Long range science scheduling for the Hubble Space Telescope

Observations with NASA's Hubble Space Telescope (HST) are scheduled with the assistance of a long-range scheduling system (SPIKE) that was developed using artificial intelligence techniques. In earlier papers, the system architecture and the constraint representation and propagation mechanisms were described. The development of high-level automated scheduling tools, including tools based on constraint satisfaction techniques and neural networks is described. The performance of these tools in scheduling HST observations is discussed

Artificial intelligence approaches to astronomical observation scheduling

Automated scheduling will play an increasing role in future ground- and space-based observatory operations. Due to the complexity of the problem, artificial intelligence technology currently offers the greatest potential for the development of scheduling tools with sufficient power and flexibility to handle realistic scheduling situations. Summarized here are the main features of the observatory scheduling problem, how artificial intelligence (AI) techniques can be applied, and recent progress in AI scheduling for Hubble Space Telescope

Corporate Financial Policy, Taxation, and Macroeconomic Risk

This paper develops a simple model of corporate financial structure intended to formalize the macroeconomic concern over excessive leverage. In particular, we attempt to rationalize why firms designing an optimal capital structure would choose a level of debt that leaves them heavily exposed to macroeconomic risk. Our starting point is a variant of the "corporate control" model often used to motivate debt as the optimal financial contract. We modify this framework in two ways. First, we include common risks, interpretable as business cycle risks, as well as idiosyncratic risks. Second, we include corporate and investor-level taxes, and consider the implications of a net tax bias against equity finance. The tax distortion confronts firms with a tradeoff ex ante between the costs of equity finance and the costs of increased exposure to macroeconomic risk accompanying debt finance. In this regard, an equilibrium with "excessive leverage" is possible. Further, despite the possibility of renegotiation, debt is in general less effective than equity in insulating the firm against aggregate risk. Our model leads to the prediction that individual firm dividends may vary with macroeconomic conditions, even after controlling for the effects of relevant firm-specific performance measures, such as earnings. We present some formal econometric evidence in support of this prediction, using a panel of individual corporations. Evidence on some related predictions is also presented.

Taxation, Corporate Capital Structure, and Financial Distress

Is corporate leverage excessive? Is the tax code distorting corporate capital structure decisions in a way that increases the possibility of an economic crisis owing to "financial instability"? Answering these kinds of questions first requires some precision in terminology. In this paper, we describe the cases for and against the trend toward high leverage, and evaluate the role played by taxation. While provision of proper incentives to managers may in part underlie the trend to the debt, high leverage may in practice be a blunt way to address the problem, and one which opens up the possibility for undue exposure to the risks of financial distress. Our story takes as given the kinds of managerial incentive problems deemed important by advocates of leverage. We maintain, however, that when a firm is subject to business-cycle risk as well as individual risk, a profit maximizing arrangement is not simple debt, but rather a contract with mixed debt and equity features. That is, the contract should index the principal obligation to aggregate and/or industry-level economic conditions. We argue that the tax system encourages corporations to absorb more business cycle risk than they would otherwise. It does so in two respects: First, it provides a relative subsidy to debt finance; second, it restricts debt for tax purposes from indexing the principal to common disturbances. At a deeper level, the issue hinges on the institutional aspects of debt renegotiation. If renegotiation were costless, then debt implicitly would have the equity features relevant for responding to business-cycle risk. However, because of the diffuse ownership pattern of much of the newly issued debt and also because of certain legal restrictions, renegotiation is likely to be a costly activity.

Factors Affecting the Unit Cost of Weapon Systems

This research identifies variables and specifies equations that can be used to estimate the unit production cost of a weapon system. It is concerned with both explanation and prediction. Three major variables identified are cumulative quantity, production rate, and change in regime. Cumulative quantity is used in learning curve theory. Production rate is found in the U-shaped short and long-run cost curves of economic theory. This study uses the term regime to refer to any major change in the production environment of a weapon system. This research attempts to integrate the use of these three variables. A change in regime may be due to a change in acquisition strategy, configuration, or manufacturing method. It is recommended that a categorical variable be used to capture the effect of a change in regime. Several specific equations are proposed and discussed. In general, they entail a shift, shift and rotation, or shift and two rotations of the cost quantity rate surface due to a change in regime. Many accepted methods of integrating learning and rate do not produce U-shaped rate curves; this study suggests one that does. Principles and equations discussed are applied in modeling the cost history of three missile systems

Compensating Differentials in Emerging Labor and Housing Markets: Estimates of Quality of Life in Russian Cities

The existence of compensating differentials in Russian labor and housing markets is examined using data from the Russian Longitudinal Monitoring Survey (RLMS) augmented by city and regional-specific characteristics from other sources. While Russia is undergoing transition to a market economy, we find ample evidence that compensating differentials for location-specific amenities exist in the labor and housing markets. Our estimated wage and housing value equations suggest that workers are compensated for differences in climate, environmental conditions, ethnic conflicts, crime rates, and health conditions, after controlling for worker characteristics, occupation, industry, and economic conditions, and various housing characteristics. Moreover, we find evidence that these compensating differentials exist even after controlling for the regional pay differences (“regional coefficients”) used by the Russian government to compensate workers for living in regions that are designated as less desirable. We rank 953 Russian cities by quality of life as measured by a group of eleven amenities. Sizable variation in the estimated quality of life across cities exists. The highest ranked cities tend to be in relatively warm areas and areas in the western, European part of the country. In addition, our quality of life index is positively correlated with net migration into a region, suggesting workers are attracted to amenity-rich locations. Overall, we find that sufficient market equilibrium exists and a model of compensating differentials with controls for disequilibrium yields useful information about values of location-specific amenities and quality of life in this large transition economy.http://deepblue.lib.umich.edu/bitstream/2027.42/40006/2/wp620.pd

Fruit and Leaf Sensing for Continuous Detection of Nectarine Water Status

Continuous assessment of plant water status indicators might provide the most precise information for irrigation management and automation, as plants represent an interface between soil and atmosphere. This study investigates the relationship of plant water status to continuous fruit diameter (FD) and inverse leaf turgor pressure rates (pp) in nectarine trees [Prunus persica (L.) Batsch] throughout fruit development. The influence of deficit irrigation treatments on stem (Ψstem) and leaf water potential, leaf relative water content, leaf hydraulic conductance and fruit growth was studied across the stages of double-sigmoidal fruit development in 'September Bright' nectarines. Fruit relative growth rate (RGR) and leaf pressure change rate (RPCR) were derived from FD and pp to represent rates of water in- and outflows in the organs, respectively. Continuous RGR and RPCR dynamics were independently and combinedly related to plant water status and environmental variables. The independent use of RGR and RPCR yielded significant associations with midday Ψstem, the most representative index of tree water status in anisohydric species. However, the combined use of nocturnal fruit and leaf parameters unveiled an even more significant relationship with Ψstem, suggesting a different fruit-to-leaf water balance in response to pronounced water deficit. In conclusion, we highlight the suitability of a multi-organ sensing approach for improved prediction of tree water status