dissertation com mai 2010 (3 résultats)

Taschenbuch. Etat : Neu. Neuware - The focus of this thesis is the study of the electronic and magnetic structure of three representative members of Fe-bearing rock-forming silicates, viz. orthoferrosilite (Fe2+2Si2O6), almandine (Fe2+3Al2(SiO4)3) and andradite (Ca3Fe3+2(SiO4)3). These minerals have attracted significant attention due to their abundance in the Earth's crust and mantle, and because crystallised silicates are main components of cosmic dust which is the most abundant raw material in the Universe. For this purpose quantum mechanical first principles electronic structure calculations are performed by the most efficient DFT method in the local spin-density approximation for calculating spectroscopic data: the spin-polarized self consistent charge Xa method.The specific feature and strength of these investigations consist in the theoretical characterization of these complex systems based on experimental results. This means that, on one hand, experimental spectroscopic and crystallographic data are being used to judge the reliability of the calculations, whereas, on the other hand, experimental data are interpreted and explained by the theoretical results.This work comprises seven chapters. After a brief introduction (Chapter 1) Chapter 2 describes the theoretical bases, ideas, approximations and advantages of the SCC- Xa method and basics of the art of cluster construction. Chapter 3 considers physical bases of crystal field theory, absorption, Mossbauer spectroscopy and magnetic interactions, as well as the calculation of spectroscopic data within the frame of the SCC-Xa method. In addition, tetragonally, trigonally and angularly distorted octahedral sites with various degrees of the distortions are calculated and analyzed. The electronic and magnetic structures of orthoferrosilite, almandine and andradite are described in the following chapters. In the case of orthoferrosilite the magnetic interactions between the iron spins within the ribbons and between neighboring ribbons are characterized. Two identical interpenetrating magnetic sublattices of circles of 10 edge-shared dodecahedra are revealed and characterized in almandine. The calculated spin structure explains and solves the controversy in the interpretation of the Mossbauer spectra of almandine below the Neel temperature. For andradite a model of the magnetic structure is proposed based on geometrical considerations and the calculated spin coupling constants for the various interaction pathways. According to this model, the magnetic structure of andradite consists of two frustrated equivalent magnetic sublattices. The spins of the Fe ions within each sublattice are coupled antiferromagnetically. The derived spin pattern explains two sextets in the Mossbauer spectra of andradite below the Neel temperature. Finally, the main results are summarized in Chapter 7.

Taschenbuch. Etat : Neu. Neuware - This study examines the socioeconomic and environmental implications of the new camu camu industry in Peru. Camu camu (Myrciaria dubia) is a small tree native to wetlands of the Amazon basin. It is especially abundant in Peruvian Amazonia. The high vitamin-C content of the fruit has generated interest in exporting camu camu products from Amazonia to more-developed countries. The government of Peru has been actively promoting this new extractive industry, as well as the planting of camu camu in rural areas. Non-governmental development organizations and private industry are now actively involved with camu camu projects and enterprises. In Peru, enthusiasm for this native species is high, because camu camu is expected to provide a much-needed and sustainable economic boost for the region. However, many questions about the environmental implications and socioeconomic impacts of the camu camu export industry need to be answered in order to understand its ecological and economic viability, and its effects on business and in rural communities.Findings indicate that camu camu has provided significantly more income to rural residents than is provided by the traditional boom and bust economies of Amazonia. Households who adopted camu camu as a new crop in their floodplain agroforestry systems farmed significantly more floodplain land than non-adopters, and were especially adept at experimenting with new innovations. Lack of agricultural credit is a major constraint to adopting camu camu as a new crop in Peru. Geographic isolation and the location of processing facilities in relation to fruit harvests present major obstacles to the economic viability of the new industry. Camu camu was found to be cultivated with a higher diversity of annual crops than is typical in floodplain fields of the region. Extraction of camu camu fruits from the wild does not appear to have a negative environmental impact, at least in the initial years of the industry. This non-timber forest product in the process of domestication can support a viable industry in the Peruvian Amazon, if agricultural extension methods and marketing channels are improved.

Taschenbuch. Etat : Neu. Neuware - A significant volume of literature has been developed that seeks to provide an explanation for the growth of FDI and its impact on less developed countries. The literature is characterized by diversity and controversy. Based on it, a range of reasons for encouraging investment have been proposed including its favorable effects on employment levels, the balance of payments and balance of trade of the host country and also the potential for acquisition of technology and skills (Cave: 1982 and Dunning: 1993). Equally, the potentially negative effects of growing levels of foreign investment on domestic market structures and national sovereignty have long been the focus of attention (Vernon: 1971 and Jenkins: 1987). More recent studies focused on the positive effect FDI can create through the integration of a host country into the global economy and the system of international division of labor based on fragmentation of production (Gereffi and Korzeniewicz: 1994, and Henderson, Decken, Hess, Coe and Yeung: 2002).Little if any research has examined the impact of FDI on the oil monarchies. Conventional expectations persisted that once they enter the post-oil phase of their histories, it will be difficult for them to uphold their political legitimacy and survive intense domestic and international pressures upon their regimes (Taeker: 1998 and O'Reilly: 1999). It has been argued that oil income enable them to pacify opponents by providing their subjects with jobs that pay well and has had detrimental effect on both economic development and political liberalization. These expectations have tended to be contradicted by actual development. The private sector has become remarkably strong in the oil monarchies and their governments were not highly resistant to change as depicted by the rentier state paradigm (Mahdavy: 1970, and Beblawi: 1987). Taking Bahrain as a case study, this thesis argues that despite its limitations as a small nation and the paucity of its oil reserves, Bahrain punched well above its weight due to its open economy and foreign direct investment. Its domestic economy is well integrated into the global market. It was able to exploit some of the opportunities that were presented by economic globalization when niches were opened or vacated within the networks of global production. It has developed energy-intensive industries (aluminium and petrochemicals) and became the major financial centre of the Middle East. Yet in spite of the government incentives, it still faces some challenges in attracting FDI in downstream activities related to oil and aluminium, which suggests that additional reforms are needed.