The Quantum-Mechanical Position Operator in Extended Systems

The position operator (defined within the Schroedinger representation in the standard way) becomes meaningless when periodic boundary conditions are adopted for the wavefunction, as usual in condensed matter physics. We show how to define the position expectation value by means of a simple many-body operator acting on the wavefunction of the extended system. The relationships of the present findings to the Berry-phase theory of polarization are discussed.Comment: Four pages in RevTe

Risk determination for the implantation process of software systems

From the analysis of software companies in Argentina, weaknesses in risk management have been observed. This impacts in quality management because risk planning is a requirement specified by all standards. As part of a general study about the implantation of software systems, the aim of this work is to analyze the risks associated to such process. This proposal envisages the activities and tasks of the ISO/IEC 12207 standard transition process. For the assessment of the proposed risks, the ISO/IEC 31010 standard is adopted. Furthermore, associated procedures are suggested to either avoid or mitigate risks. The work was tested in a real environment to determine its viability. The case study consisted of the risk analysis of the implantation of the management system module of a multinational company’s advertising agency. This revealed flaws in the management of the analyzed risks and provided feedback for the study.XVI Workshop Ingeniería de Software.Red de Universidades con Carreras en Informátic

Pérdida en cultivos causados por el invierno, en zonas de los Distritos DRI de la Regional No. 1: Cundinamarca y Boyacá, durante el período de Enero a Mayo de 1982

Presenta una evaluación aproximada de las pérdidas en cultivos debido a la alta incidencia de las lluvias. El área de cubrimiento del presente informe corresponde a los 9 distritos que atiende la Regional 1 del ICA, discriminados así : Fusagasugá y Cáqueza, en Cundinamarca, Soatá, Duitama, Chiquinquirá, Valle de Tenza y Tunja, en Boyac

Electron Localization in the Insulating State

The insulating state of matter is characterized by the excitation spectrum, but also by qualitative features of the electronic ground state. The insulating ground wavefunction in fact: (i) sustains macroscopic polarization, and (ii) is localized. We give a sharp definition of the latter concept, and we show how the two basic features stem from essentially the same formalism. Our approach to localization is exemplified by means of a two--band Hubbard model in one dimension. In the noninteracting limit the wavefunction localization is measured by the spread of the Wannier orbitals.Comment: 5 pages including 3 figures, submitted to PR

The Energy-Momentum Tensor in the 1+1 dimensional non-rotating BTZ black hole

We study the energy-momentum tensor for the real scalar field on the 1+1 dimensional BTZ black hole. We obtain closed expressions for it.Comment: 7 pages. Accepted for publication in General Relativity and Gravitation, 201

Habitat fragmentation and genetic variability of tetrapod populations

In the last two centuries, the development of human civilization has transformed large natural areas into anthropogenic landscapes, making habitat fragmentation a pervasive feature of modern landscapes. In animal populations, habitat fragmentation may alter their genetic diversity and structure due to limited gene flow and dispersion and reduced effective population sizes, potentially leading to genetic drift in small habitat patches. We tested the hypothesis that habitat fragmentation affects genetic diversity of tetrapod populations through a meta-analysis. We also examined certain life history traits of species and particular external landscape factors that may determine the magnitude of genetic erosion observed in fragmented habitats. Our results showed that habitat fragmentation reduces overall genetic diversity of tetrapod populations. Stronger negative fragmentation effects were detected for amphibians, birds, and mammals. Within each taxonomic group, species with large body size were more strongly affected by fragmentation. Particularly within mammals, we found that less vagile species with short generation times represent the most susceptible tetrapod group to lose genetic diversity in fragmented habitats. As external drivers, we found a non-significant trend of lower fragmentation effects in study systems of less than 50 years and stronger effects in older (>100 years) fragmented systems. As expected, the extent of habitat loss was also important in determining the magnitude of genetic erosion in tetrapods. Extreme habitat loss showed stronger negative effects on genetic diversity irrespectively of taxonomic groups. The information gathered in this review also highlights research bias and gaps in the literature.Fil: Rivera Ortíz, F. A.. Universidad Nacional Autonoma de Mexico. Centro de Investigaciones En Ecosistemas; MéxicoFil: Aguilar, Ramiro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Córdoba. Instituto Multidisciplinario de Biología Vegetal (p); ArgentinaFil: Arizmendi, M. D. C.. Universidad Nacional Autónoma de México; MéxicoFil: Quesada, M.. Universidad Nacional Autonoma de Mexico. Centro de Investigaciones En Ecosistemas; MéxicoFil: Oyama, K.. Universidad Nacional Autonoma de Mexico. Centro de Investigaciones En Ecosistemas; Méxic

