In this Letter we report experimental evidence that rotation enhances vertical inhomogeneity in turbulent convection, in spite of the increased columnar flow ordering under rotation. Measurements using stereoscopic particle image velocimetry have been carried out on turbulent rotating convection in water. At constant Rayleigh number Ra=1.11 x 10(9) several rotation ...

Cytoplasmic streaming circulates the contents of large eukaryotic cells, often with complex flow geometries. A largely unanswered question is the significance of these flows for molecular transport and mixing. Motivated by "rotational streaming" in Characean algae, we solve the advection-diffusion dynamics of flow in a cylinder with bidirectional helical forcing ...

Fishes use a complex, multi-branched, mechanoreceptive organ called the lateral line to detect the motion of water in their immediate surroundings. This study is concerned with a subset of that organ referred to as the lateral line trunk canal (LLTC). The LLTC consists of a long tube no more than ...

Experiments and mathematical modeling show that complex flows driven by unexpected flagellar arrangements are induced when peritrichously flagellated bacteria are confined in a thin layer of fluid, between asymmetric boundaries. The flagella apparently form a dynamic bipolar assembly rather than the single bundle characteristic of free swimming bacteria, and the ...

The effect of shear flow on the isotropic-nematic phase transition of attractive colloidal rods is investigated by a combination of simulations and experiments. The isotropic phase aligns with the flow, while the nematic phase undergoes a collective rotational motion which frustrates the merging of the coexisting regions. The location of ...

Stress from fishing capture can incite potentially lethal physiological changes in fishes. Blood acid-base status has routinely been utilized to gauge the magnitude of the stress response, which is dependent on the nature of the capture event and metabolic capacity of the species in question. The mortality induced by demersal ...

This study investigates rheological effects of blood on steady flows in a nonplanar distal end-to-side anastomosis. The shear-thinning behavior of blood is depicted by a Carreau-Yasuda model and a modified power-law model. To explore effects of nonplanarity in vessel geometry, a curved bypass graft is considered that connects to the ...

Strong shocks in rapid dense granular flows are studied theoretically and analyzed in detail to compare with benchmark experimental data. The experimental data includes particle image velocimetry measurements of dry granular flow following its continuous release from a silo. The rapidly moving material down the chute impinges on an obstruction ...

This paper describes the mechanism of formation of bubbles of nitrogen in water containing Tween 20 as a surfactant, and of droplets of water in hexadecane containing Span 80 as a surfactant. The study of these microfluidic systems compares two or four flow-focusing generators coupled through shared inlets, supplying the ...

The experimental evidence of the dependence of cell proliferation and differentiation in vitro on the mechanical environment aims to the need of characterization of porous scaffolds in terms of mechanical and flow properties. In this sense, the Young's modulus and intrinsic permeability for three types of Sponceram(R) cell carriers developed ...

We report experimental characterization of shear transformation zones (STZs) for plastic flow of bulk metallic glasses (BMGs) based on a newly developed cooperative shearing model [Johnson WL, Samwer K (2005) A universal criterion for plastic yielding of metallic glasses with a (T/T(g))(2/3) temperature dependence. Phys Rev Lett 95: 195501]. The ...

In an attempt to better understand the mechanism underlying lateral collision avoidance in flying insects, we trained honeybees (Apis mellifera) to fly through a large (95-cm wide) flight tunnel. We found that, depending on the entrance and feeder positions, honeybees would either center along the corridor midline or fly along ...

Atherosclerotic lesions are non-uniformly distributed at arterial bends and branch sites, suggesting an important role for haemodynamic factors, particularly wall shear stress (WSS), in their development. The pattern of lesions at aortic branch sites depends on age and species. Using computational flow simulations in an idealized model of an intercostal ...

Wall shear stress (WSS) has been proved to play a critical role in formation and development of atherosclerotic plaques. Our objective was to quantify local WSS in vivo in normal subjects, and to analyze spatial distribution patterns and determine the temporal gradient of WSS. Seventy-eight CCAs of 42 healthy volunteers ...

A central feature of intussusceptive angiogenesis is the development of an intravascular pillar that bridges the opposing sides of the microvessel lumen. In this report, we created polydimethyl siloxane (PDMS) microchannels with geometric proportions based on corrosion casts of the colon microcirculation. The structure of the PDMS microchannels was a ...

In karst aquifers, contaminated recharge can degrade spring water quality, but quantifying the rapid recharge (quick flow) component of spring flow is challenging because of its temporal variability. Here, we investigate the use of nitrate in a two-endmember mixing model to quantify quick flow in Barton Springs, Austin, Texas. Historical ...

Bile flow is thought to play an essential role in the pathophysiological genesis of cholelithiasis (gallstone formation) and in gallbladder pain. In this paper, we extend our previous study of the human biliary system (Li et al., 2007, J. Biomech. Eng., 129:164-173) to include two important factors: the non-Newtonian properties ...

