Página 1 dos resultados de 1168 itens digitais encontrados em 0.007 segundos

‣ Frictional contact of an anisotropic piezoelectric plate

Figueiredo, Isabel N.; Stadler, Georg
Fonte: Centro de Matemática da Universidade de Coimbra Publicador: Centro de Matemática da Universidade de Coimbra
Tipo: Pré-impressão
Português
Relevância na Pesquisa
462.3306%
The purpose of this paper is to derive and study a new asymptotic model for the equilibrium state of a thin anisotropic piezoelectric plate in frictional contact with a rigid obstacle. In the asymptotic process, the thickness of the piezoelectric plate is driven to zero and the convergence of the unknowns is studied. This leads to two-dimensional Kirchhoff-Love plate equations, in which mechanical displacement and electric potential are partly decoupled. Based on this model numerical examples are presented that illustrate the mutual interaction between the mechanical displacement and the electric potential. We observe that, compared to purely elastic materials, piezoelectric bodies yield a significantly different contact behavior.; Project ”Mathematical Analysis of Piezoelectric Problems” (POCTI/MAT/59502/2004, Fundação para a Ciência e a Tecnologia, Portugal

‣ A piezoelectric anisotropic plate model

Figueiredo, Isabel M. Narra; Leal, Carlos M. Franco
Fonte: Centro de Matemática da Universidade de Coimbra Publicador: Centro de Matemática da Universidade de Coimbra
Tipo: Pré-impressão
Português
Relevância na Pesquisa
462.3306%
We mathematically justify a reduced piezoelectric plate model. This is achieved considering the three-dimensional static equations of piezoelectricity, for a nonhomogeneous anisotropic thin plate, and using the asymptotic analysis to compute the limit of the displacement vector and electric potential, as the thickness of the plate approaches zero. We prove that the three-dimensional displacement vector converges to a Kirchhoff-Love displacement, that solves a two-dimensional piezoelectric plate model, defined on the middle surface of the plate. Moreover, the three-dimensional electric potential converges to a scalar function that is a second order polynomial with respect to the thickness variable, with coefficients that depend on the transverse component of the Kirchhoff-Love displacement. We remark that the results of this paper generalize a previous work of A. Sene (2001) for homogeneous and isotropic materials.

‣ Numerical simulation of anisotropic polymeric foams

Tita, Volnei; Caliri Junior, Mauricio Francisco
Fonte: LATIN AMER J SOLIDS STRUCTURES; RIO DE JANEIRO Publicador: LATIN AMER J SOLIDS STRUCTURES; RIO DE JANEIRO
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
483.7577%
This paper shows in detail the modelling of anisotropic polymeric foam under compression and tension loadings, including discussions on isotropic material models and the entire procedure to calibrate the parameters involved. First, specimens of poly(vinyl chloride) (PVC) foam were investigated through experimental analyses in order to understand the mechanical behavior of this anisotropic material. Then, isotropic material models available in the commercial software Abaqus (TM) were investigated in order to verify their ability to model anisotropic foams and how the parameters involved can influence the results. Due to anisotropy, it is possible to obtain different values for the same parameter in the calibration process. The obtained set of parameters are used to calibrate the model according to the application of the structure. The models investigated showed minor and major limitations to simulate the mechanical behavior of anisotropic PVC foams under compression, tension and multi-axial loadings. Results show that the calibration process and the choice of the material model applied to the polymeric foam can provide good quantitative results and save project time. Results also indicate what kind and order of error one will get if certain choices are made throughout the modelling process. Finally...

‣ Formulação alternativa para análise de domínios não-homogêneos e inclusões anisotrópicas via MEC; Alternative boundary element formulation for multi-region bodies and inclusions

