In this work, we present a second-order nonuniform time-stepping scheme for the time-fractional Allen-Cahn equation. We show that the proposed scheme preserves the discrete maximum principle, and by using the convolut...
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Stress evolution during solidification is simulated by using the phase field model. The coupling equations for phase transformation, temperature and stress/strain are derived based on thermo-dynamical theory including...
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This paper discusses a fully decentralized algorithm able to control the morphology of a modular robot, consisting of many identical modules, according to the environment encountered. One of the significant features o...
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ISBN:
(纸本)0780384636
This paper discusses a fully decentralized algorithm able to control the morphology of a modular robot, consisting of many identical modules, according to the environment encountered. One of the significant features of our approach is that we explicitly exploit "emergent phenomena" stemming from the interaction between control and mechanical dynamics in order to control the morphology in real time. To this end, we particularly focus on a "functional material" and a "mutual entrainment", the former of which is used as a connection mechanism between the modules, and the latter of which plays as the core of the control mechanism for the generation of locomotion. Simulation results indicate that the proposed algorithm can induce "protoplasmic streaming", which allows us to successfully control the morphology of modular robot in real time according to the situation without losing the coherence of the entire system.
A theoretical investigation of the electromagnetic responses of a slanted chiral sculptured thin film (STF) to both plane waves and finite sources (such as optical beams and dipolar sources) was carried out. First, a ...
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A theoretical investigation of the electromagnetic responses of a slanted chiral sculptured thin film (STF) to both plane waves and finite sources (such as optical beams and dipolar sources) was carried out. First, a rigorous coupled-wave analysis was implemented with algorithmic stability to obtain the planewave response;second, the angular-spectrum decomposition of the incident field was exploited to represent the reflected and the transmitted fields. The most prominent feature of the planewave responses is the circular Bragg phenomenon which is partially specular and angularly asymmetric for slanted, but nor for unslanted, chiral STFs. Correspondingly, the far-field radiation pattern of a Beltrami source configuration is spatially asymmetric in the presence of a slanted chiral STF. Also, optical beams are laterally shifted on reflection by chiral STFs. Two types of lateral shifts of Gaussian beams were studied: one is related to the Bragg reflection of co-handed beams, and the other is the Goos-Hänchen shift on total reflection.
Numerical methods for solving nonlinear optimization problems have been developed for over 50 years. Has this field reached maturity? What are the current research frontiers and ongoing challenges? These are questions...
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ISBN:
(纸本)0898715598
Numerical methods for solving nonlinear optimization problems have been developed for over 50 years. Has this field reached maturity? What are the current research frontiers and ongoing challenges? These are questions that this paper attempts to clarify, if not fully answer. The discussion does not explore the technical intricacies of nonlinear optimization techniques, but instead focusses on concepts and research practice. The field's vibrant nature is illustrated by a number of applications, such as adaptive lens design for spectacles, the piloting of injection of dangerous drugs to patients, the identification of parameters in biochemical models of neurons, food sterilisation or animation techniques for video games.
Large-scale, experiments of pressure vessels performed at the Oak National Laboratory (ORNL)1 in the mid 1980s validated the applicability of the linear-elastic fracture mechanics (LEFM) computational methodology for ...
