Constricted Flow Research Articles

Immunohistochemical localization of AMPA-type glutamate receptor subunits in the nucleus of the Edinger-Westphal in embryonic chick

The Edinger-Westphal nucleus (EW) in birds is responsible for the control of pupil constriction, accommodation, and choroidal blood flow. The activation of EW neurons is mediated by the neurotransmitter glutamate, in large part through AMPA-type glutamate receptors (GluRs), whose behavior varies according to the subunit composition. We investigated the developmental expression of the GluR subunits in EW of the chick ( Gallus gallus) using immunohistochemistry on tissue from embryonic days 10 through 20 (E10–E20). Of the three antibodies used, one recognized the GluR1 subunit, another the GluR4 subunit, and the third recognized a sequence common to GluR2 and GluR3 subunits. No immunolabeling of EW neurons for any GluR subunits was observed prior to E12, although immunolabeling was seen in somatic oculomotor prior to E12. At E12, immunoreactivity for each of the three antibodies was in only approximately 2% of EW neurons. By E14, the abundance of GluR1+ perikarya in EW had increased to 13%, and for GluR2/3 had increased to 48%. The perikaryal abundance of the immunoreactivity for GluR1 and GluR2/3 declined to 3% and 23%, respectively, by E16. At E14, 33% of EW neurons immunolabeled for GluR4, and their frequency increased to 43% by E16, and remained at that approximate percentage through hatching. The increased expression of GluR1 and GluR4 in EW at E14 coincides with the reported onset of the expression of the calcium-binding protein parvalbumin, and the calcium currents associated with AMPA receptors formed by these two subunits may play a role in the occurrence of parvalbumin expression.

Nonlinear scattering of crossed ultrasonic beams in a constricted flow for the detection of a simulated deep vein thrombosis.

A three phase experiment performed at the USNA Acoustics Laboratory uses turbulent flow to generate nonlinear scattering of crossed ultrasonic beams. The intent is to simulate blood flow through a vein with and without a constriction to flow and compare the nonlinear scattering effects. In phase 1, a submerged turbulent water jet (Re=4×104 and diameter=0.6 cm) interacts with overlapping crossed focused beams (f1=1.8 MHz, f2=2.0 MHz, and 15 cm focal lengths), 20 diam downstream, to create nonlinear scattering at the sum frequency (f+=f1+f2=3.8 MHz). A circular plane receiving transducer rotates azimuthally in the plane of the transmitted beam axes about the intersection to obtain angular dependent Doppler shift (about f+) and spectral broadening results. In phase 2, the turbulence at the meeting point is channeled into a simulated 30 cm long, 4.5 cm diameter “vein” with a thin, polyethylene membrane. Results show negligible nonlinearly scattered sum frequency, suggesting laminar flow. In phase 3, a constriction to flow is introduced via a 4.0 cm ping pong ball caught in a narrowed segment of vein. Results show a scattered sum frequency with narrow broadening, indicating the return of some vortices or turbulence.

Lateral constrictional flow of hot orogenic crust: Insights from the Neoarchean of south India, geological and geophysical implications for orogenic plateaux

This study provides an in situ geological perspective on fabrics produced by synconvergence lateral crustal flow of hot orogens. It is based on the example of the Neoarchean orogen of the Dharwar craton (India) and combines structural analysis and ion microprobe U-Pb zircon geochronology. We document a pervasive, three-dimensional flow mode of the lower crust, called lateral constrictional flow (LCF), which combines orogen-normal shortening, lateral constrictional stretching, and transtension. LCF achieves gravity-driven flow, lateral escape, and 3-D mass redistribution in a viscous lower crust submitted to convergence. LCF tends to mechanically and thermally homogenize the lower crust and efficiently compensates topographic relief at a shallow level in the crust. Three type-geodynamic contexts are envisaged for LCF: plateau interiors, inner parts of collisional crustal wedges or plateau edges, and throughout wide ultrahot orogens such as the Neaoarchean orogen of south India. LCF makes the lower crust act as a strain gauge between lateral gravitational collapse or tectonic thickening of the upper crust, thrust stacking in the lowermost crust (collisional crustal wedge case), crustal shortening, and/or lateral flow of the upper mantle. In the case of plateau interiors or ultrahot orogens, LCF of a thick lower crust enables coupling of upper crustal deformation with upper mantle flow through a hot and thin lithosphere being shortened coherently. LCF generates a subhorizontal lamination that should produce the strong seismic reflectivity and lateral anisotropy of the Tibetan Plateau and a variety of hot orogens.

