bluuebunny/crossref_metadata_2025_split huggingface dataset:
Photoexcitations in Poly(2,5-Thienylene Vinylene)
Authors: Samuel I. D. W. , Brassett A. J. , Colaneri N. F. , Lawrence R. A. , Bradley D. D. C. , Meyer K. E. , Friend R. H. , Murata H. , Tokito S. , Tsutsui T. , Saito S. 
Published: March 2011

ABSTRACTPoly(2,5-thienylene vinylene), PTV, can be conveniently prepared via a precursor route to give coherent films suitable for optical measurements. Photoexcitation above the band gap at 1.8 eV gives rise to two transient absorption peaks at 0.44 eV and 1.0 eV that are associated with bipolarons that live for times of order a few ms at 80 K. Photoluminescence, comparable in intensity to the Raman scattering, is found at energies above the band edge, and we assign this to a hot recombination process. Pump and probe measurements of the induced bleaching at 2 eV show a very fast rise and initial fall time, which are within the 100 fsec resolution of the measurement.
Theoretical Calculations of the Nonlinear Dielectric Function of Inhomogeneous thin Films
Authors: Risser Steven M. , Ferris Kim F. 
Published: March 2011

ABSTRACTThe dielectric function of inhomogeneous materials is composed of linear and nonlinear responses which are sensitive to the film microstructure as well as the intrinsic properties of the materials. We have developed a method to self-consistently determine the linear and non-linear contributions to the dielectric function of films with random microstructure. This method is based upon a numerical solution of the general electrostatic equations and is applicable to arbitrary shapes and orientations of model defects. This method provides near exact solutions to the linear response of the dielectric function. We have shown that the nonlinear part of the dielectric function is extremely sensitive to the void shape and void fraction.
Organic Polyradical Models for Organic Magnetic Materials
Authors: Modarelli David A. , Rossitto Frank C. , Minato Masaki , Lahti Paul M 
Published: March 2011

ABSTRACTA variety of model organic high spin molecules based upon coupled phenoxy and phenylnitrene systems has been examined by semiempirical MO-CI theory. Experimental methodology using photochemical and thermal methods in solution and solid phases to generate and study phenoxy groups for investigation of these models is presented.
An Electron Microscopy Study of the Microstructure and Microarchitecture of theStrombus GigasShell
Authors: Laraia V.J. , Aindow M. , Heuer A.H. 
Published: March 2011

AbstractA scanning and transmission electron microscopy study is presented of the microstructure of theStrombus gigasshell. The heirarchical nature of this crossed-lamellar structure and the defect content of the mineral component are described. This mineral component consists of small single crystal grains of aragonite, the metastable orthorhombic polymorph of CaCO3. The habit and morphology of the grains discussed here have not been determined previously. The observed habit and defect structure suggest that the organic matrix exerts a high degree of control over the crystal growth of the mineral phase and is responsible for the long range order in the microarchitecture. Electron beam heating of the mineral component leads to certain phase changes and these are discussed.
The Microindentation Behavior of Several Mollusk Shells
Authors: Laraia V. J. , Heuer A. H. 
Published: March 2011

AbstractAn investigation of the relationship between structure and mechanical behavior is reported for mollusk shells employing foliated, nacreous, and crossed-lamellar structures by microindentation in the Knoop and Vickers geometries. Indentation damage zones develop crack systems that reflect the micro-architecture. For the crossed-lamellar structure, the system of cracks about the indentation normally developed in a brittle material is suppressed. Previous reports that shells are harder than the corresponding minerals, calcite and aragonite, are confirmed, but it is found that this effect can be strongly dependent on orientation. This anomalous hardness is not an artifact of the identation test technique, since scratch tests confirm the relative hardness of shell over the mineral. It is suggested that microstructural organization is of central importance in producing this hardness, as opposed to intrinsic properties of the mineral or matrix phases.
Quantized Diameters in Self-assembled Cyundrical Aggregates of Chlorophylls
Authors: Worcester D. L. , Michalski T. J. , Bowman M. K. , Katz J. J. 
Published: March 2011

