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Combining Mager and Steinmetz: The Effect of Grain Size and Maximum Induction on Hysteresis Energy Loss

RODRIGUES JR., Daniel Luiz; SILVEIRA, Joao Ricardo F.; LANDGRAF, Fernando J. G.
Fonte: IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC Publicador: IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
66.2%
Twelve samples with different grain sizes were prepared by normal grain growth and by primary recrystallization, and the hysteresis dissipated energy was measured by a quasi-static method. Results showed a linear relation between hysteresis energy loss and the inverse of grain size, which is here called Mager`s law, for maximum inductions from 0.6 to 1.5 T, and a Steinmetz power law relation between hysteresis loss and maximum induction for all samples. The combined effect is better described by a Mager`s law where the coefficients follow Steinmetz law.

Determining the effect of grain size and maximum induction upon coercive field of electrical steels

LANDGRAF, Fernando Jose Gomes; SILVEIRA, Joao Ricardo Filipini da; RODRIGUES-JR, Daniel
Fonte: ELSEVIER SCIENCE BV Publicador: ELSEVIER SCIENCE BV
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
66.37%
Although theoretical models have already been proposed, experimental data is still lacking to quantify the influence of grain size upon coercivity of electrical steels. Some authors consider a linear inverse proportionality, while others suggest a square root inverse proportionality. Results also differ with regard to the slope of the reciprocal of grain size-coercive field relation for a given material. This paper discusses two aspects of the problem: the maximum induction used for determining coercive force and the possible effect of lurking variables such as the grain size distribution breadth and crystallographic texture. Electrical steel sheets containing 0.7% Si, 0.3% Al and 24 ppm C were cold-rolled and annealed in order to produce different grain sizes (ranging from 20 to 150 mu m). Coercive field was measured along the rolling direction and found to depend linearly on reciprocal of grain size with a slope of approximately 0.9 (A/m)mm at 1.0 T induction. A general relation for coercive field as a function of grain size and maximum induction was established, yielding an average absolute error below 4%. Through measurement of B(50) and image analysis of micrographs, the effects of crystallographic texture and grain size distribution breadth were qualitatively discussed. (C) 2011 Elsevier B.V. All rights reserved.

Grain size and heavy minerals of the Late Quaternary eolian sediments from the Imbituba-Jaguaruna coast, Southern Brazil: Depositional controls linked to relative sea-level changes

Sawakuchi, André Oliveira; Giannini, Paulo César Fonseca; MARTINHO, C. T.; TANAKA, A. P. B.
Fonte: ELSEVIER SCIENCE BV Publicador: ELSEVIER SCIENCE BV
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
66.33%
The stratigraphic subdivision and correlation of dune deposits is difficult, especially when age datings are not available. A better understanding of the controls on texture and composition of eolian sands is necessary to interpret ancient eolian sediments. The Imbituba-Jaguaruna coastal zone (Southern Brazil, 28 degrees-29 degrees S) stands out due to its four well-preserved Late Pleistocene (eolian generation 1) to Holocene eolian units (eolian generations 2, 3, and 4). In this study, we evaluate the grain-size and heavy-mineral characteristics of the Imbituba-Jaguartma eolian units through statistical analysis of hundreds of sediment samples. Grain-size parameters and heavy-mineral content allow us to distinguish the Pleistocene from the Holocene units. The grain size displays a pattern of fining and better sorting from generation 1 (older) to 4 (younger), whereas the content of mechanically stable (dense and hard) heavy minerals decreases from eolian generation 1 to 4. The variation in grain size and heavy-mineral content records shifts in the origin and balance (input versus output) of eolian sediment supply attributable mainly to relative sea-level changes. Dunefields submitted to relative sea-level lowstand conditions (eolian generation 1) are characterized by lower accumulation rates and intense post-depositional dissection by fluvial incision. Low accumulation rates favor deflation in the eolian system...

