bluuebunny/crossref_metadata_2025_split huggingface dataset:
Self-Assembly of Bacterial Macrofibers: A System Based Upon Hierarchies of Helices
Authors: Mendelson Neil H. 
Published: March 2011

AbstractCylindrical-shaped cells of Bacillus subtilis (0.7 by 4 μm) are the building blocks of macrofibers, highly organized, helically twisted, multifilament structures millimeters to centimeters in length. The forces responsible for self-assembly and the cylinder-helix deformation trace to the assembly of cell wall polymers and restraint of the motions generated by cell growth. An hierarchical relationship exists involving: (i) molecular level events associated with cell surface assembly, which in turn govern, (ii) cellular level events concerned with motions that accompany cell growth, and these in turn drive, (iii) multicellular level events such as the folding and plying of cell filaments to form a mature macrofiber. Cell growth generates new material and engenders twisting of the cell cylinder along a screw axis as it elongates. The helix hand and degree of twist at the cellular level eventually dictate the hand and twist of the mature multifilament macrofiber. Although several different routes can lead to the initiation of macrofiber production, once initiated a repetitive cycle of folding and plying becomes established. The self-assembly proceeds until mechanical and geometrical factors preclude further folding cycles.
An Alternate Mechanism for Porous Si Photoluminescence: Recombination in SiHx Complexes
Authors: Prokes S. M. , Glembocki O. J. , Bermudez V. M. , Kaplan R. , Friedersdorf L. E. , Searson P. C. 
Published: March 2011

ABSTRACTPorous silicon layers have been formed which exhibit photoluminescence (PL) peaks that do not blueshift with increasing porosity. Hydrogen desorption experiments have been performed in vacuum under anneals between 230°C–390°C. Simultaneous, in-situ PL measurements show that the PL intensity decreases and disappears with decreasing hydrogen content. Infrared spectroscopy (IR) measurements also show loss of hydride species in the same temperature range. These results indicate that hydrogen is important in the PL process. We suggest that silicon hydrides are the source of PL in porous SI.
Structural Studies, Surface Properties, and Photoluminescence Behaviour of Silicon Nanocrystals
Authors: Heath J. R. , Jasinski J. M. 
Published: March 2011

ABSTRACTA method for synthesizing crystalline and/or amorphous silicon nanoparticles (3 – 30 nm diameter) is discussed. The photoluminescence (PL) behaviour of these particles is studied as crystallinity, size, surface stoichiometry, and excitation frequency are varied. Orange-red photoluminescence (PL), similar to that reported for “porous silicon,” is observed. The wavelength dependence of this PL is not a function of size, but rather particle crystallinity. A separate PL feature, near 430 nm, is reported. No size dependent effects are observed for this feature.
Photoluminescence and Structure of Chemically Etched Si
Authors: Shih S. , Jung K. H. , Hsieh T. Y. , Sarathy J. , Tsai C. , Li K.-H. , Campbel J. C. , Kwong D. L. 
Published: March 2011

ABSTRACTWe demonstrate for the first time that chemical etching of Si in HF-HNO3-based solution without applying bias can produce a room temperature photoluminescent porous Si layer. Scanning electron microscope studies reveal a surface morphology similar to that of the conventionally anodized porous Si. The formation mechanism of the chemically etched (CE) film can be explained by a local anodization concept. X-ray diffraction studies on the luminescent CE porous Si show a broad amorphous peak.
Visible Light Emission from Silicon Nanoparticles
Authors: Zhang D. , Kolbas R. M. , Mehta P. , Singh A. K. , Lichtenwalner D. J. , Hsieh K. Y. , Kingon A. I. 
Published: March 2011

ABSTRACTOrange-red light emission has been observed for the first time from crystalline silicon nanoparticles produced by gas phase synthesis in a non-thermal microwave plasma. The size and crystalline nature of the particles have been confirmed by transmission electron microscopy and X-ray diffraction. Photoluminescence at 300 K and 77 K has been measured and analyzed. The emission spectra are consistent with quantum mechanical calculations based on a quantum box.
Light-Emitting Porous Silicon in High Magnetic Fields
Authors: Zheng X. L. , Chen H. C. , Wang W. , Heiman D. 
Published: March 2011

