1,671 research outputs found
Investigation of reliability attributes and accelerated stress factors on terrestrial solar cells
Major effort during this reporting period was devoted to two tasks: improvement of the electrical measurement instrumentation through the design and construction of a microcomputer controlled short interval tester, and better understanding of second quadrant behavior by developing a mathematical model relating cell temperature to electrical characteristics. In addition, some preliminary work is reported on an investigation into color changes observed after stressing
Azimuthal velocity profiles in Rayleigh-stable Taylor-Couette flow and implied axial angular momentum transport
We present azimuthal velocity profiles measured in a Taylor-Couette
apparatus, which has been used as a model of stellar and planetary accretion
disks. The apparatus has a cylinder radius ratio of , an
aspect-ratio of , and the plates closing the cylinders in the
axial direction are attached to the outer cylinder. We investigate angular
momentum transport and Ekman pumping in the Rayleigh-stable regime. The regime
is linearly stable and is characterized by radially increasing specific angular
momentum. We present several Rayleigh-stable profiles for shear Reynolds
numbers , both for
(quasi-Keplerian regime) and (sub-rotating regime)
where is the inner/outer cylinder rotation rate. None of the
velocity profiles matches the non-vortical laminar Taylor-Couette profile. The
deviation from that profile increased as solid-body rotation is approached at
fixed . Flow super-rotation, an angular velocity greater than that of
both cylinders, is observed in the sub-rotating regime. The velocity profiles
give lower bounds for the torques required to rotate the inner cylinder that
were larger than the torques for the case of laminar Taylor-Couette flow. The
quasi-Keplerian profiles are composed of a well mixed inner region, having
approximately constant angular momentum, connected to an outer region in
solid-body rotation with the outer cylinder and attached axial boundaries.
These regions suggest that the angular momentum is transported axially to the
axial boundaries. Therefore, Taylor-Couette flow with closing plates attached
to the outer cylinder is an imperfect model for accretion disk flows,
especially with regard to their stability.Comment: 22 pages, 10 figures, 2 tables, under consideration for publication
in Journal of Fluid Mechanics (JFM
Algorithm engineering for optimal alignment of protein structure distance matrices
Protein structural alignment is an important problem in computational
biology. In this paper, we present first successes on provably optimal pairwise
alignment of protein inter-residue distance matrices, using the popular Dali
scoring function. We introduce the structural alignment problem formally, which
enables us to express a variety of scoring functions used in previous work as
special cases in a unified framework. Further, we propose the first
mathematical model for computing optimal structural alignments based on dense
inter-residue distance matrices. We therefore reformulate the problem as a
special graph problem and give a tight integer linear programming model. We
then present algorithm engineering techniques to handle the huge integer linear
programs of real-life distance matrix alignment problems. Applying these
techniques, we can compute provably optimal Dali alignments for the very first
time
Universality in fully developed turbulence
We extend the numerical simulations of She et al. [Phys.\ Rev.\ Lett.\ 70,
3251 (1993)] of highly turbulent flow with Taylor-Reynolds number
up to , employing a reduced wave
vector set method (introduced earlier) to approximately solve the Navier-Stokes
equation. First, also for these extremely high Reynolds numbers ,
the energy spectra as well as the higher moments -- when scaled by the spectral
intensity at the wave number of peak dissipation -- can be described by
{\it one universal} function of for all . Second, the ISR
scaling exponents of this universal function are in agreement with
the 1941 Kolmogorov theory (the better, the large is), as is the
dependence of . Only around viscous damping leads to
slight energy pileup in the spectra, as in the experimental data (bottleneck
phenomenon).Comment: 14 pages, Latex, 5 figures (on request), 3 tables, submitted to Phys.
Rev.
On parameters of the Levi-Civita solution
The Levi-Civita (LC) solution is matched to a cylindrical shell of an
anisotropic fluid. The fluid satisfies the energy conditions when the mass
parameter is in the range . The mass per unit
length of the shell is given explicitly in terms of , which has a
finite maximum. The relevance of the results to the non-existence of horizons
in the LC solution and to gauge cosmic strings is pointed out.Comment: Latex, no figure
Perfect-fluid cylinders and walls - sources for the Levi-Civita space-time
The diagonal metric tensor whose components are functions of one spatial
coordinate is considered. Einstein's field equations for a perfect-fluid source
are reduced to quadratures once a generating function, equal to the product of
two of the metric components, is chosen. The solutions are either static fluid
cylinders or walls depending on whether or not one of the spatial coordinates
is periodic. Cylinder and wall sources are generated and matched to the vacuum
(Levi--Civita) space--time. A match to a cylinder source is achieved for
-\frac{1}{2}<\si<\frac{1}{2}, where \si is the mass per unit length in the
Newtonian limit \si\to 0, and a match to a wall source is possible for
|\si|>\frac{1}{2}, this case being without a Newtonian limit; the positive
(negative) values of \si correspond to a positive (negative) fluid density.
The range of \si for which a source has previously been matched to the
Levi--Civita metric is 0\leq\si<\frac{1}{2} for a cylinder source.Comment: 22 pages, LaTeX, one included figure. Revised version: three
(non-perfect-fluid) interior solutions are added, one of which falsifies the
original conjecture in Sec. 4, and the circular geodesics of the Levi-Civita
space-time are discussed in a footnot
Immunoseq: the identification of functionally relevant variants through targeted capture and sequencing of active regulatory regions in human immune cells
: The observation that the genetic variants identified in genome-wide association studies (GWAS) frequently lie in non-coding regions of the genome that contain cis-regulatory elements suggests that altered gene expression underlies the development of many complex traits. In order to efficiently make a comprehensive assessment of the impact of non-coding genetic variation in immune related diseases we emulated the whole-exome sequencing paradigm and developed a custom capture panel for the known DNase I hypersensitive site (DHS) in immune cells - "Immunoseq".
: We performed Immunoseq in 30 healthy individuals where we had existing transcriptome data from T cells. We identified a large number of novel non-coding variants in these samples. Relying on allele specific expression measurements, we also showed that our selected capture regions are enriched for functional variants that have an impact on differential allelic gene expression. The results from a replication set with 180 samples confirmed our observations.
: We show that Immunoseq is a powerful approach to detect novel rare variants in regulatory regions. We also demonstrate that these novel variants have a potential functional role in immune cells.This work was supported by grants from the Canadian Institute of Health Research (CIHR), the UK Medical Research Council (G1100125), the Swedish Research Council (DO283001) and Knut and Alice Wallenberg Foundation (KAW). We also acknowledge the use of subjects from the Cambridge BioResource and the support of the Cambridge NIHR Biomedical Research Centre. AM was supported by the Fond de Recherche Santé Québec Doctoral training award. TP and CL holds a Canada Research Chair
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