Removing dead transitions in timed-arc Petri nets

Timed-arc Petri nets (TAPNs) are a timed extension of Petri nets where tokens are assigned an age indicating the time elapsed from its creation, and PT-arcs (place to transition arcs) are labelled with time intervals that are used to restrict the age of the tokens that can be used to fire the adjacent transition. This is a rather pathological model, as reachability is undecidable, whereas some other known properties of Petri nets, like boundedness, coverability and even termination, are decidable. This article focuses on the problem of detecting dead transitions, i.e. transitions that can be removed from the model since they can never become enabled. We prove that this problem is decidable for TAPNs with natural times, and we present an algorithm that can be used to find dead transitions in the particular case of 1-safe TAPNs.     

CSP生产线高速钢轧辊温度场有限元分析

采用有限元软件ANSYS,结合某CSP生产线F4机架工作辊表面温度的实测值,建立轧辊二维温度场模型,对轧辊在轧制过程中的温度和热凸度变化进行研究。结果表明,轧辊在咬入弧区的换热系数为5.8×104 W/(m2·K),在非咬入弧区的水冷等效换热系数为1.1×104 W/(m2·K);在此等效换热边界条件下,使轧辊热凸度达到稳定的烫辊时间约为75min。     

Chiral separation of three agrochemical toxins enantiomers by high-performance liquid chromatography on a vancomycin crystalline degradation products-chiral stationary phase

This work aims to evaluate for the enantiomeric separations of three agrochemical toxins: haloxyfop-methyl, fenoxaprop-p-ethyl and indoxacarb on crystalline degradation products-chiral stationary phase (CDP-CSP) of high-performance liquid chromatography (HPLC) under normal and polar organic phases. In the normal phase, the mobile phase was n-hexane with alcohols including methanol and isopropanol as polar modifiers. In the polar organic phase mode, the mobile phase was methanol with different percentages of triethylammunium acetate. The influence of flow rate (0.3-0.9 mL/min), analyte concentration and silica gel particle sizes (10, 15 and 30 microm) was investigated. This new chiral stationary phase showed excellent stereoselectivity for the two enantiomers of haloxyfop-methyl and fenoxaprop-p-ethyl and chiral recognition for indoxacarb under normal-phase mode. However, under polar organic phase, only indoxacarb was separated (alpha < 1.5). The chromatographic results were compared with commercial chiral columns.     

Bibliometric Analysis on Supercritical CO2 Power Cycles for Concentrating Solar Power Applications

In recent years, supercritical CO₂ power cycles have received a large amount of interest due to their exceptional theoretical conversion efficiency above 50%, which is leading a revolution in power cycle research. Furthermore, this high efficiency can be achieved at a moderate temperature level, thus suiting concentrating solar power (CSP) applications, which are seen as a core business within supercritical technologies. In this context, numerous studies have been published, creating the need for a thorough analysis to identify research areas of interest and the main researchers in the field. In this work, a bibliometric analysis of supercritical CO₂ for CSP applications was undertaken considering all indexed publications within the Web of Science between 1990 and 2020. The main researchers and areas of interest were identified through network mapping and text mining techniques, thus providing the reader with an unbiased overview of sCO₂ research activities. The results of the review were compared with the most recent research projects and programs on sCO₂ for CSP applications. It was found that popular research areas in this topic are related to optimization and thermodynamics analysis, which reflects the significance of power cycle configuration and working conditions. Growing interest in medium temperature applications and the design of sCO₂ heat exchangers was also identified through density visualization maps and confirmed by a review of research projects.     

