A New Method for Measurement of Local Solid Flux in Gas-Solid Two-phase Flow

Previous works have shown that the suction probe cannot be used to accurately measure the upward and downward particle fluxes independently. A new method using a single optical probe to measure the local solid flux is presented. The measurement of upward, downward and net solid fluxes was carried out in a cold model circulating fluidized bed (CFB) unit. The result shows that the profile of the net solid flux is in good agreement with the previous experimental data measured with a suction probe. The comparison between the average solid flux determined with the optical measuring system and the external solid flux was made, and the maximum deviationturned out to be 22%, with the average error being about 6.9%. These confirm that the optical fiber system can be successfully used to measure the upward, downward and net solid fluxes simultaneously by correctly processing the sampling signals obtained from the optical measuring system.

Flux measurements for a DD neutron generator using neutron activation analysis

The fast and maximum thermal neutron fluxes from the DD-109 neutron generator at the University of Sharjah were experimentally measured by the activation technique using different neutron reactions. The thermal and fast neutron fluxes were found to be 2.960 × 10~6 and6.186 × 10~7 n/cm^2 s, respectively. This was done to verify the modeling results for the optimum moderator thickness needed to maximize the thermal neutron flux. The optimum moderator thickness was found to be between 3.5 and4 cm. The present data were compared with the detailed MCNP model-based calculation performed in earlier work to simulate the generator.

Direct Measurements of the Electron Energy Flux versus Electron Temperature Gradient in Tokamak Discharges

Electron thermal transport is one of the most complex processes in fusionplasmas. It is generally described by a simple thermal diffusivity in transport analyses ofdischarges, but there is evidence of critical gradient effects with moderate stiffness. By analyzingperiodic perturbations to an equilibrium, one canmeasure the variations in electron energy flux andelectron temperature gradient over the perturbation cycle, obtaining the flux as a function ofgradient over the range of parameters generated by the perturbation. Although time-dependenttransport analysis is very sensitive to noise in the input data, averaging over many cycles of aperiodic perturbation can provide data of sufficient quality. The analyses presented here are basedon the ECE temperature data with high spatial and temporal resolution and full profile coverage onDIII-D for sawteeth and modulated ECH heating.

In situ measurements of benthic oxygen fluxes in Hui-quan Bay of Qingdao by eddy correlation techniques:short term pattern variations in gravel beach

The oxygen fluxe across the sediment-water interface(SWI)in coastal region is a key measure to fully understand the regulation of biogeochemical cycles in an aquatic environment.However,studies on fluxes of dissolved oxygen in gravel beach are limited,because of the difficulty in sample collection and instrumentations deployment.In this study,benthic oxygen fluxes across rocky substratum in an intertidal zone of Huiquan Bay was estimated by using noninvasive eddy correlation techniques.A total of 10 burst measurements were analyzed.The oxygen flux fluctuated from-5.7888±2.6 to+49.3344±2.6 mmol O2 m-2/d were observed.The cospectra analysis showed that the oxygen flux at the frequency band between 0.093 and 0.279 Hz(at a period from 3.58 to 10.75 s)contributed 50.19%to the total spectrum on average.The results showed that the major contribution band moved to the high frequency region gradually and reached a steady state with increasing tidal flood.It is demonstrated that wave movement and wave breaking interaction resulted in the change of oxygen flux between gravel beach and shallow waters at the start and the end of a rising tide period,respectively.The eddy correlation techniques offer an efficient means for flux measurement over a gravel or mixed sand and gravel beaches.

Atmospheric particulate pollution of Lanzhou using magnetic measurements

To differentiate between natural and anthropogenic particulate sources in the atmosphere in Lanzhou City, samples were collected in different sites. The dust flux was calculated and magnetic measurements were conducted. Results show a distinct pattern of variation of dust flux within a year and it agrees with the shifts of atmospheric circulation regime. The magnetic parameters indicate that natural sources are the major components of atmospheric particulate during late spring and early summer, while anthropogenic sources contribute much more during winter months. The data also support the earlier findings that magnetic parameters are effective for differentiating between particulate arising from natural sources such as soil erosion and from anthropogenic sources such as coal combustion.