ABSTRACTPhotoluminescence from porous silicon was studied in a helium atmosphere and at high magnetic fields. In a magnetic field, the spectral peak had a negligible shift, amounting to +0.2 ±0.5 meV at B= 18T. If quantum confinement is the major effect, then the conduction electron would be confined to a diameter of less than 3.5 nm.
R717 Glass Alteration in the Presence of Mortar: Effect of the Cement Grade
Authors: Andriambololona Z. , Godon N. , Vernaz E. 
Published: March 2011

ABSTRACTR717 glass alteration was investigated in the presence of four mortars prepared from four different cement grades: “CPA” Portland cement (mortar M1), CPA with pozzolana additive (M2), CPA with amorphous silica additive (M3) and “CLK” blast furnace slag cement (M4). Glass specimens were also altered in Volvic mineral water and in a cement effluent. Glass corrosion in the cement media was greater than in Volvic water, but well below what could be expected from the high pH (approx 12.5). The relatively low alteration was probably related to the protective action of the calcium-enriched gel layer that formed at the glass surface. The glass corrosion rate was 2 to 3 times lower with cement containing pozzolana or silica gel additives or with CLK cement than with CPA cement alone.
Microstructure of Simulated High-Level Waste Glass Doped with Short-Lived Actinides, 238Pu and 244Cm
Authors: Inagaki Y. , Furuya H. , Idemitsu K. , Banba T. , Matsumoto S. , Muraoka S. 
Published: March 2011

ABSTRACTThe microstructural changes of a simulated waste glass irradiated with doping of 238pu and 244Cm were observed by use of a preshadowed carbon replica technique in combination with scanning electron microscopy (SEM). The irradiated glass was annealed and its microstructural changes after annealing were observed by use of the sametechnique.In the glass irradiated at a dose of 2.75x1025 α-decays/m3, bubbles with a radius from 0.15μrm to 0.35μm were observed. The average bubble radius and the bubble density were 0.23μm and 1x1017 bubbles/m3, respectively. Using these observed values, the volume change of the glass resulting from the bubble formation was estimated to be + 0.51 %. This valuoof + 0.51 % was close to the volume change of the irradiated glass measured in our previous study, which suggests a large portion of the volume change by α-irradiation results from bubble formation. In the glass annealed after irradiation the average bubbleradius was observed to decrease with annealing time. The bubble radius as a function of annealing time was analyzed on the basis of the helium diffusion model with two chemicalprocesses, i.e. trapping at bubbles and re-solution from bubbles into glass matrix. The values of the diffusion coefficient of helium, the trapping parameter and the re-solution parameter, which had been obtained experimentally in our previous study on the helium release, were applied to the calculation. The calculated curve was in good agreement with the observed data.
Remote Monitoring of Molten Radioactive Glass
Authors: Schneider Alfred , Li Kang-Wen K. , Schumacher Ray F. 
Published: March 2011

ABSTRACTAn on-line method is described for the near-continuous monitoring of the composition of a molten radioactive waste glass or, alternatively, for signaling a deviation from the target composition of a waste glass. The principle of this method, proposed by A. Schneider in 1986, is founded on the relation between two specific physical properties and composition in a ternary system. Most glasses currently considered as waste forms can be represented as pseudo-ternary systems. The pair of properties especially well suited for this purpose are the viscosity and density of the molten glass. A novel viscometry method was developed which uses the remotely determined rise velocity of carefully metered gas bubbles. The monitoring method was tested successfully with simulated Savannah River waste glasses. An integrated probe was conceived for a Joule-heated melter for the on-line determination of viscosity, temperature, density, and liquid level. A computer program calculates the glass composition from the measured data, using information from a previously developed data base.
An Aluminumsilicate Ceramic Nuclear Waste Form
Authors: Loida A. 
Published: March 2011

ABSTRACTAluminum silicate based ceramics were studied as matrix materials for the immobilizationof real TRU—wastes, as well as simulated high-level and TRU—waste mixtures. As observed by XRD and electron microscopy, isolation of radionuclides is achieved either by encapsulation of radiophases by aluminumsilicate matrix phases and by incorporation into host phases in the matrix. TRU—leach rates were found to be on the order of 5*10–3 and 1*10–2 gm–2 d–1 at room temperature after one year in MgCl2 —rich salt solution. By doping the ceramic matrix with 20 weight percent PuO2 an accumulated α-dose of 8.33*109 Gy (1*1019 α-decays*g–1) was reached after 3 years. The microstructure and the lattice constants ofthe matrix phases were not affected by a-irradiation.
Europium and Cesium Ion Immobilization in Crystalline Hosts with Magnetoplumbite or Related Type Structures
Authors: Thery J. , Borel C. , Vivien D. 
Published: March 2011

