August 2001 arXiv papers — page 6

I-Ching Yang, Irina Radinschi

We evaluate the energy distributions of the Dymnikova space-time using the Weinberg, Papapetrou, and Møller energy-momentum complexes. This result sustain the importance of the energy-momentum complexes in the evaluation of the energy distribution of a given space-time. To compare the energy distributions obtained by using several definitions, these results

I. B. Khriplovich

The spectrum of the area operator for a Schwarzschild black hole in loop quantum gravity is fixed by the demand that the entropy of a black hole is maximum. This paper has been withdrawn by the author, due a crucial error in the derivation.

Marshall Bern, Erik D. Demaine, David Eppstein, Eric Kuo

Unfolding a convex polyhedron into a simple planar polygon is a well-studied problem. In this paper, we study the limits of unfoldability by studying nonconvex polyhedra with the same combinatorial structure as convex polyhedra. In particular, we give two examples of polyhedra, one with 24 convex faces and one with 36 triangular faces, that cannot be unfolde

E. Ong, E. Lusk, W. Gropp

We describe a family of MPI applications we call the Parallel Unix Commands. These commands are natural parallel versions of common Unix user commands such as ls, ps, and find, together with a few similar commands particular to the parallel environment. We describe the design and implementation of these programs and present some performance results on a 256-

H. Zha, X. He, C. Ding, M. Gu

Many data types arising from data mining applications can be modeled as bipartite graphs, examples include terms and documents in a text corpus, customers and purchasing items in market basket analysis and reviewers and movies in a movie recommender system. In this paper, we propose a new data clustering method based on partitioning the underlying bipartite

James W. Dufty

These are notes prepared for presentation at the workshop "Challenges in Granular Matter" at the Abdus Salam Institute for Theoretical Physics, Trieste, August 2001. Revisions and figures will be added at a later date. Many features of real granular fluids under rapid flow are replicated by a system of smooth hard spheres with inelastic collisions. F

T. R. Kirkpatrick, Thomas Vojta, D. Belitz, R. Narayanan

It is argued that the phase transition in low-T_c clean itinerant ferromagnets is generically of first order, due to correlation effects that lead to a nonanalytic term in the free energy. A tricritical point separates the line of first order transitions from Heisenberg critical behavior at higher temperatures. Sufficiently strong quenched disorder suppresse

Anaël Lemaître

Constitutive equations are proposed for dense materials, based on the identification of two types of free-volume activated rearrangements associated to shear and compaction. Two situations are studied: the case of an amorphous solid in a stress-strain test, and the case of a lubricant in tribology test. Varying parameters, strain softening, shear thinning, a

K. D. Belashchenko, I. R. Pankratov, G. D. Samolyuk, V. G. Vaks

We review a series of works where the fundamental master equation is used to develop a microscopical description of evolution of non-equilibrium atomic distributions in alloys. We describe exact equations for temporal evolution of local concentrations and their correlators as well as approximate methods to treat these equations, such as the kinetic mean-fiel

Edward G. Timoshenko, Yuri A. Kuznetsov, Roman N. Basovsky

Based on large-scale Monte Carlo simulations on lattice the energy probability distribution functions are investigated for a large set of primary sequences in distinct models of copolymers at low temperatures below transitions to compacted states. Amphiphilic copolymers with hydrophobic and hydrophilic units are found to produce a single or double peak energ

Chris Beck, Xavier Siemens

In the diffusion-collision model, the unfolding rates are given by the likelihood of secondary structural cluster dissociation. In this work, we introduce an unfolding rate calculation for proteins whose secondary structural elements are $α$-helices, modeled from thermal escape over a barrier which arises from the free energy in buried hydrophobic residues.

Ronald Dickman, Wilson R. M. Rabelo, Geza Odor

We study the phase diagram and critical behavior of the one-dimensional pair contact process (PCP) with a particle source using cluster approximations and extensive simulations. The source creates isolated particles only, not pairs, and so couples not to the order parameter (the pair density) but to a non-ordering field, whose state influences the evolution

M. Grueninger, M. Windt, T. Nunner, C. Knetter

Transmission and reflectivity of La_x Ca_14-x Cu_24 O_41 two-leg spin-1/2 ladders were measured in the mid-infrared regime between 500 and 12000 1/cm. This allows us to determine the optical conductivity sigma_1 directly and with high sensitivity. Here we show data for x=4 and 5 with the electrical field polarized parallel to the rungs (E||a) and to the legs

