Showing papers by "Bell Labs published in 1981"
TL;DR: In this article, the authors derived a test for the presence of this effect and for the over-identifying restriction they use; necessary and sufficient conditions for identification of all the parameters in the model; and the asymptotically efficient instrumental variables estimator and conditions under which it differs from the within-groups estimator.
2,812 citations
TL;DR: In this paper, it was shown that the quantization of the Hall conductivity of two-dimensional metals is a consequence of gauge invariance and the existence of a mobility gap, and an estimate of the error based on thermal activation of carriers to the mobility edge is suggested.
Abstract: It is shown that the quantization of the Hall conductivity of two-dimensional metals which has been observed recently by Klitzing, Dorda, and Pepper and by Tsui and Gossard is a consequence of gauge invariance and the existence of a mobility gap. Edge effects are shown to have no influence on the accuracy of quantization. An estimate of the error based on thermal activation of carriers to the mobility edge is suggested.
1,905 citations
TL;DR: Research with texture pairs having identical second-order statistics has revealed that the pre-attentive texture discrimination system cannot globally process third- and higher- order statistics, and that discrimination is the result of a few local conspicuous features, called textons.
Abstract: Research with texture pairs having identical second-order statistics has revealed that the pre-attentive texture discrimination system cannot globally process third- and higher-order statistics, and that discrimination is the result of a few local conspicuous features, called textons. It seems that only the first-order statistics of these textons have perceptual significance, and the relative phase between textons cannot be perceived without detailed scrutiny by focal attention.
1,757 citations
TL;DR: In this article, the authors review the development of extended x-ray absorption fine structure (EXAFS) within the last decade and discuss selected examples of applications of EXAFS chosen to illustrate both the strength and limitations of this structural tool.
Abstract: The authors review the development of extended x-ray absorption fine structure (EXAFS) within the last decade. Advances in experimental techniques have been largely stimulated by the availability of synchrotron radiation. The theory of EXAFS has also matured to the point where quantitative comparison with experiments can be made. The authors review in some detail the analysis of EXAFS data, starting from the treatment of raw data to the extraction of distances and amplitude information, and they also discuss selected examples of applications of EXAFS chosen to illustrate both the strength and limitations of EXAFS as a structural tool.
1,507 citations
TL;DR: A frequencydependent quadrature model is proposed whose parameters are obtainable from single-tone measurements and is shown to fit measured data very well.
Abstract: Simple two-parameter formulas are presented for the functions involved in the amplitude-phase and the quadrature nonlinear models of a TWT amplifier, and are shown to fit measured data very well. Also, a closed-form expression is derived for the output signal of a TWT amplifier excited by two phase-modulated carriers, and an expression containing a single integral is given when more than two such earriers are involved. Finally, a frequencydependent quadrature model is proposed whose parameters are obtainable from single-tone measurements.
1,442 citations
TL;DR: In this paper, a theory of the cholesteric blue phase is presented, assuming a first-order Cholesteric-isotropic transition, and it is shown that the planar helix structure becomes unstable at temperatures near the transition point.
Abstract: We present a theory of the cholesteric blue phase, assuming a first-order cholesteric-isotropic transition. We show, on the basis of the Oseen-Frank elasticity equations, that the planar helix structure, generally associated with the cholesteric phase, becomes unstable at temperatures near the transition point. It transforms into a phase characterized by a network of disclination lines.
1,286 citations
TL;DR: In this paper, the authors proposed a heuristic approach for the analysis of the conductivity of a one-dimensional (ID) chain in which Landauer's expression was used.
Abstract: The dc conductance 1 of a finite system with static disorder is related to its transmission matrix t by the simple relation 1 = (e /2nt) Tr(t t). This relation is derived from the Kubo formula and is valid for any number of scattering channels with or without time-reversal symmetry. Differences between various definitions of the conductance of a finite system are discussed. Some time ago Landauer' proposed that the dc conductance I' of noninteracting (spinless) electrons in a disordered medium in strictly one dimension is given by I' = (e'/2vrh) ~ r ~'/~ r (' where t and r are the transmission and reflection amplitudes. A relation of this kind, especially if it can be generalized to higher dimensions, is of great interest for at least two reasons. First, the cost of numerical computation may be greatly reduced compared with the conventional use of the Kubo formula. '~ Second, such a relation emphasizes the fundamental role of the conductance which is assumed to be the only relevant variable in a recent scaling theory treatment of the localization problem. " This point of view was discussed in a recent analysis of the conductivity of a one-dimensional (ID) chain9 in which Landauer's expression was used. The argument given by Landauer is a heuristic one and not easily generalized to higher dimensions.
