NMR velocimetry of falling liquid films

First results on NMR velocimetry of falling liquid films are presented. A film of average thickness 1 mm and width 40 mm is sustained by a continuous flow of silicon oil over a vertical plate made from PMMA. The spatial distribution of velocities is measured using a double spin--echo imaging pulse sequence supplemented by a bipolar velocity encoding gradient. Spin density and velocity images as well as two-dimensional velocity maps of different situations, i.e., undisturbed and disturbed falling film flow, are discussed. Experimental and theoretical velocity data for undisturbed film flow are compared.     

Calculations of the reflection and transmission of ultrasound by cracks in steel filled with liquid sodium

The ultrasonic reflection and transmission amplitudes of idealized cracks in steel filled with liquid sodium are calculated as a function of the angle of incidence and crack width for an incident compression wave of frequency 2.25 MHz. It is concluded that it should be no more difficult to detect a liquid-sodium filled crack than an air filled crack for widths greater than 0.01 mm, which is typical of fatigue crack widths.     

Improvement of ultrasound speckle image velocimetry using image enhancement techniques

Ultrasound-based techniques have been developed and widely used in noninvasive measurement of blood velocity. Speckle image velocimetry (SIV), which applies a cross-correlation algorithm to consecutive B-mode images of blood flow has often been employed owing to its better spatial resolution compared with conventional Doppler-based measurement techniques. The SIV technique utilizes speckles backscattered from red blood cell (RBC) aggregates as flow tracers. Hence, the intensity and size of such speckles are highly dependent on hemodynamic conditions. The grayscale intensity of speckle images varies along the radial direction of blood vessels because of the shear rate dependence of RBC aggregation. This inhomogeneous distribution of echo speckles decreases the signal-to-noise ratio (SNR) of a cross-correlation analysis and produces spurious results. In the present study, image-enhancement techniques such as contrast-limited adaptive histogram equalization (CLAHE), min/max technique, and subtraction of background image (SB) method were applied to speckle images to achieve a more accurate SIV measurement. A mechanical sector ultrasound scanner was used to obtain ultrasound speckle images from rat blood under steady and pulsatile flows. The effects of the image-enhancement techniques on SIV analysis were evaluated by comparing image intensities, velocities, and cross-correlation maps. The velocity profiles and wall shear rate (WSR) obtained from RBC suspension images were compared with the analytical solution for validation. In addition, the image-enhancement techniques were applied to in vivo measurement of blood flow in human vein. The experimental results of both in vitro and in vivo SIV measurements show that the intensity gradient in heterogeneous speckles has substantial influence on the cross-correlation analysis. The image-enhancement techniques used in this study can minimize errors encountered in ultrasound SIV measurement in which RBCs are used as flow tracers instead of exogenous contrast agents.     

A proposed method for generating and receiving narrow beams of ultrasound in the Fast Reactor liquid sodium environment

In the liquid sodium coolant of the Fast Reactor there are several measurements which may be performed using ultrasonic techniques. This paper gives a brief outline of one such measurement and then describes the design of an ultrasonic waveguide for the generation and detection of ultrasound in this hostile situation. The successful laboratory tests of the device are also reported.     

Preliminary investigations of ultrasound induced acoustic streaming using particle image velocimetry

Particle image velocimetry was used to investigate ultrasound-induced acoustic streaming in a system for the enhanced uptake of substances from the aquatic medium into fish. Four distinct regions of the induced streaming in the system were observed and measured. One of the regions was identified as an preferential site for substance uptake, where the highest velocities in proximity to the fish surface were measured. A positive linear relationship was found between the ultrasound intensity and the maximum streaming velocity, where a unitless geometric factor, specific to the system, was calculated for correcting the numerical relationship between the two parameters. The results are part of a comprehensive study aimed at improving mass transdermal administrations of substances (e.g. vaccines, hormones) into fish from the aquatic medium.     

Visualizing macromolecular complexes with in situ liquid scanning transmission electron microscopy

A central focus of biological research is understanding the structure/function relationship of macromolecular protein complexes. Yet conventional transmission electron microscopy techniques are limited to static observations. Here we present the first direct images of purified macromolecular protein complexes using in situ liquid scanning transmission electron microscopy. Our results establish the capability of this technique for visualizing the interface between biology and nanotechnology with high fidelity while also probing the interactions of biomolecules within solution. This method represents an important advancement towards allowing future high-resolution observations of biological processes and conformational dynamics in real-time.     

Velocity autocorrelation in liquid sodium

The expression for the memory function of Corngold et al. has been modified using an effective potential for liquid sodium to calculate the velocity autocorrelation function and the coefficient of self diffusion. The results are found in good agreement with computer experiment results of Schiff.     

