Surfactant Mediated Microphase Separation in Miscible Block Copolymer of Poly(4-vinyl pyridine-b-hydroxybutylacrylate)

Chinese Journal of Polymer Science - Miscible disordered block copolymers (BCPs) are rarely studied due to the limits in self-assembly into ordered microstructures. Herein, we proposed a facile...     

AxMn1-xFe2O4铁氧体(A=Zn,Ni)中阳离子的占位有序化行为研究

基于尖晶石晶体结构信息,本文采用热力学三亚晶格模型,将材料热力学计算和第一性原理计算相结合,研究了Zn_xMn_(1-x) Fe_2O_4和Ni_xMn_(1-x)Fe_2O_4立方相中的Zn~(2+)、Ni~(2+)、Mn~(2+)以及Fe~(3+)在8a和16d亚晶格上的占位有序化行为。结果表明:在锰铁氧体中,室温下Mn~(2+)完全占据在8a亚晶格上,Fe~(3+)完全占据在16d亚晶格上,属于正尖晶石结构;随着热处理温度升高,在1 273 K达到热处理平衡时的占位构型为(Fe~(3+)0.09Mn~(2+)0.91)[Fe~(3+)1.91Mn~(2+)0.09]O_4,在热处理温度升至1 473 K时,达到热处理平衡时的占位构型为(Fe~(3+)0.11Mn~(2+)0.89)[Fe~(3+)1.89Mn~(2+)0.11]O_4,均与实验结果符合较好。在锌铁氧体中,室温下Zn~(2+)完全占据在8a亚晶格上,Fe~(3+)完全占据在16d亚晶格上,属于正尖晶石结构;在热处理温度较高时,Zn~(2+)和Fe~(3+)发生部分置换,符合实验结果。在镍铁氧体中,半数的Fe~(3+)在室温下占据在8a亚晶格上,Ni~(2+)与剩下另一半的Fe~(3+)共同占据在16d亚晶格上,仅在热处理温度较高的时候发生微弱变化,亦与已有的实验结果吻合。在此基础上,本文进一步通过热力学模型研究了立方相尖晶石结构的Zn_xMn_(1-x)Fe_2O_4、Ni_xMn_(1-x)Fe_2O_4复合体系中阳离子占位行为与热处理温度对占位的影响规律。     

高功率,红光至中红外可调谐腔内和频光学参量振荡器

本文利用高重复频率,高平均功率大模场面积飞秒光纤激光器作为同步抽运源,抽运以多周期极化掺氧化镁铌酸锂为非线性晶体的单共振光学参量振荡器,获得了高功率可调谐红光至中红外光,信号光调谐范围为1450—2200 nm,闲频光调谐范围为2250—4000 nm,在2 W的抽运功率下,信号光输出波长为1502 nm时获得最大输出功率374 mW,转换效率为18.7%,脉冲宽度为144 fs,此时中红外输出中心波长为3.4μm,平均功率为166 mW.再利用BBO晶体对信号光进行腔内和频,获得和频光输出波长调谐范围为610—668 nm,在4.1 W抽运的情况下,最高平均功率为615 nm处的694 mW,转换效率达16.9%.     

水下平台对卫星上行激光通信研究

在合理选择通信系统参量和通信信道参量的基础上,利用Monte Carlo方法模拟了卫星接收到的水下平台上行激光通信信号.分析了卫星接收信号的空间和时间分布特性,以及与望远镜接收视场角的关系,并计算了接收信号的信噪比,得出了3°望远镜视场角和15 μs信号积分时间的优化参量.基于计算结果,根据激光脉冲的PPM调制方式和最大似然检测方法,计算了系统的通信误码率,同时分析了海气界面、云等传输介质对通信的影响.研究结果表明:根据文中给定通信系统参量,在典型海水、海气界面、云等环境条件下,卫星与激光信号中心水平距离5 km范围内信号误码率<10－4.因此位于水下60 m的水下平台可能实现对卫星上行激光通信.     

