Name: magnetically induced rotating rayleigh-taylor instability
Uploaded: 2017-03-03T13:00:00.000+00:00
Duration: 6 min 42 s
Description: Watch this Scientific Journal Video about Magnetically Induced Rotating Rayleigh-Taylor Instability at JoVE.com

RJAH acknowledges support from EPSRC Fellowship EP/I004599/1, MMS acknowledges funding from EPSRC under grant number EP/K5035-4X/1.

注:实验装置在图示意性示出。 2。该装置的主要部分包括一个旋转平台英寸（300毫米×300 MM）安装在铜圆柱体（55毫米直径的），根据其自身重量下降到一个超导磁体（1.8 T）的强磁场与房间的温度的垂直钻孔。该平台是由通过离轴马达转动的滑动轴承带有一锁眼孔口旋转。铜柱附加到同时旋转，并且一旦所述保持针被移除下降一个钥匙形状的驱动轴。 1，非标设备的研制<ol><li>浮选船<ol><li>使船的尺寸，使得其舒适适合实验槽内而不触及两侧。 注:浮选船（ 见图3）由聚苯乙烯壁和海绵碱。 </li><li>保护海绵ST一层荣纸巾。 注:薄纸的目的是从注入船尽可能流体消散尽可能垂直动量。 </li></ol></li></ol> 2.实验准备<ol><li>液层的制备<ol><li>允许蒸馏水拿出到实验室温度（22±2℃）。大约650毫升需要对每个实验实现。 注:使混合物平衡防止形成气泡在实验中由于exsolving空气。 </li><li>分离蒸馏水入等体积在两个单独的容器中，A和B，这将被用于为密集下层和光上层分别制备的液体。 </li><li> 易地准备致密下层。集装箱A的内容: <ol><li>添加氯化钠达到0.43摩尔氯化钠的每升水的浓度为每升（约25克NaCl的水将需要）; </li><li>添加0.33克红色和蓝色的跟踪水基染料到下层的容器（ 例如 ，Cole-Parmer公司00295-16＆-18）; </li><li>加入0.1克L- -1荧光素钠。 注:下层将现在在外观不透明并具有约1012.9±1.2公斤米-3的密度。 </li></ol></li><li> 易地准备光上层。为了容器B的内容: <ol><li>加的MnCl 2盐以实现0.06摩尔的浓度的MnCl 2每升水（约12克的MnCl 2每升水）。 注:上层将在外观透明，具有大约998.2±0.5公斤米-3的密度。 </li></ol></li><li>以改变流体层的粘度，以等量添加甘油的 C 3 H 8 O 3到每一层所需的粘度直至达到。典型viscositie谎言范围1.00×10 -3 - 21.00×10 -3帕秒。各层的粘度是相同的。 注:混合物可安全地存储在其单独的容器中，直到需要。 </li><li> 易地准备密度分层的。 <ol><li>添加300毫升的容器A的内容到圆柱形内罐（参照图2）。 </li><li>从容器B内浸入液体中漂浮的船的海绵。 注:（2.1.6.2）的程序是时间敏感的经过，所以没有进行任何进一步的步骤，直到所有的磁铁，灯光，录音和机械机制已准备就绪。 </li><li>解除浮选船出容器的B，并且当它已经停止滴下，小心地将浮选船在稠密流体中的内圆柱罐中的层的顶部。 </li><li>开始从容器B向浮选小船的流速添加光层流体3毫升/分钟。作为浮选舟从两个层之间的界面升降机远逐渐增加该流速。保持该接口不被流体流的增加的动量的干扰，但足够快，该过程需要不超过20分钟的足够慢流速。保持填充直到上层中含有320毫升的流体。 注:下位层将设在约33毫米的深度，并且上层将在约39毫米的深度。 </li><li>小心地将有机玻璃盖到上层，使得每个层的层深度是相等的。允许流体和空气通过泄放孔流动，以确保没有空气的下方卡住。在有机玻璃盖顶部观察清光层液体层（约6毫米）。 注意:如果该过程已成功将有相等深度的液体两层在它们之间具有清晰的界面。扩散层的界面处的厚度将小于2μmm，在这个阶段。 </li></ol></li><li>有明确的蒸馏水外罐填充到一个高度内罐的有机玻璃盖体6毫米的位置。当观察方上会有从内筒罐所得无曲率引起的视差。 注意:由于在每一层中的液体被跨越接口在这点上连续地扩散，立即进行下面的步骤。 </li></ol></li><li>分层的自旋向上<ol><li>放置在平台上的实验罐。 </li><li>布置在磁体，通过在轨道和在位置上的保持销锁孔孔口驱动轴的孔中的铜圆柱体的位置。确保该罐是远（60厘米）从磁体使得在液体的磁力是在该位置可忽略不计。 注意:携带含有分层实验箱介绍一些困难;长，低振幅，晃动波建立与日走Ë坦克将腐烂了，有浮在上层实现时的界面质量的影响可以忽略。 </li><li>转动电机上，在0.002弧度小号-2增加旋转速度，旋转式的流体至所需旋转速率。对于16的旋转速率旋转加速时间为顺序20分钟- 60分钟。 注意:用最快的转速为13.2弧度秒-1。 </li></ol></li></ol> 3.实验执行<ol><li>确保磁铁指示1.2T的磁场强度，并且，在在该不稳定启动场梯度的高度为（毕业B 2）/ 2 = -14.3Ť2 M -1，其中B是磁感应。 </li><li>确保视频摄像机被布置为使得当该驱动轴是在它的最低位置或实验的侧面图是在焦点，或平面图处于对焦通过镜子复实验上述杆进洞。 </li><li>确保环境照明是在正确的水平，例如，没有通过摄像机拍摄的图像的饱和，而是充分反应时（灰度强度范围在0-255）。 </li><li>开始录像（240 FPS）。使用遥控器，以防止在操作记录功能移动相机。 </li><li>移除的保持销，允许罐下降，在旋转的同时，进入磁场。 </li></ol> 4.重置实验<ol><li>复位试验装置<ol><li>使用遥控器停止视频录制。 </li><li>保存电影文件到磁盘。 </li><li>用手，降低电压到电机，使得它减缓停顿。逐步执行此，以防止溢漏。 </li><li>从磁铁取出实验装置。 </li><li>适当的混合液体层处分（见锰四水氯化MSDS）。 </li><li>用水冲洗水箱（它并不需要进行蒸馏出），直到盐的所有痕迹已被冲走。避免与液体直接接触皮肤。 </li><li>用纸巾仔细擦干罐，以确保没有残余物留下可能污染后续实验。 </li></ol></li></ol> 5.图像处理<ol><li>提取每个动画帧的单个图像并保存无损.png格式。屏蔽掉每一帧的任何不需要的区域，例如在平台或铜圆柱体。 </li><li>使用离散快速傅立叶变换的不稳定性的开始之后计算2秒各图像帧的二维自相关函数16。记录的最小，平均，并在实验的旋转速度和流体层的粘度的观察波长的最大值。 </li></ol>

