3,899 research outputs found
Transport properties of isospin effective mass splitting
We investigate in detail the momentum dependence () of the effective in
medium Nucleon-Nucleon () interaction in the isovector channel. We focus
the discussion on transport properties of the expected neutron-proton ()
effective mass splitting at high isospin density. We look at observable effects
from collective flows in Heavy Ion Collisions () of charge asymmetric
nuclei at intermediate energies. Using microscopic kinetic equation simulations
nucleon transverse and elliptic collective flows in collisions are
evaluated. In spite of the reduced charge asymmetry of the interacting system
interesting effects are revealed. Good observables, particularly
sensitive to the -mass splitting, appear to be the differences between
neutron and proton flows. The importance of more exclusive measurements, with a
selection of different bins of the transverse momenta () of the emitted
particles, is stressed. In more inclusive data a compensation can be expected
from different -contributions, due to the microscopic
structure of the nuclear mean field in asymmetric matter.Comment: 18 pages, 11 figure
Modeling and Simulation of Cascading Failures in Transportation Systems During Hurricane Evacuations
Effective and timely evacuation is critical in alleviating the impact of hurricanes. As such, evacuation models are often sought to support the preparedness of evacuations. One important task in the modeling process is to evaluate exogenous factors that cause transportation system capacity loss during evacuation. Typical factors include direct damage to the roadway network due to storm surge and cascading impacts because of other facilities failures. For example, power outage can lead to signal failure and subway suspension. This paper aims to develop a macroscopic simulation-based approach to study the capacity loss of the roadway network in evacuation due to signal loss as a consequence of power outage. In particular, to simulate the case in which traffic signals lose power, a capacity-reduction model from signalized intersections to unsignalized (all-way stop control) intersections was developed and calibrated using microscopic model created in SUMO and Synchro. We used the downtown Manhattan as a case study area and created a hypothetical power-grid network in terms of neighborhoods. Six scenarios were built to simulate power loss of different neighborhoods. The simulation results give insights on how cascading failures of power network affect roadway network and evacuation process
Probing nuclear symmetry energy with the sub-threshold pion production
Within the framework of semiclassical Boltzmann-Uehling-Uhlenbeck (BUU)
transport model, we investigated the effects of symmetry energy on the
sub-threshold pion using the isospin MDI interaction with the stiff and soft
symmetry energies in the central collision of Ca + Ca at the
incident beam energies of 100, 150, 200, 250 and 300 MeV/nucleon, respectively.
We find that the ratio of of sub-threshold charged pion
production is greatly sensitive to the symmetry energy, particularly around 100
MeV/nucleon energies. Large sensitivity of sub-threshold charged pion
production to nuclear symmetry energy may reduce uncertainties of probing
nuclear symmetry energy via heavy-ion collision.Comment: 5 pages, 5 figures, typo corrections, submitted to Chinese Physics
Letter
DiffGAN-F2S: Symmetric and Efficient Denoising Diffusion GANs for Structural Connectivity Prediction from Brain fMRI
Mapping from functional connectivity (FC) to structural connectivity (SC) can
facilitate multimodal brain network fusion and discover potential biomarkers
for clinical implications. However, it is challenging to directly bridge the
reliable non-linear mapping relations between SC and functional magnetic
resonance imaging (fMRI). In this paper, a novel diffusision generative
adversarial network-based fMRI-to-SC (DiffGAN-F2S) model is proposed to predict
SC from brain fMRI in an end-to-end manner. To be specific, the proposed
DiffGAN-F2S leverages denoising diffusion probabilistic models (DDPMs) and
adversarial learning to efficiently generate high-fidelity SC through a few
steps from fMRI. By designing the dual-channel multi-head spatial attention
(DMSA) and graph convolutional modules, the symmetric graph generator first
captures global relations among direct and indirect connected brain regions,
then models the local brain region interactions. It can uncover the complex
mapping relations between fMRI and structural connectivity. Furthermore, the