Crystallization and intermittent dynamics in constricted microfluidic flows of dense suspensions

A strong coupling between shear, confinement and microstructure governs the flow of dense colloidal suspensions through narrow channels. In this paper we explore the additional complexity that arises when the channel is partially blocked by a constriction in the centre of the channel. The reduction of the particle flux due to the constriction induces a densification upstream from the constriction, resulting in the formation of extended crystalline domains. A dynamic equilibrium establishes, which is characterized by large fluctuations in the instantaneous flow velocity and the local density. In some cases, the individual events leading to this intermittent behaviour are clearly visible as transient and localized jamming and unjamming events.

Coulometric Detection of Components in Liquid Plugs by Microfabricated Flow Channel and Electrode Structures

Coulometry has been demonstrated to be effective for determining the analyte in a liquid plug on the nanoliter-scale confined in a flow channel. A plug prepared in a rhombus structure of an auxiliary flow channel was placed on a thin-film three-electrode system, and hydrogen peroxide was detected as a model analyte. Under a fixed potential, the current decayed rapidly, particularly in shallow flow channels, thus making reproducible amperometric detection difficult. On the other hand, the increasing charge during coulometry facilitated the measurements. A constricted flow channel structure with an array of platinum strips for the working electrode was effective at efficiently consuming the analyte to improve the sensitivity and lower the detection limit. Compared to the case of a single short working electrode with the same area, a 4-fold increase in sensitivity was observed for the best combination of flow channel height and interstrip distance. With an increase in the generated current while maintaining the background at a low level, the detection limit was lowered from 1.3 μM to 410 nM using working electrodes with the same area. Furthermore, the processing of solutions containing L-glutamate or L-glutamate oxidase and the detection of L-glutamate were demonstrated.

Effect of surface roughness on laminar liquid flow in micro-channels

Abstract There are three prominent theories with regard to the effects of surface roughness on the pressure drop of laminar liquid flow in micro-channels, the original constricted flow model, the constricted model containing roughness distribution and the roughness–viscosity model. However, they have only been validated with very limited data by the authors. To provide a more reliable guide for various micro-channel applications, a review of these theories was conducted based upon the broad experimental data in literature. It is found that all the normalized data of fRe can be predicted by the original constricted flow model within an error of about ±15%. It is possible that the constricted model containing roughness distribution and the roughness–viscosity model can be further improved for easier use. However, the data, which support these two theories, can also be predicted well by the original constricted flow model with similar accuracy. Furthermore, the dependence of the critical Reynolds number (transition to turbulent flow) on the relative roughness of micro-channels was examined based upon the broad and much scattered experimental data. It is interesting to find that the effects of large discrete roughness on the side walls of shallow micro-channels follow the roughness correlation of macro-channels. The critical Reynolds numbers for different kinds of rough micro-channels were correlated respectively.

An investigation into the constriction flow of a particle reinforced polystyrene melt using a combination of flow visualization and finite element simulations

This paper investigates the flow of a particle filled polystyrene melt through a constriction zone using a combination of experimental techniques and computer simulation. A special blend, containing cross-linked polystyrene beads mixed into a polydispersed polystyrene matrix, was produced for this study. This closely refractive index matched blend allowed visualization of the flow birefringence up to an equivalent particle loading of around 15 vol %. Flow birefringence through a 10:1.4 contraction, measured using a multi-pass rheometer (MPR), was compared with that predicted from finite element simulations, in a similar way to that already published for unfilled polymer melts [Collis et al., J. Rheol. 49(2), 501–522 (2005)]. Numerical predictions were obtained using the finite element solver “EUFLOW” and ranked against the experimental processing data from the MPR. An extensive study of the rheology of the particle filled polystyrene blend was conducted which provided the input to the simulations. The addition of the particles was seen to enhance the shear thinning of the melt, while debonding between the particles and the polystyrene melt during extension testing had the effect of reducing strain hardening. EUFLOW was used to evaluate how these two important aspects could affect the flow birefringence of the filled polystyrene melt.

