bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of Metal Substrate Nanometer Topography on Osteoblast Metabolic Activities
Authors: Ward Brian C. , Webster Thomas J. 
Published: April 2011

AbstractSurgeons and bioengineers have continuously been challenged by implant failure. Many of these engineers and surgeons trace implant failure to poor osseointegration (the bonding of an orthopedic implant to juxtaposed bone) and to the inability of implants to match the physical properties of surrounding bone. Researchers have recently shown that nanostructured materials (or materials with fundamental length scales less than 100 nm) enhance cell functions pertinent to effectively regenerating the tissue of numerous organs. Specifically, in a recent study, researchers demonstrated that metal surfaces utilizing low-micron to nanophase topography fostered increased adhesion of osteoblasts, the cells that create the matrix of bone. In this study, Ti, Ti6Al4V, and CoCrMo alloys were investigated, and these alloys were identical to current orthopedic implant alloys except for surface topography. The objective of this in vitro research was to determine whether these same nanophase metal surfaces not only foster osteoblast adhesion but also increase osteoblast metabolic activities leading to bone regeneration. Light microscopy and Energy Dispersion Spectroscopy (EDS) were used to verify the presence of calcium and phosphorous deposition by osteoblasts cultured on the metal substrates. Results indicated that both calcium and phosphorous are being deposited on several of the metal substrates. More importantly, compared to conventional metals, results provided the first evidence that more calcium and phosphorous was deposited by osteoblasts cultured on respective nanophase metals (Ti, Ti6Al4V, and CoCrMo). Nanophase CoCrMo had the most calcium and phosphorous minerals deposited by osteoblasts compared to any other metal substrate. Thus, the results of this study continue to provide evidence for the use of nanophase metals for the design of the next generation of more successful orthopedic implants.
Calcium Oxalate Monohydrate Precipitation at Phospholipid Monolayer Phase Boundaries
Authors: Benítez Isa O. , Talham Daniel R. 
Published: April 2011

AbstractThe precipitation of calcium oxalate monohydrate (COM) was observed at biphasic phospholipid Langmuir monolayers with the aid of Brewster angle microscopy. COM appears preferentially at phase boundaries of a monolayer of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) in a state of liquid expanded/liquid condensed coexistance. However, when the phase boundary is created by two different phospholipids that are phase segregated, such as DPPC and 1,2-dimiristoyl-sn-glycero-3-phosphocholine (DMPC), crystal formation occurs away from the interface. It is suggested that COM growth at phase boundaries is preferred only when there is molecular exchange between the phases.
Intrafibrillar demineralization study of single human dentin collagen fibrils by AFM
Authors: Balooch M. , Balooch G. , Habelitz S. , Marshall S. J. , Marshall G. W. 
Published: April 2011

AbstractIn situ atomic force microscopy (AFM) was used to investigate the kinetics of demineralization of human dentin collagen fibrils. Individual dentin collagen fibrils containing intrafibrillar mineral were isolated, transferred onto a glass slide and exposed to water for a day prior to demineralization studies. The fibrils then were exposed to trypsin for removal of non-collagenous proteins and subsequently demineralized in 10 vol % citric acid. Topographic images showed a gradual increase in gap-overlap depth of the fibril. The gap-overlap depth varied linearly with the square root of time before saturation at 7 nm in approximately sixty minutes, suggesting a diffusion process for demineralization of intrafibrillar mineral. Micro Raman studies of partially demineralized dentin revealed the existence of a phosphate peak at wave number close to 960 cm-1. The peak gradually disappeared in 60 minutes as the samples were exposed to 10% citric acid, supporting the notion that AFM topography may be correlated to the degree of intrafibrillar mineralization.
Effect of the free energies of formation of the core and shell and of the density of the casein phosphate centres on the thermodynamic stability of calcium phosphate nanoclusters
Authors: Holt Carl 
Published: April 2011

