Showing papers in "Physics Today in 1986"
275 citations
Abstract: In the 17th century the Dutch physicist Christian Huyghens observed that two clocks hanging back to back on the wall tend to synchronize their motion. This phenomenon is known as phase locking, frequency locking or resonance, and is generally present in dynamical systems with two competing frequencies. The two frequencies may arise dynamically within the system, as with Huyghens's coupled clocks, or through the coupling of an oscillator to an external periodic force, as with the swing and attendant shown in figure 1. If some parameter is varied—the length of a pendulum or the frequency of the force that drives it, for instance—the system will pass through regimes that are phase locked and regimes that are not. When systems are phase locked the ratio between their frequencies is a rational number. For weak coupling the phase‐locked intervals are narrow, so that even if there is an infinity of intervals, the motion is quasiperiodic for most driving frequencies; that is, the ratio between the two frequencies...
218 citations
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TL;DR: Dry, solution-based etching techniques were replaced in the late 1970s by dry, directional etching processes using plasmas or ion beams as mentioned in this paper, where surface atoms are removed v...
Abstract: Our ability to develop and build ever smaller microelectronic devices depends strongly on the capability to generate a desired device pattern in an image layer (photoresist) by lithography and then to transfer this pattern into the layers of materials of which the device consists. In the past the pattern transfer was almost exclusively accomplished by wet etching. Chemical dissolution of a film region that had to be removed took place in a suitable solvent. Although the wet etching processes stop precisely at a chemically different underlying layer, they typically have isotropic etch characteristics, which cost the researcher control over critical lateral dimensions. Such a tradeoff is not acceptable in the manufacture of micron‐ and submicron‐scale devices, and wet, solution‐based etching techniques were replaced in the late 1970s by dry, directional etching processes using plasmas or ion beams. Figure 1 shows a plasma‐based dry etching system at IBM. In dry etching processes, surface atoms are removed v...
122 citations
TL;DR: In this paper, the authors introduced the vacuum tunneling high over the Atlantic while flying to London in April 1982, and it proved to be the start of an adventure for our group, an adventure that still continues, undiminished in excitement.
Abstract: I was introduced to vacuum tunneling high over the Atlantic while flying to London in April 1982. For months prior to that flight I had been fretting about the future work of our microscopy research group at Stanford. We had just completed our work in acoustic microscopy and were looking for new directions. I was considering a variety of problems, such as the building of an x‐ray microscope, but nothing would fall into place. I thought that a trip to a conference in London might provide some time to get away and think. On the way to the airport I stopped by my office and picked up the latest issue of this magazine. I think we were over Iceland when I opened it and found a report (PHYSICS TODAY, April 1982, page 21) on a new form of scanning microscopy being developed in Zurich. In London, I changed my travel plans and went to Zurich. It proved to be the start of an adventure for our group, an adventure that still continues, undiminished in excitement.
120 citations
TL;DR: Our traditional approaches to science and mathematics education are based largely on intuitive notions and are, in some ways, rather unscientific as mentioned in this paper, whereas we usually tackle problems in science and engineering through the systematic use of fundamental principles, without deeper analysis.
Abstract: Our traditional approaches to science and mathematics education are based largely on intuitive notions and are, in some ways, rather unscientific. Whereas we usually tackle problems in science and engineering through the systematic use of fundamental principles, we often approach problems in science teaching by the seat of our pants, without deeper analysis. While we make great efforts in physics to understand the mechanisms that underlie observed phenomena, we are often content to consider scientists and students as “black boxes” whose internal intellectual functioning can be left largely unexamined in spite of its importance for teaching.
64 citations
45 citations
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TL;DR: For millennia we have based our views of the universe on observations in the narrow visual octave of the electromagnetic spectrum, 400-800 nm, supplemented during the last half-century by infrared and radio observations as discussed by the authors.
Abstract: For millennia we have based our views of the universe on observations in the narrow visual octave of the electromagnetic spectrum, 400–800 nm, supplemented during the last half‐century by infrared and radio observations. During the last decade, however, space research has opened the full spectrum, including the entire infrared region and the ultraviolet, x‐ray and γ‐ray regions (see the photo on the cover and figure 1).
TL;DR: The Brinkman report as discussed by the authors is devoted to the achievements in and identifying goals for the related fields of gravitation, cosmology and cosmic-ray physics, which are considered as subfields of astrophysics.
Abstract: In 1982 the Astronomy Survey Committee, under the direction of George Field, published Astronomy and Astrophysics in the 1980s (see PHYSICS TODAY, April 1982, page 96, and November 1982, page 25), a report similar in purpose to the current Brinkman report. Gravitation, cosmology and cosmic‐ray physics were then, properly, considered as subfields of astrophysics. But these three fields, because they are concerned with the nature of the fundamental forces and constituents of matter, are also of direct interest to physicists. For this reason one volume of the Brinkman report is devoted to recounting the achievements in and identifying goals for the related fields of gravitation, cosmology and cosmic‐ray physics.
