Distinct Flow Patterns Research Articles

Collateral Flow Measurement by Phase-contrast Magnetic Resonance Imaging for the Assessment of Systemic Venous Baffle Patency After Atrial Switch Repair for Transposition of the Great Arteries

We aimed to describe and compare azygos vein flow patterns of patients with obstructed and unobstructed systemic venous baffle after atrial switch repair for d-transposition of the great arteries (TGA). We hypothesized that phase-contrast magnetic resonance imaging would enable characterization of retrograde collateral flow across the azygos vein in cases of systemic venous baffle obstruction. This is a retrospective, cross-sectional study. Twelve patients with atrial switch repair for TGA were examined. Azygos flow index was measured with phase-contrast magnetic resonance imaging; comparison was made between patients with documented systemic venous baffle obstruction (n=3) and a control group of patients without baffle obstruction (n=9). Patients with systemic venous baffle obstruction had a distinctive azygos flow pattern that was retrograde and an increased amount of azygos flow compared with patients without obstruction [median (range), -436 (-455/-399) vs. 103 (51/125) mL/min/m2; P=0.01]. Patients with systemic venous baffle obstruction have a characteristic collateral flow across the azygos vein. Azygos vein flow measurement may be used for the assessment of baffle patency in patients after atrial switch repair for TGA. However, diagnostic accuracy needs to be tested in a larger population.

Reduction in sensitivity to radial optic-flow congruent with ego-motion

Visual motion, such as radial optic flow, is an important cue for perceiving direction during ego-motion. Several previous studies have reported that the perceived speed of a radial optic flow is underestimated when the represented ego-motion direction between radial optic flow and non-visual (such as vestibular or/and proprioceptive) information is congruent. In the present study, we examined whether sensitivity to different types of optic flow (radial vs. laminar) interacts with vestibular input in different ways by using another method: instead of estimating the perceived speed of the visual motion pattern, we measured motion-coherence thresholds. The results indicated that when the heading direction was represented by a radial optic-flow pattern, the radial optic-flow sensitivity was significantly lower under the condition where the visual and vestibular sensory input were congruent with the ego-motion direction than under the condition where the visuo-vestibular input and ego-motion were incongruent. These results indicated that radial optic-flow sensitivity was decreased by the congruent vestibular input during the ego-motion event. On the other hand, when the direction of ego-motion was represented by a laminar optic flow, the results were different from those observed with radial optic flows. These data suggest that vestibular input has some effect on optic-flow sensitivity but that the magnitude of the effect of vestibular input may differ between distinct flow patterns such as radial and laminar optic flows.

Role of marangoni tension effects on the melt convection in directional solidification process for multi-crystalline silicon ingots

We carried out global simulations to investigate the marangoni tension effect on the thermal and flow fields in the silicon melt of the directional solidification process for multi-crystalline silicon ingots. The argon flow rate was varied to provide different solidification conditions and to change the relative values between the argon shear stress and the marangoni tension at the melt free surface. We found that the marangoni tension together with the shear stress mainly influences the upper layer melt convection while the thermal buoyancy force dominates the bulk flow of the melt. At low argon flow rates, the argon shear stress can be neglected and the marangoni tension alone enhances the melt convection intensity near the gas–melt–crucible triple junction point. The marangoni tension is so weak that it cannot modify the melt flow pattern in this case. For medium flow rate, the marangoni tension can significantly weaken the shear stress effect at the outer part of the melt free surface, leading to a distinctive flow pattern in the silicon melt. With further increase in argon flow rate, the shear stress sharply increases and dominates the upper layer melt flow, limiting the marangoni tension effect to the triple point. The numerical results are helpful for better understanding and controlling of the directional solidification process for high quality multi-crystalline silicon ingots.

