26,715 research outputs found

    Beam Measurements of a CLOUD (Cosmics Leaving OUtdoor Droplets) Chamber

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    A striking correlation has recently been observed between global cloud cover and the flux of incident cosmic rays. The effect of natural variations in the cosmic ray flux is large, causing estimated changes in the Earth's energy radiation balance that are comparable to those attributed to greenhouse gases from the burning of fossil fuels since the Industrial Revolution. However a direct link between cosmic rays and cloud formation has not been unambiguously established. We therefore propose to experimentally measure cloud (water droplet) formation under controlled conditions in a test beam at CERN with a CLOUD chamber, duplicating the conditions prevailing in the troposphere. These data, which have never been previously obtained, will allow a detailed understanding of the possible effects of cosmic rays on clouds and confirm, or otherwise, a direct link between cosmic rays, global cloud cover and the Earth's climate. The measurements will, in turn, allow more reliable calculations to be made of the residual effect on global temperatures of the burning of fossil fuels, an issue of profound importance to society. Furthermore, light radio-isotope records indicate a correlation has existed between global climate and the cosmic ray flux extending back over the present inter-glacial and perhaps earlier. This suggests it may eventually become possible to make long-term (10-1,000 year) predictions of changes in the Earth's climate, provided a deeper understanding can be achieved of the ``geomagnetic climate'' of the Sun and Earth that modulates the cosmic-ray flux.Comment: More information and higher resolution drawings at http://cern.ch/Cloud Improved figure qualit

    Cosmic Rays and Climate

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    Among the most puzzling questions in climate change is that of solar-climate variability, which has attracted the attention of scientists for more than two centuries. Until recently, even the existence of solar-climate variability has been controversial - perhaps because the observations had largely involved temporary correlations between climate and the sunspot cycle. Over the last few years, however, diverse reconstructions of past climate change have revealed clear associations with cosmic ray variations recorded in cosmogenic isotope archives, providing persuasive evidence for solar or cosmic ray forcing of the climate. However, despite the increasing evidence of its importance, solar climate variability is likely to remain controversial until a physical mechanism is established. Although this remains a mystery, observations suggest that cloud cover may be influenced by cosmic rays, which are modulated by the solar wind and, on longer time scales, by the geomagnetic field and by the galactic environment of Earth. Two different classes of microphysical mechanisms have been proposed to connect cosmic rays with clouds: firstly, an influence of cosmic rays on the production of cloud condensation nuclei and, secondly, an influence of cosmic rays on the global electrical circuit in the atmosphere and, in turn, on ice nucleation and other cloud microphysical processes. Considerable progress on understanding ion-aerosol-cloud processes has been made in recent years, and the results are suggestive of a physically- plausible link between cosmic rays, clouds and climate. However, a concerted effort is now required to carry out definitive laboratory measurements of the fundamental physical and chemical processes involved, and to evaluate their climatic significance with dedicated field observations and modelling studies.Comment: 42 pages, 19 figure

    Taking Sides on Severed Heads: Kristeva at the Louvre

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    The theorist and philosopher Julia Kristeva is invited to curate an exhibition at the Louvre in Paris as part of a series-Parti Pris (Taking Sides)- and to turn this into a book, The Severed Head: Capital Visions. The organiser, R√©gis Michel, wants something partisan, that will challenge people to think, and Kristeva delivers in response a collection of severed heads neatly summarising her critique of the whole of western culture! Three figures dominate, providing a key to making sense of the exhibition: Freud, Bataille, and the maternal body. Using these figures, familiar from across the breadth of her work over the last half a century, she produces a witty analysis of western culture‚Äôs persistent privileging of disembodied masculine rationality; the head, ironically phallic, ironically and yet necessarily severed; the maternal body continually arousing a ‚Äújubilant anxiety‚ÄĚ (Kristeva, Severed Head 34), expressed through violence. Points of critique are raised in relation to Kristeva‚Äôs normative tendencies-could we not tell a different story about women, for example? The cultural context of the exhibition is also addressed: who are the intended viewers/readers and whose interests are being served here? Ultimately, however, this is a celebration of Kristeva‚Äôs tribute to psychic survivors

    The Schur-Horn theorem for operators with three point spectrum

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    We characterize the set of diagonals of the unitary orbit of a self-adjoint operator with three points in the spectrum. Our result gives a Schur-Horn theorem for operators with three point spectrum analogous to Kadison's result for orthogonal projections
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