bluuebunny/crossref_metadata_2025_split huggingface dataset:
IR-Visible Photoluminescence Study of Nanometer-Size Amorphous Silicon Powder Produced by Square-Wave-Modulated RF Glow Discharge
Authors: Costa J. , Roura P. , Sardin G. , Morante J.R. , Bertran E. 
Published: April 2011

ABSTRACTAmorphous silicon powder exhibiting microstructural properties such as nanometer-size, large presence of silicon-hydride groups and high surface/volume ratio has been produced in a plasma enhanced chemical vapor deposition (PECVD) reactor using pure silane gas and low frequency square-wave-modulated (SQWM) rf power (13.56 MHz). The possible crystallinity of nanometer-size domains embedded in the amorphous network was studied with Raman spectroscopy and electron diffraction analysis.Photoluminescence (PL) in the near IR-VIS region was excited by an Ar laser. The PL intensity exhibits very unusual properties: a supralinear dependence on excitation power and an exponential decrease with pressure (below 50 Pa). The analysis of PL dynamics led us to propose a mathematical model of excitation of the PL. This model involves the existence of an intermediate step, with an extremely long lifetime, that controls the PL dynamics.
A Molecular Approach to Ultrathin Multilayered Films of Titanium Dioxide
Authors: Kleinfeld Elaine R. , Ferguson Gregory S. 
Published: April 2011

ABSTRACTWe have used solution-phase inorganic chemistry to form ultrathin, covalently bonded layers of TiO2 on silicon wafers. Ellipsometry and x-ray photoelectron spectroscopy (XPS) were used to monitor the growth of the films. The ellipsometric thickness of the TiO2 films increased linearly with the number of reaction cycles, the first absorption cycle resulting in about 3–4 Å of growth, and subsequent cycles resulting in about 1 Å of growth. We attribute this limited growth to the limited number of reactive sites on the surface.
The Control of Dna Structure and Topology: An Overview
Authors: Seeman Nadrian C. , Zhang Yuwen , Du Shou Ming , Wang Hui , Mueller John E. , Wang Yinli , Liu Bing , Qi Jing , Chen Junghuei 
Published: April 2011

ABSTRACTThe control of structure on the nanoscale relies on intermolecular interactions whose specificity and geometry can be treated on a predictive basis. DNA fulfills this criterion, and provides an extremely convenient construction medium: The sticky-ended association of DNA molecules occurs with high specificity, and it results in the formation of double helical DNA, whose structure is well known. The use of stable branched DNA molecules permits one to make stick-figures. We have used this strategy to construct in solution a covalently closed DNA molecule whose helix axes have the connectivity of a cube: The molecule has twelve double helical edges; every edge is two helical turns in length, resulting in a hexacatenane, each of whose strands corresponds to a face of the object. We have developed a solid-support-based synthetic methodology that is more effective than solution synthesis. The key features of the technique are control over the formation of each edge of the object, and the topological closure of each intermediate. The isolation of individual objects on the surface of the support eliminates cross-reactions between growing products. The solid-support-based methodology has been used to construct a molecule whose helix axes have the connectivity of a truncated octahedron. This figure has 14 faces, of which six are square and eight are hexagonal; this Archimedean polyhedron contains 24 vertices and 36 edges, and is built from a 14-catenane of DNA. Knotted molecules appear to be the route for cloning DNA objects. It is possible to construct three knotted topologies, as well as a simple cyclic molecule from a single precursor, by control of solution conditions. Control of both branching and braiding topology is strong in this system, but control of 3-D structure remains elusive. Our key aim is the formation of prespecified 2-D and 3-D periodic structures for use in diffraction experiments. Another application envisioned is scaffolding for the assembly of molecular electronic devices.
Langmuir-Blodgett Films of Calcium Stearate
Authors: Costa Necesio , Aindow Mark , Marquis Peter M. 
Published: April 2011