Application of Lubrication Theory and Study of Roughness Pitch During Laminar, Transition, and Low Reynolds Number Turbulent Flow at Microscale

This work aims to experimentally examine the effects of different roughness structures on internal flows in high-aspect-ratio rectangular microchannels. Additionally, a model based on lubrication theory is compared to these results. In total, four experiments were designed to test samples with different relative roughness and pitch placed on the opposite sides forming the long faces of a rectangular channel. The experiments were conducted to study (i) sawtooth roughness effects in laminar flow, (ii) uniform roughness effects in laminar flow, (iii) sawtooth roughness effects in turbulent flow, and (iv) varying-pitch sawtooth roughness effects in laminar flow. The Reynolds number was varied from 30 to 15,000 with degassed, deionized water as the working fluid. An estimate of the experimental uncertainty in the experimental data is 7.6% for friction factor and 2.7% for Reynolds number. Roughness structures varied from a lapped smooth surface with 0.2 μ m roughness height to sawtooth ridges of height 117 μ m. Hydraulic diameters tested varied from 198 μ m to 2,349 μ m. The highest relative roughness tested was 25%. The lubrication theory predictions were good for low relative roughness values. Earlier transition to turbulent flow was observed with roughness structures. Friction factors were predictable by the constricted flow model for lower pitch/height ratios. Increasing this ratio systematically shifted the results from the constricted-flow models to smooth-tube predictions. In the turbulent region, different relative roughness values converged on a single line at higher Reynolds numbers on an f–Re plot, but the converged value was dependent on the pitch of the roughness elements.

Deformation temperatures, vorticity of flow, and strain in the Moine thrust zone and Moine nappe: Reassessing the tectonic evolution of the Scandian foreland–hinterland transition zone

Examination of deformation temperature, 3-D strain and flow vorticity ( W m) in mylonites from the Assynt-Loch More region of the Moine thrust zone (MTZ) allows quantitative kinematic and thermal characterization of shearing at the base of the Scandian (435–425 Ma) orogenic wedge. Quartz microstructures and c-axis fabric opening angles from mylonites in the immediate hangingwall and footwall to the Moine thrust suggest that deformation temperatures are highest in the eastern part of the Assynt region (including mylonites close to alkaline intrusive complexes) and decrease along strike both to the north (Stack of Glencoul – Loch More) and to the south (Knockan). Quartz c- and a-axis fabrics, together with limited 3-D strain data, indicate that deformation in both the footwall and hangingwall mylonites dominantly involved plane strain to general flattening, although domains of more constrictional flow are identified adjacent to thrust transport-parallel lineaments in the overlying Moine nappe. Rigid grain analyses indicate a remarkably constant flow vorticity for tens of kilometers along orogenic strike (40–60% pure shear) in both the hangingwall and footwall mylonites. Integration with previously reported strain and vorticity estimates from the Assynt region indicates a 50–75% sub-vertical shortening perpendicular to gently dipping foliation, that must have been accommodated by either volume loss or extrusion of material toward the synorogenic topographic surface. Extrusion implies a causal link between upper and lower crustal processes, with significant implications for the kinematic and geometric evolution of the Scandian wedge.

Structural Evolution of Colloidal Gels During Constricted Microchannel Flow

We investigate the structure of colloidal gels flowing through constrictions in microchannels using confocal microscopy. As the gel traverses the constricted region, both the average velocity and particle density increase downstream. While the average flow profile is smoothly varying, stagnation zones develop at the constriction entry, leading to markedly nonuniform local flow profiles. Dense clusters undergo shear-induced yielding at intercluster boundaries, which enhances the structural heterogeneity of the suspension at the constriction outlet.

A 3D model of first-order structural elements of the Vredefort Dome, South Africa — Importance for understanding central uplift formation of large impact structures

Based on detailed structural mapping, geophysical information and structural consideration, we generated a 3D structural model of a segment of the Vredefort Dome. This model provides insight into the mechanism of mass transfer during central uplift formation of large impact structures. The model consists of geometrically and kinematically linked km-scale radial and concentric faults that affected the overturned limb of the rim syncline to the Vredefort Dome. The faults accomplished constrictional (centripetal) rock flow followed by radial spreading of uplifted and gravitationally unstable rocks in the crater centre. More specifically, concentric faults formed likely as normal faults during transient crater rim collapse, steepened and were transformed to reverse faults during central rock uplift and finally, were overturned during gravitational collapse of the central uplift. Radial faults, by contrast, formed at a later stage of convergent rock flow towards the crater centre and retained largely their orientation during central uplift formation. Displacement on individual faults is up to 2 km. Cumulative displacement, notably on concentric faults, can account for the large displacement magnitudes predicted by numerical models.

