4,261 research outputs found

    Experiences with high definition interactive video conferencing

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    We review the design and implementation of UltraGrid, a new high definition video conferencing system, and present some experimental results. UltraGrid was the first system to support gigabit rate high definition interactive video conferencing on commodity systems and networks, and we present measurements to illustrate behavior of production networks subject to such real time traffic. We illustrate the benefits of hybrid IP/provisioned optical networks over best effort IP networks for this class of traffic, and motivate the development of congestion control algorithms for interactive conferencing on best effort IP networks

    IDEAL Symposium on the East African Lakes

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    Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94975/1/eost9699.pd

    Characteristics of successful puma kill sites of elk in the Black Hills, South Dakota

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    Elk Cervus canadensis nelsoni in the Black Hills, South Dakota, have been declining since 2006 and there is concern by resource managers and hunters that puma Puma concolor predation may be contributing to declining herds. We evaluated characteristics at sites where puma successfully killed elk in the Black Hills of South Dakota. We evaluated characteristics at coarse (79-ha plots) and fine (0.2-ha plot) scales across the landscape. Our primary objective was to obtain a better understanding of vegetation and terrain characteristics that may have facilitated greater susceptibility of elk to predation by puma. We evaluated effects of road density, terrain heterogeneity, probability of elk use, and vegetation variables at 62 puma kill sites of elk and 186 random sites to identify key landscape attributes where elk were killed by puma. Elk were killed by puma in high use areas. Elk were also killed in areas that had greater amounts of edge and intermediate ruggedness at the coarse scale. Further, elk were killed in areas with greater small tree density and woody debris at the fine scale. High germination rates of ponderosa pine trees are unique to the Black Hills and provide dense patches of cover for puma. We hypothesize that cover from small trees and woody debris provided conditions where puma could stalk elk in areas with optimal security cover for elk. We suggest managers implement vegetation management practices that reduce small tree density and woody debris in areas with greater density of meadow—forest edge if they are interested in potentially diminishing hiding cover for puma in elk high use areas

    Experimental and numerical investigation of flexural concrete wall design details

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    Reinforced concrete structural walls are common in mid- to high-rise structures in high seismic regions, and are expected to have good strength and ductility characteristics if designed in accordance with ACI 318-14. However, experimental and analytical investigations of reinforced concrete structural walls and isolated boundary element prisms indicate that the existing design provisions may be insufficient to provide ductile, flexure-dominated response under cyclic loading. Walls designed with an ACI compliant boundary element length are susceptible to shear-compression failures below the maximum ACI allowable shear stress of 10Acv√fc’. Also of concern is the frequent use of thinner walls in modern design; as the wall’s cross-sectional aspect ratio increases, such brittle shear-compression failures occur at even smaller shear stress values. In regards to detailing, special boundary elements with intermediate cross-ties exhibit a minimal improvement in confinement compared to ordinary boundary elements. This response can be linked to inadequacies in multiple code design parameters, including: vertical spacing and area of confinement steel, horizontal spacing and type of restraint to longitudinal bars, and development length provided for transverse reinforcement. Recent in-field wall failures have prompted concerns related to the minimum code required vertical and horizontal web shear reinforcement, as well as the relative amount of vertical-to-horizontal web steel. This paper examines ACI 318-14 special boundary element and web reinforcement provisions and provides design recommendations intended to improve wall performance as compared with current ACI requirements

    Reliability and validity of an auditory working memory measure: data from elderly and right-hemisphere damaged adults

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    The use of non-standardized measures in research and clinical assessments creates difficulties with interpretation and generalization of results obtained. One example of a widely used non-standardized tool is the reading/listening span paradigm for assessment of working memory (WM). WM is an important construct because of its purported relationship to language comprehension and capacity theories of cognition. This paper investigates several facets of reliability and validity for an auditory working memory measure designed for older adults and individuals with right hemisphere brain damage (RHD). Results from 28 non-brain-damaged subjects (NBD) and 11 RHD subjects indicate that the measure is internally consistent and reliable over time. Construct validity evidence, which compares favourably with evidence from existing literature, suggests that for NBD subjects this tool differentiates WR I from simple short term memory. RHD subjects do not demonstrate the same pattern of validity results as the NBD group. Further evaluation with RHD patients is warranted, because clinically this tool may be useful as a measure of severity or a prognostic indicator of language comprehension abilities for this population
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