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Search Results: 1 - 10 of 2678 matches for " Matt Gibson "
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A Characterization of Consistent Digital Line Segments in Two Dimensions
Iffat Chowdhury,Matt Gibson
Computer Science , 2015,
Abstract: Our concern is the digitalization of line segments in two dimensions as considered by Chun et al.[Discrete Comput. Geom., 2009] and Christ et al.[Discrete Comput. Geom., 2012]. The key property that differentiates the research of Chun et al. and Christ et al. from other research in digital line segment construction is that the intersection of any two segments must be connected. Such a system of segments is called a consistent digital line segments system (CDS). Chun et al. give a construction for all segments in higher dimensions that share a common endpoint (called consistent digital rays (CDR)) that has asymptotically optimal Hausdorff distance, and Christ et al. give a complete CDS in two dimensions with optimal Hausdorff distance. Christ et al. also give a characterization of CDRs in two dimensions, and they leave open the question on how to characterize CDSes in two dimensions. In this paper, we answer the most important open question regarding CDSes in two dimensions by giving the characterization asked for by Christ et al. We obtain the characterization by giving a set of necessary and sufficient conditions that a CDS must satisfy.
Decomposing Coverings and the Planar Sensor Cover Problem
Matt Gibson,Kasturi Varadarajan
Computer Science , 2009,
Abstract: We show that a $k$-fold covering using translates of an arbitrary convex polygon can be decomposed into $\Omega(k)$ covers (using an efficient algorithm). We generalize this result to obtain a constant factor approximation to the sensor cover problem where the ranges of the sensors are translates of a given convex polygon. The crucial ingredient in this generalization is a constant factor approximation algorithm for a one-dimensional version of the sensor cover problem, called the Restricted Strip Cover (RSC) problem, where sensors are intervals of possibly different lengths. Our algorithm for RSC improves on the previous $O(\log \log \log n)$ approximation.
Approximation Algorithms for Dominating Set in Disk Graphs
Matt Gibson,Imran A. Pirwani
Computer Science , 2010,
Abstract: We consider the problem of finding a lowest cost dominating set in a given disk graph containing $n$ disks. The problem has been extensively studied on subclasses of disk graphs, yet the best known approximation for disk graphs has remained $O(\log n)$ -- a bound that is asymptotically no better than the general case. We improve the status quo in two ways: for the unweighted case, we show how to obtain a PTAS using the framework recently proposed (independently)by Mustafa and Ray [SoCG 09] and by Chan and Har-Peled [SoCG 09]; for the weighted case where each input disk has an associated rational weight with the objective of finding a minimum cost dominating set, we give a randomized algorithm that obtains a dominating set whose weight is within a factor $2^{O(\log^* n)}$ of a minimum cost solution, with high probability -- the technique follows the framework proposed recently by Varadarajan [STOC 10].
On Isolating Points Using Disks
Matt Gibson,Gaurav Kanade,Kasturi Varadarajan
Computer Science , 2011,
Abstract: In this paper, we consider the problem of choosing disks (that we can think of as corresponding to wireless sensors) so that given a set of input points in the plane, there exists no path between any pair of these points that is not intercepted by some disk. We try to achieve this separation using a minimum number of a given set of unit disks. We show that a constant factor approximation to this problem can be found in polynomial time using a greedy algorithm. To the best of our knowledge we are the first to study this optimization problem.
A Characterization of Visibility Graphs for Pseudo-Polygons
Matt Gibson,Erik Krohn,Qing Wang
Computer Science , 2015,
Abstract: In this paper, we give a characterization of the visibility graphs of pseudo-polygons. We first identify some key combinatorial properties of pseudo-polygons, and we then give a set of five necessary conditions based off our identified properties. We then prove that these necessary conditions are also sufficient via a reduction to a characterization of vertex-edge visibility graphs given by O'Rourke and Streinu.
