Performance characteristics of ring-cusp thrusters with xenon propellant

The performance characteristics and operating envelope of several 30-cm ring-cusp ion thrusters with xenon propellant were investigated. Results indicate a strong performance dependence on the discharge chamber boundary magnetic fields and resultant distribution of electron currents. Significant improvements in discharge performance over J-series divergent-field thrusters were achieved for large throttling ranges, which translate into reduced cathode emission currents and reduced power dissipation which should be of significant benefit for operation at thruster power levels in excess of 10 kW. Mass spectrometry of the ion beam was documented for both the ring-cusp and J-series thrusters with xenon propellant for determination of overall thruster efficiency, and lifetime. Based on the lower centerline values of doubly charged ions in the ion beam and the lower operating discharge voltage, the screen grid erosion rate of the ring-cusp thruster is expected to be lower than the divergent-field J-series thruster by a factor of 2

Ground penetrating radar migration with uncertain parameters

The focusing principle of Kirchoff migration is described. This allows the introduction of optical focusing techniques that can be used to focus migration. Three focus measures are described that are useful for optimising migration. Simple optimisation routines are implemented that model uncertainties in the migration parameters. The focus measures are then used as cast functions to be maximised. Results show that these measures are useful in optimising migration when there are uncertainties in the parameter

Electric propulsion options for 10 kW class earth space missions

Five and 10 kW ion and arcjet propulsion system options for a near-term space demonstration experiment have been evaluated. Analyses were conducted to determine first-order propulsion system performance and system component mass estimates. Overall mission performance of the electric propulsion systems was quantified in terms of the maximum thrusting time, total impulse, and velocity increment capability available when integrated onto a generic spacecraft under fixed mission model assumptions. Maximum available thrusting times for the ion-propelled spacecraft options, launched on a DELTA II 6920 vehicle, range from approximately 8,600 hours for a 4-engine 10 kW system to more than 29,600 hours for a single-engine 5 kW system. Maximum total impulse values and maximum delta-v's range from 1.2x10(7) to 2.1x10(7) N-s, and 3550 to 6200 m/s, respectively. Maximum available thrusting times for the arcjet propelled spacecraft launched on the DELTA II 6920 vehicle range from approximately 528 hours for the 6-engine 10 kW hydrazine system to 2328 hours for the single-engine 5 kW system. Maximum total impulse values and maximum delta-v's range from 2.2x10(6) to 3.6x10(6) N-s, and approximately 662 to 1072 m/s, respectively

Electric Propulsion Options for 10 kW Class Earth-Space Missions

Five and 10 kW ion and arcjet propulsion system options for a near-term space demonstration experiment were evaluated. Analyses were conducted to determine first-order propulsion system performance and system component mass estimates. Overall mission performance of the electric propulsion systems was quantified in terms of the maximum thrusting time, total impulse, and velocity increment capability available when integrated onto a generic spacecraft under fixed mission model assumptions. Maximum available thrusting times for the ion-propelled spacecraft options, launched on a DELTA 2 6920 vehicle, range from approximately 8,600 hours for a 4-engine 10 kW system to more than 29,600 hours for a single-engine 5 kW system. Maximum total impulse values and maximum delta-v's range from 1.2x10 (exp 7) to 2.1x10 (exp 7) N-s, and 3550 to 6200 m/s, respectively. Maximum available thrusting times for the arcjet propelled spacecraft launched on the DELTA 2 6920 vehicle range from approximately 528 hours for the 6-engine 10 kW hydrazine system to 2328 hours for the single-engine 5 kW system. Maximum total impulse values and maximum delta-v's range from 2.2x10 (exp 6) to 3.6x10 (exp 6) N-s, and approximately 662 to 1072 m/s, respectively

Implications of Heavy Top

Lecture at 23 ITEP Winter School. Manifestations of heavy top at low energies (K- and B-mesons) and high energies (Z and W physics) are discussedComment: 12 pages; ps file can be found at http://venus.itep.ru/preprints/1995/95046.ps.g

Print Advertisement Characteristics and Apple Variety Attraction: A Mimic Model Approach

A structural latent variable model of apple variety demand is used to analyze the effect of variety specific newspaper advertisement characteristics on variety attraction (preferences), and in turn on variety demand. The influence of advertisement size, the use of color and the Washington apple logo were analyzed. The estimated variety attraction variable is important in explaining demand. Model specifications which exclude this variable tend to understate demand elasticities. Advertisement size has a positive impact on Granny Smith, Fuji, and Gala sales. Red Delicious sales are positively influenced by color ads, but negatively affected by ads with the Washington apple logo.Apple demand, newspaper advertisements, structural latent variable model, Marketing,

DYNAMIC COMPLEMENTARITY IN EXPORT PROMOTION: THE MARKET ACCESS PROGRAM IN FRUITS AND VEGETABLES

Government-supported promotion in foreign markets may justified when market failures exist, such as spillover externalities, where promotion of one commodity positively influences exports of another, or when market uncertainties cause planning horizons to be shorter than the persistent effects of promotion. A dynamic model of U.S. apple, almond, grape, and wine export supply is developed to test for these market failures. Promotion is viewed as an investment in establishing and maintaining a productÂ’'s image. Evidence supporting the existence of each market failure is found. Exporters and program administrators may fail to account for them in export promotion planning.International Relations/Trade,

A BILATERAL COMPARISON OF FRUIT AND VEGETABLE CONSUMPTION: U.S AND CANADA

A structural latent variable model tests the role quality and information play in explaining observed differences in Canadian and U.S. produce consumption (5.0 vs. 3.5 servings/day). Dietary health information is significant in expanding demands. Quality promotes fruit consumption in Canada, consistent with the Alchian-Allen prediction.Food Consumption/Nutrition/Food Safety,

THE ECONOMIC VALUE OF PUBLIC RELATIONS EXPENDITURES: FOOD SAFETY AND THE STRAWBERRY CASE

Food safety has become an important issue affecting public health and grower profits. Outbreaks of foodborne illnesses are typically accompanied by press accounts of the incident and a decrease in demand. This study estimates the short- and long-run impacts of adverse and positive information delivered through print media on strawberry grower profits. Positive information may arise as apart of the promotional efforts of grower associations. It is found that adverse information reduces grower profits, but that positive information can partially offset their effects. It is suggested that grower groups could redirect funds used for promotion to food safety initiatives.Food Consumption/Nutrition/Food Safety,

Native American Obesity: An Economic Model of the "Thrifty Gene" Theory

Native American obesity and the associated health conditions are generally thought to result in part from a genetic predisposition to overeating fats and carbohydrates, called the "thrifty gene." Although coined by nutritional scientists, this study maintains the origin of the thrifty gene lies in economics. Apparently harmful overconsumption and addiction constitute economically rational behavior if the increment to current utility from adding to one's stock of "consumption capital" is greater than the present value of utility lost in the future due to ill health and the costs of withdrawal. Tests of these conditions for such "rational addiction" are conducted using two-stage household production approach. The results obtained by estimating this model in a panel of Native and non-Native supermarket scanner data show that both Natives and non-Natives tend to be inherently forward-looking in their nutrient choices, but Natives tend to have far higher long-run demand elasticities for carbohydrates compared to non-Natives. Consequently, reductions in real food prices over time, primarily among foods that are dense in simple carbohydrates, leads Native Americans to over-consume potentially harmful nutrients relative to their traditional diet.Type II diabetes, household production, Native Americans, demand estimation, shadow values., Food Consumption/Nutrition/Food Safety,