Hard X-ray imaging from Explorer

Coded aperture X-ray detectors were applied to obtain large increases in sensitivity as well as angular resolution. A hard X-ray coded aperture detector concept is described which enables very high sensitivity studies persistent hard X-ray sources and gamma ray bursts. Coded aperture imaging is employed so that approx. 2 min source locations can be derived within a 3 deg field of view. Gamma bursts were located initially to within approx. 2 deg and X-ray/hard X-ray spectra and timing, as well as precise locations, derived for possible burst afterglow emission. It is suggested that hard X-ray imaging should be conducted from an Explorer mission where long exposure times are possible

Human-human haptic collaboration in cyclical Fitts' tasks

Understanding how humans assist each other in haptic interaction teams could lead to improved robotic aids to solo human dextrous manipulation. Inspired by experiments reported in Reed et al. (2004), which suggested two-person haptically interacting teams could achieve a lower movement time (MT) than individuals for discrete aiming movements of specified accuracy, we report that two-person teams (dyads) can also achieve lower MT for cyclical, continuous aiming movements. We propose a model, called endpoint compromise, for how the intended endpoints of both subjects' motion combine during haptic interaction; it predicts a ratio of /spl radic/2 between slopes of MT fits for individuals and dyads. This slope ratio prediction is supported by our data

THE PROVISION OF RAIL SERVICE: THE IMPACT OF COMPETITION

Grain transportation is one of the most important economic issues for grain producers in the Northern Plains. The reliance on export markets and the long distances to port position means that transportation costs have a significant effect on the price received by farmers. In the prairie region of Canada, rail transportation is undergoing a major transformation that will affect the competitive positions of agriculture in both the United States and Canada and influence the direction of grain flows between the two countries. Rail rates are no longer legislated although a cap is still in place), restrictions on branch line abandonment have been lifted, and further deregulation of price and car allocation is being considered. Some parties, including the railways, argue that a completely deregulated system, similar to the U.S. system, is the only way to achieve transportation efficiencies. Other groups, supporting the status quo, argue that the regulation of rates is essential to control the monopoly power of the railways. There has been very little discussion of other policy options, with the exception of a limited discussion of nationalized railbeds. The U.S. experience provides a stark view of the likely outcome of deregulation. When railways are not faced with competition from other railways or from other forms of transportation such as barges, the evidence suggests railways will price freight services at or near truck competitive rates. Freight rates in Montana, where no effective rail and/or barge competition exists, are approximately twice those at Kansas City and Denver/Commerce City, where such competition exists. The current cost-based regulated rates in Western Canada are similar to those at Kansas City and Denver/Commerce City. Given similar distances to port and the existence of only two railways (and no likelihood of new entrants), deregulation in Western Canada is likely to result in freight rates closer to those in Montana than to the current regulated level. The increase in freight costs will result in transfers from producers to the railways, distort production incentives, and create losses elsewhere in the economy. While maintenance of a regulated freight rate structure would address the freight rate issue, other problems would result. The lack of price signals reduces incentives for industry participants to perform. Branch lines are less likely to be maintained in a regulated environment because railways may be unable to charge the extra amount necessary to make them viable. Railways may also disrupt the system - as a form of bargaining - to create pressure for deregulation. This report explores the option of the government encouraging entry into rail service provision. Just as telecommunication companies are required to allow competitors to use their phone lines, existing railways could be required to make their track and switching equipment available to rail operators who wish to run train service on a line, on the condition that the access price covers the infrastructure cost. The paper examines the case of the British railway system where the ownership of the track has been separated from the operation of the rail equipment and the provision of service, and explores the applicability of this model to grain transportation on the Great Plains. In Britain, ownership of the track rests with a company called Railtrack (although Railtrack was government-owned, it has been privatized). Railtrack leases access to thirty train operators for fees that are regulated by the Office of the Rail Regulator to cover maintenance costs and provide a return on investment. The thirty rail operators then compete to provide service to customers. This model and others similar to it need to be developed and articulated before they can be considered in the public policy forum. Nevertheless, given the importance of rail transportation to the grain industry in the Northern Plains, it is imperative that options such as these be investigated to address the very thorny issue of freight rate and entry regulation.barriers to entry, competition, grain handling, grain transportation, monopoly, railroads, regulation, Public Economics, K2, L1, L9, L5,

Patterns theory and geodesic automatic structure for a class of groups

We introduce a theory of "patterns" in order to study geodesics in a certain class of group presentations. Using patterns we show that there does not exist a geodesic automatic structure for certain group presentations, and that certain group presentations are almost convex.Comment: Appeared in 2003. I am putting all my past papers on arxi

Applicability of fluidic controls to a Rankine cycle automotive engine Final report

Fluidic controls for automotive engine examined by Rankine cycle performance with water, CP-34, and freon TF and investigation for boiler and feed pump control criteri

UAV as a Reliable Wingman: A Flight Demonstration

In this brief, we present the results from a flight experiment demonstrating two significant advances in software enabled control: optimization-based control using real-time trajectory generation and logical programming environments for formal analysis of control software. Our demonstration platform consisted of a human-piloted F-15 jet flying together with an autonomous T-33 jet. We describe the behavior of the system in two scenarios. In the first, nominal state communications were present and the autonomous aircraft maintained formation as the human pilot flew maneuvers. In the second, we imposed the loss of high-rate communications and demonstrated an autonomous safe “lost wingman” procedure to increase separation and reacquire contact. The flight demonstration included both a nominal formation flight component and an execution of the lost wingman scenario

Spatial synchronization and extinction of species under external forcing

We study the interplay between synchronization and extinction of a species. Using a general model we show that under a common external forcing, the species with a quadratic saturation term in the population dynamics first undergoes spatial synchronization and then extinction, thereby avoiding the rescue effect. This is because the saturation term reduces the synchronization time scale but not the extinction time scale. The effect can be observed even when the external forcing acts only on some locations provided there is a synchronizing term in the dynamics. Absence of the quadratic saturation term can help the species to avoid extinction.Comment: 4 pages, 2 figure