石英玻璃圆环高速膨胀碎裂过程的离散元模拟

采用离散元算法模拟了石英玻璃圆环受到外加动态载荷时的力学行为. 首先基于flat-jointed粘结模型,通过标准的单轴拉压、三点弯曲等数值实验来标定了石英玻璃的微观参数. 在此模型基础上,数值模拟再现了石英玻璃圆环在不同应变率下的膨胀碎裂过程. 为定量分析数值模拟结果,需要准确确定圆环的碎裂发生时刻. 模拟发现:伴随着石英玻璃圆环的断裂,圆环外表面粒子径向膨胀速度的时程曲线会发生突然升高然后下降的跳动;详细分析表明,这种跳动源自周向的脆性断裂诱发的卸载波(周向拉伸应力急剧下降)以及伴随而来的泊松膨胀,这种径向速度跳动现象为实验中检测脆性断裂发生时刻提供了可能. 进一步的数值研究表明:(1)石英玻璃圆环的断裂应变随着应变率的提高而增大,与韧性金属材料的膨胀环实验结果一致;(2)石英玻璃圆环的碎片平均质量随着应变率的增大而减小;(3)数值计算获得的碎片平均尺寸与已有的理论和实验结果比较吻合. 利用液压膨胀环实验装置对石英玻璃圆环进行了验证性实验,回收得到的碎片形貌及碎片个数与数值模拟的结果基本一致.      

PMMA膨胀环动态拉伸碎裂实验研究

在强动载作用下, 脆性材料的碎裂问题是一个重要的研究课题, 而脆性材料在冲击拉伸载荷下的力学行为的实验研究相对较匮乏. 提出了一种动态拉伸断(碎)裂的液压膨胀环实验技术, 可用于准脆性/脆性材料的动态拉伸. 利用该技术对有机玻璃(PMMA)圆环试件进行了不同膨胀速度下的动态碎裂实验研究. 从回收碎片的断口形貌和碎片内部残余裂纹观察可知试件的破碎由环向拉伸应力造成, 碎片断口处发出的稀疏波会将周围的拉伸应力卸载, 从而抑制其他裂纹的进一步发展. 利用超高速相机记录了试件的膨胀碎裂过程, 利用DISAR激光速度干涉仪获得了试件外表面粒子的径向膨胀速度历史, 通过试件上的应变片获得了试件的应变历史和断裂应变. 实验结果表明: 在拉伸应变率150\mathrm{~}500s^{-1}范围, 材料的动态断裂应变低于准静态加载下的断裂应变, 体现出“动脆”现象; 随着加载应变率的提高, PMMA 材料的碎片尺寸减小; 无量纲化的PMMA圆环的平均碎片尺寸介于韧性碎裂模型和脆性碎裂模型的预测数值之间, 反映出材料的准脆性特性.      

Nonlinear dynamic analysis of cantilevered piezoelectric energy harvesters under simultaneous parametric and external excitations

The nonlinear dynamics of cantilevered piezoelectric beams is investigated under simultaneous parametric and external excitations. The beam is composed of a substrate and two piezoelectric layers and assumed as an Euler–Bernoulli model with inextensible deformation. A nonlinear distributed parameter model of cantilevered piezoelectric energy harvesters is proposed using the generalized Hamilton's principle. The proposed model includes geometric and inertia nonlinearity, but neglects the material nonlinearity. Using the Galerkin decomposition method and harmonic balance method, analytical expressions of the frequency–response curves are presented when the first bending mode of the beam plays a dominant role. Using these expressions, we investigate the effects of the damping, load resistance, electromechanical coupling, and excitation amplitude on the frequency–response curves. We also study the difference between the nonlinear lumped-parameter and distributedparameter model for predicting the performance of the energy harvesting system. Only in the case of parametric excitation, we demonstrate that the energy harvesting system has an initiation excitation threshold below which no energy can be harvested.We also illustrate that the damping and load resistance affect the initiation excitation threshold.     

THE NUMERICAL STUDY OF AIRFLOW ALTERATION CAUSED BY NASAL TEXTURAL ANOMALY AND DIORTHOSIS 1)

鼻腔结构的改变将伴随鼻腔空气动力学特性改变,进而促使下鼻甲等发生自适应性变化。选取鼻中隔偏曲患者并行鼻中隔偏曲矫正术,部分行下鼻甲骨折外移术,将术前和术后患者行鼻腔CT 扫描,根据CT数据对鼻腔气道进行表面三维重建,运用计算流体动力学方法分析术前和术后鼻腔气道的空气动力学特征。通过研究发现,鼻腔结构矫正手术不是以双侧鼻腔气道容积对称为目的,而是应将整个鼻腔结构看作一个整体,尽可能地保护鼻腔的\绿化带",最终达到重塑鼻腔结构之目的,使鼻腔的生理功能恢复正常。     

