Increase In Shear Stress Research Articles

Evaluation of the effect of hemodynamic factors on retinal microcirculation by using 3D confocal image-based computational fluid dynamics

PurposeTo investigate local hemodynamic changes resulting from elevated intraocular pressure (IOP) in different vasculature networks using a computational fluid dynamics model based on 3D reconstructed confocal microscopic images.MethodsThree-dimensional rat retinal vasculature was reconstructed from confocal microscopy images using a 3D U-Net-based labeling technique, followed by manual correction. We conducted a computational fluid dynamics (CFD) analysis on different retinal vasculature networks derived from a single rat. Various venule and arteriole pressures were applied to mimic the effects of elevated intraocular pressure (IOP), a major glaucoma risk factor. An increase in IOP typically correlates with a decrease in venous pressure. We also varied the percentage of capillary dropout, simulating the loss of blood vessels within the capillary network, by reducing the volume of the normal capillary network by 10%, 30%, and 50%. Based on the output of the CFD analysis, we calculated velocity, wall shear stress (WSS), and pressure gradient for different vasculature densities.ResultsArteriolar pressure, venular pressure, and capillary dropout appear to be important factors influencing wall shear stress in the rat capillary network. Our study revealed that the pressure gradient between arterioles and venules strongly affects the local wall shear stress distribution across the 3D retinal vasculature. Specifically, under a pressure gradient of 3,250 Pa, the wall shear stress was found to vary between 0 and 20 Pa, with the highest shear stress observed in the region of the superficial layer. Additionally, capillary dropout led to a 25% increase or decrease in wall shear stress in affected areas.ConclusionThe hemodynamic differences under various arteriole and venule pressures, along with different capillary dropout conditions, could help explain the development of various optic disorders, such as glaucoma, diabetic retinopathy, and retinal vein occlusion.

Failure characteristics and stress field distribution law of roadway in downward mining of deep close distance coal seam

Deep close distance coal seam mining is affected by the goaf of upper coal and remaining coal pillar, and the roadway of lower coal is difficult to maintain stability. By means of theoretical analysis, physical simulation test and numerical simulation, this paper analyzes the failure characteristics of roadway in deep close distance coal seam and the evolution law of stress field, and optimizes the reasonable layout of lower coal roadway. The results show that: (1) The analytical formula of the evolution of the floor principal stress difference with depth is derived theoretically, and the distribution law of the shear stress of the rock mass in the floor of the coal seam is obtained. (2) The airway below the goaf can maintain good stability. High stress accumulation phenomenon occurs in the transport roadway below the coal pillar, which can not keep stable. (3) Due to the stress difference under the goaf and the coal pillar, the shear stress increases and the rock mass is damaged, and the left gang of the transport roadway is prone to instability destruction. (4) By comparing the distribution characteristics of plastic zones of transport roadway at different locations, it is determined that the transport roadway is more appropriate to be arranged 45 m below the coal pillar from the goaf.

A Century of Deformation and Stress Change on Kīlauea's Décollement

AbstractKīlauea Volcano on Hawai'i Island is host to a complex volcanic and interwoven fault system. Over the last ∼120 years, a range of seismic events, including large earthquakes such as the 1975 7.7 Kalapana earthquake, creep, and slow slip events, have occurred along the décollement underlying Kilauea's south flank. We explore both the deformation and stress changes of Kīlauea from 1896 to 2018 by collating six geodetic data sets and creating an analytical model to determine the dominant deformation sources (i.e., fault planes, rifts, magma chambers) driving this system at different times. The 1975 Kalapana earthquake significantly altered the region's state of stress and deformation; we find the average slip along the décollement was reduced from 10 cm/yr prior, to 4 cm/yr after the rupture. Prior to 1975 no slip is resolved along the décollement where the earthquake nucleated, suggesting that this portion may have been locked leading up to the rupture. After 1975, décollement slip overall is smaller and more irregular, suggesting increased control by spatial variation of mechanical properties. We find increases in shear stress along the Kīlauea décollement and a decrease in normal compressive stress within the East Rift Zone prior to the Kalapana earthquake, creating favorable conditions for failure of the décollement and subsequent magmatic intrusion.