V. V. Pogosov, V. P. Kurbatsky

The effect of external strain on surface properties of simple metals is considered within the modified stabilized jellium model. The equations for the stabilization energy of the deformed Wigner-Seitz cells are derived as a function of the bulk electron density and the given deformation. The results for surface stress and work function of aluminium calculate

Valentin V. Pogosov, Walter V. Pogosov, Denis P. Kotlyarov

Analytical expressions for the binding energy of electrons and positrons in dielectric clusters, analysed in this work, neglect the elastic effects. Therefore, we present the density-functional theory for neutral liquid clusters that experience the spontaneous deformation. Using the 1/R -expansion, $R$ being the cluster radius, the exact analytical expressio

C. I. Westbrook, A. Robert, O. Sirjean, A. Browaeys

We describe our recent realization of BEC using metastable helium. All detection is done with a micruchannel plate which detects the metastables or ions coming from the trapped atom cloud. This discussion emphasizes some of the diagnostic experiments which were necessary to quantitatively analyse our results.

J. Schnack, H. -J. Schmidt, J. Richter, J. Schulenburg

For many spin systems with constant isotropic antiferromagnetic next-neighbour Heisenberg coupling the minimal energies E_{min}(S) form a rotational band, i.e. depend approximately quadratically on the total spin quantum number S, a property which is also known as Lande interval rule. However, we find that for certain coupling topologies, including recently

Ch. Niedermayer, C. Bernhard, T. Holden, R. K. Kremer

The magnetic vortex lattice (VL) of polycrystalline MgB2 has been investigated by transverse-field muon-spin-relaxation (TF-MuSR). The evolution of TF-MuSR depolarization rate, sigma, that is proportional to the second moment of the field distribution of the VL has been studied as a function of temperature and applied magnetic field. The low temperature valu

Manuel Valín-Rodríguez, Antonio Puente, Llorenç Serra

The far-infrared absorption of triangular and square two-dimensional quantum dots is studied by means of time simulations of the density oscillations within the time-dependent local-spin-density approximation. The absorption is spatially analyzed using a local-response theory that allows the identification of {\em corner} and {\em side} modes in the geometri

M. A. Novotny

The Monte Carlo with Absorbing Markov Chains (MCAMC) method is introduced. This method is a generalization of the rejection-free method known as the $n$-fold way. The MCAMC algorithm is applied to the study of the very low-temperature properties of the lifetime of the metastable state of Ising ferromagnets. This is done both for square-lattice and cubic-latt

Antonio Puente, Llorenç Serra, Vidar Gudmundsson

Time-dependent Hartree-Fock theory is used to describe density oscillations of symmetry-unrestricted two-dimensional nanostructures. In the small amplitude limit the results reproduce those obtained within a perturbative approach such as the linearized time-dependent Hartree-Fock one. The nonlinear regime is explored by studying large amplitude oscillations

Gianluca Lattanzi, Amos Maritan

A master equation approach to molecular motors allows to describe a mechano-chemical cyclic system where chemical and translational degrees of freedom are treated on an equal footing. A generalized detailed balance condition in the out of equilibrium regime is shown to be compatible with the Fokker-Planck equation in the continuum limit. The Onsager reciproc

D. Balamurugan, R. Prasad

We present results for ground state structures of small Si$_{n}$H (2 \leq \emph{n} \leq 10) clusters using the Car-Parrinello molecular dynamics. In particular, we focus on how the addition of a hydrogen atom affects the ground state geometry, total energy and the first excited electronic level gap of an Si$_{n}$ cluster. We discuss the nature of bonding of

M. J. Barber, J. W. Clark, C. H. Anderson

It has been proposed that populations of neurons process information in terms of probability density functions (PDFs) of analog variables. Such analog variables range, for example, from target luminance and depth on the sensory interface to eye position and joint angles on the motor output side. The requirement that analog variables must be processed leads i

C. -M. Chen, C. F. Schmidt, P. D. Olmsted, F. C. MacKintosh

We report experimental observations of an undulational instability of myelin figures. Motivated by this, we examine theoretically the deformation and possible instability of concentric, cylindrical, multi-lamellar membrane structures. Under conditions of osmotic stress (swelling or dehydration), we find a stable, deformed state in which the layer deformation

K. D. Belashchenko, I. R. Pankratov, G. D. Samolyuk, V. G. Vaks

The earlier-developed master equation approach and kinetic cluster methods are applied to study kinetics of L1_0 type orderings in alloys, including the formation of twinned structures characteristic of cubic-tetragonal-type phase transitions. A microscopical model of interatomic deformational interactions is suggested which generalizes a similar model of Kh

