Cavity solitons in semiconductor microresonators: Existence, stability, and dynamical properties

We apply a versatile numerical technique to establishing the existence of cavity solitons (CS) in a semiconductor microresonator with bulk GaAs or multiple quantum well GaAs/AlGaAs as its active layer. Based on a Newton method, our approach implies the evaluation of the linearized operator describing deviations from the exact stationary state. The eigenvalues of this operator determine the dynamical stability of the CS. A typical eigenspectrum contains a zero eigenvalue With which a ''neutral mode" of the CS is associated. Such neutral modes are characteristic of models with translational symmetry. All other eigenvalues typically have negative real parts large enough to cause any excitations to die out in a few medium response times. The neutral mode thus dominates the response to external random or deterministic perturbations, and its excitation induces a simple translation of the CS, which are thus stable and robust. We show how to relate the speed with which a CS moves under external perturbations to the projection of the perturbations on to the neutral mode, and give some examples, including weak gradients on the driving field and interaction with other CS. Finally, we show that the separatrix between two stable coexisting solutions: the homogeneous solution and the CS is the intervening unstable CS solution. Our results are important with a view to future applications of CS to optical information processing

Spontaneous and induced motion of optical patterns

The universality of two mechanisms of motion of patterns in nonlinear optics is demonstrated. In the first one, two-dimensional disordered patterns are shown to scroll with constant velocity after transients are discarded. In the second case, pattern motion is induced by background modulations. Spatially periodic patterns lock to maxima or minima of the underlying modulation depending on its wavevector

Psychosocial work environment and musculoskeletal symptoms among 21-year-old workers: a population-based investigation (2011-2013)

BACKGROUND: The current labour market is becoming more flexible and informal, with job insecurity selectively affecting young workers. However, the role of these increasing adverse psychosocial working conditions on health outcomes remains little known among newly employed workers. OBJECTIVE: To estimate the associations between psychosocial work environment and musculoskeletal outcomes (widespread pain syndrome features and regional pain) in a population-based sample of young workers. METHODS: Cross-sectional data from workers aged 21 years were collected during the third wave of the EPITeen cohort study (2011-2013; n=650). The Job Content Questionnaire was used to characterize the psychosocial work environment according to the demand-control-support model. Data on pain and non-pain dimensions of the widespread pain syndrome (Fibromyalgia Survey Questionnaire) as well as on regional musculoskeletal pain (Nordic Musculoskeletal Questionnaire) were also collected. Crude and adjusted odds ratios (OR) with 95% confidence intervals (95% CI) were computed using logistic regression and all estimates were adjusted for sex, education and occupational biomechanical demands. RESULTS: Job insecurity was significantly associated to the non-pain dimension of the widespread pain syndrome (adjusted OR [95% CI]=1.51 [1.08, 2.12]). Young workers with strain jobs were significantly more likely to report high levels of non-pain symptoms when compared with those with no-strain jobs and this effect was even stronger when social support was added to the main exposure: workers with strain jobs and low social support had twice the odds of reporting high levels of non-pain features than those with high strain but high social support jobs (adjusted OR=1.86, 95% CI: 1.04, 3.31). These significant associations were not observed when widespread pain or multisite regional pain were the outcomes. CONCLUSION: In the beginning of professional life, high strain jobs were associated to non-pain complaints, especially when the work environment provided also low social support.This study was supported by the Portuguese Foundation for Science and Technology (FCT, references: FCOMP-01-0124-FEDER-015750, FCT–PTDC/SAU-EPI/115254/2009). Sara Lourenço gratefully acknowledges a doctoral grant from the Portuguese Foundation for Science and Technology (FCT; reference SFRH/BD/77965/2011)