bluuebunny/crossref_metadata_2025 huggingface dataset:
Novel Technique for Quantum-Mechanical Eigenstate and Eigenvalue Calculations based on Seke's Self-Consistent Projection-Operator Method
Authors: Seke J. , Soldatov A. V. , Bogolubov N. N.
Published: October 2003

Seke's self-consistent projection-operator method has been developed for deriving non-Markovian equations of motion for probability amplitudes of a relevant set of state vectors. This method, in a Born-like approximation, leads automatically to an Hamiltonian restricted to a subspace and thus enables the construction of effective Hamiltonians. In the present paper, in order to explain the efficiency of Seke's method in particular applications, its algebraic operator structure is analyzed and a new successive approximation technique for the calculation of eigenstates and eigenvalues of an arbitrary quantum-mechanical system is developed. Unlike most perturbative techniques, in the present case each order of the approximation determines its own effective (approximating) Hamiltonian ensuring self-consistency and formal exactness of all results in the corresponding approximation order.
Ising Model over Cayley Lattices with Local 2D Geometry
Authors: Ceresole Anna , Zecchina Riccardo
Published: October 2003

A simple analysis of the thermodynamical properties of a hierarchical lattice with local 2D geometry is presented. The nonlinear maps that arise from the recursive procedure yield the thermodynamics of both the central (Bethe) region and of the complete lattice. In a particular limit, where the lattice collapses onto one with non-uniform coordination, a magnetic instability arises, preventing the appearance of a true second order transition. In the frustrated case, such an instability becomes marginally stable.
On the Torus Quantization of Two Anyons with Coulomb Interaction in a Magnetic Field
Authors: Salasnich Luca
Published: October 2003

We study two anyons with Coulomb interaction in a uniform magnetic field B. By using the torus quantization we obtain the modified Landau and Zeeman formulas for the two anyons. Then we derive a simple algebraic equation for the full spectral problem up to the second order in B.
Observation of Redshifts of Photoluminescence from Thin Films Assembled by CuCl Nanoclusters
Authors: Miao Bingyou , Hong Jianmin , Chen Pingping , Yuan Xiaoli , Han Min , Wang Guanghou
Published: October 2003

Two samples of thin films, assembled by CuCl nanoclusters, have been prepared by the gas evaporation technique. The CuCl nanoclusters were deposited on monocrystalline silicon and quartz substrates and then coated with a layer of NaCl to prevent oxidation of the CuCl nanoclusters. From transmission electron microscope and selected area diffraction, it is clear that the two samples consist of CuCl nanocrystals and Cu aggregates and the mean diameters are about 3 nm and 6 nm. From the absorption and photoluminescence (PL) spectra of the two samples carried out at ~300 K, we found that the peaks of exciton absorption do not show up and luminescence peaks shift to lower energies, possibly due to the strong coupling between exciton and phonon. At 77 K, the PL peaks of excitons broadened by exciton–phonon coupling have been observed, in approximate agreement with the values calculated by the quantum confinement model. The broad peaks of emission from trapped states or bands have also been observed at 77 K. In addition, the interaction between exciton and phonon is stronger in the sample with mean diameter about 3 nm according to a larger broadening and redshift of the PL peak from excitons, in qualitative agreement with theoretical prediction.
Generalized Exclusion Statistics in the Kondo Problem
Authors: Protogenov A. P. , Verbus V. A.
Published: October 2003

We consider the generalized exclusion statistics in the Kondo problem. The thermodynamic Bethe ansatz equations have been used for a multicomponent system of particles obeying the generalized exclusion principle. We have found a relation between the derivative of the phase shift of the scattering matrix for Fermi particles and for particles characterized by generalized exclusion statistics. We show that the statistical matrix in the Kondo problem has a universal form in the high and low temperature limits.
Walk of a Point Defect in a Model with Macroscopic Ground State Degeneracy
Authors: Bakaev A. V. , Kabanovich V. I.
Published: October 2003

Walks of the point defect in the two- and three-dimensional lattice models of colored hard spheres mimicking the q-state antiferromagnetic Potts model are considered. The walks are generated by moves of neighboring vertices which conserve the ground state energy. Various "traps" confining the walks are observed, while for the models with q≥4 and q≥5 on the square and cubic lattices respectively nonvanishing probabilities that all lattice vertices are attainable in a walk are found.
q-Deformation and Energy Deficit in Liquid Helium Phonon Spectrum
Authors: Rodrigues Ligia M. C. S. , Wulck Stenio
Published: October 2003

We present an application of an ideal bosonic q-gas in a ν0 inequivalent representation to the phonons in 4 He and discuss the role of q-deformation as a possible mechanism to supply the energy deficit that forbiddens one-phonon decay into two phonons when the constant γ in the phonon anomalous dispersion relation (ωph = c0p(1 - γp2)) is positive.
Superconductivity in the Strong Coupling Limit: Van Hove Singularity and Extended Saddle Point Singularity Scenario
Authors: Sarkar Sujit
Published: October 2003

