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For almost all interval exchange maps T_0, with combinatorics of genus g>=2, we construct affine interval exchange maps T which are semi-conjugate to T_0 and have a wandering interval.
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arxiv:0805.4737
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From the perspective of probability, the stability of growing network is studied in the present paper. Using the DMS model as an example, we establish a relation between the growing network and Markov process. Based on the concept and technique of first-passage probability in Markov theory, we provide a rigorous proof for existence of the steady-state degree distribution, mathematically re-deriving the exact formula of the distribution. The approach based on Markov chain theory is universal and performs well in a large class of growing networks.
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arxiv:0805.4765
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Transverse momentum spectra up to 4.5 GeV/c were measured around midrapidity in Pb+Pb reactions at sqrt{s_{NN}}=17.3 GeV, for pi^{+/-}, p, pbar and K^{+/-}, by the NA49 experiment. The nuclear modification factors R_{AA}, R_{AA/pA} and R_{CP} were extracted and are compared to RHIC results at sqrt{s_{NN}}=200 GeV. The modification factor R_{AA} shows a rapid increase with transverse momentum in the covered region. The modification factor R_{CP} shows saturation well below unity in the pi^{+/-} channel. The extracted R_{CP} values follow the 200 GeV RHIC results closely in the available transverse momentum range for all particle species. For pi^{+/-} above 2.5 GeV/c transverse momentum, the measured suppression is smaller than that observed at RHIC. The nuclear modification factor R_{AA/pA} for pi^{+/-} stays well below unity.
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arxiv:0805.4771
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We report the development and first results of an instrument called Low Layer Scidar (LOLAS) which is aimed at the measurement of optical-turbulence profiles in the atmospheric boundary layer with high altitude-resolution. The method is based on the Generalized Scidar (GS) concept, but unlike the GS instruments which need a 1- m or larger telescope, LOLAS is implemented on a dedicated 40-cm telescope, making it an independent instrument. The system is designed for widely separated double-star targets, which enables the high altitude-resolution. Using a 20000-separation double- star, we have obtained turbulence profiles with unprecedented 12-m resolution. The system incorporates necessary novel algorithms for autoguiding, autofocus and image stabilisation. The results presented here were obtained at Mauna Kea Observatory. They show LOLAS capabilities but cannot be considered as representative of the site. A forthcoming paper will be devoted to the site characterisation. The instrument was built as part of the Ground Layer Turbulence Monitoring Campaign on Mauna Kea for Gemini Observatory.
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arxiv:0805.4784
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Fix two points $x,\bar{x}\in S^2$ and two directions (without orientation) $\eta,\bar\eta$ of the velocities in these points. In this paper we are interested to the problem of minimizing the cost $$ J[\gamma]=\int_0^T g_{\gamma(t)}(\dot\gamma(t),\dot\gamma(t))+ K^2_{\gamma(t)}g_{\gamma(t)}(\dot\gamma(t),\dot\gamma(t)) ~dt$$ along all smooth curves starting from $x$ with direction $\eta$ and ending in $\bar{x}$ with direction $\bar\eta$. Here $g$ is the standard Riemannian metric on $S^2$ and $K_\gamma$ is the corresponding geodesic curvature. The interest of this problem comes from mechanics and geometry of vision. It can be formulated as a sub-Riemannian problem on the lens space L(4,1). We compute the global solution for this problem: an interesting feature is that some optimal geodesics present cusps. The cut locus is a stratification with non trivial topology.
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arxiv:0805.4800
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Multiplicative cascades are often used to represent the structure of multiscaling variables in many physical systems, specially turbulent flows. In processes of this kind, these variables can be understood as the result of a successive tranfer in cascade from large to small scales. For a given signal, only its optimal wavelet basis can represent it in such a way that the cascade relation between scales becomes explicit, i.e., it is geometrically achieved at each point of the system. Finding such a basis is a data-demanding, highly-complex task. In this paper we propose a formalism that allows to find the optimal wavelet in an efficient, less data-demanding way. We confirm the appropriateness of this approach by analyzing the results on synthetic signals constructed with prescribed optimal bases. Although we show the validity of our approach constrainted to given families of wavelets, it can be generalized for a continuous unconstrainted search scheme.
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arxiv:0805.4810
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We study the production of electroweak gauge bosons at high energies in the framework of kt-factorization QCD approach. Contributions from the valence quarks are calculated using the quark-gluon interaction and quark-antiquark annihilation QCD subprocesses. The total and differential cross sections (as a function of the transverse momentum and rapidity) are presented and the ratio of cross sections for W and Z boson production is investigated. The conservative error analysis is performed. In the numerical calculations two different sets of unintegrated gluon distributions in the proton are used: the one obtained from Ciafaloni-Catani-Fiorani-Marchesini evolution equation and the other from Kimber-Martin-Ryskin prescription. Theoretical results are compared with experimental data taken by the D0 and CDF collaborations at the Tevatron. We demonstrate the importance of the quark component in parton evolution in description of the experimental data. This component is very significant also at the LHC energies.
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arxiv:0805.4821
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It is shown that, in the infinite size limit, certain systems of globally coupled phase oscillators display low dimensional dynamics. In particular, we derive an explicit finite set of nonlinear ordinary differential equations for the macroscopic evolution of the systems considered. For example, an exact, closed form solution for the nonlinear time evolution of the Kuramoto problem with a Lorentzian oscillator frequency distribution function is obtained. Low dimensional behavior is also demonstrated for several prototypical extensions of the Kuramoto model, and time-delayed coupling is also considered.
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arxiv:0806.0004
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We generalise the computations of arXiv:0712.2456 to generate long wavelength, asymptotically locally AdS_5 solutions to the Einstein-dilaton system with a slowly varying boundary dilaton field and a weakly curved boundary metric. Upon demanding regularity, our solutions are dual, under the AdS/CFT correspondence, to arbitrary fluid flows in the boundary theory formulated on a weakly curved manifold with a prescribed slowly varying coupling constant. These solutions turn out to be parametrised by four-velocity and temperature fields that are constrained to obey the boundary covariant Navier Stokes equations with a dilaton dependent forcing term. We explicitly evaluate the stress tensor and Lagrangian as a function of the velocity, temperature, coupling constant and curvature fields, to second order in the derivative expansion and demonstrate the Weyl covariance of these expressions. We also construct the event horizon of the dual solutions to second order in the derivative expansion, and use the area form on this event horizon to construct an entropy current for the dual fluid. As a check of our constructions we expand the exactly known solutions for rotating black holes in global AdS_5 in a boundary derivative expansion and find perfect agreement with all our results upto second order. We also find other simple solutions of the forced fluid mechanics equations and discuss their bulk interpretation. Our results may aid in determining a bulk dual to forced flows exhibiting steady state turbulence.
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arxiv:0806.0006
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We prove uniqueness of the Kerr black holes within the connected, non-degenerate, analytic class of regular vacuum black holes.
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arxiv:0806.0016
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We study techniques for identifying highly boosted top jets, where the subsequent top decay products are not isolated. For hadronic boosted tops, we consider variables which probe the jet substructure in order to reduce the background from QCD jets with large invariant mass. Substructure variables related to two-body kinematics are least sensitive to the modeling of parton shower, while those which involve multi-body kinematics may still have discrimination power. For leptonic boosted tops, we consider variables which characterize the separation between the lepton--although not isolated by conventional criterion--and the hadronic activity in the top jet. Such variables are useful in reducing the backgrounds both from heavy-flavor jets and from accidental jet-lepton overlap. We give numerical estimates of the top identification efficiency versus background rejection rate as a functions of cuts on these variables, and find that these variables offer additional useful information above invariant mass alone.
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arxiv:0806.0023
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We show from covariant transport theory that, for a massless ideal gas equation of state, even a small shear viscosity to entropy density ratio $\eta \approx s/(4 \pi)$ generates significant 15-30% dissipative corrections to elliptic flow for conditions expected in mid-peripheral (b = 8 fm) Au+Au collisions at $\sqrt{s_{NN}} \sim 200$ GeV at RHIC.