ABSTRACTThe Langmuir Blodgett (LB) Process has been shown to be an appropriate method for use in mimicking of biological processes for producing engineering materials such as bioceramics. The main advantages of this approach are that the layers form at low temperatures, that they are fully dense and that the process of densification is by infiltration rather than by sintering. Moreover, biological hard tissues are self-assembled to perform certain functions; the architecture being controlled by an epitaxial organic matrix. Clearly, if this process can be understood in detail then it is possible that LB films may be used to replicate this architecture for engineering purposes.Atomic Force Microscopy (AFM) and X-ray diffraction (XRD) have been used to study and characterise LB films of calcium stearate obtained by the repeated dipping into and withdrawal of a (001) Si wafer from a subphase containing calcium ions and using stearic acid as the surfactant. Contact-mode AFM images of the film surface have been used to measure the thickness of the LB layers and to reveal the nature and distribution of defects in the film. The measured thickness of the calcium stearate layers is about 2.5 nm; a value consistent with that obtained by XRD, but smaller than the length of an individual calcium stearate molecules.
Adsorption of Carbon-14 on Mortar
Authors: Matsumoto Junko , Banba Tsunetaka , Muraoka Susumu 
Published: April 2011

AbstractThe sorption experiments of carbon-14 on the mortar grain (grain size : 0.50 – 1.0 mm) focused on the chemical form of the carbon-14 were carried out by the batch method. Three kinds of carbon-14 chemical form were used for the experiments : sodium carbonate (Na214CO3) as the inorganic radiocarbon, and sodium acetate (CH314COONa) and acetaldehyde (14CH314CHO) as the organic radiocarbons. 0.30 gram samples of mortar were soaked in the solution with carbon-14 at 15°C for periods of up to 160 days. At the end of each run, carbon-14 concentrations in the supernatants were determined before and after centrifugation (3,500 rpm., 1 hr.).In the mortar-sodium carbonate system, the retention process of carbon-14 related to reaction on the surface of the mortar was speculated as follows. First, 3CaO-SiO2. and 2CaO-SiO2, of the mortar components contact with water and produce Ca(OH)2. Ca(OH)2 produces Ca2+ and OH− in the solution. Then, calcite forms from Ca2+ and CO32− in the solution. Thus, the sorption ratio of carbon-14 onto mortar will be high until mortar nas been completely carbonated because Ca2+ is rich in the mortar and the solubility of calcite is low.In the mortar-organic carbon system, the soluble organic carbon-14 is hardly sorbed on the surface of the mortar. Therefore, the cementitious materials may not inhibit the release of organic radiocarbons from the low-level radioactive wastes, contrary to the case of inorganic radiocarbon.
Migration Behavior of Carbonate-14C in Tuffaceous Soil
Authors: Nagao S. , Senoo M. 
Published: April 2011

AbstractA simple closed column system was developed to study migration of bicarbonate and carbonate 14C in soil layer. Experimental data for glass beads having less the 14C adsorption indicate that the system can be performed on column experiment keeping mass balance of 14C. Migration behavior of bicarbonate and carbonate 14C in a tuffaceous sandy soil was investigated by this column system in the pH range from 8 to 12. The 14C was delayed to tritiated water, and the retardation became stronger in order, pH 12 < pH 10 < pH 8. This is considered to be due to pH-dependent adsorption of bicarbonate and carbonate ions onto the soil sample.
The Solubility of Th(IV) and U(IV) Hydrous Oxides in Concentrated Nahco3 and Na2Co3 Solutions
Authors: Rai Dhanpat , Felmy Andrew R. , Moore Dean A. , Mason Marvin J 
Published: April 2011

AbstractThe solubility of Th(IV) and U(IV) hydrous oxide was studied in the aqueous HCO3−-CO32−-OH−-H2O system extending to high concentration. The solubility of the Th(IV) and U(IV) hydrous oxides increases dramatically in both high bicarbonate and carbonate solutions and decreases with the increase in hydroxide at a fixed carbonate concentration. In general, the observed solubility of Th(IV) hydrous oxide at a given total carbonate concentration was three to four orders of magnitude higher than the solubility of U(IV) hydrous oxide. In the studies of the U(IV) system, extreme caution was used to ensure that the dissolved U was present as U(IV). Oxidation state analyses and systematic trends in the U(IV) solubility data similar to those for Th(IV), which is not redox sensitive, indicated that the dissolved U was present as U(IV).
Enhanced Recovery of Technetium(VII) by Primary Amine Extraction from Aqueous Fluoride Solutions and Aqueous Alkaline Solutions
Authors: Ito K. 
Published: April 2011

