Hamiltonian traffic dynamics in microfluidic-loop networks

Recent microfluidic experiments revealed that large particles advected in a fluidic loop display long-range hydrodynamic interactions. However, the consequences of such couplings on the traffic dynamics in more complex networks remain poorly understood. In this letter, we focus on the transport of a finite number of particles in one-dimensional loop networks. By combining numerical, theoretical, and experimental efforts, we evidence that this collective process offers a unique example of Hamiltonian dynamics for hydrodynamically interacting particles. In addition, we show that the asymptotic trajectories are necessarily reciprocal despite the microscopic traffic rules explicitly break the time reversal symmetry. We exploit these two remarkable properties to account for the salient features of the effective three-particle interaction induced by the exploration of fluidic loops

Estimating the Effect of a Retraining Program on the Re-Employment Rate of Displaced Workers

In this paper we estimate by matching techniques the effects of a French retraining program on the reemployment rate of displaced workers. This program, called "Conventions de conversion", was intended to improve reemployment prospects of displaced workers by proposing them retraining and job seeking assistance for a period of six months beginning just after the dismissal. Our empirical analysis is based upon non-experimental data collected by the French Ministry of Labour. Matching estimates show that this program succeeded in increasing the employment rate of trainees by approximately 6 points of percentage in the medium-term, namely in the second and third years after the date of entry into the program. This improvement is essentially due to an increase of their reemployment rate in regular jobs, namely jobs under long-term labour contracts.evaluation, retraining program, displaced workers, matching estimates

Phase Space Engineering in Optical Microcavities I: Preserving near-field uniformity while inducing far-field directionality

Optical microcavities have received much attention over the last decade from different research fields ranging from fundamental issues of cavity QED to specific applications such as microlasers and bio-sensors. A major issue in the latter applications is the difficulty to obtain directional emission of light in the far-field while keeping high energy densities inside the cavity (i.e. high quality factor). To improve our understanding of these systems, we have studied the annular cavity (a dielectric disk with a circular hole), where the distance cavity-hole centers, d, is used as a parameter to alter the properties of cavity resonances. We present results showing how one can affect the directionality of the far-field while preserving the uniformity (hence the quality factor) of the near-field simply by increasing the value of d. Interestingly, the transition between a uniform near- and far-field to a uniform near- and directional far-field is rather abrupt. We can explain this behavior quite nicely with a simple model, supported by full numerical calculations, and we predict that the effect will also be found in a large class of eigenmodes of the cavity.Comment: 12th International Conference on Transparent Optical Network

Impact of cutting date on carabids and spiders in a wet meadow

International audienceThe impact of different cutting dates on two dominant groups of ground-dwelling arthropods (carabids and spiders) was assessed. Short-term impacts were assessed by comparing them before and after cutting. Arthropods were collected by pitfall traps located in three plots with different cutting dates between June and August and one uncut control plot. Trapping was performed during a 4-month period in the spring and summer 2011. In total, 26,392 spiders and 12,278 carabids, representing 56 and 82 species respectively, were collected. Overall, the effects of cutting were negative and mostly visible in the long term for carabids, with reduced abundances and species richness in cut plots, and in the short-term for spiders; several parameters (proportion of predators and polyphagous species, and body length) decreased after cutting while remaining stable in the control. Long-term cutting effects revealed almost no differences between plots cut at different dates whereas the short-term effects decreased slightly over time, with respect to the overall phenology of both groups. In conclusion, this study underlines the fact that cutting has drastic effects on ground-dwelling arthropods, and even late dates, which are supposedly positive for other animals like breeding birds, are deleterious for highly diverse and species-rich grassland groups

Relative importance of management and natural flooding on spider, carabid and plant assemblages in extensively used grasslands along the Loire

International audienceIn Europe, agri-environment schemes (AES) have been implemented to counteract the effects of agricultural intensification. Studies investigating the role of management improvement induced by AES are quite numerous, but rarely take into account the effect of natural perturbations such as flooding, although severe disturbances are well known to shape community structure. Here we investigated the relative importance of management improvement and flooding to explain community parameters of two dominant arthropod groups and vegetation in alluvial meadows. Sampling took place in 2013, using suction samplers for arthropods and phytosociological relevés for vegetation, in 83 meadows distributed along 200 km of the Loire Valley (France). Pair-matched approach (by R-ANOVA) was used to assess overall effects of AES whereas a gradient analysis (GLM) was carried out to assess the impact of AES prescriptions (fertilisation and cutting-date) together with indirect (long-term) and direct (short-term) effects of flooding. No significant effect of AES was found on arthropod and plant assemblages, abundance/productivity or diversity (both α and β), but the number of rare plant species was higher in sites under AES. Prescriptions had little impact on most response variables considered; the only significant impact being the positive effect of high-amounts of fertilisers on spider α- and β-diversities. Conversely, systematic long-term effects of flooding were found on all response variables of spiders, carabids and plants, underlining the key role of this factor in alluvial meadows. Our study demonstrates that maintaining or enhancing hydrological functioning of ecosystems is even more important than regulating both the cutting-dates and the low input of fertilisers for conservation purposes in flooded, already naturally nutrient rich, meadow