Twin polaritons in semiconductor microcavities

The quantum correlations between the beams generated by polariton pair scattering in a semiconductor microcavity above the parametric oscillation threshold are computed analytically. The influence of various parameters like the cavity-exciton detuning, the intensity mismatch between the signal and idler beams and the amount of spurious noise is analyzed. We show that very strong quantum correlations between the signal and idler polaritons can be achieved. The quantum effects on the outgoing light fields are strongly reduced due to the large mismatch in the coupling of the signal and idler polaritons to the external photons

Reliability of posterolateral acromion process to examination table measurement to estimate shoulder protraction contracture

Study Design: Retrospective study. Objectives: To determine the reliability of measuring the perpendicular distance between the posterolateral acromion process and examination table to estimate passive shoulder protraction in student physical therapists. Background: Previous research has identified scapular dyskinesis to be associated with musculoskeletal shoulder pain, and commonly addressed by physical therapists. Tightness of the anterior shoulder muscles may be associated with scapular movement abnormality. Thus, reliable clinical measurements for anterior shoulder muscle length are imporrant for physical therapy care. Methods: After a 1 0-minute review session, two measurements of the distance between the posterior acromion process and examination table were obtained for both the dominant shoulders and nondominant shoulders in 12 nondisabled individuals (6 females, and 6 males age: 25.0 ± 2.4 years) by 12 student physical therapist examiners. A complete set of measurements from 10 subjects were available for analysis. Results: Mean (±standard deviation) measurements for the dominant (D) shoulder were 7.6 ± 2.0cm for Trial #1 and 7.4 ± 2.0 em for Trial #2, and 7.5 ± 2.lcm for Trial #l and 7.4 ± 2.3cm for Trial #2 for the nondominant (ND) shoulder. Tightness was determined in 85% and 86% for D and ND shoulders, respectively. The measurement demonstrated good intra-rater reliability (D: intradass correlation, formula 2,1; ICC2 _ 1 .751, 95% confidence interval; Cl: .628-.861; ND: .764, 95% CI: .645-.869) and moderate to good inter-rater reliability (D: ICC2 , 1 .651, 95% CI: .445-.876; ND: ICC2•1 = .733, 95% CI: .548-.911) considered as a continuous variable, \u3c}nd good percent agreement both within raters (94%) and between raters (90%) as a binomial variable. The coefficient of variation was acceptable (D: 25.8, ND: 28.4%). Standard error of measure was 0.99 em for D shoulders and 1.01 em for ND shoulders. Minimum detectable change outside the 95% confidence interval was 2.74 em forD shoulders and 2.80 em for ND shoulders. Conclusion: Measurement of the perpendicular distance between the posterolateral acromion process and examination table is a reliable method to estimate passive shoulder protraction in novice clinicians

The effects of exposure to a rotating environment /10 rpm/ on four aviators for a period of twelve days

Motion sickness studies of aviators exposed to rotating environment - Aerospace medicin

Quantum interference of ultrastable twin optical beams

We report the first measurement of the quantum phase-difference noise of an ultrastable nondegenerate optical parametric oscillator that emits twin beams classically phase-locked at exact frequency degeneracy. The measurement illustrates the property of a lossless balanced beam-splitter to convert number-difference squeezing into phase-difference squeezing and, thus, provides indirect evidence for Heisenberg-limited interferometry using twin beams. This experiment is a generalization of the Hong-Ou-Mandel interference effect for continuous variables and constitutes a milestone towards continuous-variable entanglement of bright, ultrastable nondegenerate beams.Comment: 4 pages, 4 figs, accepted by Phys. Rev. Let

Deformation of geometry and bifurcation of vortex rings

We construct a smooth family of Hamiltonian systems, together with a family of group symmetries and momentum maps, for the dynamics of point vortices on surfaces parametrized by the curvature of the surface. Equivariant bifurcations in this family are characterized, whence the stability of the Thomson heptagon is deduced without recourse to the Birkhoff normal form, which has hitherto been a necessary tool.Comment: 26 page

Primates are living links to our past: The contribution of comparative studies with wild vervet monkeys to the field of social cognition.

By studying the behavior of nonhuman primates, particularly in wild settings, researchers have been able to investigate a range of cognitive abilities, shedding light on the evolution of certain aspects of cognition and revealing potential evolutionary precursors of many capacities considered uniquely human. Vervet monkeys (Chlorocebus pygerythrus) have been widely investigated due to their prevalence and their suitability for experimental testing in the wild with an ecologically valid approach that is not possible with many other primates, especially apes. Here we review advances in the understanding of a number of cognitive and behavioral processes that have been gleaned from studies conducted with wild vervet monkeys over the past half century, primarily focusing on social cognitive abilities. We direct our attention to three major areas of study; communication, cooperation and trade, and social learning. We discuss how findings from this species have contributed (and continue to contribute) to our understanding of the evolution of human cognitive capacities and suggest future avenues of research with this species

Performance based seismic qualification of reinforced concrete nuclear materials processing facilities

A seismic qualification of a reinforced concrete nuclear materials processing facility using performance based acceptance criteria is presented. Performance goals are defined in terms of a minimum annual seismic failure frequency. Pushover analyses are used to determine the building`s ultimate capacity and relate the capacity to roof drift and joint rotation. Nonlinear dynamic analyses are used to quantify the building`s drift using a suite of ground motion intensities representing varying soil conditions and levels of seismic hazard. A correlation between joint rotation and building drift to damage state is developed from experimental data. The damage state and seismic hazard are convolved to determine annual seismic failure frequency. The results of this rigorous approach is compared to those using equivalent force methods and pushover techniques recommended by ATC-19 and FEMA-273

A Comparison of Polarization Observables in Electron Scattering from the Proton and Deuteron

Recoil proton polarization observables were measured for both the p($\vec {\rm e}$,e$^\prime\vec{\rm p}\,$) and d($\vec {\rm e}$,e$^\prime\vec{\rm p}\,)$n reactions at two values of Q$^2$ using a newly commissioned proton Focal Plane Polarimeter at the M.I.T.-Bates Linear Accelerator Center. The hydrogen and deuterium spin-dependent observables $D_{\ell\ell}$ and $D_{{\ell}t}$, the induced polarization $P_n$ and the form factor ratio $G^p_E/G^p_M$ were measured under identical kinematics. The deuterium and hydrogen results are in good agreement with each other and with the plane-wave impulse approximation (PWIA).Comment: 9 pages, 1 figure; accepted by Phys. Rev. Let