Cell In Flow Research Articles

Direct numerical simulations of hard particle suspensions in planar elongational flow

We present a new direct simulation technique of inertialess particle suspensions in planar elongational flow of a Newtonian fluid. The extensional bi-periodic domain concept is introduced such that a single cell problem with a small number of particles may represent a large number of repeated structures of such a cell in planar elongational flow. For implicit treatment of the hydrodynamic interaction between particles and fluid, we employ a finite-element/fictitious-domain method similar to the distributed Lagrangian multipliers (DLM) method together with a rigid-ring description of the particle. The extensional bi-periodic frame is incorporated by constraint equations with Lagrangian multipliers and is implemented by the mortar element method. In our formulation, the bulk stress is evaluated by simple boundary integrals. Concentrating on 2D circular disk particles, we present numerical examples of single-particle, two-particle and 100-particle problems in the extensional bi-periodic frame. We discuss effects of solid fraction and particle configuration on the elongational viscosity of the suspension, in comparison with simple shear flow. We found that, at zero strain, the relative elongational viscosity is almost the same as the relative shear viscosity in simple shear for moderately concentrated suspensions. There is a small increase in elongational viscosity for large strains, which is related to an anisotropic distribution of the particles.

Local Heat/Mass Transfer Phenomena in Rotating Passage, Part 2: Angled Ribbed Passage

Mass transfer experiments and numerical computations are conducted to investigate the heat/mass transfer and flow characteristics in a rotating passage with a 180-deg turn. In the present study, rectangular 70-deg rib turbulators are attached in cross and parallel arrangements on the leading and trailing surfaces of the passage. The cross-sectional area of the passage is 20 × 40 mm 2 , and the pitch-to-rib height ratio (p/e) is 7.5. The rotation number ranges from 0.0 to 0.20, whereas the Reynolds number is constant at 10,000. The results reveal that the angled rib turbulators enhance significantly heat/mass transfer in the rotating two-pass duct by generating a secondary flow. For the cross-ribbed passage, a heat/mass transfer discrepancy is observed in the second pass even for the stationary case because one asymmetric cell of secondary flow is induced in the first pass and turning region. For the parallel-ribbed passage, the flow and heat/mass transfer characteristics are less subject to the rotation number than those of the former case due to the different flow structure. At the highest tested rotation number (Ro = 0.20), the turn-induced single vortex cell becomes identical regardless of the rib configuration so that the local heat/mass transfer distributions are similar in the turning region for all of the test sections.

Peptide Blockers of the Inhibition of Neuronal Nicotinic Acetylcholine Receptors by Amyloid β

Alzheimer disease (AD) is characterized by accumulation of the neurotoxic amyloid beta peptide (Abeta) and by the loss of cholinergic neurons and nicotinic acetylcholine receptors (nAChRs) throughout the brain. Direct inhibition of nAChRs by Abeta has also been suggested to contribute to cholinergic dysfunction in AD. In an effort to find ligands capable of blocking Abeta-induced inhibition of nAChRs, we have screened a phage display library to identify peptides that bind to Abeta. Using this approach, we identified a heptapeptide denoted IQ, which binds with nanomolar affinity to Abeta and is homologous to the acetylcholine-binding protein and to most subtypes of nAChRs. Rapid kinetic whole-cell current-recording measurements showed that Abeta inhibits nAChR function in a dose-dependent manner in neuronal differentiated PC12 cells and that nanomolar concentrations of IQ completely block the inhibition by Abeta. These results indicate that the Abeta binding site in nAChRs is homologous to the IQ peptide and that this is a relevant target for Abeta neurotoxicity in AD and, more generally, for the regulation of nAChR function by soluble Abeta in a physiological context. Furthermore, the results suggest that the IQ peptide may be a lead for the development of novel drugs to block the inhibition of nAChRs in AD.

Cell Classification in Human Peripheral Blood Using the Amnis ImageStream® System.

