1,715 research outputs found
Optical phase-space reconstruction of mirror position at the attometer level
We describe an experiment in which the quadratures of the position of an
harmonically-bound mirror are observed at the attometer level. We have studied
the Brownian motion of the mirror, both in the free regime and in the
cold-damped regime when an external viscous force is applied by radiation
pressure. We have also studied the thermal-noise squeezing when the external
force is parametrically modulated. We have observed both the 50% theoretical
limit of squeezing at low gain and the parametric oscillation of the mirror for
a large gain.Comment: 10 pages, 11 figure
Agglomeration economies and firm productivity: evidence from French individual data
Geographical concentration of some industries over time is hard to explain without assuming the existence of agglomeration economies. The increasing availability of accurate individual firm data has renewed interest in the quantitative evaluation of the extent of these economies. Using three administrative files on French firms' accountancy and employment, we assess the impact on firm TFP of both urbanization economies, resulting from the size of the local market, its industrial diversity and its market potential, and of localization economies, resulting from the concentration of the same or similar activities. We find strong evidence for the former: higher density of economic activities or greater market potential in a given area increase significantly the productivity of the firms located in that area. However we do not find that industrial diversity does as well. We also find evidence of localization economies, as we observe that the more concentrated in a given area an economic activity is, the more productive the firms of this industry are. Finally we show that the more qualified the local labor force is, the more productive are the firms located in that area, suggesting that skilled workers are more prone to generate and benefit from agglomeration economies.firm productivity, agglomeration, urbanization externalities, localization externalities
Probing optomechanical correlations between two optical beams down to the quantum level
Quantum effects of radiation pressure are expected to limit the sensitivity
of second-generation gravitational-wave interferometers. Though ubiquitous,
such effects are so weak that they haven't been experimentally demonstrated
yet. Using a high-finesse optical cavity and a classical intensity noise, we
have demonstrated radiation-pressure induced correlations between two optical
beams sent into the same moving mirror cavity. Our scheme can be extended down
to the quantum level and has applications both in high-sensitivity measurements
and in quantum optics
Patterns of Localisation in the French Manufacturing and Service Industries: a Distance-Based Approach
We explore the patterns of localisation in the French manufacturing and service industries using the distance-based approach developed by Duranton and Overman (2005). The idea of this methodology is to consider the distribution of distances between pairs of plants in an industry and to compare it with that of a hypothetical industry with the same number of plants which are randomly distributed conditional on the distribution of aggregate activity. Relying on the same industrial classification as the one used by these authors, we show that their main conclusions remain valid in the case of French manufacturing industries. First, fewer manufacturing industries are found to be globally localised than usually found with discrete indices (Ellison-Glaeser, Maurel-Sédillot). Second, localisation takes place at small distance (localisation, K-density, spatial statistics, point-pattern processes
Nonlinear mechanics with photonic crystal nanomembranes
Optomechanical systems close to their quantum ground state and nonlinear
nanoelectromechanical systems are two hot topics of current physics research.
As high-reflectivity and low mass are crucial features to improve
optomechanical coupling towards the ground state, we have designed, fabricated
and characterized photonic crystal nanomembranes, at the crossroad of both
topics. Here we demonstrate a number of nonlinear effects with these membranes.
We first characterize the nonlinear behavior of a single mechanical mode and we
demonstrate its nonlocal character by monitoring the subsequent
actuation-related frequency shift of a different mode. We then proceed to study
the underlying nonlinear dynamics, both by monitoring the phase-space
trajectory of the free resonator and by characterizing the mechanical response
in presence of a strong pump excitation. We observe in particular the frequency
evolution during a ring-down oscillation decay, and the emergence of a phase
conjugate mechanical response to a weaker probe actuation. Our results are
crucial to understand the full nonlinear features of the PhC membranes, and
possibly to look for nonlinear signatures of the quantum dynamics
A micropillar for cavity optomechanics
We present a new micromechanical resonator designed for cavity optomechanics.
We have used a micropillar geometry to obtain a high-frequency mechanical
resonance with a low effective mass and a very high quality factor. We have
coated a 60-m diameter low-loss dielectric mirror on top of the pillar and
are planning to use this micromirror as part of a high-finesse Fabry-Perot
cavity, to laser cool the resonator down to its quantum ground state and to
monitor its quantum position fluctuations by quantum-limited optical
interferometry
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Memory in autism spectrum disorder: a meta-analysis of experimental studies
To address inconsistencies in the literature on memory in Autism Spectrum Disorder (ASD), we report the first ever meta-analysis of short-term (STM) and episodic long-term (LTM) memory in ASD, evaluating the effects of type of material, type of retrieval and the role of inter-item relations. Analysis of 64 studies comparing individuals with ASD and typical development (TD) showed greater difficulties in ASD compared to TD individuals in STM (Hedges’ g=-0.53 [95%CI -0.90; -0.16], p=.005, I²=96%) compared to LTM (g=-0.30 [95%CI -0.42; -0.17], p<.00001, I²=24%), a small difficulty in verbal LTM (g=-0.21, p=.01), contrasting with a medium difficulty for visual LTM (g= -0.41, p=.0002) in ASD compared to TD individuals. We also found a general diminution in free recall compared to cued recall and recognition (LTM, free recall: g=-0.38, p<.00001, cued recall: g=-0.08, p=.58, recognition: g=-0.15, p=.16; STM, free recall: g=-0.59, p=.004, recognition: g=-0.33, p=.07). We discuss these results in terms of their relation to semantic memory. The limited diminution in verbal LTM and preserved overall recognition and cued recall (supported retrieval) may result from a greater overlap of these tasks with semantic long-term representations which are overall preserved in ASD. By contrast, difficulties in STM or free recall may result from less overlap with the semantic system or may involve additional cognitive operations and executive demands. These findings highlight the need to support STM functioning in ASD and acknowledge the potential benefit of using verbal materials at encoding and broader forms of memory support at retrieval to enhance performance
Breakdown of Scaling in the Nonequilibrium Critical Dynamics of the Two-Dimensional XY Model
The approach to equilibrium, from a nonequilibrium initial state, in a system
at its critical point is usually described by a scaling theory with a single
growing length scale, , where z is the dynamic exponent
that governs the equilibrium dynamics. We show that, for the 2D XY model, the
rate of approach to equilibrium depends on the initial condition. In
particular, if no free vortices are present in the
initial state, while if free vortices are
present.Comment: 4 pages, 3 figure
Optomechanical characterization of acoustic modes in a mirror
We present an experimental study of the internal mechanical vibration modes
of a mirror. We determine the frequency repartition of acoustic resonances via
a spectral analysis of the Brownian motion of the mirror, and the spatial
profile of the acoustic modes by monitoring their mechanical response to a
resonant radiation pressure force swept across the mirror surface. We have
applied this technique to mirrors with cylindrical and plano-convex geometries,
and compared the experimental results to theoretical predictions. We have in
particular observed the gaussian modes predicted for plano-convex mirrors.Comment: 8 pages, 8 figures, RevTe
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