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201.
Electrophilic additions of hydrogen halides to alkenes in the gas phase are investigated with a high‐level ab initio method, MP2/6‐311+G(3df,2p). Based on this, the interesting features of these reactions along the IRC routes are characterized by the molecular face (MF) theory. For an alkene at the initial state, if the representative electron density (ED) encoded on the molecular face (MF) of the Markovnikov (M) carbon atom (the carbon with more hydrogen atoms) is larger than that of the anti‐Markovnikov (AM) carbon atom (the carbon with fewer hydrogen atoms), the electrophilic addition reaction is predicted to proceed along the Markovnikov addition route; in the reverse situtation, the anti‐Markovnikov addition route would be slightly preferred. It is then demonstrated that for a series of alkenes, the difference between activation energies of Markovnikov and anti‐Markovnikov addition routes [ΔE#(M?AM)] has a good linear correlation with sign(KED)K2ED, where KED is characteristic of the electron density (ED) at the π region in the initial state of the alkenes. Interestingly, there is a good linear correlation between our sign (KED)K2ED and the absolute values of difference in the core ionization energy between M and AM carbon atoms obtained by others (L. J. Sæthre, T. D. Thomas, S. Svensson J. Chem. Soc. P2 1997 , 2, 749.) in terms of the experimental study. In addition, the spatial dynamic changing features of the MF faces and interesting pictures of the electron transfer are clearly shown during the course of the electrophilic addition reactions. These results indicate that not only regioselectivity, but also activation energy and reactivity correlate with the π charge distribution in the initial state of the alkenes for electrophilic addition reactions. 相似文献
203.
《Electrophoresis》2018,39(19):2460-2470
This study uses negative dielectrophoresis and AC electroosmosis as a driving mechanism and presents an electrically driven microconcentrator that concentrates the sample in the region exterior to the electrodes (termed as exterior‐electrode electrically driven microconcentrator in this paper). The proposed microconcentrator uses a 3‐D face‐to‐face electrode pair; the top electrode is a relatively large planar electrode, and the bottom electrode is formed with three to six long and thin electrodes connected into an open ring. The sample is brought to the vicinity of the open electrode at the bottom by electroosmotic flow; then, negative dielectrophoresis is used to push the sample away from the electrode and concentrate it in the region surrounded by the open ring electrode. Concentration using an exterior‐electrode electrically driven microconcentrator offers promise for convenient use in conjunction with relevant detection systems. The results indicate that for the proposed exterior‐electrode electrically driven microconcentrator, the optimal frequency is 100 kHz and the optimal voltage is 13 Vp‐p. The corner concentration process at the corners of the bottom open electrodes enables the multi‐corner electrodes to exhibit better concentration results than that exhibited by semicircular‐shaped electrodes. The concentration performance is most favorable when the shape of the open electrode at the bottom is a five‐vertex electrode, enabling a concentration enhancement factor of 55 times for a latex particle solution and 11 times for E. coli. The experimental results also demonstrate that the concentration phenomenon in this study is not induced by non‐specific adsorption and can be repeated multiple times. 相似文献
204.