AbstractNeutron small-angle scattering measurements of several different chlorophylls hydrated in deuterated octane-toluene mixtures show that long, hollow cylinders of aggregated chlorophyll are formed. Clear secondary maxima are present in the scattering, and the cylinder diameters are well determined, but depend on the type of chlorophyll. Chlorophyll-a and Bacteriochlorophyll-a were particularly studied, and several samples of each have been measured. Other chlorophylls have also been studied. The results provide strong evidence that chlorophyll cylinders are only certain sizes, with diameters very nearly in the ratio of small integers. Thus, the cylinder diameters appear to be quantized. Neutron scattering results that further test this quantization property are presented here, together with a proposal for the stereochemical features of chlorophyll aggregation which account for the diameter quantization.
Growth-Packed PPT-A Fiber for the Replacement of Native Asbestos
Authors: Yoon Han Sik 
Published: March 2011

AbstractA now type of crystal that can be defined as a “gel crystal” was first made with oligomeric poly-p-phenyleneterephthalainide (PPT-A), associating a large amount of dimethylacetamide (DMAc) liquid molecules, in which catalytic amount of heterocyclic tertiary amine, coupled with alkali metal cations or phosphoric triamidos are incorporated. Under mechanical orientation of the growing PPT-A, before gelation of the reaction “mixture, a hark agar-like gel crystal is formed. It shows a strong optical birefrin,- gence with four clear extinction positions under crossed polarizers when the gel was sectioned either along the direction of PPT-A orientation or perpendicular to it. When the gel formed without orientation it exhibitil speckled birefringence due to a large number of tiny spherulitic crystallites. The degree of crystalline order was similar to that of lyotropic, nematic liquid crystals when evaluated from X-ray diffractograins. The same type of gel crystals with extinction positions were observed in animal and vegetable tissues. It is assumed that the gel crystal has a threedimensionally ordered molecular network structure in which oligo-PPT-A's are arranged end-to-end in parallel lines. The lines are connected laterally, to form sheets, by DMAc bridges that are linear associations of DMAc molecules, which are connected to the oligo-PPT–A at the CONH groups. PPT-A molecular growth and self-ordering occurs within this gel crystal. A similar process gives rise to wool, cotton and ol.her fibrous biological materials.The high molecular weight PPT-A fiber thus grown in the gel crystal is constructed with numerous unit fibrils which connect themselves in a three-dimensional network, that resembles native flax or ranie fibers. The molecular growth of PPT-A in the gel crystal reaches ultra high molecular weight that can rarely be attained in ordinary solvent polyinerization. The gel state of PPT-A fibrils are initially formed spontaneously by selfsubdivision of the gel crystal after the molecular growth of PPT-A. Solid fibrils and fibers are finally fortoed by removing DMAc. The PPT-A gel fibrils thus formed resemble closely “the nascent fibril” of cellulose, and the microstructure and morphology of PPT-A fibrils are consequently very similar to those of native cellulose. The thickness of PPT-A fibrils can readily be controlled by the temperature in the gel crystal before fibril formation. The direction of the fibrils depends on the initial orientation of oligo-PPT-A's immediately before the formation of the gel crystal.This growth-packed PPT-A fibril, that can be produced by a one step chemical reaction, is considered as a good candidate for the replacemerit of native asbestos, because of the lower production cost, microfibrillation property, and inherently high heat-resistance.
Elastomeric Polypeptide Biomaterials: Structure and Free Energy Transduction
Authors: Urry Dan W. 
Published: March 2011

