August 1999 arXiv papers — page 6

WA89 Collaboration, M. I. Adamovich

The production of charmed particles by Sigma- of 340 Gev/c momentum was studied in the hyperon beam experiment WA89 at the CERN-SPS, using the Omega-spectrometer. In two data-taking periods in 1993 and 1994 an integrated luminosity of 1600 microb^-1 on copper and carbon targets was recorded. From the reconstruction of 930 +- 90 charm particle decays in 10 de

YBJ Collaboration

An RPC carpet covering ~10**4 m**2 (ARGO-YBJ experiment) will be installed in the YangBaJing Laboratory (Tibet, P.R. China) at an altitude of 4300 m a.s.l.. A test-module of ~50 m**2 has been put in operation in this laboratory and about 10**6 air shower events have been collected. The carpet capability of reconstructing the shower features is presented.

Leonardo Sigalotti, Richard F. Stark

We give a preliminary report on one of the tests we have performed of a full non-axisymmetric general relativistic code. The test considered here concerns the numerical evolution of vacuum non-axisymmetric gravitational waves and their comparison at low amplitudes with theoretical waveforms obtained from linearised theory.

I. Miskovic, Dj. Sijacki

A generalization of the Dirac field equation in three-dimensional Minkowski space-time to the case of the $\bar{SL}(3,R)$ $\subset$ $\bar{SA}(3,R)$ symmetry is considered. Constraints that ensure a correct physical interpretation of the corresponding particle states are presented. Dirac-like equations based on both multiplicity-free and generic infinite-comp

Dj. Sijacki

The aim of this paper is to discuss a kinematical algebraic structure of a theory of gravity, that would be unitary, renormalizable and coupled in the same manner to both spinorial and tensorial matter fields. An analysis of the common features as well as differences of the Yang-Mills theories and gauge theories of gravity is carried out. In particular, we c

L. Rondoni, E. G. D. Cohen

Recently a number of approaches has been developed to connect the microscopic dynamics of particle systems to the macroscopic properties of systems in nonequilibrium stationary states, via the theory of dynamical systems. This way a direct connection between dynamics and Irreversible Thermodynamics has been claimed to have been found. However, the main quant

L. Bellaiche, David Vanderbilt

We present an approach to the implementation of the virtual crystal approximation (VCA) for the study of properties of solid solutions in the context of density-functional methods. Our approach can easily be applied to any type of pseudopotential, and also has the advantage that it can be used to obtain estimates of the atomic forces that would arise if the

B. Meyer, J. Padilla, David Vanderbilt

First-principles total-energy calculations are carried out for (001) surfaces of the cubic perovskite ATiO3 compounds PbTiO3, BaTiO3, and SrTiO3. Both AO-terminated and TiO2-terminated surfaces are considered, and fully-relaxed atomic configurations are determined. In general, BaTiO3 and SrTiO3 are found to have a rather similar behavior, while PbTiO3 is dif

F. Lacombe, S. Zapperi, H. J. Herrmann

We introduce a simple model to describe the frictional properties of granular media under shear. We model the friction force in term of the horizontal velocity v and the vertical position z of the slider, interpreting z as a constitutive variable characterizing the contact. Dilatancy is shown to play an essential role in the dynamic, inducing a stick-slip in

Marco Evangelisti, Juan Bartolome, Fernando Luis

The Mn cluster complexes Mn12(RCOO)16(H2O)4O12 with R=CH3 and 2ClPh (hereafter referred to as Mn12 acetate and Mn12 2-Cl benzoate, respectively) exhibit macroscopic magnetic quantum tunneling. Dynamical magnetic measurements indicate for both samples that the anisotropy energy barrier is nearly the same and that the relaxation times have sharp minima at the

A. Bock, S. Ostertun, K. -O. Subke

We investigate the Fano-type line shape of the Ba mode of Y_{1-x}Ca_xBa_2Cu_3O_{6+y} films observed in Raman spectra with A_1g symmetry. The line shape is described with an extended Fano formula that allows us to obtain the bare phonon parameters and the self-energy effects based on a phenomenological description of the real and imaginary part of the low-ene

A. Bock, S. Ostertun, R. Das Sharma, M. R"ubhausen

In Raman spectra of cuprate superconductors the gap shows up both directly, via a redistribution of the electronic background, the so-called "2Delta peaks", and indirectly, e.g. via the renormalization of phononic excitations. We use a model that allows us to study the redistribution and the related phonon self-energy effects simultaneously. We apply

J. M. Keartland, R. A. Doyle

We present results for the in-plane resistivity as a function of temperature for clean single crystal samples of BSCCO-2212 in applied magnetic fields above 0.5 T. Several fixed angles between the magnetic field and the crystal c-axis were studied. The data were analysed in terms of the vortex-glass (VG) model, as suggested by previous experimental studies.