ABSTRACTThis study deals with the incorporation of Eu3+ ions in aluminates with magnetoplumbite (MP) or mixed β alumina - MP type structure. The synthesis procedure is the coprecipitation from a nitric solution. Partial substitution of Eu3+ byLa3+ increases the thermal stability range of the phases. In these structuresEu3+ occupies several sites and in the case of Na+ containing phases, Eu3+ and Na+ coexist at some mirror planes. Some results concerning Cs+ ion immobilization in mixed β - MP structures, by ionic exchange in molten salt are also reported.
The Importance of Transuranium Solids in Solubility Studies for Nuclear Waste Repositories
Authors: Nitsche Heino 
Published: March 2011

ABSTRACTSolids obtained from laboratory solubility experiments in two different groundwaters from the Yucca Mountain region, Nevada, are described. The solubility study provided limiting solubility concentrations for neptunium(V), plutonium(IV), and americium(III) in groundwaters from Wells J-13 and UE-25p#l. The solubility-controlling solids are compared to relevant radionuclide compounds that are reported in the literature. The preparations and some characteristics of published solids that possibly may form in actinide-groundwater systems are described. The solids formed in the experiments are sodium neptunium(V) carbonates, polymeric Pu(IV) that contained small amounts of carbonate, and hexagonal or orthorhombic americium(III) hydroxycarbonates.
The Effects of the Degradation of Organic Materials in the Near Field of a Radioactive Waste Repository
Authors: Greenfield B.F. , Moreton A.D. , Spindler M.W. , Williams S.J. , Woodwark D.R. 
Published: March 2011

ABSTRACTUK Nirex Ltd are seeking to develop a deep underground repository for the disposal of solid ILW and LLW in the UK. The formation of water-soluble complexants from the degradation of the solid organic polymers and cellulosic materials present in such wastes may influence the solubility and sorption properties of a number of radioelements. A number of materials have been chemically degraded under alkaline, anaerobic conditions representative of the near field of the repository. Measurements of plutonium solubility in the leachates obtained show that the degradation of cellulose is of particular concern; the effects on the solubility can be several orders of magnitude greater than those of other organic materials. Products formed from the degradation of ion-exchange resins were found to have little effect. Solubilities of a number of other radioelements in aerobically degraded cellulose leachates are also given. The effect of reducing the ratio of celluloseto cement in the degradation experiments results in a decrease in plutonium solubility in the corresponding leachate. Several of the likely degradation products of cellulose have been individually synthesised including isosaccharinic acid, a key degradation product of cellulose. Enhanced plutonium solubilities have been measured in 10-3M solutions of these compounds. Sorption of plutonium onto cement from leachates obtained by the degradation of 10% cellulose in cement is reduced by about two orders of magnitude. Interaction with cement removes significant concentrations of complexants from solution. Thermodynamic modelling studies show that hydroxyl groups present in the compounds which result from the alkaline degradation of cellulose can strongly complex with plutonium.
Instant Release of14C,99Tc,90Sr and137Cs from Used Candu Fuel at 25°C in Distilled Deionized Water
Authors: Stroes-Gascoyne S. , Tait J.C. , Garisto N.C. , Porth R.J. , Ross J.P.M. , Glowa G.A. , Barnsdale T.R. 
Published: March 2011

ABSTRACTInstant-release fractions were measured for release of14C,99Tc,90Sr and137Cs from segments of clad used CANDU fuels in distilled deionized water at pH 8.5 and 25°C. Measured–instant release values, 0.002 to 0.07% for14C, 0.001 to 0.23% for99Tc and 0.0005 to 0.04% for 9 0 Sr, were one to two orders of magnitude lower than the estimated values currently used in the safety assessment of the Canadian concept of geological disposal of intact used CANDU fuel. The values for14C were also lower than values reported in the literature for PWR fuels.
Movement of the Redox Front at a Uranium Mine at POÇOS De Caldas
Authors: Romero Leonardo , Neretnieks Wars , Moreno Luis 
Published: March 2011

