Colloid facilitated transport in fractured rock : parameter estimation and comparison with experimental data

Many contaminants in groundwater strongly interact with the immobile porous matrix, which retards their movement relative to groundwater flow. Colloidal particles, which are often present in groundwater, have a relatively small size and large specific surface area which makes it possible for them to also adsorb pollutants. The sorption of tracers to colloids may enhance their mobility in groundwater, relative to the case where colloids are not present. A class of pollutants for which colloid-facilitated transport may be of particular significance are radioactive isotopes. A major reason for why geologic repositories are considered suitable for the disposal of spent nuclear fuel is the strong affinity of many radionuclides to adsorb onto the porous matrix. Therefore, radionuclides accidentally released, would be contained in the geological media by adsorption or filtration until sufficient decay takes place. However, the presence of colloids may enhance radionuclide mobility in the groundwater, and reduce the efficiency of geologic media to act as a natural barrier

Modeling Flow and Transport Pathways to the Potential Repository Horizon at Yucca Mountain

The isotopic ratios of {sup 36}Cl/Cl are used in conjunction with geologic interpretation and numerical modeling to evaluate flow and transport pathways, processes, and model parameters in the unsaturated zone at Yucca Mountain. By synthesizing geochemical and geologic data, the numerical model results provide insight into the validity of alternative hydrologic parameter sets, flow and transport processes in and away from fault zones, and the applicability of {sup 36}Cl/Cl ratios for evaluating alternative conceptual models

A new scheme to calculate isotope effects

We present a new scheme to calculate isotope effects. Only selected frequencies at the target level of theory are calculated. The frequencies are selected by an analysis of the Hessian from a lower level of theory. We obtain accurate isotope effects without calculating the full Hessian at the target level of theory. The calculated frequencies are very accurate. The scheme converges to the correct isotope effect

Colloid facilitated transport in fractured rocks : parameter estimation and comparison with experimental data.

Colloid-facilitated migration of plutonium in fractured rock has been implicated in both field and laboratory studies . Other reactive radionuclides may also experience enhanced mobility due to groundwater colloids. Model prediction of this process is necessary for assessment of contaminant boundaries in systems for which radionuclides are already in the groundwater and for performance assessment of potential repositories for radioactive waste. Therefore, a reactive transport model is developed and parameterized using results from controlled laboratory fracture column experiments. Silica, montmorillonite and clinoptilolite colloids are used in the experiments along with plutonium and Tritium . . The goal of the numerical model is to identify and parameterize the physical and chemical processes that affect the colloid-facilitated transport of plutonium in the fractures. The parameters used in this model are similar in form to those that might be used in a field-scale transport model

A curated online resource for SOX10 and pigment cell molecular genetic pathways

We describe the creation of a specialized web-accessible database named the Pigment Cell Gene Resource, which contains information on the genetic pathways that regulate pigment cell development and function. This manually curated database is comprised of two sections, an annotated literature section and an interactive transcriptional network diagram. Initially, this database focuses on the transcription factor SOX10, which has essential roles in pigment cell development and function, but the database has been designed with the capacity to expand in the future, allowing inclusion of many more pigmentation genes

Moiré patterns observed in bi layer graphene irradiated with high energetic protons

Customarily, it is likely that irradiated graphene yield indication of per- turbations induced by irradiation. High Resolution Transmission Electron Micros- copy (HRTEM) analysis has been performed on proton irradiated graphene. The analysis indicates the existence of Moiré patterns produced by the rotations induced by the irradiation in between planes. The rotations measured fluctuate between 3 and 5 degrees respectively. These rotations may influence the electronic properties of the material under investigation. In order to explain the observed rotations in between planes, theoretical analysis were performed under the scheme of extended Hückel tight-binding method. Average total energy of the system was careful ana- lyzed throughout the experiment composed of two graphene layers with two carbon vacancies and then the replaced carbons were intercalated in between the two lay- ers. The results obtained indicate that the system remain semi metallic. Moreover, the theoretical results yielded that the 3 degree rotation is favored, although the 5 degree rotation is not discarded. Furthermore, energy bands as well as total and projected DOS were performed in order to provide more information about the electronic changes induced by the rotations applied to the system

Molybdenum solar neutrino experiment

The goal of the molybdenum solar neutrino experiment is to deduce the /sup 8/B solar neutrino flux, averaged over the past several million years, from the concentration of /sup 98/Tc in a deeply buried molybdenum deposit. The experiment is important to an understanding of stellar processes because it will shed light on the reason for the discrepancy between theory and observation of the chlorine solar neutrino experiment. Possible reasons for the discrepancy may lie in the properties of neutrinos (neutrino oscillations or massive neutrinos) or in deficiencies of the standard solar model. The chlorine experiment only measures the /sup 8/B neutrino flux in current times and does not address possible temporal variations in the interior of the sun, which are also not considered in the standard model. In the molybdenum experiment, we plan to measure /sup 98/Tc (4.2 Myr), also produced by /sup 8/B neutrinos, and possibly /sup 97/Tc (2.6 Myr), produced by lower energy neutrinos