bluuebunny/crossref_metadata_2025 huggingface dataset:
ON CONNECTION BETWEEN TOPOLOGICAL LANDAU-GINZBURG GRAVITY AND INTEGRABLE SYSTEMS
Authors: LOSEV A. , POLYUBIN I.
Published: November 2004

We study flows on the space of topological Landau-Ginzburg theories coupled to topological gravity. We argue that flows corresponding to gravitational descendants change the target space from a complex plane to a punctured complex plane and lead to the motion of punctures. It is shown that the evolution of the topological theory due to these flows is given by the dispersionless limit of KP hierarchy. We argue that the generating function of correlators in such theories is equal to the logarithm of the tau function of the generalized Kontsevich model.
EFFECTIVE POTENTIAL FOR A NONRELATIVISTIC NON-ABELIAN CHERN-SIMONS MATTER SYSTEM IN CONSTANT BACKGROUND FIELDS
Authors: CAENEPEEL DIDIER , LEBLANC MARTIN
Published: November 2004

We present the effective potential for nonrelativistic matter coupled to non-Abelian Chern-Simons gauge fields. We perform the calculation using a functional method in constant background fields to satisfy Gauss’s law and to simplify the computation. Both the quantum gauge and matter fields are integrated over. The gauge-fixing is achieved with an Rξ gauge in the ξ→0 limit. Divergences appearing in the matter sector are regulated via operator regularization. We find no correction to the Chern-Simons coupling constant and the system experiences conformal symmetry breaking to one-loop order except at the known value of self-duality. These results agree with previous analysis of the non-Abelian Aharonov-Bohm scattering.
BOSONIC REALIZATION OF BOUNDARY OPERATORS IN SU(2)-INVARIANT THIRRING MODEL
Authors: CHAO LIU , WANG YANSHEN , YANG WENLI , HOU BOYU , SHI KANGJIE
Published: November 2004

Boundary operators and boundary states in the SU(2)-invariant Thirring model are considered from the point of view of bosonization and oscillator realizations of bulk and boundary Zamolodchikov-Faddeev algebras.
RADIATIVE SYMMETRY BREAKING IN A SUPERSYMMETRIC MODEL WITH AN EXTRA U(1)
Authors: SUEMATSU DAIJIRO , YAMAGISHI YOSHIO
Published: November 2004

Radiative symmetry breaking is studied in a superstring-inspired supersymmetric model which is extended with a low energy extra U(1) symmetry. In this model the μ problem is radiatively solved in an automatic way. The right-handed neutrino can be heavy and the seesaw mechanism will produce the small neutrino mass which makes the MSW solution applicable to the solar neutrino problem. We search a parameter region which has the favorable feature for the radiative symmetry breaking at the weak scale. A rather wide parameter region is found to be allowed. Although there are certain dependences on the soft supersymmetry breaking parameters in the estimation of masses of various fields, the upper bound of the extra Z boson mass is estimated to be mZ2≤2000 GeV for a top mass range 150 GeV ≤mt≤190 GeV within a suitable parameter region (m0<1 TeV and m1/2<200 GeV ). Some phenomenological features of the extra Z boson are also presented.
GALILEAN AND DISCRETE SPACE-TIME SYMMETRIES OF ROY-SINGH DETERMINISTIC QUANTUM MECHANICS
Authors: KUMAR ARVIND
Published: November 2004

The recent deterministic quantum theory of Roy and Singh is shown to be covariant with respect to Galilean, space reflection and time reversal transformations.
A CLOSER LOOK AT PERTURBATIVE CORRECTIONS IN THE b→c SEMILEPTONIC TRANSITIONS
Authors: SHIFMAN M. , URALTSEV N.G.
Published: November 2004

We comment on two recent calculations of the second order perturbative corrections in the heavy flavor semileptonic transitions within the Brodsky-Lepage-Mackenzie approach. It is pointed out that the results do not show significant enhancement either in the inclusive b→c decays or in the exclusive amplitudes at zero recoil provided that the expansion parameter is chosen in a way appropriate to the kinematics at hand. The values of the second order coefficients inferred from the BLM type calculations appear to be of order unity in both cases. Thus, in both cases no significant uncertainty in extracting Vcb can be attributed to perturbative effects. The theoretical accuracy is mostly determined by the existing uncertainty in [Formula: see text] nonperturbative corrections in the exclusive B→D* amplitude, and, to a lesser extent, by the uncertainty in the estimated value of the kinetic energy matrix element [Formula: see text] in the case of Γ sl (b→c). The theoretical accuracy of the inclusive method of determining Vcb seemingly competes with and even exceeds the experimental accuracy.
STABILISATION OF PARAELECTRIC PHASE BY STRONG CUBIC AND QUARTIC PHONON ANHARMONICITIES IN KDP CRYSTAL
Authors: UPADHYAY T.C. , PANWAR N.S. , SEMWAL B S.
Published: November 2004

Considering cubic and quartic phonon anharmonic interactions into the pseudospinphonon coupled mode model of Kobayashi6 expressions for shift, width, soft mode frequency and hence Curie temperature, dielectric susceptibility, Curie-Weiss constant and dielectric (tangent) loss have been evaluated for ferroelectric KDP. The method of retarded double-time thermal Green’s function and the treatment of Dyson’s equation have been used in the development. It is shown that cubic and quartic phonon anharmonic interactions render real value to the soft mode frequency in the para-phase. Results are in agreement with the experimental results of others.
MAXIMUM ENTROPY MODELS OF TRANSPORT IN MESOSCOPIC WIRES
Authors: SLEVIN KEITH , NAGAO TARO
Published: November 2004

