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Showing papers by "Bell Labs published in 1995"


Book
Vladimir Vapnik1
01 Jan 1995
TL;DR: Setting of the learning problem consistency of learning processes bounds on the rate of convergence ofLearning processes controlling the generalization ability of learning process constructing learning algorithms what is important in learning theory?
Abstract: Setting of the learning problem consistency of learning processes bounds on the rate of convergence of learning processes controlling the generalization ability of learning processes constructing learning algorithms what is important in learning theory?.

40,147 citations


Journal ArticleDOI
TL;DR: High generalization ability of support-vector networks utilizing polynomial input transformations is demonstrated and the performance of the support- vector network is compared to various classical learning algorithms that all took part in a benchmark study of Optical Character Recognition.
Abstract: The support-vector network is a new learning machine for two-group classification problems. The machine conceptually implements the following idea: input vectors are non-linearly mapped to a very high-dimension feature space. In this feature space a linear decision surface is constructed. Special properties of the decision surface ensures high generalization ability of the learning machine. The idea behind the support-vector network was previously implemented for the restricted case where the training data can be separated without errors. We here extend this result to non-separable training data. High generalization ability of support-vector networks utilizing polynomial input transformations is demonstrated. We also compare the performance of the support-vector network to various classical learning algorithms that all took part in a benchmark study of Optical Character Recognition.

37,861 citations


Book ChapterDOI
William W. Cohen1
09 Jul 1995
TL;DR: This paper evaluates the recently-proposed rule learning algorithm IREP on a large and diverse collection of benchmark problems, and proposes a number of modifications resulting in an algorithm RIPPERk that is very competitive with C4.5 and C 4.5rules with respect to error rates, but much more efficient on large samples.
Abstract: Many existing rule learning systems are computationally expensive on large noisy datasets. In this paper we evaluate the recently-proposed rule learning algorithm IREP on a large and diverse collection of benchmark problems. We show that while IREP is extremely efficient, it frequently gives error rates higher than those of C4.5 and C4.5rules. We then propose a number of modifications resulting in an algorithm RIPPERk that is very competitive with C4.5rules with respect to error rates, but much more efficient on large samples. RIPPERk obtains error rates lower than or equivalent to C4.5rules on 22 of 37 benchmark problems, scales nearly linearly with the number of training examples, and can efficiently process noisy datasets containing hundreds of thousands of examples.

4,081 citations


Journal ArticleDOI
Peter W. Shor1
TL;DR: In the mid-1990s, theorists devised methods to preserve the integrity of quantum bits\char22{}techniques that may become the key to practical quantum computing on a large scale.
Abstract: In the mid-1990s, theorists devised methods to preserve the integrity of quantum bits---techniques that may become the key to practical quantum computing on a large scale.

3,668 citations


Proceedings ArticleDOI
Tin Kam Ho1
14 Aug 1995
TL;DR: In this article, the authors proposed a method to construct tree-based classifiers whose capacity can be arbitrarily expanded for increases in accuracy for both training and unseen data, which can be monotonically improved by building multiple trees in different subspaces of the feature space.
Abstract: Decision trees are attractive classifiers due to their high execution speed. But trees derived with traditional methods often cannot be grown to arbitrary complexity for possible loss of generalization accuracy on unseen data. The limitation on complexity usually means suboptimal accuracy on training data. Following the principles of stochastic modeling, we propose a method to construct tree-based classifiers whose capacity can be arbitrarily expanded for increases in accuracy for both training and unseen data. The essence of the method is to build multiple trees in randomly selected subspaces of the feature space. Trees in, different subspaces generalize their classification in complementary ways, and their combined classification can be monotonically improved. The validity of the method is demonstrated through experiments on the recognition of handwritten digits.

2,957 citations


Book
01 Mar 1995
TL;DR: Wavelets and Subband Coding offered a unified view of the exciting field of wavelets and their discrete-time cousins, filter banks, or subband coding and developed the theory in both continuous and discrete time.
Abstract: First published in 1995, Wavelets and Subband Coding offered a unified view of the exciting field of wavelets and their discrete-time cousins, filter banks, or subband coding. The book developed the theory in both continuous and discrete time, and presented important applications. During the past decade, it filled a useful need in explaining a new view of signal processing based on flexible time-frequency analysis and its applications. Since 2007, the authors now retain the copyright and allow open access to the book.

