Ultrasonic gas flow meter with corrections for large dynamic metering range

Extreme accuracy is required in sing-around type gas flow meters in the sing-around period measurement. Thus the detection of the ultrasound is critical. Accurate detection of an ultrasound pulse transmitted through gas is not straightforward. Normally a zero crossing technique is applied, where a level trigger determines when to enable the zero crossing triggering. In a flowing gas, the ultrasound amplitude is modulated due to turbulence, humidity and changes in dynamic gas pressure. This introduces uncertainty as to the cycle in which the ultrasound pulse is detected. This in turn results in large errors in sing-around type gas flow meters. This paper discusses a new correction algorithm which will eliminate such trigger errors. To accomplish the verification of the new correction algorithm, a microprocessor-based sing-around gas flow meter, using 500 kHz ultrasound has been designed. The correction algorithm significantly increases the repeatability of this meter. Repeatability better than 0.5% over a dynamic meter range of 1 to 35 has been measured. Limitations of the sing-around method imposed by the new correction algorithm have been derived theoretically.     

Evaluation of a front-end ASIC for the readout of PMTs over a large dynamic range

The Large High Altitude Air Shower Observatory(LHAASO) project has been proposed for the survey and study of cosmic rays.In the LHAASO project,the Water Cherenkov Detector Array(WCDA) is one of the major detectors for searching for gamma ray sources.A Charge-to-Time Convertor(QTC) ASIC(Application Specification Integrated Circuit),fabricated with Global Foundry 0.35 μm CMOS technology,has been developed for readout of photomultiplier tubes(PMTs) in the WCDA.This ASIC provides both time and charge measurement of PMT signals.The input charge is converted to a pulse width based on the Time-Over-Threshold(TOT) technique and linear discharge method;as for time measurement,leading edge discrimination is employed.This paper focuses on the evaluation of this front-end readout ASIC performance.Test results indicate that the time resolution is better than 400 ps and the charge resolution is better than 1%with large input signals and remains better than 15%@1photoelectron(P.E.),both beyond the application requirement.Moreover,this ASIC has a weak ambient temperature dependence,low input rate dependence and high channel-to-channel isolation.     

数字式声呐大动态范围显示技术研究

量化比特数是衡量数字声呐性能的主要指标，增加比特数意味着更高的精度和更大的动态范围，但人机视觉接口只能显示有限字长的数据。本文从声呐显示技术出发，分析了突破这一局限的必要和可能。原理分析表明，对声呐数据实行过零基准处理，以ＧＳＣ算法配合小信号分层处理可有效地获得多比特位声呐数据的几乎无损的显示，对１６比特呐数据处理显示的实验结果表明，我们的处理方法达到了预斯要求。     

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A new arc detector with ultra wide dynamic range was developed based on three gain adjustable amplifiers and microcontroller for the RF (radio frequency) windows in the high-power microwave heating systems on HL-2A/M tokamak. The gain is digitally adjustable with 8 levels in the main amplifier and the protection threshold is adjustable from 0 to 5V with accuracy of 20mV. Both the gain and threshold are remotely controlled with the help of a microcontroller. The measured maximum response time is 2.56μs. The arcing detectors work properly in different level of background light and in complicated electromagnetic environment.     

大动态范围数控弧光探测器的研制

针对HL-2A/M 高功率微波加热系统微波窗口真空侧对弧光探测的要求,基于三级放大电路和微控制器技术,完成电路设计,研制了新型弧光探测器。增益8 挡数字可调,保护阈值以20mV 的精度0~5V 数字可调,具有远程操作和数字显示功能。在不同增益和保护阈值条件下,实验测得其响应时间最大为2.56μs,能在复杂电磁环境和不同强度干扰光的条件下稳定工作,满足系统要求。     

