bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dual Constant Composition Kinetics Studies of the Demineralization of Ceramic Plasma Coated Apatite Surfaces
Authors: Paschalis E. P. , Nancollas G. H. 
Published: March 2011

ABSTRACTCalcium phosphate phases such as hydroxyapatite (HAP) and octacalcium phosphate (OCP) have long been considered as model systems for biological minerals. Moreover such phases are involved in ceramic and plasma coated titanium (HPCTI) prosthetic devices. Most of these mineral preparations are mixtures of calcium phosphate phases, as evidenced by X-ray analysis. However, many mineralizing systems involve the formation of metastable intermediates which may subsequently undergo phase transformations. There is therefore considerable interest in investigating the simultaneous growth and dissolution of multiple mineral phases. Based on the Constant Composition (CC) method, the new Dual Constant Composition (DCC) technique has been developed for kinetics studies of the dissolution of the mixed calcium phosphate phases frequently encountered in-ceramic and plasma coated apatite surfaces.
In VitroCell Adhesion and Detachment Behavior for Various Biomaterial Substrates
Authors: Schmidt Mary Beth , Brunski John B. 
Published: March 2011

ABSTRACTCell-biomaterial interactions for different material compositions were evaluated through quantitative examination ofin vitrocell spreading behavior and shear-induced cell detachment. Biomaterial substrates consisted of identically prepared, well characterized bulk samples of implant grade cp Ti, Ti-6AI-4V, and Synamel. 3T3 fibroblasts were seeded on the substrate surfaces and incubated for 2 hours. Adherent cell morphology was then examined using scanning electron microscopy and digital image analysis. The cell detachment response was measured using a parallel plate flow chamber. When categorized according to observed cell morphology, projected cell areas were found to be lognormally distributed for all biomaterials and ln(cell area) was significantly greater for Synamel, while no difference existed between cp Ti and Ti-6AI-4V. In addition, the average post-shear fraction of adherent cells was significantly greater for Synamel substrates, as compared to cp Ti and Ti-6AI-4V substrates. The results from this study indicate thatin vitrocell adhesion and detachment behavior are measurably influenced by biomaterial substrate composition.
Bone Cell Response to Ion Implanted Silicon Wafers
Authors: Walsh W. R. , Zou L. , Lefkoe T. P. , Kelly J. C. , Howlett C. R. 
Published: March 2011

ABSTRACTResults of preliminary investigations on the electrokinetic characterization and osteoblast morphology of ion implanted silicon wafers are presented. The goal of this study is to modify the surface of a material via ion implantation to control cellular interactions at the prosthesis-body interface.
Electrical Stability of Biocompatible Electrodes
Authors: He L. , Anderson W. A. 
Published: March 2011

ABSTRACTBiocompatible electrodes were fabricated using ordinary semiconductor device processing techniques. For the purpose of identifying electrically stable electrode materials, which are biocompatible for long life, several kinds of contact metal were used. From a comparison of the metal elemental constants, it is suggested that the metal atom ionization energy, cohesive energy and the metal material conductivity may be the major factors to decide the material biocompatibility. Electrical testing shows Pd, with high atom ionization energy and low electrical conductivity, to have the best long life stability. In a test of 140 hours in saline solution with electrical power, the average maximum resistance deviation for a Pd electrode was 5%. The metal Ru, with high atom cohesive energy, has the best ability to withstand surface erosion for biocompatibility requirements. In a microscopic examination, the surface erosion for the Ru layer was invisible after 140 hours testing. The double-layer structures Pd/Ru and Mo/Ru were also tested. The maximum resistance deviations were found to be 7% and 9%, respectively.
Atomistic Study of the Clean and Hydroxylated TiO2 Surface
Authors: Podloucky R. , Steinemann S. G. , Freeman A. J. 
Published: March 2011