TL;DR: Long-range potentials have a vital role in astrophysics via Newton's law of gravitation and a significant role in nuclear physics via Coulomb's electrostatic interaction.
Abstract: Only someone with a short‐range view could fail to be aware of the great importance of long‐range interactions. Indeed, from the late 18th century, when Coulomb discovered that the electrostatic interaction has the same 1/r2 force law that Newton had found for the gravitational interaction, until perhaps the 1930s, when the strong and weak interactions began to be understood, long‐range interactions largely were the subject of physics. By long‐range interactions I mean not only those for which the potential behaves as 1/r for all r but those whose potentials behave asymptotically as some power of 1/r. These originate in 1/r potentials and include, for example, the van der Waals 1/r6 interaction (as calculated nonrelativistically) between two spherically symmetric atoms at a large separation r, and multipole interactions between charge distributions. Long‐range potentials therefore not only play a vital role in astrophysics via Newton's law of gravitation and a significant role in nuclear physics via Coulo...
TL;DR: The Delta 180 program, the first in a series known as the Delta programs, set new standards for accomplishing orbital missions in extremely short periods as discussed by the authors. But the success of the Delta series was not assured.
Abstract: The Applied Physics Laboratory first became involved with the Strategic Defense Initiative Organization (SDIO) in April 1984. Seven programs were initiated, five of which have resulted in launches; another is nearing a launch date. The teamwork between SDIO and APL, along with many other subcontractors, began with the Delta 180 program, the fIrst in a series known as the Delta programs. The Delta series set new standards for accomplishing orbital missions in extremely short periods. Although the seven programs are somewhat diverse, the constant theme throughout was to understand and develop sensors that SDro could use in a deployed architecture and that could be used from ascent through the midcourse phase of a booster trajectory.
TL;DR: In this article, the first observation of nuclear spin noise was made in a collection of chlorine nuclei, which was used to locate the source of the electrical discharge associated with focal epilepsy.
Abstract: ▸ A lonely instrument in Baja California records tiny fluctuations in the Earth's magnetic field, giving valuable information on the location of geothermal energy.▸ An extremely quiet amplifier detects electrical noise generated by the fluctuating spins in a collection of chlorine nuclei—the first observation of nuclear‐spin noise.▸ Superconducting gradiometers in liquid helium measure tiny fluctuating magnetic fields emanating from the human brain (see figure 1), pinpointing the source of the electrical discharge associated with focal epilepsy.▸ An aluminum bar weighing 4800 kg and cooled to 4.2 K rests in a vacuum chamber at Stanford University, working as the world's most sensitive monitor of gravitational radiation.
TL;DR: In the industrial world, we are seldom more than a few meters from a crystal of silicon as mentioned in this paper, and these crystals are extraordinarily perfect: No more than than one atom in 1013 is out of a proper lattice site, and the total impurity concentration may be less than 0.1 parts per billion.
Abstract: In the industrialized world, we are seldom more than a few meters from a crystal of silicon. One crystal may be strapped to our wrist, in an electronic watch; others may be buried within a nearby calculator, video recorder or auto ignition system—indeed, one may even be lurking in the quartz movement of a new “antique” clock. These crystals are extraordinarily perfect: No more than than one atom in 1013 is out of a proper lattice site, and the total impurity concentration may be less than 0.1 parts per billion. Yet a microprocessor or a megabit memory can be fabricated in a crystal of silicon costing only 15–20 cents
TL;DR: In this article, the underlying physics of electrostatic charging of amorphous materials is investigated, focusing on crystalline covalent solids, and only recently has the photoconductivity of highly insulating materials been studied.
Abstract: Electrophotographic printing and copying systems are based on two wellknown but not well‐understood physical phenomena: electrostatic charging and photoconductivity. That some materials can acquire an electric charge by contact or rubbing has been known at least since the time of Thales of Miletus, around 600 B.C., and much work has been done on understanding the phenomenology of the effect, particularly in the 18th and 19th centuries; nevertheless the underlying physics of electrostatic charging of insulators remains unclear. Photoconductivity is a considerably more recent discovery, dating back only to 1873, when Willoughby Smith discovered the effect in selenium. Early work concentrated on crystalline covalent solids; only recently has the photoconductivity of highly insulating amorphous materials been studied. In fact the invention of electrophotography was a major catalyst to research in both electrostatic charging and photoconductivity.
TL;DR: In this article, a detailed analysis of the problems and prospects of superstring theory is provided, anticipating much of the progress of the decades to follow, including the development of super-string theory.
Abstract: We provide a detailed analysis of the problems and prospects of superstring theory c. 1986, anticipating much of the progress of the decades to follow.
TL;DR: For example, this paper pointed out that science libraries all over the United States face serious financial problems associated with the increased costs of journals due to the increase in the cost of journals.
Abstract: Science libraries all over the United States face serious financial problems associated with the increased costs of journals.
