Streaming Patterns Research Articles

Low Latency Optical Switch for High Performance Computing With Minimized Processor Energy Load [Invited

Power density and cooling issues are limiting the performance of high performance chip multiprocessors (CMPs), and off-chip communications currently consume more than 20% of power for memory, coherence, PCI, and Ethernet links. Photonic transceivers integrated with CMPs are being developed to overcome these issues, potentially allowing low hop count switched connections between chips or data center servers. However, latency in setting up optical connections is critically important in all computing applications, and having transceivers integrated on the processor chip also pushes other network functions and their associated power consumption onto the chip. In this paper, we propose a low latency optical switch architecture that minimizes the power consumed on the processor chip for two scenarios: multiple-socket shared memory coherence networks and optical top-of-rack switches for data centers. The switch architecture reduces power consumed on the CMP using a control plane with a simplified send and forget server interface and the use of a hybrid Mach-Zehnder interferometer and semiconductor optical amplifier integrated optical switch with electronic buffering. Results show that the proposed architecture offers a 42% reduction in head latency at low loads compared with a conventional scheduled optical switch as well as offering increased performance for streaming and incast traffic patterns. Power dissipated on the server chip is shown to be reduced by more than 60% compared with a scheduled optical switch architecture with ring resonator switching.

Diversity of acoustic streaming in a rectangular acoustofluidic field

Diversity of acoustic streaming field in a 2D rectangular chamber with a traveling wave and using water as the acoustic medium is numerically investigated by the finite element method. It is found that the working frequency, the vibration excitation source length, and the distance and phase difference between two separated symmetric vibration excitation sources can cause the diversity in the acoustic streaming pattern. It is also found that a small object in the acoustic field results in an additional eddy, and affects the eddy size in the acoustic streaming field. In addition, the computation results show that with an increase of the acoustic medium’s temperature, the speed of the main acoustic streaming decreases first and then increases, and the angular velocity of the corner eddies increases monotonously, which can be clearly explained by the change of the acoustic dissipation factor and shearing viscosity of the acoustic medium with temperature. Commercialized FEM software COMSOL Multiphysics is used to implement the computation tasks, which makes our method very easy to use. And the computation method is partially verified by an established analytical solution.

Solidification microstructure of SiC particulate reinforced Zn–Al composites under ultrasonic exposure

Solidification microstructure of SiC particles reinforced Zn–Al composites under different kinds of ultrasonic exposure was investigated and the origin of the microstructural changes induced by ultrasonic was explained. Under continuous ultrasonic exposure, highly refined and non-dendritic globular matrix structure was achieved but serious particle clustering occurred at the top and peripheral parts of the solidified ingot. Homogeneous particle distribution as well as dramatic grain refinement of matrix metal was observed in the ingot solidified with isothermal ultrasonic processing. Strong supportive evidence showed that acoustically induced dendrite fragmentation was dominantly responsible for the formation of a refined and globular microstructure. The particle clustering was closely related to the pattern of the acoustic streaming and the interactions between the particles with the vessel and the matrix melt.

Measurement of the velocity field in parametrically excited solitary waves

AbstractParametrically excited solitary waves emerge as localized structures in high-aspect-ratio free surfaces subject to vertical vibrations. Herein, we provide the first experimental characterization of the hydrodynamics of these waves using particle image velocimetry. We show that the underlying velocity field of parametrically excited solitary waves is primarily composed of a subharmonic oscillatory component. Our results confirm the accuracy of Hamiltonian models with added dissipation in describing this field. Remarkably, our measurements also uncover the onset of a streaming velocity field which we show to be as important as other crucial nonlinear terms in the current theory. Using vorticity equations, we show that the streaming pattern arises from the coupling of the potential bulk flow with the oscillating boundary layers on the vertical walls. Numerical simulations provide good agreement between this model and experiments.

Behavior of oscillatory tube flow at liquid-gas interfaces

Oscillatory flow in a long tube is characterized by an annular axial velocity profile far away from the boundaries for which an analytical solution exists. The radial velocity component is zero. Near the entrance or free surface region, this analytic solution does not hold due to the boundary conditions. Herein, the flow behavior at a liquid-gas as well as liquid-wall interface is investigated in detail by means of flow visualization measurements and Particle Image Velocimetry. The results suggest an additional radial velocity component due to the influence of the boundary. An investigation of the phase locked flow depicts the generation of steady streaming below the free surface which could be identified by vortex rings. Their shape and velocities vary according to the boundary conditions. For low frequencies, the streaming patterns are similar for cases with liquid-gas and liquid-wall interface denoting that the surface tension does not play a role for these cases. The oscillatory amplitude dominates streaming strength. As the Womersley number increases the free surface becomes unstable and Faraday waves occur which are further analysed here. This instability interacts with the steady streaming patterns which causes a change in shape and increases the streaming strength.

