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Search Results: 1 - 10 of 201712 matches for " Christopher D. Lasher "
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Discovering Networks of Perturbed Biological Processes in Hepatocyte Cultures
Christopher D. Lasher,Padmavathy Rajagopalan,T. M. Murali
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0015247
Abstract: The liver plays a vital role in glucose homeostasis, the synthesis of bile acids and the detoxification of foreign substances. Liver culture systems are widely used to test adverse effects of drugs and environmental toxicants. The two most prevalent liver culture systems are hepatocyte monolayers (HMs) and collagen sandwiches (CS). Despite their wide use, comprehensive transcriptional programs and interaction networks in these culture systems have not been systematically investigated. We integrated an existing temporal transcriptional dataset for HM and CS cultures of rat hepatocytes with a functional interaction network of rat genes. We aimed to exploit the functional interactions to identify statistically significant linkages between perturbed biological processes. To this end, we developed a novel approach to compute Contextual Biological Process Linkage Networks (CBPLNs). CBPLNs revealed numerous meaningful connections between different biological processes and gene sets, which we were successful in interpreting within the context of liver metabolism. Multiple phenomena captured by CBPLNs at the process level such as regulation, downstream effects, and feedback loops have well described counterparts at the gene and protein level. CBPLNs reveal high-level linkages between pathways and processes, making the identification of important biological trends more tractable than through interactions between individual genes and molecules alone. Our approach may provide a new route to explore, analyze, and understand cellular responses to internal and external cues within the context of the intricate networks of molecular interactions that control cellular behavior.
A Solvable Two-Charge Ensemble on the Circle
Christopher Shum,Christopher D. Sinclair
Mathematics , 2014,
Abstract: We introduce an ensemble consisting of logarithmically repelling charge one and charge two particles on the unit circle constrained so that the total charge of all particles equals $N$, but the proportion of each species of particle is allowed to vary according to a fugacity parameter. We identify the proper scaling of the fugacity with $N$ so that the proportion of each particle stays positive in the $N \rightarrow \infty$ limit. This ensemble forms a Pfaffian point process on the unit circle, and we derive the scaling limits of the matrix kernel(s) as a function of the interpolating parameter. This provides a solvable interpolation between the circular unitary and symplectic ensembles.
Atomistic Simulations of Formation of Elementary Zr-I Systems  [PDF]
Christopher D. Taylor, Matthew L. Rossi
Open Journal of Physical Chemistry (OJPC) , 2011, DOI: 10.4236/ojpc.2011.13014
Abstract: We report results of simulations on the formation of simple zirconium iodide molecules. Previous work by Wimmer et al. [1] explored the relationship between iodine and a zirconium surface. We investigate the reaction schemes through atomistic simulations to better understand the nature of Zr-I interactions through isolated molecules. The computed energy values of varying Zr-I systems suggests a strong binding mechanism between zirconium and iodine, and offer predictions of likely reaction products. The computed results predict condensation of volatile ZrI4 with ZrI2 to form Zr2I6
Considerations for Implementing OGC WMS and WFS Specifications in a Desktop GIS  [PDF]
Christopher D. Michaelis, Daniel P. Ames
Journal of Geographic Information System (JGIS) , 2012, DOI: 10.4236/jgis.2012.42021
Abstract: An implementation of the Open Geospatial Consortium Web Feature Service (WFS) and Web Map Service (WMS) specifications in an open source desktop GIS is presented together with a discussion of considerations for improving the use of web services data in desktop applications. In our implementation, WFS and WMS services are consumed by a plug-in to MapWindow GIS [1], allowing the end user to view WFS, WMS and ArcIMS data, including data from the ESRI Geography Network, in a transparent manner that can be configured for either data analysis and modeling, or data visualization. This implementation in an open source GIS allows for others to view and use the code, improve it, and otherwise implement the suggested considerations in other GIS platforms. Specific considerations proposed here include: pre-fetching through envelope optimization, tile display, and feature complexity reduction. These strategies improve the speed and responsiveness with which data can be viewed and analyzed. Comparisons made with other web-based data access implementations are used to evaluate whether these techniques provide performance benefits, and under which circumstances.
