A band-pass frequency selective surface(FSS) with polarization rotation property is proposed. The proposed polarization rotating FSS(PR-FSS) is a two-dimensional periodic structure, its unit cell is an antenna-filter-...A band-pass frequency selective surface(FSS) with polarization rotation property is proposed. The proposed polarization rotating FSS(PR-FSS) is a two-dimensional periodic structure, its unit cell is an antenna-filter-antenna(AFA) module,and the polarization directions of the upper and lower antennas in each AFA module are orthogonal to each other, so the PR-FSS can achieve frequency selection and 90 degrees polarization rotation at the same time. The numerical simulation demonstrate that the anticipated frequency selection and polarization rotation are realized by the PR-FSS in the frequency band from 8.84 GHz to 10.30 GHz with a relative bandwidth of 15.26%, and the maximum insertion loss in the pass band is only 0.17 d B. Finally, one effective experiment validation is carried out, a reasonable agreement is observed between the experimental and simulated results except for a slight deviation caused by fabrication error and measurement tolerance.展开更多
In order to filter signal effectively according to selective center frequency, a voltage-controlled dynamic band-pass filter with gain compensation was designed based on voltage-controlled gain wideband amplifier VCA8...In order to filter signal effectively according to selective center frequency, a voltage-controlled dynamic band-pass filter with gain compensation was designed based on voltage-controlled gain wideband amplifier VCA810. The transfer function of the filter was analyzed and gain compensation voltages were given through tests; besides, a system was designed, including the gain compensation circuit and the control voltage circuit, etc. Center frequency will change from 1 kHz to 20 kHz according to control voltage on condition that bandwidth of the filter remains constant. The designed system has the advantages of simple structure, low noise, stable performance and convenient adjustment.展开更多
The application scope of the forward scatter radar(FSR)based on the Global Navigation Satellite System(GNSS)can be expanded by improving the detection capability.Firstly,the forward-scatter signal model when the targe...The application scope of the forward scatter radar(FSR)based on the Global Navigation Satellite System(GNSS)can be expanded by improving the detection capability.Firstly,the forward-scatter signal model when the target crosses the baseline is constructed.Then,the detection method of the for-ward-scatter signal based on the Rényi entropy of time-fre-quency distribution is proposed and the detection performance with different time-frequency distributions is compared.Simula-tion results show that the method based on the smooth pseudo Wigner-Ville distribution(SPWVD)can achieve the best perfor-mance.Next,combined with the geometry of FSR,the influence on detection performance of the relative distance between the target and the baseline is analyzed.Finally,the proposed method is validated by the anechoic chamber measurements and the results show that the detection ability has a 10 dB improvement compared with the common constant false alarm rate(CFAR)detection.展开更多
A novel method for noise removal from the rotating accelerometer gravity gradiometer(MAGG)is presented.It introduces a head-to-tail data expansion technique based on the zero-phase filtering principle.A scheme for det...A novel method for noise removal from the rotating accelerometer gravity gradiometer(MAGG)is presented.It introduces a head-to-tail data expansion technique based on the zero-phase filtering principle.A scheme for determining band-pass filter parameters based on signal-to-noise ratio gain,smoothness index,and cross-correlation coefficient is designed using the Chebyshev optimal consistent approximation theory.Additionally,a wavelet denoising evaluation function is constructed,with the dmey wavelet basis function identified as most effective for processing gravity gradient data.The results of hard-in-the-loop simulation and prototype experiments show that the proposed processing method has shown a 14%improvement in the measurement variance of gravity gradient signals,and the measurement accuracy has reached within 4E,compared to other commonly used methods,which verifies that the proposed method effectively removes noise from the gradient signals,improved gravity gradiometry accuracy,and has certain technical insights for high-precision airborne gravity gradiometry.展开更多
标准TCP把A d hoc网络中的移动丢包错误解释为拥塞丢包,从而不必要地启动拥塞控制,降低了TCP性能.目前绝大多数的方法都是利用中间节点的反馈信息来改善A d hoc网络中TCP性能.但当在同一条路由上同时发生多处链路中断时,现有方法在路由...标准TCP把A d hoc网络中的移动丢包错误解释为拥塞丢包,从而不必要地启动拥塞控制,降低了TCP性能.目前绝大多数的方法都是利用中间节点的反馈信息来改善A d hoc网络中TCP性能.但当在同一条路由上同时发生多处链路中断时,现有方法在路由重建后不能从正确的状态开始恢复TCP传输,使得TCP在刚恢复传输时就启动‘快速重传/快速恢复’.本文提出的TCP-FSR方法能够很好地解决这个问题,分析和试验证明此方法是有效的.展开更多
基金supported by the National Natural Science Foundation of China (Grant No. 62072378)Xi’an Science and Technology Plan Project, China (Grant No. GXYD20.4)。
文摘A band-pass frequency selective surface(FSS) with polarization rotation property is proposed. The proposed polarization rotating FSS(PR-FSS) is a two-dimensional periodic structure, its unit cell is an antenna-filter-antenna(AFA) module,and the polarization directions of the upper and lower antennas in each AFA module are orthogonal to each other, so the PR-FSS can achieve frequency selection and 90 degrees polarization rotation at the same time. The numerical simulation demonstrate that the anticipated frequency selection and polarization rotation are realized by the PR-FSS in the frequency band from 8.84 GHz to 10.30 GHz with a relative bandwidth of 15.26%, and the maximum insertion loss in the pass band is only 0.17 d B. Finally, one effective experiment validation is carried out, a reasonable agreement is observed between the experimental and simulated results except for a slight deviation caused by fabrication error and measurement tolerance.
