23,372 research outputs found
Isostaticity and the solidification of semiflexible polymer melts
Using molecular dynamics simulations of a tangent-soft-sphere bead-spring
polymer model, we examine the degree to which semiflexible polymer melts
solidify at isostaticity. Flexible and stiff chains crystallize when they are
isostatic as defined by appropriate degree-of-freedom-counting arguments.
Semiflexible chains also solidify when isostatic if a generalized isostaticity
criterion that accounts for the slow freezing out of configurational freedom as
chain stiffness increases is employed. The dependence of the average
coordination number at solidification on chains' characteristic ratio
has the same functional form [] as the
dependence of the average coordination number at jamming on
in athermal systems, suggesting that jamming-related phenomena play
a significant role in thermal polymer solidification
Stability of the Einstein static universe in f(R) gravity
We analyze the stability of the Einstein static universe by considering
homogeneous scalar perturbations in the context of f(R) modified theories of
gravity. By considering specific forms of f(R), the stability regions of the
solutions are parameterized by a linear equation of state parameter w=p/rho.
Contrary to classical general relativity, it is found that in f(R) gravity a
stable Einstein cosmos with a positive cosmological constant does indeed exist.
Thus, we are lead to conclude that, in principle, modifications in f(R) gravity
stabilize solutions which are unstable in general relativity.Comment: 7 pages, 2 figures, 2 tables; references adde
Influence of the flow on the anchoring of nematic liquid crystals on a Langmuir-Blodgett monolayer studied by optical second-harmonic generation
The influence of capillary flow on the alignment of the nematic liquid
crystal MBBA on fatty acid Langmuir-Blodgett monolayers was studied by optical
second-harmonic generation. The surface dipole sensitivity of the technique
allows probing the orientation of the first liquid crystal monolayer in the
presence of the liquid crystal bulk. It was found that capillary flow causes
the first monolayer of liquid crystal molecules in contact with the fatty acid
monolayer to be oriented in the flow direction with a large pretilt (78
degrees), resulting in a quasi-planar alignment with splay-bend deformation of
the nematic director in the bulk. itself is affected by the flow. The
quasi-planar flow-induced alignment was found to be metastable. Once the flow
ceases, circular domains of homeotropic orientation nucleate in the sample and
expand until the whole sample becomes homeotropic. This relaxation process from
flow-induced quasi-planar to surface-induced homeotropic alignment was also
monitored by SHG. It was found that in the homeotropic state the first nematic
layer presents a pretilt of 38 degrees almost isotropically distributed in the
plane of the cell, with a slight preference for the direction of the previous
flow.Comment: LaTeX2e article, 11 figures, 17 EPS files, submitte
Fermionization of a strongly interacting Bose-Fermi mixture in a one-dimensional harmonic trap
We consider a strongly interacting one-dimensional (1D) Bose-Fermi mixture
confined in a harmonic trap. It consists of a Tonks-Girardeau (TG) gas (1D Bose
gas with repulsive hard-core interactions) and of a non-interacting Fermi gas
(1D spin-aligned Fermi gas), both species interacting through hard-core
repulsive interactions. Using a generalized Bose-Fermi mapping, we determine
the exact particle density profiles, momentum distributions and behaviour of
the mixture under 1D expansion when opening the trap. In real space, bosons and
fermions do not display any phase separation: the respective density profiles
extend over the same region and they both present a number of peaks equal to
the total number of particles in the trap. In momentum space the bosonic
component has the typical narrow TG profile, while the fermionic component
shows a broad distribution with fermionic oscillations at small momenta. Due to
the large boson-fermion repulsive interactions, both the bosonic and the
fermionic momentum distributions decay as at large momenta, like in
the case of a pure bosonic TG gas. The coefficient is related to the
two-body density matrix and to the bosonic concentration in the mixture. When
opening the trap, both momentum distributions "fermionize" under expansion and
turn into that of a Fermi gas with a particle number equal to the total number
of particles in the mixture.Comment: revised version; 8 pages, 7 figure
Uniqueness of infrared asymptotics in Landau gauge Yang-Mills theory
We uniquely determine the infrared asymptotics of Green functions in Landau
gauge Yang-Mills theory. They have to satisfy both,
Dyson-Schwinger equations and functional renormalisation group equations.
Then, consistency fixes the relation between the infrared power laws of these
Green functions. We discuss consequences for the interpretation of recent
results from lattice QCD.Comment: 24 pages, 8 figure
Phasing of gravitational waves from inspiralling eccentric binaries at the third-and-a-half post-Newtonian order
We obtain an efficient description for the dynamics of nonspinning compact
binaries moving in inspiralling eccentric orbits to implement the phasing of
gravitational waves from such binaries at the 3.5 post-Newtonian (PN) order.
Our computation heavily depends on the phasing formalism, presented in [T.
Damour, A. Gopakumar, and B. R. Iyer, Phys. Rev. D \textbf{70}, 064028 (2004)],
and the 3PN accurate generalized quasi-Keplerian parametric solution to the
conservative dynamics of nonspinning compact binaries moving in eccentric
orbits, available in [R.-M. Memmesheimer, A. Gopakumar, and G. Sch\"afer, Phys.
Rev. D \textbf{70}, 104011 (2004)]. The gravitational-wave (GW) polarizations
and with 3.5PN accurate phasing should be useful for the
earth-based GW interferometers, current and advanced, if they plan to search
for gravitational waves from inspiralling eccentric binaries. Our results will
be required to do \emph{astrophysics} with the proposed space-based GW
interferometers like LISA, BBO, and DECIGO.Comment: 22 pages including 2 figures; submitted to PR
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