1,234 citations
TL;DR: This survey summarizes some of the proposed segmentation techniques in the area of biomedical image segmentation, which fall into the categories of characteristic feature thresholding or clustering and edge detection.
1,160 citations
TL;DR: In this article, a series of tables are presented to facilitate rapid determination of the selection rules for vibrational transitions for nuclear site group analysis, where the number of infrared and Raman active modes of each symmetry may be obtained without detailed analysis of the symmetry elements in the crystallographic unit cell or the construction of tables.
Abstract: The group theoretical methods by which the symmetries of normal modes in crystals may be determined are outlined, and a series of tables are presented to facilitate rapid determination of the selection rules for vibrational transitions. Emphasis is placed on the method of nuclear site group analysis in which the number of infrared and Raman active modes of each symmetry may be obtained without detailed analysis of the symmetry elements in the crystallographic unit cell or the construction of tables. By using the tables presented here for most cases identification of the crystallographic space group is sufficient information to allow determination of the vibrational mode selection rules by inspection. Several examples are included in which crystals are analyzed by each of the methods.
1,064 citations
TL;DR: It is shown that, for the important and commonly implemented policy of complete sharing, a simple one-dimensional recursion can be developed which eliminates all difficulty in computing quantities of interest-regardless of both the size and dimensionality of the underlying model.
Abstract: In recent years, considerable effort has focused on evaluating the blocking experienced by "customers" in contending for a commonly shared "resource." The customers and resource in question have typically been messages and storage space in message storage applications or data streams and bandwidth in data multiplexing applications. The model employed in these studies, a multidimensional generalization of the classical Erlang loss model, has been limited to exponentially distributed storage (or data transmission) times, questions concerning efficient computational schemes have largely been ignored, and the class of resource sharing policies considered has been unnecessarily restricted. The contribution of this paper is threefold. We first show that the state distribution (obtained by previous authors) is valid for the large class of residency time distributions which have rational Laplace transforms. Second, we show that, for the important and commonly implemented policy of complete sharing, a simple one-dimensional recursion can be developed which eliminates all difficulty in computing quantities of interest-regardless of both the size and dimensionality of the underlying model. Third, we show that the state distribution holds for completely arbitrary resource sharing policies.
1,029 citations
TL;DR: In this article, a novel passive mode-locking technique was proposed in which two synchronized counterpropagating pulses interact in a thin, saturable absorber to produce a short pulse.
Abstract: We report a novel passive mode‐locking technique in which two synchronized counterpropagating pulses interact in a thin, saturable absorber to produce a short pulse. Continuous stable trains of pulses shorter than 0.1 psec are obtained using a ring laser configuration.
TL;DR: In this article, it is argued that for the chain-store game the decision-analytic approach leads, under certain assumptions, to more realistic outcomes than the standard Nash-equilibrium approach.
11 May 1981
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.
Abstract: We propose a data structure to maintain a collection of vertex-disjoint trees under a sequence of two kinds of operations: a link operation that combines two trees into one by adding an edge, and a cut operation that divides one tree into two by deleting an edge. Our data structure requires O(log n) time per operation when the time is amortized over a sequence of operations. Using our data structure, we obtain new fast algorithms for the following problems: (1) Computing deepest common ancestors. (2) Solving various network flow problems including finding maximum flows, blocking flows, and acyclic flows. (3) Computing certain kinds of constrained minimum spanning trees. (4) Implementing the network simplex algorithm for the transshipment problem. Our most significant application is (2); we obtain an O(mn log n)-time algorithm 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.
TL;DR: In this article, a detailed structural model for covalent non-crystalline solids with order over distances of 15-30 A is presented. But this model is restricted to solids containing 30-1000 atoms.
Abstract: Characteristic order over distances of 15–30 A is indicated by various experiments on covalent non-crystalline solids. The data are reviewed and detailed structural models are developed containing 30–1000 atoms.
01 Mar 1981
TL;DR: This paper presents a tutorial overview of multirate digital signal processing as applied to systems for decimation and interpolation and discusses a theoretical model for such systems (based on the sampling theorem), and shows how various structures can be derived to provide efficient implementations of these systems.
