National Institutes of Health
The National Institutes of Health is the primary agency of the United States government responsible for biomedical and public health research. It was founded in the late 1870s and is now part of the United States Department of Health and Human Services; the majority of NIH facilities are located in Maryland. The NIH conducts its own scientific research through its Intramural Research Program and provides major biomedical research funding to non-NIH research facilities through its Extramural Research Program; as of 2013, the IRP had 1,200 principal investigators and more than 4,000 postdoctoral fellows in basic and clinical research, being the largest biomedical research institution in the world, while, as of 2003, the extramural arm provided 28% of biomedical research funding spent annually in the U. S. or about US$26.4 billion. The NIH comprises 27 separate institutes and centers of different biomedical disciplines and is responsible for many scientific accomplishments, including the discovery of fluoride to prevent tooth decay, the use of lithium to manage bipolar disorder, the creation of vaccines against hepatitis, Haemophilus influenzae, human papillomavirus.
NIH's roots extend back to the Marine Hospital Service in the late 1790s that provided medical relief to sick and disabled men in the U. S. Navy. By 1870, a network of marine hospitals had developed and was placed under the charge of a medical officer within the Bureau of the Treasury Department. In the late 1870s, Congress allocated funds to investigate the causes of epidemics like cholera and yellow fever, it created the National Board of Health, making medical research an official government initiative. In 1887, a laboratory for the study of bacteria, the Hygienic Laboratory, was established at the Marine Hospital in New York. In the early 1900s, Congress began appropriating funds for the Marine Hospital Service. By 1922, this organization changed its name to Public Health Services and established a Special Cancer Investigations laboratory at Harvard Medical School; this marked the beginning of a partnership with universities. In 1930, the Hygienic Laboratory was re-designated as the National Institute of Health by the Ransdell Act, was given $750,000 to construct two NIH buildings.
Over the next few decades, Congress would increase funding tremendously to the NIH, various institutes and centers within the NIH were created for specific research programs. In 1944, the Public Health Service Act was approved, the National Cancer Institute became a division of NIH. In 1948, the name changed from National Institute of Health to National Institutes of Health. In the 1960s, virologist and cancer researcher Chester M. Southam injected HeLa cancer cells into patients at the Jewish Chronic Disease Hospital; when three doctors resigned after refusing to inject patients without their consent, the experiment gained considerable media attention. The NIH was a major source of funding for Southam's research and had required all research involving human subjects to obtain their consent prior to any experimentation. Upon investigating all of their grantee institutions, the NIH discovered that the majority of them did not protect the rights of human subjects. From on, the NIH has required all grantee institutions to approve any research proposals involving human experimentation with review boards.
In 1967, the Division of Regional Medical Programs was created to administer grants for research for heart disease and strokes. That same year, the NIH director lobbied the White House for increased federal funding in order to increase research and the speed with which health benefits could be brought to the people. An advisory committee was formed to oversee further development of the NIH and its research programs. By 1971 cancer research was in full force and President Nixon signed the National Cancer Act, initiating a National Cancer Program, President's Cancer Panel, National Cancer Advisory Board, 15 new research and demonstration centers. Funding for the NIH has been a source of contention in Congress, serving as a proxy for the political currents of the time. In 1992, the NIH encompassed nearly 1 percent of the federal government's operating budget and controlled more than 50 percent of all funding for health research, 85 percent of all funding for health studies in universities. While government funding for research in other disciplines has been increasing at a rate similar to inflation since the 1970s, research funding for the NIH nearly tripled through the 1990s and early 2000s, but has remained stagnant since then.