Azevedo, Carlos Alberto Cabral 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 05/03/2007 Português
Relevância na Pesquisa
383.52645%
Este trabalho trata da análise de problemas planos de chapa compostos por materiais anisotrópicos, definidas em uma região ou no domínio por completo, utilizando-se o método dos elementos de contorno. As soluções fundamentais para problemas anisotrópicos, embora existentes, mostram-se difíceis de serem utilizadas devido à complexidade de sua formulação matemática ou da necessidade de se encontrar partes da solução numericamente. Nesse sentido, a formulação alternativa mostrada nesse trabalho permite o estudo de meios anisotrópicos utilizando-se as soluções fundamentais para meios isotrópicos nas representações integrais de problemas planos com campo de tensões iniciais. A região do domínio com propriedades anisotrópicas ou diferentes das propriedades elásticas de um meio isotrópico usado como referência é discretizada em células triangulares, enquanto que o contorno do problema é discretizado em elementos lineares. As componentes do tensor de tensões iniciais da região anisotrópica são definidas como uma correção das tensões elásticas do material isotrópico de referência através de uma matriz de penalização. Essa matriz, por sua vez, é obtida através de relações envolvendo as constantes elásticas de rigidez do meio desejado e os coeficientes elásticos de flexibilidade do meio isotrópico de referência. Essa técnica é particularmente adequada para a análise de inclusões anisotrópicas onde há a necessidade de discretizar apenas uma parte pequena do domínio...

‣ Modelos de material para espumas poliméricas aplicadas a estruturas aeronáuticas em material compósito sanduíche; Material models for polymeric foams applied to aircraft structures in sandwich composite materials

Caliri Junior, Mauricio Francisco
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 08/07/2010 Português
Relevância na Pesquisa
466.4876%
Estruturas aeronáuticas são em sua grande parte fabricadas em material compósito para que sejam atendidas as especificações de projeto. Entre essas estruturas destaca-se a estrutura sanduíche. A utilização desse tipo de estrutura requer estudos extensos em novos materiais, bem como na aplicação dos mesmos. Uma atenção especial para o núcleo dessas estruturas é necessária, pois este material é na verdade uma estrutura celular, como as espumas poliméricas. Esta dissertação busca concatenar a literatura com a prática ao estudar a calibração de modelos de material para descrever o comportamento mecânico de espumas poliméricas, bem como avaliar suas potencialidades e limitações. Estas espumas são estruturas celulares cujos mecanismos de falha consistem em respostas micro e macroscópicas. A identificação e quantificação desses comportamentos podem ser feitas através da investigação de modelos de material micro-mêcanicos ou fenomenológicos (macro-mecânicos) associados a ensaios e análises experimentais tanto do material celular quanto da estrutura na qual este material é utilizado. Cada abordagem, micro ou macro-mecânica, possui vantagens e desvantagens que no presente trabalho são discutidas para o material estudado (espuma polimérica rígida de PVC...

‣ Analise de trincas interfaciais em bimateriais anisotropicos usando o metodo dos elementos de contorno; Analysis of interfacial cracks in anisotropic bimaterials using the boubdary element method

Seila Vasti Faria de Paiva
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 12/12/2006 Português
Relevância na Pesquisa
374.90973%
Nesta dissertação é apresentada uma análise de problemas da mecânica da fratura elástica linear em estruturas bimateriais anisotrópicas. Utilizando o método dos elementos de contorno é possível calcular os fatores de intensidade de tensão em problemas planos (2D) devido à presença de trincas interfaciais entre as lâminas que compõem o material. A estrutura pode estar submetida à carregamento em modo I ou modo misto. O problema é modelado usando-se a técnica de sub-regiões para descrever cada um dos diferentes subdomínios, representado por cada material. Na interface das sub-regiões, em que o domínio é dividido, são impostas condições de equilíbrio de forças e continuidade de deslocamentos, exceto na região que corresponde à trinca. O comportamento singular apresentado pelo campo de tensões próximo à ponta da trinca é modelado com elementos de ponto a um quarto com singularidade de forças de superfície. São apresentados exemplos numéricos de problemas com carregamentos no plano. Foi também apresentada a análise de convergência de malhas, mostrando uma pequena dependência da discretização mesmo quando malhas pouco refinadas foram usadas. Alguns dos exemplos têm correspondentes na literatura...

