Station-Keeping Requirements for Constellations of Free-Flying Collectors Used for Astronomical Imaging in Space

The accuracy requirements on station-keeping for constellations of free-flying collectors coupled as (future) imaging arrays in space for astrophysics applications are examined. The basic imaging element of these arrays is the two-element interferometer. Accurate knowledge of two quantities is required: the \textit{projected baseline length}, which is the distance between the two interferometer elements projected on the plane tranverse to the line of sight to the target; and the \textit{optical path difference}, which is the difference in the distances from that transverse plane to the beam combiner. ``Rules-of-thumb'' are determined for the typical accuracy required on these parameters. The requirement on the projected baseline length is a \textit{knowledge} requirement and depends on the angular size of the targets of interest; it is generally at a level of half a meter for typical stellar targets, decreasing to perhaps a few centimeters only for the widest attainable fields of view. The requirement on the optical path difference is a \textit{control} requirement and is much tighter, depending on the bandwidth of the signal; it is at a level of half a wavelength for narrow (few %) signal bands, decreasing to $\approx 0.2 \lambda$ for the broadest bandwidths expected to be useful. Translation of these requirements into engineering requirements on station-keeping accuracy depends on the specific details of the collector constellation geometry. Several examples are provided to guide future application of the criteria presented here. Some implications for the design of such collector constellations and for the methods used to transform the information acquired into images are discussed.Comment: 13 pages, 6 figures, accepted 6/29/07 for the August 2007 issue of PAS

A SENSITIVITY ANALYSIS OF QUALITY OF LIFE INDICES ACROSS COUNTRIES

This paper attempts to provide a comprehensive analysis of interrelationships among the determinants of the Quality of Life (QOL). We show that various measures of well-being are highly sensitive to domains of QOL that are considered in the construction of comparative indices, and how measurable inputs into the well-being indicators are aggregated and weighted to arrive at composite measures of QOL. We present a picture of conditions among the 43 countries of the world with respect to such interrelated domains of QOL as the relationship with family and friends, emotional well-being, health, work and productivity, material well-being, feeling part of one's community, personal safety, and the quality of environment. On the basis of Borda Rule and the principal components approach, we search for factor-indices that may function as QOL indices comparatively across countries. Such indices can be useful in making QOL comparisons and evaluations with reference to both time and place. Comparing and analyzing well-being conditions among countries in this way are aimed at facilitating the discovery of extant of problems with government policies impacting QOL.quality of life, domains, Borda rule, principal components, and rankings, Institutional and Behavioral Economics, I31, D60, D63,

MEASURING THE EFFECTS OF GENERIC PRICE AND NON-PRICE PROMOTIONAL ACTIVITIES: THE CASE OF WASHINGTON APPLES

This paper develops a monthly domestic demand and supply equilibrium model for Washington apples that can be used to assess the effectiveness of price and non-price promotional activities. The econometric methodology employed takes into account market differences across the U.S. and is based on data pertaining to individual retail stores located throughout the U.S. The period of analysis is from September 1990 through August 2000 on a regional basis. A unique feature of the model is its explicit allowance for multiplier effects to exist between the level of print media (newspaper ad and flyers) expenditures provided by the Washington State Apple Commission (WAC) in support of apple demand and supplementary funds provided by retailers in support of apple promotion. In particular the model allows for the fact that Commission funds oftentimes represent only a relatively small fraction of the overall print media expenditures made in support of apple sales, and that Commission funds are often effectively only "pump priming" or serve as inducements for additional promotional activities by other entrepreneurs in the marketing chain. Also, the subset of promotional activities (print media and price reductions) provided by retailers is modeled in a dynamic fashion, whereby market conditions feedback affects the level of apple promotion provided by retailers. The overall model includes a set of retail demand equations, a set of retail-F.O.B. price linkage equations, a set of ad lines - WAC Ad buys linkage equations, and an aggregate industry supply function. Additional factors such as asymmetry in retail-F.O.B. price response, the effects of information technology in retail pricing, and the effects of the large crops and the Asian and the Mexican crises on domestic supply are all simultaneously considered. Results of this analysis indicate that, in the aggregate, price promotion is a significant factor positively impacting apple sales. Furthermore, price promotion elasticities were relatively high when compared to non-price promotional activities, leading to a conclusion that greater gains with respect to returns on promotional investment may occur when retail price reductions are pursued. Despite an increased domestic supply and the effects of the Mexican and the Asian crises, among the non-price promotional activities, results indicated that both non-trade (TV and Radio) and trade-related efforts (in store demonstrations, point of sale displays, promotional give-aways, and ad buys) have contributed to increased demand for Washington apples. Sensitivity analysis of trade and non-trade expenditures indicated that trade-related activities were more effective in increasing demand at current expenditure levels relative to non-trade activities. Promotional efforts in the form of billboards, food service expenditures, and other miscellaneous activities, which the industry also carried out during the historical period of analysis, did not have a measurable impact on demand in any of the regions. It was also found that WAC ad buy expenditures resulted in a multiplier effect on the total number of ad lines. While the direct effect of these Commission expenditures on demand would be relatively small without the supplementary efforts forthcoming from retailers, the fact that retailers multiplied the Commission's expenditures into a substantially larger promotional effort resulted in a significant positive effect on apple sales when viewing the promotion program as a whole. Key words: price and non price promotion, trade and non trade activitiesprice and non price promotion, trade and non trade activities, Marketing,

An Analysis of the Impact of European Union and United States Dairy Policies on EU-U.S. Trade in Milk Protein Concentrate