We review the maximum entropy models for the probability distribution of the transfer matrix of a disordered mesoscopic wire. We relate this distribution to the zero temperature conductance of the wire using the Landauer formula and discuss the extent to which the maximum entropy models describe accurately the weak localisation effect and universal conductance fluctuations which occur in the diffusive regime. A detailed comparison between numerical simulations and the maximum entropy models is also presented. For “long” wires there is a crossover from diffusive to localised behaviour and we review the predictions of the maximum entropy models in this regime, chiefly the symmetry dependence of the localisation length and the log-normal distribution of the conductance. In conclusion we discuss the limitations of the maximum entropy models and in particular the property of isotropy.
PARACONDUCTIVITY AND HALL EFFECT MEASUREMENTS IN THE SUPERCONDUCTING (BiPb)2(SrBa)2Ca2(Cu1−xCrx)3Oy
Authors: POP A.V. , ILONCA GH. , CIURCHEA D. , POP V. , KONOPKO L.A. , GERU I.I. , TODICĂ M. , IONCU V.
Published: November 2004

The effect of the Cu substitution by Cr in the “2223” superconductor was studied by resistivity and Hall effect measurements. The excess conductivity was analyzed by using the linear and Zou-Anderson extrapolation methods on the electrical resistivity. A crossover temperature is observed only for the x=0 sample. The sheet hole concentration per Cu-site, nHVcell is found to vary linearly with the temperature for all Cr doped samples in the 170–265 K temperature range. Deviations from linearity in the T2 dependence of the inverse Hall mobility above 250 K were evidenced.
2D ELECTRON IN AN EXTERNAL MAGNETIC FIELD IN THE PRESENCE OF DISSIPATION
Authors: CRISTOFANO G. , GIULIANO D. , MAIELLA G. , VALENTE L.
Published: November 2004

A coherent state approach is presented to analyze the behavior of a 2D electron subject to an external magnetic field, normal to the plane, in the presence of dissipation. The phenomenon of the shrinking of the Gaussian (localization), describing the electron ground state, takes place on large time scales. Its relation with the transport properties of such a system is then analyzed.
BACKWARD CAUSALITY AND THE APPARENT TIME IRREVERSIBILITY OF MEASUREMENT: A POSSIBLE RESOLUTION
Authors: CASTAGNOLI GIUSEPPE
Published: November 2004

The notion of the coexistence in the quantum framework of causality forward or backward in time is proposed as a possible way for solving the problem of measurement.
COMPUTER SIMULATION STUDY OF A TWO-DIMENSIONAL NEMATOGENIC LATTICE MODEL WITH LONG-RANGE INTERACTIONS ISOTROPIC IN SPIN SPACE
Authors: ANGELESCU N. , ROMANO S. , ZAGREBNOV V.A.
Published: November 2004

We have considered a classical spin system, consisting of n-component unit vectors (n = 2, 3) {uk, k∈Zd}, associated with a d-dimensional lattice Zd, d=1, 2, and interacting via pair potentials, isotropic in spin space, and of the long-range form [Formula: see text] Here ∊ is a positive constant setting energy and temperature scales (i.e. T*=kBT/∈), and xk denotes dimensionless lattice-site coordinates. Extending previous rigorous results, one can prove the existence of an ordering transition at finite temperature when 0<σ< d, and its absence when σ≥d. We have studied the case defined by n=3, d=2, σ=1, by means of computer simulation, Molecular Field and Two-Site Cluster theory. The Two-Site Cluster approach was found to bring about a recognizable improvement over Molecular Field; on the other hand, comparison with the Lebwohl-Lasher lattice model shows that the long-range character of the interaction tends to increase the transition temperature towards its Molecular Field limit.
CHAOS AND REGULARITY IN ADAPTIVE LATTICE DYNAMICS
Authors: SINHA SUDESHNA
Published: November 2004

We describe the rich spectrum of spatio-temporal phenomena emerging from a class of models incorporating adaptive dynamics on a lattice of nonlinear (typically chaotic) elements. The investigation is based on extensive numerical simulations which reveal many novel dynamical patterns, including scaling properties (as exemplified, for instance, by distinct 1/f spectral characteristics) emerging from processes operating over a range of time and length scales. Moreover, we study the simpler case of unidirectional adaptive dynamics rigorously, and this provides an analytical understanding of the dynamical reasons underlying the many phases found in these models.
GROUND STATE ENERGY ESTIMATION OF JELLIUM SYSTEMS BY SPATIAL GRIDDING
Authors: MOINI SHOHREH , PURI ASHOK , HABIBOLLAHZADEH DARIUSH , DAS PURNA C.
Published: November 2004

A numerical approach to estimate the ground state energy of jellium systems is explored. In this approach, the space occupied by the system is gridded, with individual grid elements small enough that the electron density within an element is considered constant. The energy of an element is then a function (and not functional) of its electron density in a given environment and the total energy of the system is obtained by summing the contributions from all the elements. A self-consistent field procedure to optimize the grid densities is then carried out resulting in the ground state energy of the system. The method is tested for known atomic and jellium models to show its validity. This approach shows enough flexibility to handle the irregular jellium shapes.
CLUSTER CALCULATION OF THE ELECTRONIC STRUCTURE OF K3C60
Authors: COUTINHO KALINE , CANUTO SYLVIO , FAZZIO A. , MOTA R.
Published: November 2004

A cluster with 188 atoms is utilized to investigate the electronic structure of K 3 C 60 within the molecular orbital model. The calculated density of states is in excellent agreement with experimental results of photoemission and inverse photoemission. The band gap is calculated using three different schemes and the results indicate a metallic system. The optical absorption spectrum is calculated from a CI procedure and indicates transitions below 15000 cm –1 not present in pristine C 60.
A UNIFIED RENORMALIZATION GROUP STUDY OF THE 1D ISING MODEL WITH TRANSVERSE FIELD
Authors: PAN C. Y. , LIN H.Q.
Published: November 2004

