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Computational and experimental study of instrumented indentation

Chollacoop, Nuwong, 1977-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 175 p.; 4637595 bytes; 6053084 bytes; application/pdf; application/pdf
ENG
Relevância na Pesquisa
105.65%
The effect of characteristic length scales, through dimensional and microstructural miniaturizations, on mechanical properties is systematically investigated by recourse to instrumented micro- and/or nanoindentation. This technique is capable of extracting mechanical properties accurately down to nanometers, via rigorous interpretation of indentation response. Such interpretation requires fundamental understandings of contact mechanics and underlying deformation mechanisms. Analytical, computational and experimental approaches are utilized to elucidate specifically how empirical constitutive relation can be estimated from the complex multiaxial stress state induced by indentation. Analytical formulations form a framework for parametric finite element analysis. The algorithms are established to predict indentation response from a constitutive relation (hereafter referred to as "forward algorithms") and to extract mechanical properties from indentation curve (hereafter referred to as "reverse algorithms"). Experimental verifications and comprehensive sensitivity analysis are conducted. Similar approaches are undertaken to extend the forward/reverse algorithms to indentations using two ore more tip geometries. Microstructural miniaturization leads to novel class of materials with a grain size smaller than 100 nm...

Nanomechnics of crystalline materials : experiments and computations

Van Vliet, Krystyn J. (Krystyn Joy), 1976-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 165 leaves; 8532263 bytes; 8532072 bytes; application/pdf; application/pdf
ENG
Relevância na Pesquisa
105.63%
In this thesis, experimental, computational and analytical approaches are employed to examine systematically the mechanisms of deformation in crystalline materials. Such insight can be used to exploit and avoid contact in actuator and sensor applications, to derive mechanical properties for engineering of materials, and to investigate the fundamental role of defects. Here, localized mechanical contact of material surfaces is utilized to elucidate the effects of length scales on the transition from elastic (reversible) to plastic (irreversible) deformation. As the mechanical response of a material can be described by parameters which range from empirical constitutive (stress-strain) relations to fundamental descriptions of atomic interactions, the deformation response can be related to global mechanical properties such as yield strength, as well as to local phenomena such as dislocation nucleation. The concurrent design and implementation of experiments including micro- and nanoindentation and uniaxial compression, in situ experiments on a model, two-dimensional crystalline analogue, and computational modeling at the continuum (finite element) and atomistic (molecular dynamics) levels presented herein provide a unique opportunity to develop and validate hypotheses and analytical algorithms. Indeed...

Size dependence of mechanical responses of materials in small-volume structures

Choi, Yoonjoon, 1967-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 144 p.; 5514870 bytes; 9747528 bytes; application/pdf; application/pdf
ENG
Relevância na Pesquisa
95.62%
The effect of length scales on mechanical responses of materials in small-volume structures, such as thin films and patterned lines on substrates, is examined. The understanding of stress evolution and deformation behavior of those materials is one of major factors in the fabrication, performance, and reliability of microelectronic devices. The length scales involved in such materials are on the order of 1 min., and the deformation characteristics of the materials exhibit a strong dependence on their physical size such as film thickness and line width, as well as their microstructural length scale such as grain size. In this thesis, analytical, experimental, and computational approaches are utilized to elucidate the effect of length scales on the time-independent inelastic deformation of materials in small-volume structures. Experiments focus on continuous thin films and patterned lines of Al on Si substrates. The inelastic deformation of a material can be described by parameters which range from global constitutive (stress-strain) relations to atomistic descriptions of defect generation. An analytical model based on the generation of an array of dislocation loops is used to rationalize the film-thickness and grain-size effect on the stress evolution of thin metallic films on thick substrates. The consequence of the dislocation generation restricted by the film thickness and grain size leads to the full description of stress-temperature histories in an Al film on a Si substrate...

