Viscoelastic Parameters Research Articles

Viscoelastic parameters derived from multifrequency MR elastography for depicting hepatic fibrosis and inflammation in chronic viral hepatitis

ObjectivesThe capability of MR elastography (MRE) to differentiate fibrosis and inflammation, and to provide precise diagnoses is crucial, whereas the coexistence of fibrosis and inflammation may obscure the diagnostic accuracy.MethodsIn this retrospective study, from June 2020 to December 2022, chronic viral hepatitis patients who underwent multifrequency MRE (mMRE) were included in, and further divided into, training and validation cohorts. The hepatic viscoelastic parameters [shear wave speed (c) and loss angle (φ) of the complex shear modulus] were obtained from mMRE. The logistic regression and receiver operating characteristic (ROC) curves were generated to evaluate performance of viscoelastic parameters for fibrosis and inflammation.ResultsA total of 233 patients were assigned to training cohort and validation cohorts (mean age, 52 years ± 13 (SD); 51 women; training cohort, n = 170 (73%), and validation cohort, n = 63 (27%)). Liver c exhibited superior performance in detecting fibrosis with ROC (95% confidence interval) of ≥ S1 (0.96 (0.92–0.99)), ≥ S2 (0.86 (0.78–0.92)), ≥ S3 (0.89 (0.84–0.95)), and S4 (0.88 (0.83–0.93)). Similarly, φ was effective in diagnosing inflammation with ROC values of ≥ G2 (0.72 (0.63–0.81)), ≥ G3 (0.88 (0.83–0.94)), and G4 (0.92 (0.87–0.98)). And great predictive discrimination for fibrosis and inflammation were shown in validation cohort (all AUCs > 0.75).ConclusionThe viscoelastic parameters derived from multifrequency MRE could realize simultaneous detection of hepatic fibrosis and inflammation.Critical relevance statementFibrosis and inflammation coexist in chronic liver disease which obscures the diagnostic performance of MR elastography, whereas the viscoelastic parameters derived from multifrequency MR elastography could realize simultaneous detection of hepatic fibrosis and inflammation.Key points• Hepatic biomechanical parameters derived from multifrequency MR elastography could effectively detect fibrosis and inflammation.• Liver stiffness is useful for detecting fibrosis independent of inflammatory activity.• Fibrosis could affect the diagnostic efficacy of liver viscosity in inflammation, especially in early-grade of inflammation.Graphical

Analysis of Love-type wave in a piezoelectric layer bonded between fiber-reinforced viscoelastic and dual porous media

Love-type wave propagation in a piezoelectric layer bonded by a layer of fiber-reinforced viscoelastic and a heterogeneous fluid-saturated cracked dual porous half-space is investigated in this paper. The heterogeneity of fracture double porous medium is assumed to be exponential distribution functions. With the help of the variable separation technique, the governing equations of each layer and half-space are solved to get the solutions of mechanical displacement and electric potential function. The results are confirmed by comparison with the classical case of Love wave, and special cases of the problem are also discussed. The phase velocity is calculated numerically and plotted graphically for various material characteristics of the layers and half-space. The analysis reveals that the phase velocity rises with an increase in viscoelastic parameters and the dielectric constant, as well as the reinforcement parameters, while it decreases with an increase in the inhomogeneity parameter, piezoelectric constant, and thickness ratio parameter. A comparative study has also been conducted to analyze the effect of these parameters on the phase velocity using two piezoelectric materials, PZT-4 and PZT-7. The importance of parameter effects increases for Love-type waves with shorter wavelengths and small guiding layer thicknesses.

Characterization on the mesostructural properties of asphalt mixtures based on meso-element equivalence method

The randomness and variation of material composition at the meso-scale lead to some limitations in the application of asphalt mixture. When all features are taken into account, the computational effort increases significantly. Therefore, the relationship can be established using the meso-element equivalence method (MEEM). In this paper, the effects of aggregate-asphalt interface, initial void defects and material damage were introduced and MEEM of asphalt mixture was established based on industrial computed tomography (ICT) and finite element method (FEM). The rationality of the model was verified by laboratory performance tests, and the effects of aggregate type, mixture gradation and mesostructural parameters on the mechanical response of MEEM were compared and analyzed. The results showed that the MEEM model captures the mechanical behavior of asphalt mixtures well, the input of visco-elastic material parameters is an important step of MEEM simulation accuracy. The aggregate type, the discrete degree of the skeleton structure and the distribution characteristics of mesostructural parameters are important factors affecting the mechanical properties of asphalt mixture in MEEM.