ABSTRACTThe coverage of an oxidized Ti-surface by amphoteric OH groups seems to be the driving mechanism for the attachement of bone material to Ti-implants. To contribute to the quantitative and fundamental understanding of this phenomenon, an ab-inito surface method was applied to calculate the electronic structure and energetics of the clean and hydroxylated (110) TiO2 rutile surface. Some of the most important relaxation and reconstruction effects of surface geometries were derived from total energy minimization.
Polymer Surface Modification Causes Change in Phenotypic Expression of Primary Bone Cells
Authors: Peel Sean A. F. , Sodhi R. N. , Duc Tran Minh , Davies John E. 
Published: March 2011

ABSTRACTPrimary rat bone marrow cells were cultured on bacteriological grade polystyrene dishes which had been treated in selected areas with concentrated sulphuric acid. X-ray photoelectron spectroscopy, angle-resolved and imaging modes, and atomic force microscopy showed that the acid treatment brought about both chemical and topographical changes in the substratum surface. While the bone marrow cells attached to both treated and untreated areas of the surfaces of the dishes, the distribution of early mineralized extracellular matrix in these areas was reproducibily different. Thus, using extracellular matrix deposition as a marker, modification of the polymer surface resulted in the cells adhering to treated and untreated areas exhibiting different phenotypes.
Calcium Phosphate Cement in a Rabbit Femoral Canal Model and a Canine Humeral Plug Model: A Pilot Investigation
Authors: Constantz B. R. , Young S. W. , Kienapfel H. , Dahlen B. L. , Sumner D. R. , Turner T. M. , Urban R. M. , Galante J. O. , Goodman S. B. , Gunasekaran S. 
Published: March 2011

ABSTRACTA new cementitious calcium phosphate biomaterial, SuperBone®, was implanted in both a rabbit femoral canal model and a canine humeral plug model. New Zealand White rabbits were implanted with cement through a novel surgical approach where cement was introduced by injection. In the canine model, a uniform gap of 3 mm around a fiber metal porous implant was filled by the cement. Undecalcified light and backscattered electron histological evaluations indicate the cement is highly biocompatible and is replaced by new bone in concert with cell-mediated resorption. Unlike the acrylic bone cement positive controls, no evidence of fibrous tissue was found around the cement.
Osteogenic Effect of Ashed Bone in Fixation of Hip Implants
Authors: Nash Alexis S. 
Published: March 2011

ABSTRACTThe purpose of this work is to discuss the role of ashed bone reinforced Ultra-High Molecular Weight Polyethylene, UHMWPE, biocomposite in bringing about early biological fixation of hip implant by combining the high damping capacity of this composite with the osteogenic characteristic of ashed bone. This paper will present the damping results obtained for this composite containing 65 weight% ashed bone over a range of frequencies, 0.1–100 rad/s, using a forced vibration technique. Some of the data obtained for lower ash content compositions are compared. The structural characteristics of bone and ashed bone are illustrated using x-ray diffractometry, XRD, and scanning electron microscopy, SEM. The optimal ashing temperature and volume fraction of ashed bone are also significant parameters which will be discussed. The 65 weight % ashed bone composite was elected to simulate the bone mineral content and use as a bioactive agent for the enhancement of bone ingrowth in the early days post-implantation.
The Evaluation of Alpha Plaster of Paris as a Osteoconductive Material in the Adult Cat Calvarium
Authors: Knuckey N. W. , Saskin H. , Yanagasawa R. , Flanagan M. 
Published: March 2011

Spontaneous new bone formation does not occur in the adult calvarium. In humans, cranial defects may require repair for brain protection, headaches or cosmetic. Over the years the search for the ideal cranioplasty material to repair such cranial defects has been extensive. We report an evaluation of alpha plaster of paris as an osteoconductive material in a cat craniectomy defect.Adult cats of either sex were anesthetized with ketamine/halothane and a 15mm biparietal craniectomy defect created. The right side was filled with alpha plaster of paris and the left served as a control. There were 4 animals in each time cohort and animals were sacrificed at 6 weeks, 6 or 12 months. The cranium was removed, fixed, stained, histologically studied and analysised for the percentage of trabecular bone formation. At all durations the control defects were bridged by proliferative fibrous tissue membrane and less than 1% trabecular bone. At six weeks the plaster of paris filled defects were either totally or nearly totally replaced by new bone formation. The plaster was completely resorbed. At 6 wks there was 28% trabecular bone which increased to 93% at 52 wks. Our experiments demonstrate the oeteoconductive potential of alpha plaster of paris in the adult calvarium. This material needs to be evaluated in humans to ascertain its potential as a biocompatible cranioplasty material.
Relativistic Multiple Scattering Theory for Space Filling Potentials
Authors: Wang Xindong , Zhang X. -G. , Butler W. H. , Harmon B. N. , Stocks G. M. 
Published: March 2011

