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Magnetomotive ultrasound (MMUS) is a promising imaging modality for detecting magnetic nanoparticles. In MMUS, an external oscillating magnetic field induces the motion of the injected magnetic nanoparticles within tissue, and phase-based tracking algorithms are used to detect the motion. However, the subwavelength scale of these displacements (often a few micrometers) makes direct visualization on conventional ultrasound B-mode images impossible. In this work, we adapt the Eulerian motion magnification technique to create a novel ultrasound display mode for identifying the nanoparticle locations, eliminating the need for displacement tracking algorithms. Phantom and in vivo experiments demonstrate that our technique successfully magnifies magnetomotion and the associated shear wave propagation in ultrasound B-mode imaging and pinpoints the nanoparticle vibration source, even in low-concentration scenarios.

The object of study is the vertical wave propagation in a sand deposit. This paper is aimed at analyzing the vertical wave propagation in a sand deposit through micromechanical modeling that inherently takes account of intergranular slips during deformation. Such a problem, which is part of the general framework of wave propagation in the soil, has long been analyzed using continuum models based on approximate behavior laws. For this purpose, a 2D Discrete Element Method (DEM) model is developed. The DEM model is based on molecular dynamics with the use of circular shaped elements. The intergranular normal forces at contacts are calculated through a linear viscoelastic law while the tangential forces are calculated through a perfectly plastic viscoelastic model. A model of rolling friction is incorporated in order to account for the damping of the grains rolling motion. Different boundary conditions of the profile have been implemented; a bedrock at the base, a free surface at the top and periodic boundaries in the horizontal direction. The sand deposit is subjected to a harmonic excitation at the base. Using this model, the fundamental and resonance frequencies of the deposit are first determined. The former is determined from the low-amplitude free vibration and the latter by performing a variable-frequency excitation test. It is noted that there is a significant gap between the two frequencies, this gap could be attributed to the degradation of the soil shear modulus in the vicinity of the resonance. Such degradation is well proven in classical soil dynamics. The effects of deposit height and confinement on resonance frequency and free-surface dynamic amplification factor are then investigated. The obtained results highlighted that the resonance frequency is inversely proportional to the deposit’s thickness whereas the dynamic amplification factor Rd increases with the deposit’s thickness. In the other hand, when the confinement increases the deposit becomes stiffer, which results in reducing the amplification. Such result is in accordance with theoretical knowledge which states that the most rigid profiles such as rocks do not amplify seismic movement. [ABSTRACT FROM AUTHOR]

In Korea, the underground silo structure for low- and intermediate-level radioactive waste disposal facilities has been constructed and operated since 2014. Large-scale earthquakes occurred in 2016 and 2017, respectively, in Gyeongju and Pohang areas near the underground silo structures, and interest in the stability of the underground silo increased significantly. In this paper, one-dimensional free-field analyses have been carried out before the three-dimensional silo dynamic analyses subjected to earthquake loadings. As an additional study, a new form of the finite element equilibrium equation is derived in terms of relative motions, which is essentially the same equation expressed in terms of total motions where the base shear force is applied to the earthquake load. The accuracy of conventional finite element solutions is evaluated by directly comparing them with closed-form solutions by frequency domain analysis such as SHAKE91.

This work provides a theoretical framework to investigate the shear wave propagation properties within an Electrostrictive cylindrical layered structure. The structure is made up of a concentric, Functionally Assessed Electrostrictive Material (FAEM) cylindrical layer of limited width and an inadequately bonded Electrostrictive material cylinder. The FAEM layer has a constant functional gradient in the radial direction, and flaws at the interface are taken seriously, mirroring actual circumstances involving structural and electrical degradation. The fundamental electromechanical connected Bessel's equations are used to simplify field differential equations by mathematical modifications. Relationships for shear wave propagation under electrically short and open circumstances are established analytically. The acquired findings are verified against predefined standards and a particular issue instance. The impact of variables on the phase velocity of shear waves, including functional range and imperfection parameters, is shown through numerical simulations and graphical displays. The research also establishes boundaries for electrically short and open circumstances, taking into account the shear defect that exists between the inner and outer cylindrical layers.

In Korea, the underground silo structure for low- and intermediate-level radioactive waste disposal facilities has been constructed and operated since 2014. Large-scale earthquakes occurred in 2016 and 2017, respectively, in Gyeongju and Pohang areas near the underground silo structures, and interest in the stability of the underground silo increased significantly. In this paper, one-dimensional free-field analyses have been carried out before the three-dimensional silo dynamic analyses subjected to earthquake loadings. As an additional study, a new form of the finite element equilibrium equation is derived in terms of relative motions, which is essentially the same equation expressed in terms of total motions where the base shear force is applied to the earthquake load. The accuracy of conventional finite element solutions is evaluated by directly comparing them with closed-form solutions by frequency domain analysis such as SHAKE91. [ABSTRACT FROM AUTHOR]

