Brownian Motion Effects on Natural Convection of Alumina–Water Nanofluid in 2‐D Enclosure

This article reports a numerical study of natural convection heat transfer in a differentially heated enclosure filled with a Al₂O₃–water nanofluid. Fluent v6.3 is used to simulate nanofluid flow. Simulations have been carried out for the pertinent parameters in the following ranges: the Rayleigh number, Ra = 10⁶, 10⁷, and the volumetric fraction of alumina nanoparticles, ? = 0 ? 4%. The effect of Brownian motion on the heat transfer is considered and examined. The numerical results show a decrease in heat transfer with an increase in particle volume fraction. Similar to experimental results, the Nusselt number increases with the Rayleigh number in the numerical results. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.21121     

Performance of two immobilized lipases for interesterification between canola oil and fully-hydrogenated canola oil under supercritical carbon dioxide

The performance and stability of Lipozyme RM IM and TL IM for the interesterification between canola oil and fully-hydrogenated canola oil (FHCO) in the presence of SCCO₂ were studied using a high pressure batch stirred reactor at 65 °C/17.5 MPa. The influence of exposure time (4, 8, and 12 h) in SCCO₂ and pressurization/depressurization cycles of up to 12 times on the enzyme's resultant activity were studied. There was no significant difference (p > 0.05) in the performance of the two enzymes over reaction time, reaching a constant degree of interesterification of about 23% after 2 h. Although FE-SEM images illustrated some morphological changes on the surface of the enzymes after 4 cycles of 7 h each, similar degrees of interesterification were achieved after each cycle. However, the amount of reaction intermediates decreased by 50–60% in the product obtained by using SCCO₂-treated enzymes after 12 pressurization/depressurization cycles compared to untreated enzymes, while there were no significant changes in the conformational and morphological structure of the treated enzymes based on FTIR and FE-SEM analysis. Findings enhance our understanding of enzymatic conversions of lipids under high pressure CO₂, targeting production of base-stock for zero-trans margarines.     

Stochastic analysis of natural gas consumption in residential and commercial buildings

Consumer consumption characteristic is an important asset for safe design and management of gas distribution networks. Different characteristics of natural gas consumption in residential and commercial buildings are studied from statistical and stochastic points of view. The technique is applied during 2008 and 2009 to a densely populated district in Tehran, Iran, with relatively large number of buildings (67,655 residential and 13,286 commercial buildings). There are different trends in the histograms of gas consumption, but there is a general trend in diagrams of probability index (the probability of gas consumption exceeding a specific value) and their regressions. The most frequent amount of gas consumption for all 45-day periods is 100 m³ as compared with the annual average of 320 m³ for residential buildings. The latter reduces to 80 m³ for the averaged periodic consumption per unit in a building. Also it seems that the most frequent amount of periodic gas consumption of residential buildings is about 31% of their respective annual average during the warm months of the year, and 150% during the cold months. Periodic consumptions less than 1500 m³ and average consumptions less than 1400 m³ are more probable in residential buildings, which are larger than that of commercial ones, but this trend reverses at higher consumption values. If actual consumption is normalized by the average consumption, the number of units in the building or the floor area, the probability index of commercial buildings is generally higher than residential ones. The binomial distribution is analytically used to predict the probability of average gas consumption exceeding 320 and 2000 m³ in two example cases of 500 and 1000 buildings.     

Concentration‐dependent minority carrier lifetime in an In0.53Ga0.47As interdigitated lateral PIN photodiode model based on spin‐on chemical fabrication methodology

The fitted parameters for the analytic function used to specify the doping dependence of minority carrier lifetimes for In_0.53Ga_0.47As (InGaAs) is described in this paper. This model together with other carrier models was used to develop an interdigitated lateral PIN photodiode utilizing InGaAs as the absorbing layer. We propose the usage of spin‐on chemicals such as spin‐on dopants and spin‐on glass to form the p+ wells, n+ wells and the surface passivation layer of the device hence providing a cheap and easy solution versus the conventional epitaxial growth methodology. The modeled device achieved dark currents of 0.21 nA and capacitance of 2.87 nF at an operating voltage of 5 V. Optical illumination at a wavelength of 1550 nm and power of 10 W/cm² enabled the device to achieve responsivity of 0.56 A/W and external quantum efficiency of 44%. The −3 dB frequency response of the device was at 8.93 GHz and signal‐to‐noise ratio is 36 dB. The developed device shows close correlation with experimentally developed devices developed using other fabrication methodologies. The results of this work would be useful in the thorough development of InGaAs‐based devices based on spin‐on chemical fabrication methodology using commercial device simulation packages. Copyright © 2010 John Wiley & Sons, Ltd.     

