5,325 research outputs found
Piezoelectric copolymer hydrophones for ultrasonic field characterization
Hydrophones to be used in the characterization of medical ultrasonic transducers have
been fabricated using a new polyvinylidene fluoride/trifluoroethylene (VF2/VF3)
copolymer. The copolymer has an advantage over VF2 in that it does not require
prestretching before poling. Thin copolymer films can be cast from solution and then
poled using the corona discharge method. As there is a need for small‐diameter
hydrophones to provide good spatial resolution in measuring highly focused ultrasonic
beams, hydrophones with diameter as small as 0.1 mm have been made. Both
needle‐type and line hydrophones have been tested and their performance reported. In
the case of line hydrophones, the output signal is proportional to the line integral of the
acoustic pressure and a computer tomographic technique has been used to reconstruct the
beam profiles
The Distance to the Coma Cluster from Surface Brightness Fluctuations
We report on the first determination of the distance to the Coma Cluster
based on surface brightness fluctuation (SBF) measurements obtained from Hubble
Space Telescope WFPC2 observations of the bright E0 galaxy NGC 4881 in the Coma
Cluster and ground-based observations of the standard E1 galaxy NGC 3379 in the
Leo-I group. Relative distances based on the I-band fluctuation magnitude,
I(SBF), are strongly dependent on metallicity and age of the stellar
population. However, the radial changes in the stellar populations of the two
giant ellipticals, NGC 3379 and NGC 4881, are well described by published Mg_2
gradients, and the ground-based measurements of I(SBF) at several radial points
in NGC 3379 are used to calibrate I(SBF) in terms of the Mg_2 index. The
distance to NGC 3379, assumed to be identical to the average SBF distance of
the Leo-I group, is combined with the new SBF measurements of NGC 4881 to
obtain a Coma Cluster distance of 102+-14 Mpc. Combining this distance with the
cosmic recession velocity of Coma (7186+-428 km/s), we find the Hubble constant
to be H_0 = 71+-11 km/s/Mpc.Comment: 12 pages, LaTex, includes aaspp4.sty and 3 eps figures. To appear in
ApJ Letter
The Sivashinsky equation for corrugated flames in the large-wrinkle limit
Sivashinsky's (1977) nonlinear integro-differential equation for the shape of
corrugated 1-dimensional flames is ultimately reducible to a 2N-body problem,
involving the 2N complex poles of the flame slope. Thual, Frisch & Henon (1985)
derived singular linear integral equations for the pole density in the limit of
large steady wrinkles , which they solved exactly for monocoalesced
periodic fronts of highest amplitude of wrinkling and approximately otherwise.
Here we solve those analytically for isolated crests, next for monocoalesced
then bicoalesced periodic flame patterns, whatever the (large-) amplitudes
involved. We compare the analytically predicted pole densities and flame shapes
to numerical results deduced from the pole-decomposition approach. Good
agreement is obtained, even for moderately large Ns. The results are extended
to give hints as to the dynamics of supplementary poles. Open problems are
evoked
Gaia eclipsing binary and multiple systems. Two-Gaussian models applied to OGLE-III eclipsing binary light curves in the Large Magellanic Cloud
The advent of large scale multi-epoch surveys raises the need for automated
light curve (LC) processing. This is particularly true for eclipsing binaries
(EBs), which form one of the most populated types of variable objects. The Gaia
mission, launched at the end of 2013, is expected to detect of the order of few
million EBs over a 5-year mission.
We present an automated procedure to characterize EBs based on the geometric
morphology of their LCs with two aims: first to study an ensemble of EBs on a
statistical ground without the need to model the binary system, and second to
enable the automated identification of EBs that display atypical LCs. We model
the folded LC geometry of EBs using up to two Gaussian functions for the
eclipses and a cosine function for any ellipsoidal-like variability that may be
present between the eclipses. The procedure is applied to the OGLE-III data set
of EBs in the Large Magellanic Cloud (LMC) as a proof of concept. The bayesian
information criterion is used to select the best model among models containing
various combinations of those components, as well as to estimate the
significance of the components.
