Showing papers by "Bell Labs published in 1972"
TL;DR: In this article, a linear specific heat at low temperatures for glass follows naturally from general considerations on the glassy state, and the experimentally observed anomalous low-temperature thermal conductivity is predicted.
Abstract: We show that a linear specific heat at low temperatures for glass follows naturally from general considerations on the glassy state. From the same considerations we obtain the experimentally observed anomalous low-temperature thermal conductivity, and we predict an ultrasonic attenuation which increases at low temperatures. Possible relationships with the linear specific heat in magnetic impurity systems are pointed out. We suggest experimental study of the relaxation of thermal and other properties.
2,578 citations
TL;DR: This article opposes the reductionist hypothesis, arguing that if everything obeys the same fundamental laws, then the only scientists who are studying anything really fundamental are those who are working on those laws.
Abstract: The reductionist hypothesis may still be a topic for controversy among philosophers, but among the great majority of active scientists I think it is accepted without question. The workings of our minds and bodies, and of all the animate or inanimate matter of which we have any detailed knowledge, are assumed to be controlled by the same set of fundamental laws, which except under certain extreme conditions we feel we know pretty well. It seems inevitable to go on uncritically to what appears at first sight to be an obvious corollary of reductionism: that if everything obeys the same fundamental laws, then the only scientists who are studying anything really fundamental are those who are working on those laws. In practice, that amounts to some astrophysicists, some elementary particle physicists, some logicians and other mathematicians, and few others. This point of view, which it is the main purpose of this article to oppose, is expressed in a rather wellknown passage by Weisskopf (1):
1,847 citations
TL;DR: A 4×4-matrix technique was introduced by Teitler and Henvis as discussed by the authors to solve the problem of reflection and transmission by cholesteric liquid crystals and other liquid crystals with continuously varying but planar ordering.
Abstract: A 4×4-matrix technique was recently introduced by Teitler and Henvis for finding propagation and reflection by stratified anisotropic media. It is more general than the 2×2-matrix technique developed by Jones and by Abeles and is applicable to problems involving media of low optical symmetry. A little later, we developed a 4×4 differential-matrix technique in order to solve the problem of reflection and transmission by cholesteric liquid crystals and other liquid crystals with continuously varying but planar ordering. Our technique is mathematically equivalent to that of Teitler and Henvis, but we used a somewhat different approach. We start with a 6×6-matrix representation of Maxwell’s equations that can include Faraday rotation and optical activity. From this, we derive expressions for 16 differential-matrix elements so that a wide variety of specific problems can be attacked without repeating a large amount of tedious algebra. The 4×4-matrix technique is particularly well suited for solving complicated reflection and transmission problems on a computer. It also serves as an illuminating alternative way to rederive closed solutions to a number of less-complicated classical problems. Teitler and Henvis described a method of solving some of these problems, briefly in their paper. We give solutions to several such problems and add a solution to the Oseen–DeVries optical model of a cholesteric liquid crystal, to illustrate the power and simplicity of the 4×4-matrix technique.
1,787 citations
TL;DR: P can be chosen to I&E the centroid oC the triangle formed by X, y and z and Express each si E S in polar coordinates th origin P and 8 = 0 in the direction of zu~ arhitnry fixed half-line L from P.
1,741 citations
Book•
01 Jan 1972TL;DR: It is the hope that the algorithms and concepts presented in this book will survive the next generation of computers and programming languages, and that at least some of them will be applicable to fields other than compiler writing.
Abstract: From volume 1 Preface (See Front Matter for full Preface)
This book is intended for a one or two semester course in compiling theory at the senior or graduate level. It is a theoretically oriented treatment of a practical subject. Our motivation for making it so is threefold.
(1) In an area as rapidly changing as Computer Science, sound pedagogy demands that courses emphasize ideas, rather than implementation details. It is our hope that the algorithms and concepts presented in this book will survive the next generation of computers and programming languages, and that at least some of them will be applicable to fields other than compiler writing.
(2) Compiler writing has progressed to the point where many portions of a compiler can be isolated and subjected to design optimization. It is important that appropriate mathematical tools be available to the person attempting this optimization.
(3) Some of the most useful and most efficient compiler algorithms, e.g. LR(k) parsing, require a good deal of mathematical background for full understanding. We expect, therefore, that a good theoretical background will become essential for the compiler designer.
While we have not omitted difficult theorems that are relevant to compiling, we have tried to make the book as readable as possible. Numerous examples are given, each based on a small grammar, rather than on the large grammars encountered in practice. It is hoped that these examples are sufficient to illustrate the basic ideas, even in cases where the theoretical developments are difficult to follow in isolation.
