bluuebunny/crossref_metadata_2025 huggingface dataset:
BIFURCATION STRUCTURE OF THE DOUBLE-WELL DUFFING OSCILLATOR
Authors: KIM SANG-YOON
Published: May 2003

We consider a forced Duffing oscillator with a double-well potential, which behaves as an asymmetric soft oscillator in each potential well. Bifurcations associated with resonances of the asymmetric attracting periodic orbits, arising from the two stable equilibrium points of the potential, are investigated in details by varying the two parameters A (the driving amplitude) and ω (the driving frequency). We thus obtain the phase diagram showing rich bifurcation structure in the ω-A plane. For the subharmonic resonances, the corresponding period-doubling bifurcation curves become folded back, within which diverse bifurcation phenomena such as "period bubblings" are observed. For the primary and superharmonic resonances, the corresponding saddle-node bifurcation curves form "horns", leaning to the lower frequencies. With decreasing ω, resonance horns with successively increasing torsion numbers recur in a similar shape. We note that recurrence of self-similar resonance horns is a "universal" feature in the bifurcation structure of many driven nonlinear oscillators.
ASPECTS OF THE STOCHASTIC BURGERS EQUATION AND THEIR CONNECTION WITH TURBULENCE
Authors: HAYOT F. , JAYAPRAKASH C.
Published: May 2003

We present results for the one-dimensional stochastically forced Burgers equation when the spatial range of the forcing varies. As the range of forcing moves from small scales to large scales, the system goes from a chaotic, structureless state to a structured state dominated by shocks. This transition takes place through an intermediate region where the system exhibits rich multifractal behavior. This is mainly the region of interest to us. We only mention in passing the hydrodynamic limit of forcing confined to large scales, where much work has taken place since that of Polyakov.1

In order to make the general framework clear, we give an introduction to aspects of isotropic, homogeneous turbulence, a description of Kolmogorov scaling, and, with the help of a simple model, an introduction to the language of multifractality which is used to discuss intermittency corrections to scaling.

We continue with a general discussion of the Burgers equation and forcing, and some aspects of three-dimensional turbulence where — because of the mathematical analogy between equations derived from the Navier–Stokes and Burgers equations — one can gain insight from the study of the simpler stochastic Burgers equation. These aspects concern the connection of dissipation rate intermittency exponents with those characterizing the structure functions of the velocity field, and the dynamical behavior, characterized by different time constants, of velocity structure functions. We also show how the exponents characterizing the multifractal behavior of velocity structure functions in the above mentioned transition region can effectively be calculated in the case of the stochastic Burgers equation.
NONLINEAR FIELD ANALYSIS OF THE HUBBARD MODEL IN ONE AND TWO DIMENSIONS IN THE CONTINUUM LIMIT
Authors: DIXON J. M. , TUSZYŃSKI J. A. , NIP M. L. A. , SEPT D. , VOS K. J. E.
Published: May 2003

We investigate the Hubbard Hamiltonian's properties in the continuum limit by implementing the procedures of the Method of Coherent Structures (MCS). We obtain field equations of motion and analyse the phase dynamics of the resultant classical spin fields. We have performed analytical and numerical calculations to find appropriate physically acceptable solutions to the equations of motion in one-dimensional space. In two-dimensional space, among other types, we have found several different spin phases of vortex type, spiral patterns and parabolic spin arrangements. Our results are consistent with earlier Hartree–Fock finite-grid numerical simulations.
COTUNNELING AND KONDO-TYPE TRANSPORT OF A QUANTUM DOT
Authors: XIONG SHI-JIE
Published: May 2003

We investigate the transport properties of a multi-level quantum dot with strong electron–electron interaction by the use of the equivalent single-particle multi-channel network and Landauer formulae. By including the effect of cotunneling to the leads the calculated results show Kondo-type transport in valleys of conductance as a function of the gate voltage which was found in recent experiments. We calculate the Kondo temperature for various parameters. We discuss the condition for observing this effect in the experiments.
PHONON SCATTERING BY BREATHERS IN THE DISCRETE NONLINEAR SCHRÖDINGER CHAIN
Authors: LEE SUNG-SIK , KIM SEUNGHWAN
Published: May 2003

Linear theory for phonon scattering by discrete breathers in the discrete nonlinear Schrödinger equation using the transfer matrix approach is presented. Transmission and reflection coefficients are obtained as a function of the wave vector of the input phonon. The occurrence of a nonzero transmission, which in fact becomes perfect for a symmetric breather, is shown to be connected with localized eigenmodes thresholds. In the weak-coupling limit, the perfect reflection is shown to exist, which requires two scattering channels. A necessary condition for a system to have a perfect reflection is also considered in a general context.
THE ROLE OF THE CARRIER MASS IN SEMICONDUCTOR QUANTUM DOTS
Authors: SINGH M. , RANJAN V. , SINGH VIJAY A.
Published: May 2003

In the present work we undertake a re-examination of effective mass theory (EMT) for a semiconductor quantum dot. We take into account the fact that the effective mass (mi) of the carrier inside the dot of radius R is distinct from the mass (m0) in the dielectric coating surrounding the dot. The electronic structure of the quantum dot is determined in crucial ways by the mass discontinuity factor β ≡mi/m0. In this connection we propose a novel quantum scale, σ, which is a dimensionless parameter proportional to β2V0R2, where V0 represents the barrier due to dielectric coating. The scale σ represents a mass modified " strength" of the potential. We show both by numerical calculations and asymptotic analysis that the charge density near the nanocrystallite surface, ρ(r=R), can be large and scales as 1/σ. This fact suggests a significant role for the surface in an EMT based model. We also show that the upshift in the ground state energy is weaker than quadratic, unlike traditional EMT based calculations, and chart its dependence on the proposed scale σ. Finally, we demonstrate that calculations based on our model compare favorably with valence band photoemission data and with more elaborate theoretical calculations.
SELF-ORGANIZING NEURAL NETWORK MODEL OF THE SENSORY-MOTOR MECHANISM
Authors: ANDRECUT M. , ALI M. K.
Published: May 2003

