Based on the particle-in-cell technology and the secondary electron emission theory, a three-dimensional simulation method for multipactor is presented in this paper. By combining the finite difference time domain met...Based on the particle-in-cell technology and the secondary electron emission theory, a three-dimensional simulation method for multipactor is presented in this paper. By combining the finite difference time domain method and the panicle tracing method, such an algorithm is self-consistent and accurate since the interaction between electromagnetic fields and particles is properly modeled. In the time domain aspect, the generation of multipactor can be easily visualized, which makes it possible to gain a deeper insight into the physical mechanism of this effect. In addition to the classic secondary electron emission model, the measured practical secondary electron yield is used, which increases the accuracy of the algorithm. In order to validate the method, the impedance transformer and ridge waveguide filter are studied. By analyzing the evolution of the secondaries obtained by our method, multipactor thresholds of these components are estimated, which show good agreement with the experimental results. Furthermore, the most sensitive positions where multipactor occurs are determined from the phase focusing phenomenon, which is very meaningful for multipactor analysis and design.展开更多
According to the dimensional tolerances on hydrodynamic journal bearing system, a nonlinear oil film force model was established,and the Reynolds' equation was solved by adopting finite difference method. In order...According to the dimensional tolerances on hydrodynamic journal bearing system, a nonlinear oil film force model was established,and the Reynolds' equation was solved by adopting finite difference method. In order to fulfill different dimensional tolerances in the system,adopting 2kfactor design and using the eccentricity ratio corresponding to the stability critical curve,the effects of the friction power loss brought by the dimensional tolerances of the dynamic viscosity,bearing width,bearing diameter and journal diameter were analyzed. The effect on dynamic characteristics of the hydrodynamic journal bearing system was quantitatively analyzed,and the nonlinear dynamic analysis, modeling and calculation methods were studied while considering the manufacturing tolerances. The results show that in contrast to the impacts of the tolerances in journal diameter,dynamic viscosity and bearing width,the bearing diameter tolerance would lead to the rise in the power loss, and the dimensional tolerances have different degrees of impacts on the journal bearing system. The friction power loss decreased as the eccentricity ratio increased, and when the eccentricity ratio was 0. 695 the power loss came to the minimum.The investigation would find the best solution and reduce energy consumption,then control varieties of nonlinear dynamical behavior effectively,and provide a theoretical basis for hydrodynamic journal bearing system in parameter design.展开更多
Objective: To assess the preoperative serum levels of vascular endothelial growth factor (VEGF) in ovarian masses compared to normal controls and to find a correlation between VEGF and Doppler indices in ovarian masse...Objective: To assess the preoperative serum levels of vascular endothelial growth factor (VEGF) in ovarian masses compared to normal controls and to find a correlation between VEGF and Doppler indices in ovarian masses. Methods: The study was conducted from December 2009 to September 2012 in the oncology and ultrasound units in department of obstetrics and gynecology, Ain Shams University on 150 patients with ovarian masses. During preoperative workup, serum Ca-125 levels and serum VEGF levels were obtained. Ultrasonographic examination included two and three dimensional power Doppler ultrasound (3DPD). Laparotomic approaches were undertaken to obtain the final pathologic results. VEGF was measured in one hundred normal cases as controls. Results: Final ovarian pathology revealed seventy three malignant ovarian masses and seventy seven were benign. Serum Ca-125 levels in malignant cases were higher compared to those in benign cases (p < 0.001). Preoperative serum VEGF revealed higher levels in malignant ovarian masses than benign conditions and normal controls (p < 0.001). Three dimensional power Doppler indices, vascularization index (VI), flow index (FI) and vascularization flow index (VFI), correlated positively with serum VEGF levels. Conclusion: Preoperative serum VEGF revealed higher levels in malignant ovarian masses than benign conditions and normal controls. These levels positively correlated with the Doppler vascular indices of the masses.展开更多
The changes in characteristics of Bose condensation of ideal Bose gas due to an external generic power law potential U =∑~d_（i=1）ci｜xi/ai｜~（ni） are studied carefully. Detailed calculation of Kim et al.（J. Phys...The changes in characteristics of Bose condensation of ideal Bose gas due to an external generic power law potential U =∑~d_（i=1）ci｜xi/ai｜~（ni） are studied carefully. Detailed calculation of Kim et al.（J. Phys. Condens. Matter 11（1999） 10269） yielded the hierarchy of condensation transitions with changing fractional dimensionality. In this manuscript, some theorems regarding specific heat at constant volume CV are presented. Careful examination of these theorems reveal the existence of hidden hierarchy of the condensation transition in trapped systems as well.展开更多
Semiconductor nanowires, with their unique capability to bridge the nanoscopic and macroscopic worlds, have been demonstrated to have potential applications in energy conversion, electronics, optoelectronics, and bios...Semiconductor nanowires, with their unique capability to bridge the nanoscopic and macroscopic worlds, have been demonstrated to have potential applications in energy conversion, electronics, optoelectronics, and biosensing devices. Onedimensional（1D） ZnO nanostructures, with coupled semiconducting and piezoelectric properties, have been extensively investigated and widely used to fabricate nanoscale optoelectronic devices. In this article, we review recent developments in 1D ZnO nanostructure based photodetectors and device performance enhancement by strain engineering piezoelectric polarization and interface modulation. The emphasis is on a fundamental understanding of electrical and optical phenomena, interfacial and contact behaviors, and device characteristics. Finally, the prospects of 1D ZnO nanostructure devices and new challenges are proposed.展开更多
基金Project supported by the National Key Laboratory Foundation,China(Grant No.9140C530103110C5301)
文摘Based on the particle-in-cell technology and the secondary electron emission theory, a three-dimensional simulation method for multipactor is presented in this paper. By combining the finite difference time domain method and the panicle tracing method, such an algorithm is self-consistent and accurate since the interaction between electromagnetic fields and particles is properly modeled. In the time domain aspect, the generation of multipactor can be easily visualized, which makes it possible to gain a deeper insight into the physical mechanism of this effect. In addition to the classic secondary electron emission model, the measured practical secondary electron yield is used, which increases the accuracy of the algorithm. In order to validate the method, the impedance transformer and ridge waveguide filter are studied. By analyzing the evolution of the secondaries obtained by our method, multipactor thresholds of these components are estimated, which show good agreement with the experimental results. Furthermore, the most sensitive positions where multipactor occurs are determined from the phase focusing phenomenon, which is very meaningful for multipactor analysis and design.
