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2350) Dental Implant
Gist
An implant is a medical device manufactured to replace a missing biological structure, support a damaged biological structure, or enhance an existing biological structure. For example, an implant may be a rod, used to strengthen weak bones.
A dental implant is a metal post that replaces the root portion of a missing tooth. A dental professional places an artificial tooth, also known as a crown, on an extension of the post of the dental implant, giving you the look of a real tooth.
Summary:
Overview
Dental implant, abutment and new tooth in jawbone to replace missing tooth
A dental implant replaces a missing tooth root. Once the implant heals, your dentist can restore it with an artificial tooth.
What are dental implants?
Dental implants are small, threaded posts that surgically replace missing teeth. In addition to filling in gaps in your smile, dental implants improve chewing function and overall oral health. Once healed, implants work much like natural teeth.
A dental implant has three main parts:
* Threaded post: You can think of this like an artificial tooth root. A provider places it in your jawbone during an oral surgery procedure.
* Abutment: This is a tiny connector post. It screws into the threaded post and extends slightly beyond your gums. It serves as the foundation for your new artificial tooth.
* Restoration: A dental restoration is any prosthetic that repairs or replaces teeth. Common dental implant restorations are crowns, bridges and dentures.
Most dental implants are titanium, but some are ceramic. Both materials are safe and biocompatible (friendly to the tissues inside of your mouth).
Missing teeth can take a toll on your oral health. But it also impacts your mental and emotional well-being. Do you avoid social situations? Or cover your mouth when you laugh? Do you rarely smile for photos? Dental implants can restore your smile and your confidence, so you don’t have to miss out on the things you enjoy.
What conditions are treated with dental implants?
Dental implants treat tooth loss, which can happen due to:
* Cavities.
* Cracked teeth.
* Gum disease.
* Teeth that never develop (anodontia).
* Teeth grinding or clenching (bruxism).
How common are dental implants?
Dental implants are a popular choice for tooth replacement. In the United States, dental providers place over 3 million implants each year.
Details
A dental implant (also known as an endosseous implant or fixture) is a prosthesis that interfaces with the bone of the jaw or skull to support a dental prosthesis such as a crown, bridge, denture, or facial prosthesis or to act as an orthodontic anchor. The basis for modern dental implants is a biological process called osseointegration, in which materials such as titanium or zirconia form an intimate bond to the bone. The implant fixture is first placed so that it is likely to osseointegrate, then a dental prosthetic is added. A variable amount of healing time is required for osseointegration before either the dental prosthetic (a tooth, bridge, or denture) is attached to the implant or an abutment is placed which will hold a dental prosthetic or crown.
Success or failure of implants depends primarily on the thickness and health of the bone and gingival tissues that surround the implant, but also on the health of the person receiving the treatment and drugs which affect the chances of osseointegration. The amount of stress that will be put on the implant and fixture during normal function is also evaluated. Planning the position and number of implants is key to the long-term health of the prosthetic since biomechanical forces created during chewing can be significant. The position of implants is determined by the position and angle of adjacent teeth, by lab simulations or by using computed tomography with CAD/CAM simulations and surgical guides called stents. The prerequisites for long-term success of osseointegrated dental implants are healthy bone and gingiva. Since both can atrophy after tooth extraction, pre-prosthetic procedures such as sinus lifts or gingival grafts are sometimes required to recreate ideal bone and gingiva.
The final prosthetic can be either fixed, where a person cannot remove the denture or teeth from their mouth, or removable, where they can remove the prosthetic. In each case an abutment is attached to the implant fixture. Where the prosthetic is fixed, the crown, bridge or denture is fixed to the abutment either with lag screws or with dental cement. Where the prosthetic is removable, a corresponding adapter is placed in the prosthetic so that the two pieces can be secured together.
The risks and complications related to implant therapy divide into those that occur during surgery (such as excessive bleeding or nerve injury, inadequate primary stability), those that occur in the first six months (such as infection and failure to osseointegrate) and those that occur long-term (such as peri-implantitis and mechanical failures). In the presence of healthy tissues, a well-integrated implant with appropriate biomechanical loads can have 5-year plus survival rates from 93 to 98 percent and 10-to-15-year lifespans for the prosthetic teeth. Long-term studies show a 16- to 20-year success (implants surviving without complications or revisions) between 52% and 76%, with complications occurring up to 48% of the time. Artificial intelligence is relevant as the basis for clinical decision support systems at the present time. Intelligent systems are used as an aid in determining the success rate of implants.
Medical uses
The primary use of dental implants is to support dental prosthetics (i.e. false teeth). Modern dental implants work through a biologic process where bone fuses tightly to the surface of specific materials such as titanium and some ceramics. The integration of implant and bone can support physical loads for decades without failure.
The US has seen an increasing use of dental implants, with usage increasing from 0.7% of patients missing at least one tooth (1999–2000), to 5.7% (2015–2016), and was projected to potentially reach 26% in 2026. Implants are used to replace missing individual teeth (single tooth restorations), multiple teeth, or to restore edentulous (toothless) dental arches (implant retained fixed bridge, implant-supported overdenture). While use of dental implants in the US has increased, other treatments to tooth loss exist.
Dental implants are also used in orthodontics to provide anchorage (orthodontic mini implants). Orthodontic treatment might be required prior to placing a dental implant.
An evolving field is the use of implants to retain obturators (removable prostheses used to fill a communication between the oral and maxillary or nasal cavities). Facial prosthetics, used to correct facial deformities (e.g. from cancer treatment or injuries), can use connections to implants placed in the facial bones. Depending on the situation the implant may be used to retain either a fixed or removable prosthetic that replaces part of the face.
Single tooth implant restoration
Single tooth restorations are individual freestanding units not connected to other teeth or implants, used to replace missing individual teeth. For individual tooth replacement, an implant abutment is first secured to the implant with an abutment screw. A crown (the dental prosthesis) is then connected to the abutment with dental cement, a small screw, or fused with the abutment as one piece during fabrication. Dental implants, in the same way, can also be used to retain a multiple tooth dental prosthesis either in the form of a fixed bridge or removable dentures.
There is limited evidence that implant-supported single crowns perform better than tooth-supported fixed partial dentures (FPDs) on a long-term basis. However, taking into account the favorable cost-benefit ratio and the high implant survival rate, dental implant therapy is the first-line strategy for single-tooth replacement. Implants preserve the integrity of the teeth adjacent to the edentulous area, and it has been shown that dental implant therapy is less costly and more efficient over time than tooth-supported FPDs for the replacement of one missing tooth. The major disadvantage of dental implant surgery is the need for a surgical procedure.
Implant retained fixed bridge or implant supported bridge
An implant supported bridge (or fixed denture) is a group of teeth secured to dental implants so the prosthetic cannot be removed by the user. They are similar to conventional bridges, except that the prosthesis is supported and retained by one or more implants instead of natural teeth. Bridges typically connect to more than one implant and may also connect to teeth as anchor points. Typically the number of teeth will outnumber the anchor points with the teeth that are directly over the implants referred to as abutments and those between abutments referred to as pontics. Implant supported bridges attach to implant abutments in the same way as a single tooth implant replacement. A fixed bridge may replace as few as two teeth (also known as a fixed partial denture) and may extend to replace an entire arch of teeth (also known as a fixed full denture). In both cases, the prosthesis is said to be fixed because it cannot be removed by the denture wearer.
Implant-supported overdenture
A removable implant-supported denture (also an implant-supported overdenture) is a removable prosthesis which replaces teeth, using implants to improve support, retention and stability. They are most commonly complete dentures (as opposed to partial), used to restore edentulous dental arches. The dental prosthesis can be disconnected from the implant abutments with finger pressure by the wearer. To enable this, the abutment is shaped as a small connector (a button, ball, bar or magnet) which can be connected to analogous adapters in the underside of the dental prosthesis.
Orthodontic mini-implants (TAD)
Dental implants are used in orthodontic patients to replace missing teeth (as above) or as a temporary anchorage device (TAD) to facilitate orthodontic movement by providing an additional anchorage point. For teeth to move, a force must be applied to them in the direction of the desired movement. The force stimulates cells in the periodontal ligament to cause bone remodeling, removing bone in the direction of travel of the tooth and adding it to the space created. In order to generate a force on a tooth, an anchor point (something that will not move) is needed. Since implants do not have a periodontal ligament, and bone remodelling will not be stimulated when tension is applied, they are ideal anchor points in orthodontics. Typically, implants designed for orthodontic movement are small and do not fully osseointegrate, allowing easy removal following treatment.[20] They are indicated when needing to shorten treatment time, or as an alternative to extra-oral anchorage. Mini-implants are frequently placed between the roots of teeth, but may also be sited in the roof of the mouth. They are then connected to a fixed brace to help move the teeth.
Small-diameter implants (mini-implants)
The introduction of small-diameter implants has provided dentists the means of providing edentulous and partially edentulous patients with immediate functioning transitional prostheses while definitive restorations are being fabricated. Many clinical studies have been done on the success of long-term usage of these implants. Based on the findings of many studies, mini dental implants exhibit excellent survival rates in the short to medium term (3–5 years). They appear to be a reasonable alternative treatment modality to retain mandibular complete overdentures from the available evidence.
Composition
A typical conventional implant consists of a titanium screw (resembling a tooth root) with a roughened or smooth surface. The majority of dental implants are made of commercially pure titanium, which is available in four grades depending upon the amount of carbon, nitrogen, oxygen and iron contained. Cold work hardened CP4 (maximum impurity limits of N .05 percent, C .10 percent, H .015 percent, Fe .50 percent, and O .40 percent) is the most commonly used titanium for implants. Grade 5 titanium, Titanium 6AL-4V (signifying the titanium alloy containing 6 percent aluminium and 4 percent vanadium alloy) is slightly harder than CP4 and used in the industry mostly for abutment screws and abutments. Most modern dental implants also have a textured surface (through etching, anodic oxidation or various-media blasting) to increase the surface area and osseointegration potential of the implant. If C.P. titanium or a titanium alloy has more than 85% titanium content, it will form a titanium-biocompatible titanium oxide surface layer or veneer that encloses the other metals, preventing them from contacting the bone.
Ceramic (zirconia-based) implants exist in one-piece (combining the screw and the abutment) or two-piece systems - the abutment being either cemented or screwed – and might lower the risk for peri‐implant diseases, but long-term data on success rates is missing.
Additional Information
Dental implant surgery replaces tooth roots with metal, screwlike posts and replaces damaged or missing teeth with artificial teeth that look and work much like real ones. Dental implant surgery can be a helpful choice when dentures or bridgework fit poorly. This surgery also can be an option when there aren't enough natural teeth roots to support dentures or build bridgework tooth replacements.
The type of implant and the condition of the jawbone guide how dental implant surgery is done. This surgery may involve several procedures. The major benefit of implants is solid support for the new teeth — a process that requires the bone to heal tightly around the implant. Because this bone healing requires time, the process can take many months.
Why it's done
Dental implants are surgically placed in your jawbone and serve as the roots of missing teeth. Because the titanium in the implants fuses with your jawbone, the implants won't slip, make noise or cause bone damage like fixed bridgework or dentures might. And the materials can't decay like your own teeth.
Dental implants may be right for you if you:
* Have one or more missing teeth.
* Have a jawbone that's reached full growth.
* Have enough bone to secure the implants or can have a bone graft.
* Have healthy tissues in your mouth.
* Don't have health conditions that can affect bone healing.
* Aren't able or willing to wear dentures.
* Want to improve your speech.
* Are willing to commit several months to the process.
* Don't smoke tobacco.
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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2351) Astrophysics/Astrophysicist
Gist
Astrophysics is a branch of space science that applies the laws of physics and chemistry to seek to understand the universe and our place in it. The field explores topics such as the birth, life and death of stars, planets, galaxies, nebulae and other objects in the universe.
Astronomers or astrophysicists study the universe to help us understand the physical matter and processes in our own solar system and other galaxies. It involves studying large objects, such as planets, as well as tiny particles.
Summary
An astrophysicist is a scientist, who studies the physical properties, processes and physics of things beyond the Earth. This includes the moon, the sun, the planets in our solar system and the galaxies which aren’t obvious to the human eye.
Working as an astrophysicist, you’ll use the expert knowledge of physics, astronomy and mathematics and apply it to explore the wonders of space such as black holes, superclusters and dark matter for example. The main purpose of the role is to figure out the origins of the universe, how it all works, what our place is within it, search for life on other planets around other stars and some, even look to predict the universe's ending.
It’s a highly skilled role where astrophysicists are educated across many disciplines.
Two types of astrophysicists complement each other's roles and they include the theoretical astrophysicist and the observational astrophysicist. Theoretical astrophysicists seek to explain observational results and observational astrophysicists help to confirm theories.
* Theoretical astrophysicists: These are the theoretical side of astrophysics, hence the name. They develop analytical or computer models to describe astronomical objects, and then use the models to pose theories about them. As what they’re analysing is too far away from reach, they’ll use properties of maths and physics to test the theories.
* Observational astrophysicists: These are the more practical side of astrophysics. Their focus is on acquiring data from celestial object observation and then analysing it, using physical. The work is similar to an astronomer, the role of observing the objects in outer space.
Responsibilities
As an astrophysicist, the responsibilities can vary, but generally, they include:
* Collaborating with other astrophysicists and working on research projects.
* Observing and analysing celestial bodies.
* Creating theories based on observations and the laws of physics.
* Testing your theories to find answers in a better understanding of the universe.
* Writing up research and essays on discoveries.
* Attending various lectures and conferences about research discoveries.
* The ability to use ground-based equipment and telescopes to explore space.
* Analysing research data and determining its purpose and significance.
* Performing presentations of your discoveries and research.
* Reviewing research from other scientists.
* Helping raise funds for scientific research and writing grant proposals.
* Teaching and training PhD candidates.
* The ability to measure emissions included infrared, gamma and x-ray from extraterrestrial sources.
* Assisting with calculating orbits and figuring out shapes, brightness, sizes and more.
Qualifications
An astrophysicist job is a master’s graduate career. Most employers at least require master’s astrophysics degrees, whilst many also require a doctoral PhD degree.
There are many relevant degrees you can study to aid your career as an astrophysicist. Before applying for your master’s you’ll need to acquire a bachelor’s (BA) degree. Any BA degree in a scientific field is useful such as astronomy degrees, physics degrees, maths degrees or a similar subject.
