81 results on '"INTERFACES (Physical sciences)"'
Search Results
2. Study on the Ge1–xSnx/HfO2 interface and its impacts on Ge1–xSnx tunneling transistor.
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Yingxin Qiu, Runsheng Wang, Qianqian Huang, and Ru Huang
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FIELD-effect transistors , *CHEMICAL bonds , *INTERFACES (Physical sciences) , *DENSITY functional theory , *SIMULATION methods & models , *MATHEMATICAL optimization - Abstract
In this paper, we employ first-principle calculation to investigate the Ge1–xSnx/HfO2 interface, and then evaluate its impacts on Ge1–xSnx tunneling field-effect transistor (TFET). First-principle calculations of Ge1–xSnx/HfO2 interfaces in the oxygen-rich process atmosphere indicate that the interface states originate from the Ge and Sn dangling bond, rather than Hf-bond. The total density of state shows that there are more interface states in the semiconductor bandgap with increasing Sn fraction. By further incorporating the material and interface parameters from density functional theory calculation into advanced device simulation, the electrical characteristics of Ge1–xSnx TFET are investigated. Removing the Sn atom from the first atom layer of Ge1–xSnx in device processes is found to be beneficial to reduce the degradations. For the degradation mechanisms, the trap-assisted-tunneling is the dominant mechanism at the low Sn fraction, and enhanced Shockley-Read-Hall recombination induced by traps becomes the dominant mechanism with increasing Sn fraction. The results are helpful for the interface optimization of Ge1–xSnx TFET. [ABSTRACT FROM AUTHOR]
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- 2014
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3. Organic solar cells: a rigorous model of the donor-acceptor interface for various bulk heterojunction morphologies.
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Raba, Adam, Leroy, Yann, and Cordan, Anne-Sophie
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SOLAR cells , *ELECTRON donor-acceptor complexes research , *INTERFACES (Physical sciences) , *CHARGE transfer , *HETEROJUNCTIONS , *BOUNDARY value problems , *SIMULATION methods & models - Abstract
Theoretical studies of organic solar cells are mostly based on one dimensional models. Despite their accuracy to reproduce most of the experimental trends, they intrinsically cannot correctly integrate the effects of morphology in cells based on a bulk heterojunction structure. Therefore, accounting for these effects requires the development of two dimensional models, in which donor and acceptor domains are explicitly distinct. In this context, we propose an analytical approach, which focuses on the description of the interface between the two domains. Assuming pinned charge transfer states, we rigorously derive the corresponding boundary conditions and explore the differences between this model and other existing models in the literature for various morphologies of the active layer. On one hand, all tested models are equivalent for an ideal interdigitated bulk heterojunction solar cell with a planar donor-acceptor interface, but divergences between the models rise for small sizes of the donor domain. On the other hand, we carried out a comparison on a less ideal case of cell, with a rough interface between the two domains. Simulations with such cells exhibit distinct behaviors for each model. We conclude that the boundary condition for the interface between the materials is of great importance for the study of solar cells with a non-planar interface. The model must account initially for the roughness of the interface. [ABSTRACT FROM AUTHOR]
- Published
- 2014
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4. Modelling interfacial coupling in thin film magnetic exchange springs at finite temperature.
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Saharan, L., Morrison, C., Miles, J. J., Thomson, T., Schrefl, T., and Hrkac, G.
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THIN film research , *TEMPERATURE , *MAGNETIZATION , *SIMULATION methods & models , *INTERFACES (Physical sciences) - Abstract
We report a numerical study that demonstrates the interface layer between a soft and hard magnetic phase, the exchange transition layer, is the dominant factor that influences the magnetization reversal process at room temperature and long measurement times. It is found that the exchange transition layer thickness affects the magnetization reversal and the coupling of a bi-layer system by lowering the switching field and changing the angle dependent magnetization reversal. We show that the change in angle dependence of reversal is due to an increased incoherency in the lateral spin behavior. Changing the value of exchange coupling in the exchange transition layer affects only the angle dependent behavior and does not lower the switching field. [ABSTRACT FROM AUTHOR]
- Published
- 2013
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5. Simulated vibrational sum frequency generation from a multilayer thin film system with two active interfaces.
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O'Brien, Daniel B. and Massari, Aaron M.
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MULTILAYERED thin films , *OPTICAL interference , *SIMULATION methods & models , *INTERFACES (Physical sciences) , *QUALITATIVE research , *SEMICONDUCTORS , *SUBSTRATES (Materials science) - Abstract
In the field of surface-specific vibrational sum frequency generation spectroscopy (VSFG) on organic thin films, optical interferences combined with the two-interface problem presents a challenge in terms of qualitative assessment of the data and quantitative modeling. The difficulty is amplified when considering systems comprised of more than a single material thin film layer. Recently, in our lab we have developed a generalized model that describes thin film interference in interface-specific nonlinear optical spectroscopies from arbitrary multilayer systems. Here, we apply the model to simulate VSFG spectra from the simplest multilayer: a system of two thin films, one of which is an organic small molecule and the other is a dielectric layer on a semiconductor substrate system where we idealize that the organic interfaces are equally VSFG active. Specifically, we consider the molecule N,N′-dioctyl-3,4,9,10-perylenedicarboximide (PTCDI-C8) deposited on a silicon wafer with a thermally grown oxide dielectric. We present results for the four polarization experiments that sample the nonzero nonlinear susceptibility elements of macroscopically centrosymmetric materials (ssp, sps, pss, and ppp) and in two mIR frequency windows (the imide carbonyl stretches around 1680 cm-1 and the alkyl stretches around 2900 cm-1) as a function of both thin film thicknesses with fixed input beam angles. We use frequency dependent refractive indices for all materials. The goal is to illustrate some of the intricacies contained in the intensity data of such systems. Of particular interest is the effect of the relative polar orientation of modes at the interfaces and the possibility of designing a system where the collected signal is exclusively attributable to a single interface. Our calculations indicate that in order to unambiguously identify the relative polar orientation one must experimentally vary an additional system parameter such as thin film thickness or input beam angle and for quantitative modeling one cannot ignore either interfacial contribution. The results show that proper modeling of thin film interference effects is essential for accurate data analysis and should include the frequency dependent refractive indices, especially for modes with larger mIR absorption cross sections, even when absorptive losses are small. [ABSTRACT FROM AUTHOR]
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- 2013
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6. Resistive switching near electrode interfaces: Estimations by a current model.
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Schroeder, Herbert, Zurhelle, Alexander, Stemmer, Stefanie, Marchewka, Astrid, and Waser, Rainer
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ELECTRODES , *INTERFACES (Physical sciences) , *SURFACES (Physics) , *SWITCHING theory , *SIMULATION methods & models - Abstract
The growing resistive switching database is accompanied by many detailed mechanisms which often are pure hypotheses. Some of these suggested models can be verified by checking their predictions with the benchmarks of future memory cells. The valence change memory model assumes that the different resistances in ON and OFF states are made by changing the defect density profiles in a sheet near one working electrode during switching. The resulting different READ current densities in ON and OFF states were calculated by using an appropriate simulation model with variation of several important defect and material parameters of the metal/insulator (oxide)/metal thin film stack such as defect density and its profile change in density and thickness, height of the interface barrier, dielectric permittivity, applied voltage. The results were compared to the benchmarks and some memory windows of the varied parameters can be defined: The required ON state READ current density of 105 A/cm2 can only be achieved for barriers smaller than 0.7 eV and defect densities larger than 3 × 1020 cm-3. The required current ratio between ON and OFF states of at least 10 requests defect density reduction of approximately an order of magnitude in a sheet of several nanometers near the working electrode. [ABSTRACT FROM AUTHOR]
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- 2013
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7. The tension of a curved surface from simulation.
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Sodt, Alexander J. and Pastor, Richard W.
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SURFACE tension , *SIMULATION methods & models , *INTERFACES (Physical sciences) , *MOLECULAR dynamics , *DEFORMATIONS (Mechanics) , *OCTANE - Abstract
This paper demonstrates a method for calculating the tension of a system with a curved interface from a molecular dynamics simulation. To do so, the pressure of a subset of the system is determined by applying a local (virtual) mechanical deformation, fitting the response to that of a bulk fluid, and then using the Young-Laplace equation to infer the tension of the interface. The accuracy of the method is tested by calculating the local pressure of a series of water simulations at various external pressures. The tension of a simulated curved octane-water interface is computed with the method and compares well with the planar tension (≈ 46.7 dyn/cm). Finally, an ambiguity is resolved between the Harasima and Irving-Kirkwood methods of calculating the local pressure as a means for computing the tension. [ABSTRACT FROM AUTHOR]
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- 2012
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8. Modified PRISM theory for confined polymers.
