The Physiology of Postharvest Tea (Camellia sinensis) Leaves,According to Metabolic Phenotypes and Gene Expression Analysis

Proper postharvest storage preserves horticultural products, including tea, until they can be processed. However, few studies have focused on the physiology of ripening and senescence during postharvest storage, which affects the flavor and quality of tea. In this study, physiological and biochemical indexes of the leaves of tea cultivar ‘Yinghong 9′ preserved at a low temperature and high relative humidity (15–18 °C and 85–95%, PTL) were compared to those of leaves stored at ambient conditions (24 ± 2 °C and relative humidity of 65% ± 5%, UTL). Water content, chromatism, chlorophyll fluorescence, and key metabolites (caffeine, theanine, and catechins) were analyzed over a period of 24 h, and volatilized compounds were determined after 24 h. In addition, the expression of key biosynthesis genes for catechin, caffeine, theanine, and terpene were quantified. The results showed that water content, chromatism, and chlorophyll fluorescence of preserved leaves were more similar to fresh tea leaves than unpreserved tea leaves. After 24 h, the content of aroma volatiles and caffeine significantly increased, while theanine decreased in both groups. Multiple catechin monomers showed distinct changes within 24 h, and EGCG was significantly higher in preserved tea. The expression levels of CsFAS and CsTSI were consistent with the content of farnesene and theanine, respectively, but TCS1 and TCS2 expression did not correlate with caffeine content. Principal component analysis considered results from multiple indexes and suggested that the freshness of PTL was superior to that of UTL. Taken together, preservation conditions in postharvest storage caused a series of physiological and metabolic variations of tea leaves, which were different from those of unpreserved tea leaves. Comprehensive evaluation showed that the preservation conditions used in this study were effective at maintaining the freshness of tea leaves for 2–6 h. This study illustrates the metabolic changes that occur in postharvest tea leaves, which will provide a foundation for improvements to postharvest practices for tea leaves.     

二氟甲基自由基反应及其在18F标记中的应用

随着正电子发射断层扫描(PET)技术的进步, 高效¹⁸F标记反应显现出重大的研究价值. 同时, 在有机氟化学的快速发展下, 研究人员已开发出一系列产生二氟甲基自由基(·CHF₂)的一碳合成子, 得以被引入到¹⁸F标记反应中. 本文从化学原理出发, 总结了近年来·CHF₂合成子、 碳氢键活化反应及¹⁸F标记的研究, 并展望了未来的研究趋势.     

一维氮掺杂碳包覆Fe3O4和Fe7S8纳米棒复合材料的制备及其储锂、储钠性能研究

以水热法制备的羟基氧化铁纳米棒作为反应原料,首先采用室温聚合法,在其表面包覆一层均匀的聚多巴胺,获得聚多巴胺包覆的羟基氧化铁,然后通过后续热处理,获得氮掺杂碳包覆的Fe3 O4和Fe7 S8复合材料(Fe3O4@NC和Fe7S8@NC).采用XRD、拉曼光谱仪、XPS、SEM以及TEM等技术对上述两种复合材料的结构和形...     

Symmetry-Protected Quantum Adiabatic Evolution in Spontaneous Symmetry-Breaking Transitions

Quantum adiabatic evolution describes the dynamical evolution of a slowly driven Hamiltonian. In most systems undergoing spontaneous symmetry-breaking transitions, the symmetry-protected quantum adiabatic evolution can still appear, even when the two lowest eigenstates become degenerate. Here, a general derivation to revisit the symmetry-dependent transition and the symmetry-dependent adiabatic condition (SDAC) is given. Further, based on the SDAC, an adiabatic-parameter-fixed sweeping scheme is used for achieving fast adiabatic evolution, which is more efficient than the linear sweeping scheme. In the limit of small adiabatic parameter, an analytic inequality is obtained for the ground state fidelity only dependent on the adiabatic parameter. The general statements are then demonstrated via two typical systems. Besides, the robustness of the symmetry-dependent adiabatic evolution against weak symmetry-breaking sources is studied. The findings can be tested via the techniques in quantum annealing and may provide promising applications in practical quantum technologies.     

半潜式海上浮式风机气动阻尼特性研究

由于海上漂浮式风机具有较大的支撑平台运动,气动阻尼效应对海上漂浮式风机的运动响应带来了重要的影响, 日渐受到相关国内外学者的关注. 为了研究海上浮式风机的气动阻尼特性,本文推导了海上浮式风机气动阻尼力的数学模型,并借助模型实验和数值计算的方法,研究了半潜式海上浮式风机的气动阻尼特性及其作用规律. 结果表明,浮式风机的风轮旋转时的气动阻尼比风轮非旋转状态时更加明显;在作业工况下,气动阻尼对半潜式浮式风机平台的纵荡、纵摇、机舱的运动有明显的抑制作用,且主要体现为对半潜式浮式风机的平台运动固有频率响应的抑制作用,对波频范围的平台运动作用甚微. 其变化规律与风速大小、波浪载荷等有关,在风机的额定工况之前,气动阻尼通常与风速呈正相关关系,但是增长率有逐渐减小的趋势;在控制系统作用下,当入流风速接近或超过风机额定风速时,容易出现气动负阻尼现象,反而进一步强化浮式风机的运动响应,此时通过降低变桨距控制器的比例系数,即降低变桨距控制器的灵敏度,有助于增加海上浮式风机的气动阻尼效果,并且在一定程度上减缓负的气动阻尼的发生,改善海上浮式风机的运动响应.      

