bluuebunny/crossref_metadata_2025 huggingface dataset:
PCNA Interacts with Indian Mung Bean Yellow Mosaic Virus Rep and Downregulates Rep Activity
Authors: Bagewadi Basavaraj , Chen Shoajiang , Lal Sunil K. , Choudhury Nirupam Roy , Mukherjee Sunil K.
Published: October 2004

Proliferative cell nuclear antigen (PCNA), a conserved plant protein as well as an important replication factor, is induced in response to geminivirus infection in the resting cells of the phloem tissues. The biochemical role of PCNA in rolling circle replication (RCR) of geminivirus DNA has not been explored in detail. The initiation of RCR of the bipartite genome of a geminivirus, Indian mung bean yellow mosaic virus (IMYMV), is mainly controlled by viral protein Rep (or AL1 or AC1). The role of host PCNA in RCR of IMYMV was revealed by studying the physical and functional interactions between recombinant PCNA and recombinant IMYMV Rep. Pea nuclear PCNA as well as recombinant pea PCNA showed binding to recombinant Rep in experiments involving both affinity chromatography and yeast two-hybrid approaches. The contacting amino acid residues of PCNA seemed to be present throughout a wide region of the trimeric protein, while those of Rep appeared to be localized only in the middle part of the protein. The site-specific nicking-closing activity and the ATPase function of IMYMV Rep were impaired by PCNA. These observations lead to interesting speculations about the control of viral RCR and dynamic profiles of protein-protein interactions at the RCR origin of the geminiviruses.
Cell Surface Delivery of the Measles Virus Nucleoprotein: a Viral Strategy To Induce Immunosuppression
Authors: Marie Julien C. , Saltel Frédéric , Escola Jean-Michel , Jurdic Pierre , Wild T. Fabian , Horvat Branka
Published: October 2004

Although only a few blood cells are infected during measles, this infectious disease is followed by acute immunosuppression, associated with high infant mortality. Measles virus nucleoprotein has been suggested to contribute to virus-induced inhibition of the immune response. However, it has been difficult to understand how this cytosolic viral protein could leave an infected cell and then perturb the immune response. Here we demonstrate that intracellularly synthesized nucleoprotein enters the late endocytic compartment, where it recruits its cellular ligand, the Fcγ receptor. Nucleoprotein is then expressed at the surfaces of infected leukocytes associated with the Fcγ receptor and is secreted into the extracellular compartment, allowing its interaction with uninfected cells. Finally, cell-derived nucleoprotein inhibits the secretion of interleukin-12 and the generation of the inflammatory reaction, both shown to be impaired during measles. These results reveal nucleoprotein egress from infected cells as a novel strategy in measles-induced immunosuppression.
Global Analysis of Host Cell Gene Expression Late during Cytomegalovirus Infection Reveals Extensive Dysregulation of Cell Cycle Gene Expression and Induction of Pseudomitosis Independent of US28 Function
Authors: Hertel Laura , Mocarski Edward S.
Published: October 2004

Replication
of human cytomegalovirus (CMV) depends on host cell gene products
working in conjunction with viral functions and leads to a dramatic
dysregulation of cell cycle gene expression. Comprehensive
transcriptional profiling was used to identify pathways most
dramatically modulated by CMV at late times during infection and to
determine the extent to which expression of the viral chemokine
receptor US28 contributed to modulating cellular gene expression. Cells
infected with the AD169 strain of virus or a fully replication
competent US28-deficient derivative (RV101) were profiled throughout
the late phase of infection (50, 72, and 98 h postinfection).
Although sensitive statistical analysis showed striking global changes
in transcript levels in infected cells compared to uninfected cells,
the expression of US28 did not contribute to these alterations. CMV
infection resulted in lower levels of transcripts encoding
cytoskeletal, extracellular matrix, and adhesion proteins, together
with small GTPases and apoptosis regulators, and in higher
levels of transcripts encoding cell cycle, DNA replication, energy
production, and inflammation-related gene products. Surprisingly, a
large number of cellular transcripts encoding mitosis-related proteins
were upmodulated at late times in infection, and these were associated
with the formation of abnormal mitotic spindles and the appearance of
pseudomitotic cells. These data extend our understanding of how broadly
CMV alters the regulation of host cell cycle gene products and
highlight the establishment of a mitosis-like environment in the
absence of cellular DNA replication as important for viral replication
and
maturation.
APOBEC3G Incorporation into Human Immunodeficiency Virus Type 1 Particles
Authors: Zennou Véronique , Perez-Caballero David , Göttlinger Heinrich , Bieniasz Paul D.
Published: October 2004

APOBEC3G is promiscuous with respect to its antiretroviral effect, requiring that it be packaged into diverse retrovirus particles. Here, we show that most virally encoded human immunodeficiency virus type 1 particle components are dispensable for APOPEC3G incorporation. However, replacement of the nucleocapsid (NC) Gag domain with a leucine zipper abolished APOBEC3G incorporation. Moreover, coprecipitation analysis showed that APOBEC3G-Gag interaction requires NC and nonspecific RNA. These observations suggest that APOBEC3G exploits an essential property of retroviruses, namely, RNA packaging, to infiltrate particles. Because it is, therefore, difficult to evolve specific sequences that confer escape from APOBEC3G, these findings may explain why lentiviruses evolved an activity that induces its destruction.
Differential Effects on the Hepatitis C Virus (HCV) Internal Ribosome Entry Site by Vitamin B12and the HCV Core Protein
Authors: Li Dongsheng , Lott William B. , Martyn John , Haqshenas Gholamreza , Gowans Eric J.
Published: October 2004

