Receive maximal-ratio combining with outdated arbitrary transmit antenna selection in Nakagami-m fading

The use of transmit antenna selection algorithms in multiple-antenna systems enables significant reduction in implementation cost and complexity while maintaining acceptable performance. An attractive and quite flexible selection algorithm is to allow the receiver to pick any of the transmit antennas that can satisfy a predetermined performance target. Such an algorithm is referred to as the arbitrarily ordered transmit antenna selection algorithm. However, the effectiveness of transmit antenna selection is decreased by several propagation impairments over the feedback channel from the receiver to the transmitter. Of these impairments, the feedback channel time delay may impose a significant impact on the achieved performance. This paper aims to investigate the impact of this time delay on the performance of receive maximal-ratio combining (MRC) diversity employing the arbitrarily ordered transmit antenna selection algorithm. In order to obtain quantitative measures for this impact, new expressions for various performance criteria are obtained by using the new derived formulas for the probability density function (pdf) and the moment generating function (MGF) of the combined signal-to-noise ratio (SNR). Numerical and simulation results are presented to illustrate the effect of delayed (i.e. outdated) feedback information on the system performance for various transmit antenna selection scenarios.     

High-gain power recycling of a Fabry-Perot Michelson interferometer for a gravitational-wave antenna

Power recycling was implemented on a fully suspended prototype interferometer with arm lengths of 20 m. A wave-front-sensing technique for alignment control of the suspended mirrors was also implemented, which allowed for several hours of stable operation. A power-recycling gain of greater than 12 was achieved, a significant increase over the highest gain in a suspended mirror Fabry-Perot Michelson interferometer reported to date.     

天线反射体的空间几何关系精密测量

采用数字工业摄影测量技术对天线反射体的空间几何关系进行精密测量和调整,并应用公共点坐标转换方法统一测量和调整过程中的坐标系。公共点坐标转换准确度可达±0.1 mm。天线主反射面表面准确度优于±0.26 mm,副反射面中心位置准确度优于0.7 mm,高度位置准确度优于0.5 mm时,某13 m口径抛物面天线接收和发送频率为f=19.6 GHz的Ka频段电磁波信号,天线反射体的电性能测试满足指标需求。与传统的天线反射体测量和调整方式相比,省去通过天线接收卫星信号扫描方向图调整副反射面姿态的大量工作,具有高准确度、高效、高可靠性等特点。     

结合天线选择和索引组合映射调制的MIMO系统研究

空间调制是一种高数据速率、低复杂度的多输入多输出无线传输技术,因其发射天线被信息序列随机激活,若被激活的信道状态不佳将导致系统误码性能下降.于是,提出一种结合天线选择和索引组合映射调制的传输方案.该方案将传统空间调制的激活天线索引比特和星座符号索引比特组合映射为一个新的调制符号,结合天线选择算法确定最佳发射天线子集,将新的调制符号通过最佳信道进行传输.在算法实现过程中采用了奇异值分解和硬限制检测等方法降低计算复杂度.实验分别仿真了两种天线选择算法下的系统性能.结果表明,提出的方案比传统的空间调制系统具有更好的误比特率特性.     

Integrated predictive maintenance strategy for manufacturing systems by combining quality control and mission reliability analysis

Predictive maintenance (PdM) is an effective means to eliminate potential failures, ensure stable equipment operation and improve the mission reliability of manufacturing systems and the quality of products, which is the premise of intelligent manufacturing. Therefore, an integrated PdM strategy considering product quality level and mission reliability state is proposed regarding the intelligent manufacturing philosophy of ‘prediction and manufacturing’. First, the key process variables are identified and integrated into the evaluation of the equipment degradation state. Second, the quality deviation index is defined to describe the quality of the product quantitatively according to the co-effect of manufacturing system component reliability and product quality in the quality–reliability chain. Third, to achieve changeable production task demands, mission reliability is defined to characterise the equipment production states comprehensively. The optimal integrated PdM strategy, which combines quality control and mission reliability analysis, is obtained by minimising the total cost. Finally, a case study on decision-making with the integrated PdM strategy for a cylinder head manufacturing system is presented to validate the effectiveness of the proposed method. The final results shows that proposed method achieves approximately 26.02 and 20.54% cost improvement over periodic preventive maintenance and conventional condition-based maintenance respectively.     

