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Kazuaki Fukamichi - One of the best experts on this subject based on the ideXlab platform.
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changes in electronic states and Magnetic Free Energy in la1 zcez fexsi1 x 13 Magnetic refrigerants
Journal of Physics D, 2011Co-Authors: Asaya Fujita, S Fujieda, Kazuaki FukamichiAbstract:The influence of partial substitution of Ce on the electronic structure and Magnetic Free Energy has been investigated for La1−zCez(FexSi1−x)13. From the Mossbauer spectroscopy of La0.7Ce0.3(Fe0.88Si0.12)13, the distribution of the electric field gradient is found to be scarcely changed, therefore, the volume reduction by partial substitution is regarded as isotropic. The change of the isomer shift to positive sign after the partial substitution is closely correlated with the 5d and/or 4f electrons of Ce.The change in Magnetic Free Energy has been examined for La0.7Ce0.3(Fe0.86Si0.14)13 having a large Magnetic entropy change ΔSm and a small hysteretic behaviour. From the results analysed by the Landau expansion theory, the large ΔSm and the small hysteresis of this compound are attributed to the magnitude and thermal variation of the fourth-order Landau coefficient in Magnetic Free Energy. Consequently, the combination of partial substitution and control of Fe concentration is useful for highly efficient Magnetic refrigerants.
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Changes in electronic states and Magnetic Free Energy in La1−zCez(FexSi1−x)13 Magnetic refrigerants
Journal of Physics D: Applied Physics, 2011Co-Authors: Asaya Fujita, S Fujieda, Kazuaki FukamichiAbstract:The influence of partial substitution of Ce on the electronic structure and Magnetic Free Energy has been investigated for La1−zCez(FexSi1−x)13. From the Mossbauer spectroscopy of La0.7Ce0.3(Fe0.88Si0.12)13, the distribution of the electric field gradient is found to be scarcely changed, therefore, the volume reduction by partial substitution is regarded as isotropic. The change of the isomer shift to positive sign after the partial substitution is closely correlated with the 5d and/or 4f electrons of Ce.The change in Magnetic Free Energy has been examined for La0.7Ce0.3(Fe0.86Si0.14)13 having a large Magnetic entropy change ΔSm and a small hysteretic behaviour. From the results analysed by the Landau expansion theory, the large ΔSm and the small hysteresis of this compound are attributed to the magnitude and thermal variation of the fourth-order Landau coefficient in Magnetic Free Energy. Consequently, the combination of partial substitution and control of Fe concentration is useful for highly efficient Magnetic refrigerants.
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Influence of spin fluctuations on thermodynamics of itinerant-electron metaMagnetic transition in La(Fe0.88Si0.12)13 compound
Journal of Magnetism and Magnetic Materials, 2004Co-Authors: Asaya Fujita, Shun Fujieda, Kazuaki FukamichiAbstract:Abstract Thermodynamic properties of the itinerant-electron metaMagnetic (IEM) transition in La(Fe 0.88 Si 0.12 ) 13 compound are discussed. Both the transition field B C and the change in magnetization at the transition Δ M show the thermal variation expected from the theory for the Magnetic Free Energy renormalized by spin fluctuations. The latent heat Δ Q obtained from B C and Δ M agrees with that obtained from heat capacity under Magnetic field. Therefore, the thermal variation of Δ Q mainly comes from the Magnetic contribution influenced by spin fluctuations.
Markus J. Aschwanden - One of the best experts on this subject based on the ideXlab platform.
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Torsional Alfvénic Oscillations Discovered in the Magnetic Free Energy during Solar Flares
The Astrophysical Journal, 2020Co-Authors: Markus J. Aschwanden, Tongjiang WangAbstract:We report the discovery of torsional Alfv\'enic oscillations in solar flares, which modulate the time evolution of the Magnetic Free Energy $E_f(t)$, while the Magnetic potential Energy $E_p(t)$ is uncorrelated, and the nonpotential Energy varies as $E_{np}(t) = E_p + E_f(t)$. The mean observed time period of the torsional oscillations is $P_{obs}=15.1 \pm 3.9$ min, the mean field line length is $L=135\pm35$ Mm, and the mean phase speed is $v_{phase} =315 \pm 120$ km s$^{-1}$, which we interpret as torsional Alfv\'enic waves in flare loops with enhanced electron densities. Most of the torsional oscillations are found to be decay-less, but exhibit a positive or negative trend in the evolution of the Free Energy, indicating new emerging flux (if positive), Magnetic cancellation, or flare Energy dissipation (if negative). The time evolution of the Free Energy has been calculated in this study with the {\sl Vertical-Current Approximation (Version 4) Nonlinear Force-Free Field (VCA4-NLFFF)} code, which incorporates automatically detected coronal loops in the solution and bypasses the non-forceFreeness of the photospheric boundary condition, in contrast to traditional NLFFF codes.