To investigate the role of the hepatitis C virus internal ribosome entry site (HCV IRES) domain IV in translation initiation and regulation, two chimeric IRES elements were constructed to contain the reciprocal domain IV in the otherwise HCV and classical swine fever virus IRES elements. This permitted an examination of the role of domain IV in the control of HCV translation. A specific inhibitor of the HCV IRES, vitamin B12, was shown to inhibit translation directed by all IRES elements which contained domain IV from the HCV and the GB virus B IRES elements, whereas the HCV core protein could only suppress translation from the wild-type HCV IRES. Thus, the mechanisms of translation inhibition by vitamin B12and the core protein differ, and they target different regions of the IRES.
A CELLULAR AUTOMATON FOR ELASTICITY EQUATIONS
Authors: EUGENIO ALBERTO , RASETTI MARIO
Published: October 2004

Cellular Automata are a very efficient numerical technique for fluid dynamics computations. In this paper, based on formal and physical analogies between the Navier-Stokes and the elasticity equations, we aim to construct a cellular automaton which simulates solid dynamics behavior. We show that, in order to describe elastic properties such as compressibility and distortion, which are typically not present in fluid dynamical simulations, higher order effects are to be taken into account.
A MODEL OF MEASUREMENT AS EVOLUTION DRIVEN BY BOTH PREVIOUS AND SUBSEQUENT CAUSES
Authors: CASTAGNOLI GIUSEPPE , RASETTI MARIO
Published: October 2004

The notion of the coexistence in the quantum framework of causality forward and backward in time, is used to develop a generalizazion of the conventional description of unitary evolutions, based on the assumption that evolutions are driven only by previous causes. Such a generalization is capable of describing basic aspects of state vector reduction.
GREEN FUNCTIONS OF STRONGLY CORRELATED ELECTRONS WITH MAGNETIC COUPLING
Authors: VAN HIEU NGUYEN
Published: October 2004

The explicit expressions for the imaginary time normal and anomalous two-point Green functions of the strongly correlated itinerant electron (or hole) system with the quantum antiferromagnetic and ferromagnetic couplings and the strong Coulomb repulsion, as well as those of the real time ones at a finite temperature, are derived in the mean field approximation. In the limit of the infinitely strong on-site Coulomb repulsion, the system becomes that with the single occupation constraint.
FINITE-SIZE SCALING FOR CELLULAR AUTOMATA WITH RANDOMIZED GRIDS AND FOR FRACTAL RANDOM FIELDS IN DISORDERED SYSTEMS
Authors: SCHÖNFISCH BIRGITT H. , VLAD MARCEL OVIDIU
Published: October 2004

The finite-size effect on the statistics of independent random point processes is analyzed in connection with the theory of cellular automata with randomized grids. The space distribution of a large but finite number N0 of independent particles confined in a large region of ds-dimensional Euclidean space of size VΣ is investigated by using the technique of characteristic functionals. Exact formal expressions are derived for all many-body correlation functions of the positions of the particles as well as for all cumulants of the concentration field. These functions are made up of the contributions of the different negative powers of the total number N0 of particles from the system [Formula: see text] where n =1, 2, … are the orders of the correlation functions or of the cumulants of the concentration field. In the thermodynamic limit N0, VΣ → ∞ with N0 / VΣ = constant only the terms An(0) survive; the other terms An(m) with m > 0 express the finite-size effects. It is shown that, even though the particles are independent, for a finite size of the system a correlation effect different from zero exists among their positions and this correlation vanishes in the limit of an infinite size. The correlation among the positions of the different particles is a finite-size effect due to the conservation of the total number of particles which is similar to the correlation among ideal bosons or fermions at low absolute temperatures. The stochastic properties of an additive scalar field generated by a random distribution of independent particles are investigated. The approach can be applied to the study of stochastic gravitational fluctuations generated by a random distribution of stars or galaxies, of the short-range mean field generated by the particles making up a disordered medium, or of the distribution of the offspring number generated by a plant population randomly distributed in space. Special attention is paid to the finite-size scaling corrections to the long-range self-similar fractal fields. The computations lead to the surprising result that for large values of the resulting field the finite size of the system has practically no influence on the tails of the probability densities of the resulting field, which obey a statistical fractal scaling law of the negative power law type. This apparent paradoxical effect is due to the fact that the very large values of the field corresponding to the tails of the probability densities are generated by the closest neighbor of the test particle considered and are not influenced by the more distant particles.
DYNAMICS OF THE CURVATURE-ENERGY-DRIVEN SURFACES
Authors: KAHNG B. , PARK K.
Published: October 2004

