A high-throughput chaotic advection microreactor for preparation of uniform and aggregated barium sulfate nanoparticles

A high-throughput (105.5 g/h) passive four-stage asymmetric oscillating feedback microreactor using chaotic mixing mechanism was developed to prepare aggregated Barium sulfate (BaSO₄) particles of high primary nanoparticle size uniformity. Three-dimensional unsteady simulations showed that chaotic mixing could be induced by three unique secondary flows (i.e., vortex, recirculation, and oscillation), and the fluid oscillation mechanism was examined in detail. Simulations and Villermaux–Dushman experiments indicate that almost complete mixing down to molecular level can be achieved and the prepared BaSO₄ nanoparticles were with narrow primary particle size distribution (PSD) having geometric standard deviation, σ_g, less than 1.43 when the total volumetric flow rate Q_total was larger than 10 ml/min. By selecting Q_total and reactant concentrations, average primary particle size can be controlled from 23 to 109 nm as determined by microscopy. An average size of 26 nm with narrow primary PSD (σ_g = 1.22) could be achieved at Q_total of 160 ml/min.     

含不凝性气体蒸汽浸没射流冷凝压力振荡实验研究

实验研究了不凝性气体（空气）含量、水温和蒸汽质量流速对蒸汽浸没射流冷凝压力振荡特性的影响，实验工况横跨冷凝振荡（CO）区和稳定冷凝（SC）区。结果表明：对于纯蒸汽射流，压力振荡主频随水温的升高而降低，振荡强度随水温的升高而升高；在CO区，振荡主频和振荡强度均随蒸汽质量流速的升高而升高；在SC区，振荡主频随蒸汽质量流速的升高而降低，振荡强度基本上不随蒸汽质量流速的变化而发生改变；对于含空气射流，随空气质量分数的增加，振荡主频总体呈下降趋势，振荡强度先迅速下降后小幅上升，在空气质量分数为0.05～0.1区域内振荡主频和振荡强度均存在极小值。     

Astrocyte Ca2+ Waves and Subsequent Non-Synchronized Ca2+ Oscillations Coincide with Arteriole Diameter Changes in Response to Spreading Depolarization

Spreading depolarization (SD) is a wave of mass depolarization that causes profound perfusion changes in acute cerebrovascular diseases. Although the astrocyte response is secondary to the neuronal depolarization with SD, it remains to be explored how glial activity is altered after the passage of SD. Here, we describe post-SD high frequency astrocyte Ca²⁺ oscillations in the mouse somatosensory cortex. The intracellular Ca²⁺ changes of SR101 labeled astrocytes and the SD-related arteriole diameter variations were simultaneously visualized by multiphoton microscopy in anesthetized mice. Post-SD astrocyte Ca²⁺ oscillations were identified as Ca²⁺ events non-synchronized among astrocytes in the field of view. Ca²⁺ oscillations occurred minutes after the Ca²⁺ wave of SD. Furthermore, fewer astrocytes were involved in Ca²⁺ oscillations at a given time, compared to Ca²⁺ waves, engaging all astrocytes in the field of view simultaneously. Finally, our data confirm that astrocyte Ca²⁺ waves coincide with arteriolar constriction, while post-SD Ca²⁺ oscillations occur with the peak of the SD-related vasodilation. This is the first in vivo study to present the post-SD astrocyte Ca²⁺ oscillations. Our results provide novel insight into the spatio-temporal correlation between glial reactivity and cerebral arteriole diameter changes behind the SD wavefront.     

