Compaction dynamics of a granular media under vertical tapping

We report new experimental results on granular compaction under consecutive vertical taps. The evolution of the mean volume fraction and of the mean potential energy of a granular packing presents a slow densification until a final steady-state, and is reminiscent to usual relaxation in glasses via a stretched exponential law. The intensity of the taps seems to rule the characteristic time of the relaxation according to an Arrhenius's type relation >. Finally, the analysis of the vertical volume fraction profile reveals an almost homogeneous densification in the packing.Comment: 7 pages, 4 figures, to appear in Europhysics Letter

Agricultural, forest and rural policy sectors' receptiveness to agroforestry intercropping systems in Quebec (Canada)

PosterIn Quebec (Canada), intercropping trees and crops is a new practice in the agricultural landscape dominated by conventional monocropping systems. As research goes on and slowly reveals the potential of these systems to address some key issues in agriculture, forestry and rural development, and as farmers’ awareness increases, there is a pressing need to find public support for these systems. In order to help the promoters of agroforestry intercropping systems in their search of support in the political arena, we conducted a comparative study of the receptiveness of the agricultural, forest and rural policy sectors to these systems. As the literature on public policy processes has stressed the importance of policy stakeholders’ ideas in the implementation of new policies, we used a conceptual framework based on cognitive schemes to compare the ideas driving these policy sectors with the ideas supporting agroforestry intercropping systems. Results based on the analysis of formal publications and semi-directed interviews conducted with agroforestry experts and policy stakeholders underline that agroforestry intercropping systems are mostly featured by their promoters as sustainable and multifunctional systems. The rural policy sector has proven to be the most receptive and the forest sector the less receptive, while the agricultural sector lies in-between, offering small-scale support to agroforestry intercropping systems. The analysis highlights that policy sectors integrating multifunctionality in their core ideas are supportive of agroforestry intercropping systems, while sectors remaining largely focused on specialization and productivity are less receptive. Our study also shows that public incentives might not be sufficient to drive the adoption of agroforestry intercropping systems since major barriers to their implementation remain in some policy sectors. Featuring these systems as productive might be a necessary argument shift to tear down policy barriers and increase public support

VHF discharges in storm cells producing microbursts

An experiment was carried out in which 3-D mapping of VHF sources was compared to a 3-D description of the reflectivity and dynamics of associated cloud cells observed by a radar network. Data from 61 microbursts were analyzed and it was found that, in 93 pct. of the cases, electrical activity precedes outflow development. The results confirm that the peak in intracloud activity precedes the maximum value of the outflow

Physiological constraints on the global distribution of <i>Trichodesmium</i> ? effect of temperature on diazotrophy

International audienceThe cyanobacterium Trichodesmium is an important link in the global nitrogen cycle due to its significant input of atmospheric nitrogen to the ocean. Attempts to incorporate Trichodesmium in ocean biogeochemical circulation models have, so far, relied on the observed correlation between temperature and Trichodesmium abundance. This correlation may result in part from a direct effect of temperature on Trichodesmium growth rates through the control of cellular biochemical processes, or indirectly through temperature influence on mixed layer depth, light and nutrient regimes. Here we present results indicating that the observed correlation of Trichodesmium with temperature in the field reflects primarily the direct physiological effects of temperature on diazotrophic growth of Trichodesmium. Trichodesmium IMS-101 (an isolate of Trichodesmium) could acclimate and grow at temperatures ranging from 20 to 34°C. Maximum growth rates (?max=0.25 day?1) and maximum nitrogen fixation rates (0.13 mmol N mol POC?1 h?1) were measured within 24 to 30°C. Combining this empirical relationship with global warming scenarios derived from state-of-the-art climate models sets a physiological constraint on the future distribution of Trichodesmium that could significantly affect the future nitrogen input into oligotrophic waters by this diazotroph

Observation of gravity-capillary wave turbulence

We report the observation of the cross-over between gravity and capillary wave turbulence on the surface of mercury. The probability density functions of the turbulent wave height are found to be asymmetric and thus non Gaussian. The surface wave height displays power-law spectra in both regimes. In the capillary region, the exponent is in fair agreement with weak turbulence theory. In the gravity region, it depends on the forcing parameters. This can be related to the finite size of the container. In addition, the scaling of those spectra with the mean energy flux is found in disagreement with weak turbulence theory for both regimes

Computing labs and Technology Classroom (ClTC) Initiative: A Model for Distributed Support

DePauw University is a small, liberal arts institution with 2200 undergraduate residential students and 222 faculty members, located in Greencastle, Indiana The challenges of supporting a campus with multiple and diverse facilities are further amplified by limited staff support resources. One of the strategies for addressing these challenges led to the formation of the Computing Labs and Technology Classrooms (CLTC) initiative. The CLTC recognizes and draws on the strengths of support specialists with a wide variety of professional training and experience, who regularly collaborate in the support and management of campus-wide labs and technology classrooms

Kinetic Monte Carlo Modelling to Study Diffusion in Zeolite. Understanding the Impact of Dual Site Isotherm on the Loading Dependence of n-Hexane and n-Heptane Diffusivities in MFI Zeolite, as Revealed by QENS Experiments

ENERGIE:MATERIAUX+HJO:NLAInternational audienceThis study concerns the diffusion of single-component molecules in zeolites, characterised by an isotherm represented by a dual-site Langmuir model with a point of inflection. The systems investigated are n-hexane and n-heptane in MFI zeolite at 300 K. Experiments conducted using the Quasi-Elastic Neutron Scattering (QENS) technique have demonstrated that this inflection has an impact on the loading dependence of the transport Dt and corrected DC diffusion coefficients of these systems. The results of these experiments are described here. A Kinetic Monte Carlo study is then conducted, showing how the energy levels of the molecule adsorption sites in a zeolite affect the loading dependence of the diffusion coefficients of these molecules

Observation of intermittency in wave turbulence

We report the observation of intermittency in gravity-capillary wave turbulence on the surface of mercury. We measure the temporal fluctuations of surface wave amplitude at a given location. We show that the shape of the probability density function of the local slope increments of the surface waves strongly changes across the time scales. The related structure functions and the flatness are found to be power laws of the time scale on more than one decade. The exponents of these power laws increase nonlinearly with the order of the structure function. All these observations show the intermittent nature of the increments of the local slope in wave turbulence. We discuss the possible origin of this intermittency.Comment: new version to Phys. Rev. Let

Interpersonal sensorimotor communication shapes intrapersonal coordination in a musical ensemble

Social behaviors rely on the coordination of multiple effectors within one’s own body as well as between the interacting bodies. However, little is known about how coupling at the interpersonal level impacts coordination among body parts at the intrapersonal level, especially in ecological, complex, situations. Here, we perturbed interpersonal sensorimotor communication in violin players of an orchestra and investigated how this impacted musicians’ intrapersonal movements coordination. More precisely, first section violinists were asked to turn their back to the conductor and to face the second section of violinists, who still faced the conductor. Motion capture of head and bow kinematics showed that altering the usual interpersonal coupling scheme increased intrapersonal coordination. Our perturbation also induced smaller yet more complex head movements, which spanned multiple, faster timescales that closely matched the metrical levels of the musical score. Importantly, perturbation differentially increased intrapersonal coordination across these timescales. We interpret this behavioral shift as a sensorimotor strategy that exploits periodical movements to effectively tune sensory processing in time and allows coping with the disruption in the interpersonal coupling scheme. As such, head movements, which are usually deemed to fulfill communicative functions, may possibly be adapted to help regulate own performance in time