14,305 research outputs found
Stability of pulse-like earthquake ruptures
Pulse-like ruptures arise spontaneously in many elastodynamic rupture
simulations and seem to be the dominant rupture mode along crustal faults.
Pulse-like ruptures propagating under steady-state conditions can be
efficiently analysed theoretically, but it remains unclear how they can arise
and how they evolve if perturbed. Using thermal pressurisation as a
representative constitutive law, we conduct elastodynamic simulations of
pulse-like ruptures and determine the spatio-temporal evolution of slip, slip
rate and pulse width perturbations induced by infinitesimal perturbations in
background stress. These simulations indicate that steady-state pulses driven
by thermal pressurisation are unstable. If the initial stress perturbation is
negative, ruptures stop; conversely, if the perturbation is positive, ruptures
grow and transition to either self-similar pulses (at low background stress) or
expanding cracks (at elevated background stress). Based on a dynamic
dislocation model, we develop an elastodynamic equation of motion for slip
pulses, and demonstrate that steady-state slip pulses are unstable if their
accrued slip is a decreasing function of the uniform background stress
. This condition is satisfied by slip pulses driven by thermal
pressurisation. The equation of motion also predicts quantitatively the growth
rate of perturbations, and provides a generic tool to analyse the propagation
of slip pulses. The unstable character of steady-state slip pulses implies that
this rupture mode is a key one determining the minimum stress conditions for
sustainable ruptures along faults, i.e., their ``strength''. Furthermore, slip
pulse instabilities can produce a remarkable complexity of rupture dynamics,
even under uniform background stress conditions and material properties
Thermopower as a Possible Probe of Non-Abelian Quasiparticle Statistics in Fractional Quantum Hall Liquids
We show in this paper that thermopower is enhanced in non-Abelian quantum
Hall liquids under appropriate conditions. This is because thermopower measures
entropy per electron in the clean limit, while the degeneracy and entropy
associated with non-Abelian quasiparticles enhance entropy when they are
present. Thus thermopower can potentially probe non-Abelian nature of the
quasiparticles, and measure their quantum dimension.Comment: 5 pages. Minor revisions in response to referee comments. Published
versio
Two types of nematicity in the phase diagram of the cuprate superconductor YBaCuO
Nematicity has emerged as a key feature of cuprate superconductors, but its
link to other fundamental properties such as superconductivity, charge order
and the pseudogap remains unclear. Here we use measurements of transport
anisotropy in YBaCuO to distinguish two types of nematicity. The
first is associated with short-range charge-density-wave modulations in a
doping region near . It is detected in the Nernst coefficient, but
not in the resistivity. The second type prevails at lower doping, where there
are spin modulations but no charge modulations. In this case, the onset of
in-plane anisotropy - detected in both the Nernst coefficient and the
resistivity - follows a line in the temperature-doping phase diagram that
tracks the pseudogap energy. We discuss two possible scenarios for the latter
nematicity.Comment: 8 pages and 7 figures. Main text and supplementary material now
combined into single articl
On the noise-induced passage through an unstable periodic orbit II: General case
Consider a dynamical system given by a planar differential equation, which
exhibits an unstable periodic orbit surrounding a stable periodic orbit. It is
known that under random perturbations, the distribution of locations where the
system's first exit from the interior of the unstable orbit occurs, typically
displays the phenomenon of cycling: The distribution of first-exit locations is
translated along the unstable periodic orbit proportionally to the logarithm of
the noise intensity as the noise intensity goes to zero. We show that for a
large class of such systems, the cycling profile is given, up to a
model-dependent change of coordinates, by a universal function given by a
periodicised Gumbel distribution. Our techniques combine action-functional or
large-deviation results with properties of random Poincar\'e maps described by
continuous-space discrete-time Markov chains.Comment: 44 pages, 4 figure
Membrane lipid order of sub-synaptic T cell vesicles correlates with their dynamics and function
During an immune response, T cells survey antigen presenting cells for antigenic peptides via the formation of an interface known as an immunological synapse. Among the complex and dynamic biophysical phenomena occurring at this interface is the trafficking of sub-synaptic vesicles carrying a variety of proximal signalling molecules. Here, we show that rather than being a homogeneous population, these vesicles display a diversity of membrane lipid order profiles, as measured using the environmentally sensitive dye di-4-ANEPPDHQ and multi-spectral TIRF microscopy. Using live-cell imaging, vesicle tracking and a variety of small molecule drugs to manipulate components of the actin and tubulin cytoskeleton, we show that the membrane lipid order of these vesicles correlate with their dynamics. Furthermore, we show that the key proximal signalling molecule Linker for Activation of T cells (LAT) is enriched in specific vesicle populations as defined by their higher membrane order. These results imply that vesicle lipid order may represent a novel regulatory mechanism for the sorting and trafficking of signalling molecules at the immunological synapse, and, potentially, other cellular structures
