全欧数字式移动无线电系统的六种中比特速率编码器的评估

自1982年以来,在欧洲邮政与电信管理联合会(CEPT)的移动通信专家组(GSM)协调下,一种数字式蜂窝状移动无线电系统在欧洲已经在研制之中。在最近的一次协调实验中,已完成了对此系统的六种待选的16kbit/s 语声编码方案输出的试听评价测试。实验包含一个规则脉冲激励编码器,一个多脉冲激励编码器,和四个子带编码器。由 CSELT(意大利)主持了一次实验性会议,在七个不同的实验室里完成其主观测试。为了比较的目的,实验中包含了对正在使用的一种蜂窝式压扩 FM 系统的测试。这六种编译码器 Codec 在主观质量,传输延迟,和实现的难易程度方面进行了比较。在这方面的对比中,没有哪个 Codec 在各方面都好。总之,规则脉冲激励的线性编测预码器(RPE-LPC)能提供最好的语声质量,它有允许的复杂性和延迟,因而被选出供进一步改进。最后,这种 Codec 的一种改进形式,即带有长期预测的规则脉冲激励 LPC(RPE—LPC)编码器被选用于欧洲数字移动系统。     

56名退伍兵带出400多个万元户

豫南大地涌现了一个万元户“体群”。这个“群体”,是由一帮泥腿子们组成的。是谁带富了这些世代贫困的农民?是一帮名不见经传的退伍兵. 确山县刘店乡独山村蕴藏着丰富的石灰石资源。多少年来,人们身居宝山不识宝,端着金碗要饭吃,世代与贫穷厮守。1983年退伍兵宋国明、孟宪章、栗保玉被选拔     

辩证认识人的特点 增强思想政治工作效益

有效的思想政治工作是建立在对教育对象的深刻分析基础上的。用辩证法来把握人的基本特点,进而揭示人的活动规律,为思想政治教育提供直接的理论指导,使思想政治教育增强感染力、针对性和有效性。主导价值观与五彩纷呈的个人价值取向兼容,要求防止和克服对人认识的定势化,思想政     

Evaluation of effectiveness of polymer coatings in reducing blast-induced deformation of steel plates

Incorporating elastomers such as polymers in protective structures to withstand high energetic dynamic loads, has gained significant interest. The main objective of this study is to investigate the influence of a Polyurea coating towards the blast-induced response in steel plates. As such, Polyurea coated steel plates were tested under near-field blast loads, produced by the detonation of 1 kg of spherical nitromethane charges, at a standoff distance of 150 mm. Mild steel (XLERPLATE 350) and high-strength steel (BIS80) plates with thicknesses of 10 mm were Polyurea coated with thicknesses of 6 mm and 12 mm on either the front (facing the charge) or the back face. The deformation profiles were measured using 3D scanning. Numerical simulations were performed using the non-linear finite element code LS-DYNA. The strain-dependent behaviour of the steel and Polyurea were represented by Johnson-cook and Money-Rivlin constitutive models, respectively. The numerical models were validated by comparing the plate deflection results obtained from the experiments and were then used in the subsequent parametric study to investigate the optimum thickness of the Polyurea coating. The results indicate that back face coating contributes towards an approximately 20% reduction in the residual deformation as well as the absence of melting of the Polyurea layer, while the front-face coating can be used a means of providing additional standoff distance to the steel plates.     

Experimental and numerical investigations of interface properties of Ti6Al4V/CP-Ti/Copper composite plate prepared by explosive welding

Explosive welding technique is widely used in many industries. This technique is useful to weld different kinds of metal alloys that are not easily welded by any other welding methods. Interlayer plays an important role to improve the welding quality and control energy loss during the collision process. In this paper, the Ti6Al4V plate was welded with a copper plate in the presence of a commercially pure titanium interlayer. Microstructure details of welded composite plate were observed through optical and scanning electron microscope. Interlayer-base plate interface morphology showed a wavy structure with solid melted regions inside the vortices. Moreover, the energy dispersive spectroscopy analysis in the interlayer-base interface reveals that there are some identified regions of different kinds of chemical equilibrium phases of Cu–Ti, i.e. CuTi, Cu₂Ti, CuTi₂, Cu₄Ti, etc. To study the mechanical properties of composite plates, mechanical tests were conducted, including the tensile test, bending test, shear test and Vickers hardness test. Numerical simulation of explosive welding process was performed with coupled Smooth Particle Hydrodynamic method, Euler and Arbitrary Lagrangian-Eulerian method. The multi-physics process of explosive welding, including detonation, jetting and interface morphology, was observed with simulation. Moreover, simulated plastic strain, temperature and pressure profiles were analysed to understand the welding conditions. Simulated results show that the interlayer base plate interface was created due to the high plastic deformation and localized melting of the parent plates. At the collision point, both alloys behave like fluids, resulting in the formation of a wavy morphology with vortices, which is in good agreement with the experimental results.     

Impact of atmospheric turbulence on coherent beam combining for laser weapon systems

The performance of a laser weapon system based on coherent beam combining (CBC) depends on its propagation properties in the atmosphere. In this study, an analytical model based on partial coherent beam combining (PCBC) for assumed coherence coefficients between beams in a CBC lattice was developed. The Kolmogorov model of atmospheric turbulence and the Hufnagel-Valley model of Cn2 dependence on atmospheric parameters were implemented. Novel simplified metrics were proposed to assess the CBC performance. Several beam profiles (super-Gaussian, truncated Gaussian, etc.) and ge-ometries were analyzed in terms of maximal intensity in the far field. An approximate formula for PCBC efficiency dependent on the Fried radius was proposed. The results of CBC modeling were compared to those of the Gaussian beam propagation model in a turbulent atmosphere. The dependence of CBC performance on the Cn2 parameter, range, and elevation angle was analyzed. It could be concluded that the application of CBC for medium and long range propagation is impractical without an effective adaptive optics system.     

Damage to aircraft composite structures caused by directed energy system: A literature review

This paper presents a comprehensive review of the research studies on direct energy system effect on aircraft composite structures to develop a good understanding of state-of-the-art research and devel-opment in this area. The review begins with the application of composite materials in the aircraft structures and highlights their particular areas of application and limitations. An overview of directed energy system is given. Some of the commonly used systems in this category are discussed and the working principles of laser energy systems are described. The experimental and numerical studies re-ported regarding the aircraft composite structures subject to the effect of directed energy systems, especially the laser systems are reviewed in detail. In particularly, the general effects of laser systems and the relevant damage mechanisms against the composite structures are reported. The review draws attention to the recent research and findings in this field and is expected to guide engineers/researchers in future theoretical, numerical, and experimental studies.     

挥师黑土地——黑龙江省民兵预备役官兵为振兴老工业基地做贡献纪实

在祖国的版图上,黑龙江省位于东北边疆,像一只迎着朝曦展翅高飞的黑天鹅。美丽富饶的黑龙江,是资源大省和边境大省。     

今天和明天的潜艇作战系统

今天典型的作战系统综合了潜艇上所有的传感器系统和武器系统。主要传感器设备通常由许多声呐系统构成,包括中频被动声呐、低频被动声纳和被动测距声呐。除声呐系统外,综合到作战系统的还有两个潜望镜、ESM接收机、各种电罗经和计程仪以及无线电导航辅助的导航系统和导航雷达。 目前潜艇上的主要武器是线导鱼雷,某些艇上还载有导弹。作战系统的典型功能包括传感器综合、决策/咨询支持以及武器使用。