bluuebunny/crossref_metadata_2025 huggingface dataset:
Theory of Detection of X-Rays by Superconductors
Authors: Krishna N. Murali , Lingam Lydia S. , Shrivastava Keshav N.
Published: October 2003

Two new processes occur in a superconducting film when it is used as a detector of X-rays. One of these processes is the scattering of the X-ray by a single electron which gives rise to the broadening of the X-ray line. Another process describes the breaking of a Cooper pair by the X-ray which also contributes to the width of the X-ray. The line arising from the single electron process depends on T4 whereas that arising from the pair breaking process varies almost as T6 at low temperatures. Lines occur at ℏωq ± 2Δ, and at ℏωq where ℏωq is the energy of the X-ray and 2Δ is the gap of the superconductor.
Dynamical Hysteresis and Stochastic Resonance in Driven Dissipative Quantum Two-State System
Authors: Pareek T. P. , Mahato Mangal C. , Jayannavar A. M.
Published: October 2003

We study the dynamics of a periodically driven two-state system coupled to thermal environment. In the high temperature limit we have obtained analytic expressions for the average position of the particle and hysteresis loop area. Both these quantities exhibit stochastic resonance behavior as a function of various parameters of the problem. These two resonances, however, occur at different values of the parameters. The resonance condition obtained from the study of phase delay exhibits resonance at a fixed frequency independent of other physical parameters.
Geometrical and Transport Properties of Disordered Fibre Networks: Analytical Results
Authors: Rodríaguez A. A. , Medina E.
Published: October 2003

We study novel geometrical and transport properties of a 2D model of disordered fibre networks. To assess the geometrical structure we determine, analytically, the probability distribution for the number of fibre intersections and resulting segment sizes in the network as a function of fibre density and length. We also determine, numerically, the probability distribution of pore perimeters and areas. We find a non-monotonous behavior of the perimeter distribution whose main features can be explained by solving for two simplified models of the line network. Finally we formulate a mean field approximation to conduction, above the percolation threshold, using the derived results. Relevance of the results to fracture networks will be discussed.
Dynamics of the Electronic States of Organic Charge-Transfer Salts in in-Phase Mode
Authors: Costa A. T. , Thomaz M. T.
Published: October 2003

We study the dimer charge oscillations of organic charge-transfer salts in in-phase mode due to the general initial condition problem. The exact time evolution of the half-filled (two-particle) case has a complex behavior. Under certain initial conditions, the average number of fermions in one-particle state, in the half-filled case, is not necessarily periodic, even though the magnetization remains periodic. We present the expressions of the magnetization and the transition dipole moment of the organic charge-transfer salts in the in-phase mode coupled to a constant external magnetic field, for arbitrary initial conditions. We show that the constant external magnetic field plays no role in this phenomena.
Ba2RESbO6 (RE = Nd, Eu and Dy); Characterization and Potential Use as Substrate for Superconducting YBCO Films
Authors: Wariar P. R. S. , Kurian J. , Sajith P. K. , Babu T. G. N. , Koshy J.
Published: October 2003

Perovskite compounds of the general formula, Ba2RESbO6 (where RE = Nd, Eu and Dy) were sintered as single phase materials by standard solid state techniques. These compounds are found to be isostructural and to have a complex perovskite structure as observed by powder X-ray diffraction measurement. No chemical reaction between YBa2Cu3O 7-δ and Ba2RESbO6 compounds, was observed even under severe heat treatment at 950°C, and the addition of Ba2RESbO6 up to 20 vol% in YBa2Cu3O 7-δ, shows no detrimental effect on the superconducting properties of YBa2Cu3O 7-δ. The dielectric constant and loss factor values of sintered specimens, are in a range suitable for their use as substrates for microwave applications. Thick films of YBCO fabricated on highly polished Ba2RESbO6 specimens, gave a superconducting zero resistance transition T c(o) of 92 K, with a critical current density, J c of 2×104 A/cm2 at 77 K.
Low Frequency Noise Behavior in Semiconductors
Authors: Melkonyan S. V. , Gasparyan F. V. , Aroutiunyan V. M.
Published: October 2003

The low frequency behavior of the generation-recombination noise in the homogeneous semiconductors is investigated. The form of Lorentz law for spectral density of noise at low frequencies is made more precise. It is shown that at superlow frequencies the spectrum of generation-recombination noise changes into the 1/f-law. The characteristic frequency of this change depends on the temperature and dimensions of the sample.
The Influence of the Impurities with Deep Levels on the Iron Behavior in Silicon
Authors: Zainabidinov S. Z. , Daliev Kh. S. , Abdurakhmanov K. P. , Utamuradova Sh. B. , Khomidjonov I. Kh. , Mirzamurodov I. A.
Published: October 2003

The influence of gold, platinum, cobalt and nickel impurities on iron atoms behavior in silicon has been studied by complex methods. The additional introducing of one of the named impurities with deep levels (DL) in Fe-doped silicon was proved to reduction of the concentration of interstitial iron ( Fe 0). The introducing of gold or nickel shows the strongest effect. The presence of iron in silicon bulk in its turn is shown to decrease the DL concentration connected with Ni, Au, Co and Pt atoms correspondingly. The conclusion is drawn about iron atoms extraction onto the silicon surface in the presence of the second impurity.
Normal Helium 3: A Mott–Stoner Liquid
Authors: Georges Antoine , Laloux Laurent
Published: October 2003