Flux-measuring approach of high temperature metal liquid based on BP neural networks

A soft-measuring approach is presented to measure the flux of liquid zinc with high temperature andcausticity. By constructing mathematical model based on neural networks, weighing the mass of liquid zinc, the fluxof liquid zinc is acquired indirectly, the measuring on line and flux control are realized. Simulation results and indus-trial practice demonstrate that the relative error between the estimated flux value and practical measured flux value islower than 1.5%, meeting the need of industrial process.

Speed Measurement Feasibility by Eddy Current Effect in the High-Speed MFL Testing

It is known that eddy current effect has a great influence on magnetic flux leakage testing(MFL).Usually,contacttype encoder wheels are used to measure MFL testing speed to evaluate the effect and further compensate testing signals.This speed measurement method is complicated,and inevitable abrasion and occasional slippage will reduce the measurement accuracy.In order to solve this problem,based on eddy current effect due to the relative movement,a speed measurement method is proposed,which is contactless and simple.In the high-speed MFL testing,eddy current induced in the specimen will cause an obvious modification to the applied field.This modified field,which is measured by Hall sensor,can be utilized to reflect the moving speed.Firstly,the measurement principle is illustrated based on Faraday’s law.Then,dynamic finite element simulations are conducted to investigate the modified magnetic field distribution.Finally,laboratory experiments are performed to validate the feasibility of the proposed method.The results show that Bmz(r1)and Bmx(r2)have a linear relation with moving speed,which could be used as an alternative measurement parameter.

THE RIEMANN PROBLEM FOR ISENTROPIC COMPRESSIBLE EULER EQUATIONS WITH DISCONTINUOUS FLUX

We consider the singular Riemann problem for the rectilinear isentropic compressible Euler equations with discontinuous flux,more specifically,for pressureless flow on the left and polytropic flow on the right separated by a discontinuity x=x(t).We prove that this problem admits global Radon measure solutions for all kinds of initial data.The over-compressing condition on the discontinuity x=x(t)is not enough to ensure the uniqueness of the solution.However,there is a unique piecewise smooth solution if one proposes a slip condition on the right-side of the curve x=x(t)+0,in addition to the full adhesion condition on its left-side.As an application,we study a free piston problem with the piston in a tube surrounded initially by uniform pressureless flow and a polytropic gas.In particular,we obtain the existence of a piecewise smooth solution for the motion of the piston between a vacuum and a polytropic gas.This indicates that the singular Riemann problem looks like a control problem in the sense that one could adjust the condition on the discontinuity of the flux to obtain the desired flow field.

2003-2005年中国通量观测研究联盟(ChinaFLUX)碳水通量观测数据集

基于微气象学理论的涡度相关通量观测技术实现了对生态系统尺度的生产力、能量平衡和温室气体交换等功能和过程的直接测定,其观测数据为陆地生态系统碳水循环过程的机理研究以及碳源/汇和水分利用的时空分布评价提供了重要的观测数据。本数据集为中国通量观测研究联盟(ChinaFLUX)首批观测站点的生态系统通量观测数据,包括森林、草地和农田在内的8个典型生态系统,并基于ChinaFLUX数据处理体系形成了标准化的生态系统碳水通量和关键气象要素数据集。本数据集可以为分析我国典型陆地生态系统对全球变化的响应及其机制提供重要的科学知识和数据基础。

Research Advances of Effects of Land Use Pattern on Greenhouse Gas Fluxes in Grassland Ecosystem

The grassland is the largest terrestrial ecosystem in China,and greenhouse gas fluxes such as CO2,CH4 and N2O play an important role in the global climate change. The differences in grazing,cultivation and management measures will affect greenhouse gas emissions in grassland ecosystem. Studies suggest that reclamation will lead to increased CO2 fluxes,and fertilization will lead to increased N2 O fluxes; no grazing in summer can reduce greenhouse gas emissions,but impacts of grazing and management measures on greenhouse gas fluxes have not yet reached the same conclusion. The different results may be related to local natural conditions,management measures and research methods. Future research should be focused on unity and standardization in these areas,making the results scientific and comparable,and finally providing the basis for emission reduction of greenhouse gases in grassland ecosystem.

