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.     

Reduced paramagnetism in γ-cerium

The electronic structure of cerium ions in cerium metal has been investigated via time-differential perturbed angular distribution (TDPAD) measurements of the paramagnetic enhancement factor at several temperatures and zero pressure. A considerable reduction of the paramagnetic enhancement in γ-cerium was observed in comparison to systems where Ce is believed to be in the trivalent state, indicating the 4f electron to be partially delocalized. The results are discussed within the framework of the valence fluctuations concept.     

Structural correlations with kinetic energy release during loss of chlorine from nineteen selected chlorinated biphenyls

Unimolecular and collision induced decompositions of the major ions of selected polychlorinated biphenyls in the field free region between the magnetic and electric sectors of a reversed Nier-Johnson instrument were studied. Loss of a single chlorine atom is associated with a wide range of kinetic energy releases but still can be correlated by a single reaction mechanism. Loss of two chlorines is interpreted as a rapid sequential loss from isomerized molecular ions for all but one compound. The decompositions which metastable ions undergo are not always the same as those of high energy ions in the source. Correlations between substituent positions and kinetic energy release can be made for the [M]^+·→[M? Cl]⁺ and [M? Cl₂]^+· processes.     

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.     

Zur Dismutierung von C1-Fluorchlorkohlenwasserstoffen an Metalloxid- und Halogenidoberflächen

Dismutation of C₁ – Fluorine Chlorine Hydro Carbons at Surfaces of Metal Oxides and halides Dismutation of C₁-fluorine chlorine hydro carbons has been investigated at surfaces of aluminium and chromium chlorides respectively fluorides. Dismutation reactions have been observed only after halogen exchange at such surfaces of solids which contain both, chloride and fluoride. A mechanism of dismutation is suggested which underlies a concerted chlorine/fluorine and fluorine/chlorine exchange between the solid and the gas phase. The results are discussed in connection with thermodynamically considerations.     

Electric quadrupole interaction of192Tl(8−) nuclei in hexagonal Tl and in tetragonal in metals

The TDPAD technique has been used to measure the electric quadrupole coupling constants for the¹⁹²Tl(8^–) isomer in hexagonal Tl at different temperatures and in tetragonal In at room temperature. The values measured weree ² qQ/h=24.0(15) MHz extrapolated toT=0K, and 33.1(16) MHz at 293K for the Tl and In hosts,respectively, The electric field gradient for Tl impurities in In was determined from systematics of isoelectric systems, yielding |Q[¹⁹²T1(8^–)]|=0.44(7)b.The almost perfect symmetry of the T1 crystalline structure makes this metal a sensitive probe to current models for electric field gradients in metals. The magnitude and temperature dependence of the field gradient in thallium metal are discussed within the framework of such models.     

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.     

A direct comparison of the visible and ultraviolet reflectance of aluminum films evaporated in conventional and ultra-high vacuum systems

Aluminum was evaporated in a conventional evaporator using an oil diffusion pump (p=3 × 10^-6torr) and in an ultra-high vacuum system evacuated by ion and titanium sublimation pumps (p=5 × 10^-9torr) and deposited at rates ranging from 2.5 Å/sec to 500 Å/sec. For aluminum deposited at rates of 300 Å /sec and greater there is no measurable difference in the visible and ultraviolet reflectance of the two types of films. However, if lower deposition rates are used the reflectance of aluminum films deposited at 5 x 10^-9 torr is much less dependent on deposition rate than that of films condensed at 3 x 10^-6 torr. Aluminum films deposited at high rates, both in conventional and ultra-high vacuum systems, show less degradation of reflectance during exposure to air than the films deposited at low rates.