bluuebunny/crossref_metadata_2025 huggingface dataset:
ORDER PARAMETERS AND PHASE TRANSITIONS IN ELECTRORHEOLOGICAL FLUIDS
Authors: TAO R.
Published: November 2004

The ground state of an induced electrorheological (ER) solid is a body-centered tetragonal (bct) lattice with conventional Bravais vectors [Formula: see text], [Formula: see text], and [Formula: see text] where a is the radius of dielectric spheres and [Formula: see text] is the field direction. The reciprocal lattice vectors are [Formula: see text], [Formula: see text], and [Formula: see text]. Three order parameters are defined as [Formula: see text], (j = 1, 2, 3), where N is the total number of particles. Among them, ρ3 characterizes the formation of chains in the z direction, while ρ1 and ρ2 characterize the structure in the x-y plane. Monte Carlo simulations of canonical ensemble have shown that three different phases and two phase transitions exist in the ER fluid. At a fixed temperature, there are two critical electric fields Ec2 < Ec1. When the applied electric field E < Ec2, ρj (j = 1, 2, 3) are all vanishing and the ER fluid is a liquid. When Ec2 < E < Ec1, ρ1 = ρ2 = 0, but ρ3 is not vanishing, indicating that the ER fluid begins to form chains between two electrodes, but the distribution of these chains is random. This state is similar to nematic liquid crystal. The second phase transition occurs as E exceeds Ec1. Then ρ1, ρ2, and ρ3 are all non-vanishing, indicating that the chains aggregate together to form thick columns which have the bct lattice structure. These two phase transitions can also be realized at a fixed field by lowering the temperature.
A NUMERICAL INVESTIGATION OF ELECTRORHEOLOGICAL MATERIAL BEHAVIOR
Authors: CHRZAN MICHAEL J. , COULTER JOHN P.
Published: November 2004

The inter-particle behavior that occurs within electrorheological (ER) materials was investigated numerically. In this initial phase of the study, a two-dimensional material assumption was adopted, and static situations were investigated. A unit cell geometry consisting of two particles separated by a fluidic carrier medium was selected, and hybrid cylindrical-numerically generated grid systems were utilized. With appropriate boundary conditions applied, electric potential distributions throughout unit cells were determined. Electric field and current distributions and resultant mechanical stresses were then calculated. Results are presented in the form of electric potential, field, and current distributions, as well as net inter-particle forces.
A MODEL FOR THE ELECTRICAL CHARACTERISTICS OF AN ER VALVE
Authors: WHITTLE M. , FIROOZIAN R. , PEEL D. J. , BULLOUGH W. A.
Published: November 2004

We present a simple model which can account for the electrical response characteristics of an Electrorheological (ER) parallel plate valve restrictor. We find that a self-consistent electrical model which can describe the current response to transient and biased sine wave voltage exitations must incorporate the non-linear dependence of current on voltage found at steady state. In addition, the steady state current characteristics are a function of the fluid flow rate. This can be described analytically and included in the model.

Analytical solutions show that non-linearity affects the detailed shape of the current response to large voltage inputs. The initial current response is well described by a numerical solution to the model differential equation using the experimental voltage as input. In the case of the relatively small fluctuations involved in the sine wave experiments, a linearised form of this model is found to be an adequate approximation.

Parameters are obtained for the model which are, within a generous margin of error, independent of valve dimension.
PASSIVE TUNEABLE FIBERS AND MATRICES
Authors: DRY CAROLYN
Published: November 2004

Active smart electrorheological fluids in building materials are expensive, need to be widely dispersed, and require large amounts of electricity. These practical considerations led to the consideration of ways of having similar effects in a matrix but using different materials. Tuneable fibers is an inexpensive dispersed passive system, requiring no electricity. The modulus of elasticity of a solid-filled fiber is very different from a liquid- or gas-filled fiber or a hollow fiber. The ability to empty and fill fibers with a material which could change phase in the fiber or in the matrix in response to some stimulus or signal from the environment is promising. In the laboratory we have used filled fibers which empty their contents into the matrix in response to a change in the environment. In this case, in which it is a substitute for ER fluid, a blast, vibration, or shaking motion could release a catalyst, monomer, or adhesive from flexed or uncoated fibers. These could cross-link with a resin or polymerize in the matrix. Passive tuneable fibers could also be used for nonbuilding applications such as radar evasion. The changing modulus profile would be, thus, an advantageous performance parameter.
NONEQUILIBRIUM GREEN’S FUNCTIONS FOR HIGH-FIELD QUANTUM TRANSPORT THEORY
Authors: BERTONCINI RITA
Published: November 2004

A formulation of the Kadanoff-Baym-Keldysh theory of nonequilibrium quantum statistical mechanics is developed in order to describe nonperturbatively the effects of the electric field on electron-phonon scattering in nondegenerate semiconductors. We derive an analytic, gauge-invariant model for the spectral density of energy states that accounts for both intracollisional field effect and collisional broadening simultaneously. A kinetic equation for the quantum distribution function is derived and solved numerically. The nonlinear drift velocity versus applied field characteristics is also evaluated numerically. Many features of our nonlinear theory bear formal resemblance to linear-response theory.
THE 1/z EXPANSION FOR MAGNETS AND JOSEPHSON ARRAYS
Authors: FISHMAN R.S.
Published: November 2004

