Two-dimensional semimetal-insulator transition in HgTe-based quantum wells induced by a longitudinal magnetic field

A metal-insulator transition in a two-dimensional semimetal based on HgTe quantum wells is discovered. The transition is induced by a magnetic field applied parallel to the plane of the quantum well. The threshold behavior of the activation energy as a function of the magnetic-field strength and an abrupt reduction of the Hall resistance at the onset of the transition suggest that the observed effect originates from the formation of an excitonic insulator.

Analysis of confinement potential fluctuation and band-gap renormalization effects on excitonic transition in GaAs/AlGaAs multiquantum wells grown on (100) and (311)A GaAs surfaces

The competition between confinement potential fluctuations and band-gap renormalization (BGR) in GaAs/AlxGa1-xAs quantum wells grown on [1 0 0] and [3 1 1]A GaAs substrates is evaluated. The results clearly demonstrate the coexistence of the band-tail states filling related to potential fluctuations and the band-gap renormalization caused by an increase in the density of photogenerated carriers during the photoluminescence (PL) experiments. Both phenomena have strong influence on temperature dependence of the PL-peak energy (E-PL(T)). As the photon density increases, the E-PL can shift to either higher or lower energies, depending on the sample temperature. The temperature at which the displacement changes from a blueshift to a redshift is governed by the magnitude of the potential fluctuations and by the variation of BGR with excitation density. A simple band-tail model with a Gaussian-like distribution of the density of state was used to describe the competition between the band-tail filling and the BGR effects on E-PL(T). (C) 2012 Elsevier B.V. All rights reserved.

Erythropoietin prevents sepsis-related acute kidney injury in rats by inhibiting NF-kappa B and upregulating endothelial nitric oxide synthase

de Souza ACCP, Volpini RA, Shimizu MH, Sanches TR, Camara NOS, Semedo P, Rodrigues CE, Seguro AC, Andrade L. Erythropoietin prevents sepsis-related acute kidney injury in rats by inhibiting nuclear factor-kappa B and upregulating endothelial nitric oxide synthase. Am J Physiol Renal Physiol 302: F1045-F1054, 2012. First published January 11, 2012; doi:10.1152/ajprenal.00148.2011.-The pathophysiology of sepsis involves complex cytokine and inflammatory mediator networks, a mechanism to which NF-kappa B activation is central. Downregulation of endothelial nitric oxide synthase (eNOS) contributes to sepsis-induced endothelial dysfunction. Erythropoietin (EPO) has emerged as a major tissue-protective cytokine in the setting of stress. We investigated the role of EPO in sepsis-related acute kidney injury using a cecal ligation and puncture (CLP) model. Wistar rats were divided into three primary groups: control (sham-operated); CLP; and CLP + EPO. EPO (4,000 IU/kg body wt ip) was administered 24 and 1 h before CLP. Another group of rats received N-nitro-L-arginine methyl ester (L-NAME) simultaneously with EPO administration (CLP + EPO + L-NAME). A fifth group (CLP + EPOtreat) received EPO at 1 and 4 h after CLP. At 48 h postprocedure, CLP + EPO rats presented significantly higher inulin clearance than did CLP and CLP + EPO + L-NAME rats; hematocrit levels, mean arterial pressure, and metabolic balance remained unchanged in the CLP + EPO rats; and inulin clearance was significantly higher in CLP + EPOtreat rats than in CLP rats. At 48 h after CLP, creatinine clearance was significantly higher in the CLP + EPO rats than in the CLP rats. In renal tissue, pre-CLP EPO administration prevented the sepsis-induced increase in macrophage infiltration, as well as preserving eNOS expression, EPO receptor (EpoR) expression, IKK-alpha activation, NF-kappa B activation, and inflammatory cytokine levels, thereby increasing survival. We conclude that this protection, which appears to be dependent on EpoR activation and on eNOS expression, is attributable, in part, to inhibition of the inflammatory response via NF-kappa B downregulation.