Quasi-Polynomial Time Approximation Schemes for Target Tracking
Matt Gibson,Gaurav Kanade,Erik Krohn,Kasturi Varadarajan
Computer Science , 2009,
Abstract: We consider the problem of tracking $n$ targets in the plane using $2n$ cameras. We can use two cameras to estimate the location of a target. We are then interested in forming $n$ camera pairs where each camera belongs to exactly one pair, followed by forming a matching between the targets and camera pairs so as to best estimate the locations of each of the targets. We consider a special case of this problem where each of the cameras are placed along a horizontal line $l$, and we consider two objective functions which have been shown to give good estimates of the locations of the targets when the distances between the targets and the cameras are sufficiently large. In the first objective, the value of an assignment of a camera pair to a target is the tracking angle formed by the assignment. Here, we are interested in maximizing the sum of these tracking angles. A polynomial time 2-approximation is known for this problem. We give a quasi-polynomial time algorithm that returns a solution whose value is at least a $(1-\epsilon)$ factor of the value of an optimal solution for any $\epsilon > 0$. In the second objective, the cost of an assignment of a camera pair to a target is the ratio of the vertical distance between the target and $l$ to the horizontal distance between the cameras in the camera pair. In this setting, we are interested in minimizing the sum of these ratios. A polynomial time 2-approximation is known for this problem. We give a quasi-polynomial time algorithm that returns a solution whose value is at most a $(1+\epsilon)$ factor of the value of an optimal solution for any $\epsilon > 0$.
Interkulturelle Online-Kommunikation: Konversationsanalyse und die Analyse asynchroner schriftlichter Diskussionen Intercultural Communication Online: Conversation Analysis and the Investigation of Asynchronous Written Discourse Comunicación intercultural en línea: Análisis de conversación y la investigación de discurso escrito asincrónico
Will Gibson
Forum : Qualitative Social Research , 2008,
Abstract: Der vorliegende Artikel arbeitet methodologische Probleme heraus, die entstehen, wenn bei der Analyse von schriftlichen, asynchronen Online-Diskussionen "Kultur" und "Interkulturalit t" als interaktiv darstellbare und beobachtbare Ph nomene behandelt werden. Insbesondere wird untersucht, wie die Konversationsanalyse mit ihrem Fokus auf Sequenzialit t und das Konzept der Zugeh rigkeitskategorisierungen die Analyse von Kultur als verschriftlichte, interaktive Leistung unterstützen k nnte. Im Beitrag wird dargelegt, dass trotz der offensichtlichen Unterschiede zwischen sequenziellen mündlichen Gespr chen und verschriftlichten Online-Diskussionen durch die Konversationsanalyse interessante Methoden bereitgestellt werden, um Online-Diskussionen zu analysieren. Die beiden Aspekte der Sequenzialit t und der Zugeh rigkeitskategorien sind dabei hilfreich, um anhand von Verschriftlichungen in Online-Foren die Konstruktion sichtbarer und als solche erkennbare, interkulturelle Diskurspraktiken nachzuzeichnen. URN: urn:nbn:de:0114-fqs0901493 This paper works through the methodological issues involved in treating "culture" and "interculturality" as interactionally demonstrable and observable phenomena in written online asynchronous discourse. In particular, the paper explores the ways that conversation analysis (CA) and its focus on sequentiality and membership categorization analysis might aid the analysis of culture as a textural interactional achievement. The paper argues that, while there are some clear differences between sequential talk and written asynchronous discourse, there are still interesting ways in which CA's analytic foci may be worked through in relation to online discourse. Both the concern with sequentiality and with membership categories may well help us to see how the construction of visible and recognizable intercultural discourse practices are accomplished through written modes in online forums. URN: urn:nbn:de:0114-fqs0901493 Este artículo aborda los temas metodológicos involucrados al tratar la "cultura" y la "interculturalidad" como fenómenos interactivamente observables y demostrables en el discurso escrito asincrónico. En particular, explora las formas en que el análisis de conversación (AC) y su foco en la secuencialidad y el análisis de categorización de membresía pueden ayudar al análisis de la cultura como una realización interactiva textual. Se argumenta que, aunque hay algunas claras diferencias entre el habla secuencial y el discurso escrito asincrónico, hay todavía formas interesantes en las que los focos analíticos del AC pueden a
Histone H4 acetylation by immunohistochemistry and prognosis in newly diagnosed adult acute lymphoblastic leukemia (ALL) patients
Anjali S Advani, Sarah E Gibson, Elizabeth Douglas, Tao Jin, Xiaoxian Zhao, Matt Kalaycio, Ed Copelan, Ronald Sobecks, Mikkael Sekeres, Shawnda Sungren, Eric D Hsi
BMC Cancer , 2010, DOI: 10.1186/1471-2407-10-387