Expansions in the inverse of the coordination number z have proved very useful in condensed matter physics. In this paper, we review the formalism of the 1/z expansion for magnetic systems and arrays of Josephson junctions. While many variations of the 1/z expansion have been developed, we concentrate on unrenormalized expansions, where the expansion coefficients are independent of the coordination number but may depend on dimension. The 1/z expansion has been used to study both first- and second-order phase transitions in a variety of systems, including the Ising and Heisenberg models, the Blume-Capel model, and Josephson-junction arrays. This expansion has also been used to study the dynamics of a Heisenberg ferromagnet. Although they sacrifice the rigor of the 1/z expansion, resummations or rearrangements of the 1/z expansion have proved useful to study critical behavior.
SMALL IS DIFFERENT
Authors: Landman Uzi , Barnett R.N. , Cleveland C.L. , Cheng Hai-Ping
Published: November 2004

Investigations of variations of physical and chemical properties of clusters as a function of size allow systematic explorations of evolutionary patterns of materials properties from the molecular scale to the condensed phase regimes. Using classical and quantum molecular dynamics simulations we discuss the dynamics of cluster collisions with surfaces leading to shock formation, dielectrons and sodium solvation in water clusters, size-evolutionary patterns of metallization of sodium-fluoride clusters, and the energetics of metal alloy clusters.
TIME-RESOLVED OPTICAL STUDIES OF PHOTO-EXCITED STATES IN C60
Authors: Thomas T.N. , Ryan J.F. , Taylor R.A. , Mihailovič D. , Zamboni R.
Published: November 2004

We have measured the relaxation of photo-excited states in C 60 by time-resolved optical absorption. An ultrafast response (~1ps) is observed which is found to be dependent on excitation density, the characteristic time decreasing with increasing laser intensity. This is consistent with a distortion of the molecule induced by the photo-excited electrons.
A Tight Binding Model for The Electronic Structure of FCC and SC C60
Authors: Tit Nacir , Kumar Vijay
Published: November 2004

Ab-initio calculations1 for K3C60 indicate that the general features of the energy bands within LDA remain nearly unchanged as compared to C60. In the electronphonon pairing mechanism of superconductivity in these materials, the variation in Tc has been attributed to changes in the lattice constant2 which affects N(EF). We have therefore fitted the valence and conduction bands of the fcc C60, obtained by Troullier and Martins3 from an LDA plane wave basis calculations, with a tight binding model and studied the energy bands as a function of the lattice constant. As the overlap between orbitals on neighbouring balls is small, the band width is found to decrease by about 30% in going from K3C60 to Rb2CsC60. The density of states, thus, obtained is used to estimate variation in Tc from McMillan’s formula. These results are in good agreement with experimental data. Calculations of the energy bands are also presented for the low temperature [Formula: see text] structure.
GLIDE OF STANDING SOLITARY WAVE IN AN INCLINED LONG WATER TROUGH
Authors: XU Y. , WEI R.
Published: November 2004

A NLS-type equation with an additional term of variable coefficient governing the modulational evolution of standing gravity waves on a water layer with slowly variable depth is obtained by using the multiple scale method to the potential-flow boundary value problem. A single solitary wave solution of this equation, that corresponds to the standing solitary wave observed by Wu et al. in a slightly inclined rectangular water trough, is given. It is found that such solitary wave moves slowly, with an acceleration, toward the shallow region.
EFFECTIVE MASS, LANDAU INTERACTION FUNCTION AND SELF-ENERGY OF AN ELECTRON LIQUID
Authors: YASUHARA HIROSHI , OUSAKA YUMI
Published: November 2004

A review is given of the calculations of the effective mass m* for an electron liquid at metallic densities. The review will be helpful to understand that a great deal of difficulties are involved in estimating the quasi-particle dispersion in the vicinity of the Fermi level. It is emphasized that a systematic consideration of vertex corrections in accordance with the Pauli principle up to higher orders in calculating the Landau interaction function fσσ'( p , p ') or the self-energy Σ( p , ε) is indispensable for the correct evaluation of m* for rs>1. It is concluded that the mass ratio m*/m is a monotonically decreasing function of rs and remains smaller than unity throughout the whole region of metallic densities. The deviation of m*/m from unity is as small as 8% even at the lowest metallic densities. From general considerations we shall also discuss the effects of Σ( p , ε) on the overall features of the quasi-particle dispersion.
SUPERCONDUCTING PROPERTIES OF INTERGRAIN AND INTRAGRAIN MATERIAL IN POLYCRYSTALLINE GdBa2Cu3O7
Authors: ROGACKI K. , SULKOWSKI C.
Published: November 2004

High quality polycrystalline GdBa 2 Cu 3 O 7−x samples with oxygen content equal to 7.0 were synthesized. Sensitive magnetization measurements were performed at low temperatures and in vicinity of T c . From these measurements the intergrain material volume was calculated. The existence of two first penetration fields was demonstrated.
THERMODYNAMICS OF THE MOLECULAR COMPLEXES WITH CHAINS OF HYDROGEN BONDS
Authors: STASYUK I.V. , IVANKIV A.L.
Published: November 2004

A pseudo-spin reduced basis model for the description of the linear hydrogen-bonds molecular systems with strong correlations between protons on the neighbouring bonds is proposed. The proton states corresponding to the high-energy proton configurations near the heavy ionic groups are excluded from the initial basis. Some aspects of thermodynamics and energy spectrum for the proton subsystem of the molecular complexes are considered in the framework of reduced basis model. It is shown that for the complexes with large but finite number of hydrogen bonds N, the polarizability is proportional to N2, the specific heat is proportional to N−1 and the spectrum includes both zone and localized proton states. At the same time it is shown that correct thermodynamic limit is obtained as N→∞ on the base of pseudo-spin model with initial basis. As a result the limits of application of reduced basis model are determined.
ELECTRONIC STRUCTURE OF THE PEROVSKITE OXIDES SrCrO3 AND PbCrO3
Authors: JAYA S. MATHI , JAGADISH R. , RAO R.S. , ASOKAMANI R.
Published: November 2004

