Magnetic alignment and patterning of cellulose fibers

The alignment and patterning of cellulose fibers under magnetic fields are reported. Static and rotating magnetic fields were used to align cellulose fibers with sizes ranging from millimeter to nanometer sizes. Cellulose fibers of the millimeter order, which were prepared for papermaking, and much smaller fibers with micrometer to nanometer sizes prepared by the acid hydrolysis of larger ones underwent magnetic alignment. Under a rotating field, a uniaxial alignment of fibers was achieved. The alignment was successfully fixed by the photopolymerization of a UV-curable resin precursor used as matrix. A monodomain chiral nematic film was prepared from an aqueous suspension of nanofibers. Using a field modulator inserted in a homogeneous magnetic field, simultaneous alignment and patterning were achieved.     

Magnetic alignment and patterning of cellulose fibers

Abstract

The alignment and patterning of cellulose fibers under magnetic fields are reported. Static and rotating magnetic fields were used to align cellulose fibers with sizes ranging from millimeter to nanometer sizes. Cellulose fibers of the millimeter order, which were prepared for papermaking, and much smaller fibers with micrometer to nanometer sizes prepared by the acid hydrolysis of larger ones underwent magnetic alignment. Under a rotating field, a uniaxial alignment of fibers was achieved. The alignment was successfully fixed by the photopolymerization of a UV-curable resin precursor used as matrix. A monodomain chiral nematic film was prepared from an aqueous suspension of nanofibers. Using a field modulator inserted in a homogeneous magnetic field, simultaneous alignment and patterning were achieved.     

Spin-Polarized Current in a Nonmagnetic Conductor and the Role of Electron–Electron Scattering

The influence of electron–electron scattering on the efficiency of certain methods for the injection and generation of spin–polarized current states in nonmagnetic conductors is discussed. We consider the effect of electron–electron collisions on the resistance to electric transport developing at the interface between a magnetic conductor (MC) and a nonmagnetic conductor (NMC). An essentially unbounded increase of the interfacial MC/NMC magnetoresistance with temperature is predicted.     

磁组装薄膜材料的结构及磁各向异性研究

在近平行方向磁场作用下,制备出有序平行线形阵列结构的纳米Fe3O4/氟碳树脂磁组装薄膜材料。利用偏光显微镜和紫外-可见-近红外分光光度计(UVPC)研究不同场强条件以及不同粉体含量对薄膜内部阵列结构的影响;采用振动样品磁强计(VSM)研究不同条件下磁组装薄膜的磁各向异性。结果表明:随着磁场强度增加,阵列变得越来越密集,随着Fe3O4含量的增加,线形阵列逐渐变粗;磁组装薄膜具有明显的磁各向异性,且随着磁场强度增加以及粉体的减少其等效磁各向异性常数逐渐增大。     

石墨烯及其复合材料在锂离子电池负极材料中的应用

石墨烯作为一种仅有单原子层厚度的新型碳材料,具有独特的结构和优异的电学、热学、力学等性能.石墨烯的产业化应用一直是国际上的研究热点.由于其高电导率、超大的比表面积、高化学稳定性等优异的物理和化学特性,石墨烯作为锂离子电池电极材料有着巨大的应用前景.综述了近5年来石墨烯及其复合材料在锂离子电池负极材料中应用的最新研究成果和进展,并对今后的研究工作进行了展望.     

Building floor analysis by the boundary element method

In this work, a boundary element formulation to analyse slabs reinforced by beams, combined or not to define a grid sub-system, is proposed. Kirchhoff s hypothesis is assumed for the plate elements. The beams elements are not required to be displayed over the plate surface, therefore eccentricity effects are taken into account. The formulation is derived by assuming a zoned body where beam elements are introduced by degenerating plate sub-regions. After finding properly a single reciprocity for the whole body, the required integral representations are derived. The integral representations derived for this complex structural element take into account the bending and stretching effects of booth structural elements working together. The standard equilibrium and compatibility conditions along interface are naturally imposed. Moreover, the amount of degrees of freedom required along the interfaces is substantially reduced, leading therefore to small and more accurate algebraic system of linear equations. Several examples are then shown to illustrate the accuracy of the formulation, comparing the obtained results with analytical and other numerical solutions.The authors wish to thank FAPESP (São Paulo State Foundation for Scientific Research) for the financial support and Prof. Selma Hissae Shimura da Nobrega by the collaboration to run the ADINA code.     

Stiffened plate bending analysis by the boundary element method

 In this work, the plate bending formulation of the boundary element method (BEM) based on the Kirchhoff's hypothesis, is extended to the analysis of stiffened elements usually present in building floor structures. Particular integral representations are derived to take directly into account the interactions between the beams forming grid and surface elements. Equilibrium and compatibility conditions are automatically imposed by the integral equations, which treat this composite structure as a single body. Two possible procedures are shown for dealing with plate domain stiffened by beams. In the first, the beam element is considered as a stiffer region requiring therefore the discretization of two internal lines with two unknowns per node. In the second scheme, the number of degrees of freedom along the interface is reduced by two by assuming that the cross-section motion is defined by three independent components only. Received 6 November 2000     

Engineering magnetic nanostructures with inverse hysteresis loops

Top-down lithography techniques allow the fabrication of nanostructured elements with novel spin configurations,which provide a new route to engineer and manipulate the magnetic response of sensors and electronic devices and understand the role of fundamental interactions in materials science.In this study, shallow nanostructure-pattemed thin films were designed to present inverse magnetization curves,i.e.,an anomalous magnetic mechanism characterized by a negative coercivity and negative remanence.This procedure involved a method for manipulating the spin configuration that yielded a negative coercivity after the patterning of a single material layer.Patterned NiFe thin films with trench depths between 15％-25％ of the total film thickness exhibited inverse hysteresis loops for a wide angular range of the applied field and the trench axis.A model based on two exchange-coupled subsystems accounts for the experimental results and thus predicts the conditions for the appearance of this magnetic behavior.The findings of the study not only advance our understanding of patterning effects and confined magnetic systems but also enable the local design and control of the magnetic response of thin materials with potential use in sensor engineering.