Properties of electrons near a Van Hove singularity

The Fermi surface of most hole-doped cuprates is close to a Van Hove singularity at the M point. A two-dimensional electronic system, whose Fermi surface is close to a Van Hove singularity shows a variety of weak coupling instabilities. It is a convenient model to study the interplay between antiferromagnetism and anisotropic superconductivity. The renormalization group approach is reviewed with emphasis on the underlying physical processes. General properties of the phase diagram and possible deformations of the Fermi surface due to the Van Hove proximity are described.Comment: Proceedings of SNS-01 to appear in the Journal of Physics and Chemistry of Solids, SNS-0

Nonlinearly charged Lifshitz black holes for any exponent z>1z>1

Charged Lifshitz black holes for the Einstein-Proca-Maxwell system with a negative cosmological constant in arbitrary dimension $D$ are known only if the dynamical critical exponent is fixed as $z=2(D-2)$. In the present work, we show that these configurations can be extended to much more general charged black holes which in addition exist for any value of the dynamical exponent $z>1$ by considering a nonlinear electrodynamics instead of the Maxwell theory. More precisely, we introduce a two-parametric nonlinear electrodynamics defined in the more general, but less known, so-called $(\mathcal{H},P)$-formalism and obtain a family of charged black hole solutions depending on two parameters. We also remark that the value of the dynamical exponent $z=D-2$ turns out to be critical in the sense that it yields asymptotically Lifshitz black holes with logarithmic decay supported by a particular logarithmic electrodynamics. All these configurations include extremal Lifshitz black holes. Charged topological Lifshitz black holes are also shown to emerge by slightly generalizing the proposed electrodynamics

Regional devolopment and solidarity in Spain: the relationship between the E.C. and the internal solidarity funds.

This paper will analyse the importance that the Regional Solidarity Funds have acquired in the financial systems of those Autonomous Communities able to benefit from them, and the influence that these Funds have had in their development. In addition, the special role that Structural Funds have had in order to bring the Autonomous Communities’ development in line with the average level of the European Member States will be referred to. Then, the different EC tools that are connected with regional development will be described and analysed; next, the Spanish regions that have benefited from these tools since Spain joined the European Union in 1986 will be studied. The Internal Solidarity Funds and their relationship with the EC Structural Funds will also be analysed. The effects of these mechanisms will be examined from three different points of view. First of all, the impact of these resources on the regional financial system will be considered; secondly, the coordination between the EC Structural Funds and the Internal Solidarity Funds, and the impact of this relationship will be analysed; and finally, whether or not these mechanisms are efficient enough to achieve the aim of regional unity will be determined, and their influence in different areas of production will also be observed. Key words: Fiscal Federalism, Spanish Autonomous Communities, Structural Funds, Inter-regional Solidarity. JEL Codes: H7, H77.

Electronic instabilities in 3D arrays of small-diameter (3,3) carbon nanotubes

We investigate the electronic instabilities of the small-diameter (3,3) carbon nanotubes by studying the low-energy perturbations of the normal Luttinger liquid regime. The bosonization approach is adopted to deal exactly with the interactions in the forward-scattering channels, while renormalization group methods are used to analyze the low-energy instabilities. In this respect, we take into account the competition between the effective e-e interaction mediated by phonons and the Coulomb interaction in backscattering and Umklapp channels. Moreover, we apply our analysis to relevant experimental conditions where the nanotubes are assembled into large three-dimensional arrays, which leads to an efficient screening of the Coulomb potential at small momentum-transfer. We find that the destabilization of the normal metallic behavior takes place through the onset of critical behavior in some of the two charge stiffnesses that characterize the Luttinger liquid state. From a physical point of view, this results in either a divergent compressibility or a vanishing renormalized velocity for current excitations at the point of the transition. We observe anyhow that this kind of critical behavior occurs without the development of any appreciable sign of superconducting correlations.Comment: 10 pages, 12 figure

Marcador tumoral antígeno carbohidrato CA 125 como herramienta para el monitoreo en el tratamiento de cáncer de ovario en muestra diagnosticadas, remitidas al Centro Nacional de Diagnóstico y Referencia Concepción Palacios CNDR-MINSA en el período de Octubre 2016-Marzo 2017