By applying a unified real space renormalization group (URG) mapping method, we study the one-dimensional spin-1/2 Ising model with a transverse field (ITF). Unlike the other real space renormalization group methods, the URG method describes the properties of the model at both zero and finite temperatures in a unified way. The results obtained are in good agreement with that obtained by other methods. Application of the URG method to other quantum spin systems is discussed.
NOVEL BINARY SPIN GLASS ALLOYS SYNTHESIZED BY MECHANICAL MILLING
Authors: ZHOU G. F. , BAKKER H.
Published: November 2004

A few novel binary spin glass alloys have been successfully synthesized by mechanical milling of ordered intermetallic compounds in a high energy ball mill. These alloys are amorphous Co 2 Ge , atomically disordered crystalline GdAl 2, and ball-milled crystalline and amorphous CoZr. The characteristic features of spin glasses are observed; these are (a) the sharp cusps at the freezing temperature T f in both ac and dc magnetic susceptibility versus temperature curves and their peculiar sensitivity to the external magnetic field; (b) the irreversibility, i.e. the difference in value and shape between the magnetisation versus temperature curves after zero field cooling (ZFC) and field cooling (FC) at temperatures below T f and (c) the displacement of the FC magnetisation curve relative to ZFC curve and the corresponding remanence in the FC curve at low temperatures. The freezing temperatures are 41, 65, 35, and 11 K, respectively, which are defined by the sharp cusps in the lowest field ac susceptibility versus temperature curves. The freezing temperatures are lowered with increasing external field. The common feature of these materials is that all are binary alloys with a rather high concentration of the magnetic component. The discovery of these novel spin glasses is of significance because they not only represent new classes of spin glass materials but also demonstrate the use of mechanical milling as a novel technique to synthesize various new materials such as spin glasses. The results are reviewed briefly.
TEMPERATURE DEPENDENCE OF SURFACE TENSION OF LIQUID CRYSTALS AT THE PHASE TRANSITION
Authors: MOLDOVAN R. , TINTARU M. , BEICA T. , FRUNZA S. , STOENESCU D. N.
Published: November 2004

The surface tension is calculated as the excess of the free energy per unit area, due to the presence of a surface layer, using Landau–de Gennes expansions, in the hypothesis of a first order transition in the bulk and taking into account the dependence of the surface free energy from the surface tilt angle. The surface order parameter is calculated and surface-ordered phase above the phase transition temperature has been found. A variety of calculated surface tension versus temperature curves with a jump at the phase transition, with positive or negative slope, well describing the experimental data from literature, have been attained.
LOW TEMPERATURE CREEP AND STRESS RELAXATION FOR PEIERLS BARRIER IN CUBIC METALS
Authors: MAJEED S. A. , FAROOQUI N. , AHMED M. A. , RAZA S. M.
Published: November 2004

The relation for low temperature creep and stress relaxation is developed for Peierls barrier in cubic metals using single barrier stochastic model, with special reference to face-centered cubic crystals. Our conjecture that the strain enhancement is responsible for an increase in activation volume is verified through nondimensionality, i.e. by shear traction number.
EXTRACTION OF PERIODIC ORBITS FROM A CHAOTIC ATTRACTOR
Authors: LIU YUDONG , BARBOSA LUIZ C.
Published: November 2004

Control of chaos present in the Lorenz system was realized numerically by using an unstable periodic oscillation produced from an identical system as a perturbation or driving signal to one of the control parameters. Two identical Lorenz systems were used as the signal system and the target system. Several unstable periodic signals from the signal system were used to control the chaotic attractor of the target system. As a result of the control of chaos, many periodic orbits were probed and extracted out from the chaotic attractor.
SOME PECULIAR FEATURES OF THE NEWEST LAYERED HIGH Tc SUPERCONDUCTORS
Authors: KRUCHININ S. P.
Published: November 2004

Some features of the high T c superconductors are analysed on the basis of the bisoliton theory. They are the dependence of the transition temperature T c on the number of layers N and the anomalous current–voltage characteristics SIN contacts. By means of the exciton theory a few normal optical properties of the high T c materials are used as well. This is a small part of the many interesting properties of high T c superconductors.
A MODEL FOR ESTIMATION OF ELECTROMECHANICAL CHARACTERISTICS OF PIEZOELECTRIC POLYMER COMPOSITE DISCS
Authors: PRASAD G. , KUMAR G. S. , BHIMASANKARAM T. , SURYANARAYANA S. V.
Published: November 2004

The constitutive equations of piezoelectric polymer composite materials used for their electromechanical characterisation are complicated and their analytical solution is difficult. Earlier models assumed either stress or strain components to be constant. In this paper we present a model for electromechanical characterisation of piezoceramic polymer composites. The assumptions are (i) the samples have complete stress free boundary conditions at the polymer piezoelectric interfaces, (ii) the materials are lossless, (iii) the coordinate axes are pure mode propagation directions, and (iv) the electric potential and the displacements are assumed to be independent degrees of freedom. Based on these assumptions, expressions for impedance, phase velocities, and electromechanical coupling constant are developed for piezoelectric polymer composites of cylindrical geometry.
ELASTIC BEHAVIOR OF Y-1-2-3/SILVER COMPOSITES
Authors: SHEKHAR S. , REDDY R. RAVINDER , REDDY P. VENUGOPAL , MULAY V. N.
Published: November 2004

