Soon: Universe's Coldest Refrigerator

The Coldest Spot in the Known Universe By Dr. Tony Phillips, NASA

Jan. 30, 2014: Everyone knows that space is cold. In the vast gulf between stars and galaxies, the temperature of gaseous matter routinely drops to 3 degrees K, or 454 degrees below zero Fahrenheit.

It’s about to get even colder.

NASA researchers are planning to create the coldest spot in the known universe inside the International Space Station.

"We’re going to study matter at temperatures far colder than are found naturally," says Rob Thompson of JPL. He’s the Project Scientist for NASA’s Cold Atom Lab, an atomic ‘refrigerator’ slated for launch to the ISS in 2016. "We aim to push effective temperatures down to 100 pico-Kelvin."

100 pico-Kelvin is just one ten billionth of a degree above absolute zero, where all the thermal activity of atoms theoretically stops. At such low temperatures, ordinary concepts of solid, liquid and gas are no longer relevant. Atoms interacting just above the threshold of zero energy create new forms of matter that are essentially ... quantum.

Quantum mechanics is a branch of physics that describes the bizarre rules of light and matter on atomic scales. In that realm, matter can be in two places at once; objects behave as both particles and waves; and nothing is certain: the quantum world runs on probability.

It is into this strange realm that researchers using the Cold Atom Lab will plunge.

"We’ll begin," says Thompson, "by studying Bose-Einstein Condensates."

In 1995, researchers discovered that if you took a few million rubidium atoms and cooled them near absolute zero, they would merge into a single wave of matter. The trick worked with sodium, too. In 2001, Eric Cornell of the National Institute of Standards & Technology and Carl Wieman of University of Colorado shared the Nobel Prize with Wolfgang Ketterle of MIT for their independent discovery of these condensates, which Albert Einstein and Satyendra Bose had predicted in the early 20^th century.

If you create two BECs and put them together, they don't mix like an ordinary gas. Instead, they can "interfere" like waves: thin, parallel layers of matter are separated by thin layers of empty space. An atom in one BEC can add itself to an atom in another BEC and produce – no atom at all.

"The Cold Atom Lab will allow us to study these objects at perhaps the lowest temperatures ever," says Thompson.

The lab is also a place where researchers can mix super-cool atomic gasses and see what happens.

"Mixtures of different types of atoms can float together almost completely free of perturbations," explains Thompson, "allowing us to make sensitive measurements of very weak interactions. This could lead to the discovery of interesting and novel quantum phenomena."

The space station is the best place to do this research. Microgravity allows researchers to cool materials to temperatures much colder than are possible on the ground.

Thompson explains why:

"It’s a basic principle of thermodynamics that when a gas expands, it cools. Most of us have hands-on experience with this. If you spray a can of aerosols, the can gets cold."

Quantum gases are cooled in much the same way. In place of an aerosol can, however, we have a ‘magnetic trap.’

"On the ISS, these traps can be made very weak because they do not have to support the atoms against the pull of gravity. Weak traps allow gases to expand and cool to lower temperatures than are possible on the ground."

No one knows where this fundamental research will lead. Even the "practical" applications listed by Thompson—quantum sensors, matter wave interferometers, and atomic lasers, just to name a few—sound like science fiction. "We’re entering the unknown," he says.

Researchers like Thompson think of the Cold Atom Lab as a doorway into the quantum world. Could the door swing both ways? If the temperature drops low enough, "we’ll be able to assemble atomic wave packets as wide as a human hair--that is, big enough for the human eye to see." A creature of quantum physics will have entered the macroscopic world.

And then the real excitement begins.

For more information about the Cold Atom Lab, visit coldatomlab.jpl.nasa.gov
  http://science.nasa.gov/science-news/science-at-nasa/2014/30jan_coldspot/

Why We Have Four Limbs

How we got four limbs? Because we
have a belly: New model for the
evolution of paired appendages

 

All of us backboned animals – at least the ones who also have jaws – have four fins or limbs, one pair in front and one pair behind. These have been modified dramatically in the course of evolution, into a marvelous variety of fins, legs, arms, flippers, and wings. But how did our earliest ancestors settle into such a consistent arrangement of two pairs of appendages? – Because we have a belly. Researchers in the Theoretical Biology Department at the University of Vienna and the Konrad Lorenz Institute for Evolution and Cognition Research have presented a new model for approaching this question in the current issue of the journal "Evolution & Development".

