Time resolved numerical modeling of oil jet cooling of a medium duty diesel engine piston

In medium to heavy duty diesel engines, ever increasing power densities are threatening piston's structural integrity at high engine loads and speeds. This investigation presents the computational results of the heat transfer between piston and an impinging oil jet, typically used to keep the pistons cool. Appropriate boundary conditions are applied and using numerical modeling, heat transfer coefficient (h) at the underside of the piston is predicted. This predicted value of heat transfer coefficient significantly helps in selecting right oil (essentially right oil grade), oil jet velocity, nozzle diameter (essentially nozzle design) and distance of the nozzle from the underside of the piston. It also predicts whether the selected grade of oil will contribute to oil fumes/mist generation. Using numerical simulation (finite element method), transient temperature profiles are evaluated for varying heat flux (simulating varying engine loads) to demonstrate the effect of oil jet cooling. The model, after experimental validation, has been used to understand the transient temperature behavior of the piston and the time taken in achieving steady state. High speed CCD camera is used to investigate the oil jet breakup, localized pool boiling and mist generation due to impinging jet on the piston's underside.     

采用光反馈控制白光LED的降压稳压器

由于大功率、高效率白光（以及其它颜色）LED的实现,采用LED的照明更受关注（参考文献1）。由于LED是一种电流控制器件,典型控制电路是调节通过LED的电流来保持一致的亮度。为了最好地利用电能,用户经常将开关转换电路用于LED,根据输入直流电压的不同,可以是降压（Buck）或升压转换器。图1是典型的降压和升压转换器白光LED驱动电路的结构。白光LED增加了串接电阻R,     

Carcass and meat quality of Assaf milk fed lambs: Effect of rearing system and sex

The effect of sex and rearing system on growth and carcass and meat characteristics of milk fed Assaf lambs was studied. Thirty-six lambs, 18 males and 18 females were used. Twelve lambs remained with their mothers throughout the experiment (NR). Within 24–36 h of birth, the rest were housed individually and fed twice a day ad libitum (AAR) or at 70% of ad libitum consumption (RAR) with reconstituted cow’s milk. Sex did not affect animal performance, yet females showed higher carcass and non-carcass fat deposits. NR lambs showed greater BWG than AAR fed lambs, and AAR, higher than the RAR. Differences between naturally and artificially reared lambs in CCW and killing out percentage were not significant. Empty digestive tract and mesenteric fat weights were greater for RAR than NR lambs, with the AAR lambs demonstrating intermediate values; conversely, omental fat was greater in NR lambs. Carcass ether extract content was greater for NR lambs, possibly due to the greater growth. Use of ad libitum cow’s milk substitute in suckling lambs twice a day resulted in less body weight gain but similar killing out percentages compared to naturally raised lambs. A 70% restricted supply increased the days in suckling and reduced carcass fatness and compactness. Except for water loss, which was less in NR than artificially fed lambs, no differences were found in meat characteristics.     

Growth and characterization of laser-deposited Ag-doped YBa2Cu3O7−x thin films on bare sapphire

Microstructural and superconducting properties of YBa₂Cu₃O_7−x thin films grownin situ on bare sapphire by pulsed laser deposition using YBa₂Cu₃O_7−x targets doped with 7 and 10 wt% Ag have been studied. Ag-doped films grown at 730°C on sapphire have shown very significant improvement over the undoped YBa₂Cu₃O_7−x films grown under identical condition. A zero resistance temperature of 90 K and a critical current density of 1·2×10⁶ A/cm² at 77 K have been achieved on bare sapphire for the first time. Improved connectivity among grains and reduced reaction rate between the substrate and the film caused due to Ag in the film are suggested to be responsible for this greatly improved transport properties.     

Photocatalytic degradation of chlorobenzene using solar and artificial UV radiation

In this work photocatalytic degradation of chlorobenzene has been studied using solar and artificial UV radiations. The effect of pH and the presence of different anions on the degradation of chlorobenzene has been studied for both cases. Chlorobenzene has been found to be a strongly adsorbing and hence rapidly degrading species when subjected to photocatalysis. The effect of pH in the range of 3–10 and the presence of different anions at a concentration of 0.1 mol dm^?3 on the adsorption was studied. Both pH and the presence of anions affect adsorption and the degradation but the overall effect is negligible (<5%). Copyright © 2004 Society of Chemical Industry     

Silver doping: A potential means to grow high quality YBa2Cu3O7?x thin films on bare sapphire

High qualityAg-doped YBa₂Cu₃O_7–x (YBCO) thin films have been grown by laser ablation on ¯1012 bare sapphire. This work demonstrates thatAg-doping can be used as very convenient means to realize good quality YBCO films on highly coveted sapphire substrates for microwave applications of highT _c thin films.     

