753 research outputs found
Automated analysis of slow crack growth in hydrous soda-lime silicate glasses
To explore the impact of ambient and structural water on static fatigue, the initiation and growth of 3279 Vickers induced median radial cracks were automatically recorded and analyzed. We find that humidity is more efficient in initiating cracks and promoting their growth than water, which is dissolved in the glass structure. In particular for slow crack
growth (< 3 Ă 10â6 m sâ1), tests in dry nitrogen showed a considerable decrease in the crack growth exponent with increasing water content of the glasses. On the other hand, if tests were performed in humid air, the crack growth exponent was independent of the water content of the hydrous glasses, while stress intensity decreased slightly. These observations indicate that water promotes the processes at the crack-tip regardless of its origin. However, ambient water is more efficient
Automated Analysis of Slow Crack Growth in Hydrous Soda-Lime Silicate Glasses
To explore the impact of ambient and structural water on static fatigue, the initiation and growth of 3279 Vickers induced median radial cracks were automatically recorded and analyzed. We find that humidity is more efficient in initiating cracks and promoting their growth than water, which is dissolved in the glass structure. In particular for slow crack growth (< 3 Ă 10â6 m sâ1), tests in dry nitrogen showed a considerable decrease in the crack growth exponent with increasing water content of the glasses. On the other hand, if tests were performed in humid air, the crack growth exponent was independent of the water content of the hydrous glasses, while stress intensity decreased slightly. These observations indicate that water promotes the processes at the crack-tip regardless of its origin. However, ambient water is more efficient
On the relevance of technical variation due to building pools in microarray experiments
Background Pooled samples are frequently used in experiments measuring gene
expression. In this method, RNA from different individuals sharing the same
experimental conditions and explanatory variables is blended and their
concentrations are jointly measured. As a matter of principle, individuals are
represented in equal shares in each pool. However, some degree of
disproportionality may arise from the limits of technical precision. As a
consequence a special kind of technical error occurs, which can be modelled by
a respective variance component. Previously published theory - allowing for
variable pool sizes - has been applied to four microarray gene expression data
sets from different species in order to assess the practical relevance of this
type of technical error in terms of significance and size of this variance
component. Results The number of transcripts with a significant variance
component due to imperfect blending was found to be 4329 (23 %) in mouse data
and 7093 (49 %) in honey bees, but only 6 in rats and none whatsoever in human
data. These results correspond to a false discovery rate of 5 % in each data
set. The number of transcripts found to be differentially expressed between
treatments was always higher when the blending error variance was neglected.
Simulations clearly indicated overly-optimistic (anti-conservative) test
results in terms of false discovery rates whenever this source of variability
was not represented in the model. Conclusions Imperfect equality of shares
when blending RNA from different individuals into joint pools of variable size
is a source of technical variation with relevance for experimental design,
practice at the laboratory bench and data analysis. Its potentially adverse
effects, incorrect identification of differentially expressed transcripts and
overly-optimistic significance tests, can be fully avoided, however, by the
sound application of recently established theory and models for data analysis
An EUV Study of the Intermediate Polar EX Hydrae
On 2000 May 5, we began a large multi-wavelength campaign to study the
intermediate polar, EX Hydrae. The simultaneous observations from six
satellites and four telescopes were centered around a one million second
observation with EUVE. Although EX Hydrae has been studied previously with
EUVE, our higher signal-to-noise observations present new results and challenge
the current IP models. Previously unseen dips in the light curve are
reminiscent of the stream dips seen in polar light curves. Also of interest is
the temporal extent of the bulge dip; approximately 0.5 in phase, implying that
the bulge extends over half of the accretion disk. We propose that the magnetic
field in EX Hydrae is strong enough (a few MG) to begin pulling material
directly from the outer edge of the disk, thereby forming a large accretion
curtain which would produce a very broad bulge dip. This would also result in
magnetically controlled accretion streams originating from the outer edge of
the disk. We also present a period analysis of the photometric data which shows
numerous beat frequencies with strong power and also intermittent and wandering
frequencies, an indication that physical conditions within EX Hya changed over
the course of the observation. Iron spectral line ratios give a temperature of
log T=6.5-6.9 K for all spin phases and a poorly constrained density of
n_e=10^10-10^11 cm^-3 for the emitting plasma. This paper is the first in a
series detailing our results from this multi-wavelength observational campaign.Comment: 27 pages, 7 figures, accepted for publication in Ap
