bluuebunny/crossref_metadata_2025 huggingface dataset:
LOCAL SYMMETRIES IN THE EXTENDED HAMILTONIAN FORMALISM
Authors: COSTA M. E. V. , GIROTTI H. O.
Published: November 2004

In this paper we study the interrelationship between local symmetries and the functional structure of the extended Hamiltonian describing the dynamics of a system possessing only first class constraints. The mathematical conditions which must be obeyed by a constrained system in order to accommodate a prescribed set of internal transformations as gauge symmetry transformations are established. A similar analysis is carried out for the case of external transformations. We arrive at the necessary and sufficient condition for a constrained system to be invariant under reparametrizations in the evolution parameter. The results in this paper are compared with those previously reported in the literature. The independent character of internal and external gauge transformations is stressed throughout the paper. We demonstrate that these transformations become isomorphic if one restricts oneself to considering only the classical trajectories.
ELASTIC S-MATRICES IN (1 + 1) DIMENSIONS AND TODA FIELD THEORIES
Authors: CHRISTE P. , MUSSARDO G.
Published: November 2004

Particular deformations of 2-D conformal field theory lead to integrable massive quantum field theories. These can be characterized by the relativistic scattering data. We propose a general scheme for classifying the elastic nondegenerate S-matrix in (1 + 1) dimensions starting from the possible boot-strap processes and the spins of the conserved currents. Their identification with the S-matrix coming from the Toda field theory is analyzed. We discuss both cases of Toda field theory constructed with the simply-laced Dynkin diagrams and the nonsimply-laced ones. We present the results of the perturbative analysis and their geometrical interpretations.
INFLATION IN KALUZA-KLEIN COSMOLOGY II: FRIEDMANN MODELS
Authors: BLEYER ULRICH , SCHMIDT HANS-JÜRGEN
Published: November 2004

The conformal relation between scale-invariant fourth-order gravity and Kaluza-Klein models as derived in the preceding paper (I) is applied to Friedmann cosmological models. Especially, the result that power-law inflation is an attractor solution can be carried over, but the conformal transformation brings power-law inflation to de Sitter-like exponential inflation, or power-law inflation a ≈ t.

The results depend essentially on the dimension of the internal space.
HOLE CONJUGATION WITHIN RELATIVISTIC FERMIONIC SYSTEM
Authors: CHAKRABARTI J. , KÖGERLER R. , SATZ H.
Published: November 2004

For a many-body relativistic fermionic system the concept of a hole state is useful. Consequently, the introduction of a field operator corresponding to these hole states is of technical convenience. We define the transformation that takes place from a particle to a hole and construct the corresponding hole-field-operator. Some physical consequences of pairing and possible condensation are explored. The advantage of the newly introduced hole-operator for symmetry considerations is shown.
TRUNCATED COMFORMAL SPACE APPROACH TO SCALING LEE-YANG MODEL
Authors: YUROV V. P. , ZAMOLODCHIKOV AL. B.
Published: November 2004

A numerical approach to 2-D relativistic field theories is suggested. Considering a field theory model as an ultraviolet conformal field theory perturbed by a suitable relevant scalar operator one studies it in finite volume (on a circle). The perturbed Hamiltonian acts in the conformal field theory space of states and its matrix elements can be extracted from the conformal field theory. Truncation of the space at a reasonable level results in a finite dimensional problem for numerical analyses. The nonunitary field theory with the ultraviolet region controlled by the minimal conformal theory [Formula: see text] is studied in detail.
A BRST APPROACH TO MASSLESS GAUGE FIELDS OF INTEGER SPIN
Authors: DOMEIJ THOMAS
Published: November 2004

We present a method based on BRST techniques for how to obtain the conventional equations for symmetric tensor gauge fields which describe free massless particles of arbitrary integer spin. We do so in a wave function representation in a flat space-time background of any dimension. A fairly straightforward way is also presented for how to obtain the equations from a gauge invariant Lagrangian of the form [Formula: see text].
LASER SPECTROSCOPY OF DYNAMICAL SURFACE PROCESSES
Authors: ZACHARIAS H.
Published: November 2004

Physical phenomena associated with energy deposition into adsorbed molecules will be discussed. This energy may be provided to the adsorbate either thermally, by a catalytic surface reaction or by laser radiation. When enough energy is supplied adsorbed molecules eventually desorb from the substrate. Observation of the desorption flux with internal state selection provides detailed information about the molecular dynamics in this process, because the internal excitations are associated with the dynamics on the potential energy hypersurface. The rotational cooling effect previously observed in molecular beam scattering has also been found for desorption. In several systems strong vibrational excitation has been observed. Recent developments permit in addition the velocity distributions of molecules to be determined with internal quantum state resolution. The complete energetics of desorbing molecules can thus be determined. Finally, making use of the polarized nature of the laser radiation, alignment effects in the desorption can be observed, permitting to analyze the vector properties of the rotational angular momentum.
FEDOROV UNIVERSAL EQUATIONS IN THE STRING AND MEMBRANE THEORIES
Authors: SHAVOKHINA N. S.
Published: November 2004

It is shown that the equation of minimal hypersurface in the Euclidean (or pseudo-Euclidean) space can be written as the universal Fedorov matrix equation with first-order partial derivatives. Time-like minimal surfaces in the pseudo-Euclidean Minkowski space describe the free motion of relativistic strings and membranes, whereas space-like minimal surfaces describe the potential in the nonlinear Born electrostatic. All of them are imaginary images of minimal surface of the Euclidean space. Spherically symmetric surfaces are found to be all the three types, the hypercatenoid of any dimensionality and its imaginary images. The Fedorov equations provide rich information on the minimal surfaces.
SUPERCONDUCTIVITY IN THE Bi-Pb-Sr-Ca-Cu-O SYSTEM DOPED WITH Sb
Authors: HEIRAS J. , KRAUSS W. , POLITIS C.
Published: November 2004

