Página 1 dos resultados de 18536 itens digitais encontrados em 0.011 segundos

Effect of anisotropy on the deep-drawing of mild steel and dual-phase steel tailor-welded blanks

Padmanabhan, R.; Baptista, A. J.; Oliveira, M. C.; Menezes, L. F.
Fonte: Universidade de Coimbra Publicador: Universidade de Coimbra
Tipo: Artigo de Revista Científica Formato: aplication/PDF
ENG
Relevância na Pesquisa
36.542334%
Tailor-welded blanks made of dissimilar, uniform or non-uniform thickness materials have potential applications in automobile industries. Compared to the base metal, the formability of tailor-welded blank is less due to the presence of weld area and strength mismatch between component blanks. Most sheet metals used to produce tailor-welded blanks have anisotropy induced during pre-processing stage due to large deformation. The orientation of the blank sheet rolling direction and the combination of the blank sheet materials has significant influence on the deformation behaviour. The effect of anisotropy in the tailor-welded blank and the orientation of blank sheets rolling direction during deep-drawing process are investigated in this study. Finite element analysis of deep-drawing mild steel and dual-phase steel tailor-welded blank models was carried out using research purpose FE code DD3IMP; to form a basis for tailor-welded blank design and development for a part. Anisotropy in the blank sheets has moderate influence and its contribution to increased material flow depends on the mechanical properties of the blank sheets. Appropriate combination of the blank sheets rolling direction orientation can significantly improve the formability of the tailor-welded blank in the deep-drawing of square cup.; http://www.sciencedirect.com/science/article/B6TGJ-4MS9JRN-1/1/0ce35db70f46b489db761aac09088a80

Upper-mantle seismic anisotropy from SKS splitting in the South American stable platform: A test of asthenospheric flow models beneath the lithosphere

ASSUMPCAO, Marcelo; GUARIDO, Marcelo; LEE, Suzan van der; DOURADO, Joao Carlos
Fonte: GEOLOGICAL SOC AMER, INC Publicador: GEOLOGICAL SOC AMER, INC
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
36.593745%
Upper-mantle seismic anisotropy has been extensively used to infer both present and past deformation processes at lithospheric and asthenospheric depths. Analysis of shear-wave splitting (mainly from core-refracted SKS phases) provides information regarding upper-mantle anisotropy. We present average measurements of fast-polarization directions at 21 new sites in poorly sampled regions of intra-plate South America, such as northern and northeastern Brazil. Despite sparse data coverage for the South American stable platform, consistent orientations are observed over hundreds of kilometers. Over most of the continent, the fast-polarization direction tends to be close to the absolute plate motion direction given by the hotspot reference model HS3-NUVEL-1A. A previous global comparison of the SKS fast-polarization directions with flow models of the upper mantle showed relatively poor correlation on the continents, which was interpreted as evidence for a large contribution of ""frozen"" anisotropy in the lithosphere. For the South American plate, our data indicate that one of the reasons for the poor correlation may have been the relatively coarse model of lithospheric thicknesses. We suggest that improved models of upper-mantle flow that are based on more detailed lithospheric thicknesses in South America may help to explain most of the observed anisotropy patterns.; CNPq (Brazilian National Research Council)[308861/2006-0]; FAPESP (Sao Paulo State Research Foundation)[01/06066-6]; FAPESP (Sao Paulo State Research Foundation)[02/00244-2]; FAPESP (Sao Paulo State Research Foundation)[05/51035-2]; ETH-Z (Federal Institute of Technology...

Anisotropia de suscetibilidade magnética dos plútons Ribeirão Branco, Sguário e Capão Bonito e implicações tectônicas para a Faixa Ribeira (Domínio Apiaí, SP); Magmatic susceptibility anisotropy of plutions Ribeirão Branco, Sguário and Capão Bonito and tectonic implication for Ribeirão belt (Apiaí Domain, SP)

