926 research outputs found
LSA silicon material task closed-cycle process development
The initial effort on feasibility of the closed cycle process was begun with the design of the two major items of untested equipment, the silicon tetrachloride by product converter and the rotary drum reactor for deposition of silicon from trichlorosilane. The design criteria of the initial laboratory equipment included consideration of the reaction chemistry, thermodynamics, and other technical factors. Design and construction of the laboratory equipment was completed. Preliminary silicon tetrachloride conversion experiments confirmed the expected high yield of trichlorosilane, up to 98 percent of theoretical conversion. A preliminary solar-grade polysilicon cost estimate, including capital costs considered extremely conservative, of $6.91/kg supports the potential of this approach to achieve the cost goal. The closed cycle process appears to have a very likely potential to achieve LSA goals
A single sub-km Kuiper Belt object from a stellar Occultation in archival data
The Kuiper belt is a remnant of the primordial Solar System. Measurements of
its size distribution constrain its accretion and collisional history, and the
importance of material strength of Kuiper belt objects (KBOs). Small, sub-km
sized, KBOs elude direct detection, but the signature of their occultations of
background stars should be detectable. Observations at both optical and X-ray
wavelengths claim to have detected such occultations, but their implied KBO
abundances are inconsistent with each other and far exceed theoretical
expectations. Here, we report an analysis of archival data that reveals an
occultation by a body with a 500 m radius at a distance of 45 AU. The
probability of this event to occur due to random statistical fluctuations
within our data set is about 2%. Our survey yields a surface density of KBOs
with radii larger than 250 m of 2.1^{+4.8}_{-1.7} x 10^7 deg^{-2}, ruling out
inferred surface densities from previous claimed detections by more than 5
sigma. The fact that we detected only one event, firmly shows a deficit of
sub-km sized KBOs compared to a population extrapolated from objects with r>50
km. This implies that sub-km sized KBOs are undergoing collisional erosion,
just like debris disks observed around other stars.Comment: To appear in Nature on December 17, 2009. Under press embargo until
1800 hours London time on 16 December. 19 pages; 7 figure
Solar System: Sifting through the debris
A quadrillion previously unnoticed small bodies beyond Neptune have been
spotted as they dimmed X-rays from a distant source. Models of the dynamics of
debris in the Solar System's suburbs must now be reworked.Comment: 3 pages, 1 figure; Nature News and Views on Chang et al. 2006,
Nature, 442, 660-66
Science with Simbol-X
Simbol-X is a French-Italian mission, with a participation of German
laboratories, for X-ray astronomy in the wide 0.5-80 keV band. Taking advantage
of emerging technology in mirror manufacturing and spacecraft formation flying,
Simbol-X will push grazing incidence imaging up to ~80 keV, providing an
improvement of roughly three orders of magnitude in sensitivity and angular
resolution compared to all instruments that have operated so far above 10 keV.
This will open a new window in X-ray astronomy, allowing breakthrough studies
on black hole physics and census and particle acceleration mechanisms. We
describe briefly the main scientific goals of the Simbol-X mission, giving a
few examples aimed at highlighting key issues of the Simbol-X design.Comment: Proc. of the workshop "Simbol-X: The hard X-ray universe in focus",
Bologna 14-16 May, 200
INTEGRAL upper limits on gamma-ray emission associated with the gravitational wave event GW150914
Using observations of the INTErnational Gamma-Ray Astrophysics Laboratory
(INTEGRAL), we put upper limits on the gamma-ray and hard X-ray prompt emission
associated with the gravitational wave event GW150914, discovered by the
LIGO/Virgo collaboration. The omni-directional view of the INTEGRAL/SPI-ACS has
allowed us to constrain the fraction of energy emitted in the hard X-ray
electromagnetic component for the full high-probability sky region of LIGO
trigger. Our upper limits on the hard X-ray fluence at the time of the event
range from erg cm to
erg cm in the 75 keV - 2 MeV energy range for typical spectral models.
Our results constrain the ratio of the energy promptly released in gamma-rays
in the direction of the observer to the gravitational wave energy
EE. We discuss the implication of gamma-ray
limits on the characteristics of the gravitational wave source, based on the
available predictions for prompt electromagnetic emission.Comment: accepted for publication in ApJ
High Momentum Probes of Nuclear Matter
We discuss how the chemical composition of QCD jets is altered by final state
interactions in surrounding nuclear matter. We describe this process through
conversions of leading jet particles. We find that conversions lead to an
enhancement of kaons at high transverse momentum in Au+Au collisions at RHIC,
while their azimuthal asymmetry v_2 is suppressed.Comment: Contribution to the 4th international workshop High-pT physics at LHC
09, Prague; 6 pages, 6 figure
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