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Xu, Mengjin, Zhang, Chen, Du, Zhongjie, and Mi, Jianguo
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APPROXIMATION theory , *INTERFACES (Physical sciences) , *DENSITY , *SURFACES (Technology) , *DENSITY functionals , *SIMULATION methods & models - Abstract
We propose a modified polymer reference interaction site model (PRISM) to describe the interfacial density profiles of polymers in contact with planar and curved solid surfaces. In the theoretical approach, a bridge function derived from density functional method is included. In description of hard-sphere polymer at planar and curved surfaces with an arbitrary external field, the effect of modification has been validated by the available simulation data, except for low density system. When extended to confined real systems, the modified theoretical model also shows an encouraging prospect in description of the interfacial structure and properties. [ABSTRACT FROM AUTHOR]
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- 2012
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9. Vapor-liquid interfacial properties of rigid-linear Lennard-Jones chains.
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Blas, F. J., Ignacio Moreno-Ventas Bravo, A., Míguez, J. M., Piñeiro, M. M., and MacDowell, L. G.
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INTERFACES (Physical sciences) , *MONOMERS , *SIMULATION methods & models , *MOLECULAR models , *THICKNESS measurement , *TEMPERATURE effect - Abstract
We have obtained the interfacial properties of short rigid-linear chains formed from tangentially bonded Lennard-Jones monomeric units from direct simulation of the vapour-liquid interface. The full long-range tails of the potential are accounted for by means of an improved version of the inhomogeneous long-range corrections of Janecˇek [J. Phys. Chem. B 110, 6264-6269 (2006)] proposed recently by MacDowell and Blas [J. Chem. Phys. 131, 074705 (2009)] valid for spherical as well as for rigid and flexible molecular systems. Three different model systems comprising of 3, 4, and 5 monomers per molecule are considered. The simulations are performed in the canonical ensemble, and the vapor-liquid interfacial tension is evaluated using the test-area method. In addition to the surface tension, we also obtain density profiles, coexistence densities, critical temperature and density, and interfacial thickness as functions of temperature, paying particular attention to the effect of the chain length and rigidity on these properties. According to our results, the main effect of increasing the chain length (at fixed temperature) is to sharpen the vapor-liquid interface and to increase the width of the biphasic coexistence region. As a result, the interfacial thickness decreases and the surface tension increases as the molecular chains get longer. The surface tension has been scaled by critical properties and represented as a function of the difference between coexistence densities relative to the critical density. [ABSTRACT FROM AUTHOR]
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- 2012
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10. Interfacial and coexistence properties of soft spheres with a short-range attractive Yukawa fluid: Molecular dynamics simulations.
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González-Melchor, Minerva, Hernández-Cocoletzi, Gregorio, López-Lemus, Jorge, Ortega-Rodríguez, Alejandro, and Orea, Pedro
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MOLECULAR dynamics , *SIMULATION methods & models , *SURFACE tension , *CRITICAL point (Thermodynamics) , *SPHERES , *INTERFACES (Physical sciences) , *FLUID dynamics - Abstract
Molecular dynamics simulations have been carried out to obtain the interfacial and coexistence properties of soft-sphere attractive Yukawa (SAY) fluids with short attraction range, κ = 10, 9, 8, 7, 6, and 5. All our simulation results are new. These data are also compared with the recently reported results in the literature of hard-core attractive Yukawa (HAY) fluids. We show that the interfacial and coexistence properties of both potentials are different. For the surveyed systems, here we show that all coexistence curves collapse into a master curve when we rescale with their respective critical points and the surface tension curves form a single master curve when we plot γ* vs. T/Tc. [ABSTRACT FROM AUTHOR]
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- 2012
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11. A scattering model for nano-textured interfaces and its application in opto-electrical simulations of thin-film silicon solar cells.
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Jäger, K., Fischer, M., van Swaaij, R. A. C. M. M., and Zeman, M.
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MATHEMATICAL models , *SCATTERING (Physics) , *INTERFACES (Physical sciences) , *NANOTECHNOLOGY , *SIMULATION methods & models , *PHOTOVOLTAIC cells - Abstract
We present a scattering model based on the scalar scattering theory that allows estimating far field scattering properties in both transmission and reflection for nano-textured interfaces. We first discuss the theoretical formulation of the scattering model and validate it for nano-textures with different morphologies. Second, we combine the scattering model with the opto-electric asa simulation software and evaluate this combination by simulating and measuring the external parameters and the external quantum efficiency of solar cells with different interface morphologies. This validation shows that the scattering model is able to predict the influence of nano-textured interfaces on the solar cell performance. The scattering model presented in this manuscript can support designing nano-textured interfaces with optimized morphologies. [ABSTRACT FROM AUTHOR]
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- 2012
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12. Studies of structural, dynamical, and interfacial properties of 1-alkyl-3-methylimidazolium iodide ionic liquids by molecular dynamics simulation.
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Ghatee, Mohammad Hadi, Zolghadr, Amin Reza, Moosavi, Fatemeh, and Ansari, Younes
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IONIC liquids , *IMIDAZOLES , *INTERFACES (Physical sciences) , *CHEMICAL structure , *MOLECULAR dynamics , *SIMULATION methods & models , *SURFACE chemistry , *MOLECULAR structure - Abstract
Bulk and surface properties of the ionic liquids 1-alkyl-3-methyl-imidazolium iodides ([Cnmim]I) were simulated by classical molecular dynamics using all atom non-polarizable force field (n = 4, butyl; 6, hexyl; 8, octyl). The structure of ionic liquids were initially optimized by density functional theory and atomic charges obtained by CHELPG method. Reduction of partial atomic charges (by 20% for simulation of density and surface tension, and by 10% for viscosity) found to improve the accuracy, while a non-polarizable force field was applied. Additionally, the simulation ensembles approach the equilibrium faster when the charge reduction is applied. By these refined force field parameters, simulated surface tensions in the range of 323-393 k are quite in agreement with the experiments. Simulation of temperature dependent surface tension of [C4mim]I well beyond room temperature (up to 700 K) permits prediction of the critical temperature in agreement with that predicted from experimental surface tension data. Simulated densities in the range of 298-450 K for the three ionic liquids are within 0.8% of the experimental data. Structural properties for [C4mim]I were found to be in agreement with the results of Car-Parrinello molecular dynamics simulation we performed, which indicates a rather well-structured cation-anion interaction and occurs essentially through the imidazolium ring cation. Diffusion coefficient changes with alkyl chain length in the order of [C8mim]I > [C6mim]I > [C4mim]I for the cation and the anion. Formation of a dense domain in subsurface region is quite evident, and progressively becomes denser as the alkyl chain length increases. Bivariate orientational analysis was used to determine the average orientation of molecule in ionic liquids surface, subsurface, and bulk regions. Dynamic bisector-wise and side-wise movement of the imodazolium ring cation in the surface region can be deduced from the bivariate maps. Atom-atom density profile and bivariate analysis indicate that the imidazolium cation takes a spoon like configuration in the surface region and the tilt of alkyl group is a function length of alkyl chain exposing as linear as possible to the vapor phase. [ABSTRACT FROM AUTHOR]
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- 2012
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13. Investigation of the interfacial tension of complex coacervates using field-theoretic simulations.
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Riggleman, Robert A., Kumar, Rajeev, and Fredrickson, Glenn H.
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SURFACE tension , *INTERFACES (Physical sciences) , *FIELD theory (Physics) , *SIMULATION methods & models , *PHASE partition , *POLYELECTROLYTES , *ADHESIVES , *COLLOCATION methods , *GIBBS' free energy - Abstract
Complex coacervation, a liquid-liquid phase separation that occurs when two oppositely charged polyelectrolytes are mixed in a solution, has the potential to be exploited for many emerging applications including wet adhesives and drug delivery vehicles. The ultra-low interfacial tension of coacervate systems against water is critical for such applications, and it would be advantageous if molecular models could be used to characterize how various system properties (e.g., salt concentration) affect the interfacial tension. In this article we use field-theoretic simulations to characterize the interfacial tension between a complex coacervate and its supernatant. After demonstrating that our model is free of ultraviolet divergences (calculated properties converge as the collocation grid is refined), we develop two methods for calculating the interfacial tension from field-theoretic simulations. One method relies on the mechanical interpretation of the interfacial tension as the interfacial pressure, and the second method estimates the change in free energy as the area between the two phases is changed. These are the first calculations of the interfacial tension from full field-theoretic simulation of which we are aware, and both the magnitude and scaling behaviors of our calculated interfacial tension agree with recent experiments. [ABSTRACT FROM AUTHOR]
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- 2012
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14. Slip length of water on graphene: Limitations of non-equilibrium molecular dynamics simulations.