Doping of Bi-Pb-Sr-Ca-Cu-O HTSC's with Sb have been attempted with the purpose of increasing the transition temperature. Several different preparation methods were investigated in which the composition and annealing conditions were varied; ρ vs T and χ vs T measurements were carried out to determine the superconducting properties of samples. X-rays, differential thermal analysis (DTA) and thermo gravimetric analysis (TG) were performed to study the structure and the melting behaviour of samples. However, it was found that, at least for the conditions tested, Sb has no effect in increasing the transition temperature of this system. The maximum superconducting transition temperature observed in the system Bi 2−x Pb x Sr 2 Ca 2 Cu 3 O y was T c,o = 108 K which was completely independent of the doping with Sb.
METASTABLE STATES IN THE HOPFIELD MODEL
Authors: PROCESI CLAUDIO , TIROZZI BRUNELLO
Published: November 2004

We describe the properties of the free energy of the Hopfield model with a finite number of patterns and describe its dynamic at zero temperature in the space of overlaps in the thermodynamic limit.
MEAN VALUES OF FIELD AND ATOMIC OPERATOR PRODUCTS IN THE PROBLEMS OF QUANTUM OPTICS
Authors: KNÖLL L. , SHUMOVSKY A. S.
Published: November 2004

Exact expressions for the mean values of the products of field and atomic operators are obtained in the general case of a chaotic, coherent or squeezed initial state of the field. These expressions permit one to eliminate the field variables from the dynamical equations.
CRITICAL TEMPERATURE OF THIRD GENERATION HIGH-TEMPERATURE SUPERCONDUCTORS
Authors: APOSTOL MARIAN , BUZATU FLORIN , LIU FANG HUA
Published: November 2004

The critical temperature of the Bi- and Tl-based superconductors is analyzed within the framework of the model of the interacting electrons and oxygen-displacive modes of the lattice. The presumable effect of the in-layer lattice modulation on the superconducting critical temperature is also estimated. The structural elements which seem to be effective in raising the critical temperature are discussed in comparison with the La- and Y-based superconductors.
EXPERIMENTAL ADVANCES IN TWO-DIMENSIONAL MAGNETISM
Authors: DÜRR W. , KERKMANN D. , PESCIA D.
Published: November 2004

This paper reviews recent experimental advances toward the physical realization of two-dimensional magnetic systems. In particular, it is shown that truly epitaxial ferromagnetic monolayers of 3-d transition metals atop a non-magnetic substrate are within reach of material science. Magnetism in these systems exhibits a rich variety of new phenomena, unknown to our three-dimensional world but in line with our theoretical picture of physcis in two dimensions.
ON THE SELF-CONSISTENT STATISTICAL THEORY OF STRUCTURAL, DYNAMICAL, AND THERMODYNAMIC SURFACE PROPERTIES OF ANHARMONIC CRYSTALS II: The Properties of Arbitrary Oriented Surfaces of the Two-Dimensional Model with Square Lattice
Authors: ZUBOV V. I. , BANYERETSE F.
Published: November 2004

The correlative unsymmetrized self-consistent field method is used to study surface properties of the two-dimensional model of an anharmonic crystal with square lattice having various Miller indices. The lattice relaxation, the amplitudes of atomic vibrations and the thermodynamic surface functions are calculated. The typical nonsingular and vicinal surfaces are considered. The dependence of thermodynamic surface functions on the surface orientation is obtained.
SQUEEZING PROPERTIES OF COUPLED NONLINEAR OSCILLATORS
Authors: BUŽEK VLADIMÍR , JEX IGOR
Published: November 2004

In this paper the squeezing properties of the two-mode radiation field interacting with a nonliner nonabsorbing Kerr-like medium modelled as a two-mode anharmonic oscillator are studied. Time evolution of the variances of the radiation field initially prepared in the two-mode coherent state as well as the two-mode squeezed vacuum state are analyzed. In particular, it is shown that in the case when the radiation field is initially prepared in the two-mode coherent state the interaction between two modes leads to a high degree of squeezing.
EXCHANGE ALGEBRA AND EXOTIC SUPERSYMMETRY IN THE CHIRAL POTTS MODEL
Authors: Bernard D. , Pasquier V.
Published: November 2004

We obtain an exchange algebra for the Chiral Potts model, the elements of which are linear in the parameters defining the rapidity curve. This enables us to connect the Chiral Potts model to a Uq(GL(2)) algebra. On the other hand, looking at the model from the S-matrix point of view relates it to a ZZ N generalisation of the supersymmetric algebra.
THE MODIFIED XXZ HEISENBERG CHAIN: CONFORMAL INVARIANCE, SURFACE EXPONENTS OF c<1 SYSTEMS AND HIDDEN SYMMETRIES OF FINITE CHAINS
Authors: GRIMM U. , RITTENBERG V.
Published: November 2004

The spin-1/2 XXZ Heisenberg chain with two types of boundary terms is considered. For the first type, the Hamiltonian is hermitian but not for the second type which includes the Uq[SU(2)] symmetric case. It is shown that for a certain “tuning” between the anisotropy angle and the boundary terms the spectra present unexpected degeneracies. These degeneracies are related to the structure of the irreducible representations of the Virasoro algebras for c<1.
C=1 COSET MODELS AND THEIR FUSION ALGEBRAS
Authors: JARVIS P.D. , ZHANG R.B.
Published: November 2004

Higher symmetry algebras, conjectured empirically in certain c=1 models in statistical mechanics, are identified with the extended conformal algebras in coset constructions of the maximal hermitian symmetric spaces. The branching functions and their modular properties are derived and associated algebras, compatible with the fusion rules are discussed.
LEVEL CROSSING, SPONTANEOUS PARITY VIOLATION, HIGH Tc SUPERCONDUCTIVITY MECHANISMS AND THE CHIRAL POTTS CHAIN
Authors: ITOYAMA Hiroshi , McCOY Barry M. , PERK Jacques H.H.
Published: November 2004