联合空间与角度的符号相干系数平面波成像北大核心CSCD

超声平面波成像是近年来一种应用较广泛的超快速超声成像方法,多角度相干平面波复合(Coherent Plane Wave Compounding,CPWC)成像在不过多损失速率的情况下,提升成像质量。但普通的CPWC方法只是简单复合多个角度延时叠加(Delay and Sum,DAS)后的数据,并未考虑到单个角度内以及多个角度之间数据的相关性。文章提出了一种联合空间与角度的符号相干系数(Angular Spatial Sign Coherence Factor,asSCF)平面波成像方法,将空间符号相干因子和角度符号相干因子创新性地融合到波束合成的过程中,充分考虑信号之间的相关性,旨在提升多角度复合成像质量。进行了仿真实验、仿体实验以及在体组织实验,对asSCF-CPWC方法、单一的符号相干系数法以及传统CPWC方法成像进行对比,结果发现asSCF-CPWC方法具有更好的横向分辨能力和成像对比度。     

Coherent beam combining: optical loss effects on power scaling

A model for a coherent array of amplifiers that has multiple stages and uses pairwise beam combining at the final stage has been developed. The model accounts for gain saturation of the individual amplifier elements, optical-coupling losses, and coherent-combining efficiency. The individual amplifier parameters are derived from experimental data. System size, efficiency, and output power are calculated as functions of optical-coupling efficiency and combining efficiency. Because of the exponential losses associated with pairwise beam combining, the coherent-combining losses are the dominant contribution to system efficiency reduction and increased system size.     

Output power limitation in a Xe laser pumped by a periodic-pulsed electric beam

We report the experimental and theoretical characteristics of generation at 1.73 μm for a Xe laser pumped with an electron beam of a pulsed electron accelerator operating at a repetition rate of up to 100 Hz. A decrease in the average output power with time is caused by electron-beam heating of the active medium.     

High cw power using an external cavity for spectral beam combining of diode laser-bar emission

In extension to known concepts of wavelength-multiplexing diode laser arrays, a new external cavity is presented. The setup simultaneously improves the beam quality of each single emitter of a standard 25 emitter broad-area stripe laser bar and spectrally superimposes the 25 beams into one. By using this external resonator in an "off-axis" arrangement, beam qualities of Mslow2<14 and Mfast2<3 with optical powers in excess of 10 W in cw operation are obtained.     

Outage probability of multiuser transmit antenna selection/maximal-ratio combining systems over arbitrary nakagami-m fading channels

The outage probability of multiuser diversity (MUD) in transmit antenna selection/maximal-ratio combining (TAS/MRC) systems is derived as an exact closed expression in independent and identically distributed (i.i.d.) Nakagami-m channels with an integer fading parameter. For a non-integer fading parameter, the exact outage probability is derived as a single infinite series of incomplete Gamma function. At high signal-to-noise ratios (SNRs), the analytical results deduce that the multiuser TAS/MRC systems can achieve a full diversity order equal to the product of the fading parameter, number of users, number of transmit antennas and number of receive antennas. The advantage of the total diversity gain becomes more pronounced on a severe fading channel. The achieved results provide an analytical framework for the assessment of multiuser TAS/MRC systems. All the derived expressions are verified by Monte Carlo simulations.     

抽水蓄能电站水泵水轮机的动静干涉与振动分析

针对抽水蓄能电站水泵水轮机运行过程中出现的振动问题,从产生共振的条件出发,分析了转轮叶片和活动导叶形成的叶栅组合的动静干涉机理。根据转轮对水力激振模式的动态响应,研究了不同叶栅组合方式对水力激振力的影响。建立流固耦合数学模型,对转轮、活动导叶、顶盖及底环等过流部件的动态特性进行了有限元分析,以7/20的叶栅组合为例,阐述了流体激发结构共振的可能性。为了避免过流部件发生共振以及由此产生的疲劳裂纹或断裂等事故,提出了最佳叶栅组合的选择原则、降低无叶区压力脉动的方法以及提高结构固有频率和降低局部应力集中系数的具体措施。     

Case study for hybrid power generation combining hydro- and photovoltaic energy resources in the Brazilian semiarid region

Clean Technologies and Environmental Policy - Hydropower is currently the primary energy resource to service the Brazilian electricity sector. However, the dry seasons in the Brazilian semiarid...     

Integrated power management circuit for piezoelectronic generator in wireless monitoring system of orthopaedic implants

Piezoelectric (PZT) materials are capable of converting the mechanical energy of compression into electrical energy. With the recent advent of extremely low-power electrical devices, PZT generators have become attractive in many kinds of applications, especially for biomedical applications. Piezoelectronic generators are used in a wireless monitoring system of orthopaedic implants. Due to their poor source characteristics, the efficiency of PZT generator is low. A hybrid direct current (DC)?DC, comprising a switched capacitor (SC) DC?DC converter and a low dropout (LDO) linear voltage regulator, is presented to improve conversion efficiency. A bandgap reference (BGR) circuit which works in sub-threshold region is also presented. Because SC DC?DC converter works in the highest voltage region in this system, small power supply current, including supply current through BGR and other auxiliary modules, means low power consumption. BGR?s power supply voltage can be varied from 3 to 16 V. Its supply current is only 3.2 μA at 125 C and its temperature coefficient is 46 ppm. Stacked switches technique is proposed to reduce leakage current in switching process of SC converter. Simulation results show that the efficiency of SC?s converter can reach 88%, that of LDO can reach 80% and that of the overall system can reach 66%, including power consumption of all auxiliary components, which is far higher than previous work.     

