An Introduction to Quantum Turbulence

Turbulence in a superfluid differs from that in a classical fluid because the flow of a superfluid is strongly influenced by quantum effects. Such turbulence is therefore often described as quantum turbulence. We give a brief historical account of the study of quantum turbulence, explaining how our understanding of it has developed. Particular attention is then paid to developments during the past ten years, which have seen the study of types of quantum turbulence that have close classical analogues. Similarities and differences between the classical and quantum cases are discussed, and aspects that are either not understood or the subject of speculation are emphasized. The paper provides an introduction to other and more detailed presentations in the Symposium.      

Dissipation and Phase Slip in Confined Superfluid Helium: Evidence for an Equilibrium Distribution of Vortices

The effects of phase slip due to the thermal creation of vortices in confined liquid ⁴He below the point is discussed. In a narrow tube there is a finite probability of thermal activation of a vortex in the superfluid helium, with the vortex not parallel to the axis of the tube. In the presence of a heat flow along the tube, the vortices experience the Magnus force, which prevents exact cancellation of the motion of thermally activated vortices traversing the cross section of the tube in opposite directions. Each crossing of the tube by a vortex causes a 2 phase slip of the superfluid order parameter along the tube. A temperature gradient results, which is proportional to the rate of phase slip, thus yielding a nonvanishing thermal resistivity below the bulk point. The calculated temperature dependence compares well with experimental data, thereby providing indirect evidence of the presence of vortices in thermal equilibrium.     

Turbulence of Second Sound Waves in Superfluid 4He: Effect of Low-Frequency Resonant Perturbations

We report the results of investigations of acoustic turbulence in a system of nonlinear second sound waves in a high-quality resonator filled with superfluid ⁴He. It was observed that subharmonics of a periodic driving force applied to the system may be generated via a parametric instability. We find that application of an additional low-frequency pumping to the turbulent system results in the generation of waves at combination frequencies of the driving forces and also leads to substantial changes in the energy spectrum of the acoustic oscillations.      

Ab Initio Values of the Thermophysical Properties of Helium as Standards

Recent quantum mechanical calculations of the interaction energy of pairs of helium atoms are accurate and some include reliable estimates of their uncertainty. We combined these ab initio results with earlier published results to obtain a helium-helium interatomic potential that includes relativistic retardation effects over all ranges of interaction. From this potential, we calculated the thermophysical properties of helium, i.e., the second virial coefficients, the dilute-gas viscosities, and the dilute-gas thermal conductivities of ³He, ⁴He, and their equimolar mixture from 1 K to 10⁴ K. We also calculated the diffusion and thermal diffusion coefficients of mixtures of ³He and ⁴He. For the pure fluids, the uncertainties of the calculated values are dominated by the uncertainties of the potential; for the mixtures, the uncertainties of the transport properties also include contributions from approximations in the transport theory. In all cases, the uncertainties are smaller than the corresponding experimental uncertainties; therefore, we recommend the ab initio results be used as standards for calibrating instruments relying on these thermophysical properties. We present the calculated thermophysical properties in easy-to-use tabular form.     

Hybrid Nanostructures and Stabilized Mechanical Properties of High-Entropy Alloy Induced by Warm Laser Shock Peening

Recently, the manufacture of high-entropy-alloy (HEA) parts by selective laser melting (SLM) has been extensively studied. However, the problems of high tensile residual stress, undesirable microstructure, and unstable mechanical properties in HEA parts caused by SLM process are difficult to be solved simultaneously. Herein, a warm laser shock peening (WLSP) process is used to obtain high strength, stable mechanical property, and favorable residual stress in SLMed FeNiCrCo HEA by regulating the microstructure in material. Experimental and simulation results show that WLSP treatment can induce high-density dislocations and nanotwins in the HEA, resulting in a 39.4% increase in the surface strength of the HEA. Moreover, because of the high atomic kinetic energy brought by high temperature in WLSP processing, WLSP-treated sample has higher density of dislocations and nanotwins than the sample treated by the LSP process at room temperature (RLSP), resulting in higher surface strength and better mechanical stability of the WLSP-treated HEA. Meanwhile, the WLSP treatment enables the tensile residual stress generated in the SLM process to be transformed into compressive residual stress, which can enhance the fatigue performance of the HEA. Therefore, WLSP has great potential in obtaining SLMed HEAs with excellent mechanical properties.     