Amnis Corporation's ImageStream® system combines the sample handling and quantitative power of flow cytometry with high-resolution brightfield, darkfield, and fluorescence cellular imagery. The system simultaneously generates up to six images of each cell in flow and can acquire data sets consisting of tens of thousands of cells in just a few minutes, while offering fluorescence sensitivity equal to or better than flow cytometry. The image data are analyzed using Amnis' IDEAS® software, which automatically calculates over 200 morphometric and photometric features and associated statistics for each cell, identifying unique cell groups based not only on their fluorescence intensity signature but also on their morphological characteristics. The software offers the ability to view the imagery associated with any cell in a scatter plot, perform “virtual cell sorts” of user-specified sub-populations, and generate custom features of biological significance (e.g. N/C ratio). The ImageStream platform's ability to quantitate morphologic and immunofluorescent differences between very large numbers of cells in suspension make it particularly well suited for hematology.In the present study, human peripheral blood mononuclear cells were stained with a fluorescent DNA binding dye to reveal nuclear morphology, as well as fluorescently labeled mAb to various CD markers. Five images of each cell were acquired: brightfield (transmitted light), darkfield (laser side scatter), and three fluorescent colors for nuclear imagery and quantitation of the CD marker abundance. The object of the study was to identify morphometric parameters in the brightfield, darkfield, and nuclear imagery that would prove useful in hematologic cell type classification. The mAb to CD antigens provided a positive control for use in the evaluation of the of the various morphometric parameters. Parameters with discriminating power included cellular size and texture, darkfield intensity and granularity, and nuclear fluorescence intensity, texture, and shape. Cell types that could be automatically discriminated using these parameters in lieu of immunofluorescent markers included neutrophils, eosinophils, monocytes, and lymphocytes (including putative activated lymphocytes).In addition to forming the basis for an advanced ImageStream hematology platform, it is envisioned that the automated morphometric classification of blood cells will act as the foundation for a wide range of image-based cellular assays performed in peripheral blood (e.g. NF-kB translocation, apoptosis, mAb compartmentalization), allowing the differential quantitation of assay results in various cell types for the purposes of basic research, drug discovery, and clinical diagnostics.

Solar Subsurface Fluid Dynamics Descriptors Derived from Global Oscillation Network Group and Michelson Doppler Imager Data

We analyze Global Oscillation Network Group (GONG) and Michelson Doppler Imager (MDI) observations obtained during Carrington rotation 1988 (2002 March 30-April 26) with a ring-diagram technique in order to measure the zonal and meridional flow components in the upper solar convection zone. We derive daily flow maps over a range of depths up to 16 Mm on a spatial grid of 75 in latitude and longitude covering ±60° in latitude and central meridian distance and combine them to make synoptic flow maps. We begin exploring the dynamics of the near-surface layers and the interaction between flows and magnetic flux by deriving fluid dynamics descriptors such as divergence and vorticity from these flow maps. Using these descriptors, we derive the vertical velocity component and the kinetic helicity density. For this particular Carrington rotation, we find that the vertical velocity component is anticorrelated with the unsigned magnetic flux. Strong downflows are more likely associated with locations of strong magnetic activity. The vertical vorticity is positive in the northern hemisphere and negative in the southern hemisphere. At locations of magnetic activity, we find an excess vorticity of the same sign as that introduced by differential rotation. The vertical gradient of the zonal flow is mainly negative except within 2 Mm of the surface at latitudes poleward of about 20°. The zonal-flow gradient appears to be related to the unsigned magnetic flux in the sense that locations of strong activity are also locations of large negative gradients. The vertical gradient of the meridional flow changes sign near about 7 Mm, marking a clear distinction between near-surface and deeper layers. GONG and MDI data show very similar results. Differences occur mainly at high latitudes, especially in the northern hemisphere, where MDI data show a counter cell in the meridional flow that is not present in the corresponding GONG data.

