热声系统中回热器特征阻抗与传播常数的研究

针对本实验室一台声驱动热声系统,采用传递函数法研究声驱动系统中回热器的特征阻抗和传播常数.通过调节谐振管长度,改变回热器表面的阻抗,从理论上分析了回热器网络传输方程中的声传播常数、特征阻抗与系统网络元件中的阻抗、导纳和流的关系.并且进一步讨论有无换热器以及不同的加热功率对回热器网络参数的影响.结论有利于进一步量化回热器的网络参数.     

反应扩散系统中波传播的锁频现象

在空间延展系统中,当增强外部光强时,作者观察到波传播的N∶N-1(N≥2)锁频现象.此现象是在光敏BZ反应实验中观察到的.通过构建一个映射函数,发现在波周期和外部光强的关系中存在魔鬼阶梯,并且此阶梯与实验数据相吻合.     

牵引变流器网侧电流谐波抑制研究

作为电力机车牵引传动系统核心部件的牵引变流器是牵引供电网的主要谐波来源之一。牵引变流器采用的单相四象限整流器,输出含有二次脉动,且工作开关频率较低,导致变流器网侧电流谐波问题严重。目前单相四象限整流器的控制脉冲产生主要采用SPWM技术。与SPWM相比,SHEPWM（特定谐波消除PWM）可以针对性的消除特定的谐波,谐波含量更小,效率更高,但其无法消除调制波中本身就存在的谐波。针对SHEPWM调制策略进行了分析设计,同时对陷波滤波器技术、PR控制策略和LC回路在降低谐波含量中的作用进行深入分析。经过合理的方案选择,有效的降低了网侧电流谐波含量,并通过MATLAB仿真实验进行了分析验证。     

川西平原还田秸秆腐解释放DOM的光谱特征

为掌握川西平原保护性耕作模式下还田秸秆腐解过程的光谱学特性,追溯还田秸秆对川西地区生态系统结构的影响过程,采集了该地区主要种植作物油菜、水稻的秸秆样本,利用紫外-可见吸收光谱(UV-Vis)、三维荧光光谱(3D-EEM)和傅里叶变换红外光谱(FTIR)三种光谱学表征手段,阐明秸秆各腐解阶段溶解性有机质(DOM)的光谱学特征,对比不同农作物秸秆快速淋溶阶段DOM(0~0.5 d)与腐解过程(0.5~90 d)的光谱学特征差异性,解析其变化机理。结果表明： 还田秸秆腐解过程中DOM的光谱学特性差异明显,伴随着芳香性物质的溶出、降解以及新生腐殖类物质的形成;由秸秆快速淋溶阶段释放DOM的E₂/E₃值最大而SUVA₂₅₄值最小可知该阶段溶出的物质芳香性和分子量相对较小;其芳香性组分的溶出主要集中在腐解前期(≤10 d),表现于该阶段E₂/E₃值逐渐减小且SUVA₂₅₄值逐渐增大,DOM中多糖峰、芳香C和酰胺峰变弱;难分解的纤维素、半纤维素和大分子蛋白质主要在腐解后期被降解;DOM中酚类、羰基类和羧酸类物质数量增加,使得DOM与有机污染物、金属离子的相互作用增强,进而调节农田土壤中污染物的迁移转化过程。本研究为川西平原秸秆还田的环境意义提供了基础数据和新证据,为该地区农业废弃物处理与资源化提供了依据。     

双面声阵列波束形成的正则化改进算法

双面声阵列波束形成能够区分识别位于不同扫描平面的相干声源,然而该算法在低信噪比条件下识别精度较低。针对此问题提出一种迭代正则化改进算法,通过迭代方法更新正则化矩阵与波束形成输出,在不断提升正则化稳定性、抑制干扰旁瓣的基础上使声学云图主瓣向实际相干声源点处聚焦。数值仿真与实验算例结果显示,改进算法在中高频代表频率下能够正确区分相干声源前后方位,并具有相对原算法更高的识别精度。从而表明:从反问题正则化角度对原算法进行优化改进是理论可行的;正则化矩阵的具体形式与广义逆波束形成输出的空间分辨率紧密相关,且可通过迭代方法将二者整合以提高声源识别精度。     