El cáncer de ovario es un crecimiento descontrolado de las células del ovario, de modo que éstas se vuelven anormales. Los ovarios están compuestos por tres tipos principales de células y cada tipo de célula se puede desarrollar en un tipo diferente de tumor. Los marcadores tumorales son sustancias de carácter bioquímico que se asocian a la presencia de un tumor, se definen como moléculas, sustancias o procesos que se alteran cualitativa o cuantitativamente como resultado de una condición precancerosa o cáncer. Por tal razón se realizó un estudio descriptivo retrospectivo de corte transversal con el objetivo de analizar el marcador tumoral antígeno carbohidrato CA125 como herramienta para el monitoreo en el tratamiento de cáncer de ovario en muestras de pacientes diagnosticadas, remitidas al Centro Nacional de Diagnóstico y Referencia Concepción Palacios CNDR-MINSA en el período de Octubre 2016 - Marzo 2017. La muestra fue de 48 pacientes diagnosticadas correspondiente al 49% del universo de pacientes, a las cuales se les realizó el marcador tumoral CA125 para cáncer de ovario. Con respecto a la variable edad, las pacientes más afectadas se encuentran entre 41-64 años con 9 casos con valores aumentados para un 50% seguidamente de las edades entre 20-40 años con 4 casos con valores aumentados que corresponde a 22%, seguido de pacientes afectadas en edades >65años con 4 casos con valores aumentados para un 22%, y por ultimo edades entre 12-19 años, 1 caso con valores aumentados equivalente al 6%. De acuerdo a las muestras analizadas mediante las determinaciones (trimestrales, semestrales y anuales) del CA 125 que se les realizó a las pacientes con cáncer de ovario; se obtuvo que existe diferencia significativa lo que indica que la respuesta al tratamiento de acuerdo al marcador está respondiendo de manera eficaz. Se recomienda al departamento de Bioanálisis clínico que implemente y apoye la realización de trabajos que abarquen esta temática, pues debido a su comportamiento asintomático se ha vuelto una problemática en el sector salud

Fitting ear contour using an ovoid model

the automatic measurement of distinctive ear features with a view to identifying or confirming the identity of the o w n e r

Variational approach to the Hubbard model in a C60 cluster

5 págs.; 4 figs.; 3 tabs.We propose a computational scheme for the Hubbard model in the C60 cluster in which the interaction with the Fermi sea of charges added to the neutral molecule is switched on sequentially. This is applied to the calculation of the balance of charging energies, within a low-energy truncation of the space of states which produces moderate errors for an intermediate range of the interaction strength. ©1996 American Physical SocietyPeer Reviewe

Phase diagram of carbon nanotube ropes

14 págs.; 9 figs.; 1 tab. ; PACS number(s): 71.20.Tx, 71.10.Pm, 74.50.1rThe zero-temperature phase diagram of carbon nanotube ropes is studied using a computational framework that incorporates the renormalization of intratube interactions and the effect of intertube Coulomb screening. This allows us to undertake a systematic analysis as a function of the number of metallic nanotubes in the rope and the effective strength of the phonon-mediated interaction. We find that there is in general a weak-coupling regime of the interactions, corresponding to Luttinger-liquid behavior in thin ropes and to superconducting behavior in sufficiently thick ropes. Furthermore, we show the existence of exotic phases in the strong-coupling regime, characterized by the appearance of charge instabilities that depend on the helicity and the doping level of the nanotubes in the rope. Our approach allows for the simultaneous analysis of the scaling of the Cooper-pair tunneling amplitude between metallic nanotubes, making it possible to discern the crossover from purely one-dimensional physics to the setting of three-dimensional Cooper-pair coherence. We provide then good estimates of the superconducting transition temperature and discuss the connection of our results with recent experiments. ©2004 American Physical SocietyJ. V. A. acknowledges support from S. Moukouri and stimulating discussions with J. Allen. J. G. acknowledges financial support from the Ministerio de Ciencia y Tecnología Grant No. BFM2003-05317.Peer Reviewe

Cultura ecológica: los jóvenes de secundaria de la ciudad de Monterrey y su área metropolitana.

Las contribuciones desde la perspectiva de la psicología social a la investigación de asuntos del medio ambiente son cada vez mayores dado que contemplan cuestiones que tienen que ver con la sociedad, lugar donde se genera la problemática ambiental. El objetivo de este trabajo fue explorar desde la teoría de las representaciones sociales aspectos de la cultura de los estudiantes de tercero de secundaria respecto a cuestiones de medio ambiente y ecología tales como el nivel de conocimiento objetivo, las atribuciones de los jóvenes sobre las fuentes de éste conocimiento y la percepción que tienen en cuanto a las actividades ecológicas que se llevan a cabo en el contexto propio. Los sujetos fueron 555 estudiantes de tercer año de secundaria de tres escuelas públicas de la ciudad de Monterrey y su área metropolitana pertenecientes a tres estratos socioeconómicos diferentes. Los datos del estudio mostraron que los estudiantes de los tres estratos socioeconómicos tienen bajos niveles de conocimiento ambiental y sobre todo, altos niveles de ignorancia referente a las cuestiones ambientales; además, que los estudiantes atribuyen como fuente de sus conocimientos en este tema en primer lugar a la familia, en segundo a la televisión y en tercero a sus maestros; asimismo refieren actividades de cuidado del ambiente principalmente en el hogar, en segundo la escuela y en tercero la colonia. No se encontraron diferencias significativas entre los estratos respecto al nivel de conocimiento y de ignorancia, sin embargo si se encontraron diferencias significativas en las actividades en el contexto familia y escuela