Magnetocaloric Effect in Sr0.4Ba1.6−x La x FeMoO6

Magnetocaloric effect in half-metallic double perovskite Sr_0.4Ba_1.6?x La _x FeMoO₆ (x = 0, 0.1, 0.2, 0.3) were investigated. It is shown that Sr_0.4Ba_1.6?x La _x FeMoO₆ exhibits the largest magnetic entropy change (ΔS _M ) of 0.086 J/kg K upon 0.2 T magnetic field variation. Furthermore, ΔS _M distribution of the Sr_0.4Ba_1.6?x La _x FeMoO₆ is much more uniform than that of gadolinium. Through these results, polycrystalline samples of Sr_0.4Ba_1.6?x La _x FeMoO₆ have some potential applications for magnetic refrigerants in a wide temperature range, including room temperature.     

Process synthesis and optimization of biorefinery configurations

Recently, there has been a growing interest in the development of cost‐effective technologies for the production of biofuels. A common approach to biofuel research is to invent or improve a biochemical or thermochemical conversion step. Subsequently, other conversion and separation steps are added to form a complete biorefinery flowsheet. Because this approach is structured around a specific conversion step, it may limit the possibilities of configuring optimal and innovative biorefineries. This article proposes a novel and systematic two‐stage approach to the synthesis and optimization of biorefinery configurations, given available feedstocks and desired products. In the synthesis stage, a systems‐based approach is developed to create a methodical way for synthesizing integrated biorefineries. This method is referred to as “forward‐backward” approach. It involves forward synthesis of biomass to possible intermediates and reverse synthesis starting with the desired products and identifying necessary species and pathways leading to them. In the optimization stage, Bellman's principle of optimality is applied to decompose the optimization problem into subproblems in which an optimal policy of available technologies is determined for every conversion step. An optimization formulation is utilized to determine the optimal configuration based on screening and connecting the optimal policies and generating the biorefinery flowsheet. A case study of alcohol‐producing pathways from lignocellulosic biomass is solved to demonstrate the merits of the proposed approach. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

A combined physicochemical and electrocatalytic study of microwave synthesized tungsten mono-carbide nanoparticles on multiwalled carbon nanotubes as a co-catalyst for a proton-exchange membrane fuel cell

Tungsten mono-carbide (WC) nanoparticles supported on multiwalled carbon nanotube (MWCNT) was synthesized by a microwave-assisted solid-state carburization. The prepared samples were used as a co-catalyst to prepare Pt-WC/MWCNT catalyst for a proton-exchange membrane fuel cell. MWCNTs with and without oxidative pretreatments were characterized as the starting precursors. The influence of the carbide formation conditions on the physicochemical characteristics of the final product were extensively investigated. According to the results, surface pretreatment of the MWCNTs can improve the yield of carbide formation. Furthermore, carburization process can improve the catalyst utilization due to increasing the number of surface defects of the MWCNT supporting materials which can be interpreted as structural effect of the carburization process. It is believed that the superior performance of electrodes modified with tungsten carbide is mostly due to the structural effect of the carburization process and synergistic effect between the electrocatalytic activity of WC and Pt.     

Impacts of user-selfishness on cooperative content caching in social wireless networks

Cooperative caching can be an effective mechanism for reducing electronic content provisioning cost in Social Wireless Networks (SWNETs). These networks are formed by a collection of mobile data enabled devices physically gathering in settings such as university campus, malls, airport and other public places. In this paper, we first propose an optimal collaborative object caching policy in order to minimize the object provisioning cost in SWNETs with homogenous user requests and a peer-rebate model for promoting collaboration. Then using an analytical model we study the impacts of user selfishness on the provisioning cost and the earned rebate when certain nodes in an SWNET selfishly deviate from the optimal policy. User selfishness is motivated in order to either increase individually earned rebate or to reduce content provisioning cost. The analytical model is validated by experimental results from simulated SWNETs using the network simulator ns2.     

Simulation of Magnetocaloric Properties of Antiperovskite Structural Ga1−X Al X CMn3

In this work, low-enhanced magnetic field magnetocaloric effect for Ga_1?X Al _X CMn₃ (X = 0, 0.05, 0.07, 0.12, and 0.15) system near a second-order phase transition from a ferromagnetic to a paramagnetic state is investigated theoretically. It is found that magnetic entropy change distribution is much more uniform than that of gadolinium, which is desirable for an Ericson-cycle magnetic refrigerator. Moreover, the results show that the magnetocaloric effect in this system is tunable by Al doping, which is beneficial for manipulating magnetocaloric refrigeration that occurs in various temperature ranges including room temperature. This makes the Ga_1?X Al _X CMn₃ samples potential candidates for practical applications.     

Optimisation and modelling green bean's ultrasound blanching

Using of ultrasound in food processing is a novel and interesting technique, which is often complementary to classical methods. This study reports on the ultrasound blanching (USB) of green bean. Response surface methodology (RSM) was used to study the effect of process variables on the USB. Three independent variables including temperature (50–90 °C), time (45–225 s) and duty cycle (0.2–0.8 s) were examined. The optimal USB conditions were obtained with a temperature of 90 °C, USB time of 58.27 s and duty cycle of 0.79 s. At these conditions, the residual peroxidase activity (RPA) determined as 9.64% and the vitamin C loss as 8.92%. The experimental values under optimal condition were in good consistent with the predicted values. According to the results, the USB process is more efficient process and as well as less damage to the product compared to the conventional blanching method.     

Influence of Lattice Defects on the Grain Growth Kinetics of Nanocrystalline Fluorite

The growth process of nanocrystalline fluorite was studied by in situ synchrotron radiation X-ray diffraction. The two studied samples had comparable crystalline domain size, but quite different content of lattice defects as a result of the different preparation procedures: ball milling of coarse CaF₂ powder or coprecipitation of CaCl₂ and NH₄F. It is shown that the high dislocation density in the ball-milled fluorite is responsible for a recrystallization process above 773 K (500 °C), which is not observed in the chemically synthesized fluorite. The linear thermal expansion coefficients of both nanocrystalline powders, as obtained and also from the in situ X-ray diffraction data, show a smaller increase with temperature than suggested by the literature on coarse-grained fluorite.