bluuebunny/crossref_metadata_2025 huggingface dataset:
Next Generation of High Temperature Structural Intermetallic Compounds
Authors: Cells Pedro B. , Ishizaki K. , Kagawa E. , Ishikawa J.
Published: March 2011

Silicon compounds with the (Mn5Si3)16H crystal structure in particular, have a high melting point, which is a necessary characteristic of high temperature structural materials. The compounds Si3Zr5 and Si3Ti2Zr3 with that crystal structure and with melting points around 2500 K, were densified by using a hot isostatic process (HIP) in a glass capsule. This crystal structure shows good creep resistance, which might be due to the particularly large silicon interatomic distance. The high melting point and good creep resistance, make these intermetallics good candidates for the next generation of high temperature structural materials.
Atmosphere Control in the HIP Treatment of Ceramics
Authors: Fujikawa Takao , Manabe Yasuo , Miyatake Takayuki
Published: March 2011

This paper describes the concept and the significance of atmosphere control in the HIP treatment of ceramics and reviews some practical methods to create desirable atmospheres during HIP treatment for some nitride and oxide ceramics by citing published experimental data. The authors propose new HIP equipment which enables atmosphere controlled HIP treatment involving a wide range of ceramics and compounds.
Collagenous Biocomposites for the Repair of Soft Tissue Injury
Authors: Christiansen David , Pins George , Wang Ming Che , Dunn Michael G. , Silver Frederick H.
Published: March 2011

Results of implantation studies in a variety of animal tissue models demonstrate that the rate of biogradation of a collagen scaffold should parallel the rate of wound healing observed in particular anatomic sites. This rapid degradation maximizes tissue regeneration and minimizes encapsulation of the implant. The following paper reviews the effects of crosslinking on the rate of tissue ingrowth and regeneration. In addition, preliminary mechanical data on newly developed soluble type I collagen fibers is presented as a possible advance in the production of high strength collagen based tissue scaffolds.
Enzyme-Pretreatment RemovesIn VitroCytoxic Effects of Dermal Sheep Collagen
Authors: van Luyn M. J. A. , van Wachem P. B. , Damink L. H. H. Olde , Dijkstra P. J. , Feijen J. , Nieuwenhuis P.
Published: March 2011

We investigated thein vitrocytotoxicity of commercially available hexamethylenediisocyanate-crosslinked dermal sheep collagen (HDSC). HDSC was found to induce medium cytotoxic effects, as measured with methylcellulose cell culture. Apart from primary cytotoxicity, due to direct release of (extractable) cytotoxic products, HDSC was found to containsecondarycytotoxicity, possibly released by enzymatic interactions. In this study we found proof for this hypothesis, by exposing extracted HDSC to enzyme-containing medium. Furthermore we observed, that enzymatic pre-treatment can remove all secondary cytotoxic products, possibly due to detachment of pendants, which are still coupled to fragments of collagen molecules. The possibility of enzymatic pretreatment of HDSC, to obtain a non-cytotoxic/biocompatible material, may be important forin vivoapplications.
Effects of Process Parameters on Physical and Biological Properties of a Small Caliber Vascular Prosthesis
Authors: Carr R. M. , Ekstein B. A. , Kemp P. D. , O'Neil K. D. , Weinberg C. B. , Garcia J. P.
Published: March 2011

A method is described for the production of collagen constructs formed from densely packed, native-banded collagen fibrils. This “Dense Fibrillar Collagen” is formed by concentrating collagen in situ prior to self assembly of the collagen into fibrils. The effect of altering the pH, ionic strength, and osmolarity of the concentrating solution was measured. Increasing the ionic strength and osmolarity of the concentrating solution increased the burst strength of the constructs; increasing the pH from 3.8 to 7.1 reduced the surface fibrillarity, degree of platelet uptake and “short term in vivo thrombogenicity. This construct is being considered as the basis of a small-caliber vascular prosthesis to support guided tissue regeneration.
Induction of Hepatocyte Differentiation by the Extracellular Matrix and an RGD-Containing Synthetic Peptide
Authors: Mooney David J. , Langer Robert , Hansen Linda K. , Vacanti Joseph P. , Ingber Donald E.
Published: March 2011

To design novel biomaterials for hepatocyte transplantation it will be necessary to determine whether specific extracellular matrix (ECM) molecule(s) or the adhesive interactions between the surface and hepatocytes are responsible for regulation of hepatocyte function. Purified ECM molecules (laminin, fibronectin, types I and IV collagen) and a synthetic peptide containing the arginine-glycine-aspartate (RGD) cell-binding sequence were precoated at defined densities to non-adhesive polystyrene dishes. Hepatocytes cultured on dishes coated with a low density of ECM molecules (1 ng/cm2) maintained a round morphology, and high liver-specific protein secretion rates. In contrast, culturing hepatocytes on increasing ECM densities (50–1000 ng/cm2) resulted in extensive cell spreading, a loss of liver-specific protein secretion, and cell growth. Hepatocytes cultured on dishes coated with the RGD-containing peptide did not spread even on a high density of the peptide (10,000 ng/cm2), and albumin secretion remained high for hepatocytes cultured on all peptide densities (1–10,000 ng/cm2). These results suggest that a variety of ECM molecules and synthetic peptides are capable of inducing hepatocyte differentiation in vitro, and these effects depend on their ability to promote cell spreading.
A New Enzyme Immunoassay for Activation of Platelets by Biomaterials: Reduced Activation by Phosphorylcholine-Coated Surfaces
Authors: Campbell Ewan J. , Wiles Martin C. , New Roger R. C. , Charles Stephen A.
Published: March 2011

An enzyme immunoassay has been developed to semi-quantitate the degree of activation of platelets adhering to biomaterials. The method employs a monoclonal mouse anti-GMP-140 antibody. The glycoprotein GMP-140 is contained in alpha granules of resting platelets and is translocated to the outer membrane of platelets during activation via the thrombin-dependent pathway. A polyclonal anti-mouse IgG peroxidase conjugate is then added and platelet activation can be semi-quantitated by use of a suitable substrate, such as OPD.

