Determination of optimal part delivery dates in a stochastic assembly line

We consider the problem of determining the optimal part delivery dates of a low volume, small lot assembly line which manufactures large and costly products. Parts are assembled at each stage to a subassembly. The arrival time of an assembly part from a vendor is assumed to be a normally distributed random variable. A dynamic programming algorithm is developed to minimize work-in-process inventory of parts and subassemblies. It is implemented on the single job problem. Its further extensions to the multi-job case and to incorporate the cost of setting delivery dates are also discussed.     

Crystal morphology of calcium aluminates hydrated for 14 days

Abstracts are not published in this journal This revised version was published online in November 2006 with corrections to the Cover Date.     

KINETICS OF BIOETHANOL PRODUCTION FROM WHEAT MILLING BY-PRODUCTS

An overview of the potential application of wheat milling by‐products as substrate for bioethanol production is presented. In order to select a suitable microorganism, model fermentations were conducted using glucose and dry baker's yeast. The overall ethanol yield was nearly stable (ca. 0.35 g/g), independent of mash glucose concentration; mashes with 100 g glucose/L resulted in an overall ethanol productivity of 3.48 g/L·h. Slurries containing low‐grade wheat flour (LG) (100, 200 or 300 g/L) were used for simultaneous saccharification and fermentation (SSF) with Zymomonas mobilis. Fermentation performance was evaluated based on ethanol concentration (P), productivity (Q_v), yield (Y_P/S), production rate (Q_p) and glucose consumption rate (Q_s). Mashes containing 200 g LG/L produced about 52 g ethanol/L, with Q_vof 2.17 g/L·h. Based on the relatively high fermentation rate of LG, reaching peak ethanol productivity within ca. 9 h of SSF, considerable savings on fermentation time was achieved. Using Z. mobilis for LG fermentation, P was about 30% higher than that obtained with Saccharomyces cerevisiae.     

Automated system for characterization and classification of malaria‐infected stages using light microscopic images of thin blood smears

In this paper, we propose a comprehensive image characterization cum classification framework for malaria‐infected stage detection using microscopic images of thin blood smears. The methodology mainly includes microscopic imaging of Leishman stained blood slides, noise reduction and illumination correction, erythrocyte segmentation, feature selection followed by machine classification. Amongst three‐image segmentation algorithms (namely, rule‐based, Chan–Vese‐based and marker‐controlled watershed methods), marker‐controlled watershed technique provides better boundary detection of erythrocytes specially in overlapping situations. Microscopic features at intensity, texture and morphology levels are extracted to discriminate infected and noninfected erythrocytes. In order to achieve subgroup of potential features, feature selection techniques, namely, F‐statistic and information gain criteria are considered here for ranking. Finally, five different classifiers, namely, Naive Bayes, multilayer perceptron neural network, logistic regression, classification and regression tree (CART), RBF neural network have been trained and tested by 888 erythrocytes (infected and noninfected) for each features’ subset. Performance evaluation of the proposed methodology shows that multilayer perceptron network provides higher accuracy for malaria‐infected erythrocytes recognition and infected stage classification. Results show that top 90 features ranked by F‐statistic (specificity: 98.64%, sensitivity: 100%, PPV: 99.73% and overall accuracy: 96.84%) and top 60 features ranked by information gain provides better results (specificity: 97.29%, sensitivity: 100%, PPV: 99.46% and overall accuracy: 96.73%) for malaria‐infected stage classification.     

采用粗空心微球低压粉末冶金法制备空心微球复合泡沫钛(英文)

在低压下采用粉末冶金法,使用粗尺寸空心微球制备出不同相对密度的钛空心微球复合泡沫材料。在压力为60~70 MPa,通过冷压制备得到不同相对密度的泡沫钛。研究冷压压力与空心微球破碎倾向和相对密度的函数关系。研究制备的泡沫钛材料的压缩变形行为,考虑到实际应用,建立了平台应力、弹性模量、致密化应变和能量吸收之间的经验关系。对比泡沫钛和致密钛的性能指标,发现在工程应用中泡沫钛是致密钛的优秀替代物。     

Electrical,rheological and electromagnetic interference shielding properties of thermoplastic polyurethane/carbon nanotube composites