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Kumar Kannam, Sridhar, Todd, B. D., Hansen, J. S., and Daivis, Peter J.
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GRAPHENE , *WATER , *PHASE equilibrium , *MOLECULAR dynamics , *SIMULATION methods & models , *CARBON , *NANOSTRUCTURED materials , *INTERFACES (Physical sciences) , *PREDICTION models - Abstract
Data for the flow rate of water in carbon nanopores is widely scattered, both in experiments and simulations. In this work, we aim at precisely quantifying the characteristic large slip length and flow rate of water flowing in a planar graphene nanochannel. First, we quantify the slip length using the intrinsic interfacial friction coefficient between water and graphene, which is found from equilibrium molecular dynamics (EMD) simulations. We then calculate the flow rate and the slip length from the streaming velocity profiles obtained using non-equilibrium molecular dynamics (NEMD) simulations and compare with the predictions from the EMD simulations. The slip length calculated from NEMD simulations is found to be extremely sensitive to the curvature of the velocity profile and it possesses large statistical errors. We therefore pose the question: Can a micrometer range slip length be reliably determined using velocity profiles obtained from NEMD simulations? Our answer is 'not practical, if not impossible' based on the analysis given as the results. In the case of high slip systems such as water in carbon nanochannels, the EMD method results are more reliable, accurate, and computationally more efficient compared to the direct NEMD method for predicting the nanofluidic flow rate and hydrodynamic boundary condition. [ABSTRACT FROM AUTHOR]
- Published
- 2012
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15. The tensile strengths of heterogeneous interfaces: A comparison of static and dynamic first-principles calculations.
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Zhu, Hongjuan and Mosey, Nicholas J.
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STRENGTH of materials , *INTERFACES (Physical sciences) , *COMPARATIVE studies , *MOLECULAR dynamics , *DENSITY functionals , *SIMULATION methods & models , *QUANTUM chemistry , *BINDING energy - Abstract
First-principles molecular dynamics (FPMD) simulations and static quantum chemical (QC) calculations are used to evaluate the tensile strengths, σc, of interfaces consisting of (0001) surfaces of α-Al2O3 separated by small organic species. The evaluation of σc with FPMD was achieved by performing simulations in which the simulation cell was extending in a direction normal to the fracture plane until rupture of the interface occurred. The static QC calculations employed an approach which treated fracture of the interface as a competition between uniform extension of the simulation cell and crack formation at the rupture site, which is analogous to that used in the construction of universal binding energy relationships. The results showed that the static QC calculations accurately reproduced the FPMD simulations with respect to tensile strength and the cell extension at which rupture occurred, provided that the rupture site employed in the static calculations matched the site at which rupture occurred during the FPMD simulations. A simple strategy for identifying the rupture site, even in complex systems containing many potential rupture sites, is proposed. Overall, the work extends the calculation of tensile strengths with static QC methods to highly heterogeneous interfaces, thus providing a computationally efficient alternative to demanding FPMD simulations for this purpose. [ABSTRACT FROM AUTHOR]
- Published
- 2011
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16. Electric field inside a 'Rossky cavity' in uniformly polarized water.
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Martin, Daniel R., Friesen, Allan D., and Matyushov, Dmitry V.
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ELECTRIC fields , *POLARIZATION (Electricity) , *ELECTRIC properties of water , *INTERFACES (Physical sciences) , *NUMERICAL analysis , *SIMULATION methods & models , *PREDICTION models , *CHARGE density waves , *SURFACES (Technology) , *ELECTROSTATICS - Abstract
Electric field produced inside a solute by a uniformly polarized liquid is strongly affected by dipolar polarization of the liquid at the interface. We show, by numerical simulations, that the electric 'cavity' field inside a hydrated non-polar solute does not follow the predictions of standard Maxwell's electrostatics of dielectrics. Instead, the field inside the solute tends, with increasing solute size, to the limit predicted by the Lorentz virtual cavity. The standard paradigm fails because of its reliance on the surface charge density at the dielectric interface determined by the boundary conditions of the Maxwell dielectric. The interface of a polar liquid instead carries a preferential in-plane orientation of the surface dipoles thus producing virtually no surface charge. The resulting boundary conditions for electrostatic problems differ from the traditional recipes, affecting the microscopic and macroscopic fields based on them. We show that relatively small differences in cavity fields propagate into significant differences in the dielectric constant of an ideal mixture. The slope of the dielectric increment of the mixture versus the solute concentration depends strongly on which polarization scenario at the interface is realized. A much steeper slope found in the case of Lorentz interfacial polarization also implies a higher free energy penalty for polarizing such mixtures. [ABSTRACT FROM AUTHOR]
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- 2011
- Full Text
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17. Reverse nonequilibrium molecular dynamics simulation of thermal conductivity in nanoconfined polyamide-6,6.
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Eslami, Hossein, Mohammadzadeh, Laila, and Mehdipour, Nargess
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POLYAMIDES , *MOLECULAR dynamics , *THERMAL conductivity , *GRAPHENE , *CHEMICAL equilibrium , *SIMULATION methods & models , *POLYMERS , *INTERFACES (Physical sciences) - Abstract
A new molecular dynamics simulation method, with coupling to external baths, is used to perform equilibrium simulations on polyamide-6,6 trimers nanoconfined between graphene surfaces, in equilibrium with the bulk polymer. The method is coupled with the reverse nonequilibrium molecular dynamics simulation technique to exchange heat in the direction normal to the surfaces. To be able to study the effect of confinement on the heat conductance in nanoconfined pores, in this work a number of simulations on systems with different pore sizes are done. It is concluded that the coefficient of heat conductivity depends on the degree of polymer layering between the surfaces and on the pore width. Our results further indicate a considerable temperature drop at the interface between the surfaces and polymer. The calculated Kapitza lengths depend on the intersurface distance and on the layering of the polymer nanoconfined between the surfaces. [ABSTRACT FROM AUTHOR]
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- 2011
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18. Molecular dynamics study of nanoparticle stability at liquid interfaces: Effect of nanoparticle-solvent interaction and capillary waves.
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Cheung, David L.
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MOLECULAR dynamics , *NANOPARTICLES , *STABILITY (Mechanics) , *INTERFACES (Physical sciences) , *CAPILLARITY , *COLLOIDS , *SURFACE tension , *SIMULATION methods & models , *MATHEMATICAL models - Abstract
While the interaction of colloidal particles (sizes in excess of 100 nm) with liquid interfaces may be understood in terms of continuum models, which are grounded in macroscopic properties such as surface and line tensions, the behaviour of nanoparticles at liquid interfaces may be more complex. Recent simulations [D. L. Cheung and S. A. F. Bon, Phys. Rev. Lett. 102, 066103 (2009)] of nanoparticles at an idealised liquid-liquid interface showed that the nanoparticle-interface interaction range was larger than expected due, in part, to the action of thermal capillary waves. In this paper, molecular dynamics simulations of a Lennard-Jones nanoparticle in a binary Lennard-Jones mixture are used to confirm that these previous results hold for more realistic models. Furthermore by including attractive interactions between the nanoparticle and the solvent, it is found that the detachment energy decreases as the nanoparticle-solvent attraction increases. Comparison between the simulation results and recent theoretical predictions [H. Lehle and M. Oettel, J. Phys. Condens. Matter 20, 404224 (2008)] shows that for small particles the incorporation of capillary waves into the predicted effective nanoparticle-interface interaction improves agreement between simulation and theory. [ABSTRACT FROM AUTHOR]
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- 2011
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19. Cavitation and crystallization in a metastable Lennard-Jones liquid at negative pressures and low temperatures.
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Baidakov, Vladimir G., Bobrov, Konstantin S., and Teterin, Aleksey S.
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CAVITATION , *CRYSTALLIZATION , *MATHEMATICAL models , *LOW temperatures , *PRESSURE , *MOLECULAR dynamics , *SIMULATION methods & models , *CHEMICAL kinetics , *NUCLEATION , *INTERFACES (Physical sciences) , *GIBBS' free energy - Abstract
Molecular dynamics simulations have been used to investigate the kinetics of spontaneous cavitation and crystallization in a Lennard-Jones liquid at negative pressures in the temperature range where these processes compete with each other. The nucleation rate has been calculated in NVE and NpT ensembles by the method of mean lifetime and the transition interface sampling method with parallel path swapping. The data obtained have been used to determine in the framework of classical nucleation theory the value of the ratio of the solid-liquid and the liquid-void interfacial free energy for critical crystals and cavities and the values of their volumes at points where the cavitation rate of the liquid is equal to the rate of its crystallization. [ABSTRACT FROM AUTHOR]
- Published
- 2011
- Full Text
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20. Effective static and high-frequency viscosities of concentrated suspensions of soft particles.
