December 2006 arXiv papers — page 45

Flore Barcellini, Françoise Détienne, Jean-Marie Burkhardt

The objective of this research is to analyse the ways members of open-source software communities participate in design. In particular we focus on how users of an Open Source (OS) programming language (Python) participate in adding new functionalities to the language. Indeed, in the OS communities, users are highly skilled in computer sciences; they do not c

Matthew Delacorte

We use the concept of a Kirchhoff resistor network (alternatively random walk on a network) to probe connected graphs and produce symmetry revealing canonical labelings of the graph(s) nodes and edges.

Kiyohisa Tanaka, W. S. Lee, D. H. Lu, A. Fujimori

We use angle-resolved photoemission spectroscopy applied to deeply underdoped cuprate superconductors Bi2Sr2(Ca,Y)Cu2O8 (Bi2212) to reveal the presence of two distinct energy gaps exhibiting different doping dependence. One gap, associated with the antinodal region where no coherent peak is observed, increases with underdoping - a behavior known for more tha

Katja Lindenberg, J. M. Sancho, A. M. Lacasta, I. M. Sokolov

We study and characterize a new dynamical regime of underdamped particles in a tilted washboard potential. We find that for small friction in a finite range of forces the particles move essentially nondispersively, that is, coherently, over long intervals of time. The associated distribution of the particle positions moves at an essentially constant velocity

Jean-Sebastien Bernier, K. Sengupta, Yong Baek Kim

We study the Mott phases and superfluid-insulator transition of spin-three bosons in an optical lattice with an anisotropic two dimensional optical trap. We chart out the phase diagrams for Mott states with $n=1$ and $n=2$ atoms per lattice site. It is shown that the long-range dipolar interaction stabilizes a state where the chains of the ferromagnetically

Lara Faoro, Lev B. Ioffe

We analyze data on the critical current and normal state resistance noise in Josephson junctions and argue that the noise in the critical current is due to a mechanism that is absent in the normal state. We estimate the noise produced by conventional Two Level Systems (TLSs) in the insulating barrier and find that it agrees both in magnitude and in temperatu

D. Inosov, S. Borisenko, I. Eremin, A. Kordyuk

Angle resolved photoemission spectroscopy (ARPES) provides a detailed view of the renormalized band structure and, consequently, is a key to the self-energy and the single-particle Green's function. Here we summarize the ARPES data accumulated over the whole Brillouin zone for the optimally doped Bi$_2$Sr$_2$CaCu$_2$O$_{8-δ}$ into a parametric model of t

R. Jaramillo, T. F. Rosenbaum, E. D. Isaacs, O. G. Shpyrko

Magnetotransport measurements on small single crystals of Cr, the elemental antiferromagnet, reveal the hysteretic thermodynamics of the domain structure. The temperature dependence of the transport coefficients is directly correlated with the real-space evolution of the domain configuration as recorded by x-ray microprobe imaging, revealing the effect of an

Yacine Ikhlef, Jesper Lykke Jacobsen, Hubert Saleur

The antiferromagnetic critical point of the Potts model on the square lattice was identified by Baxter as a staggered integrable six-vertex model. In this work, we investigate the integrable structure of this model. It enables us to derive some new properties, such as the Hamiltonian limit of the model, an equivalent vertex model, and the structure resulting

D. Sanvitto, F. P. Laussy, F. Bello, D. M. Whittaker

A single atom in a cavity is the model system of cavity quantum electrodynamics (CQED). The strong coupling regime between the atom and cavity-confined photon corresponds to the reversible exchange of energy between the two modes, and underpins a wide range of CQED phenomena with applications in quantum information science, including for example as quantum l

I. N. Zhilyaev

For a two-dimensional conductor under the conditions of the Bardeen-Cooper-Schrieffer mechanism of superconductivity, a factor resulting in economy in kinetic energy upon the transition to the superconducting state and connected to the zero oscillations of macroscopic quantum oscillator is offered. The economy, in as turn, can result in greater rigity of sup

I. L. Landau, H. Keller

We reanalyze the magnetization data collected on Bi_2Sr_2Ca_(1-x)Y_xCu_2O_(8+y) samples (Kim at al, Phys. Rev. B 72, 64525 (2005)) and argue that the method, which was used for the analysis of equilibrium magnetization data, is not adequate to the experimental situation. As a result, the temperature dependencies of the upper critical field Hc2(T) and the mag

