August 2001 arXiv papers — page 14

Lizardo H. C. M. Nunes, E. V. L. de Mello

We show that there is an effect of nonextensivity acting upon the BCS model for superconductors in the ground state that motivates its study in the Tsallis' statistical framework. We show that the weak-coupling limit superconductors are well described by $q \sim 1$, where q is a real parameter which characterizes the degree of nonextensivity of the Tsall

Edgar Bonet, Mandar M. Deshmukh, D. C. Ralph

We consider the form of the current-voltage curves generated when tunneling spectroscopy is used to measure the energies of individual electronic energy levels in nanometer-scale systems. We point out that the voltage positions of the tunneling resonances can undergo temperature-dependent shifts, leading to errors in spectroscopic measurements that are propo

C. Grazioli, Z. Hu, M. S. Golden, J. Fink K. Attenkofer

We have used temperature dependent x-ray absorption at the Ce-L3 edge to investigate the recently discovered Kondo compound Ce2Rh3Al9. The systematic changes of the spectral lineshape with decreasing temperature are analyzed and found to be related to a change in the $4f$ occupation number, n_f, as the system undergoes a transition into a Kondo state. The te

A. Lewalle, M. Pepper, C. J. B. Ford, E. H. Hwang

The effect of substrate bias and surface gate voltage on the low temperature resistivity of a Si-MOSFET is studied for electron concentrations where the resistivity increases with increasing temperature. This technique offers two degrees of freedom for controlling the electron concentration and the device mobility, thereby providing a means to evaluate the r

Yayu Wang, Z. A. Xu, T. Kakeshita, S. Uchida

The diffusion of vortices down a thermal gradient produces a Josephson signal which is detected as the vortex Nernst effect. In a recent report, Xu et al., Nature 406, 486 (2000), an enhanced Nernst signal identified with vortex-like excitations was observed in a series of La_{2-x}Sr_xCuO_4 (LSCO) crystals at temperatures 50-100 K above T_c. To pin down the

Yupeng Wang

By constructing the super-particle representation of the free boson gas, we propose a new statistics in which the particles are non-exclusive. This statistics can be considered as a generalization of Bose-Einstein's. The possible condensation of this statistical system is studied. It is found that the chemical potential below the condensation temperature

N. -C. Yeh, C. -T. Chen, G. Hammerl, J. Mannhart

Scanning tunneling spectroscopy (STS) studies reveal long-range spatial homogeneity and predominantly $d_{x^2-y^2}$-pairing spectral characteristics in under- and optimally doped $\rm YBa_2Cu_3O_{7-δ}$ superconductors, whereas STS on $\rm YBa_2(Cu_{0.9934}Zn_{0.0026}Mg_{0.004})_3O_{6.9}$ exhibits {\it microscopic} spatial modulations and strong scattering ne

Norbert Schorghofer, Sarah T. Gille

Probability density functions and conditional averages of velocity gradients derived from upper ocean observations are compared with results from forced simulations of the two-dimensional Navier-Stokes equations. Ocean data are derived from TOPEX satellite altimeter measurements. The simulations use rapid forcing on large scales, characteristic of surface wi

C. A. Clarkson, A. A. Coley, S. D. Quinlan

We study the qualitative properties of the class of spatially homogeneous Bianchi VI_o cosmological models containing a perfect fluid with a linear equation of state, a scalar field with an exponential potential and a uniform cosmic magnetic field, using dynamical systems techniques. We find that all models evolve away from an expanding massless scalar field

Milan M. Cirkovic, Srdjan Samurovic

A simple consistency argument for hypothesis of the galactic halo origin of the Ly-alpha forest absorption lines is advanced, based on the recent determination of column-density vs. impact parameter relation for the low-redshift gaseous galactic haloes. It is shown that observations of neutral hydrogen absorption around luminous galaxies are consistent with

J. E. Grindlay, C. O. Heinke, P. D. Edmonds, S. S. Murray

We report results of the Chandra deep imaging observation of the closest post-core collapse globular cluster, NGC 6397. Some 25 sources are detected within 2 arcmin of the cluster center of which about 20 are likely cluster members with L_x ~ 3x10^29 erg/s. The x-ray spectra suggest identifications with 1 quiescent low mass x-ray binary (qLMXB) detected by t

K. Treichel, L. Rudnick, M. Hardcastle, J. P. Leahy

Using spectral tomography to separate overlapping spectral features in a sample of FRII radio galaxies, we find a variety of spatial/spectral features that are not easily described in the context of current models. In particular, we find mixtures of flat and steep spectrum features in the hot spot regions, and non-monotonic spectral index gradients along jet

K. A. Venn, A. M. Brooks, D. L. Lambert, M. Lemke

Boron abundances have been derived for seven main sequence B-type stars from HST STIS spectra around the B III 2066 A line. In two stars, boron appears to be undepleted with respect to the presumed initial abundance. In one star, boron is detectable but it is clearly depleted. In the other four stars, boron is undetectable implying depletions of 1 to 2 dex.

