Noncentrosymmetric Tetrel Pnictides RuSi4P4 and IrSi3P3: Nonlinear Optical Materials with Outstanding Laser Damage Threshold

Noncentrosymmetric (NCS) tetrel pnictides have recently generated interest as nonlinear optical (NLO) materials due to their second harmonic generation (SHG) activity and large laser damage threshold (LDT). Herein nonmetal-rich silicon phosphides RuSi₄P₄ and IrSi₃P₃ are synthesized and characterized. Their crystal structures are reinvestigated using single crystal X-ray diffraction and ²⁹Si and ³¹P magic angle spinning NMR. In agreement with previous report RuSi₄P₄ crystallizes in NCS space group P1, while IrSi₃P₃ is found to crystallize in NCS space group Cm, in contrast with the previously reported space group C2. A combination of DFT calculations and diffuse reflectance measurements reveals RuSi₄P₄ and IrSi₃P₃ to be wide bandgap (E_g) semiconductors, E_g = 1.9 and 1.8 eV, respectively. RuSi₄P₄ and IrSi₃P₃ outperform the current state-of-the-art infrared SHG material, AgGaS₂, both in SHG activity and laser inducer damage threshold. Due to the combination of high thermal stabilities (up to 1373 K), wide bandgaps (≈2 eV), NCS crystal structures, strong SHG responses, and large LDT values, RuSi₄P₄ and IrSi₃P₃ are promising candidates for longer wavelength NLO materials.     

冠状动脉系统的微分积分终端滑模混沌抑制

冠状动脉系统的混沌现象会导致严重的健康问题。以非线性冠状动脉系统为研究对象，建立了不确定性冠状动脉系统动力学模型，提出了不确定性冠状动脉系统的微分积分终端滑模混沌抑制方法，针对该模型的不确定性设计了扰动观测器，根据Lyapunov理论证明了所设计控制系统的稳定性，通过仿真实验验证了所提出的混沌抑制方法的有效性和可行性。     

高压静电场协同抗氧化剂抑制大豆油氧化

高压静电场作为物理加工技术,近年来在食品领域有一定应用,但在油脂加工方面的应用鲜有报道。本研究以大豆油为原料,通过探究过氧化值、酸价、羰基价、茴香胺值及典型脂肪酸相对含量的变化,考察高压静电场对大豆油油脂氧化的影响。研究表明当高压静电场场强为150?k V/m时,对大豆油油脂氧化的抑制效果最好。在该场强下,协同考察了茶多酚、植酸、特丁基对苯二酚这3种抗氧化剂对大豆油氧化的抑制效果。结果表明:150?k V/m高压静电场结合茶多酚的方式增强了茶多酚的抗氧化效果,可以有效抑制大豆油的氧化,其对过氧化值、酸价、羰基价及茴香胺值的抑制率分别达到34.4%、67.6%、66.0%及55.0%。高压静电场结合茶多酚的处理方式,为抑制大豆油油脂氧化提供了全新的研究思路。     

分数阶PID控制对钻柱黏滑振动的抑制

钻柱黏滑振动是导致钻井设备加速磨损、钻井安全性下降以及钻井效率降低的重要原因之一。针对钻柱的扭转运动,建立了钻柱、钻杆、BHA及钻头4自由度钻柱系统扭转模型。该模型考虑了扭转自由度、钻柱阻尼以及岩石与钻头相互作用的高度非线性摩擦;通过对钻柱模型进行仿真试验,分析了钻井参数对黏滑振动的影响;为了抑制钻柱黏滑振动,设计了一种分数阶PID控制器。研究结果表明:分数阶PID控制器能够快速稳定系统,缩短调节时间,有效抑制钻柱黏滑振动,它对黏滑振动的抑制效果明显优于传统PID控制器。研究结果对抑制钻柱黏滑振动研究具有参考意义,对降低钻井工具损害、提高钻井效率以及增强作业安全性有重要的指导意义。     

Effect of O2 and temperature on the catalytic performance of Ni/Al2O3 and Ni/MgAl2O4 for the dry reforming of methane (DRM)

