Remarks on NonHamiltonian Statistical Mechanics: Lyapunov Exponents and Phase-Space Dimensionality Loss

The dissipation associated with nonequilibrium flow processes is reflected by the formation of strange attractor distributions in phase space. The information dimension of these attractors is less than that of the equilibrium phase space, corresponding to the extreme rarity of nonequilibrium states. Here we take advantage of a simple model for heat conduction to demonstrate that the nonequilibrium dimensionality loss can definitely exceed the number of phase-space dimensions required to thermostat an otherwise Hamiltonian system.Comment: 5 pages, 2 figures, minor typos correcte

Modelling the recovery of acid-sensitive Finnish headwater lakes under present emission reduction agreements

International audienceAbstract: Over the past two decades, substantial reductions in the deposition of acidifying substances (primarily sulphur) have occurred in most parts of Europe and, following recent agreements, this trend is likely to continue. The question arises as to how have sensitive ecosystems reacted, and will react in the future, to these reduced inputs of acidity? In this paper, the SMART dynamic acidification model predicts the possible recovery of 36 acid-sensitive Finnish headwater lakes, for which both catchment soil and water quality measurements were available. The model was calibrated to measurements by adjusting poorly known parameters; it was then used to simulate soil and water chemistry until 2030 under the ?current legislation scenario' resulting from implementing current European emission reduction agreements. Whereas most of the catchment soils show very little change in base saturation, the positive trends in lake ANC and the negative trends in lake sulphate concentrations, observed over the past decade, continue into the future, albeit at a slower pace. The model predicts that, during 2010?30, all lakes will have reached a positive ANC, a pre-requisite for the recovery of fish populations. Keywords: acidification, lake, catchment, recovery, SMART model, Finland</p

Lyapunov instability of fluids composed of rigid diatomic molecules

We study the Lyapunov instability of a two-dimensional fluid composed of rigid diatomic molecules, with two interaction sites each, and interacting with a WCA site-site potential. We compute full spectra of Lyapunov exponents for such a molecular system. These exponents characterize the rate at which neighboring trajectories diverge or converge exponentially in phase space. Quam. These exponents characterize the rate at which neighboring trajectories diverge or converge exponentially in phase space. Qualitative different degrees of freedom -- such as rotation and translation -- affect the Lyapunov spectrum differently. We study this phenomenon by systematically varying the molecular shape and the density. We define and evaluate ``rotation numbers'' measuring the time averaged modulus of the angular velocities for vectors connecting perturbed satellite trajectories with an unperturbed reference trajectory in phase space. For reasons of comparison, various time correlation functions for translation and rotation are computed. The relative dynamics of perturbed trajectories is also studied in certain subspaces of the phase space associated with center-of-mass and orientational molecular motion.Comment: RevTeX 14 pages, 7 PostScript figures. Accepted for publication in Phys. Rev.

Tracing the development of dust around evolved stars: The case of 47 Tuc

We observed mid-infrared (7.5-22 mum) spectra of AGB stars in the globular cluster 47 Tuc with the Spitzer telescope and find significant dust features of various types. Comparison of the characteristics of the dust spectra with the location of the stars in a logP-K-diagram shows that dust mineralogy and position on the AGB are related. A 13 mum feature is seen in spectra of low luminosity AGB stars. More luminous AGB stars show a broad feature at 11.5 mum. The spectra of the most luminous stars are dominated by the amorphous silicate bending vibration centered at 9.7 mum. For 47 Tuc AGB stars, we conclude that early on the AGB dust consisting primarily of Mg-, Al- and Fe oxides is formed. With further AGB evolution amorphous silicates become the dominant species.Comment: 2 figures, accepted for publication in ApJ Letter

Device measures conductivity and velocity of ionized gas streams

Coaxial arrangement of primary coil and two sensing secondary coils contained inside slender quartz tube inserted into ionized stream permits simultaneous determination of conductivity and linear velocity. System results agree favorably with theory

Progress in the Modelling of Critical Thresholds and Dynamic Modelling, including Impacts on Vegetation in Europe : CCE Status Report 2010

