59 research outputs found

    Structural Integrity Testing Method for PRSEUS Rod-Wrap Stringer Design

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    NASA Langley Research Center and The Boeing Company are developing an innovative composite structural concept, called PRSEUS, for the flat center section of a future environmentally friendly hybrid wing body (HWB) aircraft. The PRSEUS (Pultruded Rod Stitched Efficient Unitized Structure) concept uses dry textile preforms for the skins, frames, and stiffener webs. The highly loaded stiffeners are made from precured unidirectional carbon/epoxy rods and dry fiber preforms. The rods are wrapped with the dry fiber preforms and a resin infusion process is used to form the rod-wrap stiffeners. The structural integrity of the rod-wrap interface is critical for maintaining the panel s high strength and bending rigidity. No standard testing method exists for testing the strength of the rod-wrap bondline. Recently, Boeing proposed a rod push-out testing method and conducted some preliminary tests using this method. This paper details an analytical study of the rod-wrap bondline. The rod-wrap interface is modeled as a cohesive zone for studying the initiation and growth of interfacial debonding during push-out testing. Based on the correlations of analysis results and Boeing s test data, the adequacy of the rod-wrap testing method is evaluated, and potential approaches for improvement of the test method are proposed

    Effect of Phosphorus Amendments on Present Day Plankton Communities in Pelagic Lake Erie

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    To address questions regarding the potential impact of elevated total phosphorus (TP) inputs (due to relaxed regulations of TP loading), a series of TP enrichment experiments were conducted at pelagic stations in the 3 hydrologically distinct basins of Lake Erie. Results of nutrient assimilation measurements and assays for nutrient bioavailability suggest that the chemical speciation, and not concentration, of nitrogenous compounds may influence phytoplankton community structure; this in turn may lead to the selective proliferation of cyanobacteria in the eastern basin of the lake. Assays with cyanobacterial bioluminescent reporter systems for P and N availability as well as N-tot:P-tot assimilation ratios from on-deck incubation experiments support this work. Considered in the context of a microbial food web relative to a grazing food web, the results imply that alterations in current TP loading controls may lead to alterations in the phytoplankton community structure in the different basins of the Lake Erie system

    Applicant perspectives during selection

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    We provide a comprehensive but critical review of research on applicant reactions to selection procedures published since 2000 (n = 145), when the last major review article on applicant reactions appeared in the Journal of Management. We start by addressing the main criticisms levied against the field to determine whether applicant reactions matter to individuals and employers (“So what?”). This is followed by a consideration of “What’s new?” by conducting a comprehensive and detailed review of applicant reaction research centered upon four areas of growth: expansion of the theoretical lens, incorporation of new technology in the selection arena, internationalization of applicant reactions research, and emerging boundary conditions. Our final section focuses on “Where to next?” and offers an updated and integrated conceptual model of applicant reactions, four key challenges, and eight specific future research questions. Our conclusion is that the field demonstrates stronger research designs, with studies incorporating greater control, broader constructs, and multiple time points. There is also solid evidence that applicant reactions have significant and meaningful effects on attitudes, intentions, and behaviors. At the same time, we identify some remaining gaps in the literature and a number of critical questions that remain to be explored, particularly in light of technological and societal changes

    Colorectal Cancer Stem Cells Are Enriched in Xenogeneic Tumors Following Chemotherapy