A qualitative picture of normal 3 He is proposed, which brings together the concept of an "almost localized" liquid and the existence of ferromagnetic spin correlations. The range of these correlations is shorter than in paramagnon theory, and the spin fluctuations are never in the critical regime within our approach, even at high pressure. A lattice model is introduced, which illustrates this physical picture. We also demonstrate that a metamagnetic transition in the field-dependent magnetization is not a necessary consequence of a quasilocalized picture.
Van Der Waerden's Coloring Theorem and Classical Spin Systems
Authors: Chaudhury Ranjan , Gangopadhyay Debashis , Paul Samir K.
Published: October 2003

We find a non-invertible matrix representation for Van der Waerden's coloring theorem for two distinct colors in a one-dimensional periodic lattice. Using this, an infinite one-dimensional antiferromagnetic Ising system is mapped to a pseudo-ferromagnetic one, thereby relating the couplings. All this is reminiscent of renormalization group.
Multifractality at Transition to Chaos Complex-Temperature Singularities
Authors: Bershadskii A.
Published: October 2003

It is shown, that multifractal complex-temperature singularities can play a significant role in the critical strange sets multifractality. These singularities lead to a finite radius of convergence of the real high-temperature expansions and, therefore, to necessity to use a finite-temperature expansions (an analytic continuation). It is shown, using analytic results on multifractality of strange attractors of the baker map and results of numerical computations of the multifractal spectra on all critical points of phase transitions from period-η-tupling to chaos in 1D iterative system (Chinese Phys. Lett.3, 285 (1986) and J. Phys.A25, 589 (1992)) as well as results of a recent numerical simulation of a quantum system with multifractal spectrum (J. Phys.A28, 2717 (1995)), that the finite-temperature expansions give good approximation for the generalized dimensions Dq in a representative interval of q.
Structural Instability and Superconductivity of the Defect Cubic Structure δ-MoC1-x
Authors: Athanasiou N. S.
Published: October 2003

In this work we report the formation, characterization and superconducting transition temperatures (T c ) of homogeneous and single-phase ternary crystalline molybdenum-carbon based compounds. The required samples were prepared by conventional solidification (arc-melting). The stabilization of the cubic δ- MoC 1-x phase was successfully done by substituting Mo or C by small additions (about 1–5 at.%) of B, Ti, Zr, Ru, Hf, W, Re or Os. All substitutions of B or transition metals to pure δ- MoC 1-x phase result in a decrease of the transition temperature. The transition temperature of the single-cubic δ- MoC 1-x phase (prepared by different techniques for comparison reasons) increases from 10.15 K to 14.7 K with increasing C/Mo ratio in the homogeneity range of 0.65 ≤ C/Mo ≤ 0.75.
Kinetics, Hydrodynamics and Stochastodynamics of Cellular Structure Coarsening
Authors: Goryachev S. B.
Published: October 2003

For the first time the phenomenon of cellular structure coarsening are consistently analyzed from the positions of kinetic, hydrodynamic and stochastodynamic theories of nonequilibrium statistical systems. Thereby micro-, meso- and macroscopic levels of approach are distinguished. At the microscopic level the cellular structure is describe by a probability distribution function in a phase space of cell coordinates and of cell sizes. A kinetic equation for the function is written and a development to a hydrodynamic equation of a mesoscopic cell medium is realized. It has the form of a diffusion–reaction equation with a negative "diffusion" coefficient and with a cell interface density playing the role of concentration. Its analysis reveals a new effect of macroscopic patterning in the cell medium: existence of space-correlated stochastic fluctuations of the cell interface density.
Higher Moment Properties of k-Component (k≥3) Coherent States in a Finite Dimensional Basis
Authors: Roy Barnana
Published: October 2003

We introduce the k-component (k ≥ 3) coherent states in a finite dimensional basis and study their quadrature and higher moment squeezing properties. The results show that these states have Nth power squeezing for N = mk, m = 1,2,3, … for even and odd k and for [Formula: see text], m = 0,1,2, … for even k but none of the states exhibit quadrature squeezing.
Phase Diagram of the Semi-Infinite Ising Model in a Random Field
Authors: de Arruda A. S. , Figueiredo W.
Published: October 2003

We determine the phase diagram of the semi-infinite Ising model in a cubic lattice with a trimodal distribution of random fields on the surface. We use the mean-field renormalization group with the smallest possible clusters to show that a very small dilution of the random field at surface is sufficient to destroy the tricritical behavior.
Oxygen Pressure Dependence of Morphology of Morphology of La2-xSrxCuO4 Ultra-Thin Films
Authors: Yin H. Q. , Arakawa T. , Kaneda Y. , Yoshikawa T. , Haneji N. , Sugahara M.
Published: October 2003

La 2-x Sr x CuO 4 ultra-thin films with thickness 200 Å were fabricated by pulsed laser deposition method in oxygen ( O 2) atmosphere. The morphology of deposited films was investigated by reflection high energy electron diffraction (RHEED), atomic force microscopy (AFM) and scanning electronic microscopy (SEM). The strong oxygen ambient pressure dependence of film morphology was observed. In high oxygen ambient pressure, the film growth is dominated by island growth mode. The results imply that the experimental conditions of oxygen ambient pressure and substrate temperature are critical for the layer-by-layer growth mode.
Exact Solution of the Diffusion-Limited Recombination Process A + B → ∅
Authors: Mattis Daniel C.
Published: October 2003

