bluuebunny/crossref_metadata_2025 huggingface dataset:
SEEBECK EFFECT IN THIN FILMS AND SUPERLATTICES OF CUPRATE SUPERCONDUCTORS
Authors: PUTTI M. , MARRÈ D. , TASSISTO M. , BALESTRINO G. , MEDAGLIA P. G. , SALLUZZO M. , LIVANOV D. V. , MANOKHIN S. I.
Published: April 2003

In this paper we present thermopower measurements on Nd1 + xBa2 - xCu3O7 - δ thin films and (BaCuO2)2/(CaCuO2)n superconducting superlattices. We estimate for these systems how much charge is transferred to the CuO2 planes. For the superlattices we have clear evidence that the charge transferred by the Charge Reservoir block distributes uniformly on the available CuO2 planes. The temperature dependence of the thermopower is then compared with the prediction of a model which considers the electron-phonon-impurity interference.
CHARGE INHOMOGENEITY EFFECTS ON THE MAGNETIC PROPERTIES OF HTSC ABOVE TC
Authors: ROMANÒ L.
Published: April 2003

The anomalous diamagnetism observed in cuprate materials above Tc is justified by a presence of superconducting droplets, due to the charge inhomogeneity on the CuO plane, with Tcloc>Tcres. The phase fluctuations contribute to the magnetic properties generating vortex and antivortex which add to the flux lines induced by magnetic field. The model describes the behaviour below and above the irreversibility line and it predicts an evident upturn in the magnetization curves for T<Tirr.
EFFECTS OF Cu AND OTHER METALLIC DOPINGS ON THE SUPERCONDUCTING PROPERTIES OF MgB2
Authors: TAMPIERI A. , CELOTTI G. , SPRIO S. , RINALDI D.
Published: April 2003

Many efforts have been devoted, after the discovery of superconductivity in MgB2 [1], to understand the mechanisms of superconductivity in this system and the possible increase of its critical temperature. The aim of this work is to investigate the influence of heteroatoms doping in MgB2, substituting Mg and/or B during the classical synthesis of MgB2. Various elements were tested: mainly Cu and Ca, Sr, Cr, Mn, C and Si, devising various technological expedients when necessary to ensure an actual, even if partial, entrance of the dopants in the MgB2 lattice. Unfortunately the elements tested so far produced a decrease in Tc or a very small increase: actually Si and C seem to have a slightly positive effect on Tc. The reasons for the observed effects were analysed and tentative explanations offered: in any case some interesting deductions on the nature of superconductivity in MgB2 were drawn.
EFFECTS OF THE Al CONTENT IN MgB2: A RAMAN STUDY
Authors: DORE P. , POSTORINO P. , CONGEDUTI A. , NUCARA A. , BIANCONI A. , DI CASTRO D. , DE NEGRI S. , SACCONE A.
Published: April 2003

The partial substitution of Al for Mg in the MgB2 superconductor produces both a progressive reduction of its superconducting transition temperature Tc and the occurrence of two distinct structural phases at low and high Al content, as shown by X-ray diffraction data. To achieve a deeper understanding of the effect of the Al content, we investigated the x dependence of the Raman phonon spectrum in Mg1-xAlxB2 compounds. We analyze the evolution of the E2g Raman-active phonon mode observed on increasing x both in our measurements (0 ≤ x ≤ 0.5) and in recent experiments (0 ≤ x ≤ 1). Our analysis shows the connection between the evolution with x of the E2g phonon and the Tc suppression, thus supporting the hypothesis that superconductivity in MgB2 is mediated by a strong e-ph coupling with the E2g mode. We then derive the electron-phonon coupling constant λ in the 0-0.5 x range.
ANELASTIC SPECTROSCOPY AND NQR RELAXATION IN Sr-DOPEN La2CuO4 AROUND THE AF PERCOLATION THRESHOLD
Authors: PAOLONE A. , CANTELLI R. , CORDERO F. , CORTI M. , RIGAMONTI A. , FERRETTI M.
Published: April 2003

Anelastic spectra and 139 La NQR relaxation measurements have been carried out in La 2 - x Sr x CuO 4 (LSCO) for x around the critical value xc = 0.02 separating the antiferromagnetic (AF) from the cluster spin glass (CSG) phase for T → 0. The anelastic spectra around 10 K show step-like features common to samples pertaining to both AF and CSG phases. In the light of recent neutron scattering measurements suggesting that the spin-glass phase of LSCO with x < xc corresponds to a microscopic phase separation between regions with x ~ 0 and x ~ 0.02, the rise of the elastic energy dissipation has been attributed to the movement of the domain walls within the x ≃ xc CSG regions. The spin dynamics driving the AF transition has been investigated by means of 139 La NQR relaxation rate. The in-plane magnetic correlation length ξ2D has been extracted. In spite of the vicinity to the percolation threshold, ξ2D(x = 0.016, T) follows the temperature behavior expected in the renormalized classical regime, with spin stiffness reduced to about 0.4 of the one in pure La 2 CuO 4. Still, the 3D transition occurs when ξ2D is of the order of about 150 lattice steps, as in pure La 2 CuO 4, possibly related to the presence of AF regions unaffected by the holes.
STRAIN-INDUCED ELECTRONIC TOPOLOGICAL TRANSITIONS IN LaSrCuO THIN FILMS
Authors: ANGILELLA G. G. N. , BALESTRINO G. , CERMELLI P. , PODIO-GUIDUGLI P. , VARLAMOV A. A.
Published: April 2003