Composites based on acylated cellulose fibers and low-density polyethylene: Effect of the fiber content, degree of substitution and fatty acid chain length on final properties
Low-density polyethylene was filled with unmodified and fatty acid (hexanoic, dodecanoic, octadecanoic and docosanoic acids) esterified cellulose fibers. The thermal and mechanical properties, morphology and the water absorption behavior of the ensuing composites were investigated. The chemical modification of the cellulose fibers with fatty acids clearly improved the interfacial adhesion with the matrix and hence the mechanical properties of the composites and decreased their water uptake capacity. The performance of the composites was strongly affected by the degree of substitution (DS) and the fatty chain length as indicated by the fact that esterified cellulose fibers with low DS gave composites with better mechanical properties. (C) 2008 Elsevier Ltd. All rights reserved
Progenitors of Type Ia Supernovae: Binary Stars with White Dwarf Companions
Type Ia SNe (SNe Ia) are thought to come from carbon-oxygen white dwarfs that
accrete mass from binary companions until they approach the Chandrasekhar
limit, ignite carbon, and undergo complete thermonuclear disruption. A survey
of the observed types of binaries that contain white dwarfs is presented. We
propose that certain systems that seem most promising as SN Ia progenitors
should be more intensively observed and modeled, to determine whether the white
dwarfs in these systems will be able to reach the Chandrasekhar limit. In view
of the number of promising single-degenerate systems and the dearth of
promising double-degenerate systems, we suspect that single-degenerates produce
most or perhaps all SNe Ia, while double-degenerates produce some or perhaps
none.Comment: 34 pages, to appear in New Astronomy Review
Combined analysis of data from two granddaughter designs: A simple strategy for QTL confirmation and increasing experimental power in dairy cattle
A joint analysis of five paternal half-sib Holstein families that were part of two different granddaughter designs (ADR- or Inra-design) was carried out for five milk production traits and somatic cell score in order to conduct a QTL confirmation study and to increase the experimental power. Data were exchanged in a coded and standardised form. The combined data set (JOINT-design) consisted of on average 231 sires per grandsire. Genetic maps were calculated for 133 markers distributed over nine chromosomes. QTL analyses were performed separately for each design and each trait. The results revealed QTL for milk production on chromosome 14, for milk yield on chromosome 5, and for fat content on chromosome 19 in both the ADR- and the Inra-design (confirmed within this study). Some QTL could only be mapped in either the ADR- or in the Inra-design (not confirmed within this study). Additional QTL previously undetected in the single designs were mapped in the JOINT-design for fat yield (chromosome 19 and 26), protein yield (chromosome 26), protein content (chromosome 5), and somatic cell score (chromosome 2 and 19) with genomewide significance. This study demonstrated the potential benefits of a combined analysis of data from different granddaughter designs
Moyal star product approach to the Bohr-Sommerfeld approximation
The Bohr-Sommerfeld approximation to the eigenvalues of a one-dimensional
quantum Hamiltonian is derived through order (i.e., including the
first correction term beyond the usual result) by means of the Moyal star
product. The Hamiltonian need only have a Weyl transform (or symbol) that is a
power series in , starting with , with a generic fixed point in
phase space. The Hamiltonian is not restricted to the kinetic-plus-potential
form. The method involves transforming the Hamiltonian to a normal form, in
which it becomes a function of the harmonic oscillator Hamiltonian.
Diagrammatic and other techniques with potential applications to other normal
form problems are presented for manipulating higher order terms in the Moyal
series.Comment: 27 pages, no figure
Two Distinct Integrin-Mediated Mechanisms Contribute to Apical Lumen Formation in Epithelial Cells
Background: Formation of apical compartments underlies the morphogenesis of most epithelial organs during development. The extracellular matrix (ECM), particularly the basement membrane (BM), plays an important role in orienting the apico-basal polarity and thereby the positioning of apical lumens. Integrins have been recognized as essential mediators of matrix-derived polarity signals. The importance of b1-integrins in epithelial polarization is well established but the significance of the accompanying a-subunits have not been analyzed in detail. Principal Findings: Here we demonstrate that two distinct integrin-dependent pathways regulate formation of apical lumens to ensure robust apical membrane biogenesis under different microenvironmental conditions; 1) a2b1- and a6b4integrins were required to establish a basal cue that depends on Rac1-activity and guides apico-basal cell polarization. 2) a3b1-integrins were implicated in positioning of mitotic spindles in cysts, a process that is essential for Cdc42-driven epithelial hollowing. Significance: Identification of the separate processes driven by particular integrin receptors clarifies the functional hierarchies between the different integrins co-expressed in epithelial cells and provides valuable insight into the complexity of cell-ECM interactions thereby guiding future studies addressing the molecular basis of epithelial morphogenesis durin
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