Graphene-based bimorph microactuators

A novel graphene-on-organic film fabrication method that is compatible with a batch microfabrication process was developed and used for electromechanically driven microactuators. A very thin layer of graphene sheets was monolithically integrated and the unique material characteristics of graphene including negative thermal expansion and high electrical conductivity were exploited to produce a bimorph actuation. A large displacement with rapid response was observed while maintaining the low power consumption. This enabled the successful demonstration of transparent graphene-based organic microactuators.     

Electric and magnetic properties of ferromagnetic/piezoelectric bilayered composite

One of the most promising ways for the realization of multi-functional materials is the integration of oxides with different properties in artificial heterostructures. In this paper, a novel piezoelectric–ferromagnetic heterostructure consisting of 0.92Na_0.5Bi_0.5TiO₃–0.08BaTiO₃ (abbreviated as BNT–BT_0.08) and CoFe₂O₄ layers is fabricated on Si–Pt substrate, by sol–gel method coupled with spin-coating technique. The composite thin film shows only perovskite Bi_0.5Na_0.5TiO₃-like rhombohedral phase and CoFe₂O₄ cubic phase. The thickness of CoFe₂O₄ and BNT–BT_0.08 layers is ~?280 and?~?400 nm, respectively. BNT–BT_0.08/CoFe₂O₄ heterostructure thin film shows a saturation magnetization of 0.11 emu/g at 5 K and 0.07 emu/g at 295 K, dielectric constant of 235 at 1 kHz and tunability of 70% at 1 kHz and an electric field E?=?110 kV/cm. The results reveal that the investigated hybrid piezoelectric/ferromagnetic structure shows piezoelectric behavior, good ferroelectric and ferromagnetic properties. This bilayer composite can be used in miniature low-frequency magnetic sensor and piezoelectric sensor for biomedical domain.     

硼酸-硫酸阳极氧化2A97Al-Cu-Li合金在热带海洋大气环境中的初期腐蚀机理

采用光学显微镜、扫描电镜、能谱仪、电化学阻抗谱测试结合超薄切片,分析阳极氧化2A97Al-Cu-Li合金在大气腐蚀前后的微观形貌、化学成分及电化学性能。结果表明:在不同温度利用含有硼酸-硫酸或酒石酸-硫酸组合的电解液生长膜层时,硼酸添加和较高温度允许较大的电流密度通过,使膜生长加速;对于不同电解液,孔的几何构形和结构相似;硼酸-硫酸阳极氧化试样在热带海洋大气环境中暴露1个月后,出现主要由O,Al,Cl,Cu组成的分散性黑色锈斑,表面产生白色沉淀;随着户外暴露时间的延长,合金发生严重的点蚀并深入合金内部,腐蚀的扩展与θ相粒子有关。     

Black Hole and Sink Hole Attack Detection in Wireless Body Area Networks

In Wireless Body Area Networks (WBANs) with respect to health care, sensors are positioned inside the body of an individual to transfer sensed data to a central station periodically. The great challenges posed to healthcare WBANs are the black hole and sink hole attacks. Data from deployed sensor nodes are attracted by sink hole or black hole nodes while grabbing the shortest path. Identifying this issue is quite a challenging task as a small variation in medicine intake may result in a severe illness. This work proposes a hybrid detection framework for attacks by applying a Proportional Coinciding Score (PCS) and an MK-Means algorithm, which is a well-known machine learning technique used to raise attack detection accuracy and decrease computational difficulties while giving treatments for heartache and respiratory issues. First, the gathered training data feature count is reduced through data pre-processing in the PCS. Second, the pre-processed features are sent to the MK-Means algorithm for training the data and promoting classification. Third, certain attack detection measures given by the intrusion detection system, such as the number of data packages trans-received, are identified by the MK-Means algorithm. This study demonstrates that the MK-Means framework yields a high detection accuracy with a low packet loss rate, low communication overhead, and reduced end-to-end delay in the network and improves the accuracy of biomedical data.     

Copolymerization of the pair maleic anhydride–dicyclopentadiene: I. Copolymerization and post‐copolymerization at high conversion

The present study describes the kinetic investigation of the complex binary copolymerization system maleic anhydride (MA)—dicyclopentadiene (DCPD). All syntheses were carried out in homogeneous solution; high conversions in soluble and linear copolymer are achievable when starting from an equimolecular monomer feed. Excess of DCPD would limit the attainable conversions, while surplus of MA would induce crosslinking of the copolymers. The findings of the thorough kinetic study were sustained by structural assessment from IR and NMR spectra recorded for various copolymers, both soluble and gels. Copyright © 2004 Society of Chemical Industry     

Technology and petroleum exhaustion: Evidence from two mega-oilfields

In this paper, we use results from the Hotelling model of non-renewable resources to examine the mainstream view among economists that improvements in recovery technology can offset declines in petroleum reserves. We present empirical evidence from two well-documented mega-oilfields: the Forties in the North Sea and the Yates in West Texas. Patterns of depletion in these two fields suggest that technology temporarily increases the rates of production at the expense of more pronounced rates of depletion in later years—in line with Hotelling's predictions. Insofar as our results are generalizable, they call into question the view of most economists that technology can mitigate absolute resource scarcity. This raises concerns about the capacity of current mega-fields to meet future oil demand.     

Sensitization of as Rolled and Stable Annealed Alloy 625

Alloy 625 is used as cladding material in the oil and gas industry. Different annealing conditions are used, these are stable annealed and as rolled. Both conditions have been isothermally sensitized in a laboratory resistance furnace. The annealing temperature was up to 1050?°C and the annealing time up to 10 h. Susceptibility to intergranular corrosion has been investigated by means of a conventional immersion tests according to ASTM G28A and the Double Loop—Electrochemical Potentiokinetic Reactivation Test (DL-EPR method). Scanning electron microscopy (SEM) was used to evaluate microstructure and type of attack after testing. The chemical composition of precipitated phases was characterized by SEM and Transmission Electron Microscopy (TEM). High-resolution investigations with concentration profiles proved high molybdenum precipitates to determine the degree of sensitization.     

Molybdenum and Chromium Depletion at Grain Boundary Precipitates Alloy 926

Alloy 926 is a molybdenum-bearing stainless steel and is used in various industrial fields. This material is used as a cladding material for high diameter pipes in oil and gas industry. One opportunity of production of this material is a thermo-mechanical rolling process. Recent studies have shown that an end rolling temperature of 950 °C with subsequent water cooling has comparable corrosion properties with a solution annealed material. The impact of two different quenching and tempering processes on corrosion properties is presented. The microstructure was evaluated with high resolution SEM, and grain boundary precipitates as well as depletion zones were characterized with TEM-EDX line-scans. Isothermal annealing at 760 °C results in formation of Molybdenum rich, Chromium depleted phases. Their microstructure was not clearly detected by electron diffraction, presumably Laves phase is formed. At 900 °C and long term annealing, two s phases are present. One has a similar composition to the above mentioned Laves phase, the other is Molybdenum enriched and Chromium enriched. Thermo mechanically processed materials contains c phases with similar composition. Depletion zones of these phases are quantitatively characterized with respect to width and chemical composition and their impact on corrosion properties is discussed by use of PREN concept.