Evaluation of viscoelastic parameters and photo-based assessment of newly developed dermal substitutes modified with thermostabilized fibroblast growth factor 2

BackgroundThe purpose of dermal substitutes is to mimic the basic properties of the extracellular matrix of human skin. The application of dermal substitutes to the defect reduces the formation of hypertrophic scars and improves the scar quality. This study aims to develop an original dermal substitute enriched with stable fibroblast growth factor 2 (FGF2-STAB®) and test it in an animal model. MethodsDermal substitutes based on collagen/chitosan scaffolds or collagen/chitosan scaffolds with nanofibrous layer were prepared and enriched with FGF2-STAB® at concentrations of 0, 0.1, 1.0, and 10.0 µg ‧ cm-2. The performance of these dermal substitutes was tested in vivo on artificially formed skin defects in female swine. The outcomes were evaluated using cutometry at 3 and 6 months. In addition, visual appearance was assessed based on photos of the scars at 1-month, 3-month and 6-month follow-ups using Yeong scale and Visual Analog Scale. ResultsThe dermal substitute was fully integrated into all defects and all wounds healed successfully. FGF2-STAB®-enriched matrices yielded better results in cutometry compared to scaffolds without FGF2. Visual evaluation at 1, 3, and 6 months follow-ups detected no significant differences among groups. The FGF2-STAB® effectiveness in improving the elasticity of scar tissues was confirmed in the swine model. This effect was independently observed in the scaffolds with nanofibres as well as in the scaffolds without nanofibres. ConclusionThe formation of scars with the best elasticity was exhibited by addition 1.0 µg ‧ cm-2of FGF2-STAB® into the scaffolds, although it had no significant effect on visual appearance at longer follow-ups. This study creates the basis for further translational studies of the developed product and its progression into the clinical phase of the research.

Activation energy analysis of mobile microorganisms using conductive nanofluid flows: Mitigating toxic algal blooms in biotechnology applications

Motile microorganisms play a central role in ecosystems in both natural habitats and laboratory settings. Their contribution to nutrient cycling is crucial and their impact on human health can be significant. Furthermore, they are promising in various biotechnological applications. Ongoing studies of microbial motility represent a dynamic and evolving field of research with profound implications for our understanding of biology, ecology, and environmental science. The thermal properties of the base material are extremely advanced and enable a wide range of industrial, technical and process applications due to their thermal radiation, variable heat transfer properties and activation energy. Researchers are still working hard to find renewable energy sources that are both economical and environmentally friendly. In this regard, the past decade has seen growing interest in the potential of nanoparticles as renewable energy sources. The current study aimed to learn more about the rheological properties of thixotropic nanofluids on the surface of Riga surrounded by rotating bacteria. For this, theoretical investigations have been performed on 3D magneto-hydrodynamic micropolar-based Casson nanofluid on the surface of Riga surrounded by rotating bacteria. The influence of thermal radiation, activation energy and heat generation are considered in the present scenario. The rheology of Brownian motion, micro rotation and thermophoresis also accounted for. Classical equations of motion in the form of PDEs are transformed into ODEs by applying similarity variables. The converted ODEs are then solved with the help of a shooting algorithm using Bvp4c MATLAB software. From an engineering point of view, the impression of physical flow parameters dimensionless profiles is demonstrated graphically and in the form of tables. The outcomes show that enhancing the porosity parameter significantly reduces the velocity profiles while the opposite behaviour is noted for the viscoelastic parameter. Moreover, temperature and concentration fields are boosted by thermophoresis and concentration exponents. Present results are validated with the existing ones. The current study has the potential to improve the stability achieved by the bioconvection of nanomaterials.

The consolidation behavior of layered fractional viscoelastic soils considering groundwater

AbstractThis paper investigates the consolidation behavior of multi‐layered viscoelastic soils considering groundwater. First, the fractional Merchant viscoelastic model is introduced to describe the behavior of multi‐layered viscoelastic soils considering groundwater. Later, the governing equations are extended to a viscoelastic medium by virtue of the elastic‐viscoelastic corresponding principle in the Laplace–Hankel domain. According to the extended precise integration method, the soil layer is divided into a series of layer units. Then the relationship between general stress vector and general displacement vector on the top and bottom planes is established. Every two adjacent layer units are combined into one layer in each computational iteration. The solutions in the Laplace–Hankel domain are obtained by considering the boundary conditions, and numerical inversion is performed to obtain the solutions in the physical domain. The practicability of the present method is assessed by comparing the numerical results with those in the existing literature and done by ABAQUS. Finally, the effects of groundwater table, properties of the soils above groundwater table, load depth, viscoelastic parameters, and soil stratification are investigated.

