复合光缆地线故障暂态电流和电压分布计算与分析

故障电流和故障电压的准确计算是复合光缆地线系统热稳定校验和地线绝缘间隙选择的基础。为此建立基于相参数法的计算模型,研究一段有限长的线路,针对线路单相对地短路故障,考虑地线和相导线之间的互感的影响,利用仿真软件定量讨论了当线路在不同地点发生故障时,OPGW上的暂态电流和电压的幅值、持续时间和影响范围。结果表明:OPGW上的暂态电流峰值和暂态电压峰值分别为稳态电流峰值和稳态电压峰值的1.3～1.7倍和1.1～1.6倍;暂态过程持续0.04～0.08s;故障点两侧约8km内出现较大的暂态电流和暂态电压。

Applications of texture attribute analysis to seismic interpretation

The first generation coherence algorithm(namely C1 algorithm) is based on the statistical cross-correlation theory, which calculates the coherency of seismic data along both in-line and cross-line. The work, based on texture technique, makes full use of seismic information in different directions and the difference of multi-traces, and proposes a novel methodology named the texture coherence algorithm for seismic reservoir characterization, for short TEC algorithm. Besides, in-line and cross-line directions, it also calculates seismic coherency in 45° and 135° directions deviating from in-line. First, we clearly propose an optimization method and a criterion which structure graylevel co-occurrence matrix parameters in TEC algorithm. Furthermore, the matrix to measure the difference between multi-traces is constructed by texture technique, resulting in horizontal constraints of texture coherence attribute. Compared with the C1 algorithm, the TEC algorithm based on graylevel matrix is of the feature that is multi-direction information fusion and keeps the simplicity and high speed, even it is of multi-trace horizontal constraint, leading to significantly improved resolution. The practical application of the TEC algorithm shows that the TEC attribute is superior to both the C1 attribute and amplitude attribute in identifying faults and channels, and it is as successful as the third generation coherence.

An analogy-based method for strong convection forecasts in China using GFS forecast data

This paper describes an analogue-based method for producing strong convection forecasts with conventional outputs from numerical models.The method takes advantage of the good performance of numerical models in predicting synoptic-scale weather situations.It calculates the convective parameters as predictors to detect the favorable-occurrence environment of strong convections.Times in the past when the forecast parameters are most similar to those forecast at the current time are identified by searching a large historical numerical dataset.The observed strong convection situations corresponding to those most similar times are then used to form strong convection forecasts for the current time.The method is applied as a postprocess of the NCEP Global Forecast System(GFS)model.The historical dataset in which the analogous situations are sought comprises two years of summer(June–September)GFS 6-to 48-h forecasts.The strong convection forecast is then generated every 6 h over most regions of China,provided the availability of strong convection observations.The results show that the method performs well in predicting strong convections in different regions of China.Through comparison with another postprocessing strong convection forecast method,it is shown that the convective-parameter threshold problem can be solved by employing the analogy method,which considers the local historical conditions of strong convection occurrence.

Parameter optimization of gravity density inversion based on correlation searching and the golden section algorithm

For density inversion of gravity anomaly data, once the inversion method is determined, the main factors affecting the inversion result are the inversion parameters and subdivision scheme. A set of reasonable inversion parameters and subdivision scheme can, not only improve the inversion process efficiency, but also ensure inversion result accuracy. The gravity inversion method based on correlation searching and the golden section algorithm is an effective potential field inversion method. It can be used to invert 2D and 3D physical properties with potential data observed on flat or rough surfaces. In this paper, we introduce in detail the density inversion principles based on correlation searching and the golden section algorithm. Considering that the gold section algorithm is not globally optimized. we present a heuristic method to ensure the inversion result is globally optimized. With a series of model tests, we systematically compare and analyze the inversion result efficiency and accuracy with different parameters. Based on the model test results, we conclude the selection principles for each inversion parameter with which the inversion accuracy can be obviously improved.

Liquid holdup measurement with double helix capacitance sensor in horizontal oil-water two-phase flow pipes

This paper presents the characteristics of a double helix capacitance sensor for measurement of the liquid holdup in horizontal oil–water two-phase flow. The finite element method is used to calculate the sensitivity field of the sensor in a pipe with 20 mm inner diameter and the effect of sensor geometry on the distribution of sensitivity field is presented. Then, a horizontal oil–water two-phase flow experiment is carried out to measure the response of the double helix capacitance sensor, in which a novel method is proposed to calibrate the liquid holdup based on three pairs of parallel-wire capacitance probes. The performance of the sensor is analyzed in terms of the flow structures detected by mini-conductance array probes.