The effect of orthorhombic distortion and second nearest neighbor hopping on the transition temperature (T c ) and the isotope-shift exponent (α) have been studied for a two dimensional system, within the framework of Eliashberg formalism in the van Hove singularity scenario. The behavior of T c and α have been discussed for the case of extended saddle point singularity. A comparison of the strong coupling theory results is made with the results of weak coupling theory. From our study it reveals that the effect of singularity in the density of states (DOS) in the strong coupling limit is not so significant as that in weak coupling case.
Structure and Properties of Substitution of Fluorine for Apical Oxygen in Pb2Sr2Y0.5Ca0.5Cu3O8+δ Superconductor
Authors: Gao De , Gao Xiao-Hui , Jiang Shu-Fen , Jia Shu-Lian , Zhao Bai-Ru
Published: October 2003

Structure and properties of Pb-based superconductor with F doped as well as its synthesis are examined in this paper. Besides, substitution of F for apex oxygen O(A) atoms in CuO 5 square pyramid is confirmed by experimental results. It is pointed out that reducing the distance between carrier plane and charge reservoir will favour the hole doping and enhancement of T c .
Superconductivity and Magnetic Ordering of Pr in CaLa1-xPrxBaCu3O7 System
Authors: Awana V. P. S. , Singh Rajvir , Landinez Tellez D. A. , Ferreira J. M. , Albino Aguiar J. , Uma S. , Gmelin E. , Narlikar A. V.
Published: October 2003

We present the results of superconductivity, normal state magnetic susceptibility and heat capacity measurements on the tetragonal CaLa 1-x Pr x BaCu 3 O 7 compound. Ac susceptibility measurements show that the transition temperature T c of the unsubstituted sample decreases with an increase in the Pr concentration. Normal state dc magnetic susceptibility measurements performed in an applied field of 0.5 T show a Curie–Weiss behaviour in terms of the paramagnetic moment of Pr. The effective paramagnetic moment of Pr appears to be intermediate between those of the free Pr 3+ and Pr 4+ ions. For the nonsuperconducting samples i.e., x = 0.70 and 1.0, we observe an antiferromagnetic ordering temperature T N of nearly 4 K and 8 K respectively. The X-ray diffraction results show that the CaPrBaCu 3 O 7 compound is free from other phases, having a minor (less than 8%, in terms of peak intensity) impurity phase. The lower T N (8 K) of PrBaCaCu 3 O 7 as compared to the known antiferromagnetic ordering temperature of 17 K for PrBa 2 Cu 3 O 7 indicates a less deleterious effect of Pr in the present case.
Novel 1/N Expansion for Self-Energy and Correlation Functions of the Hubbard Model
Authors: Kulić Miodrag L. , Zeyher Roland
Published: October 2003

The novel slave-free (i.e. without slave bosons and fermions) approach to the problem of strong correlations is used in studying the Hubbard (t-J) model, where the self-energy is expressed in terms of charge and spin vertex functions of Hubbard operators. A systematic 1/N expansion (N is the number of spin components) of the self-energy is carried out. In O(1) it gives the same quasiparticle spectrum as the slave boson theory. The next order O(1/N) of the self-energy Σ(k, ω) is calculated exactly by solving analytically the integral equations for the charge and spin vertices. As an example for the feasibility of the proposed method explicit results for Σ(k, ω) are given in the case J=0. Dealing only with observable quantities our method is transparent and easily applicable to models which exclude double occupancy on lattice sites, such as the Anderson model and the Emery model for high temperature superconductors.
Normal-State c-Axis Resistivity of the High-Tc Cuprate Superconductors
Authors: Kumar N. , Pareek T. P. , Jayannavar A. M.
Published: October 2003

It is shown that a strong intraplanar incoherent scattering can effectively block the interplanar coherent tunneling between the weakly coupled planes of the highly anisotropic but clean (intrinsic) materials such as the optimally doped high-T c layered cuprate superconductors. The calculated normal-state c-axis resistivity ρ c (T) then follows the metal-like temperature dependence of the ab-plane resistivity ρab(T) at high temperatures. At low enough temperatures, however, ρ c (T) exhibits a non-metal like upturn even as ρab(T) remains metallic. Moreover, in the metallic regime, ρ c (T) is not limited by the maximum metallic resistivity of Mott–Ioffe–Regel. This correlation between the intrinsic ρ c (T) and ρab(T) is observed in the normal state of the high-T c stoichiometric cuprates.
Magnetic and Structural Characteristics of Amorphous and Crystalline α-Al2O3 High TC Superconductors
Authors: Pop Iuliu , Oprea Camelia , Burda Ioan , Pop Olivia
Published: October 2003

The amorphous and crystalline α- Al2O3 oxides were investigated from magnetic and structural point of view. The temperature dependence of the magnetic susceptibility experiences double diamagnetic transition. First diamagnetic-paramagnetic transition is connected with the superconductor-paramagnetic transition, and the second is connected with the diamagnetic-normal state transition of α- Al2O3 -amorphous and crystalline phase. The crystalline α- Al2O3 phase has the critical temperature T c (χ = 0) = 78 K and amorphous phase has the critical temperature much higher temperature T c (χ = 0)= 144 K.
Ultrasonic Shear Velocity Anomalies in Bulk Thallium-1212 High Temperature Superconductor
Authors: Abd-Shukor R.
Published: October 2003

