NMR studies of two unusual f-electron metals

We present the results of nuclear magnetic resonance (NMR) studies down to very low temperatures for two U compounds, UCu3.5Pd1.5 and U0.8Y0.2Pd3, where the conduction electrons experience strong interactions and for which the temperature dependences of the thermal and transport properties do not obey the expectations of a simple Fermi-liquid model. Also the temperature and field dependences of the nuclear magnetization recovery of UCu3.5Pd1.5 in Cu nuclear quadrupole resonance show unusual features that cannot be reconciled with common expectations for a simple metal, but they are well accounted for by the Kondo disorder model. For U0.8Y0.2Pd3, our Y NMR results indicate a distribution of internal static magnetic fields at the Y sites and a small temperature-dependent enhancement of the spin-lattice relaxation rateT 1 − with respect to YPd3. The NMR spectra are consistent with the presence of very small frozen U moments, but the temperature dependence of the spin-lattice relaxation rate indicates a more complicated situatio

Unusual magnetic properties of the low-dimensional quantum magnet Na2V3O7

We report the results of low-temperature measurements of the specific heat Cp(T), ac susceptibility chi(T) and 23Na nuclear magnetic resonance NMR of Na2V3O7. At liquid He temperatures Cp(T)/T exhibits broad field-dependent maxima, which shift to higher temperatures upon increasing the applied magnetic field H. Below 1.5 K the ac magnetic susceptibility chi(T) follows a Curie-Weiss law and exhibits a cusp at 0.086 mK which indicates a phase transition at very low temperatures. These results support the previous conjecture that Na2V3O7 is close to a quantum critical point (QCP) at mu_{0}H = 0 T. The entire data set, including results of measurements of the NMR spin-lattice relaxation 1/T1(T), reveals a complex magnetic behavior at low temperatures. We argue that it is due to a distribution of singlet-triplet energy gaps of dimerized V moments. The dimerization process evolves over a rather broad temperature range around and below 100 K. At the lowest temperatures the magnetic properties are dominated by the response of only a minor fraction of the V moments.Comment: 10.5 pages, 15 figures. Submitted to Phys. Rev.

Combinación de metodologías de predicción para el sector de las telecomunicaciones

Este documento busca ser una referencia para el OSIPTEL cuando se requiera realizar predicciones sobre valores futuros en los indicadores relevantes del sector de las telecomunicaciones. Para ello se muestran las metodologías más comunes como: Modelos de Box-Jenkins, Modelos de Suavizamiento Exponencial, Modelos de Regresiones Polinomiales y Modelos de Crecimiento Promedio

A low-dimensional spin S = 1/2 system at the quantum critical limit: Na2V2O7

We report the results of measurements of the dc-susceptibility and the 23Na-NMR response of Na2V2O7, a recently synthesized, non metallic low dimensional spin system. Our results indicate that upon reducing the temperature to below 100 K, the V^{4+} moments are gradually quenched, leaving only one moment out of 9 active. The NMR data reveal a phase transition at very low temperatures. With decreasing applied field H, the critical temperature shifts towards T = 0 K, suggesting that Na2V2O7 may be regarded as an insulator reaching a quantum critical point at H = 0.Comment: 4 pages, 5 figure

Minería, formas de urbanización y transformación del espacio en Huamachuco, La Libertad, Perú

La minería juega un papel importante en la estructuración del territorio peruano. Sin embargo, la minería es heterogénea: existen distintas escalas y formas de operación que generan distintas formas de relación con el territorio y el sistema urbano. Este artículo busca explorar los cambios que se dan en los centros urbanos que son influenciados por proyectos mineros. En primer lugar, se hace un recuento de las problemáticas que vinculan la minería con la urbanización. En segundo lugar, se explican ciertos territorios y centros mineros en el Perú. Finalmente, se expone el caso de la ciudad de Huamachuco, capital de provincia en los Andes del norte del Perú, y los efectos urbanos que pueden tener cuatro operaciones mineras actualment operativas en la zona.Les exploitations minières jouent un rôle important dans la structuration du territoire péruvien. Cependant, les activités minières sont hétérogènes : il y a plusieurs échelles et formes d’exploitation qui génèrent différents types de liens avec le territoire et le système urbain. Cet article cherche à explorer les changements que subissent les centres urbains qui sont sous l’influence de projets miniers. Tout d’abord, sont exposées les problématiques autour des liens entre exploitations minières et urbanisation. Ensuite, sont décrits certains territoires et centres miniers au Pérou. Finalement, l’auteur expose le cas de la ville de Huamachuco, capitale de province dans les Andes nord du Pérou, et les effets sur l’urbanisme issus de la présence de quatre mines proches de la ville.Mining plays an important role in the structuring of the Peruvian territory. However, mining activities are heterogeneous: there are different scales and types of mining operations that generate different kinds of linkages with the territory and the urban system. Our aim is to explore the changes that occur in urban centers that are influenced by mining operations. Firstly, we discuss the links between mining and urbanization. Secondly, we describe certain territories and mining centers in Peru. Finally we present the case of the city of Huamachuco, a provincial capital in Peru’s northern Andes, that is under the influence of four mining operations