Strain balanced quantum posts

Quantum posts are assembled by epitaxial growth of closely spaced quantum dot layers, modulating the composition of a semiconductor alloy, typically InGaAs. In contrast with most self-assembled nanostructures, the height of quantum posts can be controlled with nanometer precision, up to a maximum value limited by the accumulated stress due to the lattice mismatch. Here we present a strain compensation technique based on the controlled incorporation of phosphorous, which substantially increases the maximum attainable quantum post height. The luminescence from the resulting nanostructures presents giant linear polarization anisotropy.Comment: Submitted to Applied Physics Letters (7th March 2011). 4 pages, 4 figure

An in-the-wild study of learning to brainstorm: Comparing cards, tabletops and wall displays in the classroom

© 2016 The Author 2016. Published by Oxford University Press on behalf of The British Computer Society. Single display interactive groupware interfaces have the potential to effectively support small group work in classrooms. Our work aimed to gain understanding needed to realize that potential. First, we wanted to study how learners use these large interactive displays, compared with a more traditional method within classrooms. Second, we wanted to fill gaps in the current understanding of the effectiveness of interactive tables versus walls. Third, we wanted to do this out of the laboratory setting, in authentic classrooms, with their associated constraints. We conducted an in-the-wild study, with 51 design students, working in 14 groups, learning the brainstorming technique. Each group practiced brainstorming in three classrooms: one with vertical displays (walls); another with multi-touch tabletops; and the third with pens and index cards. The published literature suggested that tabletops would be better than the other conditions for key factors of cooperative participation, mutual awareness, maintaining interest and affective measures. Contrary to this, we found that the horizontal and vertical displays both had similar levels of benefit over the conventional method. It was only for affective measures that tabletops were better than walls. All conditions were similar for our several measures of outcome quality. We discuss the implications of our findings for designing future classrooms

Quasienergy spectrum and tunneling current in ac-driven triple quantum dot shuttles

The dynamics of electrons in ac driven double quantum dots have been extensively analyzed by means of Floquet theory. In these systems, coherent destruction of tunneling has been shown to occur for certain ac field parameters. In the present work we analyze, by means of Floquet theory, the electron dynamics of a triple quantum dot in series attached to electric contacts, where the central dot position oscillates. In particular, we analyze the quasienergy spectrum of this ac driven nanoelectromechanical system, as a function of the intensity and frequency of the ac field and of external dc voltages. For strong driving fields, we derive, by means of perturbation theory, analytical expressions for the quasienergies of the driven oscillator system. From this analysis we discuss the conditions for coherent destruction of tunneling (CDT) to occur as a function of detuning and field parameters. For zero detuning, and from the invariance of the Floquet Hamiltonian under a generalized parity transformation, we find analytical expressions describing the symmetry properties of the Fourier components of the Floquet states under such transformation. By using these expressions, we show that in the vicinity of the CDT condition, the quasienergy spectrum exhibits exact crossings which can be characterized by the parity properties of the corresponding eigenvectors

