Moduli spaces of torsion sheaves on K3 surfaces and derived equivalences

We show that for many moduli spaces M of torsion sheaves on K3 surfaces S, the functor D(S) -> D(M) induced by the universal sheaf is a P-functor, hence can be used to construct an autoequivalence of D(M), and that this autoequivalence can be factored into geometrically meaningful equivalences associated to abelian fibrations and Mukai flops. Along the way we produce a derived equivalence between two compact hyperkaehler 2g-folds that are not birational, for every g >= 2. We also speculate about an approach to showing that birational moduli spaces of sheaves on K3 surfaces are derived-equivalent.Comment: 28 pages. typos corrected. final version to appear in JLM

SU(2|2) for Theories with Sixteen Supercharges at Weak and Strong Coupling

We consider the dimensional reductions of N=4 Supersymmetric Yang-Mills theory on R x S^3 to the three-dimensional theory on R x S^2, the orbifolded theory on R x S^3/Z_k, and the plane-wave matrix model. With explicit emphasis on the three-dimensional theory, we demonstrate the realization of the SU(2|3) algebra in a radial Hamiltonian framework. Using this structure we constrain the form of the spin chains, their S-matrices, and the corresponding one- and two-loop Hamiltonian of the three dimensional theory and find putative signs of integrability up to the two-loop order. The string duals of these theories admit the IIA plane-wave geometry as their Penrose limit. Using known results for strings quantized on this background, we explicitly construct the strong-coupling dual extended SU(2|2) algebra and discuss its implications for the gauge theories.Comment: 37 pages, 1 figure. v2 some minor improvements to the text, version to appear in Phys.Rev.

NASA/JPL Aircraft SAR Workshop Proceedings

Speaker-supplied summaries of the talks given at the NASA/JPL Aircraft SAR Workshop on February 4 and 5, 1985, are provided. These talks dealt mostly with composite quadpolarization imagery from a geologic or ecologic prespective. An overview and summary of the system characteristics of the L-band synthetic aperture radar (SAR) flown on the NASA CV-990 aircraft are included as supplementary information. Other topics ranging from phase imagery and interferometric techniques classifications of specific areas, and the potentials and limitations of SAR imagery in various applications are discussed

Cramming: The Effects of School Accountability on College-Bound Students

This paper is the first to explore the effects of school accountability systems on high-achieving students' long-term performance. Using exceptional data from a large highly-selective state university, we relate school accountability pressure in high school to a student's university-level grades and study habits. We exploit a change in the state's accountability system in 1999 that led to some schools becoming newlythreatened by accountability pressure and others becoming newly-unthreatened to identify the effects of accountability pressure. We find that an accountability system based on a low-level test of basic skills apparently led to generally reduced performance by high-achieving students, while an accountability system based on a more challenging criterion-referenced exam apparently led to improved performance in college on mathematics and other technical subjects. Both types of systems are associated with increased "cramming" by students in college. The results indicate that the nature of an accountability system can influence its effectiveness.