The electronic structure calculations of the perovskite oxides SrCrO 3 and PbCrO 3 performed both in the paramagnetic and antiferromagnetic phases are reported here. The calculations were carried out using the Linear Muffin Tin Orbital method within the Atomic Sphere Approximation. The quantitative results obtained are found to give a good description of the electronic states of SrCrO 3 and are in agreement with the Goodenough’s qualitative chemical picture. However, it is not able to predict the semiconducting gap in PbCrO 3 which is an antiferromagnetic semiconductor. But the value of the theoretically calculated magnetic moment at the Cr site in PbCrO 3 is found to be in good agreement with the experimentally observed value. The calculations show strong hybridisation between the Cr -3d and O -2p orbitals and the density of states at the Fermi energy has major contributions from these hybridised orbitals.
INVESTIGATION OF THE PHONON LINE-SHAPE FOR RAMAN SCATTERING IN Tl2Ba2CuO6 AND TlBa2Cu3O7 SUPERCONDUCTORS
Authors: MISOCHKO O.V. , SHERMAN E. Ya.
Published: November 2004

The shape of the phonon Raman lines and its dependence on scattering configuration for Tl-based superconductors have been studied. The asymmetry of phonon lines and their polarization dependence can be accounted for by the participating of phonons with finite wave vector in light scattering. The reasons for violation of the wave vector conservation law have been discussed and the asymmetry value due to this factor for the fully-symmetrical phonons in high-T c superconductors has been estimated.
THE NEUTRON DIFFRACTION STUDY ON Dy2Fe17C0.5
Authors: YANG JI-LIAN , ZHANG BAI-SHENG , DING YONG-FAN , YE CHUN-TANG , LIN CHIN , JIANG HONG-WEI
Published: November 2004

A sample of Dy 2 Fe 17 C 0.5 was prepared and identified to be of a single Th 2 Ni 17 type structure by X-ray phase analysis. It is shown that a small amount of carbon raises the Curie temperature in Dy 2 Fe 17 C 0.5 from 396 K to 483 K, while the magnetic moment does not increase. In order to understand the effect of carbon on the magnetic properties, a neutron diffraction study was carried out. A preliminary discussion is given.
POLYMERS AND TOPOLOGICAL FIELD THEORY
Authors: PESANDO I. , CASSI D.
Published: November 2004

We show that the generating function for self-avoiding paths is formally obtainable from a Witten topological field theory, even if the physical quantities for polymers are not the physical quantities in the BRST approach. We argue that in the dense phase the BRST invariance should generally be broken at the quantum level.
RANDOM SEQUENTIAL ADSORPTION ON A LINEAR LATTICE: EFFECT OF DIFFUSIONAL RELAXATION
Authors: NIELABA P. , PRIVMAN V.
Published: November 2004

We offer phenomenological arguments, supported by numerical Monte Carlo data, suggesting that the asymptotic large-time behavior of the coverage in the 1D lattice deposition of k-mers with k > 3, accompanied by k-mer diffusion, is governed by the same mean-field dynamics as the lattice chemical reaction [Formula: see text]. The latter reaction is considered to occur with partial probability. The coverage in the deposition process approaches full saturation for any nonzero diffusion rate, and the void fraction decreases according to the power-law t−1/(k−1).
CHANGES IN THE SUPERCONDUCTING PROPERTIES OF HIGH-Tc CUPRATES PRODUCED BY APPLIED ELECTRIC FIELDS
Authors: MANNHART J.
Published: November 2004

By changing the concentration of mobile charge carriers, applied electric fields influence the transport properties of high-T c superconductors in the superconducting state. Experimental studies of these effects are briefly reviewed.
INVESTIGATION OF A POSSIBLE GROWTH MECHANISM OF SYNTHETIC DIAMOND FILMS
Authors: PAN BI-CAI , ZHANG WEI-PING , XIA SHANG-DA , FANG RONG-CHUAN
Published: November 2004

The binding energy and spectra of clusters related to the growth of synthetic diamond films were calculated by DV-X α method. Having analysed the binding energy and compared the calculated optical spectra with the experimental ones measured by us, we found it is probably that one of the mechanisms for the growth of synthetic diamond films is the formation and adsorption on the diamond (111) surface of the activated complex compound CH 4· H .
TWO-LEVEL ATOM UNDERGOING TWO PHOTON TRANSITION IN A QUANTIZED FIELD: THE FLUORESCENT SPECTRUM
Authors: JOSHI AMITABH , LAWANDE S. V.
Published: November 2004

The fluorescence spectrum produced by a two-photon Jaynes-Cummings model (JCM) has been analyzed using the infinity of transitions among the dressed states of its Hamiltonian. A large number of resonances in the spectra are observed which are sensitive to the mean photon numbers of the quantized coherent field. Also, the qualitative nature of these spectra are in contrast to that of the corresponding spectra of standard JCM.
RECOVERING THE PARISI–SOURLAS POLYMER THEORY FROM THE LATTICE
Authors: CASSI D. , PESANDO I.
Published: November 2004

We show explicitly how to recover the Parisi-Sourlas action from a new supersymmetric theory on the lattice for the self-avoiding walks. We also sketch how it is possible to find its topological formulation.
NONLINEAR OPTICAL RESPONSE OF C60 AND C70 FULLERENES
Authors: BLAU W. J. , CARDIN D. J.
Published: November 2004

