Amount Of Shear Stress Research Articles

A rheological study on nano-bubble assisted flotation of phosphate fine particles

ABSTRACT The application of ultrafine bubbles a.k.a. nano-bubbles (NBs) in upgrading the flotation recovery of fine particles has been extensively investigated from various perspectives over the last two decades. However, their rheological aspect has not been studied yet, which is presented for the first time in this paper. To this end, the current study addresses the effect of six crucial variables including solid content (5%, 15%, and 25% (w/w)), presence and absence of NBs, inner diameter of a Venturi tube (1.5 and 2.2 mm), pH of pulp (4.5–11) and frother dosage (3, 13, and 33 mg/L) on the variation of rheological parameters i.e. shear stress, shear tension, and viscosity. Ultrafine bubbles were generated in a conditioning tank through the hydrodynamic cavitation mechanism using a fatty-acid-based frother (Flo-Y-S), while the rheological responses were continuously monitored and measured by a rheometer and parallel plate spindle (for pulp) and a double gap spindle (for NBs). Flotation tests were conducted on a high-grade phosphate ore (d80 = 37 µm) using a mechanically agitated Denver®-type (D12) flotation cell. The experimental results revealed that fluid behavior without NBs using 13 mg/L frother was in the range of shear rates less than 1 s−1 non-Newtonian and close to the shear thinning state, while it became completely Newtonian in the range of 1 to 1500 s−1. However, the presence of NBs at the same frother content changed this tendency to non-Newtonian and Newtonian fluids at shear rates of <30 s−1 and >30 s−1, respectively. It was also found that either in acidic (5.5) or strong alkaline (11) domains, the pulp viscosity trends were almost close to each other and varied from 0.002−10 to 0.002−4 Pa.s, respectively. On the other hand, on the same trend, the amount was lowered to three times in the neutral range (7.5) and weak alkalinities (9). Diminishing the inner diameter of the Venturi tube from 2.2 mm to 1.5 mm led to an increment of shear stress and viscosity about twice at the shear rates <100 s−1. The results of evaluating frother dosage showed that an increase in the amount of frother dosage, which reduced bubble dimensions, exceeded the viscosity and the amount of shear stress. Finally, we concluded that the rheological properties significantly impacted the selective separation of NB-assisted flotation processes and need further investigations in the future.

The Impact of Rotor Axial Displacement Variation on Simulation Accuracy of Fully Magnetic Levitation Centrifugal Blood Pump.

The rotor axial displacement of the full magnetic levitation blood pump varies with the operating conditions. The effect of rotor axial displacement on simulation results is unclear. This study aimed to evaluate the effect of rotor axial displacement on the predicted blood pump flow field, hydraulic performance, and hemocompatibility through simulation. This study used the CentriMag blood pump as a model, and conducted computational fluid dynamics simulations to assess the impact of rotor displacement. Considering rotor axial displacement leads to opposite results regarding predicted residence time and thrombotic risk compared with not considering rotor axial displacement. Not considering rotor axial displacement leads to deviations in the predicted values, where the effects on the flow field within the blood pump, ratio of secondary flow, and amount of shear stress >150 Pa are significant. The variation in the back clearance of the blood pump caused by the ideal and actual rotor displacements is the main cause of the above phenomena. Given that the rotor axial displacement significantly impacts the simulation accuracy, the effect of rotor axial displacement must be considered in the simulation.

Development of a perfusable, hierarchical microvasculature-on-a-chip model.

