A Non-linear Singular Perturbation Problem Arising in the Study of Chemical Flow Reactors

This paper presents a method of obtaining the complete asymptoticsolution of boundary value problems of the form for x [0,1] where b(x) is strictly positive andfor small and positive. Physically, the problem arises in determiningthe steady-state concentration of a substance in a chemicalflow reactor. A "two-variable" expansion procedure is used.     

DISTRIBUTIONS OF FREE RADICALS AMONG AMINO ACIDS FROM LYOPHILIZED ULTRAVIOLET-IRRADIATED PROTEINS

Abstract— The effects of u.v.-irradiation at 254 nm upon lyophilized ribonuclease, lysozyme, insulin, and chymotrypsinogen have been investigated by electron spin resonance (ESR). enzymatic assay, and labeling of free radical sites with tritiated hydrogen sulfide (HST). The ESR signal of the irradiated protein diminishes on exposure to HST, and tritium becomes covalently bound to carbon. The distribution of tritium among the amino acids of each protein. studied as an indicator of the carbon free radical distribution, differs markedly from those observed previously to result from exposure to gamma radiation, electrical discharge. or hydrogen atoms. However, the earlier observation that the tritium distribution is influenced by protein conformation holds true as well for u.v.-irradiation. Moreover, the distributions of tritium among the amino acids of u.v.-irradiated proteins indicate a broad scattering of free radicals. Tyrosine and phenylalanine, residues that absorb light energy in the region of the wavelength employed, are not particularly important as radical carriers. Thus, for ribonuclease, these residues incorporated 3.8 and 1.5 per cent of the total tritium, but they absorb 51 and 12 per cent of the light, respectively. These results, together with the observed low recoveries of methionine, an amino acid that does not absorb at 254 nm, add weight to the concept that a migration of energy ensues after the initial absorption of light energy and that photolytic damage may thus be due to destruction of amino acids other than those initially absorbing the u.v.-radiation.     

Enantiospecific electrodeposition of chiral CuO films on single-crystal Cu(111)

Epitaxial films of monoclinic CuO have been electrodeposited on single-crystal Cu(111) from solutions containing either (S,S)- or (R,R)-tartrate. X-ray pole figure analysis reveals that the CuO film grown from (S,S)-tartrate exhibits a (1) out-of-plane orientation while the film grown from (R,R)-tartrate has a (11) orientation. Even though CuO does not crystallize within a chiral space group, the orientations obtained exhibit a surface chirality similar to that obtained from high index fcc metal surfaces. The films were shown to be enantioselective toward the catalytic oxidation of tartrate molecules by cyclic voltammetry. The technique should prove to be applicable to the electrodeposition of chiral surfaces of other low-symmetry materials on achiral substrates and should prove to be of use to those interested in the synthesis, separation, and detection of chiral molecules.     

A Type Calculus for Executable Modelling Languages

There is considerable current interest in the design and constructionof directly executable modelling languages for mathematicalprogramming. The present research extends contemporary modellinglanguages by specifying a type calculus for an extended dimensionalsystem that determines if the model is well formed in the sensethat the objective function and constraints consist of homogeneouscomponents. Each variable, coefficient, constant, function,constraint, input, and output of the model is assigned a typethat consists of its concepts, quantities, and units of measurementwith optional scale factors. In checking the composition offunctions and constraints, the system can do automatic unitconversions and apply user-supplied conversions. The systemallows a hierarchy of concepts that provides inheritance ofquantities and automatic concept conversion. In addition, eachset in a model is typed so the system can check the validityof operations on indices.     

Epitaxial Electrodeposition of Lead Sulfide on (100)-Oriented Single-Crystal Gold

Small lattice mismatches and gas-phase deposition are typically used for growing epitaxial films on single-crystal substrates. A 1-μm thick film of PbS can be epitaxially electrodeposited onto a Au (100) single crystal. The large lattice mismatch (45.5 %) between Au and PbS is accommodated by the formation of a coincidence lattice, in which the epitaxial film is rotated by 45 degrees relative to the substrate. The coincidence lattice reduces the mismatch to +2.9 %.