1,721 research outputs found
Recent advances in coherent optics. Filtering of spatial frequencies, holography
Applications of coherent light in areas of spatial filtering and holograph
Robotic mobile servicing platform for space station
The semi-autonomous inspection and servicing of the Space Station's major thermal, electrical, mechanical subsystems are critical needs for the safe and reliable operation of the station. A conceptual design is presented of a self-intelligent, small and highly mobile robotic platform. Equipped with suitable inspection sensors (cameras, ammonia detectors, etc.), this system's primary mission is to perform routine, autonomous inspection of the Station's primary subsystems. Typical tasks include detection of leaks from thermal fluid or refueling lines, as well as detection of micro-meteroid damage to the primary structure. Equipped with stereo cameras and a dexterous manipulator, simple teleoperator repairs and small On-orbit Replacement Unit (ORU) changeout can also be accomplished. More difficult robotic repairs would be left to the larger, more sophisticated Mobile Remote Manipulator System (MRMS). An ancillary function is to ferry crew members and equipment around the station. The primary design objectives were to provide a flexible, but uncomplicated robotic platform, one which caused minimal impact to the design of the Station's primary structure but could accept more advanced telerobotic technology as it evolves
Color Magnitude Relation and Morphology of Low-Redshift ULIRGs in SDSS
We present color-magnitude and morphological analysis of 54 low-redshift
ULIRGs, a subset of the IRAS 1Jy sample (Kim & Sanders, 1998), in the SDSS. The
ULIRGs are on average 1 magnitude brighter in M0.1r than the SDSS galaxies
within the same redshift range. The majority of the ULIRGs (~87%) have the
colors typical of the blue cloud, and only 4 sources (~7%) are located in the
red sequence. While ULIRGs are popularly thought to be precursors to a QSO
phase, we find few (~6%) in the "green valley" where the majority of the X-ray
and IR selected AGNs are found, and none of which harbors an AGN. For the 14
previously spectroscopic identified AGNs (~28%), we perform PSF subtractions
and find that on average the central point sources contribute less than one
third to the total luminosity, and that their high optical luminosities and
overall blue colors are apparently the result of star formation activity of the
host galaxies. Visual inspection of the SDSS images reveals a wide range of
disturbed morphologies. A detailed morphology analysis using Gini and M20
coefficients shows that slightly less than one half (~42% in g band) of the
ULIRGs are located in the region where most local mergers are found. The
heterogeneous distribution of ULIRGs in the G-M20 space is qualitatively
consistent with the results found by numerical simulations of disk-disk
mergers. Our study also shows that the measured morphological parameters are
systematically affected by the SNR and thus the merging galaxies can appear at
various regions in the G-M20 space. In general, our results reinforce the view
that ULIRGs contain young stellar populations and are mergers in progress. Our
study provides a uniform comparison sample for studying ULIRGs at higher
redshifts such as Spitzer mid-IR selected ULIRGs at z=1~2 and submm galaxies.Comment: 42 pages, 11 figures, ApJ accepte
Parametric tests of a traction drive retrofitted to an automotive gas turbine
The results of a test program to retrofit a high performance fixed ratio Nasvytis Multiroller Traction Drive in place of a helical gear set to a gas turbine engine are presented. Parametric tests up to a maximum engine power turbine speed of 45,500 rpm and to a power level of 11 kW were conducted. Comparisons were made to similar drives that were parametrically tested on a back-to-back test stand. The drive showed good compatibility with the gas turbine engine. Specific fuel consumption of the engine with the traction drive speed reducer installed was comparable to the original helical gearset equipped engine
Neutral Gas Properties and Ly Escape in Extreme Green Pea Galaxies
Mechanisms regulating the escape of Ly photons and ionizing radiation
remain poorly understood. To study these processes we analyze VLA 21cm
observations of one Green Pea (GP), J160810+352809 (hereafter J1608), and HST
COS spectra of 17 GP galaxies at . All are highly ionized: J1608 has the
highest [O III] /[O II] for star-forming galaxies in
SDSS, and the 17 GPs have [O III]/[O II] . We set an upper limit on
J1608's HI mass of , near or below average compared to
similar mass dwarf galaxies. In the COS sample, eight GPs show Ly
absorption components, six of which also have Ly emission. The HI
column densities derived from Ly absorption are high, cm, well above the LyC optically thick limit. Using
low-ionization absorption lines, we measure covering fractions
(f_{\mbox{cov}}) of , and find that f_{\mbox{cov}} strongly
anti-correlates with Ly escape fraction. Low covering fractions may
facilitate Ly and LyC escape through dense neutral regions. GPs with
f_{\mbox{cov}}\sim1 all have low neutral gas velocities, while GPs with lower
f_{\mbox{cov}}=0.2-0.6 have a larger range of velocities. Conventional
mechanical feedback may help establish low f_{\mbox{cov}} in some cases,
whereas other processes may be important for GPs with low velocities. Finally,
