1,721,182 research outputs found
New highly active Fe(II) pyridylamido catalysts for the ring opening polymerization and copolymerization of cyclic esters
No full textTwo Fe(II) complexes bearing chelating monoanionic [N,N]- pyridylamido ligands with bulky 2,6-dialkylphenyl substituents at both the amido and the ortho-pyridine moieties were synthesized and characterized. Single crystal X-ray diffraction analysis confirmed the formation of heteroleptic mononuclear [N,N]FeIIN(SiMe3)2 threecoordinated complexes. The two complexes were tested as catalysts for the Ring Opening Polymerization (ROP) of L-lactide (L -LA) and epsilon-caprolactone (CL) in the presence of 1 equiv. of alcohol co-initiator, resulting in high activity under both mild conditions (in solution at room temperature and low monomer/catalyst ratio) and more industrially relevant conditions (higher temperature and high monomer/catalyst ratio). The high activity and living character of the Fe(II) catalysts allowed the synthesis of stereo-multiblock polylactides by one-pot sequential addition of L -LA, D -LA and rac-LA at room temperature and in short reaction times, as well as the synthesis of di -block PCL-b-PLLA and three-block PLLA-b-PCL-b-PLLA copolymers by a similar approach
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
Electromagnetic modes and resonances of two-dimensional bodies
No full textThe electromagnetic modes and the resonances of homogeneous, finite size, two-dimensional bodies are examined in the frequency domain by a rigorous full wave approach based on an integro-differential formulation of the electromagnetic scattering problem. Using a modal expansion for the current density that disentangles the geometric and material properties of the body the integro-differential equation for the induced surface (free or polarization) current density field is solved. The current modes and the corresponding resonant values of the surface conductivity (eigenconductivities) are evaluated by solving a linear eigenvalue problem with a non-Hermitian operator. They are inherent properties of the body geometry and do not depend on the body material. The material only determines the coefficients of the modal expansion and hence the frequencies at which their amplitudes are maximum (resonance frequencies). The eigenconductivities and the current modes are studied in detail as the frequency, and the shape and the size of the body vary. Open and closed surfaces are considered. The presence of vortex current modes, in addition to the source-sink current modes (no whirling modes), which characterize plasmonic oscillations, is shown. Important topological features of the current modes, such as the number of sources and sinks, the number of vortices, and the direction of the vortices are preserved as the size of the body and the frequency vary. Unlike the source-sink current modes, in open surfaces the vortex current modes can be resonantly excited only in materials with a positive imaginary part of the surface conductivity. Eventually, as examples, the scattering by two-dimensional bodies with either a positive or negative imaginary part of the surface conductivity is analyzed and the contributions of the different modes are examined
Static Surface Mode Expansion for the Electromagnetic Scattering from Penetrable Objects
Get PDFWe introduce longitudinal and transverse static surface modes and use them to solve the scattering problem from penetrable objects with arbitrary shapes. The longitudinal static modes are the eigenmodes, with zero surface-curl, of the electrostatic integral operator that determines the tangential component of the electric field, as a function of the surface charge density. The transverse static modes are the eigenmodes, with zero surface-divergence, of the magnetostatic integral operator that determines the tangential component of the vector potential, as a function of the surface current density. These static modes are solely determined by the object's shape, thus, the same static basis can be used regardless of the operating frequency or material properties. We expand the unknown surface currents of the Poggio-Miller-Chang-Harrington-Wu-Tsai (PMCHWT) equation in terms of the static modes and solve it using Galerkin-projections. The static modes expansion allows for the regularization of the integral operators and also leads to a significant reduction in the number of unknowns compared to a discretization based on sub-domain basis functions. As a consequence, the CPU-time required for the numerical solution of the scattering problem from arrays of identical particles is significantly reduced by employing an expansion in terms of static modes of the isolated particle. © 1963-2012 IEEE
Zinc and magnesium catalysts for the synthesis for PLA and its degradation: Clues for catalyst design
Get PDFHomoleptic and heteroleptic zinc and magnesium complexes bearing phenoxy-imine pyridine ligands were synthetized and characterized. Several structural parameters such as the structure of the ancillary ligand, the nature of the metal centre and the coordination geometry were investigated for identifying design elements purposeful to improve the catalytic activity in the ring opening polymerization (ROP) of lactide and in the reverse reaction of degradation of polylactide by alcoholysis. High efficiency and control degree were reached with zinc catalysts while magnesium ones showed lower activity and a weak control degree. NMR studies demonstrated that, for the homoleptic zinc complex, an activated-monomer mechanism was active. Differently, a coordination/insertion mechanism was observed for the related homoleptic zinc complex. Significantly, the complexes that showed the best activity in the ROP of lactide revealed to be the most efficient also in the degradation reaction
Radioimmunoassay of salivary progesterone for monitoring ovarian function in female infertility
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