Observation of long-lived polariton states in semiconductor microcavities across the parametric threshold

The excitation spectrum around the pump-only stationary state of a polariton optical parametric oscillator (OPO) in semiconductor microcavities is investigated by time-resolved photoluminescence. The response to a weak pulsed perturbation in the vicinity of the idler mode is directly related to the lifetime of the elementary excitations. A dramatic increase of the lifetime is observed for a pump intensity approaching and exceeding the OPO threshold. The observations can be explained in terms of a critical slowing down of the dynamics upon approaching the threshold and the following onset of the soft Goldstone mode

Evidence for a spatial bias in the perception of sequences of brief tones

Listeners are unable to report the physical order of particular sequences of brief tones. This phenomenon of temporal dislocation depends on tone durations and frequencies. The current study empirically shows that it also depends on the spatial location of the tones. Dichotically testing a three-tone sequence showed that the central tone tends to be reported as the first or the last element when it is perceived as part of a left-to-right motion. Since the central-tone dislocation does not occur for right-to-left sequences of the same tones, this indicates that there is a spatial bias in the perception of sequences. \ua9 2013 Acoustical Society of America

Self-gravitating spheres of anisotropic fluid in geodesic flow

The fluid models mentioned in the title are classified. All characteristics of the fluid are expressed through a master potential, satisfying an ordinary second order differential equation. Different constraints are imposed on this core of relations, finding new solutions and deriving the classical results for perfect fluids and dust as particular cases. Many uncharged and charged anisotropic solutions, all conformally flat and some uniform density solutions are found. A number of solutions with linear equation among the two pressures are derived, including the case of vanishing tangential pressure.Comment: 21 page

A multi-echelon supply chain model for strategic inventory assessment through the deployment of kanbans

Thesis (M. Eng. in Logistics)--Massachusetts Institute of Technology, Engineering Systems Division, 2008.Includes bibliographical references (leaves 100-102).As global competition in the manufacturing space grows, so do corporations' needs for sophisticated and optimized management systems to enable continuous flows of information and materials across the many tiers within their supply chains. With the complexities introduced by the variability in the demand for finished goods as well as by the variability in lead-time of transportation, procurement, production and administrative activities, corporations have turned to quantitative modeling of their supply chains to address these issues. Based on the data of a heavy machinery manufacturer headquartered in the US, this research introduces a robust model for the deployment of strategic inventory buffers across a multi-echelon manufacturing system. Specifically, this study establishes a replenishment policy for inventory using a multiple bin, or Kanban, system for each part number in the assembly of products from our sponsors tractor line. We employ a numerical simulation to evaluate and optimize the various inventory deployment scenarios. Utilizing several thousand runs of the simulation, we derive a generalized treatment for each part number based on an econometric function of the parameters associated with lead-time, order frequency, inventory value and order costing. The pilot for the simulation focuses on the parts data for three earthmoving products across eight echelons, but scales to n products across m echelons. Our results show that this approach predicted the optimal quantities of Kanbans for 95% of parts to a level of accuracy +/- 3 bins.by Philip J. Hodge and Joshua D. Lemaitre.M.Eng.in Logistic

Statistical mechanics of damage phenomena

This paper applies the formalism of classical, Gibbs-Boltzmann statistical mechanics to the phenomenon of non-thermal damage. As an example, a non-thermal fiber-bundle model with the global uniform (meanfield) load sharing is considered. Stochastic topological behavior in the system is described in terms of an effective temperature parameter thermalizing the system. An equation of state and a topological analog of the energy-balance equation are obtained. The formalism of the free energy potential is developed, and the nature of the first order phase transition and spinodal is demonstrated.Comment: Critical point appeared to be a spinodal poin

Definition of the stimulated emission threshold in high-β\beta nanoscale lasers through phase-space reconstruction

Nanoscale lasers sustain few optical modes so that the fraction of spontaneous emission $\beta$ funnelled into the useful (lasing) mode is high (of the order of few 10$^{-1}$) and the threshold, which traditionally corresponds to an abrupt kink in the light in- light out curve, becomes ill-defined. We propose an alternative definition of the threshold, based on the dynamical response of the laser, which is valid even for $\beta=1$ lasers. The laser dynamics is analyzed through a reconstruction of its phase-space trajectory for pulsed excitation. Crossing the threshold brings about a change in the shape of the trajectory and in the area contained in it. An unambiguous definition of the threshold in terms of this change is shown theoretically and illustrated experimentally in a photonic crystal laser

Sketching sound with voice and gesture

Voice and gestures are natural sketching tools that can be exploited to communicate sonic interactions. In product and interaction design, sounds should be included in the early stages of the design process. Scientists of human motion have shown that auditory stimuli are important in the performance of difficult tasks and can elicit anticipatory postural adjustments in athletes. These findings justify the attention given to sound in interaction design for gaming, especially in action and sports games that afford the development of levels of virtuosity. The sonic manifestations of objects can be designed by acting on their mechanical qualities and by augmenting the objects with synthetic and responsive sound

Fireball Multi Object Spectrograph: As-built optic performances

Fireball (Faint Intergalactic Redshifted Emission Balloon) is a NASA/CNES balloon-borne experiment to study the faint diffuse circumgalactic medium from the line emissions in the ultraviolet (200 nm) above 37 km flight altitude. Fireball relies on a Multi Object Spectrograph (MOS) that takes full advantage of the new high QE, low noise 13 μm pixels UV EMCCD. The MOS is fed by a 1 meter diameter parabola with an extended field (1000 arcmin2) using a highly aspherized two mirror corrector. All the optical train is working at F/2.5 to maintain a high signal to noise ratio. The spectrograph (R~ 2200 and 1.5 arcsec FWHM) is based on two identical Schmidt systems acting as collimator and camera sharing a 2400 g/mm aspherized reflective Schmidt grating. This grating is manufactured from active optics methods by double replication technique of a metal deformable matrix whose active clear aperture is built-in to a rigid elliptical contour. The payload and gondola are presently under integration at LAM. We will present the alignment procedure and the as-built optic performances of the Fireball instrument