卫星通信在民航应用的动态

航空卫星通信最近发展较快,其原因是航线增加、航路拥挤.为了保证飞行安全,提高航运效率,为旅客提供优质的服务,许多国家的民航公司都想尽早应用卫星通信.本文介绍民用航空卫星通信的现状与未来发展趋势,并阐述实现卫星通信必须解决的一些关键技术.     

化合物半导体材料制片技术探讨

本文主要探讨化合物半导体材料磨片、抛光工艺中与表面质量有光的因素,并对一些不利因素提出了改进措施。     

CONOPT: A GRG code for large sparse dynamic nonlinear optimization problems

The paper presents CONOPT, an optimization system for static and dynamic large-scale nonlinearly constrained optimization problems. The system is based on the GRG algorithm. All computations involving the Jacobian of the constraints use sparse-matrix algorithms from linear programming, modified to deal with the nonlinearity and to take maximum advantage of the periodic structure in dynamic models. The paper presents the main features of the system, espcially the inversion routines and their data structures, the dynamic setting of tolerances in Newton’s algorithm, and the user features in the overal packaging. The difficulties with implementing a practical GRG algorithm are described in detail. Computational experience with some medium to large models is presented, idicating the viability of CONOPT for certain real-life problems, particularly those involving almost as many constraints as variables. The views and interpretations in this document are those of the author and should not be attributed to the World Bank, to its affiliated organizations or to any individual acting in their behalf.     

锁相频率合成式立体声调频器的分析与设计

锁相频率合成法调频技术不仅解决了普通调频器载频稳定度与调频性能之间的矛盾,而且具有许多独特的优点.本文分析了锁相频率合成式立体声调频器的工作原理,给出了环路参数及其部件的设计原则,并列出了一些主要测试结果.     

A solid-state frequency source for radio astronomy in the 100 to 1000 GHz range

A compact Gunn oscillator-multiplier combination can provide the for SIS receivers necessary LO power up to 1000 GHz. Frequency multiplication factors of 2 to 8 are accomplished in a single step using a Schottky mixer diode in the varistor mode.     

Bis(tetraethylthiophosphoramidoyl)methylamine as an electrochemical ligand for the simultaneous detection of iron and copper bivalent cations

A new thiophosphoramide-based electrochemical ligand was synthesized and used as a bivalent metallic cation sensor. Electrochemical studies reveal a sensitive detection process toward various cations such as Fe²⁺, Co²⁺, Ni²⁺, Cd²⁺, Cu²⁺ and Ca²⁺. The chelation process was accompanied by dramatic changes in the redox properties of the free ligand. Interestingly, the ligand shows a simultaneous sensing behavior towards iron and copper cations. The oxidation peak potentials of the two complexes can be well separated, allowing sensitive detection. Furthermore, UV–Visible spectra showed redshifts of absorbance bands of the free ligand in the presence of cations due to the coordination of the thiophosphoryl groups. Electrochemical and UV–Visible studies confirmed that the metal-ligand complexes have 1:2 stoichiometry.     

GaAlAs激光器腔面减反射涂层

通过对波长９１０ｎｍ ＧａＡｓ／ＧａＡｌＡｓ激光器谐振腔面蒸镀ＺｒＯ２膜的工艺过程，从理论和实验上分析了涂层特性，透射率由无膜时６２％提高到蒸镀膜后的９４％以上，提高了激光器的激光输出功率和工作寿命，对器件端面起到了保护作用。     

Compensation for the mutual coupling effect for the ESPRIT algorithm in single snapshot array processing

An effective method is introduced to compensate the effects of mutual coupling for the Estimation of Signal Parameter via Rotational Invariance Techniques (ESPRIT) direction finding algorithm in application of signal snapshot array processing.Changing the covariance matrix into a Teoplitz matrix can achieve high resolution in the Direction Of Arrive (DOA) estimation.How the mutual coupling affects the array antennas has been discussed and a new definition of mutual im- pedance has been used to characterize the mutual coupling effects between the array elements.Based on the new mutual impedance matrix,a practical method is presented to eliminate the effects of mutual coupling for ESPRIT in the single snapshot data processing.The simulation results show that, this new method not only properly reduces the effects of mutual coupling,but also maintains its steady performance even for weak signals.     

基于酉ESPRIT的多频带融合ISAR成像

多频带融合成像可有效提高ISAR成像的距离分辨率。传统的ESPRIT谱估计融合算法只利用了复数观测数据本身,而没有利用其共轭数据。该文提出对合成复观测数据及其共轭的酉ESPRIT法进行调整以实现基于酉ESPRIT法的多频带融合ISAR成像。酉ESPRIT法充分利用复数观测数据信息,更有利于多频带融合的频谱估计和ISAR成像。针对多频带融合中目标散射点越分辨单元徙动校正的问题,调整了传统校正处理的步骤,分别在多频带融合前进行越距离单元徙动校正和融合后进行越多普勒单元徙动校正,避免了回波中的快时间频率-慢时间耦合项以及时域相位补偿对频域融合处理的影响,从而得到效果更好的多频带融合ISAR图像。仿真和实测数据结果表明所提方法不但能得到高质量的融合ISAR图像,也具有更优的抗噪性能和更高的运算效率。

     

某数字组件电子束焊接技术改进研究

雷达产品所用某组件壳体结构复杂,气密性要求高,采用了较为先进的电子束焊接,但在实际生产中其成品率较低,对电子束焊接的主要影响因素-配合间隙、扫描参数及点焊方法进行了详细的分析,并提出了改进电子束焊接方法的具体措施.实践证明所采用的电子束改进方法是成功的,对类似问题的解决提供了有益的参考.