5,844 research outputs found

    The Kinetic Activation-Relaxation Technique: A Powerful Off-lattice On-the-fly Kinetic Monte Carlo Algorithm

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    Many materials science phenomena, such as growth and self-organisation, are dominated by activated diffusion processes and occur on timescales that are well beyond the reach of standard-molecular dynamics simulations. Kinetic Monte Carlo (KMC) schemes make it possible to overcome this limitation and achieve experimental timescales. However, most KMC approaches proceed by discretizing the problem in space in order to identify, from the outset, a fixed set of barriers that are used throughout the simulations, limiting the range of problems that can be addressed. Here, we propose a more flexible approach -- the kinetic activation-relaxation technique (k-ART) -- which lifts these constraints. Our method is based on an off-lattice, self-learning, on-the-fly identification and evaluation of activation barriers using ART and a topological description of events. The validity and power of the method are demonstrated through the study of vacancy diffusion in crystalline silicon.Comment: 5 pages, 4 figure

    Power grids vulnerability: a complex network approach

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    Power grids exhibit patterns of reaction to outages similar to complex networks. Blackout sequences follow power laws, as complex systems operating near a critical point. Here, the tolerance of electric power grids to both accidental and malicious outages is analyzed in the framework of complex network theory. In particular, the quantity known as efficiency is modified by introducing a new concept of distance between nodes. As a result, a new parameter called net-ability is proposed to evaluate the performance of power grids. A comparison between efficiency and net-ability is provided by estimating the vulnerability of sample networks, in terms of both the metrics.Comment: 16 pages, 3 figures. Figure 2 and table II modified. Typos corrected. Version accepted for publication in Chao

    Contribution of Scalar Loops to the Three-Photon Decay of the Z

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    I corrected 3 mistakes from the first version: that were an omitted Feynman integration in the function f^3_{ij}, a factor of 2 in front of log f^3_{ij} in eq.2 and an overall factor of 2 in Fig.1 c). The final result is changed drastically. Doing an expansion in the Higgs mass I show that the matrix element is identically 0 in the order (MZ/MH)^2, which is due to gauge invariance. Left with an amplitude of the order (MZ/MH)^4 the final result is that the scalar contribution to this decay rate is several orders of magnitude smaller than those of the W boson and fermions.Comment: 6 pages, plain Tex, 1 figure available under request via fax or mail, OCIP/C-93-5, UQAM-PHE-93/0

    Design, development and delivery of one /1/ breadboard and three /3/ production units of a 75 VA integrated static inverter Monthly report no. 15

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    Flip-flop arrays, power transistors, epitaxial stress, and other technological developments in integrated static inverter progra

    Global Optimization by Energy Landscape Paving

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    We introduce a novel heuristic global optimization method, energy landscape paving (ELP), which combines core ideas from energy surface deformation and tabu search. In appropriate limits, ELP reduces to existing techniques. The approach is very general and flexible and is illustrated here on two protein folding problems. For these examples, the technique gives faster convergence to the global minimum than previous approaches.Comment: to appear in Phys. Rev. Lett. (2002

    Performance and Acceptability of Legume-Fortified Yam Flours

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    Yam (Dioscoreasp.) is an annual climbing plant with edible underground tubers which is a major staple of many African and Asian countries. About 52 million tonnes of yam was produced globally in 2007, with 96% from West African (IITA, 2009). Yam has the highest calories provided per hectare when compared with other starchy tubers such as cassava and potatoes. Yam is rich in carbohydrates, dietary fibre and some minerals. Yams are usually consumed boiled, roasted, fried or pounded. The tubers are stored in-between harvests for later use which is characterized by changes in wholesomeness which may result from poor handling, wound repair, diseases, and pests infestations. Also due to its high moisture content (50- 80%), large size, and high respiration rates, it is highly perishable. Hence yam tubers are lost after 4-5 months of storage, thus causing a yearly cycle of huge post- harvest losses. In Ghana, post- harvest losses of yam have been reported to range from 10% to 50%. Although West Africa produces about 94% of the world’s yam, yams have not been processed to any significant extent commercially. However due to similarity in composition of yam to crops like potato,yams could be processed into ready to eat foods like chips, crisps flakes and fries to increase their commercial value. They can also be processed into flours for instant foods (e.g. porridge, fufu, mpotonpoton (yam porridge that is spiced with palm oil added)). Fortifying yam flours with legumes such as soyabean and cowpeas could further enhance their commercial value as the fortified products could be used for complementary feeding. This study therefore developed legume-fortified yam flours to enhance their nutritional level as well as extend the shelf-life of yam. The results showed that the blends were acceptable to trained sensory panellists at baseline and also at six months. The products were also nutritionally enhanced, and could therefore be used for complementary feeding. Keywords:Yams, Post-harvest Losses, Value-addition, Legume-fortified flour

    The WW Boson Loop Background to H -> ZZ at Photon-photon Colliders

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    We have performed a complete one-loop calculation of γγ→ZZ\gamma \gamma \rightarrow ZZ in the Standard Model, including both gauge bosons and fermions in the loop. We confirm the large irreducible continuum background from the WW-boson loop found by Jikia. We have included the photon-photon luminosity, and find that the continuum background of transverse ZZ boson pairs prohibits finding a heavy Higgs with mass \gtap 350 GeV in this decay mode.Comment: 16 pages + 4 PS figures included (uuencoded), MAD/PH/77
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