Mid- to late-Holocene paleoceanographic changes on the southeastern Brazilian shelf based on grain size records

GYLLENCREUTZ, R.; MAHIQUES, M. M.; ALVES, D. V. P.; WAINER, I. K. C.
Fonte: SAGE PUBLICATIONS LTD Publicador: SAGE PUBLICATIONS LTD
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
66.26%
; High-resolution grain size analyses of three AMS (14)C-dated cores from the Southeastern Brazilian shelf provide a detailed record of mid- to late-Holocene environmental changes in the Southwestern Atlantic Margin. The cores exhibit millennial variability that we associate with the previously described southward shift of the Inter Tropical Convergence Zone (ITCZ) average latitudinal position over the South American continent during the Holocene climatic maximum. This generated changes in the wind-driven current system of the SW Atlantic margin and modified the grain size characteristics of the sediments deposited there. Centennial variations in the grain size are associated with a previously described late-Holocene enhancement of the El Nino-Southern Oscillation (ENSO) amplitude, which led to stronger NNE trade winds off eastern Brazil, favouring SW transport of sediments from the Paraiba do Sul River. This is recorded in a core from off Cabo Frio as a coarsening trend from 3000 cal. BP onwards. The ENSO enhancement also caused changes in precipitation and wind pattern in southern Brazil, allowing high discharge events and northward extensions of the low-saline water plume from Rio de la Plata. We propose that this resulted in a net increase in northward alongshore transport of fine sediments...

Grain size effect on the structural and dielectric properties of Pb0.85La0.15TiO3 ferroelectric ceramic compound

Mesquita, Alexandre; Basso Bernardi, Maria Ines; Godart, Claude; Pizani, Paulo Sergio; Michalowicz, Alain; Mastelaro, Valmor Roberto
Fonte: ELSEVIER SCI LTD; OXFORD Publicador: ELSEVIER SCI LTD; OXFORD
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
66.27%
This paper presents a study of the influence of particle size on the structural and dielectric properties of Pb0.85La0.15TiO3 (PLT15) ferroelectric ceramic samples. The samples were prepared with average grain size of 1.69 +/- 0.08 mu m and 146 +/- 8 nm using, respectively, conventional and spark plasma sintering techniques. A decrease in the tetragonality degree as the crystallite size decreased was explained by an internal stress caused by the existence of a large amount of grain boundaries. The local structure exhibited no significant modification and the dielectric measurements showed a diffuse phase transition and a reduction in the permittivity magnitude at T-m as the average grain size decreased. The nanostructured ceramic sample prepared at a relatively lower temperature and sintering time presented a dielectric constant value of approximately 2000 at room temperature. (c) 2012 Elsevier Ltd and Techna Group S.r.l. All rights reserved.; FAPESP; FAPESP; CNPq; CNPq

O efeito do carbono no aumento do tamanho de grão e nas propriedades magnéticas de aços elétricos semiprocessados após o recozimento final.; The effect of the carbon content on the grain size coarsening and on the magnetic properties of the semi processed electrical steels after the final annealing.

Melquíades, Sérgio dos Reis
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 31/03/2006 PT
Relevância na Pesquisa
66.38%
Recozimentos realizados nos aços elétricos semiprocessados pelos fabricantes de motores sem um controle adequado da descarbonetação pode resultar em regiões das läminas com pequeno tamanho de grão e consequentemente aumento das perdas magnéticas com queda no rendimento dos motores elétricos. A maioria dos fabricantes de motores nacionais utilizam este tipo de aço e fazem internamente o recozimento final em fornos contínuos com atmosfera à base de nitrogênio com cerca de 5 a 10% de H2 e uma pequena fração de vapor dágua suficiente para gerar uma atmosfera que reaja com o carbono do aço, removendo-o. Caso esta descarbonetação não seja realizada com êxito há uma perda significativa no rendimento do motor pela aumento das perdas magnéticas. Amostras comerciais de diferentes aços com variados teores de carbono foram selecionadas para avaliar a influência do teor de carbono, do grau de redução, do tempo e da atmosfera do forno no aumento do tamanho de grão e nas perdas magnéticas. Foram realizados recozimentos a vácuo e em atmosfera descarbonetante. Medições de perdas magnéticas e do tamanho de grão além da avaliação da microestrutura foram efetuados para determinar esta influência. Foi verificado que no recozimento a vácuo...

