3,151 research outputs found
Fluctuating Elastic Rings: Statics and Dynamics
We study the effects of thermal fluctuations on elastic rings. Analytical
expressions are derived for correlation functions of Euler angles, mean square
distance between points on the ring contour, radius of gyration, and
probability distribution of writhe fluctuations. Since fluctuation amplitudes
diverge in the limit of vanishing twist rigidity, twist elasticity is essential
for the description of fluctuating rings. We find a crossover from a small
scale regime in which the filament behaves as a straight rod, to a large scale
regime in which spontaneous curvature is important and twist rigidity affects
the spatial configurations of the ring. The fluctuation-dissipation relation
between correlation functions of Euler angles and response functions, is used
to study the deformation of the ring by external forces. The effects of inertia
and dissipation on the relaxation of temporal correlations of writhe
fluctuations, are analyzed using Langevin dynamics.Comment: 43 pages, 9 Figure
Energy Dissipation and Regularity for a Coupled Navier-Stokes and Q-Tensor System
We study a complex non-newtonian fluid that models the flow of nematic liquid
crystals. The fluid is described by a system that couples a forced
Navier-Stokes system with a parabolic-type system. We prove the existence of
global weak solutions in dimensions two and three. We show the existence of a
Lyapunov functional for the smooth solutions of the coupled system and use the
cancellations that allow its existence to prove higher global regularity, in
dimension two. We also show the weak-strong uniqueness in dimension two
Note on Global Regularity for 2D Oldroyd-B Fluids with Diffusive Stress
We prove global regularity of solutions of Oldroyd-B equations in 2 spatial
dimensions with spatial diffusion of the polymeric stresses
Specific Heat of Sr4Ru3O10
We have measured the specific heat of single crystals of the triple-layer
Ruddlesden-Popper material, Sr4Ru3O10, grown both in an image furnace and by
flux-growth. The flux grown sample has a sharp mean-field-like anomaly at the
onset of magnetic order, Tc = 102 K, but a much broader anomaly, indicative of
residual heterogeneity, is observed for the image furnace sample. Even for the
flux grown sample, however, the anomaly is at least an order of magnitude
smaller than one would expect for complete ordering of the spins. Neither
sample exhibits an anomaly at Tm ~ 50 K, where magnetic measurements suggest
that basal plane antiferromagnetism sets in. Anomalous behavior (e.g.
consistent with a term in the specific heat ~ T^3/2 as would be observed for a
three-dimensional ferromagnet with weak exchange) is observed at low
temperatures for both samples, indicative of the unusual magnetic order in this
material.Comment: 14 pages including 4 figure
Cultural differences in intimacy: The influence of gender-role ideology and individualism-collectivism
Two studies examined emotional intimacy in European Canadian and Chinese Canadian dating relationships. Cultural differences in gender-role ideology and individualism–collectivism
were hypothesized to differentially contribute to selfdisclosure and responsiveness, and in turn, intimacy. Study 1 revealed that Chinese Canadians’ lower intimacy relative to European Canadians was mediated by their greater gender-role traditionalism but not by their individualism or collectivism. Study 2 further linked greater gender-role traditionalism to
lower self-disclosure, and in turn, lower intimacy. Results also revealed that Chinese Canadians’ lower intimacy mediated their lower relationship satisfaction and higher rate of relationship termination in Study 1, but that Chinese Canadians were not any more likely to terminate their relationships in Study 2
Observational Constraints on the Modified Gravity Model (MOG) Proposed by Moffat: Using the Magellanic System
A simple model for the dynamics of the Magellanic Stream (MS), in the
framework of modified gravity models is investigated. We assume that the galaxy
is made up of baryonic matter out of context of dark matter scenario. The model
we used here is named Modified Gravity (MOG) proposed by Moffat (2005). In
order to examine the compatibility of the overall properties of the MS under
the MOG theory, the observational radial velocity profile of the MS is compared
with the numerical results using the fit method. In order to obtain
the best model parameters, a maximum likelihood analysis is performed. We also
compare the results of this model with the Cold Dark Matter (CDM) halo model
and the other alternative gravity model that proposed by Bekenstein (2004), so
called TeVeS. We show that by selecting the appropriate values for the free
parameters, the MOG theory seems to be plausible to explain the dynamics of the
MS as well as the CDM and the TeVeS models.Comment: 14 pages, 3 Figures, accepted in Int. J. Theor. Phy
Spintronic properties of one-dimensional electron gas in graphene armchair ribbons
We have investigated, using effective mass approach (EMA), magnetic
properties of a one-dimensional electron gas in graphene armchair ribbons when
the electrons of occupy only the lowest conduction subband. We find that
magnetic properties of the one-dimensional electron gas may depend sensitively
on the width of the ribbon. For ribbon widths , a critical point
separates ferromagnetic and paramagnetic states while for
paramagnetic state is stable ( is an integer and is the length of
the unit cell). These width-dependent properties are a consequence of
eigenstates that have a subtle width-dependent mixture of and
states, and can be understood by examining the wavefunction
overlap that appears in the expression for the many-body exchange self-energy.
Ferromagnetic and paramagnetic states may be used for spintronic purposes.Comment: 5 pages, 6 figure
Topological Phase Transition and Electrically Tunable Diamagnetism in Silicene
Silicene is a monolayer of silicon atoms forming a honeycomb lattice. The
lattice is actually made of two sublattices with a tiny separation. Silicene is
a topological insulator, which is characterized by a full insulating gap in the
bulk and helical gapless edges. It undergoes a phase transition from a
topological insulator to a band insulator by applying external electric field.
Analyzing the spin Chern number based on the effective Dirac theory, we find
their origin to be a pseudospin meron in the momentum space. The peudospin
degree of freedom arises from the two-sublattice structure. Our analysis makes
clear the mechanism how a phase transition occurs from a topological insulator
to a band insulator under increasing electric field. We propose a method to
determine the critical electric field with the aid of diamagnetism of silicene.
Diamagnetism is tunable by the external electric field, and exhibits a singular
behaviour at the critical electric field. Our result is important also from the
viewpoint of cross correlation between electric field and magnetism. Our
finding will be important for future electro-magnetic correlated devices.Comment: 4 pages,5 figure
Collective Resistance in Microbial Communities by Intracellular Antibiotic Deactivation.
The structure and composition of bacterial communities can compromise antibiotic efficacy. For example, the secretion of β-lactamase by individual bacteria provides passive resistance for all residents within a polymicrobial environment. Here, we uncover that collective resistance can also develop via intracellular antibiotic deactivation. Real-time luminescence measurements and single-cell analysis demonstrate that the opportunistic human pathogen Streptococcus pneumoniae grows in medium supplemented with chloramphenicol (Cm) when resistant bacteria expressing Cm acetyltransferase (CAT) are present. We show that CAT processes Cm intracellularly but not extracellularly. In a mouse pneumonia model, more susceptible pneumococci survive Cm treatment when coinfected with a CAT-expressing strain. Mathematical modeling predicts that stable coexistence is only possible when antibiotic resistance comes at a fitness cost. Strikingly, CAT-expressing pneumococci in mouse lungs were outcompeted by susceptible cells even during Cm treatment. Our results highlight the importance of the microbial context during infectious disease as a potential complicating factor to antibiotic therapy
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