Hole spin dephasing time associated to hyperfine interaction in quantum dots

The spin interaction of a hole confined in a quantum dot with the surrounding nuclei is described in terms of an effective magnetic field. We show that, in contrast to the Fermi contact hyperfine interaction for conduction electrons, the dipole-dipole hyperfine interaction is anisotropic for a hole, for both pure or mixed hole states. We evaluate the coupling constants of the hole-nuclear interaction and demonstrate that they are only one order of magnitude smaller than the coupling constants of the electron-nuclear interaction. We also study, theoretically, the hole spin dephasing of an ensemble of quantum dots via the hyperfine interaction in the framework of frozen fluctuations of the nuclear field, in absence or in presence of an applied magnetic field. We also discuss experiments which could evidence the dipole-dipole hyperfine interaction and give information on hole mixing.Comment: 35 pages, 7 figures and 2 table

Bistability of the Nuclear Polarisation created through optical pumping in InGaAs Quantum Dots

We show that optical pumping of electron spins in individual InGaAs quantum dots leads to strong nuclear polarisation that we measure via the Overhauser shift (OHS) in magneto-photoluminescence experiments between 0 and 4T. We find a strongly non-monotonous dependence of the OHS on the applied magnetic field, with a maximum nuclear polarisation of 40% for intermediate magnetic fields. We observe that the OHS is larger for nuclear fields anti-parallel to the external field than in the parallel configuration. A bistability in the dependence of the OHS on the spin polarization of the optically injected electrons is found. All our findings are qualitatively understood with a model based on a simple perturbative approach.Comment: Phys Rev B (in press

Full coherent control of nuclear spins in an optically pumped single quantum dot

Highly polarized nuclear spins within a semiconductor quantum dot (QD) induce effective magnetic (Overhauser) fields of up to several Tesla acting on the electron spin or up to a few hundred mT for the hole spin. Recently this has been recognized as a resource for intrinsic control of QD-based spin quantum bits. However, only static long-lived Overhauser fields could be used. Here we demonstrate fast redirection on the microsecond time-scale of Overhauser fields of the order of 0.5 T experienced by a single electron spin in an optically pumped GaAs quantum dot. This has been achieved using full coherent control of an ensemble of 10^3-10^4 optically polarized nuclear spins by sequences of short radio-frequency (rf) pulses. These results open the way to a new class of experiments using rf techniques to achieve highly-correlated nuclear spins in quantum dots, such as adiabatic demagnetization in the rotating frame leading to sub-micro K nuclear spin temperatures, rapid adiabatic passage, and spin squeezing

Niche as a determinant of word fate in online groups

Patterns of word use both reflect and influence a myriad of human activities and interactions. Like other entities that are reproduced and evolve, words rise or decline depending upon a complex interplay between {their intrinsic properties and the environments in which they function}. Using Internet discussion communities as model systems, we define the concept of a word niche as the relationship between the word and the characteristic features of the environments in which it is used. We develop a method to quantify two important aspects of the size of the word niche: the range of individuals using the word and the range of topics it is used to discuss. Controlling for word frequency, we show that these aspects of the word niche are strong determinants of changes in word frequency. Previous studies have already indicated that word frequency itself is a correlate of word success at historical time scales. Our analysis of changes in word frequencies over time reveals that the relative sizes of word niches are far more important than word frequencies in the dynamics of the entire vocabulary at shorter time scales, as the language adapts to new concepts and social groupings. We also distinguish endogenous versus exogenous factors as additional contributors to the fates of words, and demonstrate the force of this distinction in the rise of novel words. Our results indicate that short-term nonstationarity in word statistics is strongly driven by individual proclivities, including inclinations to provide novel information and to project a distinctive social identity.Comment: Supporting Information is available here: http://www.plosone.org/article/fetchSingleRepresentation.action?uri=info:doi/10.1371/journal.pone.0019009.s00

Elucidating the mechanism of ferrocytochrome c heme disruption by peroxidized cardiolipin

