Flow-induced Changes Research Articles

Influence of Flow-Induced Polymorphism and Fiber Morphology on Mechanical Behavior in Long Discontinuous Glass Fiber Polyamide Composites

This study investigates the combined flow-induced crystallization in the polymer and fiber reorientation during compression molding of a long discontinuous glass fiber polyamide (PA 6) composite. The composite is molded from an organosheet (a semi-finished pre-impregnated mat); the composite anisotropic tensile properties are evaluated as a function of polymer crystalline morphology and fiber orientation state, both controlled by the extent of material flow in the mold. To study these effects, the full mold coverage and partial center charge of organosheet (OS)-80 %, 60 %, 50 %, and 40 % were compression molded to cause varying anisotropic material flow. Tensile specimens were cut out from the molded plates in the flow and transverse direction and tested to compare their effective tensile properties (modulus and strength). The flow-induced morphological changes in a molded composite at the glass fiber bundle microstructure scale and polymer crystalline phases nano-structure were characterized using optical microscopy and X-ray diffraction, respectively. These morphological changes contributed to the significant change in the tensile strength and modulus; a combined experimental/numerical simulation framework was used to segregate the relative contribution of each factor. Experimentally, the tensile modulus increased in the flow direction from 9.6GPa to 14.9GPa for the specimens produced by full mold coverage and OS-50 % coverage mold, respectively. The tensile strength increased from 162 MPa to 254 MPa for the full and OS-60 % mold coverage. On the contrary, the strength and modulus in the transverse direction to the flow showed a significant drop to 35 MPa and 3GPa, respectively, which was attributed to reduced fiber alignment and anisotropy in the PA6 matrix.

Under pressure: integrated endothelial cell response to hydrostatic and shear stresses.

Blood flow within the vasculature is a critical determinant of endothelial cell (EC) identity and functionality, yet the intricate interplay of various hemodynamic forces and their collective impact on endothelial and vascular responses are not fully understood. Specifically, the role of hydrostatic pressure in the EC flow response is understudied, despite its known significance in vascular development and disease. To address this gap, we developed in vitro models to investigate how pressure influences EC responses to flow. Our study demonstrates that elevated pressure conditions significantly modify shear-induced flow alignment and increase endothelial cell density. Bulk and single-cell RNA sequencing analyses revealed that, while shear stress remains the primary driver of flow-induced transcriptional changes, pressure modulates shear-induced signaling in a dose-dependent manner. These pressure-responsive transcriptional signatures identified in human ECs were conserved during the onset of circulation in early mouse embryonic vascular development, where pressure was notably associated with transcriptional programs essential to arterial and hemogenic EC fates. Our findings suggest that pressure plays a synergistic role with shear stress on ECs and emphasizes the need for an integrative approach to endothelial cell mechanotransduction, one that encompasses the effects induced by pressure alongside other hemodynamic forces.

Steady Laminar Flow Decreases Endothelial Glycolytic Flux While Enhancing Proteoglycan Synthesis and Antioxidant Pathways.

Endothelial cells in steady laminar flow assume a healthy, quiescent phenotype, while endothelial cells in oscillating disturbed flow become dysfunctional. Since endothelial dysfunction leads to atherosclerosis and cardiovascular disease, it is important to understand the mechanisms by which endothelial cells change their function in varied flow environments. Endothelial metabolism has recently been proven a powerful tool to regulate vascular function. Endothelial cells generate most of their energy from glycolysis, and steady laminar flow may reduce endothelial glycolytic flux. We hypothesized that steady laminar but not oscillating disturbed flow would reduce glycolytic flux and alter glycolytic side branch pathways. In this study, we exposed human umbilical vein endothelial cells to static culture, steady laminar flow (20 dynes/cm2 shear stress), or oscillating disturbed flow (4 ± 6 dynes/cm2 shear stress) for 24 h using a cone-and-plate device. We then measured glucose and lactate uptake and secretion, respectively, and glycolytic metabolites. Finally, we explored changes in the expression and protein levels of endothelial glycolytic enzymes. Our data show that endothelial cells in steady laminar flow had decreased glucose uptake and 13C labeling of glycolytic metabolites while cells in oscillating disturbed flow did not. Steady laminar flow did not significantly change glycolytic enzyme gene or protein expression, suggesting that glycolysis may be altered through enzyme activity. Flow also modulated glycolytic side branch pathways involved in proteoglycan and glycosaminoglycan synthesis, as well as oxidative stress. These flow-induced changes in endothelial glucose metabolism may impact the atheroprone endothelial phenotype in oscillating disturbed flow.

