Time-averaged flow characteristics and mixing properties of double-concentric jets

We examined the flow behaviors and mixing characteristics of double-concentric jets using laser-assisted smoke flow visualization method to analyze typical flow patterns and binary boundary detection technique to investigate jet spread width. Time-averaged velocity vectors, streamline patterns, velocity distributions, turbulence properties, and vorticity contours were analyzed using Particle Image Velocimetry (PIV). Topological flow patterns were analyzed to interpret the vortical flow structures. Mixing properties were investigated using a tracer-gas concentration detection method. Four characteristic modes were observed: annular flow dominated mode, transition mode, central jet dominated mode-low shear, and central jet dominated mode-high shear. The jets’ mixing properties were enhanced by two major phenomena: the merging of annular flow and central jet at the centerline and the large turbulence fluctuations produced in the flow field. The merging of the jets induced stagnation points on the central axis in the annular flow dominated mode, which caused reverse flow on the central axis and drastic turbulence fluctuations of the near field region. When the central jet penetrated the recirculation region in the other three modes, the stagnation points on the central axis and the reverse flow vanished. Therefore, the mixing behaviors were prominently enhanced in the annular flow dominated mode.     

低于13K的单级脉管制冷机性能研究

回热器是脉管制冷机的关键部件之一,其效率对脉管制冷机性能有很大影响。铅丸是常见的蓄冷材料,通常用于回热器的低温端。本文测试和分析了不同品质的国产铅丸和进口铅丸对单级G-M型脉管制冷机性能的影响。采用额定功率为6．0 kW的压缩机驱动,使用进口铅丸脉管制冷机最低制冷温度达12．9 K,这是当前单级脉管制冷机达到的最低制冷温度;40 K时的最大制冷量为57．4 W。使用国产铅丸最低制冷温度为13．6 K,40 K时的最大制冷量为55．9 W。本文对低温制冷机蓄冷材料选择具有一定的参考价值。     

风沙运动的DPM数值模拟

采用离散颗粒模型对风沙气固两相流动进行了数值计算．在该模型中,采用体平均的Navier-Stokes方程来描述气相的运动,对离散颗粒采用拉格朗日方法模拟,求解颗粒运动方程．采用硬球模型描述颗粒问碰撞作用．计算结果表明,沙粒平均水平速度廓线在0．02 m以上高度可以表示为按对数函数或幂函数规律增加,在0．02 m以下则发生偏离;在大于0．02 m的高度,输沙通量随高度按指数规律衰减,而在地面附近由于颗粒蠕移的影响发生偏离,这与已有文献结果一致。本文的模拟有助于风沙运动规律的研究与掌握。     

Topological bulk-edge effects in quantum graph transport

We examine quantum transport in periodic quantum graphs with a vertex coupling non-invariant with respect to time reversal. It is shown that the graph topology may play a decisive role in the conductivity properties illustrating this claim with two examples. In the first, the transport is possible at high energies in the bulk only being suppressed at the sample edges, while in the second one the situation is opposite, the transport is possible at the edge only.     

Photoinduced anisotropic edge states and signatures of nonequilibrium spin polarization in silicene nanoribbons

Most topological phase transitions are accompanied by the emergence of surface/edge states with spin dependence. Usually, the quantized Hall conductivity cannot characterize the anisotropic transports and spin dependence of topological states. Here, we study the intricate topological phase transition and the anisotropic behavior of edge states in silicene nanoribbon submitted to an electric field or/and a light irradiation. It is interesting to find that a circularly polarized light can induce a type-II quantum anomaly Hall phase, which is manifested as the high Chern number and the strong anisotropic edge states. Besides the measurement of the quantized Hall conductivity, we further propose to probe these topological phase transitions and the anisotropy of edge states by measuring the current-induced nonequilibrium spin polarization. It is found that the spin polarization exhibits more signatures about the behavior of surface/edge states, beyond the quantized Hall conductivity, especially for spin-dependent transports with different velocities.     

A note on the spheroidal modes vibration of an elastic sphere in linear viscoelastic fluid

Vibration characteristics of elastic nanostructures embedded in fluid medium have been used for biological and mechanical sensing, and also to investigate materials mechanical properties. An analytical approach based on the exact theory has been developed in this paper, to establish a new accurate and simple generalized frequency equation to predict spheroidal vibration of an elastic nanosphere, in a compressible viscoelastic fluid using linear Maxwell fluid model. To demonstrate the accuracy of the present approach, a comparison is made with the published theoretical results in the literature in some particular cases, which shows a very good agreement. Thus, the obtained frequency equation can be very useful to interpret the experimental measurements of vibrational dynamics of nanospheres and can serve as benchmark solution in design of liquid sensors.     

以纳米微晶纤维素为模板的酸催化水解法制备球形介孔TiO_2

以纳米微晶纤维素(NCC)为模板剂,采用酸催化水解法制备了球形介孔TiO2(SP-TiO2).并采用扫描电镜、透射电镜、X射线衍射、紫外-可见漫反射光谱和低温N2吸附-脱附等手段对其进行了表征.结果表明,所制SP-TiO2为直径100～200nm的规整球形颗粒,单个球形颗粒由粒径为10～20nm的TiO2小晶粒组成.其介孔孔径为8.2～13.5nm,且随焙烧温度的升高而增大.NCC长链结构之间羟基键合所形成的狭小空间构成的微反应器,可有效限制TiO2前驱体的生长和团聚,诱导其晶粒自组装成球形结构,并抑制由锐钛矿相向金红石相转变.600oC焙烧的SP-TiO2表现出最高的光催化活性,对苯酚降解率达89%.     

单位球中完备超曲面的一个刚性定理

本文研究了单位球中的数量曲率满足r=aH+b的完备超曲面的问题.利用极值原理的方法,获得了超曲面的一个刚性结果,推广了这一类具有常中曲率或者常数量曲率超曲面的结果.     

Au@碳球复合结构中Au颗粒位置调控光吸收

采用时域有限差分（FDTD）法研究Au纳米颗粒@碳球（AuNPs@CS）复合结构的光吸收控制。发现Au纳米颗粒@碳球复合结构中Au颗粒的位置可以控制复合结构光吸收。模型计算中选取两粒Au纳米颗粒以最佳深度（0 nm）嵌入碳球表面。当两粒Au颗粒球心与碳球球心夹角为22.5°和45°时,复合结构光吸收较单一碳球光吸收明显增强;当夹角为315°、270°、180°、90°时,光吸收增量逐渐减小;当夹角为337.5°时,光吸收量低于单一碳球。这一结果主要归因于Au纳米颗粒位置变化可引起表面等离子体光强度和光散射方向的变化。改变碳球表面Au纳米颗粒的数量和位置,可以进一步调节AuNPs@CS复合结构的光吸收。     

压气机叶栅壁面拓扑和二次流结构分析

本文从涡动力学原理出发，根据实验测量和流场显示结果，对压气机平面叶机的壁面拓扑和叶栅二次流结构进行了研究．由叶栅壁面拓扑分析和二次流结构可知，叶栅的通道涡较强，出口集中脱落涡和角区分离泡的存在，造成了叶栅两端区较高的二次流损失，并且随叶栅来流冲角的提高，旋涡出现破裂，二次流损失进一步提高．