We review a Ginzburg-Landau phenomenological model for the dependence of the critical temperature on microscopic strain in tetragonal high-T c cuprates. Such a model is in agreement with the experimental results for LSCO under epitaxial strain, as well as with the hydrostatic pressure dependence of T c in most cuprates. In particular, a nonmonotonic dependence of T c on hydrostatic pressure, as well as on in-plane or apical microstrain, is derived. From a microscopic point of view, such results can be understood as due to the proximity to an electronic topological transition (ETT). In the case of LSCO, we argue that such an ETT can be driven by a strain-induced modification of the band structure, at constant hole content, at variance with a doping-induced ETT, as is usually assumed.
NONADIABATIC EFFECTS AND THE ROLE OF SMALL FERMI ENERGY IN MgB2
Authors: CAPPELLUTI E. , GRIMALDI C. , PIETRONERO L. , STRÄSSLER S. , BOERI L. , BACHELET G. B.
Published: April 2003

There is nowadays a general agreement on a key role of the σ bands in the superconducting properties of MgB 2. We show that peculiar characteristics of the σ bands give rise to nonadiabatic and anharmonic effects which break the conventional Migdal-Eliashberg framework. Both these features are governed by the small value of the Fermi energy due to the vicinity of the hole doping level to the top of the σ bands. In this context we discuss how the nonadiabatic theory leads to a coherent interpretation of the superconducting properties of MgB 2 without invoking very large couplings and it naturally explains the role of the disorder on T c . It also leads to various specific predictions for the properties of MgB 2 and for the material optimization of these type of compounds. Anharmonicity is also investigated by means of LDA calculations. We find that the anharmonic character of the E2g phonon is essentially driven by the small Fermi energy of the σ holes. We present a simple analytic model which allows us to understand in microscopic terms the role of the small Fermi energy and of the electronic structure. The relation between anharmonicity and nonadiabaticity is pointed out and discussed in relation to various materials.
INTERPLANAR HOPPING OF W = 0 BOUND PAIRS
Authors: CALLEGARI AGNESE , PERFETTO ENRICO , STEFANUCCI GIANLUCA , CINI MICHELE
Published: April 2003

CuO 4 is the simplest of a class of repulsive Hubbard model clusters which (under well specified conditions) display W = 0 pairing; remarkably, ane also observes superconducting quantization of a magnetic flux orthogonal to the plane. Thus one can use CuO 4 units connected by weak O-O and/or Cu-Cu links to model interplanar coupling and c-axis superconductivity in Cuprates. A new analytic approximation supported by preliminary numerical evidence suggests that in such models one can study the propagation of bound pairs and also the superconducting flux quantization in a 3d geometry.
FIRST-ORDER PAIRING TRANSITION AND PHASE SEPARATION IN THE ATTRACTIVE HUBBARD MODEL
Authors: CAPONE M. , CASTELLANI C. , GRILLI M.
Published: April 2003

The normal state properties of the Hubbard model are studied by means of the Dynamical Mean-Field Theory. Even in the gauge-symmetric subspace, a first-order transition occurs between a Fermi-liquid phase and a strong-coupling bound-pairs phase, which can be thought as a "disordered" superconductor. The transition is of first order for all densities different from n = 1, and it is accompanied by a region of phase separation between the two phases at different densities.
SCANNING TUNNELING SPECTROSCOPY ON THE GdSr2RuCu2O8 COMPOUND
Authors: BOBBA F. , GIUBILEO F. , GOMBOS M. , NOCE C. , VECCHIONE A. , CUCOLO A. M. , RODITCHEV D. , LAMY R. , SACKS W. , KLEIN J.
Published: April 2003

Topographic and spectroscopic information on GdSr2RuCu2O8 sintered pellets have been obtained by a home built low temperature Scanning Tunneling Microscope (STM) operating at 4.2 K. The topographic image of the surface showed non homogeneous samples with grains of typical size of about 100 nm. In many locations studied, the Tunneling Spectroscopy reveals the presence of charging effects in the current-voltage characteristics over a voltage range up to 100 mV. Two types of charging effects are clearly distinguished: one corresponds to the reduction of the tunneling conductance around zero bias and is attributed to the Coulomb blockade, and another onw, a stepwise increasing of the current as a function of the bias voltage is identified as Coulomb staircase regime. Besides these spurious charging effects, the current-voltage characteristics often show a pronounced non-linearity around 4.0 mV. This non-linearity, disappearing above the critical temperature of the materials, is connected to the superconducting gap in the GdSr 2 RuCu 2 O 8.
INVESTIGATING THE COEXISTENCE OF MAGNETISM AND SUPERCONDUCTIVITY IN THE KONDO-HEISENBERG MODEL
Authors: ACQUARONE M. , NOCE C. , ROMANO A.
Published: April 2003

We perform a finite-size cluster study of the Kondo-Heisenberg model, describing a system of itinerant electrons locally coupled via a Kondo-type interaction to a set of magnetic ions. The ionic moments are assumed to have antiferromagnetic order, due to a nearest-neighbor Heisenberg coupling. By consecutive application of displacement and squeezing transformations, a spin polaron effective Hamiltonian is derived, which is exactly solved on a 8-site closed ring. By analyzing the behavior of suitably defined correlation functions in the variationally optimized ground state, special attention is devoted to the conditions under which a superconducting phase coexisting with spin order can be established.
POSSIBLE d + id SCENARIO IN La2-xSrxCuO4 BY POINT-CONTACT MEASUREMENTS
Authors: DAGHERO D. , GONNELLI R. S. , UMMARINO G. A. , STEPANOV V. A.
Published: April 2003