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torsional alfv enic oscillations discovered in the Magnetic Free Energy during solar flares
arXiv: Solar and Stellar Astrophysics, 2020Co-Authors: Markus J. Aschwanden, Tongjiang WangAbstract:We report the discovery of torsional Alfv\'enic oscillations in solar flares, which modulate the time evolution of the Magnetic Free Energy $E_f(t)$, while the Magnetic potential Energy $E_p(t)$ is uncorrelated, and the nonpotential Energy varies as $E_{np}(t) = E_p + E_f(t)$. The mean observed time period of the torsional oscillations is $P_{obs}=15.1 \pm 3.9$ min, the mean field line length is $L=135\pm35$ Mm, and the mean phase speed is $v_{phase} =315 \pm 120$ km s$^{-1}$, which we interpret as torsional Alfv\'enic waves in flare loops with enhanced electron densities. Most of the torsional oscillations are found to be decay-less, but exhibit a positive or negative trend in the evolution of the Free Energy, indicating new emerging flux (if positive), Magnetic cancellation, or flare Energy dissipation (if negative). The time evolution of the Free Energy has been calculated in this study with the {\sl Vertical-Current Approximation (Version 4) Nonlinear Force-Free Field (VCA4-NLFFF)} code, which incorporates automatically detected coronal loops in the solution and bypasses the non-forceFreeness of the photospheric boundary condition, in contrast to traditional NLFFF codes.
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global energetics of solar flares v Energy closure in flares and coronal mass ejections
The Astrophysical Journal, 2017Co-Authors: Markus J. Aschwanden, Amir Caspi, Ju Jing, Matthieu Kretzschmar, Eduard Kontar, James Mctiernan, Richard Mewaldt, C M Cohen, Gordon D Holman, Aidan OflannagainAbstract:In this study we synthesize the results of four previous studies on the global energetics of solar flares and associated coronal mass ejections (CMEs), which include Magnetic, thermal, nonthermal, and CME energies in 399 solar M- and X-class flare events observed during the first 3.5 yr of the Solar Dynamics Observatory (SDO) mission. Our findings are as follows. (1) The sum of the mean nonthermal Energy of flare-accelerated particles (E_(nt)), the Energy of direct heating (E_(dir)), and the Energy in CMEs (E_(CME)), which are the primary Energy dissipation processes in a flare, is found to have a ratio of E_(nt) + E_(dir) + E_(CME)/E_(mag) = 0.87 ± 0.18, compared with the dissipated Magnetic Free Energy E_(mag), which confirms Energy closure within the measurement uncertainties and corroborates the Magnetic origin of flares and CMEs. (2) The Energy partition of the dissipated Magnetic Free Energy is: 0.51 ± 0.17 in nonthermal Energy of ⩾ 6 keV electrons, 0.17 ± 0.17 in nonthermal ⩾ 1 MeV ions, 0.07 ± 0.14 in CMEs, and 0.07 ± 0.17 in direct heating. (3) The thermal Energy is almost always less than the nonthermal Energy, which is consistent with the thick-target model. (4) The bolometric luminosity in white-light flares is comparable to the thermal Energy in soft X-rays (SXR). (5) Solar energetic particle events carry a fraction ≈ 0.03 of the CME Energy, which is consistent with CME-driven shock acceleration. (6) The warm-target model predicts a lower limit of the low-Energy cutoff at e_c ≈ 6 keV, based on the mean peak temperature of the differential emission measure of T_e = 8.6 MK during flares. This work represents the first statistical study that establishes Energy closure in solar flare/CME events.