AbstractCalcium phosphate is sparingly soluble at neutral pH but the milk of nearly all species contains many times the concentrations of calcium and phosphate that this solubility allows. The explanation for this apparent paradox is that milk calcium is mainly present in the form of thermodynamically stable nanoclusters formed from casein phosphoproteins and amorphous calcium phosphate. A simplified model system comprising the main milk salts and a hydrophilic N-terminal phosphopeptide from β-casein, at or about neutral pH, forms complexes called calcium phosphate nanoclusters. It is shown that two constants, KS and y, together with the empirical chemical formula of the nanoclusters allow the concentrations of all the important chemical species in this model system to be calculated. The method has been extended successfully to the more complex problem of calculating all the important chemical species in milk. It is suggested, on the basis of a simple analysis of the thermodynamics of the formation of nanoclusters, that their size and stability is determined principally by three factors. These are the relatively low free energy of formation of the amorphous core material, the particular pattern of phosphorylation of seryl residues in the caseins that gives a large chelate effect during the sequestration of the calcium phosphate and the unfolded conformation of the caseins that allows a high density of phosphate centres on the core surface.
Conductivity Behavior of Salt Deposits on the Surface of Engineered Barrier Materials for the Potential High-Level Nuclear Waste Repository at Yucca Mountain, Nevada
Authors: Yang Lietai , Juckett Miriam R. , Pabalan Roberto T. 
Published: April 2011

AbstractThe electrical conductance or conductivity of three salt mixtures, Na-K-Cl-NO3, Ca-K-Cl and Ca-Na-Cl, were measured at 25, 50 and 70°C [77, 122, and 158 °F] as a function of relative humidity (RH). Mutual deliquescence and efflorescence RH (MDRH and MERH) values were determined based on the conductivity measurements. It was found that the conductivity of the three salt mixtures started to increase at RH values that are approximately 40 % of their MDRH and increased by 1to 2 orders of magnitude just before reaching the MDRH. At the MDRH, a significant increase in conductivity was observed. The MDRH and MERH for the Ca-K-Cl and Ca-Na-Cl mixtures were found to be approximately 15 % in the temperature range of 50 to 70 °C [122 to 158 °F]. The MDRH and MERH for the Na-K-Cl-NO3system were found to be approximately 54 % at 50 °C [122 °F] and decreased significantly with an increase in temperature.
Can Spent Nuclear Fuel Decay Heat Prevent Radionuclide Release?
Authors: Jerden James L. , Goldberg Margaret M. , Cunnane James C. , Bauer Theodore H. , Wigeland Roald A. , Nietert Russell E. 
Published: April 2011

AbstractHeat generated by radioactive decay of spent fuel represents a potentially important barrier to water accumulation on commercial spent nuclear fuel in breached waste packages. In the absence of water, fuel degradation and radionuclide release will be negligible. Thermal models for the proposed Yucca Mountain Repository suggest that, after a period of approximately 1000-4000 years (depending on loadingand ventilation conditions), the repository drift walls may decline to sub-boiling temperatures, thus allowing humidity in the drift to increase. The question thus arises, is the thermal gradient between the fuel and the drift sufficient to prevent water accumulation in a humid drift environment throughout the regulatory period? The answer depends on the balance between processes that oppose water condensation ontothe fuel (decay heat) and those that promote condensation such as the deliquescence of hygroscopic phaseswithin the fuel.Our experimental results indicate that deliquescence could lead to the condensation of water onto spent fuel despite the thermal “self-drying”effect if the following criteria are met: (1) the fission product salt CsI is present in the fuel or in the fuel-cladding gap, (2) the relative humidity in the driftexceeds 80% while temperatures in the waste package are around 90oC. Previous work suggests that these criteria may be met for some fuel pins within the proposed Yucca Mountain Repository. However,experiments that account for the role of U(VI) alteration phases suggest that deliquescence may be a self-limiting process in the sense that deliquescent components (e.g. Cs, Ba, Sr) may be incorporatedinto nondeliquescent U(VI) phases that form from the corrosion of spent fuel.
Performance Assessments of Geologic Repositories for High-Level Nuclear Waste: Are TheyNecessaryorSufficient?
Authors: Ewing Rodney C. 
Published: April 2011

