The existence of time

Of those gauge theories of gravity known to be equivalent to general relativity, only the biconformal gauging introduces new structures - the quotient of the conformal group of any pseudo-Euclidean space by its Weyl subgroup always has natural symplectic and metric structures. Using this metric and symplectic form, we show that there exist canonically conjugate, orthogonal, metric submanifolds if and only if the original gauged space is Euclidean or signature 0. In the Euclidean cases, the resultant configuration space must be Lorentzian. Therefore, in this context, time may be viewed as a derived property of general relativity.Comment: 21 pages (Reduced to clarify and focus on central argument; some calculations condensed; typos corrected

Curvature contraction of convex hypersurfaces by nonsmooth speeds

We consider contraction of convex hypersurfaces by convex speeds, homogeneous of degree one in the principal curvatures, that are not necessarily smooth. We show how to approximate such a speed by a sequence of smooth speeds for which behaviour is well known. By obtaining speed and curvature pinching estimates for the flows by the approximating speeds, independent of the smoothing parameter, we may pass to the limit to deduce that the flow by the nonsmooth speed converges to a point in finite time that, under a suitable rescaling, is round in the C^2 sense, with the convergence being exponential

Interpretation of sexual secondary characteristics (SSCs) in regulatory testing for endocrine activity in fish.

Secondary sexual characteristics (SSCs) are important features that have evolved in many fish species because of inter-individual competition for mates. SSCs are crucial not only for sexual selection, but also for other components of the reproductive process and parental care. Externally, they are especially clear in males (for instance, tubercles, fatpad, anal finnage, colouration) but are also externally present in the females (for instance, ovipositor). These characters are under hormonal control and as such there has been much interest in incorporating them as measures in fish test methods to assess the potential endocrine activity of chemicals. Here we describe the external SSCs in typical laboratory test species for endocrine testing - fathead minnow (Pimephales promelas), Japanese medaka (Oryzias latipes), zebrafish (Danio rerio) and the three-spined stickleback (Gasterosteus aculeatus L.). We also provide some examples and discuss the utility of SSC responses to the endocrine activity of chemicals in the field and the laboratory. This paper is not aimed to provide a comprehensive review of SSCs in fish but presents a view on the assessment of SSCs in regulatory testing. Due to the current regulatory importance of establishing an endocrine mode-of-action for chemicals, we also consider other, non-endocrine factors that may lead to SSC responses in fish. We conclude with recommendations for how the assessment of SSCs in fish could be usefully incorporated into the endocrine hazard and risk assessment of chemicals

Modeling Reactive Wetting when Inertial Effects are Dominant

Recent experimental studies of molten metal droplets wetting high temperature reactive substrates have established that the majority of triple-line motion occurs when inertial effects are dominant. In light of these studies, this paper investigates wetting and spreading on reactive substrates when inertial effects are dominant using a thermodynamically derived, diffuse interface model of a binary, three-phase material. The liquid-vapor transition is modeled using a van der Waals diffuse interface approach, while the solid-fluid transition is modeled using a phase field approach. The results from the simulations demonstrate an O \left( t^{-\nicefrac{1}{2}} \right) spreading rate during the inertial regime and oscillations in the triple-line position when the metal droplet transitions from inertial to diffusive spreading. It is found that the spreading extent is reduced by enhancing dissolution by manipulating the initial liquid composition. The results from the model exhibit good qualitative and quantitative agreement with a number of recent experimental studies of high-temperature droplet spreading, particularly experiments of copper droplets spreading on silicon substrates. Analysis of the numerical data from the model suggests that the extent and rate of spreading is regulated by the spreading coefficient calculated from a force balance based on a plausible definition of the instantaneous interface energies. A number of contemporary publications have discussed the likely dissipation mechanism in spreading droplets. Thus, we examine the dissipation mechanism using the entropy-production field and determine that dissipation primarily occurs in the locality of the triple-line region during the inertial stage, but extends along the solid-liquid interface region during the diffusive stage

Summer 1969

Massachusetts Turf and Lawn Grass Council Better Turf Through Research and Education Contents: New Lawn Seeds Ready to Sprout Profits by Robert W. Schery (page 3) Potash Experiments on Turf Grasses by Edward G. Konieczny (4) Understanding the Basis... Fertilizer Spreader: Spreading Relationships (9) TVA Shows Sulpher Coated Urea (13) Salinity Tolerance of Turfgrass by Jeff Wheeler (19) Poa Annua by William H. Daniel (23) Turf Management by Elwin E. Deal (26) The Art and Science of Greenskeeping by James W. Timmerman (27

Asymmetric Supernovae from Magneto-Centrifugal Jets

Strong toroidal magnetic fields generated in stellar collapse can generate magneto-centrifugal jets in analogy to those found in simulations of black hole accretion and explain why all core collapse supernovae are found to be substantially asymmetric and predominantly bi-polar. We describe two phases: the initial LeBlanc-Wilson jet and a subsequent protopulsar or toroidal jet that propagates at about the core escape velocity. The jets will produce bow shocks that tend to expel matter, including iron and silicon, into equatorial tori, accounting for observations of the element distribution in Cas A. A magnetic ``switch'' mechanism may apply in instances of low density and large magnetic field with subsequent increase in the speed and collimation of the toroidal jet, depositing relatively little momentum. The result could be enough infall to form a black hole with a third, highly relativistic jet that could catch up to the protopulsar jet after it has emerged from the star. The interaction of these two jets could generate internal shocks and explain the presence of iron lines in the afterglow. Recent estimates that typical gamma-ray burst energy is about 3x10^50 erg imply either a very low efficiency for conversion of rotation into jets, or a rather rapid turnoff of the jet process even though the black hole still rotates rapidly. Magnetars and ``hypernovae'' might arise in an intermediate parameter regime of energetic jets that yield larger magnetic fields and provide more energy than the routine case, but that are not so tightly collimated that they yield failed supernova. (slightly abridged)Comment: AASTeX, 29 pages, 2 postscript figures, accepted by ApJ, November 20, 200