ABSTRACTWe derive a relativistic full potential multiple scattering theory (MST) in direct analog to the non-relativistic full potential MST[1, 2]. The secular equation is derived fromi the Lippmann-Schwinger equation by expanding the wave function in terms of cell basis functions which are locally exact solutions of the Dirac equation. The relationship between this theory and currently widely used relativistic munffin-tin MST is also discussed.
Experiences with the Quadratic Korringa-Kohn-Rostoker Band Theory Method
Authors: Faulkner J. S. 
Published: March 2011

ABSTRACTThe Quadratic Korringa-Kohn-Rostoker method is a fast band theory method in the sense that all eigenvalues for a given k are obtained from one matrix diagonalization, but it differs from other fast band theory methods in that it is derived entirely from multiple-scattering theory, without the introduction of a Rayleigh-Ritz variational step. In this theory, the atomic potentials are shifted by Δασ(r) with Δ equal to E-E0 and σ(r) equal to one when r is inside the Wigner-Seitz cell and zero otherwise, and it turns out that the matrix of coefficients is an entire function of Δ. This matrix can be terminated to give a linear KKR, quadratic KKR, cubic KKR, …, or not terminated at all to give the pivoted multiple-scattering equations. Full potentials are no harder to deal with than potentials with a shape approximation.
Transfer of Classical Multiple Scattering theory to Quantal Multiple Scattering Theory
Authors: Korringa J. 
Published: March 2011

ABSTRACTThe transition firom classical to modern multiple scattering theory will be told in a very personal vein. The conjunction of a great teacher (Kronig). a classical problem (acoustical impedance of a porous plaster) the right reference (Kasterin's 1903 Moskau thesis) and my interest in the metallic state set the stage for a transfer from sound waves to Schroedinger waves. My 1947 Paper in Physica and Kohn and Rostoker's Physical Review paper of 1954 were shown to oe equivalent and constitute the basis of the KKR method, to the development of which Sam Faulkner has contributed more than anyone else. Details of these events will be presented.
Spin Polarised Relativistic Kkr
Authors: Staunton J.B. , Matsumoto M. , Strange P. 
Published: March 2011

ABSTRACTWe review spin polarised multiple scattering theory and show how it can provide a description of magnetic anisotropic effects in metallic systems. An interpretation in terms of the leading relativistic corrections is given; namely the interaction between spin-orbit coupling and spin polarisation. It is pointed out that it is straightforward to vary the d-rection of spin polarisation within this formalism. As simple illustrations, the cases of two and three impurities in a non-interacting relativistic' electron gas are outlined and the origin of pseudo-dipolar and Dzyaloshinski-Moriya anisotropy highlighted. We go on to compare and contrast estimates of magneto-crystalline anisotropies of transition metals with those from alternative methods. Finally we discuss the paramagnetic spin susceptibility of metals within this framework and show that this work is complementary to magnetic anisotropy energy calculations. A generalised Stoner condition for the onset and direction of the magnetisation is given. Calculations for h.c.p. metals cobalt, scandium and yttrium are presented. We conclude by pointing out that this approach can be extended to set up a theory for the dynamical susceptibility with consequent implications for anisotropy of spin wave excitations.
A Multi-Atom, Self-Consistent, Relativistic Kkr Electronic Structure Program: Numerical Aspects and Applications
Authors: Guo G. Y. , Temmerman W. M. 
Published: March 2011

