Electron transmission and phase time in semiconductor superlattices

We discuss the time spent by an electron propagating through a finite periodic system such as a semiconductor superlattice. The relation between dwell-time and phase-time is outlined. The envelopes of phase-time at maximum and minimum transmission are derived, and it is shown that the peaks and valleys of phase-time can be well described by parameters fitted at the extrema. For a many-period system this covers most of the allowed band. Comparison is made to direct numerical solutions of the time-dependent Schr\"odinger equation by Veenstra et al. [cond-mat/0411118] who compared systems with and without addition of an anti-reflection coating (ARC). With an ARC, the time delay is consistent with propagation at the Bloch velocity of the periodic system, which significantly reduces the time delay, in addition to increasing the transmissivity.Comment: 8 pages, 10 figures, based on a talk at Theory-Canada 3 in Edmonton AB, June 200

Memory effects induced by initial switching conditions

Initial-switching refers to the way in which the decay of an initially confined state begins, as the barrier isolating it from the exterior is relaxed. We study these effects in the context of Longhi's version of the Fano-Anderson model. Most authors assume the sudden approximation where the coupling is turned on instantaneously. We consider a finite rise time T, both numerically and analytically. When the coupling is ramped up linearly over a switching time T, we show that the asymptotic survival amplitude acquires a phase T and is modulated by a factor (sin T)/T. Several other results relating to the solution of the model are obtained. All site amplitudes have the same decay constant during the exponential decay regime. In the asymptotic regime, the amplitude and phase of decay oscillations depend on the initial-switching profile, but the period does not.Comment: 12 pages, 10 figures, accepted by Phys. Rev.

Hartree Fock Calculations in the Density Matrix Expansion Approach

The density matrix expansion is used to derive a local energy density functional for finite range interactions with a realistic meson exchange structure. Exchange contributions are treated in a local momentum approximation. A generalized Slater approximation is used for the density matrix where an effective local Fermi momentum is chosen such that the next to leading order off-diagonal term is canceled. Hartree-Fock equations are derived incorporating the momentum structure of the underlying finite range interaction. For applications a density dependent effective interaction is determined from a G-matrix which is renormalized such that the saturation properties of symmetric nuclear matter are reproduced. Intending applications to systems far off stability special attention is paid to the low density regime and asymmetric nuclear matter. Results are compared to predictions obtained from Skyrme interactions. The ground state properties of stable nuclei are well reproduced without further adjustments of parameters. The potential of the approach is further exemplified in calculations for A=100...140 tin isotopes. Rather extended neutron skins are found beyond 130Sn corresponding to solid layers of neutron matter surrounding a core of normal composition.Comment: Revtex, 29 pages including 14 eps figures, using epsfig.st

The grinch who stole wisdom

Dr. Seuss is wise. How the Grinch Stole Christmas (Seuss, 1957) could serve as a parable for our time. It can also be seen as a roadmap for the development of contemplative wisdom. The abiding popularity of How the Grinch Stole Christmas additionally suggests that contemplative wisdom is more readily available to ordinary people, even children, than is normally thought. This matters because from the point of view of contemplatives in any of the world's philosophies or religions, people are confused about wisdom. The content of the nascent field of wisdom studies, they might say, is largely not wisdom at all but rather what it's like to live in a particular kind of prison cell, a well appointed cell perhaps, but not a place that makes possible either personal satisfaction or deep problem solving. I believe that what the contemplative traditions have to say is important; they offer a different orientation to what personal wisdom is, how to develop it, and how to use it in the world than is presently contained in either our popular culture or our sciences. In order to illustrate this I will examine, in some detail, one contemplative path within Buddhism. Buddhism is particularly useful in this respect because its practices are nontheistic and thus avoid many of the cultural landmines associated with the contemplative aspects of Western religions

Beta-decay in odd-A and even-even proton-rich Kr isotopes

Beta-decay properties of proton-rich odd-A and even-even Krypton isotopes are studied in the framework of a deformed selfconsistent Hartree-Fock calculation with density-dependent Skyrme forces, including pairing correlations between like nucleons in BCS approximation. Residual spin-isospin interactions are consistently included in the particle-hole and particle-particle channels and treated in Quasiparticle Random Phase Approximation. The similarities and differences in the treatment of even-even and odd-A nuclei are stressed. Comparison to available experimental information is done for Gamow-Teller strength distributions, summed strengths, and half-lives. The dependence of these observables on deformation is particularly emphasized in a search for signatures of the shape of the parent nucleus.Comment: 29 pages, 16 figure

H2AX phosphorylation screen of cells from radiosensitive cancer patients reveals a novel DNA double-strand break repair cellular phenotype

