Role of convection and diffusion in a single pore with adsorptive walls

The importance of intraparticle convection during and after the pressurization step of a pressure swing adsorption process is assessed by considering a single, cylindrical, closed-end pore with adsorptive walls exposed to a binary mixture of an adsorbable component and an inert gas. Gas-phase mass transfer is comprised of pore diffusion and convection, and surface diffusion occurs in the adsorbed phase. Concentration, velocity, and flux profiles are obtained inside the pore both during and after pressurization. Solutions are obtained analytically for the limiting cases of no adsorption, no diffusion, and no inert gas. Complete solutions of the material balance equations are obtained by orthogonal collocation. The pressurization rate, the adsorptive capacity of the pore wall, and the gas-phase mole fraction are varied over a wide range to study the relative importance of convection and diffusion under different conditions. Results show that convection makes a large contribution to transport in the pore except when the adsorbable component has a small mole fraction.     

“苦学”＋“口诀”——针对《经济数学》中“差生”的策略

《经济数学》是经济类专业本科生的一门重要的必修课.本文对《经济数学》重修班的出勤情况及期末考试成绩进行分析,将重修班的学生分为＂假性差生＂与＂纯粹差生＂两类,总结了这两类学生考试不及格的原因,并针对这些原因提出了＂‘苦学’＋‘口诀’＂的策略.     

InGaAs/InP heterojunction-channel tunneling field-effect transistor for ultra-low operating and standby power application below supply voltage of 0.5 V

An In_0.53Ga_0.47As/InP heterojunction-channel tunneling field-effect transistor (TFET) with enhanced subthreshold swing (S) and on/off current ratio (I_on/I_off) is studied. The proposed TFET achieves remarkable characteristics including S of 16.5 mV/dec, on-state current (I_on) of 421 μA/μm, I_on/I_off of 1.2 × 10¹² by design optimization in doping type of In_0.53Ga_0.47As channel at low gate (V_GS) and drain voltages (V_DS) of 0.5 V. Comparable performances are maintained at V_DS below 0.5 V. Moreover, an extremely fast switching below 100 fs is accomplished by the device. It is confirmed that the proposed TFET has strong potentials for the ultra-low operating power and high-speed electron device.     

Two-dimensional threshold voltage model of a nanoscale silicon-on-insulator tunneling field-effect transistor

The tunneling field-effect transistor(TFET) is a potential candidate for the post-CMOS era.In this paper,a threshold voltage model is developed for this new kind of device.First,two-dimensional(2D) models are used to describe the distributions of potential and electric field in the channel and two depletion regions.Then based on the physical definition of threshold voltage for the nanoscale TFET,the threshold voltage model is developed.The accuracy of the proposed model is verified by comparing the calculated results with the 2D device simulation data.It has been demonstrated that the effects of varying the device parameters can easily be investigated using the model presented in this paper.This threshold voltage model provides a valuable reference to TFET device design,simulation,and fabrication.     

Characteristics of cylindrical surrounding-gate GaAs_xSb_(1-x)/In_yGa_(1-y)As heterojunction tunneling field-effect transistors

A Ⅲ-Ⅴ heterojunction tunneling field-effect transistor(TFET) can enhance the on-state current effectively,and GaAs_xSb_1_x/In_yGa_1_yAs heterojunction exhibits better performance with the adjustable band alignment by modulating the alloy composition.In this paper,the performance of the cylindrical surrounding-gate GaAs_xSb_1_x/In_yGa_1_yAs heterojunction TFET with gate-drain underlap is investigated by numerical simulation.We validate that reducing drain doping concentration and increasing gate-drain underlap could be effective ways to reduce the off-state current and subthreshold swing(SS),while increasing source doping concentration and adjusting the composition of GaAs_xSb_1_xIn_yGa_1_yAs can improve the on-state current.In addition,the resonant TFET based on GaAs_xSb_1_x/In_yGa_1_yAs is also studied,and the result shows that the minimum and average of SS reach 11 mV/decade and 20 mV/decade for five decades of drain current,respectively,and is much superior to the conventional TFET.     