Aluminoborates as Nonlinear Optical Materials

Ultraviolet (UV) and Deep-UV (DUV, λ<200 nm) nonlinear optical (NLO) materials play a significant role to convert the wavelength of laser for producing UV/DUV coherent light in the laser industry. The Al [Ne]3s²3p¹ atom with empty d orbitals can form sp³, sp³d, and sp³d² hybrid orbitals when bonding with O/F atoms, which leads to the construction of [AlO_mF_n] (m+n=4, 5, 6) units. Therein, aluminoborates have received intensive attention due to the effective structural and functional adjustment effects of the diverse Al−O/F units. Accordingly, numerous aluminoborates as candidates for the next generation of UV/DUV NLO materials were discovered. In this review, recently discovered aluminoborates are overviewed and analyzed, including their syntheses, crystal structure features, and second-order NLO performances. We aim to provide the latest progress and outlook on the crystal chemistry of aluminoborates and boost the finding of the next NLO candidates with high performances.     

Initial offset boosting coexisting attractors in memristive multi-double-scroll Hopfield neural network

Nonlinear Dynamics - Memristors are widely considered to be promising candidates to mimic biological synapses. In this paper, by introducing a non-ideal flux-controlled memristor model into a...     

Magnifying the Structural Components of Biomembranes: A Prototype for the Study of the Self-Assembly of Giant Lipids

How biomembranes are self-organized to perform their functions remains a pivotal issue in biological and chemical science. Understanding the self-assembly principles of lipid-like molecules hence becomes crucial. Herein, we report the mesostructural evolution of amphiphilic sphere-rod conjugates (giant lipids), and study the roles of geometric parameters (head–tail ratio and cross-sectional area) during this course. As a prototype system, giant lipids resemble natural lipidic molecules by capturing their essential features. The self-assembly behavior of two categories of giant lipids (I-shape and T-shape, a total of 8 molecules) is demonstrated. A rich variety of mesostructures is constructed in solution state and their molecular packing models are rationally understood. Giant lipids recast the phase behavior of natural lipids to a certain degree and the abundant self-assembled morphologies reveal distinct physiochemical behaviors when geometric parameters deviate from natural analogues.     

Phytochemical composition profile and space–time accumulation of secondary metabolites for Dracocephalum moldavica Linn. via UPLC–Q/TOF–MS and HPLC–DAD method

The aerial parts of Dracocephalum moldavica L. are extensively used in traditional ethnic medicines in China as a remedy for cardiovascular and cerebrovascular damage. However, the chemical composition and the accumulation of main secondary metabolites of D. moldavica in different natural environments remain unclear. This study aimed to conduct a qualitative and quantitative analysis of the main secondary metabolites to explore the quality variation of D. moldavica in markets. The evaluation of space–time accumulation of main secondary metabolites in D. moldavica was carried out during different growth periods and in different geographical locations. A total of 35 ingredients were detected and 24 identified, including 21 flavonoids, two phenolic acids and one coumarin by UPLC–QTOF–MS method. Furthermore, a simple and convenient HPLC method was successfully developed for the simultaneous determination of lutelin-7-O-glucuronide and tilianin and rosmarinic acid in D. moldavica. The results of space–time accumulation analysis showed the distinct variation of secondary metabolites of D. moldavica with the growth period and geographical location. Finally, the current study provided a meaningful and useful approach for comprehensively evaluating the quality of D. moldavica.     

Electrochemical determination of dopamine and uric acid using a glassy carbon electrode modified with a composite consisting of a Co(II)-based metalorganic framework (ZIF-67) and graphene oxide

A composite was prepared from a Co(II)-based zeolitic imidazolate framework (ZIF-67) and graphene oxide (GO) by an in situ growth method. The material was electrodeposited on a glassy carbon electrode (GCE). The modified GCE was used for the simultaneous voltammetric determination of dopamine (DA) and uric acid (UA), typically at working potentials of 0.11 and 0.25 V (vs. SCE). The morphology and structure of the nanocomposite were characterized by scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy and X-ray diffraction. The modified electrode exhibits excellent electroanalytical performance for DA and UA owing to the synergistic effect of the high electrical conductivity of GO and the porosity of ZIF-67. By applying differential pulse voltammetry, a linear response is found for DA in the 0.2 to 80 μM concentration range, and for UA between 0.8 and 200 μM, with detection limits of 50 and 100 nM (at S/N =?3), respectively. Further studies were performed on the effect of potential interferents, and on electrode stability and reproducibility. The modified GCE was applied to the simultaneous detection of DA and UA in spiked human urine and gave satisfying recoveries.

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Graphical abstract Schematic of the preparation procedure of GO-ZIF67 and electrochemical reaction mechanisms of UA and DA at the GO-ZIF67-modified glassy carbon electrode (GCE). GO: graphene oxide; ZIF-67: Co(II)-based zeolitic imidazolate framework.