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Aqueous solutions of isolated humic substances were investigated by laser flash photolysis. Kinetics of the decay of excited states were measured in emission and absorption. From the absorption data at least two transients with different lifetimes (order of and s) could be deduced. Quenching effects were determined for oxygen and Ni(II), Co(II), and Cd(I1). The quenching efficiency of oxygen is similar to the efficiency of the paramagnetic metal ions. The quantum yield of the singlet oxygen production sensitized by humics was determined to be 1-370 with the furfuryl alcohol method. The results are discussed with respect to the photochemistry of aquatic ecosys tems. IntroductionAwareness of the potential of photochemical reactions in the photic zone of aqueous systems has increased in the past decade (1,2). The photolysis of defined chromophores like methyl iodide, tryptophan, vitamin BI2, etc. was investigated under natural aquatic conditions. Fairly little is known about the photochemistry of complex chromophores with unknown structure like humic substances (HUS). These substances however play an important role in the aquatic ecosystems (3) and are the main light-absorbing compounds dissolved in natural water.The photophysical and photochemical properties of soil and aquatic humic materials have been reviewed recently by Choudhry (4). Zepp et al. (5) have investigated the photosensitizing effect of humic substances on various trace organic chemicals in water. The authors present evidence that an energy transfer from electronically excited humic substances to molecules like pentadiene or dimethylfuran might occur. In cases where oxygen is involved in photosensitized reactions, energy transfer can lead to singlet oxygen production.

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Some structural and mechanical properties of PHB homopolymer and copolymers containing 17 and 25-30 % PHV have been investigated. X-ray scattering, optical microscopy, density measurements and differential scanning calorimetry were used to interpret the results of load-elongation curves and thermomechanical softening measurements.

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A novel bending technique known as free-bending, which is particularly suitable for the bending of profile and tube cross-sections, is investigated. Advantageous characteristics, such as fast bending speed and an almost free definable bending geometry with transitionless bend-in-bends and spline bends, make free-bending highly applicable in the manufacture of car components. This paper gives an introduction to this new technique and presents the development of a finite element analysis (FEA) model for the simulation of this bending technology. Furthermore, a theoretical model for the determination of the bend die's control data is introduced. For the verification of the FEA model the simulation results are compared with the results from bending tests that have been carried out.