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作者什么都没有透露。

有该协议中的两个关键步骤。第一是2.1.6.4。如果光层的致密层上浮动过快，那么这两个混溶流体层的不可逆的混合发生。至关重要的是，这是避免与这两个层之间的尖锐（&lt;2mm）的接口的实现。第二个关键步骤是3.1.5。如果实验朝磁铁释放，而没有被完全纺成刚体旋转或不可视化和图像采集设备，位置和待命然后重复上述步骤（2.1.6）。 液体层的组成，磁场强度和电动机性?...

<html>包括两层的密度分层的流体系统可以在任一稳定的或不稳定的结构被布置在引力场。如果致密重层underlies密度较小，光层则系统是稳定的:扰动界面是稳定的，在重力作用下恢复，并且波可能的接口上被支持。如果重层覆盖的光层，然后系统是不稳定的和扰动的界面生长。这一基本的流体不稳定性是瑞利-泰勒不稳定性7,8。完全相同的不稳定性，可以在该朝向较重层加速非旋转系统中观察到。由于它在很多流动的规模也相差很大观察不稳定的根本性质:由小规模的薄膜现象9观察天体物理尺度特征，例如，蟹状星云EF"&gt; 10，其中观察到手指状结构，由脉冲星风创建正在通过密集的超新星遗迹加快。这是一个悬而未决的问题瑞利-泰勒不稳定性如何可以控制或影响，一旦最初的不稳定的密度差一直在界面处建立的。一种可能性是考虑系统的散装转动。该实验的目的是研究在系统上的旋转的作用，以及是否可能是稳定的路由。 我们认为由两个层重力不稳定层，是受围绕平行于重力方向的轴线转动平稳的流体系统。的扰动到不稳定两层密度分层导致斜压产生涡， 即 ，倾覆，在界面，趋于分手任何垂直结构。然而，旋转流体已知本身组织成相干垂直ST与旋转轴对齐ructures，所谓的"泰勒列"11。因此所研究的系统经受旋转的稳定效果之间的竞争，这是组织流入垂直结构并防止两层倾覆，和的致密流体的不稳定影响覆在界面产生一个翻转运动的打火机流体。具有增加的旋转速度的流体层的径向移动，以相反方向彼此以本身重新组合成一个更稳定的配置的能力，被越来越多地由泰勒普劳德曼定理12,13抑制:径向运动被减少而作为物化不稳定的发展所观察到的结构是规模较小。 图。 1所示定性旋转上形成作为不稳定拓漩涡的影响。在里面左手图像没有转动和流动是近似值经典非旋转瑞利 - 泰勒不稳定。在右手图像中的所有的实验参数是相同的，只是系统正在绕与油箱的中心对准的垂直轴线左侧的图像。它可以看出，旋转的作用是减小所形成的涡流的大小。这，反过来，将导致该比非旋转对应发展更缓慢的不稳定性。 该修改在流体中的应力张量的磁效应可以被视为以相同的方式作为修正重力场作用。因此，我们能够创造一个引力稳定层和自旋它变成固体旋转。通过施加梯度磁场产生的磁体积力则模仿修改引力场的效果。这使得该接口不稳定使得流体系统BEHAVES，以一个很好的近似，因为在旋转的古典瑞利 - 泰勒不稳定性。这种方法已被以前试图在两个维度不旋转14,15。用于与感应磁场B施加梯度磁场，施加恒定磁体积磁化率χ的流体的体积力为f =研究所（χB 2 /μ0），考虑到其中B = | C |和μ0 =4π×10 -7 NA -2是自由空间的磁导率。因此，我们可以考虑在磁铁来操作各个流体层，其中，每在强度克重力场密度ρ的流体的单位体积的有效重量用ρ 为g的有效重量- χ（∂B 2 /∂ž ）/（2μ0）。

<table><tbody><tr><td>Blue water tracing dye</td><td>Cole-Parmer</td><td>00295-18</td><td></td></tr><tr><td>Red water tracing dye</td><td>Cole-Parmer</td><td>00295-16</td><td></td></tr><tr><td>Sodium Chloride</td><td></td><td></td><td>&gt;99% purity</td></tr><tr><td>Manganese Chloride Tetrahydrate</td><td></td><td></td><td>See MSDS</td></tr><tr><td>Fluorescein sodium salt&amp;nbsp;</td><td></td><td></td><td></td></tr><tr><td>Magnet</td><td>Cryogenic Ltd. London</td><td></td><td></td></tr></tbody></table>

