Showing papers in "Physics Today in 1996"
625 citations
TL;DR: Early uses of probability arguments focused on distributions with well-defined means and variances, such as the Gaussian law of errors as discussed by the authors, in which the mean represented the most probable value from a series of repeated measurements of a fixed quantity, and the variance was related to the uncertainty of those measurements.
Abstract: Newtonian physics began with an attempt to make precise predictions about natural phenomena, predictions that could be accurately checked by observation and experiment. The goal was to understand nature as a deterministic, “clockwork” universe. The application of probability distributions to physics developed much more slowly. Early uses of probability arguments focused on distributions with well‐defined means and variances. The prime example was the Gaussian law of errors, in which the mean traditionally represented the most probable value from a series of repeated measurements of a fixed quantity, and the variance was related to the uncertainty of those measurements.
606 citations
TL;DR: A survey of recent developments in theoretical physics suggests that another revolution may be in progress, through which a new source of "fuzziness" may enter physics, and spacetime itself may be reinterpreted as an approximate, derived concept.
Abstract: Our basic ideas about physics went through several upheavals early this century. Quantum mechanics taught us that the classical notions of the position and velocity of a particle were only approximations of the truth. With general relativity, spacetime became a dynamical variable, curving in response to mass and energy. Contemporary developments in theoretical physics suggest that another revolution may be in progress, through which a new source of “fuzziness” may enter physics, and spacetime itself may be reinterpreted as an approximate, derived concept. (See figure 1.) In this article I survey some of these developments.
460 citations
TL;DR: In this article, the authors discuss advances in photochemistry and photochemistry advances in the field of photochemistry, and propose a method to improve photochemical advances in terms of photochemical properties.
Abstract: Advances in photochemistry , Advances in photochemistry , کتابخانه دیجیتال جندی شاپور اهواز
445 citations
TL;DR: In this paper, it was suggested that patterns created by the movement of grains of sand are in no small part responsible for the shape and feel of the natural world we live in.
Abstract: Victor Hugo suggested the possibility that patterns created by the movement of grains of sand are in no small part responsible for the shape and feel of the natural world we live in. Certainly, granular materials, of which sand is but one example, are ubiquitous in our daily lives. They play an important role in industries, such as mining, agriculture and construction. They also are important in geological processes, such as landslides and erosion and, on a larger scale, plate tectonics, which determine much of Earth's morphology. Practically everything we eat started out in a granular form and the clutter on our desks is often so close to the angle of repose that a chance perturbation can create an avalanche onto the floor.
412 citations
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TL;DR: Two sweeping generalizations can be made about most natural systems: They are intrinsically nonlinear and they operate in noisy environments.
Abstract: Two sweeping generalizations can be made about most natural systems: They are intrinsically nonlinear and they operate in noisy environments. Examples abound, ranging from weather systems to oscillating chemical reactions to the movements of an eel. The most complex example is arguably the human central nervous system, flooded as it is with the “noise” of modern life.
401 citations
TL;DR: In this paper, the curvature of the free energy in the vicinity of the minimum is measured as a function of temperature and pressure, which can be used to check theoretical models.
Abstract: When a new crystalline material is discovered, one of the first fundamental properties to be determined is the atomic structure, defined by the minimum in the free energy with respect to the positions of the atoms. Another fundamental characteristic of interest is the curvature of the free energy in the vicinity of the minimum, and this would be manifest in the elastic constants for the material. As derivatives of the free energy, elastic constants are closely connected to thermodynamic properties of the material. They can be related to the specific heat, the Debye temperature and the Gruneisen parameter (which relates the thermal expansion coefficient to the specific heat at constant volume), and they can be used to check theoretical models. Extensive quantitative connections among thermodynamic properties can be made if the elastic constants are known as functions of temperature and pressure. The damping of elastic waves provides information on anharmonicity and on coupling with electrons and other rela...
246 citations
Journal Article•
TL;DR: In this article, the authors present a review of the use of Resonant Ultrasound Spectroscopy (RUS) for the analysis of the mechanical resonances of solids.