Numerical modeling of microbubble backscatter to optimize ultrasound particle image velocimetry imaging: initial studies

We have developed a promising non-invasive ultrasound-based method for performing particle image velocimetry (PIV) in vivo. This method, termed echo PIV, provides multi-component blood velocity data with good (2 ms) temporal resolution. The method takes advantage of the non-linear ultrasound backscatter characteristics of small gas-filled microbubbles (ultrasound contrast) that are seeded into the blood stream. In this study, we use a numerical model to explore potential areas to focus future work in echo PIV.

Ultrasound backscatter from encapsulated microbubbles was modeled using a modified Rayleigh–Plesset equation (Church model, 1995), taking into account the protein/lipid shell layer as a thick, mass-conserving incompressible fluid surrounded by incompressible blood-like fluid. The equation of motion was solved numerically to characterize the fundamental and second harmonic components of the backscattered pressure. Results show a significant advantage in using the second harmonic component for echo PIV, especially for small bubble sizes less than 3 μm in diameter at 2.2 MHz frequency. The effect of the shell thickness ranging from 10 to 500 nm on the vibration amplitude of the bubble was examined and it is shown that the presence of the shell requires mechanical index (MI)>0.2 of incident pressure amplitude to improve bubble detectability. Analysis of the effect of pulse length shows a tradeoff between axial resolution (short pulse length) and bubble detectability (longer pulse length) will most likely be required. The effect of varying MI between 0.1 and 0.6 was also studied at a center frequency of 2.2 MHz and the results indicate that the resonance of the second harmonic is maximized for bubbles with diameter of approximately 2.75 μm. Bubble non-linearities at MI>0.2 induced a resonant frequency shift away from the integer multiple of the incident frequency in the second harmonic backscatter. For a given bubble size, there is a combination of optimal incident frequency and mechanical index range that maximizes the ratio of the second harmonic compared to the fundamental. This resonant frequency decreases with increasing bubble radius. Further, a narrow bandwidth pulse is shown to increase signal strength. Both of these effects may cause conflict with factors governing spatial resolution. Optimization of the incident frequency, microbubble size and mechanical index to enhance bubble detectability will depend on the particular clinical application. These theoretical predictions provide further understanding of the physics behind our echo PIV technique, and should be useful for guiding the design of echo PIV systems.     

Turbulent diamagnetism in flowing liquid sodium

The nature of Ohm's law is examined in a turbulent flow of liquid sodium. A magnetic field is applied to the flowing sodium, and the resulting magnetic field is measured. The mean velocity field of the sodium is also measured in an identical-scale water model of the experiment. These two fields are used to determine the terms in Ohm's law, indicating the presence of currents driven by a turbulent electromotive force. These currents result in a diamagnetic effect, generating magnetic field in opposition to the dominant fields of the experiment. The magnitude of the fluctuation-driven magnetic field is comparable to that of the field induced by the sodium's mean flow.     

Effects of red blood cell aggregates dissociation on the estimation of ultrasound speckle image velocimetry

Ultrasound speckle image of blood is mainly attributed by red blood cells (RBCs) which tend to form RBC aggregates. RBC aggregates are separated into individual cells when the shear force is over a certain value. The dissociation of RBC aggregates has an influence on the performance of ultrasound speckle image velocimetry (SIV) technique in which a cross-correlation algorithm is applied to the speckle images to get the velocity field information. The present study aims to investigate the effect of the dissociation of RBC aggregates on the estimation quality of SIV technique. Ultrasound B-mode images were captured from the porcine blood circulating in a mock-up flow loop with varying flow rate. To verify the measurement performance of SIV technique, the centerline velocity measured by the SIV technique was compared with that measured by Doppler spectrograms. The dissociation of RBC aggregates was estimated by using decorrelation of speckle patterns in which the subsequent window was shifted as much as the speckle displacement to compensate decorrelation caused by in-plane loss of speckle patterns. The decorrelation of speckles is considerably increased according to shear rate. Its variations are different along the radial direction. Because the dissociation of RBC aggregates changes ultrasound speckles, the estimation quality of SIV technique is significantly correlated with the decorrelation of speckles. This degradation of measurement quality may be improved by increasing the data acquisition rate. This study would be useful for simultaneous measurement of hemodynamic and hemorheological information of blood flows using only speckle images.     