Perceptive training of youth volleyball blockers

Este estudio analiza la eficacia de un programa de entrenamiento perceptivo basado en la orientación de la atención para la mejora de la toma de decisiones y el rendimiento en la acción de bloqueo de voleibol. 16 jugadoras juveniles fueron distribuidas en tres grupos: vídeo (n=6), que recibió ocho sesiones de entrenamiento en vídeo; mixto (n=5), que recibió 4 sesiones en vídeo y 4 sesiones de práctica en campo; y control (n=5), que completó las pruebas de evaluación. Los resultados muestran cómo el programa de entrenamiento mejoró la toma de decisiones de las jugadoras, ya que redujeron su tiempo de reacción (F(1,13)=9,237, p=0,009, ηp 2=0,415) manteniendo el mismo porcentaje de aciertos. Sin embargo, es necesaria la práctica en campo para lograr transferir dichos aprendizajes al juego real, ya que sólo el grupo mixto mejora el porcentaje de aciertos en el test de rendimiento en campo (F(2,13)=8,608, p=0,004, ηp2=0,570; t(4) =-6,216, p=0,003)This study examines the effectiveness of a training program based on perceptual orientation of attention for improving decision-making and performance in the blocking action of volleyball. 16 youth players were divided into three groups: video (n=6), which received eight perceptual training sessions by video; mixed (n=5), which received only half of the sessions by video, combined with practical training in the field; and control (n=5), which just completed pre-test and post-test tests. Results show how orientation of attention to relevant areas of information improved decision-making of the youth volleyball players because they reduced their reaction time (F(1,13)=9,237, p=0,009, ηp2=0,415) maintaining the same percentage of success. However, the practice on the field is necessary to achieve transfer those learning to the real game, because only mixed group improves the percentage of success in the field performance test (F(2,13)=8,608, p=0,004, ηp2=0,570; t(4)=-6,216, p=0,003

Microsolvation of heavy halides

The fundamental question of how intermolecular interactions lead to the stabilization of heavy halides (Br−, I−, At−) microsolvated with up to six explicit water molecules is addressed here. An exhaustive exploration of the potential energy surfaces using a random search algorithm followed by optimization of molecular geometries using pseudopotentials and at the full four component relativistic levels of theory, affords a good number of structures with high probabilities of occurrence, highlighting the important role of local minima to reproduce experimentally measured properties. Sequential hydration enthalpies for astatide are reported here for the first time in the scientific literature. Closed shell (ionic, long range) as well as intermediate character interactions (contributions from closed shell and covalent) are at play stabilizing the clusters. The ability of water molecules to either donate or to accept electron density dictates the nature and strength of the corresponding hydrogen bonds in solvation shells. Binding energies and molecular geometries are shown to be more sensitive to electron correlation than to relativistic effects

Transcriptomic analysis of the hepatic response to stress in the red cusk-eel (Genypterus chilensis): Insights into lipid metabolism, oxidative stress and liver steatosis

Indexación: Scopus.Teleosts exhibit a broad divergence in their adaptive response to stress, depending on the magnitude, duration, and frequency of stressors and the species receiving the stimulus. We have previously reported that the red cusk-eel (Genypterus chilensis), an important marine farmed fish, shows a physiological response to stress that results in increased skeletal muscle atrophy mediated by over-expression of components of the ubiquitin proteasome and autophagy-lysosomal systems. To better understand the systemic effects of stress on the red cusk-eel metabolism, the present study assessed the transcriptomic hepatic response to repetitive handling-stress. Using high-Throughput RNA-seq, 259 up-regulated transcripts were found, mostly associated with angiogenesis, gluconeogenesis, and triacylglyceride catabolism. Conversely, 293 transcripts were down-regulated, associated to cholesterol biosynthesis, PPARα signaling, fatty acid biosynthesis, and glycolysis. This gene signature was concordant with hepatic metabolite levels and hepatic oxidative damage. Moreover, the increased plasmatic levels of AST (aspartate aminotransferase), ALT (alanine aminotransferase) and AP (alkaline phosphatase), as well as liver histology suggest stress-induced liver steatosis. This study offers an integrative molecular and biochemical analysis of the hepatic response to handling-stress, and reveals unknown aspects of lipid metabolism in a non-model teleost.http://journals.plos.org/plosone/article?id=10.1371/journal.pone.017644