AbstractThe primary, secondary, tertiary and quaternary structures are presented and discussed for elastomeric polypeptides capable of undergoing inverse temperature transitions, that is, these polypeptides fold with the extrusion of water on raising the temperature through a transition. The elastomeric polypeptides, which are comprised of repeating peptide sequences, appear to be dominantly entropic elastomers. As these elastomers exhibit preferred secondary, tertiary and quarternary structure, they are not properly characterized as the random chain networks commonly ascribed to entropic elastomers. Instead, a mechanism of damping of internal chain dynamics on extension is described and referred to as the librational entropy mechanism of elasticity. Indeed, there are emerging a set of structural concepts for elastomeric polypeptides.Of particular interest is that these elastomers are capable of exhibiting free energy transduction, e.g., thermomechanical and chemomechanical. A principle is stated for thermomechanical transduction and a postulate is given for chemomechanical transduction which is supported by prediction and experimental verification. The underlying mechanism is considered to be an aqueous(hydration) mediated apolar(hydrophobic)-polar interaction free energy which arises out of a competition between apolar and polar groups for limited waters of hydration. In general, there emerges a simple structural perspective of free energy transduction in elastomeric polypeptide biomaterials that involves thermal, mechanical or chemical means of altering the equilibrium between folded and unfolded states, where the folded states are dynamic helices called β-spirals with dominantly hydrophobic intramolecular interturn contacts and the unfolded states have the hydrophobic groups exposed to water.
The Influence of Salivary Proteins on the Growth, Aggregation and Surface Properties of Hydroxyapatite Particles.
Authors: Johnsson M. , Richardson C. F. , Bergey E. J. , Scannapieco F. A. , Levine M. J. , Nancollas G. H. 
Published: March 2011

AbstractThe adsorption and crystal growth effects of salivary cystatin SA-II and non-glycosylated amylase on hydroxyapatite have been compared to the effects of the salivary cystatins SA-I and SA-III. Amylase was the least active HAP crystal growth inhibitor and adsorbed weakly to HAP. Although the three cystatins were active inhibitors of hydroxyapatite crystal growth in supersaturated solution, their affinities showed marked differences.
Bone Formation: The Rules for Fabricating a Composite Ceramic
Authors: Caplan Arnold I. 
Published: March 2011

AbstractBone, teeth and shells are complex composite ceramics which are fabricated at low temperature by living organisms. The detailed understanding of this fabrication process is required if we are to attempt to mimic this low temperature assembly process. The guiding principles and major components are outlined with the intent of establishing non-vital fabrication schemes to form a complex composite ceramic consisting of an organix matrix inorganic crystalline phase.
Air Force Applications of Biotechnology
Authors: Hedberg Frederick L. 
Published: March 2011

AbstractThe Air Force has been supporting a number of research and development programs directed at exploring the possibility of utilizing biological processes for the preparation and modification of materials with aerospace applications. Areas addressed by these programs include biosynthesis of key chemical intermediates, biological removal of materials such as paint or sealants, biodegradation for environmentally safe destruction of wastes, and biological leaching and accumulation of strategic metals, utilization of naturally occurring materials with electrooptical properties, and modeling the design of natural structures with synthetic materials.
Multifunctional Macromolecules – Some Device Options
Authors: Worboys Michael R. , Griffith Michael S. , Davies Nicholas A. 
Published: March 2011

AbstractMultifunctional macromolecules can, in principal, combine a number of active material functions such as optical nonlinearity and photoconductivity in one material. Multifunctionality may offer new options for device fabrication and implementation. However, in practice the implementation of a device which uses a range of material properties such as piezoelectricity and photoconductivity in a single layer of active material is some distance away. This is in part due to the difficulty of optimising a material simultaneously for two separate properties. Therefore the approach we have taken is to identify device configurations which rely on multilayers, each separate layer providing one of the active device functions. Initial results on the fabrication and characterisation of two such proof of principle devices, a light modulated deformable mirror and a light modulated electro-optic layer, are described.
Protective Coatings for High Temperature, Light Weight, Structural Applications
Authors: Covino J. , Klemm K. , Dykema J. 
Published: March 2011

AbstractProtective coatings for both titanium-aluminum (Ti-Al) alloys and for carbon-carbon (C-C) composites have been synthesized and characterized for high temperature, light weight, structural applications. Coatings of choice must show protection against oxygen and hydrogen in severe environments. Aluminum-silicate glass ceramics were chosen as coating candidates because they are stable to temperatures of 1500°C, are nonreactive to oxygen, and have minimal reactivity with respect to hot hydrogen.
Nanodesigning of Multifunctional Ceramic Composites
Authors: Liu J. , Sarikaya M. , Shih W. Y. , Shih W.-H. , Aksay I. A. 
Published: March 2011

