215 research outputs found

    Robot Mapping with Real-Time Incremental Localization Using Expectation Maximization

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    This research effort explores and develops a real-time sonar-based robot mapping and localization algorithm that provides pose correction within the context of a single room, to be combined with pre-existing global localization techniques, and thus produce a single, well-formed map of an unknown environment. Our algorithm implements an expectation maximization algorithm that is based on the notion of the alpha-beta functions of a Hidden Markov Model. It performs a forward alpha calculation as an integral component of the occupancy grid mapping procedure using local maps in place of a single global map, and a backward beta calculation that considers the prior local map, a limited step that enables real-time processing. Real-time localization is an extremely difficult task that continues to be the focus of much research in the field, and most advances in localization have been achieved in an off-line context. The results of our research into and implementation of realtime localization showed limited success, generating improved maps in a number of cases, but not all-a trade-off between real-time and off-line processing. However, we believe there is ample room for extension to our approach that promises a more consistently successful real-time localization algorithm

    Communication and interpretation of emotional distress within the friendships of young Irish men prior to suicide: a qualitative study

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    The potential for young men in crisis to be supported by their lay networks is an important issue for suicide prevention, due to the under-utilisation of healthcare services by this population. Central to the provision of lay support is the capability of social networks to recognise and respond effectively to young men’s psychological distress and suicide risk. The aim of this qualitative study was to explore young men’s narratives of peer suicide, in order to identify how they interpreted and responded to behavioural changes and indications of distress from their friend before suicide. In-depth qualitative interviews were conducted with 15 Irish males (aged 19-30 years) who had experienced the death by suicide of a male friend in the preceding five years. The data were analysed using a thematic approach. Through the analysis of the participants’ stories and experiences, we identified several features of young male friendships and social interactions that could be addressed in order to strengthen the support available to young men in crisis. These included: the reluctance of young men to discuss emotional or personal issues within male friendships; the tendency to reveal worries and emotion only within the context of alcohol consumption; the tendency of friends to respond in a dismissive or disapproving way to communication of suicidal thoughts; the difficulty of knowing how to interpret a friend’s inconsistent or ambiguous behaviour prior to suicide; and beliefs about the sort of person who takes their own life. Community-based suicide prevention initiatives must enhance the potential of young male social networks to support young men in crisis, through specific provisions for developing openness in communication and responsiveness, and improved education about suicide risk

    PVP2006-CPVT11-93173 MULTI-SCALE SIMULATION OF SOFT MATERIAL FLOW

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    ABSTRACT We describe a multi-scale modeling approach to model the rheology of soft matter, which can then be applied to simulate flow of viscous inorganic material in pipes and containers. Mesoscale methods, such as dissipative particle dynamics (DPD) are a key component of multi-scale modeling, as they bridge the gap between fundamental theory and continuum length scales. The paper describes a method for parameterizing DPD simulations for cements and inorganic sludges based on calculating a volume dependent cohesive energy interaction and compressive term from MD simulation with a generalized inorganic forcefield. By modifying the fluid properties through the interaction parameters one can simulate change of chemistry, such as pH or the introduction of chemicals to improve flow properties (super-plasticizers). Parameters obtained from mesoscale simulation can then be applied to simulate flow of soft matter inside pipes and containers using traditional CFD techniques. Two potential future applications in the nuclear industry are discussed in the areas of waste retrieval and encapsulation

    The molecular basis of color vision in colorful fish: Four Long Wave-Sensitive (LWS) opsins in guppies (Poecilia reticulata) are defined by amino acid substitutions at key functional sites

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    <p>Abstract</p> <p>Background</p> <p>Comparisons of functionally important changes at the molecular level in model systems have identified key adaptations driving isolation and speciation. In cichlids, for example, long wavelength-sensitive (LWS) opsins appear to play a role in mate choice and male color variation within and among species. To test the hypothesis that the evolution of elaborate coloration in male guppies (<it>Poecilia reticulata</it>) is also associated with opsin gene diversity, we sequenced long wavelength-sensitive (LWS) opsin genes in six species of the family Poeciliidae.</p> <p>Results</p> <p>Sequences of four LWS opsin genes were amplified from the guppy genome and from mRNA isolated from adult guppy eyes. Variation in expression was quantified using qPCR. Three of the four genes encode opsins predicted to be most sensitive to different wavelengths of light because they vary at key amino acid positions. This family of LWS opsin genes was produced by a diversity of duplication events. One, an intronless gene, was produced prior to the divergence of families Fundulidae and Poeciliidae. Between-gene PCR and DNA sequencing show that two of the guppy LWS opsins are linked in an inverted orientation. This inverted tandem duplication event occurred near the base of the poeciliid tree in the common ancestor of <it>Poecilia </it>and <it>Xiphophorus</it>. The fourth sequence has been uncovered only in the genus <it>Poecilia</it>. In the guppies surveyed here, this sequence is a hybrid, with the 5' end most similar to one of the tandem duplicates and the 3' end identical to the other.</p> <p>Conclusion</p> <p>Enhanced wavelength discrimination, a possible consequence of opsin gene duplication and divergence, might have been an evolutionary prerequisite for color-based sexual selection and have led to the extraordinary coloration now observed in male guppies and in many other poeciliids.</p

