The global distribution properties of Ultra Low Frequency wave (ULF) in the inner magnetospgere and its interactions with energetic particles, such as the wave-particle resonance, modulation, and particle acceleration...The global distribution properties of Ultra Low Frequency wave (ULF) in the inner magnetospgere and its interactions with energetic particles, such as the wave-particle resonance, modulation, and particle acceleration, are active topics in space physics research. These problems are fundamentally important issues to understand the energy transport from the solar wind into the magnetosphere. In this paper we briefly reviewed the recent research progress on ULF wave and its interactions with energetic particles in the inner magnetosphere; furthermore, we suggested some open questions for future study.展开更多
Background Malignant sinonasal melanoma （MSM） is a rare tumor with a perplexing signal intensity due to variable histopathologic components. This study was undertaken to delineate its MR imaging features. Methods MR...Background Malignant sinonasal melanoma （MSM） is a rare tumor with a perplexing signal intensity due to variable histopathologic components. This study was undertaken to delineate its MR imaging features. Methods MR imaging findings of 10 patients （6 women and 4 men, mean age 61.3 years old） with pathologically confirmed MSM were retrospectively reviewed. The location, size, signal intensity, enhancement, and internal imaging characteristics of all tumors were evaluated. Signal intensity and degree of enhancement was graded in comparison with the gray matter and adjacent muscle uptake, respectively. Results There were 8 tumors that were pathologically confirmed to contain melanin. Compared to gray matter of the brain, 7 of them demonstrated hyperintensity on T1WI and 6 （6/7） showed hypointensity on T2Wl. There was multiple linear, dark-signal intensity on T2Wl within the mass in 9 of the 10 patients＇ tumors. Evaluated with gadolinium-enhanced imaging, all 10 patients showed moderate enhancement within the areas that were isointense in the lesion on pregadolinium TlWl. Moreover, some parts which displayed hyperintensity on TlWl within the tumors of 7 patients showed mild enhancement that was similar to muscle on a time-intensity curve （TIC）. Conclusions MSM shows characteristic MR signal intensity （hyperintensity on TlWl and the linear, low-signal intensity on T2Wl）, which may provide valuable information for clinical diagnosis. Together with conventional MRI, TIC may be useful for indicating pleomorphic patterns of MSM.展开更多
Background Quantitative dynamic contrast enhancement MR imaging （DCE-MRI）,used to measure properties of tissue microvasculature and tumor angiogenesis,is a promising method for distinguishing benign and malignant tu...Background Quantitative dynamic contrast enhancement MR imaging （DCE-MRI）,used to measure properties of tissue microvasculature and tumor angiogenesis,is a promising method for distinguishing benign and malignant tumors and characterizing tumor response to antiangiogenic treatment.The aim of this study was to assess the feasibility of quantitative parameters derived from clinically used DCE-MRI for distinguishing benign from malignant tumors in the sinonasal area,which may be potentially useful for prediction and monitoring of treatment response to chemoradiotherapy of sinonasal tumors.Methods One hundred and forty-three patients with sinonasal tumors,including 78 malignant tumors and 65 benign tumors and tumor-like lesions,underwent clinically used DCE-MRI.Parametric maps were obtained for quantitative parameters including Ktrans,kep and ve.Two radiologists reviewed these maps and measured Ktrans,kep and ve in the tumor tissue.Data were analyzed using independent T-test or Mann-Whitney U test analysis and receiver operating characteristic curves.Results Ktrans,kep and ve showed significant differences between benign and malignant tumors in the sinonasal area （P=-0.000 1）.The accuracy of Ktrans,kep and ve in differentiation between benign and malignant sinonasal tumors were 72.0％,76.2％ and 67.1％,respectively.There were significant differences in kep and ve between malignant epithelial sinonasal tumors and lymphomas （P ＜0.05）.Using a ve value of 0.213 as the threshold value differentiated malignant epithelial tumors from lymphomas with an accuracy of 78.3％,sensitivity of 88.2％,specificity of 68.0％,positive predictive value of 66.7％,and negative predictive value of 90.9％.However,no significant difference in Ktrans and kep was found between malignant epithelial and non-epithelial tumors in the sinonasal area （P ＞0.05）.Conclusions It is feasible that quantitative parameters of tumors can be derived from clinically used DCE-MRI in the sinonasal region.Preliminary findings suggest an展开更多
