分数阶PIλDμ控制器参数λ和μ分析

针对分数阶PI^λD^μ控制器的积分阶次λ和微分阶次μ在0<λ,μ<2的范围内变化时,对分数阶控制系统的影响进行了频率特性和阶跃响应分析,给出了阶次取值的合理范围。首先采用分数阶微积分方程的数值解法,对分数阶闭环控制系统进行数值计算,且其中的分数阶微积分算子用近似计算公式来代替。然后分别采用分数阶PI^λ控制器和分数阶PD^μ控制器当积分阶次λ和微分阶次μ变化时,利用Bode图从频率特性和单位阶跃响应两方面分别对其性能进行分析,频率特性分析与实际阶跃响应的结果一致,表明分数阶PIλDμ控制器的积分阶次λ和微分阶次μ均有一较佳的取值范围。     

Development of ZnSexTe1 − x p-type contacts for high efficiency tandem structures

With a band gap of 1.7 eV CdSe is a near-ideal top cell for a tandem solar cell using CuIn_xGa_1 − xSe₂ (CIGS) as the bottom cell. We and others have demonstrated that CdSe has excellent electronic properties that should result in efficiencies of 18%. The primary obstacle to meeting that objective is low Voc due to not having an effective p-contact. We have made some progress in this regard with ZnSe and ZnTe, but each has limitations that limit Voc below the needed 1+ V. ZnSe is not easily doped p-type, and ZnTe's valence band is not as low as desired. In our recent work we have been combining the two binaries to try to get around these limitations. Films are deposited using conventional co-evaporation to be consistent with manufacturing constraints for solar cells. In one approach we are forming the ternary ZnSe_xTe_1 − x. While giving up a bit of ZnSe's favorable valence band location, we hope to enhance dopability. One of the difficulties that we encountered was maintaining stoichiometry for our targeted Te/Se ratio of 1.0. Such films are typically Zn-rich and not dopable. We found deposition techniques that allow access to stoichiometric films with the desired ratio and have measured modest conductivity. We are also investigating superlattice structures as another way of combining the properties of the binaries. This approach avoids competition between the group VI elements during deposition allowing more control over stoichiometry. However, an added difficulty is posed by the activated N dopant environment in the chamber in that it enhances loss of Te during deposition. The superlattice approach provides means of compensation and is producing stoichiometric films, but conductivity is not yet evident.     

Mg-α-SiAlON/MgO复合材料中Mg-α-SiAlON的原位合成

为改善低品位Mg基材料高温性能,采用烧结Mg砂、金属Al粉、单质Si粉和Al₂O₃粉为主要原料,制备了Mg-α-SiAlON/MgO复合材料。通过XRD、SEM及EDS等检测手段,研究了不同原料质量分数及氮化温度条件下Mg-α-SiAlON/MgO复合材料中Mg-α-SiAlON的原位合成,结合热力学分析确定了合成Mg-α-SiAlON的气氛条件并分析了合成Mg-α-SiAlON的反应机制。结果表明：1 550℃时的氮、氧分压满足合成Mg-α-SiAlON的热力学条件。当烧结Mg砂粉、Al粉、Si粉和Al₂O₃粉的质量分数之和为40wt%时,1 550℃保温3 h氮化后的Mg-α-SiAlON/MgO复合材料中板片状Mg-α-SiAlON相生成量最高可达32.1%,且相互交错构成骨架,将低熔点物相包裹其中。利用烧结Mg砂原位氮化制备Mg-α-SiAlON/MgO复合材料,有利于提高Mg基材料的抗热震性能。     

Inside Front Cover: Efficient Top‐Gate,Ambipolar, Light‐Emitting Field‐Effect Transistors Based on a Green‐Light‐Emitting Polyfluorene (Adv. Mater. 20/2006)

The inside cover shows light emission from within the channel of an ambipolar field‐effect transistor based on the green‐light‐emitting conjugated polymer F8BT in a bottom contact/top gate structure, as reported by Sirringhaus and co‐workers on p. 2708. It visually demonstrates the formation of separate electron and hole accumulation layers in ambipolar transistors and radiative recombination of charge carriers where the two layers meet (schematic), which is controlled by the applied voltages.     

