Limits of the equivalence of time and ensemble averages in shear flows

In equilibrium systems, time and ensemble averages of physical quantities are equivalent due to ergodic exploration of phase space. In driven systems, it is unknown if a similar equivalence of time and ensemble averages exists. We explore effective limits of such convergence in a sheared bubble raft using averages of the bubble velocities. In independent experiments, averaging over time leads to well-converged velocity profiles. However, the time averages from independent experiments result in distinct velocity averages. Ensemble averages are approximated by randomly selecting bubble velocities from independent experiments. Increasingly better approximations of ensemble averages converge toward a unique velocity profile. Therefore, the experiments establish that in practical realizations of nonequilibrium systems, temporal averaging and ensemble averaging can yield convergent (stationary) but distinct distributions.     

Pd(OAc)2-catalyzed fluoride-free cross-coupling reactions of arylsiloxanes with aryl bromides in aqueous medium

Mild conditions have been developed to achieve the Pd(OAc)2-catalyzed fluoride-free cross-coupling between the aryl bromides and arylsiloxanes in good to high yields in aqueous medium. The success of the reactions requires the presence of poly(ethylene glycol) (PEG) and 3 equiv of sodium hydroxide. The product was easily separated with ethyl ether extraction, and the catalytic system can be reused eight times with high efficiency.     

一种基于深度学习的视觉里程计算法

近年来,视觉里程计广泛应用于机器人和自动驾驶等领域,传统方法求解视觉里程计需基于特征提取、特征匹配和相机校准等复杂过程,同时各个模块之间要耦合在一起才能达到较好的效果,且算法的复杂度较高。环境噪声的干扰以及传感器的精度会影响传统算法的特征提取精度,进而影响视觉里程计的估算精度。鉴于此,提出一种基于深度学习并融合注意力机制的视觉里程计算法,该算法可以舍弃传统算法复杂的操作过程。实验结果表明,所提算法可以实时地估计相机里程计,并具有较高的精度和稳定性以及较低的网络复杂度。     

Theoretical study of silicon–sulfur clusters (SiS2)n− (n=1–6)

The possible geometrical structures and relative stability of silicon–sulfur clusters (SiS₂) (n=1–6) are explored by means of density functional theory (DFT) quantum chemical calculations. We also compare DFT with second‐order Møller–Plesset (MP2) and Hartree–Fock (HF) methods. The effects of polarization functions, diffuse functions, and electron correlation are included in MP2 and B3LYP quantum chemical calculations, and B3LYP is effective in larger cluster structure optimization, so we can conclude that the DFT approach is useful in establishing trends. The electronic structures and vibrational spectra of the most stable geometrical structures of (SiS₂)_n⁻ are analyzed by B3LYP. As a result, the regularity of the (SiS₂)_n⁻ cluster growing is obtained, and the calculation may predict the formation mechanism of the (SiS₂)_n⁻ cluster. © 2001 John Wiley & Sons, Inc. Int J Quant Chem 81: 280–290, 2001     

Domination critical graphs with higher independent domination numbers

We show that for each k ≥ 4 there exists a connected k-domination critical graph with independent domination number exceeding k, thus disproving a conjecture of Sumner and Blitch (J. Combinatorial Theory B 34 (1983), 65–76) in all cases except k = 3. © 1996 John Wiley & Sons, Inc.     

通道响应失配对DBF天线旁瓣电平的影响

本文研究了通道响应失配对数字波束形成(DBF)天线旁瓣电平的影响,然后分析了通道频率响应失配与脉冲响应失配的关系,进而得到通道间频率响应失配对天线旁瓣电平的影响。结果表明,用DBF技术实现超低旁瓣天线对通道频率匹配的要求相当高。最后计算机模拟验证了理论分析结果。     

群像素激光雷达多级分辨率三维点云成像技术的研究

激光三维成像雷达系统单帧获取的数据量越来越大,数据处理效率已成为亟待解决的重点问题之一.研究了群像素激光三维成像雷达的编解码数据特性,对激光三维点云回波数据进行多级分层分割处理,提高群像素激光三维点云成像雷达数据处理效率.实验结果表明,多级分层分割的成像方法可将群像素成像速度提高6倍,该方法有效地解决了群像素激光三维成...     

含氧超价化合物OK_n的结构和稳定性

运用Ｂ３ＬＹＰ－ ＤＦＴ 密度函数方法,通过３ －２１Ｇ＊ 基组,对ＯＫｎ（ｎ ＝３ ～６） 系列超价化合物几何进行了优化,计算了各分子优化几何的频率．分析了各分子的稳定构型解离出Ｋ 与Ｋ２ 的反应能,从而预测了它们的热力学稳定性     

器具开关操作引发的安全问题

对于符合 IEC 61058的器具开关,IEC 60335等大部分整机产品安全标准中只对开关的电气参数、IP 等级、动作循环周期、断开类型等提出要求,对器具开关的操作性能,例如力度、形状、位置等没有提出具体要求。实际中,如果操作器具开关需要的力度过大,会引发安全问题,例如稳定性问题以及由此引发的其它问题。提出应当制定器具开关操作力度的要求,同时还应当对器具开关的安装位置与电热元件等功能性危险源之间的距离做出规定,从而避免对器具开关的操作成为安全隐患,同时建议对此作进一步的研究。     

微波消解-电感耦合等离子体发射光谱(ICP-OES)法测定茄子中矿物元素含量

采用微波消解HNO_3+H_2O_2湿法制取样品溶液,全谱直读电感耦合等离子体发射光谱(ICPOES)法同时测定茄子中K、Na、Mg、Al、Ca、B、Ba、Cr、Cu、Fe、Sn、Mn、P、Sr、Zn 15种矿物元素,实际样品测定结果显示,Al元素含量超过国家规定标准(≤100mg/kg),微量元素Ca含量相对较高。各元素的检出限为1.0~440μg/L,标准样品的加标回收率93.5%~109%,相对标准偏差在2.1%~6.5%(n=6)。实验方法简单、重现性好,可用于测定茄子样品中各矿物元素含量。测定结果为茄子的深入研究提供基础数据。