1,721,165 research outputs found
Method of Establishing the Lewis Acidity of a Metal Fragment Based on the Relative Binding Strength of Ar-BIAN Ligands (Ar-BIAN = Bis(aryl)acenaphthenequinonediimine).
No full textThe relative coordination strength of a series of differently substituted Ar-BIAN ligands (Ar-BIAN = bis(aryl)acenaphthenequinonediimine) to a series of palladium complexes both in the formal 0 and 2 oxidation states has been determined. In all cases a good to excellent linearity of the log Keq with respect to the Hammet constants of the substituents on the aryl fragments of the ligands was observed. The resulting constant is proposed to be a good indication of the Lewis acidity of the metal fragment, a physical quantity for which experimental parameters have been determined only for a limited class of compounds. The obtained parameters allow a comparison not only of different olefin complexes among themselves, but even with respect to different metal fragment such as Pd(OAc)2, Pd(Me)Cl, or a -allyl complex. The Lewis acidity of the olefin complexes is extremely variable and ranges from the less acidic (Pd(Ar-BIAN)(DMFU), DMFU = dimethylfumarate) to two of the most acidic (Pd(Ar-BIAN)(TCNE) and Pd(Ar-BIAN)(FN); TCNE = tetracyanoethylene, FN = fumarodinitrile) complexes among those examined. A cationic -allyl complex has the highest Lewis acidity among the complexes examined. The importance of steric effects is examined in some cases
Gravity at Finite Temperature, Equivalence Principle, and Local Lorentz Invariance
No full textIn this Chapter we illustrate the close connection between the violation of
the weak equivalence principle typical of gravitational interactions at finite
temperature, and similar violations induced by a breaking of the local Lorentz
symmetry. We also discuss the physical implications of the effective repulsive
forces possibly arising in such a generalized gravitational context, by
considering, for an illustrative purpose, a quasi-Riemannian model of gravity
with rotational symmetry as the local gauge group in tangent space
Status of String Cosmology: Phenomenological Aspects
No full textI report recent studies on the evolution of perturbations in the context of the "pre-big-bang" scenario typical of string cosmology, with emphasis on the formation of a stochastic background of relic photons and gravitons, and its possible direct/indirect observable consequences. I also discuss the possible generation of a thermal microwave background by using, as example, a simple gravi-axio-dilaton model whose classical evolution connects smoothly inflationary expansion to decelerated contraction. By including the quantum back-reaction of the produced radiation the model eventually approaches the standard radiation-dominated (constant dilaton) regime. * Lecture given at the 4th Course of the International School of Astrophysics "D. Chalonge" on String gravity and physics at the Planck scale (Erice, 8-19 September 1995). To appear in the Proceedings (Kluwer Acad. Pub., Dordrecht), ed. by N. Sanchez. STATUS OF STRING COSMOLOGY: PHENOMENOLOGICAL ASPECTS M. GASPERINI Dipartimento di ..
Von Neumann and Shannon-Wehrl Entropy for Squeezed States and Cosmological Particle Production
No full textWe show that the effective coarse graining of a two-mode squeezed density matrix, implicit in the Wehrl approaches to a semiclassical phase-space distribution, leads to results in agreement with previous different definitions of entropy for the process of pair production from the vacuum. We also present, in this context, a possible interpretation of the entropy growth as an amplification (due to the squeezing) of our lack of knowledge about the initial conditions, which gives rise to an effective decoherence of the squeezed density matrix. --------------------------- To appear in the "String gravity and physics at the Planck energy scale " (World Scientific, Singapore, 1995) CERN-TH/95-37 February VON NEUMANN AND SHANNON-WEHRL ENTROPY FOR SQUEEZED STATES AND COSMOLOGICAL PARTICLE PRODUCTION M. Gasperini and M. Giovannini Dipartimento di Fisica Teorica, Universit'a di Torino, Via P.Giuria 1, 10125 Turin, Italy ABSTRACT We show that the effective coarse graining of a two-mode squeez..
Mechanical ventilation in chronic respiratory insufficiency: report on an Italian nationwide survey. The Italian Telethon Committee and the AIPO Study Group on Pulmonary Rehabilitation and Intensive Care.
No full textRespiratory home care is an important aspect of rehabilitation programmes designed for patients needing long-term mechanical ventilation. Many differences have emerged between countries in the long-term care of these patients, depending on the different ways of supplying material, managing patients and providing equipment. The results of analysis of the data obtained in a preliminary survey carried out in 1995-1996 among 115 Italian centres operating in the field of home mechanical ventilation are presented. A questionnaire (all closed-circuit items) consisting of two sections (the first epidemiological, and the second methodological and economic) was sent to all centres. Fifty-seven out of 115 (50%) centres responded to the questionnaire, with a prevalence of responses from the north of Italy (37 centres). The responding centres had been working in this field for a mean period of 6 +/- 3 yrs, and a total of 1,842 patients were surveyed. The analysis focuses on the prevalence of treated diseases, methods of mechanical ventilation, regulation of prescription, evaluations carried out during follow-up, supply of equipment, costs and reimbursement, and relations with volunteer associations. A more thorough approach to all the problems emerging from this Italian survey regarding candidates for home mechanical ventilation is warranted. A more detailed comparative analysis of indications, management and costs vis-à-vis other countries should contribute towards achieving maximum uniformity of standards throughout Europe
Phosphorus Acids as Highly Efficient Promoters for the Palladium-Phenanthroline Catalyzed Carbonylation of Nitrobenzene to Methyl Phenylcarbamate
No full textA new family of promoters, based on phosphorus acids, is reported for the catalytic carbonylation of nitrobenzene to methyl phenylcarbamate by palladium-phenanthroline complexes. With the new promoters, unprecedented reaction rates (TOF up to 6000/h) and catalyst stability (TON up to 105) could be reached. The best promoter is phosphoric acid, which is also very cheap, nontoxic and easily separable from the reaction products
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
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