Ultrasonic shear velocity of bulk TlSr2(Ca, Cr)Cu2O7 and (Tl, Bi)Sr2(Ca, Cr)Cu2O7 high temperature superconductors has been measured between 80 K and above 200 K at 8 MHz. A hardening trend was observed in both samples as the temperature was lowered. A large thermal hysteresis was observed in the TlSr2(Ca, Cr)Cu2O7 (density 3.74 g/cm3) but very much suppressed in the (Tl, Bi)Sr2(Ca, Cr)Cu2O7 (density 5.40 g/cm3) sample. Shear velocity hysteresis in these materials is very much determined by the density and microstructure and may not be directly related to high temperature superconductivity. A pronounced change in the shear velocity at about 160–190 K signifying a softening tendency was observed in the (Tl, Bi)Sr2(Ca, Cr)Cu2O7 material. Some possible mechanisms of the origin of these anomalies are discussed.
Quasicrystallinity Studies on Conventionally Solidified Aluminum-Technetium and Aluminum-Uranium Based Alloys
Authors: Athanasiou N. S.
Published: October 2003

We present quasicrystallinity investigations on conventionally solidified binary Al-Tc, ternary Al-Tc-M (M = Mn, Ni, Cu, Ru, Rh, Pd, Re, Ir, Pt), Al-Cu-U, as well as quaternary Al-Cu-Ru-U alloys. By conventional cooling (dT/dt≈103 to 102 Ksec -1) crystalline phases were formed in all the systems, except for Al-Tc-Ir system, where only icosahedral quasicrystalline phases were found. A new large (1–1.5 mm in size) icosahedral (F-type structure) quasicrystal with a pentaprismatic growth morphology was obtained in the sample with the nominal composition Al77.6Tc10Ir12.4 . The characterization of the quasicrystalline state was examined by X-ray diffractometry, scanning electron microscopy (SEM) and energy-dispersive X-ray microanalysis (EDXA).
Wigner Distribution Function for Open Quantum Systems
Authors: Baskoutas S.
Published: October 2003

Using the modified biorthonormal Heisenberg equations of motion for non-Hermitian (NH) Hamilton operators, in order to imply a consistent Lie-algebraic structure and also the equivalence between the Heisenberg and Schrödinger pictures, we have obtained the analytical form of the Wigner distribution function which is unavoidable complex. Its imaginary part accounts for the influence of additional degrees of freedom, which are always present in the phenomenological representation of dissipative systems through (NH) Hamiltonians. Applications of the above formalism can be found, for instance, in dissipative macroscopic quantum tunneling (MQT) effect for Josephson junctions, and in the dissipative tunneling of trapped atoms in optical crystals.
On the Squeezing and Displacement of nth-Order
Authors: de Almeida Norton G. , Dantas Célia M. A.
Published: October 2003

The norder expressions for the squeezed and coherent states are derived as a natural generalization of the usual squeezed coherent and coherent states. The photon number distribution of n order of squeezed coherent states that are eigenstates of the operators [Formula: see text] is derived. The n order coherent state is a particular case of the states that we are now deriving. Some mathematical and quantum statistical properties of these states are discussed.
The Electrical Resistivity and Specific Heat of NiGa
Authors: Hsu L.-S. , Yao Y. D. , Chen Y. Y.
Published: October 2003

The electrical resistivity and specific heat of NiGa were measured between 5 and 296 K and between 1.07 and 300 K, respectively, at zero magnetic field. This compound is metallic as shown from the room-temperature resistivity value (37.4 μΩ cm). The residual resistivity ratio is 1.32, which indicates the defect scattering dominates at low temperatures. The density of states at the Fermi energy and the Debye temperature obtained from the low-temperature specific-heat measurement are 1.48 states/eV formula unit and 202 K, respectively. The former is much higher than the value for NiAl. This observation suggests that the Ni d-band in NiGa is not completely filled.
Magnetic Behavior and Chemical Shift of Amorphous Cr2O3
Authors: Pop I. , Andrecut M. , Burda I. , Oprea C. , Andrecut C.
Published: October 2003

The chemical shift in cristalline and amorphous Cr2O3 was determined from the X-ray absorption Cr K edge spectra. The measurements of the temperature dependence of the reciprocal susceptibility between 100 and 1200 K show an antiferromagnetic behavior for the cristalline sample, with the Neel temperature at 318 K, and a linear dependence (Curie-Weiss law) with θp<0, for the amorphous oxide.
Vortex–Vortex Interaction Mediated Motion of Vortices in Josephson Junction Arrays
Authors: Mehrotra Ravi , Datta Sujay , Sahdev Deshdeep
Published: October 2003