T. Nattermann, T. Emig, S. Bogner

Thermal fluctuations are known to play an important role in low-dimensional systems which may undergo incommensurate-commensurate or (for an accidentally commensurate wavevector) lock-in transitions. In particular, an intermediate floating phase with algebraically decaying correlations exists only in D=2 dimensions, whereas in higher dimensions most features

M. Tissier, D. Mouhanna, B. Delamotte

We investigate the principal chiral model between two and four dimensions by means of a non perturbative Wilson-like renormalization group equation. We are thus able to follow the evolution of the effective coupling constants within this whole range of dimensions without having recourse to any kind of small parameter expansion. This allows us to identify its

S. E. Mangioni, R. R. Deza, R. Toral, H. Wio

A recently introduced lattice model, describing an extended system which exhibits a reentrant (symmetry-breaking, second-order) noise-induced nonequilibrium phase transition, is studied under the assumption that the multiplicative noise leading to the transition is colored. Within an effective Markovian approximation and a mean-field scheme it is found that

C. Bechinger, D. Rudhardt, P. Leiderer, R. Roth

The effective interaction energy of a colloidal sphere in a suspension containing small amounts of non-ionic polymers and a flat glass surface has been measured and calculated using total internal reflection microscopy (TIRM) and a novel approach within density functional theory (DFT), respectively. Quantitative agreement between experiment and theory demons

M. Stopa

We calculate the electronic structure for a modulation doped and gated T-shaped quantum wire using density functional theory. We calculate the bandgap renormalization as a function of the density of conduction band electrons, induced by the donor layer and/or the gate, for the translationally invariant wire, incorporating all growth and geometric properties

H. Potempa, L. Schweitzer

The localization properties of electrons moving in a plane perpendicular to a spatially-correlated static magnetic field of random amplitude and vanishing mean are investigated. We apply the method of level statistics to the eigenvalues and perform a multifractal analysis for the eigenstates. From the size and disorder dependence of the variance of the neare

A. Barrat, M. Weigt

We study the small-world networks recently introduced by Watts and Strogatz [Nature {\bf 393}, 440 (1998)], using analytical as well as numerical tools. We characterize the geometrical properties resulting from the coexistence of a local structure and random long-range connections, and we examine their evolution with size and disorder strength. We show that

P. E. J. Nulsen, A. C. Fabian

We consider a model for quasar formation in which massive black holes are formed and fuelled largely by the accretion of hot gas during the process of galaxy formation. In standard hierarchical collapse models, objects about the size of normal galaxies and larger form a dense hot atmosphere when they collapse. We show that if such an atmosphere forms a nearl

Kandaswamy Subramanian

Helical turbulence is thought to provide the key to the generation of large-scale magnetic fields. Turbulence also generically leads to rapidly growing small-scale magnetic fields correlated on the turbulence scales. These two processes are usually studied separately. We give here a unified treatment of both processes, in the case of random fields, incorpora

Y. Lebreton, M. -N. Perrin, R. Cayrel, A. Baglin

From an initial sample of a few hundred stars selected for an Hipparcos program, a subsample of 33 objects with direct determination of their effective temperature, bolometric magnitude and [Fe/H] has been derived. An accurate observational (logTeff, Mbol) HR diagram has been obtained, and compared to theoretical isochrones. Attention has been concentrated o

Sean A. Hartnoll, Eric G. Blackman

Flourescent iron line profiles currently provide the best diagnostic for active galactic nuclei (AGN) engine geometries. Here we construct a method for calculating the relativistic iron line profile from an arbitrarily warped accretion disc, illuminated from above and below by hard X-ray sources. This substantially generalises previous calculations of reproc