We present a solution which recovers well-known formulas for the asymptotic densities in diffusion-limited reactions of type A + B → ∅ (inert). Moreover, our solution becomes exact for all t and in all dimensions d in the low-density, continuum, limit. Following M. Doi, we use quantum field theory to analyze this many-body problem of classical, diffusing, particles undergoing a chemical reaction. We point out the crucial step at which the model becomes exactly solvable.
Diffusion and Harmonic Oscillations on Bundled Structures: Analytical Techniques and Dynamical Dimension Splitting
Authors: Cassi Davide , Regina Sofia
Published: October 2003

We present in details the general analytical techniques allowing to obtain the exact solution for random walks and harmonic oscillations problems on bundled graphs. These are networks obtained joining a copy of a fiber graph to each point of a base graph and are used as geometrical models for a wide class of real noncrystalline structures. The results show the remarkable phenomenon of dynamical dimension splitting: namely the noncoincidence of diffusive and vibrational spectral dimensions, usually supposed to be the same.
Dimensional Crossover Temperature in Presence of Two Different Josephson Couplings in High Tc Superconductors
Authors: Ghosh A. K. , Bandyopadhyay S. K. , Basu A. N.
Published: October 2003

We discuss the crossover from two dimension (2D) to three dimension (3D) in presence of two different types of Josephson couplings in high-T c superconductors. The crossover is estimated taking ab plane paraconductivity. In presence of the different coupling strengths an overlapping region is found in the case of ab plane paraconductivity where the system is neither 2D nor 3D. The role of two different types of couplings and anisotropic nature of the HTSC is discussed in controlling the overlapping region.
A Model of Bond-and-Band for the Behavior of Nitrides
Authors: Sun Chang Q.
Published: October 2003

A bond-and-band model is developed to incorporate the chemical bond and the energy band of nitrides. It is suggested that the symmetrical difference of the tetrahedral bond-structure and the similarity in the energy-band determine the performance of these compounds. The presence of bonding, nonbonding lone-pair and the lone-pair-induced antibonding features are of key importance to these materials. Well acclaimed by existing evidence, this model provided preliminary understanding of the physical properties of some nitrides and oxides and particularly, some insight into the origins of the N-enhanced magnetization, the blue-shift in nitride and oxide light emitting as well as the ultrahard and super elastic materials.
Role of Collective and Localized Modes on the Temperature-Dependent Thermal Conductivity in Polycrystalline C60 Fullerite Compacts
Authors: Tewari S. P. , Silotia Poonam , Bera Kakoli
Published: October 2003

Recently observed thermal conductivity of polycrystalline C 60 fullerite compacts has been explained on the basis of a suggested dynamical model of the fullerites which takes into account the collective acoustic phonon modes with frequency dependent relaxation time and localized libronic and orientational diffusive modes with constant relaxation times, in the temperature range 0.7–300 K. Though the bulk of the conduction is via collective modes, the localized modes, too, contribute significantly to the total thermal conductivity.
A Neural Network with Permanent and Volatile Memory
Authors: Lattanzi G. , Nardulli G. , Stramaglia S.
Published: October 2003

We discuss an attractor neural network where both neurons and synapses obey dynamical equations; it models the compresence of permanent and short-term memories. By signal-noise analysis and a discussion in terms of an energy-like function, we outline the behavior of the model.
A Simple Reverse Monte Carlo Algorithm for Structure Simulation of Multi-Component Amorphous Solids
Authors: Andrecut M.
Published: October 2003

A simple Reverse Monte Carlo algorithm for structure simulations of multi-component amorphous solids is presented. The described algorithm is based on the standard reverse Monte Carlo method,1,2 developed for the monoatomic case, the application for poliatomic case being assured by using the Warren–Krutter–Morningstar approximation.3 An application for metal-metalloid glasses is also presented.
Studies of Interfacial Roughness of GaAs/AlAs Superlattices by Grazing Incidence X-Ray Scattering
Authors: Huang S. , Ming Z. H. , Soo Y. L. , Kao Y. H. , Chang T. , Fu L. P. , Gilliland G. D. , Klem J. , Hafich M.
Published: October 2003

A series of type-II GaAs/AlAs superlattices epitaxially grown with different interrupts have been investigated using the techniques of grazing incidence X-ray scattering and diffraction. The interrupts are specifically designed to alter the interfacial roughness in the superlattices for the present study. Various structural parameters including the layer thickness, interfacial roughness, and intra-layer correlation lengths of fluctuations in the quantum-well widths have been determined. These results are compared with measurements made on the same set of samples using photoluminescence and optical imaging techniques.
Stable Divergence Angles of a Magnetic Dipole Spiral Array
Authors: Fan X. D. , Bursill L. A.
Published: October 2003