Prey handling using whole-body fluid dynamics in batoids

Fluid flow generated by body movements is a foraging tactic that has been exploited by many benthic species. In this study, the kinematics and hydrodynamics of prey handling behavior in little skates, Leucoraja erinacea, and round stingrays, Urobatis halleri, are compared using kinematics and particle image velocimetry. Both species use the body to form a tent to constrain the prey with the pectoral fin edges pressed against the substrate. Stingrays then elevate the head, which increases the volume between the body and the substrate to generate suction, while maintaining pectoral fin contact with the substrate. Meanwhile, the tip of the rostrum is curled upwards to create an opening where fluid is drawn under the body, functionally analogous to suction-feeding fishes. Skates also rotate the rostrum upwards although with the open rostral sides and the smaller fin area weaker fluid flow is generated. However, skates also use a rostral strike behavior in which the rostrum is rapidly rotated downwards pushing fluid towards the substrate to potentially stun or uncover prey. Thus, both species use the anterior portion of the body to direct fluid flow to handle prey albeit in different ways, which may be explained by differences in morphology. Rostral stiffness and pectoral fin insertion onto the rostrum differ between skates and rays and this corresponds to behavioral differences in prey handling resulting in distinct fluid flow patterns. The flexible muscular rostrum and greater fin area of stingrays allow more extensive use of suction to handle prey while the stiff cartilaginous rostrum of skates lacking extensive fin insertion is used as a paddle to strike prey as well as to clear away sand cover.

Flow regime transition for cocurrent gas–liquid flow in micro-channels

Experimental investigations of gas–liquid two-phase flow regimes in micro-channels were carried out in this work. Four distinctive flow patterns of slug flow, slug-annular flow, annular flow and parallel stratified flow were captured by a digital video recording (DVR) system and the transitions among different flow regimes were studied. The effect of fluid properties and wetting properties of the channel wall on the flow regime and flow pattern transition were studied as well. Novel empirical correlations for predicting flow pattern transitions during the steady gas–liquid flow in micro-channels have been developed with the fluid properties and the wetting properties of micro-channels incorporated, whereas the traditional flow criteria were based on gas and liquid superficial velocities only. The predictions of the present empirical models agree well with the experimental data.

Experimental Investigation on Flow Patterns of Cylindrical-Conical Spout-Fluidizing Bed

Experimental investigations on hydrodynamic characteristics of cylindrical pressurized spout-fluidizing bed were carried out. Two kinds of millet were used as bed materials. The operational pressure is 0.1MPa~0.4MPa (absolutely pressure). Five distinct flow patterns, i.e, fixed bed(FB), jet in fluidized bed with bubbles(JFB), jet in fluidized bed with slugging(JFS), spout with aeration(SA) and spout-fluidizing bed(SF) were identified. Effects of the static bed height and operational pressure on the flow pattern map were particularly studied. Typical flow pattern images obtained by a high- resolution digital CCD camera were presented for classifying these flow patterns. Typical flow pattern maps were plotted for describing the transitions between flow patterns with operating conditions

Cluster and Bed-to-wall Heat Transfer Characteristics in a Dual Circulating Fluidized Bed

The cluster and bed-to-wall heat transfer characteristics in a dual circulating fluidized bed have been determined by a particle velocity and a heat flux meters, respectively. The mean cluster length, mean cluster velocity, cluster fraction, and heat transfer coefficients increase with increasing solid circulation rate and decreasing gas velocity in the riser. The heat transfer coefficient with a solid circulation in the bubbling fluidized bed is found to be lower than that without solid circulation. With the distinct solid flow pattern, a correlation to predict convective heat transfer coefficient as a function of the operating variables is proposed. To verify the heat–transfer mechanism in a dual circulating fluidized bed, it is found that the cluster-renewal model can be utilized with high accuracy. The obtained bed hydrodynamics and the heat transfer coefficients in the dual circulating fluidized bed can be used to determine the optimum operating conditions in the gasification and combustion operations.

Flow Pattern and Pressure Drop in Highly Concentrated Slurries Transportation Pipelines

Flow pattern and pressure drop in highly concentrated slurries transportation pipelines were discussed. The particles are settling, and tend to settle down to the bottom of pipes due to the action of gravity force forming different flow patterns which can be indicated by particle concentration profile. Three distinct flow patterns can be observed for different particle size distribution at different velocities: fully stratified, partially stratified and fully suspended flow patterns. As for pressure drop, it is well known that pressure drops in pipeline flows of slurries are strongly dependent on the flow pattern developed in a pipeline. Furthermore, fine particles suspended in water make the water more viscous, and increase the friction. In case of coarse particles, having larger volume, they have the tendency to contact with the pipe wall and with the other coarse particles more times, which increase the friction of flow. Meanwhile, coarse particles are lifted by the pressure difference generated as they rotate in the liquid preventing the coarse particles from settling down which results in less friction. The mixture of particles of different sizes is helpful to reduce pressure drop in pipeline flow slurries. Narrow grading particles tend to have high frictional losses, while broad grading particles have low frictional losses at high concentrations.

