Showing papers by "Bell Labs published in 1983"
TL;DR: In this paper, the pseudodielectric functions of spectroscopic ellipsometry and refractive indices were measured using the real-time capability of the spectro-optical ellipsometer.
Abstract: We report values of pseudodielectric functions $〈\ensuremath{\epsilon}〉=〈{\ensuremath{\epsilon}}_{1}〉+i〈{\ensuremath{\epsilon}}_{2}〉$ measured by spectroscopic ellipsometry and refractive indices $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{n}=n+ik$, reflectivities $R$, and absorption coefficients $\ensuremath{\alpha}$ calculated from these data. Rather than correct ellipsometric results for the presence of overlayers, we have removed these layers as far as possible using the real-time capability of the spectroscopic ellipsometer to assess surface quality during cleaning. Our results are compared with previous data. In general, there is good agreement among optical parameters measured on smooth, clean, and undamaged samples maintained in an inert atmosphere regardless of the technique used to obtain the data. Differences among our data and previous results can generally be understood in terms of inadequate sample preparation, although results obtained by Kramers-Kronig analysis of reflectance measurements often show effects due to improper extrapolations. The present results illustrate the importance of proper sample preparation and of the capability of separately determining both ${\ensuremath{\epsilon}}_{1}$ and ${\ensuremath{\epsilon}}_{2}$ in optical measurements.
3,094 citations
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01 Jan 1983TL;DR: This paper presents a meta-trees tree model that automates the very labor-intensive and therefore time-heavy and therefore expensive process of manually selecting trees to grow in a graph.
Abstract: Foundations Disjoint Sets Heaps Search Trees Linking and Cutting Trees Minimum Spanning Trees Shortest Paths Network Flows Matchings
2,120 citations
TL;DR: In this article, a theory for vacuum tunneling between a real solid surface and a model probe with a locally spherical tip is presented, applicable to the recently developed "scanning tunneling microscope."
Abstract: A theory is presented for vacuum tunneling between a real solid surface and a model probe with a locally spherical tip, applicable to the recently developed "scanning tunneling microscope." Calculations for 2\ifmmode\times\else\texttimes\fi{}1 and 3\ifmmode\times\else\texttimes\fi{}1 reconstructions of Au(110) are in excellent agreement with recent experimental results, if an effective radius of curvature of 9 \AA{} is assumed for the tip.
2,091 citations
TL;DR: The derivation and use of a measure of similarity between two hierarchical clusterings, Bk, is derived from the matching matrix, [mij], formed by cutting the two hierarchical trees and counting the number of matching entries in the k clusters in each tree.
Abstract: This article concerns the derivation and use of a measure of similarity between two hierarchical clusterings. The measure, Bk , is derived from the matching matrix, [mij ], formed by cutting the two hierarchical trees and counting the number of matching entries in the k clusters in each tree. The mean and variance of Bk are determined under the assumption that the margins of [mij ] are fixed. Thus, Bk represents a collection of measures for k = 2, …, n – 1. (k, Bk ) plots are found to be useful in portraying the similarity of two clusterings. Bk is compared to other measures of similarity proposed respectively by Baker (1974) and Rand (1971). The use of (k, Bk ) plots for studying clustering methods is explored by a series of Monte Carlo sampling experiments. An example of the use of (k, Bk ) on real data is given.
1,376 citations
TL;DR: In this paper, the energy-band gap of an insulator is obtained from the eigenvalues of the one-particle density-functional equation for the ground state and a finite correction due to the discontinuity of the functional derivative of the exchange and correlation energy.
Abstract: The energy-band gap of an insulator is obtained from the eigenvalues of the one-particle density-functional equation for the ground state and a finite correction due to the discontinuity of the functional derivative of the exchange and correlation energy. This correction is expressed in terms of the improper self-energy and the density-functional exchange-correlation potential. It is evaluated for a two-plane-wave model including exchange only.
1,365 citations
TL;DR: The present status of high pressure research with the diamond anvil cell (DAC) is reviewed in this paper, mainly from an experimental aspect, with a view to illustrating the physics behind high-pressure phenomena, including metal-semiconductor transitions, electronic transitions, phonons and phase transitions.