As with any long-standing question in evolutionary biology, numerous ideas have been proposed to explain different aspects of the origin of paired appendages in vertebrates known as gnathostomes, which includes all living and extinct animals having both a backbone and jaw. "This group does not include the living lampreys and hagfishes, which have neither jaws nor paired fins, although they do have median fins along the midline of the back and tail", says Brian Metscher from the Department of Theoretical Biology. Any explanation must account for not only the fossil evidence, but also for the subtleties of the early development of fins and limbs.

Pairs of appendages situated at front and back ends of the body cavity
"We have drawn together a large body of molecular embryology work, as well as results from paleontology and classical morphology to work out an overall explanation of how the vertebrate embryo forms pairs of appendages along each side, and only two pairs situated at front and back ends of the body cavity," said Laura Nuño de la Rosa, lead author of the study and post-doctoral fellow at the Konrad Lorenz Institute in Altenberg, Austria.

Embryo segregates into three main layers of tissue
The proposed model incorporates results from much previous research, including information on gene expression and on interactions among the different tissues that make up an early vertebrate embryo. In its earliest stages of development, an embryo segregates into three main layers of tissue: an outer one (ectoderm) that will form the skin and nervous system, an inner layer (endoderm) that becomes the digestive tract, and an in-between layer (mesoderm) that eventually forms muscles, bones, and other organs. The early mesoderm splits into two layers that line the inside of the body cavity and the outside of the gut.

The new hypothesis proposes that fins or limbs begin to form only at the places where those two layers are sufficiently separated and interact favorably with the ectodermal tissues – namely at the two ends of the forming gut. In between, no fin/limb initiation takes place, because the two mesoderm layers maintain a narrower separation and, the authors propose, interact with the developing gut.

Behind the back end of the digestive tract (the anal opening), along the bottom of the tail, the two mesoderm layers come together as the body wall closes up, forming a single (median) fin. Along the length of the developing gut, the body wall cannot close completely, so the conditions for initiating fins or limbs occur to the left and right of the midline, allowing the development of paired instead of median fins. "You could say that the reason we have four limbs is because we have a belly," adds Laura Nuño de la Rosa.  

"The most important function of a model like this is to provide a coherent framework for formulating specific hypotheses, which can be tested with molecular and other laboratory methods," says Brian Metscher, Senior Scientist in the University of Vienna's Department of Theoretical Biology. This work is also a contribution to the ongoing discussion of the roles of changes to embryonic development in the evolution of new structures, or evolutionary novelties. Further, the focus of the hypothesis on global embryonic patterning and tissue interactions emphasizes the importance of accounting for factors other than genes (epigenetics) to understand development and evolution.

Publication in "Evolution & Development":
Laura Nuño de la Rosa, Gerd B. Müller, Brian D. Metscher: The Lateral Mesodermal Divide: An Epigenetic Model of the Origin of Paired Fins. Evolution & Development, January 2014, 38-48. DOI: 10.1111/ede.12061
Link:  onlinelibrary.wiley.com/doi/10.1111/ede.12061/full

http://medienportal.univie.ac.at/presse/aktuelle-pressemeldungen/detailansicht/artikel/wir-haben-vier-gliedmassen-weil-wir-einen-bauch-haben-kopie-1/

Singer/Activist Pete Seeger Dies

Peter "Pete" Seeger (May 3, 1919 – January 27, 2014) was an American folk singer. A fixture on nationwide radio in the 1940s, he also had a string of hit records during the early 1950s as a member of the Weavers, most notably their recording of Lead Belly's "Goodnight Irene", which topped the charts for 13 weeks in 1950. Members of the Weavers were blacklisted during the McCarthy Era. In the 1960s, he re-emerged on the public scene as a prominent singer of protest music in support of international disarmament, civil rights, counterculture and environmental causes.

