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Arxiv.org
by Natalia B. Janson; Christopher J. Marsden
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We propose an alternative approach to construct an artificial learning system, which naturally learns in an unsupervised manner. Its mathematical prototype is a dynamical system, which automatically shapes its vector field in response to the input signal. The vector field converges to a gradient of a multi-dimensional probability density distribution of the input process, taken with negative sign. The most probable patterns are represented by the stable fixed points, whose basins of attraction...
Source: http://arxiv.org/abs/1107.0674v2
Arxiv.org
by B. Luo; W. N. Brandt; Y. Q. Xue; D. M. Alexander; M. Brusa; F. E. Bauer; A. Comastri; A. C. Fabian; R. Gilli; B. D. Lehmer; D. A. Rafferty; D. P. Schneider; C. Vignali
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(abridged) We identify a numerically significant population of heavily obscured AGNs at z~0.5-1 in the Chandra Deep Field-South (CDF-S) and Extended Chandra Deep Field-South by selecting 242 X-ray undetected objects with infrared-based star formation rates (SFRs) substantially higher (a factor of 3.2 or more) than their SFRs determined from the UV after correcting for dust extinction. An X-ray stacking analysis of 23 candidates in the central CDF-S region using the 4 Ms Chandra data reveals a...
Source: http://arxiv.org/abs/1107.3148v1
Arxiv.org
by Debashish Bose; Shobha Madan
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In \cite{BCKM} it was shown that "Tiling implies Spectral" holds for a union of three intervals and the reverse implication was studied under certain restrictive hypotheses on the associated spectrum. In this paper, we reinvestigate the "Spectral implies Tiling" part of Fuglede's conjecture for the three interval case. We first show that the "Spectral implies Tiling" for two intervals follows from the simple fact that two distinct circles have at most two points of...
Source: http://arxiv.org/abs/1107.5209v1
Arxiv.org
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We consider a class of Nemytskii superposition operators that covers the nonlinear part of traveling wave models from laser dynamics, population dynamics, and chemical kinetics. Our main result is the $C^1$-continuity property of these operators over Sobolev-type spaces of periodic functions.
Source: http://arxiv.org/abs/1107.4484v2
Arxiv.org
by Hamid Hezari; Steve Zelditch
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We prove that ellipses are infinitesimally spectrally rigid among $C^{\infty}$ domains with the symmetries of the ellipse.
Source: http://arxiv.org/abs/1007.1741v3
Arxiv.org
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In this article, we consider permutation orbifold models of $C_2$-cofinite vertex operator algebras of CFT type. We show the $C_2$-cofiniteness of the 2-cyclic permutation orbifold model $(V\otimes V)^{S_2}$ for an arbitrary $C_2$-cofinite simple vertex operator algebra $V$ of CFT type. We also give a proof of the $C_2$-cofiniteness of a $\Z_2$-orbifold model $V_L^+$ of the lattice vertex operator algebra $V_L$ associated with a rank one positive definite even lattice $L$ by using our result...
Source: http://arxiv.org/abs/1107.2709v3
Arxiv.org
by Leandro M. Del Pezzo; Sandra Martinez
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In this paper we study the $H^2$ global regularity for solutions of the $p(x)-$Laplacian in two dimensional convex domains with Dirichlet boundary conditions. Here $p:\Omega \to [p_1,\infty)$ with $p\in Lip(\bar{\Omega})$ and $p_1>1$.
Source: http://arxiv.org/abs/1107.3136v2
In our previous work, we identify the Sublattice-Pairing State (SPS) in Schwinger-fermion representation as the spin liquid phase discovered in recent numerical study on a honeycomb lattice. In this paper, we show that SPS is identical to the zero-flux $Z_2$ spin liquid in Schwinger-boson representation found by Wang\cite{Wang2010} by an explicit duality transformation. SPS is connected to an \emph{unusual} antiferromagnetic ordered phase, which we term as chiral-antiferromagnetic (CAF) phase,...
Source: http://arxiv.org/abs/1007.3266v2
Arxiv.org
by Simon M. Goberstein
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A partial automorphism of a semigroup $S$ is any isomorphism between its subsemigroups, and the set all partial automorphisms of $S$ with respect to composition is the inverse monoid called the partial automorphism monoid of $S$. Two semigroups are said to be $\cPA$-isomorphic if their partial automorphism monoids are isomorphic. A class $\K$ of semigroups is called $\cPA$-closed if it contains every semigroup $\cPA$-isomorphic to some semigroup from $\K$. Although the class of all inverse...
Source: http://arxiv.org/abs/1107.4817v1
Arxiv.org
by Mauro Nacinovich; Egmont Porten
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Let $M$ be a $CR$ submanifold of a complex manifold $X$. The main result of this article is to show that $CR$-hypoellipticity at $p_0\in{M}$ is necessary and sufficient for holomorphic extension of all germs of $CR$ functions to an ambient neighborhood in $X$. As an application, we obtain that $CR$-hypoellipticity implies the existence of generic embeddings and prove holomorphic extension for a large class of $CR$ manifolds satisfying a higher order Levi pseudoconcavity condition.
Source: http://arxiv.org/abs/1107.3374v2
Arxiv.org
by A. Goasduff; S. Courtin; F. Haas; D. Lebhertz; D. G. Jenkins; C. Beck; J. Fallis; C. Ruiz; D. A. Hutcheon; P. -A. Amandruz; C. Davis; U. Hager; D. Ottewell; G. Ruprecht
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We have performed a heavy ion radiative capture reaction between two light heavy ions, $^{12}$C and $^{16}$O, leading to $^{28}$Si. The present experiment has been performed below Coulomb barrier energies in order to reduce the phase space and to try to shed light on structural effects. Obtained $\gamma$-spectra display a previously unobserved strong feeding of intermediate states around 11 MeV at these energies. This new decay branch is not fully reproduced by statistical nor semi-statistical...
Source: http://arxiv.org/abs/1107.1124v1
Arxiv.org
by M. Tamekkante; M. Chhiti; K. Louartiti
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This paper introduces and studies a particular subclass of the class of commutative rings with finite Gorenstein global dimension.
Source: http://arxiv.org/abs/1107.0446v1
Arxiv.org
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We show that $sl_2$ conformal block divisors do not cover the nef cone of $\bar{M}_{0,6}$, or the $S_9$-invariant nef cone of $\bar{M}_{0,9}$. A key point is to relate the nonvanishing of intersection numbers between these divisors and F-curves to the nonemptiness of some explicitly defined polytopes. Several experimental results and some open problems are also included.