By the 1990s, the NIH committee focus had shifted to DNA research, launched the Human Genome Project. The NIH Office of the Director is the central office responsible for setting policy for NIH, for planning and coordinating the programs and activities of all NIH components; the NIH Director plays an active role in shaping outlook. The Director is responsible for providing leadership to the Institutes and Centers by identifying needs and opportunities in efforts involving multiple Institutes. Within this Office is the Division of Program Coordination and Strategic Initiatives with 12 divisions including: Office of AIDS Research Office of Research on Women's Health Office of Disease Prevention Sexual and Gender Minority Research Office Tribal Heath Research Office Office of Program Evaluation and PerformancePrevious directors: Joseph J. Kinyoun, served August 1887 – April 30, 1899 Milton J. Rosenau, served May 1, 1899 – September 30, 1909 John F. Anderson, served October 1, 1909 – November 19, 1915 George W. McCoy, served November 20, 1915 – January 31, 1937 Lewis R. Thompson, served February 1, 1937 – January 31, 1942 R
Vacuum is space devoid of matter. The word stems from the Latin adjective vacuus for "vacant" or "void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressure. Physicists discuss ideal test results that would occur in a perfect vacuum, which they sometimes call "vacuum" or free space, use the term partial vacuum to refer to an actual imperfect vacuum as one might have in a laboratory or in space. In engineering and applied physics on the other hand, vacuum refers to any space in which the pressure is lower than atmospheric pressure; the Latin term in vacuo is used to describe an object, surrounded by a vacuum. The quality of a partial vacuum refers to how it approaches a perfect vacuum. Other things equal, lower gas pressure means higher-quality vacuum. For example, a typical vacuum cleaner produces enough suction to reduce air pressure by around 20%. Much higher-quality vacuums are possible. Ultra-high vacuum chambers, common in chemistry and engineering, operate below one trillionth of atmospheric pressure, can reach around 100 particles/cm3.
Outer space is an higher-quality vacuum, with the equivalent of just a few hydrogen atoms per cubic meter on average in intergalactic space. According to modern understanding if all matter could be removed from a volume, it would still not be "empty" due to vacuum fluctuations, dark energy, transiting gamma rays, cosmic rays and other phenomena in quantum physics. In the study of electromagnetism in the 19th century, vacuum was thought to be filled with a medium called aether. In modern particle physics, the vacuum state is considered the ground state of a field. Vacuum has been a frequent topic of philosophical debate since ancient Greek times, but was not studied empirically until the 17th century. Evangelista Torricelli produced the first laboratory vacuum in 1643, other experimental techniques were developed as a result of his theories of atmospheric pressure. A torricellian vacuum is created by filling a tall glass container closed at one end with mercury, inverting it in a bowl to contain the mercury.
Vacuum became a valuable industrial tool in the 20th century with the introduction of incandescent light bulbs and vacuum tubes, a wide array of vacuum technology has since become available. The recent development of human spaceflight has raised interest in the impact of vacuum on human health, on life forms in general; the word vacuum comes from Latin, meaning'an empty space, void', noun use of neuter of vacuus, meaning "empty", related to vacare, meaning "be empty". Vacuum is one of the few words in the English language that contains two consecutive letters'u'. There has been much dispute over whether such a thing as a vacuum can exist. Ancient Greek philosophers debated the existence of a vacuum, or void, in the context of atomism, which posited void and atom as the fundamental explanatory elements of physics. Following Plato the abstract concept of a featureless void faced considerable skepticism: it could not be apprehended by the senses, it could not, provide additional explanatory power beyond the physical volume with which it was commensurate and, by definition, it was quite nothing at all, which cannot rightly be said to exist.
Aristotle believed that no void could occur because the denser surrounding material continuum would fill any incipient rarity that might give rise to a void. In his Physics, book IV, Aristotle offered numerous arguments against the void: for example, that motion through a medium which offered no impediment could continue ad infinitum, there being no reason that something would come to rest anywhere in particular. Although Lucretius argued for the existence of vacuum in the first century BC and Hero of Alexandria tried unsuccessfully to create an artificial vacuum in the first century AD, it was European scholars such as Roger Bacon, Blasius of Parma and Walter Burley in the 13th and 14th century who focused considerable attention on these issues. Following Stoic physics in this instance, scholars from the 14th century onward departed from the Aristotelian perspective in favor of a supernatural void beyond the confines of the cosmos itself, a conclusion acknowledged by the 17th century, which helped to segregate natural and theological concerns.
Two thousand years after Plato, René Descartes proposed a geometrically based alternative theory of atomism, without the problematic nothing–everything dichotomy of void and atom. Although Descartes agreed with the contemporary position, that a vacuum does not occur in nature, the success of his namesake coordinate system and more implicitly, the spatial–corporeal component of his metaphysics would come to define the philosophically modern notion of empty space as a quantified extension of volume. By the ancient definition however, directional information and magnitude were conceptually distinct. In the medieval Middle Eastern world, the physicist and Islamic scholar, Al-Farabi, conducted a small experiment concerning the existence of vacuum, in which he investigated handheld plungers in water, he concluded that air's volume can expand to fill available space, he suggested that the concept of perfect vacuum was incoherent. However, according to Nader El-Bizri, the physicist Ibn al-Haytham and the Mu'tazili theologians disagreed with Aristotle and Al-Farabi, they supported the existence of a void.