Abstract: Resonant ultrasound spectroscopy (RUS) involves the study of the mechanical resonances of solids. The resonant response of a particular object depends on its shape, elastic constants, crystallographic orientation, density, and dissipation. It is possible to obtain the complete elastic constant matrix of relatively low-symmetry materials from a RUS spectrum on a single small sample . The measurement and the computation of the RUS spectra of solids are reviewed. Several examples of the use of the technique are discussed.
242 citations
TL;DR: A brief history of solar terrestrial physics can be found in this paper, where the authors describe the solar wind, the solar magnetic field, and the solar ionosphere of outer planets, as well as the aurora and the auroral ionosphere.
Abstract: Introduction 1. Brief history of solar terrestrial physics 2. Physics of space plasmas 3. The Sun 4. The solar wind 5. Collisionless shocks 6. Interactions with magnetized planets 7. Ionospheres 8. Interactions with unmagnetized bodies 9. Magnetopause, tail and reconnection 10. Magnetospheric configuration 11. Magnetic pulsations 12. Plasma waves 13. Magnetospheric dynamics 14. The aurora and the auroral ionosphere 15. Magnetospheres of outer planets Appendices Index.
206 citations
TL;DR: When metals are cooled, they often undergo a phase transition to a state exhibiting a new type of order as discussed by the authors, such as superconductivity and magnetization in zero-field magnetic fields.
Abstract: When metals are cooled, they often undergo a phase transition to a state exhibiting a new type of order. Metals such as iron and nickel become ferromagnetic below temperatures of several hundred degrees Celsius; electron spins order to produce a net magnetization in zero field. Other metals, such as lead and aluminum, become superconductors at cryogenic temperatures; electrons form Cooper pairs of opposite spin and momentum, leading to electrical conduction with zero resistance and to expulsion of magnetic fields.
TL;DR: The most precise confirmations of key aspects of Albert Einstein's relativistic theory of gravity are achieved by measuring features of the Moon's orbit to 1-centimeter precision using a technique known as lunar laser ranging (LLR) as mentioned in this paper.
Abstract: Three centuries ago Isaac Newton and his contemporaries sought to understand the details of lunar motion in terms of Newton's theory of gravity. Today, our most precise confirmations of key aspects of Albert Einstein's relativistic theory of gravity are achieved by measuring features of the Moon's orbit to 1‐centimeter precision using a technique known as lunar laser ranging (LLR). These present‐day measurements address some of the same questions posed by Newton. Do Earth and the Moon (figure 1) fall toward the Sun at the same rate? What, in detail, produces the precession of the lunar orbit's major axis?
TL;DR: Punctuated equilibrium, the notion that evolution in nature is stepwise rather than continuous, sometimes applies to evolution in science as well as discussed by the authors, where the seed of a scientific breakthrough may slumber for a decade or even longer without generating much interest.
Abstract: Punctuated equilibrium, the notion that evolution in nature is stepwise rather than continuous, sometimes applies to evolution in science as well. The seed of a scientific breakthrough may slumber for a decade or even longer without generating much interest. The seed may be a theoretical concept without clear predictions to test experimentally, or an intriguing but confusing experiment without a lucid interpretation. When the seed finally germinates, an entire field of science can reach maturity in a few years.
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TL;DR: Galileo Galilei was almost seventy years old, his life nearly shattered by a trial for heresy before the Inquisition, when he retired in 1633 to his villa near Florence to construct the Dialogues Concerning ‘Two New Sciences.
Abstract: Galileo Galilei was almost seventy years old, his life nearly shattered by a trial for heresy before the Inquisition, when he retired in 1633 to his villa near Florence to construct the Dialogues Concerning ‘Two New Sciences. His first science was the study of the forces that hold objects together and the conditions that cause them to fall apart—the dialogue taking place in a shipyard, triggered by observations of craftsmen building the Venetian fleet. His second science concerned local motions—laws governing the movement of projectiles.
TL;DR: The principles of quantum computing were laid out about 15 years ago by computer scientists applying the superposition principle of quantum mechanics to computer operation as mentioned in this paper, and quantum computing has recently become a hot topic in physics, with the recognition that a two-level system can be presented as a quantum bit, or “qubit,” and that an interaction between such systems could lead to the building of quantum gates obeying nonclassical logic.