The next step is applying for your master’s degree to continue your scientific studies. The master’s degree will need to be in a specific subject such as astrophysics or astronomy degrees and will take around a year to complete. The last step in qualifying is gaining your PhD in astrophysics, which can take around three to four years to complete. As part of your PhD, you will need to create a dissertation which showcases all the research and findings you’ve made when studying.
Training and development
As astrophysicists, training is usually provided when studying and on the job. Entry-level astrophysicists can expect to work closely with their supervisors and professional astrophysicists to gain industry experience and see what the day-to-day role entails.
It’s also essential for astrophysicists to take responsibility into their own hands and keep up to date with the latest industry findings, and how you can apply them to new projects. You can do this by reading relevant journals, and scientific papers, watching documentaries and staying in the know with industry news.
Skills
As an astrophysicist, skills can vary from theory-based to practical skills. These are the skills required to become an astrophysicist:
* Strong analytical skills when conducting research projects, acquiring data and writing up reports of findings.
* The ability of a good researcher, to test your theories and report back to all other professionals in your team.
* Excellent mathematics skills to help test theories and report on data.
* Good at problem-solving, relating to your research and being able to identify problems in the first place.
* Create a hypothesis and take the steps to either prove or disprove a theory.
* Confident with using computers and various programmes.
* Strong written skills and verbal communication skills.
* Great knowledge of using astrophysics equipment and tools.
* In-depth understanding of the process of raising funds for scientific research.
Career prospects
As a qualified astrophysicist, you will initially work either within a university or research institution. Through years of experience, your position may become permanent and you will move up the ranks into a more senior role, in that university, research institution or observatory.
You could also go into teaching either public or privately in schools, colleges or universities as a lecturer. There’s the option to move into journalism to share your astrophysics expertise. Alternatively, you could head down the scientific research job route in a private company, or travel around to present your research and theories worldwide.
Based on your qualifications, there’s also the option to go into other fields including private/public research and development, healthcare technology and energy production, plus many more.
Details
Astrophysics is a science that employs the methods and principles of physics and chemistry in the study of astronomical objects and phenomena. As one of the founders of the discipline, James Keeler, said, astrophysics "seeks to ascertain the nature of the heavenly bodies, rather than their positions or motions in space—what they are, rather than where they are", which is studied in celestial mechanics.
Among the subjects studied are the Sun (solar physics), other stars, galaxies, extrasolar planets, the interstellar medium, and the cosmic microwave background. Emissions from these objects are examined across all parts of the electromagnetic spectrum, and the properties examined include luminosity, density, temperature, and chemical composition. Because astrophysics is a very broad subject, astrophysicists apply concepts and methods from many disciplines of physics, including classical mechanics, electromagnetism, statistical mechanics, thermodynamics, quantum mechanics, relativity, nuclear and particle physics, and atomic and molecular physics.
In practice, modern astronomical research often involves substantial work in the realms of theoretical and observational physics. Some areas of study for astrophysicists include the properties of dark matter, dark energy, black holes, and other celestial bodies; and the origin and ultimate fate of the universe. Topics also studied by theoretical astrophysicists include Solar System formation and evolution; stellar dynamics and evolution; galaxy formation and evolution; magnetohydrodynamics; large-scale structure of matter in the universe; origin of cosmic rays; general relativity, special relativity, and quantum and physical cosmology (the physical study of the largest-scale structures of the universe), including string cosmology and astroparticle physics.
History
Astronomy is an ancient science, long separated from the study of terrestrial physics. In the Aristotelian worldview, bodies in the sky appeared to be unchanging spheres whose only motion was uniform motion in a circle, while the earthly world was the realm which underwent growth and decay and in which natural motion was in a straight line and ended when the moving object reached its goal. Consequently, it was held that the celestial region was made of a fundamentally different kind of matter from that found in the terrestrial sphere; either Fire as maintained by Plato, or Aether as maintained by Aristotle. During the 17th century, natural philosophers such as Galileo, Descartes, and Newton began to maintain that the celestial and terrestrial regions were made of similar kinds of material and were subject to the same natural laws. Their challenge was that the tools had not yet been invented with which to prove these assertions.
For much of the nineteenth century, astronomical research was focused on the routine work of measuring the positions and computing the motions of astronomical objects. A new astronomy, soon to be called astrophysics, began to emerge when William Hyde Wollaston and Joseph von Fraunhofer independently discovered that, when decomposing the light from the Sun, a multitude of dark lines (regions where there was less or no light) were observed in the spectrum. By 1860 the physicist, Gustav Kirchhoff, and the chemist, Robert Bunsen, had demonstrated that the dark lines in the solar spectrum corresponded to bright lines in the spectra of known gases, specific lines corresponding to unique chemical elements. Kirchhoff deduced that the dark lines in the solar spectrum are caused by absorption by chemical elements in the Solar atmosphere. In this way it was proved that the chemical elements found in the Sun and stars were also found on Earth.
Among those who extended the study of solar and stellar spectra was Norman Lockyer, who in 1868 detected radiant, as well as dark lines in solar spectra. Working with chemist Edward Frankland to investigate the spectra of elements at various temperatures and pressures, he could not associate a yellow line in the solar spectrum with any known elements. He thus claimed the line represented a new element, which was called helium, after the Greek Helios, the Sun personified.
In 1885, Edward C. Pickering undertook an ambitious program of stellar spectral classification at Harvard College Observatory, in which a team of woman computers, notably Williamina Fleming, Antonia Maury, and Annie Jump Cannon, classified the spectra recorded on photographic plates. By 1890, a catalog of over 10,000 stars had been prepared that grouped them into thirteen spectral types. Following Pickering's vision, by 1924 Cannon expanded the catalog to nine volumes and over a quarter of a million stars, developing the Harvard Classification Scheme which was accepted for worldwide use in 1922.
In 1895, George Ellery Hale and James E. Keeler, along with a group of ten associate editors from Europe and the United States, established The Astrophysical Journal: An International Review of Spectroscopy and Astronomical Physics. It was intended that the journal would fill the gap between journals in astronomy and physics, providing a venue for publication of articles on astronomical applications of the spectroscope; on laboratory research closely allied to astronomical physics, including wavelength determinations of metallic and gaseous spectra and experiments on radiation and absorption; on theories of the Sun, Moon, planets, comets, meteors, and nebulae; and on instrumentation for telescopes and laboratories.
Around 1920, following the discovery of the Hertzsprung–Russell diagram still used as the basis for classifying stars and their evolution, Arthur Eddington anticipated the discovery and mechanism of nuclear fusion processes in stars, in his paper The Internal Constitution of the Stars. At that time, the source of stellar energy was a complete mystery; Eddington correctly speculated that the source was fusion of hydrogen into helium, liberating enormous energy according to Einstein's equation E = m{c}^2. This was a particularly remarkable development since at that time fusion and thermonuclear energy, and even that stars are largely composed of hydrogen (see metallicity), had not yet been discovered.
In 1925 Cecilia Helena Payne (later Cecilia Payne-Gaposchkin) wrote an influential doctoral dissertation at Radcliffe College, in which she applied Saha's ionization theory to stellar atmospheres to relate the spectral classes to the temperature of stars. Most significantly, she discovered that hydrogen and helium were the principal components of stars, not the composition of Earth. Despite Eddington's suggestion, discovery was so unexpected that her dissertation readers (including Russell) convinced her to modify the conclusion before publication. However, later research confirmed her discovery.
By the end of the 20th century, studies of astronomical spectra had expanded to cover wavelengths extending from radio waves through optical, x-ray, and gamma wavelengths. In the 21st century, it further expanded to include observations based on gravitational waves.
Observational astrophysics
Observational astronomy is a division of the astronomical science that is concerned with recording and interpreting data, in contrast with theoretical astrophysics, which is mainly concerned with finding out the measurable implications of physical models. It is the practice of observing celestial objects by using telescopes and other astronomical apparatus.
Most astrophysical observations are made using the electromagnetic spectrum.
* Radio astronomy studies radiation with a wavelength greater than a few millimeters. Example areas of study are radio waves, usually emitted by cold objects such as interstellar gas and dust clouds; the cosmic microwave background radiation which is the redshifted light from the Big Bang; pulsars, which were first detected at microwave frequencies. The study of these waves requires very large radio telescopes.
* Infrared astronomy studies radiation with a wavelength that is too long to be visible to the naked eye but is shorter than radio waves. Infrared observations are usually made with telescopes similar to the familiar optical telescopes. Objects colder than stars (such as planets) are normally studied at infrared frequencies.
* Optical astronomy was the earliest kind of astronomy. Telescopes paired with a charge-coupled device or spectroscopes are the most common instruments used. The Earth's atmosphere interferes somewhat with optical observations, so adaptive optics and space telescopes are used to obtain the highest possible image quality. In this wavelength range, stars are highly visible, and many chemical spectra can be observed to study the chemical composition of stars, galaxies, and nebulae.
* Ultraviolet, X-ray and gamma ray astronomy study very energetic processes such as binary pulsars, black holes, magnetars, and many others. These kinds of radiation do not penetrate the Earth's atmosphere well. There are two methods in use to observe this part of the electromagnetic spectrum—space-based telescopes and ground-based imaging air Cherenkov telescopes (IACT). Examples of Observatories of the first type are RXTE, the Chandra X-ray Observatory and the Compton Gamma Ray Observatory. Examples of IACTs are the High Energy Stereoscopic System (H.E.S.S.) and the MAGIC telescope.
Other than electromagnetic radiation, few things may be observed from the Earth that originate from great distances. A few gravitational wave observatories have been constructed, but gravitational waves are extremely difficult to detect. Neutrino observatories have also been built, primarily to study the Sun. Cosmic rays consisting of very high-energy particles can be observed hitting the Earth's atmosphere.
Observations can also vary in their time scale. Most optical observations take minutes to hours, so phenomena that change faster than this cannot readily be observed. However, historical data on some objects is available, spanning centuries or millennia. On the other hand, radio observations may look at events on a millisecond timescale (millisecond pulsars) or combine years of data (pulsar deceleration studies). The information obtained from these different timescales is very different.
The study of the Sun has a special place in observational astrophysics. Due to the tremendous distance of all other stars, the Sun can be observed in a kind of detail unparalleled by any other star. Understanding the Sun serves as a guide to understanding of other stars.
The topic of how stars change, or stellar evolution, is often modeled by placing the varieties of star types in their respective positions on the Hertzsprung–Russell diagram, which can be viewed as representing the state of a stellar object, from birth to destruction.
Theoretical astrophysics
Theoretical astrophysicists use a wide variety of tools which include analytical models (for example, polytropes to approximate the behaviors of a star) and computational numerical simulations. Each has some advantages. Analytical models of a process are generally better for giving insight into the heart of what is going on. Numerical models can reveal the existence of phenomena and effects that would otherwise not be seen.
Theorists in astrophysics endeavor to create theoretical models and figure out the observational consequences of those models. This helps allow observers to look for data that can refute a model or help in choosing between several alternate or conflicting models.
Theorists also try to generate or modify models to take into account new data. In the case of an inconsistency, the general tendency is to try to make minimal modifications to the model to fit the data. In some cases, a large amount of inconsistent data over time may lead to total abandonment of a model.
Topics studied by theoretical astrophysicists include stellar dynamics and evolution; galaxy formation and evolution; magnetohydrodynamics; large-scale structure of matter in the universe; origin of cosmic rays; general relativity and physical cosmology, including string cosmology and astroparticle physics. Relativistic astrophysics serves as a tool to gauge the properties of large-scale structures for which gravitation plays a significant role in physical phenomena investigated and as the basis for black hole (astro)physics and the study of gravitational waves.
Some widely accepted and studied theories and models in astrophysics, now included in the Lambda-CDM model, are the Big Bang, cosmic inflation, dark matter, dark energy and fundamental theories of physics.
Popularization
The roots of astrophysics can be found in the seventeenth century emergence of a unified physics, in which the same laws applied to the celestial and terrestrial realms. There were scientists who were qualified in both physics and astronomy who laid the firm foundation for the current science of astrophysics. In modern times, students continue to be drawn to astrophysics due to its popularization by the Royal Astronomical Society and notable educators such as prominent professors Lawrence Krauss, Subrahmanyan Chandrasekhar, Stephen Hawking, Hubert Reeves, Carl Sagan and Patrick Moore. The efforts of the early, late, and present scientists continue to attract young people to study the history and science of astrophysics. The television sitcom show The Big Bang Theory popularized the field of astrophysics with the general public, and featured some well known scientists like Stephen Hawking and Neil deGrasse Tyson.
Additional Information
The branch of astronomy called astrophysics is a new approach to an ancient field. For centuries astronomers studied the movements and interactions of the sun, the moon, planets, stars, comets, and meteors. Advances in technology have made it possible for scientists to study their properties and structure. Astrophysicists collect particles from meteorites and use telescopes on land, in balloons, and in satellites to gather data. They apply chemical and physical laws to explore what celestial objects consist of and how they formed and evolved.
Spectroscopy and photography, adopted for astronomical research in the 19th century, let investigators measure the quantity and quality of light emitted by stars and nebulas (clouds of interstellar gas and dust). That allowed them to study the brightness, temperature, and chemical composition of such objects in space. Investigators soon recognized that the properties of all celestial bodies, including the planets of the solar system, could only be understood in terms of what goes on inside and around them. The trend toward using physics and chemistry to interpret celestial observations gained momentum in the early 1920s, and many astronomers began referring to themselves as astrophysicists. Since the 1960s the field has developed more rapidly.
The major areas of current interest—X-ray astronomy, gamma-ray astronomy, infrared astronomy, and radio astronomy— depend heavily on engineering for the construction of telescopes, space probes, and related equipment. The scope of both observation and theory has expanded greatly because of such technological advances as electronic radar and radio units, high-speed computers, electronic radiation detectors, Earth-orbiting observatories, and long-range planetary probes.
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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2352) Catering/Catering Technology
Gist
Catering technology can be defined as 'the application of science to the art of catering'. For this purpose catering is taken to mean the feeding of people in large groups and includes restaurants, hotels, work canteens, schools meals and hospitals as well as take-away meals such as fish and chip shops.