We analyze the results of point-contact measurements in La 2-x Sr x CuO 4 (LSCO) previously reported as a clear evidence of the separation between gap and pseudo-gap in this copper oxide. Here we show that, in addition to this, the conductance curves of our point-contact junctions – showing clear Andreev reflection features – can be interpreted as supporting a nodeless dx2 - y2 + i dxy-wave symmetry of the gap in LSCO. The results of our analysis, in particular the doping dependence of the subdominant dxy gap component, are discussed and compared to the predictions of different theoretical models.
THERMOPOWER OF THE LAYERED MULTI-BAND SUPERCONDUCTOR Sr2RuO4
Authors: CUOCO MARIO , NOCE CANIO
Published: April 2003

The dependence of in-plane thermopower and Hall coefficient of Sr 2 RuO 4 on temperature are discussed. The apparently contradiction found in experimental data in the sign of these quantities at low temperature is clarified within a simple multi-band calculation. Then, by means of the Boltzmann equation and taking into account the Fermi surface curvature and different time collisions for the electrons in the t2g bands, the calculation is extended at high temperature.
NUMERICAL CALCULATION OF THE CRITICAL STATE IN SUPERCONDUCTING TAPES ABOVE THE FULL PENETRATION FIELD
Authors: ZOLA D. , POLICHETTI M. , SENATORE C. , PACE S. , GÖMÖRY F.
Published: April 2003

The critical state with a magnetic field dependent critical current density jc(B) has been calculated numerically in superconducting tapes, for magnetic fields above the full penetration field. By using a finite element computation, the magnetic field profiles and the current distribution in the tapes have been calculated both for monofilamentary and for multifilamentary tapes with several aspect ratio of the filaments. Particular attention has been paid to the investigation of the effects of the sample geometry and of the jc(B) dependence on the field profiles and on the hysteresis loop.
AC LOSSES OF BI-2223 MULTIFILAMENTARY TAPES CARRYING AC CURRENT AND EXPOSED TO AC MAGNETIC FIELDS
Authors: GIANNI L. , GINOCCHIO S. , ROGNONI L. , ZANNELLA S. , BALDI I. , CITINO A. , SPREAFICO S. , TEBANO R.
Published: April 2003

For power applications of HTS it is crucial to predict their AC losses in the typical operating conditions. We report measurements of energy losses in Bi-2223 multifilamentary tapes carrying AC currents and exposed to AC magnetic fields oriented perpendicular or parallel to their wide surface. Losses have been evaluated at liquid nitrogen temperature by transport and magnetisation measurements. The results have been compared to the experimental values obtained by calorimetric method the values estimated by a numerical model specifically developed of evaluation of AC losses in HTS tapes.
OBSERVATION OF PORPHYRITIC TEXTURE IN HOT FILAMENT CVD DIAMOND FILMS
Authors: HAN SIJIN , FANG RONGCHUAN , SHANG NAIGUI , LIAO YUAN , LE DEFEN , LI FANQING , ZUO JIAN
Published: April 2003

The porphyritic texture of diamond films synthesized by hot filament CVD (HFCVD) is reported for the first time. The porphyritic texture has two distinct crystal habits, where phenocrysts are set in a matrix of fine grains. The morphology and quality of films were investigated by scanning electron microscopy and Raman spectroscopy. A growth model employing secondary nucleation and growth illuminates the growth mechanism of this unusual texture. We also compare the similarity and difference between Wild's and our results on the spherical shape of a multiple faceted particle, which is formed by multiple twinning.
STRUCTURAL EFFECT OF THORIUM ON THE LOCAL ORDER IN A PHOSPHATE GLASS MATRIX
Authors: SIMON S. , ARDELEAN I. , SIMON V.
Published: April 2003

The influence of ThO 2 addition on the local order of 2P 2 O 5 · Na 2 O glass matrix was investigated by IR and EPR spectroscopic analyses of non-irradiated and gamma-irradiated x ThO 2(100-x)[ 2P 2 O 5 · Na 2 O ] glass samples (0 ≤ x < 20 mol %). After the applied gamma irradiation treatments, the IR spectra are not significantly modified. The as-prepared samples and also the unirradiated samples examined after two years do not give rise to any EPR signal at the room temperature. The applied gamma irradiation treatments induce paramagnetic defects. The EPR spectra consist of doublets attributed to an electron trapped at a nonbridging oxygen vacancy.
THERMOELECTRIC POWER AND HALL EFFECT OF HIGH-Tc SUPERCONDUCTORS IN A TWO-COMPONENT MODEL
Authors: ZHANG SHUANG , ZHANG LI-YUAN , YANG XIAO-QIANG
Published: April 2003

In this paper we have succeeded in describing the thermoelectric power and the Hall coefficient in the normal state of several underdoped and nearly optimally doped high-T c superconductors within the framework of the two-subsystem (or two-component) model. We analyze the effect of pseudogap on Hall effect and get the temperature T* at which the pseudogap opens. The results agree with those of experiments. The correlation energy of the nearly local pair is in the same order of the magnitude with thermal energy (k B T), so the pairs have somewhat decomposability, therefore, we suggest that the nearly local pairs coexist with itinerant single carriers in the normal state of high-T c superconductors.
EVALUATING THE DEPLOYMENT OF FIPA STANDARDS WHEN DEVELOPING APPLICATION SERVICES
Authors: CHARLTON P. , CATTONI R.
Published: April 2003