2,793 citations


Journal ArticleDOI
TL;DR: It is proposed that in addition to double-exchange physics a strong electron-phonon interaction arising from the Jahn-Teller splitting of the outer Mn $d$ level plays a crucial role.
Abstract: The ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{MnO}}_{3}$ system with $02\ensuremath{\lesssim}x\ensuremath{\lesssim}04$ has traditionally been modeled with a ``double-exchange'' Hamiltonian in which it is assumed that the only relevant physics is the tendency of carrier hopping to line up neighboring spins We present a solution of the double-exchange model, show it is incompatible with many aspects of the data, and propose that in addition to double-exchange physics a strong electron-phonon interaction arising from the Jahn-Teller splitting of the outer Mn $d$ level plays a crucial role

2,302 citations


Journal ArticleDOI
TL;DR: A general framework for the formal specification and algorithmic analysis of hybrid systems is presented, which considers symbolic model-checking and minimization procedures that are based on the reachability analysis of an infinite state space.

2,091 citations


Journal ArticleDOI
TL;DR: An unexpectedly large magnetoresistance is seen at low temperatures in the FM phase, and is largely attributed to unusual domain wall scattering.
Abstract: The complete phase diagram of a ``colossal'' magnetoresistance material ( ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x}{\mathrm{MnO}}_{3}$) was obtained for the first time through magnetization and resistivity measurements over a broad range of temperatures and concentrations. Near $x\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.50$, the ground state changes from a ferromagnetic (FM) conductor to an antiferromagnetic (AFM) insulator, leading to a strongly first order AFM transition with supercooling of $\ensuremath{\sim}30%$ ${T}_{N}$ at $x\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.50$. An unexpectedly large magnetoresistance is seen at low temperatures in the FM phase, and is largely attributed to unusual domain wall scattering.

1,782 citations


Journal ArticleDOI
TL;DR: The results show that the notion of ``double exchange'' must be generalized to include changes in the Mn-Mn electronic hopping parameter as a result of changes inThe Mn-O-Mm bond angle.
Abstract: A detailed study of doped LaMn${\mathrm{O}}_{3}$ with fixed carrier concentration reveals a direct relationship between the Curie temperature ${T}_{c}$ and the average ionic radius of the La site $〈{r}_{A}〉$, which is varied by substituting different rare earth ions for La. With decreasing $〈{r}_{A}〉$, magnetic order and significant magnetoresistance occur at lower temperatures with increasing thermal hysteresis, and the magnitude of the magnetoresistance increases dramatically. These results show that the notion of ``double exchange'' must be generalized to include changes in the Mn-Mn electronic hopping parameter as a result of changes in the Mn-O-Mn bond angle.

1,654 citations


Journal ArticleDOI
Yoav Freund1
TL;DR: An algorithm for improving the accuracy of algorithms for learning binary concepts by combining a large number of hypotheses, each of which is generated by training the given learning algorithm on a different set of examples, is presented.
Abstract: We present an algorithm for improving the accuracy of algorithms for learning binary concepts. The improvement is achieved by combining a large number of hypotheses, each of which is generated by training the given learning algorithm on a different set of examples. Our algorithm is based on ideas presented by Schapire and represents an improvement over his results, The analysis of our algorithm provides general upper bounds on the resources required for learning in Valiant′s polynomial PAC learning framework, which are the best general upper bounds known today. We show that the number of hypotheses that are combined by our algorithm is the smallest number possible. Other outcomes of our analysis are results regarding the representational power of threshold circuits, the relation between learnability and compression, and a method for parallelizing PAC learning algorithms. We provide extensions of our algorithms to cases in which the concepts are not binary and to the case where the accuracy of the learning algorithm depends on the distribution of the instances.