Several methods have been developed for generating 3D, in vitro, organ-on-chip models of human vasculature to study vascular function, transport, and tissue engineering. However, many of these existing models lack the hierarchical nature of the arterial-to-capillary-to-venous architecture that is key to capturing a more comprehensive view of the human microvasculature. Here, we present a perfusable, multi-compartmental model that recapitulates the three microvascular compartments to assess various physiological properties such as vessel permeability, vasoconstriction dynamics, and circulating cell arrest and extravasation. Viscous finger patterning and passive pumping create the larger arterial and venular lumens, while the smaller diameter capillary bed vessels are generated through self-assembly. These compartments anastomose and form a perfusable, hierarchical system that portrays the directionality of blood flow through the microvasculature. The addition of collagen channels reduces the apparent permeability of the central capillary region, likely by reducing leakage from the side channels, enabling more accurate measurements of vascular permeability-an important motivation for this study. Furthermore, the model permits modulation of fluid flow and shear stress conditions throughout the system by using hydrostatic pressure heads to apply pressure differentials across either the arteriole or the capillary. This is a pertinent system for modeling circulating tumor or T cell dissemination and extravasation. Circulating cells were found to arrest in areas conducive to physical trapping or areas with the least amount of shear stress, consistent with hemodynamic or mechanical theories of metastasis. Overall, this model captures more features of human microvascular beds and is capable of testing a broad variety of hypotheses.

Effect of Temperature, pH and Some Salts on Physicochemical and Rheological Properties of &lt;i&gt;Nettle seed gum (NSG)&lt;/i&gt;

Nettle seed gum (NSG) or Urtica pilulifera is a novel source of hydrocolloid, in this study the physicochemical, structural, functional and rheological properties of Urtica pilulifera seed mucilage were compared with gum arabic and pectin. functional properties, water absorbance was significantly affected by temperature and with increasing temperature, water absorbance increased. In the study of urtica pilulifera oil absorbance, Urtica pilulifera had a very low oil absorbance, which can make this gum suitable for use in frying products. In the stability study, the emulsion of Urtica pilulifera mucilage was significantly higher compared to pectin and gum arabic. On the other hand, with increasing temperature, the stability of Urtica pilulifera emulsion decreased. The effect of pH on emulsion stability was also observed. Urtica pilulifera mucilage has the highest stability at pH 5. With increasing the concentration of gum, the amount of surface tension in all samples decreased and pectin gum had the highest surface tension in all concentrations. In investigating the effect of temperature and pH on particle size distribution at 70°C, pH changes had the greatest effect on particle size distribution and increased with decreasing pH, particle diameter. In the study of rheological behavior at all concentrations, with increasing shear rate, the amount of shear stress also increased and with increasing concentration, the flow behavior changed to non-Newtonian fluids or pseudoplastic. In the study of mucilage structure using FTIR, many peaks have been observed, the most important of which are related to the tensile vibrations of the hydroxyl group (fat, protein and carbohydrate), ketone groups (fat, pectin, aromatic ring with CH bond) Also to investigate the possibility of using Urtica pilulifera mucilage in foods that are exposed to low temperatures Freezing test and freezing removal were performed on it After freezing, this emulsion was unstable and completely broke.

A bioprinted composite hydrogel with controlled shear stress on cells.

In recent decades, three dimensional (3D) bio-printing technology has found widespread use in tissue engineering applications. The aim of this study is to scrutinize different parameters of the bioprinter - with the help of simulation software - to print a hydrogel so much so that avoid high amounts of shear stress which is detrimental for cell viability and cell proliferation. Rheology analysis was done on several hydrogels composed of different percentages of components: alginate, collagen, and gelatin. The results have led to the combination of percentages collagen:alginate:gelatin (1:4:8)% as the best condition which makes sol-gel transition at room temperature possible. The results have shown the highest diffusion rate and cell viability for the cross-linked sample with 1.5% CaCl2 for the duration of 1 h. Finally, we have succeeded in printing the hydrogel that is mechanically strong with suitable degradation rate and cell viability.

Computational modeling of media flow through perfusion-based bioreactors for bone tissue engineering.