Structure and formation of mud volcanoes in the South Caspian Basin according to seismic data

The South Caspian Basin (SCB) constitutes a classic province to study mud volcanoes and their associated processes. Approximately 280 active mud volcanoes have been documented in the offshore and the onshore areas of Azerbaijan, emitting water, hydrocarbons (oil and mainly methane), and fluidized muds that transport solid fragments from deep sedimentary sequences. Seismic characteristics of mud volcano systems in the Azerbaijan area of the SCB are used to address (1) the nature of the mud volcano source layer; (2) the internal geometry of the feeder systems; and (3) the processes associated with shale mobilization and extrusion. We confirm that the source layer is mainly the Maykop Suite (Oligocene-Lower Miocene), which is a thick (≤3 km) and deep (>10 km) clayey sequence rich in organic matter. This layer was quickly buried due to basin subsidence and the rapid deposition (since the Middle Miocene) of thick fluvio-lacustrine sediments of the Productive Series (PS) (Upper Miocene-Upper Pliocene), which contributed to the creation of high pore pressures and the transformation of organic matter into methane (through thermal cracking). Since the Middle Miocene and more important, during the Upper Pliocene, the Maykop shales mobilized due to an increase in shear stresses and pore pressures, which promoted a decrease in effective stresses and, as a consequence, facilitated the achievement of critical state conditions in the shales that began to flow. This process, repeated over time, allowed multiple pulses of shale mobilization to originate (as in a loading piston system). Shale piercing transporting deep-sourced fluids (and hydrocarbons) was carried out through fractures in the outer arc of anticlines, forming subvertical feeder systems. The mobilized hydrocarbons and fluids also recharged some of the younger and more permeable layers of the PS, creating shallower reservoirs in the vicinities of the mud volcano structures.

Evaluating drinking water treatment residuals as an in-situ capping material for metal-contaminated sediments

This study evaluated drinking water treatment residuals (DWTR) as an in-situ capping material for metal-contaminated sediments using Gust-chamber experiments. Metal release from non-capped and DWTR-capped sediments was measured under increasing shear stress (τ) from 0.05 to 0.4 Pa. Fathead minnow (FHM) juveniles (Pimephales promelas) were exposed to water from these sediments in 96-h bioassays to assess DWTR's efficacy in reducing metal toxicity. Sand was used as an inert capping material for comparison. Diffusive gradients in thin films (DGT) assessed DWTR's impact on vertical metal concentration profiles in sediment pore water and overlying water, with concentrations determined by ICP-MS. Without capping, increasing τ raised metal concentrations in the overlying water from 45 to 95 mg/L for Cd and Zn, 4–10 mg/L for Cu, and 2–4 mg/L for Pb. Sand capping reduced these levels, with Cd and Zn ranging from 4 to 21 mg/L, Cu from 0.26 to 0.63 mg/L, and Pb from 0.051 to 0.23 mg/L. DWTR capping significantly lowered metal concentrations in the overlying water, with Cd ranging from 1 to 8 μg/L, Zn from 30 to 40 μg/L, Cu from 2.5 to 5 μg/L, and Pb from 1 to 2 μg/L. Therefore, beyond the physical barrier effect, the DWTR cap immobilizes metals through other mechanisms such as sorption and precipitation. Bioassays showed that DWTR significantly decreased metal toxicity to FHM, while sand-capped and non-capped sediments caused 100% mortality. DGT confirmed DWTR reduced metal fluxes at the sediment-water interface by up to two orders of magnitude.

Uncovering the Fracturing Mechanism of Granite Under Compressive–Shear Loads for Sustainable Hot Dry Rock Geothermal Exploitation

