Effect of molecular structures on polyimide properties: Comparison between estimations and experiments

The density and glass transition temperature (T_g) of 11 polyimides were investigated by experiments and predictions using the connectivity indices method to explore the structure–property relationships. The predicted results are in good agreement with the experimental data. The mean interchain spacings (d‐spacings) of polyimides increase with the introduction of bridging groups, i.e., following the order: PDA < BZD < ODA < MDA < BDAF, while the densities increase in the order of MDA < BZD < PDA, and cohesive energy densities (CEDs) of polyimides change following the order of BDAF < MDA < ODA < BZD < PDA. In addition, the glass transition temperatures (T_g's) increase as the CEDs increase for the polyimides prepared from the same dianhydride and different diamines, whereas no certain correlation exists between T_g's and the values of the characteristic ratio (C_∞). This indicates that the strength of interchain interaction influences the T_g's of polyimides much stronger than the chain flexibility. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 998–1003, 2007     

Flue gas desulfurization in an internally circulating fluidized bed reactor

An internally circulating fluidized bed reactor (ICFBR) was used as a desulfurization apparatus in this study. The height of the bed was 2.5 m, and the inner diameter was 9 cm. The bed materials were calcium sorbent and silica sand. The effects of the operating parameters of the flue gas desulfurization including relative humidity, particle size of the calcium sorbent, inlet concentration of SO₂, difference between the superficial gas velocities in the draft tube and the annulus, and superficial gas velocity in the draft tube on SO₂ removal efficiency (RE) were investigated. It was found that when the relative humidity (RH) was varied from 40% to 80%, the steady state RE had a largest value of approximately 15% when the relative humidity was 60%. When RH = 50%, 60% and 70%, RE decreased initially and then increased. After that RE decreased again until a steady state was reached. In addition, RE decreased with increasing calcium particle size or inlet SO₂ concentration. A larger difference between the superficial gas velocities in the draft tube and the annulus had a higher RE resulting from increasing reactivity of the calcium sorbent caused by a higher attrition rate. Moreover, a higher attrition rate had a higher total volume of the flue gas treated. Finally, a model to predict the steady state RE in ICFBR was proposed. It assumed that the draft tube section was a bubbling fluidized bed while the annulus section was a moving bed. In addition, the effects of the calcium sorbent conversion, attrition rate and gas-bypassing fractions on RE were also taken into account in this model. It was found that the values of RE predicted by this model agreed with the experimental results.     

两电平电压源型换流器负阻性与容性效应特征指标研究

为评估两电平电压源型换流器(VSC)并网系统的谐振不稳定风险,定义了4个描述两电平VSC负阻性与容性效应的特征指标.首先,基于简化等效电路,通过奈奎斯特稳定判据论证了VSC负电阻引起谐振不稳定的简单机理.然后,通过分析两电平VSC的交流侧扰动响应特性建立其端口阻抗模型.在此基础上,通过简化分析建立VSC端口电阻和端口电抗的宽频近似模型;据此定义了VSC负阻性与容性效应的特征指标,并对其影响因素进行了分析.最后,通过电磁暂态仿真验证了宽频近似模型的准确性和特征指标的有效性.算例分析表明,文中提出的特征指标可以定性评估两电平VSC并网系统的谐振不稳定风险.     

A cost‐effective model for the gasoline blend optimization problem

Gasoline blending is a critical process with a significant impact on the total revenues of oil refineries. It consists of mixing several feedstocks coming from various upstream processes and small amounts of additives to make different blends with some specified quality properties. The major goal is to minimize operating costs by optimizing blend recipes, while meeting product demands on time and quality specifications. This work introduces a novel continuous‐time mixed‐integer linear programming (MILP) formulation based on floating time slots to simultaneously optimize blend recipes and the scheduling of blending and distribution operations. The model can handle non‐identical blenders, multipurpose product tanks, sequence‐dependent changeover costs, limited amounts of gasoline components, and multi‐period scenarios. Because it features an integrality gap close to zero, the proposed MILP approach is able to find optimal solutions at much lower computational cost than previous contributions when applied to large gasoline blend problems. © 2016 American Institute of Chemical Engineers AIChE J, 62: 3002–3019, 2016     