Changes in the electrical and viscoelastic parameters of erythrocytes in patients with manifestations of metabolic syndrome, COVID-19 convalescents, when exposed to citicoline in an in vitro experiment

Aim. To study changes in the electrical and viscoelastic parameters of erythrocytes using the method of dielectrophoresis in patients with manifestations of the metabolic syndrome who underwent COVID-19, when exposed to the drug citicoline in an in vitro experiment to reduce the severity of microcirculatory disorders.
 Materials and methods. 31 men were examined with manifestations of metabolic syndrome (50.6±9.9 years), COVID-19 convalescences, within 8 to 12 months after the disease, the diagnosis was confirmed by PCR, ELISA. The electrical and viscoelastic parameters of erythrocytes were studied by dielectrophoresis twice: the initial levels of indicators were determined and after 30 minutes of exposure with after 30 minutes of exposure to a solution of the drug Ronocyte (oral solution with the active substance citicoline sodium – 104.50 mg., which is equivalent to 100.00 mg citicoline at a concentration of 0.01 µl per 0.3 µl of red blood cell suspension in 0.3M sucrose solution (pH 7.36).
 Results. Exposure of erythrocyte suspension of patients with Ronocyte solution led to change in the levels of electrical, viscoelastic parameters: an increase in the average cell diameter (p=0.0003), the proportion of discocytes (p=0.0004), the amplitude of cell deformation at high frequencies of the electric field (p=0.000002), cell capacity (p=0.000007), the velocity of erythrocytes to the electrodes (p=0.003), dipole moment (p=0.002), polarizability at 106 and 0.5×106 Hz (p=0.000019 and p=0.0015, respectively), relative polarizability (p0.05) and, conversely, to reduce summarized rigidity (p=0.000003), viscosity (p=0.000002), electrical conductivity (p0.000001), aggregation indices (p=0.00003), destruction at frequencies of 106 Hz (p=0.003), 0.5x106 Hz (p=0.00002), 0.1×106 Hz (p0.00001), polarizability at low frequencies of the electric field (p=0.02). Under the influence of the drug, the equilibrium frequency of erythrocytes shifted to the low-frequency range compared to the initial values (p0.0000001). The revealed changes indicate an increase in the surface charge of erythrocytes, their ability to deform, and cell resistance under the action of citicoline.
 Conclusion. For the first time, the effect of the drug with the active substance citicoline, improving the rheological properties of erythrocytes, was discovered. Preparations with the active substance - citicoline should be considered promising for conducting a full-fledged clinical study to study the reduction of circulatory disorders at the microcirculatory level in patients with manifestations of metabolic syndrome who have undergone COVID-19 coronavirus infection.

Electromagnetic thermo-viscoelastic response of piezoelectric rods considering memory dependent effects

Based on the theory of nonlocal elasticity and nonlocal heat conduction, a new dual-phase-lag heat conduction model with memory dependent effect is proposed in this article to explore the thermodynamic behavior of functionally graded rotating piezoelectric rods under the action of moving heat sources. Assuming that the material properties of functionally graded piezoelectric rods vary exponentially along the length direction, the end of the rod is rigid and fixed without voltage. Use Laplace transform to transform the problem into the spatial domain and perform analytical solutions, then use inverse Laplace transform to obtain the time-domain solution. Numerical solutions were performed for dimensionless displacement, temperature, electric potential, and stress, and the variation patterns of the physical quantities involved were described in graphical form. The calculation provides the effects of functional gradient non-uniformity index, thermal nonlocal parameters, kernel function, and viscoelastic parameters on the physical quantities involved.

Evaluation of Robustness of S-Transform Based Phase Velocity Estimation in Viscoelastic Phantoms and Renal Transplants.

