2,679 research outputs found
Gas adsorption/desorption in silica aerogels: a theoretical study of scattering properties
We present a numerical study of the structural correlations associated to gas
adsorption/desorption in silica aerogels in order to provide a theoretical
interpretation of scattering experiments. Following our earlier work, we use a
coarse-grained lattice-gas description and determine the nonequilibrium
behavior of the adsorbed gas within a local mean-field analysis.
We focus on the differences between the adsorption and desorption mechanisms
and their signature in the fluid-fluid and gel-fluid structure factors as a
function of temperature. At low temperature, but still in the regime where the
isotherms are continuous, we find that the adsorbed fluid density, during both
filling and draining, is correlated over distances that may be much larger than
the gel correlation length. In particular, extended fractal correlations may
occur during desorption, indicating the existence of a ramified cluster of
vapor filled cavities. This also induces an important increase of the
scattering intensity at small wave vectors. The similarity and differences with
the scattering of fluids in other porous solids such as Vycor are discussed.Comment: 16 pages, 15 figure
Multilayered printed circuit boards inspected by X-ray laminography
Technique produces high resolution cross-sectional radiographs with close interplane spacing for inspecting multilayer boards to be used in providing circuitry routing and module structural support
Discovery of a Classic FR-II Broad Absorption Line Quasar from the FIRST Survey
We have discovered a remarkable quasar, FIRST J101614.3+520916, whose optical
spectrum shows unambiguous broad absorption features while its double-lobed
radio morphology and luminosity clearly indicate a classic Fanaroff-Riley Type
II radio source. Its radio luminosity places it at the extreme of the recently
established class of radio-loud broad absorption line quasars (Becker et al.
1997, 2000; Brotherton et al. 1998). Because of its hybrid nature, we speculate
that FIRST J101614.3+520916 is a typical FR-II quasar which has been
rejuvenated as a broad absorption line (BAL) quasar with a Compact Steep
Spectrum core. The direction of the jet axis of FIRST J101614.3+520916 can be
estimated from its radio structure and optical brightness, indicating that we
are viewing the system at a viewing angle of > 40 degrees. The position angles
of the radio jet and optical polarization are not well-aligned, differing by 20
to 30 degrees. When combined with the evidence presented by Becker et al.
(2000) for a sample of 29 BAL quasars showing that at least some BAL quasars
are viewed along the jet axis, the implication is that no preferred viewing
orientation is necessary to observe BAL systems in a quasar's spectrum. This,
and the probable young nature of compact steep spectrum sources, leads
naturally to the alternate hypothesis that BALs are an early stage in the lives
of quasars.Comment: 14 pages, 6 postscript figures; accepted for publication in the
Astrophysical Journa
Cetrorelix suppresses the preovulatory LH surge and ovulation induced by ovulation-inducing factor (OIF) present in llama seminal plasma
<p>Abstract</p> <p>Background</p> <p>The purpose of the study was to determine if the effect of llama OIF on LH secretion is mediated by stimulation of the hypothalamus or pituitary gland.</p> <p>Methods</p> <p>Using a 2-by-2 factorial design to examine the effects of OIF vs GnRH with or without a GnRH antagonist, llamas with a growing ovarian follicle greater than or equal to 8 mm were assigned randomly to four groups (n = 7 per group) and <b>a) </b>pre-treated with 1.5 mg of GnRH antagonist (cetrorelix acetate) followed by 1 mg of purified llama OIF, <b>b) </b>pre-treated with 1.5 mg of cetrorelix followed by 50 micrograms of GnRH, <b>c) </b>pre-treated with a placebo (2 ml of saline) followed by 1 mg of purified llama OIF or <b>d) </b>pre-treated with a placebo (2 ml of saline) followed by 50 micrograms of GnRH. Pre-treatment with cetrorelix or saline was given as a single slow intravenous dose 2 hours before intramuscular administration of either GnRH or OIF. Blood samples for LH measurement were taken every 15 minutes from 1.5 hours before to 8 hours after treatment. The ovaries were examined by ultrasonography to detect ovulation and CL formation. Blood samples for progesterone measurement were taken every-other-day from Day 0 (day of treatment) to Day 16.</p> <p>Results</p> <p>Ovulation rate was not different (P = 0.89) between placebo+GnRH (86%) and placebo+OIF groups (100%); however, no ovulations were detected in llamas pre-treated with cetrorelix. Plasma LH concentrations surged (P < 0.01) after treatment in both placebo+OIF and placebo+GnRH groups, but not in the cetrorelix groups. Maximum plasma LH concentrations and CL diameter profiles did not differ between the placebo-treated groups, but plasma progesterone concentrations were higher (P < 0.05), on days 6, 8 and 12 after treatment, in the OIF- vs GnRH-treated group.</p> <p>Conclusion</p> <p>Cetrorelix (GnRH antagonist) inhibited the preovulatory LH surge induced by OIF in llamas suggesting that LH secretion is modulated by a direct or indirect effect of OIF on GnRH neurons in the hypothalamus.</p
Long Range Correlation in Granular Shear Flow II: Theoretical Implications
Numerical simulations are used to test the kinetic theory constitutive
relations of inertial granular shear flow. These predictions are shown to be
accurate in the dilute regime, where only binary collisions are relevant, but
underestimate the measured value in the dense regime, where force networks of
size are present. The discrepancy in the dense regime is due to
non-collisional forces that we measure directly in our simulations and arise
from elastic deformations of the force networks. We model the non-collisional
stress by summing over all paths that elastic waves travel through force
networks. This results in an analytical theory that successfully predicts the
stress tensor over the entire inertial regime without any adjustable
parameters
Relationship of national institutes of health stroke scale to 30-day mortality in medicare beneficiaries with acute ischemic stroke.