K. Doll, G. Zwicknagl

We compute the structure of an azamacrocycle, C26H18N6. Two approximatively planar elliptical structures with C2 or CI symmetry are found to be nearly degenerate. The roughly circular conformation observed in metal complexes turns out to be ~ 0.6 eV higher in energy. We suggest that this difference is mainly due to electrostatic interactions. We discuss the

Michel Pleimling

Results of large-scale Monte Carlo simulations of three-dimensional Ising models with edges and corners are reviewed. At the ordinary transition, angle dependent critical exponents are observed, whereas at the surface transition edge and corner critical exponents are non-universal and depend on the details of the model. The results obtained at the surface tr

Shigeki Onoda, Masatoshi Imada

Metals approaching the Mott insulator generate a new hierarchy in the electronic structure accompanied by a momentum dependent electron differentiation, beyond the Mott-Hubbard, Brinkman-Rice and Slater pictures of the Mott transition. To consider such nonlinear phenomenon, we develop an analytic nonperturbative theory based on operator projections combined

T. Sato, H. Matsui, S. Nishina, T. Takahashi

Angle-resolved photoemission spectroscopy (ARPES) has been performed on the single- to triple-layered Bi-family high-{\it T$_c$} superconductors (Bi$_2$Sr$_2$Ca$_{n-1}$Cu$_n$O$_{2n+4}$, $\it{n}$=1-3). We found a sharp quasiparticle peak as well as a pseudogap at the Fermi level in the triple-layered compound. Comparison among three compounds has revealed a u

Ryotaro Arita, Yuji Suwa, Kazuhiko Kuroki, Hideo Aoki

We propose that a chain of five-membered rings (polyaminotriazole) should be ferromagnetic with an appropriate doping that is envisaged to be feasible with an FET structure. The ferromagnetism is confirmed by a spin density functional calculation, which also shows that ferromagnetism survives the Peierls instability. We explain the magnetism in terms of Miel

Ryotaro Arita, Yoshiaki Tanida, Kazuhiko Kuroki, Hideo Aoki

GW approximation is used to systematically revisit the image-potential band-gap narrowing at metal/semiconductor interfaces proposed by Inkson in the 1970's. Here we have questioned how the narrowing as calculated from quasi-particle energy spectra for the jellium/Si interface depends on $r_s$ of the jellium. The gap narrowing is found to only weakly dep

S. L. Narasimhan, P. S. R. Krishna, K. P. N. Murthy, M. Ramanadham

We propose an algorithm based on local growth rules for kinetically generating self avoiding walk configurations at any given temperature. This algorithm, called the Interacting Growth Walk (IGW) algorithm, does not suffer from attrition on a square lattice at zero temperature, in contrast to the existing algorithms. More importantly, the IGW algorithm facil

S. I. Schlachter, W. H. Fietz, K. Grube, W. Goldacker

We performed ac-susceptibility measurements of magnesium diboride powder samples under pure hydrostatic pressures up to 0.4 GPa and under quasi-hydrostatic pressure conditions up to 8 GPa in a helium gas pressure cell and a diamond-anvil cell (DAC), respectively. Furthermore, the DAC has been used to investigate the lattice compression by X-ray diffraction.

Dennis R. Crabtree, Elizabeth P. Bryson

We have investigated the productivity and impact of the Canada-France-Hawaii Telescope (CFHT) during its twenty-year history. CFHT has maintained a database of refereed publications based on data obtained with CFHT since first light in 1979. For each paper, we analysed the cumulative number of citations and the citation counts for each year, from data suppli

Peter E. Freeman, Vinay Kashyap, Robert Rosner, Donald Q. Lamb

Wavelets are scaleable, oscillatory functions that deviate from zero only within a limited spatial regime and have average value zero. In addition to their use as source characterizers, wavelet functions are rapidly gaining currency within the source detection field. Wavelet-based source detection involves the correlation of scaled wavelet functions with bin

Chadwick A. Trujillo, Jane X. Luu, Amanda S. Bosh, James L. Elliot

We present a survey for bright Kuiper Belt Objects (KBOs) and Centaurs, conducted at the Kitt Peak National Observatory (KPNO) 0.9 m telescope with the KPNO 8k Mosaic CCD. The survey imaged 164 sq deg near opposition to a limiting red magnitude of 21.1. Three bright KBOs and one Centaur were found, the brightest KBO having red magnitude 19.7, about 700 km in

