). Moderate exercise, which can be anything from brisk walking to riding a bike, for a few hours a week is helpful.

Eat a heart-healthy diet

Focusing on the things you can eat on a heart-healthy diet, instead of focusing on things you should not eat, can make this lifestyle change seem less daunting. When you’re eating for heart health and to lower cholesterol, it’s a great idea to focus on:

* lean meats
* seafood
* fat-free or low fat milk, cheese, and yogurt
* whole grains
* fruits and vegetables

Eating foods that are naturally high in fiber, like oatmeal and beans, as well as unsaturated fats, like olive oil, avocados, and nuts, are also good choices when you’re eating for heart health.

Talking with a dietician is a great way to make sure your new diet includes all the essential nutrients and vitamins you need to stay healthy and energized.

Limit alcohol

Drinking too much alcohol can raise triglycerides. When you combine elevated triglycerides with high LDL cholesterol levels, it can increase your risk for heart attack and stroke. Limiting your alcohol intake, or cutting it out entirely, can help your body recover.

Quit smoking

Smoking is difficult on your body in a number of ways, including aiding LDLs in creating narrower blood vessels. If you smoke, consider quitting. Talk with your doctor about cessation programs and other supportive resources that can help you begin the process of quitting smoking.

Outlook

Getting your cholesterol levels checked, especially if you have a family history of high cholesterol, is an essential part of staying informed about your health. If you’re younger than age 40, you may only need to get it checked every few years, but your doctor will help you decide what’s best.

If you see high LDL levels on your lipid test, remember you’re not alone. Over 93 million U.S. adults ages 20 and older have what would be considered high cholesterol. And there are many ways to treat elevated “bad” cholesterol levels, from medication to lifestyle changes.

Taking a proactive approach to lowering your cholesterol is also a positive step toward increasing your overall health — so it’s a win-win situation.

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It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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#2202 2024-07-05 14:09:51

Jai Ganesh
Administrator
Registered: 2005-06-28
Posts: 47,007

Re: Miscellany

2204) HDL

Gist

High-density lipoprotein (HDL) cholesterol is known as the "good" cholesterol because it helps remove other forms of cholesterol from your bloodstream. Higher levels of HDL cholesterol are associated with a lower risk of heart disease.

Summary

High-density lipoprotein (HDL) is one of the five major groups of lipoproteins. Lipoproteins are complex particles composed of multiple proteins which transport all fat molecules (lipids) around the body within the water outside cells. They are typically composed of 80–100 proteins per particle (organized by one, two or three ApoA). HDL particles enlarge while circulating in the blood, aggregating more fat molecules and transporting up to hundreds of fat molecules per particle.

Overview

Lipoproteins are divided into five subgroups, by density/size (an inverse relationship), which also correlates with function and incidence of cardiovascular events. Unlike the larger lipoprotein particles, which deliver fat molecules to cells, HDL particles remove fat molecules from cells. The lipids carried include cholesterol, phospholipids, and triglycerides, amounts of each are variable.

Increasing concentrations of HDL particles are associated with decreasing accumulation of atherosclerosis within the walls of arteries, reducing the risk of sudden plaque ruptures, cardiovascular disease, stroke and other vascular diseases. HDL particles are commonly referred to as "good cholesterol", because they transport fat molecules out of artery walls, reduce macrophage accumulation, and thus help prevent or even regress atherosclerosis. Higher HDL-C may not necessarily be protective against cardiovascular disease and may even be harmful in extremely high quantities, with an increased cardiovascular risk, especially in hypertensive patients.

Testing

Because of the high cost of directly measuring HDL and LDL (low-density lipoprotein) protein particles, blood tests are commonly performed for the surrogate value, HDL-C, i.e. the cholesterol associated with ApoA-1/HDL particles. In healthy individuals, about 30% of blood cholesterol, along with other fats, is carried by HDL. This is often contrasted with the amount of cholesterol estimated to be carried within low-density lipoprotein particles, LDL, and called LDL-C. HDL particles remove fats and cholesterol from cells, including within artery wall atheroma, and transport it back to the liver for excretion or re-utilization; thus the cholesterol carried within HDL particles (HDL-C) is sometimes called "good cholesterol" (despite being the same as cholesterol in LDL particles). Those with higher levels of HDL-C tend to have fewer problems with cardiovascular diseases, while those with low HDL-C cholesterol levels (especially less than 40 mg/dL or about 1 mmol/L) have increased rates for heart disease. Higher native HDL levels are correlated with lowered risk of cardiovascular disease in healthy people.

The remainder of the serum cholesterol after subtracting the HDL is the non-HDL cholesterol. The concentration of these other components, which may cause atheroma, is known as the non-HDL-C. This is now preferred to LDL-C as a secondary marker as it has been shown to be a better predictor and it is more easily calculated.

Details

In the blood, cholesterol is transported by lipoproteins known as high-density lipoprotein (HDL) and low-density lipoprotein (LDL). HDL takes cholesterol to the liver for release, while LDL brings it to the arteries. You want to aim for high HDL and low LDL levels.

Your body needs cholesterol to function properly, including making hormones and vitamin D, and supporting digestion.

Your liver generates enough cholesterol to handle these tasks, but your body doesn’t just get cholesterol this way.

Food is the main source of cholesterol, especially meat and dairy. If you eat a lot of these foods and have risk factors, your cholesterol levels may become elevated over time.

Lipoproteins are made of fat and proteins. They serve as carriers for cholesterol to move through your body.

HDL is popularly known as “good cholesterol” because it collects other types of cholesterol from the body and transports them to the liver to be released from the body.

LDL transports large amounts of cholesterol to the arteries for cell repair. Often called “bad cholesterol” because when it occurs in excess, it can build up in artery walls.

Too much cholesterol in the arteries may lead to a buildup of plaque known as atherosclerosis, which can increase the risk of blood clots.

If a blood clot breaks away and blocks an artery in your heart or brain, you may have a stroke or heart attack.

Plaque buildup may also reduce blood flow and oxygen to major organs. Oxygen deprivation to your organs or arteries may lead to other complications, like kidney disease or peripheral arterial disease.

Optimal levels of HDL can protect your body from LDL. HDL helps rid the body of excess LDL cholesterol, making it less likely to end up in the arteries.

Lifestyle factors are the main factor in cholesterol levels. You may have higher LDL levels and lower HDL levels if you:

* have obesity
* follow a diet high in red meat, full-fat dairy products, saturated fats, trans fats, and processed foods
* have a large waist circumference (over 40 inches for males or over 35 inches for females)
* do not engage in regular physical activity and exercise
* use tobacco

In some cases, high LDL is inherited. This condition is called familial hypercholesterolemia (FH). FH is caused by a genetic mutation that affects the ability of a person’s liver to get rid of extra LDL cholesterol.

This may lead to high LDL levels and an increased risk of heart attack and stroke at a young age.

Know your numbers

You may not even know if you have high cholesterol because it doesn’t cause noticeable symptoms.

The only way to find out your cholesterol levels is through a blood test that measures cholesterol in milligrams per deciliter of blood (mg/dL).

When you get your cholesterol numbers checked, you may receive results for:

* Triglycerides: This number may vary per laboratory, but it should usually be below 150 mg/dL. Triglycerides are a common type of fat. If your triglycerides are high, your LDL is also high, or your HDL is low, your risk of developing atherosclerosis may be elevated.
* HDL: The higher this number, the better. It should be at least higher than 50 mg/dL for females and 40 mg/dL for males.
* LDL: The lower this number, the better. Experts recommend LDL to be no more than 130 mg/dL if you don’t have a history of heart disease, blood vessel disease, or diabetes. If you do have a history of these conditions, LDL should be no more than 70 mg/dL or 55 mg/dL if a doctor believes you are at an increased risk.
* Total blood cholesterol: This includes your HDL, LDL, and 20% of your total triglycerides, and it should be within the normal range your laboratory sets.

How to manage suboptimal cholesterol levels

Experts often recommend lifestyle changes to manage high LDL and total cholesterol levels, including:

* eating a balanced, nutritious diet
* exercising regularly and moving more throughout the day
* managing stress
* maintaining the recommended weight for your age and height
* ceasing to use tobacco, if you smoke

Sometimes lifestyle changes aren’t enough, especially if you have FH. You may need ongoing management with one or more cholesterol-lowering medications, such as:

* statins to help your liver get rid of cholesterol
* bile-acid binding medications to help your body use extra cholesterol to produce bile
* cholesterol absorption inhibitors to prevent your small intestines from absorbing cholesterol and releasing it into your bloodstream
* injectable medications that cause your liver to absorb more LDL cholesterol

Medications and supplements to reduce triglyceride levels may also be used, such as omega-3 fatty acids and fibrates.

The takeaway

LDL refers to a low-density protein that carries cholesterol to the arteries. If there’s too much LDL cholesterol, you may have a higher risk of heart disease and stroke.

HDL is a high-density protein that collects cholesterol from the body and takes it to the liver for removal. Optimal levels of HDL help the body get rid of LDL cholesterol, so the higher your HDL, the better.

A blood test can let you know how much LDL and HDL you have, and a doctor can advise on the next steps if you have high cholesterol.

Generalized-structure-of-spherical-HDL-High-density-lipoproteins-particles-consist-of-a.jpg


It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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#2203 2024-07-06 14:05:26

Jai Ganesh
Administrator
Registered: 2005-06-28
Posts: 47,007

Re: Miscellany

2205) Spectrometer

Gist

A spectrometer is a scientific instrument used to separate and measure spectral components of a physical phenomenon. Spectrometer is a broad term often used to describe instruments that measure a continuous variable of a phenomenon where the spectral components are somehow mixed.

Summary

Spectrometer, Device for detecting and analyzing wavelengths of electromagnetic radiation, commonly used for molecular spectroscopy; more broadly, any of various instruments in which an emission (as of electromagnetic radiation or particles) is spread out according to some property (as energy or mass) into a spectrum and measurements are made at points or regions along the spectrum. As used in traditional laboratory analysis, a spectrometer includes a radiation source and detection and analysis equipment. Emission spectrometers excite molecules of a sample to higher energy states and analyze the radiation emitted when they decay to the original energy state. Absorption spectrometers pass radiation of known wavelength through a sample, varying the wavelengths to produce a spectrum of results; the detector system reveals to what extent each wavelength is absorbed. Fourier-transform spectrometers resemble absorption spectrometers but use a broad band of radiation; a computer analyzes the output to find the absorption spectrum. Different designs allow study of various kinds of samples over many frequencies, at different temperatures or pressures, or in an electric or magnetic field. Mass spectrometers spread out the atomic or molecular components in a sample according to their masses and then detect the sorted components.

Details

A spectrometer is a scientific instrument used to separate and measure spectral components of a physical phenomenon. Spectrometer is a broad term often used to describe instruments that measure a continuous variable of a phenomenon where the spectral components are somehow mixed. In visible light a spectrometer can separate white light and measure individual narrow bands of color, called a spectrum. A mass spectrometer measures the spectrum of the masses of the atoms or molecules present in a gas. The first spectrometers were used to split light into an array of separate colors. Spectrometers were developed in early studies of physics, astronomy, and chemistry. The capability of spectroscopy to determine chemical composition drove its advancement and continues to be one of its primary uses. Spectrometers are used in astronomy to analyze the chemical composition of stars and planets, and spectrometers gather data on the origin of the universe.

Examples of spectrometers are devices that separate particles, atoms, and molecules by their mass, momentum, or energy. These types of spectrometers are used in chemical analysis and particle physics.

Types of spectrometer

Optical spectrometers or optical emission spectrometer

Optical absorption spectrometers

Optical spectrometers (often simply called "spectrometers"), in particular, show the intensity of light as a function of wavelength or of frequency. The different wavelengths of light are separated by refraction in a prism or by diffraction by a diffraction grating. Ultraviolet–visible spectroscopy is an example.

These spectrometers utilize the phenomenon of optical dispersion. The light from a source can consist of a continuous spectrum, an emission spectrum (bright lines), or an absorption spectrum (dark lines). Because each element leaves its spectral signature in the pattern of lines observed, a spectral analysis can reveal the composition of the object being analyzed.

A spectrometer that is calibrated for measurement of the incident optical power is called a spectroradiometer. [2]

Optical emission spectrometers

Optical emission spectrometers (often called "OES or spark discharge spectrometers"), is used to evaluate metals to determine the chemical composition with very high accuracy. A spark is applied through a high voltage on the surface which vaporizes particles into a plasma. The particles and ions then emit radiation that is measured by detectors (photomultiplier tubes) at different characteristic wavelengths.

