A modified SPH method to model the coalescence of colliding non-Newtonian liquid droplets

This paper develops a modified smoothed particle hydrodynamics (SPH) method to model the coalescence of colliding non-Newtonian liquid droplets. In the present SPH, a van der Waals (vdW) equation of state is particularly used to represent the gas-to-liquid phase transition similar to that of a real fluid. To remove the unphysical behavior of the particle clustering, also known as tensile instability, an optimized particle shifting technique is implemented in the simulations. To validate the numerical method, the formation of a Newtonian vdW droplet is first tested, and it clearly demonstrates that the tensile instability can be effectively removed. The method is then extended to simulate the head-on binary collision of vdW liquid droplets. Both Newtonian and non-Newtonian fluid flows are considered. The effect of Reynolds number on the coalescence process of droplets is analyzed. It is observed that the time up to the completion of the first oscillation period does not always increase as the Reynolds number increases. Results for the off-center binary collision of non-Newtonian vdW liquid droplets are lastly presented. All the results enrich the simulations of the droplet dynamics and deepen understandings of flow physics. Also, the present SPH is able to model the coalescence of colliding non-Newtonian liquid droplets without tensile instability.     

Adsorption and dissociation of the methanethiol (CH3SH) molecule on the Fe(100) surface

These contributions explore interaction modes between the methanethoil (CH₃SH) molecule and the Fe(100) surface via implementing accurate density functional theory (DFT) calculations with the inclusion of van der Waals corrections. We consider three adsorption sites over the Fe(100) surface, namely, top(T), bridge (B), and hollow (H) sites as potential catalytic active sites for the molecular and dissociative adsorption of the CH₃SH molecule. The molecular adsorption structures are found to occupy either B or T sites with former sites holding higher stability by 0.17 eV. The inclusion of van der Waals corrections refound to slightly alter adsorption energies. For instance, adsorption energies increased by ~ 0.18 and ~ 0.21 eV for B and T structure, respectively, in reference to values obtained by the plain generalized gradient approximation (GGA) functional. A stability ordering of the dissociation products was found to follow the sequence (CH₄, S) > (CH₃, S, H) > (─SCH_3, H) > (─CH₃, SH). The differential charge density distributions were examined to underpin prominent electronic contributing factors. Direct fission of C─S bond in the CH₃SH molecule attains exothermic values in the range 2.0 to 2.1 eV. The most energetically favorable sites for the surface-mediated fission of the thiol's S─H bond correspond to the structure where the ─SCH₃ and H are both situated on hollow sites with an adsorption energy of −2.43 eV. Overall, we found that inclusion of van der Waals functional to change the binding energies more noticeably in case of dissociative adsorption structures. The results presented herein should be instrumental in efforts that aim to design stand-alone Fe desulfurization catalysts.     

Synthesis of thermoplastic curdlan alkyl carbamates having hydrogen bonding ability

Rigid and little moldable curdlan, a linear β-1,3-glucan having intra- and interchain hydrogen bonds, was reacted with several alkyl isocyanates, which gave thermoplastic curdlan alkyl carbamates (CrdC) with degree of substitution about 2. The alkyl carbamation at hydroxy groups in the glucan skeleton effectively broke the interchain hydrogen bonds of curdlan and increased flexibility of CrdC, while the newly formed carbamate moieties could moderately keep the hydrogen bonding ability in CrdC. Elongating the alkyl groups in the carbamate side chains increased solubility in organic solvents and thermoplasticity of CrdC, which enabled to make homogeneous and free-standing films by both methods of solution-casting and hot-pressing.     

On an approach to the study of the Jaynes–Cummings sum in quantum optics

A new approach to the study of the Jaynes–Cummings sum, which determines the atomic inversion in quantum model of a single two-level atom interacting with a single mode of the quantized radiation field, based on the number theory theorems on approximation of trigonometric sums is presented.      

