Flow Constriction Research Articles

Relieving the transfusion tissue traffic jam: a network model of radial transport in conifer needles.

Characteristic of all conifer needles, the transfusion tissue mediates the radial transport of water and sugar between the endodermis and axial vasculature. Physical constraints imposed by the needle's linear geometry introduce two potential extravascular bottlenecks where the opposition of sugar and water flows may frustrate sugar export: one at the vascular access point and the other at the endodermis. We developed a network model of the transfusion tissue to explore how its structure and composition affect the delivery of sugars to the axial phloem. To describe extravascular transport with cellular resolution, we construct networks from images of Pinus pinea needles obtained through tomographic microscopy, as well as fluorescence and electron microscopy. The transfusion tissue provides physically distinct pathways for sugar and water, reducing resistance between the vasculature and endodermis and mitigating flow constriction at the vascular flank. Dissipation of flow velocities through the transfusion tissue's branched structure allows for bidirectional transport of an inbound diffusive sugar flux against an outbound advective water flux across the endodermis. Our results clarify the structure-function relationships of the transfusion tissue under conditions free of physiological stress. The presented model framework is also applicable to different transfusion tissue morphologies in other gymnosperms.

Contractile ring mechanosensation and its anillin-dependent tuning during early embryogenesis

Cytokinesis plays crucial roles in morphogenesis. Previous studies have examined how tissue mechanics influences the position and closure direction of the contractile ring. However, the mechanisms by which the ring senses tissue mechanics remain largely elusive. Here, we show the mechanism of contractile ring mechanosensation and its tuning during asymmetric ring closure of Caenorhabditis elegans embryos. Integrative analysis of ring closure and cell cortex dynamics revealed that mechanical suppression of the ring-directed cortical flow is associated with asymmetric ring closure. Consistently, artificial obstruction of ring-directed cortical flow induces asymmetric ring closure in otherwise symmetrically dividing cells. Anillin is vital for mechanosensation. Our genetic analysis suggests that the positive feedback loop among ring-directed cortical flow, myosin enrichment, and ring constriction constitutes a mechanosensitive pathway driving asymmetric ring closure. These findings and developed tools should advance the 4D mechanobiology of cytokinesis in more complex tissues.

Elucidating the effects of microbubble pinch-off dynamics on mammalian cell viability.

In the biotechnology industry, ensuring the health and viability of mammalian cells, especially Chinese Hamster Ovary (CHO) cells, plays a significant role in the successful production of therapeutic agents. These cells are typically cultivated in aerated bioreactors, where they encounter fluid stressors from rapidly deforming bubbles. These stressors can disrupt essential biological processes and potentially lead to cell death. However, the impact of these transient, elevated stressors on cell viability remains elusive. In this study, we first employ /cgqamicrofluidics to expose CHO cells near to bubbles undergoing pinch-off, subsequently collecting and assaying the cells to quantify the reduction in viability. Observing a significant impact, we set out to understand this phenomenon. We leverage computational fluid dynamicsand numerical particle tracking to map the stressor field history surrounding a rapidly deforming bubble. Separately, we expose CHO cells to a known stressor level in a flow constriction device, collecting and assaying the cells to quantify the reduction in viability. By integrating the numerical data and results from the flow constriction device experiments, we develop a predictive model for cell viability reduction. We validate this model by comparing its predictions to the earlier microfluidic results, observing good agreement. Our findings provide critical insights into the relationship between bubble-induced fluid stressors and mammalian cell viability, with implications for bioreactor design and cell culture protocol optimization in the biotechnology sector.

The deposition kinetics of barium sulphate scale: model development

The deposition kinetics of barium sulphate scale: model development

Microfluidic techniques for mechanical measurements of biological samples.

The use of microfluidics to make mechanical property measurements is increasingly common. Fabrication of microfluidic devices has enabled various types of flow control and sensor integration at micrometer length scales to interrogate biological materials. For rheological measurements of biofluids, the small length scales are well suited to reach high rates, and measurements can be made on droplet-sized samples. The control of flow fields, constrictions, and external fields can be used in microfluidics to make mechanical measurements of individual bioparticle properties, often at high sampling rates for high-throughput measurements. Microfluidics also enables the measurement of bio-surfaces, such as the elasticity and permeability properties of layers of cells cultured in microfluidic devices. Recent progress on these topics is reviewed, and future directions are discussed.

A Fenestrated Balloon Expandable Stent System for the Treatment of Aortoiliac Occlusive Disease.

