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#1 This is Cool » Resistor » Today 00:49:47

Jai Ganesh
Replies: 0

Resistor

Gist

A resistor is a passive two-terminal electrical component that implements electrical resistance as a circuit element. In electronic circuits, resistors are used to reduce current flow, adjust signal levels, to divide voltages, bias active elements, and terminate transmission lines, among other uses.

Summary

Resistor is an electrical component that opposes the flow of either direct or alternating current, employed to protect, operate, or control the circuit. Voltages can be divided with the use of resistors, and in combination with other components resistors can be used to make electrical waves into shapes most suited for the electrical designer’s requirements. Resistors can have a fixed value of resistance, or they can be made variable or adjustable within a certain range, in which case they may be called rheostats, or potentiometers.

Details

Power resistors are required to dissipate substantial amounts of power and are typically used in power supplies, power conversion circuits, and power amplifiers; this designation is loosely applied to resistors with power ratings of 1 watt or greater. Power resistors are physically larger and may not use the preferred values, color codes, and external packages described below.

If the average power dissipated by a resistor is more than its power rating, damage to the resistor may occur, permanently altering its resistance; this is distinct from the reversible change in resistance due to its temperature coefficient when it warms. Excessive power dissipation may raise the temperature of the resistor to a point where it can burn the circuit board or adjacent components, or even cause a fire. There are flameproof resistors that will not produce flames with any overload of any duration.

Resistors may be specified with higher rated dissipation than is experienced in service to account for poor air circulation, high altitude, or high operating temperature.

All resistors have a maximum voltage rating; this may limit the power dissipation for higher resistance values.[7] For instance, among 1⁄4 watt resistors (a very common sort of leaded resistor) one is listed with a resistance of 100 MΩ[8] and a maximum rated voltage of 750 V. However even placing 750 V across a 100 MΩ resistor continuously would only result in a power dissipation of less than 6 mW, making the nominal 1⁄4 watt rating meaningless.

Nonideal properties

Practical resistors have a series inductance and a small parallel capacitance; these specifications can be important in high-frequency applications. In a low-noise amplifier or pre-amp, the noise characteristics of a resistor may be an issue.

In some precision applications, the temperature coefficient of the resistance may also be of concern.

The unwanted inductance, excess noise, and temperature coefficient are mainly dependent on the technology used in manufacturing the resistor. They are not normally specified individually for a particular family of resistors manufactured using a particular technology.[9] A family of discrete resistors may also be characterized according to its form factor, that is, the size of the device and the position of its leads (or terminals). This is relevant in the practical manufacturing of circuits that may use them.

Practical resistors are also specified as having a maximum power rating which must exceed the anticipated power dissipation of that resistor in a particular circuit: this is mainly of concern in power electronics applications. Resistors with higher power ratings are physically larger and may require heat sinks. In a high-voltage circuit, attention must sometimes be paid to the rated maximum working voltage of the resistor. While there is no minimum working voltage for a given resistor, failure to account for a resistor's maximum rating may cause the resistor to incinerate when current is run through it.

Fixed resistors

A single in line (SIL) resistor package with 8 individual 47 ohm resistors. This package is also known as a SIP-9. One end of each resistor is connected to a separate pin and the other ends are all connected together to the remaining (common) pin – pin 1, at the end identified by the white dot.

Lead arrangements

Through-hole components typically have "leads" (pronounced /liːdz/) leaving the body "axially", that is, on a line parallel with the part's longest axis. Others have leads coming off their body "radially" instead. Other components may be SMT (surface mount technology), while high power resistors may have one of their leads designed into the heat sink.

Carbon composition

Carbon composition resistors (CCR) consist of a solid cylindrical resistive element with embedded wire leads or metal end caps to which the lead wires are attached. The body of the resistor is protected with paint or plastic. Early 20th-century carbon composition resistors had uninsulated bodies; the lead wires were wrapped around the ends of the resistance element rod and soldered. The completed resistor was painted for color-coding of its value.

The resistive element in carbon composition resistors is made from a mixture of finely powdered carbon and an insulating material, usually ceramic. A resin holds the mixture together. The resistance is determined by the ratio of the fill material (the powdered ceramic) to the carbon. Higher concentrations of carbon, which is a good conductor, result in lower resistances. Carbon composition resistors were commonly used in the 1960s and earlier, but are not popular for general use now as other types have better specifications, such as tolerance, voltage dependence, and stress. Carbon composition resistors change value when stressed with over-voltages. Moreover, if internal moisture content, such as from exposure for some length of time to a humid environment, is significant, soldering heat creates a non-reversible change in resistance value. Carbon composition resistors have poor stability with time and were consequently factory sorted to, at best, only 5% tolerance. These resistors are non-inductive, which provides benefits when used in voltage pulse reduction and surge protection applications. Carbon composition resistors have higher capability to withstand overload relative to the component's size.

Carbon composition resistors are still available, but relatively expensive. Values ranged from fractions of an ohm to 22 megohms. Due to their high price, these resistors are no longer used in most applications. However, they are used in power supplies and welding controls. They are also in demand for repair of vintage electronic equipment where authenticity is a factor.

Carbon pile

A carbon pile resistor is made of a stack of carbon disks compressed between two metal contact plates. Adjusting the clamping pressure changes the resistance between the plates. These resistors are used when an adjustable load is required, such as in testing automotive batteries or radio transmitters. A carbon pile resistor can also be used as a speed control for small motors in household appliances (sewing machines, hand-held mixers) with ratings up to a few hundred watts. A carbon pile resistor can be incorporated in automatic voltage regulators for generators, where the carbon pile controls the field current to maintain relatively constant voltage. This principle is also applied in the carbon microphone.

Carbon film

In manufacturing carbon film resistors, a carbon film is deposited on an insulating substrate, and a helix is cut in it to create a long, narrow resistive path. Varying shapes, coupled with the resistivity of amorphous carbon (ranging from 500 to 800 μΩ m), can provide a wide range of resistance values. Carbon film resistors feature lower noise compared to carbon composition resistors because of the precise distribution of the pure graphite without binding. Carbon film resistors feature a power rating range of 0.125 W to 5 W at 70 °C. Resistances available range from 1 ohm to 10 megaohm. The carbon film resistor has an operating temperature range of −55 °C to 155 °C. It has 200 to 600 volts maximum working voltage range. Special carbon film resistors are used in applications requiring high pulse stability.

Printed carbon resistors

Carbon resistors (black rectangles) printed directly onto the SMD pads on the PCB of a Psion Organiser II from 1989
Carbon composition resistors can be printed directly onto printed circuit board (PCB) substrates as part of the PCB manufacturing process. Although this technique is more common on hybrid PCB modules, it can also be used on standard fibreglass PCBs. Tolerances are typically quite large and can be in the order of 30%. A typical application would be non-critical pull-up resistors.

Thick and thin film

Thick film resistors became popular during the 1970s, and most SMD (surface mount device) resistors today are of this type. The resistive element of thick films is 1000 times thicker than thin films, but the principal difference is how the film is applied to the cylinder (axial resistors) or the surface (SMD resistors).

Thin film resistors are made by sputtering (a method of vacuum deposition) the resistive material onto an insulating substrate. The film is then etched in a similar manner to the old (subtractive) process for making printed circuit boards; that is, the surface is coated with a photo-sensitive material, covered by a pattern film, irradiated with ultraviolet light, and then the exposed photo-sensitive coating is developed, and underlying thin film is etched away.

Thick film resistors are manufactured using screen and stencil printing processes.

Because the time during which the sputtering is performed can be controlled, the thickness of the thin film can be accurately controlled. The type of material also varies, consisting of one or more ceramic (cermet) conductors such as tantalum nitride (TaN), ruthenium oxide (RuO2), lead oxide (PbO), bismuth ruthenate (Bi2Ru2O7), nickel chromium (NiCr), or bismuth iridate (Bi2Ir2O7).

The resistance of both thin and thick film resistors after manufacture is not highly accurate; they are usually trimmed to an accurate value by abrasive or laser trimming. Thin film resistors are usually specified with tolerances of 1% and 5%, and with temperature coefficients of 5 to 50 ppm/K. They also have much lower noise levels, on the level of 10–100 times less than thick film resistors. Thick film resistors may use the same conductive ceramics, but they are mixed with sintered (powdered) glass and a carrier liquid so that the composite can be screen-printed. This composite of glass and conductive ceramic (cermet) material is then fused (baked) in an oven at about 850 °C.

When first manufactured, thick film resistors had tolerances of 5%, but standard tolerances have improved to 2% or 1% in the last few decades.[timeframe?] Temperature coefficients of thick film resistors are typically ±200 or ±250 ppm/K; a 40-kelvin (70 °F) temperature change can change the resistance by 1%.

Thin film resistors are usually far more expensive than thick film resistors. For example, SMD thin film resistors, with 0.5% tolerances and with 25 ppm/K temperature coefficients, when bought in full size reel quantities, are about twice the cost of 1%, 250 ppm/K thick film resistors.

Metal film

A common type of axial-leaded resistor today is the metal-film resistor. Metal Electrode Leadless Face (MELF) resistors often use the same technology.

Metal film resistors are usually coated with nickel chromium (NiCr), but might be coated with any of the cermet materials listed above for thin film resistors. Unlike thin film resistors, the material may be applied using different techniques than sputtering (though this is one technique used). The resistance value is determined by cutting a helix through the coating rather than by etching, similar to the way carbon resistors are made. The result is a reasonable tolerance (0.5%, 1%, or 2%) and a temperature coefficient that is generally between 50 and 100 ppm/K. Metal film resistors possess good noise characteristics and low non-linearity due to a low voltage coefficient. They are also beneficial due to long-term stability.

Metal oxide film

Metal-oxide film resistors are made of metal oxides which results in a higher operating temperature and greater stability and reliability than metal film. They are used in applications with high endurance demands.

Wire wound

High-power wire wound resistors used for dynamic braking on an electric railway car. Such resistors may dissipate many kilowatts for an extended length of time.

Wirewound resistors are commonly made by winding a metal wire, usually nichrome, around a ceramic, plastic, or fiberglass core. The ends of the wire are soldered or welded to two caps or rings, attached to the ends of the core. The assembly is protected with a layer of paint, molded plastic, or an enamel coating baked at high temperature. These resistors are designed to withstand unusually high temperatures of up to 450 °C. Wire leads in low power wirewound resistors are usually between 0.6 and 0.8 mm in diameter and tinned for ease of soldering. For higher power wirewound resistors, either a ceramic outer case or an aluminum outer case on top of an insulating layer is used. If the outer case is ceramic, such resistors are sometimes described as "cement" resistors, though they do not actually contain any traditional cement. The aluminum-cased types are designed to be attached to a heat sink to dissipate the heat; the rated power is dependent on being used with a suitable heat sink, e.g., a 50 W power rated resistor overheats at a fraction of the power dissipation if not used with a heat sink. Large wirewound resistors may be rated for 1,000 watts or more.

Because wirewound resistors are coils they have more undesirable inductance than other types of resistor. However, winding the wire in sections with alternately reversed direction can minimize inductance. Other techniques employ bifilar winding, or a flat thin former (to reduce cross-section area of the coil). For the most demanding circuits, resistors with Ayrton–Perry winding are used.

Applications of wirewound resistors are similar to those of composition resistors with the exception of high frequency applications. The high frequency response of wirewound resistors is substantially worse than that of a composition resistor.

Metal foil resistor

In 1960, Felix Zandman and Sidney J. Stein presented a development of resistor film of very high stability.

The primary resistance element of a foil resistor is a chromium nickel alloy foil several micrometers thick. Chromium nickel alloys are characterized by having a large electrical resistance (about 58 times that of copper), a small temperature coefficient and high resistance to oxidation. Examples are Chromel A and Nichrome V, whose typical composition is 80 Ni and 20 Cr, with a melting point of 1420 °C. When iron is added, the chromium nickel alloy becomes more ductile. The Nichrome and Chromel C are examples of an alloy containing iron. The composition typical of Nichrome is 60 Ni, 12 Cr, 26 Fe, 2 Mn and Chromel C, 64 Ni, 11 Cr, Fe 25. The melting temperature of these alloys are 1350 °C and 1390 °C, respectively.