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Mendoza, Carlos I.
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VISCOSITY , *FREQUENCIES of oscillating systems , *SUSPENSIONS (Chemistry) , *POROUS materials , *THICKNESS measurement , *INTERFACES (Physical sciences) , *SIMULATION methods & models , *HYDRODYNAMICS - Abstract
We obtain an analytic expression that allows to determine the static η and high-frequency η∞ viscosities as function of the volume fraction [lowercase_phi_synonym] of a concentrated suspension of soft spherical particles in a liquid of viscosity η0. The particles consist of a hard core of radius a covered by a porous layer of thickness d. Suspensions of hard spheres and homogeneous porous particles are limiting cases of the model. The proposed expression incorporates the results for the intrinsic viscosity obtained on the basis of a cell model [H. Ohshima, Langmuir 26, 6287 (2010)] into a recently obtained relation for the effective viscosity of concentrated colloidal suspensions [C. I. Mendoza and I. Santamaría-Holek, J. Chem. Phys. 130, 044904 (2009); J. Colloid. Interface Sci. 346, 118 (2010)]. In this model, the correlations between the particles due to crowding effects are introduced through an effective volume fraction [lowercase_phi_synonym]eff which is then used as integration variable in a differential effective medium procedure. The final expression is simple, accurate, and allows to collapse all the data in a universal master curve that is independent of the parameters characterizing the system. The only difference between the static and high-frequency cases is that in the later case [lowercase_phi_synonym]eff also incorporates hydrodynamic interactions arising from the so-called relaxation term. We have tested the accuracy of our model comparing with experimental results for spherical polymeric brushes and simulations for the high-frequency viscosity of homogeneous porous particles. In all cases the agreement with the data is extremely good. [ABSTRACT FROM AUTHOR]
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- 2011
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21. Optimizing transition interface sampling simulations.
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Borrero, Ernesto E., Weinwurm, Marcus, and Dellago, Christoph
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MATHEMATICAL optimization , *PHASE transitions , *INTERFACES (Physical sciences) , *SIMULATION methods & models , *PHASE space , *CHEMICAL kinetics , *CARBON nanotubes - Abstract
We demonstrate that a recently proposed adaptive optimization algorithm for forward flux sampling simulations [E. E. Borrero and F. A. Escobedo, J. Chem. Phys. 129, 024115 (2008)] can be easily applied within the framework of transition interface sampling. This optimization algorithm systematically identifies the kinetic bottlenecks along the order parameter used to partition phase space via interfaces and improves the statistical accuracy of the reaction rate constant estimate. In different versions of the algorithm, the number or the placement of the interfaces (or both) are varied in order to allocate the numerical effort in a balanced way. The algorithm is demonstrated for a simple two-dimensional model and for the dipole flip transition of icelike structures inside carbon nanotubes. For these test systems, the optimization yielded an efficiency increase by a factor of 2-15. [ABSTRACT FROM AUTHOR]
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- 2011
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22. Molecular theory on dielectric constant at interfaces: A molecular dynamics study of the water/vapor interface.
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Shiratori, Kazuya and Morita, Akihiro
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DIELECTRICS , *INTERFACES (Physical sciences) , *MOLECULAR theory , *MOLECULAR dynamics , *SIMULATION methods & models , *ELECTRIC properties of water , *SPECTRUM analysis - Abstract
Though the local dielectric constant at interfaces is an important phenomenological parameter in the analysis of surface spectroscopy, its microscopic definition has been uncertain. Here, we present a full molecular theory on the local field at interfaces with the help of molecular dynamics simulation, and thereby provide microscopic basis for the local dielectric constant so as to be consistent to the phenomenological three-layer model of interface systems. To demonstrate its performance, we applied the theory to the water/vapor interface, and obtained the local field properties near the interface where the simple dielectric model breaks down. Some computational issues pertinent to Ewald calculations of the dielectric properties are also discussed. [ABSTRACT FROM AUTHOR]
- Published
- 2011
- Full Text
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23. A smoothly decoupled particle interface: New methods for coupling explicit and implicit solvent.
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Wagoner, Jason A. and Pande, Vijay S.
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SOLVENTS , *INTERFACES (Physical sciences) , *DEGREES of freedom , *PARTICLES , *SIMULATION methods & models , *MATHEMATICAL models , *WATER - Abstract
A common theme of studies using molecular simulation is a necessary compromise between computational efficiency and resolution of the forcefield that is used. Significant efforts have been directed at combining multiple levels of granularity within a single simulation in order to maintain the efficiency of coarse-grained models, while using finer resolution in regions where such details are expected to play an important role. A specific example of this paradigm is the development of hybrid solvent models, which explicitly sample the solvent degrees of freedom within a specified domain while utilizing a continuum description elsewhere. Unfortunately, these models are complicated by the presence of structural artifacts at or near the explicit/implicit boundary. The presence of these artifacts significantly complicates the use of such models, both undermining the accuracy obtained and necessitating the parameterization of effective potentials to counteract the artificial interactions. In this work, we introduce a novel hybrid solvent model that employs a smoothly decoupled particle interface (SDPI), a switching region that gradually transitions from fully interacting particles to a continuum solvent. The resulting SDPI model allows for the use of an implicit solvent model based on a simple theory that needs to only reproduce the behavior of bulk solvent rather than the more complex features of local interactions. In this study, the SDPI model is tested on spherical hybrid domains using a coarse-grained representation of water that includes only Lennard-Jones interactions. The results demonstrate that this model is capable of reproducing solvent configurations absent of boundary artifacts, as if they were taken from full explicit simulations. [ABSTRACT FROM AUTHOR]
- Published
- 2011
- Full Text
- View/download PDF
24. Molecular simulations of confined liquids: An alternative to the grand canonical Monte Carlo simulations.
- Author
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Ghoufi, Aziz, Morineau, Denis, Lefort, Ronan, Hureau, Ivanne, Hennous, Leila, Zhu, Haochen, Szymczyk, Anthony, Malfreyt, Patrice, and Maurin, Guillaume
- Subjects
- *
MOLECULAR dynamics , *SIMULATION methods & models , *MONTE Carlo method , *HIGH pressure (Science) , *LOW temperatures , *QUANTUM perturbations , *INTERFACES (Physical sciences) , *METHANOL , *MESOPOROUS materials - Abstract
Commonly, the confinement effects are studied from the grand canonical Monte Carlo (GCMC) simulations from the computation of the density of liquid in the confined phase. The GCMC modeling and chemical potential (μ) calculations are based on the insertion/deletion of the real and ghost particle, respectively. At high density, i.e., at high pressure or low temperature, the insertions fail from the Widom insertions while the performing methods as expanded method or perturbation approach are not efficient to treat the large and complex molecules. To overcome this problem we use a simple and efficient method to compute the liquid's density in the confined medium. This method does not require the precalculation of μ and is an alternative to the GCMC simulations. From the isothermal-isosurface-isobaric statistical ensemble we consider the explicit framework/liquid external interface to model an explicit liquid's reservoir. In this procedure only the liquid molecules undergo the volume changes while the volume of the framework is kept constant. Therefore, this method is described in the NpnAVfT statistical ensemble, where N is the number of particles, pn is the normal pressure, Vf is the volume of framework, A is the surface of the solid/fluid interface, and T is the temperature. This approach is applied and validated from the computation of the density of the methanol and water confined in the mesoporous cylindrical silica nanopores and the MIL-53(Cr) metal organic framework type, respectively. [ABSTRACT FROM AUTHOR]
- Published
- 2011
- Full Text
- View/download PDF
25. The chemistry of acetone at extreme conditions by density functional molecular dynamics simulations.
- Author
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Ferrante, Francesco, Celso, Fabrizio Lo, Triolo, Roberto, and Taleyarkhan, Rusi P.
- Subjects
- *
ACETONE , *DENSITY functionals , *MOLECULAR dynamics , *SIMULATION methods & models , *TEMPERATURE effect , *INTERFACES (Physical sciences) , *BUBBLE dynamics , *ISOMERIZATION - Abstract
Density functional molecular dynamics simulations have been performed in the NVT ensemble (moles (N), volume (V) and temperature (T)) on a system formed by ten acetone molecules at a temperature of 2000 K and density ρ = 1.322 g cm-3. These conditions resemble closely those realized at the interface of an acetone vapor bubble in the early stages of supercompression experiments and result in an average pressure of 5 GPa. Two relevant reactive events occur during the simulation: the condensation of two acetone molecules to give hexane-2,5-dione and dihydrogen and the isomerization to the enolic propen-2-ol form. The mechanisms of these events are discussed in detail. [ABSTRACT FROM AUTHOR]
- Published
- 2011
- Full Text
- View/download PDF
26. Interface proximity effects on ionic conductivity in nanoscale oxide-ion conducting yttria stabilized zirconia: An atomistic simulation study.