Christopher J. Stockdale, W. M. Goss, John J. Cowan, R. A. Sramek

Using the Very Large Array, we have detected radio emission from the site of SN 1970G in the Sc galaxy M101. These observations are 31 years after the supernova event, making SN 1970G the longest monitored radio supernova. With flux densities of 0.12 +/- 0.020 mJy at 6 cm and 0.16 +/- 0.015 mJy at 20 cm, the spectral index of -0.24 +/- 0.20 appears to have f

H. Bushouse, K. Borne, L. Colina, R. Lucas

A sample of 27 ultraluminous infrared galaxy (ULIRG) systems has been imaged at 1.6 microns using the HST Near Infrared Camera and Multi-Object Spectrometer (NICMOS). These ULIRGs are from a larger sample also imaged with HST in the I-band. Images and catalog information for the NICMOS subsample, as well as brief morphological descriptions of each system are

John M. LoSecco, Grant J. Mathews, Yun Wang

Observers have demonstrated that it is now feasible to measure the cosmic microwave background (CMB) temperature at high redshifts. We explore the possible constraints on cosmology which might ultimately be derived from such measurements. Besides providing a consistency check on standard and alternative cosmologies, possibilities include: constraints on the

James C. Weatherall

A relativistic pair-plasma which contains a high excitation of electrostatic turbulence could produce intense radiation at brightness temperature in excess of 10^22 K by stimulated scattering. Important relativistic effects would include the broadband frequency response of the plasma and Compton-boosting of the scattered radiation. In radio-frequency relativ

S. Hony, C. Dominik, L. B. F. M. Waters, V. Icke

We report the discovery of a double ring structure in the waist of the nebula surrounding eta Carinae. The rings are detected in the mid-IR dust continuum at wavelengths of 7.9, 11.9, 12.9 and 20 micronmeter. The dust in the rings has a temperature of about 300 K. The orientation of the rings is inclined with respect to the axis of the homunculus by either 3

C. Marcella Carollo, Simon J. Lilly, Alan Stockton

We are undertaking a program to measure emission line ratios in a selected sample of $0.5 < z < 1.0$ CFRS starforming galaxies in order to compute their Interstellar Medium metallicities. The latter are derived by means of the empirically-calibrated $R_{23}$ estimator introduced by Pagel et al. (1979). Here we focus on a subsample of 15 galaxies with $L_{Hβ}

Norbert Straumann

After a brief introduction to gravitational lensing theory, a rough overview of the types of gravitational lensing statistics that have been performed so far will be given. I shall then concentrate on recent results of galaxy-galaxy lensing, which indicate that galactic halos extend much further than can be probed via rotation of stars and gas.

W. van Straten, M. Bailes, M. C. Britton, S. R. Kulkarni

Binary pulsars provide an excellent system for testing general relativity because of their intrinsic rotational stability and the precision with which radio observations can be used to determine their orbital dynamics. Measurements of the rate of orbital decay of two pulsars have been shown to be consistent with the emission of gravitational waves as predict

John P. Blakeslee

We discuss lensing properties of the nearby cluster Abell 2152. Recent work shows that Abell 2152 is actually the projection of two different clusters, one of which is a Hercules supercluster member at z=0.043, while the other is more than 3 times as distant. The cluster centers have a projected separation of only 2.4 arcmin, and our data indicate that the f

Francesco R. Ferraro, Andrea Possenti, Nichi D&#39;Amico, Elena Sabbi

We report the possible optical identification of the companion to the eclipsing millisecond pulsar PSR J1740-5340 in the globular cluster NGC 6397. A bright variable star with an anomalous red colour and optical variability which nicely correlates to the orbital period of the pulsar has been found close to the pulsar position. If confirmed, the optical light

N. D&#39;Amico, A. Possenti, R. N. Manchester, J. Sarkissian

We present the results of one year of pulse timing observations of PSR J1740-5340, an eclipsing millisecond pulsar located in the globular cluster NGC 6397. We have obtained detailed orbital parameters and a precise position for the pulsar. The radio pulsar signal shows frequent interactions with the atmosphere of the companion, and suffers significant and s

