Towards a debugging tutor for object-oriented environments

Programming has provided a rich domain for Artificial Intelligence in Education and many systems have been developed to advise students about the bugs in their programs, either during program development or post-hoc. Surprisingly few systems have been developed specifically to teach debugging. Learning environment builders have assumed that either the student will be taught these elsewhere or thatthey will be learnt piecemeal without explicit advice.This paper reports on two experiments on Java debugging strategy by novice programmers and discusses their implications for the design of a debugging tutor for Java that pays particular attention to how students use the variety of program representations available. The experimental results are in agreement with research in the area that suggests that good debugging performance is associated with a balanced use ofthe available representations and a sophisticated use of the debugging step facility which enables programmers to detect and obtain information from critical momentsin the execution of the program. A balanced use of the available representations seemsto be fostered by providing representations with a higher degree of dynamic linkingas well as by explicit instruction about the representation formalism employed in the program visualisations

Excitons and biexcitons in symmetric electron-hole bilayers

Symmetric electron-hole bilayer systems have been studied at zero temperature using the diffusion quantum Monte Carlo method. A flexible trial wave function is used that can describe fluid, excitonic and biexcitonic phases. We calculate condensate fractions and pair correlation functions for a large number of densities rs and layer separations d. At small d we find a one-component fluid phase, an excitonic fluid phase, and a biexcitonic fluid phase, and the transitions among them appear to be continuous. At d = 0, excitons appear to survive down to about rs = 0.5 a.u., and biexcitons form at rs > 2.5 a.u.Comment: 5 pages, 4 figure

The Effects of Music Genre on Cycling Performance and Perceived Exertion

Many people claim that music enhances their exercise experience. To our knowledge, no studies have analyzed the effect of music genre on exercise performance and perceived effort. Purpose: The purpose of this study was to analyze the effect of music genre on effort as well as perceived exertion while exercising. Methods: Eighteen untrained individuals, age 18-22, participated in this study. Participants performed two 25-minute exercise trials on a Monark bicycle ergometer. Participants were randomized to a music genre (either hip-hop, country or classical) and to condition (music or no music). Rating of perceived exertion (RPE), heart rate (HR), and resistance were recorded for the first ten minutes, while the same three measures and total calories burned were recorded for the final fifteen. Results: No significant difference was found in RPE between music and no music (p=0.477). The results of the Tukey post-hoc showed a significant increase in caloric expenditure between country music and hip-hop music (p=.008). There were no differences in RPE (F2,17=1.45, p=0.265) and music preference (F2,17=3.21, p=0.069) across genre. Conclusion: Based on these results, exercise performance and perceived effort were similar with or without music. When examining the effects of music genre, listening to country music increased caloric expenditure when compared to hip-hop music

Super-Extremal Spinning Black Holes via Accretion

A Kerr black hole with mass $M$ and angular momentum $J$ satisfies the extremality inequality $|J| \le M^2$. In the presence of matter and/or gravitational radiation, this bound needs to be reformulated in terms of local measurements of the mass and the angular momentum directly associated with the black hole. The isolated and dynamical horizon framework provides such quasi-local characterization of black hole mass and angular momentum. With this framework, it is possible in axisymmetry to reformulate the extremality limit as $|J| \le 2\,M_H^2$, with $M_H$ the irreducible mass of the black hole computed from its apparent horizon area and $J$ obtained using approximate rotational Killing vectors on the apparent horizon. The $|J| \le 2\,M_H^2$ condition is also equivalent to requiring a non-negative black hole surface gravity. We present numerical experiments of an accreting black hole that temporarily violates this extremality inequality. The initial configuration consists of a single, rotating black hole surrounded by a thick, shell cloud of negative energy density. For these numerical experiments, we introduce a new matter-without-matter evolution method.Comment: 11 pages, 10 figure