K. Kikoin, Y. Avishai

Recent advancement in fabrication technologies enable the construction of nano-objects with rather rich internal structures such as double or triple quantum dots, which can then be regarded as artificial molecules. The main new ingredient in the study of the Kondo effect in such artificial (and also in natural) molecules is the internal symmetry of the nano-

A. Levy Yeyati, F. S. Bergeret, A. Martin-Rodero, T. M. Klapwijk

Superconductors connected to normal metallic electrodes at the nanoscale provide a potential source of non-locally entangled electron pairs. Such states would arise from Cooper pairs splitting into two electrons with opposite spins tunnelling into different leads. In an actual system the detection of these processes is hindered by the elastic transmission of

Yoko Miura, Yukio Yasui, Masatoshi Sato, Naoki Igawa

A new-type structural transition has been found in Li2RuO3 with honeycomb lattice of edge-sharing RuO6-octahedra. With decreasing temperature T, the electrical resistivity exhibits an anomalous increase at T=Tc~540 K, suggesting the (metal to insulator)-like transition and the magnetic susceptibility also shows a sharp decrease. Detailed structure analyses h

Christian Ertler, Jaroslav Fabian

We propose a ferromagnetic spintronic system, which consists of two serial connected resonant tunneling diodes. One diode is nonmagnetic whereas the other comprises a ferromagnetic emitter and quantum well. Using a selfconsistent coherent transport model we show that the current-voltage characteristic of the ferromagnetic diode can be strongly modulated by c

L. Angelani, C. Conti, L. Prignano, G. Ruocco

We report on a statistical approach to mode-locking transitions of nano-structured laser cavities characterized by an enhanced density of states. We show that the equations for the interacting modes can be mapped onto a statistical model exhibiting a first order thermodynamic transition, with the average mode-energy playing the role of inverse temperature. T

H. Masaki, T. Ishida, R. Antos, J. Shibata

We investigate the influence of the vortex chirality on the magnetization processes of a magnetostatically coupled pair of magnetic disks. The magnetic vortices with opposite chiralities are realized by introducing asymmetry into the disks. The motion of the paired vortices are studied by measuring the magnetoresistance with lock-in resistance bridge techniq

A. Conca, M. Jourdan, H. Adrian

Epitaxial thin films of the theoretically predicted half metal Co2Cr0.6Fe0.4Al were deposited by dc magnetron sputtering on different substrates and buffer layers. The samples were characterized by x-ray and electron beam diffraction (RHEED) demonstrating the B2 order of the Heusler compound with only a small partition of disorder on the Co sites. Magnetic t

Trieu Mai, Abhishek Dhar

We study work fluctuation theorems for oscillators in non-Markovian heat baths. By calculating the work distribution function for a harmonic oscillator with motion described by the generalized Langevin equation, the Jarzynski equality (JE), transient fluctuation theorem (TFT), and Crooks' theorem (CT) are shown to be exact. In addition to this derivation

Mario De Menech, Ulf Saalmann, Martin E. Garcia

Low-temperature scanning tunneling spectroscopy allows to probe the electronic properties of clusters at surfaces with unprecedented accuracy. By means of quantum transport theory, using realistic tunneling tips, we obtain conductance curves which considerably deviate from the cluster's density of states. Our study explains the remarkably small number of

T. Waki, M. Takigawa, T. Yamauchi, J. Yamaura

We report 51V NMR experiments in the metallic phase of the quasi-one-dimensional (1D) conductor beta-Sr0.33V2O5. The Knight shift and the quadrupole splitting of all six vanadium sites were determined as a function of the direction of magnetic field perpendicular to the conducting b-axis. Magnetic properties of the three 1D structural units are remarkably he

Daisuke Tahara, Yukitoshi Motome, Masatoshi Imada

We study thermodynamic properties of an antiferromagnetic Ising model on the inverse perovskite lattice by using Monte Carlo simulations. The lattice structure is composed of corner-sharing octahedra and contains three-dimensional geometrical frustration in terms of magnetic interactions. The system with the nearest-neighbor interactions alone does not exhib

E. M. Hankiewicz, G. Vignale, Y. Tserkovnyak

We present a microscopic calculation of the Gilbert damping constant for the magnetization of a two-dimensional spin-polarized electron liquid in the presence of intrinsic spin-orbit interaction. First we show that the Gilbert constant can be expressed in terms of the auto-correlation function of the spin-orbit induced torque. Then we specialize to the case

