The existence of a critical length scale in regularised friction

We study a regularisation of Coulomb's friction law on the propagation of local slip at an interface between a deformable and a rigid solid. This regularisation, which was proposed based on experimental observations, smooths the effect of a sudden jump in the contact pressure over a characteristic length scale. We apply it in numerical simulations in order to analyse its influence on the behaviour of local slip. We first show that mesh convergence in dynamic simulations is achieved without any numerical damping in the bulk and draw a convergence map with respect to the characteristic length of the friction regularisation. By varying this length scale on the example of a given slip event, we observe that there is a critical length below which the friction regularisation does not affect anymore the propagation of the interface rupture. A spectral analysis of the regularisation on a periodic variation of Coulomb's friction is conducted to confirm the existence of this critical length. The results indicate that if the characteristic length of the friction regularisation is smaller than the critical length, a slip event behaves as if it was governed by Coulomb's law. We therefore propose that there is a domain of influence of the friction regularisation depending on its characteristic length and on the frequency content of the local slip event. A byproduct of the analysis is related to the existence of a physical length scale characterising a given frictional interface. We establish that the experimental determination of this interface property may be achieved by experimentally monitoring slip pulses whose frequency content is rich enough.Comment: 21 pages, 7 figure

Underground nuclear power plant siting

This study is part of a larger evaluation of the problems associated with siting nuclear power plants in the next few decades. This evaluation is being undertaken by the Environmental Quality Laboratory of the California Institute of Technology in conjunction with The Aerospace Corporation and several other organizations. Current efforts are directed toward novel approaches to siting plants within the State of California. This report contains the results of efforts performed by The Aerospace Corporation to provide input information to the larger evaluation relative to underground siting of large central station nuclear power plants. Projections of electric power demand in California and the country as a whole suggest that a major increase in generating capacity will be required. The problem is complicated beyond that of a large but straightforward extension of capital investment by increased emphasis on environmental factors combined with the early stage of commercial application and regulation of nuclear power sources. Hydroelectric power generation is limited by the availability of suitable sites, and fossil fueled plants are constrained by the availability of high quality fuels and the adverse environmental and/or economic impact from the use of more plentiful fuels. A substantial increase in the number of nuclear power plants is now under way. This source of power is expected to provide the maj or portion of increased capacity. Other power sources such as geothermal and nuclear fusion are unlikely to satisfy the national needs due to technical problems and the lack of a comprehensive development program. There are several problems associated with meeting the projected power demand. Chief among these is the location of acceptable and economic plant sites. Indeed a sufficient number of sites may not be found unless changes occur in the procedures for selecting sites, the criteria for accepting sites, or the type of site required. Placement of a nuclear plant underground has been suggested as an alternative to present siting practices. It is postulated that the advantages of underground siting in some situations may more than compensate for added costs so that such facilities could be preferred even where surface sites are available. By virtue of greater safety, reduced surface area requirements, and improved aesthetics, underground sites might also be found where acceptable surface sites are not available. Four small European reactors have been constructed partially underground but plans for large size commercial plants have not progressed. Consequently, the features of underground power plant siting are not well understood. Gross physical features such as depth of burial, number and size of excavated galleries, equipment layout, and access or exit shafts/tunnels must be specified. Structural design features of the gallery liners, containment structure, foundations, and gallery interconnections must also be identified. Identification of the nuclear, electrical, and support equipment appropriate to underground operation is needed. Operational features must be defined for normal operations, refueling, and construction. Several magazine articles have been published addressing underground concepts. but adequate engineering data is not available to support an evaluation of the underground concept. There also remain several unresolved questions relative to the advantages of underground siting as well as the costs and other possible penalties associated with this novel approach to siting. These include the degree of increased safety through improved containment; the extent and value of isolation from falling objects, e. g. aircraft; the value of isolation from surface storms and tidal waves; the value of protection from vandalism or sabotage; the extent by which siting constraints are relieved through reduced population-distance requirements or aggravated by underground construction requirements; and the value to be placed upon the aesthetic differences of a less visible facility. The study described in this report has been directed toward some of these questions and uncertainties. Within the study an effort has been made to identify viable configurations and structural liners for typical light water reactor nuclear power plants. Three configurations are summarized in Section 3. A discussion of the underground gallery liner design and associated structural analyses is presented in Section 4. Also addressed in the study and discussed in Section 5 are some aspects of containment for underground plants. There it is suggested that the need for large separations between the plant and population centers may be significantly reduced, or perhaps eliminated. Section 6 contains a brief discussion of operational considerations for underground plants. The costs associated with excavation and lining of the underground galleries have been estimated in Section 7. These estimates include an assessment of variations implied by different seismic loading assumptions and differences in geologic media. It is shown that these costs are a small percentage of the total cost of comparable surface plants. Finally, the parameters characterizing an acceptable underground site are discussed in Section 8. Material is also included in the appendices pertaining to foreign underground plants, span limits of underground excavations, potential siting areas for underground plants in the State of California, pertinent data from the Underground Nuclear Test Program, and other supporting technical discussions