Al₂O₃ and MgAl₂O₄ supported 10% (w/w) Ni catalysts having a dispersion of 1.5 and 2.0% are active for DRM at 600 and 750 °C. High temperature reduction of both the calcined catalysts resulted in metallic Ni being formed, suggesting strong support metal interactions. The CH₄ and CO₂ conversion during DRM are relatively constant with time-on-stream, and are higher for Ni/MgAl₂O₄ than Ni/Al₂O₃. Carbon-whiskers are also detected on both catalysts. O₂ co-feed of 2.6% (v/v) and increasing reaction temperature to 750 °C helped in decreasing the amount of carbon deposited, except for Ni/MgAl₂O₄ at 600 °C. Furthermore, higher conversions and H₂/CO ratios are achieved. It appears that on spent Ni/MgAl₂O₄ a different type of carbon species was formed, and this carbon species was difficult to remove by oxygen at 600 °C. Thus, co-feeding O₂, using an appropriate temperature, and choosing a suitable support can reduce the carbon present on the nickel catalysts during DRM.     

A two-stage vision-based method for measuring the key parameters of ball screws

Ball screws are crucial for improving the reliability and interchangeability of transmission mechanical systems; however, existing contact measurement methods that utilise stylus contact are not efficient, which precludes their use for rapid in-situ geometry evaluation. This paper presents a vision-based two-stage method for rapid measurement of key parameters (raceway arc radii and centre distance) of ball screws. The edge contour information is extracted from the acquired image using the dual-tree complex wavelet transform and non-maximal suppression. In the matching stage, a shape-matching algorithm is used for detecting approximate geometrical centres of raceway arcs. The refinement stage, on the other hand, is implemented for acquiring precise dimensional results. Furthermore, the method of averaging multiple measurements is performed to suppress random noise. A comparative experiment is presented to validate the robustness of the proposed method. Based on experimental results, the calculated mean absolute errors in the measurement of the two raceway arc radii and the centre distance are found to be 0.0082 mm, 0.0079 mm and 0.0055 mm, respectively. This study therefore paves the way for key parameter measurement without removing ball screws.     

全地域机动车驾驶室声学特性分析

以某全地域机动车驾驶室为研究对象,建立驾驶室的有限元模型,验证了有限元模型的有效性。以此有限元模型为基础构建驾驶室谐响应模型,进行谐响应分析,发现驾驶室后壁板的振动是引起驾驶室内部噪声的主要原因。研究驾驶室内部噪声特性,分别进行了声学空腔模态分析和声固耦合模态分析,发现声固耦合系统声压分布比较均匀,大部分呈现局部模态,主要原因可能是驾驶室后壁板的振动。通过驾驶员耳旁声压分析发现增加驾驶室后壁板的厚度,可以在一定程度内降低驾驶室内部噪声对驾驶员的影响,为同类驾驶室通过依靠结构改进来改善声场环境提供了案例依据。     

Mechanism of smoke suppression by melamine in rigid polyurethane foam

The smoke suppression of rigid polyurethane foam (RPUF) modified by melamine was investigated based on three sections: the condensed phase, the carbon layer, and the gas phase. In the condensed phase, the results of thermogravimetry, X‐ray photoelectron spectroscopy (XPS) N1S spectrum, and Fourier transform infrared spectroscopy indicated that melamine could suppress the degradation of RPUF by reacting with the aromatic hydrocarbons. It also reduced the smoke generation because the volatilizable aromatic hydrocarbons were the principal smoke precursors in a fire. In the carbon layer, the decrease from 38.50% to 24.76% of the inner layer oxygen content identified by XPS full‐spectrum and C1S spectrum indicated that melamine could prevent oxygen from transferring into the inner foam by the formation of an enhanced surface carbon layer, and the enhanced carbon layer could also block the release of smoke precursors. In the gas phase, the content of total aromatic hydrocarbons declined to 59.12% according to pyrolysis gaseous chromatography mass spectroscopy and indicated that melamine could reduce the smoke precursors. The results of smoke density chamber and cone calorimeter tests revealed that the addition of the melamine could decrease the smoke density of burning RPUF. Copyright © 2014 John Wiley & Sons, Ltd.