Wat weten we over de relatie tussen stikstofdepositie en biodiversiteit? Dit rapport laat zien hoe de huidige kennis het Europese luchtbeleid op dit terrein kan ondersteunen. In Europa staat de biodiversiteit onder druk door onder andere een te hoge stikstofdepositie. De opstellers gaan in op de invloed van stikstofdepositie op de bodem en relevante chemische bodemprocessen. De bodem heeft invloed op de diversiteit van plantensoorten. Het kwantificeren van het verlies aan biodiversiteit zoals dat in dit rapport staat ondersteunt het Europese milieubeleid. Voorts beschrijft het rapport de effecten van de verschillende scenario's die zijn opgesteld om emissies terug te brengen. Het gaat om het reduceren van emissies voor verzuring, vermesting en zware metalen. Deze emissies zijn destijds internationaal vastgelegd in protocollen (LRTAP Conventie Gotenburg, 1999, en Aarhus, 1998). De scenario's zijn gemaakt door het Coordination Centre for Effects (CCE) in samenwerking met haar internationale partners. Deze scenario's geven inzicht in de effecten van luchtverontreiniging op de gezondheid en het milieu. Inzichten die zowel door de verenigde naties als de Europese commissie worden gebruikt voor haar beleid.This report describes the status of the impact assessment of nitrogen, sulphur and heavy metal depositions in Europe and the progress made regarding the relation between nitrogen deposition and loss of biodiversityMinisterie van Infrastructuur en Milie

Time-oscillating Lyapunov modes and auto-correlation functions for quasi-one-dimensional systems

The time-dependent structure of the Lyapunov vectors corresponding to the steps of Lyapunov spectra and their basis set representation are discussed for a quasi-one-dimensional many-hard-disk systems. Time-oscillating behavior is observed in two types of Lyapunov modes, one associated with the time translational invariance and another with the spatial translational invariance, and their phase relation is specified. It is shown that the longest period of the Lyapunov modes is twice as long as the period of the longitudinal momentum auto-correlation function. A simple explanation for this relation is proposed. This result gives the first quantitative connection between the Lyapunov modes and an experimentally accessible quantity.Comment: 4 pages, 3 figure

A Model for Analyzing Lake Water Acidification on a Large Region Scale - Part 1: Model Structure

The International Institute for Applied Systems Analysis is developing a computer model which can be used by decision makers to evaluate policies for controlling the impact of acid rain in Europe. As part of this task, a simple dynamic model has been developed for describing the processes leading to acidification of surface waters. The simulation model is constructed of several modules, each of them providing an overview of a particular aspect of lake acidification. The meteorologic module calculates the amount of water and deposition entering the soil or the lake directly each month. The IIASA soil acidity submodel accounts for the soil solution chemistry. A simple hydrologic method is applied for simulating the routing of internal flows so that the convective flow of ions can be estimated. The lake response is calculated according to the equilibrium reactions of inorganic carbon species. These modules are described in this paper. In part 2 the application of the model on a large regional scale will be described. Monte Carlo techniques will be used to determine those ranges and combinations of input values that produce an acceptable present day lake acidity distribution, when the model is driven by a specified deposition

A Model for Analyzing Lake Water Acidification on a Large Regional Scale. Part 2: Regional Application

The International Institute for Applied Systems Analysis is developing a computer model which can be used by decision makers to evaluate policies for controlling the impact of acid rain in Europe. As part of this task, a dynamic model has been developed for describing the processes leading to acidification of surface waters. The modeling philosophy is to use a simplified approach, which is warranted for a broad geographical scope. The simulation model is constructed of several modules, each of them providing an overview of a particular aspect of lake acidification. Because of the very sparse input data available on a large regional scale, a new method is applied for estimating unknown inputs. The model is calibrated to presentday conditions by selecting input combinations from feasible ranges. Monte Carlo techniques are used to determine those combinations of inputs that produce the observed present-day lake acidity distribution, when the model is driven by a specified deposition. The ensembles obtained in the calibration procedure for each lake region are used for the scenario analysis. The usefulness of the method is compared with respect to the traditional a prtori parameter estimation technique. Results of sensitivity and uncertainty analysis are used to compare model predictions with observed values and to indicate where changes in the distributions of model parameters will affect predictions the most