曲线坐标系下孔隙介质圆柱纵向表面波的传播特性

为了研究孔隙介质圆柱纵向表面波的传播规律,分析其频散和衰减特性,在正交曲线坐标系下建立了表面波的频散方程,通过数值计算得到频散曲线,将纵向导波最低模态与表面波进行对比,并分析了曲率半径及孔隙参数对表面波频散和衰减的影响。结果表明,当频率足够大时,导波最低模态的频散曲线与表面波近似;在同一频率下,表面波的相速度随曲率半径的增大而增大,随孔隙度的增大而减小;表面波的衰减随孔隙度的增大而增大。研究结果为开展孔隙介质圆柱结构的超声无损评价提供了一定的理论参考。     

Enhanced hydrogen bonding and its dramatic impact on deformation behaviors in a biomedical poly(carbonate urethane) with fluorinated chain extender

The enhanced hydrogen bonding, manifested by significant frequency decreasing of both N? H and C?O stretching vibrations, is confirmed in a biomedical poly(carbonate urethane) with fluorinated chain extender. It gives rise to preferential association among hard segments and thus promoted microphase separation, which is responsible for the plastic deformation behaviors of the fluorinated poly(carbonate urethane). Furthermore, the segmental orientation, including both soft and hard segments, has been well correlated with the enhanced hydrogen bonding as well as promoted microphase separation. Under stretching large domains are prone to orient with their long axis along tensile direction and thus a negative orientation of hard segments is observed. Meanwhile, decreased orientation of soft segments can also find its origin in the reduced crosslinking density provided by hard domains because of preferential association among hard segments in such a biomedical material. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2198–2205, 2009     

含多重时滞非线性系统的分数阶迭代学习控制的收敛性分析

本文研究了含多重时滞非线性系统的分数阶迭代学习控制(FOILC).它包含了外部干扰和输出控制噪音,通过引入λ—范数,获得在开环和闭环迭代学习控制作用下,系统控制输入以及跟踪误差收敛的充分条件.最后,通过数值仿真验证所提方法的有效性.     

Growth mechanism of penniform BaWO4 nanostructures in catanionic reverse micelles involving polymers

The formation of penniform BaWO4 nanostructures made of nanowires or nanobelts under the direction of a block copolymer in catanionic reverse micelles has been studied in detail. On the basis of the experimental results obtained from the BaWO4 crystallization in aqueous polymer solutions and careful transmission electron microscopy (TEM) observations of BaWO4 nanostructures formed in reverse micelles containing polymers, a detailed two-stage growth mechanism has been proposed for the formation of the penniform nanostructures in reverse micelles, which involves the polymer-controlled shaft formation (Stage 1) and the mixed surfactants-controlled barb growth (Stage 2). During Stage 1, poly(ethylene glycol)-block-poly(methacrylic acid) (PEG-b-PMAA) induced the formation of c-axis-oriented shuttle-like nanocrystals and the subsequent oriented attachment of these shuttle-like nanocrystals resulted in the formation of [100]-oriented shafts with many parallel [001]-oriented pricks. During Stage 2, [001]-oriented nanowires or nanobelts grew gradually from the pricks into barbs, leading to the formation of well-defined penniform BaWO4 nanostructures with the barb morphology essentially determined by the mixing ratio r of the anionic to cationic surfactants (i.e., nanowires were formed at r=1 while nanobelts were formed at r deviating from 1). The current understanding of the growth mechanism of penniform BaWO4 nanostructures in catanionic reverse micelles involving polymers may be potentially applied for designing a new synthesis system for the controlled synthesis of other hierarchical 1D nanostructures with desired architectures.     

过硫酸盐氧化-紫外分光光度法测定气溶胶中的总氮

在120℃~124℃的碱性介质条件下,以过硫酸钾作氧化剂,将气溶胶萃取液中有机氮、NH4 、NO2-转化为NO3-,用紫外分光光度法进行分析。结果表明,溶液中有机氮的浓度在120μmol/L以下时,其回收率为97.1%~101.4%;当浓度为120μmol/L以上时,其回收率随着浓度的增大而降低。试验了共存干扰元素对总氮分析的影响,探讨了气溶胶有机氮的分析精密度与有机氮相对含量的关系。     

Potential Role of Quercetin in Polycystic Ovary Syndrome and Its Complications: A Review