The dynamics of the curvature-energy-driven surfaces such as the dynamics of the orientational roughening (OR) transition and the dynamics of the molecular beam epitaxial (MBE) growth with the lattice pinning force are studied. For the dynamics of the OR transition, we first derive the lattice pinning force of the sine-Gordon model, which is in a peculiar form of [Formula: see text] where {êk} (k =1, 2, 3) are the basis vectors of the triangular lattice. The lattice pinning force is renormalized and contributes to the coarse-grained curvature force under the dynamic renormalization group transformation introduced by Nozières and Gallet [J. Phys. (Paris) 48, 353 (1987)]. The dynamic exponent is obtained as z =4 − ∊ with ∊ =2 − d and the mobility is scaled as r−2.51 ∊ in general dimension d ≤ 2. The tilt-tilt correlation function behaves logarithmically with spatial and temporal changes of scales in two dimensions. Next, we study the dynamic equation of the OR transition with the addition of the growth-induced nonlinear term proportional to ∇2 (∇ϕ)2. It is obtained that the OR transition occurs even in the presence of the growth-induced nonlinear term, but the nature of the phase transition changes by the nonlinear term. We compare our analysis with the recent study of the growth-induced roughening transition by Hwa, Kardar and Paczuski [Phys. Rev. Lett.66, 441 (1991)]. It is also found that the lattice pinning force is irrelevant to the MBE growth.
SINGLE- TO MULTIPLE-LAYER TRANSITIONS OF FLAT AND CURVED GRAPHITE SHEETS
Authors: BOURGEOIS L. N. , BURSILL L A.
Published: October 2004

A model previously developed by the authors in order to describe the energetics of single graphitic sheets (Int. J. Mod. Phys.B9, in press 1995)1 is extended to include interlayer van der Waals forces. It is shown that above a critical size two-layer structures are energetically more favourable than single sheets. When the dangling bond energy is high this crossover size is found to be relatively large, especially for layers with free edges. This suggests the existence of a regime where single sheets are the dominant structures, the majority of which are expected to be closed in order to minimise the dangling bond energy. Partly closed structures may also occur in a slightly out-of-equilibrium environment. This theoretical result is shown to be in good agreement with high resolution transmission electron microscope observations of the sp2-microporous carbon found in conjunction with fullerene-related material. The relevance of this model in understanding the growth of single- and many-layer sp2-carbon structures of nanometric size is also discussed.
HARTREE–FOCK–BOGOLUBOV APPROXIMATION IN THE MODELS WITH GENERAL FOUR-FERMION INTERACTION
Authors: BOGOLUBOV N. N. , SOLDATOV A. V.
Published: October 2004

An approach is proposed which allows one to investigate dynamical and thermodynamical properties of models with four-fermion interaction of general type. The approach combines ideas of the standard Bogolubov's approximating Hamiltonian method for the models with separable interaction with the method of Hartree–Fock approximation based on the ideas of self-consistency.
QUANTUM SUPERCONDUCTING FLUCTUATIONS AND DISSIPATION IN VORTEX STATES
Authors: IKEDA RYUSUKE
Published: October 2004

Quantum effects on renormalized superconducting fluctuations are studied in the context of vortex states. It is argued by taking account of existing resistivity data that inclusion of dissipative (metallic) dynamics is indispensable at any nonzero temperature. Analysis is largely based on simple extensions of the usual time-dependent Ginzburg–Landau (TDGL) dynamics to quantum regime. First, phase diagram and dc conductivities resulting from a quantum GL action with purely dissipative dynamics are investigated, and it is noticed that, on (or, in the vicinity of) the transition line between the vortex lattice and the resulting quantum vortex liquid regime, the inverse of vortex flow conductance becomes a nearly universal value of the order of R q = 6.45 ( k Ω) and independent of material parameters. On the other hands, based on the usual Feynman graph analysis of Kubo formula, the superconducing (i.e. fluctuation) contribution to dc diagonal conductance decreases upon cooling in the disordered phase affected by quantum fluctuations, and becomes zero in T = 0 liquid regime [and above Hc2 (0)] irrespective of the details of dynamics. Reflecting these theoretical results, calculated resistance curves show the behavior quite similar to those observed in homogeneously disordered thin films, even though the presence of a field-tuned insulator–superconductor transition at T = 0 is neglected and the dynamics is purely dissipative. Phenomena in systems with quantum fluctuation of moderate strength are also considered. Analysis is also extended to the cases with other dynamical terms. It is pointed out that the usual (mean field) vortex flow Hall conductivity is never found in any nondissipative T = 0 liquid regime, and argued that, in general, the superconducting Hall effect itself is absent there at low enough fields irrespective of the presence of particle–hole assymmetry. Therefore, in contrast to the thermal vortex states with no pinning disorder, the dc transport phenomena at T = 0 are quite sensitive to the corresponding phase diagram, and hence, discussions based on the single vortex dynamics are even qualitatively invalid in the liquid regime at extremely low temperatures.
PHOTORESPONSE MECHANISMS OF THIN SUPERCONDUCTING FILMS AND SUPERCONDUCTING DETECTORS
Authors: SERGEEV A. V. , YU. REIZER M.
Published: October 2004

The photoresponse of ordinary and high-T c superconductors depends critically on the hierarchy of relaxation times, such as the electron–phonon and phonon–electron scattering times, the time of phonon escape from a superconducting film and also the phonon return time. For thin films of cuprates, close to the superconducting transition the following components of transient response are identified. The picosecond photoresponse is attributed to the dynamics of nonequilibrium quasiparticles and Cooper pairs. The nanosecond response is described by the thermal boundary resistance (the Kapitza resistance) between a superconducting film and a substrate. The microsecond response is associated with the phonon diffusion in the substrate. Using experimental results, we deduce the characteristic time of electron–phonon relaxation and parameters of the film-substrate interface. The kinetic inductance photoresponse of superconductors with s- and d-wave pairing far below the superconducting transition is also calculated. We study parameters (responsivity, operating speed and noise equivalent power) of a nonequilibrium detector, in which only electron states are changed under the radiation, while the film phonons stay in thermodynamic equilibrium with the substrate. Our analysis demonstrates that the nonequilibrium superconducting detectors have essential advantages compared to superconducting bolometers and other detectors.
THERMODYNAMIC RESTRICTION RULES FOR DROPLET MODELS
Authors: SHANENKO A. A. , YUKALOVA E. P. , YUKALOV V. I.
Published: October 2004