A prolific songwriter, his best-known songs include "Where Have All the Flowers Gone?" (with Joe Hickerson), "If I Had a Hammer (The Hammer Song) " (with Lee Hays of the Weavers), and "Turn! Turn! Trun!" (lyrics adapted from Ecclesiastes), which have been recorded by many artists both in and outside the folk revival movement and are sung throughout the world. "Flowers" was a hit recording for th Kingston Trio (1962); Marlene Dietrich, who recorded it in English, German and French (1962); and Johnny Rivers (1965). "If I Had a Hammer" was a hit for Peter, Paul & Mary (1962) and Trini Lopez (1963), while the Byrds had a number one hit with "Turn! Turn! Turn!" in 1965.

Seeger was one of the folksingers most responsible for popularizing the spiritual "We Shall Overcome" (also recorded by Joan Baez and many other singer-activists) that became the acknowledged anthem of the 1960s American Civil Rights Movement, soon after folk singer and activist Guy Carawan introduced it at the founding meeting of the Student Nonviolent Coordinating Committee (SNCC) in 1960. In the PBS American Masters episode "Pete Seeger: The Power of Song", Seeger stated it was he who changed the lyric from the traditional "We will overcome" to the more singable "We shall overcome".

Seeger was very active in
The Young Communist League from 1936 to 1942
The Communist Party of the USA from 1942 to 1949
Vietnam War protests
The environmental movement
　

Pete Seeger and Bob Dylan

Pete Seeger was one of the earliest backers of Bob Dylan and was responsible for urging A&R man John Hammond to produce Dylan's first LP on Columbia, and for inviting him to perform at the Newport Folk Festival, of which Seeger was a board member. There was a widely repeated story that Seeger was so upset over the extremely loud amplified sound that Dylan, backed by members of the Butterfield Blues Band, brought into the 1965 Newport Folk Festival that he threatened to disconnect the equipment. There are multiple versions of what went on, some fanciful. What is certain is that tensions had been running high between Dylan's manager, Albert Grossman, and Festival Board members (who besides Seeger also included Theodore Bikel, Bruch Jackson, Alan Lomax, festival MC Peter Yarrow and George Wein) over the scheduling of performers and other matters. Two days earlier there had been a scuffle and brief exchange of blows between Grossman and Alan Lomax; and the Board, in an emergency session, had voted to ban Grossman from the grounds, but had backed off when George Wein pointed out that Grossman also managed highly popular draws Odetta and Peter, Paul and Mary. Seeger has been portrayed as a folk "purist" who was one of the main opponents to Dylan's "going electric," but when asked in 2001 about how he recalled his "objections" to the electric style, he said:
　

I couldn't understand the words. I wanted to hear the words. It was a great song, "Maggie’s Farm," and the sound was distorted. I ran over to the guy at the controls and shouted, "Fix the sound so you can hear the words." He hollered back, "This is the way they want it." I said "Damn it, if I had an axe, I'd cut the cable right now." But I was at fault. I was the MC, and I could have said to the part of the crowd that booed Bob, "you didn't boo Howlin’ Wolf yesterday. He was electric!" Though I still prefer to hear Dylan acoustic, some of his electric songs are absolutely great. Electric music is the vernacular of the second half of the twentieth century, to use my father's old term.

Death
Seeger died on January 27, 2014, at age 94. According to his grandson, Kitama Cahill-Jackson, Seeger died peacefully in his sleep around 9:30 p.m. at New York's Presbyterian Hospital, where he had been for six days. Family members were with him at the time of his death. Cahill-Jackson said Seeger was still as active as ever, out chopping wood ten days prior to his death.

Response and reaction to Seeger's death quickly poured in. Bruce Springsteen said of Seeger's passing, "I lost a great friend and a great hero last night, Pete Seeger", before performing "We Shall Overcome" while on tour in South Africa, President Barack Obama called Seeger "America's tuning fork" who believed in "the power of song" to bring social change. "Over the years, Pete used his voice and his hammer to strike blows for workers' rights and civil rights; world peace and environmental conservation, and he always invited us to sing along. For reminding us where we come from and showing us where we need to go, we will always be grateful to Pete Seeger. Michelle and I send our thoughts and prayers to Pete's family and all those who loved him."

http://en.wikipedia.org/wiki/Pete_Seeger

Bridgman and Operationalism

Percy Williams Bridgman (21 April 1882 – 20 August 1961) was an American physicist who won the 1946 Nobel Prizer in Physics for his work on the physics of high pressures. He also wrote extensively on the scientific method and on other aspects of the philosophy of science.