The results obtained by this method compare well with scanning electron microscopy, and are shown to be less prone to the misinterpretation often associated with other conventional assay systems such as the determination of platelet adhesion by detection of ATP.

The adhesion and activation of platelets by biomaterials has been compared before and after coating these materials with phosphorylcholine (PC) derivatives. PC, in its form as a headgroup in membrane phosphoglyceride (lecithin) and ceramide (sphingomyelin) is a ubiquitous component of cell membranes, and displays extremely low interaction and binding with plasma proteins such as Factor XII [1,2], complement [2], fibrinogen [3,2], immunoglobulins [2] and albumin [2,4].

Using the immunoassay described here activation of platelets is seen to be dramatically reduced after coating surfaces, such as polyethylene, with PC compared with the untreated control. A PCcoated surface should therefore be an ideal starting point for developing tissue-inducing biomaterials. In addition endothelial cells contain GMP-140 in their secretory granules [5]. This would make this assay a potential tool in the investigation of endothelial cell - biomaterial interaction.
Quantitative Ruthenium Method for Analysis of Nitrogen Ion-Implanted Titanium Alloy (Ti-6AI-4V) and the Effect on Bacterial Adherence
Authors: Giammara Beverly L. , Williams James M. , Birch David J. , Dobbins Joanne J.
Published: March 2011

The effects of nitrogen ion implantation of Ti-6AI-4V alloy on growth ofPseudomonas aeruginosabacteria on surfaces of the alloy have been investigated. Results for ion implanted samples were compared with controls with similarly smoothly polished surfaces and with controls that had intentionally roughened surfaces. The test consisted of exposing sterile alloy samples to a microbiological broth, to which 24 hour-old cultures ofPseudomonas aeruginosahad been added. After bioassociation at normal temperature 37°C, bacteria adhering to the surface were fixed and treated with a new ruthenium tetroxide staining method, and quantified by use of scanning electron microscopy (SEM), back-scattered electron imaging and EDAX energy dispersive microanalysis. For smooth samples of the alloy, after a 12 hour growth period, the retained bacteria (revealed by the biologically incorporated ruthenium), decreased monotonically with nitrogen dose out to a total fluence of approximately 7 × 1017/cm2in an affected depth of approximately 0.1500μm. The SEM confirmed that thePseudomonas aeruginosaadhered equally to control materials. The ruthenium studies revealed that the amount of bacterial adhesion is indirectly proportional to the nitrogen ion implantation of the titanium. The greater the percentage of nitrogen ion implantation in the titanium alloy, the less bacteria colonized the disk.
Technological Development of Lipid-Based Microcylinders: Biocompatibility and Controlled Release
Authors: Spargo Barry J. , Stilwell Geoffrey E. , Cliff Richard O. , Monroy Rod L. , Rollwagen Florence M. , Rudolph Alan S.
Published: March 2011

We have developed a lipid-based microcylinder for the controlled release of biological response modifiers. Lipid microcylinders are composed of 1,2-ditricosa-10,12-diynoyl-sn-glycerol-3-phosphocholine which form hollow cylinders 50–250 μm in length with a diameter approximately 0.5–1.0 μm. Amphiphilic molecules such as ganglioside (5–6 mol%) can be incorporated into the bilayers of the microcylinder, modulating surface characteristics of the structure.

In this study, we have examined the biocompatibility of lipid microcylinders and lipid microcylinders containing 6 mol% ganglioside. The interaction of microcylinders with peripheral blood monocytes and three cell lines: U937, a histocytic monocyte; K562, an erythroblast, and; a Jurkat derivative, a lymphoblast was assessed. Toxicity, as measured by proliferative status of the cell lines, was not evident at lipid concentrations up to 100 μg/ml lipid. Peripheral blood monocytes were observed to closely associate, but not engulf lipid microcylinders. However, when ganglioside was present in the lipid microcylinders this interaction was markedly decreased.