From volume 2 Preface (See Front Matter for full Preface)
Compiler design is one of the first major areas of systems programming for which a strong theoretical foundation is becoming available. Volume I of The Theory of Parsing, Translation, and Compiling developed the relevant parts of mathematics and language theory for this foundation and developed the principal methods of fast syntactic analysis. Volume II is a continuation of Volume I, but except for Chapters 7 and 8 it is oriented towards the nonsyntactic aspects of compiler design.
The treatment of the material in Volume II is much the same as in Volume I, although proofs have become a little more sketchy. We have tried to make the discussion as readable as possible by providing numerous examples, each illustrating one or two concepts.
Since the text emphasizes concepts rather than language or machine details, a programming laboratory should accompany a course based on this book, so that a student can develop some facility in applying the concepts discussed to practical problems. The programming exercises appearing at the ends of sections can be used as recommended projects in such a laboratory. Part of the laboratory course should discuss the code to be generated for such programming language constructs as recursion, parameter passing, subroutine linkages, array references, loops, and so forth.
1,727 citations
[...]
TL;DR: In this paper, experimental evidence about the states in the gap of chalcogenide glasses is discussed and the total concentration of states is estimated from the measurements of the magnetic susceptibility and their density distribution from the optical and photo-emission measurements.
Abstract: Experimental evidence about the states in the gap of chalcogenide glasses is discussed. The total concentration of states is estimated from the measurements of the magnetic susceptibility and their density distribution from the optical and photo-emission measurements. Possible models for the interpretation of the experimental facts are considered.
1,685 citations
TL;DR: In this paper, optical transitions occur between localized states below the mobility edge and extended states of the opposite band, and they are associated with localized states in the band gap, where the authors interpret the results in terms of a model in which optical transitions are interpreted by a Gaussian distribution.
Abstract: Optical absorption measurements near the absorption edge are presented for three bulk semiconductor glasses: ${\mathrm{As}}_{2}$${\mathrm{S}}_{3}$, ${\mathrm{Ge}}_{33}$${\mathrm{As}}_{12}$${\mathrm{Se}}_{55}$, and ${\mathrm{Ge}}_{28}$${\mathrm{Sb}}_{12}$${\mathrm{Se}}_{60}$. The weak absorption tails observed below the exponential part of the edge also follow an exponential law, and they are not due to a light-scattering artifact. We associate them with localized states in the band gap. The results are interpreted in terms of a model in which optical transitions occur between localized states below the mobility edge and extended states of the opposite band.
1,157 citations
TL;DR: These effects of stimulated Raman and Brillouin scattering must be considered in the design of optical communication systems using low loss fibers especially when low loss optical fibers are used.
Abstract: The effect of stimulated Raman and Brillouin scattering on the power handling capacity of optical fibers is considered and found to be important especially when low loss optical fibers are used. A critical power below which stimulated effects may be neglected is defined for forward and backward Raman scattering and for backward Brillouin scattering. This critical power is determined by the effective core area A, the small signal attenuation constant of the fiber alpha, and the gain coefficient for the stimulated scattering process (gamma0), by the approximate relation P(crit) approximately 20Aalpha/(gamma0). For a fiber with 20-dB/km attenuation and an area of 10(-7) cm(2)P(crit) approximately 35 mW for stimulated Brillouin scattering. For stimulated Raman scattering P(crit) is approximately two orders of magnitude higher. It is concluded that these effects must be considered in the design of optical communication systems using low loss fibers.
1,080 citations
TL;DR: This article showed that elastic strain energy may account for the tendency of some nematic liquid crystals to lie parallel to the direction of rubbing on a solid surface that has been slightly deformed by rubbing, or perpendicular to a surface that is slightly rough in two dimensions.
Abstract: We show that elastic strain energy may account for the tendency of some nematic liquid crystals to lie parallel to the direction of rubbing on a solid surface that has been slightly deformed by rubbing, or perpendicular to a surface that is slightly rough in two dimensions.
782 citations
TL;DR: It is proved that the algorithm gives optimal solutions and its application to preemptive scheduling disciplines is discussed.
Abstract: Despite the recognized potential of multiprocessing little is known concerning the general problem of finding efficient algorithms which compute minimallength schedules for given computations and m?2 processors. In this paper we formulate a general model of computation structures and exhibit an efficient algorithm for finding optimal nonpreemptive schedules for these structures on two-processor systems. We prove that the algorithm gives optimal solutions and discuss its application to preemptive scheduling disciplines.
