绳系小球上升最高点速度参数的设置

在高中阶段学生所学习的曲线运动中,竖直面内的圆周运动比较典型、综合的运动,其运动过程存在较多变数和不确定性.绳系小球或者单轨光滑内侧的物体在竖直面内的圆周运动,是学习圆周运动知识过程中一个难点.其中的变数和不确定性是由设置竖直面内最低点的速度大小不同所决定的.不同的速度大小就会有不同的运动过程,比如是一般的摆动、完整的圆周运动还是圆周运动与斜上抛运动结合,求解最大高度时的方法大不相同.下面通过分析例题,总结求最大高度的方法,讨论不同难易度的题目应如何设置最低点的速度大小.     

Calculations on polarization properties of alkali metal atoms using Dirac–Fock plus core polarization method

A semi-empirical atomic structure model method is developed in the framework of a relativistic case. This method starts from Dirac-Fock calculations using B-spline basis set. The core-valence electron correction is then treated in a semiempirical core polarization potential. As an application, the polarization properties of alkali metal atoms, including the static polarizabilities and long-range two-body dispersion coefficients, have been calculated. Our results are in good agreement with the results obtained from ab initio relativistic many-body perturbation method and the available experimental measurements.     

低温凝胶燃烧法合成Y2O3∶Er3+，Yb3+纳米晶上转换发光材料

分别以柠檬酸和甘氨酸为燃烧剂,采用低温凝胶燃烧法合成了Er³⁺、Yb³⁺共掺Y₂O₃纳米晶粉体。通过TG-DSC、XRD、SEM等分析手段对两种燃烧剂所对应的反应过程及纳米晶粉体的物理性能进行了分析,结果表明甘氨酸法具有更高的反应效率、更好的粉体分散性及粒径均匀性。在980 nm激光二极管(LD)激发下,对甘氨酸法所得样品的上转换发光性能分析表明,绿光和红光发射谱带分别来自于Er³⁺的⁴S_3/2/ ²H_11/2→ ⁴I_15/2和⁴F_9/2→ ⁴I_15/2跃迁。此外,对Er³⁺和Yb³⁺掺杂浓度、粉体煅烧温度对纳米晶样品上转换发光性能的影响进行了讨论。     

基于上转换纳米粒子的低损伤神经界面技术

Optogenetics is a neuromodulation technology that combines light control technology with genetic technology, thus allowing the selective activation and inhibition of the electrical activity in specific types of neurons with millisecond time resolution. Over the past several years, optogenetics has become a powerful tool for understanding the organization and functions of neural circuits, and it holds great promise to treat neurological disorders. To date, the excitation wavelengths of commonly employed opsins in optogenetics are located in the visible spectrum. This poses a serious limitation for neural activity regulation because the intense absorption and scattering of visible light by tissues lead to the loss of excitation light energy and also cause tissue heating. To regulate the activity of neurons in deep brain regions, it is necessary to implant optical fibers or optoelectronic devices into target brain areas, which however can induce severe tissue damage. Non- or minimally-invasive remote control technologies that can manipulate neural activity have been highly desirable in neuroscience research. Upconversion nanoparticles (UCNPs) can emit light with a short wavelength and high frequency upon excitation by light with a long wavelength and low frequency. Therefore, UCNPs can convert low-frequency near-infrared (NIR) light into high-frequency visible light for the activation of light-sensitive proteins, thus indirectly realizing the NIR optogenetic system. Because NIR light has a large tissue penetration depth, UCNP-mediated optogenetics has attracted significant interest for deep-tissue neuromodulation. However, in UCNP-mediated in vivo optogenetic experiments, as the up-conversion efficiency of UCNPs is low, it is generally necessary to apply high-power NIR light to obtain up-converted fluorescence with energy high enough to activate a photosensitive protein. High-power NIR light can cause thermal damage to tissues, which seriously restricts the applications of UCNPs in optogenetic technology. Therefore, the exploration of strategies to increase the up-conversion efficiency, fluorescence intensity, and biocompatibility of UCNPs is of great significance to their wide applications in optogenetic systems. This review summarizes recent developments and challenges in UCNP-mediated optogenetics for deep-brain neuromodulation. We firstly discuss the correspondence between the parameters of UCNPs and employed opsins in optogenetic experiments, which mainly include excitation wavelengths, emission wavelengths, and luminescent lifetimes. Thereafter, we introduce the methods to enhance the conversion efficiency of UCNPs, including optimizing the structure of UCNPs and modifying the organic dyes in UCNPs. In addition, we also discuss the future opportunities in combining UCNP-mediated optogenetics with flexible microelectrode technology for the long-term detection and regulation of neural activity in the case of minimal injury.     