Transferring subsidiary knowledge in the global learning context

PurposeThe purpose of this paper is to explore organizational factors that affect the transfer of subsidiary knowledge to both parent companies and peer subsidiaries.Design/methodology/approachThe hypotheses are tested using multivariate regression, based on a survey of 81 foreign subsidiaries in South Korea.FindingsThe findings show that organizational factors that affect the transfer of subsidiary knowledge differ according to whether the recipient is the parent or the peer subsidiary. Subsidiary‐to‐parent knowledge flow is facilitated by establishing efficient formal mechanisms such as an expatriation policy, a subsidiary performance evaluation system, etc., whereas knowledge transfer to peer subsidiaries is enhanced by the length of a subsidiary's operation period and the frequency of its managers' communications with other managers in peer subsidiaries.Practical implicationsThis analysis suggests that managers of multinational companies should apply different approaches in managing these two distinct knowledge flow patterns in the MNC network.Originality/valueThis study offers new insights into the challenges of global learning by highlighting the difficulty of transferring subsidiary knowledge to peer subsidiaries through formal organizational apparatuses.

Nonlinear characterization of oil–gas–water three-phase flow in complex networks

Understanding the dynamics of oil–gas–water three-phase flow has been a challenge in the fields of nonlinear dynamics and fluid mechanics. We systematically carried out oil–gas–water three-phase flow experiments for measuring the time series of flow signals, which is studied in terms of the mapping from time series to complex networks. Two network mapping methods are proposed for the analysis and identification of flow pattern dynamics, i.e. Flow Pattern Complex Network (FPCN) and Fluid Dynamic Complex Network (FDCN). Through detecting the community structure of FPCN based on K-means clustering, distinct flow patterns can be successfully distinguished and identified. A number of FDCN's under different flow conditions are constructed in order to reveal the dynamical characteristics of three-phase flows. The network information entropy of FDCN is sensitive to the transition among different flow patterns, which can be used to characterize nonlinear dynamics of the three-phase flow. These interesting and significant findings suggest that complex networks can be a potentially powerful tool for uncovering the nonlinear dynamics of oil–gas–water three-phase flows.

Aortic flow patterns resulting from right axillary artery cannulation

Right axillary artery (RAA) cannulation is increasingly used in cardiac surgery. Little is known about resulting flow patterns in the aorta. Therefore, flow was visualized and analyzed. A mock circulatory circuit was assembled based on a compliant transparent anatomical silicon aortic model. A RAA cannula was connected to a continuous flow rotary blood pump (RBP), pulsatile heart action was provided by a pneumatic ventricular assist device (PVAD). Peripheral vascular resistance, regional flow and vascular compliance were adjusted to obtain physiological flow and pressure waveforms. Colorants were injected automatically for flow visualization. Five flow distributions with a total flow of 4l/min were tested (%PVAD:%RBP): 100:0, 75:25, 50:50, 25:75, 0:100. Colorant distribution was assessed using quantitative 2D image processing. Continuous flow from the RAA divided in a retrograde and an antegrade portion. Retro- to antegrade flow ratio increased with increasing RAA-flow. At full RBP support flow was stagnant in the ascending aorta. There were distinct flow patterns between the right- and left-sided supra-aortic branches. At full RBP support retrograde flow was demonstrated in the right carotid and right vertebral arteries. Further studies are needed to confirm and evaluate the described flow patterns.

Material Flow Visualization during Friction Surfacing

Metal flow behavior within friction surfaced coating was studied using tungsten powder as a marker. The results show that the top and bottom layers within the coating exhibit distinct flow patterns. The transport of material takes an involute path, and the material transfer starts from the advancing side of the coating to the retreating side and terminates at the center. The recirculation of material occurs at the retreating side of the coating.

