4,643 research outputs found
Effects of Nonmaternal Child Care on Inequality in Cognitive Skills
As a result of changing welfare policies, large numbers of children of poor, uneducated mothersare likely to receive care from others as their mothers enter the workforce. How will this change affect inequality in cognitive skills among young children? One view suggests that inequality will expand because children from economically advantaged families have access to better child care, and families with well-educated parents are more likely to reinforce the cognitive benefits of care. Another view argues that inequality will diminish because even though child care may be unequal, it may be less unequal than the home environments that are supplanted by nonmaternal care. A third view suggests that because the effects of care are inconsistent, there will be little overall change in inequality. Analysis of the children of mothers in the National Longitudinal Survey of Youth provides tentative evidence in support of the first view, that nonmaternal care tends to magnify inequality. Although ordinary least squares regressions reveal no effects of child care, fixed-effects models that control for differences between families indicate that children of high-income, well-educated mothers benefit from center-based care, but children of low-income, poorly educated mothers suffer a cognitive disadvantage from attending day care centers. Home-based care, however, is not associated with cognitive performance. Results from nonparametric analyses are consistent with the findings from fixed-effects models. The key results rely mainly on a relatively small sample of about 700 children in 300 families that sent their children to different types of care, and they do not pertain to families with only one child, so caution is warranted in generalizing the findings.
Convergence properties of simple genetic algorithms
The essential parameters determining the behaviour of genetic algorithms were investigated. Computer runs were made while systematically varying the parameter values. Results based on the progress curves obtained from these runs are presented along with results based on the variability of the population as the run progresses
Analytic Perturbation Theory for Practitioners and Upsilon Decay
Within the ghost-free Analytic Perturbation Theory (APT), devised in the last
decade for low energy QCD, simple approximations are proposed for 3-loop
analytic couplings and their effective powers, in both the space-like
(Euclidean) and time-like (Minkowskian) regions, accurate enough in the large
range (1--100 GeV) of current physical interest.\par Effectiveness of the new
Model is illustrated by the example of decay where the
standard analysis gives value that is
inconsistent with the bulk of data for .
Instead, we obtain that
corresponds to that is close to the world
average.\par The issue of scale uncertainty for decay is also
discussed.Comment: 12 pages, 0 figures. Model slightly modified to increase its
accuracy. Numerical results upgraded, references added. The issue of scale
uncertainty is discusse
The Estimation of the Effective Centre of Mass Energy in q-qbar-gamma Events from DELPHI
The photon radiation in the initial state lowers the energy available for the
ee collisions; this effect is particularly important at LEP2 energies
(above the mass of the Z boson). Being aligned to the beam direction, such
initial state radiation is mostly undetected. This article describes the
procedure used by the DELPHI experiment at LEP to estimate the effective
centre-of-mass energy in hadronic events collected at energies above the Z
peak. Typical resolutions ranging from 2 to 3 GeV on the effective
center-of-mass energy are achieved, depending on the event topology.Comment: 12 pages, 6 figure
Oblique Corrections To The W Width
The lowest-order expression for the partial width to , has no oblique radiative
corrections from new physics if the measured mass is used. Here GeV/ is the muon decay constant. For
the present value of GeV/, and with
GeV, one expects MeV. The total
width is also expected to lack oblique corrections from
new physics, so that . Present data are consistent with this prediction.Comment: 15 pages (LaTeX), one PostScript figure not included (available upon
request
A Precision Calculation of the Next-to-Leading Order Energy-Energy Correlation Function
The O(alpha_s^2) contribution to the Energy-Energy Correlation function (EEC)
of e+e- -> hadrons is calculated to high precision and the results are shown to
be larger than previously reported. The consistency with the leading logarithm
approximation and the accurate cancellation of infrared singularities exhibited
by the new calculation suggest that it is reliable. We offer evidence that the
source of the disagreement with previous results lies in the regulation of
double singularities.Comment: 6 pages, uuencoded LaTeX and one eps figure appended Complete paper
as PostScript file (125 kB) available at:
http://www.phys.washington.edu/~clay/eecpaper1/paper.htm
A novel series solution to the renormalization group equation in QCD
Recently, the QCD renormalization group (RG) equation at higher orders in
MS-like renormalization schemes has been solved for the running coupling as a
series expansion in powers of the exact 2-loop order coupling. In this work, we
prove that the power series converges to all orders in perturbation theory.
Solving the RG equation at higher orders, we determine the running coupling as
an implicit function of the 2-loop order running coupling. Then we analyze the
singularity structure of the higher order coupling in the complex 2-loop
coupling plane. This enables us to calculate the radii of convergence of the
series solutions at the 3- and 4-loop orders as a function of the number of
quark flavours . In parallel, we discuss in some detail the
singularity structure of the coupling at the 3- and 4-loops in
the complex momentum squared plane for . The
correspondence between the singularity structure of the running coupling in the
complex momentum squared plane and the convergence radius of the series
solution is established. For sufficiently large values, we find
that the series converges for all values of the momentum squared variable
. For lower values of , in the scheme,
we determine the minimal value of the momentum squared above
which the series converges. We study properties of the non-power series
corresponding to the presented power series solution in the QCD Analytic
Perturbation Theory approach of Shirkov and Solovtsov. The Euclidean and
Minkowskian versions of the non-power series are found to be uniformly
convergent over whole ranges of the corresponding momentum squared variables.Comment: 29 pages,LateX file, uses IOP LateX class file, 2 figures, 13 Tables.
Formulas (4)-(7) and Table 1 were relegated to Appendix 1, some notations
changed, 2 footnotes added. Clarifying discussion added at the end of Sect.
3, more references and acknowledgments added. Accepted for publication in
Few-Body System
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