2,565 research outputs found
The Commercial Application of Missile/Space Technology, Parts 1 and 2
This report is concerned with the transfer of technology from missile and space programs to non-missile/space applications in the United States. It presents the findings of a University of Denver Research Institute study sponsored by a National Aeronautics and Space Administration (NASA) grant awarded in November 1961. Initial stimulation for the unsolicited proposal leading to this study came from a 1960 Brookings Institution report to NASA, Proposed Studies on the Implications of Peaceful Space Activities for Human Affairs
Faint Stars in the Ursa Minor Dwarf Spheroidal Galaxy: Implications for the Low-Mass Stellar Initial Mass Function at High Redshift
The stellar initial mass function at high redshift is an important defining
property of the first stellar systems to form and may also play a role in
various dark matter problems. We here determine the faint stellar luminosity
function in an apparently dark-matter-dominated external galaxy in which the
stars formed at high redshift. The Ursa Minor dwarf spheroidal galaxy is a
system with a particularly simple stellar population - all of the stars being
old and metal-poor - similar to that of a classical halo globular cluster. A
direct comparison of the faint luminosity functions of the UMi Sph and of
similar metallicity, old globular clusters is equivalent to a comparison of the
initial mass functions and is presented here, based on deep HST WFPC2 and STIS
imaging data. We find that these luminosity functions are indistinguishable,
down to a luminosity corresponding to 0.3 solar masses. Our results show that
the low-mass stellar IMF for stars that formed at very high redshift is
apparently invariant across environments as diverse as those of an extremely
low-surface-brightness, dark-matter-dominated dwarf galaxy and a
dark-matter-free, high-density globular cluster within the Milky Way.Comment: Accepted by New Astronomy. 64 pages, including 9 embedded postscript
tables and 20 embedded postscript figures, plus 14 separate jpeg figures.
Postscript versions of the jpeg figures and a complete version of the paper
with all figures embedded can be found at http://tarkus.pha.jhu.edu/~mlh
Varying coefficient model for modeling diffusion tensors along white matter tracts
Diffusion tensor imaging provides important information on tissue structure
and orientation of fiber tracts in brain white matter in vivo. It results in
diffusion tensors, which are symmetric positive definite (SPD)
matrices, along fiber bundles. This paper develops a functional data analysis
framework to model diffusion tensors along fiber tracts as functional data in a
Riemannian manifold with a set of covariates of interest, such as age and
gender. We propose a statistical model with varying coefficient functions to
characterize the dynamic association between functional SPD matrix-valued
responses and covariates. We calculate weighted least squares estimators of the
varying coefficient functions for the log-Euclidean metric in the space of SPD
matrices. We also develop a global test statistic to test specific hypotheses
about these coefficient functions and construct their simultaneous confidence
bands. Simulated data are further used to examine the finite sample performance
of the estimated varying coefficient functions. We apply our model to study
potential gender differences and find a statistically significant aspect of the
development of diffusion tensors along the right internal capsule tract in a
clinical study of neurodevelopment.Comment: Published in at http://dx.doi.org/10.1214/12-AOAS574 the Annals of
Applied Statistics (http://www.imstat.org/aoas/) by the Institute of
Mathematical Statistics (http://www.imstat.org
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An ABC Transporter Is Required for Secretion of Peptide Sex Pheromones in Enterococcus faecalis
ABSTRACT Enterococci are leading causes of hospital-acquired infection in the United States and continue to develop resistances to new antibiotics. Many Enterococcus faecalis isolates harbor pheromone-responsive plasmids that mediate horizontal transfer of even large blocks of chromosomal genes, resulting in hospital-adapted strains over a quarter of whose genomes consist of mobile elements. Pheromones to which the donor cells respond derive from lipoprotein signal peptides. Using a novel bacterial killing assay dependent on the presence of sex pheromones, we screened a transposon mutant library for functions that relate to the production and/or activity of the effector pheromone. Here we describe a previously uncharacterized, but well-conserved, ABC transporter that contributes to pheromone production. Using three distinct pheromone-dependent mating systems, we show that mutants defective in expressing this transporter display a 5- to 6-order-of-magnitude reduction in conjugation efficiency. In addition, we demonstrate that the ABC transporter mutant displays an altered biofilm architecture, with a significant reduction in biofilm biomass compared to that of its isogenic parent, suggesting that pheromone activity also influences biofilm development. The conservation of this peptide transporter across the Firmicutes suggests that it may also play an important role in cell-cell communication in other species within this important phylum
Searching for Machos (and other Dark Matter Candidates) in a Simulated Galaxy
We conduct gravitational microlensing experiments in a galaxy taken from a