The macroscopic preparation of novel conjugated allotropes of carbon, the Fullerenes, has become easy to achieve and commonplace, leading to widespread study of their physical and chemical properties. In this paper we review the nonlinear optical effects observed in Fullerenes to date. Both second and third order response has been studied and the results indicate that this class of materials is highly promising for optoelectronic applications.
COULOMB BLOCKADE INDUCED BY MAGNETIC FIELD
Authors: KUSMARTSEV F. V.
Published: November 2004

We found that a Coulomb blockade can be induced by magnetic field. We illustrated this effect on the example of a ring consisting of two and many Josephson junctions. For the ring with two junctions we present an exact solution. The transition into Coulomb blockade state on a ring transforms into a real Beresinski–Kosterlitz–Thouless phase transition if the ring transforms into a linear array of Josephson junctions, although in latter case the effect of magnetic field disappears. In the state of Coulomb blockade the magnetization may be both diamagnetic and paramagnetic. The Coulomb blockade may also be removed by external magnetic field.
RANDOM WALKS ON d-DIMENSIONAL COMB LATTICES
Authors: CASSI D. , REGINA S.
Published: November 2004

Discrete time random walks on d-dimensional comb lattices are studied by analytical techniques for every integer d ≥ 1, both in unbiased and biased regime. We obtain a closed expression for the spectral dimension [Formula: see text] as a function of the embedding space dimension d, showing that it is always less than 2. We then calculate the exact asymptotic behavior of various quantities related to diffusion and show that they can all be expressed in terms of [Formula: see text].
MOTT TRANSITION IN THE HUBBARD MODEL
Authors: SHASTRY B. SRIRAM
Published: November 2004

In this article, I discuss W. Kohn’s criterion for a metal insulator transition, within the framework of a one-band Hubbard model. This and related ideas are applied to 1-dimensional Hubbard systems, and some interesting.miscellaneous results discussed. The Jordan-Wigner transformation converting the two species of fermions to two species of hardcore bosons is performed in detail, and the “extra phases” arising from odd-even effects are explicitly derived. Bosons are shown to prefer zero flux (i.e., diamagnetism), and the corresponding “happy fluxes” for the fermions identified. A curious result following from the interplay between orbital diamagnetism and spin polarization is highlighted. A“spin-statistics” like theorem, showing that the anticommutation relations between fermions of opposite spin are crucial to obtain the SU(2) invariance is pointed out.
SPONTANEOUS CURRENTS IN MESOSCOPIC RINGS
Authors: WOHLLEBEN D. , FRECHE P. , ESSER M. , ZIPPER E. , SZOPA M.
Published: November 2004

In a system of mesoscopic rings the influence of orbital magnetic interaction between the electrons is investigated. At a critical temperature Tc the system undergoes a phase transition into a current carrying state. Tc depends strongly on geometry of the system and/or its Fermi-surface, and on the quantum size gap at the Fermi level. Elastic scattering reduces Tc and eventually suppresses the transition.
MASS MATRICES AND MONOPOLES IN THREE-DIMENSIONAL FLUX PHASE MODELS
Authors: SEGRE G.C.
Published: November 2004

Chiral spin states in two dimensions can be generalized to three dimensions by introducing effective monopoles to generate the background fluxes. We explore some generalizations of chiral spin states and the consequences of chiral rotations on the charges of dyons, particle-monopole bound states.
FUNCTIONAL QUANTIZATION AROUND GW STATES OF FQHE.
Authors: DE OCA A. CABO MONTES , FELIPE R. GONZALEZ , MARTINEZ AURORA PÉREZ
Published: November 2004

Generating functional equations related to the Greiter-Wilczek ground states in FQHE are written. The Ward identities of the magnetic translation and rotational invariances allow us to determine the spatial structure of the electron propagator as in usual states. The electromagnetic linear responses again show that the Strêda formula in terms of the derivative over the real magnetic field gives the Hall conductivity. The coefficient of the Chern-Simons effective action is also determined by this expression. Calculations of the energies in the Hartree-Fock approximation are presented up to three filled Landau Levels and all the related filling factors. Under natural assumptions, the Hall resistivity versus the magnetic field curve is determined. It resembles quantitatively the experimental results for the most relevant filling fractions.
ENHANCED PHONON DENSITY OF STATES IN IMPURE ANHARMONIC CRYSTALS
Authors: INDU B.D.
Published: November 2004

The expression for the density of states of an isotopically disordered anharmonic crystal is investigated with the help of double-time thermodynamic Green’s functions. The cubic and quartic anharmonicities are taken into account besides the force constant changes and mass differences caused by the substitutional isotopic impurities. It is found that the density of states can be separated into defect, anharmonic and interference terms. The density of states is considerably enhanced due to the defects and impurities present in a real crystal and shows strong temperature and impurity concentration dependences which cannot be obtained by the traditional harmonic theory.
THE TEMPERATURE DEPENDENCE OF THE NORMAL STATE SPIN SUSCEPTIBILITY IN HIGH TEMPERATURE SUPERCONDUCTORS
Authors: DUPREE R. , HAN Z.P.
Published: November 2004