Biography
Bridgman entered Harvard University in 1900, and studied physics through to his PhD. From 1910 until his retirement, he taught at Harvard, becoming a full professor in 1919. In 1905, he began investigating the properties of matter under high pressure. A machinery malfunction led him to modify his pressure apparatus; the result was a new device enabling him to create pressures eventually exceeding 100,000 kgf/cm² (10 GPa; 100,000 atmospheres). This was a huge improvement over previous machinery, which could achieve pressures of only 3,000 kgf/cm² (0.3 GPa). This new apparatus led to an abundance of new findings, including a study of the compressibility, electric and thermal conductivity, tensile strength and viscosity of more than 100 different compounds. Bridgman is also known for his studies of electrical conduction in metals and properties of crystals. He developed the Bridgman seal and is the eponym for Bridgman’s thermodynamic equations.

Bridgman made many improvements to his high pressure apparatus over the years, and unsuccessfully attempted the synthesis of diamond many times.

His philosophy of science book The Logic of Modern Physics (1927) advocated operationalism and coined the term operational definition. He was also one of the 11 signatories to the Russell-Einstein Manifesto.

                                                        Percy Williams Bridgman

Death
Bridgman committed suicide by gunshot after living with metastic cancer for some time. His suicide note read in part, "It isn't decent for society to make a man do this thing himself. Probably this is the last day I will be able to do it myself." Bridgman's words have been quoted by many on both sides of the assisted suicide debate
　
Honors and Awards
Bridgman received Doctors, honoris causa from Stevens Institute (1934), Harvard (1939), Brooklyn Polytechnic (1941), Princeton (1950), Paris (1950), and Yale (1951). He received the Bingham Medal (1951) from the Society of Rheology, the Rumford Medal from the American Academy of Arts and Sciences, the Elliott Cresson Medal from the Franklin Institute, the Gold Medal from Bakhuys Roozeboom Fund (founder Hendrik Willem Bakhuis Roozeboom) (1933) from the Royal Netherlands Academy of Arts and Sciences, and the Comstock Prize (1933) of the National Academy of Sciences. He was a member of the American Physical Society and was its President in 1942
. He was also a member of the American Association for the Advancement of Science, the American Academy of Arts and Sciences, the American Philosophical Society, and the National Academy of Sciences. He was a Foreign Member of the Royal Society and Honorary Fellow of the Physical Society of London.
The Percy W. Bridgman House, in Massachusetts, is a U.S. National Historica Landmark designated in 1975.

http://en.wikipedia.org/wiki/Percy_Williams_Bridgman

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Operationalization
In research design, especially in psychology, social sciences, life sciences, and physics, operationalization is a process of defining the measurement of a phenomenon that is not directly measurable, though its existence is indicated by other phenomena. It is the process of defining a fuzzy concept so as to make the theoretical concept clearly distinguishable or measurable, and to understand it in terms of empirical observations. In a wider sense, it refers to the process of specifying the extension of a concept — describing what is and is not a part of that concept. For example, in medicine, the phenomenon of health might be operationalized by one or more indicators like body mass index or tobacco smoking. Thus, some phenomena are directly difficult to observe (i.e. they are latent), but their existence can be inferred by means of their observable effects.

The concept of operationalization was first presented by the British physicist N. R. Campbell in his 'Physics: The Elements' (Cambridge, 1920). This concept next spread to humanities and social sciences. It remains in use in physics.

History
Operationalization is used to specifically refer to the scientific practice of operationally defining, where even the most basic concepts are defined through the operations by which we measure them. This comes from the philosophy of science book The Logic of Modern Physics (1927), by Percu Williams Bridgman, whose methodological position is called operationalism.

Bridgman's theory was criticized because we measure "length" in various ways (e.g. it's impossible to use a measuring rod if we want to measure the distance to the Moon), "length" logically isn't one concept but many. Each concept is defined by the measuring operations used. Another example is the radius of a sphere, obtaining different values depending on the way it is measured (say, in metres and in millimeters). Bridgman said the concept is defined on the measurement. So the criticism is that we would end up with endless concepts, each defined by the things that measured the concept.