Using geometry, Ibn al-Haytham mathematically demonstrated that place is the imagined three-dimensional void between the inner surfaces of a containing body. According to Ahmad Dallal, Abū Rayhān al-Bīrūnī states that "there is no observable
Ludwig Eduard Boltzmann was an Austrian physicist and philosopher whose greatest achievement was in the development of statistical mechanics, which explains and predicts how the properties of atoms determine the physical properties of matter. Boltzmann coined the word ergodic. Boltzmann was born in the capital of the Austrian Empire, his father, Ludwig Georg Boltzmann, was a revenue official. His grandfather, who had moved to Vienna from Berlin, was a clock manufacturer, Boltzmann's mother, Katharina Pauernfeind, was from Salzburg, he received his primary education from a private tutor at the home of his parents. Boltzmann attended high school in Upper Austria; when Boltzmann was 15, his father died. Boltzmann studied physics at the University of Vienna, starting in 1863. Among his teachers were Josef Loschmidt, Joseph Stefan, Andreas von Ettingshausen and Jozef Petzval. Boltzmann received his PhD degree in 1866 working under the supervision of Stefan. In 1867 he became a Privatdozent. After obtaining his doctorate degree, Boltzmann worked two more years as Stefan's assistant.
It was Stefan. In 1869 at age 25, thanks to a letter of recommendation written by Stefan, he was appointed full Professor of Mathematical Physics at the University of Graz in the province of Styria. In 1869 he spent several months in Heidelberg working with Robert Bunsen and Leo Königsberger and in 1871 with Gustav Kirchhoff and Hermann von Helmholtz in Berlin. In 1873 Boltzmann joined the University of Vienna as Professor of Mathematics and there he stayed until 1876. In 1872, long before women were admitted to Austrian universities, he met Henriette von Aigentler, an aspiring teacher of mathematics and physics in Graz, she was refused permission to audit lectures unofficially. Boltzmann advised her to appeal. On July 17, 1876 Ludwig Boltzmann married Henriette. Boltzmann went back to Graz to take up the chair of Experimental Physics. Among his students in Graz were Svante Arrhenius and Walther Nernst, he spent 14 happy years in Graz and it was there that he developed his statistical concept of nature.
Boltzmann was appointed to the Chair of Theoretical Physics at the University of Munich in Bavaria, Germany in 1890. In 1894, Boltzmann succeeded his teacher Joseph Stefan as Professor of Theoretical Physics at the University of Vienna. Boltzmann spent a great deal of effort in his final years defending his theories, he did not get along with some of his colleagues in Vienna Ernst Mach, who became a professor of philosophy and history of sciences in 1895. That same year Georg Helm and Wilhelm Ostwald presented their position on energetics at a meeting in Lübeck, they saw energy, not matter, as the chief component of the universe. Boltzmann's position carried the day among other physicists who supported his atomic theories in the debate. In 1900, Boltzmann went on the invitation of Wilhelm Ostwald. Ostwald offered Boltzmann the professorial chair in physics, which became vacant when Gustav Heinrich Wiedemann died. After Mach retired due to bad health, Boltzmann returned to Vienna in 1902. In 1903, together with Gustav von Escherich and Emil Müller, founded the Austrian Mathematical Society.
His students included Paul Ehrenfest and Lise Meitner. In Vienna, Boltzmann taught physics and lectured on philosophy. Boltzmann's lectures on natural philosophy were popular and received considerable attention, his first lecture was an enormous success. Though the largest lecture hall had been chosen for it, the people stood all the way down the staircase; because of the great successes of Boltzmann's philosophical lectures, the Emperor invited him for a reception at the Palace. In 1906, Boltzmann's deteriorating mental condition forced him to resign his position, he committed suicide on September 5, 1906, by hanging himself while on vacation with his wife and daughter in Duino, near Trieste. He is buried in the Viennese Zentralfriedhof, his tombstone bears the inscription of Boltzmann's entropy formula: S = k ⋅ log W Boltzmann's kinetic theory of gases seemed to presuppose the reality of atoms and molecules, but all German philosophers and many scientists like Ernst Mach and the physical chemist Wilhelm Ostwald disbelieved their existence.
