4,150 research outputs found
Do Historically Black Colleges and Universities Enhance the College Attendance of African American Youths?
Recently, Historically Black Colleges and Universities (HBCUs) have become the center of intense policy debates. Do HBCUs enhance the college attendance of African American youths? Previous research has been inconclusive. Among other improvements, our study adjusts for the relative availability of HBCU enrollment opportunities in each state. We find that African Americans are more likely to choose HBCUs over other colleges if more HBCU openings are available. However, more HBCU openings don\u27t increase overall African American enrollment. As we have shown elsewhere, attendance at an HBCU does enhance African American students\u27 college graduation rates
Lattice supersymmetry
A method is proposed for latticizing a class of supersymmetric gauge
theories, including N=4 super Yang-Mills. The technique is inspired by recent
work on ``deconstruction''. Part of the target theory's supersymmetry is
realized exactly on the lattice, reducing or eliminating the need for fine
tuning. (Talk based on the paper "Supersymmetry on a Spatial Lattice",
hep-lat/0206019, by D.B.K., Emmanuel Katz and Mithat Unsal).Comment: Lattice2002(higgssusy), 3 pages, no figure
CORRUPTION, GENDER EQUALITY AND FEMINIST STRATEGIES
ABSTRACT The following arguments are presented. 1) Corruption in its various forms is a serious social ill. 2) Democracy is not a safe cure against corruption. 3) Increased gender equality seems to be one important factor behind getting corruption under control. 4) Impartiality in the exercise of public power, not least, when it "translates" into meritocratic recruitment and promotion in the public administration, has a powerful effect on lowering corruption. 5) While some aspects of impartiality are central for gender equality, research results are mixed. Some show that impartial principles promotes gender equality, others show that gender bias exists also in many processes designed to be impartial. Going from these results to policy recommendation is thus fraught with many difficulties. One is how to handle problems of legitimacy in the implementation process for various forms of preferential treatment of discriminated groups. Since these problems are impossible to handle, we may be in for a "Churchillian" argument. Like representative democracy, meritocracy may be a far from ideal solution for lowering corruption and thereby promoting human well-being, but it may be the least bad of existing alternatives
Effective field theory approach to Casimir interactions on soft matter surfaces
We utilize an effective field theory approach to calculate Casimir
interactions between objects bound to thermally fluctuating fluid surfaces or
interfaces. This approach circumvents the complicated constraints imposed by
such objects on the functional integration measure by reverting to a point
particle representation. To capture the finite size effects, we perturb the
Hamiltonian by DH that encapsulates the particles' response to external fields.
DH is systematically expanded in a series of terms, each of which scales
homogeneously in the two power counting parameters: \lambda \equiv R/r, the
ratio of the typical object size (R) to the typical distance between them (r),
and delta=kB T/k, where k is the modulus characterizing the surface energy. The
coefficients of the terms in DH correspond to generalized polarizabilities and
thus the formalism applies to rigid as well as deformable objects.
Singularities induced by the point particle description can be dealt with using
standard renormalization techniques. We first illustrate and verify our
approach by re-deriving known pair forces between circular objects bound to
films or membranes. To demonstrate its efficiency and versatility, we then
derive a number of new results: The triplet interactions present in these
systems, a higher order correction to the film interaction, and general scaling
laws for the leading order interaction valid for objects of arbitrary shape and
internal flexibility.Comment: 4 pages, 1 figur
Towers of Gravitational Theories
In this essay we introduce a theoretical framework designed to describe black
hole dynamics. The difficulties in understanding such dynamics stems from the
proliferation of scales involved when one attempts to simultaneously describe
all of the relevant dynamical degrees of freedom. These range from the modes
that describe the black hole horizon, which are responsible for dissipative
effects, to the long wavelength gravitational radiation that drains mechanical
energy from macroscopic black hole bound states. We approach the problem from a
Wilsonian point of view, by building a tower of theories of gravity each of
which is valid at different scales. The methodology leads to multiple new
results in diverse topics including phase transitions of Kaluza-Klein black
holes and the interactions of spinning black hole in non-relativistic orbits.
Moreover, our methods tie together speculative ideas regarding dualities for
black hole horizons to real physical measurements in gravitational wave
detectors.Comment: Awarded second prize for 2006 Gravity Research Foundation essay
contes
Spin induced multipole moments for the gravitational wave flux from binary inspirals to third Post-Newtonian order
Using effective field theory techniques we calculate the source multipole
moments needed to obtain the spin contributions to the power radiated in
gravitational waves from inspiralling compact binaries to third Post-Newtonian
order (3PN). The multipoles depend linearly and quadratically on the spins and
include both spin(1)spin(2) and spin(1)spin(1) components. The results in this
paper provide the last missing ingredient required to determine the phase
evolution to 3PN including all spin effects which we will report in a separate
paper.Comment: 35 pages, 7 figures. Published versio
Non-Relativistic Gravitation: From Newton to Einstein and Back
We present an improvement to the Classical Effective Theory approach to the
non-relativistic or Post-Newtonian approximation of General Relativity. The
"potential metric field" is decomposed through a temporal Kaluza-Klein ansatz
into three NRG-fields: a scalar identified with the Newtonian potential, a
3-vector corresponding to the gravito-magnetic vector potential and a 3-tensor.
The derivation of the Einstein-Infeld-Hoffmann Lagrangian simplifies such that
each term corresponds to a single Feynman diagram providing a clear physical
interpretation. Spin interactions are dominated by the exchange of the
gravito-magnetic field. Leading correction diagrams corresponding to the 3PN
correction to the spin-spin interaction and the 2.5PN correction to the
spin-orbit interaction are presented.Comment: 10 pages, 3 figures. v2: published version. v3: Added a computation
of Einstein-Infeld-Hoffmann in higher dimensions within our improved ClEFT
which partially confirms and partially corrects a previous computation. See
notes added at end of introductio
Fluid-Induced Propulsion of Rigid Particles in Wormlike Micellar Solutions
In the absence of inertia, a reciprocal swimmer achieves no net motion in a
viscous Newtonian fluid. Here, we investigate the ability of a reciprocally
actuated particle to translate through a complex fluid that possesses a network
using tracking methods and birefringence imaging. A geometrically polar
particle, a rod with a bead on one end, is reciprocally rotated using magnetic
fields. The particle is immersed in a wormlike micellar (WLM) solution that is
known to be susceptible to the formation of shear bands and other localized
structures due to shear-induced remodeling of its microstructure. Results show
that the nonlinearities present in this WLM solution break time-reversal
symmetry under certain conditions, and enable propulsion of an artificial
"swimmer." We find three regimes dependent on the Deborah number (De): net
motion towards the bead-end of the particle at low De, net motion towards the
rod-end of the particle at intermediate De, and no appreciable propulsion at
high De. At low De, where the particle time-scale is longer then the fluid
relaxation time, we believe that propulsion is caused by an imbalance in the
fluid first normal stress differences between the two ends of the particle
(bead and rod). At De~1, however, we observe the emergence of a region of
network anisotropy near the rod using birefringence imaging. This anisotropy
suggests alignment of the micellar network, which is "locked in" due to the
shorter time-scale of the particle relative to the fluid
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