964 research outputs found
Meteorological applications of fractal analysis
Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric and Planetary Sciences, 1984.Microfiche copy available in Archives and Science.Bibliography: leaves 48-49.by Michael E. Rocha.M.S
Opportunity for All: How the American Public Benefits From Internet Access at U.S. Libraries
Examines the use of free computer and Internet access in public libraries, by income level, age, race/ethnicity, and online activity. Explores libraries' role as a community resource for social media, education, employment, e-government, and other areas
Globular Clusters around Galaxies in Groups
We have obtained deep photometry of NGC 1199 (in HCG 22) and NGC 6868 (in the
Telescopium group). Both galaxies are the optically brightest galaxies of their
groups. Our analysis of B and R images taken with the Keck II and the VLT/ESO
telescopes, detected a population of globular clusters around both galaxies,
with total specific frequencies S_N=1.7\pm0.6 for NGC 1199 and S_N = 1.3\pm0.6
for NGC 6868. The color distributions of the globular cluster systems shows
bimodal peaks centered at (B-R)_0 = 1.13\pm0.10 and 1.42\pm0.10 (NGC 1199) and
(B-R)_0=1.12\pm0.10 and 1.42\pm0.10 (NGC 6868).Comment: 3 pages, 1 figure. To appear in the proceedings of IAU Symp. 207,
"Extragalactic Star Clusters", eds. E. Grebel, D. Geisler, D. Minnit
Selection and photometric properties of K+A galaxies
Two different simple measurements of galaxy star formation rate with
different timescales are compared empirically on fiber spectra of
galaxies with mag taken from the Sloan Digital Sky Survey in the
redshift range : a ratio \Aamp / \Kamp found by fitting a linear
sum of an average old stellar poplulation spectrum (\Kamp) and average A-star
spectrum (\Aamp) to the galaxy spectrum, and the equivalent width (EW) of the
\Halpha emission line. The two measures are strongly correlated, but there is
a small clearly separated population of outliers from the median correlation
that display excess \Aamp /\Kamp relative to \Halpha EW. These ``K+A'' (or
``E+A'') galaxies must have dramatically decreased their star-formation rates
over the last Gyr. The K+A luminosity distribution is very similar to
that of the total galaxy population. The K+A population appears to be
bulge-dominated, but bluer and higher surface-brightness than normal
bulge-dominated galaxies; it appears that K+A galaxies will fade with time into
normal bulge-dominated galaxies. The inferred rate density for K+A galaxy
formation is at redshift .
These events are taking place in the field; K+A galaxies don't primarily lie in
the high-density environments or clusters typical of bulge-dominated
populations.Comment: submitted to Ap
Searching for non-Gaussianity in the VSA data
We have tested Very Small Array (VSA) observations of three regions of sky
for the presence of non-Gaussianity, using high-order cumulants, Minkowski
functionals, a wavelet-based test and a Bayesian joint power
spectrum/non-Gaussianity analysis. We find the data from two regions to be
consistent with Gaussianity. In the third region, we obtain a 96.7% detection
of non-Gaussianity using the wavelet test. We perform simulations to
characterise the tests, and conclude that this is consistent with expected
residual point source contamination. There is therefore no evidence that this
detection is of cosmological origin. Our simulations show that the tests would
be sensitive to any residual point sources above the data's source subtraction
level of 20 mJy. The tests are also sensitive to cosmic string networks at an
rms fluctuation level of (i.e. equivalent to the best-fit observed
value). They are not sensitive to string-induced fluctuations if an equal rms
of Gaussian CDM fluctuations is added, thereby reducing the fluctuations due to
the strings network to rms . We especially highlight the usefulness
of non-Gaussianity testing in eliminating systematic effects from our data.Comment: Minor corrections; accepted for publication to MNRA
A Two Micron All-Sky Survey View of the Sagittarius Dwarf Galaxy: II. Swope Telescope Spectroscopy of M Giant Stars in the Dynamically Cold Sagittarius Tidal Stream
We present moderate resolution (~6 km/s) spectroscopy of 284 M giant
candidates selected from the Two Micron All Sky Survey photometry. Radial
velocities (RVs) are presented for stars mainly in the south, with a number
having positions consistent with association to the trailing tidal tail of the
Sagittarius (Sgr) dwarf galaxy. The latter show a clear RV trend with orbital
longitude, as expected from models of the orbit and destruction of Sgr. A
minimum 8 kpc width of the trailing stream about the Sgr orbital midplane is
implied by verified RV members. The coldness of this stream (dispersion ~10
km/s) provides upper limits on the combined contributions of stream heating by
a lumpy Galactic halo and the intrinsic dispersion of released stars, which is
a function of the Sgr core mass. The Sgr trailing arm is consistent with a
Galactic halo containing one dominant, LMC-like lump, however some lumpier
halos are not ruled out. An upper limit to the total M/L of the Sgr core is 21
in solar units. A second structure that roughly mimics expectations for
wrapped, leading Sgr arm debris crosses the trailing arm in the Southern
Hemisphere; however, this may also be an unrelated tidal feature. Among the <13
kpc M giants toward the South Galactic Pole are some with large RVs that
identify them as halo stars, perhaps part of the Sgr leading arm near the Sun.
The positions and RVs of Southern Hemisphere M giants are compared with those
of southern globular clusters potentially stripped from the Sgr system and
support for association of Pal 2 and Pal 12 with Sgr debris is found. Our
discussion includes description of a masked-filtered cross-correlation
methodology that achieves better than 1/20 of a resolution element RVs in
moderate resolution spectra.Comment: 41 pages, 6 figures, Astronomical Journal, in press (submitted Nov.
24, 2003; tentatively scheduled for July 2004 issue
Estimating the bispectrum of the Very Small Array data
We estimate the bispectrum of the Very Small Array data from the compact and
extended configuration observations released in December 2002, and compare our
results to those obtained from Gaussian simulations. There is a slight excess
of large bispectrum values for two individual fields, but this does not appear
when the fields are combined. Given our expected level of residual point
sources, we do not expect these to be the source of the discrepancy. Using the
compact configuration data, we put an upper limit of 5400 on the value of f_NL,
the non-linear coupling parameter, at 95 per cent confidence. We test our
bispectrum estimator using non-Gaussian simulations with a known bispectrum,
and recover the input values.Comment: 17 pages, 16 figures, replaced with version accepted by MNRAS.
Primordial bispectrum recalculated and figure 11 change
Recommended from our members
Singular value decomposition and density estimation for filtering and analysis of gene expression
We present three algorithms for gene expression analysis. Algorithm 1, known as serial correlation test, is used for filtering out noisy gene expression profiles. Algorithm 2 and 3 project the gene expression profiles into 2-dimensional expression subspaces ident ifiecl by Singular Value Decomposition. Density estimates a e used to determine expression profiles that have a high correlation with the subspace and low levels of noise. High density regions in the projection, clusters of co-expressed genes, are identified. We illustrate the algorithms by application to the yeast cell-cycle data by Cho et.al. and comparison of the results
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