Since their introduction in the 1960s, foil resistors have had the best precision and stability of any resistor available. One of the important parameters of stability is the temperature coefficient of resistance (TCR). The TCR of foil resistors is extremely low, and has been further improved over the years. One range of ultra-precision foil resistors offers a TCR of 0.14 ppm/°C, tolerance ±0.005%, long-term stability (1 year) 25 ppm, (3 years) 50 ppm (further improved 5-fold by hermetic sealing), stability under load (2000 hours) 0.03%, thermal EMF 0.1 μV/°C, noise −42 dB, voltage coefficient 0.1 ppm/V, inductance 0.08 μH, capacitance 0.5 pF.

The thermal stability of this type of resistor also has to do with the opposing effects of the metal's electrical resistance increasing with temperature, and being reduced by thermal expansion leading to an increase in thickness of the foil, whose other dimensions are constrained by a ceramic substrate.

Ammeter shunts

An ammeter shunt is a special type of current-sensing resistor, having four terminals and a value in milliohms or even micro-ohms. Current-measuring instruments, by themselves, can usually accept only limited currents. To measure high currents, the current passes through the shunt across which the voltage drop is measured and interpreted as current. A typical shunt consists of two solid metal blocks, sometimes brass, mounted on an insulating base. Between the blocks, and soldered or brazed to them, are one or more strips of low temperature coefficient of resistance (TCR) manganin alloy. Large bolts threaded into the blocks make the current connections, while much smaller screws provide volt meter connections. Shunts are rated by full-scale current, and often have a voltage drop of 50 mV at rated current. Such meters are adapted to the shunt full current rating by using an appropriately marked dial face; no change need to be made to the other parts of the meter.

Grid resistor

In heavy-duty industrial high-current applications, a grid resistor is a large convection-cooled lattice of stamped metal alloy strips connected in rows between two electrodes. Such industrial grade resistors can be as large as a refrigerator; some designs can handle over 500 amperes of current, with a range of resistances extending lower than 0.04 ohms. They are used in applications such as dynamic braking and load banking for locomotives and trams, neutral grounding for industrial AC distribution, control loads for cranes and heavy equipment, load testing of generators and harmonic filtering for electric substations.

The term grid resistor is sometimes used to describe a resistor of any type connected to the control grid of a vacuum tube. This is not a resistor technology; it is an electronic circuit topology.

Additional Information

A resistor is an electrical component that limits or regulates the flow of electrical current in an electronic circuit. Resistors can also be used to provide a specific voltage for an active device such as a transistor.

All other factors being equal, in a direct-current (DC) circuit, the current through a resistor is inversely proportional to its resistance, and directly proportional to the voltage across it. This is the well-known Ohm's Law. In alternating-current (AC) circuits, this rule also applies as long as the resistor does not contain inductance or capacitance.

Types of resistors

Resistors can be fabricated in a variety of ways.

* The most common type in electronic devices and systems is the carbon-composition resistor. Fine granulated carbon (graphite) is mixed with clay and hardened. The resistance depends on the proportion of carbon to clay; the higher this ratio, the lower the resistance.
* Another type of resistor is made from winding Nichrome or similar wire on an insulating form. This component, called a wirewound resistor, is able to handle higher currents than a carbon-composition resistor of the same physical size. However, because the wire is wound into a coil, the component acts as an inductors as well as exhibiting resistance. This does not affect performance in DC circuits, but can have an adverse effect in AC circuits because inductance renders the device sensitive to changes in frequency.

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#2 Re: This is Cool » Miscellany » Yesterday 23:08:49

2107) Iron Lung

Gist

An iron lung is a device for artificial respiration in which rhythmic alternations in the air pressure in a chamber surrounding a patient's chest force air into and out of the lungs.

Summary

Can you name any truly life-changing inventions? There have been many over the course of human history. Just look at the field of medicine, for example. In this area alone, inventions like vaccines, anesthesia, and the stethoscope have changed the world.

Today’s Wonder of the Day is about another medical invention. Before the creation of respirators, it helped people who couldn’t breathe on their own. That’s right—today, we’re learning about the iron lung.

Iron lungs aren’t common today, but there was a time when they could be found in many hospitals. Invented in 1928, they offered treatment for severe cases of polio. This illness, which affected mostly children, could lead to life-threatening issues. It could even cause paralysis.

In these cases, patients could even lose the ability to breathe. This happened when the virus affected the diaphragm, a muscle below the lungs. Many of these patients regained the ability to breathe after a few weeks or months using an iron lung. Others relied on the machine for the rest of their lives.

How do iron lungs work? They rely on air pressure. To begin the treatment, patients are put on a sliding bed. A nurse or doctor pushes the bed into the machine, which is a large metal tube. Once patients are inside the lung, only their heads are outside of the tube. A rubber seal around their neck stops air from escaping the machine.

When the iron lung is switched on, it increases air pressure inside the tube. This causes the lungs to deflate, forcing the patient to exhale. Then, the air pressure decreases. This, in turn, leads the patient to inhale as their lungs inflate.

When patients begin treatment with an iron lung, they spend most of their time inside the machine. They may be taken out for mere minutes a day until they’re able to breathe on their own. As such, they rely on nurses, doctors, and other hospital staff to help them with everyday tasks like eating and changing clothes.

Does anyone still use an iron lung today? Yes, though they are very few. One example is Paul Alexander, who was diagnosed with polio in 1952 at age six.  Today, Alexander can spend short periods of time, sometimes hours, outside of the lung. He has built a successful career as an attorney and lived a full life thanks to the breathing support he receives from this machine.

Thanks to vaccines, there hasn’t been a new case of polio in the U.S. since 1979. This has made it difficult for Alexander to find replacement parts for his iron lung. It’s also difficult to find people to repair the machine. Additionally, insurance companies no longer cover the repairs. As he relies on the machine for survival, Alexander must pay for its upkeep out-of-pocket.

Have you ever seen an iron lung in action? Today, hospitals opt for modern respirators in place of these devices. Still, the iron lung is to thank for the survival of many children who contracted polio in the 20th century. Can you think of any other medical inventions that have changed the world?

Details

An iron lung is a type of negative pressure ventilator (NPV), a mechanical respirator which encloses most of a person's body and varies the air pressure in the enclosed space to stimulate breathing. It assists breathing when muscle control is lost, or the work of breathing exceeds the person's ability. Need for this treatment may result from diseases including polio and botulism and certain poisons (for example, barbiturates, tubocurarine).

The use of iron lungs is largely obsolete in modern medicine as more modern breathing therapies have been developed and due to the eradication of polio in most of the world. However, in 2020, the COVID-19 pandemic revived some interest in the device as a cheap, readily-producible substitute for positive-pressure ventilators, which were feared to be outnumbered by patients potentially needing temporary artificially assisted respiration.

The iron lung is a large horizontal cylinder designed to stimulate breathing in patients who have lost control of their respiratory muscles. The patient's head is exposed outside the cylinder, while the body is sealed inside. Air pressure inside the cylinder is cycled to facilitate inhalation and exhalation. Devices like the Drinker, Emerson, and Both respirators are examples of iron lungs, which can be manually or mechanically powered. Smaller versions, like the cuirass ventilator and jacket ventilator, enclose only the patient's torso. Breathing in humans occurs through negative pressure, where the rib cage expands and the diaphragm contracts, causing air to flow in and out of the lungs.

The concept of external negative pressure ventilation was introduced by John Mayow in 1670. The first widely used device was the iron lung, developed by Philip Drinker and Louis Shaw in 1928. Initially used for coal gas poisoning treatment, the iron lung gained fame for treating respiratory failure caused by polio in the mid-20th century. John Haven Emerson introduced an improved and more affordable version in 1931. The Both respirator, a cheaper and lighter alternative to the Drinker model, was invented in Australia in 1937. British philanthropist William Morris financed the production of the Both–Nuffield respirators, donating them to hospitals throughout Britain and the British Empire. During the polio outbreaks of the 1940s and 1950s, iron lungs filled hospital wards, assisting patients with paralyzed diaphragms in their recovery.

Polio vaccination programs and the development of modern ventilators have nearly eradicated the use of iron lungs in the developed world. Positive pressure ventilation systems, which blow air into the patient's lungs via intubation, have become more common than negative pressure systems like iron lungs. However, negative pressure ventilation is more similar to normal physiological breathing and may be preferable in rare conditions. As of 2024, after the death of Paul Alexander, only one patient in the U.S. is still using iron lungs. In response to the COVID-19 pandemic and the shortage of modern ventilators, some enterprises developed prototypes of new, easily producible versions of the iron lung.

Design and function

The iron lung is typically a large horizontal cylinder in which a person is laid, with their head protruding from a hole in the end of the cylinder, so that their full head (down to their voice box) is outside the cylinder, exposed to ambient air, and the rest of their body sealed inside the cylinder, where air pressure is continuously cycled up and down to stimulate breathing.

To cause the patient to inhale, air is pumped out of the cylinder, causing a slight vacuum, which causes the patient's chest and abdomen to expand (drawing air from outside the cylinder, through the patient's exposed nose or mouth, into their lungs). Then, for the patient to exhale, the air inside the cylinder is compressed slightly (or allowed to equalize to ambient room pressure), causing the patient's chest and abdomen to partially collapse, forcing air out of the lungs, as the patient exhales the breath through their exposed mouth and nose, outside the cylinder.

Examples of the device include the Drinker respirator, the Emerson respirator, and the Both respirator. Iron lungs can be either manually or mechanically powered, but are normally powered by an electric motor linked to a flexible pumping diaphragm (commonly opposite the end of the cylinder from the patient's head). Larger "room-sized" iron lungs were also developed, allowing for simultaneous ventilation of several patients (each with their heads protruding from sealed openings in the outer wall), with sufficient space inside for a nurse or a respiratory therapist to be inside the sealed room, attending the patients.

Smaller, single-patient versions of the iron lung include the so-called cuirass ventilator (named for the cuirass, a torso-covering body armor). The cuirass ventilator encloses only the patient's torso, or chest and abdomen, but otherwise operates essentially the same as the original, full-sized iron lung. A lightweight variation on the cuirass ventilator is the jacket ventilator or poncho or raincoat ventilator, which uses a flexible, impermeable material (such as plastic or rubber) stretched over a metal or plastic frame over the patient's torso.

Method and use

Humans, like most mammals, breathe by negative pressure breathing: the rib cage expands and the diaphragm contracts, expanding the chest cavity. This causes the pressure in the chest cavity to decrease, and the lungs expand to fill the space. This, in turn, causes the pressure of the air inside the lungs to decrease (it becomes negative, relative to the atmosphere), and air flows into the lungs from the atmosphere: inhalation. When the diaphragm relaxes, the reverse happens and the person exhales. If a person loses part or all of the ability to control the muscles involved, breathing becomes difficult or impossible.

Invention and early use:

Initial development

In 1670, English scientist John Mayow came up with the idea of external negative pressure ventilation. Mayow built a model consisting of bellows and a bladder to pull in and expel air. The first negative pressure ventilator was described by British physician John Dalziel in 1832. Successful use of similar devices was described a few years later. Early prototypes included a hand-operated bellows-driven "Spirophore" designed by Dr Woillez of Paris (1876), and an airtight wooden box designed specifically for the treatment of polio by Dr Stueart of South Africa (1918). Stueart's box was sealed at the waist and shoulders with clay and powered by motor-driven bellows.

Drinker and Shaw tank

The first of these devices to be widely used however was developed in 1928 by Phillip Drinker and Louis Shaw of the United States. The iron lung, often referred to in the early days as the "Drinker respirator", was invented by Philip Drinker (1894–1972) and Louis Agassiz Shaw Jr., professors of industrial hygiene at the Harvard School of Public Health. The machine was powered by an electric motor with air pumps from two vacuum cleaners. The air pumps changed the pressure inside a rectangular, airtight metal box, pulling air in and out of the lungs. The first clinical use of the Drinker respirator on a human was on October 12, 1928, at the Boston Children's Hospital in the US. The subject was an eight-year-old girl who was nearly dead as a result of respiratory failure due to polio. Her dramatic recovery within less than a minute of being placed in the chamber helped popularize the new device.