We numerically study vortex motion in arrays of over- and under-damped Josephson junctions. We show quantitatively that vortex–vortex interactions (VVI) in a vortex-street are large enough to overcome the pinning potential and cause vortices to move even in a region with no external current. The experiments of van der Zant et al.1 are reinterpreted in terms of VVI without invoking ballistic motion of vortices. The discrepancy with simulations which have all failed to observe any ballistic motion is thus removed. Our results also indicate that the vortex mass is negligible for the McCumber–Stewart parameter, β c < 100.
Electric and Electro-Optic Investigations on Polymer Dispersed Liquid Crystal Films
Authors: Manaila-Maximean Doina , Bena Rodica , Albu Ana-Maria
Published: October 2003

We obtained polymer-nematic liquid crystal composite films by the solvent induced phase separation (SIPS) method. We used a novel polymer obtained by the synthesis of a macromolecular structure with a matrix basis of methyl methachrylate and a chromophore group with extended conjugation (MMA + I) and the nematic liquid crystal E3 (BDH). We studied the electro-optical effects using He–Ne lasers of two different intensities, for a.c. driving fields of different frequencies and voltages. At low frequencies, the emergent optical signal is modulated in amplitude, doubling the frequency of the a.c. driving field. At higher intensities of the incident laser beam, the variation of the transmission with the a.c. driving electric field is much smaller. In the KHz frequency range, the decrease of the fluctuations of the transmitted light intensity with the increase of the frequency was observed. We also plotted the volt-ampere (V-I) characteristics of the polymer/LC composite films in different coordinates systems in order to determine the contribution of the nonlinear effects to the electric conduction.
Potential Barrier Height Effects on the Intrasubband and Intersubband Quasi-One-Dimensional Plasmons
Authors: Machado Paulo César Miranda , Osório Francisco A. P. , Borges A. Newton
Published: October 2003

The effects of the potential barrier height on the collective excitations of a electron gas confined in a GaAs-AlxGa1-xAs quantum wire of rectangular cross-section are investigated theoretically. For several potential barrier heights, we calculated the plasmon energy, structure factor and pair-correlation function, within the Random-Phase Approximation regime, considering a three-subband model with only the lowest subband populated by electrons. We verified that the intersubband plasmon is more sensitive to the potential barrier height variation than the intrasubband plasmon. We also observed that the confining potential effect decreases with the increasing of the wire-width.
On the Two-Magnon Bound States for the Quantum Heisenberg Chain with Variable Range Exchange
Authors: Dittrich J. , Inozemtsev V. I.
Published: October 2003

The spectrum of finite-difference two-magnon operator is investigated for quantum S=1/2 chain with variable range exchange of the form h(j-k)∝ sinh -2a(j-k). It is found that usual bound state appears for some values of the total pseudomomentum of two magnons as for the Heisenberg chain with nearest-neighbor spin interaction. Besides this state, a new type of bound state with oscillating wave function appears at larger values of the total pseudomomentum.
Two-Dimensional Gases of Generalized Statistics in A Uniform Magnetic Field
Authors: Ho Choon-Lin , Liao Man-Jui
Published: October 2003

We study the low temperature properties of two-dimensional ideal gases of generalized statistics in a uniform magnetic field. The generalized statistics considered here are the parafermion statistics and the exclusion statistics. Similarity in the behaviors of the parafermion gas of finite order p and the gas with exclusion coefficient g=1/p at very low temperatures is noted. These two systems become exactly equivalent at T=0. Quantum Hall effect with these particles as charge carriers is briefly discussed.
The Energy Band Structure of Polyacene with Soliton Excitation
Authors: Li Z. J. , Xu H. B. , Yao K. L.
Published: October 2003

Starting from the extensional Su–Schrieffer–Heeger model taking into account the effects of interchain coupling, we have studied the energy spectra and electronic states of soliton excitation in polyacene. The dimerized displacement u0 is found to be similar to the case of trans-polyacetylene, and equals to 0.04 Å. The energy-band gap is 0.38 eV, in agreement with the results derived by other authors. Two new bound electronic states have been found in the conduction band and in the valence band, which is different from the one of trans-polyacetylene. There exists two degenerate soliton states in the center of energy gap. Furthermore, the distribution of charge density and spin density have been discussed in detail.
Correlated Squeezed State Approach for Complex Phonon Coupling in a Tunnelling System
Authors: Baskoutas S. , Papanikolaou P.
Published: October 2003

In the present paper we propose a method of studying a two-state system coupled linearly to a boson field with complex coupling in a correlated squeezed state approach. The complex coupling leads to the initiation of complex probability density with complex statistical averages. Exploiting the biorthonormal formalism we obtain the analytical forms of the complex expectation value E of H as well as the complex tunneling reduction factor. As it is seen from our results the localization–delocalization transition of the tunneling particle is modified for small values of the real part of the coupling constant in comparison with the conventional (g real) correlated squeezed state approach.
Theory of Spontaneous and Stimulated Emission in Two Band Intrinsic Semiconductor
Authors: Cheltsov Vladislav
Published: October 2003