Source: http://arxiv.org/abs/1107.5331v1
Arxiv.org
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Graphite oxide is an amorphous insulator. Although several models have been suggested, its structure remains controversial. To elucidate this issue, 5 samples were prepared by the Brodie process and the Staudenmaier process. The electronic structure of graphite oxide was examined with x-ray absorption near edge structure and the ratio of $sp^{2}$ to $sp^{3}$ bonded carbon atoms was investigated with x-ray photoemission spectroscopy as a function of sample preparation times. It was found that...
Source: http://arxiv.org/abs/1007.0287v2
Arxiv.org
by Ovidiu Savin; Enrico Valdinoci
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We discuss the $\Gamma$-convergence, under the appropriate scaling, of the energy functional $$ \|u\|_{H^s(\Omega)}^2+\int_\Omega W(u)dx,$$ with $s \in (0,1)$, where $\|u\|_{H^s(\Omega)}$ denotes the total contribution from $\Omega$ in the $H^s$ norm of $u$, and $W$ is a double-well potential. When $s\in [1/2,\,1)$, we show that the energy $\Gamma$-converges to the classical minimal surface functional -- while, when $s\in(0,\,1/2)$, it is easy to see that the functional $\Gamma$-converges to...
Source: http://arxiv.org/abs/1007.1725v3
Arxiv.org
by Susana Valdez-Alvarado; Ricardo Becerril; L. Arturo Urena-Lopez
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We solve numerically the Einstein-Klein-Gordon system with spherical symmetry, for a massive real scalar field endowed with a quartic self-interaction potential, and obtain the so-called $\Phi^4$-oscillatons which is the short name for oscillating soliton stars. We analyze numerically the stability of such oscillatons, and study the influence of the quartic potential on the behavior of both, the stable (S-oscillatons) and unstable (U-oscillatons) cases under small and strong radial...
Source: http://arxiv.org/abs/1107.3135v1
Arxiv.org
by Ming-Kai Du; Chun Liu
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$\Omega_b \rightarrow \Omega_c^{(*)}$ semi-leptonic decays are studied in details. Relevant helicity amplitudes are written down. Both unpolarized and polarized $\Omega_b$ cases are considered. Decay angular distributions, asymmetry parameters and semileptonic decay rates are calculated, with numerical results using leading order results of the large $N_c$ and heavy quark effective theory(HQET).
Source: http://arxiv.org/abs/1107.2535v3
Arxiv.org
by The KLOE-2 Collaboration; F. Archilli; D. Babusci; D. Badoni; I. Balwierz; G. Bencivenni; C. Bini; C. Bloise; V. Bocci; F. Bossi; P. Branchini; A. Budano; S. A. Bulychjev; P. Campana; G. Capon; F. Ceradini; P. Ciambrone; E. Czerwinski; E. Dane; E. De Lucia; G. De Robertis; A. De Santis; G. De Zorzi; A. Di Domenico; C. Di Donato; D. Domenici; O. Erriquez; G. Fanizzi; G. Felici; S. Fiore; P. Franzini; P. Gauzzi; S. Giovannella; F. Gonnella; E. Graziani; F. Happacher; B. Hoistad; E. Iarocci; M....
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The processes $e^+e^-\to e^+e^-X$, with $X$ being either the $\eta$ meson or $\pi^0\pi^0$, are studied at DA$\Phi$NE, with $e^+e^-$ beams colliding at $\sqrt{s}\simeq1$ GeV, below the $\phi$ resonance peak. The data sample is from an integrated luminosity of 240 pb$^{-1}$, collected by the KLOE experiment without tagging of the outgoing $e^+e^-$. Preliminary results are presented on the observation of the $\gamma\gamma\to\eta$ process, with both $\eta\to\pi^+\pi^-\pi^0$ and...
Source: http://arxiv.org/abs/1107.3782v1
Arxiv.org
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The octet-singlet $\eta -\eta^{\prime}$ mixing mass term could have a derivative $O(p^{2})$ term as found in recent analysis of the $\eta -\eta^{\prime}$ system. This term gives rise to an additional momentum-dependent pole contribution which is suppressed by a factor $m_{\eta}^{2}/m_{\eta^{\prime}}^{2}$ for $\eta$ relative to the $\eta^{\prime}$ amplitude. The processes with $\eta$ meson can then be described, to a good approximation, by the momentum-independent mixing mass term which gives...
Source: http://arxiv.org/abs/1005.5671v4
Arxiv.org
by B. Iochum; T. Masson; Th. Schücker; A. Sitarz
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The aim of the paper is to answer the following question: does $\kappa$-deformation fit into the framework of noncommutative geometry in the sense of spectral triples? Using a compactification of time, we get a discrete version of $\kappa$-Minkowski deformation via $C^*$-algebras of groups. The dynamical system of the underlying groups (including some Baumslag--Solitar groups) is used in order to construct \emph{finitely summable} spectral triples. This allows to bypass an obstruction to...
Source: http://arxiv.org/abs/1107.3449v1
Arxiv.org
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The strong coupling of rho meson to the nucleon produces $s$ and $p$ wave rho meson nucleon $(\rho N)$ resonances. In a nucleus, the $\rho N$ resonance-hole polarization generates the optical potential or self-energy for the rho meson. The scattering of rho meson due to this potential provides valuable informations about the $\rho N$ resonance dynamics in a nucleus. To investigate it, we use this potential to calculate the mass distribution spectrum for the $\rho$ meson produced coherently in...
Source: http://arxiv.org/abs/1005.0187v2
Arxiv.org
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In this paper we use formal asymptotic arguments to understand the stability proper- ties of equivariant solutions to the Landau-Lifshitz-Gilbert model for ferromagnets. We also analyze both the harmonic map heatflow and Schrodinger map flow limit cases. All asymptotic results are verified by detailed numerical experiments, as well as a robust topological argument. The key result of this paper is that blowup solutions to these problems are co-dimension one and hence both unstable and...
Source: http://arxiv.org/abs/1107.2620v1
Arxiv.org
by Laurent Bartholdi
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We show that contracting self-similar groups satisfy the Farrell-Jones conjectures as soon as their universal contracting cover is non-positively curved. This applies in particular to bounded self-similar groups. We define, along the way, a general notion of contraction for groups acting on a rooted tree in a not necessarily self-similar manner.
