21,099 research outputs found

    Entropic aging and extreme value statistics

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    Entropic aging consists in a progressive slowing down of the low-temperature dynamics of a glassy system due to the rarefaction of downwards directions on the energy landscape, as lower and lower energy levels are reached. A prototypical model exhibiting this scenario is the Barrat-M\'ezard model. We argue that in the zero-temperature limit, this model precisely corresponds to a dynamical realization of extreme value statistics, providing an interesting connection between the two fields. This mapping directly yields the long-time asymptotic shape of the dynamical energy distribution, which is then one of the standard extreme value distributions (Gumbel, Weibull or Fr\'echet), thus restricting the class of asymptotic energy distributions with respect to the original preasymptotic results. We also briefly discuss similarities and differences between the Barrat-M\'ezard model and undriven dissipative systems like granular gases.Comment: 8 pages, to appear in J. Phys.

    Weak Homology of Bright Elliptical Galaxies

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    Studies of the Fundamental Plane of early-type galaxies, from small to intermediate redshifts, are often carried out under the guiding principle that the Fundamental Plane reflects the existence of an underlying mass-luminosity relation for such galaxies, in a scenario where elliptical galaxies are homologous systems in dynamical equilibrium. Here I will re-examine the issue of whether empirical evidence supports the view that significant systematic deviations from strict homology occur in the structure and dynamics of bright elliptical galaxies. In addition, I will discuss possible mechanisms of dynamical evolution for these systems, in the light of some classical thermodynamical arguments and of recent N-body simulations for stellar systems under the influence of weak collisionality.Comment: 13 pages, 7 figures, to appear in "Galaxies and Chaos", Contopoulos, G. and Voglis, N. (eds), Lecture Notes in Physics, Springer-Verlag, Heidelber

    On trisecant lines to White surfaces

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    In this work we show that the only White surface in the projective 5-space having an excess of trisecant lines is the polygonal surface constructed by C. Segre. The proof follows the line of B.Gambier's beautiful approach to this question and is intended to give it modern rigour. This has some implications on the geometry of the generic point of the principal componant of the Hilbert scheme of 18 points in the projective plane special in degree 5.Comment: 25 page

    Non-Involutive Constrained Systems and Hamilton-Jacobi Formalism

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    In this work we discuss the natural appearance of the Generalized Brackets in systems with non-involutive (equivalent to second class) constraints in the Hamilton-Jacobi formalism. We show how a consistent geometric interpretation of the integrability conditions leads to the reduction of degrees of freedom of these systems and, as consequence, naturally defines a dynamics in a reduced phase space.Comment: 12 page

    On the Mahler measure of hyperelliptic families

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    We prove Boyd’s “unexpected coincidence” of the Mahler measures for two families of two-variate polynomials defining curves of genus 2. We further equate the same measures to the Mahler measures of polynomials yÂł − y + xÂł − x + kxy whose zero loci define elliptic curves for k ≠ 0, ± 3

    Septin filament organization in Saccharomyces cerevisiae.

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    Septins are a family of GTP-binding, membrane-interacting cytoskeletal proteins, highly conserved and essential in all eukaryotes (with the exception of plants). Septins play important roles in a number of cellular events that involve membrane remodeling and compartmentalization. One such event is cytokinesis, the last stage of cell division. While cytokinesis is ultimately achieved via the mechanical contraction of an actomyosin ring at the septum, determination of the location where cytokinesis will take place, and recruitment of factors involved in signaling events leading to septation requires the activity of septins. We are working towards dissecting the properties of septins from the budding yeast Saccharomyces cerevisiae, where they were first discovered as cell cycle mutants. In our studies we have employed several complementary electron microscopy techniques to describe the organization and structure of septins both in vitro and in situ

    Dust Penetrated Arm Classes: Insights from rising and falling rotation curves

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    In the last decade, near-infrared imaging has highlighted the decoupling of gaseous and old stellar disks: the morphologies of optical (Population I) tracers compared to the old stellar disk morphology, can be radically different. Galaxies which appear multi-armed and even flocculent in the optical may show significant Grand-Design spirals in the near-infrared. Furthermore, the optically determined Hubble classification scheme does not provide a sound way of classifying dust-penetrated stellar disks: spiral arm pitch angles (when measured in the near-infrared) do not correlate with Hubble type. The dust--penetrated classification scheme of Block & Puerari provides an alternative classification based on near-infrared morphology, and which is thus more closely linked to the dominant stellar mass component. Here we present near--infrared K band images of 14 galaxies, on which we have performed a Fourier analysis of the spiral structure in order to determine their near-infrared pitch angles and dust--penetrated arm classes. We have also used the rotation curve data of Mathewson et al. to calculate the rates of shear in the stellar disks of these galaxies. We find a correlation between near-infrared pitch angle and rate of shear: galaxies with wide open arms (the γ\gamma class) are found to have rising rotation curves, while those with falling rotation curves belong to the tightly wound α\alpha bin. The major determinant of near-infrared spiral arm pitch angle is the distribution of matter within the galaxy concerned. The correlation reported in this study provides the physical basis underpinning spiral arm classes in the dust-penetrated regime and underscores earlier spectroscopic findings by Burstein and Rubin that Hubble type and mass distributions are unrelated.Comment: 13 pages, accepted for publication in MNRAS. For full paper go to http://webfiles.uci.edu/mseigar/papers/Seigar_DPclass.pd