563 citations
TL;DR: In this paper, small scale statistics of the multipath propagation for vehicle travel distances on the order of 30 m along streets are presented in the following forms: 1) average power-delay profiles made up of over 200 individual profiles, 2) cumulative distributions of signal amplitude at fixed delays, and 3) radio frequency Doppler spectra at fixed delay.
Abstract: Statistical descriptions of the time delays and Doppler shifts associated with multipath propagation in a suburban mobile radio environment obtained from bandpass impulse response measurements are presented. The measuring equipment which has 0.1 \mu s resolution in time delay and a data output bandwidth of less than 5 kHz is also described. For the first time small scale statistics of the multipath propagation for vehicle travel distances on the order of 30 m along streets are presented in the following forms: 1) average power-delay profiles made up of over 200 individual profiles, 2) cumulative distributions of signal amplitude at fixed delays, and 3) radio frequency Doppler spectra at fixed delays. Delay spreads for typical suburban streets are on the order of 0.25 \mu s. Extreme cases have paths with significant amplitudes at excess delays of 5 to 7 \mu s and the square root of the second central moment delay spreads up to about 2 \mu s. Often the signal at fixed delays has a Rayleigh distributed amplitude but large departures from the Rayleigh distribution also occur. RF Doppler spectra at fixed delays indicate that some of the multipath is from one relatively discrete scattering center while at other delays several scattering centers distributed widely in angle are involved. The observed RF Doppler spectra are consistent with the cumulative amplitude distributions at the same delays.
TL;DR: In this paper, expressions for the envelope-modulation effect in spin-echo experiments of the two-and three-pulse type were obtained by partitioning the matrices which describe the evolution of the quantized system.
Abstract: Expressions have been obtained for the envelope-modulation effect in spin-echo experiments of the two- and three-pulse type by partitioning the matrices which describe the evolution of the quantized system. The initial results are quite general and may be applied to a variety of systems. Simplified expressions are derived for the case of an electron spin transition split by small nuclear hyperfine interactions. The results are given in matrix product form. The problem of computing the envelope-modulation parameters in specific instances is discussed. Algebraic results are given for $S=\frac{1}{2}$, $I=\frac{1}{2}$ and $S=\frac{1}{2}$, $I=1$.
TL;DR: In this article, a method to compensate the astigmatic distortions introduced by both the internal mirror and the cell is described, which allows the formation of a tight intracavity focus as required in applications such as CW dye lasers.
Abstract: An analysis is given of folded 3-mirror laser resonators with an internal cell set at Brewster's angle. A method is described to compensate the astigmatic distortions introduced by both the internal mirror and the cell. This compensation is achieved for a specific relation between cell thickness and folding angle. It allows the formation of a tight intracavity focus as required in applications such as CW dye lasers. A discussion is given of the mode characteristics of compensated cavities and of the limitation on beam concentration set by the thickness of the Brewster cell.
TL;DR: The experiments demonstrate that a grating is masked only by noise whose spatial frequencies are similar to the grating frequency, and provide further indication of the existence of channels in the visual system that are selectively tuned to different spatial frequencies.
Abstract: Vertical sinusoidal gratings were viewed in masking noise consisting of vertical stripes spread along the horizontal direction. Masking functions were obtained while varying the grating frequency relative to various one-octave-wide bands of noise. These functions closely resemble curves derived from previous experiments on adaptation to gratings. Masking was also measured as a function of the width of a band of noise centered on the grating frequency. Masking increased as the band was widened up to approximately ±1 octave; masking did not increase further when the band was widened beyond this range. The results demonstrate that a grating is masked only by noise whose spatial frequencies are similar to the grating frequency. The experiments provide further indication of the existence of channels in the visual system that are selectively tuned to different spatial frequencies.
TL;DR: In this paper, the power spectrum of the transmission coefficient in the multipath medium is used to determine probability distributions of amplitude and phase, correlations of fields versus time and space at mobile and base stations, level-crossing rates and durations of fades, and random frequency modulation.
Abstract: The statistical properties of radio propagation between a mobile unit and a base-station terminal are derived. The power spectrum of the transmission coefficient in the multipath medium is used to determine probability distributions of amplitude and phase, correlations of fields versus time and space at mobile and base stations, level-crossing rates and durations of fades, and random frequency modulation. Duality between the power spectrum and density of time delays is shown. The correlations versus frequency and the coherence bandwidth then follow from the density of time delays. The performance of standard diversity systems is then predicted. There is a review of results previously presented by Clarke [1], however, the derivations given herein utilize expressions of the power spectrum rather than expressions of the component waves. The power-spectral approach, used throughout, allows direct application of previous statistical analyses, particularly those of Rice [2].
