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901.
聚甲氧基二烷基醚(RO(CH2O)nR)具有高的十六烷值(CN)和含氧量,能显著改善柴油的燃烧特性,有效提高热效率,大幅减少碳烟和NOx排放,被认为是一种优良的环保型燃油组分.随着–R基碳链的增长,CN值、热值和闪点逐渐增大,密度和冷凝点逐渐降低.同时,该类化合物具有优异的溶解及渗透性能,能与许多有机溶剂互溶,低毒,可以用作溶剂或颜料分散剂.近年来,聚甲氧基二甲基醚(CH3O(CH2O)nCH3,PODEn,DMMn)的制备及应用研究受到广泛关注,而对封端基团(–R)碳数大于1的多醚类化合物的研究鲜有文献报道.本文以Br?nsted酸性离子液体为催化剂,对甲醛和二乙氧基甲烷或脂肪醇(碳数 ≥2)缩醛化反应制备聚甲氧基二烷基醚的反应性能进行了研究,考察了离子液体结构和酸性对其催化性能的影响.结果表明,–SO3H功能化的离子液体[MIMBs]HSO4在催化三聚甲醛与二乙氧基甲烷的缩醛化反应中表现出最好的催化活性.考察了催化剂用量、原料配比、反应温度、反应压力和反应时间等因素对反应性能的影响,并得到了最佳反应条件,在n([MIMBs]HSO4):n(DEM1):n(HCHO)=1:80:80,140°C下反应4 h,甲醛转化率达到了92.6%,DEM2–8选择性为95.1%.考察了不同甲醛源(三聚甲醛和多聚甲醛)与提供封端基团化合物(二乙氧基甲烷、乙醇、丙醇和丁醇)的缩醛化反应.结果发现,在反应过程中不生成水或不引入水的条件下,具有更高的反应转化率和产物选择性.分别采用静置分层和萃取实现了催化剂的分离与重复使用.推测反应机理认为,三聚甲醛首先在氢键作用下分解生成甲醛单体,甲醛和二乙氧基甲烷通过碳正离子反应机理实现了DEMn的链增长. 相似文献
902.
球形压痕技术在材料力学属性,诸如硬度,弹性模量等的测量中得到了广泛的应用。应用Twyman-Green及云纹干涉法并配合相移技术,本文对IN783合金进行了一系列的球形压痕实验研究,并对残余压痕的面内(u, v)及离面( w)变形场进行了定量测量和分析。应用面内变形测量结果,进一步对试件表面的应力-应变分布进行了分析和计算,并在离面变形场的基础上,确立了压痕周围的弹塑性边界,从而进一步应用面内的分析结果,得到材料的屈服强度。应用压痕实验的接触半径和压力并配合Tabor经验公式,本文进一步得到了材料的应力应变曲线。实验结果与已知的IN783合金相吻合。对所涉及的一系列压痕实验,本文也进行了二维有限元分析并得到了比较一致的结果。 相似文献
903.
Uniaxial ratcheting and failure behaviors of two steels 总被引:2,自引:0,他引:2
G.Z. Kang Y.G. Li J. Zhang Y.F. Sun Q. Gao 《Theoretical and Applied Fracture Mechanics》2005,43(2):199-209
The strain cyclic characteristics, ratcheting and failure behaviors of 25CDV4.11 steel and SS304 stainless steel were experimentally studied under uniaxial cyclic tests and at room temperature. The cyclic hardening/softening features of the materials were first observed under uniaxial strain cycling; and then the ratcheting and failure behaviors of the materials were researched in detail under cyclic stressing. The effects of stress amplitude and mean stress on the ratcheting and failure were discussed under uniaxial asymmetrical stress cycling. It is concluded that the ratcheting and failure behaviors of the materials depend greatly on the cyclic softening/hardening features of the materials and the stress values of cyclic loading. Some conclusions useful to understand the fatigue failure of the materials presented under asymmetrical cyclic stressing are obtained. 相似文献
904.
The newly derived dynamic-crack-branching criterion with its modifications is verified by the dynamicphotoelastic results of dynamic crack branchings in thinpolycarbonate, single-edged crack-tension specimens. Successful crack branching was observed in four specimens and unsuccessful branching in another. Crack branching consistently occurred when the necessary conditions ofK I =K I b =3.3 MPa \(\sqrt m\) and the sufficiency condition ofr o =r c =0.75 mm were satisfied simultaneously. In the unsuccessful branching test, the necessary condition was not satisfied sinceK I was always less thanK I b . 相似文献
905.
906.
