May 2006 arXiv papers — page 33

P. M. C. de Oliveira, C. M. Newman, V. Sidoravicious, D. L. Stein

The dynamic evolution at zero temperature of a uniform Ising ferromagnet on a square lattice is followed by Monte Carlo computer simulations. The system always eventually reaches a final, absorbing state, which sometimes coincides with a ground state (all spins parallel), and sometimes does not (parallel stripes of spins up and down). We initiate here the nu

Ulrich D. Jentschura, Vladimir A. Yerokhin

State-dependent quantum electrodynamic corrections are evaluated for the hyperfine splitting of nS states for arbitrary principal quantum number n. The calculations comprise both the self-energy and the vacuum-polarization correction of order alpha(Z alpha)^2 E_F and the recoil correction of order (Z alpha)^2 (m/M) E_F. Higher-order corrections are summarize

H. Matsumura, M. Orabi, Y. Suzuki, Y. Fujiwara

The ground and excited 0$^+$ states of $^{12}$C are investigated in a 3$α$ macroscopic model using the deep potential of Buck, Friedrich and Wheatley. The elimination of forbidden states is performed either by constructing the allowed state space explicitly or by using the orthogonalizing pseudopotential. The well-known enigmatic behavior of the latter appro

J. Vidal, J. M. Arias, J. Dukelsky, J. E. Garcia-Ramos

We introduce a simple two-level boson model with the same energy surface as the Q-consistent Interacting Boson Model Hamiltonian. The model can be diagonalized for large number of bosons and the results used to check analytical finite-size corrections to the energy gap and the order parameter in the critical region. \

J. Avellar, L. G. S. Duarte, S. E. S. Duarte, L. A. C. P. da Mota

Here we present/implement an algorithm to find Liouvillian first integrals of dynamical systems in the plane. In \cite{JCAM}, we have introduced the basis for the present implementation. The particular form of such systems allows reducing it to a single rational first order ordinary differential equation (rational first order ODE). We present a set of softwa

D. P. Hardin, E. B. Saff, H. Stahl

For surfaces of revolution $B$ in $\R^3$, we investigate the limit distribution of minimum energy point masses on $B$ that interact according to the logarithmic potential $\log (1/r)$, where $r$ is the Euclidean distance between points. We show that such limit distributions are supported only on the ``out-most'' portion of the surface (e.g., for a to

L. M. C. R. Barbosa, L. G. S. Duarte, C. A. Linhares, L. A. C. P. da Mota

In this paper, we are concerned with improving the forecast capabilities of the Global approach to Time Series. We assume that the normal techniques of Global mapping are applied, the noise reduction is performed, etc. Then, using the mathematical foundations behind such approaches, we propose a method that, without a great computational cost, greatly increa

Frédéric Klopp, Magali Marx

In this talk, we report on results about the width of the resonances for a slowly varying perturbation of a periodic operator. The study takes place in dimension one. The perturbation is assumed to be analytic and local in the sense that it tends to a constant at $+\infty$ and at $-\infty$; these constants may differ. Modulo an assumption on the relative pos

I. D. Feranchuk, S. I. Feranchuk

The nonperturbative analysis of the one-particle excitation of the electron-positron field is made in the paper. The standard form of quantum electrodynamics (QED) is used but the coupling constant $α_0$ is supposed to be of a large value ($α_0 \gg 1$). It is shown that in this case the quasi-particle excitation can be produced together with the non-zero sca

Kenneth R. Driessel, Alf Gerisch

Driessel ["Computing canonical forms using flows", Linear Algebra and Its Applications 2004] introduced the notion of quasi-projection onto the range of a linear transformation from one inner product space into another inner product space. Here we introduce the notion of quasi-projection onto the intersection of the ranges of two linear transformatio

Jesús A. De Loera, Raymond Hemmecke, Shmuel Onn, Robert Weismantel

In this article we study a broad class of integer programming problems in variable dimension. We show that these so-termed {\em n-fold integer programming problems} are polynomial time solvable. Our proof involves two heavy ingredients discovered recently: the equivalence of linear optimization and so-called directed augmentation, and the stabilization of ce

Jerome A. Jenquin

In a previous paper we constructed classical spin Chern-Simons for any compact Lie group $G$: a gauge theory whose action depends on the spin structure of the 3-manifold. Here we apply geometric quantization to the classical Hamiltonian theory and investigate the formal properties of the partition function in the Lagrangian theory, all in the case $G = SO_3$