直接进样的热导检测器(TCD)色谱法测定高纯氦中Ne、O2、N2

主要是通过直接进样的热导检测器色谱系统来检测高纯氦中的微量杂质(Ne、O2、N2),解决了目前高纯氦分析中始终存在的难题--氖的测定.这项工作具有技术上的突破,并且有实用、可推广的现实意义.     

蓝藻热休克诱导高效表达系统的构建

以聚球藻Synechococcus sp.PCC7942作为基因工程受体菌，构建了热休克诱导的高效表达系统。用PCR法扩增并克隆出Synechococcus sp.PCC7942自身的热休克基因groESL操纵子的强启动区（240bp），并紧靠其后组装上泛素（UB）融合的胸腺素α1（Tα1）目的基因，在下游组装的rbcSpolyA终止子。此外，还组装了一个完整的卡那霉素抗性基因作为筛选标记基因。这样，就构建了完整的蓝藻的基因表达系统。经转化蓝藻Synechococcus sp.PCC7942细胞，在42℃热诱导30min后，目的基因UB－Tα1得到较高水平表达，表达量约占可溶性蛋白的8．7％。     

空腔的流激振荡及其声激励抑制方法的数值模拟

通过数值模拟，研究了矩形空腔在亚音速外流下的流激振荡问题。采用显式ＭａｃＣｏｒｍａ－ｃｋ二步预估校正有限差分格式，求解二维雷诺平均非定常Ｎａｖｉｅｒ－Ｓｔｏｋｅｓ方程；并用Ｃｅｂｅｃｉ－Ｓｍｉｔｈ代数紊流模型作适当修正来模拟紊流效应，对有、无前缘声激励两种情况的空腔流场作了数值模拟，计算的振荡频率及振荡幅值都与实验结果基本符合，并且较好地模拟出了声激励对流场的影响。     

Measure of Entanglement States of Two Interacting Electrons in Vertically Coupled Quantum Dots Induced by a Time-Dependent Electric Field

We study the dynamics of two electrons located in two vertically tunnel-coupled quantum dots in the presence of an oscillatory electric field. By solving the time-dependent Schrödinger equation, we predict the dynamical generation of entangled electron states, such as the EPR (Einstein, Podolsky, and Rosen) pairs or Bell states. The Schmidt rank and the von Neumann entropy are evaluated to characterize the degree of entanglement of the two electron states.     

水下炮孔爆破不同方向的水中冲击波传播特性研究

水中冲击波对水中的构筑物具有很大破坏作用,研究水击波的特性对水中兵器、舰船等方面具有很大的军事意义,对于民用水下工程爆破的安全使用和推广也具有指导意义。采用ANSYS/LS—DYNA有限元软件建立简化的水下台阶爆破数学模型,探索和分析其在不同方向上的传播衰减特性。结果显示:水中冲击波的衰减规律具有方向性,在垂直水底方向水中冲击波压力衰减最快,其次是平行于坡顶线方向,最小抵抗线方向的水中冲击波压力衰减是最慢的。     

激光诱导等离子冲击波改善金属材料疲劳性能及强化机理的研究进展

激光冲击是一种利用等离子冲击波效应的表面强化技术,该技术能显著提高金属材料抗疲劳、磨损、腐蚀等性能。简要阐述了激光冲击强化技术原理、特点及激光诱导的等离子体特性。从激光冲击强化后金属的疲劳行为、强化机理及疲劳延寿机制3个方面总结了国内外激光冲击强化在金属零部件抗疲劳性能方面的研究进展。激光冲击强化机理由最初的残余压应力强化机制转变为目前普遍接受的残余压应力和表面纳米化复合强化机制。冲击后的金属零部件表层硬度显著提高,由表层向内部引入较大的残余压应力,表层晶粒碎化至纳米级,而表面粗糙度基本保持不变,尤其适合表面粗糙度要求较高的最终零部件的强化。在总结疲劳性能研究及强化机理的基础上,对目前激光冲击强化研究中存在的问题进行探讨,并指出下一步研究的关键问题。     

Fundamental Understanding of the Formation Mechanism for Graphene Quantum Dots Fabricated by Pulsed Laser Fragmentation in Liquid: Experimental and Theoretical Insight

