Showing papers in "Physics Today in 1982"

The Turning Point: Science, Society and the Rising Culture

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Astronomy and Astrophysics for the 1980s

Abstract: Astronomy is in a golden age. Discoveries since 1960 include quasars (1963), the cosmic microwave background radiation (1965), pulsars (1967), neutronstar binaries (1970), superluminal expansion of radio sources (1971), solar coronal holes (1973), evidence for gravitational radiation from a binary pulsar (1974), anomalous solar neutrino flux (1976), a super gamma‐ray burst (1979), and a gravitational lens (1979). Radio, infrared, ultraviolet, x‐ray, and gamma‐ray techniques have made it possible to study phenomena not accessible to optical astronomy alone. Physics has come to play an increasingly important role in providing both the technology for these developments and the theoretical framework for astronomy. Today, atomic, molecular, nuclear, and plasma physics are indispensable tools in interpreting astronomical data; cosmology and the study of superdense configurations depend on general relativity and, increasingly, elementary‐particle physics.

Lyotropic liquid crystals

Abstract: In mixtures of soap and water, the special properties of soap molecules cause them to form clusters—and clusters of clusters—in a variety of interesting geometrical shapes. Some of these aggregates are liquid crystals, known as lyotropic, which are quite different from thermotropic liquid crystals, the focus of most of the work described in this issue of PHYSICS TODAY. Lyotropic liquid crystals are now receiving a great deal of scientific and technological attention because of the way they reflect the unique properties of their constituent molecules.

The feasibility of inertial‐confinement fusion

Abstract: So concluded the chairman of a Department of Energy ad hoc committee of experts in 1979, after a comprehensive review of the US inertial‐confinement fusion program. In spite of this positive evaluation, the role of inertial‐confinement fusion in the total US energy program continues to be a subject of disagreement. Before I mention the issues of contention, let me describe inertial‐confinement fusion briefly. In a typical scheme, a pea‐sized target pellet containing hydrogen isotopes is projected into a reactor chamber, where it is suddenly irradiated with an intense beam of light or ions from a “driver” (see figure 1). As the surface of the target blasts away, the rocket‐like reaction forces implode the target's interior to densities and temperatures sufficient to cause the hydrogen nuclei to fuse, releasing an amount of energy equivalent to that of a barrel of oil (see PHYSICS TODAY, August 1973, page 46).

Density functional theory

Abstract: What are the energies and wavefunctions of electrons under the influence of nuclei as well as other electrons? If we could solve this general theoretical problem, we would gain a fundamental understanding of a healthy chunk of atomic, molecular and solid‐state physics.

The Physics of glass

Abstract: Some four thousand years ago man discovered glass in the embers of a fire built somewhere in the deserts of the Near East. A few years from now ultratransparent glass fibers will be transmitting more information than copper wires. Thus glass is at once both one of the oldest and one of the newest materials known to civilization. Yet the science of glass is still in its infancy, and the most basic questions remain largely unanswered.

Two‐dimensional systems

Abstract: Nearly all the microscopically small devices that are contributing to the “microtechnological” revolution are composed of thin layers of materials. Such devices are nearly two‐dimensional, and many of the questions concerning the ultimate possibilities and limitations of the technology will require investigation of the physical processes in two dimensions. Similarly, questions that arise in such diverse fields as surface physics, membrane biology and catalytic chemistry involve two‐dimensional phenomena. At least as important as these practical questions is simple intellectural curiously: How does Nature behave in a world of limited dimensionality?

How I created the theory of relativity

Abstract: It is known that when Albert Einstein was awarded the Nobel Prize for Physics in 1922, he was unable to attend the ceremonies in Stockholm in December of that year because of an earlier commitment to visit Japan at the same time. In Japan, Einstein gave a speech entitled “How I Created the Theory of Relativity” at Kyoto University on 14 December 1922. This was an impromptu speech to students and faculty members, made in response to a request by K. Nishida, professor of philosophy at Kyoto University. Einstein himself made no written notes. The talk was delivered in German and a running translation was given to the audience on the spot by J. Ishiwara, who had studied under Arnold Sommerfeld and Einstein from 1912 to 1914 and was a professor of physics at Tohoku University. Ishiwara kept careful notes of the lecture, and published his detailed notes (in Japanese) in the monthly Japanese periodical kaizo in 1923; Ishiwara's notes are the only existing notes of Einstein's talk. More recently T. Ogawa publishe...

Defects in liquid crystals

Abstract: The most striking feature of liquid crystals is the wide variety of visual patterns they display. These patterns, such as those shown in figure 1 and on the cover, are due almost entirely to the defect structure that occurs in the long‐range molecular order of the liquid. Indeed, historically, the underlying structure of the liquid‐crystal phases known as nematic and smectic‐A was discovered from a study of stable defects that characterize these phases. Such defects are easily visible in the optical microscope. By examining the thin and thick thread‐like structures observed in nematic liquid crystals, Otto Lehman and Georges Friedel deduced that this phase involves long‐range orientational ordering of the long axis of the rod‐like molecules. (The direction of this orientational ordering is what we now denote by the unit vector n, called the director.)

