998 resultados para Transition écologique
Resumo:
Nowadays any analysis of Russian economy is incomplete without taking into account the phenomenon of oligarchy. Russian oligarchs appeared after the fall of the Soviet Union and are represented by wealthy businessmen who control a huge part of natural resources enterprises and have a big political influence. Oligarchs’ shares in some natural resources industries reach even 70-80%. Their role in Russian economy is big without any doubts, however there has been very little economic analysis done. The aim of this work is to examine Russian oligarchy on micro and macro levels, its role in Russia’s transition and the possible positive and negative outcomes from this phenomenon. For this purpose the work presents two theoretical models. The first part of this thesis work examines the role of oligarchs on micro level, concentrating on the question whether the oligarchs can be more productive owners than other types of owners. To answer the question this part presents a model based on the article “Are oligarchs productive? Theory and evidence” by Y. Gorodnichenko and Y. Grygorenko. It is followed by empirical test based on the works of S. Guriev and A. Rachinsky. The model predicts oligarchs to invest more in the productivity of their enterprises and have higher returns on capital, therefore be more productive owners. According to the empirical test, oligarchs were found to outperform other types of owners, however it is not defined whether the productivity gains offset losses in tax revenue. The second part of the work concentrates on the role of oligarchy on macro level. More precisely, it examines the assumption that the depression after 1998 crises in Russia was caused by the oligarchs’ behavior. This part presents a theoretical model based on the article “A macroeconomic model of Russian transition: The role of oligarchic property rights” by S. Braguinsky and R. Myerson, where the special type of property rights is introduced. After the 1998 crises oligarchs started to invest all their resources abroad to protect themselves from political risks, which resulted in the long depression phase. The macroeconomic model shows, that better protection of property rights (smaller political risk) or/and higher outside investing could reduce the depression. Taking into account this result, the government policy can change the oligarchs’ behavior to be more beneficial for the Russian economy and make the transition faster.
Resumo:
Following growth doping strategy and using dopant oxides nanocrystals as dopant sources, we report here two different transition-metal ions doped in a variety of group II-VI semiconductor nanocrystals. Using manganese oxide and copper oxide nanocrystals as corresponding dopant sources, intense photoluminescence emission over a wide range of wavelength has been observed for different host nanocrystals. Interestingly, this single doping strategy is successful in providing such highly emissive nanocrystals considered here, in contrast with the literature reports that would suggest synthesis strategies to be highly specific to the particular dopant, host, or both. We investigate and discuss the possible mechanism of the doping process, supporting the migration of dopant ions from dopant oxide nanocrystals to host nanocrystals as the most likely scenario.
Resumo:
The use of appropriate finite elements in different regions of a stressed solid can be expected to be economical in computing its stress response. This concept is exploited here in studying stresses near free edges in laminated coupons. The well known free edge problem of [0/90], symmetric laminate is considered to illustrate the application of the concept. The laminate is modelled as a combination of three distinct regions. Quasi-three-dimensional eight-noded quadrilateral isoparametric elements (Q3D8) are used at and near the free edge of the laminate and two-noded line elements (Q3D2) are used in the region away from the free edge. A transition element (Q3DT) provides a smooth inter-phase zone between the two regions. Significant reduction in the problem size and hence in the computational time and cost have been achieved at almost no loss of accuracy.
Resumo:
A method has been suggested to accurately determine the DBTT of diffusion aluminide bond coats. Micro-tensile testing of free-standing coating samples has been carried out. The DBTT was determined based on the variation of plastic strain-to-fracture with temperature. The positive features of this method over the previously reported techniques are highlighted. (C) 2010 Elsevier B.V. All rights reserved.
Resumo:
Hollow atoms in which the K shell is empty while the outer shells are populated allow studying a variety of important and unusual properties of atoms. The diagram x-ray emission lines of such atoms, the K-h alpha(1,2) hypersatellites (HSs), were measured for the 3d transition metals, Z=23-30, with a high energy resolution using photoexcitation by monochromatized synchrotron radiation. Good agreement with ab initio relativistic multiconfigurational Dirac-Fock calculations was found. The measured HS intensity variation with the excitation energy yields accurate values for the excitation thresholds, excludes contributions from shake-up processes, and indicates domination near threshold of a nonshake process. The Z variation of the HS shifts from the diagram line K alpha(1,2), the K-h alpha(1)-K-h alpha(2) splitting, and the K-h alpha(1)/K-h alpha(2) intensity ratio, derived from the measurements, are also discussed with a particular emphasis on the QED corrections and Breit interaction.