D. Barrado-y-Navascués, M. R. Zapatero-Osorio, V. J. S. Béjar, R. Rebolo

We have obtained low resolution optical spectra of 15 isolated planetary mass objects (IPMOs) in the sigma Orionis cluster, and derived spectral types by comparison with nearby M and L dwarfs. The spectral types are in the range late M - mid L, in agreement with our expectations based on colors and magnitudes for bona fide members. Therefore, most of these o

S. Chaty, C. A. Haswell, R. I. Hynes, C. R. Shrader

We report multiwavelength observations of the two soft X-ray transients (SXTs) XTE J1859+226 and XTE J1118+480, which we observed with HST, RXTE and UKIRT. The two sources exhibited very different behaviour. XTE J1859+226 showed a thermal-viscous disc instability outburst modified by irradiation. XTE J1118+480, which we also observed with EUVE since it is lo

Chris Churchill, Jane Charlton, Joe Masiero

Our galaxy is the nearest known quasar absorption line system, and it uniquely provides us with an opportunity to probe multiple lines of sight through the same galaxy. This is essential for our interpretations of the complex kinematic profiles seen in the MgII absorption due to lines of sight through intermediate redshift galaxies. The Milky Way halo has ne

Michael Cahill, Sean Cahill, Kevin Cahill

We propose an algorithmic strategy for improving the efficiency of Monte Carlo searches for the low-energy states of proteins. Our strategy is motivated by a model of how proteins alter their shapes. In our model when proteins fold under physiological conditions, their backbone dihedral angles change synchronously in groups of four or more so as to avoid ste

Tianjun Li

We study the 6-dimensional N=2 supersymmetric grand unified theories with gauge group SU(N) and $ SO(M)$ on the extra space orbifolds $T^2/(Z_2)^3$ and $T^2/(Z_2)^4$, which can be broken down to the 4-dimensional N=1 supersymmetric $SU(3)\times SU(2)\times U(1)^{n-3}$ model for the zero modes. We also study the models which have two SU(2) Higgs doublets (zer

A. N. Petrov, N. S. Mosyagin, T. A. Isaev, A. V. Titov

A method and codes for two-step correlation calculation of heavy-atom molecules have been developed, employing the generalized relativistic effective core potential and relativistic coupled cluster (RCC) methods at the first step, followed by nonvariational one-center restoration of proper four-component spinors in the heavy cores. Electron correlation is in

Robin D. Hanson

In Everett&#39;s many worlds interpretation, quantum measurements are considered to be decoherence events. If so, then inexact decoherence may allow large worlds to mangle the memory of observers in small worlds, creating a cutoff in observable world size. Smaller world are mangled and so not observed. If this cutoff is much closer to the median measure size

BRAHMS Collaboration, I. G. Bearden

We present charged particle densities as a function of pseudorapidity and collision centrality for the 197Au+197Au reaction at sqrt{s_{NN}}=130 GeV. An integral charged particle multiplicity of 3860+/-300 is found for the 5% most central events within the pseudorapidity range -4.7 <= eta <= 4.7. At mid-rapidity an enhancement in the particle yields per parti

Peter Gorham, David Saltzberg, Allen Odian, Dawn Williams

We have investigated the possibility that large rock salt formations might be suitable as target masses for detection of neutrinos of energies about 10 PeV and above. In neutrino interactions at these energies, the secondary electromagnetic cascade produces a coherent radio pulse well above ambient thermal noise via the Askaryan effect. We describe measureme

T. G. Kovacs, E. T. Tomboulis

We examine the manner in which a linear potential results from fluctuations due to vortices linked with the Wilson loop. Our discussion is based on exact relations and inequalities between the Wilson loop and the vortex and electric flux order parameters. We show that, contrary to the customary naive picture, only vortex fluctuations of thickness of the orde

P. Q. Hung, Andrea Soddu

An extension of a model of neutrino masses to the quark sector provides an interesting link between these two sectors. A parameter which is important to describe neutrino oscillations and masses is found to be a crucial one appearing in various ``penguin&#39;&#39; operators, in particular the so-called Z penguin. This parameter is severely constrained by the

E. Bielejec, Wenhao Wu

The magnetic-field-tuned superconductor-insulator transition has been studied in ultrathin Beryllium films quench-condensed near 20 K. In the zero-current limit, a finite-size scaling analysis yields the scaling exponent product vz = 1.35 +/- 0.10 and a critical sheet resistance R_{c} of about 1.2R_{Q}, with R_{Q} = h/4e^{2}. However, in the presence of dc b