- Author
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Sankaranarayanan, Subramanian K. R. S. and Ramanathan, Shriram
- Subjects
- *
INTERFACES (Physical sciences) , *ELECTRIC conductivity , *NANOSTRUCTURED materials , *OXIDES , *ZIRCONIUM oxide , *SIMULATION methods & models , *ATOMIC theory , *THICKNESS measurement , *AMORPHOUS substances - Abstract
We present an atomistic simulation study on the size dependence of dopant distribution and the influence of nanoscale film thickness on carrier transport properties of the model oxide-ion conductor yttria stabilized zirconia (YSZ). Simulated amorphization and recrystallization approach was utilized to generate YSZ films with varying thicknesses (3-9 nm) on insulating MgO substrates. The atomic trajectories generated in the molecular dynamics simulations are used to study the structural evolution of the YSZ thin films and correlate the resulting microstructure with ionic transport properties at the nanoscale. The interfacial conductivity increases by 2 orders of magnitude as the YSZ film size decreases from 9 to 3 nm owing to a decrease in activation energy barrier from 0.54 to 0.35 eV in the 1200-2000 K temperature range. Analysis of dopant distribution indicates surface enrichment, the extent of which depends on the film thickness. The mechanisms of oxygen conductivity for the various film thicknesses at the nanoscale are discussed in detail and comparisons with experimental and other modeling studies are presented where possible. The study offers insights into mesoscopic ion conduction mechanisms in low-dimensional solid oxide electrolytes. [ABSTRACT FROM AUTHOR]
- Published
- 2011
- Full Text
- View/download PDF
27. Resistances for heat and mass transfer through a liquid-vapor interface in a binary mixture.
- Author
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Glavatskiy, K. S. and Bedeaux, D.
- Subjects
- *
MASS transfer , *MIXTURES , *INTERFACES (Physical sciences) , *KINETIC theory of liquids , *MOLECULAR dynamics , *SIMULATION methods & models , *EVAPORATION (Chemistry) - Abstract
In this paper we calculate the interfacial resistances to heat and mass transfer through a liquid-vapor interface in a binary mixture. We use two methods, the direct calculation from the actual nonequilibrium solution and integral relations, derived earlier. We verify, that integral relations, being a relatively faster and cheaper method, indeed gives the same results as the direct processing of a nonequilibrium solution. Furthermore we compare the absolute values of the interfacial resistances with the ones obtained from kinetic theory. Matching the diagonal resistances for the binary mixture we find that kinetic theory underestimates the cross coefficients. The heat of transfer is, as a consequence, correspondingly larger. [ABSTRACT FROM AUTHOR]
- Published
- 2010
- Full Text
- View/download PDF
28. Simulations of chemical vapor deposition diamond film growth using a kinetic Monte Carlo model and two-dimensional models of microwave plasma and hot filament chemical vapor deposition reactors.
- Author
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May, P. W., Harvey, J. N., Allan, N. L., Richley, J. C., and Mankelevich, Yu. A.
- Subjects
- *
CHEMICAL vapor deposition , *DIAMONDS , *SIMULATION methods & models , *MONTE Carlo method , *ADSORPTION (Chemistry) , *INTERFACES (Physical sciences) - Abstract
A one-dimensional kinetic Monte Carlo (KMC) model has been developed to simulate the chemical vapor deposition of a diamond (100) surface under conditions used to grow single-crystal diamond (SCD), microcrystalline diamond (MCD), nanocrystalline diamond (NCD), and ultrananocrystalline diamond (UNCD) films. The model considers adsorption, etching/desorption, lattice incorporation and surface migration but not defect formation or renucleation processes. Two methods have been devised for estimation of the gas phase concentrations of species at the growing diamond surface, and are used to determine adsorption rates for C1Hx hydrocarbons for the different conditions. The rate of migration of adsorbed carbon species is governed by the availability of neighboring radical sites, which, in turn, depend upon the rates of H abstraction and of surface-radical migration. The KMC model predicts growth rates and surface roughness for each of diamond types consistent with experiment. In the absence of defect formation and renucleation the average surface diffusion length, ℓ, is a key parameter controlling surface morphology. When ℓ<2, surface migration is limited by the lack of availability of surface radical sites, and the migrating surface species simply hop back and forth between two adjacent sites but do not travel far beyond their initial adsorption site. Thus, Eley-Rideal processes dominate the growth, leading to the rough surfaces seen in NCD and UNCD. The maximum or 'intrinsic' surface roughness occurs for nominally zero-migration conditions (ℓ=0) with an rms value of approximately five carbon atoms. Conversely, when migration occurs over greater distances (ℓ>2), Langmuir-Hinshelwood processes dominate the growth producing the smoother surfaces of MCD and SCD. By extrapolation, we predict that atomically smooth surfaces over large areas should occur once migrating species can travel approximately five sites (ℓ∼5). β-scission processes are found to be unimportant for MCD and SCD growth conditions, but can remove up to 5% of the adsorbing carbon for NCD and UNCD growth. C1Hx insertion reactions also contribute <1% to the growth for nearly all conditions, while C2Hx (x<2) insertion reactions are negligible due their very low concentrations at the surface. Finally, the predictions for growth rate and morphology for UNCD deposition in a microwave system were found to be anomalous compared to those for all the other growth conditions, suggesting that carbonaceous particulates created in these plasmas may significantly affect the gas chemistry. [ABSTRACT FROM AUTHOR]
- Published
- 2010
- Full Text
- View/download PDF
29. Vapor-liquid interfacial properties of fully flexible Lennard-Jones chains.
- Author
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Blas, Felipe J., MacDowell, Luis G., de Miguel, Enrique, and Jackson, George
- Subjects
- *
MOLECULAR dynamics , *INTERFACES (Physical sciences) , *VAPOR-liquid equilibrium , *SIMULATION methods & models , *MOLECULES - Abstract
We consider the computation of the interfacial properties of molecular chains from direct simulation of the vapor-liquid interface. The molecules are modeled as fully flexible chains formed from tangentially bonded monomers with truncated Lennard-Jones interactions. Four different model systems comprising of 4, 8, 12, and 16 monomers per molecule are considered. The simulations are performed in the canonical ensemble, and the vapor-liquid interfacial tension is evaluated using the test area and the wandering interface methods. In addition to the surface tension, we also obtain density profiles, coexistence densities, critical temperature and density, and interfacial thickness as functions of temperature, paying particular attention to the effect of the chain length on these properties. According to our results, the main effect of increasing the chain length (at fixed temperature) is to sharpen the vapor-liquid interface and to increase the width of the biphasic coexistence region. As a result, the interfacial thickness decreases and the surface tension increases as the molecular chains get longer. The interfacial thickness and surface tension appear to exhibit an asymptotic limiting behavior for long chains. A similar behavior is also observed for the coexistence densities and critical properties. Our simulation results indicate that the asymptotic regime is reached for Lennard-Jones chains formed from eight monomer segments. We also include a preliminary study on the effect of the cutoff distance on the interfacial properties. Our results indicate that all of the properties exhibit a dependence with the distance at which the interactions are truncated, though the relative effect varies from one property to the other. The interfacial thickness and, more particularly, the interfacial tension are found to be strongly dependent on the particular choice of cutoff, whereas the density profiles and coexistence densities are, in general, less sensitive to the truncation. [ABSTRACT FROM AUTHOR]
- Published
- 2008
- Full Text
- View/download PDF
30. The Wolf method applied to the liquid-vapor interface of water.
- Author
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Mendoza, Francisco Noé, López-Lemus, Jorge, Chapela, Gustavo A., and Alejandre, José
- Subjects
- *
ELECTROSTATIC atomization , *VAPOR-liquid equilibrium , *INTERFACES (Physical sciences) , *MOLECULAR dynamics , *SIMULATION methods & models , *SURFACE energy - Abstract
The Wolf method for the calculation of electrostatic interactions is applied in a liquid phase and at the liquid-vapor interface of water and its results are compared with those from the Ewald sums method. Molecular dynamics simulations are performed to calculate the radial distribution functions at room temperature. The interface simulations are used to obtain the coexisting densities and surface tension along the coexistence curve. The water model is a flexible version of the extended simple point charge model. The Wolf method gives good structural results, fair coexistence densities, and poor surface tensions as compared with those obtained using the Ewald sums method. [ABSTRACT FROM AUTHOR]
- Published
- 2008
- Full Text
- View/download PDF
31. Polymer chain dynamics at interfaces: Role of boundary conditions at solid interface.
- Author
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Desai, Tapan G., Keblinski, Pawel, and Kumar, Sanat K.