01 Mar 1972-Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science
TL;DR: In this article, the tensile flow and fracture behavior of three Pdo.8Sio2-based alloys in the glassy, "micro-crystalline, and fully crystalline condition has been studied.
Abstract: The tensile flow and fracture behavior of three Pdo.8Sio2-based alloys in the glassy, “microcrystalline,” and fully crystalline condition has been studied. The glassy alloys flow plastically to a total strain of approximately 0.5 pct e, and exhibit proportional limit stresses of approximatelyE x 10~2 whereE is Young’s modulus. This plastic flow is accompanied by the formation of shear deformation bands on the specimen surfaces. Fully crystalline alloys are extremely brittle and fracture via intergranular cracking. Fracture surfaces of the amorphous and “microcrystalline” alloys are inclined at 45 deg to the tensile axis and exhibit two morphologically distinct zones. One zone is relatively featureless while the other contains a “river” pattern of local necking protrusions. Detailed comparison of opposing surfaces indicates that fracture is preceded by large local plastic shear which produces the smooth zone while the local necking pattern is produced during rupture. These observations form the basis for the hypothesis that plastic flow in the glassy material occurs via localized strain concentrations and that fracture is initiated by catastrophic, “adiabatic” shear.
TL;DR: The purpose of this paper is to describe the intriguing subject of well-quasi-ordering, and to illustrate the theory, here are two definitions and an elementary result.
TL;DR: In this paper, the dynamics of electrons between the source and drain of a microwave field effect transistor (FET) have been studied using a Monte Carlo method, and the spatial dependence as well as the time dependence of the average electron velocity is presented.
Abstract: The dynamics of electrons between the source and drain of a microwave field-effect transistor (FET) have been studied using a Monte Carlo method. The spatial dependence as well as the time dependence of the average electron velocity is presented. It is shown that in silicon the relaxation time is short enough not to influence the figure of merit of the transistor. However, in direct gap polar semiconductors (e.g., GaAs), the electrons can have a velocity well above their saturation value for an appreciable length of time and, consequently, over a distance nonnegligible compared to the length of the active region of a high frequency FET. This could improve the figure of merit of the FET.
TL;DR: In this paper, the refractive indices of the ternary A^{I}B^{III}C_{2}^{VI} semiconductors CuAlSe 2, AgGaSe 2, CuGaSe2, and AgInSe 2 have been measured over most of the transparency range of these crystals.
Abstract: The refractive indices of the ternary A^{I}B^{III}C_{2}^{VI} semiconductors CuAlSe 2 , AgGaSe 2 , CuGaSe 2 , and AgInSe 2 have been measured over most of the transparency range of these crystals. The optical nonlinear coefficients for second-harmonic generation of AgGaSe 2 CuGaSe 2 , and AgInSe 2 have also been measured. Three-frequency colinear phase matching is analyzed in detail for AgGaSe 2 . The birefringences of the other three crystals are not sufficient to permit three-frequency colinear phase matching within the range of the measured index. The merits of AgGaSe 2 for nonlinear optical applications are evaluated in comparison with other promising infrared nonlinear materials.
TL;DR: The analysis and experiment demonstrated the feasibility of providing two diversity branches at UHF by polarization diversity, and the local means of the two signals were highly correlated and were with ± 3 dB for almost 90 percent of the time.
Abstract: Conventional space diversity reception at typical elevated base locations requites separation of 30λ for broadside incidence and even more for in-line incidence and is therefore difficult to implement. A polarization diversity system for mobile radio is proposed. This is a two-branch receiver diversity system with the advantage that the base station antennas can be spaced as closely as desired. An experimental program has been carried out to obtain the statistical properties of vertically and horizontally polarized electromagnetic waves in a suburban environment at 836 MHz. It was observed that signals of both polarizations were Rayleigh plus log normal, where one is uncorrelated and other is correlated irrespective of base or mobile antenna spacings. The local means of the two signals were highly correlated and were with ± 3 dB for almost 90 percent of the time. Variation of base transmitter heights appeared to have little effect on the ratio of the local means of the two signals. The analysis and experiment demonstrated the feasibility of providing two diversity branches at UHF by polarization diversity.
TL;DR: In this paper, a numerical and experimental investigation of the developing laminar free convection heat transfer in vertical parallel plate channels with asymmetric heating is presented, where the Nusselt number characterizing the total heat transfer to the fluid is found to be related to the Rayleigh number very nearly by a universal curve for all ratios of wall temperature differences.