AbstractPerformance assessments of geologic repositories for high-level nuclear waste will be used to determine regulatory compliance. The determination, that with a “reasonable expectation” regulatory limits are met, is based on the presumption that all of the relevant physical, chemical and biological processes have been modeled with enough accuracy to insure that a confident judgment of safety may be made. For the geologic disposal of high-level nuclear waste, this generally means that models must be capable of calculating radiation exposures to a specified population at distances of tens of kilometers for periods of tens to hundreds of thousands of years. A total system performance assessment will consist of a series of cascading models that are meantin tototo capture repository performance. There are numerous sources of uncertainty in these models: scenario uncertainty, conceptual model uncertainty and data uncertainty. These uncertainties will propagate through the analysis, and the uncertainty in the total system analysis must necessarily increase with time. For the highly-coupled, non-linear systems that are characteristic of many of the physical and chemical processes, one may anticipate emergent properties that cannot, in fact, be predicted. For all of these reasons, a performance assessment is not in and of itself a sufficient basis for determining the safety of a repository, but it remains a necessary part of the effort to develop a substantive understanding of a repository site.
Building Stakeholder Confidence by Reducing the Gulf between Experimental Data and Model Predictions in Assessments of Repository Performance
Authors: Hart Kaye P. 
Published: April 2011

AbstractConfidence in the ability of repository systems to isolate high level wastes from the environment can be strengthened by placing greater reliance on robust designs for the repository system, and by using multiple lines of evidence to demonstrate that parameters, models and predictions developed for the repository are relevant. A particularly useful approach is to demonstrate that models and predictions incorporate processes that have been shown to be important in existing natural systems.
Measures of Geologic Isolation
Authors: Murphy William M. 
Published: April 2011

AbstractIsolation in a geologic setting has been the generally favored solution to the high-level radioactive waste (HLW) problem since a scientific basis for nuclear waste management began to be formulated over half a century ago. Although general features of suitable settings have been enumerated, quantitative measures of the safety of geologic isolation of HLW are challenging to devise and to implement. Some regulatory measures of isolation for the proposed repository at Yucca Mountain, Nevada, have be devised and revised involving considerations of global releases, groundwater travel time, and time and space scales for isolation. In current Yucca Mountain specific regulations, the measure of long-term safety hinges on probabilistic estimates of radiation doses to the average member of a maximally exposed group of people living about 18 km down the groundwater flow gradient within 10,000 years after permanent closure of the repository. From another perspective, hydrogeochemical studies provide quantitative measures of system openness and the ability of geologic systems to isolate HLW. Hydrogeochemical data that bear on geologic isolation of HLW at Yucca Mountain include precipitation of radionuclides in stable mineralogical products of spent fuel alteration, ages of natural secondary mineralization in the mountain, uranium decay-series isotopic data for system openness, bomb-pulse isotope occurrences, and ambient carbon-14 distributions.
Diffuse reflectance spectroscopy of Pu ions in zirconolite and perovskite
Authors: Vance E. R. , Finnie K. S. , Zhang Y. , Begg B. D. 
Published: April 2011

AbstractDiffuse reflectance spectroscopy measurements at ambient temperatures have been made over the near infrared-visible range (5000-25000 cm−1) on polycrystalline ceramic zirconolite (CaZrTi2O7) and perovskite (CaTiO3) samples doped with Pu4+. The Pu concentrations were varied between 0.001 and 0.1 formula units. The Pu ions gave rise to a number of unresolved intraconfigurational f-f electronic absorption bands of a few hundred cm−1 bandwidth. Pu ions were targeted to substitute in the Ca sites as either trivalent or tetravalent species and as tetravalent species in the Zr site of zirconolite by the appropriate choice of charge compensation and firing atmosphere. There was approximate agreement of the Kubelka-Munk absorption intensities with Beer's Law for the different Pu4+ substitution schemes, apart from some “new” bands, attributed to impurities, observed in the most dilute zirconolite sample. No clear spectral differences were evident when Pu4+ was targeted to Ca or Zr sites in zirconolite. Samples prepared in reducing atmospheres with a view to producing Pu3+ were strongly absorbing, leading to suppression of Pu transitions.
Zirconolite-Based Ceramic Formulations for Immobilization of Zr-REE-Actinide Fraction of HLW
Authors: Ochkin A.V. , Stefanovsky S.V. , Ptashkin A.G. , Mikhailenko N.S. , Kirjanova O.I. 
Published: April 2011