Variations

Boston manufacturer Warren E. Collins began production of the iron lung that year. Although it was initially developed for the treatment of victims of coal gas poisoning, it was most famously used in the mid-20th century for the treatment of respiratory failure caused by polio.

Danish physiologist August Krogh, upon returning to Copenhagen in 1931 from a visit to New York where he saw the Drinker machine in use, constructed the first Danish respirator designed for clinical purposes. Krogh's device differed from Drinker's in that its motor was powered by water from the city pipelines. Krogh also made an infant respirator version.

In 1931, John Haven Emerson (1906–1997) introduced an improved and less expensive iron lung. The Emerson iron lung had a bed that could slide in and out of the cylinder as needed, and the tank had portal windows which allowed attendants to reach in and adjust limbs, sheets, or hot packs. Drinker and Harvard University sued Emerson, claiming he had infringed on patent rights. Emerson defended himself by making the case that such lifesaving devices should be freely available to all. Emerson also demonstrated that every aspect of Drinker's patents had been published or used by others at earlier times. Since an invention must be novel to be patentable, prior publication/use of the invention meant it was not novel and therefore unpatentable. Emerson won the case, and Drinker's patents were declared invalid.

The United Kingdom's first iron lung was designed in 1934 by Robert Henderson, an Aberdeen doctor. Henderson had seen a demonstration of the Drinker respirator in the early 1930s and built a device of his own upon his return to Scotland. Four weeks after its construction, the Henderson respirator was used to save the life of a 10-year-old boy from New Deer, Aberdeenshire who had poliomyelitis. Despite this success, Henderson was reprimanded for secretly using hospital facilities to build the machine.

Both respirator

The Both respirator, a negative pressure ventilator, was invented in 1937 when Australia's epidemic of poliomyelitis created an immediate need for more ventilating machines to compensate for respiratory paralysis. Although the Drinker model was effective and saved lives, its widespread use was hindered by the fact that the machines were very large, heavy (about 750 lbs or 340 kg), bulky, and expensive. In the US, an adult machine cost about $2,000 in 1930, and £2,000 delivered to Melbourne in 1936. The cost in Europe in the mid-1950s was around £1,500. Consequently, there were few of the Drinker devices in Australia and Europe.

The South Australia Health Department asked Adelaide brothers Edward and Don Both to create an inexpensive "iron lung". Biomedical engineer Edward Both designed and developed a cabinet respirator made of plywood that worked similarly to the Drinker device, with the addition of a bi-valved design which allowed temporary access to the patient's body. Far cheaper to make (only £100) than the Drinker machine, the Both Respirator also weighed less and could be constructed and transported more quickly. Such was the demand for the machines that they were often used by patients within an hour of production.

Visiting London in 1938 during another polio epidemic, Both produced additional respirators there which attracted the attention of William Morris (Lord Nuffield), a British motor manufacturer and philanthropist. Nuffield, intrigued by the design, financed the production of approximately 1700 machines at his car factory in Cowley and donated them to hospitals throughout all parts of Britain and the British Empire. Soon, the Both–Nuffield respirators were able to be produced by the thousand at about one-thirteenth the cost of the American design. By the early 1950s, there were over 700 Both-Nuffield iron lungs in the United Kingdom, but only 50 Drinker devices.

Polio epidemic

Staff in a Rhode Island hospital examine a patient in an iron lung tank respirator during a polio epidemic in 1960.
Rows of iron lungs filled hospital wards at the height of the polio outbreaks of the 1940s and 1950s, helping children, and some adults, with bulbar polio and bulbospinal polio. A polio patient with a paralyzed diaphragm would typically spend two weeks inside an iron lung while recovering.

Modern development and usage

Polio vaccination programs have virtually eradicated new cases of poliomyelitis in the developed world. Because of this, the development of modern ventilators, and widespread use of tracheal intubation and tracheotomy, the iron lung has mostly disappeared from modern medicine. In 1959, 1,200 people were using tank respirators in the United States, but by 2004 that number had decreased to just 39. By 2014, only 10 people were left with an iron lung.

Replacement

Positive pressure ventilation systems are now more common than negative pressure systems. Positive pressure ventilators work by blowing air into the patient's lungs via intubation through the airway; they were used for the first time in Blegdams Hospital, Copenhagen, Denmark, during a polio outbreak in 1952. It proved a success and by 1953 it had superseded the iron lung throughout Europe.

The positive pressure ventilator has the asset that the patient's airways can be cleared and the patient can be seated on semi-seated position in the acute phase of polio. The fatality rate on using iron lungs on respiratory paralysis patients could be as high as 80% to 90%, most patients either drowning in their own saliva as their swallowing muscles had been paralyzed, or from organ shutdown due to acidosis due to accumulated carbon dioxide in bloodstream due to clogged airways. By using the positive pressure ventilators instead of iron lungs, the Copenhagen hospital team was able to decrease the fatality rate eventually down to 11%. The first patient treated this way was a 12-year-old girl named Vivi Ebert, who had bulbar polio.

The iron lung now has a marginal place in modern respiratory therapy. Most patients with paralysis of the breathing muscles use modern mechanical ventilators that push air into the airway with positive pressure. These are generally efficacious and have the advantage of not restricting patients' movements or caregivers' ability to examine the patients as significantly as an iron lung does.

Continued use

Despite the advantages of positive ventilation systems, negative pressure ventilation is a truer approximation of normal physiological breathing and results in a more normal distribution of air in the lungs. It may also be preferable in certain rare conditions, such as central hypoventilation syndrome, in which failure of the medullary respiratory centers at the base of the brain results in patients having no autonomic control of breathing. At least one reported polio patient, Dianne Odell, had a spinal deformity that caused the use of mechanical ventilators to be contraindicated.

At least a few patients today still use the older machines, often in their homes, despite the occasional difficulty of finding replacement parts.

Joan Headley of Post-Polio Health International said that as of May 28, 2008, about 30 patients in the US were still using an iron lung. That figure may be inaccurately low; Houston alone had 19 iron lung patients living at home in 2008.

Martha Mason of Lattimore, North Carolina, died on May 4, 2009, after spending 61 of her 72 years in an iron lung.

On October 30, 2009, June Middleton of Melbourne, Australia, who had been entered in the Guinness Book of Records as the person who spent the longest time in an iron lung, died aged 83, having spent more than 60 years in her iron lung.

In 2013, the Post-Polio Health International (PHI) organizations estimated that only six to eight iron lung users were in the United States; as of 2017, its executive director knew of none. Press reports then emerged, however, of at least three (perhaps the last three) users of such devices, sparking interest amongst those in the makerspace community such as Naomi Wu in the manufacture of the obsolete components, particularly the gaskets.

In 2021, the National Public Radio programs Radio Diaries and All Things Considered gave a report on Martha Lillard, one of the last remaining Americans depending on the daily use of an iron lung, which she had been using since 1953. In her audio interview, she reported that she was having problems obtaining replacement parts to keep her machine working properly.

On March 11, 2024, Paul Alexander of Dallas, Texas, United States, died at the age of 78. He had been confined to an iron lung for 72 years from the age of six, longer than anyone, and was the last man living in an iron lung. With his death, Martha Lillard is the only person in the U.S. known to use an iron lung.

COVID-19 pandemic

In early 2020, reacting to the COVID-19 pandemic, to address the urgent global shortage of modern ventilators (needed for patients with advanced, severe COVID-19), some enterprises developed prototypes of new, readily-producible versions of the iron lung. These developments included:

* a compact, torso-sized "exovent" developed by a team in the United Kingdom, which included the University of Warwick, the Royal National Throat Nose and Ear Hospital, the Marshall Aerospace and Defence Group, the Imperial College Healthcare NHS Trust, along with teams of medical clinicians, academics, manufacturers, engineers and citizen scientists;
* a full-size iron lung developed in the United States by a team led by Hess Services, Inc., of Hays, Kansas.

Additional Information

The iron lung was born in 1927, when Philip Drinker and Louis Agassiz Shaw at Harvard University devised a machine that could maintain respiration, pulling air into and out of the lungs by changing the pressure in an airtight metal box.

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#3 Re: Dark Discussions at Cafe Infinity » crème de la crème » Yesterday 18:16:19

1431) Kai Siegbahn

Summary

According to quantum physics principles, the electrons in atoms and molecules have defined energy levels. Albert Einstein’s theory of the “photoelectric effect” says that a light particle (photon) can liberate an electron from an atom if it has sufficient energy. In the 1950s Kai Siegbahn developed methods for achieving highly accurate measurements of energy levels in atoms by irradiating them with photons and measuring the energy of the electrons emitted using the photoelectric effect.

Details

Kai Manne Börje Siegbahn (20 April 1918 – 20 July 2007) was a Swedish physicist who shared the 1981 Nobel Prize in Physics.

Biography

Siegbahn was born in Lund, Sweden, son of Manne Siegbahn the 1924 physics Nobel Prize winner. Siegbahn earned his doctorate at the University of Stockholm in 1944. He was professor at the Royal Institute of Technology 1951–1954, and then professor of experimental physics at Uppsala University 1954–1984, which was the same chair his father had held. He shared the 1981 Nobel Prize in Physics with Nicolaas Bloembergen and Arthur Schawlow. Siegbahn received half the prize "for his contribution to the development of high-resolution electron spectroscopy" while Bloembergen and Schawlow received one quarter each "for their contribution to the development of laser spectroscopy".

Siegbahn referred to his technique as Electron Spectroscopy for Chemical Analysis (ESCA); it is now usually known as X-ray photoelectron spectroscopy (XPS). In 1967 he published a book, ESCA; atomic, molecular and solid state structure studied by means of electron spectroscopy.

He was a member of several academies and societies, including the Royal Swedish Academy of Sciences, and was president of the International Union of Pure and Applied Physics from 1981 to 1984.

Siegbahn married Anna Brita Rhedin in 1944. The couple had three sons (two physicists and a biochemist).

Siegbahn died on 20 July 2007 at the age of 89. At the time of his death he was still active as a scientist at the Ångström Laboratory at Uppsala University.

Additional Information

Kai Manne Börje Siegbahn (born April 20, 1918, Lund, Swed.—died July 20, 2007, Ängelholm) was a Swedish physicist, corecipient with Nicolaas Bloembergen and Arthur Leonard Schawlow of the 1981 Nobel Prize for Physics for their revolutionary work in spectroscopy, particularly the spectroscopic analysis of the interaction of electromagnetic radiation with matter.

Siegbahn was the son of Karl Manne Siegbahn, who received the Nobel Prize for Physics in 1924 for his discoveries relating to X-ray spectroscopy. Kai was awarded his Ph.D. in physics by the University of Stockholm in 1944. In 1951 he was appointed professor at the Royal Institute of Technology in Stockholm, and in 1954 he moved to the University of Uppsala, where he taught until his retirement in 1984.

In his prize-winning work, Siegbahn formulated the principles underlying the technique called ESCA (electron spectroscopy for chemical analysis) and refined the instruments used in carrying it out. ESCA depends on a fundamental phenomenon, the photoelectric effect, which is the emission of electrons that occurs when electromagnetic radiation strikes a material. Siegbahn’s achievement was to develop ways to measure the kinetic energies of the emitted electrons accurately enough to permit the determination of their binding energies. He showed that chemical elements bind electrons with characteristic energies that are slightly modified by the molecular or ionic environment. During the 1970s ESCA was adopted all over the world for analyzing materials, including the particles in polluted air and the surfaces of solid catalysts used in petroleum refining.