Abstract: The present status of high-pressure research with the diamond anvil cell (DAC) is reviewed in this article, mainly from an experimental aspect. After a brief description of the different types of DAC's that are currently in vogue, the techniques used in conjunction with the DAC in modern high-pressure research are presented. These include techniques for low- and high-temperature studies, x-ray diffractometry, spectroscopy with the DAC, and other measurements. Results on selected materials, with a view to illustrating the physics behind high-pressure phenomena, are presented and discussed. These include metal-semiconductor transitions, electronic transitions, phonons and high-pressure lattice dynamics, and phase transitions. A whole section is devoted to the behavior of condensed gases, principally ${\mathrm{H}}_{2}$, ${\mathrm{D}}_{2}$, ${\mathrm{O}}_{2}$, ${\mathrm{N}}_{2}$, and rare-gas solids. The concluding section briefly deals with speculations on ultra-high-pressure research with the DAC in the future.
1,083 citations
TL;DR: An O(mn log n)-time algorithm is obtained to find a maximum flow in a network of n vertices and m edges, beating by a factor of log n the fastest algorithm previously known for sparse graphs.
1,042 citations
TL;DR: This paper describes the Queueing Network Analyzer (QNA), a software package developed at Bell Laboratories to calculate approximate congestion measures for a network of queues and uses two parameters to characterize the arrival processes and service times.
Abstract: This paper describes the Queueing Network Analyzer (QNA), a software package developed at Bell Laboratories to calculate approximate congestion measures for a network of queues. The first version of QNA analyzes open networks of multiserver nodes with the first-come, first-served discipline and no capacity constraints. An important feature is that the external arrival processes need not be Poisson and the service-time distributions need not be exponential. Treating other kinds of variability is important. For example, with packet-switched communication networks we need to describe the congestion resulting from bursty traffic and the nearly constant service times of packets. The general approach in QNA is to approximately characterize the arrival processes by two or three parameters and then analyze the individual nodes separately. The first version of QNA uses two parameters to characterize the arrival processes and service times, one to describe the rate and the other to describe the variability. The nodes are then analyzed as standard GI/G/m queues partially characterized by the first two moments of the interarrival-time and service-time distributions. Congestion measures for the network as a whole are obtained by assuming as an approximation that the nodes are stochastically independent given the approximate flow parameters.
1,021 citations
TL;DR: The concept of performance trade-offs between competing objectives is used to interpret the distance-time relationships observed in skilled movements, which may be useful in modeling and interpreting motor control strategies for skilled movements.
Abstract: This paper presents some elementary principles regarding constraints on movements, which may be useful in modeling and interpreting motor control strategies for skilled movements. Movements which are optimum with respect to various objectives, or "costs", are analyzed and compared. The specific costs considered are related to movement time, distance, peak velocity, energy, peak acceleration, and rate of change of acceleration (jerk). The velocity patterns for the various minimum cost movements are compared with each other and with some skilled movement patterns. The concept of performance trade-offs between competing objectives is used to interpret the distance-time relationships observed in skilled movements. Examples of arm movements during violin bowing and jaw movements during speech are used to show how skilled movements are influenced by considerations of physical economy, or "ease", of movement. Minimum-cost solutions for the various costs, which include the effect of frictional forces, are given in Appendices.
827 citations
TL;DR: It is shown that this class of database schemes, called acychc, has a number of desirable properties that have been studied by other researchers and are shown to be eqmvalent to acydicity.
Abstract: A class of database schemes, called acychc, was recently introduced. It is shown that this class has a number of desirable properties. In particular, several desirable properties that have been studied by other researchers m very different terms are all shown to be eqmvalent to acydicity. In addition, several equivalent charactenzauons of the class m terms of graphs and hypergraphs are given, and a smaple algorithm for determining acychclty is presented. Also given are several eqmvalent characterizations of those sets M of multivalued dependencies such that M is the set of muRlvalued dependencies that are the consequences of a given join dependency. Several characterizations for a conflict-free (in the sense of Lien) set of muluvalued dependencies are provided.
825 citations
TL;DR: Preattentive vision serves as an “early warning system” by pointing out those loci of texton differences that should be attended to, according to this theory, at any given instant the visual information intake is relatively modest.