- Subjects
- *
POLYMERS , *INTERFACES (Physical sciences) , *SIMULATION methods & models , *SOLVENTS , *POLYMERIZATION - Abstract
Using classical molecular dynamics simulations, we study the dynamical properties of a single polymer chain dissolved in an explicit solvent and strongly adsorbed at solid-liquid interface. To circumvent a serious challenge posed by finite size effects due to long-range hydrodynamic effects, we developed a correction procedure that substantially limits the finite size effects. Concurrently, we provide an analysis of distinctly different size effects in the directions transverse and normal to the interface. We find that on analytically smooth interfaces, corresponding to the slip boundary condition, the motions of the polymer chain and the surrounding solvent are hydrodynamically coupled. This leads to the chain diffusion coefficient D scaling with the chain degree of polymerization N as D∼N-3/4, consistent with the Zimm dynamics for strongly adsorbed chains. Introduction of transverse forces at the interface results in loss of correlation between the motion of the polymer chain and the solvent. Consequently, D∼N-1, which is a characteristic of the Rouse dynamics. [ABSTRACT FROM AUTHOR]
- Published
- 2008
- Full Text
- View/download PDF
32. Numerical integration techniques for curved-element discretizations of molecule-solvent interfaces.
- Author
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Bardhan, Jaydeep P., Altman, Michael D., Willis, David J., Lippow, Shaun M., Tidor, Bruce, and White, Jacob K.
- Subjects
- *
NUMERICAL integration , *INTERFACES (Physical sciences) , *SIMULATION methods & models , *SOLVENTS , *MOLECULES - Abstract
Surface formulations of biophysical modeling problems offer attractive theoretical and computational properties. Numerical simulations based on these formulations usually begin with discretization of the surface under consideration; often, the surface is curved, possessing complicated structure and possibly singularities. Numerical simulations commonly are based on approximate, rather than exact, discretizations of these surfaces. To assess the strength of the dependence of simulation accuracy on the fidelity of surface representation, here methods were developed to model several important surface formulations using exact surface discretizations. Following and refining Zauhar’s work [J. Comput.-Aided Mol. Des. 9, 149 (1995)], two classes of curved elements were defined that can exactly discretize the van der Waals, solvent-accessible, and solvent-excluded (molecular) surfaces. Numerical integration techniques are presented that can accurately evaluate nonsingular and singular integrals over these curved surfaces. After validating the exactness of the surface discretizations and demonstrating the correctness of the presented integration methods, a set of calculations are presented that compare the accuracy of approximate, planar-triangle-based discretizations and exact, curved-element-based simulations of surface-generalized-Born (sGB), surface-continuum van der Waals (scvdW), and boundary-element method (BEM) electrostatics problems. Results demonstrate that continuum electrostatic calculations with BEM using curved elements, piecewise-constant basis functions, and centroid collocation are nearly ten times more accurate than planar-triangle BEM for basis sets of comparable size. The sGB and scvdW calculations give exceptional accuracy even for the coarsest obtainable discretized surfaces. The extra accuracy is attributed to the exact representation of the solute-solvent interface; in contrast, commonly used planar-triangle discretizations can only offer improved approximations with increasing discretization and associated increases in computational resources. The results clearly demonstrate that the methods for approximate integration on an exact geometry are far more accurate than exact integration on an approximate geometry. A MATLAB implementation of the presented integration methods and sample data files containing curved-element discretizations of several small molecules are available online as supplemental material. [ABSTRACT FROM AUTHOR]
- Published
- 2007
- Full Text
- View/download PDF
33. Influence of interface roughness on two-dimensional electron gas streaming transport in GaN-based heterostructures.
- Author
-
Polyakov, V. M. and Schwierz, F.
- Subjects
- *
ELECTRON transport , *ELECTRON gas , *INTERFACES (Physical sciences) , *MONTE Carlo method , *SIMULATION methods & models , *SCATTERING (Physics) , *ANALYSIS of covariance , *HETEROSTRUCTURES - Abstract
Streaming transport of the two-dimensional (2D) electron gas in a model GaN-based heterostructure is investigated using the ensemble Monte Carlo simulation method. It is demonstrated that interface roughness (IFR) scattering, being, in contrast to three-dimensional (3D) transport, an additional relevant scattering mechanism, plays a crucial role in fulfilling the streaming conditions for 2D transport. For a calculation of the IFR scattering rates we use the widely adopted Gaussian and exponential autocovariance functions to quantitatively describe the interface roughness. Even neglecting the interface roughness the streaming conditions are fulfilled only at low temperatures, similar to the 3D case. Taking into account IFR scattering, the nearly quasiballistic motion of 2D electrons in the passive region (below the optical phonon energy hωLO), being one of the necessary conditions for the streaming transport, can be realized only for sufficiently smooth interfaces. [ABSTRACT FROM AUTHOR]
- Published
- 2006
- Full Text
- View/download PDF
34. Simulation studies of the protein-water interface. I. Properties at the molecular resolution.
- Author
-
Schröder, C., Rudas, T., Boresch, S., and Steinhauser, O.
- Subjects
- *
INTERFACES (Physical sciences) , *SIMULATION methods & models , *MOLECULAR dynamics , *PROTEINS , *UBIQUITIN , *PHOSPHOLIPASES - Abstract
We report molecular dynamics simulations of three globular proteins: ubiquitin, apo-calbindin D9K, and the C-terminal SH2 domain of phospholipase C-γ1 in explicit water. The proteins differ in their overall charge and fold type and were chosen to represent to some degree the structural variability found in medium-sized proteins. The length of each simulation was at least 15 ns, and larger than usual solvent boxes were used. We computed radial distribution functions, as well as orientational correlation functions about the surface residues. Two solvent shells could be clearly discerned about charged and polar amino acids. Near apolar amino acids the water density near such residues was almost devoid of structure. The mean residence time of water molecules was determined for water shells about the full protein, as well as for water layers about individual amino acids. In the dynamic properties, two solvent shells could be characterized as well. However, by comparison to simulations of pure water it could be shown that the influence of the protein reaches beyond 6 Å, i.e., beyond the first two shells. In the first shell (r≤=3.5 Å), the structural and dynamical properties of solvent waters varied considerably and depended primarily on the physicochemical properties of the closest amino acid side chain, with which the waters interact. By contrast, the solvent properties seem not to depend on the specifics of the protein studied (such as the net charge) or on the secondary structure element in which an amino acid is located. While differing considerably from the neat liquid, the properties of waters in the second solvation shell (3.5≤r≤=6 Å) are rather uniform; a direct influence from surface amino acids are already mostly shielded. [ABSTRACT FROM AUTHOR]
- Published
- 2006
- Full Text
- View/download PDF
35. Simulation studies of the protein-water interface. II. Properties at the mesoscopic resolution.
- Author
-
Rudas, T., Schröder, C., Boresch, S., and Steinhauser, O.
- Subjects
- *
INTERFACES (Physical sciences) , *MESOSCOPIC phenomena (Physics) , *SIMULATION methods & models , *MOLECULAR dynamics , *PROTEINS , *DIELECTRICS - Abstract
We report molecular dynamics (MD) simulations of three protein-water systems (ubiquitin, apo-calbindin D9K, and the C-terminal SH2 domain of phospholipase C-γ1), from which we compute the dielectric properties of the solutions. Since two of the proteins studied have a net charge, we develop the necessary theory to account for the presence of charged species in a form suitable for computer simulations. In order to ensure convergence of the time correlation functions needed for the analysis, the minimum length of the MD simulations was 20 ns. The system sizes (box length, number of waters) were chosen so that the resulting protein concentrations are comparable to experimental conditions. A dielectric component analysis was carried out to analyze the contributions from protein and water to the frequency-dependent dielectric susceptibility χ(ω) of the solutions. Additionally, an even finer decomposition into protein, two solvation shells, and the remaining water (bulk water) was carried out. The results of these dielectric decompositions were used to study protein solvation at mesoscopic resolution, i.e., in terms of protein, first and second solvation layers, and bulk water. This study, therefore, complements the structural and dynamical analyses at molecular resolution that are presented in the companion paper. The dielectric component contributions from the second shell and bulk water are very similar in all three systems. We find that the proteins influence the dielectric properties of water even beyond the second solvation shell, in agreement with what was observed for the mean residence times of water molecules in protein solutions. By contrast, the protein contributions, as well as the contributions of the first solvation shell, are system specific. Most importantly, the protein and the first water shell around ubiquitin and apo-calbindin are anticorrelated, whereas the first water shell around the SH2 domain is positively correlated. [ABSTRACT FROM AUTHOR]
- Published
- 2006
- Full Text
- View/download PDF
36. A novel algorithm to model the influence of host lattice flexibility in molecular dynamics simulations: Loading dependence of self-diffusion in carbon nanotubes.