During the 1890s Boltzmann attempted to formulate a compromise position which would allow both atomists and anti-atomists to do physics without arguing over atoms. His solution was to use Hertz's theory that atoms were Bilder, that is, pictures. Atomists could think the pictures were the real atoms while the anti-atomists could think of the pictures as representing a useful but unreal model, but this did not satisfy either group. Furthermore and many defenders of "pure thermodynamics" were trying hard to refute the kinetic theory of gases and statistical mechanics because of Boltzmann's assumptions about atoms and molecules and statistical interpretation of the second law of thermodynamics. Around the turn of the century, Boltzmann's science was being threatened by another philosophical objection; some physicists, including Mach's student, Gustav Jaumann, interpreted Hertz to mean that all electromagnetic behavior is continuous, as if there were no atoms and molecules, as if all physical behavior were ultimate
The gravitational force, or more g-force, is a measurement of the type of acceleration that causes a perception of weight. Despite the name, it is incorrect to consider g-force a fundamental force, as "g-force" is a type of acceleration that can be measured with an accelerometer. Since g-force accelerations indirectly produce weight, any g-force can be described as a "weight per unit mass"; when the g-force acceleration is produced by the surface of one object being pushed by the surface of another object, the reaction force to this push produces an equal and opposite weight for every unit of an object's mass. The types of forces involved are transmitted through objects by interior mechanical stresses; the g-force acceleration is the cause of an object's acceleration in relation to free fall. The g-force acceleration experienced by an object is due to the vector sum of all non-gravitational and non-electromagnetic forces acting on an object's freedom to move. In practice, as noted, these are surface-contact forces between objects.
Such forces cause stresses and strains on objects, since they must be transmitted from an object surface. Because of these strains, large g-forces may be destructive. Gravitation acting alone does not produce a g-force though g-forces are expressed in multiples of the acceleration of a standard gravity. Thus, the standard gravitational acceleration at the Earth's surface produces g-force only indirectly, as a result of resistance to it by mechanical forces; these mechanical forces produce the g-force acceleration on a mass. For example, the 1 g force on an object sitting on the Earth's surface is caused by mechanical force exerted in the upward direction by the ground, keeping the object from going into free fall; the upward contact force from the ground ensures that an object at rest on the Earth's surface is accelerating relative to the free-fall condition.. Stress inside the object is ensured from the fact that the ground contact forces are transmitted only from the point of contact with the ground.
Objects allowed to free-fall in an inertial trajectory under the influence of gravitation only, feel no g-force acceleration, a condition known as zero-g. This is demonstrated by the "zero-g" conditions inside an elevator falling toward the Earth's center, or conditions inside a spacecraft in Earth orbit; these are examples of coordinate acceleration without a sensation of weight. The experience of no g-force, however it is produced, is synonymous with weightlessness. In the absence of gravitational fields, or in directions at right angles to them and coordinate accelerations are the same, any coordinate acceleration must be produced by a corresponding g-force acceleration. An example here is a rocket in free space, in which simple changes in velocity are produced by the engines and produce g-forces on the rocket and passengers.. The unit of measure of acceleration in the International System of Units is m/s2. However, to distinguish acceleration relative to free fall from simple acceleration, the unit g is used.
One g is the acceleration due to gravity at the Earth's surface and is the standard gravity, defined as 9.80665 metres per second squared, or equivalently 9.80665 newtons of force per kilogram of mass. Note that the unit definition does not vary with location—the g-force when standing on the moon is about 0.181 g. The unit g is not one of the SI units. "g" should not be confused with "G", the standard symbol for the gravitational constant. This notation is used in aviation in aerobatic or combat military aviation, to describe the increased forces that must be overcome by pilots in order to remain conscious and not G-LOC. Measurement of g-force is achieved using an accelerometer. In certain cases, g-forces may be measured using suitably calibrated scales. Specific force is another name, used for g-force; the term g-force is technically incorrect. While acceleration is a vector quantity, g-force accelerations are expressed as a scalar, with positive g-forces pointing downward, negative g-forces pointing upward.