Source: http://arxiv.org/abs/1107.5339v2
Arxiv.org
by Jose A. de Azcarraga; Jose M. Izquierdo
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We use the expansion of superalgebras procedure (summarized in the text) to derive Chern-Simons (CS) actions for the (p,q)-Poincare supergravities in three-dimensional spacetime. After deriving the action for the (p,0)-Poincare supergravity as a CS theory for the expansion osp(p|2;R)(2,1) of osp(p|2;R), we find the general (p,q)-Poincare superalgebras and their associated D=3 supergravity actions as CS gauge theories from an expansion of the simple osp(p+q|2,R) superalgebras, namely...
Source: http://arxiv.org/abs/1107.2569v2
Arxiv.org
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We present a near-infrared extinction map of a large region (approximately 2200 deg^2) covering the Orion, the Monoceros R2, the Rosette, and the Canis Major molecular clouds. We used robust and optimal methods to map the dust column density in the near-infrared (NICER and NICEST) towards ~19 million stars of the Two Micron All Sky Survey (2MASS) point source catalog. Over the relevant regions of the field, we reached a 1-sigma error of 0.03 mag in the K-band extinction with a resolution of 3...
Source: http://arxiv.org/abs/1107.5096v1
Arxiv.org
by Carlo Giunti; Marco Laveder
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We present the results of fits of short-baseline neutrino oscillation data in 3+1 and 3+2 neutrino mixing schemes. In spite of the presence of a tension in the interpretation of the data, 3+1 neutrino mixing is attractive for its simplicity and for the natural correspondence of one new entity (a sterile neutrino) with a new effect (short-baseline oscillations). The allowed regions in the oscillation parameter space can be tested in near-future experiments. In the framework of 3+2 neutrino...
Source: http://arxiv.org/abs/1107.1452v3
Arxiv.org
by S. Bongard; F. Soulez; E. Thiebaut; E. Pécontal
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In this paper we present a general forward fitting method for multichannel image restoration based on regularized chi2. We introduce separable regularizations that account for the dynamic of the model and take advantage of the continuities present in the data, leaving only two hyper-parameters to tune. We illustrate a practical implementation of this method in the context of host galaxy subtraction for the Nearby SuperNova factory. We show that the image restoration obtained fulfills the...
Source: http://arxiv.org/abs/1107.4049v1
In this manuscript, the structure of broad emission line regions (BLRs) of well-mapping double-peaked emitter (AGN with broad double-peaked low-ionization emission lines) 3C390.3 is studied. Besides the best fitted results for double-peaked broad optical balmer lines of 3C390.3 by theoretical disk model, we try to find another way to further confirm the origination of double-peaked line from accretion disk. Based on the long-period observed spectra in optical band around 1995 collected from AGN...
Source: http://arxiv.org/abs/1107.0455v1
Arxiv.org
by T. D. Kitching; A. F. Heavens; L. Miller
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Here we present a number of improvements to weak lensing 3D power spectrum analysis, 3D cosmic shear, that uses the shape and redshift information of every galaxy to constrain cosmological parameters. We show how photometric redshift probability distributions for individual galaxies can be directly included in this statistic with no averaging. We also include the Limber approximation, considerably simplifying full 3D cosmic shear analysis, and we investigate its range of applicability. Finally...
Source: http://arxiv.org/abs/1007.2953v2
Arxiv.org
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We report a complete set of $^{59}$Co NMR data taken on the $x=2/3$ phase of sodium cobaltates Na$_{x}$CoO$_{2}$, for which we have formerly established the in plane Na ordering and its three dimensional stacking from a combination of symmetry arguments taken from Na and Co NQR/NMR data. Here we resolve all the parameters of the Zeeman and quadrupolar Hamiltonians for all cobalt sites in the unit cell and report the temperature dependencies of the NMR shift and spin lattice relaxation $T_{1}$...
Source: http://arxiv.org/abs/1107.3676v2
Arxiv.org
by Antonio E. Cárcamo Hernández; Riccardo Torre
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In the framework of a strong dynamics for Electro-Weak Symmetry Breaking (EWSB), both vector and scalar degrees of freedom have been studied in the literature within an effective Lagrangian approach. Here we consider the case in which both a scalar, $h$, and a vector, $V$ - respectively an iso-singlet and an iso-triplet under a custodial SU(2) - are relevant with a mass below the cut-off $\Lambda \approx 4\pi v$. We study the amplitudes for the processes $W_L W_L \to W_L W_L, hh, V_{L}V_{L},...
Source: http://arxiv.org/abs/1005.3809v3
Arxiv.org
by Taras Banakh; Magdalena Nowak
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Answering an old question of M.Hata, we construct an example of a 1-dimensional Peano continuum which is not homeomorphic to an attractor of IFS.
Source: http://arxiv.org/abs/1107.3804v1
Arxiv.org
by Warren R. Brown; Mukremin Kilic; J. J. Hermes; Carlos Allende Prieto; Scott J. Kenyon; D. E. Winget
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We have discovered a detached pair of white dwarfs (WDs) with a 12.75 min orbital period and a 1,315 km/s radial velocity amplitude. We measure the full orbital parameters of the system using its light curve, which shows ellipsoidal variations, Doppler boosting, and primary and secondary eclipses. The primary is a 0.25 Msun tidally distorted helium WD, only the second tidally distorted WD known. The unseen secondary is a 0.55 Msun carbon-oxygen WD. The two WDs will come into contact in 0.9 Myr...
Source: http://arxiv.org/abs/1107.2389v1
Arxiv.org
by Nicholas J. Wright; Michael J. Barlow; Barbara Ercolano; Thomas Rauch
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We present a 3D photoionization model of the PN NGC 6302, one of the most complex objects of its kind. Our Mocassin model is composed of an extremely dense circumstellar disk and a large pair of diffuse bipolar lobes, a combination necessary to reproduce the observed spectrum. The masses of these components gives a total nebular mass of 4.7Mo. Discrepancies between our model fit and the observations are attributed to complex density inhomogeneities in the nebula. The potential to resolve such...
Source: http://arxiv.org/abs/1107.4554v1
Arxiv.org
by Peter H. Hauschildt; E. Baron
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We discuss an implementation of our 3D radiative transfer (3DRT) framework with the OpenCL paradigm for general GPU computing. We implement the kernel for solving the 3DRT problem in Cartesian coordinates with periodic boundary conditions in the horizontal $(x,y)$ plane, including the construction of the nearest neighbor $\Lstar$ and the operator splitting step. We present the results of a small and a large test case and compare the timing of the 3DRT calculations for serial CPUs and various...
