5,543 research outputs found
Spontaneous Symmetry Breaking in General Relativity. Vector Order Parameter
Gravitational properties of a hedge-hog type topological defect in two extra
dimensions are considered in General Relativity employing a vector as the order
parameter. All previous considerations were done using the order parameter in
the form of a multiplet in a target space of scalar fields. The difference of
these two approaches is analyzed and demonstrated in detail. Regular solutions
of the Einstein equations are studied analytically and numerically. It is shown
that the existence of a negative cosmological constant is sufficient for the
spontaneous symmetry breaking of the initially plain bulk. Regular
configurations have a growing gravitational potential and are able to trap the
matter on the brane. If the energy of spontaneous symmetry breaking is high,
the gravitational potential has several points of minimum. Identical in the
uniform bulk spin-less particles, being trapped within separate minima, acquire
different masses and appear to the observer on brane as different particles
with integer spins.Comment: 23 pages, 6 figure
The protein import apparatus of chloroplasts
Routing of cytosolically synthesized precursor proteins into chloroplasts is a specific process which involves a multitude of soluble and membrane components. In this review we wil1 focus on early events of the translocation pathway of nuclear coded plastidic precursor proteins and compare import routes for polypeptide of the outer chloroplast envelope to that of internal chloroplast compartments. A number of proteins housed in the chloroplast envelopes have been implied to be involved in the translocation process, but so far a certain function has not been assigned to any of these proteins. The only exception could be an envelope localized hsc 70 homologue which could retain the import competence of a precursor protein in transit into the organelle
On the Nature of Trapped-Hole States in CdS Nanocrystals and the Mechanism of their Diffusion
Recent transient absorption experiments on CdS nanorods suggest that
photoexcited holes rapidly trap to the surface of these particles and then
undergo diffusion along the rod surface. In this paper, we present a
semiperiodic DFT model for the CdS nanocrystal surface, analyze it, and comment
on the nature of both the hole-trap states and the mechanism by which the holes
diffuse. Hole states near the top of the valence band form an energetic near
continuum with the bulk, and localize to the non-bonding sp orbitals on
surface sulfur atoms. After localization, the holes form nonadiabatic small
polarons that move between the sulfur orbitals on the surface of the particle
in a series of uncorrelated, incoherent, thermally-activated hops at room
temperature. The surface-trapped holes are deeply in the weak-electronic
coupling limit and, as a result, undergo slow diffusion.Comment: 4 figure
A Distributed Parallel Processing Environment Based upon the Linda Paradigm: A Research Prospectus
As the computing capacity of the uniprocessor is being taxed, and the high cost of parallel and super-computers is still prevalent, alternative methods of achieving parallel performance at an economical price are desired. This proposed research effort offers one such alternative, focusing on the idle CPU cycles existing on local area networks. With the increase in the computing power of workstations and their declining costs, one can effectively transform the unused computing power attached to a local area network into a parallel processing environment. Effectively exploiting such an environment, however, requires a specification and operational framework that is portable, easy to use, and efficient. The environment is constructed around the Linda parallel programming paradigm which provides an effective parallel computational framework
Where is SGR1806-20?
We apply a statistical method to derive very precise locations for soft gamma
repeaters using data from the interplanetary network. We demonstrate the
validity of the method by deriving a 600 arcsec^2 error ellipse for SGR1900+14
whose center agrees well with the VLA source position. We then apply it to
SGR1806-20, for which we obtain a 230 arcsec^2 error ellipse, the smallest
burst error box to date. We find that the most likely position of the source
has a small but significant displacement from that of the non-thermal core of
the radio supernova remnant G10.0-0.3, which was previously thought to be the
position of the repeater. We propose a different model to explain the changing
supernova remnant morphology and the positions of the luminous blue variable
and the bursting source.Comment: 12 pages and 2 color figures, accepted for publication in
Astrophysical Journal Letter
Bounding the dimensions of rational cohomology groups
Let be an algebraically closed field of characteristic , and let
be a simple simply-connected algebraic group over that is defined and
split over the prime field . In this paper we investigate
situations where the dimension of a rational cohomology group for can be
bounded by a constant times the dimension of the coefficient module. We then
demonstrate how our results can be applied to obtain effective bounds on the
first cohomology of the symmetric group. We also show how, for finite Chevalley
groups, our methods permit significant improvements over previous estimates for
the dimensions of second cohomology groups.Comment: 13 page
On the origin of the March 5, 1979 gamma ray transient: A vibrating neutron star in the Large Magellanic Cloud
It is proposed that a vibrating neutron star in the Large Magellanic Cloud is the source of the March 5 transient. Neutron star vibrations transport energy rapidly to the surface, heat the atmosphere by wave dissipation, and decay by gravitational radiation reaction. The electromagnetic emission arises from e(+)-e(-) pairs which cool and annihilate in the strong magnetic field of the neutron star. The field also confines the pairs, and this allows the production of the redshifted annihilation feature observed in the data. The redshift implies a gravitational radiation damping time which agrees with the 0.15 second duration of the impulsive phase of the event. Thus, the March 5 transient may be both the first detection of a vibrating neutron star and indirect evidence for gravitational radiation
Strange Quarks Nuggets in Space: Charges in Seven Settings
We have computed the charge that develops on an SQN in space as a result of
balance between the rates of ionization by ambient gammas and capture of
ambient electrons. We have also computed the times for achieving that
equilibrium and binding energy of the least bound SQN electrons. We have done
this for seven different settings. We sketch the calculations here and give
their results in the Figure and Table II; details are in the Physical Review
D.79.023513 (2009).Comment: Six pages, one figure. To appear in proceedings of the 2008 UCLA
coference on dark matter and dark energ
Simulations of snow distribution and hydrology in a mountain basin
We applied a version of the Regional Hydro‐Ecologic Simulation System (RHESSys) that implements snow redistribution, elevation partitioning, and wind‐driven sublimation to Loch Vale Watershed (LVWS), an alpine‐subalpine Rocky Mountain catchment where snow accumulation and ablation dominate the hydrologic cycle. We compared simulated discharge to measured discharge and the simulated snow distribution to photogrammetrically rectified aerial (remotely sensed) images. Snow redistribution was governed by a topographic similarity index. We subdivided each hillslope into elevation bands that had homogeneous climate extrapolated from observed climate. We created a distributed wind speed field that was used in conjunction with daily measured wind speeds to estimate sublimation. Modeling snow redistribution was critical to estimating the timing and magnitude of discharge. Incorporating elevation partitioning improved estimated timing of discharge but did not improve patterns of snow cover since wind was the dominant controller of areal snow patterns. Simulating wind‐driven sublimation was necessary to predict moisture losses
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