747 research outputs found
Regulating Pornography: A Public Dilemma
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73656/1/j.1460-2466.1990.tb02271.x.pd
Permutation-based Pathway Testing using the Super Learner Algorithm
Many diseases and other important phenotypic outcomes are the result of a combination of factors. For example, expression levels of genes have been used as input to various statistical methods for predicting phenotypic outcomes. One particular popular variety is the so-called gene set enrichment analysis (GSEA). This paper discusses an augmentation to an existing strategy to estimate the significance of an associations between a disease outcome and a predetermined combination of biological factors, based on a specific data adaptive regression method (the Super Learner, van der Laan et al., 2007). The procedure uses an aggressive search procedure, potentially resulting in final models that imply associations that would not be discovered using non data-adaptive procedures (e.g., multiple linear regression). A test statistic derived from the fit of the Super Learner model to the original data is compared to the permutation distribution of the same statistic, the latter being generated by permuting the outcome labels with respect to the covariate vectors. This comparison is the basis for rejection criteria for the null hypothesis of no association between a set of biological factors (e.g., gene expression levels) and binary phenotypic outcomes. We include simulations that compare the statistical power of the test derived from the Super Learner method with that of other methods for two different data generating distributions
The WHOI Moored Array Project 1963-1978 : data directory and bibliography
General information about mooring locations, durations and data
gathered by the Moored Array Project (also known as Buoy Group) between
late 1963 and 1978 is listed. Also included is a comprehensive list of
scientific and technical publications written by the Buoy Group staff.Prepared for the Office of Naval Research under Contract
N00014-76-C-0197; NR 083-400 and for the National Science
Foundation under Grant OCE 77-19403
The He abundance in the metal-deficient blue compact dwarf galaxies Tol 1214-277 and Tol 65
We present high-quality Keck telescope spectroscopic observations of the two
metal-deficient blue compact dwarf (BCD) galaxies Tol 1214-277 and Tol 65.
These data are used to derive the heavy-element and helium abundances. We find
that the oxygen abundances in Tol 1214-277 and Tol 65 are the same,
12+logO/H=7.54+/-0.01, or Zsun/24, despite the different ionization conditions
in these galaxies. The nitrogen-to-oxygen abundance ratio in both galaxies is
logN/O=-1.64+/-0.02 and lies in the narrow range found for the other most
metal-deficient BCDs. We use the five strongest HeI emission lines 3889, 4471,
5876, 6678 and 7065, to correct self-consistently their intensities for
collisional and fluorescent enhancement mechanisms and to derive the He
abundance. Underlying stellar absorption is found to be important for the HeI
4471 emission line in both galaxies, being larger in Tol 65. The weighted He
mass fractions in Tol 1214-277 and Tol 65 are respectively Y=0.2458+/-0.0039
and 0.2410+/-0.0050 when the three HeI emission lines, 4471, 5876 and 6678, are
used, and are, respectively, 0.2466+/-0.0043 and 0.2463+/-0.0057 when the HeI
4471 emission line is excluded. These values are in very good agreement with
recent measurements of the He mass fraction in others of the most
metal-deficient BCDs by Izotov and coworkers. We find that the combined effect
of the systematic uncertainties due to the underlying HeI stellar absorption
lines, ionization and temperature structure of the HII region and collisional
excitation of the hydrogen emission lines is likely small, not exceeding ~2%
(the error is 2sigma). Our results support the validity of the standard big
bang model of nucleosynthesis.Comment: 22 pages, 3 Postscript figures, accepted for publication in the
Astrophysical Journa
High-Resolution Keck Spectra of the Associated Absorption Lines in 3C 191
Associated absorption lines (AALs) are valuable probes of the gaseous
environments near quasars. Here we discuss high-resolution (6.7 km/s) spectra
of the AALs in the radio-loud quasar 3C 191 (redshift z=1.956). The measured
AALs have ionizations ranging from Mg I to N V, and multi-component profiles
that are blueshifted by ~400 to ~1400 km/s relative to the quasar's broad
emission lines. These data yield the following new results. 1) The density
based on Si II*/Si II lines is ~300 cm-3, implying a distance of ~28 kpc from
the quasar if the gas is photoionized. 2) The characteristic flow time is thus
\~3 x 10^7 yr. 3) Strong Mg I AALs identify neutral gas with very low
ionization parameter and high density. We estimate n_H > 5 x 10^4 cm-3 in this
region, compared to ~15 cm-3 where the N V lines form. 4) The total column
density is N_H < 4 x 10^18 cm-2 in the neutral gas and N_H ~ 2 x 10^20 cm-2 in
the moderately ionized regions. 5) The total mass in the AAL outflow is M ~ 2 x
10^9 Mo, assuming a global covering factor (as viewed from the quasar) of ~10%
>. 6) The absorbing gas only partially covers the background light source(s)
along our line(s) of sight, requiring absorption in small clouds or filaments
<0.01 pc across. The ratio N_H/n_H implies that the clouds have radial (line-
of-sight) thicknesses <0.2 pc. These properties might characterize a sub-class
of AALs that are physically related to quasars but form at large distances. We
propose a model for the absorber in which pockets of dense neutral gas are
surrounded by larger clouds of generally lower density and higher ionization.
This outflowing material might be leftover from a blowout associated with a
nuclear starburst, the onset of quasar activity or a past broad absorption line
(BAL) wind phase.Comment: 15 pages text plus 6 figures, in press with Ap
The afterglows of gamma-ray bursts
Gamma-ray burst astronomy has undergone a revolution in the last three years, spurred by the discovery of fading long-wavelength counterparts. We now know that at least the long duration GRBs lie at cosmological distances with estimated electromagnetic energy release of 10^51–10^53 erg, making these the brightest explosions in the Universe. In this article we review the current observational state, beginning with the statistics of X-ray, optical, and radio afterglow detections. We then discuss the insights these observations have given to the progenitor population, the energetics of the GRB events, and the physics of the afterglow emission. We focus particular attention on the evidence linking GRBs to the explosion of massive stars. Throughout, we identify remaining puzzles and uncertainties, and emphasize promising observational tools for addressing them. The imminent launch of HETE-2 and the increasingly sophisticated and coordinated ground-based and space-based observations have primed this field for fantastic growth
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