Smooth concordance of links topologically concordant to the Hopf link

It was shown by Jim Davis that a 2-component link with Alexander polynomial one is topologically concordant to the Hopf link. In this paper, we show that there is a 2-component link with Alexander polynomial one that has unknotted components and is not smoothly concordant to the Hopf link, answering a question of Jim Davis. We construct infinitely many concordance classes of such links, and show that they have the stronger property of not being smoothly concordant to the Hopf link with knots tied in the components.Comment: 8 pages, 5 figure

Effects of temperature on oocyte growth in the Mediterranean Terebellid Eupolymnia nebulosa (Annelida: Polychaeta

7 páginas, 4 figuras, 1 tabla.Eupolymnia nebulosa (Montagu) is a widely distributed terebellid polychaete that builds its tubes on the coastal shelf in areas with mixed soft and hard bottoms. From a long-term survey in the Bay of Ban- yuls, France (NW Mediterranean), we found an ad- vancement of the timing of the spawning period coin- cident with a delayed breakdown of the thermocline. We postulate that persistent high temperatures can in¯uence gamete development by stimulating oocyte growth, re- sulting in earlier spawning. During 1992 and 1993, we used a between-individuals experimental approach to assess the possible e ect of temperature on oocyte growth based on: (1) determination of the growing fraction of the oocyte population (i.e. oocyte net growth); (2) identi®cation of di erences in oocyte growth-rate among females; (3) comparison of non-sig- ni®cantly di erent size-distributions of the growing oocyte fraction (net oocyte size-distributions) at the beginning of the experiments with those at the end. No e ect of temperature on oocyte growth was detectable at the population level, but a positive individual response to prolonged high temperature was evident. Thus, the lack of a signi®cant response by the population to prolonged high temperature does not imply a lack of individual response. We propose a model of oocyte-growth dy- namics based on temperature that incorporates previous observations of extended oogenesis and oocyte growth during periods of both increasing and decreasing tem- perature and on the scattered pattern of oocyte size- distributions at the onset of spawning.This paper is a contribution to the French National Program on Re- cruitment Determinants (P.N.D.R.±G.L.O.B.E.C.), to the Marine Sciences A.E.L. and to the research project AMB94-0746 of the C.I.C.Y.T. of Spain. The ®rst and third authors were supported by grants of the C.N.R.S. and I.F.R.E.M.E.R. of France. The second author bene®ted from a fellowship of the M.E.C. of Spain (Ref. fr93 46037786) and a research contract of the C.S.I.C. of Spain.Peer reviewe

Electrochemical Processes for In-situ Treatment of Contaminated Soils

Soils at typical DOE (Department of Energy) waste sites are known to be contaminated by a host of hazardous organic chemicals, heavy metals and radionuclides. Typical hazardous organic contaminants include chlorinated solvents such as trichloroethylene (TCE), tetrachloroethylene (PCE), chloroform, and carbon tetrachloride, and polycyclic aromatic hydrocarbons (PAHs) such as naphthalene, fluorene, phenanthrene, anthracene and pyrene. It is also known that major toxic heavy metals such as Pb, Cr, As, Zn, Cu, Hg, and Cd and major radionuclides such as Tritium, U, Sr90, Pu, Cs137, and Tc are also commonly present at some DOE waste sites. Some of these chemicals are relatively mobile and can migrate down to the vadose zone and/or the aquifer region

Modelling discontinuities and Kelvin-Helmholtz instabilities in SPH

In this paper we discuss the treatment of discontinuities in Smoothed Particle Hydrodynamics (SPH) simulations. In particular we discuss the difference between integral and differential representations of the fluid equations in an SPH context and how this relates to the formulation of dissip ative terms for the capture of shocks and other discontinuities. This has important implications for many problems, in particular related to recently highlighted problems in treating Kelvin-Helmholtz instabilities across entropy gradients in SPH. The specific problems pointed out by Agertz et al. (2007) are shown to be related in particular to the (lack of) treatment of contact discontinuities in standard SPH formulations which can be cured by the simple application of an artificial thermal conductivity term. We propose a new formulation of artificial thermal conductivity in SPH which minimises dissipation away from discontinuities and can therefore be applied quite generally in SPH calculations.Comment: 31 pages, 10 figures, submitted to J. Comp. Phys. Movies + hires version available at http://www.astro.ex.ac.uk/people/dprice/pubs/kh/ . v3: modified as per referee's comments - comparison with Ritchie & Thomas formulation added, quite a few typos fixed. No major change in metho