Liquid–gas critical phenomena under confinement: small-angle neutron scattering studies of CO2 in aerogel

Small angle neutron scattering (SANS) is a well-established technique for investigating the behavior of confined binary liquid solutions, as it can probe the correlation length and susceptibility in pores on length scales 1 – 100 nm. We applied SANS to explore the influence of confinement on critical behavior of an individual fluid carbon dioxide (CO₂) in a highly porous aerogel. The results demonstrate that quenched disorder induced by aerogel significantly depresses density fluctuations. Despite the negligible volume occupied by aerogel (< 4%), the macroscopic phase separation of confined CO₂ into coexisting liquid and gaseous phases is suppressed and below the critical temperature of the bulk fluid frozen methastable microdomains are formed. Experimental data show that critical adsorption is as important as the effect of confinement in defining the behavior of confined fluids.     

Gas kinetic algorithm for flows in Poiseuille-like microchannels using Boltzmann model equation

~~Gas kinetic algorithm for flows in Poiseuille-like microchannels using Boltzmann model equation1. Feynman, R., There's plenty of room at the bottom, Journal of Microelectromechanical Systems, 1992, 1: 60 -66. 2. Piekos, E. S., Breuer, K. S., Numerical modeling of micromechanical devices using the direct simulation Monte Carlo method, Transactions of the ASME, Journal of Fluids Engineering, 1996, 118: 464-469. 3. Beskok, A., Karniadakis, G. E., Trimmer, W., Rarefaction and …     

氩-氮混合气电感耦合等离子体在元素和同位素分析中的应用进展

在传统Ar等离子体中引入其他活性气体(如氮气等)已经成为拓展其分析性能的一种重要手段。本文较系统的阐述了Ar-N₂混合气体电感耦合等离子体的基本物理化学性质,从N₂气引入引起传统Ar-ICP基本物理化学参数变化的层面出发探讨了Ar-N₂混合气等离子体特殊性质产生的机制,回顾了Ar-N₂混合气电感耦合等离子体在质谱分析中近40年的应用成果,并且展望了该技术在未来元素和同位素分析领域的应用前景。     

High-mobility two-dimensional electron gases at oxide interfaces： Origin and opportunities

Our recent experimental work on metallic and insulating interfaces controlled by interfacial redox reactions in SrTiO3-based heterostructures is reviewed along with a more general background of two-dimensional electron gas(2DEG)at oxide interfaces.Due to the presence of oxygen vacancies at the SrTiO3surface,metallic conduction can be created at room temperature in perovskite-type interfaces when the overlayer oxide ABO3has Al,Ti,Zr,or Hf elements at the B sites.Furthermore,relying on interface-stabilized oxygen vacancies,we have created a new type of 2DEG at the heterointerface between SrTiO3and a spinelγ-Al2O3epitaxial film with compatible oxygen ion sublattices.This 2DEG exhibits an electron mobility exceeding 100000 cm2·V 1·s 1,more than one order of magnitude higher than those of hitherto investigated perovskite-type interfaces.Our findings pave the way for the design of high-mobility all-oxide electronic devices and open a route toward the studies of mesoscopic physics with complex oxides.     

基于无信息变量消除法与岭极限学习机的新型变量选择方法：以CO气体浓度反演为例

变量选择是光谱分析领域一个重要的组成部分。为了克服传统区间选择法的缺点与不足,基于无信息变量消除法和岭极限学习机提出一种新型的变量选择与评价方法。首先,利用无信息变量消除法剔除整个光谱区间中无信息的波长点;其次,为了解决传统建模方法(偏最小二乘法、BP神经网络等)存在的共线性问题,采用岭极限学习机方法建立回归模型;最后,最佳的特征光谱波长点组合利用特征选择路径图和稀疏度-误差折中曲线进行确定。CO气体的浓度反演实验结果表明：(1)利用无信息变量消除法可以有效筛选出最能表征CO气体透过光谱的特征波长点;(2)岭极限学习机方法具有快速建模、避免共线性和高精度等优点(CO气体浓度反演模型的决定系数可达0.995);(3)特征选择路径图和稀疏度-误差折中曲线可以直观地帮助用户寻找出最佳的特征波长点组合。     