We describe a new biologically motivated model of the sensory-motor mechanism. The model is based on a self-organizing neural network with modifiable lateral interactions and a "master-slave" connection between the sensorial and motor modules. The results show that the described model is a useful feature that can be exploited by autonomous agents. An example of implementation in the case of a "moving virtual creature" is also presented.
SELF-ADAPTING REACTIVE AUTONOMOUS AGENTS
Authors: ANDRECUT M. , ALI M. K.
Published: May 2003

This paper describes a new self-adapting control algorithm for reactive autonomous agents. The architecture of the autonomous agents integrates the reactive behavior with reinforcement learning. We show how these components perform on-line adaptation of the autonomous agents to various complex navigation situations by constructing an internal model of the environment. Also, a discussion on cooperation and coordination of teams of agents is presented.
THE ZERO FLUX SURFACE OF THE ELECTRONIC WAVEFUNCTION'S GRADIENT
Authors: DELLE SITE L.
Published: May 2003

In a previous publication we derived a criterion for defining interatomic surfaces in condensed systems based on the zero flux surface (ZFS) of the electronic wavefunction's gradient which holds the condition of flux zero at every point. Here this criterion is examined and physical as well as mathematical properties are illustrated and discussed; in the light of this discussion we conclude that the definition illustrated in this work represents a natural extension of Bader's definition of atoms in molecules.
STUDY OF STRUCTURAL STABILITY OF WIGNER ELECTRON CRYSTAL
Authors: PALANICHAMY R. RAJESWARA , IYAKUTTI K.
Published: May 2003

The ground state energies of the non-magnetic Wigner electron crystals corresponding to sc, bcc, fcc, diamond and perovskite structures are estimated and it is found that the bcc lattice still remains to be the stable known arrangement for three-dimensional Wigner electron crystal. Perovskite structure is not the stablest as claimed in a previous work, it is preferred only after fcc and sc. The stability is analysed taking different structures and assuming the possibility of the Wigner electrons having cubic or spherical constant energy surface, the region of occupation in momentum space, for a whole range of rs values (rs=20 to 200). The structure dependent Wannier functions, which give a proper localized representation for the Wigner electrons in the crystals are constructed and employed in the present calculation.
LOW TEMPERATURE LINEAR DYNAMICAL SUSCEPTIBILITY OF THE ISING SPIN GLASS IN A TRANSVERSE FIELD
Authors: BUSIELLO G. , SABUROVA R. V.
Published: May 2003

Low-temperature equilibrium dynamical behavior of the linear ac susceptibility in d-dimensional Ising spin glass with short-range interactions between spins in transverse field is investigated in terms of droplet model. The real part of linear ac susceptibility [Formula: see text] as functions of temperature T and frequency of external ac field ω is calculated. Frequency and temperature dependence of [Formula: see text] shows a glassy behavior. For instance, we find a broad maximum for [Formula: see text] which shifts towards higher temperatures with increasing frequency of ac-field. The temperature of maximum Tf(ω) depends on frequency and increases with frequency up to the magnitude where [Formula: see text] starts to decrease.

A qualitative agreement of our calculations with experimental data, for example, in quantum dipole magnet LiHoxY1-xF4 and proton glasses, is found.
MOTT TRANSITION IN A HELIX-BASED COMPLEX
Authors: UGAJIN R. , ISHIMOTO C. , HIRATA S. , MORI Y.
Published: May 2003

We introduce a helix-based complex, which we will call a multiply-twisted helix, in which a one-dimensional array of components, e.g. atoms or nanoclusters, is twisted, producing a helix, which if itself twisted, produces a doubly-twisted helix, which we can think of as the simplest multiply-twisted helix. In the hierarchy of helical structures, the mean number of nearest neighbors can be controlled by adjusting the number of components in a round of helices. The Hubbard model is used to analyze the Mott transition in a multiply-twisted helix, where electrons can move not only along a one-dimensional array but also between sub-rounds in adjacent larger rounds. The critical strength of electron–electron interaction in a Mott transition can also be controlled by adjusting the number of components in a round, as suggested by our mean-field analysis of half-filled electrons.
DIRECTED MOTION INDUCED BY SHIFTING RATCHET
Authors: LI YUXIAO , WU XIZHEN , ZHUO YIZHONG
Published: May 2003

The motion of Brownian particles in a spatial asymmetric periodic potential is considered. In the absence of any external macroscopic driving force, when the potential transits stochastically between two configurations which are shifted by a distance relative to each other, directed motion can be induced. The dependence of the average velocity on the transition rate, the strength of thermal noise and the shift distance between the two configurations of potential are analyzed. The efficiency of the system is evaluated.
FIRST EXCITED STATE CALCULATION USING DIFFERENT PHONON BASES FOR THE TWO-SITE HOLSTEIN MODEL
Authors: CHATTERJEE JAYITA , DAS A. N.
Published: May 2003