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    Patients generally die of cancer after the failure of current therapies to eliminate residual disease. A subpopulation of tumor cells, termed cancer stem cells (CSC), appears uniquely able to fuel the growth of phenotypically and histologically diverse tumors. It has been proposed, therefore, that failure to effectively treat cancer may in part be due to preferential resistance of these CSC to chemotherapeutic agents. The subpopulation of human colorectal tumor cells with an ESA(+)CD44(+) phenotype are uniquely responsible for tumorigenesis and have the capacity to generate heterogeneous tumors in a xenograft setting (i.e. CoCSC). We hypothesized that if non-tumorigenic cells are more susceptible to chemotherapeutic agents, then residual tumors might be expected to contain a higher frequency of CoCSC.Xenogeneic tumors initiated with CoCSC were allowed to reach approximately 400 mm(3), at which point mice were randomized and chemotherapeutic regimens involving cyclophosphamide or Irinotecan were initiated. Data from individual tumor phenotypic analysis and serial transplants performed in limiting dilution show that residual tumors are enriched for cells with the CoCSC phenotype and have increased tumorigenic cell frequency. Moreover, the inherent ability of residual CoCSC to generate tumors appears preserved. Aldehyde dehydrogenase 1 gene expression and enzymatic activity are elevated in CoCSC and using an in vitro culture system that maintains CoCSC as demonstrated by serial transplants and lentiviral marking of single cell-derived clones, we further show that ALDH1 enzymatic activity is a major mediator of resistance to cyclophosphamide: a classical chemotherapeutic agent.CoCSC are enriched in colon tumors following chemotherapy and remain capable of rapidly regenerating tumors from which they originated. By focusing on the biology of CoCSC, major resistance mechanisms to specific chemotherapeutic agents can be attributed to specific genes, thereby suggesting avenues for improving cancer therapy

    Investigating the Effects of Organic Ligands on Iron and Copper Availability to Coastal and Oceanic Phytoplankton Using Continuous Cultures

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    The chemical speciation of Fe and Cu in marine waters impart a strong selective pressure on phytoplankton assemblages by influencing the availability and partitioning of these essential trace nutrients among taxa. Consequently, trace metal speciation establishes interspecific competitive interactions that largely determine the phytoplankton community structure in natural marine waters. The aim of this dissertation was to broaden the understanding of Fe and Cu availability to different phytoplankton by examining the effects of organic complexation on natural community assemblages from coastal and oceanic waters using continuous cultures. Continuous cultures provide an effective platform for investigating subtle responses in natural populations to consistent nutrient flux and speciation, as the community trajectory is amplified by dilution losses of slow-growing and noncompetitive organisms. The successful design and implementation of a novel continuous culture system for shipboard experiments with natural mixed communities is detailed here. Domoic acid (DA), a potent phycotoxin produced by the diatom genus Pseudo-nitzschia, is an Fe and Cu chelator. Dissolved DA (dDA) additions to natural phytoplankton communities from coastal and offshore regions enhanced diatom growth more than Fe or Cu additions alone, and principally selected for Pseudo-nitzschia over all other phytoplankton. These findings are consistent with evidence that Pseudo-nitzschia release dDA to enhance the Cu acquisition needed to initiate an inducible high-affinity Fe uptake mechanism. These experiments provide the first direct evidence that the production of dDA by Pseudo-nitzschia may facilitate a competitive advantage, and explain its success in coastal and offshore assemblages. Three commercially available strong Fe(III)-binding siderophores isolated from terrestrial organisms (desferrioxamine B, ferrichrome and rhodotorulic acid) were used as analogs to marine siderophores to determine Fe availability to different coastal phytoplankton taxa. While all have high conditional constants for Fe(III) in seawater, the complexation characteristics greatly influenced Fe availability, reflected in their effects on chlorophyll biomass, Fe uptake and photophysiology. Although the specific compounds comprising strong Fe and Cu complexing organic ligands in seawater are unknown, these findings strongly suggest their specific chemical nature is likely more important than their metal affinities in determining Fe availability to phytoplankton

    Injected Versus Oral Deep Vein Thrombosis Prophylactic Therapy: A Patient Satisfaction Study