Xiang-Dong Li, Subharthi Ray, Jishnu Dey, Mira Dey

The discovery of kilohertz quasi-periodic oscillations (kHz QPOs) in low-mass X-ray binaries (LMXBs) with the Rossi X-ray Timing Explorer has stimulated extensive studies of these sources. Recently, Osherovich & Titarchuk suggest a new model for kHz QPOs and the related correlations between kHz QPOs and low frequency features in LMXBs. Here we use their resu

Mauricio Bellini

I study a semiclassical approach to warm inflation scenario introduced in previous works. In this work, I define the fluctuations for the matter field by means of a new coarse - grained field with a suppression factor G. This field describes the matter field fluctuations on the now observable scale of the universe. The power spectrum for the fluctuations of

Zheng Yin

We consider a two-point spatial lattice approximation to an open string moving in a flat background with B field. It gives a constrained dipole system under the influence of a vector potential. Solving and quantizing this system recover all the essential features of a noncommutative space. In particular, open string interactions induce a canonical product st

J. J. Palacios

A projected order parameter is used to calculate, not only local minima of the Ginzburg-Landau energy functional, but also saddle points or energy barriers responsible for the metastabilities observed in superconducting mesoscopic disks (Geim et al. Nature {\bf 396}, 144 (1998)). We calculate the local minima magnetization and find the energetic instability

J. M. Pons, J. Antonio Garcia

We develop the general theory of Noether symmetries for constrained systems. In our derivation, the Dirac bracket structure with respect to the primary constraints appears naturally and plays an important role in the characterization of the conserved quantities associated to these Noether symmetries. The issue of projectability of these symmetries from tange

I. Bena, M. Copelli, C. Van den Broeck

We derive the explicit analytic expression for the Stokes' drift in one dimension in the presence of a dichotomic Markov forcing. For small amplitudes of the forcing, the drift is enhanced, but the enhancement is reduced with increasing frequency of the forcing. On the other hand, a reduction of the drift or even a flux reversal can be induced at larger

Manuel Reenders

We study a particular class of Abelian gauged Nambu-Jona-Lasinio models with global U_L(N)xU_R(N) symmetry, where N is the number of fermion flavors. We show, by treating the gauge interaction in the ladder approximation and four-fermion interactions in the leading order of the 1/N expansion, that the renormalization-group beta function of the U(1) gauge cou

C. Adloff, H1 Collaboration

The inclusive single and double differential cross-sections for neutral and charged current processes with four-momentum transfer squared Q^2 between 150 and 30,000 GeV2 and with Bjorken x between 0.0032 and 0.65 are measured in e^+ p collisions. The data were taken with the H1 detector at HERA between 1994 and 1997, and they correspond to an integrated lumi

Mickael Antoni, Stefano Ruffo, Alessandro Torcini

In this paper we review a series of results obtained for 1D and 2D simple N-body dynamical models with infinite-range attractive interactions and without short distance singularities. The free energy of both models can be exactly obtained in the canonical ensemble, while microcanonical results can be derived from numerical simulations. Both models show a pha

Inge S. Helland

The aim of this paper is to show a connection between an extended theory of statistical experiments on the one hand and the foundation of quantum theory on the other hand. The main aspects of this extension are: One assumes a hyperparameter space $Φ$ common to several potential experiments, and a basic symmetry group G associated with this space. The paramet

Inge S. Helland

A version of quantum theory is derived from a set of plausible assumptions related to the following general setting: For a given system there is a set of experiments that can be performed, and for each such experiment an ordinary statistical model is defined. The parameters of the single experiments are functions of a hyperparameter, which defines the state

Bidhan Chandra Bag, Jyotipratim Ray Chaudhuri, Deb Shankar Ray

We consider a general N-degree-of-freedom nonlinear Hamiltonian system which is chaotic and dissipative and show that the origin of chaotic diffusion lies in the correlation of fluctuation of linear stability matrix for the equation of motion of the dynamical system whose phase space variables behave as stochastic variables in the chaotic regime. Based on a

Yu Shi

According to Deutsch, a universal quantum Turing machine (UQTM) is able to perform, in repeating a fixed unitary transformation on the total system, an arbitrary unitary transformation on an arbitrary data state, by including a program as another part of the input state. We note that if such a UQTM really exists, with the program state dependent on the data

