22,984 research outputs found
Kovacs effects in an aging molecular liquid
We study by means of molecular dynamics simulations the aging behavior of a
molecular model of ortho-terphenyl. We find evidence of a a non-monotonic
evolution of the volume during an isothermal-isobaric equilibration process, a
phenomenon known in polymeric systems as Kovacs effect. We characterize this
phenomenology in terms of landscape properties, providing evidence that, far
from equilibrium, the system explores region of the potential energy landscape
distinct from the one explored in thermal equilibrium. We discuss the relevance
of our findings for the present understanding of the thermodynamics of the
glass state.Comment: RevTeX 4, 4 pages, 5 eps figure
Extreme Covariant Quantum Observables in the Case of an Abelian Symmetry Group and a Transitive Value Space
We represent quantum observables as POVMs (normalized positive operator
valued measures) and consider convex sets of observables which are covariant
with respect to a unitary representation of a locally compact Abelian symmetry
group . The value space of such observables is a transitive -space. We
characterize the extreme points of covariant observables and also determine the
covariant extreme points of the larger set of all quantum observables. The
results are applied to position, position difference and time observables.Comment: 23 page
Homogenization of the planar waveguide with frequently alternating boundary conditions
We consider Laplacian in a planar strip with Dirichlet boundary condition on
the upper boundary and with frequent alternation boundary condition on the
lower boundary. The alternation is introduced by the periodic partition of the
boundary into small segments on which Dirichlet and Neumann conditions are
imposed in turns. We show that under the certain condition the homogenized
operator is the Dirichlet Laplacian and prove the uniform resolvent
convergence. The spectrum of the perturbed operator consists of its essential
part only and has a band structure. We construct the leading terms of the
asymptotic expansions for the first band functions. We also construct the
complete asymptotic expansion for the bottom of the spectrum
On the effect of variable identification on the essential arity of functions
We show that every function of several variables on a finite set of k
elements with n>k essential variables has a variable identification minor with
at least n-k essential variables. This is a generalization of a theorem of
Salomaa on the essential variables of Boolean functions. We also strengthen
Salomaa's theorem by characterizing all the Boolean functions f having a
variable identification minor that has just one essential variable less than f.Comment: 10 page
Equilibrium and out of equilibrium thermodynamics in supercooled liquids and glasses
We review the inherent structure thermodynamical formalism and the
formulation of an equation of state for liquids in equilibrium based on the
(volume) derivatives of the statistical properties of the potential energy
surface. We also show that, under the hypothesis that during aging the system
explores states associated to equilibrium configurations, it is possible to
generalize the proposed equation of state to out-of-equilibrium conditions. The
proposed formulation is based on the introduction of one additional parameter
which, in the chosen thermodynamic formalism, can be chosen as the local minima
where the slowly relaxing out-of-equilibrium liquid is trapped.Comment: 7 pages, 4 eps figure
Oscillation mode linewidths and heights of 23 main-sequence stars observed by Kepler
Solar-like oscillations have been observed by Kepler and CoRoT in many
solar-type stars, thereby providing a way to probe the stars using
asteroseismology. We provide the mode linewidths and mode heights of the
oscillations of various stars as a function of frequency and of effective
temperature. We used a time series of nearly two years of data for each star.
The 23 stars observed belong to the simple or F-like category. The power
spectra of the 23 main-sequence stars were analysed using both maximum
likelihood estimators and Bayesian estimators, providing individual mode
characteristics such as frequencies, linewidths, and mode heights. We study the
source of systematic errors in the mode linewidths and mode heights, and we
present a way to correct these errors with respect to a common reference fit.
Using the correction, we could explain all sources of systematic errors, which
could be reduced to less than 15% for mode linewidths and heights, and
less than 5% for amplitude, when compared to the reference fit. The effect
of a different estimated stellar background and a different estimated splitting
will provide frequency-dependent systematic errors that might affect the
comparison with theoretical mode linewidth and mode height, therefore affecting
the understanding of the physical nature of these parameters. All other sources
of relative systematic errors are less dependent upon frequency. We also
provide the dependence of the so-called linewidth dip, in the middle of the
observed frequency range, as a function of effective temperature. We show that
the depth of the dip decreases with increasing effective temperature. The
dependence of the dip on effective temperature may imply that the mixing length
parameter or the convective flux may increase with effective
temperature.Comment: Accepted by A&A, 38 pages, 35 figures, 26 table
On non-completely positive quantum dynamical maps on spin chains
The new arguments based on Majorana fermions indicating that non-completely
positive maps can describe open quantum evolution are presented.Comment: published; small change
Heavy-Light Mesons with Quenched Lattice NRQCD: Results on Decay Constants
We present a quenched lattice calculation of heavy-light meson decay
constants, using non-relativistic (NRQCD) heavy quarks in the mass region of
the quark and heavier, and clover-improved light quarks. The NRQCD
Hamiltonian and the heavy-light current include the corrections at first order
in the expansion in the inverse heavy quark mass. We study the dependence of
the decay constants on the heavy meson mass , for light quarks with the tree
level ( = 1), as well as the tadpole improved clover coefficient. We
compare decay constants from NRQCD with results from clover () heavy
quarks.
Having calculated the current renormalisation constant in one-loop
perturbation theory, we demonstrate how the heavy mass dependence of the
pseudoscalar decay constants changes after renormalisation. For the first time,
we quote a result for from NRQCD including the full one-loop matching
factors at .Comment: 45 pages, latex, 24 postscript figure
Exact two-spinon dynamical correlation function of the Heisenberg model
We derive the exact contribution of two spinons to the dynamical correlation
function of the spin-1/2 Heisenberg model. For this, we use the isotropic
limits of the exact form factors that have been recently computed through the
quantum affine symmetry of the anisotropic Heisenberg model Comment: 9 pages, Latex, 2 corrections of coefficient
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