Dissertation com jun 2005 (4 Ergebnisse)

Taschenbuch. Zustand: Neu. Neuware - Young stars are surrounded by massive, rotating disks of dust and gas, which supply a reservoir of material that may be incorporated into planets or accreted onto the central star. In this dissertation, I use high angular resolution observations at a range of wavelengths to understand the structure, ubiquity, and evolutionary timescales of protoplanetary disks.First, I describe a study of Class I protostars, objects believed to be at an evolutionary stage between collapsing spherical clouds and fully-assembled young stars surrounded by protoplanetary disks. I use a Monte Carlo radiative transfer code to model new 0.9 micron scattered light images, 1.3 mm continuum images, and broadband spectral energy distributions. This modeling shows that Class I sources are probably surrounded by massive protoplanetary disks embedded in massive infalling envelopes. For the best-fitting models of the circumstellar dust distributions, I determine several important properties, including envelope and disk masses, mass infall rates, and system inclinations, and I use these results to constrain the evolutionary stage of these objects.Second, I discuss observations of the innermost regions of more evolved disks around T Tauri and Herbig Ae/Be stars, obtained with the Palomar Testbed and Keck Interferometers. I constrain the spatial and temperature structure of the circumstellar material at sub-AU radii, and demonstrate that lower-mass stars are surrounded by inclined disks with puffed-up inner edges 0.1-1 AU from the star. In contrast, the truncated inner disks around more massive stars may not puff-up, indicating that disk structure depends on stellar properties. I discuss the implications of these results for disk accretion, terrestrial planet formation and giant planet migration.Finally, I put these detailed studies of disk structure into a broader context by constraining the mass distribution and evolutionary timescales of circumstellar disks. Using the Owens Valley Millimeter Array, I mapped the millimeter continuum emission toward >300 low-mass stars in the NGC 2024 and Orion Nebula clusters. These observations demonstrate that the average disk mass in each cluster is comparable to the 'minimum-mass protosolar nebula,' and that there may be disk evolution on one million year timescales.…

Taschenbuch. Zustand: Neu. Neuware - Although the significance of '9/11' is subject to debate, it is symbolic of a general sentiment of discontinuity whereby society is vulnerable to undefined and highly disruptive events. Recent catalysts of this sentiment are eye-catching developments such as the SARS (Severe Acute Respiratory Syndrome) and bird flu outbreaks, the Enron and Parmalat scandals, political assassinations in Sweden and the Netherlands, regime changes in Iraq and Afghanistan, and terrorist attacks in Bali, Istanbul, Madrid, and various parts of the Middle East.However, recent discontinuities should not be seen as evidence that discontinuities occur more frequently now than they did before. Looking back in history we see that disruptive processes are common. For example, 25 years ago few Europeans would have predicted the upcoming upheavals on their own continent: the collapse of communism, Berlin as the capital of a reunited Germany, the wars in the former Yugoslavia, the single European currency, and the near doubling of the number of European Union member states. Changes elsewhere have been no less discontinuous and unforeseen: the fall of the Asian tigers, the emergence of the Internet and mobile telecommunication, and the presidency of Nelson Mandela.Societal discontinuity is a relatively new area of concern in policy development. Since the 1970s the consideration of change and discontinuity has gained some ground over predictive forecasting, which tended to reason from continuous developments and linear processes. Rather than making forecasting the future, it has become popular to use scenarios as a manner to consider several possible futures.Scenarios are coherent descriptions of alternative hypothetical futures that reflect different perspectives on past, present, and future developments, which can serve as a basis for action. Scenario development aims to combine analytical knowledge with creative thinking in an effort to capture a wide range of possible future developments in a limited number of outlooks. Scenario development assumes that the future is uncertain and the directions in which current developments might range from the conventional to the revolutionary.In theory, scenario development is a way to consider future discontinuity. However, there are indications that the theoretical promise is not reflected in scenario practice. Research has shown that scenarios do not consider the idea of discontinuity as a matter of course. In our research, we found that a scenario study would benefit from efforts to create and foster a 'culture of curiosity' for exploring the future and the possible discontinuities rather than simply commissioning a scenario study to provide insights about the future. Only then can one read the writing on the wall of future developments.…

Taschenbuch. Zustand: Neu. Neuware - The purpose of business is to employ capital factors in such a manner as to generate value for its customers and profits for its owners. To achieve these ends, management must make at least three distinct decisions - the operating, investment, and financing decisions. The purpose of this study is to formulate a modeling methodology that harmonically analyzes and explains how the investment decision and capital elasticity influence competitive advantage. The research explores the descriptive literature for the current states of computational modeling, accounting theory and practice, managerial finance, macroeconomics, capital theory, and harmonic analysis in order to provide evidence supporting the content validity of a proposed modeling framework, which encodes, modulates, and transforms raw financial data into waveforms suitable for harmonic analysis. The framework is operationalized algebraically, translated into a high-level computational language, and subsequently tested using simulation methods in order to analyze the computational robustness of the implementation. Finally, empirical testing shows a significant correlation exists between the model's reported results and the profitability of sole proprietorships in the U.S. providing initial evidence of the framework's construct validity. Additional empirical testing shows that the relationship between the model's reported results and net profitability is stronger than results returned from the use of raw capital magnitudes providing evidence of the model's positive capacity for recommending decisions. The study uses extant financial data obtained from the Internal Revenue Service (IRS), which maintains and releases Federal tax information extracted from its archives into the public domain through its Statistics of Income (SOI) programs.…

Taschenbuch. Zustand: Neu. Neuware - Technological cooperation is not only costly and time consuming, but also has a high attrition rate. Most literature on strategic cooperation focuses mainly on issues related to cooperation formation and the reasons why firms form these cooperative partnerships. However, a successfully formed cooperation is not always managed well enough to achieve a satisfactory performance. The knowledge of cooperative formation is necessary, but insufficient to achieve a satisfactory performance. The literature suggests that scholars know little about the underlying factors affecting cooperative performance.A comprehensive literature review was conducted to establish the possible effects of key factors on the performance of international technological cooperation, and the possible relations between key factors. A qualitative pilot study was implemented to verify the practical relevance of those 12 key factors, of which 6 factors have a relatively more significant effect on performance than the other 6 factors. By applying theoretical modeling techniques, the research framework was then constructed according to the postulated relations between 7 key factors (6 relatively more significant factors and the focal concept, performance). Strictly based on the definition of key factors, measurement items of each key factor were carefully reviewed and selected. Following the process of structural equation modeling, the structural equation model in this research was constructed. Unlike most previous cooperation studies, a structural equation model allows researchers to examine simultaneously all the relations amongst key factors. The data were collected from mangers who had experience in managing a technological cooperative project with foreign partners, and were then analyzed by LISREL, a longstanding and widely distributed structural equation modeling computer program.The result suggests that symmetric opinions, commitment, dependence, relationships, partner analyses, and rewards have effects on the performance of international technological cooperation, which confirms the results of the thorough and comprehensive literature review and of the qualitative pilot study. In addition, in the structural equation model of this research, relationships and rewards have effects on commitment, and partner analyses and rewards have effects on dependence, which are also consistent with the literature review. The findings have contributed to theory advancement in cooperation studies, and to the knowledge of international business. Managerial implications from the findings also provide advices, which managers can proactively take, to avoid the odds of success. …