bluuebunny/crossref_metadata_2025_split huggingface dataset:
Silica/Silicone Nanocomposite Films: A New Concept in Corrosion Protection
Authors: Gentle Theresa E. , Baney Ronald H. 
Published: March 2011

ABSTRACTThin films of silsesquioxane, (HSiO3/2)n, were applied to aluminum panels and to CMOS microelectronic circuit surfaces by spin or dip coating organic solutions of the silsesquioxane. Nanoporous silica was obtained by oxidation of the silsesquioxane. These nanoporous silica films were then vacuum infiltrated with various viscosities of polydimethylsiloxanes (PDMS) to form hydrophobic nanocomposites. The nanocomposite films were shown to provide superior hermetic protection against salt fog exposure when compared to PDMS and silica films alone.The composite films were characterized by FTIR and optical microscopy. FTIR spectra showed that the silica served as a skeletal framework holding the hydrophobic PDMS in place and preventing loss of adhesion. This is in contrast to PDMS films alone in which blistering of the film from the substrate can occur, thus, allowing ions and moisture to reach the surface and corrosion to take place.
Microcrystalline Ceramic Composites by Active Filler Controlled Reaction Pyrolysis of Polymers
Authors: Greil Peter , Seibold Michael , Erny Tobias 
Published: March 2011

ABSTRACTPyrolytic conversion of preceramic polymers such as polysilanes, -silazanes, or -siloxanes to ceramics may be significantly influenced by the resence of active filler dispersoids. Based on thermodynamic and microstructural considerations a variety of suitable polymer-filler systems can be found which allow the fabrication of microcrystalline composite materials with low dimensional change upon polymer- ceramic conversion. As an example the active filler controlled reaction pyrolysis of polysiloxane with addition of titanium powder was investigated. A composite material with microcrystalline titanium carbide inclusions embedded in an amorphous (< 1000 °C) or nanocrystalline (>1000 °C) silicon oxycarbide matrix was formed. Property changes with increasing pyrolysis temperature can be attributed to various microstructural transformations. Thus, a variety of potential fillers may be used to tailor the microstructure of polymer-derived ceramic composite materials in order to fabricate bulk materials and components with a broad range of compositions and properties.
Structure-Property Relationships in the Toughening of Poly(Methyl Methacrylate) by Sub-Micron Size, Multiple-Layer Particles
Authors: Archer A. C. , Lovell P. A. , McDonald J. , Sherratt M. N. , Young R. J. 
Published: March 2011

ABSTRACTRubber-toughened poly(methyl methacrylate) materials have been prepared by blending poly(methyl methacrylate) with specially-synthesised, refractive index matched particles containing two, three and four radially-alternating rubbery and glassy layers. The paper describes the effects upon mechanical properties of (i) two-, three- and four-layer particle structure and (ii) particle diameter and glassy core size for three-layer particles.
A Study on the Blends of Epoxy/Polybutadiene and the Application to the Encapsulation of a Capacitor
Authors: Ren Zhongyuan , Qui Liying 
Published: March 2011

ABSTRACTThis paper describes the blends of epoxy/polybutadiene and the application of the blends to the encapsulation of capacitors. Experiments showed that the hydroxy-carboxyl terminated polybutadiene (HCTPB) had a good toughening effect on epoxy resins, and the blends of epoxy/HTPB or epoxy/HCTPB had good craze resistance at low temperatures. The phase separation and dynamic mechanical analysis of these blends are discussed below.
Fracture Toughness and Fracture Mechanisms of PBT/PC/IM Blend
Authors: Wu Jingshen , Mai Yiu-Wing , Cotterell Brian 
Published: March 2011

ABSTRACTStatic and impact fracture toughness of a Polybutylene terephthalate (PBT)/Polycarbonate (PC)/Impact modifier (IM) blend was studied at different temperatures. The experimental results were interpreted by the specific fracture work concept and J-integral analysis. It is found that the specific fracture work concept characterizes the impact behavior of the blend very well. In the static fracture tests the specific fracture work gives the crack initiation resistance of the blend which is consistent with the JIC value obtained. The effect of temperature was also examined and the fracture mechanisms were investigated via TEM and SEM. Extensive cavitation of the impact modifiers and plastic flow of matrix in the vicinity of the crack tip is believed to be the major toughening process of the enhanced fracture toughness.
High Glass Content Non-Shrinking Sol-Gel Composites via Silicic Acid Esters
Authors: Ellsworth Mark W. , Novak Bruce M. 
Published: March 2011

