钌催化烯丙基醇的动力学拆分以及二苯基氯化膦还原的机理研究

Sat, 27 Jul 2024 02:41:53 GMT

题名: 钌催化烯丙基醇的动力学拆分以及二苯基氯化膦还原的机理研究作者: 王东浩摘要:

手性烯丙基醇结构存在于许多药物分子和生物活性分子当中，是天然化合物最重要的结构单元之一。目前，对于该结构的合成方法主要是在金属或有机催化剂的存在下对羰基化合物进行对映选择性加氢，然而该方法对于某些底物存在一定局限性。另一方面，动力学拆分能够提供与不对称氢化绝对构型相反的手性烯丙醇，可以与氢化法形成互补。本文报道了一种手性钌（II）氢转移催化剂，可以对一类含有（Z）-烯烃基团的烯丙醇底物进行有效的动力学拆分以构建对应的手性（Z）-烯丙醇，其拆分效率（s 值）位于第一梯队。该方法还能有效应用于含有 Z/E 混合物的外消旋烯丙醇的动力学拆分，以产生只含纯（Z）-烯丙醇的产物。为了探究该方法对于生物活性分子的合成应用，查阅文献设计了使用该方法合成 1,2-胺基醇缩酮（生物活性分子）的合成路线，并进行了外消旋产物的合成。使用该修饰后的方法合成了相应的 1,2-胺基醇并进行了表征。对三价膦氯化物进行转化是工业上合成各种三价膦衍生物的最重要方法，而二苯基膦作为一种非常重要的化工原料，其合成需要使用无机强还原剂进行反应。本文报道了一种使用甲酸盐进行二苯基氯化膦还原的例子，并通过理论计算解析了其反应过程，阐明了其目前产率存在上限的原因，同时提出了进一步提高产率的办法。

Influence of the Yucatan earthquake event (vol 11, 1201576, 2023)

Fri, 19 Jul 2024 09:32:13 GMT

题名: Influence of the Yucatan earthquake event (vol 11, 1201576, 2023) 作者: Li, Changcheng

Recent advances in the chemistry of isolable carbene analogues with group 13-15 elements (vol 53, pg 3896, 2024)

Fri, 19 Jul 2024 09:31:18 GMT

题名: Recent advances in the chemistry of isolable carbene analogues with group 13-15 elements (vol 53, pg 3896, 2024) 作者: He, Mian; Hu, Chaopeng; Wei, Rui; Wang, Xin-Feng; Liu, Liu Leo 摘要: Correction for 'Recent advances in the chemistry of isolable carbene analogues with group 13-15 elements' by Mian He et al., Chem. Soc. Rev., 2024, https://doi.org/10.1039/D3CS00784G.

Multi-angle tracking synthetic kinetics of phase evolution in Li-rich Mn-based cathodes (Vol 17, pg 3807, 2024)

Fri, 19 Jul 2024 09:30:57 GMT

题名: Multi-angle tracking synthetic kinetics of phase evolution in Li-rich Mn-based cathodes (Vol 17, pg 3807, 2024) 作者: Xu, Shenyang; Chen, Zhefeng; Zhao, Wenguang; Ren, Wenju; Hou, Chenxin; Liu, Jiajie; Wang, Wu; Yin, Chong; Tan, Xinghua; Lou, Xiaobing; Yao, Xiangming; Gao, Zhihai; Liu, Hao; Wang, Lu; Yin, Zuwei; Qiu, Bao; Hu, Bingwen; Li, Tianyi; Dong, Cheng; Pan, Feng; Zhang, Mingjian 摘要: Correction for 'Multi-angle tracking synthetic kinetics of phase evolution in Li-rich Mn-based cathodes' by Shenyang Xu et al., Energy Environ. Sci., 2024, https://doi.org/10.1039/d3ee04199a.

