Multichannel (e,2e) apparatus

We describe an apparatus for the coincident observation of both outgoing electrons in an electron impact ionization, or (e,2e), experiment. The device employs ten detectors arranged such that every pair corresponds to a different set of momenta for the outgoing electrons intercepted by that pair. By simultaneously monitoring the output from all ten detectors it is possible to perform 25 simultaneous (e,2e) experiments. The results of these experiments can be compared without considering temporal variations of source conditions.     

Longitudinally excited N(2) lasers without high-voltage switches

We have developed novel excitation circuits without high-voltage switches for two longitudinally excited N(2) lasers (wavelength: 337 nm). One uses a single tube without a trigger and the other uses a tandem tube with a trigger. In both systems, the discharge tube acts as a switch. In the single-tube system, the laser output energy was 125.8 microJ and the efficiency was 0.16% at 18 Torr (2.4 kPa) when a slow-rising voltage pulse of -28 kV was applied (rise time: 21.3 micros). In the tandem-tube system, the laser output energy was 259.4 microJ and the efficiency was 0.11% at 18 Torr when a slow-rising voltage pulse of -48 kV was applied (rise time: 27 micros).     

A novel method for the fabrication of AlGaN/GaN HEMTs on Si (111) substrates

In this paper, the development of a novel manufacturing process is presented for fabricating high-quality AlGaN/GaN high-electron-mobility transistors (HEMTs) on Si (111) substrates. Various material and processing approaches regarding surface passivation, gate oxide, ohmic contact metal, and post-gate annealing are evaluated in terms of device performance. In order to achieve better immunity to current collapse effects, we conducted experiments that investigate the relationship between the AlGaN/GaN HEMTs’ electrical characteristics and different passivation films by plasma-enhanced chemical vapour deposition. In order to obtain a better ohmic contact performance, we tested a Ti/Al/Ta/Au ohmic contact metallisation scheme using different annealing temperatures and annealing times to achieve a lower contact resistance, a more proper line edge definition, and a better surface morphology. A post-gate N₂ rapid thermal annealing method done after the gate metallisation process has shown better DC current–voltage output, transfer characteristics, and gate–drain breakdown voltage results compared to the as-fabricated HEMTs. A HEMT with a 0.5-μm gate length, exhibiting a maximum drain current density of 750 mA/mm, a peak transconductance of 220 mS/mm, a unity-gain cut-off frequency of 24.6 GHz, and a maximum frequency of oscillation of 45.4 GHz, was fabricated using this novel manufacturing process; the X-band power performances demonstrate a 5.8-W/mm output power density and a 51 % power-added efficiency.     

A pulse high-frequency power supply system for hyperbolic mass analyzers of space vehicles

A pulse oscillator for powering dynamic mass spectrometers with a frequency mass-spectrum scan is described. The used resonance method of forming leading edges of pulses allowed one to reduce the power consumption by a factor of 4–6 as compared to the simple charge exchange of the load capacitance. Efficient oscillators with a 4-MHz maximal pulse repetition rate, a 100-V peak-to-peak output voltage, and 1-W consumed power are designed.     

Properties of a capillary discharge-produced argon plasma waveguide for shorter wavelength source application

We report the operation of a discharge-produced argon (Ar) plasma waveguide in an alumina (Al(2)O(3)) capillary to guide a 10(16)-W/cm(2) ultrashort laser pulse for shorter wavelength light sources at high repetition rate operation. The electron density in the plasma channel was measured to be 1 × 10(18) cm(-3). Modeling with a one-dimensional magnetrohydrodynamic code was used to evaluate the degree of ionization of Ar in the preformed plasma channel. The observed spectrum of the laser pulse after propagation in the argon plasma waveguide was not modified and was well reproduced by a particle in cell simulation.     

A low-noise microwave signal source

An ultrafast electron diffraction setup is described and requirements for a signal source are determined. Taking into account these requirements, a low-noise microwave signal source with a 6.2-GHz-frequency and ≥6-W power, and 6.1-GHz additional frequency and ≥5-mW power is designed. The phase noise level at the output frequency was no higher than −115 dB/Hz when the offset from the carrier was 10 kHz. The manufactured setup was supplied to the Max-Planck Institute (Garching, Germany), experiments were performed, and the first results were obtained.     

