Light stressing

End Covers. GeneraUy it is desirable to have as few openings as possible in the waUs of a vessel, and to this end it is customary to accommodate anciUary equipment, such as stirrer glands, pipe connections, and smaU fittings for measuring instmments, in the more lightly stressed end cover. 

The effect of ozone is complicated in so far as its effect is largely at or near the surface and is of greatest consequence in lightly stressed rubbers. Cracks are formed with an axis perpendicular to the applied stress and the number of cracks increases with the extent of stress. The greatest effect occurs when there are only a few cracks which grow in size without the interference of neighbouring cracks and this may lead to catastrophic failure. Under static conditions of service the use of hydrocarbon waxes which bloom to the surface because of their crystalline nature give some protection but where dynamic conditions are encountered the saturated hydrocarbon waxes are usually used in conjunction with an antiozonant. To date the most effective of these are secondary alkyl-aryl-p-phenylenediamines such as /V-isopropyl-jV-phenyl-p-phenylenediamine (IPPD). 

Physiologically, violaxanthin is an important component of the xanthophyU cycle a high light stress-induced de-epoxidation of the violaxanthin pool to the more photoprotective zeaxanthin is mediated by violaxanthin de-epoxidase (VDE). Violaxanthin and neoxanthin, an enzymatically (NXS)-produced structural isomer, are the precursors for the abscisic acid (ABA) biosynthetic pathway (Figure 5.3.1, Pathway 4 and Figure 5.3.2). In non-photosynthetic tissues, namely ripe bell peppers, antheraxanthin and violaxanthin are precursors to the red pigments, capsanthin and capsorubin, respectively (Figure 5.3.3B). 

Verhoeven, A.S., Adams, III, W.W., Demmig-Adams, B., Croce, R., and Bassi, R. 1999. Xanthophyll cycle pigment localization and dynamics during exposure to low temperatures and light stress in low and high light-acclimated in vinca major. Plant Physiol 120 1-11. 

Nomarski differential in plants with light-stressed foliage Reveals edges in biological microscopy Scanning Surface topography, surface spectroscopy,... 

Smillie, R.M. and Hetherington, S.E., Photoabatement by anthocyanin shields photosynthetic systems from light stress, Photosynthetica, 36, 451, 1999. 

Merzlyak, M.N. and Chivkunova, O.B., Light-stress-induced pigment change and evidence for anthocyanin photoprotection in apples, J. Photochem. Photobiol. B, 55, 154, 2000. 

Alfonso, M., J.J. Pueyo, K. Gaddour, A.-L. Etienne, D. Kirilovsky, and R. Picorel (1996). Induced new mutation of D1 serine-268 in soybean photosynthetic cell cultures produced atrazine resistance, increased stability of S2QB- and S3QB- states, and increased sensitivity to light stress. Plant Physiol., 112 1499-1508. 

Fig. 5.55. IR spectral changes during degradation of MDMO-PPV in oxygen under (a) light stressing and (b) current stressing...

Stefels J, van Leeuwe MA (1998) Effects of iron and light stress on the biochemical composition of Antarctic Phaeocystis sp. (Prymnesiophyceae). I. Intracellular DMSP concentrations. J Phycol 34 486-495 Trtilek M, Kramer DM, Koblizek M, Nedbal L (1997) Dual-modulation LED kinetic fluorometer. J Lum 72-74 597-599... 

Van Leeuwe MA, Stefels J (1998) Effects of iron and light stress on the biochemical composition of Antarctic... 

The modern silk sample not subjected to heat or light stress displayed fracture Types 2, 5, 7, and 11. The dominant fracture type exhibited by these fibers was Type 7 50 of the modern silk fractures were of this type. This finding indicates that surface flaws largely govern the fracture mechanism of modern silk. A smaller number of fracture Types 2, 5, and 11 were observed. This observation indicates that at least some of these fibers also exhibit ductility, a moderate loss of interfibrillar cohesion, and large internal voids, although their influence in fiber fracture is considerably less than that of surface flaws. 

Figure 14-14. Overlay of light-stressed sample in acetonitrile.

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