ABSTRACTIn an open pit uranium mine at Pogos de Caldas (PDC) in Brazil, uranium oxide has accumulated at the redox front. The redox front forms and moves by the oxidation of pyrite in the rock by oxygen infiltrating with rainwater. The rock was formed nearly 90 million years ago by volcanic activity. Between 3 and 12 km of rock has eroded away since the formation of the rock. The redox front lies between tens and several hundred meters below the ground surface. The front is uneven and locally there are redox “fingers” which extend to depths of hundreds of meters. The redox fingers are often associated with fractures or fracture zones.
U and Nd Isotopes from the New Oklo Reactor 10 (GABON): Evidence for Radioelements Migration
Authors: Hemond C. , Menet C. , Menager M.T. 
Published: March 2011

ABSTRACTNew isotopic data on daughters of transuranium elements and fission products from the Oklo reactor 10 and its surrounding provide evidences of Nd and U migrations. Whereas Nd was released only along carbonated fissures (NdFp as high as 1.048 in the fissures compared to 1.007 in the neighbouring sandstone), U has migrated through the sandstone as well (abnormal negative 235U anomalies as low as 0.714 in both fissures and surrounding sandstone). Nevertheless the released amount of radioelements is very small and visible in the drop of the concentrations between the reactor and the surrounding sandstone [8]. As consequence, a retention effect is evidenced at the reactor-sandstone boundary.
The Alligator Rivers Analogue Project - Characterisation of the Development of the Uranium Dispersion Fan
Authors: Duerden P. 
Published: March 2011

ABSTRACTThe Koongarra uranium deposit in the Northern Territory (NT) of Australia is being studied to evaluate the processes and mechanisms involved in the hydrological/geochemical alteration of the primary uranium mineralisation and model the formation of the secondary uranium orezone and the dispersion fan. The project includes studies of groundwater flow through the orebody, the chemistry of intersecting groundwaters and the uranium distribution and mineralogy of the orezones. The work has resulted in solid phase and groundwater databases, and hydrological data from field and laboratory measurements. These are being used to test a range of geochemical, hydrological and transport models.
Diffusion of Carbon Dioxide Through Upper Layers of Yucca Mountain
Authors: Singh Ajeet , Tatterson Gary , King Franklin G. , Bardakci Tevfik 
Published: March 2011

ABSTRACTThe effective diffusivities of carbon dioxide through Tiva Canyon tuff and the lower lithophysal zone of the Topopah Spring tuff (outcrop sample of the layer above the proposed nuclear repository site layer) were determined using a steady-state method (counter diffusion). The diffusivity of carbon dioxide through the Tiva Canyon and lithophysal zone tuffs increased with temperature and decreased with percent saturation. The following correlation was obtained to estimate the effective diffusivity of carbon dioxide through the Tiva Canyon tuff as a function temperature and percent saturation.De = 1.2168×10−2 − 3.7713×10−5 T + 9.9510×10−8 T2 − 4.2220×10−5 × (Percent Saturation)where De is in cm2/sec and T in K. These units hold for all other correlations in this paper.The effective diffusivity of carbon dioxide through the lower lithophysal zone of the Topopah Spring tuff (layer right above the proposed repository site) also increased with temperature and decreased with percent saturation. For this layer, the following correlation was obtained to estimate the effective diffusivity of carbon dioxide as a function temperature and percent saturation.De = − 1.119×10−3 + 1.2512×10−5 T + 1.8288×10−9 T2 × 2.0725×10−5 × (Percent Saturation)
Applications of the Carbon-14-Polymethylmethacrylate (PMMA) Impregnation Method in Studies on Porosity and Matrix Diffusion
Authors: Hellmuth K-H. , Shtari-Kauppi M. , Lindberg A. 
Published: March 2011

ABSTRACTWe are presenting applications of a new technique for the study of porosity and diffusivity in rocks employing impregnation with labeled polymethylmethacrylate. We studied samples of different rock types and rock that has undergone various types of alteration. We have focussed special attention on fissures and fissure fillings. Association of porosity with certain mineral phases has been addressed. The spatial distribution of rock porosity exhibits a great diversity. It is a rock-typical parameter. Altered rock is, usually, characterized by inhomogenities in porosity and anisotropy of migration pathways.
Long Term Field Leaching Studies of Simulated Nuclear Waste Glass in Granite and Salt
Authors: Schulz R.L. , Clark D.E. , Lodding A.R. , Wicks G.G. 
Published: March 2011

