一种C波段雷达微带天线阵列的设计与实现

对C波段微带天线阵列在雷达方面的工程应用进行了理论和实验研究.首先根据经典理论设计微带天线阵列的基本制造因素;然后通过全波仿真软件对微带天线阵列进行数值模拟和优化,从而确定贴片单元和馈电网络的参数;最后制作了微带天线阵列实物,验证了设计方法的有效性.试验结果表明:制作的微带天线阵列测量结果与仿真结果基本吻合,满足工程要...     

蓝牙微带贴片天线的设计分析

短距离的蓝牙通信主要用于室内的无线通信，要求蓝牙天线的体积和尺寸都很小，并且要求和物体共形。根据这种需求，设计了一种可工作于蓝牙频段的微带天线，在HR娼软件进行了建模和性能仿真，并通过微带阻抗变换器对天线的输入端进行匹配，最后得到了能用于室内通信的良好性能的蓝牙微带天线。     

短距离无线通信中小型双频微带天线的研究

设计了一种小型的双频微带天线,使用曲流技术、双谐振模式分别实现了天线的小型化和双频带工作。对天线的仿真及测试结果表明,天线工作在2.4 GHz频段和5.8 GHz频段,且在两个频段上具有较一致的良好的辐射特性,二者的相对带宽分别是1.38%和3.94%。     

毫米波降雨的衰减问题研究

在分析雨滴的尺寸和外形、雨滴的介电特性基础上,提出基于ITU-R建立的雨衰减预报模型,对降雨衰减进行了计算和分析。100GHz以下的毫米波降雨衰减,则降雨衰减与降雨率、频率有强的关系,降雨率越大,频率越高,降雨衰减越大;不同极化下毫米波降雨衰减随降雨率变化关系,可得垂直极化衰减率较小,其次是圆极化,最大的是水平极化。     

浅析天线技术研究与应用

自1837年诞生了无线电通信开始,天线技术的研究与应用从未停止过。在种类繁多,功能各异的天线家族中,大到以山体为依托的巨型射电天文天线,小到各种微型无线设备中的微带天线,归纳起来就是我们通常所说的"线"天线和"面"天线两大类。随着无线通信技术的快速发展,目前,频率、时间和编码技术的潜力已发挥到极致,因此,以新型天线系统为代表的空间资源的开发越来越受到重视。本文在给出室内、外电波传播模型的基础上,着重介绍一组新型天线及研究进展。     

疲劳的火车

德国。一列高速列车在轨道上行驶着，乘客们有的在打瞌睡，有的望着窗外的景色凝想，有的在轻声交谈。谁也不会想到，一场灾难正在向他们逼近。突然，列车剧烈的颠簸起来，随着“吱吱”的急刹车声，列车发生了断裂，顷刻间，车厢七扭八歪倒在了地上，火光闪耀，浓烟四起，尖叫声、哭喊声、呻吟声交织在了一起。列车出轨，使得100多条生命瞬间陨灭。后经调查，造成事故的原因竟然是因为车轮内部疲劳断裂引起的。     

午休做梦

吃过午饭，站在阳台上，消停了一下。大概12点40分左右上床睡下了。和平时没有什么区别，不知不觉地进入了梦乡。我在一座寓所里睡觉，卧室里装饰是白色的，灰白色的床架，洁白的被单床罩，柔和的床垫，挺舒服的。不知什么时候，进来了两个小孩子在地板上玩耍，     

高家镇攻坚战

高家镇农户万元增收工程打响攻坚战，实现了六个突破。 抓组织领导，在责任落实上实现了突破；抓产业规划，在落实增收模式上实现了突破；抓技术服务，在提高致富能力上实现了突破；抓示范带动，在万元增收速度上实现了突破；抓农商对接，在凸显特色产业上实现了突破；抓结对帮扶，在帮农支农护农上实现了突破。基本形成了一户一业、一村一品的产业发展新格局。     

当家人 沼气建设热心人——王福记

王福记同志洪洞县万安镇南步亭村人。今年四十五岁，高中文化。 他在建沼气当中，多次外出取经、虚心肯学、不断请示上级，尊重上级，受到了上级的好评。由于王福记同志刻苦钻研，在沼气建设过程中，摸索出理论和实践相结合的整套方法，先后在两个乡镇建了300余个沼气池，在沼气建设工作上付出了艰辛的劳动，做出了突出的贡献，取得了可喜的成绩。     