Short-term influences of flow alteration on microbial community structure and putative metabolic functions in gravel bar hyporheic zones

Microbial communities in the hyporheic zone are important for self-purification as the riverbed is metabolically active and responsible for the retention, storage, and mineralisation of organic matter transported in the surface water. Studies exploring the response of the hyporheic microbial community to flow regime alterations remain scarce. Here, we characterised the microbial community structure over downwelling, upwelling and intermediate hyporheic zone areas within and among gravel bars at high and low discharge levels to determine flow-induced changes in a dam-regulated river using 16S rRNA gene sequencing. At low discharge, microbial composition varied across the different areas of gravel bars, reflecting heterogeneity in local abiotic conditions. However, high discharge lead to microbial community homogenisation across the three areas of the gravel bars. Microbial communities across adjacent gravel bars remained dissimilar regardless of discharge levels, likely reflecting differences in bar morphology. Our results can help better understand how anthropogenic changes in hydrologic conditions can affect microbial diversity and function in the hyporheic zone. This knowledge will help us to understand better how changes in hydrological conditions affect ecosystem functions and services in rivers affected by human impacts.

Nutrient Solution Flowing Environment Affects Metabolite Synthesis Inducing Root Thigmomorphogenesis of Lettuce (Lactuca sativa L.) in Hydroponics

The principal difference between hydroponics and other substrate cultivation methods is the flowing liquid hydroponic cultivation substrate. Our previous studies have revealed that a suitable flowing environment of nutrient solution promoted root development and plant growth, while an excess flow environment was unfavorable for plants. To explain the thigmomorphogenetic response of excess flow-induced metabolic changes, six groups of lettuce (Lactuca sativa L.), including two flow conditions and three time periods, were grown. Compared with the plants without flow, the plants with flow showed decreased root fresh weight, total root length, root surface area, and root volume but increased average root diameter and root density. The roots with flow had more upregulated metabolites than those without flow, suggesting that the flow may trigger metabolic synthesis and activity. Seventy-nine common differential metabolites among six groups were screened, and enrichment analysis showed the most significant enrichment in the arginine biosynthesis pathway. Arginine was present in all the groups and exhibited greater concentrations in roots with flow than without flow. It can be speculated from the results that a high-flowing environment of nutrient solution promotes arginine synthesis, resulting in changes in root morphology. The findings provide insights on root thigmomorphogenesis affected by its growing conditions and help understand how plants respond to environmental mechanical forces.

Endothelial cells differentially sense laminar and disturbed flows by altering the lipid order of their plasma and mitochondrial membranes.

Endothelial cells (ECs) experience two different blood flow patterns: laminar and disturbed flow. Their responses to laminar flow contribute to vascular homeostasis, whereas their responses to disturbed flow result in EC dysfunction and vascular diseases. However, it remains unclear how ECs differentially sense laminar and disturbed flow and trigger signaling that elicits different responses. Here, we showed that ECs differentially sense laminar and disturbed flows by altering the lipid order of their plasma and mitochondrial membranes in opposite directions. This results in distinct changes in mitochondrial function, namely, increased adenosine triphosphate (ATP) production for laminar flow and increased hydrogen peroxide (H2O2) release for disturbed flow, leading to ATP- and H2O2-mediated signaling, respectively. When cultured human aortic ECs were subjected to laminar or disturbed flow in flow-loading devices, the lipid order of their plasma membranes immediately decreased in response to laminar flow and increased in response to disturbed flow. Laminar flow also decreased the lipid order of mitochondrial membranes and increased mitochondrial ATP production. In contrast, disturbed flow increased the lipid order of mitochondrial membranes and increased the release of H2O2 from the mitochondria. The addition of cholesterol to the cells increased the lipid order of both membranes and abrogated laminar flow-induced ATP production, while treatment of the cells with a cholesterol-depleting reagent, methyl-β cyclodextrin, decreased the lipid order of both membranes and abolished disturbed flow-induced H2O2 release, indicating that changes in the membrane lipid order and/or cholesterol content are closely linked to flow-induced changes in mitochondrial functions.NEW & NOTEWORTHY How vascular endothelial cells (ECs) differentially sense laminar and disturbed flows and trigger intracellular signaling remains unclear. Here, we show that EC plasma membranes act as mechanosensors to discriminate between laminar and disturbed flows by undergoing opposite changes in their lipid order. Similar lipid order changes occur simultaneously in the mitochondrial membranes, which are linked to changes in mitochondrial function, that is, increased ATP production for laminar flow and increased H2O2 release for disturbed flow.

