Analysis of electron-positron momentum spectra of metallic alloys as supported by first-principles calculations

Electron-positron momentum distributions measured by the coincidence Doppler broadening method can be used in the chemical analysis of the annihilation environment, typically a vacancy-impurity complex in a solid. In the present work, we study possibilities for a quantitative analysis, i.e., for distinguishing the average numbers of different atomic species around the defect. First-principles electronic structure calculations self-consistently determining electron and positron densities and ion positions are performed for vacancy-solute complexes in Al-Cu, Al-Mg-Cu, and Al-Mg-Cu-Ag alloys. The ensuing simulated coincidence Doppler broadening spectra are compared with measured ones for defect identification. A linear fitting procedure, which uses the spectra for positrons trapped at vacancies in pure constituent metals as components, has previously been employed to find the relative percentages of different atomic species around the vacancy [A. Somoza et al. Phys. Rev. B 65, 094107 (2002)]. We test the reliability of the procedure by the help of first-principles results for vacancy-solute complexes and vacancies in constituent metals.Comment: Submitted to Physical Review B on September 19 2006. Revised version submitted on November 8 2006. Published on February 14 200

Statistical correlation of structural mode shapes from test measurements and NASTRAN analytical values

The software and procedures of a system of programs used to generate a report of the statistical correlation between NASTRAN modal analysis results and physical tests results from modal surveys are described. Topics discussed include: a mathematical description of statistical correlation, a user's guide for generating a statistical correlation report, a programmer's guide describing the organization and functions of individual programs leading to a statistical correlation report, and a set of examples including complete listings of programs, and input and output data

Natural predatory enemies of the erineum strain of Colomerus vitis (Pagenstecher) (Acari, Eriophyidae) found on wild grapevine populations from southern Spain (Andalusia)

The Eurasian wild grapevine, Vitis vinifera L. subspecies sylvestris (Gmelin,) Hegi constitutes a dioecious relative of cultivated grape varieties. It constitutes an important phytogenetic resource, threatened by human activities. The most frequent phytophagous species on this European wild vine is the erineum strain of Colomerus vitis (Pagenstecher) (Acari, Eryophyidae). The aim of the present paper is to identify the natural enemies of the cited mite in wild grapevine populations situated in southern Spain. Results indicated that such kind of predatory biocenosis is integrated by Phytoseiidae (Euseius stipulatus, Kampimodromus sp., Neoseiulella litoralis, Phytoseiulus persimilis, Typhloseiella isotricha, Typhlodromus phialatus, Typhlodromus rhenanoides), Tydeidae (Orthotydeus caudatus,Tydeus caudatus), and dipteran, Cecidomyiidae (Arthrocnodax vitis).

Nuclear emulsions for the detection of micrometric-scale fringe patterns: an application to positron interferometry

Nuclear emulsions are capable of very high position resolution in the detection of ionizing particles. This feature can be exploited to directly resolve the micrometric-scale fringe pattern produced by a matter-wave interferometer for low energy positrons (in the 10-20 keV range). We have tested the performance of emulsion films in this specific scenario. Exploiting silicon nitride diffraction gratings as absorption masks, we produced periodic patterns with features comparable to the expected interferometer signal. Test samples with periodicities of 6, 7 and 20 {\mu}m were exposed to the positron beam, and the patterns clearly reconstructed. Our results support the feasibility of matter-wave interferometry experiments with positrons.Comment: 15 pages, 10 figure

“La tierra no tiene dueño”: Las ligas agrarias correntinas y la lucha por la tierra. Aportes para una discusión.

Since the creation of the Correntinian Agrarian Leagues (CAL) at the beginning of 1972, the matter of the possession of land was acquiring greater significance within the struggle agenda until it was established as the casus belli of the most exacerbated class clashes of the organization. This article investigates the most important of such clashes, which occurred when a group of sharecroppers dedicated to the production of tobacco decided to resist by force the attempts to evict them from the field that theyhad worked for decades. By analyzing a varied corpus of sources (documentaries, newspaper reports, interviews, lyrics, etc.), it seeks to preserve the ‘subversive’ potentialities of the aspirations employed by the rebels. This inquisitive attitude led me to discuss other perspectives developed on the topic revealing, thus, a more complex picture of the conflict than the one restricted by the dichotomy “revolution” - “reaction”/“reformism” that has determined the study of the Agrarian Leagues. Desde la formación de las Ligas Agrarias Correntinas (LAC) a principios de 1972, el problema de la tenencia de la tierra fue adquiriendo mayor centralidad en su agenda de lucha hasta consagrarse como casus belli de los enfrentamientos de clases más exacerbados de la organización. En este artículo se indaga el más importante de esos enfrentamientos, acaecido cuando un grupo de aparceros/as dedicados/as a la producción de tabaco decidió resistir por la fuerza al intento de expulsión del campo que habían laborado por décadas. A partir del recurso a un variado corpus de fuentes (documentales, hemerográficas, entrevistas,letras de canciones, etc.), se busca rescatar las potencialidades ‘subversivas’ de las aspiraciones puestas en juego por los/as agentes rebeldes. Esta actitud inquisitiva me lleva a discutir con otras perspectivas desarrolladas sobre el tópico, revelando una imagen del conflicto más compleja que aquella encorsetada por la dicotomía “revolución” - “reacción”/“reformismo” que ha signado el estudio de las Ligas Agrarias

A Positron Implantation Profile Estimation Approach for the PALS Study of Battery Materials

Positron annihilation spectroscopy is a powerful probe to investigate the interfaces in materials relevant for energy storage such as Li-ion batteries. The key to the interpretation of the results is the positron implantation profile, which is a spatial function related to the characteristics of the materials forming the battery. We provide models for the positron implantation profile in a cathode of a Li-ion battery coin cell. These models are the basis for a reliable visualization of multilayer geometries and their interfaces in thin cathodes of lithium-ion batteries

How to Reduce Tire-Pavement Noise: Interim Better Practices for Constructing and Texturing Concrete Pavement Surfaces

This report describes better practices for constructing and texturing quieter concrete pavements; better practices that answer the question of how we can reduce tire-pavement noise; and better practices that don\u27t compromise the other things about the pavement that are of equal or greater importance, including safety, cost, and durability. In developing this document, the National Concrete Pavement Technology Center at Iowa State University draws from its decades of combined experience working for and alongside concrete paving contractors. This document also includes the collective experience of various contractors and equipment manufacturers with a reputation for quality. These guidelines further address the challenges that are faced in consistently producing a high-quality product in a low-bid environment. This document is intended to serve as interim guidelines and better practices for texturing. Work under the pooled fund study that sponsored the development of this document is ongoing. Additional data are being collected on both existing and new concrete paving projects that will validate the practices described herein. Given the importance of this issue, however, it is believed that many of these practices can be implemented immediately without adverse consequences. Refinements to these practices can then be implemented as necessary as changes to these better practices are made in the near future

Positron localization effects on the Doppler broadening of the annihilation line: Aluminum as a case study

The coincidence Doppler broadening (CDB) technique is widely used to measure one-dimensional momentum distributions of annihilation photons, with the aim of obtaining information on the chemical environment of open-volume defects. However, the quantitative analysis of CDB spectra needs to include also purely geometrical effects. A demonstration is given here, on the basis of CDB spectra measured in quenched and in deformed pure aluminum. The comparison of the experimental results with ab initio computations shows that the observed differences come from the difference in free volume seen by positrons trapped in quenched-in vacancies or in vacancylike defects associated to dislocations. The computation reproduces accurately all details of CDB spectra, including the peak near the Fermi break, which is due to the zero-point motion of the confined positron.Peer reviewe