Estudo da evolução do tamanho de grão na laminação a quente de barras de aço médio carbono microligado ao vanádio - 38MnSiV5.; Grain size evolution of a vanadium microalloyed steel during bar rolling mill - 38MnSiV5.

Silvério, Valdir Anderson
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 20/03/2008 PT
Relevância na Pesquisa
66.26%
Os aços microligados ao vanádio são usados em peças automotivas forjadas, tais como virabrequins e bielas. Através de equações matemáticas que descrevem a cinética de recristalização e de crescimento de grão, foi desenvolvida uma rotina em planilha para simular a evolução dos tamanhos de grão austeníticos durante os passes de laminação em função da temperatura, taxa de deformação, tempo entre passes e características do material. O resultado do tamanho de grão ferrítico calculado final, foi comparado com os tamanhos de grãos de amostras retiradas da laminação e de amostras realizadas por simulação física (ensaio de torção a quente). Esta comparação entre modelamento matemático e simulação física com o processo de laminação, demonstra que é possível calcular e descrever a evolução microestrutural e mostra que o principal mecanismo de controle do refino de grão envolvido em uma laminação de não planos com trens abertos é o de recristalização estática, para as condições existentes na usina onde foi efetuado o presente estudo.; Microalloyed steels are used as forging stock for many automotive parts such as crankshafts and connecting rods. Using mathematical equations describing the recrystallization kinetics and grain growth...

Efeito do tamanho do grão austenítico na cinética e na morfologia do produto da reação bainítica de um ferro fundido nodular austemperado.; Effect of austenite grain size on the morphology and kinetics of the bainitic reaction of an austempered ductile iron.

Azevedo, Cesar Roberto de Farias
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 05/08/1991 PT
Relevância na Pesquisa
66.29%
Investigou-se o efeito do tamanho de grão austenítico na cinética e na morfologia do produto da reação bainítica de um ferro fundido nodular austemperado (FFNA). Foram estudados 3 tamanhos de grão austeníticos, a saber: GG (grão grosseiro), GM (grao mediano); e GR (grao refinado). A condição GR foi obtida pela austenitização rápida de microestruturas martensíticas. A condição GG foi obtida por tratamento de austenitização em duas etapas, de modo a, respectivamente, provocar o crescimento de grão e manter o teor de carbono igual aos das demais condições. Na segunda etapa do tratamento da condição GG ocorreu precipitação de grafita secundária, que acelerou significativamente a taxa de reação bainítica, possibilitando estudar o efeito da.variação na quantidade de interfaces austenita/grafita e austenita/ austenita sobre a cinética e a morfologia da reação bainítica. O refino do grão austenítico acelerou a cinética de reação, aumentou a proporção de ferrita alotriomorfa de contorno de grão, refinou a microestrutura bainítica (ferrita + austenita retida) e melhorou em 14% o limite de escoamento dos FFNA. Finalmente, a predominância de ferrira alotriomorfa na condição mais fina indica que a formação de interfaces incoerentes (mecanismo difusional ao inves de reação displaciva) durante a austenitização rápida da martensita (aquecimento de 100°C/ s).; The effect of austenite grain size on the kinetics and the morphology of the bainitic reaction in an austempered ductile iron (ADI) has been investigated...

Influência do tamanho de grão, teor de silício e frequência de excitação nas perdas anômalas do aço GNO.; Influence of grain size, and content of silicon frequency excitation in anomalous loss of NO steel.

