Context. High levels of deuterium fractionation in gas-phase molecules are usually associated with cold regions, such as prestellar cores. Significant fractionation ratios are also observed in hot environments such as hot cores or hot corinos, where they are believed to be produced by the evaporation of the icy mantles surrounding dust grains, and are thus remnants of a previous cold (either ga...

PURPOSE Radiotherapy of solid tumors has been performed with various fractionation regimens such as multi- and hypofractionations. However, the ability to optimize the fractionation regimen considering the physical dose distribution remains insufficient. This study aims to optimize the fractionation regimen, in which the authors propose a graphical method for selecting the optimal number of fra...

Hydrogen-isotopic data are often interpreted using mathematical approximations originally intended for other isotopes. One of the most common, apparent in literature over the last several decades, assumes that delta values of reactants and products are separated by a constant fractionation factor: p r p/r. Because of the large fractionations that affect hydrogen isotopes, such approximations ca...

An ionization-diffusion mechanism is proposed to understand the first ionization potential (FIP) fractionation as observed in the solar corona and the solar wind. The enrichment of the low-FIP elements (<10 eV) compared to the highFIP elements in a large variety of phenomena, as e.g. slow and fast wind or polar plumes, is explained. Also the special behaviour of the heavy noble gases becomes pe...

[1] Wavelength-dependent fractionation of various isotopomers in the photodissociation of N2O is studied. The absorption cross sections are calculated by a time-independent reflection principle, related to the Prakash et al. (2005) treatment but now with an inclusion of the NN stretching coordinate and both the 2A0 and 1A00 electronic excited states. The added 1A00 state is found to have little...

Because of the general nature of the transamination reaction (1, 2), a study of the kinetics and mechanism of reaction seemed of interest. Preliminary studies of this nature have already appeared (3-5). However, these studies were carried out with crude extracts or resolved enzyme systems. In order to conduct a critical kinetic study as well as a study of the mechanism of reaction, large amount...

[1] The toxicity of mercury’s methylated species and its biomagnification in aquatic food chains and global dispersion by the atmosphere are the cause of worldwide health problems. Recent reports have observed natural mass-dependent fractionation in mercury isotopes, and recent theoretical work has demonstrated that isotopic separation in mercury is due primarily to nuclear field shifts (nuclea...

Microbial sulfate reduction exhibits a normal isotope effect, leaving unreacted sulfate enriched in S and producing sulfide that is depleted in S. However, the magnitude of sulfur isotope fractionation is quite variable. The resulting changes in sulfur isotope abundance have been used to trace microbial sulfate reduction in modern and ancient ecosystems, but the intracellular mechanism(s) under...

Isotope fractionation during sulfate reduction by natural populations of sulfate-reducing bacteria was investigated in the cyanobacterial microbial mats of Solar Lake, Sinai and the sediments of Logten Lagoon sulfuretum, Denmark. Fractionation was measured at different sediment depths, sulfate concentrations, and incubation temperatures. Rates of sulfate reduction varied between 0.1 and 37 micr...