1,238 research outputs found
The rocket ultraviolet spectrum of the planetary nebula NGC 7027
An ultraviolet spectrum of NGC 7027 was obtained with a rocket-borne telescope. The observed fluxes are given on an absolute basis and upper limits are given for the strongest predicted lines which were not observed. The extinction correction was made on the basis of the observed and calculated line ratios for the hydrogenic recombination line of He 2 at 1640A to H beta. The extinction is in agreement with ground based determinations. When corrected for extinction the C 4 resonance line at 1549A is in good agreement with the intensity calculated from models, but the C 3 intercombination line at 1909A is a factor of ten too bright. The addition of dielectronic recombination to the models sufficiently changes the C 3 concentration to reduce the discrepancy to a factor of four. The abundance of carbon is assumed to be 2 x 0.0001 that of hydrogen. Using carbon abundances for the sun, this discrepancy disappears and there must be attenuation in the C 4 line. Since the optical depth is approximately 10,000 at the line center, no appreciable number of absorbing grains can exist in the C 4 producing region of the nebula
Probiotic Potential and Antimicrobial Activity of Enterococcus faecium Isolated from Chicken Caecal and Fecal Samples
Enterococci are important inhabitants of the animal intestine and are widely used in probiotic products. A probiotic strain is expected to possess several desirable properties in order to exert beneficial effects. Therefore, the objective of this study was to isolate, characterize and identify Enterococcus sp. from chicken cecal and fecal samples to determine potential probiotic properties. Enterococci were isolated from chicken ceca and feces of thirty three clinically healthy chickens from a local farm. In vitro studies were performed to assess antibacterial activity of the isolated LAB (using agar well diffusion and cell free supernatant broth technique against Salmonella enterica serotype Enteritidis), survival in acidic conditions, resistance to bile salts, and their survival during simulated gastric juice conditions at pH 2.5. Isolates were identified by biochemical carbohydrate fermentation patterns using an API 50 CHL kit and API ZYM kits and by sequenced 16S rDNA. An isolate belonging to E. faecium species exhibited inhibitory effect against S. enteritidis. This isolate producing a clear zone as large as 10.30 mm or greater and was able to grow in the coculture medium and at the same time, inhibited the growth S. enteritidis. In addition, E. faecium exhibited significant resistance under highly acidic conditions at pH 2.5 for 8 h and survived well in bile salt at 0.2% for 24 h and showing ability to survive in the presence of simulated gastric juice at pH 2.5. Based on these results, E. faecium isolate fulfills some of the criteria to be considered as a probiotic strain and therefore, could be used as a feed additive with good potential for controlling S. Enteritidis in chickens. However, in vivo studies are needed to determine the safety of the strain
Double Quantum Dots in Carbon Nanotubes
We study the two-electron eigenspectrum of a carbon-nanotube double quantum
dot with spin-orbit coupling. Exact calculation are combined with a simple
model to provide an intuitive and accurate description of single-particle and
interaction effects. For symmetric dots and weak magnetic fields, the
two-electron ground state is antisymmetric in the spin-valley degree of freedom
and is not a pure spin-singlet state. When double occupation of one dot is
favored by increasing the detuning between the dots, the Coulomb interaction
causes strong correlation effects realized by higher orbital-level mixing.
Changes in the double-dot configuration affect the relative strength of the
electron-electron interactions and can lead to different ground state
transitions. In particular, they can favor a ferromagnetic ground state both in
spin and valley degrees of freedom. The strong suppression of the energy gap
can cause the disappearance of the Pauli blockade in transport experiments and
thereby can also limit the stability of spin-qubits in quantum information
proposals. Our analysis is generalized to an array of coupled dots which is
expected to exhibit rich many-body behavior.Comment: 14 pages, 11 pages and 1 table. Typos in text and Figs.4 and 6
correcte
Effects of subgrid-scale snow thickness variability on radiative transfer in sea ice
Snow is a principal factor in controlling heat and light fluxes through sea ice. With the goal of improving radiative and heat flux estimates through sea ice in regional and global models without the need of detailed snow property descriptions, a new parameterization including subgrid-scale snow thickness variability is presented. One-parameter snow thickness distributions depending only on the gridbox-mean snow thickness are introduced resulting in analytical solutions for the fluxes of heat and light through the snow layer. As the snowpack melts, these snow thickness distributions ensure a smooth seasonal transition of the light field under sea ice. Spatially homogenous melting applied to an inhomogeneous distribution of snow thicknesses allows the appearance of bare sea ice areas and melt ponds before all snow has melted. In comparison to uniform-thickness snow used in previous models, the bias in the under sea-ice light field is halved with this parameterization. Model results from a one-dimensional ocean turbulence model coupled with a thermodynamic sea ice model are compared to observations near Resolute in the Canadian High Arctic. The simulations show substantial improvements not only to the light field at the sea ice base which will affect ice algal growth but also to the sea ice and seasonal snowpack evolution. During melting periods, the snowpack can survive longer while sea ice thickness starts to reduce earlier. © 2015. American Geophysical Union. All Rights Reserved
Ethnicity and age as factors in sildenafil treatment of erectile dysfunction