Abstract: Recent research in texture discrimination has revealed the existence of a separate “preattentive visual system” that cannot process complex forms, yet can, almost instantaneously, without effort or scrutiny, detect differences in a few local conspicuous features, regardless of where they occur. These features, called “textons”, are elongated blobs (e.g., rectangles, ellipses, or line segments) with specific properties, including color, angular orientation, width, length, binocular and movement disparity, and flicker rate. The ends-of-lines (terminators) and crossings of line segments are also textons. Only differences in the textons or in their density (or number) can be preattentively detected while the positional relationship between neighboring textons passes unnoticed. This kind of positional information is the essence of form perception, and can be extracted only by a time-consuming and spatially restricted process that we call “focal attention”. The aperture of focal attention can be very narrow, even restricted to a minute portion of the fovea, and shifting its locus requires about 50 ms. Thus preattentive vision serves as an “early warning system” by pointing out those loci of texton differences that should be attended to. According to this theory, at any given instant the visual information intake is relatively modest.
TL;DR: The van der Waals picture focuses on the differing roles of the strong short-ranged repulsive intermolecular forces and the longer ranged attractions in determining the structure and dynamics of dense fluids and solids.
Abstract: The van der Waals picture focuses on the differing roles of the strong short-ranged repulsive intermolecular forces and the longer ranged attractions in determining the structure and dynamics of dense fluids and solids. According to this physical picture, the attractive interactions help fix the volume of the system, but the arrangements and motions of molecules within that volume are determined primarily by the local packing and steric effects produced by the repulsive forces. This very useful approach, its limitations, and its successful application to a wide variety of static and dynamic phenomena in condensed matter systems are reviewed.
TL;DR: It is shown here from the general two-soliton function that solitons in fibers exert forces on their neighbors that decrease exponentially with the distance between them and depend sinusoidally on their relative phase.
Abstract: The propagation of light pulses as solitons in optical fibers may form the basis of a viable means of communication. We show here from the general two-soliton function that solitons in fibers exert forces on their neighbors that decrease exponentially with the distance between them and depend sinusoidally on their relative phase. These forces account for the displacements suffered by solitons during collisions, and their effects must be taken into account in system design.
TL;DR: It is shown here that in these conditions a small pattern is easily detected against a background made up of many others, only if this target pattern differs from the background patterns in certain local features.
Abstract: When stimuli are available for just a brief period (approximately 100 ms) only restricted spatial information can be processed by the visual system. If the stimuli are presented very briefly, eye movements are not possible. The time during which the after-image of the stimulus is available for inspection is terminated by presentation of a masking pattern. We show here that in these conditions a small pattern is easily detected against a background made up of many others, only if this target pattern differs from the background patterns in certain local features. In this case the detectability of the target is almost independent of the number of background elements, suggesting that a parallel process is operating. Detection of patterns not differing from their backgrounds in such features requires focal attention which is a serial process. The aperture of this attention is scaled to minimize the number of shifts of attention required.
TL;DR: In this article, the reflectivity of silicon has been measured following excitation with intense 90-fsec optical pulses, which can clearly resolve in time the process of energy transfer to the crystal lattice and the dynamics of the phase transition to the melted state.
Abstract: The reflectivity of silicon has been measured following excitation with intense 90-fsec optical pulses. These measurements for the first time clearly resolve in time the process of energy transfer to the crystal lattice and the dynamics of the phase transition to the melted state.
TL;DR: In this article, the authors describe the types of externalities that one unit of government can create for non-residents through both its public goods decisions and its taxation decisions, and explore briefly what the central government might do to lessen the costs of decentralized decision-making.
Abstract: In a Federal system of government, each unit of government decides independently how much of each type of public good to provide, and what types of taxes, and which tax rates, to use in funding the public goods. In this paper we explore what types of problems can arise from this decentralized form of decision-making. In particular, we describe systematically the types of externalities that one unit of government can create for nonresidents, through both its public goods decisions and its taxation decisions. The paper also explores briefly what the central government might do to lessen the costs of decentralized decision-making.
TL;DR: Although the model was not motivated by higher nervous function, the system displays behaviours which are strikingly parallel to those needed for the hypothesized role of ‘unlearning’ in rapid eye movement (REM) sleep.