对职业教育的几点思考

1职业教育的现状 随着国家高等教育改革的实施，大学教育逐渐成为全民教育，普高升学率达到了60％～70％，随之出现的问题是，大学生就业难。在这种情况下，职高停止了师资教育，个别学校转向了培训幼儿教师，不过人数很少。但国家改革开放的步伐在加大，各地都在大上工业，搞旅游服务业，中国迎来了建国以来又一个人口大迁涉的高潮，成千上万的农民工走上了外出打工的致富路。     

Enhanced enantioselectivity in excitation of chiral molecules by superchiral light

A molecule or larger body is chiral if it cannot be superimposed on its mirror image (enantiomer). Electromagnetic fields may be chiral, too, with circularly polarized light (CPL) as the paradigmatic example. A recently introduced measure of the local degree of chiral dissymmetry in electromagnetic fields suggested the existence of optical modes more selective than circularly polarized plane waves in preferentially exciting single enantiomers in certain regions of space. By probing induced fluorescence intensity, we demonstrated experimentally an 11-fold enhancement over CPL in discrimination of the enantiomers of a biperylene derivative by precisely sculpted electromagnetic fields. This result, which agrees to within 15% with theoretical predictions, establishes that optical chirality is a fundamental and tunable property of light, with possible applications ranging from plasmonic sensors to absolute asymmetric synthesis.     

High-resolution nuclear magnetic resonance spectroscopy in a circularly polarized laser beam

Nuclei in a fluid subjected to a continuous wave circularly polarized light beam are predicted to experience a static magnetic field proportional to E(+/-) x E(+/-), where E(+/-) is the electric vector of the right or left circularly polarized wave and the dot denotes a time derivative. The field strongly depends on the local electronic structure and is present in all atoms. For an intensity of 10 watts per square centimeter propagating in the direction of the field of a magnetic resonance spectrometer, the general theory presented here predicts shifts of +/- 4 x 10(-8) hertz for protons and +/- 10(-5) hertz for fluorine-19. Larger shifts are predicted if the laser frequency is near an optical absorption.     

Frequency Dependence of Polarization of Pulsar CP 0328

The circularly polarized emission from the pulsar CP 0328 has an approximately flat spectrum in the 1-megahertz band centered at 113.6 megahertz, whereas the linearly polarized emission varies with frequency and from pulse to pulse. A simple model for the source that has a constant Faraday rotation measure fits some of the linearly polarized spectra observed for individual pulses, but changes in the rotation measure of as much as 30 radians per square meter are required between adjacent pulses. The simple model does not fit the average spectrum of the linearly polarized emission, although the average spectrum had the same form on two nights.     

Circular dichroism of biological macromolecules

Circular dichroism, the unequal absorption of right and left circularly polarized light, is a manifestation of optical activity in the vicinity of absorption bands. To the experimental scientist interested in the conformation of macromolecules and in the sensitive response of optical activity to conformational alteration, it offers a relatively new and powerful means of understanding the environment of chromophoric residues. As a tool in the elucidation of electronic spectra, it should be useful to the theoretical scientist in identifying weakly allowed absorption bands as well as in providing rotational parameters which can be compared with the developing theory of optical activity. I have stressed application of circular dichroism, to experimental aspects of protein and nucleic acid conformation in solution. Much is still uncertain in particular quantitative details. However, even these early results shed new light and yield new information on the conformation of these molecules.     

All-optical magnetic resonance in semiconductors

A scheme is proposed wherein nuclear magnetic resonance (NMR) can be induced and monitored using only optical fields. In analogy to radio-frequency fields used in traditional NMR, circularly polarized light creates electron spins in semiconductors whose hyperfine coupling could tip nuclear moments. Time-resolved Faraday rotation experiments were performed in which the frequency of electron Larmor precession was used as a magnetometer of local magnetic fields experienced by electrons in n-type gallium arsenide. Electron spin excitation by a periodic optical pulse train appears not only to prepare a hyperpolarized nuclear moment but also to destroy it resonantly at magnetic fields proportional to the pulse frequency. This resonant behavior is in many ways supportive of a simple model of optically induced NMR, but a curious discrepancy between one of the observed frequencies and classic NMR values suggests that this phenomenon is more complex.     

