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RISS 인기검색어
- 검색키워드
- 저자 : Tuzel, Erkan (검색결과 2 건)
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Particle-based mesoscale modeling of flow and transport in complex fluids
Tuzel, Erkan University of Minnesota 2007 해외박사(DDOD)
The dynamic behavior of complex liquids and soft materials is of great importance in a wide range of disciplines. Computational studies of these phenomena are particularly demanding because of the presence of disparate length and energy scales, and the complicated coupling between the embedded objects and the hydrodynamic flow field. The goal of this dissertation is to contribute to the understanding of these systems through the development and application of robust, quantitative mesoscale simulation techniques which incorporate both hydrodynamic interactions and thermal fluctuations. The work involves the further development of a specific particle-based mesoscale algorithm---stochastic rotation dynamics---which solves the hydrodynamic equations by following the discrete time dynamics of particles with continuous coordinates and velocities, using efficient multi-particle collisions. A detailed study of the long length- and time-scale properties of the algorithm, which involves analytical derivations of hydrodynamic equations, Green-Kubo relations, and transport coefficients is presented. Extensive simulations are performed to verify these results. The original algorithm is generalized to model dense fluids and binary mixtures. The equation of state and analytical expressions for the transport coefficients are derived. It is also shown that the non-ideal model exhibits an order-disorder transition and caging in the limit of large collision frequencies. The phase diagram of the entropically driven de-mixing transition of the binary mixture is presented, the surface tension for a droplet is calculated, and a detailed analysis of the capillary wave spectrum is performed. Finally, the algorithm is extended to amphiphilic mixtures in order to be able to study microemulsions and micelle formation. We have also developed a constrained dynamics algorithm for modeling the dynamical behavior of wormlike chains embedded in a mesoscale solvent. Rigorously enforced bond-length constraints permit the use of longer time steps, resulting in increased computational efficiency. It also eliminates high frequency degrees of freedom which often complicate comparison with theory and experiment. Finally, in order to provide guidance for experiments, we have modeled the behavior of thermally driven microtubules and simulated sources of experimental error that affect curvature distribution measurements used to understand the physical basis of microtubule bending in living cells.
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A level set method for an inverse problem arising in photolithography
Tuzel, Vasfiye Hande University of Minnesota 2009 해외박사(DDOD)
Photolithography is a key process used in the semiconductor industry during the fabrication of integrated circuits. It is the process in which a given circuit layout pattern is transferred onto a substrate by employing a mask. The role of the mask is to block out the ultraviolet light exposure on certain areas on the substrate, hence allowing the emergence of specific patterns after chemical post-processing. Designing the perfect mask that takes into account all optical effects, especially at nanometer resolutions, is a challenging task. In this thesis, we formulate this as an inverse problem, i.e. finding the mask that produces the desired pattern. In order to do this, we first introduce the forward problem of calculating the light intensity at the substrate, given the initial mask. We then formulate a variational problem, which minimizes the mismatch between the desired mask and the one predicted by the model. The variational problem is solved using a level-set approach. Our results show that we can successfully produce masks that match the desired patterns with an error less than 2%. We believe our algorithm can enable further automation of the mask design process, and help manufacturers design better layouts at nanometer scales.
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