Based on the two-Gaussian models, EBs with atypical LC geometries are
successfully identified in two diagrams, using the Abbe values of the original
and residual folded LCs, and the reduced . Cleaning the data set from
the atypical cases and further filtering out LCs that contain non-significant
eclipse candidates, the ensemble of EBs can be studied on a statistical ground
using the two-Gaussian model parameters. For illustration purposes, we present
the distribution of projected eccentricities as a function of orbital period
for the OGLE-III set of EBs in the LMC, as well as the distribution of their
primary versus secondary eclipse widths.Comment: 20 pages, 29 figures. Submitted to A&
The mitochondrial Na+/Ca2+ exchanger upregulates glucose dependent Ca2+ signalling linked to insulin secretion.
Mitochondria mediate dual metabolic and Ca(2+) shuttling activities. While the former is required for Ca(2+) signalling linked to insulin secretion, the role of the latter in β cell function has not been well understood, primarily because the molecular identity of the mitochondrial Ca(2+) transporters were elusive and the selectivity of their inhibitors was questionable. This study focuses on NCLX, the recently discovered mitochondrial Na(+)/Ca(2+) exchanger that is linked to Ca(2+) signalling in MIN6 and primary β cells. Suppression either of NCLX expression, using a siRNA construct (siNCLX) or of its activity, by a dominant negative construct (dnNCLX), enhanced mitochondrial Ca(2+) influx and blocked efflux induced by glucose or by cell depolarization. In addition, NCLX regulated basal, but not glucose-dependent changes, in metabolic rate, mitochondrial membrane potential and mitochondrial resting Ca(2+). Importantly, NCLX controlled the rate and amplitude of cytosolic Ca(2+) changes induced by depolarization or high glucose, indicating that NCLX is a critical and rate limiting component in the cross talk between mitochondrial and plasma membrane Ca(2+) signalling. Finally, knockdown of NCLX expression was followed by a delay in glucose-dependent insulin secretion. These findings suggest that the mitochondrial Na(+)/Ca(2+) exchanger, NCLX, shapes glucose-dependent mitochondrial and cytosolic Ca(2+) signals thereby regulating the temporal pattern of insulin secretion in β cells
Type Ia supernova parameter estimation: a comparison of two approaches using current datasets
By using the Sloan Digital Sky Survey (SDSS) first year type Ia supernova (SN
Ia) compilation, we compare two different approaches (traditional \chi^2 and
complete likelihood) to determine parameter constraints when the magnitude
dispersion is to be estimated as well. We consider cosmological constant + Cold
Dark Matter (\Lambda CDM) and spatially flat, constant w Dark Energy + Cold
Dark Matter (FwCDM) cosmological models and show that, for current data, there
is a small difference in the best fit values and 30% difference in
confidence contour areas in case the MLCS2k2 light-curve fitter is adopted. For
the SALT2 light-curve fitter the differences are less significant (
13% difference in areas). In both cases the likelihood approach gives more
restrictive constraints. We argue for the importance of using the complete
likelihood instead of the \chi^2 approach when dealing with parameters in the
expression for the variance.Comment: 16 pages, 5 figures. More complete analysis by including peculiar
velocities and correlations among SALT2 parameters. Use of 2D contours
instead of 1D intervals for comparison. There can be now a significant
difference between the approaches, around 30% in contour area for MLCS2k2 and
up to 13% for SALT2. Generic streamlining of text and suppression of section
on model selectio
Sow body condition at weaning and reproduction performance in organic piglet production
The objective was to investigate the variation in backfat at weaning and its relations to reproduction results in organic sow herds in Denmark. The study included eight herds and 573 sows. The average backfat at weaning mean�13 mm; SD�4.2 mm) ranging from 10.5 to 17.3 mm among herds shows that it is possible to avoid poor body condition at weaning even with a lactation length of seven weeks or more. No main effect of backfat at weaning on reproduction performance was found, but the probability of a successful reproduction after weaning tended to decrease with decreasing backfat for first parity sows, whereas the opposite was the case for multiparous sows
Collaborative development of the Arrowsmith two node search interface designed for laboratory investigators.
Arrowsmith is a unique computer-assisted strategy designed to assist investigators in detecting biologically-relevant connections between two disparate sets of articles in Medline. This paper describes how an inter-institutional consortium of neuroscientists used the UIC Arrowsmith web interface http://arrowsmith.psych.uic.edu in their daily work and guided the development, refinement and expansion of the system into a suite of tools intended for use by the wider scientific community
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