J. L. Chkareuli, I. G. Gogoladze, M. G. Green, D. E. Hutchcroft

A minimal lepton number violation (LNV) is proposed which could naturally appear in SUSY theories, if Yukawa and LNV couplings had a common origin. According to this idea properly implemented into MSSM with an additional abelian flavor symmetry the prototype LNV appears due to a mixing of leptons with superheavy Higgs doublet mediating Yukawa couplings. As a

Farhad H Jafarpour

We study a generalized two-species model on a ring. The original model [1] describes ordinary particles hopping exclusively in one direction in the presence of an impurity. The impurity hops with a rate different from that of ordinary particles and can be overtaken by them. Here we let the ordinary particles hop also backward with the rate q. Using Matrix Pr

Shoichi Ichinose

We present a new regularization method, for d dim (Euclidean) quantum field theories in the continuum formalism, based on the domain wall configuration in (1+d) dim space-time. It is inspired by the recent progress in the chiral fermions on the lattice. The wall "height" is given by 1/M, where M is a regularization mass parameter and appears as a 1+d

Yasuhiro Fujii, Miki Wadati

The XYZ spin chain is considered in the framework of the generalized algebraic Bethe ansatz developed by Takhtajan and Faddeev. The sum of norms of the Bethe vectors is computed and expressed in the form of a Jacobian. This result corresponds to the Gaudin hypothesis for the XYZ spin chain.

T. Hattori, T. Hasuike, S. Wakaizumi

We analyze in the four-generation model the first measurement of the branching ratio of rare kaon decay $K^+\toπ^+ν\bar{nu}$, along with the other processes of $K_L-K_S$ mass difference $Δm_K$, CP-violating parameter $ε_K, B_d-\bar{B_d}$ mixing, $B_s-\bar{B_s}$ mixing, $B(K_L\toμ\barμ)$, and the upper bound values of $D^0-\bar{D^0}$ mixing and $B(K_L\toπ^0ν\

Noboru Takigawa, Tamanna Rumin, Naoki Ihara

We present analytic expressions of the Coulomb interaction between a spherical and a deformed nuclei which are valid for all separation distance. We demonstrate their significant deviations from commonly used formulae in the region inside the Coulomb radius, and show that they remove various shortcomings of the conventional formulae.

Charles H. Bennett, Sandu Popescu, Daniel Rohrlich, John A. Smolin

In an effort to simplify the classification of pure entangled states of multi (m) -partite quantum systems, we study exactly and asymptotically (in n) reversible transformations among n'th tensor powers of such states (ie n copies of the state shared among the same m parties) under local quantum operations and classical communication (LOCC). With regard to e

J. E. Hirsch, F. Marsiglio

Anderson's interlayer tunneling model can account for up to 1% of the condensation energy of Tl_2Ba_2CuO_y. Here we account for the remaining 99%. We predict an in-plane kinetic energy gain of 1 to 3 meV per planar oxygen in the optimally doped material when it goes superconducting. It is suggested that the effect may be most easily detected in underdope

Richard A. Mould

In a previous paper, the author proposed a quantum mechanical interaction that would insure that the evolution of subjective states would parallel the evolution of biological states, as required by von Neumann's theory of measurement. The particular model for this interaction suggested an experiment that the author has now performed wih negative results.

B. Porter, P. Auchincloss, P. de Barbaro, A. Bodek

An experiment investigating the angle of Cerenkov light emitted by 3-MeV electrons traversing an acrylic detector has been developed for use in the advanced physics laboratory course at the University of Rochester. In addition to exploring the experimental phenomena of Cerenkov radiation and total internal reflection, the experiment introduces students to se

V. A. Dzuba, V. V. Flambaum.

Theories unifying gravity and other interactions suggest the possibility of spatial and temporal variation of physical ``constants''. Accuracy achieved for the atomic optical frequency standards (optical clocks) approaches the level when possible time evolution of the fine structure constant $α$ can be studied by comparisons of rates between clocks b

Sean Gavin

The dynamic separation into phases of high and low baryon density in a heavy ion collision can enhance fluctuations of the net rapidity density of baryons compared to model expectations. We show how these fluctuations arise and how they can survive through freezeout.

