Electromagnetic bandgap （EBG） materials are periodic structures capable of prohibiting the propagation of electromagnetic waves within a certain band of frequencies. This characteristic of EBG has wide application. ...Electromagnetic bandgap （EBG） materials are periodic structures capable of prohibiting the propagation of electromagnetic waves within a certain band of frequencies. This characteristic of EBG has wide application. The structures to be studied here are mainly planar EBG materials of two dimensions, which are periodic arrays of holes etched in the ground plane of a conventional microstrip line. EBG structures are calculated with finite-difference time-domain （FDTD） method in this paper. Technique of the perfectly matched layer is used for the absorption of electromagnetic waves in FDTD. The FDTD method is programmed with the blend of C++ and Matlab languages, which makes the program both simple and fast computing. A kind of new EBG structure is brought out through a lot of experiments and analyses. A filter with wide stop-band and another filter with two stop-bands are designed.展开更多
CIP （complex initial permeability） spectra of PF （polycrystalline ferrite） are studied both as intrinsic and extrinsic properties. In the former case, main steps of modeling, based on effects coming from polycryst...CIP （complex initial permeability） spectra of PF （polycrystalline ferrite） are studied both as intrinsic and extrinsic properties. In the former case, main steps of modeling, based on effects coming from polycrystal grain sizes distribution and defects, are described. The obtained relations work well in practice for PF with more or less normal MS （microstructure） and no size effects. Besides, fundamental connection between parameters of CIP and MS is found. Another case--PF with possible size effects （MnZn-ferrites） are studied experimentally for different sizes of cores, unveiling the dependence of phenomena on： dimensions of cross-section, number of turns, width of nonmagnetic gap.展开更多
The gravity field models GUCAS_EGM and GUCAS_EGM_DL are established from GOCE data (GOCE Level 2 Products from Nov. 1 to Dec. 31, 2009) based on the method of the invariants of the gravity gradient tensor, where GUCAS...The gravity field models GUCAS_EGM and GUCAS_EGM_DL are established from GOCE data (GOCE Level 2 Products from Nov. 1 to Dec. 31, 2009) based on the method of the invariants of the gravity gradient tensor, where GUCAS_EGM is derived after GOCE gravity gradient data are filtered with FIR, and GUCAS_EGM_DL is computed with an additional Durbin-Levison arithmetic apart from FIR. Since this method, different from current programs dealing with GOCE data, is introduced for the first time, some new problems are required to be discussed in advance; for example, how to filter GOCE gravity gradient data, how to compute the invariants of the gradient tensor, and how to deal with the pole gap and so on. In addition, by comparing our models with ones recommended by ESA, it can be seen that the variations of GUCAS_EGM and the models recommended by ESA to EGM08 are almost equivalent, and the variation of GUCAS_EGM_DL to EGM08 is obviously less than ones of the recommended models.展开更多
To improve the pressure capability of magnetic fluid seal with more than a 0.25 mm single edge gap,a magnetic fluid sealing structure with multiple magnetic sources which has five permanent magnets was designed.Magnet...To improve the pressure capability of magnetic fluid seal with more than a 0.25 mm single edge gap,a magnetic fluid sealing structure with multiple magnetic sources which has five permanent magnets was designed.Magnetic field distributions under the pole pieces of the magnetic fluid seal with single and multiple magnetic sources were simulated by finite element method and its sealing pressure difference could be calculated according to the theoretical formula of the magnetic fluid seal.The effects of sealing gap height and magnetic source amount on the sealing capability were investigated experimentally.The theoretical and experimental results were compared,analyzed and discussed.The results demonstrated that the magnetic fluid seal with multiple magnetic sources was an effective method to improve the sealing capability for the rotary shaft with large gaps.The theoretical results agreed well with the experimental results when the height of the single edge gap was equal to 0.4 mm.However,it was found that when the height of the single edge gap was larger than 0.4 mm,the difference between the theoretical values and experimental values increased with the gap height because part of magnetic source had less or even no effect on magnetic fluid sealing capability.展开更多