Jay Schweig

In this paper we give convex-ear decompositions for the order complexes of several classes of posets, namely supersolvable lattices with non-zero Mobius functions and rank-selected subposets of such lattices, rank-selected geometric lattices, and rank-selected face posets of shellable complexes which do not include the top rank. These decompositions give us

M. Samsonov, A. Stolin, V. Tolstoy

We propose a method of quantization of certain Lie bialgebra structures on the polynomial Lie algebras related to quasi-trigonometric solutions of the classical Yang--Baxter equation. The method is based on an affine realization of certain seaweed algebras and their quantum analogues. We also propose a method of $ω$-affinization, which enables us to quantize

Adrian Riskin

We define a new kind of crossing number which generalizes both the bipartite crossing number and the outerplanar crossing number. We calculate exact values of this crossing number for many complete bipartite graphs and also give a lower bound.

Adrian Riskin, Georgia Weidman

We prove that if $G$ is a $2r$-regular edge graceful $(p,q)$ graph with $(r,kp)=1$ then $kG$ is edge graceful for odd $k$. We also prove that for certain specific classes of $2r$-regular edge graceful graphs it is possible to drop the requirement that $(r,kp)=1$

Farrukh Mukhamedov

In the paper we completely describe the set of all solutions of a recursive equation, arising from the Bethe lattice models over $p$-adic numbers.

Joan S. Birman, Volker Gebhardt, Juan Gonzalez-Meneses

In this paper a relation between iterated cyclings and iterated powers of elements in a Garside group is shown. This yields a characterization of elements in a Garside group having a rigid power, where 'rigid' means that the left normal form changes only in the obvious way under cycling and decycling. It is also shown that, given X in a Garside group

Szabolcs Tengely

In this paper we consider the Diophantine equation $x^2+q^{2m}=2y^p$ where $m,p,q,x,y$ are integer unknowns with $m>0,$ $p$ and $q$ are odd primes and $\gcd(x,y)=1.$ We prove that there are only finitely many solutions $(m,p,q,x,y)$ for which $y$ is not a sum of two consecutive squares. We also study the above equation with fixed $y$ and with fixed $q.$

Alberto Alzati, Fabio Tonoli

The main goal of this paper is to give a general method to compute (via computer algebra systems) an explicit set of generators of the ideals of the projective embeddings of some ruled surfaces, namely projective line bundles over curves such that the fibres are embedded as smooth rational curves. Indeed, although the existence of the embeddings that we cons

Paolo Rossi

The center and radius of perception associated with a written text are defined, and algorithms for their computation are presented. Indicators for anisotropy in large scale space perception are introduced. The relevance of these notions for the analysis of literary and historical records is briefly discussed and illustrated with an example taken from medieva

Michael Baake

Discrete point sets $\mathcal{S}$ such as lattices or quasiperiodic Delone sets may permit, beyond their symmetries, certain isometries $R$ such that $\mathcal{S}\cap R\mathcal{S}$ is a subset of $\mathcal{S}$ of finite density. These are the so-called coincidence isometrie. They are important in understanding and classifying grain boundaries and twins in cr

Daryl Geller, Azita Mayeli

Let G be a stratified Lie group and L be the sub-Laplacian on G. Let 0 \neq f\in S(R^+). We show that Lf(L)δ, the distribution kernel of the operator Lf(L), is an admissible function on G. We also show that, if ξf(ξ) satisfies Daubechies' criterion, then L f(L)δgenerates a frame for any sufficiently fine lattice subgroup of G.

A. R. Gover

A new definition of canonical conformal differential operators $P_k$ ($k=1,2,...)$, with leading term a $k^{\rm th}$ power of the Laplacian, is given for conformally Einstein manifolds of any signature. These act between density bundles and, more generally, between weighted tractor bundles of any rank. By construction these factor into a power of a fundament

Jorge A. Guccione, Juan J. Guccione

Let k be a characteristic zero field, C a k-algebra and M a square zero two sided ideal of C. We obtain a new mixed complex, simpler that the canonical one, giving the Hochschild and cyclic homologies of C relative to M. This complex resembles the canonical reduced mixed complex of an augmented algebra. We begin the study of our complex showing that it has a

Stefan Friedl

We explain an algorithm for finding a boundary link Seifert matrix for a given Alexander polynomial. The algorithm depends on several choices and therefore makes it possible to find non-equivalent Seifert matrices for a given Alexander polynomial.