The effects of low-frequency workpiece vibration on low-power CO2 laser cutting of PMMA: an experimental investigation

The effect of workpiece vibration on low-power CO₂ laser cutting of polymethyl methacrylate (PMMA) has been investigated. 6-mm-thick PMMA sheets have been cut using a 70-W continuous wave CO₂ laser moving at speeds in the range of 0.1–2.0?m/min. The workpiece was vibrated in a direction parallel to the laser cut at frequencies of 0, 12, 18 and 24?Hz. The use of workpiece vibration was shown to enhance the cutting process. At 12?Hz, the cutting speed was increased to 0.4?m/min compared to 0.2?m/min for the 0-Hz sample. However, the extent of the HAZ increased when workpiece vibration was used.     

高压H2的受激拉曼散射

本文介绍了以高压H₂为工作物质,以倍频的YAG的0.532μm输出为泵浦源的受激拉曼散射实验,实现了总转换效率大于65%的目前最佳输出,得到了从紫外AS₆228.8nm到红外S₄级的4.6μm转换,扩展了脉冲染料激光器的波段,为开展从紫外到红外的光谱工作提供了理想的光频转换器件。     

Absolute calorimeter for measuring low-energy outputs from CO2 lasers

This paper describes the construction of a calibrated energy measuring device for pulsed CO(2) lasers of low output energy. An aluminium disk of low thermal capacity has been used for the detection of laser radiation. An Al(2)O(3) layer has been electrolytically deposited on the aluminium disks. It is used as a highly absorbing surface (> 95% for wavelengths between 8.5 and 11.0 microm), thus eliminating the need for calibration. The laser output energy is calculated from the measured increase of temperature of a calorimeter disk of known thermal capacity. Calculations and measurements have shown that this device is capable of measuring the energy of a single pulse of the order of 1 mJ, and in a set of 10 pulses even to 0.1 mJ, for pulses as short as 1 ps.     

涡流发生器对动态失速影响的模拟研究

基于风力机专用翼型DU91-W2-250直叶片段,采用延迟分离涡模拟（Delayed detached-eddy simulation,DDES）与k-ω SST两种CFD模拟方法,研究了涡流发生器（Vortex generators,VGs）对动态失速的影响,并对两种模拟方法的表现进行了比较。结果表明：动态失速下,光滑叶片段的分离与重新附着均出现延迟;加VGs后,上仰阶段叶片段的气动分离更加延迟,下俯阶段叶片段上表面附着流动重建的更早,气动力的迟滞现象得到明显改善。VGs对DU91-W2-250叶片段增升减阻的效果明显,其中最大升力系数增加10%,周期平均升力系数增加17.9%,最大阻力系数减少56.3%,周期平均阻力系数减少40.3%。DDES模型能更细致地反映VGs对动态失速抑制作用下叶片段表面复杂流动分离现象,k-ω SST模型则难以捕捉小尺度涡结构,模拟得到的涡结构展向呈二维分布。     

Rosen-type Pb(Mg1/3Nb2/3)O3-PbTiO3 single crystal piezoelectric transformer

In this study, a Rosen-type Pb(Mg(1/3)Nb(2/3))O(3)-PbTiO(3) single crystal piezoelectric transformer is presented. First, we simulate the operation of this transformer using the finite element method and ANSYS. By adjusting the dimensions of the piezoelectric transformer, a maximum voltage step-up ratio of 138 can be obtained at a frequency of 33.8 kHz when the output part is open. Second, we fabricate a transformer with the size of 20 mm length, 4 mm width, and 1 mm thickness to examine the simulation results. It is found that this transformer exhibits a maximum voltage step-up ratio of 134 at 37 kHz, with the efficiency over 95% when driving a liquid crystal display backlight, which shows good consistency with the numerical simulation results. Besides, we investigate the electrical properties under different frequencies and load resistances. When the input voltage increases, a maximum output power of 1 W is obtained with the temperature rise less than 10 degrees C.     

In situ fabrication and regeneration of microtips for scanning tunnelling microscopy

Progress in STM, in particular for the interpretation of the tunnel signals of corrugated surfaces, is related to the possibility of sharpening and regenerating in situ reproducible tips for use as the probe. We proposed two techniques for the production of tips with controlled geometry at the atomic level. These two techniques are based on the production of tips with equilibrium profiles obtained under heat treatments in vacuum and in the presence of an electric field. Based on the pseudo-stationary profile principle, the microtips can be sharpened in situ and in a reproducible manner, either from initial cylindrical (111)-W wire, or from breakdown tips; in both cases without the need for heavy control devices (like FIM for example).     

2D input signal reconstruction from results of measuring by digital optical systems

The algorithm for reconstructing a 2D input signal (the image measured) by a finite realization of a 2D signal at the digital optical recording system output with the use of the fast Fourier transform is analyzed. The image reconstruction error is estimated.     