We have begun to measure the release rates of growth factors such as transforming growth factor-beta (TGF-β) from lipid microcylinders. Release of TGF-β from the microcylinders follows first-order kinetics. The rate of release can be modulated by increasing the temperature which results in a thermotrophic phase transition of the lipid at 43 °C.
Physiological Cultured Skin Substitutes for Wound Healing
Authors: Halberstadt Craig , Anderson Phil , Bartel Ronnda , Cohen Ron , Naughton Gail
Published: March 2011

Physiological dermal and dermal-epidermal skin analogs have been developed in our laboratory using a novel technology for three-dimensional tissue culture. Human neonatal dermal fibroblasts are seeded on a biodegradable mesh made of polyglycolic or polyglactic acid (PGAIPGL). As the fibroblasts proliferate, they stretch across the mesh openings and secrete growth factors and human dermal matrix proteins, including collagen types I & HI and elastin. This process forms a metabolically active, three-dimensional dermal tissue around the mesh scaffolding. The mesh fibers are hydrolyzed over time and is completely resorbed in vivo within four to eight weeks. Multiple sheets of the PGA/PGL-dermal analog are grown simultaneously in a closed, continuous media-flow system, also developed in our laboratory. After attaining confluence, the dermal sheets may be seeded with keratinocytes, to create a living dermal-epidermal composite tissue.
Biological Response of Intramedullary Bone to Poly-L-Lactic Acid
Authors: Suganuma J. , Alexander H. , Traub J. , Ricci J. L.
Published: March 2011

Bioabsorbable synthetic polymers have been studied for their possible application in absorbable internal fracture fixation devices. The current study examines the biological response of intramedullary bone to PLLA (poly-L-lactic acid). PLLA degrades at a rate sufficiently slow to be useful for fracture fixation and undergoes hydrolytic deesterification to form metabolites normally found in the body. Nevertheless, the lactic-acid-rich degradation products have the potential to significantly lower the local pH in a closed space surrounded by bone. It is hypothesized that this acidity may tend to cause abnormal bone resorption and/or demineralization.
Effective Dielectric function of a Composite with Aligned Spheroidal Inclusions
Authors: Barrera Ruben G. , Giraldo Jairo , Mochan W. Luis
Published: March 2011

The effective dielectric response εM of a composite with aligned spheroidal inclusions is calculated. Using the dipolar and the mean-field approximation (MFA) an analytical expression for εM as a functional of the two-particle distribution function p(2) is obtained. It is shown that previous expressions reported in the literature correspond to different choices of p(2), thus, clarifying the origin of their discrepancies. The theory is further extended beyond the MFA by including the dipolar fluctuations through a renormalization of the polarizability tensor of the inclusions. The absorption peaks are diminished and broadened by the spatial disorder, which also yields an easily identified coupling among electromagnetic modes with perpendicular polarizations.
Multipolar Expansions for Multiple Scattering Theory
Authors: Brown R. G. , Ciftan M.
Published: March 2011

A simple derivation (based on a derived identity of integral equation theory) of fully separable, non–muffin–tin multiple scattering theory is presented. Three multipolar representations have been proposed for use in this theory: the original representation by Williams and Morgan, a more recent one by Brown and Ciftan, and a “Bloch periodic” representation by Badralexe and Freeman (which was addressed in earlier work). We study the properties of the Williams and Morgan representation in the context of the 2D empty square lattice, where the representation of Brown and Ciftan is manifestly exact and correct (so that MST derived in terms of it is a “natural” theory). We show that the representation of Williams and Morgan contains an explict divergence predicted by its implicit use of a wrong-order Green's function expansion but that MST expressed in terms of this representation is still a fairly good asymptotic approximation to the formally exact theory.
Solution of the Single-Site Aspherical Scattering Problem for the Dirac Equation
Authors: Lovatt Stephen C. , Gyorffy B.L. , Guo Guang-Yu
Published: March 2011

We study the scattering solutions of the Dirac equation numerically for anisotropic, finite range (warped muffin-tin), potentials. In particular, we calculate the partial-wave scattering matrix, ƒAA'(ε) and S-matrix SAA′(ε), for a potential characteristic of crystalline Silicon. We illustrate the consequences of aspherical scattering with reference to Silicon.
Ab Initio-Calculations of Residual Resistivities For Dilute Ni-Alloys
Authors: Mertig I. , Zeller R. , Dederichs P.H.
Published: March 2011

We report about residual resistivity calculations for dilute Ni alloys which are based on density-functional theory and the Korringa-Kohn-Rostoker Green's-function method. The transport is described quasiclassically by means of the Boltzmann equation using a two current model for the ferromagnetic host. In particular we consider 3d, 4d, 4sp and 5sp impurities in Ni and include in addition to the impurity atom one shell of perturbed host atoms in the calculation. For the residual resistivity satisfactory agreement with the experiments is obtained in practically all cases. We clarify the role of both subbands for the transport properties.
Compositional Disorder, Magnetism, and Their Interplay in Metallic Alloys
Authors: Johnson D. D. , Staunton J. B. , Pinski F. J. , Gyorffy B. L. , Stocks G. M.
Published: March 2011

Chemical disorder leads to a variety of intriguing phenomena in alloys which have yet to be fully understood, particularly those phenomena occuring when chemical and magnetic effects interplay with one another. For example, magnetic order gives rise to chemical ordering in alloys, as in Ni-rich NiFe alloys. Two examples of the interplay of chemical disorder and magnetism will be discussed. Our recently developed ab-initio Landau (mean-field) theory for calculating the chemical-chemical, magneto-chemical, and magnetic-magnetic correlation functions in substitutional random alloys is used to describe electronic/magnetic mechanisms (e.g. in FeV) which give rise to the chemical short-range order as determined by neutron, X-ray, or electron diffuse scattering intensities. New developments within this approach that account for charge rearrangement effects will be mentioned. These calculations are performed within the multiplescatteringframework, developed by Korringa, Kohn, and Rostoker (KKR), combined with the coherent potential approximation (CPA) to describe the disorder. This approach allows a firstprinciples description of the electronic structure of the high-temperature, chemically disordered state and its instability to ordering at low temperatures. This method provides not only a direct comparison of diffuse scattering data with theory but a means to understand more fully the underlying mechanisms which drive chemical and/or magnetic ordering.
Spin-Polarized Relativistic Band Structure Calculations for Dilute and Concentrated Disordered Alloys
Authors: Ebert H. , Akai H.
Published: March 2011

