7,053 research outputs found
The Damping Tail of CMB Anisotropies
By decomposing the damping tail of CMB anisotropies into a series of transfer
functions representing individual physical effects, we provide ingredients that
will aid in the reconstruction of the cosmological model from small-scale CMB
anisotropy data. We accurately calibrate the model-independent effects of
diffusion and reionization damping which provide potentially the most robust
information on the background cosmology. Removing these effects, we uncover
model-dependent processes such as the acoustic peak modulation and
gravitational enhancement that can help distinguish between alternate models of
structure formation and provide windows into the evolution of fluctuations at
various stages in their growth.Comment: 24pgs, aaspp4, 10 figs. included; supporting material (e.g. color
figures) at http://www.sns.ias.edu/~whu/pub.htm
Guidance of sentinel lymph node biopsy decisions in patients with T1-T2 melanoma using gene expression profiling.
AIM: Can gene expression profiling be used to identify patients with T1-T2 melanoma at low risk for sentinel lymph node (SLN) positivity?
PATIENTS & METHODS: Bioinformatics modeling determined a population in which a 31-gene expression profile test predicted \u3c5% SLN positivity. Multicenter, prospectively-tested (n = 1421) and retrospective (n = 690) cohorts were used for validation and outcomes, respectively.
RESULTS: Patients 55-64 years and ≥65 years with a class 1A (low-risk) profile had SLN positivity rates of 4.9% and 1.6%. Class 2B (high-risk) patients had SLN positivity rates of 30.8% and 11.9%. Melanoma-specific survival was 99.3% for patients ≥55 years with class 1A, T1-T2 tumors and 55.0% for class 2B, SLN-positive, T1-T2 tumors.
CONCLUSION: The 31-gene expression profile test identifies patients who could potentially avoid SLN biopsy
Observationally Determining the Properties of Dark Matter
Determining the properties of the dark components of the universe remains one
of the outstanding challenges in cosmology. We explore how upcoming CMB
anisotropy measurements, galaxy power spectrum data, and supernova (SN)
distance measurements can observationally constrain their gravitational
properties with minimal assumptions on the theoretical side. SN observations
currently suggest the existence of dark matter with an exotic equation of state
p/rho < -1/3 that accelerates the expansion of the universe. When combined with
CMB anisotropy measurements, SN or galaxy survey data can in principle
determine the equation of state and density of this component separately,
regardless of their value, as long as the universe is spatially flat. Combining
these pairs creates a sharp consistency check. If p/rho > -1/2, then the
clustering behavior (sound speed) of the dark component can be determined so as
to test the scalar-field ``quintessence'' hypothesis. If the exotic matter
turns out instead to be simply a cosmological constant (p/rho = -1), the
combination of CMB and galaxy survey data should provide a significant
detection of the remaining dark matter, the neutrino background radiation
(NBR). The gross effect of its density or temperature on the expansion rate is
ill-constrained as it is can be mimicked by a change in the matter density.
However, anisotropies of the NBR break this degeneracy and should be detectable
by upcoming experiments.Comment: 16 pages, 10 figures, RevTeX, submitted to PR
CMB Anisotropies: Total Angular Momentum Method
A total angular momentum representation simplifies the radiation transport
problem for temperature and polarization anisotropy in the CMB. Scattering
terms couple only the quadrupole moments of the distributions and each moment
corresponds directly to the observable angular pattern on the sky. We develop
and employ these techniques to study the general properties of anisotropy
generation from scalar, vector and tensor perturbations to the metric and the
matter, both in the cosmological fluids and from any seed perturbations (e.g.
