Hydrogen refinement during solid phase epitaxy of buried amorphous silicon layers

The effect of hydrogen on the kinetics of solid phase epitaxy (SPE) have been studied in buried amorphous Si layers. The crystallization rate of the front amorphous/crystalline (a/c) interface is monitored with time resolved reflectivity.Secondary ion mass spectrometry(SIMS) is used to examine H implanted profiles at selected stages of the anneals. The H retardation of the SPE rate is determined up to a H concentration of 2.3×10²⁰ cm¯³ where the SPE rate decreases by 80%. Numerical simulations are performed to model the H diffusion, the moving a/c interfaces and the refinement of the H profile at these interfaces. Despite the high H concentration involved, a simple Fickian diffusion model results in good agreement with the SIMS data. The segregation coefficient is estimated to be 0.07 at 575 °C. A significant fraction of the H escapes from the a-Si layer during SPE especially once the two a/c interfaces meet which is signified by the lack of H-related voids after a subsequent high temperature anneal.This research was supported by a grant from the Australian Research Council

Rotorcraft Conceptual Design Environment

Requirements for a rotorcraft conceptual design environment are discussed, from the perspective of a government laboratory. Rotorcraft design work in a government laboratory must support research, by producing technology impact assessments and defining the context for research and development; and must support the acquisition process, including capability assessments and quantitative evaluation of designs, concepts, and alternatives. An information manager that will enable increased fidelity of analysis early in the design effort is described. This manager will be a framework to organize information that describes the aircraft, and enable movement of that information to and from analyses. Finally, a recently developed rotorcraft system analysis tool is described

Toward Right-Fidelity Rotorcraft Conceptual Design

The aviation Advanced Design Office (ADO) of the US Army Aeroflightdynamics Directorate (AMRDEC) performs conceptual design of advanced Vertical Takeoff and Landing (VTOL) concepts in support of the Army's development and acquisition of new aviation systems. In particular, ADO engages in system synthesis to assess the impact of new technologies and their application to satisfy emerging warfighter needs and requirements. Fundamental to ADO being successful in accomplishing its role; is the ability to evaluate a wide array of proposed air vehicle concepts, and independently synthesize new concepts to inform Army and DoD decision makers about the tradespace in which decisions will be made (Figure 1). ADO utilizes a conceptual design (CD) process in the execution of its role. Benefiting from colocation with NASA rotorcraft researchers at the Ames Research Center, ADO and NASA have engaged in a survey of the current rotorcraft PD practices and begun the process of improving those capabilities to enable effective design and development of the next generation of VTOL systems. A unique aspect of CD in ADO is the fact that actual designs developed in-house are not intended to move forward in the development process. Rather, they are used as reference points in discussions about requirements development and technology impact. The ultimate products of ADO CD efforts are technology impact assessments and specifications which guide industry design activity. The fact that both the requirement and design are variables in the tradespace adds to the complexity of the CD process. A frequent need is ability to assess the relative "cost" of variations in requirement for a diverse set of VTOL configurations. Each of these configurations may have fundamentally different response characteristics to this requirement variation, and such insight into how different requirements drive different designs is a critical insight ADO attempts to provide decision makers. The processes and tools utilized are driven by the timeline in which questions must be answered. This can range from quick "back-of-the-envelope" assessments of a configuration made in an afternoon, to more detailed tradespace explorations that can take upwards of a year to complete. A variety of spreadsheet based tools and conceptual design codes are currently in use. The in-house developed conceptual sizing code RC (Rotorcraft) has been the preferred tool of choice for CD activity for a number of years. Figure 2 illustrates the long standing coupling between RC and solid modeling tools for layout, as well as a number of ad-hoc interfaces with external analyses. RC contains a sizing routine that is built around the use of momentum theory for rotors, classic finite wing theory, a referred parameter engine model, and semi-emperical weight estimation techniques. These methods lend themselves to rapid solutions, measured in seconds and minutes. The successful use of RC, however requires careful consideration of model input parameters and judicious comparison with existing aircraft to avoid unjustified extrapolation of results. RC is in fact a legacy of a series of codes whose development started in the early 1970s, and is best suited to the study of conventional helicopters and XV-15 style tiltrotors. Other concepts have been analyzed with RC, but typically it became necessary to modify the source code and methods for each unique configuration. Recent activity has lead to the development of a new code, NASA Design and Analysis of Rotorcraft (NDARC). NDARC uses a similar level of analytical fidelity as RC, but is built on a new framework intended to improve modularity and ability to rapidly model a wider array of concepts. Critical to achieving this capability is the decomposition of the aircraft system into a series of fundamental components which can then be assembled to form a wide-array of configurations. The paper will provide an overview of NDARC and its capabilities

Cost and Perceived Value in Obtaining a Bachelor’s Degree in Aviation Professional Flight: Will Collegiate Aviation Price Themselves Out of the Market with Technologically Advanced Aircraft?