Ultrasound shear wave elastography (SWE) methods are being used to differentiate healthy versus diseased tissue on the basis of their viscoelastic mechanical properties. Tissue viscoelasticity is often studied by analyzing shear wave phase velocity dispersion curves, which is the variation of phase velocity with frequency or wavelength. Recently, a unique approach using a generalized Stockwell transformation (GST-SFK) was proposed for the calculation of dispersion curves in viscoelastic media over expanded frequency band. In this work, the method's robustness was evaluated on data from five custom-made viscoelastic tissue-mimicking phantoms and sixty in vivo renal transplants. For each phantom, 15 shear wave motion data acquisitions were taken, while 10-13 acquisitions were acquired for renal transplants measured in the renal cortex. For each data-set mean and standard deviation (SD) of estimated phase velocity dispersion curves were studied. In addition, the viscoelastic parameters of the Zener model were examined, which were preceded by a convergence analysis. For viscoelastic phantoms scanned with a research ultrasound scanner, and for the in vivo renal transplants scanned with a clinical scanner, the decisive advantage of the GST-SFK method over the standard two-dimensional Fourier transform (2D-FT) method was shown. The GST-SFK method provided dispersion curve estimates with lower SD over a wider frequency band in comparison to the 2D-FT method. These advantages are relevant to the analysis of the mechanical properties of tissues in clinical practice to discriminate healthy from diseased tissue.

Characterization of rabbit corneal biomechanical properties after corneal refractive surgery based on rapid loading-unloading uniaxial tensile test

In order to understand how the biomechanical properties of rabbit cornea change over time after corneal ablation, 21 healthy adult rabbits were used in this study, with the left eye as experimental side and the right eye as the control side. Firstly, a lamellar knife was used to remove a portion of the anterior corneal surface tissue (30%~50% of the original corneal thickness) from the left eye of each rabbit, as an animal model simulating corneal refractive surgery. Secondly, postoperative experimental rabbits were kept for one, three, or six months until being euthanized. Strip specimens were produced using their corneas in vitro to perform a uniaxial tensile test with an average loading-unloading rate of approximately 0.16 mm/s. Finally, the visco-hyperelastic material constitutive model was used to fit the data. The results showed that there was a significant difference in the viscoelastic parameters of the corneas between the experimental and the control eyes at the first and third postoperative months. There was a difference in tangential modulus between the experimental and the control eyes at strain levels of 0.02 and 0.05 at the third postoperative month. There was no significant difference in biomechanical parameters between the experimental and the control eyes at the sixth postoperative month. These results indicate that compared with the control eyes, the biomechanical properties of the experimental eyes vary over postoperative time. At the third postoperative month, the ratio of corneal tangential modulus between the experimental and the control eyes significantly increased, and then decreased. This work lays a preliminary foundation for understanding the biomechanical properties of the cornea after corneal refractive surgery based on rapid testing data obtained clinically.

A comparison of brain retraction mechanisms using finite element analysis and the effects of regionally heterogeneous material properties

Finite element (FE) simulations of the brain undergoing neurosurgical procedures present us with the great opportunity to better investigate, understand, and optimize surgical techniques and equipment. FE models provide access to data such as the stress levels within the brain that would otherwise be inaccessible with the current medical technology. Brain retraction is often a dangerous but necessary part of neurosurgery, and current research focuses on minimizing trauma during the procedure. In this work, we present a simulation-based comparison of different types of retraction mechanisms. We focus on traditional spatulas and tubular retractors. Our results show that tubular retractors result in lower average predicted stresses, especially in the subcortical structures and corpus callosum. Additionally, we show that changing the location of retraction can greatly affect the predicted stress results. As the model predictions highly depend on the material model and parameters used for simulations, we also investigate the importance of using region-specific hyperelastic and viscoelastic material parameters when modelling a three-dimensional human brain during retraction. Our investigations demonstrate how FE simulations in neurosurgical techniques can provide insight to surgeons and medical device manufacturers. They emphasize how further work into this direction could greatly improve the management and prevention of injury during surgery. Additionally, we show the importance of modelling the human brain with region-dependent parameters in order to provide useful predictions for neurosurgical procedures.