Computational study and analysis of structural imperfections in 1D and 2D photonic crystals

Maskaly, Karlene Rosera
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 232 p.; 12921362 bytes; 12931189 bytes; application/pdf; application/pdf
ENG
Relevância na Pesquisa
115.55%
Dielectric reflectors that are periodic in one or two dimensions, also known as 1D and 2D photonic crystals, have been widely studied for many potential applications due to the presence of wavelength-tunable photonic bandgaps. However, the unique optical behavior of photonic crystals is based on theoretical models of perfect analogues. Little is known about the practical effects of dielectric imperfections on their technologically useful optical properties. In order to address this issue, a finite-difference time-domain (FDTD) code is employed to study the effect of three specific dielectric imperfections in 1D and 2D photonic crystals. The first imperfection investigated is dielectric interfacial roughness in quarter-wave tuned ID photonic crystals at normal incidence. This study reveals that the reflectivity of some roughened photonic crystal configurations can change up to 50% at the center of the bandgap for RMS roughness values around 20% of the characteristic periodicity of the crystal. However, this reflectivity change can be mitigated by increasing the index contrast and/or the number of bilayers in the crystal. In order to explain these results, the homogenization approximation, which is usually applied to single rough surfaces...

Data mining for structure type prediction

Tibbetts, Kevin (Kevin Joseph)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 42 p.; 2390590 bytes; 2390373 bytes; application/pdf; application/pdf
ENG
Relevância na Pesquisa
95.55%
Determining the stable structure types of an alloy is critical to determining many properties of that material. This can be done through experiment or computation. Both methods can be expensive and time consuming. Computational methods require energy calculations of hundreds of structure types. Computation time would be greatly improved if this large number of possible structure types was reduced. A method is discussed here to predict the stable structure types for an alloy based on compiled data. This would include experimentally observed stable structure types and calculated energies of structure types. In this paper I will describe the state of this technology. This will include an overview of past and current work. Curtarolo et al. showed a factor of three improvement in the number of calculations required to determine a given percentage of the ground state structure types for an alloy system by using correlations among a database of over 6000 calculated energies.I will show correlations among experimentally determined stable structure types appearing in the same alloy system through statistics computed from the Pauling File Inorganic Materials Database Binaries edition. I will compare a method to predict stable structure types based on correlations among pairs of structure types that appear in the same alloy system with a method based simply on the frequency of occurrence of each structure type. I will show a factor of two improvement in the number of calculations required to determine the ground state structure types between these two methods. This paper will examine the potential market value for a software tool used to predict likely stable structure types. A timeline for introduction of this product and an analysis of the market for such a tool will be included. There is no established market for structure type prediction software...

Development of stable operator splitting numerical algorithms for phase-field modeling and surface diffusion applications

Handler, Matthew Dane
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 37 leaves; 1675815 bytes; 1675298 bytes; application/pdf; application/pdf
ENG
Relevância na Pesquisa
105.55%
Implicit, explicit and spectral algorithms were used to create Allen-Cahn and Cahn-Hilliard phase field models. Individual terms of the conservation equations were approached by different methods using operator splitting techniques found in previous literature. In addition, dewetting of gold films due to surface diffusion was modeled to present the extendability and efficiency of the spectral methods derived. The simulations developed are relevant to many real systems and are relatively light in computational load because they take large time steps to drive the model into equilibrium. Results were analyzed by their relevancy to real world applications and further work in this field is outlined.; by Matthew Dane Handler.; Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2006.; Includes bibliographical references (leaves 35-37).