Rukmini Dey

Given an smooth function $K <0$ we prove a result by Berger, Kazhdan and others that in every conformal class there exists a metric which attains this function as its Gaussian curvature for a compact Riemann surface of genus $g>1$. We do so by minimizing an appropriate functional using elementary analysis. In particular for $K$ a negative constant, this prov

Georgios Michalogiorgakis, Steven S. Gubser

We calculate the beta function of non-linear sigma models with S^{D+1} and AdS_{D+1} target spaces in a 1/D expansion up to order 1/D^2 and to all orders in α&#39;. This beta function encodes partial information about the spacetime effective action for the heterotic string to all orders in α&#39;. We argue that a zero of the beta function, corresponding to a

M. Siddiq, M. Hassan

Two sets of super Riccati equations are presented which result in two linear problems of super sine-Gordon equation. The linear problems are then shown to be related to each other by a super gauge transformation and to the super Bäcklund transformation of the equation.

M. Siddiq, M. Hassan, U. Saleem

Darboux transformation is constructed for superfields of the super sine-Gordon equation and the superfields of the associated linear problem. The Darboux transformation is shown to be related to the super Bäcklund transformation and is further used to obtain $N$ super soliton solutions.

U. Saleem, M. Hassan

We present a superfield Lax formalism of superspace sigma model based on the target space ${\cal G}/{\cal H}$ and show that a one-parameter family of flat superfield connections exists if the target space ${\cal G}/{\cal H}$ is a symmetric space. The formalism has been related to the existences of an infinite family of local and non-local superfield conserve

Maxim Grigoriev

We propose a construction for nonlinear off-shell gauge field theories based on a constrained system quantized in the sense of deformation quantization. The key idea is to consider the star-product BFV--BRST master equation as an equation of motion. The construction is formulated in terms of the BRST extention of the unfolded formalism that can also be under

S. S. Afonin

Some aspects of two recent papers on parity doubling in the hadronic spectrum and its relation to restoration of linearly realized chiral symmetry are critically discussed.

D. S. O&#39;Brien, N. H. Buttimore

Relativistic formulae for spin averaged and spin dependent one photon exchange differential cross sections are developed for spin half fermion fermion elastic scattering. Spin transfer cross sections are important for the Polarized Antiproton eXperiments (PAX) project at GSI Darmstadt. In particular, cross sections for polarization transfer in antiproton ele

E. Ramirez Barreto, Y. A. Coutinho, J. Sá Borges

We obtain bounds for the mass of the extra neutral gauge boson, ${Z^\prime}$, predicted by two versions of ${SU (3)_C \times SU (3)_L \times U (1)_X}$ model, namely one corresponding to its minimal version and another where the neutrinos are allowed to have right-handed projection. We explore $\sqrt s$ from 0.5 TeV to 5 TeV region, that will be accessible in

Gurpreet Sidana

Two body non-leptonic decays: are investigated. Baryon form factors of the heavy quark effective theory are employed. Form factors for renormalization in full QCD are also considered. We find that contributions of the non-factorizable terms are negligible in b-decays. Comparison with calculations in other models shows that form factors for renormalization in

M. Jamin, A. Pich, J. Portoles

With the newly available data sets on hadronic tau decays from the B-factories BABAR and BELLE, and future data from BESIII, precise information on the decay distributions will soon become available. This calls for an improvement of the decay spectra also on the theoretical side. In this work, the distribution function for the decay tau -> nu_tau K pi will b

Seung-il Nam, Hyun-Chul Kim

We investigate the effects of flavor SU(3)-symmetry breaking on the QCD condensates, based on the nonlocal effective chiral action from the instanton vacuum, focusing on the quark-gluon mixed one. We employ two different parameterizations for the dependence of the momentum-dependent dynamical quark mass on the strange current quark mass. We obtain the ratios

J. O. Eeg, K. Kumericki, I. Picek

Intriguing B --> K eta&#39; decays provide a unique opportunity to study a joining of two-gluon configurations arising from the penguin b --> sG and b --> sGG transitions, with those inherent to the eta&#39; particle. We employ the heavy-light chiral quark model, applied previously to a somewhat related B --> D eta&#39; decay, as a calculational tool account

CDF Collaboration, A. Abulencia

We present a measurement of R_B, the ratio of the branching fraction for the rare decay D0 -> K+ pi- to that for the Cabibbo-favored decay D0 -> K- pi+. Charge conjugate decays are implicitly included. A signal of 2005 +/- 104 events for the decay D0 -> K+ pi- is obtained using the CDF II detector at the Fermilab Tevatron collider. The data set corresponds t