The interaction of peroxidized cardiolipin with ferrocytochrome c induces two kinetically and chemically distinct processes. The first is a rapid oxidation of ferrocytochrome c, followed by a slower, irreversible disruption of heme c. The oxidation of ferrocytochrome c by peroxidized cardiolipin is explained by a Fenton-type reaction. Heme scission is a consequence of the radical-mediated reactions initiated by the interaction of ferric heme iron with peroxidized cardiolipin. Simultaneously with the heme c disruption, generation of hydroxyl radical is detected by EPR spectroscopy using the spin trapping technique. The resulting apocytochrome c sediments as a heterogeneous mixture of high aggregates, as judged by sedimentation analysis. Both the oxidative process and the destructive process were suppressed by nonionic detergents and/or high ionic strength. The mechanism for generating radicals and heme rupture is presented

Solitary fibrous tumour of the genitourinary tract: a clinicopathological study of 11 cases and their association with the NAB2-STAT6 fusion gene

Aims To characterise clinicopathological features and clinical outcomes of the genitourinary tract solitary fibrous tumours, incorporating NAB2-STAT6 gene fusion status. Methods The presence of the molecular hallmark NAB2-STAT6 gene fusion and for the defining fusion partner product STAT6 was assessed in 11 cases of the genitourinary tract solitary fibrous tumours. NAB2-STAT6 gene fusion analysis was performed using a break-apart fluorescence in situ hybridisation (FISH) probe using a probe cocktail with Bacterial artificial chromosome (BAC) clones for STAT6 and NAB2. Results Eleven solitary fibrous tumours were diagnosed in eight male patients and three female patients with a mean age of 46 years (range: 11–64 years). Four of the tumours had malignant histological features, and three were considered moderate risk for metastasis. With a mean follow-up time of 61 months, 1 recurred locally and 2 presented at distant metastatic sites. Using a break-apart FISH probe cocktail, we found the NAB2-STAT6 gene fusion and nuclear STAT6 expression in 58% and 91% of cases, respectively. However, the NAB2-STAT6 fusion status was not correlated with STAT6 expression or useful in discriminating between malignant histological features or subsequent clinical outcomes in the genitourinary solitary fibrous tumours. Conclusions A subset of solitary fibrous tumours of the genitourinary tract behaved aggressively. Using a break-apart FISH probe cocktail, we found the NAB2-STAT6 gene fusion in 64% of cases. However, the NAB2-STAT6 fusion status was not correlated with STAT6 expression or useful in discriminating between low-risk or high-risk tumours and subsequent clinical outcomes

The STRIPES Trial - Support to Rural India's Public Education System

Background Performance of primary school students in India lags far below government expectations, and major disparity exists between rural and urban areas. The Naandi Foundation has designed and implemented a programme using community members to deliver after-school academic support for children in over 1,100 schools in five Indian states. Assessments to date suggest that it might have a substantial effect. This trial aims to evaluate the impact of this programme in villages of rural Andhra Pradesh and will compare test scores for children in three arms: a control and two intervention arms. In both intervention arms additional after-school instruction and learning materials will be offered to all eligible children and in one arm girls will also receive an additional 'kit' with a uniform and clothes. Methods/Design The trial is a cluster-randomised controlled trial conducted in conjunction with the CHAMPION trial. In the CHAMPION trial 464 villages were randomised so that half receive health interventions aiming to reduce neonatal mortality. STRIPES will be introduced in those CHAMPION villages which have a public primary school attended by at least 15 students at the time of a baseline test in 2008. 214 villages of the 464 were found to fulfil above criteria, 107 belonging to the control and 107 to the intervention arm of the CHAMPION trial. These latter 107 villages will serve as control villages in the STRIPES trial. A further randomisation will be carried out within the 107 STRIPES intervention villages allocating half to receive an additional kit for girls on the top of the instruction and learning materials. The primary outcome of the trial is a composite maths and language test score. Discussion The study is designed to measure (i) whether the educational intervention affects the exam score of children compared to the control arm, (ii) if the exam scores of girls who receive the additional kit are different from those of girls living in the other STRIPES intervention arm. One of the goals of the STRIPES trial is to provide benefit to the controls of the CHAMPION trial. We will also conduct a cost-benefit analysis in which we calculate the programme cost for 0.1 standard deviation improvement for both intervention arms