defects) that may be present. The simpler, more transparent form and derivation
of the Boltzmann equations brings out the geometric and model-independent
aspects of temperature and polarization anisotropy formation. Large angle
scalar polarization provides a robust means to distinguish between isocurvature
and adiabatic models for structure formation in principle. Vector modes have
the unique property that the CMB polarization is dominated by magnetic type
parity at small angles (a factor of 6 in power compared with 0 for the scalars
and 8/13 for the tensors) and hence potentially distinguishable independent of
the model for the seed. The tensor modes produce a different sign from the
scalars and vectors for the temperature-polarization correlations at large
angles. We explore conditions under which one perturbation type may dominate
over the others including a detailed treatment of the photon-baryon fluid
before recombination.Comment: 32 pg., 10 figs., RevTeX, minor changes reflect published version,
minor typos corrected, also available at http://www.sns.ias.edu/~wh
Unusual raptor nests around the world
From surveys in many countries, we report using unusual nesting materials (e.g., paper money, rags, metal, antlers, and large bones) and unusual nesting situations. For example, we documented nests of Steppe Eagles [Aquila nipalensis] and Upland Buzzards [Buteo hemilasius] on the ground beside well-traveled roads, Saker Falcon [Falco cherrug] eyries in attics and a cistern, and Osprey [Pandian haliaetus] nests on the masts of boats and on a suspended automobile. Other records include a Golden Eagle [A. chrysaelos] nest 7.0 m in height, believed to be the tallest nest ever described, and, for the same species, we report nesting in rudimentary, nests. Some nest sites are within a Few meters of known predators or competitors. These unusual observations may be important in revealing the plasticity of a species' behavioral repertoire
UV/Optical Nuclear Activity in the gE Galaxy NGC 1399
Using HST/STIS, we have detected far-ultraviolet nuclear activity in the
giant elliptical galaxy NGC 1399, the central and brightest galaxy in the
Fornax I cluster. The source reached a maximum observed far-UV luminosity of
\~1.2 x 10e39 ergs/s in January 1999. It was detectable in earlier HST archival
images in 1996 (B band) but not in 1991 (V band) or 1993 (UV). It faded by a
factor of ~4x by mid-2000. The source is almost certainly associated with the
low luminosity AGN responsible for the radio emission in NGC 1399. The
properties of the outburst are remarkably similar to the UV-bright nuclear
transient discovered earlier in NGC 4552 by Renzini et al. (1995). The source
is much fainter than expected from its Bondi accretion rate (estimated from
Chandra high resolution X-ray images), even in the context of "radiatively
inefficient accretion flow" models, and its variability also appears
inconsistent with such models. High spatial resolution UV monitoring is a
valuable means to study activity in nearby LLAGNs.Comment: 18 pages, 2 figures, 1 table; accepted for publication in Ap
Distinguishing Causal Seeds from Inflation
Causal seed models, such as cosmological defects, generically predict a
distinctly different structure to the CMB power spectrum than inflation, due to
the behavior of the perturbations outside the horizon. We provide a general
analysis of their causal generation from isocurvature initial conditions by
analyzing the role of stress perturbations and conservation laws in the causal
evolution. Causal stress perturbations tend to generate an isocurvature pattern
of peak heights in the CMB spectrum and shift the first compression, i.e.~main
peak, to smaller angular scales than in the inflationary case, unless the
pressure and anisotropic stress fluctuations balance in such a way as to
reverse the sense of gravitational interactions while also maintaining constant
gravitational potentials. Aside from this case, these causal seed models can be
cleanly distinguished from inflation by CMB experiments currently underway.Comment: 22pgs, revtex, 5 figs.; revision clarifies discussion of
astro-ph/9604172, includes new supporting sections on assumptions and
anisotropic stresses, and discusses astro-ph/9607109; main conclusions
unchanged; supporting material at http://www.sns.ias.edu/~wh
A measurement of the W boson mass using large rapidity electrons
We present a measurement of the W boson mass using data collected by the D0
experiment at the Fermilab Tevatron during 1994--1995. We identify W bosons by
their decays to e-nu final states where the electron is detected in a forward
calorimeter. We extract the W boson mass, Mw, by fitting the transverse mass
and transverse electron and neutrino momentum spectra from a sample of 11,089 W
-> e nu decay candidates. We use a sample of 1,687 dielectron events, mostly
due to Z -> ee decays, to constrain our model of the detector response. Using
the forward calorimeter data, we measure Mw = 80.691 +- 0.227 GeV. Combining
the forward calorimeter measurements with our previously published central
calorimeter results, we obtain Mw = 80.482 +- 0.091 GeV
Improved W boson mass measurement with the D0 detector
We have measured the W boson mass using the D0 detector and a data sample of
82 pb^-1 from the Tevatron collider. This measurement used W -> e nu decays,
where the electron is close to a boundary of a central electromagnetic
calorimeter module. Such 'edge' electrons have not been used in any previous D0
analysis, and represent a 14% increase in the W boson sample size. For these
electrons, new response and resolution parameters are determined, and revised
backgrounds and underlying event energy flow measurements are made. When the
current measurement is combined with previous D0 W boson mass measurements, we
obtain M_W = 80.483 +/- 0.084 GeV. The 8% improvement from the previous D0
measurement is primarily due to the improved determination of the response
parameters for non-edge electrons using the sample of Z bosons with non-edge
and edge electrons.Comment: submitted to Phys. Rev. D; 20 pages, 18 figures, 9 table
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