Kerstin Weis, Michael F. Corcoran, Kris Davidson

The extremely luminous and unstable star Eta Carinae is surrounded by ejecta formed during the star's giant eruption around 1843. The optical nebula consists of an inner region, the bipolar Homunculus and the outer ejecta. The X-ray emission as detected in ROSAT and CHANDRA shows a hook shaped emission structure mainly at the position of the outer ejecta

Peter E. Freeman, Stephen Doe, Aneta Siemiginowska

The ever-increasing quality and complexity of astronomical data underscores the need for new and powerful data analysis applications. This need has led to the development of Sherpa, a modeling and fitting program in the CIAO software package that enables the analysis of multi-dimensional, multi-wavelength data. In this paper, we present an overview of Sherpa

Heath Jones

Tunable imaging filters have been used for a variety of science programmes on the Anglo-Australian and William Herschel Telescopes during the last five years. This contribution describes these novel devices and reviews the science (both Galactic and extragalactic) done with them. Possible strategies for implementing a tunable filter at the VLT are also discu

J. C. Wilson, J. Davy Kirkpatrick, J. E. Gizis, M. F. Skrutskie

We present two confirmed wide separation L-dwarf common proper motion companions to nearby stars and one candidate identified from the Two Micron All Sky Survey. Spectral types from optical spectroscopy are L0 V, L2.5 V, and L8 V. Near-infrared low resolution spectra of the companions are provided as well as a grid of known objects spanning M6 V -- T dwarfs

S. M. Kanbur, D. Iono, N. R. Tanvir, M. A. Hendry

We show how Principal Component Analysis can be used to analyse the structure of Cepheid light curves. This method is more efficient than Fourier analysis at bringing out changes in light curve shape as a function of period. Using this technique, we study the shape of fundamental and first overtone mode Cepheid light curves in the Galaxy, LMC and SMC over a

Leticia Carigi

I study the effect of the galaxies of the Milky Way subgroup on the chemical enrichment of the diffuse gas within the Local Group. The preferred model predicts that the present-day intergalactic medium mass is 1/22 of the initial baryonic mass and its metallicity is 1/20 $Z_\odot$. Nearly 80 % of intergalactic metals were produced in the Galactic bulge.

V. Šimon, R. Hudec, G. Pizzichini, N. Masetti

Results of the study of the color indices and luminosities of 17 optical afterglows (OAs) of GRBs are presented. We show that the color variations during the decline of OAs (except for GRB000131) are relatively small during t-T_0 < 10 days and allow a comparison among them, even for the less densely sampled OAs. The colors in the observer frame, corrected fo

O. Fors, J. Nunez, A. Richichi

A CCD drift-scanning technique for lunar occultation (LO) observations is presented. While this approach has been addressed before by Sturmann (1994) for the case of large telescopes, the technical validity has never been discussed for sub-meter class telescopes. In contrast to Sturmann&#39;s scheme, the proposed technique places the CCD in the image plane o

M. Feroci, L. A. Antonelli, P. Soffitta, J. J. M. in &#39;t Zand

We present the X- and $γ$-ray detection of GRB 990704 and the discovery and study of its X-ray afterglow, 1SAX J1219.5-0350. Two pointed BeppoSAX observations with the narrow field instruments were performed on this source, separated in time by one week. The decay of the X-ray flux within the first observation appears unusually slow, being best-fit by a powe

Daigo Tomono, Yoshiyuki Doi, Tomonori Usuda, Tetsuo Nishimura

The central region of the Seyfert 2 galaxy NGC 1068 is imaged in the mid infrared (MIR) using the Mid-Infrared Test Observation System on the 8.2 m Subaru Telescope. The oversampling pixel scale associated with shift-and-add method shows 0.1 arcsec resolution images with a high dynamic range after deconvolution. Along with an extended structure at a position

Junichiro Makino

We present a novel, highly efficient algorithm to parallelize O(N^2) direct summation method for N-body problems with individual timesteps on distributed-memory parallel machines such as Beowulf clusters. Previously known algorithms, in which all processors have complete copies of the N-body system, has the serious problem that the communication-computation

Tomohiro Harada

A direct method is developed to reconstruct the equation of state for high-density nuclear matter from the relationship between any two properties of neutron stars, such as masses, radii, moments of inertia, baryonic masses, binding energies, gravitational redshifts, and their combinations.