Simulations of polymeric membrane formation in 2D and 3D

Zhou, Bo, Ph. D. Massachusetts Institute of Technology
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 213 p.; 5095015 bytes; 5217969 bytes; application/pdf; application/pdf
ENG
Relevância na Pesquisa
105.55%
The immersion precipitation process makes most commercial polymeric membranes, which enjoy widespread use in water filtration and purification. In this work, a ternary Cahn-Hilliard formulation incorporating a Flory-Huggins homogeneous free energy function is used to model both initial diffusion and the liquid-liquid demixing stage of the immersion precipitation process, which determines much of the final morphology of membranes. Simulations start with a simple non-solvent/solvent/polymer ternary system with periodic boundary conditions and uniform initial conditions with small random fluctuations in 2D. Results in 2D demonstrate the effects of mobilities (Mij) and gradient penalty coefficients (Kij) on phase separation behavior. A two-layer polymer-solvent/non-solvent initial condition is then used to simulate actual membrane fabrication conditions. 2D simulation results demonstrate an asymmetric structure of membrane morphology, which strongly agrees with the experimental observation. A mass transfer boundary condition is developed to model the interaction between the polymer solution and the coagulation bath more efficiently. Simulation results show an asymmetric membrane with connected top layer.; (cont.) Then a wide range of initial compositions are used in both the polymer solution and the coagulation bath...

Micro and nano mechanics of materials response during instrumented frictional sliding

Bellemare, Simon C. (Simon Claude)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 109 p.
ENG
Relevância na Pesquisa
105.55%
Over the past decade, many computational studies have explored the mechanics of instrumented normal indentation. In contrast, very few studies have investigated quantitative aspects of frictional sliding contact in the elasto-plastic regime. In this thesis, a new framework was developed to establish relationships between the frictional sliding response, material properties and contact parameters. Dimensional analysis enabled to define scaling variables and dimensionless functions. Finite element methods were used to simulate the process of steady-state frictional sliding and evaluate the dimensionless functions. In frictional sliding, the representative plastic strain was found to be more than four times as large as in normal indentation. Further comparison with indentation indicated a three fold increase in the maximum pile-up height and an increased influence of the strain hardening on hardness. Experimental studies were conducted with and without a liquid lubricant in selected material systems. Quantitative agreements with numerical predictions were observed in all cases. The strong influence of the strain hardening exponent on the pile-up height was illustrated from frictional sliding results obtained in copper and copper-zinc specimens of different grain sizes.; (cont.) Also...

Computational studies of cation and anion ordering in cubic yttria stabilized zirconia

Predith, Ashley P. (Ashley Page)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 137 p.
ENG
Relevância na Pesquisa
105.55%
The investigation of ordering and phase stability in the ZrO2-Y203 system involves two sets of calculations. The first set of calculations uses the cluster expansion method. A guide to the practical implementation of the cluster expansion outlines methods for defining a goal and choosing structures and clusters that best model the system of interest. The cluster expansion of the yttria stabilized zirconia system considers 447 configurations across the ZrO2-Y203 composition range. The effective cluster interaction for pair clusters show electrostatic repulsion between anions and little interaction between cations. Triplet anion terms largely modify the energy contributions of the pair terms. Separate cluster expansions using structures at single compositions show that cation clusters become more important at high yttria composition. The cluster expansion led to the discovery of three previously unidentified ordered ground state structures at 25, 29, and 33 % Y on the cubic fluorite lattice. The ground state with 33 % Y is stable with respect to the calculated energies of monoclinic ZrO2 and the Y4Zr3012 ground state. The ground states have the common ordering feature of yttrium and vacancies in [1 1 2] chains, and Monte Carlo simulations show that vacancy ordering upon cooling is contingent on cation ordering.; (cont.) The second set of calculations consider three driving forces for order: ionic relaxation...

Numerical modeling of interface dynamics and transport phenomena in transport-limited electrolysis processes

Pongsaksawad, Wanida
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 117 p.
ENG
Relevância na Pesquisa
105.61%
Electrochemical reactions in materials and processes induce morphological instability on the cathode, which can lead to porous deposits or system failure. The growth of the protrusion is a complex phenomenon which involves chemical, electrical, and momentum driving forces in the system. Thus, it is important to understand the effect of electrochemistry in phase boundary evolution in order to optimize the performance of such processes. This thesis contributes to predicting and controlling such interface instability phenomena by developing a computational model that captures them. Successful application of the model to emerging metal extraction processes demonstrates its usefulness. A phase field model of electrochemical interface is developed for transport-limited electrolysis with rapid charge redistribution. This new Cahn-Hillard phase field formulation includes a model electrostatic free energy term, which captures the behavior of the diffuse interface under the applied electric field, in addition to transport by free energy gradient and convection. The model agrees with published stability criterion for a solid cathode. When the electrodes and electrolyte are low-viscosity fluids, flow stabilizes the interface.; (cont.) A new stability criterion for metal reduction in a liquid-liquid system is derived and agrees well with the model results. Next...

