54 research outputs found
The First Stars in The Universe
Large telescopes have allowed astronomers to observe galaxies that formed as
early as 850 million years after the Big Bang. We predict when the first star
that astronomers can observe formed in the universe, accounting for the first
time for the size of the universe and for three essential ingredients: the
light travel time from distant galaxies, Poisson and density fluctuations on
all scales, and the effect of very early cosmic history on galaxy formation. We
find that the first observable star is most likely to have formed 30 million
years after the Big Bang (at redshift 65), much earlier than previously
expected. Also, the first galaxy as massive as our own Milky Way likely formed
when the universe was only 400 Myr old (at redshift 11). We also show that
significant modifications are required in current methods of numerically
simulating the formation of galaxies at redshift 20 and above.Comment: 5 pages, 4 figures, MNRAS Letters, revised versio
Self contamination effects in the TAUVEX UV Telescope: Ground testing and computer simulation
The contamination effects due to outgassing from construction materials of the TAUVEX (Tel Aviv University UV Telescope) were evaluated using a combination of ground testing and computer simulations. Tests were performed from the material level of the system level including: (1) High sensitivity CVCM(10(exp -3 percent) measurements of critical materials. (2) Optical degradation measurements of samples specially contaminated by outgassing products at different contamination levels. (3) FTIR studies of chemical composition of outgassed products on above samples. (4) High resolution AFM studies of surface morphology of contaminated surfaces. The expected degradation of TAUVEX performance in mission was evaluated applying a computer simulation code using input parameters determined experimentally in the above tests. The results have served as guidelines for the proper selection of materials, cleanliness requirements, determination of the thermal conditions of the system and bakeout processes
TAUVEX: status in 2011
We present a short history of the TAUVEX instrument, conceived to provide
multi-band wide-field imaging in the ultraviolet, emphasizing the lack of
sufficient and aggressive support on the part of the different space agencies
that dealt with this basic science mission. First conceived in 1985 and
selected by the Israel Space Agency in 1989 as its first priority payload,
TAUVEX is fast becoming one of the longest-living space project of space
astronomy. After being denied a launch on a national Israeli satellite, and
then not flying on the Spectrum X-Gamma (SRG) international observatory, it was
manifested since 2003 as part of ISRO's GSAT-4 Indian satellite to be launched
in the late 2000s. However, two months before the launch, in February 2010, it
was dismounted from its agreed-upon platform. This proved to be beneficial,
since GSAT-4 and its launcher were lost on April 15 2010 due to the failure of
the carrier rocket's 3rd stage. TAUVEX is now stored in ISRO's clean room in
Bangalore with no firm indications when or on what platform it might be
launched.Comment: Invited contribution presented at the "UV Universe 2010". Accepted
for publication in Astrophysics & Space Scienc
Isolated Hypoxic Hepatic Perfusion with Retrograde Outflow in Patients with Irresectable Liver Metastases; A New Simplified Technique in Isolated Hepatic Perfusion
Background: Isolated hepatic perfusion with high-dose chemotherapy is a treatment option for patients with irresectable metastases confined to the liver. Prolonged local control and impact on survival have been claimed. Major drawbacks are magnitude and costs of the procedure. We developed an isolated hypoxic h
A. B. C. D. de la taille des arbres fruitiers /
Mode of access: Internet
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