Summary
Before you consider starting a catering business, it is crucial to understand the types of catering and what is catering. Knowing the basic concepts of catering will help you run a successful catering business, be a better caterer and draft your catering business plan.
So, what is catering? First, let’s review all you need to know about catering business basics and the types of catering.
What Is Catering?
Catering is the process or business of preparing food and providing food services for clients at remote locations, such as hotels, restaurants, offices, concerts, and events. Companies that offer food, drinks, and other services to various customers, typically for special occasions, make up the catering sector.
Some restaurant businesses may contract their cooking to catering businesses or even offer catering services to customers. For instance, customers may love a particular dish so much that they want the same food to be served at their event.
Catering is more than just preparing food and cleaning up after the party. Sometimes, catering branches into event planning and management. For example, if you offer corporate catering services, you will be required to work with large crowds and handle the needs of corporate clients.
A catering business may use its chefs to create food or buy food from a vendor or third party to deliver to the client. In addition, you may be asked to plan the food menu for corporate events such as picnics, holiday celebrations, and other functions. So, what is a caterer? Let’s find out.
What Is a Caterer?
A caterer is a person or business that prepares, cooks, and serves food and beverages to clients at remote locations and events. The caterer may be asked to prepare seasonal menu options and provide the equipment such as dishes, spoons, place settings, and wine glasses needed to serve guests at an event.
Starting a catering business is the ideal venture for you if you enjoy interacting with guests and producing a wide range of dishes that are delicious to eat as well as beautiful to look at. A caterer is inventive in novel recipes, culinary presentations, and menus.
In addition, caterers excel at multitasking. For instance, if professional wait staff will be serving each course of dinner to guests, the caterer must be ready to prepare all the dishes for the event at once.
To ensure attendees enjoy their time at events, caterers always offer a delicious, relaxing dinner. Additionally, caterers may deal with particular demands and design menus for unique events directly with clients.
Usually, a catering service sends waiters, waitresses, and busboys to set tables and serve meals during sit-down dining occasions. The caterer may send staff to prepare chafing dishes, bowls, and platters filled with food for buffets and casual gatherings, replace them, and serve food to guests.
4 Types of Catering
It is essential to choose a catering specialty when starting your catering business. With many catering types to choose from, it’s only logical to research your options and pick a niche that will suit your target market and improve your unique selling proposition.
Let’s look at the types of catering:
What Is Event Catering?
Event catering is planning a menu, preparing, delivering, and serving food at social events and parties. Catering is an integral part of any event.
As you know, events revolve around the food and drink menu. Party guests may even say that the success of any event depends on the catering services.
Birthday celebrations, retirement parties, grand openings, housewarming parties, weddings, and baby showers are a few exceptional events that fall under this category. In addition, catering packages for event catering sometimes include things like appetizers, decorations, bartenders, and servers.
Types of Event Catering
* Stationary Platters
* Hors D’oeuvres
* Small Plates and Stations
* Three-Course Plated Dinner
* Buffet
* Outdoor BBQ
What Is Full-Service Catering?
Full-service catering manages every facet of an event, including meal preparation, decorations, and clean-up following the event. Unlike regular event catering, where the caterer just prepares and serves food and drinks, a full-service caterer handles every event detail based on clients' specifications.
Some logistics, such as dinnerware, linens, serving utensils, and dedicated staff to help on-site, are handled by full-service catering. The head caterer oversees every aspect of the event according to what will appeal to each guest.
What Does a Full-service Catering Business Offer?
* Venue setup
* Menu planning
* Dining setup
* Food preparation
* After-party cleanup.
Details
Catering is the business of providing food services at a remote site or a site such as a hotel, hospital, pub, aircraft, cruise ship, park, festival, filming location or film studio.
History of catering
The earliest account of major services being catered in the United States was an event for William Howe of Philadelphia in 1778. The event served local foods that were a hit with the attendees, who eventually popularized catering as a career. The official industry began to be recognized around the 1820’s, with the caterers being disproportionately African-American. The catering business began to form around 1820, centered in Philadelphia.
Robert Bogle
The industry began to professionalize under the reigns of Robert Bogle who is recognized as "the originator of catering." Catering was originally done by servants of wealthy elites. Butlers and house slaves, which were often black, were in a good position to become caterers. Essentially, caterers in the 1860s were "public butlers" as they organized and executed the food aspect of a social gathering. A public butler was a butler working for several households. Bogle took on the role of public butler and took advantage of the food service market in the hospitality field.
Caterers like Bogle were involved with events likely to be catered today, such as weddings and funerals. Bogle also is credited with creating the Guild of Caterers and helping train other black caterers. This is important because catering provided not only jobs to black people but also opportunities to connect with elite members of Philadelphia society. Over time, the clientele of caterers became the middle class, who could not afford lavish gatherings and increasing competition from white caterers led to a decline in black catering businesses.
Evolution of catering
By the 1840s many restaurant owners began to combine catering services with their shops. Second-generation caterers grew the industry on the East Coast, becoming more widespread. Common usage of the word "caterer" came about in the 1880s at which point local directories began to use these term to describe the industry. White businessmen took over the industry by the 1900’s, with the Black Catering population disappearing.
In the 1930s, the Soviet Union, creating more simple menus, began developing state public catering establishments as part of its collectivization policies. A rationing system was implemented during World War II, and people became used to public catering. After the Second World War, many businessmen embraced catering as an alternative way of staying in business after the war. By the 1960s, the home-made food was overtaken by eating in public catering establishments.
By the 2000s, personal chef services started gaining popularity, with more women entering the workforce.[citation needed] People between 15 and 24 years of age spent as little as 11–17 minutes daily on food preparation and clean-up activities in 2006-2016, according to figures revealed by the American Time Use Survey conducted by the US Bureau of Labor Statistics. There are many types of catering, including Event catering, Wedding Catering and Corporate Catering.
Event catering
An event caterer serves food at indoor and outdoor events, including corporate and workplace events and parties at home and venues.
Mobile catering
A mobile caterer serves food directly from a vehicle, cart or truck which is designed for the purpose. Mobile catering is common at outdoor events such as concerts, workplaces, and downtown business districts. Mobile catering services require less maintenance costs when compared with other catering services. Mobile caterers may also be known as food trucks in some areas. Mobile catering is popular throughout New York City, though sometimes can be unprofitable. Ice cream vans are a familiar example of a catering truck in Canada, the United States and the United Kingdom.
Seat-back catering
Seat-back catering was a service offered by some charter airlines in the United Kingdom (e.g., Court Line, which introduced the idea in the early 1970s, and Dan-Air) that involved embedding two meals in a single seat-back tray. "One helping was intended for each leg of a charter flight, but Alan Murray, of Viking Aviation, had earlier revealed that 'with the ingenious use of a nail file or coin, one could open the inbound meal and have seconds'. The intention of participating airlines was to "save money, reduce congestion in the cabin and give punters the chance to decide when to eat their meal". By requiring less galley space on board, the planes could offer more passenger seats.
According to TravelUpdate's columnist, "The Flight Detective", "Salads and sandwiches were the usual staples," and "a small pellet of dry ice was put into the compartment for the return meal to try to keep it fresh." However, in addition to the fact that passengers on one leg were able to consume the food intended for other passengers on the following leg, there was a "food hygiene" problem, and the concept was discontinued by 1975.
Canapé catering
A canapé caterer serves canapés at events. They have become a popular type of food at events, Christmas parties and weddings. A canapé is a type of hors d'oeuvre, a small, prepared, and often decorative food, consisting of a small piece of bread or pastry. They should be easier to pick up and not be bigger than one or two bites. The bite-sized food is usually served before the starter or main course or alone with drinks at a drinks party.
Wedding catering
A wedding caterer provides food for a wedding reception and party, traditionally called a wedding breakfast. A wedding caterer can be hired independently or can be part of a package designed by the venue. Catering service providers are often skilled and experienced in preparing and serving high-quality cuisine. They offer a diverse and rich selection of food, creating a great experience for their customers. There are many different types of wedding caterers, each with their approach to food.
Shipboard catering
Merchant ships – especially ferries, cruise liners, and large cargo ships – often carry Catering Officers. In fact, the term "catering" was in use in the world of the merchant marine long before it became established as a land-bound business.
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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2353) Bun
Gist
A bun is a type of bread roll, typically filled with savory fillings (for example hamburger). A bun may also refer to a sweet cake in certain parts of the world. Though they come in many shapes and sizes, buns are most commonly round, and are generally hand-sized or smaller.
Summary:
Ingredient List
For the food processor buns:
* 3 cups bread or all-purpose flour (may be part whole wheat flour)
* 2 tablespoons granulated sugar
* 1 teaspoon salt
* 1 (¼ ounce) package instant yeast
* 3 tablespoons unsalted butter or margarine, cubed
* 1 cup lukewarm water (90°F)
Instructions
For the food processor buns:
In bowl of food processor fitted with dough blade, add flour, sugar, salt, yeast and butter. Place lid on processor and pulse 10 seconds.
Begin processing, pouring 1 cup warm water through tube. When dough forms a ball, stop adding water. All may not be needed. Process dough an additional 60 seconds to knead.
Remove dough and smooth into a ball; cover with bowl and let rest 15 minutes.
Divide dough into 8 buns and flatten into 3 ½” disks. Place buns two inches apart on greased or parchment-lined baking sheet. Cover; let rise in a warm place until doubled. Near the end of the rise, preheat oven to 400°F.
Bake 12 – 15 minutes, until golden and internal temperature registers 190°F – 195°F. Remove buns to rack and cool before slicing.
Nutrition Information Per Serving (1 Bun, 91g): 240 calories, 45 calories from fat, 5g total fat, 3g saturated fat, 0g trans fat, 10mg cholesterol, 300mg sodium, 41g total carbohydrate, 1g dietary fiber, 3g sugars, 7g protein, 97mcg folate, 2mg vitamin C, 2mg iron.
Details
A bun is a type of bread roll, typically filled with savory fillings (for example hamburger). A bun may also refer to a sweet cake in certain parts of the world. Though they come in many shapes and sizes, buns are most commonly round, and are generally hand-sized or smaller.
In the United Kingdom, the usage of the term differs greatly in different regions. In Southern England, a bun is a hand-sized sweet cake, while in Northern England, it is a small round of ordinary bread. In Ireland, a bun refers to a sweet cake, roughly analogous to an American cupcake.
Buns are usually made from a dough of flour, milk, yeast and small amounts of sugar and/or butter. Sweet bun dough is distinguished from bread dough by the addition of sugar, butter and sometimes egg. Common sweet varieties contain small fruit or nuts, topped with icing or caramel, and filled with jam or cream.
Chinese baozi, with savory or sweet fillings, are often referred to as "buns" in English.
Additional Information:
How to Make Hamburger Buns
It couldn't be easier to make these homemade hamburger buns. You'll find the step-by-step recipe below — but here's a brief overview of what you can expect:
* Make the dough.
* Let the dough rise.
* Form the buns.
* Bake the buns, then let them cool completely.
* Slice the buns in half lengthwise.
Begin by proofing the yeast with some of the flour. Once the yeast is foamy, add the remaining flour, an egg, butter, sugar, and salt. Fit a stand mixer with a dough hook and knead the dough, scraping the sides often, until it's soft and sticky.
Transfer the dough to a floured surface and form into a smooth, round ball. Tuck the ends underneath and return the dough to an oil-drizzled stand mixer bowl. Ensure the dough is coated with oil, then cover and allow to rise in a warm place until it has doubled in size.
Transfer the dough back to the floured work surface. Pat into a slightly rounded rectangle, then cut into eight equal squares. Use your hands to shape and pat the squares into discs. Arrange the buns on a floured baking sheet, cover, and let rise until they've doubled in size.
Brush the buns with an egg wash and sprinkle with sesame seeds. Bake in a preheated oven until lightly browned. Remove from the oven, allow the buns to cool, and slice in half lengthwise to serve.
How to Store Hamburger Buns
Store the homemade hamburger buns in an airtight container or wrapped in foil at room temperature for up to five days. Avoid short term refrigeration, as this will dry them out.
Can You Freeze Hamburger Buns?
Yes, you can freeze homemade hamburger buns (though they're best enjoyed fresh). Transfer the cooled buns to a freezer-safe container, then wrap in a layer of foil. Label with the date and freeze for up to two months. Thaw on a paper towel at room temperature. When it's about halfway thawed, flip the bun, and replace the paper towel.
Allrecipes Community Tips and Praise
"This recipe was so simple and fun to make," according to Kris Allfrey. "The hamburger buns were so light and the crumb texture was perfect. I followed the recipe and Chef John's instructions to the letter. I wouldn't change a thing about this recipe. They are excellent for pulled-pork sandwiches."
"I didn't make any changes except for what I put on top of the buns. I put dried onion, parsley, sesame seeds, and poppy seeds," says Ron Doty-Tolaro. "Also, as a rule of thumb, when making any kind of rising bread, lightly push in on the dough with one finger. If the dough is ready it will bounce back out. If the indentation stays in, knead it more."
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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2354) Hypertension
Gist
Hypertension (high blood pressure) is when the pressure in your blood vessels is too high (140/90 mmHg or higher). It is common but can be serious if not treated. People with high blood pressure may not feel symptoms. The only way to know is to get your blood pressure checked.
Summary
High blood pressure (also called hypertension) can lead to serious problems like heart attacks or strokes. But lifestyle changes and blood pressure medicines can help you stay healthy.
Check if you're at risk of high blood pressure
High blood pressure is very common, especially in older adults. There are usually no symptoms, so you may not realise you have it.
Things that increase your chances of having high blood pressure include:
* your age – you're more likely to get high blood pressure as you get older
* having close relatives with high blood pressure
* your ethnicity – you're at higher risk if you have a Black African, Black Caribbean or South Asian ethnic background
* having an unhealthy diet – especially a diet that's high in salt
* being overweight
* smoking
* drinking too much alcohol
* feeling stressed over a long period
Non-urgent advice:Get your blood pressure checked at a pharmacy or GP surgery if:
* you think you might have high blood pressure or might be at risk of having high blood pressure
* you're aged 40 or over and have not had your blood pressure checked for more than 5 years.
Some pharmacies may charge for a blood pressure check.
Some workplaces also offer blood pressure checks. Check with your employer.
Symptoms of high blood pressure
High blood pressure does not usually cause any symptoms.
