Thin spray film thickness measuring technique

Thin spray film application depths, in the 0.0002 cm to 0.002 cm range, are measured by portable, commercially available, light density measuring device used in conjunction with glass plate or photographic film. Method is automated by using mechanical/electrical control for shutting off film applicator at desired densitometer reading

New measurements of magnetic fields of roAp stars with FORS1 at the VLT

Magnetic fields play a key role in the pulsations of rapidly oscillating Ap (roAp) stars since they are a necessary ingredient of all pulsation excitation mechanisms proposed so far. This implies that the proper understanding of the seismological behaviour of the roAp stars requires knowledge of their magnetic fields. However, the magnetic fields of the roAp stars are not well studied. Here we present new results of measurements of the mean longitudinal field of 14 roAp stars obtained from low resolution spectropolarimetry with FORS1 at the VLT.Comment: 5 pages, accepted for publication in A&

Viscosity methods giving uniqueness for martingale problems

Let $E$ be a complete, separable metric space and $A$ be an operator on $C_b(E)$. We give an abstract definition of viscosity sub/supersolution of the resolvent equation $\lambda u-Au=h$ and show that, if the comparison principle holds, then the martingale problem for $A$ has a unique solution. Our proofs work also under two alternative definitions of viscosity sub/supersolution which might be useful, in particular, in infinite dimensional spaces, for instance to study measure-valued processes. We prove the analogous result for stochastic processes that must satisfy boundary conditions, modeled as solutions of constrained martingale problems. In the case of reflecting diffusions in $D\subset {\bf R}^d$, our assumptions allow $D$ to be nonsmooth and the direction of reflection to be degenerate. Two examples are presented: A diffusion with degenerate oblique direction of reflection and a class of jump diffusion processes with infinite variation jump component and possibly degenerate diffusion matrix

Genealogical constructions of population models

Representations of population models in terms of countable systems of particles are constructed, in which each particle has a `type', typically recording both spatial position and genetic type, and a level. For finite intensity models, the levels are distributed on $[0,\lambda ]$, whereas in the infinite intensity limit $\lambda\rightarrow\infty$, at each time $t$, the joint distribution of types and levels is conditionally Poisson, with mean measure $\Xi (t)\times \ell$ where $\ell$ denotes Lebesgue measure and $\Xi (t)$ is a measure-valued population process. The time-evolution of the levels captures the genealogies of the particles in the population. Key forces of ecology and genetics can be captured within this common framework. Models covered incorporate both individual and event based births and deaths, one-for-one replacement, immigration, independent `thinning' and independent or exchangeable spatial motion and mutation of individuals. Since birth and death probabilities can depend on type, they also include natural selection. The primary goal of the paper is to present particle-with-level or lookdown constructions for each of these elements of a population model. Then the elements can be combined to specify the desired model. In particular, a non-trivial extension of the spatial $\Lambda$-Fleming-Viot process is constructed

HD 97394: a magnetic Ap star with high cerium overabundance

We report a spectroscopic analysis of the chemically peculiar Ap star HD 97394. The stellar spectrum is rich in lines of rare earth elements with large overabundances, especially cerium, gadolinium and europium. Enhancement of the abundances of these rare earths shows this star to be one of the most peculiar stars. Very large overabundances were found for lines of Ce iii and Eu iii. Abundances obtained from second ionization lines of Nd, Ce and Eu are about 2 dex higher than for those of the first ionization. From partially split Zeeman components of the Fe ii 6149.258 Å line and from synthetic modelling, a global magnetic field of 3.1 kG was measured. We tested for pulsation of the star with high time resolution spectroscopy obtained with the ESO Very Large Telescope. We place an upper limit to any pulsation amplitude of 30–40 m s−1 for individual lines of rare earth elements, of 10–20 m s−1 for the combination of several lines, and of 6–10 m s−1 for cross-correlation over large spectral bands