6,489 research outputs found

    Variational Principles for Natural Divergence-free Tensors in Metric Field Theories

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    Let Tab=Tba=0T^{ab}=T^{ba}=0 be a system of differential equations for the components of a metric tensor on RmR^m. Suppose that TabT^{ab} transforms tensorially under the action of the diffeomorphism group on metrics and that the covariant divergence of TabT^{ab} vanishes. We then prove that TabT^{ab} is the Euler-Lagrange expression some Lagrangian density provided that TabT^{ab} is of third order. Our result extends the classical works of Cartan, Weyl, Vermeil, Lovelock, and Takens on identifying field equations for the metric tensor with the symmetries and conservation laws of the Einstein equations

    Some thoughts on GAIA and the sulfur cycle

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    The data hypothesis states that the composition, oxidation reduction state, and temperature of the troposphere are actively regulated by the biota for the biota. One of the early predictions of the Gaia hypothesis was that there should be a sulfur compound made by the biota in the oceans. It would need to be stable enough against oxidation in water to allow its transfer to the air. Either the sulfur compound itself or its atmospheric oxidation product would have to return sulfur from the sea to the land surfaces. The most likely candidate for this role was dimethyl sulfide. Another sulfur compound of interest from a Gaian viewpoint CS2 (carbon disulfide) is discussed. Theories on the production of dimethyl sulfide and carbon disulfide related to the Gaian hypothesis are examined

    Daisyworld: a review

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    Daisyworld is a simple planetary model designed to show the long-term effects of coupling between life and its environment. Its original form was introduced by James Lovelock as a defense against criticism that his Gaia theory of the Earth as a self-regulating homeostatic system requires teleological control rather than being an emergent property. The central premise, that living organisms can have major effects on the climate system, is no longer controversial. The Daisyworld model has attracted considerable interest from the scientific community and has now established itself as a model independent of, but still related to, the Gaia theory. Used widely as both a teaching tool and as a basis for more complex studies of feedback systems, it has also become an important paradigm for the understanding of the role of biotic components when modeling the Earth system. This paper collects the accumulated knowledge from the study of Daisyworld and provides the reader with a concise account of its important properties. We emphasize the increasing amount of exact analytic work on Daisyworld and are able to bring together and summarize these results from different systems for the first time. We conclude by suggesting what a more general model of life-environment interaction should be based on

    Martian atmospheric compositional analysis- its biological significance first quarterly progress report, 15 may - 15 aug. 1965

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    Biological significance of Martian atmospheric compositional analysis, and life detection studies of chemical free energy in surface matte

    On the naturalness of Einstein's equation

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    We compute all 2-covariant tensors naturally constructed from a semiriemannian metric which are divergence-free and have weight greater than -2. As a consequence, it follows a characterization of the Einstein tensor as the only, up to a constant factor, 2-covariant tensor naturally constructed from a semiriemannian metric which is divergence-free and has weight 0 (i.e., is independent of the unit of scale). Since these two conditions are also satisfied by the energy-momentum tensor of a relativistic space-time, we discuss in detail how these theorems lead to the field equation of General Relativity.Comment: 12 pages, added references, corrected typo

    Catching a Catfish: Constructing the ‘good’ social media user in reality television

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    This article interrogates the cultural work of ‘old’ media texts which take social media use as a narrative focus. Employing the MTV reality show Catfish: The TV Show as a case study, I argue that, in this program, the specific conventions of reality television - authenticity, confession and self-realization – work to produce and circulate normative scripts of “appropriate” and “inappropriate” ways to articulate the self on social media, which align with reality TV’s established investment in the concept of the ‘authentic’ self. Further, I argue that the show’s representations of social media use valorize the primacy of connecting with and accepting one’s ‘real’ self, making legible a subject position which speaks particularly to young people – the program’s target demographic – in the contemporary juncture of 2010s ‘crisis’ neoliberalism, by transposing political questions into personal crises

    Galactic Potentials

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    The information contained in galactic rotation curves is examined under a minimal set of assumptions. If emission occurs from stable circular geodesic orbits of a static spherically symmetric field, with information propagated to us along null geodesics, observed rotation curves determine galactic potentials without specific reference to any metric theory of gravity. Given the potential, the gravitational mass can be obtained by way of an anisotropy function of this field. The gravitational mass and anisotropy function can be solved for simultaneously in a Newtonian limit without specifying any specific source. This procedure, based on a minimal set of assumptions, puts very strong constraints on any model of the "dark matter".Comment: A somewhat longer form of the final version to appear in Physical Review Letters.Clarification and further reference

    “I Am…”: Caitlyn Jenner, Jazz Jennings and the cultural politics of transgender celebrity

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    In the twenty-first century, the visibility of transgender celebrities appears greater than ever. Whilst scholarly work has analysed, and continues to analyse, representations of trans celebrities, this research has largely approached these figures as significant because they make transgender visible, rather than because of the more specific fact that they are celebrities. This article interrogates the role of discourses and tropes of celebrity itself in enabling particular incarnations of trans subjectivity to become intelligible within popular culture. Focusing upon the examples of Caitlyn Jenner and Jazz Jennings, two of the most widely circulated trans celebrities in the contemporary moment, I argue that the tropes of authenticity, self-reflexivity, self-revelation and manufacture central to celebrity culture, have functioned as core discursive frameworks through which Jenner and Jennings’ transgender identities have been rationalised within the popular media. In becoming legible as transgender through celebrity, I argue that Jenner and Jennings’ media narratives have worked to confer recognisability to a highly limited model of transgender life, fraught with exclusions around race and gender normativity

    On the static Lovelock black holes

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    We consider static spherically symmetric Lovelock black holes and generalize the dimensionally continued black holes in such a way that they asymptotically for large r go over to the d-dimensional Schwarzschild black hole in dS/AdS spacetime. This means that the master algebraic polynomial is not degenerate but instead its derivative is degenerate. This family of solutions contains an interesting class of pure Lovelock black holes which are the Nth order Lovelock {\Lambda}-vacuum solu- tions having the remarkable property that their thermodynamical parameters have the universal character in terms of the event horizon radius. This is in fact a characterizing property of pure Lovelock theories. We also demonstrate the universality of the asymptotic Einstein limit for the Lovelock black holes in general.Comment: 19 page