1,167 research outputs found
IS THERE A ROLE FOR GOVERNMENT SPONSORED ENTITIES WITHIN THE ORIGINATE-TO-DISTRIBUTE MODEL? EVIDENCE FROM PRIME AND SUBPRIME MORTGAGES
This paper examines a role for Government Sponsored Entity’s (GSE) within theoriginate-to-distribute model (OTD). The research determines if originated residential prime and subprime mortgages in the OTD market, have a positive correlation with housing foreclosures, by analyzing residential OTD rates in 2007 and comparing it to foreclosure rates in 2008 for all 51 states in the United States. This paper breaks down OTD mortgages into purchaser and loan typein order to determine a relationship between GSE OTD/government mortgage guarantees and foreclosure rates. The paper has limited scope due to data limitations; however, our results indicate that higher levels of residential mortgage OTD rates on a state-wide level, causes foreclosure rates to increase in the US between 2007 and 2008
Dynamical Expansion of H II Regions from Ultracompact to Compact Sizes in Turbulent, Self-Gravitating Molecular Clouds
The nature of ultracompact H II regions (UCHRs) remains poorly determined. In
particular, they are about an order of magnitude more common than would be
expected if they formed around young massive stars and lasted for one dynamical
time, around 10^4 yr. We here perform three-dimensional numerical simulations
of the expansion of an H II region into self-gravitating, radiatively cooled
gas, both with and without supersonic turbulent flows. In the laminar case, we
find that H II region expansion in a collapsing core produces nearly spherical
shells, even if the ionizing source is off-center in the core. This agrees with
analytic models of blast waves in power-law media. In the turbulent case, we
find that the H II region does not disrupt the central collapsing region, but
rather sweeps up a shell of gas in which further collapse occurs. Although this
does not constitute triggering, as the swept-up gas would eventually have
collapsed anyway, it does expose the collapsing regions to ionizing radiation.
We suggest that these regions of secondary collapse, which will not all
themselves form massive stars, may form the bulk of observed UCHRs. As the
larger shell will take over 10^5 years to complete its evolution, this could
solve the timescale problem. Our suggestion is supported by the ubiquitous
observation of more diffuse emission surrounding UCHRs.Comment: accepted to ApJ, 40 pages, 13 b/w figures, changes from v1 include
analytic prediction of radio luminosity, better description of code testing,
and many minor changes also in response to refere
The Inability of Ambipolar Diffusion to set a Characteristic Mass Scale in Molecular Clouds
We investigate the question of whether ambipolar diffusion (ion-neutral
drift) determines the smallest length and mass scale on which structure forms
in a turbulent molecular cloud. We simulate magnetized turbulence in a mostly
neutral, uniformly driven, turbulent medium, using a three-dimensional,
two-fluid, magnetohydrodynamics (MHD) code modified from Zeus-MP. We find that
substantial structure persists below the ambipolar diffusion scale because of
the propagation of compressive slow MHD waves at smaller scales. Contrary to
simple scaling arguments, ambipolar diffusion thus does not suppress structure
below its characteristic dissipation scale as would be expected for a classical
diffusive process. We have found this to be true for the magnetic energy,
velocity, and density. Correspondingly, ambipolar diffusion leaves the clump
mass spectrum unchanged. Ambipolar diffusion appears unable to set a
characteristic scale for gravitational collapse and star formation in turbulent
molecular clouds.Comment: 16 pages, 5 figures. ApJ accepte
A Bayesian regression tree approach to identify the effect of nanoparticles' properties on toxicity profiles
We introduce a Bayesian multiple regression tree model to characterize
relationships between physico-chemical properties of nanoparticles and their
in-vitro toxicity over multiple doses and times of exposure. Unlike
conventional models that rely on data summaries, our model solves the low
sample size issue and avoids arbitrary loss of information by combining all
measurements from a general exposure experiment across doses, times of
exposure, and replicates. The proposed technique integrates Bayesian trees for
modeling threshold effects and interactions, and penalized B-splines for dose-
and time-response surface smoothing. The resulting posterior distribution is
sampled by Markov Chain Monte Carlo. This method allows for inference on a
number of quantities of potential interest to substantive nanotoxicology, such
as the importance of physico-chemical properties and their marginal effect on
toxicity. We illustrate the application of our method to the analysis of a
library of 24 nano metal oxides.Comment: Published at http://dx.doi.org/10.1214/14-AOAS797 in the Annals of
Applied Statistics (http://www.imstat.org/aoas/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Effects of contextual interference (CI) in basic squash shots practice / Ebby Waqqash and Jeffrey Low
The purpose of this study was to compare block and random practice in learning basic squash
shots. Eight university students were randomly assigned to two groups; the block practice group
and the random practice group. The block practice group performed 10 minutes of forehand
stroke, followed by another 10 minutes of backhand stroke. The random practice group played
against themselves in a 1 on 1 real-match situation for 20 minutes. Three tests were administered
to evaluate the participants’ performance: pretest, posttest (acquisition) and retention test.
Results showed the block practice (M=16, SD=.816) has better skill learning effect in the
acquisition phase compared to random practice (M=15.75, SD=2.22). However, the random
practice (M=18.25, SD=2.22) outperformed the block practice (M=10.25, SD=1.26) in the
retention phase. Based on the finding of this study, unstructured and real-match situation
practice facilitates better learning by reconstructing the learners’ action plan each time a skill is
performed
Fitness implications of seasonal climate variation in Columbian ground squirrels
The influence of climate change on the fitness of wild populations is often studied in the context of the spring onset of the reproductive season. This focus is relevant for climate influences on reproductive success, but neglects other fitness- relevant periods (e.g., autumn preparation for overwintering). We examined variation in climate variables (temperature, rainfall, snowfall, and snowpack) across the full annual cycle of Columbian ground squirrels (Urocitellus columbianus) for 21 years. We investigated seasonal climate variables that were associated with fitness variables, climate variables that exhibited directional changes across the study period, and finally observed declines in fitness (-0.03 units/year; total decline = 37%) that were associated with directional changes in climate variables. Annual fitness of adult female ground squirrels was positively associated with spring temperature (r = 0.69) and early summer rainfall (r = 0.56) and negatively associated with spring snow conditions (r = -0.44 to -0.66). Across the 21 years, spring snowmelt has become significantly delayed (r = 0.48) and summer rainfall became significantly reduced (r = -0.53). Using a standardized partial regression model, we found that directional changes in the timing of spring snowmelt and early summer rainfall (i.e., progressively drier summers) had moderate influences on annual fitness, with the latter statistically significant (rho = -0.314 and 0.437, respectively). The summer period corresponds to prehibernation fattening of young and adult ground squirrels. Had we focused on a single point in time (viz. the onset of the breeding season), we would have underestimated the influences of climate change on our population. Rather, we obtained a comprehensive understanding of the influences of climate change on individual fitness by investigating the full lifecycle
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