Magnetic properties of novel superparamagnetic MRI contrast agents based on colloidal nanocrystals

Novel systems based on colloidal magnetic nanocrystals (NCs), potentially useful as superparamagnetic (SP) contrast agents for magnetic resonance imaging (MRI) have been investigated. The NCs we have studied comprise organic-capped single-crystalline maghemite (γ-Fe₂O₃) cores possessing controlled sizes and shapes. We have comparatively examined spherical and tetrapod-like NCs, the latter being branched particles possessing four arms which depart out at tetrahedral angles from a central point. The as-synthesized NCs are passivated by hydrophobic surfactant molecules and thus are fully dispersible in nonpolar media only. The NCs have been made soluble in aqueous solution by applying a procedure based on the surface intercalation and coating with an amphiphilic polymer shell. NMR relaxivities R₁ and R₂ were compared with ENDOREM^®, one of the standard commercial SP-MRI contrast agent. We found that the spherical NCs exhibit R₁ and R₂ relaxivities slightly lower than those of ENDOREM^®, over the whole frequency range; on the contrary, tetrapods show relaxivities about one order of magnitude lower. The physical origin of such difference in relaxivities between tetrapod- and spheres-based nanostructures is under investigation and it is possibly related to different sources of the magnetic anisotropy.     

铝合金表面复合陶瓷防火涂层的制备及性能研究

以无机胶粘剂及陶瓷粉体为原料,制备用于地铁内饰的铝合金板表面阻燃陶瓷涂层.研究了胶粘剂、无机阻燃剂的加入量及料浆粒度与涂层致密度的关系.按照饰面型防火涂料的国家标准(GB12441-2005)和材料非燃性的英国标准(BS476-4)对涂层的理化性能进行检测.结果表明:当粘结剂的用量为60;、添加剂粒度为1～2 μm时,涂层表面均匀、致密、无缩孔.所制备的陶瓷涂层均达到上述标准.涂层的耐火极限高于30 min,不燃,不脱落,无烟,不产生有毒的气体,具有很好的防火阻燃作用.     

On the Synthesis of 1,4,7-Tris(tert-butoxycarbonylmethyl)-1,4,7,10-tetraazacyclododecane

1,4,7-Tris(tert-butoxycarbonylmethyl)-1,4,7,10-tetraazacyclododecane is widely used as an intermediate in the preparation of medically important DO3A and DOTA metal chelators. Despite its commercial availability and importance, the literature describing the preparation and properties of the free base is limited and sometimes unclear. We present herein an efficient synthesis of the hydrobromide salt of 1,4,7-tris(tert-butoxycarbonylmethyl)-1,4,7,10-tetraazacyclododecane, characterize this compound spectroscopically and by X-ray crystallographic analysis, describe its simple conversion to the corresponding free base, characterize this compound spectroscopically and by X-ray crystallographic analysis, and make observations on the reactivity of this interesting and useful compound.     

十六烷基三甲基溴化铵辅助作用下球形、蠕虫状和网状Pd纳米粒子的制备与表征

以十六烷基三甲基溴化铵(CTAB)为表面活性剂,NaBH4为还原剂,通过调节水相体系中CTAB和NaBH4浓度,合成了一系列不同形貌的Pd纳米粒子,合成过程简便易行且环境友好.结果表明,随着CTAB浓度的增加,Pd粒子形貌由纳米微球逐渐向纳米线网络形态转变.CTAB浓度和NaBH4浓度是决定Pd粒子形貌的两个重要因素.     

政府委托下应急物资代储系统激励契约设计

政府委托企业代储应急物资是现实中普遍采用的一种应急物资管理策略,代储企业的努力程度对于保障应急物资的可靠供应具有关键性的作用,但由于代储企业与政府之间存在追求目标的差异,以及信息透明化方面受客观条件制约等因素,代储企业可能会因为长期的“太平无事”而产生倦怠,或者为追求经济效益而减少应有的付出,导致总体的努力程度下降,给应急条件下的物资供应带来隐患。鉴于此,论文采用供应链契约激励的理论,建立政企之间的利益博弈模型,分析政府的激励方式和激励数额对应急物资代储企业努力程度的影响,通过数值仿真寻找最优的参数设置,在此基础上,设计符合实际需要的应急物资代储激励契约,制定相应的奖惩规则,从而为政府有效管理应急物资代储企业,提高其努力程度,提升应急条件下应急物资供应保障能力提供了理论支撑。     

关于大经济金融市场

在Aumann大经济框架下，本文给出具有可测空间经纪人的大金融市场模型；讨论了资产结构完全时均衡的存在性；给出了以经纪人代表效用表出形式的金融资产定价公式，它推广[3]中相关内容。模型更贴近于具有对称信息充分竞争的涵义．     

基于多Agent的心理战效果评估方法研究

心理作战系统是典型的复杂适应系统。以复杂适应系统理论为指导,运用多Agent建模仿真方法,建立了心理战效果评估模型,开发了心理战智能体仿真平台PSYOPASP,对5种心理战防御方案进行仿真实验。     

用线性规划方法求网络计划的最低成本日程

网络计划优化的一个重要内容是研究项目的最低成本日程。本文假定工序在可压缩范围内,直接成本呈线性变化的前提下,以线性规范为工具,提出了一种最低成本日程的优化方法。当借助计算机求解时,该方法更加简单实用。     

一个具有双重反馈作用的异类经纪人herding模型

一个具有双重反馈作用的异类经纪人herding模型被提出.该模型认为,金融市场是由不同大小和行为倾向的经纪人集团组成.当两个不同行为倾向的经纪人集团相遇时,他们有可能发生一次交易;当两个同种行为倾向的经纪人集团相遇时,他们可能合并成一个更大的经纪人集团.交易或合并的成功率跟市场上一次波动程度有关.当两个经纪人集团发生一次交易后,处于亏损方的经纪人集团有可能分化和翻转,分化和翻转的概率取决于经纪人集团的亏损程度和市场信念等因素.数值计算表明,该模型能较好地反映市场的经济行为和动力学特性.