Pulsatile flow in stenotic geometries: flow behaviour and stability

Pulsatile inlet flow through a circular tube with an axisymmetric blockage of varying size is studied both numerically and experimentally. The geometry consists of a long, straight tube and a blockage, semicircular in cross-section, serving as a simplified model of an arterial stenosis. The stenosis is characterized by a single parameter, the aim being to highlight fundamental behaviours of constricted pulsatile flows. The Reynolds number is varied between 50 and 700 and the stenosis degree by area between 0.20 and 0.90. Numerically, a spectral element code is used to obtain the axisymmetric base flow fields, while experimentally, results are obtained for a similar set of geometries, using water as the working fluid. For low Reynolds numbers, the flow is characterized by a vortex ring which forms directly downstream of the stenosis, for which the strength and downstream propagation velocity vary with the stenosis degree. Linear stability analysis is performed on the simulated axisymmetric base flows, revealing a range of absolute instability modes. Comparisons are drawn between the numerical linear stability analysis and the observed instability in the experimental flows. The observed flows are less stable than the numerical analysis predicts, with convective shear layer instability present in the experimental flows. Evidence is found of Kelvin–Helmholtz-type shear layer roll-ups; nonetheless, the possibility of the numerically predicted absolute instability modes acting in the experimental flow is left open.

Steady inlet flow in stenotic geometries: convective and absolute instabilities

Steady inlet flow through a circular tube with an axisymmetric blockage of varying size is studied both numerically and experimentally. The geometry consists of a long, straight tube and a blockage, semicircular in cross-section, serving as a simplified model of an arterial stenosis. The stenosis is characterized by a single parameter, the aim being to highlight fundamental behaviours of constricted flows, in terms of the total blockage. The Reynolds number is varied between 50 and 2500 and the stenosis degree by area between 0.20 and 0.95. Numerically, a spectral-element code is used to obtain the axisymmetric base flow fields, while experimentally, results are obtained for a similar set of geometries, using water as the working fluid. At low Reynolds numbers, the flow is steady and characterized by a jet flow emanating from the contraction, surrounded by an axisymmetric recirculation zone. The effect of a variation in blockage size on the onset and mode of instability is investigated. Linear stability analysis is performed on the simulated axisymmetric base flows, in addition to an analysis of the instability, seemingly convective in nature, observed in the experimental flows. This transition at higher Reynolds numbers to a time-dependent state, characterized by unsteadiness downstream of the blockage, is studied in conjunction with an investigation of the response of steady lower Reynolds number flows to periodic forcing.

UNSTEADY RESPONSE OF BLOOD FLOW THROUGH A COUPLE OF IRREGULAR ARTERIAL CONSTRICTIONS TO BODY ACCELERATION

A two-dimensional (2D) nonlinear mathematical model to study the response of the pulsatile flow of blood through a couple of irregular stenoses influenced by externally imposed periodic body acceleration is developed. The model is 2D and axisymmetric with an outline of the stenosis obtained from the three-dimensional (3D) casting of a mildly stenosed artery. The combined influence of an asymmetric shape and surface irregularities of the constrictions is explored in a computational study of blood flow through arterial stenoses with 48% areal occlusion. The arterial wall is treated as an elastic (moving wall) cylindrical tube having a couple of stenoses in its lumen, while the streaming blood is considered to be Newtonian. Solutions of the time-dependent nonlinear Navier–Stokes equations in the cylindrical coordinate system are obtained using a finite difference method based on the nonuniform and nonstaggered grids. The finite difference approximation helps to estimate the effects of body acceleration on the doubly constricted flow phenomena through several graphical representations quantitatively in order to validate the applicability of the present, improved mathematical model.

Experimental study of turbulent flow sound production in presence of a simplified vocal tract constriction

Sound production due to turbulence is widely shown to be an important phenomenon involved in a.o. fricatives, singing, whispering and speech pathologies. In spite of it relevance, only a few recent models are dealing with turbulence consequences during voiced sound production. The current study presents preliminary results of an experimental characterisation of the aeroacoustical effects of a turbulent flow in case of a constricted channel flow, by means of measuring the velocity fluctuations and the acoustic field downstream of the constriction. Aiming a future application in speech production, the influence of typical vocal tract shape parameters on the velocity distribution and sound field is explored: the tube shape and length as well as the degree, geometry and position of the constriction. The influence of the Reynolds number of the upstream flow is also observed. Results are discussed with respect to the upper airways and human sound production and will be exploited with respect to simplified models for velocity fluctuations and sound production.