Thus, a g-force is a vector of acceleration. It is an acceleration that must be produced by a mechanical force, cannot be produced by simple gravitation. Objects acted upon only by gravitation experience no g-force, are weightless. G-forces, when multiplied by a mass upon which they act, are associated with a certain type of mechanical force in the correct sense of the term force, this force produces compressive stress and tensile stress; such forces result in the operational sensation of weight, but the equation carries a sign change due to the definition of positive weight in the direction downward, so the direction of weight-force is opposite to the direction of g-force acceleration: Weight = mass × −g-forceThe reason for the minus sign is that the actual force on an object produced by a g-force is in the opposite direction to the sign of the g-force, since in physics, weight is not the force that produces the acceleration, but rather the equal-and-opposite reaction force to it. If the direction upward is taken as positive positive g-force produces a force/w
A macromolecule is a large molecule, such as protein created by the polymerization of smaller subunits. They are composed of thousands of atoms or more; the most common macromolecules in biochemistry are large non-polymeric molecules. Synthetic macromolecules include common plastics and synthetic fibers as well as experimental materials such as carbon nanotubes; the term macromolecule was coined by Nobel laureate Hermann Staudinger in the 1920s, although his first relevant publication on this field only mentions high molecular compounds. At that time the phrase polymer, as introduced by Berzelius in 1833, had a different meaning from that of today: it was another form of isomerism for example with benzene and acetylene and had little to do with size. Usage of the term to describe large molecules varies among the disciplines. For example, while biology refers to macromolecules as the four large molecules comprising living things, in chemistry, the term may refer to aggregates of two or more molecules held together by intermolecular forces rather than covalent bonds but which do not dissociate.
According to the standard IUPAC definition, the term macromolecule as used in polymer science refers only to a single molecule. For example, a single polymeric molecule is appropriately described as a "macromolecule" or "polymer molecule" rather than a "polymer," which suggests a substance composed of macromolecules; because of their size, macromolecules are not conveniently described in terms of stoichiometry alone. The structure of simple macromolecules, such as homopolymers, may be described in terms of the individual monomer subunit and total molecular mass. Complicated biomacromolecules, on the other hand, require multi-faceted structural description such as the hierarchy of structures used to describe proteins. In British English, the word "macromolecule" tends to be called "high polymer". Macromolecules have unusual physical properties that do not occur for smaller molecules. Another common macromolecular property that does not characterize smaller molecules is their relative insolubility in water and similar solvents, instead forming colloids.
Many require particular ions to dissolve in water. Many proteins will denature if the solute concentration of their solution is too high or too low. High concentrations of macromolecules in a solution can alter the rates and equilibrium constants of the reactions of other macromolecules, through an effect known as macromolecular crowding; this comes from macromolecules excluding other molecules from a large part of the volume of the solution, thereby increasing the effective concentrations of these molecules. All living organisms are dependent on three essential biopolymers for their biological functions: DNA, RNA and proteins; each of these molecules is required for life since each plays a distinct, indispensable role in the cell. The simple summary is that DNA makes RNA, RNA makes proteins. DNA, RNA, proteins all consist of a repeating structure of related building blocks. In general, they are all unbranched polymers, so can be represented in the form of a string. Indeed, they can be viewed as a string of beads, with each bead representing a single nucleotide or amino acid monomer linked together through covalent chemical bonds into a long chain.
In most cases, the monomers within the chain have a strong propensity to interact with other amino acids or nucleotides. In DNA and RNA, this can take the form of Watson-Crick base pairs, although many more complicated interactions can and do occur; because of the double-stranded nature of DNA all of the nucleotides take the form of Watson-Crick base pairs between nucleotides on the two complementary strands of the double-helix. In contrast, both RNA and proteins are single-stranded. Therefore, they are not constrained by the regular geometry of the DNA double helix, so fold into complex three-dimensional shapes dependent on their sequence; these different shapes are responsible for many of the common properties of RNA and proteins, including the formation of specific binding pockets, the ability to catalyse biochemical reactions. DNA is an information storage macromolecule that encodes the complete set of instructions that are required to assemble and reproduce every living organism. DNA and RNA are both capable of encoding genetic information, because there are biochemical mechanisms which read the information coded within a DNA or RNA sequence and use it to generate a specified protein.