Incidence of debris discs around FGK stars in the solar neighbourhood

Debris discs are a consequence of the planet formation process and constitute the fingerprints of planetesimal systems. Their solar system's counterparts are the asteroid and Edgeworth-Kuiper belts. The aim of this paper is to provide robust numbers for the incidence of debris discs around FGK stars in the solar neighbourhood. The full sample of 177 FGK stars with d<20 pc proposed for the DUNES survey is presented. Herschel/PACS observations at 100 and 160 micron complemented with data at 70 micron, and at 250, 350 and 500 micron SPIRE photometry, were obtained. The 123 objects observed by the DUNES collaboration were presented in a previous paper. The remaining 54 stars, shared with the DEBRIS consortium and observed by them, and the combined full sample are studied in this paper. The incidence of debris discs per spectral type is analysed and put into context together with other parameters of the sample, like metallicity, rotation and activity, and age. The subsample of 105 stars with d<15 pc containing 23 F, 33 G and 49 K stars, is complete for F stars, almost complete for G stars and contains a substantial number of K stars to draw solid conclusions on objects of this spectral type. The incidence rates of debris discs per spectral type 0.26 (6 objects with excesses out of 23 F stars), 0.21 (7 out of 33 G stars) and 0.20 (10 out of 49 K stars), the fraction for all three spectral types together being 0.22 (23 out of 105 stars). Uncertainties corresponding to a 95% confidence level are given in the text for all these numbers. The medians of the upper limits of L_dust/L_* for each spectral type are 7.8E-7 (F), 1.4E-6 (G) and 2.2E-6 (K); the lowest values being around 4.0E-7. The incidence of debris discs is similar for active (young) and inactive (old) stars. The fractional luminosity tends to drop with increasing age, as expected from collisional erosion of the debris belts.Comment: 31 pages, 15 figures, 10 tables, 2 appendice

Efficient metallic spintronic emitters of ultrabroadband terahertz radiation

Terahertz electromagnetic radiation is extremely useful for numerous applications such as imaging and spectroscopy. Therefore, it is highly desirable to have an efficient table-top emitter covering the 1-to-30-THz window whilst being driven by a low-cost, low-power femtosecond laser oscillator. So far, all solid-state emitters solely exploit physics related to the electron charge and deliver emission spectra with substantial gaps. Here, we take advantage of the electron spin to realize a conceptually new terahertz source which relies on tailored fundamental spintronic and photonic phenomena in magnetic metal multilayers: ultrafast photo-induced spin currents, the inverse spin-Hall effect and a broadband Fabry-P\'erot resonance. Guided by an analytical model, such spintronic route offers unique possibilities for systematic optimization. We find that a 5.8-nm-thick W/CoFeB/Pt trilayer generates ultrashort pulses fully covering the 1-to-30-THz range. Our novel source outperforms laser-oscillator-driven emitters such as ZnTe(110) crystals in terms of bandwidth, terahertz-field amplitude, flexibility, scalability and cost.Comment: 18 pages, 10 figure

New measurement of the scattering cross section of slow neutrons on liquid parahydrogen from neutron transmission

Liquid hydrogen is a dense Bose fluid whose equilibrium properties are both calculable from first principles using various theoretical approaches and of interest for the understanding of a wide range of questions in many body physics. Unfortunately, the pair correlation function $g(r)$ inferred from neutron scattering measurements of the differential cross section $d\sigma \over d\Omega$ from different measurements reported in the literature are inconsistent. We have measured the energy dependence of the total cross section and the scattering cross section for slow neutrons with energies between 0.43~meV and 16.1~meV on liquid hydrogen at 15.6~K (which is dominated by the parahydrogen component) using neutron transmission measurements on the hydrogen target of the NPDGamma collaboration at the Spallation Neutron Source at Oak Ridge National Laboratory. The relationship between the neutron transmission measurement we perform and the total cross section is unambiguous, and the energy range accesses length scales where the pair correlation function is rapidly varying. At 1~meV our measurement is a factor of 3 below the data from previous work. We present evidence that these previous measurements of the hydrogen cross section, which assumed that the equilibrium value for the ratio of orthohydrogen and parahydrogen has been reached in the target liquid, were in fact contaminated with an extra non-equilibrium component of orthohydrogen. Liquid parahydrogen is also a widely-used neutron moderator medium, and an accurate knowledge of its slow neutron cross section is essential for the design and optimization of intense slow neutron sources. We describe our measurements and compare them with previous work.Comment: Edited for submission to Physical Review