Journal ArticleDOI
B. B. Hu1, Martin C. Nuss1
TL;DR: This work presents what is to their knowledge the first imaging system based on optoelectronic terahertz time-domain spectroscopy, and demonstrates applications to package inspection and chemical content mapping in biological objects.
Abstract: We present what is to our knowledge the first imaging system based on optoelectronic terahertz time-domain spectroscopy Terahertz time-domain waveforms are downconverted from the terahertz to the kilohertz frequency range, and the waveform for each pixel is frequency analyzed in real time with a digital signal processor to extract compositional information at that point We demonstrate applications to package inspection and chemical content mapping in biological objects

Journal ArticleDOI
TL;DR: The magnetic moments determined from the integrals of these spectra are found to be in excellent agreement (within 3%) for the orbital to spin moment ratios, and in good agreement for the individual moments, with those obtained from Einstein--de Haas gyromagnetic ratio measurements.
Abstract: High precision, $L$${}_{2,3}$-edge photoabsorption and magnetic circular dichroism spectra of iron and cobalt were measured in transmission with in situ grown thin films, eliminating experimental artifacts encountered by the indirect methods used in all previous measurements. The magnetic moments determined from the integrals of these spectra are found to be in excellent agreement (within 3%) for the orbital to spin moment ratios, and in good agreement (within 7%) for the individual moments, with those obtained from Einstein--de Haas gyromagnetic ratio measurements, demonstrating decisively the applicability of the individual orbital and spin sum rules.

Journal ArticleDOI
TL;DR: In this article, the Lanczos process is used to compute the Pade approximation of Laplace-domain transfer functions of large linear networks via a Lanczos Process (PVL) algorithm.
Abstract: In this paper, we introduce PVL, an algorithm for computing the Pade approximation of Laplace-domain transfer functions of large linear networks via a Lanczos process. The PVL algorithm has significantly superior numerical stability, while retaining the same efficiency as algorithms that compute the Pade approximation directly through moment matching, such as AWE and its derivatives. As a consequence, it produces more accurate and higher-order approximations, and it renders unnecessary many of the heuristics that AWE and its derivatives had to employ. The algorithm also computes an error bound that permits to identify the true poles and zeros of the original network. We present results of numerical experiments with the PVL algorithm for several large examples. >

Journal ArticleDOI
Colin L. Mallows1
TL;DR: In this paper, the interpretation of C p -plots and how they can be calibrated in several ways are discussed, including using the display as a basis for formal selection of a subset-regression model and extending the range of application of the device to encompass arbitrary linear estimates of the regression coefficients.
Abstract: We discuss the interpretation of C p -plots and show how they can be calibrated in several ways. We comment on the practice of using the display as a basis for formal selection of a subset-regression model, and extend the range of application of the device to encompass arbitrary linear estimates of the regression coefficients, for example Ridge estimates.

Journal ArticleDOI
Frank H. Stillinger1
31 Mar 1995-Science
TL;DR: Various static and dynamic phenomena displayed by glass-forming liquids, particularly those near the so-called "fragile" limit, emerge as manifestations of the multidimensional complex topography of the collective potential energy function.
Abstract: Various static and dynamic phenomena displayed by glass-forming liquids, particularly those near the so-called "fragile" limit, emerge as manifestations of the multidimensional complex topography of the collective potential energy function. These include non-Arrhenius viscosity and relaxation times, bifurcation between the α- and β-relaxation processes, and a breakdown of the Stokes-Einstein relation for self-diffusion. This multidimensional viewpoint also produces an extension of the venerable Lindemann melting criterion and provides a critical evaluation of the popular "ideal glass state" concept.

