867 research outputs found

    Discovery of a ~5 day characteristic timescale in the Kepler power spectrum of Zw 229-15

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    We present time series analyses of the full Kepler dataset of Zw 229-15. This Kepler light curve --- with a baseline greater than three years, composed of virtually continuous, evenly sampled 30-minute measurements --- is unprecedented in its quality and precision. We utilize two methods of power spectral analysis to investigate the optical variability and search for evidence of a bend frequency associated with a characteristic optical variability timescale. Each method yields similar results. The first interpolates across data gaps to use the standard Fourier periodogram. The second, using the CARMA-based time-domain modeling technique of Kelly et al. (2014), does not need evenly-sampled data. Both methods find excess power at high frequencies that may be due to Kepler instrumental effects. More importantly both also show strong bends ({\Delta}{\alpha} ~ 2) at timescales of ~5 days, a feature similar to those seen in the X-ray PSDs of AGN but never before in the optical. This observed ~5 day timescale may be associated with one of several physical processes potentially responsible for the variability. A plausible association could be made with light-crossing, dynamical or thermal timescales, depending on the assumed value of the accretion disk size and on unobserved disk parameters such as {\alpha} and H/R. This timescale is not consistent with the viscous timescale, which would be years in a ~10^7 Solar mass AGN such as Zw 229-15. However there must be a second bend on long (>~1 year) timescales, and that feature could be associated with the viscous timescale.Comment: 10 pages, 5 figures, 1 table. To appear in the Astrophysical Journal, Part

    Small Scale Fish Farming for Food Security and Income Generation. Progress Report; September 1999 - February 2000

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    This short progress report is the third progress report prepared for the NAROIMAAIF Fish Farming Project. It has been prepared in advance of the third Steering Committee Meeting scheduled for March 28/11 2000. at which it will be used as the main reporting document. The report describes progress during the period, (September 1999 - February 2000 and is organised in a similar manner to the Jun-Aug 99 report. It follows the format of the Logical Framework with the first 4 sections focusing on the four Project logical framework outputs. The Logical Framework has been slightly revised as a result of the Inception Review in September 1999 and can be found in Appendix 1. The wording of the four Project Outputs has been revised and these are now as follows: 1) Improved institutional capacity and linkages for poverty focused aquaculture development established at district and national level involving public sector, NCO's and local organisations. 2) The identification of improved aquaculture technologies and indigenous species fish strains appropriate for use by the rural poor within the existing fanning system. 3) Improved delivery of poverty focused extension services addressing the needs offanners with ponds at district and sub county levels. 4) An improved in Jonnation base on small-scale aquaculture for planning and monitoring. This report also includes the following sections. 5) Reports Produced. 6) Project Expenditure Sept 1999 - Feb 2000 7) Proposed work-plan for the period Mar - Aug 2000. 8) Annexes 1) The revised Logical Framework 2) A summary of Recommendations from the Project Inception Mission

    Design Optimization of an Above-Knee Prosthesis with Energy Regeneration

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    Above-knee amputees who use a prosthetic leg typically have to compensate for its shortcomings with unnatural hip motions. This compensation eventually leads to adverse health issues such as arthritis. We propose an active prosthesis to improve performance. The motor in our prosthetic knee allows the patient to move his hip normally, thus reducing the possibility of ancillary health issues. To improve the efficiency of the prosthesis, we use the braking phase of the prosthesis to regenerate energy. By storing energy in a supercapacitor during braking, the prosthesis lasts longer between each charge than it would without regenerative braking. We are considering two knee motor designs—a gear drive and a ball screw drive. Both designs appear to have the potential for regeneration. Several parameters characterize the prosthesis design. We use biogeography-based optimization (BBO) to determine these parameters. We are currently optimizing the prosthesis design to achieve accurate tracking of the knee angle. Future optimization criteria will include efficient energy use and generation.https://engagedscholarship.csuohio.edu/u_poster_2013/1009/thumbnail.jp

    Markov Models for Biogeography-based Optimization

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    Biogeography-based optimization (BBO) is a population-based evolutionary algorithm that is based on the mathematics of biogeography. Biogeography is the science and study of the geographical distribution of biological organisms. In BBO, problem solutions are analogous to islands, and the sharing of features between solutions is analogous to the migration of species. This paper derives Markov models for BBO with selection, migration, and mutation operators. Our models give the theoretically exact limiting probabilities for each possible population distribution for a given problem. We provide simulation results to confirm the Markov models

    Analytical and Numerical Comparisons of Biogeography-based Optimization and Genetic Algorithms.