Background Distinguishing inverted papilloma （IP） from malignant tumors in the nasal cavity is difficult in a substantial number of cases,thus hindering the administration of appropriate therapeutic strategies.This ...Background Distinguishing inverted papilloma （IP） from malignant tumors in the nasal cavity is difficult in a substantial number of cases,thus hindering the administration of appropriate therapeutic strategies.This study aimed to evaluate whether magnetic resonance imaging （MRI）,including dynamic contrast enhanced MRI （DCE-MRI）,could improve differentiation between IP and malignant tumors,and to identify which MRI features were the best in discriminating IP from malignant tumors in the nasal cavity.Methods Non-enhanced,static,and dynamic contrast enhanced MRI was performed in 88 patients with an IP or a malignant tumor in the nasal cavity that had been confirmed by histological results.MRI features of IP and malignant tumors including side,margin,T1 signal intensity,T1 homogeneity,T2 signal intensity,T2 homogeneity,lobulation signs,convoluted cerebriform pattern,extra-sinonasal involvement,pattern of enhancement,Tpeak,Tmax,Clmax,and TIC type were evaluated and correlated with histological findings.Results There were significant differences between IP and malignant tumors in T2 homogeneity,Iobulation signs,convoluted cerebriform pattern,extra-sinonasal involvement,Tpeak,Tmax and TIC types.A convoluted cerebriform pattern had a higher sensitivity and specificity in diagnosis of IP while washout-type TIC had a higher sensitivity and specificity in diagnosis of malignant tumors in the nasal cavity.Non-enhanced combined with static and dynamic enhancement MRI was significantly superior to non-enhanced combined with static enhancement MRI in the differentiation of IP and malignant tumors in the nasal cavity.Multivariate logistic regression analysis identified that the best MRI features were a convoluted cerebriform pattern,extra-sinonasal involvement,and washout-type TIC for both observers （Wang XY and Zhang ZY）.Conclusion Non-enhanced and static combined with dynamic contrast-enhanced MRI improves differentiation of IP and malignant tumors in the nasal cavity.展开更多
Based on observations obtained by Cluster C1, GOES 10, 12, and Polar, the global ULF wave properties are studied during the recovery phase of a very intense magnetic storm-Halloween storm (October 31, 2003, 21:00–23:...Based on observations obtained by Cluster C1, GOES 10, 12, and Polar, the global ULF wave properties are studied during the recovery phase of a very intense magnetic storm-Halloween storm (October 31, 2003, 21:00–23:00 UT). The results indicate that the ULF waves’ properties observed by different satellites, such as amplitude, period, etc. show large variations. This can be interpreted as that Field Line Resonance (FLR) might take place in the region where Cluster C1 passed. The compressional wave of the cavity mode coupled with FLR’s shear Alfven wave and fed energy to the latter, forming a large-amplitude toroidal mode. From the point of period, Cluster C1 observed the shortest period, GOES 10, 12 observed the middle, while Polar observed the longest. The wave period of toroidal mode observed by Cluster C1 kept almost unchanging when Cluster C1 passed L range from 11.7 to 5.3. Using the Squared Wavelet Coherence analysis method, we estimated that the FLR region in the dayside magnetosphere could expand to at least 4 local time widths. The toroidal mode observed by Polar was a standing wave, while the poloidal mode was a propagating wave, the observation results could be well explained by the waveguide mode theory. Since the solarwind speed V <SUB>x</SUB> was −800 km/s and the dynamic pressure varied little, we speculated that the source of the ULF wave was the Kelvin-Helmholtz instability at the magnetopause triggered by high speed solarwind.展开更多
The cavity-mode resonance effect could result in significant degradation of the shielding effectiveness （SE） of a shielding enclosure around its resonance frequencies. In this paper, the influence of coated wall los...The cavity-mode resonance effect could result in significant degradation of the shielding effectiveness （SE） of a shielding enclosure around its resonance frequencies. In this paper, the influence of coated wall loss on the suppression of the resonance effect is investigated. For this purpose, an equivalent circuit model is employed to analyze the SE of an apertured rectangular cavity coated with an inside layer of resistive material. The model is developed by extending Robinson＇s equivalent circuit model through incorporating the effect of the wall loss into both the propagation constant and the characteristic impedance of the waveguide. Calculation results show that the wall loss could lead to great improvement on the SE for frequencies near the resonance but almost no effect on the SE for frequencies far away from the resonance.展开更多