A series of Y-1-2-3/Ag high T c superconducting composites have been prepared using the sol–gel method by sintering at three different sintering temperatures, viz. 910°C, 945°C, and 975°C. After the usual characterization by XRD, electrical resistance, bulk density, and porosity measurements, the longitudinal (V1) and shear wave (V s ) velocities were measured by the pulse transmission technique. Using the experimental data, several elasticity parameters such as Young's modulus (E), rigidity modulus (G), etc. were evaluated. The variation of elastic constants with dopant concentration has been explained in terms of the binding forces between various atoms of the superconductor. A linear relationship between the superconducting transition temperature (T c ) and the Debye temperature (θ D ) has also been obtained.
C–T MEASUREMENTS ON LINEARLY GRADED GE DIODES
Authors: ASGHAR MUHAMMAD , AFZAL M. , ZAFAR N.
Published: November 2004

This study is aimed to investigate the capacitance–temperature (C–T) measurements of linearly graded junction diodes of germanium. We have established a definite relationship between the capacitance and temperature over a range (77 K to 400 K) of temperature. These C–T measurements were carried out at different reverse biases applied to the device to see the biasing effects on the C–T variations.
QUANTUM HALL EFFECT OF HARD CORE BOSONS
Authors: JAIN J. K. , RAO SUMATHI
Published: November 2004

Motivated by a mean field approach, which has been employed for anyon superfluidity and the fractional quantum Hall effect, the quantum Hall effect (QHE) of hard core bosons is investigated. It is shown that QHE is possible only in the thermodynamic limit. The filling factors where QHE may be expected are obtained with the help of two adiabatic schemes.
GROUP THEORY OF THE NUMBER-PHASE QUANTIZATION
Authors: BARONE V. , PENNA V.
Published: November 2004

A formalism for the number-phase quantization, based on the doubting of the degrees of freedom, is studied from a group-theoretical viewpoint. The so-called relative number states are shown to be a standard basis of unitary irreducible representations of both SU(2) and SU(1, 1). The algebraic meaning of the relevant operators is elucidated and their eigenstates are constructed. As an example, the dynamics of the quantum-damped harmonic oscillator is worked out.
A NUMERICAL METHOD FOR EVALUATING FEYNMAN PATH INTEGRALS
Authors: CRESWICK RICHARD J.
Published: November 2004

A method for numerically evaluating Feynman path integrals based on the density of actions is presented. The method is illustrated by calculating the propagator for the free particle and the simple harmonic oscillator.
EFFECT OF SINGLE PARTICLE HOPPING AND OUT OF PLANE MAGNETIC IMPURITY ON COUPLED PLANAR SUPERCONDUCTORS
Authors: SARDAR MANAS , SA DEBANAND
Published: November 2004

It is shown that the single particle band motion along the c axis is harmful for superconductivity in anisotropic systems. Variation of T c with c axis hopping parameter is shown for both the conventional Josephson coupled, planar superconductors and for interlayer pair tunneling mechanism of Wheatley, Hsu, and Anderson (WHA). Effect of out-of-plane magnetic impurity substitution is shown to suppress T c more for conventional superconductors whereas there is a very sharp decrease of T c in the WHA mechanism at larger concentrations.
ENHANCEMENT OF Tc IN Y2Ba4Cu7O14+y BY Ca DOPING
Authors: JEYABALAN K. , RAVIKUMAR S. , ASOKAMANI R. , NATARAJAN S.
Published: November 2004

The effect of Ca 2+ substitution for Y 3+ in Y 2 Ba 4 Cu 7 O 14+y on the superconducting properties and the high pressure electrical resistivity behavior of the system at ambient temperature were studied. The samples were obtained for x = 0.1, 0.2 and 0.5. The susceptibility measurements showed a maximum T c for the concentration x = 0.1. The high pressure studies performed on the system revealed the metallic behavior up to 80 kbar.
SYNCHRONIZATION IN RANDOMLY DRIVEN SYSTEMS
Authors: JAYANNAVAR A.M.
Published: November 2004

We have solved analytically a simple model of evolution of particles driven by identical noise. We show that the trajectories of all particles collapse into a single trajectory at long time. This synchronization also leads to violation of the law of large numbers.
A MONTE CARLO SIMULATION OF CONFINED MAGNETIC SYSTEMS WITH RADIAL BOUNDARY CONDITIONS
Authors: CHICCOLI CESARE , PASINI PAOLO , SEMERIA FRANCO , ZANNONI CLAUDIO
Published: November 2004

We present a computer simulation of a confined magnetic system. We study a Heisenberg model microsphere with radial boundary conditions, the influence of the homeo-tropic surface alignment on the magnetic ordering inside the sphere and the consequent changes induced in the thermodynamic behavior. Comparisons with the case of nematic liquid crystal droplets are provided.
LEARNING INTERFERENCE REDUCTION IN NEURAL NETWORKS
Authors: ZANIN DIEGO , ZECCHINA RICCARDO
Published: November 2004

The learning and generalization properties of a modified learning cost function for Neural Networks models are discussed. We show that the introduction of a “cross-talk” term allows for an improvement of performance based on the control of the convergence subspaces of the network outputs. In the case of an unbiased distribution of binary patterns, we derive analytically the learning performance of the single layer architecture whereas we investigate numerically the generalization capabilities. An enhancement of computational performance is observed for multi-classification purposes, and also for imperfectly classified training sets.
SUPERCONDUCTING GAP NODAL SURFACE AND FERMI SURFACE: THEIR PARTIAL OVERLAP IN CUPRATES
Authors: BASKARAN G. , BASU RAHUL , ARJUNWADKAR MIHIR , KANHERE D.G.
Published: November 2004

Electron correlation in cuprates leads to a global constraint Σk Δk=0 on the gap function Δk, resulting in a gap nodal surface. We give numerical results and qualitative physical arguments supported by some experimental results to argue that correlations also lead to a local constraint on charge fluctuations in k-space close to the Fermi surface, which may result in a substantial overlap of the Fermi surface with the gap nodal surface.
HIGH PRESSURE STUDY ON SOME HIGH-Tc SUPERCONDUCTORS
Authors: HUANG C. Y. , LIN J. G. , HUANG Z. J.
Published: November 2004