The static spin susceptibility in high-temperature superconductors can be accurately determined by Nuclear Magnetic Resonance (NMR) measurements which show that it has a systematic doping and temperature dependence in the normal state. The similarity in the temperature dependence of the 89Y, 63Cu and 17O Knight shifts for YBa2Cu3O7−δ as well as for YBa2Cu4O8 demonstrate that all of them probe the same spin susceptibility, Xs(T). This provides strong evidence in favor of the one-band model in which the Cu 3d and O 2p orbitals hybridize strongly and form a single quantum spin fluid in the Cu−O plane. Furthermore, recent NMR work has revealed a common behavior in the underdoped regime: similar magnitudes and temperature dependences of Xs(T) in different double layered superconducting cuprates are related to their similar Tc, suggesting a strong correlation between Tc, the hole density and the spin susceptibility. Possible explanations of the common behavior as well as the systematic doping and temperature dependence of the spin susceptibility in high-Tc cuprates are discussed.
HEAVILY DOPED HARMONIC CONFINED QUANTUM WIRES
Authors: LIMA I.C. DA CUNHA , SILVA A. FERREIRA DA
Published: November 2004

Quasi-one-dimensional channels have already been fabricated by holographic lithography on semiconductor heterostructures. We study the formation of an impurity band for shallow donors located inside the channels assuming they have been created by applying a modulated gate voltage in a quantum well of AlxGa1−xAs−GaAs. We calculate the changes in the impurity density of states as a function of the gate voltage. It is shown that the increase of the applied gate voltage leads to higher binding energy and larger impurity bandwidth.
ISOTOPE EFFECT IN SURFACE PHOTOCHEMICAL PROCESSES: EXPERIMENT AND THEORY
Authors: ZHU X.-Y.
Published: November 2004

A photochemical process in the adsorbate state has an inherent isotope or mass effect. This is because the presence of a solid surface introduces efficient relaxation channels for the electronically excited molecule. Competition between the chemical event and the quenching process is mass-dependent. Depending on the details of the dynamic energy transfer process, the isotope effect in a surface photochemical event can depend on either the mass or the internal reduced mass of the desorbing/dissociating particle. Measurements of isotope effect in UV surface photochemistry have provided insight into two mechanistic models, i.e., the classic Menzel-Gomer-Redhead (MGR) model and its recent variation, the vibration-mediated UV photodesorption (VMPD) model.
ENHANCED DONOR ELECTRIC SUSCEPTIBILITY IN SEMICONDUCTOR SYSTEMS
Authors: MOTA F. DE BRITO , DA SILVA A. FERREIRA
Published: November 2004

The electric susceptibility due to interacting donor-pair molecules are presented for a random distribution of uncompensated phosphorus-doped silicon at T=0 K. The results yield a critical exponent and susceptibility enhancement observed in optical measurements.
SHORT-PERIOD OSCILLATIONS OF THE MAGNETIC COUPLING OF EPITAXIAL GROWN Fe/Mo/Fe SANDWICHES ON Mo(100)
Authors: QIU Z. Q. , PEARSON J. , BADER S. D.
Published: November 2004

Epitaxial Fe / Mo / Fe sandwiches grown onto a Mo (100) single crystal were characterized in situ by electron diffraction and the magneto-optic Kerr effect. The intervening Mo layer is wedge shaped to facilitate the study of the magnetic coupling between the two (14-monolayer thick) Fe films as a function of Mo thickness. The exchange coupling between the Fe films across Mo was found to exhibit oscillatory behavior between antiferromagnetic (AF) and ferromagnetic coupling with a periodicity of ~3 ML of Mo . The shape of the hysteresis loop of the AF-coupled samples was calculated from a simple model that reproduces most of the experimental features.
AHARONOV–CASHER EFFECT IN HALF-INTEGER SPIN ANTIFERROMAGNETS
Authors: KRIVE I. V. , ZVYAGIN A. A.
Published: November 2004

The manifestation of the Aharonov–Casher effect in condensed media is considered. In the one-dimensional Hubbard model with arbitrary band filling we derived analytical expressions for the oscillating part of the ground state energy of mesoscopic ring with twisted boundary conditions which model the influence of Aharonov–Bohn (AB) and/or Aharonov–Casher (AC) fields. It is shown that in the limit of strong on-site repulsion AB-oscillations disappear for half-filled band, but the amplitude of the AC-oscillations, on the contrary, attains its maximum. The period of the AC-oscillations in this case equals hc/2 μ B (μ B is the Bohr magneton).
STABILITY OF LARGE OPTICAL SINGLET BIPOLARONS, MANY-PARTICLE EFFECTS AND HIGH TEMPERATURE SUPERCONDUCTIVITY
Authors: CHATTERJEE ASHOK , SIL SHREEKANTHA
Published: November 2004

The stability criteria for large optical bipolarons are obtained variationally for the entire range of the coupling parameters in both two and three dimensions. The size and the effective mass of these bipolarons are calculated and their variations with the material parameters are discussed. Two compounds are suggested which in the form of thin films should be tested for large bipolaronic effects. The theory is finally applied to La 2 CuO 4 and some of its normal state and superconductive properties are explained using the large bipolaronic mechanism.
LOWER CRITICAL MAGNETIC FIELD OF SUPERCONDUCTING Rb3C60
Authors: BUNTAR V. , ECKERN U. , POLITIS C.
Published: November 2004

The lower critical magnetic field Hc1 of superconducting Rb 3 C 60 (Tc=28.5 K ) is estimated by different methods. The zero temperature value is found to be given by Hc1=16.2±1.0 mT, and the penetration depth is λL=215±10 nm . The Bean model analysis leads to threshold fields of 5.3 mT for T=5 K , and 4.0 mT for T=17 K . The big influence of intergranular connections on Hc1 is demonstrated. Good agreement between the low- and the high-field analysis is found.
ESR STUDY OF CuO BULK POWDER AND THIN FILMS
Authors: PUNNOOSE ALEX , MATHEW JILSON , MAURYA B. P. , UMAR MOHD. , SINGH R. J.
Published: November 2004