Salazar, Carlos Alejandro
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 19/05/2010 PT
Relevância na Pesquisa
36.542334%
A trama de magmas graníticos alojados na crosta intermediária e superior pode-se originar pela ação de forças de corpo (ascensionais, convectivas) e/ou tectônicas. Diferentes mecanismos podem concorrer para a formação de tramas, embora a interação entre a deformação magmática e a tectônica regional seja um dos mecanismos fundamentais, notadamente nos granitos alojados em faixas orogênicas. No Domínio Apiaí da Faixa Ribeira (SP - PR), os batólitos graníticos alongados têm sido historicamente classificados como sintectônicos, ou seja, colocados durante o desenvolvimento de um arco magmático continental neoproterozóico. Os plútons menores, de forma circular a ovalada, geralmente discordantes e com típica coloração avermelhada, são considerados pós-tectônicos ou alojados após a colisão continental entre os diferentes blocos litosféricos que formaram a Faixa Ribeira. Essa classificação esquemática tem sido baseada em geoquímica e geocronologia dos granitos. Este trabalho identificou e mapeou a trama interna dos plútons sin-tectônicos (Ribeirão Branco) e pós-tectônicos (Capão Bonito e Sguário) utilizando a anisotropia de suscetibilidade magnética (ASM), de forma a inserí-los propriamente nos modelos de classificação tectônica...

Anisotropias induzidas em ligas ferromagnéticas amorfas; Induced anisotropy in amorphous ferromagnetic alloys

Santos, Antonio Domingues dos
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 07/03/1991 PT
Relevância na Pesquisa
36.593745%
Apresentaremos uma série de estudos realizados sobre o tema anisotropias magnéticas induzidas (Kind) em 1igas amorfas. Foram usados vários tipos de tratamentos térmico, com o objetivo de obtermos uma visão amp1a do assunto. A análise teórica dos dados de Kind e de "after-effect" magnético (MAE) foi feita com um modelo baseado em sistemas de dois níveis (TLS). A partir da análise dos dados experimentais obtém-se um largo espectro de energias de ativação. Estas energias estão relacionadas aos tempos de re1axação, através da equação de Arrhenius: = 0 exp (E/kT), onde o pré-fator 0 é da ordem do inverso da frequência de Debye. Construiu-se um forno para tratamentos térmicos em ligas amorfas, que opera em um eletroimã de 6 kOe e desenvolveu-se os programas para análise de dados experimentais. Essas facilidades, associadas ao traçador de curvas de histerese, permitiram os seguintes estudos de anisotropias induzidas em ligas amorfas ferromagnéticas: 1. Estudo da cinética de indução de anisotropia por tratamentos térmicos na faixa de temperatura de 190 a 250 °C, para fitas amorfas "as cast" de composição C070.4Fe4.6 Si15B10. Com o modelo TLS pode-se obter o espectro de energias de ativação, que se apresentou na faixa de energia de 1.50 a 1.85eV...

Estudo da anisotropia de emissão luminescente de filmes poliméricos ordenados; Study of the luminescence emission anisotropy of polymeric ordered films

Longaresi, Rafael Henriques
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 12/12/2012 PT
Relevância na Pesquisa
36.632617%
Processos fotofísicos em polímeros conjugados estão intimamente relacionados com a conformação dos segmentos moleculares. Filmes finos de polímeros conjugados apresentam uma anisotropia intrínseca resultante da conformação dos segmentos moleculares tornando esses materiais atrativos em estudos fotofísicos pela emissão polarizada apresentada quando excitado via radiação eletromagnética ou sob aplicação de uma diferença de potencial elétrico. Neste trabalho procuramos correlacionar o espectro de emissão fotoluminescente de filmes finos de um derivado do polifluoreno, nominalmente poli(9,9-dioctilfluorenil-2-7-diil) terminado com dimetilfenil, com sua anisotropia molecular. Filmes finos mecanicamente estirados sofrem um processo de reordenamento molecular induzindo a emissão de luz polarizada predominantemente na direção de estiramento. O estiramento ocasiona ainda um aumento no comprimento de conjugação efetivo dos segmentos moleculares influenciando no acoplamento elétron-fônon. Através da técnica de elipsometria, foi possível determinar os estados de polarização da luz (através dos parâmetros de Stokes) e medidas de fotoluminescência estacionária dependente da temperatura nos possibilitou aferirmos sobre o acoplamento elétron-fônon a partir do Princípio de Franck-Condon. Medidas de fotoluminescência de excitação (PLE) determinou que o espectro da PL consiste da sobreposição espectral de duas espécies emissoras: a espécie isolada e a espécie agregada. Para baixas temperaturas a PL apresenta picos de emissão bem definidos como resultado da dinâmica molecular do PFO correspondendo ao favorecimento de emissão da espécie isolada. Para temperaturas acima da temperatura de transição 'beta' (~270 K)...