An analytical model is introduced for the experiment of Douady and Couder [Phys. Rev. Lett.68, 2098 (1992), where phyllotactic patterns appear as a dynamical result of the interaction between magnetic dipoles. The difference equation for the divergence angle (i.e. the angle between successive radial vectors) is obtained by solving the equations of motion with a second nearest neighbor (SNN) approximation. A one-dimensional map analysis as well as a comprehensive analytical proof shows that the divergence angle always converges to a single attractor regardless of the initial conditions. This attractor is approximately the Fibonacci angle(~ 138°) within variations due to a growth factor μ of the pattern. The system is proved to be stable with the SNN approximation. Further analysis with a third nearest neighbor approximation (TNN) shows extra linearly stable attractors may appear around the Lucas angle (~ 99.5°).
Optical Constants of TiO2/Ag/TiO2 Three-Layer Thin Films
Authors: Baskoutas S. , Athanasiou N. S.
Published: October 2003

In the present work we discuss a theoretical model based on the classical electromagnetism, which determines the reflectance and transmittance of multi-layer thin films used as transparent heat mirrors. For normal light incidence the calculations have pointed out, that the most suitable combination, in order to obtain optima heat mirror properties, is the silver film (18 nm thickness) sandwiched between two layers of titanium dioxide (18 nm thickness). We found that the reflectivity in the infrared is about 98% and the visible transmission is approximately 85%.
Error Avoiding Quantum Codes
Authors: Zanardi Paolo , Rasetti Mario
Published: October 2003

The existence is proved of a class of open quantum systems that admits a linear subspace [Formula: see text] of the space of states such that the restriction of the dynamical semigroup to the states built over [Formula: see text] is unitary. Such subspace allows for error-avoiding (noiseless) encoding of quantum information.
Geometrical Universality in Vibrational Dynamics
Authors: Burioni Raffaella , Cassi Davide
Published: October 2003

A good generalization of the Euclidean dimension to disordered systems and noncrystalline structures is commonly required to be related to large scale geometry and it is expected to be independent of local geometrical modifications. The spectral dimension, defined according to the low frequency density of vibrational states, appears to be the best candidate as far as dynamical and thermodynamical properties are concerned. In this letter we give the rigorous analytical proof of its independence of finite scale geometry. We show that the spectral dimension is invariant under local rescaling of couplings and under addition of finite range couplings, or infinite range couplings decaying faster then a characteristic power law. We also prove that it is left unchanged by coarse graining transformations, which are the generalization to graphs and networks of the usual decimation on regular structures. A quite important consequence of all these properties is the possibility of dealing with simplified geometrical models with nearest-neighbors interactions to study the critical behavior of systems with geometrical disorder.
Spectral Correspondence to the Evolution of Chemical Bond and Valence Band in Oxidation
Authors: Sun Chang Q. , Zhang Sam , Hing Peter , Wei Jun , Xie Hong , Wee Andrew T. S.
Published: October 2003

Spectroscopy covering energies around Fermi level of a metal is of particular interest as it does give direct information of bond forming and its consequence on the energy states (DOS). However, the origin of some outstanding spectral features from metal surface with chemisorbed oxygen has not yet been well established. It is shown in this letter that a bond-to-band model for oxidation enables the nature of a sum of spectral features to be consistently defined. All the spectral changes in the STS, XPS, UPS, photoemission spectroscopy (PES) and the thermal desorption spectroscopy (TDS) are classified by four DOS features around Fermi level and three bonding processes. Such a definition leads not only to new knowledge of the nature of O-metal interaction but also to a direct understanding of the bond-and-band forming dynamics.
Nature of the O-fcc(110) Surface-Bond Networking
Authors: Sun Chang Q.
Published: October 2003

New insight into the nature and formation of the multiphase ordering of oxygen onto threefold sites of fcc(110) (Rh, Pd and [Formula: see text] analogue) is presented. By including bond-to-band model and the potential-barrier for oxygen-metal chemisorption with theoretical and experimental observations, it is shown that the multiphase ordering, composed of (2×1)pmg, (2×1)p2mg and (2×2)p2mg structures, originates from the hybridized- O -2 forming at different oxygen coverages with a specific bonding environment. Unlike the long-bridge sited O -2 ions on the Cu(Ni, Ag)(110) which give the missing-row type reconstruction, the threefold-coordinated O -2 ions on the Rh(Pd)(110) form a tetrahedron through one bond to the metal atom underneath and two nonbonding lone pairs acting on its two neighbors in the first layer. In the (2×1)p2mg structure, the lack of one metal atom for the tetrahedron is compensated by a virtual bond pulling the electron-cloud of the dipoles that are induced by the lone pairs of other O -2 ions. The tetrahedron in the (2×2)pg structure requires an electron from a metal atom in the next nearest row at the surface. Therefore, the bond network interlocks all the surface atoms; and thereby, no atoms are missing. The zigzag protrusions in the STM images are recognized as metal dipoles deformed by the lone pairs of O -2 ions. The depressions correspond to rows of M + metal ions other than missing-row vacancies as had been expected previously.
On the Possibility of the Creation of Radically New Type Detectors of Particles and Radiation Based on High-Tc Superconductors
Authors: Gevorgyan S. G. , Movsisyan A. A. , Movsesyan G. D. , Shindyan V. A. , Shirinyan H. G.
Published: October 2003