Bioreactor system has been used in bone tissue engineering in order to simulate dynamic nature of bone tissue environments. Perfusion bioreactors have been reported as the most efficient types of shear-loading bioreactor. Also, combination of forces, such as rotation plus perfusion, has been reported to enhance cell growth and osteogenic differentiation. Mathematical modeling using sophisticated infrastructure processes could be helpful and streamline the development of functional grafts by estimating and defining an effective range of bioreactor settings for better augmentation of tissue engineering. This study is aimed to conduct computational modeling for newly designed bioreactors in order to alleviate the time and material consuming for evaluating bioreactor parameters and effect of fluid flow hydrodynamics (various amounts of shear stress) on osteogenesis. Also, biological assessments were performed in order to validate similar parameters under implementing the perfusion or rotating and perfusion fluid motions in bioreactors' prototype. Finite element method was used to investigate the effect of hydrodynamic of fluid flow inside the bioreactors. The equations used in the simulation to calculate the velocity values and consequently the shear stress values include Navier-Stokes and Brinkman equations. It has been shown that rotational fluid motion in rotating and perfusion bioreactor produces more velocity and shear stress compared with perfusion bioreactor. Moreover, implementing the perfusion together with rotational force in rotating and perfusion bioreactors has been shown to have more cell proliferation and higher activity of alkaline phosphatase enzyme as well as formation of extra cellular matrix sheet, as an indicator of bone-like tissue formation.

Pressure‐Driven Poiseuille Flow: A Major Component of the Torque‐Balance Governing Pacific Plate Motion

AbstractThe Pacific Plate is thought to be driven mainly by slab pull, associated with subduction along the Aleutians‐Japan, Marianas‐Izu‐Bonin, and Tonga‐Kermadec trenches. This implies that viscous flow within the sub‐Pacific asthenosphere is mainly generated by overlying plate motion (i.e., Couette flow) and that the associated shear stresses at the lithosphere's base are resisting such motion. Recent studies on glacial isostatic adjustment and lithosphere dynamics provide tighter constraints on the viscosity and thickness of Earth's asthenosphere and, therefore, on the amount of shear stress that asthenosphere and lithosphere mutually exchange, by virtue of Newton's third law of motion. In light of these constraints, the notion that subduction is the main driver of present‐day Pacific Plate motion becomes somewhat unviable, as the pulling force that would be required by slabs exceeds the maximum available from their negative buoyancy. Here we use coupled global models of mantle and lithosphere dynamics to show that the sub‐Pacific asthenosphere features a significant component of pressure‐driven (i.e., Poiseuille) flow and that this has driven at least 50% of the Pacific Plate motion since, at least, 15 Ma. A corollary of our models is that a sublithospheric pressure difference as high as ±50 MPa is required across the Pacific domain.

Using lower extremity muscle activity to obtain human ankle impedance in the external–internal direction

The human ankle has a critical role in locomotion and estimating its impedance is essential for human gait rehabilitation. The ankle is the first major joint that regulates the contact forces between the human body and the environment, absorbing shocks during the stance, and providing propulsion during walking. Its impedance varies with the level of the muscle activation. Hence, characterizing the complex relation between the ankle impedance and the lower leg’s muscle activation levels may improve our understanding of the neuromuscular characteristics of the ankle. Most ankle–foot prostheses do not have a degree of freedom in the transverse plane, which can cause high amounts of shear stress to be applied to the socket and can lead to secondary injuries. Quantifying the ankle impedance in the transverse plane can guide the design for a variable impedance ankle–foot prosthesis that can significantly reduce the shear stress on the socket. This paper presents the results of applying artificial neural networks (ANN) to learn and estimate the relation between the ankle impedance in the transverse plane under non-load bearing condition using electromyography signals (EMG) from the lower leg muscles. The Anklebot was used to apply pseudorandom perturbations to the human ankle in the transverse plane while the other degrees of freedom (DOF) in the sagittal and frontal planes were constrained. The mechanical impedance of the ankle was estimated using a previously proposed stochastic identification method that describes the ankle impedance as a function of the applied disturbances torques and the ankle motion output. The ankle impedance with relaxed muscles and with the lower leg’s muscle activations at 10 and 20% of the maximum voluntary contraction were estimated. The proposed ANN effectively predicts the ankle impedance within 85% accuracy (±5 Nm/rad absolute) for nine out of ten subjects given the root-mean-squared (rms) of the EMG signals. The main contribution of this paper is to quantify the relationship between lower leg muscle EMG signals and the ankle impedance in the transverse plane to pave the way towards designing and controlling this degree of freedom in a future ankle–foot prosthesis.

