Synthesis and self-assembly behaviors of four-armed amphiphilic polystyrene-b-poly(N-isopropylacrylamide) copolymers

Four-armed amphiphilic block copolymers polystyrene-b-poly(N-isopropyl acrylamide) (PSt-b-PNIPAAM)₄ were synthesized by atom transfer radical polymerization (ATRP) in two steps. Star narrow dispersed polystyrene, (PSt-Br)₄, with controlled number-average molecular weight was firstly synthesized by ATRP of styrene (St) using pentaerythritol tetrakis (2-bromoisobutyrate) (4Bri-Bu) as four-armed initiator. Then, (PSt-b-PNIPAAM)₄ was prepared using (PSt-Br)₄ as macroinitiator by ATRP. The structures of (PSt-Br)₄ and (PSt-b-PNIPAAM)₄ were confirmed by characterization by nuclear magnetic resonance (¹H NMR). The apparent viscosity of the four-armed (PSt-b-PNIPAAM)₄ was significantly lower than that of the linear PSt-b-PNIPAAM with the same amount of repeat units of PSt and PNIPAAM. The self-assembly behavior of the four-armed amphiphilic block copolymers (PSt-b-PNIPAAM)₄ in mixed solution (DMF/H₂O) and the lower critical solution temperature (LCST) of the resulting micelles were investigated by scanning electron microscopy (SEM), dynamic light scattering (DLS) and UV-VIS spectroscopy. The results show that the size of the mono-dispersed spherical micelles decreased with the increment of the chain length of PNIPAAM in the block copolymers, while LCST increased.     

非线性一致同时逼近

设Ω是紧Ｈａｕｓｄｏｒｆｆ空间,Ｃ（Ω）表示定义在Ω上取值于实数域的所有实连续函数全体组成的空间,在Ｃ（Ω）上定义一致范数则Ｃ（Ω）构成一个Ｂａｎａｃｈ空间．定义其中 ｜｜· ｜｜Ｂ是Ｒｍ中给定的范数． 设Ｇ是Ｃ（Ω）的一个非空子集,ｆ１,…,ｆｍ是Ｃ（Ω）中给定的ｍ个函数．若存在ｆ∈Ｇ,满足那么称这样的ｆ是Ｇ对Ｆ的最佳一致同时逼近,其全体记为ＰＧ（Ｆ）． 近年来．最佳同时逼近问题作为单元最佳逼近问题的推广,受到了广泛的关注．文［１－６］在一般的Ｂａｎａｃｈ空间中研究了各种意义下的最佳同时逼近的特征…     

颗粒介质的离散态特性研究

回顾了颗粒介质中应力的分布和传播模式以及物体在颗粒介质中运动所受阻力的研究进展，并报道了我们对颗粒体系中代表离散特性的颗粒尺寸效应对颗粒介质特性影响的研究.研究发现物体由于自身重量在颗粒介质中下沉的深度随着颗粒尺寸的增大单调减小；球体在下陷过程中受到的颗粒床的支撑力，除了在约1 mm范围的表面作用区域以外，与下陷深度之间满足很好的幂率关系，幂值在1.5—1.0之间，并且此幂值随着颗粒尺寸的增大而单调减小.颗粒床的支撑力与下陷深度的幂率关系可解释为颗粒介质内部应力结构重组的宏观反应结果. 关键词： 颗粒物质 离散介质力学     

Spatio-temporal expression of a novel neuron-derived neurotrophic factor (NDNF) in mouse brains during development

Background  

Neuron-derived neurotrophic factor (NDNF) is evolutionarily well conserved, being present in invertebrate animals such as the nematode, Caenorhabditis elegans, as well as in the fruit fly, Drosophila melanogaster. Multiple cysteines are conserved between species and secondary structure prediction shows that NDNF is mainly composed of beta-strands. In this study, we aimed to investigate the function of NDNF.     