P. Zweber

Using 20.7 pb^-1 of e+e- annihilation data taken at sqrt{s} = 3.671 GeV with the CLEO-c detector, precision measurements of the electromagnetic form factors of the charged pion, charged kaon, and proton have been made for timelike momentum transfer of |Q^2| = 13.48 GeV^2 by the reaction e+e- to h+h-. The measurements are the first ever with identified pions

B. Aubert et al

We present a search for the rare B-meson decay B0 to a1+- rho-+ with a_1+- to pi+ pi- pi+-. We use (110 +/- 1.2) x 10^6 Upsilon(4S) to BBbar decays collected with the BaBar detector at the PEP-II asymmetric-energy B Factory at SLAC. We obtain an upper limit of 30 x 10-6 (90% C.L.) for the branching fraction product B(B0 to a_1+- rho-+)B(a_1+- to pi+ pi- pi+-

P. R. Silva

We propose intuitive derivations of the Hawking temperature and the Bekenstein-Hawking entropy of a Schwarzschild black hole.

V. Faraoni, M. N. Jensen, S. A. Theuerkauf

In the context of scalar-tensor models of dark energy and inflation, the dynamics of vacuum scalar-tensor cosmology are analysed without specifying the coupling function or the scalar field potential. A conformal transformation to the Einstein frame is used and the dynamics of general relativity with a minimally coupled scalar field are derived for a generic

Georg Schmidt, Vladimir R. Sidorenko

The problem of finding the shortest linear shift-register capable of generating t finite length sequences over some field F is considered. A similar problem was already addressed by Feng and Tzeng. They presented an iterative algorithm for solving this multi-sequence shift-register synthesis problem, which can be considered as generalization of the well know

Stefano Guerrini, Andrea Masini

Continuation Passing Style (CPS) is one of the most important issues in the field of functional programming languages, and the quest for a primitive notion of types for continuation is still open. Starting from the notion of ``test&#39;&#39; proposed by Girard, we develop a notion of test for intuitionistic logic. We give a complete deductive system for test

Marcus Hutter

Consider an agent interacting with an environment in cycles. In every interaction cycle the agent is rewarded for its performance. We compare the average reward U from cycle 1 to m (average value) with the future discounted reward V from cycle k to infinity (discounted value). We consider essentially arbitrary (non-geometric) discount sequences and arbitrary

Tran Cao Son, Enrico Pontelli, Islam Elkabani

The paper presents two equivalent definitions of answer sets for logic programs with aggregates. These definitions build on the notion of unfolding of aggregates, and they are aimed at creating methodologies to translate logic programs with aggregates to normal logic programs or positive programs, whose answer set semantics can be used to defined the semanti

Filip Radlinski, Thorsten Joachims

Clickthrough data is a particularly inexpensive and plentiful resource to obtain implicit relevance feedback for improving and personalizing search engines. However, it is well known that the probability of a user clicking on a result is strongly biased toward documents presented higher in the result set irrespective of relevance. We introduce a simple metho

James E. Magee, Victor R. Vasquez, Leo Lue

We present Monte Carlo simulation results for square-well homopolymers at a series of bond lengths. Although the model contains only isotropic pairwise interactions, under appropriate conditions this system shows spontaneous chiral symmetry breaking, where the chain exists in either a left- or a right-handed helical structure. We investigate how this behavio

C. A. Linhares, A. P. C. Malbouisson, Y. W. Milla, I. Roditi

In the context of the Ginzburg--Landau theory for critical phenomena, we consider the Euclidean $λϕ^4+ηϕ^6$ model bounded by two parallel planes, a distance $L$ separating them. This is supposed to describe a sample of a superconducting material undergoing a first-order phase transition. We are able to determine the dependence of the transition temperature $

Grzegorz Szamel, Elijah Flenner

We study the four-point dynamic susceptibility $χ_4(t)$ obtained from Brownian dynamics computer simulations of the Kob-Andersen Lennard-Jones mixture. We compare the results of the simulations with qualitative predictions of the mode-coupling theory. In addition, we test an estimate of the four-point susceptibility recently proposed by Berthier \textit{et a

K. Kikoin, V. Fleurov

We extend the model of ferromagnetic superexchange in dilute magnetic semiconductors to the ferromagnetically ordered highly insulating compounds (dilute magnetic dielectrics). The intrinsic ferromagnetism without free carriers is observed in oxygen-deficient films of anatase TiO_2 doped with transition metal impurities in cation sublattice. We suppose that

