Radiation induced zero-resistance states: a dressed electronic structure effect

Recent results on magnetoresistance in a two dimensional electron gas under crossed magnetic and microwave fields show a new class of oscillations, suggesting a new kind of zero-resistance states. A complete understanding of the effect is still lacking. We consider the problem from the point of view of the electronic structure dressed by photons due to a in plane linearly polarized ac field. The dramatic changes in the dressed electronic structure lead to a interpretation of the new magnetoresistance oscillations as a persistent-current like effect, induced by the radiation field.Comment: 5 pages, 5 figures, revtex4, changes in introduction and added reference

Managing the gap: the psychology of personal transition

Thesis (Ed.D.)--Boston UniversityChange is an increasing factor in our daily lives as well as in our life stories. "Change" can be distinguished from "transition;" change denotes an alteration, or perceived alteration, in a condition or circumstance. Transition, on the other hand, refers to the process, or the result of the process, by which an individual adapts to change and re-establishes a sense of stability. Change is a catalyst for transition; transition re-aligns the self in relation to the environment. This dissertation proposes a new theoretical model of personal transition based on concepts of self and identity. The model, referred to as The Gap Management Model, is proposed as a tool for both applied and theoretical use. It explores how people cope with change and why some responses are functional while others are dysfunctional. The model accounts for factors that have been identified by others as influencing the difficulty of transition such as timeliness, desirability, scope, etc., and is consistent with the phases of transition described in existing transition process models. Although existing models are useful, none thus far has been applicable to all types of transition (driven by changes that are internal or external, expected or unexpected) while at the same time explaining why people react to change the way they do and how they attempt to regain a sense of normalcy in their lives. The proposed model will link existing, well-accepted theory and research in creating a unified model of personal transition. The three-part ritual structure of stability-liminality-stability is mirrored in the psychological processes of transition as they have been observed. The model explores the middle phase of liminality as an important step in psychological realignment. The central concept of the model is that people strive for a sense of congruity between their internal sense of self and the roles and relationships they maintain. Lack of congruity creates uncertainty and distress, feelings characteristic of the liminal experience. Three different applications of the model are presented: adolescence, the college to post-college transition, and WWII-era Civil Resettlement Units for ex-POWs. The author's own research data is employed for the college to post-college example

Terra incognita—cerebellar contributions to neuropsychiatric and cognitive dysfunction in behavioral variant frontotemporal dementia

Although converging evidence has positioned the human cerebellum as an important relay for intact cognitive and neuropsychiatric processing, changes in this large structure remain mostly overlooked in behavioral variant frontotemporal dementia (bvFTD), a disease which is characterized by cognitive and neuropsychiatric deficits. The present study assessed whether degeneration in specific cerebellar subregions associate with indices of cognition and neuropsychiatric performance in bvFTD. Our results demonstrate a relationship between cognitive and neuropsychiatric decline across various domains of memory, language, emotion, executive, visuospatial function, and motivation and the degree of gray matter degeneration in cerebellar lobules V–VII. Most notably, bilateral cerebellar lobule VII and the posterior vermis emerged as distinct for memory processes, the right cerebellar hemisphere underpinned emotion, and the posterior vermis was highlighted in language dysfunction in bvFTD. Based on cortico-cerebellar connectivity maps, these findings in the cerebellum are consistent with the neural connections with the cortices involved in these domains in patients with bvFTD. Overall, the present study underscores the significance of cortical-cerebellar networks associated with cognition and neuropsychiatric dysfunction in bvFTD

Resources and student achievement – evidence from a Swedish policy reform

This paper utilizes a policy change to estimate the effect of teacher density on student performance. We find that an increase in teacher density has a positive effect on student achievement. The baseline estimate – obtained by using the grade point average as the outcome variable – implies that resource increases corresponding to the class-size reduction in the STAR-experiment (i.e., a reduction of 7 students) improves performance by 2.6 percentile ranks (or 0.08 standard deviations). When we use test score data for men, potentially a more objective measure of student performance, the effect of resources appears to be twice the size of the baseline estimate.Student performance; teacher/student ratio; policy reform; differences-in-differences

Long-Range Excitons in Optical Absorption Spectra of Electroluminescent Polymer Poly(para-phenylenevinylene)

The component of photoexcited states with large spatial extent is investigated for poly(para-phenylenevinylene) using the intermediate exciton theory. We find a peak due to long-range excitons at the higher-energy side of the lowest main feature of optical spectra. The fact that the onset of long-range excitons is located near the energy gap is related to the mechanisms of large photocurrents measured in such energy regions. We show that a large value of the hopping integral is realistic for characterizing optical excitations.Comment: To be published in J. Phys. Soc. Jpn. (Letters