61,446 research outputs found
An intelligent position-specific training system for mission operations
Marshall Space Flight Center's (MSFC's) payload ground controller training program provides very good generic training; however, ground controller position-specific training can be improved by including position-specific training systems in the training program. This report explains why MSFC needs to improve payload ground controller position-specific training. The report describes a generic syllabus for position-specific training systems, a range of system designs for position-specific training systems, and a generic development process for developing position-specific training systems. The report also describes a position-specific training system prototype that was developed for the crew interface coordinator payload operations control center ground controller position. The report concludes that MSFC can improve the payload ground controller training program by incorporating position-specific training systems for each ground controller position; however, MSFC should not develop position-specific training systems unless payload ground controller position experts will be available to participate in the development process
Growth of Sr1-xCaxRuO3 thin films by metalorganic aerosol deposition
We report the growth of thin films of Sr1-xCaxRuO3 on SrTiO3 and MgO
substrates by metalorganic aerosol deposition. The structure and microstructure
is characterized by X-ray diffraction and room-temperature scanning tunnelling
microscopy (STM), respectively. STM indicates in-plane epitaxy and a small
surface roughness for films on SrTiO3. The high-quality of the films is
supported by large residual resistivity ratios up to 29.Comment: 4 Pages, 2 Figures, submitted to Proceedings of ICM 2009 (Karlsruhe
Implications of the isotope effects on the magnetization, magnetic torque and susceptibility
We analyze the magnetization, magnetic torque and susceptibility data of
La2-xSrxCu(16,18)O4 and YBa2(63,65)CuO7-x near Tc in terms of the universal
3D-XY scaling relations. It is shown that the isotope effect on Tc mirrors that
on the anisotropy. Invoking the generic behavior of the anisotropy the doping
dependence of the isotope effects on the critical properties, including Tc,
correlation lengths and magnetic penetration depths are traced back to a change
of the mobile carrier concentration.Comment: 5 pages, 3 figure
Superluminal Caustics of Close, Rapidly-Rotating Binary Microlenses
The two outer triangular caustics (regions of infinite magnification) of a
close binary microlens move much faster than the components of the binary
themselves, and can even exceed the speed of light. When , where
is the caustic speed, the usual formalism for calculating the lens
magnification breaks down. We develop a new formalism that makes use of the
gravitational analog of the Li\'enard-Wiechert potential. We find that as the
binary speeds up, the caustics undergo several related changes: First, their
position in space drifts. Second, they rotate about their own axes so that they
no longer have a cusp facing the binary center of mass. Third, they grow larger
and dramatically so for . Fourth, they grow weaker roughly in
proportion to their increasing size. Superluminal caustic-crossing events are
probably not uncommon, but they are difficult to observe.Comment: 12 pages, 7 ps figures, submitted to Ap
Angular Radii of Stars via Microlensing
We outline a method by which the angular radii of giant and main sequence
stars in the Galactic bulge can be measured to a few percent accuracy. The
method combines ground-based photometry of caustic-crossing bulge microlensing
events, with a handful of precise astrometric measurements of the lensed star
during the event, to measure the angular radius of the source, theta_*. Dense
photometric coverage of one caustic crossing yields the crossing timescale dt.
Less frequent coverage of the entire event yields the Einstein timescale t_E
and the angle phi of source trajectory with respect to the caustic. The
photometric light curve solution predicts the motion of the source centroid up
to an orientation on the sky and overall scale. A few precise astrometric
measurements therefore yield theta_E, the angular Einstein ring radius. Then
the angular radius of the source is obtained by theta_*=theta_E(dt/t_E)
sin(phi). We argue that theta_* should be measurable to a few percent accuracy
for Galactic bulge giant stars using ground-based photometry from a network of
small (1m-class) telescopes, combined with astrometric observations with a
precision of ~10 microarcsec to measure theta_E. We find that a factor of ~50
times fewer photons are required to measure theta_E to a given precision for
binary-lens events than single-lens events. Adopting parameters appropriate to
the Space Interferometry Mission (SIM), ~7 min of SIM time is required to
measure theta_E to ~5% accuracy for giant sources in the bulge. For
main-sequence sources, theta_E can be measured to ~15% accuracy in ~1.4 hours.
With 10 hrs of SIM time, it should be possible to measure theta_* to ~5% for
\~80 giant stars, or to 15% for ~7 main sequence stars. A byproduct of such a
campaign is a significant sample of precise binary-lens mass measurements.Comment: 13 pages, 3 figures. Revised version, minor changes, required SIM
integration times revised upward by ~60%. Accepted to ApJ, to appear in the
March 20, 2003 issue (v586
Reconstruction of Cluster Masses using Particle Based Lensing I: Application to Weak Lensing
We present Particle-Based Lensing (PBL), a new technique for gravitational
lensing mass reconstructions of galaxy clusters. Traditionally, most methods
have employed either a finite inversion or gridding to turn observational
lensed galaxy ellipticities into an estimate of the surface mass density of a
galaxy cluster. We approach the problem from a different perspective, motivated
by the success of multi-scale analysis in smoothed particle hydrodynamics. In
PBL, we treat each of the lensed galaxies as a particle and then reconstruct
the potential by smoothing over a local kernel with variable smoothing scale.
In this way, we can tune a reconstruction to produce constant signal-noise
throughout, and maximally exploit regions of high information density.
PBL is designed to include all lensing observables, including multiple image
positions and fluxes from strong lensing, as well as weak lensing signals
including shear and flexion. In this paper, however, we describe a shear-only
reconstruction, and apply the method to several test cases, including simulated
lensing clusters, as well as the well-studied ``Bullet Cluster'' (1E0657-56).
In the former cases, we show that PBL is better able to identify cusps and
substructures than are grid-based reconstructions, and in the latter case, we
show that PBL is able to identify substructure in the Bullet Cluster without
even exploiting strong lensing measurements. We also make our codes publicly
available.Comment: Accepted for publication in ApJ; Codes available at
http://www.physics.drexel.edu/~deb/PBL.htm ; 12 pages,9 figures, section 3
shortene
Exact gravitational lensing and rotation curve
Based on the geodesic equation in a static spherically symmetric metric we
discuss the rotation curve and gravitational lensing. The rotation curve
determines one function in the metric without assuming Einstein's equations.
Then lensing is considered in the weak field approximation of general
relativity. From the null geodesics we derive the lensing equation and
corrections to it.Comment: 12 pages, 1 figur
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