The Molecular Biogeography of the Indo-Pacific: Testing Hypotheses With Multispecies Genetic Patterns

Aim: To test hypothesized biogeographic partitions of the tropical Indo-Pacific Ocean with phylogeographic data from 56 taxa, and to evaluate the strength and nature of barriers emerging from this test. \u3eLocation: The Indo-Pacific Ocean. Time Period: Pliocene through the Holocene. Major Taxa Studied: Fifty-six marine species. Methods: We tested eight biogeographic hypotheses for partitioning of the Indo-Pacific using a novel modification to analysis of molecular variance. Putative barriers to gene flow emerging from this analysis were evaluated for pairwise ΦST, and these ΦST distributions were compared to distributions from randomized datasets and simple coalescent simulations of vicariance arising from the Last Glacial Maximum. We then weighed the relative contribution of distance versus environmental or geographic barriers to pairwise ΦST with a distance-based redundancy analysis (dbRDA). Results: We observed a diversity of outcomes, although the majority of species fit a few broad biogeographic regions. Repeated coalescent simulation of a simple vicariance model yielded a wide distribution of pairwise ΦST that was very similar to empirical distributions observed across five putative barriers to gene flow. Three of these barriers had median ΦST that were significantly larger than random expectation. Only 21 of 52 species analysed with dbRDA rejected the null model. Among these, 15 had overwater distance as a significant predictor of pairwise ΦST, while 11 were significant for geographic or environmental barriers other than distance. Main Conclusions: Although there is support for three previously described barriers, phylogeographic discordance in the Indo-Pacific Ocean indicates incongruity between processes shaping the distributions of diversity at the species and population levels. Among the many possible causes of this incongruity, genetic drift provides the most compelling explanation: given massive effective population sizes of Indo-Pacific species, even hard vicariance for tens of thousands of years can yield ΦST values that range from 0 to nearly 0.5

Isotope sensitive measurement of the hole-nuclear spin interaction in quantum dots

Decoherence caused by nuclear field fluctuations is a fundamental obstacle to the realization of quantum information processing using single electron spins. Alternative proposals have been made to use spin qubits based on valence band holes having weaker hyperfine coupling. However, it was demonstrated recently both theoretically and experimentally that the hole hyperfine interaction is not negligible, although a consistent picture of the mechanism controlling the magnitude of the hole-nuclear coupling is still lacking. Here we address this problem by performing isotope selective measurement of the valence band hyperfine coupling in InGaAs/GaAs, InP/GaInP and GaAs/AlGaAs quantum dots. Contrary to existing models we find that the hole hyperfine constant along the growth direction of the structure (normalized by the electron hyperfine constant) has opposite signs for different isotopes and ranges from -15% to +15%. We attribute such changes in hole hyperfine constants to the competing positive contributions of p-symmetry atomic orbitals and the negative contributions of d-orbitals. Furthermore, we find that the d-symmetry contribution leads to a new mechanism for hole-nuclear spin flips which may play an important role in hole spin decoherence. In addition the measured hyperfine constants enable a fundamentally new approach for verification of the computed Bloch wavefunctions in the vicinity of nuclei in semiconductor nanostructures

The transition of people’s preferences for the intervention of the government in the economy of re-unified Germany

Covering the first fifteen years immediately after German re- unification, this paper analyzes the people’s support to the transition. The focus is on individuals’ preferences for the intervention of the government in the economy and on the opinion about competition per se. Eastern German data are compared with Western German data. Using suitable data that allow for interpersonal comparisons, the paper shows that Eastern Germans have always preferred an intervention of the public hand in the economy deeper than Western Germans; these different positions have hardly converged during the examined period of time. However there are no significant differences with respect to how Germans perceive competition per se: it is considered as a good by the people living in both parts of the country.info:eu-repo/semantics/publishedVersio