Spectral Characteristics of Fluctuating Aerodynamic Forces Acting on Rectangular Prisms

The present work is devoted to the role of boundary layer turbulence on the spectral characteristics of fluctuating wind loads on large aspect-ratio rectangular prisms. Seven rectangular rigid models with different side ratios (1/4~4) were created, and simultaneous pressure experiments were conducted under the boundary layer turbulence flows. Using the measured data, the power spectrums of the fluctuating aerodynamic forces were calculated, and then, the spectral characteristics under different turbulent boundary layer flows were analyzed. In contrast to the typical power spectrum model, the main factors affecting the spectral characteristics of the fluctuating aerodynamic loads are presented and discussed in this study. The power spectrum of the rectangular prism was significantly impacted by the turbulent wind field, primarily because higher turbulence intensity levels result in a lower spectral peak and a wider spectral bandwidth, which also redistributes spectral energy. In particular, the effect on the spectral properties of across-wind fluctuating loads was stronger, and the turbulent disturbance modified the lateral separation flow structure, causing the reattachment phenomenon to occur earlier on rectangular prisms with small side ratios, which effectively altered the spectral properties. Thus, a normalized across-wind fluctuating wind load spectrum model is proposed, taking into account the effects of incoming turbulence, the side ratio, vortex shedding, separation reattachment flow-induced spectral bandwidth changes, and high-frequency fluctuations.

Platelet Mechanotransduction: Regulatory Cross Talk Between Mechanosensitive Receptors and Calcium Channels.

Blood flow-induced hemodynamic changes result in mechanical stress on blood cells and vessel walls. Increased shear stress can activate platelets and other circulating cells, triggering the rapid activation of receptors, calcium channels, and related signaling mechanisms. Shear stress can also modify the folding of extracellular molecules and directly activate mechanosensitive receptors and calcium channels. The mechanical movement of the extracellular matrix and the intracellular cortical actin cytoskeleton can change the conformation of platelet receptors and gate channel pores in the plasma membrane. Mechanosensitive platelet receptors and their downstream signaling events and metabolic products can also indirectly activate calcium channels. While the molecular composite of mechanotransduction pathways has been described in mammals, shear stress-induced platelet receptors and their cross talk with calcium channels have been incompletely characterized. In this review, we discuss current knowledge about the role of mechanosensitive platelet receptors and calcium channels in shear-dependent platelet activation and arterial thrombus formation.

Viscous flow through macroscopic spherical cavities in an arbitrary configuration in a granular material

Viscous flow through macroscopic spherical cavities in a granular material is theoretically investigated. Number, size and configuration of the cavities are arbitrary, except that cavities are sufficiently distant to allow asymptotic analysis on their interaction, which is taken into account up to , where a and l are the characteristic radius and inter-cavity distance, respectively. Dependence of the flow field, flux into respective cavities and stress field etc on the cavity size, separation distance and orientation are analyzed. As further examples, 1D-, 2D-, and 3D-array of equal size cavities are examined, by which onset of the collapse of cavity and development of the collapsed region are elucidated. The latter may predict landslides and other flow-induced catastrophic changes in the material with quasi-equilibrium solid structure, as well as microscale waterway formation in human tissue known as angiogenesis.

In silico study of the effects of cerebral circulation on source localization using a dynamical anatomical atlas of the human head

Objective. This study focuses on the effects of dynamical vascular modeling on source localization errors in electroencephalography (EEG). Our aim of this in silico study is to (a) find out the effects of cerebral circulation on the accuracy of EEG source localization estimates, and (b) evaluate its relevance with respect to measurement noise and interpatient variation. Approach. We employ a four-dimensional (3D + T) statistical atlas of the electrical properties of the human head with a cerebral circulation model to generate virtual patients with different cerebral circulatory conditions for EEG source localization analysis. As source reconstruction techniques, we use the linearly constraint minimum variance (LCMV) beamformer, standardized low-resolution brain electromagnetic tomography (sLORETA), and the dipole scan (DS). Main results. Results indicate that arterial blood flow affects source localization at different depths and with varying significance. The average flow rate plays an important role in source localization performance, while the pulsatility effects are very small. In cases where a personalized model of the head is available, blood circulation mismodeling causes localization errors, especially in the deep structures of the brain where the main cerebral arteries are located. When interpatient variations are considered, the results show differences up to 15 mm for sLORETA and LCMV beamformer and 10 mm for DS in the brainstem and entorhinal cortices regions. In regions far from the main arteries vessels, the discrepancies are smaller than 3 mm. When measurement noise is added and interpatient differences are considered in a deep dipolar source, the results indicate that the effects of conductivity mismatch are detectable even for moderate measurement noise. The signal-to-noise ratio limit for sLORETA and LCMV beamformer is 15 dB, while the limit is under 30 dB for DS. Significance. Localization of the brain activity via EEG constitutes an ill-posed inverse problem, where any modeling uncertainty, e.g. a slight amount of noise in the data or material parameter discrepancies, can lead to a significant deviation of the estimated activity, especially in the deep structures of the brain. Proper modeling of the conductivity distribution is necessary in order to obtain an appropriate source localization. In this study, we show that the conductivity of the deep brain structures is particularly impacted by blood flow-induced changes in conductivity because large arteries and veins access the brain through that region.