Laser annealing of silicon

Abstract: Silicon is one of the most studied and best understood of all materials because of its importance to the integrated circuit industry. The emergence of laser annealing (1,2) in the last ten years has brought about new insight into some of its basic properties and new ways of processing. A quick look at the way integrated circuits are made reveals the reasons for the interest in laser annealing. To make integrated circuits, manufacturers slice very pure crystals of Si into thin wafers. Then they use complex fabrication techniques to produce electrically doped regions close to the surface of the Si and to produce insulating and conducting films that overlay the surface. These doped regions and films can be as thin as a few hundred atomic layers.

Thermodynamics of excitons in semiconductors

Abstract: During the few microseconds between its laser‐induced creation in a pure semiconductor crystal and its destruction by recombination, a bound electron–hole pair, or exciton, is very active. Like the negative and positive charge carriers from which it forms, the exciton exhibits great mobility, whether it is coaxed by an applied force or simply moves under its own thermal energy. And like an atom in free space, it is bound by Coulomb forces, has discrete energy levels and may combine with other excitons into molecules or even condense into a liquid‐like state. In a semiconductor crystal such as silicon, all of this occurs at temperatures below about 30 K, for these weakly bound neutral particles ionize easily into electrons and holes at higher temperatures. The study of these particles and their products has occupied many physicists over the last couple of decades, and the investigations continue to uncover interesting new phenomena.

Polymeric Liquid Crystals

Abstract: Soft contact lenses and ablative heat shields for spacecraft require materials with vastly different physical properties. Yet the materials for both—permeable elastic membranes and tenacious high‐temperature composities—are products of polymer science.

Solid electrolytes—the beta aluminas

Abstract: Electrolytes conduct electricity by the movement of ions, whereas metals conduct by the flow of electrons. Until recently, almost all electrolytes known to have high conductivities were liquids, such as molten salts or aqueous solutions of salts. But research over the last twenty years has uncovered many solid electrolytes—substances that have a high ionic conductivity even though they are insulators to the flow of electrons. Physicists often call these solids “superionic conductors” because a number of the compounds have electrical conductivities comparable with those of liquid electrolytes. (But we will avoid this term to prevent a possible mistaken identification with superconductors.)

My work with Millikan on the oil‐drop experiment

Abstract: Lorena (Chipman) and I were married on 9 September 1908. Soon after we left by train for Chicago. On arrival there, we found a small apartment near the University.

Search for the sparking of the vacuum

Abstract: Our concept of the nature of the vacuum has been evolving for the last 25 centuries. Indeed, some aspects of today's perception of the vacuum, established by modern experimental probes, date back to ancient Greek philosophers.

Phases and phase transitions

Abstract: In this first sentence of his seminal book “The Physics of Liquid Crystals,” Pierre Gilles de Gennes has succinctly stated the appeal that liquid crystals have for all of us working in this field. The term “liquid crystal,” in fact, refers to a number of distinct states of matter that have structural order intermediate between that of conventional liquids and solids.

The molecular physics of liquid‐crystal devices

Abstract: Liquid‐crystal displays are now ubiquitous in homes, stores, businesses and laboratories—on pocket calculators, wrist watches, clocks and so forth; only 14 years after RCA's initial disclosure of potentially useful liquid‐crystal displays, these devices provide the basis for the second largest display industry, second only in dollar volume to cathode‐ray tubes. This remarkable growth has been based on the development of a sophisticated understanding of the molecular properties of liquid crystals.

Solving physics problems—how do we do it?

Abstract: Scribblings on the back of an envelope are as much a part of the professional mystique of the physicist as they are of the story of the Gettysburg Address.

Harold Urey and the discovery of deuterium

Abstract: It was on Thanksgiving day in 1931 that Harold Clayton Urey found definitive evidence of a heavy isotope of hydrogen. Urey's discovery of deuterium is a story of the fruitful use of primitive nuclear and thermodynamic models. But it is also a story of missed opportunity and errors—errors that are particularly interesting because of the crucial positive role that some of them played in the discovery. A look at the nature of the theoretical and experimental work that led to the detection of hydrogen of mass 2 reveals much about the way physics and chemistry were done half a century ago.

The solar cycle

Abstract: Nearly 140 years have elapsed since the German apothecary and amateur astronomer Samuel Heinrich Schwabe reported discovery of the solar cycle. “From my earlier observations,” Schwabe wrote in 1843, “it appears that there is a certain periodicity in the appearance of sunspots and this theory seems more and more probable from the results of this year.” Schwabe had been looking for new planets crossing the Sun's disk. The day‐to‐day records of sunspots he kept for 18 years as part of that search led him to realize that solar behavior is cyclic.