Electron spectroscopy

Some forms of spectroscopy involve analysis of electron energy rather than photon energy. X-ray photoelectron spectroscopy is an example.

Mass spectrometer

A mass spectrometer is an analytical instrument that is used to identify the amount and type of chemicals present in a sample by measuring the mass-to-charge ratio and abundance of gas-phase ions.

Time-of-flight spectrometer

The energy spectrum of particles of known mass can also be measured by determining the time of flight between two detectors (and hence, the velocity) in a time-of-flight spectrometer. Alternatively, if the particle-energy is known, masses can be determined in a time-of-flight mass spectrometer.

Magnetic spectrometer

When a fast charged particle (charge q, mass m) enters a constant magnetic field B at right angles, it is deflected into a circular path of radius r, due to the Lorentz force. The momentum p of the particle is then given by

,

where m and v are mass and velocity of the particle. The focusing principle of the oldest and simplest magnetic spectrometer, the semicircular spectrometer, invented by J. K. Danisz, is shown on the left. A constant magnetic field is perpendicular to the page. Charged particles of momentum p that pass the slit are deflected into circular paths of radius r = p/qB. It turns out that they all hit the horizontal line at nearly the same place, the focus; here a particle counter should be placed. Varying B, this makes possible to measure the energy spectrum of alpha particles in an alpha particle spectrometer, of beta particles in a beta particle spectrometer, of particles (e.g., fast ions) in a particle spectrometer, or to measure the relative content of the various masses in a mass spectrometer.

Since Danysz' time, many types of magnetic spectrometers more complicated than the semicircular type have been devised.

Resolution

Generally, the resolution of an instrument tells us how well two close-lying energies (or wavelengths, or frequencies, or masses) can be resolved. Generally, for an instrument with mechanical slits, higher resolution will mean lower intensity.

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It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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#2204 2024-07-07 14:20:31

Jai Ganesh
Administrator
Registered: 2005-06-28
Posts: 47,007

Re: Miscellany

2206) Spirit lamp

Gist

An alcohol burner or spirit lamp is a piece of laboratory equipment used to produce an open flame. It can be made from brass, glass, stainless steel or aluminium.

Spirit lamps are often used for heating small test tubes, performing flame tests, and for simple chemistry experiments. They are also commonly used in medical settings for heating surgical instruments and for sterilizing small equipment.

Details

An alcohol burner or spirit lamp is a piece of laboratory equipment used to produce an open flame. It can be made from brass, glass, stainless steel or aluminium.

Uses

Alcohol burners are preferred for some uses over Bunsen burners for safety purposes, and in laboratories where natural gas is not available. Their flame is limited to approximately 5 centimeters (two inches) in height, with a comparatively lower temperature than the gas flame of the Bunsen burner.

While they do not produce flames as hot as other types of burners, they are sufficiently hot for performing some chemistries, standard microbiology laboratory procedures, and can be used for flame sterilization of other laboratory equipment.

A small alcohol burner is also preferred for camping when the need for fire is modest. It burns the alcohol vapor that rises due to the heat from the flame through the holes on the top perimeter of the container.

Operation

Typical fuel is denatured alcohol, methanol, or isopropanol. A cap is used as a snuffer for extinguishing the flame.

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It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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#2205 2024-07-07 22:11:07

Jai Ganesh
Administrator
Registered: 2005-06-28
Posts: 47,007

Re: Miscellany

2207) Rib cage

Gist

The rib cage consists of 24 ribs (2 sets of 12), which are attached to a long, flat bone in the centre of the chest called the sternum. The ribs are connected to the sternum with a strong, somewhat flexible material called cartilage.

Summary

Rib cage, in vertebrate anatomy, basketlike skeletal structure that forms the chest, or thorax, and is made up of the ribs and their corresponding attachments to the sternum (breastbone) and the vertebral column. The rib cage surrounds the lungs and the heart, serving as an important means of bony protection for these vital organs.In total, the rib cage consists of the 12 thoracic vertebrae and the 24 ribs, in addition to the sternum. With each succeeding rib, from the first, or uppermost, the curvature of the rib cage becomes more open. The rib cage is semirigid but expansile, able to increase in size. The small joints between the ribs and the vertebrae permit a gliding motion of the ribs on the vertebrae during breathing and other activities.

The first seven ribs in the rib cage are attached to the sternum by pliable cartilages called costal cartilages; these ribs are called true ribs. Of the remaining five ribs, which are called false, the first three have their costal cartilages connected to the cartilage above them. The last two, the floating ribs, have their cartilages ending in the muscle in the abdominal wall. The configuration of the lower five ribs gives freedom for the expansion of the lower part of the rib cage and for the movements of the diaphragm, which has an extensive origin from the rib cage and the vertebral column. The motion is limited by the ligamentous attachments between ribs and vertebrae.

Details

The rib cage or thoracic cage is an endoskeletal enclosure in the thorax of most vertebrates that comprises the ribs, vertebral column and sternum, which protect the vital organs of the thoracic cavity, such as the heart, lungs and great vessels and support the shoulder girdle to form the core part of the axial skeleton.

A typical human thoracic cage consists of 12 pairs of ribs and the adjoining costal cartilages, the sternum (along with the manubrium and xiphoid process), and the 12 thoracic vertebrae articulating with the ribs. The thoracic cage also provides attachments for extrinsic skeletal muscles of the neck, upper limbs, upper abdomen and back, and together with the overlying skin and associated fascia and muscles, makes up the thoracic wall.

In tetrapods, the rib cage intrinsically holds the muscles of respiration (diaphragm, intercostal muscles, etc.) that are crucial for active inhalation and forced exhalation, and therefore has a major ventilatory function in the respiratory system.

Structure

There are thirty-three vertebrae in the human vertebral column. The rib cage is associated with TH1−TH12. Ribs are described based on their location and connection with the sternum. All ribs are attached posteriorly to the thoracic vertebrae and are numbered accordingly one to twelve. Ribs that articulate directly with the sternum are called true ribs, whereas those that do not articulate directly are termed false ribs. The false ribs include the floating ribs (eleven and twelve) that are not attached to the sternum at all.

Attachment

The terms true ribs and false ribs describe rib pairs that are directly or indirectly attached to the sternum respectively. The first seven rib pairs known as the fixed or vertebrosternal ribs are the true ribs (Latin: costae verae) as they connect directly to the sternum via their own individual costal cartilages. The next five pairs (eighth to twelfth) are the false ribs (Latin: costae spuriae) or vertebrochondral ribs, which do not connect directly to the sternum. The first three pairs of vertebrochondral ribs (eighth to tenth) connect indirectly to the sternum via the costal cartilages of the ribs above them, and the overall elasticity of their articulations allows the bucket handle movements of the rib cage essential for respiratory activity.

The phrase floating rib (Latin: costae fluctuantes) or vertebral rib refers to the two lowermost (the eleventh and twelfth) rib pairs; so-called because they are attached only to the vertebrae and not to the sternum or any of the costal cartilages. These ribs are relatively small and delicate, and include a cartilaginous tip.

The spaces between the ribs are known as intercostal spaces; they contain the instrinsic intercostal muscles and the neurovascular bundles containing intercostal nerves, arteries and veins. The superficial surface of the rib cage is covered by the thoracolumbar fascia, which provides external attachments for the neck, back, pectoral and abdominal muscles.

Parts of rib

Each rib consists of a head, neck, and a shaft. All ribs are attached posteriorly to the thoracic vertebrae. They are numbered to match the vertebrae they attach to – one to twelve, from top (T1) to bottom. The head of the rib is the end part closest to the vertebra with which it articulates. It is marked by a kidney-shaped articular surface which is divided by a horizontal crest into two articulating regions. The upper region articulates with the inferior costal facet on the vertebra above, and the larger region articulates with the superior costal facet on the vertebra with the same number. The transverse process of a thoracic vertebra also articulates at the transverse costal facet with the tubercle of the rib of the same number. The crest gives attachment to the intra-articular ligament.

The neck of the rib is the flattened part that extends laterally from the head. The neck is about 3 cm long. Its anterior surface is flat and smooth, whilst its posterior is perforated by numerous foramina and its surface rough, to give attachment to the ligament of the neck. Its upper border presents a rough crest (crista colli costae) for the attachment of the anterior costotransverse ligament; its lower border is rounded.

On the posterior surface at the neck, is an eminence—the tubercle that consists of an articular and a non-articular portion. The articular portion is the lower and more medial of the two and presents a small, oval surface for articulation with the transverse costal facet on the end of the transverse process of the lower of the two vertebrae to which the head is connected. The non-articular portion is a rough elevation and affords attachment to the ligament of the tubercle. The tubercle is much more prominent in the upper ribs than in the lower ribs.

The angle of a rib (costal angle) may both refer to the bending part of it, and a prominent line in this area, a little in front of the tubercle. This line is directed downward and laterally; this gives attachment to a tendon of the iliocostalis muscle. At this point, the rib is bent in two directions, and at the same time twisted on its long axis.

The distance between the angle and the tubercle is progressively greater from the second to the tenth ribs. The area between the angle and the tubercle is rounded, rough, and irregular, and serves for the attachment of the longissimus dorsi muscle.

Bones:

Ribs and vertebrae

The first rib (the topmost one) is the most curved and usually the shortest of all the ribs; it is broad and flat, its surfaces looking upward and downward, and its borders inward and outward.

The head is small and rounded, and possesses only a single articular facet, for articulation with the body of the first thoracic vertebra. The neck is narrow and rounded. The tubercle, thick and prominent, is placed on the outer border. It bears a small facet for articulation with the transverse costal facet on the transverse process of T1. There is no angle, but at the tubercle, the rib is slightly bent, with the convexity upward, so that the head of the bone is directed downward. The upper surface of the body is marked by two shallow grooves, separated from each other by a slight ridge prolonged internally into a tubercle, the scalene tubercle, for the attachment of the anterior scalene; the anterior groove transmits the subclavian vein, the posterior the subclavian artery and the lowest trunk of the brachial plexus. Behind the posterior groove is a rough area for the attachment of the medial scalene. The under surface is smooth and without a costal groove. The outer border is convex, thick, and rounded, and at its posterior part gives attachment to the first digitation of the serratus anterior. The inner border is concave, thin, and sharp, and marked about its center by the scalene tubercle. The anterior extremity is larger and thicker than that of any of the other ribs.

The second rib is the second uppermost rib in humans or second most frontal in animals that walk on four limbs. In humans, the second rib is defined as a true rib since it connects with the sternum through the intervention of the costal cartilage anteriorly (at the front). Posteriorly, the second rib is connected with the vertebral column by the second thoracic vertebra. The second rib is much longer than the first rib, but has a very similar curvature. The non-articular portion of the tubercle is occasionally only feebly marked. The angle is slight and situated close to the tubercle. The body is not twisted so that both ends touch any plane surface upon which it may be laid; but there is a bend, with its convexity upward, similar to, though smaller than that found in the first rib. The body is not flattened horizontally like that of the first rib. Its external surface is convex, and looks upward and a little outward; near the middle of it is a rough eminence for the origin of the lower part of the first and the whole of the second digitation of the serratus anterior; behind and above this is attached the posterior scalene. The internal surface, smooth, and concave, is directed downward and a little inward: on its posterior part there is a short costal groove between the ridge of the internal surface of the rib and the inferior border. It protects the intercostal space containing the intercostal veins, intercostal arteries, and intercostal nerves.

The ninth rib has a frontal part at the same level as the first lumbar vertebra. This level is called the transpyloric plane, since the pylorus is also at this level.

The tenth rib attaches directly to the body of vertebra T10 instead of between vertebrae like the second through ninth ribs. Due to this direct attachment, vertebra T10 has a complete costal facet on its body.

The eleventh and twelfth ribs, the floating ribs, have a single articular facet on the head, which is of rather large size. They have no necks or tubercles, and are pointed at their anterior ends. The eleventh has a slight angle and a shallow costal groove, whereas the twelfth does not. The twelfth rib is much shorter than the eleventh rib, and only has a one articular facet.

Sternum

The sternum is a long, flat bone that forms the front of the rib cage. The cartilages of the top seven ribs (the true ribs) join with the sternum at the sternocostal joints. The costal cartilage of the second rib articulates with the sternum at the sternal angle making it easy to locate.

