Ultraviolet shield

Iwashina, T. et ak, Flavonoids in translucent bracts of the Himalayan Rheum nobile (Polygona-ceae) as ultraviolet shields, J. Plant Res., 117, 101, 2004. 

Phoenix VR, Konhauser KO, Adams DG, Bottrell SH (2001) Role of biomineralization as an ultraviolet shield implications for Archean life. Geology 29 823-826... 

Because ozone selectively absorbs these deleterious wavelengths of solar radiation, it serves as an ultraviolet shield. As such, stratospheric ozone helps to protect humans and other organisms on Earth s surface from some of the harmful effects of exposure to this high-energy electromagnetic radiation, hi fact, without the protective action of the stratospheric ozone layer, it is likely that... 

Ozone has been an important reagent of the organic chemist almost from the time of its discovery by Schonbein in 1840. With the discovery of the ozone layer in the upper atmosphere, and its all-important role as an ultraviolet shield, the properties and reactions of ozone became of intense interest in an entirely different field of science. 

If the additive acts only as ultraviolet shield then A=L In the case when the additive acts as sensitizer, then A1 then effect of overshielding. 

Value A for all investigated light stabilizers is less than 1. Hence it follows that HAC acts not only as ultraviolet shields, but as photosensitizer too. It is seen from Table 13A that the best light stabilizers are HAC-1, P-3 and HAC-4, for which value A is the highest. Introduction of HAC inhibits the process of photomechanical CDA destruction by 5,1-5,9 times. 

If the additive does not act as inhibitor, but only as ultraviolet shield and photosensitizer, then dependence of quantum yield of photooxidation OOo on light intensity lo at full absorption of incident light should be described by well-known equation (5)... 

A simple and convenient method of polymer modification is to introduce an additive. This method is most effectively utilized in the modification of nylon fibers. For antistatic and conductive properties, hygroscopic polymeric materials and conductive materials such as carbon and metal powders are incorporated, respectively. For flame retardant properties, antimony trioxide is added. To impart ultraviolet shielding properties, ultraviolet absorbents are included and inoiganic particles of metal such as silver and zeolite containing metal ions are used for antibacterial and odor preventing properties. 

On the whole, most ultraviolet shielded fibers are manufactured by blend spinning with ultraviolet shielding substances or by coating with ultraviolet shielding substances in the finishing stage. 

It is also necessary to ultraviolet stabilize the coating because the pipes are stored outside before laying in any case, if high continuous service temperatures are expected, it is advisable to reduce the direct sun exposure time and/or to give a coat of paint or to use other kinds of ultraviolet shielding. 

Carbon black might be described as an ideal universal additive it can provide pigmentation, reinforcement, ultraviolet shielding, and anti-static properties -but always provided that the final colour is black. It is used in several different forms, produced by different production processes for its various applications. There are about 100 different grades today, each of which Is matched to an individual application. In thermosetting resins, most carbon blacks tend to inhibit cure and should be avoided. 

This ozone is formed near ground level and is an irritant ozone at stratospheric levels is a benign ultraviolet shield. Now keep your eye on the ozone molecule. In one instance we see it collide with an NO molecule, which plucks off one of ozone s O atoms, forming NO2 and letting O3 revert to O2. 

Applicabdity Limitations Photolysis is appropriate for difficult-to-treat chemicals (e.g., pesticides, dioxins, chlorinated organics), nitrated wastes, and those chemicals in media which permits photolyzing the waste. The waste matrix can often shield chemicals from the light (e.g., ultraviolet light absorbers, suspended solids, solid wastes). The photolysis process typically requires pretreatment to remove suspended materials, and the by-products formed may be more toxic than the parent molecules. 

A representation of the stratospheric system that shields terrestrial life from excessive solar ultraviolet radiation is presented in Figure 4. Our primary concern is the decrease of stratospheric ozone, most striking in the Antarctic, which has been linked to increases in CFCs from the troposphere, and the possible increased transport of these compounds between the stratosphere and the troposphere by increased temperature driven circulation. 

Caution The photochemical reaction in Part C should be carried out behind a light-absorbent cover or shield. Protective goggles should be worn to avoid exposure of the eyes to ultraviolet light. 

It is advisable to wrap the entire apparatus with aluminum foil to avoid exposure to ultraviolet light. The reaction solution can be observed through a small hole in the aluminum foil which is shielded from the direct radiation of the lamp. 

The collagen shield, fabricated from procine scleral tissue, is a spherical contact lens-shaped film whose thickness can be made to vary from 0.027 to 0,071 mm. It has a diameter of 14.5 mm and a base curve of 9 mm. Once the shield is hydrated by tear fluid and begins to dissolve, it softens and conforms to the corneal surface. Dissolution rates can be varied from 2 to as long as 72 hr by exposing the shields to ultraviolet radiation in order to achieve varying degrees of crosslinking. 

Sunblocks are opaque substances such as zinc oxide, titanium dioxide, and iron oxide that protect by forming a shield on the skin, which reflects and scatters incident radiation. In essence, sunblocks provide physical protection against sun exposure, including both visible and ultraviolet light. Sunscreens are substances that chemically absorb ultraviolet light in the top layer of the epidermis, protecting the underlying layers. 

All of the ionizing air systems at Longhorn are located in areas where ultraviolet sensors are used in conjunction with deluge systems for fire protection. Care must be taken to shield the ultraviolet detectors from the ion generating corona source. The systems used at Longhorn are individually shielded with PVC tubing or with hoods. 

Uses. In ultraviolet stabilizers and smoke depressants for polymers to increase the burn rate of rocket propellants to prevent erosion of space capsule shields to improve the viscosity of lubricants to catalyze polymerization reactions to catalyze combustion some derivatives used as hematinic agents... 

Burchard, P., Bilger, W., and Weissenbock, G., Contribution of hydroxycinnamates and flavonoids to epidermal shielding of UV-A and UV-B radiation in developing rye primary leaves as assessed by ultraviolet-induced chlorophyll fluorescence measurements, Plant Cell Environ., 23, 1373, 2000. 

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