Advanced propulsion concepts for orbital transfer vehicles

Studies of the United States Space Transportation System show that in the mid-to-late 1990s expanded capabilities for Orbital Transfer Vehicles (OTV) will be needed to meet increased payload requirements for transporting materials and possible men to geosynchronous orbit. NASA is conducting a technology program in support of an advanced propulsion system for future OTVs. This program is briefly described with results to date of the first program element, the Conceptual Design and Technology Definition studies

Effect of degree of fuel vaporization upon emissions for a premixed prevaporized combustion system

An experimental and analytical study of the combustion of partially vaporized fuelair mixtures was performed to assess the impact of the degree of fuel vaporization upon emissions for a premixing-prevaporizing flametube combustor. Data collected show near linear increases in nitrogen oxide emissions with decreasing vaporization at equivalence ratios of 0.6. For equivalence ratio of 0.72, the degree of vaporization had very little impact on nitrogen oxide emissions. A simple mechanism which accounts for the combustion of liquid droplets in partially vaporized mixtures was found to agree with the measured results with fair accuracy with respect to both trends and magnitudes

Manrating orbital transfer vehicle propulsion

The expended capabilities for Orbital Transfer Vehicles (OTV) which will be needed to meet increased payload requirements for transporting materials and men to geosynchronous orbit are discussed. The requirement to provide manrating offers challenges and opportunities to the propulsion system designers. The propulsion approaches utilized in previous manned space vehicles of the United States are reviewed. The principals of reliability analysis are applied to the Orbit Transfer Vehicle. Propulsion system options are characterized in terms of the test requirements to demonstrate reliability goals and are compared to earlier vehicle approaches

Job-related stress and burnout

Occupational stress is a topic of substantial interest to organizational researchers and managers, as well as society at large. Stress arising from work conditions can be pervasive and significant in its impact on individuals, their families and organizations. There is also a widespread belief that management of job stress is a key factor for enhancing individual performance on the job, hence increasing organizational effectiveness. Sethi and Schuler 1984 outlined four major reasons why job stress and coping have become prominent issues: a concern for individual employee health and well-being; b the financial impact on organizations including days lost due to stress-related illness; c organizational effectiveness; and d legal obligations on employers to provide safe and healthy working environments

The economics of labor adjustment: mind the gap

We study inferences about the dynamics of labor adjustment obtained by the "gap methodology" of Caballero and Engel [1993] and Caballero, Engel and Haltiwanger [1997]. In that approach, the policy function for employment growth is assumed to depend on an unobservable gap between the target and current levels of employment. Using time series observations, these studies reject the partial adjustment model and find that aggregate employment dynamics depend on the cross-sectional distribution of employment gaps. Thus, nonlinear adjustment at the plant level appears to have aggregate implications. We argue that this conclusion is not justified: these findings of nonlinearities in time series data may reflect mismeasurement of the gaps rather than the aggregation of plant-level nonlinearities.Labor supply ; Econometric models

Mind the (approximation) gap: a robustness analysis

This note continues the discussion of the results reported by Ricardo Caballero and Eduardo Engel (1993), hereafter CE, and Ricardo Caballero, Eduardo Engel, and John Haltiwanger (1997), hereafter CEH, by responding to the results reported in Christian Bayer (2008). Russell Cooper and Jonathan Willis (2004), hereafter CW, find that the aggregate nonlinearities reported in CE and CEH may be the consequence of mismeasurement of the employment gap rather than nonlinearities in plant-level adjustment. Bayer reassesses this finding in the context of the CE model in the case where static employment gaps are observed and concludes that the CW result is not robust to alternative shock processes. We concur with Bayer's assessment that the nonlinearity finding is sensitive to the aggregate profitability shock process. We argue, however, that Bayer's finding does not imply that the mismeasurement problem goes away. Instead, the nonlinearity created by mismeasurement is directly related to the level of the aggregate shock. Once the empirical specification properly incorporates the aggregate shock, the nonlinearity test is robust to alternative shock processes and confirms the results in CW. More importantly, we demonstrate that the CW findings are robust to alternative shock processes for the natural case of unobserved gaps as examined by CE and CEH.

Coordination of expectations in the recent crisis: private actions and policy responses

Some of the events of the recent financial crisis have made clear the importance of expectations in an economy. The economic choices individuals make are often based on their expectations of what other people will do—in what economists call a “coordination game.” In such situations, changes in the beliefs of what others may do can affect the actions of individuals. A key element in such situations is that, as the collective beliefs change and individuals respond to these altered expectations, the outcome in the marketplace can change. In the recent crisis, the coordination of expectations played a key role in areas such as financial markets, the housing market, and the automobile sector. ; When the coordination of expectations results in a crisis or a panic, policymakers are the primary group with the ability to alter the expectations of individuals. By using various policy tools, policymakers can lessen the damage from the crisis. Such tools include providing guarantees and changing marketplace incentives such as interest rates and tax rates. ; Cooper and Willis develop a framework to illustrate how the coordination of expectations was instrumental in the economic and financial crisis. The framework also helps describe the actions policymakers took to limit the severity of the downturn by coordinating expectations to achieve more positive outcomes.