2,594 research outputs found
Extreme gravitational lensing in vicinity of Schwarzschild-de Sitter black holes
We have developed a realistic, fully general relativistic computer code to
simulate optical projection in a strong, spherically symmetric gravitational
field. The standard theoretical analysis of optical projection for an observer
in the vicinity of a Schwarzschild black hole is extended to black hole
spacetimes with a repulsive cosmological constant, i.e, Schwarzschild-de Sitter
spacetimes. Influence of the cosmological constant is investigated for static
observers and observers radially free-falling from the static radius.
Simulations include effects of the gravitational lensing, multiple images,
Doppler and gravitational frequency shift, as well as the intensity
amplification. The code generates images of the sky for the static observer and
a movie simulations of the changing sky for the radially free-falling observer.
Techniques of parallel programming are applied to get a high performance and a
fast run of the BHC simulation code
Acoustic Attenuation by Two-dimensional Arrays of Rigid Cylinders
In this Letter, we present a theoretical analysis of the acoustic
transmission through two-dimensional arrays of straight rigid cylinders placed
parallelly in the air. Both periodic and completely random arrangements of the
cylinders are considered. The results for the sound attenuation through the
periodic arrays are shown to be in a remarkable agreement with the reported
experimental data. As the arrangement of the cylinders is randomized, the
transmission is significantly reduced for a wider range of frequencies. For the
periodic arrays, the acoustic band structures are computed by the plane-wave
expansion method and are also shown to agree with previous results.Comment: 4 pages, 3 figure
Development of modeling tools to describe the corrosion behavior of uncoated EUROFER in flowing Pb-17Li and their validation by performing of corrosion tests at T up to 550⁰C
Equatorial circular orbits in the Kerr-de Sitter spacetimes
Equatorial motion of test particles in the Kerr-de Sitter spacetimes is
considered. Circular orbits are determined, their properties are discussed for
both the black-hole and naked-singularity spacetimes, and their relevance for
thin accretion discs is established.Comment: 24 pages, 19 figures, REVTeX
Effects of disorder in location and size of fence barriers on molecular motion in cell membranes
The effect of disorder in the energetic heights and in the physical locations
of fence barriers encountered by transmembrane molecules such as proteins and
lipids in their motion in cell membranes is studied theoretically. The
investigation takes as its starting point a recent analysis of a periodic
system with constant distances between barriers and constant values of barrier
heights, and employs effective medium theory to treat the disorder. The
calculations make possible, in principle, the extraction of confinement
parameters such as mean compartment sizes and mean intercompartmental
transition rates from experimentally reported published observations. The
analysis should be helpful both as an unusual application of effective medium
theory and as an investigation of observed molecular movements in cell
membranes.Comment: 9 pages, 5 figure
Molecular motion in cell membranes: analytic study of fence-hindered random walks
A theoretical calculation is presented to describe the confined motion of
transmembrane molecules in cell membranes. The study is analytic, based on
Master equations for the probability of the molecules moving as random walkers,
and leads to explicit usable solutions including expressions for the molecular
mean square displacement and effective diffusion constants. One outcome is a
detailed understanding of the dependence of the time variation of the mean
square displacement on the initial placement of the molecule within the
confined region. How to use the calculations is illustrated by extracting
(confinement) compartment sizes from experimentally reported published
observations from single particle tracking experiments on the diffusion of
gold-tagged G-protein coupled mu-opioid receptors in the normal rat kidney cell
membrane, and by further comparing the analytical results to observations on
the diffusion of phospholipids, also in normal rat kidney cells.Comment: 10 pages, 5 figure
A new triclinic modification of the pyrochlore-type KOs2O6 superconductor
A new modification of KOs2O6, the representative of a new structural type
(Pearson symbol aP18, a=5.5668(1)A, b=6.4519(2)A, c=7.2356(2)A, space group
P-1, no.2) was synthesized employing high pressure technique. Its structure was
determined by single-crystal X-ray diffraction. The structure can be described
as two OsO6 octahedral chains relating to each other through inversion and
forming big voids with K atoms inside. Quantum chemical calculations were
performed on the novel compound and structurally related cubic compound.
High-pressure X-ray study showed that cubic KOs2O6 phase was stable up to
32.5(2) GPa at room temperature.Comment: 23 pages, 9 figures,6 tables. Accepted for J. Solid State Che
Improving NLO-parton shower matched simulations with higher order matrix elements
In recent times the algorithms for the simulation of hadronic collisions have
been subject to two substantial improvements: the inclusion, within parton
showering, of exact higher order tree level matrix elements (MEPS) and,
separately, next-to-leading order corrections (NLOPS). In this work we examine
the key criteria to be met in merging the two approaches in such a way that the
accuracy of both is preserved, in the framework of the POWHEG approach to
NLOPS. We then ask to what extent these requirements may be fulfilled using
existing simulations, without modifications. The result of this study is a
pragmatic proposal for merging MEPS and NLOPS events to yield much improved
MENLOPS event samples. We apply this method to W boson and top quark pair
production. In both cases results for distributions within the remit of the NLO
calculations exhibit no discernible changes with respect to the pure NLOPS
prediction; conversely, those sensitive to the distribution of multiple hard
jets assume, exactly, the form of the corresponding MEPS results.Comment: 38 pages, 17 figures. v2: added citations and brief discussion of
related works, MENLOPS prescription localized in a subsection. v3: cited 4
more MEPS works in introduction
Endogenous Sex Steroid Hormones, Lipid Subfractions, and Ectopic Adiposity in Asian Indians
Background: Estradiol, testosterone (T), and sex hormone binding globulin (SHBG) levels are associated with lipid subfractions in men and women. Our objective was to determine if associations are independent from adipose tissue area among Asian Indians. Methods: We used data from 42 women and 57 Asian Indian men who did not use exogenous steroids or lipid-lowering medications. Lipoprotein subfractions including low-density lipoprotein cholesterol (LDL), very low-density lipoprotein cholesterol (VLDL), and intermediate density lipoprotein (IDL) were assessed by ion mobility spectrometry. Intra-abdominal adiposity was assessed by computed tomography. Multivariable regression models estimated the association between sex hormones with lipoprotein subfractions before and after adjustment for adiposity. Results: Among women, lower logSHBG levels were associated with smaller logLDL particle size and higher logtriglycerides, logVLDL, and logIDL, although these associations were attenuated with adjustment for visceral adiposity in particular. Among women, lower logSHBG levels was significantly associated with lower logmedium LDL and logsmall LDL concentrations even after consideration of visceral and hepatic adiposity and insulin resistance as represented by the homeostasis model assessment of insulin resistance (HOMA-IR). Among men, lower logSHBG was also associated with smaller logLDL peak diameter size and higher logtriglycerides and logVLDL, even after adjustment for HOMA-IR and adiposity. Relationships between sex steroids and lipid subfractions were not significant among women. Among men, higher total testosterone was associated with higher logHDL and logLDL particle size, and lower logtriglycerides and logVLDL, but these associations were partially attenuated with adjustment for adiposity and HOMA-IR. Conclusions: Among Asian Indians, SHBG is associated with more favorable lipid subfraction concentrations, independent of hepatic and visceral fat.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/140166/1/met.2015.0063.pd
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