magnetically induced rotating rayleigh-taylor instability

调查瑞利-泰勒不稳定经典技术包括使用压缩气体1，火箭2或线性电动机3反转重力的有效方向，并加快向致密流体较轻流体。其他作者如: 4，5，6已分离的重力不稳定层与被除去以发起的流动的障碍。然而，在一个旋转的分层的情况下，抛物线初始界面施加显著技术困难实验。我们希望能够在分层自旋成固体旋转，然后才开始流为了研究旋转时瑞利 - 泰勒不稳定的影响。我们在这里所采用的方法是使用的磁场超导磁体操纵两种液体的有效重量以引发流动。我们创建一个使用标准浮选技术的重力稳定两层分层。上部层比下部层的密度小，因此该系统是瑞利 - 泰勒稳定。然后，该分层纺丝机，直到两个层都是在固体旋转和抛物线界面观察。这些实验使用具有低磁化率，流体|χ| 〜10 -6 - 10 -5相比，一个铁磁流体。磁场的占主导地位的影响施加车身力每一层改变有效重量。上层是弱顺磁性，而下层是弱抗磁性。当施加的磁场，而上层朝向磁铁吸引下层从磁铁排斥。瑞利 - 泰勒不稳定与高梯度磁场中的应用来实现。我们还观察到，INC。reasing流体的动态粘度在每一层，增加长度尺度的不稳定性。

图。图4示出在两种流体之间的界面处的瑞利-泰勒不稳定的发展，用于四种不同的旋转速率:Ω= 1.89弧度-1（顶行），Ω= 3.32弧度-1，Ω= 4.68弧度秒- 1，和Ω= 8.74弧度-1（底行）。界面示出从T时刻演进= 0秒（左手列）为0.5秒的增量进行到t = 3.0秒（右栏）。因此右手列表示分别0.90，1.59，2.23，和4.17整圈从上到下一?...

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Magnetically Induced Rotating Rayleigh-Taylor Instability

We present a protocol for preparing a two-layer density-stratified liquid that can be spun-up into solid body rotation and subsequently induced into Rayleigh-Taylor instability by applying a gradient magnetic field.

磁感应旋转瑞利 - 泰勒不稳定性

Classical techniques for investigating the Rayleigh-Taylor instability include using compressed gasses1, rocketry2 or linear electric motors3 to reverse ...

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Universidad San Sebastian

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Unit 1

Fluid Statics

Rotation and Rigid Bodies

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9.5K 次观看.  University of Nottingham. We present a protocol for preparing a two-layer density-stratified liquid that can be spun-up into solid body rotation and subsequently induced into Rayleigh-Taylor instability by applying a gradient magnetic field.

视频: Magnetically Induced Rotating Rayleigh-Taylor Instability

Methods for Measuring the Orientation and Rotation Rate of 3D-printed Particles in Turbulence

Experimental methods are presented for measuring the rotational and translational motion of anisotropic particles in turbulent fluid flows. 3D printing technology is used to fabricate particles with slender arms connected at a common center. Shapes explored are crosses (two perpendicular rods), jacks (three perpendicular rods), triads (three rods in triangular planar symmetry), and tetrads (four arms in tetrahedral symmetry). Methods for producing on the order of 10,000 fluorescently dyed particles are described. Time-resolved measurements of their orientation and solid-body rotation rate are obtained from four synchronized videos of their motion in a turbulent flow between oscillating grids with R&#955; = 91. In this relatively low-Reynolds number flow, the advected particles are small enough that they approximate ellipsoidal tracer particles. We present results of time-resolved 3D trajectories of position and orientation of the particles as well as measurements of their rotation rates.

We use 3D printing to fabricate anisotropic particles in the shapes of jacks, crosses, tetrads, and triads, whose alignments and rotations in turbulent fluid flow can be measured from multiple simultaneous video images.

测量的方向和旋转速率方法3D打印在湍流颗粒

Experimental methods are presented for measuring the rotational and translational motion of anisotropic particles in turbulent fluid flows. 3D printing ...