水泵水轮机开机过程压力脉动的试验研究

水泵水轮机机组的压力脉动是影响机组稳定性的一个非常重要的因素,而转轮与活动导叶之间的无叶区的压力脉动具有振幅最大、振源复杂的特点。本文通过某抽水蓄能电站的真机的试验数据分析,对机组开机过程中无叶区的压力脉动进行了较为深入的研究,获得了水轮机的开机过程及水泵的开机过程中无叶区的压力脉动的幅值和频谱特性,并对其特点进行了分析。     

Regiospecific and diastereoselective aldol reaction of chiral N-sulfinyl metalloenamines with α,β-unsaturated trifluoromethyl ketones: Asymmetric synthesis of tertiary trifluoromethyl allylic carbinols

Regiospecific and diastereoselective aldol type reaction of chiral N-sulfinyl metalloenamines with α,β-unsaturated trifluoromethyl ketones was reported, which affords the corresponding tertiary trifluoromethyl allylic carbinols in high yields with good diastereoselectivities (dr up to 90:10). The reduction of the condensation product 3a with LiBHEt₃ and Catecholborane provides CF₃-substituted syn- and anti-1,3-amino alcohols 5a and 5b in high yields with excellent diastereoselectivities (dr > 99:1).     

RhIII-Catalyzed C6-Selective Oxidative C−H/C−H Crosscoupling of 2-Pyridones with Thiophenes

A rhodium(III)-catalyzed C6-selective dehydrogenative cross-coupling of 2-pyridones with thiophenes was developed for the synthesis of 6-thiophenyl pyridin-2(1H)-one derivatives. In this reaction, the excellent site selectivity was controlled by the 2-pyridyl directing group on the nitrogen of the pyridone ring. Control experiments indicated that the N-pyridyl was essential for the transformation. To the best of our knowledge, this procedure is the first successful example of the direct C6 heteroarylation of 2-pyridones with electron-rich thiophene derivatives. 4-Pyridone was also used as substrate to generate the corresponding C2 heteroarylated product. Moreover, this pyridyl directing group was readily removable to generate the biheteroaryl structures with a free N−H group.     

Regio- and diastereoselective Reformatsky reaction of chiral fluoroalkyl α,β-unsaturated N-tert-butanesulfinyl ketimines: Efficient asymmetric synthesis of β-fluoroalkyl β-vinyl β-amino esters

Highly regio- and diastereoselective Reformatsky reaction of stable, chiral fluoroalkyl α,β-unsaturated N-tert-butanesulfinyl ketimines was developed, which provided an efficient method for the asymmetric synthesis of structurally diverse β-tetrasubstituted β-fluoroalkyl β-vinyl β-amino esters in good yields and with excellent diastereoselectivities (dr up to 96:4).     

介孔空心球状WC微球结构与晶相形成机理

采用喷雾干燥微球化处理-气固反应法制备了介孔空心球状WC微球，应用扫描电子显微镜(SEM)对微球的形貌变化进行了表征。结果表明，介孔空心球状结构是逐步形成的。其中，空心球状结构形成于前驱体微球化处理过程中，介孔结构形成于空心微球还原碳化过程中。在与样品制备工艺条件相同的情况下，采用原位X射线衍射技术(in situ XRD)对样品的晶相演变规律进行了监测。结果表明，样品在CO/CO₂气氛中进行还原碳化时，当温度缓慢而连续上升到750 ℃时，其晶相变化遵循AMT → WO₃ → WO₂ → W₂C → WC规律;当采用“阶跃式”升温，即温度缓慢而连续上升到400 ℃，然后再快速上升到750 ℃，并在750 ℃下进行还原碳化时，其晶相变化规律为AMT → WO₃ → WO₂ → WC。这说明，样品的晶相演变不仅与还原碳化温度和时间有关，而且与升温方式和升温速率有关。