AbstractNanodesigning of multifunctional ceramic composites with colloids is discussed from a fundamental point of view. We start with one-component systems, where packing density is the primary concern. Then we extend the discussion to binary systems and deal with the problem of homogeneity. We show that the structure is controlled by the nature of bonding between the particles and by the particle-particle interaction. Surfactants are used to modiy these properties, by, first, protecting the active particle surfaces to prevent solid bond formation, and, second, altering the interparticle interaction to provide a “lubricating” effect. In weakly attractive multicomponent systems, not only are we able to achieve high-density packing through restructuring, but we can also control the scale of homogeneity.
Periodic Area Minimization Surfaces in Microstructural Science
Authors: Thomas Edwin L. , Gido Samuel P. 
Published: March 2011

AbstractAn A/B block copolymer consists of two macromolecules bonded together. In forming an equilibrium structure, such a material may separate into distinct phases, creating domains of component A and of component B. A dominant factor in the determination of the domain morphology is area-minimization of the intermaterial surface, subject to fixed volume fractions. Surfaces that satisfy this mathematical condition are said to have constant mean curvature. The geometry of such surfaces strongly influences material physical properties. We have discovered domain structures in microphase-separated diblock copolymers that closely approximate periodic surfaces of constant mean curvature. Transmission electron microscopy and computer-simulation are used to deduce the three dimensional microstructure by comparison of tilt series with two-dimensional image projection simulations of three-dimensional mathematical models. Two structures are discussed: First is the double diamond microdomain morphology, associated with a newly discovered family of triply periodic constant mean curvature surfaces. Second, a doubly periodic boundary between lamellar microdomains, corresponding to a classically known minimal surface (Scherk's First Surface), is described.
Modelling Microstructiure in Materials that Contain Anisotropic Particles
Authors: Viney Christopher , Chick Larry A. 
Published: March 2011

AbstractThe spontaneous alignment of molecules in liquid crystalline solutions is characteristic of other materials that contain rodlike particles. We are developing a model to predict the evolution of microstructure in these systems. Its starting point is Flory's thermodynamic analysis of liquid crystalline phase separation. Our preferred method dispenses with the traditional lattice model in favor of a Monte Carlo simulation to calculate entropy. Some advantages and consequences of our approach are explored in this paper
Exploratory Studies of New NLO and Piezoelectric Polymers
Authors: Hall H. K. , Padias Anne B. , Fuso Francesco , NI Zhende , Mitchell Michael A. , Leslie Thomas M. 
Published: March 2011

AbstractSynthetic efforts toward novel NLO and piezoelectric polymers are described. NLO-phores are incorporated in the main chain of a polymer with all the dipoles in the same direction by polycondensation of AB-monomers. The polymers containing p-alkoxy-α-cyanocinnamate units in the backbone show cooperative enhancement of SHG in solution. For comparison, p-thio-α-cyanocinnamate is incorporated in the main chain and in the side chain of polymers. Novel potentially piezoelectric polymers synthesized include polymers containing multicyanocyclobutyl or -cyclopropyl groups and acrylonitrile copolymers.
Design, Characterization, and Optical Properties of Phosphazene-Based Polymers
Authors: Exarhos Gregory J. , Samuels William D. 
Published: March 2011

AbstractPhysical properties intrinsic to linear inorganic polymer systems can be modified through replacement of chemical groups external to the chain backbone. This substitution also perturbs chemical bonding along the chain which can further influence polymer properties. Several phosphazene polymers deposited as thin dielectric films exhibit extended ultraviolet transmission. Second harmonic generation (SHG) has been observed in these polymers as well as in cyclic polymer precursors. The relative magnitude of SHG is found to correlate both with the nature of the substitutional group and molecular conformation. Influence of these parameters on substrate-film adhesion and measured optical properties is discussed in terms of substitutional group electronegativity, and electronic charge localization in the polymer chain which is probed using molecular spectroscopic techniques.
Lognormal Simulation of Pore Evolution During Cement and Mortar Hardening
Authors: Shi Dexiang , Ma Weiping , Brown Paul W. 
Published: March 2011