We present a brief review on the pressure effects of some high temperature super-conductors. The examined systems include RBa 2 Cu 3 O 7, (R, Pr)Ba 2 Cu 3 O 7 and (ZnPc) y Bi 2 Sr 2 Ca 2 Cu 3 O 10, with R=rare earth elements and Pc=phthalocyanine. The results of the presssure effects on the superconducting transition temperature T c in these materials have, thus, not only revealed the origin of the T c -variation induced by the chemical substitution or intercalation, but have also confirmed the important roles played by the carrier concentration and T co (maximum T c ) on determining T c . Based on our experimental results, along with good agreement between our data and theory, we have clearly demonstrated that the variation of T c dominantly originates from the strains induced by the variation of the ionic radii or the intercalation of foreign molecules.
NONRELATIVISTIC LAMB-SHIFT CALCULATIONS FOR S-STATES OF HYDROGENIC ATOMS
Authors: SEKE J.
Published: November 2004

It is shown, for the first time to our knowledge, that the Lamb shift for S-states of hydrogenic atoms can be almost completely calculated by applying the methods of nonrelativistic quantum electrodynamics and without using the Dirac equation and the second quantization for the electron. By taking into account the spin-radiation-field interaction the Lamb shift to order of α5 is calculated for different S-states.
TOPOLOGY OF THE HALL FLUID AND BERRY PHASE
Authors: BANERJEE DIPTI , BASU BANASRI
Published: November 2004

We have shown here that when the spin of the quantized Hall particle is taken into account we have to consider the internal topology of the particle, and as a result an additional quantum number comes into the picture. This will lead to a change in the Berry phase of the Hall particle.
ELECTRICAL RESISTIVITY OF COBALT-BORON LQA ALLOYS
Authors: NAQVI S. M. M. R. , RIZVI S. DABIR H. , JAMILA SAJIDA , RIZVI SHABANA , RAZA S. MOHSIN , GORMANI MUSHTAQ AHMED , FAROOQI N.
Published: November 2004

Activation energies determined from Arrhenius plot for cobalt-boron liquid quenched amorphous alloys in the temperature range 40 K < T < 300 K , suggest vacancy and interstitial formation to nucleate crystalline phases in an amorphous matrix preferably at sites where dangling bonds are present. Nucleation of crystallites with preferential tetragonal or orthorhombic structures is a self-evolving process due to catalytic presence of dangling bonds in an amorphous material and that the occurrence of negative activation energies support this evidence.
PHASE FLUCTUATION OF Pr AND Ca DOPED YBa2Cu3O7−δ COMPOUNDS IN A MICROSCOPIC AREA
Authors: POON T. C. , GAO J.
Published: November 2004

Experimental investigations have been made on the compound Y 1−x Pr x Ba 2 Cu 3 O 7−δ with increasing praseodymium concentration x. 'Internal temperature gradient' in a muffle furnace would suffice to induce a small-scale melt texture growth to proceed, resulting in a single crystal block with (relatively) regular shape. The ingredients of the materials in the such crystal block, though randomly oriented and sometimes irregular in shape, can be investigated in a systematic way by using techniques such as energy dispersive X-ray analysis. The phase amounts along the crystal layers have been correlated with atomic percentages based on simple, plausible assumptions. This provides us sensible and useful clues to understand the compositions of various samples. Besides, the physical nature of this material has been studied and discussed. Various theoretical models, including the magnetic pair-breaking mechanism and the hole-filling mechanism, were compared with the obtained results.
SURFACE STATES IN THIN VERSUS THICK ORGANIC QUANTUM WELLS
Authors: AN NGUYEN BA , HANAMURA EIICHI
Published: November 2004

Surface states are studied in dependence on thickness of organic quantum wells within the nearest layer approximation. It is shown that there is a material-dependent critical thickness. Structures that have thickness thinner or thicker than the critical one, exhibit qualitatively different characteristics of surface states. Criteria for existence and sign rules for location of energy levels of surface states are established which are general and contain the results of the previous works as particular cases.
THE NEW MEAN FIELD RENORMALIZATION GROUP FROM EFFECTIVE FIELD THEORY
Authors: COELHO F. O. , PLASCAK J. A.
Published: November 2004

The new mean field renormalization group is used to study the Ising model through the calculation of the order parameter by means of the effective field theory based on Callen–Suzuki identity. By considering one- and two-spin clusters, better results are obtained when compared to the previous treatment using the usual mean field approximation.
AN ELASTIC CONTINUUM MODEL FOR FULLERENE ENERGETICS
Authors: XIAOYU XIA , JI-XING LIU , ZHONG-CAN OU-YANG
Published: November 2004

By analogy with the elastic theory of solid shells1 and fluid membranes,2 it has been suggested that fullerenes, at least large ones, might somehow resemble the classic elastic continuum, as indicated by Schnur.3 Some related works dealt with nanotubes do show positive evidence for this suggestion.4 Here we propose an elastic continuum model appropriate to graphite-like networks. Applying it to various shapes of fullerenes, such as spheres, tubes, tori, and minimal surfaces, we found good agreement between this model and previous numerical results given by approaches of ab initio or empirical potential. Furthermore, this model enables one to understand the puzzling phenomena such as why Schwarzite P216 and Schwarzite D216 have nearly identical bending energies while their geometric forms are very different (see Fig. 1). The prospect of this model is also discussed.
WAVEFUNCTION RENORMALIZATION OF ONE HOLE IN A STRONGLY CORRELATED SYSTEM
Authors: PANAT P.V. , DEY B. , KANHERE D.G. , AMRITKAR R.E.
Published: November 2004

