Ion Beam Analysis and Normal-State Conduction Mechanisms for (Bi, Pb)-2223 and (Tl, Pb)/Sr-1212 Superconducting Phases Substituted by Ruthenium

Superconducting samples of type Bi_1.8Pb_0.4Sr₂Ca_2.1Cu_3−x Ru _x O_10+δ , (Bi, Pb)-2223, with 0.0≤x≤0.4 and type Tl_0.5Pb_0.5Sr_1.6Ba_0.4CaCu_2−x Ru _x O_7−δ , (Tl, Pb)/Sr-1212, with 0.0≤x≤0.525 were synthesized using the standard solid-state reaction technique. The lattice parameters and the surface morphology for these samples were determined using X-ray powder diffraction (XRD) and scanning electron microscope (SEM) measurements, respectively. All element-contents of the samples prepared were estimated from the electron dispersive X-ray (EDX) technique, and their results were compared with those obtained from particle-induced X-ray emission (PIXE). In addition, the oxygen-content was determined using elastic Rutherford backscattering spectroscopy (RBS) technique at 3 MeV proton beam. The superconducting transition temperature T _c and the hole carrier concentration P were determined from the electrical resistivity measurement. The data of both T _c and P for Bi_1.8Pb_0.4Sr₂Ca_2.1Cu_3−x Ru _x O_10+δ and Tl_0.5Pb_0.5Sr_1.6Ba_0.4CaCu_2−x Ru _x O_7−δ phases increased up to x=0.05 and 0.075, respectively and then they decreased as x increased. The superconductivity was completely destroyed around x=0.4 and 0.525 for (Bi, Pb)-2223 and (Tl, Pb)/Sr-1212 phases, respectively. The normal-state electrical resistivity data were analyzed using the two and three dimensional variable range hopping (2D-VRH and 3D-VRH) and the Coulomb gab (CG).     

Coating of a lignocellulosic aggregate with pectin/polyethylenimin mixtures: Effects on flax shive and cement-shive composite properties

Lignocellulosic lightweight concretes are a potential contributor to sustainable development. However, lignocellulosic aggregates are not always fully compatible with cement matrices leading to setting delays, significant dimensional variations and low mechanical strengths. An aggregate treatment, reducing water absorption and water-soluble molecule release, can avoid or reduce these drawbacks. In this study a coating treatment, using a pectin/polyethylenimin (PP) mixture, was applied to flax shives, which is a lignocellulosic by-product. Before shive coating, a dilution with distilled water or a micro-wave heating were conducted to decrease PP mixture viscosity.The PP treatment involved a decrease in shive water absorption. Compared to standard shive concrete, treated shive concrete exhibited a decrease in setting delay with an increase in cement hydration enthalpy, an increase in mechanical strengths and a significant reduction in dimensional variations. Although a slight increase in thermal conductivity and bulk density was measured, the cement-shive composite obtained still belongs to the insulating concrete category.     

Transmission pricing and recovery of investment costs in the deregulated power system based on optimal circuit prices

Transmission pricing has become a major issue in the discussions about the deregulated electricity markets.Conse-quently,open access to the transmission system is one of the basic topics to allow compe...     

In vitro mesenchymal stem cell responses on laser-welded NiTi alloy

The biocompatibility of NiTi after laser welding was studied by examining the in vitro (mesenchymal stem cell) MSC responses at different sets of time varying from early (4 to 12 h) to intermediate phases (1 and 4 days) of cell culture. The effects of physical (surface roughness and topography) and chemical (surface Ti/Ni ratio) changes as a consequence of laser welding in different regions (WZ, HAZ, and BM) on the cell morphology and cell coverage were studied. The results in this research indicated that the morphology of MSCs was affected primarily by the topographical factors in the WZ: the well-defined and directional dendritic pattern and the presence of deeper grooves. The morphology of MSCs was not significantly modulated by surface roughness. Despite the possible initial Ni release in the medium during the cell culture, no toxic effect seemed to cause to MSCs as evidenced by the success of adhesion and spreading of the cells onto different regions in the laser weldment. The good biocompatibility of the NiTi laser weldment has been firstly reported in this study.     

Charge transport mechanism of graphite‐nanosheet‐loaded rubber nanocomposites

Nitrile butadiene rubber loaded with different concentrations of thin graphite nanosheets have been successfully prepared by using a two‐roll mill. The percolation concentration of the nanocomposites was 0.5 phr. The I–V characteristic curves showed that the nanocomposites exhibited ohmic behaviour at a certain voltage and then non‐linear behaviour. The Richardson–Schottky and Poole–Frenkel models were used to investigate the reason for the space charge. The experimental data fit the Schottky model well. The conductivity as a function of temperature was also studied and the data were fitted by using the Mott relation. The Mott relation showed that as the concentration of graphite nanosheets in the rubber composite increases, the hopping distance between the graphite nanosheet layers decreases, which enhances the conductivity of the nanocomposite at low concentrations. Copyright © 2011 Society of Chemical Industry     

Control of a robotic orthosis for gait rehabilitation

Robot assisted gait training may help in producing rapid improvements in functional gait parameters. This paper presents new experimental results with an intrinsically compliant robotic gait training orthosis. The newly developed robotic orthosis has 6 degrees of freedom (DOFs). A trajectory tracking controller based on the boundary layer augmented sliding control (BASMC) law was implemented to guide the subject’s limbs on physiological gait trajectories. The compliance of the robotic orthosis sagittal plane hip and knee joints was also controlled, independently of the trajectory tracking control. The robotic orthosis and the control scheme were evaluated on three neurologically intact subjects walking on a treadmill. A maximum trajectory tracking error of 10° was recorded at the hip and knee sagittal plane joints. The results showed that subjects can walk in the robotic orthosis with comfort and the BASMC law was able to guide the subject’s limbs on reference physiological trajectories.     

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.