The single-electron energy and static charge-lattice deformation correlations have been calculated for the first excited state of a two-site Holstein model within perturbative expansions using different standard phonon bases obtained through Lang–Firsov (LF) transformation, LF with squeezed phonon states, modified LF, modified LF transformation with squeezed phonon states, and also within weak-coupling perturbation approach. Comparisons of the convergence of the perturbative expansions for different phonon bases reveal that modified LF approach works much better than other approaches for major range of the coupling strength.
ONE-DIMENSIONAL SPIN-ONE HEISENBERG ANTIFERROMAGNET WITH SINGLE-ION ANISOTROPY IN A MAGNETIC FIELD: SCHWINGER BOSON THEORY
Authors: SU GANG , XING HUAIZHONG , XUE DESHENG , CHEN ZIYU , LI FASHEN
Published: May 2003

The one-dimensional spin-one Heisenberg antiferromagnet with single-ion anisotropy in the presence of the applied magnetic field is explored in terms of the Schwinger boson mean-field theory. The temperature and anisotropy dependences of the specific heat, the susceptibility and the magnetization are thoroughly discussed. New features of the specific heat as a function of temperature as well as anisotropy are found. A transition from an antiferromagnetic phase to a spin-canting phase is observed, and meanwhile, a schematic phase diagram is proposed.
EFFECT OF THE COUPLING BETWEEN THE NORMAL AND LATERAL DEGREES OF FREEDOM ON LOCALIZED ELECTRONIC STATES IN SUPERLATTICE'S WITH STRUCTURAL DEFECTS
Authors: CHEN KE-QIU , WANG XUE-HUA , GU BEN-YUAN
Published: May 2003

Using a effect-barrier height method, we investigate the effect of coupling between normal and lateral degree of freedom of an electron on the localized electronic states at zero and finite magnetic fields perpendicular to interfaces in SL's with structural defect layer within the framework of effective-mass theory. The numerical calculations for GaAs/AlxGa1-xAs material show that minibands, minigaps and localized levels is obviously dependent on the transverse wave number kxy. Magneto-coupling effect brings about not only the splitting of the localized electron levels but also the definite dependence of the minibands, minigaps, localized levels and localization degree on magnetic field and Landau indices. It is believed that applying an appropriate magnetic field may provide a available way to control the minibands, minigaps and localized levels in structural defect superlattice's to match practice requirements.
CHAOTIC HIERARCHY IN HIGH DIMENSIONS
Authors: POSTNOV D. E. , BALANOV A. G. , SOSNOVTSEVA O. V. , MOSEKILDE E.
Published: May 2003

The paper suggests a new mechanism for the development of higher-order chaos in accordance with the concept of a chaotic hierarchy. A discrete-time model is proposed which demonstrates how the creation of coexisting chaotic attractors combined with boundary crises can produce a continued growth of the Lyapunov dimension of the resulting chaotic behavior.
ANISOTROPIC COMPRESSION IN DIMER C60 FULLERENE SOLID
Authors: KAUR NARINDER , BAJWA NAVDEEP , DHARAMVIR K. , JINDAL V. K.
Published: May 2003

Dimer C60 solids are monoclinic crystals with molecular longer axis aligned along the c-axis. A simple model based on atom-atom potential used to calculate various bulk, structural and thermodynamic properties of this fullerite, has also been used to investigate the pressure and temperature dependent properties such as bulk modulus, lattice and orientational structure, phonon dispersion relations, Gruneisen parameters, heat capacity and entropy. An important feature of this solid evidently concerns its anisotropic pressure compression. We calculate these directional compressibilities and find the anisotropy for pressure compression very significant. It is expected that the properties of dimer solid C60 calculated here will motivate further experimentation on this solid.
A STRONG-COUPLING EXPANSION FOR THE HUBBARD MODEL
Authors: DUPUIS N. , PAIRAULT S.
Published: May 2003

We reconsider the strong-coupling expansion for the Hubbard model recently introduced by Sarker and Pairault et al. By introducing slave particles that act as projection operators onto the empty, singly occupied and doubly occupied atomic states, the perturbation theory around the atomic limit distinguishes between processes that do conserve or do not conserve the total number of doubly occupied sites. This allows for a systematic t/U expansion that does not break down at low temperature (t being the intersite hopping amplitude and U the local Coulomb repulsion). The fermionic field becomes a two-component field, which reflects the presence of the two Hubbard bands. The single-particle propagator is naturally expressed as a function of a 2×2 matrix self-energy. Furthermore, by introducing a time- and space-fluctuating spin-quantization axis in the functional integral, we can expand around a "non-degenerate" ground-state where each singly occupied site has a well defined spin direction (which may fluctuate in time). This formalism is used to derive the effective action of charge carriers in the lower Hubbard band to first order in t/U. We recover the action of the t–J model in the spin-hole coherent-state path integral. We also compare our results with those previously obtained by studying fluctuations around the large-U Hartree–Fock saddle point.
SUPERCONDUCTIVITY OF SYSTEMS WITH COEXISTING ITINERANT ELECTRONS AND LOCAL PAIRS
Authors: CZART WOJCIECH R. , ROBASZKIEWICZ STANISŁAW
Published: May 2003