Mobilidade da hélice 12 de receptores nucleares: comparação entre simulações de dinâmica molecular e experimentos de anisotropia de fluorescência; Nucler receptor's helix 12 mobility: comparison between molecular dynamics simulations and fluorescence anisotropy experiments

Batista, Mariana Raquel Bunoro
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 15/02/2013 PT
Relevância na Pesquisa
36.542334%
Receptores nucleares formam uma superfamília de proteínas responsáveis pela regulação da expressão de genes. Estruturalmente, são formados por três domínios: um domínio N-terminal bastante variável, um domínio altamente conservado de ligação com o DNA e um domínio C-terminal, menos conservado, denominado domínio de ligação com o ligante (LDB). Diversos experimentos mostram que a interação com o ligante afeta a estrutura e a mobilidade da hélice C-terminal dos receptores nucleares (hélice 12 do domínio de ligação com o ligante), sendo o principal mecanismo de ativação e repressão da transcrição. As primeiras estruturas de LBDs de receptores nucleares revelaram importantes diferenças entre estruturas contendo ligantes (holo) e estruturas apo, principalmente no que diz respeito a posição da hélice 12: em estruturas apo, foi observada a H12 em uma conformação aberta, expondo o sítio de ligação com o ligante, enquanto que em estruturas holo, foi observada a H12 em uma conformação fechada, dobrada sobre o corpo do LBD e envolvendo completamente o ligante. Essa diferença sugeriu um mecanismo para a entrada e saída de ligantes do sítio de ligação denominado modelo da ratoeira, entretanto, esse modelo apresenta diversas inconsistências e tem sido desacreditado. Estudos experimentais e teóricos recentes mostram que a hélice 12 é mais móvel na ausência de ligantes...

Evaluation of the anisotropy field for fine-particle systems from low-field thermomagnetic curves

Geshev, Julian Penkov; Martinez, Lluiz Martinez; Muñoz, Juan Santiago; Schmidt, Joao Edgar; Mikhov, Mihail
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
36.542334%
A method for evaluating the temperaturedependent magnetic anisotropy field from thermomagnetic curves for Stoner–Wohlfarth-like systems is proposed. It allows the anisotropy parameters of a sample with unknown spontaneous magnetization to be obtained by using magnetic fields considerably lower than the anisotropy field.

Effect of structural anisotropy on electrical and magnetic properties of polyaniline conducting films

Fedorko, P.; Faure-Vincent, J.; Fier, I.; Walmsley, L.; Sniechowski, M.; Jacquot, J. F.; Pron, A.; Travers, J. P.; Djurado, D.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 63-69
ENG
Relevância na Pesquisa
36.66304%
It is shown that highly conducting films of polyaniline protonated with di-esters of sulfosuccinic and sulfophthalic acids which contain alkyl- or alkoxy-type substituents exhibit highly anisotropic structural, electrical and magnetic properties. The layered-like structure of these films can be described as consisting of polyaniline chains which are mainly oriented parallel to the plane of the film and form regular out-of-plane stacks. These stacks are separated by bilayers of the dopant anions. Accordingly, the main anisotropy observed for solution cast films implies in-plane and out-of-plane measurements. An electrical anisotropy of about 80 is found for the in-plane and out-of-plane electronic conductivities at 5 K. The temperature dependences of the in-plane and out-of-plane conductivities are qualitatively similar and have been fitted as a series combination of variable-range-hopping-type and power law contributions. A maximum is observed in the temperature dependence of the electrical anisotropy at low temperature. The films also show a clear anisotropy of magnetization whose temperature and field characteristics depend on the chemical structure of the dopant anion. © 2013 Elsevier B.V.