Band gap optimization in Cu(In1 − xGax)(Se1 − ySy)2 by controlled Ga and S incorporation during reaction of Cu-(In,Ga) intermetallics in H2Se and H2S

A large number of companies around the world are developing a variety of manufacturing approaches aimed at low-cost, high throughput, large area CIS-based photovoltaic modules that maintain laboratory-scale cell efficiencies. The most critical technological issue, which directly impacts on the cost-of-ownership of large-scale production, is the specific technology employed for the deposition of the chalcopyrite absorber film. In standard reactive annealing processes, the complex reaction kinetics during the chalcogenization of the precursor film, results in phase segregated multinary alloys. This in turn results in compositionally graded absorber films, which could adversely affect the performance of devices, if grading is not carefully controlled through proper process control. Against this background, a clear understanding of the reaction paths for the formation of the chalcopyrite multinary alloys is essential. In this paper, the details of a fast solid-state reaction process producing single-phase homogeneous Cu(In_1 − xGa_x)(Se_1 − yS_y)₂ alloys, are discussed. The most significant material properties of the resulting single-phase chalcopyrite alloys, as well as the corresponding device characteristics, are also reviewed. This technology has been successfully demonstrated in a pilot facility at the University of Johannesburg and is currently been applied on a commercial level by Johanna Solar Technology GmbH.     

4πγ井型NaI晶体测量装置开展医用核素99Tcm活度测量的国际比对

⁹⁹Tc^m为目前在核医学领域应用最为广泛的短寿命放射性核素,其活度值的准确性至关重要,为此国际计量局组织了⁹⁹Tc^m核素活度国际关键比对。2012 年3月,中国计量科学研究院电离辐射所采用4πγ井型NaI晶体国际参考系统传递仪器（SIRTI）完成了医用核素99Tcm的比对实验。稳定性测试结果表明SIRTI仪器工作状态满足比对要求,比对核素⁹⁹Tc^m的活度当量测量结果在12.580 kBq左右。     

超声辅助制备β-磷酸三钙/Mg-Zn-Ca生物复合材料及性能

在生物Mg合金基体中添加β-磷酸三钙（β-TCP）颗粒可以调控其力学性能及腐蚀降解性能,满足人体不同植入部位的服役需求。本研究在机械搅拌铸造的基础上,采用超声方法对Mg基复合材料的熔体进行辅助处理,制备了β-TCP添加量为1%（质量比）、Zn含量为3%（质量比）、Ca含量为0.2%（质量比）的β-TCP/Mg-Zn-Ca可降解生物复合材料,对超声处理制备的β-TCP/Mg-Zn-Ca复合材料的显微组织、力学性能和腐蚀行为与未超声处理制备的β-TCP/Mg-Zn-Ca复合材料进行了对比研究。结果表明：超声处理可以细化β-TCP/Mg-Zn-Ca复合材料的显微组织,有利于β-TCP复合颗粒的均匀分散;β-TCP/Mg-Zn-Ca复合材料在模拟体液环境下的耐蚀性得到提高;其屈服强度、抗拉强度和伸长率分别为211.54 MPa、334.32 MPa和7.28%,与未超声处理的β-TCP/Mg-Zn-Ca复合材料相比,分别提高了8.44%、4.67%和17.99%。     