Many people have it without realising it.
Rarely, high blood pressure can cause symptoms such as:
* headaches
* blurred vision
* chest pain
But the only way to find out if you have high blood pressure is to get your blood pressure checked.
Details
Hypertension, also known as high blood pressure, is a long-term medical condition in which the blood pressure in the arteries is persistently elevated. High blood pressure usually does not cause symptoms itself. It is, however, a major risk factor for stroke, coronary artery disease, heart failure, atrial fibrillation, peripheral arterial disease, vision loss, chronic kidney disease, and dementia. Hypertension is a major cause of premature death worldwide.
High blood pressure is classified as primary (essential) hypertension or secondary hypertension. About 90–95% of cases are primary, defined as high blood pressure due to nonspecific lifestyle and genetic factors. Lifestyle factors that increase the risk include excess salt in the diet, excess body weight, smoking, physical inactivity and alcohol use. The remaining 5–10% of cases are categorized as secondary hypertension, defined as high blood pressure due to a clearly identifiable cause, such as chronic kidney disease, narrowing of the kidney arteries, an endocrine disorder, or the use of birth control pills.
Blood pressure is classified by two measurements, the systolic (first number) and diastolic (second number) pressures. For most adults, normal blood pressure at rest is within the range of 100–140 millimeters mercury (mmHg) systolic and 60–90 mmHg diastolic. For most adults, high blood pressure is present if the resting blood pressure is persistently at or above 130/80 or 140/90 mmHg. Different numbers apply to children. Ambulatory blood pressure monitoring over a 24-hour period appears more accurate than office-based blood pressure measurement.
Lifestyle changes and medications can lower blood pressure and decrease the risk of health complications. Lifestyle changes include weight loss, physical exercise, decreased salt intake, reducing alcohol intake, and a healthy diet. If lifestyle changes are not sufficient, blood pressure medications are used. Up to three medications taken concurrently can control blood pressure in 90% of people. The treatment of moderately high arterial blood pressure (defined as >160/100 mmHg) with medications is associated with an improved life expectancy. The effect of treatment of blood pressure between 130/80 mmHg and 160/100 mmHg is less clear, with some reviews finding benefit and others finding unclear benefit. High blood pressure affects 33% of the population globally. About half of all people with high blood pressure do not know that they have it. In 2019, high blood pressure was believed to have been a factor in 19% of all deaths (10.4 million globally).
Signs and symptoms
Hypertension is rarely accompanied by symptoms. Half of all people with hypertension are unaware that they have it. Hypertension is usually identified as part of health screening or when seeking healthcare for an unrelated problem.
Some people with high blood pressure report headaches, as well as lightheadedness, vertigo, tinnitus (buzzing or hissing in the ears), altered vision or fainting episodes. These symptoms, however, might be related to associated anxiety rather than the high blood pressure itself.
Long-standing untreated hypertension can cause organ damage with signs such as changes in the optic fundus seen by ophthalmoscopy. The severity of hypertensive retinopathy correlates roughly with the duration or the severity of the hypertension. Other hypertension-caused organ damage include chronic kidney disease and thickening of the heart muscle.
Secondary hypertension
Secondary hypertension is hypertension due to an identifiable cause, and may result in certain specific additional signs and symptoms. For example, as well as causing high blood pressure, Cushing's syndrome frequently causes truncal obesity, glucose intolerance, moon face, a hump of fat behind the neck and shoulders (referred to as a buffalo hump), and purple abdominal stretch marks. Hyperthyroidism frequently causes weight loss with increased appetite, fast heart rate, bulging eyes, and tremor. Renal artery stenosis may be associated with a localized abdominal bruit to the left or right of the midline, or in both locations. Coarctation of the aorta frequently causes a decreased blood pressure in the lower extremities relative to the arms, or delayed or absent femoral arterial pulses. Pheochromocytoma may cause abrupt episodes of hypertension accompanied by headache, palpitations, pale appearance, and excessive sweating.
Hypertensive crisis
Severely elevated blood pressure (equal to or greater than a systolic 180 mmHg or diastolic of 120 mmHg) is referred to as a hypertensive crisis. Hypertensive crisis is categorized as either hypertensive urgency or hypertensive emergency, according to the absence or presence of end organ damage, respectively.
In hypertensive urgency, there is no evidence of end organ damage resulting from the elevated blood pressure. In these cases, oral medications are used to lower the BP gradually over 24 to 48 hours.
In hypertensive emergency, there is evidence of direct damage to one or more organs. The most affected organs include the brain, kidney, heart and lungs, producing symptoms which may include confusion, drowsiness, chest pain and breathlessness. In hypertensive emergency, the blood pressure must be reduced more rapidly to stop ongoing organ damage; however, there is a lack of randomized controlled trial evidence for this approach.
Pregnancy
Hypertension occurs in approximately 8–10% of pregnancies. Two blood pressure measurements six hours apart of greater than 140/90 mmHg are diagnostic of hypertension in pregnancy. High blood pressure in pregnancy can be classified as pre-existing hypertension, gestational hypertension, or pre-eclampsia. Women who have chronic hypertension before their pregnancy are at increased risk of complications such as premature birth, low birthweight or stillbirth. Women who have high blood pressure and had complications in their pregnancy have three times the risk of developing cardiovascular disease compared to women with normal blood pressure who had no complications in pregnancy.
Pre-eclampsia is a serious condition of the second half of pregnancy and following delivery characterised by increased blood pressure and the presence of protein in the urine. It occurs in about 5% of pregnancies and is responsible for approximately 16% of all maternal deaths globally. Pre-eclampsia also doubles the risk of death of the baby around the time of birth. Usually there are no symptoms in pre-eclampsia and it is detected by routine screening. When symptoms of pre-eclampsia occur the most common are headache, visual disturbance (often "flashing lights"), vomiting, pain over the stomach, and swelling. Pre-eclampsia can occasionally progress to a life-threatening condition called eclampsia, which is a hypertensive emergency and has several serious complications including vision loss, brain swelling, seizures, kidney failure, pulmonary edema, and disseminated intravascular coagulation (a blood clotting disorder).
In contrast, gestational hypertension is defined as new-onset hypertension during pregnancy without protein in the urine.
There have been significant findings on how exercising can help reduce the effects of hypertension just after one bout of exercise. Exercising can help reduce hypertension as well as pre-eclampsia and eclampsia.
The acute physiological responses include an increase in cardiac output (CO) of the individual (increased heart rate and stroke volume). This increase in CO can inadvertently maintain the amount of blood going into the muscles, improving functionality of the muscle later. Exercising can also improve systolic and diastolic blood pressure making it easier for blood to pump to the body. Through regular bouts of physical activity, blood pressure can reduce the incidence of hypertension.
Aerobic exercise has been shown to regulate blood pressure more effectively than resistance training. It is recommended to see the effects of exercising, that a person should aim for 5-7 days/ week of aerobic exercise. This type of exercise should have an intensity of light to moderate, utilizing ~85% of max heart rate (220-age). Aerobic has shown a decrease in SBP by 5-15mmHg, versus resistance training showing a decrease of only 3-5mmHg. Aerobic exercises such as jogging, rowing, dancing, or hiking can decrease SBP the greatest. The decrease in SBP can regulate the effect of hypertension ensuring the baby will not be harmed. Resistance training takes a toll on the cardiovascular system in untrained individuals, leading to a reluctance in prescription of resistance training for hypertensive reduction purposes.
Children
Failure to thrive, seizures, irritability, lack of energy, and difficulty in breathing can be associated with hypertension in newborns and young infants. In older infants and children, hypertension can cause headache, unexplained irritability, fatigue, failure to thrive, blurred vision, nosebleeds, and facial paralysis.
Causes:
Primary hypertension
Primary (also termed essential) hypertension results from a complex interaction of genes and environmental factors. More than 2000 common genetic variants with small effects on blood pressure have been identified in association with high blood pressure, as well as some rare genetic variants with large effects on blood pressure. There is also evidence that DNA methylation at multiple nearby CpG sites may link some sequence variation to blood pressure, possibly via effects on vascular or renal function.
Blood pressure rises with aging in societies with a western diet and lifestyle, and the risk of becoming hypertensive in later life is substantial in most such societies. Several environmental or lifestyle factors influence blood pressure. Reducing dietary salt intake lowers blood pressure; as does weight loss, exercise training, vegetarian diets, increased dietary potassium intake and high dietary calcium supplementation. Increasing alcohol intake is associated with higher blood pressure, but the possible roles of other factors such as caffeine consumption, and vitamin D deficiency are less clear. Average blood pressure is higher in the winter than in the summer.
Depression is associated with hypertension and loneliness is also a risk factor. Periodontal disease is also associated with high blood pressure. Chemical element As exposure through drinking water is associated with elevated blood pressure. Air pollution is associated with hypertension. Whether these associations are causal is unknown. Gout and elevated blood uric acid are associated with hypertension and evidence from genetic (Mendelian Randomization) studies and clinical trials indicate this relationship is likely to be causal. Insulin resistance, which is common in obesity and is a component of syndrome X (or metabolic syndrome), can cause hyperuricemia and gout and is also associated with elevated blood pressure.
Events in early life, such as low birth weight, maternal smoking, and lack of breastfeeding may be risk factors for adult essential hypertension, although strength of the relationships is weak and the mechanisms linking these exposures to adult hypertension remain unclear.
Secondary hypertension
Secondary hypertension results from an identifiable cause. Kidney disease is the most common secondary cause of hypertension. Hypertension can also be caused by endocrine conditions, such as Cushing's syndrome, hyperthyroidism, hypothyroidism, acromegaly, Conn's syndrome or hyperaldosteronism, renal artery stenosis (from atherosclerosis or fibromuscular dysplasia), hyperparathyroidism, and pheochromocytoma. Other causes of secondary hypertension include obesity, sleep apnea, pregnancy, coarctation of the aorta, excessive eating of liquorice, excessive drinking of alcohol, certain prescription medicines, herbal remedies, and stimulants such as cocaine and methamphetamine.
A 2018 review found that any alcohol increased blood pressure in males while over one or two drinks increased the risk in females.
Additional Information
Hypertension is a condition that arises when the blood pressure is abnormally high. Hypertension occurs when the body’s smaller blood vessels (the arterioles) narrow, causing the blood to exert excessive pressure against the vessel walls and forcing the heart to work harder to maintain the pressure. Although the heart and blood vessels can tolerate increased blood pressure for months and even years, eventually the heart may enlarge (a condition called hypertrophy) and be weakened to the point of failure. Injury to blood vessels in the kidneys, brain, and eyes also may occur.
Blood pressure is actually a measure of two pressures, the systolic and the diastolic. The systolic pressure (the higher pressure and the first number recorded) is the force that blood exerts on the artery walls as the heart contracts to pump the blood to the peripheral organs and tissues. The diastolic pressure (the lower pressure and the second number recorded) is residual pressure exerted on the arteries as the heart relaxes between beats. A diagnosis of hypertension is made when blood pressure reaches or exceeds 140/90 mmHg (read as “140 over 90 millimeters of mercury”).
Classification
When there is no demonstrable underlying cause of hypertension, the condition is classified as essential hypertension. (Essential hypertension is also called primary or idiopathic hypertension.) This is by far the most common type of high blood pressure, occurring in 90 to 95 percent of patients. Genetic factors appear to play a major role in the occurrence of essential hypertension. Secondary hypertension is associated with an underlying disease, which may be renal, neurologic, or endocrine in origin; examples of such diseases include Bright disease (glomerulonephritis; inflammation of the urine-producing structures in the kidney), atherosclerosis of blood vessels in the brain, and Cushing syndrome (hyperactivity of the adrenal glands). In cases of secondary hypertension, correction of the underlying cause may cure the hypertension. Various external agents also can raise blood pressure. These include cocaine, amphetamines, cold remedies, thyroid supplements, corticosteroids, nonsteroidal anti-inflammatory drugs (NSAIDs), and oral contraceptives.
Malignant hypertension is present when there is a sustained or sudden rise in diastolic blood pressure exceeding 120 mmHg, with accompanying evidence of damage to organs such as the eyes, brain, heart, and kidneys. Malignant hypertension is a medical emergency and requires immediate therapy and hospitalization.
Epidemiology
Elevated arterial pressure is one of the most important public health problems in developed countries. In the United States, for instance, nearly 30 percent of the adult population is hypertensive. High blood pressure is significantly more prevalent and serious among African Americans. Age, race, gender, smoking, alcohol intake, elevated serum cholesterol, salt intake, glucose intolerance, obesity, and stress all may contribute to the degree and prognosis of the disease. In both men and women, the risk of developing high blood pressure increases with age.
Hypertension has been called the “silent killer” because it usually produces no symptoms. It is important, therefore, for anyone with risk factors to have their blood pressure checked regularly and to make appropriate lifestyle changes.
Complications
The most common immediate cause of hypertension-related death is heart disease, but death from stroke or renal (kidney) failure is also frequent. Complications result directly from the increased pressure (cerebral hemorrhage, retinopathy, left ventricular hypertrophy, congestive heart failure, arterial aneurysm, and vascular rupture), from atherosclerosis (increased coronary, cerebral, and renal vascular resistance), and from decreased blood flow and ischemia (myocardial infarction, cerebral thrombosis and infarction, and renal nephrosclerosis). The risk of developing many of these complications is greatly elevated when hypertension is diagnosed in young adulthood.
Treatment
Effective treatment will reduce overall cardiovascular morbidity and mortality. Nondrug therapy consists of: (1) relief of stress, (2) dietary management (restricted intake of salt, calories, cholesterol, and saturated fats; sufficient intake of potassium, magnesium, calcium, and vitamin C), (3) regular aerobic exercise, (4) weight reduction, (5) smoking cessation, and (6) reduced intake of alcohol and caffeine.