The manubrium is the wider, superior portion of the sternum. The top of the manubrium has a shallow, U-shaped border called the jugular (suprasternal) notch. The clavicular notch is the shallow depression located on either side at the superior-lateral margins of the manubrium. This is the site of the sternoclavicular joint, between the sternum and clavicle. The first ribs also attach to the manubrium.

The transversus thoracis muscle is innervated by one of the intercostal nerves and superiorly attaches at the posterior surface of the lower sternum. Its inferior attachment is the internal surface of costal cartilages two through six and works to depress the ribs.

Development

Expansion of the rib cage in males is caused by the effects of testosterone during puberty. Thus, males generally have broad shoulders and expanded chests, allowing them to inhale more air to supply their muscles with oxygen.

Variation

Variations in the number of ribs occur. About 1 in 200–500 people have an additional cervical rib, and there is a female predominance. Intrathoracic supernumerary ribs are extremely rare. The rib remnant of the 7th cervical vertebra on one or both sides is occasionally replaced by a free extra rib called a cervical rib, which can mechanically interfere with the nerves (brachial plexus) going to the arm.

In several ethnic groups, most significantly the Japanese, the tenth rib is sometimes a floating rib, as it lacks a cartilaginous connection to the seventh rib.

Function

The human rib cage is a component of the human respiratory system. It encloses the thoracic cavity, which contains the lungs. An inhalation is accomplished when the muscular diaphragm, at the floor of the thoracic cavity, contracts and flattens, while the contraction of intercostal muscles lift the rib cage up and out.

Expansion of the thoracic cavity is driven in three planes; the vertical, the anteroposterior and the transverse. The vertical plane is extended by the help of the diaphragm contracting and the abdominal muscles relaxing to accommodate the downward pressure that is supplied to the abdominal viscera by the diaphragm contracting. A greater extension can be achieved by the diaphragm itself moving down, rather than simply the domes flattening. The second plane is the anteroposterior and this is expanded by a movement known as the 'pump handle'. The downward sloping nature of the upper ribs are as such because they enable this to occur. When the external intercostal muscles contract and lift the ribs, the upper ribs are able also to push the sternum up and out. This movement increases the anteroposterior diameter of the thoracic cavity, and hence aids breathing further. The third, transverse, plane is primarily expanded by the lower ribs (some say it is the 7th to 10th ribs in particular), with the diaphragm's central tendon acting as a fixed point. When the diaphragm contracts, the ribs are able to evert (meaning turn outwards or inside out) and produce what is known as the bucket handle movement, facilitated by gliding at the costovertebral joints. In this way, the transverse diameter is expanded and the lungs can fill.

The circumference of the normal adult human rib cage expands by 3 to 5 cm during inhalation.

Clinical significance

Rib fractures are the most common injury to the rib cage. These most frequently affect the middle ribs. When several adjacent ribs incur two or more fractures each, this can result in a flail chest which is a life-threatening condition.

A dislocated rib can be painful and can be caused simply by coughing, or for example by trauma or lifting heavy weights.

One or more costal cartilages can become inflamed – a condition known as costochondritis; the resulting pain is similar to that of a heart attack.

Abnormalities of the rib cage include pectus excavatum ("sunken chest") and pectus carinatum ("pigeon chest"). A bifid rib is a bifurcated rib, split towards the sternal end, and usually just affecting one of the ribs of a pair. It is a congenital defect affecting about 1.2% of the population. It is often without symptoms though respiratory difficulties and other problems can arise.

Rib removal is the surgical removal of one or more ribs for therapeutic or cosmetic reasons.

Rib resection is the removal of part of a rib.

Regeneration

The ability of the human rib to regenerate itself has been appreciated for some time. However, the repair has only been described in a few case reports. The phenomenon is has been appreciated particularly by craniofacial surgeons, who use both cartilage and bone material from the rib for ear, jaw, face, and skull reconstruction.

The perichondrium and periosteum are fibrous sheaths of vascular connective tissue surrounding the rib cartilage and bone respectively. These tissues containing a source of progenitor stem cells that drive regeneration..

Additional Information

The rib cage is also known as the thoracic cage, and the primary rib cage function is to protect the organs inside the chest. These organs include the heart and lungs, which are two of our most important organs.

The thoracic cage bones include more than just the ribs, though. They also include the sternum and the thoracic vertebrae, where the ribs form.

Unfortunately, while the ribs protect the heart and lungs, they can become damaged for various reasons.

What Is the Rib Cage?

The rib cage is part of the axial skeleton. The average human is born with the same number of ribs regardless of gender. The ribs articulate with the thoracic vertebra. For example, the first rib, or rib 1, is the most significant and corresponds to the T1 thoracic vertebrae. Rib 2 corresponds to the T2 thoracic vertebra, rib 3 corresponds to the T3 thoracic vertebrae, and so on.

Where Is the Rib Cage?

The chest is where the rib cage is located. It surrounds the heart and lungs and is positioned posteriorly to the thoracic vertebrae. Each rib has two ends, one with various components and bumps, while the other is rounded and smooth.

How Many Ribs Do We Have?

The average person is born with 24 ribs—12 on each side. The ribs are located in the thoracic cage and thorax, along with their costal cartilages and the sternum. Each rib is made up of a few different components: the head, the neck, the tubercle, the angle, and the body.

Rib Cage Injuries and Conditions

Rib deformities occur in some babies during childbirth or due to genetic mutations inherited from one or both parents. In some cases, these deformities may happen spontaneously. This is known as de novo gene mutations. These deformities can range in severity from mild to life-threatening.

Some deformities can cause the lungs to constrict, which can cause difficulty breathing. Other deformities include:

* Extra ribs
* Missing ribs
* Short ribs
* Abnormally shaped ribs
* Ribs that have been fused

One condition relating to the ribs is called thoracic insufficiency syndrome. This occurs when the ribs are deformed, creating a small chest where healthy lungs cannot develop correctly.

Most of the time, these deformities happen due to genetic mutations. Sometimes these mutations happen as a result of genes passed down from the parents. Other times, these mutations occur on their own.

Rib deformities can happen in isolated incidents or alongside other issues. For example, patients with Down syndrome are often born with extra ribs. Sometimes, patients with Down syndrome are also born with a missing pair of ribs. In these cases, it is rare for health issues to occur.

There are also other conditions in which rib deformities appear. These include:

* Juene syndrome: This condition occurs when the chest and rib cage are abnormally small. As a result, severe breathing difficulties occur.
* Spondylocostal dysplasia: This condition is rare and occurs when abnormalities in the development of the spine and ribs occur. It is common for patients with this condition to have fused or missing ribs and an abnormally curved spine.
* Spondylothoracic dysplasia: This condition occurs when ribs are fused near the spine. In addition, vertebrae are misshapen or fused. Babies born with spondylothoracic dysplasia have small chests and severe breathing difficulties.

If rib deformities are minor, they are unlikely to cause symptoms. These deformities are usually only detected during x-rays. Children with minor deformities, such as an extra or missing rib, are unlikely to have health issues.

Symptoms of rib deformities that are more severe include:

* A chest that is narrow or smaller than normal
* A crooked chest
* Trouble breathing
* A lower abdomen that expands abnormally during inhalation

Additionally, other symptoms can happen when deformities occur alongside other conditions, such as:

* Short height
* Abnormally short legs and arms
* Shortened torso
* Rigid neck
* Scoliosis
* Extra toes or fingers

Rib deformities can be detected during pregnancy through ultrasound imaging. If ultrasounds do not detect deformities, though, x-rays may be necessary when the child is born, mainly if symptoms such as a small chest and breathing problems occur.

Genetic testing can also be done in cases where parents are concerned about inherited conditions.

Treating Rib Deformities

Treatment will vary depending on the severity and type of deformity. No health issues are present in minor cases, and treatment isn’t needed. However, if the deformity causes significant health issues such as difficulty breathing or harms the development of the lungs, your child may require breathing support. This could include intubation or a tracheotomy.

Vertical expandable prosthetic titanium rib (VEPTR) surgery may be recommended. This surgery allows your child’s rib, spine, and lungs to grow correctly and expand by implanting titanium ribs into your child’s body. This treatment will require surgical adjustment until your child’s skeletal muscles reach full maturity. Once maturity is reached, an additional surgery known as spinal fusion may be necessary.

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It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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#2206 2024-07-08 14:06:58

Jai Ganesh
Administrator
Registered: 2005-06-28
Posts: 47,007

Re: Miscellany

2208) Murphy bed

Gist

Murphy bed is a bed with a frame that can be folded into a space in a wall.

Murphy beds are used for space-saving purposes, much like trundle beds, and are popular where floor space is limited, such as small houses, apartments, hotels, mobile homes and college dormitories. In recent years, Murphy bed units have included options such as lighting, storage cabinets, and office components.

Details

A Murphy bed (also known as a pull-down bed, fold-down bed, or wall bed) is a bed that is hinged at one end to store vertically against the wall, or inside a closet or cabinet. Since they often can be used as both a bed or a closet, Murphy beds are multifunctional furniture.

History

The Murphy bed is named after William Lawrence Murphy (1876–1957), president of the Murphy Bed and Door Company.

Pre-Murphy folding beds

Under the name "bureau bedstead" the fold-up bed appeared in the 18th century, but never gained popularity. When closed, the bed looked like a bureau with fake drawers, hence the name. Gloag points to three 18th century pieces: one manufactured by Gillows of Lancaster and London in 1788, another one advertised by John Taylor in 1769, and the third one with a description published in the Prices for Cabinet Work in 1797.

Foldup beds were offered in the US through the Sears, Roebuck & Co. catalog, before Murphy's inventions.

Murphy

Murphy applied for his first patents around 1900. According to legend, he was wooing an opera singer, but living in a one-room apartment in San Francisco, and the moral code of the time frowned upon a woman entering a man's bedroom. Murphy's invention converted his bedroom into a parlor, enabling him to entertain.

Murphy introduced pivot and counterbalanced designs for which he received a series of patents, including one for a "Disappearing Bed" on June 18, 1912, and another for a "Design for a Bed" on June 27, 1916.

Murphy beds are used for space-saving purposes, much like trundle beds, and are popular where floor space is limited, such as small houses, apartments, hotels, mobile homes and college dormitories. In recent years, Murphy bed units have included options such as lighting, storage cabinets, and office components. They saw a resurgence in popularity in the early 2010s due to the weak economy, with children moving back in with their parents and families choosing to renovate homes rather than purchasing larger ones.

In 1989, the United States Court of Appeals for the Second Circuit ruled that the term "Murphy Bed" had entered common usage so thoroughly that it was no longer eligible for trademark protection.

Designs and models

Few Murphy beds have box springs. Instead, the mattress usually lies on a wood platform or wire mesh and is held in place so as not to sag when in a closed position. The mattress is attached to the bed frame, often with elastic straps to hold the mattress in position when the unit is folded upright. Pistons-lifts or torsion springs make modern Murphy beds easy to lower and raise.

Since the first model several other variations and designs have been created, including: sideways-mounted Murphy beds, Murphy bunk beds, and solutions that include other functions. Murphy beds exist with tables or desks that fold down when the bed is folded up, and there are also models with sofas and shelving solutions.

Risks

If not secured or used properly, a Murphy bed could collapse on the operator. A 1945 court case in Illinois found that a tenant assumed the risk of injury from a wall bed installed in a rented inn room. In 1982, a drunk man suffocated inside a closed Murphy bed, and two women were entrapped and suffocated by an improperly installed wall bed in 2005. A 2014 lawsuit alleged that a defective Murphy bed led to the death of a Staten Island man. In April 2022, Bestar Wall Beds of Quebec, Canada, recalled 129,000 beds in the United States and 53,000 beds in Canada after a 79-year-old woman was killed and 60 others injured by falling beds. Later that year, Cyme Tech, also of Quebec, Canada, recalled 8,200 beds after 146 reports of falling beds resulting in 62 injuries.

In popular culture

Murphy beds were a common setup for comic scenes in early cinema, including in silent films. The earliest known film to feature a Murphy bed is the lost 1900 Biograph Company film A Bulletproof Bed, which was remade in 1903 by Edison Pictures as the extant film Subub Surprises the Burglar. It was a recurrent slapstick element in many Keystone Studios productions of the 1910s, including Cursed by His Beauty (1914), Fatty's Reckless Fling (1915), He Wouldn't Stay Down (1915), and Bath Tub Perils (1916). Charlie Chaplin's 1916 One AM also features an exaggerated encounter with a Murphy bed.