撞击流反应器撞击面稳定性研究进展

撞击流技术因其良好的混合特性近些年用于强化制备超细粉体反应中的混合过程。撞击面的稳定影响反应器内的混合效果，所以本文对撞击面稳定性的研究进行了综述。撞击流反应器不同结构形式包括平面撞击流、轴对称撞击流和微型撞击流等。文中简述了撞击流稳定性的实验研究手段，分析轴对称撞击流反应器的径向偏转振荡的起止条件和不同喷嘴间距下的轴向偏移振荡规律，并且分析平面撞击流反应器的撞击面偏转周期以及偏转振荡的起止条件。得出轴对称撞击流与平面撞击流撞击面驻点的振荡对混合都有促进作用，并且偏移振荡周期不定，轴对称撞击面偏移振幅与喷嘴间距和雷诺数相关。平面撞击流的偏转振荡周期与进口流速成反比，反应器结构参数是撞击流稳定性的影响因素之一。根据轴对称撞击流偏移振荡对混合的促进作用，本文提出一种新型的预设流量波形双组撞击流反应器。新型撞击流反应器的独特结构克服了物料反应通道单一缺点，通过预设波形控制其进口流量，增大其撞击面偏移振幅，消除撞击面无序振荡，使流动轨迹扩展，扩大混合区域，并设计实验装置与方法讨论动态流量撞击流反应器撞击面稳定性对混合效果的影响。最后，本文对轴对称撞击流反应器的混合性能研究前景进行展望。     

燕窝及其伪品电化学指纹图谱的研究

基于BrO3--Ce2+-H+-丙二酸振荡反应体系,以燕窝水解液为底物,在反应温度为35℃,搅拌速度为500 r/min的条件下,可得到重现性好的稳定电化学指纹图谱。不同种类燕窝及燕窝伪品的电化学指纹图谱不尽相同,指纹图谱峰形、振荡周期、振荡寿命等特征参数可作为燕窝及其伪品鉴别的有效依据。     

Structure of turbulent rich hydrogen‐air premixed flames

In the present article, series of experiments were conducted to study the structure characteristics of premixed flames in turbulent rich hydrogen‐air mixtures within a constant‐volume turbulent combustion system, 7 equivalence ratios (1.2, 1.4, 1.6, 1.8, 2.0, 2.2, and 2.5), and 5 turbulent intensity (0, 0.494, 0.742, 1.080, and 1.309 m/s) were studied. With the increase of turbulent intensity, the cellularity degree was obviously enhanced for turbulence promoted the formation and the development of initial cracks by wrinkling flame‐front; furthermore, the enhanced hydrodynamic instability was also one important reason. Turbulence would change the linear growth of critical radius to equivalence ratio into nonlinear, but the variation extents had limitation. The wrinkling index of flame‐front would rise as flame expanded, and the wrinkling index on flames with similar size would be increased with the increase of turbulence once the turbulent intensity was sufficiently high. From the variations of the root mean square of related oscillation on flame‐front, it could be found that the partial amount of oscillation induced by sole turbulence was declined as flame expanded for the breakup of large eddies.     

Experimental study on the propagation characteristics of hydrogen/methane/air premixed flames in a narrow channel

This work is focused on the explosion characteristics of premixed gas containing different volume fractions of hydrogen in a narrow channel (1000 mm × 50 mm × 10 mm) under the circumstance of stoichiometric ratio. The ignition positions were set in the closed end and the middle of the pipeline respectively. The results showed that when the gas was ignited at the pipeline closed end, the propagating flame was tulip structure for different premixed gas. When the hydrogen volume fraction was less than 40%, the flame propagation speed increased significantly with the rise of hydrogen volume fraction, and the overpressure peak also appeared obviously in advance. However, when the volume fraction of hydrogen was more than 40%, the increase of flame propagation speed and the overpressure peak occurrence time varied slightly. Furthermore, when the ignition position was placed in the middle of the pipeline, the flame propagation speed propagating to the opening end was much faster than that propagating to the closing end, and there was no tulip shape when the flame propagates to the opening end. The flame propagating to the closed end appeared tulip shape under the influence of airflow, and high-frequency flame oscillation occurred during the propagation. This work shows that the hydrogen volume fraction and ignition position significantly affected the flame structure, flame front speed, and explosion overpressure.     

教室声学环境的分析及改善

对于教室内声学环境的要求,国内及国外一些有关规范都只停留在中频段(500～1 000 Hz)。这样的要求是不够的。在这样的声学环境中,教师健康和学生听课效果均受到影响。文章分析了达到优良室内声学环境的几个重要因素,着重减低低频噪声和控制低频混响时间。利用简单的吸声构件,得到几乎平直的混响时间频率特性。叙述了"掩蔽效应"对中、高频的影响并叙述了"哈斯效应"及在声学处理时要利用有利反射声的注意事项。为得到室内优良的音质环境,提出建议并给出工程实践结果的实例。