The wavefunction renormalization factor Zk of a hole injected in a half-filled band in a strongly correlated system in two dimensions is evaluated analytically using the extended quasiparticle operator introduced by Dagotto and Schrieffer. A model Hamiltonian for such an extended hole is proposed. We analytically calculate Zk for different parameter values and observe that the Zk value increases as compared with what it would be if a bare hole operator is used. This is in conformity with the numerical observation of Dagotto and Schrieffer.
HOLE QUASIPARTICLE DYNAMICS IN THE DOPED 2D QUANTUM ANTIFERROMAGNET
Authors: KUZEMSKY A.L. , MARVAKOV D.
Published: November 2004

The spectrum of hole quasiparticles and the role of magnetic correlations are investigated in the self-consistent Irreducible Green Functions formalism motivated from Strongly Correlated Electron systems in the framework of spin-fermion model. It was clearly pointed out on the self-energy level, beyond Hartree-Fock approximation, how the one-and two-magnon processes define the true nature of carriers in HTSC.
NON-FERMI LIQUID BEHAVIOR OF A SYSTEM WITH SADDLE POINTS IN THE ENERGY
Authors: CRISAN M. , MOCA C.P.
Published: November 2004

We present a simple demonstration that the two-dimensional fermionic system with the energy ε(k)=kxky has a non-Fermi behavior. The calculation of the wave function renormalization constant Z will be performed using the “poor man’s renormalization” method and we will show that Z→0 with the infrared cutoff Λ as Z(Λ)=Λζ where ζ is a constant.
CENTRAL PEAK ANOMALIES IN MACROSCOPIC AND IN SCATTERING EXPERIMENTS DUE TO ENTROPY FLUCTUATIONS
Authors: SCHRANZ W. , HAVLIK D. , FALLY M.
Published: November 2004

The study of dynamical properties of crystals near structural phase transitions is still of great importance. Especially the interest on ultralow-frequency dynamics, i.e. the so called “Central-Peak question” was renewed nowadays through some recent work on the observation of Entropy Fluctuations in macroscopic susceptibilities. This so called Heat-Diffusion Central Peak was previously found in scattering experiments, and the corresponding theory was originally formulated for scattering experiments.

In this work we present an overview on previous light scattering measurements of Entropy Fluctuations and very recent results concerning the observation of a Heat-Diffusion Central Peak in macroscopic properties at ultralow frequencies, which provide a new insight into the “old” Central Peak problem. The crossover functions from isothermal to adiabatic behaviour are calculated for the macroscopic susceptibilities.
COHERENT STATES OF QUANTUM NONLINEAR SYSTEMS
Authors: HABA Z.
Published: November 2004

Quantum dynamics of integrable systems is discussed. Localized wave packets generalizing the conventional coherent states of minimal uncertainty are constructed. The wave packet moves along a certain trajectory and does not change its shape for times of order [Formula: see text].
THE RECURRENT EQUATIONS AND THEIR SOLUTIONS FOR KINETIC COEFFICIENTS OF DISORDERED SYSTEMS
Authors: SKAL ASYA S.
Published: November 2004

All equations of kinetic coefficients in physics give only the first order response to the external forces and fields. However the perturbation theory provides the possibility, to obtain a new recurrence equations with recurrent solutions for all orders of responses of the Hall and Seebeck coefficients and the Poisson ratio for the conductivity in a magnetic field, for the thermopower and the elasticity of disordered systems.

Zero order solution of Lame equilibrium equation expresses the Poisson ratio as νe~(p−pc)k, k=0.3, whereas the first order solution gives mean values of effective lateral displacements or forces when lateral boundaries are fixed.
A COMPUTATIONAL MODEL FOR MARTENSITIC THIN FILMS WITH COMPOSITIONAL FLUCTUATION
Authors: BĚLÍK PAVEL , LUSKIN MITCHELL
Published: November 2004

We develop a computational model for the martensitic first-order structural phase transformation in a single crystal thin film, and we use this model to study the effect of spatial compositional fluctuation, spatial temporal noise, and the loss of stability of the metastable phase at temperatures sufficiently far from the transformation temperature.
PROBLEMS OF GLOBAL NETWORKS OF GRAVITATIONAL DETECTORS
Authors: KUCHIK E.K. , RUDENKO V.N.
Published: November 2004

We describe the network of gravitational wave detectors which now exist in the world: Stanford-Louisiana-Pert-Geneva-Moscow. A computer simulation of a gravitational wave detection is performed. Proposals for the creation of a global observational gravitational wave service are made.
PRELIMINARY TEST OF NEW ALGORITHM FOR SEARCHING GRAVITATIONAL-WAVE PERTURBATION IN EARTH CRUST NOISES
Authors: KRAVCHUK V.K. , GUSEV A.V. , RUDENKO V.N.
Published: November 2004

A new algorithm for optimal filtration of gravitational wave signals in Earth crust noises is described. Digital synchronous data recorded from two pairs of European seismic stations—Moxa (Germany)-Membach (Belgium) and Obninsk (Russia)-Moskva (Russia)—are used. New upper limit of gravitational wave background for a seismic detection of GW bursts in low-frequency range ν=(0.01–0.1) Hz is obtained.
THE PAPAPETROU EQUATIONS AND MOTION OF A TEST BODY IN GRAVITATIONAL FIELD
Authors: KHRAPKO R.I.
Published: November 2004

The Papapetrou equations for a dipole particle are criticized in favor of the evolution equations obtained by Dixon and Madore. It is concluded that an additional condition (Pirani, Dixon, Corinaldesi, etc.) which permits the calculation of a unique world line of a particle is a substitute for data of a particle structure. Equations of motion of an extended test body in terms of multipoles are presented.
NONLOCAL THEORY OF GRAVITY
Authors: NOVELLO M. , DUQUE S.L.S.
Published: November 2004