Source: http://arxiv.org/abs/1107.5719v2
Arxiv.org
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For the description of the early inflation, and acceleration expansion of the Universe, compatible with observational data, the 5D noncompact Kaluza--Klein cosmology is investigated. It is proposed that the 5D space is filled with a null perfect fluid, resulting a perfect fluid in 4D universe, plus one along the fifth dimension. By analyzing the reduced field equations for flat FRW model, we show the early inflationary behavior and current acceleration of the universe.
Source: http://arxiv.org/abs/1005.3140v2
Arxiv.org
by Xi Chen; Simon P. Ellingsen; Zhi-Qiang Shen; Anita Titmarsh; Cong-Gui Gan
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We report the results of a systematic survey for 95 GHz class I methanol masers towards a new sample of 192 massive young stellar object (MYSO) candidates associated with ongoing outflows (known as extended green objects or EGOs) identified from the Spitzer GLIMPSE survey. The observations were made with the Australia Telescope National Facility (ATNF) Mopra 22-m radio telescope and resulted in the detection of 105 new 95 GHz class I methanol masers. For 92 of the sources our observations...
Source: http://arxiv.org/abs/1107.2914v1
Arxiv.org
by C. Adam; J. Sanchez-Guillen; A. Wereszczynski
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Within the set of generalized Skyrme models, we identify a submodel which has both infinitely many symmetries and a Bogomolny bound which is saturated by infinitely many exact soliton solutions. Concretely, the submodel consists of the square of the baryon current and a potential term only. Further, already on the classical level, this BPS Skyrme model reproduces some features of the liquid drop model of nuclei. Here, we review the properties of the model and we discuss the semiclassical...
Source: http://arxiv.org/abs/1107.5433v2
Arxiv.org
by Sangjib Kim; Oded Yacobi
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The symplectic group branching algebra, B, is a graded algebra whose components encode the multiplicities of irreducible representations of Sp(2n-2,C) in each irreducible representation of Sp(2n,C). By describing on B an ASL structure, we construct an explicit standard monomial basis of B consisting of Sp(2n-2,C) highest weight vectors. Moreover, B is known to carry a canonical action of the n-fold product SL(2) \times ... \times SL(2), and we show that the standard monomial basis is the unique...
Source: http://arxiv.org/abs/1005.2320v2
Arxiv.org
by Xiaolei Xun; Bani Mallick; Raymond J. Carroll; Peter Kuchment
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The article addresses the problem of detecting presence and location of a small low emission source inside of an object, when the background noise dominates. This problem arises, for instance, in some homeland security applications. The goal is to reach the signal-to-noise ratio (SNR) levels on the order of $10^{-3}$. A Bayesian approach to this problem is implemented in 2D. The method allows inference not only about the existence of the source, but also about its location. We derive Bayes...
Source: http://arxiv.org/abs/1107.2980v1
Arxiv.org
by A. R. Conn; G. F. Lewis; R. A. Ibata; Q. A. Parker; D. B. Zucker; A. W. McConnachie; N. F. Martin; M. J. Irwin; N. Tanvir; M. A. Fardal; A. M. N. Ferguson
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We present a new approach for identifying the Tip of the Red Giant Branch (TRGB) which, as we show, works robustly even on sparsely populated targets. Moreover, the approach is highly adaptable to the available data for the stellar population under study, with prior information readily incorporable into the algorithm. The uncertainty in the derived distances is also made tangible and easily calculable from posterior probability distributions. We provide an outline of the development of the...
Source: http://arxiv.org/abs/1107.3206v1
Arxiv.org
by Eric B. Ford; Althea V. Moorhead; Dimitri Veras
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We present a Bayesian surrogate model for the analysis of periodic or quasi-periodic time series data. We describe a computationally efficient implementation that enables Bayesian model comparison. We apply this model to simulated and real exoplanet observations. We discuss the results and demonstrate some of the challenges for applying our surrogate model to realistic exoplanet data sets. In particular, we find that analyses of real world data should pay careful attention to the effects of...
Source: http://arxiv.org/abs/1107.4047v1
Arxiv.org
by Yuriy Mishchencko; Joshua T. Vogelstein; Liam Paninski
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Deducing the structure of neural circuits is one of the central problems of modern neuroscience. Recently-introduced calcium fluorescent imaging methods permit experimentalists to observe network activity in large populations of neurons, but these techniques provide only indirect observations of neural spike trains, with limited time resolution and signal quality. In this work we present a Bayesian approach for inferring neural circuitry given this type of imaging data. We model the network...
Source: http://arxiv.org/abs/1107.4228v1
Arxiv.org
by Philipp Gubler; Makoto Oka
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QCD sum rules are analyzed with the help of the Maximum Entropy Method. We develop a new technique based on the Bayesion inference theory, which allows us to directly obtain the spectral function of a given correlator from the results of the operator product expansion given in the deep euclidean 4-momentum region. The most important advantage of this approach is that one does not have to make any a priori assumptions about the functional form of the spectral function, such as the "pole +...
Source: http://arxiv.org/abs/1005.2459v2
Arxiv.org
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We consider scheduling packets with values in a capacity-bounded buffer in an online setting. In this model, there is a buffer with limited capacity $B$. At any time, the buffer cannot accommodate more than $B$ packets. Packets arrive over time. Each packet is associated with a non-negative value. Packets leave the buffer only because they are either sent or dropped. Those packets that have left the buffer will not be reconsidered for delivery any more. In each time step, at most one packet in...
Source: http://arxiv.org/abs/1005.3835v3
Arxiv.org
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The Boltzmann collision operator for a dilute granular gas of inelastic rough hard spheres is much more intricate than its counterpart for inelastic smooth spheres. Now the one-body distribution function depends not only on the translational velocity of the center of mass but also on the angular velocity of the particle. Moreover, the collision rules couple both velocities, involving not only the coefficient of normal restitution but also the coefficient of tangential restitution. The aim of...
Source: http://arxiv.org/abs/1007.0700v2
Arxiv.org
by Blanca Ayuso de Dios; Ariel Lombardi; Paola Pietra; Ludmil Zikatanov
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We consider an exponentially fitted discontinuous Galerkin method and propose a robust block solver for the resulting linear systems.
Source: http://arxiv.org/abs/1107.2831v1
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by Daoyuan Fang; Ruizhao Zi; Ting Zhang
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We establish a blow-up criterion in terms of the upper bound of the density and temperature for the strong solution to 2D compressible viscous heat-conductive flows. The initial vacuum is allowed.
