102,741 research outputs found
Effects of pregnancy, childbirth, and motherhood on high school dropout
This paper uses data from the National Longitudinal Survey of Youth to explore the effect of fertility on high school dropout, and differences in that effect by age at first birth. Fertility is conceptualized as a series of states: pregnancy, childbirth, postpartum, and motherhood. Pregnant students and mothers are much more likely to drop out than students who are not pregnant or mothers. Models including a wide variety of controls for social background, ability, schooling factors, and adolescent behaviors show that the net effects of pregnancy and motherhood on dropout are substantively and statistically significant. The effects of fertility on dropout are strongest for the youngest students.
Borel singularities at small x
D.I.S. at small Bjorken is considered within the dipole cascade
formalism. The running coupling in impact parameter space is introduced in
order to parametrize effects that arise from emission of large size dipoles.
This results in a new evolution equation for the dipole cascade. Strong
coupling effects are analyzed after transforming the evolution equation in
Borel () space. The Borel singularities of the solution are discussed first
for the universal part of the dipole cascade and then for the specific process
of D.I.S. at small . In the latter case the leading infrared renormalon is
at indicating the presence of power corrections for the
small- structure functions.Comment: 5 pages, Latex (Talk presented at DIS'97, Chicago, IL
Development of strain tolerant thermal barrier coating systems, tasks 1 - 3
Insulating ceramic thermal barrier coatings can reduce gas turbine airfoil metal temperatures as much as 170 C (about 300 F), providing fuel efficiency improvements greater than one percent and durability improvements of 2 to 3X. The objective was to increase the spalling resistance of zirconia based ceramic turbine coatings. To accomplish this, two baseline and 30 candidate duplex (layered MCrAlY/zirconia based ceramic) coatings were iteratively evaluated microstructurally and in four series of laboratory burner rig tests. This led to the selection of two candidate optimized 0.25 mm (0.010 inch) thick plasma sprayed partially stabilized zirconia ceramics containing six weight percent yttria and applied with two different sets of process parameters over a 0.13 mm (0.005 inch) thick low pressure chamber sprayed MCrAlY bond coat. Both of these coatings demonstrated at least 3X laboratory cyclic spalling life improvement over the baseline systems, as well as cyclic oxidation life equivalent to 15,000 commercial engine flight hours
Variable conductance heat pipe technology
Research and development programs in variable conductance heat pipe technology were conducted. The treatment has been comprehensive, involving theoretical and/or experimental studies in hydrostatics, hydrodynamics, heat transfer into and out of the pipe, fluid selection, and materials compatibility, in addition to the principal subject of variable conductance control techniques. Efforts were not limited to analytical work and laboratory experimentation, but extended to the development, fabrication and test of spacecraft hardware, culminating in the successful flight of the Ames Heat Pipe Experiment on the OAO-C spacecraft
The Energy Transfer Process in Planetary Flybys
We illustrate the energy transfer during planetary flybys as a function of
time using a number of flight mission examples. The energy transfer process is
rather more complicated than a monotonic increase (or decrease) of energy with
time. It exhibits temporary maxima and minima with time which then partially
moderate before the asymptotic condition is obtained. The energy transfer to
angular momentum is exhibited by an approximate Jacobi constant for the system.
We demonstrate this with flybys that have shown unexplained behaviors: i) the
possible onset of the "Pioneer anomaly" with the gravity assist of Pioneer 11
by Saturn to hyperbolic orbit (as well as the Pioneer 10 hyperbolic gravity
assist by Jupiter) and ii) the Earth flyby anomalies of small increases in
energy {\it in the geocentric system} (Galileo-I, NEAR, and Rosetta, in
additioon discussing the Cassini and Messenger flybys). Perhaps some small, as
yet unrecognized effect in the energy-transfer process can shed light on these
anomalies.Comment: 29 pages, 43 images combined into 13 figures. Additions to answer
comments of refere
STOL Simulation Requirements for Development of Integrated Flight/propulsion Control Systems
The role and use of simulation as a design tool in developing integrated systems where design criteria is largely unavailable is well known. This paper addresses additional simulation needs for the development of Integrated Flight/Propulsion Control Systems (IFPCS) which will improve the probability of properly interpreting simulation results. These needs are based on recent experience with power approach flying qualities evaluations of an advanced fighter configuration which incorporated Short Takeoff and Landing (STOL) technologies and earlier experiences with power approach flying qualities evaluations on the AFTI/F-16 program. The use of motion base platforms with axial and normal degrees of freedom will help in evaluating pilot coupling and workload in the presence of high frequency low amplitude axial accelerations produced by high bandwidth airspeed controllers in a gusty environment
Therapeutic Opportunities in Infectious Diseases: Highlights from the Society of Medicines Research Symposium, held on March 14th 2013 at the National Heart & Lung Institute, London, UK
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