bluuebunny/crossref_metadata_2025_split huggingface dataset:
Synthesis and Characterization of Periodic Polypeptides Containing Repeating —(AlaGly)xGluGly— Sequences
Authors: Deguchi Yoshikuni , Krejchi Mark T. , Borbely Janos , Fournier Maurille J. , Mason Thomas L. , Tirrell David A. 
Published: March 2011

AbstractWe have expressed in E. coli a series of periodic polypeptides represented by sequence 1. Our objective has been an understanding of the role of chemical sequence in determining the chain folding behavior of periodic macromolecules. Molecular organization has been examined by infrared spectroscopy and 1H and 13C NMR methods and a preliminary model of the folded structure has been developed.
Processing Natural and Reconstituted Silk Solutions Under Equilibrium and Non-Equilibrium Conditions
Authors: Viney Christopher , Huber Anne E. , Dunaway Dwayne L. , Case Steven T. , Kaplan David L. 
Published: March 2011

AbstractA variety of natural silk secretions (from spiders, silkworms and aquatic insect larvae), and also reconstituted silk solutions, are able to form a nematic liquid crystalline phase. The anisotropic structures that self-assemble in this phase are formed from the isotropic phase by aggregation of molecules, rather than by individual molecules undergoing a conformational change to a rod-like form. This enables the molecules to retain their solubility in water while, simultaneously, the viscosity of the solution is reduced. The liquid crystalline phase is stable under a wide range of equilibrium conditions, but its ability to form is sensitive to the rate at which the initially isotropic solution is allowed to dry. The kinetics of phase transitions exhibited by solutions of silk proteins must be taken into account if solutions of silk fibroin are to be successfully processed in vitro.
Chiral Symmetry Breaking and Pattern Formation in Two-Dimensional Films
Authors: Selinger Jonathan V. , Wang Zhen-Gang , Bruinsma Robijn F. 
Published: March 2011

AbstractThin films of organic molecules, such as Langmuir monolayers and freely suspended smectic films, can exhibit a spontaneous breaking of chiral symmetry. This chiral symmetry breaking can occur through at least three possible mechanisms: (1) the relation between tilt order and bond-orientational order in a tilted hexatic phase, (2) a special packing of non-chiral molecules on a two-dimensional surface, and (3) phase separation of a racemic mixture. Because the chiral order parameter is coupled to variations in the direction of molecular tilt, chiral symmetry breaking leads to the formation of patterns in the tilt direction with one-dimensional or two-dimensional order. Using a Landau theory, we investigate these patterns and predict the critical behavior near the chiral symmetry breaking transition.
Genetic Coding in Biomineralization of Microlaminate Composites
Authors: Morse Daniel E. , Cariolou Marios A. , Stucky Galen D. , Zaremba Charlotite M. , Hansma Paul K. 
Published: March 2011

AbstractBiomineralization is precisely controlled by complex templating relationships ultimately encoded in the genes. In the formation of the molluscan shell, polyanionic pleated sheet proteins serve as templates for the nucleation and epitaxial growth of calcium carbonate crystalline domains to yield microlaminate composites of exceptional strength and crystal ordering. The strength and fracture-resistance of these composites far exceed those of the minerals themselves, as a result of both the capacity for flexible deformation of the organic matrix layers and the retardation of crack propagation at each mineral-organic interface. The basic principles controlling low temperature biosynthesis of these materials thus are of both fundamental and applied importance. The abalone shell consists of microlaminates with a remarkable regularity of lamina thickness (ca. 0.5 micron), the formation of which defies present understanding. We have found that shells of abalone larvae formed prior to metamorphosis contain only aragonite, whereas the adult shell made after metamorphosis contains both aragonite and calcite. This transition is accompanied by a switch in genetic expression of the template proteins, suggesting that the premetamorphic protein may serve as a template for aragonite nucleation and growth, while template proteins synthesized after metamorphosis may direct crystallization of calcite. These analyses are based on improvements we recently reported for the detection and purification of proteins from the demineralized shell matrix. Genetic cloning experiments now in progress are aimed at discovering additional protein sequences responsible for the programmed control of crystal phase termination, since it is the termination and reinitiation of mineralization that is responsible for the regularity of highly ordered microlaminates produced in nature.
Characterization of New Ionically Conducting Peo-Based Networks by Diffusion, Elasticity Modulus and Ionic Conductivity Measurements
Authors: Cheradame Herve , Desbat F. , Mercier-Niddam P. , Boileau S. 
Published: March 2011