We draw upon various practical experiences of designing and implementing complex systems through a multiagent approach which supports engineering of dynamic open distributed services. The general scope of multiagent system software engineering is reviewed with focus on the analysis and evaluation of certain aspects of the current specification standards provided by FIPA (Foundation of Intelligent Physical Agents). The benefits and drawbacks of a multiagent approach, using the FIPA standards as a benchmark, are evaluated and further illustrated through the deployment of an audio–video entertainment broadcasting (AVEB) system. The development and testing of the AVEB application was part of an EU project called FACTS (acts AC317). A main result of using agent engineering paradigm for complex distributed development, especially apparent in FIPA standards, has been the identification of the usefulness and power of its protocols. The reason for the importance of the protocols in developing multiagent systems (MAS) is it provides a degree of expressing cooperation within MAS architecture. As the protocols stand currently they are not sufficient to capture a complete explicit model of the cooperative requirements in multiagent systems. However, they provide a basis from which to start. We examine this feature of FIPA further in order to evaluate its role as a bridge between the mental agency and social agency requirements in the development of cooperation in multiagent systems.
RECOGNITION OF 2D STANDALONE AND OCCLUDED OBJECTS USING WAVELET TRANSFORM
Authors: TSANG K. M.
Published: April 2003

A planar curve descriptor which is invariant to translation, size, rotation and starting point in tracing the boundary is developed based on the periodized wavelet transform. Coefficients obtained from the transform are divided into different bands, and feature vectors are extracted for the recognition of two-dimensional closed boundary curves. The weight vectors which include the width of different bands are also derived to differentiate spurious results arising from noisy samples. The technique is further extended for the recognition of occluded objects by incorporating local features into the features vector to form a feature map. Matching the likeliness of a part of the feature map with that of the reference feature maps indicates which class the occluded object belongs to. Experimental results were obtained to show the effectiveness of the proposed technique.
CHARACTERIZATION OF STATIC BIFURCATIONS IN THE FREQUENCY DOMAIN
Authors: ITOVICH GRISELDA R. , MOIOLA JORGE L.
Published: April 2003

In this paper two-dimensional systems with static bifurcations are considered. An analysis of the bifurcation behavior is proposed using a frequency domain approach. The analyzed bifurcations are known as elementary since they are the building blocks to understand other more complex singularities.
DETERMINATION OF THE DYNAMICAL PROPERTIES OF FERROELECTRICS USING NONLINEAR TIME SERIES ANALYSIS
Authors: KAPSCH RALF-PETER , KANTZ HOLGER , HEGGER RAINER , DIESTELHORST MARTIN
Published: April 2003

We investigate the behavior of an experimental electric resonance circuit with a nonlinear capacitor. Triglycine sulfate (TGS) was used as nonlinear dielectric material. This is the most thoroughly investigated ferroelectric with a second-order phase transition. Its static dielectric small signal behavior is well described in the framework of the Landau theory of phase transitions. The dynamic behavior however is strongly related to relaxation phenomena due to switching of domains. Here the theoretical situation is still unclear.

By mere data analysis we construct an ordinary differential equation which describes the dynamical behavior of the circuit, and which is simple in the sense of Ockham's razor. The structure of this equation is closely related to the dynamical properties of the ferroelectric. We are therefore able to gain some insights into the dynamical behavior of ferroelectrics, which may give some hints for a more exhaustive analysis of nonequilibrium properties of ferroelectrics.
FRACTALS AND CLOSURES OF LINEAR DYNAMICAL SYSTEMS EXCITED STOCHASTICALLY BY TEMPORAL INPUTS
Authors: WADA RYOICHI , GOHARA KAZUTOSHI
Published: April 2003

Fractals and closures of two-dimensional linear dynamical systems excited by temporal inputs are investigated. The continuous dynamics defined by the set of vector fields in the cylindrical phase space is reduced to the discrete dynamics defined by the set of iterated functions on the Poincaré section. When all iterated functions are contractions, it has already been shown theoretically that a trajectory in the cylindrical phase space converges into an attractive invariant set with a fractal-like structure. Calculating analytically the Lipschitz constants of iterated functions, we show that, under some conditions, noncontractions often appear. However, we numerically show that, even for noncontractions, an attractive invariant set with a fractal-like structure exists. By introducing the interpolating system, we can also show that the set of trajectories in the cylindrical phase space is enclosed by the tube structure whose initial set is the closure of the fractal set on the Poincaré section.
SYNCHRONIZATION AND SECURE COMMUNICATION FOR CHAOTIC SYSTEMS: THE MODULATED FUZZY SYSTEM DESIGN
Authors: LIAN KUANG-YOW , CHIANG TUNG-SHENG , LIU PETER , CHIU CHIAN-SONG
Published: April 2003

This paper presents a modulated T–S fuzzy model that can be applied to both continuous/discrete chaotic synchronization, chaotic model following and secure communication. The modulated T–S fuzzy model is constructed by choosing the common factor or the only variable of nonlinear terms in chaotic systems as the premise variable of fuzzy rules and output signal. Following this model, fuzzy chaotic synchronization is achieved by utilizing linear matrix inequalities design and some restricting conditions can be relaxed. This simplified design framework can be applied to many well-known chaotic systems. Also, for chaotic communications, this modulated T–S fuzzy model illustrates asymptotical recovering of the message. Moreover, the usage of combinational states as the coupling signal for Luré type systems is taken into consideration. In this case, the receiver design for synchronization and secure communication is also proposed. The simulation results are shown with expected satisfactory performance.
GLOBAL ANALYSIS FOR A NONLINEAR VIBRATION ABSORBER WITH FAST AND SLOW MODES
Authors: ZHANG WEI , LI JING
Published: April 2003