Reconstruction of conductivity distribution of brain tissue from two components magnetic flux density

In this paper the recent Magnetic resonance electrical impedance imaging (MREIT) technique is used to image non-invasively the three-dimensional continuous conductivity distribution of the head tissues. With the feasibility of the human head being rotated twice in the magnetic resonance imaging (MRI) system, a continuous conductivity reconstruction MREIT algorithm based on two components of the measured magnetic flux density is introduced. The reconstructed conductivity image could be obtained through solving iter- atively a non-linear matrix equation. According to the present algorithm of using two magnetic flux den- sity components, numerical simulations were per- formed on a concentric three-sphere and realistic human head model (consisting of the scalp, skull and brain) with the uniform and non-uniform isotropic target conductivity distributions. Based on the algorithm, the reconstruction of scalp and brain conductivity ratios could be figured out even under the condition that only one current is injected into the brain. The present results show that the three-dimensional continuous conductivity reconstruction method with two magnetic flux density components for the realistic head could get better results than the method with only one magnetic flux density component. Given the skull conductivity ratio, the relative errors of scalp and brain conductivity values were reduced to less than 1% with the uniform conductivity distribution and less than 6.5% with the non-uniform distribution for different noise levels. Furthermore, the algorithm also shows fast convergence and improved robustness against noise.

Tower-based observation of air-sea momentum flux:comparisons between onshore and offshore winds

We investigate the air-sea momentum flux in the marine atmospheric boundary layer using a tower-based direct measurement method.First,we compare the collected data with previous observations,and the results are roughly consistent.Next,in the low-to-moderate winds,the exchange coefficients(or drag coefficients)deviate between onshore and offshore winds,which exhibits the influence of surface wave on the momentum flux.Furthermore,we use a surface-wave-involved parameterization scheme to explain the dependence of momentum flux on surface wave.The results consolidate the influence of surface wave on momentum flux on the one hand,and validate the surface-wave-involved parameterization scheme on the other hand.

Flux Pinning in Y- and Ag-Doped MgB₂

High temperature superconductor research is presently concentrated upon the flux pinning properties of the Abrikosov lattice of the mixed-mode superconducting phase. The temperature thermal fluctuations, current and magnetic field unpin the flux vortices and so cause electromagnetic resistivity in high temperature superconductors. Materials with higher vortex pinning exhibit less resistivity and are more attractive for industrial uses. In the present article, we measured and correlated the pinning flux energy barrier, determined by AC magnetic measurements, and transmission electron microscopy measurements to the critical current Jc in Yttrium- and Silver-doped MgB2 superconductors. The energy of the flux vortex was evaluated as a function of the magnetic field. The energy barrier curves suggest an optimal doping level to occur in doped materials. This result only depends on the optimal size and distribution of precipitates, and not on their chemical composition. The energy barriers have been compared with that of undoped MgB2 in literature.

Influence of Molecular Vibrational Energy Accommodation Modeling on Cone Surface Heat FLUX at Mach 10

In order to assess the influence of high vibrational temperatures typically found in shock-tunnel-generated flows on model surface heat flux, measurements are compared to simulations using the DSMC （direct simulation Monte Carlo） method. The two limiting cases of either full accommodation of molecular vibrational energy to the surface temperature or none at all are simulated for three shock tunnel conditions using Nitrogen （N2） as a test gas. The conditions mainly differ by an order of magnitude in density, however, all three comparisons to the corresponding measurements suggest that vibrational surface relaxation happens only to a small extent. While model surface pressure is not affected, heat fluxes differ by up to 20%, depending on the modelling. Furthermore, lower flow densities generally lead to higher differences.