La（Fe, Si）13-based compounds have been considered as promising candidates for magnetic refrigerants particularly near room temperature. Herein we review recent progress particularly in the study of the effects of in...La（Fe, Si）13-based compounds have been considered as promising candidates for magnetic refrigerants particularly near room temperature. Herein we review recent progress particularly in the study of the effects of interstitial H and/or C atoms on the magnetic and magnetocaloric properties of La（Fe, Si）13 compounds. By introducing H and/or C atoms, the Curie temperature Tc increases notably with the increase of lattice expansion which makes the Fe 3d band narrow and reduces the overlap of the Fe 3d wave functions. The first-order itinerant-electron metamagnetic transition is conserved and the MCE still remains high after hydrogen absorption. In contrast, the characteristic of magnetic transition varies from first-order to second-order with the increase of C concentration, which leads to remarkable reduction of thermal and magnetic hysteresis. In addition, the introduc- tion of interstitial C atoms promotes the formation of NaZnl3-type （1：13） phase in La（Fe, Si）13 compounds, and thus reducing the annealing time significantly from 40 days for LaFe11.7Sil.3 to a week for LaFell.7Sil.3C0.2. The pre-occupied interstitial C atoms may depress the rate of hydrogen absorption and release, which is favorable to the accurate control of hydrogen content. It is found that the reduction of particle size would greatly depress the hysteresis loss and improve the hydrogenation process. By the incorporation of both H and C atoms, large MCE without hysteresis loss can be obtained in La（Fe, Si）13 compounds around room temperature, for instance, La0.7Pr0.3Fe115Si15C0.2H12 exhibits a large IASM[ of 22.1 J/（kg＇K） at Tc = 321 K without hysteresis loss for a field change of 0-5 T.展开更多
This article reviews low-temperature heat transport studies of spin-gapped quantum magnets in the last few decades. Quantum magnets with small spins and low dimensionality exhibit a variety of novel phenomena. Among t...This article reviews low-temperature heat transport studies of spin-gapped quantum magnets in the last few decades. Quantum magnets with small spins and low dimensionality exhibit a variety of novel phenomena. Among them, some systems are characteristic of having quantum-mechanism spin gap in their magnetic excitation spectra, including spin-Peierls systems, S=1Haldane chains, S= 1/2 spin ladders, and spin dimmers. In some particular spin-gapped systems, the XY-type antiferromagnetic state induced by magnetic field that closes the spin gap can be described as a magnon Bose-Einstein condensation(BEC). Heat transport is effective in probing the magnetic excitations and magnetic phase transitions, and has been extensively studied for the spin-gapped systems. A large and ballistic spin thermal conductivity was observed in the two-leg Heisenberg S=1/2 ladder compounds. The characteristic of magnetic thermal transport of the Haldane chain systems is quite controversial on both the theoretical and experimental results. For the spin-Peierls system, the spin excitations can also act as heat carriers. In spin-dimer compounds, the magnetic excitations mainly play a role of scattering phonons. The magnetic excitations in the magnon BEC systems displayed dual roles, carrying heat or scattering phonons, in different materials.展开更多
文摘Electromagnetic bandgap （EBG） materials are periodic structures capable of prohibiting the propagation of electromagnetic waves within a certain band of frequencies. This characteristic of EBG has wide application. The structures to be studied here are mainly planar EBG materials of two dimensions, which are periodic arrays of holes etched in the ground plane of a conventional microstrip line. EBG structures are calculated with finite-difference time-domain （FDTD） method in this paper. Technique of the perfectly matched layer is used for the absorption of electromagnetic waves in FDTD. The FDTD method is programmed with the blend of C++ and Matlab languages, which makes the program both simple and fast computing. A kind of new EBG structure is brought out through a lot of experiments and analyses. A filter with wide stop-band and another filter with two stop-bands are designed.
文摘CIP （complex initial permeability） spectra of PF （polycrystalline ferrite） are studied both as intrinsic and extrinsic properties. In the former case, main steps of modeling, based on effects coming from polycrystal grain sizes distribution and defects, are described. The obtained relations work well in practice for PF with more or less normal MS （microstructure） and no size effects. Besides, fundamental connection between parameters of CIP and MS is found. Another case--PF with possible size effects （MnZn-ferrites） are studied experimentally for different sizes of cores, unveiling the dependence of phenomena on： dimensions of cross-section, number of turns, width of nonmagnetic gap.
基金supported by National Natural Science Foundation of China (Grant No.41074015)Program of Chinese Academy of Sciences (Grant No.XMXX280730)
文摘The gravity field models GUCAS_EGM and GUCAS_EGM_DL are established from GOCE data (GOCE Level 2 Products from Nov. 1 to Dec. 31, 2009) based on the method of the invariants of the gravity gradient tensor, where GUCAS_EGM is derived after GOCE gravity gradient data are filtered with FIR, and GUCAS_EGM_DL is computed with an additional Durbin-Levison arithmetic apart from FIR. Since this method, different from current programs dealing with GOCE data, is introduced for the first time, some new problems are required to be discussed in advance; for example, how to filter GOCE gravity gradient data, how to compute the invariants of the gradient tensor, and how to deal with the pole gap and so on. In addition, by comparing our models with ones recommended by ESA, it can be seen that the variations of GUCAS_EGM and the models recommended by ESA to EGM08 are almost equivalent, and the variation of GUCAS_EGM_DL to EGM08 is obviously less than ones of the recommended models.
