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Looking Back and Pressing Forward: Lessons for Today Found in the Story of Barbara Smith Conrad
Educatio
Incompressibility in finite nuclei and nuclear matter
The incompressibility (compression modulus) of infinite symmetric
nuclear matter at saturation density has become one of the major constraints on
mean-field models of nuclear many-body systems as well as of models of high
density matter in astrophysical objects and heavy-ion collisions. We present a
comprehensive re-analysis of recent data on GMR energies in even-even Sn and Cd and earlier data on 58 A 208
nuclei. The incompressibility of finite nuclei is expressed as a
leptodermous expansion with volume, surface, isospin and Coulomb coefficients
, , and . \textit{Assuming}
that the volume coefficient is identified with , the
= -(5.2 0.7) MeV and the contribution from the curvature
term KA in the expansion is neglected, compelling
evidence is found for to be in the range 250 315
MeV, the ratio of the surface and volume coefficients to be between -2.4 and -1.6 and between -840 and -350 MeV.
We show that the generally accepted value of = (240 20) MeV
can be obtained from the fits provided -1, as predicted by the
majority of mean-field models. However, the fits are significantly improved if
is allowed to vary, leading to a range of , extended to higher
values. A self-consistent simple (toy) model has been developed, which shows
that the density dependence of the surface diffuseness of a vibrating nucleus
plays a major role in determination of the ratio K and
yields predictions consistent with our findings.Comment: 26 pages, 13 figures; corrected minor typos in line with the proof in
Phys. Rev.
EDUCATION ON PUBLIC POLICY IN AGRICULTURE THROUGH THE LEAGUE OF WOMEN VOTERS
Teaching/Communication/Extension/Profession,
The plasma dynamics of hypersonic spacecraft: Applications of laboratory simulations and active in situ experiments
Attempts to gain an understanding of spacecraft plasma dynamics via experimental investigation of the interaction between artificially synthesized, collisionless, flowing plasmas and laboratory test bodies date back to the early 1960's. In the past 25 years, a number of researchers have succeeded in simulating certain limited aspects of the complex spacecraft-space plasma interaction reasonably well. Theoretical treatments have also provided limited models of the phenomena. Several active experiments were recently conducted from the space shuttle that specifically attempted to observe the Orbiter-ionospheric interaction. These experiments have contributed greatly to an appreciation for the complexity of spacecraft-space plasma interaction but, so far, have answered few questions. Therefore, even though the plasma dynamics of hypersonic spacecraft is fundamental to space technology, it remains largely an open issue. A brief overview is provided of the primary results from previous ground-based experimental investigations and the preliminary results of investigations conducted on the STS-3 and Spacelab 2 missions. In addition, several, as yet unexplained, aspects of the spacecraft-space plasma interaction are suggested for future research
The Effect of the Hall Term on the Nonlinear Evolution of the Magnetorotational Instability: II. Saturation Level and Critical Magnetic Reynolds Number
The nonlinear evolution of the magnetorotational instability (MRI) in weakly
ionized accretion disks, including the effect of the Hall term and ohmic
dissipation, is investigated using local three-dimensional MHD simulations and
various initial magnetic field geometries. When the magnetic Reynolds number,
Re_M \equiv v_A^2 / \eta \Omega (where v_A is the Alfven speed, \eta the
magnetic diffusivity, and \Omega the angular frequency), is initially larger
than a critical value Re_{M, crit}, the MRI evolves into MHD turbulence in
which angular momentum is transported efficiently by the Maxwell stress. If
Re_M < Re_{M, crit}, however, ohmic dissipation suppresses the MRI, and the
stress is reduced by several orders of magnitude. The critical value is in the
range of 1 - 30 depending on the initial field configuration. The Hall effect
does not modify the critical magnetic Reynolds number by much, but enhances the
saturation level of the Maxwell stress by a factor of a few. We show that the
saturation level of the MRI is characterized by v_{Az}^2 / \eta \Omega, where
v_{Az} is the Alfven speed in the nonlinear regime along the vertical component
of the field. The condition for turbulence and significant transport is given
by v_{Az}^2 / \eta \Omega \gtrsim 1, and this critical value is independent of
the strength and geometry of the magnetic field or the size of the Hall term.
If the magnetic field strength in an accretion disk can be estimated
observationally, and the magnetic Reynolds number v_A^2 / \eta \Omega is larger
than about 30, this would imply the MRI is operating in the disk.Comment: 43 pages, 8 tables, 20 figures, accepted for publication in ApJ,
postscript version also available from
http://www.astro.umd.edu/~sano/publications
School Choice and Student Performance: Are Private Schools Really Better?
Are private schools really better than public schools, or is it simply that better students attend private schools? Although a number of recent studies find that students perform better in private schools (more specifically, Catholic schools), others do not. Typically, however, the instruments used to adjust for nonrandom selection are weak. This study employs uniquely detailed local instruments and jointly models selection into religious and nonreligious private high schools, relative to public high schools—improving instrument power in predicting private sector attendance to roughly three times that of prior studies. Failing to correct adequately for selection leads to a systematic upward bias in the estimated treatment effect for religious schools, but a downward bias for nonreligious private schools. With adequate correction, religious schools are modestly inferior in mathematics and science, while nonreligious schools are substantially superior. However, minority students, particularly in urban areas, benefit from religious schools. Other factors that may make both religious and nonreligious private schools attractive include possibly better retention rates, increased security and discipline, and greater opportunities for a variety of specialized school-day and extracurricular activities.
Tests of a single tube-in-shell water-boiling heat exchanger with a helical-wire insert and several inlet flow-stabilizing devices
Single tube-in-shell water-boiling heat exchanger performance with helical wire insert and flow stabilizing device
Local heat transfer for water in entrance regions of tubes with tapered flow areas and nonuniform heat fluxes
Convective heat transfer data for water flow in heated circular tubes with varying heat fluxes and flow area
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