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Kimlien Nguyen - One of the best experts on this subject based on the ideXlab platform.
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fast and accurate calculation of myocardial t1 and t2 values using deep learning Bloch Equation simulations deepbless
Magnetic Resonance in Medicine, 2020Co-Authors: Jiaxin Shao, Vahid Ghodrati, Kimlien NguyenAbstract:PURPOSE To propose and evaluate a deep learning model for rapid and accurate calculation of myocardial T1 /T2 values based on a previously proposed Bloch Equation simulation with slice profile correction (BLESSPC) method. METHODS Deep learning Bloch Equation simulations (DeepBLESS) models are proposed for rapid and accurate T1 estimation for the MOLLI T1 mapping sequence with balanced SSFP readouts and T1 /T2 estimation for a radial simultaneous T1 and T2 mapping (radial T1 -T2 ) sequence. The DeepBLESS models were trained separately based on simulated radial T1 -T2 and MOLLI data, respectively. The DeepBLESS T1 -T2 estimation accuracy was evaluated based on simulated data with different noise levels. The DeepBLESS model was compared with BLESSPC in simulation, phantom, and in vivo studies for the MOLLI sequence at 1.5 T and radial T1 -T2 sequence at 3 T. RESULTS After DeepBLESS was trained, in phantom studies, DeepBLESS and BLESSPC achieved similar accuracy and precision in T1 -T2 estimations for both MOLLI and radial T1 -T2 (P > .05). For in vivo, DeepBLESS and BLESSPC generated similar myocardial T1 /T2 values for radial T1 -T2 at 3 T (T1 : 1366 ± 31 ms for both methods, P > .05; T2 : 37.4 ms ± 0.9 ms for both methods, P > .05), and similar myocardial T1 values for the MOLLI sequence at 1.5 T (1044 ± 20 ms for both methods, P > .05). DeepBLESS generated a T1 /T2 map in less than 1 second. CONCLUSION The DeepBLESS model offers an almost instantaneous approach for estimating accurate T1 /T2 values, replacing BLESSPC for both MOLLI and radial T1 -T2 sequences, and is promising for multiparametric mapping in cardiac MRI.
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fast and accurate calculation of myocardial t 1 and t 2 values using deep learning Bloch Equation simulations deepbless
Magnetic Resonance in Medicine, 2020Co-Authors: Jiaxin Shao, Vahid Ghodrati, Kimlien NguyenAbstract:Purpose To propose and evaluate a deep learning model for rapid and accurate calculation of myocardial T1 /T2 values based on a previously proposed Bloch Equation simulation with slice profile correction (BLESSPC) method. Methods Deep learning Bloch Equation simulations (DeepBLESS) models are proposed for rapid and accurate T1 estimation for the MOLLI T1 mapping sequence with balanced SSFP readouts and T1 /T2 estimation for a radial simultaneous T1 and T2 mapping (radial T1 -T2 ) sequence. The DeepBLESS models were trained separately based on simulated radial T1 -T2 and MOLLI data, respectively. The DeepBLESS T1 -T2 estimation accuracy was evaluated based on simulated data with different noise levels. The DeepBLESS model was compared with BLESSPC in simulation, phantom, and in vivo studies for the MOLLI sequence at 1.5 T and radial T1 -T2 sequence at 3 T. Results After DeepBLESS was trained, in phantom studies, DeepBLESS and BLESSPC achieved similar accuracy and precision in T1 -T2 estimations for both MOLLI and radial T1 -T2 (P > .05). For in vivo, DeepBLESS and BLESSPC generated similar myocardial T1 /T2 values for radial T1 -T2 at 3 T (T1 : 1366 ± 31 ms for both methods, P > .05; T2 : 37.4 ms ± 0.9 ms for both methods, P > .05), and similar myocardial T1 values for the MOLLI sequence at 1.5 T (1044 ± 20 ms for both methods, P > .05). DeepBLESS generated a T1 /T2 map in less than 1 second. Conclusion The DeepBLESS model offers an almost instantaneous approach for estimating accurate T1 /T2 values, replacing BLESSPC for both MOLLI and radial T1 -T2 sequences, and is promising for multiparametric mapping in cardiac MRI.
