1,720,964 research outputs found
Ab initio MO study of the internal rotation process in alpha-chlorinated picolines.
No full textConformational properties and barriers to internal rotation for the three isomeric picolines mono- bi- and trichlorosubstituted at the methyl group were studied at the theoretical level with ab initio MO calculations. Energy profiles for internal rotation of the chlorinated methyl group were obtained at the 6-31G* level with full molecular geometry relaxation, and the energy of critical points was recalculated at the MP2/6-311G** level of theory. The conformational minima and maxima of these derivatives are qualitatively similar to those found for benzene derivatives, yet differences are found in the heights of the barriers to internal rotation and in the presence of two rotational minima or maxima in the molecules with lower rotational symmetry. The origin of the barriers to rotation and of the different energy content of conformational minima is discussed in the light of the natural bond orbital (NBO) approach within the donor-acceptor viewpoint of intramolecular interactions, and electrostatic interactions between the rotating group and the ring
L'evoluzione della tutela della salute a livello internazionale ed europeo. Le sfide future
No full text1. Osservazioni introduttive. L’affermazione del diritto alla salute nel contesto internazionale. – 2. Il percorso storico giuridico del diritto alla salute nell’Unione europea. – 3. Programmi d’azione in materia di sanità pubblica e di Sistemi sanitari nell’Unione europea. – 4. Le sfide future del diritto alla salute
Exocyclic push-pull conjugated compounds. Part 4. rotational barriers in poorly polarized push-pull ethylenes
No full textThe rotational barrier for substituted ethylenes was calculated with MO ab initio methods, both in the Hartree-Fock (HF) single determinant scheme and with multiconfigurational self-consistent field (MCSCF) approaches. The HF model affords reliable results only when applied to molecules substituted with strong electron donor groups, assigning a push-pull character to the molecule. The MCSCF approach was employed for calculating rotational barriers in poorly polarized ethylenes not directly amenable to the HF methods; however, this method was found hard to handle for low symmetry molecules with substituents interacting with the double bond. A method is proposed based on the interpolation of the energy of the perpendicular conformation from a Fourier truncated function constructed with HF molecular energies calculated for frozen conformations twisted up to 60 degrees, The application of HF theory for studying internal rotation in substituted ethylenes with poorly polarized character is discussed and an upper limit of 35-40 kcal/mol can be set up for having reliable barriers from the calculated energy of the rotational transition state at this level of theory. (C) 2001 Elsevier Science B.V. All rights reserved
Exocyclic push-pull conjugated compounds. Part 1. Theoretical study of the effect of ring size on the structure, electronic properties and rotational barriers of cyclic analogoues of 1,1-diamino-2,2-dicyanoethylene
No full textAn MO theoretical ab initio study was performed on 2-exo-methylene push-pull derivatives having as donor groups nitrogen atoms, components of a heterocyclic ring, and as acceptors CN and COOEt groups. Five-, six- and seven-membered ring derivatives were considered. Calculations were also performed on a number of push-pull ethylenes whose experimental properties were reported in the chemical literature in order to test the soundness of the conclusions from theoretical approaches. The physical properties calculated for the latter molecules were compared with known experimental values, in order to check the predictive ability of the theoretical approaches employed. Geometrical features and torsional barriers in solution are satisfactorily reproduced. Results were obtained with different basis sets, second-order Moller-Plesset theory, in order to perform comparisons at different theoretical levels with a view to carrying out calculations in larger molecular systems. The widest range of comparisons between calculated values for the different molecules were carried out at the HF/6-31G*//HF/6-31G* level. The origin of the torsional barrier for isomer interconversion as a function of the electronic properties of these molecules is discussed, in particular by examining the polarized character of the exo double bond. The role of the lone pairs of the nitrogen atoms in the push-pull mechanism is investigated, also in competition with an unsaturated bond within the ring. The different conjugation patterns that can be exploited within these molecules is examined within the donor-acceptor model and Natural Bond Orbital (NBO) theory. Empirical correlations are proposed in order to estimate dipole moments and absorption wavelengths for the family of push-pull olefins. (C) 2000 Elsevier Science B.V. All rights reserved
Exocyclic push-pull conjugated compounds. Part 2. The effect of donor and acceptor substituents on the rotational barrier of push-pull ethylenes
No full textThe energy of the rotational barriers and electronic structure of the transition state in substituted ethylenes are discussed in the light of the results obtained from different theoretical MO ab initio approaches. The 6-31G* basis set at Hartree-Fock (HF) level and with second-order Moller-Plesset perturbation theory (MP2) was employed, critical points were localized through Full geometry relaxation and characterized by vibrational analysis. A multiconfigurational approach (MCSCF) with different active spaces was also employed. For alkenes the correct rotational transition state is obtained only from the MCSCF approach, whereas for push-pull olefins the HF approach with correlation corrections at MP2 level provides correct answers for the internal rotation around C(sp(2))-C(sp(2)) bonds. The choice is more critical when only acceptor or donor groups are present, especially when change of hybridization occurs at the atoms at the edges of the C-C bond in the critical points. (C) 2000 Published by Elsevier Science B.V. All rights reserved
L'apertura dei sistemi sanitari alla diversità culturale : quale spazio per le medicine "non convenzionali" ?
No full textLa ricerca di una contemporanea declinazione del diritto alla salute è al centro del Progetto Alma Idea Diversità culturale come cura, cura della diversità culturale, che indaga la dimensione anche culturale della salute, in contesti caratterizzati da un alto tasso di diversità e da risorse limitate. Il presente contributo indaga i multiformi profili connessi all'integrabilità delle "medicine altre" nei sistemi sanitari nazionali. ALMA IDEA 2017 - Diversità culturale come cura, cura della diversità cultural
La salute dello straniero entro e oltre lo Stato: quale spazio nell’ambito della Cedu?
No full textIl contributo analizza il grado di riconoscimento e tutela del diritto alla salute a favore degli stranieri. L'oggetto di indagine viene affrontato con un multi-level approach che tenga conto dei diversi piani e/o livelli ordinamentali di tutela dello straniero. Il riconoscimento e la tutela effettiva del diritto alla salute si inscrive, infatti, nel quadro della tutela multilivello dei diritti, in un intersecarsi di piani ordinamentali e di status soggettivi.
Il contributo si concentra, in specie, sul sistema convenzionale di tutela, con particolare attenzione alla giurisprudenza della Corte Edu
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
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