Shear-dominated hazards, such as induced earthquakes, pose an escalating threat to the sustainability and safety of the geothermal exploitation. Variations in fault orientations and compression–shear stress ratios exert a profound influence on the failure processes underlying these disasters. To better understand these effects on the shear failure mechanisms of hot dry rocks, mode-II fracturing tests on granites were conducted at varying loading angles (specifically, 55°, 60°, 65°, and 70°). These tests were accompanied by a comprehensive analysis of the mechanical properties, energy dissipation behavior, acoustic emission (AE) responses, and digital image correlation (DIC)-extracted displacement fields. The tensile–shear properties of stress-induced microcracks were discerned via AE characteristic parameter analysis and DIC displacement decomposition, and the mode-II fracture energy release rate was quantitatively characterized. The results reveal that with increasing compression–shear loading angles, the mechanical properties of granites are weakened, and the elastic strain energy at peak stress gradually decreases, while the slip-related dissipated energy increases. Throughout the fracturing process, the AE count progressively climbs and reaches a peak near catastrophic failure, with an upsurge in low-frequency and high-amplitude AE events. Microcrack distribution concentrates aggregation along the shear plane, reflecting the emergent displacement discontinuities evident in DIC contours. Both the AE characteristic parameter analysis and DIC displacement decomposition demonstrate that shear-sliding constitutes the paramount mechanism, and the fraction of shear-oriented microcracks and the ratio of tangential versus normal displacement escalate with increases in shear stress. This analysis is supported by the heightened propensity for transgranular microcracking events observed through scanning electron microscopy. As the shear-to-compression stress increases, the energy concentration along the shear band intensifies, with the gradient of the fitting line between cumulative AE energy and slip displacement steepening, indicative of a heightened mode-II energy release rate. These results contribute to a deeper understanding of the mode-II fracture mechanism of rocks, thereby providing a foundational basis for early warnings of shear-dominant geomechanical disasters, and improving the safety and sustainability of subsurface rock engineering.

Local carotid stiffness, hemodynamic forces and blood viscosity in patients with cerebral lacunar infarctions.

The carotid stiffness is an important factor in the pathogenesis of cerebrovascular small vessel disease. Our study aimed to evaluate the relation of the local arterial stiffness of the common carotid artery (CCA) to the hemodynamic forces and blood viscosity in patients with cerebral lacunar infarctions (LI). Twenty-two patients with chronic LI and 15 age-matched controls were examined. An ultrasound examination of the CCA intima-media thickness (IMT), the parameters of local CCA stiffness: distensibility (DC) and compliance coefficients (CC), α and β stiffness indices and pulse wave velocity (PWV) was performed. The local hemodynamic forces were calculated: circumferential wall tension (CWT) and wall shear stress (WSS). Whole blood viscosity (WBV) and shear stresses at shear rates of 0.277 s-1 to 94.5 s-1 were measured in patients and controls. Higher values of IMT, a significant decrease of DC and CC and an increase of α and β stiffness indices and PWV in the LI patients compared to the controls were obtained. A parallel significant increase in CWT and a decrease in WSS was found. An increase in WBV and a significant increase in shear stresses were detected. In the LI patients, the increased stiffness indices were associated with an increase in age, cholesterol and WBV at higher shear rates in the left CCA. In the controls, the IMT and stiffness indices correlated significantly with the hemodynamic factors and WBV in both CCAs, while the stiffness indices correlated with the hemodynamic forces in the left CCA. The results of the present study demonstrate different associations of the local carotid stiffness indices with the hemodynamic forces and WBV in patients with LI and controls.

Monotonic simple shear characteristics of K0 highly over-consolidated and remolded Wenzhou clay

The over consolidated clay is widely distributed in the seabed. Monotonic simple shear tests on K 0 consolidated clays with an over consolidation ratio (OCR) of 1 ∼ 14 were conducted through a multidirectional cyclic simple shear apparatus. The stress–strain relationship, pore pressure evolution, and shear strength variation under different OCRs were revealed, and differences between over and normally consolidated clay were compared. When OCR is below 8, peak values of shear stress and negative excess pore pressure both increase linearly with increasing OCR. However, the peak values tend to stabilize when OCR is above 8. Correspondingly, the occurrences of peak values no longer delay linearly, and the failure line is also shifted towards stronger strengths. An exponential formula is purposed and validated on accordance with numerous experimental data to describe the aforementioned pattern more precisely compared with the traditional power formula. Therefore, shear strengths of over consolidated clays with various OCRs and consolidation pressures can be accurately predicted according to the exponential formula and the shear strength of a normally consolidated sample with a certain consolidation pressure.