The behavior of a single mode of radiation field coupled to an excited two band intrinsic semiconductor has been investigated with the help of the commutator version of evolution operator method. As dependent on the excitation level three states of the field has been shown to exist: the equilibrium with the number of photons determined by the Bose–Einstein distribution with nonzero chemical potential; the quasi-equilibrium with the average number of photons equal to unity and accompanied by fluctuations; the state of photon avalanche.
Percolation Conductivity and Fractal Behavior in an YBaCuO Sample
Authors: Patapis S. K. , Moraitakis E. , Vekinis G. , Niarchos D. , Clippe P.
Published: October 2003

From the fluctuation conductivity behavior of a system information concerning its dimensionality and its change with temperature can be studied and the cross-over point of this change can be determined as well. Besides the above characteristics sometimes, depending on the relations of some constants of the material, percolative fractal behavior emerges in the fluctuation behavior. The above behavior has been recognized out of paraconductivity measurements in a polycrystal YBaCuO sample as it has been also observed in some other samples.
A Proposed Experiment of Direct Detecting of the Vector Potential within Classical Electrodynamics
Authors: Onoochin V.
Published: October 2003

An experiment within the framework of classical electrodynamics is proposed, to demonstrate Boyer's suggestion of a change in the velocity of a charged particle as it passes close to a solenoid. The moving charge is replaced by an ultra-short pulse (USP), whose characteristics should depend on the current in the coil. This dependence results from the exchange of energy between the electromagnetic field of the pulse and the magnetic field within the solenoid. This energy exchange could only be explained, by assuming that the vector potential of the solenoid has a direct influence on the pulse.
Electric Field Investigation of the Microcracks in Metal Oxide Film
Authors: Duś-Sitek M. , Szymura S. , Pisarek J. , Całusiński B. , Małachowski M. J. , Dabrowski R.
Published: October 2003

According to the model explaining the kinetics of the exoelectron emission, the uniaxial stretching of metals is accompanied by electrons emission in the electric field of the charged microcracks presented during the deformation process. In this paper, using the polarization effect of a liquid crystal deposited onto the surface of the stretched metal, the evolution of a such microcrack was observed.
Phase Distribution in a Disordered Chain and the Emergence of a Two-Parameter Scaling in the Quasiballistic to the Mildly Localized Regime
Authors: Sen Asok K.
Published: October 2003

We study the phase distribution of the complex reflection coefficient in different configurations as a disordered 1D system evolves in length, and its effect on the distribution of the 4-probe resistance R4. The stationary (L → ∞) phase distribution is almost always strongly non-uniform and is in general double-peaked with their separation decaying algebraically with growing disorder strength to finally give rise to a single narrow peak at infinitely strong disorder. Further in the length regime where the phase distribution still evolves with length (i.e. in the quasiballistic to the mildly localized regime), the phase distribution affects the distribution of the resistance in such a way as to make the mean and the variance of log (1+R4) diverge independently with length with different exponents. As L → ∞, these two exponents become identical (unity). Obviously, these facts imply two relevant parameters for scaling in the quasiballistic to the mildly localized regime finally crossing over to one-parameter scaling in the strongly localized regime.
The Glauber and Metropolis Transition Rates on the Stationary States of the Ising Model
Authors: Paula G. L. S. , Figueiredo W.
Published: October 2003

We have applied the Glauber and Metropolis prescriptions to investigate the stationary states of the Ising model in one and two dimensions. We have employed the formalism of the master equation to follow the evolution of the system towards the stationary states. Although the Glauber and Metropolis transition rates lead the system to the same equilibrium states for the Ising model in the Monte Carlo simulations, we show that they can predict different results if we disregard the correlations between spins. The critical temperature of the one-dimensional Ising model cannot even be found by using the Metropolis algorithm and the mean field approximation. However, taking into account only correlations between nearest neighbor spins, the resulting stationary states become identical for both Glauber and Metropolis transition rates.
Many Band Effects in Cuprate Superconductors
Authors: Kruchinin S. P. , Yaremko A. M. , Mozdor E. V.
Published: October 2003

The new theoretical approach is proposed for study the states responsible for superconductivity of crystals. Within the frameworks of worked out approach it is shown that in electron–phonon system a class of new so-called coupled states arises. Postulated in BCS method electron-pair states k1 + k2 = 0, s + s′ = 0 are in natural manner included in this class. The model numerical calculations have shown that SC gap depends on number of bands crossing the Fermi level on the momenta k1+k2 = K≠ 0 of interacting electrons and that the temperature dependence of SC gap for HTSC is more complicated (in agreement with the recent experimental data) then predicted in BCS approach.
Ferromagnetic Instanton Interference in Magnetic Fields — Detailed Calculation of Tunneling-Rate
Authors: Lü Rong , Zhu Jia-Lin , Wu Jian , Chen Xi , Chang Lee , Kawazoe Yoshiyuki
Published: October 2003

Macroscopic quantum coherence and tunneling of small ferromagnetic particles in the presence of a magnetic field are investigated by using the instanton method. Both the Wentzel–Kramers–Brillouin exponent and the van Vleck fluctuation determinant are obtained for each case. The topological quenching at H=0 for half-integral spin particles is evident and such effect can be destroyed by a large applied magnetic field. The oscillating relations of the tunneling rate with the weak applied magnetic field are clearly shown and the quenching of tunneling at some definite values of the field is predicted. The experiment condition for observing the topological quenching is suggested.
Extension of the High Temperature Susceptibility Expansion for General Ising Systems
Authors: Soehianie A. , Oitmaa J.
Published: October 2003