Prediction of creep failure life for unidirectional CFRP with heat-resistant epoxy resin as matrix exposed to high temperature under tension load

The accelerated testing methodology (ATM) developed by the authors is the methodology for predicting statistically long-term life of CFRP structures based on the viscoelasticity including the time-temperature superposition principle for matrix resin. The formulae of ATM are expressed as the product of static strength at room temperature, its dispersion, and the viscoelastic parameter of matrix resin that changes with time and temperature history. This methodology ATM was applied to the prediction of long-term creep failure life for unidirectional CFRP with heat-resistant epoxy resin as matrix under heat degradation in this study. Resin impregnated CFRP strands with heat-resistant epoxy resin were molded using a filament winding system as virgin specimens of unidirectional CFRP. Then, heat-degraded specimens were prepared by exposing the virgin specimens under acceleration conditions determined based on the time-temperature superposition principle for chemical deterioration assuming the condition of practical temperature 110°C and period 10 years. Second, the creep strengths of virgin and heat-degraded CFRP strands were statistically predicted based on ATM and the effect of heat degradation on the long-term life of CFRP strands was evaluated. As results, it was cleared that when the creep strength of CFRP strands undergoes thermal aging at the practical condition, in addition to the strength decrease to time due to the viscoelasticity of the resin, a comparable decrease in static strength and increase in this scatter occur.

Magnetic resonance elastography resolving all gross anatomical segments of the kidney during controlled hydration.

Introduction: Magnetic resonance elastography (MRE) is a non-invasive method to quantify biomechanical properties of human tissues. It has potential in diagnosis and monitoring of kidney disease, if established in clinical practice. The interplay of flow and volume changes in renal vessels, tubule, urinary collection system and interstitium is complex, but physiological ranges of in vivo viscoelastic properties during fasting and hydration have never been investigated in all gross anatomical segments simultaneously. Method: Ten healthy volunteers underwent two imaging sessions, one following a 12-hour fasting period and the second after a drinking challenge of >10mL per kg body weight (60-75min before the second examination). High-resolution renal MRE was performed using a novel driver with rotating eccentric mass placed at the posterior-lateral wall to couple waves (50Hz) to the kidney. The biomechanical parameters, shear wave speed (cs in m/s), storage modulus (Gd in kPa), loss modulus (Gl in kPa), phase angle and attenuation (α in 1/mm) were derived. Accurate separation of gross anatomical segments was applied in post-processing (whole kidney, cortex, medulla, sinus, vessel). Results: High-quality shear waves coupled into all gross anatomical segments of the kidney (mean shear wave displacement: 163 ± 47μm, mean contamination of second upper harmonics <23%, curl/divergence: 4.3 ± 0.8). Regardless of the hydration state, median Gd of the cortex and medulla (0.68 ± 0.11kPa) was significantly higher than that of the sinus and vessels (0.48 ± 0.06kPa), and consistently, significant differences were found in cs, , and Gl (all p < 0.001). The viscoelastic parameters of cortex and medulla were not significantly different. After hydration sinus exhibited a small but significant reduction in median Gd by -0.02 ± 0.04kPa (p = 0.01), and, consequently, the cortico-sinusoidal-difference in Gd increased by 0.04 ± 0.07kPa (p = 0.05). Only upon hydration, the attenuation in vessels became lower (0.084 ± 0.013 1/mm) and differed significantly from the whole kidney (0.095 ± 0.007 1/mm, p = 0.01). Conclusion: High-resolution renal MRE with an innovative driver and well-defined 3D segmentation can resolve all renal segments, especially when including the sinus in the analysis. Even after a prolonged hydration period the approach is sensitive to small hydration-related changes in the sinus and in the cortico-sinusoidal-difference.

Determination of Penetration Depth and Excited Volume of Rubber in Klüppel Friction Theory from Friction Law

ABSTRACT This article aims to determine the excited volume and penetration depth in the theoretical friction model of rubber sliding on a corundum surface. The theoretical procedure of the Klüppel friction theory was implemented using the power spectral density of the corundum surface and viscoelastic model for rubber. The power spectral density was obtained with a power-law mode using the height difference correlation function parameters calculated from a surface measurement taken with a profilometer. Viscoelastic model parameters for the rubber were derived from a dynamic mechanical analyzer. Empirical law for friction coefficient obtained from the side force experiments and simulations of a laboratory abrasion tester (LAT 100) were used in this work. The friction coefficient from the theoretical procedure was matched with the empirical friction coefficient to estimate the penetration depth and excited volume of rubber. The correlation between the theoretical and empirical model was satisfactory. Estimating the penetration depth and excited volume of sliding rubber provides an insight into the contact conditions near surface asperities and the volume of rubber contributing to energy dissipation during the frictional process.