Applications of the spin-polarized relativistic version of multiple scattering theory (SPRKKR) to study the electronic properties of dilute and concentrated disordered alloys are presented. This approach, developed recently, allows to investigate magnetic systems containing heavy elements and also gives access to a detailed discussion of phenomena, which are linked to the simultanous presence of spin-polarisation and spin-orbit coupling. This is demonstrated by discussing the hyperfine properties of 5d-transition metals dissolved substitutionally in Fe, where pronounced relativistic effects could be found. In addition the magnetic X-ray dichroism (MXD), denoting the difference in absorption of left and right circularly polarized radiation, is studied for these dilute alloys.

To be able to deal also with concentrated alloys, we have combined the Coherent Potential Approximation (CPA) alloy theory with the SPRKKR-formalism. Results for the spin-orbit induced orbital contributions to the magnetic moments as well as the MXD in FexCol-x and CoxPtl-x clearly show that remarkable relativistic effects are present even for relatively light elements.
A Full-Potential KKR-GREEN's Function Method to Calculate the Electronic Structure of Surfaces
Authors: Zeller R. , Lang P. , Drittler B. , Dederichs P.H.
Published: March 2011

We present a multiple-scattering Green's function method to calculate the electronic structure of ideal surfaces and surfaces with point defects. In our method we use the full potential in each atomic cell and describe the surface as a twodimensional defect of the bulk crystal by removing several (three to five) adjacent layers. We have implemented our method within density-functional theory in the local-spin-density approximation and present first results for the Cu (001)-surface, for magnetic monolayers on this surface and for such monolayers in bulk Cu.
A Simple Derivation of the Layer-Kkr Theory of Leed
Authors: Marcus P.M.
Published: March 2011

The equations of the layer-KKR method for finding the intensities of electrons diffracted by a semi-infinite layered structure are derived in a simple way by use of three identities relating spherical and plane waves and by use of a compact notation. The third identity, which transforms a sum of outgoing spherical waves on a twodimensional array intoa sum of plane waves or beams, is a very useful simplification of the derivation, which does not appear in texts on LEED. Explicit linear equations are derived for amplitudes of outgoing spherical waves produced by diffraction of an incident beam first by a singleBravais net and then generalized to a composite layer made up of several Bravais nets; matrix elements of the beam reflection and transmission matrices for a single Bravais netand for a composite layer are given, and also the exact interlayer matrix equation for the reflection matrix of the semi-infinite structure.
Advanced Multiple Scattering Theories of Low-Energy Electron Diffraction (LEED)
Authors: Hove M.A. Van
Published: March 2011

Recent advances in the theory of low-energy electron diffraction (LEED) are reviewed. They primarily concern methods to handle the multiple scattering of electrons in an atomiclattice. These advances have allowed the structure determination by LEED of complex surface structures, including large-unit-cell overlayers of molecules, disordered and incommensurate overlayers, complex reconstructions and adsorbate-induced relaxations.
Multiple Scattering of Electrons in Condensed Matter Physics: An Overview
Authors: Gyorffy B.L.
Published: March 2011

The Multiple Scattering strategy for studying electrons in condensed matter is reviewed. It is emphasized that this approach is effective for the Dirac and Bogoliubov-de Gennes equations, describing relativistic and superconducting quasi-particles respectively, as well as the usual Schrödinger's equation which arises during the implementation of the Density Functional Theory.
Classical Appucations of Multiple Scattering Theory, an Overview
Authors: Weaver Richard L
Published: March 2011

It appears that the most salient of the issues that a brief overview might address in this symposium concerns the relationship - the differences, the parallels, and the similarities - between research in classical wave applications of multiple scattering theory and that research whose chief focus is electronic. Each desires the solution to a linear partial differential equation, usually a wave equation such as the Schrodinger equation or Maxwell's equations, in a heterogeneous medium, and each seeks to derive bulk properties from knowledge of the properties of the constituents. As with the Schrodinger equation, Korringa-Kohn-Rostoker like equations are often used for classical waves, and expansions in spherical harmonics and outgoing and regular solutions of the wave equation in the bare medium used to represent the equations. There remain, however, substantial differences in their respective formulations and methodologies. These appear to be traceable, at least in part, to differences in the questions that are asked about the field in the heterogeneous medium, to differences in the prior information available in regard to the microstructure, and to different symmetry classes of the microphysics. It is perhaps these differences which can account for the otherwise rather surprising absence of interaction between researchers in classical applications and those in electronic structure.
Hierarchy in Extended Chain Polymers
Authors: Klunzinger P. E. , Eby R. K. , Adams W. W.
Published: March 2011

