An integrated capacitance bridge for high-resolution, wide temperature range quantum capacitance measurements

We have developed a highly sensitive integrated capacitance bridge for quantum capacitance measurements. Our bridge, based on a GaAs HEMT amplifier, delivers attofarad (aF) resolution using a small AC excitation at or below k(B)T over a broad temperature range (4-300 K). We have achieved a resolution at room temperature of 60?aF/√Hz for a 10 mV ac excitation at 17.5 kHz, with an improved resolution at cryogenic temperatures, for the same excitation amplitude. We demonstrate the utility of our bridge for measuring the quantum capacitance of nanostructures by measuring the capacitance of top-gated graphene devices and cleanly resolving the density of states.     

Differential capacitance sensor as position detector for a magnetic suspension densimeter

A differential capacitance sensor has been used in the servosystem of a magnetic suspension densimeter to detect the position of a magnetic buoy. This type of sensor has not previously been used in this application. Its design, performance, and advantages are described.     

库仑阵列电化学检测器高效液相色谱仪的日常使用与维护

在使用库仑阵列电化学检测器高效液相色谱仪(HPLC-ECD)的过程中,难免碰到各种各样的问题,本文参考该仪器厂家的技术文献,结合本实验室的使用经验,从仪器系统各组成部分、色谱柱以及流动相等几个方面,探讨影响该设备正常使用的因素、常见故障的成因及解决方法,为HPLC-ECD仪器的使用人员提供技术参考。     

Mutual inductance bridge for low-temperature thermometry and susceptibility measurements

We describe a solid-state mutual inductance bridge suitable for low-temperature thermometry and susceptibility measurements. The design features an electronically simulated variable mutual inductance. Particular care is taken to reduce spurious capacitive effects. The bridge is highly stable and linear. It has a resolution of 10(-4) over the range 15 microH to 150 mH, and a noise limited sensitivity of 55 I(p) (-1) nH with a l-s time constant, where I(p) is the rms primary current in mA. Application to thermometry is discussed.     

电容层析成像系统传感器设计新方法

在电容层析成像系统中,为了提高重建图像的精度,常用的方法是提高成像传感器的极板数目,以获得较多的图像重建所需的独立电容测量值数目,但这种方法是以牺牲检测场的灵敏度为代价的。该文提出了一种在有限极板数条件下通过改变极板的组合方式成倍提高成像系统的独立电容测量值数目的方法。仿真结果表明该方法在不降低检测场灵敏度的前提下提高了电容测量值数目,从而提高了图像重建质量。     

Mass filter and focusing ion detector for use with time-of-flight velocity distribution measurements

A novel mass filter and focusing ion detector for time-of-flight studies of dissociative ionization fragments is described. The filter-dector combination is particularly suited for measuring the kinetic energy released in the molecular dissociation process. The mass filter utilizes a computer-controlled, time-dependent retarding potential synchronized with, and located a distance L from, a pulsed electron-bombardment ion source. Ions arriving at the filter at time t have a kinetic energy of mL(2)/2t(2). The retarding potential varies with time as mL(2)/2et(2), thus deflecting ions with masses less than m. Operation of the filter in a mode which provides unity mass resolution at 16 amu has been demonstrated. The detector consists of a channel electron multiplier and a focusing electrode configuration approximating that of a charged sphere above a grounded conducting plane. The planar input aperture of the detector is located just behind the mass filter along the ion flight path. The detector features high efficiency, large input aperture, low background, and simple operation. Ion transit times through the detector are small and essentially independent of the initial ion kinetic energy.     

Comparative study on the heat transfer performance of micro-grooved anodized thermosyphon with R134a,R600a and R717 for low-temperature applications

Journal of Mechanical Science and Technology - A comparative heat transfer performance of an internally grooved anodized thermosyphon with eco-friendly refrigerants is presented in this study....     

The use of a segmented cathode of a drift tube for designing a track detector with a high rate capability

Detector rate capability is one of the main parameters for designing a new detector for high energy physics due to the permanent rise of the beam luminosity of modern accelerators. One of the widely used detectors for particle track reconstruction is a straw-detector based on drift tubes. The rate capability of such detectors is limited by the parameters of readout electronics. The traditional method of increasing detector rate capability consists in increasing their granularity (the number of “elementary” detectors = readout channels) by reducing the straw diameter and/or by dividing the straw anode wire into two parts (for decreasing the rate per readout channel). A new method of designing straw detectors with a high rate capability is presented and tested. The method is based on dividing the straw cathode into parts and the independent readout of each part.     

