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The paper presents an analytical control solution to the problem of transient stabilization of lossy multi-machine power systems. Firstly, a new form of control Lyapunov function candidates with a flexible potential-energy-like term is proposed. This is achieved mainly by introducing an auxiliary state that contributes to the derivation of a cross-term. Based on the Lyapunov function candidates, a new control law ensuring asymptotic stability of the desired closed-loop operating equilibrium is proposed. Finally, a case study on the model of a two-machine system to illustrate the effectiveness of the proposed control solution is presented.

The density of T300 carbon fiber, as well as the amount of sizing and micro-structure were measured, before and after removing the sizing. The results showed that there was apparent stratification when measuring the density of the carbon fiber by the sink/float method, without removing the sizing. The upper sample layer was seriously flocculated with an excessive sizing amount of 2.17%, while the bottom-layer also flocculated. Two methods including acetone extraction and pyrolysis, were conducted to removing the sizing. It was shown that the measured amounts of sizing for the two methods were 1.20% and 1.53%, respectively. For the sample after immersion in acetone, there was still stratification in the sink/float test, with the upper sample layer flocculated because of the remaining sizing; while samples at the bottom dispersed relatively well. However, for the thermally treated samples the sizing was adequately removed, which resulted in the uniform density and dispersion during the test. This indicates that the non-uniform distribution of sizing agent on the surface of the CFs is the main reason for stratification during the density measurement. Therefore, the sizing must be fully removed in order to obtain an accurate density for the carbon fibers. Moreover, it can be seen that pyrolysis is an effective way to remove the CF sizing agent.

Background: Fresh pine needles, which evergreen, renewable and can be collected at any time, have abundant essential oil. The pine needle essential oil possess various biological activities, including antimicrobial, antioxidant, anti-inflammatory, cardioprotective properties etc., and can be widely used as medicine or medical raw materials, fragrances etc. So in order to make full use of pine needle plant resources, especially essential oil, the identification and quantification of essential oil were investigated.Materials and Methods: GC-MS was used to identified compounds in pine needle essential oil of Pinus massoniana Lamb. from Zhejiang, and GC method was developed for determining 5 compounds (namely α-pinene, β-pinene, limonene, bornyl acetate, β-caryophyllene) in pine needle essential oil from different habitats of Pinus massoniana Lamb. and different species (Pinus koraiensis Sieb. et Zucc., Pinus sylvestris var. mongolica Litv., Abies holophylla Maxim.). Hierarchical clustering analysis (HCA) was used to evaluate homogeneity of pine needles in China.Results: 42 compounds(monoterpenes and sesquiterpenes) were identified by GC-MS, which accounted for 99.62% of total essential oil, particularly contained α-and β-pinene (45.23%). Quantification results showed content of bornyl acetate were the lowest, while content of α-pinene, β-pinene were all high except Sichuan, among them α-pinene were higher than β-pinene except for Shandong and Jiangsu, and total content of essential oil in Guangxi is the highest, Jiangsu was the lowest within Pinus massoniana from different habitats. Within pine needle from different species, the highest total content was Pinus koraiensis, the lowest was Pinus sylvestris, Interestingly, the highest content of bornyl acetate was Abies holophylla. By HCA, samples were sorted into two clusters, Abies holophylla and the other, that is Abies holophylla is different from Pinus massoniana, Pinus koraiensis and Pinus sylvestris. Pinus massoniana from Sichuan is different from other Pinus, in which limonene was the highest in all samples.Conclusions: Compounds of pine needle essential oil vary greatly between genus, while smaller between species, so composition differences among pine needle essential oil was related with genus and species. Abies holophylla is different from other pinus species, and Pinus massoniana from Sichuan is different from other habitats. Pine needle essential oil contains abundant α-and β-pinene, which can be used as an alternative raw materials source of pinene. And Abies holophylla and Pinus massoniana from Sichuan can become bornyl acetate and limonene alternative source of raw materials.Keywords: pine needle, essential oil, terpene, GC-MS, GC

The aim of this work is to investigate the effect of moisture on the measured tensile strength of polyacrylonitrile (PAN) carbon fibers immersed in epoxy matrix under various moisture conditions. Tensile tests are carried out for the specimens, and a sharp decrease in measured tensile strength of the carbon fibers/epoxy system A immersed under high-moisture conditions is observed. Scanning electron microscope (SEM) is used to observe the effect of moisture on the surface structures of specimens. The results show that the decrease in the measured tensile strength is attributed to the microvoids of epoxy matrix formed in the preparation of the specimens. And the formation of microvoids in carbon fiber/epoxy matrix depends on viscosity change and curing condition of epoxy system. During the early stage of epoxy curing, both the solvent and absorbed water in the epoxy system escape from the immersed carbon fibers and form channels in the epoxy matrix. Once the viscosity of the epoxy system increased rapidly at a low curing temperature, the channels cannot be filled quickly by the surrounding resin and form microvoids finally. In order to verify these results, epoxy system B with a high curing temperature is chosen to prepare the specimens for tensile tests, and SEM images demonstrate that there are no microvoids that can be observed on the surfaces of specimens, even at such a high-moisture condition. And the measured tensile strengths remain unaffected in both low and high-moisture conditions. These results indicate that epoxy system with a high curing temperature is suitable for preparing the specimens for tensile tests regardless of moisture condition in the surrounding air.

The aim of this work is to investigate the effect of a process-induced resin bead on the measured tensile strength of polyacrylonitrile-based carbon fibers. It is found that the resin bead was formed on the surface of carbon fiber specimens if the carbon fibers impregnated with resin were positioned horizontally during the tensile specimen preparation. Mechanical testing results indicated that the measured tensile strength of carbon fibers noticeably decreased by about 10 % due to the formation of the resin bead, and the initial fracture of carbon fibers usually occurred around the resin bead. Moreover, the bending of the filaments in the resin bead had been observed by optical microscope. It is concluded that the flowing and curing of excess resin lead to the bending of loose filaments in carbon fiber tow during specimen preparation; thus, internal stress was subsequently formed in the fiber specimen, which is detrimental to the measured tensile strength. Finally, based on the microscopic observations, theoretical analysis under the maximum stress criterion was employed to predict the tensile strength of carbon fibers with a resin bead, and the theoretical results agree well with the experimental results. It is verified that the bending angle and the fraction of the bending filaments in the resin bead play important roles in deteriorating the measured tensile strength. These conclusions can help to improve the tensile testing method for accurately measuring the tensile strength of high modulus carbon fibers.

Based on DEA-Tobit model, the efficiency of occupational training for rural migrant workers of 30 provinces and cities was studied in this paper. The results indicated that there are significant differences among these 30 provinces and cities. Technical efficiency of East areas is lower than average level. Moreover, there is a significant negative correlation between the efficiency and Average education attainment, and a significant positive correlation between the efficiency and proportion of rural population.

Through literature research and expert interviews, we extract 10 variables influencing the new generation migrant workers' employability, and establish the comprehensive evaluation model of the new generation migrant workers' employability. Using factor analysis, we derive that the model includes three factors: skill literacy, relationship literacy and basic literacy. The weights of each factor are 0.580, 0.244 and 0.174 8, respectively. Skill literacy is affected by skill level, learning ability, career aspiration, ability to analyze problems, physical health status and other factors. Relationship literacy is affected by the sense of teamwork, interpersonal skills, social support and other factors. Basic literacy is affected by educational level, hardworking spirit and other factors. According to the results, we put forth the following recommendations to improve the new generation migrant workers' employability: strengthening the vocational skill training; coordinating the vocational education resources.