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#4 Jokes » Celery Quotes - I » Yesterday 17:39:35

Jai Ganesh
Replies: 0

Q: Why did the gardener quit?
A: Because his celery wasn't high enough!
* * *
Q: What water yields award winning Celery plants?
A: Perspiration!
* * *
Q: What vegetable might you find in your basement?
A: Cellar-y!
* * *
Q: Why was the Hamster upset with his job?
A: It didn't pay enough salary (celery).
* * *
Q: Why did the chef quit?
A: They cut his celery.
* * *

#5 Dark Discussions at Cafe Infinity » Chairman Quotes » Yesterday 17:25:48

Jai Ganesh
Replies: 0

Chair Quotes - II

1. There is only one boss. The customer. And he can fire everybody in the company from the chairman on down, simply by spending his money somewhere else. - Sam Walton

2. I have no desire to be a politician. The role of chairman is not a politically aligned role, although it's all based in Canberra so I'm over there a lot. - Adam Gilchrist

3. At age 26, I was chairman of UB Group but living like a 26-year-old. I lived my age. Which youngster doesn't like a Ferrari? Which youngster doesn't like a good time?... but my contemporaries were R. S. Goenka and Dhirubhai Ambani, captains of the industry but twice my age. You wouldn't necessarily expect them to be driving around in Ferraris. - Vijay Mallya

4. I'm the non-executive chairman of nine or so major companies, and on the nine companies, it's a little trying because you jump from one industry to another, as the case might be. But one had the reasonable knowledge of those nine activities, and it's been an exciting job. - Ratan Tata

5. I served as the chairman of the India-Israel Parliamentary Friendship Group for three years, during which I also had the pleasure of visiting Israel. - Sushma Swaraj

6. I was chairman of the steering committee for agriculture when we set up the target of 4% growth rate. I had written that if you want to achieve 4% growth rate in agriculture, you should have 8% growth in animal husbandry and fisheries and 8% in horticulture. - M. S. Swaminathan

7. I was the chairman of the IT committee of Parliament for 5 years. - Anurag Thakur.

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#8 Re: Jai Ganesh's Puzzles » Doc, Doc! » Yesterday 15:55:09

Hi,

#2538. What does the medical term Jugular venous pressure mean?

#9 Re: Jai Ganesh's Puzzles » General Quiz » Yesterday 15:36:49

Hi,

#9731. What does the term in Geography Waterfall mean?

#9732. What does the term in Geography Water-meadow mean?

#10 Re: Jai Ganesh's Puzzles » English language puzzles » Yesterday 15:15:44

Hi,

#5715. What does the verb (used with object) crumble mean?

#5716. What does the verb (used with object) crunch mean?

#12 This is Cool » Server » Yesterday 00:22:37

Jai Ganesh
Replies: 0

Server

Gist

A server is a computer or system that provides resources, data, services, or programs to other computers, known as clients, over a network.

Summary

A server is a hardware device or software that processes requests sent over a network and replies to them. A client is the device that submits a request and waits for a response from the server. The computer system that accepts requests for online files and transmits those files to the client is referred to as a “server” in the context of the Internet.

What is a Server?

A Server is a program or a device that provides functionality for called clients which are other programs or devices. This architecture is called the client-server model.

A single overall computation is distributed across multiple processes or devices. Servers can provide various functionalities called services. These services include sharing data or resources among multiple clients or performing computations for a client. Multiple clients can be served by a single server, and a single client can use multiple servers.

Uses of Servers

A client process may run on the same device. It can also connect over a network to a server to run on a different device. Examples of servers may include database servers, mail servers, print servers, file servers, web servers, application servers, and game servers. Most frequently client-server systems are implemented by the request-response communication., i.e., a client sends a request to the server. In this model, the server performs some action and sends a response back to the client, typically with a result or acknowledgement.

Designating a computer as server-class hardware means that it is specialized for running servers on it. This implies that it is more powerful and reliable than standard personal computers. However large computing clusters may comprise many relatively simple, replaceable server components.

Details

A server is a software or hardware device that accepts and responds to requests made over a network. The device that makes the request, and receives a response from the server, is called a client. On the Internet, the term "server" commonly refers to the computer system that receives requests for a web files and sends those files to the client.

What are they used for?

Servers manage network resources. For example, a user may set up a server to control access to a network, send/receive e-mail, manage print jobs, or host a website. They are also proficient at performing intense calculations. Some servers are committed to a specific task or one website, often called dedicated servers. However, many servers today are shared servers that take on the responsibility of e-mail, DNS (domain name system), FTP, and multiple websites in the case of a web server.

Why are servers always on?

Because they are commonly used to deliver services that are constantly required, most servers are never turned off. Consequently, when servers fail, they can cause the network users and company many problems. To alleviate these issues, servers are commonly set up to be fault tolerant.

Examples of servers

The following list contains links to various server types.

* Application server
* Blade server
* Cloud server
* Database server
* Dedicated server
* Domain name service
* File server
* Mail server
* Print server
* Proxy server
* Standalone server
* Web server

How do other computers connect to a server?

With a local network, the server connects to a router or switch that all other computers on the network use. Once connected to the network, other computers can access that server and its features. For example, with a web server, a user could connect to the server to view a website, search, and communicate with other users on the network.

An Internet server works the same way as a local network server, but on a much larger scale. The server is assigned an IP address by InterNIC, or by web host.

Usually, users connect to a server using its domain name, which is registered with a domain name registrar. When users connect to the domain name (such as "computerhope.com"), the name is automatically translated to the server's IP address by a DNS resolver.

The domain name makes it easier for users to connect to the server, because the name is easier to remember than an IP address. Also, domain names enable the server operator to change the IP address of the server without disrupting the way that users access the server. The domain name can always remain the same, even if the IP address changes.

Where are servers stored?

In a business or corporate environment, a server and other network equipment are often stored in a closet or glass house. These areas help isolate sensitive computers and equipment from people who should not access them.

Servers that are remote or not hosted on-site are located in a data center. With these types of servers, the hardware is managed by another company and configured remotely by you or your company.

What is a Linux server?

A Linux server is a computer running a version of Linux that's connected to a network or the Internet. For example, many of the web servers that host web pages on the Internet are Linux servers.

Can my computer be a server?

Yes. Any computer, even a home desktop or laptop computer, can act as a server with the right software. For example, you could install an FTP server program on your computer to share files between other users on your network.

Although it is possible to have your home computer act as a server, keep the following ideas in mind.

* Your computer and the related server software must always be running to be accessible.
* When your computer is used as a server, its resources (e.g., processing and bandwidth) is taken away from what you have available to do other things.
* Connecting a computer to a network and the Internet can open up your computer to new types of attacks.
* If the service you're providing becomes popular, a typical computer may not have the necessary resources to handle all of the requests.

Additional Information

In computing, a server is a piece of computer hardware or software (computer program) that provides functionality for other programs or devices, called "clients". This architecture is called the client–server model. Servers can provide various functionalities, often called "services", such as sharing data or resources among multiple clients or performing computations for a client. A single server can serve multiple clients, and a single client can use multiple servers. A client process may run on the same device or may connect over a network to a server on a different device. Typical servers are database servers, file servers, mail servers, print servers, web servers, game servers, and application servers.

Client–server systems are usually most frequently implemented by (and often identified with) the request–response model: a client sends a request to the server, which performs some action and sends a response back to the client, typically with a result or acknowledgment. Designating a computer as "server-class hardware" implies that it is specialized for running servers on it. This often implies that it is more powerful and reliable than standard personal computers, but alternatively, large computing clusters may be composed of many relatively simple, replaceable server components.

Operation

Strictly speaking, the term server refers to a computer program or process (running program). Through metonymy, it refers to a device used for (or a device dedicated to) running one or several server programs. On a network, such a device is called a host. In addition to server, the words serve and service (as verb and as noun respectively) are frequently used, though servicer and servant are not. The word service (noun) may refer to the abstract form of functionality, e.g. Web service. Alternatively, it may refer to a computer program that turns a computer into a server, e.g. Windows service. Originally used as "servers serve users" (and "users use servers"), in the sense of "obey", today one often says that "servers serve data", in the same sense as "give". For instance, web servers "serve [up] web pages to users" or "service their requests".

The server is part of the client–server model; in this model, a server serves data for clients. The nature of communication between a client and server is request and response. This is in contrast with peer-to-peer model in which the relationship is on-demand reciprocation. In principle, any computerized process that can be used or called by another process (particularly remotely, particularly to share a resource) is a server, and the calling process or processes is a client. Thus any general-purpose computer connected to a network can host servers. For example, if files on a device are shared by some process, that process is a file server. Similarly, web server software can run on any capable computer, and so a laptop or a personal computer can host a web server.

While request–response is the most common client-server design, there are others, such as the publish–subscribe pattern. In the publish-subscribe pattern, clients register with a pub-sub server, subscribing to specified types of messages; this initial registration may be done by request-response. Thereafter, the pub-sub server forwards matching messages to the clients without any further requests: the server pushes messages to the client, rather than the client pulling messages from the server as in request-response.

Hardware

Hardware requirement for servers vary widely, depending on the server's purpose and its software. Servers often are more powerful and expensive than the clients that connect to them.

The name server is used both for the hardware and software pieces. For the hardware servers, it is usually limited to mean the high-end machines although software servers can run on a variety of hardwares.

Since servers are usually accessed over a network, many run unattended without a computer monitor or input device, audio hardware and USB interfaces. Many servers do not have a graphical user interface (GUI). They are configured and managed remotely. Remote management can be conducted via various methods including Microsoft Management Console (MMC), PowerShell, SSH and browser-based out-of-band management systems such as Dell's iDRAC or HP's iLo.

Large servers

Large traditional single servers would need to be run for long periods without interruption. Availability would have to be very high, making hardware reliability and durability extremely important. Mission-critical enterprise servers would be very fault tolerant and use specialized hardware with low failure rates in order to maximize uptime. Uninterruptible power supplies might be incorporated to guard against power failure. Servers typically include hardware redundancy such as dual power supplies, RAID disk systems, and ECC memory, along with extensive pre-boot memory testing and verification. Critical components might be hot swappable, allowing technicians to replace them on the running server without shutting it down, and to guard against overheating, servers might have more powerful fans or use water cooling. They will often be able to be configured, powered up and down, or rebooted remotely, using out-of-band management, typically based on IPMI. Server casings are usually flat and wide, and designed to be rack-mounted, either on 19-inch racks or on Open Racks.

These types of servers are often housed in dedicated data centers. These will normally have very stable power and Internet and increased security. Noise is also less of a concern, but power consumption and heat output can be a serious issue. Server rooms are equipped with air conditioning devices.

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#13 Re: This is Cool » Miscellany » 2024-03-27 22:54:29

2106) Muscular System

Gist

The muscular system is composed of specialized cells called muscle fibers. Their predominant function is contractibility. Muscles, attached to bones or internal organs and blood vessels, are responsible for movement. Nearly all movement in the body is the result of muscle contraction.

Summary

The muscular system is composed of specialized cells called muscle fibers. Their predominant function is contractibility. Muscles, attached to bones or internal organs and blood vessels, are responsible for movement. Nearly all movement in the body is the result of muscle contraction. Exceptions to this are the action of cilia, the flagellum on sperm cells, and amoeboid movement of some white blood cells.

The integrated action of joints, bones, and skeletal muscles produces obvious movements such as walking and running. Skeletal muscles also produce more subtle movements that result in various facial expressions, eye movements, and respiration.

In addition to movement, muscle contraction also fulfills some other important functions in the body, such as posture, joint stability, and heat production. Posture, such as sitting and standing, is maintained as a result of muscle contraction. The skeletal muscles are continually making fine adjustments that hold the body in stationary positions. The tendons of many muscles extend over joints and in this way contribute to joint stability. This is particularly evident in the knee and shoulder joints, where muscle tendons are a major factor in stabilizing the joint. Heat production, to maintain body temperature, is an important by-product of muscle metabolism. Nearly 85 percent of the heat produced in the body is the result of muscle contraction.

Details

Muscles play a part in every function of the body. The muscular system is made up of over 600 muscles. These include three muscle types: smooth, skeletal, and cardiac.

Only skeletal muscles are voluntary, meaning you can control them consciously. Smooth and cardiac muscles act involuntarily.

Each muscle type in the muscular system has a specific purpose. You’re able to walk because of your skeletal muscles. You can digest because of your smooth muscles. And your heart beats because of your cardiac muscle.

The different muscle types also work together to make these functions possible. For instance, when you run (skeletal muscles), your heart pumps harder (cardiac muscle), and causes you to breathe heavier (smooth muscles).

Keep reading to learn more about your muscular system’s functions.

1. Mobility

Your skeletal muscles are responsible for the movements you make. Skeletal muscles are attached to your bones and partly controlled by the central nervous system (CNS).

You use your skeletal muscles whenever you move. Fast-twitch skeletal muscles cause short bursts of speed and strength. Slow-twitch muscles function better for longer movements.

