9,476 research outputs found
Dyon Spectrum in CHL Models
We propose a formula for the degeneracy of quarter BPS dyons in a class of
CHL models. The formula uses a modular form of a subgroup of the genus two
modular group Sp(2,Z). Our proposal is S-duality invariant and reproduces
correctly the entropy of a dyonic black hole to first non-leading order for
large values of the charges.Comment: LaTeX file, 38 pages, minor changes in section 3.3(v2), minor changes
in introduction, appendix A and C(v3
Peer Evaluation of Video Lab Reports in a Blended Introductory Physics Course
The Georgia Tech blended introductory calculus-based mechanics course
emphasizes scientific communication as one of its learning goals, and to that
end, we gave our students a series of four peer-evaluation assignments intended
to develop their abilities to present and evaluate scientific arguments. Within
these assignments, we also assessed students' evaluation abilities by comparing
their evaluations to a set of expert evaluations. We summarize our development
efforts and describe the changes we observed in student evaluation behavior.Comment: 4 pages, 1 table, 2 figures, submitted to Summer 2014 PERC
Proceeding
Two-photon interference with thermal light
The study of entangled states has greatly improved the basic understanding
about two-photon interferometry. Two-photon interference is not the
interference of two photons but the result of superposition among
indistinguishable two-photon amplitudes. The concept of two-photon amplitude,
however, has generally been restricted to the case of entangled photons. In
this letter we report an experimental study that may extend this concept to the
general case of independent photons. The experiment also shows interesting
practical applications regarding the possibility of obtaining high resolution
interference patterns with thermal sources.Comment: Added reference 1
The Initial State of Students Taking an Introductory Physics MOOC
As part of a larger research project into massively open online courses
(MOOCs), we have investigated student background, as well as student
participation in a physics MOOC with a laboratory component. Students completed
a demographic survey and the Force and Motion Conceptual Evaluation at the
beginning of the course. While the course is still actively running, we have
tracked student participation over the first five weeks of the eleven-week
course.Comment: Accepted to PERC Proceedings 201
Coherent versus Incoherent Light Scattering from a Quantum Dot
We analyze the light scattered by a single InAs quantum dot interacting with
a resonant continuous-wave laser. High resolution spectra reveal clear
distinctions between coherent and incoherent scattering, with the laser
intensity spanning over four orders of magnitude. We find that the fraction of
coherently scattered photons can approach unity under sufficiently weak or
detuned excitation, ruling out pure dephasing as a relevant decoherence
mechanism. We show how spectral diffusion shapes spectra, correlation
functions, and phase-coherence, concealing the ideal radiatively-broadened
two-level system described by Mollow.Comment: to appear in PRB 85, 23531
Bright light therapy to promote sleep in mothers of low-birth-weight infants: a pilot study
Having a low-birth-weight (LBW) infant in a neonatal intensive care unit (NICU) can intensify a mother’s sleep disturbances due to both stress and the dim lighting in the ICU setting, which desynchronizes circadian rhythms. The purpose of this pilot study was to examine the effectiveness of a 3-week bright light therapy intervention on sleep and health outcomes of mothers with LBW infants in the NICU. Controlled stratified randomization was used to assign 30 mothers to a treatment or control group. Data were collected at pretreatment (second week postpartum) and after the 3-week intervention. Sleep data were assessed by wrist actigraph (total sleep time [TST], circadian activity rhythms [CARs]) and the General Sleep Disturbance scale. Other outcome variables were measured by the Lee’s Fatigue scale, Edinburgh Postpartum Depression scale, and the Medical Outcomes Short Form 36, version 2. Mothers averaged 26.6 (SD = 6.3) years of age, and the majority were Black (73%). The mean gestational age for the infants was 27.7 (SD = 2.0) weeks. Small to large effect sizes were found when comparing the pre- to posttreatment differences between groups. Although none of the differences were statistically significant in this small sample, for mothers in the treatment group nocturnal TST (d = .33), CAR (d = 1.06), morning fatigue (d = .22), depressive symptoms (d = .40), physical health–related quality of life (d = .33), and mental health–related quality of life (d = .60) all improved compared to the control group. Bright light therapy is feasible for mothers with infants in an NICU. Clinically significant improvements have been evidenced; a larger-scale trial of effectiveness is needed
Low energy physical properties of high-Tc superconducting Cu oxides: A comparison between the resonating valence bond and experiments
In a recent review by Anderson and coworkers\cite{Vanilla}, it was pointed
out that an early resonating valence bond (RVB) theory is able to explain a
number of unusual properties of high temperature superconducting (SC)
Cu-oxides. Here we extend previous calculations \cite{anderson87,FC
Zhang,Randeria} to study more systematically low energy physical properties of
the plain vanilla d-wave RVB state, and to compare results with the available
experiments. We use a renormalized mean field theory combined with variational
Monte Carlo and power Lanczos methods to study the RVB state of an extended
model in a square lattice with parameters suitable for the hole doped
Cu-oxides. The physical observable quantities we study include the specific
heat, the linear residual thermal conductivity, the in-plane magnetic
penetration depth, the quasiparticle energy at the antinode , the
superconducting energy gap, the quasiparticle spectra and the Drude weight. The
traits of nodes (including , the Fermi velocity and the velocity
along Fermi surface ), as well as the SC order parameter are also
studied. Comparisons of the theory and the experiments in cuprates show an
overall qualitative agreement, especially on their doping dependences.Comment: 12 pages, 14 figures, 1 tabl
Additive Expression of Consolidated Memory through Drosophila Mushroom Body Subsets
Associative olfactory memory in Drosophila has two components called labile anesthesia-sensitive memory and consolidated anesthesia-resistant memory (ARM). Mushroom body (MB) is a brain region critical for the olfactory memory and comprised of 2000 neurons that can be classified into alphabeta, alpha'beta', and gamma neurons. Previously we demonstrated that two parallel pathways mediated ARM consolidation: the serotonergic dorsal paired medial (DPM)-alphabeta neurons and the octopaminergic anterior paired lateral (APL)-alpha'beta' neurons. This finding prompted us to ask how this composite ARM is retrieved. Here, we showed that blocking the output of alphabeta neurons and that of alpha'beta' neurons each impaired ARM retrieval, and blocking both simultaneously had an additive effect. Knockdown of radish and octbeta2R in alphabeta and alpha'beta' neurons, respectively, impaired ARM. A combinatorial assay of radish mutant background rsh1 and neurotransmission blockade confirmed that ARM retrieved from alpha'beta' neuron output is independent of radish. We identified MBON-beta2beta'2a and MBON-beta'2mp as the MB output neurons downstream of alphabeta and alpha'beta' neurons, respectively, whose glutamatergic transmissions also additively contribute to ARM retrieval. Finally, we showed that alpha'beta' neurons could be functionally subdivided into alpha'beta'm neurons required for ARM retrieval, and alpha'beta'ap neurons required for ARM consolidation. Our work demonstrated that two parallel neural pathways mediating ARM consolidation in Drosophila MB additively contribute to ARM expression during retrieval
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