Numerical simulation of 3D boundary-driven acoustic streaming in microfluidic devices

This article discusses three-dimensional (3D) boundary-driven streaming in acoustofluidic devices. Firstly, the 3D Rayleigh streaming pattern in a microchannel is simulated and its effect on the movement of microparticles of various sizes is demonstrated. The results obtained from this model show good comparisons with 3D experimental visualisations and demonstrate the fully 3D nature of the acoustic streaming field and the associated acoustophoretic motion of microparticles in acoustofluidic devices. This method is then applied to another acoustofluidic device in order to gain insights into an unusual in-plane streaming pattern. The origin of this streaming has not been fully described and its characteristics cannot be explained from the classical theory of Rayleigh streaming. The simulated in-plane streaming pattern was in good agreement with the experimental visualisation. The mechanism behind it is shown to be related to the active sound intensity field, which supports our previous findings on the mechanism of the in-plane acoustic streaming pattern visualised and modelled in a thin-layered capillary device.

Experimental investigation of acoustic streaming in a cylindrical wave guide up to high streaming Reynolds numbers

Measurements of streaming velocity are performed by means of Laser Doppler Velocimetry and Particle Image Velociimetry in an experimental apparatus consisting of a cylindrical waveguide having one loudspeaker at each end for high intensity sound levels. The case of high nonlinear Reynolds number ReNL is particularly investigated. The variation of axial streaming velocity with respect to the axial and to the transverse coordinates are compared to available Rayleigh streaming theory. As expected, the measured streaming velocity agrees well with the Rayleigh streaming theory for small ReNL but deviates significantly from such predictions for high ReNL. When the nonlinear Reynolds number is increased, the outer centerline axial streaming velocity gets distorted towards the acoustic velocity nodes until counter-rotating additional vortices are generated near the acoustic velocity antinodes. This kind of behavior is followed by outer streaming cells only and measurements in the near wall region show that inner streaming vortices are less affected by this substantial evolution of fast streaming pattern. Measurements of the transient evolution of streaming velocity provide an additional insight into the evolution of fast streaming.

Hybrid Collision Detection Algorithm based on Image Space

Collision detection is an important application in the field of virtual reality, and efficiently completing collision detection has become the research focus. For the poorly real-time defect of collision detection, this paper has presented an algorithm based on the hybrid collision detection, detecting the potential collision object sets quickly with the mixed bounding volume hierarchy tree, and then using the streaming pattern collision detection algorithm to make an accurate detection. With the above methods, it can achieve the purpose of balancing load of the CPU and GPU and speeding up the detection rate. The experimental results show that compared with the classic Rapid algorithm, this algorithm can effectively improve the efficiency of collision detection. DOI: http://dx.doi.org/10.11591/telkomnika.v11i12.3744

Arabidopsis ACTIN-DEPOLYMERIZING FACTOR7 Severs Actin Filaments and Regulates Actin Cable Turnover to Promote Normal Pollen Tube Growth

Actin filaments are often arranged into higher-order structures, such as the longitudinal actin cables that generate the reverse fountain cytoplasmic streaming pattern present in pollen tubes. While several actin binding proteins have been implicated in the generation of these cables, the mechanisms that regulate their dynamic turnover remain largely unknown. Here, we show that Arabidopsis thaliana actin-depolymerizing factor7 (ADF7) is required for turnover of longitudinal actin cables. In vitro biochemical analyses revealed that ADF7 is a typical ADF that prefers ADP-G-actin over ATP-G-actin. ADF7 inhibits nucleotide exchange on actin and severs filaments, but its filament severing and depolymerizing activities are less potent than those of the vegetative ADF1. ADF7 primarily decorates longitudinal actin cables in the shanks of pollen tubes. Consistent with this localization pattern, the severing frequency and depolymerization rate of filaments significantly decreased, while their maximum lifetime significantly increased, in adf7 pollen tube shanks. Furthermore, an ADF7-enhanced green fluorescent protein fusion with defective severing activity but normal G-actin binding activity could not complement adf7, providing compelling evidence that the severing activity of ADF7 is vital for its in vivo functions. These observations suggest that ADF7 evolved to promote turnover of longitudinal actin cables by severing actin filaments in pollen tubes.