ABSTRACTA KKR program for self-consistent electronic structure and total energy calculations of complex solids has been developed. This program has been used to study structural, electronic and magnetic properties of a number of solids. In this paper, we give a description of several numerical techniques used in this KKR program which might be of use to other practitioners. We also present some results obtained using this program: c/a ratio of hexagonal Y, elastic constants of Mo, TiC and MgO, and static spin susceptibility of Pd.
Self-Consistent Electronic-Structure Calculations for Interface Geometries
Authors: Sowa Erik C. , MacLaren J. M. , Zhang X. -G. , Gonis A. 
Published: March 2011

ABSTRACTWe describe a technique for computing self-consistent electronic structures and total energies of planar defects, such as interfaces, which are embedded in an otherwise perfectcrystal. As in the Layer Korringa-Kohn-Rostoker approach, the solid is treated as a set of coupled layers of atoms, using Bloch's theorem to take advantage of the two-dimensional periodicity of the individual layers. The layers are coupled using the techniques of the Real-Space Multiple-Scattering Theory, avoiding artificial slab or supercell boundary conditions. A total-energy calculation on a Cu crystal, which has been split apart at a (111) plane, is used to illustrate the method.
Multiple Scattering Calculations Applied to XAS: A Structure and Electronic Sensitive Tool
Authors: Sainctavit Philippe , Petiau J. 
Published: March 2011

ABSTRACTWe present an application of multiple scattering theory with “muffin-tin” potentials to the calculation of X-ray absorption cross section. We have measured and calculated the K-edge spectra of atoms in compounds with zincblende structure : SiC, ZnS. We show that some spectral features can be precisely related to the local environnement around the absorbing atom.
Positron 2D-Acar Experiments and Electron-Positron Momentum Density in YBa2Cu307−x
Authors: Smedskjaer L.C. , Bansil A. , Welp U. , Fang Y. , Bailey K.G. 
Published: March 2011

ABSTRACTWe discuss positron annihilation (2D-ACAR) measurements in the c-projection on an untwinned metallic single crystal of YBa2Cu3O7-x as a function of temperature, for five temperatures ranging from 30K to 300K. The measured 2D-ACAR intensities are interpreted in terms of the electron-positron momentum density obtained within the KKR-band theory framework. The temperature dependence of the 2D-ACAR spectra is used to extract a ‘background corrected’ experimental spectrum which is in remarkable accord with the corresponding band theory predictions, and displaysin particular clear signatures of the electron ridge Fermi surface.
Full Potential Electronic Structure Calculations and the Concept of Stress Fields and Energy Densities for Total Energy Calculations
Authors: Ziesche P. 
Published: March 2011

ABSTRACTWith the availability of reliable full atomic cell orbitals the possibility arises to calculate pressure or stress, restoring or relaxation driving Hellmann -Feynman forces, and total energies (especially of defects) alternatively and directly via stress tensor fields and energy densities, two local quantities. Although quantum mechanical stress field and energy density can not be defined uniquely, there is a recent interest in these quantities, because integrals with physical meaning are gauge invariant.The mentioned fields can be defined (i) for the full many-body description with the exact one-particle density matrix and pair distribution function as well as (ii) for the Kohn-Sham one-particle description with LDA or beyond (gradient expansion approximation). If the local stress field for a special system once is constructed, then the global stress tensor and /or forces on nuclei can be calculated via the stress theorem and the force theorem by means of unit cell surface integrals. The energy density can be derived from the terms of the stress field by taking the trace and can be used to calculate defect energies without bothering about the thermodynamic limit.
An Updated Gas Source Focused Ion Beam Instrument for TEM Specimen Preparation
Authors: Alani Reza , Jones Joseph S. , Swann Peter R. 
Published: March 2011