The deposition of intralumenal thrombus in intracranial aneurysms adds a risk of thrombo-embolism over and above that posed by mass effect and rupture. In addition to biochemical factors, hemodynamic factors that are governed by lumenal geometry and blood flow rates likely play an important role in the thrombus formation and ...

The objective of this work is to develop understanding of the local fluid dynamic mechanisms that underpin gas exchange in high-frequency oscillatory ventilation (HFOV). The flow field during HFOV was investigated experimentally using particle image velocimetry in idealized and realistic models of a single bifurcation. Results show that inspiratory and ...

Flows of dense emulsions show many complex features among which long range nonlocal effects pose a problem for macroscopic characterization. In order to get around this problem, we study the flows of several dense emulsions, with droplet size ranging from 0.3to40microm , in a wide-gap Couette geometry. We couple macroscopic ...

We study the rheology of sheared granular flows close to a jamming transition. We use the approach of partially fluidized theory (PFT) with a full set of equations extending the thin layer approximation derived previously for the description of the granular avalanches phenomenology. This theory provides a picture compatible with ...

An updated numerical simulation of unsteady generalized Newtonian blood flow through differently shaped distensible arterial stenoses is developed. A shear-thinning fluid modelling the deformation dependent viscosity of blood is considered for the characterization of generalized Newtonian behaviour of blood. The arterial model is treated as two-dimensional and axisymmetric with an ...

Secondary flows that are absent in Newtonian flows are found for semidilute lambda -DNA solutions in abrupt planar 90 degrees microbends at modest levels of elasticity. Flow visualization and microparticle image velocimetry experiments show that a vortex, which is present in the inner, upstream corner of the bend, grows with ...

BACKGROUND: The carotid bifurcation is one of the most susceptible locations for atherosclerotic plaques. It is important to assess wall shear stress (WSS) and blood flow patterns in this area. PURPOSE: To assess local WSS and blood flow patterns at the origin of the internal carotid artery (ICA). MATERIAL AND ...

Exposure of endothelial cells (EC) to shear stress reduces their response to tumour necrosis factor-alpha (TNF). We tested how shear-conditioned EC responded to reduction in flow, either by spontaneously binding leukocytes, or by increasing sensitivity to TNF. Human umbilical vein EC were exposed to shear stress of 2.0 Pa (20 ...

We have numerically investigated the axisymmetric motion of a finite-sized nearly occluding air bubble through a shear-thinning Casson fluid flowing in blood vessels of circular cross section. The numerical solution entails solving a two-layer fluid model--a cell-free layer and a non-Newtonian core together with the gas bubble. This problem is ...

The autoregulation of blood flow, the maintenance of almost constant blood flow in the face of variations in arterial pressure, is characteristic of many tissue types. Here, contributions to the autoregulation of pressure-dependent, shear stress-dependent, and metabolic vasoactive responses are analyzed using a theoretical model. Seven segments, connected in series, ...

When one contemplates the one-parameter family of steady inviscid shear flows discovered by J. T. Stuart in 1967, an obvious thought is that these flows resemble a row of vortices diffusing in a viscous fluid, with the parameter playing the role of a reversed time. In this paper, we ask ...

Stress, whether physical or emotional, is known to challenge the hypothalamus-pituitary-adrenal axis and to induce important changes in the biochemical parameters of organ functions. The fascia is an elastic tissue that envelops the organs and reacts to stress by tightening, thus contributing to the dysfunction of the body. One of ...

Accurate evaluation of damping in laterally oscillating microstructures is challenging due to the complex flow behavior. In addition, device fabrication techniques and surface properties will have an important effect on the flow characteristics. Although kinetic approaches such as the direct simulation Monte Carlo (DSMC) method and directly solving the Boltzmann ...

The inspiratory flow characteristics in a CT-scanned human lung model were numerically investigated using low Reynolds number (LRN) kappa-omega turbulent model. The five-generation airway is extracted from the trachea to segmental bronchi of a 60-year-old Chinese male patient. Computations were carried out in the Reynolds number range of 900-2100, corresponding ...

Little is known about endothelial responses to the impinging flow hemodynamics that occur at arterial bifurcation apices, where intracranial aneurysms usually form. Such hemodynamic environments are characterized by high wall shear stress (WSS >40 dynes/cm(2)) and high wall shear stress gradients (WSSG >300 dynes/cm(3)). In this study, confluent bovine aortic ...

The flow field at inspiration and expiration in the upper human airways consisting of the trachea down to the sixth generation of the bronchial tree is numerically simulated. The three-dimensional steady flow at a hydraulic diameter-based Reynolds number Re(D)=1250 is computed via a lattice-Boltzmann method (LBM). The simulation is validated ...

