Impingement Cooling of Concave Surfaces With Lines of Circular Air Jets

An experimental study of the heat transfer characteristics between single lines of circular jets and concave cylindrical surfaces is presented. It is intended to model a practically important class of impingement cooling configurations for which existing heat transfer correlations are not obviously applicable. The results clarify the present uncertain position with regard to the optimum spacing between the jet nozzle and the heat transfer surface and with regard to the center-to-center spacing between the jets. Some limited results for a two-dimensional jet impinging on the concave surfaces are also presented.

Inhibition of the Hill Reaction by Tris and Restoration by Electron Donation to Photosystem II

Experiments in which chloroplasts were washed with tris and tricine buffers at different pH's indicated that the non-protonated (uncharged) form of tris was inhibitory to the Hill reaction while the protonated form of tris and the zwitterionic forms of tricine were non-inhibitory. Buffers analogous to tris and tricine gave similar results. Photoreduction of NADP could be restored to the inhibited chloroplasts by adding the reduced forms of p-hydroquinone, p-aminophenol, p-phenylenediamine, benzidine, semicarbazide, and dihydroxydiphenyl, all of which donated electrons to photosystem II. Photoreduction of ferricyanide was shown with those donor systems (benzidine and semicarbazide) which did not react chemically with ferricyanide. Photophosphorylation was also restored with all of the electron donors except semicarbazide.

Photoreduction and photophosphorylation with tris-washed chloroplasts

The artificial electron donor compounds p-phenylenediamine (PD), N, N, N', N'-tetramethyl-p-phenylenediamine (TMPD), and 2,6-dichlorophenol-indophenol (DCPIP) restored the Hill reaction and photophosphorylation in chloroplasts that had been inhibited by washing with 0.8 m tris (hydroxymethyl) aminomethane (tris) buffer, pH 8.0. The tris-wash treatment inhibited the electron transport chain between water and photosystem II and electron donation occurred between the site of inhibition and photosystem II. Photoreduction of nicotinamide adenine dinucleotide phosphate (NADP) supported by 33 mum PD plus 330 mum ascorbate was largely inhibited by 1 mum 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) while that supported by 33 mum TMPD or DCPIP plus ascorbate was relatively insensitive to DCMU. Experiments with the tris-washed chloroplasts indicated that electron donors preferentially donate electrons to photosystem II but in the presence of DCMU the donors (with the exception of PD at low concentrations) could also supply electrons after the DCMU block. The PD-supported photoreduction of NADP showed the relative inefficiency in far-red light characteristic of chloroplast reactions requiring photosystem II. With phosphorylating systems involving electron donors at low concentrations (33 mum donor plus 330 mum ascorbate) photophosphorylation, which occurred with P/e(2) ratios approaching unity, was completely inhibited by DCMU but with higher concentrations of the donor systems, photophosphorylation was only partially inhibited.

Inhibition of chloroplasts by UV-irradiation and heat-treatment

The site of inhibition in UV-irradiated and heat-treated chloroplasts was examined by using artificial electron donor compounds such as p-phenylenediamine and hydroquinone which donated electrons specifically to photosystem II. In both cases the electron donors restored the photoreduction of nicotinamide adenine dinucleotide phosphate and the restored activity was inhibited by 3-(3,4-dichlorophenyl)-1,1-dimethyl urea. The fluorescence of variable yield was eliminated by both inhibitory treatments and was partially restored by the electron donors in the heat-treated but not the UV-irradiated chloroplasts. The results suggest that the sites of inhibition of UV-radiation and heat treatment are in the photosynthetic electron transport chain between water and photosystem II.