Ferron逐时比色法中显色剂Ferron浓度对Al-Ferron体系反应动力学的影响

Ferron逐时比色法中Al-Ferron体系反应动力学常被视为准一级反应,由此可推得相应的拟合方程并测得相应的反应速率常数kb,显色剂Ferron作为反应物之一其用量必然直接影响测量的结果。以不同OH/Al比的聚合氯化铝溶液为研究对象,抓住Ferron浓度这一核心要素,对Al-Ferron体系反应动力学过程进行了系统研究。结果表明,[Ferron]≥2.0×10^(-3)mol/L是确保动力学速率常数kb准确测量的基本保证。     

基于并行环境的模型检查技术研究与实现

针对实时系统模型检查中的突出问题：状态组合爆炸,提出一种基于并行环境的实时系统模型检查技术,用邻接表存储时钟带,用C＋＋和MPI设计并实现了一个并行实时系统模型检查器———PRAModelChecker,选择一个典型的实例对PRAModelChecker的性能进行分析.实验表明,随着系统复杂性的增加,不但能提高工作效率,而且能处理的系统规模可伸缩,从而为从根本上解决状态组合爆炸问题提供了一种新的途径.     

键合型聚丙烯酰胺衍生物手性固定相的制备与手性识别性能

高效液相色谱(HPLC)被广泛认为是分离制备光学纯单一对映体的最有效方法。在高效液相色谱手性拆分中,手性固定相(CSP)的性能直接影响到色谱柱的手性分离能力。在众多手性固定相中,键合型手性固定相具有溶剂耐受性好,分离模式灵活等优点,已经发展成为一类重要的手性固定相。本文通过两步化学反应合成了新型的光学活性丙烯酰胺衍生物--(S)-1-丙烯酰-2-(N-苯基甲酰胺基)吡咯烷((S)-APACP),采用核磁共振氢谱表征了(S)-APACP的化学结构;通过3步化学反应制备了键合型聚丙烯酰胺衍生物手性固定相,采用热重分析法表征了聚合物的键合量,采用HPLC评价了键合型手性固定相的识别能力,分析了影响其手性识别能力的因素。研究结果表明,APACP聚合物成功地键合到硅胶表面制备了具有良好溶剂耐受性的键合型手性固定相,其聚合物键合量为10.2%~11.8%,该键合型手性固定相对若干种对映体显示了较好的手性识别能力。     

CSP结晶器内钢液流动及凝固的数值模拟

应用数值模拟方法,建立CSP漏斗型结晶器内钢液流动及凝固传热耦合模型。针对结晶器内铸坯角部受到强冷的特点,对结晶器内热流密度采用修正方程进行计算,分析热流密度修正系数对铸坯凝固坯壳表面温度计算精度的影响。通过比较不同拉坯速率下结晶器内钢液凝固的特点,研究凝固坯壳对结晶器内钢液流动行为的影响。结果表明,采用热流密度修正系数后,铸坯凝固坯壳角部温度的计算值与实际情况更相符;提高拉坯速率可使铸坯凝固坯壳厚度减小;拉坯速率较大时凝固坯壳厚度随铸坯距弯月面距离的增大基本呈线性增长,拉坯速率为3m/min时,凝固坯壳在生长过程中厚度的增长有短暂的停滞现象;凝固坯壳对钢液流动的影响较大,主要是由钢液有效流动区域减少及两相区额外动量阻损造成的。     

一种基于时间自动机网络的实时系统形式化验证方法

介绍了时间自动机形式模型,在此基础上给出了时间自动机网络的形式语法和语义,然后给出一种基于时间自动机网络的实时系统形式化验证方法,并采用基于时间自动机网络的模型检测工具UPPAAL对一个经典的实时系统实例进行了验证．     

硅胶负载手性氨基醇聚合物的合成及其应用

以L-亮氨酸(L-Leu)为手性源,经酯化、格氏化、酰胺化等步骤制备手性单体(L-NALAA),以该单体为手性识别基团,在引发剂偶氮二异丁腈和交联剂乙二醇二甲基丙烯酸酯(EDMA)的作用下,与烯化功能硅胶发生自由基共聚反应,制备了新型键合硅胶手性固定相,其结构经FT-IR、TGA、EA表征。以4种对映异构体为模型药物对手性材料手性固定相的手性拆分性能进行研究,结果表明,手性材料手性固定相对奥美拉唑和兰索拉唑的拆分效果较好。