Numerical study on mixed convection from a constant wall temperature circular cylinder in zero-mean velocity oscillating cooling flows

Fluid flow and heat transfer of mixed convection from a constant wall temperature circular cylinder in zero-mean velocity oscillating cooling flows have been simulated based on the projection method with two dimensional exponential stretched staggered cylindrical meshes. Cycle mean temperature and secondary streaming are obtained by the method of partial sums of the Fourier series. Present numerical results are validated by comparing the heat transfer results of free convection and the secondary streaming of pure oscillating flow over a circular cylinder to published experimental and numerical results. The complete structures of the cycle mean temperature and secondary streaming patterns are provided by numerical simulations over wide ranges of the Reynolds number, the Keulegan–Carpenter number and the Richardson number. Based on turning points of the curves of the overall Nusselt numbers versus Reynolds numbers and the characteristics of the cycle averaged temperature and flow patterns, the heat transfer can be divided into three linear regimes (conduction, laminar convection, and turbulent convection dominated regimes) and two non-linear transition regimes. The effects of wave directions, amplitudes, frequencies, and buoyancy forces on the enhancement of heat transfer are also investigated. The effective ranges of the governing parameters for heat transfer enhancement are identified.

Finite element simulation of a two-dimensional standing wave thermoacoustic engine

A finite element analysis has been performed on a theoretical two-dimensional standing wave thermoacoustic engine using the linearized thermoacoustic equations in the frequency domain. This analysis is used to obtain the stability curve of the thermoacoustic engine, which in turn is used to calculate the oscillation onset temperature difference across the stack. The results are compared with existing theory including the long-pore approximation, as originally derived by Rott et al. In addition, the time-averaged effects of the acoustic wave are obtained using weakly nonlinear thermoacoustic theory. This includes the second order time-averaged equations for energy, momentum, and continuity. The saturation amplitude of the acoustic pressure oscillation and the required heat input to sustain the oscillation is obtained. The theory allows for calculation of acoustic streaming patterns. The particle path calculations provide insight to the minor loss mechanism occurring at the interface between the stack and the free tube for low acoustic velocity amplitudes (laminar flow).

Droplet Streaming and Nebulization Induced by the Shear Horizontal Surface Acoustic Wave

Droplet streaming and nebulization on a shear horizontal surface acoustic wave device made of 36o Y-cut LiTaO3 have been reported. The streaming pattern inside the droplet is sensitive to the droplet shape, the position to the interdigital transducer, and the aperture size. Droplet nebulization was enhanced with the increased aperture size of the driven IDTs and mainly occurred in horizontal direction along two lateral sides of the droplet, which is perpendicular to the designed SAW propagation direction. The atomization duration increases with the droplet size and decreases with the driven power at a given droplet size. The maximum rate of the atomization is ~0.2 μL/s at an applied power of 6.7 W. This provides a simple and effective method of the integration of both bio-liquid sensing and fluid manipulation on a single substrate for lab-on-chip biosensing platform.

Acoustic streaming in the transducer plane in ultrasonic particle manipulation devices

In acoustofluidic manipulation and sorting devices, Rayleigh streaming flows are typically found in addition to the acoustic radiation forces. However, experimental work from various groups has described acoustic streaming that occurs in planar devices in a plane parallel to the transducer face. This is typically a four-quadrant streaming pattern with the circulation parallel to the transducer. Understanding its origins is essential for creating designs that limit or control this phenomenon. The cause of this kind of streaming pattern has not been previously explained as it is different from the well-known classical streaming patterns such as Rayleigh streaming and Eckart streaming, whose circulation planes are generally perpendicular to the face of the acoustic transducer. In order to gain insight into these patterns we present a numerical method based on Nyborg's limiting velocity boundary condition that includes terms ignored in the Rayleigh analysis, and verify its predictions against experimental PIV results in a simple device. The results show that the modelled particle trajectories match those found experimentally. Analysis of the dominant terms in the driving equations shows that the origin of this kind of streaming pattern is related to the circulation of the acoustic intensity.