科研

工程学

Direct Imaging of Laser-driven Ultrafast Molecular Rotation

We present a method for visualizing laser-induced, ultrafast molecular rotational wave packet dynamics. We have developed a new 2-dimensional Coulomb explosion imaging setup in which a hitherto-impractical camera angle is realized. In our imaging technique, diatomic molecules are irradiated with a circularly polarized strong laser pulse. The ejected atomic ions are accelerated perpendicularly to the laser propagation. The ions lying in the laser polarization plane are selected through the use of a mechanical slit and imaged with a high-throughput, 2-dimensional detector installed parallel to the polarization plane. Because a circularly polarized (isotropic) Coulomb exploding pulse is used, the observed angular distribution of the ejected ions directly corresponds to the squared rotational wave function at the time of the pulse irradiation. To create a real-time movie of molecular rotation, the present imaging technique is combined with a femtosecond pump-probe optical setup in which the pump pulses create unidirectionally rotating molecular ensembles. Due to the high image throughput of our detection system, the pump-probe experimental condition can be easily optimized by monitoring a real-time snapshot. As a result, the quality of the observed movie is sufficiently high for visualizing the detailed wave nature of motion. We also note that the present technique can be implemented in existing standard ion imaging setups, offering a new camera angle or viewpoint for the molecular systems without the need for extensive modification.

We present a protocol for creating a real-time movie of a molecular rotational wave packet using a high-resolution Coulomb explosion imaging setup.

激光驱动的超快分子旋转直接成像

We present a method for visualizing laser-induced, ultrafast molecular rotational wave packet dynamics. We have developed a new 2-dimensional Coulomb ...

化学

Visually Based Characterization of the Incipient Particle Motion in Regular Substrates: From Laminar to Turbulent Conditions

Two different experimental methods for determining the threshold of particle motion as a function of geometrical properties of the bed from laminar to turbulent flow conditions are presented. For that purpose, the incipient motion of a single bead is studied on regular substrates that consist of a monolayer of fixed spheres of uniform size that are regularly arranged in triangular and quadratic symmetries. The threshold is characterized by the critical Shields number. The criterion for the onset of motion is defined as the displacement from the original equilibrium position to the neighboring one. The displacement and the mode of motion are identified with an imaging system. The laminar flow is induced using a rotational rheometer with a parallel disk configuration. The shear Reynolds number remains below 1. The turbulent flow is induced in a low-speed wind tunnel with open jet test section. The air velocity is regulated with a frequency converter on the blower fan. The velocity profile is measured with a hot wire probe connected to a hot film anemometer. The shear Reynolds number ranges between 40 and 150. The logarithmic velocity law and the modified wall law presented by Rotta are used to infer the shear velocity from the experimental data. The latter is of special interest when the mobile bead is partially exposed to the turbulent flow in the so-called hydraulically transitional flow regime. The shear stress is estimated at onset of motion. Some illustrative results showing the strong impact of the angle of repose, and the exposure of the bead to shear flow are represented in both regimes.

Two different methods for characterizing the incipient particle motion of a single bead as a function of the sediment bed geometry from laminar to turbulent flow are presented.

从层流到湍流条件下的规则基底表面初始粒子运动的可视化表征

Two different experimental methods for determining the threshold of particle motion as a function of geometrical properties of the bed from laminar to ...

Measurements of Local Instantaneous Convective Heat Transfer in a Pipe - Single and Two-phase Flow