Locating Current Leakage Point of Subway and HVDC with Multi Components Geoelectrical Potential Monitoring

Fri, 19 Jul 2024 09:15:45 GMT

题名: Locating Current Leakage Point of Subway and HVDC with Multi Components Geoelectrical Potential Monitoring 作者: Zhang, Xin; Han, Peng; Yang, Xiaodong; Huang, Yuanmin; Wu, Xiaoping 摘要: Significant disturbances of stray currents caused by subway leakage and unbalanced high-voltage direct current (HVDC) have a significant impact on grounded motors. To obtain the subway leakage current and HVDC ground current, two types of multi-pole distance devices with 6/8 electrodes for orthogonal combination are used. The template matching method is applied to identify the spontaneous potential (SP) pulses generated by subway train start/stop, and daily variation correction is utilized to determine geoelectric field (GEF) step changes caused by HVDC. The results show that (1) the number of SP pulses picked up after template matching corresponds to the number of running trains and the combination of pulses from multiple component orientations reflects the orientation of leakage point; (2) the method for locating current leakage sources can identify the positions of two HVDC converter stations after daily variation correction by analyzing the GEF observation from numerous stations; (3) there are slight dissimilarities between the HVDC simulation and GEF observation due to local electromagnetic environment and electrical structure factors. Therefore, accurate signals of orthogonal observation and positioning methods are crucial for confirming the interference source; after correction in the normal signals, results of good electromagnetic observation can be obtained.

Adaptive online mean-variance portfolio selection with transaction costs

Fri, 19 Jul 2024 09:15:40 GMT

题名: Adaptive online mean-variance portfolio selection with transaction costs 作者: Guo, Sini; Gu, Jia-Wen; Ching, Wai-Ki; Lyu, Benmeng 摘要: Online portfolio selection is attracting increasing attention in both artificial intelligence and finance communities due to its efficiency and practicability in deriving optimal investment strategies in real investment activities where the market information is constantly renewed every second. The key issues in online portfolio selection include predicting the future returns of risky assets accurately given historical data and providing optimal investment strategies for investors in a short time. In the existing online portfolio selection studies, the historical return data of one risky asset is used to estimate its future return. In this paper, we incorporate the peer impact into the return prediction where the predicted return of one risky asset not only depends on its past return data but also the other risky assets in the financial market, which gives a more accurate prediction. An adaptive moving average method with peer impact (AOLPI) is proposed, in which the decaying factors can be adjusted automatically in the investment process. In addition, the adaptive mean-variance (AMV) model is firstly applied in online portfolio selection where the variance is employed to measure the investment risk and the covariance matrix can be linearly updated in the investment process. The adaptive online moving average mean-variance (AOLPIMV) algorithm is designed to provide flexible investment strategies for investors with different risk preferences. Finally, numerical experiments are presented to validate the effectiveness and advantages of AOLPIMV.

Wafer-scale single-crystalline MoSe₂ and WSe₂ monolayers grown by molecular-beam epitaxy at low-temperature - the role of island-substrate interaction and surface steps

Fri, 19 Jul 2024 09:12:36 GMT

题名: Wafer-scale single-crystalline MoSe₂ and WSe₂ monolayers grown by molecular-beam epitaxy at low-temperature - the role of island-substrate interaction and surface steps 作者: Xia, Yipu; Ding, Degong; Xiao, Ke; Zhang, Junqiu; Xu, Shaogang; He, Daliang; Yue, Xingyu; Rao, Qing; Wang, Xiong; Ding, Sujuan; Gao, Guoyun; Xue, Hongxia; Wang, Yueyang; Yuan, Mengfei; Ho, Wingkin; Ki, Dong-Keun; Xu, Hu; Cui, Xiaodong; Jin, Chuanhong; Xie, Maohai 摘要: Ultrathin two-dimensional transition-metal dichalcogenides (TMDs) have been pursued extensively in recent years for interesting physics and application potentials. For the latter, it is essential to synthesize crystalline TMD monolayers at wafer-scale. Here, we report growth of single-crystalline MSe2 (M = Mo, W) monolayers at wafer-scale by molecular-beam epitaxy at low temperatures (200-400degree celsius) on nominally flat Au(1 1 1) substrates. The epifilms have low intrinsic defect densities of low 10(12) cm(-2). The grown films have then been exfoliated and transferred onto SiO2/Si by a wet chemical process, on which some optical measurements are performed, revealing high spatial uniformity of the samples. We also establish that MSe2 grows on Au via the van der Waals epitaxy mechanism, where a continuous film extends across the whole surface, overhangs atomic-layer steps on substrate. We identify that the growth of highly crystalline MSe2 is promoted by an enhanced interaction between Au substrate and MSe2 islands rather than by the guidance of surface steps on substrate. The latter only arrests MSe2 lateral growth if they are multilayer high.Key points:center dot MBE growth of wafer-scale highly crystalline TMD monolayers at low-temperature is achieved.center dot Island-substrate interaction is found to play a critical role in vdW epitaxy of single-crystalline TMDs on on-axis substates.center dot The TMD monolayers are of high uniformity and low intrinsic defect density.