Phase diagrams and electromagnetic properties of the system of coexisting itinerant (c)-electrons and localized (d)-electrons which can form real space local pairs are analyzed. The model considered assumes arbitrary value of the on-site density interaction of d-electrons U d , which allows investigation of the effects of reduced d-pair binding energy. The phase diagrams of the system have been evaluated within the approach which treats the on-site interaction term U d exactly and the remaining interactions within the broke symmetry HFA. Within the linear response theory the electromagnetic kernels are calculated and basic superfluid characteristics of the system are determined as a function of electron concentration, interactions and relative position of the bands. Depending on parameters the model is found to exhibit several kinds of superconducting behaviors ranging from the BCS-like to the local pair-like. The relevance of obtained results to the interpretation of experimental data for short-coherence length superconductors is pointed out.
NANO-CRYSTALS OF c-DIAMOND, n-DIAMOND AND i-CARBON GROWN IN CARBON-ION IMPLANTED FUSED QUARTZ
Authors: PENG J. L. , ORWA J. O. , JIANG B. , PRAWER S. , BURSILL L. A.
Published: May 2003

Combined high-resolution transmission electron microscopy, selected area electron diffraction and parallel electron energy loss spectroscopy are used to characterise carbon nano-phases found embedded in fused quartz. These appear after implantation of 1 MeV carbon ions, followed by annealing in argon, oxygen and forming gas for 1 hour at 1100°C. For Ar, virtually all of the carbon diffuses out of the substrate with no observable carbon clusters for all doses studied. After annealing in oxygen, a crystalline CO x phase is identified at the end of range, following a dose of 5×1017 C/cm 2.

Three nano-crystalline carbon phases, including diamond, appear after annealing in forming gas: these form a layer 170 nm beneath the fused quartz surface for all ion doses. The average size of these clusters and the corresponding phases depend on the ion dose; the smallest size of 5–7 nm diameter crystallise as fcc [Formula: see text] diamond following a dose of 0.5× 1017 C/cm 2, whereas clusters of 8–13 nm diameter, for a higher dose of 2× 1017 C/cm 2, have a [Formula: see text] modified phase of diamond known as n-diamond. The largest clusters, diameter 15–40 nm, for a dose of 5× 1017 C/cm 2, have the cubic P2 13 (or P4 232) structure known as i-carbon.

These buried layered diamond and diamond-related materials may have applications for field emission and optical waveguide type devices.
OSCILLATIONS OF SPHERICAL AND CYLINDRICAL SHELLS
Authors: ERDIN SERKAN , POKROVSKY VALERYC L.
Published: May 2003

We have found the complete spectrum and eigenstates for harmonic oscillations of ideal spherical and cylindrical shells, both being infinetely thin. The spectrum of the cylindrical shell has an infinite number of Goldstone modes corresponding to folding deformations. This infrared catastrophe is overcome by accounting for curvature-dependent part of energy.
COOPERATIVE PHASE DYNAMICS IN COUPLED NEPHRONS
Authors: POSTNOV D. E. , SOSNOVTSEVA O. V. , MOSEKILDE E. , HOLSTEIN-RATHLOU N.-H.
Published: May 2003

The individual functional unit of the kidney (the nephron) displays oscillations in its pressure and flow regulation at two different time scales: Relatively fast oscillations associated with the myogenic dynamics of the afferent arteriole, and slower oscillations related with a delay in the tubuloglomerular feedback. Neighboring nephrons interact via vascularly propagated signals. We study the appearance of various forms of coherent behavior in a model of two such interacting nephrons. Among the observed phenomena are in-phase and anti-phase synchronization of chaotic dynamics, multistability, and partial phase synchronization in which the nephrons attain a state of chaotic phase synchronization with respect to their slow dynamics, but the fast dynamics remains desynchronized.
QUANTUM–CLASSICAL PHASE TRANSITION OF NUCLEATION RATE IN A ONE-DIMENSIONAL UNIAXIAL HEISENBERG MODEL WITH A MAGNETIC FIELD AT AN ARBITRARY DIRECTION
Authors: ZHOU BIN , LIANG JIU-QING
Published: May 2003

We study crossover from quantum tunneling to thermal activation of nucleation rate in a one-dimensional uniaxial Heisenberg model with a magnetic field applied at an arbitrary direction. Considering the periodical boundary condition of spatial coordinate, the type of transition depends critically on the length of ferromagnetic chain. In the low barrier limit two different critical parameter values distinguishing the types of transition are obtained for different angles between the direction of magnetic field and the easy axis (π/2≪ φ H ≪ π and φ H =π).
EPR STUDY OF Fe3+ AND Mn2+ DOPED AMORPHOUS AND CRYSTALLINE ALUMINUM BORATES
Authors: SIMON S. , ARDELEAN I. , PETEANU M. , POP M. , STEFAN R.
Published: May 2003

Amorphous and crystalline aluminum borates prepared by sol–gel method doped with iron and manganese were studied by electron paramagnetic resonance in order to determine the matrix effects on Fe3+ and Mn2+ environments during their consolidation by heat treatment up to 860°C. In amorphous matrices, after heat treatments up to 600°C, the Fe3+ environment is almost unaffected but the vicinity of Mn2+ ions is relatively strongly disordered. In partial crystalline alumina and aluminum borate samples, obtained after heat treatments applied at 860°C, the Fe3+ sites are subjected to completely different crystalline fields, as regards intensity and symmetry. If in crystalline alumina we have both sites typical for α and γ phases in crystalline aluminum borate, the well-known spectrum of Fe3+ in disordered systems seems to be solved, suggesting more than one well-defined site. In the case of manganese-doped samples, only a diminishing of hyperfine resolution with increasing heat treatment temperature is observed as a result of environment distortion by improvement of alumina borate sample crystallinity.
MEASUREMENT OF A QUANTUM SYSTEM COUPLED TO INDEPENDENT HEAT-BATH AND POINTER MODES
Authors: MOZYRSKY DIMA , PRIVMAN VLADIMIR
Published: May 2003

