碳纤维复合材料内部缺陷深度的定量红外检测

利用脉冲红外热成像技术对碳纤维复合材料试件内部的模拟脱黏缺陷的深度进行测量, 研究在被测物热属性参数未知情况下,碳纤维增强塑料中缺陷深度的测量方法. 分析了平板材料在脉冲热源激励下的一维热传导模型;给出了内部缺陷深度的红外测量原理; 选用对数温度二阶微分峰值时刻作为特征时间测量缺陷深度; 考虑单点标定测量深度可能产生较大的随机误差,提出利用最小二乘法多项式拟合建立阶梯件中阶梯深度与其对应的对数温度时间二阶微分曲线峰值时间两者之间的标定关系式的方法, 选择在相对误差平方和最小情形下的拟合关系式作为脱黏缺陷深度测量的标定关系式. 实验结果表明,利用该方法测量脱黏缺陷深度的精度优于单点法标定测量结果, 实现了在被检测材料热属性参数未知的情况下仍能较准确地测量脱黏缺陷深度.     

新型宽温区高热稳定性微波功率SiGe 异质结双极晶体管

宽温区大电流下的热不稳定性严重制约着功率SiGe 异质结双极晶体管 (HBT) 在射频和微波电路中的应用.为改善器件的热不稳定性, 本文利用SILVACO TCAD建立的多指功率SiGe HBT模型, 分析了器件纵向结构中基区Ge组分分布对微波功率SiGe HBT电学特性和热学特性的影响. 研究表明, 对于基区Ge组分为阶梯分布的HBT, 由于Ge组分缓变引入了少子加速电场, 使它与均匀基区Ge组分HBT相比, 具有更高的特征频率f_T, 且电流增益β和f_T随温度变化变弱, 这有利于防止器件在宽温区工作时电学特性的漂移.同时, 器件整体温度有所降低, 但器件各指温度分布均匀性较差.考虑多指HBT各发射极指散热能力存在差异, 在器件纵向结构设计为基区Ge组分阶梯分布的同时, 对其横向版图进行发射极指间距渐变结构设计, 用于改善器件各指温度分布的均匀性, 进而提高HBT的热稳定性.结果表明, 与基区Ge组分为均匀分布的等发射极指间距结构HBT相比, 新器件各指温度分布均匀性明显改善, f_T保持了较高的值, 且β和f_T 随温度变化不敏感, 热不稳定性得到显著改善, 显示了新器件在宽温区大电流下工作的优越性. 关键词： SiGe 异质结双极晶体管 Ge组分分布 发射极指间距渐变技术 热稳定性     

改进的三维电磁PIC系统模拟并行算法

为了更好地实现对大尺度器件的模拟,以及更系统地验证和解决高功率微波系统在设计和实验中负载变化等影响,在进一步深入研究电磁PIC并行算法的基础上,运用MPI消息传递函数做出了改进。提出了一种整体建模、分段解析的并行算法,并从并行时序算法入手,通过减少一次同步提高了计算的效率。最后经过一个磁绝缘线振荡器进行验证,改进的算法正确,并且当计算进程数4个增加到16个时,计算速度能提高2.5倍左右。     

A Simple Hydrothermal Method for the Growth of ZnO Crystals

ZnO microstructures have been grown from zinc chloride (ZnCl₂) and ammonia solution at 100 °C for 1 – 24 hours. X‐ray diffraction, scanning electron microscope and field‐emission scanning microscope were utilized to investigate the structural properties and morphology of the ZnO crystals. Structural investigations show that phase‐pure hexagonal structure ZnO has been successfully synthesized, and the hexagonal structure ZnO can be achieved in solutions with an appropriate range of concentrations. Under our experimental conditions, several different morphologies of ZnO structures were obtained, including flower‐like and bar flower‐like. The relationship between the morphology and experimental conditions are discussed.     

Mo/Si aperiodic multilayer broadband reflective mirror for 12.5-28.5-nm wavelength range

Aperiodic molybdenum/silicon (Mo/Si) multilayer designed as a broadband reflective mirror with mean reflectivity of 10% over a wide wavelength range of 12.5-28.5 nm at incidence angle of 5° is developed using a numerical optimized method. The multilayer is prepared using direct current magnetron sputtering technology. The reflectivity is measured using synchrotron radiation. The measured mean reflectivity is 7.0% in the design wavelength range of 12.5-28.5 nm. This multilayer broadband reflective mirror can be used in extreme ultraviolet measurements and will greatly simplify the experimental arrangements.     

