1,559 research outputs found
Method and apparatus for relative navigation using reflected GPS signals
A method and system to passively navigate an orbiting moving body towards an orbiting target using reflected GPS signals. A pair of antennas is employed to receive both direct signals from a plurality of GPS satellites and a second antenna to receive GPS signals reflected off an orbiting target. The direct and reflected signals are processed and compared to determine the relative distance and position of the orbiting moving body relative to the orbiting target
Wide-field weak lensing by RXJ1347-1145
We present an analysis of weak lensing observations for RXJ1347-1145 over a
43' X 43' field taken in B and R filters on the Blanco 4m telescope at CTIO.
RXJ1347-1145 is a massive cluster at redshift z=0.45. Using a population of
galaxies with 20<R<26, we detect a weak lensing signal at the p<0.0005 level,
finding best-fit parameters of \sigma_v=1400^{+130}_{-140} km s^{-1} for a
singular isothermal sphere model and r_{200} = 3.5^{+0.8}_{-0.2} Mpc with c =
15^{+64}_{-10} for a NFW model in an \Omega_m = 0.3, \Omega_\Lambda = 0.7
cosmology. In addition, a mass to light ratio M/L_R =90 \pm 20 M_\odot /
L_{R\odot} was determined. These values are consistent with the previous weak
lensing study of RXJ1347--1145 by Fischer and Tyson, 1997, giving strong
evidence that systemic bias was not introduced by the relatively small field of
view in that study. Our best-fit parameter values are also consistent with
recent X-ray studies by Allen et al, 2002 and Ettori et al, 2001, but are not
consistent with recent optical velocity dispersion measurements by Cohen and
Kneib, 2002.Comment: accepted to ApJ, tentative publication 10 May 2005, v624
The Case for a New Frontiers–Class Uranus Orbiter: System Science at an Underexplored and Unique World with a Mid-scale Mission
Current knowledge of the Uranian system is limited to observations from the flyby of Voyager 2 and limited remote observations. However, Uranus remains a highly compelling scientific target due to the unique properties of many aspects of the planet itself and its system. Future exploration of Uranus must focus on cross-disciplinary science that spans the range of research areas from the planet’s interior, atmosphere, and magnetosphere to the its rings and satellites, as well as the interactions between them. Detailed study of Uranus by an orbiter is crucial not only for valuable insights into the formation and evolution of our solar system but also for providing ground truths for the understanding of exoplanets. As such, exploration of Uranus will not only enhance our understanding of the ice giant planets themselves but also extend to planetary dynamics throughout our solar system and beyond. The timeliness of exploring Uranus is great, as the community hopes to return in time to image unseen portions of the satellites and magnetospheric configurations. This urgency motivates evaluation of what science can be achieved with a lower-cost, potentially faster-turnaround mission, such as a New Frontiers–class orbiter mission. This paper outlines the scientific case for and the technological and design considerations that must be addressed by future studies to enable a New Frontiers–class Uranus orbiter with balanced cross-disciplinary science objectives. In particular, studies that trade scientific scope and instrumentation and operational capabilities against simpler and cheaper options must be fundamental to the mission formulation
Clinical and laboratory practice for lupus anticoagulant testing : an International Society of Thrombosis and Haemostasis Scientific and Standardization Committee survey
Background Current guidelines have contributed to more uniformity in the performance and interpretation of lupus anticoagulant (LA) testing. However, points to reconsider include testing for LA in patients on anticoagulation, cut-off values, and interpretation of results. Objectives The aim of this International Society of Thrombosis and Haemostasis Scientific and Standardization committee (ISTH SSC) questionnaire was to capture the spectrum of clinical and laboratory practice in LA detection, focusing on variability in practice, so that the responses could inform further ISTH SSC recommendations. Methods Members of the ISTH SSC on Lupus Anticoagulant/Antiphospholipid Antibodies and participants of the Lupus Anticoagulant/Antiphospholipid Antibodies Programme of the External quality Control of diagnostic Assays and Tests Foundation were invited to complete a questionnaire on LA testing that was placed on the ISTH website using RedCap, with data tallied using simple descriptive statistics. Results There was good agreement on several key recommendations in the ISTH and other guidelines on LA testing, such as sample processing, principles of testing, choice of tests, repeat testing to confirm persistent positivity and the use of interpretative reporting. However, the results highlight that there is less agreement on some other aspects, including the timing of testing in relation to thrombosis or pregnancy, testing in patients on anticoagulation, cut-off values, and calculation and interpretation of results. Conclusions Although some of the variability in practice in LA testing reflects the lack of substantive data to underpin evidence-based recommendations, a more uniform approach, based on further guidance, should reduce the inter-center variability of LA testing
A Deep 150 MHz GMRT Survey in Eridanus
We present results of a 150 MHz survey of a field centered on Epsilon
Eridani, undertaken with the Giant Metrewave Radio Telescope (GMRT). The survey
covers an area with a diameter of 2 deg, has a spatial resolution of 30" and a
noise level of 3.1 mJy at the pointing centre. These observations provide a
deeper and higher resolution view of the 150 MHz radio sky than the 7C survey
(although the 7C survey covers a much larger area). A total of 113 sources were
detected, most are point-like, but 20 are extended. We present an analysis of
these sources, in conjunction with the NVSS (at 1.4 GHz) and VLSS (at 74 MHz).