‣ Development of a general purpose nonlinear solid-shell element and its application to anisotropic sheet forming simulation; Desenvolvimento de um elemento sólido-casca não linear para aplicação em simulações de conformação plástica de chapas anisotrópicas

Sousa, Ricardo José Alves de
Fonte: Universidade de Aveiro Publicador: Universidade de Aveiro
Tipo: Tese de Doutorado
Português
Relevância na Pesquisa
382.09574%
A utilização dos métodos computacionais na Engenharia Mecânica tem assumido cada vez mais relevância, contribuindo para uma melhor compreensão dos processos de conformação plástica em chapa, especialmente aqueles que lidam com materiais anisotrópicos, como é o caso das ligas de alumínio. Dentre estes, o método dos elementos finitos (FEM) tem progredido substancialmente nas últimas duas décadas, em parte devido ao rápido desenvolvimento da arquitectura dos computadores. Para a correcta modelação dos processos de conformação plástica em chap: o desenvolvimento de um elemento finito preciso e eficiente, vocacionado para a modelação de estruturas com parede fina, como é o caso das chapas de metal; o estudo e implementação de modelos constitutivos, considerando a anisotropia material a três dimensões. Assim, é proposto um novo elemento finito sólido-casca, suportando um número arbitrário de pontos de integração numérica ao longo da sua espessura. Devido à sua topologia sólida com oito nós físicos, esta formulação avalia naturalmente variações de espessura, contacto simultâneo em duas faces e modelos constitutivos tridimensionais, aspectos cruciais neste tipo de aplicações. Do lado constitutivo...

‣ Remarks on orthotropic elastic models applied to wood

Mascia,Nilson Tadeu; Lahr,Francisco Antônio Rocco
Fonte: ABM, ABC, ABPol Publicador: ABM, ABC, ABPol
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/09/2006 Português
Relevância na Pesquisa
474.90973%
Wood is generally considered an anisotropic material. In terms of engineering elastic models, wood is usually treated as an orthotropic material. This paper presents an analysis of two principal anisotropic elastic models that are usually applied to wood. The first one, the linear orthotropic model, where the material axes L (Longitudinal), R( radial) and T(tangential) are coincident with the Cartesian axes (x, y, z), is more accepted as wood elastic model. The other one, the cylindrical orthotropic model is more adequate of the growth caracteristics of wood but more mathematically complex to be adopted in practical terms. Specifically due to its importance in wood elastic parameters, this paper deals with the fiber orientation influence in these models through adequate transformation of coordinates. As a final result, some examples of the linear model, which show the variation of elastic moduli, i.e., Young´s modulus and shear modulus, with fiber orientation are presented.

‣ Numerical simulation of anisotropic polymeric foams

Tita,Volnei; Caliri Júnior,Mauricio Francisco
Fonte: Associação Brasileira de Ciências Mecânicas Publicador: Associação Brasileira de Ciências Mecânicas
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/04/2012 Português
Relevância na Pesquisa
483.7577%
This paper shows in detail the modelling of anisotropic polymeric foam under compression and tension loadings, including discussions on isotropic material models and the entire procedure to calibrate the parameters involved. First, specimens of poly(vinyl chloride) (PVC) foam were investigated through experimental analyses in order to understand the mechanical behavior of this anisotropic material. Then, isotropic material models available in the commercial software AbaqusTM were investigated in order to verify their ability to model anisotropic foams and how the parameters involved can influence the results. Due to anisotropy, it is possible to obtain different values for the same parameter in the calibration process. The obtained set of parameters are used to calibrate the model according to the application of the structure. The models investigated showed minor and major limitations to simulate the mechanical behavior of anisotropic PVC foams under compression, tension and multi-axial loadings. Results show that the calibration process and the choice of the material model applied to the polymeric foam can provide good quantitative results and save project time. Results also indicate what kind and order of error one will get if certain choices are made throughout the modelling process. Finally...

‣ Effect of Specimen-Specific Anisotropic Material Properties in Quantitative Computed Tomography-Based Finite Element Analysis of the Vertebra

Unnikrishnan, Ginu U.; Barest, Glenn D.; Berry, David B.; Hussein, Amira I.; Morgan, Elise F.
Fonte: American Society of Mechanical Engineers Publicador: American Society of Mechanical Engineers
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
478.2846%
Intra- and inter-specimen variations in trabecular anisotropy are often ignored in quantitative computed tomography (QCT)-based finite element (FE) models of the vertebra. The material properties are typically estimated solely from local variations in bone mineral density (BMD), and a fixed representation of elastic anisotropy (“generic anisotropy”) is assumed. This study evaluated the effect of incorporating specimen-specific, trabecular anisotropy on QCT-based FE predictions of vertebral stiffness and deformation patterns. Orthotropic material properties estimated from microcomputed tomography data (“specimen-specific anisotropy”), were assigned to a large, columnar region of the L1 centrum (n = 12), and generic-anisotropic material properties were assigned to the remainder of the vertebral body. Results were compared to FE analyses in which generic-anisotropic properties were used throughout. FE analyses were also performed on only the columnar regions. For the columnar regions, the axial stiffnesses obtained from the two categories of material properties were uncorrelated with each other (p = 0.604), and the distributions of minimum principal strain were distinctly different (p ≤ 0.022). In contrast, for the whole vertebral bodies in both axial and flexural loading...

