28,598 research outputs found
Parabolic Problems with Nonlinear Boundary Conditions in Cell Tissues
In this paper we consider reaction diffusion problems with nonlinear boundary conditions in two dimensional domains for which the diffusion is large except in a neighborhood of a one dimensional set where it becomes small. We regard the domain as a cell tissue
Real space mapping of topological invariants using artificial neural networks
Topological invariants allow to characterize Hamiltonians, predicting the
existence of topologically protected in-gap modes. Those invariants can be
computed by tracing the evolution of the occupied wavefunctions under twisted
boundary conditions. However, those procedures do not allow to calculate a
topological invariant by evaluating the system locally, and thus require
information about the wavefunctions in the whole system. Here we show that
artificial neural networks can be trained to identify the topological order by
evaluating a local projection of the density matrix. We demonstrate this for
two different models, a 1-D topological superconductor and a 2-D quantum
anomalous Hall state, both with spatially modulated parameters. Our neural
network correctly identifies the different topological domains in real space,
predicting the location of in-gap states. By combining a neural network with a
calculation of the electronic states that uses the Kernel Polynomial Method, we
show that the local evaluation of the invariant can be carried out by
evaluating a local quantity, in particular for systems without translational
symmetry consisting of tens of thousands of atoms. Our results show that
supervised learning is an efficient methodology to characterize the local
topology of a system.Comment: 9 pages, 6 figure
Probing quantum fluctuation theorems in engineered reservoirs
Fluctuation Theorems are central in stochastic thermodynamics, as they allow
for quantifying the irreversibility of single trajectories. Although they have
been experimentally checked in the classical regime, a practical demonstration
in the framework of quantum open systems is still to come. Here we propose a
realistic platform to probe fluctuation theorems in the quantum regime. It is
based on an effective two-level system coupled to an engineered reservoir, that
enables the detection of the photons emitted and absorbed by the system. When
the system is coherently driven, a measurable quantum component in the entropy
production is evidenced. We quantify the error due to photon detection
inefficiency, and show that the missing information can be efficiently
corrected, based solely on the detected events. Our findings provide new
insights into how the quantum character of a physical system impacts its
thermodynamic evolution.Comment: 9 pages, 4 figure
Correlations around an interface
We compute one-loop correlation functions for the fluctuations of an
interface using a field theory model. We obtain them from Feynman diagrams
drawn with a propagator which is the inverse of the Hamiltonian of a
Poschl-Teller problem. We derive an expression for the propagator in terms of
elementary functions, show that it corresponds to the usual spectral sum, and
use it to calculate quantities such as the surface tension and interface
profile in two and three spatial dimensions. The three-dimensional quantities
are rederived in a simple, unified manner, whereas those in two dimensions
extend the existing literature, and are applicable to thin films. In addition,
we compute the one-loop self-energy, which may be extracted from experiment, or
from Monte Carlo simulations. Our results may be applied in various scenarios,
which include fluctuations around topological defects in cosmology,
supersymmetric domain walls, Z(N) bubbles in QCD, domain walls in magnetic
systems, interfaces separating Bose-Einstein condensates, and interfaces in
binary liquid mixtures.Comment: RevTeX, 13 pages, 6 figure
SiUinde: A collaborative platform to share conditions for near-the-shore activities
Currently, a large number of near-the-shore activities (sports and leisure) with a huge set of practitioners (growing everyday) exist. Also, the number of commercial companies, such as sport schools, that explore such type of costal activities are also on the rising. These kind of coastal activities are dependent of a set of conditions (in particular on what concerns the sun, the wind and waves) that affect directly or indirectly, the type of activity – mostly sportive – that can be practiced (surf, windsurf, paddle, kite surfing, canoeing, paragliding and others) on a given spot at a given time. This paper presents a platform, called SiUinde that was developed to allow users to collaboratively communicate reports about the coastal conditions, using several parameters, which include the wind conditions and the sea conditions, through a smartphone or tablet, permitting other users to have an in-depth and timely overview of the best places to enjoy their near-the-shore activities. This collaborative platform, takes advantage from the concept of collaborative intelligence and crowdsourcing to provide to the end-users the best possible recommendations for their preferred near-the-shore activities.info:eu-repo/semantics/submittedVersio
Probing the Circumnuclear Stellar Populations of Starburst Galaxies in the Near-infrared
We employ the NASA Infrared Telescope Facility's near-infrared spectrograph
SpeX at 0.8-2.4m to investigate the spatial distribution of the stellar
populations (SPs) in four well known Starburst galaxies: NGC34, NGC1614,
NGC3310 and NGC7714. We use the STARLIGHT code updated with the synthetic
simple stellar populations models computed by Maraston (2005, M05). Our main
results are that the NIR light in the nuclear surroundings of the galaxies is
dominated by young/intermediate age SPs (yr), summing from
40\% up to 100\% of the light contribution. In the nuclear aperture of
two sources (NGC1614 and NGC3310) we detected a predominant old SP component
(yr), while for NGC34 and NGC7714 the younger component
prevails. Furthermore, we found evidence of a circumnuclear star formation
ring-like structure and a secondary nucleus in NGC1614, in agreement with
previous studies. We also suggest that the merger/interaction experienced by
three of the galaxies studied, NGC1614, NGC3310 and NGC7714 can explain the
lower metallicity values derived for the young SP component of these sources.
In this scenario the fresh unprocessed metal poorer gas from the
destroyed/interacting companion galaxy is driven to the centre of the galaxies
and mixed with the central region gas, before star formation takes place. In
order to deepen our analysis, we performed the same procedure of SP synthesis
using Maraston (2011, M11) EPS models. Our results show that the newer and
higher resolution M11 models tend to enhance the old/intermediate age SP
contribution over the younger ages
Supergiant Barocaloric Effects in Acetoxy Silicone Rubber over a Wide Temperature Range: Great Potential for Solid-state Cooling
Solid-state cooling based on caloric effects is considered a viable
alternative to replace the conventional vapor-compression refrigeration
systems. Regarding barocaloric materials, recent results show that elastomers
are promising candidates for cooling applications around room-temperature. In
the present paper, we report supergiant barocaloric effects observed in acetoxy
silicone rubber - a very popular, low-cost and environmentally friendly
elastomer. Huge values of adiabatic temperature change and reversible
isothermal entropy change were obtained upon moderate applied pressures and
relatively low strains. These huge barocaloric changes are associated both to
the polymer chains rearrangements induced by confined compression and to the
first-order structural transition. The results are comparable to the best
barocaloric materials reported so far, opening encouraging prospects for the
application of elastomers in near future solid-state cooling devices.Comment: 19 pages, 7 figures, 2 table
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