Mild to moderate hypertension may be controlled by a single-drug regimen, although more severe cases often require a combination of two or more drugs. Diuretics are a common medication; these agents lower blood pressure primarily by reducing body fluids and thereby reducing peripheral resistance to blood flow. However, they deplete the body’s supply of potassium, so it is recommended that potassium supplements be added or that potassium-sparing diuretics be used. Beta-adrenergic blockers (beta-blockers) block the effects of epinephrine (adrenaline), thus easing the heart’s pumping action and widening blood vessels. Vasodilators act by relaxing smooth muscle in the walls of blood vessels, allowing small arteries to dilate and thereby decreasing total peripheral resistance. Calcium channel blockers promote peripheral vasodilation and reduce vascular resistance. Angiotensin-converting enzyme (ACE) inhibitors inhibit the generation of a potent vasoconstriction agent (angiotensin II), and they also may retard the degradation of a potent vasodilator (bradykinin) and involve the synthesis of vasodilatory prostaglandins. Angiotensin receptor antagonists are similar to ACE inhibitors in utility and tolerability, but instead of blocking the production of angiotensin II, they completely inhibit its binding to the angiotensin II receptor. Statins, best known for their use as cholesterol-lowering agents, have shown promise as antihypertensive drugs because of their ability to lower both diastolic and systolic blood pressure. The mechanism by which statins act to reduce blood pressure is unknown; however, scientists suspect that these drugs activate substances involved in vasodilation.
Other agents that may be used in the treatment of hypertension include the antidiabetic drug semaglutide and the drug aprocitentan. Semaglutide is used specifically in patients who are obese or overweight. The drug acts as a glucagon-like peptide-1 (GLP-1) receptor agonist; GLP-1 interacts with receptors in the brain involved in the regulation of appetite, and thus semaglutide effectively triggers a reduction in appetite and thereby helps relieve symptoms of weight-related complications, such as hypertension. Aprocitentan acts as an inhibitor at endothelin A and endothelin B receptors, preventing binding by endothelin-1, which is a key protein involved in the activation of vasoconstriction and inflammatory processes in blood vessels.
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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2355) Hypotension
Gist
Low blood pressure is a condition in which the force of the blood pushing against the artery walls is too low. It's also called hypotension. Blood pressure is measured in millimeters of mercury (mm Hg). In general, low blood pressure is a reading lower than 90/60 mm Hg.
Low blood pressure occurs when blood pressure is much lower than normal. This means the heart, brain, and other parts of the body may not get enough blood. Normal blood pressure is mostly between 90/60 mmHg and 120/80 mmHg. The medical word for low blood pressure is hypotension.
Summary
Hypotension, also known as low blood pressure, is a cardiovascular condition characterized by abnormally reduced blood pressure. Blood pressure is the force of blood pushing against the walls of the arteries as the heart pumps out blood and is indicated by two numbers, the systolic blood pressure (the top number) and the diastolic blood pressure (the bottom number), which are the maximum and minimum blood pressures within the cardiac cycle, respectively. A systolic blood pressure of less than 90 millimeters of mercury (mmHg) or diastolic of less than 60 mmHg is generally considered to be hypotension. Different numbers apply to children. However, in practice, blood pressure is considered too low only if noticeable symptoms are present.
Symptoms may include dizziness, lightheadedness, confusion, feeling tired, weakness, headache, blurred vision, nausea, neck or back pain, an irregular heartbeat or feeling that the heart is skipping beats or fluttering, sweating, and fainting. Hypotension is the opposite of hypertension, which is high blood pressure. It is best understood as a physiological state rather than a disease. Severely low blood pressure can deprive the brain and other vital organs of oxygen and nutrients, leading to a life-threatening condition called shock. Shock is classified based on the underlying cause, including hypovolemic shock, cardiogenic shock, distributive shock, and obstructive shock.
Hypotension can be caused by strenuous exercise, excessive heat, low blood volume (hypovolemia), hormonal changes, widening of blood vessels, anemia, vitamin B12 deficiency, anaphylaxis, heart problems, or endocrine problems. Some medications can also lead to hypotension. There are also syndromes that can cause hypotension in patients including orthostatic hypotension, vasovagal syncope, and other rarer conditions.
For many people, excessively low blood pressure can cause dizziness and fainting or indicate serious heart, endocrine or neurological disorders.
For some people who exercise and are in top physical condition, low blood pressure could be normal. A single session of exercise can induce hypotension and water-based exercise can induce a hypotensive response.
Treatment depends on what causes low blood pressure. Treatment of hypotension may include the use of intravenous fluids or vasopressors. When using vasopressors, trying to achieve a mean arterial pressure (MAP) of greater than 70 mmHg does not appear to result in better outcomes than trying to achieve an MAP of greater than 65 mmHg in adults.
Details
Low blood pressure is a reading below 90/60 mm Hg. Many issues can cause low blood pressure. Treatment varies depending on what’s causing it. Symptoms of low blood pressure include dizziness and fainting, but many people don’t have symptoms. The cause also affects your prognosis.
Symptoms of low blood pressure include feeling tired or dizzy.
What is low blood pressure?
Hypotension, or low blood pressure, is when your blood pressure is much lower than expected. It can happen either as a condition on its own or as a symptom of a wide range of conditions. It may not cause symptoms. But when it does, you may need medical attention.
Types of low blood pressure
Hypotension has two definitions:
* Absolute hypotension: Your resting blood pressure is below 90/60 millimeters of mercury (mm Hg).
* Orthostatic hypotension: Your blood pressure stays low for longer than three minutes after you stand up from a sitting position. (It’s normal for your blood pressure to drop briefly when you change positions, but not for that long.) The drop must be 20 mm Hg or more for your systolic (top) pressure and 10 mm Hg or more for your diastolic (bottom) pressure. Another name for this is postural hypotension because it happens with changes in posture.
Measuring blood pressure involves two numbers:
Systolic (top number): This is the pressure on your arteries each time your heart beats.
Diastolic (bottom number): This is how much pressure your arteries are under between heartbeats.
What is considered low blood pressure?
Learn how blood pressure is measured.
Low blood pressure is below 90/60 mm Hg. Normal blood pressure is above that, up to 120/80 mm Hg.
How common is low blood pressure?
Because low blood pressure is common without any symptoms, it’s impossible to know how many people it affects. However, orthostatic hypotension seems to be more and more common as you get older. An estimated 5% of people have it at age 50, while that figure climbs to more than 30% in people over 70.
Who does low blood pressure affect?
Hypotension can affect people of any age and background, depending on why it happens. However, it’s more likely to cause symptoms in people over 50 (especially orthostatic hypotension). It can also happen (with no symptoms) to people who are very physically active, which is more common in younger people.
Symptoms and Causes:
What are the symptoms of low blood pressure?
Low blood pressure symptoms include:
* Dizziness or feeling lightheaded.
* Fainting or passing out (syncope).
* Nausea or vomiting.
* Distorted or blurred vision.
* Fast, shallow breathing.
* Fatigue or weakness.
* Feeling tired, sluggish or lethargic.
* Confusion or trouble concentrating.
* Agitation or other unusual changes in behavior (a person not acting like themselves).
For people with symptoms, the effects depend on why hypotension is happening, how fast it develops and what caused it. Slow decreases in blood pressure happen normally, so hypotension becomes more common as people get older. Fast decreases in blood pressure can mean certain parts of your body aren’t getting enough blood flow. That can have effects that are unpleasant, disruptive or even dangerous.
Usually, your body can automatically control your blood pressure and keep it from dropping too much. If it starts to drop, your body tries to make up for that, either by speeding up your heart rate or constricting blood vessels to make them narrower. Symptoms of hypotension happen when your body can’t offset the drop in blood pressure.
For many people, hypotension doesn’t cause any symptoms. Many people don’t even know their blood pressure is low unless they measure their blood pressure.
What are the possible signs of low blood pressure?
Your healthcare provider may observe these signs of low blood pressure:
* A heart rate that’s too slow or too fast.
* A skin color that looks lighter than it usually does.
* Cool kneecaps.
* Low cardiac output (how much blood your heart pumps).
* Low urine (pee) output.
What causes low blood pressure?
Hypotension can happen for a wide range of reasons. Causes of low blood pressure include:
* Orthostatic hypotension: This happens when you stand up too quickly and your body can’t compensate with more blood flow to your brain.
* Central nervous system diseases: Conditions like Parkinson’s disease can affect how your nervous system controls your blood pressure. People with these conditions may feel the effects of low blood pressure after eating because their digestive systems use more blood as they digest food.
* Low blood volume: Blood loss from severe injuries can cause low blood pressure. Dehydration can also contribute to low blood volume.
* Life-threatening conditions: These conditions include irregular heart rhythms (arrhythmias), pulmonary embolism (PE), heart attacks and collapsed lung. Life-threatening allergic reactions (anaphylaxis) or immune reactions to severe infections (sepsis) can also cause hypotension.
* Heart and lung conditions: You can get hypotension when your heart beats too quickly or too slowly, or if your lungs aren’t working as they should. Advanced heart failure (weak heart muscle) is another cause.
* Prescription medications: Hypotension can happen with medications that treat high blood pressure, heart failure, erectile dysfunction, neurological problems, depression and more. Don’t stop taking any prescribed medicine unless your provider tells you to stop.
* Alcohol or recreational drugs: Recreational drugs can lower your blood pressure, as can alcohol (for a short time). Certain herbal supplements, vitamins or home remedies can also lower your blood pressure. This is why you should always include these when you tell your healthcare provider what medications you’re taking.
* Pregnancy: Orthostatic hypotension is possible in the first and second trimesters of pregnancy. Bleeding or other complications of pregnancy can also cause low blood pressure.
* Extreme temperatures: Being too hot or too cold can affect hypotension and make its effects worse.
What are the complications of low blood pressure?
Complications that can happen because of hypotension include:
* Falls and fall-related injuries: These are the biggest risks with hypotension because it can cause dizziness and fainting. Falls can lead to broken bones, concussions and other serious or even life-threatening injuries. If you have hypotension, preventing falls should be one of your biggest priorities.
* Shock: When your blood pressure is low, that can affect your organs by reducing the amount of blood they get. That can cause organ damage or even shock (where your body starts to shut down because of limited blood flow and oxygen).
* Heart problems or stroke: Low blood pressure can cause your heart to try to compensate by pumping faster or harder. Over time, that can cause permanent heart damage and even heart failure. It can also cause problems like deep vein thrombosis (DVT) and stroke because blood isn’t flowing like it should, causing clots to form.
Diagnosis and Tests:
How is low blood pressure diagnosed?
Hypotension itself is easy to diagnose. Taking your blood pressure is all you need to do. But figuring out why you have hypotension is another story. If you have symptoms, a healthcare provider will likely use a variety of tests to figure out why it’s happening and if there’s any danger to you because of it.
What tests will be done to diagnose low blood pressure?
Your provider may recommend the following tests:
Lab testing
Tests on your blood and pee (urine) can look for any potential problems, like:
* Diabetes.
* Vitamin deficiencies.
* Thyroid or hormone problems.
* Low iron levels (anemia).
* Pregnancy (for anyone who can become pregnant).
Imaging
If providers suspect a heart or lung problem is behind your hypotension, they’ll likely use imaging tests to see if they’re right. These tests include:
* X-rays.
* Computed tomography (CT) scans.
* Magnetic resonance imaging (MRI).
* Echocardiogram or similar ultrasound-based tests.
Diagnostic testing
These tests look for specific problems with your heart or other body systems.
* Electrocardiogram (ECG or EKG).
* Exercise stress testing.
* Tilt table test (can help in diagnosing orthostatic hypotension).
Additional Information
Hypotension is a condition in which the blood pressure is abnormally low, either because of reduced blood volume or because of increased blood-vessel capacity. Though not in itself an indication of ill health, it often accompanies disease.
Extensive bleeding is an obvious cause of reduced blood volume that leads to hypotension. There are other possible causes. A person who has suffered an extensive burn loses blood plasma—blood minus the red and white blood cells and the platelets. Blood volume is reduced in a number of conditions involving loss of salt and water from the tissues—as in excessive sweating and diarrhea—and its replacement with water from the blood. Loss of water from the blood to the tissues may result from exposure to cold temperatures. Also, a person who remains standing for as long as one-half hour may temporarily lose as much as 15 percent of the blood water into the tissues of the legs.
Orthostatic hypotension—low blood pressure upon standing up—seems to stem from a failure in the autonomic nervous system. Normally, when a person stands up, there is a reflex constriction of the small arteries and veins to offset the effects of gravity. Hypotension from an increase in the capacity of the blood vessels is a factor in fainting (see syncope). Hypotension is also a factor in poliomyelitis, in shock, and in overdose of depressant drugs, such as barbiturates.
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.
Offline
2356) Mathematician
Gist
A mathematician is someone who uses an extensive knowledge of mathematics in their work, typically to solve mathematical problems. Mathematicians are concerned with numbers, data, quantity, structure, space, models, and change.
Summary
Mathematics is the science of structure, order, and relation that has evolved from elemental practices of counting, measuring, and describing the shapes of objects. It deals with logical reasoning and quantitative calculation, and its development has involved an increasing degree of idealization and abstraction of its subject matter. Since the 17th century, mathematics has been an indispensable adjunct to the physical sciences and technology, and in more recent times it has assumed a similar role in the quantitative aspects of the life sciences.
In many cultures—under the stimulus of the needs of practical pursuits, such as commerce and agriculture—mathematics has developed far beyond basic counting. This growth has been greatest in societies complex enough to sustain these activities and to provide leisure for contemplation and the opportunity to build on the achievements of earlier mathematicians.
All mathematical systems (for example, Euclidean geometry) are combinations of sets of axioms and of theorems that can be logically deduced from the axioms. Inquiries into the logical and philosophical basis of mathematics reduce to questions of whether the axioms of a given system ensure its completeness and its consistency. For full treatment of this aspect, see mathematics, foundations of.
As a consequence of the exponential growth of science, most mathematics has developed since the 15th century ce, and it is a historical fact that, from the 15th century to the late 20th century, new developments in mathematics were largely concentrated in Europe and North America. For these reasons, the bulk of this article is devoted to European developments since 1500.
This does not mean, however, that developments elsewhere have been unimportant. Indeed, to understand the history of mathematics in Europe, it is necessary to know its history at least in ancient Mesopotamia and Egypt, in ancient Greece, and in Islamic civilization from the 9th to the 15th century. The way in which these civilizations influenced one another and the important direct contributions Greece and Islam made to later developments are discussed in the first parts of this article.
India’s contributions to the development of contemporary mathematics were made through the considerable influence of Indian achievements on Islamic mathematics during its formative years. A separate article, South Asian mathematics, focuses on the early history of mathematics in the Indian subcontinent and the development there of the modern decimal place-value numeral system. The article East Asian mathematics covers the mostly independent development of mathematics in China, Japan, Korea, and Vietnam.