Anisotropia magnética em tricamadas epitaxiais Fe/Mn/Fe; Magnetic anisotropy Fe/Mn/Fe trilayers

Pessoa, Marcio Solino
Fonte: Universidade Federal de Goiás; Brasil; UFG; Programa de Pós-graduação em Fisica (IF); Instituto de Física - IF (RG) Publicador: Universidade Federal de Goiás; Brasil; UFG; Programa de Pós-graduação em Fisica (IF); Instituto de Física - IF (RG)
Tipo: Dissertação Formato: application/pdf
POR
Relevância na Pesquisa
36.593745%
The ferromagnetic resonance (FMR) technique at the microwave frequencies of X-band (9.79 GHz) and Q-band (34 Ghz) was used to study, at room temperature, the magnetic anisotropy of Fe/Mn/Fe trilayers. The samples studied were grown by molecular beam epitaxy onto MgO substrates at the temperatures of 50 ° C, 150 ° C and 175 ° C, at the pressure of 4 x 10-11 Torr. The thicknesses of the distinct layers were 5 or 10 nm for the bottom Fe layer grown onto the MgO substrate, varied from 0.8 to 1.35 nm, for the Mn spacer layer, and was kept constant and equal to 5 nm, for the top Fe layer. The FMR spectra of the symmetrical trilayer at X and Q-band microwave frequencies show only the uniform resonance mode. Asymmetrical trilayers also show non resonant and/or non aligned modes at X-band frequency, but only the uniform mode at Q-band frequency. For some samples this result gives evidence of a non-collinear coupling between the Fe layers in the presence of low intensity magnetic fields. The out-of-plane angular dependence of the absorption fields show that the magnetization for all trilayers studied is in the plane of the sample. The magnetic anisotropy was deduced from the in-plane angular dependence of the uniform resonance mode at Q-band frequency...

Current absolute plate motion from seismic anisotropy and hotspot tracks; bounds on the latitudinal shift of the Hawaiian hotspot during formation of the Hawaiian island and seamount chain

Zheng, Lin
Fonte: Universidade Rice Publicador: Universidade Rice
Relevância na Pesquisa
36.632617%
Hotspots, the volcanic regions thought to be fed by underlying mantle that is anomalously hot compared with the mantle elsewhere, can serve as a reference frame to track the motion of the plates relative to the mantle beneath the asthenosphere. The application of the hotspot reference frame, however, is limited by the relative hotspot motion ranging from a few mm a-1 [Morgan, 1971; Duncan, 1981; Muller et al., 1993; Koivisto et al. 2013] to 80 mm a-1 [Raymond et al., 2000]. This dissertation aims to evaluate the hotspot reference frame. In the first part, I estimate the plate motion relative to the sub-asthenospheric mantle from seismic anisotropy data [Kreemer, 2009]. Prior studies based on seismic anisotropy assume that errors in the azimuths inferred from shear-wave splitting are uncorrelated. In this dissertation, I show that the residuals of azimuths inferred from shear-wave splitting beneath any one tectonic plate are strongly correlated with other residuals from the same plate. I account for these correlations in an inversion for absolute plate angular velocity by adopting a two-tier analysis of plate absolute velocities. First I find the pole of rotation and confidence limits for each plate individually. Then I perform a global inversion in which each plate is represented not by multiple individual estimates of the orientation of seismic anisotropy but by a single best-fitting pole and confidence limits. In the second part...

Anisotropy studies of the HiRes EHECR.

Bellido Caceres, Jose Alfredo
Fonte: Universidade de Adelaide Publicador: Universidade de Adelaide
Tipo: Tese de Doutorado
Publicado em //2002
Relevância na Pesquisa
36.593745%
In this thesis I present studies of the EHtrCR (E > 10¹⁸ eV) arrival directions using the data from the HiRes cosmic ray detector. The aims are to look for evidence of any cosmic ray anisotropy in any particular direction, especially in the directions of a priori, selected source candidates (Cygnus X-3, Virgo A, the AGASA triplet and the supergalactic plane). To perform these anisotropy studies it was necessary to determine in advance the uncertainties of the reconstructed cosmic ray arrival directions. The early chapters of my thesis give an introduction to cosmic ray physics and a review of anisotropy studies undertaken by several groups. In Chapter 4, I describe in some detail the High Resolution Fly's Eye (HiRes) detector. In Chapters 5, 6, and 7, I present details of the geometry reconstruction of the arrival directions of cosmic rays (monocular and stereo events) and estimations of the uncertainties in the reconstructed arrival directions. In Chapter 8, I present the results of the arrival direction anisotropy analysis. Finally in Chapter 9, I present a summary and conclusions.; Thesis (Ph.D.) -- University of Adelaide, Dept. of Physics and Mathematical Physics, 2002