In aortoiliac occlusive disease, atherosclerotic plaques can occlude the distal aortic bifurcation and proximal bilateral iliac artery and thus cause ischemia in the lower extremity. This is typically treated by restoring patency with balloon expandable stents. Stents are typically deployed in a "kissing stent" configuration into the bilateral iliac arteries and into the distal aortic bifurcation lumen to restore antegrade arterial flow. However, these stents typically become re-occluded by plaques. To understand the reasons for this and look for solutions, we simulated flow dynamics in the aortic bifurcation in the presence and absence of stents using computational fluid dynamics. Results demonstrated that the kissing stent configuration was associated with high levels of vorticity and flow constriction. These prothrombotic variables were alleviated in an alternative, aortoiliac fenestrated (AIFEN), tapered, and balloon-expandable stent design. Our findings suggest that stent design can be tailored to improve flow fields for aortoiliac stenting.

Gas Migration Episodes Observed During Peridotite Alteration in the Samail Ophiolite, Oman.

Serpentinization and carbonation of mantle rocks (peridotite alteration) are fundamentally important processes for a spectrum of geoscience topics, including arc volcanism, earthquake processes, chemosynthetic biological communities, and carbon sequestration. Data from a hydrophone array deployed in the Multi-Borehole Observatory (MBO) of the Oman Drilling Project demonstrates that free gas generated by peridotite alteration and/or microbial activity migrates through the formation in discrete bursts of activity. We detected several, minutes-long, swarms of gas discharge into Hole BA1B of the MBO over the course of a 9month observation interval. The episodic nature of the migration events indicates that free gas accumulates in the permeable flow network, is pressurized, and discharges rapidly into the borehole when a critical pressure, likely associated with a capillary barrier at a flow constriction, is reached. Our observations reveal a dynamic mode of fluid migration during serpentinization, and highlight the important role that free gas can play in modulating pore pressure, fluid flow, and alteration kinetics during peridotite weathering.

Trocar site hernia after laparoscopy: Early recognition prevents catastrophic sequelae

BackgroundTrocar site hernia is a rare but potentially serious complication of laparoscopic surgery that may lead to bowel incarceration and strangulation. Prompt diagnosis by emergency physicians facilitates timely intervention that prevents bowel necrosis. We report a case of trocar site hernia presenting to the emergency department (ED) with abdominal pain that was correctly diagnosed and promptly managed. Case ReportA 25-year-old woman, gravida 2, abortion 2, underwent outpatient surgery and laparoscopic removal of a ruptured right-sided tubal pregnancy without any intraoperative difficulties. However, 48 h later, she presented to the ED complaining of acute abdominal pain and nausea. Computed tomography revealed a loop of small bowel herniating through a 12-mm right lower quadrant trocar site defect in the fascia. She was taken back to the operating room, where the computed tomography findings were confirmed and the entrapped bowel was successfully reduced and the fascial defect repaired. The patient was discharged home feeling much improved. Why Should an Emergency Physician Be Aware of This?Trocar site hernia is a rare but potentially dangerous complication that can present with acute symptoms or be asymptomatic if late in onset. Intestinal necrosis begins as soon as 6 h after constriction of blood flow to entrapped bowel, so timely intervention is critically important. Therefore, trocar site hernias should be considered in patients presenting with abdominal complaints after laparoscopic surgery and included in the differential diagnosis of bowel obstruction.

Experimental Investigations and Numerical Assessment of Liquid Velocity Profiles and Turbulence for Single- and Two-phase Flow in a Constricted Vertical Pipe

In this work, the capabilities of state-of-the-art turbulence models are compared for a three-dimensional flow (3D) field within a constricted vertical pipe. The considered flow domain is a vertical pipe section with a baffle-shaped flow constriction which leads to the development of a jet flow through and a recirculation flow region behind the constriction. Different Reynolds-Averaged Navier-Stokes (RANS) and Large Eddy Simulation (LES) models were tested for single- and two-phase flow simulations. In the two-phase simulations, bubble-induced turbulence (BIT) was also considered by adding source terms in the k and ε/ω equations. The results are validated against experimental data. We employed hot-film anemometry (HFA) for liquid velocity measurement and combined it with ultrafast X-ray computed tomography (UFXCT), which provides gas phase data. Based on the local phase-indicator function obtained from the tomographic image data, we can correct HFA signals, which become corrupted by bubble contacts. We found that for single-phase flow all RANS models predict axial velocity well while radial velocity prediction is inadequate. LES models, however, achieve a better prediction of the latter. For two-phase flow, the axial component of the liquid velocity is well captured by all RANS models and the radial component of the liquid velocity is predicted better than for single-phase flow. In general, the computationally less costly RNG k-ε model performs similar to the SSG RSM model and can therefore be recommended for simulation of complex flow scenarios.