AbstractThe extraction behavior of technetium from aqueous hydrofluoric acid solution has been investigated. The recovery of Tc using two techniques, primary amine extraction in mixed heptane and 1–octanol solution and stripping with a mixed aqueous ammonium hydroxide – ammonium carbonate solution has been studied. The determination of distribution ratios and percentages of technetium in both extraction and stripping cycles was established as were the volume ratios between organic and aqueous phases. The stripping mechanism in the aqueous solution has also been investigated by the slope analysis method.
Recycle Processes for Metal Fuels by Dissolution into Organic Solution
Authors: Sano Y. , Hayami H. , Miyake C. , Horie M. 
Published: April 2011

AbstractThe dissolution behavior of actinide and fission product metals into THF with 10 vol% Br2 was examined in this study. The solubilities of niobium, ruthenium, rhodium, zirconium and molybdenum in both aerated and nitrogenated THF solutions with 10 vol% Br2 are negligible. On the other hand, the solubilities of lanthanum, neodymium, samarium and strontium in aerated and nitrogenated THF solutions with 10 vol% Br2 are large. Among metals examined in this study, uranium had the largest solubility in nitrogenated THF with 10 vol% Br2 and under this condition uranium will be separated from other metals. In the nitrogenated organic solution U(IV), U(V) and UO22+ (VI) coexist, while only UO22+ (VI) exists in the aerated organic solution.
Development of the Hydrogeological Survey Method Using the Natural Dissolved Noble Gases for the Site-Characterization for Radwastes Disposal
Authors: Mahara Yasunori 
Published: April 2011

AbstractThis study focused on developing the tracer method using the dissolved natural noble gases. The method measures precisely helium and neon dissolved in groundwater for dating. Since the dissolved helium consists of three different components (Atmospheric He, Radiogenic He and Mantle He), if it is possible to separate total dissolved helium into each component, the mixing rate between young groundwater and ancient will be predicted in in-situ groundwater. Then, dating of young groundwater is determined by measuring tritium and tritiogenic 3He in a groundwater sample. On the other hand, the dating method for old groundwater is not still verified. In this study, the old groundwater age is predicted by the accumulating rate of radiogenic helium through the alpha decay of uranium and thorium contained in rock.This tracing method was applied to a confined aquifer in the Kumamoto plain (10km × 20km ), where the groundwater flow and the geohydrological formation of aquifer was investigated in detail in the past. The groundwater in the area consists of mixture of young groundwater (less than 20 yrs old) and ancient isolated groundwater (more than 1000 yrs old). Furthermore, the drastic change in the helium isotopic ratio revealed unexpectedly the existence of active faults covered in groundwater basins. Consequently, the method using the dissolved noble gases is practicably available for investigating the geohydrologic formation of aquifer at the early stage of the site characterization.
Effects of Alpha Decay on the Properties of Actual Nuclear Waste Glass
Authors: Banba T. , Matsumoto S. , Muraoka S. , Yamada K. , Saito M. , Ishikawa H. , Sasaki N. 
Published: April 2011

