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Lin L.,Princeton University | Morrone J.A.,Princeton University | Morrone J.A.,Columbia University | Car R.,Princeton University | Parrinello M.,Computational Sciences, LLC
Physical Review Letters

The proton momentum distribution, accessible by deep inelastic neutron scattering, is a very sensitive probe of the potential of mean force experienced by the protons in hydrogen-bonded systems. In this work we introduce a novel estimator for the end-to-end distribution of the Feynman paths, i.e., the Fourier transform of the momentum distribution. In this formulation, free particle and environmental contributions factorize. Moreover, the environmental contribution has a natural analogy to a free energy surface in statistical mechanics, facilitating the interpretation of experiments. The new formulation is not only conceptually but also computationally advantageous. We illustrate the method with applications to an empirical water model, ab initio ice, and one dimensional model systems. © 2010 The American Physical Society. Source

Clayton J.D.,Impact Physics | Knap J.,Computational Sciences, LLC
International Journal of Fracture

Phase field theory is developed for solids undergoing potentially large deformation and fracture. The elastic potential depends on a finite measure of elastic strain. Surface energy associated with fracture can be anisotropic, enabling description of preferred cleavage planes in single crystals, or isotropic, applicable to amorphous solids such as glass. Incremental solution of the Euler–Lagrange equations corresponds to local minimization of an energy functional for the solid, enabling prediction of equilibrium crack morphologies. Predictions are in close agreement with analytical solutions for pure mode I or pure mode II loading, including the driving force for a crack to extend from a pre-existing plane onto a misoriented cleavage plane. In an isotropic matrix, the tendency for a crack to penetrate or deflect around an inclusion is shown to depend moderately on the ratio of elastic stiffness in matrix and inclusion and strongly on their ratio of surface energy. Cracks are attracted to (shielded by) inclusions softer (stiffer) than the surrounding matrix. The theory and results apparently report the first fully three-dimensional implementation of phase field theory of fracture accounting for simultaneous geometric nonlinearity, nonlinear elasticity, and surface energy anisotropy. © 2014, Springer Science+Business Media Dordrecht (outside the USA). Source

Stone C.P.,Computational Sciences, LLC | Davis R.L.,University of California at Davis
Journal of Propulsion and Power

The cost of integrating detailed finite rate chemical kinetics mechanisms can be prohibitive in turbulent combustion simulations. Techniques that can significantly reduce these simulation times are of great interest to model developers and the broader propulsion and power community. Two new integration methods using graphical processing units are presented that can rapidly integrate the nonlinear ordinary differential equations at each grid point. The explicit graphical processing-unit-enabled fourth-order-accurate Runge-Kutta-Fehlberg ordinary differential equation solver achieved a maximum speed up of 20.2x over the baseline implicit fifth-order-accurate DVODE CPU run time for large numbers of independent ordinary differential equation systems with comparable accuracy. The graphical processing unit implementation of DVODE achieved a maximum speed up of 7.7x over the baseline CPU run time. The performance impact of mapping one graphical processing unit thread to each ordinary differential equation system was compared with mapping an entire graphical processing unit thread block per ordinary differential equation (i.e., multiple threads per ordinary differential equation). The one-thread-per- ordinary-differentialequation approach achieved greater overall speed up but only when the number of independent ordinary differential equations was large. The one-block-per-ordinary-differential-equation implementation of Runge-Kutta-Fehlberg and DVODE both achieved lower peak speed ups, but outperformed the serial CPU performance with as few as 100 ordinary differential equations. The new graphical processing-unit-enabled ordinary differential equation solvers demonstrate a method to significantly reduce the computational cost of detailed finite rate combustion simulations. Copyright © 2013 by the American Institute of Aeronautics and Astronautics, Inc. Source

Lin L.,Princeton University | Morrone J.A.,Princeton University | Morrone J.A.,Columbia University | Car R.,Princeton University | Parrinello M.,Computational Sciences, LLC
Physical Review B - Condensed Matter and Materials Physics

By analyzing the momentum distribution obtained from path integral and phonon calculations we find that the protons in hexagonal ice experience an anisotropic quasiharmonic effective potential with three distinct principal frequencies that reflect molecular orientation. Due to the importance of anisotropy, anharmonic features of the environment cannot be extracted from existing experimental distributions that involve the spherical average. The full directional distribution is required, and we give a theoretical prediction for this quantity that could be verified in future experiments. Within the quasiharmonic context, anharmonicity in the ground-state dynamics of the proton is substantial and has quantal origin, a finding that impacts the interpretation of several spectroscopies. © 2011 American Physical Society. Source

Computational Sciences, LLC | Date: 2013-02-14

A dual use of a heater core that enables heating the cabin, cooling the engine or both on demand regardless of the passengers cabin heating and cooling requirements. This use of the heater core is enabled by an HVAC airbox system with a cooling door that can be selectively positioned such that at least some of the air moving through the heater core is directed to the underhood area of a vehicle thereby providing supplemental engine cooling on demand regardless of the passengers cabin heating and cooling requirements. The cooling door can be positioned automatically by the Engine Control Unit (ECU) dependent on any parameter, or combination of parameters, of the engine such as the engine coolant temperature or the engine oil temperature. The blower speed and the position of the cooling door are adjusted by the ECU depending on the whether and how much supplemental engine cooling is required.

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