20,067 research outputs found
Models of dynamic extraction of lipid tethers from cell membranes
When a ligand that is bound to an integral membrane receptor is pulled, the
membrane and the underlying cytoskeleton can deform before either the membrane
delaminates from the cytoskeleton or the ligand detaches from the receptor. If
the membrane delaminates from the cytoskeleton, it may be further extruded and
form a membrane tether. We develop a phenomenological model for this processes
by assuming that deformations obey Hooke's law up to a critical force at which
the cell membrane locally detaches from the cytoskeleton and a membrane tether
forms. We compute the probability of tether formation and show that they can be
extruded only within an intermediate range of force loading rates and pulling
velocities. The mean tether length that arises at the moment of ligand
detachment is computed as are the force loading rates and pulling velocities
that yield the longest tethers.Comment: 16 pages, 7 figure
Ising metamagnets in thin film geometry: equilibrium properties
Artificial antiferromagnets and synthetic metamagnets have attracted much
attention recently due to their potential for many different applications.
Under some simplifying assumptions these systems can be modeled by thin Ising
metamagnetic films. In this paper we study, using both the Wang/Landau scheme
and importance sampling Monte Carlo simulations, the equilibrium properties of
these films. On the one hand we discuss the microcanonical density of states
and its prominent features. On the other we analyze canonically various global
and layer quantities. We obtain the phase diagram of thin Ising metamagnets as
a function of temperature and external magnetic field. Whereas the phase
diagram of the bulk system only exhibits one phase transition between the
antiferromagnetic and paramagnetic phases, the phase diagram of thin Ising
metamagnets includes an additional intermediate phase where one of the surface
layers has aligned itself with the direction of the applied magnetic field.
This additional phase transition is discontinuous and ends in a critical end
point. Consequently, it is possible to gradually go from the antiferromagnetic
phase to the intermediate phase without passing through a phase transition.Comment: 8 figures, accepted for publication in Physical Review
Ward Identities in Non-equilibrium QED
We verify the QED Ward identity for the two- and three -point functions at
non-equilibrium in the HTL limit. We use the Keldysh formalism of real time
finite temperature field theory. We obtain an identity of the same form as the
Ward identity for a set of one loop self-energy and one loop three-point vertex
diagrams which are constructed from HTL effective propagators and vertices.Comment: 19 pages, RevTex, 4 PostScript figures, revised version to be
published in Phys. Rev.
Direct measurement of decoherence for entanglement between a photon and stored atomic excitation
Violations of a Bell inequality are reported for an experiment where one of
two entangled qubits is stored in a collective atomic memory for a user-defined
time delay. The atomic qubit is found to preserve the violation of a Bell
inequality for storage times up to 21 microseconds, 700 times longer than the
duration of the excitation pulse that creates the entanglement. To address the
question of the security of entanglement-based cryptography implemented with
this system, an investigation of the Bell violation as a function of the
cross-correlation between the generated nonclassical fields is reported, with
saturation of the violation close to the maximum value allowed by quantum
mechanics.Comment: 4 pages, 3 figures. Minor changes. Published versio
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Health-related quality of life and depression among participants in the Sjögren's International Collaborative Clinical Alliance registry.
