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This paper reports on the results of an experiment to test the use of a Peer Instruction (PI) pedagogical model in a small class, high school environment. The study reports findings based on a population of 213 high school students attending algebra based physics courses, both Honors and A level, taught by 5 different instructors. The results show a correlation between use of Peer Instruction and improved student conceptual understanding, as demonstrated by gains on a pre-/post- assessment instrument (FCI). However, there also appears to be a number of other factors that strongly influence the resulting gains. In addition to instructor differences, the data seem to indicate that students who are more "physics-inclined" and can answer questions correctly prior to instruction and prior to any Peer Instruction discussion subsequently achieve higher gains as measured by the FCI. While this is to be expected, the use of normalized gains is intended to mitigate this result, but it appears to be prevalent nonetheless. This raises questions as to what degree the FCI gains can be attributed to the use of Peer Instruction, to teacher differences, to student ability level or to simply increased familiarity with the question types presented on the FCI.
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A total of 1067 speckle observations of 345 binary stars are presented. Of these, 161 are double stars first resolved by Hipparcos, 17 are resolved for the first time in the observations presented here, and 21 are stars previously discovered by our program and reported in earlier papers in the series. In 947 cases, a magnitude difference is reported along with the relative astrometry. When comparing to systems with very well-known orbits, we find that the root mean square (rms) deviation in separation residuals is 2.81 0.28 mas, and the rms deviation in position angle residuals is 0.88 0.07°. The magnitude difference measures show no significant deviation from Hipparcos photometry, and have average standard deviation of approximately 0.10 mag as judged from repeat observations. Five important systems discovered by Hipparcos are discussed. © 2008. The American Astronomical Society. All rights reserved..
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The "dynamic" Hubbard Hamiltonian describes interacting fermions on a lattice whose on-site repulsion is modulated by a coupling to a fluctuating bosonic field. We investigate one such model, introduced by Hirsch, using the determinant quantum Monte Carlo method. Our key result is that the extended s -wave pairing vertex, repulsive in the usual static Hubbard model, becomes attractive as the coupling to the fluctuating Bose field increases. The sign problem prevents us from exploring a low enough temperature to see if a superconducting transition occurs. We also observe a stabilization of antiferromagnetic correlations and the Mott gap near half-filling, and a near linear behavior of the energy as a function of particle density which indicates a tendency toward phase separation. © 2008 The American Physical Society.
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