Passive and reversible area regulation of supported lipid bilayers in response to fluid flow

Biological and model membranes are frequently subjected to fluid shear stress. However, membrane mechanical responses to flow remain incompletely described. This is particularly true of membranes supported on a solid substrate, and the influences of membrane composition and substrate roughness on membrane flow responses remain poorly understood. Here, we combine microfluidics, fluorescence microscopy, and neutron reflectivity to explore how supported lipid bilayer patches respond to controlled shear stress. We demonstrate that lipid membranes undergo a significant, passive, and partially reversible increase in membrane area due to flow. We show that these fluctuations in membrane area can be constrained, but not prevented, by increasing substrate roughness. Similar flow-induced changes to membrane structure may contribute to the ability of living cells to sense and respond to flow.

Monitoring of false lumen thrombosis in type B aortic dissection by impedance cardiography - A multiphysics simulation study.

Aortic dissection is caused by a tear on the aortic wall that allows blood to flow through the wall layers. Usually, this tear involves the intimal and partly the medial layer of the aortic wall. As a result, a new false lumen develops besides the original aorta, denoted then as the true lumen. The local hemodynamic conditions such as flow disturbances, recirculations and low wall shear stress may cause thrombus formation and growth in the false lumen. Since the false lumen status is a significant predictor for late-dissection-related deaths, it is of great importance in the medical management of patients with aortic dissection. The hemodynamic changes in the aorta also alter the electrical conductivity of blood. Since the blood is much more conductive than other tissues in the body, such changes can be identified with non-invasive methods such as impedance cardiography. Therefore, in this study, the capability of impedance cardiography in monitoring thrombosis in the false lumen is studied by multiphysics simulations to assist clinicians in the medical management of patients under treatment. To tackle this problem, a 3D computational fluid dynamics simulation has been set up to model thrombosis in the false lumen and its impact on the blood flow-induced conductivity changes. The electrical conductivity changes of blood have been assigned as material properties of the blood-filled aorta in a 3D finite element electric simulation model to investigate the impact of conductivity changes on the measured impedance from the body's surface. The results show remarkable changes in the electrical conductivity distribution in the measurement region due to thrombosis in the false lumen, which significantly impacts the morphology of the impedance cardiogram. Thus, frequent monitoring of impedance cardiography signals may allow tracking the thrombus formation and growth in the false lumen.

Development of a New Rheometry and Its Application to Study of Flow-Induced Structural Changes

Development of a New Rheometry and Its Application to Study of Flow-Induced Structural Changes

Rheo-Dielectrics and Diffusion of Type-A Rouse Chain under Fast Shear Flow: Method of Evaluation of Non-Equilibrium Parameters for FENE, Friction-Reduction, and Brownian Force Intensity Variation

