A novel highly accurate current mirror

A novel complementary metal-oxide semiconductor (CMOS) current mirror that can work in weak and strong inversion is proposed. The mirror is capable of accurately copying current in the nano-ampere range. The proposed scheme eliminates the DC matching error caused by the difference between drain-to-source voltages of both the input and output transistors. The proposed circuit was verified using ORCAD simulator in 0.8 μm CMOS process technology. Simulation results confirm the functionality and accuracy of the circuit.     

A CMOS current-mode log(x) and log(1/x) functions generator

A novel Complementary Metal Oxide Semiconductor (CMOS) current-mode low-voltage and low-power controllable logarithmic function circuit is presented. The proposed design utilises one Operational Transconductance Amplifier (OTA) and two PMOS transistors biased in weak inversion region. The proposed design provides high dynamic range, controllable amplitude, high accuracy and is insensitive to temperature variations. The circuit operates on a ±0.6 V power supply and consumes 0.3 μW. The functionality of the proposed circuit was verified using HSPICE with 0.35 μm 2P4M CMOS process technology.     

Characterisation of microwave phase conjugate signal generation using nonlinearly loaded wire frequency selective surface (FSS)

Both experimental and theoretical information regarding the scattering and phase conjugate mixing properties of a 2D double-periodic array of wires loaded with nonlinear/linear lumped elements have been provided. An experimental means for assessing the phase conjugate energy production capability for the array is given. These investigations enable identification of the fundamental operational characteristics and underlying mechanisms associated with the production of phase conjugate energy by this type of artificial electromagnetic media. Means for enhancing the phase conjugate energy production capability of the structure by using additional linear lumped loads is examined theoretically and limits on the production of phase conjugate energy established. Theoretical far-field prediction of the behaviour of the structure indicates that retro-directive reflector action as well as negative refraction should be possible.     

Reactive Synthesis and Phase Stability Investigations in the Aluminum Nitride–Silicon Carbide System

The effect of AlN on the structure formation of SiC was investigated. SiC was synthesized in the presence of AlN under vacuum at 1500°C, and the result was cubic SiC. The synthesis of AlN–SiC composites through the reaction Si₃N₄+ 4Al + 3C = 3SiC + 4AlN was also investigated and compared with synthesis via field-activated self-propagating combustion (FASHS). Reactants were heated in a vacuum furnace at temperatures ranging from 1130° to 1650°C. Below 1650°C, the reaction is not complete and at this temperature the product phases are AlN and cubic SiC. At 1650°C, the product contained an outer layer which contained β-SiC only and an inner region which contained AlN and cubic SiC. 2H-SiC and AlN composites synthesized via field-activated self-propagating combustion were annealed at 1700°C under vacuum. The AlN dissociated and evaporated and the 2H-SiC transformed to the cubic β phase. Reasons for the differences in products of furnace heating and FASHS are discussed.     

Mass Spectrometric Study of the Vaporization Kinetics of Potassium Bromide Single Crystals

A mass-spectrometric method was used to investigate the kinetics of the vaporization of potassium bromide single crystals. In electron-impact-ionization mass spectra of molecular fluxes vaporized from a free-surface of KBr, ions of K⁺, KBr⁺, Br⁺, and K₂Br⁺ originating from KBr and K₂Br₂ molecular precursors were detected in the temperature range 724–918 K. The temperature dependencies of ion currents, ln I_iT – 1/ T, of the most abundant ions (K⁺, KBr⁺, and K₂Br⁺) revealed a departure from the linearity. From a comparison between the equilibrium and nonequilibrium vaporization rates, it was concluded that the value of the vaporization coefficient for monomers and dimers passes through a maximum at about 800 and 825 K, respectively. An electron-impact-fragmentation pattern of KBr molecules, I(K⁺)/I(KBr⁺), was observed to pass reproducibly through a minimum at the temperatures of about 800 to 830 K. In the fluxes from a free surface and from one inside a Knudsen cell, the dimer-to-monomer ratios were found to vary with temperature in different ways. The difference in the equilibrium and nonequilibrium rates of vaporization, the temperature dependence of the fragmentation pattern, and the mechanism of association reactions are discussed in light of the terrace-ledge-kink and surface-charge models.     