Later films which use Murphy beds as comic props (often to cause injury or frustration, or to hide a clandestine guest) include Laurel and Hardy's Be Big (1930), Jimmy Stewart and Ginger Rogers's Vivacious Lady (1938), Buster Keaton's Spite Marriage (1929) and Nothing But Pleasure (1940), Abbott and Costello's Hit the Ice (1943), several Three Stooges shorts (including 1952's Corny Casanovas), It's a Mad, Mad, Mad, Mad World, the Popeye cartoon Shuteye Popeye, Bob Hope's Boy, Did I Get a Wrong Number (1966), the James Bond film You Only Live Twice, The Night They Raided Minsky's, Mel Brooks's Silent Movie, The Pink Panther Strikes Again, The Great Muppet Caper, Police Academy 2, Who Framed Roger Rabbit, Spy Hard, and Freddy vs. Jason. Murphy beds have also been used in television series; for example, an episode of Laverne and Shirley (re-creates scenes from Chaplin's One A.M.) and Love American Style ("Love and the Murphy's Bed"), Australian prime time soap opera, Number 96, and Caroline Channing's Murphy bed in 2 Broke Girls. Murphy beds were a routine enough feature of comic film to invite commentary from retailers; one store based in Vancouver, British Columbia remarked in an advertisement, "Gone are the days of Laurel and Hardy where the beds were portrayed as a fold away trap for your worst enemies."

In comics, the Murphy bed is depicted in the Tintin book Red Rackham's Treasure
as being an invention of Professor Calculus.

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It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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#2207 2024-07-09 13:28:36

Jai Ganesh
Administrator
Registered: 2005-06-28
Posts: 47,007

Re: Miscellany

2209) Bunsen burner

Gist

A Bunsen burner is a type of gas burner that is used in many chemistry procedures in a laboratory setting. It is used to heat substances, to combust substances, and to sterilize objects on high heat. Many different types of gases can be used in a burner such as methane, butane, propane, or a mixture of them.

Summary

Bunsen burner, device for combining a flammable gas with controlled amounts of air before ignition; it produces a hotter flame than would be possible using the ambient air and gas alone. Named for Robert Bunsen, the German chemist who introduced it in 1855 (from a design by Peter Desdega, who likely modified an earlier design by Michael Faraday), the Bunsen burner was the forerunner of the gas-stove burner and the gas furnace. The Bunsen burner consists of a metal tube on a base with a gas inlet at the lower end of the tube, which may have an adjusting valve; openings in the sides of the tube can be regulated by a collar to admit as much air as desired. The mixture of air and gas (optimally about 1 part gas to 3 parts air) is forced by gas pressure to the top of the tube, where it is ignited with a match. It burns with a pale blue flame, the primary flame, seen as a small inner cone, and a secondary, almost colourless flame, seen as a larger, outer cone, which results when the remaining gas is completely oxidized by the surrounding air.

The hottest part of the Bunsen flame, which is found just above the tip of the primary flame, reaches about 1,500 °C (2,700 °F). With too little air, the gas mixture will not burn completely and will form tiny carbon particles that are heated to glowing, making the flame luminous. With too much air, the flame may burn inside the burner tube; that is, it may strike back. The Meker and Fisher burners, variations of the original Bunsen burner, have metallic grids to increase the turbulence of the mixture and keep the flame at the top of the tube. The Fisher burner uses forced air. There is no secondary flame dependent on surrounding air, because these improvements introduce sufficient air for complete combustion, and the heat of the primary flame is augmented.

Details

A Bunsen burner, named after Robert Bunsen, is a kind of ambient air gas burner used as laboratory equipment; it produces a single open gas flame, and is used for heating, sterilization, and combustion.

The gas can be natural gas (which is mainly methane) or a liquefied petroleum gas, such as propane, butane, or a mixture. Combustion temperature achieved depends in part on the adiabatic flame temperature of the chosen fuel mixture.

History

In 1852, the University of Heidelberg hired Bunsen and promised him a new laboratory building. The city of Heidelberg had begun to install coal-gas street lighting, and the university laid gas lines to the new laboratory.

The designers of the building intended to use the gas not just for lighting, but also as fuel for burners for laboratory operations. For any burner lamp, it was desirable to maximize the temperature of its flame, and minimize its luminosity (which represented lost heating energy). Bunsen sought to improve existing laboratory burner lamps as regards economy, simplicity, and flame temperature, and adapt them to coal-gas fuel.

While the building was under construction in late 1854, Bunsen suggested certain design principles to the university's mechanic, Peter Desaga, and asked him to construct a prototype. Similar principles had been used in an earlier burner design by Michael Faraday, and in a device patented in 1856 by gas engineer R. W. Elsner. The Bunsen/Desaga design generated a hot, sootless, non-luminous flame by mixing the gas with air in a controlled fashion before combustion. Desaga created adjustable slits for air at the bottom of the cylindrical burner, with the flame issuing at the top. When the building opened early in 1855, Desaga had made 50 burners for Bunsen's students. Two years later Bunsen published a description, and many of his colleagues soon adopted the design. Bunsen burners are now used in laboratories around the world.

Operation

The device in use today safely burns a continuous stream of a flammable gas such as natural gas (which is principally methane) or a liquefied petroleum gas such as propane, butane, or a mixture of both.

The hose barb is connected to a gas nozzle on the laboratory bench with rubber tubing. Most laboratory benches are equipped with multiple gas nozzles connected to a central gas source, as well as vacuum, nitrogen, and steam nozzles. The gas then flows up through the base through a small hole at the bottom of the barrel and is directed upward. There are open slots in the side of the tube bottom to admit air into the stream using the Venturi effect, and the gas burns at the top of the tube once ignited by a flame or spark. The most common methods of lighting the burner are using a match or a spark lighter.

The amount of air mixed with the gas stream affects the completeness of the combustion reaction. Less air yields an incomplete and thus cooler reaction, while a gas stream well mixed with air provides oxygen in a stoichiometric amount and thus a complete and hotter reaction. The air flow can be controlled by opening or closing the slot openings at the base of the barrel, similar in function to the choke in a carburettor.

If the collar at the bottom of the tube is adjusted so more air can mix with the gas before combustion, the flame will burn hotter, appearing blue as a result. If the holes are closed, the gas will only mix with ambient air at the point of combustion, that is, only after it has exited the tube at the top. This reduced mixing produces an incomplete reaction, producing a cooler but brighter yellow, which is often called the "safety flame" or "luminous flame". The yellow flame is luminous due to small soot particles in the flame, which are heated to incandescence. The yellow flame is considered "dirty" because it leaves a layer of carbon on whatever it is heating. When the burner is regulated to produce a hot, blue flame, it can be nearly invisible against some backgrounds. The hottest part of the flame is the tip of the inner flame, while the coolest is the whole inner flame. Increasing the amount of fuel gas flow through the tube by opening the needle valve will increase the size of the flame. However, unless the airflow is adjusted as well, the flame temperature will decrease because an increased amount of gas is now mixed with the same amount of air, starving the flame of oxygen.

Generally, the burner is placed underneath a laboratory tripod, which supports a beaker or other container. The burner will often be placed on a suitable heatproof mat to protect the laboratory bench surface.

A Bunsen burner is also used in microbiology laboratories to sterilise pieces of equipment and to produce an updraft that forces airborne contaminants away from the working area.

Variants

Other burners based on the same principle exist. The most important alternatives to the Bunsen burner are:

Teclu burner – The lower part of its tube is conical, with a round screw nut below its base. The gap, set by the distance between the nut and the end of the tube, regulates the influx of the air in a way similar to the open slots of the Bunsen burner. The Teclu burner provides better mixing of air and fuel and can achieve higher flame temperatures than the Bunsen burner.

Meker burner – The lower part of its tube has more openings with larger total cross-section, admitting more air and facilitating better mixing of air and gas. The tube is wider and its top is covered with a wire grid. The grid separates the flame into an array of smaller flames with a common external envelope, and also prevents flashback to the bottom of the tube, which is a risk at high air-to-fuel ratios and limits the maximum rate of air intake in a conventional Bunsen burner. Flame temperatures of up to 1,100–1,200 °C (2,000–2,200 °F) are achievable if properly used. The flame also burns without noise, unlike the Bunsen or Teclu burners.

Tirrill burner – The base of the burner has a needle valve which allows the regulation of gas intake directly from the burner, rather than from the gas source. Maximum temperature of flame can reach 1560 °C.

Additional information

A Bunsen burner is a type of gas burner commonly used as a heat source in laboratory experiments. The burner consists of a flat base with a straight tube extending vertically, known as the barrel or chimney. Natural gas (predominantly methane) or a liquified petroleum gas such as propane or butane is supplied at the bottom of the chimney.

Bunsen burners are normally fitted with a hose barb at the base of the chimney to allow rubber tubing to supply the gas from a gas nozzle on the laboratory bench. There may also be a gas value on the Bunsen burner. The other critical component of a Bunsen burner is the air hole. This is located near the bottom of the chimney, just above the gas inlet. The air hole allows pre-mixing of air and gas before combustion occurs at the top of the chimney. A collar around the base of the chimney, with a hole that aligns with the air hole, acts as an air regulator, allowing the air in the pre-mixture to be adjusted.

Air is drawn into the air hole due to the Venturi effect. A fluid flow transfers energy in three ways, potential energy, pressure and kinetic energy. Bernoulli’s principle states that, due to conservation of energy, a change in velocity must result in either a change in the potential energy or a change in the fluid’s pressure. When a fluid flow increases in velocity, normally it is the pressure which decreases. Because the gas in a Bunsen burner is flowing through the chimney, it has a lower pressure than the static air surrounding it. This difference in pressure causes air to be drawn into the air hole as the gas flows past it, a phenomenon known as the Venturi effect.

As the air hole is opened the flame progresses from an unsteady orange flame to a more steady orange, a steady purple and finally a roaring blue flame. This progression results in increasing flame temperature. The unsteady orange flame produced when the air hole is completely closed is highly visible and of lower temperature. This safety flame is, therefore, used for lighting and as the default position when the Bunsen burner is not in use.

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It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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#2208 2024-07-10 15:01:32

Jai Ganesh
Administrator
Registered: 2005-06-28
Posts: 47,007

Re: Miscellany

2210) Cuticle

Gist

1. an area of hard skin at the base of the nails on your fingers and toes.
2. a hard outer layer that covers and protects a plant.

Summary

Cuticle, the outer layer or part of an organism that comes in contact with the environment. In many invertebrates the dead, noncellular cuticle is secreted by the epidermis. This layer may, as in the arthropods, contain pigments and chitin; in humans the cuticle is the epidermis.

In some higher plants, the cuticle is a water-impervious protective layer covering the epidermal cells of leaves and other parts and limiting water loss. It consists of cutin, a waxy, water-repellent substance allied to suberin, which is found in the cell walls of corky tissue. Cutin is especially noticeable on many fruits—e.g., apple, nectarine, and cherry, which can be buffed to a high gloss. Carnauba wax is derived from the cuticles of the leaves of Copernicia cerifera, a Brazilian palm.

Details

A cuticle, or cuticula, is any of a variety of tough but flexible, non-mineral outer coverings of an organism, or parts of an organism, that provide protection. Various types of "cuticle" are non-homologous, differing in their origin, structure, function, and chemical composition.

Human anatomy

In human anatomy, "cuticle" can refer to several structures, but it is used in general parlance, and even by medical professionals, to refer to the thickened layer of skin surrounding fingernails and toenails (the eponychium), and to refer to the superficial layer of overlapping cells covering the hair shaft (cuticula pili), consisting of dead cells, that locks the hair into its follicle. It can also be used as a synonym for the epidermis, the outer layer of skin.

Cuticle of invertebrates

In zoology, the invertebrate cuticle or cuticula is a multi-layered structure outside the epidermis of many invertebrates, notably arthropods and roundworms, in which it forms an exoskeleton.

The main structural components of the nematode cuticle are proteins, highly cross-linked collagens and specialised insoluble proteins known as "cuticlins", together with glycoproteins and lipids.