Statistical systems whose particles can coagulate, forming compact bound objects called droplets or clusters are considered. We analyze the methods of constructing effective thermodynamic potentials for such systems and of calculating their thermodynamic characteristics. The central point of our paper is the formulation of thermodynamic restriction rules which permit a correct definition of thermodynamic characteristics; not following these rules may lead to unphysical results. The application of the restriction rule is illustrated by a statistical model of quark–gluon clustering matter.
EXCITONS IN A HIGH MAGNETIC FIELD
Authors: KOROLEV ANDREI V. , LIBERMAN MICHAEL A.
Published: October 2004

A high magnetic field, such that the distance between the Landau levels exceeds the binding energy of an exciton, gives an opportunity to create various new states of matter, i.e. exciton crystal, molecular compexes, Bose–Einstein condensation an exciton gas in a semiconductor, depending on the dimensionality of the system. We consider the problem of excitonic interaction in a semiconductor in its multi-electron formulation, starting from the second-quantization representation of the Hamiltonian of interacting electrons and holes in a high magnetic field. A system of excitons in its ground state in a high magnetic field is similar to a weakly non-ideal Bose gas; whereas the excited states may be strongly bounded. It is shown that different types of exciton complexes in a quasi-one-dimensional semiconductor quantum wire, from crystals to molecular chains, can be obtained both by varying the direction and intensity of the magnetic field and by changing the exciton density. The existence and the stability of the Bose condensate in a bulk semiconductor due to an essential decrease of the interaction between excitons and an increase of their binding energy in a high magnetic field are established at a high density of excitons. Existence of the built-in condensate of excitons in a broad density range significantly changes the excitation spectrum of coupled excitons and photons in a high magnetic field and results in a number of interesting optical phenomena.
POSSIBILITY OF GEOMETRIC DESCRIPTION OF QUASIPARTICLES IN SOLIDS
Authors: DANILOV YU. A. , ROZHKOV A. V. , SAFONOV V. L.
Published: October 2004

New phenomenological approach for the description of elementary collective excitations is proposed. The crystal is considered to be an anisotropic space-time vacuum with a prescribed metric tensor in which the information on electromagnetic crystalline fields is included. The quasiparticles in this space are supposed to be described by the equations structurally similar to the relativistic wave equations for particles in empty space. The generalized Klein–Gordon–Fock equation and the generalized Dirac equation in external electromagnetic field are considered. The applicability of the proposed approach to the case of conduction electron in a crystal is discussed.
A FIELD THEORY FOR THE READ OPERATOR
Authors: RAJARAMAN R. , SONDHI S. L.
Published: October 2004

We introduce a new field theory for studying quantum Hall systems. The quantum field is a modified version of the bosonic operator introduced by Read. In contrast to Read's original work we do not work in the lowest Landau level alone, and this leads to a much simpler formalism. We identify an appropriate canonical conjugate field, and write a Hamiltonian that governs the exact dynamics of our bosonic field operators. We describe a Lagrangian formalism, derive the equations of motion for the fields and present a family of mean-field solutions. Finally, we show that these mean field solutions are precisely the Laughlin states. We do not, in this work, address the treatment of fluctuations.
THE EXOTIC BARIUM BISMUTHATES
Authors: TARAPHDER A. , PANDIT RAHUL , KRISHNAMURTHY H. R. , RAMAKRISHNAN T. V.
Published: October 2004

We review the remarkable properties, including superconductivity, charge-density-wave ordering and metal–insulator transitions, of lead- and potassium-doped barium bismuthate. We will discuss some of the early theoretical studies of these systems. Our recent theoretical work, on the negative-U, extended-Hubbard model for these systems, will also be described. Both the large- and intermediate-U regimes of this model were examined, using mean-field and random-phase approximations, particularly with a view to fitting various experimental properties of these bismuthates. On the basis of our studies, we point out possibilities for exotic physics in these systems. We also emphasize the different consequences of electronic and phonon-mediated mechanisms for the negative U. We show that, for an electronic mechanism, the semiconducting phases of these bismuthates must be unique, with their transport properties dominated by charge±2eCooperon bound states. This can explain the observed difference between the optical and transport gaps. We propose other experimental tests for this novel mechanism of charge transport and comment on the effects of disorder.
RAPIDLY ANNEALED Bi(Pb)SrCaCuO THIN FILMS PREPARED BY A 2223 STOICHIOMETRIC TARGET SPUTTERING
Authors: HIGO S. , KOBA S. , HAKURAKU Y. , OGUSHI T. , KAWANO I. , NAKAO A.
Published: October 2004