The Extended Superomedial Pedicle: Advancing Mammaplasty Techniques  [PDF]
Albert Losken, Christopher D. Funderburk, Claire Duggal
Modern Plastic Surgery (MPS) , 2013, DOI: 10.4236/mps.2013.31005
Abstract:

Many variations can be applied to traditional mammoplasty techniques to improve outcomes in certain situations. The purpose of this report was to demonstrate the indications and benefits of mammoplasty autoaugmentation using an extended superomedial pedicle. All patients who underwent transfer of an extended superopedicleto other parts of the breast for autoaugmentation were included. Indications were determined and outcomes were assessed. Forty-eight patients were included in the series. The average follow-up was 2.1 years. Indications were categorized into reconstruction of a partial mastectomy defect (oncoplastic group, n = 18), upper pole volume in the contralateral mastopexy (implant reconstruction group, n = 9), and volume improvement and suspension (massive weight loss group, n = 21). The overall complication rate was 15% (n = 7/48), with a revision rate of 10% (5/48). The extended superomedial pedicle is a reliable and versatile adjunct to regular mastopexy techniques for various indications. It gives us the ability to transfer vascularized tissue from the lower pole to areas that require autoaugmentation.

Acute liver failure following levetiracetam therapy for seizure prophylaxis in traumatic brain injury  [PDF]
Aasim Ali Syed, Christopher D. Adams
Case Reports in Clinical Medicine (CRCM) , 2012, DOI: 10.4236/crcm.2012.12010
Abstract: This case report investigates an uncommon occurrence of drug induced acute liver injury directly associated with the administration of levetiracetam in a patient following traumatic brain injury.
The distribution of Mahler's measures of reciprocal polynomials
Christopher D. Sinclair
International Journal of Mathematics and Mathematical Sciences , 2004, DOI: 10.1155/s0161171204312469
Abstract: We study the distribution of Mahler's measures of reciprocal polynomials with complex coefficients and bounded even degree. We discover that the distribution function associated to Mahler's measure restricted to monic reciprocal polynomials is a reciprocal (or antireciprocal) Laurent polynomial on [1,∞) and identically zero on [0,1). Moreover, the coefficients of this Laurent polynomial are rational numbers times a power of π. We are led to this discovery by the computation of the Mellin transform of the distribution function. This Mellin transform is an even (or odd) rational function with poles at small integers and residues that are rational numbers times a power of π. We also use this Mellin transform to show that the volume of the set of reciprocal polynomials with complex coefficients, bounded degree, and Mahler's measure less than or equal to one is a rational number times a power of π.
Atomistic Modeling of Corrosion Events at the Interface between a Metal and Its Environment
Christopher D. Taylor
International Journal of Corrosion , 2012, DOI: 10.1155/2012/204640
Abstract: Atomistic simulation is a powerful tool for probing the structure and properties of materials and the nature of chemical reactions. Corrosion is a complex process that involves chemical reactions occurring at the interface between a material and its environment and is, therefore, highly suited to study by atomistic modeling techniques. In this paper, the complex nature of corrosion processes and mechanisms is briefly reviewed. Various atomistic methods for exploring corrosion mechanisms are then described, and recent applications in the literature surveyed. Several instances of the application of atomistic modeling to corrosion science are then reviewed in detail, including studies of the metal-water interface, the reaction of water on electrified metallic interfaces, the dissolution of metal atoms from metallic surfaces, and the role of competitive adsorption in controlling the chemical nature and structure of a metallic surface. Some perspectives are then given concerning the future of atomistic modeling in the field of corrosion science. 1. Introduction to Corrosion Mechanisms The following statement was made by Pletnev in regards to the corrosion of iron by chlorides in acidic media. It is a common point of view that the chemical nature and structure of the surface of a metal, which is in contact with an electrolyte, are decisive in the kinetics of electrochemical reactions that proceed on this surface [1]. This “common point of view” is manifested in the great body of work in corrosion science that proposes mechanisms that explain how corrosion reactions occur (see, for instance, the monograph edited by Marcus) [2]. Corrosion in aqueous environments proceeds via an electrochemical mechanism, in which the coupled anodic and cathodic reactions take place at unique sites within the material/environment interface. The reactions themselves involve transfer of electrons or ions—often both—across the electrochemical double layer [3]. For this reason, the mechanisms via which corrosion proceeds can be strongly influenced by perturbations in the surface and interfacial environment. In many cases, the chemical reactions that together constitute a proposed mechanism or reaction scheme should be considered as placeholders: representative entities that subsume a host of microkinetic processes such as mass transport, surface adsorption and desorption, and bond-making/bond-breaking chemical reactions. Pltenev’s “chemical nature and structure” of the materials/environment interface are, in fact, rather complex quantities. Figure 1 contains an illustration that
