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991.
992.
Wen-mei Wei Ren-hui Zheng Yan Tian Tian-jing He Li He Dong-ming Chen Fan-chen Liu 《化学物理学报(中文版)》2007,20(2):126-134
The complex potential energy surface and reaction mechanisms for the unimolecular isomerization and decomposition of methyl-nitramine (CH3NHNO2) were theoretically probed at the QCISD(T)/6-311+G*//B3LYP/6-311+G* level of theory. The results demonstrated that there are four low-lying energy channels: (i) the NN bond fission pathway; (ii) a sequence of isomerization reactions via CH3NN(OH)O; (IS2a); (iii) the HONO elimination pathway; (iv) the isomerization and the dissociation reactions via CH3NHONO (IS3). The rate constants of each initial step (rate-determining step) for these channels were calculated using the canonical transition state theory. The Arrhenius expressions of the channels over the temperature range 298-2000 K are k6(T)=1014:8e-46:0=RT , k7(T)=1013:7e-42:1=RT , k8(T)=1013:6e-51:8=RT and k9(T)=1015:6e-54:3=RT s-1, respectively. The calculated overall rate constants is 6.9£10-4 at 543 K, which is in good agreement with the experimental data. Based on the analysis of the rate constants, the dominant pathway is the isomerization reaction to form CH3NN(OH)O at low temperatures, while the NN bond fission and the isomerization reaction to produce CH3NHONO are expected to be competitive with the isomerization reaction to form CH3NN(OH)O at high temperatures. 相似文献
993.
运用量子化学方法优化了硫代樟脑的最低5个电子态(S0, T1, S1, T2和S2)的结构, 并计算了它们的相对能量. 计算结果表明: S1, T1和T2态的能量非常接近, 而S2的能量远远高于T2态, 这与之前对几种小的硫代羰基化合物的研究结论一致. 确定了硫代樟脑分子在T1态发生β-插入反应和类Norrish II型反应的机理, 计算的势垒相对于S0的振动零点分别为314.1和332.6 kJ/mol. 在400 nm波长的光的照射下, 分子被激发到S1态, 此时分子没有足够的能量发生反应, 只能通过内转换回到基态. 当激发光波长在254 nm时, 硫代樟脑分子被激发到S2态, 这时候体系有了足够的内部能量使反应发生. 实验上已经观察到此激发光波长下, 气态硫代樟脑可以发生β-插入反应和类Norrish II型反应. 相似文献
994.
许多生理过程都通过分子间相互作用来实现。氢键则是最基本的化学作用力之一。具有碱性和酸性双官能团的芳香族化合物能与水作用形成氢键网络,对于实现生物体系的物质转移(质子转移、离子转移)起着十分重要的作用。在非水溶剂中,通过氢键发生质子转移反应动力学实验特征也己进行了广泛的研究。本文用密度泛函B3LYP方法在6-311G^*基组水平上对7-羟基喹啉-水复合物相互作用进行了研究,从成键特征及氢键复合物的稳定关系方面进行了理论计算。 相似文献
995.
Metakaolin-based geopolymer microspheres (MGM) with hierarchical pore structures were prepared by suspension dispersion method in dimethicone at 80 °C. The hydrothermal modification of MGM was carried out at a lower temperature of 80 °C, and a NaA molecular sieve converted from metakaolin-based geopolymer (NMGM) with good crystal structure was prepared and applied in thermal catalytic cracking of low-density polyethylene (LDPE) reaction. The one-pot two-stage thermal catalytic cracking of LDPE was carried out in a 100 mL micro-autoclave under normal pressure. In this work, the optimal proportions and optimal reaction conditions of catalysts for NMGM thermal catalytic cracking of LDPE waste to fuel oil were investigated. The NMGM catalyst showed high selectivity to the liquid product of thermal catalytic cracking of waste LDPE. Under the reaction conditions of reaction time of 1 h and reaction temperature of 400 °C, the liquid-phase yield of thermal catalytic cracking of LDPE reached a high of 88.45%, of which the content of gasoline components was 10.14% and the content of diesel components was 80.97%. 相似文献
996.