TL;DR: The 1970s were the decade of bulk phenomena in solidstate physics as mentioned in this paper, and it was during this decade that we made enormous strides in understanding crystal energy bands, developed clever computational schemes and became experimentally and theoretically adept at characterizing solid crystals.
Abstract: In my view of the evolution of solidstate physics, the 1970s were the decade of bulk phenomena. We made enormous strides in understanding crystals—we mapped their energy bands, developed clever computational schemes and became experimentally and theoretically adept at characterizing solid crystals. At the same time, we developed the tools to study surfaces, and we continue to make amazing progress in this area, as Shuk Y. Tong explained in a recent article (PHYSICS TODAY, August 1984, page 50).
TL;DR: The recent appearance of the Aharonov-Bohm effect in a rather different context may eventually have a profound effect on our view of the solid state on a "mesoscopic" scale.
Abstract: Ever since Yakir Aharonov and David Bohm pointed out, in 1959, that electrons propagating around a magnetic field through a field‐free vacuum should exhibit a quite surprising interference effect, its experimental and theoretical investigation has been contributing to our understanding of the fundamental character of the quantum theory. The recent appearance of this Aharonov–Bohm effect in a rather different context may eventually have a profound effect on our view of the solid state on a “mesoscopic” scale—between the microscopic and the truly macroscopic.
TL;DR: The resulting “integrated circuits” have revolutionized electronics ranging from radio to computers, and a decade ago these circuits surpassed discrete devices in use by the microelectronics industry.
Abstract: For more than a decade after the invention of the transistor in 1948, all semiconductor circuits consisted of discrete devices either connected by wires or mounted on printed circuit boards. Such circuits offered tremendous advantages over the vacuum‐tube circuits that they replaced: less power consumption, higher speed, higher reliability, lower cost, less weight and smaller size. In 1958–59, a major technological breakthrough led to the realization of all these advantages for a second time: Working independently, Jack S. Kilby, an engineer at Texas Instruments, and Robert N. Noyce, a scientist at Fairchild, showed how one could form interconnected transistors, diodes, resistors, capacitors and other active and passive components on a single piece of silicon. The resulting “integrated circuits” have revolutionized electronics ranging from radio to computers, and a decade ago these circuits surpassed discrete devices in use by the microelectronics industry. In recognition of their invention, the National ...
TL;DR: In this paper, a family of selenium-based organic compounds, known as Bechgaard salts, were shown to be superconducting below about 1.5 K.
Abstract: Seven years ago Klaus Bechgaard of the University of Copenhagen synthesized a family of selenium‐based organic compounds now known as Bechgaard salts (see figure 1). A few months later his collaborators at the University of Paris, Orsay, found these materials to be superconducting below about 1.5 K, culminating the search for organic superconductivity that began in the early 1960s. (See PHYSICS TODAY, February 1981, page 17.)
TL;DR: The authors of as mentioned in this paper have assembled enough information from interviews, plant records and computer simulations to describe the chronology of events leading to a severe accident that destroyed a nuclear reactor at Chernobyl on 26 April and spread radiation over much of Europe.
Abstract: Some—but by no means all—of the Chernobyl story can now be told. Soviet scientists have assembled enough information from interviews, plant records and computer simulations to describe the chronology of events leading to a severe accident that destroyed a nuclear reactor at Chernobyl on 26 April and spread radiation over much of Europe. A Soviet delegation of 28 specialists headed by V. A. Legasov (Kurchatov Institute) presented a very frank report on the accident's causes and consequences to an experts' meeting sponsored by the International Atomic Energy Agency in Vienna on 25–29 August. Their report places heavy blame on the reactor staff for committing numerous violations of operating rules, one of which left the reactor operating at a power level where the consequences of further violations were greatly exacerbated.
TL;DR: In this paper, the authors consider analog components, where the signal frequency, signal level, or data rate is not compatible with digital processing, and propose to use analog components for analog applications.
Abstract: Because of inherent advantages in dynamic range and noise rejection, digital signal processing is used whenever possible in modern systems. Critical applications remain for analog components, however, where the signal frequency, signal level, or the data rate is not compatible with digital processing.
TL;DR: The best known example is the giant dipole resonance, which is stimulated when the electric field of an incident gamma ray exerts a force on the positively charged protons in a nucleus, moving them relative to the uncharged neutrons as discussed by the authors.
Abstract: Nuclei interact with the external environment through a number of different fields—electromagnetic, weak and hadronic. The collective excitations induced by these interactions are known as giant resonances. The best‐known example is the giant dipole resonance, which is stimulated when the electric field of an incident gamma ray exerts a force on the positively charged protons in a nucleus, moving them relative to the uncharged neutrons (see figures 1 and 2). Other giant resonances that have been studied are the monopole, quadrupole and spin‐isospin modes of oscillation. The spin‐isospin mode involves charge‐changing processes, in particular beta decay. The quadrupole and monopole giant resonances are most easily seen with fields that act equally on neutrons and protons, because in these modes the neutrons and protons oscillate in the same mode.