Solar Radiation UV Light

Solar radiation is normally accompanied by heating of the surface of materials. Very seldom cold solar radiation takes place, such as in high mountain areas. Therefore, effect of solar radiation is difficult to separate from thermal effects on plastics and plastic-based composites. Deck surface temperatures under direct sunlight and in a shade, are quite different from each other. In a shade, deck surface temperature is practically equal to air temperature, whereas under direct sunlight it is about 40°F higher in the north of the United States, and 50°F higher in the south. Flence, an effect of solar radiation practically always carries a thermal component. 

The loose layer gradually becomes deeper and deeper, as if plastic disappears from the composite material, leaving only loose filler behind. In fact, plastic disappears indeed because its polymer chain becomes shorter and shorter, and after a while it is not a plastic anymore. If the board is hollow, soon the upper panel collapses (Figs. 15.11 and 15.12) exposing ribs and inner channels of the board. The bottom panel of the hollow board still holds, as it was subjected only to thermal effect, not to UV light. 

Another example can be given with a tongue-and-groove composite hollow board. A control board showed a break point at an average load of 2666 + 32 lb. A weathered, crumbled sample of the same size showed a partial break load at 1408 lb (53% 

Because UV degradation along with heat creates the same—by nature—free radicals, as the heat alone (see above), the same antioxidants as described above can be used for board protection against oxidative degradation. In other words, it does not matter what causes free radicals, heat or UV light When free radicals got into bulk of the composite board and propagate there, antioxidants stop them there, provided that antioxidants are used in sufficient amounts. 

TABLE 15.21 UV embrittlement times (in hours) for polypropylene films containing pigments, with and without stabilizing additives [11] 

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Snow load, 272- 274 Snow on a deck, 272 Softwood fiber, 86, 100 Soil Block test, 431 Soil-block cultures, 434 Solar radiant exposure, 615 Solar radiation (UV light), 531 Solid board, 2, 16, 36, 267, 280, 281, 288, 311 Soundwall, 252, 269, 281-286 Bending moment, 282... 

Solar radiation - visible light infrared (IR) radiation - UV radiation... 

Because of UV filters are substances designed to absorb solar energy, photolysis and photocatalysis have been tested as a feasible treatment to degrade the recalcitrant compounds. To date, very few studies have examined UV filters response under UV radiation when exposed in aqueous samples [41-44], Results indicate that the extent of degradation is quite variable, from no photodegradation of BP3 to complete mineralization of BP1 after 24 h of UV light irradiation. 

It responds well to a wide range of hydrocarbon fires and is blind to welding arcs except when very close to the detector. It can see through smoke and other contaminates that could blind a UV detector. It generally ignores lightning, electrical arcs and other forms of radiation. It is blind to solar radiation and resistant to most forms of artificial lighting. 

Photocatalysis uses semiconductor materials as catalysts. The photoexcitation of semiconductor particles generates electron-hole pairs due to the adsorption of 390 run or UV light of low wavelength (for Ti02). If the exciting energy employed comes from solar radiation, the process is called solar photocatalysis [21],... 

Vitamin D hormone is derived from vitamin D (cholecalciferol). Vitamin D can also be produced in the body it is formed in the skin from dehydrocholesterol during irradiation with UV light. When there is lack of solar radiation, dietary intake becomes essential, cod liver oil being a rich source. Metaboli-cally active vitamin D hormone results from two successive hydroxylations in the liver at position 25 ( calcifediol) and in the kidney at position 1 ( calci-triol = vit. D hormone). 1-Hydroxylation depends on the level of calcium homeostasis and is stimulated by parathormone and a fall in plasma levels of Ca or phosphate. Vit D hormone promotes enteral absorption and renal reabsorption of Ca and phosphate. As a result of the increased Ca + and phosphate concentration in blood, there is an increased tendency for these ions to be deposited in bone in the form of hydroxyapatite crystals. In vit D deficiency, bone mineralization is inadequate (rickets, osteomalacia). Therapeutic Liillmann, Color Atlas of Pharmacology... 

All these photoreactions caused by uv light prevent H-bonding between base pairs which is fundamental to the replication and propagation of life (Figure 9.1). Some of these damages can be repaired, others are permanent and lethal to life. Therefore the importance of ozone screen in cutting off these deleterious radiations from the solar spectrum. 

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