Some aspects of high-T c superconductors (HTSC) electrophysical properties, which could be successfully applied to the detection of particles and radiation are discussed. The possibilities and the perspectives of the creation of completely new type detectors of elementary particles and ionizing radiation, based on HTSC materials, are considered. At this, the use of the unusual open-flat measuring (pick-up) coils made of, in particular, the HTSC materials, as a detecting element in known tunnel diode oscillator technique it seems of considerable promise and may find also a number of other applications in different areas of science and technology. The results of the HTSC thin-film structures real use for the detection of the visible and infrared spectrum radiations as well as constant magnetic fields and also direct currents passing through the HTSC film structures are presented. Three designs of these detectors are proposed suitable for various applications. The achieved up-to-date sensitivity is about 10-11 Wt/cm2/Hz-1/2 for the 0.63 μm and 0.8 μm wavelength radiations, about 0.1 mOe/cm2/Hz-1/2 for the constant magnetic fields and about 0.1 μA/cm2/Hz-1/2 for the direct currents passing through the HTSC thin-film structures. Capabilities of new detectors are evaluated and possible directions of further essential improvement of their parameters are also suggested.
Hysteretic Phenomena in the Critical Current of High-Tc Superconductors
Authors: Svistunov V. M. , Aomine T. , Fukami T. , Yamamoto T. , D'Yachenko A. I.
Published: October 2003

Models describing the appearance of an abnormal hysteresis in the critical current of granular superconductors are analyzed. It has been revealed that the most suitable for High T c Superconductors ( H T c S ) is a model based on an irreversibility of the grain surface current that determines the critical current of the Josephson weak links or depairing current of narrow superconducting part in ( H T c S ) oxides. This leads to the irreversibility phenomena in ( H T c S ) at the high magnetic fields H≫ H c1 .
Superfluidity of q-Deformed Bosons with Weak Interaction
Authors: Hui-Yun Pan , Hai Jun Wang , Zu Sen Zhao
Published: October 2003

Superfluidity of q-deformed bosons with weak interaction is studied. Bogoliubov's method of approximate second quantization is applied to this case. Under the condition p2/m ≫ ([N]/V)U0, the spectrum of elementary excitations is found to be of the roton-type, and hence superfluidity is predicted.
Coherent State Representation for Generalized Bosonic Bogolyubov Transformation
Authors: Fan Hong-Yi , Fan Yue
Published: October 2003

We show that the generalized bosonic Bogolyubov transformation generator [Formula: see text] where G is a n×n matrix, has the manifest coherent state representation [Formula: see text] This expression has the advantage of exhibiting the transition from classical transformation to its quantum mechanical correspondence apparent and providing us with a convenient approach for calculating some Bogolyubov transformed states.
Anomalous Thermoelectric Power of Sol–Gel Prepared NdNiO3-δ
Authors: Tiwari Ashutosh , Rajeev K. P.
Published: October 2003

We are reporting, for the first time, the detailed measurement of the thermoelectric power S(T) of sol–gel prepared NdNiO 3-δ (with δ =0.12) in the temperature range of 77–300 K. Resistivity and d.c. magnetization measurements of the same piece of the sample are also being reported in the temperature ranges of 1.2–300 K and 4.2–185 K respectively. The resistivity of the sample shows a transition at around 180 K but no such transition is reflected in the thermoelectric power of the sample. A careful analysis of the data reveals that even below 180 K the material is a metal.
Crystal Structures and Peculiar Magnetic Properties of α- and γ-Al2O3 Powders
Authors: Liu R. S. , Shi W. C. , Cheng Y. C. , Huang C. Y.
Published: October 2003

The crystal structure and magnetic properties of the α- Al2O 3 and γ- Al2O 3 samples were investigated. The α- Al2O 3 and γ- Al2O 3 powders have the trigonal and cubic symmetries, respectively. Moreover, the α- Al2O 3 powders have better crystallinity than γ- Al2O 3 material. A peculiar magnetic behavior in these two materials was found. The weak diamagnetic signal appeared at the temperature range between room temperature and 100 K. Moreover, both materials have antiferromagnetic-like transitions at the temperature range between 30 K and 100 K. The materials changed to paramagnetic-like behavior at the temperature lower than 30 K. Based on our studies, we did not find any superconducting diamagnetic signal at the temperature range from 300 K to 5 K.
Structural, Magnetic and Superconducting Properties of the Y1-xZrxBa2-2xCa2xCu3O7-δ Compounds
Authors: Deac Iosif Gr. , Pop Iuliu , Pop Viorel , Burda Ioan
Published: October 2003

Samples with stoichiometric composition Y 1-x Zr x Ba 2-2x Ca 2x Cu3O7-δ with x=0.0, 0.1, 0.2, 0.3 were prepared by the solid state reaction method. The effect of Zr and Ca, doped at the Y and respectively Ba sites simultaneously in the Y:123 composition was studied. The phase and lattice parameters of the compounds were determined by X-ray powder diffraction measurements. We also discuss the distribution of the Ca ions between the Y and Ba sites when Y is partially replaced by Zr. Superconductivity was analyzed by both electrical resistivity and magnetic susceptibility measurements. The results suggest the assumption that the substitutions could increase the number of isolated Cu 2+ spin 1/2 defects and/or to change the energy of the spin fluctuations.
Crystal Structure of Red Lead Titanate Thin Films
Authors: Bursill L. A. , Peng J. L. , Jiang B. , Li X.
Published: October 2003