Measurement of Apex Offsets for Fiber Connector End Faces

As one of the most important geometric parameters for a PC-type fiber connector end face, apex offset can contribute to high insertion loss and high back-reflection reading. A novel measurement method for the parameter, connector rotating-π method, is proposed. With the method, the apex offset of a common connector end face is measured. The result is compared with that measured by a Norland 3000 fiber connector end face interferometer. It is found that the difference between two results is 1.8μm. Meantime, the influences of relevant error resources on apex offset measurement under rotating-π method and apex-core method are respectively analyzed, and two error equations are derived. The analytical result shows that, compared with apex-core method, if two additional sub-tilts of axis within and in the direction perpendicular to principal plane caused by its rotation are not bigger than the original axis tilt angle, the max. measurement error will then be reduced by at least 22.5% with rotating-π method. The practicability of the method is confirmed by the experiments.

From Allan Variance to Phase Noise:A New Conversion Approach

A new mathematical method is proposed to convert the oscillator instability parameters from Allan variance to Spectrum Density(SD)of random phase fluctuations,which is the inversion of the classic transformation formula from SD to Allan variance.Due to the fact that Allan variance does not always determine a unique SD function,power-law model of the SD of oscillator phase fluctuations is introduced to the translating algorithm and a constrained maximum likelihood solution is presented.Considering that the inversion is an ill-posed problem,a regularization method is brought forward in the process.Simulation results show that the converted SD of phase fluctuations from Allan variance parameters agrees well with the real SD function.Furthermore,the effects of the selected regularization factors and the input Allan variances are analyzed in detail.

Seasonal and interannual variations of ecosystem photosynthetic characteristics in a semi-arid grassland of Northern China

The ecosystem apparent quantum yield(α),maximum rate of gross CO_(2) assimilation(Pmax)and daytime ecosystem respiration rate(R.),reflecting the physiological functioning of ecosystem,are vital photosynthetic parameters for the estimation of ecosystem carbon budget.Climatic drivers may affect photosynthetic parameters both directly and indirectly by altering the response of vegetation.However,the relative contribution and regulation pathway of environmental and physiological controls remain unclear,especially in semi-arid grasslands.We analyzed seasonal and interannual variations of photosynthetic parameters derived from eddy-covariance observation in a typical semi-arid grassland in Inner Mongolia,Northern China,over 12 years from 2006 to 2017.Regression analyses and a structural equation model(SEM)were adopted to separate the contributions of environmental and physiological effects.The photosynthetic parameters showed unimodal seasonal patterns and significantly interannual variations.Variations of air temperature(T,)and soil water content(SWC)drove the seasonal patterns of photosynthetic parameters,while SWC predominated their interannual variations.Moreover,contrasting with the predominant roles of T,onαand Ra,SWC explained more variance of Pmax than T,Results of SEM revealed that environmental factors impacted photosynthetic parameters both directly and indirectly through regulating physiological responses reflected by stomatal conductance at the canopy level.Moreover,leaf area index(LAl)directly affectedα,Pmax and R,and dominated the variation of Pmax.On the other hand,SWC influenced photosynthetic parameters indirectly through LAl and canopy surface conductance(gc).Our findings highlight the importance of physiological regulation on the photosynthetic parameters and carbon assimilation capacity,especially in water-limitedgrassland ecosystems.

The jet over a stretching wall with suction or injection

The steady laminar wall jet over a stretching surface in the presence of lateral suction or injection is considered. Similarity solutions absent in previous publications are found in some new ranges of parameters in the governing equation. The accuracy and reliability of the solutions have been checked through detailed convergence study and compared with the solutions from the numerical method and analytic method, and excellent agreement has been found. This gives the strongest evidence that those solutions are indeed new ones.

GROUP CONTINGENCY TEST FOR TWO OR SEVERAL INDEPENDENT SAMPLES

This paper proposes a new and distribution-free test called ＂Group Contingency＂ test （GC, for short） for testing two or several independent samples. Compared with traditional nonparametric tests, GC test tends to explore more information based on samples, and it＇s location-, scale-, and shapesensitive. The authors conduct some simulation studies comparing GC test with Wilcoxon rank sum test （W）, Kolmogorov-Smirnov test （KS） and Wald-Wolfowitz runs test （WW） for two sample case, and with Kruskal-Wallis （KW） for testing several samples. Simulation results reveal that GC test usually outperforms other methods.

Optimization of Pyrolysis Properties using TGA and Cone Calorimeter Test

The present paper describes an optimization work to obtain the properties related to a pyrolysis process in the solid material such as density, specific heat, conductivity of virgin and char, heat of pyrolysis and kinetic parameters used for deciding pyrolysis rate. A repulsive particle swarm optimization algorithm is used to obtain the pyrolysis-related properties. In the previous study all properties obtained only using a cone calorimeter but in this paper both the cone calorimeter and thermo gravimetric analysis (TGA) are used for precisely optimizing the pyrolysis properties. In the TGA test a very small mass is heated up and conduction and heat capacity in the specimen is negligible so kinetic parameters can first be optimized. Other pyrolysis-related properties such as virgin/char specific heat and conductivity and char density are also optimized in the cone calorimeter test with the already decided parameters in the TGA test.