An airborne sampling system using a spin trapping method has been developed to determine the concentration of hydroxyl radical in the troposphere. Hydroxyl radical was trapped In a «-4-pyrldyl-Af-fert-butylnltrone a-1-oxide (4-PO-BN) In situ to form a stable hydroxy adduct of 4-POBN and determined by electron spin resonance (ESR) later In the laboratory. The concentration of hydroxyl radical ranged from less than 5 X 10s molecules/cm3 at an altitude of 10 km to a maximum of 5 X 106 molecules/cm3 at an altitude of 6 km at 37°N 140°E during the period of May 1980 to Feb 1981. The limit of detection of the present system was about 5 X 10s molecules/cm3 If 200 m3 of air was sampled. The uncertainty of the concentration was estimated to be less than 30%.is now recognized to be of prime importance (2-4). It controls the concentration of various trace species such as CH4, CO,

A Timoshenko beam finite element suitable for vehicle-track vibration analysis is proposed and is applied to a jointed railway track. In several simulation models, the track vibration excited by a train running on the rail is formulated as a dynamic problem where a sequence of concentrated loads moves on the discretely supported Timoshenko beam. The external force is then defined by the concentrated load. The Timoshenko beam subjected to concentrated loads deforms with the slope discontinuity at the loading points. This deformation cannot be represented by the usual finite elements, which causes the fictitious responses of the beam. The present finite element model removes the undesirable response by completely modelling the slope discontinuity. This is achieved by the TIM7 element with the piecewise-linear hat functions. The jointed track model constructed by this finite element is employed to predict the impulsive wheel-track contact force excited by the wheel passage on rail joints. The rail joints with fishplates are of great concern to track deterioration, the settlement of ballast track and the failure of track components. In the present paper the effects of train speed and gap size of the joints on the impact force are assessed from simulation results.

SUMMARYA boundary element method is developed for the topology optimization problem. The topological change is captured using the level set method. The level set function which is defined by signed distance from the boundary contour is assigned to fixed grid points. Boundary elements are developed along the zero contour of the level set function. The design sensitivity analysis is performed for the boundary element equation, and then the boundary velocity is obtained. The velocity field which leads the level set function to optimal material distribution is obtained by the extension of the boundary velocity. Numerical examples show that the proposed method is valid for the topology optimization problems.

The predominance of planar C–H/O=C approached conformations in methyl 3-formyl-2-, 2-formyl-3-, and 4-formyl-3-thiophenecarboxylates was shown experimentally by the chemical shifts of the formyl protons, the unusually large 1JCH values of the formyl groups, and their infrared C–H and C=O absorptions. The stability of the C–H/O=C approached conformation was attributed to the hydrogen-bond-like interaction between the two groups. The considerably large positive bond population between non-bonded H/O and the additional charge separation indicated by the MNDO calculations supported the presence of the intramolecular hydrogen bond.

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