A two-degree-of-freedom model of a nonlinear vibration absorber is considered in this paper. Both the global bifurcations and chaotic dynamics of the nonlinear vibration absorber are investigated. The nonlinear equations of motion of this model are derived. The method of multiple scales is used to find the averaged equations. Based on the averaged equations, the theory of normal form is used to obtain the explicit expressions of normal form associated with a double zero and a pair of pure imaginary eigenvalues by Maple software program. The fast and slow modes may simultaneously exist in the averaged equations. On the basis of the normal form, the global bifurcation and the chaotic dynamics of the nonlinear vibration absorber are analyzed by a global perturbation method developed by Kovacic and Wiggins. The chaotic motion of this model is also found by numerical simulation.
MAGNETIC-BEARING RELATED CHAOTIC ELECTROMECHANICAL OSCILLATOR
Authors: HOREN Y. , KAPLAN B. Z.
Published: April 2003

The work deals with a switching mode control of a magnetic levitation system that possesses a symmetrical geometry similar to that usually found in magnetic bearings. The control depends on switching the current in two attracting electromagnets installed on both sides of the suspended object. The underlying idea is to use merely discrete (noncontinuous) position sensors for the control. It is unfortunate that relying merely on one such sensor cannot enable stabilization. We observe, however, that two such sensors (mounted symmetrically on both sides of the symmetry plane) are sufficient for stabilizing the system. The dynamic features of the system are considered theoretically and also investigated by simulation work. An interesting dynamics that is associated with chaotic behavior is revealed. Namely, the region of stability of the suspended object is characterized by being related to a strange attractor. It is shown that the chaotic dynamic behavior is closely similar to that exhibited by certain purely electronic oscillators where feedback is channelled through hysteresis. The main tool employed for assessing the present chaotic behavior is a discrete map constructed for the sequence of velocities exhibited at the switching instances.
ELECTRO-OSMOTIC SLIP OF THE SECOND KIND AND INSTABILITY IN CONCENTRATION POLARIZATION AT ELECTRODIALYSIS MEMBRANES
Authors: RUBINSTEIN I. , ZALTZMAN B.
Published: April 2003

Theories of electro-osmotic slip, of either the equilibrium (first) or nonequilibrium (second) kind at a permselective conductive surface (ion exchange electrodialysis membrane, electrode) are reviewed. A slip condition for electro-osmosis of the second kind, relevant for a developed concentration polarization at an electrodialysis membrane, is derived through a boundary layer analysis of the appropriate convective electrodiffusion problem. Linear hydrodynamic stability of the quiescent concentration polarization in a diffusion layer at a cation exchange electrodialysis membrane is studied. It is shown that electro-osmotic slip of the second kind, as opposed to that of the first kind, yields instability for realistic conditions. Numerical calculations for the resulting nonlinear convection show that the latter provides an efficient mixing mechanism for the diffusion layer, capable of accounting for the overlimiting conductance in concentration polarization at a cation exchange membrane.
OVERCOMING THE CHRISTMAS TREE SYNDROME
Authors: GRÉGOIRE E. , ANSART D.
Published: April 2003

We propose a new computational approach to logic-based systems that should reason in a fast but logically sound and complete manner about large-scale complex critical devices and systems that can exhibit unexpected faulty behaviors. The approach is original from at least two points of view. First, it makes use of local search techniques while preserving logical deductive completeness. Second, it proves experimentally efficient for very large knowledge bases thanks to new heuristics in the use of local search techniques.
3D OBJECT FEATURE EXTRACTION BASED ON SHAPE SIMILARITY
Authors: SONG JEONG-JUN , GOLSHANI FOROUZAN
Published: April 2003

We introduce two complementary feature extraction methods for shape similarity based retrieval of 3D object models. The proposed methods lead us to achieve effectiveness and robustness in searching similar 3D models, and eventually support two essential query modes, namely, query by 3D model and query by 2D image. Our feature extraction scheme is inspired by the observation of human behavior in recognizing 3D objects. The process of extracting spatial arrangement from a 3D object can be considered as using human tactile sensation without visual information. On the other hand, the process of extracting 2D features from multiple views can be considered as examining an object by moving the viewing points (or camera positions). We propose a hybrid method of 3D model identification by object-centered feature extraction, which utilizes the Extended Gaussian Image (EGI) surface normal distribution and distance distributions between object surface points and origin. Another technique need in parallel is a hybrid method using view-centered features, which adopts simple geometric attributes such as circularity, rectangularity and eccentricity. To generate a signature for view-centered features, we have measured distances of a feature between different views and constructing histogram of the distance. We also address the fundamental problem of obtaining sample points on an object surface, which is important to extract reliable features from the object model.
WEB INFORMATION MANAGEMENT AND ITS APPLICATION TO ELECTRONIC COMMERCE
Authors: THURAISINGHAM BHAVANI
Published: April 2003

This paper describes various aspects of web information management with particular emphasis on its application to electronic commerce. We first provide a brief overview of the web. Then we discuss concepts for web database management, as database management is a key part of information management. These include data models and architectures, query processing, transaction management, metadata management, storage issues, and integrity and security. Then we discuss various web information management technologies such as multimedia, visualization, data mining and warehousing, and knowledge management. Then we discuss emerging standards such as Java Database Connectivity, Extended Markup Language (XML), and middleware standards such as Object Request Brokers (ORB) and Remote Method Invocation (RMI). Finally we discuss how web data management technologies can be applied to the important area of electronic commerce.
PREPROCESSING AND INTEGRATION OF DATA FROM MULTIPLE SOURCES FOR KNOWLEDGE DISCOVERY
Authors: CERUTI MARION G. , KAMEL MAGDI N.
Published: April 2003

