Search Results (7 total)

The paper reports on how educational research informed and supported both the process of refinement of introductory physics laboratory instruction and student development of scientific abilities. In particular we focus on how the action research approach paradigm combined with instructional approaches such as scaffolding and formative assessment can be used to design the learning environment, investigate student learning, revise curriculum materials, and conduct subsequent assessment. As the result of the above efforts we found improvement in students’ scientific abilities over the course of three years. We suggest that the process used to improve the curriculum under study can be extended to many instructional innovations.

The paper introduces a set of formative assessment tasks and rubrics that were developed for use in an introductory physics instruction to help students acquire and self-assess various scientific process abilities. We will describe the rubrics, tasks, and the student outcomes in courses where the tasks and rubrics were used.

In the context of the dynamical mean-field theory (DMFT) of the Hubbard model, we study the behavior of the compressibility near the density driven Mott transition at finite temperatures. We demonstrate this divergence using DMFT and quantum Monte Carlo simulations in the one-band and the two-band Hubbard model. We supplement this result with considerations based on the Landau theory framework, and discuss the relevance of our results to the α-γ end point in cerium.

The electric-dipole moment (edm) of the ground state of cesium has been measured using a two-laser method that does not require the presence of an external B field. The measured value d_Cs=(-1.8±6.7±1.8)×10^-24 e cm implies that the electron EDM is d_e=(-1.5±5.5±1.5)×10^-26 e cm. This result represents more than an order-of-magnitude improvement over all previous limits.

The dc Stark shift of the cesium D lines is observed in the low-field limit where the induced shift is small compared with the various hyperfine splittings. On the D2 line, modification by the electric field of the dipole transition rates to the various excited-state hyperfine levels must be taken into account in order to interpret our results. From our observations the following atomic polarizabilities in units of 10^-24 cm³ are deduced: α₀(6P_1/2)-α₀(6S_1/2)=143.8±1.4, α₀(6p_3/2)-α₀(6S_1/2)=187.3±1.9, and α₂(6P_3/2)=-38.6±1.2.

A new technique involving detection of both fragments associated with each fission event by two thin-film scintillation detectors is investigated to obtain information about fragment mass and energy. The functional behavior of the film response to fission fragments of specified E / M and Z is obtained by combining the specific luminescence and specific energy loss data for heavy ions. The analysis of the scintillation data gives fragment mass and energy distributions and mass-energy correlations whose main features are in good agreement with those of semiconductor detector measurements. In addition it is found that the scintillation data are capable of revealing information on the average charge to mass relation of the fragments in the symmetric region.

NUCLEAR REACTIONS, FISSION Fragment mass-energy investigation with thin-film scintillation detectors.

The average emission times of K x rays emitted from U²³⁶ fission fragments and the multiplicities of K x rays from Cf²⁵² fission fragments of specified atomic numbers have been determined. The average emission times of K x rays from U²³⁶ fragments were determined by detecting the x rays in the two cases of the emitting fragments moving towards and away from the x-ray detector in the time ranges of 110 and 1000 nsec after fission. The most striking delayed K x-ray emitter is found to be ₅₂Te, wherein (79±5)% of the K x rays are emitted in the time interval 110-1000 nsec. Information about the cascade emission of K x rays from Cf²⁵² fission fragments of specified atomic numbers was obtained by measuring the energy spectra of coincident K x rays with two Si(Li) x-ray detectors operated in coincidence with each other and with fission. From the analysis of these spectra the first and second moments of the x-ray emission distribution function were determined. A noteworthy feature of these results is that there exists a significantly large probability for a cascade emission of K x rays in several cases. The cascade emission is found to be, in general, more predominant in the heavy-fragment group as compared to the light-fragment group. In the heavy group, a strong odd-even effect is reflected on the cascade-emission probability. The observed effect on the average K x-ray yield per fragment, if only those events are selected in which the complementary fragment charge has emitted a K x ray, is also discussed.