Study on the Shear Degradation Law of Polymer Drag Reducing Agents

Abstract The use of drag reducing agents in oil pipeline transportation can reduce driving energy consumption and has certain energy-saving benefits. However, irreversible degradation occurs when polymer drag reducing agents are sheared through pumping. In order to study the viscosity loss of polymer drag reducing agents caused by mechanical shear during the pumping process, the combination of methods such as a rotational rheometer and an indoor drag reducing loop testing system was used to test and analyze the rheological and drag reducing properties of the drag reducing agent solution, and to study the shear degradation law of polymer drag reducing agent solution under different conditions. The results showed that the shear stress of the polymer drag reducing agent solution increased with the increase in shear rate, and the viscosity increased with the increase of shear stress, showing shear thickening. When the polymer drag reducing agent solution is not sheared, the drag reduction rate increases and then decreases with the increase of concentration, and reaches the maximum value at 20 mg·L−1. However, after shear, the drag reduction performance decreases rapidly, but the high concentration still maintains a good drag reduction rate. The research results provide a theoretical basis for improving the performance of polymer drag reducing agents under different operating conditions and play a guiding role in further improving and perfecting the polymer drag reducing technology.

Breaking Strong Alkynyl-Phenyl Bonds: Poly(para-phenylene ethynylene)s under Mechanical Stress.

Stronger chemical bonds withstand higher mechanical forces; thus, the rupture of single bonds is preferred over the rupture of double or triple bonds or aromatic rings. We investigated bond scission in poly(dialkyl-p-phenylene ethynylene)s (PPEs), a fully conjugated polymer. In a scale-bridging approach using electron-paramagnetic resonance spectroscopy and gel permeation chromatography of cryomilled samples, in combination with density functional theory calculations and coarse-grained simulations, we conclude that mechanical force cleaves the sp-sp2 bond of PPEs (bond dissociation energy as high as 600 kJ mol-1). Bond scission primarily occurs in shear bands with locally increased shear stresses. The scission occurs in the middle of the PPE chains. Breaking sp-sp2 bonds into free radicals thus is feasible but requires significant mechanical force and an efficient stress concentration.

Computational Model for Early-Stage Aortic Valve Calcification Shows Hemodynamic Biomarkers.

Heart disease is a leading cause of mortality, with calcific aortic valve disease (CAVD) being the most prevalent subset. Being able to predict this disease in its early stages is important for monitoring patients before they need aortic valve replacement surgery. Thus, this study explored hydrodynamic, mechanical, and hemodynamic differences in healthy and very mildly calcified porcine small intestinal submucosa (PSIS) bioscaffold valves to determine any notable parameters between groups that could, possibly, be used for disease tracking purposes. Three valve groups were tested: raw PSIS as a control and two calcified groups that were seeded with human valvular interstitial and endothelial cells (VICs/VECs) and cultivated in calcifying media. These two calcified groups were cultured in either static or bioreactor-induced oscillatory flow conditions. Hydrodynamic assessments showed metrics were below thresholds associated for even mild calcification. Young's modulus, however, was significantly higher in calcified valves when compared to raw PSIS, indicating the morphological changes to the tissue structure. Fluid-structure interaction (FSI) simulations agreed well with hydrodynamic results and, most notably, showed a significant increase in time-averaged wall shear stress (TAWSS) between raw and calcified groups. We conclude that tracking hemodynamics may be a viable biomarker for early-stage CAVD tracking.

Thermal analysis in unsteady oscillatory Darcy blood flow through stenosed artery

This study aims to provide an extensive overview of the consequences of heat source and thermal radiation on blood flow in stenosed arteries through Casson fluid. We examine the behaviour of an unsteady non-Newtonian fluid under oscillatory Darcy flow. This analysis explores the impact of blood flow in the stenosed arteries on the momentum and energy profiles of the Casson fluid. In addition, this study examines a parametric analysis to illustrate the impact of the Nusselt number and Casson parameter. Higher values of the thermal radiation and Casson-Viscous parameters result in enhanced velocity fields. The Brinkman model accurately represents the resistance to flow caused by the porous material, known as Darcy resistance. The inner space of the coronary artery generates cholesterol-rich fatty plaques and blood clots that block the artery, simulating the diseased condition of blood circulation in this study. We employ a set of non-dimensional variables to convert the governing equations of the current flow into dimensionless partial differential equations. Analytical methods have derived a solution for the studied problem. The discovery is pertinent to the natural circulation of blood through coronary arteries, which are highly porous. A particular artery pathology creates a permeable structure within the arterial lumen. The current study demonstrates that blood flow may be manipulated by adjusting the intensity of the external magnetic field, while the temperature of the blood can be managed by either increasing or decreasing its thermal conductivity. The graphical representation demonstrates the impact of different physical parameters on velocity, temperature, and concentration profiles. The significant results of the current studies are that, the fluid velocity diminishes with rising magnetic and Biot numbers but exhibits an increase when considering the Darcy number and Hall parameter. There is a gentle increase in the wall shear stress as the Casson parameter (β) increases from 0.1 to 0.3. For β= 0.3, the percentage change along the axial direction (x) is more pronounced. This is because the wall shear stress is proportional to the number of Casson parameters.

