7,235 research outputs found
Tumbleweeds and airborne gravitational noise sources for LIGO
Gravitational-wave detectors are sensitive not only to astrophysical
gravitational waves, but also to the fluctuating Newtonian gravitational forces
of moving masses in the ground and air around the detector. This paper studies
the gravitational effects of density perturbations in the atmosphere, and from
massive airborne objects near the detector. These effects were previously
considered by Saulson; in this paper I revisit these phenomena, considering
transient atmospheric shocks, and the effects of sound waves or objects
colliding with the ground or buildings around the test masses. I also consider
temperature perturbations advected past the detector as a source of
gravitational noise. I find that the gravitational noise background is below
the expected noise floor even of advanced interferometric detectors, although
only by an order of magnitude for temperature perturbations carried along
turbulent streamlines. I also find that transient shockwaves in the atmosphere
could potentially produce large spurious signals, with signal-to-noise ratios
in the hundreds in an advanced interferometric detector. These signals could be
vetoed by means of acoustic sensors outside of the buildings. Massive
wind-borne objects such as tumbleweeds could also produce gravitational signals
with signal-to-noise ratios in the hundreds if they collide with the
interferometer buildings, so it may be necessary to build fences preventing
such objects from approaching within about 30m of the test masses.Comment: 15 pages, 10 PostScript figures, uses REVTeX4.cls and epsfig.st
Two-Gaussian excitations model for the glass transition
We develop a modified "two-state" model with Gaussian widths for the site
energies of both ground and excited states, consistent with expectations for a
disordered system. The thermodynamic properties of the system are analyzed in
configuration space and found to bridge the gap between simple two state models
("logarithmic" model in configuration space) and the random energy model
("Gaussian" model in configuration space). The Kauzmann singularity given by
the random energy model remains for very fragile liquids but is suppressed or
eliminated for stronger liquids. The sharp form of constant volume heat
capacity found by recent simulations for binary mixed Lennard Jones and soft
sphere systems is reproduced by the model, as is the excess entropy and heat
capacity of a variety of laboratory systems, strong and fragile. The ideal
glass in all cases has a narrow Gaussian, almost invariant among molecular and
atomic glassformers, while the excited state Gaussian depends on the system and
its width plays a role in the thermodynamic fragility. The model predicts the
existence of first-order phase transition for fragile liquids.Comment: 12 pages, 12 figure
Structural change of vortex patterns in anisotropic Bose-Einstein condensates
We study the changes in the spatial distribution of vortices in a rotating
Bose-Einstein condensate due to an increasing anisotropy of the trapping
potential. Once the rotational symmetry is broken, we find that the vortex
system undergoes a rich variety of structural changes, including the formation
of zig-zag and linear configurations. These spatial re-arrangements are well
signaled by the change in the behavior of the vortex-pattern eigenmodes against
the anisotropy parameter. The existence of such structural changes opens up
possibilities for the coherent exploitation of effective many-body systems
based on vortex patterns.Comment: 5 pages, 4 figure
Immunofluorescent Examination of Biopsies from Long-Term Renal Allografts
Immunofluorescent examination of open renal biopsies revealed clear-cut glomerular localization of immunoglobulins not related clearly to the quality of donor-recipient histocompatibility in 19 of 34 renal allografts. The biopsies were obtained 18 to 31 months after transplantations primarily from related donors with a variable quality of histocompatibility match. IgG was the predominant immunoglobulin class fixed in 13 biopsies, and IgM in six. The pattern of immunoglobulin deposition was linear, connoting anti-GBM antibody in four of the 19; it was granular and discontinuous, connoting antigen–antibodycomplex deposits, in 13. An immune process may affect glomeruli of renal allografts by mechanisms comparable to those that cause glomerulonephritis in native kidneys. The transplant glomerulonephritis may represent a persistence of the same disease that originally destroyed the host kidneys or the consequence of a new humoral antibody response to allograft antigens. © 1970, Massachusetts Medical Society. All rights reserved
Low-density, one-dimensional quantum gases in a split trap
We investigate degenerate quantum gases in one dimension trapped in a
harmonic potential that is split in the centre by a pointlike potential. Since
the single particle eigenfunctions of such a system are known for all strengths
of the central potential, the dynamics for non-interacting fermionic gases and
low-density, strongly interacting bosonic gases can be investigated exactly
using the Fermi-Bose mapping theorem. We calculate the exact many-particle
ground-state wave-functions for both particle species, investigate soliton-like
solutions, and compare the bosonic system to the well-known physics of Bose
gases described by the Gross-Pitaevskii equation. We also address the
experimentally important questions of creation and detection of such states.Comment: 7 pages, 5 figure
Self-adjoint Lyapunov variables, temporal ordering and irreversible representations of Schroedinger evolution
In non relativistic quantum mechanics time enters as a parameter in the
Schroedinger equation. However, there are various situations where the need
arises to view time as a dynamical variable. In this paper we consider the
dynamical role of time through the construction of a Lyapunov variable - i.e.,
a self-adjoint quantum observable whose expectation value varies monotonically
as time increases. It is shown, in a constructive way, that a certain class of
models admit a Lyapunov variable and that the existence of a Lyapunov variable
implies the existence of a transformation mapping the original quantum
mechanical problem to an equivalent irreversible representation. In addition,
it is proved that in the irreversible representation there exists a natural
time ordering observable splitting the Hilbert space at each t>0 into past and
future subspaces.Comment: Accepted for publication in JMP. Supercedes arXiv:0710.3604.
Discussion expanded to include the case of Hamiltonians with an infinitely
degenerate spectru
Rapid online buffer exchange for screening of proteins, protein complexes and cell lysates by native mass spectrometry
It is important to assess the identity and purity of proteins and protein complexes during and after protein purification to ensure that samples are of sufficient quality for further biochemical and structural characterization, as well as for use in consumer products, chemical processes and therapeutics. Native mass spectrometry (nMS) has become an important tool in protein analysis due to its ability to retain non-covalent interactions during measurements, making it possible to obtain protein structural information with high sensitivity and at high speed. Interferences from the presence of non-volatiles are typically alleviated by offline buffer exchange, which is time-consuming and difficult to automate. We provide a protocol for rapid online buffer exchange (OBE) nMS to directly screen structural features of pre-purified proteins, protein complexes or clarified cell lysates. In the liquid chromatography coupled to mass spectrometry (LC-MS) approach described in this protocol, samples in MS-incompatible conditions are injected onto a short size-exclusion chromatography column. Proteins and protein complexes are separated from small molecule non-volatile buffer components using an aqueous, non-denaturing mobile phase. Eluted proteins and protein complexes are detected by the mass spectrometer after electrospray ionization. Mass spectra can inform regarding protein sample purity and oligomerization, and additional tandem mass spectra can help to further obtain information on protein complex subunits. Information obtained by OBE nMS can be used for fast (<5 min) quality control and can further guide protein expression and purification optimization
Vortex shear effects in layered superconductors
Motivated by recent transport and magnetization measurements in BSCCO samples
[B. Khaykovich et. al., Phys. Rev. B 61, R9261 (2000)], we present a simple
macroscopic model describing effects of inhomogeneous current distribution and
shear in a layered superconductor. Parameters of the model are deduced from a
microscopic calculation. Our model accounts for the strong current
non-linearities and the re-entrant temperature dependence observed in the
experiment.Comment: 11 pages, 7 figures, submitted to Phys. Rev.
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