脉冲编码器、测速发电机性能自动测试分析系统

脉冲编码器、测速发电机是传动系统中常用的速度传感器,其性能分坏直接影响控制系统的品质指标。本文设计实现了一种基于微机脉冲编码器,测速发电机性能自动测试系统,对该系统的硬件构成和软件分析功能进行了详细讨论。     

汽车发动机性能试验台监控系统设计

介绍了由RS485总线组成的分布式汽车发动机性能参数测试系统的设计。对组成该系统的现场采集单元、通信网络单元、系统管理单元进行了分析与阐述。经现场实验验证,该分布式测控系统具有数据测量准确可靠,可扩展性强,性价比高,维护方便等特点。     

Flat-response, subkiloelectronvolt x-ray detector with a subnanosecond time response

A detector that has a flat response to x rays with energies between 100 eV and 1.5 keV has been built. It has been used to measure x rays emitted from gold disks irradiated by the Argus laser at Lawrence Livermore Laboratory. Results from this detector are in good agreement with results from other techniques.     

Note: a high performance pulse energy detector for Q-switched laser based on photoacoustic effect

A high performance pulse energy detector is developed based on photoacoustic effect. Different from the detectors reported before which also utilized photoacoustic effect, our detector can measure the energy of each pulse output from a Q-switched laser and monitor the pulse energy fluctuation in real time owing to the signal processing circuit designed. By comparing with a commercial laser energy meter, our detector is proved to be of high sensitivity and accuracy. We test the detector under illumination of different pulse energy at varied wavelengths, and the results demonstrate that the detector has a broad spectral response and a dynamical energy range. Besides, the measurements of this detector will not be affected by the background light according to the principle of photoacoustic effect.     

Simple adaptation of the Bridgman high pressure technique for use with liquid media

We present a simple novel technique to adapt a standard Bridgman cell for the use of a liquid pressure transmitting medium. The technique has been implemented in a compact cell, able to fit in a commercial Quantum Design PPMS system, and would also be easily adaptable to extreme conditions of very low temperatures or high magnetic fields. Several media have been tested and a mix of fluorinert FC84:FC87 has been shown to produce a considerable improvement over the pressure conditions in the standard steatite solid medium, while allowing a relatively easy setup procedure. For optimized hydrostatic conditions, the success rate is about 80% and the maximum pressure achieved so far is 7.1 GPa. Results are shown for the heavy fermion system YbAl(3) and for NaV(6)O(15), an insulator showing charge order.     

Refrigeration oils for use with non-CFC,non-ozone-depleting refrigerants — key performance and retrofitting issues

This paper compares the performance of polyol ester base fluids — in key areas such as miscibility, stability, transport property, and antiwear protection — with other candidate oils proposed for use with HFC-134a and with naphthenic oils conventionally employed with ozone-depleting CFC refrigerants such as CFC-12. The data demonstrate that properly selected polyol ester-based fluids meet key lubricant requirements for use with ‘ozone friendly’ refrigerant HFC-134a. In addition, the paper describes key issues in retrofitting existing CF C/naphthenic oil-based systems to run with HFC-134a and polyol ester.     

Design and characterisation of a single-reflection,solid-state detector with high discrimination against backscattered electrons for cathodoluminescence microscopy

Aportable solid-state detector (SSD) for cathodoluminescence (CL) has been constructed and tested. The detector geometry utilises a parabolic reflector to direct light towards the solid-state detection element. The photo-sensitive area of the solid-state photodiodes is situated at a level in line with or sightly below the top surface of the specimen to minimise the collection of backscattered electrons (BSEs) coming directly from the beam impact point. The components have been integrated into a single unit to enhance portability. In comparison with a commercial CL detection system, the new geometry shows excellent efficiency in rejecting BSE contribution during CL operation. A light collection solid angle close to 1.97π steradian is realised in this geometry, higher than other SSD-CL systems. A method for characterising CL detection system performance has been developed.     

