3,046 research outputs found
A finite-difference program for stresses in anisotropic, layered plates in bending
The interlaminar stresses induced in a layered laminate that is bent into a cylindrical surface are studied. The laminate is modeled as a continuum, and the resulting elasticity equations are solved using the finite difference method. The report sets forth the mathematical framework, presents some preliminary results, and provides a listing and explanation of the computer program. Significant among the results are apparent symmetry relationships that will reduce the numerical size of certain problems and an interlaminar stress behavior having a sharp rise at the free edges
Nanoscale magnetic structure of ferromagnet/antiferromagnet manganite multilayers
Polarized Neutron Reflectometry and magnetometry measurements have been used
to obtain a comprehensive picture of the magnetic structure of a series of
La{2/3}Sr{1/3}MnO{3}/Pr{2/3}Ca{1/3}MnO{3} (LSMO/PCMO) superlattices, with
varying thickness of the antiferromagnetic (AFM) PCMO layers (0<=t_A<=7.6 nm).
While LSMO presents a few magnetically frustrated monolayers at the interfaces
with PCMO, in the latter a magnetic contribution due to FM inclusions within
the AFM matrix was found to be maximized at t_A~3 nm. This enhancement of the
FM moment occurs at the matching between layer thickness and cluster size,
where the FM clusters would find the optimal strain conditions to be
accommodated within the "non-FM" material. These results have important
implications for tuning phase separation via the explicit control of strain.Comment: 4 pages, submitted to PR
Berry's phase contribution to the anomalous Hall effect of gadolinium
When conduction electrons are forced to follow the local spin texture, the
resulting Berry phase can induce an anomalous Hall effect (AHE). In gadolinium,
as in double-exchange magnets, the exchange interaction is mediated by the
conduction electrons and the AHE may therefore resemble that of chromium
dioxide and other metallic double-exchange ferromagnets. The Hall resistivity,
magnetoresistance, and magnetization of single crystal gadolinium were measured
in fields up to 30 T. Measurements between 2 K and 400 K are consistent with
previously reported data. A scaling analysis for the Hall resistivity as a
function of the magnetization suggests the presence of a Berry's-phase
contribution to the anomalous Hall effect.Comment: 6 pages, 7 figures, submitted to Phys. Rev.
Initial recommendations of MOOCs characteristics for academic discipline clusters
Massive Open Online Courses (known as MOOCs) have been introduced as an extensive and pervasive learning style in order to increase students’ performance. Many academics and students in Malaysian higher education institutions have begun to show their interest in applying MOOCs to deliver course material or conduct distance education in an innovative way. However, there are no guidelines available to assist the application of MOOCs; in particular, there are no guidelines to help academics develop their own MOOCs based on their area of expertise. In the education domain, usually these areas of expertise are arranged according to certain groups referred to as academic discipline clusters. This study investigates existing MOOCs characteristics and recommends specific characteristics in relation to academic discipline clusters. Content analysis was carried out by exploring MOOCs characteristics implemented successfully in six universities worldwide. This included an examination of the platforms used and the courses that applied MOOCs. Based on the results, the desirable characteristics of MOOCs are recommended with regard to academic discipline clusters, with the Universiti Teknologi Malaysia used as a case study
Magnetocrystalline anisotropic effect in GdCoFeAsO ()
From a systematic study of the electrical resistivity , magnetic
susceptibility , isothermal magnetization and the specific
heat , a temperature-magnetic field (-) phase diagram has been
established for GdCoFeAsO ( and ) polycrystalline
compounds. GdCoAsO undergoes two long-range magnetic transitions: ferromagnetic
(FM) transition of Co electrons () and
antiferromagnetic (AFM) transition of Gd electrons
(). For the Fe-doped sample (), an extra
magnetic reorientation transition takes place below ,
which is likely associated with Co moments. The two magnetic species of Gd and
Co are coupled antiferromagnetically to give rise to ferrimagnetic (FIM)
behavior in the magnetic susceptibility. Upon decreasing the temperature (), the magnetocrystalline anisotropy breaks up the FM
order of Co by aligning the moments with the local easy axes of the various
grains, leading to a spin reorientation transition at
. By applying a magnetic field,
monotonically decreases to lower temperatures, while
the is relatively robust against the external field.
On the other hand, the applied magnetic field pulls the magnetization of grains
from the local easy direction to the field direction via a first-order
reorientation transition, with the transition field () increasing
upon cooling the temperature.Comment: accepted by physical Review B 6 figures and 7 page
Doping of inorganic materials in microreactors – preparation of Zn doped Fe₃O₄ nanoparticles
Microreactor systems are now used more and more for the continuous production of metal nanoparticles and metal oxide nanoparticles owing to the controllability of the particle size, an important property in many applications. Here, for the first time, we used microreactors to prepare metal oxide nanoparticles with controlled and varying metal stoichiometry. We prepared and characterised Zn-substituted Fe₃O₄ nanoparticles with linear increase of Zn content (ZnxFe₃−xO₄ with 0 ≤ x ≤ 0.48), which causes linear increases in properties such as the saturation magnetization, relative to pure Fe₃O₄. The methodology is simple and low cost and has great potential to be adapted to the targeted doping of a vast array of other inorganic materials, allowing greater control on the chemical stoichiometry for nanoparticles prepared in microreactors
A -Vertex Kernel for Maximum Internal Spanning Tree
We consider the parameterized version of the maximum internal spanning tree
problem, which, given an -vertex graph and a parameter , asks for a
spanning tree with at least internal vertices. Fomin et al. [J. Comput.
System Sci., 79:1-6] crafted a very ingenious reduction rule, and showed that a
simple application of this rule is sufficient to yield a -vertex kernel.
Here we propose a novel way to use the same reduction rule, resulting in an
improved -vertex kernel. Our algorithm applies first a greedy procedure
consisting of a sequence of local exchange operations, which ends with a
local-optimal spanning tree, and then uses this special tree to find a
reducible structure. As a corollary of our kernel, we obtain a deterministic
algorithm for the problem running in time
Finite Element Analysis of Poroelastic Composites Undergoing Thermal and Gas Diffusion
A theory for time-dependent thermal and gas diffusion in mechanically time-rate-independent anisotropic poroelastic composites has been developed. This theory advances previous work by the latter two authors by providing for critical transverse shear through a three-dimensional axisymmetric formulation and using it in a new hypothesis for determining the Biot fluid pressure-solid stress coupling factor. The derived governing equations couple material deformation with temperature and internal pore pressure and more strongly couple gas diffusion and heat transfer than the previous theory. Hence the theory accounts for the interactions between conductive heat transfer in the porous body and convective heat carried by the mass flux through the pores. The Bubnov Galerkin finite element method is applied to the governing equations to transform them into a semidiscrete finite element system. A numerical procedure is developed to solve the coupled equations in the space and time domains. The method is used to simulate two high temperature tests involving thermal-chemical decomposition of carbon-phenolic composites. In comparison with measured data, the results are accurate. Moreover unlike previous work, for a single set of poroelastic parameters, they are consistent with two measurements in a restrained thermal growth test
A Renormalization Proof of the KAM Theorem for Non-Analytic Perturbations
We shall use a Renormalization Group (RG) scheme in order to prove the
classical KAM result in the case of a non-analytic perturbation (the latter
will be assumed to have continuous derivatives up to a sufficiently large
order). We shall proceed by solving a sequence of problems in which the
perturbations are analytic approximations of the original one. We shall finally
show that the sequence of the approximate solutions will converge to a
differentiable solution of the original problem.Comment: 33 pages, no figure
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