Sergey Frolov, Igor R. Klebanov, Arkady A. Tseytlin

We study leading string corrections to the type IIB supergravity solution dual to the ${\cal N}=1$ supersymmetric $SU(N+M)\times SU(N)$ gauge theory coupled to bifundamental chiral superfields $A_i, B_j$, $i,j=1,2$. This solution was found in hep-th/0007191, and its asymptotic form describing logarithmic RG flow was constructed in hep-th/0002159. The leading

P. F. Borges, H. Boschi-Filho, Marcelo Hott

From spinor and scalar 2+1 dimensional QED effective actions at finite temperature and density in a constant magnetic field background, we calculate the corresponding virial coefficients for particles in the lowest Landau level. These coefficients depend on a parameter theta related to the time-component of the gauge field, which plays an essential role for

R. P. Malik

We show the existence of some new local, covariant and continuous symmetries for the BRST invariant Lagrangian density of a free two ($1 + 1$)-dimensional (2D) Abelian U(1) gauge theory in the framework of superfield formalism. The Noether conserved charges corresponding to the above local continuous symmetries find their geometrical origin as the translatio

Vineer Bhansali, Mark B. Wise

The instability of historical risk factor correlations renders their use in estimating portfolio risk extremely questionable. In periods of market stress correlations of risk factors have a tendency to quickly go well beyond estimated values. For instance, in times of severe market stress, one would expect with certainty to see the correlation of yield level

M. A. Cirone, K. Rzazewski, W. P. Schleich, F. Straub

In a two-dimensional world a free quantum particle of vanishing angular momentum experiences an attractive force. This force originates from a modification of the classical centrifugal force due to the wave nature of the particle. For positive energies the quantum anti-centrifugal force manifests itself in a bunching of the nodes of the energy wave functions

A. Mikovic

We construct a class of spin foam models describing matter coupled to gravity, such that the gravitational sector is described by the unitary irreducible representations of the appropriate symmetry group, while the matter sector is described by the finite-dimensional irreducible representations of that group. The corresponding spin foam amplitudes in the fou

Ram Brustein, Stefano Foffa, Avraham E. Mayo

The conditions for validity of the Causal Entropy Bound (CEB) are verified in the context of non-singular cosmologies with classical sources. It is shown that they are the same conditions that were previously found to guarantee validity of the CEB: the energy density of each dynamical component of the cosmic fluid needs to be sub-Planckian and not too negati

R. X. Xu, G. J. Qiao

Pulsar braking torques due to magnetodipole radiation and to unipolar generator are considered, which results in braking index being less than 3 and could be employed to test the emission models. Improved equations to obtain pulsar braking index and magnetic field are presented if we deem that the rotation energy loss rate equals to the sum of the dipole rad

Gert Brodin, Mattias Marklund, Lennart Stenflo

We present a novel method for detecting nonlinearities, due to quantum electrodynamics through photon-photon scattering, in Maxwell&#39;s equation. The photon-photon scattering gives rise to self-interaction terms, which are similar to the nonlinearities due to the polarisation in nonlinear optics. These self-interaction terms vanish in the limit of parallel

A. El Rhalami, E. M. Sahraoui, E. H. Saidi

We develop the non commutative Chern-Simons gauge model analysis modeling the description of the hierarchical states of fractional quantum Hall fluids. For a generic level $n$ of the hierarchy, we show that the order parameter matrix $K_{ab}$ is given by $ θ^{-2}Tr(τ_a τ_b)$, where $\{τ_a, 1\leq a \leq n \}$ define a specific set of $n\times n$ matrices depe

Shahrokh Parvizi

Dynamics of D-branes on $SU(2)/U(1)$ gauged WZW model are investigated. We find the effective action for infinite $k$, where $k$ is the level of WZW model. We also consider finite $k$ correction to the effective action which is compatible with Fedosov&#39;s deformation quantization of the background.

Johannes Berg, Anita Mehta

We discuss the use of a ferromagnetic spin model on a random graph to model granular compaction. A multi-spin interaction is used to capture the competition between local and global satisfaction of constraints characteristic for geometric frustration. We define an athermal dynamics designed to model repeated taps of a given strength. Amplitude cycling and th

D. A. Head, A. Ajdari, M. E. Cates

We study the strain response to steady imposed stress in a spatially homogeneous, scalar model for shear thickening, in which the local rate of yielding Γ(l) of mesoscopic `elastic elements&#39; is not monotonic in the local strain l. Despite this, the macroscopic, steady-state flow curve (stress vs. strain rate) is monotonic. However, for a broad class of Γ

A. Gashi, G. C. Oades, G. Rasche, W. S. Woolcock

We calculate the electromagnetic corrections needed to obtain isospin invariant hadronic pion-pion s-wave scattering lengths a^0, a^2 from the elements a_cc, a_0c of the s-wave scattering matrix for the (π^+ π^-, π^0 π^0) system at the π^+ π^- threshold. These elements can be extracted from experiments on pionium. Our calculation uses energy independent hadr

Kazuo Hosomichi

We study Liouville theory on worldsheets with boundary using the solutions of Knizhnik-Zamolodchikov equation involving a degenerate representation of the Virasoro algebra. The expression for bulk-boundary propagator on a disc is proposed.