人工湿地温室气体排放影响因素及相关作用机制研究进展

概述了人工湿地的发展历史,分析了其温室气体排放研究现状,详细阐述了湿地类型、基质种类、进水C/N、植物种类及溶解氧浓度等对人工湿地温室气体排放的影响。在此基础上,综述了人工湿地温室气体减排的具体措施及其效果。最后,对人工湿地温室气体减排研究的发展方向进行了展望。

基于拉普拉斯变换的瞬态热流测量方法

针对航空发动机热端部件表面瞬态热流测量的问题,面向一种当前较为先进的横向测温差薄膜热流计结构,针对其瞬态测量的导热模型,在稳态测量原理方程中加入时间项,建立瞬态导热微分方程组,采用拉普拉斯变换方法并结合解卷积方法对导热方程进行求解,提出该型薄膜热流计瞬态条件下的表面热流测量方法;采用数值模拟手段,对所提方法进行验证。结果表明:所提方法突破了原始的稳态测量局限,可用于固体表面瞬态热流测量,计算得到的热流计表面热流与真实值符合较好;在表面阶跃热流条件下,测量精度约为8.2%;在100 Hz正弦热流条件下,测量精度约为4.0%。

Schmidt–Boelter热流传感器的改进和性能测评

为满足常规高超声速风洞连续变迎角试验动态热流测量需求,改进了一种小尺寸Schmidt–Boelter热流传感器。以热流标定装置进行了静态校准和动态测试,得到改进后传感器的灵敏度系数为57.67μV·m^(2)/kW,响应时间约26 ms,截止频率26 Hz,可覆盖1~130 kW/m^(2)的热流范围。基于特征响应时间常数,建立了变迎角速度与最大测量误差的定量关系;参照某阶梯变迎角试验测得的热流数据,对该传感器在一定误差范围内能够满足的最大连续变迎角速度进行了评估。

双膜量子点表面热流密度场测量技术

现有热流密度场测量技术主要局限在分辨率低、瞬态响应慢、成本高等方面。为解决这一问题,本文提出了一种测量热流密度场的新技术。量子点是一种纳米级的光致发光半导体材料,其光致荧光光谱强度随温度的变化呈现线性变化趋势。基于该效应,设计并制作了双膜量子点试片,搭建了量子点热流密度场测量实验系统,开展了标定与测量实验。结果表明:在本研究实验范围内,量子点膜的平均光致荧光强度随温度的升高呈现线性下降趋势;测得在本研究实验条件下10s内纯水液滴受热蒸发过程中底层平均热流密度约为3.4×10^(4)W/m^(2),测量不确定度为0.14;本研究测量方法的空间分辨率可达30μm级,响应时间为秒级,实现了对表面热流密度场的高分辨率、低延迟测量。基于分辨率高、延迟低的优势,本研究可以有效应用于旋转叶片、高速飞行器、微纳米元件等传统测量方法难以开展的测试环境。

基于红外激光积分球的硅探测器响应非线性研究

0.9μm是我国高温标准光电和辐射法热力学温度测量的主要工作波段之一,因此对该波段下滤光片辐射计的非线性的研究十分重要。基于单相干光源双光路的光通量倍增法设计并搭建了硅探测器光谱响应非线性测量系统,利用双紫外熔融石英分光镜实现光通量的调控,通过积分球使探测器视场被完全充满,提高入射光在探测器光敏面作用区域的重复性,采用高吸收光阱避免光通量调控过程中的多次反射。实验通过切换中性密度滤波片来实现对光电流范围扩展,表征了0.9μm滤光片辐射计在1.6×10-8~8×10-6 A光电流范围内的非线性,单次测量的非线性值为-8.7×10-5~4.8×10-5,单次测量结果标准不确定度优于3.7×10-4,累积测量的非线性值为-2.7×10-4,标准不确定度优于7.6×10-4。

弧板型电容式鼓位探测器的结构设计方法研究及特性分析

高通量试验堆采用控制鼓部件作为功率调节装备,通过改变控制鼓与堆芯的相对角度,可调节堆内的核反应性。控制鼓的旋转角度信号是高通量堆运行过程中最重要的待测参数之一,该信号需由鼓位探测器进行识别。电容传感技术可应用于角度信号测量,本文基于弧板构型,进行了电容式鼓位探测器结构的初步设计,明确了鼓位探测器边缘效应的影响范围,提出了边缘误差的补偿方法,完成了鼓位探测器的结构改进设计,获得了电容式鼓位测量系统的总体性能。研究结果表明,完成边缘误差补偿后,在0°~180°的角度范围内,电容式鼓位测量系统的最大测量误差在±0.004°以内,可满足高通量堆控制鼓鼓位的测量精度需求。