AbstractIonically conducting materials containing PEO were prepared from telechelic di(methyl-diethoxy-silane) PEO, synthesized by the hydrosilylation of telechelic diallyl-PEO with methyldiethoxysilane. The network is obtained by the usual sol-gel chemistry. Then, it is filled with LiClO4 by diffusion of the salt and further drying. A comparison is made with the same kind of materials crosslinked using urethane chemistry. Diffusion studies show that the diffusion coefficient of solvent is similar for both types of materials, whilst the ionic conductivity is higher for the networks crosslinked with siloxane bonds. An experiment of diffusion of LiClO4 without solvent showed that this salt has a diffusion coefficient of the order of 2.10-8 cm2.sec-1 at 34°C. The conductivity calculated from this determination is compatible with the mechanism of lithium cation transport by the diffusion of salt molecules. Elasticity modulus measurements show that the salt aggregates are essentially located within the crosslinks at low concentration, but also in the PEO chains for salt concentrations higher than 1 mol/l.
Ion Insertion in Highly Conjugated Polypyrrole
Authors: Skaarup S. , West K. , Zachau-Christiansen B. , Careem M.A. 
Published: March 2011

AbstractPolypyrrole has been synthesized electrochemically at current densities from 6.4 μA/cm2 to 3.84 mA/cm2. Low current density is crucial to the formation of a highly conjugated modification as shown by the low value of the π-π* transition energy (2.83 eV). The low current form displays a cyclic voltammogram with a detailed structure with narrow peaks. Following the presence and evolution of the peaks is a powerful diagnostic method of monitoring the state of the polymer. The solvent (water-free propylene carbonate or acetonitrile) can be reversibly exchanged during oxidation/reduction cycling and has little effect on the nature of the polymer formed, but influences the properties during the doping process greatly. In contrast, the ion present during polymerization (ClO4 or CF3SO3) seems to irreversibly influence the morphology of the film. The highly conjugated, low current form is to be preferred as a well-defined point of reference close to the intrinsic properties of pure polypyrrole.
Variable Microwave Transmission Attenuation by Conducting Polymers
Authors: Rupich Martin W. , Liu Ying Ping , Kon Alan B. 
Published: March 2011

AbstractThe microwave properties of polypyrrole, polyaniline and poly(3-hydroquinonylpyrrole) films were examined as a function of doping level, conductivity, counter anion and thickness. The microwave transmittance of the polymer films was varied from less than 10% to greater than 90%; by oxidizing and reducing the polymers. The potential use of conductive polymers in the design of an electromagnetic modulator for the tunable attenuation of microwave radiation is described.
Structure and Dynamics of Network Glasses at Large Positive and Negative Pressures - a Molecular Dynamics Study
Authors: Vashishta Priya , Kalia Rajiv K. 
Published: March 2011

AbstractUsing the molecular dynamics (MD) method, the nature of crystalline fragments in SiSe2 glass (a-SiSe2) at normal pressure, structural transformation and the loss of intermediate range order in SiO2 glass at very large positive pressures, and the modification of SiO2 glass network at very large negative pressures have been investigated. Implementations of the MD algorithm on the Connection Machine and Intel iPSC/860 machine are discussed.
Structural and Dynamical Correlations in Stishovite and High Density Silica Glass
Authors: Jin Wei , Kalia Rajiv K. , Vashishta Priya 
Published: March 2011

AbstractPressure-induced structural transformation from tetrahedral to octahedral coordination and the destruction of intermediate-range order (IRO) are studied in silica glass (a-SiO 2) using the molecular-dynamics (MD) method. Changes in the position and height of the first sharp diffraction peak (FSDP) in the static structure factor, bond lengths, coordination numbers, bond-angle distributions, and statistics of rings are investigated as a function of density. Modifications of the vibrational density of states and participation ratio are also discussed.
Cation Ordering in Brownmillerite-Perovskite Intergrowth Structures
Authors: Thomas Julie K. , Krause Wendy E. , Loye Hans-Conrad Zur 
Published: March 2011