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arxiv:0806.0026
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Herbig-Haro (HH) jets are commonly thought of as homogeneous beams of plasma traveling at hypersonic velocities. Structure within jet beams is often attributed to periodic or ``pulsed'' variations of conditions at the jet source. Simulations based on this scenario result in knots extending across the jet diameter. Observations and recent high energy density laboratory experiments shed new light on structures below this scale and indicate they may be important for understanding the fundamentals of jet dynamics. In this paper we offer an alternative to ``pulsed'' models of protostellar jets. Using direct numerical simulations we explore the possibility that jets are chains of sub-radial clumps propagating through a moving inter-clump medium. Our models explore an idealization of this scenario by injecting small ($r<r_{jet}$), dense ($\rho>\rho_{jet}$) spheres embedded in an otherwise smooth inter-clump jet flow. The spheres are initialized with velocities differing from the jet velocity by $\sim15$%. We find the consequences of shifting from homogeneous to heterogeneous flows are significant as clumps interact with each other and with the inter-clump medium in a variety of ways. Structures which mimic what is expected from pulsed-jet models can form, as can previously unseen ``sub-radial'' behaviors including backward facing bow shocks and off-axis working surfaces. While these small-scale structures have not been seen before in simulation studies, they are found in high resolution jet observations. We discuss implications of our simulations for the interpretation of protostellar jets with regard to characterization of knots by a ``lifetime'' or ``velocity history'' approach as well as linking observed structures with central engines which produce the jets.
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arxiv:0806.0038
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To investigate the effects of muscle fatigue on force sense at the ankle joint, 10 young healthy adults were asked to perform an isometric contra-lateral force ankle-matching task in two experimental conditions of: (1) no-fatigue and (2) fatigue of the plantar-flexor muscles. Measures of the overall accuracy and the variability of the force matching performances were determined using the absolute error and the variable error, respectively. Results showed less accurate and less consistent force matching performances in the fatigue than no fatigue condition, as indicated by decreased absolute and variable errors, respectively. The present findings evidence that muscle fatigue degrades force sense at the ankle joint.
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arxiv:0806.0084
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We present a catalog of point gamma-ray sources detected by the EGRET detector aboard the Compton Gamma Ray Observatory. We have used the whole gamma-ray dataset of reprocessed photons at energies above 100 MeV together with new Galactic interstellar emission models based on recent CO, HI, dark gas, and interstellar radiation field data. Two different assumptions have been used for the cosmic-ray distribution in the Galaxy to explore the resulting systematic uncertainties in source detection and characterization. We have used the same 2-dimensional maximum-likelihood detection method as for the 3rd EGRET catalogue. The revised catalogue lists 188 sources, 14 of which are marked as confused, compared to the 271 entries of the 3rd EGRET (3EG) catalogue. 107 former sources have not been confirmed because of the additional structure in the interstellar background. The vast majority of them were unidentified and marked as possibly extended or confused in the 3EG catalogue. In particular, we do not confirm most of the 3EG sources associated with the local clouds of the Gould Belt. Alternatively, we find 30 new sources with no 3EG counterpart. The new error circles for the confirmed 3EG sources largely overlap the previous ones, but several counterparts of particular interest that had been discussed in the litterature, such as Sgr A*, radiogalaxies and several microquasars are now found outside the error circles. We have cross-correlated the source positions with a large number of radio pulsars, pulsar wind nebulae, supernova remnants, OB associations, blazars and flat radiosources and we find a surprising large number of sources (87) at all latitudes with no counterpart among the potential gamma-ray emitters.
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arxiv:0806.0113
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The canonical analysis and subsequent quantization of the (2+1)-dimensional action of pure gravity plus a cosmological constant term is considered, under the assumption of the existence of one spacelike Killing vector field. The proper imposition of the quantum analogues of the two linear (momentum) constraints reduces an initial collection of state vectors, consisting of all smooth functionals of the components (and/or their derivatives) of the spatial metric, to particular scalar smooth functionals. The demand that the midi-superspace metric (inferred from the kinetic part of the quadratic (Hamiltonian) constraint) must define on the space of these states an induced metric whose components are given in terms of the same states, which is made possible through an appropriate re-normalization assumption, severely reduces the possible state vectors to three unique (up to general coordinate transformations) smooth scalar functionals. The quantum analogue of the Hamiltonian constraint produces a Wheeler-DeWitt equation based on this reduced manifold of states, which is completely integrated.
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arxiv:0806.0137
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We report on the magnetic excitation spectrum of the coupled spin tetrahedral system Cu$_{2}$Te$_{2}$O$_{5}$Cl$_{2}$ using Raman scattering on single crystals. The transition to an ordered state at T$_{N}^{Cl}$=18.2 K evidenced from thermodynamic data leads to the evolution of distinct low-energy magnetic excitations superimposed by a broad maximum. These modes are ascribed to magnons with different degree of localization and a two-magnon continuum. Two of the modes develop a substantial energy shift with decreasing temperature similar to the order parameter of other Neel ordered systems. The other two modes show only a negligible temperature dependence and dissolve above the ordering temperature in a continuum of excitations at finite energies. These observations point to a delicate interplay of magnetic inter- and intra-tetrahedra degrees of freedom and an importance of singlet fluctuations in describing a spin dynamics.
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arxiv:0806.0147
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A full nexus between Newtonian and relativistic mechanics is set. Contrarily to what is commonly thought, Newtonian mechanics can be amended to suit all speeds up to c. It is demonstrated that when introducing the fact that the pulse of oscillators, i.e. emitters and clocks, is sensitive to speed, the Newtonian framework can be extended to all speeds. For this aim, it is formulated the concept of actor scenario vs. observer scenario. This differentiation is essential to avoid confusion between effective reality (actor scenario) and appearance (observer scenario). Measurements are subjected to kinematical aberrations, the observer scenario being inertial. These must be removed to attain intrinsic reality, i.e. that of actors. The lack of demarcation between the two scenarios leads to conceptual confusions. The amended Newtonian mechanics is of full application. Here, it has been mainly applied to the Newtonian Doppler effect, amended to suit all speeds.
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arxiv:0806.0171
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We investigate sub-gap transport through a single-level quantum dot tunnel coupled to one superconducting and two normal-conducting leads. Despite the tendency of a large charging energy to suppress the equilibrium proximity effect, a finite Andreev current through the dot can be achieved in non-equilibrium situations. We propose two schemes to identify non-local Andreev transport. In one of them, the presence of strong Coulomb interaction leads to negative values of the non-local conductance as a clear signal of non-local Andreev transport.
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arxiv:0806.0237
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P. J. Kelly conjectured in 1968 that every diregular tournament on (2n+1) points can be decomposed in directed Hamilton circuits [1]. We define so called leading diregular tournament on (2n+1) points and show that it can be decomposed in directed Hamilton circuits when (2n+1) is a prime number. When (2n+1) is not a prime number this method does not work and we will need to devise some another method. We also propose a general method to find Hamilton decomposition of certain tournament for all sizes.
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arxiv:0806.0251
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We study the question of whether or not contractive representations of logmodular algebras are completely contractive. We prove that a 2-contractive representation of a logmodular algebra extends to a positive map on the enveloping C*-algebra, which we show generalizes a result of Foias and Suciu on uniform logmodular algebras. Our proof uses non-commutative operator space generalizations of classical results on 2-summing maps and semispectral measures. We establish some matrix factorization results for uniform logmodular algebras
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arxiv:0806.0284
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We report neutron diffuse scattering measurements on a single crystal of 68%Pb(Mg1/3Nb2/3)O3-32%PbTiO3. Strong diffuse scattering is observed at low temperatures. An external field applied along the [001] direction affects the diffuse scattering in the (HK0) plane significantly, suggesting a redistribution occurs between polar nanoregions of different polarizations perpendicular to the field. By contrast, the [001] field has no effect on the diffuse scattering in the (HOL) and (0KL) zones.
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arxiv:0806.0288
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The dispersion relation for the electrostatic waves below the electron plasma frequency in a dense quantum plasma is derived by using the magnetohydrodynamic model. It is shown that in the classical case the dispersion relation reduces to the expression obtained for the well-known Trivelpiece-Gould (TG) modes. Attention is also devoted to the case of solitary waves associated with the nonlinear TG modes.
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arxiv:0806.0346
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We calculate the prompt neutrino flux from atmospheric charm production by cosmic rays, using the dipole picture in a perturbative QCD framework, which incorporates the parton saturation effects present at high energies. We compare our results with the next-to-leading order perturbative QCD result and find that saturation effects are large for neutrino energies above 10^6 GeV, leading to a substantial suppression of the prompt neutrino flux. We comment on the range of prompt neutrino fluxes due to theoretical uncertainties.