We use recent results on the integrable Chiral Potts chains, the t-J model, and the bilinear-biquadratic spin-1 model to discuss the level crossing-spontaneous parity violating mechanism for high Tc superconductivity.
OFF THE CRITICAL POINT BY PERTURBATION (II): THE ISING MODEL SPIN-SPIN CORRELATOR IN A MAGNETIC FIELD
Authors: Dotsenko Vl. S.
Published: November 2004

An extension of the analytic regularization technique based on the conform 1 theory is suggested for the case of the spin-spin correlation function of the Ising model in a magnetic field, <σ0σR>h=F(t)/(R)1/4, t=hR15/8. Several first terms of the expansion of the scaling function F(t) are given.
C*-ALGEBRAIC METHODS IN STATISTICAL MECHANICS AND FIELD THEORY
Authors: EVANS David E.
Published: November 2004

We survey the recent work in non-commutative operator algebras (especially AF-algebras, those which are inductive limits of finite dimensional C*-algebras) and which arise in studying critical phenomena in classical statistical mechanics and conformal field theory, from a C*- or topological viewpoint, rather than a von Neumann algebra/measure theoretic one.
ENTROPY INCREASE AND K-SYSTEMS IN QUANTUM THEORY
Authors: Thirring W.
Published: November 2004

It is shown that the relative entropy converges to its equilibrium value when the states converge strongly. This can happen only for subalgebras for which the clustering is uniform. It happens for K-systems for which this uniformity in clustering has the maximal extent which is possible.
BLOCH AND THE NEW SUPERCONDUCTORS
Authors: LITTLE WILLIAM A.
Published: November 2004

Bob Hofstadter gave a very complete description of the work that Felix had done in many different areas. I would like to touch only on those areas which are connected with superconductivity, and of these, those areas in which I have had personal contact with Felix. This, I hope, will give you a different view of working with Felix, and a view of the kind of interaction that a colleague could have had with him.
BOUND SMALL POLARONS IN HIGH-Tc SUPERCONDUCTORS
Authors: SZYMCZAK H. , GENZEL L. , WITTLIN A.
Published: November 2004

The thermal and acoustic anomalies in high-Tc superconductors are interpreted in terms of contributions arising from the tunneling motion of bound small polarons. The small polarons arise in YBa 2 Cu 3 O 7 oxides due to the localization of the holes on one of the four O 2− ions surrounding the Cu(2) site in the CuO2 plane. The optical absorption band located at 0.4 eV is explained as a light-induced transfer of holes between the equivalent O 2− sites. It is argued that the strong hole-lattice interaction is responsible for the enhanced oscillator strength of optical phonons in YBa 2 Cu 3 O 7.
SURFACE CRITICAL BEHAVIOUR OF SOME TWO-DIMENSIONAL LATTICE MODELS
Authors: STELLA A.L. , VANDERZANDE C.
Published: November 2004

A review is given of recent work on the ordinary surface critical behaviour of systems in two dimensions. Several models of interest in statistical mechanics are considered: Potts model, percolation, Ising clusters, ZN-model, O(n) model and polymers. Numerical results for surface exponents, obtained by suitable finite size scaling extrapolations, are discussed in the light of recent advances based on the conformal invariance approach.

Surface exponents are often seen as important tests of conformal invariance predictions. In other cases these exponents provide important information for a location of the problem within the classification schemes offered by the conformal approach, and a determination of its universality class. A relevant example of the first aspect is the study of the q-state Potts model with q near 4, for which an analytical study of logarithmic scaling corrections is needed to achieve a successful test. The latter point of view applies, e.g., to the more controversial cases of polymers at the theta point and critical Ising clusters. Emphasis is put on the importance of an integrated study of both bulk and surface properties. Relevant issues, like the possible existence of analytical expressions for the indices in particular model families, or of general relationships between bulk and surface exponents, are critically discussed.

The new problem of critical behaviour at fractal boundaries is also considered for random (RW) and self-avoiding walks (SAW). From the numerical analysis of this problem remarkable universalities of the surface exponents seem to emerge, which, in the case of SAW’s, are still far from being understood.
X-RAY ABSORPTION STUDY OF INTERMEDIATE VALENCE IN Sm1−xGdxS ALLOYS
Authors: SINGHAL R.K. , RAO K.V.R. , CHANDRA U. , JAIN D.C. , GARG K.B.
Published: November 2004

X-ray Absorption Near Edge Structure (XANES) measurements above LII edge of Sm are employed to study the intermediate valence in Sm 1−x Gd x S (0.05≤x≤0.30) alloys. The split white lines at the LII edge of Sm are used to determine the average valence of Sm in these alloys, The internal chemical pressure generated by substitution of smaller trivalent cation, Gd, for Sm drives the latter to a higher valence. Sm valence increases smoothly first and then undergoes an abrupt increment at a critical concentration of 16 at.% of Gd. At concentration of Gd higher than 16 at.% the increase in Sm valence is smooth and small. The data for Sm average valence for Sm 1−x Gd x S alloys obtained by LII absorption edges shows fair agreement with other techniques.
SQUEEZING OF THE SQUARE OF THE FIELD AMPLITUDE IN THE TWO-ATOM ONE-MODE MODEL WITH MULTIPHOTON TRANSITIONS
Authors: BASHKIROV E.K. , SHUMOVSKY A.S.
Published: November 2004

The squeezing of the square of the field amplitude in the two-atom one-mode model with multiphoton transitions is investigated. The time-dependent squeezing factors are calculated. The conditions for the optimum squeezing are shown.
EXACT RESULTS FOR THE AREA-WEIGHTED MOMENTS OF CONVEX POLYGONS ON THE SQUARE LATTICE
Authors: LIN K.Y.
Published: November 2004

