5,533 research outputs found
Computing probabilities of very rare events for Langevin processes: a new method based on importance sampling
Langevin equations are used to model many processes of physical interest,
including low-energy nuclear collisions. In this paper we develop a general
method for computing probabilities of very rare events (e.g. small fusion
cross-sections) for processes described by Langevin dynamics. As we demonstrate
with numerical examples as well as an exactly solvable model, our method can
converge to the desired answer at a rate which is orders of magnitude faster
than that achieved with direct simulations of the process in question.Comment: 18 pages + 7 figures, to appear in Nucl.Phys.
Investigation of magnetopause reconnection models using two colocated, lowâaltitude satellites: A unifying reconnection geometry
Ion precipitation data from two co-orbiting Defense Meteorological Satellite Program satellites (F6 and F8) are used to investigate magnetopause reconnection models. We examine differential fluxes between 30 eV and 30 keV, from a Southern Hemisphere, prenoon pass during the morning of January 10, 1990. Data from the first satellite to pass through the region (F6) show two distinct ion energy dispersions âą-1 Ăž of latitude apart, between 76 Ăž and 79 Ăž magnetic latitude. The electron data exhibit similar features at around the same region but with no or little energy dispersion, consistent with their high velocities. We suggest that the two energy dispersions can be explained by two separate injections resulting from two bursts of magnetopause reconnection. Data from the second satellite (F8), which moved through the same region I rain later, reveal the same energy-dispersed structures, only further poleward and with less overall flux. This temporal evolution is consistent with two recently reconnected flux tubes releasing their plasma as they move antisunward away from dayside merging sites. However, an observed overlap between the two ion energy dispersions suggests a more complex reconnection geometry than usual models can accommodate. We propose a generalized reconnection scenario that unifies the Bursty Single X-Line and the Multiple X-Line Reconnection models. A simple time-of-flight particle precipitation model is constructed to reproduce the ion dispersions and their overlap. The modeling results suggest that for time-dependent reconnection the dispersion overlap is observed clearly at low altitudes only for a short period compared with the evolution timescale of the ion precipitation
Analysis of the second order exchange self energy of a dense electron gas
We investigate the evaluation of the six-fold integral representation for the
second order exchange contribution to the self energy of a three dimensional
electron gas at the Fermi surface.Comment: 6 page
Onsager reciprocity relations without microscopic reversibility
In this paper we show that Onsager--Machlup time reversal properties of
thermodynamic fluctuations and Onsager reciprocity relations for transport
coefficients can hold also if the microscopic dynamics is not reversible. This
result is based on the explicit construction of a class of conservative models
which can be analysed rigorously.Comment: revtex, no figure
Anomalous scaling of passive scalar in turbulence and in equilibrium
We analyze multi-point correlation functions of a tracer in an incompressible
flow at scales far exceeding the scale at which fluctuations are generated
(quasi-equilibrium domain) and compare them with the correlation functions at
scales smaller than (turbulence domain). We demonstrate that the scale
invariance can be broken in the equilibrium domain and trace this breakdown to
the statistical integrals of motion (zero modes) as has been done before for
turbulence. Employing Kraichnan model of short-correlated velocity we identify
the new type of zero modes, which break scale invariance and determine an
anomalously slow decay of correlations at large scales
Cyclotron radiation and emission in graphene
Peculiarity in the cyclotron radiation and emission in graphene is
theoretically examined in terms of the optical conductivity and relaxation
rates to propose that graphene in magnetic fields can be a candidate to realize
the Landau level laser, proposed decades ago [H. Aoki, Appl. Phys. Lett. {\bf
48}, 559 (1986)].Comment: 4 pages, 3 figure
Fluctuation relations for a driven Brownian particle
We consider a driven Brownian particle, subject to both conservative and
non-conservative applied forces, whose probability evolves according to the
Kramers equation. We derive a general fluctuation relation, expressing the
ratio of the probability of a given Brownian path in phase space with that of
the time-reversed path, in terms of the entropy flux to the heat reservoir.
This fluctuation relation implies those of Seifert, Jarzynski and
Gallavotti-Cohen in different special cases
The analysis of Polyakov loop and spin correlators in finite volumes
We derive an analytic expression for point to point correlation functions of
the Polyakov loop based on the transfer matrix formalism. The contributions
from the eigenvalues of the transfer matrix including and beyond the mass gap
are investigated both for the Ising model and in finite temperature
gauge theory. We find that the leading matrix element shows similar
scaling properties in both models. Just above the critical point we obtain for
a Debye screening mass , independent of the volume.
Sorry, figures are not included and can be sent by ordinary mail.Comment: TALK GIVEN AT THE LATTICE '93 INTERNATIONAL SYMPOSIUM LATTICE FIELD
THEORY, DALLAS, USA, OCTOBER 12--16, 1993 3 pages preprint HU
BERLIN--IEP--93/5 and BIELEFELD BI-TP--93/63, November 199
A Trip from St. Paul Minn. to Los Angeles, California in a Ford Car
Diary of a cross country trip by automobile in 1920.https://digitalcommons.andrews.edu/books/1099/thumbnail.jp
Experiences with a Service Dog of an Adolescent with Spinal Muscular Atrophy
Adolescents with Spinal Muscular Atrophy (SMA) may receive occupational therapy services and may at times use service dogs. Literature suggests that service dogs can provide social and physical benefits to children and adults with physical disabilities, however little research has been published, especially with adolescents. A qualitative methodology was used to best gain insight on the daily life experiences with a service dog of a thirteen year old female adolescent with a diagnosis of SMA and her mother. Major themes that emerged from interviews included: A Process, A Special Bond, A Sense of Security, Increased Independence and Participation in Life, Empowering, Social Aspects, and The Future. The information gained from this study may lead occupational therapists to suggest clients apply for a service dog, assist clientâs with the transition of obtaining a service dogs, and incorporate service dogs into occupational therapy interventions
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