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arxiv:0806.0418
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We extend a tight-binding method to include the effects of spin-orbit coupling, and apply it to the study of the electronic properties of the actinide elements Th, U, and Pu. These tight-binding parameters are determined for the fcc crystal structure using the equivalent equilibrium volumes. In terms of the single particle energies and the electronic density of states, the overall quality of the tight-binding representation is excellent and of the same quality as without spin-orbit coupling. The values of the optimized tight-binding spin-orbit coupling parameters are comparable to those determined from purely atomic calculations.
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arxiv:0806.0420
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The circular descent of a permutation $\sigma$ is a set $\{\sigma(i)\mid \sigma(i)>\sigma(i+1)\}$. In this paper, we focus on the enumerations of permutations by the circular descent set. Let $cdes_n(S)$ be the number of permutations of length $n$ which have the circular descent set $S$. We derive the explicit formula for $cdes_n(S)$. We describe a class of generating binary trees $T_k $ with weights. We find that the number of permutations in the set $CDES_n(S)$ corresponds to the weights of $T_k$. As a application of the main results in this paper, we also give the enumeration of permutation tableaux according to their shape.
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arxiv:0806.0433
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We calculate photons from jet plasma interaction in a collisional energy loss scenario. It is shown that the PHENIX photon data is well reproduced when photons from initial hard collisions are taken into account.
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arxiv:0806.0481
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We present mid-IR spectro-interferometry of the Seyfert type 1 nucleus of NGC 3783. The dusty circumnuclear environment is spatially resolved and the wavelength dependence of the compact emission is discussed. The observations were carried out with the MIDI instrument at the Very Large Telescope Interferometer in the N-band. Spectra and visibilities were derived with a spectral resolution of 30 in the wavelength range from 8 to 13 micron. For the interpretation we developed a simple dusty disk model with small and variable covering factor. At baselines of 65 and 69 m, visibilities in the range of 0.4 to 0.7 were measured. The N-band spectra show a monotonic increase of the measured flux with wavelength with no apparent silicate feature around 10 micron. We find that the mid-IR emission from the nucleus can be reproduced by an extended dust disk or torus with a small covering factor of the radiating dust clouds. Our mid-IR observations of NGC 3783 are consistent with a clumpy circumnuclear dust environment. The interpretation in terms of a dusty torus with low covering factor supports a clumpy version of the unified scheme for AGN. The inferred sizes and luminosities are in good agreement with dust reverberation sizes and bolometric luminosities from optical and X-ray observations.
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arxiv:0806.0531
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We integrate numerically the Kardar-Parisi-Zhang (KPZ) equation in 1+1 and 2+1 dimensions using an Euler discretization scheme and the replacement of ${(\nabla h)}^2$ by exponentially decreasing functions of that quantity to suppress instabilities. When applied to the equation in 1+1 dimensions, the method of instability control provides values of scaling amplitudes consistent with exactly known results, in contrast to the deviations generated by the original scheme. In 2+1 dimensions, we spanned a range of the model parameters where transients with Edwards-Wilkinson or random growth are not bserved, in box sizes $8\leq L\leq 128$. We obtain roughness exponent $0.37\leq \alpha\leq 0.40$ and steady state height distributions with skewness $S= 0.25\pm 0.01$ and kurtosis $Q= 0.15\pm 0.1$. These estimates are obtained after extrapolations to the large $L$ limit, which is necessary due to significant finite-size effects in the estimates of effective exponents and height distributions. On the other hand, the steady state roughness distributions show weak scaling corrections and evidence of stretched exponentials tails. These results confirm previous estimates from lattice models, showing their reliability as representatives of the KPZ class.
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arxiv:0806.0588
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We show that the factor ordering ambiguities associated with the loop quantisation of the gravitational part of the cosmological Hamiltonian constraint, disappear at the level of Wheeler-DeWitt equation only for a particular choice of lattice refinement model, which coincides with constraints imposed from phenomenological and consistency arguments.
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arxiv:0806.0595
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We examine the linear stability of static, spherically symmetric wormhole solutions of Einstein's field equations coupled to a massless ghost scalar field. These solutions are parametrized by the areal radius of their throat and the product of the masses at their asymptotically flat ends. We prove that all these solutions are unstable with respect to linear fluctuations and possess precisely one unstable, exponentially in time growing mode. The associated time scale is shown to be of the order of the wormhole throat divided by the speed of light. The nonlinear evolution is analyzed in a subsequent article.
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arxiv:0806.0608
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We model the hot and dense strongly interacting mater produced in high energy heavy ion collisions using relativistic hydrodynamics. Several different sources of real photons produced during these collisions are considered and their relative importance is assessed. We include contributions from QCD jets, which are allowed to loose and gain energy as they proceed through the hot matter. This is treated within the AMY formalism. We obtain photon spectra, R_{AA}, and v_2 in agreement with measurements performed by the PHENIX collaboration.
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arxiv:0806.0610
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The simplest decomposition of a Toffoli gate acting on three qubits requires {\em five} 2-qubit gates. If we restrict ourselves to controlled-sign (or controlled-NOT) gates this number climbs to six. We show that the number of controlled-sign gates required to implement a Toffoli gate can be reduced to just {\em three} if one of the three quantum systems has a third state that is accessible during the computation, i.e. is actually a qutrit. Such a requirement is not unreasonable or even atypical since we often artificially enforce a qubit structure on multilevel quantums systems (eg. atoms, photonic polarization and spatial modes). We explore the implementation of these techniques in optical quantum processing and show that linear optical circuits could operate with much higher probabilities of success.
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arxiv:0806.0654
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In the Born-Infeld 'harmonic gauge' description of M-branes moving in R^{M+1} the underlying M+2 dimensional Poincare - invariance gives rise to an interesting system of conservation laws showing signs of integrability.
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arxiv:0806.0656
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Let GF(q)[x,y] be the polynomial algebra in two variables over the finite field GF(q) with q elements. We give an exact formula and the asymptotics for the number p(n) of automorphisms (f,g) of GF(q)[x,y] such that max{deg(f),deg(g)}=n. We describe also the Dirichlet series generating function p(1)/1^s+p(2)/2^s+p(3)/3^s+.... The same results hold for the automorphisms of the free associative algebra GF(q)<x,y>. We have also obtained analogues for free algebras with two generators in Nielsen - Schreier varieties of algebras.
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arxiv:0806.0681
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We show that the group of holomorphic automorphisms of a Stein manifold X of dimension greater than 1 is infinite-dimensional, provided X is a homogeneous space of a holomorphic action of a complex Lie group.
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arxiv:0806.0693
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Nuclear physics can be applied in various ways to the study of neutron stars. This thesis reports on one such application, where the relativistic mean-field approximation has been employed to calculate the equations of state of matter in the neutron star interior. In particular the equations of state of nuclear and neutron star matter of the NL3, PK1 and FSUGold parameter sets were derived. A survey of available literature on neutron stars is presented and we use the derived equations of state to reproduce the properties of saturated nuclear matter as well as the mass-radius relationship of a static, spherical symmetric neutron star. Results are compared to published values of the properties of saturated nuclear matter and to available observational data of the mass-radius relationship of neutron stars.
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arxiv:0806.0747
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Studies of the production of W/Z + jets are important for a variety of reasons. W/Z + inclusive jets is a valuable high statistics sample that allows one to probe the validity of predictions from perturbative Quantum Chromodynamics (pQCD) at both leading and next-to-leading order. W/Z + heavy flavor jets (those originating from b or c production) is a significant background to top and Higgs at the Tevatron and will play an important role at the LHC as well. Herein the latest Tevatron results on these production mechanisms are reviewed with an emphasis on comparison of data results to the latest theoretical models.