A. De Virgiliis, K. Binder

Transport phenomena are studied for a binary (AB) alloy on a rigid square lattice with nearest-neighbor attraction between unlike particles, assuming a small concentration $c_v$ of vacancies $V$ being present, to which $A(B)$ particles can jump with rates $Γ_A (Γ_B)$ in the case where the nearest neighbor attractive energy $ε_{AB}$ is negligible in compariso

Elbert E. M. Chia, H. J. Lee, Namjung Hur, E. D. Bauer

Ultrafast time-resolved photoinduced reflectivity is measured for the itinerant antiferromagnet UNiGa$_{5}$ ($T_{N} \approx$85 K) from room temperature to 10 K. The relaxation time $τ$ shows a sharp increase at $T_{N}$ consistent with the opening of a spin gap. In addition, the temperature dependence of $τ$ below $T_{N}$ is consistent with the opening of a s

Stefano Sanvito, Alexandre Reily Rocha

Spintronics is the ability of injecting, manipulating and detecting electron spins into solid state systems. Molecular-electronics investigates the possibility of making electronic devices using organic molecules. Traditionally these two burgeoning areas have lived separate lives, but recently a growing number of experiments have indicated a possible pathway

Yuri Martinez-Raton, Enrique Velasco, Luis Mederos

We investigate the effect of three-body correlations on the phase behavior of hard rectangle two-dimensional fluids. The third virial coefficient, $B_3$, is incorporated via an equation of state that recovers scaled particle theory for parallel hard rectangles. This coefficient, a functional of the orientational distribution function, is calculated by Monte

Zhi-Feng Huang, Jorge Vinals

We introduce a model constitutive law for the dissipative stress tensor of lamellar phases to account for low frequency and long wavelength flows. Given the uniaxial symmetry of these phases, we argue that the stress tensor must be the same as that of a nematic but with the local order parameter being the slowly varying lamellar wavevector. This assumption l

O. Pozo, N. Olivi-Tran

A Molecular Dynamics approach has been used to compute the shear force resulting from the shearing of disks. Two-dimensional monodisperse disks have been put in an horizontal and rectangular shearing cell with periodic boundary conditions on right and left hand sides. The shear is applied by pulling the cover of the cell either at a constant rate or by pulli

Mesfin Asfaw, Mulugeta Bekele

We model a tiny heat engine as a Brownian particle that moves in a viscous medium in a sawtooth potential (with or without load) assisted by $\it {alternately}$ placed hot and cold heat baths along its path. We find closed form expression for the steady state current as a function of the model parameters. This enables us to deal with the energetics of the mo

Florian Marquardt

We describe a scheme for the efficient generation of microwave photon pairs by parametric downconversion in a superconducting transmission line resonator coupled to a Cooper pair box serving as an artificial atom. By properly tuning the first three levels with respect to the cavity modes, the down-conversion probability may become higher than in the most eff

Georges Raseev, Eric Charron

In the long wavelength domain, typically for wavelengths lambda > 100 angstroms, the laser fields are usually taken as independent of the spatial coordinate. However, at the gas-solid interface the electron density of the material and the incident laser fields vary sharply on a scale of few angstroms. Instead of solving Maxwell equations, we present here a t

R. Oszwałdowski, J. A. Majewski, T. Dietl

Intrinsic domain-wall resistance (DWR) in (Ga,Mn)As is studied theoretically and compared to experimental results. The recently developed model of spin transport in diluted ferromagnetic semiconductors [Van Dorpe et al., Phys. Rev. B 72, 205322 (2005)] is employed. The model combines the disorder-free Landauer-Büttiker formalism with the tight-binding descri

A. Fledderjohann, A. Langari, K. -H. Muetter

The emergence of phase separation is investigated in the framework of a 2D t-J model by means of a variational product ansatz, which covers the infinite lattice by two types of L x L clusters. Clusters of the first type are completely occupied with electrons, i.e. they carry maximal charge Q_e=L^2 and total spin 0, and thereby form the antiferromagnetic back

Marco Evangelisti, Esperanca Manuel, Marco Affronte, Masashi Okubo

We experimentally show that the magnetocaloric properties of molecule-based Prussian blue analogues can be adjusted by controlling during the synthesis the amount of intrinsic vacancies. For Cs_xNi^II_4[Cr^III(CN)_6]_(8+x)/3}, we find indeed that the ferromagnetic phase transition induces significantly large magnetic entropy changes, whose maxima shift from