基于“1+2”模式的结构化学课程在线教学实践

Since the outbreak of novel coronavirus pneumonia (NCP) at the beginning of this year, Chinese government acted immediately and made some regulations to control the epidemic NCP and promote the recovery of society and industry including education. Chinese universities stayed on the online courses without suspension on teaching and learning. Herein, we report online teaching of structural chemistry course based on the teaching mode of online live broadcast platform, online course resources and management platforms ("1 + 2" mode). This may promote online teaching, and take advantage of online live broadcast and massive open online courses, which achieves good teaching and learning experiences on structural chemistry course.     

维生素 E型人工膝关节在ISO标准步态与上楼梯运动下的磨损情况对比

为研究人工膝关节假体在ISO标准步态与上楼梯运动负载下的摩擦磨损情况,通过对日常活动频次及动力学和运动学的研究与分析,基于人工膝关节磨损试验机,以新型Vitamin E型人工膝关节为对象进行500万次标准步态磨损测试加200万次上楼梯运动磨损测试. 结果表明正常步态阶段的磨损率为4.34 mg/mc,上楼梯运动阶段的磨损率为5.95 mg/mc. 上楼梯运动相比标准步态对半月板衬垫的磨损量造成更大的影响,半月板衬垫表面形貌相较标准步态磨损后表面形貌也发生了显著变化,出现了条纹图案和局部凹陷,这种表面形貌结果更接近于临床半月板衬垫取出物的表面形貌,目前对于人工膝关节假体的标准磨损测试方式不够全面,需要进一步改进整个测试的方案才能更好地体现体外磨损测试的意义.      

基于光滑粒子流体动力学的滑油泵数值仿真

基于光滑粒子流体动力学方法,构建齿轮泵壳体及内部流体的粒子模型,对内啮合齿轮泵在不同工况下的流量特性进行数值模拟。首先设置了均匀分布的油泵出入口压强,计算得到的流量结果与试验结果吻合,且在中低转速下流量与转速呈线性关系;针对高转速下油泵流量降低的问题,通过适当减小周期模型内部的流体粒子数反映流量降低,获得了与试验值相吻合的连续转速流量的模拟结果;针对影响齿轮泵性能的间隙和空化现象,结合模型特点给出了相应的近似处理方法。通过以上研究,将SPH方法成功地应用于滑油泵问题的分析计算。     

点阵式上转换板在激光光斑采集中的应用研究

 通过在镜头前加装上转换板,利用其快速的红外上转换功能可以提高CCD对于低频窄脉冲光斑的采集效率。然而在利用传统面阵式工艺制成的上转换板采集光斑的过程中,普遍存在因上转换材料内部漫反射及局部饱和效应造成的光斑形状和光强分布的失真。针对上述问题,提出了一种新的点阵式上转换板制作工艺,并设计了点阵式上转换板光斑采集成像质量对比实验。实验结果表明,点阵式上转换板对低频窄脉冲光斑有更好的采集效果。为评价点阵式上转换板所采集光斑的成像质量,建立了相应的评价模型。     

基于SOI非对称马赫曾德尔结构的集成矢量和微波光子移相器(英文)

设计和分析了一种基于SOI(绝缘体上的硅)脊型波导非对称马赫曾德尔结构的集成矢量和微波光子移相器。对于10 GHz的微波信号,设定非对称两臂的长度差为3 983μm时,其相应的时间延迟约为47 ps。分别在两臂上集成了一个热光可调谐可变光衰减器用于光学调谐,当衰减单元的折射率在0～6×10-3变化时,实现了10 GHz微波信号在0～180°的相位调谐。该器件尺寸小、结构紧凑,易于实现片上集成,在光控相控阵雷达中很有应用前景。     

Yb~(3+)/Er~(3+)掺杂氟氧化物微晶玻璃的制备与发光性能

采用高温熔融法制备了Yb3+/Er3+掺杂的氟氧化物发光微晶玻璃,确定了最佳熔化温度(1 100℃)和退火温度(440℃,480℃)。测定得到基质玻璃的透过率为85%,掺入稀土后,透过率有所下降,并出现了稀土离子的特征吸收峰。980 nm半导体激光器(LD)激发下样品的上转换发射光谱存在4个明显的发射峰,分别为410,532,546和656 nm,对应于2H9/2→4I15/2,2H11/2→4I15/2,4S3/2→4I15/2和4F9/2→4I15/2跃迁。研究了不同Yb3+/Er3+(摩尔分数)和Er3+浓度对上转换发光强度的影响,当Yb3+∶Er3+=4∶1、Er3+摩尔分数为1.5%时,上转换发光强度达到最高。根据发光强度与泵浦功率之间的关系,确定了上转换发射均为双光子过程。讨论了Yb3+,Er3+离子间的能量传递,建立了上转换发光机制。