Program development for performance analysis of a steam turbine system with the use of overload valve

The global energy market has grown steadily as various energy technologies have been developed. Renewable energy has been used widely but conventional power plants are still used as major electric power sources, including steam turbines and gas turbines. Recently, flexible power plant operation in terms of load management has become important in the power generation industry. For flexible operation, overload valve operation has been introduced for ultra-supercritical steam turbine plants. Overload valve operation is an operation wherein some of the steam at the control valve is bypassed into the middle of the high pressure turbine. In this study, an in-house program is developed for the analysis of ultra-supercritical steam turbines using overload valve operation. A full off-design analysis is performed based on theoretical and empirical correlations. Four kinds of operations were comparatively investigated; control valve operation, sliding pressure operation, and two types of overload valve operation. The influence of the overload valve is analyzed in terms of operating characteristics and performance.

     

Development and performance of a magnetic ionic liquid for use in vacuum-compatible non-contact seals

For the electron-beam machining of optical media, a very low rotational speed is required to enable the precise fabrication of grooves of various depths and widths. In addition, a lubricant with a very low vapour pressure, such as an ionic liquid, and a vacuum chamber are needed to avoid contamination of workpieces. Accordingly, the development of a vacuum-compatible hydrostatic bearing using an ionic liquid is required to satisfy these rotational conditions and nanometre-order machining accuracy. To use a hydrostatic bearing in a vacuum environment, a non-contact vacuum seal is needed to avoid leakage of the ionic liquid used as the lubricant. Furthermore, making a non-contact seal using an ionic liquid requires the development of a new type of magnetic ionic liquid. Therefore, this paper describes the development of such a magnetic ionic liquid, which consists of magnetite (Fe₃O₄) particles, a newly synthesized dispersant, and a pyridinium-based ionic liquid. The outgassed products from this magnetic ionic liquid were measured when it was applied to a non-contact seal in a vacuum of about 10⁻⁶ Pa. In addition, its mechanical properties, such as viscosity and burst pressure as a non-contact seal, were measured. From these investigations, it was found that the developed magnetic ionic liquid would meet the requirements for non-contact seals to be used in vacuum-compatible hydrostatic bearings.     

Object-marking,a bridge between light and analytical electron microscopy for particles characterization

In problems of air or water pollution, or in evaluation of exposure to pathogenic dusts from biological specimens ( e.g., asbestos fibers) some typical particles can be used as tracers. As far as they have sufficiently typical properties (shape, color, anisotropy,…) particles are rapidly recognized and quantified by light microscopy (LM), even if they are very scarce or dispersed among large amounts of unsignificant ones. For accurate characterization, analytical electron microscopy (scanning or transmission) is required, but cannot be efficiently applied for low concentrations of particles. A technique using a high precision object-marker under LM has been developed in the past by Jedwab (1975) to be used with SEM, but there is actually no equivalent for TEM. Such a technique is proposed in this paper. Its major interest resides in the greater amount of analytical data available for one single particle (high magnification morphology, crystallographic structure, chemistry). Practical results were obtained with asbestos fibers and bodies recovered from biological specimens, but the technique can be extended to many other problems concerning micron-sized particles.     

关于红外探测器与红外焦平面阵列探测器性能参数描述方法的商榷

对中国国标GB/T 13584与GB/T17444关于红外探测器和红外焦平面阵列探测器噪声和相关性能参量定义方法提出了异议和见解.在国标中关于噪声的定义没有说明背景辐亮度和信号辐照度水平,因此容易导致关于噪声和相关参量的模糊观念.当信号很强时,光子噪声占主导地位,信噪比(SNR)与信号水平不成正比,此时由信噪比导出噪声等效功率(NEP)和D*时应格外小心.当信号很弱时,可以忽略光子噪声,由信噪比导出NEP和D^*就变为很简单.     

甲烷化氢火焰离子化检测器专用微型转化炉的研制

制作了一种目前属国内先进的微型转化炉。转化炉由大口径玻璃毛细管或金属管制成。将一定粒度的Ni触媒与Al(OH)3溶胶混合,形成较稳定的悬浮液,用动态法将悬浮液涂渍在管内壁上,形成均匀的Ni触媒涂层,经过老化即可使用。当一氧化碳、二氧化碳加氢通过该管时,在一定的转化温度下,一氧化碳、二氧化碳会转化成甲烷被气相色谱-氢火焰离子化检测器检测。甲烷化微型转化炉转化率达到95%以上,一氧化碳、二氧化碳的最小检测量为5μg/g。