BACKGROUND: About 1-5% of cancer patients suffer from significant normal tissue reactions as a result of radiotherapy (RT). It is not possible at this time to predict how most patients' normal tissues will respond to RT. DNA repair dysfunction is implicated in sensitivity to RT particularly in genes that mediate the repair of DNA double-strand breaks (DSBs). Phosphorylation of histone H2AX (phosphorylated molecules are known as gammaH2AX) occurs rapidly in response to DNA DSBs, and, among its other roles, contributes to repair protein recruitment to these damaged sites. Mammalian cell lines have also been crucial in facilitating the successful cloning of many DNA DSB repair genes; yet, very few mutant cell lines exist for non-syndromic clinical radiosensitivity (RS).\ud \ud METHODS: Here, we survey DNA DSB induction and repair in whole cells from RS patients, as revealed by gammaH2AX foci assays, as potential predictive markers of clinical radiation response.\ud \ud RESULTS: With one exception, both DNA focus induction and repair in cell lines from RS patients were comparable with controls. Using gammaH2AX foci assays, we identified a RS cancer patient cell line with a novel ionising radiation-induced DNA DSB repair defect; these data were confirmed by an independent DNA DSB repair assay.\ud \ud CONCLUSION: gammaH2AX focus measurement has limited scope as a pre-RT predictive assay in lymphoblast cell lines from RT patients; however, the assay can successfully identify novel DNA DSB repair-defective patient cell lines, thus potentially facilitating the discovery of novel constitutional contributions to clinical RS

Exercise-induced improvements in liver fat and endothelial function are not sustained 12 months following cessation of exercise supervision in non-alcoholic fatty liver disease (NAFLD).

AIMS: Supervised exercise reduces liver fat and improves endothelial function, a surrogate of cardiovascular disease risk, in non-alcoholic fatty liver disease (NAFLD). We hypothesised that after a 16-week supervised exercise program, patients would maintain longer-term improvements in cardiorespiratory fitness, liver fat and endothelial function. MATHERIALS AND METHODS: Ten NAFLD patients [5/5 males/females, age 51±13years, BMI 31±3 kg.m(2) (mean±s.d.)] underwent a 16-week supervised moderate-intensity exercise intervention. Biochemical markers, cardiorespiratory fitness (VO2peak), subcutaneous, visceral and liver fat (measured by magnetic resonance imaging and spectroscopy respectively) and brachial artery flow-mediated dilation (FMD) were assessed at baseline, after 16 weeks supervised training and 12-months after ending supervision. RESULTS: Despite no significant change in body weight, there were significant improvements in VO2peak [6.5 ml.kg(-1).min(-1) (95% CI 2.8, 10.1); P=0.003], FMD [2.9% (1.5, 4.2); P=0.001], liver transaminases (P0.05) and liver fat [1.4% (-13.0, 15.9); P=0.83] were not significantly different from baseline. CONCLUSIONS: Twelve months following cessation of supervision, exercise-mediated improvements in liver fat and other cardiometabolic variables had reversed with cardiorespiratory fitness at baseline levels. Maintenance of high cardiorespiratory fitness and stability of body weight are critical public health considerations for the treatment of NAFLD.International Journal of Obesity accepted article preview online, 21 July 2016. doi:10.1038/ijo.2016.123

Nucleation of dislocations and their dynamics in layered oxide cathode materials during battery charging

Defects and their interactions in crystalline solids often underpin material properties and functionality as they are decisive for stability, result in enhanced diffusion, and act as a reservoir of vacancies. Recently, lithium-rich layered oxides have emerged among the leading candidates for the next-generation energy storage cathode material, delivering 50 % excess capacity over commercially used compounds. Oxygen-redox reactions are believed to be responsible for the excess capacity, however, voltage fading has prevented commercialization of these new materials. Despite extensive research the understanding of the mechanisms underpinning oxygen-redox reactions and voltage fade remain incomplete. Here, using operando three-dimensional Bragg coherent diffractive imaging, we directly observe nucleation of a mobile dislocation network in nanoparticles of lithium-rich layered oxide material. Surprisingly, we find that dislocations form more readily in the lithium-rich layered oxide material as compared with a conventional layered oxide material, suggesting a link between the defects and the anomalously high capacity in lithium-rich layered oxides. The formation of a network of partial dislocations dramatically alters the local lithium environment and contributes to the voltage fade. Based on our findings we design and demonstrate a method to recover the original high voltage functionality. Our findings reveal that the voltage fade in lithium-rich layered oxides is reversible and call for new paradigms for improved design of oxygen-redox active materials