Unimolecular activation–deactivation: Impulsive collision theory

A theory of collisional energy transfer based on microcanonical relaxation in the limit of infinitesimal collision lifetimes is developed. In distinction to the recently formulated ergodic collision theory the potential energy is now frozen due to the short time scale, and only kinetic energy is available for redistribution. As a consequence, the rate of energy transfer is decreased, and agreement with experimentally based estimates generally improved.     

The use of computed tomography in non-destructive testing of polymeric materials, aluminium and concrete: Part 1—basic principles

In 1895 Wilhelm C. Röntgen discovered the X-ray as an important instrument for medical diagnosis. During the first 50 years of the 20th century X-ray technology developed slowly. It is only within the last decade that growth in imaging technology in the range of techniques available has been rapid. In the 1970s computed tomography (CT) was discovered by Cormack^1,2 and Hounsfield³. This article describes the principal differences between X-radiography and computed tomography.     

Dispersion of carbon black

Satisfactory dispersion of the carbon black is essential to the production of rubber compounds possessing the maximum possible resistance to wear, tensile strength and abrasion resistance. The methods used to measure/estimate the degree of dispersion are reviewed in this paper.Most current methods are based on some form of microscopy. Light microscopy (at small magnifications) of cryomicrotomed rubber specimens in transmitted light is used to some extent. However, the preparation of the specimen is too time-consuming to warrant the use of the method for routine inspection. This has led to the development of an instrument—the Dispergator—which employs split field microscopy of freshly-cut samples to reduce the total time of testing (including the time required for specimen preparation) to about 1 min.     

In silico prediction of drug solubility: 1. Free energy of hydration

As a first step in the computational prediction of drug solubility the free energy of hydration, DeltaG*(vw) in TIP4P water has been computed for a data set of 48 drug molecules using the free energy of perturbation method and the optimized potential for liquid simulations all-atom force field. The simulations were performed in two steps, where first the Coulomb and then the Lennard-Jones interactions between the solute and the water molecules were scaled down from full to zero strength to provide physical understanding and simpler predictive models. The results have been interpreted using a theory assuming DeltaG*(vw) = A(MS)gamma + E(LJ) + E(C)/2 where A(MS) is the molecular surface area, gamma is the water-vapor surface tension, and E(LJ) and E(C) are the solute-water Lennard-Jones and Coulomb interaction energies, respectively. It was found that by a proper definition of the molecular surface area our results as well as several results from the literature were found to be in quantitative agreement using the macroscopic surface tension of TIP4P water. This is in contrast to the surface tension for water around a spherical cavity that previously has been shown to be dependent on the size of the cavity up to a radius of approximately 1 nm. The step of scaling down the electrostatic interaction can be represented by linear response theory.     

Ueber die Bindung des Jods an Stärke. II

Ohne Zusammenfassung     

The generalized transition state method

Current theories of unimolecular reaction rates are based on the transition state method which replaces internal reactant dynamics by an assumption of internal equilibrium. The present work is devoted to the development of generalized transition state method which allows effects such as nonergodicity and non-exponential decay to be accounted for within a simple theoretical framework. The derivation is quantum mechanical and not limited by any weak perturbation assumption. An effective hamiltonian is constructed for the reactant dynamics. The loss of amplitude due to reaction is accounted for by a dissipative term in the hamiltonian which is obtained on a phenomenological basis. The diagonalization of the hamiltonian allows the decay of reactant state to be predicted. The decay information is then used to set up a non-markovian master equation which in turn yields the rate coefficient for the reaction. The accuracy of the method is tested in one-dimensional model calculations in which particular attention is paid to decay by quantum mechanical tunneling through a potential barrier.     

Polymer track developments

This article summarizes the development of tracks for cross-country vehicles and emphasizes the importance of a very well defined specification of the needs to be able control the development work. It also points out that it is absolutely essential for the manufacturers involved to work very closely together to ascertain the most suitable design of track vehicle.     

Trace analysis of polychlorinated dibenzo-p-dioxins, dibenzofurans and WHO polychlorinated biphenyls in food using comprehensive two-dimensional gas chromatography with electron-capture detection

Trace analysis of 2,3,7,8-polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs) and the 12 WHO-PCBs (four non-ortho and eight mono-ortho congeners that have been assigned toxic equivalence factors, TEFs, by the World Health Organisation) was conducted by comprehensive two-dimensional gas chromatography with a micro electron-capture detector (GC x GC-microECD). Four food matrices (fish oil from herring, spiked cows' milk, vegetable oil and an eel extract) were analysed by two GC x GC laboratories, and four GC-HRMS laboratories generated reference values. The two GC x GC laboratories used different column combinations for separating the target analytes. For the first dimension, non-polar DB-XLB and VF-1 columns were used, and for the second dimension, an LC-50 liquid crystalline column with unique selectivity for planar compounds. The congener-specific and total toxic equivalence (TEQ) data obtained using DB-XLB x LC-50 were in good agreement with results obtained by the GC-HRMS laboratories. The WHO-PCB data obtained with the VF-1 x LC-50 combination was also good, but the PCDD/F concentrations were sometimes overestimated due to matrix interferences. GC x GC-microECD using DB-XLB x LC-50 seems to fulfil the European Community requirements of a screening method for PCDD/F and WHO-PCB TEQ in food.