The main structural component of arthropod cuticle is chitin, a polysaccharide composed of N-acetylglucosamine units, together with proteins and lipids. The proteins and chitin are cross-linked. The rigidity is a function of the types of proteins and the quantity of chitin. It is believed that the epidermal cells produce protein and also monitors the timing and amount of protein to be incorporated into the cuticle.

Often, in the cuticle of arthropods, structural coloration is observed, produced by nanostructures. In the mealworm beetle, Tenebrio molitor, cuticular color may suggest pathogen resistance in that darker individuals are more resistant to pathogens compared to more tan individuals.

Botany

In botany, plant cuticles are protective, hydrophobic, waxy coverings produced by the epidermal cells of leaves, young shoots and all other aerial plant organs. Cuticles minimize water loss and effectively reduce pathogen entry due to their waxy secretion. The main structural components of plant cuticles are the unique polymers cutin or cutan, impregnated with wax. Plant cuticles function as permeability barriers for water and water-soluble materials. They prevent plant surfaces from becoming wet and also help to prevent plants from drying out. Xerophytic plants such as cacti have very thick cuticles to help them survive in their arid climates. Plants that live in range of sea's spray also may have thicker cuticles that protect them from the toxic effects of salt.

Some plants, particularly those adapted to life in damp or aquatic environments, have an extreme resistance to wetting. A well-known example is the sacred lotus. This adaptation is not purely the physical and chemical effect of a waxy coating but depends largely on the microscopic shape of the surface. When a hydrophobic surface is sculpted into microscopic, regular, elevated areas, sometimes in fractal patterns, too high and too closely spaced for the surface tension of the liquid to permit any flow into the space between the plateaus, then the area of contact between liquid and solid surfaces may be reduced to a small fraction of what a smooth surface might permit. The effect is to reduce wetting of the surface substantially.

Structural coloration is also observed in the cuticles of plants.

Mycology

"Cuticle" is one term used for the outer layer of tissue of a mushroom's basidiocarp, or "fruit body". The alternative term "pileipellis", Latin for "skin" of a "cap" (meaning "mushroom") might be technically preferable, but is perhaps too cumbersome for popular use. It is the part removed in "peeling" mushrooms. On the other hand, some morphological terminology in mycology makes finer distinctions, such as described in the article on the "pileipellis". Be that as it may, the pileipellis (or "peel") is distinct from the trama, the inner fleshy tissue of a mushroom or similar fruiting body, and also from the spore-bearing tissue layer, the hymenium.

Additional information

The cuticle is a layer of clear skin located along the bottom edge of your finger or toe, which is called the nail bed. The cuticle protects new nails from bacteria when they grow out from the nail root.

The area around the cuticle is delicate. It can get dry, damaged, and infected. It’s important to care for the entire nail area and keep it clean so that your nails stay healthy.

Cuticle vs. nail lunula

The cuticle is the transparent skin located above and around the nail base. The lunula is the half-moon shape seen at the base of the nail. The lunula is located above the cuticle.

Hair cuticles

Human hair also contains cuticles. These are different from nail cuticles but have a similar function. Hair cuticles serve as a protective layer for the hair. They’re composed of dead, overlapping cells.

When healthy, these cuticles give your hair shine and protect its inner layers from damage.

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It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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#2209 2024-07-11 14:10:31

Jai Ganesh
Administrator
Registered: 2005-06-28
Posts: 47,007

Re: Miscellany

2211) Sleep Apnea

Gist

Sleep Apnea is a potentially serious sleep disorder in which breathing repeatedly stops and starts. If you snore loudly and feel tired even after a full night's sleep, you might have sleep apnea.

Summary

Sleep Apnea is a common condition in which your breathing stops and restarts many times while you sleep. This can prevent your body from getting enough oxygen. You may want to talk to your healthcare provider about sleep apnea if someone tells you that you snore or gasp during sleep, or if you experience other symptoms of poor-quality sleep, such as excessive daytime sleepiness.

There are two types of sleep apnea.

* Obstructive sleep apnea happens when your upper airway becomes blocked many times while you sleep, reducing or completely stopping airflow. This is the most common type of sleep apnea. Anything that could narrow your airway such as obesity, large tonsils, or changes in your hormone levels can increase your risk for obstructive sleep apnea.
* Central sleep apnea happens when your brain does not send the signals needed to breathe. Health conditions that affect how your brain controls your airway and chest muscles can cause central sleep apnea.

To diagnose sleep apnea, your provider may have you do a sleep study. Breathing devices such as continuous positive air pressure (CPAP) machines and lifestyle changes are common sleep apnea treatments. If these treatments do not work, surgery may be recommended to correct the problem that is causing your sleep apnea. If your sleep apnea is not diagnosed or treated, you may not get enough good quality sleep. This can lead to trouble concentrating, making decisions, remembering things, or controlling your behavior. Sleep apnea is also linked to serious health problems.

Details

Sleep apnea is a serious sleep disorder that happens when your breathing stops and starts while you're asleep. If it goes untreated, it can cause loud snoring, daytime tiredness, or more serious problems like heart trouble or high blood pressure.

This condition is different from regular, or primary, snoring. Primary snoring may be caused by nose or throat conditions, your sleep style (especially back sleeping), being overweight or older, or using alcohol or other depressants. While both types of snoring happen when tissues in the back of your throat vibrate, people with sleep apnea tend to:

* Snore much more loudly than those with regular snoring
* Pause for over 10 seconds while they breathe
* Take shallow breaths, gasp, or choke
* Be restless during sleep

Is sleep apnea dangerous?

Sleep apnea itself isn't thought to be fatal. But research has found that people who have the condition are twice as likely to die suddenly within a given time period than those who don't--especially if it's not treated. That's because of its links to serious conditions like high blood pressure, heart disease, stroke, and diabetes.

Sleep Apnea Types

There are three types of sleep apnea:

* Obstructive sleep apnea. This is the most common type. It results when your airways repeatedly get completely or partially blocked as you sleep . This usually happens because the soft tissue at the back of your throat collapses when the muscles in your face and neck relax while you sleep. During these episodes, your diaphragm and chest muscles must work harder than normal to open your airways. You may start to breathe with loud gasps, and your body may jerk. This can affect your sleep, lower the flow of oxygen to your vital organs, and lead to abnormal heart rhythms.

* Central sleep apnea. With this type, your airway doesn't get blocked. Instead, your brain fails to tell your muscles to breathe because of issues in your respiratory control center. It's related to the function of your central nervous system. This type most often affects people with neuromuscular disease such as amyotrophic lateral sclerosis (ALS, or Lou Gehrig's disease), those who've had a stroke, or those who have heart failure or other forms of heart, kidney, or lung disease.

* Complex sleep apnea syndrome. With this condition, you have a combination of obstructive and central sleep apnea. When you have the obstructive type but it turns into the central type after you get treatment, that's called treatment-emergent central sleep apnea.

Effects of Sleep Apnea

When you briefly stop breathing because of sleep apnea, the oxygen levels in your blood drop. This triggers a brain reflex that wakes you up long enough to  start breathing again.

These repeated awakenings keep you from spending enough time in the deep stages of sleep. The more serious your condition is, the more often your sleep will be interrupted.

Losing sleep makes you feel tired during the day. You may be less productive at work or school, and feel irritable, moody, or sad. You might be forgetful or find it hard to concentrate. And you're more likely to have accidents at work or while driving. 

Sleep Apnea Causes

What causes sleep apnea depends on what type you have: 

* Obstructive sleep apnea. Things that narrow your airway or interfere with your airflow, including obesity, enlarged tonsils or adenoids, or a thick neck, can cause this type.

* Central sleep apnea. Anything that affects your brain's control of your breathing and chest muscles can cause this type. This includes hormone levels as well as certain health conditions. Opioid use can have this effect, as can changes that come with aging.

Some research has indicated that apnea might run in families.

Sleep Apnea Risk Factors

This condition can affect anyone, but some things put you more at risk:

* Being overweight
* A large neck circumference that could make your airways more narrow
* A narrowed airway that you inherited or developed from large tonsils or adenoids
* Being male (or having been identified as male at birth)
* Older age
* A family history of sleep apnea
* Smoking
* Use of alcohol, sedatives, or tranquilizers
* Nasal congestion
* Medical conditions such as type 2 diabetes, congestive heart failure, high blood pressure, Parkinson's disease, PCOS, hormonal disorders,  a previous stroke, or chronic lung diseases like asthma

Sleep Apnea Symptoms

You probably won't notice your first symptoms of obstructive sleep apnea, but your bed partner may make you aware of them. The most common signs are:

* Snoring
* Fatigue or sleepiness during the day
* Restlessness while sleeping, or often waking up at night
* Dry mouth or sore throat when you wake up
* Waking up suddenly after gasping or choking
* Trouble concentrating, forgetfulness, or crankiness
* Depression or anxiety
* Frequent need to get up to pee at night
* Night sweats
* Sexual dysfunction
* Headaches

People with central sleep apnea usually say they wake up a lot or have insomnia. They also might have a choking or gasping sensation when they awaken.

Sleep apnea symptoms in women

Women (and those who were identified as female at birth) who have the condition may be less less likely than men to snore. For them, signs of sleep apnea may include:

* Fatigue
* Daytime drowsiness
* Anxiety or depression
* Headaches, often in the morning
* Trouble sleeping, including often waking up during the night

Sleep apnea symptoms in children

The symptoms might not be as obvious in children. Warning signs include:

* Sluggishness or sleepiness, which could be mistaken for laziness in the classroom
* Hyperactivity or problems focusing at school
* Poor academic performance
* Trouble swallowing
* Daytime mouth breathing
* An inward movement of the rib cage when inhaling
* Sweating a lot at night
* Heartburn
* Unusual sleeping positions, like sleeping on their hands and knees, or with the neck extended
* Often moving their arms or legs during sleep
* Loud snoring
* Bedwetting.

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It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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#2210 2024-07-12 14:33:26

Jai Ganesh
Administrator
Registered: 2005-06-28
Posts: 47,007

Re: Miscellany

2212) Coffee bean

A coffee bean is a seed from the Coffea plant and the source for coffee. It is the pit inside the red or purple fruit. This fruit is often referred to as a coffee cherry, and like the cherry, it is a fruit with a pit. Even though the coffee beans are not technically beans, they are referred to as such because of their resemblance to true beans. The fruits most commonly contain two stones with their flat sides together. A small percentage of cherries contain a single seed, called a "peaberry". Peaberries make up only around 10% to 15% of all coffee beans. It is a fairly common belief that they have more flavour than normal coffee beans. Like Brazil nuts (a seed) and white rice, coffee beans consist mostly of endosperm.

The two most economically important varieties of coffee plants are the Arabica and the Robusta; approximately 60% of the coffee produced worldwide is Arabica and ~40% is Robusta. Arabica beans consist of 0.8–1.4% caffeine and Robusta beans consist of 1.7–4.0% caffeine. As coffee is one of the world's most widely consumed beverages, coffee beans are a major cash crop and an important export product, accounting for over 50% of some developing nations' foreign exchange earnings. This has made coffee very important in culture and food around the world. In 2017, 70% of total coffee production was exported, worth US$19.9 billion. The global coffee industry is massive and valued at $495.50 billion as of 2023, the biggest producer of coffee and coffee beans is Brazil. Other main exporters of coffee beans are Colombia, Vietnam and Ethiopia.

History

Significant dates

* According to legend, the coffee plant was discovered in Ethiopia by a goat herder named Kaldi around 850 AD, who observed increased physical activity in his goats after they consumed coffee beans.
* The coffee plant was first found in the mountains of Yemen. Then by 1500, it was exported to the rest of the world through the port of Mokha, Yemen.
* First cultivation in India (Chikmagalur) – 1600
* First cultivation in Europe – 1616
* First cultivation in Java – 1699
* First cultivation in Caribbean (Cuba, Hispaniola, Jamaica, Puerto Rico) – 1715–1730
* First cultivation in South America – 1730
* First cultivation in Dutch East Indies – 1720
* Roasted beans first sold on retail market (Pittsburgh) – 1865
* Important spray-drying techniques developed in 1950s, which along with freeze drying are a method to create instant coffee

Distribution

Brazil produces about 45% of the world's total coffee exports. The United States imports more coffee than any other nation. As of 2015, Americans consumed approximately 400 million cups of coffee per day, making the United States the leading consumer of coffee in the world.

Coffee plants grow within a defined area between the tropics of Cancer and Capricorn, termed the bean belt or coffee belt.