Michael Tews, Daniela Pfannkuche

The influence of the tip-substrate bias induced electrical field in a scanning tunneling spectroscopy experiment on colloidal InAs nanocrystals has been studied. Calculating the Stark induced splitting of the degenerate 1P_e state perturbatively within a particle-in-a-sphere model, revealed a possible explanation of recently published experimental wave funct

G. A. Ummarino, R. S. Gonnelli

In a recent paper (J.H. Schon, Ch. Kloc, R.C. Haddon and B. Batlogg, Nature 408 (2000) 549) a large increase in the superconducting critical temperature was observed in C60 doped with holes by application of a high electric field. We demonstrate that the measured Tc versus doping curves can be explained by solving the (four) s-wave Eliashberg equations in th

Arnab Rai Choudhuri, Sushan Konar

A possible mechanism for screening of the surface magnetic field of an accreting neutron star, by the accreted material, is investigated. We model the material flow in the surface layers of the star by an assumed 2-D velocity field satisfying all the physical requirements. Using this model velocity we find that, in the absence of magnetic buoyancy, the surfa

Y. S. Myung

We study issues of the quintessence in the brane cosmology. The initial bulk spacetime consists of two 5D topological anti de Sitter black hole joined by the brane (moving domain wall). Here we do not introduce any conventional radiation and matter. Instead we include a localized scalar on the brane as a stress-energy tensor, and thus we find the quintessenc

Andreas Winter

We consider two apparently separated problems: in the first part of the paper we study the concept of a scalable (approximate) programmable quantum gate (SPQG). These are special (approximate) programmable quantum gates, with nice properties that could have implications on the theory of universal computation. Unfortunately, as we prove, such objects do not e

Tohru Eguchi, Yuji Sugawara

We construct modular invariant partition functions for strings propagating on non-compact manifolds of G_2 holonomy. Our amplitudes involve a pair of N=1 minimal models M_m, M_{m+2} (m=3,4,...) and are identified as describing strings on manifolds of G_2 holonomy associated with A_{m-2} type singularity. It turns out that due to theta function identities our

Volodymyr Krasnoholovets

The two opposite concepts - multiphoton and effective photon - readily describing the photoelectric effect under strong irradiation in the case that the energy of the incident light is essentially smaller than the ionisation potential of gas atoms and the work function of the metal are treated. Based on the submicroscopic construction of quantum mechanics de

Xinhua Peng, Xiwen Zhu, Ximing Fang, Mang Feng

Using nuclear magnetic resonance (NMR) techniques with three-qubit sample, we have experimentally implemented the highly structured algorithm for the 1-SAT problem proposed by Hogg. A simplified temporal averaging procedure was employed to the three-qubit spin pseudo-pure state. The algorithm was completed with only a single evaluation of structure of the pr

R. Freivalds, A. Winter

We introduce quantum finite state transducers (qfst), and study the class of relations which they compute. It turns out that they share many features with probabilistic finite state transducers, especially regarding undecidability of emptiness (at least for low probability of success). However, like their `little brothers&#39;, the quantum finite automata, t

M. A. Kiselev, P. Lesieur, A. M. Kisselev, M. Ollivon

Ice formation in model biological membranes is studied by SAXS and WAXS in the presence of cryoprotectors: dimethyl sulfoxide and glycerol. Three types of phospholipid membranes: DPPC, DMPC, DSPC are chosen for the investigation as well-studied model biological membranes. A special cryostat is used for sample cooling from 14.1C to -55.4C. The ice formation i

T. A. Isaev, N. S. Mosyagin, A. V. Titov, A. B. Alekseyev

The correlation calculation of the electronic structure of PbH is carried out with the Generalized Relativistic Effective Core Potential (GRECP) and MultiReference single- and Double-excitation Configuration Interaction (MRD-CI) methods. The 22-electron GRECP for Pb is used and the outer core 5s, 5p and 5d pseudospinors are frozen using the level-shift techn

Maria B. Barbaro

The impact of pionic correlations and meson-exchange currents on the quasi-elastic electromagnetic response functions is studied in a fully relativistic framework.

