bluuebunny/crossref_metadata_2025_split huggingface dataset:
ISING SPIN GLASS: RECENT PROGRESS IN THE FIELD THEORY APPROACH
Authors: DOMINICIS C. DE , KONDOR I. , TEMESVARI T. 
Published: November 2004

A loop expansion around Parisi's replica symmetry breaking mean field theory is constructed, in zero field. We obtain the equation of state (and associated Parisi's solution) below the upper critical dimension du=6, and, in particular, explicit corrections in εlnt and (εlnt)2 with t=(Tc−T)/Tc and ε=6−d. This allows us to verify that standard scaling is satisfied with β=1+ε/2+0(ε2). We have also investigated the transverse (replicon) correlation function, particularly at zero overlap. Near du, G00 (p) ~ t/P4 (for p~0) is the most obvious obstacle to a meaningful theory in d=3. If we make the twofold assumption that (i) scaling applies, and (ii) the replicon propagator is dominated by the spectrum of the (small) transverse masses, we obtain the softer behavior G00(p) ~ (1/p2–η). (t/p1/v)β and a prediction for a soft replicon spectrum in tγk2γ/β γ/β instead of tk2 at du. We have checked tγ to one loop and work is in progress to check k2γ/β to the same order. Taking the above divergence in p−(d+2−η)/2 as the leading divergence defines the lower critical dimension d ℓ by d ℓ=2−η (d ℓ). Known values of η (at d=6, from the ε expansion at Tc, or from numerical work at d=4, 3) are compatible with d ℓ ~ 2.5±.3.
MEAN FIELD APPROXIMATION FOR ANYONS IN A MAGNETIC FIELD
Authors: WESTERBERG ERIK 
Published: November 2004

The mean field equations for anyons in an external homogeneous magnetic field are studied and two classes of mean field solutions are explicitly constructed. The first class of solutions, corresponding to one filled Landau level in the combined external and smeared out statistical magnetic fields, is compared to the corresponding exact groundstate solutions. The energies are found to agree well at low densities and when the statistical field is not too strong compared to the background field. At high densities the fermi pressure increases the mean field energy indefinitely. The mean field solutions also miss the lower part of the energy spectrum. To the second class of mean field solutions no corresponding anyon state is known. These solutions represent the anyonic continuation of the fermi state with two filled Landau levels.
CHAOS AND COMPLEXITY IN ABNORMAL OSCILLATIONS OF TWO EXCITABLE NEURONS AND A 2D NETWORK MODEL COUPLED VIA GAP JUNCTIONS
Authors: GE MANLING , GUO HONGYONG , SUN MINGUI , GUSPHYL JUSTIN , DONG GUOYA , ZHAO TONGJUN , YAN WEILI 
Published: November 2004

Many electrophysiological experiments have shown that epileptic seizures often originate from the synchronous activities of abnormally excitable neurons. The dynamic process of epilepsy is very complex, and characterized by a seemingly rapid and dramatic birth of new oscillations, essentially leading to a propagation and amplification of the original aberrant activity. It is very difficult to thoroughly understand the mechanism from a theoretical standpoint, however some special work can prove helpful. Here we present a theoretical framework to investigate chaos and complexity in the synchrony of excitable neurons in an effort to study the collective oscillations within a neural network. As endogenous rhythms, oscillations arise because most cellular processes contain feedback. The Chay model of excitable neurons is chosen because the model describes the abnormal process, where spiking can be transformed into bursting via bifurcation. In our study, the Chay model is regarded as an abnormal oscillator and coupled via a resistor representing the effect of gap junctions (electrical synapses). In this paper, we present some models developed from the original Chay model, for the synchrony of two cells and a 2D neural network. Lyapunov exponent and phase portrait are utilized to evaluate the chaotic dynamics. Finally, approximate entropy is utilized to measure its complexity. Our results show that the synchrony of abnormal oscillations can occur when the coupling strength of the gap junction is sufficiently large. It is also found that the concentration of Ca 2+ ions does not synchronize. In the 2D network, approximate entropies of different oscillations with strong coupling strength are greater than those with weak coupling strength. It is indicated that synchronous neurons have greater ability to produce new oscillations than asynchronous ones. This work shows that nonlinear analytical methods may prove useful in elucidating the mechanisms of pathologic conditions, where new oscillations are born and propagated, such as in epilepsy.
BEHAVIOR OF STEP EDGES ON Si(001)
Authors: ZANDVLIET H.J.W. , ELSWIJK H.B. 
Published: November 2004