Flow analysis of acoustic streaming pattern produced by ultrasonic transducer using stereoscopic PIV

Quantitative flow fields from the acoustic streaming were measured experimentally using the stereoscopic PIV. The acoustic streaming pattern between the ultrasonic transducer and stationary plate, maximum acoustic streaming velocity, velocity variation at resonance and non-resonance, variation of flow pattern and velocity with gap variation were experimentally verified. The maximum acoustic velocity between the gap in the open channel at resonance and non-resonance was located at the ultrasonic transducer center at radial direction and at the neighborhood of the ultrasonic transducer at axial direction. In the vicinity of the ultrasonic transducer surface, larger average acoustic velocity occurred at the edge of the transducer than at the transducer center at the resonant gap. At non-resonant gap, the maximum acoustic velocity exists toward the edge of the transducer. The turbulent intensity varied with gap size and maximum value existed at the transducer center with radial direction and at surface of the stationary plate or transducer with axial direction. At resonant gaps, there was almost zero radial acoustic streaming velocity at the ultrasonic transducer center and there existed only axial streaming velocity. For axial directions, maximum acoustic streaming velocity was located at z position of − 16 mm.

Numerical simulation of nonlinear acoustic streaming in a resonator using gas-kinetic scheme

The acoustic streaming motion in a compressible air-filled two-dimensional cylindrical resonator driving by a piston is simulated by using the gas-kinetic scheme, and the effects of acoustic field intensity on the formation process of flow structure as well as streaming pattern are investigated numerically for the practical applications of high-intensity acoustic devices. Therefore, five cases with different excitation amplitudes are considered in simulation ranging from the linear to highly nonlinear regions. The validation of the developed model is verified by comparing the numerical results of streaming velocities with the theoretical ones for the linear case. The wave form of pressure and velocity and the transient flow field structure as well as the resulting streaming pattern are found to be strongly correlated to the excitation amplitude. Be observed for the linear case is a sine wave and a uniform of quasi-one-dimensional flow field as well as classical Rayleigh streaming. Periodic shock waves and strongly two-dimensional flow fields as well as the irregular acoustic streaming fields have been observed for the nonlinear cases. And some new physical phenomena have also been revealed for the highly nonlinear case, and these facts are that the wave form will deviate from typical “shock wave”-type toward a more distorted type, and at the same time, the two-dimensional transient flow fields are characterized by the changing flow direction and circulatory flow pattern, which are all correlated to a turbulent streaming with various scales of irregular and unsteady vortices throughout the resonator. Detailed explanations are provided for these nonlinear phenomena, and a critical Reynolds number for the transition to turbulence is also numerically obtained which is consistent with the experiment result from the previous publication. The present work has demonstrated that the gas-kinetic scheme is capable of resolving large Reynolds number of nonlinear acoustic problems with no any restriction on the nonlinearity level.

CFD analysis of nonlinear processes in pulse tube refrigerators: Streaming induced by vortices

Streaming in the pulse tube refrigerator is a crucial nonlinear flow and heat transfer phenomenon which considerably affects the refrigeration temperature and performance. The third type streaming in the pulse tube refrigerator is studied using computational fluid dynamics method for the first time. A two-dimensional simulation of an inline inertance tube pulse tube refrigerator (ITPTR) is performed for different operating frequencies with the help of the FLUENT® package. The streaming is found to be formed due to the generation, evolution and shedding of vortices and pressure drops which are induced by the hydrodynamic and thermodynamic asymmetries along the refrigeration system. The pressure drops due to abrupt changes of the tube cross sections at both hot and cold ends in the pulse tube are calculated and the mass flow rate of the streaming is predicted. The geometry, temperature gradient and especially frequency are revealed as the main factors influencing the streaming patterns and final refrigeration performance. The numerical results agree well with the substantial experiments and indicate further suppression and optimization methods.