Simulation of blood flow in three-dimensional geometrically complex arterial networks involves many inlets and outlets and requires large-scale parallel computing. It should be based on physiologically correct boundary conditions, which are accurate, robust, and simple to implement in the parallel framework. While a secondary closure problem can be solved to ...

Amorphous glassy materials of diverse nature-concentrated emulsions, granular materials, pastes, molecular glasses-display complex flow properties, intermediate between solid and liquid, which are at the root of their use in many applications. A general feature of such systems, well documented yet not really understood, is the strongly nonlinear nature of the ...

Rotation and shear flows are ubiquitous features of many astrophysical and geophysical bodies. To understand their origin and effect on turbulent transport in these systems, we consider a forced turbulence and investigate the combined effect of rotation and shear flow on the turbulence properties. Specifically, we study how rotation and ...

We present a study of sediment transport in the creeping and saltation regimes. In our model, a bed of particles is simulated with the conventional event-driven method. The particles are considered as hard disks in a two-dimensional domain with periodic boundary conditions in the horizontal direction. The flow of the ...

Recently, analytical solutions for the nonlinear Couette flow demonstrated the relevance of the lattice Boltzmann (LB) models to hydrodynamics beyond the continuum limit [S. Ansumali, Phys. Rev. Lett. 98, 124502 (2007)]. In this paper, we present a systematic study of the simplest LB kinetic equation-the nine-bit model in two dimensions--in ...

OBJECTIVE: The goal of this report is to analyze the hemodynamic characteristics of low- and high-flow arteriovenous malformations (AVM) using computerized electrical models. METHODS: Two electrical models of brain AVMs were created. These models consist of electrical resistors that simulate AVM vessels. In both models, a low-flow AVM and a ...

The three-dimensional flow around a hemispherical bubble sliding and growing on a wall in a viscous linear shear flow is studied numerically by solving the full Navier-Stokes equations in a boundary-fitted domain. The main goal of the present study is to provide a complete description of the forces experienced by ...

A model was developed for the analysis of steady and unsteady bubble generation frequencies in a microfluidic flow-focusing device. In both cases, the generation frequency depends on the downstream influence of bubbles created by the flow-focusing device, which provides a source of feedback. For steady-state generation of bubbles, this feedback ...

We investigate the structure and flow behavior of colloidal gels in microchannels using confocal microscopy. Silica particles are first coated with a cationic polyelectrolyte and then flocculated by the addition of an anionic polyelectrolyte. In the quiescent state, the suspension is an isotropic and homogeneous gel. Under shear flow, the ...

The effect of preferential concentration of heavy particles in a homogeneous stably stratified turbulent flow is studied by means of direct numerical simulations. Particle distributions show different clustering patterns in horizontal and vertical directions, thereby representing the anisotropy of the flow. Preferential concentration in stably stratified turbulence can be quantified ...

The Arnhem Anti-Tank Range (Canadian Forces Base [CFB] Valcartier, Canada, in operation since the 1970s) has been characterized, including the drilling, installation, and characterization of 25 wells and a ground-penetrating radar survey. The observed particular features of this site include highly variable flow velocities (from < 3 to 1200 m/yr) ...

Large-Eddy simulation (LES) is performed to study pulsatile blood flow through a 3D model of arterial stenosis. The model is chosen as a simple channel with a biological type stenosis formed on the top wall. A sinusoidal non-additive type pulsation is assumed at the inlet of the model to generate ...

BACKGROUND AND PURPOSE: That certain vessels might be at so-called geometric risk of atherosclerosis rests on assumptions of wide interindividual variations in disturbed flow and of a direct relationship between disturbed flow and lumen geometry. In testing these often-implicit assumptions, the present study aimed to determine whether investigations of local ...

OBJECTIVES: In light of the ongoing discussion about flow-mediated arterial remodeling, it was the aim of this report to demonstrate the detailed assessment of 3-dimensional vascular hemodynamics by high-field magnetic resonance imaging in healthy volunteers and to illustrate its potential in comparison with results in a patient with stenosis. MATERIALS ...

Computational fluid dynamics techniques employing primarily steady Reynolds-Averaged Navier-Stokes (RANS) methodology have been recently used to characterize the transitional/turbulent flow field in human airways. The use of RANS implies that flow phenomena are averaged over time, the flow dynamics not being captured. Further, RANS uses two-equation turbulence models that are ...

Tracer particles on the surface of a turbulent flow have a very intermittent distribution. This preferential concentration effect is studied in a two-dimensional synthetic compressible flow, both in the inertial (self-similar) and in the dissipative (smooth) range of scales, as a function of the compressibility C . The second moment ...

Atherosclerotic plaques with high likelihood of rupture often show local temperature increase with respect to the surrounding arterial wall temperature. In this work, atherosclerotic plaque temperature was numerically determined during the different levels of blood flow reduction produced by the introduction of catheters at the vessel lumen. The temperature was ...