Student evaluations of teaching effectiveness: the interpretation of observational data and the principle of faute de mieux

Student opinion surveys are important but widely misunderstood tools for evaluating teaching effectiveness. In this brief review, an analogy is drawn between the use and interpretation of observational data for public health and biomedical research and the use of student opinion data in evaluating teach ing effectiveness. Sources of systematic error in the form of selection bias, information bias, and confounding are defined and illustrated. Original data concerning intermittent quid pro quo confounding (i.e., the effect of expected grades on student evaluations of teaching) are presented. Finally, the principle of faute de mieux ( lack of anything better ) and the interpretation of less-than-pristine data are considered

Quantum Kinetic Equations for Plasmas and Radiation; Part II. Cyclotron Instabilities in a Bounded Plasma

The procedure for obtaining kinetic equations for internal distribution functions of a system was first developed by Bogoliubov* (1) in his study of.the properties of un-ionized gases. Bogoliubov also indicated some of the problems which would be encountered in a similar development for systems interacting through long-range Coulomb forces . Born and Green (3) , Kirkwood and collaborators (13, 25) and Yvon (37 ) also studied classical and quantum systems, using techniques similar to those developed by Bogolilibov. However, they too were primarily interested in un-ionized gases and liquids. Recently, Rosenbluth and Rostoker (26) derived kinetic equations for a classical plasma, assuming only Coulomb interactions . Simon and Harris (30) extended the theory to include transverse electromagnetic interactions . Most of the investigations of quantum plasmas have employed techniques differing somewhat from those used here . Several texts have been devoted to the methods appropriate for various many-body problems, but some of them most often employed in plasma studies will be indicated here. Perhaps the best known treatment is due to Bohm and Pines (2). Here, collective variables replace the usual coordinates of the system, facilitating the solution of problems in which the individual particle nature is not as important as the gross features of the system. In particular, Bohm and Pines obtained a dispersion relation for the frequencies of collective oscillations of a quantum plasma. This same relation has been obtained by several other authors (8, 15, 29, 39) in different ways and will also be derived in this investigation. Of especial interest is the work of Klimontovich and Selin (7), in which kinetic equations for the quantum plasma were obtained and applied to several problems, including the small-amplitude Coulomb disturbances. Ehrenreich and Cohen (8) have also studied this problem, obtaining the quantum dispersion relation by means of the one-particle Liouville equation and the self-consistent field approximation for the Coulomb potential. Finally, von Roos (36), formulating the problem in terms of a quantum mechanical distribution function similar to that used first by Wigner (37), obtained the dispersion relation mentioned above and showed how exchange affects the relation. None of the above treatments have included a development of kinetic equations for particles and the electromagnetic field, although Osborn and Klevans (24) initiated an investigation of this problem at about the same time that the present study was begun. However, the direction of these authors\u27 work seems to be somewhat different from this dissertatio

Population inversion in optically pumped asymmetric quantum well terahertz lasers

Intersubband carrier lifetimes and population ratios are calculated for three- and four-level optically pumped terahertz laser structures. Laser operation is based on intersubband transitions between the conduction band states of asymmetric GaAs-Ga(1 – x)Al(x)As quantum wells. It is shown that the carrier lifetimes in three-level systems fulfill the necessary conditions for stimulated emission only at temperatures below 200 K. The addition of a fourth level, however, enables fast depopulation of the lower laser level by resonant longitudinal optical phonon emission and thus offers potential for room temperature laser operation. © 1997 American Institute of Physics

Antitrust Laws- Judicial Relief for Violations of Section Seven of the Clayton Act - Disenfranchisement in \u3cem\u3eUnited States v. E. I. du Pont de Nemours & Co.\u3c/em\u3e

This comment will approach section 7 relief questions and solutions primarily in the light of du Pont\u27s unique facts, which included a vertical stock acquisition made thirty years before the judicial proceeding plus the complicating factors of vast financial interests, numerous innocent investors and several corporate interrelationships. Thereby were posed complex problems regarding (1) parties to the relief determination, (2) interests to be affected by the decree and (3) the manner of affecting those interests

Stabilizing All Geometric Moduli in Heterotic Calabi-Yau Vacua

We propose a scenario to stabilize all geometric moduli - that is, the complex structure, Kahler moduli and the dilaton - in smooth heterotic Calabi-Yau compactifications without Neveu-Schwarz three-form flux. This is accomplished using the gauge bundle required in any heterotic compactification, whose perturbative effects on the moduli are combined with non-perturbative corrections. We argue that, for appropriate gauge bundles, all complex structure and a large number of other moduli can be perturbatively stabilized - in the most restrictive case, leaving only one combination of Kahler moduli and the dilaton as a flat direction. At this stage, the remaining moduli space consists of Minkowski vacua. That is, the perturbative superpotential vanishes in the vacuum without the necessity to fine-tune flux. Finally, we incorporate non-perturbative effects such as gaugino condensation and/or instantons. These are strongly constrained by the anomalous U(1) symmetries which arise from the required bundle constructions. We present a specific example, with a consistent choice of non-perturbative effects, where all remaining flat directions are stabilized in an AdS vacuum.Comment: 24 pages, 2 figure

The Minimum Wiener Connector

The Wiener index of a graph is the sum of all pairwise shortest-path distances between its vertices. In this paper we study the novel problem of finding a minimum Wiener connector: given a connected graph $G=(V,E)$ and a set $Q\subseteq V$ of query vertices, find a subgraph of $G$ that connects all query vertices and has minimum Wiener index. We show that The Minimum Wiener Connector admits a polynomial-time (albeit impractical) exact algorithm for the special case where the number of query vertices is bounded. We show that in general the problem is NP-hard, and has no PTAS unless $\mathbf{P} = \mathbf{NP}$. Our main contribution is a constant-factor approximation algorithm running in time $\widetilde{O}(|Q||E|)$. A thorough experimentation on a large variety of real-world graphs confirms that our method returns smaller and denser solutions than other methods, and does so by adding to the query set $Q$ a small number of important vertices (i.e., vertices with high centrality).Comment: Published in Proceedings of the 2015 ACM SIGMOD International Conference on Management of Dat