Electrically conducting polymers: preparation and investigation of oxidized poly(acetylene) by EFTEM

Energy-filtering transmission electron microscopy (EFTEM) was used to demonstrate that the oxidation of poly(acetylene), necessary to produce a highly conducting phase, proceeds homogeneously on a scale of 100 nm to several micrometres. The distribution of the anions BF₄⁻ and PF₆⁻ serves as indicator for the penetration of poly(acetylene) by the oxidizing agent. The sample preparation necessitates prevention of sample degradation by air and moisture. It was possible to synthesize, orientate, oxidize, embed and section poly(acetylene) samples under inert conditions. Only mounting of the grids into the sample holder of the electron microscope was performed under ambient conditions. EFTEM was possible for phosphorus and boron, but not for fluorine owing to irradiation damage leading to loss of fluorine from the sample. Polyvinylbutyral was chosen as the embedding medium because it allows embedding of the sample prior to oxidation. Embedding of a previously oxidized poly(acetylene) sample leads to migration of the anions from the interior of the sample into the embedding medium.     

On efficiency of both single fuel cells and stacks I

A method to estimate the efficiency of a stack of several identical cells is described on the basis of the electrochemical behavior of a single cell. Efficiency of fuel cell stacks is defined by means of a combination of semi-empirical models of polarization curves and dimensionless variables such as reaction extent and utilization. The connection of flows among the cells is basically divided in two extreme cases and one intermediate case. Higher efficiencies are obtained when the same main flow (both anodic and cathodic) passes consecutively through the stack cells (Chain Flow), because it is favored thermodynamically. It is less favored when the main flow is strictly divided among all the cells (Separate Flow). In the intermediate case, the main flow is divided among all the stack cells and all the outlets are collected in one flow. The latter can spontaneously evolve to the more thermodynamically stable behavior of Chain Flow.     

MAKING BETTER USE OF NATURAL LIGHT WITH A LIGHT-REDIRECTING DOUBLE-GLAZING SYSTEM

The subject of the present paper is a fixed daylighting system known as the LIF light guide. The system consists of a fixed arrangement for capturing sunlight incident at various angles and re-directing it by means of an optical wave-guide which provides diffuse ceiling illumination. The light guide is generally sandwiched between two glass panes and mounted above the windows to avoid obstructing visibility. Its intended function is to furnish offices and other working areas with a uniform level of natural illumination while avoiding glare.     

On efficiency of both single fuel cells and stacks II

The model developed in the first part of this work is used to predict the cell potentials and the irreversible Gibbs free energy of a stack of 15 cells. The model starts from a phenomenological equation of a polarization curve with the extent of reaction as the independent variable. Two extreme kinds of flow of reagents, defined as Chain and Separate Flows respectively, are considered. The cell potentials are obtained by a combination of the potential of the two extreme cases of flow. The stack cell potentials and the efficiencies, estimated by the model, reproduce the general characteristics obtained by the experiments.     

Effects of Immobilization and Permeabilization Procedures on Growth of Chenopodium rubrum Cells and Amaranthin Concentration

Cultures of Chenopodium rubrum were subjected to permeabilization and immobilization procedures to examine their potential for pigment production. Amaranthin content of culture media was highest for cultures treated with dimethylsulfoxide (DMSO) or dissolved chitosan. Labelling of the cells with L-(U-¹⁴C) tyrosine revealed that amaranthin was released from the cells but degraded rapidly. Product degradation in chitosan immobilized cells was delayed by 12–24 hr. Sufficient cell growth was observed in cultures treated with 0.77 mg chitosan per gram fresh biomass, with 0.42 ml.g^-1 DMSO, or when immobilized in a complex Ca-alginate-chitosan gel system. All other treatments resulted in inhibition of growth.     

MATHEMATICAL MODELS FOR DEVELOPING REGIONAL SOLID WASTE MANAGEMENT POLICIES

Various mathematical programming models are applied to evaluate operational (static one-period) and dynamic investment. (multiperiod) policies of regional solid waste management (SWM). Special attention is paid to the use of mixed integer programming (MIP) models for dynamic investment policies.

The common objective of minimizing the present value of overall investment and/or management costs is extended to deal explicitly with land-use policies by evaluating the sequencing of landfilling operations. The question of abandonment or upgrading of facilities is introduced into the mathematical framework because of its importance in the light of more restrictive standards. The decision as to which process should be installed at what location and at what time, as well as the decision which landfill should be operated and when, is identified in the MIP model.

Considering the limitations of the data base and the model formalism, the question of the usefulness of relying on one optimal solution from a model is discussed. The insensitivity of the ordinary present value criterion is displayed by analyzing substantially different policies which have only slightly different values of the criterion function. Attempts at introducing the notion of regret for the policy selection are presented in the context of Paretian environmental analysis.     

Solubilization Kinetics of Triacyl Glycerol and Hydrocarbon Emulsion Droplets in a Micellar Solution

Solubilization of oil molecules in surfactant micelles can have pronounced effects on the physicochemical properties of oil-in-water emulsions, e.g., reaction rates, distribution of nonpolar ingredients, emulsion stability and controlled flavor release. Static light-scattering was used to compare the solubilization kinetics of corn oil droplets with those of n-hexadecane droplets (ø= 0.02 wt%, d₃₂= 0.3 μm) in a micellar surfactant solution (2 wt% Tween 20). The n-hexadecane droplets were completely solubilized by the micelles within 5 days, but no change was observed in the corn oil emulsíon Possible reasons for the observed differences in solubilization kinetics were related to the molecular geometry and size of the oil molecules.