Thin films of BiSrCaCuO were prepared on MgO (100) by a single target sputtering. This deposition process yielded c-axis oriented superconducting thin films with a smooth surface. The as-grown films grown at 670–690°C showed 2223 single phase and zero resistivity at about 60 K. The as-grown films were directly placed on a Bi(Pb)SrCaCuO bulk sample, and then rapidly annealed at 835–845°C within 40 s in air. The superconducting properties of the annealed Bi(Pb)SrCaCuO films were greatly improved by optimizing the temperature and time during rapid annealing. Films annealed at 840°C for 30s in air showed zero resistivity at 100 K and had the critital current of about 1×106 A/cm 2 at 77 K. The surfaces of these films on MgO were black and smooth. The film quality is greatly improved by means of annealing process at 840°C for a very short time of 30 s in air after deposition.
TRANSPORT PROPERTIES AND AC SUSCEPTIBILITIES OF (Bi1.6Pb0.4)(Sr1.8Ba0.2)Ca2(Cu1–xNix)3Oy SUPERCONDUCTOR
Authors: POP A. V. , ILONCA GH. , CIURCHEA D. , YE M. , DELTOUR R. , GERU I. I. , KANTSER V. G. , KONOPKO L.A. , GERU V.I.
Published: October 2004

The effect of the partial substitution of Cu by Ni in the stabilized 108 K phase was investigated by electrical resistance and a.c. susceptibility measurements. Up to a Ni concentration x = 0.02 the bending of the R (T) curve above T c can be described in the terms of the Lawrence-Doniach theory. The intergrain and intragrain critical transition temperatures decrease to ∆T CG = 9 K and ∆T j = 10.9 K respectively by the Ni substitution in the Cu-O pyramids.
CLASSICAL BAND STRUCTURE OF PERIODIC ELASTIC COMPOSITES
Authors: KUSHWAHA MANVIR S.
Published: October 2004

The rich diversity and the fundamental character of the essential theoretical problems associated with it have given band theory a width of interest which contrasts strongly with the apparent narrowness of its subject matter. This review, dealing mainly with the classical band structures of periodic elastic and acoustic binary systems, offers briefly a systematic survey of the historical development of the principles, tools, and applications of band theory for electrons, phonons, photons, and vibrations giving what may be called the "background" to the more recent developments in the fields of photonic and phononic band-gap crystals. Attention is given to survey the physical conditions required to achieve the complete spectral gaps within which the respective propagating modes are utterly forbidden irrespective of the direction of propagation. The existence of complete spectral gaps for cleverly synthesized photonic crystals guarantees the observability of classical Anderson localization of photons and the influence on the spontaneous emission which was, until the 1980's, often regarded as a natural and uncontrollable phenomenon. The phononic band-gap crystals, on the other hand, offer the feasibility of constructing the ultrasound filters, polarization filters, and improvements in designing the transducers, as well as the observability of classical elastic or acoustic wave localization. Abiding by the central theme of the review, numerous theoretical results on the band structure related problems for periodic elastic and acoustic binary sytems have been gathered and reviewed. This survey is preceded by a detailed mathematical machinery that provides the reader with numerous useful analytical results applicable to a wide range of systems of varying interest. Finally, the report concludes with a summary of anticipated implications of photonic and phononic band-gap crystals and proposes some interesting relevant problems concerned with the spectral gaps and the classical wave localization. Our satisfaction in writing this review, like any other review which covers a considerably longer period, was to reach a reasonably self-contained unity by wanting to "leave nothing unexplained". The background provided is believed to make less formidable the task of future writers of reviews in this rather general field and hence enable them to deal more readily with particular aspects of the subject, or with recent advances in those directions in which notable progress may have been made.
ON SELF-ORGANIZED CRITICALITY AND SYNCHRONIZATION IN LATTICE MODELS OF COUPLED DYNAMICAL SYSTEMS
Authors: PÉREZ CONRAD J. , CORRAL ÁLVARO , DÍAZ-GUILERA ALBERT , CHRISTENSEN KIM , ARENAS ALEX
Published: October 2004

Lattice models of coupled dynamical systems lead to a variety of complex behaviors. Between the individual motion of independent units and the collective behavior of members of a population evolving synchronously, there exist more complicated attractors. In some cases, these states are identified with self-organized critical phenomena. In other situations, they are identified with clusterization or phase-locking. The conditions leading to such different behaviors in models of integrate-and-fire oscillators and stick-slip processes are reviewed.
LOW FREQUENCY MODES PROBED BY TIME-DOMAIN OPTICAL KERR EFFECT SPECTROSCOPY
Authors: KINOSHITA S. , KAI Y. , ARIYOSHI T. , SHIMADA Y.
Published: October 2004

The principle and application of ultrafast optical Kerr effect (OKE) spectroscopy have been reviewed. This spectroscopy is shown to be very useful to investigate low frequency modes in disordered materials and the obtained data are directly comparable with frequency-domain light scattering spectroscopy. Experimental study to show the consistency between the time- and frequency-domain spectroscopy has been performed for liquid nitrobenzene and the excellent agreement is attained over three orders of magnitude in frequency range. It is also shown that the result obtained by the OKE measurement is consistent with that obtained by four wave mixing spectroscopy. Combination of these spectroscopic techniques is particularly suited for the investigation of low frequency modes because a wide frequency range is covered with great accuracy. Several remarks concerning the OKE spectroscopy are presented such as the breakdown of Debye relaxation model and various interference effects which may distort the time-domain data.
QUANTUM DENSITY OF PROBABILITY AT THE CLASSICAL PECULIAR POINT
Authors: BUONANNO L. , RENNA M. , PAVLOTSKY I.P.
Published: October 2004

The so-called no-interaction theorem of D.G. Currie, T.F. Jordan, E.C. Sudarshan, H. Leutwyler, G. Marmo and N. Mukunda makes it possible to construct relativistic quasi-classical particle dynamics in the post-Galilean approximation only.1−4 In this approximation the Lagrangians are singular on some surfaces of the phase space. The dynamical properties are essentially peculiar on the singular surfaces.5−8 In the particular case of the rectilinear motion of two electrons the peculiar point appears when the distance between the particles r=r0, where r0=e2/mc2 (the so-called “radius of an electron”). Here m and e are respectively the mass and the charge of the electron, c is the speed of light.