Hypergolic Continuous Detonation with Space-Storable Propellants and Additively Manufactured Injector Design

Initiation and sustained detonation of hypergolic liquid rocket propellants have been assessed in an annular combustor. An established impinging injector design was modified for additive manufacturing to improve hydraulic characteristics. Computational fluid dynamics analysis was used to verify decreased flow resistance and increased relative backflow resistance afforded by tapered propellant passageways enabled by additive manufacturing. Two injectors were manufactured and a honing process was employed on one of the injectors to reduce surface roughness associated with additive manufacturing. Cold-flow testing confirmed decreased hydraulic resistance due to tapering of the injector passageways and due to the honing process. The detonability of hypergolic space-storable propellants in an annular combustor with the injectors was assessed experimentally with dinitrogen tetroxide as the oxidizer and monomethylhydrazine as the fuel. The presence of rotating detonation waves was verified via multiple instrumentation methods, including a high-speed camera. The performance of the combustor was seen to increase with the total number of detonation waves, the total propellant flow rate, and the presence of a downstream flow constriction. The work demonstrates continuous detonability of hypergolic space-storable propellants under various operation conditions relevant to in-space rocket propulsion concepts, as well as several benefits of utilizing additive manufacturing for injection-system design.

Model for hot spots and Q -slope behavior in granular niobium thin film superconducting rf cavities

We propose a model to explain power dissipation leading to the formation of hot spots in the inner walls of niobium thin film superconducting rf cavities. The physical mechanism that we explore is due to the constriction of surface electrical current flow at grain interface boundaries. This constriction creates an additional electrical contact resistance which induces localized punctual heat dissipation. The temperature at these spots is derived; and the electrical contact resistance is shown to depend on the magnetic field, on the grain contact size over which dissipation occurs, and on other key parameters, including the effective London penetration depth and the frequency. The surface resistance and the quality factors are determined using our model and are shown to be in excellent agreement with experimental data.

Abstract 12848: Patient-Specific in silico Models Demonstrate Hemodynamic Effect of LAMPOON in Transcatheter Mitral Valve Replacement

Introduction: The purpose of this study was to investigate the hemodynamic impact of LAMPOON (Laceration of the Anterior Mitral leaflet to Prevent Outflow ObstructioN) in transcatheter mitral valve replacement (TMVR) using patient-specific in silico modeling. Methods: Eight subjects from the LAMPOON investigational device exemption trial were included. All subjects were at prohibitive risk of outflow tract obstruction from TMVR based on computed tomography (CT), and underwent successful LAMPOON immediately followed by TMVR. A validated computational fluid dynamics (CFD) model was used to compare simulated hemodynamics and 3D flow patterns between two modeled conditions: 1) TMVR with LAMPOON and 2) TMVR without LAMPOON. Using the post-procedure CT scans, anatomical models of TMVR with LAMPOON were created for each subject. The open transcatheter valve cells were then virtually closed to model TMVR without LAMPOON for each subject. Finally, CFD was performed for each condition to simulate the systolic flow fields. Results: As compared to TMVR without LAMPOON, TMVR with LAMPOON resulted in lower peak velocity, lower peak LVOT gradient, and higher peak LVOT effective orifice area by 13 ± 6% (p=0.004), 28 ± 14% (p=0.008), and 15 ± 8% (p=0.002), respectively. LAMPOON provided flow communication through exposed cells of the transcatheter valve, thereby decreasing the flow constriction and reducing flow stasis in the vicinity of the neo-LVOT (Figure). The hemodynamic benefit of LAMPOON was observed to be greater in subjects with a smaller neo-LVOT area measured post-implant (p<0.001). Conclusions: In silico modeling allowed for a quantitative patient-specific comparison of TMVR with and without LAMPOON, which is impossible to study clinically. The LAMPOON procedure improved simulated hemodynamics in all subjects, with a greater hemodynamic impact observed in subjects with a smaller post-implant neo-LVOT area.

Wax Deposition Characterization under Flowing Conditions Using an Oscillatory Flow Setup

Wax deposition is a significant flow assurance issue in oil/gas production and transportation, often leading to significant flow constrictions with eventual blockages of flowlines. Wax deposition i...