Brian D. Taylor

Using random variables as motivation, this paper presents an exposition of the formalisms developed by Rota and Taylor for the classical umbral calculus. A variety of examples are presented, culminating in several descriptions of sequences of binomial type in terms of umbral polynomials.

Brian D. Taylor

We produce a new basis for the Schur and Weyl modules associated to a row-convex shape, D. The basis is indexed by new class of "straight" tableaux which we introduce by weakening the usual requirements for standard tableaux. Spanning is proved via a new straightening algorithm for expanding elements of the representation into this basis. For skew sh

V. Manuilov

We study the $C^*$-algebras related to Mishchenko's version of asymptotic homomorphisms. In particular we show that their different versions are weakly homotopy equivalent but not isomorphic to each other. We give also the continuous version for these algebras.

Norman Danner

We investigate the relationship between (countable) transfinite iteration and ordinal arithmetic. The nice connection between finite iteration and addition, multiplication, and exponentiation is lost when passing to the transfinite. In this note, we investigate a new equivalence relation on ordinal functionals with respect to which we restore the connection.

L. Andrew Campbell

The Jacobian Conjecture would follow if it were known that real polynomial maps with a unipotent Jacobian matrix are injective. The conjecture that this is true even for $C^1$ maps is explored here. Some results known in the polynomial case are extended to the $C^1$ context, and some special cases are resolved.

Stéphane Druel

Nous montrons que le revêtement universel des variétés algébriques projectives dont le fibré tangent est totalement décomposé et vérifie certaines conditions d'intégrabilité est produit de surfaces de Riemann et que la décomposition de $T_{X}$ est induite par la décomposition du tangent au revêtement universel; lorsque la variété est minimale les conditi

Phung Ho Hai

We compute the integral on matrix quantum (super) groups of type $A_{r|s}$ and derive from it the quantum analogue of (super) HCIZ integral.

E. D'Hoker, D. Z. Freedman, S. D. Mathur, A. Matusis

The non-renormalization of the 3-point functions $tr X^{k_1} tr X^{k_2} tr X^{k_3}$ of chiral primary operators in N=4 super-Yang-Mills theory is one of the most striking facts to emerge from the AdS/CFT correspondence. A two-fold puzzle appears in the extremal case, e.g. k_1 = k_2 + k_3. First, the supergravity calculation involves analytic continuation in

Antonio Liguori, Mihail Mintchev, Luigi Pilo

In this letter we study 1+1 anyon fields at finite temperature and density with non-vanishing chemical potentials. Our approach is based on an operator formalism for bosonization at finite temperature; the correlation functions for the system are given in an explicit form. Two are the main results of this construction: we point out the existence of persisten

R. Blumenhagen, A. Font, A. Kumar, D. Lust

A construction of compact tachyon-free orientifolds of the non-supersymmetric Type 0B string theory is presented. Moreover, we study effective non-supersymmetric gauge theories arising on self-dual D3-branes in Type 0B orbifolds and orientifolds.

K. Ghoroku, K. Kaneko

We examine the solutions of world-volume action for a D3-brane being put near other D3-brane which is replaced by the background configuration of bulk space. It is shown that the BPS solutions are not affected by the D3-brane background, and they are interpreted as dyonic strings connecting two branes. On the contrary, the non-BPS configurations are largely

Tamiaki Yoneya

The large N behavior of Matrix theory is discussed on the basis of the previously proposed generalized conformal symmetry. The concept of `oblique' AdS/CFT correspondence, in which the conformal symmetry involves both the space-time coordinates and the string coupling constant, is proposed. Based on the explicit predictions for two-point correlators, pos

N. Gurappa, Prasanta K. Panigrahi

A method is developed to construct the solutions of one and many variable, linear differential equations of arbitrary order. Using this, the $N$-particle Sutherland model, with pair-wise inverse sine-square interactions among the particles, is shown to be equivalent to free particles on a circle. Applicability of our method to many other few and many-body pr

M. B. Voloshin

The dependence of inclusive weak decay rates of heavy hadrons on light spectator quarks is considered. The analysis of a previous work on relating the effects in b baryons to those in charmed baryons is extended to explicit evaluation of the matrix elements of certain four-quark operators over heavy baryons. It is shown that the usually postulated color anti