Ravi Subrahmanyan

Australia Telescope Compact Array (ATCA) observations in sky regions selected to be low in foreground confusion have been used to infer limits on arcmin-scale CMB anisotropy in total intensity and polarization. These deep searches have, hitherto, been made using the East-West ATCA in an ultra-compact 1-D array configuration and in the highest available frequ

B. W. Miller, A. E. Dolphin, M. G. Lee, S. C. Kim

We have determined the distance and star formation history of the Local Group dwarf galaxy LGS 3 from deep Hubble Space Telescope WFPC2 observations. LGS 3 is intriguing because ground-based observations showed that, while its stellar population is dominated by old, metal-poor stars, there is a handful of young, blue stars. Also, the presence of HI gas makes

W. Buchmuller, D. Wyler

We study neutrino masses and mixings based on the simplest SO(10) mass relations and the seesaw mechanism. We find that the requirement of large neutrino mixings determines the relative magnitude of the heavy Majorana neutrino masses in terms of the known quark mass hierarchy. This leads to specific predictions for the structure of the neutrino mixing matrix

Christian Korff, Itzhak Roditi

We consider integrable vertex models whose Boltzmann weights (R-matrices) are trigonometric solutions to the graded Yang-Baxter equation. As is well known the latter can be generically constructed from quantum affine superalgebras $U_{q}(\hat g)$. These algebras do not form a symmetry algebra of the model for generic values of the deformation parameter $q$ w

Wang Xiang-Bin, Matsumoto Keiji

Motivated for the fault tolerant quantum computation, quantum gate by adiabatic geometric phase shift is extensively investigated. In this paper, we demonstrate the nonadiabatic scheme for the geometric phase shift and conditional geometric phase shift. Essentially, the new scheme is simply to add an appropriate additional field. With this additional field,

Vadim V. Varlamov

Finite-dimensional representations of the proper orthochronous Lorentz group are studied in terms of spinor representations of the Clifford algebras. The Clifford algebras are understood as an `algebraic covering&#39; of a full system of the finite-dimensional representations of the Lorentz group. Space-time discrete symmetries P, T and PT, represented by fu

G. W. Gibbons, H. Lu, C. N. Pope, K. S. Stelle

Supersymmetric domain-wall spacetimes that lift to Ricci-flat solutions of M-theory admit generalized Heisenberg (2-step nilpotent) isometry groups. These metrics may be obtained from known cohomogeneity one metrics of special holonomy by taking a &#34;Heisenberg limit&#34;, based on an Inönü-Wigner contraction of the isometry group. Associated with each suc

Stephon Alexander, Robert Brandenberger, Joao Magueijo

We show how a radiation dominated universe subject to space-time quantization may give rise to inflation as the radiation temperature exceeds the Planck temperature. We consider dispersion relations with a maximal momentum (i.e. a mimimum Compton wavelength, or quantum of space), noting that some of these lead to a trans-Planckian branch where energy increas

Gia Dvali, Matias Zaldarriaga

If the recent observations suggesting a time variation of the fine structure constant are correct, they imply the existence of an ultra light scalar particle. This particle inevitably couples to nucleons through the α-dependence of their masses and thus mediates an isotope-dependent long-range force. The strength of the coupling is within a couple of orders

Katherine A. Seaton

Some universal amplitude ratios appropriate to the $ϕ_{2,1}$ peturbation of the c=7/10 minimal field theory, the subleading magnetic perturbation of the tricritical Ising model, are explicitly demonstrated in the dilute A$_3$ model, in regime 1.

Subir Sachdev

We argue that aspects of the anomalous, low temperature, spin and charge dynamics of the high temperature superconductors can be understood by studying the corresponding physics of undoped Mott insulators. Such insulators display a quantum transition from a magnetically ordered Neel state to a confining paramagnet with a spin gap; the latter state has bond-c

Ken Ebisawa, Yoshitomo Maeda, Hidehiro Kaneda, Shigeo Yamauchi

The Galactic plane is a strong hard x-ray emitter and the emission forms a narrow continuous ridge. The currently known hard x-ray sources are far too few to explain the ridge x-ray emission, and the fundamental question as to whether the ridge emission is ultimately resolved into numerous dimmer discrete sources or truly diffuse emission has not yet been se

Etienne Boaknin, R. W. Hill, Cyril Proust, C. Lupien

The thermal conductivity of borocarbide superconductor LuNi_2B_2C was measured down to 70 mK (T_c/200) in a magnetic field perpendicular to the heat current from H = 0 to above H_c2 = 7 T. As soon as vortices enter the sample, the conduction at T -> 0 grows rapidly, showing unambiguously that delocalized quasiparticles are present at the lowest energies. The