In this paper it is shown that in the simple case of a one-dimensional system of two electrons with the symmetrical initial condition v1=−v2 (v1 and v2 are the velocities of the particles), the density of probability tends to zero when the distance between electrons tends to r0. In other words, the point of the classical phase-space, which cannot be crossed by the trajectory of the system, reflects at the point where the corresponding quantum system has the vanishing probability.
SELF-CONSISTENT SUBBAND STRUCTURE OF MODULATION-DOPED AlxGa1−xAs-GaAs-AlxGa1−xAs DOUBLE QUANTUM WELLS
Authors: XU W.
Published: October 2004

A detailed theoretical study of the electronic subband structure of a two-dimensional semiconductor system is presented for low temperatures. By considering Si modulationdoped Al x Ga 1−x As-GaAs-Al x Ga 1−x As-GaAs-Al x Ga 1−x As double quantum wells (DQWs), a model is developed in which the interested electronic properties, such as confining potential, energy and wavefunction of the electronic subband, electron density, depletion length, etc., can be calculated self-consistently as function of known material properties, sample growth parameters and experimental conditions. We study the influence of the sample parameters and the applied gate voltage on the electronic properties of the DQWs. The main results are: (i) the electronic properties (e.g. electron density, electronic subband energy, depletion length, etc.) of a DQW are very sensitive to the sample growth parameters and to the applied gate voltage; (ii) the energy separation of symmetric and antisymmetric levels in a DQW depends strongly on the widths of the well layer, the separation of the two quantum wells, and on the gate voltage; (iii) the asymmetric modulation-doping has a relatively weak effect on the electronic subband energies of the DQW; and (iv) the electron density and the population of electrons to the electronic subband in the structure can be varied by applying the gate voltage and/or by changing the width of quantum well.
ELECTRON-PHONON COUPLING CLOSE TO A METAL-INSULATOR TRANSITION IN ONE DIMENSION
Authors: FABRIZIO MICHELE , CASTELLANI CLAUDIO , DI CASTRO CARLO
Published: October 2004

We consider a one-dimensional system of electrons interacting via a short-range repulsion and coupled to phonons close to the metal-insulator transition at half-filling. We argue that the metal-insulator transition can be described as a standard one-dimensional incommensurate to commensurate transition, even if the electronic system is coupled to the lattice distortion. By making use of known results for this transition, we prove that low-momentum phonons, with the inclusion of the 4kF (≃2π near half-filling) scattering, do not play any relevant role close to the metal-insulator transition, unless their coupling to the electrons is large in comparison with the other energy scales present in the problem. In other words the effective strength of the low-momentum transferred electron-phonon coupling does not increase close to the metal-insulator transition, even though the effective velocity of the mobile carriers is strongly diminished.
QUANTUM ANALYSIS, NONEQUILIBRIUM DENSITY MATRIX AND ENTROPY OPERATOR
Authors: SUZUKI MASUO
Published: October 2004

The present paper gives a brief review of the new concept of quantum analysis and derives several basic equations on the nonequilibrium density matrix and entropy operator, using the quantum analysis.
p-ADIC HILBERT SPACE REPRESENTATION OF QUANTUM SYSTEMS WITH AN INFINITE NUMBER OF DEGREES OF FREEDOM
Authors: ALBEVERIO SERGIO , KHRENNIKOV ANDREW
Published: October 2004

Gaussian measures on infinite-dimensional p-adic spaces are introduced and the corresponding L2-spaces of p-adic valued square integrable functions are constructed. Representations of the infinite-dimensional Weyl group are realized in p-adic L2-spaces. p-adic Hilbert space representations of quantum Hamiltonians for systems with an infinite number of degrees of freedom are constructed. Many Hamiltonians with potentials which are too singular to exist as functions over reals are realized as bounded symmetric operators in L2-spaces with respect to a p-adic Gaussian measure.
ABOUT THE OVERLAP DISTRIBUTION IN MEAN FIELD SPIN GLASS MODELS
Authors: GUERRA FRANCESCO
Published: October 2004

We continue our presentation of mathematically rigorous results about the Sherrington-Kirkpatrick mean field spin glass model. Here we establish some properties of the distribution of overlaps between real replicas. They are in full agreement with the Parisi accepted picture of spontaneous replica symmetry breaking. As a byproduct, we show that the self-averaging of the Edwards-Anderson fluctuating order parameter, with respect to the external quenched noise, implies that the overlap distribution is given by the Sherrington-Kirkpatrick replica symmetric Ansatz. This extends previous results of Pastur and Scherbina. Finally, we show how to generalize our results to realistic short range spin glass models.
SOLITON SECTOR OF THE XY MODEL
Authors: ARAKI HUZIHIRO
Published: October 2004

