Arc Phenomena in low-voltage current limiting circuit breakers

Circuit breakers are an important safety feature in most electrical circuits, and they act to prevent excessive currents caused by short circuits, for example. Low-voltage current limiting circuit breakers are activated by a trip solenoid when a critical current is exceeded. The solenoid moves two contacts apart to break the circuit. However, as soon as the contacts are separated an electric arc forms between them, ionising the air in the gap, increasing the electrical conductivity of air to that of the hot plasma that forms, and current continues to flow. The currents involved may be as large as 80,000 amperes. Critical to the success of the circuit breaker is that it is designed to cause the arc to move away from the contacts, into a widening wedge-shaped region. This lengthens the arc, and then moves it onto a series of separator plates called an arc divider or splitter. The arc divider raises the voltage required to sustain the arcs across it, above the voltage that is provided across the breaker, so that the circuit is broken and the arcing dies away. This entire process occurs in milliseconds, and is usually associated with a sound like an explosion and a bright ash from the arc. Parts of the contacts and the arc divider may melt and/or vapourise. The question to be addressed by the Study Group was to mathematically model the arc motion and extinction, with the overall aim of an improved understanding that would help the design of a better circuit breaker. Further discussion indicated that two key mechanisms are believed to contribute to the movement of the arc away from the contacts, one being self-magnetism (where the magnetic field associated with the arc and surrounding circuitry acts to push it towards the arc divider), and the other being air flow (where expansion of air combined with the design of the chamber enclosing the arc causes gas flow towards the arc divider). Further discussion also indicated that a key aspect of circuit breaker design was that it is desirable to have as fast a quenching of the arc as possible, that is, the faster the circuit breaker can act to stop current flow, the better. The relative importance of magnetic and air pressure effects on quenching speed is of central interest to circuit design

Comparison of Alternative Safety Net Programs for the 2000 Farm Bill

As Congress begins its debate for the 2002 farm bill, there have been calls for a counter cyclical safety net that will provide a better basis for targeting longer term planning than exists with ad hoc emergency assistance. Further subsidization of the multi-peril crop insurance (MPCI) program has been proposed, as well as reliance on a farm and ranch risk management (FARRM) account to help farmers. A whole farm revenue income support program and several variations of national income supplement programs have been put forward. A comprehensive analysis of different safety net alternatives using a common methodology is needed so farmers and policy makers can make objective comparisons. The objective of this paper is to quantitatively analyze the economic effects of alternative safety net/insurance programs on farmers in the Southern United States. The objective is accomplished by simulating representative crop farms in the South over the 2001-2005 planning horizon for alternative safety net options. The simulated net present value distributions for the farms are compared using certainty equivalents to determine the value of alternative safety net options to feed grain, cotton and rice farms in the South.Agricultural and Food Policy,

Assessing the Impact of Premier Information Systems Research over Time

In this study we examine the influence of premier information systems research over time to assess the maturity of the Information Systems (IS) field and its impact on subsequent IS and non-IS research. 19,357 citations from the Social Science Citation Index (SSCI) (1982-2004) are attributed to 879 articles published in MIS Quarterly (MISQ), Information Systems Research (ISR), and the IS articles from Management Science (MS) between 1982 and 2004, and this number continues to increase over time. The results suggest that research in premier IS journals has an influence on other disciplines as 7,137 citations come from outside the IS discipline and this number continues to increase over time. Of particular note is the consistent increase over time in citations of premier IS research articles from the management, engineering and physical sciences, organizational behavior, and computer science disciplines. Given recent debates regarding the IT artifact, we also directly test the impact of articles that address the IT artifact and those that do not. We find that articles that directly address the IT artifact are cited significantly more often than those that do not, consistent with arguments made by Benbasat et al. [2003]

Assessing Leading Institutions, Faculty, and Articles in Premier Information Systems Research Journals

This study provides a current assessment of the impact of various Information Systems (IS) articles, and the productivity of IS researchers and institutions. Using a data set of Information Systems articles that spans 15 years, we conducted a scientometric study of the field. The articles are drawn from three premier IS journals. We use citation analysis to demonstrate the impact of articles on institutions and individuals in the IS field. In addition, we identify IS topics with the highest impact. The results indicate that leading productive institutions have changed over time, and problematically, institutions outside of North America are poorly represented. We compare our results with earlier productivity findings created using alternative metrics

Lenalidomide, bortezomib and dexamethasone induction therapy for the treatment of newly diagnosed multiple myeloma : a practical review

For patients with newly diagnosed multiple myeloma, survival outcomes continue to improve significantly: however, nearly all patients will relapse following induction treatment. Optimisation of induction therapy is essential to provide longer term disease control and the current standard of care for most patients incorporates an immunomodulatory agent and proteasome inhibitor, most commonly lenalidomide and bortezomib in combination with dexamethasone (RVD), with maintenance until progression. Historically there has been limited access to RVD as an induction strategy outside of the United States; fortunately, there is now increasing access worldwide. This review discusses the rationale for use of RVD as induction therapy and aims to provide guidance in prescribing this regimen in order to optimise efficacy while minimising the toxicities of treatment. We also highlight the increasing evidence for the utility of addition of a monoclonal antibody to the RVD backbone to deepen responses and potentially provide longer disease control.Peer reviewe

Representative Farm Analysis of the H.R. 2646 Farm Bill Proposal

Agricultural and Food Policy,

Unstable fingering patterns of Hele-Shaw flows as a dispersionless limit of the KdV hierarchy

We show that unstable fingering patterns of two dimensional flows of viscous fluids with open boundary are described by a dispersionless limit of the KdV hierarchy. In this framework, the fingering instability is linked to a known instability leading to regularized shock solutions for nonlinear waves, in dispersive media. The integrable structure of the flow suggests a dispersive regularization of the finite-time singularities.Comment: Published versio

Evaluating Active U: an Internet-mediated physical activity program.

Background: Engaging in regular physical activity can be challenging, particularly during the winter months. To promote physical activity at the University of Michigan during the winter months, an eight-week Internet-mediated program (Active U) was developed providing participants with an online physical activity log, goal setting, motivational emails, and optional team participation and competition. Methods: This study is a program evaluation of Active U. Approximately 47,000 faculty, staff, and graduate students were invited to participate in the online Active U intervention in the winter of 2007. Participants were assigned a physical activity goal and were asked to record each physical activity episode into the activity log for eight weeks. Statistics for program reach, effectiveness, adoption, and implementation were calculated using the Re-Aim framework. Multilevel regression analyses were used to assess the decline in rates of data entry and goal attainment during the program, to assess the likelihood of joining a team by demographic characteristics, to test the association between various predictors and the number of weeks an individual met his or her goal, and to analyze server load. Results: Overall, 7,483 individuals registered with the Active U website (≈16% of eligible), and 79% participated in the program by logging valid data at least once. Staff members, older participants, and those with a BMI < 25 were more likely to meet their weekly physical activity goals, and average rate of meeting goals was higher among participants who joined a competitive team compared to those who participated individually (IRR = 1.28, P < .001). Conclusion: Internet-mediated physical activity interventions that focus on physical activity logging and goal setting while incorporating team competition may help a significant percentage of the target population maintain their physical activity during the winter months