On-line delta(18)O measurement of organic and inorganic substances

A method for the automated sample conversion and on-line oxygen isotope ratio (delta(18)O) determination for organic and inorganic substances is presented. The samples are pyrolytically decomposed at 1400 degrees C in the presence of nickelized graphite. With the system presented organic as well as inorganic samples such as nitrates, sulphates and phosphates of 50-100 &mgr;g O can be analyzed for their delta(18)O values with a standard deviation usually better than 0.5 per thousand. Additionally, carbon isotope ratios of organic substances and nitrogen isotope ratios of inorganic nitrogenous compounds are available in the same sample run. Data for international and some inter-laboratory reference materials are presented to show the accuracy and reliability of the method. The effect of some additives on the CO yield was checked for substances which do not pyrolyze completely. Copyright 1999 John Wiley & Sons, Ltd.     

Wave scattering effects in elastic percolation models

The study of the propagation of waves in randomly diluted models is presented. Porosity (crack-like) models are simulated by constructing typical elastic percolation networks with random microscopic heterogeneities in order to resemble rock media. Central and bond-bending forces (Born Hamiltonian) models are considered. For each experimental case, the elastic energy of the system is relaxed in equilibrium and then the model is excited by a pulse source in order to produce wave propagation. First, a review is presented of the well established velocity-porosity relationship from rock physics, which shows a linear trend from small porosities up to the critical porosity (percolation threshold) where the rocks fall apart. From the wave propagation analysis a general trend is observed for the attenuation of waves, from the small to the large porosity models, suggesting multiple scattering effects similar to those reported from effective-medium approximations of wave scattering due to random heterogeneities. Finally, the results are compared with those obtained from laboratory experiments on dry rocks with different porosities and different applied stress regimes.     

Experimental determination of the internal photoemission contribution to KLM Auger spectra of Na,Mg and Al

Photoemission from the 2p levels of the light metals excited by internally generated K_α1,2 X-rays has been observed, and the intensities compared with valence band to 2p intensity ratios obtained from X-ray photoemission spectroscopy. It is found that internal photoemission from the valence band contributes 0.5% of the intensity of the KL_2,3M Auger peak.     

The structure of the turbulent boundary layer over a mobile and deformable boundary

The structure of the velocity field above a propagating water wave of fixed frequency was investigated in order to evaluate the transport of wind momentum to water waves and the influence of a mobile and deformable boundary on the bursting cycle. The vertical and horizontal velocities were measured in a transformed Eulerian wave-following frame of reference with the aid of a cross hot film, in a wind-wave research facility at Stanford University.The mean velocity profiles have a log-linear form with a wake free-stream characteristic. The wave-coherent motion in the free-stream is irrotational; in the boundary layer, it has a strong shear behavior related to the wave-associated stress. The wave-induced velocity field and the wave-perturbed turbulence depend strongly on the ratio of the wave-speed to the mean free-stream velocity, c/U ₀.The presence of the propagating waves affects the bursting cycle, making the contribution of sweeps and ejections almost equal and dependent on the ratio c/U ₀. The magnitudes of the contribution of the bursting events are generally enhanced by the presence of water waves. The time interval between ejections or sweeps does not scale with either the inner and/or outer flow variables.This paper was presented at the Ninth Symposium on Turbulence, University of Missouri-Rolla, October 1–3, 1984     

A geminate recombination model for photoluminescence decay in plasma-deposited amorphous Si:H

We develop a model of geminate electron-hole recombination, including tunnelling and diffusion, to account for photoluminescence decay in amorphous semiconductors. The model correctly predicts the shape of the decay, the luminescence quantum efficiency, and the microscopic electron mobility.     

FEATURES OF BIOECONOMICS MODELS FOR THE OPTIMAL MANAGEMENT OF A FISHERY EXPLOITED BY TWO DIFFERENT FLEETS

ABSTRACT. After the extension of the Exclusive Economic Zone, in 1977, to 200 miles, most fish stocks came under jurisdiction of the adjacent coastal states. This development opened prospects of effective management of the open sea fisheries. Coastal states have the right to plan out the operation of so-called by Clarke and Munro “distant water fishing nations” from their Exclusive Economic Zone. Under some arrangements, a foreign fleet is allowed to harvest the resource in the Exclusive Economic Zone area. Clarke and Munro, in [1987] and [1991], focus on the issue of optimum terms and conditions of access and, in doing so, built a multiobjective model. The main goal of the present work is the development of a more general model including more variables and parameters related to the presence of a domestic fleet as well as a distant water fishing nation. The main difficulty resides in sharing the harvesting between the two fleets. The study responds to the realistic problemof coastal states who own enough resource stocks to allow harvesting by several kinds of fleets. Two optimal scenarios are developed, in each of them a solution is given.     

Generalizations of the Sweedler Dual

As left adjoint to the dual algebra functor, Sweedler’s finite dual construction is an important tool in the theory of Hopf algebras over a field. We show in this note that the left adjoint to the dual algebra functor, which exists over arbitrary rings, shares a number of properties with the finite dual. Nonetheless the requirement that it should map Hopf algebras to Hopf algebras needs the extra assumption that this left adjoint should map an algebra into its linear dual. We identify a condition guaranteeing that Sweedler’s construction works when generalized to noetherian commutative rings. We establish the following two apparently previously unnoticed dual adjunctions: For every commutative ring R the left adjoint of the dual algebra functor on the category of R-bialgebras has a right adjoint. This dual adjunction can be restricted to a dual adjunction on the category of Hopf R-algebras, provided that R is noetherian and absolutely flat.     

An algebra containing the two-sided convolution operators

We present an intrinsically defined algebra of operators containing the right and left invariant Calderón–Zygmund operators on a stratified group. The operators in our algebra are pseudolocal and bounded on L^p (1<p<∞). This algebra provides an example of an algebra of singular integrals that falls outside of the classical Calderón–Zygmund theory.