Almeida, Adriano Alex de
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 20/09/2013 PT
Relevância na Pesquisa
66.34%
Este trabalho discute o efeito do tamanho de grão, frequência de excitação e resistividade elétrica nas perdas magnéticas, destacando-se a perda anômala. Também é proposto um método de sobreposição de histereses onde é revelada a região de ocorrência da perda anômala durante o ciclo de magnetização e desmagnetização, e posteriormente a curva de histerese da perda anômala é construída. Para tal, três ligas de aço de grão não orientado, com teor de silício de 2,05%, 2,45%, 3,3%, foram tratadas termicamente para aumento do tamanho de grão por crescimento. Cada liga foi tratada sobre a mesma sequência de temperatura, em recozimento contínuo. Os tamanhos de grão das amostras foram medidos pelo método de interceptos. A caracterização das propriedades magnéticas foi realizada por meio do quadro de Epstein. As amostras, no total de 21 conjuntos, foram ensaiadas em regime de frequência de 50, 60, 100, 150 e 200 Hz e regime quase estático (5mHz), ambos a 1 e 1,5 T. Possibilitando desta forma, a construção da histerese da perda histerética e total. Por meio dos resultados da perda total, histerética e parasita, a perda anômala pode ser calculada. Os resultados mostraram o comportamento da perda anômala (Pa) em função do tamanho de grão (l) do tipo Pa ∝ l0...

Determination of net sediment transport patterns in Lirquén Harbor, Chile, through grain-size trend analysis: a test of methods

Ríos, Felipe; Ulloa, Raúl; Correa, Iran Carlos Stalliviere
Fonte: Universidade Federal do Rio Grande do Sul Publicador: Universidade Federal do Rio Grande do Sul
Tipo: Artigo de Revista Científica Formato: application/pdf
ENG
Relevância na Pesquisa
66.2%
During June 1997, bottom sediment samples were collected at 76 stations on a rectangular grid in a small port (Lirquén Harbor, south-central Chile) facing siltation problems. The spatial changes in grain-size parameters, analyzed by using three different methodologies to infer net sediment transport paths, are compared with the measured water circulation of the study area and sediment dispersal patterns on aerial photographs. A Geographical Information System (GIS) is used to determine the degree of similarity between the results of the three grain-size trend methodologies. The results of this study confirm that because of its formulation and underlying assumptions, the McLaren-Bowles methodology tends to confuse the space-scale of sediment transport processes. In this way, the obtained transport patterns are in poor correlation with the observed hydrodynamics and aerial photographs and they seem to represent a combination of the spatial macroscale and mesoscale sediment transport processes existing in Concepcion Bay and in Lirquén Harbor, respectively. On the contrary, because the results yielded by the Gao-Collins and Le Roux methodologies correlate well with these studies, it is suggested that both methodologies be applied in combination to allow a better representation of local net sediment transport patterns...

Seasonal sediment transport pathways in Lirquen Harbor, Chile, as inferred from grain-size trends

Ríos, Felipe; Cisternas, Marcos; Le Roux, Jacobus; Correa, Iran Carlos Stalliviere
Fonte: Universidade Federal do Rio Grande do Sul Publicador: Universidade Federal do Rio Grande do Sul
Tipo: Artigo de Revista Científica Formato: application/pdf
SPA
Relevância na Pesquisa
66.3%
En junio y diciembre de 1997 se realizaron dos campañas de muestreo sedimentológico en un puerto afectado por el embancamiento (Puerto Lirquén, Región del Biobío, Chile) con el fin de determinar la circulación sedimentaria del área de estudio a través de la aplicación de tres metodologías basadas en el análisis de los câmbios espaciales de los parámetros granulométricos de los sedimentos. Se estudia la relación entre los regímenes meteorológicos-oceanográficos y de transporte de sedimentos, los resultados de este análisis indican que la movilidad de los sedimentos está asociada a los eventos altamente energéticos que afectan a la Región. Los patrones de transporte obtenidos mediante las metodologías de McLaren-Bowles (1985), Gao-Collins (1992) y Le Roux (1994b), se comparan con el patrón residual de circulación de las aguas y con fotografías aéreas del área de estudio. Los resultados mostrados por las dos últimas metodologías reconocen una variación estacional en el patrón de transporte de sedimentos, concordando así con la variabilidad estacional de las condiciones meteorológicas y hidrodinámicas prevalecientes. Por lo tanto, se sugiere que los patrones de transporte obtenidos a través de las metodologías de Gao-Collins y Le Roux estarían representando la circulación de sedimentos a una mesoescala espacial. Sobre la base de los patrones de transporte de sedimentos inferidos...

