Li-Tien Cheng²³, Myungjoo Kang⁴, Stanley Osher⁴, Hyeseon Shim⁴, Yen-Hsi Tsai⁵

CMES-Computer Modeling in Engineering & Sciences, Vol.5, No.4, pp. 347-360, 2004, DOI:10.3970/cmes.2004.005.347

Abstract Geometric optics makes its impact both in mathematics and real world applications related to ray tracing, migration, and tomography. Of special importance in these problems are the wavefronts, or points of constant traveltime away from sources, in the medium. Previously in [Osher, Cheng, Kang, Shim, and Tsai(2002)], we initiated a level set approach for the construction of wavefronts in isotropic media that handled the two major algorithmic issues involved with this problem: resolution and multivalued solutions. This approach was quite general and we were able to construct wavefronts in the presence of refraction, reflection, higher dimensions, and, in [Qian, Cheng,… More >

P. Castillo², J. Koning³, R. Rieben⁴, D. White⁵

CMES-Computer Modeling in Engineering & Sciences, Vol.5, No.4, pp. 331-346, 2004, DOI:10.3970/cmes.2004.005.331

Abstract In this article, we present a computational framework for solving problems arising in electromagnetism. The framework is derived from a modern geometrical approach and is based on differential forms (or p-forms). These geometrical entities provide a natural framework for modeling of physical quantities such as electric potentials, electric and magnetic fields, electric and magnetic fluxes, etc. We have implemented an object oriented class library, called FEMSTER. The library is designed for high order finite element approximations. In addition, it can be expanded by including user-defined data types or by deriving new classes. Finally, the versatility of the software is shown… More >

Oscar P. Bruno¹

CMES-Computer Modeling in Engineering & Sciences, Vol.5, No.4, pp. 319-330, 2004, DOI:10.3970/cmes.2004.005.319

Abstract We present a new set of high-order algorithms and methodologies for the numerical solution of problems of scattering by complex bodies in three-dimensional space. These methods, which are based on integral equations, high-order integration and Fast Fourier Transforms, can be used in the solution of problems of electromagnetic and acoustic scattering by surfaces and penetrable scatterers---even in cases in which the scatterers contain geometric singularities such as corners and edges. The solvers presented here exhibit high-order convergence, they run on low memories and reduced operation counts, and they result in solutions with a high degree of accuracy. More >

E. Bleszynski¹, M. Bleszynski¹, T. Jaroszewicz¹

CMES-Computer Modeling in Engineering & Sciences, Vol.5, No.4, pp. 295-318, 2004, DOI:10.3970/cmes.2004.005.295

Abstract We describe elements of our current work on the development of new methods for high frequency electromagnetic scattering, based on the wavefront (WF) representation of propagating fields and on the asymptotic but rigorous solution of integral equations for surface currents. In the wavefront evolution technique, surfaces of constant phase are constructed and treated not merely as collections of independent rays, but as well defined geometrical objects endowed with the full connectivity information. Hence, a precise determination of shadow and reflection boundaries, a construction of (multiply) diffracted wavefronts, a dynamic adjustment of the number of rays, an approximately constant ray-ray distance,… More >

F. Reitich¹, K. K. Tamma²

CMES-Computer Modeling in Engineering & Sciences, Vol.5, No.4, pp. 287-294, 2004, DOI:10.3970/cmes.2004.005.287

Abstract This article has no abstract. More >

Gerhard Klimeck^1,2, Fabiano Oyafuso², Timothy B. Boykin³, R. Chris Bowen², Paul von Allmen⁴

CMES-Computer Modeling in Engineering & Sciences, Vol.3, No.5, pp. 601-642, 2002, DOI:10.3970/cmes.2002.003.601

Abstract Material layers with a thickness of a few nanometers are common-place in today's semiconductor devices. Before long, device fabrication methods will reach a point at which the other two device dimensions are scaled down to few tens of nanometers. The total atom count in such deca-nano devices is reduced to a few million. Only a small finite number of "free'' electrons will operate such nano-scale devices due to quantized electron energies and electron charge. This work demonstrates that the simulation of electronic structure and electron transport on these length scales must not only be fundamentally quantum mechanical, but it must… More >

Amitesh Maiti¹

CMES-Computer Modeling in Engineering & Sciences, Vol.3, No.5, pp. 589-600, 2002, DOI:10.3970/cmes.2002.003.589

Abstract Atomistic modeling and simulations are becoming increasingly important in the design of new devices at the nanoscale. In particular, theoretical modeling of carbon nanotubes have provided useful insight and guidance to many experimental efforts. To this end, we report simulation results on the electronic, structural and transport properties for two different applications of carbon nanotube-based devices: (1) effect of adsorbates on field emission; and (2) effect of mechanical deformation on the electronic transport. The reported simulations are based on First Principles Density Functional Theory (DFT), classical molecular mechanics, and tight-binding transport based on the recursive Green's function formalism. More >

Susan B. Sinnott¹, Zugang Mao,², Ki-Ho Lee

CMES-Computer Modeling in Engineering & Sciences, Vol.3, No.5, pp. 575-588, 2002, DOI:10.3970/cmes.2002.003.575

Abstract Nanofluidics is an area that has been under study for some time in zeolites and ideal nanoporous systems. Computational studies of the behavior of molecules in nanoporous structures have played an important role in understanding this phenomenon as experimental studies of molecular behavior in nanometer-scale pores are difficult to perform. In this paper computational work to study molecular motion and the separation of molecular mixtures in carbon nanotube systems is reported. The systems examined include organic molecules, such as CH₄, C₂H₆, n-C₄H₁₀, and i-C₄H₁₀, and inorganic molecules, such as CO₂. The interatomic forces in the molecular dynamics simulations are calculated… More >

Al Globus¹, Madhu Menon², Deepak Srivastava¹

CMES-Computer Modeling in Engineering & Sciences, Vol.3, No.5, pp. 557-574, 2002, DOI:10.3970/cmes.2002.003.557

Abstract A genetic algorithm procedure has been developed for fitting parameters for many-body interatomic force field functions. Given a physics or chemistry based analytic form for the force field function, parameters are typically chosen to fit a range of structural and physical properties given either by experiments and/or by higher accuracy tight-binding or ab-initio simulations. The method involves using both near equilibrium and far from equilibrium configurations in the fitting procedure, and is unlikely to be trapped in local minima in the complex many-dimensional parameter space. As a proof of concept, we demonstrate the procedure for Stillinger-Weber (S-W) potential by (a)… More >

Leonid V. Zhigilei¹, Avinash M. Dongare¹

CMES-Computer Modeling in Engineering & Sciences, Vol.3, No.5, pp. 539-556, 2002, DOI:10.3970/cmes.2002.003.539

Abstract Computational modeling has a potential of making an important contribution to the advancement of laser-driven methods in nanotechnology. In this paper we discuss two computational schemes developed for simulation of laser coupling to organic materials and metals and present a multiscale model for laser ablation and cluster deposition of nanostructured materials. In the multiscale model the initial stage of laser ablation is reproduced by the classical molecular dynamics (MD) method. For organic materials, the breathing sphere model is used to simulate the primary laser excitations and the vibrational relaxation of excited molecules. For metals, the two temperature model coupled to… More >