针对螺旋线型脉冲形成线放电过程的匝间击穿问题,采用数值模拟的方法研究了影响螺旋线上轴向电场的因素,模拟结果表明:螺旋线的螺旋角越大、开关的上升沿越小、负载的阻值越小则越容易造成匝间击穿;针对输出波形的前沿上冲和下凹问题,通过数值模拟和实验方法研究了加速器内阻抗不匹配段对输出波形的影响,结果表明: 改变螺旋线与开关之间连接段的阻抗以及开关和二极管之间过渡段的阻抗,使之接近于螺旋线阻抗,并使电长度减小,可以消除波形的前沿上冲和下凹,得到近似方波的高电压脉冲输出。 相似文献
997.
This paper proves the optimal estimations of a low-order spatial-temporal fully discrete method for the non-stationary Navier-Stokes Problem. In this paper, the semi-implicit scheme based on Euler method is adopted for time discretization, while the special finite volume scheme is adopted for space discretization. Specifically, the spatial discretization adopts the traditional triangle trial function pair, combined with macro element form to ensure local stability. The theoretical analysis results show that under certain conditions, the full discretization proposed here has the characteristics of local stability, and we can indeed obtain the optimal theoretic and numerical order error estimation of velocity and pressure. This helps to enrich the corresponding theoretical results. 相似文献
998.
999.
Yazhou Qin Fan Mo Sen Yao Yuanzhao Wu Yingsheng He Weixuan Yao 《Molecules (Basel, Switzerland)》2022,27(12)
Porous noble metal nanomaterials have attracted extensive attention due to their high specific surface area and surface plasmon resonance effect. However, it is difficult to form porous structures due to the high mobility and low reduction potential of noble metal precursors. In this article, we developed a facile method for preparing porous Ag with a controllable structure at room temperature. Two kinds of Ag crystals with different porous structures were successfully prepared by using AgCl cubes as sacrificial templates. Through the galvanic replacement reaction of Zn and AgCl, Ag crystals with a sponge-like porous structure were successfully prepared. Additionally, using NaBH4 as the reducing agent, we prepared granular porous Ag cubes by optimizing the amount of reducing agent. Both the sponge-like and granular porous Ag cubes have clean and accessible surfaces. In addition, we used the prepared two porous Ag cubes as substrate materials for SERS detection of five kinds of methamphetamine analogs. The experimental results show that the enhancement effect of granular porous Ag is better than that of sponge-like porous Ag. Furthermore, we probed the hot spot distribution of granular porous Ag by Raman mapping. By using granular porous Ag as the substrate material, we have achieved trace detection of 5 kinds of methamphetamine analogs including Ephedrine, Amphetamine, N-Methyl-1-(benzofuran-5-yl)propan-2-amine (5-MAPB), N-Methyl-1-(4-methoxyphenyl)propan-2-amine (PMMA) and N-Methyl-1-(4-fluorophenyl)propan-2-amine (4-FMA). Furthermore, to achieve qualitative differentiation of analogs with similar structures we performed density functional theoretical (DFT) calculations on the Raman spectra of the above analogs. The DFT calculations provided the vibrational frequencies, Raman activities, and normal mode assignment for each analog, enabling the qualitative differentiation of the above analogs. 相似文献
1000.
Qinghui He Congcong Si Zhenjiao Sun Yuhui Chen Xin Zhang 《Molecules (Basel, Switzerland)》2022,27(12)
The imbalance of intestinal microbiota can cause the accumulation of endotoxin in the main circulation system of the human body, which has a great impact on human health. Increased work and life pressure have led to a rise in the number of people falling into depression, which has also reduced their quality of life. The gut–brain axis (GBA) is closely related to the pathological basis of depression, and intestinal microbiota can improve depressive symptoms through GBA. Previous studies have proven that prebiotics can modulate intestinal microbiota and thus participate in human health regulation. We reviewed the regulatory mechanism of intestinal microbiota on depression through GBA, and discussed the effects of prebiotics, including plant polysaccharides and polyphenols on the regulation of intestinal microbiota, providing new clues for the prevention and treatment of depression. 相似文献