Anomalous Behavior of Spin Systems with Dipolar Interactions

We study the properties of spin systems realized by cold polar molecules interacting via dipole-dipole interactions in two dimensions. Using a spin wave theory, that allows for the full treatment of the characteristic long-distance tail of the dipolar interaction, we find several anomalous features in the ground state correlations and the spin wave excitation spectrum, which are absent in their counterparts with short range interaction. The most striking consequence is the existence of true long-range order at finite temperature for a two-dimensional phase with a broken U(1) symmetry.Comment: 6 pages, 3 figure

Spin dynamics of coupled spin ladders near quantum criticality in Ba2CuTeO6

We report inelastic neutron scattering measurements of the magnetic excitations in Ba2CuTeO6, proposed by ab initio calculations to magnetically realize weakly coupled antiferromagnetic two-leg spin-1/2 ladders. Isolated ladders are expected to have a singlet ground state protected by a spin gap. Ba2CuTeO6 orders magnetically, but with a small Neel temperature relative to the exchange strength, suggesting that the interladder couplings are relatively small and only just able to stabilize magnetic order, placing Ba2CuTeO6 close in parameter space to the critical point separating the gapped phase and Neel order. Through comparison of the observed spin dynamics with linear spin wave theory and quantum Monte Carlo calculations, we propose values for all relevant intra- and interladder exchange parameters, which place the system on the ordered side of the phase diagram in proximity to the critical point. We also compare high field magnetization data with quantum Monte Carlo predictions for the proposed model of coupled ladders.Comment: 14 pages, 12 figure

Publisher Correction: Rapid Adaptation to the Timbre of Natural Sounds.

An amendment to this paper has been published and can be accessed via a link at the top of the paper

New Tools for Aspect-oriented Programming in Music and Media Programming Environments

(Abstract to follow

Reexamining Student-Athlete GPA: Traditional vs. Athletic Variables

A sample of 674 first-year student-athletes at a midsize Midwestern university were examined each year over a five-year period (2004–2008) to determine if athletic variables were powerful enough to be used in conjunction with traditional predictors of college success to predict GPA. The four specific athletic variables unique to student-athletes (i.e., sport, coaching change, playing time, team winning percentage), were hypothesized to be as predictive as traditional variables. Pearson correlations revealed student-athletes were more likely to earn a high first-year GPA if they were female (r = .35), Caucasian (r = -.33), scored well on standardized tests (r = -.47), had a respectable high school GPA (r = .64), were ranked high in their graduating high school class (r = -.58), had a relatively large high school graduating class (r = .15) were not undecided about major (r = -.11), were not a member of a revenue sport (r = .33), and earned a considerable amount of playing time in their first year (r = -.15). Least squares linear regression demonstrated the traditional variables of gender (B = .16), race (B = -.26), standardized test scores (B = .03), high school GPA (B = .41), high school rank (B < -.01), and size of high school graduating class (B < .01) were most influential in predicting first-year student-athlete GPA

Control Improvisation

We formalize and analyze a new automata-theoretic problem termed control improvisation. Given an automaton, the problem is to produce an improviser, a probabilistic algorithm that randomly generates words in its language, subject to two additional constraints: the satisfaction of an admissibility predicate, and the exhibition of a specified amount of randomness. Control improvisation has multiple applications, including, for example, generating musical improvisations that satisfy rhythmic and melodic constraints, where admissibility is determined by some bounded divergence from a reference melody. We analyze the complexity of the control improvisation problem, giving cases where it is efficiently solvable and cases where it is #P-hard or undecidable. We also show how symbolic techniques based on Boolean satisfiability (SAT) solvers can be used to approximately solve some of the intractable cases