Traditional academic baccalaureate degree programs have become increasingly expensive throughout the US. For collegiate aviation students, this news is even more daunting. Students obtaining a bachelor\u27s degree in aviation with a professional flight emphasis face unique challenges in today\u27s colleges and universities not typified by a majority of 4-year degree programs. Perhaps the most distinctive challenge lays in the financial arena of cost and return on investment for a bachelor\u27s degree in professional flight. This article will examine the various barriers associated with a typical bachelor\u27s degree aviation student majoring in professional flight

Not So Fast

President Barack Obama and the Republican leadership in Congress are trying to pass fast track legislation in order to push through major economic agreements with eleven countries of the Pacific region (the Trans-Pacific Partnership) and Europe (the Trans-Atlantic Trade and Investment Partnership) without the possibility for Congressional amendments. Both are being sold generally as trade agreements, yet they involve key areas of business law and regulation far beyond trade. Before Congress approves fast track, these agreements need to be made public and exposed to thorough public scrutiny

Why Fast Track Is a Dangerous Gift to Corporate Lobbies

The Obama Administration is now on track to get fast track legislation through the Senate, heading towards a close vote in the House. The end goal is to conclude two major business treaties: the Trans-Atlantic Trade and Investment Partnership Agreement (TTIP) and the Trans-Pacific Partnership Agreement (TPP). The House Democrats are right to withhold their support until key treaty positions favored by the White House are dropped

Investor-State Dispute Settlement, Public Interest and U.S. Domestic Law

As negotiations are ongoing in the Trans-Pacific Partnership (TPP) and the Trans-Atlantic Trade and Investment Partnership Agreement (TTIP), CCSI staff and Jeffrey Sachs discuss the implications of investor-state dispute settlement (ISDS) for domestic law and policy, focusing on effects within the US. The paper concludes that the risks ISDS poses for domestic law are significant and unjustified, and that there are preferable policy alternatives to pursue as a means of protecting the rights of investors operating overseas

INCOME, WEALTH, AND THE ECONOMIC WELL-BEING OF FARM HOUSEHOLDS

Agricultural policy is rooted in the 1930s notion that providing transfers of money to the farm sector translates into increased economic well-being of farm families. This report shows that changes in income for the farm sector or for any particular group of farm businesses do not necessarily reflect changes confronting farm households. Farm households draw income from various sources, including off-farm work, other businesses operated, and increasingly nonfarm investments. Likewise, focus on a single indicator of well-being, like income, overlooks other indicators such as the wealth held by the household and the level of consumption expenditures for health care, food, housing, and other items. Using an expanded definition of economic well-being, we show that farm households as a whole are relatively better off than the average U.S. household, but that about 6 percent remain economically disadvantaged relative to the rest of the population.Consumption, farm households, income, wealth, well-being, off-farm employment, Consumer/Household Economics,

Managing variability in the semiconductor supply chain

Thesis (S.M.)--Massachusetts Institute of Technology, Engineering Systems Division, 2005.Includes bibliographical references (leaves 88-92).Within the semiconductor industry, the variability in both supply and demand is quite high; this uncertainty makes supply chain planning very difficult. We analyze the current tools and processes at a large semiconductor manufacturing company and then propose a framework for improvement based on hierarchical production planning. We present an appropriate decomposition for this specific planning problem and illustrate some limitations of traditional inventory models. New safety stock equations are developed for this planning problem based on a simple analysis using the basic ideas from probability theory. We also devise a new method to determine lead times that more accurately captures the actual lead time seen in the supply chain. Finally, an algorithm is developed to determine appropriate inventory levels and production allocation. These ideas, when used together, provide a powerful framework to properly manage supply chains in highly stochastic environments.by Jeffrey D. Johnson.S.M

Life-Cycle Impacts of Forest Resource Activities in the Pacific Northwest and Southeast United States

A more intensive management alternative was created for each region by reallocating acres to higher management intensity classes. Harvesting activities were segmented into five stages to allow development of all inputs and outputs: (1) felling, (2) processing (bucking, limbing, cutting to length), (3) secondary transportation (skidding and yarding), (4) loading, and (5) hauling to a process point. The costs and consumption rates of energy and materials for these activities drove the log outputs, emissions, and carbon pools. Logs are allocated to wood product facilities, the primary product of the analysis, or pulp and paper mills as a co-product from the forest. Non-merchantable slash is generally left on site and is disposed of through site preparation activities. Transportation-related activities and the required diesel fuel produce by far the largest contribution to emission outputs. However, fertilizer use contributes to much of the change in emissions as acreage shifts to higher intensity management alternatives