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The solution of energy-balance model of the Earth global climate and the EPICA Dome C and Vostok experimental data of the Earth surface palaeotemperature evolution over past 420 and 740 kyr are compared. In the framework of proposed bifurcation model (i) the possible sharp warmings of the Dansgaard-Oeschger type during the last glacial period due to stochastic resonance is theoretically argued; (ii) the concept of climatic sensitivity of water in the atmosphere, whose temperature instability has the form of so-called hysteresis loop, is proposed, and based of this concept the time series of global ice volume over the past 1000 kyr, which is in good agreement with the time series of delta O-18 concentration in the sea sediments, is obtained; (iii) the so-called "CO2 doubling" problem is discussed
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arxiv:0803.2766
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We demonstrate that there is an intimate relationship between the magnetic properties of Derrida's random energy model (REM) of spin glasses and the problem of joint source--channel coding in Information Theory. In particular, typical patterns of erroneously decoded messages in the coding problem have ``magnetization'' properties that are analogous to those of the REM in certain phases, where the non--uniformity of the distribution of the source in the coding problem, plays the role of an external magnetic field applied to the REM. We also relate the ensemble performance (random coding exponents) of joint source--channel codes to the free energy of the REM in its different phases.
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arxiv:0803.2789
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High resolution (0.15") Very Large Array observations of 7 mm continuum and H53a line emission toward the hypercompact H II region G28.20-0.04N reveal the presence of large-scale ordered motions. We find a velocity gradient of 1000 km/s/pc along the minor axis of the continuum source. Lower resolution (1.0"-2.3") radio recombination line observations indicate a systematic increase of line width from H30alpha to H92alpha. Under the assumption that the H30alpha line does not suffer significant pressure broadening, we have deconvolved the contributions of statistical broadening (thermal, turbulent, and pressure) from large-scale motions. The pressure broadening of the H53alpha, H76alpha, and H92alpha lines implies an electron density of 6.9E+06, 8.5E+05, and 2.8E+05 cm^(-3), respectively.
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arxiv:0803.2872
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An analytical solution of Einstein-Maxwell equations with a static fluid as a source is presented. The spacetime is represented by the axially symmetric Weyl metric and the energy-momentum tensor describes a coupling of a fluid with an electromagnetic field. When appropriate limits are performed we recover the well-known solutions of Gutsunaev-Manko and Schwarzschild. Also, using Eckart's thermodynamics, we calculated the temperature, the mechanical pressure, the charge density and the energy density of the system. The analysis of thermodynamic quantities suggests that the solution can be used to represent a magnetized compact stellar object surrounded by a charged fluid.
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arxiv:0803.2899
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Let $\sum_{\beta\in\nats^d} F_\beta x^\beta$ be a multivariate power series. For example $\sum F_\beta x^\beta$ could be a generating function for a combinatorial class. Assume that in a neighbourhood of the origin this series represents a nonentire function $F=G/H^p$ where $G$ and $H$ are holomorphic and $p$ is a positive integer. Given a direction $\alpha\in\pnats^d$ for which the asymptotics are controlled by a smooth point of the singular variety $H = 0$, we compute the asymptotics of $F_{n \alpha}$ as $n\to\infty$. We do this via multivariate singularity analysis and give an explicit formula for the full asymptotic expansion. This improves on earlier work of R. Pemantle and the second author and allows for more accurate numerical approximation, as demonstrated by our examples.
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arxiv:0803.2914
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We investigated electronic structure of 5d transition-metal oxide Sr2IrO4 using angle-resolved photoemission, optical conductivity, and x-ray absorption measurements and first-principles band calculations. The system was found to be well described by novel effective total angular momentum Jeff states, in which relativistic spin-orbit (SO) coupling is fully taken into account under a large crystal field. Despite of delocalized Ir 5d states, the Jeff-states form so narrow bands that even a small correlation energy leads to the Jeff = 1/2 Mott ground state with unique electronic and magnetic behaviors, suggesting a new class of the Jeff quantum spin driven correlated-electron phenomena.
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arxiv:0803.2927
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In many applications of multiple hypothesis testing where more than one false rejection can be tolerated, procedures controlling error rates measuring at least $k$ false rejections, instead of at least one, for some fixed $k\ge 1$ can potentially increase the ability of a procedure to detect false null hypotheses. The $k$-FWER, a generalized version of the usual familywise error rate (FWER), is such an error rate that has recently been introduced in the literature and procedures controlling it have been proposed. A further generalization of a result on the $k$-FWER is provided in this article. In addition, an alternative and less conservative notion of error rate, the $k$-FDR, is introduced in the same spirit as the $k$-FWER by generalizing the usual false discovery rate (FDR). A $k$-FWER procedure is constructed given any set of increasing constants by utilizing the $k$th order joint null distributions of the $p$-values without assuming any specific form of dependence among all the $p$-values. Procedures controlling the $k$-FDR are also developed by using the $k$th order joint null distributions of the $p$-values, first assuming that the sets of null and nonnull $p$-values are mutually independent or they are jointly positively dependent in the sense of being multivariate totally positive of order two (MTP$_2$) and then discarding that assumption about the overall dependence among the $p$-values.
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arxiv:0803.2934
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Baryon resonance state with strangeness $S = +1$ observed in systems $p K^0$ and $n K^+$ is interpreted as a result of the decay $N^{*+} \to p \eta$ of the well-known resonance $N^*(1535)$ (with spin-parity $j^P = {1/2}^-$ and mass $m \approx 1.54$ GeV) and the subsequent oscillation $\eta \rightleftarrows K^0$. It is argued that the latter is noticeably enhanced by the neighbourhood of the $\eta$ and $K^0$ levels and the gluon exchanges of the "penguin" form.
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arxiv:0803.2936
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We establish a general criterion for the validity of inequalities of the following form: A certain convex combination of the values of a convex function at n points and of its value at a weighted mean of these n points is always greater or equal to a convex combination of the values of the function at some other weighted means of these points. Here, the left hand side contains only one weighted mean, while the right hand side may contain as many as possible, as long as there are finitely many. The weighted mean on the left hand side must have positive weights, while those on the right hand side must have nonnegative weights. The most prominent example of such kind of inequalities, Popoviciu's inequality in its most general form, follows from the general criterion. As another application, a result by Vasile Cirtoaje is sharpened.
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arxiv:0803.2958
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In the discussed model, the cold dark matter consists of Dirac spin-1/2 fermions, sterile from all Standard Model charges, where masses are generated by a nonzero vacuum expectation value of a field of scalar bosons, also assumed to be sterile. For convenience, these sterile particles have beeen called sterinos and sterons, respectively. It has been conjectured that our sterile world of sterinos and sterons can communicate with the familiar Standard Model world not only through gravity, but also through a photonic portal provided by a very weak effective interaction involving the electromagnetic field F_{\mu \nu} = \partial_\mu A_\nu - \partial_\nu A_\mu coupled to the sterino and steron fields.
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arxiv:0803.2977
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We propose a three dimensional generalization of the geometric McKay correspondence described by Gonzales-Sprinberg and Verdier in dimension two. We work it out in detail when G is abelian and C^3/G has a single isolated singularity. More precisely, we show that the Bridgeland-King-Reid derived category equivalence induces a natural geometric correspondence between irreducible representations of G and subschemes of the exceptional set of G-Hilb (C^3). This correspondence appears to be related to Reid's recipe.
