Creep motion of a model frictional system

We report on the dynamics of a model frictional system submitted to minute external perturbations. The system consists of a chain of sliders connected through elastic springs that rest on an incline. By introducing cyclic expansions and contractions of the springs we observe a reptation of the chain. We account for the average reptation velocity theoretically. The velocity of small systems exhibits a series of plateaus as a function of the incline angle. Due to elastic e ects, there exists a critical amplitude below which the reptation is expected to cease. However, rather than a full stop of the creep, we observe in numerical simulations a transition between a continuous-creep and an irregular-creep regime when the critical amplitude is approached. The latter transition is reminiscent of the transition between the continuous and the irregular compaction of granular matter submitted to periodic temperature changes

An international prospective general population-based study of respiratory work disability

Background: Previous cross-sectional studies have shown that job change due to breathing problems at the workplace (respiratory work disability) is common among adults of working age. That research indicated that occupational exposure to gases, dust and fumes was associated with job change due to breathing problems, although causal inferences have been tempered by the cross-sectional nature of previously available data. There is a need for general population-based prospective studies to assess the incidence of respiratory work disability and to delineate better the roles of potential predictors of respiratory work disability.Methods: A prospective general population cohort study was performed in 25 centres in 11 European countries and one centre in the USA. A longitudinal analysis was undertaken of the European Community Respiratory Health Survey including all participants employed at any point since the baseline survey, 6659 subjects randomly sampled and 779 subjects comprising all subjects reporting physician-diagnosed asthma. The main outcome measure was new-onset respiratory work disability, defined as a reported job change during follow-up attributed to breathing problems. Exposure to dusts (biological or mineral), gases or fumes during follow-up was recorded using a job-exposure matrix. Cox proportional hazard regression modelling was used to analyse such exposure as a predictor of time until job change due to breathing problems.Results: The incidence rate of respiratory work disability was 1.2/1000 person-years of observation in the random sample (95% CI 1.0 to 1.5) and 5.7/1000 person-years in the asthma cohort (95% CI 4.1 to 7.8). In the random population sample, as well as in the asthma cohort, high occupational exposure to biological dust, mineral dust or gases or fumes predicted increased risk of respiratory work disability. In the random sample, sex was not associated with increased risk of work disability while, in the asthma cohort, female sex was associated with an increased disability risk (hazard ratio 2.8, 95% CI 1.3 to 5.9).Conclusions: Respiratory work disability is common overall. It is associated with workplace exposures that could be controlled through preventive measures

Prélèvement et échantillonnage dans les petits bassins-versants ruraux

Cet article traite de la représentativité des prélèvements d'eau effectués dans le cadre de suivis de bassins versants ou de rivières.Les réflexions proposées sont en premier lieu basées sur des expérimentations de laboratoire et de terrain destinées à comparer divers systèmes et modalités de prélèvements. Les résultats obtenus montrent en particulier que les prélèvements de matières en suspension de dimensions > 100 µm sont peu fiables alors que ce type de particules présente, dans certain cas, une contribution non négligeable aux flux de phosphore total.Les suivis réalisés en divers points représentatifs de petits bassins expérimentaux fournissent des éléments de discussion complémentaires sur le choix des sites des prélèvements et sur les pas de temps de ceux-ci. Nous montrons entre autre, toute l'importance de saisir le début des crues dans les bassins à forte pollution ponctuelle et de considérer des suivis des périodes suffisamment longues pour intégrer les divers fonctionnements hydrochimiques du bassin versant étudié.Water and suspended matter sampling in hydrographic networks is studied through various sampling systems and procedures, and through devices used in fields and in laboratories (fig. 1).Large size particles tend to be underestimated whatever the sampling procedure (manual or automatic) (fig. 2, 3). On the other hand, the sampling for soluble elements and small site particles (less man 50 µm) is very reliable. This is observed in suspended matter concentrations, eg < 2 g.l-1.The largest particles of suspended matter sometimes contribute to nutrient transfer, e.g. phosphorous. This however depends upon the presence of soil microaggregates and nutrient geochemistry. Moreover, natural hydrological variations give rise to another problem for sampling, especially for suspended matter (fig. 7, 9, 10, table 2).Comparatively the variation due to preservation of water is of secondary importance (fig. 11).However, thanks to results from monitoring in experimental watersheds, it is possible to find the best sampling station and the hast time to carry out sampling (fig. 12, 13; fable 3).Duration of survey and intervals between each sample depend, of course, upon the objectives of the study, but also upon watershed characteristics. Considering these characteristics, we propose an example of sampling stategy in the text (table 6, fig. 5)

