50,541 research outputs found
A New Monte Carlo Method and Its Implications for Generalized Cluster Algorithms
We describe a novel switching algorithm based on a ``reverse'' Monte Carlo
method, in which the potential is stochastically modified before the system
configuration is moved. This new algorithm facilitates a generalized
formulation of cluster-type Monte Carlo methods, and the generalization makes
it possible to derive cluster algorithms for systems with both discrete and
continuous degrees of freedom. The roughening transition in the sine-Gordon
model has been studied with this method, and high-accuracy simulations for
system sizes up to were carried out to examine the logarithmic
divergence of the surface roughness above the transition temperature, revealing
clear evidence for universal scaling of the Kosterlitz-Thouless type.Comment: 4 pages, 2 figures. Phys. Rev. Lett. (in press
Driven diffusive systems with mutually interactive Langmuir kinetics
We investigate the simple one-dimensional driven model, the totally
asymmetric exclusion process, coupled to mutually interactive Langmuir
kinetics. This model is motivated by recent studies on clustering of motor
proteins on microtubules. In the proposed model, the attachment and detachment
rates of a particle are modified depending upon the occupancy of neighbouring
sites. We first obtain continuum mean-field equations and in certain limiting
cases obtain analytic solutions. We show how mutual interactions increase
(decrease) the effects of boundaries on the phase behavior of the model. We
perform Monte Carlo simulations and demonstrate that our analytical
approximations are in good agreement with the numerics over a wide range of
model parameters. We present phase diagrams over a selective range of
parameters.Comment: 9 pages, 8 Figure
Active biopolymer networks generate scale-free but euclidean clusters
We report analytical and numerical modelling of active elastic networks,
motivated by experiments on crosslinked actin networks contracted by myosin
motors. Within a broad range of parameters, the motor-driven collapse of active
elastic networks leads to a critical state. We show that this state is
qualitatively different from that of the random percolation model.
Intriguingly, it possesses both euclidean and scale-free structure with Fisher
exponent smaller than . Remarkably, an indistinguishable Fisher exponent and
the same euclidean structure is obtained at the critical point of the random
percolation model after absorbing all enclaves into their surrounding clusters.
We propose that in the experiment the enclaves are absorbed due to steric
interactions of network elements. We model the network collapse, taking into
account the steric interactions. The model shows how the system robustly drives
itself towards the critical point of the random percolation model with absorbed
enclaves, in agreement with the experiment.Comment: 6 pages, 7 figure
The nuclear shell effects near the r-process path in the relativistic Hartree-Bogoliubov theory
We have investigated the evolution of the shell structure of nuclei in going
from the r-process path to the neutron drip line within the framework of the
Relativistic Hartree-Bogoliubov (RHB) theory. By introducing the quartic
self-coupling of meson in the RHB theory in addition to the non-linear
scalar coupling of meson, we reproduce the available data on the shell
effects about the waiting-point nucleus Zn. With this approach, it is
shown that the shell effects at N=82 in the inaccessible region of the
r-process path become milder as compared to the Lagrangian with the scalar
self-coupling only. However, the shell effects remain stronger as compared to
the quenching exhibited by the HFB+SkP approach. It is also shown that in
reaching out to the extreme point at the neutron drip line, a terminal
situation arises where the shell structure at the magic number is washed out
significantly.Comment: 18 pages (revtex), 8 ps figures, to appear in Phys. Rev.
Conductivity of Highly Concentrated Aqueous Electrolyte Solutions: Ammonium Nitrate-Water System
84-8
Upper atmosphere chemical release study Final report
Chemical release experiments to study upper atmosphere including night sky oxygen emissio
Spectroscopic accuracy directly from quantum chemistry: application to ground and excited states of beryllium dimer
We combine explicit correlation via the canonical transcorrelation approach
with the density matrix renormalization group and initiator full configuration
interaction quantum Monte Carlo methods to compute a near-exact beryllium dimer
curve, {\it without} the use of composite methods. In particular, our direct
density matrix renormalization group calculations produce a well-depth of
=931.2 cm which agrees very well with recent experimentally derived
estimates =929.7~cm [Science, 324, 1548 (2009)] and
=934.6~cm [Science, 326, 1382 (2009)]], as well the best composite
theoretical estimates, =938~cm [J. Phys. Chem. A, 111,
12822 (2007)] and =935.1~cm [Phys. Chem. Chem. Phys., 13,
20311 (2011)]. Our results suggest possible inaccuracies in the functional form
of the potential used at shorter bond lengths to fit the experimental data
[Science, 324, 1548 (2009)]. With the density matrix renormalization group we
also compute near-exact vertical excitation energies at the equilibrium
geometry. These provide non-trivial benchmarks for quantum chemical methods for
excited states, and illustrate the surprisingly large error that remains for
1 state with approximate multi-reference configuration
interaction and equation-of-motion coupled cluster methods. Overall, we
demonstrate that explicitly correlated density matrix renormalization group and
initiator full configuration interaction quantum Monte Carlo methods allow us
to fully converge to the basis set and correlation limit of the
non-relativistic Schr\"odinger equation in small molecules
Temperature enhanced effects of ozone on cardiovascular mortality in 95 large US communities, 1987-2000 - assessment using the NMMAPS data
A few studies examined interactive effects between air pollution and temperature on health outcomes. This study is to examine if temperature modified effects of ozone and cardiovascular mortality in 95 large US cities. A nonparametric and a parametric regression models were separately used to explore interactive effects of temperature and ozone on cardiovascular mortality during May and October, 1987-2000. A Bayesian meta-analysis was used to pool estimates. Both models illustrate that temperature enhanced the ozone effects on mortality in the northern region, but obviously in the southern region. A 10-ppb increment in ozone was associated with 0.41 % (95% posterior interval (PI): -0.19 %, 0.93 %), 0.27 % (95% PI: -0.44 %, 0.87 %) and 1.68 % (95% PI: 0.07 %, 3.26 %) increases in daily cardiovascular mortality corresponding to low, moderate and high levels of temperature, respectively. We concluded that temperature modified effects of ozone, particularly in the northern region
Lockdown lifted: measuring spatial resilience from London’s public transport demand recovery
The disruptive effects of the COVID-19 pandemic has rapidly shifted how individuals navigate in cities. Governments are concerned that travel behavior will shift toward a car-driven and homeworking future, shifting demand away from public transport use. These concerns place the recovery of public transport in a possible crisis. A resilience perspective may aid the discussion around recovery–particularly one that deviates from pre-pandemic behavior. This paper presents an empirical study of London’s public transport demand and introduces a perspective of spatial resilience to the existing body of research on post-pandemic public transport demand. This study defines spatial resilience as the rate of recovery in public transport demand within census boundaries over a period after lockdown restrictions were lifted. The relationship between spatial resilience and urban socioeconomic factors was investigated by a global spatial regression model and a localized perspective through Geographically Weighted Regression (GWR) model. In this case study of London, the analysis focuses on the period after the first COVID-19 lockdown restrictions were lifted (June 2020) and before the new restrictions in mid-September 2020. The analysis shows that outer London generally recovered faster than inner London. Factors of income, car ownership and density of public transport infrastructure were found to have the greatest influence on spatial patterns in resilience. Furthermore, influential relationships vary locally, inviting future research to examine the drivers of this spatial heterogeneity. Thus, this research recommends transport policymakers capture the influences of homeworking, ensure funding for a minimum level of service, and advocate for a polycentric recovery post-pandemic
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