电场激活燃烧合成( TiB2)PNi/Ni3Al/ Ni功能梯度材料

采用电场激活压力辅助合成技术(FAPAS)制备了(TiB₂)_PNi/(TiB₂)_PNi₃Al/Ni₃Al/Ni梯度材料,主要研究电场激活燃烧合成过程中电场对材料合成及层界面扩散连接的作用。分析了梯度材料各层的界面微观组织及相组成和材料的硬度分布。结果表明,采用FAPAS 技术结合机械合金化工艺制备的(TiB₂)_PNi/(TiB₂)_PNi₃Al/Ni₃Al/Ni 功能梯度材料具有快速、简便和组织均匀密实的特点。梯度材料的陶瓷复合层、Ni₃Al层和Ni板的界面区产生成分的互扩散,形成了良好的冶金结合。从Ni板到陶瓷复合层的硬度呈梯度分布。     

Ambient belonging: How stereotypical cues impact gender participation in computer science.

People can make decisions to join a group based solely on exposure to that group’s physical environment. Four studies demonstrate that the gender difference in interest in computer science is influenced by exposure to environments associated with computer scientists. In Study 1, simply changing the objects in a computer science classroom from those considered stereotypical of computer science (e.g., Star Trek poster, video games) to objects not considered stereotypical of computer science (e.g., nature poster, phone books) was sufficient to boost female undergraduates’ interest in computer science to the level of their male peers. Further investigation revealed that the stereotypical broadcast a masculine stereotype that discouraged women’s sense of ambient belonging and subsequent interest in the environment (Studies 2, 3, and 4) but had no similar effect on men (Studies 3, 4). This masculine stereotype prevented women’s interest from developing even in environments entirely populated by other women (Study 2). Objects can thus come to broadcast stereotypes of a group, which in turn can deter people who do not identify with these stereotypes from joining that group. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Formation Mechanism of AlN–SiC Solid Solution by Combustion Nitridation in Si3N4–Si-Al-C System

The synthesis of solid solutions of AlN–SiC was investigated through the combustion reaction between Si₃N₄, aluminum, and carbon powders and nitrogen gas at pressures ranging from 0.1 to 6.0 MPa. The combustion reaction was initiated locally and then the wave front propagated spontaneously, passing through the cylindrical bed containing the loose powder. In the presence of Si₃N₄ as a reactant, it was feasible to synthesize solid solutions at an ambient pressure (0.1 MPa). The relationship between nitrogen pressure and full-width at half-maximum of the (110) peak of the product showed that lower pressures produced more-homogeneous solid solutions. Some aspects of formation of the AlN–SiC solid solutions were discussed with special emphasis on the influence of nitrogen pressure and reactant stoichiometry.     

Discovery of Five New Ethylene-Forming Enzymes for Clean Production of Ethylene in E. coli

Ethylene is an essential platform chemical with a conjugated double bond, which can produce many secondary chemical products through copolymerisation. At present, ethylene production is mainly from petroleum fractionation and cracking, which are unsustainable in the long term, and harmful to our environment. Therefore, a hot research field is seeking a cleaner method for ethylene production. Based on the model ethylene-forming enzyme (Efe) {"type":"entrez-protein","attrs":{"text":"AAD16440.1","term_id":"4323597","term_text":"AAD16440.1"}}AAD16440.1 (6vp4.1.A) from Pseudomonas syringae pv. phaseolicol, we evaluated five putative Efe protein sequences using the data derived from phylogenetic analyses and the conservation of their catalytic structures. Then, pBAD expression frameworks were constructed, and relevant enzymes were expressed in E. coli BL21. Finally, enzymatic activity in vitro and in vivo was detected to demonstrate their catalytic activity. Our results show that the activity in vitro measured by the conversion of α-ketoglutarate was from 0.21–0.72 μmol ethylene/mg/min, which varied across the temperatures. In cells, the activity of the new Efes was 12.28–147.43 μmol/gDCW/h (DCW, dry cellular weight). Both results prove that all the five putative Efes could produce ethylene.     

Corrosion susceptibilities of various metals and alloys in synthetic geothermal brines

The corrosion susceptibilities of various pure metals and alloys were investigated in synthetic geothermal fluids. Rates of corrosion of AISI 1010 steel, types 304 and 316 stainless steels, Monel 400 and nickel were determined at three temperatures (296, 333 and 368 K); and those of the molybdenum, niobium and titanium were determined at 368 K only. Type 304 stainless steel appears to undergo an active-passive transition at a temperature range between 333 and 368 K. In the passive state type 304 steel has essentially the same corrosion rate as type 316. At 368 K the corrosion rate of pure nickel was approximately 2.5 times that of Monel, which in turn was twice that of type 316 stainless steel. The corrosion rates of Mo, Nb and Ti were less than one mdd at the highest experimental temperature.