BackgroundThe National Institutes of Health Stroke Scale (NIHSS), a well-validated tool for assessing initial stroke severity, has previously been shown to be associated with mortality in acute ischemic stroke. However, the relationship, optimal categorization, and risk discrimination with the NIHSS for predicting 30-day mortality among Medicare beneficiaries with acute ischemic stroke has not been well studied.Methods and resultsWe analyzed data from 33102 fee-for-service Medicare beneficiaries treated at 404 Get With The Guidelines-Stroke hospitals between April 2003 and December 2006 with NIHSS documented. The 30-day mortality rate by NIHSS as a continuous variable and by risk-tree determined or prespecified categories were analyzed, with discrimination of risk quantified by the c-statistic. In this cohort, mean age was 79.0 years and 58% were female. The median NIHSS score was 5 (25th to 75th percentile 2 to 12). There were 4496 deaths in the first 30 days (13.6%). There was a strong graded relation between increasing NIHSS score and higher 30-day mortality. The 30-day mortality rates for acute ischemic stroke by NIHSS categories were as follows: 0 to 7, 4.2%; 8 to 13, 13.9%; 14 to 21, 31.6%; 22 to 42, 53.5%. A model with NIHSS alone provided excellent discrimination whether included as a continuous variable (c-statistic 0.82 [0.81 to 0.83]), 4 categories (c-statistic 0.80 [0.79 to 0.80]), or 3 categories (c-statistic 0.79 [0.78 to 0.79]).ConclusionsThe NIHSS provides substantial prognostic information regarding 30-day mortality risk in Medicare beneficiaries with acute ischemic stroke. This index of stroke severity is a very strong discriminator of mortality risk, even in the absence of other clinical information, whether used as a continuous or categorical risk determinant. (J Am Heart Assoc. 2012;1:42-50.)
Capillary condensation in disordered porous materials: hysteresis versus equilibrium behavior
We study the interplay between hysteresis and equilibrium behavior in
capillary condensation of fluids in mesoporous disordered materials via a
mean-field density functional theory of a disordered lattice-gas model. The
approach reproduces all major features observed experimentally. We show that
the simple van der Waals picture of metastability fails due to the appearance
of a complex free-energy landscape with a large number of metastable states. In
particular, hysteresis can occur both with and without an underlying
equilibrium transition, thermodynamic consistency is not satisfied along the
hysteresis loop, and out-of-equilibrium phase transitions are possible.Comment: 4 pages, 4 figure
Adsorption in non interconnected pores open at one or at both ends: A reconsideration of the origin of the hysteresis phenomenon
We report on an experimental study of adsorption isotherme of nitrogen onto
porous silicon with non interconnected pores open at one or at both ends in
order to check for the first time the old (1938) but always current idea based
on Cohan's description which suggests that the adsorption of gaz should occur
reversibly in the first case and irreversibly in the second one. Hysteresis
loops, the shape of which is usually associated to interconnections in porous
media, are observed whether the pores are open at one or at both ends in
contradiction with Cohan's model.Comment: 5 pages, 4 EPS figure
Electrons in a ferromagnetic metal with a domain wall
We present theoretical description of conduction electrons interacting with a
domain wall in ferromagnetic metals. The description takes into account
interaction between electrons. Within the semiclassical approximation we
calculate the spin and charge distributions, particularly their modification by
the domain wall. In the same approximation we calculate local transport
characteristics, including relaxation times and charge and spin conductivities.
It is shown that these parameters are significantly modified near the wall and
this modification depends on electron-electron interaction.Comment: 10 pages with 4 figure
The FIRST Bright Quasar Survey. II. 60 Nights and 1200 Spectra Later
We have used the VLA FIRST survey and the APM catalog of the POSS-I plates as
the basis for constructing a new radio-selected sample of optically bright
quasars. This is the first radio-selected sample that is competitive in size
with current optically selected quasar surveys. Using only two basic criteria,
radio-optical positional coincidence and optical morphology, quasars and BL
Lacs can be identified with 60% selection efficiency; the efficiency increases
to 70% for objects fainter than magnitude 17. We show that a more sophisticated
selection scheme can predict with better than 85% reliability which candidates
will turn out to be quasars.
This paper presents the second installment of the FIRST Bright Quasar Survey
with a catalog of 636 quasars distributed over 2682 square degrees. The quasar
sample is characterized and all spectra are displayed. The FBQS detects both
radio-loud and radio-quiet quasars out to a redshift z>3. We find a large
population of objects of intermediate radio-loudness; there is no evidence in
our sample for a bimodal distribution of radio characteristics. The sample
includes ~29 broad absorption line quasars, both high and low ionization, and a
number of new objects with remarkable optical spectra.Comment: 41 pages plus 39 gifs which contain all quasar spectra. Accepted for
publication in the Astrophysical Journal Supplement Serie
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