5,402 research outputs found
Neutron star properties in the Thomas-Fermi model
The modern nucleon-nucleon interaction of Myers and Swiatecki, adjusted to
the properties of finite nuclei, the parameters of the mass formula, and the
behavior of the optical potential is used to calculate the properties of
--equilibrated neutron star matter, and to study the impact of this
equation of state on the properties of (rapidly rotating) neutron stars and
their cooling behavior. The results are in excellent agreement with the outcome
of calculations performed for a broad collection of sophisticated
nonrelativistic as well as relativistic models for the equation of state.Comment: 23 pages, LaTeX, 15 ps-figure
Multilevel Monte Carlo for Random Degenerate Scalar Convection Diffusion Equation
We consider the numerical solution of scalar, nonlinear degenerate
convection-diffusion problems with random diffusion coefficient and with random
flux functions. Building on recent results on the existence, uniqueness and
continuous dependence of weak solutions on data in the deterministic case, we
develop a definition of random entropy solution. We establish existence,
uniqueness, measurability and integrability results for these random entropy
solutions, generalizing \cite{Mishr478,MishSch10a} to possibly degenerate
hyperbolic-parabolic problems with random data. We next address the numerical
approximation of random entropy solutions, specifically the approximation of
the deterministic first and second order statistics. To this end, we consider
explicit and implicit time discretization and Finite Difference methods in
space, and single as well as Multi-Level Monte-Carlo methods to sample the
statistics. We establish convergence rate estimates with respect to the
discretization parameters, as well as with respect to the overall work,
indicating substantial gains in efficiency are afforded under realistic
regularity assumptions by the use of the Multi-Level Monte-Carlo method.
Numerical experiments are presented which confirm the theoretical convergence
estimates.Comment: 24 Page
Observation Uncertainty in Reversible Markov Chains
In many applications one is interested in finding a simplified model which captures the essential dynamical behavior of a real life process. If the essential dynamics can be assumed to be (approximately) memoryless then a reasonable choice for a model is a Markov model whose parameters are estimated by means of Bayesian inference from an observed time series. We propose an efficient Monte Carlo Markov Chain framework to assess the uncertainty of the Markov model and related observables. The derived Gibbs sampler allows for sampling distributions of transition matrices subject to reversibility and/or sparsity constraints. The performance of the suggested sampling scheme is demonstrated and discussed for a variety of model examples. The uncertainty analysis of functions of the Markov model under investigation is discussed in application to the identification of conformations of the trialanine molecule via Robust Perron Cluster Analysis (PCCA+)
Building CMS Pixel Barrel Detectur Modules
For the barrel part of the CMS pixel tracker about 800 silicon pixel detector
modules are required. The modules are bump bonded, assembled and tested at the
Paul Scherrer Institute. This article describes the experience acquired during
the assembly of the first ~200 modules.Comment: 5 pages, 7 figures, Vertex200
Importance sampling in path space for diffusion processes with slow-fast variables
Importance sampling is a widely used technique to reduce the variance of a Monte Carlo estimator by an appropriate change of measure. In this work, we study importance sampling in the framework of diffusion process and consider the change of measure which is realized by adding a control force to the original dynamics. For certain exponential type expectation, the corresponding control force of the optimal change of measure leads to a zero-variance estimator and is related to the solution of a Hamilton-Jacobi-Bellmann equation. We focus on certain diffusions with both slow and fast variables, and the main result is that we obtain an upper bound of the relative error for the importance sampling estimators with control obtained from the limiting dynamics. We demonstrate our approximation strategy with a simple numerical example
Measuring competition in the Olympic Winter Games 1992–2014 using economic indices
Since the early 1990s, competition in the Olympic Winter Games has changed notably in terms of events contested and nations taking part. Despite, these changes, which are overseen by the International Olympic Committee (IOC), the number of medal-winning nations has remained relatively stable. As a first attempt to illustrate this issue on a discipline by discipline basis, economic techniques are used to examine the outcome of competition between 1992 and 2014. The purpose of this paper is to measure: market size; the number of competing nations; and the balance between competitive nations in six disciplines. Focusing on competitive balance, the Herfindahl–Hirschman Index is applied to measure the concentration of domination; while the Przeworski Index is used to quantify instability over time. Important changes are identified in biathlon (2010) and short track (2014). While the change in the former is consistent with the IOC’s substantial increase in biathlon events, the latter can be attributed to athletes changing their nationality. IOC policy-makers can benefit from this research as it provides a method by which to monitor competition in a discipline. This method provides the potential for evaluating the likely effects of governing the Olympic Games by increasing the number of events
High-resolution [OI] line spectral mapping of TW Hya consistent with X-ray driven photoevaporation
Theoretical models indicate that photoevaporative and magnetothermal winds
play a crucial role in the evolution and dispersal of protoplanetary disks and
affect the formation of planetary systems. However, it is still unclear what
wind-driving mechanism is dominant or if both are at work, perhaps at different
stages of disk evolution. Recent spatially resolved observations by Fang et al.
(2023) of the [OI] 6300 Angstrom spectral line, a common disk wind tracer, in
TW Hya revealed that about 80% of the emission is confined to the inner few au
of the disk. In this work, we show that state-of-the-art X-ray driven
photoevaporation models can reproduce the compact emission and the line profile
of the [OI] 6300 Angstrom line. Furthermore, we show that the models also
simultaneously reproduce the observed line luminosities and detailed spectral
profiles of both the [OI] 6300 Angstrom and the [NeII] 12.8 micron lines. While
MHD wind models can also reproduce the compact radial emission of the [OI] 6300
Angstrom line, they fail to match the observed spectral profile of the [OI]
6300 Angstrom line and underestimate the luminosity of the [NeII] 12.8 micron
line by a factor of three. We conclude that, while we cannot exclude the
presence of an MHD wind component, the bulk of the wind structure of TW Hya is
predominantly shaped by a photoevaporative flow.Comment: 7 pages, 4 figures, accepted for publication in Astrophysical Journal
Letter
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