Plan Nacional de Transferencia de Tecnología Agropecuaria PLANTRA para 1990-1994: resumen consolidado nacional.

Se tratan aspectos generales relacionados con la transferencia de tecnología en Colombia y se menciona el objetivo general y los específicos del Plan Nacional de Transferencia de Tecnología Agropecuaria (PLANTRA) para el período 1990-94. Se describe la metodología utilizada para la obtención de la información en los aspectos de diagnóstico (necesidades tecnológicas y circunstancias cindicionantes de los productores, oferta tecnológica disponible y situación actual de la transferencia de tecnología), confrontación de las necesidades tecnológicas con la oferta tecnológica disponible y los productos resultantes del proceso (perfiles de proyectos). Se resumen los principales resultados obtenidos y una lista de documentos generados en la reformulación del PLANTR

Mangarara Formation: exhumed remnants of a middle Miocene, temperate carbonate, submarine channel-fan system on the eastern margin of Taranaki Basin, New Zealand

The middle Miocene Mangarara Formation is a thin (1–60 m), laterally discontinuous unit of moderately to highly calcareous (40–90%) facies of sandy to pure limestone, bioclastic sandstone, and conglomerate that crops out in a few valleys in North Taranaki across the transition from King Country Basin into offshore Taranaki Basin. The unit occurs within hemipelagic (slope) mudstone of Manganui Formation, is stratigraphically associated with redeposited sandstone of Moki Formation, and is overlain by redeposited volcaniclastic sandstone of Mohakatino Formation. The calcareous facies of the Mangarara Formation are interpreted to be mainly mass-emplaced deposits having channelised and sheet-like geometries, sedimentary structures supportive of redeposition, mixed environment fossil associations, and stratigraphic enclosure within bathyal mudrocks and flysch. The carbonate component of the deposits consists mainly of bivalves, larger benthic foraminifers (especially Amphistegina), coralline red algae including rhodoliths (Lithothamnion and Mesophyllum), and bryozoans, a warm-temperate, shallow marine skeletal association. While sediment derivation was partly from an eastern contemporary shelf, the bulk of the skeletal carbonate is inferred to have been sourced from shoal carbonate factories around and upon isolated basement highs (Patea-Tongaporutu High) to the south. The Mangarara sediments were redeposited within slope gullies and broad open submarine channels and lobes in the vicinity of the channel-lobe transition zone of a submarine fan system. Different phases of sediment transport and deposition (lateral-accretion and aggradation stages) are identified in the channel infilling. Dual fan systems likely co-existed, one dominating and predominantly siliciclastic in nature (Moki Formation), and the other infrequent and involving the temperate calcareous deposits of Mangarara Formation. The Mangarara Formation is an outcrop analogue for middle Miocene-age carbonate slope-fan deposits elsewhere in subsurface Taranaki Basin, New Zealand

Background studies and shielding effects for the TPC detector of the CAST experiment

Sunset solar axions traversing the intense magnetic field of the CERN Axion Solar Telescope (CAST) experiment may be detected in a Time Projection Chamber (TPC) detector, as X-rays signals. These signals could be masked, however, by the inhomogeneous background of materials in the experimental site. A detailed analysis, based on the detector characteristics, the background radiation at the CAST site, simulations and experimental results, has allowed us to design a shielding which reduces the background level by a factor of ~4 compared to the detector without shielding, depending on its position, in the energy range between 1 and 10 keV. Moreover, this shielding has improved the homogeneity of background measured by the TPC.Comment: 14 pages, 5 figures, accepted in New Journal of Physic