Magnetophotoluminescence study of GaAs/AlGaAs coupled double quantum wells with bimodal heterointerface roughness

This work reports on the results of magnetophotoluminescence (MPL) measurements carried out in a sample containing two Al0.35Ga0.65As/GaAs, coupled double quantum wells (CDQWs), with inter-well barriers of different thicknesses, which have the heterointerfaces characterized by a distribution of bimodal roughness. The MPL measurements were performed at 4 K, with magnetic fields applied parallel to the growth direction, and varying from 0 to 12 T. The diamagnetic shift of the photoluminescence (PL) peaks is more sensitive to changes in the confinement potential, due to monolayer variations in the mini-well thickness, rather than to the exciton localization at the local potential fluctuations. As the magnetic field increases, the relative intensities of the two peaks in each PL band inverts, what is attributed to the reduction in the radiative lifetime of the delocalized excitons, which results in the radiative recombination, before the excitonic migration between the higher and lower energy regions in each CDQW occurs. The dependence of the full width at half maximum (FWHM) on magnetic field shows different behaviors for each PL peak, which are attributed to the different levels and correlation lengths of the potential fluctuations present in the regions associated with each recombination channel. (C) 2011 Elsevier B.V. All rights reserved.

Theoretical and experimental study of the excitonic binding energy in GaAs/AlGaAs single and coupled double quantum wells

This paper discusses the theoretical and experimental results obtained for the excitonic binding energy (Eb) in a set of single and coupled double quantum wells (SQWs and CDQWs) of GaAs/AlGaAs with different Al concentrations (Al%) and inter-well barrier thicknesses. To obtain the theoretical Eb the method proposed by Mathieu, Lefebvre and Christol (MLC) was used, which is based on the idea of fractional-dimension space, together with the approach proposed by Zhao et al., which extends the MLC method for application in CDQWs. Through magnetophotoluminescence (MPL) measurements performed at 4 K with magnetic fields ranging from 0 T to 12 T, the diamagnetic shift curves were plotted and adjusted using two expressions: one appropriate to fit the curve in the range of low intensity fields and another for the range of high intensity fields, providing the experimental Eb values. The effects of increasing the Al% and the inter-well barrier thickness on Eb are discussed. The Eb reduction when going from the SQW to the CDQW with 5 Å inter-well barrier is clearly observed experimentally for 35% Al concentration and this trend can be noticed even for concentrations as low as 25% and 15%, although the Eb variations in these latter cases are within the error bars. As the Zhao's approach is unable to describe this effect, the wave functions and the probability densities for electrons and holes were calculated, allowing us to explain this effect as being due to a decrease in the spatial superposition of the wave functions caused by the thin inter-well barrier.

The Gemini NICI planet-finding campaign: the frequency of giant planets around young B and A stars

We have carried out high contrast imaging of 70 young, nearby B and A stars to search for brown dwarf and planetary companions as part of the Gemini NICI Planet-Finding Campaign. Our survey represents the largest, deepest survey for planets around high-mass stars (≈1.5-2.5 M ☉) conducted to date and includes the planet hosts β Pic and Fomalhaut. We obtained follow-up astrometry of all candidate companions within 400 AU projected separation for stars in uncrowded fields and identified new low-mass companions to HD 1160 and HIP 79797. We have found that the previously known young brown dwarf companion to HIP 79797 is itself a tight (3 AU) binary, composed of brown dwarfs with masses 58$^{+21}_{-20}$ M Jup and 55$^{+20}_{-19}$ M Jup, making this system one of the rare substellar binaries in orbit around a star. Considering the contrast limits of our NICI data and the fact that we did not detect any planets, we use high-fidelity Monte Carlo simulations to show that fewer than 20% of 2 M ☉ stars can have giant planets greater than 4 M Jup between 59 and 460 AU at 95% confidence, and fewer than 10% of these stars can have a planet more massive than 10 M Jup between 38 and 650 AU. Overall, we find that large-separation giant planets are not common around B and A stars: fewer than 10% of B and A stars can have an analog to the HR 8799 b (7 M Jup, 68 AU) planet at 95% confidence. We also describe a new Bayesian technique for determining the ages of field B and A stars from photometry and theoretical isochrones. Our method produces more plausible ages for high-mass stars than previous age-dating techniques, which tend to underestimate stellar ages and their uncertainties.