Source: http://arxiv.org/abs/1107.4663v1
Arxiv.org
by Walid Hachem; Malika Kharouf; Jamal Najim; Jack W. Silverstein
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In this article, we study the fluctuations of the random variable: $$ {\mathcal I}_n(\rho) = \frac 1N \log\det(\Sigma_n \Sigma_n^* + \rho I_N),\quad (\rho>0) $$ where $\Sigma_n= n^{-1/2} D_n^{1/2} X_n\tilde D_n^{1/2} +A_n$, as the dimensions of the matrices go to infinity at the same pace. Matrices $X_n$ and $A_n$ are respectively random and deterministic $N\times n$ matrices; matrices $D_n$ and $\tilde D_n$ are deterministic and diagonal, with respective dimensions $N\times N$ and $n\times...
Source: http://arxiv.org/abs/1107.0145v1
Arxiv.org
by Luc Simard; J. Trevor Mendel; David R. Patton; Sara L. Ellison; Alan W. McConnachie
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We perform two-dimensional, Point-Spread-Function-convolved, bulge+disk decompositions in the $g$ and $r$ bandpasses on a sample of 1,123,718 galaxies from the Legacy area of the Sloan Digital Sky Survey Data Release Seven. Four different decomposition procedures are investigated which make improvements to sky background determinations and object deblending over the standard SDSS procedures that lead to more robust structural parameters and integrated galaxy magnitudes and colors, especially in...
Source: http://arxiv.org/abs/1107.1518v1
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We use a Stochastic Differential Equation satisfied by Brownian motion taking values in the unit sphere $S_{n-1}subsetmathbb{R}^{n}$ and we obtain a Central Limit Theorem for a sequence of such Brownian motions. We also generalize the results to the case of the $n$-dimensional Ornstein-Uhlenbeck processes.
Source: http://arxiv.org/abs/1107.3230v3
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New observations show that the lightcurve of Kuiper belt contact binary (139775) 2001 QG298 has changed substantially since the first observations in 2003. The 2010 lightcurve has a peak-to-peak photometric of range \Deltam{2010}=0.7\pm0.1 mag, significantly lower than in 2003, \Deltam{2003}=1.14\pm0.04 mag. This change is most simply interpreted if 2001 QG298 has an obliquity near 90 deg. The observed decrease in \Deltam is caused by a change in viewing geometry, from equator-on in 2003 to...
Source: http://arxiv.org/abs/1107.3507v1
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by H. R. Jacobson; C. A. Pilachowski; E. D. Friel
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We present a detailed chemical abundance study of evolved stars in 10 open clusters based on Hydra multi-object echelle spectra obtained with the WIYN 3.5m telescope. From an analysis of both equivalent widths and spectrum synthesis, abundances have been determined for the elements Fe, Na, O, Mg, Si, Ca, Ti, Ni, Zr, and for two of the 10 clusters, Al and Cr. To our knowledge, this is the first detailed abundance analysis for clusters NGC 1245, NGC 2194, NGC 2355 and NGC 2425. These 10 clusters...
Source: http://arxiv.org/abs/1107.4139v1
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by Shin Isojima; Junkichi Satsuma
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A class of special solutions are constructed in an intuitive way for the ultradiscrete analog of $q$-Painlev\'e II ($q$-PII) equation. The solutions are classified into four groups depending on the function-type and the system parameter.
Source: http://arxiv.org/abs/1107.4416v1
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The derivation of the Born rule by Zurek uses a "splitting procedure" where a physical state is subdivided into a number of states. It is argued that in quantum field theory, which encompasses quantum mechanics, such a procedure would in general modify the physics.
Source: http://arxiv.org/abs/1107.3736v1
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by Joshua D. Simon; Marla Geha; Quinn E. Minor; Gregory D. Martinez; Evan N. Kirby; James S. Bullock; Manoj Kaplinghat; Louis E. Strigari; Beth Willman; Philip I. Choi; Erik J. Tollerud; Joe Wolf
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We present the results of a comprehensive Keck/DEIMOS spectroscopic survey of the ultra-faint Milky Way satellite galaxy Segue 1. We have obtained velocity measurements for 98.2% of the stars within 67 pc (10 arcmin, or 2.3 half-light radii) of the center of Segue 1 that have colors and magnitudes consistent with membership, down to a magnitude limit of r=21.7. Based on photometric, kinematic, and metallicity information, we identify 71 stars as probable Segue 1 members, including some as far...
Source: http://arxiv.org/abs/1007.4198v3
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by W. P. Birmingham; C. J. Meek
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We propose a model for errors in sung queries, a variant of the hidden Markov model (HMM). This is a solution to the problem of identifying the degree of similarity between a (typically error-laden) sung query and a potential target in a database of musical works, an important problem in the field of music information retrieval. Similarity metrics are a critical component of query-by-humming (QBH) applications which search audio and multimedia databases for strong matches to oral queries. Our...
Source: http://arxiv.org/abs/1107.0054v1
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The notion of weak truth-table reducibility plays an important role in recursion theory. In this paper, we introduce an elaboration of this notion, where a computable bound on the use function is explicitly specified. This elaboration enables us to deal with the notion of asymptotic behavior in a manner like in computational complexity theory, while staying in computability theory. We apply the elaboration to sets which appear in the statistical mechanical interpretation of algorithmic...
Source: http://arxiv.org/abs/1107.3746v1
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by R. A. Gutermuth; J. L. Pipher; S. T. Megeath; P. C. Myers; L. E. Allen; T. S. Allen
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We report the discovery and characterization of a power law correlation between the local surface densities of Spitzer-identified, dusty young stellar objects and the column density of gas (as traced by near-IR extinction) in eight molecular clouds within 1 kpc and with 100 or more known YSOs. This correlation, which appears in data smoothed over size scales of ~1 pc, varies in quality from cloud to cloud; those clouds with tight correlations, MonR2 and Ophiuchus, are fit with power laws of...
Source: http://arxiv.org/abs/1107.0966v1
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by Sundar Vishwanathan
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We give a counting based proof of the Graham Pollak Theorem
Source: http://arxiv.org/abs/1007.1553v2
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by M. Ferrero; D. Salgado; J. L. Sanchez-Gomez
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It is argued that the traditional "realist" methodology of physics, according to which human concepts, laws and theories can grasp the essence of reality, is incompatible with the most fruitful interpretation of quantum formalism. The proof rests on the violation by quantum mechanics of the foundational principles of that methodology. An alternative methodology, in which the construction of sciences finishes at the level of human experience, as standard quantum theory strongly...