Abstract: Patients ≥18 years of age and an available diagnostic bone marrow biopsy were evaluated. Cox proportional hazards analysis was used to identify univariate and multivariate correlates of CR, RFS, and OS. The variables histone H4 acetylation (positive or negative), white blood count, cytogenetic (CG) risk group (CALGB criteria), and age were used in multivariate analysis.On multivariate analysis, histone acetylation was associated with a trend towards an improved OS (for all CG risk groups) (HR = 0.51, p = 0.09). In patients without poor risk CG, there was an impressive association between the presence of histone acetylation and an improved CR rate (OR 3.43, p = 0.035), RFS (HR 0.07, p = 0.005), and OS (HR 0.24, p = 0.007). This association remained statistically significant in multivariate analysis.These data provide a rationale for the design of novel regimens incorporating HDAC inhibitors in ALL.Histones are small basic proteins that complex with DNA to form nucleosomes [1]. Five types occur in humans: histone linker H1 and core histones H2A, H2B, H3, and H4. The core histones are targets for post-translational modification such as acetylation [1]. Histone acetylation is determined by the opposing actions of histone acetyltransferases and histone deacetylases (HDACs) [2-4]. Imbalances in histone acetylation can lead to transcriptional dysregulation of genes involved in cell cycle progression and/or apoptosis by nucleosome remodeling. Increased acetylation of histones H3 and H4 has been associated with transcriptional activation of several genes involved in the suppression of tumor growth [1,5,6]. Histone acetylation and expression of HDACs affect prognosis in a number of cancers. Toh et al [7] demonstrated a favorable prognosis in patients with esophageal squamous cell cancer who demonstrated higher levels of acetylated histone H4. Acetylation correlated inversely with depth of cancer invasion, pathologic stage, and expression of the metastasis-associated-protein-1
Developing Framework for Alternative Funding Options in Water Infrastructure Projects  [PDF]
Matt Nafziger, Dan Koo
Journal of Building Construction and Planning Research (JBCPR) , 2015, DOI: 10.4236/jbcpr.2015.31004
Abstract: The United States is facing a crisis in which less financial resources are available to maintain the quality and to meet increasing demand of our water infrastructure system. Water utility owners across the nation are faced with the incredible challenge of finding ways to invest because of limited government funding, from local to federal levels. The funding gap between available and necessary funds has been increasing and expected to increase in the future. With government unable to provide adequate funding, water utility owners should consider alternative funding sources such as private partnerships and investment. There are many key aspects of an effective funding strategy for water utility owners to achieve successful water infrastructure planning and development. This paper presents various funding alternatives and provides a framework for utilizing alternative funding in water infrastructure planning and development to help alleviate funding gaps while simultaneously encouraging future sustainability in public water infrastructure.
Calcium Homeostasis in Articular Chondrocytes of Two Different Animal Species  [PDF]
Rachel White, John Stanley Gibson
Open Journal of Veterinary Medicine (OJVM) , 2018, DOI: 10.4236/ojvm.2018.88012
Abstract: Introduction: Intracellular calcium concentration ([Ca2+]i) is a critical parameter in cellular homeostasis, including articular chondrocytes. Perturbed [Ca2+]i of chondrocytes may be associated with joint disease. The objective of the study was to compare large animal models for investigating Ca2+ homeostasis in chondrocytes. Materials and Methods: The gross anatomy of the metacarpophalangeal joint (MCP) of cattle and sheep was compared, along with the effect of various manoeuvres used to study the mechanisms of Ca2+ homeostasis in chondrocytes from load-bearing areas. The gross anatomy was observed before and after dissection, and internal architecture was examined after sectioning. Cartilage thickness was measured with a digital micrometer. Chondrocyte yield was determined after isolation. Chondrocytes were incubated with Fura-2 and Ca2+i followed in different extracellular conditions. A hypotonic shock (HTS) was used to mimic removal of a load. Results: The results showed that ovids and bovids were skeletally immature and aspects of Ca2+ homeostasis were similar. Ovine chondrocytes had higher resting fluorescence, consistent with elevated resting Ca2+ levels. Results from ion substitution experiments were consistent with a role for Na+/Ca2+ exchange, and swelling-induced Ca2+ enters into the cytoplasm via the plasma membrane and intracellular stores. Conclusions: Ca2+ homeostasis in chondrocytes from both species behaved in a similar manner to HTS and ion substitutions. Differences in resting [Ca2+]i could be associated with species, stage of maturation, or Fura-2 itself and require further investigation. These findings contribute to our understanding of the physiology of articular cartilage in different species, and their potential use as models for studying joint disease in humans.
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