Etymology

The Oxford English Dictionary suggests that the European languages generally appear to have gotten the name from Turkish kahveh, about 1600, perhaps through Italian caffè. Arab qahwah, in Turkish pronounced kahveh, the name of the infusion or beverage; said by Arab lexicographers to have originally meant "wine" or some type of wine, and to be a derivative of a verb-root qahiya "to have no appetite". Another common theory is that the name derives from Kaffa Province, Ethiopia, where the species may have originated.

Coffee plant

The coffee tree averages from 5–10 m (16–33 ft) in height. As the tree gets older, it produces less fruit and slowly loses any pest- and disease-resistance. The coffee beans come from the seeds which contained in fruits from trees and shrubs naturally grown in African forests. Humans produce coffee by roasting, grinding and brewing the green coffee beans.

Coffee plants are often grown in rows spaced apart depending on the desired density chosen by the farmer. Some farmers plant other trees, such as shade trees or other cash-crop trees, such as orange trees around them or plant the coffee on the sides of hills, because they need specific conditions to flourish. Ideally, Arabica coffee beans are grown at temperatures between 15 and 24 °C (59 and 75 °F) and Robusta between 24 and 30 °C (75 and 86 °F) and receive between 500 and 3,000 mm (20 and 118 in) of rainfall per year. More rain is needed at the beginning of the season when the fruit is developing and less later in the season as it ripens.

Two lesser known species grown for consumption are Coffea liberica and Coffea racemosa.

Processing

When the fruit is ripe, it is almost always handpicked, using either "selective picking", where only the ripe fruit is removed, or "strip-picking", where all of the fruit is removed from a limb all at once. Selective picking is often used to produce higher quality coffee because the cherries are picked at their ripest. Strip-picking is indiscriminate and will harvest unripe, ripe, and over-ripe fruit. To improve quality after strip-picking, the harvest must be sorted.

Two methods are primarily used to process coffee berries. The first, "wet" or "washed" process, has historically usually been carried out in Central America and areas of Africa. The flesh of the cherries is separated from the seeds and then the seeds are fermented – soaked in water for about two days. This softens the mucilage, which is a sticky pulp residue that is still attached to the seeds. Then this mucilage is washed off with water.

The "dry processing" method, cheaper and simpler, was historically used for lower-quality beans in Brazil and much of Africa, but now brings a premium when done well. Twigs and other foreign objects are separated from the berries and the fruit is then spread out in the sun on concrete, bricks or raised beds for 2–3 weeks, turned regularly for even drying.

In Asia a third type of processing exists, where the Asian palm civet eats coffee berries and excretes the beans. Because the civet prefers the taste of the ripest cherries, the civet selectively harvests the cherries. Its digestive system then processes the beans by breaking down the mucilage and pulp surrounding the seed. Once the seeds are excreted by the civet, they can be harvested, processed and sold as a niche product. Once they are finally processed, these beans are called kopi luwak, and are often marketed as a rare and expensive coffee.

Composition

The term "green coffee bean" refers to unroasted mature or immature coffee beans. These have been processed by wet or dry methods to remove the outer pulp and mucilage and have an intact wax layer on the outer surface. When immature, they are green. When mature, they have a brown to yellow or reddish color and typically weigh 300 to 330 mg per dried coffee bean. Nonvolatile and volatile compounds in green coffee beans, such as caffeine, deter many insects and animals from eating them. Further, both nonvolatile and volatile compounds contribute to the flavor of the coffee bean when it is roasted. Nonvolatile nitrogenous compounds (including alkaloids, trigonelline, proteins, and free amino acids) and carbohydrates are of major importance in producing the full aroma of roasted coffee and for its biological action. Since the mid-2000s, green coffee extract has been sold as a nutritional supplement and has been clinically studied for its chlorogenic acid content and for its lipolytic and weight-loss properties.

Nonvolatile alkaloids

Caffeine (1,3,7-trimethylxanthine) is the alkaloid most present in green and roasted coffee beans. The content of caffeine is between 1.0% and 2.5% by weight of dry green coffee beans. The content of caffeine does not change during maturation of green coffee beans, but higher caffeine content is found in plants grown at higher altitudes. Lower concentrations of theophylline, theobromine, paraxanthine, liberine, and methylliberine can be found. The concentration of theophylline, an alkaloid noted for its presence in green tea, is reduced during the roasting process, usually about 15 minutes at 230 °C (446 °F), whereas the concentrations of most other alkaloids are not changed. The solubility of caffeine in water increases with temperature and with the addition of chlorogenic acids, citric acid, or tartaric acid, all of which are present in green coffee beans. For example, 1 g (0.035 oz) of caffeine dissolves in 46 mL (1.6 US fl oz) of water at room temperature, and 5.5 mL (0.19 US fl oz) at 80 °C (176 °F). The xanthine alkaloids are odorless, but have a bitter taste in water, which is masked by organic acids present in green coffee.

Trigonelline (N-methyl-nicotinate) is a derivative of vitamin B3 that is not as bitter as caffeine. In green coffee beans, the content is between 0.6% and 1.0%. At a roasting temperature of 230 °C (446 °F), 85% of the trigonelline is degraded to nicotinic acid, leaving small amounts of the unchanged molecule in the roasted beans.

Proteins and amino acids

Proteins account for 8% to 12% of dried green coffee beans. A majority of the proteins are of the 11-S storage kind (alpha – component of 32 kDa, beta – component of 22 kDa), most of which are degraded to free amino acids during maturation of green coffee beans. Further, 11-S storage proteins are degraded to their individual amino acids under roasting temperature, thus are an additional source of bitter components due to generation of Maillard reaction products. High temperature and oxygen concentration and low pH degrade 11-S storage proteins of green coffee beans to low-molecular-weight peptides and amino acids. The degradation is accelerated in the presence of organic acids such as chlorogenic acids and their derivatives. Other proteins include enzymes, such as catalase and polyphenol oxidase, which are important for the maturation of green coffee beans. Mature coffee contains free amino acids (4.0 mg amino acid/g robusta coffee and up to 4.5 mg amino acid/g arabica coffee). In Coffea arabica, alanine is the amino acid with the highest concentration, i.e. 1.2 mg/g, followed by asparagine of 0.66 mg/g, whereas in C. robusta, alanine is present at a concentration of 0.8 mg/g and asparagine at 0.36 mg/g. The free hydrophobic amino acids in fresh green coffee beans contribute to the unpleasant taste, making it impossible to prepare a desirable beverage with such compounds. In fresh green coffee from Peru, these concentrations have been determined as: isoleucine 81 mg/kg, leucine 100 mg/kg, valine 93 mg/kg, tyrosine 81 mg/kg, phenylalanine 133 mg/kg. The concentration of gamma-aminobutyric acid (a neurotransmitter) has been determined between 143 mg/kg and 703 mg/kg in green coffee beans from Tanzania. Roasted coffee beans do not contain any free amino acids; the amino acids in green coffee beans are degraded under roasting temperature to Maillard products (reaction products between the aldehyde group of sugar and the alpha-amino group of the amino acids). Further, diketopiperazines, e.g. cyclo(proline-proline), cyclo(proline-leucine), and cyclo(proline-isoleucine), are generated from the corresponding amino acids, and are the major source of the bitter taste of roasted coffee. The bitter flavor of diketopiperazines is perceptible at around 20 mg/liter of water. The content of diketopiperazines in espresso is about 20 to 30 mg, which is responsible for its bitterness.

Carbohydrates

Carbohydrates make up about 50% of the dry weight of green coffee beans. The carbohydrate fraction of green coffee is dominated by polysaccharides, such as arabinogalactan, galactomannan, and cellulose, contributing to the tasteless flavor of green coffee. Arabinogalactan makes up to 17% of dry weight of green coffee beans, with a molecular weight of 90 kDa to 200 kDa. It is composed of beta-1-3-linked galactan main chains, with frequent members of arabinose (pentose) and galactose (hexose) residues at the side chains comprising immunomodulating properties by stimulating the cellular defense system (Th-1 response) of the body. Mature brown to yellow coffee beans contain fewer residues of galactose and arabinose at the side chain of the polysaccharides, making the green coffee bean more resistant to physical breakdown and less soluble in water. The molecular weight of the arabinogalactan in coffee is higher than in most other plants, improving the cellular defense system of the digestive tract compared to arabinogalactan with lower molecular weight. Free monosaccharides are present in mature brown to yellow-green coffee beans. The free part of monosaccharides contains sucrose (gluco-fructose) up to 9000 mg/100 g of arabica green coffee bean, a lower amount in robustas, i.e. 4500 mg/100 g. In arabica green coffee beans, the content of free glucose was 30 to 38 mg/100 g, free fructose 23 to 30 mg/100 g; free galactose 35 mg/100 g and mannitol 50 mg/100 g dried coffee beans, respectively. Mannitol is a powerful scavenger for hydroxyl radicals, which are generated during the peroxidation of lipids in biological membranes.

Lipids

The lipids found in green coffee include: linoleic acid, palmitic acid, oleic acid, stearic acid, arachidic acid, diterpenes, triglycerides, unsaturated long-chain fatty acids, esters, and amides. The total content of lipids in dried green coffee is 11.7–14 g/100 g. Lipids are present on the surface and in the interior matrix of green coffee beans. On the surface, they include derivatives of carboxylic acid-5-hydroxytryptamides with an amide bond to fatty acids (unsaturated C6 to C24) making up to 3% of total lipid content or 1200 to 1400 microgram/g dried green coffee bean. Such compounds form a wax-like cover on the surface of the coffee bean (200–300 mg lipids/100 g dried green coffee bean) protecting the interior matrix against oxidation and insects. Further, such molecules have antioxidative activity due to their chemical structure. Lipids of the interior tissue are triglycerides, linoleic acid (46% of total free lipids), palmitic acid (30% to 35% of total free lipids), and esters. Arabica beans have a higher content of lipids (13.5–17.4 g lipids/100 g dried green coffee beans) than robustas (9.8–10.7 g lipids/100 g dried green coffee beans). The content of diterpenes is about 20% of the lipid fraction. The diterpenes found in green coffee include cafestol, kahweol and 16-O-methylcafestol. Some of these diterpenes have been shown in in vitro experiments to protect liver tissue against chemical oxidation. In coffee oil from green coffee beans the diterpenes are esterified with saturated long chain fatty acids.

Nonvolatile chlorogenic acids

Chlorogenic acids belong to a group of compounds known as phenolic acids, which are antioxidants. The content of chlorogenic acids in dried green coffee beans of arabica is 65 mg/g and of robusta 140 mg/g, depending on the timing of harvesting. At roasting temperature, more than 70% of chlorogenic acids are destroyed, leaving a residue less than 30 mg/g in the roasted coffee bean. In contrast to green coffee, green tea contains an average of 85 mg/g polyphenols. These chlorogenic acids could be a valuable, inexpensive source of antioxidants. Chlorogenic acids are homologous compounds comprising caffeic acid, ferulic acid and 3,4-dimethoxycinnamic acid, which are connected by an ester bond to the hydroxyl groups of quinic acid. The antioxidant capacity of chlorogenic acid is more potent than of ascorbic acid (vitamin C) or mannitol, which is a selective hydroxy-radical scavenger. Chlorogenic acids have a bitter taste in low concentrations such as 50 mg/L water. At higher concentrations of 1 g/L water, they have a sour taste. Chlorogenic acids increase the solubility of caffeine and are important modulators of taste.

Volatile compounds

Volatile compounds of green coffee beans include short-chain fatty acids, aldehydes, and nitrogen-containing aromatic molecules, such as derivatives of pyrazines (green-herbaceous-earthy odor). Briefly, such volatile compounds are responsible for the less pleasing odor and taste of green coffee versus roasted coffee. Commercial success was realized by Starbucks in creating Green Bean Refreshers using a process that primarily isolates the caffeine from the green beans but does not actually use steeped liquid from the beans. Many consumers experiment with creating green bean "extract" by steeping green coffee beans in hot water. Often, the recommended times of steeping (20 minutes to 1 hour) extract too much caffeine to provide a pleasant taste. A steeping time of 12 minutes or under provides a more palatable liquid that can be used as a base for a drink containing more of the nutrients and less caffeine that using just isolated caffeine extract. The alkaline stock base that results can be paired with acidic or fruity extracts, with or without sweetener, to mask the vegetable-like taste of the extract.