- Author
-
Jakobtorweihen, S., Lowe, C. P., Keil, F. J., and Smit, B.
- Subjects
- *
MOLECULAR dynamics , *SIMULATION methods & models , *LATTICE dynamics , *INTERFACES (Physical sciences) , *NANOTUBES , *CARBON - Abstract
We describe a novel algorithm that includes the effect of host lattice flexibility into molecular dynamics simulations that use rigid lattices. It uses a Lowe-Andersen thermostat for interface-fluid collisions to take the most important aspects of flexibility into account. The same diffusivities and other properties of the flexible framework system are reproduced at a small fraction of the computational cost of an explicit simulation. We study the influence of flexibility on the self-diffusion of simple gases inside single walled carbon nanotubes. Results are shown for different guest molecules (methane, helium, and sulfur hexafluoride), temperatures, and types of carbon nanotubes. We show, surprisingly, that at low loadings flexibility is always relevant. Notably, it has a crucial influence on the diffusive dynamics of the guest molecules. [ABSTRACT FROM AUTHOR]
- Published
- 2006
- Full Text
- View/download PDF
37. Simple analytical model for 2kT current in forward-biased p-n junctions.
- Author
-
Abenante, Luigi
- Subjects
- *
SEMICONDUCTOR junctions , *EQUATIONS , *DIODES , *SIMULATION methods & models , *INTERFACES (Physical sciences) , *PHYSICAL sciences - Abstract
The junction space-charge region (JSCR) is modeled as a separate region with carrier recombination at the surface and in the bulk. Bulk recombination is modeled according to the idealized model of C. T. Sah, R. N. Noyce, and W. Shockley [Proc. IRE45, 1228 (1957)]. JSCR surface recombination is modeled by combining at high biases the approaches of A. S. Grove [Physics and Technology of Semiconductor Devices (Wiley, New York, 1967), pp. 301–302] and of C. H. Henry, R. A. Logan, and F. R. Merrit [J. Appl. Phys. 49, 3530 (1978)]. In the treatment, it is assumed that the densities of states in the bulk and at the surface are related to each other. The transport equations are solved in JSCR at high biases and an expression for the JSCR recombination current is obtained. The model is adjusted for Si emitters and diodes, in such a way that it agrees with the numerical simulation program PC1D at all voltages. [ABSTRACT FROM AUTHOR]
- Published
- 2005
- Full Text
- View/download PDF
38. Numerical simulation of ZnSe/GaAs interface reflectance difference spectroscopy.
- Author
-
Kwok, Tat-Kun and Yang, Z.
- Subjects
- *
SIMULATION methods & models , *REFLECTANCE spectroscopy , *INTERFACES (Physical sciences) - Abstract
Proposes a numerical method for simulating the non-normal incidence reflectance difference spectroscopy (RDS) spectra of biaxial anisotropic multilayer systems. Description on the RDS spectra of a typical ZnSe/GaAs sample; Presentation of the theory for the biaxial ZnSe/GaAs interface RDS; Overview on the numerical simulation.
- Published
- 1996
- Full Text
- View/download PDF
39. Simulations at conducting interfaces: Boundary conditions for electrodes and electrolytes.
- Author
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Perram, J. W. and Ratner, Mark A.
- Subjects
- *
INTERFACES (Physical sciences) , *SIMULATION methods & models , *BOUNDARY value problems , *ELECTRODES , *ELECTROLYTES - Abstract
The purpose of this paper is to derive a set of boundary conditions appropriate for simulating a wide variety of electrochemical and biophysical systems which are not necessarily electrically neutral. This is done by using the method of Green’s function, a generalization of the method of images, for solving the Poisson equation to provide boundary conditions for simulating electrochemical reactions involving ions confined between metal electrodes as well as ions in membranes enclosed between regions of aqueous electrolytes. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]
- Published
- 1996
- Full Text
- View/download PDF
40. Comparative molecular dynamics simulation study of the benzene–graphite and the benzene–1,12-dodecanediol–graphite interface.
- Author
-
Winkler, Roland G. and Hentschke, Reinhard
- Subjects
- *
MOLECULAR dynamics , *INTERFACES (Physical sciences) , *SIMULATION methods & models - Abstract
Using the molecular dynamics simulation technique, we study the effect of a highly ordered physisorbed alkyl monolayer on the surface induced liquid structure near a smooth solid–liquid interface. The system considered here is 1,12-dodecanediol adsorbed at the benzene–graphite interface. We compare the results on the graphite–1,12-dodecanediol–benzene interface to previous simulations on the bare graphite–benzene interface. We find that the surface induced liquid structure near the adsorbate covered interface differs from the structure induced by the bare interface only within the first solvation shell. Beyond the first solvation shell, there is no discernible difference, even though the surface induced structure is still pronounced. In addition, we study the structure of the hydrogen bond stabilized molecular adsorbate network. Here we find that the hydrogen bonds link the 1,12-dodecanediol molecules in a chain-like fashion across the boundaries of the herringbone structure formed by the adsorbate. [ABSTRACT FROM AUTHOR]
- Published
- 1994
- Full Text
- View/download PDF
41. Hygro-thermo-mechanical Modeling of Transport Phenomena for Simulation of Building Envelopes Detachment.
- Author
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Madĕra, J., Koudelka, T., and Kruis, Jaroslav
- Subjects
- *
BUILDING envelopes , *HYGROTHERMOELASTICITY , *PROBLEM solving , *INTERFACES (Physical sciences) , *SIMULATION methods & models - Abstract
Plaster detachment is serious problem with strong influence on the structure durability. This contribution describes numerical simulation of the plaster detachment. The simulation is based on the coupled thermo-hydro-mechanical analysis of masonry and plaster. Interface finite elements are used between the masonry and plaster. Material parameters were obtained from laboratory test. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
42. Area dependence of the surface tension of a Lennard-Jones fluid from molecular dynamics simulations.
- Author
-
Chen, Li-Jen
- Subjects
- *
MOLECULAR dynamics , *SIMULATION methods & models , *INTERFACES (Physical sciences) , *FLUIDS - Abstract
Molecular dynamics simulations are used to study the structure of the vapor–liquid interface of three-dimensional fluids. Particles interact via a truncated Lennard-Jones pair potential in the absence of external fields. The effect of the surface area on the surface tension is investigated. It is found that the surface tension increases with the decrease of the surface area. However, this finite-size effect is pronounced only in small surface areas. In addition, our simulation results show that the finite-size correction of the surface tension is directly proportional to the reciprocal of the surface area, in accord with the prediction of the Gaussian model of capillary waves. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]
- Published
- 1995
- Full Text
- View/download PDF
43. Front-tracking Lattice Boltzmann Simulation of a Wedge Water Entry.
- Author
-
Zarghami, Ahad, Porfiri, Maurizio, Jannelli, Elio, and Ubertini, Stefano
- Subjects
- *
LATTICE Boltzmann methods , *GAS dynamics , *MOMENTUM (Mechanics) , *INTERFACES (Physical sciences) , *SURFACES (Technology) , *SIMULATION methods & models - Abstract
In this work, we present the implementation of a front-tracking variant of the lattice Boltzmann method to model water entry problems. In this method, the fluid is considered incompressible, the gas dynamics is neglected and the free surface is represented through a layer of interface cells, whose dynamics is described using the mass and momentum fluxes across it. The consistency and accuracy of the computations is demonstrated through comparisons with theoretical solutions and experimental data reported in the literature. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