On-chip micromanipulation by AC-EWOD driven twin bubbles

A novel on-chip micromanipulation method has been developed by which the streaming generated by oscillating twin bubbles actuated by alternating current electrowetting-on-dielectric (AC-EWOD) was used to manipulate micro/bio-objects in an aqueous medium. First, the behavior of a bubble placed on a plain EWOD electrode submerged in a water chamber was investigated under different AC-EWOD actuation conditions such as various frequencies and voltages using high-speed images. The results showed that the bubble oscillation amplitude highly depended on the applied frequency and was proportional to the strength of the bubble-induced streaming. To investigate the effect of the streaming, the forces generated by the oscillating bubble-induced streaming were indirectly measured using Stokes’ drag approximation under the different AC-EWOD actuation conditions at various distances between the bubble and a fish egg. The maximum force was calculated as 9μN. To improve the controllability for manipulating objects, a system of twin bubbles was proposed, and twin-bubble-induced streaming patterns at different distances between the twin bubbles were experimentally studied on microfabricated AC-EWOD chips to determine the optimum distance. To transport twin bubbles on microfluidic chips, the arrays of EWOD electrodes were microfabricated, and EWOD signals were controlled by a digital I/O board using custom-programmed Labview code. The transportation of twin bubbles was successfully demonstrated by sequentially activating the arrays of EWOD electrodes. Finally, as proof of the feasibility of the proposed method, the manipulation of a fish egg by AC-EWOD driven twin bubbles was experimentally achieved.

Ultrasonic cleaning of the root canal

A crucial step during a root canal treatment is the irrigation, where an antimicrobial fluid is injected into the root canal to eradicate all bacteria from the root canal system. Agitation of the fluid using a miniature file oscillating at 30 kHz has shown a significant improvement in the cleaning efficacy over conventional syringe irrigation. However, the exact cleaning mechanisms, being acoustic streaming, cavitation or an enhanced chemical effect, are not fully understood. Here we investigate ultrasonically activated irrigation through experiments and numerical simulations in order to understand the relative importance of each of the three cleaning mechanisms. We combine high-speed imaging and micro-Particle Imaging Velocimetry to visualize the flow pattern and cavitation in a root canal model (sub-millimeter dimensions), at timescales relevant to the cleaning processes (microseconds). Measurements of the acoustic streaming are coupled to the oscillation characteristics of the file as simulated numerically and measured with a laser vibrometer. Comparison between the streaming pattern inside the root canal and in the free field shows the importance of the confinement of the root canal on the acoustic streaming. The results give new insight into the role of acoustic streaming for the cleaning of root canals.

Shear horizontal surface acoustic wave induced microfluidic flow

In this letter, we demonstrate that surface acoustic waves (SAWs) excited on 36°Y-X LiTaO3 have both Rayleigh and shear horizontal components, which can result in different acoustic streaming patterns in micro-droplets. The shear horizontal surface acoustic wave streaming pattern exhibits a quasi-stable counterflow in the SAW propagation direction with velocities of up to 16 mm/s, with minimal damping observed within the droplets. A pumping function was realized at a threshold power of 30 dBm with a large rotation vector on hydrophobically treated devices.

Association of Intrathoracic Herniation of the Liver with Left Heart Hypoplasia in Fetuses with a Left Diaphragmatic Hernia but not in Fetuses with a Right Diaphragmatic Hernia

Predominant left heart hypoplasia is commonly observed in human fetuses with left diaphragmatic hernia and intrathoracic liver herniation ("liver-up"). In contrast, marked left/right heart disproportion has not been described in fetuses with right diaphragmatic hernia, despite intrathoracic herniation of large parts of the liver. We analyzed the data of 15 fetuses with left diaphragmatic hernia and 10 fetuses with right diaphragmatic hernia and all with intrathoracic liver herniation ("liver-up") that were examined with fetal echocardiography between 21 weeks + 1 day and 35 weeks + 0 days of gestation. The inflow and outflow dimensions and Z-scores of the two groups were statistically compared. In addition, ductus venosus streaming patterns were examined. Despite the presence of intrathoracic liver herniation, predominant left heart hypoplasia, defined as a mitral valve Z-score < - 2 in combination with a tricuspid valve Z-score that was at least 2 Z larger than the mitral valve Z-score in an individual fetus, was observed in 11 of the 15 fetuses with left diaphragmatic hernia but in none of the 10 fetuses (p < 0.001) with right diaphragmatic hernia. Preferential streaming to the right heart was observed in 14 of the 15 fetuses with left hernia but in none of the 7 fetuses with right diaphragmatic hernia in whom this flow information was available (p < 0.0001). Intrathoracic herniation of the liver ("liver-up") is associated with predominant left heart hypoplasia in left diaphragmatic hernia but not right fetal diaphragmatic hernia. Our observations indicate that this difference may result from different ductus venosus streaming sites in these conditions.