Jochen Bartels, Carlo Ewerz

The high energy limit of QCD is investigated in the generalized leading logarithmic approximation. We study unitarity corrections to the BFKL Pomeron containing t-channel states with up to six gluons. Special attention is given to the field theory structure of the corresponding multi-gluon amplitudes. We discuss the transition from two to six gluons in the t

M. E. Bracco, F. S. Navarra, M. Nielsen

The NKY coupling constant for $Y = Λ$ and $Σ$ is evaluated in a QCD sum rule calculation. We discuss and extend the result of a previous analysis in the $\rlap{/}{q}iγ_5$ structure and compare it with the result obtained with the use of the $γ_5 σ_{μν}$ structure. We find a huge violation of the SU(3) symmetry in the $γ_5 σ_{μν}$ structure.

Masataka Fukugita, Guo-Chin Liu, Naoshi Sugiyama

We consider the effect of three species of neutrinos with nearly degenerate mass on the cosmic structure formation in a low matter-density universe within a hierarchical clustering scenario with a flat initial perturbation spectrum. The matching condition for fluctuation powers at the COBE scale and at the cluster scale leads to a strong upper limit on neutr

Bronislav G. Zakharov

I demonstrate that the Baier-Katkov approach to the Landau-Pomeranchuk-Migdal effect based on their quasiclassical operator method is conceptually wrong in quantum regime of interaction of the charged particles with the medium constituents which takes place for electrons and positrons in real media.

Kai Hencken, Dirk Trautmann, Gerhard Baur

We calculate the probability for dilepton production in central relativistic heavy ion collisions due to the gamma-gamma mechanism. This is a potential background to more interesting mechanisms. We find that this mechanism is negligible in the CERES experiments. Generally, the contribution due to this mechanism is small in the central region, while it can be

Tuomas Multamaki, Iiro Vilja

Stable non-topological solitons, Q-balls, are studied using analytical and numerical methods. Three different physically interesting potentials that support Q-ball solutions are considered: two typical polynomial potentials and a logarithmic potential inspired by supersymmetry. It is shown that Q-balls in these potentials exhibit different properties in the

Akira Kitagawa, Katsuji Yamamoto, Seishi Matsuki

Quantum calculations are developed on the dynamical system consisting of the cosmic axions, photons and Rydberg atoms which are interacting in the resonant microwave cavity. The time evolution is determined for the number of Rydberg atoms in the upper state which are excited by absorbing the axion-converted and thermal background photons. The calculations ar

A. A. Kozhevnikov

Two new effects of interaction of the gauge string with a homogeneous density of fermions are considered in a gauge model with an anomalous coupling of vector fields with fermions. First, the presence of an induced nonzero magnetic-like helicity on the straight string is demonstrated. Second, it is shown that the equation of motion of the string is modified

Hitoshi Murayama

I first motivate why we may want to look at possible new physics contributions to epsilon' given relatively clear experimental but unclear theoretical situations. I reexamine the supersymmetric contribution to epsilon' and find an important one generally missed in the literature. Based on rather model-independent arguments based on flavor symmetries,

M. Suzuki

Reference to recent papers and experimental feasibility are added. The paper will not be published in a hard-copy journal.

S. Capitani, M. Göckeler, R. Horsley, B. Klaus

We evaluate the contribution of a class of higher-twist operators to the lowest moment of the Structure Functions, by computing appropriate matrix elements of six four-fermion operators in the quenched approximation. Their perturbative renormalization constants and mixing coefficients are calculated in the 't Hooft-Veltman scheme of dimensional regulariz

ALEPH Collaboration, R. Barate

A preliminary search for neutral Higgs bosons is performed in the data collected by ALEPH in 1999, corresponding to integrated luminosities of 29.0 and 69.5 pb^-1 at centre-of-mass energies of 191.6 and 195.6 GeV respectively. No evidence for a signal is found. Combined with the lower energy ALEPH data, this observation leads to a 95% confidence level lower

Ulf S Nilsson, C. Uggla, J. Wainwright

To understand the observational properties of cosmological models, in particular, the temperature of the cosmic microwave background radiation, it is necessary to study their null geodesics. Dynamical systems theory, in conjunction with the orthonormal frame approach, has proved to be an invaluable tool for analyzing spatially homogeneous cosmologies. It is