Orange-red lead titanate thin films are examined by high-resolution transmission electron microscopy and diffraction. It is remarkable that the structure is based on that of tetragonal-tungsten-bronze (TTB) rather than perovskite-type. The chemical basis for this result is examined, it is deduced that the TTB structure is stabilized by inclusion of hydroxyl ions during synthesis by a sol–gel route involving hydrolysis of n-Butyl titanate.
High Pressure Electrical Resistivity Study of Sm0.85Nd0.15Se
Authors: Ariponnammal S. , Natarajan S.
Published: October 2003

The study of rare-earth monochalcogenides have received much attention because of their interesting electrical properties. They crystallize in the NaCl type structure and are semiconducting if the rare earth ion is in the divalent state and metalic if trivalent state. The effect of substitution of trivalent rare earth ion in divalent rare earth has been studied. We present the results of electrical resistivity measurements and lattice parameter study on Sm0.85Nd0.15Se . The structure of the sample is confirmed by the theoretical calculation of X-ray intensities using Lazy-Pulverix programme. The electrical resistivity is found to be decreasing with the increase of pressure.
2D Saddle Potential Schrödinger Green's Function in the Presence of an Arbitrary Time-Dependent Electric Field
Authors: Horing Norman J. M. , Sabeeh Kashif
Published: October 2003

We derive the retarded nonrelativistic Green's function for a Schrödinger electron confined to a plane and subject to a parabolic saddle potential and an electric field having arbitrary time dependence and orientation on the plane. This derivation is carried out using Heisenberg equations of motion for position and momentum operators, following an earlier analysis of Schwinger, to obtain the retarded Green's function in closed form, as an explicit function of position and time variables.
Confinement Dependence of Bound Polaronic Energies in Anisotropic Quantum Dots under Magnetic Fields
Authors: Chen Chuanyu , Jin Pei-Wan , Lin D. L.
Published: October 2003

Energy levels of a polaron bound to hydrogenic impurities in anisotropic double-parabolic quantum dots are investigated by the second order perturbation theory. The polaronic energy corrections are expressed as a function of the confinement strength in different directions and the magnetic field applied along the growth direction. With characteristic parameters pertaining to GaAs, it is found that as the effective thickness reduces, the energy correction to higher subbands increases at a much larger rate than that to the lower subband. The polaron binding energy for higher subbands may become larger than that for the lower subband in the case of sufficiently thin quantum dots, in contrast to the normal energy level structure.
The Alexander–Orbach Conjecture is Corrected
Authors: Skal Asya S.
Published: October 2003

Using the Einstein relation [Formula: see text] the new critical exponents for regular diffusion are introduced [Formula: see text] where t is the conductivity critical exponents, g = -0.6 is the Hall coefficient critical exponents above the threshold for two-component composite.

This result allows us to correct the Alexander–Orbach conjecture1 that an effective dimensionality of the random walk, is d w = 2+(t-g)/ν by changing β on g and obtaining a universal fraction dimension d s = 4/3 in two and three-dimensional spaces. The Alexander and Orbach suggestion is nothing else but a rigorous relation for dynamic exponents of conductivity, the Hall and diffusion coefficients, similar to those for the phase-transition static critical exponents. It allows us to verify our value of fractal dimension of the backbone [Formula: see text] instead of customary [Formula: see text] for three-dimensional space and also to calculate the Hall coefficient critical exponent and the backbone fractal dimension in high dimension spaces.
Cooperative Quantum Phase Mixing Effect or Why the Continuous (He-Ne)-Laser Operates Without Inversion
Authors: Cheltsov Vladislav
Published: October 2003

Cooperative phase mixing effect (CPME) in the system of N-two-level atoms coupled to one and two resonance modes is described. Caused by irrationality of cooperative energy eigenvalues the CPME leads to quasi-periodic dynamics giving rise to superposition of states with both positive and negative inversions, so that the averaged inversion should be close to zero. To check inversionless operation of the continuous (He-Ne)-laser the nonperturbative theory of beatings in a rotating ring laser (RGL) has been suggested. The derived formula for beating frequency displays two states: with split frequencies of opposite modes and the lock-in regime. Comparison of this formula with the observed lock-in threshold rotation velocity has given the estimation (N_/V)~ (10-5-10-11) cm-3 as dependent on geometry and operation conditions.
Dechanneling by Ionized Point Defects in Solids: Double Screening Effects
Authors: Siddiqui Azher M. , Kiran A. , Pathak Anand P.
Published: October 2003

The interaction between an external probe particle and host lattice is described by a screened Coulomb potential which gets modified due to the presence of impurities in the lattice. A double screened potential was earlier derived and we extend the formulation to include higher order terms in the dielectric function ε(q) which defines the screening parameters of this potential. The weakly decaying nature of the potential thus derived manifests itself in dechanneling process and scattering cross-section. It will also be evident from this formulation that the conduction electrons of the host lattice play an important role in the interaction between the probe particle and impurities. Dechanneling cross-sections are modified for various charge states of impurity in different planar directions when we consider the effect of both atomic electrons of the impurity and conduction electrons of the host lattice. The results for α-particle dechanneling in palladium (by C or H impurities) and for muon dechanneling by oxygen in tantalum are compared with earlier calculations and available experimental results.
Liquid Crystal, Synergetical System? New Considerations on the Self-Organization and Structural Stability in LC State
Authors: Honciuc Maria , Bǎdrǎgan I. , Slavnicu Elena , Ploşceanu Carmina
Published: October 2003