基金supported by the National Natural Science Foundation of China(Grant No.50875017)
文摘To improve the pressure capability of magnetic fluid seal with more than a 0.25 mm single edge gap,a magnetic fluid sealing structure with multiple magnetic sources which has five permanent magnets was designed.Magnetic field distributions under the pole pieces of the magnetic fluid seal with single and multiple magnetic sources were simulated by finite element method and its sealing pressure difference could be calculated according to the theoretical formula of the magnetic fluid seal.The effects of sealing gap height and magnetic source amount on the sealing capability were investigated experimentally.The theoretical and experimental results were compared,analyzed and discussed.The results demonstrated that the magnetic fluid seal with multiple magnetic sources was an effective method to improve the sealing capability for the rotary shaft with large gaps.The theoretical results agreed well with the experimental results when the height of the single edge gap was equal to 0.4 mm.However,it was found that when the height of the single edge gap was larger than 0.4 mm,the difference between the theoretical values and experimental values increased with the gap height because part of magnetic source had less or even no effect on magnetic fluid sealing capability.
基金supported by the National Natural Science Foundation of Chinathe Hi-Tech Research and Development program of China+2 种基金the Key Research Program of the Chinese Academy of Sciencesthe National Basic Research Program of Chinathe Fundamental Research Funds for the Central Universities
文摘La（Fe, Si）13-based compounds have been considered as promising candidates for magnetic refrigerants particularly near room temperature. Herein we review recent progress particularly in the study of the effects of interstitial H and/or C atoms on the magnetic and magnetocaloric properties of La（Fe, Si）13 compounds. By introducing H and/or C atoms, the Curie temperature Tc increases notably with the increase of lattice expansion which makes the Fe 3d band narrow and reduces the overlap of the Fe 3d wave functions. The first-order itinerant-electron metamagnetic transition is conserved and the MCE still remains high after hydrogen absorption. In contrast, the characteristic of magnetic transition varies from first-order to second-order with the increase of C concentration, which leads to remarkable reduction of thermal and magnetic hysteresis. In addition, the introduc- tion of interstitial C atoms promotes the formation of NaZnl3-type （1：13） phase in La（Fe, Si）13 compounds, and thus reducing the annealing time significantly from 40 days for LaFe11.7Sil.3 to a week for LaFell.7Sil.3C0.2. The pre-occupied interstitial C atoms may depress the rate of hydrogen absorption and release, which is favorable to the accurate control of hydrogen content. It is found that the reduction of particle size would greatly depress the hysteresis loss and improve the hydrogenation process. By the incorporation of both H and C atoms, large MCE without hysteresis loss can be obtained in La（Fe, Si）13 compounds around room temperature, for instance, La0.7Pr0.3Fe115Si15C0.2H12 exhibits a large IASM[ of 22.1 J/（kg＇K） at Tc = 321 K without hysteresis loss for a field change of 0-5 T.
基金supported by the National Natural Science Foundation of China(Grant Nos.11374277,11574286,11404316,U1532147)the National Basic Research Program of China(Grant Nos.2015CB921201,2016YFA0300103)the Opening Project of Wuhan National High Magnetic Field Center(Grant No.2015KF21)
文摘This article reviews low-temperature heat transport studies of spin-gapped quantum magnets in the last few decades. Quantum magnets with small spins and low dimensionality exhibit a variety of novel phenomena. Among them, some systems are characteristic of having quantum-mechanism spin gap in their magnetic excitation spectra, including spin-Peierls systems, S=1Haldane chains, S= 1/2 spin ladders, and spin dimmers. In some particular spin-gapped systems, the XY-type antiferromagnetic state induced by magnetic field that closes the spin gap can be described as a magnon Bose-Einstein condensation(BEC). Heat transport is effective in probing the magnetic excitations and magnetic phase transitions, and has been extensively studied for the spin-gapped systems. A large and ballistic spin thermal conductivity was observed in the two-leg Heisenberg S=1/2 ladder compounds. The characteristic of magnetic thermal transport of the Haldane chain systems is quite controversial on both the theoretical and experimental results. For the spin-Peierls system, the spin excitations can also act as heat carriers. In spin-dimer compounds, the magnetic excitations mainly play a role of scattering phonons. The magnetic excitations in the magnon BEC systems displayed dual roles, carrying heat or scattering phonons, in different materials.