Charles J. Horowitz, Jorge Piekarewicz

A new relation between the neutron skin of a heavy nucleus and the radius of a neutron star is proposed: the larger the neutron skin of the nucleus the larger the radius of the star. Relativistic models that reproduce a variety of ground-state observables can not determine uniquely the neutron skin of a heavy nucleus. Thus, a large range of neutron skins is

Amruta Mishra, Jitendra C. Parikh, Walter Greiner

The medium modification of vector meson masses is studied taking into account the quantum correction effects for the hot and dense hadronic matter. In the framework of Quantum Hadrodynamics, the quantum corrections from the baryon and scalar meson sectors were earlier computed using a nonperturbative variational approach through a realignment of the ground s

Kei Iida, Gentaro Watanabe, Katsuhiko Sato

Formation and decay of rod-like and slab-like nuclei, as may be encountered in the outer parts of neutron stars, are examined within a zero-temperature stability analysis with respect to perturbations inducing fission and proton clustering. The nonspherical nuclei are found to be stable against these perturbations, implying the possibility that the size of t

P. Huovinen

We use a hydrodynamical model to describe the evolution of the collision system at collision energies sqrt{s}=130 and 200 GeV. At lower sqrt{s}=130 GeV energy we compare the results obtained assuming fast or slow thermalization (thermalization times tau_0=0.6 and 4.1 fm/c, respectively) and show that slow thermalization fails to reproduce the observed anisot

B. Lenkeit, NA60-Collaboration

NA60, a follow-up of NA38/50 at the CERN-SPS, is a third generation heavy-ion experiment finally approved in November 2000 for heavy-ion runs in 2002 and 2003. This article will report about the main motivations which lead to this experiment, the main detector concept and the foreseen physics performance.

Guillaume Bal, George Papanicolaou, Leonid Ryzhik

We give a detailed mathematical analysis of the radiative transport limit for the average phase space density of solutions of the Schroedinger equation with time dependent random potential. Our derivation is based on the construction of an approximate martingale for the random Wigner distribution.

Mark Adler, Pierre van Moerbeke

Given the Hermitian, symmetric and symplectic ensembles, it is shown that the probability that the spectrum belongs to one or several intervals satisfies a nonlinear PDE. This is done for the three classical ensembles: Gaussian, Laguerre and Jacobi. For the Hermitian ensemble, the PDE (in the boundary points of the intervals) is related to the Toda lattice a

Mark Goresky, Yung sheng Tai

For appropriate $N\ge 3$ and $d<0,$ the moduli space of principally polarized abelian surfaces with level $N$ structure and anti-holomorphic multiplication by $\mathcal O_d$ (the ring of integers in $\mathbb Q(\sqrt{d})$) is shown to consist of the real points of a quasi-projective algebraic variety defined over $\mathbb Q$, and to coincide with finitely man

Károly Bezdek, Robert Connelly

We give a proof of the planar case of a longstanding conjecture of Kneser (1955) and Poulsen (1954). In fact, we prove more by showing that if a finite set of disks in the plane is rearranged so that the distance between each pair of centers does not decrease, then the area of the union does not decrease, and the area of the intersection does not increase.

Eric Weber

We extend Robertson&#39;s theorem to apply to frames generated by the action of a discrete, countable abelian unitary group. Within this setup we use Stone&#39;s theorem and the theory of spectral multiplicity to analyze wandering frame collections. Motivated by wavelet theory, we explicitly apply our results to the action of the integers given by translatio

Shesansu Sekhar Pal

The noncommutative string theory is described by embedding open string theory in a constant second rank antisymmetric $B_{μν}$ field and the noncommutative gauge theory is defined by a deformed $\star$ product. As a check, study of various scattering amplitudes in both noncommutative string and noncommutative gauge theory confirm that in the $α^{&#39;}\to 0$

M. R. Gaberdiel, A. Recknagel, G. M. T. Watts

For the case of the SU(2) WZW model at level one, the boundary states that only preserve the conformal symmetry are analysed. Under the assumption that the usual Cardy boundary states as well as their marginal deformations are consistent, the most general conformal boundary states are determined. They are found to be parametrised by group elements in SL(2,C)

Juan Maldacena, Gregory Moore, Nathan Seiberg

We discuss some physical issues related to the K-theoretic classification of D-brane charges, putting an emphasis on the role of D-brane instantons. The relation to D-instantons provides a physical interpretation to the mathematical algorithm for computing K-theory known as the ``Atiyah-Hirzebruch spectral sequence.&#39;&#39; Conjecturally, a formulation in