The substantive branches of mathematics are treated in several articles. See algebra; analysis; arithmetic; combinatorics; game theory; geometry; number theory; numerical analysis; optimization; probability theory; set theory; statistics; trigonometry.
Ancient mathematical sources
It is important to be aware of the character of the sources for the study of the history of mathematics. The history of Mesopotamian and Egyptian mathematics is based on the extant original documents written by scribes. Although in the case of Egypt these documents are few, they are all of a type and leave little doubt that Egyptian mathematics was, on the whole, elementary and profoundly practical in its orientation. For Mesopotamian mathematics, on the other hand, there are a large number of clay tablets, which reveal mathematical achievements of a much higher order than those of the Egyptians. The tablets indicate that the Mesopotamians had a great deal of remarkable mathematical knowledge, although they offer no evidence that this knowledge was organized into a deductive system. Future research may reveal more about the early development of mathematics in Mesopotamia or about its influence on Greek mathematics, but it seems likely that this picture of Mesopotamian mathematics will stand.
From the period before Alexander the Great, no Greek mathematical documents have been preserved except for fragmentary paraphrases, and, even for the subsequent period, it is well to remember that the oldest copies of Euclid’s Elements are in Byzantine manuscripts dating from the 10th century ce. This stands in complete contrast to the situation described above for Egyptian and Babylonian documents. Although, in general outline, the present account of Greek mathematics is secure, in such important matters as the origin of the axiomatic method, the pre-Euclidean theory of ratios, and the discovery of the conic sections, historians have given competing accounts based on fragmentary texts, quotations of early writings culled from nonmathematical sources, and a considerable amount of conjecture.
Many important treatises from the early period of Islamic mathematics have not survived or have survived only in Latin translations, so that there are still many unanswered questions about the relationship between early Islamic mathematics and the mathematics of Greece and India. In addition, the amount of surviving material from later centuries is so large in comparison with that which has been studied that it is not yet possible to offer any sure judgment of what later Islamic mathematics did not contain, and therefore it is not yet possible to evaluate with any assurance what was original in European mathematics from the 11th to the 15th century.
In modern times the invention of printing has largely solved the problem of obtaining secure texts and has allowed historians of mathematics to concentrate their editorial efforts on the correspondence or the unpublished works of mathematicians. However, the exponential growth of mathematics means that, for the period from the 19th century on, historians are able to treat only the major figures in any detail. In addition, there is, as the period gets nearer the present, the problem of perspective. Mathematics, like any other human activity, has its fashions, and the nearer one is to a given period, the more likely these fashions will look like the wave of the future. For this reason, the present article makes no attempt to assess the most recent developments in the subject.
Details
A mathematician is someone who uses an extensive knowledge of mathematics in their work, typically to solve mathematical problems. Mathematicians are concerned with numbers, data, quantity, structure, space, models, and change.
History
One of the earliest known mathematicians was Thales of Miletus (c. 624 – c. 546 BC); he has been hailed as the first true mathematician and the first known individual to whom a mathematical discovery has been attributed. He is credited with the first use of deductive reasoning applied to geometry, by deriving four corollaries to Thales's theorem.
The number of known mathematicians grew when Pythagoras of Samos (c. 582 – c. 507 BC) established the Pythagorean school, whose doctrine it was that mathematics ruled the universe and whose motto was "All is number". It was the Pythagoreans who coined the term "mathematics", and with whom the study of mathematics for its own sake begins.
The first woman mathematician recorded by history was Hypatia of Alexandria (c. AD 350 – 415). She succeeded her father as librarian at the Great Library and wrote many works on applied mathematics. Because of a political dispute, the Christian community in Alexandria punished her, presuming she was involved, by stripping her naked and scraping off her skin with clamshells (some say roofing tiles).
Science and mathematics in the Islamic world during the Middle Ages followed various models and modes of funding varied based primarily on scholars. It was extensive patronage and strong intellectual policies implemented by specific rulers that allowed scientific knowledge to develop in many areas. Funding for translation of scientific texts in other languages was ongoing throughout the reign of certain caliphs, and it turned out that certain scholars became experts in the works they translated, and in turn received further support for continuing to develop certain sciences. As these sciences received wider attention from the elite, more scholars were invited and funded to study particular sciences. An example of a translator and mathematician who benefited from this type of support was Al-Khawarizmi. A notable feature of many scholars working under Muslim rule in medieval times is that they were often polymaths. Examples include the work on optics, maths and astronomy of Ibn al-Haytham.
The Renaissance brought an increased emphasis on mathematics and science to Europe. During this period of transition from a mainly feudal and ecclesiastical culture to a predominantly secular one, many notable mathematicians had other occupations: Luca Pacioli (founder of accounting); Niccolò Fontana Tartaglia (notable engineer and bookkeeper); Gerolamo Cardano (earliest founder of probability and binomial expansion); Robert Recorde (physician) and François Viète (lawyer).
As time passed, many mathematicians gravitated towards universities. An emphasis on free thinking and experimentation had begun in Britain's oldest universities beginning in the seventeenth century at Oxford with the scientists Robert Hooke and Robert Boyle, and at Cambridge where Isaac Newton was Lucasian Professor of Mathematics & Physics. Moving into the 19th century, the objective of universities all across Europe evolved from teaching the "regurgitation of knowledge" to "encouraging productive thinking." In 1810, Alexander von Humboldt convinced the king of Prussia, Fredrick William III, to build a university in Berlin based on Friedrich Schleiermacher's liberal ideas; the goal was to demonstrate the process of the discovery of knowledge and to teach students to "take account of fundamental laws of science in all their thinking." Thus, seminars and laboratories started to evolve.
British universities of this period adopted some approaches familiar to the Italian and German universities, but as they already enjoyed substantial freedoms and autonomy the changes there had begun with the Age of Enlightenment, the same influences that inspired Humboldt. The Universities of Oxford and Cambridge emphasized the importance of research, arguably more authentically implementing Humboldt's idea of a university than even German universities, which were subject to state authority. Overall, science (including mathematics) became the focus of universities in the 19th and 20th centuries. Students could conduct research in seminars or laboratories and began to produce doctoral theses with more scientific content. According to Humboldt, the mission of the University of Berlin was to pursue scientific knowledge. The German university system fostered professional, bureaucratically regulated scientific research performed in well-equipped laboratories, instead of the kind of research done by private and individual scholars in Great Britain and France. In fact, Rüegg asserts that the German system is responsible for the development of the modern research university because it focused on the idea of "freedom of scientific research, teaching and study."
Required education
Mathematicians usually cover a breadth of topics within mathematics in their undergraduate education, and then proceed to specialize in topics of their own choice at the graduate level. In some universities, a qualifying exam serves to test both the breadth and depth of a student's understanding of mathematics; the students who pass are permitted to work on a doctoral dissertation.
Activities:
Applied mathematics
Mathematicians involved with solving problems with applications in real life are called applied mathematicians. Applied mathematicians are mathematical scientists who, with their specialized knowledge and professional methodology, approach many of the imposing problems presented in related scientific fields. With professional focus on a wide variety of problems, theoretical systems, and localized constructs, applied mathematicians work regularly in the study and formulation of mathematical models. Mathematicians and applied mathematicians are considered to be two of the STEM (science, technology, engineering, and mathematics) careers.
The discipline of applied mathematics concerns itself with mathematical methods that are typically used in science, engineering, business, and industry; thus, "applied mathematics" is a mathematical science with specialized knowledge. The term "applied mathematics" also describes the professional specialty in which mathematicians work on problems, often concrete but sometimes abstract. As professionals focused on problem solving, applied mathematicians look into the formulation, study, and use of mathematical models in science, engineering, business, and other areas of mathematical practice.
Pure mathematics
Pure mathematics is mathematics that studies entirely abstract concepts. From the eighteenth century onwards, this was a recognized category of mathematical activity, sometimes characterized as speculative mathematics, and at variance with the trend towards meeting the needs of navigation, astronomy, physics, economics, engineering, and other applications.
Another insightful view put forth is that pure mathematics is not necessarily applied mathematics: it is possible to study abstract entities with respect to their intrinsic nature, and not be concerned with how they manifest in the real world. Even though the pure and applied viewpoints are distinct philosophical positions, in practice there is much overlap in the activity of pure and applied mathematicians.
To develop accurate models for describing the real world, many applied mathematicians draw on tools and techniques that are often considered to be "pure" mathematics. On the other hand, many pure mathematicians draw on natural and social phenomena as inspiration for their abstract research.
Mathematics teaching
Many professional mathematicians also engage in the teaching of mathematics. Duties may include:
* teaching university mathematics courses;
* supervising undergraduate and graduate research; and
* serving on academic committees.
Consulting
Many careers in mathematics outside of universities involve consulting. For instance, actuaries assemble and analyze data to estimate the probability and likely cost of the occurrence of an event such as death, sickness, injury, disability, or loss of property. Actuaries also address financial questions, including those involving the level of pension contributions required to produce a certain retirement income and the way in which a company should invest resources to maximize its return on investments in light of potential risk. Using their broad knowledge, actuaries help design and price insurance policies, pension plans, and other financial strategies in a manner which will help ensure that the plans are maintained on a sound financial basis.
As another example, mathematical finance will derive and extend the mathematical or numerical models without necessarily establishing a link to financial theory, taking observed market prices as input. Mathematical consistency is required, not compatibility with economic theory. Thus, for example, while a financial economist might study the structural reasons why a company may have a certain share price, a financial mathematician may take the share price as a given, and attempt to use stochastic calculus to obtain the corresponding value of derivatives of the stock.
Occupations
In 1938 in the United States, mathematicians were desired as teachers, calculating machine operators, mechanical engineers, accounting auditor bookkeepers, and actuary statisticians.
According to the Dictionary of Occupational Titles occupations in mathematics include the following.
* Mathematician
* Operations-Research Analyst
* Mathematical Statistician
* Mathematical Technician
* Actuary
* Applied Statistician
* Weight Analyst
Prizes in mathematics
There is no Nobel Prize in mathematics, though sometimes mathematicians have won the Nobel Prize in a different field, such as economics or physics. Prominent prizes in mathematics include the Abel Prize, the Chern Medal, the Fields Medal, the Gauss Prize, the Nemmers Prize, the Balzan Prize, the Crafoord Prize, the Shaw Prize, the Steele Prize, the Wolf Prize, the Schock Prize, and the Nevanlinna Prize.
The American Mathematical Society, Association for Women in Mathematics, and other mathematical societies offer several prizes aimed at increasing the representation of women and minorities in the future of mathematics.
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.
Offline
2357) Mortar
Gist
Mortar is a combination of sand, a binding agent like cement or lime and water, used in masonry buildings to bridge the space between building blocks. It is applied in the form of a paste which then hardens and binds the masonry units such as stones, bricks, or concrete used in the construction.
Common mortar specifications include 1:3, 1:2:9 or 1:1:6 mixes. The first one or two digits refer to the binder content (lime, cement or both) and the last digit always refers to the filler, which is usually sand. So a 1:3 mix could mean one part by volume of lime or cement to three parts by volume of sand.
Summary
Mortar, in technology, is material used in building construction to bond brick, stone, tile, or concrete blocks into a structure. Mortar consists of inert siliceous (sandy) material mixed with cement and water in such proportions that the resulting substance will be sufficiently plastic to enable ready application with the mason’s trowel and to flow slightly but not collapse under the weight of the masonry units. Slaked lime is often added to promote smoothness, and sometimes colouring agents are also added. Cement is the most costly ingredient and is held to the minimum consistent with desired strength and watertightness.
Mortar hardens into a stonelike mass and, properly applied, distributes the load of the structure uniformly over the bonding surfaces and provides a weathertight joint.
Details
Mortar is a workable paste which hardens to bind building blocks such as stones, bricks, and concrete masonry units, to fill and seal the irregular gaps between them, spread the weight of them evenly, and sometimes to add decorative colours or patterns to masonry walls. In its broadest sense, mortar includes pitch, asphalt, and soft clay, as those used between bricks, as well as cement mortar. The word "mortar" comes from the Old French word mortier, "builder's mortar, plaster; bowl for mixing."
Cement mortar becomes hard when it cures, resulting in a rigid aggregate structure; however, the mortar functions as a weaker component than the building blocks and serves as the sacrificial element in the masonry, because mortar is easier and less expensive to repair than the building blocks. Bricklayers typically make mortars using a mixture of sand, a binder, and water. The most common binder since the early 20th century is Portland cement, but the ancient binder lime (producing lime mortar) is still used in some specialty new construction. Lime, lime mortar, and gypsum in the form of plaster of Paris are used particularly in the repair and repointing of historic buildings and structures, so that the repair materials will be similar in performance and appearance to the original materials. Several types of cement mortars and additives exist.
Ancient mortar
The first mortars were made of mud and clay, as demonstrated in the 10th millennia BCE buildings of Jericho, and the 8th millennia BCE of Ganj Dareh.
According to Roman Ghirshman, the first evidence of humans using a form of mortar was at the Mehrgarh of Baluchistan in what is today Pakistan, built of sun-dried bricks in 6500 BCE.
Gypsum mortar, also called plaster of Paris, was used in the construction of many ancient structures. It is made from gypsum, which requires a lower firing temperature. It is therefore easier to make than lime mortar and sets up much faster, which may be a reason it was used as the typical mortar in ancient, brick arch and vault construction. Gypsum mortar is not as durable as other mortars in damp conditions.
In the Indian subcontinent, multiple cement types have been observed in the sites of the Indus Valley civilization, with gypsum appearing at sites such as the Mohenjo-daro city-settlement, which dates to earlier than 2600 BCE.
Gypsum cement that was "light grey and contained sand, clay, traces of calcium carbonate, and a high percentage of lime" was used in the construction of wells, drains, and on the exteriors of "important looking buildings." Bitumen mortar was also used at a lower-frequency, including in the Great Bath at Mohenjo-daro.
In early Egyptian pyramids, which were constructed during the Old Kingdom (~2600–2500 BCE), the limestone blocks were bound by a mortar of mud and clay, or clay and sand. In later Egyptian pyramids, the mortar was made of gypsum, or lime. Gypsum mortar was essentially a mixture of plaster and sand and was quite soft.