Alteration of cement rheological properties and setting-hardening: Novel insight into the impact of polyaluminum sulfate

The accelerator significantly influences the setting and hardening performance of shotcrete, in order to develop novel setting components, this study investigates the underlying mechanisms through which polyaluminum sulfate (PAS) facilitates the setting of cement paste. QXRD, Isothermal calorimetry, Zeta potential and Rheological test were employed to analyze the effects of PAS addition on the setting and hardening behavior, hydration kinetics, and rheological properties of cement paste. When the dosage of PAS is 10 %, the initial and final setting times are reduced by 54.39 % and 38.57 % respectively, meanwhile the compressive strength after 6 hours increases by 659.09 %. The influence of PAS on cement setting acceleration and rheological properties were analyzed using the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory and the Water Film Thickness (WFT) theory. PAS leads to an acceleration in particle aggregation rate and an increase in shear stress and plastic viscosity of the cement paste. Furthermore, the accelerated hydration effect of PAS promotes the formation of additional hydration products, strengthens the interparticle connectivity, and facilitates the formation of a rigid network. This study highlights a novel pathway for understanding the rapid setting mechanism of aluminum-based accelerators.

Investigation of turbulence and interfacial exchange features of the gap area within the fully developed Shallow-Submerged canopy flow

The flow patterns within a longitudinal gap area formed by discontinuous distributions of submerged canopy, as well as the momentum and mass exchange characteristics between the gap area and the overlying free-flow, were studied using high-resolution Large Eddy Simulation (LES). The gap area is located within the fully developed region of submerged canopy flow. The simulations considered four aspect ratios of the gap area, L/h (ranging from 1 to 4), where L and h represent the span of the gap area and the height of the canopy, respectively, and two canopy densities, ϕ = 0.08 and 0.15. Results indicate that recirculation vortices appear only at ϕ = 0.15 and penetrate the downstream canopy patches to varying extents, with the distance of invasion decreasing as L/h increases. Influenced by the recirculation vortices, the bed shear stress in the downstream part of the gap area and the initial section of the downstream canopy patch is significantly increased compared to the fully developed region of the upstream canopy patch. Within the parameter range covered, vertical penetration of the mixing layer into the gap area always occurs, consistently falling into the shear layer growth regime, with significant enhancement of turbulence within the gap area even at L/h = 1. The high momentum entrainment elevates longitudinal velocity and turbulence intensity in the upper corner regions of the downstream canopy patch’s leading edge, combined with localized increases in bed shear stress, potentially destabilizing plants at the forefront of the downstream canopy patch. Although the total momentum exchange across the interface between the gap area and the upper free-flow layer is approximately independent of L/h, larger canopy densities lead to stronger momentum transport, and turbulent transport always dominates. Mass exchange generally increases with L/h, with more efficient vertical mass exchange in ϕ = 0.15 cases at L/h = 3 and 4.

Electromagnetohydrodynamic flow and thermal performance in a rotating rough surface microchannel

Rough surfaces in microchannels effectively enhance liquid mixing, thermal performance, and chemical reactions in electrically actuated microfluidic devices. Rotation of the microchannel with surface roughness intensifies this enhancement. We investigate the combined effects of electromagnetohydrodynamics and surface roughness on transient rotating flow in microchannels. We present a mathematical model considering the variable zeta potential, heat transfer characteristics, and entropy generation within the microchannel. We obtain analytical solutions using the separation of variables method and Fourier series expansion. The surface roughness of the microchannel, when combined with rotation, impacts the temperature enhancement. Higher rotation rates result in the formation of multiple vortices. The secondary flow pushes the primary velocity toward the boundary layer, which affects the flow pattern. Surface roughness and electroosmotic flow significantly affect secondary flow, resulting in complex flow patterns and reversals. The interaction between centrifugal and viscous forces results in maximum velocities at the boundary layers. Higher roughness and electromagnetic effects enhance temperature by intensifying fluid-solid friction and joule heating. Surface roughness causes an increase in wall shear stress and friction factor, resulting in a higher Poiseuille number. Moreover, surface roughness increases entropy production by enhancing fluid mixing and internal friction despite improved heat transfer. Higher rotation also elevates entropy generation due to additional vortices induced by secondary flow.