AbstractTwo ceramics for immobilization of a Zr-REE-actinide fraction of high level waste (HLW) based on zirconolite or/and pyrochlore structures with minor brannerite/lucasite, and fluorite-structured dioxide-based solid solution, were synthesized and characterized. The samples were produced by melting of oxide mixtures at 1500 °C followed by controlled cooling for crystallization. Phase compositions of the samples obtained and waste elements partitioning among co-existing phases were investigated in detail using powder X-ray diffraction, scanning electron microscopy with energy dispersive spectroscopy, and transmission electron microscopy. Cerium enters cerianite-based solid solution, lucasite (if present), and to a lesser extent, pyrochlore and zirconolite. Europium and gadolinium enter predominantly zirconolite and pyrochlore. The highest uranium concentrations were found in a uraninite-based cubic solid solution or pyrochlore and zirconolite.
Investigation of Pu Incorporation into Zircon Single Crystal
Authors: Hanchar John M. , Burakov Boris E. , Zamoryanskaya Maria V. , Garbuzov Vladimir M. , Kitsay Alexander A. , Zirlin Vladimir A. 
Published: April 2011

AbstractIn order to obtain Pu-doped zircon, (Zr,Pu)SiO4, with a maximum Pu content in the form of solid solution, zircon single crystals have been grown using the flux method from starting materials overloaded with Pu. The crystals obtained ranged from 0.2-0.5 to 3.5-4.5 mm in size, are transparent, and characterized by deep pink-brown color. No inclusions of separate Pu phases were observed in the crystals. The distribution of Pu in crystals is zoned and the Pu content varying from approximately 5 to 14 wt.% el. The zircon unit cell parameters calculated from XRD data of bulk powdered sample were: a=6.620(1); c=5.989(2). The results obtained allow us to conclude that the capacity of the zircon structure to incorporate Pu exceeds 10 wt.% el.; however, additional research is required to study the extent of solid solution, (Zr,Pu)SiO4, at higher Pu contents.
REE and TRU Incorporation into Monazite Structure Ceramics
Authors: Rovnyi S. I. , Medvedev G. M. , Aloy A. S. , Koltsova T. I. , Samoylov S. E. 
Published: April 2011

AbstractOne of the high levels of actinide, and in particular Cm, waste streams at the Russian radiochemical Production Association (PA) Mayak was generated during spent fuel reprocessing. Using oxalate precipitation, the rare earth elements (REE) and transuranic elements (TRU) settled out in the form of oxalate residues. Due to in high REE contents in this residue, the mineral-like matrix based on (REE)PO4 solid solution, with monlclinic monazite structure have been proposed to use as a suitable ceramics form for final actinide immobilization. For this purpose the synthetic REE oxalates were first transformed into REE orthophosphates in a thin-film evaporator (TFE). Then the (REE)PO4 powder was compacted both by either hot uniaxial pressing (HUP) or cold uniaxial pressing followed by sintering (CUP). This ceramic with the monazite structure has a high density and exhibits chemical durability by leaching.
Effect of Alpha Decay on Nuclear Borosilicate Glass Properties
Authors: Peuget Sylvain , Jégou Christophe , Broudic Véronique , Roudil Danièle , Deschanels Xavier , Bart Jean-Michel 
Published: April 2011

AbstractThe properties of actinide glasses are studied in the context of high-level waste management programs. Reprocessing high burnup fuels in particular will increase the minor actinide content in the glass package, resulting in higher cumulative alpha decay doses in the glass, and raising the question of the glass matrix behavior and especially its containment properties. The effect of alpha self-irradiation on the glass behavior is evaluated by doping the glass with a short-lived actinide (244Cm) to reach in several years the alpha dose received by the future glass packages over several thousand years. “R7T7” borosilicate glasses were doped with 3 different curium contents (0.04 wt%, 0.4 wt% and 1.2 wt% 244CmO2). The glass homogeneity was characterized by SEM and XRD. Chemical analysis after dissolution of the glass confirmed the chemical composition. The curium content and its distribution in the glass specimens were checked by calorimetry measurements and gamma spectrometry on 243Cm and 245Cm isotopes. The density and mechanical properties of the curium-doped glasses were characterized up to 2 × 1018 α/g, revealing only a slight evolution of the macroscopic behavior of R7T7 glass in this range. The leaching behavior of curium-doped glass was also studied by Soxhlet tests. The results do not show any significant evolution of the initial alteration rate with the alpha dose.
Corrosion mechanisms of low level vitrified radioactive waste in a loamy soil
Authors: Ojovan M.I. , Lee W.E. , Barinov A.S. , Ojovan N.V. , Startceva I.V. , Bacon D.H. , Mcgrail B.P. , Vienna J.D. 
Published: April 2011