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arxiv:0803.2990
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There is no doubt that management practices are linked to the productivity and performance of a company. However, research findings are mixed. This paper provides a multi-disciplinary review of the current evidence of such a relationship and offers suggestions for further exploration. We provide an extensive review of the literature in terms of research findings from studies that have been trying to measure and understand the impact that individual management practices and clusters of management practices have on productivity at different levels of analysis. We focus our review on Operations Management (om) and Human Resource Management (hrm) practices as well as joint applications of these practices. In conclusion, we can say that taken as a whole, the research findings are equivocal. Some studies have found a positive relationship between the adoption of management practices and productivity, some negative and some no association whatsoever. We believe that the lack of universal consensus on the effect of the adoption of complementary management practices might be driven either by measurement issues or by the level of analysis. Consequently, there is a need for further research. In particular, for a multi-level approach from the lowest possible level of aggregation up to the firm-level of analysis in order to assess the impact of management practices upon the productivity of firms.
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arxiv:0803.2995
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The magneto-optical absorption properties of graphene multilayers are theoretically studied. It is shown that the spectrum can be decomposed into sub-components effectively identical to the monolayer or bilayer graphene, allowing us to understand the spectrum systematically as a function of the layer number. Odd-layered graphenes always exhibit absorption peaks which shifts in proportion to sqrt(B), with B being the magnetic field, due to the existence of an effective monolayer-like subband. We propose a possibility of observing the monolayer-like spectrum even in a mixture of multilayer graphene films with various layers numbers.
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arxiv:0803.3023
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We observe the dynamics of waves propagating on the surface of a ferrofluid under the influence of a spatially and temporarily modulated field. In particular, we excite plane waves by a travelling lamellar modulation of the magnetization. By this external driving both the wavelength and the propagation velocity of the waves can be controlled. The amplitude of the excited waves exhibits a resonance phenomenon similar to that of a forced harmonic oscillator. Its analysis reveals the dispersion relation of the free surface waves, from which the critical magnetic field for the onset of the Rosensweig instability can be extrapolated.
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arxiv:0803.3038
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We study orbital excitations in the optical absorption spectra of YVO3 and HoVO3. We focus on an orbital absorption band observed at 0.4 eV for polarization E parallel c. This feature is only observed in the intermediate, monoclinic phase. By comparison with the local crystal-field excitations in VOCl and with recent theoretical predictions for the crystal-field levels we show that this absorption band cannot be interpreted in terms of a local crystal-field excitation. We discuss a microscopic model which attributes this absorption band to the exchange of two orbitals on adjacent sites, i.e., to the direct excitation of two orbitons. This model is strongly supported by the observed dependence on polarization and temperature. Moreover, the calculated spectral weight is in good agreement with the experimental result.
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arxiv:0803.3046
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We compare three notions of effectiveness on uncountable structures. The first notion is that of a $\real$-computable structure, based on a model of computation proposed by Blum, Shub, and Smale, which uses full-precision real arithmetic. The second notion is that of an $F$-parameterizable structure, defined by Morozov and based on Mal'tsev's notion of a constructive structure. The third is $\Sigma$-definability over $HF(\real)$, defined by Ershov as a generalization of the observation that the computably enumerable sets are exactly those $\Sigma_1$-definable in $HF(\mathbb{N})$. We show that every $\real$-computable structure has an $F$-parameterization, but that the expansion of the real field by the exponential function is $F$-parameterizable but not $\real$-computable. We also show that the structures with $\real$-computable copies are exactly the structures with copies $\Sigma$-definable over $HF(\real)$. One consequence of this equivalence is a method of approximating certain $\real$-computable structures by Turing computable structures.
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arxiv:0803.3073
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Upon commissioning on Gemini South, FLAMINGOS-2 will be one of the most powerful wide-field near-infrared imagers and multi-object spectrographs ever built for use on 8-meter-class telescopes. In order to take best advantage of the strengths of FLAMINGOS-2 early in its life cycle, the instrument team has proposed to use 21 nights of Gemini guaranteed time in 3 surveys -- the FLAMINGOS-2 Early Science Surveys (F2ESS). The F2ESS will encompass 3 corresponding science themes -- the Galactic Center, galaxy evolution, and star formation. In this paper, I review the design performance and status of FLAMINGOS-2, and describe the planned FLAMINGOS-2 Galactic Center Survey.
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arxiv:0803.3084
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Discussion of ``The Dantzig selector: Statistical estimation when $p$ is much larger than $n$'' [math/0506081]
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arxiv:0803.3135
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We establish a relation between several entanglement properties in the Lipkin-Meshkov-Glick model, which is a system of mutually interacting spins embedded in a magnetic field. We provide analytical proofs that the single-copy entanglement and the global geometric entanglement of the ground state close to and at criticality behave as the entanglement entropy. These results are in deep contrast to what is found in one- dimensional spin systems where these three entanglement measures behave differently.
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arxiv:0803.3151
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A complex algebraic variety defined over the reals is maximal when the sum of its Betti numbers for Borel Moore homology with $\zz$ coefficients coincides with the sum of the Betti numbers of its real part. We will show in this paper that toric varieties of dimension 4 are maximal.
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arxiv:0803.3196
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We report on the spectroscopic transit of the massive hot-Jupiter CoRoT-Exo-2b observed with the high-precision spectrographs SOPHIE and HARPS. By modeling the radial velocity anomaly occurring during the transit due to the Rossiter-McLaughlin (RM) effect, we determine the sky-projected angle between the stellar spin and the planetary orbital axis to be close to zero lambda=7.2+-4.5 deg, and we secure the planetary nature of CoRoT-Exo-2b. We discuss the influence of the stellar activity on the RM modeling. Spectral analysis of the parent star from HARPS spectra are presented.
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arxiv:0803.3209
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In unparticle dark matter (unmatter) models the equation of state of the unmatter is given by $p=\rho/(2d_U+1)$, where $d_U$ is the scaling factor. Unmatter with such equations of state would have a significant impact on the expansion history of the universe. Using type Ia supernovae (SNIa), the baryon acoustic oscillation (BAO) measurements and the shift parameter of the cosmic microwave background (CMB) to place constraints on such unmatter models we find that if only the SNIa data is used the constraints are weak. However, with the BAO and CMB shift parameter data added strong constraints can be obtained. For the $\Lambda$UDM model, in which unmatter is the sole dark matter, we find that $d_U > 60$ at 95% C.L. For comparison, in most unparticle physics models it is assumed $d_U<2$. For the $\Lambda$CUDM model, in which unmatter co-exists with cold dark matter, we found that the unmatter can at most make up a few percent of the total cosmic density if $d_U<10$, thus it can not be the major component of dark matter.
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arxiv:0803.3223
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We consider quantum-memory assisted protocols for discriminating quantum channels. We show that for optimal discrimination of memory channels, memory assisted protocols are needed. This leads to a new notion of distance for channels with memory. For optimal discrimination and estimation of sets of unitary channels memory-assisted protocols are not required.
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arxiv:0803.3237
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Motivated by the relationship of classical modular functions and Picard--Fuchs linear differential equations of order 2 and 3, we present an analogous concept for equations of order 4 and 5.
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arxiv:0803.3322
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We consider the general model of zero-sum repeated games (or stochastic games with signals), and assume that one of the players is fully informed and controls the transitions of the state variable. We prove the existence of the uniform value, generalizing several results of the literature. A preliminary existence result is obtained for a certain class of stochastic games played with pure strategies.
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arxiv:0803.3345
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Let $R$ be an associative ring with identity, $C(R)$ denote the center of $R$, and $g(x)$ be a polynomial in the polynomial ring $C(R)[x]$. $R$ is called strongly $g(x)$-clean if every element $r \in R$ can be written as $r=s+u$ with $g(s)=0$, $u$ a unit of $R$, and $su=us$. The relation between strongly $g(x)$-clean rings and strongly clean rings is determined, some general properties of strongly $g(x)$-clean rings are given, and strongly $g(x)$-clean rings generated by units are discussed.
