1,512 research outputs found
Classical Strongly Coupled QGP I: The Model and Molecular Dynamics Simulations
We propose a model for the description of strongly interacting quarks and
gluon quasiparticles at , as a classical and nonrelativistic
colored Coulomb gas. The sign and strength of the inter-particle interactions
are fixed by the scalar product of their classical {\it color vectors} subject
to Wong's equations. The model displays a number of phases as the Coulomb
coupling is increased ranging from a gas, to a liquid, to a crystal with
antiferromagnetic-like color ordering. We analyze the model using Molecular
Dynamics (MD) simulations and discuss the density-density correlator in real
time. We extract pertinent decorrelation times, diffusion and viscosity
constants for all phases. The classical results when extrapolated to the sQGP
suggest that the phase is liquid-like, with a diffusion constant and a bulk viscosity to entropy density ratio .Comment: 11 pages, 14 figure
Long-Range Exciton Diffusion in Two-Dimensional Assemblies of Cesium Lead Bromide Perovskite Nanocrystals
F\"orster Resonant Energy Transfer (FRET)-mediated exciton diffusion through
artificial nanoscale building block assemblies could be used as a new
optoelectronic design element to transport energy. However, so far nanocrystal
(NC) systems supported only diffusion length of 30 nm, which are too small to
be useful in devices. Here, we demonstrate a FRET-mediated exciton diffusion
length of 200 nm with 0.5 cm2/s diffusivity through an ordered, two-dimensional
assembly of cesium lead bromide perovskite nanocrystals (PNC). Exciton
diffusion was directly measured via steady-state and time-resolved
photoluminescence (PL) microscopy, with physical modeling providing deeper
insight into the transport process. This exceptionally efficient exciton
transport is facilitated by PNCs high PL quantum yield, large absorption
cross-section, and high polarizability, together with minimal energetic and
geometric disorder of the assembly. This FRET-mediated exciton diffusion length
matches perovskites optical absorption depth, opening the possibility to design
new optoelectronic device architectures with improved performances, and
providing insight into the high conversion efficiencies of PNC-based
optoelectronic devices
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Lagrangian continuum dynamics in ALEGRA.
Alegra is an ALE (Arbitrary Lagrangian-Eulerian) multi-material finite element code that emphasizes large deformations and strong shock physics. The Lagrangian continuum dynamics package in Alegra uses a Galerkin finite element spatial discretization and an explicit central-difference stepping method in time. The goal of this report is to describe in detail the characteristics of this algorithm, including the conservation and stability properties. The details provided should help both researchers and analysts understand the underlying theory and numerical implementation of the Alegra continuum hydrodynamics algorithm
Computational fluid dynamics modeling of symptomatic intracranial atherosclerosis may predict risk of stroke recurrence.
BackgroundPatients with symptomatic intracranial atherosclerosis (ICAS) of ≥ 70% luminal stenosis are at high risk of stroke recurrence. We aimed to evaluate the relationships between hemodynamics of ICAS revealed by computational fluid dynamics (CFD) models and risk of stroke recurrence in this patient subset.MethodsPatients with a symptomatic ICAS lesion of 70-99% luminal stenosis were screened and enrolled in this study. CFD models were reconstructed based on baseline computed tomographic angiography (CTA) source images, to reveal hemodynamics of the qualifying symptomatic ICAS lesions. Change of pressures across a lesion was represented by the ratio of post- and pre-stenotic pressures. Change of shear strain rates (SSR) across a lesion was represented by the ratio of SSRs at the stenotic throat and proximal normal vessel segment, similar for the change of flow velocities. Patients were followed up for 1 year.ResultsOverall, 32 patients (median age 65; 59.4% males) were recruited. The median pressure, SSR and velocity ratios for the ICAS lesions were 0.40 (-2.46-0.79), 4.5 (2.2-20.6), and 7.4 (5.2-12.5), respectively. SSR ratio (hazard ratio [HR] 1.027; 95% confidence interval [CI], 1.004-1.051; P = 0.023) and velocity ratio (HR 1.029; 95% CI, 1.002-1.056; P = 0.035) were significantly related to recurrent territorial ischemic stroke within 1 year by univariate Cox regression, respectively with the c-statistics of 0.776 (95% CI, 0.594-0.903; P = 0.014) and 0.776 (95% CI, 0.594-0.903; P = 0.002) in receiver operating characteristic analysis.ConclusionsHemodynamics of ICAS on CFD models reconstructed from routinely obtained CTA images may predict subsequent stroke recurrence in patients with a symptomatic ICAS lesion of 70-99% luminal stenosis
Quantum interest in two dimensions
The quantum interest conjecture of Ford and Roman asserts that any
negative-energy pulse must necessarily be followed by an over-compensating
positive-energy one within a certain maximum time delay. Furthermore, the
minimum amount of over-compensation increases with the separation between the
pulses. In this paper, we first study the case of a negative-energy square
pulse followed by a positive-energy one for a minimally coupled, massless
scalar field in two-dimensional Minkowski space. We obtain explicit expressions
for the maximum time delay and the amount of over-compensation needed, using a
previously developed eigenvalue approach. These results are then used to give a
proof of the quantum interest conjecture for massless scalar fields in two
dimensions, valid for general energy distributions.Comment: 17 pages, 4 figures; final version to appear in PR
Analysis of ocean power extraction capabilites of a rotary wave energy conversion system
Gemstone Team WAVES (Water and Versatile Energy Systems)In recent years, there has been a shift towards renewable energy sources to help alleviate the dependence on fossil fuels. Many industries have started to investigate wind, solar, and other alternative energy sources. Our research aimed to provide additional insight into the field of wave energy as a component of a comprehensive energy solution. We selected a unique wave energy converter design and analyzed potential modifications that could improve its performance. After developing design modifications, we constructed and tested a prototype of a Rotary Wave Energy Collector (R-WEC). We tested the rotor under two mooring configurations and collected data on the relationship between power output and wavelength. We also analyzed the rotor's performance under single and multiple frequency wave environments. In addition, we investigated the implementation of a full-scale device through a study of three coastal regions in the mid-Atlantic U.S. area. This research showed that our R-WEC design could be implemented in shallow water, single frequency wave environments to generate usable power
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