Stochastic resonance is a phenomenon in which adding random noise to a system enhances the detection or transmission of a weak signal. It occurs when the noise interacts with the system's nonlinearity, thus improv...Stochastic resonance is a phenomenon in which adding random noise to a system enhances the detection or transmission of a weak signal. It occurs when the noise interacts with the system's nonlinearity, thus improving signal-to-noise ratio and increasing sensitivity. Although parametric resonances in an atomic spinor Bose-Einstein condensate have been investigated, the question of whether one can observe stochastic resonance in such a system persists. In this study we propose a scheme for generating stochastic resonance in a cavity-spinor Bose-Einstein condensate coupling system. We demonstrate stochastic resonance through numerical calculations using the mean-field theory and truncated Wigner approximation methods. Furthermore, the characteristics of the system's response to noise and periodic signals are studied in detail. This study unravels a new scheme for observing stochastic resonance via linking atomic many-body physics with cavity quantum electrodynamics.展开更多
In dielectrometry,traditional analytical and numerical algorithms are difficultly employed in complex resonant cavities.For a special kind of structure(a rotating resonant cavity),the body of revolution finite-element...In dielectrometry,traditional analytical and numerical algorithms are difficultly employed in complex resonant cavities.For a special kind of structure(a rotating resonant cavity),the body of revolution finite-element method(BOR-FEM)is employed to calculate the resonant parameters and dielectric parameters.In this paper,several typical resonant structures are selected for analysis and verification.Compared with the resonance parameter values in the literature and the simulation results of commercial software,the error of the BOR-FEM calculation is less than 0.9%and a single solution time is less than 1 s.Reentrant coaxial resonant cavities loaded with dielectric materials are analyzed using this method and compared with simulation results,showing good agreement.Finally,in this paper,the established BOR-FEM method is successfully applied with a machined cavity for the accurate measurement of the complex dielectric constant of dielectric materials.The test specimens were machined from polytetrafluoroethylene,fused silica and Al_(2)O_(3),and the test results showed good agreement with the literature reference values.展开更多
基金the National Natural Science Foundation of China (Grant Nos. 40528005 and 40390152)
文摘The global distribution properties of Ultra Low Frequency wave (ULF) in the inner magnetospgere and its interactions with energetic particles, such as the wave-particle resonance, modulation, and particle acceleration, are active topics in space physics research. These problems are fundamentally important issues to understand the energy transport from the solar wind into the magnetosphere. In this paper we briefly reviewed the recent research progress on ULF wave and its interactions with energetic particles in the inner magnetosphere; furthermore, we suggested some open questions for future study.
基金This study was tSnancally supported by the China Postdoctoral Science Foundation （No. 20090461433）, and the National Natural Science Foundation of China （No. 30900352）.
文摘Background Malignant sinonasal melanoma （MSM） is a rare tumor with a perplexing signal intensity due to variable histopathologic components. This study was undertaken to delineate its MR imaging features. Methods MR imaging findings of 10 patients （6 women and 4 men, mean age 61.3 years old） with pathologically confirmed MSM were retrospectively reviewed. The location, size, signal intensity, enhancement, and internal imaging characteristics of all tumors were evaluated. Signal intensity and degree of enhancement was graded in comparison with the gray matter and adjacent muscle uptake, respectively. Results There were 8 tumors that were pathologically confirmed to contain melanin. Compared to gray matter of the brain, 7 of them demonstrated hyperintensity on T1WI and 6 （6/7） showed hypointensity on T2Wl. There was multiple linear, dark-signal intensity on T2Wl within the mass in 9 of the 10 patients＇ tumors. Evaluated with gadolinium-enhanced imaging, all 10 patients showed moderate enhancement within the areas that were isointense in the lesion on pregadolinium TlWl. Moreover, some parts which displayed hyperintensity on TlWl within the tumors of 7 patients showed mild enhancement that was similar to muscle on a time-intensity curve （TIC）. Conclusions MSM shows characteristic MR signal intensity （hyperintensity on TlWl and the linear, low-signal intensity on T2Wl）, which may provide valuable information for clinical diagnosis. Together with conventional MRI, TIC may be useful for indicating pleomorphic patterns of MSM.
基金This work was supported by grants from Beijing Excellent Talents Foundation （No.2010D003034000033）,Beijing Municipal Natural Science Foundation （No.7112030）,High Levels of Health Technical Personnel in Beijing City （No.2011-3-047） and China Postdoctoral Science Foundation （No.2011M500026）.