Abstract: The concepts of digital signal processing are playing an increasingly important role in the area of multirate signal processing, i.e. signal processing algorithms that involve more than one sampling rate. In this paper we present a tutorial overview of multirate digital signal processing as applied to systems for decimation and interpolation. We first discuss a theoretical model for such systems (based on the sampling theorem) and then show how various structures can be derived to provide efficient implementations of these systems. Design techniques for the linear-time-invariant components of these systems (the digital filter) are discussed, and finally the ideas behind multistage implementations for increased efficiency are presented.
TL;DR: In this paper, the authors discuss the theory and experiments dealing with the pulsed optoacoustic effect (i.e., generation of a transient acoustic wave by absorption of an optical pulse) in condensed matter.
Abstract: The authors discuss the theory and experiments dealing with the pulsed optoacoustic effect (i.e., generation of a transient acoustic wave by absorption of an optical pulse) in condensed matter. Their primary interest lies in the measurement of small absorption coefficients (\ensuremath{\ll}${10}^{\ensuremath{-}1}$ ${\mathrm{cm}}^{\ensuremath{-}1}$). At present an experimental capability of measuring absorption coefficients as small as ${10}^{\ensuremath{-}6}$ ${\mathrm{cm}}^{\ensuremath{-}1}$ has been demonstrated, and further improvement is foreseen. The pulsed optoacoustic absorption measurement technique has been applied to the following linear spectroscopic studies: (1) precise measurements of the optical absorption spectra of ${\mathrm{H}}_{2}$O and ${\mathrm{D}}_{2}$O; (b) accurate determination of absorption strengths and profiles of high harmonics ($n=6, 7, \mathrm{and} 8$) of vibrational modes in transparent organic liquids (e.g., benzene); (c) quantitative absorption spectra of thin (\ensuremath{\sim} 1-10 \ensuremath{\mu}m) liquid films; and (d) quantitative absorption spectra of solids and finely powdered crystals. The usefulness of the pulsed optoacoustic technique to nonlinear spectroscopy has been demonstrated in the following studies: (a) quantitative two-photon absorption spectroscopy of the weak two-photon ($^{1}B_{2\ensuremath{\mu}}\ensuremath{\leftarrow}^{1}A_{1g}$) transition in benzene; and (b) optoacoustic Raman-gain spectra for a variety of liquids where an ability to measure Raman gains as small as ${10}^{\ensuremath{-}5}$ ${\mathrm{cm}}^{\ensuremath{-}1}$ has been demonstrated. In addition to reviewing the above studies the authors discuss future possible applications and compare the pulsed optoacoustic spectroscopy technique with other optoacoustic absorption measurement techniques.
TL;DR: In this article, the authors derived the asymptotic distribution of their test under sequences of contiguous alternatives to the null hypothesis of homoscedasticity, and proposed a modification of the test which corrects this defect.
TL;DR: This paper infer the details of individual programmers’ chunks of key programming concepts using the Reitman-Rtreter technique for inferring tree structures from recall orders.
TL;DR: In this paper, the nature of random coupling between normal modes of polarization is analyzed and discussed in connection with various applications, such as fibers with very small or very large birefringence for polarization dependent applications.
Abstract: Recent research on fibers with very small or very large birefringence for polarization-dependent applications is reviewed. The nature of random coupling between normal modes of polarization is analyzed and discussed in connection with various applications.
TL;DR: In this paper, the conductance for a two-dimensional tight-binding model with on-site disorder is calculated numerically with use of the Kubo formula. And the magnetoresistance is found to be negative in both the logarithmic and exponential localization regimes.
Abstract: The conductance for a two-dimensional tight-binding model with on-site disorder is calculated numerically with use of the Kubo formula. For weak disorder logarithmic localization is observed, in agreement with the scaling theory. The magnetoresistance is found to be negative in both the logarithmic and exponential localization regimes. Results for a model with random complex hopping matrix elements are also presented.
TL;DR: The key notion of the correlation of two strings is introduced, which is a representation of how the second string can overlap into the first, and this notion is used to state and prove a formula for the generating function that enumerates the q -ary strings of length n which contain none of a given finite set of patterns.
TL;DR: In this paper, the authors considered the problem of estimating a diffusion in independent Wiener processes by solving the stochastic DE dx t =f(x t )dt+dw t on the basis of noisy observations defined bydy t =x t dt+db t.
