2,107 research outputs found

    Autonomous spacecraft attitude control using magnetic torquing only

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    Magnetic torquing of spacecraft has been an important mechanism for attitude control since the earliest satellites were launched. Typically a magnetic control system has been used for precession/nutation damping for gravity-gradient stabilized satellites, momentum dumping for systems equipped with reaction wheels, or momentum-axis pointing for spinning and momentum-biased spacecraft. Although within the small satellite community there has always been interest in expensive, light-weight, and low-power attitude control systems, completely magnetic control systems have not been used for autonomous three-axis stabilized spacecraft due to the large computational requirements involved. As increasingly more powerful microprocessors have become available, this has become less of an impediment. These facts have motivated consideration of the all-magnetic attitude control system presented here. The problem of controlling spacecraft attitude using only magnetic torquing is cast into the form of the Linear Quadratic Regulator (LQR), resulting in a linear feedback control law. Since the geomagnetic field along a satellite trajectory is not constant, the system equations are time varying. As a result, the optimal feedback gains are time-varying. Orbit geometry is exploited to treat feedback gains as a function of position rather than time, making feasible the onboard solution of the optimal control problem. In simulations performed to date, the control laws have shown themselves to be fairly robust and a good candidate for an onboard attitude control system

    Is there a common core of religious experience?

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    In recent years many scholars in the study of religions have emphasised the differences between religions to such an extent that doubt has even been cast on whether it is useful to use the term 'religion' any more. It has been said that religious terms can only be properly understood within the context of their own 'language games', and that it is misleading to try to take them out of context and compare them with terms from very different traditions. If that is so, to speak of a 'common core' of religious experience, underlying the obvious differences between religious doctrines, is a doomed enterprise. It is such an enterprise upon which I wish to embark. I wish to argue that there is something common to a great many major religious traditions, a range of core experiences that are recognisably similar beneath many doctrinal differences. I will set out my argument by considering two religious traditions that seem almost as different as possible. I will try to establish that, beneath the doctrinal oppositions, there are clear convergences of experience. So I hope this test case will provide a pattern for similar studies with regard to many other apparently diverse traditions too. Religions are different, and they often disagree on doctrines. But it is possible to identify a set of religious experiences that are very similar across diverse religious traditions, and this may help to support the thesis that there are deep and important convergences underlying the obvious disagreements between religions. The two traditions I will consider are Vedanta and Christianity, both extremely complex and themselves containing many diverse strands. Nevertheless, they form identifiable religious traditions that are very often treated as in almost complete opposition. I will ask to what extent this is so, and to what extent they may rather be treated as complementary, or even as different ways of construing basically similar religious experiences and attitudes

    Classifying textile designs using region graphs

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    A Phenomenological Study of the Transition of Veterans into the Civilian Workforce

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    Military veterans face various challenges during their transition into the civilian workforce, including mental health problems. Veterans experience challenges like emotional trauma and physical distress while transitioning into the civilian workforce. The challenges result from the nature of the civilian work. The purpose of this phenomenological study was to explore the challenges among veterans in California and Michigan while transitioning into the civilian life. The study participants included 30 veterans from California and Michigan who had retired and those who were expecting to retire from the military within six months at the time of conducting the study. Schoenberg\u27s 4S transition theory was used as a conceptual framework. Data, collected through semi-structured interviews were analyzed using thematic analysis to develop themes for each research question. The findings indicated that transition challenges were related to emotional trauma and physical distress. Themes identified in relation to coping strategies that veterans can use to cope with the transition challenges include physical exercise, social interaction/open communication, and mutual support. The results of this study have significant social change implications. Leaders in the military and civilian workforce, government, and future military veterans could benefit from the findings by understanding the traditional challenges faced while transitioning into the civilian workforce. The study\u27s findings could benefit policymakers and senior leaders in developing and implementing strategies that ensure smooth transition by military veterans into the civilian workforce

    Realism and idealism in the political thought of Reinhold Niebuhr.

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    Methods and systems for production of organically derived ammonia/ammonium

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    Disclosed are methods for forming ammonia and ammonium that can be utilized in certifiably organic farming productions according to most if not all known certification standards. Also disclosed are bioreactors that can be utilized in carrying out disclosed methods. Methods and systems utilize obligate anaerobic bacteria to breakdown organic protein substrates, i.e., compounds containing bound nitrogen, to provide nitrogen in an unbound plant available form, and particularly, ammonia and/or ammonium. Obligate anaerobic bacteria include high ammonia producing bacteria such as Peptostreptococcus anaerobius, Clostridium sticklandii, and Clostridium aminophilum

    If You Can't Trust the Farmer, Who Can You Trust? The Effect of Certification Types on Purchases of Organic Produce

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    An information asymmetry exists in the market for organic produce since consumers cannot determine whether produce is organically or conventionally grown. Various methods may solve this problem including signaling, reputation, and certification. Signaling and reputation may not work well, because signals are noisy, and reputation may be difficult for a producer to establish. Certification of the farm and its growing methods shows the most promise. A survey instrument testing the efficacy of certification is presented along with empirical analysis suggesting that no notable difference existed between independent certification methods, although independent certification had significantly different effects than self-certification.Asymmetric information, Certification, Ordered probit, Organic produce, Agribusiness,
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