Micromechanical Coupled Study of Crack Growth Initiation Criterion in Pressure Vessel Steel

We present results of the combined design-theoretical investigation of the mechanism of crack growth at the onset of ductile fracture of NPP reactor pressure vessels. Micromechanical approach to the prediction of ductile fracture has been applied, according to which the volume fraction of voids in the deformed material is determined by the finite-element method. On the basis of CT-specimen tests and known damage parameters, determined for smooth spherical specimens, we propose a micromechanical criterion of crack growth initiation for ductile fracture.     

褐煤树脂醇类化学组成与分布特征

对云南潦浒及寻甸褐煤树脂中醇类化学成分进行了GC-MS研究，探索褐煤树脂醇类作为药用资源的可能性．实验结果表明，树脂醇由正构烷醇、正构酮(甲基酮)、甾醇类、五环三萜醇及五环三萜酮所组成．褐煤树脂醇中均存在24-甲基-5β(H)-胆甾烷-3β-醇(C28H50O，MW．402)，24-乙基胆甾-5，22-二烯-3β-醇(C29H48O，MW．412)，24-乙基-5α(H)-胆甾烷-3β-醇(C29H52O，MW．416)，23，24-二甲基胆甾-5-烯一3β-醇(C29H50O，MW．414)，C29-5β(H)，3β(OH)-甾醇(C29H52O，MW．416)，24-异丙基胆甾-5，24(28)E-二烯-3β-醇(C30H50O，MW．426)等甾类物质．化学组成表明褐煤树脂作为药用资源是可能的．     

柚皮提取物不同级分的抗氧化活性研究

为柚皮资源的精细化利用提供参考依据，采用弱极性的DM130大孔吸附树脂为吸附剂、以不同浓度的乙醇溶液对柚皮提取物进行梯度洗脱，得到5种洗脱级分。采用二苯代苦肼自由基法和硫氰酸铁盐比色法对该5种级分的抗氧化活性进行了测定。结果显示：5种洗脱级分表现出不同程度的清除DPPH自由基和抗亚油酸过氧化活性，其作用大小依次为：水级分、20％乙醇级分、40％乙醇级分、60％乙醇级分和80％乙醇级分，5种洗脱级分的抗氢化活性均高干柚皮苷，但均低于二丁基羟基甲苯。柚皮提取物不同洗脱级分具有不同的抗氧化活性。     

Solid particle erosion behaviour of hardfacing deposits on cast iron—Influence of deposit microstructure and erodent particles

Solid particle erosion (SPE) behaviour of different hardfacing electrodes deposited on gray cast iron (ASTM 2500) was studied using quartz sand and iron ore as erodent particles. Erosion test was carried out as per ASTM G76 test method. Considerable differences in erosion rates were found among different hardfacing electrodes at normal impact. Both volume fraction of carbides and type of carbides played an important role in the erosion behaviour of the deposits when quartz sand was used as erodent particles. On the other hand, only volume fraction of carbides irrespective of carbide type mainly controlled the erosion rate of the same deposits when iron ore was used as erodent particles. Such difference is attributed due to difference in metal removal mechanisms by the two erodent particles used. Hard quartz sand particles were capable of causing damage to most of the carbides while relatively softer iron ore particles were unable to fracture any carbides present in the microstructures. Furthermore, relatively brittle matrix led to high erosion rate which is significant in case of quartz sand as erodent, but not in case of iron ore particles. Like abrasion resistance, hardness is not a true index of erosion resistance of hardfacing deposits.     

Capacitive measuring system for two-phase flow monitoring. Part 1: Hardware design and evaluation

Two-phase flows are commonly found in many industrial applications, such as oil and gas production. The monitoring of such flows is performed either in field applications or in pilot plant studies. In both cases, simple and robust measuring techniques are required. Capacitive probes have been applied for void fraction measurement in pipes in research and industry. However, capacitive measuring systems applied so far are tailored for specific applications and may not be easily adaptable. In addition, more and more soft-computing methods are applied for advanced data processing and parameter extraction which requires more computational power of sensor systems for online data processing. We develop a capacitive system provided with a microcontroller in which necessary routines for data processing may be embedded. System design is detailed explained and system's performance is evaluated, showing appropriate accuracy and time response for the investigation of two-phase flows.     

