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Yang Xiang - One of the best experts on this subject based on the ideXlab platform.
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dislocation dynamics formulation for self climb of dislocation loops by vacancy pipe diffusion
International Journal of Plasticity, 2019Co-Authors: Xiaohua Niu, Yang XiangAbstract:Abstract It has been shown in experiments that self-climb of prismatic dislocation loops by pipe diffusion plays important roles in their dynamical behaviors, e.g., coarsening of prismatic loops upon annealing, as well as the physical and mechanical properties of materials with irradiation. In this paper, we show that the dislocation dynamics self-climb formulation that we derived in (Niu et al., 2017) is able to quantitatively describe the properties of self-climb of prismatic loops that were observed in experiments and atomistic simulations. This dislocation dynamics formulation applies to self-climb by pipe diffusion for any configurations of dislocations, and is able to recover the available models in the literature for rigid self-climb motion of small prismatic loops. We also present implementation method of this self-climb formulation. Simulations performed show evolution, translation and coalescence of prismatic loops as well as prismatic loops driven by an edge dislocation by self-climb motion and the Elastic Interaction between them. These results are in excellent agreement with available experimental and atomistic results. We have also performed systematic analyses of the behaviors of a prismatic loop under the Elastic Interaction with an infinite, straight edge dislocation by motions of self-climb and glide.
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continuum approximation of the peach koehler force on dislocations in a slip plane
Journal of The Mechanics and Physics of Solids, 2009Co-Authors: Yang XiangAbstract:Abstract We derive a continuum model for the Peach–Koehler force on dislocations in a slip plane. To represent the dislocations, we use the disregistry across the slip plane, whose gradient gives the density and direction of the dislocations. The continuum model is derived rigorously from the Peach–Koehler force on dislocations in a region that contains many dislocations. The resulting continuum model can be written as the variation of an Elastic energy that consists of the contribution from the long-range Elastic Interaction of dislocations and a correction due to the line tension effect.
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an active contour model for image segmentation based on Elastic Interaction
Journal of Computational Physics, 2006Co-Authors: Yang Xiang, Albert C S ChungAbstract:The task of image segmentation is to partition an image into non-overlapping regions based on intensity or textural information. The active contour methods provide an effective way for segmentation, in which the boundaries of the objects are detected by evolving curves. In this paper, we propose a new edge-based active contour method, which uses a long-range and orientation-dependent Interaction between image boundaries and the moving curves while maintaining the edge fidelity. As a result, this method has a large capture range, and is able to detect sharp features of the images. The velocity field for the moving curves generated by this Elastic Interaction is calculated using the fast Fourier transform (FFT) method. Level set representation is used for the moving curves so that the topological changes during the evolution are handled automatically. This new method is derived based on the Elastic Interaction between line defects in solids (dislocations). Although it is derived originally for two dimensional segmentation, we also extend it to three dimensions. The features of the new method are examined by experiments on both synthetic images and medical images of blood vessels. Comparisons are made with the existing active contour methods.
Yongjiang Guo - One of the best experts on this subject based on the ideXlab platform.
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dark solitons Interaction for a 2 1 dimensional nonlinear schrodinger equation in the heisenberg ferromagnetic spin chain
Superlattices and Microstructures, 2016Co-Authors: Xuehui Zhao, Bo Tian, Deyin Liu, Jun Chai, Yongjiang GuoAbstract:Abstract Under investigation in this paper is a (2 + 1)-dimensional nonlinear Schrodinger equation in the Heisenberg ferromagnetic spin chain. Via the symbolic computation and Hirota method, the bilinear forms, dark one-, two- and three-soliton solutions are derived. Propagation and Interaction for the dark solitons are illustrated graphically: Amplitude and shape of the dark one soliton keep invariant during the propagation, which imply the transport of the energy is stable in the (2 + 1)-dimensional Heisenberg ferromagnetic spin chain. Through the asymptotic analysis, Elastic and inElastic Interactions between the dark two solitons are discussed. For the Elastic Interaction, oblique, head-on and overtaking Interactions between the dark two solitons are displayed, where the amplitudes and shapes remain unchanged after Interaction except for certain phase shifts. However, in the area of the inElastic Interaction, amplitudes of the dark two solitons vanish after Interaction. For the Elastic Interaction among the dark three solitons, oblique, overtaking and Interaction among the dark two parallel solitons and a single one are presented, whose characteristics are similar to those of the dark two solitons. InElastic-Elastic Interaction is investigated as well. Linear stability analysis is used to analyze modulation instability and prove the dark solitons are stable.
Y.w. Liu - One of the best experts on this subject based on the ideXlab platform.
