5,465 research outputs found
Supercurrent conservation in the lattice Wess-Zumino model with Ginsparg-Wilson fermions
We study supercurrent conservation for the four-dimensional Wess-Zumino model
formulated on the lattice. The formulation is one that has been discussed
several times, and uses Ginsparg-Wilson fermions of the overlap (Neuberger)
variety, together with an auxiliary fermion (plus superpartners), such that a
lattice version of U(1)_R symmetry is exactly preserved in the limit of
vanishing bare mass. We show that the almost naive supercurrent is conserved at
one loop. By contrast we find that this is not true for Wilson fermions and a
canonical scalar action. We provide nonperturbative evidence for the
nonconservation of the supercurrent in Monte Carlo simulations.Comment: 19 pages, 5 figure
Target shape dependence in a simple model of receptor-mediated endocytosis and phagocytosis
Phagocytosis and receptor-mediated endocytosis are vitally important particle
uptake mechanisms in many cell types, ranging from single-cell organisms to
immune cells. In both processes, engulfment by the cell depends critically on
both particle shape and orientation. However, most previous theoretical work
has focused only on spherical particles and hence disregards the wide-ranging
particle shapes occurring in nature, such as those of bacteria. Here, by
implementing a simple model in one and two dimensions, we compare and contrast
receptor-mediated endocytosis and phagocytosis for a range of biologically
relevant shapes, including spheres, ellipsoids, capped cylinders, and
hourglasses. We find a whole range of different engulfment behaviors with some
ellipsoids engulfing faster than spheres, and that phagocytosis is able to
engulf a greater range of target shapes than other types of endocytosis.
Further, the 2D model can explain why some nonspherical particles engulf
fastest (not at all) when presented to the membrane tip-first (lying flat). Our
work reveals how some bacteria may avoid being internalized simply because of
their shape, and suggests shapes for optimal drug delivery.Comment: 18 pages, 5 figure
Scrambling and thermalization in a diffusive quantum many-body system
Out-of-time ordered (OTO) correlation functions describe scrambling of
information in correlated quantum matter. They are of particular interest in
incoherent quantum systems lacking well defined quasi-particles. Thus far, it
is largely elusive how OTO correlators spread in incoherent systems with
diffusive transport governed by a few globally conserved quantities. Here, we
study the dynamical response of such a system using high-performance
matrix-product-operator techniques. Specifically, we consider the
non-integrable, one-dimensional Bose-Hubbard model in the incoherent
high-temperature regime. Our system exhibits diffusive dynamics in time-ordered
correlators of globally conserved quantities, whereas OTO correlators display a
ballistic, light-cone spreading of quantum information. The slowest process in
the global thermalization of the system is thus diffusive, yet information
spreading is not inhibited by such slow dynamics. We furthermore develop an
experimentally feasible protocol to overcome some challenges faced by existing
proposals and to probe time-ordered and OTO correlation functions. Our study
opens new avenues for both the theoretical and experimental exploration of
thermalization and information scrambling dynamics.Comment: 7+4 pages, 8+3 figures; streamlined versio
Composite space antenna structures: Properties and environmental effects
The thermal behavior of composite spacecraft antenna reflectors has been investigated with the integrated Composites Analyzer (ICAN) computer code. Parametric studies have been conducted on the face sheets and honeycomb core which constitute the sandwich-type structures. Selected thermal and mechanical properties of the composite faces and sandwich structures are presented graphically as functions of varying fiber volume ratio, temperature, and moisture content. The coefficients of thermal expansion are discussed in detail since these are the critical design parameters. In addition, existing experimental data are presented and compared to the ICAN predictions
N-body Efimov states from two-particle noise
The ground state energies of universal N-body clusters tied to Efimov
trimers, for N even, are shown to be encapsulated in the statistical
distribution of two particles interacting with a background auxiliary field at
large Euclidean time when the interaction is tuned to the unitary point.
Numerical evidence that this distribution is log-normal is presented, allowing
one to predict the ground-state energies of the N-body system.Comment: Extended discussion of results; published versio
Dileptons in a coarse-grained transport approach
We calculate dilepton spectra in heavy-ion collisions using a coarse-graining
approach to the simulation of the created medium with the UrQMD transport
model. This enables the use of dilepton-production rates evaluated in
equilibrium quantum-field theory at finite temperatures and chemical
potentials.Comment: 4 pages, 2 figures, contribution to the proceedings of "The 15th
International Conference on Strangeness in Quark Matter" (SQM 2015), 06-11
July in Dubna, Russi
Convergence and Divergence of Themes in Successful Psychotherapy: An Assimilation Analysis
Theme convergence is the linking of seemingly unrelated problem domains as they advance through assimilation stages-a developmental sequence of cognitive and affective changes through which problematic content is hypothesized to pass during successful psychotherapy. Theme divergence is the contradiction or conflict of solutions to different problems, so that progress in one domain leads to stagnation or regression in another domain. An intensive qualitative method called assimilation analysis was used to examine theme convergence and divergence in a successful psychodynamic psychotherapy with a 20–yr–old female patient. Because specific problems often fail to progress monotonically, even in successful psychotherapy cases, it is suggested that clients\u27 problems cannot be resolved in isolation; instead, they may influence each other toward resolution or stagnation in complex and unpredictable ways
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