726 research outputs found

    Network Effects in OSS Development: The Impact of Users and Developers on Project Performance

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    The ability to acquire knowledge is an important determinant of performance for organizations. Developers and users can contribute knowledge to multiple OSS projects, and thereby create links between them through which knowledge can flow and facilitate performance. The contributions a project receives will affect its performance differently depending on the role of the participant and their relationship to other projects. The ability of projects to implement knowledge contributions into code will depend on the level of competition in the knowledge niche in which they exist. We examine how project performance is affected by user- and developer networks, and propose hypotheses relating network density, diversity, and competition to a project’s knowledge contributions and implementation

    Mechanisms for maintaining genomic integrity during chromosome segregation in budding yeast

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    Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Biology, 2009.Cataloged from PDF version of thesis.Includes bibliographical references.Maintaining genomic integrity is crucial for an organism's fitness and survival. Regulation of chromosome segregation requires complex surveillance mechanisms that vary for different loci within the genome. This thesis focuses on two complexes, monopolin (made up of Lrs4, Csml and Maml) and condensin, a protein complex required for chromosome condensation, and their roles in chromosome segregation during mitosis and meiosis. During mitosis, Lrs4-Csml and condensiin reside in the nucleolus where they regulate the maintenance and segregation of the budding yeast ribosomal DNA array, a highly repetitive and transcriptionally active locus. Here I show that Lrs4 and Csml bind the RENT complex at the non-transcribed space region 1 within the rDNA array and via cohesin or condensin inhibit unequal exchange between sister chromatids. This complex is released during anaphase, during which Lrs4 and Csml localize to kinetochores, where they play a role in mitotic chromosome segregation. Although their role in meiotic chromosome Here we show that Lrs4 and Csml collaborate with condensins at kinetochores to control mitotic and meiotic chromosome segregation. During meiosis, diploid cells must first segregate homologous chromosomes before sister chromatids can separate. Lrs4-Csml and condensin are required during the first meiotic division to bring about the co-segregation of sister chromatids towards one pole and for the binding of monopolin subunit Maml. In summary, I show here that condensins and Lrs4-Csml are required at various chromosomal locations to provide linkages between sister chromatids to promote high fidelity chromosome segregation.by Ilana L. Brito.Ph.D

    OMCat: Catalogue of Serendipitous Sources Detected with the XMM-Newton Optical Monitor

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    The Optical Monitor Catalogue of serendipitous sources (OMCat) contains entries for every source detected in the publicly available XMM-Newton Optical Monitor (OM) images taken in either the imaging or ``fast'' modes. Since the OM is coaligned and records data simultaneously with the X-ray telescopes on XMM-Newton, it typically produces images in one or more near-UV/optical bands for every pointing of the observatory. As of the beginning of 2006, the public archive had covered roughly 0.5% of the sky in 2950 fields. The OMCat is not dominated by sources previously undetected at other wavelengths; the bulk of objects have optical counterparts. However, the OMCat can be used to extend optical or X-ray spectral energy distributions for known objects into the ultraviolet, to study at higher angular resolution objects detected with GALEX, or to find high-Galactic-latitude objects of interest for UV spectroscopy.Comment: 25 pages, 22 figures, submitted to PAS

    Assessing the Performance of Sampling Designs for Measuring the Abundance of Understory Plants

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    Accurate estimation of responses of understory plants to disturbance is essential for understanding the efficacy of management activities. However, the ability to assess changes in the abundance of plants may be hampered by inappropriate sampling methodologies. Conventional methods for sampling understory plants may be precise for common species but may fail to adequately characterize abundance of less common species. We tested conventional (modified Whittaker plots and Daubenmire and point–line intercept transects) and novel (strip adaptive cluster sampling [SACS]) approaches to sampling understory plants to determine their efficacy for quantifying abundance on control and thinned-and-burned treatment units in Pinus ponderosa forests in western Montana, USA. For species grouped by growth-form and for common species, all three conventional designs were capable of estimating cover with a 50% relative margin of error with reasonable sample sizes (3–36 replicates for growth-form groups; 8–14 replicates for common species); however, increasing precision to 25% relative margin of error required sample sizes that may be infeasible (11–143 replicates for growth-form groups; 28–54 replicates for common species). All three conventional designs required enormous sample sizes to estimate cover of nonnative species as a group (29–60 replicates) and of individual less common species (62–118 replicates), even with a 50% relative margin of error. SACS was the only design that efficiently sampled less common species, requiring only 6–11% as many replicates relative to conventional designs. Conventional designs may not be effective for estimating abundance of the majority of forest understory plants, which are typically patchily distributed with low abundance, or of newly establishing nonnative plants. Novel methods such as SACS should be considered in investigations when cover of these species is of concern

    Central Executive Dysfunction and Deferred Prefrontal Processing in Veterans with Gulf War Illness.

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    Gulf War Illness is associated with toxic exposure to cholinergic disruptive chemicals. The cholinergic system has been shown to mediate the central executive of working memory (WM). The current work proposes that impairment of the cholinergic system in Gulf War Illness patients (GWIPs) leads to behavioral and neural deficits of the central executive of WM. A large sample of GWIPs and matched controls (MCs) underwent functional magnetic resonance imaging during a varied-load working memory task. Compared to MCs, GWIPs showed a greater decline in performance as WM-demand increased. Functional imaging suggested that GWIPs evinced separate processing strategies, deferring prefrontal cortex activity from encoding to retrieval for high demand conditions. Greater activity during high-demand encoding predicted greater WM performance. Behavioral data suggest that WM executive strategies are impaired in GWIPs. Functional data further support this hypothesis and suggest that GWIPs utilize less effective strategies during high-demand WM

    Service Robots Rising:How Humanoid Robots Influence Service Experiences and Elicit Compensatory Consumer Responses

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    Interactions between consumers and humanoid service robots (HSRs; i.e., robots with a human-like morphology such as a face, arms, and legs) will soon be part of routine marketplace experiences. It is unclear, however, whether these humanoid robots (compared with human employees) will trigger positive or negative consequences for consumers and companies. Seven experimental studies reveal that consumers display compensatory responses when they interact with an HSR rather than a human employee (e.g., they favor purchasing status goods, seek social affiliation, and order and eat more food). The authors investigate the underlying process driving these effects, and they find that HSRs elicit greater consumer discomfort (i.e., eeriness and a threat to human identity), which in turn results in the enhancement of compensatory consumption. Moreover, this research identifies boundary conditions of the effects such that the compensatory responses that HSRs elicit are (1) mitigated when consumer-perceived social belongingness is high, (2) attenuated when food is perceived as more healthful, and (3) buffered when the robot is machinized (rather than anthropomorphized)
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