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arxiv:0806.0825
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Constrictions in fractional quantum Hall (FQH) systems not only facilitate backscattering between counter-propagating edge modes, but also may reduce the constriction filling fraction $\nu_c$ with respect to the bulk filling fraction $\nu_b$. If both $\nu_b$ and $\nu_c$ correspond to incompressible FQH states, at least part of the constriction region is surrounded by composite edges, whose low energy dynamics is characterized by a charge mode and one or several neutral modes. In the incoherent regime, decay of neutral modes describes the equilibration of composite FQH edges, while in the limit of coherent transport, the presence of neutral modes gives rise to universal conductance fluctuations. In addition, neutral modes renormalize the strength of scattering across the constriction, and thus can determine the relative strength of forward and backwards scattering.
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arxiv:0806.0869
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We propose to detect the Mott insulator-superfluid quantum phase transition in an array of coupled cavities by studying the polariton and photon fluctuations in a block of linear dimension M (in units of the lattice constant of the array). We explicitly show this for a one-dimensional array; the analysis can be however extended to higher dimensions. In the Mott phase polariton fluctuations are independent of the block size. In the superfluid phase they grow logarithmically with M, the prefactor being related to the compressibility of the system. In the case of photon fluctuations, the critical behaviour is encoded in the subleading scaling with the block dimension, while the leading behaviour is linear in M and non-critical. Our results have been obtained by means of the density matrix renormalization group numerical algorithm.
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arxiv:0806.0942
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We present and compare the predictions of various cosmic-ray Monte Carlo models for the energy (dE/deta) and particle (dN/deta) flows in p-p, p-Pb and Pb-Pb collisions at sqrt(s) = 14, 8.8, and 5.5 TeV respectively, in the range covered by forward LHC detectors like CASTOR or TOTEM (5.2<|eta|<6.6) and ZDC or LHCf (|eta|>8.1 for neutrals).
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arxiv:0806.0944
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The spin polarized charge transport is systematically analyzed as a thermally driven stochastic process. The approach is based on Kramers' equation describing the semiclassical motion under the inclusion of stochastic and damping forces. Due to the relativistic spin-orbit coupling the damping experiences a relativistic correction leading to an additional contribution within the spin Hall conductivity. A further contribution to the conductivity is originated from the averaged underlying crystal potential, the mean value of which depends significantly on the electric field. We derive an exact expression for the electrical conductivity. All corrections are estimated in lowest order of a relativistic approach and in the linear response regime.
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arxiv:0806.0948
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We study the action of a nilpotent group G with finite generating set S on its horofunction boundary. We show that there is one finite orbit associated to each facet of the polytope obtained by projecting S into the infinite component of the abelianisation of G. We also prove that these are the only finite orbits of Busemann points. To finish off, we examine in detail the Heisenberg group with its usual generators.
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arxiv:0806.0966
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Any hint of non-gaussianity in the cosmological initial conditions will provide us with a unique window into the physics of early universe. We show that the impact of a small local primordial non-gaussianity (generated on super-horizon scales) on the statistics of collapsed objects (such as galaxies or clusters) can be approximated by using slightly modified, but gaussian, initial conditions, which we describe through simple analytic expressions. Given that numerical simulations with gaussian initial conditions are relatively well-studied, this equivalence provides us with a simple tool to predict signatures of primordial non-gaussianity in the statistics of collapsed objects. In particular, we describe the predictions for non-gaussian mass function, and also confirm the recent discovery of a non-local bias on large scales (arXiv:0710.4560, arXiv:0801.4826) as a signature of primordial non-gaussianity. We then study the potential of galaxy surveys to constrain non-gaussianity using their auto-correlation and cross-correlation with the CMB (due to the Integrated Sachs-Wolfe effect), as a function of survey characteristics, and predict that they will eventually yield an accuracy of Delta f_{NL} ~ 0.1 and 3 respectively, which will be better than or competitive with (but independent of) the best predicted constraints from the CMB. Interestingly, the cross-correlation of CMB and NVSS galaxy survey already shows a hint of a large local primordial non-gaussianity: f_{NL} = 236 +/- 127.
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arxiv:0806.1046
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We study M-theory compactified on a specific class of seven-dimensional manifolds with SU(3) structure. The manifolds can be viewed as a fibration of an arbitrary Calabi-Yau threefold over a circle, with a U-duality twist around the circle. In some cases we find that in the four dimensional low energy effective theory a (broken) non-Abelian gauge group appears. Furthermore, such compactifications are shown to be dual to previously analyzed compactifications of the heterotic string on K3 x T^2, with background gauge field fluxes on the T^2.
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arxiv:0806.1051
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The ordering temperature of a quasi-one-dimensional system, consisting of weakly interacting quantum spin-1/2 chains with antiferromagnetic spin-frustrating couplings (or zig-zag ladder) is calculated. The results show that a quantum critical point between two phases of the one-dimensional subsystem plays a crucial role. If the one-dimensional subsystem is in the antiferromagnetic-like phase in the ground state, similar to the phase of a spin chain without frustration, weak couplings yield magnetic ordering of the Neel type. For intra-chain spin-frustrating interactions larger than the critical one (at which the quantum phase transition takes place), the quasi-one-dimensional spin system manifests a spiral magnetic incommensurate ordering. The obtained results of our quantum theory are compared with the quasi-classical approximations. The calculated features of magnetic ordering are expected to be generic for weakly coupled quantum spin chains with gapless excitations and spin-frustrating nearest and next-nearest neighbor interactions.
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arxiv:0806.1074
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A central problem in comparative genomics consists in computing a (dis-)similarity measure between two genomes, e.g. in order to construct a phylogeny. All the existing measures are defined on genomes without duplicates. However, we know that genes can be duplicated within the same genome. One possible approach to overcome this difficulty is to establish a one-to-one correspondence (i.e. a matching) between genes of both genomes, where the correspondence is chosen in order to optimize the studied measure. In this paper, we are interested in three measures (number of breakpoints, number of common intervals and number of conserved intervals) and three models of matching (exemplar, intermediate and maximum matching models). We prove that, for each model and each measure M, computing a matching between two genomes that optimizes M is APX-hard. We also study the complexity of the following problem: is there an exemplarization (resp. an intermediate/maximum matching) that induces no breakpoint? We prove the problem to be NP-Complete in the exemplar model for a new class of instances, and we show that the problem is in P in the maximum matching model. We also focus on a fourth measure: the number of adjacencies, for which we give several approximation algorithms in the maximum matching model, in the case where genomes contain the same number of duplications of each gene.
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arxiv:0806.1103
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We provide a rigorous mathematical derivation of the convergence in the long-wave transonic limit of the minimizing travelling waves for the two-dimensional Gross-Pitaevskii equation towards ground states for the Kadomtsev-Petviashvili equation (KP I).
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arxiv:0806.1122
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We report on visible light emission from Si-nanocrystal based optically active microdisk resonators. The room temperature photoluminescence (PL) from single microdisks shows the characteristic modal structure of whispering-gallery modes. The emission is both TE and TM-polarized in 300 nm thick microdisks, while thinner ones (135 nm) support only TE-like modes. Thinner disks have the advantage to filter out higher order radial mode families, allowing for measuring only the most intense first order modal structure. We reveal subnanometer linewidths and corresponding quality factors as high as 2800, limited by the spectral resolution of the experimental setup. Moreover,we observe a modification of mode linewidth by a factor 13 as a function of pump power. The origin of this effect is attributed to an excited carrier absorption loss mechanism.
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arxiv:0806.1128
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The equilibrium points and their linear stability has been discussed in the generalized photogravitational Chermnykh's problem. The bigger primary is being considered as a source of radiation and small primary as an oblate spheroid. The effect of radiation pressure has been discussed numerically. The collinear points are linearly unstable and triangular points are stable in the sense of Lyapunov stability provided $\mu< \mu_{Routh}=0.0385201$. The effect of gravitational potential from the belt is also examined. The mathematical properties of this system are different from the classical restricted three body problem.
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arxiv:0806.1132
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In quasi-persistent neutron star transients, long outbursts cause the neutron star crust to be heated out of thermal equilibrium with the rest of the star. During quiescence, the crust then cools back down. Such crustal cooling has been observed in two quasi-persistent sources: KS 1731-260 and MXB 1659-29. Here we present an additional Chandra observation of MXB 1659-29 in quiescence, which extends the baseline of monitoring to 6.6 yr after the end of the outburst. This new observation strongly suggests that the crust has thermally relaxed, with the temperature remaining consistent over 1000 days. Fitting the temperature cooling curve with an exponential plus constant model we determine an e-folding timescale of 465 +/- 25 days, with the crust cooling to a constant surface temperature of kT = 54 +/- 2 eV (assuming D=10 kpc). From this, we infer a core temperature in the range 3.5E7-8.3E7 K (assuming D=10 kpc), with the uncertainty due to the surface composition. Importantly, we tested two neutron star atmosphere models as well as a blackbody model, and found that the thermal relaxation time of the crust is independent of the chosen model and the assumed distance.