AbstractAn accelerated experiment using the actinide doping technique was performed to investigate the effects of alpha decay on the properties of actual nuclear waste glass at high radiation doses. A fully radioactive borosilicate waste glass, containing the actual high-level radioactive liquid waste generated from the Tokai Reprocessing Plant of PNC, was prepared by JAERI, and a powder mixture of the ground fully radioactive glass and 244CmO2 was melted at 1200°C for 2 hrs. The radioactivity concentration of 244Cm was 1.0 } 1010 Bq/g-glass at the date of preparation. The homogeneity of curium-doped glass samples was confirmed by the density measurement, heat load measurement and alpha autoradiography. The properties of the irradiated samples were investigated by the mass spectrometer for helium determination, the optical microscope, the electron probe microanalyzer, the densitometer, the Soxhlet and MCC-1 leach testing apparatus. By measuring the amount of helium released from the curium-doped glass samples, more than 99% of helium remained in the matrix at room temperature. The density of the sample slightly decreased with the increase of cumulative alpha decays and the decrease of 0.77% was observed at a dose of 1.55 } 1018 alpha decays/g, corresponding to an equivalent age of 150000 yrs. Optical and scanning electron micrographs showed that no cracks were observed on all samples having up to a dose of 1.5 } 1018 alpha decays/g. The leach rates, based on weight loss, in both the Soxhlet (100°C, 7 days) and MCC-1 (90°C, 28 days) tests did not significantly change with alpha decay dose.
Experimental Investigation on the Active Range of Sulfate-Reducing Bacteria for Geological Disposal
Authors: Fukunaga S. , Yoshikawa H. , Fujiki K. , Asano H. 
Published: April 2011

AbstractThe active range ofDesulfovibrio desulfuricans. a species of sulfate-reducing bacteria, was examined in terms of pH and Eh using a fermenter at controlled pH and Eh. Such research is important because sulfate-reducing bacteria (SRB) are thought to exist underground at depths equal to those of supposed repositories for high-level radioactive wastes and to be capable of inducing corrosion of the metals used in containment vessels.SRB activity was estimated at 35°C, with lactate as an electron donor, at a pH range from 7 to 11 and Eh range from 0 to -380 mV. Activity increased as pH approached neutral and Eh declined. The upper pH limit for activity was between 9.9 and 10.3, at Eh of -360 to -384 mV. The upper Eh limit for activity was between -68 and -3 mV, at pH 7.1. These results show that SRB can be made active at higher pH by decreasing Eh, and that the higher pH levels of 8 to 10 produced by use of the buffer material bentonite does not suppress SRB completely.A chart was obtained showing the active range ofDesulfovibrio desulfuricansin terms of pH and Eh. Such charts can be used to estimate the viability of SRB and other microorganisms when the environmental conditions of a repository are specified.
Experimental Validation of a Speciation Model Applied to Organic-Rich Groundwaters
Authors: Crawford M. B. , Higgo J. J. W. , Davis J. 
Published: April 2011

AbstractNatural organic compounds can play an important role in the transport of radionuclides through the geosphere, but the inclusion of polyelectrolytic fulvic and humic acids into geochemical speciation codes is not straightforward. Schubert ion-exchange experiments have been used to parameterise an equilibrium-based, discrete site-electrostatic model, Model V, which is concerned with predicting trace metal-humic interactions in solution. However, before such a model can be applied to natural groundwaters, its ability to deal with competition between trace cations and anionic ligands has to be tested.PHREEQEV, which incorporates Model V with the inorganic speciation code PHREEQE, has been used to guide experiments based on a modified Hummel-Dreyer method. To improve speed and precision, these experiments used a HPLC method rather than Sephadex gel, and measured the effect of Ca on Co and Ni binding to fulvic acid. The results were compared with the predictions made by PHREEQEV. Although the system was further complicated by the need to add citric acid to prevent binding of metals to the HPLC column, predictions at pH 5 were good for both metals. At pH 7, the Co binding results were not well predicted and the reasons for this are still unclear. Comparisons between the Schubert and Hummel-Dreyer-type experiments show that the two methods are compatible.
Permeability Variation of Bentonite-Sand Mixture Due to Shear Strain
Authors: Zhang Ming , Esaki T. , Mitani Y. 
Published: April 2011

AbstractThe objective of this study is to investigate the permeability variation of the compacted bento-nite-sand mixture, a candidate material to be used in low level radioactive nuclear waste geotechnical disposal facility, due to shear deformation which might occur in the mixture caused by the earthquake and/or the nonuniform deformation in its long term performance. To execute the study systematically, a coupled shear and permeability testing apparatus was firstly developed in which a hollow cylindric specimen and the constant flow pump was adopted. It enabled us to measure the permeability along the shear plane in the specimen successfully and rapidly. The result of this study revealed that the permeability of the compacted bentonite-sand mixture with 15% of bentonite was not significantly influenced by the shear deformation. This has tentatively shown the effectiveness of both the new coupled shear and permeability testing apparatus and the bentonite-sand mixture to be used for retarding the radionuclide migration around the radioactive waste repository accompanying water movement.
Simultaneous Transport of Synthetic Colloids and a Nonsorbing Solute Through Single Saturated Natural Fractures
Authors: Reimus Paul W. , Robinson B. A. , Nuttall H. E. , Kale R. 
Published: April 2011