We have obtained the graphs and weights for the twelfth and thirteenth terms of the high temperature multigraph expansion for the susceptibility of general Ising systems. As applications we have computed the coefficients through thirteenth order for the square lattice with first and second neighbor interactions and first and third neighbor interactions.
Critical Relaxation and Critical Exponents
Authors: Luo H. J. , Zheng B.
Published: October 2003

Dynamic relaxation of the XY model and fully frustrated XY model quenched from an initial ordered state to the critical temperature or below is investigated with Monte Carlo methods. Universal power law scaling behavior is observed. The dynamic critical exponent z and the static exponent η are extracted from the time-dependent Binder cumulant and magnetization. The results are competitive to those measured with traditional methods.
Dissipative Model for a Gas System with Constant External Force
Authors: López G. , Murguía M. , Sosa M.
Published: October 2003

The thermodynamic characteristics of a system consisting in a mixture of two gases affected by a constant external force (gravity, for example) with dissipation are derived. Assuming a long narrow-square shape pipe container for the gas, the pressure as a function of the altitude is determined using the partition function of the classical mechanics. The limit case for α and f going to zero is studied, where α and f are the parameters which characterize the dissipation and the constant force.
Magnetic and Magnetoelectric Studies in Polycrystalline LaBi4FeTi3O15
Authors: James A. R. , Kumar G. S. , Kumar Mahendra , Suryanarayana S. V. , Bhimasankaram T.
Published: October 2003

LaBi4FeTi3O15 is a 4-layered ferroelectromagnetic material belonging to the Aurivillius' family of compounds having an orthorhombic distortion. Polycrystalline samples of this compound were prepared by uniaxial pressing and cold isostatic pressing with a view to study the effect of different compaction techniques and its impact on the physical properties. The scanning electron micrographs of the samples showed differences in microstructures. Magnetization measurements were carried out from 80 K to room temperature and B–H loop traces indicated a small hysteresis around the origin. Dc magnetoelectric studies were performed and outputs of 2.52 mV/cm/Oe and 2.49 mV/cm/Oe respectively were obtained for the unixially and isostatically pressed samples.
A Simple Phenomenological Model of the Stress Relaxation in Slowly Evolving 3D Polycrystalline Materials
Authors: Gadomski A.
Published: October 2003

The phenomenon of propagation of a stress field through complex 3d polycrystalline materials along the grain boundaries performing very slow random motion is studied. After applying the Hall–Petch coupling relation it turns out that the relaxation process proceeds in time anomalously. As a consequence, a fractional evolution equation of order one half for the relaxation function is postulated and its solutions are presented. Interpretations of the process in terms of the diffusion on a comb-like structure (antipersistent Random Walk with d w =4 and/or the generalized Gauss–Kolmogorov (in)homogeneous turbulence scenario with the Hurst exponent of H = 1/4 are proposed.
Application of the Recursion Method to the Electronic Structures of Simple-Cubic Na2CsC60 and Body-Centered-Cubic K6C60
Authors: Lu Jing , Zhang Liyuan , Liu Yun
Published: October 2003

Electronic structures of simple cubic (sc) Na2CsC60 and body-centered-cubic (bcc) K6C60 are studied using the tight-binding recursion method. We find that the orientational disorder modifies the electronic states of sc Na2CsC60 significantly. The ground state of K6C60 is found to be insulating with a gap of 0.20 eV. The valence electrons of the alkali-metal atoms in both Na2CsC60 and K6C60 are almost completely transferred to the lowest unoccupied bands of the C 60 molecular solid. The strength of the interaction between the alkali-metal atom and the C 60 molecule is estimated.
Optical Absorption Spectra in Zigzag Fullerene Tubes
Authors: Jiang Jie
Published: October 2003

The optical absorption spectra of zigzag fullerene tubes have been studied by using the extended Su–Schrieffer–Heeger model with the Coulomb interaction included. The numerical results indicate that the carbon number and the Coulomb interaction have great effects on the optical absorption spectra.
Structural and Dynamical Properties of Nanocrystalline Krypton
Authors: Athanasiou N. S.
Published: October 2003

In this paper we discuss structural and dynamical properties of nano-clusters. The study is based on molecular dynamics calculations. In particular, the behavior of the following functions have been studied: single-particle distribution function, velocity autocorrelation function and the generalized phonon density of states (PDOS). The calculations have been done for krypton since for this material a realistic pair potential is available (Barker et al. potential). In order to have more informations about the nano-cluster properties, we also performed molecular dynamics calculations for the bulk. The comparison of the bulk results with the nano-cluster results shows that the shift of the cluster PDOS to low frequencies, caused from the different number of particles.
Formal Requirements and Design Specifications: The Clepsydra Methodology
Authors: Ciaccia P. , Ciancarini P. , Penzo W.
Published: October 2003