We study soliton sectors of the XY model by using known results and methods about its ground states. In the regions of parameters for which ground states are not unique, we show that (1) there are two soliton sectors depending on parameters of the model analytically in a well-defined sense, (2) the only sectors with “finite energy” are ground state and soliton sectors, and (3) the sudden appearance of additional ground states at a pair of specific values of parameters (despite analytic dependence of other ground states on parameters at those specific values), which were found in earlier study of ground states, can be understood as the degeneracy of one particle energy in the soliton sector (which has a continuous spectrum at other values of parameters) to a single point spectrum with infinite multiplicity at the specific values of parameters.
MEMBRANE VACUUM AS A TYPE II SUPERCONDUCTOR
Authors: Ansoldi S. , Aurilia A. , Spallucci E.
Published: October 2004

We study a functional field theory of membranes coupled to a rank-three tensor gauge potential. We show that gauge field radiative corrections lead to membrane condensation which turns the gauge field into a massive spin-0 field. This is the Coleman-Weinberg mechanism for membranes. An analogy is also drawn with a type-II superconductor. The ground state of the system consists of a two-phase medium in which the superconducting background condensate is “pierced” by four-dimensional domains, or “bags”, of non-superconducting vacuum. Bags are bounded by membranes whose physical thickness is of the order of the inverse mass acquired by the gauge field.
YANGIAN SYMMETRY OF THE TWO-COMPONENT FERMIONIC NONLINEAR SCHRÖDINGER MODEL
Authors: MURAKAMI SHUICHI , WADATI MIKI
Published: October 2004

The quantum nonlinear Schrödinger model with two-component fermions exhibits a Yangian symmetry when considered on an infinite interval. We construct the generators of the Yangian using one representation of the degenerate affine Hecke algebra. We discuss the connection between the Yangian symmetry and the quantum inverse scattering method. Under the Yangian algebra the space of states with a fixed particle number forms a tensor product representation of fundamental representations.
SOME PROPERTIES OF THE POSITIVE-U AND NEGATIVE-U HUBBARD MODEL
Authors: MANCINI F. , MARINARO M. , MATSUMOTO H.
Published: October 2004

In this article we review the properties of the 2D Hubbard model by considering at the same time the cases of repulsive and attractive interaction. The paramagnetic solution is studied by means of the composite operator method in the static approximation for the case of half-filling. Some properties of the two models, as the double occupancy and the spin magnetic susceptibility, are calculated for various values of interaction and temperature and compared. In particular, the different role played by thermal fluctuations is analyzed. Analytical and numerical calculations show that there is a critical value of the interaction, Uc, where the system exhibits a metal-insulator transition. At zero temperature it is found that Uc=−W for the negative-U model and Uc≈1.68W for the positive-U model, where W is the band width. At zero temperature, when the strength of the attractive interaction equals the band width, the system exhibits a phase transition to a pair state, where all the electrons are locally paired. The temperature Tp which controls the crossover to the pair state is calculated as a function of U. For strong attractive interaction χ0 is strongly depressed; increases by increasing T and tends to zero as T→TP.
CLUES TO THE EXISTENCE OF DETERMINISTIC CHAOS IN RIVER FLOW
Authors: PORPORATO AMILCARE , RIDOLFI LUCA
Published: October 2004

The present work investigates the existence of a component of deterministic chaos in the discharge time series of a river. The first part of the work is concerned with the reconstruction of the attractor and the calculation of the correlation integral; in the second part the analysis is conducted with the aid of nonlinear prediction. Some clues emerge as to the possible presence of chaos, probably immersed in a phenomenon altogether more extensive and manifold. If confirmed, this presence could provide interesting openings for a better comprehension of the formation mechanism of river flow, and a more precise forecasting of floods.
QUASIPARTICLE MANY-BODY DYNAMICS OF THE ANDERSON MODEL
Authors: KUZEMSKY A.L.
Published: October 2004

The paper addresses the many-body quasiparticle dynamics of the Anderson impurity model at finite temperatures in the framework of the equation-of-motion method. We find a new exact identity relating the one-particle and many-particle Green’s functions. Using this identity we present a consistent and general scheme for a construction of generalized mean fields (elastic scattering corrections) and self-energy (inelastic scattering) in terms of Dyson equation. A new approach for the complex expansion for the single-particle propagator in terms of Coulomb repulsion U and hybridization V is proposed. Using the exact identity, the essentially new many-body dynamical solution of SIAM has been derived. This approach offers a new way for the systematic construction of the approximative interpolating dynamical solutions of the strongly correlated electron systems.
ANALYTIC RESULTS FOR THE DIFFUSION COEFFICIENT OF A PIECEWISE LINEAR MAP
Authors: TSENG HSEN-CHE , CHEN HUNG-JUNG
Published: October 2004

For a piecewise linear map parameterized by a parameter a which exhibits deterministic diffusion, we have previously found, using computer experiment, that the diffusion coefficient D depends on the parameter a in an interesting and unexpected way.6 In that study, D was exactly calculated for six values of a. In this follow-up study, we use Markov diagrams within the framework of cycle expansions to determine D analytically for thirty-eight values of a between zero and one. We have found, interestingly, that for some cases the pruning rules of the system are infinite but recurrent. Whence, as the complexity of their symbolic dynamics increases, more and more values of a with soluble D’s are expected to be found systematically. Thus, we hope, the profile of D could be fully understood.
MEAN-FIELD STUDY OF SURFACE AND INTERFACE PROPERTIES IN TERMS OF NONLINEAR MAPS
Authors: TRALLORI LEONARDO , GLORIA PINI MARIA , RETTORI ANGELO , MACCIÒ MONICA , POLITI PAOLO
Published: October 2004

