Determination of picomolar levels of flavins in natural waters by solid-phase ion-pair extraction and liquid chromatography

A method is described for the rapid determination of flavins in sea water, based on solid-phase extraction followed by ion-pair high-performance liquid chromatography (HPLC) with fluorescence detection. Riboflavin, flavin mononucleotide (FMN), and flavin adenine dinucleotide (FAD) and their photochemical breakdown products, lumiflavin, formylmethylflavin, and lumichrome can be determined with subpicomolar detection limits. The method was used at sea in the analysis of coastal and open ocean waters. In both environments, riboflavin, lumiflavin and lumichrome were routinely observed at concentrations in the picomolar range; lumiflavin and lumichrome were generally confined to the photic zone while riboflavin was present throughout the water column. Formylmethylflavin, FMN, and FAD were only occasionally observed; when present, these flavins were observed at consistently higher concentrations than riboflavin, lumiflavin and lumichrome.     

Deposition and characterization of sputtered ZnO films

Zinc oxide thin films were deposited by radio frequency magnetron sputtering at room temperature using a metallic zinc target in a gas mixture of argon and oxygen. Plasma power, oxygen /argon gas ratio, gas pressure, and substrate temperature were varied, and an experimental design method was used to optimize these deposition parameters by considering their interdependence. Crystalline structures and film stresses were examined. Post-deposition rapid thermal annealing was also carried out to observe its effects on the film properties. Statistical analysis was then used to find the optimal sputtering conditions. Results indicated that plasma power and gas pressure have the largest effects on film crystallization and stress and that postdeposition annealing can be used to improve the quality of the film properties.     

Detonation in heterogeneous mixtures of liquids and particles

The mechanisms of detonation propagation in heterogeneous systems comprising closely packed particles and a liquid explosive are not fully understood. Recent experimental work has suggested the presence of two distinct modes of detonation propagation. One mode is valid for small particles (which is the regime we will address in this paper) with another mode for large particles. In this work we model numerically the detail of the wave interactions between the detonating liquid and the solid particles. The generic system of interest in our work is nitromethane and aluminium but our methodology can be applied to other liquids and particles. We have exercised our numerical models on the experiments described above. Our models can now qualitatively explain the observed variation in critical diameter with particle size. We also report some initial discrepancies in our predictions of wave speeds in nominally one dimensional experiments which can be explained by detailed modelling. We find that the complex wave interaction in the flow behind the leading shock in the detonating system of liquid and particles is characterised by at least two sonic points. The first is the standard CJ point in the reacting liquid. The second is a sonic point with respect to the sound speed in the inert material. This leads to a steady state zone in the flow behind the leading shock which is much longer than the reaction zone in the liquid alone. The width of this region scales linearly with particle size. Since the width of the subsonic region strongly influences the failure diameter we believe that this property of the flow is the origin of the observed increase in failure diameter with particle size for small inert particles. Received 3 December 1999 / Accepted 5 July 2000     

A comparison of ion-induced electron emission and secondary ion yields

Ion-induced electron emission from solid surfaces is studied using a beam of caesium ions. Features of the spectra obtained during depth profiling of layered structures suggest a novel technique for investigating ion-induced Auger processes. Depth profiles are presented in terms of measured secondary ion signals, electron-induced Auger emission, and the intensities of features in the ion-induced electron spectra. It is shown that changes in features of the ion-induced electron spectra can be related to changes of chemical composition and sputtering probability. These help in the interpretation of variations in secondary-ion yields with matrix composition during depth profiling.     

A Comparison of Two Stock Control Models

Two methods of computing re-order levels are compared under an assumed state of nature. The results indicate that the difference, measured in terms of the expected lost sales is significant.     

Novel UV cured coatings and adhesives based on the photoinitiated cyclopolymerization of derivatives of diallylamine

A new family of non-acrylate UV cured three-dimensional polymeric networks for coatings and adhesives based on the photoinitiated cyclopolymerization of diallylamine salts and diallylamides using a low power (75 W) UVA domestic sunlamp is described.     

Schur functions and the invariant polynomials characterizing U(n) tensor operators

We give a direct formulation of the invariant polynomials _μG_q⁽ⁿ⁾(, Δ_i,;, x_{i,i + 1},) characterizing U(n) tensor operators p, q, …, q, 0, …, 0 in terms of the symmetric functions S_λ known as Schur functions. To this end, we show after the change of variables Δ_i = γ_i − δ_i and x_{i, i + 1} = δ_i − δ_{i + 1} that_μG_q⁽ⁿ⁾(,Δ_i;, x_{i, i + 1},) becomes an integral linear combination of products of Schur functions S_α(, γ_i,) · S_β(, δ_i,) in the variables {γ₁,…, γ_n} and {δ₁,…, δ_n}, respectively. That is, we give a direct proof that _μG_q⁽ⁿ⁾(,Δ_i,;, x_{i, i + 1},) is a bisymmetric polynomial with integer coefficients in the variables {γ₁,…, γ_n} and {δ₁,…, δ_n}. By making further use of basic properties of Schur functions such as the Littlewood-Richardson rule, we prove several remarkable new symmetries for the yet more general bisymmetric polynomials _μ^mG_q⁽ⁿ⁾(γ₁,…, γ_n; δ₁,…, δ_m). These new symmetries enable us to give an explicit formula for both _μ^mG₁⁽ⁿ⁾(γ; δ) and ₁G₂⁽ⁿ⁾(γ; δ). In addition, we describe both algebraic and numerical integration methods for deriving general polynomial formulas for _μ^mG_q⁽ⁿ⁾(γ; δ).     

Hypergeometric series well-poised in SU(n) and a generalization of Biedenharn's G-functions

We prove that Holman's hypergeometric series well-poised in SU(n) satisfy a general difference equation. We make use of the “path sum” function developed by Biedenharn and this equation to show that a special class of these series, multiplied by simple products, may be regarded as a U(n) generalization of Biedenharn and Louck's G(Δ; X) functions for U(3). The fact that these generalized G-functions are polynomials follows from a detailed study of their symmetries and zeros. As a further application of our general difference equations, we give an elementary proof of Holman's U(n) generalization of the ₅F₄(1) summation theorem.