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    We show that biogeography-based optimization (BBO) is a generalization of a genetic algorithm with global uniform recombination (GA/GUR). Based on the common features of BBO and GA/GUR, we use a previously-derived BBO Markov model to obtain a GA/GUR Markov model. One BBO characteristic which makes it distinctive from GA/GUR is its migration mechanism, which affects selection pressure (i.e., the probability of retaining certain features in the population from one generation to the next). We compare the BBO and GA/GUR algorithms using results from analytical Markov models and continuous optimization benchmark problems. We show that the unique selection pressure provided by BBO generally results in better optimization results for a set of standard benchmark problems. We also present comparisons between BBO and GA/GUR for combinatorial optimization problems, include the traveling salesman, the graph coloring, and the bin packing problems

    Metamorphic Temperature Investigation of Coexisting Calcite and Dolomite Marble––Examples from Nikani Ghar Marble and Nowshera Formation, Peshawar Basin, Pakistan

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    Using marble samples from the Nikani Ghar marble and Nowshera Formation from Northern Pakistan the determination of the temperature of metamorphism was undertaken with the help of calcite-dolomite solvus geothermometer. Two types of marbles, that is, calcite-dolomite marble and quartz-bearing calcite-dolomite marble were selected. Petrographic and scanning electron microscope analysis of dolomite samples indicated different grain sizes. X-ray diffraction technique indicated the calcites MgCO3 content up to 7.93 mol.%. Nikani Ghar marble samples have shown lower contents of MgCO3 as compared to samples from Nowshera Formation. The calcite-dolomite-quartz marble has also showed relatively lower MgCO3 content and hence rather low temperature (~500 °C). The temperature reached during peak metamorphism of the investigated marble occurrence, based on calcitedolomite solvus was 628 °C. Metamorphic temperatures derived from the present study were shown as a linear graph and values were in good agreement with the published literature

    Towards a flexible Decision Support Tool for MSY-based Marine Protected Area design for skates and rays

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    Peer-reviewed Paper. This is a pre-copyedited, author-produced version of an article accepted for publication in ICES Journal of Marine Science following peer review. The version of record Dedman, S., Officer, R., Brophy, D., Clarke, M., & Reid, D. G. (2017). Towards a flexible Decision Support Tool for MSY-based Marine Protected Area design for skates and rays. Ices Journal of Marine Science, 74(2), 576–587. https://doi.org/10.1093/icesjms/fsw147 is available online at: https://academic.oup.com/icesjms/article/74/2/576/2669563 & https://doi.org/10.1093/icesjms/fsw147.It is recommended that demersal elasmobranchs be managed using spatial proxies for Maximum Sustainable Yield. Here we combine escapement biomass—the percentage of the stock which must be retained each year to conserve it—with maps of predicted Catch Per Unit Effort (CPUE) of four ray species [cuckoo (Leucoraja naevus), thornback (Raja clavata), blonde (Raja brachyura), and spotted (Raja montagui)], created using Boosted Regression Tree modelling. We then use a Decision Support Tool to generate location and size options for Marine Protected Areas to protect these stocks, based on the priorities of the various stakeholders, notably the minimisation of fishing effort displacement. Variations of conservation/fishing priorities are simulated, as well as differential priorities for individual species, with a focus on protecting nursery grounds and spawning areas. Prioritizing high CPUE cells results in a smaller closed area that displaces the most fishing effort, whereas prioritizing low fishing effort results in a larger closed area that displaces the least fishing effort. The final result is a complete software package that produces maps of predicted species CPUE from limited survey data, and allows disparate stakeholders and policymakers to discuss management options within a mapping interface
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