15,216 research outputs found

    Collisions with ice-volatile objects: Geological implications

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    The collision of the Earth with extra-terrestrial ice-volatile bodies is proposed as a mechanism to produce rapid changes in the geologic record. These bodies would be analogs of the ice satellites found for the Jovian planets and suspected for comets and certain low density bodies in the Asteroid belt. Five generic end-members are postulated: (1) water ice; (2) dry ice: carbon-carbon dioxide rich, (3) oceanic (chloride) ice; (4) sulfur-rich ice; (5) ammonia hydrate-rich ice; and (6) clathrate: methane-rich ice. Due to the volatile nature of these bodies, evidence for their impact with the Earth would be subtle and probably best reflected geochemically or in the fossil record. Actual boloids impacting the Earth may have a variable composition, generally some admixture with water ice. However for discussion purposes, only the effects of a dominant component will be treated. The general geological effects of such collisions, as a function of the dominant component would be: (1) rapid sea level rise unrelated to deglaciation, (2) decreased oceanic pH and rapid climatic warming or deglaciation; (3) increased paleosalinities; (4) increased acid rain; (5) increased oceanic pH and rapid carbonate deposition; and (6) rapid climatic warming or deglaciation

    K3-fibered Calabi-Yau threefolds I, the twist map

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    A construction of Calabi-Yaus as quotients of products of lower-dimensional spaces in the context of weighted hypersurfaces is discussed, including desingularisation. The construction leads to Calabi-Yaus which have a fiber structure, in particular one case has K3 surfaces as fibers. These Calabi-Yaus are of some interest in connection with Type II -heterotic string dualities in dimension 4. A section at the end of the paper summarises this for the non-expert mathematician.Comment: 31 pages LaTeX, 11pt, 2 figures. To appear in International Journal of Mathematics. On the web at http://personal-homepages.mis.mpg.de/bhunt/preprints.html , #

    “It’s Just Nice Having a Real Teacher”: Student Perceptions of Online versus Face-to-Face Instruction

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    With recent increases in online enrollment, undergraduate students are far more likely to experience an online learning environment than they were in the past. While existing literature provides general insight into reasons why students may or may not prefer online instruction, it is unclear whether these preferences are shaped by student’s perceptions of online learning or actual experience with online courses. To address this gap, undergraduate students enrolled in either online (n=370) or face-to-face (n=360) courses were surveyed about their course format preference. A content analysis of the responses was performed with the findings suggesting that 1) student perceptions may be based on old typologies of distance education akin to correspondence courses, regardless of actual experience with online courses, and 2) course preferences are related to issues involving teaching presence and self-regulated learning. The implications of this research for developing more effective online pedagogy are discussed

    The deep human prehistory of global tropical forests and its relevance for modern conservation

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    Significant human impacts on tropical forests have been considered the preserve of recent societies, linked to large-scale deforestation, resource mining, livestock grazing, and plantation industries. Cumulative archaeological evidence now demonstrates, however, that Homo sapiens has actively manipulated tropical forest ecologies for at least 45,000 years. It is clear that these millennia of impacts need to be taken into account when studying and conserving tropical forest ecosystems today. Nevertheless, archaeology has so far provided minimal practical insight into contemporary human-tropical forest interactions. Here, we review significant archaeological evidence for impacts of prehistoric hunter-gatherers, agriculturalists, and urban settlements on global tropical forests. We compare the challenges faced, as well as the solutions adopted, by these groups with those confronting present-day societies, which rely on tropical forests for ecosystem services, ranging from the maintenance of global carbon sinks to bioprospection for medicinal plants. We emphasise archaeology’s importance in not only promoting natural and cultural heritage in tropical forests, but also taking an active role in informing modern conservation and policy-making

    Spatial patterns of desynchronization bursts in networks

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    We adapt a previous model and analysis method (the {\it master stability function}), extensively used for studying the stability of the synchronous state of networks of identical chaotic oscillators, to the case of oscillators that are similar but not exactly identical. We find that bubbling induced desynchronization bursts occur for some parameter values. These bursts have spatial patterns, which can be predicted from the network connectivity matrix and the unstable periodic orbits embedded in the attractor. We test the analysis of bursts by comparison with numerical experiments. In the case that no bursting occurs, we discuss the deviations from the exactly synchronous state caused by the mismatch between oscillators

    Are Drug Companies Living Up to Their Human Rights Responsibilities? Moving Toward Assessment

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    As one viewpoint of three in the PLoS Medicine Debate on whether drug companies are living up to their human rights responsibilities, Sofia Gruskin and Zyde Raad argue that companies' actions to promote access to medicines, including their interactions with state and non-state actors, must be better monitored

    Fluid flow at the interface between elastic solids with randomly rough surfaces

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    I study fluid flow at the interface between elastic solids with randomly rough surfaces. I use the contact mechanics model of Persson to take into account the elastic interaction between the solid walls and the Bruggeman effective medium theory to account for the influence of the disorder on the fluid flow. I calculate the flow tensor which determines the pressure flow factor and, e.g., the leak-rate of static seals. I show how the perturbation treatment of Tripp can be extended to arbitrary order in the ratio between the root-mean-square roughness amplitude and the average interfacial surface separation. I introduce a matrix D(Zeta), determined by the surface roughness power spectrum, which can be used to describe the anisotropy of the surface at any magnification Zeta. I present results for the asymmetry factor Gamma(Zeta) (generalized Peklenik number) for grinded steel and sandblasted PMMA surfaces.Comment: 16 pages, 14 figure

    From ‘other’ to involved: User involvement in research: An emerging paradigm

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    This article has been made available through the Brunel Open Access Publishing Fund. Copyright @ 2013 The Author(s). This is an Open Access article. Non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly attributed, cited, and is not altered, transformed, or built upon in any way, is permitted. The moral rights of the named author(s) have been asserted.This article explores the issue of ‘othering’ service users and the role that involving them, particularly in social policy and social work research may play in reducing this. It takes, as its starting point, the concept of ‘social exclusion’, which has developed in Europe and the marginal role that those who have been included in this construct have played in its development and the damaging effects this may have. The article explores service user involvement in research and is itself written from a service user perspective. It pays particular attention to the ideological, practical, theoretical, ethical and methodological issues that such user involvement may raise for research. It examines problems that both research and user involvement may give rise to and also considers developments internationally to involve service users/subjects of research, highlighting some of the possible implications and gains of engaging service user knowledge in research and the need for this to be evaluated
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