Redox Modulation of the Reactivity and Regioselectivity in Diels–Alder Reaction of Metallofullerene La@C82 with Cyclopentadiene

Modulation of the reactivity of metallofullerenes is critical for production of metallofullerene derivatives with desired properties and functionalities. In this study, we investigate the effects of reduction and oxidation on the reactivity and regioselectivity in Diels–Alder reaction of metallofullerene La@C₈₂ by means of density functional theory calculations. Because of the enhanced electron-deficiency characteristic upon oxidation, the oxidized metallofullerene exhibits higher thermodynamic and kinetic reactivity as compared with neutral La@C₈₂. The regioselectivity in the reaction of La@C₈₂ with cylcopentadiene is remarkably changed after oxidation of the metallofullerene, which is explained in terms of the changes in the geometrical structure and the electronic structure of the metallofullerene. Quantitative analysis based on the activation-strain model demonstrates that the low activation energy barrier for the reaction of the cation La@C₈₂⁺ with cyclopentadiene originates from small strain energy and large interaction energy between the reactants. Energy decomposition analysis on the transition states of the reactions reveals that the exchange-repulsion interaction energy is one of the critical factors that determine the kinetic reactivity of the metallofullerene. This study not only provides new theoretical insights on how to modulate the reactivity of metallofullerenes, but also offers guideline for future experimental synthesis of new metallofullerene derivatives.     

Improved heat resistance in poly (lactic acid)/ethylene butyl methacrylate glycidyl methacrylate terpolymer blends by controlling highly filled talc particles

Journal of Thermal Analysis and Calorimetry - Heat resistance poly(lactic acid) PLA/ethylene butyl methacrylate glycidyl methacrylate terpolymer (GEBMA)/talc composites were fabricated by melt...     

基于畸变相位波前分形特征产生矩形湍流相屏

在包含时间进程的光波大气传输及其自适应光学相位校正的数值模拟研究中,如长曝光成像和自适应光学系统的动态控制过程,矩形湍流相屏的产生和应用尤为重要.而现在通常使用的功率谱反演法产生的是正方形的湍流相屏,只采用其中的矩形部分显然造成计算机资源的浪费;并且谱反演法产生的湍流相屏需要进行低频补偿,从而明显地增加计算量.基于大气湍流所造成的畸变相位波前的分形特征,提出了一种产生矩形湍流相屏的新方法,并与解析理论结果进行对比,验证了这种矩形相屏产生方法的正确性.与已有的方法相比,此算法具有两个明显的优点:算法简单、计算效率高,节省计算机资源;与大气湍流介质统计特性无论在高频部分还是在低频部分均符合得较好.     

大型设备中金属跌落零件的声学定位问题研究

针对金属跌落零碰金属板产生的冲击信号，比较了时域初始过零点法和能量比法两种时间延心估计方法。     

Extraction of weak crack signals based on sparse code shrinkage combined with wavelet packet filtering

Early crack signals in critical infrastructure components of major equipment are hardly to be extracted due to its low signal noise ratio (SNR). A de-noising method combined wavelet packet (WP) technology with sparse code shrinkage (SCS) is proposed in this study. Firstly, WP reconstruction technology is used to reserve the crack signal with a specified frequency range. That is, the signal is decomposed by Meyer wavelet into five layers, and the signal with the frequency range from 187.5 kHz to 609.375 kHz is reserved. Then SCS method removes noise within the specified frequency range. Namely, the probability density function (PDF) of the signal independent coefficients is estimated via the generalized Gaussian model (GGM) in the independent component analysis (ICA) space. The nonlinear de-noising is finished by utilizing maximum a posteriori (MAP) estimate. The results obtained by the combined method are compared with those generated by the SCS method and the WP de-noising method. It demonstrates that the combined method is the best one among the three methods in extracting weak signals. Its output SNR is −2.38 dB and the correlation coefficient (CC) is 0.54 when the input SNR is −20 dB. They are higher than those obtained by the SCS method (SNR −4.46 dB and CC 0.51). The WP method is the worst (SNR −3.54 dB and CC −0.003). Therefore, the combined method is quite suitable for weak signal extraction.     

