870 research outputs found
Correlation of Preston-tube data with laminar skin friction (Log No. J12984)
Preston tube data within laminar boundary layers obtained on a sharp ten-degree cone in the NASA Ames eleven-foot transonic wind tunnel are correlated with the corresponding values of theoretical skin friction. Data were obtained over a Mach number range of 0.30 to 0.95 and unit Reynolds numbers of 9.84, 13.1, and 16.4 million per meter. The rms scatter of skin friction coefficient about the correlation is of the order of one percent, which is comparable to the reported accuracy for calibrations of Preston tubes in incompressible pipe flows. In contrast to previous works on Preston tube/skin friction correlations, which are based on the physical height of the probe's face, this satisfactory correlation for compressible boundary layer flows is achieved by accounting for the effects of a variable "effective" height of the probe. The coefficients, which appear in the correlation, are dependent on the particular tunnel environment. The general procedure can be used to define correlations for other wind tunnels
First-principles phase diagram calculations for the HfCâTiC, ZrCâTiC, and HfCâZrC solid solutions
We report first-principles phase diagram calculations for the binary systems HfCâTiC, TiCâZrC, and HfCâZrC. Formation energies for superstructures of various bulk compositions were computed with a plane-wave pseudopotential method. They in turn were used as a basis for fitting cluster expansion Hamiltonians, both with and without approximations for excess vibrational free energies. Significant miscibility gaps are predicted for the systems TiCâZrC and HfCâTiC, with consolute temperatures in excess of 2000 K. The HfCâZrC system is predicted to be completely miscibile down to 185 K. Reductions in consolute temperature due to excess vibrational free energy are estimated to be ~7%, ~20%, and ~0%, for HfCâTiC, TiCâZrC, and HfCâZrC, respectively. Predicted miscibility gaps are symmetric for HfCâZrC, almost symmetric for HfCâTiC and asymmetric for TiCâZrC
New optical polarization measurements of the Crab pulsar
The Crab nebula and its pulsar have been observed for about 3 hours with the
high-speed photo-polarimeter OPTIMA in January 2002 at the Calar Alto 3.5m
telescope. The Crab pulsar intensity and polarization are determined at all
phases of rotation with higher statistical accuracy than ever. Therefore, we
were able to separate the so-called 'off-pulse' phase emission (with an
intensity of about 1.2% compared to the main peak, assumed to be present at all
phases) from the pulsed emission and show the 'net' polarization of the pulsed
structures. Recent theoretical results indicate that the measured optical
polarization of the Crab pulsar is similar to expectations from a two-pole
caustic emission model or a striped pulsar wind model.Comment: AIP Conference Proceedings "Astrophysical Sources of High Energy
Particles and Radiation", eds. T. Bulik et al. (NY:AIP), Volume 801, 2005,
pp. 306-31
Pressure data from a 64A010 airfoil at transonic speeds in heavy gas media of ratio of specific heats from 1.67 to 1.12
A NACA 64A010 pressure-instrumented airfoil was tested at transonic speeds over a range of angle of attack from -1 to 12 degrees at various Reynolds numbers ranging from 2 to 6 million in air, argon, Freon 12, and a mixture of argon and Freon 12 having a ratio of specific heats corresponding to air. Good agreement of results is obtained for conditions where compressibility is not significant and for the air and comparable argon-Freon 12 mixture. Comparison of heavy gas results with air, when adjusted for transonic similarity, show improved, but less than desired agreement
The Spectral Variability of Cygnus X-1 at MeV Energies
In previous work, we have used data from the first three years of the CGRO
mission to assemble a broad-band -ray spectrum of the galactic black
hole candidate Cygnus X-1. Contemporaneous data from the COMPTEL, OSSE and
BATSE experiments on CGRO were selected on the basis of the hard X-ray flux
(45--140 keV) as measured by BATSE. This provided a spectrum of Cygnus X-1 in
its canonical low X-ray state (as measured at energies below 10 keV), covering
the energy range from 50 keV to 5 MeV. Here we report on a comparison of this
spectrum to a COMPTEL-OSSE spectrum collected during a high X-ray state of
Cygnus X-1 (May, 1996). These data provide evidence for significant spectral
variability at energies above 1 MeV. In particular, whereas the hard X-ray flux
{\it decreases} during the high X-ray state, the flux at energies above 1 MeV
{\it increases}, resulting in a significantly harder high energy spectrum. This
behavior is consistent with the general picture of galactic black hole
candidates having two distinct spectral forms at soft -ray energies.