Rigid rod polymers are of potential use in fibers for composites because of their high specific tensile strength and modulus as well as their high thermal stability. Some other common properties of systems meeting these criteria are a nonlinear elasticity (increasing Young's modulus with increasing tensile stress) and a negative coefficient of thermal expansion along the fiber axis. In composites, these two properties can combine to cause an increase of Young's modulus with increasing temperature and can lead to yielding or interfacial failure. The source of the nonlinear elasticity resides at two length scales: 1) the scale of the crystallites, (the reversible realignment of the crystallites along the fiber axis with increasing stress), and 2) at the scale of the molecules, (an inherent nonlinear elasticity of the molecules themselves). The former effect is reviewed and computational results for the latter are presented along with computational results for the molecular origin of the negative coefficient of thermal expansion.
Polymer Microlayer Composites
Authors: Hiltner A. , Sung K. , Shin E. , Bazhenov S. , Im J. , Baer E.
Published: March 2011

Continuous microlayer composites of polycarbonate (PC), a ductile glassy polymer, and styrene-acrylonitrile copolymer (SAN), a glassy relatively brittle polymer, were discussed. Microlayered systems composed of 49 to 776 continuous layers, in which the primary variable was the variation in thickness of the continuous layers between 30 and 2μm, were emphasized. The bulk properties of these microlayered composites showed a dramatic improvement in the toughness or ductility and in the fatigue properties as the layer thickness decreased. Investigation of the irreversible deformation processes revealed that when the layers were thicker (30μm, 49 layers) the SAN layers crazed and the PC shear banded in the usual manner. Subsequently the composite system fractured in a relatively brittle manner due to the development of large voids in the SAN layers. When the layer thickness was reduced to 2μm (776 layers) the entire system behaved in a ductile manner and both the PC and SAN shear banded due to a new cooperative process. This was analyzed by considering the micromechanics of these irreversible processes at the PC-SAN interface. As a result of this work, it is expected that ultra-thin layered structures of other alternating composite systems will reveal synergistic properties if the interfacial properties are designed so that the ductile component will dominate the yield and failure characteristics of the entire system.
Failure Problems In Composites
Authors: Mcgarry Frederick J.
Published: March 2011

Fiber reinforced polymer matrix composites have become very useful in chemical processing systems, in transportation applications such as automobiles, aircraft and boats, in electrical hardware and in sports equipment. Failures in these rarely involve gross cohesive fracture; usually leaks develop, the stiffness decreases, local delamination occurs, the dielectric properties degrade or the strength declines. Almost all of these failures can be traced to local cracking, either at the fiber matrix interface or within the matrix itself. The cracks are generated by mechanical loads, by thermal excursions or by fluid absorption, because the relevant properties of the fiber and the matrix often differ by orders of magnitude. Current technology attempts to avoid the cracks by maximizing the fiber-matrix adhesion and great progress has been made in this area. An alternative interposes a thin compliant layer, rubber, between the two constituents thereby reducing the stress concentrations which exist because of their greatly different properties. Cracking is inhibited, composite strength is increased and its energy absorption also rises; if the rubber layer is thin (a few thousand Angstroms) no loss of stiffness or heat resistance is evident.
Imaging Of Hierarchically Structured Materials
Authors: Sarikaya Mehmet , Aksay Ilhan A.
Published: March 2011

We describe techniques used to characterize hierarchically structured synthetic and biological materials. These techniques decipher the structures through the dimensional spectrum from the molecular and atomic scales (10.−10m) to the macro scales (10−3m) where the overall shape of the material emerges. Techniques used to image surfaces and internal structures can be categorized according to their wavelength and thus spatial resolution as light, x-ray, and electron microscopy. We also discuss newly emerging microscopy techniques that image surfaces at the atomic level without a focusing lens, such as scanning tunneling and atomic force microscopies, with the aid of field ion microscope and scanned probe microscopes. Transmission electron microscopy (TEM), a unique tool for multipurpose imaging, provides structural information through direct imaging, diffraction, and spectroscopic analysis. We illustrate the major TEM techniques used to analyze structural hierarchy with examples of synthetic and biological materials. We also describe light optical microscopy and scanning probe microscopy techniques, which cover the opposite ranges of the dimensional spectrum at the micrometer and subangstrom levels.
Hierarchical Structures that Arise from Self-Assembling Systems
Authors: Marzio Edmund A. Di
Published: March 2011

A working definition of the term hierarchy that is consistent with past usage is that a hierarchy is an assemblage of assemblages. Self-assembling systems are essential to those hierarchical structures that contain structure on micro and nano distance scales since these tiny structures being so large in number can not be manipulated individually as is possible for larger structures. It is shown how self-assembling structures are nothing more than materials that have undergone a structure inducing phase transition. The induced structures can be either equilibrium structures (example lamellar block copolymers) or kinetic patterns (example snowflakes). Polymer systems provide a rich source of phase transitions. There are at least ten classes of polymer phase transitions. [1] helixrandom coil [2) polymerization or one-dimensional crystallization [3] adsorption [4] collapse transition [5] coilfstretch transition [6] liquidliquid transitions [7] crystallization [8] liquid crystals-plastic crystals [9] glass-amorphous and sol-gel transitions [10] soaps-membranes-micellesvesicles-block copolymers. These phase transitions can interact with each other creating an even richer overlay of self-assembled systems. We discuss three aspects of the building of Hierarchical structures from selfassembling systems.
Hierarchical Cellular Materials
Authors: Gibson L. J. , Ashby M. F.
Published: March 2011

Cellular materials are made up of an interconnecting network of strut- or plate-like members. Natural cellular materials include wood, cancellous bone, cork, palm and leaves. Engineering cellular materials are either in the form of honeycombs, with two-dimensional, prismatic cells, or foams with three-dimensional, polyhedral cells. Natural cellular materials usually have multiple phases at multiple scales while engineering cellular materials use a single phase at a single scale.

