1,404 research outputs found
Childhood Conditions that Predict Survival to Advanced Ages Among African Americans
This paper investigates the social and economic circumstances of childhood that predict the probability of survival to age 85. It uses a unique study design in which survivors are linked to their records in U.S. Censuses of 1900 and 1910. A control group of age and race-matched children is drawn from Public Use Samples for these censuses. It concludes that the factors most predictive of survival are farm background, having literate parents, and living in a two-parent household. Results support the interpretation that death risks are positively correlated over the life cycle
An Archaeological Survey of a Pipeline Right-of-way along Loop 1604 from IH-37 to the San Antonio River, Southeast Bexar County, Texas
In February 1997, the Center for Archaeological Research (CAR) of The University of Texas at San Antonio was contracted by the San Antonio Water Systems (SAWS) to conduct an intensive archaeological survey and geomorphological study along a proposed 5 .5-km water main right-of-way, from the junction of ill -3 7 and Loop 1604 to the San Antonio River in southeast Bexar County. Upon completion of a 1 DO-percent pedestrian survey, 10 backhoe trenches, and 152 shovel tests, CAR concluded that no significant cultural remains would be impacted by excavations for the proposed water main, and recommends that no further archaeological work is required prior to construction.
Eulerian simulation of the fluid dynamics of helicopter brownout
A computational model is presented that can be used to simulate the development of the dust cloud
that can be entrained into the air when a helicopter is operated close to the ground in desert or dusty
conditions. The physics of this problem, and the associated pathological condition known as âbrownoutâ
where the pilot loses situational awareness as a result of his vision being occluded by dust suspended in the
flow around the helicopter, is acknowledged to be very complex. The approach advocated here involves
an approximation to the full dynamics of the coupled particulate-air system. Away from the ground, the
model assumes that the suspended particles remain in near equilibrium under the action of aerodynamic
forces. Close to the ground, this model is replaced by an algebraic sublayer model for the saltation and
entrainment process. The origin of the model in the statistical mechanics of a distribution of particles
governed by aerodynamic forces allows the validity of the method to be evaluated in context by comparing
the physical properties of the suspended particulates to the local properties of the flow field surrounding
the helicopter. The model applies in the Eulerian frame of reference of most conventional Computational
Fluid Dynamics codes and has been coupled with Brownâs Vorticity Transport Model. Verification of the
predictions of the coupled model against experimental data for particulate entrainment and transport in
the flow around a model rotor are encouraging. An application of the coupled model to analyzing the
differences in the geometry and extent of the dust clouds that are produced by single main rotor and
tandem-rotor configurations as they decelerate to land has shown that the location of the ground vortex
and the size of any regions of recirculatory flow, should they exist, play a primary role in governing the
extent of the dust cloud that is created by the helicopter
Generic Airspace Research Phase 5 Report
Human-in-the-loop testing was completed to assess the subjective preferences, usage, and operational benefits of Integrated and Separated Controller Information Tools (CITs) in support of Generic Airspace Research. Participants controlled traffic in in a busy, high altitude sector with the aid of the CITs. When the participants were asked which CIT that they preferred to use, they overwhelmingly chose the integrated version of the CIT. The primary reason for this seemed to be that it allowed participants to remain focused on the traffic situation, whereas the Standalone CIT required them to focus their attention for short periods away from the radar presentation. In contrast to their preference, there were little or no differences in the CIT usage and the operational differences. There were similar numbers of losses of separation and participants accessed each CIT equally. Although the information accessed was the similar for the two conditions, participants actively turned off the data on the Integrated CIT, presumably to reduce the clutter on the radar scope. Further work is needed to isolate which information can and should be available to controllers in the Integrated vs. Standalone format