We use a three-index tensor Aμνα to describe spin-2 fields. This quantity acts as the potential of the standard variable hμν. We apply the new variables to examine the coherence of a nonlocal nonlinear theory of gravity.
SCATTERING OF DIRAC PARTICLES BY GRAVITATIONAL PLANE WAVES
Authors: BINI DONATO , FERRARI VALERIA
Published: November 2004

We find a complete set of solutions of the Dirac equation in the background of a gravitational plane wave. The Bogoliubov transformation relating the in and the out modes and the scattering cross-section is also derived.
THE WHEELER-DEWITT EQUATION FOR THE HETEROTIC SUPERSTRING THEORY INCLUDING TERMS QUARTIC IN THE RIEMANN TENSOR
Authors: POLLOCK M.D.
Published: November 2004

The Wheeler-DeWitt equation for the wave function of the Universe Ψ can be derived for the heterotic superstring, after reduction of the effective action, including terms [Formula: see text] quartic in the Riemann tensor, from ten dimensions to [Formula: see text] dimensions, where [Formula: see text]. If the compactified space is Ricci flat, then no terms ℛ3 appear, since the coefficient of [Formula: see text] in the ten-dimensional action vanishes. The reduced Lagrangian, ignoring all non-gravitational fields, is then L=(16πG)−1R+a2ℛ2+a4α′2ℛ4, where G is the Newton gravitational constant, α′ is the Regge slope parameter, and a2 and a4 are dimensionless coefficients. Including only the first two terms, in the Friedmann space-time ds2=dt2−e2α(t)dx2, leads to the Schrödinger equation i∂Ψ/∂t=[−AMe−Mα∂2/∂ξ2+ VM,K(α, ξ)]Ψ, where AM is a positive constant, ξ≡dα/dt and K is the curvature of the M-space dx2. After the Wick rotation [Formula: see text], this equation becomes [Formula: see text], where [Formula: see text]. The requirement that both V and [Formula: see text] are positive semi-definite leads to the conditions M=3, K=0, which state that space is three-dimensional and flat.

Here, a more complete Schrödinger equation is derived, via a perturbative treatment of the terms a4α′2ℛ4, which lifts the degeneracy of the potential V3,0 under Wick rotations, the Lorentzian signature being energetically favoured over the Euclidean signature. This corroborates results concerning supersymmetry and the quantum mechanical consistency of the string theory on the world sheet, for which the Lorentzian signature is also necessary, as it is argued to be for the Feynman path-integral formulation of Ψ.
TYPICAL SCALES IN THE CLUSTERING OF THE UNIVERSE
Authors: FANG LI-ZHI , DENG ZU-GAN , XIA XIAO-YANG
Published: November 2004

The cosmic density perturbations are not completely scale-free, i.e. preferential scales should exist in the clustering of the universe. Observations do show the existence of the typical scales, namely, the distribution of various objects cannot be described by a simple fractal law. However, the standard two-point correlation function statistic is ineffective in detecting the typical scales. A better method based on identifying the periodic components in two-point correlation functions was developed. Using this method, the typical scales have been systematically searched for in samples of galaxies, clusters of galaxies, quasars and absorption lines of quasars. It showed the existence of typical scales in the range of 20–130 h−1 Mpc with high confidence. In particular, two typical scales, 60−1 Mpc and 130−1 Mpc, have been detected in all the samples being analysed. Such “universal” scales are probably the characteristic scales in the primordial fluctuations of the universe. Other theoretical implications of the detected typical scales have also been reviewed.
SN1993J: CHALLENGING NEW INSIGHTS FOR STELLAR STRUCTURE AND SUPERNOVA THEORIES
Authors: PARUI RAMEN KUMAR
Published: November 2004

The appearance of supernova SN1993J in our nearby galaxy M81 is an important event in the modern study of supernovae. From the very beginning it created puzzles regarding its supernova type; then in its evolution further puzzles particularly in its spectra, light curve, nature of progenitor, X-ray and γ-ray emission, polarization, etc. Various puzzles have been solved with the help of both theoretical and observational investigations. Still many problems remain. In this present review we examine the gradual development of the various puzzles along with the evolution of SN1993J. We have also presented the unsolved problems as well as the important aspects which are to be measured. We particularly emphasize on the measurements of the shell structure of a radio supernova and of the asymmetry of the scattering envelope as a test to verify the prediction of shell structure in supernova theory i.e. supernova SN1993J will give us an opportunity to verify various aspects of supernova theory.
ASYMPTOTICALLY FLAT SPACETIMES AT SPATIAL INFINITY: THE FIELD APPROACH AND THE LAGRANGIAN DESCRIPTION
Authors: PETROV A.N.
Published: November 2004

An asymptotically flat spacetime (AFST) at spatial infinity is studied. The technique of the field formulation of general relativity developed earlier is used. The properties of the latter are similar to those of an ordinary gauge field theory in a fixed background spacetime. We give a definition of an AFST. The role of a background is played by Minkowski space. Integrals of motion are defined with the use of a stress-energy tensor of the gravitational field together with its sources and Killing vectors of the background spacetime. For each of the following AFST characteristics, namely the definition and the values of the integrals of motion and the action integral, we have found the weakest asymptotics for gauge transformations such that this characteristic does not change under the gauge transformations. These three kinds of falloff conditions are compared. The suggested approach is discussed and compared with some known results and methods.
DIRAC EQUATION IN SPATIALLY NONFLAT ROBERTSON-WALKER SPACE-TIMES: II
Authors: BARUT A.O. , SINGH LAMBODAR P.
Published: November 2004