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electro Elastic Interaction between a moving screw dislocation and collinear interfacial rigid lines
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2006Co-Authors: Qihong Fang, Y.w. LiuAbstract:Abstract This paper attempts to investigate the problem for the electro-Elastic Interaction between a piezoelectric moving dislocation and interfacial collinear rigid lines under combined longitudinal shear and in-plane electric field. Using Riemann–Schwarz's symmetry principle integrated with the analysis singularity of complex functions, we present the general Elastic solution of this problem and the closed form solution for interface containing single rigid line. The expressions of electro-Elastic fields and image force acting on moving dislocation are derived explicitly. The results show that the velocity of moving dislocation has significant effect on the image force. The present solutions contain previously known results as the special cases.
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size dependent Elastic Interaction of a screw dislocation with a circular nano inhomogeneity incorporating interface stress
Scripta Materialia, 2006Co-Authors: Y.w. LiuAbstract:Effect of interface stress upon the Interaction between a screw dislocation and a nano-inhomogeneity is investigated. By using the complex variable method, the image force acting on the screw dislocation is obtained. The results indicate that the influence of interface stress on the motion of the dislocation near the inhomogeneity becomes significant when the radius of the inhomogeneity is reduced to nanometer scale, leading to that the normalized image force depends on the inhomogeneity size which differs from the size-independent classical solution.
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electro Elastic Interaction between a piezoelectric screw dislocation and circular interfacial rigid lines
International Journal of Solids and Structures, 2003Co-Authors: Y.w. Liu, Qihong FangAbstract:Abstract The electro-Elastic Interaction between a piezoelectric screw dislocation located either outside or inside inhomogeneity and circular interfacial rigid lines under anti-plane mechanical and in-plane electrical loads in linear piezoelectric materials is dealt with in the framework of linear Elastic theory. Using Riemann–Schwarz’s symmetry principle integrated with the analysis of singularity of complex functions, the general solution of this problem is presented in this paper. For a special example, the closed form solutions for electro-Elastic fields in matrix and inhomogeneity regions are derived explicitly when interface containing single rigid line. Applying perturbation technique, perturbation stress and electric displacement fields are obtained. The image force acting on piezoelectric screw dislocation is calculated by using the generalized Peach–Koehler formula. As a result, numerical analysis and discussion show that soft inhomogeneity can repel screw dislocation in piezoelectric material due to their intrinsic electro-mechanical coupling behavior and the influence of interfacial rigid line upon the image force is profound. When the radian of circular rigid line reaches extensive magnitude, the presence of interfacial rigid line can change the Interaction mechanism.
Jinwei Yang - One of the best experts on this subject based on the ideXlab platform.
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dark solitonic Interaction and conservation laws for a higher order 2 1 dimensional nonlinear schrodinger type equation in a heisenberg ferromagnetic spin chain with bilinear and biquadratic Interaction
Annals of Physics, 2015Co-Authors: Qimin Wang, Yitian Gao, Bingqing Mao, Zhe Gao, Jinwei YangAbstract:Abstract In this paper, a higher-order ( 2 + 1 ) -dimensional nonlinear Schrodinger-type equation is investigated, which describes the nonlinear spin dynamics of the ( 2 + 1 ) -dimensional Heisenberg ferromagnetic spin chain with bilinear and biquadratic Interaction. Lax pair and infinite-number conservation laws are constructed, which could prove the existence of the multi-soliton solutions. Via the auxiliary function, bilinear forms and dark-soliton solutions are derived. Properties and Interaction patterns for the dark solitons are investigated: (i) Effects on the dark solitons arising from the bilinear Interaction, biquadratic Interaction and lattice parameter are discussed. (ii) Through the asymptotic analysis, Elastic and inElastic Interaction between the two solitons is discussed analytically and graphically, respectively. Due to the Elastic Interaction, amplitudes and velocities of the two dark solitons remain unchanged with the distortion of the Interaction area, except for certain phase shifts. However, in virtue of the inElastic Interaction, amplitudes of the dark solitons reduce to zero, without the distortion. (iii) Elastic Interaction among the three dark solitons is investigated, which implies that the properties of the Elastic Interaction among the three are similar to that between the two, except for the more complicated distortion. InElastic–Elastic Interaction is also investigated, which implies that the Interaction between the inElastic region and the dark soliton is Elastic. (iv) Linear stability analysis is proposed, which is used to analyze the properties of modulation instability and proves that the dark solitons are modulationally stable.
Seiji Miyashita - One of the best experts on this subject based on the ideXlab platform.