Angel J. Moreno, Walter Kob

We present molecular dynamics simulations of the motion of a single rigid rod in a disordered static 2d-array of disk-like obstacles. Two different configurations have been used for the latter: A completely random one, and which thus has an inhomogeneous structure, and an homogeneous ``glassy&#39;&#39; one, obtained from freezing a liquid of soft disks in eq

D. Poilblanc, C. Weber, F. Mila, M. Sigrist

We propose that the inhomogeneous patterns seen by STM in some underdoped superconducting cuprates could be related to a bond-order-wave instability of the staggered flux state, one of the most studied &#34;normal&#34; state proposed to compete with the d-wave RVB superconductor. A checkerboard pattern is obtained by a Gutzwiller renormalized mean-field theo

Y. Sidor, B. Partoens, F. M. Peeters, N. Schildermans

The magnetic field dependence of the excitonic states in unstrained GaAs/AlGaAs quantum dots is investigated theoretically and experimentally. The diamagnetic shift for the ground and the excited states are studied in magnetic fields of varying orientation. In the theoretical study, calculations are performed within the single band effective mass approximati

A. Hernandez-Cabrera, P. Aceituno, F. T. Vasko

Modifications of spin-splitting dispersion relations and density of states for electrons in non-symmetric heterostructures under in-plane magnetic field are studied within the envelope function formalism. Spin-orbit interactions, caused by both a slow potential and the heterojunction potentials (which are described by the boundary conditions) are taken into

L. A. Fernandez, V. Martin-Mayor, P. Verrocchio

A new Monte Carlo algorithm is introduced for the simulation of supercooled liquids and glass formers, and tested in two model glasses. The algorithm is shown to thermalize well below the Mode Coupling temperature and to outperform other optimized Monte Carlo methods. Using the algorithm, we obtain finite size effects in the specific heat. This effect points

M. R. Graeber, M. Weiss, C. Schoenenberger

We report the experimental realization of double quantum dots in single-walled carbon nanotubes. The device consists of a nanotube with source and drain contact, and three additional top-gate electrodes in between. We show that, by energizing these top-gates, it is possible to locally gate a nanotube, to create a barrier, or to tune the chemical potential of

E. Bernardi, A. Lascialfari, A. Rigamonti, L. Romano&#39;

High resolution SQUID magnetization measurements in lead nanoparticles are used to study the fluctuating diamagnetism in zero-dimensional condition, namely for particle size d lesser than the coherence length. The diamagnetic magnetization Mdia (H, T= const) as a function of the field H at constant temperature is reported in the critical region and compared

J. C. Phillips

The entirely orbital self-organized dopant percolative filamentary model describes many counter-intuitive chemical trends in oxide superconductors quantitatively, especially the high superconductive transition temperatures Tc. According to rules previously used successfully for network glasees, the host networks are marginally stable mechanically, and the hi

A. Oosawa, K. Kakurai, Y. Nishiwaki, T. Kato

Polarized neutron inelastic scattering experiments have been carried out in the quasi-1D Ising-like antiferromagnet TlCoCl$_3$. We observed the longitudinal magnetic fluctuation $S_{zz} (Q, ω)$ for the spin-wave excitation continuum, which has not been observed in the unpolarized neutron inelastic scattering experiments of the quasi-1D Ising-like antiferroma

J. Y. Gan, Yan Chen, F. C. Zhang

Motivated by the recent discovery of a low temperature spin liquid phase in layered organic compound $κ$-(ET)$_2$Cu$_2$(CN)$_3$ which becomes a superconductor under pressure, we examine the phase transition of Mott insulating and superconducting (SC) states in a Hubbard-Heisenberg model on an anisotropic triangular lattice. We use a renormalized mean field t

Marius Costeniuc, Richard S. Ellis, Hugo Touchette

It is well-known that the entropy of the microcanonical ensemble cannot be calculated as the Legendre transform of the canonical free energy when the entropy is nonconcave. To circumvent this problem, a generalization of the canonical ensemble which allows for the calculation of nonconcave entropies was recently proposed. Here, we study the mean-field Curie-

Guo-qing Zheng, Kazuaki Matano, D. P. Chen, C. T. Lin

We report a ^{59}Co Knight shift measurement in a single crystal of the cobalt oxide superconductor Na_{x}CoO_2\cdot1.3H_2O (T_c=4.25 K). We find that the shift due to the spin susceptibility, K^s, is substantially large and anisotropic, with the spin shift along the a-axis K^s_a being two times that along the c-axis K^s_c. The shift decreases with decreasin

Hiroki Saito, Masahito Ueda

A self-trapped Bose-Einstein condensate in three-dimensional free space is shown to be stabilized by feedback control of the interatomic interaction through nondestructive measurement of the condensate&#39;s peak column density. The stability is found to be robust against poor resolution and experimental errors in the measurement.

