Publications

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This paper focuses on the extraction of skeletons of CAD models and its applications in finite element (FE) mesh generation. The term 'skeleton of a CAD model' can be visualized as analogous to the 'skeleton of a human body'. The skeletal representations covered in this paper include medial axis transform (MAT), Voronoi diagram (VD), chordal axis transform (CAT), mid surface, digital skeletons, and disconnected skeletons. In the literature, the properties of a skeleton have been utilized in developing various algorithms for extracting skeletons. Three main approaches include: (1) the bisection method where the skeleton exists at equidistant from at least two points on boundary, (2) the grassfire propagation method in which the skeleton exists where the opposing fronts meet, and (3) the duality method where the skeleton is a dual of the object. In the last decade, the author has applied different skeletal representations in all-quad meshing, hex meshing, mid-surface meshing, mesh size function generation, defeaturing, and decomposition. A brief discussion on the related work from other researchers in the area of tri meshing, tet meshing, and anisotropic meshing is also included. This paper concludes by summarizing the strengths and weaknesses of the skeleton-based approaches in solving various geometry-centered problems in FE mesh generation. The skeletons have proved to be a great shape abstraction tool in analyzing the geometric complexity of CAD models as they are symmetric, simpler (reduced dimension), and provide local thickness information. However, skeletons generally require some cleanup, and stability and sensitivity of the skeletons should be controlled during extraction. Also, selecting a suitable application-specific skeleton and a computationally efficient method of extraction is critical.

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In recent years, a successful method for generating experimental dynamic substructures has been developed using an instrumented fixture, the transmission simulator. The transmission simulator method solves many of the problems associated with experimental substructuring. These solutions effectively address: (1) rotation and moment estimation at connection points; (2) providing substructure Ritz vectors that adequately span the connection motion space; and (3) adequately addressing multiple and continuous attachment locations. However, the transmission simulator method may fail if the transmission simulator is poorly designed. Four areas of the design addressed here are: (1) designating response sensor locations; (2) designating force input locations; (3) physical design of the transmission simulator; and (4) modal test design. In addition to the transmission simulator design investigations, a review of the theory with an example problem is presented.

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Results of several experiments aimed at remedying photoresist adhesion failure during spray wet chemical etching of InGaP/GaAs NPN HBTs are reported. Several factors were identified that could influence adhesion and a Design of Experiment (DOE) approach was used to study the effects and interactions of selected factors. The most significant adhesion improvement identified is the incorporation of a native oxide etch immediately prior to the photoresist coat. In addition to improving adhesion, this pre-coat treatment also alters the wet etch profile of (100) GaAs so that the reaction limited etch is more isotropic compared to wafers without surface treatment; the profiles have a positive taper in both the [011] and [011] directions, but the taper angles are not identical. The altered profiles have allowed us to predictably yield fully probe-able HBTs with 5 x 5 {micro}m emitters using 5200 {angstrom} evaporated metal without planarization.

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Scoping studies have demonstrated that ceragenins, when linked to water-treatment membranes have the potential to create biofouling resistant water-treatment membranes. Ceragenins are synthetically produced molecules that mimic antimicrobial peptides. Evidence includes measurements of CSA-13 prohibiting the growth of and killing planktonic Pseudomonas fluorescens. In addition, imaging of biofilms that were in contact of a ceragenin showed more dead cells relative to live cells than in a biofilm that had not been treated with a ceragenin. This work has demonstrated that ceragenins can be attached to polyamide reverse osmosis (RO) membranes, though work needs to improve the uniformity of the attachment. Finally, methods have been developed to use hyperspectral imaging with multivariate curve resolution to view ceragenins attached to the RO membrane. Future work will be conducted to better attach the ceragenin to the RO membranes and more completely test the biocidal effectiveness of the ceragenins on the membranes.

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Objectives of the Office of Energy Efficiency and Renewable Energy (EERE) 2009-2010 Studies (Solar, Wind, Geothermal, & Combustion Engine R&D) are to: (1) Demonstrate to investors that EERE research and technology development (R&D) programs & subprograms are 'Worth It'; (2) Develop an improved Benefit-Cost methodology for determining realized economic and other benefits of EERE R&D programs - (a) Model government additionality more thoroughly and on a case-by-case basis; (b) Move beyond economic benefits; and (c) Have each study calculate returns to a whole EERE program/subprogram; and (3) Develop a consistent, workable Methods Guide for independent contractors who will perform the evaluation studies.

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