    Financing Direct Democracy: Revisiting the Research on Campaign Spending and Citizen Initiatives

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    The conventional view in the direct democracy literature is that spending against a measure is more effective than spending in favor of a measure, but the empirical results underlying this conclusion have been questioned by recent research. We argue that the conventional finding is driven by the endogenous nature of campaign spending: initiative proponents spend more when their ballot measure is likely to fail. We address this endogeneity by using an instrumental variables approach to analyze a comprehensive dataset of ballot propositions in California from 1976 to 2004. We find that both support and opposition spending on citizen initiatives have strong, statistically significant, and countervailing effects. We confirm this finding by looking at time series data from early polling on a subset of these measures. Both analyses show that spending in favor of citizen initiatives substantially increases their chances of passage, just as opposition spending decreases this likelihood

    Impaired Striatal Akt Signaling Disrupts Dopamine Homeostasis and Increases Feeding

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    DOI is broken and has been reportedThe prevalence of obesity has increased dramatically worldwide. The obesity epidemic begs for novel concepts and therapeutic targets that cohesively address “food-abuse” disorders. We demonstrate a molecular link between impairment of a central kinase (Akt) involved in insulin signaling induced by exposure to a high-fat (HF) diet and dysregulation of higher order circuitry involved in feeding. Dopamine (DA) rich brain structures, such as striatum, provide motivation stimuli for feeding. In these central circuitries, DA dysfunction is posited to contribute to obesity pathogenesis. We identified a mechanistic link between metabolic dysregulation and the maladaptive behaviors that potentiate weight gain. Insulin, a hormone in the periphery, also acts centrally to regulate both homeostatic and reward-based HF feeding. It regulates DA homeostasis, in part, by controlling a key element in DA clearance, the DA transporter (DAT). Upon HF feeding, nigro-striatal neurons rapidly develop insulin signaling deficiencies, causing increased HF calorie intake. Methodology/Principal Findings We show that consumption of fat-rich food impairs striatal activation of the insulin-activated signaling kinase, Akt. HF-induced Akt impairment, in turn, reduces DAT cell surface expression and function, thereby decreasing DA homeostasis and amphetamine (AMPH)-induced DA efflux. In addition, HF-mediated dysregulation of Akt signaling impairs DA-related behaviors such as (AMPH)-induced locomotion and increased caloric intake. We restored nigro-striatal Akt phosphorylation using recombinant viral vector expression technology. We observed a rescue of DAT expression in HF fed rats, which was associated with a return of locomotor responses to AMPH and normalization of HF diet-induced hyperphagia. Conclusions/Significance Acquired disruption of brain insulin action may confer risk for and/or underlie “food-abuse” disorders and the recalcitrance of obesity. This molecular model, thus, explains how even short-term exposure to “the fast food lifestyle” creates a cycle of disordered eating that cements pathological changes in DA signaling leading to weight gain and obesity.National Institutes of Health (U.S.) (grant DA14684)National Institutes of Health (U.S.) (grant DK085712

    CowN Sustains Nitrogenase Turnover in the Presence of the Inhibitor Carbon Monoxide

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    Nitrogenase is the only enzyme capable of catalyzing nitrogen fixation, the reduction of dinitrogen gas (N2) to ammonia (NH3). Nitrogenase is tightly inhibited by the environmental gas carbon monoxide (CO). Nitrogen-fixing bacteria rely on the protein CowN to grow in the presence of CO. However, the mechanism by which CowN operates is unknown. Here, we present the biochemical characterization of CowN and examine how CowN protects nitrogenase from CO. We determine that CowN interacts directly with nitrogenase and that CowN protection observes hyperbolic kinetics with respect to CowN concentration. At a CO concentration of 0.001 atm, CowN restores nearly full nitrogenase activity. Our results further indicate that CowN’s protection mechanism involves decreasing the binding affinity of CO to nitrogenase’s active site approximately tenfold without interrupting substrate turnover. Taken together, our work suggests CowN is an important auxiliary protein in nitrogen fixation that engenders CO tolerance to nitrogenase

    MicroRNAs in pulmonary arterial remodeling

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    Pulmonary arterial remodeling is a presently irreversible pathologic hallmark of pulmonary arterial hypertension (PAH). This complex disease involves pathogenic dysregulation of all cell types within the small pulmonary arteries contributing to vascular remodeling leading to intimal lesions, resulting in elevated pulmonary vascular resistance and right heart dysfunction. Mutations within the bone morphogenetic protein receptor 2 gene, leading to dysregulated proliferation of pulmonary artery smooth muscle cells, have been identified as being responsible for heritable PAH. Indeed, the disease is characterized by excessive cellular proliferation and resistance to apoptosis of smooth muscle and endothelial cells. Significant gene dysregulation at the transcriptional and signaling level has been identified. MicroRNAs are small non-coding RNA molecules that negatively regulate gene expression and have the ability to target numerous genes, therefore potentially controlling a host of gene regulatory and signaling pathways. The major role of miRNAs in pulmonary arterial remodeling is still relatively unknown although research data is emerging apace. Modulation of miRNAs represents a possible therapeutic target for altering the remodeling phenotype in the pulmonary vasculature. This review will focus on the role of miRNAs in regulating smooth muscle and endothelial cell phenotypes and their influence on pulmonary remodeling in the setting of PAH
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