NUMERICAL SIMULATION OF THE EFFECT OF VENOUS NEEDLE'S FLOW ON FLOW PARAMETERS OF HEMODIALYSIS GRAFT AND ITS HEMODYNAMIC CONSEQUENCES

Arterio-Venous (AV) grafts which are used for hemodialysis, frequently develop intimal hyperplasia (IH) in venous anastomosis and ultimately leads to graft failure which is the major cause of morbidity and mortality in patients with the end stage renal disease (ESRD). Although the high AV access blood flow has been implicated in the pathogenesis of graft stenosis, the potential role of needle turbulence during hemodialysis is relatively unexplored. In the current study, a numerical survey is carried out to investigate the effect of venous needle's flow on hemodynamic parameters of the flow inside a hemodialysis graft. Two cases include the individual graft flow and the graft flow combined with a needle flow which both of them are evaluated and their results are compared to the cell morphology are represented in this research. Blood is considered as an incompressible Newtonian fluid with density of 1050 [Kg/(m3)] and dynamic viscosity of 0.0035 [Pa.s] and the graft was considered as a rigid vessel due to its low compliance. Flow rates were considered 500 and 100 [mL/min] as inlet conditions of the graft and the needle, respectively. Results show that the presence of the needle's flow causes to increase the amount of shear stress and nonuniformity of the shear stress distribution on the graft wall, where the cell alignment is lost in the presence of needle flow. These findings suggest the presence of potential relationship between venous needle flow during hemodialysis and endothelial dysfunction which may lead to vascular injury and graft failure.

Evaluation of the Thickness and Bond Quality of Three-Layered Media using Zero-Group-Velocity Lamb Waves

Bonding conditions such as jointing agent thickness and bond strength (quality) at the interface between two components is a critical concern in an assembled product because the jointing area is often the weakest component in products. Using a laser ultrasonic technique, zero-group-velocity (ZGV) Lamb waves were utilized to characterize the thickness of an adhesive layer for an epoxy-bonded sample and the bond quality for brazed samples. Using two modes of the ZGV Lamb waves, the thickness of the adhesive layer ranging from 0.2 to 0.8 mm can be estimated with high accuracy. In bond quality measurements, poor bond quality lowered the frequency of ZGV Lamb waves. The decrease in the frequency depended on the amount of shear stress along the interface caused by ZGV Lamb waves.

Numerical evaluation of interfibre joint strength measurements in terms of three-dimensional resultant forces and moments

The interfibre joint is one of the key elements in creating the strength of self-binding fibrous materials such as paper and board. In order evaluate the strength properties of interfibre joints using direct measurements, a greater understanding on how the mode of loading influences the results is desirable. The methods reported in the literature do not in general distinguish between the contributions of normal and shear stresses in the bonded region. This paper presents a numerical analysis procedure, based on the finite element method, for evaluating interfibre joint strength measurements in terms of the normal, shear, and moment loading components during testing. The target is to estimate the resultant forces and moments, that acts in the interfibre joint region at rupture, of Kraft pulp interfibre joints tested under two principally different modes of loading. The results show that for a typical interfibre joint test, modes of loading other than pure shear cannot, in general, be neglected, and are strongly dependent on the structural geometry of the fibre–fibre crosses. In addition, the resultant forces and moments were scaled in terms of the interface area and the twisting and bending resistance of the interface approximated as an ellipse to account for differences in interface area between the measurements. These scaled resultants were used to quantify how the mode of loading influences the relation between the amount of normal stress and the amount of shear stress that develop in the interfibre joint.