When green coffee beans are roasted, other molecules with the typical pleasant aroma of coffee are generated, which are not present in fresh green coffee. During roasting, the major part of the unpleasant-tasting volatile compounds are neutralised. Unfortunately, other important molecules such as antioxidants and vitamins present in green coffee are destroyed. Volatile compounds with nauseating odor for humans have been identified, including acetic acid (pungent, unpleasant odor), propionic acid (odor of sour milk, or butter), butanoic acid (odor of rancid butter, present in green coffee with 2 mg/100 g coffee beans), pentanoic acid (unpleasant fruity flavor, present in green coffee at 40 mg/100 g in coffee beans), hexanoic acid (fatty-rancid odor), heptanoic acid (fatty odor), octanoic acid (repulsive oily rancid odor); nonanoic acid (mild nut-like fatty odor); decanoic acid (sour repulsive odor), and derivatives of such fatty acids – 3-methyl-valeric acid (sour, green-herbaceous, unpleasant odor), acetaldehyde (pungent-nauseating odor, even when highly diluted, present in dried green coffee beans at concentrations of about 5 mg/kg), propanal (choking effect on respiratory system, penetrating-nauseating), butanal (nauseating effect, present in dried green coffee beans at 2–7 mg/kg), or pentanal (very repulsive nauseating effect).

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It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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#2211 Yesterday 14:44:20

Jai Ganesh
Administrator
Registered: 2005-06-28
Posts: 47,007

Re: Miscellany

2213) Electron Shell

Gist

An electron shell is the outside part of an atom around the atomic nucleus. It is a group of atomic orbitals with the same value of the principal quantum number n. Electron shells have one or more electron subshells, or sublevels.

Details

In chemistry and atomic physics, an electron shell may be thought of as an orbit that electrons follow around an atom's nucleus. The closest shell to the nucleus is called the "1 shell" (also called the "K shell"), followed by the "2 shell" (or "L shell"), then the "3 shell" (or "M shell"), and so on farther and farther from the nucleus. The shells correspond to the principal quantum numbers (n = 1, 2, 3, 4 ...) or are labeled alphabetically with the letters used in X-ray notation (K, L, M, ...). A useful guide when understanding electron shells in atoms is to note that each row on the conventional periodic table of elements represents an electron shell.

Each shell can contain only a fixed number of electrons: the first shell can hold up to two electrons, the second shell can hold up to eight (2 + 6) electrons, the third shell can hold up to 18 (2 + 6 + 10) and so on. The general formula is that the nth shell can in principle hold up to 2(n^2) electrons. For an explanation of why electrons exist in these shells, see electron configuration.

Each shell consists of one or more subshells, and each subshell consists of one or more atomic orbitals.

History

In 1913, Niels Bohr proposed a model of the atom, giving the arrangement of electrons in their sequential orbits. At that time, Bohr allowed the capacity of the inner orbit of the atom to increase to eight electrons as the atoms got larger, and "in the scheme given below the number of electrons in this [outer] ring is arbitrary put equal to the normal valency of the corresponding element". Using these and other constraints, he proposed configurations that are in accord with those now known only for the first six elements.

The shell terminology comes from Arnold Sommerfeld's modification of the 1913 Bohr model. During this period Bohr was working with Walther Kossel, whose papers in 1914 and in 1916 called the orbits "shells". Sommerfeld retained Bohr's planetary model, but added mildly elliptical orbits (characterized by additional quantum numbers ℓ and m) to explain the fine spectroscopic structure of some elements. The multiple electrons with the same principal quantum number (n) had close orbits that formed a "shell" of positive thickness instead of the circular orbit of Bohr's model which orbits called "rings" were described by a plane.

The existence of electron shells was first observed experimentally in Charles Barkla's and Henry Moseley's X-ray absorption studies. Moseley's work did not directly concern the study of electron shells, because he was trying to prove that the periodic table was not arranged by weight, but by the charge of the protons in the nucleus. However, because the number of electrons in an electrically neutral atom equals the number of protons, this work was extremely important to Niels Bohr who mentioned Moseley's work several times in his 1962 interview. Moseley was part of Rutherford's group, as was Niels Bohr. Moseley measured the frequencies of X-rays emitted by every element between calcium and zinc and found that the frequencies became greater as the elements got heavier. This led to the theory that electrons were emitting X-rays when they were shifted to lower shells. This led to the conclusion that the electrons were in Kossel's shells with a definite limit per shell, labeling the shells with the letters K, L, M, N, O, P, and Q. The origin of this terminology was alphabetic. Barkla, who worked independently from Moseley as an X-ray spectrometry experimentalist, first noticed two distinct types of scattering from shooting X-rays at elements in 1909 and named them "A" and "B". Barkla described these two types of X-ray diffraction: the first was unconnected with the type of material used in the experiment and could be polarized. The second diffraction beam he called "fluorescent" because it depended on the irradiated material. It was not known what these lines meant at the time, but in 1911 Barkla decided there might be scattering lines previous to "A", so he began at "K". However, later experiments indicated that the K absorption lines are produced by the innermost electrons. These letters were later found to correspond to the n values 1, 2, 3, etc. that were used in the Bohr model. They are used in the spectroscopic Siegbahn notation.

The work of assigning electrons to shells was continued from 1913 to 1925 by many chemists and a few physicists. Niels Bohr was one of the few physicists who followed the chemist's work of defining the periodic table, while Arnold Sommerfeld worked more on trying to make a relativistic working model of the atom that would explain the fine structure of the spectra from a classical orbital physics standpoint through the Atombau approach. Einstein and Rutherford, who did not follow chemistry, were unaware of the chemists who were developing electron shell theories of the periodic table from a chemistry point of view, such as Irving Langmuir, Charles Bury, J.J. Thomson, and Gilbert Lewis, who all introduced corrections to Bohr's model such as a maximum of two electrons in the first shell, eight in the next and so on, and were responsible for explaining valency in the outer electron shells, and the building up of atoms by adding electrons to the outer shells. So when Bohr outlined his electron shell atomic theory in 1922, there was no mathematical formula for the theory. So Rutherford said he was hard put "to form an idea of how you arrive at your conclusions". Einstein said of Bohr's 1922 paper that his "electron-shells of the atoms together with their significance for chemistry appeared to me like a miracle – and appears to me as a miracle even today". Arnold Sommerfeld, who had followed the Atombau structure of electrons instead of Bohr who was familiar with the chemists' views of electron structure, spoke of Bohr's 1921 lecture and 1922 article on the shell model as "the greatest advance in atomic structure since 1913". However, the electron shell development of Niels Bohr was basically the same theory as that of the chemist Charles Rugeley Bury in his 1921 paper.

As work continued on the electron shell structure of the Sommerfeld-Bohr Model, Sommerfeld had introduced three "quantum numbers n, k, and m, that described the size of the orbit, the shape of the orbit, and the direction in which the orbit was pointing." Because we use k for the Boltzmann constant, the azimuthal quantum number was changed to ℓ. When the modern quantum mechanics theory was put forward based on Heisenberg's matrix mechanics and Schrödinger's wave equation, these quantum numbers were kept in the current quantum theory but were changed to n being the principal quantum number, and m being the magnetic quantum number.

However, the final form of the electron shell model still in use today for the number of electrons in shells was discovered in 1923 by Edmund Stoner, who introduced the principle that the nth shell was described by 2(n^2). Seeing this in 1925, Wolfgang Pauli added a fourth quantum number, "spin", during the old quantum theory period of the Sommerfeld-Bohr Solar System atom to complete the modern electron shell theory.

Subshells

Each shell is composed of one or more subshells, which are themselves composed of atomic orbitals. For example, the first (K) shell has one subshell, called 1s; the second (L) shell has two subshells, called 2s and 2p; the third shell has 3s, 3p, and 3d; the fourth shell has 4s, 4p, 4d and 4f; the fifth shell has 5s, 5p, 5d, and 5f and can theoretically hold more in the 5g subshell that is not occupied in the ground-state electron configuration of any known element.

* The first column is the "subshell label", a lowercase-letter label for the type of subshell. For example, the "4s subshell" is a subshell of the fourth (N) shell, with the type (s) described in the first row.
* The second column is the azimuthal quantum number (ℓ) of the subshell. The precise definition involves quantum mechanics, but it is a number that characterizes the subshell.
* The third column is the maximum number of electrons that can be put into a subshell of that type. For example, the top row says that each s-type subshell (1s, 2s, etc.) can have at most two electrons in it. Each of the following subshells (p, d, f, g) can have 4 more electrons than the one preceding it.
* The fourth column says which shells have a subshell of that type. For example, looking at the top two rows, every shell has an s subshell, while only the second shell and higher have a p subshell (i.e., there is no "1p" subshell).
* The final column gives the historical origin of the labels s, p, d, and f. They come from early studies of atomic spectral lines. The other labels, namely g, h, and i, are an alphabetic continuation following the last historically originated label of f.

Number of electrons in each shell

Each subshell is constrained to hold 4ℓ + 2 electrons at most, namely:

* Each s subshell holds at most 2 electrons
* Each p subshell holds at most 6 electrons
* Each d subshell holds at most 10 electrons
* Each f subshell holds at most 14 electrons
* Each g subshell holds at most 18 electrons

Therefore, the K shell, which contains only an s subshell, can hold up to 2 electrons; the L shell, which contains an s and a p, can hold up to 2 + 6 = 8 electrons, and so forth; in general, the nth shell can hold up to 2n^2 electrons.

Although that formula gives the maximum in principle, in fact that maximum is only achieved (in known elements) for the first four shells (K, L, M, N). No known element has more than 32 electrons in any one shell. This is because the subshells are filled according to the Aufbau principle. The first elements to have more than 32 electrons in one shell would belong to the g-block of period 8 of the periodic table. These elements would have some electrons in their 5g subshell and thus have more than 32 electrons in the O shell (fifth principal shell).

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It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

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#2212 Today 00:03:51

Jai Ganesh
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Registered: 2005-06-28
Posts: 47,007

Re: Miscellany

2214) Shopping Mall

A shopping mall (or simply mall) is a large indoor shopping center, usually anchored by department stores. The term mall originally meant a pedestrian promenade with shops along it, but in the late 1960s, it began to be used as a generic term for the large enclosed shopping centers that were becoming increasingly commonplace. In the United Kingdom and other countries, shopping malls may be called shopping centers.

In recent decades, malls have declined considerably in North America, particularly in subprime locations, and some have closed and become so-called "dead malls". Successful exceptions have added entertainment and experiential features, added big-box stores as anchors, or converted to other specialized shopping center formats such as power centers, lifestyle centers, factory outlet centers, and festival marketplaces. In Canada, shopping centres have frequently been replaced with mixed-use high-rise communities. In many European countries and Asian countries, shopping malls continue to grow and thrive.

Terminology

In the United States, Persian Gulf countries, and India, the term shopping mall is usually applied to enclosed retail structures (and is generally abbreviated to simply mall), while shopping center usually refers to open-air retail complexes; both types of facilities usually have large parking lots, face major traffic arterials, and have few pedestrian connections to surrounding neighborhoods. Outside of North America, the terms shopping precinct and shopping arcade are also used.

In the U.K., such complexes are considered shopping centers (Commonwealth English: shopping centre), though shopping center covers many more sizes and types of centers than the North American mall. Other countries follow U.K. usage. In Canadian English, and often in Australia and New Zealand, the term mall may be used informally but shopping center or merely center will feature in the name of the complex (such as Toronto Eaton Centre). The term mall is less-commonly a part of the name of the complex.

Types

The International Council of Shopping Centers, based in New York City, classifies two types of shopping centers as malls: regional malls and superregional malls. A regional mall, per the International Council of Shopping Centers, is a shopping mall with 400,000 sq ft (37,000 m^2) to 800,000 sq ft (74,000 m^2) gross leasable area with at least two anchor stores. A super-regional mall, per the International Council of Shopping Centers, is a shopping mall with over 800,000 sq ft (74,000 m^2) of gross leasable area, three or more anchors, mass merchant, more variety, fashion apparel, and serves as the dominant shopping venue for the region (25 miles or 40 km) in which it is located. Not classified as malls are smaller formats such as strip malls and neighborhood shopping centers, and specialized formats such as power centers, festival marketplaces, and outlet centers.

