A simple and efficient biphasic method for the preparation of 4-nitrophenyl N-methyl- and N-alkylcarbamates

Treatment of 4-nitrophenyl chloroformate with alkylammonium hydrochloride salts and solid anhydrous Na₂CO₃ in either CH₂Cl₂ or CH₃CN gave 4-nitrophenyl N-methylcarbamate and other N-alkylcarbamate analogues in excellent yields. Of particular interest is the observation that 4-nitrophenyl N-methylcarbamate, a safer alternative to the highly toxic methyl isocyanate, is obtained in quantitative yield (?95% pure as determined by ¹H NMR) after simple filtration and solvent evaporation.     

Improving amplitude-modulated signals by re-scaled and twice sampling vibrational resonance methods

Quantum chemical calculations have been employed to study the molecular effects produced by \(\hbox {Cr}_{2}\hbox {O}_{3}/\hbox {SnO}_{2}\) optimised structure. The theoretical parameters of the transparent conducting metal oxides were calculated using DFT / B3LYP / LANL2DZ method. The optimised bond parameters such as bond lengths, bond angles and dihedral angles were calculated using the same theory. The non-linear optical property of the title compound was calculated using first-order hyperpolarisability calculation. The calculated HOMO–LUMO analysis explains the charge transfer interaction between the molecule. In addition, MEP and Mulliken atomic charges were also calculated and analysed.     

悬浮振子对中耳声传播特性影响的数值研究

为研究悬浮式中耳植入式助听装置中悬浮振子对中耳声传播特性的一些影响,建立了包括绑定悬浮振子的中耳有限元模型. 该模型基于一无任何听力损伤病史的成年志愿者的左耳,利用CT扫描和逆向成型技术建成. 模型的可靠性通过鼓膜及镫骨底板的位移计算结果与国外文献实验测得数据进行对比加以验证. 研究结果表明:悬浮振子的绑定会显著恶化中耳的高频传输特性;振子输出8.9\times10^5N的激振力才能激起100dB声压所对应的激振效果;振子在砧骨长突上的绑定位置离砧镫关节越近,高频段激振效果越好.      

Unknown bearing fault diagnosis under time-varying speed conditions and strong noise background

The bearing vibration signal shows strong non-stationary property under time-varying speed conditions. In addition, the weak bearing fault characteristic is often submerged in strong background noise. How to accurately extract the unknown fault characteristic from the non-stationary vibration signal is the primary problem of bearing fault diagnosis. Stochastic resonance has been proved to be an effective weak signal enhancement method. Therefore, an unknown bearing fault detection technology of speed variation is proposed, which breaks through the periodicity limitation of the classical stochastic resonance on the input signal. It enables stochastic resonance suitable for the enhancement of non-stationary fault signal. Firstly, the non-stationary vibration signal is processed by the computed order tracking to obtain the stationary signal in angular domain. To extract the potential feature information, the bearing imaginary fault order index is constructed from the angular domain order spectrum. Then, the resonance response at the imaginary fault order is obtained. Finally, the coherence resonance theory is introduced to judge the bearing fault pattern through the resonance factor index of response order spectrum. The proposed method overcomes the fuzzy mapping relationship between the signal symptom and the bearing fault caused by speed variation. The experimental data analysis results provide effective support for the proposed method.