The use of formal methods early in the development process has been advocated as a way of improving the quality of software products and their production process. Here we study the influence of a formal requirements document on the next phase in the software process, that is design. We suggest that formal design should coherently follow from formal requirements. We show that two different formal notations can be effectively used, one for writing requirements specification and one for design specification. We also consider how a design specification can be formally checked with respect to requirements specification. The notations we choose are well known: the Z notation for requirements and the Larch two-tiered language for design. We show how a number of tools based on these notations can be used to improve the quality of the documents produced during the development process.
Data Flow Analysis of System Specifications in Lotos
Authors: van der Schoot Hans , Ural Hasan
Published: October 2003

In LOTOS, a system is specified as a behaviour expression describing the externally observable behaviour of the system in terms of possible sequences of interactions between the system and its environment. The desired control flow and data flow that must be established by a possible implementation of the system are specified in the behaviour expression as implicit enumerations of allowed sequences of interaction identifiers and relationships among interaction parameters, respectively. A model exposing the desired flow of data within the allowed control flow expressed in a system specification in LOTOS is presented. Based on the explicit information provided by the model, data flow anomaly detection and data flow oriented test selection are facilitated. A comprehensive example, i.e. an alternating bit protocol specification, is used to illustrate both these validation activities. An error in this specification is revealed by the analysis of a data flow anomaly detected within the specification. A set of test paths is derived from the specification by the application of an existing data flow oriented test selection criterion, called all-uses criterion.
Writing and Analyzing System Specifications by Integrated Linguistic Tools
Authors: Abate A. F. , D'apolito C. , Nota G. , Pacini G.
Published: October 2003

The literature offers several examples of executable specification languages, ranging from mathematically based notation to visual formalisms. In this paper, an analysis environment for executable system specifications based on the language RSF (Requirement Specification Formalism) is presented. The analysis environment also contains two other linguistic tools — RSQ (Requirement Specification Querying), and SEF (Specification Execution Filtering). Using RSQ, classes of execution paths with certain properties can be exercised, so that selected behavioral aspects can be observed. Using SEF, the amount of information and the times at which it is output can be controlled, making the behavior analysis more effective. The paper shows how the notation of RSF, with its few basic concepts, is naturally exploited as a nucleus for the other tools, which are easily integrated to produce the final analysis environment. The combination of RSQ and SEF allows the planning of testing and analysis activities. A working session is shown for a specification describing a telephone switch call handler.
Specifying Active Database Systems in an Object-Oriented Framework
Authors: Campin Jack , Paton Norman , Williams M. Howard
Published: October 2003

This paper presents a framework for the formal specification of active database systems, and shows how the framework can be used to describe the functionality of three well known example systems, namely Starburst, POSTGRES and Ariel. The framework has been developed using Object-Z to structure specifications in a way that emphasises commonalities and key differences between the designs, and that is readily extensible to support new constructs and systems. Such a formal framework can be used to provide formal descriptions of systems that have previously been described only informally, to compare the functionalities of different systems by contrasting support for fundamental concepts, and as a basis for reasoning about rule bases in the context of different active rule systems. The paper also demonstrates the applicability of object-oriented formal methods to the specification of advanced database functionality.
Integration Object-Oriented Software Testing and Metrics
Authors: Chung Chi-Ming , Shih Timothy K. , Wang Chun-Chia , Lee Ming-Chi
Published: October 2003

Software testing methodologies and metrics are key issues to improve and assure software quality. They are important areas in the research of Software Engineering. However, not many focus on the testing criteria and metrics evaluation of a class hierarchy. This paper introduces an important concept named URI (Unit Repeated Inheritance) to realize integrated object-oriented testing and object-oriented metrics. The approach describes an ILT (Inheritance Level Technique) method as a guide to test object-oriented software errors and measure the software complexity of a class hierarchy. The proposed technique shows that inheritance has a close relation to object-oriented software complexity and reveals that overuse of repeated(multiple) inheritance will increase software complexity and be prone to implicit software errors. Also, two test criteria: intra level first and inter level first are presented.
Transforming an HCI Model to a Software Design Model
Authors: Olson Andrew M.
Published: October 2003

The software engineering and human factors communities are seeking ways to integrate their methodologies. This paper outlines an amplified, software engineering methodology that extends beyond requirements gathering to encompass human factors analyses. The methodology employs an object model that is uniform throughout the software project. It involves a procedure that seamlessly transforms a task action grammar model, from HCI theory, directly into a specification model based on user/machine dialog and, thence, into a software design model. The model's object-oriented structure makes it feasible to trace the effects of the user's needs throughout the amplified project life cycle to the final code. A case study documents evidence concerning how effectively the procedure supports the software engineering process. An examination of the extent of metamorphosis the model undergoes in the case study indicates that the transition through the amplified life history is well controlled; in particular, the transition from the software specification to the design model is more controlled than that under traditional methodologies.
A New Framework for Improving Software Development Process on Small Computer Systems
Authors: Sakai Makoto , Matsumoto Ken-Ichi , Torii Koji
Published: October 2003

While small computer systems have provided us with a wide array of development and operational environments, implementation methods, and domains of the software to be developed, it has also made the software development more risky.