Bioconvection Pumping of Nanofluid Flows in a Curved Conduit with Electromagnetic Fields, Thermal Radiation and Joule Heating

This study analyses the electroosmotic transport of Jeffrey nanofluids containing gyrotactic microorganisms in a two-dimensional curved microchannel enduring peristalsis. In the presence of magnetic field, variable properties, viscous dissipation, Ohmic dissipation, thermal radiation, thermophoresis, and Brownian motion in a wave frame of reference in curvilinear coordinates, the formulation of the problem has been made. The governing equations are solved using Mathematica’s software, yielding numerical solutions. Detailed physical reasoning is used to graphically depict the consequences of the dimensionless variables involved. It has been observed that mobile microorganisms improve both the efficiency of heat transfer and the stability of nanoparticles. It is observed that the irreversibility rate decreases as the viscoelastic parameter, Darcy number, and radiation parameter increase. For small values of the curvature parameter, the nanofluid’s axial velocity is not symmetric about the centerline. Increases in the viscous dissipation parameter, Hartmann number, and Joule heating parameter intensify the temperature distribution, while increases in the radiation parameter have the opposite effect. The nanoparticle concentration decreases as thermophoresis advances and increases as the Brownian motion parameter rises. Electroosmotic phenomenon and magnetic parameter increase the rate of heat and mass transfer along the channel walls.

Nonlinear electro-rheological instability of two moving cylindrical fluids: An innovative approach

The present article examines the nonlinear stability of two viscoelastic electrified cylindrical fluids immersed in permeable media. The current structure consists of two endless vertical cylinders containing two electrified fluids. An axial unchanged electric field (EF) is applied to the entire construction; additionally, the impact of the surface tension is reflected. The main driving force for understanding this challenge has increasing significance in atmospheric and oceanic dynamics. The viscous potential theory is employed to ease the mathematical processes. The fundamental hydrodynamic equations are combined with Maxwell's equations in the quasi-static approximation to set the boundary-value problem. The appropriate boundary conditions (BCs) are expressed in a nonlinear form; this nonlinearity is achieved by addressing the linearized controlling equations of the motion. The viscoelastic impacts are considered to illustrate how the BCs produce their contributions. Consequently, the equations of motion are tackled without the effects of viscoelasticity parameters. The interface displacement consequently interacts vertically along with the cylindrical axis. The Rayleigh Helmholtz–Duffing oscillator describes the propagation of the interface between the two fluids. The non-perturbative approach (NPA), based on the He's frequency formula, transforms the typical nonlinear differential equation (NDE) into a linear one. The non-dimensional analysis reveals a lot of dimensionless physical numerals. These non-dimensional physical characteristics can be utilized to study the fundamental character of the liquid movement. They are also used to reduce the quantity of variables that are needed to comprehend the framework. A quick explanation of NPA is also presented. The stability study reveals the real/complex coefficients of the NDE. The numerical simulations show that there is a consistent solution and that the increases in the axial EF, as well as axial wavenumber, stabilize the system. The obtained findings help to understand and explain diverse nonlinear progressions that have taken place in fluid mechanics. To show the impact of the different factors and the efficiency of the stability approach, diverse PolarPlot diagrams are graphed for both actual and hypothetical portions.

Characterization of viscoelastic behavior of basalt fiber asphalt mixtures based on discrete and continuous spectrum models.

In order to analyze the differences between the master curves of relaxation modulus E(t) and creep compliance J(t) obtained from discrete and continuous spectrum models, and to comprehensively evaluate the effect of basalt fiber content on the viscoelastic behavior of asphalt mixtures, complex modulus tests were conducted for asphalt mixtures with fiber content of 0%, 0.1%, 0.2% and 0.3%, respectively. Consequently, the master curves of Viscoelastic Parameters of asphalt mixtures were constructed according to the generalized Sigmoidal model(GSM) and the approximate Kramers-Kronig (K-K) relationship. Then, transformation of master curves using discrete and continuous spectrum models to obtain the models of E(t) and J(t) containing all viscoelastic information. Also, the accuracy of the models of E(t) and J(t) was evaluated. The results show that the addition of basalt fibers improves the strength, stress relaxation and deformation resistance of asphalt mixtures. It is worth noting that basalt fibers achieve the improvement of asphalt mixtures by changing their internal structure. Considering the different viscoelastic master curves at four dosages, the optimum fiber dosage was 0.2%. In addition, both discrete and continuous model conversion methods can obtain high accuracy conversion results.

A novel ultrasonic method for measuring minute sinusoidal displacement by network analyzer.