Abstract: The principles of quantum computing were laid out about 15 years ago by computer scientists applying the superposition principle of quantum mechanics to computer operation. Quantum computing has recently become a hot topic in physics, with the recognition that a two‐level system can be presented as a quantum bit, or “qubit,” and that an interaction between such systems could lead to the building of quantum gates obeying nonclassical logic. (See PHYSICS TODAY, October 1995, page 24 and March 1996, page 21.)
TL;DR: The linking number as discussed by the authors is a topological invariant that depends only on the type of link, and not on the geometry of the topology, and it was introduced by Listing in 1847.
Abstract: The use of topological ideas in physics and fluid mechanics dates back to the very origin of topology as an independent science. In a brief note in 1833 Karl Gauss, while lamenting the lack of progress in the “geometry of position” (or Geometria Situs, as topology was then known I, gives a remarkable example of the relationship between topology and measurable physical quantities such as electric currents. He considers two inseparably linked circuits, each of them a copper wire with ends joined, and flowing electric current. Without comment he puts forward a formula that gives the relationship between the magnetic action induced by the currents and a pure number that depends only on the type of link, and not on the geometry. This number is a topological invariant now known as the linking number. The formula, as well as the very first studies in topology done by Johann Benedict Listing in 1847, became known to Kelvin (then William Thomson), James Clerk Maxwell and Peter Guthrie Tait in Britain.
TL;DR: An elderly gentleman with heart disease was admitted to hospital for treatment of an abnormal heart rhythm called ventricular tachycardia, which occurs days, or even years, after a heart attack.
Abstract: An elderly gentleman with heart disease was admitted to hospital for treatment of an abnormal heart rhythm called ventricular tachycardia. This potentially fatal rhythm can occur days, or even years, after a heart attack. It is associated with an abnormally rapid heartbeat that arises from tissue in the heart attack‐damaged portions of the ventricles—the two main pumping chambers of the heart. (See the box on page 41.)
TL;DR: The creation of a gaseous Bose-Einstein condensate in Boulder, Colorado, last summer marked the opening of a door to a new world of physics, the realm of wealdy interacting, quantum degenerate atomic gases as mentioned in this paper.
Abstract: If the creation of a gaseous Bose–Einstein condensate in Boulder, Colorado, last summer marked the opening of a door to a new world of physics—the realm of wealdy interacting, quantum degenerate atomic gases—then today we have unlocked multiple entrances to that domain. Furthermore, each entrance has a different architecture and looks out across a unique landscape.
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TL;DR: In this paper, the effect of randomness and disorder on condensed phases of matter is discussed and a special issue of PHYSICS TODAY dedicated to disordered solids is devoted to the topic.
Abstract: An important theme that threads through many areas of current interest in condensed matter physics is the effect of randomness and disorder. Prior to the 1960s, disorder and impurities were often viewed as unavoidable nuisances that masked the true behavior of ideal systems. We have since learned that disorder itself can bring forth fascinating and often unexpected new phenomena in condensed phases of matter. (See the December 1988 special issue of PHYSICS TODAY, dedicated to disordered solids.)
TL;DR: The Internet offers a wide variety of possibilities for accomplishing this goal as mentioned in this paper, and it can be used to make the exchange of information among scientists faster and better, at reasonable cost.
Abstract: Scientific societies were founded to foster communication among their members. As we move into the era of enhanced electronic communication, the research community is seeking to make the exchange of information among scientists faster and better, at reasonable cost. The Internet offers a wide variety of possibilities for accomplishing this goal.
TL;DR: In this paper, the authors focus primarily on these weapons-related discharges because of their size and less-well-known nature, and they focus mainly on these discharges.
Abstract: Over a 50‐year period, the Soviet Union and the United States developed the largest nuclear weapons complexes in the world. In doing so, they also created the world's largest inventories of radioactive waste. Although some of the waste has been stored in safely managed systems such as tanks or converted into stable and storable forms such as glass, significant amounts of it have been released into the environment. This article focuses primarily on these weapons‐related discharges because of their size and less‐well‐known nature.
TL;DR: The Making of the Atomic Bomb as discussed by the authors is the definitive, often shocking story of the politics and the science behind the development of the hydrogen bomb and the birth of the Cold War.
