全面了解高清晰度电视兼议地面广播移动接收

高清晰度电视(以下简称高清电视)是在现代微电子技术、通信技术和信息技术高度发展的基础上集多方面的成就于一身的高科技产物,在我国已是热门话题。它的发展标志着一个国家的技术水平和经济实力,并能带动整个电子信息技术及相关产业领域的发展,成为技术发展的驱动器和经济发展的倍增器。高清电视是在现行三大彩色电视广播制式存在着一系列缺陷的情况下开发研制出来的新的电视系统。日本N H K率先从上世纪六十年代末开始探索新的电视系统,提出了H D T V这个术语并被各国普遍接受。“高清晰度电视”一词名称的概念是不完整、不确切的,它容…     

陶瓷湿度传感器

我国(日本)很早就处于高温多湿的环境下,过去一直致力于以温度为中心的环境控制.但为了能更好地进行环境控制须同时控制温度和湿度.又由于整个工业界都在进行系统化,所度要求研制包括湿度传感器在内的各种传感器.即如家庭用的电气产品中的冷暖房设备的湿度控制,检测干燥机的水分以及电子炉等的食品烹调器的湿度检测等等,都是属于湿度传感器的应用范围.但在这些用途中,由于要求高精的并能稳定地计测宽范围的湿度,所以     

7Li2分子B1Ⅱu以及X1∑+g态的准确平衡几何、离解能及谐振频率

使用SAC/SAGCI方法,利用6-311G,6.311++G,6-311G(3df,3pd),D95V(d,p),D95,D95V,6-311++C（3af,3Pd),D95(3df,3t,d)、cc-PVTZ和AUG-cc-PVTZ等基组.对Li2分子的B1Ⅱu及X1∑+8态的平衡几何进行了优化计算.同时,在优化得到的平衡位置附近、于同一条件下通过精细的单点能扫描,也获得了相应基组下的平衡核间距.发现优化计算结果与精细的单点能扫描结果不一致.分析表明由单点能扫描获得的平衡核间距应更为合理.通过对平衡按间距及计算离解能的比较,得出了对B1ⅡU态而言AUG-OC-P扩12基组为最优基组的结论.在AUG-cc-PyIZ基组下,于0.135～l.5 nm范围內,利用SAC的GSUM(Group Sum of Operators)方法对X1∑+8态、SAC-CI的GSUM方法对月B1Ⅱu态进行单点能扫描、井用正規方程组拟合出了相应的解析势能函数.利用解析势能函数的物理意义并结合RKR方法,计算出了X1∑+8态及B1Ⅱu态的谐振频率,理论计算结果与实验值较为一致.     

Coherent Scattering of Light by Bose-Einstein Condensation in a Tight Confinement

We have observed strong scattering of a probe light by dilute Bose-Einstein condensate （BEC） ^87Rb gas in a tight magnetic trap. The scattering light forms fringes at the image plane. It is found that we can infer the real size of the condensation and the number of the atoms by modelling the imaging system. We present a quantitative calculation of light scattering by the condensed atoms. The calculation shows that the experimental results agree well with the prediction of the generalized diffraction theory, and thus we can directly observe the phase transition of BEC in a tight trap.     

解读"十一五"发展纲要中推进三网融合的含义

2006年3月14日我国政府正式公布的“十一五”发展纲要提出：“加强宽带通信网、数字电视网和下一代互联网等信息基础设施建设,推进‘三网融合’,健全信息安全保障体系”,对前一个五年规划中“促进电信、电视、计算机三网融合”的提法做了进一步的界定.     

7Li2分子23Πu激发态的解析势能函数、振动能级及其转动惯量

使用Gaussian03程序包中的“对称性匹配簇-组态相互作用”方法、在0.13—2.0nm的核间距范围内利用6-311 G(d,p)基组对7Li2(23Πu)分子的势能曲线进行了计算,同时使用最小二乘法将计算结果拟合成了解析势能函数.利用拟合出的解析势能函数并结合Rydberg-Klein-Rees方法,计算了该态的谐振频率,进而计算了该态的其他光谱常数,分别为Te=3.6701eV,De=1.0764eV,Re=0.3000nm,ωe=285.69cm-1,ωeχe=1.8351cm-1,αe=0.00942cm-1和Be=0.5340cm-1,其中光谱常数Te,De,Re和ωe的值与文献值相符很好.以得到的解析势能函数为基础,通过求解双原子分子核运动的径向Schr dinger方程,发现J=0时7Li2(23Πu)分子存在67个振动态,求出了相应于每一振动态的振动能级、振动经典转折点及转动惯量.     

All-Optical RZ-to-NRZ Format Conversion with a Tunable Fibre Based Delay Interferometer

All-optical format conversion from return-to-zero （RZ） to non-return-to-zero （NRZ） is demonstrated with temperaturecontrolled all-fibre delay interferometer （DI） at 20 Gb/s. The operation principle is theoretical analysed with the help of numerical simulation and spectra analysis. Theoretical analysis results are consistent well with the experimental results. The format conversion can be achieved with power penalty of 0.54 dB and with output extinction ratio 20 dB.     

Growth and Characterization of A1GaN/A1N/GaN HEMT Structures with a Compositionally Step-Graded A1GaN Barrier Layer

A new A1GaN/A1N/GaN high electron mobility transistor （HEMT） structure using a compositionally step-graded A1GaN barrier layer is grown on sapphire by metalorganic chemical vapour deposition （MOCVD）. The structure demonstrates significant enhancement of two-dimensional electron gas （2DEG） mobility and smooth surface morphology compared with the conventional HEMT structure with high A1 composition A1GaN barrier. The high 2DEG mobility of 1806 cm2/Vs at room temperature and low rms surface roughness of 0.220 nm for a scan area of 5μm×5 μm are attributed to the improvement of interracial and crystal quality by employing the stepgraded barrier to accommodate the large lattice mismatch stress. The 2DEG sheet density is independent of the measurement temperature, showing the excellent 2DEG confinement of the step-graded structure. A low average sheet resistance of 314.5Ω/square, with a good resistance uniformity of 0.68%, is also obtained across the 50 mm epilayer wafer. HEMT devices are successfully fabricated using this material structure, which exhibits a maximum extrinsic transconductance of 218 mS/ram and a maximum drain current density of 800 mA/mm.     

Ab Initio Comparative Study of Zincblende and Wurtzite ZnO

By employing the first-principles pseudopotential plane-wave method, the physical properties of zincblende ZnO are investigated in comparison with those of the common wurtzite structure. Zincblende ZnO is predicted to be a direct gap semiconductor. Compared to the wurtzite structure, the zincblende ZnO is characterized by smaller bandgap and pressure coefficient, larger electron effective mass, increasing static dielectric constants and more covalent bonding. Furthermore, the optical properties including dielectric function and energy loss function of zincblende ZnO were obtained and analysed with some features. These aspects reveal promising applications of zincblende ZnO in optoelectronic devices.     

一种宽带贴片天线的设计与仿真

介绍了微带贴片天线的特点、原理和设计方法，针对孔径耦合的馈电方式，运用以有限元法为原理的软件对设计的贴片天线进行仿真，并对天线参数进行优化，结果表明孔径耦合微带贴片天线结构简单，可以达到21％的相对带宽（VSWR〈2），和较高的增益。同时对影响天线性能的主要参数进行仿真对比，得出了实用性的结论，对方便有效地改进电子对抗装备性能有一定的意义。