942 resultados para Instability criterion


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This paper describes the aggregate rural capital markets of the EU and the main differences between the markets of its member countries. The results of our study suggest that the agricultural credit markets are still quite segmented and the segments are country- rather than currency- or region specific. Financial instability in Europe is also penetrating the agricultural sector and the variation of interest rates for agricultural credit is increasing across countries. Perhaps the most dramatic signal of growing financial instability is that the financial leverage (gearing rate) of European farms rose in 2008 by almost 4 percentage points, from 14 to 18%. The 4 percentage-point annual rise was twice the 2 percentage-point rise observed during the economic recession in the late 1980s and early 1990s. The distribution of the financial leverage of agriculture across countries does not, however, reflect the distribution of country-specific risk premiums in the manner that they are observed in government bond yields. Therefore, in those countries that have the weakest financial situation in the public sector and in which the bond markets are encumbered with high country-specific risk premiums, the agricultural sector is not directly exposed to a very large risk of increasing interest rates, since it is not so highly leveraged. For example in Greek and Spanish agriculture, the financial leverage (gearing) rate is only 0.6% and 2.2% respectively, while the highest gearing rates are found elsewhere (in Denmark), reaching 50%.

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Kazakhstan: Kazakhstan can boast economic development like no other country in Central Asia. In contrast to other countries of the region, which have rich natural resources, Kazakhstan has managed to use its economic potential in a way that yields concrete benefits now and, at the same time, creates prospects for further sustainable economic growth. Tajikistan: Tajikistan in its present state has been built on the civil war experiences and provisions of the peace accords signed in 1997. These have had a great impact on the present form of the state, its political scene and power mechanisms. President Emomali Rakhmonov is the central figure in the state. The political system, which he has cocreated, is based on - unique in this region - political pluralism (the existence of the Islamic party), decentralisation (far-going independence of the regions and relatively limited potential of the central structures) and compromise as the basic way of resolving conflicts. Such a system has so far guaranteed stabilisation and normalisation of the country. Uzbekistan: With its geographic location, potential, ambitions and political priorities, Uzbekistan could play a leading role in Central Asia. The international community has perceived the country as the pillar of stability in the region. This perception was further reinforced after 11th September 2001 and was certainly among the factors that inspired the United States to start closer political and military cooperation with Tashkent. The administration in Washington had expected that closer contacts might galvanise political, economic and social change in Uzbekistan, thus reinforcing positive trends in other countries of the region as well. But the relations between Washington and Tashkent are in crisis (which the United States will certainly try to overcome), and we have seen rapprochement between Uzbekistan and Russia and China.

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The present understanding of the initiation of boudinage and folding structures is based on viscosity contrasts and stress exponents, considering an intrinsically unstable state of the layer. The criterion of localization is believed to be prescribed by geometry-material interactions, which are often encountered in natural structures. An alternative localization phenomenon has been established for ductile materials, in which instability emerges for critical material parameters and loading rates from homogeneous conditions. In this thesis, conditions are sought under which this type of instability prevails and whether localization in geological materials necessarily requires a trigger by geometric imperfections. The relevance of critical deformation conditions, material parameters and the spatial configuration of instabilities are discussed in a geological context. In order to analyze boudinage geometries, a numerical eigenmode analysis is introduced. This method allows determining natural frequencies and wavelengths of a structure and inducing perturbations on these frequencies. In the subsequent coupled thermo-mechanical simulations, using a grain size evolution and end-member flow laws, localization emerges when material softening through grain size sensitive viscous creep sets in. Pinch-and-swell structures evolve along slip lines through a positive feedback between the matrix response and material bifurcations inside the layer, independent from the mesh-discretization length scale. Since boudinage and folding are considered to express the same general instability, both structures should arise independently of the sign of the loading conditions and for identical material parameters. To this end, the link between material to energy instabilities is approached by means of bifurcation analyses of the field equations and finite element simulations of the coupled system of equations. Boudinage and folding structures develop at the same critical energy threshold, where dissipative work by temperature-sensitive creep overcomes the diffusive capacity of the layer. This finding provides basis for a unified theory for strain localization in layered ductile materials. The numerical simulations are compared to natural pinch-and-swell microstructures, tracing the adaption of grain sizes, textures and creep mechanisms in calcite veins. The switch from dislocation to diffusion creep relates to strain-rate weakening, which is induced by dissipated heat from grain size reduction, and marks the onset of continuous necking. The time-dependent sequence uncovers multiple steady states at different time intervals. Microstructurally and mechanically stable conditions are finally expressed in the pinch-and-swell end members. The major outcome of this study is that boudinage and folding can be described as the same coupled energy-mechanical bifurcation, or as one critical energy attractor. This finding allows the derivation of critical deformation conditions and fundamental material parameters directly from localized structures in the field.

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We perform density functional calculations to investigate the structure of the intermetallic alloy FeRh under epitaxial strain. Bulk FeRh exhibits a metamagnetic transition from a low-temperature antiferromagnetic (AFM) phase to a ferromagnetic phase at 350 K, and its strain dependence is of interest for tuning the transition temperature to the room-temperature operating conditions of typical memory devices. We find an unusually strong dependence of the structural energetics on the choice of exchange-correlation functional, with the usual local density approximation yielding the wrong ground-state structure, and generalized gradient (GGA) extensions being in better agreement with the bulk experimental structure. Using the GGA we show the existence of a metastable face-centered-cubic-like AFM structure that is reached from the ground-state body-centered-cubic-like AFM structure by following the epitaxial Bain path. We show that the behavior is well described using nonlinear elasticity theory, which captures the softening and eventual sign change of the orthorhombic shear modulus under compressive strain, consistent with this structural instability. Finally, we predict the existence of an additional unit-cell-doubling lattice instability, which should be observable at low temperature.

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"The project reported herein was performed pursuant to a grant from the U.S. Office of Education, Department of Health, Education and Welfare."

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Texas Department of Transportation, Austin

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National Highway Traffic Safety Administration, Washington, D.C.

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"UILU-ENG 77 1714."

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Report year runs ends June 30.

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"Classification cancelled or changed to UNCLASSIFIED by authority of TIS Change Notice No. 1849 by ASB TISOR, date 8/14/55."

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"Contract AT(30-1)2101."

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pt. 1. Basic studies of rotating stall flow mechanisms.--pt. 2. Investigation of flow-instability sensing devices.

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Mode of access: Internet.