1,720,952 research outputs found
Cobalt catalysts towards parahydrogen induced polarization
Get PDFMagnetic resonance imaging (MRI) and nuclear magnetic resonance (NMR) spectroscopy are two techniques that hold great importance to the fields of medicine and chemistry, respectively. Used daily by researchers and medical practitioners alike, these techniques provide critical diagnostic information for molecular structure determination and irregularities in the body’s internal structures which is often key in early detection of diseases. Despite the frequent use of these two techniques, both suffer from the same inherent sensitivity issue which often increases the time required to collect highly resolved data. To address these problems, several techniques have been developed, with one of them relying on the use of a spin isomer of hydrogen gas termed parahydrogen (p-H2).
Parahydrogen has been used in conjunction with rhodium and iridium homogeneous catalysts in the field of Parahydrogen Induced Polarization (PHIP) to yield large signal enhancements over the standard signals traditionally achieved in MRI and NMR spectroscopy. This field has advanced to yield enhancements via both hydrogenative (incorporation of p-H2 into the substrate) and non-hydrogenative methods, however, expansion of the field beyond the use of standardized rhodium and iridium catalysts is limited. This work builds on the application of the established hydrogenation catalyst, (MesCCC)Co-py [MesCCC = bis(2,4,6-trimethylphenyl-benzimidazol-2-ylidene)phenyl), py = pyridine] , towards hyperpolarization of substrates via PHIP chemistry.
In Chapter 2, the development of structural and electronic variants of the CCC ligand platform is discussed. The synthesis of a chiral ligand and a tolyl variant is achieved through modification of the established Buchwald-Hartwig coupling of the respective amine precursor with 2-bromoiodobenzene. Metalation of the variants is reported with varying degrees of success using cobalt, nickel, and zirconium metal sources. Additionally, the synthesis of an electron rich CCC ligand was explored via the installation of amine, methoxy, and tert¬-butyl moieties in the backbone of the ligand. Success was achieved in the synthesis and isolation of the (MesCCCtBu)CoCl2py complex. Characterization of that complex, as well as its derivatives, was done via NMR and IR spectroscopies as well as X-ray diffraction studies. The application of the (MesCCCtBu)Co(N2)PPh3 towards the semi-hydrogenation of alkynes is discussed and a comparison to the (MesCCC)Co(N2)PPh3 and (MesCCCCF3)Co(N2)PPh3 complexes is made.
Interested in further probing these electronic variants’ impact on PHIP chemistry, Chapter 3 reports the use of the (MesCCCtBu)Co-py and (MesCCCCF3)Co-py complexes towards the hyperpolarization of ethyl propionate via ALTADENA (adiabatic longitudinal transfer after dissociation engenders net alignment). Additionally, the substrate scope of the (MesCCC)Co-py-catalyzed ATLADENA chemistry is expanded, with long-lived hyperpolarization being achieved in the parahydrogenation of alkynes. The impact of the ligands flanking group on catalysis was examined in the application of the (DippCCC)Co(N2) towards ALTADENA hyperpolarization. And finally, the application of rhodium and iridium derivatives of the CCC ligand towards hyperpolarization is described.
In Chapter 4, the expansion beyond hydrogenative hyperpolarization with the (MesCCC)Co-py catalyst is discussed with the enhancement of structurally intact olefins. A variety of olefinic substrates bearing different functional group is tolerated for non-hydrogenative hyperpolarization of both 1H and 13C nuclei, both with and without the use of microtesla fields. Mechanistic studies to probe the route of hyperpolarization were conducted, leading to the attribution of the enhancement to a net-non-hydrogenative route termed PHIP-IE, PHIP via Insertion and Elimination. The application of the previously discussed catalysts to this chemistry and the influence of catalytic parameters were examined.
Finally, Chapter 5 describes the development and synthesis of novel cobalt and copper complexes for application towards PHIP chemistry. The metalation of two bidentate ligands as well as a CCN ligand is explored with various metal salts, with the use of Co2(CO)8 proving the most successful. Lastly, synthesis of a (ArCCC)Cu, (Ar = Mes or Dipp), complex is investigated with three different metalations routes: direct metalation, zwitterion formation, and transmetalation from a zirconium complex.Submission published under a 24 month embargo labeled 'U of I Access', the embargo will last until 2023-08-01The student, Safiyah Muhammad, accepted the attached license on 2021-07-07 at 18:03.The student, Safiyah Muhammad, submitted this Dissertation for approval on 2021-07-07 at 18:34.This Dissertation was approved for publication on 2021-07-09 at 17:32.DSpace SAF Submission Ingestion Package generated from Vireo submission #16791 on 2022-01-12 at 12:53:52Made available in DSpace on 2022-01-12T22:35:05Z (GMT). No. of bitstreams: 2
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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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
Author Under Sail The Imagination of Jack London, 1893-1902
No full textIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Intro -- Title Page -- Copyright Page -- Dedication -- Contents -- Acknowledgments -- Introduction -- 1. Spirit Truth -- 2. From Absorption to Theatricality and Back Again -- 3. "I Will Build a New Present" -- 4. Sons as Authors -- 5. Fathers as Publishers -- 6. The Daughter as Author -- 7. Lovers as Authors -- 8. At Sea with the Family -- 9. Yellow News, Yellow Stories -- 10. The Return Home -- Notes -- Bibliography -- Index -- About Jay WilliamsIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Description based on publisher supplied metadata and other sources.Electronic reproduction. Ann Arbor, Michigan : ProQuest Ebook Central, YYYY. Available via World Wide Web. Access may be limited to ProQuest Ebook Central affiliated libraries
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