22,519 research outputs found
Collapse transition in polymer models with multiple monomers per site and multiple bonds per edge
We present results from extensive Monte Carlo simulations of polymer models
where each lattice site can be visited by up to monomers and no restriction
is imposed on the number of bonds on each lattice edge. These \textit{multiple
monomer per site} (MMS) models are investigated on the square and cubic
lattices, for and , by associating Boltzmann weights ,
and to sites visited by 1, 2 and
3 monomers, respectively. Two versions of the MMS models are considered for
which immediate reversals of the walks are allowed (RA) or forbidden (RF). In
contrast to previous simulations of these models, we find the same
thermodynamic behavior for both RA and RF versions. In three-dimensions, the
phase diagrams - in space - are featured by coil and
globule phases separated by a line of points, as thoroughly
demonstrated by the metric , crossover and entropic
exponents. The existence of the -lines is also confirmed by the second
virial coefficient. This shows that no discontinuous collapse transition exists
in these models, in contrast to previous claims based on a weak bimodality
observed in some distributions, which indeed exists in a narrow region very
close to the -line when . Interestingly, in
two-dimensions, only a crossover is found between the coil and globule phases
Bump-on-tail instability of twisted excitations in rotating cold atomic clouds
We develop a kinetic theory for twisted density waves (phonons), carrying a
finite amount of orbital angular momentum, in large magneto optical traps,
where the collective processes due to the exchange of scattered photons are
considered. Explicit expressions for the dispersion relation and for the
kinetic (Landau) damping are derived and contributions from the orbital angular
momentum are discussed. We show that for rotating clouds, exhibiting
ring-shaped structures, phonons carrying orbital angular momentum can cross the
instability threshold and grow out of noise, while the usual plane wave
solutions are kinetically damped.Comment: 5 pages, 5 figure
A class of cubic Rauzy Fractals
In this paper, we study arithmetical and topological properties for a class
of Rauzy fractals given by the polynomial
where is an integer. In particular, we prove the number of neighbors
of in the periodic tiling is equal to . We also give
explicitly an automaton that generates the boundary of . As a
consequence, we prove that is homeomorphic to a topological
disk
Locally Inertial Reference Frames in Lorentzian and Riemann-Cartan Spacetimes
In this paper we scrutinize the concept of locally inertial reference frames
(LIRF) in Lorentzian and Riemann-Cartan spacetime structures. We present
rigorous mathematical definitions for those objects, something that needs
preliminary a clear mathematical distinction between the concepts of observers,
reference frames, naturally adapted coordinate functions to a given reference
frame and which properties may characterize an inertial reference frame (if
any) in the Lorentzian and Riemann-Cartan structures. We hope to have clarified
some eventual obscure issues associated to the concept of LIRF appearing in the
literature, in particular the relationship between LIRFs in Lorentzian and
Riemann-Cartan spacetimes and Einstein's most happy though, i.e., the
equivalence principle.Comment: In this version a new reference has been added, some misprints and
typos have been corrected and some few sentences in two remarks and in the
conclusions have been changed for better intelligibilit
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