This manuscript provides step by step description of the manufacturing process of a test section designed to measure the local instantaneous heat transfer coefficient as a function of the liquid flow rate in a transparent pipe. With certain amendments, the approach is extended to gas-liquid flows, with a particular emphasis on the effect of a single elongated (Taylor) air bubble on heat transfer enhancement. A non-invasive thermography technique is applied to measure the instantaneous temperature of a thin metal foil heated electrically. The foil is glued to cover a narrow slot cut in the pipe. The thermal inertia of the foil is small enough to detect the variation in the instantaneous foil temperature. The test section can be moved along the pipe and is long enough to cover a considerable part of the growing thermal boundary layer.
At the beginning of each experimental run, a steady state with a constant water flow rate and heat flux to the foil is attained and serves as the reference. The Taylor bubble is then injected into the pipe. The heat transfer coefficient variations due to the passage of a Taylor bubble propagating in a vertical pipe is measured as function of the distance of the measuring point from the bottom of the moving Taylor bubble. Thus, the results represent the local heat transfer coefficients. Multiple independent runs preformed under identical conditions allow accumulating sufficient data to calculate reliable ensemble-averaged results on the transient convective heat transfer. In order to perform this in a frame of reference moving with the bubble, the location of the bubble along the pipe has to be known at all times. Detailed description of measurements of the length and of the translational velocity of the Taylor bubbles by optical probes is presented.

This manuscript describes methods aimed at measuring the local instantaneous convective heat transfer coefficients in a single or two-phase pipe flow. A simple optical method to determine the length and the propagation velocity of an elongated (Taylor) air bubble moving at a constant velocity is also presented.

管道单、两相流局部瞬时对流换热的测量

This manuscript provides step by step description of the manufacturing process of a test section designed to measure the local instantaneous heat transfer ...

Uncoupling Coriolis Force and Rotating Buoyancy Effects on Full-Field Heat Transfer Properties of a Rotating Channel

An experimental method for exploring the heat transfer characteristics of an axially rotating channel is proposed. The governing flow parameters that characterize the transport phenomena in a rotating channel are identified via the parametric analysis of the momentum and energy equations referring to a rotating frame of reference. Based on these dimensionless flow equations, an experimental strategy that links the design of the test module, the experimental program and the data analysis is formulated with the attempt to reveal the isolated Coriolis-force and buoyancy effects on heat transfer performances. The effects of Coriolis force and rotating buoyancy are illustrated using the selective results measured from rotating channels with various geometries. While the Coriolis-force and rotating-buoyancy impacts share several common features among the various rotating channels, the unique heat transfer signatures are found in association with the flow direction, the channel shape and the arrangement of heat transfer enhancement devices. Regardless of the flow configurations of the rotating channels, the presented experimental method enables the development of physically consistent heat transfer correlations that permit the evaluation of isolated and interdependent Coriolis-force and rotating-buoyancy effects on the heat transfer properties of rotating channels.

Here, we present an experimental method for decoupling the interdependent Coriolis-force and rotating-buoyancy effects on full-field heat transfer distributions of a rotating channel.

解耦科里奥利力和旋转浮力对旋转通道全场传热性能的影响

An experimental method for exploring the heat transfer characteristics of an axially rotating channel is proposed. The governing flow parameters that ...

Construction and Operation of a Light-driven Gold Nanorod Rotary Motor System

The possibility to generate and measure rotation and torque at the nanoscale is of fundamental interest to the study and application of biological and artificial nanomotors and may provide new routes towards single cell analysis, studies of non-equilibrium thermodynamics, and mechanical actuation of nanoscale systems. A facile way to drive rotation is to use focused circularly polarized laser light in optical tweezers. Using this approach, metallic nanoparticles can be operated as highly efficient scattering-driven rotary motors spinning at unprecedented rotation frequencies in water.
In this protocol, we outline the construction and operation of circularly-polarized optical tweezers for nanoparticle rotation and describe the instrumentation needed for recording the Brownian dynamics and Rayleigh scattering of the trapped particle. The rotational motion and the scattering spectra provides independent information on the properties of the nanoparticle and its immediate environment. The experimental platform has proven useful as a nanoscopic gauge of viscosity and local temperature, for tracking morphological changes of nanorods and molecular coatings, and as a transducer and probe of photothermal and thermodynamic processes.

Plasmonic gold nanorods can be trapped in liquids and rotated at kHz frequencies using circularly-polarized optical tweezers. Introducing tools for Brownian dynamics analysis and light scatteringspectroscopy leads to a powerful system for research and application in numerous fields of science.

