Self-healing slip pulses and the friction of gelatin gels

We present an extensive experimental study and scaling analysis of friction of gelatin gels on glass. At low driving velocities, sliding occurs via propagation of periodic self-healing slip pulses whose velocity is limited by collective diffusion of the gel network. Healing can be attributed to a frictional instability occurring at the slip velocity $v = V_c$. For $v > V_c$, sliding is homogeneous and friction is ruled by the shear-thinning rheology of an interfacial layer of thickness of order the (nanometric) mesh size, containing a semi-dilute solution of polymer chain ends hanging from the network. Inspite of its high degree of confinement, the rheology of this system does not differ qualitatively from known bulk ones. The observed ageing of the static friction threshold reveals the slow increase of adhesive bonding between chain ends and glass. Such structural ageing is compatible with the existence of a velocity-weakening regime at velocities smaller than $V_c$, hence with the existence of the healing instability.Comment: 9 pages, 16 figure

A Model of Perinatal Ischemic Stroke in the Rat: 20 Years Already and What Lessons?

Neonatal hypoxia-ischemia (HI) and ischemia are a common cause of neonatal brain injury resulting in cerebral palsy with subsequent learning disabilities and epilepsy. Recent data suggest a higher incidence of focal ischemia-reperfusion located in the middle cerebral artery (MCA) territory in near-term and newborn babies. Pre-clinical studies in the field of cerebral palsy research used, and still today, the classical HI model in the P7 rat originally described by Rice et al. (1). At the end of the 90s, we designed a new model of focal ischemia in the P7 rat to explore the short and long-term pathophysiology of neonatal arterial ischemic stroke, particularly the phenomenon of reperfusion injury and its sequelae (reported in 1998). Cerebral blood-flow and cell death/damage correlates have been fully characterized. Pharmacologic manipulations have been applied to the model to test therapeutic targets. The model has proven useful for the study of seizure occurrence, a clinical hallmark for neonatal ischemia in babies. Main pre-clinical findings obtained within these 20 last years are discussed associated to clinical pattern of neonatal brain damage

Self healing slip pulses along a gel/glass interface

We present an experimental evidence of self-healing shear cracks at a gel/glass interface. This system exhibits two dynamical regimes depending on the driving velocity : steady sliding at high velocity (> Vc = 100-125 \mu m/s), caracterized by a shear-thinning rheology, and periodic stick-slip dynamics at low velocity. In this last regime, slip occurs by propagation of pulses that restick via a ``healing instability'' occuring when the local sliding velocity reaches the macroscopic transition velocity Vc. At driving velocities close below Vc, the system exhibits complex spatio-temporal behavior.Comment: 4 pages, 6 figure

Maged1, a new regulator of skeletal myogenic differentiation and muscle regeneration

<p>Abstract</p> <p>Background</p> <p>In normal adult skeletal muscle, cell turnover is very slow. However, after an acute lesion or in chronic pathological conditions, such as primary myopathies, muscle stem cells, called satellite cells, are induced to proliferate, then withdraw definitively from the cell cycle and fuse to reconstitute functional myofibers.</p> <p>Results</p> <p>We show that Maged1 is expressed at very low levels in normal adult muscle but is strongly induced after injury, during the early phase of myoblast differentiation. By comparing in vitro differentiation of myoblasts derived from wild-type or Maged1 knockout mice, we observed that Maged1 deficiency results in reduced levels of p21^CIP1/WAF1, defective cell cycle exit and impaired myotube maturation. In vivo, this defect results in delayed regeneration of injured muscle.</p> <p>Conclusions</p> <p>These data demonstrate for the first time that Maged1 is an important factor required for proper skeletal myoblast differentiation and muscle healing.</p

Non-contrast-enhanced MR angiography using time-spin labelling inversion pulse technique for detecting crossing renal vessels in children with symptomatic ureteropelvic junction obstruction: comparison with surgical findings.

OBJECTIVES: Investigate the feasibility and evaluate the accuracy of non-contrast-enhanced MR angiography (NC-MRA) using time-spin labelling inversion pulse (time-SLIP)to identify crossing renal vessels (CRVs) in children requiring surgical treatment of ureteropelvic junction (UPJ) obstructionand compare to laparoscopic findings. MATERIALS AND METHODS: Nineteen children ranging from 6 to 16 years of age underwent NC-MRA using the time-SLIP technique before surgery. Two independent readers analysed the MRA images. Number of renal arteries and presence or absence of CRVs were identified and compared with surgicalfindings. Image quality was assessed, as well as the presence of CRVs and measurement of renal pelvis diameter. Intra and inter-reader agreement was calculated using Cohen's kappa coefficient and Bland-Altman plots. RESULTS: The overall image quality was fair or good in 88% of cases. NC-MRA demonstrated CRVs at the level of the obstruction in 10 children and no CRV in 9 children. All were confirmed intra-operatively except in one of the nine children. Sensitivity, specificity, NPV, PPV for predicting CRVs were 92%, 100%, 100% and 87.5%, respectively, for both readers. CONCLUSION: NC-MRA is a good alternative to contrast-enhanced MRA and CT scanning for identifying CRVs in children with symptomatic UPJ. KEY POINTS: • Time-SLIP technique offers acceptable imaging quality for identifying crossing renal vessel. • Time-SLIP technique is easy to apply to the renal MRA examination. • Time-SLIP technique is an alternative to contrast-enhanced MRA and CT scanning