ABSTRACTField leaching studies were carried out in granite at the Stripa site in Sweden and also in salt in the Materials Interface Interaction Test at the Waste Isolation Pilot Plant (MIIT/WIPP) in New Mexico. The goal of these studies is to assess the durability of various glass compositions engineered to isolate high-level nuclear waste from the biosphere. An additional goal of the MIIT study is to determine how the glasses interact with a wide array of proposed materials that may be a part of the multi-barrier waste package. These substances include metals, geological host specimens,, as well as engineered backfill and overpack materials.Two year data on the SRLY (165/TDS) glass compositions has been extracted from both studies (Stripa and WIPP/MIIT) and five year data has recently become available from the MIIT study. Results from SEM/EDS, SIMS and FTIRRS analyses on glass/glass interfaces are presented in this paper.
Transient Diffusion from the Near-Field, A 3-D Model
Authors: Bengtsson A. , Grundfelt B. , Widén H. 
Published: March 2011

ABSTRACTA study of near-field radionuclide migration is presented. The study [1] has been performed in the context of the SKB91 study which is a comprehensive performance assessment of disposal of spent fuel. The objective of the present study has been to enable the assessment of which nuclides can be screened out because they decay to insignificant levels already in the near-field of the repository.A numerical model has been used which describes the transient transport of radionuclides through a small hole in a spent fuel canister imbedded in bentonite clay into a fracture in the rock outside the bentonite. Calculations for more than twenty nuclides, nuclides with both high and low solubility, have been made. The effect of sorption in the bentonite backfill is included. Materials data for bentonite where taken from [2]. The size of the penetration hole was assumed to be constant up to the time when the calculations were terminated, 500 000 years after the deposition. The mass transport rate is controlled by diffusion. The model is three dimensional.This paper describes the geometry of the modelled system, the assumptions concerning the transport resistances at the boundary conditions, the handling of the source term and obtained release curves.
Release of Radionuclides from the Near Field by Various Pathways. The Influence by the Sorption Properties in the Near Field.
Authors: Romero Leonardo , Neretnieks Wars , Moreno Luis 
Published: March 2011

ABSTRACTRadionuclides from a damaged canister for spent fuel will leak out through a damage in the canister wall and spread through the surrounding backfill. They will further migrate into water bearing fractures in the rock, up through the backfill into the damaged zone around the drift and into the drift itself. Some substance may also diffuse through the rock to adjacent fracture zones. Underway the nuclides will sorb on the materials along the transport paths. This very complex and variable transport geometry has been modelled using a compartment model which is based on simplifying a full 3 dimensional integrated finite difference model. The simplifications are supplemented by introducing analytical and semianalytical solutions at sensitive locations such as entrances and exits from damages and fractures and in the flowing water. The model has been tested against full 3D solutions with good results. Sample calculations are presented and discussed for a nuclide with the chemical properties of Pu-239.
The Effect of Precipitation Fronts Induced by Radionuclide Chain Decay and Elemental Solubility Limits on Near-Field Mass Transport
Authors: Worcan Karen J. , Apted Michael J. 
Published: March 2011

ABSTRACTThe formation and impact of precipitation fronts on the diffusional mass transport of radionuclides from a high-level nuclear waste canister through a bentonite buffer has been investigated in a series of numerical simulations. The precipitation fronts arise from chain decay and ingrowth, coupled with differences in elemental solubility limits and sorption properties. The fronts influence particularly the behavior of uranium, plutonium and neptunium isotopes. The isotopic concentration profiles across the buffer differ considerably from results obtained with models that employ elemental solubility limits simply as a boundary condition at the waste-bentonite interface.
A Possibility for Hlw Disposal in Very Deep Boreholes
Authors: Byalko A.V. 
Published: March 2011

ABSTRACTRecently we proposed [1] that high-level nuclear waste be deposited in very deep boreholes, filled with a substance of low melting temperature, of high density, not generating gases and water-insoluble.The first paper outlined nuclear waste disposal in deep boreholes, discussions of physical and chemical processes in a filled borehole and preliminarily comments on the ecological safety of the disposal. The given paper covers some economical aspects of the new proposal as well as the principal steps of implementation of the R&D program.