526 research outputs found

    The Number of Seymour Vertices in Random Tournaments and Digraphs

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    Seymour's distance two conjecture states that in any digraph there exists a vertex (a "Seymour vertex") that has at least as many neighbors at distance two as it does at distance one. We explore the validity of probabilistic statements along lines suggested by Seymour's conjecture, proving that almost surely there are a "large" number of Seymour vertices in random tournaments and "even more" in general random digraphs.Comment: 14 page

    Experimental study of energy-minimizing point configurations on spheres

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    In this paper we report on massive computer experiments aimed at finding spherical point configurations that minimize potential energy. We present experimental evidence for two new universal optima (consisting of 40 points in 10 dimensions and 64 points in 14 dimensions), as well as evidence that there are no others with at most 64 points. We also describe several other new polytopes, and we present new geometrical descriptions of some of the known universal optima.Comment: 41 pages, 12 figures, to appear in Experimental Mathematic

    Overview: Computer vision and machine learning for microstructural characterization and analysis

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    The characterization and analysis of microstructure is the foundation of microstructural science, connecting the materials structure to its composition, process history, and properties. Microstructural quantification traditionally involves a human deciding a priori what to measure and then devising a purpose-built method for doing so. However, recent advances in data science, including computer vision (CV) and machine learning (ML) offer new approaches to extracting information from microstructural images. This overview surveys CV approaches to numerically encode the visual information contained in a microstructural image, which then provides input to supervised or unsupervised ML algorithms that find associations and trends in the high-dimensional image representation. CV/ML systems for microstructural characterization and analysis span the taxonomy of image analysis tasks, including image classification, semantic segmentation, object detection, and instance segmentation. These tools enable new approaches to microstructural analysis, including the development of new, rich visual metrics and the discovery of processing-microstructure-property relationships.Comment: submitted to Materials and Metallurgical Transactions

    The architecture of convention hotels in the United States, 1940-1976

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    The convention hotel emerged as a distinct building type in the years of the Second World War and its aftermath. The earliest examples of convention hotels were distinguished from their pre-war counterparts by the design of their meeting facilities and the layout of public areas. In these projects, new techniques in architectural design were used only where they were critical to hotel operation. As the number of hotels increased in the fifties, competition for business required new approaches to design. For some hotel companies, the policy was to improve a hotel's capability for handling groups in order to attract sizable conventions to the property. In resort cities, hotel operators found that innovations in style and decor enhanced popular appeal, thereby increasing business. In the late fifties and early sixties, the participation of developers and corporations outside the hotel industry in building new properties brought about an increasing diversity. In the projects, design was based on potential profitability regardless of traditional hotel principles. At the same time, the inclusion of convention hotels in large-scale urban developments called for innovations in site planning and expansion of public amenities. While these hotels and their predecessors of the fifties rarely displayed architectural excellence, their contribution to guidelines for modern hotel design was critical to later, more spectacular developments of the building type. One project of the late sixties, the Hyatt Regency Atlanta, dramatically explored the potential of new approaches to hotel architecture. The astounding design of the public spaces, the integration of the hotel with surrounding development, and the hotel's subsequent popularity have served to transform this commercial building type into significant public architecture. The success of the. Atlanta Hyatt has led to a repetition of the concept by the hotel company, while inspiring new experiments by the architect. In the early seventies, a series of hotels of remarkable design opened in the United States. Their public appeal confirmed the value of good architecture to the successful operation of a hotel. Hotel professionals were forced to reconsider the necessary elements of hotel design, while architects were encouraged to re-examine the possibilities inherent in this commercial building type

    Instance Segmentation for Direct Measurements of Satellites in Metal Powders and Automated Microstructural Characterization from Image Data

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    We propose instance segmentation as a useful tool for image analysis in materials science. Instance segmentation is an advanced technique in computer vision which generates individual segmentation masks for every object of interest that is recognized in an image. Using an out-of-the-box implementation of Mask R-CNN, instance segmentation is applied to images of metal powder particles produced through gas atomization. Leveraging transfer learning allows for the analysis to be conducted with a very small training set of labeled images. As well as providing another method for measuring the particle size distribution, we demonstrate the first direct measurements of the satellite content in powder samples. After analyzing the results for the labeled data dataset, the trained model was used to generate measurements for a much larger set of unlabeled images. The resulting particle size measurements showed reasonable agreement with laser scattering measurements. The satellite measurements were self-consistent and showed good agreement with the expected trends for different samples. Finally, we provide a small case study showing how instance segmentation can be used to measure spheroidite content in the UltraHigh Carbon Steel Database, demonstrating the flexibility of the technique.Comment: 16 pages, 12 figure
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