To wet or not to wet: that is the question

Wetting transitions have been predicted and observed to occur for various combinations of fluids and surfaces. This paper describes the origin of such transitions, for liquid films on solid surfaces, in terms of the gas-surface interaction potentials V(r), which depend on the specific adsorption system. The transitions of light inert gases and H2 molecules on alkali metal surfaces have been explored extensively and are relatively well understood in terms of the least attractive adsorption interactions in nature. Much less thoroughly investigated are wetting transitions of Hg, water, heavy inert gases and other molecular films. The basic idea is that nonwetting occurs, for energetic reasons, if the adsorption potential's well-depth D is smaller than, or comparable to, the well-depth of the adsorbate-adsorbate mutual interaction. At the wetting temperature, Tw, the transition to wetting occurs, for entropic reasons, when the liquid's surface tension is sufficiently small that the free energy cost in forming a thick film is sufficiently compensated by the fluid- surface interaction energy. Guidelines useful for exploring wetting transitions of other systems are analyzed, in terms of generic criteria involving the "simple model", which yields results in terms of gas-surface interaction parameters and thermodynamic properties of the bulk adsorbate.Comment: Article accepted for publication in J. Low Temp. Phy

Threshold criterion for wetting at the triple point

Grand canonical simulations are used to calculate adsorption isotherms of various classical gases on alkali metal and Mg surfaces. Ab initio adsorption potentials and Lennard-Jones gas-gas interactions are used. Depending on the system, the resulting behavior can be nonwetting for all temperatures studied, complete wetting, or (in the intermediate case) exhibit a wetting transition. An unusual variety of wetting transitions at the triple point is found in the case of a specific adsorption potential of intermediate strength. The general threshold for wetting near the triple point is found to be close to that predicted with a heuristic model of Cheng et al. This same conclusion was drawn in a recent experimental and simulation study of Ar on CO_2 by Mistura et al. These results imply that a dimensionless wetting parameter w is useful for predicting whether wetting behavior is present at and above the triple temperature. The nonwetting/wetting crossover value found here is w circa 3.3.Comment: 15 pages, 8 figure

Industriavløpsvannets innvirkning på Rambekk kjemiske kloakkrenseanlegg. Fellingskjemikalier. Hydrauliske forhold. HPA-22/75

Rambekk renseanlegg (sekundærfelling) renser avløpet fra Gjøvik. Det har vært problemer med å oppnå gode renseresultater. En har undersøkt mulig innvirkning av meieri- og slakteriavløp på renseresultatene. Felling med alternative kjemikalier (aluminiumsulfat, jernklorid, jernklorid/kalk) er vurdert. En har også undersøkt betydningen av hydraulisk belastning for renseresultater samt kommentert detaljer og endringer av konstruksjonsmessig utformin

Bangkok's forurensningsproblemer. Situasjonsanalyse med forslag til tiltak fra norsk side

Rapporten beskriver forurensningssituasjonen i Bangkok's kanaler og i elven Chao Phraya. Rapporten belyser også lovverket og håndhevingen av dette. Tekniske løsninger med modifisering av kanalene med ombygging til renseanlegg vurderes, likeså andre tiltak for å bekjempe forurensninger.Statens forurensningstilsyn (SFT

Design of convergent switched systems

In this paper we deal with the problem of rendering hybrid/nonlinear systems into convergent closed-loop systems by means of a feedback law or switching rules. We illustrate our approach to this problem by means of two examples: the anti-windup design for a marginally stable system with input saturation, and the design of a switching rule for a piece-wise affine system operating in different modes