基于最新势能面的C(1D)+H2反应的环聚合分子动力学研究

本文利用环聚合分子动力学方法对C(¹D)+H₂反应开展了详细的理论研究. 计算中使用了最近构建的Zhang-Ma-Bian(ZMB)从头算势能面,该势能面对锥形交叉附近区域以及范德华区域均有精确的描述. 环聚合分子动力学计算得到的热反应速率常数与最新实验值吻合很好. 与前人计算结果比较,发现在?¹A′电子基态的ZMB-a势能面上获得的反应速率常数远大于前人构建的RKHS势能面上的结果,这是由于ZMB势能面上的范德华鞍具有与之前势能面上的范德华阱完全不同的动态学作用,表明环聚合分子动力学方法能够处理范德华作用引起的势能面拓扑结构所导致的动态学效应. 本文还揭示了b¹A′′电子激发态ZMB-b势能面以及量子效应对反应的重要性.     

二维范德瓦尔斯异质结构的制备与物性研究

二维范德瓦尔斯材料(可简称二维材料)已发展成为备受瞩目的材料大家族,而由其衍生的二维范德瓦尔斯异质结构的集成、性能及应用是现今凝聚态物理和材料科学领域的研究热点之一.二维范德瓦尔斯异质结构为探索丰富多彩的物理效应和新奇的物理现象,以及构建新型的自旋电子学器件提供了灵活而广阔的平台.本文从二维材料的转移技术着手,介绍二维范德瓦尔斯异质结构的构筑、性能及应用.首先,依据湿法转移和干法转移的分类,详细介绍二维范德瓦尔斯异质结构的制备技术,内容包括转移技术的通用设备、常用转移方法的具体操作步骤、三维操纵二维材料的方法、异质界面清洁.随后介绍二维范德瓦尔斯异质结构的性能和应用,重点介绍二维磁性范德瓦尔斯异质结构,并列举在二维范德瓦尔斯磁隧道结和摩尔超晶格领域的应用.因此,二维材料转移技术的发展和优化将进一步助力二维范德瓦尔斯异质结构在基础科学研究和实际应用上取得突破性的成果.     

基于PdSe2/GaAs异质结的高灵敏近红外光伏型探测器的制备和图像传感的应用

本文制备了一种基于PdSe₂/GaAs异质结的高灵敏近红外光电探测器,该探测器是通过将多层PdSe₂薄膜转移到平面GaAs上制成的. 所制备的PdSe₂/GaAs异质结器件在808 nm光照下表现出明显的光伏特性,这表明近红外光电探测器可以用作自驱动器件. 进一步的器件分析表明,这种杂化异质结在零偏电压和808 nm光照下具有1.16×10⁵的高开关比. 光电探测器的响应度和比探测度分别约为171.34 mA/W和2.36×10¹¹ Jones. 而且,该器件显示出优异的稳定性和可靠的重复性. 在空气中2个月后,近红外光电探测器的光电特性几乎没有下降,这归因于PdSe₂的良好稳定性. 最后,基于PdSe₂/GaAs的异质结器件还可以用作近红外光传感器.     

Effect of defects on the electronic structure of a PbI2/MoS2 van der Waals heterostructure: A first-principles study

PbI2/MoS2,as a typical van der Waals(vdW)heterostructure,has attracted intensive attention owing to its remarkable electronic and optoelectronic properties.In this work,the effect of defects on the electronic structures of a PbI2/MoS2 heterointerface has been systematically investigated.The manner in which the defects modulate the band structure of PbI2/MoS2,including the band gap,band edge,band alignment,and defect energy-level density within the band gap is discussed herein.It is shown that sulfur defects tune the band gaps,iodine defects shift the positions of the band edge and Fermi level,and lead defects realize the conversions between the straddling-gap band alignment and valence-band-aligned gap,thus enhancing the light-absorption ability of the material.     

C1 Solutions of the Iterative Equation G(x, f(x), ..., fn(x)) =F(x)

In this paper we consider the iterative equation G(x,f(x),...,f n(x)) = F(x) on R,and give the existence of C 1 solutions near the fixed point of F,which generalize some results on the leading coefficient problem from the form of the polynomial-like iterative equations to the general form.