Bridgman notes that in the theory of relativity we see how a concept like "duration" can split into multiple different concepts. As part of the process of refining a physical theory, it may be found that what was one concept is, in fact, two or more distinct concepts. However, Bridgman proposes that if we only stick to operationally defined concepts, this will never happen.

Operationalization and Relativity
The practical 'operational definition' is generally understood as relating to the theoretical definitions that describe reality through the use of theory.

The importance of careful operationalization can perhaps be more clearly seen in the development of General Relativity. Einstein discovered that there were two operational definitions of "mass" being used by scientists: inertial, defined by applying a force and observing the acceleration, from Newton’s Second Law of Motion; and gravitational, defined by putting the object on a scale or balance. Previously, no one had paid any attention to the different operations used because they always produced the same results, but the key insight of Einstein was to posit the Principle of Equivalence that the two operations would always produce the same result because they were equivalent at a deep level, and work out the implications of that assumption, which is the General Theory of Relativity. Thus, a breakthrough in science was achieved by disregarding different operational definitions of scientific measurements and realizing that they both described a single theoretical concept. Einstein's disagreement with the operationalist approach was criticized by Bridgman as follows: "Einstein did not carry over into his general relativity theory the lessons and insights he himself has taught us in his special theory."

http://en.wikipedia.org/wiki/Operationalism

Strength of Materials

Mechanics of materials, also called strength of materials, is a subject which deals with the behavior of solid objects subject to stresses and strains. The complete theory began with the consideration of the behavior of one and two dimensional members of structures, whose states of stress can be approximated as two dimensional, and was then generalized to three dimensions to develop a more complete theory of the elastic and plastic behavior of materials. An important founding pioneer in mechanics of materials was Stephen Timoshenko.

The study of strength of materials often refers to various methods of calculating the stresses and strains in structural members, such as beams, columns, and shafts. The methods employed to predict the response of a structure under loading and its susceptibility to various failure modes takes into account the properties of the materials such as its yield strength, ultimate strength,Young’s Modulus, and Poisson’s ratio; in addition the mechanical element's macroscopic properties (geometric properties), such as it length, width, thickness, boundary constraints and abrupt changes in geometry such as holes are considered.

Definition
In materials science, the strength of a material is its ability to withstand an applied stress without failure. The field of strength of materials deals with forces and deformations that result from their acting on a material. A load applied to a mechanical member will induce internal forces within the member called stresses when those forces are expressed on a unit basis. The stresses acting on the material cause deformation of the material. Deformation of the material is called strain when those deformations too are placed on a unit basis. The applied loads may be axial (tensile or compressive), or shear. The stresses and strains that develop within a mechanical member must be calculated in order to assess the load capacity of that member. This requires a complete description of the geometry of the member, its constraints, the loads applied to the member and the properties of the material of which the member is composed. With a complete description of the loading and the geometry of the member, the state of stress and of state of strain at any point within the member can be calculated. Once the state of stress and strain within the member is known, the strength (load carrying capacity) of that member, its deformations (stiffness qualities), and its stability (ability to maintain its original configuration) can be calculated. The calculated stresses may then be compared to some measure of the strength of the member such as its material yield or ultimate strength. The calculated deflection of the member may be compared to a deflection criteria that is based on the member's use. The calculated buckling load of the member may be compared to the applied load. The calculated stiffness and mass distribution of the member may be used to calculate the member's dynamic response and then compared to the acoustic environment in which it will be used.

Material strength refers to the point on the engineering stress-strain curve (yield stress) beyond which the material experiences deformations that will not be completely reversed upon removal of the loading and as a result the member will have a permanent deflection. The ultimate strength refers to the point on the engineering stress-strain curve corresponding to the stress that produces fracture.

Failure Theories
There are four important failure theories: maximum shear stress theory, maximum normal stress theory, maximum strain energy theory, and maximum distortion energy theory. Out of these four theories of failure, the maximum normal stress theory is only applicable for brittle materials, and the remaining three theories are applicable for ductile materials. Of the latter three, the distortion energy theory provides most accurate results in majority of the stress conditions. The strain energy theory needs the value of Poisson’s ratio of the part material, which is often not readily available. The maximum shear stress theory is conservative. For simple unidirectional normal stresses all theories are equivalent, which means all theories will give the same result.