基于石英增强光声光谱的HCl痕量气体高灵敏度探测研究

HCl是一种有毒有害气体,对其高灵敏度探测具有非常重要的意义,然而到目前为止,采用激光光谱的手段对其探测的研究报道很少。石英增强光声光谱(QEPAS)是近年来发展起来的一种痕量气体探测技术,具有系统体积小、价格低廉、探测灵敏度高等优点。以5 000 ppm HCl∶N₂混合气作为待测目标,采用输出波长为1 742.38 nm的分布反馈连续波单纵模半导体激光器,开展对基于QEPAS技术的HCl高灵敏度探测研究。为了提高信噪比和简化数据处理过程,QEPAS传感器系统采用波长调制和2次谐波探测技术。研究中,首先对声波探测系统中微共振腔强声波增强特性进行了讨论,选择了“共轴”形式的声波微共振腔,并对其尺寸进行了优化,选择的微共振管长度为4 mm、内径为0.5 mm。实验中研究了激光波长调制深度对QEPAS系统产生的信号幅度的影响,当QEPAS系统积分时间为1 s、激光波长调制深度为0.23 cm-1时,获得了815 ppb的优异检测极限,归一化噪声等效吸收系数为7.41×10-9 cm-1·W·Hz-1/2。在后续的实验中,可在待测HCl气体中加入水汽分子,提高HCl分子的热弛豫速率,进一步提高HCl-QEPAS传感器系统的信号强度。     

基于QEPAS技术的乙炔微量气体高灵敏度检测研究

石英增强光声光谱(QEPAS)是近年来发展起来的一种痕量气体探测技术,具有系统体积小、价格低廉、探测灵敏度高等优点。乙炔(C₂H₂)是一种化学性质活泼的有毒气体,对它进行高灵敏度检测在变压器故障诊断、环境监测等领域有着重要的意义,基于此,采用QEPAS技术对C₂H₂微量气体展开高灵敏度检测研究。采用输出波长为1.53 μm的连续波分布反馈半导体激光器作为激发光源。为了提高信噪比和简化数据处理过程,QEPAS传感器系统采用波长调制和2次谐波探测技术。为了提高QEPAS系统信号幅值,相比于常见的共振频率为32.768 kHz的石英音叉,采用了共振频率较低的30.72 kHz石英音叉作为声波传导器,同时还优化了石英音叉与激光束的空间位置、激光波长调制深度,并添加了声波微共振腔,选择的微共振腔长度为4 mm、内径为0.5 mm,最终获得了2.7 ppm的优异检测极限,归一化噪声等效吸收系数为1.3×10-8 cm-1·W·Hz-1/2。     

Growth of oxide thin films for optical gas sensor applications

Tungsten trioxide and titanium dioxide thin films were synthesised by pulsed laser deposition. We used for irradiations of oxide targets an UV KrF* (λ = 248 nm, τ_FWHM ≅ 20 ns, ν = 2 Hz) excimer laser source, at 2 J/cm² incident fluence value. The experiments were performed in low oxygen pressure. The (0 0 1) SiO₂ substrates were heated during the thin film deposition process at temperature values within the 300-500 °C range. The structure and crystalline status of the obtained oxide thin films were investigated by high resolution transmission electron microscopy. Our analyses show that the films are composed by nanoparticles with average diameters from a few to a few tens of nm. Moreover, the films deposited at substrate temperatures higher than 300 °C are crystalline. The tungsten trioxide films consist of a mixture of triclinic and monoclinic phases, while the titanium dioxide films structure corresponds to the tetragonal anatase phase. The oxide films average transmittance in the visible-infrared spectral range is higher than 80%, which makes them suitable for sensor applications.     

微槽道气体流动的统计模拟

利用基于分子模型的统计模拟方法——信息保存方法(IP)统计模拟了实验条件下微槽道气体流动,仔细讨论了用IP方法模拟长槽道稀薄气流时遇到的问题,并给出了解决的方法,即采取守恒形式的控制方程避免质量流量计算误差积累,并利用超松弛方法使收敛过程加速.将IP计算结果与压力分布和质量流量实验数据进行了比较.     

The operational performance of the Yale ESTU

The ESTU began operation in 1988 and achieved the design voltage of 20 MV in 1990. Since that time, improvements to the gas handling system, negative ion injector, accelerator terminal and control system have greatly increased its capability and reliability. Today, the ESTU can efficiently produce an extensive assortment of stable ions at wide-ranging energies in support of low-energy nuclear physics.