2. Circulation

The involuntary cardiac and smooth muscles help your heart beat and blood flow through your body by producing electrical impulses. The cardiac muscle (myocardium) is found in the walls of the heart. It’s controlled by the autonomic nervous system responsible for most bodily functions.

The myocardium also has one central nucleus like a smooth muscle.

Your blood vessels are made up of smooth muscles, and also controlled by the autonomic nervous system.

3. Respiration

Your diaphragm is the main muscle at work during quiet breathing. Heavier breathing, like what you experience during exercise, may require accessory muscles to help the diaphragm. These can include the abdominal, neck, and back muscles.

4. Digestion

Digestion is controlled by smooth muscles found in your gastrointestinal tract. This comprises the:

* mouth
* esophagus
* stomach
* small and large intestines
* rectum
* the last part of the digestive tract

The digestive system also includes the liver, pancreas, and gallbladder.

Your smooth muscles contract and relax as food passes through your body during digestion. These muscles also help push food out of your body through defecation, or vomiting when you’re sick.

5. Urination

Smooth and skeletal muscles make up the urinary system. The urinary system includes the:

* kidneys
* bladder
* ureters
* urethra
* male or female reproductive organs
* prostate

All the muscles in your urinary system work together so you can urinate. The dome of your bladder is made of smooth muscles. You can release urine when those muscles tighten. When they relax, you can hold in your urine.

6. Childbirth

Smooth muscles are found in the uterus. During pregnancy, these muscles grow and stretch as the baby grows. When a woman goes into labor, the smooth muscles of the uterus contract and relax to help push the baby through the math.

7. Vision

Your eye sockets are made up of six skeletal muscles that help you move your eyes. And the internal muscles of your eyes are made up of smooth muscles. All these muscles work together to help you see. If you damage these muscles, you may impair your vision.

8. Stability

The skeletal muscles in your core help protect your spine and help with stability. Your core muscle group includes the abdominal, back, and pelvic muscles. This group is also known as the trunk. The stronger your core, the better you can stabilize your body. The muscles in your legs also help steady you.

9. Posture

Your skeletal muscles also control posture. Flexibility and strength are keys to maintaining proper posture. Stiff neck muscles, weak back muscles, or tight hip muscles can throw off your alignment. Poor posture can affect parts of your body and lead to joint pain and weaker muscles. These parts include the:

* shoulders
* spine
* hips
* knees

The bottom line

The muscular system is a complex network of muscles vital to the human body. Muscles play a part in everything you do. They control your heartbeat and breathing, help digestion, and allow movement.

Muscles, like the rest of your body, thrive when you exercise and eat healthily. But too much exercise can cause sore muscles. Muscle pain can also be a sign that something more serious is affecting your body.

The following conditions can affect your muscular system:

* myopathy (muscle disease)
* muscular dystrophy
* multiple sclerosis (MS)
* Parkinson’s disease
* fibromyalgia

Talk to your doctor if you have one of these conditions. They can help you find ways to manage your health. It’s important to take care of your muscles so they stay healthy and strong.

Additional Information

The muscular system is an organ system consisting of skeletal, smooth, and cardiac muscle. It permits movement of the body, maintains posture, and circulates blood throughout the body. The muscular systems in vertebrates are controlled through the nervous system although some muscles (such as the cardiac muscle) can be completely autonomous. Together with the skeletal system in the human, it forms the musculoskeletal system, which is responsible for the movement of the body.

Types

There are three distinct types of muscle: skeletal muscle, cardiac or heart muscle, and smooth (non-striated) muscle. Muscles provide strength, balance, posture, movement, and heat for the body to keep warm.

There are approximately 640 muscles in an adult male human body. A kind of elastic tissue makes up each muscle, which consists of thousands, or tens of thousands, of small muscle fibers. Each fiber comprises many tiny strands called fibrils, impulses from nerve cells control the contraction of each muscle fiber.

Skeletal

Skeletal muscle, is a type of striated muscle, composed of muscle cells, called muscle fibers, which are in turn composed of myofibrils. Myofibrils are composed of sarcomeres, the basic building blocks of striated muscle tissue. Upon stimulation by an action potential, skeletal muscles perform a coordinated contraction by shortening each sarcomere. The best proposed model for understanding contraction is the sliding filament model of muscle contraction. Within the sarcomere, actin and myosin fibers overlap in a contractile motion towards each other. Myosin filaments have club-shaped myosin heads that project toward the actin filaments, and provide attachment points on binding sites for the actin filaments. The myosin heads move in a coordinated style; they swivel toward the center of the sarcomere, detach and then reattach to the nearest active site of the actin filament. This is called a ratchet type drive system.

This process consumes large amounts of adenosine triphosphate (ATP), the energy source of the cell. ATP binds to the cross-bridges between myosin heads and actin filaments. The release of energy powers the swiveling of the myosin head. When ATP is used, it becomes adenosine diphosphate (ADP), and since muscles store little ATP, they must continuously replace the discharged ADP with ATP. Muscle tissue also contains a stored supply of a fast-acting recharge chemical, creatine phosphate, which when necessary can assist with the rapid regeneration of ADP into ATP.

Calcium ions are required for each cycle of the sarcomere. Calcium is released from the sarcoplasmic reticulum into the sarcomere when a muscle is stimulated to contract. This calcium uncovers the actin-binding sites. When the muscle no longer needs to contract, the calcium ions are pumped from the sarcomere and back into storage in the sarcoplasmic reticulum.

There are approximately 639 skeletal muscles in the human body.

Cardiac

Heart muscle is striated muscle but is distinct from skeletal muscle because the muscle fibers are laterally connected. Furthermore, just as with smooth muscles, their movement is involuntary. Heart muscle is controlled by the sinus node influenced by the autonomic nervous system.

Smooth

Smooth muscle contraction is regulated by the autonomic nervous system, hormones, and local chemical signals, allowing for gradual and sustained contractions. This type of muscle tissue is also capable of adapting to different levels of stretch and tension, which is important for maintaining proper blood flow and the movement of materials through the digestive system.

Physiology:

Contraction

Neuromuscular junctions are the focal point where a motor neuron attaches to a muscle. Acetylcholine, (a neurotransmitter used in skeletal muscle contraction) is released from the axon terminal of the nerve cell when an action potential reaches the microscopic junction called a synapse. A group of chemical messengers across the synapse and stimulate the formation of electrical changes, which are produced in the muscle cell when the acetylcholine binds to receptors on its surface. Calcium is released from its storage area in the cell's sarcoplasmic reticulum. An impulse from a nerve cell causes calcium release and brings about a single, short muscle contraction called a muscle twitch. If there is a problem at the neuromuscular junction, a very prolonged contraction may occur, such as the muscle contractions that result from tetanus. Also, a loss of function at the junction can produce paralysis.

Skeletal muscles are organized into hundreds of motor units, each of which involves a motor neuron, attached by a series of thin finger-like structures called axon terminals. These attach to and control discrete bundles of muscle fibers. A coordinated and fine-tuned response to a specific circumstance will involve controlling the precise number of motor units used. While individual muscle units contract as a unit, the entire muscle can contract on a predetermined basis due to the structure of the motor unit. Motor unit coordination, balance, and control frequently come under the direction of the cerebellum of the brain. This allows for complex muscular coordination with little conscious effort, such as when one drives a car without thinking about the process.

Tendon

A tendon is a piece of connective tissue that connects a muscle to a bone.[8] When a muscle intercept, it pulls against the skeleton to create movement. A tendon connects this muscle to a bone, making this function possible.

Aerobic and anaerobic muscle activity

At rest, the body produces the majority of its ATP aerobically in the mitochondria without producing lactic acid or other fatiguing byproducts. During exercise, the method of ATP production varies depending on the fitness of the individual as well as the duration and intensity of exercise. At lower activity levels, when exercise continues for a long duration (several minutes or longer), energy is produced aerobically by combining oxygen with carbohydrates and fats stored in the body.

During activity that is higher in intensity, with possible duration decreasing as intensity increases, ATP production can switch to anaerobic pathways, such as the use of the creatine phosphate and the phosphagen system or anaerobic glycolysis. Aerobic ATP production is biochemically much slower and can only be used for long-duration, low-intensity exercise, but produces no fatiguing waste products that can not be removed immediately from the sarcomere and the body, and it results in a much greater number of ATP molecules per fat or carbohydrate molecule. Aerobic training allows the oxygen delivery system to be more efficient, allowing aerobic metabolism to begin quicker. Anaerobic ATP production produces ATP much faster and allows near-maximal intensity exercise, but also produces significant amounts of lactic acid which render high-intensity exercise unsustainable for more than several minutes. The phosphagen system is also anaerobic. It allows for the highest levels of exercise intensity, but intramuscular stores of phosphocreatine are very limited and can only provide energy for exercises lasting up to ten seconds. Recovery is very quick, with full creatine stores regenerated within five minutes.

Clinical significance

Multiple diseases can affect the muscular system.

Muscular Dystrophy

Muscular dystrophy is a group of disorders associated with progressive muscle weakness and loss of muscle mass. These disorders are caused by mutations in a person’s genes. The disease affects between 19.8 and 25.1 per 100,000 person-years globally.

There are more than 30 types of muscular dystrophy. Depending on the type, muscular dystrophy can affect the patient's heart and lungs, and/or their ability to move, walk, and perform daily activities. The most common types include:

* Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD)
* Myotonic dystrophy
* Limb-Girdle (LGMD)
* Facioscapulohumeral dystrophy (FSHD)
* Congenital dystrophy (CMD)
* Distal (DD)
* Oculopharyngeal dystrophy (OPMD)
* Emery-Dreifuss (EDMD).

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#14 Re: Dark Discussions at Cafe Infinity » crème de la crème » 2024-03-27 19:00:45

1430) Arthur Leonard Schawlow

Summary

Arthur L. Schawlow (born May 5, 1921, Mount Vernon, New York, U.S.—died April 28, 1999, Palo Alto, California) American physicist and corecipient, with Nicolaas Bloembergen of the United States and Kai Manne Börje Siegbahn of Sweden, of the 1981 Nobel Prize for Physics for his work in developing the laser and in laser spectroscopy.

As a child, Schawlow moved with his family to Canada. He attended the University of Toronto, receiving his Ph.D. in 1949. In that year he went to Columbia University, where he began collaborating with Charles Townes on the development of the maser (a device that produces and amplifies electromagnetic radiation mainly in the microwave region of the spectrum), the laser (a device similar to the maser that produces an intense beam of light of a single colour), and laser spectroscopy. Schawlow worked on the project that led to the construction of the first working maser in 1953 (for which Townes received a share of the 1964 Nobel Prize for Physics). Schawlow was a research physicist at Bell Telephone Laboratories from 1951 to 1961. In 1958 he and Townes published a paper in which they outlined the working principles of the laser, though the first such working device was built by another American physicist, Theodore Maiman, in 1960. In 1961 Schawlow became a professor at Stanford University. He became a world authority on laser spectroscopy, and he and Bloembergen earned their share of the 1981 Nobel Prize by using lasers to study the interactions of electromagnetic radiation with matter. His works include Infrared and Optical Masers (1958) and Lasers and Their Uses (1983). A few years after winning the Nobel Prize, Schawlow wrote an article on the laser for Encyclopædia Britannica’s 1987 Yearbook of Science and the Future.

Details

Arthur Leonard Schawlow (May 5, 1921 – April 28, 1999) was an American physicist and co-inventor of the laser with Charles Townes. His central insight, which Townes overlooked, was the use of two mirrors as the resonant cavity to take maser action from microwaves to visible wavelengths. He shared the 1981 Nobel Prize in Physics with Nicolaas Bloembergen and Kai Siegbahn for his work using lasers to determine atomic energy levels with great precision.

Biography

Schawlow was born in Mount Vernon, New York. His mother, Helen (Mason), was from Canada, and his father, Arthur Schawlow, was a Jewish immigrant from Riga (then in the Russian Empire, now in Latvia). Schawlow was raised in his mother's Protestant religion. When Arthur was three years old, they moved to Toronto, Ontario, Canada.