The propagation of uncertainties in stellar population synthesis modeling I: The relevance of uncertain aspects of stellar evolution and the IMF to the derived physical properties of galaxies
The stellar masses, mean ages, metallicities, and star formation histories of
galaxies are now commonly estimated via stellar population synthesis (SPS)
techniques. SPS relies on stellar evolution calculations from the main sequence
to stellar death, stellar spectral libraries, phenomenological dust models, and
stellar initial mass functions (IMFs). The present work is the first in a
series that explores the impact of uncertainties in key phases of stellar
evolution and the IMF on the derived physical properties of galaxies and the
expected luminosity evolution for a passively evolving set of stars. A
Monte-Carlo Markov-Chain approach is taken to fit near-UV through near-IR
photometry of a representative sample of low- and high-redshift galaxies with
this new SPS model. Significant results include the following: 1) including
uncertainties in stellar evolution, stellar masses at z~0 carry errors of ~0.3
dex at 95% CL with little dependence on luminosity or color, while at z~2, the
masses of bright red galaxies are uncertain at the ~0.6 dex level; 2) either
current stellar evolution models, current observational stellar libraries, or
both, do not adequately characterize the metallicity-dependence of the
thermally-pulsating asymptotic giant branch phase; 3) conservative estimates on
the uncertainty of the slope of the IMF in the solar neighborhood imply that
luminosity evolution per unit redshift is uncertain at the ~0.4 mag level in
the K-band, which is a substantial source of uncertainty for interpreting the
evolution of galaxy populations across time; 4) The more plausible assumption
of a distribution of stellar metallicities, rather than a fixed value as is
usually assumed, can have significant effects on the interpretation of colors
blueward of the V-band. (ABRIDGED)Comment: 21 pages, 17 figures, ApJ in pres
The propagation of uncertainties in stellar population synthesis modeling III: model calibration, comparison, and evaluation
Stellar population synthesis (SPS) provides the link between the stellar and
dust content of galaxies and their observed spectral energy distributions. In
the present work we perform a comprehensive calibration of our own flexible SPS
(FSPS) model against a suite of data. Several public SPS models are
intercompared, including the models of Bruzual & Charlot (BC03), Maraston (M05)
and FSPS. The relative strengths and weaknesses of these models are evaluated,
with the following conclusions: 1) The FSPS and BC03 models compare favorably
with MC data at all ages, whereas M05 colors are too red and the age-dependence
is incorrect; 2) All models yield similar optical and near-IR colors for old
metal-poor systems, and yet they all provide poor fits to the integrated J-K
and V-K colors of both MW and M31 star clusters; 4) All models predict ugr
colors too red, D4000 strengths too strong and Hdelta strengths too weak
compared to massive red sequence galaxies, under the assumption that such
galaxies are composed solely of old metal-rich stars; 5) FSPS and, to a lesser
extent, BC03 can reproduce the optical and near-IR colors of post-starburst
galaxies, while M05 cannot. Reasons for these discrepancies are explored. The
failure at predicting the ugr colors, D4000, and Hdelta strengths can be
explained by some combination of a minority population of metal-poor stars,
young stars, blue straggler and/or blue horizontal branch stars, but not by
appealing to inadequacies in either theoretical stellar atmospheres or
canonical evolutionary phases (e.g., the main sequence turn-off). We emphasize
that due to a lack of calibrating star cluster data in regions of the
metallicity-age plane relevant for galaxies, all of these models continue to
suffer from serious uncertainties that are difficult to quantify. (ABRIDGED)Comment: 26 pages, 16 figures, submitted to ApJ. The FSPS code can be
downloaded at http://www.astro.princeton.edu/~cconroy/SPS
Field Blue Stragglers and Related Mass Transfer Issues
This chapter contains my impressions and perspectives about the current state
of knowledge about field blue stragglers (FBS) stars, drawn from an extensive
literature that I searched. I conclude my review of issues that attend FBS and
mass transfer, by a brief enumeration of a few mildly disquieting observational
facts.Comment: Chapter 4, in Ecology of Blue Straggler Stars, H.M.J. Boffin, G.
Carraro & G. Beccari (Eds), Astrophysics and Space Science Library, Springe
- âŠ