文摘Background Quantitative dynamic contrast enhancement MR imaging （DCE-MRI）,used to measure properties of tissue microvasculature and tumor angiogenesis,is a promising method for distinguishing benign and malignant tumors and characterizing tumor response to antiangiogenic treatment.The aim of this study was to assess the feasibility of quantitative parameters derived from clinically used DCE-MRI for distinguishing benign from malignant tumors in the sinonasal area,which may be potentially useful for prediction and monitoring of treatment response to chemoradiotherapy of sinonasal tumors.Methods One hundred and forty-three patients with sinonasal tumors,including 78 malignant tumors and 65 benign tumors and tumor-like lesions,underwent clinically used DCE-MRI.Parametric maps were obtained for quantitative parameters including Ktrans,kep and ve.Two radiologists reviewed these maps and measured Ktrans,kep and ve in the tumor tissue.Data were analyzed using independent T-test or Mann-Whitney U test analysis and receiver operating characteristic curves.Results Ktrans,kep and ve showed significant differences between benign and malignant tumors in the sinonasal area （P=-0.000 1）.The accuracy of Ktrans,kep and ve in differentiation between benign and malignant sinonasal tumors were 72.0％,76.2％ and 67.1％,respectively.There were significant differences in kep and ve between malignant epithelial sinonasal tumors and lymphomas （P ＜0.05）.Using a ve value of 0.213 as the threshold value differentiated malignant epithelial tumors from lymphomas with an accuracy of 78.3％,sensitivity of 88.2％,specificity of 68.0％,positive predictive value of 66.7％,and negative predictive value of 90.9％.However,no significant difference in Ktrans and kep was found between malignant epithelial and non-epithelial tumors in the sinonasal area （P ＞0.05）.Conclusions It is feasible that quantitative parameters of tumors can be derived from clinically used DCE-MRI in the sinonasal region.Preliminary findings suggest an
基金This work was supported by Beijing Excellent Talents Foundation （No. 2010D003034000033）, Beijing Municipal Natural Science Foundation （No. 7112030）, and High Levels of Health Technical Personnel in Beijing City （No. 2011-3-047）.
文摘Background Distinguishing inverted papilloma （IP） from malignant tumors in the nasal cavity is difficult in a substantial number of cases,thus hindering the administration of appropriate therapeutic strategies.This study aimed to evaluate whether magnetic resonance imaging （MRI）,including dynamic contrast enhanced MRI （DCE-MRI）,could improve differentiation between IP and malignant tumors,and to identify which MRI features were the best in discriminating IP from malignant tumors in the nasal cavity.Methods Non-enhanced,static,and dynamic contrast enhanced MRI was performed in 88 patients with an IP or a malignant tumor in the nasal cavity that had been confirmed by histological results.MRI features of IP and malignant tumors including side,margin,T1 signal intensity,T1 homogeneity,T2 signal intensity,T2 homogeneity,lobulation signs,convoluted cerebriform pattern,extra-sinonasal involvement,pattern of enhancement,Tpeak,Tmax,Clmax,and TIC type were evaluated and correlated with histological findings.Results There were significant differences between IP and malignant tumors in T2 homogeneity,Iobulation signs,convoluted cerebriform pattern,extra-sinonasal involvement,Tpeak,Tmax and TIC types.A convoluted cerebriform pattern had a higher sensitivity and specificity in diagnosis of IP while washout-type TIC had a higher sensitivity and specificity in diagnosis of malignant tumors in the nasal cavity.Non-enhanced combined with static and dynamic enhancement MRI was significantly superior to non-enhanced combined with static enhancement MRI in the differentiation of IP and malignant tumors in the nasal cavity.Multivariate logistic regression analysis identified that the best MRI features were a convoluted cerebriform pattern,extra-sinonasal involvement,and washout-type TIC for both observers （Wang XY and Zhang ZY）.Conclusion Non-enhanced and static combined with dynamic contrast-enhanced MRI improves differentiation of IP and malignant tumors in the nasal cavity.
