Multi-train modeling and simulation integrated with traction power supply solver using simplified Newton–Raphson method

Multi-train modeling and simulation plays a vital role in railway electrification during operation and planning phase. Study of peak power demand and energy consumed by each traction substation needs to be deter- mined to verify that electrical energy flowing in its railway power feeding system is appropriate or not. Gauss-Seidel, conventional Newton-Raphson, and current injection methods are well-known and widely accepted as a tool for electrical power network solver in DC railway power supply study. In this paper, a simplified Newton-Raphson method has been proposed. The proposed method employs a set of current-balance equations at each electrical node instead of the conventional power-balance equation used in the conventional Newton-Raphson method. This concept can remarkably reduce execution time and computing complexity for multi-train simulation. To evaluate its use, Sukhumvit line of Bangkok transit system （BTS） of Thai- land with 21.6-km line length and 22 passenger stopping stations is set as a test system. The multi-train simulation integrated with the proposed power network solver is developed to simulate 1-h operation service of selected 5-min headway. From the obtained results, the proposed method is more efficient with approximately 18 % faster than the conventional Newton-Raphson method and just over 6 % faster than the current injection method.

Novel Cascade Refrigeration Cycle for Cold Supply Chain of COVID-19 Vaccines at Ultra-Low Temperature -80°C Using Ethane (R170) Based Hydrocarbon Pair

Several media report highlight on that the pharmaceutical companies require ultra-low temperatures -80°C to transport and store its COVID-19 vaccines. This research presents the thermodynamic analysis on cascade refrigeration system (CRS) with several refrigerant pairs which are R32/R170, R123/R170, R134a/R170, R404A/R170, R407c/R170, R410/R170, and the hydrocarbon (HC) refrigerant pair Propane/Ethane, namely R290/R170. Besides, the results of R22/R170 pair, which is not recommended to be used due to phase out of R22 as per Montréal Protocol, are included as base case to compare the novel hydrocarbon pairs in CRS and the old trend of refrigerant pairs. Thermodynamic properties of all these pairs were investigated and compared under different intermediate temperature used in CRS heat exchanger, which thermally connected both the Low and High temperature cycles (LTC) and (HTC). By applying the first law of thermodynamics, the coefficients of performance (COPs) and the specific power consumptions (SPC) in kW/TR are presented and compared. In addition, by applying the second law of thermodynamics the exergetic efficiencies were estimated. The results reveal the promising opportunity of using the HC pair (R290/R170). The minimum SPC in kW/TR is recorded for the pair R123/R170. One the other hand, the highest exegetic efficiency values are observed to be 40%, 38%, and 35% for the pairs R123/R170, R290/R170, and R134/R170, respectively. This research concludes that the HC pair (R290/R170) is highly recommended for CRS applications either to transport the COVID-19 or store it in cold storage rooms in hospitals and clinics. All precautionary measures should be carefully applied in design and operation of HC pair (R290/R170) due to its flammability hazard.

我国区域航空市场客运运力供需均衡研究

区域航空市场作为民航运输市场的重要组成部分,在服务于区域航空旅客和带动区域经济发展方面发挥着不可替代的作用。借助供需均衡理论,对我国区域航空市场客运运力供需进行了研究,得出我国区域航空市场客运运力供需不均衡的结论,提出了我国区域航空市场客运运力供需均衡实现的4条途径,即政府的高度重视,区域优势的利用,区域航空枢纽的建设及航空公司的积极参与。

广东高职院校建筑类专业人才供需平衡现状分析

以广东工程职业技术学院为例,从数量、结构、质量等方面对建筑类专业人才的供需现状进行分析,分析结果为人才供需失衡。建筑业的快速发展、市场信息的不对称、人才激励机制的不健全、人才培养模式的不完善是导致其不平衡的重要原因。政校行企深度融合是实现广东高职院校建筑类专业人才供需平衡的重要途径。

Integrated Knitwear Production for Hong Kong and the Interior of China

Hong Kong knitwear manufacturers were among the pioneers to invest in the Pearl River Delta region of Guang-dong,China.Owing to limitations on technological levelat the time of the initial investments,the content of pro-duction-sharing for the Inland in China were basically of simple technology and labour intensive in nature.Through venturing hardships,the investment has been able to boost the economy of Guangdong and foster close trade relationship,especially in outward processing trade,By now,the co-operative production

带电源适配器(USB)插座温升试验标准分析

随着科学技术的发展以及消费者需求的多样化,为适应不同场合的多种用途,插座产品的功能越来越丰富。带电源适配器(USB POWER SUPPLY)的插座产品,将交流和直流输出两种功能集于一体,满足了消费者同时给各类电子设备充电和大功率用电设备用电需求。但是,由于带电源适配器(USB POWER SUPPLY)插座的结构特殊性,国内外相关插座标准,对该类产品的温升试验方法尚未形成一致要求。本文通过对比分析国家标准GB/T 2099.1-2008(及其报批稿)、英国BS 1363-2:2016+A1:2018标准、现行IEC 60884-1:2002+A1:2006+A2:2013标准以及新版IEC FDIS 60884-3-1:2021标准草案,对带电源适配器(USB POWER SUPPLY)插座温升试验的不同要求;并依据不同方法对同一插座样品进行试验,归纳出不同试验方法对温升试验结果的影响。同时介绍分析即将发布的新版IEC 60884-3-1:2021标准的温升试验方法。

Machining of circular micro holes by electrochemical micro-machining process

Machining of micro holes with micro electro- chemical machining （micro ECM） process has been carried out with an indigenously developed set up. This paper describes relevant problems and solutions for the circular micro holes machining process on 304 stainless steel sheets with 60 μm thickness using high speed steel cylindrical tool of diameter 500 ~tm and using dilute I-I2SO4 as elec- trolyte. The taper angle variation of the machined hole is analyzed and reported for different experimental setting parameters. The minimum value of the taper angle of machined holes is achieved at the parameter setting of 0.4 mol/L H2504, 700 kHz, 600 ns and 21 V, for stainless steel sheets and HSS tool.