Flame Retardancy and Properties of Thermoplastic Vulcanizates from Dibutyl Phosphate-Bound Natural Rubber/Ethylene Vinyl Acetate Blends

ABSTRACT Dibutyl phosphate-bound epoxidized natural rubber (DBNR) was synthesized from natural rubber latex via epoxidation using a 20 mol% intermediate. Successful formation of epoxidized natural rubber (ENR-20) and DBNR was confirmed by FTIR analysis. Thermoplastic vulcanizates (TPVs) were prepared by dynamically vulcanizing blends of DBNR and ethylene-vinyl acetate copolymer (EVA). The 50/50 DBNR/EVA TPV exhibited higher mixing torque during vulcanization, indicative of increased shear stress, shear rate, and tensile strength. This was attributed to finer dispersion of vulcanized rubber domains in the EVA matrix, leading to enhanced interfacial adhesion. Elongation at break decreased with increasing EVA content, while hardness and tension set increased, suggesting reduced elasticity at higher EVA proportions. Under heat aging, TPVs experienced degradation of mechanical properties and increased tension set, indicating loss of elastomeric behavior. Significantly, DBNR exhibited a low burning rate of 0.2 mm/s, imparting inherent flame retardancy. The burning rate of DBNR/EVA TPVs decreased with increasing DBNR content, demonstrating improved flame retardancy. Overall, DBNR/EVA TPVs exhibited favorable mechanical properties and flame retardancy, making them suitable for applications requiring flame-retardant elastomeric materials.

Variable stiffness performance analysis of layer jamming actuator based on bionic adhesive flaps

Soft actuators made of soft materials cannot generate precisely efficient output forces compared to rigid actuators. It is a promising strategy to equip soft actuators with variable stiffness modules of layer jamming mechanism, which could increase their stiffness as needed. Inspired by the gecko's the array of setae, bionic adhesive flaps with inclined micropillars are applied in layer jamming mechanism. In this paper, after the manufacturing process of the layer jamming actuator based on the bionic adhesive flaps is described, the equivalent stiffness models of the whole actuator are established in the unjammed and jammed states. And the shear adhesive force of a single micropillar is calculated based on the Kendall viscoelastic band model. The finite element simulation results of two bionic adhesive flaps show that the interlaminar shear stress and stiffness increase with the increase of pressure. The measurement of shear adhesive force show that the critical shear adhesive force of the bionic adhesive material is 3.2 times that of polyethylene terephthalate (PET) material, and exhibit the ability of anisotropic adhesion behavior. The variable stiffness performance of the layer jamming actuator based on bionic adhesive flaps is evaluated by three test methods, and the max stiffness reaches 8.027 N mm-1, which is 1.5 times higher than the stiffness of the layer jamming actuator based on the PET flaps. All results of simulation and experiment effectively verify the validity and superiority of applying the bionic adhesive flaps to the layer jamming mechanism to enhance the stiffness.

Rheology and Structure of Model Smectite Clay: Insights From Molecular Dynamics

AbstractThe low frictional strength of smectite minerals, such as montmorillonite, is thought to play a critical role in controlling the rheology and the stability of clay‐rich faults. In this study, we perform molecular dynamics simulations on a model clay system. Clay platelets are simplified as oblate ellipsoids interacting via the Gay‐Berne potential. We study the rheology and structural development during shear in this model system, which is sheared at constant strain rates for 10 strains after compression and equilibrium. We find that the system exhibits velocity‐strengthening behavior over a range of normal stresses from 1.68 to 56.18 MPa and a range of strain rates from 6.93 × 105 to 6.93 × 108/s. The relationship between shear stress and strain rate follows the Herschel‐Bulkley model. Shear localization is observed at lower strain rates despite the velocity‐strengthening friction, while homogeneous shear is realized at higher strain rates. The structure change due to shear is analyzed from various aspects: the porosity, particle orientation, velocity profile, and the parallel radial distribution function. We find that particle rearrangement and compaction dominate at the early stage of shear when the shear stress increases. The shear band starts to form in the later stage as the shear stress decreases and relaxes to a steady‐state value. The structural development at low strain rates is similar to previous experimental observations. The stacking structure is reduced during shear and restores logarithmically with time in the rest period.

