6,794 research outputs found
Reactive Palladium Carbenes: Migratory Insertion and Other Carbene-Hydrocarbyl Coupling Reactions on Well-Defined Systems
ProducciĂłn CientĂficaPalladium complexes with carbene ligands are among the best known and more extensively used catalysts. Those carbenes are usually NHC or N,N-disubstituted derivatives and their use relies on the robust nature of the carbene ligands and their role as auxiliary ligands that modify the metal's elec- tronic and steric features. In contrast, there are other types of carbenes that, when coordinated to palladium, lead to transfor- mations in which the carbene fragment is involved. In the last decade, palladium-catalyzed reactions have been extended to the use of carbene precursors that can be functionalized with the formation of several CâC bonds in one reaction step. Plausi- ble mechanisms have been proposed where a carbeneâhydro- carbyl coupling occurs in the palladium coordination sphere. This microreview aims to collect and discuss the examples of organometallic reactions in well-characterized palladium com- plexes where the carbene is one of the fragments involved in CâC bond formation. These examples are key in understanding and supporting the mechanisms proposed for the Pd-catalyzed of CâC coupling reactions of carbenes.MINECO (SGPI, grant CTQ2016-80913-P)Junta de Castilla y LeoÌn (grants VA062G18 and VA051P17
Evaluation of magnetic terms in Cu4O4 cubane-like systems from selected configuration interaction calculations: A case study of polynuclear transition-metal systems
We present the evaluation of magnetic terms in a Cu4O4 cubane-like system from truncated CI calculations, as a case study of polynuclear transition-metal complexes. We employ a new excitation
selected configuration interaction (EXSCI) method based on the use of local orbitals. Taking advantage of the locality and then of the fact that the interactions vanish when the distance is large, the
dimension of the CI is largely reduced. To the best of our knowledge these CI calculations are the
largest one performed for polynuclear transition metal systems so far. The results show the presence
of two leading ferromagnetic interactions between bridged Cu ions. Also the interactions between
the unbridged Cu ions are ferromagnetic, but very weak, in contrast to the experimental data. The
nature and amplitude of all the computed interactions are consistent with the relative orientation
of the magnetic orbitals in the molecule, and correctly reproduce the susceptibility versus temperature curve. Our results indicate that it is possible to obtain similar fittings with sets of parameters
representing different physical effects and put in evidence the drawbacks of the fitting based on oversimplified magnetic models. In this context, the presented computational strategy can be considered
as a useful tool to help in the interpretation of the magnetic data and the validation of the magnetic interaction model in the polynuclear magnetic systems.Ministerio de Ciencia e Innovación de España-CTQ2009-0776
Vinylic Addition Polynorbornene in Catalysis
Vinylic addition polynorbornenes (VA-PNB) result from the insertion polymerization of norbornene or specific norbornene derivatives catalyzed by transition metal com- plexes. The VA-PNB skeleton is completely aliphatic and keeps the bicyclic structure of norbornene. This saturated polymer is thermally and chemically very stable and it is a very robust scaffold to support catalysts or reagents for catalytic applications. Several VA-PNBs are now available with suitable functional groups (halogen, alkenyl, carbonates) that can be used as starting materials to introduce the functionalization of choice by post-polymerization reactions. This has been applied to anchor organocatalysts on VA-PNB as well as ligands that can be used to synthesize supported metal catalysts. The reported examples of the use of VA-PNB-linked catalysts and their recyclability will be presented. VA-PNBs have also proved useful in the context of organotin chemistry to solve the problem of tin contamination by an efficient separation and the reuse of tin byproducts. Its uses in the Stille cross-coupling reaction and tin-hydride radical proc- esses will be discussed.MINECO (SGPI, grant CTQ2016-80913-P)Junta de Castilla y LeoÌn (grants VA062G18 and VA051P17 and a fellowship to RGL
On the solvability of the Yakubovich linear-quadratic infinite horizon minimization problem
The Yakubovich Frequency Theorem, in its periodic version and in its general
nonautonomous extension, establishes conditions which are equivalent to
the global solvability of a minimization problem of infinite horizon type,
given by the integral in the positive half-line of a quadratic functional
subject to a control system. It also provides the unique minimizing pair
\lq\lq solution, control\rq\rq~and
the value of the minimum. In this paper we establish less restrictive conditions
under which the problem is partially solvable, characterize the set of
initial data for which the minimum exists, and obtain its value as well a
minimizing pair. The occurrence of exponential dichotomy and the
null character of the rotation number for a nonautonomous
linear Hamiltonian system defined
from the minimization problem are fundamental in the analysis.Ministerio de EconomĂa y Competitividad / FEDER, MTM2015-66330-PMinisterio de Ciencia, InnovaciĂłn y Universidades, RTI2018-096523-B-I00European Commission, H2020-MSCA-ITN-2014INDAM -- GNAMPA Project 201
LiâYorke chaos in nonautonomous Hopf bifurcation patterns - I
We analyze the characteristics of the global attractor of a type of
dissipative nonautonomous dynamical systems
in terms of the Sacker and Sell spectrum of its linear part.
