Dispersion phenomena in reactors for flow analysis

Both coiled open tubular reactors and packed-bed reactors can be used in flow analysis. Band broadening and pressure drop in these reactors are discussed. Theoretical analysis shows that packed-bed reactors are to be preferred. It is shown that for a given residence time and equal band-broadening values the pressure drop over a packed-bed reactor is lower than over a coiled open tubular reactor. Rules for optimal design are given for coiled tubular reactors and packed-bed reactors. The application of both reactors is shown for the spectrophotometric determination of phosphate with a vanadomolybdate reagent yielding a yellow colour.     

Determination of iron(II) and iron(III) by flow injection and amperometric detection with a glassy carbon electrode

Flow injection analysis can be used for the determination of both iron(II) and iron(III) with an amperometric detector. The flow-through cell contains a glassy carbon electrode. Selection of the appropriate voltammetric technique, choice of the indication potentials, sample size, composition of the carrier stream, etc., are discussed. The limit of determination is about 10^-6 M; the calibration curves are linear in the concentration ranges 10^-3–10^-5 M for iron(III) and 5 × 10^-4–10^-5 M for iron(II). To illustrate the potentialities of the proposed method, standard rocks have been analysed.     

Polarographic analysis for corticosteroids: Part 4. Determination of Corticosteroids in Multicomponent and Complex Pharmaceutical Preparations

Differential pulse polarographic methods for determination of corticosteroids in multicomponent and complex pharmaceutical preparations are described. The influence of other reducible common components of such preparations and excipients on the height of the reduction peaks of corticosteroids and the accuracy of the results was investigated, as well as the interference of excipients by adsorption processes at the electrode or at solid particles of the preparations. In the procedures developed, variations in composition of the supporting electrolyte according to the lipophilicity of the preparation, and the use of standard additions, produce results quickly and reliably. Standard deviations vary from 0.8 to 2.8%.     

Zeeman experiments on the 3Eu α 1A1g transition of platinum porphein in an n-alkane single crystal at 4.2

We report absorption spectra from the ground state to the photoexcited triplet state of platinum porphin (PtP) in single crystals of n-octane (C₈) and n-decane (C₁₀) at 4.2 K, with and without a magnetic field. For PtP in C₁₀ the same transition was studied in emission. From the experiments, values are derived of the spin-orbit coupling parameter Z, the crystal field splitting δ and the orbital angular momentum A for PtP in the two hosts: Z = 76 ± 2 cm^?1 (C₈, C₁₀), δ = 71 ± 1 cm^?1 (C₈), 55 ± 1 cm^?1 (C₁₀) and A = 1.6 ± 0.1 (C₈, C₁₀). For the ratio of the in-plane and the z-polarized electric dipole transition moments we obtain ¦Mx,y¦/¦Mz¦=76± 0.3 (C₈).     

Diffusion of additives and plasticizers in poly(vinyl chloride)—II: The self-diffusion of the stabilizers dibutyltin dilaurate and dibutyltin bismonobutylmaleate in plasticized poly(vinyl chloride)

The self-diffusion coefficient, D, of dibutyltin dilaurate and dibutyltin bismonobutylmaleate have been obtained at 35, 45 and 55° in samples of poly(vinyl chloride) plasticized with 34, 60 and 100 phr of di(2-ethylhexyl)phthalate. D at 2 phr of the laurate is 3–5 times larger than for the smaller maleate molecule. In all cases, D increases with increasing plasticizer concentration, an effect interpreted in terms of the free volume theory of diffusion. D for the laurate increases by a factor of about 2.7 when the laurate diffusant concentration is increased from 0 to 4 phr. The activation energies for diffusion, E_D, lie between 50 and 90 kJ mol^?1. They increase with increasing plasticizer concentration but become constant at higher plasticizer concentrations (60–100 phr). It is impossible to correlate all the known data on diffusion in plasticized PVC with an equation of the form log D₀ = C₁ + C₂ E_D/RT     

Neural network survival analysis for personal loan data

Traditionally, credit scoring aimed at distinguishing good payers from bad payers at the time of the application. The timing when customers default is also interesting to investigate since it can provide the bank with the ability to do profit scoring. Analysing when customers default is typically tackled using survival analysis. In this paper, we discuss and contrast statistical and neural network approaches for survival analysis. Compared to the proportional hazards model, neural networks may offer an interesting alternative because of their universal approximation property and the fact that no baseline hazard assumption is needed. Several neural network survival analysis models are discussed and evaluated according to their way of dealing with censored observations, time-varying inputs, the monotonicity of the generated survival curves and their scalability. In the experimental part, we contrast the performance of a neural network survival analysis model with that of the proportional hazards model for predicting both loan default and early repayment using data from a UK financial institution.     

Orthogonal similarity transformation into block‐semiseparable matrices of semiseparability rank k

Very recently, an algorithm, which reduces any symmetric matrix into a semiseparable one of semi‐ separability rank 1 by similar orthogonality transformations, has been proposed by Vandebril, Van Barel and Mastronardi. Partial execution of this algorithm computes a semiseparable matrix whose eigenvalues are the Ritz‐values obtained by the Lanczos' process applied to the original matrix. Also a kind of nested subspace iteration is performed at each step. In this paper, we generalize the above results and propose an algorithm to reduce any symmetric matrix into a similar block‐semiseparable one of semiseparability rank k, with k ∈ ?, by orthogonal similarity transformations. Also in this case partial execution of the algorithm computes a block‐semiseparable matrix whose eigenvalues are the Ritz‐values obtained by the block‐Lanczos' process with k starting vectors, applied to the original matrix. Subspace iteration is performed at each step as well. Copyright © 2005 John Wiley & Sons, Ltd.     

Well‐posedness of the equations governing the motions of a one‐dimensional hybrid thermo‐elastic structure

In this paper a model for the vibrations of a one‐dimensional hybrid thermo‐elastic structure consisting of an extensible thermo‐elastic beam which is hinged at one end, with a rigid body attached to its free end, is studied with a view to establishing the existence of a unique solution in a weak sense. The model takes account of the effect of stretching on bending and rotational inertia. By treating eigenvalue problems with the spectral parameter also in the boundary conditions, we are able to employ the method of Faedo–Galerkin approximations. Copyright © 2004 John Wiley & Sons, Ltd.     

A supplement to precise asymptotics in the law of the iterated logarithm

Let be a sequence of real-valued i.i.d. random variables with E(X)=0 and E(X²)=1, and set , n?1. This paper studies the precise asymptotics in the law of the iterated logarithm. For example, using a result on convergence rates for probabilities of moderate deviations for obtained by Li et al. [Internat. J. Math. Math. Sci. 15 (1992) 481-497], we prove that, for every b∈(−1/2,1],

     

Multiple Wilson and Jacobi–Piñeiro polynomials

We introduce multiple Wilson polynomials, which give a new example of multiple orthogonal polynomials (Hermite–Padé polynomials) of type II. These polynomials can be written as a Jacobi–Piñeiro transform, which is a generalization of the Jacobi transform for Wilson polynomials, found by Koornwinder. Here we need to introduce Jacobi and Jacobi–Piñeiro polynomials with complex parameters. Some explicit formulas are provided for both Jacobi–Piñeiro and multiple Wilson polynomials, one of them in terms of Kampé de Fériet series. Finally, we look at some limiting relations and construct a part of a multiple AT-Askey table.