10,204 research outputs found
Deep space network
Background, current status, and sites of Deep Space Network stations are briefly discussed
Tracking and data systems support for the Helios project. Volume 3: DSN support of Project Helios May 1976 - June 1977
Spacecraft extended mission coverage does not generally carry a high priority, but Helios was fortunate in that a combination of separated viewperiods and unique utilization of the STDN Goldstone antenna have provided a considerable amount of additional science data return, particularly at key times such a perihelion and/or solar occultation
Tracking and data systems support for the Helios project. Volume 2: DSN support of Project Helios April 1975 - May 1976
Deep Space Network activities in the development of the Helios B mission from planning through entry of Helios 2 into first superior conjunction (end of Mission Phase II) are summarized. Network operational support activities for Helios 1 from first superior conjunction through entry into third superior conjunction are included
Hydrogen absorption properties of amorphous (Ni0.6Nb0.4−yTay)100−xZrx membranes
Ni based amorphous materials have great potential as hydrogen purification membranes. In the present work
the melt spun (Ni0.6Nb0.4−yTay)100−xZrx with y=0, 0.1 and x=20, 30 was studied. The result of X-ray diffraction
spectra of the ribbons showed an amorphous nature of the alloys. Heating these ribbons below T < 400 °C, even
in a hydrogen atmosphere (1−10 bar), the amorphous structure was retained. The crystallization process was
characterized by differential thermal analysis and the activation energy of such process was obtained. The
hydrogen absorption properties of the samples in their amorphous state were studied by the volumetric method,
and the results showed that the addition of Ta did not significantly influence the absorption properties, a clear
change of the hydrogen solubility was observed with the variation of the Zr content. The values of the
hydrogenation enthalpy changed from ~37 kJ/mol for x=30 to ~9 kJ/mol for x=20. The analysis of the
volumetric data provides the indications about the hydrogen occupation sites during hydrogenation, suggesting
that at the beginning of the absorption process the deepest energy levels are occupied, while only shallower
energy levels are available at higher hydrogen content, with the available interstitial sites forming a continuum
of energy levels
Ionization Structure and the Reverse Shock in E0102-72
The young oxygen-rich supernova remnant E0102-72 in the Small Magellanic
Cloud has been observed with the High Energy Transmission Grating Spectrometer
of Chandra. The high resolution X-ray spectrum reveals images of the remnant in
the light of individual emission lines of oxygen, neon, magnesium and silicon.
The peak emission region for hydrogen-like ions lies at larger radial distance
from the SNR center than the corresponding helium-like ions, suggesting passage
of the ejecta through the "reverse shock". We examine models which test this
interpretation, and we discuss the implications.Comment: 4 pages, 6 figures; To appear in "Young Supernova Remnants" (11th
Annual Astrophysics Conference in Maryland), S. S. Holt & U. Hwang (eds),
AIP, New York (2001
Predicting the Starquakes in PSR J0537-6910
We report on more than 7 years of monitoring of PSR J0537-6910, the 16 ms
pulsar in the Large Magellanic Cloud, using data acquired with the RXTE. During
this campaign the pulsar experienced 23 sudden increases in frequency
(``glitches'') amounting to a total gain of over six ppm of rotation frequency
superposed on its gradual spindown of d(nu)/d(t) = -2e-10 Hz/s. The time
interval from one glitch to the next obeys a strong linear correlation to the
amplitude of the first glitch, with a mean slope of about 400 days ppm (6.5
days per uHz), such that these intervals can be predicted to within a few days,
an accuracy which has never before been seen in any other pulsar. There appears
to be an upper limit of ~40 uHz for the size of glitches in_all_ pulsars, with
the 1999 April glitch of J0537 as the largest so far. The change in the
spindown of J0537 across the glitches, Delta(d(nu)/d(t)), appears to have the
same hard lower limit of -1.5e-13 Hz/s, as, again, that observed in all other
pulsars. The spindown continues to increase in the long term,
d(d(nu)/d(t))/d(t) = -1e-21 Hz/s/s, and thus the timing age of J0537 (-0.5 nu
d(nu)/d(t)) continues to decrease at a rate of nearly one year every year,
consistent with movement of its magnetic moment away from its rotational axis
by one radian every 10,000 years, or about one meter per year. J0537 was likely
to have been born as a nearly-aligned rotator spinning at 75-80 Hz, with a
|d(nu)/d(t)| considerably smaller than its current value of 2e-10 Hz/s. The
pulse profile of J0537 consists of a single pulse which is found to be flat at
its peak for at least 0.02 cycles.Comment: 54 pages, 12 figures. Accepted for publication in The Astrophysical
Journal. Cleaner figure 2. V4 -- in line with version accepted by Ap
Spectral Line Imaging Observations of 1E0102.2-7219
E0102-72 is the second brightest X-ray source in the Small Magellanic Cloud
and the brightest supernova remnant in the SMC. We observed this SNR for ~140
ksec with the High Energy Transmission Gratings (HETG) aboard the Chandra X-ray
Observatory. The small angular size and high surface brightness make this an
excellent target for HETG and we resolve the remnant into individual lines. We
observe fluxes from several lines which include O VIII Ly, Ly,
and O VII along with several lines from Ne X, Ne IX and Mg XII. These line
ratios provide powerful constraints on the electron temperature and the
ionization age of the remnant.Comment: To appear in "Young Supernova Remnants" (11th Annual Astrophysics
Conference in Maryland), S. S. Holt & U. Hwang (eds), AIP, New York (2001
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