为了解决装配式钢框架中节点区域构造复杂和传力机制不明的问题,提出一种考虑组合楼板作用的端板螺栓连接节点。设计并制作了2组端板连接的装配式梁柱节点,进行了低周往复循环荷载试验,建立了节点试件的数值模型,分析组合楼板对节点的破坏模式、滞回性能、承载能力、半刚性性能、受力特征的影响作用。结果表明,端板连接节点主要破坏模式为端板的弯曲变形,组合楼板的加入会使滞回曲线产生一定的捏拢现象,同时会产生组合楼板开裂破坏现象;增加组合楼板后,端板连接节点的初始转动刚度、极限承载力、耗能能力分别增加了约22%,13%,22%;组合楼板和钢梁上翼缘共同作用时,荷载通过组合楼板传递至柱腹板;与闭口型压型钢板-混凝土组合楼板的节点相比,采用开口型压型钢板-混凝土组合楼板的节点初始转动刚度和极限承载力分别提高13%和9%。组合楼板能有效提高端板连接节点的抗震性能,扩大节点核心区的传力范围,增强梁柱传力机制,可为进一步提高装配式节点性能提供参考。 相似文献
907.
A method for determination of intracellular acyl‐coenzyme A esters in Clostridium acetobutylicum (CA) by high performance liquid chromatography (HPLC) was developed and validated. In our experiment, two important intermediates acyl‐coenzyme A esters including acetyl‐CoA, butyryl‐CoA could be baseline separated on a Zobax‐C18 column with mobile phase composed of the acetonitrile and phosphate buffer (pH 5.0). Samples treated with freeze‐thaw and protein precipitated by addition of trichloroacetic acid could be directly injected for determination of acetyl‐CoA, butyryl‐CoA with a recovery higher than 73%. With this method, the metabolite profiling of the acyl‐coenzyme A esters of CA was obtained. The comparison of the metabolite profiling between the model strain ATCC 824 and a mutant strain EA 2018, which produces higher butanol than the former was performed. Some useful information was concluded for understanding the mechanism of CA for selectively producing the solvent. 相似文献
908.
Xiu-li Wang Bao Mu Hong-yan Lin Guo-cheng Liu Ai-xiang Tian Jin Li Zhen-hui Kang 《Transition Metal Chemistry》2010,35(8):967-971
A new Keggin-type polyoxometalate-based compound {[Cu2(L)4(H2O)4](PW11VIWVO40)}·16H2O (1) constructed from PW11VIWVO40
4−, N,N′-bis(4-pyridylformyl) piperazine (L) and Cu(II) has been hydrothermally synthesized and structurally characterized by elemental analyses, IR and single-crystal
X-ray diffraction analysis. Single-crystal X-ray diffraction analysis reveals that the semi-rigid piperazine-based ligands
L coordinate to the Cu(II) atoms to constitute a two dimensional coordination network. The 2D (4, 4) cationic layers are stacked
together in a perpendicular mode, resulting in the formation of twofold interpenetrating frameworks with large cavities. The
PW12 anions reside in the large cubic-like cavities, serving as non-coordinating templates. The compound 1 displays good electrocatalytic activity toward the reduction of nitrite in 1 M H2SO4 aqueous solution. 相似文献
909.
Sunwoo Kang Sang Joo Lee Shihai Yan Kye Chun Nam Jin Yong Lee 《Journal of inclusion phenomena and macrocyclic chemistry》2010,66(1-2):67-73
We investigated the binding nature of the 1,2,3-alternate calix[6]arene with one piperidine, two piperidines, and two triethyl amines with a special emphasis on the hydrogen bonding networks by density functional theory calculations. The 1,2,3-alternate calix[6]arene strongly binds with piperidines and triethylamines at two different binding sites, exo and endo sites. In the two binding sites, the hydrogen bonding nature shows a characteristic difference. In the exo site, there formed only one hydrogen bond, while in the endo site, two hydrogen bonds except for the triethylamine. The proton transfer within the hydrogen bonding and the hydrogen bonding types, normal hydrogen bonding (NHB), short strong hydrogen bond (SSHB), and low barrier hydrogen bonding (LBHB), will be discussed in detail. 相似文献
910.
Sunwoo Kang Sang Joo Lee Shihai Yan Kye Chun Nam Jin Yong Lee 《Journal of inclusion phenomena and macrocyclic chemistry》2010,66(1-2):75-79
The variations in geometry structure, IR spectra, as well as the molecular orbitals upon anion recognition for polyamide cryptand are explored with the hybrid density functional theory. The cavity generated by six amide NH groups shrinks upon F ? recognition because of the strong hydrogen bonds between the amide protons and F ? , while the cavity expands upon Cl ? binding because of the strong electron repulsion between the p electron of Cl ? and the lone pair electrons of the nitrogen atom of the pyridine moieties. The “electropositive field space” …Cl ? coupling exists when Cl ? is recognized. The strong anion binding energy with F ? indicates that the polyamide cryptand prefers F ? to Cl ? . 相似文献