天祝煤MRF工艺热解焦油的组成分析

本文对天祝煤ＭＲＦ（ＭｕｔｉｓｔａｇｅＲｏｔａｒｙＦｕｒｎａｃｅ）热解焦油进行了常规及元素分析，了解其基本特性；用毛细管色谱分别对焦油各馏分进行了分析，共定性定量了１０３种化合物，酚类化合物以低级酚（苯酚、甲酚）为主，中性化合物为多烷基芳烃衍生物、脂肪族链状烷烃和烯烃。上述分析结果为从焦油中提取酚类化工原料或将其加工成各种燃料油的可行性提供了依据。     

A Sub‐50‐nm Monosized Superparamagnetic Fe3O4@SiO2 T2‐Weighted MRI Contrast Agent: Highly Reproducible Synthesis of Uniform Single‐Loaded Core–Shell Nanostructures

Oleic acid stabilized superparamagnetic iron oxide nanoparticles (SPION) were selected as the cores for fabrication of sub‐50‐nm monodisperse single‐loaded SPION@SiO₂ core–shell nanostructures. Parameters that influence the formation of SPION@SiO₂ in the water‐in‐oil reverse microemulsion system have been systematically investigated. The sufficiently high concentration of well‐dispersed SPION, together with an appropriately low injection rate of tetraethoxysilane, were found to be the keys to efficiently prevent the homogeneous nucleation of silica and obtain a high‐quality single‐loaded core–shell nanocomposite. A more detailed mechanism for incorporating oleic acid capped inorganic functional nanoparticles into silica is proposed on the basis of previous reports and our new experimental results. Finally, the as‐synthesized SPION@SiO₂ nanospheres are exploited as an MRI‐enhanced contrast agent, and their contrast effect in solution is tested by using a clinical MRI instrument.     

Optical properties of AgI/Ag infrared hollow fiber in the visible wavelength region

We report on AgI/Ag infrared hollow fiber with low-loss in visible region. Improved methods of silver plating and iodination were proposed to fabricate the hollow fiber. The surface roughness of the silver layer and the silver iodide layer was reduced by the pretreatment with an SnCl2 solution and low iodination temperature. Losses for the Er:YAG and green laser light were 0.4 and 7dB/m. The loss property of green laser beam was low to deliver a pilot beam for the invisible infrared laser light. Owing to the smooth and uniform AgI film, the loss spectrum of the hollow fiber showed clear interference peaks in the visible region. An empirical formula for AgI material dispersion was derived, which is of special importance for the design of high-performance AgI/Ag hollow fiber.     

改进的Herriott型光学长程池

用凹面反射镜和平面反射镜组成结构简单、光路易调的光多次反射装置,计算了这种光学系统的稳定性条件。考察实际入射光束的直径和发射角,给出了最大反射次数的求法。制成适用于钛宝石激光光声光谱仪的光56次通过的长程池。理论计算的反射光斑分布与实验观测一致。这个技术有利于提高光声光谱和吸收光谱的探测灵敏度。     

航天相机主动热控测试系统设计

为了检测航天相机主动热控系统的功能、性能及可靠性,设计了主动热控仿真测试系统。依据传热学基本定律、航天器轨道理论和热控策略,给出了计算航天相机温度场的热网络数学模型,使主动热控系统能在模拟的空间热环境中连续工作,实现了对主动热控系统的闭环仿真测试。采用两个数字电位器相串联的方法模拟温度传感器的走势,得到的最大阻值为100 kΩ,精度达到10Ω,符合设计中对总电阻和电阻变化率的需求,实现了对主动热控系统的功能、性能以及可靠性的仿真测试。     

扩展的Jacobi椭圆函数展开法和Zakharov方程组的新的精确周期解

对Jacobi椭圆函数展开法进行了扩展，且利用这一方法求出了Zakharov方程组的一系列新的精确周期解，在极限情况下可得到相应的孤波解，补充了前面研究的结果. 关键词： Jacobi椭圆函数展开法 非线性发展方程 精确解 周期解