Molecular Dynamics Simulations of Field Emission From a Prolate Spheroidal Tip

High resolution molecular dynamics simulations with full Coulomb interactions of electrons are used to investigate field emission from a prolate spheroidal tip. The space charge limited current is several times lower than the current calculated with the Fowler-Nordheim formula. The image-charge is taken into account with a spherical approximation, which is good around the top of the tip, i.e. region where the current is generated.Comment: 6 pages, 8 figure

Inducing R&D investment with price ceilings

Though government intervention is prevalent in the market for research and development (R&D), most literature has focused on the use of subsidies, patents or joint research ventures to obtain the efficient R&D investment. By using a two-stage duopoly model in which firms first choose the level of investment and then output, our paper shows that the introduction of a price ceiling by the regulator will result in the optimal level of R&D. This interesting but counterintuitive result contrasts with the existing literature and advances our understanding about price ceilings.Research and development; Subsidy; Price ceiling

Enhanced imaging of microcalcifications in digital breast tomosynthesis through improved image-reconstruction algorithms

PURPOSE: We develop a practical, iterative algorithm for image-reconstruction in under-sampled tomographic systems, such as digital breast tomosynthesis (DBT). METHOD: The algorithm controls image regularity by minimizing the image total $p$-variation (TpV), a function that reduces to the total variation when $p=1.0$ or the image roughness when $p=2.0$. Constraints on the image, such as image positivity and estimated projection-data tolerance, are enforced by projection onto convex sets (POCS). The fact that the tomographic system is under-sampled translates to the mathematical property that many widely varied resultant volumes may correspond to a given data tolerance. Thus the application of image regularity serves two purposes: (1) reduction of the number of resultant volumes out of those allowed by fixing the data tolerance, finding the minimum image TpV for fixed data tolerance, and (2) traditional regularization, sacrificing data fidelity for higher image regularity. The present algorithm allows for this dual role of image regularity in under-sampled tomography. RESULTS: The proposed image-reconstruction algorithm is applied to three clinical DBT data sets. The DBT cases include one with microcalcifications and two with masses. CONCLUSION: Results indicate that there may be a substantial advantage in using the present image-reconstruction algorithm for microcalcification imaging.Comment: Submitted to Medical Physic

AstroGrid-D: Enhancing Astronomic Science with Grid Technology

We present AstroGrid-D, a project bringing together astronomers and experts in Grid technology to enhance astronomic science in many aspects. First, by sharing currently dispersed resources, scientists can calculate their models in more detail. Second, by developing new mechanisms to efficiently access and process existing datasets, scientific problems can be investigated that were until now impossible to solve. Third, by adopting Grid technology large instruments such as robotic telescopes and complex scientific workflows from data aquisition to analysis can be managed in an integrated manner. In this paper, we present prominent astronomic use cases, discuss requirements on a Grid middleware and present our approach to extend/augment existing middleware to facilitate the improvements mentioned above

Health Beliefs and Behaviors of College Women

Background: Lifestyle factors are known contributors to chronic disease states, a major factor in increasing health care costs. Promoting healthier lifestyles is a current emphasis worldwide. Emerging adulthood is an important window of opportunity since lifestyle patterns are often set during this time period. Women are more likely to make family health care decisions. Understanding factors affecting lifestyle patterns in a population of emerging adult women will support the design of interventions aimed at prevention of chronic disorders in this population, which may additionally have positive effects on lifestyles in their families.Purpose: The purpose of this study was to investigate the factors that influence healthy lifestyle beliefs and behaviors in college women. Design: This study used the Health Belief Model as a framework and employed a mixed methods design including surveys, pedometers, and nominal group technique (NGT). Women, 18 to 25 years of age, were recruited from an urban, women's centered university in Pittsburgh, PA.Results: Analysis of 109 completed data sets demonstrated that health beliefs of perceived benefits and barriers related to eating behavior and physical activity were more predictive of healthy behaviors than beliefs of perceived susceptibility and seriousness. Perceived diet benefits accounted for over 15% of the variance seen in eating behavior. Perceived exercise barriers accounted for 35% of the variance, and exercise benefits explained 4% of the variance in physical activity. The association between health beliefs and behaviors was increased when the effect of modifying factors was considered. Socioeconomic factors including race, income, living environment, medical supervision, and knowledge moderated the relationship between health beliefs and health behaviors increasing variance explained from 15% to 30% in eating behaviors and from 39% to 49% in physical activity behaviors. NGT results suggested that mood, aesthetics, and practical issues such as cost and availability, were important factors in decision making related to healthy eating behaviors and participation in physical activity.Conclusions: Emerging adult (college) women are more motivated by higher perceived immediate benefits and lower perceived barriers to health behaviors. Framing interventions toward immediate benefit to the individual may be the most appropriate avenue in this population