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arxiv:0806.1166
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Let s<t be two fixed positive integers. We study what are the minimum degree conditions for a bipartite graph G, with both color classes of size n=k(s+t), which ensure that G has a K_{s,t}-factor. Exact result for large n is given. Our result extends the work of Zhao, who determined the minimum degree threshold which guarantees that a bipartite graph has a K_{s,s}-factor.
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arxiv:0806.1192
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Controlling domain wall motion is important due to the impact on the viability of proposed nanowire devices. One hurdle is slow domain wall speed when driven by fields greater than the Walker field, due to nucleation of vortices in the wall. We present simulation results detailing the dynamics of these vortices; including the nucleation and subsequent fast ejection of the vortex core leading to fast domain wall speeds. The ejection is due to the reversal of the core moments by an out-of-plane field. The technique can be used to produce domain walls of known orientation independent of the initial state.
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arxiv:0806.1205
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We review the history of analytical approaches to particle production from external strong fields in QED and QCD, and numerical studies of the back reaction problem for the electric field in QED. We discuss the formulation of the backreaction problem for the chromoelectric field in QCD both in leading and next to leading order in flavor large-N QCD.
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arxiv:0806.1249
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The exponential of the triangular matrix whose entries in the diagonal at distance $n$ from the principal diagonal are all equal to the sum of the inverse of the divisors of $n$ is the triangular matrix whose entries in the diagonal at distance $n$ from the principal diagonal are all equal to the number of partitions of $n$. A similar result is true for any pair of sequences satisfying a special recurrence.
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arxiv:0806.1273
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An analytic pair of dimension n and center V is a pair (V, M) where M is a complex manifold of (complex) dimension n and V is a closed totally real analytic submanifold of dimension n. To an analytic pair (V, M) we associate the class of the functions u from M to a positive bounded interval which are plurisubharmonic in M and such that u(p) = 0 for each p in V. If the class admits a maximal function u, the triple (V, M, u) is said to be a maximal plurisubharmonic model. After defining a pseudo-metric E(V,M) on the center V of an analytic pair (V, M) we prove (see Theorem 4.1, Theorem 5.1) that maximal plurisubharmonic models provide a natural generalization of the Monge-Ampere models introduced by Lempert and Szoke in [16].
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arxiv:0806.1275
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In the last few years we have developed stellar model atmospheres which included effects of anomalous abundances and strong magnetic field. The full treatment of anomalous Zeeman splitting and polarized radiative transfer were introduced in the model atmosphere calculations for the first time. In this investigation we present results of modelling the atmosphere of one of the most extreme magnetic chemically peculiar stars, HD137509. This Bp SiCrFe star has the mean surface magnetic field modulus of about 29kG. We use the recent version of the line-by-line opacity sampling stellar model atmosphere code LLmodels, which incorporates the full treatment of Zeeman splitting of spectral lines, detailed polarized radiative transfer and arbitrary abundances. We compare model predictions with photometric and spectroscopic observations of the star, aiming to reach a self-consistency between the abundance pattern derived from high-resolution spectra and abundances used for model atmosphere calculation. Based on magnetic model atmospheres, we redetermined abundances and fundamental parameters of HD137509 using spectroscopic and photometric observations. This allowed us to obtain a better agreement between observed and theoretical parameters compared to non-magnetic models with individual or scaled-solar abundances. We confirm that the magnetic field effects should be taken into account in the stellar parameter determination and abundance analysis.
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arxiv:0806.1296
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In a long-term observing project we have imaged a complete sample of FRII quasars and radio galaxies with z < 1.0 at high resolution and high sensitivity with the VLA and MERLIN. This sample of 98 sources includes 15 quasars, 11 broad line radio galaxies and 57 narrow line radio galaxies, allowing unification to be considered in terms of source morphological properties. Radio maps of all the targets have been presented in earlier papers. Here we carry out a systematic analysis of the properties of the jets, cores, lobes and hotspots of objects in the sample. The majority of the tests that we perform show that the data are consistent with a model in which quasars and broad-line radio galaxies are unified with narrow-line objects. Relativistic beaming is the main effect that determines the properties of kiloparsec-scale jets, and it may also have some effect on hotspots. However, some properties of the sample are difficult to account for in simple unified models.
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arxiv:0806.1313
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From the study of a functional equation of Gibbs measures we calculate the limiting free energy of the Sherrington-Kirkpatrick spin glass model at a particular value of (low) temperature. This implies the following lower bound for the ground state energy $\epsilon_0$ \[\epsilon_0\geq -0.7833\cdots,\] close to the replica symmetry breaking and numerical simulations values.
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arxiv:0806.1380
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The particular properties of synchronization are discussed for the system of coupled van der Pol - Duffing oscillators. The arrangement of synchronization tongues and the particular properties of their internal structure in the parameter space are revealed. The features of attractors in the phase space and in the Poincare section are considered.
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arxiv:0806.1402
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We report ^{59}Co NMR studies in single crystals of cobalt oxide superconductor Na_{0.42}CoO_{2}\cdot1.3H_{2}O (T_c=4.25K) and its parent compound Na_{0.42}CoO_{2}. We find that both the magnitude and the temperature (T) dependence of the Knight shifts are identical in the two compounds above T_c. The spin-lattice relaxation rate (1/T_1) is also identical above T_0 \sim60 K for both compounds. Below T_0, the unhydrated sample is found to be a non-correlated metal that well conforms to Fermi liquid theory, while spin fluctuations develop in the superconductor. These results indicate that water intercalation does not change the density of states but its primary role is to bring about spin fluctuations. Our result shows that, in the hydrated superconducting compound, the in-plane spin fluctuation around finite wave vector is much stronger than that along the c-axis, which indicates that the spin correlation is quasi-two-dimensional.
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arxiv:0806.1412
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We present a detailed optical study of the ultra-compact X-ray binary 4U0614+091. We have used 63 hrs of time-resolved optical photometry taken with three different telescopes (IAC80, NOT and SPM) to search for optical modulations. The power spectra of each dataset reveals sinusoidal modulations with different periods, which are not always present. The strongest modulation has a period of 51.3 mins, a semi-amplitude of 4.6 mmags, and is present in the IAC80 data. The SPM and NOT data show periods of 42 mins and 64 mins respectively, but with much weaker amplitudes, 2.6 mags and 1.3 mmags respectively. These modulations arise from either X-ray irradiation of the inner face of the secondary star and/or a superhump modulation from the accretion disc, or quasi-periodic modulations in the accretion disc. It is unclear whether these periods/quasi-periodic modulations are related to the orbital period, however, the strongest period of 51.3 mins is close to earlier tentative orbital periods. Further observations taken over a long base-line are encouraged.
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arxiv:0806.1419
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We show that a special choice of light-cone gauge can greatly simplify the calculation of the classical color field created in the initial stages of nucleus-nucleus collisions. Within this gauge, we can in particular construct explicitly the conserved color current and calculate exactly the gauge field immediately after the collision. This field is used as a boundary condition in an iterative solution of the Yang-Mills equations in the forward light-cone. In leading order, which corresponds to a linearization of the Yang-Mills equation in the forward light-cone, we obtain a simple formula for the spectrum of gluons produced in nucleus-nucleus collisions. This formula reproduces exactly the known formula for proton-nucleus collisions, where $k_t-$factorization is recovered, while the latter property apparently breaks down in the case of nucleus-nucleus collisions.
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arxiv:0806.1422
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We examine the incipient infinite cluster (IIC) of critical percolation in regimes where mean-field behavior has been established, namely when the dimension d is large enough or when d>6 and the lattice is sufficiently spread out. We find that random walk on the IIC exhibits anomalous diffusion with the spectral dimension d_s=4/3, that is, p_t(x,x)= t^{-2/3+o(1)}. This establishes a conjecture of Alexander and Orbach. En route we calculate the one-arm exponent with respect to the intrinsic distance.
