3,654 research outputs found
Warsaw, Town of and International Brotherhood of Teamsters Local 264
In the Matter of Impasse in Negotiations between TOWN OF WARSAW and INTERNATIONAL BROTHERHOOD OF TEAMSTERS LOCAL 264 (WARSAW HIGHWAY DEPARTMENT). PERB Case M2006-282. Edward A. Schmidt, Fact Finder
TWO NEW SHORT-PERIOD CEPHEIDS
The General Catalogue of Variable Stars gives periods of slightly less than three-quarters of a day for the stars NO Cas and CN Tau. However, new photometry demonstrates that their periods are actually 2.6 and 1.8 days, respectively, and they are thus classical Cepheids. Fourier decompositions of their light curves are performed, and they are found to be members of a class of Cepheids with periods less than three days which may be related to the s-Cepheids. These two stars represent the shortest and longest known members of this class and thus are very useful in defining its properties in the Fourier diagrams
Reconciliation of the Surface Brightness Fluctuations and Type Ia Supernovae Distance Scales
We present Hubble Space Telescope measurements of surface brightness
fluctuations (SBF) distances to early-type galaxies that have hosted Type Ia
supernovae (SNIa). The agreement in the relative SBF and SNIa multicolor light
curve shape and delta-m_15 distances is excellent. There is no systematic scale
error with distance, and previous work has shown that SBF and SNIa give
consistent ties to the Hubble flow. However, we confirm a systematic offset of
about 0.25 mag in the distance zero points of the two methods, and we trace
this offset to their respective Cepheid calibrations. SBF has in the past been
calibrated with Cepheid distances from the H_0 Key Project team, while SNIa
have been calibrated with Cepheid distances from the team composed of Sandage,
Saha, and collaborators. When the two methods are calibrated in a consistent
way, their distances are in superb agreement. Until the conflict over the
``long'' and ``short'' extragalactic Cepheid distances among many galaxies is
resolved, we cannot definitively constrain the Hubble constant to better than
about 10%, even leaving aside the additional uncertainty in the distance to the
Large Magellanic Cloud, common to both Cepheid scales. However, recent
theoretical SBF predictions from stellar population models favor the Key
Project Cepheid scale, while the theoretical SNIa calibration lies between the
long and short scales. In addition, while the current SBF distance to M31/M32
is in good agreement with the RR Lyrae and red giant branch distances,
calibrating SBF with the longer Cepheid scale would introduce a 0.3 mag offset
with respect to the RR Lyrae scale.Comment: 13 pages, 3 PostScript figures, LaTeX with AASTeX 5.02 and natbib.sty
v7.0 (included). Accepted for publication in The Astrophysical Journa
Experimental study of ultracold neutron production in pressurized superfluid helium
We have investigated experimentally the pressure dependence of the production
of ultracold neutrons (UCN) in superfluid helium in the range from saturated
vapor pressure to 20bar. A neutron velocity selector allowed the separation of
underlying single-phonon and multiphonon pro- cesses by varying the incident
cold neutron (CN) wavelength in the range from 3.5 to 10{\AA}. The predicted
pressure dependence of UCN production derived from inelastic neutron scattering
data was confirmed for the single-phonon excitation. For multiphonon based UCN
production we found no significant dependence on pressure whereas calculations
from inelastic neutron scattering data predict an increase of 43(6)% at 20bar
relative to saturated vapor pressure. From our data we conclude that applying
pressure to superfluid helium does not increase the overall UCN production rate
at a typical CN guide.Comment: 18 pages, 8 figures Version accepted for publication in PR
PromoterPlot: a graphical display of promoter similarities by pattern recognition
PromoterPlot (http://promoterplot.fmi.ch) is a web-based tool for simplifying the display and processing of transcription factor searches using either the commercial or free TransFac distributions. The input sequence is a TransFac search (public version) or FASTA/Affymetrix IDs (local install). It uses an intuitive pattern recognition algorithm for finding similarities between groups of promoters by dividing transcription factor predictions into conserved triplet models. To minimize the number of false-positive models, it can optionally exclude factors that are known to be unexpressed or inactive in the cells being studied based on microarray or proteomic expression data. The program will also estimate the likelihood of finding a pattern by chance based on the frequency observed in a control set of mammalian promoters we obtained from Genomatix. The results are stored as an interactive SVG web page on our serve
PromoterPlot: a graphical display of promoter similarities by pattern recognition
PromoterPlot () is a web-based tool for simplifying the display and processing of transcription factor searches using either the commercial or free TransFac distributions. The input sequence is a TransFac search (public version) or FASTA/Affymetrix IDs (local install). It uses an intuitive pattern recognition algorithm for finding similarities between groups of promoters by dividing transcription factor predictions into conserved triplet models. To minimize the number of false-positive models, it can optionally exclude factors that are known to be unexpressed or inactive in the cells being studied based on microarray or proteomic expression data. The program will also estimate the likelihood of finding a pattern by chance based on the frequency observed in a control set of mammalian promoters we obtained from Genomatix. The results are stored as an interactive SVG web page on our server
M32+/-1
WFPC-2 images are used to study the central structure of M31, M32, and M33.
