Design of a geodetic database and associated tools for monitoring rock-slope movements: the example of the top of Randa rockfall scar

International audienceThe need for monitoring slope movements increases with the increasing need for new areas to inhabit and new land management requirements. Rock-slope monitoring implies the use of a database, but also the use of other tools to facilitate the analysis of movements. The experience and the philosophy of monitoring the top of the Randa rockfall scar which is sliding down into the valley near Randa village in Switzerland are presented. The database includes data correction tools, display facilities and information about benchmarks. Tools for analysing the movement acceleration and spatial changes and forecasting movement are also presented. Using the database and its tools it was possible to discriminate errors from critical slope movement. This demonstrates the efficiency of these tools in monitoring the Randa scar

Kinematics of the 1991 Randa rockslides (Valais, Switzerland)

International audienceAbout 22 mio m3 of rock fell from a cliff near the village of Randa (10 km north of Zermatt, Switzerland) on 18 April 1991. A second retrogressive rockslide of about 7 mio m3 followed on 9 May 1991. At present, a rock mass situated above the scarp is still slowly moving toward the valley, involving several mio m 3 of rock. A kinematic approach to study of this well-documented rockslide was made "a posteriori" in order to identify the parameters relevant to the detection of such failures involving large volumes of rock. A 3-D model of the pre-rockslide geometry is presented, and is used to interpret the geostructural, hydrogeological, and chronological data. The steepness of the cliff, the massive lithology (mainly orthogneiss), the location on a topographic ridge outcropping at the confluence between a glacial cirque and the main valley, and the existence of previous events of instability were the preexisting field conditions that affected the stability of the area. The structural cause of instability was a 30 dipping, more than 500-m-long, persistent fault, which cut the base of the rock face. Together with a steeply dipping set of persistent joints, this basal discontinuity delimited a 20- mio-m 3 rock block, with a potential sliding direction approximately parallel to the axis of the valley. To the North, the fractures delimiting the unstable mass were less persistent and separated by rock bridges; this rock volume acted as key block. This topographic and structural configuration was freed from glacier support about 15 000 years BP. The various mechanisms of degradation that led to the final loss of equilibrium required various amounts of time. During the late-and post-glacial periods, seismic activity and weathering of the orthogneiss along the fissure network due to infiltration of meteoric water, joined to reduce the mechanical resistance of the sliding surfaces and the rocks bridges. In addition, crystallisation of clay minerals due to mineralogical alteration of the fault gouge accumulated along the sliding surface, reducing its angle of internal friction, and sealing the surface against water circulation. Once this basal fracture began to act as an aquiclude, the seasonal increase of the hydraulic head in the fissures promoted hydraulic fracturing on the highly stressed edges of the key block. Acceleration of this mechanical degradation occurred during the 20-year period before the 1991 rockslides, giving rise to an increasing rockfall activity, that constituted a forewarning sign. The final triggering event corresponded to a snow-melt period with high water table, leading to fracturation around the key block. On 18 April 1991, the key block finally failed, allowing subsidiary orthogneiss blocks to slide. They fell in turn over a period of several hours. The 9 May 1991, rockslide was the first of a series of expected future retrogressive reequilibrium stages of the very fractured and decompressed paragneisses, which lie on the orthogneiss base cut by the 18 April event

Role of capsid sequence and immature nucleocapsid proteins p9 and p15 in Human Immunodeficiency Virus type 1 genomic RNA dimerization

