30,107 research outputs found
Plasma accelerator Patent
Crossed-field plasma accelerator for laboratory simulation of atmospheric reentry condition
Development and initial operating characteristics of the 20 megawatt linear plasma accelerator facility
A 20-megawatt linear plasma accelerator facility, a steady flow, Faraday-type plasma accelerator facility for high velocity aerodynamic testing, was constructed, developed, and brought to an operational status. The accelerator has a 63.5-mm-square and 0.5-meter-long channel and utilizes nitrogen-seeded with 2 % mole fraction of cesium vapor. Modification of the original accelerator design characteristics and the improvements necessary to make the arc heater a suitable plasma source are described. The measured accelerator electrode current distribution and the electrode-wall potential distributions are given. The computed and the measured values are in good agreement. Measured pitot pressure indicates that an accelerator exit velocity of 9.2 km/sec, is obtained with 30 of the 36 electrode pairs powered and corresponds to a velocity increase to about 2 1/4 times the computed entrance velocity. The computed stagnation enthalpy at the accelerator exit is 92 MJ/kg, and the mass density corresponds to an altitude of about 58 km. The 92 MJ/kg stagnation enthalpy corresponds to a kinetic energy content at low temperature equivalent to a velocity of 13.6 km/sec
Research on a one-inch-square linear d-c plasma accelerator
One-inch-square linear d-c plasma accelerator using cesium seeded nitroge
A Post-AGB Star in the Small Magellanic Cloud Observed with the Spitzer Infrared Spectrograph
We have observed an evolved star with a rare combination of spectral
features, MSX SMC 029, in the Small Magellanic Cloud (SMC) using the
low-resolution modules of the Infrared Spectrograph on the Spitzer Space
Telescope. A cool dust continuum dominates the spectrum of MSX SMC 029. The
spectrum also shows both emission from polycyclic aromatic hydrocarbons (PAHs)
and absorption at 13.7 micron from C2H2, a juxtaposition seen in only two other
sources, AFGL 2688 and IRAS 13416-6243, both post-asymptotic giant branch (AGB)
objects. As in these sources, the PAH spectrum has the unusual trait that the
peak emission in the 7-9 micron complex lies beyond 8.0 micron. In addition,
the 8.6 micron feature has an intensity as strong as the C-C modes which
normally peak between 7.7 and 7.9 micron. The relative flux of the feature at
11.3 micron to that at 8 micron suggests that the PAHs in MSX SMC 029 either
have a low ionization fraction or are largely unprocessed. The 13-16 micron
wavelength region shows strong absorption features similar to those observed in
the post-AGB objects AFGL 618 and SMP LMC 11. This broad absorption may arise
from the same molecules which have been identified in those sources: C2H2,
C4H2, HC3N, and C6H6. The similarities between MSX SMC 029, AFGL 2688, and AFGL
618 lead us to conclude that MSX SMC 029 has evolved off the AGB in only the
past few hundred years, making it the third post-AGB object identified in the
SMC.Comment: 4 figures, Fig. 4 color; to appear in the 20 November 2006
Astrophysical Journal Letter
Identifying short motifs by means of extreme value analysis
The problem of detecting a binding site -- a substring of DNA where
transcription factors attach -- on a long DNA sequence requires the recognition
of a small pattern in a large background. For short binding sites, the matching
probability can display large fluctuations from one putative binding site to
another. Here we use a self-consistent statistical procedure that accounts
correctly for the large deviations of the matching probability to predict the
location of short binding sites. We apply it in two distinct situations: (a)
the detection of the binding sites for three specific transcription factors on
a set of 134 estrogen-regulated genes; (b) the identification, in a set of 138
possible transcription factors, of the ones binding a specific set of nine
genes. In both instances, experimental findings are reproduced (when available)
and the number of false positives is significantly reduced with respect to the
other methods commonly employed.Comment: 6 pages, 5 figure
Development of Stresses in Cohesionless Poured Sand
The pressure distribution beneath a conical sandpile, created by pouring sand
from a point source onto a rough rigid support, shows a pronounced minimum
below the apex (`the dip'). Recent work of the authors has attempted to explain
this phenomenon by invoking local rules for stress propagation that depend on
the local geometry, and hence on the construction history, of the medium. We
discuss the fundamental difference between such approaches, which lead to
hyperbolic differential equations, and elastoplastic models, for which the
equations are elliptic within any elastic zones present .... This displacement
field appears to be either ill-defined, or defined relative to a reference
state whose physical existence is in doubt. Insofar as their predictions depend
on physical factors unknown and outside experimental control, such
elastoplastic models predict that the observations should be intrinsically
irreproducible .... Our hyperbolic models are based instead on a physical
picture of the material, in which (a) the load is supported by a skeletal
network of force chains ("stress paths") whose geometry depends on construction
history; (b) this network is `fragile' or marginally stable, in a sense that we
define. .... We point out that our hyperbolic models can nonetheless be
reconciled with elastoplastic ideas by taking the limit of an extremely
anisotropic yield condition.Comment: 25 pages, latex RS.tex with rspublic.sty, 7 figures in Rsfig.ps.