History:

Forerunners to the shopping mall

In 1798, the first covered shopping passage was built in Paris, the Passage du Caire. The Burlington Arcade in London was opened in 1819. The Arcade in Providence, Rhode Island, built in 1828, claims to be the first shopping arcade in the United States. Western European cities in particular built many arcade-style shopping centers. The Galleria Vittorio Emanuele II in Milan, which opened in 1877, was larger than its predecessors, and inspired the use of the term "galleria" for many other shopping arcades and malls.

In the mid-20th century, with the rise of the suburb and automobile culture in the United States, a new style of shopping center was created away from downtowns. Early shopping centers designed for the automobile include Market Square, Lake Forest, Illinois (1916), and Country Club Plaza, Kansas City, Missouri (1924).

The suburban shopping center concept evolved further in the United States after World War II, with larger open-air shopping centers anchored by major department stores, such as the 550,000-square-foot (51,000 m^2) Broadway-Crenshaw Center in Los Angeles, built in 1947 and anchored by a five-story Broadway and a May Company California.

Downtown pedestrian malls and use of term mall

In the late 1950s and into the 1960s, the term "shopping mall" was first used, but in the original sense of the word "mall", meaning a pedestrian promenade in the U.S., or in U.K. usage, a "shopping precinct". Early downtown pedestrianized malls included the Kalamazoo Mall (the first, in 1959), "Shoppers' See-Way" in Toledo, Lincoln Road Mall in Miami Beach, Santa Monica Mall (1965).

Although Bergen Mall opened in 1957 using the name "mall" and inspired other suburban shopping centers to rebrand themselves as malls, these types of properties were still referred to as "shopping centers" until the late 1960s.

Enclosed malls

The enclosed shopping center, which would eventually be known as the shopping mall, did not appear in mainstream until the mid-1950s. One of the earliest examples was the Valley Fair Shopping Center in Appleton, Wisconsin, which opened on March 10, 1955. Valley Fair featured a number of modern features including central heating and cooling, a large outdoor parking area, semi-detached anchor stores, and restaurants. Later that year the world's first fully enclosed shopping mall was opened in Luleå, in northern Sweden (architect: Ralph Erskine) and was named Shopping; the region now claims the highest shopping center density in Europe.

The idea of a regionally-sized, fully enclosed shopping complex was pioneered in 1956 by the Austrian-born architect and American immigrant Victor Gruen. This new generation of regional-size shopping centers began with the Gruen-designed Southdale Center, which opened in the Twin Cities suburb of Edina, Minnesota, United States in October 1956. For pioneering the soon-to-be enormously popular mall concept in this form, Gruen has been called the "most influential architect of the twentieth century" by Malcolm Gladwell.

The first retail complex to be promoted as a "mall" was Paramus, New Jersey's Bergen Mall, which opened with an open-air format on November 14, 1957, and was later enclosed in 1973. Aside from Southdale Center, significant early enclosed shopping malls were Harundale Mall (1958) in Glen Burnie, Maryland, Big Town Mall (1959) in Mesquite, Texas, Chris-Town Mall (1961) in Phoenix, Arizona, and Randhurst Center (1962) in Mount Prospect, Illinois.

Other early malls moved retailing away from the dense, commercial downtowns into the largely residential suburbs. This formula (enclosed space with stores attached, away from downtown, and accessible only by automobile) became a popular way to build retail across the world. Gruen himself came to abhor this effect of his new design; he decried the creation of enormous "land wasting seas of parking" and the spread of suburban sprawl.

Even though malls mostly appeared in suburban areas in the U.S., some U.S. cities facilitated the construction of enclosed malls downtown as an effort to revive city centers and allow them to compete effectively with suburban malls. Examples included Main Place Mall in Buffalo (1969) and The Gallery (1977, now Fashion District Philadelphia) in Philadelphia. Other cities created open-air pedestrian malls.

In the United States, developers such as A. Alfred Taubman of Taubman Centers extended the concept further in 1980, with terrazzo tiles at the Mall at Short Hills in New Jersey, indoor fountains, and two levels allowing a shopper to make a circuit of all the stores. Taubman believed carpeting increased friction, slowing down customers, so it was removed. Fading daylight through glass panels was supplemented by gradually increased electric lighting, making it seem like the afternoon was lasting longer, which encouraged shoppers to linger.

Decline of shopping malls in the United States

In the United States, in the mid-1990s, malls were still being constructed at a rate of 140 a year. But in 2001, a PricewaterhouseCoopers study found that underperforming and vacant malls, known as "greyfield" and "dead mall" estates, were an emerging problem. In 2007, a year before the Great Recession, no new malls were built in America, for the first time in 50 years. City Creek Center Mall in Salt Lake City, which opened in March 2012, was the first to be built since the recession.

Malls began to lose consumers to open-air power centers and lifestyle centers during the 1990s, as consumers preferred to park right in front of and walk directly into big-box stores with lower prices and without the overhead of traditional malls (i.e., long enclosed corridors).

Another issue was that the growth-crazed American commercial real estate industry had simply built too many nice places to shop—far more than could be reasonably justified by the actual growth of the American population, retail sales, or any other economic indicator. The number of American shopping centers exploded from 4,500 in 1960 to 70,000 by 1986 to just under 108,000 by 2010.

Thus, the number of dead malls increased significantly in the early 21st century. The economic health of malls across the United States has been in decline, as revealed by high vacancy rates. From 2006 to 2010, the percentage of malls that are considered to be "dying" by real estate experts (have a vacancy rate of at least 40%), unhealthy (20–40%), or in trouble (10–20%) all increased greatly, and these high vacancy rates only partially decreased from 2010 to 2014. In 2014, nearly 3% of all malls in the United States were considered to be "dying" (40% or higher vacancy rates) and nearly one-fifth of all malls had vacancy rates considered "troubling" (10% or higher). Some real estate experts say the "fundamental problem" is a glut of malls in many parts of the country creating a market that is "extremely over-retailed". By the time shopping mall operator Unibail-Rodamco-Westfield decided to exit the American market in 2022, the United States had an average of 24.5 square feet of retail space per capita (in contrast to 4.5 square feet per capita in Europe).

In 2019, The Shops & Restaurants at Hudson Yards opened as an upscale mall in New York City with "a 'Fifth Avenue' mix of shops", such as H&M, Zara, and Sephora below them. This is one of the first two malls built recently, along with American Dream in which both opened in 2019 since City Creek Center.

Online shopping has also emerged as a major competitor to shopping malls. In the United States, online shopping has accounted for an increasing share of total retail sales. In 2013, roughly 200 out of 1,300 malls across the United States were going out of business. To combat this trend, developers have converted malls into other uses including attractions such as parks, movie theaters, gyms, and even fishing lakes. In the United States, the 600,000 square foot Highland Mall will be a campus for Austin Community College. In France, the So Ouest mall outside of Paris was designed to resemble elegant, Louis XV-style apartments and includes 17,000 square metres (180,000 sq ft) of green space. The Australian mall company Westfield launched an online mall (and later a mobile app) with 150 stores, 3,000 brands and over 1 million products.

The COVID-19 pandemic also significantly impacted the retail industry. Government regulations temporarily closed malls, increased entrance controls, and imposed strict public sanitation requirements.

Design:

Vertical malls

High land prices in populous cities have led to the concept of the "vertical mall", in which space allocated to retail is configured over a number of stories accessible by elevators and/or escalators (usually both) linking the different levels of the mall. The challenge of this type of mall is to overcome the natural tendency of shoppers to move horizontally and encourage shoppers to move upwards and downwards. The concept of a vertical mall was originally conceived in the late 1960s by the Mafco Company, former shopping center development division of Marshall Field & Co. The Water Tower Place skyscraper in Chicago, Illinois was built in 1975 by Urban Retail Properties. It contains a hotel, luxury condominiums, and office space and sits atop a block-long base containing an eight-level atrium-style retail mall that fronts on the Magnificent Mile.

Vertical malls are common in densely populated conurbations in East and Southeast Asia. Hong Kong in particular has numerous examples such as Times Square, Dragon Centre, Apm, Langham Place, ISQUARE, Hysan Place and The One.

A vertical mall may also be built where the geography prevents building outward or there are other restrictions on construction, such as historic buildings or significant archeology. The Darwin Shopping Centre and associated malls in Shrewsbury, UK, are built on the side of a steep hill, around the former town walls; consequently the shopping center is split over seven floors vertically – two locations horizontally – connected by elevators, escalators and bridge walkways. Some establishments incorporate such designs into their layout, such as Shrewsbury's former McDonald's, split into four stories with multiple mezzanines which featured medieval castle vaults – complete with arrowslits – in the basement dining rooms.

Components:

Food court

A common feature of shopping malls is a food court: this typically consists of a number of fast food vendors of various types, surrounding a shared seating area.

Department stores

When the shopping mall format was developed by Victor Gruen in the mid-1950s, signing larger department stores was necessary for the financial stability of the projects, and to draw retail traffic that would result in visits to the smaller stores in the mall as well. These larger stores are termed anchor stores or draw tenants. In physical configuration, anchor stores are normally located as far from each other as possible to maximize the amount of traffic from one anchor to another.

Regional differences:

Europe

There are a reported 222 malls in Europe. In 2014, these malls had combined sales of US$12.47 billion. This represented a 10% bump in revenues from the prior year.

U.K. and Ireland

In the United Kingdom and Ireland, both open-air and enclosed centers are commonly referred to as shopping centres. Mall primarily refers to either a shopping mall – a place where a collection of shops all adjoin a pedestrian area – or an exclusively pedestrianized street that allows shoppers to walk without interference from vehicle traffic.

The majority of British enclosed shopping centres, the equivalent of a U.S. mall, are located in city centres, usually found in old and historic shopping districts and surrounded by subsidiary open air shopping streets. Large examples include West Quay in Southampton; Manchester Arndale; Bullring Birmingham; Liverpool One; Trinity Leeds; Buchanan Galleries in Glasgow; St James Quarter in Edinburgh; and Eldon Square in Newcastle upon Tyne. In addition to the inner city shopping centres, large UK conurbations will also have large out-of-town "regional malls" such as the Metrocentre in Gateshead; Meadowhall Centre, Sheffield serving South Yorkshire; the Trafford Centre in Greater Manchester; White Rose Centre in Leeds; the Merry Hill Centre near Dudley; and Bluewater in Kent. These centres were built in the 1980s and 1990s, but planning regulations prohibit the construction of any more. Out-of-town shopping developments in the UK are now focused on retail parks, which consist of groups of warehouse style shops with individual entrances from outdoors. Planning policy prioritizes the development of existing town centres, although with patchy success. Westfield London (White City) is the largest shopping centre in Europe.

Russia

In Russia, on the other hand, as of 2013 a large number of new malls had been built near major cities, notably the MEGA malls such as Mega Belaya Dacha mall near Moscow. In large part they were financed by international investors and were popular with shoppers from the emerging middle class.

Management and legal issues:

Shopping property management firms

A shopping property management firm is a company that specializes in owning and managing shopping malls. Most shopping property management firms own at least 20 malls. Some firms use a similar naming scheme for most of their malls; for example, Mills Corporation puts "Mills" in most of its mall names and SM Prime Holdings of the Philippines puts "SM" in all of its malls, as well as anchor stores such as The SM Store, SM Appliance Center, SM Hypermarket, SM Cinema, and SM Supermarket. In the UK, The Mall Fund changes the name of any center it buys to "The Mall (location)", using its pink-M logo; when it sells a mall the center reverts to its own name and branding, such as the Ashley Centre in Epsom. Similarly, following its rebranding from Capital Shopping Centres, intu Properties renamed many of its centres to "intu (name/location)" (such as intu Lakeside); again, malls removed from the network revert to their own brand (see for instance The Glades in Bromley).

Legal issues

One controversial aspect of malls has been their effective displacement of traditional main streets or high streets. Some consumers prefer malls, with their parking garages, controlled environments, and private security guards, over central business districts (CBD) or downtowns, which frequently have limited parking, poor maintenance, outdoor weather, and limited police coverage.

In response, a few jurisdictions, notably California, have expanded the right of freedom of speech to ensure that speakers will be able to reach consumers who prefer to shop, eat, and socialize within the boundaries of privately owned malls. The Supreme Court decision Pruneyard Shopping Center v. Robins was issued on 9 June 1980 which affirmed the decision of the California Supreme Court in a case that arose out of a free speech dispute between the Pruneyard Shopping Center in Campbell, California, and several local high school students.

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It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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