Proceedings ArticleDOI
22 May 1995
TL;DR: A fast algorithm to map objects into points in some k-dimensional space (k is user-defined), such that the dis-similarities are preserved, and this method is introduced from pattern recognition, namely, Multi-Dimensional Scaling (MDS).
Abstract: A very promising idea for fast searching in traditional and multimedia databases is to map objects into points in k-d space, using k feature-extraction functions, provided by a domain expert [25]. Thus, we can subsequently use highly fine-tuned spatial access methods (SAMs), to answer several types of queries, including the 'Query By Example' type (which translates to a range query); the 'all pairs' query (which translates to a spatial join [8]); the nearest-neighbor or best-match query, etc.However, designing feature extraction functions can be hard. It is relatively easier for a domain expert to assess the similarity/distance of two objects. Given only the distance information though, it is not obvious how to map objects into points.This is exactly the topic of this paper. We describe a fast algorithm to map objects into points in some k-dimensional space (k is user-defined), such that the dis-similarities are preserved. There are two benefits from this mapping: (a) efficient retrieval, in conjunction with a SAM, as discussed before and (b) visualization and data-mining: the objects can now be plotted as points in 2-d or 3-d space, revealing potential clusters, correlations among attributes and other regularities that data-mining is looking for.We introduce an older method from pattern recognition, namely, Multi-Dimensional Scaling (MDS) [51]; although unsuitable for indexing, we use it as yardstick for our method. Then, we propose a much faster algorithm to solve the problem in hand, while in addition it allows for indexing. Experiments on real and synthetic data indeed show that the proposed algorithm is significantly faster than MDS, (being linear, as opposed to quadratic, on the database size N), while it manages to preserve distances and the overall structure of the data-set.

Journal ArticleDOI
14 Apr 1995-Science
TL;DR: The thiophene oligomer α-hexathienylene (α-6T) has been successfully used as the active semiconducting material in thin-film transistors and optimized methods of device fabrication have resulted in high field-effect mobilities and on/off current ratios of > 106.
Abstract: The thiophene oligomer α-hexathienylene (α-6T) has been successfully used as the active semiconducting material in thin-film transistors. Field-induced conductivity in thin-film transistors with α-6T active layers occurs only near the interfacial plane, whereas the residual conductivity caused by unintentional doping scales with the thickness of the layer. The two-dimensional nature of the field-induced conductivity is due not to any anisotropy in transport with respect to any molecular axis but to interface effects. Optimized methods of device fabrication have resulted in high field-effect mobilities and on/off current ratios of > 106. The current densities and switching speeds are good enough to allow consideration of these devices in practical large-area electronic circuits.

Journal ArticleDOI
27 Jan 1995-Science
TL;DR: The phenomenology of these patterns, and of the shapes of their constituent domains, is reviewed here from a point of view that interprets these patterns as a manifestation of modulated phases.
Abstract: A wide variety of two- and three-dimensional physical-chemical systems display domain patterns in equilibrium. The phenomenology of these patterns, and of the shapes of their constituent domains, is reviewed here from a point of view that interprets these patterns as a manifestation of modulated phases. These phases are stabilized by competing interactions and are characterized by periodic spatial variations of the pertinent order parameter, the corresponding modulation period generally displaying a dependence on temperature and other external fields. This simple picture provides a unifying framework to account for striking and substantial similarities revealed in the prevalent "stripe" and "bubble" morphologies as well as in commonly observed, characteristic domain-shape instabilities. Several areas of particular current interest are discussed.

Journal ArticleDOI
Rafael Yuste1, Winfried Denk1
22 Jun 1995-Nature
TL;DR: In this paper, the authors used two-photon microscopy to image fluorescence with high resolution in strongly scattering tissue, and measured calcium dynamics in spines from CA1 pyramidal neurons in slices of rat hippocampus.
Abstract: Most excitatory synaptic connections occur on dendritic spines. Calcium imaging experiments have suggested that spines constitute individual calcium compartments, but recent results have challenged this idea. Using two-photon microscopy to image fluorescence with high resolution in strongly scattering tissue, we measured calcium dynamics in spines from CA1 pyramidal neurons in slices of rat hippocampus. Subthreshold synaptic stimulation and spontaneous synaptic events produced calcium accumulations that were localized to isolated spines, showed stochastic failure, and were abolished by postsynaptic blockers. Single somatic spikes induced fast-peaking calcium accumulation in spines throughout the cell. Pairing of spikes with synaptic stimulation was frequently cooperative, that is, it resulted in supralinear calcium accumulations. We conclude: (1) calcium channels exist in spine heads; (2) action potentials invade the spines; (3) spines are individual calcium compartments; and (4) spines can individually detect the temporal coincidence of pre- and postsynaptic activity, and thus serve as basic functional units of neuronal integration.