A. D. Thakur, T. V. Chandrasekhar Rao, S. Uji, T. Terashima

We have explored the presence of a two-peak feature spanning the peak effect (PE) region in the ac susceptibility data and the magnetization hysteresis measurements over a wide field-temperature regime in few weakly pinned single crystals of $2H$-NbSe$_2$, which display reentrant characteristic in the PE curve near $T_c$(0). We believe that the two-peak feat

Olav F. Syljuasen

The plaquette phase of the square lattice quantum dimer model is studied using a continuous-time reptation quantum Monte Carlo method for lattices of sizes up to 48x48 sites. We determine the location of the phase transition between the columnar and plaquette phases to occur at V_c/J=0.60 +- 0.05 which is significantly larger than inferred from previous exac

Alexander Vilenkin

The smallness of the vacuum energy density and its near coincidence with the average matter density of the universe are naturally explained by anthropic selection. An alternative explanation, based on the cyclic model of Steinhardt and Turok, does not address the coincidence problem and is therefore less convincing. This article appeared in ``Science&#39;&#3

J. P. Grimes, T. Heckman, C. Hoopes, D. Strickland

We have analyzed FUSE, XMM, and Chandra observations of VV 114, a local galaxy merger with strong similarities to typical high-redshift Lyman Break Galaxies (LBGs). Diffuse thermal X-ray emission encompassing VV114 has been observed by Chandra and XMM. This region of hot (kT~0.59 keV) gas has an enhanced alpha to iron element ratio relative to solar abundanc

Julie A. Rathbun, John R. Spencer

Loki Patera is the most powerful volcano in the solar system. We have obtained measurements of Loki&#39;s 3.5 micron brightness from NASA&#39;s Infrared Telescope Facility (IRTF) and have witnessed a change from the periodic behavior previously noted. While Loki brightened by a factor of several every 540 days prior to 2001, from 2001 through 2004 Loki remai

Rachael L. Beaton, Steven R. Majewski, Puragra Guhathakurta, Michael F. Skrutskie

A new, 2.8 deg^2 J,H,K_s infrared survey from the 2MASS 6x program across the extent of the optical disk of the Andromeda (M31) galaxy provides a clear view of the M31 center almost completely unfettered by dust extinction, and reveals a high contrast bulge with extremely boxy isophotes dominating the NIR light to a semi-major axis of ~700&#39;&#39;(2.6 kpc)

E. S. Voges, R. A. M. Walterbos

We present spectroscopic observations of diffuse ionized gas (DIG) in M33 near the HII region NGC 604. We present the first detection of [OI] 6300 in the DIG of M33, one of the critical lines for distinguishing photo- from shock ionization models. We measure [OI]/Ha in the range of 0.04 to 0.10 and an increase in this ratio with decreasing emission measure.

F. Panessa, L. Bassani, M. Cappi, M. Dadina

We investigate the relation between X-ray nuclear emission, optical emission line luminosities and black hole masses for a sample of 47 Seyfert galaxies. The sample, which has been selected from the Palomar optical spectroscopic survey of nearby galaxies (Ho, Filippenko & Sargent 1997), covers a wide range of nuclear powers, from L_{2-10 keV} ~ 10^{43} erg/s

M. J. Barlow, A. S. Hales, P. J. Storey, X. -W. Liu

We have acquired high spectral resolution observations (R=150,000) of the planetary nebulae NGC 7009 and NGC 6153, using bHROS on Gemini South. Observations of this type may provide a key to understanding why optical recombination lines (ORLs) yield systematically higher heavy element abundances for photoionized nebulae than do the classical forbidden collis

Ryuichi Kurosawa, Tim J. Harries, Neil H. Symington

We present radiative transfer models of the circumstellar environment of classical T Tauri stars, concentrating on the formation of the H-alpha emission. The wide variety of line profiles seen in observations are indicative of both inflow and outflow, and we therefore employ a circumstellar structure that includes both magnetospheric accretion and a disc win