‣ Measurement of the intrinsic attenuation of longitudinal waves in anisotropic material from uncorrected raw data

SELDIS Thomas
Fonte: ELSEVIER SCIENCE BV Publicador: ELSEVIER SCIENCE BV
Tipo: Articles in Journals Formato: Printed
Português
Relevância na Pesquisa
469.1443%
Among the physical parameters characterising the interaction of the ultrasonic beam with its supporting medium, ultrasonic attenuation is an important input parameter to simulate wave propagation and defect-beam phenomena. The measurement of the intrinsic attenuation in anisotropic material however is a difficult task. The paper presents an approach to determine intrinsic attenuation in anisotropic materials such as austenitic stainless steel welds and cladding. It deals with improvements on the initial device, based on measurements on two samples with different thicknesses (10 mm and 20 mm). A previous paper presented preliminary results with this new approach for isotropic materials.; JRC.F.4-Nuclear Reactor Integrity Assessment and Knowledge Management

‣ Estudo de criterios de resistencia de materiais anisotropicos aplicados a madeira; Study of anisotropic material failure criteria, applied to wood

Elias Antonio Nicolas
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 30/06/2006 Português
Relevância na Pesquisa
469.1443%
Esta pesquisa refere-se ao estudo de critérios de resistência de materiais anisotrópicos, especialmente o critério tensorial de resistência de TSAI- WU, com aplicações teóricas e experimentais para a madeira. Neste sentido foi realizada uma revisão teórica dos principais temas relacionados à presente pesquisa, como: critérios gerais de resistência, fórmula de hankinson, critério de TSAIWU, modos de ruptura da madeira, fatores que influenciam na resistência da madeira,equipamentos e corpos-de-prova para realização de ensaios uniaxiais e biaxiais, prescrições de cálculo das normas de estruturas de madeira. O objetivo principal deste trabalho foi determinar os parâmetros de resistência do critério tensorial de TSAI-WU, com a finalidade de definir uma superfície de ruptura, para a espécie de madeira estudada, cupiúba (Goupia glabra), e comparar os dados dos ensaios com as estimativas do critério. No estudo experimental foram realizados os seguintes ensaios: tração e compressão, uniaxiais, com ângulos das fibras inclinados em relação ao carregamento (0°, 15°, 30°, 45°, 60°, 75° e 90°); ensaios de cisalhamento paralelo às fibras e ensaios de compressão biaxial. As estimativas do critério de TSAI- WU ficaram próximas das estimativas da fórmula de Hankinson e também dos dados dos ensaios uniaxiais de tração e compressão. Por outro lado...

‣ Effective medium theory for anisotropic metamaterials

Zhang, Xiujuan; Wu, Ying
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Artigo de Revista Científica
Publicado em 20/01/2015 Português
Relevância na Pesquisa
376.5044%
Materials with anisotropic material parameters can be utilized to fabricate many fascinating devices, such as hyperlenses, metasolids, and one-way waveguides. In this study, we analyze the effects of geometric anisotropy on a two-dimensional metamaterial composed of a rectangular array of elliptic cylinders and derive an effective medium theory for such a metamaterial. We find that it is possible to obtain a closed-form analytical solution for the anisotropic effective medium parameters, provided the aspect ratio of the lattice and the eccentricity of the elliptic cylinder satisfy certain conditions. The derived effective medium theory not only recovers the well-known Maxwell-Garnett results in the quasi-static regime, but is also valid beyond the long-wavelength limit, where the wavelength in the host medium is comparable to the size of the lattice so that previous anisotropic effective medium theories fail. Such an advance greatly broadens the applicable realm of the effective medium theory and introduces many possibilities in the design of structures with desired anisotropic material characteristics. A real sample of a recently theoretically proposed anisotropic medium, with a near-zero index to control the flux, is achieved using the derived effective medium theory...