Stephen R. Williams, Denis J. Evans, Emil Mittag

Linear irreversible thermodynamics asserts that the instantaneous local spontaneous entropy production is always nonnegative. However for a viscoelastic fluid this is not always the case. Given the fundamental status of the Second Law, this presents a problem. We provide a new derivation of the Second Law, from first principles, which is valid for the approp

A. E. Kobryn, F. Hirata

We present results of theoretical description of ultrasonic phenomena in molecular liquids. In particular, we are interested in the development of microscopical, i.e., statistical-mechanical framework capable to explain the long living puzzle of the excess ultrasonic absorption in liquids. Typically, ultrasonic wave in a liquid can be generated by applying t

Sven Aerts, Diederik Aerts, Franklin E. Schroeck, Jurgen Sachs

We study the statistical performance and applicability of a simple quantum state discrimination technique for the analysis of data from nuclear quadrupole resonance experiments on a TNT sample. The target application is remote detection of anti-personnel landmines.We show that, even for data that allows the determination of only one time dependent component

Takahumi Suzuki, Sei-ichiro Suga

We investigate NMR relaxation rates 1/T_1 of quantum spin chains in magnetic fields. Universal properties for the divergence behavior of 1/T_1 are obtained in the Tomonaga-Luttinger-liquid state. The results are discussed in comparison with experimental results.

T. Fragos, B. Willems, N. Ivanova, V. Kalogera

In recent years, an increasing number of proper motions have been measured for Galactic X-ray binaries. When supplemented with accurate determinations of the component masses, orbital period, and donor luminosity and effective temperature, these kinematical constraints harbor a wealth of information on the systems' past evolution. The constraints on comp

L. Carigi

I present a review of chemical evolution models of the solar neighborhood. I give special attention to the necessary ingredients to reproduce the observed [Xi/Fe] ratios in nearby metal and super metal rich stars, and to the chemical properties of the solar vicinity focusing on [Fe/H] > -0.1. I suggest that the observed abundance trends are due to material s

Demosthenes Kazanas, Apostolos Mastichiadis, Markos Georganopoulos

We present the general notions and observational consequences of the "Supercritical Pile" GRB model; the fundamental feature of this model is a detailed process for the conversion of the energy stored in relativistic protons in the GRB Relativistic Blast Waves (RBW) into relativistic electrons and then into radiation. The conversion is effected throu

Benjamin Levrard, Alexandre Morgado Correia, Gilles Chabrier, Isabelle Baraffe

Eccentricity or obliquity tides have been proposed as the missing energy source that may explain the anomalously large radius of some transiting ``hot Jupiters''. To maintain a non-zero and large obliquity, it was argued that the planets can be locked in a Cassini state, i.e. a resonance between spin and orbital precessions. We compute the tidal heat

A. Gianninas, P. Bergeron, G. Fontaine

Although the Sloan Digital Sky Survey has permitted the discovery of an increasing number of new ZZ Ceti stars, recent published analyses have shown that there are still many relatively bright (V < 17) ZZ Ceti stars waiting to be found. We will discuss the discovery of several such objects in addition to a number of DA stars in which we detected no photometr

M. Wold, M. S. Brotherton, Z. Shang

In order to investigate the dependence of quasar variability on fundamental physical parameters like black hole mass, we have matched quasars from the QUEST1 Variability Survey with broad-lined objects from the Sloan Digital Sky Survey. The matched sample contains approximately 100 quasars, and the Sloan spectra are used to estimate black hole masses and bol

Michele Trenti

We present an indirect dynamical evidence, based on the measure of the core to half mass radius ratio (rc/rh), that a significant fraction of globular clusters in our galaxy with an age greater than 10 half-mass relaxation times (t_rh) host an intermediate mass black hole (IMBH). In fact, after a few t_rh much of the memory about the details of initial condi

Dejan Vinkovic, Tomislav Jurkic

We present a new model-independent method of comparison of NIR visibility data of YSOs. The method is based on scaling the measured baseline with the YSO&#39;s distance and luminosity, which removes the dependence of visibility on these two variables. We use this method to compare all available NIR visibility data and demonstrate that it distinguishes YSOs o

A. C. Goncalves, S. Collin, A. -M. Dumont

We have studied the thermal instabilities in the context of Active Galactic Nuclei (AGN), addressing the cases of thin and thick (stratified) X-ray illuminated media. For that, we have compared the behaviour of different models in pressure equilibrium. Ionized gas in pressure equilibrium show temperature discontinuities which, however difficult to tackle, ca