Resolved CFD-DEM simulation of blood flow with a reduced-order RBC model

Mathematical modeling of the blood flow with a resolved description of biological cells mechanics such as red blood cell (RBC) has been a challenge in the past decades as it involves physical complexities and demands high computational costs. In the present study, we propose an approach for efficient simulation of blood flow with several suspended RBCs. In this approach, we employ our previously proposed reduced-order model for deformable particles (Nair et al. in Comput Part Mech 7:593–601, 2020) to mimic the mechanical behavior of an individual RBC as a cluster of overlapping spheres interconnected by flexible mathematical bonds. This discrete element method-based model is then coupled with a fluid flow solver using the immersed boundary method with continuous forcing in the context of computational fluid dynamics-discrete element method (CFD-DEM) coupling. The present computational method is tested with a couple of validation cases in which the single RBC dynamics, as well as the blood flow with several RBCs, were tested in comparison with existing literature date. First, the RBC deformation index in shear flow at different shear rates is studied with a good accuracy. Then, the blood flow in micro-tubes of different diameters and hematocrits was simulated. The key characteristics of blood flow such as cell-free layer (CFL) thickness, Fahraeus effect and the relative apparent viscosity are used as the validation metrics. The proposed approach can predict the formation of the migration of RBC toward the tube center-line and the CFL thickness in good agreement with previous measurement and simulations. Furthermore, the model is employed to study the CFL enhancement for plasma separation based on channel constriction. The simulation results compute the CFL thickness downstream of the channel constriction in good agreement with the experiments in a wide range of flow rates and constriction lengths. The original contribution of this study lies in proposing an efficient resolved CFD-DEM simulation method for blood flows with many RBCs which can be employed for numerical investigation of bio-microfluidic applications.

The influence of mean flow velocity and direction on the acoustic transmission behavior of right-angled duct bends

Many duct systems transporting air flow also transport unwanted noise. The geometrical parameters of duct bends can be tailored to reduce the noise emission by blocking sound transmission through ducts. However, the flow velocity has an influence on sound propagation. So far, it is not clear to what extent this limits the transmission loss of bends and their usage for noise reduction. In this work, the influence of flow on the transmission loss of duct bends is studied numerically on the basis of a right-angled sharp bend with rectangular cross-section. The numerical method consists of two steps: First, a CFD flow simulation is done. These results are used as an input for the subsequent finite element acoustic simulation where the Helmholtz equation is solved. Thereby, the usage of two different flow models allows differing influences purely related to the uniform movement of the fluid from those related to additional flow phenomena like the flow constriction zone downstream of the bend. It is revealed that the impact of mean flow velocities up to 40 m/s is mostly negligible. However, flow direction plays an important role when higher order modes propagate, leading to significant differences between upstream and downstream transmission loss. Inter-modal acoustic scattering as well as mode transformation in the flow constriction zone have been identified as the reasons for these differences. The numerical results are confirmed by measurements.

Proteolytic activation of Growth-blocking peptides triggers calcium responses through the GPCR Mthl10 during epithelial wound detection.

The presence of a wound triggers surrounding cells to initiate repair mechanisms, but it is not clear how cells initially detect wounds. In epithelial cells, the earliest known wound response, occurring within seconds, is a dramatic increase in cytosolic calcium. Here, we show that wounds in the Drosophila notum trigger cytoplasmic calcium increase by activating extracellular cytokines, Growth-blocking peptides (Gbps), which initiate signaling in surrounding epithelial cells through the G-protein-coupled receptor Methuselah-like 10 (Mthl10). Latent Gbps are present in unwounded tissue and are activated by proteolytic cleavage. Using wing discs, we show that multiple protease families can activate Gbps, suggesting that they act as a generalized protease-detector system. We present experimental and computational evidence that proteases released during wound-induced cell damage and lysis serve as the instructive signal: these proteases liberate Gbp ligands, which bind to Mthl10 receptors on surrounding epithelial cells, and activate downstream release of calcium.