Material transport in dip-pen nanolithography

Dip-pen na.nolithography （DPN） is a useful method for directly printing materials on surfaces with sub-50nm resolution. Because it, involves the physical transport of materials from a scanning probe tip to a surface and the subsequent chemical interaction of that material with the surface, there are many factors to consider when attempting to understand DPN. In this review, we overview the physical and chemical processes that are known to play a role in DPN, Through a detailed review of the literature, we classify inks into three general categories based on their transport properties, and highlight the myriad ways that. DPN can be used to perform chemistry at the tip of a scanning probe.     

Room-Temperature Magnetism Realized by Doping Fe into Ferroelectric LiTaO3

We synthesize LiTal-x FexO3-σ （LTFO） remain single phase up to x = 0.09 ceramics by the conventional solid-state reaction method. The samples The magnetic measurements show that the doping of Fe successfully realizes ferromagnetism of LTFO at room temperature. The dielectric measurements indicate that LTFO is ferroelectric, similarly to LiTaO3 （LTO）, but its ferroelectric Curie temperature seems to decrease with the increasing Fe content. By means of doping Fe ions into LTO, the coexistence of spontaneous electric polarization and spontaneous magnetic moment is realized at room temperature.     

Microwave-assisted synthesis of Cu2ZnSnS4 nanocrystals as a novel anode material for lithium ion battery

One-dimensional ordered quantum-ring chains are fabricated on a quantum-dot superlattice template by molecular beam epitaxy. The quantum-dot superlattice template is prepared by stacking multiple quantum-dot layers and quantum-ring chains are formed by partially capping quantum dots. Partially capping InAs quantum dots with a thin layer of GaAs introduces a morphological change from quantum dots to quantum rings. The lateral ordering is introduced by engineering the strain field of a multi-layer InGaAs quantum-dot superlattice.     

基于单次旋转的旋转非对称面形误差绝对检测技术研究

绝对检测技术是剔除干涉仪系统误差进而提高面形检测精度的有效手段。基于单次旋转的绝对检测技术由被测球面绕光轴旋转前后的检测数据,采用基于最小二乘法的Zernike多项式拟合,剔除系统误差,获得被测面的旋转非对称面形误差。详细推导了理论计算公式,分析了单次旋转角度对算法检测精度的影响,并和多次旋转法作了对比,其残差均方根(RMS)值约为1.5nm。该方法只需一次旋转两次检测,在保证检测精度的同时简化了检测过程。     

Corrosion resistance and blood compatibility of lanthanum ion implanted pure iron by MEVVA

Pure iron is a potential material applying for coronary artery stents based on its biocorrodible and nontoxic properties. However, the degradation characteristics of pure iron in vivo could reduce the mechanical stability of iron stents prematurely. The purpose of this work was to implant the lanthanum ion into pure iron specimens by metal vapor vacuum arc (MEVVA) source at an extracted voltage of 40 kV to improve its corrosion resistance and biocompatibility. The implanted fluence was up to 5 × 10¹⁷ ions/cm². The X-ray photoelectron spectroscopy (XPS) was used to characterize the chemical state and depth profiles of La, Fe and O elements. The results showed lanthanum existed in the +3 oxidation state in the surface layer, most of the oxygen combined with lanthanum and form a layer of oxides. The lanthanum ion implantation layer could effectively hold back iron ions into the immersed solution and obviously improved the corrosion resistance of pure iron in simulated body fluids (SBF) solution by the electrochemical measurements and static immersion tests. The systematic evaluation of blood compatibility, including in vitro platelets adhesion, prothrombin time (PT), thrombin time (TT), indicated that the number of platelets adhesion, activation, aggregation and pseudopodium on the surface of the La-implanted samples were remarkably decreased compared with pure iron and 316L stainless steel, the PT and TT were almost the same as the original plasma. It was obviously showed that lanthanum ion implantation could effectively improve the corrosion resistance and blood compatibility of pure iron.