On the other hand, the sequence information of a protein molecule is not used by cells to functionally encode genetic information. DNA has three primary attributes that allow it to be far better than RNA at encoding genetic information. First, it is double-stranded, so that there are a minimum of two copies of the information encoding each gene in every cell. Second, DNA has a much greater stability against breakdown than does RNA, an attribute associated with the absence of the 2'-hydroxyl group within every nucleotide of DNA. Third sophisticated DNA surveillance and repair systems are present which monitor damage to the DNA and repair the sequence when necessary. Analogous systems have not evolved for repairing damaged RNA molecules. Chromosomes can contain many billions of atoms, arranged in a specific chemical structure. Proteins are functional macromolecules responsible for catalysing the biochemical reactions that sustain life. Proteins carry out all functions of an organism, for example p
Temperature is a physical quantity expressing hot and cold. It is measured with a thermometer calibrated in one or more temperature scales; the most used scales are the Celsius scale, Fahrenheit scale, Kelvin scale. The kelvin is the unit of temperature in the International System of Units, in which temperature is one of the seven fundamental base quantities; the Kelvin scale is used in science and technology. Theoretically, the coldest a system can be is when its temperature is absolute zero, at which point the thermal motion in matter would be zero. However, an actual physical system or object can never attain a temperature of absolute zero. Absolute zero is denoted as 0 K on the Kelvin scale, −273.15 °C on the Celsius scale, −459.67 °F on the Fahrenheit scale. For an ideal gas, temperature is proportional to the average kinetic energy of the random microscopic motions of the constituent microscopic particles. Temperature is important in all fields of natural science, including physics, Earth science and biology, as well as most aspects of daily life.
Many physical processes are affected by temperature, such as physical properties of materials including the phase, solubility, vapor pressure, electrical conductivity rate and extent to which chemical reactions occur the amount and properties of thermal radiation emitted from the surface of an object speed of sound is a function of the square root of the absolute temperature Temperature scales differ in two ways: the point chosen as zero degrees, the magnitudes of incremental units or degrees on the scale. The Celsius scale is used for common temperature measurements in most of the world, it is an empirical scale, developed by a historical progress, which led to its zero point 0 °C being defined by the freezing point of water, additional degrees defined so that 100 °C was the boiling point of water, both at sea-level atmospheric pressure. Because of the 100-degree interval, it was called a centigrade scale. Since the standardization of the kelvin in the International System of Units, it has subsequently been redefined in terms of the equivalent fixing points on the Kelvin scale, so that a temperature increment of one degree Celsius is the same as an increment of one kelvin, though they differ by an additive offset of 273.15.
The United States uses the Fahrenheit scale, on which water freezes at 32 °F and boils at 212 °F at sea-level atmospheric pressure. Many scientific measurements use the Kelvin temperature scale, named in honor of the Scots-Irish physicist who first defined it, it is a absolute temperature scale. Its zero point, 0 K, is defined to coincide with the coldest physically-possible temperature, its degrees are defined through thermodynamics. The temperature of absolute zero occurs at 0 K = −273.15 °C, the freezing point of water at sea-level atmospheric pressure occurs at 273.15 K = 0 °C. The International System of Units defines a scale and unit for the kelvin or thermodynamic temperature by using the reliably reproducible temperature of the triple point of water as a second reference point; the triple point is a singular state with its own unique and invariant temperature and pressure, along with, for a fixed mass of water in a vessel of fixed volume, an autonomically and stably self-determining partition into three mutually contacting phases, vapour and solid, dynamically depending only on the total internal energy of the mass of water.
For historical reasons, the triple point temperature of water is fixed at 273.16 units of the measurement increment. There is a variety of kinds of temperature scale, it may be convenient to classify them theoretically based. Empirical temperature scales are older, while theoretically based scales arose in the middle of the nineteenth century. Empirically based temperature scales rely directly on measurements of simple physical properties of materials. For example, the length of a column of mercury, confined in a glass-walled capillary tube, is dependent on temperature, is the basis of the useful mercury-in-glass thermometer; such scales are valid only within convenient ranges of temperature. For example, above the boiling point of mercury, a mercury-in-glass thermometer is impracticable. Most materials expand with temperature increase, but some materials, such as water, contract with temperature increase over some specific range, they are hardly useful as thermometric materials. A material is of no use as a thermometer near one of its phase-change temperatures, for example its boiling-point.