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    Deep vein thrombosis (DVT) is a serious complication of total knee replacement (TKA). While the need for post op prophylaxis is accepted, controversy exists as to which regimen(s) to use. ASA use has seen resurgence due to its efficacy, safety profile, and easy administration. To date no study has evaluated patient satisfaction and compliance with ASA chemoprophylaxis after TKA. Ninety-six TKA patients were surveyed after randomization to receive either oral ASA or injected low molecular weight heparin. Satisfaction was significantly greater in the ASA group. Confidence in treatment was equivalent between the groups. Patient satisfaction withanticoagulation after TKA should not be overlooked. We have demonstrated increased satisfaction with ASA treatment without affecting perceptions of efficacy. Our findings should be considered when prescribing postoperative prophylaxi

    Confirmation of post-harvest spectral recovery from Landsat time series using measures of forest cover and height derived from airborne laser scanning data

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    Landsat time series (LTS) enable the characterization of forest recovery post-disturbance over large areas; however, there is a gap in our current knowledge concerning the linkage between spectral measures of recovery derived from LTS and actual manifestations of forest structure in regenerating stands. Airborne laser scanning (ALS) data provide useful measures of forest structure that can be used to corroborate spectral measures of forest recovery. The objective of this study was to evaluate the utility of a spectral index of recovery based on the Normalized Burn Ratio (NBR): the years to recovery, or Y2R metric, as an indicator of the return of forest vegetation following forest harvest (clearcutting). The Y2R metric has previously been defined as the number of years required for a pixel to return to 80% of its pre-disturbance NBR (NBRpre) value. In this study, the Composite2Change (C2C) algorithm was used to generate a time series of gap-free, cloud-free Landsat surface reflectance composites (1985–2012), associated change metrics, and a spatially-explicit dataset of detected changes for an actively managed forest area in southern Finland (5.3 Mha). The overall accuracy of change detection, determined using independent validation data, was 89%. Areas of forest harvesting in 1991 were then used to evaluate the Y2R metric. Four alternative recovery scenarios were evaluated, representing variations in the spectral threshold used to define Y2R: 60%, 80%, and 100% of NBRpre, and a critical value of z (i.e. the year in which the pixel's NBR value is no longer significantly different from NBRpre). The Y2R for each scenario were classified into five groups: recovery within 17 years, and not recovered. Measures of forest structure (canopy height and cover) were obtained from ALS data. Benchmarks for height (>5 m) and canopy cover (>10%) were applied to each recovery scenario, and the percentage of pixels that attained both of these benchmarks for each recovery group, was determined for each Y2R scenario. Our results indicated that the Y2R metric using the 80% threshold provided the most realistic assessment of forest recovery: all pixels considered in our analysis were spectrally recovered within the analysis period, with 88.88% of recovered pixels attaining the benchmarks for both cover and height. Moreover, false positives (pixels that had recovered spectrally, but not structurally) and false negatives (pixels that had recovered structurally, but not spectrally) were minimized with the 80% threshold. This research demonstrates the efficacy of LTS-derived assessments of recovery, which can be spatially exhaustive and retrospective, providing important baseline data for forest monitoring.Peer reviewe

    Monitoring Forest Change in Landscapes Under-Going Rapid Energy Development: Challenges and New Perspectives

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    The accelerated development of energy resources around the world has substantially increased forest change related to oil and gas activities. In some cases, oil and gas activities are the primary catalyst of land-use change in forested landscapes. We discuss the challenges associated with characterizing ecological change related to energy resource development using North America as an exemplar. We synthesize the major impacts of energy development to forested ecosystems and offer new perspectives on how to detect and monitor anthropogenic disturbance during the Anthropocene. The disturbance of North American forests for energy development has resulted in persistent linear corridors, suppression of historical disturbance regimes, novel ecosystems, and the eradication of ecological memory. Characterizing anthropogenic disturbances using conventional patch-based disturbance measures will tend to underestimate the ecological impacts of energy development. Suitable indicators of anthropogenic impacts in forests should be derived from the integration of multi-scalar Earth observations. Relating these indicators to ecosystem condition will be a capstone in the progress toward monitoring forest change in landscapes undergoing rapid energy development.Forestry, Faculty ofNon UBCForest and Conservation Sciences, Department ofForest Resources Management, Department ofReviewedFacult
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