2,340 research outputs found
Parents and children talk: the family dynamics of English language proficiency
This paper extends the analysis of the acquisition of destination language proficiency
among immigrants by explicitly incorporating dynamics among family membersâ
mother, father and children. Single equation, bivariate, and four-state (multivariate)
probit analyses are employed. Immigrant English language skills are greater the
younger the age at migration, the longer the duration of residence, the higher the
level of education, and for immigrants not from Asia. Large positive correlations in
the unmeasured determinants of proficiency exist between spouses, between
siblings, and between parents and children, although the latter relationship is
stronger for the mother
A mathematical model of fluid flow in a scraped-surface heat exchanger
A simple mathematical model of fluid flow in a common type of scraped-surface heat exchanger in which the gaps between the blades and the device walls are narrow, so that a lubrication-theory description of the flow is valid, is presented. Specifically steady isothermal flow of a Newtonian fluid around a periodic array of pivoted scraper blades in a channel with one stationary and one moving wall, when there is an applied pressure gradient in a direction perpendicular to the wall motion, is analysed. The flow is three-dimensional, but decomposes naturally into a two-dimensional "transverse" flow driven by the boundary motion and a "longitudinal" pressure-driven flow. First details of the structure of the transverse flow are derived, and, in particular, the equilibrium positions of the blades are calculated. It is shown that the desired contact between blades and the moving wall will be attained, provided that the blades are pivoted sufficiently close to their ends. When the desired contact is achieved, the model predicts that the forces and torques on the blades are singular, and so the model is generalised to include three additional physical effects, namely non-Newtonian power-law behaviour, slip at rigid boundaries, and cavitation in regions of very low pressure, each of which is shown to resolve these singularities. Lastly the nature of the longitudinal flow is discussed
Southern Hemisphere Observations of a eV Cosmic Ray Source Near the Direction of the Galactic Centre
We report on an analysis of data from the southern hemisphere SUGAR cosmic
ray detector. We confirm the existence of an excess of eV cosmic rays
from a direction close to the Galactic Centre, first reported by the AGASA
group. We find that the signal is consistent with that from a point source, and
we find no evidence for an excess of cosmic rays coming from the direction of
the Galactic Centre itself.Comment: 14 pages including 5 postscript figures, corrected the title
(replaced "Cosmic Ray Source" instead of "Cosmic Ray"
Effective scraping in a scraped surface heat exchanger: some fluid flow analysis
An outline of mathematical models that have been used to understand the behaviour of scraped surface heat exchangers is presented. In particular the problem of the wear of the blades is considered. A simple model, exploiting known behaviour of viscous flow in corners and in wedges, and accounting for the forces on the blade is derived and solutions generated. The results shows initial rapid wear but that the wear rate goes to zero
Minimizing Effective Many-Body Interactions
A simple two-level model is developed and used to test the properties of
effective interactions for performing nuclear structure calculations in
truncated model spaces. It is shown that the effective many-body interactions
sensitively depend on the choice of the single-particle basis and they appear
to be minimized when a self- consistent Hartree-Fock basis is used.Comment: (15 pages of text and 1 postscript figure (Figure available upon
request), Preprint Number not assigned ye
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Recurrent Connectivity Can Account for the Dynamics of Disparity Processing in V1
Disparity tuning measured in the primary visual cortex (V1) is described well by the disparity energy model, but not all aspects of disparity tuning are fully explained by the model. Such deviations from the disparity energy model provide us with insight into how network interactions may play a role in disparity processing and help to solve the stereo correspondence problem. Here, we propose a neuronal circuit model with recurrent connections that provides a simple account of the observed deviations. The model is based on recurrent connections inferred from neurophysiological observations on spike timing correlations, and is in good accord with existing data on disparitytuning dynamics.Wefurther performedtwo additional experimentstotest predictions ofthe model. First, we increased the size of stimuli to drive more neurons and provide a stronger recurrent input. Our model predicted sharper disparity tuning for larger stimuli. Second, we displayed anticorrelated stereograms, where dots of opposite luminance polarity are matched between the left- and right-eye images and result in inverted disparity tuning in the disparity energy model. In this case, our model predicted reduced sharpening and strength of inverted disparity tuning. For both experiments, the dynamics of disparity tuning observed from the neurophysiological recordings in macaque V1 matched model simulation predictions. Overall, the results of this study support the notion that, whilethe disparity energy model provides a primary account of disparitytuning in V1 neurons, neural disparity processing in V1 neurons is refined by recurrent interactions among elements in the neural circuit
Nuclear shell-model calculations for 6Li and 14N with different NN potentials
Two ``phase-shift equivalent'' local NN potentials with different
parametrizations, Reid93 and NijmII, which were found to give nearly identical
results for the triton by Friar et al, are shown to yield remarkably similar
results for 6Li and 14N in a (0+2)hw no-core space shell-model calculation. The
results are compared with those for the widely used Hamada-Johnson hard-core
and the original Reid soft-core potentials, which have larger deuteron D-state
percentages. The strong correlation between the tensor strength and the nuclear
binding energy is confirmed. However, many nuclear-structure properties seem to
be rather insensitive to the details of the NN potential and, therefore, cannot
be used to test various NN potentials. (Submitted to Phys. Rev. C on Nov. 9,
1993 as a Brief Report.)Comment: 12 text pages and 1 figure (Figure available upon request),
University of Arizona Physics Preprint (Number not yet assigned
Auxiliary potential in no-core shell-model calculations
The Lee-Suzuki iteration method is used to include the folded diagrams in the
calculation of the two-body effective interaction between
two nucleons in a no-core model space. This effective interaction still depends
upon the choice of single-particle basis utilized in the shell-model
calculation. Using a harmonic-oscillator single-particle basis and the
Reid-soft-core {\it NN} potential, we find that overbinds
^4\mbox{He} in 0, 2, and model spaces. As the size of the
model space increases, the amount of overbinding decreases significantly. This
problem of overbinding in small model spaces is due to neglecting effective
three- and four-body forces. Contributions of effective many-body forces are
suppressed by using the Brueckner-Hartree-Fock single-particle Hamiltonian.Comment: 14 text pages and 4 figures (in postscript, available upon request).
AZ-PH-TH/94-2
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