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arxiv:0806.1442
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We study models of correlated percolation where there are constraints on the occupation of sites that mimic force-balance, i.e. for a site to be stable requires occupied neighboring sites in all four compass directions in two dimensions. We prove rigorously that $p_c<1$ for the two-dimensional models studied. Numerical data indicate that the force-balance percolation transition is discontinuous with a growing crossover length, with perhaps the same form as the jamming percolation models, suggesting the same underlying mechanism driving the transition in both cases. In other words, force-balance percolation and jamming percolation may indeed belong to the same universality class. We find a lower bound for the correlation length in the connected phase and that the correlation function does not appear to be a power law at the transition. Finally, we study the dynamics of the culling procedure invoked to obtain the force-balance configurations and find a dynamical exponent similar to that found in sandpile models.
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arxiv:0806.1552
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We study the angular resolution of the gravitational wave detector LISA and show that numerical relativity can drastically improve the accuracy of position location for coalescing Super Massive Black Hole (SMBH) binaries. For systems with total redshifted mass above $10^7 M_{\odot}$, LISA will mainly see the merger and ring-down of the gravitational wave (GW) signal, which can now be computed numerically using the full Einstein equations. Using numerical waveforms that also include about ten GW cycles of inspiral, we improve inspiral-only position estimates by an order of magnitude. We show that LISA localizes half of all such systems at $z=1$ to better than 3 arcminutes and the best 20% to within one arcminute. This will give excellent prospects for identifying the host galaxy.
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arxiv:0806.1591
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In this paper we compute the leading order Casimir energy for the electromagnetic field (EM) in an open ended perfectly conducting rectangular waveguide in three spatial dimensions by a direct approach. For this purpose we first obtain the second quantized expression for the EM field with boundary conditions which would be appropriate for a waveguide. We then obtain the Casimir energy by two different procedures. Our main approach does not contain any analytic continuation techniques. The second approach involves the routine zeta function regularization along with some analytic continuation techniques. Our two approaches yield identical results. This energy has been calculated previously for the EM field in a rectangular waveguide using an indirect approach invoking analogies between EM fields and massless scalar fields, and using complicated analytic continuation techniques, and the results are identical to ours. We have also calculated the pressures on different sides and the total Casimir energy per unit length, and plotted these quantities as a function of the cross-sectional dimensions of the waveguide. We also present a physical discussion about the rather peculiar effect of the change in the sign of the pressures as a function of the shape of the cross-sectional area.
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arxiv:0806.1628
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In this work it is shown that a necessary condition for the completeness of the geodesics of left invariant pseudo-Riemannian metrics on Lie groups is also sufficient in the case of 3-dimensional unimodular Lie groups, and not sufficient for 3-dimensional non unimodular Lie groups. As a consequence it is possible to identify, amongst the compact locally homogeneous Lorentzian 3-manifolds with non compact (local) isotropy group, those that are geodesically complete.
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arxiv:0806.1632
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We study the interaction of small amplitude, long wavelength solitary waves in the Fermi-Pasta-Ulam model with general nearest-neighbor interaction potential. We establish global-in-time existence and stability of counter-propagating solitary wave solutions. These solutions are close to the linear superposition of two solitary waves for large positive and negative values of time; for intemediate values of time these solutions describe the interaction of two counterpropagating pulses. These solutions are stable with respect to perturbations in $\ell^2$ and asymptotically stable with respect to perturbations which decay exponentially at spatial $\pm \infty$.}
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arxiv:0806.1637
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We extend the concept of generalized synchronization of chaos, a phenomenon that occurs in driven dynamical systems, to the context of autonomous spatiotemporal systems. It means a situation where the chaotic state variables in an autonomous system can be synchronized to each other but not to a coupling function defined from them. The form of the coupling function is not crucial; it may not depend on all the state variables nor it needs to be active for all times for achieving generalized synchronization. The procedure is based on the analogy between a response map subject to an external drive acting with a probability p and an autonomous system of coupled maps where a global interaction between the maps takes place with this same probability. It is shown that, under some circumstances, the conditions for stability of generalized synchronized states are equivalent in both types of systems. Our results reveal the existence of similar minimal conditions for the emergence of generalized synchronization of chaos in driven and in autonomous spatiotemporal systems.
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arxiv:0806.1642
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We study the weighted heat trace asymptotics of an operator of Laplace type with Dirichlet boundary conditions where the weight function exhibits radial blowup. We give formulas for the first few terms in the expansion in terms of geometrical data.
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arxiv:0806.1706
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Precision data from cosmology suggest neutrinos stream freely and hence interact very weakly around the epoch of recombination. We study this issue in a simple framework where neutrinos recouple instantaneously and stop streaming freely at a redshift z_i. The latest cosmological data imply z_i < 1500, the exact constraint depending somewhat on the assumed prior on z_i. This bound translates into a limit on the coupling strength between neutrinos and majoron-like particles phi, implying tau > 1 x 10^10 s (m_2/50 meV)^3 for the decay nu_2 -> nu_1+phi.
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arxiv:0806.1735
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Adding rewriting to a proof assistant based on the Curry-Howard isomorphism, such as Coq, may greatly improve usability of the tool. Unfortunately adding an arbitrary set of rewrite rules may render the underlying formal system undecidable and inconsistent. While ways to ensure termination and confluence, and hence decidability of type-checking, have already been studied to some extent, logical consistency has got little attention so far. In this paper we show that consistency is a consequence of canonicity, which in turn follows from the assumption that all functions defined by rewrite rules are complete. We provide a sound and terminating, but necessarily incomplete algorithm to verify this property. The algorithm accepts all definitions that follow dependent pattern matching schemes presented by Coquand and studied by McBride in his PhD thesis. It also accepts many definitions by rewriting, containing rules which depart from standard pattern matching.
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arxiv:0806.1749
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When implementing a propagator for a constraint, one must decide about variants: When implementing min, should one also implement max? Should one implement linear equations both with and without coefficients? Constraint variants are ubiquitous: implementing them requires considerable (if not prohibitive) effort and decreases maintainability, but will deliver better performance. This paper shows how to use variable views, previously introduced for an implementation architecture, to derive perfect propagator variants. A model for views and derived propagators is introduced. Derived propagators are proved to be indeed perfect in that they inherit essential properties such as correctness and domain and bounds consistency. Techniques for systematically deriving propagators such as transformation, generalization, specialization, and channeling are developed for several variable domains. We evaluate the massive impact of derived propagators. Without derived propagators, Gecode would require 140000 rather than 40000 lines of code for propagators.
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arxiv:0806.1806
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We present an efficient routing approach for delivering packets in complex networks. On delivering a message from a node to a destination, a node forwards the message to a neighbor by estimating the waiting time along the shortest path from each of its neighbors to the destination. This projected waiting time is dynamical in nature and the path through which a message is delivered would be adapted to the distribution of messages in the network. Implementing the approach on scale-free networks, we show that the present approach performs better than the shortest-path approach and another approach that takes into account of the waiting time only at the neighboring nodes. Key features in numerical results are explained by a mean field theory. The approach has the merit that messages are distributed among the nodes according to the capabilities of the nodes in handling messages.
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arxiv:0806.1843
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Let $X$ be a smooth algebraic curve. Suppose that there exists a triple covering $f : X \to Y$ where $Y$ is a smooth algebraic curve. In this paper, we investigate the existence of morphisms from $X$ to the projective line $\mathbf{P}^1$ which do not factor through the covering $f$. For this purpose, we generalize the classical results of Maroni concerning base-point-free pencils on trigonal curves to the case of triple covers of arbitrary smooth irrational curves.