At the age of 16, he completed high school at Vaughan Road Academy (then Vaughan Collegiate Institute), and received a scholarship in science at the University of Toronto (Victoria College). After earning his undergraduate degree, Schawlow continued in graduate school at the University of Toronto which was interrupted due to World War II. At the end of the war, he began work on his Ph.D at the university with Professor Malcolm Crawford. He then took a postdoctoral position with Charles H. Townes at the physics department of Columbia University in the fall of 1949.

He went on to accept a position at Bell Labs in late 1951. He left in 1961 to join the faculty at Stanford University as a professor. He remained at Stanford until he retired to emeritus status in 1996.

Although his research focused on optics, in particular, lasers and their use in spectroscopy, he also pursued investigations in the areas of superconductivity and nuclear resonance. Schawlow shared the 1981 Nobel Prize in Physics with Nicolaas Bloembergen and Kai Siegbahn for their contributions to the development of laser spectroscopy.

Schawlow coauthored the widely used text Microwave Spectroscopy (1955) with Charles Townes. Schawlow and Townes were the first to publish the theory of laser design and operation in their seminal 1958 paper on "optical masers", although Gordon Gould is often credited with the "invention" of the laser, due to his unpublished work that predated Schawlow and Townes by a few months. The first working laser was made in 1960 by Theodore Maiman.

In 1991, the NEC Corporation and the American Physical Society established a prize: the Arthur L. Schawlow Prize in Laser Science. The prize is awarded annually to "candidates who have made outstanding contributions to basic research using lasers."

Science and religion

He participated in science and religion discussions. Regarding God, he stated, "I find a need for God in the universe and in my own life."

Personal life

In 1951, he married Aurelia Townes, younger sister of his postdoctoral advisor, Charles Townes. They had three children: Arthur Jr., Helen, and Edith. Arthur Jr. is autistic, with very little speech ability.

Schawlow and Professor Robert Hofstadter at Stanford, who also had an autistic child, teamed up to help each other find solutions to the condition. Arthur Jr. was put in a special center for autistic individuals, and later, Schawlow put together an institution to care for people with autism in Paradise, California. It was later named the Arthur Schawlow Center in 1999, shortly before his death. Schawlow was a promoter of the controversial method of facilitated communication with patients of autism.

He considered himself to be an orthodox Protestant Christian, and attended a Methodist church. Arthur Schawlow was an intense fan and collector of traditional American jazz recordings, as well as a supporter of instrumental groups performing this type of music.

Schawlow died of leukemia in Palo Alto, California, on April 28, 1999, at the age 77.

Additional Information

Electrons in atoms and molecules have fixed energy levels, according to the principles of quantum physics. When there are transitions among different energy levels, light with certain frequencies is emitted or absorbed. This allows atoms and molecules to be analyzed with the help of the absorbed light’s spectrum. With the laser’s coherent and intense light, the measurement phenomenon can occur. In the 1960s, Arthur Schawlow made use of this to eliminate the Doppler effect, allowing him to determine energy levels with great precision.

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#15 Jokes » Carrot Jokes - IV » 2024-03-27 18:15:38

Jai Ganesh
Replies: 0

Q: Why did the Ukrainian turn his carrot around?
A: He wanted to start the orange revolution!
* * *
Q: What did the rabbit say to the carrot?
A: It's been nice gnawing you.
* * *
Q: What's a vegetable's favourite casino game?
A: Baccarrot!
* * *
Q: What does the Carrot priest say at church?
A: "Lettuce Pray".
* * *
Q: What's orange and never shuts up?
A: A carrot reading the bible!
* * *

#16 Dark Discussions at Cafe Infinity » Chair Quotes - I » 2024-03-27 18:03:52

Jai Ganesh
Replies: 0

Chair Quotes - I

1. Worrying is like a rocking chair, it gives you something to do, but it gets you nowhere. - Glenn Turner

2. If it's the right chair, it doesn't take too long to get comfortable in it. - Robert De Niro

3. The discontented man finds no easy chair. - Benjamin Franklin

4. A table, a chair, a bowl of fruit and a violin; what else does a man need to be happy? - Albert Einstein

5. When I was in junior high school, the teachers voted me the student most likely to end up in the electric chair. - Sylvester Stallone

6. It is totally different making films in the East than in the West. In the East, I make my own Jackie Chan films, and it's like my family. Sometimes I pick up the camera because I choreograph all the fighting scenes, even when I'm not fighting. I don't have my own chair. I just sit on the set with everybody. - Jackie Chan

7. I have always thought it a great privilege to have as my colleague in the Palit Chair of Chemistry such a distinguished pioneer in scientific research and education in Bengal as Sir Prafulla Ray. It has been invariably my experience that I could count on his cooperation and sympathy in every matter concerning my scientific work. - C. V. Raman

8. In 1979, just after I became governor, I asked Hillary to chair a rural health committee to help expand health care to isolated farm and mountain areas. They recommended to do that partly by deploying trained nurse practitioners in places with no doctors to provide primary care they were trained to provide. - William J. Clinton

9. When I received my first paycheck from my now known day job, I spent it on a period Craftsman chair and a Frank Lloyd Wright-wannabe lamp. With my second paycheck, I bought a stereo. - Brad Pitt

10. If you really want to torture me, sit me in a room strapped to a chair and put Mariah Carey's records on. - Cameron Diaz

11. This is a very superficial job. I sit in a chair for two hours and get hair and makeup done and talk about myself in interviews. That's a very vain thing to do. And I do get caught up in it sometimes. - Selena Gomez

12. When I hear something that comes from me that makes me fall down off my chair, it's not often. - Celine Dion.

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#19 Re: Jai Ganesh's Puzzles » Doc, Doc! » 2024-03-27 16:23:25

Hi,

#2537. What does the medical term Skin grafting mean?

#20 Re: Jai Ganesh's Puzzles » General Quiz » 2024-03-27 16:06:00

Hi,

#9729. What does the term in Chemistry Surfactants mean?

#9730. What does the term in Chemistry Substitution reaction mean?

#21 Re: Jai Ganesh's Puzzles » English language puzzles » 2024-03-27 15:34:31

Hi,

#5713. What does the verb (used with object) condone mean?

#5714. What does the noun confectionary mean?

#23 This is Cool » Blue Green Algae » 2024-03-27 00:38:20

Jai Ganesh
Replies: 0

Blue Green Algae

Gist

Cyanobacteria, formerly known as blue-green algae, are photosynthetic microscopic organisms that are technically bacteria. They were originally called blue-green algae because dense growths often turn the water green, blue-green or brownish-green. These algae are found in all lakes and are a natural part of the lake ecosystem. Unfortunately, high nutrient concentrations can promote a population explosion of these organisms and result in algal blooms, especially during warm weather.

Summary

Blue-green algae are any of a large, heterogeneous group of prokaryotic, principally photosynthetic organisms. Cyanobacteria resemble the eukaryotic algae in many ways, including morphological characteristics and ecological niches, and were at one time treated as algae, hence the common name of blue-green algae. Algae have since been reclassified as protists, and the prokaryotic nature of the blue-green algae has caused them to be classified with bacteria in the prokaryotic kingdom Monera.

Like all other prokaryotes, cyanobacteria lack a membrane-bound nucleus, mitochondria, Golgi apparatus, chloroplasts, and endoplasmic reticulum. All of the functions carried out in eukaryotes by these membrane-bound organelles are carried out in prokaryotes by the bacterial cell membrane. Some cyanobacteria, especially planktonic forms, have gas vesicles that contribute to their buoyancy. Chemical, genetic, and physiological characteristics are used to further classify the group within the kingdom. Cyanobacteria may be unicellular or filamentous. Many have sheaths to bind other cells or filaments into colonies.

Cyanobacteria contain only one form of chlorophyll, chlorophyll a, a green pigment. In addition, they contain various yellowish carotenoids, the blue pigment phycobilin, and, in some species, the red pigment phycoerythrin. The combination of phycobilin and chlorophyll produces the characteristic blue-green colour from which these organisms derive their popular name. Because of the other pigments, however, many species are actually green, brown, yellow, black, or red.

Most cyanobacteria do not grow in the absence of light (i.e., they are obligate phototrophs); however, some can grow in the dark if there is a sufficient supply of glucose to act as a carbon and energy source.

In addition to being photosynthetic, many species of cyanobacteria can also “fix” atmospheric nitrogen—that is, they can transform the gaseous nitrogen of the air into compounds that can be used by living cells. Particularly efficient nitrogen fixers are found among the filamentous species that have specialized cells called heterocysts. The heterocysts are thick-walled cell inclusions that are impermeable to oxygen; they provide the anaerobic (oxygen-free) environment necessary for the operation of the nitrogen-fixing enzymes. In Southeast Asia, nitrogen-fixing cyanobacteria often are grown in rice paddies, thereby eliminating the need to apply nitrogen fertilizers.

Cyanobacteria range in size from 0.5 to 60 micrometres, which represents the largest prokaryotic organism. They are widely distributed and are extremely common in fresh water, where they occur as members of both the plankton and the benthos. They are also abundantly represented in such habitats as tide pools, coral reefs, and tidal spray zones; a few species also occur in the ocean plankton. On land, cyanobacteria are common in soil down to a depth of 1 m (39 inches) or more; they also grow on moist surfaces of rocks and trees, where they appear in the form of cushions or layers.

Cyanobacteria flourish in some of the most inhospitable environments known. They can be found in hot springs, in cold lakes underneath 5 m of ice pack, and on the lower surfaces of many rocks in deserts. Cyanobacteria are frequently among the first colonizers of bare rock and soil. Various types of associations take place between cyanobacteria and other organisms. Certain species, for example, grow in a mutualistic relationship with fungi, forming composite organisms known as lichens.

Cyanobacteria reproduce asexually, either by means of binary or multiple fission in unicellular and colonial forms or by fragmentation and spore formation in filamentous species. Under favourable conditions, cyanobacteria can reproduce at explosive rates, forming dense concentrations called blooms. Cyanobacteria blooms can colour a body of water. For example, many ponds take on an opaque shade of green as a result of overgrowths of cyanobacteria, and blooms of phycoerythrin-rich species cause the occasional red colour of the Red Sea. Cyanobacteria blooms are especially common in waters that have been polluted by nitrogen wastes; in such cases, the overgrowths of cyanobacteria can consume so much of the water’s dissolved oxygen that fish and other aquatic organisms perish.

Details

Cyanobacteria, also called Cyanobacteriota or Cyanophyta, are a phylum of autotrophic gram-negative bacteria that can obtain biological energy via photosynthesis. The name 'cyanobacteria' refers to their color (from Ancient Greek 'blue'), which similarly forms the basis of cyanobacteria's common name, blue-green algae, although they are not scientifically classified as algae. They appear to have originated in a freshwater or terrestrial environment.

Cyanobacteria are probably the most numerous taxon to have ever existed on Earth and the first organisms known to have produced oxygen. By producing and releasing oxygen as a byproduct of photosynthesis, cyanobacteria are thought to have converted the early oxygen-poor, reducing atmosphere into an oxidizing one, causing the Great Oxidation Event and the "rusting of the Earth", which dramatically changed the composition of life forms on Earth.

Cyanobacteria use photosynthetic pigments, such as various forms of chlorophyll, carotenoids, phycobilins to convert the energy in sunlight to chemical energy. Unlike heterotrophic prokaryotes, cyanobacteria have internal membranes. These are flattened sacs called thylakoids where photosynthesis is performed. Phototrophic eukaryotes such as green plants perform photosynthesis in plastids that are thought to have their ancestry in cyanobacteria, acquired long ago via a process called endosymbiosis. These endosymbiotic cyanobacteria in eukaryotes then evolved and differentiated into specialized organelles such as chloroplasts, chromoplasts, etioplasts, and leucoplasts, collectively known as plastids.

Sericytochromatia, the proposed name of the paraphyletic and most basal group, is the ancestor of both the non-photosynthetic group Melainabacteria and the photosynthetic cyanobacteria, also called Oxyphotobacteria.

The cyanobacteria Synechocystis and Cyanothece are important model organisms with potential applications in biotechnology for bioethanol production, food colorings, as a source of human and animal food, dietary supplements and raw materials. Cyanobacteria produce a range of toxins known as cyanotoxins that can cause harmful health effects in humans and animals.

