21,514 research outputs found
Entropic aging and extreme value statistics
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
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
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
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
We prove Boydâs âunexpected coincidenceâ 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 â y + xÂł â x + kxy whose zero loci define elliptic curves for k â 0, ± 3
Septin filament organization in Saccharomyces cerevisiae.
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
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
class) are found to have rising rotation curves, while those with
falling rotation curves belong to the tightly wound 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
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