Source: http://arxiv.org/abs/1107.3366v1
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The bin packing problem is to find the minimum number of bins of size one to pack a list of items with sizes $a_1,..., a_n$ in $(0,1]$. Using uniform sampling, which selects a random element from the input list each time, we develop a randomized $O({n(\log n)(\log\log n)\over \sum_{i=1}^n a_i}+({1\over \epsilon})^{O({1\over\epsilon})})$ time $(1+\epsilon)$-approximation scheme for the bin packing problem. We show that every randomized algorithm with uniform random sampling needs $\Omega({n\over...
Source: http://arxiv.org/abs/1007.1260v3
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by Y. Fukui; H. Sano; J. Sato; K. Torii; H. Horachi; T. Hayakawa; N. M. McClure-Griffiths; G. Rowell; T. Inoue; S. Inutsuka; A. Kawamura; H. Yamamoto; T. Okuda; N. Mizuno; T. Onishi; A. Mizuno; H. Ogawa
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RX J1713.7$-$3946 is the most remarkable TeV $\gamma$-ray SNR which emits $\gamma$-rays in the highest energy range. We made a new combined analysis of CO and \ion{H}{1} in the SNR and derived the total protons in the interstellar medium (ISM). We have found that the inclusion of the \ion{H}{1} gas provides a significantly better spatial match between the TeV $\gamma$-rays and ISM protons than the H$_2$ gas alone. In particular, the southeastern rim of the $\gamma$-ray shell has a counterpart...
Source: http://arxiv.org/abs/1107.0508v4
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This paper considers sparse linear discriminant analysis of high-dimensional data. In contrast to the existing methods which are based on separate estimation of the precision matrix $\O$ and the difference $\de$ of the mean vectors, we introduce a simple and effective classifier by estimating the product $\O\de$ directly through constrained $\ell_1$ minimization. The estimator can be implemented efficiently using linear programming and the resulting classifier is called the linear programming...
Source: http://arxiv.org/abs/1107.3442v1
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by Tony Gherghetta; Alex Pomarol
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We show that when supersymmetry is broken at the TeV scale by strong dynamics, the Higgs sector of the MSSM can be drastically modified. This arises from possible sizeable mixings of the Higgs with the resonances of the strong sector. In particular the mass of the lightest Higgs boson can be significantly above the MSSM bound (~130 GeV). Furthermore only one Higgs doublet is strictly necessary, because the Yukawa couplings can have a very different structure compared to the MSSM. Using the...
Source: http://arxiv.org/abs/1107.4697v2
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by Ermin Wei; Asuman Ozdaglar; Ali Jadbabaie
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Most existing work uses dual decomposition and subgradient methods to solve Network Utility Maximization (NUM) problems in a distributed manner, which suffer from slow rate of convergence properties. This work develops an alternative distributed Newton-type fast converging algorithm for solving network utility maximization problems with self-concordant utility functions. By using novel matrix splitting techniques, both primal and dual updates for the Newton step can be computed using iterative...
Source: http://arxiv.org/abs/1005.2633v2
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We show that the three-dimensional layers-of-maxima problem can be solved in $o(n\log n)$ time in the word RAM model. Our algorithm runs in $O(n(\log \log n)^3)$ deterministic time or $O(n(\log\log n)^2)$ expected time and uses O(n) space. We also describe an algorithm that uses optimal O(n) space and solves the three-dimensional layers-of-maxima problem in $O(n\log n)$ time in the pointer machine model.
Source: http://arxiv.org/abs/1007.1593v2
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by Necdet Serhat Aybat; Garud Iyengar
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We propose a first-order augmented Lagrangian algorithm (FAL) for solving the basis pursuit problem. FAL computes a solution to this problem by inexactly solving a sequence of L1-regularized least squares sub-problems. These sub-problems are solved using an infinite memory proximal gradient algorithm wherein each update reduces to "shrinkage" or constrained "shrinkage". We show that FAL converges to an optimal solution of the basis pursuit problem whenever the solution is...
Source: http://arxiv.org/abs/1005.5582v2
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by Mark D. Roberts
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In a certain sense a perfect fluid is a generalization of a point particle. This leads to the question as to what is the corresponding generalization for extended objects. The lagrangian formulation of a perfect fluid is much generalized and this has as a particular example a fluid which is a classical generalization of a membrane, however there is as yet no indication of any relationship between their quantum theories.
Source: http://arxiv.org/abs/hep-th/0406164v2
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We study twisted ideal sheaves of small length on an irreducible principally polarized abelian surface (T,l). Using Fourier-Mukai techniques we associate certain jumping schemes to such sheaves and completely classify such loci. We give examples of applications to the enumerative geometry of T and show that no smooth genus 5 curve on such a surface can contain a g^1_3. We also describe explicitly the singular divisors in the linear system |2l|.
Source: http://arxiv.org/abs/1107.2549v2
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by Bing Zeng; Xueming Tang; Chingfang Hsu
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We present a framework for fully-simulatable $h$-out-of-$n$ oblivious transfer ($OT^{n}_{h}$) with security against non-adaptive malicious adversaries. The framework costs six communication rounds and costs at most $40n$ public-key operations in computational overhead. Compared with the known protocols for fully-simulatable oblivious transfer that works in the plain mode (where there is no trusted common reference string available) and proven to be secure under standard model (where there is no...
Source: http://arxiv.org/abs/1005.0043v3
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by Salvatore Catanese; Emilio Ferrara; Giacomo Fiumara; Francesco Pagano
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The process of design and development of virtual environments can be supported by tools and frameworks, to save time in technical aspects and focusing on the content. In this paper we present an academic framework which provides several levels of abstraction to ease this work. It includes state-of-the-art components we devised or integrated adopting open-source solutions in order to face specific problems. Its architecture is modular and customizable, the code is open-source.
Source: http://arxiv.org/abs/1107.0690v1
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by Albert Banchs; Andres Garcia-Saavedra; Pablo Serrano; Joerg Widmer
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Distributed Opportunistic Scheduling (DOS) is inherently harder than conventional opportunistic scheduling due to the absence of a central entity that has knowledge of all the channel states. With DOS, stations contend for the channel using random access; after a successful contention, they measure the channel conditions and only transmit in case of a good channel, while giving up the transmission opportunity when the channel conditions are poor. The distributed nature of DOS systems makes them...
Source: http://arxiv.org/abs/1107.4452v1
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Using ergodic theory, in this paper we present a Gel'fand-type spectral radius formula which states that the joint spectral radius is equal to the generalized spectral radius for a matrix multiplicative semigroup $\bS^+$ restricted to a subset that need not carry the algebraic structure of $\bS^+$. This generalizes the Berger-Wang formula. Using it as a tool, we study the absolute exponential stability of a linear switched system driven by a compact subshift of the one-sided Markov shift...