AbstractBrownmillerite-perovskite intergrowths of the type m(A2B2O5)*n(ABO3), where m = 1 and n = 1, were investigated with respect to cation ordering. It was found that Sr31n2ZrO8, Sr31n2HfO8, Ba3Sc2TiO8 and Ba31n2TiO8 form in a disordered cubic structure, while Sr3Sc2ZrO8 and Ba3Sc2ZrO8 form an ordered cation arrangement. The Arrhenius plots of the oxygen ion conductivity of Ba3Sc2ZrO8, Sr31n2HfO8, and Ba31n2TiO8 contain discontinuities that appear to be caused by an oxygen vacancy order-disorder transition. High temperature powder-X ray diffraction did not show any evidence for cation ordering that might otherwise have created the changes in activation energy in the conductivity plots.
Electrical Behavior of Ca(UO2PO4)2.10.5H2O Films in Contact with the Generating Electrolytes
Authors: J.R. Ramos Barrado , J Benavente , S. Bruque , M. Martinez 
Published: March 2011

AbstractThe electrical response of a self -supported film (CaUP) in contact with different electrolyte media was studied by impedance spectroscopy for electrolyte concentrations ranging between 10−4 M and 10−2 M.The film was placed separating two aqueous solutions of the generating electrolytes, at the same concentrations, and two systems: i) UO2(NO3)2/CaUP/H3PO4; ii)Ca(NO3)2/CaUP/H3PO4, were considered.The film equivalent circuit and characteristic parameters (Rf and Wf) for both systems were determined. Result show an important dependence of Rf values with concentration, whlckis related to the electrolyte invasion into the film matrix, but no significant changes in Wf values were found. Due to the film nature, the ionic diffusion process associated to this circuit element is mainly attributed to the protons.
Dielectric Properties of the Solid Solution Formed in the System LiTao3 - “Li2MnO4 ”
Authors: Villafuerte-Castrejón M.E. , Pineda J.L. , Huanosta A. 
Published: March 2011

AbstractImpedance spectroscopy methods were used to characterize the electrical properties of the solid solution formed in the system LiTaO3 -“Li2Mn4O9”.Involved parameters were calculated using equialent circuits. Activation energy values were decreasing from around 1.3 eV for lowest concentration of Mn4+ until around 0.8 eV for higher Mn4+ contents. Results will be discused in terms of Z' vs Z" and Arrhenius plots. The ferroelectric character was stablished using the real part of the permittivity against temperature. Curie temperature values Tc were found decreasing toward higher concentration of Mn4+ in the range 630-580°C.
Femtosecond Spectroscopy of Ferroelectric Perovskites: Explanation of Anomalous Polariton Dynamics in Lithium Tantalate
Authors: Wiederrecht Gary P. , Dougherty T. P. , Dhar L. , Nelson K. A. 
Published: March 2011

AbstractTime resolved impulsive stimulated Raman scattering (ISRS) is used to characterize the lowest frequency A1 phonon-polariton mode in lithium tantalate. The anomalously high and wavevector-dependent damping rates observed are explained in terms of coupling of the polariton to a weakly Raman-active relaxational mode and to two heavily damped vibrational modes. The dynamics of the relaxational mode are explored further through temperature dependent ISRS studies. Femtosecond optical pulse shaping is used for multiple pulse ISRS at temperatures lower than 120K where single pulse excitation led to photorefractive damage.
In Situ X-Ray Investigation of Novel Protonic Conductors
Authors: Shekhtman Veniamin Sh. , Dilanyan Ruben A. 
Published: March 2011

AbstractSystematic X-ray diffraction studies of thermal expansion in CsHSO4, CsDSO4, RbHSO4 and Rb3H(SeO4)2 crystals have been carried out. An analysis of the results showed that the fast protonic conductivity is closely connected with the characteristic features of the structure, symmetry and orientation of hydrogens bonds in the crystals of MeXAO4 (Me=NI4, Rb, Cs; X= D,H; A= S,Se) family.
Fundamental Study on the Solidification of Cs+ and Sr2+ with Hydrous TiIV Oxide Modified with Si and Zr
Authors: Inoue Y. , Yamazaki H. , Erza R. 
Published: March 2011