某抽水蓄能电站地下厂房热湿环境测试分析

水电站地下厂房的通风空调系统对维持厂房内的热湿环境,使其满足人员工作及设备运行的要求有着重要作用。为了对某抽水蓄能电站地下厂房的热湿环境进行评估,对主厂房各层空间空气的热湿参数及通风量进行测试,并结合室外天气状况得出室外天气对厂房内的热湿环境的影响。在测试过程中发现,其蜗壳层设备及管路表面结露问题严重。根据对结露现象的分析,提出相应的解决方案,为水电站地下厂房的热湿环境的调控提供参考。     

Synchronously pumped optical parametric oscillation in periodically poled lithium niobate with 1-w average output power

We report on a rugged all-solid-state laser source of near-IR radiation in the range of 1461-1601 nm based on a high-power Nd:YVO(4) laser that is mode locked by a semiconductor saturable Bragg reflector as the pump source of a synchronously pumped optical parametric oscillator with a periodically poled lithium niobate crystal. The system produces 34-ps pulses with a high repetition rate of 235 MHz and an average output power of 1 W. The relatively long pulses lead to wide cavity detuning tolerances. The comparatively narrow spectral bandwidth of <15 GHz is suitable for applications such as pollutant detection.     

一管多机布置抽水蓄能电站非线性动力学建模与瞬态分析

一管多机布置抽水蓄能电站存在共用管段引水系统,其中共用管段的水力耦合相互作用是抽水蓄能电站系统动力学建模的关键.考虑共用管段水力系统耦合作用,将其分解成多个仅依赖于各子管段流量的单变量函数,通过结合水泵水轮机组动态特性,建立一管多机布置抽水蓄能电站非线性动力学模型.利用数值模拟探究了两机在额定工况并列运行时,一机突甩全...     

Assessment of fire vulnerability for nuclear power plant safety systems by combining fault-and success-oriented logic with physical models

The time behaviour of potential accident sequences may carry important information regarding nuclear power plant (NPP) safety operation and shutdown. In the case of external and environmental events, the ability of NPP components to operate correctly can be changed dramatically in a short time. In contrast to the failures caused by internal events, these two groups of undesirable events may lead to dynamic dependent failures among components of one or several systems. Such kinds of failure should be taken into account in the models of NPP behaviour. To evaluate how successfully the tasks of the safety systems will be carded out, logical models such as fault trees are usually used. The fault trees are not efficient at describing the short-term changes of the failure probabilities for system components. A method that has some advantages over the pure fault tree logic is proposed. The main features of the method are demonstrated by using examples.     

Dielectric resonator probe arrays with sectoral hard horn for wideband spatial power combiners/dividers

Analysis of dielectric resonator probe (DRP) arrays operating in an oversized hard waveguide with sectoral hard horn excitation is presented. A single DRP excited by a coaxial probe is first investigated inside a hollow rectangular waveguide and a waveguide loaded with hard walls, respectively. Simulation results are compared with measurement results and show a good agreement. Then, a one-dimensional DRP array is analysed inside a dielectric-loaded, oversized waveguide with sectoral hard horn excitation. A full-wave analysis based on the region-by-region finite-difference time-domain technique is applied for the optimisation of array parameters such as inter-element coupling, active reflection coefficients and uniform excitation. Numerical results are compared with those generated by using commercial software and exhibit a very good agreement.     

High efficiency, diode pumped Nd:YAG ceramics slab laser with 230 W continuous-wave output power

Diode pumped zig-zag slab lasers are widely adopted for continuous-wave high power or pulsed high energy applications. Recently [J. Eur. Opt. Soc.-Rapid 6, 11041 (2011)] we started to investigate a new thin slab format in which pumping radiation input is obtained through the thin lateral faces (edge pumping) and the beam propagation takes place bouncing on these same lateral faces ("edge zig-zag"). We report on the optimized operation of a ceramic Nd:YAG laser, based on this geometry, extracting 230 W at a 43% output power to diode power conversion efficiency. Thorough investigation of the thermal lens effect allows us to analyze the optical cavity and thus to define the main aspects limiting the present laser configuration.     

All-fiber quasi-continuous wave supercontinuum generation in single-mode high-nonlinear fiber pumped by submicrosecond pulse with low peak power

We demonstrate quasi-continuous wave supercontinuum generation in a single-mode high-nonlinear fiber (HNLF) in 1.55 μm band, which is pumped by the amplified passively Q-switched submicrosecond pulse. The pump wavelength is in the normal dispersion region of HNLF and near to the zero-dispersion wavelength. The broad SC spectral range from 1200 to 2260 nm is obtained with the low pump peak power of 17.8 W. The 20 dB bandwidth of 922 nm from 1285 to 2207 nm is obtained with the assumption that the peak near 1560 nm is filtered. The spectrum density for the 20 dB bandwidth is from -27.5 to -7.5 dbm/nm.