Source: http://arxiv.org/abs/1107.0124v1
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by Fano W. G.; S. Boggi; A. C. Razzitte
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This paper is devoted to the study and the obtaining of the general relation between the real part and the imaginary part of the magnetic susceptibility function in the Laplace domain. This new theoretical technique is general, and can be applied to any magnetic material, that can be considered like causal and Linear time invariant (LTI). A discussion of the causality which is extensively used in Physics has been done. To obtain the relations, some important concepts like Titchmarsh's theorem...
Source: http://arxiv.org/abs/1107.0419v1
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In a previous paper, we defined an operation $\mu$ that generalizes Turaev's cobracket for loops on a surface. We showed that, in contrast to the cobracket, this operation gives a formula for the minimum number of self-intersections of a loop in a given free homotopy class. In this paper we consider the corresponding question for virtual strings. We show that $\mu$ gives a bound on the minimal self-intersection number of a virtual string which is stronger than a bound given by Turaev's virtual...
Source: http://arxiv.org/abs/1107.4718v1
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The definition and measurement of magnetic reconnection in three-dimensional magnetic fields with multiple reconnection sites is a challenging problem, particularly in fields lacking null points. We propose a generalization of the familiar two-dimensional concept of a magnetic flux function to the case of a three-dimensional field connecting two planar boundaries. Using hyperbolic fixed points of the field line mapping, and their global stable and unstable manifolds, we define a unique flux...
Source: http://arxiv.org/abs/1107.0594v1
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A lower bound on the minimum error probability for multihypothesis testing is established. The bound, which is expressed in terms of the cumulative distribution function of the tilted posterior hypothesis distribution given the observation with tilting parameter theta larger than or equal to 1, generalizes an earlier bound due the Poor and Verdu (1995). A sufficient condition is established under which the new bound (minus a multiplicative factor) provides the exact error probability in the...
Source: http://arxiv.org/abs/1107.3474v1
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by Aaron Smith
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We determine the mixing time of a simple Gibbs sampler on the unit simplex, confirming a conjecture of D. Aldous. The upper bound is based on a two-step coupling, where the first step is a simple contraction argument and the second step is a non-Markovian coupling. We also present a MCMC-based perfect sampling algorithm that is based on our proof and which can be applied to Gibbs samplers that are harder to analyze.
Source: http://arxiv.org/abs/1107.5829v1
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We review an approach to observation-theory comparisons we call "Taste-Testing." In this approach, synthetic observations are made of numerical simulations, and then both real and synthetic observations are "tasted" (compared) using a variety of statistical tests. We first lay out arguments for bringing theory to observational space rather than observations to theory space. Next, we explain that generating synthetic observations is only a step along the way to the...
Source: http://arxiv.org/abs/1107.2827v1
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by Jason Baggett; Odile Bastille; Alexei Rybkin
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We discuss a new numerical schema for solving the initial value problem for the Korteweg-de Vries equation for large times. Our approach is based upon the Inverse Scattering Transform that reduces the problem to calculating the reflection coefficient of the corresponding Schr\"odinger equation. Using a step-like approximation of the initial profile and a fragmentation principle for the scattering data, we obtain an explicit recursion formula for computing the reflection coefficient,...
Source: http://arxiv.org/abs/1107.3540v1
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by Cyril Imbert; Régis Monneau; Hasnaa Zidani
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This paper is concerned with the study of a model case of first order Hamilton-Jacobi equations posed on a "junction", that is to say the union of a finite number of half-lines with a unique common point. The main result is a comparison principle. We also prove existence and stability of solutions. The two challenging difficulties are the singular geometry of the domain and the discontinuity of the Hamiltonian. As far as discontinuous Hamiltonians are concerned, these results seem to...
Source: http://arxiv.org/abs/1107.3250v2
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In Type III seesaw model the heavy neutrinos are contained in leptonic triplet representations. The Yukawa couplings of the triplet fermion and the left-handed neutrinos with the doublet Higgs field produce the Dirac mass terms. Together with the Majorana masses for the leptonic triplets, the light neutrinos obtain non-zero seesaw masses. We point out that it is also possible to have a quadruplet Higgs field to produce the Dirac mass terms to facilitate the seesaw mechanism. The vacuum...
Source: http://arxiv.org/abs/1107.5879v2
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by Chris Aholt; Bernd Sturmfels; Rekha Thomas
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Multiview geometry is the study of two-dimensional images of three-dimensional scenes, a foundational subject in computer vision. We determine a universal Groebner basis for the multiview ideal of n generic cameras. As the cameras move, the multiview varieties vary in a family of dimension 11n-15. This family is the distinguished component of a multigraded Hilbert scheme with a unique Borel-fixed point. We present a combinatorial study of ideals lying on that Hilbert scheme.
Source: http://arxiv.org/abs/1107.2875v1
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by Bum-Hoon Lee; Da-Wei Pang; Chanyong Park
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We give a review on our recent work arXiv:1006.0779 [hep-th] and arXiv:1006.1719 [hep-th], in which properties of holographic strange metals were investigated. The background is chosen to be anisotropic scaling solution in Einstein-Maxwell-Dilaton theory with a Liouville potential. The effects of bulk Maxwell field, an extra U(1) gauge field and probe D-branes on the DC conductivity, the DC Hall conductivity and the AC conductivity are extensively analyzed. We classify behaviors of the...
Source: http://arxiv.org/abs/1107.5822v2
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by Sakura Schafer-Nameki; Carlos Tamarit; Gonzalo Torroba
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We construct composite Higgs models admitting a weakly coupled Seiberg dual description. We focus on the possibility that only the up-type Higgs is an elementary field, while the down-type Higgs arises as a composite hadron. The model, based on a confining SQCD theory, breaks supersymmetry and electroweak symmetry dynamically and calculably. This simultaneously solves the \mu/B_\mu problem and explains the smallness of the bottom and tau masses compared to the top mass. The proposal is then...
Source: http://arxiv.org/abs/1005.0841v3
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by Raphaël Danchin; Piotr Bogus\law Mucha
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Here we investigate the Cauchy problem for the inhomogeneous Navier-Stokes equations in the whole $n$-dimensional space. Under some smallness assumption on the data, we show the existence of global-in-time unique solutions in a critical functional framework. The initial density is required to belong to the multiplier space of $\dot B^{n/p-1}_{p,1}(\R^n)$. In particular, piecewise constant initial densities are admissible data \emph{provided the jump at the interface is small enough}, and...