Viscoelastic flows in mixing-separating cells

The flow of Newtonian and viscoelastic fluids in a mixing-separating geometry that consists of two opposed channel flows interacting through a gap in the common separating wall is investigated. The flow in this type of geometry was studied experimentally by Cochrane et al. (Philos Trans R Soc Lond A301:163-181, 1981) using Newtonian and viscoelastic fluids at low Reynolds numbers (Re < 50). In this numerical study, by use of a finite-volume method, the effects of Deborah (De) and Reynolds numbers and gap size on the two-dimensionalflow dynamics are assessed. The normalized gap size varies between 0 and 5, Re varies between 0 and 50 and De varies between 0 and the maximum attainable value. Due to the anti-symmetry of the fully developed inlet conditions and the symmetry of the flow geometry, the Newtonian creeping flow is anti-symmetric. Increasing the gap size of the separating walls leads to an increase of the reversed flow-rate ratio (Rr), which is defined as the ratio of the reversed and the total flow rate. For creeping flow of viscoelastic fluids, here described by the upper-convected Maxwell model, two distinct flow patterns are observed. Below a critical gap size, the reversed flow is slightly enhanced when the Deborah number increases. Further increase of De leads to a subsequent decrease in Rr towards zero. For a supercritical gap size, increasing the Deborah number leads to a monotonic increase in Rr.

Investigation on Flow Patterns and Transitions in a Multiple-Spouted Bed

Experimental studies on flow patterns and transitions were carried out in a visible multiple-spouted bed. The bed combines three spouted bed cells, each with a cross-section of 100 × 30 mm, and each cell has an independent spout nozzle of 10 mm in width. Polypropylene beads with a density of 900 kg/m3 and mean diameter of 2.8 mm were used as bed materials. Six distinct flow patterns, i.e., fixed bed (FB), internal jet (IJ), internal jet with bubble (IJB), single spouting (SS), multi-spouting (MS), and internal jet with slugging (IJS), were determined on the basis of criteria as well as schematic diagrams and typical flow pattern images obtained from a high-resolution digital charge coupled device (CCD) camera. Typical flow regime maps at three static bed heights were plotted to describe the transitions of flow patterns with central and auxiliary spouting gases. Besides, some important flow characteristics associated with flow patterns and transitions, i.e., minimum spouted velocity and pressure drop, were...

Flow Boiling Visualization of R-134a in a Vertical Channel of Small Diameter

The present work reports on flow boiling visualization of refrigerant R-134a in a vertical circular channel with an internal diameter of 1.33 mm and 235 mm in heated length. A quartz tube with a homogeneous Indium Tin Oxide coating is used to allow heating and simultaneous visualization. Flow patterns have been observed along the heated length with the aid of high-speed complementary metal oxide semiconductor (CMOS) digital camera. From the flow boiling visualization, seven distinct two-phase flow patterns have been observed: isolated bubbly flow, confined bubbly flow, slug flow, churn flow, slug-annular flow, annular flow, and mist flow. Two-phase flow pattern observations are presented in the form of flow pattern maps. The effects of the saturation temperature and the inlet subcooling degree on the two-phase flow pattern transitions are elucidated. Finally, the experimental flow pattern map is compared with models developed for conventional sizes as well as to a microscale map for air-water mixtures available in literature, showing a large discrepancy.

Contribution of experimental fluid mechanics to the design of vertical slot fish passes

This paper presents the main results of an experimental study of mean and turbulent characteristics of flow in a scale model of a vertical slot fish pass with varying width and slope (from 5% to 15%). Experimental hydraulic modelling was combined with the study of fish behaviour in the model. The discharge coefficient, which significantly affects the design of such facilities, varied from 0.67 to 0.89 and was strongly influenced by the slope. Two distinct flow patterns were observed, depending on the slope and the fish pass width. The point of transition between the two states was determined. Low velocity areas are likely resting zones for fish and particular attention was paid to evaluating these areas. Slope was found to affect both the volume of the low velocity zone, and the value of turbulent kinetic energy in these areas. The statistical characteristics of turbulent kinetic energy in the pools were linked primarily to the maximum velocity in the jet. An analysis of the behaviour of juvenile brown trout (Salmo trutta ) in the scale model clearly showed that the fish avoided the areas of high velocities in the jet, except at the slot itself where they took advantage of the jet’s non-stationary character. Low-velocity areas were not frequented uniformly by fish, which stayed most frequently in the zone located just downstream from the slot and behind the small side baffle. It is suggested that future studies might investigate lower pool-length to slot-width ratios, which might make it possible to increase the slope significantly and should also examine ways of improving hydraulic conditions for fish by carefully distributing obstacles in pools.

