1,721,657 research outputs found
Presentation by Xing Fang, 1988
No full textXing Fang (China) speaks with students at Bell Park Academic Centre during Multicultural Week in the Spring of 1988. This photo is part of the International Education Centre fonds (1998.12). Additional photos available
Mechanisms of cytotoxicity induced by halobenzoquinone water disinfection byproducts
Get PDFDrinking water disinfection effectively kills pathogens and prevents waterborne diseases, but it also generates a large number of water disinfection byproducts (DBPs). Epidemiological studies have consistently linked long-term consumption of chlorinated water with an increased risk of developing bladder cancer; however, the responsible DBP or DBPs have not been identified. Halobenzoquinones (HBQs) are an emerging class of DBPs that are predicted to be potent bladder carcinogens. However, little is known about the toxicological effects of HBQs. This thesis investigated the cytotoxicity and potential mechanism of toxicity induced by HBQs. The cytotoxicity of HBQs was demonstrated in several cell lines: T24 human bladder carcinoma cells, CHO-K1 Chinese hamster ovary cells, and SV-HUC-1 human uroepithelial cells. At μM levels HBQs induced significantly higher toxicity than the regulated DBPs. HBQs generated significant intracellular reactive oxygen species (ROS), weakened the glutathione (GSH) antioxidant system, and caused severe oxidative DNA and protein damage (i.e., increased cellular level of 8-hydroxydeoxyguanosine (8-OHdG) and protein carbonyls). Additionally, toxicogenomic analysis showed that HBQs activate the nuclear factor E2-related factor 2 (Nrf2) antioxidant pathway; the major transcripts differentially up-regulated at both early and late exposure times were HMOX1, followed by NQO1, PTGS2 and TXNRD1. These results support oxidative stress as a key mechanism of HBQ-induced cytotoxicity. Structure–toxicity relationship analysis demonstrated that formation of ROS, cytotoxicity, and genotoxicity were strongly affected by the structure of HBQs (i.e., position, type, and number of substitutions of halogens on the benzoquinone ring). Halogen substitution groups, isomeric structure, and electron distribution were shown to affect toxicity. The cytotoxicity of di-halogenated HBQs followed the trend: iodo- > bromo- > chloro-HBQs. Additionally, 2,5-HBQs induced greater toxicity than their corresponding 2,6-HBQ isomers. Furthermore, HBQ toxicity was influenced by two major structural descriptors: the lowest unoccupied molecular orbital energy (ELUMO) and dipole moment. An established human embryonic kidney (HEK293) cell model, expressing specific multidrug resistance proteins (MRPs), was used to indirectly examine the role of MRPs on the cellular export of HBQs. Compared to the HEK-empty vector, HEK-MRP4 cells significantly decreased HBQ cytotoxicity and cellular ROS generation, supporting the role of MRP4 in the cellular detoxification of HBQs. The detoxification of HBQs by MRP4 was dependent on GSH. This research provides several original contributions to the field. 1) HBQ DBPs can cause high toxicity in multiple human cell lines, and show significantly higher toxicity than regulated DBPs in CHO cells. 2) The structure–toxicity analysis of HBQs identified ELUMO and dipole moment as a key parameter of HBQ toxicity. 3) Toxicogenomic analysis supports oxidative stress pathways as one of the key mechanisms of toxicity of HBQ DBPs. 4) The first study of MRPs and the toxicity of DBPs demonstrated the role of MRP4 in detoxifying HBQs. These results provide useful insight into the mechanisms of toxic effects of HBQs in in vitro systems
Application of the G'/G expansion method in ultrashort pulses in nonlinear optical fibers
Get PDFWith the increasing input power in optical fibers, the dispersion problem is becoming a severe restriction on wavelength division multiplexing (WDM). With the aid of solitons, in which the shape and speed can remain constant during propagation, it is expected that the transmission of nonlinear ultrashort pulses in optical fibers can effectively control the dispersion. The propagation of a nonlinear ultrashort laser pulse in an optical fiber, which fits the high-order nonlinear Schrödinger equation (NLSE), has been solved using the expansion method. Group velocity dispersion, self-phase modulation, the fourth-order dispersion, and the fifth-order nonlinearity of the high-order NLSE were taken into consideration. A series of solutions has been obtained such as the solitary wave solutions of kink, inverse kink, the tangent trigonometric function, and the cotangent trigonometric function. The results have shown that the expansion method is an effective way to obtain the exact solutions for the high-order NLSE, and it provides a theoretical basis for the transmission of ultrashort pulses in nonlinear optical fiber
News: Dr. Xing-Fang Li receives Environment Research and Development Award from the Chemical Institute of Canada
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Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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