A. V. Efremov, K. Goeke, P. Schweitzer

Recently HERMES has observed an azimuthal asymmetry in electro-production of neutral pions in semi-inclusive deep-inelastic scattering of unpolarized positrons off longitudinally polarized protons. This asymmetry (like those observed in the production of charged pions) is well reproduced theoretically by using the non-perturbative calculation of the proton t

Pantelis S. Apostolopoulos, Michael Tsamparlis

All hypersurface homogeneous locally rotationally symmetric spacetimes which admit conformal symmetries are determined and the symmetry vectors are given explicitly. It is shown that these spacetimes must be considered in two sets. One set containing Ellis Class II and the other containing Ellis Class I, III LRS spacetimes. The determination of the conformal

C. L. Herzenberg

A new conceptual approach for examining the origin of cosmic rays is developed by considering the characteristics of particle trajectory distributions in four-dimensional Euclidean space-time. Transformation of an isotropic distribution into a velocity distribution in ordinary three-dimensional space results in a spatially isotropic flux of highly relativist

S. Gilad

The promise and limitations of studying nuclear structure and reactions using (e,e&#39;p) reactions are discussed. A(e,e&#39;p)A-1 reactions on complex nuclei are used to test new relativistic mean-field calculations and their ingredients such as ground-state wave function, current operators, final-state interactions and two-body currents, and to assess the

E. Ben-Naim, P. L. Krapivsky

We study an elementary two-player card game where in each round players compare cards and the holder of the smallest card wins. Using the rate equations approach, we treat the stochastic version of the game in which cards are drawn randomly. We obtain an exact solution for arbitrary initial conditions. In general, the game approaches a steady state where the

Sergei V. Ketov

Born-Infeld theory is the non-linear generalization of Maxwell electrodynamics. It naturally arises as the low-energy effective action of open strings, and it is also part of the world-volume effective action of D-branes. The N=1 and N=2 supersymmetric generalizations of the Born-Infeld action are closely related to partial spontaneous breaking of rigid exte

Masaru Kamata, Atsushi Nakamula

In the preceding paper (Phys. Lett. B463 (1999) 257), the authors presented a q-analog of the ADHMN construction and obtained a family of anti-selfdual configurations with a parameter q for classical SU(2) Yang-Mills theory in four-dimensional Euclidean space. The family of solutions can be seen as a q-analog of the single BPS monopole preserving (anti-)self

G. Wilk, Z. Wlodarczyk

We present an overview of possible imprints of non-extensitivity in particle and nucler physics. Special emphasis is put on the intrinsic fluctuations present in the system under consideration as the possible source of nonextensivity. The possible connection of nonextensivity and the self organized criticality apparently being observed in some cosmic rays an

Pervez Hoodbhoy

By means of an explicit one-loop calculation, it is shown that the leading twist contribution to the exclusive electroproduction of transversely polarized vector mesons from the nucleon vanishes. This confirms the all-orders proof by Collins and Diehl.

F. Becattini, G. Pettini

We suppose that overall strangeness production in both high energy elementary and heavy ion collisions can be described within the framework of an equilibrium statistical model in which the effective degrees of freedom are constituent quarks as used in effective lagrangian models. In this picture, the excess of relative strangeness production in heavy ion co

L. C. Garcia de Andrade

A new class of spacetime defect solutions of Einstein Field equations of Edelen&#39;s direct Poincaré Gauge Field theory without biaxial symmetry is presented. The interior solution describes a core of defects where curvature vanishes and Cartan torsion is nonvanishing. Outside the core (in vacuum) the solution represents a spacetime with vanishing curvature

Pantelis S. Apostolopoulos, Michael Tsamparlis

It is shown that the results of the paper by Contreras et al. [Contreras, G., Nunez, L. A., Percoco, U. &#34;Ricci Collineations for Non-degenerate, Diagonal and Spherically Symmetric Ricci Tensors&#34; (2000) Gen. Rel. Grav. 32, 285-294] concerning the Ricci Collineations in spherically symmetric space-times with non-degenerate and diagonal Ricci tensor do

Aviel D. Rubin

This paper discusses the security considerations for remote electronic voting in public elections. In particular, we examine the feasibility of running national federal elections over the Internet. The focus of this paper is on the limitations of the current deployed infrastructure in terms of the security of the hosts and the Internet itself. We conclude th

