Ultraviolet exposure

Sun worshipers and those who work outside can protect themselves from ultraviolet exposure with skin creams that contain UV-absorbing molecules. The UV-absorbing molecule in the first sunscreens was PABA, para-aminobenzoic acid. However, this compound may have toxic effects of its own. The UV-absorbing components of current sunscreens are derivatives of cinnamic acid and benzophenone. 

The frequency of application of sunscreen is guided by the SPF (sun protection factor) of the preparation. This derived value is the ratio of the time of ultraviolet exposure that causes erythema with the sunscreen to the time that causes erythema without the sunscreen. The higher the SPF, the less frequent the needed application of sunscreen. SPFs of available preparations vary from 2 to 50. 

The blank curve in the graph below shows the response when the sample compartment contains just electrolyte. Before irradiation, no current is observed. Ultraviolet radiation causes a spike in the current with a rapid decrease to a steady level near 40 jxA. This current arises from oxidation of water at the TiOz surface under ultraviolet exposure. The upper curve shows the same experiment, but with... 

Ultraviolet Exposure. A combination fluorescent ultraviolet and fluorescent blacklight lamp assembly (2) was used which yields an ultraviolet spectrum similar to that of the ultraviolet portion of sunlight (9). 

Karentz, D., McEuen, F. S., Land, M. C., and Dunlap, W. C., Survey of microsporine-like amino acid compounds in Antarctic marine organisms potential protection from ultraviolet exposure, Mar. Biol. 

Pacansky et al. (1987) described the fabrication of dual-layer photoreceptors by radiation curing. The layers were coated with a polymerizable acrylate monomer or oligomer as the liquid component, then cured by a 175 kV electron beam or ultraviolet exposure. These methods were used for the preparation of generation layers containing bisazo and hydroxysquaraine pigments. 

Figure 75 The field dependencies of the hole mobility of DEH doped PC that had received ultraviolet exposures prior to the mobility measurements.

Enokida et al. (1991) measured hole mdbilities of PMPS before and after ultraviolet exposures. The exposures were of the order of 1 erg/s-cm2. Prior to the exposures, the mobilities were approximately 10-4 cm2/Vs and weakly field dependent. Following the exposures, a decrease in the mobility was observed. Under vacuum exposure conditions, a decrease of approximately 40% was observed for a 1 h exposure. Under atmospheric conditions, however, the decrease was approximately a factor of 4. Enokida et al. attributed the decrease in mobility to the formation of Si-O-Si bonds in the Si backbone chain. A similar study of PMPS was described by Naito et al. (1991). While the field and temperature dependencies of the mobility were not affected by the ultraviolet exposures, the dispersion in transit times increased significantly. The change in dispersion could be removed by subsequent annealing. The authors attributed the increase in transit time dispersion to a reduction in the hole lifetime, induced by Si dangling bonds created by the ultraviolet radiation. 

Enokida et al. (1991) reported that ultraviolet-induced fatigue of a photoreceptor using poly(methylphenylsilylene) (PMPS) as the transport layer could be explained by photodecomposition of the transport layer. The PMPS was both decomposed and cross-linked by the ultraviolet exposures. 

Fair-skiimed humans face a dilemma because ultraviolet light exposure carries the risks of carcinogenesis and skin aging, whereas insufficient ultraviolet light carries the risk of vitamin Ds (94, Fig. 11) insufficiency. The case is unique in so far as an endogenous biosynthetic pathway is subject to regulation by external lifestyle factors such as ultraviolet exposure and the use of chemical and physical sunscreens. Recent studies... 

Konig K et al (1996) Effects of ultraviolet exposure and near infrared laser tweezers on human spermatozoa. Hum Reprod 11(10) 2162-2164... 

Other human-health effects of ultraviolet exposure include increased risks of developing cataracts and other damage to the cornea, damage to the retina, a suppressed immune system, sunburns of exposed skin, skin allergies, and an accelerated aging of the skin. 

Dozens of phytochemicals are under study for their potential effects in humans. The benefits may be similar to the roles they are known to perform for the plant itself. In plants, phytochemicals defend against disease invaders, ultraviolet exposure, bacteria, viruses, fungi, DNA and cell damage, and destructive free radicals. 

The problems of ozone depletion in the upper atmosphere have led to increased problems of exposure of the skin to solar ultraviolet radiation [74]. Ultraviolet radiation to earth, due to the above effect could gradually affect human s immune system. Ailments like cataract, lung diseases and skin cancer would increase. Approximately 90% of non-melanoma and 65% of melanoma skin cancers have been attributed to ultraviolet exposure. 

D. Karentz, F.S. McEuen, M.C. Land, W.C. Dunlap (1991). Survey of mycosporine-like amino acids in Antarctic marine organisms Potential protection form ultraviolet exposure. Mar. Biol., 108,157-166. 

NickelO).—Ultraviolet exposure of the nickel (ii) complex of NiVN N -tetramethyl-phenylenediamine produces a new nickel(i) species ( n = 2.37, = 2.128). ° The... 

Seidl, H., Kreimer-Erlacher, H., Back, B., Soyer, H.P., Hofler, G., Kerl, H., and Wolf, P. (2001) Ultraviolet exposure as the main initiator of p53 mutations in basal cell carcinomas from psoralen and ultraviolet A-treated patients with psoriasis, J. Invest Dermatol., 117 365-370. 

---