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myocardial t1 mapping at 3 0 tesla using an inversion recovery spoiled gradient echo readout and Bloch Equation simulation with slice profile correction blesspc t1 estimation algorithm
Journal of Magnetic Resonance Imaging, 2016Co-Authors: Jiaxin Shao, Stanislas Rapacchi, Kimlien NguyenAbstract:Background To develop an accurate and precise myocardial T1 mapping technique using an inversion recovery spoiled gradient echo readout at 3.0 Tesla (T). Theory and Methods The modified Look-Locker inversion-recovery (MOLLI) sequence was modified to use fast low angle shot (FLASH) readout, incorporating a BLESSPC (Bloch Equation Simulation with Slice Profile Correction) T1 estimation algorithm, for accurate myocardial T1 mapping. The FLASH-MOLLI with BLESSPC fitting was compared with different approaches and sequences with regards to T1 estimation accuracy, precision and image artifact based on simulation, phantom studies, and in vivo studies of 10 healthy volunteers and three patients at 3.0 Tesla. Results The FLASH-MOLLI with BLESSPC fitting yields accurate T1 estimation (average error = −5.4 ± 15.1 ms, percentage error = −0.5% ± 1.2%) for T1 from 236–1852 ms and heart rate from 40–100 bpm in phantom studies. The FLASH-MOLLI sequence prevented off-resonance artifacts in all 10 healthy volunteers at 3.0T. In vivo, there was no significant difference between FLASH-MOLLI-derived myocardial T1 values and “ShMOLLI+IE” derived values (1458.9 ± 20.9 ms versus 1464.1 ± 6.8 ms, P = 0.50); However, the average precision by FLASH-MOLLI was significantly better than that generated by “ShMOLLI+IE” (1.84 ± 0.36% variance versus 3.57 ± 0.94%, P < 0.001). Conclusion The FLASH-MOLLI with BLESSPC fitting yields accurate and precise T1 estimation, and eliminates banding artifacts associated with bSSFP at 3.0T. J. Magn. Reson. Imaging 2015.
Gengchiau Liang - One of the best experts on this subject based on the ideXlab platform.
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damping like spin orbit torque induced magnetization dynamics in ferrimagnets based on landau lifshitz Bloch Equation
Journal of Applied Physics, 2018Co-Authors: Zhifeng Zhu, Xuanyao Fong, Gengchiau LiangAbstract:A theoretical model based on the Landau-Lifshitz-Bloch Equation is developed to study the effect of damping-like spin-orbit torque in ferrimagnets, which can capture many experimental findings. For example, the sample changes from Gd to FeCo dominate by increasing temperature, the damping-like spin-orbit torque has a peak at the magnetization compensation temperature, and angular-momentum compensation temperature increases as a function of Gd concentration. In contrast to the ferromagnet system, the switching trajectory in ferrimagnets is found to be precession free. The two sublattices are not always collinear, which produce a large exchange field affecting the magnetization dynamics. The study of material composition shows the existence of an oscillation region at intermediate current density, induced by the nondeterministic switching. Compared to the Landau-Lifshitz-Gilbert model, our developed model based on the Landau-Lifshitz-Bloch Equation enables the systematic study of the spin-torque effect and the evaluation of ferrimagnet-based devices.A theoretical model based on the Landau-Lifshitz-Bloch Equation is developed to study the effect of damping-like spin-orbit torque in ferrimagnets, which can capture many experimental findings. For example, the sample changes from Gd to FeCo dominate by increasing temperature, the damping-like spin-orbit torque has a peak at the magnetization compensation temperature, and angular-momentum compensation temperature increases as a function of Gd concentration. In contrast to the ferromagnet system, the switching trajectory in ferrimagnets is found to be precession free. The two sublattices are not always collinear, which produce a large exchange field affecting the magnetization dynamics. The study of material composition shows the existence of an oscillation region at intermediate current density, induced by the nondeterministic switching. Compared to the Landau-Lifshitz-Gilbert model, our developed model based on the Landau-Lifshitz-Bloch Equation enables the systematic study of the spin-torque effect and ...
