867 research outputs found
Uniqueness of Current Cosmic Acceleration
One of the strongest arguments against the cosmological constant as an
explanation of the current epoch of accelerated cosmic expansion is the
existence of an earlier, dynamical acceleration, i.e. inflation. We examine the
likelihood that acceleration is an occasional phenomenon, putting stringent
limits on the length of any accelerating epoch between recombination and the
recent acceleration; such an epoch must last less than 0.05 e-fold (at z>2) or
the matter power spectrum is modified by more than 20%.Comment: 6 pages, 5 figures; v2 corrected typo in Eq.
H-Ras signaling and K-Ras signaling are differentially dependent on endocytosis
dEndocytosis is required for efficient mitogen-activated protein kinase (MAPK) activation by activated growth factor receptors. We examined if H-Ras and K-Ras proteins, which are distributed across different plasma membrane microdomains, have equal access to the endocytic compartment and whether this access is necessary for downstream signaling. Inhibition of endocytosis by dominant interfering dynamin-K44A blocked H-Ras but not K-Ras-mediated PC12 cell differentiation and selectively inhibited H-Ras- but not K-Ras-mediated Raf-1 activation in BHK cells. H-Ras- but not K-Ras-mediated Raf-1 activation was also selectively dependent on phosphoinositide 3-kinase activity. Stimulation of endocytosis and endocytic recycling by wildtype Rab5 potentiated H-Ras-mediated Raf-1 activation. In contrast, Rab5-Q79L, which stimulates endocytosis but not endocytic recycling, redistributed activated H-Ras from the plasma membrane into enlarged endosomes and inhibited H-Ras-mediated Raf-1 activation. Rab5-Q79L expression did not cause the accumulation of wild-type H-Ras in enlarged endosomes. Expression of wild-type Rab5 or Rab5-Q79L increased the specific activity of K-Ras-activated Raf-1 but did not result in any redistribution of K-Ras from the plasma membrane to endosomes. These results show that H-Ras but not K-Ras signaling though the Raf/MEK/MAPK cascade requires endocytosis and enclocytic recycling. The data also suggest a mechanism for returning Raf-1 to the cytosol after plasma membrane recruitment
Paper Session I-A - Weather Impacts on Space Operations
The 45th Weather Squadron of the United States Air Force provides weather support to Patrick Air Force Base, Cape Canaveral Air Force Station (CCAFS), Eastern Range, and Kennedy Space Center (KSC). The support includes weather observations, forecasts, climatological studies and consultant services to a wide variety of Range users. The most visible to the general public is weather support to space vehicles, particularly the Space Shuttle. That support includes resource protection, ground processing, launch, and Ferry Flight; as well as consultant to the Spaceflight Meteorology Group (at Johnson Space Center) for landing forecasts
Weighing the local dark matter with RAVE red clump stars
We determine the Galactic potential in the solar neigbourhood from RAVE
observations. We select red clump stars for which accurate distances, radial
velocities, and metallicities have been measured. Combined with data from the
2MASS and UCAC catalogues, we build a sample of 4600 red clump stars within a
cylinder of 500 pc radius oriented in the direction of the South Galactic Pole,
in the range of 200 pc to 2000 pc distances. We deduce the vertical force and
the total mass density distribution up to 2 kpc away from the Galactic plane by
fitting a distribution function depending explicitly on three isolating
integrals of the motion in a separable potential locally representing the
Galactic one with four free parameters. Because of the deep extension of our
sample, we can determine nearly independently the dark matter mass density and
the baryonic disc surface mass density. We find (i) at 1kpc Kz/(2piG) = 68.5 pm
1.0 Msun/pc2, and (ii) at 2 kpc Kz/(2piG) = 96.9 pm 2.2 Msun/pc2. Assuming the
solar Galactic radius at R0 = 8.5 kpc, we deduce the local dark matter density
rhoDM (z=0) = 0.0143 pm 0.0011Msun pc3 = 0.542 pm 0.042 Gev/cm3 and the
baryonic surface mass density Sigma = 44.4 pm 4.1 Msun/pc2 . Our results are in
agreement with previously published Kz determinations up to 1 kpc, while the
extension to 2 kpc shows some evidence for an unexpectedly large amount of dark
matter. A flattening of the dark halo of order 0.8 can produce such a high
local density in combination with a circular velocity of 240 km/s . Another
explanation, allowing for a lower circular velocity, could be the presence of a
secondary dark component, a very thick disc resulting either from the deposit
of dark matter from the accretion of multiple small dwarf galaxies, or from the
presence of an effective phantom thick disc in the context of effective
galactic-scale modifications of gravity.Comment: 14 pages, 13 figures, accepted to Astronomy and Astrophysic
Romantic Relationships and Criminal Desistance: Pathways and Processes
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/107362/1/socf12088.pd
SparsePak: A Formatted Fiber Field-Unit for The WIYN Telescope Bench Spectrograph. II. On-Sky Performance
We present a performance analysis of SparsePak and the WIYN Bench
Spectrograph for precision studies of stellar and ionized gas kinematics of
external galaxies. We focus on spectrograph configurations with echelle and
low-order gratings yielding spectral resolutions of ~10000 between 500-900nm.