‣ The factorization method for a defective region in an anisotropic material

Cakoni, Fioralba; Harris, Isaac
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 14/10/2014 Português
Relevância na Pesquisa
476.11035%
In this paper we consider the inverse acoustic scattering (in \mathbb{R}^3) or electromagnetic scattering (in \mathbb{R}^2, for the scalar TE-polarization case) problem of reconstructing possibly multiple defective penetrable regions in a known anisotropic material of compact support. We develop the factorization method for a non-absorbing anisotropic background media containing penetrable defects. In particular, under appropriate assumptions on the anisotropic material properties of the media we develop a rigorous characterization for the support of the defective regions from the given far field measurements. Finally we present some numerical examples in the two dimensional case to demonstrate the feasibility of our reconstruction method including examples for the case when the defects are voids (i.e. subregions with refractive index the same as the background outside the inhomogeneous hosting media).

‣ What is the Brillouin Zone of an Anisotropic Photonic Crystal?

Sivarajah, P.; Maznev, A. A.; Ofori-Okai, B. K.; Nelson, K. A.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
380.0735%
The concept of the Brillouin zone (BZ) in relation to a photonic crystal fabricated in an optically anisotropic material is explored both experimentally and theoretically. In experiment, we used femtosecond laser pulses to excite THz polaritons and image their propagation in lithium niobate and lithium tantalate photonic crystal (PhC) slabs. We directly measured the dispersion relation inside PhCs and observed that the lowest bandgap expected to form at the BZ boundary forms inside the BZ in the anisotropic lithium niobate PhC. Our analysis shows that in an anisotropic material the BZ - defined as the Wigner-Seitz cell in the reciprocal lattice - is no longer bounded by Bragg planes and thus does not conform to the original definition of the BZ by Brillouin. We construct an alternative Brillouin zone defined by Bragg planes and show its utility in identifying features of the dispersion bands. We show that for an anisotropic 2D PhC without dispersion, the Bragg plane BZ can be constructed by applying the Wigner-Seitz method to a stretched or compressed reciprocal lattice. We also show that in the presence of the dispersion in the underlying material or in a slab waveguide, the Bragg planes are generally represented by curved surfaces rather than planes. The concept of constructing a BZ with Bragg planes should prove useful in understanding the formation of dispersion bands in anisotropic PhCs and in selectively tailoring their optical properties.; Comment: 9 pages...

‣ Enhancement of non-resonant dielectric cloaks using anisotropic composites

Takezawa, Akihiro; Kitamura, Mitsuru
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
378.74445%
Cloaking techniques conceal objects by controlling the flow of electromagnetic waves to minimize scattering. Herein, the effectiveness of homogenized anisotropic materials in non-resonant dielectric multilayer cloaking is studied. Because existing multilayer cloaking by isotropic materials can be regarded as homogenous anisotropic cloaking from a macroscopic view, anisotropic materials can be efficiently designed through optimization of their physical properties. Anisotropic properties can be realized in two-phase composites if the physical properties of the material are within appropriate bounds. The optimized anisotropic physical properties are identified by a numerical optimization technique based on a full-wave simulation using the finite element method. The cloaking performance measured by the total scattering width is improved by about 2.8% and 25% in eight- and three-layer cylindrical cloaking materials, respectively, compared with multilayer cloaking by isotropic materials. In all cloaking examples, the optimized microstructures of the two-phase composites are identified as the simple lamination of two materials, which maximizes the anisotropy. The same performance as published for eight-layer cloaking by isotropic materials is achieved by three-layer cloaking using the anisotropic material. Cloaking with an approximately 50% reduction of total scattering width is achieved even in an octagonal object. Since the cloaking effect can be realized using just a few layers of the laminated anisotropic dielectric composite...