We present an exact derivation of a process in which a microscopic measured system interacts with the heat-bath and pointer modes of a measuring device, via a coupling involving a general Hermitian operator Λ of the system. In the limit of strong interaction with these modes, over a small time interval, we derive the exact effective many-body density matrix of the measured system plus pointer. We then discuss the interpretation of the dynamics considered as the first stage in the process of quantum measurement, eventually involving the wave-function collapse due to interactions with "the rest of the universe". We establish that the effective density matrix represents the required framework for the measured system and the pointer part of the measuring device to evolve into a statistical mixture described by direct-product states such that the system is in each eigenstate of Λ with the correct quantum-mechanical probability, whereas the expectation values of the pointer-space operators retain amplified information of the system's eigenstate.
THE THERMAL DENATURATION OF DNA IN THE PEYRARD–BISHOP MODEL
Authors: NYEO SU-LONG , YANG I-CHING
Published: May 2003

The statistical mechanics of DNA denaturation is studied with the Morse potential. We point out that the results of Peyrard and Bishop do not correctly reflect the statistics relation  ≥ 2, at the region of delocalized states, for the DNA interstrand separation y. The correct results are given.
LYAPUNOV SPECTRA OF CORRELATED RANDOM MATRIX PRODUCTS
Authors: OKABE TSUNEYASU , YAMADA HIROAKI
Published: May 2003

We have numerically studied the Lyapunov spectra and the maximal Lyapunov exponent (MLE) in products of real symplectic correlated random matrices, each of which is produced by a modified Bernoulli map. As a statistical property, it has been well studied that the correlation function of the sequence of the map shows power-low decay. We can systematically investigate the influence of the correlation on the Lyapunov spectra and the fluctuation-strength dependence of the MLE. It is shown that the form of the scaled Lyapunov spectra does not change even if the correlation increases in the stationary region of the sequence, and in the nonstationary region, the form is quite different from the one in the stationary region. The power of the scaling law for the fluctuation-strength dependence of the MLE becomes small as the correlation increases, and a different scaling law can be observed in the strongly correlated nonstationary region as from the δ-correlated case.
ELECTRICAL PROPERTIES OF Na2O–CdO–P2O5 GLASSES
Authors: CHAUDHRY M. A. , ALTAF M.
Published: May 2003

The direct current (dc) electrical conductivity of the Na 2 O – CdO – P 2 O 5 glasses has been determined in the temperature range 293–423 K. Activation energy of the samples lies in the range 0.56–0.96 eV. The field-lowering coefficient β has also been determined.
LOW ENERGY PROPERTIES OF A FRUSTRATED ANTIFERROMAGNETIC SPIN-1/2 LADDER
Authors: WANG XIAOQUN
Published: May 2003

Using the density matrix renormalization group method, we determined the phase diagram of a frustrated antiferromagnetic spin-[Formula: see text] ladder at zero temperature. Two spin-gapped phases, the Haldane phase and the singlet phase, are identified. In particular, impurity effects are experimentally detectable for the Haldane phase. A phase transition between the two phases occurs at any nonzero value of frustration coupling J×. On the phase boundary, the spin gap vanishes for sufficiently small J×. Crossing this line of gapless states, the transition is of second order, while it is of first order for larger J×.
ON THE INFRARED HALL EFFECT ABOVE Tc IN YBCO
Authors: FUJITA SHIGEJI , KIM YOUNG-GI
Published: May 2003

A kinetic theory is developed for the infrared Hall effect. Expressions for the dynamic conductivity σ(ω), ω = laser frequency, and other transport coefficients are shown to be obtained by applying the conversion rule: γ0 → γ -iω to those for the static coefficients, where γ0 (γ) are the static (dynamic) scattering rates. The observed T2-law of [Formula: see text] in YBa 2 Cu 3 O 7 are shown to arise from the drift velocity of the low-energy Cooper pairs (pairons) moving with the linear dispersion relation: ε = (2/π) v F p, where v F is the Fermi velocity.
KINETIC THEORY OF INFRARED HALL EFFECT IN SIMPLE METALS
Authors: FUJITA SHIGEJI , KIM YOUNG-GI , OKAMURA YOSHINOBU
Published: May 2003

A kinetic theory is developed for the infrared (IR) Hall effect. The dynamic transport coefficients including the conductivity σ, cot θ H (θ H = Hall angle ) and the Hall coefficient R H for a system of conduction electrons ("electrons" or "holes") are shown to be obtained by applying the conversion rule: γ0 → γ(ω) -iω to the expressions for the static coefficients, where γ0 [γ(ω)] are static (dynamic) scattering rates which depend on the frequency ω and temperature T. If the real (Re) and imaginary (Im) parts of σ(ω) are measured, the ratio Re [σ(ω)]/ Im [σ(ω)] is equal to γ/ω, which directly gives the dynamic rate γ(ω, T). The ratio Re [ cot θ H ]/ Im [ cot θ H ] = -γ H (ω, T)/ω yields the dynamic Hall rate γ H (ω, T). The IR Hall effect experiments give a remarkable result: γ H (ω, T) = γ H , 0(T), that is, the dynamic Hall scattering rate is equal to the static rate up to mid-IR ~1000 cm -1.
THE PROCESS OF PHASE CHANGE OF TRANSMISSION THROUGH A MESOSCOPIC RING WITH A QUANTUM DOT
Authors: ZHANG GANG , CAO ZHILIANG , GU BING-LIN
Published: May 2003

