2,703 research outputs found
White noise flashing Brownian pump
A Brownian pump of particles powered by a stochastic flashing ratchet
mechanism is studied. The pumping device is embedded in a finite region and
bounded by particle reservoirs. In the steady state, we exactly calculate the
spatial density profile, the concentration ratio between both reservoirs and
the particle flux. A simple numerical scheme is presented allowing for the
consistent evaluation of all such observable quantities
Self-sustained spatiotemporal oscillations induced by membrane-bulk coupling
We propose a novel mechanism leading to spatiotemporal oscillations in
extended systems that does not rely on local bulk instabilities. Instead,
oscillations arise from the interaction of two subsystems of different spatial
dimensionality. Specifically, we show that coupling a passive diffusive bulk of
dimension d with an excitable membrane of dimension d-1 produces a
self-sustained oscillatory behavior. An analytical explanation of the
phenomenon is provided for d=1. Moreover, in-phase and anti-phase
synchronization of oscillations are found numerically in one and two
dimensions. This novel dynamic instability could be used by biological systems
such as cells, where the dynamics on the cellular membrane is necessarily
different from that of the cytoplasmic bulk.Comment: Accepted for publication in Physical Review Letter
Measuring School Engagement: Validation and Measurement Equivalence of the Student Engagement Scale on Angolan Male and Female Adolescents
School engagement is defined primarily in relation to the participation of the student in academic achievement, and it is viewed as a multidimensional and integrative construct, or macroconstruct made up of several dimensions. The most repeated typology recognizes three specific dimensions: Cognitive, behavioral, and emotional (affective). Recently, a fourth new dimension, personal agency, has been proposed, which reflects students’ constructive engagement with the academic instructions. F. Veiga has been the first to present a self-report instrument, in Portuguese, to measure these four components, the Student Engagement Scale-4 dimensions (SES-4DS). This research has studied the validity and reliability of this scale and its gender invariance in a sample of 2034 Angolan students. Results have shown a clear scalar invariant factor structure, some reliability problems, and adequate convergent and nomological validity. Latent differences were found between males and females for cognitive and affective engagement. Results are discussed in light of the existing literature
Pinning and switching of magnetic moments in bilayer graphene
We examine the magnetic properties of the localized states induced by lattice
vacancies in bilayer graphene with an unrestricted Hartree-Fock calculation. We
show that with realistic values of the parameters and for experimentally
accessible gate voltages we can have a magnetic switching between an
unpolarized and a fully polarized system.Comment: 9 pages, 4 figure
Self-energy corrections to anisotropic Fermi surfaces
The electron-electron interactions affect the low-energy excitations of an
electronic system and induce deformations of the Fermi surface. These effects
are especially important in anisotropic materials with strong correlations,
such as copper oxides superconductors or ruthenates. Here we analyze the
deformations produced by electronic correlations in the Fermi surface of
anisotropic two-dimensional systems, treating the regular and singular regions
of the Fermi surface on the same footing. Simple analytical expressions are
obtained for the corrections, based on local features of the Fermi surface. It
is shown that, even for weak local interactions, the behavior of the
self-energy is non trivial, showing a momentum dependence and a self-consistent
interplay with the Fermi surface topology. Results are compared to experimental
observations and to other theoretical results.Comment: 13 pages, 10 figure
From subdiffusion to superdiffusion of particles on solid surfaces
We present a numerical and partially analytical study of classical particles
obeying a Langevin equation that describes diffusion on a surface modeled by a
two dimensional potential. The potential may be either periodic or random.
Depending on the potential and the damping, we observe superdiffusion,
large-step diffusion, diffusion, and subdiffusion. Superdiffusive behavior is
associated with low damping and is in most cases transient, albeit often long.
Subdiffusive behavior is associated with highly damped particles in random
potentials. In some cases subdiffusive behavior persists over our entire
simulation and may be characterized as metastable. In any case, we stress that
this rich variety of behaviors emerges naturally from an ordinary Langevin
equation for a system described by ordinary canonical Maxwell-Boltzmann
statistics
High-throughput screening methodology to identify alpha-synuclein aggregation inhibitors
An increasing number of neurodegenerative diseases are being found to be associated with the abnormal accumulation of aggregated proteins in the brain. In Parkinson’s disease, this process involves the aggregation of alpha-synuclein (a-syn) into intraneuronal inclusions. Thus, compounds that inhibit a-syn aggregation represent a promising therapeutic strategy as disease-modifying agents for neurodegeneration. The formation of a-syn amyloid aggregates can be reproduced in vitro by incubation of the recombinant protein. However, the in vitro aggregation of a-syn is exceedingly slow and highly irreproducible, therefore precluding fast high throughput anti-aggregation drug screening. Here, we present a simple and easy-to-implement in-plate method for screening large chemical libraries in the search for a-syn aggregation modulators. It allows us to monitor aggregation kinetics with high reproducibility, while being faster and requiring lower protein amounts than conventional aggregation assays. We illustrate how the approach enables the identification of strong aggregation inhibitors in a library of more than 14, 000 compounds
Deformation of anisotropic Fermi surfaces due to electron-electron interactions
We analyze the deformations of the Fermi surface induced by electron-electron
interactions in anisotropic two dimensional systems. We use perturbation theory
to treat, on the same footing, the regular and singular regions of the Fermi
surface. It is shown that, even for weak local coupling, the self-energy
presents a nontrivial behavior showing momentum dependence and interplay with
the Fermi surface shape. Our scheme gives simple analytical expressions based
on local features of the Fermi surface.Comment: 7 pages, 3 figure
Noise-Induced Phase Separation: Mean-Field Results
We present a study of a phase-separation process induced by the presence of
spatially-correlated multiplicative noise. We develop a mean-field approach
suitable for conserved-order-parameter systems and use it to obtain the phase
diagram of the model. Mean-field results are compared with numerical
simulations of the complete model in two dimensions. Additionally, a comparison
between the noise-driven dynamics of conserved and nonconserved systems is made
at the level of the mean-field approximation.Comment: 12 pages (including 6 figures) LaTeX file. Submitted to Phys. Rev.
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