Application of a Hydraulic Gradient Technique for Modeling the Uplift Behavior of Piles in Sand

Abstract A scale modeling technique is presented for simulating the uplift behavior of piles in sand, which satisfies stress and strain similitude with full-scale prototypes. A hydraulic gradient approach was used to increase the body forces in the scale model tests, until the stresses became representative of reasonable field-scale conditions. The associated model scaling laws that are used with this technique are presented and discussed. Eight pile pullout tests were conducted, at varying magnitudes of hydraulic gradient; one of these tests was conducted on a pile instrumented with strain gages. From the results of this study, it was concluded that the hydraulic gradient technique can be effectively applied to induce reasonable prototype stresses in a scale model, allowing for reasonable simulation of the uplift behavior of piles in sand. The hydraulic gradient technique was found to be particularly sensitive to the distribution of the hydraulic gradient in the soil profile, which is not surprising, given the nature of the scaling laws for this particular modeling technique. Analysis of the results from the pile instrumented with strain gages indicated that (1) very little shear stress was mobilized in the upper 25 % of the pile, even at applied uplift loads approaching the ultimate pullout force; (2) the largest amount of shear stress for each applied uplift force was typically mobilized at a point somewhere between 60 % and 80 % of the length of the pile; and (3) at failure, the mobilized shear stress distribution was clearly not triangular, as is postulated by commonly used pile uplift design approaches. Post-failure investigations conducted after the completion of each pullout test indicated that the failure shear surface in each of the model tests developed along the pile-soil interface.

Shear Control of Elastomer Shear Pads for Variable Remote Center Compliance

Research is performed to design a new variable remote center compliance (VRCC) device with elastomer shear pads (ESP) for robot assembly. The proposed ESP VRCC has a shear controller that can change the fixed point on the top side of the ESP which is attached to the upper plate of the VRCC while the bottom side remains fixed. In this case, the ESP is under shear stress, while the axial/lateral stiffness of the ESP changes according to the amount of shear stress. Therefore, the position of the compliance center can be controlled with the shear controller because the axial/lateral stiffness of the ESP is one of the design parameters that determines the position of the compliance on the ESP VRCC. To verify the effectiveness of the proposed design, the stiffness variation of the ESP and the position of the compliance center of the new VRCC are measured at various shear stresses.

Ageing and vascular adrenoceptor desensitization: too little, too late?

Ageing and vascular adrenoceptor desensitization: too little, too late?

Cardiovascular physiology during fetal development and implications for tissue engineering.

Shear stress in fluid dynamics has a well-known impact on vascular cell morphology, proliferation, orientation, and the organization and composition of extracellular matrix. There is an increasing interest in the field of tissue engineering to use defined shear stress in bioreactors for tissue conditioning and guided tissue formation. Especially for cardiovascular structures like heart valves or blood vessels, the type and appropriate amount of shear stress needed to improve tissue formation remains speculative. The authors believe that fetal-like conditions may be more optimal for new tissue formation in a bioreactor. The purpose of this review is to delineate parameters of cardiovascular physiology during embryonic and fetal development that may have a potential impact on the design and setting of bioreactors for cardiovascular tissue engineering.

A reexamination of the performance of demagnetizing coils on finely ground natural magnetite

Since the last period of intensive study of the demagnetization process for magnetite during the 1950s, our understanding of the physical basis of the magnetism of small particles has increasing exponentially. In light of this improved understanding, the demagnetization process, particularly as applied to finely ground particles of natural magnetite, was reexamined. Magnetometer measurements showed that the coercivity and remanent magnetization increase markedly as the particle size decreases below 10 μm. Although industry-standard 60-Hz demagnetizing coils reduced the remanent magnetization of these particles to a significant extent, the particles remained strongly magnetized, forming magnetic agglomerates of 100 particles or more under quiescent conditions. Although in previous work with high-coercivity synthetic magnetite, it had been found that increasing the strength and frequency of the applied field gave improved demagnetization, applying the same conditions to finely ground natural magnetite gave no significant improvement. The sizable remanent magnetization of the fine natural magnetite particles after all known demagnetization processes is a fundamental property related to the limited number of magnetic domains in each particle. Whether these particles behave as individual particles or as larger agglomerates in any particular unit operation depends upon the amount of shear stress to which the particles are subjected.

