51 research outputs found
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Access to Dual Enrollment in the United States: Implications for Equity and Stratification
Dual enrollment (DE) programs are on the rise nationally. This study uses recently available nationally representative data to examine which student and school characteristics predict participation in DE in the United States. We connect DE participation to human capital theory and related educational policy values of equity, excellence, and efficiency. Using logistic regressions, we find that, on average, 9thgrade GPA and attendance as well as higher socioeconomic status increased the odds that a student participates in DE. Our analysis also detects geographic disparities with students in rural areas and the South being more likely to take DE. We discuss implications for educational and economic policy.Educatio
The Cosmological Gene Project: cluster analysis of the atmospheric fluctuations on arcmin-scale imaging of the Cosmic Microwave Background
We discuss some aspects of the Cosmological Gene Project started at the
Special Astrophysical Observatory (Russia) in 1999. The goal of the project is
to measure the anisotropy and polarization of the Cosmic Microwave Background
(CMB) and investigation of atmospheric fluctuations and foreground on
arcmin-scales using the radio-telescope RATAN-600. We develop the cluster
analysis of one-dimensional random fields for the application to the RATAN-600
scans. We analyze the specific properties of peak clusterisation in the
RATAN-600 scans which to separate the primordial CMB signal from noise.Comment: Submitted to Astronomy & Astrophysic
Peculiarities of anisotropy and polarization as an indicator of noises in the CMB maps
We discuss some new problems of the modern cosmology which arose after the
BOOMERANG and MAXIMA-1 successful missions. Statistics of high peaks of the CMB
anisotropy is analyzed and we discuss possible inner structure of such peaks in
the observational data of future MAP and PLANCK missions. We have investigated
geometrical and statistical properties of the CMB polarization around such high
isolated peaks of anisotropy in the presence of a polarized pixel noise and
point sources. The structure of polarization fields in the vicinity of singular
points with zero polarization is very sensitive to the level of pixel noises
and point sources in the CMB maps.Comment: 9 pages, 2 figure
Scale-Invariant Correlation Functions of Cosmological Density Fluctuations in the Strong Clustering Regime
We have investigated the scale-invariant solutions of the BBGKY equations for
spatial correlation functions of cosmological density fluctuations and the mean
relative peculiar velocity in the strongly nonlinear regime.
It is found that the solutions for the mean relative physical velocity depend
on the three-point spatial correlation function and the skewness of the
velocity fields. We find that the stable condition in which the mean relative
physical velocity vanishes on the virialized regions is satisfied only under
the assumptions which Davis \& Peebles took in his paper. It is found, however,
that their assumptions may not be general in real.
The power index of the two-point correlation function in the strongly
nonlinear regime depends on the mean relative peculiar velocity, the
three-point correlation function and the skewness. If the self-similar
solutions exist, the power index in the strongly nonlinear regime is related to
the power index of the initial power spectrum and its relation depends on the
three-point correlation function and the skewness through the mean relative
peculiar velocity.
Furthermore it is found that the mean relative physical velocity should have
the values between 0 and the Hubble expanding velocity. When the mean relative
physical velocity equals to the Hubble expanding velocity, there might exist
self-similar solutions in which the power index of the two-point correlation
function in the strongly nonlinear regime is independent of the initial power
index .Comment: 24 pages, no figures, uses aaspp4.sty, Submitted to Ap
Universality in the distribution of caustics in the expanding Universe
We numerically investigate the long--time evolution of density perturbations
after the first appearance of caustics in an expanding cosmological model with
one--dimensional `single--wave' initial conditions. Focussing on the
time--intervals of caustic appearances and the spatial distribution of caustics
at subsequent times, we find that the time--intervals of caustic appearances
approach a constant, i.e., their time--subsequent ratio converges to 1; it is
also found that the spatial distribution of caustics at a given time features
some universality rules, e.g., the ratio between the position of the nearest
caustic from the center and that of the second nearest caustic from the center
approaches a constant. Furthermore we find some rules for the mass distribution
for each caustic. Using these universality constants we are in the position to
predict the spatial distribution of caustics at an arbitrary time in order to
give an estimate for the power spectral index in the fully--developed
non--dissipative turbulent (`virialized') regime.Comment: 23 pages, 19 figure
Recommended from our members
Forest fires in California, 1911-1920 : an analytical study
Gerald W. Williams Collectio
Recommended from our members
Cover type and fire control in the national forests of northern California
Gerald W. Williams Collectio
Smart windows: cation internal and anion external activation for electrochromic films of nickel hydroxide
Two methods - internal and external - were used for improving the electrochemical activity and electrochromic properties of Ni(OH)2 films. In the case of internal activation, Al3+ ions were added to the electrolyte composition during the electrochemical precipitation process. In the case of external activation, [Fe(CN)6]4â ions were used in the electrolyte during the cycling process. In all the experiments there were used Ni(OH)2 films synthesized by the electrochemical template method with polyvinyl alcohol (PVA) addition to the electrolyte composition. It was shown that the addition of [Fe(CN)6]4â ions into the electrolyte for cycling leads to significant improvement of electrochemical and electrochromic (colorization-bleaching) properties. At the same time, the addition of Al3+ ions into the electrolyte for Ni(OH)2 films precipitation leads to drastic worsening of their properties. Also, possible mechanisms of Al3+ and [Fe(CN)6]4â ions influence were considered in this work
Blue spectra and induced formation of primordial black holes
We investigate the statistical properties of primordial black hole (PBH)
formation in the very early Universe. We show that the high level of
inhomogeneity of the early Universe leads to the formation of the first
generation PBHs. %The existence of these PBHs This causes later the appearance
of a dust-like phase of the cosmological expansion. We discuss here a new
mechanism for the second generation of PBH formation during the dust-like
phase. This mechanism is based on the coagulation process. We demonstrate that
the blue power spectrum of initial adiabatic perturbations after inflation
leads to overproduction of primordial black holes with gg if the power index is .Comment: 16 pages, 2 figure
Perturbation Spectra in the Warm Inflationary Scenario
We investigate the phenomenology of warm inflation and present generic
results about the evolution of the inflaton and radiation fields. The general
conditions required for warm inflation to take place are derived and discussed.
A comprehensive approach is presented for the generation of thermally induced
adiabatic and isocurvature perturbations and the amplitude of their spectra
calculated. In addition we derive the ratio of tensor-to-scalar perturbations
and find the spectral indices for adiabatic, isocurvature and tensor
perturbations formed in the warm inflationary era. These results are presented
in a simplified and compact approach that is generally applicable. Our results
are illustrated by inflation models with polynomial and exponential potentials.
We compare our analytic results against numerical models and find excellent
agreement. Finally, presently available data is used to put constraints on warm
inflation and we discuss how near--future observations may distinguish the warm
inflationary scenario from standard supercooled inflation. The main observable
difference is the different scalar-to- tensor ratio, and that the consistency
relation between this and the slope of tensor perturbations does not hold for
warm inflation.Comment: 12 pages, Latex, Accepted by Phys Rev D., minor change
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