Abstract: Crick and Mitchison have presented a hypothesis for the functional role of dream sleep involving an 'unlearning' process. We have independently carried out mathematical and computer modelling of learning and 'unlearning' in a collective neural network of 30-1,000 neurones. The model network has a content-addressable memory or 'associative memory' which allows it to learn and store many memories. A particular memory can be evoked in its entirety when the network is stimulated by any adequate-sized subpart of the information of that memory. But different memories of the same size are not equally easy to recall. Also, when memories are learned, spurious memories are also created and can also be evoked. Applying an 'unlearning' process, similar to the learning processes but with a reversed sign and starting from a noise input, enhances the performance of the network in accessing real memories and in minimizing spurious ones. Although our model was not motivated by higher nervous function, our system displays behaviours which are strikingly parallel to those needed for the hypothesized role of 'unlearning' in rapid eye movement (REM) sleep.
TL;DR: In this paper, model-coupling equations for the resistive drift-wave instability were derived and numerically solved to study the properties of turbulence near a plasma edge, and the wavenumber spectrum of the turbulence was found to exhibit an inverse cascade to form an isotropic, two-dimensional Kolmogorov spectrum, in the large wave-number regime.
Abstract: Model mode-coupling equations for the resistive drift-wave instability are derived and numerically solved to study the properties of turbulence near a plasma edge. The wavenumber spectrum of the turbulence is found to exhibit an inverse cascade to form an isotropic, two-dimensional Kolmogorov spectrum, ${k}^{\ensuremath{-}3}$, in the large-wave-number regime. The turbulence has a broad frequency spectrum with a large saturation level and produces Bohm-type particle diffusion.
TL;DR: The narrowing of pulses to widths as small as 0.26 psec by various lengths, short relative to the soliton period, of single-mode, low-loss optical fiber is reported to be in at least semiquantitative agreement with prediction based on the nonlinear Schrödinger equation.
Abstract: We report the narrowing of pulses, initially 7 psec FWHM, to widths as small as 0.26 psec by various lengths, short relative to the soliton period, of single-mode, low-loss optical fiber. Since the ~1.5-μm wavelength lies in the region of negative group-velocity dispersion (∂νg/∂λ 10) soliton number. We show these results to be in at least semiquantitative agreement with prediction based on the nonlinear Schrodinger equation.
TL;DR: Gigawatt white-light continuum pulses that permit spectroscopic measurements with a time resolution of 80 fsec are obtained that are consistent with self-phase modulation having a prominent role in generation of the continuum.
Abstract: We obtain gigawatt white-light continuum pulses that permit spectroscopic measurements with a time resolution of 80 fsec. These pulses extend continuously from 0.19 to 1.6 μm and have time sweeps as small as 10 fsec/1000 A. We find temporal, spatial, and spectral properties that are consistent with self-phase modulation having a prominent role in generation of the continuum.
14 Apr 1983
TL;DR: The aim is to determine the extent to which the bit rate of LPC parameters can be reduced without sacrificing speech quality.
Abstract: This paper describes a method for efficient coding of LPC log area parameters. It is now well recognized that sample-by-sample quantization of LPC parameters is not very efficient in minimizing the bit rate needed to code these parameters. Recent methods for reducing the bit rate have used vector and segment quantization methods. Much of the past work in this area has focussed on efficient coding of LPC parameters in the context of vocoders which put a ceiling on achievable speech quality. The results from these studies cannot be directly applied to synthesis of high quality speech. This paper describes a different approach to efficient coding of log area parameters. Our aim is to determine the extent to which the bit rate of LPC parameters can be reduced without sacrificing speech quality. Speech events occur generally at non-uniformly spaced time intervals. Moreover, some speech events are slow while others are fast. Uniform sampling of speech parameters is thus not efficient. We describe a non-uniform sampling and interpolation procedure for efficient coding of log area parameters. A temporal decomposition technique is used to represent the continuous variation of these parameters as a linearly-weighted sum of a number of discrete elementary components. The location and length of each component is automatically adapted to speech events. We find that each elementary component can be coded as a very low information rate signal.
TL;DR: A new data structure is introduced, called the y- fast trie, which uses Θ ( N ) space and log log M) time for range queries on a random access machine.