The explosive growth in the generation and collection of data has generated an urgent need for a new generation of techniques and tools that can assist in transforming these data intelligently and automatically into useful knowledge. Knowledge discovery is an emerging multidisciplinary field that attempts to fulfill this need. Knowledge discovery is a large process that includes data selection, cleaning, preprocessing, integration, transformation and reduction, data mining, model selection, evaluation and interpretation, and finally consolidation and use of the extracted knowledge. This paper addresses the issues of data cleaning and integration for knowledge discovery by proposing a systematic approach for resolving semantic conflicts that are encountered during the integration of data from multiple sources. Illustrated with examples derived from military databases, the paper presents a heuristics-based algorithm for identifying and resolving semantic conflicts at different levels of information granularity.
VIRTUAL MODEL BASED ADAPTIVE DYNAMIC CONTROL OF A BIPED WALKING ROBOT
Authors: HU JIANJUEN J. , PRATT JERRY E. , CHEW CHEE-MENG , HERR HUGH M. , PRATT GILL A.
Published: April 2003

The robustness of bipedal walking robots can be enhanced by the use of adaptive control techniques. In this paper, we extend a previous control approach. "Virtual Model Control" (VMC) [6] to create "Adaptive Virtual Model Control" (AVMC). The adaptation compensates for external disturbances and unmodelled dynamics, enhancing robustness in the control of height, pitch, and forward speed. The state machine used to modulate the virtual model components and to select the appropriate virtual to physical transformations (as in traditional VMC) is also used to inform the adaptation about the robot's changing configuration.

The design procedure for AVMC is described in this paper and simulation results are presented for a planar walking biped.
INTELLIGENT CONTROL OF A SIMULATED RUNNING JOINTED LEG: THE LANDING PHASE
Authors: DOERSCHUK PEGGY ISRAEL , LIN QING
Published: April 2003

Controlling the running movement of a machine with jointed legs is a difficult problem in robotics. The control of a single running stride can be broken down into three phases; takeoff, ballistic, and landing. This paper describes the development of an intelligent controller for the landing phase of a simulated jointed leg's running stride. The landing controller takes control when the tool touches the ground after the airborne ballistic phase of the stride. It lears from experience to control the leg so as to recover from the impact with the ground and to reposition the leg for the takeoff of the next running stride. Very accurate control is achieved even during the first attempt at the running stride.
IMPROVING EVOLUTIONARY ALGORITHMS FOR EFFICIENT CONSTRAINT SATISFACTION
Authors: STUCKEY PETER , TAM VINCENT
Published: April 2003

Hard or large-scale constraint satisfaction and optimization problems, occur widely in artificial intelligence and operations research. These problems are often difficult to solve with global search methods, but many of them can be efficiently solved by local search methods. Evolutionary algorithms are local search methods which have considerable success in tackling difficult, or ill-defined optimization problems. In contrast they have not been so successful in tackling constraint satisfaction problems. Other local search methods, in particular GENET and EGENET are designed specifically for constraint satisfaction problems, and have demonstrated remarkable success in solving hard examples of these problems. In this paper we examine how we can transfer the mechanisms that were so successful in (E)GENET to evolutionary algorithms, in order to tackle constraint satisfaction algorithms efficiently. An empirical comparison of our evolutionary algorithm improved by mechanisms from EGENET and shows how it can markedly improve on the efficiency of EGENET in solving certain hard instances of constraint satisfaction problems.
TOWARDS A DNA SOLUTION TO THE SHORTEST COMMON SUPERSTRING PROBLEM
Authors: GLOOR GREG , KARI LILA , GAASENBEEK MICHELLE , YU SHENG
Published: April 2003

This paper proposes a DNA algorithm for solving an NP-complete problem (The Shortest Common Superstring Problem) by manipulation of biomolecules, and presents partial results of the experiment that implements our algorithm. We also discuss practical constraints that have to be taken into account when implementing the algorithm, propose a coding system as a solution to these practical restrictions, and discuss the control experiments performed for establishing the parameters controlling the specificity of the assay.
A GAUSSIAN WEAVE FOR KINEMATICAL LOOP QUANTUM GRAVITY
Authors: CORICHI A. , REYES J. M.
Published: April 2003

Remarkable efforts in the study of the semiclassical regime of kinematical loop quantum gravity are currently underway. In this note, we construct a "quasicoherent" weave state using Gaussian factors. In a similar fashion to some other proposals, this state is peaked in both the connection and the spin network basis. However, the state constructed here has the novel feature that, in the spin network basis, the main contribution for this state is given by the fundamental representation, independently of the value of the parameter that regulates the Gaussian width.
A RELATION AMONG THE EFFECTIVE NUCLEON MASS, THE INCOMPRESSIBILITY AND THE EFFECTIVE σ-MESON MASS IN NUCLEAR MATTER
Authors: IWASAKI YOSHITAKA , KOUNO HIROAKI , HASEGAWA AKIRA , NAKANO MASAHIRO
Published: April 2003

