Effective Parameter Interpretation and Extrapolation of Dispersion Simulations by Means of a Simple Two-Velocity Model

The investigation of dispersion by microscopic simulations yields a lot of detailed information. To identify characteristic behaviours, it is useful to condense this information into a few effective parameters, which describe the transport process in the model geometry on a larger scale. For this purpose, a very simple two-velocity model has been developed, which models the transition from reversible to irreversible spreading of a tracer volume. It is shown that this model is very similar to Taylor–Aris dispersion and that it is quite suitable to approximate the time dependence of dispersion. The model is applied to characterize the effect of dead end pores on dispersion with a single correlation parameter. Up to Péclet numbers of about 500, 'hold-up'-dispersion similar to Taylor–Aris-dispersion is found. The simulations have been performed by the lattice Bhatnagar–Gross–Krook (BGK) method, which is a particular type of cellular automata and therefore allows an easy implementation of complicated geometries. The fully irreversible asymptotic dispersion is reached in an exponential process, the parameters of which can be identified by the two-velocity model after the mixing has noticeably begun. These are used to extrapolate the process which reduces the computational effort by about one order of magnitude.     

Physical aging and dye diffusion in polysulfone below the glass transition temperature

The effect of physical aging on the tracer diffusion coefficient D of camphorquinone in polysulfone is investigated. It is shown that if the sample is sufficiently annealed and physical aging is nearly complete, the temperature dependence of D will reflect the primary α-relaxation process of the host polymer. In the temperature range between T_g (=185°C) and 165°C, D is found to be a function of time, and the time dependence of D is given by D = At^?μ, with μ approximately equal to unity. © 1994 John Wiley & Sons, Inc.     

Finite Time Approach to Equilibrium in a Fractional Brownian Velocity Field

We consider the solution of the equation r(t) = W(r(t)), r(0) = r ₀ > 0 where W(⋅) is a fractional Brownian motion (f.B.m.) with the Hurst exponent α∈ (0,1). We show that for almost all realizations of W(⋅) the trajectory reaches in finite time the nearest equilibrium point (i.e. zero of the f.B.m.) either to the right or to the left of r ₀, depending on whether W(r ₀) is positive or not. After reaching the equilibrium the trajectory stays in it forever. The problem is motivated by studying the separation between two particles in a Gaussian velocity field which satisfies a local self-similarity hypothesis. In contrast to the case when the forcing term is a Brownian motion (then an analogous statement is a consequence of the Markov property of the process) we show our result using as the principal tools the properties of time reversibility of the law of the f.B.m., see Lemma 2.4 below, and the small ball estimate of Molchan, Commun. Math. Phys. 205 (1999) 97–111.     

Local and non-local sources of airborne particulate pollution at Beijing——The ratio of Mg/Al as an element tracer for estimating the contributions of mineral aerosols from outside Beijing

1 Introduction The long-range transport of airborne particulatematter is one of the most important pathways of globalbiogeochemistry cycle. As an important component oftroposphere aerosols, mineral aerosol is estimatedabout one half of total amounts of tr…     

Gaschromatographische Reinigung von radioaktiv markierten Kohlenwasserstoffen

Zur Reinigung ¹⁴C-markierter Kohlenwasserstoffe wird ein präparativer Gaschromatograph verwendet. Die analytische Kontrolle vor und nach der pröparativen Abtrennung erfolgt mit einem Radiogaschromatographen. Technische Einzelheiten beider Geräte sowie einige präparative Tremmimgem werden beschrieben.     

Cost Benefit Ratio of Industrial Tracer Applications

Simple relations are given, which could help to estimate the expected annual savings resulting from the application of radioisotope methods for the mixing time, segregation effect or residence time distribution determination. Criteria for estimation of benefit at optimum transition of the continuous production from one quality to another, criteria for estimate the benefits on basis of known holdup and for estimate of benefits resulting from knowledge of the distribution function of residence time and of the kinetics of chemical reaction are presented. Further are demonstrated two examples of evaluation of the economic effect of the results of a system analysis in chemical industry where beside the measurements od residence time distribution by help of radiotracers are used also results of other experimental methods and that practically without increasing production cost.     

Teil I. Verweilzeit als zweidimensionale Zufallsvariable — Klassifikation der Alters- und Restverweilzeitverteilungsfunktionen

Die mit Hilfe radioaktiver Indikatoren meβbare Verweilzeit wird auf Grund des Stochastischen Charakters des Stofftransports in Strömungssystemen als Zufallsvariable dargestellt. Eine erweiterte Beschreibung der inneren Struktur von Strömungs-systemen führt zur Einteilung der Verweilzeit in Alter und Restverweilzeit. Beide Gröβen sind gleichfalls als Zufallsvariable aufzufassen, so daβ die innere Verweilzeitstruktur als zweidimensionaler Zufallsvektor beschrieben warden kann. Die ihm zugeordneten Verteilungsfunktionen warden als reine Ensemblefunktioen klassifiziert und am Schluβ der Arbeit tablelarisch zusammengefaβt. Die Betrachtungen bilden die Grundlage für die in Teil 2 Dargelegte physikalische und technologische Interpretation von Indikatorkonzentrationskurven.     

A Theory for the Quantitative Estimation of Bed Load Transport Using Radioisotopes

In this paper an attempt has been made to develop a simple theory for the application of radiotracer techniques to estimate the quantum of bed material transported in rivers, estuaries, etc. The emphasis is mainly on the physical concepts involved. Certain assumptyions made in the theory are later verified experimentally.     

Ergebnisse und Erfahrungen bei der Amwendung von Radioisotopen in der Metallurgie der ČSSR

Die Anwendung von Radionukliden hat im tschechoslowakischen Hüttenwesen eine langjährige Tradition. Geräte zur radiometrischen Dickenmessung, Feuchtigkeitsbestimmung und Nivcaukontrolle warden produziert und in groβer Zuhl in der Industrie eingesetzt. Seit 1970 werden keine eigenen radiometrischen Betriebsmeβgeräte mehr produziert. Der Bedarf wird aus Importen, vorwiegend aus der Sowjetunion, gedeckt.

Mit offenen Radionukliden werden u. a. in groβem Umfany Untersuchungen über die Herkunft nichtmetallischer Verunreinigungen in Stahl durchgeführt. Auf diesem Gebiet sind zur Zeit Untersuchungen über die Entstchung exo- und endogener Einschlüsse durch radioaktive und inaktive Markierung im Gauge.     

Electrochemical Studies of Polymeric Carbons. II. Surface Layer Formation on Glassy Carbon Electrodes in Chloride Solutions as Studied by Radiotracer Techniques

The interaction of chloride ions with glassy carbon electrodes is studied by means of ³⁶Cl as radiotracer. Chloride ions are bonded on the electrode in case of anodization depending on electrode potential and duration of the polarization. Strong interaction is observed at electrode potentials more positive than +1.3 V. A significant part of the chloride ions bonded at the glassy carbon can not be displaced neither by cathodic polarization nor by rinsing with water or non-labelled solutions. It is concluded that chloride ions are chemically bonded at the surface and the surface region of glassy carbon.