S. Manoff

A generalized definition of a frame of reference in spaces with affine connections and metrics is proposed based on the set of the following differential-geometric objects: (a) a non-null (non-isotropic) vector field, (b) the orthogonal to the vector field sub space, (c) an affine connection and the related to it covariant differential operator determining a

Andrew D. Kent, Yicheng Zhong, Louisa Bokacheva, Daniel Ruiz

Precise magnetic hysteresis measurements of small single crystals of Mn$_{12}$ acetate of spin 10 have been conducted down to 0.4 K using a high sensitivity Hall magnetometer. At higher temperature (>1.6K) step-like changes in magnetization are observed at regularly spaced magnetic field intervals, as previously reported. However, on lowering the temperature

C. D. Batista, K. Hallberg, A. A. Aligia

We calculate the electron paramagnetic resonance (EPR) spectra of the antiferromagnetic spin-1 chain compound Y(2)BaNi(1-x)Mg(x)O(5) for different values of x and temperature T much lower than the Haldane gap (~100K). The low-energy spectrum of an anisotropic Heisenberg Hamiltonian, with all parameters determined from experiment, has been solved using DMRG.

L. A. Braunstein, R. C. Buceta, N. Giovambattista

Reply to ``Comment on [Phys. Rev. Lett. 81, 630 (1998)]''

David E Logan, Matthew T Glossop

A local moment approach is developed for the single-particle excitations of a symmetric Anderson impurity model (AIM), with a soft-gap hybridization vanishing at the Fermi level with a power law r > 0. Local moments are introduced explicitly from the outset, and a two-self-energy description is employed in which the single-particle excitations are coupled dy

J. M. Wills, P. H. Andersson, L. Nordstrom, P. Soderlind

In a recent paper by Jones et al., it is argued, based on FP-LAPW band-structure calculations, that previous calculations of ground-state properties for actinides, using the FP-LMTO method implemented by J. M. Wills, are in error. We demonstrate in this paper that the conclusions of Jones et. al. are unfounded. Calculations using the FP-LMTO method are compa

L. A. Braunstein, R. C. Buceta, C. D. Archubi, G. Costanza

We present an analytical continuous equation for the Tang and Leschhorn model [Phys. Rev A {\bf 45}, R8309 (1992)] derived from his microscopic rules using a regularization procedure. As well in this approach the nonlinear term $(\nabla h)^2$ arises naturally from the microscopic dynamics even if the continuous equation is not the Kardar-Parisi-Zhang equatio

M. Arrayas, R. Mannella, P. V. E. McClintock, A. J. McKane

The currents generated by noise-induced activation processes in a periodic potential are investigated analytically, by digital simulation and by performing analogue experiments.

R. Onofrio, D. S. Durfee, C. Raman, M. Kohl

Surface modes in a Bose-Einstein condensate of sodium atoms have been studied. We observed excitations of standing and rotating quadrupolar and octopolar modes. The modes were excited with high spatial and temporal resolution using the optical dipole force of a rapidly scanning laser beam. This novel technique is very flexible and should be useful for the st

N. Markovic, M. A. H. Dohmen, H. S. J. van der Zant

The collective charge density wave (CDW) conduction is modulated by a transverse single-particle current in a transistor-like device. Nonequilibrium conditions in this geometry lead to an exponential reduction of the depinning threshold, allowing the CDWs to slide for much lower bias fields. The results are in excellent agreement with a recently proposed dyn

Matthew T Glossop, David E Logan

We consider a symmetric Anderson impurity model, with a soft-gap hybridization vanishing at the Fermi level with a power law r > 0. Three facets of the problem are examined. First the non-interacting limit, which despite its simplicity contains much physics relevant to the U > 0 case: it exhibits both strong coupling (SC) states (for r < 1) and local moment

David Carpentier, Pierre Le Doussal

We study the two dimensional XY model with quenched random phases and its Coulomb gas formulation. A novel renormalization group (RG) method is developed which allows to study perturbatively the glassy low temperature XY phase and the transition at which frozen topological defects (vortices) proliferate. This RG approach is constructed both from the replicat

