9,013 research outputs found

    Insect Pests of Christmas Trees

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    PDF pages: 2

    The "backdoor pathway" of androgen synthesis in human male sexual development.

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    Mammalian sex determination (male versus female) is largely controlled by genes, whereas sex differentiation (development of reproductive structures) is largely controlled by hormones. Work in the 20th century indicated that female external anatomy was a "default" pathway of development not requiring steroids, whereas male genital development required testicular testosterone plus dihydrotestosterone (DHT) made in genital skin according to a "classic" pathway. Recent work added the description of an alternative "backdoor" pathway of androgen synthesis discovered in marsupials. Unique "backdoor steroids" are found in human hyperandrogenic disorders, and genetic disruption of the pathway causes disordered male sexual development, suggesting it plays an essential role. O'Shaughnessy and colleagues now show that the principal human backdoor androgen is androsterone and provide strong evidence that it derives from placental progesterone that is metabolized to androsterone in nontesticular tissues. These studies are essential to understanding human sexual development and its disorders

    Iterative Row Sampling

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    There has been significant interest and progress recently in algorithms that solve regression problems involving tall and thin matrices in input sparsity time. These algorithms find shorter equivalent of a n*d matrix where n >> d, which allows one to solve a poly(d) sized problem instead. In practice, the best performances are often obtained by invoking these routines in an iterative fashion. We show these iterative methods can be adapted to give theoretical guarantees comparable and better than the current state of the art. Our approaches are based on computing the importances of the rows, known as leverage scores, in an iterative manner. We show that alternating between computing a short matrix estimate and finding more accurate approximate leverage scores leads to a series of geometrically smaller instances. This gives an algorithm that runs in O(nnz(A)+dω+θϵ2)O(nnz(A) + d^{\omega + \theta} \epsilon^{-2}) time for any θ>0\theta > 0, where the dω+θd^{\omega + \theta} term is comparable to the cost of solving a regression problem on the small approximation. Our results are built upon the close connection between randomized matrix algorithms, iterative methods, and graph sparsification.Comment: 26 pages, 2 figure

    Parallel Graph Decompositions Using Random Shifts

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    We show an improved parallel algorithm for decomposing an undirected unweighted graph into small diameter pieces with a small fraction of the edges in between. These decompositions form critical subroutines in a number of graph algorithms. Our algorithm builds upon the shifted shortest path approach introduced in [Blelloch, Gupta, Koutis, Miller, Peng, Tangwongsan, SPAA 2011]. By combining various stages of the previous algorithm, we obtain a significantly simpler algorithm with the same asymptotic guarantees as the best sequential algorithm

    Your Lawn

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    Congressional Reform: Toward a Modern Congress

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    Improved Parallel Algorithms for Spanners and Hopsets

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    We use exponential start time clustering to design faster and more work-efficient parallel graph algorithms involving distances. Previous algorithms usually rely on graph decomposition routines with strict restrictions on the diameters of the decomposed pieces. We weaken these bounds in favor of stronger local probabilistic guarantees. This allows more direct analyses of the overall process, giving: * Linear work parallel algorithms that construct spanners with O(k)O(k) stretch and size O(n1+1/k)O(n^{1+1/k}) in unweighted graphs, and size O(n1+1/klogk)O(n^{1+1/k} \log k) in weighted graphs. * Hopsets that lead to the first parallel algorithm for approximating shortest paths in undirected graphs with O(m  polylog  n)O(m\;\mathrm{polylog}\;n) work

    FARM-LEVEL RESPONSE TO AGRICULTURAL EFFLUENT CONTROL STRATEGIES: THE CASE OF THE WILLAMETTE VALLEY

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    This article examines economic incentives and other mechanisms to offset non-point source pollution from agriculture. A biophysical simulator to estimate technical relationships is linked to linear programming models for representative farms in the Willamette Valley of Oregon. The models are then optimized for profit maximization under alternative non-point pollution control policies. The results indicate that site-specific resource conditions and production possibilities greatly influence policy effectiveness and the cost of achieving pollution abatement. Nevertheless, some abatement is possible on all farms for relatively little cost.Environmental Economics and Policy,
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