Antigen detection based on background fluorescence quenching immunochromatographic assay

Gold immunochromatographic assay (GICA) has been around for quite a while, but it is qualitative in the vast majority of applications. A fast, simple and quantitative GICA is in call for better medicine. In the current study, we have established a novel, quantitative GICA based on fluorescence quenching and nitrocellulose membrane background signals, called background fluorescence quenching immunochromatographic assay (bFQICA). Using model analyte alpha-fetoprotein (AFP), the present study assessed the performance of bFQICA in numerous assay aspects. With serial dilutions of the international AFP standard, standard curves for the calculation of AFP concentration were successfully established. At 10 and 100 ng mL⁻¹ of the international AFP standard, the assay variability was defined with a coefficient of variance at 10.4% and 15.2%, respectively. For samples with extended range of AFP levels, bFQICA was able to detect AFP at as low as 1 ng mL⁻¹. Fluorescence in bFQICA strips stayed constant over months. A good correlation between the results from bFQICA and from a well-established Roche electrochemiluminescence immunoassay was observed in 27 serum samples (r = 0.98, p < 0.001). In conclusion, our study has demonstrated distinctive features of bFQICA over conventional GICA, including utilization of a unique fluorescence ratio between nitrocellulose membrane background and specific signals (F1/F2) to ensure accurate measurements, combined qualitative and quantitative capabilities, and exceptionally high sensitivity for detection of very low levels of antigens. All of these features could make bFQICA attractive as a model for antigen-antibody complex based GICA, and could promote bFQICA to a broad range of applications for investigation of a variety of diseases.     

Finiteness and Dehn functions of automatic monoids having directed fellow traveller property

A left-cancellative automatic monoid having directed fellow traveller property is finitely presented, and the first order Dehn functions of such automatic monoids are bounded above by a quadratic function. These results coincide with those of automatic groups. The research of X. Wang was partially supported by China National Science Funds (No:10771077 and 10671114).     

Investigation of structure and magnetic characteristics of Ni-implanted AlGaN films

The structural, valence of elements and magnetic characteristics of Ni-implanted Al_0.5Ga_0.5N films, deposited on Al₂O₃ substrates by metalorganic chemical vapor deposition (MOCVD), were reported. Ni ions were implanted into Al_0.5Ga_0.5N films by Metal Vapor Arc (MEVVA) sources under the energy of 100 keV for 3 h. The films were annealed at 900 K in the furnace for the transference of Ni ions from interstitial sites to substitutional sites in AlGaN and activating the Ni³⁺ ions. Characterizations were carried out in situ using X-ray diffraction (XRD), X-ray photoemission spectroscopy (XPS) and Vibrating sample magnetometer (VSM), indicating that the films have wurtzite structure without forming a secondary phase after annealing. Ni ions were successfully implanted into substitutional sites of Al_0.5Ga_0.5N films and the chemical bonding states of Ni³⁺ is Ni–N. The apparent hysteresis loops prove the films exhibited ferromagnetism at 300 K. The room temperature (RT) M_s and H_c obtained were approximately 0.22 emu/g and 32.97 Oe, respectively. From the first-principles calculation, A total magnetic moment of 2.86 μB per supercell is calculated: the local magnetic moment of NiN₄ tetrahedron, 2.38 μB, makes the primary contribution. The doped Ni atom hybridizes with its four nearby N atoms in NiN₄ tetrahedron, then N atoms are spin polarized and couple with Ni atom with strong magnetization, which result in ferromagnetism. Therefore, the p-d exchange mechanism is responsible for ferromagnetism in Ni-doped AlGaN. It is expected that the room temperature ferromagnetic Ni-doped Al_0.5Ga_0.5N films can make it possible to the applications for the spin electric devices.     

久坐对脊椎肌肉sEMG信号的影响

采集18名女性受试者在不同久坐时间下,颈夹肌和竖脊肌在最大用力收缩（MVC）过程中的表面肌电（surface electromyography, sEMG）信号,分别考察其初始1.5 s的线性时频指标AEMG、MPF、非线性分析指标%DET的差异,以及全程MVC过程中MPF的变化趋势,以探讨久坐对脊椎肌肉活动水平和功能状态的影响.发现：在久坐前、久坐1.5 h、久坐3 h之后3种状态下,颈夹肌和竖脊肌在MVC的前1.5 s信号中,其时频信号AEMG、MPF及非线性信号%DET均无明显变化;在1 min脊椎持续MVC过程中,颈夹肌MPF均呈现线性递减趋势,且下降速率依次增大;竖脊肌MPF则呈现线性递增趋势,且上升速率依次减小.由此可得,久坐对于脊椎肌肉的最大收缩力量并无影响,但是对其维持最大收缩力量的能力有所改变.