Fractionated Crystallization Kinetics and Polymorphic Homocrystalline Structure of Poly(L-lactic acid)/Poly(D-lactic acid) Blends: Effect of Blend Ratio

Stereocomplex (SC) crystallization has been an effective way to improve the physical performances of stereoregular polymers. However, the competition between homo and SC crystallizations can lead to more complicated crystallization kinetics and polymorphic crystalline structure in stereocomplexable polymers, which influences the physical properties of obtained materials. Herein, we select the medium-molecular-weight (MMW) poly(_L-lactic acid)/poly(_D-lactic acid) (PLLA/PDLA) asymmetric blends with different PDLA fractions (f_D=0.01–0.5) as the model system and investigate the effects of f_D and crystallization temperature (T_c) on the crystallization kinetics and polymorphic crystalline structure. We observe the fractionated (i.e., multistep) crystallization kinetics and the formation of peculiar β-form homocrystals (HCs) in the asymmetric blends under quiescent conditions, which are strongly influenced by both f_D and T_c. Precisely, crystallization of β-form HCs is favorable in the MMW PLLA/PDLA blends with high f_D (≥0.2) at a low T_c (80–100 °C). It is proposed that the formation of metastable β-form HCs is attributed to the conformational matching between β-form HCs and SCs, and the stronger constrain effects of precedingly-formed SCs in the early stage of crystallization. Such effects can also cause the multistep crystallization kinetics of MMW PLLA/PDLA asymmetric blends in the heating process.

     

从乌龟坐标在动态Vaidya黑洞上的推广谈起

从一类参数未定的一般形式的乌龟坐标变换出发, 找出了在动态Vaidya黑洞背景下能将波动方程化为标准形式且无发散的乌龟坐标所满足的条件. 结果表明, 以乌龟坐标变换为主要特征的Damour-Ruffini方法, 用来计算动态黑洞的Hawking辐射时, 只适用于事件视界, 无法应用于表观视界.     

x射线在毛细导管中传输的模拟计算

阐述了x射线在毛细导管中传输的基本理论，根据光线追迹原理建立了x射线在毛细导管中传输的计算模型.在此基础上使用MATLAB编写程序，实现了对x光经过x光单导管的传输效率和光强分布的模拟计算.计算结果和实验数据进行比较，得到了很好的符合. 关键词： 模拟计算 毛细导管 光线追迹 传输效率 光强分布     

低能He~(2+)入射He原子转移电离实验中出射电子成像研究

利用反应显微谱仪对70keV He2+-He转移电离过程中的出射电子进行了成像,研究了出射电子的空间速度分布特征.结果表明:电子主要集中在散射平面内;在散射平面内,电子速度分布介于零与入射离子速度Vp之间(即前向出射)且在散射离子和靶核核间轴处有一极小值,呈现出典型的双峰结构.出射电子的上述分布特征可由出射电子波函数σ振幅和π振幅的干涉进行定性解释,σ振幅和π振幅对出射电子波函数的贡献与碰撞参数相关.在小碰撞参数下,π振幅的贡献更加明显;而在大碰撞参数下,σ振幅的贡献更加显著.     

Gas–liquid two phase flow measurement method based on combination instrument of turbine flowmeter and conductance sensor

In order to solve the flowrate measurement problem of gas–liquid two phase flow widely existing in gas wells of Daqing oil field in China, a new method has been developed, which is based on the combination instrument of turbine flowmeter and conductance sensor with petal type concentrating flow diverter. The turbine and conductance signals under 104 different flow conditions have been acquired through oil–gas–water three phase flow loop experimental facility. To determine the flow pattern in measurement channel, attractor morphologic characteristics are extracted from the conductance signals. For the total flowrate measurement, based on the turbine fluctuant signals of gas–liquid two phase flow, a statistical model with the average error of 7.9% is set up. With regard to the water cut measurement, the characteristics in time and frequency domains are extracted from the fluctuant conductance signals, and then employing the Support Vector Machine (SVM) soft measurement model used in high-dimension data fitting, the water cut prediction is realized with the average error of 0.038. The results show that the combination instrument of turbine flowmeter and conductance sensor with petal type concentrating flow diverter would be useful in measuring the total flowrate and water cut of gas–liquid two phase flow in gas production wells.     