Xavier Calmet, Harald Fritzsch

Astrophysical observations indicate a time variation of the proton-electron mass ratio and of the fine-structure constant. We discuss this phenomenon in models of Grand Unification. In these models a time variation of the fine-structure constant and of the proton mass are expected, if either the unified coupling constant or the scale of unification changes,

W. Gieren, G. Pietrzynski, K. Nalewajko, I. Soszynski

We have measured near-infrared magnitudes in the J and K bands for 56 Cepheid variables in the Local Group galaxy NGC 6822 with well-determined periods and optical light curves in the V and I bands. Using the template light curve approach of Soszynski, Gieren and Pietrzynski, accurate mean magnitudes were obtained from these data which allowed us to determin

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

The study of the early high-energy emission from both long and short Gamma-ray bursts has been revolutionized by the Swift mission. The rapid response of Swift shows that the non-thermal X-ray emission transitions smoothly from the prompt phase into a decaying phase whatever the details of the light curve. The decay is often categorized by a steep-to-shallow

Pietro Ubertini

The recent completion and operation of the High Energy Stereoscopic System, an array of ground based imaging Cherenkov telescopes, has provided a survey with unprecedented sensitivity of the inner part of the Galaxy and revealed a new population of very high energy gamma-rays sources emitting at E$>$100 GeV. Most of them were reported to have no known radio

A. Stroeer, A. Vecchio

The Laser Interferometer Space Antenna (LISA) guarantees the detection of gravitational waves by monitoring a handful of known nearby galactic binary systems, the so-called ``verification binaries&#39;&#39;. We consider the most updated information on the source parameters for the thirty more promising verification binaries. We investigate which of them are

G. Pietrzynski, W. Gieren, A. Udalski, I. Soszynski

We have obtained mosaic images of NGC 3109 in the V and I bands on 74 nights, spanning approximately one year. From these data, we have conducted an extensive search for Cepheid variables over the entire field of the galaxy, resulting in the discovery of 113 variables with periods ranging from 3.4 to 31.4 days. In this sample, 76 Cepheids, including many lon

S. P. Littlefair, V. S. Dhillon, T. R. Marsh, T. Shahbaz

We present multi-colour photometry of four field ultracool dwarfs with the triple-beam photometer ultracam. Data were obtained simultaneously in the Sloan-g&#39; band and a specially designed narrow-band NaI filter. The previously reported 1.8-hr period of Kelu-1 is here recovered in the g&#39;-band, but the lack of any significant variability in the NaI lig

H. M. A. Thompson, F. P. Keenan, P. L. Dufton, R. S. I. Ryans

An analysis of high-resolution Anglo-Australian Telescope (AAT)/ University College London Echelle Spectrograph (UCLES) optical spectra for the ultraviolet (UV)-bright star ROA 5701 in the globular cluster omega Cen (NGC 5139) is performed, using non-local thermodynamic equilibrium (non-LTE) model atmospheres to estimate stellar atmospheric parameters and ch

Laura Magrini

The Local Group (LG) represents the best environment to study in detail the PN population in a large number of morphological types of galaxies. The closeness of the LG galaxies allows to investigate the faintest side of the PN luminosity function and to detect PNe also in the less luminous galaxies, the dwarf galaxies, where a small number of them is expecte

Didier Fraix-Burnet, Philippe Choler, Emmanuel J. P. Douzery

Context: The Hubble tuning fork diagram has always been the preferred scheme for classification of galaxies. It is based on morphology only. At the opposite, biologists have long taken into account the genealogical relatedness of living entities for classification purposes. Aims: Assuming branching evolution of galaxies as a &#39;descent with modification&#3

M. Ausseloos, C. Aerts, K. Lefever, J. Davis

We present methodology to derive high-precision estimates of the fundamental parameters of double-lined spectroscopic binaries. We apply the methods to the case study of the double-lined beta Cephei star beta Centauri. We also present a detailed analysis of beta Centauri&#39;s line-profile variations caused by its oscillations. We point out that a systematic

Remo Collet, Martin Asplund, Regner Trampedach

We investigate the impact of realistic 3D hydrodynamical model stellar atmospheres on the determination of elemental abundances in the carbon-rich, hyper iron-poor stars HE0107-5240 and HE1327-2326. We derive the chemical compositions of the two stars by means of a detailed 3D analysis of spectral lines under the assumption of local thermodynamic equilibrium