Shaz Qadeer

The memory model of a shared-memory multiprocessor is a contract between the designer and programmer of the multiprocessor. The sequential consistency memory model specifies a total order among the memory (read and write) events performed at each processor. A trace of a memory system satisfies sequential consistency if there exists a total order of all memor

Junji Ito, Kunihiko Kaneko

As a model of temporally evolving networks, we consider a globally coupled logistic map with variable connection weights. The model exhibits self-organization of network structure, reflected by the collective behavior of units. Structural order emerges even without any inter-unit synchronization of dynamics. Within this structure, units spontaneously separat

Xiao Yang, Chetan Nayak

We compute the electrical and thermal conductivities and Hall conductivities of the $d$-density wave (DDW) state in the low-temperature impurity-scattering-dominated regime for low-dopings, at which they are dominated by nodal quasiparticles. We show that the longitudinal conductivity in this limit in the DDW state is not Drude-like. However, the thermal con

Stefano Sanvito, Nicola A. Hill

MnAs/GaAs superlattices, made by $δ$-doping GaAs with Mn, are known as digital ferromagnetic heterostructures. Here we present a theoretical density functional study of the electronic, magnetic and transport properties of such heterostructures. In the absence of intrinsic donors these systems show an half metallic density of states, with an exchange interact

Y. Chou, J. E. Grindlay

We present timing analysis results for Rossi x-ray Timing Explorer (RXTE) observations of x-ray binary source 4U 1820$-$30 located in the globular cluster NGC 6624. The light curves of observations made between October 1996 and September 1997 show that the maximum of the 685s binary period modulation folded by the linear ephemeris from previous observations

P. R. Bolton, J. E. Clendenin, D. H. Dowell, M. Ferrario

The design of the Linac Coherent Light Source assumes that a low-emittance, 1-nC, 10-ps beam will be available for injection into the 15-GeV linac. The proposed rf photocathode injector that will provide a 150-MeV beam with rms normalized emittances of 1 mm in both the transverse and longitudinal dimensions is based on a 1.6-cell S-band rf gun that is equipp

M. Kellogg, I. B. Spielman, J. P. Eisenstein, L. N. Pfeiffer

The frictional drag between parallel two-dimensional electron systems has been measured in a regime of strong interlayer correlations. When the bilayer system enters the excitonic quantized Hall state at total Landau level filling factor ν_T=1 the longitudinal component of the drag vanishes but a strong Hall component develops. The Hall drag resistance is ob

Gautam Rupak, Xin-wei Kong

We present a power counting to include Coulomb effects in the three-nucleon system in a low-energy pionless effective field theory (EFT). With this power counting, the quartet S-wave proton-deuteron elastic scattering amplitude is calculated. The calculation includes next-to-leading order (NLO) Coulomb effects and next-to-next-to-leading order (NNLO) strong

Bing Zhang, Peter Meszaros

(Abridged) We discuss a Gamma-ray burst (GRB) fireball with an additional energy injection, either in the form of a Poynting-flux-dominated outflow or a kinetic-energy-dominated matter shell injected after the burst. A total injection energy comparable to that of the impulsive energy in the initial fireball is required to make a detectable signature in the a

O. Almaini, S. E. Scott, J. S. Dunlop, J. C. Manners

We explore the relationship between the hard X-ray and sub-mm populations using deep Chandra observations of a large, contiguous SCUBA survey. In agreement with other recent findings, we confirm that the direct overlap is small. Of the 17 sub-mm sources detected in this field at 850 microns, only one is coincident with a Chandra source. The resulting limits

Ernest Ma

Using the particle content of the fundamental {27} supermultiplet of E_6, naturally small Dirac neutrino masses are obtained in the context of SU(3)_C times SU(2)_L times U(1)_Y times U(1)_{chi}, where U(1)_{chi} comes from the decomposition E_6 to SO(10) times U(1)_{psi}, then SO(10) to SU(5) times U(1)_{chi}. New observable consequences are predicted at th

R. Jin, J. He, J. R. Thompson, M. F. Chisholm

Experimental investigation of the resistivity $ρ$, susceptibility $χ$, specific heat C$_p$, and Hall coefficient R$_H$ of the pyrochlore Cd$_2$Re$_2$O$_7$ reveals the presence of a continuous phase transition of uncertain origin with critical temperature T* = 200 K. Electron and X-ray diffraction measurements indicate that a commensurate structural transform

