Large area microchannel plate detector with amorphous silicon pixel array readout for fast neutron radiography

Fast neutron radiography is a non-destructive testing technique with a variety of industrial applications and the capability for element sensitive imaging for contraband and explosives detection.

Commonly used position sensitive detectors for fast neutron radiography are based on charge coupled devices (CCDs) and scintillators. The limited format of CCDs implies that complex optical systems involving lenses and mirrors are required to indirectly image areas that are larger than 8.6 cm×11.05 cm. The use of optics reduces the light collection efficiency of the imaging system, while the efficiency of hydrogen rich scintillators exploiting the proton recoil reaction is limited by the hydrogen concentration and the magnitude of the neutron scattering cross-section.

The light conversion step inevitably involves a tradeoff in scintillator thickness between light yield and spatial resolution.

The development of large area amorphous silicon (a-Si) panel flat panel photodiode arrays and direct neutron-to-charge converters based on microchannel plates, provide an attractive new form of high resolution, large area, fast neutron imaging detector for the non-destructive imaging of large structures. This paper describes some recent results of both Monte Carlo simulations and measurements for such a detector.     

Micro-nano structured VNb9O25 anode with superior electronic conductivity for high-rate and long-life lithium storage

The oxygen vacancies and micro-nano structure can optimize the electron/Li+migration kinetics in anode materials for lithium batteries(LIBs).Here,porous micro-nano structured VNb9O25 composites with rich oxygen vacancies were reasonably prepared via a facile solvothermal method combined with annealing treatment at 800℃for 30 h(VNb9 O25-30 h).This micro-nano structure can enhance the contact of active material/electrolyte,and shorten the Li+diffusion distance.The introduction of oxygen vacancies can further boosts the intrinsic conductivity of VNb9O25-30 h for achieving excellent LIB performance.The as-prepared VNb9O25-30 h anode showed advanced rate capability with reversible capacity of 122.2 mA h g-1 at 4 A g-1,and delivered excellent capacity retention of～100％after 2000 cycles.Meanwhile,VNb9O25-30 h provides unexpected long-cycle life(i.e.,reversible capacity of 165.7 mA h g-1 at 1 A g-1 with a high capacity retention of 85.6％even after 8000 cycles).Additionally,coupled with the LiFePO4 cathode,the LiFePO4//VNb9O25-30 h full cell delivers superior LIB properties with high reversible capacities of 91.6 mA h g-1 at 5C for 1000 cycles.Thus,such reasonable construction method can assist in other high-performance niobium-based oxides in LIBs.     

板带轧机随机干扰模型与ARMA谱分析

板带轧机随机干扰模型不易建模,是制约轧机随机动力特性研究的主要难点之一。基于某铝热连轧机轧制１２３５铝合金的轧制力随机数据,得到平稳、正态、零均值的时间序列,采用时序分析法建立轧制力的ＡＲＭＡ模型及轧机动态干扰功率谱密度模型,分析了轧制力的ＡＲＭＡ谱特性,采用麦夸特法＋通用全局优化算法,得出便于工程应用的轧制力功率谱表达式,构建轧制力随机干扰模型。对轧制力的预报、轧机动刚度的确定及对轧机与轧制过程的随机动态性研究与分析具有一定的意义。     

A simple power supply and control unit for pulsed operation of a microchannel plate imaging detector

A simple power supply and control electronic system to operate microchannel plate (MCP) detectors for imaging transient events such as X-ray emission from laser-produced plasmas is described. The power supply consists of two parts, viz. a high voltage pulse generator of 1 kV amplitude with a variable pulse duration of 100 μs to 1 ms for the MCP input, and a regulated 5 kV d.c. for biasing the phosphor screen. The control unit synchronizes the high voltage pulse with the event and operates a safety switch to guard the detector against any accidental rise in the background pressure. A signal-to-noise ratio ≥ 75 is obtained, limited by the noise contribution of the Charge Coupled Device (CCD)-frame grabber combination attached to the MCP. The system is compact, has provision for both positive and negative pulses, is extendable to higher voltages for operating two-stage MCP, and is immune to electromagnetic interference.     