Photocatalytic degradation of nitrobenzene using titanium dioxide and concentrated solar radiation: chemical effects and scaleup

Photocatalytic degradation of nitrobenzene (NB) using titanium dioxide (Degussa P-25) as photocatalyst and concentrated solar radiation has been studied. The effects of various factors, such as the presence of anions common in the industrial wastewater, the initial pH and the addition of FeSO(4), were investigated. The intermediates detected were o, p,m-nitrophenols and dihhydroxy derivatives indicating that degradation proceeds via z.rad;OH radicals. Degradation of NB was studied in three reactors of different diameters to ascertain the effect of photon penetration depth on the degradation.     

Understanding nitrate reactions with zerovalent iron using tafel analysis and electrochemical impedance spectroscopy

This study investigated the reaction mechanisms of nitrate (NO3-) with zerovalent iron (ZVI) media under conditions relevantto groundwatertreatment using permeable reactive barriers (PRB). Reaction rates of NO3- with freely corroding and with cathodically or anodically polarized iron wires were measured in batch reactors. Tafel analysis and electrochemical impedance spectroscopy (EIS) were used to investigate the reactions occurring on the iron surfaces. Reduction of NO3- by corroding iron resulted in near stoichiometric production of NO2-, which did not measurably react in the absence of added Fe(II). Increasing NO3- concentrations resulted in increasing corrosion currents. However, EIS and Tafel analyses indicated that there was little direct reduction of NO3- at the ZVI surface, despite the presence of water reduction. This behavior can be attributed to formation of a microporous oxide on the iron surfaces that blocked reduction of NO3- and NO2- but did not block water reduction. This finding is consistent with previous observations that NO3- impedes reduction of organic compounds by ZVI. Nitrite concentrations greater than 4 mM resulted in anodic passivation of the iron, but passivation was not observed with NO3- concentrations as high as 96 mM. This indicates that the passivating oxide preventing NO3- reduction was permeable toward cation migration. Since reaction with Fe(0) can be excluded asthe mechanism for NO3- and NO2- reduction, reaction with Fe(II)-containing oxides coating the iron surface is the most likely reaction mechanism. This suggests that short-term batch tests requiring little turnover of reactive sites on the iron surface may overestimate long-term rates of NO3- removal because the effects of passivation are not apparent in batch tests conducted with high initial Fe(II) to NO3- ratios.     

Investigating the fault tolerance of neural networks

Particular levels of partial fault tolerance (PFT) in feedforward artificial neural networks of a given size can be obtained by redundancy (replicating a smaller normally trained network), by design (training specifically to increase PFT), and by a combination of the two (replicating a smaller PFT-trained network). This letter investigates the method of achieving the highest PFT per network size (total number of units and connections) for classification problems. It concludes that for non-toy problems, there exists a normally trained network of optimal size that produces the smallest fully fault-tolerant network when replicated. In addition, it shows that for particular network sizes, the best level of PFT is achieved by training a network of that size for fault tolerance. The results and discussion demonstrate how the outcome depends on the levels of saturation of the network nodes when classifying data points. With simple training tasks, where the complexity of the problem and the size of the network are well within the ability of the training method, the hidden-layer nodes operate close to their saturation points, and classification is clean. Under such circumstances, replicating the smallest normally trained correct network yields the highest PFT for any given network size. For hard training tasks (difficult classification problems or network sizes close to the minimum), normal training obtains networks that do not operate close to their saturation points, and outputs are not as close to their targets. In this case, training a larger network for fault tolerance yields better PFT than replicating a smaller, normally trained network. However, since fault-tolerant training on its own produces networks that operate closer to their linear areas than normal training, replicating normally trained networks ultimately leads to better PFT than replicating fault-tolerant networks of the same initial size.     

Final Shape of Precision Molded Optics: Part I—Computational Approach,Material Definitions and the Effect of Lens Shape

Coupled thermomechanical finite element models were developed in ABAQUS to simulate the precision glass lens molding process, including the stages of heating, soaking, pressing, cooling and release. The aim of the models was the prediction of the deviation of the final lens profile from that of the mold, which was accomplished to within one-half of a micron. The molding glass was modeled as viscoelastic in shear and volume using an n-term, prony series; temperature dependence of the material behavior was taken into account using the assumption of thermal rheological simplicity (TRS); structural relaxation as described by the Tool-Narayanaswamy-Moynihan (TNM)-model was used to account for temperature history dependent expansion and contraction, and the molds were modeled as elastic taking into account both mechanical and thermal strain. In Part I of this two-part series, the computational approach and material definitions are presented. Furthermore, in preparation for the sensitivity analysis presented in Part II, this study includes both a bi-convex lens and a steep meniscus lens, which reveals a fundamental difference in how the deviation evolves for these different lens geometries. This study, therefore, motivates the inclusion of both lens types in the validations and sensitivity analysis of Part II. It is shown that the deviation of the steep meniscus lens is more sensitive to the mechanical behavior of the glass, due to the strain response of the newly formed lens that occurs when the pressing force is removed.