Source: http://arxiv.org/abs/1107.2763v1
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by Matthew D. Johnston; David Siegel; Gábor Szederkényi
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A numerically effective procedure for determining weakly reversible chemical reaction networks that are linearly conjugate to a known reaction network is proposed in this paper. The method is based on translating the structural and algebraic characteristics of weak reversibility to logical statements and solving the obtained set of linear (in)equalities in the framework of mixed integer linear programming. The unknowns in the problem are the reaction rate coefficients and the parameters of the...
Source: http://arxiv.org/abs/1107.1659v1
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by Tomasz Kociumaka; Marcin Kubica; Jakub Radoszewski; Wojciech Rytter; Tomasz Walen
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Periodicity in words is one of the most fundamental areas of text algorithms and combinatorics. Two classical and natural variations of periodicity are seeds and covers (also called quasiperiods). Linear-time algorithms are known for finding all the covers of a word, however in case of seeds, for the past 15 years only an $O(n\log{n})$ time algorithm was known (Iliopoulos, Moore and Park, 1996). Finding an $o(n\log{n})$ time algorithm for the all-seeds problem was mentioned as one of the most...
Source: http://arxiv.org/abs/1107.2422v1
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by Can Baskent
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Notion of strategy in game theory is static and presumably constructed before the game play. The static, pre-determined notion of strategies falls short analyzing perfect information games. Because, we, people, do not strategize as such even in perfect information games - largely because we are not logically omniscient, and we have limited computational power and bounded memory. In this paper, we focus on what we call move updates where some moves become unavailable during the game. Our goal...
Source: http://arxiv.org/abs/1107.4931v1
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We review and then combine two aspects of the theory of bundle gerbes. The first concerns lifting bundle gerbes and connections on those, developed by Murray and Gomi. Lifting gerbes represent obstructions against extending the structure group of a principal bundle. The second is the transgression of gerbes to loop spaces, initiated by Brylinski and McLaughlin and with recent contributions of the author. Combining these two aspects, we obtain a new formulation of lifting problems in terms of...
Source: http://arxiv.org/abs/1007.5373v2
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by James W. Anderson; Aaron Wootton
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We prove that the number of distinct group actions on compact Riemann surfaces of a fixed genus $\sigma \geq 2$ is at least quadratic in $\sigma$. We do this through the introduction of a coarse signature space, the space $\mathcal{K}_\sigma$ of {\em skeletal signatures} of group actions on compact Riemann surfaces of genus $\sigma$. We discuss the basic properties of $\mathcal{K}_\sigma$ and present a full conjectural description.
Source: http://arxiv.org/abs/1107.3433v2
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by Calanit Dotan; Elena M. Rossi; Nir J. Shaviv
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We consider a scenario where supermassive black holes form through direct accumulation of gas at the centre of proto-galaxies. In the first stage, the accumulated gas forms a super-massive star whose core collapses when the nuclear fuel is exhausted, forming a black hole of $M_{\rm BH} \approx 100 M_{\sun}$. As the black hole starts accreting, it inflates the surrounding dense gas into an almost hydrostatic self-gravitating envelope, with at least 10-100 times the mass of the hole. We find that...
Source: http://arxiv.org/abs/1107.3562v1
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by Fabien Campillo; Dominique Hervé; Angelo Raherinirina; Rivo Rakotozafy
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The application of the Markov chain to modeling agricultural succession is well known. In most cases, the main problem is the inference of the model, i.e. the estimation of the transition matrix. In this work we present methods to estimate the transition matrix from historical observations. In addition to the estimator of maximum likelihood (MLE), we also consider the Bayes estimator associated with the Jeffreys prior. This Bayes estimator will be approximated by a Markov chain Monte Carlo...
Source: http://arxiv.org/abs/1107.0785v1
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by Jie Sun; Erik M. Bollt; Mason A. Porter; Marian S. Dawkins
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We formulate a mathematical model for daily activities of a cow (eating, lying down, and standing) in terms of a piecewise affine dynamical system. We analyze the properties of this bovine dynamical system representing the single animal and develop an exact integrative form as a discrete-time mapping. We then couple multiple cow "oscillators" together to study synchrony and cooperation in cattle herds. We comment on the relevant biology and discuss extensions of our model. With this...
Source: http://arxiv.org/abs/1005.1381v2
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by D. Cohen; M. Cooper; P. Jeavons; A. Krokhin
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Many researchers in artificial intelligence are beginning to explore the use of soft constraints to express a set of (possibly conflicting) problem requirements. A soft constraint is a function defined on a collection of variables which associates some measure of desirability with each possible combination of values for those variables. However, the crucial question of the computational complexity of finding the optimal solution to a collection of soft constraints has so far received very...
Source: http://arxiv.org/abs/1107.0043v1
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by D. T. O'Dea; C. N. Clark; C. R. Contaldi; C. J. MacTavish
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The upcoming generation of cosmic microwave background (CMB) experiments face a major challenge in detecting the weak cosmic B-mode signature predicted as a product of primordial gravitational waves. To achieve the required sensitivity these experiments must have impressive control of systematic effects and detailed understanding of the foreground emission that will influence the signal. In this paper, we present templates of the intensity and polarisation of emission from one of the main...
Source: http://arxiv.org/abs/1107.4612v2
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We propose new equations of motion under the theory of the Brownian motion to connect the states of quantum, diffusion, soliton, and periodic localization. The new equations are nothing but the classical equations of motion with two additional terms and the one of them can be regarded as the the quantum potential. By choosing a parameter space, various important states are obtained. Further, the equations contain other interesting phenomena such as general dynamics of diffusion process,...
Source: http://arxiv.org/abs/1107.4329v1
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by D. W. Longcope; S. E. Guidoni
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Super-hot looptop sources, detected in some large solar flares, are compact sources of HXR emission with spectra matching thermal electron populations exceeding 30 megakelvins. High observed emission measure, as well as inference of electron thermalization within the small source region, both provide evidence of high densities at the looptop; typically more than an order of magnitude above ambient. Where some investigators have suggested such density enhancement results from a rapid enhancement...
Source: http://arxiv.org/abs/1107.2441v1
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by Michael G. Gowanlock; David R. Patton; Sabine M. McConnell
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We present a model of the Galactic Habitable Zone (GHZ), described in terms of the spatial and temporal dimensions of the Galaxy that may favour the development of complex life. The Milky Way galaxy is modelled using a computational approach by populating stars and their planetary systems on an individual basis using Monte-Carlo methods. We begin with well-established properties of the disk of the Milky Way, such as the stellar number density distribution, the initial mass function, the star...
Source: http://arxiv.org/abs/1107.1286v1