Numerical simulation of the flow-induced deformation of red blood cells.

A theoretical model is presented for describing the flow-induced deformation of red blood cells. The cells are modeled as deformable liquid capsules enclosed by a membrane that is nearly incompressible and exhibits elastic response to shearing and bending deformation. In the mathematical formulation, the hydrodynamics is coupled with the membrane mechanics by means of surface equilibrium equations expressed in global Cartesian coordinates. Numerical simulations are carried out to investigate the deformation of a cell in simple shear flow, in the physiological range of physical properties and flow conditions. The results show that the cell performs flipping motion accompanied by periodic deformation in which the cross section of the membrane in the plane that is perpendicular to the vorticity of the shear flow alternates between the nearly biconcave resting shape and a reverse S shape. The period of the overall rotation is in good agreement with the experimental observations of Goldsmith and Marlow for red blood cells suspended in plasma. Parametric investigations reveal that, in the range of shear rates considered, membrane compressibility has a secondary influence on the cell deformation and on the effective viscosity of a dilute suspension. The numerical results illustrate in quantitative terms the distribution of the membrane tensions developing due to the flow-induced deformation, and show that the membrane is subjected to stretching and compression in the course of the rotation.

A Coupled Approach to Predict Microscopic Temperature Distribution Inside a Unit Cell of Nonisothermal Laminar Flow in Periodic Porous Media

A Coupled Approach to Predict Microscopic Temperature Distribution Inside a Unit Cell of Nonisothermal Laminar Flow in Periodic Porous Media

Bioengineering. Flow around Cells Adhered to a Microvessel Wall. III. Effects of Neighboring Cells in Channel Flow.

The flow past cells adherent to the bottom plate of a parallel-plate channel is numerically analyzed in the zero-Reynolds-number limit, and the effect of the neighboring adherent cells on the drag force exerted on an adherent cell is examined. The cells are modeled as rigid spherical particles and they are assumed to be attached to the channel wall regularly in a square array. It is found that, when the size ratio of the cell-to-channel height is smaller than approximately 0.2, the drag force exerted on an adherent cell is well approximated by a linear function of the size ratio, almost independently of the separation distances between neighboring cells except for the cases of very narrow spacing. For larger size ratios, the drag force on an adherent cell in channel flow is generally smaller than the corresponding value in tube flow, but both values vary considerably, depending on the size ratios and the separation distances.

Regional calcium transients during spontaneously occurred morphological changes in endothelial cell and effect of fluid flow

Regional calcium transients during spontaneously occurred morphological changes in endothelial cell and effect of fluid flow

Analysis of mass and momentum transfer in an annular electrodialysis cell in pulsed flow

An analysis of mass and momentum transfer in an annular pulsating electrodialysis cell has been made. The mass and momentum balance equations are solved numerically for the case of reversing and non-reversing oscillatory flow. The numerical mass transfer is compared with the experimental results obtained from the determination of the limiting current density in an electrodialysis cell. From the numerical calculations and the experimental results, an enhancement of mass transfer due to superimposed pulsation can take place in the case of reversing flow. Increases in frequency and amplitude of pulsation improve the mass transfer coefficient, the effect of frequency being greater.

Mass transfer during gas absorption in a vertical gas-liquid slug flow with small bubbles in liquid plugs

A model is developed for the analysis of mass transfer during isothermal absorption in a vertical gas-liquid slug flow at large Reynolds numbers with liquid plugs containing small bubbles. Simple formulas for mass flux from the N-th unit cell of gas-liquid slug flow and for total mass flux from N unit cells are derived. In the limiting case the derived formulas for mass transfer during gas absorption in a slug flow with liquid plugs containing small bubbles recover the derived expressions for mass transfer in slug flow without small bubbles in the liquid plugs. Using the developed model recommendations concerning the design of the absorber operating in a slug flow regime are suggested.