梁与正交各向异性板弯曲波的传递特性研究

以正交各向异性板与各向同性梁耦合系统弹性波传递特性为研究对象,基于弯曲波传播的动力学分析,推导出子系统间的功率流传递系数(power flow transmission coefficient,PTC)和耦合边界处的耦合损耗因子(coupling loss factor,CLF)表达式.计算分析了内损耗因子、频率和方向...     

电容器盖板自动预压机及其控制系统设计

针对电容器盖板预压工序存在自动化程度低、劳动强度大等不足,设计了电容器盖板自动预压机及其控制系统.对电容器盖板自动预压机的机械系统进行了详细设计,包括铝壳放置转盘组件、电容器定位组件、盖板预压组件、电容器推出组件、电容器接收组件等;采用可编程序逻辑控制器(programmable logic controller,PLC)作为控制系统的主控制器,实现多种规格电容器盖板的自动预压;依据电容器高度的不同,通过图形操作终端(graphic operating terminal,GOT)设置和调整生产参数.该设备已投入实际生产使用,运行结果表明:整机性能稳定,实际运行状况良好,满足了生产线高柔性化、高效率、高质量的自动化加工要求.     

Novel method for determining the fast axis and phase retardation of a wave plate using Fresnel Rhomb

In this study, an optical scheme based on the measurement of light intensity and a proper orientation of the Fresnel Rhomb is successfully developed for simultaneous determination of the phase retardation and fast axis of a wave plate. The theoretical analysis of the principle of measuring the reflection-induced retardance of the Fresnel Rhomb and the phase retardation of a wave plate is given taking Stokes–Mueller Formalism as a mathematical tool. In this method, the fast axis position of the wave plate need not be determined in advance. In addition, the measured result is free of the intensity fluctuation of light source. An application example is also demonstrated. The measured result of the example is verified with an experiment. Some of the merits of the method, such as, a simple optical set-up, high stability and high accuracy, low cost and easier operation, are presented, and the validity of the method is demonstrated.     

姿控飞轮电控系统共模辐射分析与抑制

 为降低飞轮电控系统对其他星载电子设备的电磁干扰,以PWM全桥电路共模辐射源为研究对象,重点分析由开关管和散热片协同导致的共模辐射．建立铝制带鳍散热片计算模型,应用有限元数值计算法分析散热器能量耦合及辐射发射机理,以屏蔽作为主要抑制手段,研究屏蔽板尺寸、放置位置及通风孔对共模辐射抑制效应,并进一步提出屏蔽板改进结构．计算结果表明：使用2块屏蔽板在正确放置时就可有效抑制辐射,且屏蔽板越长,对共模辐射抑制效果越好;屏蔽板上有孔缝存在,对应的辐射就要比无孔时高,开孔个数本身对辐射的影响并不大．改进后的结构对共模辐射抑制效果更优于原结构,尤其体现在3.9 GHz窄频带范围内．     

Multi-state reliability assessment for shipboard hybrid turbine-diesel generation system with redundancy and aging effects

Complex system structures, dynamic energy demands, and tough operating environment pose a huge challenge to reliability assessment and risk control. Taking multi-state, redundant structure and aging impact into account, reliability assessment for shipboard hybrid turbine-diesel generation system is studied. This work adopts a comprehensive method combining the Markov method and universal generating function (UGF): the Markov method is used for reliability modeling at the unit level, and then synthesized and calculated through UGFs to obtain system-level reliability. Based on the above methodology, this work presents a multi-state system (MSS) model with different configuration structures and failure rate types, then compares the availability evaluation results of the single power generation system, the hybrid power system with redundancy and aging effects. The results show that (1) redundant design effectively improves system availability to meet power supply requirements; (2) in the case of system aging and imperfect repair, redundant configuration and power distribution can significantly improve the availability of power supply to be almost unaffected by aging, and effectively reduce the risk of performance failure; and (3) when the redundancy is applied, the system power supply availability is not sensitive in the high-value range of the redundant installed capacity ratio, but sensitive in the high-value range of effective coefficient about power compensation control.