452 research outputs found
Development of buried wire gages for measurement of wall shear stress in Blastane experiments
Buried Wire Gages operated from a Constant Temperature Anemometer System are among the special types of instrumentation to be used in the Boundary Layer Apparatus for Subsonic and Transonic flow Affected by Noise Environment (BLASTANE). These Gages are of a new type and need to be adapted for specific applications. Methods were developed to fabricate Gage inserts and mount those in the BLASTANE Instrumentation Plugs. A large number of Gages were prepared and operated from a Constant Temperature Anemometer System to derive some of the calibration constants for application to fluid-flow wall shear-stress measurements. The final stage of the calibration was defined, but could not be accomplished because of non-availability of a suitable flow simulating apparatus. This report provides a description of the Buried Wire Gage technique, an explanation of the method evolved for making proper Gages and the calibration constants, namely Temperature Coefficient of Resistance and Conduction Loss Factor
PMS68 GRAND: THE GERMAN RETROSPECTIVE COHORT ANALYSIS ON NON-ADHERENCE IN OSTEOPOROSIS PATIENTS TREATED WITH ORAL BISPHOSPHONATES
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
COMPTEL upper limits for Seyfert galaxies
The gammaâray emission of Seyfert galaxies has fallen far short of preâGRO expectations. No single object of this class has been detected by either COMPTEL or EGRET, and OSSE has detected only a fraction of the Seyferts expected. To derive a more stringent upper limit to the emission from these objects in the energy ranges 0.75 to 1 and 1 to 3 MeV, we have summed a large number of COMPTEL observations acquired during Phase 1 of the GRO mission. From a total of 47 observations of 23 individual Xâray selected Seyfert galaxies, we derive preliminary upper limits of 8Ă10â8 photons/(cm2 s keV) in the 0.75â1 MeV band and 1Ă10â8 photons/(cm2 s keV) in the 1â3 MeV band
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.
COMPTEL observations of the quasar PKS 0528+134 during the first 3.5 years of the CGRO mission
The COMPTEL observations of the blazar-type quasar PKS 0528+134 in the energy
range 0.75 MeV to 30 MeV carried out between April 1991 and September 1994 have
been analyzed. During the first two years PKS 0528+134 was most significantly
detected at energies above 3 MeV. During the last year there is only evidence
for the quasar at energies below 3 MeV indicating a spectral change. The
time-averaged COMPTEL energy spectrum between 0.75 MeV and 30 MeV is well
represented by a power-law shape. Spectra collected from different
observational periods reveal different power-law shapes: a hard state during
flaring observations reported by EGRET, and a soft state otherwise. The
combined simultaneous EGRET and COMPTEL spectra indicate these two spectral
states as well. During low intensisty gamma-ray phases no spectral break is
obvious from the combined COMPTEL and EGRET measurements. For the gamma-ray
flaring phases however, the combined COMPTEL and EGRET data require a spectral
bending at MeV-energies. By fitting broken power-law functions the best-fit
values for the break in photon index range between 0.6 and 1.7, and for the
break energy between ~5 MeV and ~20 MeV. Because the flux values measured by
COMPTEL below 3 MeV in both states are roughly equal, the observations would be
consistent with an additional spectral component showing up during gamma-ray
flaring phases of PKS 0528+134. Such a component could be introduced by e.g. a
high-energy electron-positron population with a low-energy cutoff in their bulk
Lorentz factor distribution. The multiwavelength spectrum of PKS 0528+134 for
gamma-ray flaring phases shows that the major energy release across the entire
electro-magnetic spectrum is measured at MeV-energies.Comment: 10 pages, 8 postscript figures, latex, to appear in: A&A 328, 33
(1997
COMPTEL Observations of AGN at MeV-Energies
The COMPTEL experiment aboard CGRO, exploring the previously unknown sky at
MeV-energies, has so far detected 10 Active Galactic Nuclei (AGN): 9 blazars
and the radio galaxy Centaurus A. No Seyfert galaxy has been found yet. With
these results COMPTEL has opened the field of extragalactic Gamma-ray astronomy
in the MeV-band.Comment: 4 pages, 2 figures including 1 color plot, to appear in the
Proceedings of the 3rd INTEGRAL Workshop "The Extreme Universe", held in
Taormina, Italy, 14-18 September 199
The Hard X-ray Emission of Cen A
The radio galaxy Cen A has been detected all the way up to the TeV energy
range. This raises the question about the dominant emission mechanisms in the
high-energy domain. Spectral analysis allows us to put constraints on the
possible emission processes. Here we study the hard X-ray emission as measured
by INTEGRAL in the 3-1000 keV energy range, in order to distinguish between a
thermal and non-thermal inverse Compton process. The hard X-ray spectrum of Cen
A shows a significant cut-off at energies Ec = 434 (+106 -73) keV with an
underlying power law of photon index 1.73 +- 0.02. A more physical model of
thermal Comptonisation (compPS) gives a plasma temperature of kT = 206+-62 keV
within the optically thin corona with Compton parameter y = 0.42 (+0.09 -0.06).
The reflection component is significant at the 1.9 sigma level with R = 0.12
(+0.09 -0.10), and a reflection strength R>0.3 can be excluded on a 3 sigma
level. Time resolved spectral studies show that the flux, absorption, and
spectral slope varied in the range f(3-30 keV) = (1.2 - 9.2)e-10 erg/cm**2/s,
NH = (7 - 16)e22 1/cm**2, and photon index 1.75 - 1.87. Extending the cut-off
power law or the Comptonisation model to the gamma-ray range shows that they
cannot account for the high-energy emission. On the other hand, also a broken
or curved power law model can represent the data, therefore a non-thermal
origin of the X-ray to GeV emission cannot be ruled out. The analysis of the
SPI data provides no sign of significant emission from the radio lobes and
gives a 3 sigma upper limit of f(40-1000 keV) < 0.0011 ph/cm**2/s. While
gamma-rays, as detected by CGRO and Fermi, are caused by non-thermal (jet)
processes, the main process in the hard X-ray emission of Cen A is still not
unambiguously determined, being either dominated by thermal inverse Compton
emission, or by non-thermal emission from the base of the jet.Comment: 8 pages, 6 figures, accepted for publication in A&
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