A relation among the effective nucleon mass M*, the incompressibility K and the effective σ-meson mass [Formula: see text] in nuclear matter is studied by using the relativistic nuclear model. We found that there is a strong correlation between M* and [Formula: see text], while there is only a weak correlation between K and [Formula: see text]. At the normal density, [Formula: see text] is smaller than the one at zero density, if M* is smaller than 0.8 times of the nucleon mass at zero density. It is also found that the off-shell effective mass [Formula: see text] is related directly to K and M* at the normal density.
TWO-OSCILLATOR BASIS EXPANSION FOR THE SOLUTION OF RELATIVISTIC MEAN FIELD EQUATIONS
Authors: SASTRY S. V. S. , JAIN ARUN K. , GAMBHIR Y. K.
Published: April 2003

In the relativistic mean field (RMF) calculations usually the basis expansion method is employed. For this one uses single harmonic oscillator (HO) basis functions. A proper description of the ground state nuclear properties of spherical nuclei requires a large (around 20) number of major oscillator shells in the expansion. In halo nuclei where the nucleons have extended spatial distributions, the use of single HO basis for the expansion is inadequate for the correct description of the nuclear properties, especially that of the surface region. In order to rectify these inadequacies, in the present work an orthonormal basis composed of two HO basis functions having different sizes is proposed. It has been shown that for a typical case of (A=11) the ground state constructed using two-HO wave functions extends much beyond the second state or even third excited state of the single HO wave function. To demonstrate its usefulness explicit numerical RMF calculations have been carried out using this procedure for a set of representative spherical nuclei ranging from 16 O to 208 Pb . The binding energies, charge radii and density distributions have been correctly reproduced in the present scheme using a much smaller number of major shells (around 10) in the expansion.
FRACTAL MORPHOLOGY OF DEPOSITS IN HEAT EXCHANGERS AND THEIR PHYSICAL PROPERTIES
Authors: GOMATAM JAGANNATHAN , MULHOLLAND ANTHONY J.
Published: April 2003

Our fundamental hypothesis in this paper is that aggregated deposits grown on a substrate can be construed as media endowed with fractal properties over a finite range of temporal and spatial scales. We present image analysis of industrial deposits that confirm their fractal morphology and then derive an equation governing the thermal conductivity which displays an explicit dependence on the box-counting fractal dimension. We also study the percolation properties of shuffled Sierpinski carpets (SSC) by developing a real space renormalization group (RSRG) theory approach. The theoretical results are critically discussed with reference to the numerical solution of the steady-state heat equation in simulated fouling material.
TRANSIENT DYNAMICS AND SCALING PHENOMENA IN URBAN GROWTH
Authors: MANRUBIA SUSANNA C. , ZANETTE DAMIÁN H. , SOLÉ RICARD V.
Published: April 2003

Urban centers present all over the world striking similarities which translate into universal laws describing their growth and morphology. In this paper, we study a simple two-dimensional cellular automata model containing what we identify as essential ingredients in the demographic change. The slow addition of population to an initially empty area (mimicking migration) added with a reaction diffusion process (representing reorganization of the population) allow us to recover many real data and provide us with a better understanding of the main processes forming and shaping the modern metropolis.
FRACTALITY OF RAINFALL: IDENTIFICATION OF TEMPORAL SCALING LAW
Authors: LIN SHU-CHEN , LIU CHANG-LING , LEE TZONG-YEANG
Published: April 2003

This paper introduces the concept of point-fractal to analyze the time-scale variability of rainfall data on the northern and southern regions of Taiwan. It is evident that scale invariance exists in time and clustering will decrease in accord with the increase of threshold. Under the variation of threshold, it can be verified that the maximum values of the homogenous scale-invariant interval are just the same. In addition, taking the probability-scale law on different levels of threshold, the relation can be established between the saturation scale (return period) and the threshold (design hydrologic variable). The methodology is different from the traditional one, i.e. frequency analysis method. When both methods are compared, it is found that the former does not require either the probability density function or the calculation of parameters. We conclude that this study provides a new alternative method in computation.
BRITTLE-DUCTILE TRANSITION AND SCALE DEPENDENCE: FRACTAL DIMENSION OF FRACTURE SURFACE OF MATERIALS
Authors: IKESHOJI TOSHITAKA , SHIOYA TADASHI
Published: April 2003

The fractal dimension of fracture surfaces obtained within brittle-ductile transition regime is evaluated at various observation scales. Fracture surfaces are generated by the tensile fracture test. The brittle-ductile transition is accomplished by using the round-notched bar specimens with various notch radii, which cause the variation in stress triaxiality. The specimens are manufactured from mild steel, steel and cast-iron bar. The fracture model is identified according to the observation through scanning electron micrographs.

The fractal dimension for ductile fracture surfaces is almost constant despite variations in observing scale and changes in stress triaxiality. Meanwhile, the fractal dimension on brittle fracture surfaces shows the different values for macroscopic and microscopic observing scales. This transition-like scale dependence of fractal dimension for brittle fracture surfaces is considered to reflect such a characteristic of the fracture i.e. its specific length in microscopic fracture mechanism. The existence of transition in fractal dimension with observing scale is considered to be an index, used to distinguish the ductile fracture surface from the brittle fracture one.
INVESTIGATING CLUSTERING STRUCTURES IN TIME-OCCURRENCE SEQUENCES OF SEISMIC EVENTS OBSERVED IN THE IRPINIA-BASILICATA REGION (SOUTHERN ITALY)
Authors: TELESCA L. , CUOMO V. , LANFREDI M. , LAPENNA V. , MACCHIATO M.
Published: April 2003