The transitions from the solid crystal to liquid crystal, from isotropic liquid crystal as well as the transitions between different mesomorphic states could be interpreted in terms of synergetic and nonlinear dynamics.
The Role of Dimensionality in the Stability of a Confined Condensed Bose Gas
Authors: Salasnich Luca
Published: October 2003

We study analytically the ground-state stability of a Bose–Einstein condensate (BEC) confined in an harmonic trap with repulsive or attractive zero-range interaction by minimizing the energy functional of the system. In the case of repulsive interaction the BEC mean radius grows by increasing the number of bosons, instead in the case of attractive interaction the BEC mean radius decreases by increasing the number of bosons: to zero if the system is one-dimensional and to a constant minimum radius, with a maximum number of bosons, if the system is three-dimensional.
Penetration Depth in Anyon Superconductivity on Torus
Authors: Farajian Amir Abbas , Brojeny Ali Akbar Babaei
Published: October 2003

We present a model for studying the Meissner effect in anyon superconductivity on torus. By obtaining the explicit forms of screening currents for different geometries of external magnetic fields, we calculate the penetration depth and its dependence on relevant parameters. We find a difference between our model and London theory of bulk superconductors. This can be traced back to the two-dimensional character of electric charge carriers that obey anyonic statistics. Our calculations show that for ground state configuration the fractional statistical nature of carriers is washed out of the final results, whereas for excited states the screening currents — and hence the penetration depth — explicitly depend on the fractional phase of the model.
Equivalence Between Squeezed-State and Twin-Beam Communication Channels
Authors: D'Ariano G. M. , Sacchi M. F.
Published: October 2003

We show the equivalence between two different communication schemes that employ a couple of modes of the electromagnetic field. One scheme uses unconventional heterodyne detection, with correlated signal and image band modes in a twin-beam state from parametric downconversion. The other scheme is realized through a complex-number coding over quadrature-squeezed states of two uncorrelated modes, each detected by ordinary homodyning. This equivalence concerns all the stages of the communication channel: the encoded state, the optimal amplifier for the channel, the master equation modeling the loss, and the output measurement scheme. The unitary transformation that connects the two communication schemes is realized by a frequency conversion device.
Quantum Signal Splitting that Avoids Initialization of the Targets
Authors: Mozyrsky Dima , Privman Vladimir
Published: October 2003

The classical signal splitting and copying are not possible in quantum mechanics. Specifically, one cannot copy the basis up and down states of the input (I) two-state system (qubit, spin) into the copy (C) and duplicate-copy (D) two-state systems if the latter systems are initially in an arbitrary state. We consider instead a quantum evolution in which the basis states of I at time t are duplicated in at least two of the systems I, C, D, at time t+Δt. In essence, the restriction on the initial target states is exchanged for uncertainty as to which two of the three qubits retain copies of the initial source state.
Differential Conductance for Tunnel Junctions: Effects of d-Wave Gap
Authors: Chattopadhyay Biplab , Lahiri Joydev , Das A. N.
Published: October 2003

Tunneling conductance for N-I-S and S-I-S tunnel junctions are calculated within the framework of an extended van-Hove singularity in the single particle density of states of the superconducting electrode. Results from our calculations are compared with the conductance data of N-I-S and S-I-S junctions consisting of high-T c superconductors. Possible interpretation of the photoemission intensity curves, in terms of the quasiparticle density of states, is considered and predictions are made for conductance including a d-wave pseudogap in the quasiparticle dispersion.
Field-Induced Phase Transition in S=1 XXZ Chain with Biquadratic Exchange Interaction
Authors: Sato Ryutaro
Published: October 2003

We study the magnetization process of the S=1 XXZ chain with biquadratic exchange interaction at zero temperature. This system can be regarded as a quantum lattice gas composed of "particles" with Sz=0, ±1. We introduce an approximate nested Bethe ansatz (ANBA) to examine the possibility of phase transition induced by the magnetic field. In the high-magnetization region σ≥σ0 for certain σ0, the ANBA gives the exact ground state energies. For σ<σ0 the ANBA gives approximate solutions. The analysis shows that a phase transition occurs at σ0 across which the magnetic susceptibility changes discontinuously. Comparing with the finite-size diagonalization, we argue that σ0 is the exact critical magnetization.
Polaron Dissociation at the Insulator-to-Metal Transition
Authors: Quémerais P. , Fratini S.
Published: October 2003

Considering the long range Coulomb interactions between large polarons in dielectrics, we propose a model for their crystallization when no bipolarons are formed. As the density increases, the melting is examined at T=0 K. One possibility is the delocalization towards a liquid state of polarons. However, we show that this cannot happen if the electron-phonon coupling is larger than some critical value. The other competing mechanism is the dissociation of the polarons themselves, favored owing to their large mass at strong coupling. Finally, we propose a phase diagram for the insulator-to-metal transition as a function of the density and electron–phonon coupling.
Shift in Quantum Hall-Fluids and Topological Aspects of Chiral Anomaly
Authors: Basu B. , Bandyopadhyay P.
Published: October 2003