The morphology of monatomic step edges on vicinal Si (001) surfaces is briefly reviewed. With increasing miscut angle, the Si (001) surface exhibits an interesting sequence of phase transitions. For a miscut angle smaller than about 0.03°, a hilly structure with step loops is found, whereas a phase of wavy steps coexisting with a phase of straight steps is observed in the range of 0.03°–0.1°. If the miscut angle lies in the range of 0.1° up to about 3°, two types, one much straighter than the other, of monatomic step edges develop. For even larger miscut angles, a phase of straight biatomic step edges is found. The fundamental energetic parameters, like kink formation energies, step edge energies and step-step interactions, which govern the thermodynamic behavior are determined using Scanning Tunneling Microscopy (STM) images of 0.5° misoriented Si (001). Despite the weak strength of energetic and entropic step-step interactions as compared to the interactions along the step edge, i.e. the kink formation and step edge energies, they have a profound effect on the meandering of the step edges. Both entropic and energetic step-step interactions are proportional to L−2 (where L is the average terrace length). The behavior of the step edges at temperatures above room temperature will be addressed with the aid of a high-temperature STM. The freeze-out temperature, T f , of the monatomic step edges is estimated to be higher than 600–700 K. The temperature T f is significantly above the roughening temperature, Tr, of the step edges. This means that at room temperature, the monatomic step edges on vicinal Si (001) are always rough.
A SPEECH UNDERSTANDING SYSTEM FOR INFORMATION RETRIEVAL
Authors: BAGGIA P. , FISSORE L. , GIACHIN E. , MICCA G. , RULLENT C. , LAFACE P. 
Published: November 2004

This paper describes a Continuous Speech Understanding System that allows information services to be accessed through the telephone line. It accepts queries within a restricted semantic domain, expressed in free but syntactically correct natural language, with a lexicon of the order of 800 words. In the implementation here described, a user can access an electronic mailbox or a train information service through a PABX telephone line. The architecture of the system is based on two main modules that represent and use different knowledge sources. A speaker independent recognition module generates, for each utterance, a lattice of word hypotheses which is the interface to an understanding module that performs the syntactic and semantic analysis. The recognition module is based on Hidden Markov Models of subword units, and performs the acoustic decoding process according to a beam search strategy. The understanding module finds the most likely sequence of words and represents its meaning in a format which facilitates the access to a database. It makes use of a modified caseframe analysis guided by the word hypotheses scores. Experiments were performed with 600 sentences from 10 speakers on the E-Mail application task. Using 15 Gaussian mixtures per state, a word accuracy of 75.7 was obtained with a test vocabulary of 787 words and no linguistic constraints. Linguistic processing of the corresponding lattices achieved a sentence understanding rate of 82%.
KNOWLEDGE-BASED TECHNIQUES IN ACOUSTIC-PHONETIC DECODING OF SPEECH: INTEREST AND LIMITATIONS
Authors: FOHR DOMINIQUE , HATON JEAN-PAUL , LAPRIE YVES 
Published: November 2004

A major step in the process of speech understanding is the acoustic-phonetic decoding which can be defined as the automatic mapping of the continuous speech wave into a set of predetermined linguistic units such as phones, diphones, syllables, etc. This paper relates to the approach of this problem which consists in exploiting an explicit description of all kinds of available knowledge about the speech communication phenomena, in the general framework of an artificial intelligence knowledge-based system. We will first recall the main difficulties of acoustic-phonetic decoding with a practical example. We will then present the APHODEX system that we have been designing for the past eight years, in terms of software architecture and of knowledge representation and reasoning. The practical evaluation of this system will then be carried out at the different levels of feature extraction, segmentation and labelling. Finally, we will discuss the limitations of our approach and present the ongoing effort to overcome these limitations, especially through the use of abductive reasoning.
ACOUSTIC-PHONETIC DECODING OF SPANISH CONTINUOUS SPEECH
Authors: GALIANO I. , SANCHIS E. , CASACUBERTA F. , TORRES I. 
Published: November 2004