Polycystic ovary syndrome (PCOS) is a common multisystem disease with reproductive, metabolic and psychological abnormalities. It is characterized by a high prevalence rate in women of childbearing age and highly heterogeneous clinical manifestations, which seriously harm women’s physical and mental health. Quercetin (QUR) is a natural compound of flavonoids found in a variety of foods and medicinal plants. It can intervene with the pathologic process of PCOS from multiple targets and channels and has few adverse reactions. It is mentioned in this review that QUR can improve ovulation disorder, relieve Insulin resistance (IR), reduce androgen, regulate lipid metabolism, regulate gut microbiota and improve vascular endothelial function, which is of great significance in the treatment of PCOS.     

Ultrathin defective high-entropy layered double hydroxides for electrochemical water oxidation

One of the fundamental driving forces in the materials science community is the hunt for new materials with specific properties that meet the requirements of ra...     

An option for green and sustainable future:Electrochemical conversion of ammonia into nitrogen

Green and sustainable options are needed to ease the current energy and environmental crisis,and alle-viate the greenhouse effect and energy shortage.As an alte...     

Modulation of the superficial electronic structure via metal–support interaction for H2 evolution over Pd catalysts

Electronic interactions can radically enhance the performance of supported metal catalysts and are critical for fundamentally understanding the nature of catalysts. However, at the microscopic level, the details of such interactions tuning the electronic properties of the sites on the metal particle''s surface and metal–support interface remain obscure. Herein, we found polarized electronic metal–support interaction (pEMSI) in oxide-supported Pd nanoparticles (NPs) describing the enhanced accumulation of electrons at the surface of NPs (superficial Pd^δ−) with positive Pd atoms distributed on the interface (interfacial Pd^δ+). More superficial Pd^δ− species mean stronger pEMSI resulting from the synergistic effect of moderate Pd–oxide interaction, high structural fluxionality and electron transport activity of Pd NPs. The surface Pd^δ− species are responsible for improved catalytic performance for H₂ evolution from metal hydrides and formates. These extensive insights into the nature of supported-metal NPs may open new avenues for regulating a metal particle''s electronic structure precisely and exploiting high-performance catalysts.

A new type of electronic effect, polarized metal-support interaction (pEMSI), in oxide-supported Pd nanoparticles describing the enhanced accumulation of electrons at the superficial surface is responsible for improved catalytic H₂ evolution.     

Enabling highly (R)-enantioselective epoxidation of styrene by engineering unique non-natural P450 peroxygenases

Unlike the excellent (S)-enantioselective epoxidation of styrene performed by natural styrene monooxygenases (ee > 99%), the (R)-enantioselective epoxidation of styrene has not yet achieved a comparable efficiency using natural or engineered oxidative enzymes. This report describes the H₂O₂-dependent (R)-enantioselective epoxidation of unfunctionalized styrene and its derivatives by site-mutated variants of a unique non-natural P450BM3 peroxygenase, working in tandem with a dual-functional small molecule (DFSM). The observed (R)-enantiomeric excess (ee) of styrene epoxidation is up to 99% with a turnover number (TON) of 918 by the best enantioselective mutant F87A/T268I/L181Q, while the best active mutant F87A/T268I/V78A/A184L (with 98% ee) gave a catalytic TON of 4350, representing the best activity of a P450 peroxygenase towards styrene epoxidation to date. Following this approach, a set of styrene derivatives, such as o-, m-, p-chlorostyrenes and fluorostyrenes, could also be epoxidized with modest to very good TONs (362–3480) and high (R)-enantioselectivities (95–99% ee). The semi-preparative scale synthesis of (R)-styrene oxide performed at 0 °C with high conversion, maintaining enantioselectivity, and moderate isolated yields, further suggests the potential application of the current P450 enzymatic system in styrene epoxidation. This study indicates that the synergistic use of protein engineering and an exogenous DFSM constitutes an efficient strategy to control the enantioselectivity of styrene epoxidation, thus substantially expanding the chemical scope of P450 enzymes as useful bio-oxidative catalysts.

H₂O₂-dependent epoxidation of unfunctionalized styrenes is achieved with high (R)-enantioselectivity and moderate to excellent TONs by combining site-mutated variants of cytochrome P450BM3 monooxygenase and a dual-functional small molecule (DFSM).