A general method to derive the generating functions for the area-weighted moments of the number of convex polygons on the square lattice is described. We apply this method to calculate the generating functions for the jth moments up to j=10. The empirical formula of Enting and Guttmann for the second moment is verified.
OVERVIEW OF POLYMER TOPOLOGY
Authors: NECHAEV SERGEI
Published: November 2004

The modern state of the theory of topological constraints in statistical physics of polymers is reviewed. Attention is paid mainly to the most general problems concerning the topological properties of polymers represented as Markov paths. The different approaches and methods used for solving the concrete topological problems are systematized. On the phenomenological level the role of topological constraints in kinetics of polymers is investigated.
MACROSCOPICAL THEORY OF LAYERED SUPERCONDUCTORS
Authors: BULAEVSKII L.N.
Published: November 2004

The macroscopical Ginzburg-Landau models with effective-mass tensor and Josephson coupling of the layers are used to describe the magnetic properties of layered superconductors (dichalcogenides of transition metals and intercalated compounds, organic superconductors and high-Tc copper oxide compounds). In the framework of such models the magnetic critical fields, Abrikosov lattice, torque, Josephson oscillations, Gaussian fluctuations are considered and the validity of mean field theory in the model with Josephson coupling is discussed. The layeredcompounds with different superconducting layers are also studied including the dependence of critical temperature on the strength of coupling and temperature dependence of magnetic anisotropy. The experimental data of high-Tc superconductors are discussed to show that in Bi- and Tl-compounds the conditions of Josephson coupling of layers is fulfilled.
NEW LOCAL RELATIONS FOR LATTICE MODELS
Authors: AVAN J. , MAILLARD J-M. , TALON M. , VIALLET C.
Published: November 2004

We describe new local relations leading to non-trivial (non-homogeneous) equations for the row-to-row transfer matrices of arbitrary size for two dimensional I.R.F. and vertex models. We sketch the connection between this relation and the Yang-Baxter equations, and we describe the example of the hard hexagon model.
PATTERN FORMATION IN CONDENSED MATTER
Authors: MOURITSEN OLE G.
Published: November 2004

A mini-review is given of complex pattern formation in hard and soft condensed matter with special emphasis on the dynamics of random networks of interfaces and growth of tenuous structures. The elementary principles of describing such phenomena are outlined together with a discussion based on a number of specific examples, including domain growth and dynamics of ordering processes as well as diffusion-limited aggregation and impurity-controlled solidification. Results obtained from simple model calculations are presented and it is also demonstrated how pattern-formation phenomena in space and time may be described using the concepts of fractal geometry and dynamical scaling. The possibility of a universal classification of ordering dynamics and growth of fractal structures will be discussed.
TWO-DIMENSIONAL HUME-ROTHERY PHASES
Authors: MARKIEWICZ R. S.
Published: November 2004

The traditional Hume-Rothery phases are Cu-bronzes or other (three-dimensional) alloys, which show a series of phase transitions at fixed electron-per-atom ratios, independent of the particular atomic constituents. The transitions are driven by Fermi surface nesting within the individual phases. It is shown that similar transitions appear to be a pervasive feature of two-dimensional systems. Examples are given involving graphite intercalation compounds, organic superconductors, and the new high T c oxide superconductors.
EFFECTIVE POTENTIAL FOR TWO-BODY INTERACTIONS
Authors: VAIA RUGGERO , TOGNETTI VALERIO
Published: November 2004

A new kind of effective potential, which permits the calculation of the quantum equilibrium averages of configuration dependent observables in a classical-like way, is used for calculating the quantum pair correlation function of a two-body system. The main feature of this effective potential is the capability to fully account for the quantum harmonic effects, so it proves much more efficient than the analogous one defined by the Wigner expansion. Applications and comparisons with exact data are made for the Lennard-Jones interaction, with the characteristic parameters of helium atoms and hydrogen molecules.
HIGH-DENSITY EXPANSION FOR THE SPINLESS FERMION MODEL III: GREEN'S FUNCTIONS
Authors: BARTKOWIAK M. , MÜNGER P. , CHAO K. A.
Published: November 2004

The single-particle electron Green's function and the charge-fluctuation Green's function for the spin-polarized fermion lattice gas are calculated within the framework of the high-density expansion up to the first order in 1/z. Violation of some conditions of consistency of diagrammatic perturbation expansion approximation schemes are discussed. Relations between the Green's functions and corresponding approximate free energy are established. Two kinds of approximations for Green's functions for the charge ordered phase are constructed and applied to determine the band structure of the spinless fermion model. The Green's functions for the nonordered phase are used to study the phase diagram of the model for finite temperatures and arbitrary band filling.
SOLVABLE MODEL OF A METAL-INSULATOR TRANSITION
Authors: SHANKAR R.
Published: November 2004

A solvable model of d = 1 spinless fermions at half-filling which exhibits a Mott transition is studied in detail. Many response functions are computed: at zero and nonzero temperatures, in the insulating and metallic sites, at the transition, and at q ≃ 0, 2k F . Some quantities are computed exactly, others only upto a scale factor. Some results are old, but mentioned here for completeness. Some are rederived using new tools such as conformal invariance. The rest are new. Next, the effect of randomness on the Mott state is explored. It is found, on the basis of Imry-Ma type arguments that no matter how large the gap is, the Mott insulator turns into an Anderson insulator immediately.
VARIATIONAL TRANSITION STATE THEORY FOR ACTIVATED RATE PROCESSES IN DISSIPATIVE SYSTEMS
Authors: POLLAK ELI
Published: November 2004

Variational upper bounds are derived for the spatial and energy diffusion limited escape rate of a particle trapped in a metastable well and interacting with a dissipative medium. The theory is well defined for arbitrary memory friction and accounts explicitly for the nonlinearity of the potential governing the motion of the escaping particle.
QUENCHING OF THE HALL RESISTANCE IN A NOVEL GEOMETRY
Authors: CHANG A.M.
Published: November 2004