ABSTRACTA model to describe the pore sizes in cement paste and mortar, as determined by high pressure mercury intrusion porosimetry, has been developed. The model describes porosity using a compound lognormal distribution. For given material under a given set of curing conditions, the weighing factors and shape parameters of two sub-distributions in the lognormal model may be considered as constants, while the location parameters may be related to curing time and the relationship can be quantified. Therefore, it is possible to predict both the pore size distribution in cement and mortar at any age as well as the evolution in pore size during curing.
Modelling of the Evolution of Porewater Chemistry in a Cementitious Repository
Authors: Haworth A. , Sharland S.M. , Tweed C.J. 
Published: March 2011

ABSTRACTThe current concept for disposal of low- or intermediate-level nuclear waste in the UK includes a largely cementitious backfill. An important factor in determining nuclide release rates from the repository is the pH in the near-field. In this paper, we describe development of a coupled chemistry/transport model of cement degradation and its application in determining the evolution of the chemistry within the repository. In particular, the effect of the cement formulation and interaction with groundwater species on the evolution of the pH is examined. The model is sufficiently flexible to consider a number of different repository scenarios.
Prediction of Radioactive Waste Glass Durability by the Hydration Thermodynamic Model: Application to Saturated Repository Environments
Authors: Jantzen Carol M. , Ramsey W. Gene 
Published: March 2011

ABSTRACTThe effects of groundwater chemistry on glass durability were examined using the hydration thermodynamic model. The relative durabilities of SiO2, obsidian, basalt, nuclear waste glasses, medieval window glasses, and a frit glass were determined in tuffaceous (J–13) groundwater, basaltic (GR–4) groundwater, WIPP–A brine, and Permian Basin brine (PBB–3) using the monolithic MCC–I durability test. In the groundwater–dominated MCC–l experiments, the interaction of the glasses and the initial groundwater (leachant) caused the formation of unique assemblages of secondary phases. The secondary phase formation, in turn, controlled the final groundwater (leachate) pH and ionic strength, I[t].Correlations of the final leachate pH and I[t] with the Si release from the glass indicated that it is the influence of the secondary phase formation on the leachate pH and I[t] that controls the final dissolution rate of the glass. Since I[t] and the pH of the leachates are functions of the precipitation reactions, inclusion of the experimentally determined solution pH in the free energy of hydration model provides for the functional dependence of the dissolution rate on the secondary precipitation. Therefore, superposition of the linear equation for the groundwater and deionized water experiments occurs and the hydration free energy model can be used to compare glass durability in deionized water and in repository groundwaters.
In-Situ Testing of Nuclear Waste Glasses in a Clay Laboratory - Results After Two Years Corrosion
Authors: Iseghem P. Van , Timmermans W. , Neerdael B. 
Published: March 2011

ABSTRACTThe first retrieval of an in-situ experiment on the interaction waste form - clay host in the underground laboratory under the Mol site has been finished successfully. The test consisted in a two years exposure of various candidate simulated waste glasses at 90°C to Boom clay. The retrieval was done by overcoring. The experimental data showed satisfactorily correspondence between in-situ and laboratory simulation tests both for mass loss and surface analytical data, supporting the validity of the in-situ test as it was performed. The thickness of waste form dissolved within two years varies between 40 and 325 μm (case of the high-level waste glasses), depending on the composition. Matrix dissolution is expected to be the major mechanism of interaction.
The Interaction Between Nuclear Waste Glasses and Clay-II
Authors: Iseghem P. Van , Berghman K. , Timmermans W. 
Published: March 2011

ABSTRACTThe interaction between simulated HLW glasses and clay has been investigated, as part of a larger programme to evaluate the performance of vitrified HLW in repository conditions. Experimental conditions were carefully chosen to simulate repository conditions as close as possible. The glass corrosion seems to be controlled by a diffusion process, but there are indications of a (small) final corrosion rate. The leaching of 134Cs, 90Sr, 239Pu and 241Am is characterized by extremely small mobile concentrations leached (for 239pu and 241Am, below detection limit). The presence of a gamma irradiation field does not increase the glass dissolution. The production of radiolythic hydrogen is strongly reduced by the presence of clay.