Polychromatic, defined

The in vivo micronucleus test is used for the detection of damage to chromosomes as well as the mitotic apparatus in bone marrow or peripheral blood cells of rodents. The assay system has been well standardized.14-17 The basic features of the test system are (1) the effect of the test chemical is observed in anucleated polychromatic erythrocytes (PCEs) (2) PCEs have a relatively short lifespan, so that any micronuclei they contain must have been generated as a result of recently induced chromosome damage (3) micronuclei are readily identifiable and their distribution is well defined and (4) the frequency of induced micronuclei in PCEs is dependent on sampling times. 

One of the interesting consequences of eqs. (11-25) and (11-26) is the dependence of the probability of the molecule being in a given nonstationary state on the time correlations in the coupled radiation field. In most experimental studies the radiation field employed consists of a superposition of many frequencies with random phases. It is convenient to represent that form of field in terms of a correlation function d>(t, t"), which is defined in eq. (6-16). Introducing, because of the polychromaticity of the radiation field, the averages of eqs. (11-25) and (11-26), choosing the same representation for the field correlation function as did Bixon and Jortner, and using the conservation of probability, we find for the probability of dissociation of the molecule the relation ... 

For novel devices like the polymer solar cells described in this chapter, measurement procedures are not nearly so well-established as for inorganic devices, ft was reported earlier that all kinds of ill-defined efficiencies can be found in the literature [87]. This makes a meaningful comparison of efficiency values extremely difficult or even impossible, when they are measured at different institutes and using different measuring techniques. This section describes a procedure for obtaining better defined polychromatic efficiencies. 

Early studies with PDT employed complex mixtures of poorly defined porphyrins known as hemato-porphyrin derivative (photofrin I) or a partially purified mixture known as porfimer sodium (PHOTOFRIN II) that was administered parenterally with subsequent irradiation using polychromatic light sources. The major problem with this approach was the prolonged period (4-6 weeks) of photosensitivity caused by skin retention of the porphyrin formulations. This led to a search for compounds that could be administered topically and that were eliminated more readily from the skin. The porphyrin precursor S-aminolevulinic acid (ALA) is converted to various porphyrins, particularly protoporphyrin (proto), in tissues including the skin (see below). Protoporphyrin subsequently is eliminated rapidly from the body, thereby minimizing the period of skin photosensitivity to a few hours. Topically applied ALA HCl (20% wA>) and, more recently, the methyl ester of ALA have been used successfully for the PDT of various types of nonmelanoma skin cancers and premalignant lesions. 

Studies of the photodissociation of cyanogen halides in the vacuum ultraviolet can be separated into two broad types (i) those which employed polychromatic flash photolysis and which were primarily concerned with the detection of electronic and/or vibrational laser action in the CN fragments, and (ii) those which employed continuous monochromatic photolysis sources and were primarily concerned with the branching ratios and energy disposal following dissociation from well-defined initially populated levels. 

Action and activation spectra can be experimentally determined from studies employing exposure of samples to either monochromatic or polychromatic UV-visible radiation. Rather lax use of these terms in the literature on wavelength sensitivity has led to some degree of confusion. It is convenient to define these terms in a manner consistent with most of the reported literature by making a clear distinction between the different experimental approaches. 

For monochromatic incident radiation, these properties are called spectral and when that radiation is polychromatic they are defined as total (Sandu, 1986). Materials may be classified based on their transmissivity, depending on the physical state of the body where the radiation impinges. A body that does not allow the radiation to be transmitted through it is called opaque and is characterized by r = 0. Examples of these are most solids. On the other hand, liquids and some solids like rock salt or glass have a defined transmissivity so they are transparent to radiation. 

Quantum yields are defined only for specific wavelengths. They are not applicable to polychromatic light sources, especially in combination with broad absorption of the irradiated systems, and must be substituted by empirically determined irradiation times. Studies of the variation in the quantum efficiencies of various primary photochemical processes in polymers show very little dependence on molecular weight [858, 871]. 

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