Modeling the hourly solar diffuse fraction in Taiwan

Using the data for global and diffuse radiation in Tainan, Taiwan, for the years of 2011 and 2012, respectively, four correlation models with five predictors: the hourly clearness index (k_t), solar altitude, apparent solar time, daily clearness index and a measure of persistence of global radiation level, are constructed to relate the hourly diffuse fraction on a horizontal surface (d) to the clearness index. Two models use a single logistic equation for all k_t values, Eqs. (6), (7), and the other two models use a set of piece-wise linear equations for four k_t intervals, Eqs. (8), (9). The proposed models are compared respectively with the fourteen models available in the literature, in terms of the four statistical indicators: the mean bias error, the root-mean-square error, the t-statistic and the Bayesian Information Criterion, using the out-of-sample dataset for Tainan, Taiwan. It is concluded from the analysis that the proposed piece-wise linear models perform well in predicting the diffuse fraction, while the performances of the proposed logistic models are more case-dependent. Among those fourteen models considered in this study, the models developed by Erbs et al., Chandrasekaran and Kumar, and Boland et al. have competitive performances as the proposed piece-wise linear models do, when applying to the prediction of diffuse fraction in Tainan, Taiwan.     

Determination of bone mineral volume fraction using impedance analysis and Bruggeman model

Measurements by impedance spectroscopy and Bruggeman effective medium approximation model were employed in order to determine the mineral volume fraction of dry bone. This approach assumes that two or more phases are present into the composite: the matrix (environment) and the other ones are inclusion phases. A fragment of femur diaphysis dense bone from a young pig was investigated in its dehydrated state. Measuring the dielectric properties of bone and its main components (hydroxyapatite and collagen) and using the Bruggeman approach, the mineral volume filling factor was determined. The computed volume fraction of the mineral volume fraction was confirmed by a histogram test analysis based on the SEM microstructures. In spite of its simplicity, the method provides a good approximation for the bone mineral volume fraction. The method which uses impedance spectroscopy and EMA modeling can be further developed by considering the conductive components of the bone tissue as a non-invasive in situ impedance technique for bone composition evaluation and monitoring.     

Sweet and sour potential of yeast from the Yarrowia clade

The food industry is witnessing a growing demand for food additives. Microbial fermentation is an attractive way to produce them using microorganisms, including the yeast Yarrowia lipolytica. Twelve species of the Yarrowia clade were screened for erythritol, mannitol and citric acid production from pure glycerol, glucose or fructose in four different media. During shake-flask cultures, only Y. lipolytica was able to secrete citric acid. Glycerol was found to be the best substrate for erythritol and mannitol biosynthesis by all the species. The six best candidate species for sweetener biosynthesis were cultivated in bioreactors. Up to 69.8 g dm⁻³ of total polyols with a yield of 0.59 g g⁻¹ was obtained for Candida oslonensis, the best sweetener producer. It secreted 44.6 g dm⁻³ of erythritol (Q_Ery = 1.16 g dm⁻³ h⁻¹ and Y_Ery/S = 0.4 g g⁻¹) and 34 g dm⁻³ of mannitol (0.29 g g⁻¹). Additionally, Candida hollandica and Yarrowia divulgata represent promising species for which media composition and culture parameters still have to be optimized.     

Intrusive Effect of Wire Mesh Tomography on Gas-liquid Flow Measurement

To investigate the accuracy of wire mesh tomography (WMT) for gas-liquid flow measurement, the experimental study focused on its intrusive feature has been carried out. The WMT principle is based on the dependency upon electrical conductivity on the local void fraction. The applied wire mesh sensor (WMS) consists of two measuring planes. Each plane has 8x32 crossing points with spatial resolution of2.22x3.03 mm² and wire diameter of 0.125 mm.

The disturbance level is estimated from the deviation of flow properties between each measuring plane of WMT and also from the alternative image processing for low gas intensity range. The results show the dependency of disturbance level on the void fraction shape. Furthermore, the contribution of deceleration and deformation on the flow disturbance related to the flow condition are presented. In addition, the capability of gas velocity evaluation method is confirmed and the intrusive effect becomes only one important parameter for gas velocity measurement.     

较大管径中两相流动漂移流模型研究

漂移流模型作为一种简单实用的模型，在反应堆热工水力及安全分析，特别是在空泡份额的计算方面，应用非常广泛。针对不同的通道及流型，研究者提出了多种基于漂移流模型的计算方法。通过较大通道中两相流动过程的实验研究，对5种空泡份额计算模型进行评价分析。结果表明，基于常规通道的Hibiki-Ishii模型与实验值吻合较好，平均相对误差为14.1%。结合对气泡运动过程的研究，发现在〈J_g〉β<0.027区，分布参数C₀<1，据此，给出了在较大管径通道中计算精度更高的模型关系式。