In this paper, the efficiencies of various natural cellular materials are estimated by analyzing their behavior at various microstructural scales. The results of the analysis suggest microstructural design of hierarchically structured engineering cellular materials.
Biomimetic Mineralization of an Aligned, Self-Assembled Collagenous Matrix.
Authors: Christiansen David , Silver Frederick H.
Published: March 2011

An in-vitro method of mineralizing an aligned, self-assembled collagenous matrix is presented. Reconstituted collagen fibers were mineralized by exposure to saturated solutions of calcium and phosphate of varying pH in a double diffusion chamber for seven days at room temperature. Microscopic investigation of the mineral precipitate within the fibers indicate the formation of hydroxyapatite crystals with features comparable to mineral observed in bone and avian tendon. Mechanical test results indicate that tensile strength and tangent modulus increase after mineralization in comparison to unmineralized control fibers. These results suggest that mineralization of collagen fiber in-vitro may parallel some of the events seen in mineralization of bone and turkey tendon. In addition, mineralized collagen fibers may be useful in the design of composites for the replacement or augmentation of hard tissue
Hierarchical and Modulable Hydrophobic Folding and Self-assembly in Elastic Protein-based Polymers: Implications for Signal Transduction
Authors: Urry D. W. , Luan C.-H. , Peng S. O. , Parker T. M. , Gowda D. C.
Published: March 2011

When the hydrophobic (apolar) and polar moieties of elastomeric polypeptides are properly balanced, the polypeptides are soluble in water at lower temperatures but undergo folding and assembly transitions to increased order on raising the temperature. The temperatures, Tt, and heats, ΔHt, of these inverse temperature transitions are determined by differential scanning calorimetry for a series of elastomeric polypentapeptides: poly(VPAVG), poly(IPAVG), poly(VPGVG), poly(IPGVG), poly[0.5(VPGVG),0.5(IPGVG)] and poly[0.82(IPGVG),0.18(IPGEG)] where V = Val, P = Pro, A = Ala, G = Gly, I = lle and E = Glu.

On increasing the hydrophobicity as when replacing V(Val) by I(lle) which is the addition of one CH2moiety per pentamer, the temperature of the transition is lowered by 15 to 20°C and the heat of the transition is increased by more than one kcal/mole, for the above examples, by more than a factor of two.

When differential scanning calorimetry thermograms are obtained on mixtures of poly(VPAVG) plus poly(IPAVG) or of poly(VPGVG) plus poly(IPGVG), it is found that the polypentapeptides self-separate, i.e., they de-mix, even though in the latter case the conformations have been shown to be essentially identical before and after their respective transitions.

When the polymer, poly[0.82(IPGVG),0.18(IPGEG)], is studied as a function of pH, increasing the degree of ionization is found to increase the temperature and to decrease the heat of the transition such that, with the correct balance of I with the variable E(GluCOO−), the values of Ttand ΔHtcan be made to approach those of poly(VPGVG). Acid-base titration studies indicate that less than one Glu(COO−) in 200 residues can raise the value of Ttby 25°C and decrease ΔHtby 90%.

These and additional data are interpreted to mean that there exists an hierarchical hydrophobic folding, that the hierarchical hydrophobic folding can be modulated by changing the degree of ionization or by changes in a number of intensive variables, that changes in these intensive variables can be used to drive folding/unfolding-assembly/disassembly transitions under isothermal conditions, and that these unfolding/folding and disassembly/assembly transitions can be used to achieve signal transduction. This is called the ΔTtmechanism of free energy (signal) transduction.
Polymer Liquid Crystals and Their Blends: A Hierarchy of Structures
Authors: Brostow Witold , Hess Michael
Published: March 2011

Hierarchical structures are possible in polymer liquid crystals (PLCs) since each molecule contains at least two kinds of building blocks that are not homeomorphic to each other. We discuss some examples of molecular structures and phase structures of monomer liquid crystals (MLCs) and PLCs: smectic phases formed by interdigitated MLC molecules; PLC molecule classification based on increasing complexity – and its consequences on properties of the materials; and formation and phase structures of LC-rich islands in PLCs and in PLC blends. Some rules pertaining to hierarchical structures are formulated. The knowledge of hierarchies is neccessary – but not sufficient – for intelligent procesing of PLCs and their blends and for achieving properties defined in advance. Computer modelling represents another important element of building materials to order.
Si Nanostructure Fabrication by Ga+ FIB Selective Doping and Anisotropic Etching
Authors: Steckl A. J. , Mogul H. C. , Mogren S.
Published: March 2011

A novel fabrication technique involving the use of focused ion beam (FIB) selective implantation to fabricate nanostructures on crystalline Si substrates in conjunction with anisotropic etching is described. Using this maskless & resistless approach, Si nanostructures were fabricated by FIB implantation of Ga+ at doses from 1015 to 1016/cm 2. Wet etching in KOH/IPA does not attack the implanted region, while it removes the underlying Si anisotropically, with a very low etch rate on the {111} planes. The result is a cantilever-like structure whose thickness is dependent on the implantation energy and dose. Pre-etching rapid thermal annealing at 600°C for 30 sec does not prevent structure fabrication and post-etching RTA does not affect the shape of the structures.
Reversible Luminescence Quenching of Porous Si by Solvents
Authors: Lauerhaas Jeffrey M. , Credo Grace M. , Heinrich Julie L. , Sailor Michael J.
Published: March 2011