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arxiv:0803.3353
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We consider a class of nonlinear Schroedinger equation in three space dimensions with an attractive potential. The nonlinearity is local but rather general encompassing for the first time both subcritical and supercritical (in $L^2$) nonlinearities. We study the asymptotic stability of the nonlinear bound states, i.e. periodic in time localized in space solutions. Our result shows that all solutions with small initial data, converge to a nonlinear bound state. Therefore, the nonlinear bound states are asymptotically stable. The proof hinges on dispersive estimates that we obtain for the time dependent, Hamiltonian, linearized dynamics around a careful chosen one parameter family of bound states that "shadows" the nonlinear evolution of the system. Due to the generality of the methods we develop we expect them to extend to the case of perturbations of large bound states and to other nonlinear dispersive wave type equations.
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arxiv:0803.3377
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Archival Spitzer observations of 41 starburst galaxies that span a wide range in metallicity reveal for the first time a correlation between the [FeII]/[NeII] 26.0/12.8 micron ratio and the electron gas density as traced by the 18.7/33.4 micron [SIII] ratio, with the [FeII]/[NeII] ratio decreasing with increasing gas density. We also find a strong correlation between the gas density and the PAH peak to continuum strength. Using shock and photoionization models, we see the driver of the observed [FeII]/[NeII] ratios is metallicity. The majority of [FeII] emission in low metallicity galaxies may be shock-derived, whilst at high metallicity, the [FeII] emission may be instead dominated by contributions from HII and in particular from dense PDR regions. However, the observed [FeII]/[NeII] ratios may instead be following a metallicity-abundance relationship, with iron being less depleted onto grains in low metallicity galaxies - a result that would have profound implications for the use of iron emission lines as unambiguous tracers of shocks.
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arxiv:0803.3403
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We define the hitting (or absorbing) time for the case of continuous quantum walks by measuring the walk at random times, according to a Poisson process with measurement rate $\lambda$. From this definition we derive an explicit formula for the hitting time, and explore its dependence on the measurement rate. As the measurement rate goes to either 0 or infinity the hitting time diverges; the first divergence reflects the weakness of the measurement, while the second limit results from the Quantum Zeno effect. Continuous-time quantum walks, like discrete-time quantum walks but unlike classical random walks, can have infinite hitting times. We present several conditions for existence of infinite hitting times, and discuss the connection between infinite hitting times and graph symmetry.
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arxiv:0803.3446
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Several research groups are giving special attention to quantum walks recently, because this research area have been used with success in the development of new efficient quantum algorithms. A general simulator of quantum walks is very important for the development of this area, since it allows the researchers to focus on the mathematical and physical aspects of the research instead of deviating the efforts to the implementation of specific numerical simulations. In this paper we present QWalk, a quantum walk simulator for one- and two-dimensional lattices. Finite two-dimensional lattices with generic topologies can be used. Decoherence can be simulated by performing measurements or by breaking links of the lattice. We use examples to explain the usage of the software and to show some recent results of the literature that are easily reproduced by the simulator.
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arxiv:0803.3459
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In this article we consider the anisotropic Calderon problem and related inverse problems. The approach is based on limiting Carleman weights, introduced in Kenig-Sjoestrand-Uhlmann (Ann. of Math. 2007) in the Euclidean case. We characterize those Riemannian manifolds which admit limiting Carleman weights, and give a complex geometrical optics construction for a class of such manifolds. This is used to prove uniqueness results for anisotropic inverse problems, via the attenuated geodesic X-ray transform. Earlier results in dimension $n \geq 3$ were restricted to real-analytic metrics.
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arxiv:0803.3508
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A parametrization of the Bose-Einstein correlation function of pairs of identical pions produced in hadronic e+e- annihilation is proposed within the framework of a model (the tau-model) in which space-time and momentum space are very strongly correlated. Using information from the Bose-Einstein correlations as well as from single-pion spectra,it is then possible to reconstruct the space-time evolution of pion production.
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arxiv:0803.3528
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We study the holographic map between long open strings, which stretch between D-branes separated in the bulk space-time, and operators in the dual boundary theory. We focus on a generalization of the Sakai-Sugimoto holographic model of QCD, where the simplest chiral condensate involves an operator of this type. Its expectation value is dominated by a semi-classical string worldsheet, as for Wilson loops. We also discuss the deformation of the model by this operator, and in particular its effect on the meson spectrum. This deformation can be thought of as a generalization of a quark mass term to strong coupling. It leads to the first top-down holographic model of QCD with a non-Abelian chiral symmetry which is both spontaneously and explicitly broken, as in QCD. Other examples we study include half-supersymmetric open Wilson lines, and systems of D-branes ending on NS5-branes, which can be analyzed using worldsheet methods.
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arxiv:0803.3547
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We analyze an interacting particle system with a Markov evolution of birth-and-death type. We have shown that a local competition mechanism (realized via a density dependent mortality) leads to a globally regular behavior of the population in course of the stochastic evolution.
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arxiv:0803.3565
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We use a tight-binding Bogoliubov-de Gennes (BdG) formalism to self-consistently calculate the proximity effect, Josephson current, and local density of states in ballistic graphene SNS Josephson junctions. Both short and long junctions, with respect to the superconducting coherence length, are considered, as well as different doping levels of the graphene. We show that self-consistency does not notably change the current-phase relationship derived earlier for short junctions using the non-selfconsistent Dirac-BdG formalism but predict a significantly increased critical current with a stronger junction length dependence. In addition, we show that in junctions with no Fermi level mismatch between the N and S regions superconductivity persists even in the longest junctions we can investigate, indicating a diverging Ginzburg-Landau superconducting coherence length in the normal region.
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arxiv:0803.3574
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We decribe the correspondence between normalised $\omega$-operads and certain lax monoidal structures on the category of globular sets. As with ordinary monoidal categories, one has a notion of category enriched in a lax monoidal category. Within the aforementioned correspondence, we provide also an equivalence between the algebras of a given normalised $\omega$-operad, and categories enriched in globular sets for the induced lax monoidal structure.
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arxiv:0803.3594
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Massive stars undergo a violent death when the supply of nuclear fuel in their cores is exhausted, resulting in a catastrophic "core-collapse" supernova. Such events are usually only detected at least a few days after the star has exploded. Observations of the supernova SNLS-04D2dc with the Galaxy Evolution Explorer space telescope reveal a radiative precursor from the supernova shock before the shock reached the surface of the star and show the initial expansion of the star at the beginning of the explosion. Theoretical models of the ultraviolet light curve confirm that the progenitor was a red supergiant, as expected for this type of supernova. These observations provide a way to probe the physics of core-collapse supernovae and the internal structures of their progenitor stars
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arxiv:0803.3596
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We present a numerical study of Gamma-Ray Burst - Circumburst Medium interaction and plasma preconditioning via Compton scattering. The simulation tool employed is a unique hybrid model; it combines a highly parallelized (Vlasov) particle-in-cell approach with continuous weighting of particles and a sub-Debye Monte-Carlo binary particle interaction framework. These first results from 3D simulations with this new simulation tool, the PhotonPlasma code, suggests that magnetic fields and plasma density filaments are created in the wakefield of prompt gamma-ray bursts, and that the photon flux density gradient has a significant impact on particle acceleration in the burst head and wakefield. We discuss some possible implications of the circumburst medium preconditioning for the trailing afterglow, and also discuss which additional processes will be needed to improve future studies within this unique and powerful simulation framework.
