粉末PET固相缩聚的研究

系统地研究了粉末聚酯(PET)固相缩聚,得到了有效的干燥结晶条件:140℃干燥120 min,180℃再结晶45 min,切片含水率低于30μg／g;研究了反应温度,粉末粒径和N2流量对PET固相缩聚的影响,分析粉末固相缩聚存在N2流量阈值的机理。结果表明:反应温度越高,颗粒越小,固相缩聚反应速度越快;粉末 PET预聚体在一定温度下固相缩聚,存在N2流量阈值。在此流量下,达到该温度下的该粒径粉末的最大界面扩散速率和固相缩聚的最大反应速度。相同反应温度下,粉末粒径越小,阈值N2流量越大。     

混凝土工程中常见裂缝问题的预防与处理措施

1前言 混凝土是一种由砂石骨料、水泥、水及其他外加材料混合而形成的非均质脆性材料.     

竞争PSO在多序列联配中的应用

本文提出了一种求解多序列联配的竞争粒子群优化算法,算法根据适应值分类设计了粒子群的惯性权重以及其飞行速度范围,并进行了动态调整,提高了算法的收敛速度和精度;引入了重新初始化机制,有效的避免粒子群优化算法可能出现的早熟现象;提出了一种全新的速度更新模式和竞争策略,增强了算法的能力。实验表明该算法是有效的。     

Numerical study of scattering Legendre moments and effect of anisotropic scattering on SN shielding calculation

The main purpose of this work was to perform a rigorous computational study on scintimammography with a Mura-mask based on Monte Carlo simulation of voxelized breast phantoms. Three main objectives were addressed:(1) verification of Geant4 version 10.4,(2)optimization of the imaging setup, and(3) small tumor detection and localization. We successfully verified the Geant4-based imaging of a commonly used phantom in the field. We used a Mura-mask with a 41× 41 array pattern with adjustable thickness, material, and hole shape(box and cylinder); a low-energy high-resolution collimator with different hole shapes(cylinder and hexagon); and a voxelized breast phantom with different sizes(small, medium,and large) and glandularity percentages(low, medium, and high). We also compared the detector crystal outputs of CdZnTe and NaI(Tl). The simulation was followed by a deconvolution procedure, and the data(images) were statistically emphasized. Statistical metrics indicate that the Mura-mask(W material with 1.5 mm thickness and box holes) combined with a CdZnTe detector leads to the optimum point spread function. Finally, a preliminary study on small-sized tumor detection and localization was conducted with different tumor-to-background ratios(from2 to 12). Tumors with diameters of 5 and 8 mm could be detected, while those of 2 mm were undetectable. Nevertheless, this study enhances our understanding of the early detection of tumors in the field of scintimammography.     

Silk Sericin Enrichment through Electrodeposition and Carbonous Materials for the Removal of Methylene Blue from Aqueous Solution

The recycling and reuse of biomass waste for the preparation of carbon-based adsorbents is a sustainable development strategy that has a positive environmental impact. It is well known that a large amount of silk sericin (SS) is dissolved in the wastewater from the silk industry. Utilizing the SS instead of discharging it into the environment without further treatment would reduce environmental and ecological problems. However, effective enrichment of the SS from the aqueous solution is a challenge. Here, with the help of carboxymethyl chitosan (CMCS), which can form a gel structure under low voltage, an SS/CMCS hydrogel with SS as the major component was prepared via electrodeposition at a 3 V direct-current (DC) voltage for five minutes. Following a carbonization process, an SS-based adsorbent with good performance for the removal of methylene blue (MB) from an aqueous solution was prepared. Our results reveal that the SS/CMCS hydrogel maintains a porous architecture before and after carbonization. Such structure provides abundant adsorption sites facilitating the adsorption of MB molecules, with a maximum adsorptive capacity of 231.79 mg/g. In addition, it suggests that the adsorption is an exothermic process, has a good fit with the Langmuir model, and follows the intra-particle diffusion model. The presented work provides an economical and feasible path for the treatment of wastewater from dyeing and printing.     