Effects of nanoscale film thickness on apparent stiffness of and cell-mediated strains in polymers

Oommen, Binu K
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 70 leaves
ENG
Relevância na Pesquisa
105.55%
The mechanical properties of compliant materials such as polymeric films and biological membranes that are of nanoscale in thickness are increasingly extracted from scanning probe microscope-enabled nanoindentation. These films are applied in various fields that require multiaxial loading conditions. The Hertzian contact models developed for linear elastic materials of semi-infinite thickness fail to accurately predict the elastic modulus E for these compliant materials. This makes it necessary to understand the evolution of stress and strain fields of these nanoscale structures. In this thesis we employ computational simulations that are based on experimental parameters for contact based analysis of compliant polymer thin films, to decouple the effect of thickness and angle of indentation on calculated mechanical properties. Traction applied by living cells to these compliant films are studied in detail. We thus identify the range of strains and material thickness for which contact models could be used to accurately predict the elastic stiffness of these polymeric films of nanoscale (<100 nm) thickness using scanning probe microscope-enabled experiments, and the volumes over which adhered cells deform these films. The key results of this thesis enable accurate experimental analysis of polymeric thin film elastic properties...

Blind benchmark predictions of the NACOK air ingress tests using the CFD code FLUENT

Brudieu, Marie-Anne V
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 127, [84] p.
ENG
Relevância na Pesquisa
95.62%
The JAERI and NACOK experiments examine the combined effects of natural convection during an air ingress event: diffusion, onset of natural circulation, graphite oxidation and multicomponent chemical reactions. MIT has been benchmarking JAERI tests using the FLUENT code for approximately three years [1]. This work demonstrated that the three fundamental physical phenomena of diffusion, natural circulation and then chemical reactions can be effectively modeled using computational fluid dynamics. The latest series of tests conducted at the NACOK facility were two graphite corrosion experiments: The first test consisted of an open chimney configuration heated to 650C with a pebble bed zones of graphite pebbles and graphite reflectors. The second test is a similar test with a cold leg adjacent to the hot channel with an open return duct below the hot channel. Natural circulation, diffusion and graphite corrosion were studied for both tests. Using and adapting previous computational methods, the FLUENT code is used to blind benchmark these experiments. The objective is to assess the adequacy of the modeling method used in this blind bench-marking analysis by comparing these blind test predictions to the actual data and then modify the model to improve predictive capability. Ultimately...

A machine learning approach to crystal structure prediction

Fischer, Christopher Carl
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 147 p.
ENG
Relevância na Pesquisa
95.56%
This thesis develops a machine learning framework for predicting crystal structure and applies it to binary metallic alloys. As computational materials science turns a promising eye towards design, routine encounters with chemistries and compositions lacking experimental information will demand a practical solution to structure prediction. We review the ingredients needed to solve this problem and focus on structure search. This thesis develops and argues for a search strategy utilizing a combination of machine learning and modern quantum mechanical methods. Structure correlations in a binary alloy database are extracted using probabilistic graphical models. Specific correlations are shown to reflect well-known structure stabilizing mechanisms. Two probabilistic models are investigated to represent correlation: an undirected graphical model known as a cumulant expansion, and a mixture model. The cumulant expansion is used to efficiently guide Density Functional Theory predictions of compounds in the Ag-Mg, Au-Zr, and Li-Pt alloy systems. Cross-validated predictions of compounds present in 1335 binary alloys are used to demonstrate predictive ability over a wide range of chemistries - providing both efficiency and confidence to the search problem. Inconsistencies present in the cumulant expansion are analyzed...