Proceedings ArticleDOI
01 Oct 1995
TL;DR: This paper provides a plausible physical explanation for the occurrence of self-similarity in high-speed network traffic based on convergence results for processes that exhibit high variability and is supported by detailed statistical analyses of real-time traffic measurements from Ethernet LAN's at the level of individual sources.
Abstract: A number of recent empirical studies of traffic measurements from a variety of working packet networks have convincingly demonstrated that actual network traffic is self-similar or long-range dependent in nature (i.e., bursty over a wide range of time scales) - in sharp contrast to commonly made traffic modeling assumptions. In this paper, we provide a plausible physical explanation for the occurrence of self-similarity in high-speed network traffic. Our explanation is based on convergence results for processes that exhibit high variability (i.e., infinite variance) and is supported by detailed statistical analyses of real-time traffic measurements from Ethernet LAN's at the level of individual sources.Our key mathematical result states that the superposition of many ON/OFF sources (also known as packet trains) whose ON-periods and OFF-periods exhibit the Noah Effect (i.e., have high variability or infinite variance) produces aggregate network traffic that features the Joseph Effect (i.e., is self-similar or long-range dependent). There is, moreover, a simple relation between the parameters describing the intensities of the Noah Effect (high variability) and the Joseph Effect (self-similarity). An extensive statistical analysis of two sets of high time-resolution traffic measurements from two Ethernet LAN's (involving a few hundred active source-destination pairs) confirms that the data at the level of individual sources or source-destination pairs are consistent with the Noah Effect. We also discuss implications of this simple physical explanation for the presence of self-similar traffic patterns in modern high-speed network traffic for (i) parsimonious traffic modeling (ii) efficient synthetic generation of realistic traffic patterns, and (iii) relevant network performance and protocol analysis.

Proceedings ArticleDOI
27 Jun 1995
TL;DR: A model for analyzing software rejuvenation in continuously-running applications is presented and express downtime and costs due to downtime during rejuvenations in terms of the parameters in that model and Threshold conditions for rejuvenation to be beneficial are derived.
Abstract: Software rejuvenation is the concept of gracefully terminating an application and immediately restarting it at a clean internal state. In a client-server type of application where the server is intended to ran perpetually for providing a service to its clients, rejuvenating the server process periodically during the most idle time of the server increases the availability of that service. In a long-running computation-intensive application, rejuvenating the application periodically and restarting it at a previous checkpoint increases the likelihood of successfully completing the application execution. We present a model for analyzing software rejuvenation in such continuously-running applications and express downtime and costs due to downtime during rejuvenation in terms of the parameters in that model. Threshold conditions for rejuvenation to be beneficial are also derived. We implemented a reusable module to perform software rejuvenation. That module can be embedded in any existing application on a UNIX platform with minimal effort. Experiences with software rejuvenation in a billing data collection subsystem of a telecommunications operations system and other continuously-running systems and scientific applications in AT&T are described. >

Book
Robert P. Kurshan1
06 Feb 1995
TL;DR: Theories of L-automaton/L-process, L-matrix, and String Acceptors are compared to Boolean Algebra, which describes the construction of language-based Algebra.
Abstract: Preface Introduction 2 Boolean Algebra 3 L-matrix 4 L-language 5 String Acceptors 6 [omega]-theory: L-automaton/L-process 7 The Selection/Resolution Model 8 Reduction of Verification 9 Structural Induction 10 Binary Decision Diagrams Appendices Bibliography Glossary Index


Book ChapterDOI
01 Jun 1995
TL;DR: A tableau-based algorithm for obtaining an automaton from a temporal logic formula that can be constructed simultaneously with, and guided by, the generation of the model, and which can be used in model checking in an “on-the-fly” fashion.
Abstract: We present a tableau-based algorithm for obtaining an automaton from a temporal logic formula. The algorithm is geared towards being used in model checking in an “on-the-fly” fashion, that is the automaton can be constructed simultaneously with, and guided by, the generation of the model. In particular, it is possible to detect that a property does not hold by only constructing part of the model and of the automaton. The algorithm can also be used to check the validity of a temporal logic assertion. Although the general problem is PSPACE-complete, experiments show that our algorithm performs quite well on the temporal formulas typically encountered in verification. While basing linear-time temporal logic model-checking upon a transformation to automata is not new, the details of how to do this efficiently, and in “on-the-fly” fashion have never been given.