ABSTRACTFundamental data are provided for the potential use of hydrous TiIV-si oxide (TS) and hydrous TiIV-Zr oxide (TZ) as the solidification media of radioactive Cs+ and Sr2+. The sorption capacity for Cs+ and Sr2+, at various conditions, and the structure and the composition of the exchangers in these ionic forms, at high temperature, were investigated, followed by measuring the leaching rate from the calcined exchangers into water at room temperature. TS uptakes more Cs+ and Sr2+ than TZ does. The leaching rate from calcined TS is much lower than that from calcined TZ, due to the formation of titanium silicates of Cs+ or Sr2+. Based on these results, TS is considered to be superior to TZ, in sorption capacity, and the fixation capability of Cs+ and Sr2+, on the exchanger matrix.
Dissolution of R7T7 Glass in Static and Flowing Conditions: Influence of Si Diffusion Mechanism in the Leached Layer
Authors: Delage F. , Larche F. , Vernaz E. 
Published: March 2011

ABSTRACTLeach tests with R7T7 nuclear waste glass in distilled water were conducted at 50 and 90°C under static and slow flowing conditions, with an SA/V ratio of 50 m−1. A computer model for glass dissolution (LIXIVER) Was used to interpret the experimental data. This mechanistic model is based on a combination of the first-order law governing surface reactions, the silicon mass transport equation for the interstitial solution in the alteration film, and an empirical law for partial silicon retention in the alteration layer. The LIXIVER model satisfactorily accounts for most of the experimental results. The importance of the silicon diffusion mechanism in the diffusion layer is stressed. Values are indicated for the apparent silicon diffusion coefficient, Dsi, which ranged from 10−16 to 10−14 m2·s−1 at 50°C, and from 10−15 to 10−13 m2·s−1 at 90°C.
High-Level Nuclear-Waste Borosilicate Glass: A Compendium of Characteristics
Authors: Cunnane J. C. , Bates J. K. , Ebert W. L. , Feng X. , Mazer J. J. , Wronkiewicz D. J. , Sproull J. , Bourcier W. L. , Mcgrail B. P. 
Published: March 2011

ABSTRACTWith the imminent startup, in the United States, of facilities for vitrification of high-level nuclear waste, a document has been prepared that compiles the scientific basis for understanding the alteration of the waste glass products under the range of service conditions to which they may be exposed during storage, transportation, and eventual geologic disposal. A summary of selected parts of the content of this document is provided.Waste glass alterations in a geologic repository may include corrosion of the glass network due to groundwater and/or water vapor contact. Experimental testing results are described and interpreted in terms of the underlying chemical reactions and physical processes involved. The status of mechanistic modeling, which can be used for long-term predictions, is described and the remaining uncertainties associated with long-term simulations are summarized.
Borate Substituted Ettringites
Authors: Csetenyi Laszlo J. , Glasser F. P. 
Published: March 2011

ABSTRACTThe setting of cement is adversely affected by soluble borates. To reduce interference, the extent to which borate can be insolubilized has been investigated. One specific mechanism of insolubilization is by inclusion into ettringite. Ettringite, Ca6Al2(SO4)3(OH)12·26H2O, is a normal and stable constituent of Portland cement. It has an open but non-zeolitic framework. Borate can substitute partially or fully for sulfate.Formation conditions, solubility and stability of borate ettringites, Ca6Al2(BO4)2-4(OH,O)12·26H2O, are characterised using XRD, IR, DTA, and SEM.The potential durability of borate ettringites in a repository environment have been assessed by exposing it to Na-sulfate and Na-carbonate attack at different concentrations. Ion exchange occurs; back substitution of borate by sulfate is incomplete; high carbonate concentrations can, however, decompose borate ettringite.On heat treatment up to 85°C the crystalline morphology and the OH arrangement of the structure are altered, but the X-ray powder pattern, and hence its structural framework are largely unaffected.It is concluded that ettringite has potential to reduce the solubility of borate.
Mobility of Chelated Radionuclides in Engineered Concrete Barriers
Authors: Dicke Craig A. , Smith Robert W. 
Published: March 2011

