Nucleation of Slip-Weakening Rupture Instability in Landslides by Localized Increase of Pore Pressure

We model landslide initiation as slip surface growth driven by local elevated pore pressure, with particular reference to submarine slides. Assuming an elastic medium and friction that weakens with slip, solutions exist in which the slip surface may dynamically grow, without further pore pressure increases, at a rate of the order of the sediment shear wave speed, a situation comparable to earthquake nucleation. The size of the rupture at this transition point depends weakly on the imposed pore pressure pro file; however, the amount of slip at the transition depends strongly on whether the pore pressure was broadly or sharply elevated. Sharper profiles may result in pore pressures reaching the total slope-normal stress before dynamic rupture is nucleated. While we do not account for modes of failure other than pure slip on a failure surface, this may be an indication that additional modes involving liquefaction or hydraulic cracking may be factors in the initiation of shallow slope failure. We identify two lengthscales, one geometrical (h, depth below the free surface) and one material (l, determined by the frictional weakening rate) and a transition in nucleation behavior between effectively "deep" and "shallow" limits dependent on their ratio. Whether dynamic propagation of failure is indefinite or arresting depends largely on whether the background shear stress is closer to nominal peak or residual frictional strength. This is determined in part by background pore pressures, and to consider the submarine case we simplify a common sedimentation/consolidation approach to reflect interest in near-seafloor conditions.Earth and Planetary SciencesEngineering and Applied Science

Transfer Student-Athletes: Prominent but Vulnerable

Transfer students play a prominent role in Division I athletics, but the effects of transferring can often be detrimental to their academic performance. Providing a formal orientation course especially designed for new transfer student-athletes can be an effective means of helping them bridge the intercollegiate experience. This gives an example transfer orientation program from Oregon State University

Off-Fault Plasticity and Earthquake Rupture Dynamics: 2. Effects of Fluid Saturation

We present an analysis of inelastic off-fault response in fluid-saturated material during earthquake shear rupture. The analysis is conducted for 2-D plane strain deformation using an explicit dynamic finite element formulation. Along the fault, linear slip-weakening behavior is specified, and the off-fault material is described using an elastic-plastic description of the Drucker-Prager form, which characterizes the brittle behavior of rocks under compressive stress when the primary mode of inelastic deformation is frictional sliding of fissure surfaces, microcracking and granular flow. In this part (part 1), pore pressure changes were neglected in materials bordering the fault. In part 2, we more fully address the effects of fluid saturation. During the rapid stressing by a propagating rupture, the associated undrained response of the surrounding fluid-saturated material may be either strengthened or weakened against inelastic deformation. We consider poroelastoplastic materials with and without plastic dilation. During nondilatant undrained response near a propagating rupture, large increases in pore pressure on the compressional side of the fault decrease the effective normal stress and weaken the material, and decreases in pore pressure on the extensional side strengthen the material. Positive plastic dilatancy reduces pore pressure, universally strengthening the material. Dilatantly strengthened undrained deformation has a diffusive instability on a long enough timescale when the underlying drained deformation is unstable. Neglecting this instability on the short timescale of plastic straining, we show that undrained deformation is notably more resistant to shear localization than predicted by neglect of pore pressure changes.Earth and Planetary SciencesEngineering and Applied Science

The Contribution of Household and Small Manufacturing Establishments to Indonesian Economic Development 1986-2000

Household and small manufacturing industries (HMIs and SMIs) are very important especially in terms of employment generation in the densely populated areas of Indonesia like Java. This is because in 1996 they accounted for 44% and 17% of manufacturing industry employment respectively, but only 6% and 5% of manufacturing industry value-added. They were even more important in rural areas because 95% and 59% of HMI and SMI employees were in rural areas and 92% and 44% of their value-added. Many of the establishments in rural areas processed imported raw materials instead of locally produced materials. The rates of growth of household and small manufacturing industries real value-added were high from 1986 to 1996 in spite of unfavourable government policies, 7.2% and 12.3% per annum, but lower than medium/large establishments at 16.4%. HMS and SMIs were hit hard by the economic crisis of 1997, especially those selling fully or partially non-tradeable goods using fully tradable inputs, although they recovered quite quickly. There is a good potential for firther development of HMIs and SMIs that can be facilitated by the expansion and improvement of financial institutions and supplies of privately delivered business services, and improved foreign direct investment and marketing, micro-establishment retailing, and local government economic policies

The fracture energy of ruptures driven by flash heating

We present a model for dynamic weakening of faults based on local flash heating at microscopic asperity contacts coupled to bulk heating at macroscopic scale. We estimate the fracture energy G associated with that rheology and find that for constant slip rate histories G scales with slip δ as math formula at small slip, while math formula at large slip. This prediction is quantitatively consistent with data from laboratory experiments conducted on dry rocks at constant slip rate. We also estimate G for crack-like ruptures propagating at constant speed and find that math formula in the large slip limit. Quantitative estimates of G in that regime tend to be several orders of magnitude lower than seismologically inferred values of G. We conclude that while flash heating provides a consistent explanation for the observed dynamic weakening in laboratory experiments with kinematically imposed slip, its contribution to the energy dissipation during earthquakes becomes negligible for large events when considering the elastodynamic coupling between strength and slip evolution

Nuclear safety policy working group recommendations on nuclear propulsion safety for the space exploration initiative

An interagency Nuclear Safety Working Group (NSPWG) was chartered to recommend nuclear safety policy, requirements, and guidelines for the Space Exploration Initiative (SEI) nuclear propulsion program. These recommendations, which are contained in this report, should facilitate the implementation of mission planning and conceptual design studies. The NSPWG has recommended a top-level policy to provide the guiding principles for the development and implementation of the SEI nuclear propulsion safety program. In addition, the NSPWG has reviewed safety issues for nuclear propulsion and recommended top-level safety requirements and guidelines to address these issues. These recommendations should be useful for the development of the program's top-level requirements for safety functions (referred to as Safety Functional Requirements). The safety requirements and guidelines address the following topics: reactor start-up, inadvertent criticality, radiological release and exposure, disposal, entry, safeguards, risk/reliability, operational safety, ground testing, and other considerations

Simulating Humans as Integral Parts of Spacecraft Missions

The Collaborative-Virtual Environment Simulation Tool (C-VEST) software was developed for use in a NASA project entitled "3-D Interactive Digital Virtual Human." The project is oriented toward the use of a comprehensive suite of advanced software tools in computational simulations for the purposes of human-centered design of spacecraft missions and of the spacecraft, space suits, and other equipment to be used on the missions. The C-VEST software affords an unprecedented suite of capabilities for three-dimensional virtual-environment simulations with plug-in interfaces for physiological data, haptic interfaces, plug-and-play software, realtime control, and/or playback control. Mathematical models of the mechanics of the human body and of the aforementioned equipment are implemented in software and integrated to simulate forces exerted on and by astronauts as they work. The computational results can then support the iterative processes of design, building, and testing in applied systems engineering and integration. The results of the simulations provide guidance for devising measures to counteract effects of microgravity on the human body and for the rapid development of virtual (that is, simulated) prototypes of advanced space suits, cockpits, and robots to enhance the productivity, comfort, and safety of astronauts. The unique ability to implement human-in-the-loop immersion also makes the C-VEST software potentially valuable for use in commercial and academic settings beyond the original space-mission setting