A systematic Electron Spin Resonance investigation is carried out in CuO bulk powder and thin films, after calcining them to different temperatures ranging from 100°C to 1000°C. In CuO powder, two separate signals (one broad and one sharp) were observed at calcination temperature of 500°C, for the fist time. They got intensified, came closer and amalgamated on further heating upto 800°C, indicating complete destruction of antiferromagnetic ordering in this powdered compound. In thin films of CuO, the first appearance of the signal at 200°C and its intensification and shifting on further heating indicates that in thin film form, the destruction of antiferromagnetism takes place much earlier.
THE SPIN-POLARON PAIRING AND THE x DEPENDENCE OF THE Tc IN (La1-xSrx)2CuO4
Authors: MOTA R. , LIMA G. A. R. , FAZZIO A.
Published: November 2004

We present a study of superconducting correlations associated to the mechanism of spin-polaron pairing resulting from an attractive exchange interaction between spin-polarons. The spin-polarons associated with itinerant holes in CuO 2 are assumed to be created by strong intra-atomic exchange interaction with quasi-localized spins. The interplay of Hund's coupling and superexchange between quasi-localized spins gives rise to an attractive interaction between spin-polarons which leads to the formation of spin-singlet spin-polaron-pairs. The two-particle Green function in the ladder approximation for the itinerant holes with this attractive interaction is used to calculate in ( La 1-x Sr x)2 CuO 4 the dependence on the hole concentration of the critical temperature T c . The obtained results reproduce the experimental observations satisfactorily.
RESONANT PROPERTIES OF INELASTIC LIGHT SCATTERING IN Bi2Sr2CaCu2O8-x SUPERCONDUCTING SINGLE CRYSTALS
Authors: MISOCHKO O. V. , KH. ARSLANBEKOV A.
Published: November 2004

The resonant properties of Raman scattering in Bi 2 Sr 2 CaCu 2 O 8-x single crystals for four diagonal phonons and electronic scattering as well have been investigated for different polarizations. The resonance profiles for the phonons were of similar character, but the resonant profiles of the two components of electronic scattering, by contrast, were different.
SYSTEM IDENTIFICATION WITH ARTIFICIAL NEURAL NETWORKS
Authors: TISDALE E. ROBERT , KARPLUS WALTER J.
Published: November 2004

System identification is the term scientists and engineers use to refer to the process of building mathematical models of dynamical systems based on observed data. This paper approaches system identification as a pattern recognition problem. We use computers to simulate the system response for a variety of different mathematical models. For each distinct system model, simulated system responses tend to remain segregated in one or more amorphous regions of system response space despite (1) large variations in system parameters, (2) experimental errors, and (3) noise. The actual system response is classified with the model corresponding to the region of system response space where it is found. The classifier is an Artificial Neural Network (ANN) which implements a Generalized Vector Quantizer (GVQ). A small number of simple but powerful discriminant functions facilitate the correct classification of most of the responses in any given region. The required distribution of discriminants among the regions evolves automatically as they learn their respective functions.
IMAGE RECOGNITION AND RECONSTRUCTION USING ASSOCIATIVE MAGNETIC PROCESSING
Authors: GOODWIN JAMES M. , ROSEN BRUCE E. , VIDAL JACQUES J.
Published: November 2004

This paper presents a technique for image recognition, reconstruction, and processing using a novel massively parallel system. This device is a physical implementation of a Boltzmann machine type of neural network based on the use of magnetic thin films and opto-magnetic control. Images or patterns in the form of pixel arrays are imposed on the magnetic film using a laser in an external magnetic field. These images are learned and can be recalled later when a similar image is presented. A stored image is recallable even when a partial, noisy, or corrupted version of that image is imposed on the film. The system can also be used for feature detection and image compression. The operation and construction of the physical system is described, together with a discussion of the physical basis for its operation.

The authors have developed Monte Carlo style computer simulations of the system for a variety of platforms, including serial workstations and hypercube configured parallel systems. They describe here some of the factors involved in computer simulations of the system, which can be fast and relatively simple in implementation. Simulation results are presented and, in particular, the behavior of the model under simulated annealing in the light of statistical physics is discussed. The simulation itself can be used as a neural network model capable of the functions ascribed to the physical device.
APPLICATION OF GUARDED FUZZY-ATTRIBUTE CONTEXT FREE GRAMMAR TO SYNTACTIC PATTERN RECOGNITION
Authors: CHAN KWOK-PING
Published: November 2004

High-dimensional grammars such as web grammars and plex grammars were used in syntactic recognition of complex 2-D or 3-D objects. In this paper, we present a simple modification, borrowing the concept of guards from concurrent programming to attributed grammar proposed by D. E. Knuth. We show that the resultant grammar can handle patterns described by the high-dimensional grammars. The only problem is that we may not have a simple ordering of the terminal symbols or pattern primitives. In some applications, such as on-line character recognition, the problem does not exist and hence presents a good candidate for the application. We also discuss the incorporation of fuzzy attributes and the necessary modification is hence introduced. Finally, the error transformations proposed by K. S. Fu can easily be taken into consideration and a powerful yet simple scheme presented.
AN EFFICIENT ALGORITHM FOR FOLEY–SAMMON OPTIMAL SET OF DISCRIMINANT VECTORS BY ALGEBRAIC METHOD
Authors: LIU KE , CHENG YONG-QING , YANG JING-YU , LIU XIAO
Published: November 2004