文摘粪肠球菌是难治性根尖周炎(refractory apical periodontitis,RAP)的主要致病菌,该细菌可耐受严苛环境,引发根尖周免疫炎症反应,造成根管内外持续性感染。粪肠球菌黏附于根管牙本质壁形成生物膜,其耐药和抗冲刷能力显著增强,是介导其致病的关键因素。粪肠球菌与牙本质的黏附包括非特异性和特异性黏附,后者由黏附相关毒力因子介导,主要包括肠球菌胶原结合蛋白(adhesin of collagen from enterococci,Ace)、表面蛋白(extracellular surface protein,Esp)、明胶酶(gelatinase,GelE)和丝氨酸蛋白酶(serine prtease,SprE)、菌毛以及聚集物质,且受到多个双组份系统调控。Fsr双组份系统在群体密度增加时可以促进gelE及sprE的表达,GelE进一步减少表面肠球菌胶原结合蛋白Ace,而GrvRS双组份系统则在响应血清环境时直接下调ace的表达。CroRS双组份系统及WalRK双组份系统也可能分别促进和抑制包括ace及gelE在内的多种毒力因子的表达,进而影响粪肠球菌的黏附性。此外,根管机械/化学预备、根管内环境因素等均可对粪肠球菌牙本质黏附产生影响。根管治疗中避免粪肠球菌的引入和使用干扰黏附的药物可以有效预防粪肠球菌的黏附,而多种活化荡洗方法也可以有效增加根管内粪肠球菌的清除率。针对粪肠球菌牙本质黏附关键因子与调控因素为靶点设计合理药物,有望为根管感染控制提供新的思路与手段。本文就粪肠球菌与牙本质的黏附性及其影响因素进行综述。
文摘In order to filter signal effectively according to selective center frequency, a voltage-controlled dynamic band-pass filter with gain compensation was designed based on voltage-controlled gain wideband amplifier VCA810. The transfer function of the filter was analyzed and gain compensation voltages were given through tests; besides, a system was designed, including the gain compensation circuit and the control voltage circuit, etc. Center frequency will change from 1 kHz to 20 kHz according to control voltage on condition that bandwidth of the filter remains constant. The designed system has the advantages of simple structure, low noise, stable performance and convenient adjustment.
基金This work was supported by the National Natural Science Foundation of China(62071475,61890541,62171447).
文摘The application scope of the forward scatter radar(FSR)based on the Global Navigation Satellite System(GNSS)can be expanded by improving the detection capability.Firstly,the forward-scatter signal model when the target crosses the baseline is constructed.Then,the detection method of the for-ward-scatter signal based on the Rényi entropy of time-fre-quency distribution is proposed and the detection performance with different time-frequency distributions is compared.Simula-tion results show that the method based on the smooth pseudo Wigner-Ville distribution(SPWVD)can achieve the best perfor-mance.Next,combined with the geometry of FSR,the influence on detection performance of the relative distance between the target and the baseline is analyzed.Finally,the proposed method is validated by the anechoic chamber measurements and the results show that the detection ability has a 10 dB improvement compared with the common constant false alarm rate(CFAR)detection.
文摘A novel method for noise removal from the rotating accelerometer gravity gradiometer(MAGG)is presented.It introduces a head-to-tail data expansion technique based on the zero-phase filtering principle.A scheme for determining band-pass filter parameters based on signal-to-noise ratio gain,smoothness index,and cross-correlation coefficient is designed using the Chebyshev optimal consistent approximation theory.Additionally,a wavelet denoising evaluation function is constructed,with the dmey wavelet basis function identified as most effective for processing gravity gradient data.The results of hard-in-the-loop simulation and prototype experiments show that the proposed processing method has shown a 14%improvement in the measurement variance of gravity gradient signals,and the measurement accuracy has reached within 4E,compared to other commonly used methods,which verifies that the proposed method effectively removes noise from the gradient signals,improved gravity gradiometry accuracy,and has certain technical insights for high-precision airborne gravity gradiometry.
文摘标准TCP把A d hoc网络中的移动丢包错误解释为拥塞丢包,从而不必要地启动拥塞控制,降低了TCP性能.目前绝大多数的方法都是利用中间节点的反馈信息来改善A d hoc网络中TCP性能.但当在同一条路由上同时发生多处链路中断时,现有方法在路由重建后不能从正确的状态开始恢复TCP传输,使得TCP在刚恢复传输时就启动‘快速重传/快速恢复’.本文提出的TCP-FSR方法能够很好地解决这个问题,分析和试验证明此方法是有效的.