Hydrogeophysical Characterization of Anisotropy in the Biscayne Aquifer Using Geophysical Methods

Yeboah-Forson, Albert
Fonte: FIU Digital Commons Publicador: FIU Digital Commons
Tipo: Artigo de Revista Científica Formato: application/pdf
Relevância na Pesquisa
36.76151%
The anisotropy of the Biscayne Aquifer which serves as the source of potable water for Miami-Dade County was investigated by applying geophysical methods. Electrical resistivity imaging, self potential and ground penetration radar techniques were employed in both regional and site specific studies. In the regional study, electrical anisotropy and resistivity variation with depth were investigated with azimuthal square array measurements at 13 sites. The observed coefficient of electrical anisotropy ranged from 1.01 to 1.36. The general direction of measured anisotropy is uniform for most sites and trends W-E or SE-NW irrespective of depth. Measured electrical properties were used to estimate anisotropic component of the secondary porosity and hydraulic anisotropy which ranged from 1 to 11% and 1.18 to 2.83 respectively. 1-D sounding analysis was used to models the variation of formation resistivity with depth. Resistivities decreased from NW (close to the margins of the everglades) to SE on the shores of Biscayne Bay. Porosity calculated from Archie's law, ranged from 18 to 61% with higher values found along the ridge. Higher anisotropy, porosities and hydraulic conductivities were on the Atlantic Coastal Ridge and lower values at low lying areas west of the ridge. The cause of higher anisotropy and porosity is attributed to higher dissolution rates of the oolitic facies of the Miami Formation composing the ridge. The direction of minimum resistivity from this study is similar to the predevelopment groundwater flow direction indicated in published modeling studies. Detailed investigations were carried out to evaluate higher anisotropy at West Perrine Park located on the ridge and Snapper Creek Municipal well field where the anisotropy trend changes with depth. The higher anisotropy is attributed to the presence of solution cavities oriented in the E-SE direction on the ridge. Similarly...

A search for anisotropy in the arrival directions of ultra high energy cosmic rays recorded at the Pierre Auger Observatory

Abreu, P.; Aglietta, M.; Ahlers, M.; Ahn, E. J.; Albuquerque, Ivone Freire da Mota e; Allard, D.; Allekotte, I.; Allen, J.; Allison, P.; Almela, A.; Alvarez Castillo, J.; Alvarez-Muniz, J.; Ambrosio, M.; Aminaei, A.; Anchordoqui, L.; Andringa, S.; Antici'
Fonte: IOP PUBLISHING LTD; BRISTOL Publicador: IOP PUBLISHING LTD; BRISTOL
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
36.593745%
Observations of cosmic rays arrival directions made with the Pierre Auger Observatory have previously provided evidence of anisotropy at the 99% CL using the correlation of ultra high energy cosmic rays (UHECRs) with objects drawn from the Veron-Cetty Veron catalog. In this paper we report on the use of three catalog independent methods to search for anisotropy. The 2pt-L, 2pt+ and 3pt methods, each giving a different measure of self-clustering in arrival directions, were tested on mock cosmic ray data sets to study the impacts of sample size and magnetic smearing on their results, accounting for both angular and energy resolutions. If the sources of UHECRs follow the same large scale structure as ordinary galaxies in the local Universe and if UHECRs are deflected no more than a few degrees, a study of mock maps suggests that these three method can efficiently respond to the resulting anisotropy with a P-value = 1.0% or smaller with data sets as few as 100 events. using data taken from January 1, 2004 to July 31, 2010 we examined the 20, 30, ... , 110 highest energy events with a corresponding minimum energy threshold of about 49.3 EeV. The minimum P-values found were 13.5% using the 2pt-L method, 1.0% using the 2pt+ method and 1.1% using the 3pt method for the highest 100 energy events. In view of the multiple (correlated) scans performed on the data set...