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damping like spin orbit torque induced magnetization dynamics in ferrimagnets based on landau lifshitz Bloch Equation
Journal of Applied Physics, 2018Co-Authors: Zhifeng Zhu, Xuanyao Fong, Gengchiau LiangAbstract:A theoretical model based on the Landau-Lifshitz-Bloch Equation is developed to study the effect of damping-like spin-orbit torque in ferrimagnets, which can capture many experimental findings. For example, the sample changes from Gd to FeCo dominate by increasing temperature, the damping-like spin-orbit torque has a peak at the magnetization compensation temperature, and angular-momentum compensation temperature increases as a function of Gd concentration. In contrast to the ferromagnet system, the switching trajectory in ferrimagnets is found to be precession free. The two sublattices are not always collinear, which produce a large exchange field affecting the magnetization dynamics. The study of material composition shows the existence of an oscillation region at intermediate current density, induced by the nondeterministic switching. Compared to the Landau-Lifshitz-Gilbert model, our developed model based on the Landau-Lifshitz-Bloch Equation enables the systematic study of the spin-torque effect and the evaluation of ferrimagnet-based devices.
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spin torque induced magnetization dynamics in ferrimagnets based on landau lifshitz Bloch Equation
arXiv: Materials Science, 2018Co-Authors: Zhifeng Zhu, Xuanyao Fong, Gengchiau LiangAbstract:A theoretical model based on the Landau-Lifshitz-Bloch Equation is developed to study the spin-torque effect in ferrimagnets. Experimental findings, such as the temperature dependence, the peak in spin torque, and the angular-momentum compensation, can be well captured. In contrast to the ferromagnet system, the switching trajectory in ferrimagnets is found to be precession free. The two sublattices are not always collinear, which produces large exchange field affecting the magnetization dynamics. The study of material composition shows the existence of an oscillation region at intermediate current density, induced by the nondeterministic switching. Compared to the Landau-Lifshitz-Gilbert model, our developed model based on the Landau-Lifshitz-Bloch Equation enables the systematic study of spin-torque effect and the evaluation of ferrimagnet-based devices.
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theoretical proposal for determining angular momentum compensation in ferrimagnets
Physical Review B, 2018Co-Authors: Zhifeng Zhu, Xuanyao Fong, Gengchiau LiangAbstract:This work demonstrates that the magnetization and angular momentum compensation temperatures (${T}_{\mathrm{MC}}$ and ${T}_{\mathrm{AMC}}$) in ferrimagnets can be unambiguously determined by performing two sets of temperature-dependent current switching, with the symmetry reversals at ${T}_{\mathrm{MC}}$ and ${T}_{\mathrm{AMC}}$, respectively. A theoretical model based on the modified Landau-Lifshitz-Bloch Equation is developed to systematically study the spin torque effect under different temperatures, and numerical simulations are performed to corroborate our proposal. Furthermore, we demonstrate that the recently reported linear relation between ${T}_{\mathrm{AMC}}$ and ${T}_{\mathrm{MC}}$ can be explained using the Curie-Weiss theory.
Zhifeng Zhu - One of the best experts on this subject based on the ideXlab platform.
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damping like spin orbit torque induced magnetization dynamics in ferrimagnets based on landau lifshitz Bloch Equation
Journal of Applied Physics, 2018Co-Authors: Zhifeng Zhu, Xuanyao Fong, Gengchiau LiangAbstract:A theoretical model based on the Landau-Lifshitz-Bloch Equation is developed to study the effect of damping-like spin-orbit torque in ferrimagnets, which can capture many experimental findings. For example, the sample changes from Gd to FeCo dominate by increasing temperature, the damping-like spin-orbit torque has a peak at the magnetization compensation temperature, and angular-momentum compensation temperature increases as a function of Gd concentration. In contrast to the ferromagnet system, the switching trajectory in ferrimagnets is found to be precession free. The two sublattices are not always collinear, which produce a large exchange field affecting the magnetization dynamics. The study of material composition shows the existence of an oscillation region at intermediate current density, induced by the nondeterministic switching. Compared to the Landau-Lifshitz-Gilbert model, our developed model based on the Landau-Lifshitz-Bloch Equation enables the systematic study of the spin-torque effect and the evaluation of ferrimagnet-based devices.A theoretical model based on the Landau-Lifshitz-Bloch Equation is developed to study the effect of damping-like spin-orbit torque in ferrimagnets, which can capture many experimental findings. For example, the sample changes from Gd to FeCo dominate by increasing temperature, the damping-like spin-orbit torque has a peak at the magnetization compensation temperature, and angular-momentum compensation temperature increases as a function of Gd concentration. In contrast to the ferromagnet system, the switching trajectory in ferrimagnets is found to be precession free. The two sublattices are not always collinear, which produce a large exchange field affecting the magnetization dynamics. The study of material composition shows the existence of an oscillation region at intermediate current density, induced by the nondeterministic switching. Compared to the Landau-Lifshitz-Gilbert model, our developed model based on the Landau-Lifshitz-Bloch Equation enables the systematic study of the spin-torque effect and ...