The pulsed laser fragmentation in liquid (PLFL) process is a promising technique for the synthesis of carbon‐based functional materials. In particular, there has been considerable attention on graphene quantum dots (GQDs) derived from multiwalled carbon nanotubes (MWCNTs) by the PLFL process, owing to the low cost and rapid processing time involved. However, a fundamental deep understanding of the formation of GQDs from MWCNTs by PLFL has still not been achieved despite the high demand. In this work, a mechanism for the formation of GQDs from MWCNTs by the PLFL process is reported, through the combination of experimental and theoretical studies. Both the experimental and computational results demonstrate that the formation of GQDs strongly depends on the pulse laser energy. Both methods demonstrate that the critical energy point, where a plasma plume is generated on the surface of the MWCNTs, should be precisely maintained to produce GQDs; otherwise, an amorphous carbon structure is favorably formed from the scattered carbons.     

Investigation of the Short-Time Photodissociation Dynamics of Furfural in S₂ State by Resonance Raman and Quantum Chemistry Calculations

Raman (resonance Raman, FT-Raman), IR and UV-visible spectroscopy and quantum chemistry calculations were used to investigate the photodissociation dynamics of furfural in S₂ state. The resonance Raman(RR) spectra indicate that the photorelaxation dynamics for the S₀→S₂ excited state is predominantly along nine motions: C=O stretch ν₅ (1667 cm^-1), ring C=C antisymmetric stretch ν₆ (1570 cm^-1), ring C=C symmetric stretch ν₇ (1472 cm^-1), C2-O6-C5 symmetric stretch/C1-H8 rock in plane ν₈ (1389 cm^-1), C3-C4 stretch/ C1-H8 rock in plane ν₉ (1370 cm^-1), C5-O6 stretch in plane ν₁₂ (1154 cm^-1), ring breath ν₁₃ (1077 cm^-1), C3-C4 stretch ν₁₄ (1020 cm^-1), C3-C2-O6 symmetric stretch ν₁₆ (928 cm^-1 ). Stable structures of S₀, S₁, S₂, T₁ and T₂ states with Cs point group were optimized at CASSCF method in Franck-Condon region there are S₂/S₁ conical intersection was found by state average method and RR spectra.     

The Role of Liquid Ink Transport in the Direct Placement of Quantum Dot Emitters onto Sub‐Micrometer Antennas by Dip‐Pen Nanolithography

Dip‐pen nanolithography (DPN) is used to precisely position core/thick‐shell (“giant”) quantum dots (gQDs; ≥10 nm in diameter) exclusively on top of silicon nanodisk antennas (≈500 nm diameter pillars with a height of ≈200 nm), resulting in periodic arrays of hybrid nanostructures and demonstrating a facile integration strategy toward next‐generation quantum light sources. A three‐step reading‐inking‐writing approach is employed, where atomic force microscopy (AFM) images of the pre‐patterned substrate topography are used as maps to direct accurate placement of nanocrystals. The DPN “ink” comprises gQDs suspended in a non‐aqueous carrier solvent, o‐dichlorobenzene. Systematic analyses of factors influencing deposition rate for this non‐conventional DPN ink are described for flat substrates and used to establish the conditions required to achieve small (sub‐500 nm) feature sizes, namely: dwell time, ink‐substrate contact angle and ink volume. Finally, it is shown that the rate of solvent transport controls the feature size in which gQDs are found on the substrate, but also that the number and consistency of nanocrystals deposited depends on the stability of the gQD suspension. Overall, the results lay the groundwork for expanded use of nanocrystal liquid inks and DPN for fabrication of multi‐component nanostructures that are challenging to create using traditional lithographic techniques.     

三维编织复合材料的热激波传播衰减特性

采用保护环式石英压电测量技术 ,在“闪光 2号”脉冲电子束加速器上 ,进行了三维编织复合材料的热激波传播衰减特性实验研究。实验结果表明 :(1)在电子束能注量为 5 70～ 970J cm2 ,对厚度为 10mm的三维编织复合材料 ,其热激波应力峰值约为 0 15～ 0 39GPa ,只有相同条件下LY - 12铝的 6 %左右。这说明三维编织复合材料具有良好的衰减热激波的性能 ;(2 )热激波在三维编织材料的传播中 ,相对LY - 12而言 ,其上升和作用时间都被明显展宽