Rouse model is the basic molecular model for unentangled linear polymer chains in melts. Recent studies suggest that the Rouse parameters characterizing the unentangled melts, the spring strength κ , the segmental friction coefficient ζ, and the mean-square Brownian force intensity B, change under fast flow thereby providing significant rheological nonlinearities with those melts (Matsumiya et al., Macromolecules, 51, 9710 (2018)). This article theoretically analyzes effects of the flow-induced changes of these parameters on the dielectric and diffusion behavior of the Rouse chain having so-called type-A dipoles parallel along the chain backbone. It turned out that the dielectric behavior under steady shear is determined by non-equilibrium parameters, rκ = κ/κeq and rζ,ij = ζij/ζeq but irrelevant to rB,ij = B ij/Beq, where the subscript “eq” stands for the quantities at equilibrium and the subscripts “ij” denote the spatial direction under shear flow: i and/or j = x, y, and z for the velocity, velocity gradient, and vorticity directions, respectively. Specifically, the complex dielectric permittivity ε* is analytically expressed in terms of the parameters rκ and rζ,ij, which in turn enables us to evaluate these parameters from data of the dielectric relaxation time and intensity under steady shear (obtained in future experiments). In contrast, the advective diffusion behavior under steady shear is determined by rζ,ij and rB,ij but irrelevant to rκ. The mean-square displacement ‹Δr2CM› of the center of mass defined with respect to the known non-diffusive advection point is analytically expressed in terms of rζ,ij and rB,ij, thereby allowing us to evaluate rB,ij from the diffusion data under steady shear and the dielectrically determined rζ,ij. The method of experimental evaluation of the non-equilibrium parameters presented in this article provides us with a complementary basis for analyzing nonlinear rheological behavior of unentangled melts.

Numerical investigation of eutectic growth dynamics under convection by 3D phase-field method

Control of eutectic growth trajectory is a technologically important subject in metallurgy and applied physics. The interaction between solute transport and interface capillary determines eutectic growth under convection. By employing a multiphase-field lattice-Boltzmann method, together with a parallel-adaptive mesh refinement algorithm, the effect of convection on 3D eutectic growth is quantified including lamellar and rod eutectics. The flow-induced solute distribution changes eutectic growth dynamics by establishing a new solute transport equilibrium. The growth behaviors of different eutectic patterns are investigated, and the eutectic growth dynamics is largely dependent on the constitutional undercooling and the curvature undercooling ahead of the solidification front. The natural convection changes the width ratio of coexisting solid phases, while the forced convection causes a tilt band for both lamellar and rod eutectics. Rod-to-lamellar transition under larger convection intensity, which is first predicted by numerical techniques, is discussed and good agreement with previous works is achieved. The deep understanding of the convection effect can help guide how to regulate eutectic patterns through changing the solidification condition.

Simulating Local Deformations in the Human Cortex Due to Blood Flow-Induced Changes in Mechanical Tissue Properties: Impact on Functional Magnetic Resonance Imaging.

Investigating human brain tissue is challenging due to the complexity and the manifold interactions between structures across different scales. Increasing evidence suggests that brain function and microstructural features including biomechanical features are related. More importantly, the relationship between tissue mechanics and its influence on brain imaging results remains poorly understood. As an important example, the study of the brain tissue response to blood flow could have important theoretical and experimental consequences for functional magnetic resonance imaging (fMRI) at high spatial resolutions. Computational simulations, using realistic mechanical models can predict and characterize the brain tissue behavior and give us insights into the consequent potential biases or limitations of in vivo, high-resolution fMRI. In this manuscript, we used a two dimensional biomechanical simulation of an exemplary human gyrus to investigate the relationship between mechanical tissue properties and the respective changes induced by focal blood flow changes. The model is based on the changes in the brain’s stiffness and volume due to the vasodilation evoked by neural activity. Modeling an exemplary gyrus from a brain atlas we assessed the influence of different potential mechanisms: (i) a local increase in tissue stiffness (at the level of a single anatomical layer), (ii) an increase in local volume, and (iii) a combination of both effects. Our simulation results showed considerable tissue displacement because of these temporary changes in mechanical properties. We found that the local volume increase causes more deformation and consequently higher displacement of the gyrus. These displacements introduced considerable artifacts in our simulated fMRI measurements. Our results underline the necessity to consider and characterize the tissue displacement which could be responsible for fMRI artifacts.

Modeling the effect of flow-induced mechanical erosion during coffee filtration

The espresso extraction process involves a complex transport inside a geometry-changing porous medium. Large solid grains forming the majority of the porous medium can migrate, swell, and consolidate, and they can also morphologically change during flow, i.e., being mechanically eroded by hydrodynamic forces. These processes can, in turn, have a significant back-effect on the flow and the related coffee extraction profiles. In this article, we devise a bottom–up erosion model in the framework of smoothed dissipative particle dynamics to consider flow-induced morphological changes of the coffee grains. We assume that the coffee grains are not completely wetted and remain brittle. We found that heterogeneity in both the filtration direction and the transverse direction can be induced. The former is controlled by the angle of internal friction while the latter is controlled by both the cohesion parameter and the angle of internal friction. Not restricted to the modeling of espresso extraction, our model can also be applied to other eroding porous media. Our results suggest that, under ideal porous flow conditions, we can control the heterogeneity (in both the pressure drop direction and the transverse direction) of an eroding medium by tuning the yield characteristics of the eroding material.