Eirik G. Flekkoy, Peter V. Coveney

A procedure is introduced for deriving a coarse-grained dissipative particle dynamics from molecular dynamics. The rules of the dissipative particle dynamics are derived from the underlying molecular interactions, and a Langevin equation is obtained that describes the forces experienced by the dissipative particles and specifies the associated canonical Gibb

I. P. Goudemond, J. M. Keartland, M. J. R. Hoch, G. A. Saunders

The spin dynamics of rare earth ions (Er, Nd, Sm and Gd) in heavily doped phosphate glasses have been investigated using 31P NMR. Correlation times in the range 10^-2 to 10^-12 s have been obtained for temperatures between 4 K and 100 K. No evidence of spin-spin coupling between the ions has been found and spin relaxation occurs via conventional phonon proce

T. Dahm, D. J. Scalapino

Despite several efforts the nonlinear Meissner effect in d-wave superconductors, as has been discussed by Yip and Sauls in 1992, has not been verified experimentally in high-Tc superconductors at present. Here, we reinvestigate the nonlinear response expected in a d-wave superconductor. While the linear H field dependence of the penetration depth, predicted

E. A. Jagla

A model based on the existence of two different competing local structures in water is described. It is shown that it can explain the transition between fragile and strong behavior that supercooled water has around 220 K. The high temperature behavior is similar to that observed in standard fragile glass-formers. The strong behavior at low temperatures is as

Sutapa Mukherji, Somendra M. Bhattacharjee

We discuss the features of nonequilibrium growth problems, their scaling description and their differences from equilibrium problems. The emphasis is on the Kardar-Parisi-Zhang equation and the renormalization group point of view. Some of the recent developments along these lines are mentioned.

A. Guarino, R. Scorretti, S. Ciliberto

The statistical properties of failure are studied in a fiber bundle model with thermal noise. We find that in agreement with recent experiments the macroscopic failure is produced by a thermal activation of microcracks. Most importantly the effective temperature of the system is amplified by the spatial disorder (heterogeneity) of the fiber bundle.

H. J. J. Verheijen, M. W. J. Prins

We derive a model for voltage-induced wetting, so-called electrowetting, from the principle of virtual displacement. Our model includes the possibility that charge is trapped in or on the wetted surface. Experimentally, we show reversible electrowetting for an aqueous droplet on an insulating layer of 10 micrometer thickness. The insulator is coated with a h

C. W. J. Beenakker, P. W. Brouwer

The scattering-matrix product SS+ of a weakly absorbing medium is related by a unitary transformation to the time-delay matrix without absorption. It follows from this relationship that the eigenvalues of SS+ for a weakly absorbing chaotic cavity are distributed according to a generalized Laguerre ensemble.

S. Sakamoto, H. Matsumoto, T. Koyama, M. Machida

By use of the multi-Josephson junction model, we investigate voltage-biased I-V characteristics. Differently from the case of the single junction, I-V characteristics show a complicated behavior due to inter-layer couplings among superconducting phase differences mediated by the charging effect. We show that there exist three characteristic regions, which ar

Robert Shrock

We present exact calculations of the zero-temperature partition function of the $q$-state Potts antiferromagnet (equivalently the chromatic polynomial) for Moebius strips, with width $L_y=2$ or 3, of regular lattices and homeomorphic expansions thereof. These are compared with the corresponding partition functions for strip graphs with (untwisted) periodic l

V. C. Galarza, R. A. M. Walterbos, R. Braun

We present results of KPNO 4-m optical spectroscopy of discrete emission-line nebulae and regions of diffuse ionized gas (DIG) in M31. Long-slit spectra of 16 positions in the NE half of M31 were obtained over a 5-15 kpc range in radial distance from the center of the galaxy. The spectra have been used to confirm 16 supernova remnant candidates from the Brau

Rodrigo A. Ibata, Harvey B. Richer, Ronald L. Gilliland, Douglas Scott

The deepest optical image of the sky, the Hubble Deep Field (HDF), obtained with the Hubble Space Telescope (HST) in December 1995, has been compared to a similar image taken in December 1997. Two very faint, blue, isolated and unresolved objects are found to display a substantial apparent proper motion, 23+/-5 mas/yr and 26+/-5 mas/yr; a further three objec