We developed a method for generating continuous sinusoidal displacements of an object to estimate viscoelastic parameters. However, the amplitude of the displacement caused by the ultrasonic excitation force under safe guidelines was small (a few micrometers), and it was difficult to stably measure the displacement. Therefore, to stably measure the amplitude of sinusoidal displacement as small as the order of micrometers, we proposed a novel method using a network analyzer. Ultrasonic waves were irradiated using an ultrasonic transducer on an object vibrating sinusoidally. The S parameter of the first reflected wave received from the surface of the object was measured using a network analyzer. The S parameter and the inverse Fourier transform were formulated theoretically, and the amplitude of the sinusoidal displacement of the object was estimated from the amplitude characteristics of the inverse Fourier-transformed signal. The proposed method was applied to measure sinusoidal displacements on the order of micrometers from 10 to 300Hz on an object using a water tank experiment. The obtained sinusoidal displacement agreed well with the reference values measured using a laser displacement meter. The proposed method can accurately measure minute sinusoidal displacements that occur on an object.

Interaction between eye movements and adhesion of extraocular muscles

The contact and pull-off tests and finite element simulations were used to study the extraocular muscle-sclera adhesion and its variation with eye movement in this research. The effect of the adhesion on the eye movements was also determined using equilibrium equations of eye motion. The contact and pull-off tests were performed using quasi-static and non-quasi-static unloading velocities. Finite element models were developed to simulate these tests in cases with high unloading velocity which could not be achieved experimentally. These velocities range from the eye's fixation to saccade movement. The tests confirmed that the pull-off force is related to the unloading velocity. As the unloading velocity increases, the pull-off force increases, with an insignificant increase at the high ocular saccade velocities. The adhesion moment between the extraocular muscles and the sclera exhibited the same trend, increasing with higher eye movement velocities and higher separation angles between the two interfaces. The adhesion moment ratio to the total moment was calculated by the traditional model and the active pulley model of eye movements to assess the effect of adhesion behavior on eye movements. At the high ocular saccade velocities (about 461 deg/s), the adhesion moment was found to be 0.53% and 0.50% of the total moment based on the traditional and active pulley models, respectively. The results suggest that the adhesion behavior between the extraocular muscles and the sclera has a negligible effect on eye movements. At the same time, this adhesion behavior can be ignored in eye modeling, which simplifies the model reasonably well. Statement of Significance1. Adhesion behavior between the extraocular muscles and the sclera at different indenter unloading velocities determined by contact and pull-off tests. 2. A finite element model was developed to simulate the adhesive contact between the extraocular muscles and the sclera at different indenter unloading velocities. The bilinear cohesive zone model was used for adhesive interactions. 3. The elastic modulus and viscoelastic parameters of the extraocular muscle along the thickness direction were obtained by using compressive stress-relaxation tests. 4. The influence of the adhesion moment between the extraocular muscles and the sclera on eye movement was obtained according to the equation of oculomotor balance. The adhesion moment between the extraocular muscles and the sclera was found to increase with increased eye movement velocity and increased separation angle between the two interfaces.

3D flow of variable properties viscoelastic nanofluids with impacts of Arrhenius energy and Cattaneo–Christov double-diffusion

In several situations, particularly, flow of viscoelastic nanofluids, the dynamic viscosity and thermal conductivity should be considered as variables due to their roles in various practical applications. Therefore, this article aims applying the Cattaneo–Christov double-diffusion theory to investigate the three-dimensional (3D) forced flow of second-grade viscoelastic nanofluids over a permeable stretching surface. The properties of the mixture are considered to be variables where the dynamic viscosity is exponentially varied with temperature and the thermal conductivity and Brownian motion are linearly dependent on temperature and concentration, respectively. The included medium is isotropic porous, and both heat generation and thermal radiation impacts are assumed. At the surface, the nanoparticles are either active or passively controlled, and the convective boundary conditions are considered for the surface temperature. The solution methodology is based on similarity transformations, and the numerical technique is based on 4th-order Runge-Kutta method. The major outcomes revealed that the growth in thermal relaxation time δ e and viscoelastic parameter K causes gradually decreases in temperature and nanoparticles features. Also, constant dynamic viscosity gives higher velocity features compared to the variable case. Furthermore, the considered range of thermal conductivity coefficient ε 1 gives an enhancement in rate of the heat transfer by 5.26%.