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arxiv:0803.3618
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In this paper we extend current perspectives in engineering reservoirs by producing a time-dependent master equation leading to a nonstationary superposition equilibrium state that can be nonadiabatically controlled by the system-reservoir parameters. Working with an ion trapped inside a nonindeal cavity we first engineer effective Hamiltonians that couple the electronic states of the ion with the cavity mode. Subsequently, two classes of decoherence-free evolution of the superposition of the ground and decaying excited levels are achieved: those with time-dependent azimuthal or polar angle. As an application, we generalise the purpose of an earlier study [Phys. Rev. Lett. 96, 150403 (2006)], showing how to observe the geometric phases acquired by the protected nonstationary states even under a nonadiabatic evolution.
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arxiv:0803.3709
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Comment on ``Tests of scaling and universality of the distributions of trade size and share volume: Evidence from three distinct markets" by Plerou and Stanley, Phys. Rev. E 76, 046109 (2007)
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arxiv:0803.3733
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In quantum field theory (QFT), the vacuum expectation value of a normal product of creation and annihilation operators is always zero. This simple property paves the way to the classical treatment of perturbative QFT. This is no longer the case in the presence of initial correlations, that is if the vacuum is replaced by a general state. As a consequence, the combinatorics of correlated systems such as the ones occurring in many-body physics is more complex than that of quantum field theory and the general theory has made very slow progress. Similar observations hold in statistical physics or quantum probability for the perturbation series arising from the study of non Gaussian measures. In this work, an analysis of the Hopf algebraic aspects of quantum field theory is used to derive the structure of Green functions in terms of connected and one-particle irreducible Greeen functions for perturbative QFT in the presence of initial correlations.
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arxiv:0803.3747
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We present first results of Hertz/VPM, the first submillimeter polarimeter employing the dual Variable-delay Polarization Modulator (dual-VPM). This device differs from previously used polarization modulators in that it operates in translation rather than mechanical rotation. We discuss the basic theory behind this device, and its potential advantages over the commonly used half wave plate (HWP). The dual-VPM was tested both at the Submillimeter Telescope Observatory (SMTO) and in the lab. In each case we present a detailed description of the setup. We discovered nonideal behavior in the system. This is at least in part due to properties of the VPM wire grids (diameter, spacing) employed in our experiment. Despite this, we found that the dual-VPM system is robust, operating with high efficiency and low instrumental polarization. This device is well suited for air and space-borne applications.
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arxiv:0803.3759
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Applying squashing transformation to Kerr-Godel black hole solutions, we present a new type of a rotating Kaluza-Klein black hole solution to the five-dimensional Einstein-Maxwell theory with a Chern-Simon term. The new solutions generated via the squashing transformation have no closed timelike curve everywhere outside the black hole horizons. At the infinity, the metric asymptotically approaches a twisted S^1 bundle over a four-dimensional Minkowski space-time. One of the remarkable features is that the solution has two independent rotation parameters along an extra dimension associated with the black hole's rotation and the Godel's rotation. The space-time also admits the existence of two disconnected ergoregions, an inner ergoregion and an outer ergoregion. These two ergoregions can rotate in the opposite direction as well as in the same direction.
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arxiv:0803.3873
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In 2004 the Dutch Department of Social Affairs conducted a survey to assess the extent of noncompliance with social security regulations. The survey was conducted among 870 recipients of social security benefits and included a series of sensitive questions about regulatory noncompliance. Due to the sensitive nature of the questions the randomized response design was used. Although randomized response protects the privacy of the respondent, it is unlikely that all respondents followed the design. In this paper we introduce a model that allows for respondents displaying self-protective response behavior by consistently giving the nonincriminating response, irrespective of the outcome of the randomizing device. The dependent variable denoting the total number of incriminating responses is assumed to be generated by the application of randomized response to a latent Poisson variable denoting the true number of rule violations. Since self-protective responses result in an excess of observed zeros in relation to the Poisson randomized response distribution, these are modeled as observed zero-inflation. The model includes predictors of the Poisson parameters, as well as predictors of the probability of self-protective response behavior.
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arxiv:0803.3891
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Multi-sample microarray experiments have become a standard experimental method for studying biological systems. A frequent goal in such studies is to unravel the regulatory relationships between genes. During the last few years, regression models have been proposed for the de novo discovery of cis-acting regulatory sequences using gene expression data. However, when applied to multi-sample experiments, existing regression based methods model each individual sample separately. To better capture the dynamic relationships in multi-sample microarray experiments, we propose a flexible method for the joint modeling of promoter sequence and multivariate expression data. In higher order eukaryotic genomes expression regulation usually involves combinatorial interaction between several transcription factors. Experiments have shown that spacing between transcription factor binding sites can significantly affect their strength in activating gene expression. We propose an adaptive model building procedure to capture such spacing dependent cis-acting regulatory modules. We apply our methods to the analysis of microarray time-course experiments in yeast and in Arabidopsis. These experiments exhibit very different dynamic temporal relationships. For both data sets, we have found all of the well-known cis-acting regulatory elements in the related context, as well as being able to predict novel elements.
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arxiv:0803.3904
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When designing systems that are complex, dynamic and stochastic in nature, simulation is generally recognised as one of the best design support technologies, and a valuable aid in the strategic and tactical decision making process. A simulation model consists of a set of rules that define how a system changes over time, given its current state. Unlike analytical models, a simulation model is not solved but is run and the changes of system states can be observed at any point in time. This provides an insight into system dynamics rather than just predicting the output of a system based on specific inputs. Simulation is not a decision making tool but a decision support tool, allowing better informed decisions to be made. Due to the complexity of the real world, a simulation model can only be an approximation of the target system. The essence of the art of simulation modelling is abstraction and simplification. Only those characteristics that are important for the study and analysis of the target system should be included in the simulation model.
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arxiv:0803.3905
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We applied our recently proposed empirical formula, a formula quite successful in describing essential trends of the lowest excitation energies of the natural parity even multipole states, to the lowest excitation energies of the natural parity odd multipole states in even-even nuclei throughout the entire periodic table. Even though the systematic behavior of the lowest excitation energies of odd multipole states is quite different from those of even multipole states, we have shown that the same empirical formula also holds reasonably well for the odd multipole states with the exception of a few certain instances.
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arxiv:0803.3927
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A boundary layer turbulence index (TIBL) product has been developed to assess the potential for turbulence in the lower troposphere, generated using RUC-2 numerical model data. The index algorithm approximates boundary layer turbulent kinetic energy by parameterizing vertical wind shear, responsible for mechanical production of TKE, and kinematic heat flux, parameterized by the vertical temperature lapse rate and responsible for buoyant production of TKE. Validation for the TIBL product has been conducted for selected nonconvective wind events during the 2008 winter season over the Idaho National Laboratory mesonet domain. This paper presents studies of four significant wind events between December 2007 and February 2008 over southeastern Idaho. Based on the favorable results highlighted from validation statistics and in the case studies, the RUC TIBL product has demonstrated operational utility in assessing turbulence hazards to low-flying aircraft and ground transportation, and in the assessment of wildfire threat.
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arxiv:0803.3945
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We prove that for given integers b and c, the diophantine equation x^2+bx+c=y^2, has finitely many integer solutions(i.e. pairs in ZxZ),in fact an even number of such solutions(including the zero or no solutions case).We also offer an explicit description of the solution set. Such a description depends on the form of the integer b^2-4c. Some Corollaries do follow. Furthermore, we show that the said equation has exactly two integer solutions, precisely when b^2-4c= 1,4,16,-4,or-16. In each case we list the two solutions in terms of the coefficients b and c.