STM Imaging of Flux Line Arrangements in the Peak Effect Regime

We present the results of a study of vortex arrangements in the peak-effect regime of 2H-NbSe_2 by scanning tunneling microscopy. By slowly increasing the temperature in a constant magnetic field, we observed a sharp transition from collective vortex motion to positional fluctuations of individual vortices at the temperature which coincides with the onset of the peak effect in ac-susceptibility. We conclude that the peak effect is a disorder driven transition, with the pinning energy winning from the elastic energy.Comment: 4 pages, 4 figures included Manuscript has been submitte

Atlas.txt : Exploring Lingusitic Grounding Techniques for Communicating Spatial Information to Blind Users

Peer reviewedPostprin

On the elliptic nonabelian Fourier transform for unipotent representations of p-adic groups

In this paper, we consider the relation between two nonabelian Fourier transforms. The first one is defined in terms of the Langlands-Kazhdan-Lusztig parameters for unipotent elliptic representations of a split p-adic group and the second is defined in terms of the pseudocoefficients of these representations and Lusztig's nonabelian Fourier transform for characters of finite groups of Lie type. We exemplify this relation in the case of the p-adic group of type G_2.Comment: 17 pages; v2: several minor corrections, references added; v3: corrections in the table with unipotent discrete series of G

Experimental observation of nonlinear Thomson scattering

A century ago, J. J. Thomson showed that the scattering of low-intensity light by electrons was a linear process (i.e., the scattered light frequency was identical to that of the incident light) and that light's magnetic field played no role. Today, with the recent invention of ultra-high-peak-power lasers it is now possible to create a sufficient photon density to study Thomson scattering in the relativistic regime. With increasing light intensity, electrons quiver during the scattering process with increasing velocity, approaching the speed of light when the laser intensity approaches 10^18 W/cm^2. In this limit, the effect of light's magnetic field on electron motion should become comparable to that of its electric field, and the electron mass should increase because of the relativistic correction. Consequently, electrons in such high fields are predicted to quiver nonlinearly, moving in figure-eight patterns, rather than in straight lines, and thus to radiate photons at harmonics of the frequency of the incident laser light, with each harmonic having its own unique angular distribution. In this letter, we report the first ever direct experimental confirmation of these predictions, a topic that has previously been referred to as nonlinear Thomson scattering. Extension of these results to coherent relativistic harmonic generation may eventually lead to novel table-top x-ray sources.Comment: including 4 figure

Genome-wide transcription analysis of clinal genetic variation in Drosophila.

Clinal variation in quantitative traits is widespread, but its genetic basis awaits identification. Drosophila melanogaster shows adaptive, clinal variation in traits such as body size along latitudinal gradients on multiple continents. To investigate genome wide transcription differentiation between North and South that might contribute to the clinal phenotypic variation, we compared RNA expression patterns during development of D. melanogaster from tropical northern and temperate southern populations using whole genome tiling arrays. We found that genes that were differentially expressed between the cline ends were generally associated with metabolism and growth, and experimental alteration of expression of a sample of them generally resulted in altered body size in the predicted direction, sometimes significantly so. We further identified the serpent (srp) transcription factor binding sites to be enriched near genes up-regulated in expression in the south. Analysis of clinal populations revealed a significant cline in the expression level of srp. Experimental over-expression of srp increased body size, as predicted from its clinal expression pattern, suggesting that it may be involved in regulating adaptive clinal variation in Drosophila. This study identified a handful of genes that contributed to clinal phenotypic variation through altered gene expression level, yet misexpression of individual gene led to modest body size change

Modified triangular posterior osteosynthesis of unstable sacrum fracture

We report preliminary results for unstable sacral fractures treated with a modified posterior triangular osteosynthesis. Seven patients were admitted to our trauma center with an unstable sacral fracture. The average age was 31years (22-41). There were four vertical shear lesions of the pelvis and three transverse fracture of the upper sacrum. The vertical shear injuries were initially treated with an anterior external fixator inserted at the time of admission. Definitive surgery was performed at a mean time of 9days after trauma. The operation consisted in a posterior fixation combining a vertebropelvic distraction osteosynthesis with pedicle screws and a rod system, whereby the transverse fixation was obtained using a 6mm rod as a cross-link between the two main rods. Late displacement of the posterior pelvis or fracture was measured on X-ray films according to the criteria of Henderson. The patients were followed-up for a minimum time of 12months. Four patients who presented with a pre-operative perineal neurological impairment made a complete recovery. No iatrogenic nerve injury was reported. One case of deep infection was managed successfully with surgical debridement and local antibiotics. All patients complained of symptoms related to the prominence of the iliac screws. The metalwork was removed in all cases after healing of the fracture, at a mean time of 4.3months after surgery. No loss of reduction of fracture was seen at final radiological follow-up. The preliminary results are promising. The fixation is sufficiently stable to allow an immediate progressive weight-bearing, and safe nursing care in polytrauma cases. The only problem seems to be related to prominent heads of the distal screw