The double velocity correlation function of homogeneous turbulence with constant mean velocity gradient

In this article, as the velocity gradient is taken as a constant value, we obtain the solutions of the equation of fluctuation velocity after Fourier transform. When the mean velocity gradient is small, they represent the picture of eddies, of which the homogeneous turbulence (both isotropic and nonisotropic) of the final period is composed. By using the eddies of these types at different times, we may compose the steady turbulent field with the constant velocity gradient and this field may represent the turbulent field in the central part of the channel flow or pipe flow approximately. Then we may obtain the double velocity correlation function of this turbulent field, which involves both longitudinal correlation coefficient and the transversal correlation coefficient . We compare these theoretical coefficients with the experimental data of these coefficients at initial period and final period of isotropic homogeneous turbulence. And then we obtain the relationship between the turbulent double velocity correlation coefficient and the mean velocity gradient. Finally, we get the expressions of the Reynolds stress and the eddy viscosity coefficient.     

Protective Effects of Jujubosides on 6-OHDA-Induced Neurotoxicity in SH-SY5Y and SK-N-SH Cells

6-hydroxydopamine (6-OHDA) is used to induce oxidative damage in neuronal cells, which can serve as an experimental model of Parkinson’s disease (PD). Jujuboside A and B confer free radical scavenging effects but have never been examined for their neuroprotective effects, especially in PD; therefore, in this study, we aimed to investigate the feasibility of jujubosides as protectors of neurons against 6-OHDA and the underlying mechanisms. 6-OHDA-induced neurotoxicity in the human neuronal cell lines SH-SY5Y and SK-N-SH, was used to evaluate the protective effects of jujubosides. These findings indicated that jujuboside A and B were both capable of rescuing the 6-OHDA-induced loss of cell viability, activation of apoptosis, elevation of reactive oxygen species, and downregulation of the expression levels of superoxide dismutase, catalase, and glutathione peroxidase. In addition, jujuboside A and B can reverse a 6-OHDA-elevated Bax/Bcl-2 ratio, downregulate phosphorylated PI3K and AKT, and activate caspase-3, -7, and -9. These findings showed that jujubosides were capable of protecting both SH-SY5Y and SK-N-SH neuronal cells from 6-OHDA-induced toxicity via the rebalancing of the redox system, together with the resetting of the PI3K/AKT apoptotic signaling cascade. In conclusion, jujuboside may be a potential drug for PD prevention.     

Ultrasound Plus Vacuum-System-Assisted Biocatalytic Synthesis of Octyl Cinnamate and Response Surface Methodology Optimization

Cinnamic acid is one of the phenolic compounds that is isolated from cinnamon, or other natural plants, and has a wide range of physiological activities. However, the application of cinnamic acid is limited due to its poor solubility and low oral bioavailability. In this study, the feasibility of producing octyl cinnamate by ultrasonic assistance, combined with a rotary evaporation under vacuum, was studied using methyl cinnamate and octanol as the starting materials. A Box–Behnken design (BBD) was employed to evaluate the effects of the operation parameters, including reaction temperature (55–75 °C), reaction time (4–12 h), and ultrasonic power (90–150 W) on the production of octyl cinnamate. Meanwhile, the synthesis process was further optimized by the modeling response surface methodology (RSM). The data indicated that octyl cinnamate was efficiently synthesized from methyl cinnamate and octanol using the ultrasound plus vacuum system; further, this system was superior to the conventional method. According to the RSM model for the actual experiments, a reaction temperature of 74.6 °C, a reaction time of 11.1 h, and an ultrasound power of 150 W were determined to be the best conditions for the maximum molar conversion of octyl cinnamate (93.8%). In conclusion, the highly efficient synthesis of octyl cinnamate by a rotary evaporator with an ultrasound plus vacuum system was achieved via RSM optimization.     

Cryptanalysis of a Semi-Quantum Bi-Signature Scheme Based on W States

Recently, Zhao et al. proposed a semi-quantum bi-signature (SQBS) scheme based on W states with two quantum signers and just one classical verifier. In this study, we highlight three security issues with Zhao et al.’s SQBS scheme. In Zhao et al.’s SQBS protocol, an insider attacker can perform an impersonation attack in the verification phase and an impersonation attack in the signature phase to capture the private key. In addition, an eavesdropper can perform a man-in-the-middle attack to obtain all of the signer’s secret information. All of the above three attacks can pass the eavesdropping check. Without considering these security issues, the SQBS protocol could fail to ensure the signer’s secret information.     

机器学习在大型粒子加速器中的应用回顾与展望

机器学习技术在近十几年发展迅猛,并被广泛地用于解决复杂的科学和工程问题。最近十年间,基于机器学习的粒子加速器相关研究也开始呈现出井喷式发展趋势。国际上许多加速器实验室开始尝试用机器学习和大数据技术处理加速器中的海量复杂数据,以期解决加速器及其子系统中的诸多物理和技术问题。不过,迄今为止,机器学习在加速器中的应用仍处于初步探索阶段,不同机器学习算法在解决具体加速器问题的效果及其适用范围尚待摸索,机器学习在实际加速器中的应用仍非常有限。因此,有必要对加速器领域中的机器学习研究做一个整体回顾和总结。将回顾机器学习在大型粒子加速器（以储存环加速器和直线加速器为主）中的加速器技术、束流物理以及加速器整体性能优化等研究方向中已取得的研究成果,并探讨机器学习在加速器领域的未来发展方向和应用前景。

     

A Drying‐Free,Water‐Based Process for Fabricating Mixed‐Matrix Membranes with Outstanding Pervaporation Performance

Despite much progress in the development of mixed matrix membranes (MMMs) for many advanced applications, the synthesis of MMMs without particle agglomeration or phase separation at high nanofiller loadings is still challenging. In this work, we synthesized nanoporous zeolitic imidazole framework (ZIF‐8) nanoparticles with a particle size of 60 nm and a pore size of 0.34 nm in water and directly added them into an aqueous solution of the organic polymer poly(vinyl alcohol) (PVA) without an intermediate drying process. This approach led to a high‐quality PVA/ZIF‐8 MMM with enhanced performance in ethanol dehydration by pervaporation. The permeability of this MMM is three times higher than that of pristine PVA, and the separation factor is nearly nine times larger than that of pristine PVA. The significantly improved separation performance was attributed to the increase in the fractional free volume in the membranes.     

Stereoselective Michael-alkylation and Michael-oxidation reactions of chiral 1,3-dioxolanones

A highly diastereoselective Michael-alkylation/oxidation methodology has been developed for the synthesis of optically active α-hydroxy-1,5-diester subunits. Inverse stereochemistry at the C_2′ position could be achieved by using a Michael acceptor equipped with a suitable group followed by a highly stereoselective protonation. This methodology has been applied to the enantioselective synthesis of the upper fragment of (+)-retusine.