Environment-induced anisotropy and the sensitivity of the radical pair mechanism in the avian compass = Anisotropia induzida pelo ambiente e a sensibilidade do mecanismo de pares radicais na orientação magnética aviária; Anisotropia induzida pelo ambiente e a sensibilidade do mecanismo de pares radicais na orientação magnética aviária

Alejandro Carrillo Lozada
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 04/04/2013 PT
Relevância na Pesquisa
36.687495%
O campo magnético da Terra é essencial na orientação de pássaros migratórios. A explicação mais promissora para esta orientação utiliza o mecanismo de pares ra-dicais (PR) criados em uma reação foto-estimulada, a qual é conjecturada ocorrer em fotorreceptores criptocromo. Esta última conjectura foi particularmente reforçada recentemente pela evidência de sensibilidade magnética do criptocromo humano. Os radicais devem ter uma anisotropia intrínseca, a fim de definir um quadro de referência para esse tipo de bússola. Esta anisotropia, quando introduzida através de interação hiperfinas, impõe imobilidade ao RP formado dentro do olho do pássaro, e implica na preservação do emaranhamento entre os elétrons desemparelhados do PR por tempos longos (de centenas de microssegundos). Consequentemente, os tempos de coerência são também longos, mesmo que o papel do emaranhamento na reação permaneça desconhecido. Mostra-se que esse tipo de anisotropia devido às interações hiperfinas não é necessário para o funcionamento da bússola. Pares radicais isotrópicos, isto é, moléculas que executam um movimento de rotação ou de difusão capaz de remover qualquer anisotropia no Hamiltoniano quando submetidos a um processo de decoerência rápida...

Probability of radial anisotropy in the deep mantle

Visser, K; Trampert, Jeannot; Lebedev, S; Kennett, Brian
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
36.632617%
It is well established that the Earth's uppermost mantle is anisotropic, but observations of anisotropy in the deeper mantle have been more ambiguous. Radial anisotropy, the discrepancy between Love and Rayleigh waves, was included in the top 220 km of P

Control of the perpendicular magnetic anisotropy of FePd films via Pd capping deposition

Clavero Pérez, César; Skuza, J. R.; Choi, Y.; Haskel, D.; García-Martín, José Miguel; Cebollada, Alfonso; Lukaszew, R. A.
Fonte: American Institute of Physics Publicador: American Institute of Physics
Tipo: Artículo Formato: 464633 bytes; application/pdf
ENG
Relevância na Pesquisa
36.632617%
We have investigated the influence of two capping layers (MgO and Pd) on the magnetic anisotropy of highly anisotropic L10 FePd films. While we mainly found perpendicular magnetic anisotropy in MgO capped films, we observed that the Pd capping layer induces formation of an additional new phase near the FePd/Pd interface that exhibits in-plane magnetic anisotropy. The combined effect of these two anisotropies results in global canted magnetic anisotropy. Thus, our findings illustrate a mechanism to influence the magnetic anisotropy in FePd highly ordered alloys via adequate choice of capping layer materials.; Peer reviewed

Using exchange bias to extend the temperature range of square loop behavior in [Pt/Co] multilayers with perpendicular anisotropy

Sort Viñas, Jordi; Suriñach, Santiago
Fonte: Universidade Autônoma de Barcelona Publicador: Universidade Autônoma de Barcelona
Tipo: Artigo de Revista Científica Formato: application/pdf
Publicado em //2005 ENG
Relevância na Pesquisa
36.593745%
This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics.; The temperature dependence of the magnetic properties of [Pt/Co]multilayers (ML), exhibiting perpendicular anisotropy, with and without exchange biasing with an antiferromagnet(AFM) has been investigated. Upon heating, a loss of the out-of-plane anisotropy and, consequently, of the remanence to saturation ratio is observed in these systems. However, such effect occurs at higher temperatures in the [Pt/Co] ML exchange coupled to the AFM than for the unbiased ML. This is attributed to the additional anisotropy induced to the ML by the ferromagnetic-antiferromagnetic exchange coupling.

