924 research outputs found
Ozone Response to Aircraft Emissions: Sensitivity Studies with Two-dimensional Models
Our first intercomparison/assessment of the effects of a proposed high-speed civil transport (HSCT) fleet on the stratosphere is presented. These model calculations should be considered more as sensitivity studies, primarily designed to serve the following purposes: (1) to allow for intercomparison of model predictions; (2) to focus on the range of fleet operations and engine specifications giving minimal environmental impact; and (3) to provide the basis for future assessment studies. The basic scenarios were chosen to be as realistic as possible, using the information available on anticipated developments in technology. They are not to be interpreted as a commitment or goal for environmental acceptability
Graphical User Interface Development and Design to Support Airport Runway Configuration Management
The objective of this effort was to develop a graphical user interface (GUI) for the National Aeronautics and Space Administration's (NASA) System Oriented Runway Management (SORM) decision support tool to support runway management. This tool is expected to be used by traffic flow managers and supervisors in the Airport Traffic Control Tower (ATCT) and Terminal Radar Approach Control (TRACON) facilities
Rotational velocities of low-mass stars in the Pleiades and Hyades
We have obtained high-resolution spectra of 89 M dwarf members of the
Pleiades and Hyades and have derived radial velocities, H-alpha equivalent
widths, and spectroscopic rotational velocities for these stars. Typical masses
of the newly-observed Pleiades and Hyades stars are ~ 0.4 M_{\sun} and ~ 0.2
M_{\sun}, respectively. We combine our new observations with previously
published data to explore the rotational evolution of young stars with M < 0.4
M_\sun. The average rotation rate in the Hyades (age 600 Myr) is about 0.4 that
of the Pleiades (110 Myr), and the mean equivalent widths of H-alpha are also
lower. As found in previous studies, the correlation between rotation and
chromospheric activity is identical in both clusters, implying that the lower
activity in the Hyades is a result of the lower rotation rates. We show that a
simple scaling of the Pleiades rotational distribution for M \leq 0.4 M_{\sun},
corrected for the effects of structural evolution, matches that of the Hyades
if the average angular momentum loss from the Pleiades to the Hyades age is
factor of \approx 6. This suggests that the distribution of initial angular
momenta and disk-locking lifetimes for the lowest mass stars was similar in
both clusters. We argue that this result provides further evidence for a
saturation of the angular momentum loss rate at high rotational velocities.Comment: 22 pages, 11 figures, accepted for publication in The Astronomical
Journal, tentatively scheduled for March 200
Rotational Studies of Late-Type Stars. VII. M34 (NGC 1039) and the Evolution of Angular Momentum and Activity in Young Solar-Type Stars
We analyze Keck Hires observations of rotation in F, G, and K dwarf members
of the open cluster M34 (NGC 1039), which is 250 Myr old, and we compare them
to the Pleiades, Hyades, and NGC 6475. The upper bound to rotation seen in M34
is about a factor of two lower than for the 100 Myr-old Pleiades, but most M34
stars are well below this upper bound, and it is the overall convergence in
rotation rates that is most striking. A few K dwarfs in M34 are still rapid
rotators, suggesting that they have undergone core-envelope decoupling,
followed by replenishment of surface angular momentum from an internal
reservoir. Our comparison of rotation in these clusters indicates that the time
scale for the coupling of the envelope to the core must be close to 100 Myr if
decoupling does, in fact, occur.Comment: 16 pages + 1 table + 5 figure
Epigenetic Alterations and an Increased Frequency of Micronuclei in Women with Fibromyalgia
Fibromyalgia (FM), characterized by chronic widespread pain, fatigue, and cognitive/mood disturbances, leads to reduced workplace productivity and increased healthcare expenses. To determine if acquired epigenetic/genetic changes are associated with FM, we compared the frequency of spontaneously occurring micronuclei (MN) and genome-wide methylation patterns in women with FM () to those seen in comparably aged healthy controls ( (MN); (methylation)). The mean (sd) MN frequency of women with FM (51.4 (21.9)) was significantly higher than that of controls (15.8 (8.5)) (; df = 1; ). Significant differences ( sites) in methylation patterns were observed between cases and controls considering a 5% false discovery rate. The majority of differentially methylated (DM) sites (91%) were attributable to increased values in the women with FM. The DM sites included significant biological clusters involved in neuron differentiation/nervous system development, skeletal/organ system development, and chromatin compaction. Genes associated with DM sites whose function has particular relevance to FM included BDNF, NAT15, HDAC4, PRKCA, RTN1, and PRKG1. Results support the need for future research to further examine the potential role of epigenetic and acquired chromosomal alterations as a possible biological mechanism underlying FM
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Rates of lobar atrophy in asymptomatic MAPT mutation carriers.