IntroductionSildenafil has been evaluated in >16Â 000 men with erectile dysfunction (ED) in doubleâ blind, placeboâ controlled trials.AimTo assess efficacy and safety of sildenafil in ED by ethnicity (white, black Asian) and age (â ¤45, 46â 60, â ¥61Â years).MethodsData were pooled from 38 doubleâ blind, placeboâ controlled, flexibleâ dose trials. Most had starting sildenafil doses of 50Â mg once daily, ~1Â hour before sexual activity, with adjustment to 100 or 25Â mg as needed.Main Outcome MeasuresChange from baseline in International Index of Erectile Function erectile function (IIEFâ EF) domain score assessed with analysis of covariance and a Global Assessment Question (GAQ; â Did the treatment improve your erections?â ) at endpoint assessed with logistic regression analysis.Results4120 and 3714 men received sildenafil and placebo, respectively (2740 and 2671 White; 407 and 385 Black; 973 and 658 Asian). For sildenafil vs. placebo groups, overall treatment differences for IIEFâ EF domain and GAQ were significant for each ethnic and age group (P<.0001); significant treatmentâ byâ ethnicity and treatmentâ byâ age interactions were also observed for change in IIEFâ EF domain scores (P<.05), with differences significantly greater for White vs. Black (P<.0001), White vs. Asian (P=.0163), and Asian vs. Black (P=.0036) men. A significant treatmentâ byâ ethnicity interaction was observed for GAQ (P=.0004). The OR comparison for GAQ was significantly greater (P=.0001) with sildenafil vs. placebo in White (OR=11.2) or Asian (OR=12.4) men vs. Black men (OR=5.1). Adverseâ event rates were generally similar, with some age variations.ConclusionsSildenafil is effective and wellâ tolerated regardless of ethnicity or age; however, treatment effects can vary.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/137386/1/ijcp12945_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/137386/2/ijcp12945.pd
A Comparison of Ultraviolet, Optical, and X-Ray Imagery of Selected Fields in the Cygnus Loop
During the Astro-1 and Astro-2 Space Shuttle missions in 1990 and 1995, far
ultraviolet (FUV) images of five 40' diameter fields around the rim of the
Cygnus Loop supernova remnant were observed with the Ultraviolet Imaging
Telescope (UIT). These fields sampled a broad range of conditions including
both radiative and nonradiative shocks in various geometries and physical
scales. In these shocks, the UIT B5 band samples predominantly CIV 1550 and the
hydrogen two-photon recombination continuum. Smaller contri- butions are made
by emission lines of HeII 1640 and OIII] 1665. We present these new FUV images
and compare them with optical Halpha and [OIII], and ROSAT HRI X-ray images.
Comparing the UIT images with those from the other bands provides new insights
into the spatial variations and locations of these different types of emission.
By comparing against shock model calculations and published FUV spectroscopy at
select locations, we surmise that resonance scattering in the strong FUV
permitted lines is widespread in the Cygnus Loop, especially in the bright
optical filaments typically selected for observation in most previous studies.Comment: 21 pages with 10 figures. See http://www.pha.jhu.edu/~danforth/uit/
for full-resolution figure
Universality in Four-Boson Systems
We report recent advances on the study of universal weakly bound four-boson
states from the solutions of the Faddeev-Yakubovsky equations with zero-range
two-body interactions. In particular, we present the correlation between the
energies of successive tetramers between two neighbor Efimov trimers and
compare it to recent finite range potential model calculations. We provide
further results on the large momentum structure of the tetramer wave function,
where the four-body scale, introduced in the regularization procedure of the
bound state equations in momentum space, is clearly manifested. The results we
are presenting confirm a previous conjecture on a four-body scaling behavior,
which is independent of the three-body one. We show that the correlation
between the positions of two successive resonant four-boson recombination peaks
are consistent with recent data, as well as with recent calculations close to
the unitary limit. Systematic deviations suggest the relevance of range
corrections.Comment: Accepted for publication in special issue of Few-Body Systems devoted
to the Sixth Workshop on the Critical Stability of Quantum Few-Body Systems,
October 2011, Erice, Sicily, Ital
BEC-BCS Crossover of a Trapped Two-Component Fermi Gas with Unequal Masses
We determine the energetically lowest lying states in the BEC-BCS crossover
regime of s-wave interacting two-component Fermi gases under harmonic
confinement by solving the many-body Schrodinger equation using two distinct
approaches. Essentially exact basis set expansion techniques are applied to
determine the energy spectrum of systems with N=4 fermions. Fixed-node
diffusion Monte Carlo methods are applied to systems with up to N=20 fermions,
and a discussion of different guiding functions used in the Monte Carlo
approach to impose the proper symmetry of the fermionic system is presented.
The energies are calculated as a function of the s-wave scattering length a_s
for N=2-20 fermions and different mass ratios \kappa of the two species. On the
BEC and BCS sides, our energies agree with analytically-determined first-order
correction terms. We extract the scattering length and the effective range of
the dimer-dimer system up to \kappa = 20. Our energies for the
strongly-interacting trapped system in the unitarity regime show no shell
structure, and are well described by a simple expression, whose functional form
can be derived using the local density approximation, with one or two
parameters. The universal parameter \xi for the trapped system for various
\kappa is determined, and comparisons with results for the homogeneous system
are presented.Comment: 11 pages, 6 figures, extended versio
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