We review experiments on the observation of Hall resistance anomalies in ballistic Hall junctions of novel geometries, in submicron GaAs-Al x Ga 1−x As heterostructure devices. We demonstrate that the low magnetic field Hall resistance is greatly influenced by the junction geometry, and that particular geometries are required to give rise to a phenomenon known as “quenching” of the Hall resistance where the conventional linear Hall resistance is suppressed to nearly zero, and to a related plateau feature at slightly higher magnetic fields, known as the “last plateau.” These anomalies are explained in terms of the collimation of ballistic electron beams by specific geometric structures and the scattering properties of the Hall junction side walls.
SYNTHESIS AND CONDUCTIVITY OF PALLADIUM POLYMETHACRYLATE
Authors: CHOHAN M.H. , KHAWJA FARID. A. , REHAMN AZIZ UR , ZULFIQAR M. , TAHIR M.
Published: November 2004

Synthesis of palladium polymethacrylate and its dc conductivity have been investigated. Infrared spectra of the palladium acetate and palladium polymethacrylate are taken and compared. The palladium polymethacrylate spectrum indicates that Pd is not attached with —COOH, instead it forms a complex with carboxylic group. Measurements indicate that conduction in this material cannot be attributed to a single conduction process.
INTERFERENCE OF THE FERMI EDGE SINGULARITY WITH AN EXCITONIC RESONANCE IN DOPED SEMICONDUCTORS
Authors: MUELLER JOACHIM F. , RUCKENSTEIN ANDREI E. , SCHMITT-RINK STEFAN
Published: November 2004

Low-temperature emission spectra are calculated for an n-doped semiconductor in which the Fermi level is almost degenerate with an exciton of a higher conduction band. It is shown that in such a sample the virtual transitions of electrons from the Fermi surface into the excitonic state can lead to a strong enhancement of the optical oscillator strength. In particular, due to this effect, the Fermi edge singularity, which is usually only seen in absorption, can become visible also in the emission spectrum. This explains the optical spectra recently obtained in experiments on modulation-doped heterostructures.
CORRELATION IDENTITIES FOR NEAREST-PARTICLE SYSTEMS AND THEIR APPLICATIONS TO ONE-DIMENSIONAL CONTACT PROCESS
Authors: KONNO NORIO , KATORI MAKOTO
Published: November 2004

A series of identities of correlation functions K(n1, n2, …, nN) are given in the nearest-particle system. The above correlation identities are applied to the one-dimensional contact process. The decoupling induced by a renewal measure yields the first approximation: [Formula: see text] for the critical value and [Formula: see text] for the order parameter, which makes a rigorous bound as proved by Holley and Liggett. Furthermore, introducing a new decoupling procedure, improved estimations of [Formula: see text] and [Formula: see text] are calculated.
CONTROL OF SURFACE PHOTOREACTIONS BY ALKALI COADSORPTION
Authors: YING Z.C. , HO W.
Published: November 2004

Recent experimental studies of the promotion and suppression of photoreactions of molecules on solid surfaces by coadsorption of alkali atoms are reviewed.
ON RECURSIVE DEFINITION OF THE GREEN FUNCTION OF FINITE DIFFERENCE AND DIFFERENTIAL OPERATORS
Authors: KABANOVICH V.I. , ERMILOV A.N. , KURBATOV A.M.
Published: November 2004

The possibility of recursive definition of the Green function of finite difference operators with constant coefficients is considered. New equations for the Green functions are found. In particular cases a representation for the Green functions in the form of a series of rational functions is obtained. Generalization for the case of differential operators is carried out. The general problems of the Green functions recursive definition are formulated.
STUDY OF CRYSTAL STRUCTURE AND PHYSICAL PROPERTIES OF THE COMPOUND Bi-Pb-Sr-Ca-Ba-Cu-O
Authors: ZHIQIANG MAO , SUNLI HUANG , YU WANG , ZHAOJIA CHENG , LI YANG , CHENGGAO FAN , GUIEN ZHOU , YUHENG ZHANG
Published: November 2004

With the aid of transmission electron microscopy, the phenomenon of additional superstructure along [Formula: see text] direction was observed for a sample of Bi 1.7 Pb 0.3Sr2 Ca 1.8 Ba 0.2 Cu 3 O y, and two kinds of modulation mode along b axis was found to coexist in this sample. The images of SEM showed that the addition of Ba ions improved the property of two-dimensional growth. The results of XRD indicated that the substitution of Ba 2+ for Ca 2+ increased the volume fraction of the high-Tc phase (Tc>100 K). From the initial part of dc magnetization curve, it is estimated that about 36 percent of the sample volume is in the 110 K superconducting phase at 77 K. Its frozen magnetic flux density is about 8.6 G, which is 5–6 G higher than that of general Pb-doped sample, and its zero-resistance temperature can reach as high as 111 K. These changes of physical properties may be related to the adjustment of the microstructure.
THE EFFECT OF HIGH PRESSURE TREATMENT ON BiPbSrCaCuO SUPERCONDUCTORS
Authors: WU B.Q. , YAO Y.S. , JIN C.Q. , WANG W.K.
Published: November 2004

The effect of high pressure on the superconducting properties of BiPbSrCaCuO ceramic was investigated. We applied cold pressing method on the powder of the prepared samples as well as on the as-prepared samples directly. The former showed a serious destruction of superconductivity, and the latter, however, showed only broadening of the superconducting transitions. It was believed that the structural deformation of the superconducting phases was the main reason for the drastic changes in the electric and magnetic properties of the superconductors.
QUANTUM EFFECT ON SHOT NOISE SUPPRESSION IN TRANSPORT THROUGH MICROSTRUCTURES
Authors: CHEN L.Y. , LEVINE G. , YANG J. , TING C.S.
Published: November 2004