• Maximum Shear stress Theory- This theory postulates that failure will occur if the magnitude of the maximum shear stress in the part exceeds the shear strength of the material determined from uniaxial testing.
• Maximum normal stress theory - This theory postulates that failure will occur if the maximum normal stress in the part exceeds the ultimate tensile stress of the material as determined from uniaxial testing. This theory deals with brittle materials only. The maximum tensile stress should be less than or equal to ultimate tensile stress divided by factor of safety. The magnitude of the maximum compressive stress should be less than ultimate compressive stress divided by factor of safety.
• Maximum strain energy theory - This theory postulates that failure will occur when the strain energy per unit volume due to the applied stresses in a part equals the strain energy per unit volume at the yield point in uniaxial testing.
• Maximum distortion energy theory - This theory is also known as shear energy theory or von Mises hencky theory. This theory postulates that failure will occur when the distortion energy per unit volume due to the applied stresses in a part equals the distortion energy per unit volume at the yield point in uniaxial testing. The total elastic energy due to strain can be divided into two parts: one part causes change in volume, and the other part causes change in shape. Distortion energy is the amount of energy that is needed to change the shape.
• Fracture mechanics was established by Alan Arnold Griffith and George Rankine Irwin. This important theory is also known as numeric conversion of toughness of material in the case of crack existence.
• Fractology was proposed by Takeo Yokobori because each fracture law, including creep rupture criterion, must be combined nonlinially.

  http://en.wikipedia.org/wiki/Strength_of_materials

Ductility in Materials Science

In materials science, ductility is a solid material's ability to deform under tensile stress; this is often characterized by the material's ability to be stretched into a wire. Malleability, a similar property, is a material's ability to deform under compressive stress; this is often characterized by the material's ability to form a thin sheet by hammering or rolling. Both of these mechanical properties are aspects of plasticity, the extent to which a solid material can be plastically deformed without fracture. Also, these material properties are dependent on temperature and pressure (investigated by Percy Williams Bridgman as part of his Nobel Prize winning work on high pressures).

Ductility and malleability are not always coextensive – for instance, while gold has high ductility and malleability, lead has low ductility but high malleability. The word ductility is sometimes used to embrace both types of plasticity.

Materials Science
Ductility is especially important in metalworking, as materials that crack, break or shatter under stress cannot be manipulated using metal forming processes, such as hammering, rolling and drawing. Malleable materials can be formed using stamping or pressing, whereas brittle metals and plastiucs must be molded.

High degrees of ductility occur due to metallic bonds, which are found predominantly in metals and leads to the common perception that metals are ductile in general. In metallic bonds valence shell electrons are delocalized and shared between many atoms. The delocalized electrons allow metal atoms to slide past one another without being subjected to strong repulsive forces that would cause other materials to shatter.

Ductility can be quantified by the fracture strain, which is the engineering strain at which a test specimen fractures during a uniaxial tensile test. Another commonly used measure is the reduction of area at fracture . The ductility of steel varies depending on the alloying constituents. Increasing levels of carbon decreases ductility. Many plastics and amorphous solids, such as Play-Doh, are also malleable. The most ductile metal is platinum and the most malleable metal is gold.

Ductile-brittle transition temperature
The ductile–brittle transition temperature (DBTT), nil ductility temperature (NDT), or nil ductility transition temperature of a metal represents the point at which the fracture energy passes below a pre-determined point (for steels typically 40 J for a standard Charpy impact test). DBTT is important since, once a material is cooled below the DBTT, it has a much greater tendency to shatter on impact instead of bending or deforming. For example, zamak 3 exhibits good ductility at room temperature but shatters at sub-zero temperatures when impacted. DBTT is a very important consideration in materials selection when the material in question is subject to mechanical stresses. A similar phenomenon, the glass transition temperature, occurs with glasses and polymers, although the mechanism is different in these amorphous materials.