Laser output power stabilization for direct laser writing system by using an acousto-optic modulator

We present experimental results on the output power stabilization of an Ar(+) laser for a direct laser writing system (LWS). Instability of the laser output power in the LWS cause resolution fluctuations of being fabricated diffractive optical elements or computer-generated holograms. For the purpose of reducing the power fluctuations, we have constituted a feedback loop with an acousto-optic modulator, a photodetector, and a servo controller. In this system, we have achieved the stability of +/-0.20% for 12 min and the relative intensity noise level of 2.1 x 10(-7) Hz(-12) at 100 Hz. In addition, we applied our system to a 2 mW internal mirror He-Ne laser. As a consequence, we achieved the output power stability of +/-0.12% for 25 min.     

基于数据包络分析的制造系统的C2R及其扩展投资决策模型

为评价制造系统投资决策的有效性,将系统输入分解为信息流、物料流及能量流,将系统输出分解为稳定性、自组性和整体性,分别用可测度的特定参数表示。在此基础上,建立了基于技术与规模同时有效的多投入多产出的C^2R数据包络分析决策模型。为单独评价制造系统的技术有效性,将C^2R模型扩展为C2GS2模型;为在决策过程中引入投资决策者的主观偏好,将C^2R模型扩展为带有决策者偏好锥的C2WH模型。     

A Device for the Formation of Short Microwave Pulses in a High Quality Factor Cavity

Microwave pulses at a frequency of 2.45 GHz with a duration of 30–55 ns (at the base level) were obtained using the effect of fast energy transfer in a pair of coupled cavities. The pulse repetition rate reached 40 kHz, and the maximum magnetic-induction amplitude was 0.32 mT at a 20-W generator power.     

Detection of lower hybrid waves within a plasma by microwave scattering

The spatial distribution and intensity of electrostatic waves injected into a hot plasma may be inferred from the scattering of millimeter microwaves. We report measurements on the 30 degrees scattering of 8.6-mm microwaves by a 500-W, 2.45-GHz slow wave excited in a linear plasma by a phased array of two waveguides. From the magnitude of the scattered signal and auxiliary measurements with probes, we infer that a large fraction of the injected power penetrates to the center of the overdense test plasma.     

Data-driven output-feedback fault-tolerant L2 control of unknown dynamic systems

This paper studies the data-driven output-feedback fault-tolerant L₂-control problem for unknown dynamic systems. In a framework of active fault-tolerant control (FTC), three issues are addressed, including fault detection, controller reconfiguration for optimal guaranteed cost control, and tracking control. According to the data-driven form of observer-based residual generators, the system state is expressed in the form of the measured input–output data. On this basis, a model-free approach to L₂ control of unknown linear time-invariant (LTI) discrete-time plants is given. To achieve tracking control, a design method for a pre-filter is also presented. With the aid of the aforementioned results and the input–output data-based time-varying value function approximation structure, a data-driven FTC scheme ensuring L₂-gain properties is developed. To illustrate the effectiveness of the proposed methodology, two simulation examples are employed.     

涡轴发动机稳态性能参数随机误差极限(REL)计算方法

输出轴功率是涡轴发动机的重要性能参数,它的不确定度由固定偏差和随机误差两部分组成。本文分别采用对输入参数进行随机误差合成计算(方法一)和直接对输出参数进行随机误差计算(方法二)的方法,对某涡轴发动机在高度Hp=1 000 m,四种工作状态下的稳态试验数据进行计算分析,得出采用上述两种方法计算分别得到的换算轴功率Nzhco及其平均值Nzhco的随机误差极限REL(Nzhco)和REL(Nzhco)数量级一致,均在±1.3%和±0.20%以内。计算结果表明,这两种随机误差极限计算方法都适用于涡轴发动机。     

Study of the slow-fast preamplifier input parameter’s effects on output image for LYSO scintillator with PS-PMT based animal PET

We developed a small animal positron emission tomography with four detector heads, each one composed of 2 × 2 cm² of pixilated LYSO matrix of 10 × 10 crystals, 2 × 2 mm wide and 10 mm deep coupled to position sensitive photomultiplier (PS-PMT, Hamamatsu R8900U-00-C12). Anger-type logic discretized positioning circuit (DPC) multiplexed readout connected to PMT of each head. The fast-slow preamplifier is used in the fabricated animal PET. We showed that the input capacitance of the preamplifier (the capacitance in the output node of the resistive network) has a direct effect on output image. Image broadening, peak to valley ratio and the geometry distortion of crystal illustration are studied for different input capacitance of preamplifier. The input capacitance of 1 nF resulted in the best image by keeping all the parameters at the proper level with no geometry distortion at the edge of the image.