Ultraviolet radiation definition

Ultraviolet radiation, 797 Undeipotential deposition, 1121, 1313 alloy formation during, 1316 causes of, 1315 definition, 1313 displacement potential, 1316 kinetics of, 1316 lead deposition, 1313 one-dimensional phase formation in, 1316 scanning tunneling microscopy used to study, 1313, 1315... 

Goetz (5), writing about maritime haze particles, said that the degrading of particles by ultraviolet radiation appears to be definite proof for the significant, if not occasional dominant, presence of various hydrocarbons in the aerocolloidal matter. ... 

You are probably aware of some of the damaging effects of ultraviolet radiation from the Sun if you have ever suffered from a sunburn. Overexposure to ultraviolet radiation also is harmful to plants and animals, lowering crop yields and disrupting food chains. Living things can exist on Earth because ozone, a chemical in Earth s atmosphere, absorbs most of this radiation before it reaches Earth s surface. A chemical is any substance that has a definite composition. Ozone is a substance that consists of three particles of oxygen. 

ABA is a C, organic acid with one asymmetric carbon atom at C-1 (Fig. 1). The naturally occurring form is 5-( + )-ABA the side chain of ABA is by definition 2-cis,4-trans [2]. The optical rotatory dispersion (ORD) spectrum of ABA exhibits an intense Cotton effect. This property was initially exploited to identify and measure ABA in purified extracts of a number of plants [11]. ABA in organic solvents can be photo-isomerized by ultraviolet radiation to give a mixture of approximately 50% ABA and 50% 2-trans,4 trans-ABA (f-ABA) (Fig. 1). The latter compound is biologically inactive. 

Experimental Aspects of Excitation and Emission. Although there are many pathways for a species to reach the excited state, photoluminescence by definition must involve photoexcitation, which may occur by absorption of one of the following forms of radiant energy (1) sunlight, (2) visible radiation, including room light, (3) ultraviolet radiation, or (4) x-rays. 

Figure 4-10. Hair fiber exposed to ultraviolet radiation and then bleached for 15 min with alkaline peroxide. Note the decreased scale definition. SEM kindly provided by Sigrid Ruetsch of Textile Research Institute/Princeton.

This general definition of corrosion includes reactions of widely varying material classes, such as the degradation of polymers by ultraviolet radiation, and the attack of refractory bricks during steelmaking. However, the focus of much of the field of corrosion is on the degradation of metals, which will be the focus of this volume. The corrosion of metals can take many forms, which are important to understand since the best methods of corrosion prevention depend upon the form of corrosion. 

The first "true" terrestrial vertebrates, whether taxonomically amphibians or reptiles, were definitely not lizards. However, there is good reason to imagine that they behaved like lizards (Maderson, 1972a 164). Data are available that suggest that a superficial corneous layer of the epidermis, wherein the cells synthesized 3-keratin, was an adaptation protecting the living cells from the deleterious effects of ultraviolet radiation (Maderson et al., 1984, and in preparation). 

A variety of melting points have been reported for [57]. Although the presence of geometric isomers has been su ested to explain these discrepancies, there is as yet no evidence to support this proposal. At least a partial explanation is to be found in the observation that 57 undergoes photodimeiization slowly in ordinary light and more rapidly when exposed to ultraviolet radiation. The monomer and dimer can be separated by vacuum sublimation. Infrared, ultraviolet, and proton magnetic resonance spectra of the dimer support the cyclobutane structure 58, although the stereochemistry has not been definitely established. 

A chemical is any substance that has a definite composition. Ozone is a chemical that is made up of three particles of oxygen. Ozone forms a thick blanket above the clouds in the stratosphere. This layer of ozone protects Earth from overexposure to ultraviolet radiation from the Sun. You are probably familiar with the damage that exposure to ultraviolet radiation can do to your skin in the form of sunburn. Ultraviolet radiation can also harm other animals and plants. In the 1980s, scientists documented that the ozone layer arovmd Earth was becoming measurably thinner in some spots. 

In spectrophotometric analysis a source of radiation is used that extends into the ultraviolet region of the spectrum. From this, definite wavelengths of radiation are chosen possessing a bandwidth of less than 1 nm. This process necessitates the use of a more complicated and consequently more expensive instrument. The instrument employed for this purpose is a spectrophotometer. 

From the perspective of the atomic spectroscopist, desirable properties of plasmas include high thermal temperature and sufficient energy to excite and ionize atoms which are purposefully introduced for the purposes of analysis. In terms of atomic spectrometry, this means that we would generally wish to measure the absorption or emission of radiation in the near-ultraviolet (180-350 nm) and visible (350-770 nm) parts of the spectrum. In this sense, plasmas have been variously described as electrical flames or partially ionized gases. A working definition for atomic spectrometry could be as follows ... 

Medium Pressure Lamp.—A lamp filled with mercury vapor and operated at a pressure of about 1 atmosphere. The total intensity in the near ultraviolet and visible is lower than that of high pressure lamps, but photochemically useful light at wavelengths less than 3000 A. is produced. The ultraviolet spectrum consists of reasonably narrow lines with only a weak continuum. Hence, in conjunction with a filter or monochromator it is a good source for monochromatic radiation including reversed 2537-A. radiation (see definition below). 

Historically, the photochemistry of oxygen and ozone has been of considerable interest because of the importance of oxygen and ozone in the atmosphere. In 1881 Hartley (39) postulated that ozone was a normal constituent of the upper atmosphere and that absorption of solar radiation by ozone could account for the limitation of the solar spectrum at about 3000 A. These speculations were not definitely corroborated until 1913 by Fabry and Buisson (26). The formation of ozone from oxygen in ultraviolet light in the region 1400-1900 A. was first reported by Lenard (53) in 1900 and afterwards confirmed by Goldstein (34) in 1903. 

The term surface layer is used interchangeably for somewhat different concepts in the literature. It might refer to the parts of the disk that are optically thin to (generally ultraviolet or visible) radiation from the central star, i.e. along a line of sight from the disk surface to the star. This is a physical definition because the... 

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