Protein flotation assay to isolate lipid rafts from soft tissue or cells

on-line protocol: Bio-protocol: http://www.bio-protocol.org/wenzhang.aspx?id=854The arrangement in eukaryotic cell membranes of liquid-ordered states surrounded by liquid-disordered phases allows for the existence of organized membrane microdomains called rafts. Rafts play a crusial role in signal-transduction events, in lipid transport and in various internalization processes, and for all these reasons need to be purified for further characterization

A fast method for computing convolutions with structural Green's functions: application to tyre dynamic contact problems

International audienceTyre/road contact is the main source of car noise at speeds greater than 50 km/h. In this context, we have developed a new approach for modelling tyre vibrations and contact with rigid road surfaces during rolling. For tyres, a periodic model is used to compute Green's functions. The response of tyres can, thus, be modelled over a large frequency range. Then, a fast convolution and a new contact model are developed and examples of computations of contact stress are given for real road textures. Spectra of stress for different tyre velocities are also compute

A fast algorithm for computing dynamic tyre road contact forces

International audienceTire/road contact is the principal source of car noise at speeds greater than 50 km/h. In this context, we have developed a new approach for modelling the tire vibrations and the contact with the rigid road surfaces during rolling. For the tire, a periodic model is used to compute Green's functions. The response of the tire can thus be modelled over a large frequency range. Then a fast convolution and contact model is developed and examples of computations of contact forces are given for real road textures. Spectra of forces for different tire velocities are also computed

Dawn- and dusk-phased circadian transcription rhythms coordinate anabolic and catabolic functions in Neurospora

Background: Circadian clocks control rhythmic expression of a large number of genes in coordination with the 24 hour day-night cycle. The mechanisms generating circadian rhythms, their amplitude and circadian phase are dependent on a transcriptional network of immense complexity. Moreover, the contribution of post-transcriptional mechanisms in generating rhythms in RNA abundance is not known. Results: Here, we analyzed the clock-controlled transcriptome of Neurospora crassa together with temporal profiles of elongating RNA polymerase II. Our data indicate that transcription contributes to the rhythmic expression of the vast majority of clock-controlled genes (ccgs) in Neurospora. The ccgs accumulate in two main clusters with peak transcription and expression levels either at dawn or dusk. Dawn-phased genes are predominantly involved in catabolic and dusk-phased genes in anabolic processes, indicating a clock-controlled temporal separation of the physiology of Neurospora. Genes whose expression is strongly dependent on the core circadian activator WCC fall mainly into the dawn-phased cluster while rhythmic genes regulated by the glucose-dependent repressor CSP1 fall predominantly into the dusk-phased cluster. Surprisingly, the number of rhythmic transcripts increases about twofold in the absence of CSP1, indicating that rhythmic expression of many genes is attenuated by the activity of CSP1. Conclusions: The data indicate that the vast majority of transcript rhythms in Neurospora are generated by dawn and dusk specific transcription. Our observations suggest a substantial plasticity of the circadian transcriptome with respect to the number of rhythmic genes as well as amplitude and phase of the expression rhythms and emphasize a major role of the circadian clock in the temporal organization of metabolism and physiology

Une méthode rapide pour calculer un produit de convolution avec une fonction de Green : application au problème de contact dynamique

International audienceDans ce travail, nous proposons une nouvelle démarche pour calculer le produit de convolution de façon rapide et efficace. L'idée est de simplifier la fonction de Green dans le domaine fréquentiel en la décomposant dans une base modale. Les paramètres modaux identifiés sont ensuite utilisés pour construire une convolution rapide. Cette démarche a été adaptée au problème de contact dynamique. Pour illustrer l'efficacité de la méthode, deux exemples sont présentés. Les déplacements et les forces de contact obtenus par cette méthode sont comparés à ceux obtenus à l'aide de la convolution classique

Numerical evaluation of tyre/road contact pressures using a multi-asperity approach

International audienceThe interaction between the tyre and the road surface is responsible for many physical problems such as skid resistance, rolling resistance or noise generation. This paper deals with the numerical study of tyre/road contact. A two-scale iterative method is used for solving the contact problem between a multi-asperity road surface and an elastic half-space. This method has been used successfully for idealized rough surfaces. However, for efficient applications to real surfaces, an appropriate partition of the surfaces is required. A partitioning method is proposed to describe road surfaces using classical image processing and a new load/penetration relation for a single road asperity is introduced. In order to evaluate the efficiency of the method, numerical results for a small sample of road are compared to a classical matrix inversion method, which show at macro-scale a rather good accuracy to predict tyre/road noise. At micro-scale both methods give the same results, but the multi-asperity method is much less time-consuming. Then numerical evaluation of tyre/road static contact pressures for different road textures at full contact area is presented. This approach with new preconditioning can be a reliable and efficient method to simulate contact problems with large surfaces

Vibrational Spectroscopy of Selected Natural Uranyl Vanadates

Raman spectroscopy has been used to study a selection of uranyl vanadate minerals including carnotite, curienite, francevillite, tyuyamunite and metatyuyamunite. The minerals are characterised by an intense band in the 800 to 824 cm-1 region, assigned to the ν1 symmetric stretching vibrations of the (UO2)2+ units. A second intense band is observed in the 965 to 985 cm-1 range and is attributed to the ν1 (VO3) symmetric stretching vibrations in the (V2O8) units. This band is split with a second component observed at around 963 cm-1. A band of very low intensity is observed around 948 cm-1 and is assigned to the ν3 antisymmetric stretching vibrations of the (VO3) units. Bands in the range 608-655 cm-1 may be attributed to molecular water librational modes or the stretching modes ￮(V2O2) units. Bands in the range 573-583 cm-1 may be connected with the ￮ (U-Oequatorial) vibrations or ￮ (V2O2) units. Bands located in the range 467-539 cm-1 may be also attributed to the ￮ (U-Oequatorial) units vibrations. The bending modes of the (VO3) units are observed in the 463 to 480 cm-1 range – there may be some coincidence with ￮ (U-Oequatorial). The bending modes of the (V2O2) in the (V2O8) units are located in a series of bands around 407, 365 and 347 cm-1 (ν2). Two intense bands are observed in the 304 to 312 cm-1 range and 241 to 264 cm-1 range and are assigned to the doubly degenerate ν2 modes of the (UO2)2+ units. The study of the vibrational spectroscopy of uranyl vanadates is complicated by the overlap of bands from the (VO3) and (UO2)2+ units. Raman spectroscopy has proven most useful in assigning bands to these two units since Raman bands are sharp and well separated as compared with infrared bands. The uranyl vanadate minerals are often found as crystals on a host matrix and Raman spectroscopy enables their in-situ characterisation without sample preparation