TL;DR: In this article, a method is described which provides estimates to first order of the number of either power or envirionmenta1 cyc1es 1eading to so1der joint fai1ure.
Abstract: An ana1ytica1 method is described which provides estimates to first order of the number of either power or envirnnmenta1 cyc1es 1eading to so1der joint fai1ure. Vari0us parameter variations such as so1der joint height, ceramic chip carrier (CCC) size, printed c1rcuit substrate (PCS) materia1, etc. are investigated and discussed and samp1e estimates for a 0.65 x 0.65-in CCC are given.
TL;DR: In this paper, it was shown that the additional phase changes also give rise to line shape structure in the form of additional peaks separated from the main peak by multiples of the relaxation oscillation frequency.
Abstract: Spontaneous emission alters the phase and amplitude of the laser field. The amplitude changes induce relaxation oscillations, which cause additional phase changes while restoring the field amplitude to the steady state value. It was previously shown that the additional phase changes greatly enhance the linewidth. We show here that the additional phase changes also give rise to line shape structure in the form of additional peaks separated from the main peak by multiples of the relaxation oscillation frequency. The calculated mean square phase change and power spectrum are in good agreement with published observations.
TL;DR: The silicon molecular beam epitaxy (MBE) technique has only been used in silicon device applications in the last 5 years as discussed by the authors, and it is expected that in the near future silicon MBE will be applied to a much wider range of silicon devices including silicon integrated circuits.
TL;DR: In this article, a taxonomy of kinds of environmental scenes, where perceived attributes are obtained as a byproduct, is presented, based on measures of cognition, behavior, and communication.
TL;DR: In this paper, the authors study theories of preferences under risk that do not use the independence axiom of the von Neumann-Morgenstern theory and show that preferences are transitive.
TL;DR: In this article, the dynamics of the structural changes that take place on a silicon surface following excitation with an intense optical pulse are observed with 90-fs time resolution, and the threefold rotational symmetry of the silicon surface becomes rotationally isotropic within a picosecond after excitation consistent with a transition from the crystalline to the liquid molten state.
Abstract: The dynamics of the structural changes that take place on a silicon surface following excitation with an intense optical pulse are observed with 90-fs time resolution. The threefold rotational symmetry of the silicon $〈111〉$ surface becomes rotationally isotropic within a picosecond after excitation consistent with a transition from the crystalline to the liquid molten state.
TL;DR: In this paper, the authors used the self-consistent, scalar-relativistic, linear augmented plane-wave (LAPW) method and the virtual-crystal approximation.
Abstract: Electronic-structure calculations have been carried out for representative members of the $\mathrm{Ba}{\mathrm{Pb}}_{1\ensuremath{-}x}{\mathrm{Bi}}_{x}{\mathrm{O}}_{3}$ alloy series with the use of the self-consistent, scalar-relativistic, linear augmented plane-wave (LAPW) method and the virtual-crystal approximation. The study includes LAPW calculations for the high-temperature cubic ($x=0,0.3, 1$) as well as the room-temperature tetragonal ($x=0.3$) and monoclinic ($x=1$) phases. The cubic results exhibit nearly-rigid-band---like behavior and feature a ten-band $\mathrm{O}(2p)\ensuremath{-}[\mathrm{Pb}(6s),\mathrm{Bi}(6s)]$ complex near ${E}_{F}$ containing a pair of broad (\ensuremath{\sim}16 eV) $\ensuremath{\sigma}$-bonding $2p\ensuremath{-}6s$ subbands that are approximately centered on nonbonding O $2p$ states. $6s\ensuremath{-}2p$ band overlap and metallic properties are predicted for all $x$ in the cubic phase. The principal features of the cubic band structure survive the tetragonal distortion, predicting a nearly spherical Fermi surface and a low density of states at ${E}_{F}$ in the concentration range $0.05\ensuremath{\le}x\ensuremath{\le}0.30$ where high-temperature superconductivity (${T}_{c}\ensuremath{\approx}13$ K) is observed. A strong Fermi-surface instability is shown to occur in the terminal ($x=1$) BaBi${\mathrm{O}}_{3}$ compound, explaining both the stability of the monoclinic phase as well as its semiconducting properties.