Computational studies of hydrogen storage materials and the development of related methods

Mueller, Timothy Keith
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 199 p.
ENG
Relevância na Pesquisa
105.62%
Computational methods, including density functional theory and the cluster expansion formalism, are used to study materials for hydrogen storage. The storage of molecular hydrogen in the metal-organic framework with formula unit Zn40(02C-C6H6-COD3 is considered. It is predicted that hydrogen adsorbs at five sites near the metal-oxide cluster, in good agreement with recent experimental data. It is also shown that the metal-oxide cluster affects the electronic structure of the organic linker, qualitatively affecting the way in which hydrogen binds to the linker. Lithium imide (Li2NH), a material present in several systems being considered for atomic hydrogen storage, is extensively investigated. A variation of the cluster expansion formalism that accounts for continuous bond orientations is developed to search for the ground state structure of this material, and a structure with a calculated energy lower than any known is found. Two additional discrete cluster expansions are used to predict that the experimentally observed phase of lithium imide is metastable at temperatures below approximately 200 K and stabilized primarily by vibrational entropy at higher temperatures. A new structure for this low-temperature phase that agrees well with experimental data is proposed. A method to improve the predictive power of cluster expansions through the application of statistical learning theory is developed...

Computational studies of stress and structure development resulting from the coalescence of metallic islands

Takahashi, Andrew Rikio
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 65 leaves
ENG
Relevância na Pesquisa
105.55%
Thin film component properties are critical design elements in almost all industries. These films are particularly important in the performance of micro- and nano-electromechanical systems (MEMS and NEMS). Residual stress in thin film components is often treated as an unavoidable side effect of processing steps and the degree of residual stress can drastically affect the performance and properties of the final product. While high levels of residual stress are often detrimental to performance, control of the stress and stress gradients can also be used to enhance performance and even generate new capabilities. The work presented in this thesis examines the role of island coalescence in the development of structure and stress in thin films. The primary methods of investigation are molecular dynamics (MD) and finite element analysis (FEA). The semi-empirical MD calculations show that coalescence is a very rapid process for unconstrained spheres and for hemispheres allowed to slide on a frictionless substrate. Particle rotations are commonly observed during the coalescence calculations. The extent of neck formation between 2 particles is consistent with continuum models even down to length scales which would normally be outside the range in which the models might be expected to be applicable. The MD calculations also show that internal island defects may be induced by the island coalescence process...

Indentation of plastically graded materials

Choi, In-Suk, Ph. D. Massachusetts Institute of Technology
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 126 p.
ENG
Relevância na Pesquisa
95.58%
The introduction of certain controlled gradients in plastic properties is known to promote resistance to the onset of damage at contact surfaces during some tribological applications. Gradients in composition, microstructure and plastic properties can also be deleterious to contact-damage resistance in some situations. In order to realize such potentially beneficial or deleterious effects of plastic property gradients in tribological applications, it is essential first to develop a comprehensive understanding of the effects of yield strength and strain hardening exponent on frictionless normal indentation. To date, however, systematic studies of plasticity gradient effects on indentation response have not been completed. A comprehensive parametric study of the mechanics of indentation of plastically graded materials is completed in this work by recourse to finite element (FE) computations. On the basis of a large number of detailed computational simulations, a general methodology for assessing instrumented indentation response of plastically graded materials is formulated so that quantitative interpretations of depth-sensing indentation experiments could be performed. The specific case of linear gradient in yield strength is explored in detail.; (cont.) The FE analysis leads to a universal dimensionless function to predict load displacement curves for plastically graded engineering materials. Experimental validation of the analysis is performed by choosing the model system of an electrodeposited nanostructured Ni-W alloy...

