Refining treatment techniques

Preparation of the highest purity rare earth metals usually includes SSE as part of the refining treatment. A DC electric field is applied along a rod of metal and the resulting electron flow sweeps many impurities, but in particular O, H, N and C, to the anode end of the rod. The heating effect of the current serves to enhance impurity transport rates. The processing is carried out in a UHV chamber to prevent environmental recontamination. The re-distribution of impurities yields a section of the rod with substantially reduced impurity levels. Jordan (1974), Beaudry and Gschneidner (1978) and more recently Fort (1987) have reviewed the technique and its application to the rare earths. 

The refining process most commonly used involves treatment with hot aqueous alkaH to convert free fatty acids to soaps, followed by bleaching, usually with hydrogen peroxide, although sodium chlorite, sodium hypochlorite, and ozone have also been used. Other techniques include distillation, steam stripping, neutralization by alkaH, Hquid thermal diffusion, and the use of active adsorbents, eg, charcoal and bentonite, and solvent fractionation... 

In good solvents, the mean force is of the repulsive type when the two polymer segments come to a close distance and the excluded volume is positive this tends to swell the polymer coil which deviates from the ideal chain behavior described previously by Eq. (1). Once the excluded volume effect is introduced into the model of a real polymer chain, an exact calculation becomes impossible and various schemes of simplification have been proposed. The excluded volume effect, first discussed by Kuhn [25], was calculated by Flory [24] and further refined by many different authors over the years [27]. The rigorous treatment, however, was only recently achieved, with the application of renormalization group theory. The renormalization group techniques have been developed to solve many-body problems in physics and chemistry. De Gennes was the first to point out that the same approach could be used to calculate the MW dependence of global properties... 

The use of computer simulations to study internal motions and thermodynamic properties is receiving increased attention. One important use of the method is to provide a more fundamental understanding of the molecular information contained in various kinds of experiments on these complex systems. In the first part of this paper we review recent work in our laboratory concerned with the use of computer simulations for the interpretation of experimental probes of molecular structure and dynamics of proteins and nucleic acids. The interplay between computer simulations and three experimental techniques is emphasized (1) nuclear magnetic resonance relaxation spectroscopy, (2) refinement of macro-molecular x-ray structures, and (3) vibrational spectroscopy. The treatment of solvent effects in biopolymer simulations is a difficult problem. It is not possible to study systematically the effect of solvent conditions, e.g. added salt concentration, on biopolymer properties by means of simulations alone. In the last part of the paper we review a more analytical approach we have developed to study polyelectrolyte properties of solvated biopolymers. The results are compared with computer simulations. 

In this article, we will not focus on recent developments in refinement techniques, which benefited recently from better statistical treatments such as maximum likelihood targets for refinement (Adams et al., 1999), but rather will describe in detail some of the newest developments in MR to get the best... 

A convenient procedure for assessing the digestibility of forages is the cellulase digestibility technique. This was refined by Jones and Hayward (1973) at the Welsh Plant Breeding Station (WPBS) in Aberystwyth (since 1992, the Institute for Grassland and Environmental Research). It was later extended to a two-stage procedure with a pepsin pre-treatment (Jones and Hayward, 1975). 

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