Less-deformable erythrocyte subpopulations biomechanically induce endothelial inflammation in sickle cell disease

AbstractSickle cell disease (SCD) is canonically characterized by reduced red blood cell (RBC) deformability, leading to microvascular obstruction and inflammation. Although the biophysical properties of sickle RBCs are known to influence SCD vasculopathy, the contribution of poor RBC deformability to endothelial dysfunction has yet to be fully explored. Leveraging interrelated in vitro and in silico approaches, we introduce a new paradigm of SCD vasculopathy in which poorly deformable sickle RBCs directly cause endothelial dysfunction via mechanotransduction, during which endothelial cells sense and pathophysiologically respond to aberrant physical forces independently of microvascular obstruction, adhesion, or hemolysis. We demonstrate that perfusion of sickle RBCs or pharmacologically-dehydrated healthy RBCs into small venule-sized “endothelialized” microfluidics leads to pathologic physical interactions with endothelial cells that directly induce inflammatory pathways. Using a combination of computational simulations and large venule-sized endothelialized microfluidics, we observed that perfusion of heterogeneous sickle RBC subpopulations with varying deformability, as well as suspensions of dehydrated normal RBCs admixed with normal RBCs, leads to aberrant margination of the less-deformable RBC subpopulations toward the vessel walls, causing localized, increased shear stress. Increased wall stress is dependent on the degree of subpopulation heterogeneity and oxygen tension and leads to inflammatory endothelial gene expression via mechanotransductive pathways. Our multifaceted approach demonstrates that the presence of sickle RBCs with reduced deformability leads directly to pathological physical (ie, direct collisions and/or compressive forces) and shear-mediated interactions with endothelial cells and induces an inflammatory response, thereby elucidating the ubiquity of vascular dysfunction in SCD.

Microstructure and mechanical properties of a severely cold-rolled and annealed dual-phase compositionally complex alloy (CCA) with an exceptionally deformable Laves phase

A novel CCA was designed by substituting Nb in (FCC + C14 Laves) CoCrFeNi2.1(Nb)0.2 CCA by (Hf + Nb + Ta). The (HfNbTa)0.2 CCA was homogenized, heavily cold-rolled, and isothermally annealed at 800 °C and 1000 °C for different time intervals. The (HfNbTa)0.2 alloy revealed the presence of a Hf and Ni enriched cubic C15 Laves phase. The considerations of site occupancy behavior, formation energy, and highly off-stoichiometric composition stabilized the (Hf, Ni) rich cubic C15 Laves phase. In contrast to the brittle hexagonal C14 Laves phase in (Nb)0.2 CCA, the C15 Laves phase in (HfNbTa)0.2 CCA showed exceptional deformability owing to the high propensity for nano-twin formation. Meanwhile, the FCC matrix developed a deformation-induced nano-lamellar structure with a spacing of ∼45 nm. Annealing resulted in ultrafine recrystallized FCC matrix and precipitation of DO19 structured ε nano-precipitates. The isothermal grain growth kinetics revealed a high grain growth exponent (n) ∼7, which confirmed a Zener-drag mediated process due to the ε nano-precipitates. The Hall-Petch analysis of the hardness data showed relatively high friction stress originating from the dissolution of Hf, Nb, and Ta in the FCC matrix. A high Hall-Petch coefficient indicated increased shear stress for plastic flow across the boundaries, resulting from the elongated Laves phase at the boundaries. The highly deformable Laves phase, ultrafine grain size, and ε nano-precipitates resulted in high yield strength (∼975 MPa) and superior ductility (∼16 %) in the (HfNbTa)0.2 CCA, even surpassing the (Nb)0.2 CCA. It was envisaged that strong yet deformable Laves phases could pave the pathway for developing Laves phase-based CCAs for advanced structural applications.