ObjectiveTo examine health-related quality of life (HRQoL) and depression among participants in an international Sjögren's syndrome (SS) registry, comparing those with and without SS.MethodsCross-sectional study of participants in the Sjögren's International Collaborative Clinical Alliance (SICCA) registry. The 2016 American College of Rheumatology/European League Against Rheumatism SS classification criteria were used to determine disease status. HRQoL was assessed using the Short Form 12, version 2 Health Survey to derive scores for physical component summary (PCS) and mental component summary (MCS). Depression was assessed using the 9-Item Patient Health Questionnaire. Multivariate linear and logistic regression analyses were performed to identify predictors of HRQoL and depression while controlling for potential confounders.ResultsAmong 2401 SICCA participants who had symptoms of dry eyes and dry mouth, 1051 had SS (44%) and 1350 did not (56%). After controlling for confounders, when compared with non-SS participants, those with SS had better PCS (p<0.001, β=2.43, 95% CI 1.57 to 3.29), MCS (p=0.002, β=1.37, 95% CI 0.50 to 2.23) and lower adjusted odds of depression (p<0.001, OR 0.67, 95% CI 0.55 to 0.81). Other significant predictors of HRQoL and depression included employment, country of residence and use of medication with anticholinergic effect or for management of SS-related signs and symptoms.ConclusionOur results suggest that among symptomatic patients, having a diagnosis of SS may be associated with better emotional and psychological well-being compared with patients without a diagnosis. Having a definitive diagnosis of SS may encourage patients to obtain a better understanding of their disease and have coping mechanisms in place to better manage their symptoms
X-ray Scattering Study of the spin-Peierls transition and soft phonon behavior in TiOCl
We have studied the S=1/2 quasi-one-dimensional antiferromagnet TiOCl using
single crystal x-ray diffraction and inelastic x-ray scattering techniques. The
Ti ions form staggered spin chains which dimerize below Tc1 = 66 K and have an
incommensurate lattice distortion between Tc1 and Tc2 = 92 K. Based on our
measurements of the intensities, wave vectors, and harmonics of the
incommensurate superlattice peaks, we construct a model for the incommensurate
modulation. The results are in good agreement with a soliton lattice model,
though some quantitative discrepancies exist near Tc2. The behavior of the
phonons has been studied using inelastic x-ray scattering with ~2 meV energy
resolution. For the first time, a zone boundary phonon which softens at the
spin-Peierls temperature Tsp has been observed. Our results show reasonably
good quantitative agreement with the Cross-Fisher theory for the phonon
dynamics at wave vectors near the zone boundary and temperatures near Tsp.
However, not all aspects of the data can be described, such as the strong
overdamping of the soft mode above Tsp. Overall, our results show that TiOCl is
a good realization of a spin-Peierls system, where the phonon softening allows
us to identify the transition temperature as Tsp=Tc2=92 KComment: 14 pages, 14 figure
Tau Polarizations in the Three-body Slepton Decays with Stau as the NLSP
In the gauge-mediated supersymmetry breaking models with scalar tau as the
next-to-lightest supersymmetric particle, a scalar lepton may decay dominantly
into its superpartner, tau lepton, and the lightest scalar tau particle. We
give detailed formulas for the three-body decay amplitudes and the polarization
asymmetry of the outgoing tau lepton . We find that the tau polarizations are
sensitive to the model parameters such as the stau mixing angle, the neutralino
to slepton mass ratio and the neutralino mixing effect.Comment: 13 pages, 5 figures, RevTe
Variational Thomas-Fermi Theory of a Nonuniform Bose Condensate at Zero Temperature
We derive a description of the spatially inhomogeneous Bose-Einstein
condensate which treats the system locally as a homogeneous system. This
approach, similar to the Thomas-Fermi model for the inhomogeneous many-particle
fermion system, is well-suited to describe the atomic Bose-Einstein condensates
that have recently been obtained experimentally through atomic trapping and
cooling. In this paper, we confine our attention to the zero temperature case,
although the treatment can be generalized to finite temperatures, as we shall
discuss elsewhere.Comment: 24 pages, latex, 6 ps figures, BoxedEPS include
Magic-Angle Semimetals with Chiral Symmetry
We construct and solve a two-dimensional, chirally symmetric model of Dirac
cones subjected to a quasiperiodic modulation. In real space, this is realized
with a quasiperiodic hopping term. This hopping model, as we show, at the Dirac
node energy has a rich phase diagram with a semimetal-to-metal phase transition
at intermediate amplitude of the quasiperiodic modulation, and a transition to
a phase with a diverging density of states and sub-diffusive transport when the
quasiperiodic hopping is strongest. We further demonstrate that the
semimetal-to-metal phase transition can be characterized by the multifractal
structure of eigenstates in momentum space and can be considered as a unique
"unfreezing" transition. This unfreezing transition in momentum space generates
flat bands with a dramatically renormalized bandwidth in the metallic phase
similar to the phenomena of the band structure of twisted bilayer graphene at
the magic angle. We characterize the nature of this transition numerically as
well as analytically in terms of the formation of a band of topological zero
modes. For pure quasiperiodic hopping, we provide strong numerical evidence
that the low-energy density of states develops a divergence and the eigenstates
exhibit Chalker (quantum-critical) scaling despite the model not being random.
At particular commensurate limits the model realizes higher-order topological
insulating phases. We discuss how these systems can be realized in experiments
on ultracold atoms and metamaterials.Comment: 20+4 pages, 24 figures, published versio
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