Gas-dynamic shock heating of post-flare loops due to retraction following localized, impulsive reconnection

We present a novel model in which shortening of a magnetic flux tube following localized, three-dimensional reconnection generates strong gas-dynamic shocks around its apex. The shortening releases magnetic energy by progressing away from the reconnection site at the Alfven speed. This launches inward flows along the field lines whose collision creates a pair of gas-dynamic shocks. The shocks raise both the mass density and temperature inside the newly shortened flux tube. Reconnecting field lines whose initial directions differ by more that 100 degrees can produce a concentrated knot of plasma hotter that 20 MK, consistent with observations. In spite of these high temperatures, the shocks convert less than 10% of the liberated magnetic energy into heat - the rest remains as kinetic energy of bulk motion. These gas-dynamic shocks arise only when the reconnection is impulsive and localized in all three dimensions; they are distinct from the slow magnetosonic shocks of the Petschek steady-state reconnection model

A SLAM II simulation model for analyzing space station mission processing requirements

Space station mission processing is modeled via the SLAM 2 simulation language on an IBM 4381 mainframe and an IBM PC microcomputer with 620K RAM, two double-sided disk drives and an 8087 coprocessor chip. Using a time phased mission (payload) schedule and parameters associated with the mission, orbiter (space shuttle) and ground facility databases, estimates for ground facility utilization are computed. Simulation output associated with the science and applications database is used to assess alternative mission schedules

Evaluation of work-related psychosocial factors and regional musculoskeletal pain: results from a EULAR Task Force

Objectives: to establish whether review articles provide consistent conclusions on associations between workplace psychosocial factors and musculoskeletal pain and, if differences exist, to explore whether this is related to the methods used.Methods: reviews, reported up to February 2007, that included consideration of workplace psychosocial factors and upper limb, back or knee pain were identified through searches of multiple databases. The specific work-related psychosocial factors considered were job demands, support, job autonomy and job satisfaction. The conclusions of each review on one or more of the psychosocial/musculoskeletal pain associations were extracted.Results: 15 review articles were identified that considered one or more of the regional pain syndromes included in the study. For back pain, the most consistent conclusions (four reviews positive out of six) were with high job demands and low job satisfaction. The studies of upper limb pain were exclusively related to shoulder and/or neck pain, and the most consistent positive conclusions were with high and low job demands (four reviews positive out of six and two reviews positive out of three, respectively). For knee pain, only a single review was identified. For individual reviews of back and upper limb pain, there were marked differences in the number of associations concluded to be positive between reviews.Conclusions: the reasons for reviews coming to different conclusions included that they were often evaluating different bodies of evidence (according to their search criteria, the year when the review was conducted, the role that quality assessment played in whether studies contributed to evidence, and the combination of risk factors addressed in individual studies), but more important was whether the review specified explicit criteria for making conclusions on strength of evidence. These conclusions emphasise the importance of developing standardised methods for conducting such evaluations of existing evidence and the importance of new longitudinal studies for clarifying the temporal relationship between psychosocial factors and musculoskeletal pain in the workplac

Paper Session III-B - A Combined Probabilistic and Expert System Approach for Assigning Repair Start-Times at the NASA Shuttle Logistics Depot

The NASA Shuttle Logistics Depot (NSLD) is tasked with the responsibility for repair and manufacture of Line Replaceable Unit (LRU) hardware and components to support the Space Shuttle Orbiter. Due to shrinking budgets, cost effective repair of LRUs becomes a primary objective. To achieve this objective, it is imperative that resources can be assigned to those LRUs which have the greatest expectation of being needed as a spare. Forecasting the times at which spares are needed requires consideration of many significant factors including, for example, failure rate, flight rate, spares availability, and desired level of support, among others. This paper summarizes the results of the research and development work that has been accomplished in producing an automated system for assisting in the assignment of effective repair start-times for LRUs at the NSLD. This system, called the Repair Start-time Assignment System (RSAS), combines probabilistic modeling and expert system technology to generate an expected future need date. The result is a mathematically calculated value that has been adjusted heuristically to produce a date for beginning the repair that has significantly greater confidence (in the sense that a desired probability of support is assured) than dates produced using other techniques. Since an important output of RSAS is the longest repair turn-around time that will ensure a desired probability of support, RSAS has the potential for being applied to operations at any repair depot where spares are on-hand and repair start-times are of interest. In addition, RSAS incorporates tenants of Just-In-Time (JIT) techniques in the connotation that the latest repair start-time (i.e., the latest time at which repair resources must be committed) may be calculated for every failed unit. This could aid in reducing the spares inventory for certain items, without significantly increasing the risk of unsatisfied demand

Paper Session I-A - Modeling Current and Future Launch Vehicle Processing Using Object-Oriented Simulation Techniques

STARSIM, an acronym for Space Transportation Activities and Resources Simulation, is an objectoriented, menu-driven, user-friendly, decision support system for simulating National Space Transportation System (NSTS) processing, as well as Personnel Launch System (PLS)-National Launch System (NLS), PLS-Proton, PLS-Titan IV, Hermes-Ariane 5 and Cargo Transfer Return Vehicle (CTRV) processing. For each launch system modeled, output is displayed numerically (for global statistical information), in pie chart form (to visualize percentages of subcategories associated with a main category) and in Gantt chart form (for visualizing when and where each launch vehicle experiences waiting, processing, blocking and maintenance periods, and the reasons for blocking). Users may input a comprehensive set of system parameters (e.g., number of launch vehicles, processing times at each facility, number of bays at a particular facility) using a window-based environment, or by supplying an existing input data file. Data for existing launch systems and representative data for proposed systems are used to illustrate output for the models mentioned above. The object-oriented methodology employed in the initial model (i.e., NSTS processing) permitted additional models to be implemented in a minimum amount of time and effort

Patchy Reconnection in a Y-Type Current Sheet

We study the evolution of the magnetic field in a Y-type current sheet subject to a brief, localized magnetic reconnection event. The reconnection produces up- and down-flowing reconnected flux tubes which rapidly decelerate when they hit the Y-lines and underlying magnetic arcade loops at the ends of the current sheet. This localized reconnection outflow followed by a rapid deceleration reproduces the observed behavior of post-CME downflowing coronal voids. These simulations support the hypothesis that these observed coronal downflows are the retraction of magnetic fields reconnected in localized patches in the high corona.Comment: 4 pages, 3 figure

A Model for Patchy Reconnection in Three Dimensions

We show, theoretically and via MHD simulations, how a short burst of reconnection localized in three dimensions on a one-dimensional current sheet creates a pair of reconnected flux tubes. We focus on the post-reconnection evolution of these flux tubes, studying their velocities and shapes. We find that slow-mode shocks propagate along these reconnected flux tubes, releasing magnetic energy as in steady-state Petschek reconnection. The geometry of these three-dimensional shocks, however, differs dramatically from the classical two-dimensional geometry. They propagate along the flux tube legs in four isolated fronts, whereas in the two-dimensional Petschek model, they form a continuous, stationary pair of V-shaped fronts. We find that the cross sections of these reconnected flux tubes appear as teardrop shaped bundles of flux propagating away from the reconnection site. Based on this, we argue that the descending coronal voids seen by Yohkoh SXT, LASCO, and TRACE are reconnected flux tubes descending from a flare site in the high corona, for example after a coronal mass ejection. In this model, these flux tubes would then settle into equilibrium in the low corona, forming an arcade of post-flare coronal loops.Comment: 27 pages plus 16 figure