These data extend this picture, for the first time, to energies above 1 MeV.Comment: 5 pages, 4 figures, to be published in AIP Conf. Proc., "The Fifth
Compton Symposium
Recent results from COMPTEL observations of Cygnus Xâ1
The COMPTEL experiment on the Compton GammaâRay Observatory (CGRO) has now observed Cyg Xâ1 on four separate occasions during phase 1 and phase 2 of its orbital mission (April, 1991 to August, 1993). Here we report on the results of the latest analysis of these data, which provide a spectrum extending to energies greater than 2 MeV. A spectral analysis of these data, in the context of a classical Comptonization model, indicates an electron temperature much higher than previous hard Xâray measurements would suggest (200 keV vs 60â80 keV). This implies either some limitations in the standard Comptonization model and/or the need to incorporate a reflected component in the hard Xâray spectrum. Although significant variability near 1 MeV has been observed, there is no evidence for any âMeV excess.
ADAMTSL2 gene variant in patients with features of autosomal dominant connective tissue disorders
This is the peer reviewed version of the following article: Steinle, J, Hossain, WA, Lovell, S, Veatch, OJ, Butler, MG. ADAMTSL2 gene variant in patients with features of autosomal dominant connective tissue disorders. Am J Med Genet Part A. 2021; 185A: 743â 752. https://doi.org/10.1002/ajmg.a.62030, which has been published in final form at https://doi.org/10.1002/ajmg.a.62030. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions. This article may not be enhanced, enriched or otherwise transformed into a derivative work, without express permission from Wiley or by statutory rights under applicable legislation. Copyright notices must not be removed, obscured or modified. The article must be linked to Wileyâs version of record on Wiley Online Library and any embedding, framing or otherwise making available the article or pages thereof by third parties from platforms, services and websites other than Wiley Online Library must be prohibited.Ehlers-Danlos syndrome (EDS) consists of a heterogeneous group of genetically inherited connective tissue disorders. A family with three affected members over two generations with features of Dermatosparaxic EDS (dEDS) autosomal dominant transmission was reported by Desai et al. and having a heterozygous nonsynonymous missense variant of ADAMTSL2 (c.1261Gâ>âA; p. Gly421Ser). Variation in this gene is also reported to cause autosomal recessive geleophysic dysplasia. We report five unrelated patients with the Gly421Ser variant identified from a large series of patients presenting with features of connective tissue disorders, each with a positive family history consistent with autosomal dominant transmission. Clinical features of a connective tissue disorder included generalized joint hypermobility and pain with fragility of internal and external tissues including of skin, dura, and arteries. Overall, our analyses including bioinformatics, protein modeling, and gene-protein interactions with the cases described would add evidence for the Gly421Ser variant in ADAMTSL2 as causative for variable expressivity of autosomal dominant connective tissue disorders
Observations of Seyferts by OSSE and parameters of their X-ray/gamma-ray sources
We present a summary of spectra of Seyfert galaxies observed by the OSSE
detector aboard Compton Gamma Ray Observatory. We obtain average spectra of
Seyferts of type 1 and 2, and find they are well fitted by thermal
Comptonization. We present detailed parameter ranges for the plasma temperature
and the Compton parameter in the case of spherical and slab geometries. We find
both the average and individual OSSE spectra of Seyfert 2s are significantly
harder than those of Seyfert 1s, which difference can be due to anisotropy of
Compton reflection and/or Thomson-thick absorption.Comment: ApJ, 10 Nov. 2000, in press, 13 page
On the nature of the ultraluminous X-ray transient in Cen~A (NGC 5128)
We combine 9 ROSAT, 9 Chandra, and 2 XMM-Newton observations of the Cen~A
galaxy to obtain the X-ray light curve of 1RXH J132519.8-430312 (=CXOU
J132519.9430317) spanning 1990 to 2003. The source reached a peak 0.1-2.4
keV flux F_X>10^{-12} ergs cm^{-2} s^{-1} during a 10~day span in 1995 July.
The inferred peak isotropic luminosity of the source therefore exceeded 3
10^{39} ergs s^{-1}, which places the source in the class of ultra-luminous
X-ray sources. Coherent pulsations at 13.264 Hz are detected during a second
bright episode (F_X >3 times 10^{-13} ergs cm^{-2} s^{-1}) in 1999 December.
The source is detected and varies significantly within three additional
observations but is below the detection threshold in 7 observations. The X-ray
spectrum in 1999 December is best described as a cut-off power law or a
disk-blackbody (multi-colored disk). We also detect an optical source, m_F555W
~ 24.1 mag, within the Chandra error circle of 1RXH J132519.8-430312 in HST
images taken 195~days before the nearest X-ray observation. The optical
brightness of this source is consistent with a late O or early B star at the
distance of Cen A. If the optical source is the counterpart, then the X-ray and
optical behavior of 1RXH J132519.8-430312 are similar to the transient Be/X-ray
pulsar A 0538-66.Comment: 7 pages, 8 figures. ApJ (accepted
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