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arxiv:0806.1849
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The pair separation model of Goto and Vassilicos (S Goto and J C Vassilicos, 2004, New J.Phys., 6, p.65) is revisited and placed on a sound mathematical foundation. A DNS of two dimensional homogeneous isotropic turbulence with an inverse energy cascade and a k^{-5/3} power law is used to investigate properties of pair separation in two dimensional turbulence. A special focus lies on the time asymmetry observed between forward and backward separation. Application of the present model to this data suffers from finite inertial range effects and thus, conditional averaging on scales rather than on time has been employed to obtain values for the Richardson constants and their ratio. The Richardson constants for the forward and backward case are found to be (1.066 +/- 0.020) and (0.999 +/- 0.007) respectively. The ratio of Richardson constants for the backwards and forwards case is therefore g_b/g_f = (0.92 +/- 0.03), and hence exhibits a qualitatively different behavior from pair separation in three dimensional turbulence, where g_b > g_f (J Berg et al., 2006, Phys.Rev.E, 74(1), p.016304). This indicates that previously proposed explanations for this time asymmetry based on the strain tensor eigenvalues are not sufficient to describe this phenomenon in two dimensional turbulence. We suggest an alternative qualitative explanation based on the time asymmetry related to the inverse versus forward energy cascade. In two dimensional turbulence, this asymmetry manifests itself in merging eddies due to the inverse cascade, leading to the observed ratio of Richardson constants.
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arxiv:0806.1867
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Stimulated by the recent debate on the physical relevance and on the predictivity of q-Gaussian formalism, we present specific analytical expressions for the parameters characterizing non-Gaussian distributions, such as the nonextensive parameter q, expressions that we have proposed for different physical systems, an important example being plasmas in the stellar cores.
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arxiv:0806.1870
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The first optical spectrum of an isolated polycyclic aromatic hydrocarbon large enough to survive the photophysical conditions of the interstellar medium is reported. Vibronic bands of the first electronic transition of the all benzenoid polycyclic aromatic hydrocarbon hexa-peri-hexabenzocoronene were observed in the 4080-4530 Angstrom range by resonant 2-color 2-photon ionization spectroscopy. The strongest feature at 4264 Angstrom is estimated to have an oscillator strength of f=1.4x10^-3, placing an upper limit on the interstellar abundance of this polycyclic aromatic hydrocarbon at 4x10^12 cm^-2, accounting for a maximum of ~0.02% of interstellar carbon. This study opens up the possibility to rigorously test neutral polycyclic aromatic hydrocarbons as carriers of the diffuse interstellar bands in the near future.
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arxiv:0806.1888
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We study localized plasma configurations in 3+1 dimensional massive field theories obtained by Scherk-Schwarz compactification of 4+1 dimensional CFT to predict the thermodynamic properties of localized blackholes and blackrings in Scherk-Schwarz compactified $AdS_6$ using the AdS/CFT correspondence. We present an exact solution to the relativistic Navier-Stokes equation in the thin ring limit of the fluid configuration. We also perform a thorough numerical analysis to obtain the thermodynamic properties of the most general solution. Finally we compare our results with the recent proposal for the phase diagram of blackholes in six flat dimensions and find some similarities but other differences.
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arxiv:0806.1897
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Let $X$ be an affine algebraic variety with a transitive action of the algebraic automorphism group. Suppose that $X$ is equipped with several non-degenerate fixed point free $SL_2$-actions satisfying some mild additional assumption. Then we show that the Lie algebra generated by completely integrable algebraic vector fields on $X$ coincides with the set of all algebraic vector fields. In particular, we show that apart from a few exceptions this fact is true for any homogeneous space of form $G/R$ where $G$ is a linear algebraic group and $R$ is its proper reductive subgroup.
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arxiv:0806.1935
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We investigate the vacuum polarization effects associated with a charged massless spin-1/2 field in a higher-dimensional space-time, induced by a composite topological defect. The defect is constituted by a global monopole living on a three-brane and two-dimensional conical space transverse to the latter. In addition, we assume the presence of an extra magnetic flux along the core of the conical space. The heat kernel and the Feynman Green function are presented in the form of a sum of two terms. The first one corresponds to the contribution coming from the bulk with global monopole in the absence of conical structure of the orthogonal two-space, and the second one is induced by this structure and the magnetic flux. We explicitly evaluate the part in the vacuum expectation value of the energy-momentum tensor induced by the flux carrying conical structure. As in pure cosmic string geometries, only the fractional part of the ratio of the magnetic flux to flux quantum leads to non-trivial effects. The vacuum energy-momentum tensor is an even function of this parameter. We show that for strong gravitational fields corresponding to large values of the solid angle deficit, the effects induced by the conical structure and flux are exponentially suppressed.
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arxiv:0806.1944
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We report the observation of beatings of the coincidence event rate in a Hong-Ou-Mandel interference (HOMI) between signal and idler photons from a parametric downconversion (PDC) process inside a multi-mode KTP waveguide. As explanation we introduce bi-photonic states entangled in their broadband frequency modes generated by waveguide mode triples and propose a suitable entanglement detection scheme.
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arxiv:0806.1961
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We study the single-transverse spin asymmetry for open charm production in the semi-inclusive lepton-hadron deep inelastic scattering. We calculate the asymmetry in terms of the QCD collinear factorization approach for $D$ mesons at high enough $P_{h\perp}$, and find that the asymmetry is proportional to the twist-three tri-gluon correlation function in the proton. With a simple model for the tri-gluon correlation function, we estimate the asymmetry for both COMPASS and eRHIC kinematics, and discuss the possibilities of extracting the tri-gluon correlation function in these experiments.
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arxiv:0806.1970
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We present progress on a comprehensive, modular, interactive modeling environment centered on overall regulation of blood pressure and body fluid homeostasis. We call the project SAPHIR, for "a Systems Approach for PHysiological Integration of Renal, cardiac, and respiratory functions". The project uses state-of-the-art multi-scale simulation methods. The basic core model will give succinct input-output (reduced-dimension) descriptions of all relevant organ systems and regulatory processes, and it will be modular, multi-resolution, and extensible, in the sense that detailed submodules of any process(es) can be "plugged-in" to the basic model in order to explore, eg. system-level implications of local perturbations. The goal is to keep the basic core model compact enough to insure fast execution time (in view of eventual use in the clinic) and yet to allow elaborate detailed modules of target tissues or organs in order to focus on the problem area while maintaining the system-level regulatory compensations.
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arxiv:0806.2005
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We consider scale invariant theories of continuous mass fields, and show how interactions of these fields with the standard model can reproduce unparticle interactions. There is no fixed point or dimensional transmutation involved in this approach. We generalize interactions of the standard model to multiple unparticles in this formalism and explicitly work out some examples, in particular we show that the product of two scalar unparticles behaves as a normalized scalar unparticle with dimension equal to the sum of the two composite unparticle dimensions. Extending the formalism to scale invariant interactions of continuous mass fields, we calculate three point function of unparticles.
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arxiv:0806.2009
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Dissimilarity measures for (possibly weighted) phylogenetic trees based on the comparison of their vectors of path lengths between pairs of taxa, have been present in the systematics literature since the early seventies. But, as far as rooted phylogenetic trees goes, these vectors can only separate non-weighted binary trees, and therefore these dissimilarity measures are metrics only on this class. In this paper we overcome this problem, by splitting in a suitable way each path length between two taxa into two lengths. We prove that the resulting splitted path lengths matrices single out arbitrary rooted phylogenetic trees with nested taxa and arcs weighted in the set of positive real numbers. This allows the definition of metrics on this general class by comparing these matrices by means of metrics in spaces of real-valued $n\times n$ matrices. We conclude this paper by establishing some basic facts about the metrics for non-weighted phylogenetic trees defined in this way using $L^p$ metrics on these spaces of matrices.
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arxiv:0806.2035
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We show that with GLAST there will be the possibility to detect, within the UHECR skimming at atmosphere edges, the showers generated by very high energy upward and horizontal Tau. The effective area, thanks to the large area covered by the showers at 550 Km, is less than that of AUGER, but its efficiency is comparable because the lower detection threshold and the consequent event rate may lead to a few EeV and-or few Glashow resonant signals within a decade.