Abstract: Let and be independent Wiener processes, and consider the task of estimating a diffusion solving the stochastic DE dx t =f(x t )dt+dw t on the basis of noisy observations defined bydy t =x t dt+db t . This problem is governed by the filtering equation for the unnormalized conditional density with A * the forwarded operator Theorem: if then the fundamental solution of the filtering equation can be written explicity in terms of a small number of statistics satisfying a matrixvector equation. The Lie algebraic interpretation of this result is studied and described. Extensions to many dimensions and applications to optimal stochastic control readily follow.
TL;DR: This paper describes some of the features of POSSE (Product Optimization and Selected Segment Evaluation), a general procedure for optimizing product/service designs in marketing research that uses input data based on conjoint analysis methods.
Abstract: This paper describes some of the features of POSSE (Product Optimization and Selected Segment Evaluation), a general procedure for optimizing product/service designs in marketing research. The appr...
TL;DR: A hybrid end-point detector is proposed which gives a rejection rate of less than 0.5 percent, while providing recognition accuracy close to that obtained from hand-edited endpoints.
Abstract: Accurate location of the endpoints of an isolated word is important for reliable and robust word recognition. The endpoint detection problem is nontrivial for nonstationary backgrounds where artifacts (i.e., nonspeech events) may be introduced by the speaker, the recording environment, and the transmission system. Several techniques for the detection of the endpoints of isolated words recorded over a dialed-up telephone line were studied. The techniques were broadly classified as either explicit, implicit, or hybrid in concept. The explicit techniques for endpoint detection locate the endpoints prior to and independent of the recognition and decision stages of the system. For the implicit methods, the endpoints are determined solely by the recognition and decision stages of the system, i.e., there is no separate stage for endpoint detection. The hybrid techniques incorporate aspects from both the explicit and implicit methods. Investigations showed that the hybrid techniques consistently provided the best estimates for both of the word endpoints and, correspondingly, the highest recognition accuracy of the three classes studied. A hybrid end-point detector is proposed which gives a rejection rate of less than 0.5 percent, while providing recognition accuracy close to that obtained from hand-edited endpoints.
TL;DR: In this article, the light and heavy-hole two-dimensional exciton term values are determined directly from the excitation spectra of GaAs-${\mathrm{Al}}_{x}{\mathrm-Ga}}_{1\ensuremath{-}x}\mathrm {As}$ heterostructures with GaAs well widths from 42 to 145 \AA{}.
Abstract: The light- and heavy-hole two-dimensional exciton term values are determined directly from the excitation spectra of GaAs-${\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}$ heterostructures with GaAs well widths $L$ from 42 to 145 \AA{}. these values are in excellent agreement with a theoretical model which contains no adjustable parameters. This theory also gives integrated strengths for the excitons which agree with experiment, and ground-state binding energies as a function of $L$.
TL;DR: In this article, the electromigration resistance of Al-0.5%Cu meander lines was found to increase with increasing grain size s and degree of {111} preferred orientation and with decreasing spread σ in the grain size distribution.
TL;DR: In this paper, a systematic increase of the linewidth of luminescence, absorption and excitation spectra of undoped GaAs-Ga 1-x A l x As Multi-Quantum structures with decreasing layer thickness was reported.
01 Sep 1981
TL;DR: In this article, a transmission rate of ≃1 Tbits/sec (≃0.1 T bits/s) per 30 km can be achieved using envelope solitons with peak power of approximately 10 W in a monomode optical fiber, respectively.
Abstract: A transmission rate of ≃1 Tbits/sec (≃0.1 Tbits/s) per 30 km can be achieved using envelope solitons with peak power of ≃10 W (≃10 mW) in a monomode optical fiber, respectively. Unlike the linear pulse in which the bit rate is limited by the group dispersion, the bit rate of soliton transmission is limited by the fiber loss and the input power. Conditions for achieving optimum transmission rate using solitons are theoretically obtained including the effects of fiber loss and second order group dispersion.
TL;DR: Theory and practice of plasma etching are reviewed in this article, and some unifying principles are extended to explain a large body of experimental data, encompassing more than 20 substrate materials in dozens of etchant gas mixtures.
Abstract: Theory and practice of plasma etching are critically reviewed. Some unifying principles are extended to explain a large body of experimental data, encompassing more than 20 substrate materials in dozens of etchant gas mixtures. These basic concepts can be used to select new etchants and plasma etching parameters.