In some materials this transition is sharper than others. For example, the transition is generally sharper in materials with a body-centered cubic (BCC) lattice than those with a face-centefed cubic (FCC) lattice. DBTT can also be influenced by external factors such as neutron radiation, which leads to an increase in internal lattice defects and a corresponding decrease in ductility and increase in DBTT.

The most accurate method of measuring the BDT or DBT temperature of a material is by fracture testing. Typically, four point bend testing at a range of temperatures is performed on pre-cracked bars of polished material. For experiments conducted at higher temperatures, dislocation activity increases. At a certain temperature, dislocations shield the crack tip to such an extent the applied deformation rate is not sufficient for the stress intensity at the crack-tip to reach the critical value for fracture (K_iC). The temperature at which this occurs is the ductile–brittle transition temperature. If experiments are performed at a higher strain rate, more dislocation shielding is required to prevent brittle fracture and the transition temperature is raised.

http://en.wikipedia.org/wiki/Ductility

Annealing Metals and Materials

Annealing, in metallurgy and materials science, is a heat treatment that alters a material to increase its ductility and to make it more workable. It involves heating a material to above its critical temperature, maintaining a suitable temperature, and then cooling. Annealing can induce ductility, soften material, relieve internal stresses, refine the structure by making it homogeneous, and improve cold working properties.

In the cases of copper, steel, silver, and brass, this process is performed by heating the material (generally until glowing) for a while and then slowly letting it cool to room temperature in still air. Copper, silver and brass can be cooled slowly in air, or quickly by quenching in water, unlike ferrous metals, such as steel, which must be cooled slowly to anneal. In this fashion, the metal is softened and prepared for further work—such as shaping, stamping, or forming.

Annealing occurs by the diffusion of atoms within a solid material, so that the material progresses towards its equilibrium state. Heat increases the rate of diffusion by providing the energy needed to break bonds.
The movement of atoms has the effect of redistributing and destroying the dislocations in metals and (to a lesser extent) in ceramics. This alteration in dislocations allows metals to deform more easily, so increases their ductility.

The amount of process-initiating Gibbs free energy in a deformed metal is also reduced by the annealing process. In practice and industry, this reduction of Gibbs free energy is termed stress relief.

The relief of internal stresses is a thermodynamically spontaneous process; however, at room temperatures, it is a very slow process. The high temperatures at which annealing occurs serve to accelerate this process.

Stages
The three stages of the annealing process that proceed as the temperature of the material is increased are: recovery, recrystallization, and grain growth. The first stage is recovery, and it results in softening of the metal through removal of primarily linear defects called dislocations and the internal stresses they cause. Recovery occurs at the lower temperature stage of all annealing processes and before the appearance of new strain-free grains. The grain size and shape do not change. The second stage is recrystallization, where new strain-free grains nucleate and grow to replace those deformed by internal stresses. If annealing is allowed to continue once recrystallization has completed, then grain growth (the third stage) occurs. In grain growth, the microstructure starts to coarsen and may cause the metal to lose a substantial part of its original strength. This can however be regained with hardening.

Controlled Atmospheres
Typically, large ovens are used for the annealing process. The inside of the oven is large enough to place the workpiece in a position to receive maximum exposure to the circulating heated air. For high volume process annealing, gas fired conveyor furnaces are often used. For large workpieces or high quantity parts, car-bottom furnaces are used so workers can easily move the parts in and out. Once the annealing process is successfully completed, workpieces are sometimes left in the oven so the parts cool in a controllable way. While some workpieces are left in the oven to cool in a controlled fashion, other materials and alloys are removed from the oven. Once removed from the oven, the workpieces are often quickly cooled off in a process known as quench hardening. Typical methods of quench hardening materials involve media such as air, water, oil, or salt. Salt is used as a medium for quenching usually in the form of brine (salt water). Brine provides faster cooling rates than water. This is because when an object is quenched in water air bubbles form on the surface of the object reducing the surface area the water is in contact with. The salt in the brine reduces the formation of air bubbles on the objects surface, meaning there is a larger surface area of the object in contact with the water, providing faster cooling rates. Quench hardening is generally applicable to some ferrous alloys, but not copper alloys.

http://en.wikipedia.org/wiki/Annealing_(metallurgy)