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arxiv:0803.3956
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We prove a sharp stability estimate for the problem of reconstructing a symmetric 2-tensor from its integrals along all maximal geodesics on a simple manifold.
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arxiv:0803.3958
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Using a compilation of measurements of the stellar mass density as a function of redshift we can infer the cosmic star formation history. For z < 0.7 there is good agreement between the two star formation histories. At higher redshifts the instantaneous indicators suggest star formation rates larger than that implied by the evolution of the stellar mass density. This discrepancy peaks at z = 3 where instantaneous indicators suggest a star formation rate around 0.6 dex higher than those of the best fit to the stellar mass history. We discuss a variety of explanations for this inconsistency, such as inaccurate dust extinction corrections, incorrect measurements of stellar masses and a possible evolution of the stellar initial mass function.
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arxiv:0803.4024
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We study the size effect on the energy levels of the D-dimensional isotropic harmonic oscillator confined within a box of radius $r_c$ with impenetrable walls. Two different approaches are used to obtain the energy eigenvalues and eigenfunctions for D=1,2,...,5. In the first we solve the Schroedinger equation exactly. In the second we use a series expansion of the wave function. The numerical results obtained are extremely accurate; these values are reported with 50 decimal places.
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arxiv:0803.4029
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We present an analysis of the stellar populations in a sample of ~7000 galaxies from the 6dF Galaxy Survey (6dFGS). We derive ages and metallicities using stellar population models. We also derive dynamical masses and dynamical mass-to-light ratios by combining central velocity dispersions with global photometry in B, R and K bands. Together, these data allow to reduce the degeneracies between age, metallicity and star formation burst-strength that have limited previous studies. We find old galaxies exhibit a mass-metallicity relation with slope d[Fe/H]/dlogM = 0.25, while young galaxies show slopes consistent with zero. When we account for the effects of the mass-metallicity relation, we obtain a single, consistent relation between mass-to-light ratio and mass for old galaxies in all passbands. As we have accounted for stellar population effects, this relation must have a dynamical origin. However, we demonstrate that any simple trend between mass-to-light-ratio and mass or luminosity is inconsistent with the observations, and that a more complex relationship must exist. We find the central regions of galaxies often exhibit young stellar populations. However it is only in the lowest-mass galaxies (~10^{10} M$_{\odot}$) that these populations are evident in the global photometry. In higher-mass galaxies, young central populations have decreasing influence on the global photometry, with there being no discernible impact in galaxies more massive than ~2x10^{11} M$_{\odot}$. We conclude that the young stellar populations detected in spectroscopic studies are generally centrally concentrated, and that there is an upper limit on the mass of star-forming events in massive galaxies. These results have ramifications for mass-to-light ratios estimated from photometric observations.
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arxiv:0803.4032
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We consider the Ising model on a cylindrical lattice of L columns, with fixed-spin boundary conditions on the top and bottom rows. The spontaneous magnetization can be written in terms of partition functions on this lattice. We show how we can use the Clifford algebra of Kaufman to write these partition functions in terms of L by L determinants, and then further reduce them to m by m determinants, where m is approximately L/2. In this form the results can be compared with those of the Ising case of the superintegrable chiral Potts model. They point to a way of calculating the spontaneous magnetization of that more general model algebraically.
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arxiv:0803.4036
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Recent advances of information technology in biomedical sciences and other applied areas have created numerous large diverse data sets with a high dimensional feature space, which provide us a tremendous amount of information and new opportunities for improving the quality of human life. Meanwhile, great challenges are also created driven by the continuous arrival of new data that requires researchers to convert these raw data into scientific knowledge in order to benefit from it. Association studies of complex diseases using SNP data have become more and more popular in biomedical research in recent years. In this paper, we present a review of recent statistical advances and challenges for analyzing correlated high dimensional SNP data in genomic association studies for complex diseases. The review includes both general feature reduction approaches for high dimensional correlated data and more specific approaches for SNPs data, which include unsupervised haplotype mapping, tag SNP selection, and supervised SNPs selection using statistical testing/scoring, statistical modeling and machine learning methods with an emphasis on how to identify interacting loci.
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arxiv:0803.4065
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The electromagnetic mean squared radii, <r^2>_E and <r^2>_M, of Lambda(1405) are calculated in the chiral unitary model. We describe the excited baryons as dynamically generated resonances in the octet meson and octet baryon scattering. We evaluate values of <r^2>_E and <r^2>_M for the Lambda(1405) on the resonance pole and obtain their complex values. We also consider Lambda(1405) obtained by neglecting decay channels. For the latter case, we obtain negative and larger absolute electric mean squared radius than that of typical ground state baryons. This implies that Lambda(1405) has structure that K^- is widely spread around p.
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arxiv:0803.4068
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Models where the accelerated expansion of our Universe is caused by a quintessence scalar field are reviewed. In the framework of high energy physics, the physical nature of this field is discussed and its interaction with ordinary matter is studied and explicitly calculated. It is shown that this coupling is generically too strong to be compatible with local tests of gravity. A possible way out, the chameleon effect, is also briefly investigated.
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arxiv:0803.4076
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We describe the results and the current status of our program to search for intracluster planetary nebulae (ICPNe) in the Virgo and the Coma clusters of galaxies. For the Virgo cluster, ICPNe candidates were detected with narrow band imaging combined with broad band imaging. The use of two narrow band filters for H$\alpha$ and [O III] lines tuned for the cluster redshift enabled us to detect secure ICPNe candidates. Kinematics of the detected ICPNe confirm that the Virgo cluster is in a highly unrelaxed state. In order to detect ICPNe in the Coma cluster, which is more than five times more distant than the Virgo cluster, we devised a multi-slit imaging spectroscopy technique and successfully detected 35 secure ICPNe candidates for the first time in this cluster. We have found a hint that the Coma cluster is currently in the midst of a subcluster merger.
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arxiv:0803.4077
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We consider dipole oscillations of a trapped dilute Bose-Einstein condensate in the presence of a scattering potential consisting either in a localized defect or in an extended disordered potential. In both cases the breaking of superfluidity and the damping of the oscillations are shown to be related to the appearance of a nonlinear dissipative flow. At supersonic velocities the flow becomes asymptotically dissipationless.
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arxiv:0803.4116
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We give the complete proof of a conjecture of Georges Gras which claims that, for any extension $K/k$ of number fields in which at least one infinite place is totally split, every ideal $I$ of $K$ principalizes in the compositum $Kk^{ab}$ of $K$ with the maximal abelian extension $k^{ab}$ of $k$
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arxiv:0803.4147
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We consider an arbitrary linear elliptic first--order differential operator A with smooth coefficients acting between sections of complex vector bundles E,F over a compact smooth manifold M with smooth boundary N. We describe the analytic and topological properties of A in a collar neighborhood U of N and analyze various ways of writing A|U in product form. We discuss the sectorial projections of the corresponding tangential operator, construct various invertible doubles of A by suitable local boundary conditions, obtain Poisson type operators with different mapping properties, and provide a canonical construction of the Calderon projection. We apply our construction to generalize the Cobordism Theorem and to determine sufficient conditions for continuous variation of the Calderon projection and of well--posed selfadjoint Fredholm extensions under continuous variation of the data.
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arxiv:0803.4160
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The periodic eclipses of the pre-main-sequence binary, KH 15D, have been explained by a circumbinary dust ring inclined to the orbital plane, which causes occultations of the stars as they pass behind the ring edge. We compute the extinction and forward scattering of light by the edge of the dust ring to explain (1) the gradual slope directly preceding total eclipse, (2) the gradual decline at the end of ingress, and (3) the slight rise in flux at mid-eclipse. The size of the forward scattering halo indicates that the dust grains have a radius of a ~ 6 (D/3 AU) microns, where D is the distance of the edge of the ring from the system barycenter. This dust size estimate agrees well with estimates of the dust grain size from polarimetry, adding to the evidence that the ring lies at several AU. Finally, the ratio of the fluxes inside and outside eclipse independently indicates that the ring lies at a few astronomical units.
