589 research outputs found

    Phytophthora ramorum

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    Phytophthora ramorum is a recently emerged plant pathogen and causal agent of one of the most destructive and devastating diseases currently affecting US horticulture and forests (Rizzo et al. 2002, 2005). This oomycete pathogen was discovered in Marin County, California, in the mid-1990s, causing sudden oak death on coast live oak (Quercus agrifolia) and tanoak (Notholithocarpus densiflorus) and simultaneously discovered in Europe causing foliar blight on Rhododendron and Viburnum (Rizzo et al. 2002; Werres et al. 2001). It is now known to affect more than 100 plant species, including economically important nursery and forest host species (Frankel 2008; Rizzo et al. 2005; Tooley et al. 2004; Tooley and Kyde 2007)

    The No-Free-Lunch Theorems of Supervised Learning

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    The no-free-lunch theorems promote a skeptical conclusion that all possible machine learning algorithms equally lack justification. But how could this leave room for a learning theory, that shows that some algorithms are better than others? Drawing parallels to the philosophy of induction, we point out that the no-free-lunch results presuppose a conception of learning algorithms as purely data-driven. On this conception, every algorithm must have an inherent inductive bias, that wants justification. We argue that many standard learning algorithms should rather be understood as model-dependent: in each application they also require for input a model, representing a bias. Generic algorithms themselves, they can be given a model-relative justification

    The q-exponential family in statistical physics

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    The notion of generalised exponential family is considered in the restricted context of nonextensive statistical physics. Examples are given of models belonging to this family. In particular, the q-Gaussians are discussed and it is shown that the configurational probability distributions of the microcanonical ensemble belong to the q-exponential family.Comment: 18 pages, 4 figures, proceedings of SigmaPhi 200

    ТЕХНОГЕННІ РОДОВИЩА ТА ЇХ КЛАСИФІКАЦІЯ

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    На багатьох гірничодобувних підприємствах тих, що забезпечують мінера-льною сировиною чорну і кольорову металургію України та країн СНД, виник-ла проблема з розвіданими запасами. Резерв запасів багатьох видів корисних копалини на експлуатованих родовищах недостатній для забезпечення повної проектної потужності. Стан сировинних баз багатьох найважливіших гірничо-добувних регіонів і підприємств, що діють, різко погіршав у зв'язку з висна-женням запасів, зниженням їх якісних і економічних характеристик ускладнен-ням умов відробітку в результаті тривалої і інтенсивної експлуатації раніше освоєних родовищ. Основною причиною ситуації, що створилася, можна назва-ти зниження фінансування геологорозвідувальних робіт для освоєння нових ро-довищ необхідної мінеральної сировини

    Transitions between Inherent Structures in Water

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    The energy landscape approach has been useful to help understand the dynamic properties of supercooled liquids and the connection between these properties and thermodynamics. The analysis in numerical models of the inherent structure (IS) trajectories -- the set of local minima visited by the liquid -- offers the possibility of filtering out the vibrational component of the motion of the system on the potential energy surface and thereby resolving the slow structural component more efficiently. Here we report an analysis of an IS trajectory for a widely-studied water model, focusing on the changes in hydrogen bond connectivity that give rise to many IS separated by relatively small energy barriers. We find that while the system \emph{travels} through these IS, the structure of the bond network continuously modifies, exchanging linear bonds for bifurcated bonds and usually reversing the exchange to return to nearly the same initial configuration. For the 216 molecule system we investigate, the time scale of these transitions is as small as the simulation time scale (1\approx 1 fs). Hence for water, the transitions between each of these IS is relatively small and eventual relaxation of the system occurs only by many of these transitions. We find that during IS changes, the molecules with the greatest displacements move in small ``clusters'' of 1-10 molecules with displacements of 0.020.2\approx 0.02-0.2 nm, not unlike simpler liquids. However, for water these clusters appear to be somewhat more branched than the linear ``string-like'' clusters formed in a supercooled Lennar d-Jones system found by Glotzer and her collaborators.Comment: accepted in PR
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