These configurations are of general relevance to the spectrograph performance.
Benchmarks include spectral resolution, sampling, vignetting, scattered light,
and an estimate of the system absolute throughput. Comparisons are made to
other, existing, fiber feeds on the WIYN Bench Spectrograph. Vignetting and
relative throughput are found to agree with a geometric model of the optical
system. An aperture-correction protocol for spectrophotometric standard-star
calibrations has been established using independent WIYN imaging data and the
unique capabilities of the SparsePak fiber array. The WIYN
point-spread-function is well-fit by a Moffat profile with a constant power-law
outer slope of index -4.4. We use SparsePak commissioning data to debunk a
long-standing myth concerning sky-subtraction with fibers: By properly treating
the multi-fiber data as a ``long-slit'' it is possible to achieve precision sky
subtraction with a signal-to-noise performance as good or better than
conventional long-slit spectroscopy. No beam-switching is required, and hence
the method is efficient. Finally, we give several examples of science
measurements which SparsePak now makes routine. These include H
velocity fields of low surface-brightness disks, gas and stellar
velocity-fields of nearly face-on disks, and stellar absorption-line profiles
of galaxy disks at spectral resolutions of ~24,000.Comment: To appear in ApJSupp (Feb 2005); 19 pages text; 7 tables; 27 figures
(embedded); high-resolution version at
http://www.astro.wisc.edu/~mab/publications/spkII_pre.pd
Chemical gradients in the Milky Way from the RAVE data. II. Giant stars
We provide new constraints on the chemo-dynamical models of the Milky Way by
measuring the radial and vertical chemical gradients for the elements Mg, Al,
Si, Ti, and Fe in the Galactic disc and the gradient variations as a function
of the distance from the Galactic plane (). We selected a sample of giant
stars from the RAVE database using the gravity criterium 1.7log g2.8. We
created a RAVE mock sample with the Galaxia code based on the Besan\c con model
and selected a corresponding mock sample to compare the model with the observed
data. We measured the radial gradients and the vertical gradients as a function
of the distance from the Galactic plane to study their variation across the
Galactic disc. The RAVE sample exhibits a negative radial gradient of
dex kpc close to the Galactic plane ( kpc)
that becomes flatter for larger . Other elements follow the same trend
although with some variations from element to element. The mock sample has
radial gradients in fair agreement with the observed data. The variation of the
gradients with shows that the Fe radial gradient of the RAVE sample has
little change in the range kpc and then flattens. The iron
vertical gradient of the RAVE sample is slightly negative close to the Galactic
plane and steepens with . The mock sample exhibits an iron vertical
gradient that is always steeper than the RAVE sample. The mock sample also
shows an excess of metal-poor stars in the [Fe/H] distributions with respect to
the observed data. These discrepancies can be reduced by decreasing the number
of thick disc stars and increasing their average metallicity in the Besan\c con
model.Comment: 13 pages, 9 figures, 5 tables, A&A accepte
High resolution infrared spectra of bulge globular clusters: Liller~1 and NGC 6553
Using the NIRSPEC spectrograph at Keck II, we have obtained echelle spectra
covering the range 1.5-1.8um for 2 of the brightest giants in Liller 1 and NGC
6553, old metal rich globular clusters in the Galactic bulge. We use spectrum
synthesis for the abundance analysis, and find [Fe/H]=-0.3 +/- 0.2 and
[O/H]=+0.3 +/- 0.2 dex. The composition of the clusters is similar to that of
field stars in the bulge and is consistent with a sceanrio in which the
clusters formed early, with rapid enrichment. We have dificulty achieveing a
good fit to the spectrum of NGC 6553 using either the low or the high values
recently reported in the literature, unless unusually large, or no
alpha-element enhancements are adopted, respectively.Comment: To appear in the Astronomical Journal, March 200
Deciphering The Last Major Invasion of the Milky Way Galaxy
We present first results from a spectroscopic survey of 2000 F/G stars
0.5--5kpc from the Galactic plane, obtained with the 2dF facility on the AAT.
These data show the mean rotation velocity of the thick disk about the Galactic
center a few kpc from the plane is very different than expectation, being about
100km/s, rather than the predicted ~180km/s. We propose that our sample is
dominated by stars from a disrupted satellite which merged with the disk of the
Milky Way Galaxy some 10-12Gyr ago. We do not find evidence for the many
substantial mergers expected in hierarchical clustering theories. We find yet
more evidence that the stellar halo retains kinematic substructure, indicative
of minor mergersComment: ApJ Letter in pres
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