6,577 research outputs found
Computational study on microstructure evolution and magnetic property of laser additively manufactured magnetic materials
Additive manufacturing (AM) offers an unprecedented opportunity for the quick
production of complex shaped parts directly from a powder precursor. But its
application to functional materials in general and magnetic materials in
particular is still at the very beginning. Here we present the first attempt to
computationally study the microstructure evolution and magnetic properties of
magnetic materials (e.g. Fe-Ni alloys) processed by selective laser melting
(SLM). SLM process induced thermal history and thus the residual stress
distribution in Fe-Ni alloys are calculated by finite element analysis (FEA).
The evolution and distribution of the -Fe-Ni and FeNi phase
fractions were predicted by using the temperature information from FEA and the
output from CALculation of PHAse Diagrams (CALPHAD). Based on the relation
between residual stress and magnetoelastic energy, magnetic properties of SLM
processed Fe-Ni alloys (magnetic coercivity, remanent magnetization, and
magnetic domain structure) are examined by micromagnetic simulations. The
calculated coercivity is found to be in line with the experimentally measured
values of SLM-processed Fe-Ni alloys. This computation study demonstrates a
feasible approach for the simulation of additively manufactured magnetic
materials by integrating FEA, CALPHAD, and micromagnetics.Comment: 20 pages, 15 figure
A phase-field model of relaxor ferroelectrics based on random field theory
A mechanically coupled phase-field model is proposed for the first time to
simulate the peculiar behavior of relaxor ferroelectrics. Based on the random
field theory for relaxors, local random fields are introduced to characterize
the effect of chemical disorder. This generic model is developed from a
thermodynamic framework and the microforce theory and is implemented by a
nonlinear finite element method. Simulation results show that the model can
reproduce relaxor features, such as domain miniaturization, small remnant
polarization and large piezoelectric response. In particular, the influence of
random field strength on these features are revealed. Simulation results on
domain structure and hysteresis behavior are discussed and compared with
related experimental results.Comment: 8 figure
Multiscale examination of strain effects in Nd-Fe-B permanent magnets
We have performed a combined first-principles and micromagnetic study on the
strain effects in Nd-Fe-B magnets. First-principles calculations on Nd2Fe14B
reveal that the magnetocrystalline anisotropy (K) is insensitive to the
deformation along c axis and the ab in-plane shrinkage is responsible for the K
reduction. The predicted K is more sensitive to the lattice deformation than
what the previous phenomenological model suggests. The biaxial and triaxial
stress states have a greater impact on K. Negative K occurs in a much wider
strain range in the ab biaxial stress state. Micromagnetic simulations of
Nd-Fe-B magnets using first-principles results show that a 3-4% local strain in
a 2-nm-wide region near the interface around the grain boundaries and triple
junctions leads to a negative local K and thus decreases the coercivity by
~60%. The local ab biaxial stress state is more likely to induce a large loss
of coercivity. In addition to the local stress states and strain levels
themselves, the shape of the interfaces and the intergranular phases also makes
a difference in determining the coercivity. Smoothing the edge and reducing the
sharp angle of the triple regions in Nd-Fe-B magnets would be favorable for a
coercivity enhancement.Comment: 9 figure
Chlorido{N-[(diethylÂamino)ÂdimethylÂsilÂyl]anilido-κN}(N,N,N′,N′-tetraÂmethylÂethane-1,2-diamine-κ2 N,N′)cobalt(II)
In the title cobalt(II) compound, [Co(C12H21N2Si)Cl(C6H16N2)], the ethane-1,2-diamine donor molÂecule coordinÂates the metal atom in an N,N′-chelating mode, with Co—N distances of 2.136 (2) and 2.140 (3) Å. An anilide ligand connects to the CoII atom with a σ–bond, the Co—Nanilide distance being 1.931 (2) Å. The four-coordinate CoII atom demonstrates a slightly distorted tetraÂhedral geometry
A Self-Consistent Field Solution for Robust Common Spatial Pattern Analysis
The common spatial pattern analysis (CSP) is a widely used signal processing
technique in brain-computer interface (BCI) systems to increase the
signal-to-noise ratio in electroencephalogram (EEG) recordings. Despite its
popularity, the CSP's performance is often hindered by the nonstationarity and
artifacts in EEG signals. The minmax CSP improves the robustness of the CSP by
using data-driven covariance matrices to accommodate the uncertainties. We show
that by utilizing the optimality conditions, the minmax CSP can be recast as an
eigenvector-dependent nonlinear eigenvalue problem (NEPv). We introduce a
self-consistent field (SCF) iteration with line search that solves the NEPv of
the minmax CSP. Local quadratic convergence of the SCF for solving the NEPv is
illustrated using synthetic datasets. More importantly, experiments with
real-world EEG datasets show the improved motor imagery classification rates
and shorter running time of the proposed SCF-based solver compared to the
existing algorithm for the minmax CSP
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