À ma famille passée, présente et future 5 Table of contents Abbreviations 6 Abstract 7 Publication list 8 Introduction 9 Stable isotopes 11 General considerations 11 Definitions 12 Mechanisms of isotope fractionation 13 1) Physical fractionations 13 2) Chemical fractionations 14 Isotopomers 16 Measurements of isotope and isotopomer abundance 17 1) IRMS 17 3) FTIR 19 2) NMR 19 Climate change 23 ...

In wavelength routed optical networks, wavelength converters can potentially reduce the requirement on the number of wavelengths. A recent study [Proceedings of 9th ACM-SIAM Symposium on Discrete Algorithms (1998)] raised the following problem: choose a minimum number of nodes in a WDM network to place wavelength converters so that any set of paths requires the same number of wavelengths as if ...

Let $R$ be a commutative ring with identity and let $M$ be an $R$-module. In this paper we introduce a new graph associated to modules over commutative rings. We study the relationship between the algebraic properties of modules and their associated graphs. A topological characterization for the completeness of the special subgraphs is presented. Also modules whose associated graph is complete...

Swiss needle cast (SNC) is a fungal disease of Douglas-fir (Pseudotsuga menziesii) that has recently become prevalent in coastal areas of the Pacific Northwest. We used growth measurements and stable isotopes of carbon and oxygen in tree-rings of Douglas-fir and a non-susceptible reference species (western hemlock, Tsuga heterophylla) to evaluate their use as proxies for variation in past SNC i...

Clear-cutting of forests affects the nitrogen cycle and the nitrogen isotopic composition of bioavailable ammonium and nitrate in the soil. Here, we have used nitrogen isotopic variations of tree-rings in red oak (Quercus rubra) and white oak (Quercus alba) as indicators of changes in the nitrogen cycle on a local scale. The delta15N values of late-wood from trees at two remnant forest stands i...