Semiclassical spacetimes at super-Planckian scales from delocalized sources

Fri, 19 Jul 2024 09:06:27 GMT

题名: Semiclassical spacetimes at super-Planckian scales from delocalized sources 作者: Akil, A.; Cadoni, M.; Modesto, L.; Oi, M.; Sanna, A. P. 摘要: We derive the gravitational field and the spacetime metric generated by sources in quantum super-position of different locations. We start by working in a Newtonian approximation, in which the effective gravitational potential is computed as the expectation value of the gravitational potential operator in a Gaussian distribution of width R for the position of the source. The effective gravitational potential is then covariantly uplifted to a fully relativistic metric in general relativity, describing the spacetime generated by averaging over the state of such sources. These results are then rederived and extended by adopting an independent construction in terms of quantum reference frames. We find three classes of quantum effective metrics which are all asymptotically flat and reproduce the Schwarzschild metric at great distances. The solutions differ, however, in the inner core. The quantum uncertainty Delta r similar to R in the position of the source prevents the radius of the transverse two-sphere to shrink to zero. Depending on the strength of the quantum superposition effects, we have either a nonsingular black hole with a "quantum hair" and an event horizon, a one-way wormhole with a critical null throat or a traversable wormhole. We also provide a detailed study of the geometric and thermodynamic properties of the spacetime structure for each of these three families of models, as well as their phenomenology.

Quantum interference in the Kerr spacetime

Fri, 19 Jul 2024 09:04:18 GMT

题名: Quantum interference in the Kerr spacetime 作者: Mo, Zhongyou; Modesto, Leonardo 摘要: The gravitational induced interference is studied here in the framework of teleparallel gravity. We derive the gravitational phase difference and we apply the result to the case of a Kerr spacetime. Afterwards, we compute the fringe shifts in an interference experiment of particles and discuss how to increase their values by changing the given parameters that include the area in between the paths, the energy of the particles, the distance from the black hole, the mass, and the spin of the black hole. It turns out that it is more difficult to detect the fringe shifts for massless particles than for massive particles. As a further application, we show how the mass of the black hole and its angular momentum can be obtained from the measurement of the fringe shifts. Finally, we compare the phase difference derived in teleparallel gravity with a previous work in general relativity.

Photocatalytic degradation of different types of microplastics by TiO_x/ZnO tetrapod photocatalysts

Fri, 19 Jul 2024 09:03:26 GMT

题名: Photocatalytic degradation of different types of microplastics by TiO_x/ZnO tetrapod photocatalysts 作者: He, Yanling; Rehman, Atta Ur; Xu, Muxian; Not, Christelle A.; Ng, Alan M. C.; Djurisic, Aleksandra B. 摘要: We investigated the use of titania coated ZnO tetrapods for photocatalytic degradation of two common types of microplastics, namely polyethylene (PE) microparticles and polyester (PES) microfibers. We found that the plastics morphology affects the rate of degradation, and that the use of electron scavengers is needed to maintain the reactivity of the photocatalysts over a prolonged period of time. Complete mass loss of PE and PES is achieved under UV illumination for 480 h and 624 h, respectively. In addition to pristine microplastics, the degradation of environmental microplastics sample (consisting primarily of polypropylene) was also demonstrated, though in this case longer degradation time (similar to 816 h) was needed to achieve complete mass loss of the samples.

钌催化烯丙基醇的动力学拆分以及二苯基 氯化膦还原的机理研究