cosmological N-body simulation. Hypothetical observers measure the optical
depth and event rate toward hypothetical LMCs and compare their results with
model predictions. Since we control the accuracy and sophistication of the
model, we can determine how good it has to be for statistical errors to
dominate over systematic ones. Several thousand independent microlensing
experiments are performed. When the ``best-fit'' triaxial model for the mass
distribution of the halo is used, the agreement between the measured and
predicted optical depths is quite good: by and large the discrepancies are
consistent with statistical fluctuations. If, on the other hand, a spherical
model is used, systematic errors dominate. Even with our ``best-fit'' model,
there are a few rare experiments where the deviation between the measured and
predicted optical depths cannot be understood in terms of statistical
fluctuations. In these experiments there is typically a clump of particles
crossing the line of sight to the hypothetical LMC. These clumps can be either
gravitationally bound systems or transient phenomena in a galaxy that is still
undergoing phase mixing. Substructure of this type, if present in the Galactic
distribution of Machos, can lead to large systematic errors in the analysis of
microlensing experiments. We also describe how hypothetical WIMP and axion
detection experiments might be conducted in a simulated N-body galaxy.Comment: 18 pages of text (LaTeX, AASTeX) with 12 figures. submitted to the
Astrophysical Journa
The American Academy of Social Work and Social Welfare: History and Grand Challenges
Conceptualized by social work deans and actualized with the support of major social work organizations, the American Academy
of Social Work and Social Welfare was established in 2009. This article describes the historical context and creation of the
Academy, whose objectives include recognizing outstanding social work scholars and practitioners; informing social policy by
serving as a signal scientific source of information for the social work profession and agencies seeking information; promoting the
examination of social policy and the application of research to the design and development of more effective public policies, social
welfare programs, and social work practice; and celebrating excellence in research, education, and practice. The Academy's 72
members have been selected using the methods of the National Academy of Science. The Academy's first substantive effort is the
Grand Challenges of Social Work Initiative, designed to help transform social work science, education, and practice around
visionary and achievable challenges
Estimating the Magnitude of Illicit Cigarette Trade in Bangladesh:Protocol for a Mixed-Methods Study
The illicit tobacco trade undermines the effectiveness of tobacco tax policies; increases the availability of cheap cigarettes, which, in turn, increases tobacco use and tobacco related deaths; and causes huge revenue losses to governments. There is limited evidence on the extent of illicit tobacco trade particularly cigarettes in Bangladesh. The paper presents the protocol for a mixed-methods study to estimate the extent of illicit cigarette trade in Bangladesh. The study will address three research questions: (a) What proportion of cigarettes sold as retail are illicit? (b) What are the common types of tax avoidance and tax evasion? (c) Can pack examination from the trash recycle market be considered as a new method to assess illicit trade in comparison to that from retailers and streets? Following an observational research method, data will be collected utilizing empty cigarette packs from three sources: (a) retailers; (b) streets; and (c) trash recycle market. In addition, a structured questionnaire will be used to collect information from retailers selling cigarettes. We will select post codes as Primary Sampling Unit (PSU) using a multi-stage random sampling technique. We will randomly select eight districts from eight divisions stratified by those with land border and non-land border; and within each district, we will randomly select ten postcodes, stratified by rural (five) and urban (five) PSU to ensure maximum geographical variation, leading to a total of eighty post codes from eight districts. The analysis will report the proportions of packs that do not comply with the study definition of illicit. Independent estimates of illicit tobacco are rare in low-and middle-income countries such as Bangladesh. Findings will inform efforts by revenue authorities and others to address the effects of illicit trade and counter tobacco industry claims
Exploring the Local Milky Way: M Dwarfs as Tracers of Galactic Populations
We have assembled a spectroscopic sample of low-mass dwarfs observed as part
of the Sloan Digital Sky Survey along one Galactic sightline, designed to
investigate the observable properties of the thin and thick disks. This sample
of ~7400 K and M stars also has measured ugriz photometry, proper motions, and
radial velocities. We have computed UVW space motion distributions, and
investigate their structure with respect to vertical distance from the Galactic
Plane. We place constraints on the velocity dispersions of the thin and thick
disks, using two-component Gaussian fits. We also compare these kinematic
distributions to a leading Galactic model. Finally, we investigate other
possible observable differences between the thin and thick disks, such as
color, active fraction and metallicity.Comment: 11 pages, 12 figures, Accepted by A
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