2nd millennia BCE Babylonian constructions used lime or pitch for mortar.
Historically, building with concrete and mortar next appeared in Greece. The excavation of the underground aqueduct of Megara revealed that a reservoir was coated with a pozzolanic mortar 12 mm thick. This aqueduct dates back to c. 500 BCE. Pozzolanic mortar is a lime based mortar, but is made with an additive of volcanic ash that allows it to be hardened underwater; thus it is known as hydraulic cement. The Greeks obtained the volcanic ash from the Greek islands Thira and Nisiros, or from the then Greek colony of Dicaearchia (Pozzuoli) near Naples, Italy. The Romans later improved the use and methods of making what became known as pozzolanic mortar and cement. Even later, the Romans used a mortar without pozzolana using crushed terra cotta, introducing aluminum oxide and silicon dioxide into the mix. This mortar was not as strong as pozzolanic mortar, but, because it was denser, it better resisted penetration by water.
Hydraulic mortar was not available in ancient China, possibly due to a lack of volcanic ash. Around 500 CE, sticky rice soup was mixed with slaked lime to make an inorganic−organic composite sticky rice mortar that had more strength and water resistance than lime mortar.
It is not understood how the art of making hydraulic mortar and cement, which was perfected and in such widespread use by both the Greeks and Romans, was then lost for almost two millennia. During the Middle Ages when the Gothic cathedrals were being built, the only active ingredient in the mortar was lime. Since cured lime mortar can be degraded by contact with water, many structures suffered over the centuries from wind-blown rain.
Ordinary Portland cement mortar
Ordinary Portland cement mortar, commonly known as OPC mortar or just cement mortar, is created by mixing powdered ordinary Portland cement, fine aggregate and water.
It was invented in 1794 by Joseph Aspdin and patented on 18 December 1824, largely as a result of efforts to develop stronger mortars. It was made popular during the late nineteenth century, and had by 1930 became more popular than lime mortar as construction material. The advantages of Portland cement is that it sets hard and quickly, allowing a faster pace of construction. Furthermore, fewer skilled workers are required in building a structure with Portland cement.
As a general rule, however, Portland cement should not be used for the repair or repointing of older buildings built in lime mortar, which require the flexibility, softness and breathability of lime if they are to function correctly.
In the United States and other countries, five standard types of mortar (available as dry pre-mixed products) are generally used for both new construction and repair. Strengths of mortar change based on the mix ratio for each type of mortar, which are specified under the ASTM standards. These premixed mortar products are designated by one of the five letters, M, S, N, O, and K. Type M mortar is the strongest, and Type K the weakest.
These type letters are taken from the alternate letters of the words "MaSoN wOrK".
Polymer cement mortar
Polymer cement mortars (PCM) are the materials which are made by partially replacing the cement hydrate binders of conventional cement mortar with polymers. The polymeric admixtures include latexes or emulsions, redispersible polymer powders, water-soluble polymers, liquid thermoset resins and monomers. Although they increase cost of mortars when used as an additive, they enhance properties. Polymer mortar has low permeability that may be detrimental to moisture accumulation when used to repair a traditional brick, block or stone wall. It is mainly designed for repairing concrete structures. The use of recovered plastics in mortars is being researched and is gaining ground. Depolymerizing PET to use as a polymeric binder to enhance mortars is actively being studied.
Lime mortar
The setting speed can be increased by using impure limestone in the kiln, to form a hydraulic lime that will set on contact with water. Such a lime must be stored as a dry powder. Alternatively, a pozzolanic material such as calcined clay or brick dust may be added to the mortar mix. Addition of a pozzolanic material will make the mortar set reasonably quickly by reaction with the water.
It would be problematic to use Portland cement mortars to repair older buildings originally constructed using lime mortar. Lime mortar is softer than cement mortar, allowing brickwork a certain degree of flexibility to adapt to shifting ground or other changing conditions. Cement mortar is harder and allows little flexibility. The contrast can cause brickwork to crack where the two mortars are present in a single wall.
Lime mortar is considered breathable in that it will allow moisture to freely move through and evaporate from the surface. In old buildings with walls that shift over time, cracks can be found which allow rain water into the structure. The lime mortar allows this moisture to escape through evaporation and keeps the wall dry. Re−pointing or rendering an old wall with cement mortar stops the evaporation and can cause problems associated with moisture behind the cement.
Pozzolanic mortar
Pozzolana is a fine, sandy volcanic ash. It was originally discovered and dug at Pozzuoli, nearby Mount Vesuvius in Italy, and was subsequently mined at other sites, too. The Romans learned that pozzolana added to lime mortar allowed the lime to set relatively quickly and even under water. Vitruvius, the Roman architect, spoke of four types of pozzolana. It is found in all the volcanic areas of Italy in various colours: black, white, grey and red. Pozzolana has since become a generic term for any siliceous and/or aluminous additive to slaked lime to create hydraulic cement.
Finely ground and mixed with lime it is a hydraulic cement, like Portland cement, and makes a strong mortar that will also set under water.
The fact that the materials involved in the creation of pozzolana are found in abundance within certain territories make its use more common there, with areas inside of Central Europe as well as inside of Southern Europe being an example (significantly because of the many European volcanoes of note). It has, as such, been commonly associated with a variety of large structures constructed by the Roman Empire.
Radiocarbon dating
As the mortar hardens, the current atmosphere is encased in the mortar and thus provides a sample for analysis. Various factors affect the sample and raise the margin of error for the analysis. Radiocarbon dating of mortar began as early as the 1960s, soon after the method was established (Delibrias and Labeyrie 1964; Stuiver and Smith 1965; Folk and Valastro 1976). The very first data were provided by van Strydonck et al. (1983), Heinemeier et al.(1997) and Ringbom and Remmer (1995). Methodological aspects were further developed by different groups (an international team headed by Åbo Akademi University, and teams from CIRCE, CIRCe, ETHZ, Poznań, RICH and Milano-Bicocca laboratory. To evaluate the different anthropogenic carbon extraction methods for radiocarbon dating as well as to compare the different dating methods, i.e. radiocarbon and OSL, the first intercomparison study (MODIS) was set up and published in 2017.
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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2358) Oceanography/Oceanology
Gist
Oceanography is the study of all aspects of the ocean. Oceanography covers a wide range of topics, from marine life and ecosystems to currents and waves, the movement of sediments, and seafloor geology.
Oceanology is an area of Earth Science that deals with oceans. Oceanology, also called as Oceanography, is a vast subject covering a range of topics in the sub field areas of Physical, Chemical, Biological and Geological oceanography.
Summary
Oceanography is the study of the physical, chemical, and biological features of the ocean, including the ocean’s ancient history, its current condition, and its future. In a time when the ocean is threatened by climate change and pollution, coastlines are eroding, and entire species of marine life are at risk of extinction, the role of oceanographers may be more important now than it has ever been.
Indeed, one of the most critical branches of oceanography today is known as biological oceanography. It is the study of the ocean’s plants and animals and their interactions with the marine environment. But oceanography is not just about study and research. It is also about using that information to help leaders make smart choices about policies that affect ocean health. Lessons learned through oceanography affect the ways humans use the sea for transportation, food, energy, water, and much more.
For example, fishermen with the Northwest Atlantic Marine Alliance (NAMA) are working with oceanographers to better understand how pollutants are reducing fish populations and posing health risks to consumers of the fish. Together, NAMA and ocean scientists hope to use their research to show why tighter pollution controls are needed.
Oceanographers from around the world are exploring a range of subjects as wide as the ocean itself. For example, teams of oceanographers are investigating how melting sea ice is changing the feeding and migration patterns of whales that populate the ocean’s coldest regions. National Geographic Explorer Gabrielle Corradino, a North Carolina State University 2017 Global Change Fellow, is also interested in marine ecosystems, though in a much warmer environment. Corradino is studying how the changing ocean is affecting populations of microscopic phytoplankton and the fish that feed off of them. Her field work included five weeks in the Gulf of Mexico filtering seawater to capture phytoplankton and protozoa—the tiniest, but most important, parts of the sea’s food chain.
Of course, oceanography covers more than the living organisms in the sea. A branch of oceanography called geological oceanography focuses on the formation of the seafloor and how it changes over time. Geological oceanographers are starting to use special GPS technology to map the seafloor and other underwater features. This research can provide critical information, such as seismic activity, that could lead to more accurate earthquake and tsunami prediction.
In addition to biological and geological oceanography, there are two other main branches of sea science. One is physical oceanography, the study of the relationships between the seafloor, the coastline, and the atmosphere. The other is chemical oceanography, the study of the chemical composition of seawater and how it is affected by weather, human activities, and other factors.
About 70 percent of Earth’s surface is covered by water. Nearly 97 percent of that water is the saltwater swirling in the world’s ocean. Given the size of the ocean and the rapid advancements in technology, there is seemingly no end to what can and will be uncovered in the science of oceanography.
Details
Oceanography, also known as oceanology, sea science, ocean science, and marine science, is the scientific study of the ocean, including its physics, chemistry, biology, and geology.
It is an Earth science, which covers a wide range of topics, including ocean currents, waves, and geophysical fluid dynamics; fluxes of various chemical substances and physical properties within the ocean and across its boundaries; ecosystem dynamics; and plate tectonics and seabed geology.
Oceanographers draw upon a wide range of disciplines to deepen their understanding of the world’s oceans, incorporating insights from astronomy, biology, chemistry, geography, geology, hydrology, meteorology and physics.
History:
Early history
Humans first acquired knowledge of the waves and currents of the seas and oceans in pre-historic times. Observations on tides were recorded by Aristotle and Strabo in 384–322 BC. Early exploration of the oceans was primarily for cartography and mainly limited to its surfaces and of the animals that fishermen brought up in nets, though depth soundings by lead line were taken.
The Portuguese campaign of Atlantic navigation is the earliest example of a systematic scientific large project, sustained over many decades, studying the currents and winds of the Atlantic.
The work of Pedro Nunes (1502–1578) is remembered in the navigation context for the determination of the loxodromic curve: the shortest course between two points on the surface of a sphere represented onto a two-dimensional map. When he published his "Treatise of the Sphere" (1537), mostly a commentated translation of earlier work by others, he included a treatise on geometrical and astronomic methods of navigation. There he states clearly that Portuguese navigations were not an adventurous endeavour:
"nam se fezeram indo a acertar: mas partiam os nossos mareantes muy ensinados e prouidos de estromentos e regras de astrologia e geometria que sam as cousas que os cosmographos ham dadar apercebidas (...) e leuaua cartas muy particularmente rumadas e na ja as de que os antigos vsauam" (were not done by chance: but our seafarers departed well taught and provided with instruments and rules of astrology (astronomy) and geometry which were matters the cosmographers would provide (...) and they took charts with exact routes and no longer those used by the ancient).
His credibility rests on being personally involved in the instruction of pilots and senior seafarers from 1527 onwards by Royal appointment, along with his recognized competence as mathematician and astronomer. The main problem in navigating back from the south of the Canary Islands (or south of Boujdour) by sail alone, is due to the change in the regime of winds and currents: the North Atlantic gyre and the Equatorial counter current will push south along the northwest bulge of Africa, while the uncertain winds where the Northeast trades meet the Southeast trades (the doldrums) leave a sailing ship to the mercy of the currents. Together, prevalent current and wind make northwards progress very difficult or impossible. It was to overcome this problem and clear the passage to India around Africa as a viable maritime trade route, that a systematic plan of exploration was devised by the Portuguese. The return route from regions south of the Canaries became the 'volta do largo' or 'volta do mar'. The 'rediscovery' of the Azores islands in 1427 is merely a reflection of the heightened strategic importance of the islands, now sitting on the return route from the western coast of Africa (sequentially called 'volta de Guiné' and 'volta da Mina'); and the references to the Sargasso Sea (also called at the time 'Mar da Baga'), to the west of the Azores, in 1436, reveals the western extent of the return route. This is necessary, under sail, to make use of the southeasterly and northeasterly winds away from the western coast of Africa, up to the northern latitudes where the westerly winds will bring the seafarers towards the western coasts of Europe.
The secrecy involving the Portuguese navigations, with the death penalty for the leaking of maps and routes, concentrated all sensitive records in the Royal Archives, completely destroyed by the Lisbon earthquake of 1775. However, the systematic nature of the Portuguese campaign, mapping the currents and winds of the Atlantic, is demonstrated by the understanding of the seasonal variations, with expeditions setting sail at different times of the year taking different routes to take account of seasonal predominate winds. This happens from as early as late 15th century and early 16th: Bartolomeu Dias followed the African coast on his way south in August 1487, while Vasco da Gama would take an open sea route from the latitude of Sierra Leone, spending three months in the open sea of the South Atlantic to profit from the southwards deflection of the southwesterly on the Brazilian side (and the Brazilian current going southward - Gama departed in July 1497); and Pedro Álvares Cabral (departing March 1500) took an even larger arch to the west, from the latitude of Cape Verde, thus avoiding the summer monsoon (which would have blocked the route taken by Gama at the time he set sail).[9] Furthermore, there were systematic expeditions pushing into the western Northern Atlantic (Teive, 1454; Vogado, 1462; Teles, 1474; Ulmo, 1486).
The documents relating to the supplying of ships, and the ordering of sun declination tables for the southern Atlantic for as early as 1493–1496, all suggest a well-planned and systematic activity happening during the decade long period between Bartolomeu Dias finding the southern tip of Africa, and Gama's departure; additionally, there are indications of further travels by Bartolomeu Dias in the area. The most significant consequence of this systematic knowledge was the negotiation of the Treaty of Tordesillas in 1494, moving the line of demarcation 270 leagues to the west (from 100 to 370 leagues west of the Azores), bringing what is now Brazil into the Portuguese area of domination. The knowledge gathered from open sea exploration allowed for the well-documented extended periods of sail without sight of land, not by accident but as pre-determined planned route; for example, 30 days for Bartolomeu Dias culminating on Mossel Bay, the three months Gama spent in the South Atlantic to use the Brazil current (southward), or the 29 days Cabral took from Cape Verde up to landing in Monte Pascoal, Brazil.