Data representation has been one of the core topics in 3D graphics and pattern recognition in high-dimensional data. Although the high-resolution geometrical information of a physical object can be well preserved in the form of metrical data, e.g., point clouds/triangular meshes, from a regular data (e.g., image/audio) processing perspective, they also bring excessive noise in the course of feature abstraction and regression. For 3D face recognition, preceding attempts focus on treating the scan samples as signals laying on an underlying discrete surface (mesh) or morphable (statistic) models and by embedding auxiliary information, e.g., texture onto the regularized local planar structure to obtain a superior expressive performance to registration-based methods, but environmental variations such as posture/illumination will dissatisfy the integrity or uniform sampling condition, which holistic models generally rely on. In this paper, a geometric deep learning framework for face recognition is proposed, which merely requires the consumption of raw spatial coordinates. The non-uniformity and non-grid geometric transformations in the course of point cloud face scanning are mitigated by modeling each identity as a stochastic process. Individual face scans are considered realizations, yielding underlying inherent distributions under the appropriate assumption of ergodicity. To accomplish 3D facial recognition, we propose a windowed solid harmonic scattering transform on point cloud face scans to extract the invariant coefficients so that unrelated variations can be encoded into certain components of the scattering domain. With these constructions, a sparse learning network as the semi-supervised classification backbone network can work on reducing intraclass variability. Our framework obtained superior performance to current competing methods; without excluding any fragmentary or severely deformed samples, the rank-1 recognition rate (RR1) achieved was on the Face Recognition Grand Challenge (FRGC) v2.0 dataset and on the Bosphorus dataset. 相似文献
205.
分子形貌(Molecular face, MF)定义分子的内禀电子转折边界面,同时在其上计算并描绘出前沿电子密度(MFED). MF不仅能显示分子的形状和大小,还能够指示分子的化学反应性.应用M06-2X/6-311++G(d,p)理论方法,对单线态和三线态羟基卡宾分子及其衍生物的质子化反应进行研究并计算了这些反应的活化能.结果表明,吸电性和供电性较强的取代基,均使单线态反应活化能增大,只有吸电性较强的─CN才能使三线态反应活化能增大.应用分子形貌理论研究了上述反应,不仅展示出分子的形貌变化、与反应位点的关联,以及有关物理量的变化倾向,而且还定量地显示出,单线态羟基卡宾及其衍生物分子边界面上前沿电子密度极大值与极小值的差值,与其质子转移反应的活化能之间存在线性相关. 相似文献
206.
RHT模型普遍用于混凝土的数值模拟当中, 但该模型的相关参数较难获得. 利用SHPB实验测得C40混凝土应力应变曲线, 并从该曲线中选取RHT模型中弹性极限面和失效强度面对应的应力状态点进行数值拟合, 从而得到RHT模型参数A、N、δ、α. 并引进当前面所对应的归一化静水压参量和应变增量, 改进了损伤量D的描述, 从而改进了在混凝土数值计算中广泛应用的RHT模型. 结果表明: 改进RHT模型得到的理论应力应变曲线与实验曲线吻合良好, 可作为获得RHT模型参数的有效方法. 相似文献
207.
208.
Yinyu Ye 《Mathematical Programming》1992,57(1-3):325-335
It has been shown [8] that numerous interior-point algorithms for linear programming (LP) generate solution sequences that converge to strict complementarity solutions, or interior solutions on the optimal face. In this note we further establish a theoretical base for Gay's test (Gay, 1989) to identify the optimal face, and develop a new termination procedure to obtain an exact solution on the optimal face. We also report some numerical results for solving a set of LP test problems, each of which has a highly degenerate and unbounded optimal face.Research supported in part by NSF Grant DDM-8922636, The Iowa Business School Summer Grant, and the Interdisciplinary Research Grant of the University of Iowa Center for Advanced Studies. 相似文献
209.
210.
Yan‐Li Ding En‐Bo Li Li‐Dong Gong 《International journal of quantum chemistry》2012,112(12):2515-2524
We perform a systematical investigation on the dynamic changing feature of the molecular shape and size and electron density distribution in the process of a rare‐gas atom (He, Ne, Ar, and Kr) approaching a hydrogen molecule by an ab initio method. In terms of the molecular face (MF) theory, the polarization effect in the above processes is vividly demonstrated. There is a good linear correlation between our average variation rate (Saver) of molecular intrinsic characteristic radius at the contacting point and the experimental polarizability of the rare‐gas atoms. This indicates that the MF theory can well represent the intermolecular polarization effect. Interestingly, the pictures of shape changing, charge‐flow, and exchange repulsion processes especially on the reacting active areas have been clearly observed. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011 相似文献