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arxiv:0803.4275
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Let S be a connected orientable surface with finitely many punctures, finitely many boundary components, and genus at least 6. Then any C^1 action of the mapping class group of S on the circle is trivial. The techniques used in the proof of this result permit us to show that products of Kazhdan groups and certain lattices cannot have C^1 faithful actions on the circle. We also prove that for n > 5, any C^1 action of Aut(F_n) or Out(F_n) on the circle factors through an action of Z/2Z.
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arxiv:0803.4281
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It is proposed four dimensional curved space-time with de-Sitter group of motion. Theory contain free dimension constants of length, impulse and action. Under infinite values of these parameters theory pass to usual Minkowski space-time with Poincare group of motion. In modified space gauge invariant field theory is constructed.
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arxiv:0803.4289
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Energy-efficient real-time task scheduling has been actively explored in the past decade. Different from the past work, this paper considers schedulability conditions for stochastic real-time tasks. A schedulability condition is first presented for frame-based stochastic real-time tasks, and several algorithms are also examined to check the schedulability of a given strategy. An approach is then proposed based on the schedulability condition to adapt a continuous-speed-based method to a discrete-speed system. The approach is able to stay as close as possible to the continuous-speed-based method, but still guaranteeing the schedulability. It is shown by simulations that the energy saving can be more than 20% for some system configurations
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arxiv:0803.4308
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The electronic structure of the new superconductor, SmO$_{1-x}$F$_x$FeAs ($x=0.15$), has been studied by angle-integrated photoemission spectroscopy. Our data show a sharp feature very close to the Fermi energy, and a relative flat distribution of the density of states between 0.5 eV and 3 eV binding energy, which agrees best with band structure calculations considering an antiferromagnetic ground state. No noticeable gap opening was observed at 12 Kelvin below the superconducting transition temperature, indicating the existence of large ungapped regions in the Brillouin zone.
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arxiv:0803.4328
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The transversal and longitudinal resistance in the quantum Hall effect regime was measured in a Si MOSFET sample in which a slot-gate allows one to vary the electron density and filling factor in different parts of the sample. In case of unequal gate voltages, the longitudinal resistances on the opposite sides of the sample differ from each other because the originated Hall voltage difference is added to the longitudinal voltage only on one side depending on the gradient of the gate voltages and the direction of the external magnetic field. After subtracting the Hall voltage difference, the increase in longitudinal resistance is observed when electrons on the opposite sides of the slot occupy Landau levels with different spin orientations.
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arxiv:0803.4432
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The NA48/2 experiment at the CERN SPS carried out data taking in 2003 and 2004. Analysis of the selected data samples of 7,146 $K^\pm\to\pi^\pm e^+e^-$ decay candidates with 0.6% background, 1,164 $K^\pm\to\pi^\pm\gamma\gamma$ candidates with 3.3% background, and 120 $K^\pm\to\pi^\pm\gamma e^+e^-$ candidates with 6.1% background allowed precise measurements of branching fractions and other characteristics of these rare kaon decays.
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arxiv:0803.4475
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We present a dynamical spectral model for Large Eddy Simulation of the incompressible magnetohydrodynamic (MHD) equations based on the Eddy Damped Quasi Normal Markovian approximation. This model extends classical spectral Large Eddy Simulations for the Navier-Stokes equations to incorporate general (non Kolmogorovian) spectra as well as eddy noise. We derive the model for MHD and show that introducing a new eddy-damping time for the dynamics of spectral tensors in the absence of equipartition between the velocity and magnetic fields leads to better agreement with direct numerical simulations, an important point for dynamo computations.
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arxiv:0803.4499
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A binary 1-error-correcting code can always be embedded in a 1-perfect code of some larger length
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arxiv:0804.0006
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We propose a new computational framework that combines the recently developed time-parallel (TP) and the compound wavelet matrix (CWM) methods. The framework, termed tpCWM, offers significant computational acceleration by making multiscale/multiphysics simulations computationally scalable in time and space domains. We demonstrate the accuracy and the scalability of the method on a prototype problem with oscillatory trajectory. The method corrects the coarse solution by iterative use of the CWM, which compounds the fine and the coarse solutions for the processes. Computational savings, over the fine solution as well as the TP method, in terms of the real time required to perform the simulations, can reach several orders of magnitude. We believe that this method is general enough to be applicable to a wide-class of computational physics problems. Tendency towards large number of cores and processors in parallel computers is compatible with the computational scalability of the algorithm.
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arxiv:0804.0017
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We give a mathematical framework for manipulating indeterminate-length quantum bit strings. In particular, we define prefixes, fragments, tensor products and concatenation of such strings of qubits, and study their properties and relationships. The results are then used to define prefix-free Hilbert spaces in a more general way than in previous work, without assuming the existence of a basis of length eigenstates. We prove a quantum analogue of the Kraft inequality, illustrate the results with some examples and discuss the relevance of prefix-free Hilbert spaces for lossless compression.
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arxiv:0804.0022
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While a set of covariance matrices corresponding to different populations are unlikely to be exactly equal they can still exhibit a high degree of similarity. For example, some pairs of variables may be positively correlated across most groups, while the correlation between other pairs may be consistently negative. In such cases much of the similarity across covariance matrices can be described by similarities in their principal axes, the axes defined by the eigenvectors of the covariance matrices. Estimating the degree of across-population eigenvector heterogeneity can be helpful for a variety of estimation tasks. Eigenvector matrices can be pooled to form a central set of principal axes, and to the extent that the axes are similar, covariance estimates for populations having small sample sizes can be stabilized by shrinking their principal axes towards the across-population center. To this end, this article develops a hierarchical model and estimation procedure for pooling principal axes across several populations. The model for the across-group heterogeneity is based on a matrix-valued antipodally symmetric Bingham distribution that can flexibly describe notions of ``center'' and ``spread'' for a population of orthonormal matrices.
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arxiv:0804.0031
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Two novel (and proprietary) strategies for the structural identification of a nanocrystal from either a single high-resolution (HR) transmission electron microscopy (TEM) image or a single precession electron diffraction pattern are proposed and their advantages discussed in comparison to structural fingerprinting from powder X-ray diffraction patterns. Simulations for cubic magnetite and maghemite nanocrystals are used as examples. This is an expanded and updated version of a conference paper that has been published in Suppl. Proc. of TMS 2008, 137th Annual Meeting & Exhibition, Volume 1, Materials Processing and Properties, pp. 25-32.
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arxiv:0804.0063
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We consider a cosmological solution which can explain anisotropic evolution of spatial dimensions and the stabilization of extra dimensions in brane gas formalism. We evaluate the effective potentials, induced by brane gas, bulk flux and supergravity particles, which govern the sizes of the observed three and the extra dimensions. It is possible that the wrapped internal volume can oscillate between two turning points or sit at the minimum of the potential while the unwrapped three dimensional volume can expand monotonically. Including the supergravity particles makes the effective potential steeper as the internal volume shrinks.
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arxiv:0804.0073
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Discussion of ``Statistical analysis of an archeological find'' by Andrey Feuerverger [arXiv:0804.0079]
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arxiv:0804.0080
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Discussion of ``Statistical analysis of an archeological find'' by Andrey Feuerverger [arXiv:0804.0079]
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arxiv:0804.0090
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In this work, we construct commutative rings of two variable matrix differential operators that are isomorphic to a ring of meromorphic functions on a rational manifold obtained from the $CP^1\times CP^1$ by identification of two lines with the pole on a certain rational curve.