AbstractField experiments have run for over 14 years to evaluate the behaviour of the same high-sodium content radioactive waste borosilicate glass buried in a loamy soil (glass K-26) and in an open testing area (glass Bs-10). Processing of field data for glass Bs-10 tested in an open area has resulted in a dissolution rate r = 0.42 µm/y and caesium diffusion coefficient D ≍ 1.8 10−20 m2/s at testing temperatures up to 19 oC. Both ion-exchange and hydrolysis control the corrosion of this glass. Processing of field data for K-26 glass revealed an insignificant role of glass dissolution. The caesium diffusion coefficient was estimated as D ≍ (3.4-5.1) 10−21 m2/s. Due to the relatively low storage temperatures (4.5 oC) used the leaching behaviour of glass K-26 is believed to be controlled by ion exchange processes. This mechanism is likely to remain dominant until the decay of 137Cs in the glass is below exemption levels.
Characterization of Chromium(III) Hydroxide Solids and Their Oxidation by Hydrogen Peroxide
Authors: Zhang Zhicheng , Rao Linfeng , Rai Dhanpat , Clark Sue B. 
Published: April 2011

AbstractChromium is of great concern in the vitrification of high-level nuclear waste sludges because it forms separate crystallites in the molten glass. Inadequate removal of chromium from sludges could result in the production of an unacceptably large volume of HLW glass. Alkaline oxidative leaching is considered one of the pretreatment strategies to remove chromium before the vitrification.In this study, Cr(III) hydroxide solids were prepared under different conditions and characterized by EXAFS and IR. The rate of oxidation of the solids by hydrogen peroxide in alkaline solutions was studied by UV absorption spectroscopy. EXAFS and IR experiments indicate that the degree of oligomerization in the Cr(III) hydroxide solids increases with the increase in the concentration of NaOH in solution, the aging temperature and the aging time. The rate of oxidation of the solids follows the same order previously observed for Cr(III) oligomers in solution, i.e., species with higher degree of oligomerization are oxidized more slowly.
Formation Rate and Compositions of the Actinide Hosts with Garnet Structure
Authors: Ioudintseva Tatiana S. , Chae Soo-Chun 
Published: April 2011

AbstractGarnet phases have been considered as a durable crystalline waste form for hosting actinide. The garnet-structure phases with stoichiometries of Ca2,5Ce0,5Zr2Fe3O12, Ca2CeZrFeFe3O12, and Ca1,5GdCe0,5ZrFeFe3O12 were synthesized through cold pressing and sintering in air and oxygen to determine the optimum parameters for the formation of actinide waste forms. Cerium (Ce) was used as an imitator of plutonium due to its similarity in oxidation state and ionic radii. Gadolinium (Gd) plays a major role as an absorber of neutrons that prevents nuclear chain reaction. It also serves as imitators of the trivalent actinides. Ce-garnet or (Ce,Gd)-garnet is chemically analogous to the garnets with plutonium and/or trivalent actinides. The results of XRD and SEM-EDS examination of the products of experiments reveal that equilibrium state was reached at the temperatures of 1300 °C and 1200 °C for 1 and 5 hours heating, respectively.
Analytical STEM of Borosilicate Glasses Containing Molybdates.
Authors: Short Rick J. , Möbus Günter , Yang Guang , Hand Russell J. , Hyatt Neil , Lee William E. 
Published: April 2011

AbstractBorosilicate nuclear waste glasses with various amounts of simulated waste elements have been examined by analytical TEM. This preliminary Scanning Transmission Electron Microscopy (STEM) study evaluates the capability of EELS for mapping coordination parameters of the base glass structure, to apply EDX-mapping and HAADF Z-contrast mapping for the characterisation and shape-mapping of common precipitates in nuclear glasses, such as molybdates, and to study irradiation effects.