Philosophical Transactions A, Royal Society, submitted 02/9
Fermi LAT Gamma-ray Detections of Classical Novae V1369 Centauri 2013 and V5668 Sagittarii 2015
We report the Fermi Large Area Telescope (LAT) detections of high-energy
(>100 MeV) gamma-ray emission from two recent optically bright classical novae,
V1369 Centauri 2013 and V5668 Sagittarii 2015. At early times, Fermi
target-of-opportunity observations prompted by their optical discoveries
provided enhanced LAT exposure that enabled the detections of gamma-ray onsets
beginning ~2 days after their first optical peaks. Significant gamma-ray
emission was found extending to 39-55 days after their initial LAT detections,
with systematically fainter and longer duration emission compared to previous
gamma-ray detected classical novae. These novae were distinguished by multiple
bright optical peaks that encompassed the timespans of the observed gamma rays.
The gamma-ray light curves and spectra of the two novae are presented along
with representative hadronic and leptonic models, and comparisons to other
novae detected by the LAT are discussed.Comment: 13 pages, 6 figures, 4 tables, ApJ accepte
Characterization of a branchial epithelial calcium channel (ECaC) in freshwater rainbow trout (Oncorhynchus mykiss)
The entry of calcium (Ca2+) through an apical membrane epithelial calcium channel (ECaC) is thought to a key step in piscine branchial Ca2+ uptake. In mammals, ECaC is a member of the transient receptor potential (TRP) gene family of which two sub-families have been identified, TRPV5 and TPRV6. In the present study we have identified a single rainbow trout (Oncorhynchus mykiss) ECaC (rtECaC) that is similar to the mammalian TRPV5 and TRPV6. Phylogenetic analysis of the protein sequence suggests that an ancestral form of the mammalian genes diverged from those in the lower vertebrates prior to the gene duplication event that gave rise to TRPV5 and TRPV6. The putative model for Ca2+ uptake in fish proposes that the mitochondria-rich cell (also termed ionocyte or chloride cell) is the predominant or exclusive site of transcellular Ca2+ movements owing to preferential localisation of ECaC to the apical membrane of these cells. However, the results of real-time PCR performed on enriched gill cell populations as well as immunocytochemistry and in situ hybridisation analysis of enriched cells, cell cultures and whole gill sections strongly suggest that ECaC is not exclusive to mitochondria-rich cells but that it is also found in pavement cells. Not only was ECaC protein localized to areas of the gill normally having few mitochondria-rich cells, but there was also no consistent co-localization of ECaC- and Na+/K+-ATPase-positive (a marker of mitochondria rich cells) cells. Taken together, the results of the present study suggest that although ECaC (mRNA and protein) does exist in trout gill, its cellular distribution is more extensive than previously thought, thus suggesting that Ca2+ uptake may not be restricted to mitochondria-rich cells as was proposed in previous models
Chandra and Swift observations of the quasi-persistent neutron star transient EXO 0748-676 back to quiescence
The quasi-persistent neutron star X-ray transient and eclipsing binary EXO
0748-676 recently started the transition to quiescence following an accretion
outburst that lasted more than 24 years. We report on two Chandra and twelve
Swift observations performed within five months after the end of the outburst.
The Chandra spectrum is composed of a soft, thermal component that fits to a
neutron star atmosphere model with kT^inf~0.12 keV, joined by a hard powerlaw
tail that contributes ~20% of the total 0.5-10 keV unabsorbed flux. The
combined Chandra/Swift data set reveals a relatively hot and luminous quiescent
system with a temperature of kT^inf~0.11-0.13 keV and a bolometric thermal
luminosity of ~8.1E33-1.6E34 (d/7.4 kpc)^2 erg/s. We discuss our results in the
context of cooling neutron star models.Comment: Accepted for publication in MNRAS Letters, moderate revision
according to referee report, added one plot to figure 2 and included new
Swift observations, 5 pages, 2 figure
Comparative study of hormonal counterregulation during GCIIS-guided hypoglycemia tests using human Proinsulin and Human Insulin (recombinant DNA)
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