ABSTRACTThe application of the sol-gel process for the formation. of inorganic-organic composites has received a great deal of attention in recent years. We have focused our efforts in this area toward the development of simultaneous polymerization/sol-gel reactions for the developement of inorganic-organic composites with a wide range of polymers. Further research in this area has led to the design and synthesis of tetraalkoxysilanes, and more recently, poly(silicic acid esters) possessing polymerizable alkoxides for the synthesis of non-shrinking sol-gel composites.
Effect of Pressure on Order and Stability in Alloys: The Case of Al-Ge
Authors: Turchi P. E. A. , Sluiter M. , Stocks G. M. 
Published: March 2011

ABSTRACTA parameter-free approach to phase stability in substitutional alloys is applied to the influence of pressure on order-disorder phenomena in Al-Ge. The methodology is based upon an application of the Generalized Perturbation Method to the Korringa-Kohn-Rostoker scattering formulation of the Coherent Potential Approximation. For fcc-based Al-Ge alloys, it is shown that the tendency towards phase separation at normal pressure originates from a structural difference between the pure species. By applying pressure, the structural energy difference is reduced, and a significant increase in the tendency towards order, especially for Al-rich alloys, is theoretically observed, leading, as an example, to the possible observation of a DO22 ordered state around 25 at. pct. Ge. The electronic origin of the ordering tendencies induced by pressure is discussed and the theoretical predictions are related to experimental facts.
A Tight-Binding-Bond Approach to Interatomic Forces in Disordered Transition Metal Alloys
Authors: Pasturel A. 
Published: March 2011

ABSTRACTA tight-binding-bond approach to interatomic forces in disordered transition metal-Aluminium alloys is presented. The bond-order is calculated on a Bethe lattice reference system, well adapted to topologically disordered alloy. It is shown that the bond-order depends strongly on the strength of the pd hybridization in the AB alloy, leading to non additive potentials with a strong preference for the formation of pair of unlike atoms and short bond-distances in the A-B pairs. This is illustrated by studying the structural properties of liquid Al80Ni20 and Al80Mn20 alloys using molecular dynamics simulations and by comparing our results with the available experimental ones.
Kinetics of Ordering in Cu3Au : An Atomistic Approach
Authors: Xi Zhigang , Chakraborty Bulbul 
Published: March 2011

ABSTRACTWe study the kinetics of ordering in Cu3Au using a model Hamiltonian derived from the effective medium theory of chemical bonding. Monte Carlo simulations are used to investigate universal and non-universal features of the growth kinetics. Anisotropic scaling of the structure factor is observed in late-stage growth of ordered domains. The anisotropy is a non-universal feature determined by the details of the microscopic model, and we find that the anisotropy observed in the simulations is in excellent agreement with experiments on Cu3Au. The simulations are discussed in the context of theories of unstable growth. To our knowledge, this is the first study of kinetics in a realistic model Hamiltonian describing the material-specific properties of Cu3Au.
Real-Space Descriptions of Structural Energies in Metals
Authors: Carlsson A. E. , Zou J. 
Published: March 2011

ABSTRACTTwo real-space methods for treating structural energetics of transition metals and compounds are described. The first uses a local description of the electronic density of states (DOS) in a tight-binding model to obtain an angular-force method containing up to four-body interaction terms. It is shown that this method yields bond-strengthening effects at surfaces which exceed those obtained by previous many-body potentials. Structural-energy calculations show that for W, several Frank-Kasper phases are only slightly higher in energy than the ground-state bcc structure; this near-degeneracy is driven by the energetic favorability of icosahedral sites. The second method uses a free-electron type approach to generate pair potentials for transition-metal solutes in Al. The calculated potentials have an oscillating form, with a much larger magnitude than those in Al. The potential is applied to complex Al-Mn phases, including the icosahedral quasicrystal. The results indicate that the oscillating pair potentials make a major contribution to stabilizing the complex phases.
Self Diffusion Parameters from Non-empirical Pair Potentials
Authors: Dorfman S. , Fuks D. , Pelleg J. , Rashkeev S. 
Published: March 2011