ABSTRACTConcrete is a major component in many low-level radioactive waste (LLW) disposal facilities. The use of concrete is widespread because of its physical and structural properties and because it provides geochemical control on metal and radionuclide releases. Organic compounds are often disposed with radionuclides in LLW disposal facilities. Interactions between radionuclides and chelating agents must be evaluated to estimate mobility of radionuclides in concrete vaults. This paper quantifies the effects of two common organic components [citric acid and ethylenediaminetetraacetic acid (EDTA)] on radionuclide mobility in concrete barriers by using equilibrium geochemical calculations.Equilibrium speciation calculations indicate that some radionuclides are chelated in groundwater (pH 7) but are destabilized in the highly alkaline (pH 13) concrete pore fluids. Radionuclides complexed by EDTA and citrate are replaced by calcium in the concrete pore fluids. In addition, the citrate nuclide complex reacts to form uncomplexed citrate in concrete pore fluids. The chemical performance of concrete LLW disposal facilities should not be compromised by small amounts of chelating agents disposed with some radionuclides. However, EDTA may form significant nickel and cobalt complexes above the pH important in the long-term service life of concrete barriers.
The Radiation Stability of Ground Granulated Blast Furnace Slag/ordinary Portland Cement Grouts Containing Organic Admixtures
Authors: Palmer John D , Fairhall Graham A 
Published: March 2011

ABSTRACTAt the British Nuclear Fuels (BNFL) Sellafield reprocessing plant in the United Kingdom, cement grouts based on ground granulated blast-furnace slag (BFS) and ordinary Portland cement (OPC) are used extensively for immobilising radioactive wastes. These grouts have excluded organic admixtures in order to reduce process complexity and uncertainties, regarding the performance of organic admixtures with BFS/OPC grouts, particularly under irradiation.This study has investigated the effects of sulfonated melamine formaldehyde and naphthalene condensates on grout properties. The results show grout settlement and strengths increase on addition of additives, with the additives remaining largely in the pore solution. Under irradiation the additives breakdown liberating hydrogen and carbon dioxide. Strength and product dimensions are unaffected by irradiation.
Ancient Metallurgy and Nuclear Waste Containment
Authors: Goodway Martha 
Published: March 2011

ABSTRACTArchaeological artifacts of glass, ceramic, and metal provide examples of long term durability and as such have been surveyed by the nuclear agencies of several countries as a possible guide to choices of materials for the containment of nuclear waste. In the case of metals evaluation is difficult because of the loss of many artifacts to recycling and corrosion processes, as well as by uncertainty as to the environmental history under which the remainder survived. More recently the study of ancient metallurgy has expanded to included other materials associated with metals processing.It is suggested that an impermeable ceramic composite used in ancient metals processing installations should be reproduced and tested for its resistance to radiation damage. This material was synthesized more than two millennia ago and has a proven record of durability. These installations have had no maintenance but are intact, some still holding water.
Research Needs in HLW Disposal Programmes
Authors: Hadermann Joerg , Mccombie Charles 
Published: March 2011

ABSTRACTA repository for high-level radioactive waste (HLW) will not be in operation in Switzerland (or elsewhere) before the turn of the century. However, extensive investigations for disposal in specific regions or sites are ongoing and formal safety analyses have been performed in many countries. Broadly speaking, these analyses show the feasibility of the chosen options for deep geological disposal. At the present stage, before a licensing application, performance assessments have another important application: to identify further needs to improve system understanding, and to guide the necessary research activities. Performance assessments are thus indispensable tools for focussing in on research requirements and discriminating between necessary, and merely desirable or interesting, research projects.Based on experience from assessments of HLW disposal in the crystalline of Northern Switzerland (Project Gewähr, KRISTALLIN-I) we consider in detail the chain of models resulting from a scenario analysis. For each model block (e.g., engineered barrier performance, hydrology, radionuclide transport), the adequacy of understanding is addressed and the necessary research needs pointed out. These needs cover a wide span, from a requirement for more reliable input numbers (example: long-term corrosion rate of glass) to a better understanding of important features (example: excavation-damaged-zone) and key mechanisms (example: sorption).