From semiclassical transport to quantum Hall effect under low-field Landau quantization

The crossover from the semiclassical transport to quantum Hall effect is studied by examining a two-dimensional electron system in an AlGaAs/GaAs heterostructure. By probing the magneto-oscillations, it is shown that the semiclassical Shubnikov-de Haas (SdH) formulation can be valid even when the minima of the longitudinal resistivity approach zero. The extension of the applicable range of the SdH theory could be due to the damping effects resulting from disorder and temperature. Moreover, we observed plateau-plateau transition like behavior with such an extension. From our study, it is important to include the positive magnetoresistance to refine the SdH theory.Comment: 11 pages, 5 figure

Temperature-Sensitive Alleles of Radially Swollen2 Link the KORRIGAN Endo-1,4-fl-Glucanase to Cellulose Synthesis and Cytokinesis

An 8.5-kb cosmid containing the KORRIGAN gene complements the cellulose-deficient rsw2-1 mutant of Arabidopsis. Three temperature-sensitive alleles of rsw2show single amino acid mutations in the putative endo-1,4-β-glucanase encoded by KOR. The F1 from crosses betweenkor-1 and rsw2 alleles shows a weak, temperature-sensitive root phenotype. The shoots ofrsw2-1 seedlings produce less cellulose and accumulate a short chain, readily extractable glucan resembling that reported forrsw1 (which is defective in a putative glycosyltransferase required for cellulose synthesis). The double mutant (rsw2-1 rsw1) shows further reductions in cellulose production relative to both single mutants, constitutively slow root growth, and enhanced temperature-sensitive responses that are typically more severe than in either single mutant. Abnormal cytokinesis and severely reduced birefringent retardation in elongating root cell walls of rsw2 link the enzyme to cellulose production for primary cell walls and probably cell plates. The Rsw2− phenotype generally resembles the Kor−and cellulose-deficient Rsw1− phenotypes, but anther dehiscence is impaired in Rsw2-1−. The findings link a second putative enzyme activity to cellulose synthesis in primary cell walls of Arabidopsis and further increases the parallels to cellulose synthesis in Agrobacterium tumefaciens where thecelA and celC genes are required and encode a putative glycosyltransferase and an endo-1,4-β-glucanase related to RSW1 and KOR, respectively

Síndrome intra-selar: análise de 506 cirurgias transesfenoidais

Entre 506 cirurgias transesfenoidais realizadas pelo autor, foram selecionados para análise 404 casos assim distribuidos: 396 tumores hipofisários, 4 cistos intra-selares e 4 selas vazias. Com base nos sintomas apresentados pelos pacientes delineou-se a "síndrome intra-selar" caracterizada por cefaléia, desordens visuais e desendocrinias. Esta tríade pode às vezes aparecer incompleta. Chama-se atenção para casos de tumor intra-selar com RX da sela turcica normal, onde o diagnóstico se faz apenas pelo perfil endocrinológico. Mostra o autor que o reconhecimento da síndrome intra-selar pode ser feito precocemente se está atento para ela. Enfim o tratamento pela cirurgia transesfenoidal é simples e de excelentes resultados. A mortalidade na casuística do autor foi de 0,2%