The model gives rise to a pattern of nonautonomous Hopf bifurcation
which can be understood as a generalization of the classical autonomous one.
We pay special attention to the dynamics at the bifurcation point,
showing the possibility of occurrence of Li-Yorke chaos in the
corresponding attractor and hence of a high degree of unpredictability.MINECO/FEDER, MTM2015-66330-PEuropean Commission, H2020-MSCA-ITN-201
Non-Atkinson perturbations of nonautonomous linear Hamiltonian systems: exponential dichotomy and nonoscillation
ProducciĂłn CientĂficaWe analyze the presence of exponential dichotomy (ED) and of global existence of Weyl functions for one-parametric families of finite-dimensional nonautonomous linear Hamiltonian systems defined along the orbits of a compact metric space, which are perturbed from an initial one in a direction which does not satisfy the classical Atkinson condition: either they do not have ED for any value of the parameter; or they have it for at least all the nonreal values, in which case the Weyl functions exist and are Herglotz. When the parameter varies in the real line, and if the unperturbed family satisfies the properties of exponential dichotomy and global existence of , then these two properties persist in a neighborhood of 0 which agrees either with the whole real line or with an open negative half-line; and in this last case, the ED fails at the right end value. The properties of ED and of global existence of are
fundamental to guarantee the solvability of classical minimization problems given by linear-quadratic control processes.MINECO/FEDER, MTM2015-66330-PEuropean Commission, H2020-MSCA-ITN-201
Evaluation of subsidies programs to sell green cars: Impact on prices, quantities and efficiency
During the recent period of economic crisis, many countries have introduced scrappage schemes to boost the sale and production of vehicles, particularly of vehicles designed to pollute less. In this paper, we analyze the impact of a particular scheme in Spain (Plan2000E) on vehicle prices and sales figures as well as on the reduction of polluting emissions from vehicles on the road. We considered the introduction of this scheme an exogenous policy change and because we could distinguish a control group (non-subsidized vehicles) and a treatment group (subsidized vehicles), before and after the introduction of the Plan, we were able to carry out our analysis as a quasi-natural experiment. Our study reveals that manufacturers increased vehicle prices by the same amount they were granted through the Plan (1,000 âŹ). In terms of sales, econometric estimations revealed an increase of almost 5% as a result of the implementation of the Plan. With regard to environmental efficiency, we compared the costs (inverted quantity of money) and the benefits of the program (reductions in polluting emissions and additional fiscal revenues) and found that the Plan would only be beneficial if it boosted demand by at least 30%.Subsidies; Automobile sector; Difference-in-Difference estimator; Green policies.
HomeopatĂa: aportaciones a su historia, legislaciĂłn y clĂnica
En este trabajo se trata de establecer una visiĂłn clara sobre quĂ© es la homeopatĂa mediante el enlace de tĂ©cnicas histĂłricas, normativas y clĂnicas.
La homeopatĂa es un mĂ©todo terapĂ©utico que lleva empleĂĄndose por diferentes profesionales de la salud desde hace mĂĄs de dos siglos.
En una primera revisiĂłn bibliogrĂĄfica se pone en situaciĂłn el marco histĂłrico que acoge a la homeopatĂa y a su evoluciĂłn hasta nuestros dĂas para acercarnos la visiĂłn de esta terapĂ©utica, la cual lleva empleĂĄndose ya mĂĄs de tres siglos. Comenzamos con el nacimiento de la homeopatĂa y todo lo relacionado a su fundador para exponer unas nociones bĂĄsicas sobre cĂłmo surge y cĂłmo, despuĂ©s de Ă©l, otros clĂnicos la adaptan a su forma de proceder. AdemĂĄs, pondremos en valor diversos mĂ©dicos homeĂłpatas relevantes en España y profundizaremos en las fuentes primarias a nuestro alcance.
Asimismo, nos acercamos a la clĂnica mĂ©dica a travĂ©s de la colaboraciĂłn con una podĂłloga que tiene, en una de sus vĂas de tratamiento, la homeopatĂa. Dentro de esta secciĂłn de la revisiĂłn se encuentra, de forma breve y resumida, la regulaciĂłn de estos medicamentos en nuestro paĂs como parte de las cuestiones sanitarias que se recogen en la norma, ofreciĂ©ndose una visiĂłn escueta y clara en cuanto a las nociones bĂĄsicas a tener en cuenta entorno al registro de los medicamentos homeopĂĄticos, la calidad y normas de correcta fabricaciĂłn de ellos, la dispensaciĂłn o la farmacovigilancia. Para completar el estudio, abordamos un caso clĂnico que ha ofrecido un profesional sanitario y completamos esta monografĂa con una entrevistaUniversidad de Sevilla. Grado en Farmaci
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