Computational structure analysis of multicomponent oxides

Hinuma, Yoyo
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 138 p.
ENG
Relevância na Pesquisa
105.55%
First principles density functional theory (DFT) energy calculations combined with the cluster expansion and Monte Carlo techniques are used to understand the cation ordering patterns of multicomponent oxides. Specifically, the lithium ion battery cation material LiNi0.5Mn0.5O2 and the thermoelectric material P2-NaxCoO2 (0.5 =/< x =/< 1) are investigated in the course of this research. It is found that at low temperature the thermodynamically stable state of LiNi0.5Mn0.5O2 has almost no Li/Ni disorder between the Li-rich and transition metal-rich (TM) layer, making it most suitable for battery applications. Heating the material above ~600°C causes an irreversible transformation, which yields a phase with 10~12% Li/Ni disorder and partial disorder of cations in the TM layer. Phase diagrams for the NaxCoO2 system were derived from the results of calculations making use of both the Generalized Gradient Approximation (GGA) to DFT and GGA with Hubbard U correction (GGA+U). This enabled us to study how hole localization, or delocalization, on Co affects the ground states and order-disorder transition temperatures of the system. Comparison of ground states, c lattice parameter and Na1/Na2 ratio with experimental observations suggest that results from the GGA...

Towards first-principles electrochemistry

Dabo, Ismaila
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 151 p.
ENG
Relevância na Pesquisa
95.67%
This doctoral dissertation presents a comprehensive computational approach to describe quantum mechanical systems embedded in complex ionic media, primarily focusing on the first-principles representation of catalytic electrodes under electrochemical conditions. The accurate electrostatic description of electrified metal-solution interfaces represents a persistent challenge for ab-initio simulations and an essential requisite for predicting the electrical response of electrochemical convertors-i.e., the correspondence between the macroscopic voltage and the microscopic interfacial charge distribution. The approach consists of controlling the electrode voltage via its conjugate extensive variable, namely, the charge of the system. As a preliminary to the study of electrified interfaces in ionic media, we analyze charged slabs in vacuum subject to periodic boundary conditions. We show that the corrective potential (defined as the difference between the exact open-boundary potential and the periodic potential obtained from a Fourier transform) varies smoothly over space, allowing for its determination on a coarse mesh using optimized electrostatic solvers. Because this scheme takes into account exact open boundary conditions, its performance is considerably superior to that of conventional corrective methods. Extending this computational scheme...

Attractive electrostatic self-assembly of ordered and disordered heterogeneous colloids

Maskaly, Garry R. (Garry Russell), 1978-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 193 p.; 7064851 bytes; 7064543 bytes; application/pdf; application/pdf
ENG
Relevância na Pesquisa
105.55%
Ionic colloidal crystals are here defined as multicomponent ordered colloidal structures stabilized by attractive electrostatic interactions. These crystals are colloidal analogues to ionic materials including zincblende, rocksalt, cesium chloride, and fluorite. A thermodynamic study revealed that the screening ratio, charge ratio, and monodispersity are critical parameters in ionic colloidal crystal (ICC) formation. Experimentally, small ordered regions were observed under ideal thermodynamic conditions. However, no larger crystalline regions were found in these samples. The kinetics of ICC formation was studied using a variety of computational techniques, including Brownian dynamics, Monte Carlo, and a Newton's method solver. These techniques have each elucidated properties and processing conditions that are important to crystallization. The Brownian dynamics and Monte Carlo simulations showed that the previous experiments were highly undercooled. Furthermore, a narrow crystallization window was found, demonstrating the need to create particle systems that meet the narrow parameter space where ICCs should be stable. Pair interaction potentials were evaluated for their accuracy using a Poisson-Boltzmann (PB) equation solver. The PB solver was also used to further refine crystalline formation energies so that systems can be more accurately tailored. A surprising result from the PB solver showed that the lowest formation energy occurs when the quantity of surface charges on both particles are equal. Although this result is not predicted by any colloidal pair potentials...

Education for Computational Science and Engineering

Grcar, Joseph F.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
95.6%
Computational science and engineering (CSE) has been misunderstood to advance with the construction of enormous computers. To the contrary, the historical record demonstrates that innovations in CSE come from improvements to the mathematics embodied by computer programs. Whether scientists and engineers become inventors who make these breakthroughs depends on circumstances and the interdisciplinary extent of their educations. The USA currently has the largest CSE professorate, but the data suggest this prominence is ephemeral.; Comment: 9 pages, 2 figures, 1 table