Individual and collective behavior of dust particles in a protoplanetary nebula

We study the interaction between gas and dust particles in a protoplanetary disk, comparing analytical and numerical results. We first calculate analytically the trajectories of individual particles undergoing gas drag in the disk, in the asymptotic cases of very small particles (Epstein regime) and very large particles (Stokes regime). Using a Boltzmann averaging method, we then infer their collective behavior. We compare the results of this analytical formulation against numerical computations of a large number of particles. Using successive moments of the Boltzmann equation, we derive the equivalent fluid equations for the average motion of the particles; these are intrinsically different in the Epstein and Stokes regimes. We are also able to study analytically the temporal evolution of a collection of particles with a given initial size-distribution provided collisions are ignored.Comment: 15 pages, 9 figures, submitted to Ap

Treatment of old disused mine openings

International audienceAccording to French regulations, the main objectives for the treatment of old abandoned mines consist of : preventing collapses and dangerous subsidence, controlling mine gas emissions and closing old abandoned mine openings. In the Herault coal basin, underground exploitation started very early, in particular by the way of shallow adits dug in hillsides. Today more than 600 adits have been listed on old maps but a lot of them have not yet been precisely located. Charbonnages de France and INERIS have analyzed all risks generated by these old openings and have established a methodology able to determine the closure procedure which can guarantee the safety of the opening. This methodology can be adapted to an adit (size, state of...) and to the physical characteristics of the site (gas, water, location...). In order to limit the number of configurations, two of the above factors have been retained : the state and the location of the gallery. After analyzing all the possible configurations, closure principles have been determined for each of them. The paper : discusses geographical and historical background of the Herault basin exploitation, list the specific parameters which influence the choice of process able to secure the adits, present the general methodology used. Finally, the treatment of an adit located under inhabited areas is presented

Temporal Coordination of Hippocampal Neurons Reflects Cognitive Outcome Post-febrile Status Epilepticus

AbstractThe coordination of dynamic neural activity within and between neural networks is believed to underlie normal cognitive processes. Conversely, cognitive deficits that occur following neurological insults may result from network discoordination. We hypothesized that cognitive outcome following febrile status epilepticus (FSE) depends on network efficacy within and between fields CA1 and CA3 to dynamically organize cell activity by theta phase. Control and FSE rats were trained to forage or perform an active avoidance spatial task. FSE rats were sorted by those that were able to reach task criterion (FSE-L) and those that could not (FSE-NL). FSE-NL CA1 place cells did not exhibit phase preference in either context and exhibited poor cross-theta interaction between CA1 and CA3. FSE-L and control CA1 place cells exhibited phase preference at peak theta that shifted during active avoidance to the same static phase preference observed in CA3. Temporal coordination of neuronal activity by theta phase may therefore explain variability in cognitive outcome following neurological insults in early development

MAX: Development of a Laue diffraction lens for nuclear astrophysics

The next generation of instrumentation for nuclear astrophysics will have to achieve an improvement in sensitivity by a factor of 10-100 over present technologies. With the focusing gamma-ray telescope MAX we take up this challenge and propose to combine the required sensitivity with high spectral and angular resolution, and the capability to measure the polarization of the photons. MAX is a space-borne crystal diffraction telescope, featuring a broad-band Laue lens optimized for the observation of compact sources in two wide energy bands of high astrophysical relevance. Gamma rays will be focused from the large collecting area of a crystal diffraction lens onto a very small detector volume. As a consequence, the signal to background ratio is greatly enhanced, leading to unprecedented sensitivities

Ascaroside Expression in Caenorhabditis elegans Is Strongly Dependent on Diet and Developmental Stage

Background: The ascarosides form a family of small molecules that have been isolated from cultures of the nematode Caenorhabditis elegans. They are often referred to as “dauer pheromones” because most of them induce formation of long-lived and highly stress resistant dauer larvae. More recent studies have shown that ascarosides serve additional functions as social signals and mating pheromones. Thus, ascarosides have multiple functions. Until now, it has been generally assumed that ascarosides are constitutively expressed during nematode development. Methodology/Principal Findings: Cultures of C. elegans were developmentally synchronized on controlled diets. Ascarosides released into the media, as well as stored internally, were quantified by LC/MS. We found that ascaroside biosynthesis and release were strongly dependent on developmental stage and diet. The male attracting pheromone was verified to be a blend of at least four ascarosides, and peak production of the two most potent mating pheromone components, ascr#3 and asc#8 immediately preceded or coincided with the temporal window for mating. The concentration of ascr#2 increased under starvation conditions and peaked during dauer formation, strongly supporting ascr#2 as the main population density signal (dauer pheromone). After dauer formation, ascaroside production largely ceased and dauer larvae did not release any ascarosides. These findings show that both total ascaroside production and the relative proportions of individual ascarosides strongly correlate with these compounds' stage-specific biological functions. Conclusions/Significance: Ascaroside expression changes with development and environmental conditions. This is consistent with multiple functions of these signaling molecules. Knowledge of such differential regulation will make it possible to associate ascaroside production to gene expression profiles (transcript, protein or enzyme activity) and help to determine genetic pathways that control ascaroside biosynthesis. In conjunction with findings from previous studies, our results show that the pheromone system of C. elegans mimics that of insects in many ways, suggesting that pheromone signaling in C. elegans may exhibit functional homology also at the sensory level. In addition, our results provide a strong foundation for future behavioral modeling studies