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global energetics of solar flares v Energy closure in flares and coronal mass ejections
arXiv: Solar and Stellar Astrophysics, 2017Co-Authors: Markus J. Aschwanden, Amir Caspi, Ju Jing, Matthieu Kretzschmar, Eduard Kontar, James Mctiernan, Richard Mewaldt, C M Cohen, Gordon D Holman, Aidan OflannagainAbstract:In this study we synthesize the results of four previous studies on the global energetics of solar flares and associated coronal mass ejections (CMEs), which include Magnetic, thermal, nonthermal, and CME energies in 399 solar M and X-class flare events observed during the first 3.5 years of the Solar Dynamics Observatory (SDO) mission. Our findings are: (1) The sum of the mean nonthermal Energy of flare-accelerated particles ($E_{\mathrm{nt}}$), the Energy of direct heating ($E_{\mathrm{dir}}$), and the Energy in coronal mass ejections ($E_{\mathrm{CME}}$), which are the primary Energy dissipation processes in a flare, is found to have a ratio of $(E_{\mathrm{nt}}+E_{\mathrm{dir}}+ E_{\mathrm{CME}})/E_{\mathrm{mag}} = 0.87 \pm 0.18$, compared with the dissipated Magnetic Free Energy $E_{\mathrm{mag}}$, which confirms Energy closure within the measurement uncertainties and corroborates the Magnetic origin of flares and CMEs; (2) The Energy partition of the dissipated Magnetic Free Energy is: $0.51\pm0.17$ in nonthermal Energy of $\ge 6$ keV electrons, $0.17\pm0.17$ in nonthermal $\ge 1$ MeV ions, $0.07\pm0.14$ in CMEs, and $0.07\pm0.17$ in direct heating; (3) The thermal Energy is almost always less than the nonthermal Energy, which is consistent with the thick-target model; (4) The bolometric luminosity in white-light flares is comparable with the thermal Energy in soft X-rays (SXR); (5) Solar Energetic Particle (SEP) events carry a fraction $\approx 0.03$ of the CME Energy, which is consistent with CME-driven shock acceleration; and (6) The warm-target model predicts a lower limit of the low-Energy cutoff at $e_c \approx 6$ keV, based on the mean differential emission measure (DEM) peak temperature of $T_e=8.6$ MK during flares. This work represents the first statistical study that establishes Energy closure in solar flare/CME events.
Tongjiang Wang - One of the best experts on this subject based on the ideXlab platform.
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Torsional Alfvénic Oscillations Discovered in the Magnetic Free Energy during Solar Flares
The Astrophysical Journal, 2020Co-Authors: Markus J. Aschwanden, Tongjiang WangAbstract:We report the discovery of torsional Alfv\'enic oscillations in solar flares, which modulate the time evolution of the Magnetic Free Energy $E_f(t)$, while the Magnetic potential Energy $E_p(t)$ is uncorrelated, and the nonpotential Energy varies as $E_{np}(t) = E_p + E_f(t)$. The mean observed time period of the torsional oscillations is $P_{obs}=15.1 \pm 3.9$ min, the mean field line length is $L=135\pm35$ Mm, and the mean phase speed is $v_{phase} =315 \pm 120$ km s$^{-1}$, which we interpret as torsional Alfv\'enic waves in flare loops with enhanced electron densities. Most of the torsional oscillations are found to be decay-less, but exhibit a positive or negative trend in the evolution of the Free Energy, indicating new emerging flux (if positive), Magnetic cancellation, or flare Energy dissipation (if negative). The time evolution of the Free Energy has been calculated in this study with the {\sl Vertical-Current Approximation (Version 4) Nonlinear Force-Free Field (VCA4-NLFFF)} code, which incorporates automatically detected coronal loops in the solution and bypasses the non-forceFreeness of the photospheric boundary condition, in contrast to traditional NLFFF codes.
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torsional alfv enic oscillations discovered in the Magnetic Free Energy during solar flares
arXiv: Solar and Stellar Astrophysics, 2020Co-Authors: Markus J. Aschwanden, Tongjiang WangAbstract:We report the discovery of torsional Alfv\'enic oscillations in solar flares, which modulate the time evolution of the Magnetic Free Energy $E_f(t)$, while the Magnetic potential Energy $E_p(t)$ is uncorrelated, and the nonpotential Energy varies as $E_{np}(t) = E_p + E_f(t)$. The mean observed time period of the torsional oscillations is $P_{obs}=15.1 \pm 3.9$ min, the mean field line length is $L=135\pm35$ Mm, and the mean phase speed is $v_{phase} =315 \pm 120$ km s$^{-1}$, which we interpret as torsional Alfv\'enic waves in flare loops with enhanced electron densities. Most of the torsional oscillations are found to be decay-less, but exhibit a positive or negative trend in the evolution of the Free Energy, indicating new emerging flux (if positive), Magnetic cancellation, or flare Energy dissipation (if negative). The time evolution of the Free Energy has been calculated in this study with the {\sl Vertical-Current Approximation (Version 4) Nonlinear Force-Free Field (VCA4-NLFFF)} code, which incorporates automatically detected coronal loops in the solution and bypasses the non-forceFreeness of the photospheric boundary condition, in contrast to traditional NLFFF codes.
Asaya Fujita - One of the best experts on this subject based on the ideXlab platform.
