Phosphoramidite Gold(I)-Catalyzed Diastereo- and Enantioselective Synthesis of 3,4-Substituted Pyrrolidines

In this article the utility of phosphoramidite ligands in enantioselective AuI catalysis was explored in the development of highly diastereo- and enantioselective AuI-catalyzed cycloadditions of allenenes. A Au^I-catalyzed synthesis of 3,4-disubstituted pyrrolidines and γ-lactams is described. This reaction proceeds through the enantioselective AuI-catalyzed cyclization of allenenes to form a carbocationic intermediate that is trapped by an exogenous nucleophile, resulting in the highly diastereoselective construction of three contiguous stereogenic centers. A computational study (DFT) was also performed to gain some insight into the underlying mechanisms of these cycloadditions. The utility of this new methodology was demonstrated through the formal synthesis of (−)-isocynometrine

Marginal Fermi liquid behavior from 2d Coulomb interaction

A full, nonperturbative renormalization group analysis of interacting electrons in a graphite layer is performed, in order to investigate the deviations from Fermi liquid theory that have been observed in the experimental measures of a linear quasiparticle decay rate in graphite. The electrons are coupled through Coulomb interactions, which remain unscreened due to the semimetallic character of the layer. We show that the model flows towards the noninteracting fixed-point for the whole range of couplings, with logarithmic corrections which signal the marginal character of the interaction separating Fermi liquid and non-Fermi liquid regimes.Comment: 7 pages, 2 Postscript figure

Modelos matemáticos a partir del modelo nomológico–deductivo de la explicación científica

Mostraremos a continuación la posibilidad de generar modelos matemáticos simples a partir de la explicación de un hecho físico. El marco teórico de partida es el de la explicación científica con la estructura del modelo nomológico deductivo. El uso de modelos matemáticos en este marco genera herramientas didácticas de distinto tipo, en este articulo desarrollamos brevemente el diseño de proyectos de investigación para los alumnos. El docente puede generar y luego utilizar estos proyectos de distintos modos, por ejemplo, como actividad de cierre de un curso, o también para generar una discontinuidad en el transcurso de la cursada, como actividad en paralelo que ocupe algún momento de las clases, etc

On algebraic classification of quasi-exactly solvable matrix models

We suggest a generalization of the Lie algebraic approach for constructing quasi-exactly solvable one-dimensional Schroedinger equations which is due to Shifman and Turbiner in order to include into consideration matrix models. This generalization is based on representations of Lie algebras by first-order matrix differential operators. We have classified inequivalent representations of the Lie algebras of the dimension up to three by first-order matrix differential operators in one variable. Next we describe invariant finite-dimensional subspaces of the representation spaces of the one-, two-dimensional Lie algebras and of the algebra sl(2,R). These results enable constructing multi-parameter families of first- and second-order quasi-exactly solvable models. In particular, we have obtained two classes of quasi-exactly solvable matrix Schroedinger equations.Comment: LaTeX-file, 16 pages, submitted to J.Phys.A: Math.Ge

Spectroscopic analysis of peculiar stars. : II. HD 192913 and HD 224801

High dispersion spectra of HD 192913 and HD 224801, two objects belonging to the so called "Si - λ4200" group have been analysed. Both stars show differences in the line intensities of several elements. Hd 192913 contains iron in three stages of ionization, shows C II and has V, Cr and Zr intensified. HD 224801 shows only normal Fe and no V, Cr and Zr. The only abnormalities of this object are the enhancement of Si, Mn and some rare-earths. The paper will be published in full somewhere else.Asociación Argentina de Astronomí

Spectroscopic analysis of peculiar stars. : II. HD 192913 and HD 224801

High dispersion spectra of HD 192913 and HD 224801, two objects belonging to the so called "Si - λ4200" group have been analysed. Both stars show differences in the line intensities of several elements. Hd 192913 contains iron in three stages of ionization, shows C II and has V, Cr and Zr intensified. HD 224801 shows only normal Fe and no V, Cr and Zr. The only abnormalities of this object are the enhancement of Si, Mn and some rare-earths. The paper will be published in full somewhere else.Asociación Argentina de Astronomí

The anatomy of urban social networks and its implications in the searchability problem

The appearance of large geolocated communication datasets has recently increased our understanding of how social networks relate to their physical space. However, many recurrently reported properties, such as the spatial clustering of network communities, have not yet been systematically tested at different scales. In this work we analyze the social network structure of over 25 million phone users from three countries at three different scales: country, provinces and cities. We consistently find that this last urban scenario presents significant differences to common knowledge about social networks. First, the emergence of a giant component in the network seems to be controlled by whether or not the network spans over the entire urban border, almost independently of the population or geographic extension of the city. Second, urban communities are much less geographically clustered than expected. These two findings shed new light on the widely-studied searchability in self-organized networks. By exhaustive simulation of decentralized search strategies we conclude that urban networks are searchable not through geographical proximity as their country-wide counterparts, but through an homophily-driven community structure

Spectroscopic analysis of peculiar stars. : II. HD 192913 and HD 224801

High dispersion spectra of HD 192913 and HD 224801, two objects belonging to the so called "Si - λ4200" group have been analysed. Both stars show differences in the line intensities of several elements. Hd 192913 contains iron in three stages of ionization, shows C II and has V, Cr and Zr intensified. HD 224801 shows only normal Fe and no V, Cr and Zr. The only abnormalities of this object are the enhancement of Si, Mn and some rare-earths. The paper will be published in full somewhere else.Asociación Argentina de Astronomí