Interaction of the solvents tetrahydrofuran, diethyl ether, methylene chloride, toluene, o-xylene, benzene, and methanol with luminescent porous n- Si (PS) results in reversible quenching of the luminescence associated with this material. The degree of quenching ranges from 99% – 50%, and scales with solvent dipole moment. Reaction with gaseous Cl2, Br2, or I2 results in irreversible quenching, associated with a surface reaction that removes Si-H bonds. Total luminescence quenching is observed on treatment of a PS wafer with a solution of the electron donor ferrocene in toluene, suggesting that charge transfer quenching may also be operative in this material. Luminescence is partially recovered by rinsing the PS in pure toluene. The data show that photoluminescence of PS is highly sensitive to surface adsorbates, suggesting that carrier trapping is easily induced in this material.
Microstructural Characterization of Photoluminescent Porous Silicon
Authors: Macaulay J. M. , Ross F. M. , Searson P. C. , Sputz S. K. , People R. , Friedersdorf L. E.
Published: March 2011

We have used electron microscopy to examine the microstructure of porous silicon films over a wide range of doping levels, and photoluminescence spectroscopy to study their optical properties. We discuss the impact of our experimental results on models from the literature which were proposed to explain visible luminescence from porous silicon.
Effect of Surface Finish on Nuclear Glass Dissolution Rate
Authors: Dussossoy J.L. , Dubois C. , Vernaz E. , Chambaudet A.
Published: March 2011

The influence of the surface finish on nuclear glass dissolution was investigated. Seven different surface finishes were tested: a specimen as cut, three specimens polished with 220, 600 and 4000 mesh SiC paper and one with 1 μm diamond powder, a flame-polished specimen and a thermal rupture specimen.

The initial glass corrosion rates were measured after 7 and 28 days of Soxhlet leaching at 100°C. The surface finish of each glass coupon was also assessed by three-dimensional analysis before and after leaching for 28 days. Leaching solution analyses showed that the mean apparent leach rate for the first 7 days was highly dependent on the surface finish: the measured rates ranged from 3.8·g.m-2d-1 for the as-cut specimen to 1.3 g·m-2d-1 for the flamepolished specimen. The differences in the leach rates diminished considerably after 28 days of leaching: the mean rate measured between 7 and 28 days for the as-cut and polished specimens was identical (1.7 g·m-2d-1), but was still lower for the remaining two specimens. Three-dimensional surface analysis showed that leaching revealed surface defects (superficial microcracks) produced by cutting or polishing. These effects were less perceptible on the flame-polished or thermally ruptured specimens. The actual surface area of the cut and polished specimens exceeded the apparent geometrical area.

In another experiment, the leach rates measured for as-cut specimens and flamepolished specimens were measured over periods of five months or more using a thermogravity balance placed above the Soxhlet device. The experiment confirmed the existence of an initial period during which the dissolution rate for the as-cut specimen was much higher than the mean corrosion rate.
Materials Interface Interactions Test (MIIT); in-Situ Testing of Simulated Hlw Forms in Salt- Performance of Srs Simulated Waste Glass After up to 5 Years of Burial at the Waste Isolation Pilot Plant (WIPP)
Authors: Wicks G.G. , Lodding A.R. , Macedo P.B. , Clark D.E.
Published: March 2011

The first field tests conducted in the United States involving burial of simulated high-level waste [HLW] forms and package components, were started in July of 1986. The program, called the Materials Interface Interactions Test or MIIT, is the largest cooperative field-testing venture in the international waste management community. Included in the study are over 900 waste form samples comprising 15 different systems supplied by 7 countries. Also included are approximately 300 potential canister or overpack metal samples along with more than 500 geologic and backfill specimens. There are almost 2000 relevant interactions that characterize this effort which is being conducted in the bedded salt site at the Waste Isolation Pilot Plant (WIPP), near Carlsbad, New Mexico. The MIIT program represents a joint endeavor managed by Sandia National Laboratories in Albuquerque, N.M., and Savannah River Laboratory in Aiken, S.C. and sponsored by the U.S. Department of Energy. Also involved in MIIT are participants from various laboratories and universities in France, Germany, Belgium, Canada, Japan, Sweden, the United Kingdom, and the United States. In July of 1991, the experimental portion of the 5-yr. MIIT program was completed. Although only about 5% of all MIIT samples have been assessed thus far, there are already interesting findings that have emerged. The present paper will discuss results obtained for SRS 165/TDS waste glass after burial of 6 mo., 1 yr. and 2 yrs., along with initial analyses of 5 yr. samples.
Time-Dependence of Volatilization of 137Cs and 106Ru Over High-Level Waste Glass in a Canister
Authors: Kamizono Hiroshi , Muraoka Susumu
Published: March 2011

Volatility of 137Cs and 106Ru at 600ºC over high-level waste glass in a canister is numerically analyzed. The time-dependence of normalized concentrations of each radionuclide is traced by a differential equation based on a simple model consisting of competitive forward and backward steps. It is assumed that, as time proceeds, a surface layer forms on the glass and serves as a protective barrier against volatilization. It is found that the forward rate of volatilization for 137Cs is about 140 times greater than that of 106Ru at 600ºC. The effects of the glass surface area and plenum volume on the concentration excursion inside the canister are closely estimated by the differential equation.
Structures and Stabilities of Trivalent and Tetravalent Rare Earth Ions in Sevenfold Andeightfold Coordination in Fluorite-Related Complex Oxides
Authors: Morss Lester R.
Published: March 2011