ABSTRACTA scheme for construction of the pair potential from non-empirical calculations of electronic structure of solids is suggested. As an example, parameters of Lennard-Jones potential are obtained for fccCs, based on LMTO calculations of energy parameters. Vacancy formation and migration energies for fccCs are calculated from this first-principles pair potential. In addition, the frequency of vibration and the jump probability of an atom are calculated and it is shown that they are direction dependent.
Molecular Mechanics and Dynamics Studies of Chemisorbed Monolayers of Alkanethiolates
Authors: Shnidman Yitzhak , Eilers James E. , Ulman Abraham , Sellers Harrell 
Published: March 2011

ABSTRACTWe study ordering within closely packed monolayers of thiol derivatives self-assembled on gold substrates by chemisorption from solution. We discuss constant stress molecular mechanics and dynamics simulations of alkanethiolate monolayers on Au(111) and Au(l00) surfaces. In the first case, we use the MM2 force field augmented with classical chemisorption parameters obtained from fitting to results of ab initioquantum mechanical calculations. In the second, the chemisorption to the Au(l00) surface was accomplished by using harmonic constraints to restrict the thiolate groups to the square lattice. It is shown that two chemisorption modes of alkanethiolate on Au(l11) exist, and that both give closely packed ordered monolayers. In the system on Au(100), rearrangement towards close-packing is achieved at the expense of distortions that increase the intrachain elastic energy.
Exact Diagonalization Study of Real Materials
Authors: Chen Changfeng 
Published: March 2011

ABSTRACTWe report some recent developments in theoretical modeling of real 3d magnetic materials, particularly interface and ultrathin-film structures. We focus on many-body correlation effects and describe the method of modeling realistic strongly correlated electron systems using and going beyond die local-density-approximation single-particle electronic structures. Group-theoretical techniques and high-performance computing facilities are systematically used in this work. Fundamental spectroscopic properties of several prototypical 3d transition-metal systems have been obtained and new features induced by many-body correlation have been discovered. Results will be presented and discussed.
Ground State Analysis on the Fcc Lattice With Four Pair Interactions
Authors: Garbulsky Gerardo D. , Tepesch Patrick D. , Ceder Gerbrand 
Published: March 2011

ABSTRACTWe have partially solved the ground state problem of binary alloys on the fcc lattice with pair interactions up to the fourth nearest neighbor distance. Our results extend the study presented by Kanamori and Kakehashi [1], releasing the constraint they imposed on the nearest neighbor correlation. The solution we present increases the number of possible ground state structures by an order of magnitude with respect to previous results. We have applied both the polyhedron and the enumeration method. The latter proved more powerful when including interactions beyond the second nearest neighbor distance.
Parallel Algorithms for Molecular-Dynamics Simulations of Coulombic Systems
Authors: Li Wei , Kalia Rajiv K. , Leeuw Simon De , Nakano Aiichiro , Greenwell Donald , Vashishta Priya 
Published: March 2011

ABSTRACTIn molecular-dynamics simulations for the long-range Coulomb interaction, a great deal of effort is devoted to reducing the computational complexity of the usual N2operations in the direct calculation. For bulk systems, we have designed a parallel algorithm based on the domain-decomposition strategy for the Ewald summation. The performance of the algorithm is evaluated on the in-house iPSC/860 system. We find that this algorithm reduces the computational complexity to O(N). For a 64,000-particle plasma in three dimension, the execution time on an 8-node system is 27.4 sec per MD time step. The interprocessor communication is a small fraction of the total execution time. We find linear speedups and a parallel efficiency of 0.85. For comparison, parallel algorithms are also designed for the Fast Multipole Method (FMM) - a divide and conquer scheme in which the system is divided into cubic subdomains and interactions between distant charged regions are calculated with a truncated multipole expansion. The performance of the FMM on Touchstone Delta machine is discussed.
Statistical Modelling in Materials Research
Authors: Pouskouleli G. , Ahmad A. , Wheat T.A. , Varma S. , Prasad S.E. 
Published: March 2011