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changes in electronic states and Magnetic Free Energy in la1 zcez fexsi1 x 13 Magnetic refrigerants
Journal of Physics D, 2011Co-Authors: Asaya Fujita, S Fujieda, Kazuaki FukamichiAbstract:The influence of partial substitution of Ce on the electronic structure and Magnetic Free Energy has been investigated for La1−zCez(FexSi1−x)13. From the Mossbauer spectroscopy of La0.7Ce0.3(Fe0.88Si0.12)13, the distribution of the electric field gradient is found to be scarcely changed, therefore, the volume reduction by partial substitution is regarded as isotropic. The change of the isomer shift to positive sign after the partial substitution is closely correlated with the 5d and/or 4f electrons of Ce.The change in Magnetic Free Energy has been examined for La0.7Ce0.3(Fe0.86Si0.14)13 having a large Magnetic entropy change ΔSm and a small hysteretic behaviour. From the results analysed by the Landau expansion theory, the large ΔSm and the small hysteresis of this compound are attributed to the magnitude and thermal variation of the fourth-order Landau coefficient in Magnetic Free Energy. Consequently, the combination of partial substitution and control of Fe concentration is useful for highly efficient Magnetic refrigerants.
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Changes in electronic states and Magnetic Free Energy in La1−zCez(FexSi1−x)13 Magnetic refrigerants
Journal of Physics D: Applied Physics, 2011Co-Authors: Asaya Fujita, S Fujieda, Kazuaki FukamichiAbstract:The influence of partial substitution of Ce on the electronic structure and Magnetic Free Energy has been investigated for La1−zCez(FexSi1−x)13. From the Mossbauer spectroscopy of La0.7Ce0.3(Fe0.88Si0.12)13, the distribution of the electric field gradient is found to be scarcely changed, therefore, the volume reduction by partial substitution is regarded as isotropic. The change of the isomer shift to positive sign after the partial substitution is closely correlated with the 5d and/or 4f electrons of Ce.The change in Magnetic Free Energy has been examined for La0.7Ce0.3(Fe0.86Si0.14)13 having a large Magnetic entropy change ΔSm and a small hysteretic behaviour. From the results analysed by the Landau expansion theory, the large ΔSm and the small hysteresis of this compound are attributed to the magnitude and thermal variation of the fourth-order Landau coefficient in Magnetic Free Energy. Consequently, the combination of partial substitution and control of Fe concentration is useful for highly efficient Magnetic refrigerants.
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Influence of spin fluctuations on thermodynamics of itinerant-electron metaMagnetic transition in La(Fe0.88Si0.12)13 compound
Journal of Magnetism and Magnetic Materials, 2004Co-Authors: Asaya Fujita, Shun Fujieda, Kazuaki FukamichiAbstract:Abstract Thermodynamic properties of the itinerant-electron metaMagnetic (IEM) transition in La(Fe 0.88 Si 0.12 ) 13 compound are discussed. Both the transition field B C and the change in magnetization at the transition Δ M show the thermal variation expected from the theory for the Magnetic Free Energy renormalized by spin fluctuations. The latent heat Δ Q obtained from B C and Δ M agrees with that obtained from heat capacity under Magnetic field. Therefore, the thermal variation of Δ Q mainly comes from the Magnetic contribution influenced by spin fluctuations.
P. F. Chen - One of the best experts on this subject based on the ideXlab platform.
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A STATISTICAL STUDY OF FLARE PRODUCTIVITY ASSOCIATED WITH SUNSPOT PROPERTIES IN DIFFERENT Magnetic TYPES OF ACTIVE REGIONS
The Astrophysical Journal, 2017Co-Authors: Y. H. Yang, Min-shiu Hsieh, P. F. ChenAbstract:It is often believed that intense flares preferentially originate from the large-size active regions (ARs) with strong Magnetic fields and complex Magnetic configurations. This work investigates the dependence of flare activity on the AR properties and clarifies the influence of AR Magnetic parameters on the flare productivity, based on two data sets of daily sunspot and flare information as well as the GOES soft X-ray measurements and HMI vector magnetograms. By considering the evolution of Magnetic complexity, we find that flare behaviors are quite different in the short- and long-lived complex ARs and the ARs with more complex Magnetic configurations are likely to host more impulsive and intense flares. Furthermore, we investigate several Magnetic quantities and perform the two-sample Kolmogorov–Smirnov test to examine the similarity/difference between two populations in different types of ARs. Our results demonstrate that the total source field strength on the photosphere has a good correlation with the flare activity in complex ARs. It is noted that intense flares tend to occur at the regions of strong source field in combination with an intermediate field-weighted shear angle. This result implies that the Magnetic Free Energy provided by a complex AR could be high enough to trigger a flare eruption even with a moderate Magnetic shear on the photosphere. We thus suggest that the Magnetic Free Energy represented by the source field rather than the photospheric Magnetic complexity is a better quantity to characterize the flare productivity of an AR, especially for the occurrence of intense flares.
