3,567 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
AON: Towards Arbitrarily-Oriented Text Recognition
Recognizing text from natural images is a hot research topic in computer
vision due to its various applications. Despite the enduring research of
several decades on optical character recognition (OCR), recognizing texts from
natural images is still a challenging task. This is because scene texts are
often in irregular (e.g. curved, arbitrarily-oriented or seriously distorted)
arrangements, which have not yet been well addressed in the literature.
Existing methods on text recognition mainly work with regular (horizontal and
frontal) texts and cannot be trivially generalized to handle irregular texts.
In this paper, we develop the arbitrary orientation network (AON) to directly
capture the deep features of irregular texts, which are combined into an
attention-based decoder to generate character sequence. The whole network can
be trained end-to-end by using only images and word-level annotations.
Extensive experiments on various benchmarks, including the CUTE80,
SVT-Perspective, IIIT5k, SVT and ICDAR datasets, show that the proposed
AON-based method achieves the-state-of-the-art performance in irregular
datasets, and is comparable to major existing methods in regular datasets.Comment: Accepted by CVPR201
USCID fourth international conference
Presented at the Role of irrigation and drainage in a sustainable future: USCID fourth international conference on irrigation and drainage on October 3-6, 2007 in Sacramento, California.Includes bibliographical references.Studying the impact of microtopography on irrigation performance is important for improving the management of basin irrigation systems. However, the limitation of field experiments will restrict the studies on the impact of microtopography spatial variability on basin irrigation performance. Thus, firstly this paper analyzed the spatial variability characteristics of field-measured Surface Relative Elevations (SRE). The correlations between the field geometry parameters and the spatial variability characteristics of SRE were evaluated, and the estimation methods for parameters of the semi-variogram of SRE were determined. Secondly, a microtopography stochastic generating model was built up based on the Monte-Carlo and the Kriging interpolation techniques. Lastly, the effect of spatial variability of microtopography on the performance of basin irrigation was evaluated by using of the numerical simulation model. Results showed that the microtopography undulation degree and the spatial distribution difference of undulation location had obvious effect on the basin irrigation performance. The average irrigation depth (Z'avg), corresponding to the water just cover the whole basin surface is increased while the irrigation application efficiency (Ea) and the irrigation uniformity (CU) is decreased when the field elevation non-uniformity, measured by the standard deviation of SRE (Sd) is increased. The effect of spatial distribution of undulation location on the irrigation performance was dependent upon the microtopography undulation degree, when Sd is less than 2cm the impacts can be neglected, while Sd is greater than 2cm, the influence should be considered
Phase-field modeling of paramagnetic austenite-ferromagnetic martensite transformation coupled with mechanics and micromagnetics
A three-dimensional phase-field model is proposed for simulating the magnetic
martensitic phase transformation. The model considers a paramagnetic cubic
austenite to ferromagnetic tetragonal martensite transition, as it occurs in
magnetic Heusler alloys like Ni2 MnGa, and is based on a Landau 2-3-4
polynomial with temperature dependent coefficients. The
paramagnetic-ferromagnetic transition is recaptured by interpolating the
micromagnetic energy as a function of the order parameter for the ferroelastic
domains. The model is numerically implemented in real space by finite element
(FE) method. FE simulations in the martensitic state show that the model is
capable to correctly recapture the ferroelastic and -magnetic microstructures,
as well as the influence of external stimuli. Simulation results indicate that
the paramagnetic austenite to ferromagnetic martensite transition shifts
towards higher temperatures when a magnetic field or compressive stress is
applied. The dependence of the phase transition temperature shift on the
strength of the external stimulus is uncovered as well. Simulation of the phase
transition in magnetocaloric materials is of high interest for the development
of energy-efficient magnetocaloric cooling devices
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