22,316 research outputs found
Numerical analysis and simulation of an assured crew return vehicle flow field
A lifting body was proposed as a candidate for the Assured Crew Return Vehicle (ACRV) which will serve as a crew rescue vehicle for the Space Station Freedom. The focus is on body surface definition, both surface and volume grid definition, and the computation of inviscid flow fields about the vehicle at wind tunnel conditions. Very good agreement is shown between the computed aerodynamic characteristics of the vehicle at M(sub infinity) = 10 and those measured in wind tunnel tests at high Reynolds numbers
Evidence for Antiferromagnetic Order in LaCeCuO from Angular Magnetoresistance Measurements
We investigated the in-plane angular magnetoresistivity (AMR) of -phase LaCeCuO (LCCO) thin films () fabricated by a pulsed laser deposition technique. The in-plane
AMR with shows a twofold symmetry instead of the
fourfold behavior found in other electron-doped cuprates such as PrCeCuO and NdCeCuO. The twofold AMR
disappears above a certain temperature, . The is well above
for ( K), and decreases with increasing doping,
until it is no longer observed above at . This twofold AMR
below is suggested to originate from an antiferromagnetic or spin
density wave order.Comment: to be published in Phys. Rev. B, Vol. 80 (2009
Andreev Reflection in Heavy-Fermion Superconductors and Order Parameter Symmetry in CeCoIn_5
Differential conductance spectra are obtained from nanoscale junctions on the
heavy-fermion superconductor CeCoIn along three major crystallographic
orientations. Consistency and reproducibility of characteristic features among
the junctions ensure their spectroscopic nature. All junctions show a similar
conductance asymmetry and Andreev reflection-like conductance with reduced
signal (~ 10%-13%), both commonly observed in heavy-fermion superconductor
junctions. Analysis using the extended Blonder-Tinkham-Klapwijk model indicates
that our data provide the first spectroscopic evidence for
symmetry. To quantify our conductance spectra, we propose a model by
considering the general phenomenology in heavy fermions, the two-fluid
behavior, and an energy-dependent density of states. Our model fits to the
experimental data remarkably well and should invigorate further investigations.Comment: 4 pages, 4 figures; Phys. Rev. Lett., published versio
Recommended from our members
Obesity-induced Upper Extremity Lymphedema
Summary: Obesity increases the risk of upper extremity lymphedema following treatment for breast cancer and can cause lower extremity lymphatic dysfunction in extremely obese individuals. We report the first patient with obesity-induced upper extremity lymphedema. A 62-year-old man with a previous body mass index (BMI) of 105.6, presented with a BMI 60.3 following weight loss. He complained of lymphedema of all 4 extremities, which was confirmed by lymphoscintigraphy. Because the upper limbs are more resistant to lymphedema than the lower extremities, a higher BMI threshold may be necessary to cause upper extremity lymphatic dysfunction
Genomic variations associated with attenuation in Mycobacterium avium subsp paratuberculosis vaccine strains
BACKGROUND: Mycobacterium avium subspecies paratuberculosis (MAP) whole cell vaccines have been widely used tools in the control of Johne's disease in animals despite being unable to provide complete protection. Current vaccine strains derive from stocks created many decades ago; however their genotypes, underlying mechanisms and relative degree of their attenuation are largely unknown.
RESULTS: Using mouse virulence studies we confirm that MAP vaccine strains 316 F, II and 2e have diverse but clearly attenuated survival and persistence characteristics compared with wild type strains. Using a pan genomic microarray we characterise the genomic variations in a panel of vaccine strains sourced from stocks spanning over 40 years of maintenance. We describe multiple genomic variations specific for individual vaccine stocks in both deletion (26-32 Kbp) and tandem duplicated (11-40 Kbp) large variable genomic islands and insertion sequence copy numbers. We show individual differences suitable for diagnostic differentiation between vaccine and wild type genotypes and provide evidence for functionality of some of the deleted MAP-specific genes and their possible relation to attenuation.
CONCLUSIONS: This study shows how culture environments have influenced MAP genome diversity resulting in large tandem genomic duplications, deletions and transposable element activity. In combination with classical selective systematic subculture this has led to fixation of specific MAP genomic alterations in some vaccine strain lineages which link the resulting attenuated phenotypes with deficiencies in high reactive oxygen species handling
A New Sample of Low-mass Black Holes in Active Galaxies
We present an expanded sample of low-mass black holes (BHs) found in galactic
nuclei. Using standard virial mass techniques to estimate BH masses, we select
from the Fourth Data Release of the Sloan Digital Sky Survey all broad-line
active galaxies with masses < 2 x 10^6 M_sun. BHs in this mass regime provide
unique tests of the relationship between BHs and galaxies, since their
late-type galaxy hosts do not necessarily contain classical bulges.
Furthermore, they provide observational analogs of primordial seed BHs and are
expected, when merging, to provide strong gravitational signals for future
detectors such as LISA. From our preliminary sample of 19, we have increased
the total sample by an order of magnitude to 174, as well as an additional 55
(less secure) candidates. The sample has a median BH mass of = 1.3 x
10^6 M_sun, and in general the objects are radiating at high fractions of their
Eddington limits. We investigate the broad spectral properties of the sample;
55 are detected by \rosat, with soft X-ray luminosities in the range 10^40 to 7
x 10^43 ergs/sec. Much like the preliminary sample, these objects are
predominantly radio-quiet (R = f_6cm/f_4400A < 10), but 11 objects are detected
at 20 cm, with radio powers (10^21-10^23 W/Hz) that may arise from either star
formation or nuclear activity; only 1% of the sample is radio-loud. We further
confirm that, with =-19.3 and = 0.7 mag, the host galaxies are
low-mass, late-type systems. At least 40% show disk-like morphologies, and the
combination of host galaxy colors and higher-order Balmer absorption lines
indicate intermediate-age stellar populations in a subset of the sample.Comment: to appear in ApJ; 13 pages, 8 figure
SDSS J143030.22-001115.1: A misclassified narrow-line Seyfert 1 galaxy with flat X-ray spectrum
We used multi-component profiles to model H and [O III]4959,5007 lines for SDSS J143030.22-001115.1, a narrow-line Seyfert 1
galaxy (NLS1) in a sample of 150 NLS1s candidates selected from the Sloan
Digital Sky Survey (SDSS) Early Data Release (EDR). After subtracting the
H contribution from narrow line regions (NLRs), we found that its full
width half maximum (FWHM) of broad H line is nearly 2900 \kms,
significantly larger than the customarily adopted criterion of 2000 \kms. With
its weak Fe II multiples, we think that SDSS J143030.22-001115.1 can't be
classified as a genuine NLS1. When we calculate the virial black hole masses of
NLS1s, we should use the H linewidth after subtracting the H
contribution from NLRs.Comment: 7 pages, 1 table, accepted by ChJA
- …