TNJ涂料及涂装技术在化纤厂的应用

介绍一种新型的专门适用于化纤行业使用的防腐涂料——TNJ涂料及配套的涂装技术,详细说明了该涂料的优点和喷涂施工中应掌握的要点。     

多相同步电动机中压变频调速装置系统集成

电力电子系统集成对于中大功率电力电子装置而言是要实现其系统结构和部件的标准化.作者以多相同步电动机中压变频调速装置为研究背景,探索了复杂大电力电子装置中的系统集成问题.作者对大电力电子装置进行模块化研究,首先分析如何选择主电路的一级标准模块,如三电平逆变单元的一级标准模块为一相NPC三电平桥臂;然后又分析了如何划分系统的二级标准模块,如整流模块、逆变模块、励磁模块等;随后作者又以多相同步电动机调速系统为例对控制系统进行分层研究,设计了各控制管理层的任务及各层问的信息流通信方式.利用这些研究成果,作者设计、制作了模块化的同步电机调速装置,试验取得了成功.     

Insight into crystal growth and upconversion luminescence property of tetragonal Ba3Sc2F12 nanocrystals

Sc-based nanomaterials have attracted consid-erable attention due to their unique optical properties dif-ferent from those of Ln/Y-based nanomaterials.However,s...     

Molecular Identification of the G-Protein Genes and Their Expression Profiles in Response to Nitrogen Deprivation in Brassica napus

Heterotrimeric guanine nucleotide binding protein (G-protein) consisting of Gα, Gβ, and Gγ subunits is one of the key signal transducers in plants. Recent studies indicated that G-protein has been proposed as an important mediator of nitrogen responses in rice, wheat, and Arabidopsis. However, little is known about these G-proteins in Brassica napus (B. napus), except for three identified G-proteins, BnGA1, BnGB1, and BnGG2. Therefore, the aim of the present study is to characterize the members of the G-protein gene family in allotetraploid B. napus and to analyze their expression profiles in response to nitrogen deprivation. In total, 21 G-protein family members were identified in B. napus, encoding two Gα, six Gβ, and 13 Gγ. Sequence and phylogenetic analyses showed that although genome-wide triploid events increased the number of genes encoding Gα, Gβ, and Gγ subunits, the gene structure and protein properties of the genes encoding each G-protein subunit were extremely conserved. Collinearity analysis showed that most G-protein genes in B. napus had syntenic relationships with G-protein members of Arabidopsis, Brassica rape (B. rapa), and Brassica oleracea (B. oleracea). Expression profile analysis indicated that Gα and C-type Gγ genes (except BnGG10 and BnGG12 were highly expressed in flower and ovule) were barely expressed in most organs, whereas most Gβ and A-type Gγ genes tended to be highly expressed in most organs. G-protein genes also showed various expression patterns in response to nitrogen-deficient conditions. Under nitrogen deficiency, Gα and five C-type Gγ genes were upregulated initially in roots, while in leaves, Gα was downregulated initially and five C-type Gγ genes were highly expressed in different times. These results provide a complex genetic dissection of G-protein genes in B. napus, and insight into the biological functions of G-protein genes in response to nitrogen deficiency.     

Research on the stability of nearly zero flattened dispersion of photonic crystal fibers

To analyze the stability of nearly zero flattened dispersion, the dispersion deviations for three kinds of PCFs are calculated when the hole diameters deviate from their designed values. Numerical results show that around the wavelength of 1.55 μm, the dispersion deviations of both the PCF with three-fold symmetry core and the PCF with hexagonal lattice are much less than that of the PCF with different hole diameters in different rings. Therefore, the stabilities of nearly zero flattened dispersion of the first two kinds of PCFs are much better than that of the last one. Considering the confinement loss, the PCF with three-fold symmetry core is preferable to practical use.