Numerical modelling of a low power non-transferred arc plasma reactor for methane conversion

Thermal flow characteristics and the methane conversion reaction in a low power arc plasma reactor for efficient storage and transport of methane, which is the main component of shale gas, were simulated. The temperature and velocity distributions were calculated according to the type of discharge gases and arc current level by a self-developed magnetohydrodynamics (MHD) code and a commercial ANSYS-FLUENT code; the transport of chemical species was analyzed as including the chemical reactions of methane conversion. The simulated results were verified by the comparison of calculated and measured arc voltages with permissible low error as under 4%. Three C₂ hydrocarbon gases with ethane (C₂H₆), ethylene (C₂H₄), and acetylene (C₂H₂) were selected as the converted species of methane from experimental data. The mass fraction of C₂ hydrocarbons and hydrogen as the product of the conversion reaction at the reactor was also calculated. Those values show good agreement with the actual experimental results in that the major conversion reaction occurred in C₂H₂ and hydrogen, and the conversions to C₂H₆, C₂H₄, and hydrogen were minor reactions of methane pyrolysis conversion.     

Etching characteristics of thin SiON films using a liquefied perfluorocarbon precursor of C6F12O with a low global warming potential

Perfluorocarbon gas is widely used in the semiconductor industry. However, perfluorocarbon has a negative effect on the global environment owing to its high global warming potential (GWP) value. An alternative solution is essential. Therefore, we evaluated the possibility of replacing conventional perfluorocarbon etching gases such as CHF₃ with C₆F₁₂O, which has a low GWP and is in a liquid state at room temperature. In this study, silicon oxynitride (SiON) films were plasma-etched using inductively coupled CF₄ +C₆F₁₂O+O₂ mixed plasmas. Subsequently, the etching characteristics of the film, such as etching rate, etching profile, selectivity over Si, and photoresist, were investigated. A double Langmuir probe was used and optical emission spectroscopy was performed for plasma diagnostics. In addition, a contact angle goniometer and x-ray photoelectron spectroscope were used to confirm the change in the surface properties of the etched SiON film surface. Consequently, the etching characteristics of the C₆F₁₂O mixed plasma exhibited a lower etching rate, higher SiON/Si selectivity, lower plasma damage, and more vertical etched profiles than the conventional CHF₃ mixed plasma. In addition, the C₆F₁₂O gas can be recovered in the liquid state, thereby decreasing global warming. These results confirmed that the C₆F₁₂O precursor can sufficiently replace the conventional etching gas.     

平流层通信新思路——谷歌气球计划

平流层通信具有低延迟、信道衰落小、造价低廉、机动灵活等特点,在军事应用和应急通信领域都有重要的战略价值,也曾经引起各国的重视,并成为研究热点。然而平流层通信平台的稳定性对各国研究者而言一直是一个挑战,谷歌公司从鸟群飞行中得到启发,开启了Google Loon项目,其目的是为全球偏远地区2/3人口提供速度较快、价格可承受的互联网接入服务,同时为自然灾害发生地区提供通信服务。文中分析了谷歌气球的技术细节,谷歌气球初次试验的情况,以及谷歌气球面临的挑战。谷歌气球计划为平流层通信提供了又一新思路。     

关于住居能源碳排放量影响因素的研究——基于中国省际面板数据的实证分析

以中国省级行政单位为研究对象对与居民生活息息相关的住居领域内所产生的能源消费与CO2排放的地区间差异性进行研究,并在此基础上对产生这一差异性的影响因素进行了深入的分析。以人均碳排放量为因变量,分别从人口、社会和经济特征及区域环境特征两大方面出发选取了10个影响因素作为自变量构建了从2002—2011年10年间以全国28个省份为对象的4个均衡面板数据模型并进行了估计分析。从模型估计结果来看,个人属性以及家庭结构等都对住居领域的碳排放有着显著性的影响;城镇居民的人均住宅建筑面积越大其碳排放量就越高。基于此,研究认为在制定有关节能减排措施时,要充分考虑到个人属性、家庭结构等人口和社会经济性因素以及住宅类型、城市形态等区域环境因素所带来的影响,根据各个地区不同的经济发展水平和实际情况因地制宜地制定和实施节能减排政策。     

Relation between etching profile and voltage–current shape of sintered SiC etching by atmospheric pressure plasma

Sintered silicon carbide (SiC) was etched by a dielectric barrier discharge source. A high voltage bipolar pulse was used with helium gas for the plasma generation. One stable filament plasma was generated and could be used for SiC etching. As the processing gas (NF₃) mixing rate increased, the width and depth of the etching profile became narrower and deeper. The differentiated V–Q Lissajous method was used for measuring the capacitances (C_eq) of the electrode after the plasma turned on. The width of the etching profile was proportional to C_eq. As the current peak value I_smx of the substrate current increased, the volume removal rate of SiC increased. The etch depth was proportional to the ratio of I_smx to C_eq. Additionally, because of the different characteristics of the plasma disks on SiC substrate by the voltage polarity, the etching profile was unstable. However, in high NF₃ mixing process, the etching profile became stable and deeper.     

Computational study on influence of RF shielding box on inductance of coil

Despite the fact that a radio frequency (RF) shielding box affects a coil inductance used in matching network, RF engineers have used a coil inductance measured in open space on designing matching networks since it is difficult to precisely measure the coil inductance within the RF shielding box. In this work, we investigate the influences of the RF shielding box on the coil inductance via a 3D full electromagnetic wave simulation. Simulation results shows that the coil inductance decreases from -6.0% to -11.9% compared with its ideal inductance depending on coil positions within the RF shielding box. Both inductive and capacitive coupling between the coil and surfaces of the RF shielding box contribute to the reduction of the coil inductance. We expect that these results would be useful for those who design RF matching networks.     

Efficiency enhancement of dye-sensitized solar cells with addition of additives (single/binary) to ionic liquid electrolyte

The effect of addition of single and binary additives on the performance of dye-sensitized TiO₂ solar cells based on electrolytes containing an ionic liquid (IL), 1,2-dimethyl-3-propylimidazolium iodide (DMPII) has been studied. Among the seven additives used, the addition of 2-(dimethylamino)-pyridine (DMAP) to IL resulted in best cell efficiency, which showed further enhancement with the addition of 5-chloro-1-ethyl-2-methylimidazole (CEMI) as second additive. The efficiency of the dye-sensitized solar cell (DSC) based on an electrolyte containing binary additives (DMAP and CEMI in equal molar ratios) has been found to increase by 62·5% from 4·35 to 7·07%. The dependence of different photovoltaic performance parameters (V _oc, J _sc, ff, η) of DSC upon temperature has been studied over a 30–120°C range and only a small decrease in conversion efficiency has been observed. The electrolyte containing binary additives (DMAP and CEMI) shows best cell performance up to 120°C.     

Performance improvement using time delays in multivariable controller design

A new controller for linear multivariable ordinary systems is suggested in which distributed delays are included in the feedback loop. A general design approach to obtain this type of controller is suggested. It is shown that the resulting closed-loop system is asymptotically stable under some sufficient conditions. Sufficient conditions are derived under which the disturbance attenuation, the robustness against parameter variations, and the time-delay stability margins are improved by the proposed controller. The state feedback tracking controller and the dual-state observer are obtained by modification of the proposed controller.