1,146 research outputs found

    The Role of the ICC in the Administration of the National Transportation Policy

    Get PDF

    Species Invasion Shifts the Importance of Predator Dependence

    Get PDF
    The strength of interference between foraging individuals can influence per capita consumption rates, with important consequences for predator and prey populations and system stability. Here we demonstrate how the replacement of a previously established invader, the predatory crab Carcinus maenas, by the recently invading predatory crab Hemigrapsus sanguineus shifts predation from a species that experiences strong predator interference (strong predator dependence) to one that experiences weak predator interference (weak predator dependence). We demonstrate using field experiments that differences in the strength of predator dependence persist for these species both when they forage on a single focal prey species only (the mussel Mytilus edulis) and when they forage more broadly across the entire prey community. This shift in predator dependence with species replacement may be altering the biomass across trophic levels, consistent with theoretical predictions, as we show that H. sanguineus populations are much larger than C. maenas populations throughout their invaded ranges. Our study highlights that predator dependence may differ among predator species and demonstrates that different predatory impacts of two conspicuous invasive predators may be explained at least in part by different strengths of predator dependence

    INFRARED ELLPSOMETER/ POLARMETER SYSTEM, METHOD OF CALIBRATION, AND USE THEREOF

    Get PDF
    A sample system investigation system, such as an ellipsometer or polarimeter system, for use in investigating sample systems with electromagnetic wavelengths in the infrared range, and a calibration method for compensating nonidealities in multi-dimensional system rotated and non-rotated component representing matricies, are disclosed. An essentially achromatic compensator of dual-rhomb construction, which introduces a (3*LAMBDA/4) phase shift, but essentially no deviation in the direction of propagation of a polarized beam of electromagnetic wavelengths caused to pass there through, even when said compensator is caused to continuously rotate, is also disclosed

    Experimental Demonstration of Accelerated Extinction in Source-Sink Metapopulations

    Get PDF
    Population extinction is a fundamental ecological process which may be aggravated by the exchange of organisms between productive (source) and unproductive (sink) habitat patches. The extent to which such source-sink exchange affects extinction rates is unknown. We conducted an experiment in which metapopulation effects could be distinguished from source-sink effects in laboratory populations of Daphnia magna. Time-to-extinction in this experiment was maximized at intermediate levels of habitat fragmentation, which is consistent with a minority of theoretical models. These results provided a baseline for comparison with experimental treatments designed to detect effects of concentrating resources in source patches. These treatments showed that source-sink configurations increased population variability (the coefficient of variation in abundance) and extinction hazard compared with homogeneous environments. These results suggest that where environments are spatially heterogeneous, accurate assessments of extinction risk will require understanding the exchange of organisms among population sources and sinks. Such heterogeneity may be the norm rather than the exception because of both the intrinsic heterogeneity naturally exhibited by ecosystems and increasing habitat fragmentation by human activity

    A Finite Element Analysis of the Utah Thistle Failure

    Get PDF
    In the Spring of 1983, a large landslide occurred near the town of Thistle, Utah which blocked major transportation routes and impounded the Spanish Fork River, inundating the town with 200 feet of water. While much attention has been given to the slide and its impact, very little has been directed toward a quantitative understanding of its causes. An analysis was performed of the Thistle landslide using the SEEPSLOPE finite element system in order to evaluate the mechanisms, factors, and causes of the failure. An elastic, perfectly-plastic stress-strain curve was employed in the analysis to model the behavior of the overconsolidated clay soils. It is concluded that the landslide was a compound, progressive failure which initiated at the toe and progressed uphill. Seepage forces played a significant role in the failure

    Exploiting Machine Learning to Subvert Your Spam Filter

    Get PDF
    Using statistical machine learning for making security decisions introduces new vulnerabilities in large scale systems. This paper shows how an adversary can exploit statistical machine learning, as used in the SpamBayes spam filter, to render it uselessā€”even if the adversaryā€™s access is limited to only 1 % of the training messages. We further demonstrate a new class of focused attacks that successfully prevent victims from receiving specific email messages. Finally, we introduce two new types of defenses against these attacks.

    Near-Optimal Evasion of Convex-Inducing Classifiers

    Full text link
    Classifiers are often used to detect miscreant activities. We study how an adversary can efficiently query a classifier to elicit information that allows the adversary to evade detection at near-minimal cost. We generalize results of Lowd and Meek (2005) to convex-inducing classifiers. We present algorithms that construct undetected instances of near-minimal cost using only polynomially many queries in the dimension of the space and without reverse engineering the decision boundary.Comment: 8 pages; to appear at AISTATS'201
    • ā€¦
    corecore