Local light-activation of the Src oncoprotein in an epithelial monolayer promotes collective extrusion

International audienceTransformed isolated cells are usually extruded from normal epithelia and subsequently eliminated. However, multicellular tumors outcompete healthy cells, highlighting the importance of collective effects. Here, we investigate this situation in vitro by controlling in space and time the activity of the Src oncoprotein within a normal Madin-Darby Canine Kidney (MDCK) epithelial cell monolayer. Using an optogenetics approach with cells expressing a synthetic light-sensitive version of Src (optoSrc), we reversibly trigger the oncogenic activity by exposing monolayers to well-defined light patterns. We show that small populations of activated optoSrc cells embedded in the non-transformed monolayer collectively extrude as a tridimensional aggregate and remain alive, while the surrounding normal cells migrate towards the exposed area. This phenomenon requires an interface between normal and transformed cells and is partially reversible. Traction forces show that Src-activated cells either actively extrude or are pushed out by the surrounding cells in a non-autonomous way

Des pistes pour améliorer les compétences en lecture des élèves

La dernière enquête pancanadienne sur les compétences en lecture des élèves du secondaire dresse un portrait peu flatteur des élèves québécois par comparaison avec leurs pairs de l’Ontario, de l’Alberta ou de la Colombie-Britannique. Profitant de la diffusion de ces résultats accablants, la ministre de l’Éducation, du Loisir et du Sport a annoncé un certain nombre de mesures visant à rectifier le tir en matière d’enseignement de la lecture, répondant ainsi en partie à des revendications portées depuis quelque temps par les instances syndicales. Les mesures annoncées concernent la révision des orientations du programme du préscolaire et du primaire pour les premiers apprentissages, l’ajout d’une épreuve d’évaluation à la fin du deuxième cycle du primaire ainsi qu’un engagement à débloquer des fonds non négligeables pour des recherches relatives à la question de l’acquisition de la compétence en lecture

Spoken Corpora Good Practice Guide 2006

International audienceThere is currently a vast amount of fundamental or applied research, which is based on the exploitation of oral corpora (organized recorded collections of oral and multimodal language productions). Created as a result of linguists becoming aware of the importance to ensure the durability of sources and a diversified access to the oral documents they produce, this Guide to good practice mainly deals with “oral corpora”, created for and used by linguists. But the questions raised by the creation and documentary exploitation of these corpora can be found in numerous disciplines: ethnology, anthropology, sociology, psychology, demography, oral history notably use oral surveys, testimonies, interviews, life stories. Based on a linguistic approach, this Guide also touches on the preoccupations of other researchers who use oral corpora (for example in the field of speech synthesis and recognition), even if their specific needs aren’t consistently dealt with in the present document

Corpus oraux, Guide des bonnes pratiques 2006. Version allemande

International audienceViele Grundlagen- oder angewandte Forschungen beruhen zur Zeit auf der Auswertung von „Korpora der gesprochenen Sprache“ (geordneten Sammelwerken der Aufnahmen von mündlichen und multimodalen sprachlichen Produktionen). Dieses Handbuch der guten Praktiken entsteht aus der Erkenntnis von Sprachwissenschaftlern, die darauf bedacht sind, den Fortbestand der Quellen und einen verschiedenartigen Zugang zu den mündlichen von ihnen produzierten Produktionen zu sichern ; es schneidet zuerst die „Korpora der gesprochenen Sprache“ an, die von Sprachwissenschaftlern und für sie geschaffen und verwendet wurden. Die durch die Erschaffung und die dokumentarische Auswertung dieser Korpora hervorgerufenen Fragen trifft man aber in vielen Fächern : die Völkerkunde, die Anthropologie, die Soziologie, die Psychologie, die Demographie, die mündlich überlieferte Geschichte gebrauchen vor allem die verbale Befragung, die Aussage, das Interview, die Lebensgeschichte. Dieses Handbuch beruft sich auf das Verfahren der Sprachwissenschaftler, es stimmt aber mit den Beschäftigungen anderer Forscher überein, die Korpora der gesprochenen Sprache (z. B. in Sprachsynthese und -entzifferung) gebrauchen, auch wenn ihre spezifischen Bedürfnisse im vorliegenden Dokument nicht systematisch angeschnitten werden