Lattice congruences of the weak order
We study the congruence lattice of the poset of regions of a hyperplane
arrangement, with particular emphasis on the weak order on a finite Coxeter
group. Our starting point is a theorem from a previous paper which gives a
geometric description of the poset of join-irreducibles of the congruence
lattice of the poset of regions in terms of certain polyhedral decompositions
of the hyperplanes. For a finite Coxeter system (W,S) and a subset K of S, let
\eta_K:w \mapsto w_K be the projection onto the parabolic subgroup W_K. We show
that the fibers of \eta_K constitute the smallest lattice congruence with
1\equiv s for every s\in(S-K). We give an algorithm for determining the
congruence lattice of the weak order for any finite Coxeter group and for a
finite Coxeter group of type A or B we define a directed graph on subsets or
signed subsets such that the transitive closure of the directed graph is the
poset of join-irreducibles of the congruence lattice of the weak order.Comment: 26 pages, 4 figure
A Study of Water Clusters Using the Effective Fragment Potential and Monte Carlo Simulated Annealing
Simulated annealing methods have been used with the effective fragment potential to locate the lowest energy structures for the water clusters (H2O)n with n=6, 8, 10, 12, 14, 16, 18, and 20. The most successful method uses a local minimization on each Monte Carlo step. The effective fragment potential method yielded interaction energies in excellent agreement with those calculated at the ab initio Hartree–Fock level and was quite successful at predicting the same energy ordering as the higher-level perturbation theory and coupled cluster methods. Analysis of the molecular interaction energies in terms of its electrostatic,polarization, and exchange-repulsion/charge-transfer components reveals that the electrostatic contribution is the dominant term in determining the energy ordering of the minima on the (H2O)n potential energy surfaces, but that differences in the polarization and repulsion components can be important in some cases
Atomic Spectral Features During Thermonuclear Flashes on Neutron Stars
The gravitational redshift measured by Cottam, Paerels and Mendez for the
neutron star (NS) in the low-mass X-ray binary EXO 0748-676 depends on the
identification of an absorption line during a type I burst as the H
line from hydrogenic Fe. We show that Fe is present above the photosphere as
long as during the burst. In
this limit, the total Fe column is for incident material of solar abundances and only depends on the
nuclear physics of the proton spallation. The Fe destruction creates many heavy
elements with which may imprint photo-ionization edges on the NS spectra
during a radius expansion event or in a burst cooling tail. Detecting these
features in concert with those from Fe would confirm a redshift measurement. We
also begin to address the radiative transfer problem, and find that a
concentrated Fe layer with and column (depending on the line depth) above the hotter
continuum photosphere is required to create the H line of the observed
strength. This estimate must be refined by considerations of non-LTE effects as
well as resonant line transport. Until these are carried out, we cannot say
whether the Fe column from accretion and spallation is in conflict with the
observations. We also show that hydrogenic Fe might remain in the photosphere
due to radiative levitation from the high burst flux.Comment: Substantially revised version, to appear in Ap J Letter
Professional attitudes to sex offenders: implications for multiagency and collaborative working
Recent years have seen the development and implementation of a range of multi-disciplinary and partnership approaches to managing risk in known sex offenders, involving collaboration between justice and human services agencies. Potential barriers to the development of effective multidisciplinary practices arise when participating professionals hold different attitudes about those they are responsible for managing. This paper examines differences in attitudes towards sex offenders in two professional groups – police officers and allied health workers. The results suggest that police officers tend to hold more negative views than those who deliver treatment and support services. They are more likely to believe that offenders cannot change their behaviour and should be subject to more punitive sanctions. These findings are discussed in relation to judgements of both risk and dangerousness and associated decisions about the appropriate management of sex offenders in multi-agency and multi-disciplinary working forums
- …