Mesh stiffness analysis of beveloid gears for the rotating vector transmission

Journal of Mechanical Science and Technology - This paper investigates the meshing stiffness of beveloid gears in the beveloid rotate vector (BRV) transmission. It is a new kind of transmission...     

中国建筑话语中的“文脉”(1980年代-1990年代)

对"文脉"一词进入中国建筑话语的历史作出概览式的回顾,并分别以"阙里宾舍"和"西单商业大楼"为例,从设计者的自述与建筑界的评论入手,探讨1980年代末到1990年代初"文脉热"兴起的可能原因。指出对"复古主义"的批判和创作有"民族特色"建筑的愿望是"文脉"一词背后潜在的诉求,同时,也警醒地看到,基于特定时代背景,中国建筑界对西方后现代主义等建筑思潮不可避免地片面理解和吸收,也造成了"文脉"逐渐丧失了其本应具有的批判性与创造力。     

鄂尔多斯盆地延安气田南部岩溶古地貌分级识别及有利区预测

延安气田南部地区古地貌研究程度较差,难以满足精细勘探要求。综合利用钻井、测井、录井、二维地震资料,对延安气田南部下古生界奥陶系顶部风化壳岩溶古地貌进行精细恢复,结合钻井试气成果,明确了岩溶古地貌对气藏分布的控制作用,并划分有利目标区。研究结果表明:研究区划分为西部岩溶台地、中部岩溶斜坡以及东部岩溶盆地3个二级古地貌单元,在二级古地貌单元上进一步分级识别出三级古地貌单元;沟槽两翼及高地洼地转换地岩溶作用强烈,储层物性较好,为最有利目标区,沟槽、洼地以及远离沟槽处物性较差。具体优选吴起志丹部分地区、甘泉地区、西南部黄陵富县西地区为有利岩溶储层区。该研究可有效提高钻井成功率,为后期气田增储上产提供有力支撑。     

剂油比对煤焦油沥青质加氢过程的影响

以中低温煤焦油沥青质为原料,采用NiMoW/γ-Al_2O_3商业催化剂,在反应温度380℃、反应压力8 MPa和反应时间1.5 h条件下,分别在不同剂油质量比(1∶25、1∶20、1∶15、1∶10)条件下进行加氢实验,通过采用元素分析、FT-IR、XRD、~1H-NMR和XPS等分析表征手段,考察不同剂油质量比对中低温煤焦油沥青质加氢转化过程的影响。结果表明,随着剂油质量比的增加,沥青质转化率提高,加氢产物分布也发生大幅变化,沥青质和芳香分轻质化转化为饱和分。但随着剂油质量比的进一步提高,同时也发生了更多的裂化反应和缩合反应,剂油质量比在合适范围能够很好地起到加氢轻质化且抑制结焦的效果。     

中低温煤焦油基炭微球的制备

通过馏分切割、温和加氢相结合对中低温煤焦油进行精制处理，精制后的原料采用分级热聚制备中间相炭微球。考察了精制处理条件对原料性质、中间相炭微球宏观外貌及微晶结构的影响。采用FTIR、GC-MS、族组成、元素分析对原料进行表征，采用SEM、XRD对中间相炭微球进行表征。结果表明：中低温煤焦油中300～430℃馏分油是制备中间相炭微球的较佳馏分。300～430℃馏分油中正庚烷可溶物（HS）质量分数高达84.76%，吡啶不溶物（PI）质量分数低至0.23%，杂原子含量低，芳烃化合物的环数为2～4环。300～430℃馏分油在T_H=350℃、p=8MPa、t=1.5h、剂油比1∶40（质量比）的条件下温和加氢得到的精制原料，经420℃热聚6h得制备的中间相炭微球宏观外貌、微晶结构较好。中低温煤焦油基炭微球的粒径范围为5～15μm，小球表面光滑，微观结构为地球仪型，经1450℃高温煅烧后，石墨化度达到12.33%。     

Bi@Bi4Ti3O12/TiO2 films on glass with photocatalytic and self-cleaning performance

A stable and translucent Bi@Bi₄Ti₃O₁₂/TiO₂ film was fabricated on conventional glass substrates for the first time. The film exhibited a good photocatalytic performance and efficient self-cleaning capability against organic dyes under full spectral irradiation and visible light irradiation. Bi₄Ti₃O₁₂/TiO₂ film was first prepared on a glass substrate with colloidal silica as a high temperature binder, followed by implantation of nanoscale Bi in it by an in-situ partially reduction of Bi₄Ti₃O₁₂ to generate Bi@Bi₄Ti₃O₁₂/TiO₂ films. The improved photocatalytic ability is probably attributed to the surface plasmon resonance of Bi atom as well as the enhanced electron transfer efficiency and synergistic effect of Bi₄Ti₃O₁₂ and TiO₂. According to trapping experiments, hydroxyl radicals (OH) were active species in the photocatalytic degradation of dyes under full spectral light irradiation and possible photocatalytic mechanism was proposed. The film prepared in this work may well have potential practical applications in many aspects, such as cleansing treatments for high building external decorative panels and also systematic characterization of the film suggests that the in-situ reduction is an effective and simple way to produce nanoscale Bi@Bi₄Ti₃O₁₂.     

牦牛肉品质特性研究进展

牦牛肉是我国青藏高原的重要畜牧产品之一，在当地居民的膳食及高原地区的经济发展中占据重要地位。了解牦牛肉的肉质特性对于牦牛肉的精深加工和牦牛资源的合理开发有重要意义。本文综合近几年国内外相关研究，从营养品质、食用品质和加工品质3 个方面对牦牛肉的品质特性进行概述和分析，以期为牦牛肉的品质改善和产品开发提供参考和思路。牦牛肉营养价值高、绿色无污染、市场潜力大，但嫩度较差，今后需借助适当饲养方式和宰后处理方式对其嫩度进行改善。     

Effects of pre-imidization on rheological behaviors of polyamic acid solution and thermal mechanical properties of polyimide film: an experiment and molecular dynamics simulation

A series of polyamic acid (PAA) solutions and corresponding polyimide (PI) films with different chemical structures were prepared through a partial pre-imidization process, and the rheological behavior of PAA solutions and thermal mechanical properties of PI films were investigated in detail. The FT-IR spectra indicate that the pre-imidization degree (pre-ID) of PI could be accurately controlled by adjusting the amount of dehydration reagents. The PI films with a certain pre-ID exhibit better mechanical properties and lower coefficient of thermal expansion. The viscosity curves of PAA solution with varying shear rate show that the PAA solutions with high pre-ID have low shear sensitivity, which exhibits a lower viscosity at the low shear rate, but retains almost the same viscosity at high shear rate. Chain conformation variations with pre-IDs and solvent content were investigated by molecular dynamic (MD) simulation. The MD results indicate that a sudden increase in cohesive energy density leads to gel at a certain pre-ID and the mobility of molecular chain decreases greatly with solvent volatilization. It is supposed that the molecular chain orientation induced by the pre-imidization will be preserved in the subsequent thermal imidization process. Therefore, the PI films with a certain pre-IDs exhibit more excellent thermal mechanical properties, especially for the PI with rigid-rod segments.