Comparison of fracture surface and plane section analysis for ceramic grain size characterisation

Horovistiz, A. L.; Frade, JR; Hein, LRO
Fonte: Elsevier B.V. Publicador: Elsevier B.V.
Tipo: Artigo de Revista Científica Formato: 619-626
ENG
Relevância na Pesquisa
66.26%
A method has been developed to obtain quantitative information about grain size and shape from fractured surfaces of ceramic materials. One elaborated a routine to split intergranular and transgranular grains facets of ceramic fracture surfaces by digital image processing. A commercial ceramic (ALCOA A-16, Al2O3-1.5% of CrO) was used to test the proposed method. Microstructural measurements of grain shape and size taken from fracture surfaces have been compared through descriptive statistics of distributions, with the corresponding measurements from polished and etched surfaces. The agreement between results, with the expected bias on grain size values from fractures, obtained for both types of surfaces allowed to infer that this new technique can be used to extract the relevant microstructural information from fractured surfaces, thus minimising the time consuming steps of sample preparation. (C) 2003 Elsevier Ltd. All rights reserved.

Development of image analysis methods to evaluate barley / malt grain size

Amaral, A. L.; Rocha, Orlando; Gonçalves, Cristina; Ferreira, António Augusto; Ferreira, E. C.
Fonte: Universidade do Minho Publicador: Universidade do Minho
Tipo: Conferência ou Objeto de Conferência
Publicado em //2005 ENG
Relevância na Pesquisa
66.26%
It is known that the barley / malt grain size is an important factor regarding the uniformity of malting process and hence the brewery process. For that purpose an image processing and analysis system was built for the evaluation of grain / malt size, on the ImageJ public domain platform. A programme was developed for the barley / malt images treatment and determination of several morphological parameters as well as the grain size distribution. The results showed that for the Prestige and Scarlett barley varieties good correlations could be obtained between the standard weight distribution and the proposed image analysis method. For the Esterel malt and barley as well as for the Nevada barley reasonable to good correlations were also obtained upon the introduction of a density correction factor.

A new and practical method to obtain grain size measurements in sandy shores based on digital image acquisition and processing

Baptista, Paulo; Cunha, Telmo; Gama, Cristina; Bernardes, Cristina
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
66.26%
Modern methods for the automated evaluation of sediment size in sandy shores relay on digital image processing algorithms as an alternative to time-consuming traditional sieving methodologies. However, the requirements necessary to guarantee that the considered image processing algorithm has a good grain identification success rate impose the need for dedicated hardware setups to capture the sand surface images. Examples are specially designed camera housings that maintain a constant distance between the camera lens and the sand surface, tripods to fix and maintain the camera angle orthogonal to the sand surface, external illumination systems that guarantee the light level necessary for the image processing algorithms, and special lenses and focusing systems for close proximity image capturing. In some cases, controlled image-capturing conditions can make the fieldwork more laborious which incurs in significant costs formonitoring campaigns considering large areas. To circumvent this problem, it is proposed a new automated image-processing algorithm that identifies sand grains in digital images acquired with a standard digital camera without any extra hardware attached to it. The accuracy and robustness of the proposed algorithm are evaluated in this work by means of a laboratory test on previously controlled grain samples...