In this paper, we study the transmission through a mesoscopic ring with a quantum dot embedded in one of its arms with the one-dimensional wave guide theory. We discuss the detailed process of the phase change when a resonant tunneling through the dot occurs. We find that when the state of the dot is far from a resonance, the transmission coefficient is periodic with a period equal to the flux quantum Φ0. However, when a resonant tunneling through the dot occurs, the transmission coefficient is a periodic function of Φ with a period [Formula: see text]. This phenomenon is consistent with the experimental results.
Mg–Mn–Al FERRITES FOR HIGH FREQUENCY APPLICATIONS
Authors: SINGH M. , SUD S. P.
Published: May 2003

The effect of substitution of nonmagnetic Al 3+ ions on the electrical and magnetic properties of Mg–Mn ferrites was studied in the ferrite series Mg 0.9 Mn 0.1 Al x Fe 2-x O 4 where x varied from 0–0.5 in steps of 0.1. The incorporation of Al 3+ ions in place of Fe 3+ ions results in a decrease of the lattice parameter owing to the smaller size of the substituted ions. The increase in dc resistivity has been observed at the expense of the deterioration of magnetic properties. A significant reduction in the values of the initial permeability, saturation magnetization and Curie temperature has been observed with successive increase of Al 3+ ions. These changes in properties have been explained on the basis of various models and other relevant factors, like modified cation distribution and magnetic interactions. The high dc resistivity, thereby lowering the dielectric losses, and the low value of the saturation magnetization are the desired characteristics of aluminium-substituted Mg–Mn ferrites used to prepare microwave devices operating in L, S and C bands.
PROPERTIES AND PREPARATION OF AlN THIN FILMS BY REACTIVE LASER ABLATION WITH NITROGEN DISCHARGE
Authors: WANG HONG-HAI
Published: May 2003

Highly oriented AlN thin films have been deposited on (100) and (111) Si wafers by reactive laser ablation with nitrogen discharge at low substrate temperature. The composition and microstructure of films strongly depend on deposition parameters. X-ray photoelectron spectra showed that nitrogen discharge is of great importance to the composition of the films. The effect of substrate temperature on the preferred orientation of films has been investigated carefully by means of X-ray diffraction. Under optimizing deposition parameters — 1.0 J/cm 2 laser fluence, 5 Hz pulse frequency, 100 mTorr nitrogen pressure, 650 V discharge voltage and 200°C substrate temperature — the AlN films deposited on silicon substrates were smooth, dense and stoichiometric with very good preferred orientation. The orientation relationships between films and substrates were AlN(100)//Si(100) and AlN(110)//Si(111). The average refractive index was found to be 2.05 with the usage of an ellipsometer. The films had a band gap of 6.2 eV as measured by UV–visible absorption. The IR spectrum had an absorption characteristic of AlN. Examination of electric properties of films that was carried out on the metal–insulator–semiconductor structure of Au/AlN/Si showed that the dielectric constant, resistivity and breakdown field were 8.3, 2 × 1013 Ω· cm and 3 × 106 V/cm , respectively.
THERMAL STRESS RELAXATION BY A COMPOSITION-GRADED INTERMEDIATE LAYER
Authors: HOU Q.-R. , GAO J.
Published: May 2003

A simple model has been proposed to calculate the thermal stress distribution for diamond-like carbon films deposited on silicon substrates with a composition-graded intermediate layer. In this model, the intermediate layer is divided into many thin layers, and the thermal stress in one thin layer is caused by the difference in thermal expansion coefficients between this layer and the adjacent layer. It is found that the thermal stress distribution in the intermediate layer is strongly dependent on the composition profile of the intermediate layer. By choosing a proper composition profile, the thermal stress near the interlayer/substrate interface will be very small and this small stress is beneficial to enhancing adhesion of the film. For diamond-like carbon films deposited on silicon substrates, the experimental results are in agreement with the theoretical prediction qualitatively.
BINDING ENERGY OF BIEXCITONS IN A QUANTUM DISK
Authors: XIE WENFANG , LIN D. L.
Published: May 2003

The method of few-body physics is applied to treat a system of two excitons in a quantum disk. The binding energy of a biexciton is calculated for various confinements. It is found that the biexciton binding energy drops sharply to zero, i.e. there exists a critical radius RC, such that if R>RC (R<RC), the biexciton configuration is stable (unstable). From [Formula: see text], we obtain RC~0.5[Formula: see text], indicating the existence of a repulsive core of interaction between the two neutral excitons. The dependence of the ratio of biexciton binding energy to that of the exciton on the disk thickness is also investigated.
TUNNELING TRANSPORT IN STM-TIP–NANOTUBE–SUBSTRATE SYSTEMS
Authors: ZHANG GANG , CAO ZHILIANG , GU BING-LIN
Published: May 2003

In this paper, we considered a single-wall carbon nanotube deposited on a substrate and probed by a scanning probe. We calculated the current and differential conductance dI/dV versus the bias voltage V in this system. We found that currents through nanotubes become saturated in high voltages. This result shows the one-dimensional characteristic of carbon nanotubes. Our results are consistent with experiments which were carried out in low bias voltage regime and can be tested easily by experiments in higher bias voltage regime.
CHARACTERISTICS OF GeV ELECTRON BUNCHES ACCELERATED BY INTENSE LASERS IN VACUUM
Authors: WANG P. X. , HO Y. K. , KONG Q. , YUAN X. Q. , CAO N. , FENG L.
Published: May 2003