Global azimuthal seismic anisotropy and the unique plate-motion deformation of Australia

Debayle, E; Kennett, Brian; Priestley, K
Fonte: Macmillan Publishers Ltd Publicador: Macmillan Publishers Ltd
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
36.750876%
Differences in the thickness of the high-velocity lid underlying continents as imaged by seismic tomography, have fuelled a long debate on the origin of the 'roots' of continents1-5. Some of these differences may be reconciled by observations of radial anisotropy between 250 and 300 km depth, with horizontally polarized shear waves travelling faster than vertically polarized ones2. This azimuthally averaged anisotropy could arise from present-day deformation at the base of the plate, as has been found for shallower depths beneath ocean basins6. Such deformation would also produce significant azimuthal variation, owing to the preferred alignment of highly anisotropic minerals7. Here we report global observations of surface-wave azimuthal anisotropy, which indicate that only the continental portion of the Australian plate displays significant azimuthal anisotropy and strong correlation with present-day plate motion in the depth range 175-300 km. Beneath other continents, azimuthal anisotropy is only weakly correlated with plate motion and its depth location is similar to that found beneath oceans. We infer that the fast-moving Australian plate contains the only continental region with a sufficiently large deformation at its base to be transformed into azimuthal anisotropy. Simple shear leading to anisotropy with a plunging axis of symmetry may explain the smaller azimuthal anisotropy beneath other continents.

Continental scale shear wave splitting analysis: Investigation of seismic anisotropy underneath the Australian continent

Heintz, M.; Kennett, Brian
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
36.750876%
The structure of the upper mantle beneath the Australian continent is investigated using teleseismic shear wave splitting to extract seismic anisotropy. Measurements have been performed on data recorded at 190 sites with portable broadband seismic recorders, spanning almost the entire surface of the continent since 1992. The average time span of the various deployments, primarily designed for surface wave tomography, is 6 months, which is rather limited for shear wave splitting analysis. However, the data set provides a full continental scale survey using the reasonably favourable distribution of seismicity to Australia. Seismic anisotropy has the potential to provide insights into the lithospheric structure and the possible mechanical coupling between the crust and the upper mantle, but prior results for Australia have indicated relatively small levels of splitting and a complex pattern. These results are confirmed with our new and far more extensive measurements across the whole continent. The pattern of seismic anisotropy from shear wave splitting beneath Australia is rather complex and is not correlated with the almost north-south absolute plate motion (APM) from recent models. Deviation of the asthenospheric mantle flow around the lithospheric roots associated with the extensive Archaean and Proterozoic zones of central and western Australia could be occurring...

Anisotropy in the Australasian upper mantle from Love and Rayleigh waveform inversion

Debayle, E; Kennett, Brian
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
36.750876%
Records of both Rayleigh and Love waves have been analyzed to determine the pattern of anisotropy in the Australasian region. The approach is based on a two-stage inversion. Starting from a smooth PREM model with transverse isotropy about a vertical symmetry axis, the first step is an inversion of the waveforms of surface waves to produce path specific one-dimensional (1-D) upper mantle models. Under the assumption that the I-D models represent averages along the paths, the results from 1584 Love and Rayleigh wave seismograms are combined in a tomographic inversion to provide a representation of three-dimensional structure for wavespeed heterogeneities and anisotropy. Polarization anisotropy with SH faster than SV is retrieved in the upper 200-250 km of the mantle for most of Precambrian Australia. In this depth interval, significant lateral variations in the level of polarization anisotropy are present. Locally, the anisotropy can be large, reaching an extreme value of 9% that is difficult to reconcile with current mineralogical models. However, the discrepancy may be explained in part by the presence of strong lateral heterogeneities along the path, or by effects introduced by the simplifying assumption of transverse isotropy for each path. The consistency between the location of polarization and azimuthal anisotropy in depth suggests that both observations share a common origin. The observation of polarization anisotropy down to at least 200 km supports a two-layered anisotropic model as constrained by the azimuthal anisotropy of SV waves. In the upper layer...