In systems with free surfaces and interfaces, the absence of translational invariance may result in a completely different behavior with respect to the corresponding bulk system, so that many new and interesting phenomena may take place, as for example, the occurrence of a surface reconstruction phenomenon, characterized by an order at the surface different from the one which occurs deep in the sample. This article reviews the mean-field approach to surface and interface properties as a problem in nonlinear dynamics. We focus our attention on magnetic films and superlattices, whose properties are studied in terms of area-preserving maps; the emphasis is put on the effect of the surfaces, which are introduced as appropriate boundary condition, and which let exotic solution become physically relevant, though the infinitely extended system is trivially solvable. The importance of the discreteness of the lattice and of chaotic regimes in the map phase space is stressed. Some specific applications are given: (i) the magnetic field dependence of the ground state of semi-infinite uniaxial antiferromagnets and films, so that the anomalous behavior of the magnetic susceptibility experimentally observed in Fe/Cr(211) superlattices is easily accounted for as related to the chaotic nature of the corresponding map; (ii) the ground state and the temperature dependence of the magnetization of a ferromagnet with an enhanced surface exchange, and with a surface anisotropy favoring the spins to lie perpendicularly to the film plane, while a bulk anisotropy favors an in plane spin configuration.
PHENOMENOLOGICAL THEORY OF THE DIELECTRIC RESPONSE OF LEAD MAGNESIUM NIOBATE AND LEAD SCANDIUM TANTALATE
Authors: QIAN H. , BURSILL L.A.
Published: October 2004

The influence of the random field effects originating from charged chemical defects and nano-domain textures on the formation and dynamics of polar clusters is analyzed. The spatial distribution of the local fields is not totally random but contains some correlations in direction and strength.

Polar clusters are classified to be dynamic or frozen according to their dynamic characteristics in the random fields. The relaxation formula of a dipolar moment in an anisotropic double-well potential is deduced. Two percolation models are introduced, one to account for frustration effects associated with multiple orientations of polar clusters, which results in a broad diffuse dielectric response and the second to account for the case whereby there may be a phase transition to a ferroelectric state. The dielectric permittivity and dissipation factor of the typical relaxors lead magnesium niobate and lead scandium tantalate are predicted as a function of both temperature and frequency, which results are in good agreement with the experimental measurements.
RANDOM-FIELD POTTS MODEL FOR THE POLAR DOMAINS OF LEAD MAGNESIUM NIOBATE AND LEAD SCANDIUM TANTALATE
Authors: QIAN H. , BURSILL L.A.
Published: October 2004

A random field Potts model is used to establish the spatial relationship between the nanoscale distribution of charged chemical defects and nanoscale polar domains for the perovskite-based relaxor materials lead magnesium niobate (PMN) and lead scandium tantalate (PST). The random fields are not set stochastically but are determined initially by the distribution of B-site cations (Mg,Nb) or (Sc,Ta) generated by Monte Carlo NNNI-model simulations for the chemical defects. An appropriate random field Potts model is derived and algorithms developed for a 2D lattice. It is shown that the local fields are strongly correlated with the chemical domain walls and that polar nanodomains tend to nucleate about the latter. The evolution of the polar domains as a function of decreasing temperature is simulated for the two cases of PMN and PST. The dynamics of the polar clusters is also discussed. The results are used in an accompanying paper (H. Qian and L.A. Bursill, Int. J. Mod. Phys.B10, 2007, 1996) in order to predict the temperature and frequency dependence of the dielectric response of these two relaxors.
RELATION BETWEEN A CLASS OF QUASIPERIODIC LATTICES GENERATED BY THE SUBSTITUTION METHOD AND THE GENERALIZED CONTINUED FRACTION EXPANSION
Authors: YOSHIKAWA TOSHIO , IGUCHI KAZUMOTO
Published: October 2004

The continued fraction expansion for a positive real number is generalized to that for a set of positive real numbers. For arbitrary integer n≥2, this generalized continued fraction expansion generates (n−1) sequences of positive integers {ak}, {bk}, … , {yk} from a given set of (n−1) positive real numbers α, β, …ψ. The sequences {ak}, {bk}, … ,{yk} determine a sequence of substitutions Sk: A → Aak Bbk…Yyk Z, B → A, C → B,…,Z → Y, which constructs a one-dimensional quasiperiodic lattice with n elements A, B, … , Z. If {ak}, {bk}, … , {yk} are infinite periodic sequences with an identical period, then the ratio between the numbers of n elements A, B, … , Z in the lattice becomes a : β : … : ψ : 1. Thereby the correspondence is established between all the sets of (n−1) positive real numbers represented by a periodic generalized continued fraction expansion and all the one-dimensional quasiperiodic lattices with n elements generated by a sequence of substitutions with a finite period.
POSSIBLE ELECTRONIC STRUCTURE OF DOMAIN WALLS IN MOTT INSULATORS
Authors: NAYAK CHETAN , WILCZEK FRANK
Published: October 2004

We discuss the quantum numbers of domain walls of minimal length induced by doping Mott insulators, carefully distinguishing between holon and hole walls. We define a minimal wall hypothesis that uniquely correlates the observed spatial structure with the doping level for the low-temperature commensurate insulating state of La 2−x Ba x CuO 4 and related materials at x = ⅛. We remark that interesting walls can be supported not only by conventional antiferromagnetic but also by orbital antiferromagnetic (staggered flux phase, d-density) bulk order. We speculate on the validity of the minimal wall hypothesis more generally, and argue that it plausibly explains several of the most striking anomalous features of the cuprate high-temperature superconductors.