IntroductionThe aim of this study was to investigate the rates of lobar atrophy in the asymptomatic microtubule-associated protein tau (MAPT) mutation carriers.MethodsMAPT mutation carriers (n = 14; 10 asymptomatic, 4 converters from asymptomatic to symptomatic) and noncarriers (n = 13) underwent structural magnetic resonance imaging and were followed annually with a median of 9.2 years. Longitudinal changes in lobar atrophy were analyzed using the tensor-based morphometry with symmetric normalization algorithm.ResultsThe rate of temporal lobe atrophy in asymptomatic MAPT mutation carriers was faster than that in noncarriers. Although the greatest rate of atrophy was observed in the temporal lobe in converters, they also had increased atrophy rates in the frontal and parietal lobes compared to noncarriers.DiscussionAccelerated decline in temporal lobe volume occurs in asymptomatic MAPT mutation carriers followed by the frontal and parietal lobe in those who have become symptomatic. The findings have implications for monitoring the progression of neurodegeneration during clinical trials in asymptomatic MAPT mutation carriers
The Problem of Hipparcos Distances to Open Clusters. II. Constraints from Nearby Field Stars
This paper examines the discrepancy between distances to nearby open clusters
as determined by parallaxes from Hipparcos compared to traditional main
sequence fitting. The biggest difference is seen for the Pleiades, and our
hypothesis is that if the Hipparcos distance to the Pleiades is correct, then
similar subluminous ZAMS stars should exist elsewhere, including the immediate
solar neighborhood. We examine a color-magnitude diagram of very young and
nearby solar-type stars and show that none of them lie below the traditional
ZAMS, despite the fact that the Hipparcos Pleiades parallax would place its
members 0.3 magnitude below that ZAMS. We also present analyses and
observations of solar-type stars that do lie below the ZAMS and show that they
are subluminous because of low metallicity and that they have the kinematics of
old stars.Comment: 22 pages (including 4 tables) plus 6 figure
Hydrodynamics of high-redshift galaxy collisions: From gas-rich disks to dispersion-dominated mergers and compact spheroids
Disk galaxies at high redshift (z~2) are characterized by high fractions of
cold gas, strong turbulence, and giant star-forming clumps. Major mergers of
disk galaxies at high redshift should then generally involve such turbulent
clumpy disks. Merger simulations, however, model the ISM as a stable,
homogeneous, and thermally pressurized medium. We present the first merger
simulations with high fractions of cold, turbulent, and clumpy gas. We discuss
the major new features of these models compared to models where the gas is
artificially stabilized and warmed. Gas turbulence, which is already strong in
high-redshift disks, is further enhanced in mergers. Some phases are
dispersion-dominated, with most of the gas kinetic energy in the form of
velocity dispersion and very chaotic velocity fields, unlike merger models
using a thermally stabilized gas. These mergers can reach very high star
formation rates, and have multi-component gas spectra consistent with
SubMillimeter Galaxies. Major mergers with high fractions of cold turbulent gas
are also characterized by highly dissipative gas collapse to the center of
mass, with the stellar component following in a global contraction. The final
galaxies are early-type with relatively small radii and high Sersic indices,
like high-redshift compact spheroids. The mass fraction in a disk component
that survives or re-forms after a merger is severely reduced compared to models
with stabilized gas, and the formation of a massive disk component would
require significant accretion of external baryons afterwards. Mergers thus
appear to destroy extended disks even when the gas fraction is high, and this
lends further support to smooth infall as the main formation mechanism for
massive disk galaxies.Comment: ApJ accepte
The transcriptional response of Caenorhabditis elegans to ivermectin exposure identifies novel genes involved in the response to reduced food intake
We have examined the transcriptional response of Caenorhabditis elegans following exposure to the anthelmintic drug ivermectin (IVM) using whole genome microarrays and real-time QPCR. Our original aim was to identify candidate molecules involved in IVM metabolism and/or excretion. For this reason the IVM tolerant strain, DA1316, was used to minimise transcriptomic changes related to the phenotype of drug exposure. However, unlike equivalent work with benzimidazole drugs, very few of the induced genes were members of xenobiotic metabolising enzyme families. Instead, the transcriptional response was dominated by genes associated with fat mobilization and fatty acid metabolism including catalase, esterase, and fatty acid CoA synthetase genes. This is consistent with the reduction in pharyngeal pumping, and consequential reduction in food intake, upon exposure of DA1316 worms to IVM. Genes with the highest fold change in response to IVM exposure, cyp-37B1, mtl-1 and scl-2, were comparably up-regulated in response to short–term food withdrawal (4 hr) independent of IVM exposure, and GFP reporter constructs confirm their expression in tissues associated with fat storage (intestine and hypodermis). These experiments have serendipitously identified novel genes involved in an early response of C. elegans to reduced food intake and may provide insight into similar processes in higher organisms
Evidence for Reflected Light from the Most Eccentric Exoplanet Known
This is an author-created, un-copyedited version of an article published in The Astrophysical Journal. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at https://doi.org/10.3847/0004-637X/821/1/65.Planets in highly eccentric orbits form a class of objects not seen within our solar system. The most extreme case known among these objects is the planet orbiting HD20782, with an orbital period of 597days and an eccentricity of 0.96. Here we present new data and analysis for this system as part of the Transit Ephemeris Refinement and Monitoring Survey. We obtained CHIRON spectra to perform an independent estimation of the fundamental stellar parameters. New radial velocities from Anglo-Australian Telescope and PARAS observations during periastron passage greatly improve our knowledge of the eccentric nature of the orbit. The combined analysis of our Keplerian orbital and Hipparcos astrometry show that the inclination of the planetary orbit is >1.22, ruling out stellar masses for the companion. Our long-term robotic photometry show that the star is extremely stable over long timescales. Photometric monitoring of the star during predicted transit and periastron times using Microvariability and Oscillations of STars rule out a transit of the planet and reveal evidence of phase variations during periastron. These possible photometric phase variations may be caused by reflected light from the planet’s atmosphere and the dramatic change in star–planet separation surrounding the periastron passage.Peer reviewedFinal Accepted Versio
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