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arxiv:0804.0117
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Signals of bimodality have been investigated in experimental data of quasi-projectile decay produced in Au+Au collisions at 35 AMeV. This same data set was already shown to provide several signals characteristic of a first order, liquid-gas-like phase transition. Different event sortings proposed in the recent literature are analyzed. A sudden change in the fragmentation pattern is revealed by the distribution of the charge of the largest fragment, compatible with a bimodal behavior.
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arxiv:0804.0205
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This paper presents a sensitive and comprehensive IRAC 3-8 $\mu$m photometric survey of white dwarfs for companions in the planetary mass regime with temperatures cooler than the known T dwarfs. The search focuses on descendents of intermediate mass stars with $M\ga3$ $M_{\odot}$ whose inner, few hundred AU regions cannot be probed effectively for massive planets and brown dwarfs by any alternative existing method. Furthermore, examination for mid-infrared excess explores an extensive range of orbital semimajor axes, including the intermediate 5-50 AU range poorly covered and incompletely accessible by other techniques at main sequence or evolved stars. Three samples of white dwarfs are chosen which together represent relatively young as well as older populations of stars: 9 open cluster white dwarfs, 22 high mass field white dwarfs, and 17 metal-rich field white dwarfs. In particular, these targets include: 7 Hyads and 4 field white dwarfs of similar age; 1 Pleiad and 19 field white dwarfs of similar age; van Maanen 2 and 16 similarly metal-rich white dwarfs with ages between 1 and 7 Gyr. No substellar companion candidates were identified at any star. By demanding a 15% minimum photometric excess at 4.5 $\mu$m to indicate a companion detection, upper limits in the planetary mass regime are established at 34 of the sample white dwarfs, 20 of which have limits below 10 $M_{\rm J}$ according to substellar cooling models. Specifically, limits below the minimum mass for deuterium burning are established at all Pleiades and Hyadeswhite dwarfs, as well as similarly young field white dwarfs, half a dozen of which receive limits at or below 5 $M_{\rm J}$. Two IRAC epochs at vMa 2 rule out $T\ga200$ K proper motion companions within 1200 AU.
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arxiv:0804.0237
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We investigate the transmission of electrons between conducting nanoribbon leads oriented at multiples of 60 degrees with respect to one another, connected either directly or through graphene polygons. A mode-matching analysis suggests that the transmission at low-energies is sensitive to the precise way in which the ribbons are joined. Most strikingly, we find that armchair leads forming 120-degree angles can support either a large transmission or a highly suppressed transmission, depending on the specific geometry. Tight-binding calculations demonstrate the effects in detail, and are also used to study transmission at higher energies as well as for zigzag ribbon leads.
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arxiv:0804.0246
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Dynamical systems studies of differential equations often focus on the behavior of solutions near critical points and on invariant manifolds, to elucidate the organization of the associated flow. In addition, effective methods, such as the use of Poincare maps and phase resetting curves, have been developed for the study of periodic orbits. However, the analysis of transient dynamics associated with solutions on their way to an attracting fixed point has not received much rigorous attention. This paper introduces methods for the study of such transient dynamics. In particular, we focus on the analysis of whether one component of a solution to a system of differential equations can overtake the corresponding component of a reference solution, given that both solutions approach the same stable node. We call this phenomenon tolerance, which derives from a certain biological effect. Here, we establish certain general conditions, based on the initial conditions associated with the two solutions and the properties of the vector field, that guarantee that tolerance does or does not occur in two-dimensional systems. We illustrate these conditions in particular examples, and we derive and demonstrate additional techniques that can be used on a case by case basis to check for tolerance. Finally, we give a full rigorous analysis of tolerance in two-dimensional linear systems.
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arxiv:0804.0248
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Vacuum birefringence is a signature of Lorentz-symmetry violation. Here we report on a recent search for birefringence in the cosmic microwave background. Polarization data is used to place constraints on certain forms of Lorentz violation.
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arxiv:0804.0269
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Modeling the evolution of a financial index as a stochastic process is a problem awaiting a full, satisfactory solution since it was first formulated by Bachelier in 1900. Here it is shown that the scaling with time of the return probability density function sampled from the historical series suggests a successful model. The resulting stochastic process is a heteroskedastic, non-Markovian martingale, which can be used to simulate index evolution on the basis of an auto-regressive strategy. Results are fully consistent with volatility clustering and with the multi-scaling properties of the return distribution. The idea of basing the process construction on scaling, and the construction itself, are closely inspired by the probabilistic renormalization group approach of statistical mechanics and by a recent formulation of the central limit theorem for sums of strongly correlated random variables.
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arxiv:0804.0331
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Using series expansions and spin-wave theory we calculate the spin-stiffness anisotropy $\rho_{sx}/\rho_{sy}$ in Heisenberg models on the square lattice with anisotropic couplings $J_x,J_y$. We find that for the weakly anisotropic spin-half model ($J_x\approx J_y$), $\rho_{sx}/\rho_{sy}$ deviates substantially from the naive estimate $\rho_{sx}/\rho_{sy} \approx J_x/J_y$. We argue that this deviation can be responsible for pinning the electronic liquid crystal direction, a novel effect recently discovered in YBCO. For completeness, we also study the spin-stiffness for arbitrary anisotropy $J_x/J_y$ for spin-half and spin-one models. In the limit of $J_y/J_x\to 0$, when the model reduces to weakly coupled chains, the two show dramatically different behavior. In the spin-one model, the stiffness along the chains goes to zero, implying the onset of Haldane-gap phase, whereas for spin-half the stiffness along the chains increases monotonically from a value of $0.18 J_x$ for $J_y/J_x=1$ towards $0.25 J_x$ for $J_y/J_x\to 0$. Spin-wave theory is extremely accurate for spin-one but breaks down for spin-half presumably due to the onset of topological terms.
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arxiv:0804.0400
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We propose and demonstrate the functioning of a special Rapid Single Flux Quantum (RSFQ) circuit with frequency-dependent damping. This damping is achieved by shunting individual Josephson junctions by pieces of open-ended RC transmission lines. Our circuit includes a toggle flip-flop cell, Josephson transmission lines transferring single flux quantum pulses to and from this cell, as well as DC/SFQ and SFQ/DC converters. Due to the desired frequency-dispersion in the RC line shunts which ensures sufficiently low noise at low frequencies, such circuits are well-suited for integrating with the flux/phase Josephson qubit and enable its efficient control.
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arxiv:0804.0442
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The most difficult aspect of the realistic modeling of granular materials is how to capture the real shape of the particles. Here we present a method to simulate granular materials with complex-shaped particles. The particle shape is represented by the classical concept of a Minkowski sum, which permits the representation of complex shapes without the need to define the object as a composite of spherical or convex particles. A well defined interaction force between these bodies is derived. The algorithm for identification of neighbor particles reduces force calculations to O(N), where $N$ is the number of particles. The algorithm is much more efficient, accurate and easier to implement than other models. We investigate the existence of a statistical equilibrium in granular systems with circular non-spherical particles in the collisional. regime. We also investigate the limit state of dissipative granular materials using biaxial test simulations. The results are consistent with the classical assumption of the statistical mechanics for non-dissipative systems, and the critical state theory of soils mechanics for dissipative granular materials.
