Performance of IEEE 802.15.4 Clusters with Power Management and Key Exchange

The IEEE 802.15.4 specification is a recent low data rate wireless personal area network standard.While basic security services are provided for,there is a lack of more advanced techniques which are indispensable in modern personal area network applications.In addition,performance implications of those services are not known.In this paper,we describe a secure data exchange protocol based on the ZigBee specification and built on top of IEEE 802.15.4 link layer.This protocol includes a key exchange mechanism.We assume that all nodes are applying power management technique based on the constant event sensing reliability required by the coordinator.Power management generates random sleep times by every node which in average fairly distributes the sensing load among the nodes.Key exchange is initiated by a cluster coordinator after some given number of sensing packets have been received by the coordinator.We develop and integrate simulation model of the key exchange and power management technique into the cluster's reliable sensing function.We evaluate the impact of security function and its periodicity on cluster performance.     

Promotional roles of second metals in catalyzing methane decomposition over the Ni-based catalysts for hydrogen production: A critical review

The thermocatalytic decomposition (TCD) of methane is considered as a milestone towards the production of valuable CO_x-free hydrogen and carbon nanomaterials without the use of steam or O₂. Previous reviews have been aimed at methane decomposition over the different catalysts, such as nickel-based catalysts, non-nickel-based catalysts, metal oxide-supported catalysts, and carbon-supported catalysts. The Ni-based catalysts are suitably applied for methane TCD process due to their high activity and low cost. However, the loss of activity and/or stability with reaction time is one of the most notable challenges in the use of Ni-based catalysts, and a number of studies on the roles of various factors in overcoming such a problem can be found in the literature. Recently, the use of the second metal as a promoter to control catalyst deactivation has attracted much attention. The present review focuses on classification of the different promoters based on the periodic table of elements, such as alkali metals, alkaline earth, transition metals, noble metals, and rare earth metals, and makes a detailed discussion on promotional roles in influencing their physicochemical properties and catalytic performance of the Ni-based catalysts. The generalized structure-performance relationship of the metals-doped catalysts may give an appreciated reference to the design of catalysts with highly pure hydrogen production and carbon nanomaterials. In addition, this review also covers the works on effects of the promoters on nature and morphology of the formed carbon nanomaterials. The use of transition metals (Fe, Co or Cu), noble metal (Pd or Pt), and rare earth metal (La) with a suitable loading as a promoter influenced performance and lifespan of the catalyst and the interaction of Ni particles with the support. Among these promoters, Cu, Pd, La, and Cu–Pd as a dopant have demonstrated superior performance, which was attributed to the capability of these elements in prohibiting carbon accumulation on the active Ni components.     

Thermocatalytic decomposition of methane over mesoporous Ni/xMgO·Al2O3 nanocatalysts

This paper describes a facile method to produce mesoporous nanostructure Ni/Al₂O₃, Ni/MgO, and Ni/xMgO.Al₂O₃ (x: MgO/Al₂O₃ molar ratio) catalysts prepared by “one-pot” evaporation-induced self-assembly (EISA) method with some modifications for investigating in the thermocatalytic decomposition of methane. Detailed characterizations of the material were performed with X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) and N₂ adsorption/desorption, hydrogen temperature-programmed reduction (H₂-TPR), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and temperature-programmed oxidation (TPO). The characterizations demonstrated that the synthesized catalysts with various MgO/Al₂O₃ molar ratios possessed mesoporous structure with the high BET area in the range of 216.79 to 31.74 m² g^?1. The effect of different surfactants and calcination temperatures on the characterizations and catalytic activity of the catalysts were also examined in details. The experimental results showed that the catalysts exhibited high catalytic potential in this process and the 55 wt.% Ni/2 MgO·Al₂O₃ catalyst calcined at 600^οC possessed an acceptable methane conversion (～60%) under the harsh reaction conditions (GHSV = 48000 (mL h^?1 g_cat^?1)).     

A highly active and stable chromium free iron based catalyst for H2 purification in high temperature water gas shift reaction

In this work mesoporous nanocrystalline chromium free Fe–Al–Ni catalysts with various Fe/Al and Fe/Ni ratios were prepared by coprecipitation method for high temperature water gas shift reaction. The prepared catalysts were characterized using X-ray diffraction (XRD), N₂ adsorption (BET), temperature-programmed reduction (TPR) and transmission electron microscopy (TEM) techniques. The catalytic results revealed that the catalyst with Fe/Al = 10 and Fe/Ni = 5 weight ratios exhibited the highest catalytic activity among the prepared catalysts and the commercial chromium containing one. This catalyst possessed a high surface area of 177.4 m² g⁻¹ with an average pore size of 4.3 nm with a high stability during 20 h time on stream. Furthermore, the effect of calcination temperature, GHSV and steam/gas ratio on the structural properties and catalytic performance of the catalyst with the highest activity was investigated.     

