16,434 research outputs found
Observations: test driving the Internet
Shopping for a new car over the Internet.Electronic commerce ; Automobile industry and trade
Patching the Pipeline: Addressing Teacher Satisfaction and Retention in Duval County
In "Patching the Pipeline: Addressing Teacher Satisfaction and Retention in Duval County," the Jacksonville Public Education Fund provides a comprehensive look at the last five cohorts of new teachers in Duval County Public Schools, and conducts a survey of all teachers in the district to get their opinions about a wide variety of different factors.This report details the turnover among new teachers in Duval County Public Schools -- half leave in the first five years -- and raises the voices of teachers themselves about what factors keep them in the classroom
Space-Time Noncommutativity from Particle Mechanics
We exploit the reparametrization symmetry of a relativistic free particle to
impose a gauge condition which upon quantization implies space-time
noncommutativity. We show that there is an algebraic map from this gauge back
to the standard `commuting' gauge. Therefore the Poisson algebra, and the
resulting quantum theory, are identical in the two gauges. The only difference
is in the interpretation of space-time coordinates. The procedure is repeated
for the case of a coupling with a constant electromagnetic field, where the
reparametrization symmetry is preserved. For more arbitrary interactions, we
show that standard dynamical system can be rendered noncommutative in space and
time by a simple change of variables.Comment: 13 p
Strings in plane-fronted gravitational waves
Brinkmann's plane-fronted gravitational waves with parallel rays --~shortly
pp-waves~-- are shown to provide, under suitable conditions, exact string vacua
at all orders of the sigma-model perturbation expansion.Comment: 7 pages, no figure
Finite unions of balls in C^n are rationally convex
It is shown that the rational convexity of any finite union of disjoint
closed balls in C^n follows easily from the results of Duval and Sibony.Comment: V.2 - minor edits, 2 page
Rapid and persistent selection of the K103N mutation as a majority quasispecies in a HIV1-patient exposed to efavirenz for three weeks: a case report and review of the literature
<p>Abstract</p> <p>Introduction</p> <p>Selection of the K103N mutation is associated with moderately reduced in vitro fitness of HIV. Strains bearing K103N in vivo tend to persist, even in the absence of additional drug pressure, as minority quasispecies, often undetectable in genotyping resistance testing assays, performed at standard conditions. Here, we report on the rapid and long lasting selection of a K103N bearing strain as the dominant quasispecies after very short exposure to efavirenz in vivo.</p> <p>Case presentation</p> <p>A 55-year-old Caucasian man was switched to efavirenz, zidovudine and lamivudine in February 2003, while on viral suppression in his first-line highly active anti-retroviral treatment regimen. One month later, he reported inconsistent adherence and his viremia level was 5700 c/mL. He did not attend further checkups until September 2005, when his viral load was 181,000 c/mL. The patient reported interrupting his medications approximately three weeks after simplification. The genotyping resistance testing assay was performed both on HIV RNA and HIV DNA from plasma, yielding an identical pattern with the isolate presence of the K103N mutation in the prevalent strain.</p> <p>Conclusion</p> <p>Persistence of the K103N mutation as a majority quasispecies may ensue after a very short exposure to efavirenz. Our case would therefore suggest that the presence of the K103N mutation should always be ruled out by genotyping resistance testing assays, even after minimal exposures to efavirenz.</p
Conserved quantities in non-abelian monopole fields
Van Holten's covariant Hamiltonian framework is used to find conserved
quantities for an isospin-carrying particle in a non-Abelian monopole-like
field. For a Wu-Yang monopole we find the most general scalar potential such
that the combined system admits a conserved Runge-Lenz vector. It generalizes
the fine-tuned inverse-square plus Coulomb potential, found before by McIntosh
and Cisneros, and by Zwanziger, for a charged particle in the field of a Dirac
monopole. Following Feh\'er, the result is interpreted as describing motion in
the asymptotic field of a self-dual Prasad-Sommerfield monopole. In the
effective non-Abelian field for nuclear motion in a diatomic molecule due to
Moody, Shapere and Wilczek, a conserved angular momentum is constructed,
despite the non-conservation of the electric charge. No Runge-Lenz vector has
been found.Comment: 8 pages, RevTex no figures. An error corrected and a new Section
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