Phonons in MgB2 by Polarized Raman Scattering on Single Crystals

The paper presents detailed Raman scattering study of the unusually broad E2g phonon mode in MgB2 crystal. For the first time, it is shown by the polarized Raman scattering on few-micron-size crystallites with natural faces that the observed broad Raman feature really does obey the selection rules of an E2g mode. Raman spectra on high quality polycrystalline superconducting MgB2 wires reveal a very symmetric E2g phonon line near 615 1/cm with the room temperature linewidth of 260 1/cm only. Additional scattering of different polarization dependence, observed in certain crystallites is interpreted as weighted phonon density of states induced by lattice imperfections.Comment: 4 pages + 7 figure

Custos de operações florestais: noções e conceitos.

A base conceitual; Os fatores de produção; Objetivos das empresas florestais; Os diferentes níveis financeiros; Os custos; Tipos de custos; Custos fixos e custos variáveis; O comportamento dos custos; Os momentos de custos empresariais; As categorias de análise financeira; Análise econômica versus análise financeira Análise financeira dos diferentes níveis; Limitações da análise financeira; Análise de investimentos; Cálculo de investimento; Avaliação de risco; Consideração de outros aspectos; Proposta de controle de custos; O sistema de registros; Inventário patrimonial; Os custos comuns; Os mecanismos de análise.bitstream/item/51985/1/DOC-373.pdfVersão eletrônica

Equilibrum Composition of Thermal Plasma with Copper and Chromium Vapours Admixtures

Thermal plasma of electric arc is widely used in various technological applications: welding, cutting, lamps, spraying, protection of electrical installations, etc. Process efficiency is defined by different parameters that determine arc operation and influence the energy transfer within the medium. All energy exchanges depend on the medium, which is modified by the presence of the arc and more particularly by the appearance of new species from contact erosion. Sintered Cu-Cr composites are widely used as electrical contacts for vacuum circuit breakers. These materials take advantage of the high thermal and electrical conductivity of Cu and of the refractory and oxygen getter properties of reinforcing Cr particles. The aim of this paper is to give results of the calculation of the equilibrium composition of argon and air plasma with various admixtures of Cu and Cr

SHRINKAGE IN TERNARY MIXES OF CONTAINER MEDIA

Based on functional relationships established for binary mixes of container media, a mathematical model is proposed for ternary component mixtures. Shrinkage values are generated for three-component mixtures based on mathematical equations. Empirically observed shrinkage values for corresponding three-component mixtures are determined and used as the basis for assessing the reliability of the proposed mathematical model for characterizing shrinkage in mixtures of container media. . Regression equations were developed and compared for both theoretical and empirical results

New, nearby bright southern ultracool dwarfs

We report the discovery of twenty-one hitherto unknown bright southern ultracool dwarfs with spectral types in the range M7 to L5.5, together with new observations of a further three late M dwarfs previously confirmed. Three more objects are already identified in the literature as high proper motion stars;we derive their spectral types for the first time. All objects were selected from the 2MASS All Sky and SuperCOSMOS point source databases on the basis of their optical/near-infrared colours, $J$-band magnitudes and proper motions. Low resolution (R $\sim$ 1000) $JH$ spectroscopy with the ESO/NTT SOFI spectrograph has confirmed the ultracool nature of 24 targets, out of a total of 25 candidates observed. Spectral types are derived by direct comparison with template objects and compared to results from H$_2$O and FeH indices. We also report the discovery of one binary, as revealed by SOFI acquisition imaging; spectra were taken for both components. The spectral types of the two components are L2 and L4 and the distance $\sim$ 19 pc. Spectroscopic distances and transverse velocities are derived for the sample. Two $\sim$ L5 objects lie only $\sim$ 10 pc distant. Such nearby objects are excellent targets for further study to derive their parallaxes and to search for fainter, later companions with AO and/or methane imaging.Comment: 11 pages, 10 figures, accepted to MNRA

Note: Non-invasive optical method for rapid determination of alignment degree of oriented nanofibrous layers

This paper presents a rapid non-destructive method that provides information on the anisotropic internal structure of nanofibrous layers. A laser beam of a wavelength of 632.8 nm is directed at and passes through a nanofibrous layer prepared by electrostatic spinning. Information about the structural arrangement of nanofibers in the layer is directly visible in the form of a diffraction image formed on a projection screen or obtained from measured intensities of the laser beam passing through the sample which are determined by the dependency of the angle of the main direction of polarization of the laser beam on the axis of alignment of nanofibers in the sample. Both optical methods were verified on Polyvinyl alcohol (PVA) nanofibrous layers (fiber diameter of 470 nm) with random, single-axis aligned and crossed structures. The obtained results match the results of commonly used methods which apply the analysis of electron microscope images. The presented simple method not only allows samples to be analysed much more rapidly and without damaging them but it also makes possible the analysis of much larger areas, up to several square millimetres, at the same time

Realfast: Real-Time, Commensal Fast Transient Surveys with the Very Large Array

Radio interferometers have the ability to precisely localize and better characterize the properties of sources. This ability is having a powerful impact on the study of fast radio transients, where a few milliseconds of data is enough to pinpoint a source at cosmological distances. However, recording interferometric data at millisecond cadence produces a terabyte-per-hour data stream that strains networks, computing systems, and archives. This challenge mirrors that of other domains of science, where the science scope is limited by the computational architecture as much as the physical processes at play. Here, we present a solution to this problem in the context of radio transients: realfast, a commensal, fast transient search system at the Jansky Very Large Array. Realfast uses a novel architecture to distribute fast-sampled interferometric data to a 32-node, 64-GPU cluster for real-time imaging and transient detection. By detecting transients in situ, we can trigger the recording of data for those rare, brief instants when the event occurs and reduce the recorded data volume by a factor of 1000. This makes it possible to commensally search a data stream that would otherwise be impossible to record. This system will search for millisecond transients in more than 1000 hours of data per year, potentially localizing several Fast Radio Bursts, pulsars, and other sources of impulsive radio emission. We describe the science scope for realfast, the system design, expected outcomes, and ways real-time analysis can help in other fields of astrophysics.Comment: Accepted to ApJS Special Issue on Data; 11 pages, 4 figure

Southern Infrared Proper Motion Survey I: Discovery of New High Proper Motion Stars From First Full Hemisphere Scan

We present the first results from the Southern Infrared Proper Motion Survey. Using 2 Micron All Sky Survey data along with that of the SuperCOSMOS sky survey we have been able to produce the first widefield infrared proper motion survey. Having targeted the survey to identify nearby M, L and T dwarfs we have discovered 72 such new objects with proper motions greater than 0.5''/yr with 10 of these having proper motions in excess of 1''/yr. The most interesting of these objects is SIPS1259-4336 a late M dwarf. We have calculated a trigonometric parallax for this object of $\pi = 276 \pm 41$ milliarcseconds yielding a distance of $3.62\pm0.54$pc. We have also discovered a common proper motion triple system and an object with a common proper motion with LHS 128. The survey completeness is limited by the small epoch differences between many 2MASS and UKI observations. Hence we only recover 22% of Luyten objects with favourable photometry. However the Luyten study is itself unquantifiably incomplete. We discuss the prospect of enhancing the survey volume by reducing the lower proper motion limit.Comment: 20 pages, 11 figures, accepted for publication in Astronomy and Astrophysic