ABSTRACTThe role of statistical modelling in materials research is examined. It is shown that considerable benefits can be derived by following an appropriate full factorial design, in which a number of factors (process parameters) are varied simultaneously while the responses (materials properties) are monitored. It is also shown that by using a fractional factorial matrix, essentially the same conclusions can be drawn with a significantly smaller number of experimental trials. Examples drawn from recent materials research on glasses and ceramics are presented to demonstrate the effectiveness of this approach.
Interatomic Potentials From First-Principles Calculations
Authors: Ercolessi Furio , Adams James B. 
Published: March 2011

ABSTRACTWe propose a new scheme to extract “optimal” interatomic potentials starting from a large number of atomic configurations (and their forces) obtained from first-principles calculations. The method appears to be able to overcome the difficulties encountered by traditional fitting approaches when using rich and complex analytical forms, and constitute a step forward towards large-scale simulations of condensed matter systems with a degree of accuracy comparable to that obtained by ab initio methods. A first exploratory application to aluminum is presented.
Long Time Dynamics of the Transverse Ising Model - Comparison With Data onLiTbF4
Authors: Sen Surajit , Florencio João , Cai Zhi-Xiong 
Published: March 2011

ABSTRACTWe use the continued fraction formalism (CFF) to obtain the zz- component of the dynamical spin pair correlations of a transverse Ising model (TIM) in 2D at T = ∞ for the first time. Our calculations suggest that the correlation function decays algebraically at long times as t−α, 1.5 < α < 2.2, which is slower than gaussian decay found for the corresponding dynamical correlation in 1D. The calculations suggest that the corresponding dynamical correlation in 3 D is also likely to exhibit a power law decay. Our results compare favorably with the neutron scattering data on LiTbF4, for T > Tc, an induced moment ferromagnet.
Parallel Molecular Dynamics With the Embedded Atom Method
Authors: Plimpton Steven J. , Hendrickson Bruce A. 
Published: March 2011

ABSTRACTParallel computing offers new capabilities for using molecular dynamics (MD) to simulate larger numbers of atoms and longer time scales. In this paper we discuss two methods we have used to implement the embedded atom method (EAM) formalism for molecular dynamics on multiple-instruction/multiple-data (MIMD) parallel computers. The first method (atom-decomposition) is simple and suitable for small numbers of atoms. The second method (force-decomposition) is new and is particularly appropriate for the EAM because all the computations are between pairs of atoms. Both methods have the advantage of not requiring any geometric information about the physical domain being simulated. We present timing results for the two parallel methods on a benchmark EAM problem and briefly indicate how the methods can be used in other kinds of materials MD simulations.
Diffusion of Metallic Impurities in Semiconductor Thin Film
Authors: Vaysleyb Alexander V. 
Published: March 2011

ABSTRACTThe diffusion transport of metal impurities in semiconductors is considered. Critical magnitude of dislocation density and critical sample size are obtained at which the diffusion kinetics change from the interstitial impurity regime of diffusion transport to the self-interstitial regime or the vacancy regime. It is predicted that the critical density of dislocations decreases with increasing temperature.
A Method for the Determination of Real-Space Interatomic Force-Constants.
Authors: Quong Andrew A. , Liu Amy Y. , Klein Barry M. 
Published: March 2011

ABSTRACTWe present a method for the self-consistent determination of inter-atomic force-constants. Using non-local ab-initio pseudopotentials to represent the ion-electron interaction and linear response theory to calculate the self-consistent change in the electron density, we are able to calculate the dynamical matrices at arbitrary points in the Brillouin zone. Diagonalization of the dynamical matrix yields phonon eigenvectors and eigenvalues, and fourier inversion yields the real-space interatomic force-constants. We present numerical results for the phonon-dispersion of a variety of metals.
Reconstruction of Twist Grain Boundaries in Gold
Authors: Phillpot S. R. 
Published: March 2011

ABSTRACTThe reconstruction of high-angle twist grain boundaries on the four densest atomic planes in gold are investigated using the recently developed method of grand-canonical simulated quenching. It is found that the grain boundaries on the two densest planes, (111) and (100), do not reconstruct, while those on the (110) and (113) planes do.
Theoretical Prediction of the Donor/Acceptor Site-Dependence on First Hyperpolarizabilities in Conjugated Systems Containing Azomethine Bonds
Authors: Matsuura Azuma , Hayano Tomoaki 
Published: March 2011

