Novel structure of GaAs-based interdigital-gated HEMT plasma devices for solid-state THz wave amplifier

Theoretical analysis of potential distribution in the interdigital-gated high electron mobility transistor (HEMT) plasma wave device was carried out. The dc I–V characteristics of capacitively coupled interdigital structure showed that uniformity of electric field under the interdigital gates was improved compared to the dc-connected interdigital gate structure. Admittance measurements of capacitively coupled interdigital gate structure in the microwave region of 10–40 GHz showed the conductance modulation by drain–source voltage. These results indicate the existence of plasma wave interactions.     

一种基于改进的博客观点检索算法研究

近年来博客逐渐成为一种新的主流媒体及网络形式,已成为人们获取信息的重要渠道。通过分析博客的相关功能,提出一种基于博客的观点检索方法,并且设计了一种基于负规则的极性检测算法,以提高极性检测部分的性能。通过相关实验数据验证,结果证明了提出的方法的有效性,该改进算法能够显著提高系统的MAP值。     

Nano-Al2O3/PANI composites with high negative permittivity

Polyaniline (PANI) composites filled with ferroferric oxide and barium titanate were discovered to have metamaterial characteristics in recent years. In this paper, based on micron-Al₂O₃/PANI composites with negative permittivity, the dielectric properties of nano-Al₂O₃/PANI composites were studied. Nano-Al₂O₃/PANI composites had negative permittivity, which was considerably higher than that of PANI and micron-Al₂O₃/PANI composites. The higher negative permittivity was caused by the better dispersibility of nano-Al₂O₃, resulting in the enlargement of polarization voltage on a greater range of PANI molecular chain. Moreover, nano-Al₂O₃/PANI composite with 5 wt% nano-Al₂O₃ has the largest negative permittivity (−2.24 × 10⁶) that has not been reported so far in oxide/PANI composites.     

Perforated Sheets Exhibiting Negative Poisson's Ratios

Sheets made from readily available conventional materials containing diamond or star shaped perforations are shown to exhibit various Poisson's ratio values which could also be negative (auxetic). This behavior may be exhibited in both tension and compression and can be explained through models based on “rotating rigid units.” This provides an easy manner for the manufacture of auxetic or conventional systems at any scale which can be tailor made to exhibit particular values of the Poisson's ratio.     

Impact of mass balance calculations on adsorption capacities in microporous shale gas reservoirs

Determination of the adsorbed reservoir capacity of gas shales by adsorption analyses as done routinely by mass balance maybe in significant error if the effects of pore-size dependent void volume (porosity) is not considered. It is shown here that with increasing pressure, helium, which is invariably used to measure void volume, can access pores that are not available for adsorption to gases with larger kinetic diameters as highlighted by experiments with zeolites of known pore-size distribution. Helium can diffuse and/or adsorb in restricted pores of the microporous samples, as indicated by a larger void volume with pressure. The error in adsorption calculations due to helium void volume calibrations for high pressure methane isotherms is most significant with low organic-carbon content, moisture-equilibrated shales and mudrocks in which the overall adsorptive capacity is low. In such samples negative adsorption can be calculated due to the void volume of helium used in the mass balance calculations exceeding the void volume to methane – a reflection of greater pore-space accessibility of the smaller helium molecule than methane. The amount of the error introduced by using helium void volume in mass balance calculations is pore-size and pore-size distribution dependent. Organic-rich shales and mudrocks or coals which do not show negative methane adsorption also maybe in error but the error is masked by their larger adsorbed gas capacities. Such findings underline the importance of analysis gas-type as kinetic diameter size will influence the penetrability/diffusion of the gas through the sample and hence the calculated adsorbed gas capacities.     

Asymmetric electric double layer capacitors using carbon electrodes with different pore size distributions

Asymmetric capacitors composed of carbon electrodes with different pore size distributions (PSD) were constructed in order to study the fundamental relationship between the PSD of positive and negative carbon electrodes and the performance of electric double layer capacitors. The performance of asymmetric capacitors in a non-aqueous electrolyte solution (TEMA·BF₄/PC) was found to be governed by the PSD of the carbon used in the negative electrode. Capacitance depends on the BET surface area of the negative electrode and the rate performance depends on its mesoporous surface area. These results were explained by the fact that it is more difficult to adsorb large solvated cations (TEMA⁺) in micropores (less than 2 nm wide) than in mesopores (2-50 nm wide), and that this is more difficult with a higher rate of charge-discharge.     

A kinetic interpretation of a negative time constant in impedance equivalent circuits for the dissolution/passive transition

A theoretical impedance function is proposed for the active/passive transition of nickel in an acid sulphate medium. It is considered that passivating species progressively covers the electrode surface. This approximated model predicts the appearance of negative time constants in the impedance spectra when coverage coefficient θ values for passive species are greater than 0.5.     

负压差移动床立管料斗中散作颗粒流动特征──Ⅳ立管中科面高度对流落特征的影响

通过负压差移动床立管中料面高度对散体颗粒通过其下方连接的锥形料斗流落特征影响的研究，结果表明：当锥形料斗的半锥角不大于10．2°及料面高度大于0．30m时，立管中料面高度对散体颗粒流落时的流区特征、压力波动特征和散体颗粒平均质量流率等影响甚微；而当料面高度不大于0．30m时．料斗中压力波动强度减小。当锥形料斗的半锥角大于10．2°，无论立管中料面高度为0．55m还是0．30m，散体颗粒流落特征满足压力控制区，而立管中料面高度为1．65m时，散体颗粒流落时出现气泡控制区特征。     

对气测全量曲线“负漂”的认识及资料应用价值的探讨

对于TDC—综合录井仪的气测全量曲线“负漂”成因机理,通过理论分析和现场试验,有了初步认识。全量曲线“负漂”峰是惠斯顿电桥鉴定器测量低导热系数气体的正常反应,它对判断CO_2气体和N_2气体的存在有较好的应用价值。它可为今后进一步研究地层中高矿化度水层、油水同层和气水同层的解释方法提供一项特殊价值的气测分析资料。     

Characteristics of negative electron beam resists, ma-N2410 and ma-N2405

We have characterized the electron beam lithography (EBL) properties of the new negative tone resists, ma-N2410 and ma-N2405. These negative resists reacts under low electron dose values from 10 to 140 μC/cm², tested using 10, 20, 28 keV electron beam. There was negligible loss of pattern height, which was attributed to the combined dose of the incident electron beam and the backscattered electrons. Experimental tests were performed under various EBL writing conditions of dose value, developing time, line-width and resist thickness. Our investigation showed that these new commercially available resists have high resolution and high contrast with non-chemical amplification, useful for micro-fabrication application.