Use of needle track detection to quantify the displacement of stranded seeds following prostate brachytherapy

We aim to compute the movement of permanent stranded implant brachytherapy radioactive sources (seeds) in the prostate from the planned seed distribution to the intraoperative fluoroscopic distribution, and then to the postimplant computed tomography (CT) distribution. We present a novel approach to matching the seeds in these distributions to the plan by grouping the seeds into needle tracks. First, we identify the implantation axis using a sample consensus algorithm. Then, we use a network flow algorithm to group seeds into their needle tracks. Finally, we match the needles from the three stages using both their transverse plane location and the number of seeds per needle. We validated our approach on eight clinical prostate brachytherapy cases, having a total of 871 brachytherapy seeds distributed in 193 needles. For the intraoperative and postimplant data, 99.31% and 99.41% of the seeds were correctly assigned, respectively. For both the preplan to fluoroscopic and fluoroscopic to CT registrations, 100% of the needles were correctly matched. We show that there is an average intraoperative seed displacement of 4.94±2.42 mm and a further 2.97±1.81 mm of postimplant movement. This information reveals several directional trends and can be used for quality control, treatment planning, and intraoperative dosimetry that fuses ultrasound and fluoroscopy.     

A game theoretic approach to video streaming over peer-to-peer networks

We consider the problem of foresighted multimedia resource reciprocation in peer-to-peer (P2P) networks, which consist of rational peers aiming at maximizing their individual utilities. We introduce an artificial currency (credit) to take into account the characteristics of different parts of the video signal. The resource reciprocation with the proposed credit metric can be formulated as a stochastic game, in which the peers determine their optimal strategies using Markov Decision Process (MDP) framework. The introduced framework can be applied to the general video coding, and in particular, is suitable for the scalable video where various parts of the encoded bit stream have significantly different importance for the video quality.     

A simplified two-phase macroscopic model for reinforced soils

This paper presents the formulation of a macroscopic model for reinforced soil structures in which the interface is taken into consideration as a rigid-plastic contact. The model is formulated in the framework of a so-called multiphase model recently introduced for reinforced soil masses. The proposed simplified two-phase model can be considered as an optimal solution between extremely simplified perfect bonding model on one hand, and using a third phase for the interface on the other hand, which results in a more complicated and time-consuming model. The introduced platform is implemented in a numerical code. The proposed model is evaluated by simulating (a) the failure of laboratorial plane strain compression tests; (b) the behavior of a 1-g reinforced soil retaining wall model under external loading, and (c) the deformation of a reinforced soil structure under its own weight, which has been analyzed by another homogenization approach including elastoplastic interface model. The results indicate that the deformation of reinforced soil structures can be satisfactorily predicted by the proposed model.     

Effect of path planning on the laser powder deposition process: thermal and structural evaluation

In this study, ANSYS finite element software is used to simulate the temperature and stress field in the laser powder deposition process. The model is used to determine the effect of the deposition pattern on the final stress distribution. Four deposition patterns are defined to cover the same area: long bead, short bead, spiral in, and spiral out. The results show that the deposition pattern significantly affects the temperature history of the process, and consequently, the stress distribution. Among the four deposition patterns, the spiral-in pattern shows the highest and the short-bead pattern shows the lowest maximum residual stress. The modeling results are verified with experiments.     

A method for reserve clearing in disaggregated model considering lost opportunity cost

In this paper, a new formulation for clearing reserve market in a deregulated environment with separated energy and reserve market is introduced. In the proposed method, reserve market is cleared such that the costs associated with capacity reservation, producing energy in real-time, opportunity cost of those units which are accepted in the energy market and backed down from the accepted values to participate in the reserve market are minimized. This optimization problem is formulated and solved using linear programming method. Finally, the proposed method is applied to a six units test system to examine the applicability and effectiveness of the proposed method.