The design of current acoustic-phonetic decoders for a specific language involves the selection of an adequate set of sublexical units, and a choice of the mathematical framework for modelling the corresponding units. In this work, the baseline chosen for continuous Spanish speech consists of 23 sublexical units that roughly correspond to the 24 Spanish phonemes. The process of selection of such a baseline was based on language phonetic criteria and some experiments with an available speech corpora. On the other hand, two types of models were chosen for this work, conventional Hidden Markov Models and Inferred Stochastic Regular Grammars. With these two choices we could compare classical Hidden Markov modelling where the structure of a unit-model is deductively supplied, with Grammatical Inference modelling where the baseforms of model-units are automatically generated from training samples. The best speaker-independent phone recognition rate was 64% for the first type of modelling, and 66% for the second type.
COMPONENT-ORIENTED ALGORITHMS FOR SIGNATURE VERIFICATION
Authors: DIMAURO G. , IMPEDOVO S. , PIRLO G. 
Published: November 2004

Signing is a complex and highly variable process. It results from simple bodily motions of a ballistic nature whose combined effects produce the fundamental components of the signature. Therefore, signature verification can be performed by adopting local verification strategies for the detection of personal characteristics in fundamental components. In this paper, an on-line component-oriented signature verification system is presented. During the training phase, the set of fundamental components of each signer is derived and a suitable component-oriented knowledge-base is created by an automated technique. The verification is accomplished through a step-wise process. In the first step the structural organization of the signature is checked. In the second step each component is examined using spectral analysis. The experimental result shows the effectiveness of this approach compared with other techniques in the literature.
AUTOMATIC INPUT OF LOGIC DIAGRAMS BY RECOGNIZING LOOP-SYMBOLS AND RECTILINEAR CONNECTIONS
Authors: KIM SOO HYUNG , KIM JIN HYUNG 
Published: November 2004

An automatic system that reads an image of a logic diagram, digitized by a document scanner, and generates a description of the diagram in terms of logic symbols and their interconnections is proposed. The digitized image is converted into a set of line segments by way of a sequence of picture processing operations, Then symbols and connections are recognized by identifying loops and rectilinear polylines. Graphical description of a set of symbol models is provided as prior knowledge about input diagrams. Experiments show that the system can recognize more than 96% of logic symbols and connections and that an A4 size diagram (210×297 mm ) of average complexity can be processed within 10 seconds on a workstation.
THE THEORY OF CONFINORS IN CHUA’S CIRCUIT: ACCURATE ANALYSIS OF BIFURCATIONS AND ATTRACTORS
Authors: LOZI RENÉ , USHIKI SHIGEHIRO 
Published: November 2004

We apply the new concept of confinors and anti-confinors, initially defined for ordinary differential equations constrained on a cusp manifold, to the equations governing the circuit dynamics of Chua’s circuit. We especially emphasize some properties of the confinors of Chua’s equation with respect to the patterns in the time waveforms. Some of these properties lead to a very accurate numerical method for the computation of the half-Poincaré maps which reveal the precise structures of Chua’s strange attractors and the exact bifurcation diagrams with the help of a special sequence of change of coordinates. We also recall how such accurate methods allow the reliable numerical observation of the coexistence of three distinct chaotic attractors for at least one choice of the parameters. Chua’s equation seemssurprisingly rich in very new behaviors not yet reported even in other dynamical systems. The application of the theory of confinors to Chua’s equation and the use of sequences of Taylor’s coordinates could give new perspectives to the study of dynamical systems by uncovering very unusual behaviors not yet reported in the literature. The main paradox here is that the theory of confinors, which could appear as a theory of rough analysis of the phase portrait of Chua’s equation, leads instead to a very accurate analysis of this phase portrait.
ADAPTIVE FILTERING AND PREDICTION OF NOISY MULTIVARIATE SIGNALS: AN APPLICATION TO SUBANNUAL VARIABILITY IN ATMOSPHERIC ANGULAR MOMENTUM
Authors: KEPPENNE CHRISTIAN L. , GHIL MICHAEL 
Published: November 2004