Cohesive Relations for Surface Atoms in the Iron-Technetium Binary System
Christopher D. Taylor
Journal of Metallurgy , 2011, DOI: 10.1155/2011/954170
Abstract: Iron-technetium alloys are of relevance to the development of waste forms for disposition of radioactive technetium-99 obtained from spent nuclear fuel. Corrosion of candidate waste forms is a function of the local cohesive energy ( ) of surface atoms. A theoretical model for calculating is developed. Density functional theory was used to construct a modified embedded atom (MEAM) potential for iron-technetium. Materials properties determined for the iron-technetium system were in good agreement with the literature. To explore the relationship between local structure and corrosion, MEAM simulations were performed on representative iron-technetium alloys and intermetallics. Technetium-rich phases have lower , suggesting that these phases will be more noble than iron-rich ones. Quantitative estimates of based on numbers of nearest neighbors alone can lead to errors up to 0.5?eV. Consequently, atomistic corrosion simulations for alloy systems should utilize physics-based models that consider not only neighbor counts, but also local compositions and atomic arrangements. 1. Introduction The development of long-term containment strategies for spent nuclear fuel requires a combination of careful experiments and theoretical studies so that the realistic lifetimes of these strategies can be confidently predicted. Currently, a number of different containment strategies are being considered, one of which involves the storage of certain fission products within a metallic alloy waste form [1]. Chief among these fission products is technetium-99, which has a half-life of ~105 years [2]. Studies have demonstrated that technetium can be alloyed with stainless steel with significant mass-loadings and that these waste forms have considerable corrosion resistance [3]. Predictions of the long-term stability of this material can be obtained through the coupling of the results of accelerated testing studies with a rigorous, physics-based theoretical model. Corrosion is believed to be the chief process by which stored, spent nuclear fuel will degrade over time and have the potential to release radionuclides to the environment [1, 4, 5]. Modeling corrosion at long-time scales requires a thorough and fundamental understanding of the electrochemical stability of such systems, particularly the surface phenomena (Figure 1) [6]. Surface processes that are important to consider include passivation (formation of protective oxide films), depassivation (the rupture of such films by localized dissolution, mechanical damage, or presence of deleterious chemistries), mass-transport (at the
Fishery-Independent Data Reveal Negative Effect of Human Population Density on Caribbean Predatory Fish Communities
Christopher D. Stallings
PLOS ONE , 2009, DOI: 10.1371/journal.pone.0005333
Abstract: Background Understanding the current status of predatory fish communities, and the effects fishing has on them, is vitally important information for management. However, data are often insufficient at region-wide scales to assess the effects of extraction in coral reef ecosystems of developing nations. Methodology/Principal Findings Here, I overcome this difficulty by using a publicly accessible, fisheries-independent database to provide a broad scale, comprehensive analysis of human impacts on predatory reef fish communities across the greater Caribbean region. Specifically, this study analyzed presence and diversity of predatory reef fishes over a gradient of human population density. Across the region, as human population density increases, presence of large-bodied fishes declines, and fish communities become dominated by a few smaller-bodied species. Conclusions/Significance Complete disappearance of several large-bodied fishes indicates ecological and local extinctions have occurred in some densely populated areas. These findings fill a fundamentally important gap in our knowledge of the ecosystem effects of artisanal fisheries in developing nations, and provide support for multiple approaches to data collection where they are commonly unavailable.
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