基金National Natural Science Foundations of China(No.11272100,No.50865001)
文摘According to the dimensional tolerances on hydrodynamic journal bearing system, a nonlinear oil film force model was established,and the Reynolds' equation was solved by adopting finite difference method. In order to fulfill different dimensional tolerances in the system,adopting 2kfactor design and using the eccentricity ratio corresponding to the stability critical curve,the effects of the friction power loss brought by the dimensional tolerances of the dynamic viscosity,bearing width,bearing diameter and journal diameter were analyzed. The effect on dynamic characteristics of the hydrodynamic journal bearing system was quantitatively analyzed,and the nonlinear dynamic analysis, modeling and calculation methods were studied while considering the manufacturing tolerances. The results show that in contrast to the impacts of the tolerances in journal diameter,dynamic viscosity and bearing width,the bearing diameter tolerance would lead to the rise in the power loss, and the dimensional tolerances have different degrees of impacts on the journal bearing system. The friction power loss decreased as the eccentricity ratio increased, and when the eccentricity ratio was 0. 695 the power loss came to the minimum.The investigation would find the best solution and reduce energy consumption,then control varieties of nonlinear dynamical behavior effectively,and provide a theoretical basis for hydrodynamic journal bearing system in parameter design.
文摘Objective: To assess the preoperative serum levels of vascular endothelial growth factor (VEGF) in ovarian masses compared to normal controls and to find a correlation between VEGF and Doppler indices in ovarian masses. Methods: The study was conducted from December 2009 to September 2012 in the oncology and ultrasound units in department of obstetrics and gynecology, Ain Shams University on 150 patients with ovarian masses. During preoperative workup, serum Ca-125 levels and serum VEGF levels were obtained. Ultrasonographic examination included two and three dimensional power Doppler ultrasound (3DPD). Laparotomic approaches were undertaken to obtain the final pathologic results. VEGF was measured in one hundred normal cases as controls. Results: Final ovarian pathology revealed seventy three malignant ovarian masses and seventy seven were benign. Serum Ca-125 levels in malignant cases were higher compared to those in benign cases (p < 0.001). Preoperative serum VEGF revealed higher levels in malignant ovarian masses than benign conditions and normal controls (p < 0.001). Three dimensional power Doppler indices, vascularization index (VI), flow index (FI) and vascularization flow index (VFI), correlated positively with serum VEGF levels. Conclusion: Preoperative serum VEGF revealed higher levels in malignant ovarian masses than benign conditions and normal controls. These levels positively correlated with the Doppler vascular indices of the masses.
文摘The changes in characteristics of Bose condensation of ideal Bose gas due to an external generic power law potential U =∑~d_（i=1）ci｜xi/ai｜~（ni） are studied carefully. Detailed calculation of Kim et al.（J. Phys. Condens. Matter 11（1999） 10269） yielded the hierarchy of condensation transitions with changing fractional dimensionality. In this manuscript, some theorems regarding specific heat at constant volume CV are presented. Careful examination of these theorems reveal the existence of hidden hierarchy of the condensation transition in trapped systems as well.
基金Project supported by the National Major Research Program of China(Grant No.2013CB932602)the National Key Research and Development Program of China(Grant No.2016YFA0202701)+6 种基金the Program of Introducing Talents of Discipline to Universities,China(Grant No.B14003)the National Natural Science Foundation of China(Grant Nos.51527802,51232001,51602020,51672026,and 51372020)China Postdoctoral Science Foundation(Grant Nos.2015M580981 and 2016T90033)Beijing Municipal Science&Technology Commission,Chinathe State Key Laboratory for Advanced Metals and Materials,China(Grant No.2016Z-06)the Fundamental Research Funds for the Central Universities,ChinaJST in Japan,Research and Education Consortium for Innovation of Advanced Integrated Science
文摘Semiconductor nanowires, with their unique capability to bridge the nanoscopic and macroscopic worlds, have been demonstrated to have potential applications in energy conversion, electronics, optoelectronics, and biosensing devices. Onedimensional（1D） ZnO nanostructures, with coupled semiconducting and piezoelectric properties, have been extensively investigated and widely used to fabricate nanoscale optoelectronic devices. In this article, we review recent developments in 1D ZnO nanostructure based photodetectors and device performance enhancement by strain engineering piezoelectric polarization and interface modulation. The emphasis is on a fundamental understanding of electrical and optical phenomena, interfacial and contact behaviors, and device characteristics. Finally, the prospects of 1D ZnO nanostructure devices and new challenges are proposed.