John Ellis, Murat Gunaydin, Marco Zagermann

Motivated by the possibility that physics may be effectively five-dimensional over some range of distance scales, we study the possible gaugings of five-dimensional N=2 supergravity. Using a constructive approach, we derive the conditions that must be satisfied by the scalar fields in the vector, tensor and hypermultiplets if a given global symmetry is to be

S. Y. Choi, J. Kalinowski, G. Moortgat-Pick, P. M. Zerwas

Charginos $\tildeχ^\pm$ and neutralinos $\tildeχ^0$ in supersymmetric theories can be produced copiously at $e^+e^-$ colliders and their properties can be measured with high accuracy. Consecutively to the chargino system, in which the SU(2) gaugino parameter $M_2$, the higgsino mass parameter $μ$ and $\tanβ$ can be determined, the remaining fundamental super

P. R. Crompton

The reweighting method developed in Glasgow to circumvent the lattice action becoming complex at finite density suffers from a pathological onset transition thought to be due to the reweighting. We present a new reweighting scheme based on this approach in which we combine ensembles to alleviate the sampling bias we identify in the polynomial coefficients of

S. Carlip

The problem of reconciling general relativity and quantum theory has fascinated and bedeviled physicists for more than 70 years. Despite recent progress in string theory and loop quantum gravity, a complete solution remains out of reach. I review the status of the continuing effort to quantize gravity, emphasizing the underlying conceptual issues and the var

Gert Brodin, Mattias Marklund, Peter Dunsby

A general system of equations is derived, using the 1+3 orthonormal tetrad formalism, describing the influence of a plane-fronted-parallel gravitational wave on a warm relativistic two-component plasma. We focus our attention on phenomena that are induced by terms that are higher order in the gravitational wave amplitude. In particular, it is shown that para

T. Eiter, M. Fink, G. Sabbatini, H. Tompits

The search for information on the web is faced with several problems, which arise on the one hand from the vast number of available sources, and on the other hand from their heterogeneity. A promising approach is the use of multi-agent systems of information agents, which cooperatively solve advanced information-retrieval problems. This requires capabilities

Daniel Duque, Xiao-jun Li, Kirill Katsov, Michael Schick

Effects of the mismatch between the hydrophobic length, d, of transmembrane alpha helices of integral proteins and the hydrophobic thickness, D_h, of the membranes they span are studied theoretically utilizing a microscopic model of lipids. In particular, we examine the dependence of the period of a lamellar phase on the hydrophobic length and volume fractio

Farhan Rana, Rajeev J. Ram

A comprehensive model for the photon number fluctuations and the current noise in quantum cascade lasers is presented. It is shown that the photon intensity noise in quantum cascade lasers exhibits little amplitude squeezing even when noise in the drive current is suppressed below the shot noise value. This is in contrast to interband semiconductor diode las

Anton Bovier, Beat Niederhauser

We study the Hopfield model with pure $p$-spin interactions with even $p\geq 4$, and a number of patterns, M(N) growing with the system size, $N$, as $M(N) = \a N^{p-1}$. We prove the existence of a critical temperature $\b_p$ characterized as the first time quenched and annealed free energy differ. We prove that as $p\uparrow\infty$, $\b_p\to\sqrt {\a 2\ln

Paulo Murilo Castro de Oliveira

Computer modelling for evolutionary systems consists in: 1) to store in the memory the individual features of each member of a large population; and 2) to update the whole system repeatedly, as time goes by, according to some prescribed rules (reproduction, death, ageing, etc) where some degree of randomness is included through pseudo-random number sequences

D. G. Polyakov, F. Evers, I. V. Gornyi

We study the dynamical properties of an electron gas scattered by impenetrable antidots in the presence of a strong magnetic field. We find that the lineshape of the cyclotron resonance is very different from the Lorentzian and is not characterized by the Drude scattering rate. We show that the dissipative dynamical response of skipping orbits, $S_c(ω)$, is

H. Tanaka, Y. Sekine, S. Saito, H. Takayanagi

We propose a scheme for entangled state measurement at flux qubits (quantum bits) depending on the sensitivity measurement of a DC-SQUID (Superconducting QUantum Interference Device). The DC-SQUID is used as a flux qubit readout device. The switching current distribution of a DC-SQUID is sufficiently narrow to distinguish between two ground states of three J