This process allowed us to identify 5 Ultra Steep Spectrum (USS) radio sources
that are candidate high redshift radio galaxies (HzRGs). In addition, we have
derived the dN/dS distribution for these observations and compare our results
with other low frequency radio surveys.Comment: 12 pages, 11 figures, 3 tables, accepted for publication in MNRA
Tailored photon-pair generation in optical fibers
We experimentally control the spectral structure of photon pairs created via
spontaneous four-wave mixing in microstructured fibers. By fabricating fibers
with designed dispersion, one can manipulate the photons' wavelengths, joint
spectrum, and, thus, entanglement. As an example, we produce photon-pairs with
no spectral correlations, allowing direct heralding of single photons in
pure-state wave packets without filtering. We achieve an experimental purity of
, while theoretical analysis and preliminary tests suggest 94.5%
purity is possible with a much longer fiber
New Extremely Metal-Poor Stars in the Galactic Halo
We present a detailed abundance analysis based on high resolution and high
signal-to-noise spectra of eight extremely metal poor (EMP) stars with [Fe/H] <
-3.5-$2429, another sample
star, has excesses of N and Sc with respect to Fe. The strong outliers in
abundance ratios among the Fe-peak elements in these C-normal stars, not found
at somewhat higher metallicities, are definitely real. They suggest that at
such low metallicities we are beginning to see the anticipated and long sought
stochastic effects of individual supernova events contributing to the Fe-peak
material within a single star. A detailed comparison of the results of the
analysis procedures adopted by our 0Z project compared to those of the First
Stars VLT Large Project finds a systematic difference for [Fe/H] of ~0.3 dex,
our values always being higher.Comment: Accepted to the Ap
Evidence for Large-Scale Structure at z=2.4 From Lyman-alpha Imaging
We present deep wide-field medium-band imaging in redshifted Lyman alpha of
fields surrounding HST detections of faint emitters, to characterize their
larger-scale environment. The radio galaxy 53W002 was previously found to be
part of a rich grouping at z=2.39, including 5 confirmed, compact, star-forming
objects. This is now shown to be part of a larger structure traced by bright
AGN, all contained within a projected span of 6.8 arcmin (3.2 Mpc). Of the 14
candidate emitters, six have been spectroscopically confirmed as active nuclei
in the range z=2.390 +/- 0.008. Various statistical tests give a significance
of 95-99% for the reality of this structure on the sky. This grouping is more
extended than a relaxed King model, at the 90% confidence level. Either this
configuration has yet to decouple fully from the Hubble expansion, or it
consists of subgroups which will themselves form a more compact, relaxed
structure. The redshift range for measured members is comparable to the Hubble
flow across the structure, which may imply that the structure is seen near
turnaround.
We surveyed two additional fields at z=2.4, and three contiguous fields at
z=2.6. Only a single candidate at z=2.4 was found, with six at z=2.6.
Comparison with the WFPC2 surveys suggests that the field-to-field contrast is
larger for brighter objects. From this survey alone, groupings such as the
53W002 "cluster" must have an area covering fraction <0.04 in this redshift
range.Comment: 28 pages including 8 figures, uses aaspp4.sty. Accepted for Dec. 1999
A
Robotic-assisted laparoscopic donor nephrectomy: Decreasing length of stay
Background: The number of robotic operations performed with the da Vinci Surgical System has increased during the past decade. This system allows for greater maneuverability and control than hand-assisted laparoscopic procedures, resulting in less tissue manipulation and irritation
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