Steuer- und Transferpolitik auf dem Weg in die Sackgasse: Eine Analyse der Umverteilungswirkung

Abbildungsverzeichnis Vorbemerkung 1. Finanzpolitik in einer globalisierten Welt 2. Mechanismen und Verteilungseffekte der Steuerpolitik 3. Entwicklungen der Umverteilungseffekte in der Steuer- und Transferpolitik 3.1 Entwicklung in der Umverteilungsleistung der Einkommensteuer 3.2 Entwicklung in der Umverteilungsleistung der Sozialversicherungsbeiträge 3.3 Entwicklung in der Umverteilungsleistung der Mehrwertsteuer 3.4 Entwicklung vermögensbezogener Steuern 3.5 Entwicklung des gesamten Steuermixes 3.6 Entwicklung in der Umverteilungsleistung der Transferprogramme 3.7 Bewertung der Messergebnisse und der Entwicklung des Gesamteffekts 4. Fazit Literaturhinweise Der Auto

Alpine vascular plant species richness: the importance of daily maximum temperature and pH

Species richness in the alpine zone varies dramatically when communities are compared. We explored (i) which stress and disturbance factors were highly correlated with species richness, (ii) whether the intermediate stress hypothesis (ISH) and the intermediate disturbance hypothesis (IDH) can be applied to alpine ecosystems, and (iii) whether standing crop can be used as an easily measurable surrogate for causal factors determining species richness in the alpine zone. Species numbers and standing crop were determined in 14 alpine plant communities in the Swiss Alps. To quantify the stress and disturbance factors in each community, air temperature, relative air humidity, wind speed, global radiation, UV-B radiation, length of the growing season, soil suction, pH, main soil nutrients, waterlogging, soil movement, number of avalanches, level of denudation, winter dieback, herbivory, wind damage, and days with frost were measured or observed. The present study revealed that 82% of the variance in␣vascular species richness among sites could be explained by just two abiotic factors, daily maximum temperature and soil pH. Daily maximum temperature and pH affect species richness both directly and via their effects on other environmental variables. Some stress and disturbance factors were related to species richness in a monotonic way, others in an unimodal way. Monotonic relationships suggest that the harsher the environment is, the fewer species can survive in such habitats. In cases of unimodal relationships (ISH and IDH) species richness decreases at both ends of the gradients due to the harsh environment and/or the interaction of other environmental factors. Competition and disturbance seemed only to play a secondary role in the form of fine-tuning species richness in specific communities. Thus, we concluded that neither the ISH nor the IDH can be considered useful conceptual models for the alpine zone. Furthermore, we found that standing crop can be used as an easily measurable surrogate for causal factors determining species richness in the alpine zone, even though there is no direct causalit

Welding-base metal investigation Final report, 27 Jun. 1964 - 28 Jul. 1965

Weld defects associated with aluminum alloys - monitoring weld shielding gas purit

SUPERPOSED MESOSCOPIC FOLDS IN THE BUENAVISTA ANTICLINE, COLOMBIAN LLANOS FOOTHILLS.

    The structural evolution of the Llanos foothills, Eastern Cordillera of Colombia, involves the reactivation of deep-seated faults, the origin of which has to be sought for in Late Paleozoic and Early Cretaceous rift events. These faults are blind and refer to major, E-vergent anticlines which make up the eastern deformation front of this mountain chain. Their ge-ometry can be simulated using the "tri-shear" model. For our study area we perform a structural analysis at map scale by the contouring of the basement-cover interface and compare observations at outcrop scale. Both scales display N-S and E-W trending folds. E-W trending folds have not been reported so far from the Eastern Cordillera and, discussing their origin, we evoke three hypotheses: 1) a regional N-S contraction; 2) their formation in a relay zone during a sinistral fault reactivation; and 3), local down-slope mass movements on the fanks of a major E-W trending structural high.   Key Words: Blind faults, fault reactivation, superposed folds, oblique contraction, Llanos foothills of Colombia.  La evolución del frente de deformación del piedemonte llanero se caracteriza por la reactivación de fallas corticales cuyo origen se debe a eventos distensivos del Paleozoico Superior y del Cretáceo Inferior. Estas fallas son típicamente ciegas y se asocian a pliegues con una vergencia pronunciada hacia el E. Una posible simulación cinemática para su formación se apoya en el mecanismo de una zona de cizalla triangular ("tri-shear"). Para el área de estudio presentamos un análisis estructural a nivel de mapa por medio de un contorneo de la interfase basamento-cobertera y observaciones relacionadas a los aforamientos. En ambas escalas se evidencian pliegues de dirección N-S y de dirección E-W. Para explicar los plie­gues de dirección E-W discutimos tres hipótesis, una primera evocando un acortamiento N-S regional, otra atribuyendo el acortamiento N-S a una reactivación sinestral de fallas mayores y una ultima basada en movimientos de masa de las unidades lodosas del Cretáceo Inferior.   Palabras clave: Fallas ciegas, reactivación de fallas, pliegues sobrepuestos, contracción oblicua, piedemonte llanero.     &nbsp