浅议油罐消防泡沫管线的腐蚀问题

针对油罐消防泡沫管线的腐蚀问题,通过对管线施工及使用过程中各种影响因素的分析,得出管线产生腐蚀的几种可能原因,进而采取相应的措施。     

中线平移互交视线测设法在斜交桥梁定位的应用

以福建某高速公路尤溪段源湖中桥为例,阐述了中线平移互交视线测设法在斜交桥梁墩台定位的应用情况,实践证明该方法能很好地解决斜交桥梁墩台定位的问题。     

A study on sensitivity correction factor of gamma camera in whole body bone image

The aim of this study was to calculate a reasonable correction factor that could be corrected when the sensitivity of each gamma camera is measured and a whole body bone scan is performed as a follow-up examination. Seven pieces of equipment were used to analyse the sensitivity measurements of each gamma camera based on the source sensitivity measurement method recommended by the IAEA. These were BRIGHTVIEW, PRECEDENCE, ECAM, ECAM signature, ECAM Plus, SYMBIA T2 and INFINIA. The ^99mTc line source for the sensitivity measurement was generated in 4–7 kcps, which are the common values in a whole body bone scan. All the cameras were equipped with a low-energy and high-resolution parallel multi-hole collimator and set at a window width and photo peak of 15% and 140 keV, respectively. After placing the ^99mTc source as closely as possible to the collimator, the count was measured for 60 and 120 seconds to calculate correction factor. To determine if the correction factor calculated using the ^99mTc line source could be applied to a whole body bone scan of a real patient, a whole body bone scan was performed on 27 patients before applying the correction factor for comparative analysis. According to the experimental results using the ^99mTc line source, the gamma camera sensitivity was the highest for ECAM plus, followed in order by the gamma cameras, ECAM signature, SYMBIA T2, ECAM, BRIGHTVIEW, INFINIA and PRECEDENCE. When the results were used to calculate the correction factor based on the ECAM gamma camera, which had a medium-degree of sensitivity, the respective correction factors were 1·07, 1·05, 1·03, 1·00, 0·90, 0·83 and 0·72. The correction factors calculated based on the experiment using a ^99mTc line source were similar to those calculated based on the whole body bone scan. Clinical application of correction factor for measured sensitivity enables estimation of factor correction depending on difference in equipment when image is read, which improves accuracy and reliability of examination, and is expected to be used especially for continuous follow-up examination.     

Simultaneous extraction of source and drain resistances in top contact organic thin film transistors from a single test structure

A method of extraction of source and drain resistances in linear mode of operation from a single transistor is described. The proposed method can also be used to measure source resistance over the entire operating range from linear to saturation mode of operation. The method uses two floating probes outside the channel, one adjacent to the source and the other to the drain to sense the voltage under these contacts. Using transmission line analysis, the source and drain resistances are directly extracted from these measurements. 2D numerical simulation results confirm the validity of the proposed technique and sensitivity analysis shows that the method is more accurate than the conventional gated four probe technique, especially, when the source resistance is much smaller than the channel resistance. Experimental results obtained with Pentacene top-contact transistors are used to illustrate the proposed technique. Analysis of two devices with very different source resistance is carried out to highlight the ability of the proposed technique to offer insight into the different contributing factors. Current crowding under the source contact and accurate estimation of mobility without the distorting effects of source resistance are also described.     

One‐dimensional low‐profile slot‐loaded epsilon‐negative zeroth‐order antenna with improved radiation efficiency

A novel low‐profile slot‐loaded epsilon‐negative (ENG) transmission line (TL) is proposed for efficiency‐improved zeroth‐order resonant antennas. It is demonstrated that the quality factor of the ENG TL‐based zeroth‐order resonator can be remarkably reduced by enlarging the slot size, therefore, a highly efficient radiating resonator can be designed with higher gain at the zeroth‐order frequency. Two one‐dimensional zeroth‐order resonant antennas with identical unit cell size but different unit cell number are fabricated and measured, each of which can realize a monopole‐like radiation pattern at nearly the same frequency. A maximum gain of 1.96 dBi is generated for the electrically small two‐unit‐cell configuration together with an improved efficiency from 57.0% to 69.1%, while the compact four‐unit‐cell antenna can realize a maximum gain of 3.86 dBi with an improved efficiency from 71.0% to 82.4%. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.     