The Danish expedition to Arabia 1761–67 can be said to be the world's first oceanographic expedition, as the ship Grønland had on board a group of scientists, including naturalist Peter Forsskål, who was assigned an explicit task by the king, Frederik V, to study and describe the marine life in the open sea, including finding the cause of mareel, or milky seas. For this purpose, the expedition was equipped with nets and scrapers, specifically designed to collect samples from the open waters and the bottom at great depth.
Although Juan Ponce de León in 1513 first identified the Gulf Stream, and the current was well known to mariners, Benjamin Franklin made the first scientific study of it and gave it its name. Franklin measured water temperatures during several Atlantic crossings and correctly explained the Gulf Stream's cause. Franklin and Timothy Folger printed the first map of the Gulf Stream in 1769–1770.
Information on the currents of the Pacific Ocean was gathered by explorers of the late 18th century, including James Cook and Louis Antoine de Bougainville. James Rennell wrote the first scientific textbooks on oceanography, detailing the current flows of the Atlantic and Indian oceans. During a voyage around the Cape of Good Hope in 1777, he mapped "the banks and currents at the Lagullas". He was also the first to understand the nature of the intermittent current near the Isles of Scilly, (now known as Rennell's Current). The tides and currents of the ocean are distinct. Tides are the rise and fall of sea levels created by the combination of the gravitational forces of the Moon along with the Sun (the Sun just in a much lesser extent) and are also caused by the Earth and Moon orbiting each other. An ocean current is a continuous, directed movement of seawater generated by a number of forces acting upon the water, including wind, the Coriolis effect, breaking waves, cabbeling, and temperature and salinity differences.
Sir James Clark Ross took the first modern sounding in deep sea in 1840, and Charles Darwin published a paper on reefs and the formation of atolls as a result of the second voyage of HMS Beagle in 1831–1836. Robert FitzRoy published a four-volume report of Beagle's three voyages. In 1841–1842 Edward Forbes undertook dredging in the Aegean Sea that founded marine ecology.
The first superintendent of the United States Naval Observatory (1842–1861), Matthew Fontaine Maury devoted his time to the study of marine meteorology, navigation, and charting prevailing winds and currents. His 1855 textbook Physical Geography of the Sea was one of the first comprehensive oceanography studies. Many nations sent oceanographic observations to Maury at the Naval Observatory, where he and his colleagues evaluated the information and distributed the results worldwide.
Modern oceanography
Knowledge of the oceans remained confined to the topmost few fathoms of the water and a small amount of the bottom, mainly in shallow areas. Almost nothing was known of the ocean depths. The British Royal Navy's efforts to chart all of the world's coastlines in the mid-19th century reinforced the vague idea that most of the ocean was very deep, although little more was known. As exploration ignited both popular and scientific interest in the polar regions and Africa, so too did the mysteries of the unexplored oceans.
HMS Challenger undertook the first global marine research expedition in 1872.
The seminal event in the founding of the modern science of oceanography was the 1872–1876 Challenger expedition. As the first true oceanographic cruise, this expedition laid the groundwork for an entire academic and research discipline. In response to a recommendation from the Royal Society, the British Government announced in 1871 an expedition to explore world's oceans and conduct appropriate scientific investigation. Charles Wyville Thomson and Sir John Murray launched the Challenger expedition. Challenger, leased from the Royal Navy, was modified for scientific work and equipped with separate laboratories for natural history and chemistry. Under the scientific supervision of Thomson, Challenger travelled nearly 70,000 nautical miles (130,000 km) surveying and exploring. On her journey circumnavigating the globe, 492 deep sea soundings, 133 bottom dredges, 151 open water trawls and 263 serial water temperature observations were taken. Around 4,700 new species of marine life were discovered. The result was the Report Of The Scientific Results of the Exploring Voyage of H.M.S. Challenger during the years 1873–76. Murray, who supervised the publication, described the report as "the greatest advance in the knowledge of our planet since the celebrated discoveries of the fifteenth and sixteenth centuries". He went on to found the academic discipline of oceanography at the University of Edinburgh, which remained the centre for oceanographic research well into the 20th century. Murray was the first to study marine trenches and in particular the Mid-Atlantic Ridge, and map the sedimentary deposits in the oceans. He tried to map out the world's ocean currents based on salinity and temperature observations, and was the first to correctly understand the nature of coral reef development.
In the late 19th century, other Western nations also sent out scientific expeditions (as did private individuals and institutions). The first purpose-built oceanographic ship, Albatros, was built in 1882. In 1893, Fridtjof Nansen allowed his ship, Fram, to be frozen in the Arctic ice. This enabled him to obtain oceanographic, meteorological and astronomical data at a stationary spot over an extended period.
In 1881 the geographer John Francon Williams published a seminal book, Geography of the Oceans. Between 1907 and 1911 Otto Krümmel published the Handbuch der Ozeanographie, which became influential in awakening public interest in oceanography. The four-month 1910 North Atlantic expedition headed by John Murray and Johan Hjort was the most ambitious research oceanographic and marine zoological project ever mounted until then, and led to the classic 1912 book The Depths of the Ocean.
The first acoustic measurement of sea depth was made in 1914. Between 1925 and 1927 the "Meteor" expedition gathered 70,000 ocean depth measurements using an echo sounder, surveying the Mid-Atlantic Ridge.
In 1934, Easter Ellen Cupp, the first woman to have earned a PhD (at Scripps) in the United States, completed a major work on diatoms that remained the standard taxonomy in the field until well after her death in 1999. In 1940, Cupp was let go from her position at Scripps. Sverdrup specifically commended Cupp as a conscientious and industrious worker and commented that his decision was no reflection on her ability as a scientist. Sverdrup used the instructor billet vacated by Cupp to employ Marston Sargent, a biologist studying marine algae, which was not a new research program at Scripps. Financial pressures did not prevent Sverdrup from retaining the services of two other young post-doctoral students, Walter Munk and Roger Revelle. Cupp's partner, Dorothy Rosenbury, found her a position teaching high school, where she remained for the rest of her career. (Russell, 2000)
Sverdrup, Johnson and Fleming published The Oceans in 1942, which was a major landmark. The Sea (in three volumes, covering physical oceanography, seawater and geology) edited by M.N. Hill was published in 1962, while Rhodes Fairbridge's Encyclopedia of Oceanography was published in 1966.
The Great Global Rift, running along the Mid Atlantic Ridge, was discovered by Maurice Ewing and Bruce Heezen in 1953 and mapped by Heezen and Marie Tharp using bathymetric data; in 1954 a mountain range under the Arctic Ocean was found by the Arctic Institute of the USSR. The theory of seafloor spreading was developed in 1960 by Harry Hammond Hess. The Ocean Drilling Program started in 1966. Deep-sea vents were discovered in 1977 by Jack Corliss and Robert Ballard in the submersible DSV Alvin.
In the 1950s, Auguste Piccard invented the bathyscaphe and used the bathyscaphe Trieste to investigate the ocean's depths. The United States nuclear submarine Nautilus made the first journey under the ice to the North Pole in 1958. In 1962 the FLIP (Floating Instrument Platform), a 355-foot (108 m) spar buoy, was first deployed.
In 1968, Tanya Atwater led the first all-woman oceanographic expedition. Until that time, gender policies restricted women oceanographers from participating in voyages to a significant extent.
From the 1970s, there has been much emphasis on the application of large scale computers to oceanography to allow numerical predictions of ocean conditions and as a part of overall environmental change prediction. Early techniques included analog computers (such as the Ishiguro Storm Surge Computer) generally now replaced by numerical methods (e.g. SLOSH.) An oceanographic buoy array was established in the Pacific to allow prediction of El Niño events.
1990 saw the start of the World Ocean Circulation Experiment (WOCE) which continued until 2002. Geosat seafloor mapping data became available in 1995.
Study of the oceans is critical to understanding shifts in Earth's energy balance along with related global and regional changes in climate, the biosphere and biogeochemistry. The atmosphere and ocean are linked because of evaporation and precipitation as well as thermal flux (and solar insolation). Recent studies have advanced knowledge on ocean acidification, ocean heat content, ocean currents, sea level rise, the oceanic carbon cycle, the water cycle, Arctic sea ice decline, coral bleaching, marine heatwaves, extreme weather, coastal erosion and many other phenomena in regards to ongoing climate change and climate feedbacks.
In general, understanding the world ocean through further scientific study enables better stewardship and sustainable utilization of Earth's resources. The Intergovernmental Oceanographic Commission reports that 1.7% of the total national research expenditure of its members is focused on ocean science.
Branches:
The study of oceanography is divided into these five branches:
Biological oceanography
Biological oceanography investigates the ecology and biology of marine organisms in the context of the physical, chemical and geological characteristics of their ocean environment.
Chemical oceanography
Chemical oceanography is the study of the chemistry of the ocean. Whereas chemical oceanography is primarily occupied with the study and understanding of seawater properties and its changes, ocean chemistry focuses primarily on the geochemical cycles. The following is a central topic investigated by chemical oceanography.
Ocean acidification
Ocean acidification describes the decrease in ocean pH that is caused by anthropogenic carbon dioxide (CO2) emissions into the atmosphere. Seawater is slightly alkaline and had a preindustrial pH of about 8.2. More recently, anthropogenic activities have steadily increased the carbon dioxide content of the atmosphere; about 30–40% of the added CO2 is absorbed by the oceans, forming carbonic acid and lowering the pH through ocean acidification. The pH is expected to reach 7.7 by the year 2100.
An important element for the skeletons of marine animals is calcium, but calcium carbonate becomes more soluble with pressure, so carbonate shells and skeletons dissolve below the carbonate compensation depth. Calcium carbonate becomes more soluble at lower pH, so ocean acidification is likely to affect marine organisms with calcareous shells, such as oysters, clams, sea urchins and corals, and the carbonate compensation depth will rise closer to the sea surface. Affected planktonic organisms will include pteropods, coccolithophorids and foraminifera, all important in the food chain. In tropical regions, corals are likely to be severely affected as they become less able to build their calcium carbonate skeletons, in turn adversely impacting other reef dwellers.
The current rate of ocean chemistry change seems to be unprecedented in Earth's geological history, making it unclear how well marine ecosystems will adapt to the shifting conditions of the near future. Of particular concern is the manner in which the combination of acidification with the expected additional stressors of higher ocean temperatures and lower oxygen levels will impact the seas.
Geological oceanography
Geological oceanography is the study of the geology of the ocean floor including plate tectonics and paleoceanography.
Physical oceanography
Physical oceanography studies the ocean's physical attributes including temperature-salinity structure, mixing, surface waves, internal waves, surface tides, internal tides, and currents. The following are central topics investigated by physical oceanography.
Ocean currents
Since the early ocean expeditions in oceanography, a major interest was the study of ocean currents and temperature measurements. The tides, the Coriolis effect, changes in direction and strength of wind, salinity, and temperature are the main factors determining ocean currents. The thermohaline circulation (THC) (thermo- referring to temperature and -haline referring to salt content) connects the ocean basins and is primarily dependent on the density of sea water. It is becoming more common to refer to this system as the 'meridional overturning circulation' because it more accurately accounts for other driving factors beyond temperature and salinity.
Examples of sustained currents are the Gulf Stream and the Kuroshio Current which are wind-driven western boundary currents.
Ocean heat content
Oceanic heat content (OHC) refers to the extra heat stored in the ocean from changes in Earth's energy balance. The increase in the ocean heat play an important role in sea level rise, because of thermal expansion. Ocean warming accounts for 90% of the energy accumulation associated with global warming since 1971.
Paleoceanography
Paleoceanography is the study of the history of the oceans in the geologic past with regard to circulation, chemistry, biology, geology and patterns of sedimentation and biological productivity. Paleoceanographic studies using environment models and different proxies enable the scientific community to assess the role of the oceanic processes in the global climate by the reconstruction of past climate at various intervals. Paleoceanographic research is also intimately tied to palaeoclimatology.
Oceanographic institutions
The earliest international organizations of oceanography were founded at the turn of the 20th century, starting with the International Council for the Exploration of the Sea created in 1902, followed in 1919 by the Mediterranean Science Commission. Marine research institutes were already in existence, starting with the Stazione Zoologica Anton Dohrn in Naples, Italy (1872), the Biological Station of Roscoff, France (1876), the Arago Laboratory in Banyuls-sur-mer, France (1882), the Laboratory of the Marine Biological Association in Plymouth, UK (1884), the Norwegian Institute for Marine Research in Bergen, Norway (1900), the Laboratory für internationale Meeresforschung, Kiel, Germany (1902). On the other side of the Atlantic, the Scripps Institution of Oceanography was founded in 1903, followed by the Woods Hole Oceanographic Institution in 1930, the Virginia Institute of Marine Science in 1938, the Lamont–Doherty Earth Observatory at Columbia University in 1949, and later the School of Oceanography at University of Washington. In Australia, the Australian Institute of Marine Science (AIMS), established in 1972 soon became a key player in marine tropical research.
In 1921 the International Hydrographic Bureau, called since 1970 the International Hydrographic Organization, was established to develop hydrographic and nautical charting standards.
Additional Information
Oceanography is a scientific discipline concerned with all aspects of the world’s oceans and seas, including their physical and chemical properties, their origin and geologic framework, and the life forms that inhabit the marine environment.
Traditionally, oceanography has been divided into four separate but related branches: physical oceanography, chemical oceanography, marine geology, and marine ecology. Physical oceanography deals with the properties of seawater (temperature, density, pressure, and so on), its movement (waves, currents, and tides), and the interactions between the ocean waters and the atmosphere. Chemical oceanography has to do with the composition of seawater and the biogeochemical cycles that affect it. Marine geology focuses on the structure, features, and evolution of the ocean basins. Marine ecology, also called biological oceanography, involves the study of the plants and animals of the sea, including life cycles and food production.
Oceanography is the sum of these several branches. Oceanographic research entails the sampling of seawater and marine life for close study, the remote sensing of oceanic processes with aircraft and Earth-orbiting satellites, and the exploration of the seafloor by means of deep-sea drilling and seismic profiling of the terrestrial crust below the ocean bottom. Greater knowledge of the world’s oceans enables scientists to more accurately predict, for example, long-term weather and climatic changes and also leads to more efficient exploitation of the Earth’s resources. Oceanography also is vital to understanding the effect of pollutants on ocean waters and to the preservation of the quality of the oceans’ waters in the face of increasing human demands made on them.
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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