A. V. Dooglav, M. V. Eremin, Yu. A. Sakhratov, A. V. Savinkov

Systematic measurements of the $^{63}$Cu(2) NQR line width were performed in underdoped YBa$_2$Cu$_3$O$_{7-y}$ samples over the temperature range 4.2 K $<T<300$ K. It was shown that the copper NQR line width monotonically increases upon lowering temperature in the below-critical region, resembling temperature behavior of the superconducting gap. The observed

Paolo Grigolini, Deborah Leddon, Nicola Scafetta

We analyze the waiting time distribution of time distances $τ$ between two nearest-neighbor flares. This analysis is based on the joint use of two distinct techniques. The first is the direct evaluation of the distribution function $ψ(τ)$, or of the probability, $Ψ(tau)$, that no time distance smaller than a given $τ$ is found. We adopt the paradigm of the i

Irene D&#39;Amico, Giovanni Vignale

We study the effect of the electron-electron interaction on the transport of spin polarized currents in metals and doped semiconductors in the diffusive regime. In addition to well-known screening effects, we identify two additional effects, which depend on many-body correlations and exchange and reduce the spin diffusion constant. The first is the &#34;spin

H. -S. Sim, H. -W. Lee, K. J. Chang

With the aid of the Friedel sum rule, we perform first-principles calculations of conductances through monatomic Na wires, taking into account the sharp tip geometry and discrete atomic structure of electrodes. We find that conductances (G) depend on the number (L) of atoms in the wires; G is G_0 (= 2e^2/h) for odd L, independent of the wire geometry, while

D. J. Singh, P. Blaha, K. Schwarz, J. O. Sofo

First principles density functional calculations within the local spin density approximation (LSDA) and the generalized gradient approximation (GGA) are reported for pyrochlore Cd$_2$Os$_2$O$_7$ and Cd$_{2}$Re$_{2}$O$_7$. The transition metal $t_{2g}$ manifolds are found to be well separated in energy from the O $2p$ bands and from the higher lying $e_g$ and

T. del Rio Gaztelurrutia, J. M. Pitarke

We report various many-body theoretical approaches to the nonlinear decay rate and energy loss of charged particles moving in an interacting free electron gas. These include perturbative formulations of the scattering matrix, the self-energy, and the induced electron density. Explicit expressions for these quantities are obtained, with inclusion of exchange

H. Kitano, R. Inoue, T. Hanaguri, A. Maeda

We have measured the temperature- and frequency dependence of the microwave and millimeter wave conductivity $σ_1(T,ω)$ along both the ladder (c-axis) and the leg (a-axis) directions in Sr$_{14}$Cu$_{24}$O$_{41}$. Below a temperature $T^*$($\sim$170 K), we observed a stronger frequency dependence in $σ_1^c(T,ω)$ than that in $σ_1^a(T,ω)$, forming a small res

Altje Latununuwe, Pepen Arifin, Euis Sustini, Horasdia Saragih

The temperature variation of partial mobility and effective mobility for undoped p-GaSb have been calculated using Matthiessen rule. The effective mobility depends on the ionized, acoustic, polar optical and non-polar optical scattering processes. The analysis shows that the effective mobility for undoped p-GaSb at room temperature is about 905 cm^2/Vs with

Robert S. Maier, D. L. Stein

We study a spatially extended model of noise-induced magnetization reversal: a classical Ginzburg-Landau theory, restricted to a bounded interval and perturbed by weak spatiotemporal noise. We compute the activation barrier and Kramers prefactor. As the interval length increases, a transition between activation regimes occurs, at which the prefactor diverges

N. Z. Scoville, M. Polletta, S. Ewald, S. R. Stolovy

(first paragraph) We have obtained Halpha and Palpha emission line images covering the central 3 - 4 arcmin of M51 using the WFPC2 and NICMOS cameras on HST to study the high-mass stellar population. The 0.1 - 0.2 arcsec pixels provide 4.6 - 9 pc resolution in M51 and the Halpha/Palpha line ratios are used to obtain extinction estimates. A sample of 1373 Hal

Vinod B. Johri

We report a significant finding in Quintessence theory that the the scalar fields with tracker potentials have a model-independent scaling behaviour in the expanding universe. So far widely discussed exponential,power law or hyperbolic potentials can simply mimic the tracking behaviour over a limited range of redshift. In the small redshift range where the v

O. De Marco, P. A. Crowther, M. J. Barlow, G. C. Clayton

The hydrogen-deficient carbon-rich [WCL] type central star HD167362 and its oxygen-rich planetary nebula (PN) SwSt~1 are investigated. The nebular chemistry might indicate a recent origin for the carbon-rich stellar spectrum. Its stellar and nebular properties might therefore provide further understanding of the origin of the [WCL] central star class. The UV