轻型金纳米旋转电机系统的施工与运行

The possibility to generate and measure rotation and torque at the nanoscale is of fundamental interest to the study and application of biological and ...

Measuring Magnetically-Tuned Ferroelectric Polarization in Liquid Crystals

Materials showing coupling phenomena between magnetism and (ferro)electricity, i.e., magnetoelectric effects, have attracted a great deal of attention due to their potential applications for future device technologies such as sensors and storage. However, conventional approaches, which usually utilize materials containing magnetic metal ions (or radicals), have a major problem: only a few materials have been found to show the coupling phenomena at room temperature. Recently, we proposed a new approach to achieve room-temperature magnetoelectrics. In contrast to conventional approaches, our alternative proposal focuses on a completely different material, a &#34;liquid crystal&#34;, free from magnetic metal ions. In such liquid crystals, a magnetic field can be utilized to control the orientational state of constituent molecules and the corresponding electric polarization through magnetic anisotropy of the molecules; it is an unprecedented mechanism of the magnetoelectric effect. In this context, this paper provides a protocol to measure ferroelectric properties induced by a magnetic field, that is, the direct magnetoelectric effect, in a liquid crystal. With the method detailed here, we successfully detected magnetically-tuned electric polarization in the chiral smectic C phase of a liquid crystal at room temperature. Taken together with the flexibility of constituent molecules, which directly affects the magnetoelectric responses, the introduced method will serve to allow liquid crystal cells to acquire more functions as room-temperature magnetoelectrics and associated optical materials.

In this report, we present a protocol to examine direct magnetoelectric effects, i.e., induction of ferroelectric polarization by applying magnetic fields, in liquid crystals. This protocol provides a unique approach, supported by the softness of liquid crystals, to achieve room-temperature magnetoelectrics.

液晶中磁调谐铁电极化的测量

Materials showing coupling phenomena between magnetism and (ferro)electricity, i.e., magnetoelectric effects, have attracted a great deal of attention due ...

Analyzing Mixing Inhomogeneity in a Microfluidic Device by Microscale Schlieren Technique

In this paper, we introduce the use of microscale schlieren technique to measure mixing inhomogeneity in a microfluidic device. The microscale schlieren system is constructed from a Hoffman modulation contrast microscope, which provides easy access to the rear focal plane of the objective lens, by removing the slit plate and replacing the modulator with a knife-edge. The working principle of microscale schlieren technique relies on detecting light deflection caused by variation of refractive index1-3. The deflected light either escapes or is obstructed by the knife-edge to produce a bright or a dark band, respectively. If the refractive index of the mixture varies linearly with its composition, the local change in light intensity in the image plane is proportional to the concentration gradient normal to the optical axis. The micro-schlieren image gives a two-dimensional projection of the disturbed light produced by three-dimensional inhomogeneity.
To accomplish quantitative analysis, we describe a calibration procedure that mixes two fluids in a T-microchannel. We carry out a numerical simulation to obtain the concentration gradient in the T-microchannel that correlates closely with the corresponding micro-schlieren image. By comparison, a relationship between the grayscale readouts of the micro-schlieren image and the concentration gradients presented in a microfluidic device is established. Using this relationship, we are able to analyze the mixing inhomogeneity from associate micro-schlieren image and demonstrate the capability of microscale schlieren technique with measurements in a microfluidic oscillator4. For optically transparent fluids, microscale schlieren technique is an attractive diagnostic tool to provide instantaneous full-field information that retains the three-dimensional features of the mixing process.

Herein, we describe a procedure that employs microscale schlieren technique to measure mixing inhomogeneity in a microfluidic device. Through calibration, distribution of concentration gradient can be derived from the micro-schlieren image.

由微型条纹分析技术在微流控设备混合不均匀

In this paper, we introduce the use of microscale schlieren technique to measure mixing inhomogeneity in a microfluidic device. The microscale schlieren ...