This paper reports the preparation and characterization of a series of oxides containing3+ or 4+ lanthanide (M = Ce, Pr, or Tb) ions, with different ionic sizes and varying M4+/M3+ reduction potentials, in nearly cubic coordination. The objective of the study was to demonstrate how oxidation-reduction characteristics and ionic-size trends explain the properties of these oxides and to compare the oxidation-reduction stability of M3+ and M4+ lanthanide ions in high (CN 7 or 8) coordination in fluorite-related oxides versus low (CN 6) coordination in perovskite oxies. Efficient preparative methods are reported, as well as powder diffraction and thermogravimetric measurements for oxides CaMTi2O7-x and CaMZr2O7-x. These oxides were characterized by X-ray powder diffraction and by thermogravimetric analysis. CaCeTi2O7 is a pyrochlore, a = 10.142(4) Å with Ce4+ much more easily reducible than in the perovskite BaCeO3. By contrast, a preparation with the stoichiometry “CaPrTi2O7-x” is a two-phase mixture of perovskite CaTiO3 and a presumably Pr3+-rich pyrochlore Pr2Ti2O7(?). CaTbTi2O7-x appears to be a Tb3+ pyrochlore, a = 10.149(2) Å. CaCeZr2O7 is a pyrochlore, a = 10.524(1) sÅ. A preparation of “CaPrZr2O7-x” also appeared to yield a two-phase mixture, perovskite CaZrO3 and pyrochlore Pr2Zr2O7. In this paper, the structures, f-element ion sites, and M(IV)- MM1I stability trends in the CaMTi2O7-x and CaMZr2O7-x oxides are compared with the structural and stability trends in the perovskites BaMO3 which have M4+ ions in sixfold (tilted octahedra) coordination.
Enthalpies of Formation of Rare Earth and Actinide(III) Hydroxides; their Acid-Base Relationships and Estimation of their Thermodynamic Properties
Authors: Morss Lester R. , Williams Clayton W.
Published: March 2011

This paper reviews the literature on rare earth(III) and actinide(III) hydroxide thermodynamics, in particular the determination of their enthalpies of formation at 25 ºC. The hydroxide unit-cell volumes, lanthanide/actinide ion sizes, and solid-solution stability trends have been correlated with a generalized acid-base strength model for oxides to estimate properties for heterogeneous equilibria that are relevant to nuclear waste modeling and to characterization of potential actinide environmental interactions. Enthalpies of formation and solubility-product constants of actinide(III) hydroxidesare estimated
SIMULATING THE BEHAVIOUR OF FISSION PRODUCTS IN UO2
Authors: Grimes Robin W.
Published: March 2011

Fission products in nuclear fuels exhibit a significant variation in solubility and stability. To understand better the reasons for this variation, the Mott-Littleton simulation technique has been used to calculate solution energies of the fission products Br, Kr, Rb, Sr, Y, Zr, Te, I, Xe, Cs, Ba, La and Ce. Nonstoichiometry and variable charge state are important components of the model.
The Critical Condition for the Initiation of Localized Corrosion of Mild Steels in Contact with Bentonite Used For Nuclear Waste Package
Authors: Nakayama Guen , Akashi Masatsune
Published: March 2011

It has been established that the mild steels which undergo the general corrosion in the acidic to neutral environments, attain the passivity status in alkaline environments, thereby becoming liable to the localized corrosion, such as pitting corrosion and crevice corrosion. Now, for the case of using bentonite as a buffer to stand between the hostrock and the geological disposal packages of high level nuclear waste, localized corrosion behaviors of mild steel as a candidate for such a package has been studied quantitatively for environments where the the otherwise neutral ground water would be turned slightly alkaline with pH = 9.5 - 10.0.

In view of the lack of quantitative data on the passivity-to-localized corrosion of mild steel in natural water environments of weak alkalinity, the present authors have previously determined an empirical E-pH diagram for mild steel with a 20 °C, 1 m mol/L [HC03-], 10 ppm [CI -] solution simulating the natural water environment concerned; it has been shown that the general corrosion-to-passivity transition condition was determined to be pHd =9.4, and the mild steel was shown to be liable to localized corrosion over a large portion of the passivity domain. The present paper discusses behaviors, mechanisms, and critical conditions for initiation of localized corrosion in mild steel placed in bentonitesuspending natural water environment, in terms of the critical potentials for pitting (Vc), and crevice corrosion (ER,CREV). Bentonite was addid to the solution in varying amounts to give bentonite-to-solution ratios up to 0.1, while the pHvalue was adjusted appropriately with sodium carbonate, always keeping the bentonite particles in suspension.

It is demonstrated that bentonite particles suspended in water will deposit upon the steel on receipt of Fe2 + ions, thereby promoting pitting corrosion by preventing repassivation and promoting crevice corrosion by acting as an effective crevice, once the environment conditions become favorable for localized corrosion.

We conclude therefore that disposal package made of mild steel and placed in an underground water environment with bentonite as buffer will be liable to localized corrosion.