Applications of ultrasound in processing of liquid foods: A review

Ultrasonic processing of a variety of liquids, drinks and beverages has generated much interest with published literature papers increasing within this area in recent years. Benefits include enhanced emulsification with improved homogenization and fat globule size reduction being recorded. In dairy systems increased creaming rates are observed on sonication in a process known as fractionation. Whilst fruit juices exhibit retention or enhancement of quality parameters whilst increasing levels of bioactive compounds. Sterilization of liquids is a large feature of ultrasonic treatment with microbial activity of a range of fruit juices being monitored over time as increased stability and reduced spoilage is observed. Progress has also been made towards scale up of ultrasonic processes with several examples of batch and continuous processes being studied with reduced processing times and temperatures being quoted as a result of ultrasonic treatment. This short review covers the effect of sonication on liquids and beverages with a specific focus towards dairy and fruit juices and covers emulsification, fractionation, sterilization and some pilot scale initiatives.     

Three-dimensional particle image velocimetry: a low-cost 35 mm angular stereoscopic system for liquid flows

A low-cost 35 mm PIV stereoscopic system for liquid flows is presented which has an imaging component cost under US$9000. The system uses an angular configuration, rotating mirror image shifting and in-situ calibration techniques. Image processing algorithms based on cross correlation and bicubic interpolation are also used to calculate the 3D data from the PIV images. Results from an error analysis have shown the system to have in plane errors ranging from 4.15 to 5.95% and out of plane errors of 7.01% providing an f-number of f2 is fixed for all imaging. Subsequent application of the system to a flow field generated by a free falling sphere in wheat syrup have produced results which when compared to previous flow visualisation give good qualitative agreement. Suggested improvements to the PIV system costing US$1300 would allow operation at f-numbers down to f by modifying the cameras for the Scheimpflug condition and using a corrective liquid prism.     

Visualization of turbulence structure in unsteady non-penetrative thermal convection using liquid crystal thermometry and stereo velocimetry

Temperature and velocity fields in unsteady non-penetrative turbulent thermal convection of a horizontal fluid layer are measured in horizontal and vertical planes simultaneously using the combined liquid-crystal thermometry and stereo particle image velocimetry (PIV) with high spatial and temporal resolution. The result shows the formation of convection pattern across the fluid layer, which originates from the spoke structure over the heated surface. The upward fluid motion is generated from the intersection of the bursting lines of the spoke structure, while the downward motion is induced by the low temperature fluid directing toward the center of the spoke structure. Thus, the large-scale convective motion is produced in the fluid layer through the motion of spoke structure. The POD analysis of the temperature and velocity eigenfunctions shows the existence of large-scale motion in the fluid layer, which supports the observed convection pattern near the heated boundary and in the middle of the fluid layer.     

Gas bubble detection in liquid metals by means of the ultrasound transit-time-technique

In this work the ultrasound-transit time technique is introduced as a versatile method to analyze the bubble dynamics in liquid-metal-gas flows. After discussing the principle of operation and the implementation of the technique, the methods used to extract the positions of the bubbles, their velocities, or their diameters are explained. Finally, the performance of the method is demonstrated for a liquid-metal-gas flow with and without a magnetic field.     

Plasma discharge with bulk glow in the liquid phase exposed to ultrasound

It is shown that a specific form of the electric discharge with bulk glow in the entire space between electrodes and an increasing current-voltage characteristic inherent to the anomalous glow discharge in gas can exist in a liquid exposed to an intense ultrasonic field above the cavitation threshold. Such a discharge can be initiated between planar or rod electrodes in liquid in the mode of developed cavitation excited by an ultrasonic acoustic field. It is found that a plasma pinch is formed during cavitation between electrodes immersed into liquid. The pinch is stable at relatively low voltages (??30?C60 V) and currents (4?C8 A).     

分子波函数的直接观测

2011年,IBM苏黎世实验室根据量子力学中隧道效应的“微商定则”,用一氧化碳分子作为扫描隧道显微镜的探头,观测到了两种有机分子的波函数的波节面和叶片在空间中的分布,证明了分子波函数的波节面和叶片结构是可以直接观测的物理实在。反映上述研究工作结果的文章发表一年多以来,已获得物理学界和化学界的普遍认同。这一实验发现将帮助未来几代的化学家对分子的性质有直观的了解,从而引导他们在化学的所有领域中获得新的解决方案。     

分子波函数的直接观测

2011年,IBM苏黎世实验室根据量子力学中隧道效应的“微商定则”,用一氧化碳分子作为扫描隧道显微镜的探头,观测到了两种有机分子的波函数的波节面和叶片在空间中的分布,证明了分子波函数的波节面和叶片结构是可以直接观测的物理实在。反映上述研究工作结果的文章发表一年多以来,已获得物理学界和化学界的普遍认同。这一实验发现将帮助未来几代的化学家对分子的性质有直观的了解,从而引导他们在化学的所有领域中获得新的解决方案。