The dimmer peak, P2, of the M31 double nucleus is centered on the bulge to
0.1", implying that it is the dynamical center of M31. P2 contains a compact
source discovered by King et al. (1995) at 1700 A. This source is resolved,
with r_{1/2} approx0.2 pc. It dominates the nucleus at 3000 A, and is
consistent with late B-early A stars. This probable cluster may consist of
young stars and be an older version of the cluster of hot stars at the center
of the Milky Way, or it may consist of heavier stars built up from collisions
in a possible cold disk of stars orbiting P2. In M32, the central cusp rises
into the HST limit with gamma approx0.5, and the central density
rho_0>10^7M_sol pc^-3. The V-I and U-V color profiles are flat, and there is no
sign of an inner disk, dust, or any other structure. This total lack of
features seems at variance with a nominal stellar collision time of 2 X 10^10
yr, which implies that a significant fraction of the light in the central pixel
should come from blue stragglers. InM33, the nucleus has an extremely steep
gamma=1.49 power-law profile for 0.05"<r<0.2" that becomes shallower as the HST
resolution limit is approached. The profile for r<0.04" has either a gamma
approx 0.8 cusp or a small core with r_c ~<0.13 pc. The central density is
rho_0 > 2 10^6M_sol pc^-3, and the implied relaxation time is only ~3 X 10^6
yr, indicating that the nucleus is highly relaxed. The accompanying short
collision time of 7 X 10^9 yr predicts a central blue straggler component
quantitatively consistent with the strong V-I and B-R color gradients seen with
HST and from the ground.Comment: 44 pages, 22 figures (7 as separate JPEG images), submitted to The
Astronomical Journal. Full postscript image available at
http://www.noao.edu/noao/staff/lauer/lauer_paper
"Hidden" Seyfert 2 Galaxies and the X-ray Background
Obscured active galactic nuclei, which are classified optically as type 2
(narrow-line) Seyfert galaxies in the local universe, are by far the most
promising candidates for the origin of the hard (2-10 keV) X-ray background
radiation. However, optical follow-up observations of faint X-ray sources in
deep Chandra images have revealed surprising numbers of apparently normal
galaxies at modest redshift. Such objects represent ~40-60% of the sources
classified in deep Chandra surveys, raising the possibility that the X-ray
galaxy population has evolved with cosmic time. Alternatively, most of the
faint X-ray galaxies in question are so distant that their angular diameters
are comparable to the slit widths used in ground-based spectroscopic
observations; thus, their nuclear spectral features may be overwhelmed
(``hidden'') by host-galaxy light. To test this hypothesis, we have obtained
integrated spectra of a sample of nearby, well-studied Seyfert 2 galaxies. The
data, which accurately simulate observations of distant Chandra sources,
demonstrate convincingly that the defining spectral signatures of Seyfert 2s
can be hidden by light from their host galaxies. In fact, 60% of the observed
objects would not be classified as Seyfert 2s on the basis of their integrated
spectra, similar to the fraction of faint X-ray sources identified with
``normal'' galaxies. Thus, the numbers of narrow-line active galaxies in deep
Chandra surveys (and perhaps all ground-based spectroscopic surveys of distant
galaxies) are likely to have been underestimated.Comment: 9 pages, including 1 figure. To appear in ApJ Letter
A Composite Seyfert 2 X-ray Spectrum: Implications for the Origin of the Cosmic X-ray Background
We present a composite 1-10 keV Seyfert 2 X-ray spectrum, derived from ASCA
observations of a distance-limited sample of nearby galaxies. All 29 observed
objects were detected. Above ~3 keV, the composite spectrum is inverted,
confirming that Seyfert 2 galaxies as a class have the spectral properties
necessary to explain the flat shape of the cosmic X-ray background spectrum.
Integrating the composite spectrum over redshift, we find that the total
emission from Seyfert 2 galaxies, combined with the expected contribution from
unabsorbed type 1 objects, provides an excellent match to the spectrum and
intensity of the hard X-ray background. The principal uncertainty in this
procedure is the cosmic evolution of the Seyfert 2 X-ray luminosity function.
Separate composite spectra for objects in our sample with and without polarized
broad optical emission lines are also presented.Comment: 11 pages (AASTeX), including 3 figures. Accepted for publication in
ApJ Letter
Ultra-Slow Light and Enhanced Nonlinear Optical Effects in a Coherently Driven Hot Atomic Gas
We report the observation of small group velocities of order 90 meters per
second, and large group delays of greater than 0.26 ms, in an optically dense
hot rubidium gas (~360 K). Media of this kind yield strong nonlinear
interactions between very weak optical fields, and very sharp spectral
features. The result is in agreement with previous studies on nonlinear
spectroscopy of dense coherent media
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