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arxiv:0806.2046
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Some recent efforts in compiling data for astrophysical purposes are introduced, which were discussed during a JINA-CARINA Collaboration meeting on "Nuclear Physics Data Compilation for Nucleosynthesis Modeling" held at the ECT* in Trento/ Italy from May 29th- June 3rd, 2007. The main goal of this collaboration is to develop an updated and unified nuclear reaction database for modeling a wide variety of stellar nucleosynthesis scenarios. Presently a large number of different reaction libraries (REACLIB) are used by the astrophysics community. The "JINA Reaclib Database" on http://www.nscl.msu.edu/\~nero/db/ aims to merge and fit the latest experimental stellar cross sections and reaction rate data of various compilations, e.g. NACRE and its extension for Big Bang nucleosynthesis, Caughlan and Fowler, Iliadis et al., and KADoNiS. The KADoNiS (Karlsruhe Astrophysical Database of Nucleosynthesis in Stars, http://nuclear-astrophysics.fzk.de/kadonis) project is an online database for neutron capture cross sections relevant to the s process. The present version v0.2 is already included in a REACLIB file from Basel university (http://download.nucastro.org/astro/reaclib). The present status of experimental stellar $(n,\gamma)$ cross sections in KADoNiS is shown. A "high priority list" for measurements and evaluations for light charged-particle reactions set up by the JINA-CARINA collaboration is presented. The central web access point to submit and evaluate new data is provided by the Oak Ridge group via the http://www.nucastrodata.org homepage. "Workflow tools" aim to make the evaluation process transparent and allow users to follow the progress.
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arxiv:0806.2070
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Motivated by recent experiments and a theoretical analysis of the gap equation for the propagator of Dirac quasiparticles, we assume that the physics underlying the recently observed removal of sublattice and spin degeneracies in graphene in a strong magnetic field is connected with the generation of both Dirac masses and spin gaps. The consequences of such a scenario for the existence of the gapless edge states with zigzag and armchair boundary conditions are discussed. In the case of graphene on a half-plane with a zigzag edge, there are gapless edge states in the spectrum only when the spin gap dominates over the mass gap. In the case of an armchair edge, however, the existence of the gapless edge states depends on the specific type of mass gaps.
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arxiv:0806.2136
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Strong magnetization makes the disks surrounding young stellar objects rotate at rates that are too sub-Keplerian to enable the thermal launching of disk winds from their surfaces unless the rate of gas diffusion across field lines is dynamically fast. This under-appreciated implication of disk magnetization poses a considerable challenge for disk-wind theory.
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arxiv:0806.2137
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We propose a super-resolution quantum lithography scheme based on coherent population trapping in lambda-type atoms coupled to temporally-cascaded standing-wave driving fields. By realizing effective multiplication of optical intensity profiles on an atomic state density distribution, the scheme enables an arbitrarily high degree of resolution enhancement without modifying the atomic level structure of the photographic medium or the light source configuration. It is also shown that the visibility of the super-resolution patterns is preserved under a significant atomic state decoherence rate.
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arxiv:0806.2175
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We investigate the Taylor expansion of the baryon number susceptibility, and hence, pressure, in a series in the baryon chemical potential (mu_B) through a lattice simulation with light dynamical staggered quarks at a finer lattice cutoff a=1/6T. We determine the QCD cross over coupling at mu_B=0. We find the radius of convergence of the series at various temeperatures, and bound the location of the QCD critical point to be T^E/T_c = 0.94 and mu_B^E/T < 1.8. We also investigate the extrapolation of various susceptibilities and linkages to finite chemical potential.
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arxiv:0806.2233
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A set of universal relations between various properties of any few-body or many-body system consisting of fermions with two spin states and a large but finite scattering length have been derived by Shina Tan. We derive generalizations of the Tan relations for a two-channel model for fermions near a Feshbach resonance that includes a molecular state whose detuning energy controls the scattering length. We use quantum field theory methods, including renormalization and the operator product expansion, to derive these relations. They reduce to the Tan relations as the scattering length is made increasingly large.
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arxiv:0806.2277
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We constrain the physical nature of dark matter using the newly identified massive merging galaxy cluster MACSJ0025.4-1222. As was previously shown by the example of the Bullet Cluster (1E0657-56), such systems are ideal laboratories for detecting isolated dark matter, and distinguishing between cold dark matter (CDM) and other scenarios (e.g. self-interacting dark matter, alternative gravity theories). MACSJ0025.4-1222 consists of two merging subclusters of similar richness at z=0.586. We measure the distribution of X-ray emitting gas from Chandra X-ray data and find it to be clearly displaced from the distribution of galaxies. A strong (information from highly distorted arcs) and weak (using weakly distorted background galaxies) gravitational lensing analysis based on Hubble Space Telescope observations and Keck arc spectroscopy confirms that the subclusters have near-equal mass. The total mass distribution in each of the subclusters is clearly offset (at >4sigma significance) from the peak of the hot X-ray emitting gas (the main baryonic component), but aligned with the distribution of galaxies. We measure the fractions of mass in hot gas (0.09^{+0.07}_{-0.03}) and stars (0.010^{+0.007}_{-0.004}), consistent with those of typical clusters, finding that dark matter is the dominant contributor to the gravitational field. Under the assumption that the subclusters experienced a head-on collision in the plane of the sky, we obtain an order-of-magnitude estimate of the dark matter self-interaction cross-section of sigma/m < 4cm^2/g, re-affirming the results from the Bullet Cluster on the collisionless nature of dark matter.
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arxiv:0806.2320
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We examine bosons hopping on a one-dimensional lattice in the presence of a random potential at zero temperature. Bogoliubov excitations of the Bose-Einstein condensate formed under such conditions are localized, with the localization length diverging at low frequency as $\ell(\omega)\sim 1/\omega^\alpha$. We show that the well known result $\alpha=2$ applies only for sufficiently weak random potential. As the random potential is increased beyond a certain strength, $\alpha$ starts decreasing. At a critical strength of the potential, when the system of bosons is at the transition from a superfluid to an insulator, $\alpha=1$. This result is relevant for understanding the behavior of the atomic Bose-Einstein condensates in the presence of random potential, and of the disordered Josephson junction arrays.
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arxiv:0806.2322
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We revisit the problem of constructing type IIA orientifolds on T^6/(Z2 x Z2) which admit (non)-factorisable lattices. More concretely, we consider a (Z2 x Z2') orientifold with torsion, where D6-branes wrap rigid 3-cycles. We derive the model building rules and consistency conditions in the case where the compactification lattice is non-factorisable. We show that in this class of configurations, (semi) realistic models with an odd number of families can be easily constructed, in contrast to compactifications where the D6-branes wrap non-rigid cycles. We also show that an odd number of families can be obtained in the factorisable case, without the need of tilted tori. We illustrate the discussion by presenting three family Pati-Salam models with no chiral exotics in both factorisable and non-factorisable toroidal compactifications.
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arxiv:0806.2328
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Randomized sampling has recently been demonstrated to be an efficient technique for computing approximate low-rank factorizations of matrices for which fast methods for computing matrix vector products are available. This paper describes an extension of such techniques to a wider class of matrices that are not themselves rank-deficient, but have off-diagonal blocks that are. Such matrices arise frequently in numerical analysis and signal processing, and there exist several methods for rapidly performing algebraic operations (matrix-vector multiplications, matrix factorizations, matrix inversion, \textit{etc}) on them once low-rank approximations to all off-diagonal blocks have been constructed. The paper demonstrates that if such a matrix can be applied to a vector in O(N) time, where the matrix is of size $N\times N$, and if individual entries of the matrix can be computed rapidly, then in many cases, the task of constructing approximate low-rank factorizations for all off-diagonal blocks can be performed in $O(N k^{2})$ time, where $k$ is an upper bound for the numerical rank of the off-diagonal blocks.
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arxiv:0806.2339
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In this paper, we study a curvaton model described by a Dirac-Born-Infeld-like action. We calculate the spectrum of curvature perturbation induced by DBI-curvaton and estimate its non-Gaussianity. We find that in the limit of low sound speed the amplitude of curvature perturbation is enhanced more than that in DBI inflation. This result also means that the inflationary scale with DBI-curvaton may be lower than that in usual curvaton model. In addition, we also find that the local non-Gaussianity level in DBI-curvaton is generally about 10 times larger than that in usual curvaton model, which is interesting for current observations. This work in some sense explores a new application of brane-cosmology in inflation.
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arxiv:0806.2363
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We report simulations of a two-dimensional, dense, bidisperse system of inelastic hard disks falling down a vertical tube under the influence of gravity. We examine the approach to jamming as the average flow of particles down the tube is slowed by making the outlet narrower. Defining coarse-grained velocity and stress fields, we study two-point temporal and spatial correlation functions of these fields in a region of the tube where the time-averaged velocity is spatially uniform. We find that fluctuations in both velocity and stress become increasingly correlated as the system approaches jamming. We extract a growing length scale and time scale from these correlations.
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arxiv:0806.2413
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