A stochastic process with repulsive correlations is proposed to simulate the nonequilibrium electronic transport through microstructures under finite bias voltage. Since an electron needs to stay a finite time τ0 on a channel state while traversing the constriction structure, electrons following within time τ0 cannot get through the same channel state because of the Pauli exclusion. This quantum effect induces a repulsive correlation and suppresses the shot noise. The Monte Carlo results are compared with experimental measurements.
INFRARED REFLECTION IN Bi(Pb)-Sr-Ca-Cu-O SUPERCONDUCTING CERAMIC SAMPLES OF MIXED 2212 AND 2223 PHASES
Authors: LIU J, Q. , HE Y.S. , REVAULT M. , FORGERIT J.P.
Published: November 2004

Investigations of superconducting energy gap with IR reflectance measurements above and below Tc have been performed in Bi(Pb)-Sr-Ca-Cu-O ceramic samples of mixed 2212 and 2223 phases. The failure to get the two gap’s values simultaneously in the same sample from the maxima in the Rs/Rn curve and a comparison between our results and those obtained previously by other authors for YBaCuO compounds showed the insensitivity of these maxima to Tc in high-Tc superconductors. This means that it might be difficult to deduce the gap’s value directly from the Rs/Rn curve as has been done in conventional BCS superconductors.
A GRASSMANIAN LOOP SPACE APPROACH FOR FERMIONIC BELL FUNCTIONAL INTEGRAL
Authors: BOTELHO LUIZ C.L.
Published: November 2004

We propose a Generalization of the usual Bell Functional Integral for the case of existence of explicit spin interaction.
SURFACE RECONSTRUCTION OF NOBLE METALS: MODELS AND CONSEQUENCES
Authors: TOSATTI E. , ERCOLESSI F.
Published: November 2004

We review recent work on the theory of noble metal surface reconstructions. We put strong emphasis on gold, chosen as a representative prototype system, and discuss in detail its three main faces, Au(100), (110) and (111), a class of (100) vicinals and small clusters. In particular, we discuss the microscopic modeling of these surfaces via a particular many-particle classical Hamiltonian, the so-called glue model, which we have developed in Trieste. Optimal surface structures, obtained by molecular dynamics annealing, are amusingly rich, and can explain several facts known from experiment.
THE ANNEALED MANY-BONDS ISING MODEL
Authors: MARKO P. , KUPKA M. , KOPČANSKÝ P.
Published: November 2004

The random bond problem with many kinds of bonds for Ising lattice is studied. The transformation was found from the Ising model with many kinds of bonds to the Ising problem with one effective bond. The method of transformation is illustrated on the 2D square lattice with ferromagnetic and antiferromagnetic interactions.
TRANSITIONS BETWEEN FRACTIONAL QUANTUM HALL STATES
Authors: GOLDMAN V.J. , JAIN J.K. , SHAYEGAN M.
Published: November 2004

We have studied transitions between adjacent incompressible states by measuring the positions of the longitudinal resistance peaks in the fractional quantum Hall regime and comparing results with the theoretical predictions. We have found that the peak positions agree well with those predicted by theory in which quantum effects are crucial to the existence of extended states.
THE INVERSE BLACKBODY RADIATION PROBLEM
Authors: LAKHTAKIA A.
Published: November 2004

The inverse blackbody radiation problem is of great importance in remote sensing, and has been tackled with some success during the last decade. Progress made in solving this problem is reviewed here.
XPS SPECTRA OF Y-Ba-Cu-O AND ITS DOPED SYSTEMS
Authors: Zhang H. , Feng S.Q. , Feng Q.R. , Zhu X.
Published: November 2004

An XPS study was carried out on the samples of pure Y-Ba-Cu-O and its doped systems. The experiment gave several important results about the electronic states of Y-Ba-Cu-O system. First, the presence of Cu 3+ oxidation state has correlation with the oxygen content and the formal valence state of Cu , but has no direct relationship with the magnitude of Tc; second, there is strong correlation among the electronic states of O, Ba and Cu ; third, the subtle difference in the electronic states of the elements may induce local structure change.
A COMPARISON OF RESISTANCE BROADENING IN MAGNETIC FIELD OF SINGLE CRYSTAL YBa2Cu3O7−δ AND THE ORGANIC SUPERCONDUCTOR κ-(BEDT-TTF)2Cu[N(CN)2]Br
Authors: KWOK W.K.
Published: November 2004

AC resistivity measurements in fields up to 8 Tesla in fully oxygenated and oxygen deficient single crystals of YBa 2 Cu 3 O 7−δ are presented. Fully oxygenated crystals show the characteristic ‘fantail’ broadening in magnetic field where the onset temperature remains virtually independent of the applied magnetic field and the zero resistance temperature decreases dramatically. However, in oxygen deficient crystals, the temperature dependence of the resistivity undergoes a change in shape at high magnetic fields. These results are compared with the recently discovered highest Tc=11.6 K organic superconductor κ- (ET) 2 Cu[N(CN) 2] Br where the shape of the resistive transition for H||b undergoes a change from a ‘fantail’ resistive broadening in magnetic field to that of a more conventional low Tc superconductor.
INTERRELATION BETWEEN CHARGE EXCHANGE AND ENERGY LOSS OF PARTICLES INTERACTING WITH SURFACES: A BRIEF REVIEW AND RECENT RESULTS
Authors: NÄRMANN A.
Published: November 2004

In the interaction of particles approaching a surface energy dissipation to the surface and charge exchange processes between the incoming ion or atom and the surface are two features which have found continuous interest over decades. Only few workers tried to resolve the interrelation of the change of the charge state of the incoming particle and the energy lost during the interaction. Here a brief review of earlier work in this field is given and some recently obtained new experimental and theoretical results are presented concerning the interaction of slow (2–5 keV) incoming He ions with a Ni(110) surface.
ABOUT THE CORRELATION LENGTHS OF QUANTUM HEISENBERG FERRO AND ANTIFERROMAGNETS
Authors: JOLICOEUR TH. , LE GUILLOU J.C.
Published: November 2004

