Metal-superconductor transition at zero temperature: A case of unusual scaling

An effective field theory is derived for the normal metal-to-superconductor quantum phase transition at T=0. The critical behavior is determined exactly for all dimensions d>2. Although the critical exponents \beta and \nu do not exist, the usual scaling relations, properly reinterpreted, still hold. A complete scaling description of the transition is given, and the physics underlying the unusual critical behavior is discussed. Quenched disorder leads to anomalously strong T_c-fluctuations which are shown to explain the experimentally observed broadening of the transition in low-T_c thin films.Comment: 4 pp., no figs, final version as publishe

Anderson-Mott Transition in a Magnetic Field: Corrections to Scaling

It is shown that the Anderson-Mott metal-insulator transition of paramagnetic, interacting disordered electrons in an external magnetic field is in the same universality class as the transition from a ferromagnetic metal to a ferromagnetic insulator discussed recently. As a consequence, large corrections to scaling exist in the magnetic-field universality class, which have been neglected in previous theoretical descriptions. The nature and consequences of these corrections to scaling are discussed.Comment: 5pp., REVTeX, no figs, final version as publishe

Factors Related to Persistence in the Study of French at the College Level

The current study was conducted to address the problem of declining enrollments in French classes. The purpose was to identify those factors that are responsible for student persistence in the study of French beyond the level required to obtain a general degree from the University. Research questions included the following topics: 1) students’ perception of their motivation for language learning, 2) the relationship of certain activities, the classroom climate, the role of the teacher, and the use of technology, to their motivation for language learning, 3) reasons students give for not continuing with their foreign language studies, and 4) factors language majors and minors attribute to the decision making process that led them to continue with the advanced courses. Using an emergent case study design, the researcher surveyed and interviewed French 102 students and French majors and minors. Classroom observations and a focus group meeting were conducted as a way of triangulating the data. Participants attributed their motivation primarily to two factors — the value of knowing a second language and the beliefs they had developed regarding language study. Beliefs included notions such as the extensive time and study commitment needed to effectively learn a foreign language and the age at which students best acquire language skills. In terms of the French classroom environment, students indicated that any materials other than the textbook were the most motivating and beneficial, including the use of games, songs, and varied media forms. They also stressed the importance of the professor in motivating students. The most non-motivating activity was anything that was required; students insisted on the need for choice in their assignments and content. Students were somewhat indifferent about the use of technology in the French classroom, perhaps because their use of technology was extremely limited. Further research is recommended in the areas of foreign language teacher education and the use of technology in the foreign language classroom, as it becomes more widespread. In addition, research is suggested at the secondary and middle school level, where students may acquire some of the beliefs alluded to during this study

Phase diagram of glassy systems in an external field

We study the mean-field phase diagram of glassy systems in a field pointing in the direction of a metastable state. We find competition among a ``magnetized'' and a ``disordered'' phase, that are separated by a coexistence line as in ordinary first order phase transitions. The coexistence line terminates in a critical point, which in principle can be observed in numerical simulations of glassy models.Comment: 4 pages, 5 figure

Individual tests of school children.

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Advances in large-diameter liquid encapsulated Czochralski GaAs

The purity, crystalline perfection, and electrical properties of n- and p-type GaAs crystals grown by the liquid encapsulated Czochralski (LEC) technique are evaluated. The determination of the dislocation density, incidence of twinning, microstructure, background purity, mobility, and minority carrier diffusion length is included. The properties of the LEC GaAs crystals are generally comparable to, if not superior to those of small-diameter GaAs material grown by conventional bulk growth techniques. As a result, LEC GaAs is suitable for application to minority carrier devices requiring high-quality and large-area substrates