15,424 research outputs found
Simulation of Ultra-Relativistic Electrons and Positrons Channeling in Crystals with MBN Explorer
A newly developed code, implemented as a part of the \MBNExplorer package
\cite{MBN_ExplorerPaper,MBN_ExplorerSite} to simulate trajectories of an
ultra-relativistic projectile in a crystalline medium, is presented. The motion
of a projectile is treated classically by integrating the relativistic
equations of motion with account for the interaction between the projectile and
crystal atoms. The probabilistic element is introduced by a random choice of
transverse coordinates and velocities of the projectile at the crystal entrance
as well as by accounting for the random positions of the atoms due to thermal
vibrations. The simulated trajectories are used for numerical analysis of the
emitted radiation. Initial approbation and verification of the code have been
carried out by simulating the trajectories and calculating the radiation
emitted by \E=6.7 GeV and \E=855 MeV electrons and positrons in oriented
Si(110) crystal and in amorphous silicon. The calculated spectra are compared
with the experimental data and with predictions of the Bethe-Heitler theory for
the amorphous environment.Comment: 41 pages, 11 figures. Initially submitted on Dec 29, 2012 to Phys.
Rev.
Particles held by springs in a linear shear flow exhibit oscillatory motion
The dynamics of small spheres, which are held by linear springs in a low
Reynolds number shear flow at neighboring locations is investigated. The flow
elongates the beads and the interplay of the shear gradient with the nonlinear
behavior of the hydrodynamic interaction among the spheres causes in a large
range of parameters a bifurcation to a surprising oscillatory bead motion. The
parameter ranges, wherein this bifurcation is either super- or subcritical, are
determined.Comment: 4 pages, 5 figure
Research on Geometrical Errors of Geokhod Prototype Shell Based on Coordinate Control Data
The article contains results of a research on geometric accuracy of a geokhod prototype shell. The article outlines the general structural features of geokhod bodies, and the main principles of manufacturing in test production. An overview of approaches to modeling of shell error occurrence is given. The researches were conducted on the basis of data obtained by coordinate control over the stabilizing section shell. The data were studied by statistical methods and analyzed in terms of their compliance with previously proposed mathematical models of formation of geokhod shell inaccuracies. It is shown that available mathematical models can not completely explain the origin of all the errors. The authors attribute unexplained geokhod shell errors as deformations caused by welding
Non-Markovian quantum state diffusion for absorption spectra of molecular aggregates
In many molecular systems one encounters the situation where electronic
excitations couple to a quasi-continuum of phonon modes. That continuum may be
highly structured e.g. due to some weakly damped high frequency modes. To
handle such a situation, an approach combining the non-Markovian quantum state
diffusion (NMQSD) description of open quantum systems with an efficient but
abstract approximation was recently applied to calculate energy transfer and
absorption spectra of molecular aggregates [Roden, Eisfeld, Wolff, Strunz, PRL
103 (2009) 058301]. To explore the validity of the used approximation for such
complicated systems, in the present work we compare the calculated
(approximative) absorption spectra with exact results. These are obtained from
the method of pseudomodes, which we show to be capable of determining the exact
spectra for small aggregates and a few pseudomodes. It turns out that in the
cases considered, the results of the two approaches mostly agree quite well.
The advantages and disadvantages of the two approaches are discussed
Probing the Earth's interior with a large-volume liquid scintillator detector
A future large-volume liquid scintillator detector would provide a
high-statistics measurement of terrestrial antineutrinos originating from
-decays of the uranium and thorium chains. In addition, the forward
displacement of the neutron in the detection reaction
provides directional information. We investigate the requirements on such
detectors to distinguish between certain geophysical models on the basis of the
angular dependence of the geoneutrino flux. Our analysis is based on a
Monte-Carlo simulation with different levels of light yield, considering both
unloaded and gadolinium-loaded scintillators. We find that a 50 kt detector
such as the proposed LENA (Low Energy Neutrino Astronomy) will detect
deviations from isotropy of the geoneutrino flux significantly. However, with
an unloaded scintillator the time needed for a useful discrimination between
different geophysical models is too large if one uses the directional
information alone. A Gd-loaded scintillator improves the situation
considerably, although a 50 kt detector would still need several decades to
distinguish between a geophysical reference model and one with a large neutrino
source in the Earth's core. However, a high-statistics measurement of the total
geoneutrino flux and its spectrum still provides an extremely useful glance at
the Earth's interior.Comment: 21 pages, 9 figures. Minor changes, version accepted for publication
in Astroparticle Physic
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