Resumo:
The K-shell diagram (K alpha(1,2) and K beta(1,3)) and hypersatellite (HS) (K-h alpha(1,2)) spectra of Y, Zr, Mo, and Pd have been measured with high energy-resolution using photoexcitation by 90 keV synchrotron radiation. Comparison of the measured and ab initio calculated HS spectra demonstrates the importance of quantum electrodynamical (QED) effects for the HS spectra. Phenomenological fits of the measured spectra by Voigt functions yield accurate values for the shift of the HS from the diagram lines, the splitting of the HS lines, and their intensity ratio. Good agreement with theory was found for all quantities except for the intensity ratio, which is dominated by the intermediacy of the coupling of the angular momenta. The observed deviations imply that our current understanding of the variation of the coupling scheme from LS to jj across the periodic table may require some revision.
Resumo:
The resistivities of zinc borate glasses containing Fe2O3, V2O5, and Fe2O3 + V2O5 have been measured as a function of composition and temperature. The values of resistivity and activation energy decrease as the transition metal oxide content is increased. The conductivities of the glasses containing Fe2O3 + V2O5 are more than the sum of those of the glasses containing only Fe2O3 or V2O5 (i.e. the activation energies are less than the sum of those in the glasses containing only Fe2O3 or V2O5). The results are discussed in terms of existing theories.
Resumo:
X-ray and ultraviolet photoelectron spectroscopy as well as x-ray absorption spectroscopy have been employed to investigate transition metal oxide perovskites of the general formula ABOs (A=La or rare-earth ion, B=trivalent transition metalion). Systematics in the core levels and in the valence bands in the series of LaBOa compounds have been discussed. Lanthanum chemical shifts in the x-ray absorption spectra in this series show interesting trends. Photoelectron spectra of the solid solutions, LaNil_x Coxes, LaNix_x FexO8 and LaFel_x Coxes show that the rigid band model is applicable to these systems. It is shown that x-ray photoelectron spectroscopy can be employed to identify multiple oxidation states of transition metal ions in oxide perovskites.
Resumo:
Boundary-layer transition at different free-stream turbulence levels has been investigated using the particle-image velocimetry technique. The measurements show organized positive and negative fluctuations of the streamwise fluctuating velocity component, which resemble the forward and backward jet-like structures reported in the direct numerical simulation of bypass transition. These fluctuations are associated with unsteady streaky structures. Large inclined high shear-layer regions are also observed and the organized negative fluctuations are found to appear consistently with these inclined shear layers, along with highly inflectional instantaneous streamwise velocity profiles. These inflectional velocity profiles are similar to those in the ribbon-induced boundary-layer transition. An oscillating-inclined shear layer appears to be the turbulent spot-precursor. The measurements also enabled to compare the actual turbulent spot in bypass transition with the simulated one. A proper orthogonal decomposition analysis of the fluctuating velocity field is carried out. The dominant flow structures of the organized positive and negative fluctuations are captured by the first few eigenfunction modes carrying most of the fluctuating energy. The similarity in the dominant eigenfunctions at different Reynolds numbers suggests that the flow prevails its structural identity even in intermittent flows. This analysis also indicates the possibility of the existence of a spatio-temporal symmetry associated with a travelling wave in the flow.
Resumo:
We discuss the results of an extensive mean-field investigation of the half-filled Hubbard model on a triangular lattice at zero temperature. At intermediate U we find a first-order metal-insulator transition from an incommensurate spiral magnetic metal to a semiconducting state with a commensurate linear spin density wave ordering stabilized by the competition between the kinetic energy and the frustrated nature of the magnetic interaction. At large U the ground state is that of a classical triangular antiferromagnet within our approximation. In the incommensurate spiral metallic phase the Fermi surface has parts in which the wave function renormalization Z is extremely small. The evolution of the Fermi surface and the broadening of the quasi-particle band along with the variation of the plasma frequency and a charge stiffness constant with U/t are discussed.
Resumo:
The nature of the chemisorbed states of nitrogen on various transition metal surfaces is discussed comprehensively on the basis of the results of electron spectroscopic investigations augmented by those from other techniques such as LEED and thermal desorption. A brief discussion of the photoemission spectra of free N2, a comparison of adsorbed N2 and CO as well as of physisorption of N2 on metal surfaces is also presented. We discuss the chemisorption of N2 on the surfaces of certain metals (e.g. Ni, Fe, Ru and W) in some detail, paying considerable attention to the effect of electropositive and electronegative surface modifiers. Features of the various chemisorbed states (one or more weakly chemisorbed gamma-states, strongly chemisorbed alpha-states with bond orders between 1 and 2. and dissociative chemisorbed beta-states) on different surfaces are described and relations between them indicated. While the gamma-state could be a precursor of the alpha-state, the alpha-state could be the precursor of the beta-state and this kind of information is of direct relevance to ammonia synthesis. The nature of adsorption of N2 on the surfaces of some metals (e.g. Cr, Co) deserves further study and such investigations might as well suggest alternative catalysts for ammonia synthesis.