The mass gap for the two-dimensional O (3) non-linear sigma model has been recently extracted from the Bethe Ansatz solution. Combining this result with the Renormalization Group treatment of the Quantum Heisenberg Ferromagnet as well as the Quantum non-linear sigma model we present new formulas for the correlation length of the square lattice quantum ferro and antiferromagnet.
A NEW 1212-TYPE PHASE: Cr-SUBSTITUTED TlSr2CaCu2O7 WITH Tc UP TO ABOUT 110 K
Authors: SHENG Z.Z. , GU D.X. , XIN Y. , PEDERSON D.O. , FINGER L.W. , HADIDIACOS C.G. , HAZEN R.M.
Published: November 2004

Superconductivity up to about 110 K in the CrTlSrCaCuO system was observed by resistance and ac susceptibility measurements. Powder X-ray diffraction analyses showed that a 1212-type phase, Cr -substituted TlSr 2 CaCu 2 O 7, is responsible for the observed superconductivity. This is the first time that single-element substitution for TlSr 2 CaCu 2 O 7 increases Tc of the 1212 phase to above 100 K. The Cr -substituted TlSr 2 CaCu 2 O 7 is easily prepared and has very good quality suitable for practical applications.
A UNIVERSAL CONDUCTANCE DISTRIBUTION AT THE MOBILITY EDGE
Authors: SHAPIRO B.
Published: November 2004

An ensemble of disordered electronic samples at the mobility edge is considered. It is shown that the conductance distribution function PL(g), for samples of size L, approaches a universal function P*(g) when L→∞. This limiting function does not depend on any parameters of the model and contains only the spatial dimensionality d. The calculation is limited to d=2+∊ where ∊ is a small number.
SINGLE MOLECULE SPECTROSCOPY
Authors: ORRIT M. , BERNARD J.
Published: November 2004

We report unambiguous optical detection of single molecules of pentacene in p-terphenyl crystal. The relative shift of the molecular resonance frequencies with temperature changes demonstrates the phenomenon of activated spectral diffusion. These results show the feasibility of the optical study of a single molecule and its local environment.
SUPERCONDUCTIVITY IN Bi-Sr-Ca-Mg-Cu-OXIDE
Authors: KHAN A.Y. , MOHAMMAD M. , SHAHNAZ M. , HASNAIN S.K.
Published: November 2004

A Mg -substituted material with nominal composition Bi 2 Sr 2 Ca 3 Mg 2 Cu 6 O x, prepared by partial substitution of Ca by isovalent Mg in the 2256 composition of Bi-Sr-Ca-Cu-O , has been studied by the measurements of electrical resistance, magnetic susceptibility and X-ray diffraction pattern. Results show the existence of a superconducting phase with onset T c at 112.5±1 K along with a minor phase with onset T c =88 K . The material retained superconducting characteristics (Meissner effect and T c onset ) even after a period of six months.
RAMAN AND NMR STUDY IN MgO-DOPED LiNbO3 CRYSTAL
Authors: HU L.J. , CHANG Y.H. , CHANG C.S. , YANG S.J. , HU M.L. , TSE W.S.
Published: November 2004

The MgO -doped LiNbO 3 crystal has been grown and studied by NMR and Raman techniques. The solubility of MgO in the LiNbO 3 crystal is as much as 30 mole %. It is shown in NMR spectra that the number of Nb 5+ cations at A-site (Li-site) decrease as Mg concentration increased when the Mg content is lower than 5 mole %. The vibration of ( NbO 6) octahedron and translations involving Li + and Mg 2+ cations motion can be identified by replacing Nb 5+ and Li + cations with Ta 5+ and Mg 2+ cations through Raman spectra. The 115 cm −1 and 151 cm −1 peaks are due to the translational modes of Mg 2+ and Li + cations. The doping mechanisms of MgO are proposed.
THERMAL DIFFUSE SCATTERING IN SOME FCC ALLOYS
Authors: ABBAS TAHIR , ZIYA AMER BASHIR
Published: November 2004

Thermal diffuse scattering (TDS) intensity has been calculated for some fcc alloys. The effects of variation of temperature and atomic concentration on TDS have been studied. A systematic change in TDS is observed for various atomic concentrations and temperatures.
MONTE CARLO STUDY OF THE SPIN-1/2 HEISENBERG MODEL IN 1, 2, AND 3 DIMENSIONS
Authors: CRESWICK RICHARD J. , SISSON CYNTHIA J.
Published: November 2004

The properties of the spin-1/2 Heisenberg model on 1, 2, and 3-dimensional lattices are calculated using the Decoupled Cell Method of Homma et al., and these results are compared with high temperature and spin-wave expansions, and with other numerical approaches. The DCM has advantages over other Monte Carlo methods currently in wide use in that the transition probability is positive definite, there is no need to introduce an additional imaginary time, or Trotter, dimension, and the acceptance rate for transitions is comparable to that of classical lattice models. We find very good agreement between the DCM and the high temperature expansion in the temperature region where the high temperature expansion is valid, and reasonably good agreement at low temperatures with spin wave theory. The DCM fails for temperatures T < Tc which decreases with the size of the cell.
THEORY OF THE QUANTIZED ADIABATIC PARTICLE TRANSPORT
Authors: NIU QIAN
Published: November 2004

A localized formulation is presented for the quantized adiabatic particle transport (APT) induced by a slow and cyclic potential variation. Finite size effects are studied for the ring geometry and a realistic geometry. The localized description of APT is shown to be equivalent to the Laughlin's gauge invariant argument for the quantum Hall effect. The effect of quantum fluctuation and the possibility of fractionally quantized APT are also discussed.
INVESTIGATION OF THE SAMARIUM ROLE IN THE PHYSICAL PROPERTIES OF Sm0.5Re0.5Ba2Cu3O7−δ COMPOUNDS IN THE ORTHORHOMBIC AND TETRAGONAL STRUCTURES
Authors: GUSKOS N. , LIKODIMOS W. , LONDOS C. A. , TRIKALINOS Ch. , KOUFOUDAKIS A. , MITROS C. , GAMARI-SEALE H. , NIARCHOS D. , PARASKEVAS S. M.
Published: November 2004

