1,514 research outputs found

    Very-high-energy gamma radiation from supernova remnants as seen with H.E.S.S

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    Very-high-energy (VHE, E > 100 GeV) gamma radiation has already been detected from several supernova remnants (SNRs). These objects, which are well-studied in radio, optical and X-ray wavelengths, constitute one of the most intriguing source classes in VHE astronomy. H.E.S.S., an array of four imaging atmospheric Cherenkov telescopes in Namibia, has recorded an extensive dataset of VHE gamma-ray observations covering the central region of the Milky Way, both from pointed observations as well as from the Galactic Plane Survey conducted in the inner region of the Galaxy. From radio observations, several hundred SNRs are known in the Milky Way, but until now only few of them have been identified as VHE gamma-ray emitters. Using the H.E.S.S. dataset and a large ensemble of radio SNRs localized in the inner region of the Galaxy, the standard framework that links the origin of cosmic rays to the gamma-ray visibility of SNRs can now be tested. Here we present the ensemble of investigated SNRs and discuss constraints on the parameter space used within a theoretical model of hadronic VHE gamma-ray production.Comment: Proceeding of the 32nd ICRC, August 11-18 2011, Beijing, Chin

    SQG-Differential Evolution for difficult optimization problems under a tight function evaluation budget

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    In the context of industrial engineering, it is important to integrate efficient computational optimization methods in the product development process. Some of the most challenging simulation-based engineering design optimization problems are characterized by: a large number of design variables, the absence of analytical gradients, highly non-linear objectives and a limited function evaluation budget. Although a huge variety of different optimization algorithms is available, the development and selection of efficient algorithms for problems with these industrial relevant characteristics, remains a challenge. In this communication, a hybrid variant of Differential Evolution (DE) is introduced which combines aspects of Stochastic Quasi-Gradient (SQG) methods within the framework of DE, in order to improve optimization efficiency on problems with the previously mentioned characteristics. The performance of the resulting derivative-free algorithm is compared with other state-of-the-art DE variants on 25 commonly used benchmark functions, under tight function evaluation budget constraints of 1000 evaluations. The experimental results indicate that the new algorithm performs excellent on the 'difficult' (high dimensional, multi-modal, inseparable) test functions. The operations used in the proposed mutation scheme, are computationally inexpensive, and can be easily implemented in existing differential evolution variants or other population-based optimization algorithms by a few lines of program code as an non-invasive optional setting. Besides the applicability of the presented algorithm by itself, the described concepts can serve as a useful and interesting addition to the algorithmic operators in the frameworks of heuristics and evolutionary optimization and computing

    Fostering sustainability through technology-mediated interactions: Conviviality and reciprocity in the sharing economy

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    Purpose: This article addresses the lack of scholarly attention paid to the sharing economy from a sociological perspective, with respect to the technology-mediated interactions between sharing economy users. The paper provides a critical overview of the sharing economy and its impact on business and communities and explores how information technology can facilitate authentic, genuine sharing, through exercising and enabling conviviality and non-direct reciprocity. Approach: The paper begins with a critique of the technology-mediated sharing economy; introduces the concept of conviviality as a tool to grow and shape community and sustainability within the sharing economy; then explores reciprocity and sharing behaviour. Finally, the paper draws upon social exchange theory to illustrate conviviality and reciprocity, using four case studies of technology-enabled sharing. Findings: The paper contributes to the emerging debate around how the sharing economy, driven by information systems and technology affects social cohesion and personal relationships. The paper elucidates the central role conviviality and reciprocity play in explaining the paradoxes, tensions and impact of the sharing economy on society. Conviviality and reciprocity are positioned as key capabilities of a more sustainable version of the sharing economy, enabled via information technology. Originality and value: The findings reveal that information technology mediated sharing enterprises should promote conviviality and reciprocity in order to deliver more positive environmental, economic and social benefits. The diversity of existing operations indicated by he findings and the controversies discussed will guide the critical study of the social potential of sharing economy to avoid treating all sharing alike

    Never the twain shall meet: a critical appraisal of the combination of discourse and psychoanalytic theory in studies of men and masculinity

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    In recent years there has been a number of attempts by different researchers to study men and masculinity using a combination of discourse theory and psychoanalysis. The main reason for this development is the sense that, on its own, discourse theory provides an incomplete account of masculine subjectivity. Psychoanalysis is thought to be able to fill those gaps. In this paper I want to begin by reviewing these arguments. I will provide an outline of the alleged deficiencies in discursive approaches to men and masculinity before going on to examine some of the work that has attempted the above synthesis. What I aim to show is that, for a number of reasons, such attempts are bound to fail. Instead, I will argue that better progress can be made in studies of masculinity by remaining within the theoretical boundaries of Discursive Psychology

    Exoplanets and SETI

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    The discovery of exoplanets has both focused and expanded the search for extraterrestrial intelligence. The consideration of Earth as an exoplanet, the knowledge of the orbital parameters of individual exoplanets, and our new understanding of the prevalence of exoplanets throughout the galaxy have all altered the search strategies of communication SETI efforts, by inspiring new "Schelling points" (i.e. optimal search strategies for beacons). Future efforts to characterize individual planets photometrically and spectroscopically, with imaging and via transit, will also allow for searches for a variety of technosignatures on their surfaces, in their atmospheres, and in orbit around them. In the near-term, searches for new planetary systems might even turn up free-floating megastructures.Comment: 9 page invited review. v2 adds some references and v3 has other minor additions and modification
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