1,720,961 research outputs found
Stereoregular [m,n]-polyurethanes derived from D-mannitol
Full text linkNovel linear carbohydrate-derived [m,n]-polyurethanes are successfully prepared using D-mannitol as renewable and low cost starting material. The key comonomer, 1,6-di-O-phenylcarbonyl-2,3,4,5-tetra-O-methyl-D-mannitol is polymerized with a diamine synthesized from D-mannitol or with alkylenediamines. These polymerization reactions afford, respectively, a [6,6]-polyurethane entirely based on a carbohydrate derivative or [m,n]-polyurethanes constituted by a poly-O-methyl substituted unit alternating with a polymethylene chain. All these polymers are stereoregular, as result of the C2 axis of symmetry of mannitol. The optically active polyurethanes are characterized by standard methods (FTIR, RMN, GPC, TGA, and DSC). Thus, GPC analysis reveals weight-average molecular weights between 18,000 and 25,000 Da. Thermal studies (DSC) indicate that the polymers obtained are amorphous materials with Tg values dependent on the structure and chain length of the diamine constituent.Fil: Fidalgo, Daniela Marina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones En Hidratos de Carbono; ArgentinaFil: Kolender, Adriana Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones En Hidratos de Carbono; ArgentinaFil: Varela, Oscar Jose. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones En Hidratos de Carbono; Argentin
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
Diseño, síntesis sustentable y caracterización de poliuretanos, politriazoles y oligotriazoles derivados de hidratos de carbono. Estudio de sus interacciones con iones
No full textLos azúcares son los componentes mayoritarios de la biomasa renovable. Por su abundancia, bajo costo y por poseer una estereoquímica definida son compuestos de partida útiles en la preparación de polímeros estereorregulares, principalmente cuando se los requiere quirales. Entre los polímeros, los poliuretanos son muy importantes por sus variadas aplicaciones, particularmente en el campo de la biomedicina. Por esta razón uno de los objetivos de esta Tesis fue la síntesis sustentable de poliuretanos, mediante el desarrollo de polimerizaciones benignas para el medio ambiente, con ahorro energético y evitando la manipulación de isocianatos o fosgeno. En primer término, se sintetizaron [m,n]-poliuretanos estereorregulares a partir de diaminas y di-O-fenilcarbonatos derivados de D-manitol. Estos comonómeros se diseñaron de modo que presentaran simetría C2. Los nuevos materiales tenían Mn en el rango 11000-18000 y eran esencialmente amorfos. Sus valores de Tg correlacionaban con la estructura de la diamina. Otro objetivo de la Tesis fue la síntesis de poli(amida-triazol)es mediante la reacción click entre azida y alquino catalizada por Cu(I) (CuAAC) como polimerización sustentable. Así, a partir de D-glucono-1,5-lactona se diseñaron y prepararon azido-N-alquinilamidas con longitud variable de la cadena alquílica. Se condujo la polimerización click CuAAC, que fue altamente regioselectiva en favor de los anillos triazol 1,4-disustituidos, o bien la cicloadición térmica en ausencia de Cu(I) (CuFAAC) para dar polímeros no-regiorregulares (1,4- y 1,5-disustituidos). Se observaron valores de Mn moderados, con valores mayores para las polimerizaciones CuAAC respecto de las térmicas. Los poli(amida-triazol)es eran estables hasta más de 300 ºC y poseían valores de Tg notablemente elevados, con la tendencia general de que Tg disminuía con la longitud de la cadena alquílica y con la proporción de anillos triazol 1,5-disustituidos en el polímero. Los nuevos materiales eran altamente insolubles en agua y poseían un alto contenido de nitrógeno, por lo que se estudió su capacidad para capturar Cu(II) y Cr(VI) de soluciones acuosas, en vistas a remediar efluentes industriales. Un estudio computacional preliminar y evidencias espectroscópicas sugirieron la estabilización de estructuras secundarias para uno de los poli(amida-triazol)es, con la participación del CH de triazol en enlaces hidrógeno frente a aniones. Para comprobar esta situación, se sintetizó una serie homóloga de oligo(amida-triazol)es lineales, que contenían de uno a cuatro unidades triazólicas. Sobre estos oligómeros se estudiaron cualitativamente las interacciones con halogenuros (Cl−, Br−, I−) por RMN y por espectrometría de masa (ID-ESI). Se verificó que los compuestos presentaban mayor afinidad hacia Cl−. Se determinaron las estequiometrias y las constantes de afinidad de las especies formadas por combinación de los oligómeros con Cl−. Es de destacar que se comprobó que el oligómero con cuatro unidades de triazol adquiría una conformación helicoidal en solución. Estos oligo(amida-triazol)es podrían aplicarse como receptores aniónicos para sensar Cl− por ESI-MS.Fil: Fidalgo, Daniela Marina
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
Poly(amide-triazole)s obtained by regioselective, microwave-assisted click polymerization of bio-based monomers
No full textThe Cu(I)-catalyzed, microwave-assisted click polymerization of bio-based -azide--alkyne monomers afforded, with high regioselectivity, stereoregular poly(amide-triazole)s. The monomers were prepared starting from d-glucono-1,5-lactone as a renewable resource. The synthetic route involves the selective protection of this sugar lactone with formaldehyde to give a gluconic acid derivative, which was subjected to amidation of the carboxylic acid function with alkynylamines (2-propynyl, 3-butynyl, and 4-pentynylamines) and substitution of the primary hydroxyl group by azide. The regioselective click polymerization of these AB-type alkyne/azide monomers led to a series of linear biosourced poly(amide-triazole)s containing mostly (>95%) 1,4-disubstituted triazole linkages. In contrast, the thermal, metal-free click polymerization led to random distribution of 1,4- and 1,5-disubstituted triazoles in the polymer backbone. The length of the methylene chain linked to the amide of the monomer and the cycloaddition regioselectivity strongly affected the properties of the materials, mainly the Tg values, which were unexpectedly high.Fil: Fidalgo, Daniela Marina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones en Hidratos de Carbono. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones en Hidratos de Carbono; ArgentinaFil: Kolender, Adriana Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones en Hidratos de Carbono. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones en Hidratos de Carbono; ArgentinaFil: Varela, Oscar Jose. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones en Hidratos de Carbono. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones en Hidratos de Carbono; Argentin
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
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