Electrically conducting rubbery composites based on thermoplastic polyurethane (TPU) and carbon nanotubes (CNTs) were prepared through melt blending using a torque rheometer equipped with a mixing chamber. The electrical conductivity, morphology, rheological properties and electromagnetic interference shielding effectiveness (EMI SE) of the TPU/CNT composites were evaluated and also compared with those of carbon black (CB)‐filled TPU composites prepared under the same processing conditions. For both polymer systems, the insulator–conductor transition was very sharp and the electrical percolation threshold at room temperature was at CNT and CB contents of about 1.0 and 1.7 wt%, respectively. The EMI SE over the X‐band frequency range (8–12 GHz) for TPU/CNT and TPU/CB composites was investigated as a function of filler content. EMI SE and electrical conductivity increased with increasing amount of conductive filler, due to the formation of conductive pathways in the TPU matrix. TPU/CNT composites displayed higher electrical conductivity and EMI SE than TPU/CB composites with similar conductive filler content. EMI SE values found for TPU/CNT and TPU/CB composites containing 10 and 15 wt% conductive fillers, respectively, were in the range ?22 to ?20 dB, indicating that these composites are promising candidates for shielding applications. © 2013 Society of Chemical Industry     

Effect of Flow Distribution to the Channels on the Thermal Performance of the Multipass Plate Heat Exchangers

Over last two decades, plate heat exchangers (PHEs) have presented themselves as a viable alternative to the conventional shell and tube heat exchangers in the process and power industries. The thermal theory available for plate heat exchangers in the literature largely works on the assumption of equal flow in each channel. However, it is well known that the distribution of fluid from port to channel in PHE is far from being uniform. The present study brings about this port to channel flow distribution effect on the thermal behavior of multipass plate heat exchangers. The variation of the heat transfer coefficient due to flow variation from channel to channel has also been taken into consideration. Heat exchangers with both equal and unequal passes of the fluids have been studied. The results indicate that the flow maldistribution severely affects the performance of plate heat exchangers, and multipassing can act as an important tool to reduce the deterioration in performance due to maldistribution. The results show that with a low number of passes, the increase of velocity of fluid may be counterproductive in terms of heat transfer enhancement. Also, adding plates in order to increase the heat transfer surface may not be effective due to an increase in flow maldistribution. The correlations for 1-1, 1-2, 2-2, and 2-3 pass plate heat exchangers with the maldistribution index as a parameter are also presented.     

Self-propagating high temperature synthesis (SHS) of titanium carbide

Abstracts are not published in this journal This revised version was published online in November 2006 with corrections to the Cover Date.     

Effect of zinc on the electrocrystallization of cobalt

The effects of zinc on the current efficiency, power consumption, deposit quality and contamination of cathode deposit during electrocrystallization of cobalt were studied. The presence of zinc affected current efficiency at all temperatures and the effect was intensified at lower temperature. Increase in power consumption was significant at lower temperature. The quantity of zinc in the electrodeposited cobalt invariably increased with increase in zinc concentration in the electrolyte, however, the zinc content of the deposit was significantly low at higher temperature. The tolerance limit of zinc in the electrolyte with respect to deposit quality was also greater at higher temperature. Increase in current density decreased the current efficiency, increased the power consumption and lowered the cathode contamination.     

Application of a stochastic modelling framework to characterize the influence of different oxide scales on the solid particle erosion behaviour of boiler grade steel

An earlier developed stochastic model has been applied to describe the relative rate of material loss from the steel surface subjected to simultaneous action of high temperature oxidation involving multiple oxides and mechanical erosion. Different oxide scale growths, namely, nickel, iron and chromium have been treated deterministically and erosion is described using a literature based probabilistic framework. Oxidation is described with a power law (parabolic) approach to quantify the rate of growth of all the three oxide scales. In consonance with the published model, erosion is treated using a probabilistic methodology as spatially random phenomena on the oxide surface. The concept of ‘erosion footprint’ has been incorporated in the present model to characterize the erosion-induced damage on the steel surface. The model has been applied to predict the relative material loss as a function of time resulted from erosion–oxidation interaction pertaining to nickel, iron and chromium oxides in dimensionless form. This investigation is expected to provide a quantitative understanding of relative material loss due to solid particle erosion for oxide scales, (composed of multiple oxides) formed on the steel components of coal-fired boilers.