Preparation and evaluation of Ni/γ-Al2O3 catalysts promoted by alkaline earth metals in glycerol reforming with carbon dioxide

Glycerol is the main by-product in the biodiesel process and can be considered as a promising and renewable source for hydrogen generation through the reforming process. In this work, catalysts with 15 wt% Ni supported on 3 wt% M ? Al₂O₃ (M = MgO, CaO, SrO, and BaO) were prepared and employed in the glycerol dry reforming (GDR) reaction to produce hydrogen and carbon monoxide. The textural characteristics of the fresh and spent catalysts were determined using the ICP, BET, TPR, TPO, and SEM analyses. Based on the obtained results, the catalyst promoted by SrO had the highest catalytic activity. The results indicated that adding various alkaline-earth oxides into the catalyst support decreased the Ni crystalline size from 17.2 nm to 7.4–10.9 nm. Moreover, all promoted catalysts showed better catalytic performance and the promoted sample with 3 wt% SrO possessed higher stability than unpromoted catalyst during 20 h on stream.     

Effect of process parameters on the synthesis of nanocrystalline magnesium oxide with high surface area and plate-like shape by surfactant assisted precipitation method

A surfactant assisted precipitation method was employed for the preparation of nanocrystalline magnesium oxide with high specific surface area and plate-like shape. Ammonium hydroxide and polyvinyl alcohol (PVA) were used as precipitant and polymeric surfactant, respectively. The effects of several process parameters such as refluxing time, refluxing temperature and magnesium oxide to PVA monomer unit mole ratio (MgO/PVA) were investigated on the structural properties of the powders. The obtained results showed that the increase in refluxing time and temperature increased the specific surface area and decreased the crystallite size. The results revealed that the polymeric surfactant (PVA) has a significant effect on the synthesis of MgO nanocrystals and led to obtain a powder with higher surface area and plate-like shape.     

Coprecipitated Ni‐Co Bimetallic Nanocatalysts for Methane Dry Reforming

Methane dry reforming was studied over nanostructure bimetallic Ni‐Co‐MgO catalysts. The catalysts were prepared by coprecipitation with different Ni‐Co contents and characterized by XRD, BET, N₂ adsorption/desorption, temperature‐programmed reduction (TPR), SEM, and temperature‐programmed oxidation (TPO) techniques. XRD results let conclude that all samples contained MgO crystallite phases. With a higher Ni content the intensity of the diffraction peaks became stronger, indicating growth of the crystallite size of the prepared solid solutions. BET analysis demonstrated that a higher Ni‐Co content decreased the surface area. The optimal catalyst could be determined which had the highest activity and a good stability in dry reforming reaction.     

Kinetic modeling of mass transfer during deep fat frying of shrimp nugget prepared without a pre-frying step

The objective of this study was to evaluate the effect of different batter formulation on mass transfer during deep fat frying of shrimp nuggets prepared without a pre-frying step. The effects of soy and corn flour (5, 10%) addition to the batter formulation, frying temperature and time on mass transfer were determined. The results showed an interaction effect of these processing conditions on mass transfer. The most reduction in fat absorption was observed when samples were coated with batter contained 10% soy flour and fried at 190 °C. The first order kinetic based on the Fick's law were used to describe moisture transfer data. The effective moisture diffusivity ranged between 2.05 × 10⁻⁸ and 5.71 × 10⁻⁸ m²/s with R² between 0.91 and 0.98, and fat transfer rate constant was between 3.5 × 10⁻³ and 7.8 × 10⁻³ s⁻¹ with R² from 0.82 to 0.99. Activation energy obtained from the Arrhenius plot for the effective moisture diffusivity ranged between 18.42 and 23.84 kJ/mol.     

Coordination of bioenergy supply chains under government incentive policies: a game-theoretic analysis

Clean Technologies and Environmental Policy - Biomass as an abundant renewable energy source can play a vital role in controlling the greenhouse gas emissions. The distributed nature of biomass and...     

Pd doped WO3 films prepared by sol–gel process for hydrogen sensing

The sol gel method was employed to prepare peroxopolytungstic acid (P-PTA). Palladium chloride salt was dissolved in the sol with different Pd:W molar ratios and coated on Al₂O₃ substrates by spin coating method. XRD and XPS techniques were used to analyze the crystal structure and chemical composition of the films before and after heat treatment at 500 °C. We observed that Pd can modify the growth kinetic of tungsten trioxide nanoparticles by reducing the crystallite size and as a result can improve hydrogen sensitivity. Resistance-sensing measurements indicated sensitivity of about 2.5 × 10⁴ at room temperature in hydrogen concentration of 0.1% in air. Considering all sensing parameters, an optimum working temperature of 100 °C was obtained.