Principal component analysis (PCA) in the space and time domains is applied to filter adaptively the dominant modes of subannual (SA) variability of a 12-year long multivariate time series of Northern Hemisphere atmospheric angular momentum (AAM); AAM is computed in 23 latitude bands of equal area from operational analyses of the U.S. National Meteorological Center. PCA isolates the leading empirical orthogonal functions (EOFs) of spatial dependence, while multivariate singular spectrum analysis (M-SSA) yields filtered time series that capture the dominant low-frequency modes of SA variability. The time series prefiltered by M-SSA lend themselves to prediction by the maximum entropy method (MEM). Whole-field predictions are made by combining the forecasts so obtained with the leading spatial EOFs obtained by PCA. The combination of M-SSA and MEM has predictive ability up to about a month. These methods are essentially linear but data-adaptive. They seem to perform well for short, noisy, multivariate time series, to which purely nonlinear, deterministically based methods are difficult to apply.
DYNAMICAL SYNTHESIS OF POINCARÉ MAPS
Authors: BROWN RAY , CHUA LEON O. 
Published: November 2004

We present a theory of constructive Poincaré maps. The basis of our theory is the concept of irreducible nonlinear maps closely associated to concepts from Lie groups. Irreducible nonlinear maps are, heuristically, nonlinear maps which cannot be made simpler without removing the nonlinearity. A single irreducible map cannot produce chaos or any complex nonlinear effect. It can be implemented in an electronic circuit, and there are only a finite number of families of irreducible maps in any n-dimensional space. The composition of two or more irreducible maps can produce chaos and most of the maps studied today that produce chaos are compositions of two or more irreducible maps. The composition of a finite number of irreducible maps is called a completely reducible map and a map which can be approximated pointwise by completely reducible maps is called a reducible map. Poincaré maps from sinusoidally forced oscillators are the most familiar examples of reducible maps. This theoretical framework provides an approach to the construction of "closed form" Poincaré maps having the properties of Poincaré maps of systems for which the Poincaré map cannot be obtained in closed form. In particular, we derive a three-dimensional ODE for which the Hénon map is the Poincaré map and show that there is no two-dimensional ODE which can be written down in closed form for which the Hénon map is the Poincaré map. We also show that the Chirikov (standard) map is a Poincaré map for a two-dimensional closed form ODE. As a result of our theory, these differential equations can be mapped into electronic circuits, thereby associating them with real world physical systems. In order to clarify our results with respect to the abstract mathematical concept of suspension, which says that every C1 invertible map is a Poincaré map, we introduce the concept of a constructable Poincaré map. Not every map is a constructable Poincaré map and this is an important distinction between dynamical synthesis and abstract nonlinear dynamics. We also show how to use any one-dimensional map to induce a two-dimensional Poincaré map which is a completely reducible map and hence for a very broad class of maps that includes the logistic map we derive closed form ODEs for which these one-dimensional maps are "embedded" in a Poincaré map. This provides an avenue for the study of one-dimensional maps, such as the logistic map, as two-dimensional Poincaré maps that arise from square-wave forced electronic circuits.
REGULAR AND CHAOTIC PULSATIONS IN LASER DIODE WITH DELAYED FEEDBACK
Authors: GRIGORIEVA E. V. , KASHCHENKO S. A. 
Published: November 2004

