System-size effect on the friction at liquid-solid interfaces

The friction at the liquid-solid interfaces is widely involved in various phenomena ranging from nanometer to micrometer scales. By the molecular dynamic(MD)simulation, the friction properties of liquid-solid interfaces at the molecular level are calculated via the Green-Kubo relation. It is found that the system size will influence the value of the friction coefficient, especially for the solid surfaces with the larger polar charge. The value of the friction coefficient decreases with the increase in the system size and converges at large system sizes. The large polar charge will lead to a significant friction coefficient. However, the diffusion of water molecules on this surface is almost a constant, indicating that the diffusion coefficient seems to be independent of the system size and polar charge. This work provides insights for the selection of the system size in modeling the frictional properties of hydrophobic/hydrophilic surfaces.     

毛冬青总皂苷对大鼠脑缺血再灌注损伤的保护作用及血液微量元素影响

目的研究毛冬青总皂苷对脑缺血再灌注损伤的保护作用,并初步探讨其血液微量元素的影响。方法动物随机分为假手术组、模型组、毛冬青总皂苷(高、中、低)剂量组及阳性药物对照组,运用大鼠大脑中动脉栓塞,制作脑缺血再灌注损伤模型,缺血10 min后,给药组及阳性药物组于舌下静脉给予高、中、低剂量的毛冬青总皂苷及假手术组、模型组给予等体积的溶剂。缺血60 min再灌注24 h后,每组取8只大鼠断头取脑,TTC染色,测定脑梗死体积;取血,测定血液中3种微量元素Ca、Zn、Cu的含量。结果毛冬青总皂苷组与模型组相比,毛冬青总皂苷治疗组脑梗死体积减小,病理变化较轻;模型组与假手术组比较血液中Ca、Cu含量增加明显有统计学意义,Zn含量明显降低与假手术组比较有统计学意义(P0.05),毛冬青高、中、低剂量组与模型组比较Ca、Cu含量明显降低,Zn含量明显升高,而且呈明显的量效关系,与模型组比较有统计学意义(P0.05)。结论毛冬青总皂苷对脑缺血再灌注损伤具有一定的保护作用,其保护机制与毛冬青总皂苷抗氧化作用及增强氧自由基的清除有关。     

Synthesis of Indolophanes by Photochemical Macrocyclization

Herein, we report the synthetically practical, short, and general access to novel indolophane architectures by means of a photochemical C?H activation process—the Witkop cyclization. These highly strained scaffolds were obtained by photoinduced ring closure and feature atropisomerism as well as aromatic ring current effects, which both have been investigated. The prevailing regioselectivity of theWitkop cyclization reaction was completely reversed by the presence of a quaternary carbon center, exerting a strong Thorpe–Ingold effect on the system for which experimental‐evidence is provided.     

Lanthanum trilactate: Vibrational spectroscopic study − infrared/Raman spectroscopy

In this study lanthanum trilactate was prepared by neutralization reaction of lactic acid and lanthanum oxide, purified and identified by X-ray powder diffraction. Infrared spectra (Mid-IR region 4000–650 cm⁻¹) and Raman spectra (Stokes region 4000–100 cm⁻¹) of the high quality crystalline samples have been recorded and presented for the first time. For comparison DFT calculations were performed using Gaussian 09 D.01 and agreement between predicted and measured spectral data has been achieved. Acquired information can be utilized for substance identification for example in various industrial applications or in biological systems.     

Salt effect on molecular orientation at air/liquid methanol interface

The salt effects on molecular orientation at air/liquid methanol interface were investigated by the polarization-dependent sum frequency generation vibrational spectroscopy(SFG-VS). We clarified that the average tilting angle of the methyl group to be u = 308 58 at the air/pure methanol surface assuming a d-function orientational distribution. Upon the addition of 3 mol/L Na I, the methyl group tilts further away from the surface normal with a new u = 418 38. This orientational change does not explain the enhancement of the SFG-VS intensities when adding Na I, implying the number density of the methanol molecules with a net polar ordering in the surface region also changed with the Na I concentrations. These spectroscopic findings shed new light on the salt effects on the surfaces structures of the polar organic solutions. It was also shown that the accurate determination of the bulk refractive indices and Raman depolarization ratios for different salt concentrations is crucial to quantitatively interpret the SFG-VS data.     