Optimization of gas hydrate reactors with slug flow

A model of heat transfer during gas hydrate formation at a gas-liquid interface in gas-liquid slug flow with liquid plugs containing small bubbles is suggested. Under the assumption of perfect mixing of liquid in liquid plugs, recurrent relations for temperature in the n-th liquid plug and heat and mass fluxes from the n-th unit cell in a gas-liquid slug flow are derived. The ratio of the total mass flux during gas hydrate formation in a cluster with N unit cells to the mass flux in a cluster with an infinite number of unit cells is determined. The number of unit cells that yield 95% of the total amount of gas hydrates in an infinite cluster of unit cells is calculated and formula for an optimal length of a gas hydrate slug flow reactor is derived.

Microcinematographic studies of flow patterns in the excised rabbit aorta and its major branches

Arterial fluid mechanics may play a role as a localizing factor for early atherosclerosis. Flow patterns in natural rabbit aortas rendered transparent were studied using a microcinematographic visualization technique. The aortic arch exhibited a single cell of clockwise-rotating helical secondary flow along the ventral and inner walls. Flow separation occurred proximal to the two arch branches with flow reversal proximal to the brachiocephalic artery. Sinusoidal flow rendered the helical motion more pronounced in systole, while the reverse flow zone periodically expanded and contracted. Steady flow in the abdominal aorta revealed streamlines which follow slow looping trajectories lateral to ostia before tracing helical paths into the branches. Flow separation was present along the dorsal wall of the aorta opposite the superior mesenteric artery. With the exception of the left renal artery, steady flow wall shear stresses were higher distal to ostia than proximal. Spatial gradients of wall shear stress were larger around branches than elsewhere. Similar to observed flow patterns, sites of enhanced macromolecular permeability, as observed previously in the normal rabbit aorta, follow a clockwise helical pattern in the arch and exhibit a distribution around ostia that correlates to some degree with regions of elevated shear stress gradients.

Velocity profiles and limiting current in an annular electrodialysis cell in pulsed flow

Hydrodynamics and mass transfer in an annular electrodialysis cell with pulsed flow have been studied. Velocities were obtained solving the momentum equations, in the annular space between two concentric cylinders. The instantaneous velocity can be broken down into two components: a steady component with a parabolic profile, and an oscillatory component which presents two maxima in the nearby of the cylinder walls. The fundamental dimensionless groups that describe the velocity profiles are the Reynolds number, Re = v D eq v , the dimensionless velocity, α 0 = αω v , and the pulse Reynolds number, α 1 = D eq ( ω v ) 1 2 . Mass transfer through the membrane was investigated in terms of the limiting current. For a given value of α 0, frequency has a more significant effect on the limiting current than amplitude.

An Investigation of the Transition from Multicell to Supercell Storms

Abstract Nearly 2½ hours of dual-Doppler radar data with high temporal and spatial resolution are used to examine the evolution and morphology of a thunderstorm that evolved from a complex of small cells into a supercell storm. Individual storm cells and updrafts moved east-northeastward, nearly with the mean wind, while the storm complex, which encompassed the individual cells, propagated toward the south–southeast. Cells were first detected at middle levels (5–10 km) on the storm's right flank and dissipated on the left flank. Generally, the storm contained three cells—a forming cell, a mature cell, and a dissipating cell; life stages were apparently dictated by the source of updraft air. During the growth stage, cell inflow had a southerly component. As the cell moved through the storm complex, it started ingesting stable air from the north and soon dissipated. A storm-environment feedback mechanism of updraft–downdraft interactions, in conjunction with increasing environmental vertical wind shear and ...

Motion of the Red Blood Cell in the Blood Flow

Motion of the Red Blood Cell in the Blood Flow

Motion and deformation of a red blood cell in a shear flow: a two-dimensional simulation of the wall effect.