海南省高新技术产业发展的灰色关联度评价研究

对我国高新技术产业的发展进行评价研究具有重要的理论意义和现实的指导意义。作者首先建立了高新技术产业的评价指标体系，在此基础上对海南省2000～2005年6年间高新技术产业在经济效益、创新能力及发展潜力等方面的历史数据进行了灰色关联度分析。     

辽宁省县区科技进步综合评价研究

县区科技进步是推动地方经济和社会发展的关键因素，对县区科技进步总体情况进行综合评价，对于县区合理配置科技资源、促进区域经济发展和社会全面进步具有重要的实践意义.首先明确了县区科技进步评价的目的，在此基础上建立了县区科技进步综合评价层级指标体系，并运用专家访谈法确定了指标权重，提出了评价指标标准化的方法，然后运用评价模型可以综合评价县区科技进步的总体情况，最后以辽宁省的部分县区为例进行了实证分析，证明所建立的指标体系和评价方法是有效的.     

Economical and Technical Indices of Decomposition Processes of Typical Rare Earth Minerals in China

The typical treatment processes we of main rare earth resources in China, especially the economical and technical indices of the minerals decomposition of such as ionic adsorptive rare earth deposit ore, bastnasite and mixed with monazite in Baotou, was presented. The dispersive ionic adsorptive rare earth deposit ore, which is enriched on valuable middle and heavy elements, concentrated by bicarbonate precipitation after exchanging with ammonium sulphate solution. Planting and waste liquid should be focused. Bastnasite and/or monazite, which is enriched light rare earth, centralized with high content and capacity,concentrated by gravimetric, magnetic, floating, then decomposed by calcinations and leaching. Waste liquid, gases and dregs should be treated properly. Investors interested in RE industry can find out the technical and economic characters and history of various RE minerals. Engineers and workers in RE industry can also find the differences of the plants, so as to make more efforts on improving management. However, solving environment protection problems for each process should be committed extraordinarily in order to make a sustainable development of RE industry.     

番茄秧苗模拟运贮中质量下降机理研究

采用信号物质含量变化和生理指标测定以及电子显微透射观察等方法进行番茄秧苗运贮试验,结果表明:运贮期间番茄秧苗信号物质含量以及某些生理因素指标发生明显而定向的变化,番茄叶片细胞叶绿体超微结构及叶绿体数量和体积均发生改变。这些变化表明番茄秧苗运贮期间的质量下降的实质是由于“断光”“断水”而引起的不同于“衰老”的整株型“胁迫性生理衰变”。这种衰变具有“急剧性”“胁迫性”和“可恢复性”的特征。     

Capability Indices and Conformance to Specification: The Motivation for Using Cpm

Proposed is a perspective on quality that is different from but consistent with the current Six Sigma thinking. The focus is still squarely on the customer, but the concept of a “defect” is reevaluated. This new perspective can be used to help define key characteristics, process capability, and evaluate overall product quality using a loss function. This article focuses on the concept of process capability using this perspective. Central to the proposed quality perspective is ability to meet the customer's product specifications rather than ability to meet the component feature specifications. Current product and component quality metrics can drive the wrong decisions and wrong behaviors. This can add significant cost to internal processes and suppliers, and inadequately protect the customers from defective products. The new perspective defines component and process quality based on the probability of meeting the product specifications rather than the individual component feature specifications. Cpm is a simple process capability metric that can indicate the probability of meeting the customer's product specification. Cpm can be used to better estimate the cost of poor quality than can be estimated by using Cpk, and thus can be used to better manage product quality to the customer.     

One‐sided Process Capability Assessment in the Presence of Measurement Errors

In the manufacturing industry, many product characteristics are of one‐sided specifications. The well‐known process capability indices C_PU and C_PL are often used to measure process performance. Most capability research works have assumed no measurement errors. Unfortunately, such an assumption is not realistic even if the measurement is conducted using highly sophisticated advanced measuring instruments. Therefore, conclusions drawn regarding process capability are not reliable. In this paper, we consider the estimation and testing of C_PU and C_PL with the presence of measurement errors, to obtain adjusted lower confidence bounds and critical values for true process capability, which can be used to determine whether the factory processes meet the capability requirement when the measurement errors are unavoidable. Copyright © 2005 John Wiley & Sons, Ltd.