A. C. Goncalves, R. Soria

We assess the claim that Ultra-luminous X-ray sources (ULXs) host intermediate-mass black holes (BH) by comparing the cool disc-blackbody model with a range of other models, namelly a more complex physical model based on a power-law component slightly modified at various energies by smeared emission/absorption lines from highly-ionized gas. Our main conclusi

A. C. Goncalves, S. Collin, A. -M. Dumont, L. Chevallier

A photoionized gas in thermal equilibrium can display a thermal instability, with 3 or more solutions in the multi-branch region of the S-shape curve giving the temperature versus the radiation-to-gas-pressure ratio. Many studies have been devoted to this curve and to its dependence on different parameters, always in the optically thin case. The purpose of o

Chongshan Zhao, Heidi Jo Newberg

We calculate the transformation from the Sloan Digital Sky Survey (SDSS) photometric system to the Johnson-Morgan-Cousins System in the HK Survey. This research was done in late 2001, so the SDSS photometry was taken from the database prior to the release of DR1. This paper is being posted because it is referenced in other papers in the literature, but will

Rodger I. Thompson, Daniel Eisenstein, Xiaohui Fan, Marcia Rieke

NICMOS observations of the resolved object fluxes in the Hubble Deep Field North and the Hubble Ultra Deep Field are significantly below the fluxes attributed to a 1.4 - 1.8 microns Near InfraRed Background Excess (NIRBE) from previous low spatial resolution NIRS measurements. Tests placing sources in the NICMOS image with fluxes sufficient to account for th

R. Willingale, P. T. O&#39;Brien, J. P. Osborne, O. Godet

We show that all X-ray decay curves of GRBs measured by Swift can be fitted using one or two components both of which have exactly the same functional form comprised of an early falling exponential phase followed by a power law decay. The 1st component contains the prompt gamma-ray emission and the initial X-ray decay. The 2nd component appears later, has a

G. Houdek, D. O. Gough

We investigate the influence of the ionization of helium on the low-degree acoustic oscillation frequencies in model solar-type stars. The signature in the oscillation frequencies characterizing the ionization-induced depression of the first adiabatic exponent $γ$ is a superposition of two decaying periodic functions of frequency $ν$, with `frequencies&#39;

D. E. Trilling, J. A. Stansberry, K. R. Stapelfeldt, G. H. Rieke

We observed 69 A3-F8 main sequence binary star systems using the Multiband Imaging Photometer for Spitzer onboard the Spitzer Space Telescope. We find emission significantly in excess of predicted photospheric flux levels for 9(+4/-3)% and 40(+7/-6)% of these systems at 24 and 70 microns, respectively. Twenty two systems total have excess emission, including

T. Misawa, M. Eracleous, J. C. Charlton, R. Ganguly

We present statistical and monitoring results of narrow absorption lines that are physically related to quasars (i.e., intrinsic NALs). We use Keck/HIRES spectra of 37 optically bright quasars at z=2-4, and identify 150 NAL systems that contain 124 C IV, 12 N V, and 50 Si IV doublets. Among them, 39 are classified as intrinsic systems based on partial covera

Qizhou Zhang, Todd R. Hunter, H. Beuther, T. K. Sridharan

We present studies of a massive protocluster AFGL5142 in the J=2-1 transition of the CO isotopologues, SO, CH_3OH and CH_3CN lines, as well as continuum at 225 GHz and 8.4 GHz. The 225 GHz continuum emission reveals three prominent peaks MM-1, MM-2 and MM-3. MM-1 and MM-2 are associated with strong CH_3CN emission with temperatures of 90 \pm 20 and 250 \pm 4

Guido De Marchi, Luigi Pulone

We have studied the stellar main sequence (MS) of the globular cluster NGC2298 using deep HST/ACS observations in the F606W and F814W bands covering an area of 3.4&#39; x 3.4&#39; around the cluster centre or about twice the cluster&#39;s half-mass radius. The colour-magnitude diagram that we derive in this way reveals a narrow and well defined MS extending

G. Houdek, D. O. Gough

We present an improved model for an asteroseismic diagnostic contained in the frequency spacing of low-degree acoustic modes. By modelling in a realistic manner regions of rapid variation of dynamically relevant quantities, which we call acoustic glitches, we can derive signatures of the gross properties of those glitches. In particular, we are interested in

G. Houdek

A review on acoustic mode damping and excitation in solar-type stars is presented. Current models for linear damping rates are discussed in the light of recent low-degree solar linewidth measurements with emphasis on the frequency-dependence of damping rates of low-order modes. Recent developments in stochastic excitation models are reviewed and tested again