CeO2对CuCl/活性炭吸附剂C2H4/C2H6吸附分离性能促进作用

通过等体积浸渍方法制备了添加CeO₂助剂的用于C₂H₄/C₂H₆吸附分离的CuCl/活性炭(AC)吸附剂,使用氮气吸附-脱附曲线、X射线衍射(XRD)、X射线光电子能谱(XPS)、扫描电子显微镜(SEM)、能量分散X射线光谱(EDX)等分析方法对吸附剂进行了表征.结果表明,吸附剂表面Cu(II)在氮气气氛焙烧过程中被部分还原成Cu(I).重点研究了Ce元素的添加对于吸附剂的C₂H₄/C₂H₆吸附分离性能的影响,等温吸附曲线结果表明添加了CeO₂的吸附剂通过降低乙烷的吸附容量从而显著提高了吸附分离性能. XRD及XPS结果表明,和未添加助剂样品相比,其表面晶体团簇较小,分散性更好, Cu(II)还原程度更高.添加CeO₂的吸附剂样品5Ce50Cu(CeO₂和CuCl2的质量分数(w)分别为5%和50%)获得了最好的吸附分离效果,相对于未添加CeO₂的样品50Cu,其在660 kPa下的吸附选择性由4.2提升到8.7.     

Optimum design of photoresist thickness for 90-nm critical dimension based on ArF laser lithography

In this work,a 90-nm critical dimension(CD) technological process in an ArF laser lithography system is simulated,and the swing curves of the CD linewidth changing with photoresist thickness are obtained in the absence and presence of bottom antireflection coating(BARC).By analysing the simulation result,it can be found that in the absence of BARC the CD swing curve effect is much bigger than that in the presence of BARC.So,the BARC should be needed for the 90-nm CD manufacture.The optimum resist thickness for 90-nm CD in the presence of BARC is obtained,and the optimizing process in this work can be used for reference in practice.     

捕集高湿烟气中CO2的变压吸附技术

变压吸附法在捕集烟气中的CO₂这一领域中显示出强大的优越性,但实际电厂烟气含有少量的水蒸气,这对利用常规吸附剂捕集CO₂造成很大挑战。为解决上述瓶颈问题,改进变压吸附工艺以及开发对湿度不敏感、高效的吸附剂成为最主要的途径。本文详细介绍了两种常用的变压吸附工艺,即多层变压吸附及微波辅助真空再生法分离高湿烟气的研究进展,综述了近年来研发的适于捕集高湿烟气的高效吸附剂,系统阐述了各种吸附剂的物理化学特性及其吸附CO₂、H₂O的机制,并在此基础上讨论了变压吸附技术捕集高湿烟气时存在的问题,提出了研究展望。相信随着人们对变压吸附工艺的改进以及对新型高效吸附剂的进一步研发,必将显著降低捕集高湿烟气中CO₂的成本,这将对燃煤电厂等高湿CO₂排放源的温室气体减排具有重要意义。     

非对称经济相位协变量子克隆的最优性

我们严格的证明两维空间中1→2非对称经济型相位协变量子克隆的最优性。证明中,我们得出另一种独立的幺正变换。我们的结果涵盖了以前的结果[Durt T, et, al, Phys. Rev. A, 2004, 69: 062316]。     

一维链状氢键型甘氨酸超分子化合物[(Gly)2+ (18-crown-6)2(MnCl4)2‒]的合成、 结构及介电性质

以甘氨酸(Gly)、 18-冠醚-6、 二氯化锰(MnCl₂)和盐酸为原料, 通过蒸发法获得一种新型相变一维链状氢键型甘氨酸超分子化合物[(Gly)₂⁺ (18-crown-6)₂(MnCl₄)^2?](1). 通过元素分析、 变温X射线单晶衍射和介电测试等手段对其进行了表征和解析. 实验结果表明, 该晶体属于单斜晶系, 空间群从P2₁/c(100 K)转化为C2/c(293 K). 随着温度升高, [MnCl₄]^2?呈现无序状态的共棱双四面体结构. 质子化甘氨酸分子和分子内羟基(—OH)发生动态摆动, 引起O—H…Cl型一维氢键链产生明显伸缩运动, 导致化合物1在一定温度范围内出现结构相变及介电异常.