Sediment Transport using Grain Size Trend Analysis: A Case Study in SW of Portugal

Du, XIAOQIN; Gama, Cristina; Liu, James
Fonte: Asia Oceania Geosciences Society- AOGS 2011 Publicador: Asia Oceania Geosciences Society- AOGS 2011
Tipo: Aula
ENG
Relevância na Pesquisa
66.3%
As a embayed coast, the main sediment sources are fluvial discharges, sea-cliff erosion and sand carried by longshore currents [1]. The particles are transported in suspended load or bedload pattern under the coactions of tidal currents and waves. In response to sediment transport processes, the spatial variations in the grain-size parameters exist, that reflect the net particles transport trend and the dynamic conditions. Thus, the grain size trend analysis was developed to study the net sediment transport. The study area is an embayed coast from Troia to Sines in SW of Portugal. There is a cape in the south end while the north end is a mountain belt with 35 km in length and 500 m in height [2]. A river with small discharge lies in the north. The tidal range varies between 1.5~3.5 m while the swell and winds from the west and northwest are dominant [3]. Therefore, the study area is sheltered from persist winds from north in summer and exposed to the storm waves from southwest in winter. The surfical sediment was sampled in the shallow water in 1980, 1983 and 1985, respectively. In order to obtain the important sediment source and sediment transport trend, three approaches were used: (1) the EOF (Empirical Orthogonal Function) analysis technique; (2) the McLaren Model; (3) grain size trend analysis. The wave is dominant in the study area. The result of EOF analysis shows that the most important sediment source is cliff erosion. The sediment eroded from cliffs during storms and high waves was transported off-shore and southward in the south part during high energy effect...

A new and practical method to obtain grain size measurements in sandy shores based

Baptista, Paulo; Cunha, Telmo; Gama, Cristina; Bernardes, Cristina
Fonte: Sedimentary Geology Publicador: Sedimentary Geology
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
66.26%
Modern methods for the automated evaluation of sediment size in sandy shores relay on digital image processing algorithms as an alternative to time-consuming traditional sieving methodologies. However, the requirements necessary to guarantee that the considered image processing algorithm has a good grain identification success rate impose the need for dedicated hardware setups to capture the sand surface images. Examples are specially designed camera housings that maintain a constant distance between the camera lens and the sand surface, tripods to fix and maintain the camera angle orthogonal to the sand surface, external illumination systems that guarantee the light level necessary for the image processing algorithms, and special lenses and focusing systems for close proximity image capturing. In some cases, controlled image-capturing conditions can make the fieldwork more laborious which incurs in significant costs for monitoring campaigns considering large areas. To circumvent this problem, it is proposed a new automated image-processing algorithm that identifies sand grains in digital images acquired with a standard digital camera without any extra hardware attached to it. The accuracy and robustness of the proposed algorithm are evaluated in this work by means of a laboratory test on previously controlled grain samples...

Evaluating the performance of species richness estimators: sensitivity to sample grain size

Hortal, Joaquín; Borges, Paulo A. V.; Gaspar, Clara
Fonte: Wiley-Blackwell Publicador: Wiley-Blackwell
Tipo: Artigo de Revista Científica
Publicado em /01/2006 ENG
Relevância na Pesquisa
66.28%
Copyright © 2006 British Ecological Society.; 1. Fifteen species richness estimators (three asymptotic based on species accumulation curves, 11 nonparametric, and one based in the species-area relationship) were compared by examining their performance in estimating the total species richness of epigean arthropods in the Azorean Laurisilva forests. Data obtained with standardized sampling of 78 transects in natural forest remnants of five islands were aggregated in seven different grains (i.e. ways of defining a single sample): islands, natural areas, transects, pairs of traps, traps, database records and individuals to assess the effect of using different sampling units on species richness estimations. 2. Estimated species richness scores depended both on the estimator considered and on the grain size used to aggregate data. However, several estimators (ACE, Chao1, Jackknife1 and 2 and Bootstrap) were precise in spite of grain variations. Weibull and several recent estimators [proposed by Rosenzweig et al. (Conservation Biology, 2003, 17, 864-874), and Ugland et al. (Journal of Animal Ecology, 2003, 72, 888-897)] performed poorly. 3. Estimations developed using the smaller grain sizes (pair of traps, traps, records and individuals) presented similar scores in a number of estimators (the above-mentioned plus ICE...