we compare f_{\mbox{cov}} with proposed indicators of LyC escape. Ionizing
photon escape likely depends on a combination of neutral gas geometry and
kinematics, complicating the use of emission-line diagnostics for identifying
LyC emitters.Comment: 21 pages, 11 figures, accepted for publication in Ap
Evaluation of sleepiness in space robotics task performance and discussing sleep with high school students in a museum
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics; and, (S.M. in Technology and Policy)--Massachusetts Institute of Technology, Engineering Systems Division, Technology and Policy Program, 2012.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student submitted PDF version of thesis.Includes bibliographical references (p. 47-50).Sleepiness impacts performance in all aspects of life. This thesis addresses the impact of sleepiness on astronauts and adolescents in their everyday tasks. The first part describes the results of an experiment assessing the effect of sleepiness and workload on performance in simulated space telerobotics tasks. The second part describes the results of a forum discussion with high school students about school start time based on information about adolescent sleep biology and various stakeholder perspectives. Astronauts must maintain a high level of performance during space robotics operations, despite sleep schedules that hinder their cognitive function, response time, and attention. This study aimed to determine the usefulness of secondary tasks to assess sleepiness and workload during simulated space robotics performance. 13 naive subjects were trained to perform two types of robotics tasks and two types of secondary tasks measuring response time. Subjects completed two 2-hour robotics sessions, one at midday after approximately 4 hours awake, and one at night after 18 hours awake. Comparing 18 hours awake versus 4, Karolinska Sleepiness Scale scores increased by at least 2 points. Subjects maintained primary robotics task performance at the night session, but secondary task measures such as inverse response time showed significant changes, with moderate Hedges' g (0.35 to 0.74) effect sizes. For a passive monitoring of arm movement primary task, a simple response secondary task metric proved more sensitive to time awake than a two choice response secondary task, but the converse was found when the primary task involved track and capture manual control. Our visual secondary task was sensitive to changes in primary task workload and sleepiness. Secondary task workload measures are a potentially useful adjunct to primary task drowsiness metrics like PVT and deserve further investigation. In Part II, we hypothesized that informed high school students can make strong recommendations about school start time after learning about the biology of their sleep needs and participating in a discussion forum to consider various stakeholder perspectives. 26 high school students from Fenway High School participated in a forum at the Museum of Science. Before the forum, they completed a survey about their sleep habits. During the forum, they participated in a role play exercise, taking on the roles of parent, sleep researcher, administrator, student, and teacher and negotiating tradeoffs about school start time. In the post-forum survey, students showed learning about sleep and made good recommendations to share with their peers. They value sleep and think that getting enough sleep is important, yet by their self-reported actions they seem to value other activities more."Part I of this research was supported by the NSBRI through NASA Contract NCC 9-58"--PDF p. 3by Caroline Lowenthal.S.M.in Technology and PolicyS.M
Total Molecular Gas Masses of Planck - Herschel Selected Strongly Lensed Hyper Luminous Infrared Galaxies
We report the detection of CO(1 - 0) line emission from seven Planck and
Herschel selected hyper luminous (LIR(8-1000um) > 10^13Lsun) infrared galaxies
with the Green Bank Telescope (GBT). CO(1 - 0) measurements are a vital tool to
trace the bulk molecular gas mass across all redshifts. Our results place tight
constraints on the total gas content of these most apparently luminous high-z
star-forming galaxies (apparent IR luminosities of LIR > 10^(13-14) Lsun),
while we confirm their predetermined redshifts measured using the Large
Millimeter Telescope, LMT (zCO = 1.33 - 3.26). The CO(1 - 0) lines show similar
profiles as compared to Jup = 2 -4 transitions previously observed with the
LMT. We report enhanced infrared to CO line luminosity ratios of
= 110 (pm 22) Lsun(K km s^-1 pc^-2)^-1 compared to normal
star-forming galaxies, yet similar to those of well-studied IR-luminous
galaxies at high-z. We find average brightness temperature ratios of =
0.93 (2 sources), = 0.34 (5 sources), and = 0.18 (1 source). The
r31 and r41 values are roughly half the average values for SMGs. We estimate
the total gas mass content as uMH2 = (0.9 - 27.2) x 10^11(alphaCO/0.8)Msun,
where u is the magnification factor and alphaCO is the CO line luminosity to
molecular hydrogen gas mass conversion factor. The rapid gas depletion times
are, on average, tau = 80 Myr, which reveal vigorous starburst activity, and
contrast the Gyr depletion timescales observed in local, normal star-forming
galaxies.Comment: published in MNRAS, 9pages, 5fig
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