Twin-spool turbopumps for ''low'' net positive suction pressure operations

Modified single-shaft turbopump incorporates inducer and main pump, each separately driven at different speeds through coaxial-shaft arrangement. Inducer operates at low speed for low net positive suction pressure, main pump operates at high speed to generate high pressure. This arrangement requires no external control for the inducer

Stochastic modelling of intermittent scrape-off layer plasma fluctuations

Single-point measurements of fluctuations in the scrape-off layer of magnetized plasmas are generally found to be dominated by large-amplitude bursts which are associated with radial motion of blob-like structures. A stochastic model for these fluctuations is presented, with the plasma density given by a random sequence of bursts with a fixed wave form. Under very general conditions, this model predicts a parabolic relation between the skewness and kurtosis moments of the plasma fluctuations. In the case of exponentially distributed burst amplitudes and waiting times, the probability density function for the fluctuation amplitudes is shown to be a Gamma distribution with the scale parameter given by the average burst amplitude and the shape parameter given by the ratio of the burst duration and waiting times.Comment: 11 pages, 1 figur

Myths and Realities about Online Forums in Open Source Software Development: An Empirical Study

The use of free and open source software (OSS) is gaining momentum due to the ever increasing availability and use of the Internet. Organizations are also now adopting open source software, despite some reservations, in particular regarding the provision and availability of support. Some of the biggest concerns about free and open source software are post release software defects and their rectification, management of dynamic requirements and support to the users. A common belief is that there is no appropriate support available for this class of software. A contradictory argument is that due to the active involvement of Internet users in online forums, there is in fact a large resource available that communicates and manages the provision of support. The research model of this empirical investigation examines the evidence available to assess whether this commonly held belief is based on facts given the current developments in OSS or simply a myth, which has developed around OSS development. We analyzed a dataset consisting of 1880 open source software projects covering a broad range of categories in this investigation. The results show that online forums play a significant role in managing software defects, implementation of new requirements and providing support to the users in open source software and have become a major source of assistance in maintenance of the open source projects

Exploring User Satisfaction in a Tutorial Dialogue System

Abstract User satisfaction is a common evaluation metric in task-oriented dialogue systems, whereas tutorial dialogue systems are often evaluated in terms of student learning gain. However, user satisfaction is also important for such systems, since it may predict technology acceptance. We present a detailed satisfaction questionnaire used in evaluating the BEETLE II system (REVU-NL), and explore the underlying components of user satisfaction using factor analysis. We demonstrate interesting patterns of interaction between interpretation quality, satisfaction and the dialogue policy, highlighting the importance of more finegrained evaluation of user satisfaction

The Impact of Interpretation Problems on Tutorial Dialogue

Supporting natural language input may improve learning in intelligent tutoring systems. However, interpretation errors are unavoidable and require an effective recovery policy. We describe an evaluation of an error recovery policy in the BEE-TLE II tutorial dialogue system and discuss how different types of interpretation problems affect learning gain and user satisfaction. In particular, the problems arising from student use of non-standard terminology appear to have negative consequences. We argue that existing strategies for dealing with terminology problems are insufficient and that improving such strategies is important in future ITS research.

Caught On Tape: Institutional Order Flow and Stock Returns

Many questions about institutional trading can only be answered if one can track high-frequency changes in institutional ownership. In the US, however, institutions are only required to report their ownership quarterly in 13-F filings. We infer daily institutional trading behavior from the "tape", the Transactions and Quotes database of the New York Stock Exchange, using both a naive approach and a sophisticated method that best matches quarterly 13-F data. Increases in our measures of institutional flows negatively predict returns, particularly when institutions are selling. We interpret this as evidence that 13-F institutions compensate more patient investors for the service of providing liquidity. We also find that both very large and very small trades signal institutional activity, while medium size trades signal activity by the rest of the market.

Caught on Tape: Predicting Institutional Ownership With Order Flow

Many questions about institutional trading can only be answered if one can track institutional equity ownership continuously. However, these data are only available on quarterly reporting dates. We infer institutional trading behavior from the "tape," the Transactions and Quotes database of the New York Stock Exchange, by regress- ing quarterly changes in reported institutional ownership on quarterly buy and sell volume in different trade size categories. Our regression method predicts institutional ownership signifcantly better than the simple cutoff rules used in previous research. We also find that total buy (sell) volume predicts increasing (decreasing) institutional ownership, consistent with institutions demanding liquidity in aggregate. Furthermore, institutions tend to trade in large or very small sizes: buy (sell) volume at these sizes predicts increasing (decreasing) institutional ownership, while the pattern reverses at intermediate trade sizes that appear favored by individuals. We then explore changes in institutional trading strategies. Institutions appear to prefer medium size trades on high volume days and large size trades on high volatility days.