Crystallization of Arthrobacter sp. strain 1C N-(1-D-carboxyethyl)-L-norvaline dehydrogenase and its complex with NAD+

The novel NAD+-linked opine dehydrogenase from a soil isolate Arthrobacter sp. strain 1C belongs to an enzyme superfamily whose members exhibit quite diverse substrate specificites. Crystals of this opine dehydrogenase, obtained in the presence or absence of co-factor and substrates, have been shown to diffract to beyond 1.8 ? resolution. X-ray precession photographs have established that the crystals belong to space group P21212, with cell parameters a = 104.9, b = 80.0, c = 45.5 ? and a single subunit in the asymmetric unit. The elucidation of the three-dimensional structure of this enzyme will provide a structural framework for this novel class of dehydrogenases to enable a comparison to be made with other enzyme families and also as the basis for mutagenesis experiments directed towards the production of natural and synthetic opine-type compounds containing two chiral centres.     

57Fe Mössbauer-effect studies of quadrupole splitting distributions in icosahedral Al-TM-Fe quasicrystals

Room temperature⁵⁷Fe Mössbauer effect spectra of several Al-TM-Fe icosahedral quasicrystals are reported. Results of fits to discrete sites and to various distributions of quadrupole splittings are presented. Mean isomer shifts, \(\overline \delta \) , and quadrupole splittings, Δ, are shown to be insensitive to the fitting procedure used. Trends in \(\overline \delta \) and \(\overline \Delta \) for the icosahedral phase may be indicative of a Hume-Rothery stabilization mechanism.     

Elements of specified order in simple algebraic groups

In this paper we let be a simple algebraic group and be a natural number, and consider the codimension in of the variety of elements satisfying . We shall obtain a lower bound for this codimension which is independent of characteristic, and show that it is attained if is of adjoint type.

     

Two-phase hydrodynamic experiments with axial flow through seven-rod clusters

Hydrodynamic experiments have been carried out with upflow of air-water mixtures through vertical seven-rod clusters at atmospheric pressure. Results obtained from measurements of flow characteristics, including pressure drops, local velocity and voidage distribution, are discussed in terms of relations developed for two-phase flow in round tubes. Effects on the flow characteristics of spacer elements and bowing of a cluster are also discussed.     

Computable error bounds for pointwise derivatives of a Neumann problem

In this paper we discuss the recovery of derivatives and thecomputation of rigorous and useful upper bounds for the pointwiseerror in the recovered derivatives, for finite element approximationsof the Laplace equation with Neumann boundary conditions, especiallyat points close to or on a smooth, curved boundary. We analyzethe dipole image technique for the case of curved boundaries,and show how to compute reliable recovered derivatives and errorbounds even in the limiting case of points lying on the curvedboundary. Numerical experiments show reasonably tight errorbounds for points both close to and away from a curved boundary.     

Prediction of the incidence of motion sickness from the magnitude, frequency, and duration of vertical oscillation

A method is proposed by which the incidence of motion sickness may be predicted from measurement of the motion exposure. The method is based on data from both field and laboratory studies involving large numbers of people and is applicable to marine and other environments where vertical oscillation occurs at frequencies below 0.5 Hz. The dependence of motion sickness on the frequency of oscillation requires the use of a weighting function between 0.1 and 0.5 Hz. The dependence of sickness on the duration of exposure is incorporated by the use of a cumulative measure of motion dose based on the product of root-mean-square (rms) acceleration magnitude and the square root of stimulus duration. The influence of population variables such as sex, age, and motion experience is discussed. The method enables separate predictions to be made of vomiting incidence and of feelings of illness. The prediction procedure, while not seeking to explain the underlying mechanisms of motion sickness occurrence, provides a generally applicable method which is simple to use and has an accuracy consistent with the experimental data on which it is based.