AbstractThe construction and performance of an updated gas source precision ion milling system are described. The system is based on an existing focused ion beam machine which is able to image and mill selected areas of specimens that are too thick for TEM studies. The specimen image is formed using either secondary electrons or secondary ions, captured by a dual detector. The work chamber consists of three major components: the ion gun, the ion column and the specimen chamber. The ion gun is an electron impact ionization type with an optimized source size and allows the use of variety of gases. The updated system employs an objective lens with shorter focal length to enhance the resolution. The specimen chamber with an improved specimen eucentric stage, accepts side entry TEM specimen holders. This enables the specimen to move between the TEM and the instrument for further precision thinning as required without removal of the specimen from the holder and consequent risk of damage. The upgraded system resolves features <1μm in thickness. Its point milling rate for Ni is 1.4μm/min. The ability of the instrument for imaging and localized milling is demonstrated by a number of TEM images of semiconductors, metals, ceramics and composites.
Characterizing Hierarchical Structures of Natural Ivory
Authors: Zhang H. B. , Cui F. Z. , Wang S. , Li H. D. 
Published: March 2011

AbstractThis paper presents a detailed investigation of the hierarchical and structural organization of the collagen-based aggregates in ivory. Ivory from African elephants is selected as the prototype in this study. A sophisticated architecture composed of collagen fibers and hydroxyapatite-like particles is revealed by optical microscopy, scanning electron microscopy and transmission electron microscopy. X-ray diffraction and TEN with selected area diffraction are employed to analyze the structure. Electron spectroscopy for chemical analysis and infrared absorption spectroscopy give information about the composition and chemical environment of the atoms in ivory. It is found that the structure of ivory has a three-level hierarchical organization, which includes both organic and inorganic materials. In the structure the inorganic material exists inside an organic framework, located outside of the collagen fibrils in the extrafibrillar volume. This inorganic structure has a polycrystalline form. Both the chemical compositions and the chemical environment of the atoms in the hydroxyapatite-like particles in ivory are different from those in natural hydroxyapatite.
Cluster Assembly of Hierarchical Nanostructures
Authors: Siegel Richard W. 
Published: March 2011

AbstractIn the past few years, atom clusters with diameters in the range of 2–20 nm of a variety of materials, including both metals and ceramics, have been synthesized by evaporation and condensation in high-purity gases and subsequently consolidated in situ under ultrahigh vacuum conditions to create nanophase materials. These new ultrafine-grained materials have properties that are often significantly different and considerably improved relative to those of their coarser-grained counterparts owing to both their small grain-size scale and the large percentage of their atoms in grain boundary environments. Since their properties can be engineered during the synthesis and processing steps, cluster-assembled materials appear to have significant potential for the introduction of a hierarchy of both structure and properties. Some of the recent research on nanophase materials related to properties and scale are reviewed and some of the possibilities for synthesizing hierarchical nanostructures via cluster assembly are considered.
Hierarchical Design Of Electrochromic Glasses
Authors: Demiryont Hulya 
Published: March 2011

AbstractLayered electrochromic glass was investigated in order to test the feasibility of using hierarchical designs for new electrochromic devices. Matrix-type synthetic electrochromic structures were designed, and two types of matrix devices, polarization and plating, were produced and evaluated. The application and device requirements of electrochromic glasses are discussed.
Physics of Complex-Biological Membranes and Cell Interfaces
Authors: Evans Evan 
Published: March 2011

AbstractNature has developed exceptional designs for resilient “soft” materials and for interfacing “soft-hard” materials which show capabilities well-beyond our present day technology. Most of the properties of biological materials – and a great deal of biological function – emanate from chemical and physical characteristics of interfacial structures (membranes). Although material interfaces in biology are complicated, it appears that these structures have been invariably optimized (with respect to harsh-environmental requirements) by the slow “evolutionary-driven” engineering. Some “hierarchical” features and characteristic length scales for biological membranes are directly related to architecture; but others are more subtle and arise because conformations of much of the molecular structure are randomized by thermal fluctuations.
Disorder and Scaling in Regular and Hierarchical Composites
Authors: Duxbury P. M. 
Published: March 2011

AbstractWe first summarize the scaling behavior of breakdown strengths and transport and elastic moduli of random two phase composites. We then consider the effect of disorder on two hierarchical structures. The first, a tree-like structure illustrates the fact that disordered trees, such as occur in many natural circulatory systems, show large fluctuations in their conductance and current flow. The second, a continuous fiber composite (CFC), leads us to suggest that, due to its greater flaw tolerance, a hierarchical microstructural design may improve the longitudinal and transverse toughness of CFC's.