Counterpoint: There is not capillary recruitment in active skeletal muscle during exercise

The notion that a substantial proportion of capillaries do not contain moving red blood cells (RBCs) in muscle at rest but are “recruited,” i.e., begin flowing with RBCs during contractions, is one basis for our present understanding of blood-muscle exchange during exercise ([20][1], [28][2]).

Effect of Sawtooth Roughness on Pressure Drop and Turbulent Transition in Microchannels

Roughness elements affect internal flows in different ways. One effect is the transition from laminar to turbulent flow at a lower Reynolds number than the predicted Re = 2300. Initial work at RIT in the subject area was performed by Schmitt and Kandlikar [1] and Kandlikar et al. [2], and this study is an extension of these efforts. The channel used in this study is rectangular, with varying separation between walls that have machined roughness elements. The roughness elements are saw-tooth in structure, with element heights of 107 and 117 μ m for two pitches of 405 μ m and 815 μ m, respectively. The resulting hydraulic diameters and Reynolds numbers based on the constricted flow area range from 424 μ m to 2016 μ m and 210 to 2400, respectively. Pressure measurements are taken at sixteen locations along the flow length of 88.9 mm to determine the local pressure gradients. The results for friction factors and transition to turbulent flow are obtained and compared with the data reported by Schmitt and Kandlikar [1]. The roughness elements cause an early transition to turbulent flow, and the friction factors in the laminar region are predicted accurately using the hydraulic diameter based on the constricted flow area.

A fourth-order accurate compact scheme for the solution of steady Navier–Stokes equations on non-uniform grids

This paper deals with the formulation of a higher-order compact (HOC) scheme on non-uniform grids in complex geometries to simulate two-dimensional (2D) steady incompressible viscous flows governed by the Navier–Stokes (N–S) equations. The proposed scheme which is spatially fourth-order accurate is then tested on three nonlinear problems, namely (i) a problem governed by N–S equations with a constructed analytical solution, (ii) lid-driven cavity flow problem, and (iii) constricted channel flow problem. In the process, we have also expanded the scope of fourth-order 9-point compact schemes to geometries beyond rectangular. It is seen to efficiently capture steady-state solutions of the N–S equations with Dirichlet as well as Neumann boundary conditions. In addition to this, it captures viscous flows involving free and wall bounded shear layers which invariably contain spatial scale variations. Our results are in excellent agreement with analytical and numerical results whenever available and they clearly demonstrate the superior scale resolution of the proposed scheme.

Computational simulation for the constricted flow of argon plasma arc

A two-dimensional mathematical model has been developed to research the behavior of the transferred-type argon plasma arc constricted by a torch. The model includes a part of torch and tungsten electrode to achieve more reasonable results. Solving the model, the arc temperature and flow fields have been derived. And the distributions of the current density and electromagnetic force have been gotten, as well as the voltage drop of the plasma arc and the distributions of heat flux, pressure at the anode. The arc pressure and current density distributions at the anode are measured experimentally to show the simulated results believable. The influences of welding parameters on the distribution of the arc pressure at the anode have been studied. The result shows that the arc pressure is much dependent on the current and plasma gas flow rate, while is not sensitive to the arc length in the study range.

Cathode Plasma Jet Pinching and Intense X-Ray Emission in a Moderate-Current Laser-Triggered Vacuum Discharge

Occurrence of cathode plasma jet pinching and its dependence on anode-cathode separation (d=2-10 mm) in a moderate-current (~10 kA) low-energy (les 20 J) vacuum discharge is presented. Discharge was created between a planar titanium cathode and a conical point-tip titanium anode by producing plasma on the cathode using 27-ps-duration laser pulses. For d=2-3 mm, constricted flow of cathode plasma jet up to anode was observed along with multiple feeble local pinchings. A neck formation was observed for d=5-6 mm, whereas multiple pinching occurred for larger separations. Temporal profiles of the X-ray emission from the anode due to bombardment by electrons extracted from the expanding cathode plasma, for different anode-cathode separations, were consistent with the characteristics of cathode plasma jet pinching