The topological aspects of the quantum number shift for the quantum Hall fluid has been discussed here. It is shown that this effectively represents the deviation of the Berry phase associated with the chiral anomaly arising out of the quantization procedure of a fermion from that of a quantum Hall particle induced by the external magnetic field. Also it is argued that there should not be any shift when the curvature of space vanishes.
Spiral Waves in a Cyclic Cellular Automaton Model for Excitable Media
Authors: Andrecut Mircea
Published: October 2003

We present a cyclic cellular automaton for excitable media. The model exhibits the complex dynamics of patterns observed in excitable media. Spatial patterns dynamics provides an important example of spatio-temporal self-organization in distributed active systems. The global behavior of the cellular automaton model is described in terms of point correlation functions. The Fouries analysis pointed out the quasi-oscillatory and chaotic behavior of these functions.
Determination of Transient Currents in Nematic Liquid Crystals by Using a Time Dependent Thermodynamical Model
Authors: Rosu Constantin , Motoc Cornelia
Published: October 2003

The behavior of transient currents in nematic liquid crystals is examined by using a theoretical model based on a time dependent thermodynamical model. The transient current exhibits a peak which is due to the dynamics of molecular reorientation under electric field. The time evolution of the transient current, its dependence on temperature and on field strength are in good agreement with the experimental data obtained for the nematic 5CB.
A Fully Distributed Architecture for Large Scale Workflow Enactment
Authors: Filho Roberto Silveira Silva , Wainer Jacques , Madeira Edmundo R. M.
Published: October 2003

Standard client-server workflow management systems are usually designed as client-server systems. The central server is responsible for the coordination of the workflow execution and, in some cases, may manage the activities database. This centralized control architecture may represent a single point of failure, which compromises the availability of the system. We propose a fully distributed and configurable architecture for workflow management systems. It is based on the idea that the activities of a case (an instance of the process) migrate from host to host, executing the workflow tasks, following a process plan. This core architecture is improved with the addition of other distributed components so that other requirements for Workflow Management Systems, besides scalability, are also addressed. The components of the architecture were tested in different distributed and centralized configurations. The ability to configure the location of components and the use of dynamic allocation of tasks were effective for the implementation of load balancing policies.
W-RBAC — A Workflow Security Model Incorporating Controlled Overriding of Constraints
Authors: Wainer Jacques , Barthelmess Paulo , Kumar Akhil
Published: October 2003

This paper presents a pair of role-based access control models for workflow systems, collectively known as the W-RBAC models. The first of these models, W0-RBAC is based on a framework that couples a powerful RBAC-based permission service and a workflow component with clear separation of concerns for ease of administration of authorizations. The permission service is the focus of the work, providing an expressive logic-based language for the selection of users authorized to perform workflow tasks, with preference ranking. W1-RBAC extends the basic model by incorporating exception handling capabilities through controlled and systematic overriding of constraints.
A Feature Selection and Classification Technique for Text Categorization
Authors: Girgis M. R. , Aly A. A.
Published: October 2003

Text categorization is the automated assigning of documents to predefined categories based on their contents. It involves two main tasks — feature selection and document classification. This paper discusses the weak points of the text categorization technique developed by Maron and modified by Lewis. Then, it introduces a technique for text categorization that uses new formulas for feature selection and document classification. These formulas have been formulated to overcome the weak points of Maron's and Lewis' techniques. Also, the paper describes the design of an experimental text categorization system that is composed of the same set of processes as the MAXCAT system developed by Lewis. The paper presents and analyses the results of applying the system on a set of training and test documents by using Lewis' and the proposed formulas. In addition, a method for separately evaluating the effectiveness of feature selection is given. Finally, the impact of the feature set size on the effectiveness of the classification system is investigated, using the system and applying one of the proposed classification formulas with different feature set sizes.
A Three-Level Framework for Process and Data Management of Complex E-Services
Authors: Grefen Paul , Ludwig Heiko , Angelov Samuil
Published: October 2003

Service outsourcing is the business paradigm in which an organization has part of its business process performed by a service provider. In dynamic markets, service providers can be selected on the fly during process enactment. The cooperation between the parties is specified in a dynamically made electronic contract. This contract includes a process specification that is tailored towards service brokering and cross-organizational process enactment and, hence, has to conform to market and specification standards. Process enactment, however, relies on intra-organizational process specifications that have to comply with the infrastructure available in an organization for process and data management. In this paper, we present a three-level process and data specification framework for dynamic contract-based outsourcing of complex services. We focus on services with an externally visible control flow, as opposed to simple, black-box web services. The framework relates the two process specification levels through a third, conceptual level. This approach is inspired by the well-known ANSI-SPARC model for data management. We discuss an abstract architecture for dynamic service outsourcing based on the three-level framework. We show how the framework and architecture can be placed in the context of existing infrastructures for cross-organizational process support. As service outsourcing is used more and more for core business processes requiring reliable execution, we pay special attention to transaction management.
ON THE COMPACTNESS OF MANIFOLDS
Authors: LI XUE-MEI , WANG FENG-YU
Published: October 2003

It is believed that the family of Riemannian manifolds with negative curvatures is much richer than that with positive curvatures. In fact there are many results on the obstruction of furnishing a manifold with a Riemannian metric whose curvature is positive. In particular any manifold admitting a Riemannian metric whose Ricci curvature is bounded below by a positive constant must be compact. Here we investigate such obstructions in terms of certain functional inequalities which can be considered as generalized Poincaré or log-Sobolev inequalities. A result of Saloff-Coste is extended.