Spin-polarized hydrogen atoms from molecular photodissociation

The production of spin-polarized hydrogen atoms from the photodissociation of hydrogen chloride with circularly polarized 193-nanometer light is inferred from the measurement of the complete angular momentum distributions of ground state Cl(2P3/2)and excited state Cl(2P1/2)cofragments by slice imaging. The experimentally measured and ab initio predicted a q(k) (p)parameters, which describe the single-surface and multiple-surface-interference contributions to the angular momentum distributions, are in excellent agreement. For laser pulses longer than about 0.7 ns, the polarization of the electron and the proton are both 36%.     

The opposition effect of the moon: the contribution of coherent backscatter

The opposition effect, the sharp surge in brightness of an astronomical object observed near zero phase angle, which has been known for more than a century, has generally been explained by shadow hiding. The reflectances of several Apollo lunar soil samples have been measured as a function of phase angle in linearly and circularly polarized light. All samples exhibited a decrease in the linear polarization ratio and an increase in the circular polarization ratio in the opposition peak. This provides unequivocal proof that most of the lunar opposition effect is caused by coherent backscatter, not shadow hiding. This result has major implications for the interpretation of photometric observations of bodies in the solar system, including the Earth.     

Direct measurement of the preferred sense of NO rotation after collision with argon

The preferred sense of product molecule rotation (clockwise or counterclockwise) in a bimolecular collision system has been measured. Rotationally inelastic collisions of nitric oxide (NO) molecules with Ar atoms were studied by combining crossed molecular beams, circularly polarized resonant multiphoton ionization probing, and velocity-mapped ion imaging detection. The observed sense of NO product rotation varies with deflection angle and is a strong function of the NO final rotational state. The largest preferences for sense of rotation are observed at the highest kinematically allowed product rotational states; for lower rotational states, the variation with deflection angle becomes oscillatory. Quantum calculations on the most recently reported NO-Ar potential give good agreement with the observed oscillation patterns in the sense of rotation.     

Impact of reader antenna polarisation, distance, inlay design, conveyor speed, tag location and orientation on the coupling of UHF RFID as applied to modified atmosphere packaged meat

Undetected RFID tags make the potential benefits of RFID unattainable. This study aimed to determine the most significant factors that affect RFID and particularly its application to the traceability of meat. Experimental parameters included five RFID tag inlays, two levels of conveyor speeds, five variations of beef sample and an empty container, 12 tags per test sample, three distances and two types of reader antenna polarisations. Tag detection rates were determined in three replicates per combination of test parameters. A GLM ANOVA was carried out on tag detection rate. In decreasing order of significance in terms of the effect on mean tag detection rate were distance, sample, inlay design, conveyor speed and reader antenna polarisation. Interaction of these factors also proved significant, in decreasing order of importance were reader antenna * inlay, sample type * distance, inlay * distance, sample type * inlay, sample type * reader antenna, distance * speed, sample type * speed and finally sample type * distance * speed. Linearly polarised antenna preformed better overall at detecting tags, with 63% mean detection rate compared with circularly polarised antenna with 57% mean detection rate. Varying the tag inlay resulted in mean detection rates of between 62% and 88%. Ideal transponder location on package was reader antenna polarisation dependent, but generally tags facing reader antennas exhibited better detection rate. Results revealed that the under side of the package was the most un-detectable transponder location, considering the placement of reader antennas on top, left and right sides of the sample. Conveyor speed also proved significant with a variation from 0.5 to 1.0 m/s resulting in an average detection rate ranging from 62% to 57%, respectively. Circularly polarised antennas are believed to perform better in cases of random tag orientation on products. It can be concluded that RFID systems implementation in the meat supply chain requires a holistic approach where distances, polarisations, inlay type, meat composition and conveyor speed need to be considered.     

Direct spectroscopic detection of a zwitterionic excited state

Two electrons in two weakly coupled orbitals give rise to two states (diradical) with electrons residing in separate orbitals and two states (zwitterionic) with both electrons paired in one orbital or the other. This two-electron, two-orbital state manifold has eluded experimental confirmation because the zwitterionic states have been difficult to locate. Two-photon excitation of fluorescence from Mo(2)CI(4)(PMe(3))(4) (D2d) has been measured with linearly and circularly polarized light. From the polarization ratio and the energy of the observed transition, the 2(1)A(1) (delta*delta*) excited state has been located and characterized. In conjunction with the one-photon allowed (1)B(2) (deltadelta*) excited state, the zwitterionic state manifold for the quadruply bonded metal-metal class of compounds is thus established.