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tutorial on Elastic Interaction models for multistep spin crossover transitions
Journal of Applied Physics, 2021Co-Authors: Masamichi Nishino, Yogendra Singh, Kamel Boukheddaden, Seiji MiyashitaAbstract:Spin-crossover (SC) compounds are fascinating materials that exhibit colorful phase transitions induced by temperature, pressure, photoirradiation, etc. From the microscopic point of view, the electronic (spin) state of a molecule changes between the low-spin (LS) and high-spin (HS) states by such stimuli, and a variation of the molecular size follows through the vibronic coupling between the electronic state and structure in the molecule. This causes an Elastic distortion and then an Elastic Interaction. The Elastic Interaction is essential in cooperative properties of SC phenomena. In this paper, we present a tutorial study on Elastic Interaction models for SC phenomena, which are the recent trend of modeling of SC compounds. We focus on multistep transitions, which are a topic of SC phenomena. We analyze the phase diagrams including the metastable phases for several SC systems, in which antiferromagnetic-like and ferrimagnetic-like phases are associated in addition to the LS and HS phases. Making use of the phase diagrams, we show various patterns of thermally induced SC transition with steps. We also investigate SC transitions with steps in a core-shell SC nanocomposite composed of two different SC compounds. We focus on two cases: the core has a lower transition temperature than the shell, and the core has a higher transition temperature. We show characteristic features of difference in the two systems.
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nontrivial phase diagram for an Elastic Interaction model of spin crossover materials with antiferromagnetic like short range Interactions
APS, 2018Co-Authors: Masamichi Nishino, Seiji Miyashita, Per Arne RikvoldAbstract:We study the phase diagram of an Elastic Interaction model for spin crossover (SC) materials with antiferromagnetic-like short-range Interactions. In this model, the interplay between the short-range Interaction and the long-range Interaction of Elastic origin causes complex phase transitions. For relatively weak Elastic Interactions, the phase diagram is characterized by tricritical points, at which antiferromagnetic (AF) -like and ferromagnetic (F) -like spinodal lines and a critical line merge. On the other hand, for relatively strong Elastic Interactions, unusual ``horn structures,'' which are surrounded by the F-like spinodal lines, disorder (D) spinodal lines, and the critical line, are realized at higher temperatures. These structures are similar to those obtained in our previous study [Phys. Rev. B 93, 064109 (2016)] of an Ising antiferromagnet with infinite-range ferromagnetic Interactions, and we find universal features caused by the interplay between the competing short-range and long-range Interactions. The long-range Interaction of Elastic origin is irrelevant (inessential) for the critical line. In contrast, the AF-like, F-like, and D spinodal lines result from the long-range Interaction of Elastic origin. This difference causes qualitatively different features of domain formation or nucleation of the new phase: clustering occurs in the former case, while clustering is absent in the latter. Based on the phase diagrams, we discuss the patterns and clustering features of two-step SC transitions, in which the AF-like phase is realized in the intermediate temperature region.
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Elastic Interaction among transition metals in one dimensional spin crossover solids
Physical Review B, 2007Co-Authors: Kamel Boukheddaden, Seiji Miyashita, Masamichi NishinoAbstract:We present an exact examination of a one-dimensional (1D) spin-phonon model describing the thermodynamical properties of spin-crossover (SC) solids. This model has the advantage of giving a physical mechanism for the Interaction between the SC units. The origin of the Interaction comes from the fact that the Elastic constant of the spring linking two atoms depends on their electronic states. This leads to local variation of the Elastic constant. Up to now, all the statistical studies of this model have been performed in the frame of the mean-field (MF) approach, which is not adequate to describe 1D systems with short-range Interactions. An alternative method, based on the variational approach and taking into account the short-range correlations between neighboring molecules, was also suggested, but it consists in an extension of the previous MF approximation. Here, we solve exactly this Hamiltonian in the frame of classical statistical mechanics using the transfer-matrix technique. The temperature dependence of the high spin fraction and that of the total energy are obtained analytically. Our results clearly show that there is a clear tendency to a sharp transition when we tune the Elastic constants adequately, which indicates that first-order phase transition takes place at higher dimensions. In addition, we demonstrate the existence of an interesting isomorphism between the present model and Ising model under effective Interaction and effective ligand field energy, in which both depend linearly on temperature and both come from the phonon contribution. We have also studied the effect of the pressure (the tension) on the thermodynamical properties of the high spin (HS) fraction and have found a nontrivial pressure effect that while for weak tension values, the low spin state is stabilized for the pressure above a threshold value, it enhances the Interaction between the HS states. Finally, we have also introduced Elastic Interactions between the chains. Treating exactly (in mean field) the intrachain (interchain) contributions, we found that our model leads us to obtain first-order spin transitions when both short- and long-range Interactions are ferroElastic. We show also that competing (antiferroElastic short-range and ferroElastic long-range) Interactions between spin-state ions reproduce qualitatively the two-step-like spin-crossover transitions.