In spite of these restrictions, most used practical thermometers are of the empirically based kind. It was used for calorimetry, which contributed to the discovery of thermodynamics. Empirical thermometry has serious drawbacks when judged as a basis for theoretical physics. Empirically based thermometers, beyond their base as simple direct measurements of ordinary physical properties of thermometric materials, can be re-calibrated, by use of theoretical physical reasoning, this can extend their range of adequacy. Theoretically-based temperature scales are based directly on theoretical arguments those of thermodynamics, kinetic theory and quantum mechanics, they rely on theoretical properties of idealized materials. They are more or less comparable with feasible physical devices and materials. Theoretically based temperature scales are used to provide calibrating standards for practi
A catastrophic failure is a sudden and total failure from which recovery is impossible. Catastrophic failures lead to cascading systems failure; the term is most used for structural failures, but has been extended to many other disciplines in which total and irrecoverable loss occurs. Such failures are investigated using the methods of forensic engineering, which aims to isolate the cause or causes of failure. For example, catastrophic failure can be observed in steam turbine rotor failure, which can occur due to peak stress on the rotor. In firearms, catastrophic failure refers to a rupture or disintegration of the barrel or receiver of the gun when firing it; some possible causes of this are an out-of-battery gun, an inadequate headspace, the use of incorrect ammunition, the use of ammunition with an incorrect propellant charge, a or obstructed barrel, or weakened metal in the barrel or receiver. A failure of this type, known colloquially as a "kaboom", or "kB" failure, can pose a threat not only to the user but many bystanders.
In chemical engineering, thermal runaway can cause catastrophic failure. Examples of catastrophic failure of engineered structures include: The Tay Rail Bridge disaster of 1879, where the center half mile of the bridge was destroyed while a train was crossing in a storm; the bridge was badly designed and its replacement was built as a separate structure upstream of the old. The failure of the South Fork Dam in 1889 released 4.8 billion US gallons of water and killed over 2,200 people. The collapse of the St. Francis Dam in 1928 released 12.4 billion US gallons of water, resulting in a death toll of nearly 600 people. The collapse of the first Tacoma Narrows Bridge of 1940, where the main deck of the road bridge was destroyed by dynamic oscillations in a 40 miles per hour wind; the De Havilland Comet disasters of 1954 determined to be structural failures due to metal fatigue that had not been anticipated at the corners of square windows used by the Comet 1. The 62 Banqiao Dams failure event in China in 1975, due to Typhoon Nina.
86,000 people died from flooding and another 145,000 died from subsequent diseases, total of 231,000 deaths. The Hyatt Regency walkway collapse of 1981, where a suspended walkway in a hotel lobby in Kansas City, collapsed killing over 100 people on and below the structure; the Space Shuttle Challenger disaster of 1986, in which an O-ring of a rocket booster failed, causing the external fuel tank to break up and making the shuttle veer off course, subjecting it to aerodynamic forces beyond design tolerances. The nuclear reactor at the Chernobyl power plant, which exploded in 1986 causing the release of a substantial amount of radioactive materials; the collapse of the Warsaw radio mast of 1991, which had up to that point held the title of world's tallest structure. The Sampoong Department Store collapse of 1995, which happened due to structural weaknesses, killed 502 people and injured 937; the terrorist attacks and subsequent fire at the World Trade Center on September 11, 2001 weakened the floor joists to the point of catastrophic failure.
The Space Shuttle Columbia disaster of 2003, where damage to a wing during launch resulted in total loss upon re-entry. The collapse of the multi-span I-35W Mississippi River bridge on August 1, 2007. List of bridge disasters Seismic performance Structural collapse Structural failure Resonance disaster Risks to civilization and planet Earth Dragon King Theory Feynman, Richard. What Do You Care What Other People Think?. W. W. Norton. ISBN 0-553-17334-0. Lewis, Peter R.. Beautiful Railway Bridge of the Silvery Tay: Reinvestigating the Tay Bridge Disaster of 1879. Tempus. ISBN 0-7524-3160-9