The seismological signature of temperature and grain size variation in the upper mantle

Faul, Ulrich; Jackson, Ian
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
66.36%
The shear modulus and attenuation of pure and therefore genuinely melt-free polycrystalline aggregates of Fo90 olivine have recently been measured over a wide range of mean grain size at upper mantle temperatures and seismic frequencies [1,2] [B.H. Tan, I. Jackson, J.D. Fitz Gerald, High-temperature viscoelasticity of fine-grained polycrystalline olivine, Phys. Chem. Miner. 28 (2001) 641-664; I. Jackson, J.D. Fitz Gerald, U.H. Faul, B.H. Tan, Grain-size sensitive seismic wave attenuation in polycrystalline olivine, J. Geophys. Res. 107 (B12 2360) (2002) doi:10.1029/2001JB001225]. Here for the first time we fit the experimental shear modulus and attenuation data to a common model that provides an internally consistent description of the observed variations with frequency, temperature and grain size. This model is used to perform indicative calculations of shear wave speed (V s) and attenuation (Q) along geotherms representative of both oceanic and continental settings, intended to highlight the sensitivity of Vs and Q to variations of temperature and grain size. Comparison of the results of these calculations with seismological models suggests the following: (1) The low velocity zone (LVZ), commonly observed below ocean basins, and its tendency to become less pronounced and deeper with increasing lithospheric age...

Relationship among grain-size, plant communities, and fluvial and eolian processes in a piedmont of the central Andes in Argentina

González Loyarte,María M
Fonte: Ecología austral Publicador: Ecología austral
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2003 EN
Relevância na Pesquisa
66.27%
The relationship among modern geomorphological processes, grain-size of surface sediments, and vegetation was analyzed in an alluvial fan in the piedmont of the Cordillera Frontal (Andes Mountains). Statistical parameters of grain-size distribution were calculated according to a standard graphical method. Plant communities were studied by applying a standard floristic-ecological method. A sensitivity analysis of grain-size parameters and plant communities in relation to geomorphological processes was made, based on literature, to compare results. Indicator species of fluvial, eolian and soil erosion processes were identified. Contemporary surface modifications by fluvial and eolian processes produce distinct surface sediment size parameters (mean diameter, standard deviation, skewness and kurtosis). The vegetation pattern follows these differences since communities with riparian species (Proustia cuneifolia var. mendocina and Eupatorium buniifolium) characterize the terraces and the young alluvial fan with fluvial processes, and psammophytes (Grindelia chiloensis, Aristida subulata, Poa lanuginosa, Glandularia parodii) characterize different communities developed under eolian activity.

Control of the grain size distribution of the raw material mixture in the production of iron sinter

Lwamba,E.; Garbers-Craig,A.M.
Fonte: Journal of the Southern African Institute of Mining and Metallurgy Publicador: Journal of the Southern African Institute of Mining and Metallurgy
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/05/2008 EN
Relevância na Pesquisa
66.32%
The aim of this study was to examine the effect of grain size distribution control of the raw material mixture on the permeability of the green sinter bed and the properties of the produced sinter. This was achieved by evaluating the granulation characteristics of the sinter mixture (moisture content, ranulation time and mean granule diameter) in terms of its green bed permeability, and evaluating the productivity of the sinter bed, the coke rate, tumble index (TI), abrasion index (AI), reduction disintegration index (RDI) and reducibility (RI) of the produced sinter. The raw sinter mixtures contained combinations of Thabazimbi iron ore, Sishen iron ore, coke, lime and return fines. The grain size distributions were controlled by removing the -0.5 mm size fractions of the return fines and coke, and the -1 mm size fraction of lime. Of the examined mixtures, a mixture of 20 mass% Thabazimbi iron ore, 80 mass% Sishen iron ore and fluxes where the coke, lime and return fines were all sized had the highest granulation effectiveness and permeability. The sintering properties of the mixtures in which the grain size distributions were controlled, were very similar for all the mixtures, but superior to the base case mixture in which the grain size distribution was not controlled.