AbstractHIV-1 genomic RNA (gRNA) dimerization is important for viral infectivity and is regulated by proteolytic processing of the Gag precursor protein (Pr55gag) under the direction of the viral protease. The processing occurs in successive steps and, to date, the step associated with formation of a wild-type (WT) level of gRNA dimers has not been identified. The primary cleavage divides Pr55gag into two proteins. The C-terminal polypeptide is termed NCp15 (NCp7–p1–p6) because it contains the nucleocapsid protein (NC), a key determinant of gRNA dimerization and packaging. To examine the importance of precursor polypeptides NCp15 and NCp9 (NCp7–p1), we introduced mutations that prevented the proteolytic cleavages responsible for the appearance of NCp9 or NCp7. Using native Northern blot analysis, we show that gRNA dimerization was impaired when both the secondary (p1–p6) and tertiary (p7–p1) cleavage sites of NCp15 were abolished, but unaffected when only one or the other site was abolished. Though processing to NCp9 therefore suffices for a WT level of gRNA dimerization, we also show that preventing cleavage at the p7–p1 site abolished HIV-1 replication. To identify the minimum level of protease activity compatible with a WT level of gRNA dimers, we introduced mutations Thr26Ser and Ala28Ser in the viral protease to partially inactivate it, and we prepared composite HIV-1 resulting from the cotransfection of various ratios of WT and protease-inactive proviral DNAs. The results reveal that a 30% processing of Pr55gag into mature capsid proteins (CA/CA-p2) yielded a WT level of gRNA dimers, while a 10% Pr55gag processing hardly increased gRNA dimerization above the level seen in protease-inactive virions. We found that full gRNA dimerization required less than 50% WT NC in complementation asssays. Finally, we show that if we destroy alpha helix 1 of the capsid protein (CA), gRNA dimerization is impaired to the same extent as when the viral protease is inactivated. Cotransfection studies show that this CA mutation, in contrast to the NC-disabling mutations, has a dominant negative effect on HIV-1 RNA dimerization, viral core formation, and viral replication. This represents the first evidence that a capsid mutation can affect HIV-1 RNA dimerization

The projection from auditory cortex to cochlear nucleus in guinea pigs: an in vivo anatomical and in vitro electrophysiological study

Previous anatomical experiments have demonstrated the existence of a direct, bilateral projection from the auditory cortex (AC) to the cochlear nucleus (CN). However, the precise relationship between the origin of the projection in the AC and the distribution of axon terminals in the CN is not known. Moreover, the influence of this projection on CN principal cells has not been studied before. The aim of the present study was two-fold. First, to extend the anatomical data by tracing anterogradely the distribution of cortical axons in the CN by means of restricted injections of biotinylated dextran amine (BDA) in physiologically characterized sites in the AC. Second, in an in vitro isolated whole brain preparation (IWB), to assess the effect of electrical stimulation of the AC on CN principal cells from which intracellular recordings were derived. BDA injections in the tonotopically organized primary auditory cortex and dorsocaudal auditory field at high and low best frequency (BF) sites resulted in a consistent axonal labeling in the ipsilateral CN of all injected animals. In addition, fewer labeled terminals were observed in the contralateral CN, but only in the animals subjected to injections in low BF region. The axon terminal fields consisting of boutons en passant or terminaux were found in the superficial granule cell layer and, to a smaller extent, in the three CN subdivisions. No axonal labeling was seen in the CN as result of BDA injection in the secondary auditory area (dorsocaudal belt). In the IWB, the effects of ipsilateral AC stimulation were tested in a population of 52 intracellulary recorded and stained CN principal neurons, distributed in the three CN subdivisions. Stimulation of the AC evoked slow late excitatory postsynaptic potentials (EPSPs) in only two cells located in the dorsal CN. The EPSPs were induced in a giant and a pyramidal cell at latencies of 20ms and 33ms, respectively, suggesting involvement of polysynaptic circuits. These findings are consistent with anatomical data showing sparse projections from the AC to the CN and indicate a limited modulatory action of the AC on CN principal cell

Faciliter le déplacement des aveugles avec une carte numérique et une interface vocale

Le récepteur GPS permet à la personne de se localiser sous certaines conditions de visibilité des satellites et de réception de leurs signaux. Lorsque ces conditions ne sont pas remplies, il est nécessaire d'utiliser d'autres capteurs pour saisir le déplacement de la personne et son orientation. Ce mécanisme est appelé navigation à l'estime (Dead Reckoning)