Viscoelastic material behavior: models and discretization used in process simulator DIOS

It is a known fact that melted glass, such as SiO/sub 2/, shows viscoelastic behavior. But in the range of processing temperatures the mechanical properties of SiO/sub 2/ vary strongly. While below 800/spl deg/C the material behaves like an elastic solid, at temperatures above 1000/spl deg/C it shows nearly pure viscous properties. In this paper, the governing equation, the so-called constitutive equation, describing viscoelastic behavior, and its discretization are presented. The oxide viscosity depends on the local amount of shear stresses which leads to inhomogeneous material behavior and a nonlinear theory. This new mechanical model was implemented into the process simulator DIOS-ISE. Some obtained simulation results are shown and discussed.

Deviatoric stress accumulation and vertical motions forced by lithospheric density anomalies

Abstract We built a viscoelastic model earth that is appropriate to study the rate of vertical motion and shear stress accumulation driven by lithospheric density anomalies. The lateral extension of these heterogeneities is allowed to vary in the lateral direction to simulate tectonic transport. This model accounts for the effects of sphericity and discontinuities of tectonic phases. Our approach is different from the one followed by Quinlan and Beaumont (1984) and Jordan (1981) in which attention was drawn to the total deflection of the lithosphere beneath the overthrust. We provide the explicit expression for the inverse of the fundamental matrix entering the solution of the system for ordinary differential equations that control the time dependent deformation of an incompressible, viscoelastic solid in spherical symmetry. We found that sphericity plays a crucial role for vertical motions induced by elongated lithospheric anomalies of hundreds of kilometers. When the model is applied to the study of vertical deformation due to the overthrusting of the Apennines in the Mediterranean region, we obtained a lithospheric viscosity ranging between 10 22 –10 23 Pa·s, with the subsidence of the plate underlying the active front of the overthrust around 0.5 – 1.0 mm/year. This is consistent with the amount of sedimentation in the Adriatic foredeep. We analyzed the effects of discontinuities in the tectonic phases on vertical movements in collision zones. We discovered that the rate of vertical motion is a very sensitive function of lithospheric viscosity, horizontal velocity of overthrusting and timing of tectonic phases. We thus found a strong correlation between horizontal and vertical motions: this result suggests that altimetric geodetic surveying along levelling lines of a few hundred kilometers can constrain the tectonic style of a geologic region. Crustal deformation data obtained from satellite missions will provide another set of information on the horizontal motions that are needed in our modelling. Wegener/Medlas project will furnish, in the future, geodetic data on the relative velocities between different plates in the Mediterranean region (Wilson et al. , 1985). Analysis of the stress field induced by an overthrusting load shows that principal stress differences of a few bars can be accumulated on a time scale of 10 2 –10 3 year. These findings are consistent with the stress drop and recurrence times of the earthquakes in the northern Apennines. We conclude that lateral density variations are less effective in triggering earthquakes when comparison is made with other mechanisms, such as transcurrent motions along active plate margins. Discontinuity of tectonic phases plays an important role in controlling the amount of shear stress due to density anomalies.

Scanning Electron Microscopic Analyses of Fiber Reinforced Metals

Recent scanning electron microscopic analyses have shown the comparison of the apparent failure modes of biaxially loaded boron reinforced aluminum composites versus uniaxial, off-axis tensile loading. Additionally, degradation of the longitudinal mechanical properties of both boron reinforced aluminum and Borsic reinforced titanium has been correlated with the growth of deleterious reaction products formed during diffusion bonding of plate and tubular specimens.Combined loading composite theory has been based on off-axis tensile and beam specimens relying on Mohr's Circle transformation of stress to introduce designated stress ratios of ‘transverse to longitudinal stresses. Inherent in these transformations is the high amount of shear stresses applied to the orthotropic axes of the material. Figure 1 shows the fracture surface of off-axis tensile specimens depicting the variation in failure mode from filament normal tensile failure at 5° to matrix and interface shearing at 15° to matrix tensile failure at 90°.