spatially connected consistency loss is devised to constrain the generator to
preserve global-local topological information for accurate intrinsic SC
prediction. Testing on the public Alzheimer's Disease Neuroimaging Initiative
(ADNI) dataset, the proposed model can effectively generate empirical
SC-preserved connectivity from four-dimensional imaging data and shows superior
performance in SC prediction compared with other related models. Furthermore,
the proposed model can identify the vast majority of important brain regions
and connections derived from the empirical method, providing an alternative way
to fuse multimodal brain networks and analyze clinical disease.Comment: 12 page
Relativistic effects in the search for high density symmetry energy
Intermediate energy heavy ion collisions open the unique possibility to
explore the Equation of State () of nuclear matter far from saturation, in
particular the density dependence of the symmetry energy. Within a relativistic
transport model it is shown that the isovector-scalar -meson, which
affects the high density behavior of the symmetry energy density, influences
the dynamics of heavy ion collisions in terms of isospin collective flows. The
effect is largely enhanced by a relativistic mechanism related to the covariant
nature of the fields contributing to the isovector channel. Results for
reactions induced by radioactive beams are presented. The elliptic
flows of nucleons and light isobars appear to be quite sensitive to microscopic
structure of the symmetry term, in particular for particles with large
transverse momenta, since they represent an earlier emission from a compressed
source. Thus future, more exclusive, experiments with relativistic radioactive
beams should be able to set stringent constraints on the density dependence of
the symmetry energy far from ground state nuclear matter.Comment: 11 pages, 4 figures inserted in the text. Elsevier preprint format
(Latex) Version with a new figure for the more physical 132Sn+124Sn cas
Isospin Dynamics in Heavy Ion Collisions: EoS-sensitive Observables
Heavy Ion Collisions (HIC) represent a unique tool to probe the in-medium
nuclear interaction in regions away from saturation and at high nucleon
momenta. In this report we present a selection of reaction observables
particularly sensitive to the isovector part of the interaction, i.e. to the
symmetry term of the nuclear Equation of State (EoS) At low energies the
behavior of the symmetry energy around saturation influences dissipation and
fragment production mechanisms. Predictions are shown for deep-inelastic and
fragmentation collisions induced by neutron rich projectiles. Differential flow
measurements will also shed lights on the controversial neutron/proton
effective mass splitting in asymmetric matter. The high density symmetry term
can be derived from isospin effects on heavy ion reactions at relativistic
energies (few AGeV range), that can even allow a ``direct'' study of the
covariant structure of the isovector interaction in the hadron medium. Rather
sensitive observables are proposed from collective flows and from pion/kaon
production. The possibility of the transition to a mixed hadron-quark phase, at
high baryon and isospin density, is finally suggested. Some signatures could
come from an expected ``neutron trapping'' effect.Comment: 10 pages, 5 figures; espcrc1 style; IX Int.Conf. on Nucleus-Nucleus
Collisions, Rio de Janeiro Aug.2006; to appear in Nucl.Phys.
Stability and Dark Hysteresis Correlate in NiO-Based Perovskite Solar Cells
© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim In perovskite solar cells (PSCs), the interfaces are a weak link with respect to degradation. Electrochemical reactivity of the perovskite's halides has been reported for both molecular and polymeric hole selective layers (HSLs), and here it is shown that also NiO brings about this decomposition mechanism. Employing NiO as an HSL in pâiân PSCs with power conversion efficiency (PCE) of 16.8%, noncapacitive hysteresis is found in the dark, which is attributable to the bias-induced degradation of perovskite/NiO interface. The possibility of electrochemically decoupling NiO from the perovskite via the introduction of a buffer layer is explored. Employing a hybrid magnesium-organic interlayer, the noncapacitive hysteresis is entirely suppressed and the device's electrical stability is improved. At the same time, the PCE is improved up to 18% thanks to reduced interfacial charge recombination, which enables more efficient hole collection resulting in higher Voc and FF
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