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damping like spin orbit torque induced magnetization dynamics in ferrimagnets based on landau lifshitz Bloch Equation
Journal of Applied Physics, 2018Co-Authors: Zhifeng Zhu, Xuanyao Fong, Gengchiau LiangAbstract:A theoretical model based on the Landau-Lifshitz-Bloch Equation is developed to study the effect of damping-like spin-orbit torque in ferrimagnets, which can capture many experimental findings. For example, the sample changes from Gd to FeCo dominate by increasing temperature, the damping-like spin-orbit torque has a peak at the magnetization compensation temperature, and angular-momentum compensation temperature increases as a function of Gd concentration. In contrast to the ferromagnet system, the switching trajectory in ferrimagnets is found to be precession free. The two sublattices are not always collinear, which produce a large exchange field affecting the magnetization dynamics. The study of material composition shows the existence of an oscillation region at intermediate current density, induced by the nondeterministic switching. Compared to the Landau-Lifshitz-Gilbert model, our developed model based on the Landau-Lifshitz-Bloch Equation enables the systematic study of the spin-torque effect and the evaluation of ferrimagnet-based devices.
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spin torque induced magnetization dynamics in ferrimagnets based on landau lifshitz Bloch Equation
arXiv: Materials Science, 2018Co-Authors: Zhifeng Zhu, Xuanyao Fong, Gengchiau LiangAbstract:A theoretical model based on the Landau-Lifshitz-Bloch Equation is developed to study the spin-torque effect in ferrimagnets. Experimental findings, such as the temperature dependence, the peak in spin torque, and the angular-momentum compensation, can be well captured. In contrast to the ferromagnet system, the switching trajectory in ferrimagnets is found to be precession free. The two sublattices are not always collinear, which produces large exchange field affecting the magnetization dynamics. The study of material composition shows the existence of an oscillation region at intermediate current density, induced by the nondeterministic switching. Compared to the Landau-Lifshitz-Gilbert model, our developed model based on the Landau-Lifshitz-Bloch Equation enables the systematic study of spin-torque effect and the evaluation of ferrimagnet-based devices.
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theoretical proposal for determining angular momentum compensation in ferrimagnets
Physical Review B, 2018Co-Authors: Zhifeng Zhu, Xuanyao Fong, Gengchiau LiangAbstract:This work demonstrates that the magnetization and angular momentum compensation temperatures (${T}_{\mathrm{MC}}$ and ${T}_{\mathrm{AMC}}$) in ferrimagnets can be unambiguously determined by performing two sets of temperature-dependent current switching, with the symmetry reversals at ${T}_{\mathrm{MC}}$ and ${T}_{\mathrm{AMC}}$, respectively. A theoretical model based on the modified Landau-Lifshitz-Bloch Equation is developed to systematically study the spin torque effect under different temperatures, and numerical simulations are performed to corroborate our proposal. Furthermore, we demonstrate that the recently reported linear relation between ${T}_{\mathrm{AMC}}$ and ${T}_{\mathrm{MC}}$ can be explained using the Curie-Weiss theory.
Unai Atxitia - One of the best experts on this subject based on the ideXlab platform.
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the classical two sublattice landau lifshitz Bloch Equation for all temperatures
Low Temperature Physics, 2015Co-Authors: P Nieves, Roy W. Chantrell, Unai Atxitia, Chubykalo O FesenkoAbstract:Micromagnetic modeling has proved itself as a widely used tool, complimentary in many respects to experimental measurements. The Landau–Lifshitz Equation provides a basis for this modeling, especially where the dynamical behaviour is concerned. However, this approach is strictly valid only for zero temperature and for high temperatures must be replaced by a more thermodynamically consistent approach such as the Landau–Lifshitz–Bloch (LLB) Equation. Here we review the recently derived LLB Equation for two-sublattice systems and extend its derivation for temperatures above the Curie temperature. We present comparison with many-body atomistic simulations and show that this Equation can describe the ultra-fast switching in ferrimagnets, observed experimentally.