Abstract: Here, for the first time, in a brilliant, panoramic portrait by the Pulitzer Prize-winning author of \"The Making of the Atomic Bomb, \" is the definitive, often shocking story of the politics and the science behind the development of the hydrogen bomb and the birth of the Cold War. Based on secret files in the United States and the former Soviet Union, this monumental work of history discloses how and why the United States decided to create the bomb that would dominate world politics for more than forty years.
TL;DR: Health Effects of Exposure to Low-Level Ionizing Radiation as discussed by the authors presents a comprehensive and understandable discussion of radiation sources, health effects, radiation protection, and worker and public perception and education about radiat
Abstract: The question of the risks associated with low-level exposure to ionizing radiation and the associated statutory limitations on exposure remains a topic of vigorous debate amongst medical and health physicists, clinical radiologists and members of the public. DEGREESIHealth Effects of Exposure to Low-Level Ionizing Radiation presents a comprehensive, consideration of these issues within a solid historical and scientific framework. It provides a thorough and understandable discussion of radiation sources, health effects, radiation protection, and worker and public perception and education about radiat
TL;DR: In this article, the first bulk applications of high-temperature superconductors are discussed, including current leads, fault current limiters, and wire for power transmission cables, with a transition temperature higher than that of liquid nitrogen.
Abstract: Ten years after Georg Bed‐norz and Alex Muller discovered the first high‐temperature superconductors, and nine years after superconductivity was found with a transition temperature higher than that of liquid nitrogen, considerable progress is being made in bulk applications of high‐temperature superconductors. Electronics applications and thin‐film technology are even more advanced. (See PHYSICS TODAY, March 1995, page 20.) Among the first bulk applications are: current leads, fault current limiters, and wire for power transmission cables.
TL;DR: The hydroxyl molecules (OH) in the troposphere make their presence known as mentioned in this paper, and the life cycle of a single molecule can be estimated in less than one second, compared to carbon dioxide levels, which are a few hundred parts per million.
Abstract: There aren't many hydroxyl molecules (OH) in the troposphere, but the few that are there certainly make their presence known. More than any other species in the troposphere (the atmospheric layer between Earth's surface and an altitude of 8–18 km), the OH radical determines the lifetimes of such common atmospheric constituents as carbon monoxide, methane and sulfur dioxide. Yet, because of its short atmospheric lifetime (a single molecule sticks around less than one second) and low concentrations (a few tenths of a part per trillion, compared, for example to carbon dioxide levels, which are a few hundred parts per million), the OH radical has defied accurate measurement. Not any more.
TL;DR: In this paper, a diode based on gallium nitride (GaN) was reported to operate at a wavelength of 417 nanometers, giving forth a blue-violet light.
Abstract: Researchers at Nichia Chemical Industries in Tbkushima, Japan, reported in January that they had succeeded in getting a diode based on gallium nitride to lase at a wavelength of 417 nanometers, giving forth a blueviolet light. (See the figure on page 19.) Since then, at the International Symposium on Blue Lasers and Light‐Emitting Diodes held in Chiba, Japan, last month, a team from Meijo University in Nagoya announced GaN‐based diode lasers operating both in the blue (402 nm) and ultraviolet (376 nm).
TL;DR: In this article, the development of structurally stronger composite conductors has made feasible the design of pulsed magnets capable of nondestructively delivering 10−ms 100−T (that is, megagauss) pulses.
Abstract: Because high‐magnetic‐field experiments have proved to be valuable tools for illuminating the physics of phenomena ranging from the quantum Hall effect to high‐temperature superconductivity, magnet laboratories around the world are constantly striving to produce more intense magnetic fields, using both continuous‐ and pulsed‐field magnets. To date, magnetic fields above 100 tesla have been achieved only by self‐destructing (exploding or imploding) magnet technologies. These intense magnetic fields persist for only a few microseconds, and most of the destructive‐magnet technologies also destroy the sample. However, the recent development of structurally stronger composite conductors has made feasible the design of pulsed magnets capable of nondestructively delivering 10‐ms 100‐T (that is, megagauss) pulses. (See the box on page 41). During the past five years, researchers in both Europe and the US have proposed building such magnets, along with experiments to exploit this new experimental regime.