11,430 research outputs found
Slider-Block Friction Model for Landslides: Application to Vaiont and La Clapiere Landslides
Accelerating displacements preceding some catastrophic landslides have been
found empirically to follow a time-to-failure power law, corresponding to a
finite-time singularity of the velocity [{\it Voight},
1988]. Here, we provide a physical basis for this phenomenological law based on
a slider-block model using a state and velocity dependent friction law
established in the laboratory and used to model earthquake friction. This
physical model accounts for and generalizes Voight's observation: depending on
the ratio of two parameters of the rate and state friction law and on the
initial frictional state of the sliding surfaces characterized by a reduced
parameter , four possible regimes are found. Two regimes can account for
an acceleration of the displacement. We use the slider-block friction model to
analyze quantitatively the displacement and velocity data preceding two
landslides, Vaiont and La Clapi\`ere. The Vaiont landslide was the catastrophic
culmination of an accelerated slope velocity. La Clapi\`ere landslide was
characterized by a peak of slope acceleration that followed decades of ongoing
accelerating displacements, succeeded by a restabilizing phase. Our inversion
of the slider-block model on these data sets shows good fits and suggest to
classify the Vaiont (respectively La Clapi\`ere) landslide as belonging to the
velocity weakening unstable (respectively strengthening stable) sliding regime.Comment: shortened by focusing of the frictional model, Latex document with
AGU style file of 14 pages + 11 figures (1 jpeg photo of figure 6 given
separately) + 1 tabl
A cellular automaton for the factor of safety field in landslides modeling
Landslide inventories show that the statistical distribution of the area of
recorded events is well described by a power law over a range of decades. To
understand these distributions, we consider a cellular automaton to model a
time and position dependent factor of safety. The model is able to reproduce
the complex structure of landslide distribution, as experimentally reported. In
particular, we investigate the role of the rate of change of the system
dynamical variables, induced by an external drive, on landslide modeling and
its implications on hazard assessment. As the rate is increased, the model has
a crossover from a critical regime with power-laws to non power-law behaviors.
We suggest that the detection of patterns of correlated domains in monitored
regions can be crucial to identify the response of the system to perturbations,
i.e., for hazard assessment.Comment: 4 pages, 3 figure
Influence of woven ply degradation on fatigue crack growth in thin notched composites under tensile loading
This paper deals with the fatigue of the through the-thickness crack propagation in thin notched composite laminates made of two glass woven plies. It highlights the different crack growths between warp and weft directions of the woven ply. Experimental results show a decrease of the crack growth rate per cycle with the increase of the crack initiation time. Moreover, it has been shown that it is necessary to take into account the fatigue damage of the woven plies in term of loss of rigidity in the initiation phase. The fatigue crack growth rates are then quantified using Paris law type equations and linear elastic fracture mechanics (LEFM)
Large scale gas injection test (Lasgit) performed at the Äspö Hard Rock Laboratory: summary report 2007
The deposition hole was closed on the 1st February 2005 signifying the start of the hydration
phase. Groundwater inflow through a number of conductive discrete fractures resulted in
elevated porewater pressures leading to the formation of conductive channels (piping), the
extrusion of bentonite from the hole and the discharge of groundwater to the gallery floor. This
problem was addressed by drilling two pressure-relief holes in the surrounding rock mass.
Artificial hydration began on the 18th May 2005 after 106 days of testing. Initial attempts to raise
porewater pressure in the artificial hydration arrays often resulted in the formation of preferential
pathways. These pressure dependent features were not focused in one location but occurred at
multiple sites at different times in the test history. These pathways appear to be relatively short
lived, closing when water pressure is reduced.
It was determined that both pressure relief holes should remain open until the bentonite had
generated sufficient swelling pressure to withstand the high water pressure in the system when
these holes are closed. Packers were installed into the pressure relief holes on 23rd March 2006
and sections in them closed off over the period to 5th July 2006. There was no repeat of the
formation of piping through discrete channels so, on 20th November 2006, pressures to the
artificial hydration filters on the canister were increased to 2350 kPa
Ames life science telescience testbed evaluation
Eight surrogate spaceflight mission specialists participated in a real-time evaluation of remote coaching using the Ames Life Science Telescience Testbed facility. This facility consisted of three remotely located nodes: (1) a prototype Space Station glovebox; (2) a ground control station; and (3) a principal investigator's (PI) work area. The major objective of this project was to evaluate the effectiveness of telescience techniques and hardware to support three realistic remote coaching science procedures: plant seed germinator charging, plant sample acquisition and preservation, and remote plant observation with ground coaching. Each scenario was performed by a subject acting as flight mission specialist, interacting with a payload operations manager and a principal investigator expert. All three groups were physically isolated from each other yet linked by duplex audio and color video communication channels and networked computer workstations. Workload ratings were made by the flight and ground crewpersons immediately after completing their assigned tasks. Time to complete each scientific procedural step was recorded automatically. Two expert observers also made performance ratings and various error assessments. The results are presented and discussed
Institutional paraconsciousness and its pathologies
This analysis extends a recent mathematical treatment of the Baars consciousness model to analogous, but far more complicated, phenomena of institutional cognition. Individual consciousness is limited to a single, tunable, giant component of interacting cognitive modules, instantiating a Global Workspace. Human institutions, by contrast, support several, sometimes many, such giant components simultaneously, although their behavior remains constrained to a topology generated by cultural context and by the path-dependence inherent to organizational history. Such highly parallel multitasking - institutional paraconsciousness - while clearly limiting inattentional blindness and the consequences of failures within individual workspaces, does not eliminate them, and introduces new characteristic dysfunctions involving the distortion of information sent between global workspaces. Consequently, organizations (or machines designed along these principles), while highly efficient at certain kinds of tasks, remain subject to canonical and idiosyncratic failure patterns similar to, but more complicated than, those afflicting individuals. Remediation is complicated by the manner in which pathogenic externalities can write images of themselves on both institutional function and therapeutic intervention, in the context of relentless market selection pressures. The approach is broadly consonant with recent work on collective efficacy, collective consciousness, and distributed cognition
- …