The Dirac equation is generalised to the Robertson-Walker space-time in a Cartesian tetrad gauge. Its relationship with the Dirac equation in the diagonal tetrad gauge is established. The time dependence of the solution for different models of the expanding Universe is discussed.
THE CONSTRAINT ALGEBRA OF QUANTUM GRAVITY IN THE LOOP REPRESENTATION
Authors: GAMBINI RODOLFO , GARAT ALCIDES , PULLIN JORGE
Published: November 2004

We study the algebra of constraints of quantum gravity in the loop representation based on Ashtekar’s new variables. We show by direct computation that the quantum commutator algebra reproduces the classical Poisson bracket one, in the limit in which regulators are removed. The calculation illustrates the use of several computational techniques for the loop representation.
SPIN-$\frac{3}{2}$ POTENTIALS IN BACKGROUNDS WITH BOUNDARY
Authors: ESPOSITO GIAMPIERO , GIONTI GABRIELE , KAMENSHCHIK ALEXANDER YU. , MISHAKOV IGOR V. , POLLIFRONE GIUSEPPE
Published: November 2004

This paper studies the two-spinor form of the Rarita-Schwinger potentials subject to local boundary conditions compatible with local supersymmetry. The massless Rarita-Schwinger field equations are studied in four-real-dimensional Riemannian backgrounds with boundary. Gauge transformations on the potentials are shown to be compatible with the field equations providing the background is Ricci-flat, in agreement with previous results in the literature. However, the preservation of boundary conditions under such gauge transformations leads to a restriction of the gauge freedom. The recent construction by Penrose of secondary potentials which supplement the Rarita-Schwinger potentials is then applied. The equations for the secondary potentials, jointly with the boundary conditions, imply that the background four-geometry is further restricted to be totally flat. The analysis of other gauge transformations confirms that, in the massless case, the only admissible class of Riemannian backgrounds with boundary is totally flat.
SQUEEZED STATE REPRESENTATION OF THE SCALAR FIELD AND VACUUM FLUCTUATIONS IN THE EARLY UNIVERSE
Authors: SURESH P.K. , KURIAKOSE V.C. , JOSEPH K. BABU
Published: November 2004

A squeezed state representation valid even near the singularity is constructed for each mode of a quantized scalar field in a spatially homogeneous and anisotropic background cosmology, and the problem of particle creation in an external field is examined by means of the squeezed state formalism of quantum optics. Using the squeezed state formalism the expectation values of the stress-energy tensor of the scalar field in curved space-time have been calculated. Quantum fluctuations of density and anisotropic pressure have also been calculated.
GROUND BAND ENERGIES OF TRANSITIONAL NUCLEI II
Authors: DRENSKA S. , GEORGIEVA A. , IVANOV M. , MAVRODIEV S. , ROUSSEV R. , RAYCHEV P.
Published: November 2004

An unified description of the low-lying excited states of the ground bands of the transitional nuclei throughout the periodic table is obtained. A new variable in the geometrical part of the interaction characterizing the transitions is evaluated and analyzed. A phenomenological formula for the dynamical coefficient of the interaction, depending on the nuclear shell quantum numbers, is derived. A good agreement between the so-obtained theoretical ground band energies and the experimental ones is obtained for 474 low-lying states of 159 transitional nuclei from five major shells.
AN ESTIMATE OF CENTRE-OF-MASS EFFECTS IN QUARK POTENTIAL MODELS
Authors: ADAM R.M. , GAVIN E.J.O. , MILLER H.G. , SHITIKOVA K.V. , YEN G.D.
Published: November 2004

The correction to the mass for the spurious centre-of-mass motion in a three-quark system is calculated exactly in the nonrelativistic constituent quark model for the Cornell potential. The result is somewhat higher than MIT bag model estimates but similar to that of a soliton bag model and a relativistic oscillator model.
NUCLEAR FORM FACTORS AND NUCLEON MOMENTUM DISTRIBUTIONS IN NUCLEI
Authors: GARISTOV VLADIMIR P.
Published: November 2004

A simultaneous description of nuclear form factors and momentum distributions for ground and collective excited states is presented using a simple liquid drop model with an oscillating nuclear surface. The influence of the nuclear surface diffuseness over nuclear form factors and nucleon momentum distributions for a large region of mass number is investigated. Mean square radii of nuclei in one-phonon excited states are discussed. Quasi-elastic electron scattering y-scaling functions are presented and compared with those extracted from experimental data.
COMPARISON OF TWO-NEUTRON TRANSFER INTENSITIES IN RARE EARTH NUCLEI WITH PREDICTIONS OF MICROSCOPIC MODELS
Authors: SHIHAB-ELDIN A.A. , RASMUSSEN J.O. , STOYER M.A. , BURKE D.G. , GARRETT P.E.
Published: November 2004

The microscopic structure of 0+ states in well-deformed even-even nuclei was generated within a framework of exact diagonalization of the residual pairing and n−p forces in a seniority-zero Nilsson orbital basis. Available experimental results on the fraction of the L=0 two-neutron transfer intensity which goes to excited 0+ states are compared with microscopic model calculations, giving good overall agreement. Some prominent features of the experimental systematics appear to depend on details of the single-particle states, and are therefore better explained with a microscopic description than with the IBM.
NUMBER-PROJECTED QUASIPARTICLE PHONON COUPLING APPLIED TO ODD-MASS Te ISOTOPES
Authors: CENEVIVA C.A.P. , LOSANO L. , DIAS H.
Published: November 2004

The structure of low-lying levels in odd-mass Te isotopes (115≤A≤131) is examined in the framework of the projected-quasiparticle-phonon coupling model (PQPC). Effects of particle number symmetry restoration are discussed through the comparison with usual quasiparticle phonon coupling calculations (QPC). Excitation energies, dipole and quadrupole moments are calculated and compared with the experimental data.

Nuclear Structure: 115−131 Te ; calculated levels J, π, S, μ, and Q. Number-projected quasiparticle-phonon coupling.