溶剂热插层法制备荧光石墨相氮化碳量子点及其在Fe3+检测中的应用

利用溶剂热法, 基于氢氧化钾的插层作用制备了荧光氮化碳量子点(g-C₃N₄ QDs). 所获得的氮化碳量子点具有良好的水溶性和荧光稳定性. 透射电子显微镜(TEM)照片显示, 氮化碳量子点的粒径约为2.3 nm; X射线光电子能谱(XPS)和红外光谱(FTIR)结果表明, 氮化碳量子点表面存在大量的亲水基团; 荧光发射光谱(PL)结果表明, 氮化碳量子点具有激发波长依赖性. 基于三价铁离子(Fe³⁺)对荧光氮化碳量子点荧光的猝灭现象, 构建了一种用于检测Fe³⁺的荧光传感器, 在Fe³⁺浓度为5~100 μmol/L范围内, 检测体系表现出良好的线性关系, 检出限约为0.5 μmol/L, 实现了对Fe³⁺的高效、 灵敏、 选择性检测.     

A novel approach to designing cylindrical-surface shimcoils for a superconducting magnet of magnetic resonance imaging

For a superconducting magnet of magnetic resonance imaging (MRI), the novel approach presented in this paper allows the design of cylindrical gradient and shim coils of finite length. The method is based on identification of the weighting of harmonic components in the current distribution that will generate a magnetic field whose z-component follows a chosen spherical harmonic function. Mathematical expressions which relate the harmonic terms in the cylindrical current distribution to spherical harmonic terms in the field expansion are established. Thus a simple matrix inversion approach can be used to design a shim coil of any order pure harmonic. The expressions providing a spherical harmonic decomposition of the field components produced by a particular cylindrical current distribution are novel. A stream function was applied to obtain the discrete wire distribution on the cylindrical-surface. This method does not require the setting of the target-field points. The discussion referring to matrix equations in terms of condition numbers proves that this novel approach has no ill-conditioned problems. The results also indicate that it can be used to design cylindrical-surface shim coils of finite length that will generate a field variation which follows a particular spherical harmonic over a reasonably large-sized volume.     

基于生灭过程的多斑块毒杂草入侵模型及空间模拟

本文将生灭过程模型应用到多斑块毒杂草入侵问题中,研究毒杂草与周围有限数量斑块的可食牧草之间的入侵关系.借助生灭过程理论,利用全期望公式构建微分方程,计算出毒杂草的期望值.通过讨论极限期望,分析得出毒杂草成功入侵至周围斑块的条件.采用元胞自动机理论将入侵模型扩展到空间网格进行模拟研究,分析毒杂草属的空间分布类型,为毒杂草的控制提供数据支持.研究结果表明:(1)若毒杂草的内禀增长率大于死亡率且内禀增长率和死亡率之差大于毒杂草的入侵率时,毒杂草成功入侵至可食牧草的概率变大,增加了可食牧草灭绝的风险,不利于可食牧草的续存;(2)若毒杂草的内禀增长率小于死亡率或内禀增长率和死亡率之差小于毒杂草的入侵率时,毒杂草没有足够的生物量向可食牧草入侵,毒杂草成功入侵至可食牧草的概率变小;(3)毒杂草的入侵作用影响了毒杂草种群的空间分布特征,加快了空间分布的聚集程度.     

Ab-Initio Study of Electronic Structure and Magnetic Properties of Pipz-H2 [MnF4（HF2）]

The full-potential linearized augmented plane wave method was applied to study the electronic and the magnetic properties of the compound pipz-H2[MnF4(HF2)](pipz=piperazine). The band structure, the total density of states, the partial density of states and the electron density were calculated to explain the electronic and the magnetic properties of pipz-H2[MnF4(HF2)] in the ferromagnetic state. It is found that the magnetic moment of the molecule mainly comes from the Mn atoms with partial contribution from the F atoms. The symmetrical σ/σ bonds via H atoms along Mn-F-H-F-Mn chains and the weak direct-exchange interaction between F(2), F(3) and Mn atoms have effect on the electronic structure and the magnetism of pipz-H2 [MnF4(HF2)].     

带电球面和带电球体电场强度和电势分布求解探讨

在大学物理静电场的教学中, 与球形有关的问题很典型, 比如带电球面和带电球体周围空间的电场强 度和电势分布问题, 不同电荷密度分布带电球体周围空间的电场强度和电势分布的求解问题, 本文对这些球形带电 体系进行分析探讨, 分别根据定义式求解和高斯定理求解, 并找出了其规律式和特点     

冷凝泵型稀释制冷机实验研究

极低温(<1 K)环境对于凝聚态物理、天文观测和量子计算等前沿领域具有重要意义,其中稀释制冷是应用最广泛的极低温制冷技术.针对小冷量应用的冷凝泵型稀释制冷机利用冷凝泵实现³He的低温循环,无需复杂的机械泵组和连接气路,具有结构紧凑、操作便利、成本低等优势,从而成为新的研究热点.本文围绕冷凝泵型稀释制冷机,介绍了其制冷原理和系统架构,设计并搭建了预冷系统、稀释低温系统和测量系统,并对整机进行了实验研究.辅助多测温点测量系统,通过多次实验总结了稀释低温循环过程,由吸附制冷机预冷、稀释循环启动和稀释制冷三个阶段组成,并且分析了系统启动和运行特性.经过测试,实验最低温度可达108 mK.该制冷机可以很方便地拓展低温平台的制冷温区,为凝聚态物理、材料、医学研究等前沿领域提供重要支撑.     

卷烟烟气总粒相物中氟节胺含量的检测方法

建立了气相色谱电子捕获器法检测卷烟抽吸过程中氟节胺向主流烟气总粒相物中转移量的方法,卷烟在标准条件下抽吸,用剑桥滤片捕集主流烟气总粒相物,经乙腈提取、石墨碳黑固相萃取柱或自制混合层析柱净化、GC/ECD检测后,外标法定量.氟节胺在0.02 ～20 mg/L范围内线性关系良好,检出限为9.14×10-6 g/L.加标量为...     

水热法快速制备荧光氧化石墨烯量子点及其在细胞成像中的应用

作为一种新型荧光纳米材料,氧化石墨烯量子点(GO QDs)凭借其良好的水溶性和生物相容性得到广泛的关注。以氧化石墨烯为原料,过氧化氢为氧化剂,一步水热法在90 min内快速制备氧化石墨烯量子点,实现了快速、高效及绿色制备氧化石墨烯量子点。所制备得到的氧化石墨烯量子点分布均匀,透射电镜(TEM)图片表明氧化石墨烯量子点粒径分布在2.25～5.25 nm,傅里叶红外光谱(FTIR)和X射线电子能谱(XPS)显示氧化石墨烯量子点表面含有大量的羟基、羧基、羰基等含氧功能团,表明氧化石墨烯量子点具有很好的水溶性。荧光发射光谱(PL)表明氧化石墨烯量子点具有激发波长依赖性。基于其独特的纳米结构,良好的光学性能和生物相容性,氧化石墨烯量子点可替代传统荧光纳米材料应用于细胞成像。