We reveal the existence of clustering properties in the temporal distribution of the earthquakes observed in a seismic active area of Southern Apennine Chain (Italy) by means of quantitatively fractal tools (Fano Factor and Allan Factor). Data consist in a sequence of seismic events instrumentally recorded during the period 1983–1995 in the Irpinia-Basilicata Region (Southern Italy), in which in past and recent years, many destructive events occurred. The analysis of the Fano and Allan Factors shows that the sequence of the occurrence times of events with magnitude M th ≥2.5 is characterized by a scale-invariant behavior from the time scale τ ~ 5 · 103s with a scaling coefficient α ~ 0.3. By gradually increasing the threshold magnitude up to M th =3.1, the value of the scaling coefficient monotonically decreases, pointing out a falling-off in the correlation strength. Although the increasing of the threshold magnitude seems to act as a randomizing filter which removes clustered structures, no firm sign of Poissonian, memoryless behavior is detectable in our analysis.
LOCALIZATION NATURE OF VIBRATIONAL EXCITATIONS ON CLUSTER-CLUSTER AGGREGATION
Authors: TERAO TAKAMICHI , KOIZUMI TAKUYA , SUZUKI SHINICHIRO , NAKAYAMA TSUNEYOSHI
Published: April 2003

We study the vibrational dynamics of cluster-cluster aggregations(CCA) by computer simulation with emphasis on the localization nature of vibrational excitations on the CCA. The frequency dependence of the inverse participation ratio P-1(ω) obeys a power law such as P-1(ω)∝ω1.07±0.06 in two-dimensional system. In addition, we show that the time development of the average cluster size can be scaled by a characteristic time tc. After a sufficiently long time, the cluster size obeys the power law behavior, depending on the sticking probability between particles.
EIGENVALUES FOR HIGH ORDER ELLIPTIC OPERATORS IN A FRACTAL STRING
Authors: DENG HONG , PENG GONGWEN
Published: April 2003

In this paper, we study the spectrum of order 2m (m≥1) elliptic operator A in a bounded open set Ω∈R1, with fractal boundary Γ=∂Ω and Minkowski dimension D∈(0, 1), thus proving the corresponding modified Weyl-Berry conjecture to be true, namely [Formula: see text] where N(λ, A, Ω) is the counting function, [Formula: see text], C1, D =2-(1-D) π-D(1-D)(-ζ(D)), ζ(D) is the classical Riemann–zeta function, and ℳ(D, Γ) is the Minkowski measure of Γ.
HOW IS THE DYNAMICS OF KÖNIG ITERATION FUNCTIONS AFFECTED BY THEIR ADDITIONAL FIXED POINTS?
Authors: DRAKOPOULOS V.
Published: April 2003

König iteration functions are a generalization of Newton–Raphson method to determine roots of equations. These higher-degree rational functions possess additional fixed points, which are generally different from the desired roots. We first prove two new results: firstly, about these extraneous fixed points and, secondly, about the Julia sets of the König functions associated with the one-parameter family of quadratic polynomials. Then, after finding all the critical points of the König functions as applied to a one-parameter family of cubic polynomials, we examine the orbits of the ones available for convergence to an attracting periodic cycle, should such a cycle exist.
ANALYTICAL PROPERTIES OF SCATTERED INTENSITY FROM GAUSSIAN D-MANIFOLDS AND TWO-DIMENSIONAL MEMBRANES
Authors: ZEGHAIDER MUSTAPHA , BENHAMOU MABROUK
Published: April 2003

The purpose of the present work is a systematic and analytical study of the scattering properties of Gaussian D-manifolds (1≤D<2) and two-dimensional membranes (D=2). Here, D is the spectral (or internal) dimension of the polymeric complex. We first determine exactly their gyration radius and the higher order moments. Then, we construct a simple integral representation of the structure factor, in the case of D-manifolds (1≤D<2). By analytical continuation in dimension D, this representation enables us to get much information about those polymeric systems of non-integer internal dimension (ideal branched polymers, Gaussian polymeric fractals, etc.). For ideal linear polymers, with D=1, we recover the classical Debye function. An exact expression of the structure factor for Gaussian large two-dimensional membranes is also derived.
A REVIEW OF INFINITE ELEMENT METHODS FOR EXTERIOR HELMHOLTZ PROBLEMS
Authors: GERDES KLAUS
Published: April 2003

This work is devoted to review infinite element discretizations for the Helmholtz equation in exterior domains, which have become popular in recent years, as many research papers on this topic have appeared in the literature. The early contributions were mostly motivated by engineering considerations and the variational formulations have, in general, not been stated in a mathematically precise way. Only recently, theoretical aspects of the infinite element methodology have been analyzed and helped to put the different formulations into a mathematical framework. We build upon this, and present and compare the infinite element formulations within this context.
GENERALIZATION OF ZWIKKER AND KOSTEN THEORY FOR SOUND ABSORPTION IN FLEXIBLE POROUS MEDIA TO THE CASE OF VARIABLE PARAMETERS
Authors: SHOSHANI YAKIR , YAKUBOV YAKOV
Published: April 2003

The paper suggests a generalization of Zwikker and Kosten theory for sound absorption in porous flexible media. We have considered the case in which the intrinsic characteristics of the medium, such as its porosity or compressibility, are varied along the direction of propagation of the sound wave. The eigenvalue problem was reformulated to encompass variable intrinsic properties, and several theorems which justify the numerical evaluation of the approximated solutions, were thoroughly analyzed and proved. We believe that this work might serve as a guideline for the design of acoustic blankets or barriers made of multilayer combination of nonwoven fiber webs of different characteristics.