Anisotropic thermopiezoelectric solids with an elliptic inclusion or a hole under uniform heat flow

The two-dimensional problem of a thermopiezoelectric material containing an elliptic inclusion or a hole subjected to a remote uniform heat flow is studied. Based on the extended Lekhnitskii formulation for thermopiezoelectricity, conformal mapping and Laurent series expansion, the explicit and closed-form solutions are obtained both inside and outside the inclusion (or hole). For a hole problem, the exact electric boundary conditions on the hole surface are used. The results show that the electroelastic fields inside the inclusion or the electric field inside the hole are linear functions of the coordinates. When the elliptic hole degenerates into a slit crack, the electroelastic fields and the intensity factors are obtained. The effect of the heat flow direction and the dielectric constant of air inside the crack on the thermal electroelastic fields are discussed. Comparison is made with two special cases of which the closed solutions exist and it is shown that our results are valid.     

组织策略在化学教学中的运用

由于缺乏应有的组织,学生头脑中的化学知识往往处于无序状态的堆积方式,这种无序状态堆积的知识不但不易贮存,在需要使用时也难以被充分激活。因此,在化学教学中教师要运用好组织策略,帮助学生把握知识的内在联系,归纳知识纲目要点,建构知识网络。     

Dielectric Properties Investigation of Metal–Insulator–Metal (MIM) Capacitors

This study presents the construction and dielectric properties investigation of atomic-layer-deposition Al₂O₃/TiO₂/HfO₂ dielectric-film-based metal–insulator–metal (MIM) capacitors. The influence of the dielectric layer material and thickness on the performance of MIM capacitors are also systematically investigated. The morphology and surface roughness of dielectric films for different materials and thicknesses are analyzed via atomic force microscopy (AFM). Among them, the 25 nm Al₂O₃-based dielectric capacitor exhibits superior comprehensive electrical performance, including a high capacitance density of 7.89 fF·µm⁻², desirable breakdown voltage and leakage current of about 12 V and 1.4 × 10⁻¹⁰ A·cm⁻², and quadratic voltage coefficient of 303.6 ppm·V⁻². Simultaneously, the fabricated capacitor indicates desirable stability in terms of frequency and bias voltage (at 1 MHz), with the corresponding slight capacitance density variation of about 0.52 fF·µm⁻² and 0.25 fF·µm⁻². Furthermore, the mechanism of the variation in capacitance density and leakage current might be attributed to the Poole–Frenkel emission and charge-trapping effect of the high-k materials. All these results indicate potential applications in integrated passive devices.     

疏水/亲水大孔聚二乙烯基苯/聚(N-2-氨基乙基丙烯酰胺)IPN树脂的合成及对水杨酸吸附性能研究

采用分步悬浮聚合法制备了聚二乙烯基苯/聚丙烯酸甲酯(PDVB/PMA)大孔互穿聚合物网络,将其中的聚丙烯酸甲酯用乙二胺氨解,合成了具有疏水/亲水性能的聚二乙烯基苯/聚(N-2-氨基乙基丙烯酰胺)(PDVB/PNAEAM)大孔互穿聚合物网络(IPN);测定了该树脂的孔结构、含水量、弱碱交换量和溶胀性能;测定了该树脂对水杨酸在不同温度下的吸附等温线,利用热力学函数关系计算出了吸附焓、自由能和熵.推测PDVB/PNAEAM IPN树脂中疏水性的PDVB一网具有疏水作用吸附能力、亲水性的PNAEAM一网具有氢键作用吸附能力.动态吸附及脱附实验表明湿态PDVB/PNAEAM IPN树脂对水溶液中水杨酸的饱和吸附量达到46.1mg/mL.树脂可以通过4%NaOH溶液再生.PDVB/PNAEAM IPN树脂在分离工业废水中水杨酸等芳香有机酸有良好的应用前景.     

Small-angle X-ray scattering study on the microstructure evolution of zirconia nanoparticles during calcination

Zirconia nanoparticles have been synthesized from zirconium hydroxide precipitates followed by a supercritical CO₂ extraction. The microstructure evolution of these zirconia nanoparticles during the calcination at the moderate temperature has been investigated. Assisted by the analyses of TEM and XRD, small-angle X-ray scattering (SAXS) study offers possibilities to a comprehensive and quantitative characterization of the structural evolution on the nanometer scales. The as-synthesized zirconia sample exhibits a mass fractal structure constructed by the surface fractal particles. Such a structure can be preserved up to 300 °C. After calcination at 400 °C, considerable structural rearrangement occurs. In the interior of nanoparticles zirconia nanocrystallites emerge. It is the scattering from such zirconia nanoparticles that give rise to the broadened crossover in the ln[J(q)] vs. ln q plot and the scattering peak in the ln[q³J(q)] vs. q² plot. With a further increase in the calcination temperature, the power-law region at large-q in ln J(q) vs. ln q plot expands, and the peak in ln[q³J(q)] vs. q² plot shifts towards lower q values, indicating size increases in both the nanocrystallites and nanoparticles. Besides, the mass fractal structure constructed by zirconia nanoparticles can be largely preserved during the moderate temperature calcination.     

掺铒光纤放大器在多路模拟光纤传输系统中应用

对应用掺铒光纤放大器的副载波频分复用模拟电视光纤传输系统的噪声和失真进行了实验研究，利用掺铒光纤放大器作为系统的功率提升和中继放大器，分别成功地进行了１８５ｋｍ和２１５ｋｍ的系统传输试验     

Experimental Study on High Power and Efficiency Fiber Amplifier Module

l.IntroductionErbium-doPedfiberamp1ifier(EDFA)isattractiveinall-opticalcommunicationsys-temsduetoitSsuperiorityofhighgain,broadbandwidth,lownoiseandhighPOwer.Whenusedinhigh-sPeed,long-haulcommunicationanddistributionsystems,suchassolitoncommunication,WDM,FDM,AM-VSB,CATV,etc.,EDFAisdemandedofhighsignaloutputPowerbesidebroadbandwidth,lowdistortionandcrossta]k.ToobtainlargeoutputPowerwil1relatetomanyproblemslikethefibermaterial,pumpinglaser,fibcrcomPonent,manufacturetechnologyanddesig…     

最高阶元个数是4p的有限群

本文证明了如果有限群G恰有4p个最高阶元,p为素数,则群G为可解群,除非G同构于S5.     

The Fiber Soliton Communication System with Stochastic Variation of Gain

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Soliton switching in twin-core fibers with gain and loss

Soliton propagation and switching in twin-core nonlinear fibers with gain and loss have been investigated based on a pair of coupled nonlinear Schr?dinger equations. We have found the fiber with equal amount of gain in both cores has the minimum ascending energy Δɛ of 1.5K, while the fiber with a certain amount of gain in one core and the same amount of loss in the other core has the minimum switching thresholdɛ _th of 2.05K. A new vector field is defined and its potential function is derived, which explains the switching behavior of the minimumɛ _th switch satisfactorily.