This paper studies the characteristics of GeV electron bunches driven by ultra-intense lasers in vacuum based on the mechanism of capture and violent acceleration scenario [CAS, see, e.g. J. X. Wang et al., Phys. Rev.E58, 6575 (1998)], which shows an interesting prospect of becoming a new principle of laser-driven accelerators. It has been found that the accelerated GeV electron bunch is a macro-pulse composed of a lot of micro-pulses, which is analogous to the structure of the bunches produced by conventional linacs. The macro-pulse corresponds to the duration of the laser pulse while the micro-pulse corresponds to the periodicity of the laser wave. Therefore, provided that the incoming electron bunch with comparable sizes as that of the laser pulse synchronously impinges on the laser pulse, the total fraction of electrons captured and accelerated to GeV energy can reach more than 20%. These results demonstrate that the mechanisms of CAS is a relatively effective accelerator mechanism.
GROWTH AND CHARACTERIZATION OF Cd1-xZnxS FILMS BY CHEMICAL BATH DEPOSITION
Authors: NAYEEM ABDUL , VAJRALINGAM G. , YADAIAH K. , NAGABHOOSHANAM M.
Published: May 2003

Thin films of C d 1-x Zn xS solid solutions are grown by the chemical bath deposition method with 0≤x<1. The films are characterized by X-ray, optical and electrical measurements. X-ray studies have indicated that the films have polycrystalline nature. Optical studies have also shown that the films possess polycrystalline nature with tiny crystallites in the form of platelets. Electrical conductivity studies have revealed two activation energies in solid solutions for x≤0.2 and one activation energy value for x>0.2. The results are explained in terms of mixed hexagonal and cubic crystalline structures.
PHASE DIAGRAMS OF TWO FKD MODELS WITH DIFFERENT TRIPLE-WELL INTERACTIONS
Authors: XU HAIBO , XU AIGUO , WANG GUANGRUI , CHEN SHIGANG
Published: May 2003

We introduce two typical Frenkel–Kontorova–Devonshire (FKD) models where the interactions are of different triple-well potentials and the external potentials are of the same parabolic type. The exact phase diagrams are worked out by the use of the effective potential method with the numerical implementation. We also analyze the periodicity of the phase diagrams and find that the properties of the phase structures are closely related to the period of the external potential D.
TRANSFER OF PROTON AND ELECTRON IN HYDROGEN-BONDED CHAINS
Authors: ZHOU BIN , XU JI-ZHONG , LIANG JIU-QING
Published: May 2003

In this paper, we suggest a mechanism of charge transport in hydrogen-bonded chains where one electron is trapped by an antikink defect in proton sublattice. The bell-shaped electronic wave function, localized in the compression area of the proton sublattice, is found. It is called the electrosoliton state. The electrosoliton and the antikink defect in proton sublattice form an electrosoliton-antikink pair.
ALGEBRAIC EQUIVALENCE BETWEEN CERTAIN MODELS FOR SUPERFLUID–INSULATOR TRANSITION
Authors: AMICO LUIGI
Published: May 2003

Algebraic contraction is proposed to realize mappings between Hamiltonian models. This transformation contracts the algebra of the degrees of freedom underlying the Hamiltonian. The rigorous mapping between the anisotropic XXZ Heisenberg model, the quantum phase model and the Bose Hubbard model is established as the contractions of the algebra u(2) underlying the dynamics of the XXZ Heisenberg model.
PHOTOELECTRON SPECTROSCOPY ON IRON-CONTAINING CaO–SiO2–P2O5GLASS CERAMICS
Authors: SIMON V. , CHIUZBĂIAN S. G. , NEUMANN M. , ENIU D. , INDREA E. , TÖRÖK-KISS A. , SIMON S.
Published: May 2003

The influence of isochronous heat treatments, applied at different temperatures between 1000 and 2000°C under the same conditions and schedules, on the elemental composition of iron-containing CaO–SiO2–P2O5glass ceramics was investigated by X-ray-induced photoelectron spectroscopy. Differences in the elemental composition, with the exception of the oxygen content, are observed. Major modifications are obtained for the glass ceramic resulting after the heat treatment carried out at 1000°C. It contains the highest iron concentration on the investigated surface and has a Ca/P ratio about three times higher than the untreated sample.
THEORY OF TURBULENT SHEAR STRESS
Authors: DEKKER H.
Published: May 2003

Using dynamical response functions for 3D turbulent shear flow, I calculate the Reynolds stress spectrum on the basis of the inertial range energy spectrum.
KERNEL WHITENING FOR ONE-CLASS CLASSIFICATION
Authors: TAX DAVID M. J. , JUSZCZAK PIOTR
Published: May 2003

In one-class classification one tries to describe a class of target data and to distinguish it from all other possible outlier objects. Obvious applications are areas where outliers are very diverse or very difficult or expensive to measure, such as in machine diagnostics or in medical applications. In order to have a good distinction between the target objects and the outliers, good representation of the data is essential. The performance of many one-class classifiers critically depends on the scaling of the data and is often harmed by data distributions in (nonlinear) subspaces. This paper presents a simple preprocessing method which actively tries to map the data to a spherical symmetric cluster and is almost insensitive to data distributed in subspaces. It uses techniques from Kernel PCA to rescale the data in a kernel feature space to unit variance. This transformed data can now be described very well by the Support Vector Data Description, which basically fits a hypersphere around the data. The paper presents the methods and some preliminary experimental results.
SCALING LARGE LEARNING PROBLEMS WITH HARD PARALLEL MIXTURES
Authors: COLLOBERT RONAN , BENGIO YOSHUA , BENGIO SAMY
Published: May 2003