This paper presents a new method for computing the discriminant vectors of the Foley–Sammon optimal set. First, an equivalent criterion is presented to replace the Fisher criterion; then, the problem of computing the discriminant vectors in Rn is transformed into the maximum problem in a subspace. Several theorems relating to the method are also presented. Experimental results show that the present method is superior to the positive pseudoinverse method, and the perturbation method in terms of correct classification rate.
INTEGRA — AN INTEGRATED SYSTEM FOR RANGE IMAGE UNDERSTANDING
Authors: BHANDARKAR SUCHENDRA M. , SIEBERT ANDREAS
Published: November 2004

Segmentation, feature extraction, recognition and localization are the four stages in range image understanding. Conventional approaches to range image understanding have treated these stages in isolation with a largely bottom-up flow of control and data through these various stages. Strictly bottom-up approaches have proved to be fragile in the face of errors in segmentation due to noise and limitations on sensor resolution and accuracy. Synergetic interaction of these various stages is essential for an image understanding system to exhibit robust behavior. This paper describes the design and implementation of INTEGRA, a range image understanding system that attempts to exploit the synergy between the various stages in the image understanding process. The salient features of INTEGRA are: (i) A synergetic combination of edge- and surface-based segmentation processes that results in more accurate segmentation than would have been possible with either of them alone and (ii) the ability to correct errors made during segmentation in the matching and localization stages. INTEGRA at this time, is limited to recognition and localization of polyhedral objects and is in the process of being enhanced to handle objects with curved surfaces of quadratic order such as spherical, ellipsoidal, cylindrical, and conical surfaces. Experimental results on real range images containing single and multiple polyhedral objects are presented. Future enhancements to INTEGRA are discussed.
CHARACTERIZING ONE-LAYER ASSOCIATIVE NEURAL NETWORKS WITH OPTIMAL NOISE-REDUCTION ABILITY
Authors: WANG TAO , XING XIAOLIANG , ZHUANG XINHUA
Published: November 2004

In this paper, we describe an optimal learning algorithm for designing one-layer neural networks by means of global minimization. Taking the properties of a well-defined neural network into account, we derive a cost function to measure the goodness of the network quantitatively. The connection weights are determined by the gradient descent rule to minimize the cost function. The optimal learning algorithm is formed as either the unconstraint-based or the constraint-based minimization problem. It ensures the realization of each desired associative mapping with the best noise reduction ability in the sense of optimization.

We also investigate the storage capacity of the neural network, the degree of noise reduction for a desired associative mapping, and the convergence of the learning algorithm in an analytic way. Finally, a large number of computer experimental results are presented.
MEDIAN BASED IDEMPOTENT FILTERS
Authors: HAAVISTO P. , GABBOUJ M. , NEUVO Y.
Published: November 2004

Idempotent filters produce a root signal in a single filter pass, i.e. the filter output is invariant to further filterings with the same filter. In this paper median based idempotent filter structures are introduced. Two approaches to generate these filters are studied: weighted median filters and median filter cascades.

Two subclasses of n-dimensional idempotent weighted median filters, called Class 1 and Class 2 filters in the paper, are introduced. It is shown that both Class 1 and Class 2 filters suppress impulsive noise from n-dimensional input signals and yet have almost no effect on the non-corrupted parts of the signal. These filters are therefore well-suited for example for preprocessing purposes. An application to speech processing is described. Other likely applications of these filters are in image processing and, also, in image sequence processing, where the filter mask is typically 3-dimensional.

Sufficient conditions for a filter cascade to be idempotent are given. Two idempotent median filter cascades and their advantages are discussed.
AN ARTIFICIAL INTELLIGENCE APPROACH TO ANALOG CIRCUIT DESIGN
Authors: WAWRYN KRZYSZTOF
Published: November 2004

This article deals with a new approach to an intelligent analog circuit design. The iterative closed loop design methodology adopts an expert system approach to provide topological synthesis, the SPICE circuit simulator to evaluate the circuit performance and a new approach of the diagnostic expert system to provide advice on how to improve the design. Unlike previous design methods, this approach introduces formal circuit representation for both numerical and heuristic knowledge of the design system. The predicate logic circuit representation is proposed to introduce a new concept of a formal analog circuit description language. The language syntax and semantics provide precise symbolic description of analog circuits functionality at different levels of hierarchy and connectivities together with transistor sizes of CMOS circuits at the transistor level. Different levels of hierarchy with circuit structures and performance parameters are presented in detail. It is shown how sentence conversion rules of language grammar can be used to derive transistor level circuits from input performance specifications through all intermediate levels of hierarchy. The implementation of the methodology and associated experimental results for CMOS operational amplifier designs are presented.
A PARALLEL ALGORITHM FOR MINIMUM DUAL-COVER WITH APPLICATION TO CMOS LAYOUT
Authors: HUANG Y.M. , SARRAFZADEH M.
Published: November 2004

In a pair of planar graphs (G, Gd), with Gd being the dual graph of G, a sequence of distinct edges is a dual-Euler trail if it is a trail both in G and in Gd. A set of disjoint dual-Euler trails that simultaneously cover G and Gd is called a dual-cover. We present an O( log n) time and O(n) processors algorithm, in PRAM model, based on the graph separator theory, for obtaining a minimum cardinality dual-cover in a pair of series-parallel graphs (G, Gd), where n is the total number of edges. We employ the proposed algorithm to obtain a minimum-area VLSI layout of CMOS functional cells. Our algorithm, when implemented in a serial environment performs better than previous algorithms and produces more compact layouts.
A NEW COMPREHENSIVE PROCEDURE FOR THE EXACT DESIGN OF CANONIC LDI-TYPE SC LADDER FILTERS
Authors: KAELIN AUGUST , MOSCHYTZ GEORGE S.
Published: November 2004