44. PFC2D simulation of thermally induced cracks in concrete specimens.
- Author
-
Liu, Xinghong, Chang, Xiaolin, Zhou, Wei, and Li, Shuirong
- Subjects
- *
CRACKING of concrete , *INTERFACES (Physical sciences) , *STRENGTH of materials , *FRACTURE mechanics , *MECHANICAL behavior of materials , *SIMULATION methods & models - Abstract
The appearance of cracks exposed to severe environmental conditions can be critical for concrete structures. The research is to validate Particle Flow Code(PFC2D) method in the context of concrete thermally-induced cracking simulations. First, concrete was discreted as meso-level units of aggregate, cement mortar and the interfaces between them. Parallel bonded-particle model in PFC2D was adapted to describe the constitutive relation of the cementing material. Then, the concrete mechanics meso-parameters were obtained through several groups of biaxial tests, in order to make the numerical results comply with the law of the indoor test. The concrete thermal meso-parameters were determined by compared with the parameters in the empirical formula through the simulations imposing a constant heat flow to the left margin of concrete specimens. At last, a case of 1000mm×500mm concrete specimen model was analyzed. It simulated the formation and development process of the thermally-induced cracks under the cold waves of different durations and temperature decline. Good agreements in fracture morphology and process were observed between the simulations, previous studies and laboratory data. The temperature decline limits during cold waves were obtained when its tensile strength was given as 3MPa. And it showed the feasibility of using PFC2D to simulate concrete thermally-induced cracking. [ABSTRACT FROM AUTHOR]
- Published
- 2013
- Full Text
- View/download PDF
45. The simulation study of protein-protein interfaces based on the 4-helix bundle structure.
- Author
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Fukuda, Masaki, Komatsu, Yu, Morikawa, Ryota, Miyakawa, Takeshi, Takasu, Masako, Akanuma, Satoshi, and Yamagishi, Akihiko
- Subjects
- *
PROTEIN-protein interactions , *INTERFACES (Physical sciences) , *INTERMOLECULAR interactions , *MOLECULAR structure , *SIMULATION methods & models , *MIXING - Abstract
Docking of two protein molecules is induced by intermolecular interactions. Our purposes in this study are: designing binding interfaces on the two proteins, which specifically interact to each other; and inducing intermolecular interactions between the two proteins by mixing them. A 4-helix bundle structure was chosen as a scaffold on which binding interfaces were created. Based on this scaffold, we designed binding interfaces involving charged and nonpolar amino acid residues. We performed molecular dynamics (MD) simulation to identify suitable amino acid residues for the interfaces. We chose YciF protein as the scaffold for the protein-protein docking simulation. We observed the structure of two YciF protein molecules (I and II), and we calculated the distance between centroids (center of gravity) of the interfaces' surface planes of the molecules I and II. We found that the docking of the two protein molecules can be controlled by the number of hydrophobic and charged amino acid residues involved in the interfaces. Existence of six hydrophobic and five charged amino acid residues within an interface were most suitable for the protein-protein docking. [ABSTRACT FROM AUTHOR]
- Published
- 2013
- Full Text
- View/download PDF
46. Role of varying interface conditions on the eddy current response from cracks in multilayer structures.
- Author
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Cherry, Aaron, Knopp, Jeremy, Aldrin, John C., Sabbagh, Harold A., Boehnlein, Thomas, and Mooers, Ryan
- Subjects
- *
FRACTURE mechanics , *INTERFACES (Physical sciences) , *EDDY current testing , *STRUCTURAL engineering , *ENGINEERING inspection , *AIRFRAMES , *SIMULATION methods & models - Abstract
There is a need to improve the understanding of the role of interface conditions on eddy current inspections for cracks in multilayer aircraft structures. This paper presents initial experimental and simulated results studying the influence of gaps and contact conditions between two plates with a notch in the second layer. Simulations show an amplification of the eddy current signal for a subsurface notch adjacent to an air gap as opposed to a submerged notch in a solid plate. [ABSTRACT FROM AUTHOR]
- Published
- 2013
- Full Text
- View/download PDF
47. Investigation on a coupled CFD/DSMC method for continuum-rarefied flows.
- Author
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Tang, Zhenyu, He, Bijiao, and Cai, Guobiao
- Subjects
- *
COMPUTATIONAL fluid dynamics , *SIMULATION methods & models , *MONTE Carlo method , *CONTINUUM mechanics , *INTERFACES (Physical sciences) , *HYPERSONIC flow - Abstract
The purpose of the present work is to investigate the coupled CFD/DSMC method using the existing CFD and DSMC codes developed by the authors. The interface between the continuum and particle regions is determined by the gradient-length local Knudsen number. A coupling scheme combining both state-based and flux-based coupling methods is proposed in the current study. Overlapping grids are established between the different grid systems of CFD and DSMC codes. A hypersonic flow over a 2D cylinder has been simulated using the present coupled method. Comparison has been made between the results obtained from both methods, which shows that the coupled CFD/DSMC method can achieve the same precision as the pure DSMC method and obtain higher computational efficiency. [ABSTRACT FROM AUTHOR]
- Published
- 2012
- Full Text
- View/download PDF
48. Dependence of near-surface dopant pile-up on post-implant annealing conditions.
- Author
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Gorai, Prashun, Kondratenko, Yevgeniy V., and Seebauer, Edmund G.
- Subjects
- *
DOPING agents (Chemistry) , *ION implantation , *ANNEALING of metals , *SILICON surfaces , *INTERFACES (Physical sciences) , *SILICA , *CONTINUUM mechanics , *SIMULATION methods & models - Abstract
Near-surface dopant pile-up at Si/SiO2 interfaces during post-implant annealing can affect the electrical performance of devices with shallow dopant profiles. Pile-up results from alterations in the charge state of dopant-related point defects, induced by near-surface band bending. The effects of annealing conditions on the evolution of pile-up are little known. The present work employs continuum simulations coupled with experiments in the case of B implanted into Si to show that annealing temperature, ramp rate, interface potential and annihilation probability, besides other factors, determine the growth kinetics and extent of pile-up. Annealing conditions under which pile-up is absent have also been identified. [ABSTRACT FROM AUTHOR]
- Published
- 2012
- Full Text
- View/download PDF
49. Numerical simulation of drop coalescence in the presence of film soluble surfactant.
- Author
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Bazhlekov, I.
- Subjects
- *
NUMERICAL analysis , *SIMULATION methods & models , *DROPLETS , *THIN films , *SURFACE active agents , *NAVIER-Stokes equations , *INTERFACES (Physical sciences) , *BOUNDARY value problems , *APPROXIMATION theory - Abstract
Numerical method is presented for simulation of the deformation, drainage and rupture of axisymmetric film (gap) between colliding drops in the presence of film soluble surfactants under the influence of van der Waals forces at small capillary and Reynolds numbers and small surfactant concentrations. The mathematical model is based on the lubrication equations in the gap between drops and the creeping flow approximation of Navier-Stokes equations in the drops, coupled with velocity and stress boundary conditions at the interfaces. A non-uniform surfactant concentration on the interfaces, related with that in the film, leads to a gradient of the interfacial tension which in turn leads to additional tangential stress on the interfaces (Marangoni effects). Both film and interface surfactant concentrations, related via adsorption isotherm, are governed by a convection-diffusion equation. The numerical method consists of: Boundary integral method for the flow in the drops; Finite difference method for the flow in the gap, the position of the interfaces and the surfactant concentration on the interfaces, as well as in the film. Second order approximation of the spatial terms on adaptive non-uniform mesh is constructed in combination with Euler explicit scheme for the time discretization. For the convection-diffusion equation in the film first order implicit and Crank-Nicolson time integration schemes are used as well. Tests and comparisons are performed to show the accuracy and stability of the presented numerical method. [ABSTRACT FROM AUTHOR]
- Published
- 2012
- Full Text
- View/download PDF
50. Further testing and development of simulation models for UT inspections of armor.
- Author
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Margetan, Frank J., Richter, Nathaniel, and Thompson, R. Bruce
- Subjects
- *
MATERIALS testing , *SIMULATION methods & models , *THICKNESS measurement , *DENSITY , *ATTENUATION (Physics) , *INTERFACES (Physical sciences) , *PREDICTION models - Abstract
In previous work we introduced an approach for simulating ultrasonic pulse/echo immersion inspections of multi-layer armor panels. Model inputs include the thickness, density, velocity and attenuation of each armor layer, the focal properties of the transducer, and a measured calibration signal. The basic model output is a response-versus-time waveform (ultrasonic A-scan) which includes echoes from all interfaces including those arising from reverberations within layers. Such A-scans can be predicted both for unflawed panels and panels containing a large disbond at any given interface. In this paper we continue our testing of the simulation software, applying it now to an armor panel consisting of SiC ceramic tiles fully embedded in a titanium-alloy matrix. An interesting specimen of such armor became available in which some tile/metal interfaces appear to be well bonded, while others have disbonded areas of various sizes. We compare measured and predicted A-scans for UT inspections, and also demonstrate an extension of the model to predict ultrasonic C-scans over regions containing a small, isolated disbond. [ABSTRACT FROM AUTHOR]
- Published
- 2012
- Full Text
- View/download PDF
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