A challenge for statistical learning is to deal with large data sets, e.g. in data mining. The training time of ordinary Support Vector Machines is at least quadratic, which raises a serious research challenge if we want to deal with data sets of millions of examples. We propose a "hard parallelizable mixture" methodology which yields significantly reduced training time through modularization and parallelization: the training data is iteratively partitioned by a "gater" model in such a way that it becomes easy to learn an "expert" model separately in each region of the partition. A probabilistic extension and the use of a set of generative models allows representing the gater so that all pieces of the model are locally trained. For SVMs, time complexity appears empirically to local growth linearly with the number of examples, while generalization performance can be enhanced. For the probabilistic version of the algorithm, the iterative algorithm probably goes down in a cost function that is an upper bound on the negative log-likelihood.
A FAST SVM TRAINING ALGORITHM
Authors: DONG JIAN-XIONG , SUEN CHING Y. , KRZYŻAK ADAM
Published: May 2003

A fast support vector machine (SVM) training algorithm is proposed under SVM's decomposition framework by effectively integrating kernel caching, digest and shrinking policies and stopping conditions. Kernel caching plays a key role in reducing the number of kernel evaluations by maximal reusage of cached kernel elements. Extensive experiments have been conducted on a large handwritten digit database MNIST to show that the proposed algorithm is much faster than Keerthi et al.'s improved SMO, about nine times. Combined with principal component analysis, the total training for ten one-against-the-rest classifiers on MNIST took less than an hour. Moreover, the proposed fast algorithm speeds up SVM training without sacrificing the generalization performance. The 0.6% error rate on MNIST test set has been achieved. The promising scalability of the proposed scheme paves a new way to solve more large-scale learning problems in other domains such as data mining.
REAL-TIME PEDESTRIAN DETECTION USING SUPPORT VECTOR MACHINES
Authors: KANG SEONGHOON , BYUN HYERAN , LEE SEONG-WHAN
Published: May 2003

In this paper, we present a real-time pedestrian detection method in outdoor environments. It is necessary for pedestrian detection to implement obstacle and face detection which are major parts of a walking guidance system for the visually impaired. It detects foreground objects on the ground, discriminates pedestrians from other noninterest objects, and extracts candidate regions for face detection and recognition. For effective real-time pedestrian detection, we have developed a method using stereo-based segmentation and the SVM (Support Vector Machines), which works well particularly in binary classification problem (e.g. object detection). We used vertical edge features extracted from arms, legs and torso. In our experiments, test results on a large number of outdoor scenes demonstrated the effectiveness of the proposed pedestrian detection method.
SUPPORT VECTOR LEARNING FOR GENDER CLASSIFICATION USING AUDIO AND VISUAL CUES
Authors: WALAVALKAR L. , YEASIN M. , NARASIMHAMURTHY A. , SHARMA R.
Published: May 2003

Computer vision systems for monitoring people and collecting valuable demographic information in a social environment is an important research problem. It is expected that such a system will play an increasingly important role in enhancing user's experience and can significantly improve the intelligibility of a human computer interaction (HCI) system. For example, a robust gender classification system can provide a basis for passive surveillance and access to a smart building using demographic information or can provide valuable consumer statistics in a public place. The option of an audio cue in addition to the visual cue promises a robust solution with high accuracy and ease-of-use in human computer interaction systems.

This paper investigates gender classification using Support Vector Machines (SVMs). The visual (thumbnail frontal face) and the audio (features from speech data) cues were considered for designing the classifier. Three different representations of the data, namely, raw data, principle component analysis (PCA) and non-negative matrix factorization (NMF) were used for the experimentation with visual signal. For speech, mel-cepstral coefficient and pitch were used for the experimentation. It was found that the best overall classification rates obtained using the SVM for the visual and speech data were 95.31% and 100%, respectively, on data set collected in laboratory environment. The performance of the SVM was compared with two simple classifiers namely, the nearest prototype neighbor and the k-nearest neighbor on all feature sets. It was found that the SVM outperformed the other two classifiers on all datasets. To further understand the robustness issues, the proposed approach has been applied on a large balanced (roughly equal distribution of gender, ethnicity and age group) data-base consisting of 8000 faces collected in real world environment. While, the results are very promising it indicates more to be done to make a statistically meaningful conclusion.
COMPUTER INTRUSION DETECTION WITH CLASSIFICATION AND ANOMALY DETECTION, USING SVMs
Authors: FUGATE MIKE , GATTIKER JAMES R.
Published: May 2003

This paper describes experiences and results applying Support Vector Machine (SVM) to a Computer Intrusion Detection (CID) dataset. First, issues in supervised classification are discussed, then the incorporation of anomaly detection enhancing the modeling and prediction of cyber-attacks. SVM methods are seen as competitive with benchmark methods and other studies, and are used as a standard for the anomaly detection investigation. The anomaly detection approaches compare one class SVMs with a thresholded Mahalanobis distance to define support regions. Results compare the performance of the methods and investigate joint performance of classification and anomaly detection. The dataset used is the DARPA/KDD-99 publicly available dataset of features from network packets, classified into nonattack and four-attack categories.
A SURVEY ON PATTERN RECOGNITION APPLICATIONS OF SUPPORT VECTOR MACHINES
Authors: BYUN HYERAN , LEE SEONG-WHAN
Published: May 2003

In this paper, we present a survey on pattern recognition applications of Support Vector Machines (SVMs). Since SVMs show good generalization performance on many real-life data and the approach is properly motivated theoretically, it has been applied to wide range of applications. This paper describes a brief introduction of SVMs and summarizes its various pattern recognition applications.