‣ Effective medium theory for anisotropic metamaterials

Zhang, Xiujuan; Wu, Ying
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 03/09/2014 Português
Relevância na Pesquisa
376.5044%
We present an effective medium theory that can predict the effective permittivity and permeability of a geometrically anisotropic two-dimensional metamaterial composed with a rectangular array of elliptical cylinders. It is possible to obtain a closed-form analytical solution for the anisotropic effective medium parameters if the aspect ratio of the lattice and the eccentricity of elliptical cylinder satisfy certain conditions. The derived effective medium theory can recover the well-known Maxwell-Garnett results in the quasi-static regime. More importantly, it is valid beyond the long-wavelength limit, where the wavelength in the host medium is comparable to the size of the lattice so that previous anisotropic effective medium theories fail. The validity of the derived effective medium theory is verified by band structure calculations. A real sample of a recent theoretically proposed anisotropic medium with near-zero index to control flux is achieved from the derived effective medium theory and control of electromagnetic waves in the sample is clearly demonstrated. The accuracy of the theory is further systematically studied as material and geometric parameter varies, and we find the derived effective medium theory applies over a large range in the parameter space. Such applicability greatly broadens the applicable realm of the effective medium theory and opens many vistas in the design of structures with desired anisotropic material characteristics.; Comment: Paper draft. An updated formal version is under review

‣ Review of Anisotropic Terahertz Material Response

Arikawa, T.; Zhang, Q.; Ren, L.; Belyanin, A. A.; Kono, J.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 08/05/2013 Português
Relevância na Pesquisa
376.11035%
Anisotropy is ubiquitous in solids and enhanced in low-dimensional materials. In response to an electromagnetic wave, anisotropic absorptive and refractive properties result in dichroic and birefringent optical phenomena both in the linear and nonlinear optics regimes. Such material properties have led to a diverse array of useful polarization components in the visible and near-infrared, but mature technology is non-existent in the terahertz (THz). Here, we review several novel types of anisotropic material responses observed in the THz frequency range, including both linear and circular anisotropy, which have long-term implications for the development of THz polarization optics. We start with the extreme linear anisotropy of macroscopically aligned carbon nanotubes, arising from their intrinsically anisotropic dynamic conductivity. Magnetically induced anisotropy will then be reviewed, including the giant Faraday effects observed in semiconductors, semimetals, and two-dimensional electron systems.; Comment: 26 pages, 11 figures

‣ Brewster's angle for anisotropic material from the extinction theorem

Shu, Weixing; Ren, Zhongzhou; Luo, Hailu; Li, Fei
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
479.79457%
By the extinction theorem we explore the Brewster effect in the external and internal reflections of electromagnetic wave associated with an anisotropic material that is both dielectric and magnetic, including metamaterials. We obtain Fresnel's coefficients and the condition of Brewster's angle, and give microscopic explanations from the view point of molecular optics. The Brewster angle is the incidence of angle at which the contribution of all electric and magnetic dipoles in the anisotropic material to the reflection field becomes zero. Distinct from isotropic media, the anisotropic material can exhibit Brewster angle for both TE and TM waves due to the anisotropy of the material.; Comment: 16 pages, 9 figures

‣ COBRA, an Arabidopsis Extracellular Glycosyl-Phosphatidyl Inositol-Anchored Protein, Specifically Controls Highly Anisotropic Expansion through its Involvement in Cellulose Microfibril Orientation

Roudier, Francois; Fernandez, Anita G; Fujita, Machiko; Himmelspach, Regina; Borner, Georg H H; Schindelman, Gary; Song, Shuang; Baskin, Tobias I; Dupree, Paul; Wasteneys, Geoffrey; Benfey, Philip N
Fonte: American Society of Plant Biologists Publicador: American Society of Plant Biologists
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
469.6907%
The orientation of cell expansion is a process at the heart of plant morphogenesis. Cellulose microfibrils are the primary anisotropic material in the cell wall and thus are likely to be the main determinant of the orientation of cell expansion. COBRA (COB) has been identified previously as a potential regulator of cellulose biogenesis. In this study, characterization of a null allele, cob-4, establishes the key role of COB in controlling anisotropic expansion in most developing organs. Quantitative polarized-light and field-emission scanning electron microscopy reveal that loss of anisotropic expansion in cob mutants is accompanied by disorganization of the orientation of cellulose microfibrils and subsequent reduction of crystalline cellulose. Analyses of the conditional cob-1 allele suggested that COB is primarily implicated in microfibril deposition during rapid elongation. Immunodetection analysis in elongating root cells revealed that, in agreement with its substitution by a glycosylphosphatidylinositol anchor, COB was polarly targeted to both the plasma membrane and the longitudinal cell walls and was distributed in a banding pattern perpendicular to the longitudinal axis via a microtubule-dependent mechanism. Our observations suggest that COB...