During 1996-2000, U.S. imports of milk protein concentrate (MPC) increased rapidly. At the same time, Commodity Credit Corporation (CCC) stocks of non-fat dry milk (NFDM) went from nothing to more than 500 million pounds. Consequently, U.S. milk producers attributed low milk prices and dairy farmer income during this period to the increased imports of MPC. U.S. milk producers were especially concerned with MPC imports for two reasons. First, MPC between 40 and 90 percent protein had been classified in subheading 0404.90.10 of the Harmonized Tariff Schedule of the United States (HTS). Thus, MPC was not subject to the tariff-rate quotas applied to many other dairy products. Second, MPC produced in the European Union (EU) and exported to the United States was eligible for production and export subsidies. Along with the high U.S. internal milk protein prices maintained by the Dairy Price Support Program, and volatile world prices of NFDM, these policies created economic rents for trade in MPC between the European Union and the United States. To test the relationship between these policies and U.S. imports of MPC, these economic rents, which were not directly observable, were estimated by combing a set of identifiable variables: (1) the CCC purchase price, (2) the EU export refund, (3) EU casein production aid, and (4) the world price of NFDM as expressed by the Western Europe export price. A vector autoregression model was then estimated using monthly U.S. imports of MPC and the estimate of economic rents. This estimation showed that nearly 40 percent of the variability in U.S. MPC imports was attributable to the estimate of economic rents. These results demonstrate that U.S. and EU policies can not be analyzed in isolation when evaluating the impact of dairy policies on U.S. MPC imports.Agricultural and Food Policy, International Relations/Trade,

Thermal coatings for titanium-aluminum alloys

Titanium aluminides and titanium alloys are candidate materials for use in hot structure and heat-shield components of hypersonic vehicles because of their good strength-to-weight characteristics at elevated temperature. However, in order to utilize their maximum temperature capability, they must be coated to resist oxidation and to have a high total remittance. Also, surface catalysis for recombination of dissociated species in the aerodynamic boundary layer must be minimized. Very thin chemical vapor deposition (CVD) coatings are attractive candidates for this application because of durability and very light weight. To demonstrate this concept, coatings of boron-silicon and aluminum-boron-silicon compositions were applied to the titanium-aluminides alpha2 (Ti-14Al-21Nb), super-alpha2 (Ti-14Al-23-Nb-2V), and gamma (Ti-33Al-6Nb-1Ta) and to the titanium alloy beta-21S (Ti-15Mo-3Al-3Nb-0.2Si). Coated specimens of each alloy were subjected to a set of simulated hypersonic vehicle environmental tests to determine their properties of oxidation resistance, surface catalysis, radiative emittance, and thermal shock resistance. Surface catalysis results should be viewed as relative performance only of the several coating-alloy combinations tested under the specific environmental conditions of the LaRC Hypersonic Materials Environmental Test System (HYMETS) arc-plasma-heated hypersonic wind tunnel. Tests were also conducted to evaluate the hydrogen transport properties of the coatings and any effects of the coating processing itself on fatigue life of the base alloys. Results are presented for three types of coatings, which are as follows: (1) a single layer boron silicon coating, (2) a single layer aluminum-boron-silicon coating, and (3) a multilayer coating consisting of an aluminum-boron-silicon sublayer with a boron-silicon outer layer

Permanent Housing for Seasonal Workers? A Generalized Peak Load Investment Model for Farm Worker Housing

Many seasonal workers are housed in transitory accommodations, including tents and vehicles. In this study, we analyze the supply side of this problem by assuming that a public agent must house the workers through direct public investment. A peak load model is adapted to develop investment rules for the least-cost provision of seasonal worker housing, adding an interacting multi-season component to existing models. Based on this model and the data from three prototype projects, the majority of the least-cost investment would be in permanent, but seasonally occupied, housing.farmworker housing, investment rules, peak load model, public housing, seasonal labor, Farm Management, Labor and Human Capital, Public Economics, R31, H75, J43, G31,

Hourly Electricity Prices in Day-Ahead Markets

This paper focuses on the characteristics of hourly electricity prices in day-ahead markets. In these markets, quotes for day-ahead delivery of electricity are submitted simultaneously for all hours in the next day. The same information set is used for quoting all hours of the day. The dynamics of hourly electricity prices does not behave as a time series process. Instead, these prices should be treated as a panel in which the prices of 24 cross-sectional hours vary from day to day. This paper introduces a panel model for hourly electricity prices in day-ahead markets and examines their characteristics. The results show that hourly electricity prices exhibit hourly specific mean-reversion and that they oscillate around an hourly specific mean price level. Furthermore, a block structured cross-sectional correlation pattern between the hours is apparent

Housing careers, intergenerational support and family relations

The home and family have always been mutually embedded, with the former central to the realization and reproduction of the latter. More recently, this mutuality has taken on a more critical salience as realignments in housing markets, employment and welfare states in many countries have worked together to undermine housing access for new households. In this context, families have become increasingly involved in smoothening the routes of young adults members up the ‘housing ladder’ into home ownership. Intergenerational support appears to have become much more widespread and not just confined to familialistic welfare regimes. The role of intergenerational support for housing remains, however, highly differentiated across countries, cities and regions, as well as uneven between social and income classes. This introduction to the Special Issue explores how the role of housing wealth transfers has impacted the renegotiation of the generational contract. In doing so, it sets the scene for the articles that follow, each of which contribute significantly to advancing understanding of housing as a key driver of contemporary social relations and inequalities