AbstractTracer transport experiments involving colloids that showed little tendency to attach to rock surfaces and a nonsorbing solute (iodide) were conducted in three different well-characterized natural fractures in tuff. The objective was to investigate the potential for using nonattaching colloids in tracer experiments to (1) obtain a measure of the dispersion in a fractured system in the absence of diffusion into the matrix or into stagnant zones along the fracture walls, and (2) provide insights into predicting colloid transport in fractures under conditions of minimal deposition.In the experiments, the colloids always arrived earlier in the effluent than the iodide, which we believe is evidence of (1) hydrodynamic chromatography and/or (2) the fact that the colloids experience a smaller effective volume in the fracture because they diffuse too slowly to enter low-velocity regions (dead zones) along the rough fracture walls. The iodide also approached the inlet concentration in the effluent more slowly than the colloids, with the concentration at a given elution volume being greater at higher flow rates. By contrast, the rate of approach of the colloid concentration to the inlet concentration did not vary with flow rate. We attribute this behavior to matrix diffusion of the iodide, with the colloids being too large/nondiffusive to experience this phenomenon. Dispersion of all tracers was greatest in the fracture of widest average aperture and least in the fracture of narrowest aperture, which is consistent with Taylor dispersion theory.The tracer experiments were modeled/interpreted using a three-step approach that involved (1) estimating the aperture distribution in each fracture using surface profiling techniques, (2) predicting the flow field in the fractures using a localized parallel-plate approximation, and (3) predicting tracer transport in the fractures using particle-tracking techniques. Although considered preliminary at this time, the model results were in qualitative agreement with the experiments.
Hydrologic Imaging of Fractured Rock
Authors: Karasaki Kenzi , Cohen Andrew , Cook Paul , Freifeld Barry , Grossenbacher Ken , Peterson John , Vasco Don 
Published: April 2011

AbstractVarious geophysical and hydrologic tests were conducted in a cluster of nine wells to image the hydrologic connections of a fractured rock mass. Results of intra-borehole flow surveys and cross-hole radar and seismic tomography surveys correlated very well, and indicated that there is a major feature at a depth of 30m. Systematic injection tests were conducted in all nine wells. Three to four intervals in each well were isolated using pneumatic packers. Each interval was equipped with a high resolution pressure transducer. Some 130 injection tests were conducted, and more than 4,100 cross-hole transient pressure measurements were obtained. A computer algorithm was developed to analyze such massive interference data systematically. As a result of the analysis, an image of the fracture connections emerged which is consistent with the geophysical data.
A Channel-Network-Model for Radionuclide Transport in Fractured Rock-Testing Against Field Data
Authors: Gylling Björn , Moreno Luis , Neretnieks Ivars 
Published: April 2011

AbstractA new model concept for describing flow and transport in fractured rock has been tested on some field tracer experiments. The flowing water in the rock is envisaged to take place in a three-dimensional network of channels with stochastic properties. For times of interest for deep geological repositories for nuclear waste it has been found that the volume of the channels, i.e. the flow porosity of the rock, has no practical influence on the Residence Time Distribution of the nuclides. It is totally dominated by the matrix diffusion effects. The specific Flow Wetted Surface, FWS, of the channels therefore needs to be known. A method to evaluate the FWS from hydraulic measurements in boreholes is presented.Tracer tests at the Swedish ÄSPÖ rock laboratory have been predicted using this model and data obtained in the way outlined in the paper. The main tracer test was predicted reasonably well without using any adjustable parameters. Some other tracers also used were not detected in the tests as they were expected to be. We discuss some of the possible reasons for this in relation to geological observations made in the expected pathways for these tracers. The sensitivity of results to uncertainties in parameter values is also discussed.