Structural and Superconductivity Properties of BaFe<Subscript>2−<Emphasis Type="Italic">x</Emphasis></Subscript>Pt<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>As<Subscript>2</Subscript>

Extraordinary magnetic behaviors, resistivity properties, and lattice parameters of the main sample BaFe₂As₂ and BaFe_2?x Pt _x As₂ in the variation of x from 0 to 0.4 with the step of 0.1 were investigated. The bulk materials have been prepared by the solid-state reaction method and sealed into a quartz tube. The crystal structure of all samples exhibited the ThCr₂Si₂-type crystal structure which is in harmony with earlier studies in the literature. The superconducting states with magnetization measurements have been detailed in the wide temperature range 5–170 K, up to a field of 20 Oe. Increasing Pt and decreasing Fe elements in the BaFe_2?x Pt _x As₂ compound deteriorated superconductivity. Using magnetization measurement data, we present the variation of superconducting critical temperature (T _c) correlating with a Pt dopant rate from x = 0 to x = 0.4. The dopant rate of x = 0.3 exhibited the limit rate for maximum T _c; deterioration of superconductivity was revealed with a dopant rate of more than x = 0.3. This should be explained by varying T _c related to a lattice shrinking and pressure effect (geometric factor).     

Some Properties of Composite Panels Made from Wood Flour and Recycled Polyethylene

This study investigated the effect of board type (unmodified vs. MAPE modified) on the surface quality and thickness swelling-water absorption properties of recycled high density polyethylene (HDPE) based wood plastic composites. Additionally, two commercially available coatings (cellulosic coating and polyurethane lacquer coating) were also applied to composite surfaces and their adhesion strength, abrasion and scratch resistance, and gloss values were determined. This study showed that modification of the composites with MAPE coupling agent increased the surface smoothness and reduced the water absorption and thickness swelling of the panels. Abrasion resistance of the composites was also improved through MAPE modification. Regardless of board type, higher scratch resistance and gloss values were observed for polyurethane lacquer coated samples compared to those of cellulosic varnish coated ones. Improvement of adhesion strength was also seen on SEM micrographs.     

Secure data aggregation in wireless sensor networks: A comprehensive overview

Wireless sensor networks often consists of a large number of low-cost sensor nodes that have strictly limited sensing, computation, and communication capabilities. Due to resource restricted sensor nodes, it is important to minimize the amount of data transmission so that the average sensor lifetime and the overall bandwidth utilization are improved. Data aggregation is the process of summarizing and combining sensor data in order to reduce the amount of data transmission in the network. As wireless sensor networks are usually deployed in remote and hostile environments to transmit sensitive information, sensor nodes are prone to node compromise attacks and security issues such as data confidentiality and integrity are extremely important. Hence, wireless sensor network protocols, e.g., data aggregation protocol, must be designed with security in mind. This paper investigates the relationship between security and data aggregation process in wireless sensor networks. A taxonomy of secure data aggregation protocols is given by surveying the current “state-of-the-art” work in this area. In addition, based on the existing research, the open research areas and future research directions in secure data aggregation concept are provided.     

Plasma sprayed cast iron coatings containing solid lubricant graphite and h-BN structure

Water-atomized cast iron powder of Fe-2.17 at.%C-9.93at.%Si-3.75at.%Al were deposited onto an aluminum alloy substrate by atmospheric direct current plasma spraying to improve its tribological properties. Preannealing of the cast iron powder allows the precipitation of considerable amounts of graphite structure in the powder. However, significant reduction in graphitized carbon in cast iron coatings is inevitable after plasma spraying in air atmosphere due to the in-flight burning and dissolution into molten iron droplets. Hexagonal boron nitride (h-BN) powders, which have excellent lubricating properties like graphite, were incorporated into the cast iron powder as a solid lubricant by the sintering process (1300°C) to obtain protective coatings with a low friction coefficient. The performance of each coating was evaluated using a ring-on-disk-type wear tester under a paraffin-based oil condition in an air atmosphere. A conventional cast iron liner, which had a flaky graphite embedded in the pearlitic matrix, was also tested under similar conditions for comparison. Sections of worn surfaces and debris were characterized, and the wear behavior of plasma-sprayed coatings was discussed. The original version of this paper was published in the CD ROM Thermal Spray Connects: Explore Its Surfacing Potential, International Thermal Spray Conference, sponsored by DVS, ASM International, and HW International Institute of Welding, Basel, Switzerland, May 2–4, 2005, DVS-Verlag GmbH, Düsseldorf, Germany.     

In-process exothermic reaction in high-velocity oxyfuel and plasma spraying with SiO<Subscript>2</Subscript>/Ni/Al-Si-Mg composite powder

Reactive thermal spraying, in which thermodynamically stable compounds are formed by expected inprocess reactions, has attracted considerable attention as a result of the wide availability of in situ composite coatings. Such in-process reactions occur differently in high-velocity oxyfuel (HVOF) and plasma spraying because of differences in the flame temperature and speed. In the current study, a composite powder of SiO₂/Ni/Al-Si-Mg was deposited onto an aluminum substrate to fabricate in situ composite coatings by both spraying methods. The coating hardness sprayed with Al-Si-Mg core powder increases with silicon and magnesium content, whereas the coatings by HVOF spraying show higher hardness than those by plasma spraying. In the present reactive spraying, the exothermic reaction of SiO₂ with molten Al-Si-Mg alloy leads to composite materials of MgAl₂O₄, Mg₂Si, and Al-Si matrix. Moreover, a rapid formation of aluminide (NiAl₃), which is introduced by an exothermic reaction of plated nickel with Al-Si-Mg core powder, enhances the reduction of SiO₂, especially in HVOF spraying. A series of in-process reactions proceed mainly during splat layering on a substrate instead of during droplet flight even in plasma spraying. Plasma-sprayed composite coatings become much harder because of the great progress of in-process reactions.