A new procedure is given for the exact design of canonic LDI-type SC ladder filters realizing any elliptic discrete-time transfer function, including highpass functions. We show that, in contrast to known exact design procedures, the underlying prototype network should be terminated with so-called half-unit delays in order to preserve the capability of realizing any filter type. We will show, based on such ladder prototypes, simple and stray-insensitive LDI-type SC ladder filters can be derived, which are canonical for any filter type (i.e., every filter pole requires for its realization one stray-insensitive SC integrator without the need for additional amplifiers). Compared to common exact design procedures, simpler SC ladder structures are obtained, in particular, for highpass-type filters. Exact designs of canonic SC highpass ladder filters are presented and compared with corresponding biquad designs.
HEURISTIC PREDICTION OF THE OPTIMUM NUMBER OF SPARES IN DEFECT-TOLERANT INTEGRATED CIRCUITS
Authors: THIBEAULT C. , SAVARIA Y. , HOULE J.L.
Published: November 2004

This paper presents a heuristic method that efficiently approximates the optimum number of spares predicted by yield models through figures of merit. This method, which is based on simple approximate functions, offers a very good trade-off between CPU time and accuracy. Indeed, the CPU time required is negligible compared to what is needed for a direct prediction of the optimum number of spares using yield models and figures of merit. Also, the approximations provided by the proposed heuristic method are very close to the exact values predicted by yield models over a wide range of parameters. A hybrid prediction method, that makes it possible to accelerate the prediction of the optimum amount of redundancy without precision losses, is also presented. This hybrid method, which uses results from the heuristic method as starting points around which yield models and figures of merit are applied, is almost optimum in terms of CPU time over the parameter range considered.
ALGORITHM FOR WIRE SIZING OF POWER AND GROUND NETWORKS IN VLSI DESIGNS
Authors: DUTTA ROBI , MAREK-SADOWSKA MALGORZATA
Published: November 2004

Distributing power and ground to the elements present in a VLSI chip is a very crucial task in the design process. Power networks carry substantial currents and wires carrying them have to be carefully designed to avoid damage caused by electromigration and should not experience significant voltage drops. This paper presents a fast and efficient method for sizing power/ground networks. No restrictions on network topology or the number of supplying pads are imposed. Wire widths are calculated such that the weighted area of wire segments is minimized while electromigration and voltage drops constraints are fulfilled. The algorithm proposed here runs 50% faster for unrestricted topologies than the best methods reported in literature for tree type networks.
TRANSITION TO CHAOS FROM A TWO-TORUS IN A DELAYED FEEDBACK SYSTEM
Authors: BOE EUGENE , CHANG HSUEH-CHIA
Published: November 2004

By using the center manifold and normal form theories of dynamical systems, we were able to show that when a "resonant" system, with a maximum in its amplitude Bode plot, is placed under delayed negative feedback, two-torus attractors appear near specific values of delay and feedback gain [Boe & Chang, 1989]. The two-torus attractors of a classical liquid-level control experiment with cascaded feedback are studied both numerically and experimentally here to complete the local analysis of the previous paper. Like other two-torus systems, we observe a Devil's staircase of frequency-locked tori with a fractal dimension 0.87. A torus-wrinkling mechanism for the transition to chaos, as proposed by Ostlund et al. [1983], is supported by our experiments.
GRID IMAGING FOR A TWO-DIMENSIONAL MAP
Authors: JUDD K. , MEES A. I. , AIHARA K. , TOYODA M.
Published: November 2004

By examining images of grids as they fold and stretch under the action of two-dimensional maps, we determine the geometry of the maps and use this to study their dynamics and bifurcations. In particular, we explain important features of the complicated dynamics and rich bifurcation structure of a map designed as a model of two coupled neurons.
ON MODELING DRIVEN OSCILLATORS BY MAPS
Authors: PARLITZ U. , SCHEFFCZYK C. , KURZ T. , LAUTERBORN W.
Published: November 2004

A family of two-dimensional maps showing essential features of the bifurcation set of some periodically driven, strictly dissipative oscillators is constructed.
BIFURCATION AND CHAOS OF THE SINUSOIDALLY-DRIVEN CHUA'S CIRCUIT
Authors: MURALI K. , LAKSHMANAN M.
Published: November 2004

The effect of an external sinusoidal signal on the familiar Chua's piecewise-linear autonomous circuit is experimentally investigated. Under the influence of such a periodic excitation an immense variety of bifurcation phenomena like period doubling, period adding, quasiperiodicity, and intermittency has been observed. Also, equal periodic bifurcation, hysteresis, and coexistence of multiple attractors are reported. A two-parameter (drive amplitude–drive frequency) bifurcation diagram is constructed, which classifies the observed rich bifurcation sequences and chaotic structures.
NONLINEAR TIME SEQUENCE ANALYSIS
Authors: GRASSBERGER PETER , SCHREIBER THOMAS , SCHAFFRATH CARSTEN
Published: November 2004

We review several aspects of the analysis of time sequences, and concentrate on recent methods using concepts from the theory of nonlinear dynamical systems. In particular, we discuss problems in estimating attractor dimensions, entropies, and Lyapunov exponents, in reducing noise and in forecasting. For completeness and since we want to stress connections to more traditional (mostly spectrum-based) methods, we also give a short review of spectral methods.