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Large-scale, experiments of pressure vessels performed at the Oak National Laboratory (ORNL)1 in the mid 1980s validated the applicability of the linear-elastic fracture mechanics (LEFM) computational methodology for application to fracture analysis of reactor pressure vessels (RPVs) in nuclear power plants. The current federal regulations to insure that nuclear RPVs maintain their structural integrity, when subjected to transients such as pressurized thermal shock (PTS) events, were derived in the early-mid 1980s from a comprehensive computational methodology of which LEFM is a major element. Recently, the United States Nuclear Regulatory Commission (USNRC) has conducted the PTS re-evaluation project that has the objective to establish a technical basis for a potential relaxation to the current PTS regulations which could have profound implications for plant license-extension considerations. The PTS re-evaluation project has primarily consisted of the development and application of an updated risk-based computational methodology that has been implemented into the Fracture Analysis of Vessels: Oak Ridge (FAVOR) computer code. LEFM continues to be a major element of the updated computational methodology. As part of the PTS re-evaluation program, there has been an extensive effort to validate that FAVOR has an accurate implementation of the LEFM methodology. This effort has consisted of the successful benchmarking of thermal analysis, stress analysis, and LEFM fracture analysis results between FAVOR and ABAQUS, a commercial general-purpose finite element computer code that has fracture mechanics capabilities, for a range of transient descriptions. The NRC has also participated in international round-robin benchmarking exercises in which FAVOR-generated solutions to well-specified PTS problems have been compared to solutions generated by other research institutions. A more fundamental aspect of the ongoing validation of FAVOR is demonstration that FAVOR can be used to
Conventional strain-based mechanics theory does not account for contributions from strain gradients. Failure to include the strain gradient contributions can lead to underestimates of stresses and size-dependent behav...
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Conventional strain-based mechanics theory does not account for contributions from strain gradients. Failure to include the strain gradient contributions can lead to underestimates of stresses and size-dependent behaviors in small-scaled structure. This paper focus on the structural size effects on torsion of cylinders. The torsional stiffness of cylinders can be higher than conventional expectation when the cylinder size is in the nanometer - or micron-scale. Following the Saint-Venant theory of torsion, we established the equation of torsion in terms of the warping function on the basis of the nano-mechanical theory of elasticity. The torsional equations contain two higher order material length scale parameters and two conventional Lame constants. The equilibrium equation is a fourth order partial differential equation which can be reduced to two second order equations. Two formulations in terms of pseudo warping function and stress function are presented. Closed-form solutions for circular and thin wall section and series solutions for rectangular microbars have been obtained. The total torque depends only on the stresses conjugated to the strain and is only implicitly dependent on the higher order stress metrics. The solution reveals that the torsional rigidity is dependent on the higher order length scale parameters and strain gradients and increases asymptotically upward when the cylinder size is reduced to the size of the higher order length scale material parameters. The increase is most marked for thin walled cylinders, stiffening to more then 10 times the conventional value when the cylinder size is near that of the higher order length scaled parameters.
Color histograms are effective for representing color visual features. However, the high dimensionality of feature vectors results in high computational cost. Several transformations, including singular value decompos...
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Color histograms are effective for representing color visual features. However, the high dimensionality of feature vectors results in high computational cost. Several transformations, including singular value decomposition (SVD) and principal component analysis (PCA), have been proposed to reduce the dimensionality. In PCA, the dimensionality reduction is achieved by projecting the data to a subspace which contains most of the variance. As a common observation, the PCA basis function with the lowest frquency accounts for the highest variance. Therefore, the PCA subspace may not be the optimal one to represent the intrinsic features of data. In this paper, we apply independent component analysis (ICA) to extract the features in color histograms. PCA is applied to reduce the dimensionality and then ICA is performed on the low-dimensional PCA subspace. The experimental results show that the proposed method (1) significantly reduces the feature dimensions compared with the original color histograms and (2) outperforms other dimension reduction techniques, namely the method based on SVD of quadratic matrix and PCA, in terms of retrieval accuracy.
The implementation of a three-dimensional (3D) finite difference time domain (FDTD) scheme for simulating wave propagation in surface plasmon polaritons bandgap (SPPBG) waveguides, was investigated. An SPPBG structure...
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The implementation of a three-dimensional (3D) finite difference time domain (FDTD) scheme for simulating wave propagation in surface plasmon polaritons bandgap (SPPBG) waveguides, was investigated. An SPPBG structure resulted on introducing a doubly periodic perturbation in planar dielectric-plasma interface. In the direction normal to dielectric-plasma interface, the plasma half space was truncated by a perfect electrically conducting plate. The results show that straight SPPBG waveguide section allows signals to propagate with small losses.
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