(3S,4S)-4-氨基-3-羟基-6-甲基庚酸的合成

价廉易得的L-亮氨酸先以苄基同时保护氨基及羧基得(S)-2-(二苄胺基)-4-甲基戊酸苄酯,进而在碱性条件下与乙腈发生亲核取代反应得(S)-4-(二苄胺基)-6-甲基-3-氧代庚腈,再经硼氢化钠选择性还原羰基得(3S,4S)-4-(二苄胺基)-3-羟基-6-甲基庚腈,用双氧水氧化得(3S,4S)-4-(二苄胺基)-3-羟基-6-甲基庚酸,最后在Pd(OH)2/C-H2作用下脱掉苄基得到(3S,4S)-4-氨基-3-羟基-6-甲基庚酸,即(3S,4S)-statine。整个合成路线总产率为33.6%。     

椭圆偏振法测定在线Low-E玻璃的可见-近红外光学常数与膜厚

从在线Low-E玻璃光学机理出发,用椭圆偏振光谱仪对在线Low-E玻璃功能层和过渡层的可见-近红外波段的光学常数进行研究.测量了样品在三个不同入射角的椭偏参数,分别用Lorentz双振子模型和Cauchy模型来描述Low-E玻璃功能层和过渡层的光学色散特性.通过拟合椭偏参数获得在线Low-E玻璃的光学常数及每层膜厚度,并用扫描电镜对样品的膜厚进行表征.结果表明,Lorentz双振子模型和Cauchy模型能很好地解释在线Low-E玻璃的光学特性;同时,椭圆偏振法也为多层膜系统提供了一种测定光学常数和膜厚的可靠方法.     

Modeling and testing of snow penetration

Penetration by a cone into snow is commonly used to characterize snow properties. However, the effects of the diameter and half-angle of the cone on the mechanical properties of snow have not been systematically studied. In addition, no estimation of material parameters in a physically-based model has been made such that the results from penetration provide only an index of snow properties. In this paper, modeling and experimental methods are used to examine the effects of cone geometry on the maximum penetration force and associated hardness, with penetrometers ranging from 2.5 to 4 mm in diameter, 15° to 45° in cone half-angle, and testing both fine-grained and coarse-grained snows. The material point method, in conjunction with the Drucker–Prager cap plasticity model, was used to obtain the theoretical penetration force-distance relationship. Global sensitivity studies were conducted that indicate that the cohesion accounts for 86% of the penetration force, followed distantly by friction angle which accounts for 27%. A general trend, for the simulation results was established: for a given half-angle, the penetration force increases with the increase of diameter which holds for most of the test data as well; for a given diameter, the penetration force decreases with the increase of half-angle, which holds for some of the test data. In addition, for a given half-angle, the hardness decreases with the increase of diameter; for a given diameter, the hardness decreases with the increase of half-angle. To take into consideration the uncertainty of test data, a simple interval-based metric was used to compare test data with simulation results; the comparison was satisfactory. The material parameters from the simulations can thus be considered as calibrated ones for the snow studied.     

Intermolecular Stetter reaction of aromatic aldehydes with (E)-(2-nitrovinyl)cyclohexane induced by N-heterocyclic carbene and thiourea

Intermolecular Stetter reaction of aromatic aldehydes with (E)-(2-nitrovinyl)cyclohexane catalyzed by thiazolium A has been developed. The reaction rate and efficiency are profoundly impacted by the presence of thiourea B. The reaction affords moderate to good yields of the Stetter product. Some factors influencing yield were discussed.