TiO2对琼胶-κ-卡拉胶膜性能的影响

采用热铸法,制备了琼胶膜、κ-卡拉胶膜及其两者的共混膜,并在共混膜中添加质量分数为0.8%的TiO₂粉末,制得TiO₂/琼胶-κ-卡拉胶复合膜。对这4种膜的SEM、XRD、力学性能、透光率、不透明度和对水的阻抗性进行测试。结果表明：琼胶-κ-卡拉胶膜的力学性能、透光率、不透明度和对水的阻抗性均介于琼胶膜和κ-卡拉胶膜之间,琼胶和κ-卡拉胶之间有良好的共混性,并且在共混膜中形成了分子间作用力。TiO₂/琼胶-κ-卡拉胶复合膜的拉伸强度（45.44 MPa）比其他3种膜的拉伸强度都大,其中比琼胶-κ-卡拉胶膜的拉伸强度（31.06 MPa）提高46.30%,但断裂伸长率（15.73%）却比其他3种膜的都低,TiO₂与复合膜基质分子间形成强相互作用力,增强复合膜的拉伸强度;在相同波长下,TiO₂/琼胶-κ-卡拉胶复合膜的透光率比其他3种膜都低,在200~400 nm的紫外光区,TiO₂/琼胶-κ-卡拉胶复合膜的透光率明显低于其他3种膜,添加TiO₂的复合膜对紫外光有显著的屏蔽作用,但在600 nm波长处,不透明度（0.96）比其他3种膜都高;TiO₂/琼胶-κ-卡拉胶复合膜对水的阻抗性高于琼胶-κ-卡拉胶膜。     

离子液体/磷酸锆抗菌材料的制备及耐热性研究

以α-磷酸锆(分子式: Zr(HPO₄)₂·H₂O, 以下简称α-ZrP)为载体, 三种季铵型离子液体: 溴化十六烷基三甲基咪唑(C₁₆MIMBr)、氯化十六烷基二甲基苄基铵(C₁₆HDBACCl)和氯化十六烷基三甲基铵(C₁₆CTACCl)被引入α-ZrP层间, 制备得到三种离子液体/α-磷酸锆(IL-ZrP)复合抗菌材料. 通过X射线衍射法(XRD)、红外光谱分析(FTIR)、热重-红外联用分析(TG-FTIR)对材料的结构、组成和热稳定性进行表征. XRD结果表明: 相对于α-ZrP, 三种复合抗菌材料的层间距明显增大, 这证明离子液体已经成功地嵌入到α-ZrP的层间. TG-FTIR实验显示三种离子液体在复合抗菌材料中分别占53.11wt%、50.65wt%和51.25wt%. 三种纯离子液体的热分解起始温度分别为174℃、198℃和219℃, 而离子液体/α-ZrP(IL-ZrP)复合抗菌材料中所含的离子液体的热分解起始温度为219℃、225℃和263℃, 这表明α-ZrP能有效提高离子液体的耐热性. 抗菌性能检测结果表明: 在三种复合材料中, C₁₆MIMBr-ZrP具有较好的抗菌效果(在24 h内, 其对大肠杆菌、金色葡萄球菌的最小抑菌浓度均小于19 mg/L).     

AC conductivity, density related and magnetic properties of Ni1 − xZnxFe2O4 ferrites with the variation of zinc concentration

AC conductivity, density related and magnetic properties are reported for Ni_1 − xZn_xFe₂O₄ ferrites with the variation of zinc concentration prepared by the standard solid state reaction technique. X-ray powder diffraction patterns confirmed the spinel structure of the prepared compounds. AC conductivity (lnσ_ac) increases from − 10.045 (S/m) to − 3.781 (S/m) with the increase in zinc concentration from 0.0 to 1.0 at the frequency of 1 kHz. Lattice parameters, sintered density and grain size increase whereas X-ray density and porosity decrease with the increase in zinc concentration. Saturation magnetization increases with the increase in zinc concentration up to x = 0.4 and after that it decreases with the increase in zinc concentration. Remanence magnetization and magnetic moment almost have the similar trend as that of saturation magnetization. Yafet-Kittel angles increase with the increase in zinc concentration. The possible reasons responsible for these changes are undertaken.     

Nanobelts,Nanowires, and Nanodiskettes of Semiconducting Oxides—From Materials to Nanodevices

Novel nanostructures of semiconducting oxides are reviewed here. It is shown that nanobelts, nanowires, and nanodiskettes of materials such as zinc oxide, gallium oxide, silica, and tin oxide can be fabricated using a vapor‐phase evaporation method. Two applications of these materials—in field effect transistors and as gas sensors—are highlighted.