一种实验教学用蒸发结晶装置的设计

针对目前蒸发结晶实验教学的需要,以实验室常用玻璃器材为主,设计了一种蒸发结晶装置。该装置包括数显加热搅拌装置、蒸发瓶、滴液装置、H型管、套管式换热器、冷凝液接收装置、连接装置和原料液储罐等8个部分,结构简单、占用空间小。并以硫酸铜溶液的蒸发结晶过程为例,对其使用方法进行了研究。通过外形的设计,可实现装置安装时长在15 min内,用时短,拆卸方便;通过控制原料液浓度和流速,实现对晶体的生长速度和形状的调控;原料液可循环使用,原料节约;玻璃器材为主,原理展示清晰;以硫酸铜水溶液为原料液,颜色鲜艳,便于演示。该装置能较好地满足高校工程类专业实验教学的需求。     

SBA-15表面改性及其对介孔La0.8Sr0.2CoO3钙钛矿型催化剂结构和性能的影响

Mesoporous SBA-15 with mesopore diameter up to 10.1 nm was prepared by a hydrothermal method, and was further functionalized to obtain different surface properties. Thus-prepared SBA-15 was employed as a template to synthesize rhombohedrally crystallized mesoporous La_0.8Sr_0.2CoO₃ perovskite via a nanocasting method. The surface properties of the SBA-15 were adjusted by treatment with concentrated hydrochloric acid, trimethylchlorosilane (TMCS), and 3-aminopropyltriethoxysilane (APTES). A series of characterization techniques verified that all the synthesized templates possessed ordered two-dimensional hexagonal mesoporous structure, and the surface was successfully modified with methyl and amino groups. The mesoporous perovskite structure was formed in the samples and the surface properties of SBA-15 significantly influenced the structure and properties of La_0.8Sr_0.2CoO₃ perovskite oxides. Wide-angle X-ray diffraction patterns suggested that the modified silica templates were conducive to the formation of pure perovskite frameworks with good crystallinity. The catalysts also possessed mesoporous structure, as confirmed by small-angle XRD patterns, high-resolution transmission electron microscopy images, and nitrogen adsorption analysis. Moreover, the La_0.8Sr_0.2CoO₃ materials synthesized using surface-functionalized templates exhibited relatively higher catalytic activity and stability in CO oxidation. Complete CO conversion could be achieved at 140℃ using the thus-prepared La_0.8Sr_0.2CoO₃ materials, and no significant loss in catalytic activity was observed after 100 h of on-stream reaction experiments. X-ray photoelectron spectroscopy, H₂ temperature-programmed reduction, and O₂ temperature-programmed desorption experiments revealed that the existence of Co⁴⁺, Sr enrichment in the perovskite structure, and high content of adsorbed oxygen species play a critical role in the enhanced catalytic activity of the catalysts. We also proposed the possible reasons for the effect of surface properties of the silica templates on the structure and properties of the La_0.8Sr_0.2CoO₃ nanomaterials.     

Diastereospecific entry to pyrrolidinyldispirooxindole skeletons via three-component 1,3-dipolar cycloadditions

Practical and diastereospecific three-component 1,3-dipolar cycloaddition reactions of methyleneindolinones, isatins and diverse primary amino acids have been well established. A range of pyrrolidinyldispirooxindole scaffolds with wide structural diversity and complexity were obtained facilely in excellent yields under mild conditions, which hold promising applications in their further pharmacological studies.     

One-pot synthesis of 2-bromo-4,5-diazafluoren-9-one via a tandem oxidation-bromination-rearrangement of phenanthroline and its hammer-shaped donor-acceptor organic semiconductors

An unexpected one-pot tandem procedure of 2-bromo-4,5-diazafluoren-9-one starting from phenanthroline with a yield of up to 50% has been described. The conversion mechanism involves three consecutive oxidation, bromination, and rearrangement reactions. A series of its hammer-shaped donor-acceptor organic semiconductors with solvent-dependent fluorescence have also been constructed via Ullman and/or Friedel-Crafts reaction. Diazafluorenes (DAFs) and derivatives are regarded as promising building blocks or candidates for donor-acceptor organic semiconductors.     

Photoinduced Single-Electron Transfer as an Enabling Principle in the Radical Borylation of Alkenes with NHC–Borane

A photoinduced SET process enables the direct B−H bond activation of NHC–boranes. In contrast to common hydrogen atom transfer (HAT) strategies, this photoinduced reaction simply takes advantage of the beneficial redox potentials of NHC–boranes, thus obviating the need for extra radical initiators. The resulting NHC–boryl radical was used for the borylation of a wide range of α-trifluoromethylalkenes and alkenes with diverse electronic and structural features, providing facile access to highly functionalized borylated molecules. Labeling and photoquenching experiments provide insight into the mechanism of this photoinduced SET pathway.