19,519 research outputs found
Ascent from the lunar surface
Ascent from lunar surface problem with solution by variational calculu
The space station: Human factors and productivity
Human factor researchers and engineers are making inputs into the early stages of the design of the Space Station to improve both the quality of life and work on-orbit. Effective integration of the human factors information related to various Intravehicular Activity (IVA), Extravehicular Activity (EVA), and teletobotics systems during the Space Station design will result in increased productivity, increased flexibility of the Space Stations systems, lower cost of operations, improved reliability, and increased safety for the crew onboard the Space Station. The major features of productivity examined include the cognitive and physical effort involved in work, the accuracy of worker output and ability to maintain performance at a high level of accuracy, the speed and temporal efficiency with which a worker performs, crewmember satisfaction with their work environment, and the relation between performance and cost
Substructure in clusters containing wide-angle tailed radio galaxies. I. New redshifts
We present new redshifts and positions for 635 galaxies in nine rich clusters
containing Wide-Angle Tailed (WAT) radio galaxies. Combined with existing data,
we now have a sample of 18 WAT-containing clusters with more than 10 redshifts.
This sample contains a substantial portion of the WAT clusters in the VLA 20 cm
survey of Abell clusters, including 75% of WAT clusters in the complete survey
(z0.09. It is a representative sample
which should not contain biases other than selection by radio morphology. We
graphically present the new data using histograms and sky maps. A
semi-automated procedure is used to search for emission lines in the spectra in
order to add and verify galaxy redshifts. We find that the average apparent
fraction of emission line galaxies is about 9% in both the clusters and the
field. We investigate the magnitude completeness of our redshift surveys with
CCD data for a test case, Abell 690. This case indicates that our galaxy target
lists are deeper than the detection limit of a typical MX exposure, and they
are 82% complete down to R=19.0. The importance of the uniformity of the
placement of fibers on targets is posited, and we evaluate this in our
datasets. We find some cases of non-uniformities which may influence dynamical
analyses. A second paper will use this database to look for correlations
between the WAT radio morphology and the cluster's dynamical state.Comment: 15 pages, 5 figures, 7 tables. To appear in the Astronomical Journa
The Arecibo Galaxy Environments survey IV: the NGC7448 region and the HI mass function
In this paper we describe results from the Arecibo Galaxy Environments Survey
(AGES). The survey reaches column densities of ~3x10^18 cm^-2 and masses of
~10^7 M_O, over individual regions of order 10 sq deg in size, out to a maximum
velocity of 18,000 km s^-1. Each surveyed region is centred on a nearby galaxy,
group or cluster, in this instance the NGC7448 group. Galaxy interactions in
the NGC7448 group reveal themselves through the identification of tidal tails
and bridges. We find ~2.5 times more atomic gas in the inter-galactic medium
than in the group galaxies. We identify five new dwarf galaxies, two of which
appear to be members of the NGC7448 group. This is too few, by roughly an order
of magnitude, dwarf galaxies to reconcile observation with theoretical
predictions of galaxy formation models. If they had observed this region of sky
previous wide area blind HI surveys, HIPASS and ALFALFA, would have detected
only 5% and 43% respectively of the galaxies we detect, missing a large
fraction of the atomic gas in this volume. We combine the data from this paper
with that from our other AGES papers (370 galaxies) to derive a HI mass
function with the following Schechter function parameters alpha=-1.52+/-0.05,
M^*=5.1+/-0.3x10^9 h_72^-2 M_O, phi=8.6+/-1.1x10-3 h_72^3 Mpc^-3 dex-1.
