微带线实现环形交叉耦合带通滤波器的设计

本文设计一种应用于小型化微波系统的微带线环形交叉耦合带通滤波器,可以更好改善系统的性能,应用较广泛.     

基于GIS的北京城市公园绿地景观格局分析

运用景观生态学和地理信息系统的理论与方法,按照斑块大小对北京城八区的公园绿地进行分类统计,计算出不同类型公园绿地的面积、数量等景观单元特征指数,计算出不同类型公园绿地的多样性指数、破碎化指数、分离度等景观异质性指数,在此基础上,进行公园绿地景观格局分维分析,得出如下结论:1)城市公园绿地类型组成不协调,大型公园比例偏大,小型、中小型公园比例偏小;2)城市公园绿地的布局不尽合理,城市中心缺乏“绿心”,局部过于分散。3)城市公园绿地多样性不高,景观破碎度大,特别是小型斑块,人为影响严重。在城八区中,海淀区的绿地景观相对比较好。4)公园绿地边界简单,分维数普遍较低,不利于生物多样性的保护。通过对公园绿地的景观格局分析,为北京公园绿地规划及绿色奥运建设提供决策支持。     

Glutamate and γ-aminobutyric acid receptors and their characteristics in retina

Glutamate and Ⅱ-aminobutyric acid (GABA) are important neurotransmitters in the retinal neuronal circuitry. Using the whole-cell patch clamp technique and a rapid solution changer, glutamate and GABA receptors in the retina have been extensively investigated. Results indicate that glutamate receptors on horizontal cells may be an AMPA preferring subtype, which predominantly consists of flop splice variants. GABAA and GABAC receptors coexist in bipolar cells, with the latter showing significant desensitization. Kinetics analysis has demonstrated that the activation, deactivation and desensitization of the GABAC receptor-mediated response of these cells are overall slower than those of the GABAA response. Endogenous modulator Zn2 + in the retina has been found to differentially modulate the kinetic characteristics of the GABAC and GABAA responses.     

超高频RFID读写器天线的设计与仿真

基于RFID系统对天线的要求,针对单馈电微带天线回波损耗和轴比之间的矛盾,利用理论计算和Ansoft HFSS软件仿真优化的方法设计出了一种用于RFID读写器的新型超高频圆极化微带天线.该天线采用背馈的方法,相对于侧馈有效地减小了天线的尺寸.为实现良好的圆极化性能,该天线利用空气作为介质层.并且采用非对称矩形切角,相对于当前普遍采用的对称等腰直角三角形切角更容易加工和调整.经过仿真分析得出了各种参数的曲线图,验证了该天线的优越性能.     

Modulation of presynaptic nAChRs on postsynaptic GABA receptor in optic tectum of juvenile<Emphasis Type="Italic">Xenopus</Emphasis>

Using the blind patch-clamp technique with the whole-cell mode,we have studied the modulation presynaptic receptor on postsynaptic γ-raminobutyric acid (GABA) receptor measuring miniature inhibitory postsynaptic currents (mIPSCs)in optic tectum of Xenopus during critical peroid.It was demonstrated that compared with mature neurons,mIPSCs recorded from immature neurons had smaller amplitude and longer decay time.mIPSCs are mediated by GABAa receptor.The nicotinic acetylcholine receptor agonists(carbachol,cytisine,nicotine,DMPP and so on) could increase the frequency of mIPSCs.The enhancement of mIPSCs frequency induced by nAChR agonists was calcium-dependent.However,the choline,a product of hydrolyzed acetylcholine,could not increase the frequency of mIPSCs.DH-β-E,a competitive antagonist of nAChR,blocked the increase of mIPSCs frequency induced by carbachol.Mecamyllamine,an α3β4 subtype of nAChR antagonist,also blocked the carbachol-induced enhancement of mIPSCs.On the other hand,MLA,α7 subtype of nAChR antagonist,had no effect on it .Thus,it seems that nAChR could presynaptically modulate the mIPSCs and α3β4 subtype of nAChR might be involved.But α7 nAChR subtype of nAChR would not be involved.The modulation is calcium-dependent.Meanwhile,we found that Ca^2 -free solution could elicit giant PSCs.The frequency of mIPSCs also is related with the level of HP.     

制造公差对悬置微带天线性能的影响

根据修改的微带天线的腔模理论,利用电磁场理论推导了悬置矩形微带天线的谐振频率的理论计算公式,为了减小微带天线制作中的各种因素所引起的谐振频率的偏移,对微带天线的不准确性进行误差分析和仿真研究,结果表明,各种制造公差对谐振频率的影响程度不同。     

土地整理对区域景观格局的影响——以湖北省安陆市辛榨乡基本农田整理项目为例

土地整理是区域景观变化的主要驱动力之一,其生态影响可以通过景观格局的变化表现出来．结合国家投资基本农田整理项目的空间数据与属性数据。选取景观单元特征指数、景观多样性指数、景观破碎化指数等三大类指数与9小类指标,在AutoCAD与MapGIS平台上提取与处理空间数据和属性数据。并计算出各指标量整理前后的变化．结果表明：土地整理后斑块密度指数减少,景观多样性指数降低,破碎度指数减小,水田的优势度增高且更具有连通性,景观异质程度下降,景观类型有向单一化和非均衡化方向发展的趋势。景观中各类型斑块在空间上的分布也出现非均衡化．     

用馈电校正优化设计双馈点圆极化微带天线

该文提出用馈电校正的方法来改善圆极化天线的轴比性能.通过增加附加并联枝节改变双馈电点处信号幅度和相位的相对分布,抵消高次模辐射和馈电网络寄生辐射的影响,将高次模辐射和寄生辐射都考虑在内,来实现馈电校正.在X波段采用全波一体化优化方法设计出双馈点宽带圆极化微带天线.该文给出了仿真结果及实测数据.获得的实测结果为:中心频率为10GHz,电压驻波比小于2的带宽为33.85%,圆极化轴比小于3dB的带宽为22.4%.与校正前的结果相比,轴比带宽从16.2%提高到22.4%.     

超宽带宽缝天线的设计与仿真

改进了一种基于宽缝微带天线结构的超宽带天线.利用Ansoft公司的HFSS对其进行了仿真计算,给出了反射损耗曲线和辐射方向图.该天线采用较低的介电常数(ε=2.2)和薄基板(h=0.8mm),获得了150%的阻抗带宽(S11≤-10 dB),频率范围是1.40~9.69 GHz.仿真结果和理论结果相符.