The dynamics of a semiconductor laser with delayed feedback are investigated on the basis of single-mode rate equations with retarded argument. Spontaneous emission in lasing mode, limited bandwidth of optoelectronic feedback and the presence of an impurity with saturable absorption are also taken into account. The existence of a hierarchy of multistable periodic attractors with different structures (slowly and rapidly oscillating ones) are found. Complex temporal structures: metastable chaotic regimes, quasiperiodic regimes and intermittency are obtained as a result of different bifurcations of multidimensional maps.
ORTHOGONAL SHORTEST ROUTE QUERIES AMONG AXES PARALLEL RECTANGULAR OBSTACLES
Authors: ELGINDY HOSSAM , MITRA PINAKI 
Published: November 2004

Given a set ℬ of n barriers, the shortest route query SRQ problem asks for a preprocessing of ℬ such that a description of the shortest route between two points (origin and destination) can be reported efficiently. In this manuscript we present efficient sequential and parallel algorithms for the SRQ problem where the barriers in ℬ are disjoint planar rectangles whose sides are parallel to the coordinate axes, and subsequent queries ask for the shortest L1 route between two arbitrary points which avoids the barriers in ℬ. The segments forming such route are also restricted to be parallel to the coordinate axes. For this problem we we present sequential and parallel preprocessing algorithms which allow for reporting the shortest distance between two arbitrary query points in O( log n) time with a single processor. The route itself can also be constructed in time proportional to its number of segments. Our method is based on constructing three planar graphs, called carrier graphs, that contain the shortest route information in a succinct form. Each graph can then be searched using graph theoretic techniques. Using the same techniques we also present a parallel algorithm for computing the orthogonal shortest distance between two points among rectangular obstacles which runs in poly-logarithmic time using sub-quadratic number of processors on the CREW PRAM model of computation.
NOGOOD RECORDING FOR STATIC AND DYNAMIC CONSTRAINT SATISFACTION PROBLEMS
Authors: SCHIEX THOMAS , VERFAILLIE GÉRARD 
Published: November 2004

Many AI synthesis problems such as planning, scheduling or design may be encoded in a constraint satisfaction problems (CSP). A CSP is typically defined as the problem of finding any consistent labeling for a fixed set of variables satisfying all given constraints between these variables. However, for many real tasks, the set of constraints to consider may evolve because of the environment or because of user interactions. The notion of dynamic CSP (DCSP) [DD88] has been proposed to represent such evolutions. The problem we consider here is the solution maintenance problem in a DCSP. Naively applying usual satisfaction algorithms to this problem results in redundant search and inefficiency. A general approach to suppress redundancies in case of both restrictions and relaxations is to concisely represent the frontier of the solution space and justifications of this frontier in terms of set of constraints. This paper proposes a new class of constraint recording algorithms called nogood recording that may be used for solving both dynamic CSPs and usual CSP (called static CSPs here). It offers an interesting compromise, polynomially bounded in space, between an ATMS-like (Assumption-based Truth Maintenance System) approach, that would give a precise and exhaustive description of the frontier, and the usual constraint satisfaction algorithms (that discover a new frontier at each execution). We first introduce the principles used for nogood generation and then examine various recording schemes, on top of different tree search algorithms, characterizing the tradeoffs between the amount of recorded constraints and the pruning achieved. We then present experimental results and comparisons with various existing techniques for solving static or dynamic CSP.
CONCEPT AND REALIZATION OF A HYBRID AI TOOL APPLIED TO COMPUTER VISION
Authors: DVORAK J. , BUNKE H. 
Published: November 2004

Computer vision includes a variety of tasks of different natures, and there are many applications that have a strong need for knowledge representation and use. Typical knowledge representation methods used in computer vision include frames, rules, logic, constraints, and attributed prototype graphs. Although the advantages of hybrid approaches to knowledge representation have been recognized, no hybrid tool for high-level computer vision is available yet. In this paper we first present a general framework for a hybrid knowledge representation tool. It is based on object-oriented programming and offers distinctive features such as high flexibility, coherence, and a clean integration of a collection of knowledge-based techniques. Then we give a brief overview of our computer vision tool VISTO, which was created along the framework discussed in the first part of the paper. With an application example we illustrate the use of VISTO and the advantages of hybrid knowledge representation in comparison to non-hybrid approaches.