763 research outputs found

    Foundations for a theory of gravitation theories

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    A foundation is laid for future analyses of gravitation theories. This foundation is applicable to any theory formulated in terms of geometric objects defined on a 4-dimensional spacetime manifold. The foundation consists of (i) a glossary of fundamental concepts; (ii) a theorem that delineates the overlap between Lagrangian-based theories and metric theories; (iii) a conjecture (due to Schiff) that the weak equivalence principle implies the Einstein equivalence principle; and (iv) a plausibility argument supporting this conjecture for the special case of relativistic, Lagrangian-based theories

    Rhizobium radiobacter Endophthalmitis following Intravitreal Ranibizumab Injection.

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    We present the first reported case of acute endophthalmitis due to Rhizobium radiobacter after an intravitreal injection of ranibizumab for neovascular age-related macular degeneration

    Active Mass Under Pressure

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    After a historical introduction to Poisson's equation for Newtonian gravity, its analog for static gravitational fields in Einstein's theory is reviewed. It appears that the pressure contribution to the active mass density in Einstein's theory might also be noticeable at the Newtonian level. A form of its surprising appearance, first noticed by Richard Chase Tolman, was discussed half a century ago in the Hamburg Relativity Seminar and is resolved here.Comment: 28 pages, 4 figure

    A relativistic formalism for computation of irrotational binary stars in quasi equilibrium states

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    We present relativistic hydrostatic equations for obtaining irrotational binary neutron stars in quasi equilibrium states in 3+1 formalism. Equations derived here are different from those previously given by Bonazzola, Gourgoulhon, and Marck, and have a simpler and more tractable form for computation in numerical relativity. We also present hydrostatic equations for computation of equilibrium irrotational binary stars in first post-Newtonian order.Comment: 5 pages, corrected eqs.(2.10), (2.11) and (3.1

    Evidence for deficits in behavioural and physiological responses in aged mice relevant to the psychiatric symptom of apathy

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    Apathy is widely reported in patients with neurological disorders or post viral infection but is also seen in otherwise-healthy aged individuals. This study investigated whether aged male mice express behavioural and physiological changes relevant to an apathy phenotype. Using measures of motivation to work for reward, we found deficits in the progressive ratio task related to rate of responding. In an effort-related decision-making task, aged mice were less willing to exert effort for high value reward. Aged mice exhibited reduced reward sensitivity but also lower measures of anxiety in the novelty supressed feeding test and an attenuated response to restraint stress with lower corticosterone and reduced paraventricular nucleus c-fos activation. This profile of affective changes did not align with those observed in models of depression but suggested emotional blunting. In a test of cognition (novel object recognition), aged mice showed no impairments, but activity was lower in a measure of exploration in a novel environment. Together, these data suggest aged mice show changes across the domains of motivated behaviour, reward sensitivity and emotional reactivity and may be a suitable model for the pre-clinical study of the psychiatric symptom of apathy

    Self-Screening Hawking Atmosphere in the Presence of a Bulk Viscosity

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    The recent theory of 't Hooft [ Nucl. Phys. Suppl. {\bf 68}, 174 (1998)] models the black hole as a system endowed with an envelope of matter that obeys an equation of state in the form p=(γ1)ρ p=(\gamma -1)\rho, and acts as a source in Einstein's equations. The present paper generalizes the 't Hooft theory so as to take into account a bulk viscosity ζ\zeta in the fluid. It is shown that even a slight positive value of ζ\zeta will suffice to yield complete agreement with the Hawking formula for the entropy of the black hole, if the value of the constant γ\gamma takes a value that is slightly less than 4/3. The value γ=4/3\gamma=4/3 corresponds to a radiation fluid.Comment: 12 pages, LaTeX, no figures, minor extensions of the discussion. To appear in PR

    Effects of 7.5% carbon dioxide inhalation on anxiety and mood in cigarette smokers

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    Cigarette smoking is associated with elevated risk of anxiety and mood disorder. Using the 7.5% carbon dioxide (CO(2)) inhalation model of anxiety induction, we examined the effects of smoking status and abstinence from smoking on anxiety responses. Physiological and subjective responses to CO(2) and medical air were compared in smokers and non-smokers (Experiment One) and in overnight abstinent and non-abstinent smokers (Experiment Two). CO(2) induced greater increases in blood pressure in non-smokers compared with smokers (ps < 0.043), and greater increases in anxiety (p = 0.005) and negative affect (p = 0.054) in non-abstinent compared with abstinent smokers. CO(2) increased physiological and subjective indices of anxiety. There were differences across smoking groups indicating that the CO(2) inhalation model is a useful tool for examining the relationship between smoking and anxiety. The findings suggested that both acute smoking and acute abstinence may protect against anxious responding. Further investigation is needed in long-term heavy smokers
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