ABSTRACTWe calculated frequency-dependent first hyperpolarizabilities for electro-optic Pockels effect, β(ω; 0, ω), in π-conjugated molecules containing azomethine bonds using the CNDO/S-CI sum-over-states method. First, we examined the dependence of static β on formulas for the two-center Coulomb integral, γAB. The choice of the γAB formula has little effect on the relative β value, but a considerable effect on the absolute value. Then we investigated the relationship between the magnitude of β(ω; 0, ω) and the donor/acceptor substitution sites. We found that the molecule with no donors or acceptors can be divided into donor and acceptor regions whose existence causes the donor/acceptor site-dependence of β(ω; 0, ω).
Angular Dependence of the Magnetic Properties of Steels Under the Action of Uniaxial Stress
Authors: Kaminski D. A. , Jiles D.C. , Biner S.B. , Sablik M.J. 
Published: March 2011

ABSTRACTAngular dependence of structure sensitive magnetic properties such as coercivity and permeability has never been adequately explained by a quantitative physical model or theory. The present study investigates the angular dependence of magnetic properties of materials with different microstructures. Measurements were taken under compressive and tensile uniaxial stress. The materials investigated were plain carbon steels with compositions of 0.1 % -0.8% carbon. Alloy steels with compositions of 2.25 % Cr and 1.0 % Mo were also investigated. The effects of uniaxial stress on permeability along the direction of the stress can be described by including an effective field Hσ given by:Experimental results are compared to model using Hσ.
Anharmonic Effects at the (100) and (110) Surfaces of Ni
Authors: Beaudet Yvon , Lewis Laurent J. , Persson Mats 
Published: March 2011

ABSTRACTWe present the results of a detailed molecular-dynamics investigation of anharmonic effects at the (100) and (110) surfaces of Ni, with the interactions between atoms described using embedded-atom potentials. We find both surfaces to suffer an anomalously large thermal expansion, with a concomitant rapid increase of the mean-square amplitudes of vibration. For the (100) surface, our results for the surface expansion can be directly compared to the low-energy electron diffraction (LEED) measurements of Cao and Conrad;1 the agreement is excellent. The anomalies appear at a temperature of about 900 K for the (100) surface, well below the onset of disordering, thereby confirming that the observed anomalies indeed arise from anharmonicities. Our simulated LEED intensities are found to reproduce well the observed intensities. The phonon spectra in the anharmonic regime will be discussed, and a detailed comparison between the two surfaces will be established.
A Tight-Binding Molecular Dynamics Simulation of the Melting and Solidification of Silicon
Authors: Horsfield Andrew , Clancy Paulette 
Published: March 2011

ABSTRACTThe melting of crystalline silicon and the cooling of liquid silicon are investigated using Molecular Dynamics. Both the Stillinger-Weber (SW) potential and the Tight-Binding Bond Model are used to calculate the forces. The electrical properties are investigated using an empirical pseudopotential method with a plane wave basis. The melting point of the solid is found to be about 2300K. The dependency of this temperature with cell size is investigated. On cooling, there are changes in some of the properties of the liquid: the energy per particle decreases, the diffusion constant decreases, and the low frequency electrical conductivity decreases slightly as the temperature decreases. Between 1180K and 980K the liquid undergoes a transition to a glassy phase. There are large changes in the pair correlation function, the SW three-body energy distribution, the diffusion constant, the density of electron single particle states and the electrical conductivity. All of these changes are consistent with increased tetrahedral bonding.
Molecular Dynamics Simulations and Theory of Interfaces of Oligomers
Authors: Harris Jonathan G. , Wang Yantse 
Published: March 2011

ABSTRACTThese proceedings summarize recent work in our group studying the structure of interfaces involving molecular fluids. Two types of systems are discussed. First, we summarize simulations of the structure and surface tension of liquid-vapor interfaces of the alkanes eicosane and decane. Then, we describe the results of simulations of the confined films studied in surface force apparatus and atomic force microscopy experiments. Our simulations show that in both films of normal and branched alkanes, the formation of a layered structure is observed. The branching inhibits this layering, especially in the narrowest pores. In addition an examination of the molecular motions indicates that a transition to a solid or glassy state is not a prerequisite for layering or oscillating solvation forces.