F. Cocchia, F. Fiore, C. Vignali, M. Mignoli

(Abridged) We present the results of the photometric and spectroscopic identification of 110 hard X-ray selected sources (6e-15<F(2-10 keV)<4e-14 cgs) from 5 additional XMM-Newton fields, nearly doubling the original HELLAS2XMM sample. We spectroscopically identified 59 new sources, bringing the completeness of the full HELLAS2XMM sample to ~70%. We found op

Carlo Schimd, Ismael Tereno

A light scalar field, minimally or not-minimally coupled to the metric field, is a well-defined candidate for the dark energy, overcoming the coincidence problem intrinsic to the cosmological constant and avoiding the difficulties of parameterizations. We present a general description of the weak gravitational lensing valid for every metric theory of gravity

S. E. Arena, G. Bertin

In this paper we study the infall, by dynamical friction, of rigid &#34;satellites&#34; taken in a variety of initial configurations and models. We thus measure how dynamical friction depends on the density concentration and on the pressure anisotropy of the host galaxy and, separately, the response of the galaxy during the process. The investigation is carr

Tom Mauch, Elaine M. Sadler

We have identified 7824 radio sources from the 1.4GHz NRAO VLA Sky Survey (NVSS) with galaxies brighter than K=12.75 mag. in the Second Incremental Data Release of the 6dF Galaxy Survey (6dFGS DR2). The resulting sample of redshifts and optical spectra for radio sources over an effective sky area of 7076 square degrees (about 17% of the celestial sphere) is

J. C. Muñoz-Mateos, A. Gil de Paz, S. Boissier, J. Zamorano

We present specific Star Formation Rate (sSFR) radial profiles for a sample of 161 relatively face-on spiral galaxies from the GALEX Atlas of Nearby Galaxies. The sSFR profiles are derived from GALEX & 2MASS (FUV-K) color profiles after a proper SFR calibration of the UV luminosity and K-band mass-to-light ratio are adopted. The (FUV-K) profiles were first c

HESS Collaboration, F. A. Aharonian

The detection of fast variations of the TeV (10^12 eV) gamma-ray flux, on time-scales of days, from the nearby radio galaxy M 87 is reported. These variations are ~10 times faster than that observed in any other waveband and imply a very compact emission region with a dimension similar to the Schwarzschild radius of the central black hole. We thus can exclud

W. Domainko, M. Ruffert

We investigate the long-term evolution and observability of remnants originating from the merger of compact binary systems and discuss the differences to supernova remnants. Compact binary mergers expel much smaller amounts of mass at much higher velocities, as compared to supernovae, which will affect the dynamical evolution of their remnants. The ejecta of

A. Cassan, D. Kubas

Microlensing has recently proven to be a valuable tool to search for extrasolar planets of Neptune- to super-Earth-mass planets at orbits of few AU. Since planetary signals are of very short duration, an intense and continuous monitoring is required, which is achieved by PLANET : ``Probing Lensing Anomalies NETwork&#39;&#39;. Up to now the detection number a

A. T. Kearsley, G. A. Graham, M. J. Burchell, M. J. Cole

The known encounter velocity (6.1kms-1) and particle incidence angle (perpendicular) between the Stardust spacecraft and the dust emanating from the nucleus of comet Wild 2 fall within a range that allows simulation in laboratory light gas gun experiments designed to validate analytical methods for the interpretation of dust impacts on the aluminum foil comp

A. V. Yushkov, A. A. Lagutin

Self-consistency of interaction models QGSJET 01, SIBYLL 2.1, NEXUS 3.97 and QGSJET II is checked in terms of their ability to reproduce simultaneously experimental data on fluxes of muons and hadrons. From this point of view SIBYLL 2.1 gives the most acceptable, though not quite satisfactory, results. Analysis of the situation for muons supports our previou

R. Davies, R. Genzel, L. Tacconi, F. Mueller Sanchez

We present results from a survey of nearby AGN using the near infrared adaptive optics integral field spectrograph SINFONI. These data enable us to probe the distribution and kinematics of the gas and stars at spatial resolutions as small as 0.085arcsec. We find strong evidence for recent but short lived starbursts residing in very dense nuclear disks. On sc

Smadar Naoz, Rennan Barkana

We investigate the suppression of the baryon density fluctuations compared to the dark matter in the linear regime. Previous calculations predict that the suppression occurs up to a characteristic mass scale of ~ 1,000,000 solar masses, which suggests that pressure has a central role in determining the properties of the first luminous objects at early times.