电子束蒸发沉积Ir膜真空紫外反射特性

Ir是一种重要的真空紫外反射材料,在太阳物理、宇宙物理、生命科学、大气物理、同步辐射等方面有着十分重要的应用.对电子束蒸发沉积Ir膜在真空紫外波段的反射特性进行了系统的理论和实验研究.根据吸收材料基底上单层金属膜数学计算模型,对不同基片上各种厚度的Ir膜真空紫外反射率进行了优化计算.根据计算和前期实验结果,采用电子束蒸发方法,在石英、K9玻璃基片上沉积了不同厚度的Ir膜,在入射波长120 nm处获得了近30%正入射反射率,对应的Ir膜厚度为12 nm.过厚或过薄均不利于Ir膜反射率的提高.经退火处理后,Ir膜中张应力有所释放但并未消除,同时晶粒平均尺寸显著增大,反射率下降.     

The Inhibition of Gastric Cancer Cells’ Progression by 23,24-Dihydrocucurbitacin E through Disruption of the Ras/Raf/ERK/MMP9 Signaling Pathway

Gastric cancer is considered to be one of the most common causes of cancer death worldwide due to its high recurrence and metastasis rates. The molecule 23,24-Dihydrocucurbitacin E (DHCE) is a cucurbitacin-derived tetracyclic triterpenoid compound that has anti-tumor activity, but the exact mechanism remains to be elucidated. This research aimed to explore the effects of DHCE on human gastric cancer cells and the possible mechanisms. The results showed that DHCE suppressed proliferation, migration, and invasion of gastric cancer cells, as well as induced apoptosis and G2/M phase arrest. Mechanistically, the potential targets and pathways of DHCE were predicted using database screening and verified using a molecular docking study, fluorescence staining, and Western blot. The results indicated that DHCE obviously inhibited the kinase activity of ERK2 via targeting its ATP-binding domain, destroyed F-actin microfilament, and reduced the expression levels of Ras, p-c-Raf, ERK, p-ERK, and MMP9 proteins. Collectively, our study demonstrated that DHCE suppressed gastric cancer cells’ proliferation, migration, and invasion through targeting ERK2 and disrupting the Ras/Raf/ERK/MMP9 signaling pathway. These properties make DHCE a promising candidate drug for the further design and development of novel and effective Ras/Raf/ERK/MMP9 pathway inhibitors for treating gastric cancer.     

Rate dependence of temperature fields and energy dissipations in non-static pseudoelasticity

The temperature fields and the energy dissipations of shape memory alloys during the stress-induced martensitic transformations are studied theoretically and experimentally. The effect of the loading rate is analyzed. It was found that the temperature field inside a shape memory alloy sample varies strongly in space and time. The increase rate of the temperature is given by the difference between the rate of the latent heat release and the rate of the heat convection and conduction. The notion and the rate dependence of the energy dissipation are discussed in connection with the stress–strain hysteresis, the entropy production, and the Clausius–Duhem inequality.     

Enhanced visible-light photoelectrochemical and photoelectrocatalytic activity of nano-TiO2/polyimide/Ni foam photoanode

Research on Chemical Intermediates - We report a novel method for fabrication of a nano-TiO2/polyimide (PI)/Ni foam photoanode. Characterization results indicated that porous nanostructured TiO2...     

Doubly stereocontrolled asymmetric Michael addition of acetylacetone to nitroolefins promoted by an isosteviol-derived bifunctional thiourea

A novel class of chiral bifunctional thioureas bearing a chiral lipophilic beyerane scaffold and a tertiary amino group was designed and prepared. The thioureas were proven to be effective for catalyzing the doubly stereocontrolled asymmetric Michael addition between acetylacetone and nitroolefins. The corresponding adducts were obtained in high yields (up to 95%) and with good to excellent enantioselectivities (up to 97%). In addition, the reaction of tert-butyl acetoacetate and trans-β-nitrostyrene also proceeded smoothly with good enantioselectivity.