Overview

* Cyanobacteria are found almost everywhere. Sea spray containing marine microorganisms, including cyanobacteria, can be swept high into the atmosphere where they become aeroplankton, and can travel the globe before falling back to earth.
* Cyanobacteria are a very large and diverse phylum of photosynthetic prokaryotes. They are defined by their unique combination of pigments and their ability to perform oxygenic photosynthesis. They often live in colonial aggregates that can take on a multitude of forms. Of particular interest are the filamentous species, which often dominate the upper layers of microbial mats found in extreme environments such as hot springs, hypersaline water, deserts and the polar regions, but are also widely distributed in more mundane environments as well. They are evolutionarily optimized for environmental conditions of low oxygen. Some species are nitrogen-fixing and live in a wide variety of moist soils and water, either freely or in a symbiotic relationship with plants or lichen-forming fungi (as in the lichen genus Peltigera).

Cyanobacteria are globally widespread photosynthetic prokaryotes and are major contributors to global biogeochemical cycles. They are the only oxygenic photosynthetic prokaryotes, and prosper in diverse and extreme habitats. They are among the oldest organisms on Earth with fossil records dating back at least 2.1 billion years. Since then, cyanobacteria have been essential players in the Earth's ecosystems. Planktonic cyanobacteria are a fundamental component of marine food webs and are major contributors to global carbon and nitrogen fluxes. Some cyanobacteria form harmful algal blooms causing the disruption of aquatic ecosystem services and intoxication of wildlife and humans by the production of powerful toxins (cyanotoxins) such as microcystins, saxitoxin, and cylindrospermopsin. Nowadays, cyanobacterial blooms pose a serious threat to aquatic environments and public health, and are increasing in frequency and magnitude globally.

Cyanobacteria are ubiquitous in marine environments and play important roles as primary producers. They are part of the marine phytoplankton, which currently contributes almost half of the Earth's total primary production. About 25% of the global marine primary production is contributed by cyanobacteria.

Within the cyanobacteria, only a few lineages colonized the open ocean: Crocosphaera and relatives, cyanobacterium UCYN-A, Trichodesmium, as well as Prochlorococcus and Synechococcus. From these lineages, nitrogen-fixing cyanobacteria are particularly important because they exert a control on primary productivity and the export of organic carbon to the deep ocean, by converting nitrogen gas into ammonium, which is later used to make amino acids and proteins. Marine picocyanobacteria (Prochlorococcus and Synechococcus) numerically dominate most phytoplankton assemblages in modern oceans, contributing importantly to primary productivity. While some planktonic cyanobacteria are unicellular and free living cells (e.g., Crocosphaera, Prochlorococcus, Synechococcus); others have established symbiotic relationships with haptophyte algae, such as coccolithophores. Amongst the filamentous forms, Trichodesmium are free-living and form aggregates. However, filamentous heterocyst-forming cyanobacteria (e.g., Richelia, Calothrix) are found in association with diatoms such as Hemiaulus, Rhizosolenia and Chaetoceros.

Marine cyanobacteria include the smallest known photosynthetic organisms. The smallest of all, Prochlorococcus, is just 0.5 to 0.8 micrometres across. In terms of numbers of individuals, Prochlorococcus is possibly the most plentiful genus on Earth: a single millilitre of surface seawater can contain 100,000 cells of this genus or more. Worldwide there are estimated to be several octillion ({10}^{27}, a billion billion billion) individuals. Prochlorococcus is ubiquitous between latitudes 40°N and 40°S, and dominates in the oligotrophic (nutrient-poor) regions of the oceans. The bacterium accounts for about 20% of the oxygen in the Earth's atmosphere.

Morphology

Cyanobacteria are variable in morphology, ranging from unicellular and filamentous to colonial forms. Filamentous forms exhibit functional cell differentiation such as heterocysts (for nitrogen fixation), akinetes (resting stage cells), and hormogonia (reproductive, motile filaments). These, together with the intercellular connections they possess, are considered the first signs of multicellularity.

Many cyanobacteria form motile filaments of cells, called hormogonia, that travel away from the main biomass to bud and form new colonies elsewhere. The cells in a hormogonium are often thinner than in the vegetative state, and the cells on either end of the motile chain may be tapered. To break away from the parent colony, a hormogonium often must tear apart a weaker cell in a filament, called a necridium.

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#24 Re: This is Cool » Miscellany » 2024-03-27 00:02:51

2105) Anatomy

Gist

The study of the structure of a plant or animal. Human anatomy includes the cells, tissues, and organs that make up the body and how they are organized in the body.

Summary

Anatomy is the study of the structure of living things – animal, human, plant – from microscopic cells and molecules to whole organisms as large as whales.

Anatomy Is Everywhere

* Anthropologists study cultures around the world.
* Paleontologists use cutting-edge technology to discover the ancient world.
* Archeologists uncover our history one artifact at a time.
* Veterinarians help humans care for pets and farm animals.
* Zoologists ensure captive animals – from backyard critters to endangered species – receive optimal care.
* Medical students learn anatomy before becoming nurses, doctors, and dentists.
* Inventors create exoskeletons to give people mobility.
* Biomedical engineers create better pacemakers and prosthetics.
* Physical therapists find remedies for their patients’ challenges.

Who Are Anatomists?

An anatomist broadly describes someone who studies, researches, or teaches in the anatomical sciences, including the study of extinct species, such as dinosaurs and Neanderthals. They help us understand how things are formed and constructed, which has enormous impact. However, not everyone who studies, applies, or researches anatomy calls themselves ‘anatomists.’

WHAT ANATOMISTS DO

Anatomists work with students and researchers to better understand humans and animals, in order to teach the next generation of doctors, nurses, physical therapists, dentists, and veterinarians. Their research into cell and molecular anatomy means that conditions such as cleft palate, congenital heart defects, neurological disorders, and cancer biology are better understood – and can be treated.

WHERE ANATOMISTS WORK

Anatomists work in universities, research institutions, and private industry. They teach anatomy in medical, dental, and veterinary schools, as well as at large undergraduate universities. They run their own research labs at organizations and universities, and they work together in teams of scientists, postdoctoral researchers, and students to uncover discoveries that lead to better understanding of our biology.

Details

Anatomy (from Ancient Greek anatomḗ) 'dissection') is the branch of biology concerned with the study of the structure of organisms and their parts. Anatomy is a branch of natural science that deals with the structural organization of living things. It is an old science, having its beginnings in prehistoric times. Anatomy is inherently tied to developmental biology, embryology, comparative anatomy, evolutionary biology, and phylogeny, as these are the processes by which anatomy is generated, both over immediate and long-term timescales. Anatomy and physiology, which study the structure and function of organisms and their parts respectively, make a natural pair of related disciplines, and are often studied together. Human anatomy is one of the essential basic sciences that are applied in medicine, and is often studied alongside physiology.

Anatomy is a complex and dynamic field that is constantly evolving as new discoveries are made. In recent years, there has been a significant increase in the use of advanced imaging techniques, such as MRI and CT scans, which allow for more detailed and accurate visualizations of the body's structures.

The discipline of anatomy is divided into macroscopic and microscopic parts. Macroscopic anatomy, or gross anatomy, is the examination of an animal's body parts using unaided eyesight. Gross anatomy also includes the branch of superficial anatomy. Microscopic anatomy involves the use of optical instruments in the study of the tissues of various structures, known as histology, and also in the study of cells.

The history of anatomy is characterized by a progressive understanding of the functions of the organs and structures of the human body. Methods have also improved dramatically, advancing from the examination of animals by dissection of carcasses and cadavers (corpses) to 20th-century medical imaging techniques, including X-ray, ultrasound, and magnetic resonance imaging.

Etymology and definition

Derived from the Greek "dissection" (from "I cut up, cut open" from "up", and "I cut"), anatomy is the scientific study of the structure of organisms including their systems, organs and tissues. It includes the appearance and position of the various parts, the materials from which they are composed, and their relationships with other parts. Anatomy is quite distinct from physiology and biochemistry, which deal respectively with the functions of those parts and the chemical processes involved. For example, an anatomist is concerned with the shape, size, position, structure, blood supply and innervation of an organ such as the liver; while a physiologist is interested in the production of bile, the role of the liver in nutrition and the regulation of bodily functions.

The discipline of anatomy can be subdivided into a number of branches, including gross or macroscopic anatomy and microscopic anatomy. Gross anatomy is the study of structures large enough to be seen with the naked eye, and also includes superficial anatomy or surface anatomy, the study by sight of the external body features. Microscopic anatomy is the study of structures on a microscopic scale, along with histology (the study of tissues), and embryology (the study of an organism in its immature condition). Regional anatomy is the study of the interrelationships of all of the structures in a specific body region, such as the abdomen. In contrast, systemic anatomy is the study of the structures that make up a discrete body system—that is, a group of structures that work together to perform a unique body function, such as the digestive system.

Anatomy can be studied using both invasive and non-invasive methods with the goal of obtaining information about the structure and organization of organs and systems. Methods used include dissection, in which a body is opened and its organs studied, and endoscopy, in which a video camera-equipped instrument is inserted through a small incision in the body wall and used to explore the internal organs and other structures. Angiography using X-rays or magnetic resonance angiography are methods to visualize blood vessels.

The term "anatomy" is commonly taken to refer to human anatomy. However, substantially similar structures and tissues are found throughout the rest of the animal kingdom, and the term also includes the anatomy of other animals. The term zootomy is also sometimes used to specifically refer to non-human animals. The structure and tissues of plants are of a dissimilar nature and they are studied in plant anatomy.

Animal tissues

The kingdom Animalia contains multicellular organisms that are heterotrophic and motile (although some have secondarily adopted a sessile lifestyle). Most animals have bodies differentiated into separate tissues and these animals are also known as eumetazoans. They have an internal digestive chamber, with one or two openings; the gametes are produced in multicellular gender organs, and the zygotes include a blastula stage in their embryonic development. Metazoans do not include the sponges, which have undifferentiated cells.

Unlike plant cells, animal cells have neither a cell wall nor chloroplasts. Vacuoles, when present, are more in number and much smaller than those in the plant cell. The body tissues are composed of numerous types of cells, including those found in muscles, nerves and skin. Each typically has a cell membrane formed of phospholipids, cytoplasm and a nucleus. All of the different cells of an animal are derived from the embryonic germ layers. Those simpler invertebrates which are formed from two germ layers of ectoderm and endoderm are called diploblastic and the more developed animals whose structures and organs are formed from three germ layers are called triploblastic. All of a triploblastic animal's tissues and organs are derived from the three germ layers of the embryo, the ectoderm, mesoderm and endoderm.

Animal tissues can be grouped into four basic types: connective, epithelial, muscle and nervous tissue.

Connective tissue

Connective tissues are fibrous and made up of cells scattered among inorganic material called the extracellular matrix. Connective tissue gives shape to organs and holds them in place. The main types are loose connective tissue, adipose tissue, fibrous connective tissue, cartilage and bone. The extracellular matrix contains proteins, the chief and most abundant of which is collagen. Collagen plays a major part in organizing and maintaining tissues. The matrix can be modified to form a skeleton to support or protect the body. An exoskeleton is a thickened, rigid cuticle which is stiffened by mineralization, as in crustaceans or by the cross-linking of its proteins as in insects. An endoskeleton is internal and present in all developed animals, as well as in many of those less developed.[16]

Epithelium

Epithelial tissue is composed of closely packed cells, bound to each other by cell adhesion molecules, with little intercellular space. Epithelial cells can be squamous (flat), cuboidal or columnar and rest on a basal lamina, the upper layer of the basement membrane, the lower layer is the reticular lamina lying next to the connective tissue in the extracellular matrix secreted by the epithelial cells. There are many different types of epithelium, modified to suit a particular function. In the respiratory tract there is a type of ciliated epithelial lining; in the small intestine there are microvilli on the epithelial lining and in the large intestine there are intestinal villi. Skin consists of an outer layer of keratinized stratified squamous epithelium that covers the exterior of the vertebrate body. Keratinocytes make up to 95% of the cells in the skin. The epithelial cells on the external surface of the body typically secrete an extracellular matrix in the form of a cuticle. In simple animals this may just be a coat of glycoproteins. In more advanced animals, many glands are formed of epithelial cells.