基金the National Natural Science Foundation of China(Grant Nos. 40425004, 40528005, 40390152)the National Basic Research Program of China (Grant No. 2006CB806305)
文摘Based on observations obtained by Cluster C1, GOES 10, 12, and Polar, the global ULF wave properties are studied during the recovery phase of a very intense magnetic storm-Halloween storm (October 31, 2003, 21:00–23:00 UT). The results indicate that the ULF waves’ properties observed by different satellites, such as amplitude, period, etc. show large variations. This can be interpreted as that Field Line Resonance (FLR) might take place in the region where Cluster C1 passed. The compressional wave of the cavity mode coupled with FLR’s shear Alfven wave and fed energy to the latter, forming a large-amplitude toroidal mode. From the point of period, Cluster C1 observed the shortest period, GOES 10, 12 observed the middle, while Polar observed the longest. The wave period of toroidal mode observed by Cluster C1 kept almost unchanging when Cluster C1 passed L range from 11.7 to 5.3. Using the Squared Wavelet Coherence analysis method, we estimated that the FLR region in the dayside magnetosphere could expand to at least 4 local time widths. The toroidal mode observed by Polar was a standing wave, while the poloidal mode was a propagating wave, the observation results could be well explained by the waveguide mode theory. Since the solarwind speed V <SUB>x</SUB> was −800 km/s and the dynamic pressure varied little, we speculated that the source of the ULF wave was the Kelvin-Helmholtz instability at the magnetopause triggered by high speed solarwind.
基金supported by the National Natural Science Foundation of China(Grant No.51037001)
文摘The cavity-mode resonance effect could result in significant degradation of the shielding effectiveness （SE） of a shielding enclosure around its resonance frequencies. In this paper, the influence of coated wall loss on the suppression of the resonance effect is investigated. For this purpose, an equivalent circuit model is employed to analyze the SE of an apertured rectangular cavity coated with an inside layer of resistive material. The model is developed by extending Robinson＇s equivalent circuit model through incorporating the effect of the wall loss into both the propagation constant and the characteristic impedance of the waveguide. Calculation results show that the wall loss could lead to great improvement on the SE for frequencies near the resonance but almost no effect on the SE for frequencies far away from the resonance.
基金supported by the Innovation Program for Quantum Science and Technology (Grant No. 2021ZD0303200)the National Natural Science Foundation of China (Grant Nos. 12074120, 12234014, 11654005, 11964014, and 12364046)+4 种基金the Shanghai Municipal Science and Technology Major Project (Grant No. 2019SHZDZX01)the National Key Research and Development Program of China (Grant No. 2016YFA0302001)the Innovation Program of the Shanghai Municipal Education Commision (Grant No. 202101070008E00099)the Major Discipline Academic and Technical Leader Training Program of Jiangxi Province (Grant No. 20204BCJ23026)the Fundamental Research Funds for the Central Universities。
文摘Stochastic resonance is a phenomenon in which adding random noise to a system enhances the detection or transmission of a weak signal. It occurs when the noise interacts with the system's nonlinearity, thus improving signal-to-noise ratio and increasing sensitivity. Although parametric resonances in an atomic spinor Bose-Einstein condensate have been investigated, the question of whether one can observe stochastic resonance in such a system persists. In this study we propose a scheme for generating stochastic resonance in a cavity-spinor Bose-Einstein condensate coupling system. We demonstrate stochastic resonance through numerical calculations using the mean-field theory and truncated Wigner approximation methods. Furthermore, the characteristics of the system's response to noise and periodic signals are studied in detail. This study unravels a new scheme for observing stochastic resonance via linking atomic many-body physics with cavity quantum electrodynamics.
基金the National Natural Science Foundation of China(Grant No.62001083)the Guangdong Provincial Key Research and Development Project,China(Grant No.2020B010179002).
文摘In dielectrometry,traditional analytical and numerical algorithms are difficultly employed in complex resonant cavities.For a special kind of structure(a rotating resonant cavity),the body of revolution finite-element method(BOR-FEM)is employed to calculate the resonant parameters and dielectric parameters.In this paper,several typical resonant structures are selected for analysis and verification.Compared with the resonance parameter values in the literature and the simulation results of commercial software,the error of the BOR-FEM calculation is less than 0.9%and a single solution time is less than 1 s.Reentrant coaxial resonant cavities loaded with dielectric materials are analyzed using this method and compared with simulation results,showing good agreement.Finally,in this paper,the established BOR-FEM method is successfully applied with a machined cavity for the accurate measurement of the complex dielectric constant of dielectric materials.The test specimens were machined from polytetrafluoroethylene,fused silica and Al_(2)O_(3),and the test results showed good agreement with the literature reference values.