Proceedings ArticleDOI
Brenda S. Baker1
14 Jul 1995
TL;DR: A program called dup can be used to locate instances of duplication or near-duplication in a software system and is shown to be both effective at locating duplication and fast.
Abstract: This paper describes how a program called dup can be used to locate instances of duplication or near-duplication in a software system. Dup reports both textually identical sections of code and sections that are the same textually except for systematic substitution of one set of variable names and constants for another. Further processing locates longer sections of code that are the same except for other small modifications. Experimental results from running dup on millions of lines from two large software systems show dup to be both effective at locating duplication and fast. Applications could include identifying sections of code that should be replaced by procedures, elimination of duplication during reengineering of the system, redocumentation to include references to copies, and debugging.

Journal ArticleDOI
TL;DR: This work determines the complexity of testing whether a finite state, sequential or concurrent probabilistic program satisfies its specification expressed in linear-time temporal logic and addresses questions for specifications described by ω-automata or formulas in extended temporal logic.
Abstract: We determine the complexity of testing whether a finite state, sequential or concurrent probabilistic program satisfies its specification expressed in linear-time temporal logic. For sequential programs, we present an algorithm that runs in time linear in the program and exponential in the specification, and also show that the problem is in PSPACE, matching the known lower bound. For concurrent programs, we show that the problem can be solved in time polynomial in the program and doubly exponential in the specification, and prove that it is complete for double exponential time. We also address these questions for specifications described by o-automata or formulas in extended temporal logic.

Journal ArticleDOI
28 Jul 1995-Science
TL;DR: In this model, the fluctuations in the force distribution arise because of variations in the contact angles and the constraints imposed by the force balance on each bead in the pile.
Abstract: Experimental observations and numerical simulations of the large force inhomogeneities present in stationary bead packs are presented. Forces much larger than the mean occurred but were exponentially rare. An exactly soluble model reproduced many aspects of the experiments and simulations. In this model, the fluctuations in the force distribution arise because of variations in the contact angles and the constraints imposed by the force balance on each bead in the pile.

Proceedings Article
20 Aug 1995
TL;DR: It is observed that three different types of handwritten digit classifiers construct their decision surface from strongly overlapping small subsets of the data base, which opens up the possibility of compressing data bases significantly by disposing of theData which is not important for the solution of a given task.
Abstract: We report a novel possibility for extracting a small subset of a data base which contains all the information necessary to solve a given classification task: using the Support Vector Algorithm to train three different types of handwritten digit classifiers, we observed that these types of classifiers construct their decision surface from strongly overlapping small (≈ 4%) subsets of the data base. This finding opens up the possibility of compressing data bases significantly by disposing of the data which is not important for the solution of a given task. In addition, we show that the theory allows us to predict the classifier that will have the best generalization ability, based solely on performance on the training set and characteristics of the learning machines. This finding is important for cases where the amount of available data is limited.

Journal ArticleDOI
TL;DR: This work shows how current TCP implementations introduce unacceptably long pauses in communication during cellular handoffs, and proposes an end-to-end fast retransmission scheme that can reduce these pauses to levels more suitable for human interaction.
Abstract: We explore the performance of reliable data communication in mobile computing environments. Motion across wireless cell boundaries causes increased delays and packet losses while the network learns how to route data to a host's new location. Reliable transport protocols like TCP interpret these delays and losses as signs of network congestion. They consequently throttle their transmissions, further degrading performance. We quantify this degradation through measurements of protocol behavior in a wireless networking testbed. We show how current TCP implementations introduce unacceptably long pauses in communication during cellular handoffs (800 ms and longer), and propose an end-to-end fast retransmission scheme that can reduce these pauses to levels more suitable for human interaction (200 ms). Our work makes clear the need for reliable transport protocols to differentiate between motion-related and congestion-related packet losses and suggests how to adapt these protocols to perform better in mobile computing environments. >