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quantum landau lifshitz Bloch Equation and its comparison with the classical case
Physical Review B, 2014Co-Authors: P Nieves, Unai Atxitia, D Serantes, O ChubykalofesenkoAbstract:The detailed derivation of the quantum Landau-Lifshitz-Bloch (qLLB) Equation for simple spin-flip scattering mechanisms based on spin-phonon and spin-electron interactions is presented and the approximations are discussed. The qLLB Equation is written in a form suitable for comparison with its classical counterpart. The temperature dependence of the macroscopic relaxation rates is discussed for both mechanisms. It is demonstrated that the magnetization dynamics is slower in the quantum case than in the classical one.
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landau lifshitz Bloch Equation for ferrimagnetic materials
Physical Review B, 2012Co-Authors: Unai Atxitia, P Nieves, O ChubykalofesenkoAbstract:We derive the Landau-Lifshitz-Bloch (LLB) Equation for a two-component magnetic system valid up to the Curie temperature. As an example, we consider disordered GdFeCo ferrimagnet where the ultrafast optically induced magnetization switching under the action of heat alone has been recently reported. The two-component LLB Equation contains the longitudinal relaxation terms responding to the exchange fields from the proper and the neighboring sublattices. We show that the sign of the longitudinal relaxation rate at high temperatures can change depending on the dynamical magnetization value and a dynamical polarisation of one material by another can occur. We discuss the differences between the LLB and the Baryakhtar Equation, recently used to explain the ultrafast switching in ferrimagnets. The two-component LLB Equation forms basis for the largescale micromagnetic modeling of nanostructures at high temperatures and ultrashort timescales.
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landau lifshitz Bloch Equation for ferrimagnetic materials
Physical Review B, 2012Co-Authors: Unai Atxitia, P Nieves, O ChubykalofesenkoAbstract:We derive the Landau-Lifshitz-Bloch (LLB) Equation for a two-component magnetic system valid up to the Curie temperature. As an example, we consider disordered GdFeCo ferrimagnet where the ultrafast optically induced magnetization switching under the action of heat alone has been recently reported. The two-component LLB Equation contains the longitudinal relaxation terms responding to the exchange fields from the proper and the neighboring sublattices. We show that the sign of the longitudinal relaxation rate at high temperatures can change depending on the dynamical magnetization value and a dynamical polarization of one material by another can occur. We discuss the differences between the LLB and the Baryakhtar Equations, recently used to explain the ultrafast switching in ferrimagnets. The two-component LLB Equation forms the basis for the large-scale micromagnetic modeling of nanostructures at high temperatures and ultrashort time scales.
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Stochastic form of the Landau-Lifshitz-Bloch Equation
Physical Review B, 2012Co-Authors: Richard F. L. Evans, Denise Hinzke, Ulrich Nowak, Roy W. Chantrell, Unai Atxitia, Oksana Chubykalo-fesenkoAbstract:The Landau-Lifshitz-Bloch Equation is a formulation of dynamic micromagnetics valid at all temperatures, treating both the transverse and longitudinal relaxation components important for high-temperature applications. In this paper we discuss two stochastic forms of the Landau-Lifshitz-Bloch Equation. Both of them are consistent with the fluctuation-dissipation theorem. We derive the corresponding Fokker-Planck Equations and show that only the stochastic form of the Landau-Lifshitz-Bloch Equation proposed in the present paper is consistent with the Boltzmann distribution at high temperatures. The previously used form does not satisfy this requirement in the vicinity of the Curie temperature. We discuss the stochastic properties of both Equations and present numerical simulations for distribution functions and the average magnetization value as a function of temperature.
Rongrong Jia - One of the best experts on this subject based on the ideXlab platform.
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new soliton solutions for the 2 1 dimensional schrodinger maxwell Bloch Equation
Superlattices and Microstructures, 2017Co-Authors: Run Zhou, Huiqin Hao, Rongrong JiaAbstract:Abstract In this paper, the (2+1)-dimensional Schrodinger-Maxwell-Bloch Equation (SMBE) is analytically investigated. Based on the Lax pair, the two-fold Darboux transformation (DT) is constructed for this Equation. In addition, the two different kinds of soliton solutions (multi-line soliton and multi-parabola soliton solutions) are derived under the zero background. Also, the dynamic characteristics of solitons are discussed through theoretical analysis and graphical description.