Perovskites of type Sm 0.5 Re 0.5 Ba 2 Cu 3 O 7−δ (Re=Y, La, Nd, Eu, Gd, Dy, Ho, Er, Tm, Yb, and Lu) have been investigated by XRD, magnetic and EPR measurements in both orthorhombic and tetragonal phases. In the former case the usual superconducting phase transition in the range 90 to 95 K has been detected. In all the compounds an EPR spectrum of Cu 2+ ions has been observed. In the tetragonal phase, the EPR spectra of trivalent rare earth ions have been recorded for some members of the series. The observation of a broad EPR signal, tentatively attributed to superexchange interaction over the oxygen bridges < O 2), has also been recorded. Furthermore, the intensity of low-field microwave absorption has been found to depend strongly on the nature of the substituted rare earth ion at the sites of Y ions of the YBa 2 Cu 3 O 7−δ type compounds.
POSSIBLE CORRELATION OF THE ANOMALOUS THERMAL BEHAVIOR OF NbSe3 TO MOBILE DEFECTS
Authors: BÂLDEA IOAN
Published: November 2004

The model of quasi-regular impurity (defect) distribution driven by CDW is used to suggest a possible explanation of the anomalous thermal behavior (thermal hysteresis, latent heats, etc.) found at the CDW transitions in the linear chain compound NbSe 3.
SPECTRAL SPLITTING DUE TO A CIRCULARLY POLARISED PUMP LASER: LASER ZEEMAN SPECTROSCOPY
Authors: EVANS M. W.
Published: November 2004

Theoretical prediction is made for various types of molecular Zeeman spectroscopy due to a circularly polarised pump laser, in which optical rectification produces a pattern of spectral splitting mediated by the imaginary antisymmetric part of the frequency-dependent molecular polarisability. The hyperfine part of this splitting, in which the nuclear spin quantum number plays a role, leads to the expectation of laser-induced resonance effects akin to conventional nuclear magnetic resonance (NMR) and electron spin resonance (ESR). Experimental conditions for the observation of "laser Zeeman" spectral effects are defined using double resonance and saturation in mode-locked lasers for ultra high resolution.
PRODUCTION OF ELECTRON-POLARIZED BEAMS OF MULTIPLY-CHARGED IONS: THEIR USE IN TESTS OF FUNDAMENTAL ATOMIC PHYSICS
Authors: LIU C. J. , DUNFORD R. W.
Published: November 2004

We discuss the prospects for production of an electron-polarized beam of multiply-charged ions by the technique of single-electron capture in a polarized atomic target. In addition, we suggest two atomic physics experiments which could utilize such beams. One of these is a test of the Standard Model of the Weak and Electromagnetic Interactions in a simple one-electron system. The other is a measurement of the hyperfine splitting of the ground state of a multiply-charged lithium-like system.
TWO-PHOTON-ABSORPTION SPECTRA OF QUANTUM-WELL EXCITONS IN STATIC ELECTRIC FIELDS
Authors: FUJII KAZUHITO , SHIMIZU AKIRA , BERGQUIST JOHAN , IKEDA SOTOMITSU , SAWADA TAKESHI
Published: November 2004

We have measured two-photon-absorption spectra of GaAs/Al 0.4 Ga 0.6 As quantum-well structures in a static electric field for photon energies near half the band gap energy, and found drastic field-induced-changes in the spectra. The two-photon-absorption peak at half the energy of the lowest light-hole exciton is induced by the static electric field normal to the quantum well layers, in agreement with a theory that takes account of quasi-two-dimensional exciton effects. With increasing the electric field, however, this peak grows more drastically than the theoretical prediction, and it approaches a large value predicted by another simplified theory based on a two-level model.
MICROSCOPIC MODELS OF PHASE TRANSITIONS IN THE CsHSO4 TYPE CRYSTALS
Authors: RUSTAMOV K. A. , JAVADOV N. A.
Published: November 2004

Microscopic models for the phase transitions described by two wave vectors (corresponding to the centre and the boundary of the Brillouin zone) in the CsHSO 4 type crystals are presented. On the basis of the symmetry analysis, obtained recently, molecular field and cluster approximations are considered. Limitation of this analysis is related to the large number of parameters. Possible phase diagrams within the MFA are presented. In the case of CA within the Slater type model in KDP the necessity of taking into account the parameter of long range interaction is shown.
INFLUENCE OF THE ANTIFERROMAGNETIC CORRELATIONS ON THE CRITICAL TEMPERATURE OF THE HIGH TEMPERATURE SUPERCONDUCTORS
Authors: VERES T. , CRISAN M.
Published: November 2004

The decreasing of the critical temperature of a high temperature superconductor due to the antiferromagnetic correlations and impurities has been calculated using a phenomenological model for the dynamic susceptibility considered in the explanations of the nuclear magnetic resonance, neutron scattering, tunneling experiments and the photoemission spectra. A good agreement with the experimental data has been obtained taking realistic values for the fit parameters.
EPR SPECTRA OF BULK TEXTURED SAMPLES OF THE YBa2Cu3Ox SUPERCONDUCTOR
Authors: CALAMIOTOU M. , GUSKOS N. , LEVENTOURI TH. , PARASKEVAS S. M. , HASCICEK Y. S.
Published: November 2004

EPR and specific conductivity measurements are presented for a series of bulk partially oriented YBa 2 Cu 3 O x samples. The intensities of the EPR signals from the samples as pellets are several times lower than the corresponding ones from the samples in powder form. This difference in intensity is attributed to the "skin effect".