UV-B rays

UV-A and UV-B rays are defined as wavelengths between 320—400 nm and 290-320 nm, respectively. Rays with wavelengths longer than 270 nm and an intensity distribution similar to UV-A and UV-B rays were produced by a 660 watt xenon-arc lamp (Suntester XF-180, Shimadzu, Japan). The UV-A and UV-B were prepared by excluding wavelengths shorter than 320 nm and 290 nm, respectively, from the xenon-arc lamp using special filters. The UV-B contains both UV-B and UV-A rays while UV-A contains only UV-A rays. The intensity of UV-B between 290—320 nm was approximately double the intensity of actual UV-B rays and the intensity of UV-A between 320—400 nm was identical to that of actual UV-A. 

Ultraviolet wavelengths of 290-310 nm from the UV-B band of radiation constitute the principal tissue-damaging rays of the sun, which are not fully atmospherically filtered. An hour s exposure to the summer sun and its damaging rays can produce a painful burn with a characteristic erythema. The skin has natural mechanisms to prevent or minimize such sun-induced trauma, but it takes time to set these into place. Upon... 

Figure 2. Survival curves for f. coli B, B/r and Bs-i. (A) UV. (B) X-rays. (Hill, 1958. Reprinted with kind permission of Elsevier Science—NL, Sara Burgerhartstraat 25, 1055 KV Amsterdam, The Netherlands.

Ultraviolet (UV) rays Radiation from the sun that can be useful or potentially harmful. UV rays from one part of the spectrum (UV-A) enhance plant life. UV rays from other parts of the spectrum (UV-B) can cause skin cancer or other tissue damage. The ozone layer in the atmosphere partly shields us from ultraviolet rays reaching the Earth s surface. 

Re-cover the beaker with crystallizing dish and irradiate contents of the beaker with UV (Blak-Ray B-100A lamp) with stirring for 12 h. 

Fig. 4.60 Time dependencies of the mechanical breaking stress (MBS) of draglines (mean value standard error) secreted from a N. clavata spider weighing 540 mg. Draglines were irradiated with UV rays of UV-A or UV-B, respectively. The horizontal line is drawn using a value of 1.2 GPa as the starting point. UV-A, o UV-B. ...

Many cyanobacteria live in tropical zones in the vicinity of the water surface and are thus subjected to solar radiation, in particular the ultraviolet B (UV B) wavelength (280-320 nm). Certain species thus developed antiradical systems to protect themselves from this radiation. One of these substances is scytonemin, a brown-yellow dimeric pigment of heteroaromatic nature, of which the first observation was made by Nageli in 1849, who obtained it from a species of the genus Scytonema. This compormd, the structure of which was established in 1993, stiU seems to be specific to cyanobacteria, and in a more general way to prokaryotes, although it is present in very many species (Proteau et al, 1993). For an overview on the anti-UV substances of cyanobacteria, of phytoplankton and macro-algae, see Sinha et ol. (1998). Scytonemin absorbs in the three fields of the ultraviolet rays UV-A (325—425 nm) UV-B (280-320 nm) and UV-C (250 nm). 

Reminder the sun s ultraviolet rays can be divided into UV-A (wavelength (380-315 nm) and UV-B (315-280nm). The latter are the more dangerous and may cause melanoma however, they are absorbed by the o2one layer. UV-C (100-280 nm) rays in the range 260-270 nm are used as a disinfectant. 

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