Integrating the mass function leads to a cosmic mass density of atomic hydrogen
of Omega_HI=5.3+/-0.8x10^-4 h_72^-1. Our mass function is steeper than that
found by both HIPASS and ALFALFA (alpha=1.37 and 1.33 respectively), while our
cosmic mass density is consistent with ALFALFA, but 1.7 times larger than found
by HIPASS
Status of Outer Planet Global Reference Atmospheric Model (GRAM) Upgrades
The inability to test planetary spacecraft in the flight environment prior to a mission requires engineers to rely on ground-based testing and models of the vehicle and expected environments. One of the most widely used engineering models of the atmosphere is the Global Reference Atmospheric Model (GRAM) developed and maintained by the NASA Marshall Space Flight Center (MSFC). The NASA Science Mission Directorate (SMD) has provided funding support to upgrade the GRAMs
Recoverin Regulates Light-dependent Phosphodiesterase Activity in Retinal Rods
The Ca2+-binding protein recoverin may regulate visual transduction in retinal rods and cones, but its functional role and mechanism of action remain controversial. We compared the photoresponses of rods from control mice and from mice in which the recoverin gene was knocked out. Our analysis indicates that Ca2+-recoverin prolongs the dark-adapted flash response and increases the rod's sensitivity to dim steady light. Knockout rods had faster Ca2+ dynamics, indicating that recoverin is a significant Ca2+ buffer in the outer segment, but incorporation of exogenous buffer did not restore wild-type behavior. We infer that Ca2+-recoverin potentiates light-triggered phosphodiesterase activity, probably by effectively prolonging the catalytic activity of photoexcited rhodopsin
The Socratic Method: Empirical Assessment of a Psychology Capstone Course
Although students make some epistemological progress during college, most graduate without developing meaning-making strategies that reflect an understanding that knowledge is socially constructed. Using a pre-test–post-test design and a within-subjects 2 × 2 mixed-design ANOVA, this study reports on empirical findings which support the Socratic method of teaching as effective in challenging and changing psychology capstone students’ levels of epistemological maturity as measured by the Learning Environment Preferences survey and Perry’s model of intellectual maturity
Finite Difference Modeling of Attenuation and Anisotropy
A nite difference scheme which includes the effects of attenuation and anisotropy is tested for seismic reflection and borehole acoustic models. The validity of the scheme is established using a 3D homogenous isotropic model to compare results to the discrete wavenumber method. Three models are then investigated. First, reflections from a 3D at layered model are analyzed for o set and azimuthal dependence of attenuation. Second, discrete fractures are included in a 2D
at layered model to examine their effect on reservoir top and bottom reflections. Third, a 3D borehole in both hard and soft formations is modeled to test the effect of attenuation on guided waves.Massachusetts Institute of Technology. Earth Resources LaboratoryUnited States. Dept. of Energy (Grant DE-FC26-02NT15346)Eni S.p.A. (Firm
Frequency Dependence Of Seismic Data From Nigeria: Preliminary Results
Seismic data from the Niger Delta is used to test processing sequences involved in
prestack and poststack amplitude and frequency analysis of marine seismic data. Water
bottom reverberations are found to present a formidable challenge in poststack frequency
and amplitude analysis. However, reflectors with anomalously high amplitudes show low
frequency content both in deconvolved poststack data and in the near offsets of prestack
data with no deconvolution, which agrees with results in the literature. Lack of detailed
knowledge of the lithology prevents investigation of the physical nature of the amplitude
and frequency variations.Massachusetts Institute of Technology. Borehole Acoustics and Logging ConsortiumMassachusetts Institute of Technology. Earth Resources Laboratory. Reservoir Delineation
Consortiu
A Compact EMAT Receiver for Ultrasonic Testing at Elevated Temperatures
For the past several years, the AISI and several national laboratories have cooperated on a program to develop ultrasonic transducers that can be used in steel mills at the highest temperatures encountered during the processing of the solid metal {1}. To date, pulsed laser light focused on the surface appears to make a satisfactory generator or transmitter for ultrasonic pulses while the EMAT or Electromagnetic Acoustic Transducer appears to hold the greatest promise for the receiver {2}. Both of these essentially noncontact devices can be made to withstand the very hot environmnent and they are not very sensitive to the quality of the surface
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