Accurate pointing of tungsten welding electrodes

Thoriated-tungsten is pointed accurately and quickly by using sodium nitrite. Point produced is smooth and no effort is necessary to hold the tungsten rod concentric. The chemically produced point can be used several times longer than ground points. This method reduces time and cost of preparing tungsten electrodes

Cold machining of high density tungsten and other materials

Cold machining process, which uses a sub-zero refrigerated cutting fluid, is used for machining refractory or reactive metals and alloys. Special carbide tools for turning and drilling these alloys further improve the cutting performance

Exploiting geometry, topology, and optimization for knowledge discovery in big data

2013 Summer.Includes bibliographical references.In this dissertation, we consider several topics that are united by the theme of topological and geometric data analysis. First, we consider an application in landscape ecology using a well-known vector quantization algorithm to characterize and segment the color content of natural imagery. Color information in an image may be viewed naturally as clusters of pixels with similar attributes. The inherent structure and distribution of these clusters serves to quantize the information in the image and provides a basis for classification. A friendly graphical user interface called Biological Landscape Organizer and Semi-supervised Segmenting Machine (BLOSSM) was developed to aid in this classification. We consider four different choices for color space and five different metrics in which to analyze our data, and results are compared. Second, we present a novel topologically driven clustering algorithm that blends Locally Linear Embedding (LLE) and vector quantization by mapping color information to a lower dimensional space, identifying distinct color regions, and classifying pixels together based on both a proximity measure and color content. It is observed that these techniques permit a significant reduction in color resolution while maintaining the visually important features of images. Third, we develop a novel algorithm which we call Sparse LLE that leads to sparse representations in local reconstructions by using a data weighted 1-norm regularization term in the objective function of an optimization problem. It is observed that this new formulation has proven effective at automatically determining an appropriate number of nearest neighbors for each data point. We explore various optimization techniques, namely Primal Dual Interior Point algorithms, to solve this problem, comparing the computational complexity for each. Fourth, we present a novel algorithm that can be used to determine the boundary of a data set, or the vertices of a convex hull encasing a point cloud of data, in any dimension by solving a quadratic optimization problem. In this problem, each point is written as a linear combination of its nearest neighbors where the coefficients of this linear combination are penalized if they do not construct a convex combination, revealing those points that cannot be represented in this way, the vertices of the convex hull containing the data. Finally, we exploit the relatively new tool from topological data analysis, persistent homology, and consider the use of vector bundles to re-embed data in order to improve the topological signal of a data set by embedding points sampled from a projective variety into successive Grassmannians

Reflections on Math Students’ Circles: Two Personal Stories from Colorado

Math Students’ Circles provide an opportunity for mathematicians to work in their communities to engage young students in mathematics as a human, aesthetic, and social endeavor. Sometimes referred to simply as Math Circles, these venues give mathematicians experience in introducing children to topics not typically seen in school curricula in an exciting, hands-on format. This article explores two Math Students’ Circles (MSCs) in the state of Colorado from the point of view of two pre-tenure faculty members. One participated in MSCs for four years while working on her Ph.D. in mathematics, the other started an MSC as an offshoot of a successful professional development program for middle school mathematics teachers. We discuss how and why MSCs have influenced our professional lives

Topological Data Analysis of Biological Aggregation Models

We apply tools from topological data analysis to two mathematical models inspired by biological aggregations such as bird flocks, fish schools, and insect swarms. Our data consists of numerical simulation output from the models of Vicsek and D'Orsogna. These models are dynamical systems describing the movement of agents who interact via alignment, attraction, and/or repulsion. Each simulation time frame is a point cloud in position-velocity space. We analyze the topological structure of these point clouds, interpreting the persistent homology by calculating the first few Betti numbers. These Betti numbers count connected components, topological circles, and trapped volumes present in the data. To interpret our results, we introduce a visualization that displays Betti numbers over simulation time and topological persistence scale. We compare our topological results to order parameters typically used to quantify the global behavior of aggregations, such as polarization and angular momentum. The topological calculations reveal events and structure not captured by the order parameters.Comment: 25 pages, 12 figures; second version contains typo corrections, minor textual additions, and a brief discussion of computational complexity; third version fixes one typo and adds small paragraph about topological stabilit

Interview with Lois Mallory

An interview with Lois Mallor regarding her experiences in a one-room school house.https://scholars.fhsu.edu/ors/1165/thumbnail.jp

Process analysis and material behavior of thermoplastic elastomers throughout the laser sintering processing chain

Laser sintering (LS), an additive manufacturing (AM) technology, allows for the production of 3-dimensional parts by fusing together successive layers of polymer powder without the need for tooling. Its potential and applicability, however, is still constrained due to the limited repertoire of materials available and the lack of detail in understanding both the important process-material interactions and consequently the requirements for the development of new materials. Past research has mainly focused on polyamide 12 (PA12) as the standard material, hence most of the empirically grown or theoretical, often idealized, process models are based on this polymer. As a result, it was shown that there are strong interactions between the material and the process leading to an undesired deviation of part properties. Thermoplastic elastomers (TPEs) for LS have gained more and more popularity for the production of, for example flexible parts in the recent past but they are a group of polymers that is neither well studied nor understood regarding their use in LS. Therefore, this PhD investigation has focused on TPEs in order to reveal their process specifics throughout the processing chain in LS. As the properties of parts manufactured by LS are, amongst others, influenced by the packing and flow efficiencies of the powders, the bulk (static) and flow (dynamic) characteristics of the observed TPEs were examined on the powder scale as well as their effects on the process and parts. The resulting part properties were evaluated in terms of their tensile properties, surface roughness and density. In contrast to previous studies which have rarely taken into account the characteristics of the un-sintered particles, this work provided a novel approach quantifying and describing the interconnection between the powder characteristics as well as its performance and the part properties, thus providing valuable input on future material design. As mentioned before, for typical semi-crystalline thermoplastics such as PA12, different idealized process models describing the Pre-Process specifics exist, but they might not necessarily be applicable for thermoplastic elastomers with significantly different thermal characteristics. Consequently, the important interactions during processing of TPEs have been studied by high speed and high resolution thermography helping to indicate the most important material properties in combination with calorimetric analysis. The resulting understanding of crystallization and melting behaviour helped to derive a design of experiments revealing the possible range for the process management in terms of temperature control as well as energy input and the resulting part properties. Moreover, it is known that polymers used in LS change their intrinsic properties due to processing conditions that are close to the crystalline melting temperature. As a result, within this PhD investigation the ageing behaviour of TPEs was studied. Both the powder and the sintered parts were examined for chemical and physical ageing effects. The results showed that the materials observed could be used without refreshing throughout the applied ageing cycles, however, changes in the processing behaviour as well as in the parts’ mechanical properties were evident. These changes were due to the differing ageing states of the LS-powder showing an increase in the particle size affecting the bulk materials packing density. In the literature, modifications in the rheological properties due to thermal loads during LS are already known on basis of PA12. It was shown that they tend to experience an increase in molecular weight with increasing processing cycles. In this work it was found that TPEs exhibit the exact opposite trend in a slight decrease of molecular weight likely to reduce the mechanical strength of tensile specimens. By using novel process adapted methods in order to reveal vital interactions of TPE powders for LS, this thesis makes a significant contribution to an AM database. In addition, the comprehensive observation and applications of these methods over the whole processing chain helped expanding the understanding of important requirements for the development of new polymers for LS and builds a substantial basis for future work and quality assurance