Expert systems for chemical analysis (ESPRIT Project 1570)

Summary This paper gives an overview of the structure and processes going on in the project Expert Systems for Chemical Analysis (ESCA), an international project within the ESPRIT research programme of the European Community. The application area, HPLC method development, is explained and broken down into four domains. The methods used for representing knowledge in the project are discussed.     

Phase equilibria in polymer solutions

A theoretical study of phase equilibria in multicomponent polymer solutions is presented. The treatment is based on the virial expansion of the osmotic pressure. A program for the numerical determination of phase diagrams is worked out and applied to the polystyrene-cyclohexane system. The present approach is compared with the Flory-Huggins theory of polymer solutions, which is shown to represent a special class of approximations in the present treatment.     

Precision measurements of osmotic pressure in concentrated polymer solutions—II

Precision measurements of osmotic pressure have been carried out with several polymers (polystyrene, polymethylmethacrylate and polyvinyl acetate) in organic solvents. The concentration dependence of the osmotic pressure over a wide range of concentrations (up to 0·2 g/cm³) was established and the osmotic virial coefficients were evaluated. From the temperature dependence of the osmotic pressure, the partial molar heats and entropies of mixing were also determined. In the system polystyrene-cyclohexane, measurements were carried out near the θ-temperature; variation of the virial coefficients with temperature and molecular weight was studied. It was found that the conventionally defined θ-temperature is molecular weight dependent. At the θ-temperature, the third virial coefficient is positive and tends to a nonzero limit when the molecular weight tends to infinity.     

The role of the spectral sensitivity curve in the selection of relevant biological dosimeters for solar UV monitoring

To estimate the risk of enhanced UV-B radiation due to stratospheric ozone depletion, phage T7 and uracil thin-layer biological dosimeters have been developed, which weight the UV irradiance according to induced DNA damage. To study the molecular basis of the biological effects observed after UV irradiation, the spectral sensitivity curves of the two dosimeters and induction of the two major DNA photoproducts, cyclobutane pyrimidine dimers (CPDs) and 6-4 photoproducts ((6-4)PDs), in phage T7 have been determined for polychromatic UV sources. CPDs and (6-4)PDs are determined by lesion-specific monoclonal antibodies in an immunodotblot assay. Phage T7 and uracil biological dosimeters together with a Robertson-Berger (RB) meter have been used for monitoring environmental radiation from the polar region to the equator. The biologically effective dose (BED) established with the three different dosimeters increases according to the changes in the solar angle and ozone column, but the degree of the change differs significantly. The results can be explained based on the different spectral sensitivities of the dosimeters. A possible method for determining the trend of the increase in the biological risk due to ozone depletion is suggested.     

Isotropic-nematic interfacial tension of hard and soft rods: application of advanced grand canonical biased-sampling techniques

Coexistence between the isotropic and the nematic phase in suspensions of rods is studied using grand canonical Monte Carlo simulations with a bias on the nematic order parameter. The biasing scheme makes it possible to estimate the interfacial tension gamma(IN) in systems of hard and soft rods. For hard rods with LD=15, we obtain gammaIN approximately 1.4kBT/L2, with L the rod length, D the rod diameter, T the temperature, and kB the Boltzmann constant. This estimate is in good agreement with theoretical predictions, and the order of magnitude is consistent with experiments.     

Biological consequences of cyclobutane pyrimidine dimers.

In the skin many molecules may absorb ultraviolet (UV) radiation upon exposure. In particular, cellular DNA strongly absorbs shorter wavelength solar UV radiation, resulting in various types of DNA damage. Among the DNA photoproducts produced the cyclobutane pyrimidine dimers (CPDs) are predominant. Although these lesions are efficiently repaired in the skin, this CPD formation results in various acute effects (erythema, inflammatory responses), transient effects (suppression of immune function), and chronic effects (mutation induction and skin cancer). The relationships between the presence of CPD in skin cells and the subsequent biological consequences are the subject of the present review.     

New bounds for Morse clusters

This paper presents new, simple arguments improving the lower bounds for the total energy and the minimal inter-particle distance in minimal energy atom cluster problems with interactions given by a Morse potential, where the atom separation problem is difficult due to the finite energy at zero atom separation. Apart from being sharper than previously known bounds, they also apply for a wider range ρ ≥ 4.967 of the parameter in the Morse potential. Most results also hold for more general pair potentials.     

Determination of amitrole in plant tissues and sandy soils by capillary gas chromatography with alkali flame ionization detection

Summary A rapid and specific method has been developed for the determination of amitrole in plant tissues and sandy soils. Amitrole is extracted with ethanol, adsorbed on resin and desorbed with ammonia. After acetylation with acetic anhydride and a clean-up over a SEP-PAK silica cartridge, the amitrole-acetyl derivative is determined by gas chromatography with alkali-flame ionization detection. The gas chromatographic separation is performed simultaneously on two capillary columns of different polarity. The limit of detection for both plant tissues and sandy soils is 0.01 mg/kg. The average recoveries are 81 and 96% respectively.     

Minority carrier lifetime in p-type gallium phosphide

The decay time of the luminescence involving bound minority carriers shortens above some temperature with increasing temperature owing to thermal quenching. However, above some higher temperature there will be a plateau since the luminescence decay cannot be faster than the decay of the excited free minority carriers.     

ESR of a Mn-S nearest neighbour complex in GaP

ESR measurements on a manganese-sulphur nearest neighbour complex having axial symmetry along 〈111〉 axes are reported. The spin Hamiltonian parameters are found to be g = 2.002 ± 0.001, A = (-57 ±1) × 10^-4 cm^-1, D = (-306 ± 2) × 10^-4 cm^-1 and (a − F) = (+12 ±2) × 10^-4 cm^-1. The formation of these complexes is discussed. briefly.