P02-159 - Magnetic resonance imaging of baseline brain perfusion in major depressive disorder

IntroductionContinuous arterial spin labelling (cASL) is a non-invasive magnetic resonance imaging method increasingly used to study human brain function and perfusion physiology.ObjectivesIn this study, we investigated distinct patterns of cerebral blood flow (CBF) in MDD patients by means of resting state cASL.Methods11 healthy controls and 11 patients with MDD according to DSM-IV criteria were included. The individual cASL images underwent data preprocessing steps including the generation of perfusion-weighted images, followed by conversion to quantified CBF. An analysis of temporally coherent CBF patterns was performed using a spatial Independent Component Analysis.ResultsBoth groups showed distinct blood flow patterns in a medial frontoparietal and lateral temporal component (“default mode” network), a medial temporal and anterior cingulate component (“limbic” network) and bilateral prefrontal and parietal component (“cognitive” network). Within the “limbic” network, MDD patients showed a pattern of increased CBF in the bilateral ventrolateral prefrontal, cingulate, striatal and hippocampal regions. Within the “cognitive” network, MDD patients showed a pattern of increased CBF in left dorsolateral prefrontal and the inferior parietal areas. Decreased perfusion in MDD patients was found in the right precuneus, the right inferior parietal cortex, the left posterior cingulate and the left lateral temporal cortex.ConclusionsThese preliminary data demonstrate the sensitivity of cASL techniques for detecting resting state CBF changes in MDD patients. Thus, cASL studies in MDD could provide valuable information with regard to neurobiologically characterized endophenotypes, while resting state CBF measures could serve as objective predictors of treatment response in future studies.

An electrohydrodynamic flow in ac electrowetting

In ac electrowetting, hydrodynamic flows occur within a droplet. Two distinct flow patterns were observed, depending on the frequency of the applied electrical signal. The flow at low-frequency range was explained in terms of shape oscillation and a steady streaming process in conjunction with contact line oscillation. The origin of the flow at high-frequency range has not yet been explained. We suggest that the high-frequency flow originated mainly from the electrothermal effect, in which electrical charge is generated due to the gradient of electrical conductivity and permittivity, which is induced by the Joule heating of fluid medium. To support our argument, we analyzed the flow field numerically while considering the electrical body force generated by the electrothermal effect. We visualized the flow pattern and measured the flow velocity inside the droplet. The numerical results show qualitative agreement with experimental results with respect to electric field and frequency dependence of flow velocity. The effects of induced-charge electro-osmosis, natural convection, and the Marangoni flow are discussed.

Use of color flow Doppler ultrasonography to diagnose a bleeding neuroendocrine tumor in the gallbladder of a dog

A 13-year-old neutered female Keeshond-cross was evaluated because of a history of melena, anemia, hematemesis, vomiting, and high serum liver enzyme activities over a 1.5-year period. Abdominal ultrasonography revealed a hyperechoic mass in the gallbladder. In the gallbladder mass itself, a distinct linear blood flow pattern was detected by use of color flow Doppler ultrasonography. A cholecystectomy was performed, and clinical signs resolved. Samples of the mass were examined histologically and immunohistochemically, and findings supported a diagnosis of neuroendocrine tumor of the gallbladder. Tumors of the biliary tree are a potential source of blood loss into the gastrointestinal tract. Color flow Doppler ultrasonography in conjunction with conventional grayscale ultrasonography may be useful in evaluation of the gallbladder in dogs. When echogenic material is detected in the gallbladder, it is important to evaluate the region for blood flow.

Simulation and experiment research on vaporizing liquid micro-thruster

In the present work, a micro-thruster chip with dimension of 19.5 mm × 9.5 mm was fabricated with MEMS technologies for the experiment study of vaporizing liquid micro-thruster. In addition, a full 3D computational model was constructed to simulate the aft section of a vaporizing liquid micro-thruster for investigating flow characteristics. The results show that there were four distinct flow patterns observed in this study including snake flow, vapor-droplet flow, vapor-droplet-jet flow, and vapor flow. To prevent the failure of micro-thruster chip from generating of snake flow, the heating treatment of an empty micro-thruster chip at 300 °C for 2 h was the key factor. The generation of vapor flow preliminarily proved that the concept of vaporizing liquid micro-thruster chip was feasible. Furthermore, the numerical model in this study successfully provided the thrust estimation. The channel cross-section of 1 mm × 100 μm designed in this study was fit for developing a micro-thruster of O(mN) (ranging from 1 to 6 mN approximately). The numerical simulation could match better with the experiment results for the vapor flow cases if the flow oscillation was taken into consideration, and the heating channel of micro-thruster was lengthened to completely vaporize the liquid water.