Turbulent flow of liquid lead alloy in oxygen-controlled corrosion erosion test facility

The CORELLA (CORrosion Erosion test facility for Liquid Lead Alloy) facility allows corrosion erosion tests in molten lead alloys at controlled oxygen content and temperature under flowing conditions. Its exposure chamber consists of a cylindrical container, partially filled with the liquid metal. An inner rotating cylinder drives the liquid metal flow. The specimens of interest are fixed vertically inside the chamber such that the lead alloy flows around the specimens on both sides. In this numerical study, the turbulent flow of liquid lead–bismuth eutectic is solved for various specimen configurations, filling heights, and rotational speeds of the inner cylinder. Hereby, the deformation of the free liquid surface is taken into account using a rotationally symmetric approximation. Highly turbulent flow is found even for 200 rpm (revolutions per minute), the lowest rotational speed investigated. The velocity of the liquid metal along the specimens’ lateral surfaces reaches values up to 1.5 m/s for a rotational speed of 1200 rpm, the limit of experimentally stable conditions. Due to the sudden flow constrictions and expansions around the specimens, a much higher effect of the flow on corrosion erosion is expected than for simple pipe flow at the same bulk velocity.

Injection Molding and Near-Complete Densification of Monolithic and Al2O3 Fiber-Reinforced Ti2AlC MAX Phase Composites.

Near-net shape components composed of monolithic Ti2AlC and composites thereof, containing up to 20 vol.% Al2O3 fibers, were fabricated by powder injection molding. Fibers were homogeneously dispersed and preferentially oriented, due to flow constriction and shear-induced velocity gradients. After a two-stage debinding procedure, the injection-molded parts were sintered by pressureless sintering at 1250 °C and 1400 °C under argon, leading to relative densities of up to 70% and 92%, respectively. In order to achieve near-complete densification, field assisted sintering technology/spark plasma sintering in a graphite powder bed was used, yielding final relative densities of up to 98.6% and 97.2% for monolithic and composite parts, respectively. While the monolithic parts shrank isotropically, composite assemblies underwent anisotropic densification due to constrained sintering, on account of the ceramic fibers and their specific orientation. No significant increase, either in hardness or in toughness, upon the incorporation of Al2O3 fibers was observed. The 20 vol.% Al2O3 fiber-reinforced specimen accommodated deformation by producing neat and well-defined pyramidal indents at every load up to a 30 kgf (~294 N).

Evaluating Friction and Inertial Losses From Slug Tests Conducted in a Multilevel System

AbstractEngineered multilevel systems (MLS) are one of the few viable options for collecting spatial and temporal datasets in 3‐D complex groundwater flow systems. However, these monitoring systems present challenges for hydraulic testing due to small port tubing diameters. In this study, an equipment was developed to enable a pneumatic slug testing of a G360 MLS, fitted with 1/2‐inch ID open tubes that extend from the monitoring ports to the surface. Of the eight ports tested, four exhibited overdamped slug test responses, while underdamped responses were observed in the remaining four ports. It is expected that friction in the small diameter tubing is not negligible, and additional flow constrictions are introduced when installing a transducer in the tubing, effectively changing the open tube geometry to an annulus around the transducer body and around the transducer cable. Steady flow models for annular flow, widely available in the literature, were used to assess tube friction for the overdamped tests. However, for underdamped tests that oscillate quickly, a mathematical solution for unsteady oscillatory flow through an annulus was derived. The results of this study show that it is important to account for frictional and inertial losses to obtain good transmissivity (T) estimates from slug tests conducted in small diameter tubing. Assuming steady flow through small annuli will not introduce an appreciable error when calculating the water level; however, if steady flow through the open tube below the transducer is assumed when calculating the formation head, T values can be underestimated by as much as 80%.

Drying crack patterns of sessile drops with tuned contact line

Drying cracks formed in the deposits of films, paints, and coatings make the deposits failure and limit the corresponding applications. Extensive experimental attempts and theoretical understanding have been made to discover the underlying mechanisms and avoid cracks in the cases of uniform films. However, crack formation from drying drops is greatly complicated due to the strong coupling of the mass, internal flow and geometry constriction by the presence of the contact line, resulting in the heterogeneity of the deposit thickness. Interestingly, the complex physicochemical influences from colloidal particle, solution, surroundings can be geometrically reflected by the motion of the contact line, while the effect on crack formation is still lack of investigations. Hence, in this paper, we propose a model system to examine the dynamical motion of the contact line and correlate the corresponding mechanism of crack formation. The wettability of supporting substrates are successfully tuned in order to control the drop shapes with different contact angles, i.e. from hydrophilic to hydrophobic. Three drying regimes are recognized as pinned, stick-slip and receding by tuning the mobility of the contact line. The correlation between the crack spacing and the local thickness of deposits near the contact line is found as approximately linear, which is qualitatively discussed in the analysis of the scaling law. Finally, suppression of the cracks deposits are practically realized by freely moving contact line on the slippery substrates in receding cases with a wide range of suspension concentration.