Z箍缩丝阵动态烧蚀的二维数值模拟

采用FOI-PERFECT程序对局域欧姆加热主导的动态烧蚀进行了数值模拟研究,定量诊断并比较了烧蚀率、先驱电流和烧蚀时间,考查烧蚀阶段之初的丝等离子体的直径和丝阵的丝数对烧蚀的影响,结果表明,在等离子体流建立后,随丝数或者丝径的增加,烧蚀率增大,先驱电流减少,烧蚀时间减小。     

Z箍缩丝阵动态烧蚀的二维数值模拟

采用FOI-PERFECT程序对局域欧姆加热主导的动态烧蚀进行了数值模拟研究, 定量诊断并比较了烧蚀率、先驱电流和烧蚀时间, 考查烧蚀阶段之初的丝等离子体的直径和丝阵的丝数对烧蚀的影响, 结果表明, 在等离子体流建立后, 随丝数或者丝径的增加, 烧蚀率增大, 先驱电流减少, 烧蚀时间减小。     

A linearity interrogation technique with enlarged dynamic range for fiber Bragg grating sensing

An exact linearity interrogation technique with enlarged dynamic range for fiber Bragg grating (FBG) sensor has been analyzed theoretically and demonstrated experimentally. The technique bases on two matched FBGs for receiving the reflected signal from the sensor FBG and two photodiodes (PDs) for collecting the reflected signal from the two receiver FBGs. The linear expression between the nature logarithm of the output ratio of the two PDs and Bragg wavelength of the sensor FBG is obtained on the condition that the bandwidths of the two receiver FBGs being equal to each other. The wavelength of the sensor FBG can be interrogated simply and accurately by the linearity technique according to the expression. In addition, a new tunable paralleled matched gratings interrogation scheme is proposed. The interrogation range can be enlarged and multiple FBG sensors can be interrogated simultaneously with the tunable interrogation scheme.     

New data-processing technique for measurement of metallic foil thickness with differential white-light interferometry

The thickness of metallic foil was measured by differential white-light interferometry (DWLI). Two tandem Michelson interferometers (MI), in which the reflective surfaces measured are the surfaces of the metallic foil, were used as a basic interferometry system to obtain interference fringes on a spectrometer. Therefore, the interference fringes depend only on the path differences caused by the thickness of the metallic foil. The interference fringes were analyzed using a modified extremum method based on the least root-mean-square (RMS) deviation. Experimental results for thickness measurements are presented. Measurement time is only 100 ms or less for a thickness of 1–80 μm.     

Entangledlike chain dynamics in nonentangled polymer blends with large dynamic asymmetry

We discuss simulations of a simple model for polymer blends in the framework of the Rouse model. At odds with standard predictions, large dynamic asymmetry between the two components induces strong nonexponentiality of the Rouse modes for the fast component. Despite chains being much shorter than the entanglement length, it also induces dynamic features resembling a crossover to entangledlike chain dynamics. This unusual behavior is associated with strong memory effects which break down the assumption of time uncorrelation of the external forces acting on the tagged chain.     

纹影技术在直喷式柴油机燃烧过程研究中的应用

本文叙述了作者所设计建立的高速纹影摄影光路系统,给出了利用该系统所拍摄的纹影照片,并通过照片简单分析了柴油机缸内的喷雾和燃烧过程。结果表明,纹影技术是研究发动机缸内空气运动和喷雾燃烧过程的有效手段。     

Resonant fermi gases with a large effective range

We calculate the equation of state of a Fermi gas with resonant interactions when the effective range is appreciable. Using an effective field theory for a large scattering length and large effective range, we show how calculations in this regime become tractable. Our results are model independent, and as an application, we study the neutron matter equation of state at low densities of astrophysical interest 0.002 fm(-3) < rho < 0.02 fm(-3), for which the interparticle separation is comparable to the effective range. We compare our simple results with those of conventional many-body calculations.     