TL;DR: In this article, a scaling theory for thermodynamic functions and spin correlations near the surface is developed, and relations among the exponents of the half-space are found among the sparsification terms.
Abstract: Phase transitions in Ising models with tree surfaces are studied from various points of view, including a phenomenological Landau theory, high-temperature series expansions, and a scaling theory for thermodynamic quantities and correlation functions. In the presence of a surface a number of new critical exponents must be defined. These arise because of the existence of "surface" terms in the thermodynamic functions, and because of the anisotropy of space and lack of translational symmetry introduced by the surface. The need for these new critical exponents already appears in the phenomenological theory, which is discussed in detail and related to the microscopic mean-field approximation. The essential new parameter appearing in this theory is an extrapolation length $\ensuremath{\lambda}$ which enters the boundary condition on the magnetization at the surface. For magnetic systems this length is of the order of the interaction range, in contrast to superconductors, where it is usually much larger. In order to go beyond the mean-field theory, high-temperature series expansions are carried out for the Ising half-space, to tenth order in two dimensions and to eighth order in three dimensions. A scaling theory is developed both for thermodynamic functions and for spin correlations near the surface, and relations are found among the exponents of the half-space. Both the scaling theory and the numerical calculations are compared with the exact solution of the Ising half-plane (two dimensions) by McCoy and Wu, and agreement is found wherever the theory is applicable. In analogy to the bulk situation, the scaling theory is found to agree with mean-field theory in four dimensions. The prediction of the present work which is most easily accessible to experiment is the temperature dependence of the magnetization at the surface, with critical exponent estimated to be ${\ensuremath{\beta}}_{1}=\frac{2}{3}$. The mean-field result, ${\ensuremath{\beta}}_{1}=1$, seems to agree more closely with presently available experiment, and more work is needed to clarify the situation.
TL;DR: In this paper, X-ray scattering intensities from unoriented samples of cholesteryl nonanoate and myristate are reported for several temperatures in the smectic $A, cholesteric, and isotropic liquid phases.
Abstract: X-ray scattering intensities from unoriented samples of cholesteryl nonanoate and myristate are reported for several temperatures in the smectic $A$, cholesteric, and isotropic liquid phases. The measured Bragg-scattering intensities from the smectic planes are used to test a recent theoretical model of the smectic $A$ phase. Strong pretransition scattering (short-range-order or order-parameter fluctuations) are observed in the cholesteric phase and a Landau theory is constructed to describe this effect.
TL;DR: In this article, the transition from ballistic to second sound to diffusive propagation of heat pulses in the semimetal bismuth in the temperature range of 1.2 to 4.0 K was observed.
Abstract: We have observed the transition from ballistic to second sound to diffusive propagation of heat (phonon) pulses in the semimetal bismuth in the temperature range of 1.2 to 4.0 K. The saturated second-sound velocity is found to be independent of orientation and has a a value of (0.78\ifmmode\pm\else\textpm\fi{}0.05)\ifmmode\times\else\texttimes\fi{}${10}^{5}$ cm/sec ($\frac{1}{3}\sqrt{3}$ times the Debye velocity). The inverse of the normal process phonon lifetime has a value ${{T}_{N}}^{\ensuremath{-}1}=4.49\ifmmode\times\else\texttimes\fi{}{10}^{4}{T}^{4}$ ${\mathrm{sec}}^{\ensuremath{-}1}$. Scattering due to the hole-phonon interaction is observed for ballistic $L$ modes propagating along the ${C}_{3}$ axis.
TL;DR: A deductive method of fault simulation is described, which "deduces" the faults defected by a test at the same time that it simulates explicitly only the good behavior of logic circuit.
Abstract: A deductive method of fault simulation is described, which "deduces" the faults defected by a test at the same time that it simulates explicitly only the good behavior of logic circuit. For large logic circuits (at least several thousand gates) it is expected to be faster than "parallel" fault simulators, but uses much more computer memory than do parallel simulators.
TL;DR: This paper analyzes a queuing model consisting of a system of queues that are attended periodically in a given order by a single server and shows how the moments of these distributions can be calculated.
Abstract: This paper analyzes a queuing model consisting of a system of queues that are attended periodically in a given order by a single server. The server empties each queue before proceeding to the next queue in sequence. A changeover time is required whenever the server switches from one queue to another. For a stationary process expressions are obtained for the Laplace-Stieltjes transforms of the waiting-time and intervisit-time distributions at each queue. It is also shown how the moments of these distributions can be calculated.