Muscle tissue

Muscle cells (myocytes) form the active contractile tissue of the body. Muscle tissue functions to produce force and cause motion, either locomotion or movement within internal organs. Muscle is formed of contractile filaments and is separated into three main types; smooth muscle, skeletal muscle and cardiac muscle. Smooth muscle has no striations when examined microscopically. It contracts slowly but maintains contractibility over a wide range of stretch lengths. It is found in such organs as sea anemone tentacles and the body wall of sea cucumbers. Skeletal muscle contracts rapidly but has a limited range of extension. It is found in the movement of appendages and jaws. Obliquely striated muscle is intermediate between the other two. The filaments are staggered and this is the type of muscle found in earthworms that can extend slowly or make rapid contractions. In higher animals striated muscles occur in bundles attached to bone to provide movement and are often arranged in antagonistic sets. Smooth muscle is found in the walls of the uterus, bladder, intestines, stomach, oesophagus, respiratory airways, and blood vessels. Cardiac muscle is found only in the heart, allowing it to contract and pump blood round the body.

Nervous tissue

Nervous tissue is composed of many nerve cells known as neurons which transmit information. In some slow-moving radially symmetrical marine animals such as ctenophores and cnidarians (including sea anemones and jellyfish), the nerves form a nerve net, but in most animals they are organized longitudinally into bundles. In simple animals, receptor neurons in the body wall cause a local reaction to a stimulus. In more complex animals, specialized receptor cells such as chemoreceptors and photoreceptors are found in groups and send messages along neural networks to other parts of the organism. Neurons can be connected together in ganglia. In higher animals, specialized receptors are the basis of sense organs and there is a central nervous system (brain and spinal cord) and a peripheral nervous system. The latter consists of sensory nerves that transmit information from sense organs and motor nerves that influence target organs. The peripheral nervous system is divided into the somatic nervous system which conveys sensation and controls voluntary muscle, and the autonomic nervous system which involuntarily controls smooth muscle, certain glands and internal organs, including the stomach.

Vertebrate anatomy

All vertebrates have a similar basic body plan and at some point in their lives, mostly in the embryonic stage, share the major chordate characteristics: a stiffening rod, the notochord; a dorsal hollow tube of nervous material, the neural tube; pharyngeal arches; and a tail posterior to the math. The spinal cord is protected by the vertebral column and is above the notochord, and the gastrointestinal tract is below it. Nervous tissue is derived from the ectoderm, connective tissues are derived from mesoderm, and gut is derived from the endoderm. At the posterior end is a tail which continues the spinal cord and vertebrae but not the gut. The mouth is found at the anterior end of the animal, and the math at the base of the tail. The defining characteristic of a vertebrate is the vertebral column, formed in the development of the segmented series of vertebrae. In most vertebrates the notochord becomes the nucleus pulposus of the intervertebral discs. However, a few vertebrates, such as the sturgeon and the coelacanth, retain the notochord into adulthood. Jawed vertebrates are typified by paired appendages, fins or legs, which may be secondarily lost. The limbs of vertebrates are considered to be homologous because the same underlying skeletal structure was inherited from their last common ancestor. This is one of the arguments put forward by Charles Darwin to support his theory of evolution.

Mammal anatomy

Mammals are a diverse class of animals, mostly terrestrial but some are aquatic and others have evolved flapping or gliding flight. They mostly have four limbs, but some aquatic mammals have no limbs or limbs modified into fins, and the forelimbs of bats are modified into wings. The legs of most mammals are situated below the trunk, which is held well clear of the ground. The bones of mammals are well ossified and their teeth, which are usually differentiated, are coated in a layer of prismatic enamel. The teeth are shed once (milk teeth) during the animal's lifetime or not at all, as is the case in cetaceans. Mammals have three bones in the middle ear and a cochlea in the inner ear. They are clothed in hair and their skin contains glands which secrete sweat. Some of these glands are specialized as mammary glands, producing milk to feed the young. Mammals breathe with lungs and have a muscular diaphragm separating the thorax from the abdomen which helps them draw air into the lungs. The mammalian heart has four chambers, and oxygenated and deoxygenated blood are kept entirely separate. Nitrogenous waste is excreted primarily as urea.

Mammals are amniotes, and most are viviparous, giving birth to live young. Exceptions to this are the egg-laying monotremes, the platypus and the echidnas of Australia. Most other mammals have a placenta through which the developing foetus obtains nourishment, but in marsupials, the foetal stage is very short and the immature young is born and finds its way to its mother's pouch where it latches on to a nipple and completes its development.

Human anatomy

In humans, dexterous hand movements and increased brain size are likely to have evolved simultaneously.
Humans have the overall body plan of a mammal. Humans have a head, neck, trunk (which includes the thorax and abdomen), two arms and hands, and two legs and feet.

Generally, students of certain biological sciences, paramedics, prosthetists and orthotists, physiotherapists, occupational therapists, nurses, podiatrists, and medical students learn gross anatomy and microscopic anatomy from anatomical models, skeletons, textbooks, diagrams, photographs, lectures and tutorials and in addition, medical students generally also learn gross anatomy through practical experience of dissection and inspection of cadavers. The study of microscopic anatomy (or histology) can be aided by practical experience examining histological preparations (or slides) under a microscope.

Human anatomy, physiology and biochemistry are complementary basic medical sciences, which are generally taught to medical students in their first year at medical school. Human anatomy can be taught regionally or systemically; that is, respectively, studying anatomy by bodily regions such as the head and chest, or studying by specific systems, such as the nervous or respiratory systems. The major anatomy textbook, Gray's Anatomy, has been reorganized from a systems format to a regional format, in line with modern teaching methods. A thorough working knowledge of anatomy is required by physicians, especially surgeons and doctors working in some diagnostic specialties, such as histopathology and radiology.

Academic anatomists are usually employed by universities, medical schools or teaching hospitals. They are often involved in teaching anatomy, and research into certain systems, organs, tissues or cells.

Additional Information

Anatomy is a field in the biological sciences concerned with the identification and description of the body structures of living things. Gross anatomy involves the study of major body structures by dissection and observation and in its narrowest sense is concerned only with the human body. “Gross anatomy” customarily refers to the study of those body structures large enough to be examined without the help of magnifying devices, while microscopic anatomy is concerned with the study of structural units small enough to be seen only with a light microscope. Dissection is basic to all anatomical research. The earliest record of its use was made by the Greeks, and Theophrastus called dissection “anatomy,” from ana temnein, meaning “to cut up.”

Comparative anatomy, the other major subdivision of the field, compares similar body structures in different species of animals in order to understand the adaptive changes they have undergone in the course of evolution.

Gross anatomy

This ancient discipline reached its culmination between 1500 and 1850, by which time its subject matter was firmly established. None of the world’s oldest civilizations dissected a human body, which most people regarded with superstitious awe and associated with the spirit of the departed soul. Beliefs in life after death and a disquieting uncertainty concerning the possibility of bodily resurrection further inhibited systematic study. Nevertheless, knowledge of the body was acquired by treating wounds, aiding in childbirth, and setting broken limbs. The field remained speculative rather than descriptive, though, until the achievements of the Alexandrian medical school and its foremost figure, Herophilus (flourished 300 BCE), who dissected human cadavers and thus gave anatomy a considerable factual basis for the first time. Herophilus made many important discoveries and was followed by his younger contemporary Erasistratus, who is sometimes regarded as the founder of physiology. In the 2nd century CE, Greek physician Galen assembled and arranged all the discoveries of the Greek anatomists, including with them his own concepts of physiology and his discoveries in experimental medicine. The many books Galen wrote became the unquestioned authority for anatomy and medicine in Europe because they were the only ancient Greek anatomical texts that survived the Dark Ages in the form of Arabic (and then Latin) translations.

Owing to church prohibitions against dissection, European medicine in the Middle Ages relied upon Galen’s mixture of fact and fancy rather than on direct observation for its anatomical knowledge, though some dissections were authorized for teaching purposes. In the early 16th century, the artist Leonardo da Vinci undertook his own dissections, and his beautiful and accurate anatomical drawings cleared the way for Flemish physician Andreas Vesalius to “restore” the science of anatomy with his monumental De humani corporis fabrica libri septem (1543; “The Seven Books on the Structure of the Human Body”), which was the first comprehensive and illustrated textbook of anatomy. As a professor at the University of Padua, Vesalius encouraged younger scientists to accept traditional anatomy only after verifying it themselves, and this more critical and questioning attitude broke Galen’s authority and placed anatomy on a firm foundation of observed fact and demonstration.

From Vesalius’s exact descriptions of the skeleton, muscles, blood vessels, nervous system, and digestive tract, his successors in Padua progressed to studies of the digestive glands and the urinary and reproductive systems. Hieronymus Fabricius, Gabriello Fallopius, and Bartolomeo Eustachio were among the most important Italian anatomists, and their detailed studies led to fundamental progress in the related field of physiology. William Harvey’s discovery of the circulation of the blood, for instance, was based partly on Fabricius’s detailed descriptions of the venous valves.

Microscopic anatomy

The new application of magnifying glasses and compound microscopes to biological studies in the second half of the 17th century was the most important factor in the subsequent development of anatomical research. Primitive early microscopes enabled Marcello Malpighi to discover the system of tiny capillaries connecting the arterial and venous networks, Robert Hooke to first observe the small compartments in plants that he called “cells,” and Antonie van Leeuwenhoek to observe muscle fibres and spermatozoa. Thenceforth attention gradually shifted from the identification and understanding of bodily structures visible to the naked eye to those of microscopic size.

The use of the microscope in discovering minute, previously unknown features was pursued on a more systematic basis in the 18th century, but progress tended to be slow until technical improvements in the compound microscope itself, beginning in the 1830s with the gradual development of achromatic lenses, greatly increased that instrument’s resolving power. These technical advances enabled Matthias Jakob Schleiden and Theodor Schwann to recognize in 1838–39 that the cell is the fundamental unit of organization in all living things. The need for thinner, more transparent tissue specimens for study under the light microscope stimulated the development of improved methods of dissection, notably machines called microtomes that can slice specimens into extremely thin sections. In order to better distinguish the detail in these sections, synthetic dyes were used to stain tissues with different colours. Thin sections and staining had become standard tools for microscopic anatomists by the late 19th century. The field of cytology, which is the study of cells, and that of histology, which is the study of tissue organization from the cellular level up, both arose in the 19th century with the data and techniques of microscopic anatomy as their basis.

In the 20th century anatomists tended to scrutinize tinier and tinier units of structure as new technologies enabled them to discern details far beyond the limits of resolution of light microscopes. These advances were made possible by the electron microscope, which stimulated an enormous amount of research on subcellular structures beginning in the 1950s and became the prime tool of anatomical research. About the same time, the use of X-ray diffraction for studying the structures of many types of molecules present in living things gave rise to the new subspecialty of molecular anatomy.

Anatomical nomenclature

Scientific names for the parts and structures of the human body are usually in Latin; for example, the name musculus biceps brachii denotes the biceps muscle of the upper arm. Some such names were bequeathed to Europe by ancient Greek and Roman writers, and many more were coined by European anatomists from the 16th century on. Expanding medical knowledge meant the discovery of many bodily structures and tissues, but there was no uniformity of nomenclature, and thousands of new names were added as medical writers followed their own fancies, usually expressing them in a Latin form.

By the end of the 19th century the confusion caused by the enormous number of names had become intolerable. Medical dictionaries sometimes listed as many as 20 synonyms for one name, and more than 50,000 names were in use throughout Europe. In 1887 the German Anatomical Society undertook the task of standardizing the nomenclature, and, with the help of other national anatomical societies, a complete list of anatomical terms and names was approved in 1895 that reduced the 50,000 names to 5,528. This list, the Basle Nomina Anatomica, had to be subsequently expanded, and in 1955 the Sixth International Anatomical Congress at Paris approved a major revision of it known as the Paris Nomina Anatomica (or simply Nomina Anatomica). In 1998 this work was supplanted by the Terminologia Anatomica, which recognizes about 7,500 terms describing macroscopic structures of human anatomy and is considered to be the international standard on human anatomical nomenclature. The Terminologia Anatomica, produced by the International Federation of Associations of Anatomists and the Federative Committee on Anatomical Terminology (later known as the Federative International Programme on Anatomical Terminologies), was made available online in 2011.

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