The motion and deformation of a single red blood cell in a simple shear flow between two parallel walls is studied theoretically. A two-dimensional deformable microcapsule is adopted as a model for the cell, which has a thin moving membrane, like a tank-tread, around the interior and is deformed into an elliptical shape with a constant area. Applying the finite element method to the Stokes equations, the tank-tread motion and deformation is determined in a stationary motion, under fluid dynamic interaction between the cell and the walls. It is shown that the motion and deformation of the microcapsule crucially depends on the channel width between the two walls. As the width decreases, the microcapsule is more elongated and the frequency of tank-tread motion decreases at a constant shear rate. In addition, the angle of inclination decreases at the low range of the viscosity ratio of internal to external fluids and increases at the high range. The results obtained are compared with experimental observations and applied to the behavior of cells under mutual interaction.

Numerical approach to the motion of a red blood cell in Couette flow.

The motion of a red blood cell in a plane Couette flow is studied theoretically, introducing a two-dimensional microcapsule model for the cell. It is assumed that the microcapsule is deformed into an elliptical shape with a constant area and that its membrane moves like a tank-tread around the interior. The flow fields both inside and outside the microcapsule are analyzed using the finite element method in the Stokes equations and the obtained viscous forces on the membrane are used to determine its deformation and tank-treading motion. It is shown that a decrease in viscosity ratio of internal to external fluids causes the microcapsule to be more elongated, with its inclination angle increasing, whereas the microcapsule becomes more elongated at a smaller inclination angle with a longer tank-treading period as the elastic compliance of the membrane or the shear rate of the Couette flow increases. The force acting on the wall is also examined in relation to the abnormal viscosity of blood.

Two-dimensional approach to the motion of a red blood cell in a plane couette flow of plasma

In relation to microrheology of blood, a theoretical approach to the motion of a red blood cell in a plane Couette flow between two parallel plates is made with emphasis on effects of wall. The red blood cell is assumed to be an elliptic cylindrical particle with a thin, inextensible membrane moving like a tank-tread along its perimeter and to contain a Newtonian fluid inside. Fluid motions are analysed numerically both inside and outside the particle on the basis of the Stokes equations, using the finite element method. A quasi-static equilibrium condition leads to the solution for the motion of the particle. It is shown that two types of motion exist (a stationary orientation motion and a flipping motion), depending on the viscosity ratio of inner to outer fluid, the axis ratio of the elliptic cylinder and the ratio of particle size to channel width. The results are applied to capillary blood flow.

A network model of glomerular function

A model has been developed to establish the determinants of glomerular function by means of a network analysis. The topological and dimensional parameters of the capillary network were obtained by reconstructing the lobular structures of two Wistar rat glomeruli. Calculation of the hydrostatic pressure drop from the afferent to the efferent extremity of the network ( ε = (P c a − P c e ) P c a ) was based on the concept of the additional pressure drop per red cell in single-file flow, or, in multiple-layer flow, on in vitro experimental data relating apparent viscosity of blood to dynamic hematocrit and capillary radius. Partition of red cells at bifurcations was calculated as a function of the velocity ratio within the branches. The micropuncture data obtained in Munich-Wistar rats at distal pressure disequilibrium (net ultrafiltration pressure greater than 0) were used to establish the validity of the model. ε was found to be 3.1%. The efferent ultrafiltration pressure was close to the value predicted from the micropuncture data. At distal pressure disequilibrium, 100% of the glomerular surface area was utilized for filtration. In this case, the mean integrated ultrafiltration pressure and the filtration coefficient were close to the values reported by R. C. Blantz, F. C. Rector, Jr., and D. W. Seldin ((1974) Kidney Int. 6, 209–225) using the single-tube model of W. M. Deen, C. R. Robertson, and B. M. Brenner ((1972) Amer. J. Physiol. 223, 1178–1183). The hydraulic conductance was estimated between 0.046 and 0.09 μl sec −1 mm Hg −1 cm −2 S.A. but was dependent on the value chosen for the glomerular surface area.