3,459 research outputs found

    Topology and Phases in Fermionic Systems

    Full text link
    There can exist topological obstructions to continuously deforming a gapped Hamiltonian for free fermions into a trivial form without closing the gap. These topological obstructions are closely related to obstructions to the existence of exponentially localized Wannier functions. We show that by taking two copies of a gapped, free fermionic system with complex conjugate Hamiltonians, it is always possible to overcome these obstructions. This allows us to write the ground state in matrix product form using Grassman-valued bond variables, and show insensitivity of the ground state density matrix to boundary conditions.Comment: 4 pages, see also arxiv:0710.329

    Potential of Natural Ventilation in Shopping Centres

    Get PDF

    Not Quite Equal Odds: Openness to Experience Moderates the Relation Between Quantity and Quality of Ideas in Divergent Production

    Get PDF
    Since brainstorming was introduced as a technique in 1953 it has been assumed that the best way to produce good ideas is through the production of many ideas, which has later been named the equal-odds rule. However, this finding that productivity often leads to creative quality has rarely been examined in psychometric studies of creative cognition. To close this knowledge gap, we examined the relationship between individual differences in creative personality, as assessed by the personality trait openness to experience, and both the quantity and quality of ideas produced in a divergent thinking task. Across 154 graduate students we found a positive and significant relationship between creative personality and the number of ideas produced, as well as their creative value. The present results indicate that while quantity does breed quality in creative production, the effect is moderated by individual differences, specifically the personality trait Openness to Experience. As the level of Openness to Experience increases, the relation of quantity of ideas to average Creative value gradually becomes positive and significant. We discuss the possible reasons for and implications of our findings

    Potential toxicity of some traditional leafy vegetables consumed in Nyang’oma division, western Kenya

    Get PDF
    Traditional leafy vegetables are those plants whose leaves or aerial parts have been integrated in a community’s culture for use as food over a long span of time. These vegetables are highly recommended due to their relatively high nutritional value  compared to the introduced varieties, and are also important in food security. Qualitative phytochemical screening, using  standard laboratory procedure, was carried out for alkaloids, saponins, cardenolides, flavonoids and polyphenols on traditional  leafy vegetables consumed amongst the Luo, an agro-pastoral community living along the shores of lake Victoria, Western  Kenya. The vegetables were: Amaranthus hybridus L. (subsp.hybridus), Asystasia mysorensis T. Anderson, Coccinia grandis (L) Voigt, Crotalaria ochroleuca (Kotschy) Polhill, Cucurbita maxima Duchesne ex Lam, Portulaca quadrifida L., Sesamum calycimum Welw. var. angustifolium (Oliv.) Ihlenf. and Siedenst., Senna occidentalis L. and Sida acuta Burm. F. All the vegetables were found to contain polyphenols and flavanoids while other classes of phytochemicals varied from species to species Brine shrimp lethality tests  revealed that S. calycimum var. angustifolium (LC50 84.8 μg/ml), S. occidentalis (LC5099.5 μg/ml), S. acuta (LC50 99.4 μg/ml), C. grandis (LC50  100.6 μg/ml) and A. mysorensis (LC50 207.7 μg/ml) exhibited marked levels of toxicity. C. ochroleuca (Sunnhemp) contained all the five classes of  phytochemicals, but proved less toxic (LC50 4511.3 μg/ml). This vegetable is highly utilized in Nyang’oma, and seventy per cent of the respondents consume this species. A. hybridus (African spinach, or Amaranth) was found to be the least toxic (LC50 6233.6 μg/ml) and this vegetable is recommended for consumption. From the results, five vegetables contain possible agents that can cause acute or chronic toxicities when consumed in large quantities or over a long period of  time. Hence some vegetables should be consumed with great care. Though further studies are required to determine which of the phytochemicals are lethal to mammals.Key words: Traditional vegetables, phytochemicals, toxicity, Luo, Nyang’om

    Relativistic quantum clocks

    Full text link
    The conflict between quantum theory and the theory of relativity is exemplified in their treatment of time. We examine the ways in which their conceptions differ, and describe a semiclassical clock model combining elements of both theories. The results obtained with this clock model in flat spacetime are reviewed, and the problem of generalizing the model to curved spacetime is discussed, before briefly describing an experimental setup which could be used to test of the model. Taking an operationalist view, where time is that which is measured by a clock, we discuss the conclusions that can be drawn from these results, and what clues they contain for a full quantum relativistic theory of time.Comment: 12 pages, 4 figures. Invited contribution for the proceedings for "Workshop on Time in Physics" Zurich 201
    • …
    corecore