Wohlbefinden, Gesundheit und kognitive Kompetenz im Alter : Ergebnisse der Basler Interdisziplinären Altersstudie IDA

Hier wird ein Überblick über den aktuellen Forschungsstand zu Wohlbefinden, Gesundheit und Gedächtnis im Alter gegeben, der ergänzt wird mit Ergebnissen einer grossen interdisziplinären Studie, die u.a. auf folgende Themenkomplexe eingeht -> Stellenwert des Gesundheitsverhaltens Ernährung, Vitaminstatus, Sport, Rauchen) und sozialer Netzwerke in Bezug auf Wohlbefinden, Gesundheit und Gedächtnis. -> Effiziez vn Interventionsmöglichkeiten (Gedächtnistraining, Schauspieltraining, Krafttraining) für die Erhaltung von Wohlbefinden, Gesundheit udn geistiger Leistungsfähigkeit. -> Welche Rolle spielen diesbezüglich Persönlichkeit und Selbstverantwortlichkeit? Angesichts der grossen sozialpolitischen Bedeutung, die den Fragen nach den Determinanten gesunden und autonomen Alterns zukommt, gibt dieses Buch neue Impulse für prophylaktische und diagnostische Interventionsmassnahmen.

Benjamin Disraeli : zum 50. Todestage am 19. April 1931

B. Segalowitsch

Exchange Market Pressure on the Pound-Dollar Exchange Rate: 1925-1931

An investigation of exchange market pressure against the pound sterling during the inter-war period. The main findings are that a) the behavior of UK fundamentals relative to those of the USA help to explain exchange market pressure against the pound; b) during the run up to devaluation in September 1931 the monetary authorities in the UK were acting to reduce domestic credit; but that c) additional pressure was brought against the pound from speculative sources. These findings relate to current thinking on the choice of exchange rate regime as even well behaved fundamentals may not be sufficient to sustain a currency on its peg.

Silberne B'somimbüchsen [Illustration]

Scan von Monochrom-Mikroform

Rechtsanwalt Wassili Bermann : (3. September 1862 - 18. März 1896)

G. B.

El discurso en su devenir : Variantes de escritura y de lectura en 'De la anarquía' de J. B. Alberdi

El presente trabajo propone una aproximación a la operatoria escritural de J.B. Alberdi a partir del estudio de las variantes de escritura y de lectura relevadas en la edición genética, que he realizado, de De la anarquía y sus dos causas principales, del gobierno y sus dos elementos necesarios en la República Argentina con motivo de su reorganización por Buenos Aires (1862). Alberdi es el primer lector de su texto, un lector exigente que reescribe, censura y modifica. A través de las sucesivas modificaciones del texto, dadas por la sustitución, la supresión, el desplazamiento de sentido y la adición, se ofrece el discurso escrito en su devenir y, por ende, el pensamiento en movimiento. Por un lado, actúa un escritor-lector que, simultáneamente, escribe y lee, y a veces interrumpe el ritmo para reescribir al correr de la pluma (variantes de escritura). En otras ocasiones, el escritor hace una pausa para (re)leer y revisar lo escrito hasta ese momento y surgen las reescrituras (variantes de lectura). Las escrituras y reescrituras leídas simultáneamente son el ámbito ideal para estudiar la lucha alberdiana entre la pasión y el intelecto, entre la subjetividad y la objetividad

El discurso en su devenir : Variantes de escritura y de lectura en 'De la anarquía' de J. B. Alberdi

El presente trabajo propone una aproximación a la operatoria escritural de J.B. Alberdi a partir del estudio de las variantes de escritura y de lectura relevadas en la edición genética, que he realizado, de De la anarquía y sus dos causas principales, del gobierno y sus dos elementos necesarios en la República Argentina con motivo de su reorganización por Buenos Aires (1862). Alberdi es el primer lector de su texto, un lector exigente que reescribe, censura y modifica. A través de las sucesivas modificaciones del texto, dadas por la sustitución, la supresión, el desplazamiento de sentido y la adición, se ofrece el discurso escrito en su devenir y, por ende, el pensamiento en movimiento. Por un lado, actúa un escritor-lector que, simultáneamente, escribe y lee, y a veces interrumpe el ritmo para reescribir al correr de la pluma (variantes de escritura). En otras ocasiones, el escritor hace una pausa para (re)leer y revisar lo escrito hasta ese momento y surgen las reescrituras (variantes de lectura). Las escrituras y reescrituras leídas simultáneamente son el ámbito ideal para estudiar la lucha alberdiana entre la pasión y el intelecto, entre la subjetividad y la objetividad