基于致动线模型的风力机尾流场数值模拟

本文基于致动线模型求解三维Navier-Stokes方程的方法,对NTNU的"BlindTest1"风力机尾流场进行了数值模拟。该方法避免了求解实际叶片的表面边界层,无需使用动网格,从而大大降低了网格量和计算时间,非常适用于尾流场的模拟。该文所有计算均基于OpenFOAM自定义的求解器ALMpisoFoam。推力和功率的计算值与实验值吻合得很好,验证了求解器的正确性。3个典型叶尖速比下的轴向诱导因子、湍动能和尾涡结构等也在文中进行了简要分析。     

Effects of VSC based HVDC system on distance protection of transmission lines

The priority to reactive power contribution from the Voltage Source Converter (VSC) based High Voltage Direct Current (HVDC) connection to support the grid during faults as suggested by the modern Network Code (NC) for HVDC affects the distance protection of transmission lines. Moreover, suppressing the negative sequence current during an unbalanced condition also interferes with the proper operation of the distance relays. This is because the current contribution from the converter is limited in magnitude and modified in the waveform in order to protect the power electronic devices during the fault in comparison to the synchronous generator fault current characteristics. This paper discusses the cause as well as the severity of the problems faced by the distance protection of transmission lines connected to the VSC based HVDC system by analyzing the apparent impedance analytically and in the simulation. The response of the relay to balanced and unbalanced faults lying on transmission lines is investigated. It is shown that the VSC limited reactive support and suppressed negative sequence current affect fault detection, forcing the relay to malfunction. The results of this paper can be used as a reference for understanding the effects of VSC-HVDC system on the operation of the distance protection during faults.     

Two-sided assembly line balancing problem of type I: Improvements,a simple algorithm and a comprehensive study

Many meta-heuristic methods have been applied to solve the two-sided assembly line balancing problem of type I with the objective of minimizing the number of stations, but some of them are very complex or intricate to be extended. In addition, different decoding schemes and different objectives have been proposed, leading to the different performances of these algorithms and unfair comparison. In this paper, two new decoding schemes with reduced search space are developed to balance the workload within a mated-station and reduce sequence-depended idle time. Then, graded objectives are employed to preserve the minor improvements on the solutions. Finally, a simple iterated greedy algorithm is extended for the two-sided assembly line balancing problem and modified NEH-based heuristic is introduced to obtain a high quality initial solution. And an improved local search with referenced permutation and reduced insert operators is developed to accelerate the search process. Computational results on benchmark problems prove the efficiency of the proposed decoding schemes and the new graded objectives. A comprehensive computational comparison among 14 meta-heuristics is carried out to demonstrate the efficiency of the improved iterated greedy algorithm.     

Cold model experiment on dynamic behavior of dross in hot dip plating bath

The motions of top and bottom dross in a continuous hot dip plating bath were investigated using a transparent cold model vessel with a reduced scale of one-tenth. The flow field in the model bath was classified into three regions as usual; the entry region, the exit region, and the region enclosed with a belt. This belt was used as a model for a strip. Polystyrene particles were used as models both for the top and bottom dross while NaCl aqueous solutions of different densities were used as models for plating melts. The motions of model particles were observed by eye inspection and by using a high-speed video camera. Local particle frequency and particle holdup were measured with a newly developed sensor. Typical streak lines for the top and bottom dross particles were similar to main stream lines in the bath. Both the top and bottom dross particles were rich in the region enclosed with the belt. A lot of top dross particles floated on the bath surface near the side walls, while many bottom dross particles stayed on the bottom wall in the entry region.     

混凝土坝基防渗帷幕体老化的基本模式及识别指标

采用综合分析方法,对混凝土坝基防渗帷幕体的老化模式以及识别指标进行了系统的探讨。基于相对防渗效率,把帷幕体老化分为相对稳定型、缓慢变化型以及阶段性变化型3种基本模式;在分析时段内,不同的模式具有不同的防渗效率。用于识别帷幕体老化的指标有3类:第一类为渗流的微观动态要素,包括析钙量、TDS值、pH值、无机质和有机质等,可用于揭示帷幕体的老化机制;第二类为渗流的宏观动态要素,包括扬压力、排水量等,可用于判断帷幕体的老化程度及其基本模式;第三类为数值分析指标,包括饱和指数和渗漏水源比例系数等,可用于量化分析帷幕体的老化过程。3类指标的识别有助于构建混凝土坝基防渗帷幕体老化评估体系。