生物工程

Spectral and Angle-Resolved Magneto-Optical Characterization of Photonic Nanostructures

Photonic crystals are periodic nanostructures that can support a variety of confined electromagnetic modes. Such confined modes are usually accompanied by local enhancement of electric field intensity that strengthens light-matter interactions, enabling applications such as surface-enhanced Raman scattering (SERS) and surface plasmon enhanced sensing. In the presence of magneto-optically active materials, the local field enhancement gives rise to anomalous magneto-optical activity. Typically, the confined modes of a given photonic crystal depend strongly on the wavelength and incidence angle of the incident electromagnetic radiation. Thus, spectral and angular-resolved measurements are needed to fully identify them as well as to establish their relationship with the magneto-optical activity of the crystal. In this article, we describe how to use a Fourier-plane (back focal plane) microscope to characterize magneto-optically active samples. As a model system, here we use a plasmonic grating built out of magneto-optically active Au/Co/Au multilayer. In the experiments, we apply a magnetic field on the grating in situ and measure its reciprocal space response, obtaining the magneto-optical response of the grating over a range of wavelengths and incident angles. This information enables us to build a complete map of the plasmonic band structure of the grating and the angle and wavelength dependent magneto-optical activity. These two images allow us to pinpoint the effect that the plasmon resonances have on the magneto-optical response of the grating. The relatively small magnitude of magneto-optical effects requires a careful treatment of the acquired optical signals. To this end, an image processing protocol for obtaining magneto-optical response from the acquired raw data is laid out.

Photonic band structure enables understanding how confined electromagnetic modes propagate within a photonic crystal. In photonic crystals that incorporate magnetic elements, such confined and resonant optical modes are accompanied by enhanced and modified magneto-optical activity. We describe a measurement procedure to extract the magneto-optical band structure by Fourier space microscopy.

光子纳米结构的光谱和角度解析磁-光学特性

Photonic crystals are periodic nanostructures that can support a variety of confined electromagnetic modes. Such confined modes are usually accompanied by ...

Induction of Microstreaming by Nonspherical Bubble Oscillations in an Acoustic Levitation System

When located near biological barriers, oscillating microbubbles may increase cell membrane permeability, allowing for drug and gene internalization. Experimental observations suggest that the temporary permeabilization of these barriers may be due to shear stress that is exerted on cell tissues by cavitation microstreaming. Cavitation microstreaming is the generation of vortex flows which arise around oscillating ultrasound microbubbles. To produce such liquid flows, bubble oscillations must deviate from purely spherical oscillations and include either a translational instability or shape modes. Experimental studies of bubble-induced flows and shear stress on nearby surfaces are often restricted in their scope due to the difficulty of capturing shape deformations of microbubbles in a stable and controllable manner. We describe the design of an acoustic levitation chamber for the study of symmetry-controlled nonspherical oscillations. Such control is performed by using a coalescence technique between two approaching bubbles in a sufficiently intense ultrasound field. The control of nonspherical oscillations opens the way to a controlled cavitation microstreaming of a free surface-oscillating microbubble. High-frame rate cameras allow investigating quasi-simultaneously the nonspherical bubble dynamics at the acoustic timescale and the liquid flow at a lower timescale. It is shown that a large variety of fluid patterns may be obtained and that they are correlated to the modal content of the bubble interface. We demonstrate that even the high-order shape modes can create large-distance fluid patterns if the interface dynamics contain several modes, highlighting the potential of nonspherical oscillations for targeted and localized drug delivery.

A fast and reliable technique is proposed to control the shape oscillations of a single, trapped acoustic bubble that is based on coalescence technique between two bubbles. The steady-state, symmetry-controlled bubble shape oscillations allow analysis of the fluid flow generated in the vicinity of the bubble interface.

声学悬浮系统中非球形气泡振荡诱导微流

When located near biological barriers, oscillating microbubbles may increase cell membrane permeability, allowing for drug and gene internalization. ...