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arxiv:0804.0474
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The charge dynamics in weakly hole doped high temperature superconductors is studied in terms of the accurate numerical solution to a model of a single hole interacting with a quantum lattice in an antiferromagnetic background, and accurate far-infrared ellipsometry measurements. The experimentally observed two electronic bands in the infrared spectrum can be identified in terms of the interplay between the electron correlation and electron-phonon interaction resolving the long standing mystery of the mid-infrared band.
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arxiv:0804.0479
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The moduli space of flat connections for maximally supersymmetric Yang-Mills theories, in a space-time of the form T^3xR, contains isolated points, corresponding to normalizable zero energy states, for certain simple gauge groups G. We consider the low energy effective field theories in the weak coupling limit supported on such isolated points and find that when quantized they consist of an infinite set of harmonic oscillators whose angular frequencies are completely determined by the Lie algebra of G. We then proceed to find the isolated flat connections for all simple G and subsequently specify the corresponding effective field theories.
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arxiv:0804.0503
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We consider Kemp's q-analogue of the binomial distribution. Several convergence results involving the classical binomial, the Heine, the discrete normal, and the Poisson distribution are established. Some of them are q-analogues of classical convergence properties. Besides elementary estimates, we apply Mellin transform asymptotics.
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arxiv:0804.0534
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We study the quantum dynamics/fluctuation of the cycloidal helical magnet in terms of the Schwinger boson approach. In sharp contrast to the classical fluctuation, the quantum fluctuation is collinear in nature which gives rise to the collinear spin density wave state slightly above the helical cycloidal state as the temperature is lowered. Physical properties such as the reduced elliptic ratio of the spiral, the neutron scattering and infrared absorption spectra are discussed from this viewpoint with the possible relevance to the quasi-one dimensional LiCu$_2$O$_2$ and LiCuVO$_4$.
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arxiv:0804.0669
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The many peculiarities of Ap stars (not only chemical ones, but also magnetic field and slow rotation) may vary during the main-sequence evolution of these stars. We review here briefly the evidences found in the last thirty years for such evolution, with an emphasis on the more recent research. The position in the HR diagram of low mass Ap stars with a significant surface magnetic field (as measured by us) is reviewed as well.
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arxiv:0804.0711
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Generalized Parton Distributions of the pion are evaluated in chiral quark models with the help of double distributions. As a result the polynomiality conditions are automatically satisfied. In addition, positivity constraints, proper normalization and support, sum rules, and soft pion theorems are fulfilled. We obtain explicit expressions holding at the low-energy quark-model scale, which exhibit no factorization in the t-dependence. The crucial QCD evolution of the quark-model distributions is carried out up to experimental or lattice scales. The obtained results for the Parton Distribution Function and the Parton Distribution Amplitude describe the available experimental and lattice data, confirming that the quark-model scale is low, around 320 MeV.
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arxiv:0804.0718
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We present a method of obtaining information about spin lifetimes in quantum dots from measurements of electrical transport. The dot is under resonant microwave irradiation and at temperatures comparable to or larger than the Zeeman energy. We find that the ratio of the spin coherence times T_{1}/T_{2} can be deduced from a measurement of current through the quantum dot as a function the applied magnetic field. We calculate the noise power spectrum of the dot current and show that a dip occurs at the Rabi frequency with a line width given by 1/T_{1}+1/T_{2}.
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arxiv:0804.0771
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Recently developed methods for PT-symmetric models can be applied to quantum-mechanical matrix and vector models. In matrix models, the calculation of all singlet wave functions can be reduced to the solution a one-dimensional PT-symmetric model. The large-N limit of a wide class of matrix models exists, and properties of the lowest-lying singlet state can be computed using WKB. For models with cubic and quartic interactions, the ground state energy appears to show rapid convergence to the large-N limit. For the special case of a quartic model, we find explicitly an isospectral Hermitian matrix model. The Hermitian form for a vector model with O(N) symmetry can also be found, and shows many unusual features. The effective potential obtained in the large-N limit of the Hermitian form is shown to be identical to the form obtained from the original PT-symmetric model using familiar constraint field methods. The analogous constraint field prescription in four dimensions suggests that PT-symmetric scalar field theories are asymptotically free.
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arxiv:0804.0778
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We present joint theoretical-experimental study of the correlation effects in the electronic structure of (pyH)$_3$[Mn$_4$O$_3$Cl$_7$(OAc)$_3$]$\cdot$2MeCN molecular magnet (Mn$_4$). Describing the many-body effects by cluster dynamical mean-field theory, we find that Mn$_4$ is predominantly Hubbard insulator with strong electron correlations. The calculated electron gap (1.8 eV) agrees well with the results of optical conductivity measurements, while other methods, which neglect many-body effects or treat them in a simplified manner, do not provide such an agreement. Strong electron correlations in Mn$_4$ may have important implications for possible future applications.
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arxiv:0804.0792
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We generalise the analysis carried out in [arXiv:0710.5796], and find that our previous results can be extended beyond the case of SL(N,C). In particular, we show that an equivalence--at the level of the holomorphic chiral algebra--between a bosonic string on a smooth coset manifold G/B and a B-gauged version of itself on G, will imply an isomorphism of classical W-algebras and a level relation which underlie a geometric Langlands correspondence for the simply-laced, complex ADE-groups. In addition, as opposed to line operators and branes of an open topological sigma-model, the Hecke operators and Hecke eigensheaves, can, instead, be physically interpreted in terms of the correlation functions of local operators in the holomorphic chiral algebra of a closed, quasi-topological sigma-model. Our present results thus serve as an alternative physical interpretation--to that of an electric-magnetic duality of four-dimensional gauge theory demonstrated earlier by Kapustin and Witten in [arXiv:hep-th/0604151]--of the geometric Langlands correspondence for complex ADE-groups. The cases with tame and mild "ramifications" are also discussed.
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arxiv:0804.0804
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We study the linear conductance through a double-quantum-dot system consisting of an interacting dot in its Kondo regime and an effectively noninteracting dot, connected in parallel to metallic leads. Signatures in the zero-bias conductance at temperatures $T>0$ mark a pair of quantum (T=0) phase transitions between a Kondo-screened many-body ground state and non-Kondo ground states. Notably, the conductance features become more prominent with increasing $T$, which enhances the experimental prospects for accessing the quantum-critical region through tuning of gate voltages in a single device.
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arxiv:0804.0805
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We study finiteness conditions on large tilting modules over arbitrary rings. We then turn to a hereditary artin algebra R and apply our results to the (infinite dimensional) tilting module L that generates all modules without preprojective direct summands. We show that the behaviour of L over its endomorphism ring determines the representation type of R. A similar result holds true for the (infinite dimensional) tilting module W that generates the divisible modules. Finally, we extend to the wild case some results on Baer modules and torsion-free modules proven in [AHT] for tame hereditary algebras.
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arxiv:0804.0815
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We discuss whether some perturbed Friedmann-Robertson-Walker (FRW) universes could be creatable, i. e., could have vanishing energy, linear momentum and angular momentum, as it could be expectable if the Universe arose as a quantum fluctuation. On account of previous results, the background is assumed to be either closed (with very small curvature) or flat. In the first case, fully arbitrary linear perturbations are considered; whereas in the flat case, it is assumed the existence of: (i) inflationary scalar perturbations, that is to say, Gaussian adiabatic scalar perturbations having an spectrum close to the Harrison-Zel'dovich one, and (ii) arbitrary tensor perturbations. We conclude that, any closed perturbed universe is creatable, and also that, irrespective of the spectrum and properties of the inflationary gravitational waves, perturbed flat FRW universes with standard inflation are not creatable. Some considerations on pre-inflationary scalar perturbations are also presented. The creatable character of perturbed FRW universes is studied, for the first time, in this paper.
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arxiv:0804.0861
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