Combining green LiDAR bathymetry, aerial images and telemetry data to derive mesoscale habitat characteristics for European grayling and brown trout in a Norwegian river

While many studies provide microscale relationships between fish and habitat characteristics, studies covering longer river reaches are scarce. Modern remote sensing techniques may enable new and effective ways of mapping and assessing mesoscale habitat characteristics. Using green LIDAR-derived bathymetry and hydraulic modelling, we tested how mesoscale depth and velocity were related to fish counts of adult European grayling (Thymallus thymallus L.) and brown trout (Salmo trutta L.) in 500 m river sections in three separate periods during the year. Using riverbank sinuosity from aerial images and a Froude number-based index from the hydraulic model as proxies for mesoscale spatial and hydraulic heterogeneity, we tested for temporal correlations with river section fish counts of adult European grayling and brown trout. Results showed that mesoscale mean depth and velocity were correlated to period fish counts of adult European grayling. Using mixed model analysis we found that riverbank sinuosity and the Froude number-based index were significantly correlated with river section occurrence of adult European grayling during spawning. The results can be used to assess how flow-induced changes and channel adjustments at the mesoscale level can influence access to and use of relevant habitats in rivers occupied by European grayling and brown trout.

Lipid Bilayer Passive Area Regulation in Response to Fluid Flows

Mechanotransduction is the cellular process in which mechanical stimuli are converted into biochemical signals to induce specific cellular responses, enabling the cell to sense and respond to mechanical forces. Although many cells exhibit this behavior, vascular endothelial cells (ECs) are of considerable interest as they effectively respond to fluid shear stress, adapting their morphology, functions and gene expression to maintain the homeostasis of the vascular system. Fundamentally, these processes rely on the transduction of intracellular signals through the lipid membrane, and several studies have already demonstrated that shear stress induces significant changes in lipid order and viscosity of ECs plasma membrane. Despite such extensive study, the underlying molecular mechanisms that control this change to membrane lipid order and viscosity remain unclear. Supported lipid bilayers provide an ideal platform for the investigation of the molecular mechanisms behind shear induced biophysical changes in membrane structure. As a minimal model system, they are suited for isolating the physical role of lipid bilayer in membrane shear response, in the absence of active biological processes. Here, combining microfluidics and fluorescence microscopy, we examine how the application of controlled fluid flows on supported lipid bilayer patches alters their physical properties. We observe a reversible and significant ∼10% increase in SLB area (when physiological shear stresses of 1-2 Pa are applied). Such area fluctuations have been a previously suggested response to fluid shear stress but have not directly observed. Furthermore, we determine how these membrane area fluctuations in response to fluid flows depend on lipid composition and surface roughness. Identifying the origin of such flow-induced changes in membrane structure could reveal an underlying mechanism utilized by biology to sense and direct changes in membrane order and viscosity in response to shear flows.

The structure factor in flowing wormlike micellar solutions

Abstract In this work we present theoretical and experimental studies on the structure factor in micellar systems. Cetyl trimethyl ammonium tosilate (CTAT) solutions in absence of salts exhibit a flow behavior similar to polymer solutions, while upon an increase in the ionic strength with NaCl, their behavior changes to that of a kinetic-controlled breakage-reformation process. The relaxation mechanism thus changes from that of a spectrum of relaxation times into an averaged dominant relaxation mode, representative of reversible kinetics. Micellar solutions exhibit mechanical instabilities under flow, which may be increased by concentration fluctuations. Elastic stresses increase concentration fluctuations, which are experimentally observed by rheo-optical techniques, such as Rheo-SALS, depicting characteristic “butterfly” patterns. Scattering patterns provide information on the structure factor, arising from concentration fluctuations of the flowing solution. Upon addition of salt to a CTAT solution, we observe agreement with the Cox-Merz rule, revealing that the solution is in the fast-breaking regime approaching a single relaxation time kinetics. This behavior cannot be predicted by polymer solution theories which do not incorporate the breakage-reformation kinetics. Here, we propose a kinetic model by which the structure factor can be calculated for these micellar solutions. A shift in the maximum of the scattering patterns as the shear rate is increased is predicted by the new theory, which can be explained by considering flow-induced changes in the structure of the solutions with the underlying kinetics of breakage-reformation. Agreement with experiments is exhibited.