Simple derivation of the frequency dependent complex heat capacity

This paper gives a simple derivation of the well-known expression of the frequency dependent complex heat capacity in modulated temperature experiments. It aims at clarified again that the generalized calorimetric susceptibility is only due to the non-equilibrium behaviour occurring in the vicinity of thermodynamic equilibrium of slow internal degrees of freedom of a sample when the temperature oscillates at a well determined frequency

Switching Current vs. Magnetoresistance in Magnetic Multilayer Nanopillars

We study current-driven magnetization switching in nanofabricated magnetic trilayers, varying the magnetoresistance in three different ways. First, we insert a strongly spin-scattering layer between the magnetic trilayer and one of the electrodes, giving increased magnetoresistance. Second, we insert a spacer with a short spin-diffusion length between the magnetic layers, decreasing the magnetoresistance. Third, we vary the angle between layer magnetizations. In all cases, we find an approximately linear dependence between magnetoresistance and inverse switching current. We give a qualitative explanation for the observed behaviors, and suggest some ways in which the switching currents may be reduced.Comment: 3 pages, 4 figure

Neutron skin uncertainties of Skyrme energy density functionals

Background: Neutron-skin thickness is an excellent indicator of isovector properties of atomic nuclei. As such, it correlates strongly with observables in finite nuclei that depend on neutron-to-proton imbalance and the nuclear symmetry energy that characterizes the equation of state of neutron-rich matter. A rich worldwide experimental program involving studies with rare isotopes, parity violating electron scattering, and astronomical observations is devoted to pinning down the isovector sector of nuclear models. Purpose: We assess the theoretical systematic and statistical uncertainties of neutron-skin thickness and relate them to the equation of state of nuclear matter, and in particular to nuclear symmetry energy parameters. Methods: We use the nuclear superfluid Density Functional Theory with several Skyrme energy density functionals and density dependent pairing. To evaluate statistical errors and their budget, we employ the statistical covariance technique. Results: We find that the errors on neutron skin increase with neutron excess. Statistical errors due to uncertain coupling constants of the density functional are found to be larger than systematic errors, the latter not exceeding 0.06 fm in most neutron-rich nuclei across the nuclear landscape. The single major source of uncertainty is the poorly determined slope L of the symmetry energy that parametrizes its density dependence. Conclusions: To provide essential constraints on the symmetry energy of the nuclear energy density functional, next-generation measurements of neutron skins are required to deliver precision better than 0.06 fm.Comment: 5 pages, 4 figure

Sensitivity of Vertebrate Embryos to Heavy Metals as a Criterion of Water Quality

Embryonic and/or larval stages of the leopard frog (Rana pipiens), domestic fowl (Gallus domesticus) and the goldfish (Carassiua auratus) were treated with cadmium chloride, mercuric chloride, lead chloride, zinc chloride and sodium arsenite. The principal objectives were (1) to determine the sensitivity of vertebrate embryos to certain metals which are of consequence in water pollution, and (2) to ascertain the suitalility of vertebrate embryos as bioassay organisms for monitoring metallic pollutants within water resources. Vertebrate embryos are found to be highly sensitive to the toxic effects of all the metals studied. Concentrations of mercury as low as 10 ppb, with continuous treatment, produced a 100% kill of frog embryos and a significant degree of lethality in chick embryos. Cadmium and lead also produced detectable levels of lethality and/or anomalous development when administered to chick embryos at concentrations of 10 ppb. At 0.5 ppm mercury and cadmium produced 100% lethality in populations of goldfish embryos treated for four days. Lead and zinc were less toxic to the latter, producing approximately 80% lethality under simitar conditions. These results indicate that vertebrate embryos are substantially more sensitive to metallic pollutants than are adult forms, and that they may constitute a valuable tool for monitoring the quality of water resources

Current-Driven Magnetic Excitations in Permalloy-Based Multilayer Nanopillars

We study current-driven magnetization switching in nanofabricated Ni84Fe16/Cu/Ni84Fe16 trilayers at 295 K and 4.2 K. The shape of the hysteretic switching diagram at low magnetic field changes from 295 K to 4.2 K. The reversible behavior at higher field involves two phenomena, a threshold current for magnetic excitations closely correlated with the switching current, and a peak in differential resistance characterized by telegraph noise, with average period that decreases exponentially with current and shifts with temperature. We interpret both static and dynamic results at 295 K and 4.2 K in terms of thermal activation over a potential barrier, with a current dependent effective magnetic temperature.Comment: 4 pages, 4 Figure

Manipulating Current-Induced Magnetization Switching

We summarize our recent findings on how current-driven magnetization switching and magnetoresistance in nanofabricated magnetic multilayers are affected by varying the spin-scattering properties of the non-magnetic spacers, the relative orientations of the magnetic layers, and spin-dependent scattering properties of the interfaces and the bulk of the magnetic layers. We show how our data are explained in terms of current-dependent effective magnetic temperature.Comment: 6 pages, 6 figures, submitted to MMM'04 proceeding

An Avoidance Response Bioassay for Aquatic Pollutants

Avoidance response bioassays were conducted with eight aquatic contaminants, including cadmium, copper, mercury, zinc, chloroform, dioctyl phthalate (DOP), trisodium nitrilotriacetic acid (NTA), and phenol. Tests were performed in a dual-channel fluviarium system, and the toxicant injection procedure used provided good regulation of exposure concentrations. Juvenile stages of largemouth bass (Micropterus salmoides), bluegill sunfish (Lepomis macrochirus), and rainbow trout (Salmo gairdneri), and tadpoles of the American toad (Bufo americanus) proved to be suitable animals for evaluating avoidance or attraction responses. The trout was the most sensitive species tested. Avoidance was significant in tests with cadmium, phenol, and zinc, and significant attraction resulted from exposures to chloroform, COP, and mercury. Animals generally avoided lower concentrations of copper but were attracted to higher exposure levels. NTA produced variable responses. In tests With trout, threshold concentrations for avoidance or attraction were estimated to fall at 0.0002 mg/1 mercury, 0.047 mg/1 zinc, 0.052 mg/1 cadmium, 0.074 mg/1 copper, 11.9 mg/1 chloroform, and 56.6 mg/1 NTA. The threshold for phenol, determined using bluegill, was 39.0 mg/1. Results from fish embryo-larval toxicity tests were used to gauge sensitivity of the avoidance response bioassay. Toxicant concentrations which produced embryo-larval lethality or teratogenesis at frequencies of 10% (LC10) and 1% (LC1) were compared to behavioral threshold concentrations. The avoidance test was observed to be a less sensitive procedure for evaluating the effects of all the selected toxicants, except zinc. However, the behavioral test provided valuable information which was not obtainable using other bioassay methodologies

A Standard Input Format for Computer Codes Which Solve Stochastic Programs with Recourse and a Library of Utilities to Simplify its Use

We explain our suggestions for standardizing input formats for computer codes which solve stochastic programs with recourse. The main reason to set some conventions is to allow programs implementing different methods of solution to be used interchangeably. The general philosophy behind our design is a) to remain fairly faithful to the de facto standard for the statement of LP problems established by IBM for use with MPSX and subsequently adopted by the authors of MINOS, b) to provide sufficient flexibility so that a variety of problems may be expressed in the standard format, c) to allow problems originally formulated as deterministic LP to be converted to stochastic problems with a minimum of effort, d) to permit new options to be added as the need arises, and e) to provide some routines to facilitate the task of reading files specified in the standard format