L. D. Cooley, X. Song, J. Jiang, D. C. Larbalestier

The nanostructure and magnetic properties of polycrystalline MgCNi_3 were studied by x-ray diffraction, electron microscopy, and vibrating sample magnetometry. While the bulk flux-pinning force curve F_p(H) indicates the expected grain-boundary pinning mechanism just below T_c = 7.2 K, a systematic change to pinning by a nanometer-scale distribution of core

Justin Khoury, Burt A. Ovrut, Nathan Seiberg, Paul J. Steinhardt

We consider conditions under which a universe contracting towards a big crunch can make a transition to an expanding big bang universe. A promising example is 11-dimensional M-theory in which the eleventh dimension collapses, bounces, and re-expands. At the bounce, the model can reduce to a weakly coupled heterotic string theory and, we conjecture, it may be

Mustapha Ishak, Kayll Lake

The stability of transparent spherically symmetric thin shells (and wormholes) to linearized spherically symmetric perturbations about static equilibrium is examined. This work generalizes and systematizes previous studies and explores the consequences of including the cosmological constant. The approach shows how the existence (or not) of a domain wall domi

J. S. Dunlop, R. J. McLure, M. J. Kukula, S. A. Baum

We present the final results from our deep HST imaging study of the hosts of radio-quiet quasars (RQQs), radio-loud quasars (RLQs) and radio galaxies (RGs). We describe new WFPC2 R-band observations for 14 objects and model these images in conjunction with the data already reported in McLure et al (1999). We find that spheroidal hosts become more prevalent w

A. L. Chudnovskiy, D. Pfannkuche

Influence of disorder on the ferromagnetic phase transition in diluted (III,Mn)V semiconductors is investigated analytically. The regime of small disorder is addressed, and the enhancement of the critical temperature by disorder is found both in the mean field approximation and from the analysis of the zero temperature spin stiffness. Due to disorder, the sp

S. G. Schirmer, J. V. Leahy, A. I. Solomon

Precise definitions for different degrees of controllability for quantum systems are given, and necessary and sufficient conditions are discussed. The results are applied to determine the degree of controllability for various atomic systems with degenerate energy levels and transition frequencies.

J. P. J. Hetherington

The Minimal Supersymmetric Standard Model (MSSM) can include two soft breaking terms which are often neglected: a non-analytic scalar trilinear coupling and a Higgsino bilinear term. A set of high-scale boundary conditions consistent with the reparameterisation invariance which the model possesses is obtained. The three-family renormalisation group equations

S. Groot Nibbelink

An extension of dimensional regularization to the case of compact dimensions is presented. The procedure preserves the Kaluza-Klein tower structure, but has a regulator specific to the compact dimension. Possible 5 and 4 dimensional divergent as well as manifest finite contributions of (one-loop) Feynman graphs can easily be identified in this scheme.

M. Ausloos, K. Ivanova

The multifractal structure of the temporal dependence of the Deutsche Aktienindex (DAX) is analyzed. The $q$-th order moments of the structure functions and the singular measures are calculated. The generalized Hurst exponent $H(q)$ and the $h(γ(q))$ curve indicate a hierarchy of power law exponents. This approach leads to characterizing the nonstationarity

Jose Natario

Given a (d+1)-dimensional spacetime (M,g), one can consider the set N of all its null geodesics. If (M,g) is globally hyperbolic then this set is naturally a smooth (2d-1)-manifold. The sky of an event x in M is the set X of all null geodesics through x, and is an embedded submanifold of N diffeomorphic to S^{d-1}. Low conjectured that if d=2 then x,y are ca

Naofumi Kitsunezaki, Shozo Uehara

We evaluate $N$ dependences of correlation functions in the bosonic part of the IIB matrix model by the Monte Carlo method. We also evaluate those in two sorts of regularized Schild models and find that the $N$ dependences are different from those in the matrix model. In particular, the distribution of the eigenvalues are logarithmically divergent in the reg

E. L. Bratkovskaya

The dilepton production from $pC$ and $pCu$ collisions at $T_{lab}=12$ GeV is calculated using the semi-classical BUU transport model, that includes the off-shell propagation of vector mesons nonperturbatively and calculates the width of the vector mesons dynamically. It is found that the collisional broadening of the vector meson width and dropping vector m

Masashi Naganuma, Muneto Nitta, Norisuke Sakai

BPS walls and junctions are studied in ${\cal N}=1$ SUSY nonlinear sigma models in four spacetime dimensions. New BPS junction solutions connecting N discrete vacua are found for nonlinear sigma models with several chiral scalar superfields. A nonlinear sigma model with a single chiral scalar superfield is also found which has a moduli space of the topology