1,720,954 research outputs found
NMR in oriented media : new methodologies and studies on new alignment media
Full text linkThis thesis describes the development and application of new methodologies for the structural determination of small organic molecules based on nuclear magnetic resonance (NMR) in aligned media. Nuclear Magnetic Resonance is the most important technique in the structural study of organic molecules in solution. In the last decade, residual dipolar couplings (RDCs) emerged as a powerful tool for the structural determination of the relative configuration of small- to medium-size organic molecules in solution. In cases where the classical 3JAB and NOE analysis is not enough to provide an unambiguous solution to the structural elucidation problem and crystallization is not possible, RDCs proved to be extremely helpful. The technique is based on the use of an alignment medium, normally a cross-linked polymer or a lyotropic liquid crystal, that imposes a certain degree of anisotropy in a sample. One of the effects of this anisotropy is the appearance of a new NMR observable, the so-called residual dipolar coupling, which encodes non-local angular information between spin pairs.
Three main topics will be described in this work:
• Application of RDCs to several practical cases and description of an automatic procedure for the structural determination from molecular formula to the 3D absolute configuration of natural products aided by Automatic Structural Elucidation Software and RDCs.
• Study of the properties of disodium cromoglicic salt (cromolyn) as alignment media in aqueous media.
• Synthesis of organic soluble cromolyn mimetizers.
After a description of the theoretical basis of residual dipolar couplings, the experiments normally used to acquire the data, how it is treated afterwards and which are the main alignment phases developed to date, the first topic of the thesis is developed through Chapters 2, 3 and 4. Chapter 2 shows a real case in which RDCs were used as tool to determine the final product of a reaction in which a photochemical ring closure can give rise to two different structures, impossible to discern by classical 3JAB and NOE analysis. A new experimental approach (combined use of JSB-HSQC and JSB-HSQC/HMBC experiments) to the assignment of prochiral methylene protons in natural products is described in Chapter 3. Last, Chapter 4 shows the development of an automatic procedure for the determination of the absolute configuration of relatively rigid small organic molecules in solution combining automatic structural determination software with RDCs and computation of the electronic circular dichroism of several commercially available natural products.
The second topic is developed through Chapters 5 and 6. In Chapter 5, the use as alignment media of cromolyn, a compound that gives its name to a family of water-soluble lyotropic liquid crystals is described. The studies comprise the preparation of the different cromolyn/water liquid crystals, temperature and concentration studies to determine the limits of the LC phase depending on those two variables, and 2D-pseudo imaging NMR studies that show the homogeneity of the phases depending on their concentration. 3D Diffusion studies of N-methyl codeinium iodide are also described here. The LC was also doped first with NaCl and then with L-alanine. The addition of NaCl has an effect on the concentration needed to form the LC phase, whereas L-alanine turns the LC from nematic to cholesteric. Chapter 6 shows the full characterization of the cromolyn liquid crystalline phase when it is doped with L-alanine by using polarization optical microscopy (POM), rheology, differential scanning calorimetry (DSC), X-ray diffraction powder and 2H NMR. Also, experiments to test the enantiodiscriminating properties of the cholesteric liquid crystal phase are shown in this chapter.
Cromolyn showed outstanding properties as alignment media, but its main disadvantage is its own nature, since it is a water-soluble mesogen. This fact led to the synthesis of organic solvent compatible molecules with planar structures as cromolyn, and with different substitution patterns in order to try to mimic in organic solvents the properties of cromolyn in water. Synthetic procedures, gelation tests and optical micrographs for the different compounds synthesized are summarized in Chapter 7.La resonancia magnética nuclear (RMN) en medios alineados experimentó en la última década grandes avances en su aplicación a la determinación estructural de compuestos orgánicos, permitiendo la determinación simultánea de varios estereocentros.
En este proyecto de tesis pretendemos explorar nuevas metodologías y áreas de aplicación de esta técnica. El primer objetivo de esta tesis será la exploración de la posibilidad del uso de las constantes dipolares residuales (RDCs) en la determinación de la estructura de complejos “host-guest” como pueden ser los complejos entre ciclodextrinas y diversos ligandos orgánicos. Investigaremos diferentes medios de alineamiento compatibles con el medio acuoso. Si esta investigación tiene éxito investigaremos las aproximaciones computacionales necesarias para la determinación de la estructura tridimensional de estos complejos usando las RDCs obtenidas.
Otro objetivo de esta tesis es la extensión de la técnica de RDCs a la determinación estructural de compuestos fluorados. Investigaremos mediante técnicas computacionales la influencia de la parte anisótropa del tensor de acoplamiento escalar en la medida de las RDCs e implementaremos el software necesario para el análisis del tensor de alineamiento en esos compuestos.
Finalmente investigaremos, como objetivo final, la influencia del disolvente sobre el tensor de alineamiento para distintos medios de alineamiento. Para ésto mediremos distintos compuestos orgánicos en distintas combinaciones de medios de alineamiento y disolventes, lo que nos dará información valiosa sobre la naturaleza del proceso de alineamiento. Por otra parte esta investigación será reforzada mediante simulaciones de dinámica molecular en cajas de disolvente anisótropas, como un modelo simple del medio de alineamiento.A resonancia magnética nuclear (RMN) en medios alineados experimentou na última década grandes avances na súa aplicación á determinación estructural de compostos orgánicos, permitindo a determinación simultánea de varios estereocentros.
Neste proxecto de tese pretendemos explorar novas metodoloxías e áreas de aplicación desta técnica. O primeiro obxectivo desta tese será a exploración da posibilidade do uso das constantes dipolares residuais (RDCs) na determinación da estructura de complexos “host-guest” como poden ser os complexos entre ciclodextrinas e diversos ligandos orgánicos. Investigaremos diferentes medios de alineamento compatíbeis co medio acuoso. Se esta investigación ten éxito investigaremos as aproximacións computacionais necesarias para a determinación da estructura tridimensional destes complexos usando os RDCs obtidos.
Outro obxectivo desta tese e a extensión da técnica de RDCs á determinación estructural de compostos fluorados. Investigaremos mediante técnicas computacionais a influencia da parte anisótropa do tensor de acoplamento escalar na medida dos RDCs e implementaremos o software necesario para a análise do tensor de alineamento neses compostos.
Finalmente investigaremos, como obxectivo final, a influencia do disolvente sobre o tensor de alineamento para distintos medios de alineamento. Para isto mediremos distintos compostos orgánicos en distintas combinacións de medios de alineamento e disolventes, o que fornecerá información valiosa sobre a natureza do proceso de alineamento. Por outra parte esta investigación será reforzada mediante simulacións de dinámica molécular en caixas de disolvente anisótropas, como un modelo simple do medio de alineamento
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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
Full text linkWe 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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