Diode laser spectrometer for high-resolution spectroscopy in the visible range

A high-resolution diode laser spectrometer operating at 657 nm is described. To achieve a narrow linewidth and a high power, a master-slave laser system is employed. The master laser is an extended cavity diode laser whose linewidth is reduced to less than 100 Hz by the FM sideband technique. The slave laser is an AR-coated diode laser and characteristics of injection locking are experimentally studied. The injection current of the slave laser is utilized to stabilize the output power or to produce pulsed output. Using this spectrometer, we probed the intercombination line of Ca and observed high-contrast optical Ramsey fringes with a linewidth of 10 kHz. A velocity-selective Ramsey fringe is also observed in the pulse-mode operation.     

Study of linearity for a high dynamic range calorimeter

A high dynamic range calorimeter has been designed for the DArk Matter Particles Explore(DAMPE) satellite. It consists of 308 BGO crystals, multi-dynode readout PMTs and front end electronics system. We have built on previous research to show that BGO fluorescence should not be saturated by high electron energy density under DAMPE's energy range. A BGO fluorescence simulator is set up to calibrate the energy range of the dynodes, while a cosmic-ray unit is used to calibrate 1 MIP with the ADC count in dynode 8. Linearity is achieved for the dynamic range from 0.5 MIPs to 1.26×105MIPs. The requirements of DAMPE can thus be satisfied.     

Temperature-insensitive FBG tilt sensor with a large measurement range

A novel two-dimensional tilt sensor with a large measurement range is demonstrated by using four fiber Bragg gratings (FBGs) attached on a cylindrical cantilever-based pendulum. Experimental results show that tilt accuracy of ±0.2° and resolution of 0.013° have been achieved in the range of −40°-40°. The temperature effect is automatically eliminated without additional temperature compensation elements.     

Realization of a resonant Fermi gas with a large effective range

We have measured the interaction energy and three-body recombination rate for a two-component Fermi gas near a narrow Feshbach resonance and found both to be strongly energy dependent. Even for de Broglie wavelengths greatly exceeding the van der Waals length scale, the behavior of the interaction energy as a function of temperature cannot be described by atoms interacting via a contact potential. Rather, energy-dependent corrections beyond the scattering length approximation are required, indicating a resonance with an anomalously large effective range. For fields where the molecular state is above threshold, the rate of three-body recombination is enhanced by a sharp, two-body resonance arising from the closed-channel molecular state which can be magnetically tuned through the continuum. This narrow resonance can be used to study strongly correlated Fermi gases that simultaneously have a sizable effective range and a large scattering length.     

An optical power-equalized amplifier with a wide dynamic range

An optical power equalization amplifier with a wide dynamic range is proposed and demonstrated with no electronic control. It shows constant and equalized outputs when a power difference between input channels and a total input power are changed. It has more than a 15 dB dynamic range for input signals between −30 dBm and −5 dBm. The structure of this amplifier can be more promising when it is applied to a planar waveguide device.     

Visualization and analysis of muzzle flow fields using the Background-Oriented Schlieren technique

Several experimental and numerical studies on muzzle blast and flow fields have been performed. However, due to the extremely short duration and the spatiotemporal evolution of these flows, experimental quantitative techniques are limited. As a consequence, the number of validated numerical calculations is limited as well. On the other hand, despite the development of computer models that have succeeded in predicting the measured pressure and velocity, they show unrealistic temperatures and densities. Therefore, temperature and/or density measurements are required to validate these codes, thus the motivation of this research. The present paper focuses on the development of a density-sensitive and non-intrusive measurement technique and the implementation of a quantitative flow visualization method based on Background-Oriented Schlieren (BOS) combined with a high-speed camera. In BOS, the experimental setup of conventional Schlieren (mirrors, lenses, and knife-edge) is replaced by a background pattern and a single digital camera. The muzzle flow fields and the flow field around a 5.56-mm projectile in flight were successfully visualized. Indeed, the implemented experimental high-speed BOS setup has demonstrated its ability to capture clearly the salient features of the precursor and the propellant gas flow fields and their interactions. The captured structures such as vortex, barrel shock, Mach disk, and blast wave show a good agreement with that issued from a realized conventional Schlieren setup and the bibliography, confirming the BOS capability to visualize complex density flow fields.