基于硅杂蒽类染料的荧光探针及其应用

近年来,荧光成像技术为人们研究活体细胞及组织内的化学生物学过程提供了有效的研究工具,可以无损、实时、原位地以高时空分辨率实现对目标物进行生物荧光成像与分析。荧光成像技术在生物学、环境监测、临床诊断和药物发现等诸多研究领域发挥着越来越重要的作用。生物荧光成像技术的最新进展对发展新型小分子荧光染料及探针提出了更高的要求。激发和发射波长位于近红外光区（600~900 nm）的荧光染料及探针由于具有光毒性低、生物分子自发荧光干扰小、光散射低、组织穿透能力强等优点,非常适合用于生物荧光成像领域。通过将罗丹明分子中O桥原子用Si代替,得到了一类新型的探针分子--硅杂蒽类荧光探针。这类染料分子在保留了氧杂蒽荧光染料优越的光学性质的同时,光谱发生明显红移,满足了近红外荧光检测的要求,具有良好的生物相容性。本文综述了近年来基于硅杂蒽及其衍生物荧光探针的合成及在金属离子、pH值、小分子、生物酶等检测方面的研究进展,并且简要阐述了基于硅杂蒽类探针分子的识别检测机理以及其在生物成像等方面的应用。     

Preparation of Corn Stalk-Walnut Shell Mix-based Activated Carbon and Its Adsorption of Malachite Green

The mix-based activated carbon derived from corn stalk and walnut shell was prepared by chemical activation method using phosphoric acid as the activator. The optimized conditions for preparation were obtained by the orthogonal experiment, the characterizations of the activated carbon were performed by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy(FTIR), Boehm's titration method and nitrogen adsorption. For the prepared mix-based activated carbon, the highest iodine number, methylene blue number and BET surface area are 720.5 mg/g, 195.0 mg/g and 1187 m²/g, respectively, and the pores are mainly mesopores. The mix-based activated carbon shows the higher adsorption capacity for malachite green than the raw materials, the activated carbons prepared only from corn stalk or walnut shell and the commercial activated carbon. The kinetics and thermodynamics of the adsorption can be satisfactorily described by the pseudo-second-order kinetic model and the Langmuir isotherm model, separately.     

MRI梯度预加重模块的分时复用设计

为获得更优的成像质量和更快的成像速度,磁共振成像（MRI）系统的梯度预加重模块需要具有更多的补偿通道和调节参数,常规预加重模块的设计方案使现场可编程门阵列（FPGA）面临巨大的资源消耗.为解决高性能梯度预加重模块的资源消耗大的问题,本文提出了一种基于分时复用技术的梯度预加重实现方案,以常规方案1/44的资源实现了11通道×4组参数的梯度预加重模块.将该模块用于0.35 T MRI系统,测试了补偿前后的涡流曲线和磁共振图像,结果表明该模块有效降低了系统的涡流,减小了磁共振图像中的涡流伪影.     

Anticancer Activity of Copper Complex of (4R)-(-)-2-Thioxo-4-thiazolidinecarboxylic Acid and 3-Rhodaninepropionic Acid on Prostate and Breast Cancer Cells by Fluorescent Microscopic Imaging

Copper complexes with strong anticancer activity are promising new drugs for treatment of patients with metastatic cancer. Copper 8-hydroxyquinoline-2-carboxaldehyde-thiosemicarbazide (CuHQTS) and copper 8-hydroxyquinoline-2-carboxaldehyde-4,4-dimethyl-3-thiosemicarbazide (CuHQDMTS) were found to have strong anticancer activity against cisplatin-resistant neuroblastoma cells and prostate cancer cells. This study aimed to synthesize and characterize two new anticancer copper complexes, copper complex of (4R)-(?)-2-Thioxo-4-thiazolidinecarboxylic acid (CuTTDC), and copper complex of 3-Rhodaninepropionic acid-copper complex (CuRDPA). Cell growth inhibition and cytotoxicity of CuTTDC and CuRDPA on prostate and breast cancer cells were evaluated with Cell Counting Kits-8 (CCK8) assay and fluorescent microscopic imaging respectively. Strong anticancer activity of CuTTDC and CuRDPA was demonstrated by growth inhibition and cytotoxicity of prostate and breast cancer cells treated with these two copper complexes, supporting further investigation of potential use of these two new anticancer complexes for treatment of prostate and breast cancer metastasis.     

A Quninolylthiazole Derivatives as an ICT-Based Fluorescent Probe of Hg(II) and its Application in Ratiometric Imaging in Live HeLa Cells

As a structural analogue of pyridylthiazole, 2-(2-benzothiazoyl)-phenylethynylquinoline (QBT) was designed as a fluorescent probe for Hg(II) based on an intramolecular charge transfer (ICT) mechanism. The compound was synthesized in three steps starting from 6-bromo-2-methylquinoline, with moderate yield. Corresponding studies on the optical properties of QBT indicate that changes in the fluorescence ratio of QBT in response to Hg(II) could be quantified based on dual-emission changes. More specifically, the emission spectrum of QBT before and after interactions with Hg(II) exhibited a remarkable red shift of about 120 nm, which is rarely reported in ICT-based fluorescent sensors. Finally, QBT was applied in the two-channel imaging of Hg(II) in live HeLa cells.     

Bimetallic NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript> synthesized via confined carburization in NiFe-MOFs for efficient oxygen evolution reaction

Transition metal oxides that derived from metal–organic framework (MOF) precursor have intensively received attention because of their numerous electrochemical applications. Bimetallic Ni-Fe oxides have been rarely reported on the basis of MOF-related strategy. Herein, a bimetallic NiFe₂O₄ was successfully synthesized via confined carburization in NiFe-MOF precursors and characterized by XRD, XPS, SEM, and TEM. After conducting an investigation of oxygen evolution reaction (OER), the as-synthesized NiFe₂O₄ material exhibited good catalytic efficiency and high stability and durability in alkaline media. The as-synthesized NiFe₂O₄ material would promote the development of MOFs in non-noble-metal OER catalyst.