Radiation, migration rate

An order of magnitude higher radiation parameter R was needed than reported in the literature to match the observed migration rate. 

The rate and extent of electron and hole migration within DNA had been a topic of intense experimental [1] and theoretical [2] interest and dispute. However, as other chapters in this volume point out, the overall picture is now becoming increasingly understood. Several earlier reviews have dealt with the radiation damage to DNA and subsequent chemical processes including electron and hole transfer [3]. This chapter will focus on recent contributions to hole and electron transfer in DNA from high-energy radiation studies. We first present a brief overview on electron transfer processes in DNA from radiation studies and describe in more detail our most recent results on electron and hole transfer in DNA at low temperatures. 

The dose required for amorphization is a function of the kinetics of simultaneous dynamic recovery processes. The recovery process is accelerated at elevated temperatures and, in many cases, is greatly increased by radiation-enhanced defect migration. These simultaneous recovery processes may be associated with defect recombination or annihilation, epitaxial recrystallization at crystalline-amorphous interfaces (Carter and Nobes 1991), or nucleation and growth recrystallization in the bulk of the amorphous state. For any crystalline solid, there is a critical temperature, above which the rate of amorphization is less than the rate of recovery, thus amorphization cannot occur. However, Tc also depends on the energy and mass of the incident beam, as well as the dose rate. 

We expect that the ablation rate of the Elephant Moraine is reduced by the layer of rock clasts of which it is composed and by the discontinuous patches of snow that migrate across it driven by the prevailing wind. The presence of rock clasts may reduce the ablation rate because the clasts cover the surface of the ice. They may also increase the ablation rate because the clasts, which are primarily composed of dark-brown weathered dolerite, absorb solar radiation. The resulting increase in the temperature of the air above the moraine accelerates ablation by sublimation and even causes melting of the ice, especially under boulders that are warmed by solar radiation. 

Atmospheric—Atmospheric corrosion is responsible for a large fraction of the total corrosion in the world. Factors that affect the atmospheric corrosion of materials in a marine environment are the time of wetness, temperature, material, atmospheric contaminants and pollutants, solar radiation, composition of the corrosion products, wind velocity, and biological species [fO]. Atmospheric corrosion of a passive alloy tends to be localized. For electrochemical processes related to corrosion to occur, an electrolyte must be present to allow current to pass via diffusion and electrochemical migration of cations and anions. Seawater is a very conductive electrolyte. The severity of corrosion in an atmospheric environment is related to the time of wetness during which electrochemical processes and corrosion take place. There is also a direct relationship between atmospheric salt content and measured corrosion rates [/O]. 

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