This paper proposes a new framework for improving the software development process on small computer systems to reduce software development risks. The key idea of the proposed framework is that the solutions to the software development problems can be extracted by the project manager, with relatively low overload, from the development processes that were actually executed in order to reduce the development risks, and then be formalized and stored in a database. The formalized solutions can be used not only for process improvement, but also for devising new solutions if new problems should occur in the future. We believe that the proposed framework is capable of making up for the difficulties in implementing CMM on small computer systems, and it encourages us to apply CMM to such risky software development.
Enriching Software Process Support by Knowledge-Based Techniques
Authors: Dellen Barbara , Maurer Frank , Münch Jürgen , Verlage Martin
Published: October 2003

Representations of activities dealing with the development or maintenance of software are called software process models. Process models allow for communication, reasoning, guidance, improvement, and automation. Two approaches for modeling processes and instantiating and managing the process models, namely CoMo-Kit and MVP-E, are combined to build a more powerful one. CoMo-Kit is based on AI/KE technology; it is a support tool system for general complex design processes, and was not been developed specifically with software development processes in mind. MVP-E is a process-sensitive software engineering environment for modeling and analyzing software development processes, and guides software developers. Additionally, it provides services to establish and run measurement programmes in software organizations. Because both approaches were developed independently from one another, major integration efforts had to be made to combine both their advantages. This article concentrates on the resulting language concepts, and their operationalization necessary for building automated process support.
Method of Cumulative Sums and Problems of Optimal Control by Technological Processes
Authors: Mazalov Vladimir V.
Published: October 2003

We consider the problem of optimal control by some technological process using the model of "disorder". The most important parameters of the cumulative sum method (mean delay, false alarm) may be determined by computing. Some explicit expressions of the mean delay and false alarm for the cumulative sum method in the exponential case are given.
Knowledge Aspects of Resource Allocation Problems with Saturation
Authors: Cherenkov A. P.
Published: October 2003

In this paper we consider some knowledge aspects which arise when investigating problems of optimal resource allocation with saturation. Among them we mention information state before resource allocation, utilization of lexicographical variables, space transformations, some principles used for finding solutions, finding quality form of solution on the basis of the necessary conditions of optimality, inner and outer parametrization, essential reduction of dimension of solved problems, reasons of solution non-uniqueness, utilization of continual problems for solution of analogous discrete problems.

We shall try to show the mutual interplay between software engineering and knowledge engineering. Examples of problems solved with attraction of methods discussed in this paper exist in papers [1–10] and others.
The Stabilization Problem for Certain Class of Ecological Systems
Authors: Kirillov A. N.
Published: October 2003

The stabilization problem for dynamical systems is to find control providing stability of some sets in phase space. This problem is not solved in general for nonlinear systems. The ecological systems are nonlinear, as usual, with restrictions on phase coordinates and controls.

In this paper we consider piecewise constant control stabilization. Some general results are obtained. A new class of population dynamical systems is introduced, for which the constructive method of global stabilization and controllability is given. The set of attraction is found.
An Experience with the Use of Systems Engineer Case Tool
Authors: Bieliková Mária , Návrat Pavol
Published: October 2003

Systems Engineer is a client/server CASE tool for supporting software system development on PC machines under Windows. It compares fairly satisfactorily with other similar tools of the same category. Systems Engineer offers various supporting techniques which address the full software life cycle, from planning and design to code generation, reengineering and maintenance. It supports system engineers working in a team.
Knowledge-Assisted Retrieval of Spatiotemporal Content in Multimedia Databases
Authors: Yoshitaka Atsuo , Hirakawa Masahito , Ichikawa Tadao
Published: October 2003

Retrieval is one of the challenging issues in multimedia database studies. Components of multimedia data such as image, video, and audio convey various meaning depending on the standpoint in viewing the data. Deriving the meaning of data, therefore, is not an easy task. At the same time, components of multimedia data inherently possess spatial and/or temporal relationships among them. These two aspects of multimedia data make data retrieval difficult without the support of specific knowledge for the proper interpretation of data and queries.

In this paper, we provide an overview of existing approaches related to the issue of implementing content-based retrieval of multimedia databases and then describe a framework for enabling knowledge-assisted retrieval of audio visual content and their spatio-temporal relationship based on user cognition.
A Survey of Access Methods for Image Data
Authors: Chan Chee-Yong , Pau Louis F.
Published: October 2003

The feasibility of storing large amount of digital images and the pictorial-oriented nature of many applications have attracted much interest in pictorial information systems. An important issue in such systems is the efficient retrieval of image based on its contents. Supporting content-based retrieval of image data is a difficult problem and embraces different technologies including image processing, user interface design, and database management. To provide efficient content-based retrieval, efficient access methods based on image features are required. This paper presents a survey of indexing techniques that support content-based retrieval of images. In particular, we examine access methods for three types of image features, namely, object shape, semantic objects, and spatial relationships among semantic objects. For each image feature, we look at how various approaches represent and organize the image features and how they support similarity retrieval.