Highlights: Shear wave propagation across frictional joints has been studied using Split Shear Plate (SSP) test facility. The laboratory experiments were conducted to obtain the energy coefficients and transmission amplitude coefficients across joints of various orientations. Energy transmission, displacement amplitudes and frequency of the waves propagated across joints are presented. [ABSTRACT FROM AUTHOR]

Fabric evolution monitoring of sandy specimens during shearing up to critical state is characterized by continuous, bidirectional shear wave velocity measurements along the vertical and horizontal directions (V&H). The specimens are prepared by water sedimentation methods and then subjected to drained compression and extension loading paths. The results exhibit a significant differences between shear wave velocities in two orthogonal directions, and subsequently shear moduli, as shear develops. Not only do the differences between shear wave velocities in V and H directions illuminate a severe and increasing soil anisotropy during the shearing, but the results also signify promising information related to the current fabric and stress state. Comparison between compression and extension results highlight different fabric evolution trends and consequently dissimilar fabric states at the critical state. Considering the conforming results with recent findings on the basis of the discrete element method (DEM), the proposed method can be used as an experimental method facilitating the macroscopic investigation of the effects of fabric anisotropy on the soil elastic response. The fabric anisotropy and its evolution are assessed consecutively using three methods, including quantitative evaluation of shear moduli, proposing a fabric function to account for the soil fabric, and 3D microscopic inspection of Micro-CT slices. The findings of the mentioned methods agree on the importance of fabric anisotropy in shear wave propagation and microscopic variations towards the critical state evolving from the initial state to dissimilar anisotropic states at the critical state under different shear modes. [ABSTRACT FROM AUTHOR]

This short communication identifies some inconsistencies in the numerical predictions of three advanced soil constitutive models. The chosen constitutive models are subject to simple numerical tests in the small-strain range relevant to the cyclic response of soil in seismic, offshore and urban applications. The numerical tests comprise a cyclic simple shear test in the small-strain range, a simple shear test with very small strain unloading-reloading loops and a test on the dependence of the rate of the shear stiffness degradation on the changing mean confining stress. The results are briefly discussed and, in some cases, the reasons for the observed inconsistencies and potential improvements in the formulations of the investigated constitutive models are initially drafted. [ABSTRACT FROM AUTHOR]

Ligaments and tendons undergo nonuniform deformation during movement. While deformations can be imaged, it remains challenging to use such information to infer regional tissue loading. Shear wave tensiometry is a promising noninvasive technique to gauge axial stress and is premised on a tensioned beam model. However, it is unknown whether tensiometry can predict regional stress in a nonuniformly loaded structure. The objectives of this study were to (1) determine whether regional shear wave speed tracks regional axial stress in nonuniformly loaded fibrous soft tissues, and (2) determine the sensitivity of regional axial stress and shear wave speed to nonuniform load distribution and fiber alignment. We created a representative set of 12,000 dynamic finite element models of a fibrous soft tissue with probabilistic variations in fiber alignment, stiffness, and aspect ratio. In each model, we applied a randomly selected nonuniform load distribution, and then excited a shear wave and tracked its regional propagation. We found that regional shear wave speed was an excellent predictor of the regional axial stress (RMSE = 0.57 MPa) and that the nature of the regional shear wave speed-stress relationship was consistent with a tensioned beam model (R2 = 0.99). Variations in nonuniform load distribution and fiber alignment did not substantially alter the wave speed-stress relationship, particularly at higher loads. Thus, these findings suggests that shear wave tensiometry could provide a quantitative estimate of regional tissue stress in ligaments and tendons. [ABSTRACT FROM AUTHOR]

Abstract: Dynamic elastography is a virtual palpation tool that aims at investigating the mechanical response of biological soft tissues in vivo. The objective of this study is to develop a finite element model (FEM) with low computational cost for reproducing realistically wave propagation for magnetic resonance elastography in heterogeneous soft tissues. Based on the first‐order shear deformation theory for moderately thick structures, this model is developed and validated through comparison with analytical formulations of wave propagating in heterogeneous, viscoelastic infinite medium. This 2D‐FEM is then compared to experimental data and a 3D‐FEM using a commercial software. Our FEM is a powerful promising tool for investigations of magnetic resonance elastography. [ABSTRACT FROM AUTHOR]

Shear wave tensiometry is a noninvasive approach for gauging tendon loads based on shear wave speed. Transient shear waves are induced and tracked via sensors secured to the skin overlying a superficial tendon. Wave speeds measured in vivo via tensiometry modulate with tendon load but are lower than that predicted by a tensioned beam model of an isolated tendon, which may be due to the added inertia of adjacent tissues. The objective of this study was to investigate the effects of adjacent fat tissue on shear wave propagation measurements in axially loaded tendons. We created a layered, dynamic finite element model of an elliptical tendon surrounded by subcutaneous fat. Transient shear waves were generated via an impulsive excitation delivered across the tendon or through the subcutaneous fat. The layered models demonstrated dispersive behavior with phase velocity increasing with frequency. Group shear wave speed could be ascertained via dispersion analysis or time-to-peak measures at sequential spatial locations. Simulated wave speeds in the tendon and adjacent fat were similar and modulated with tendon loading. However, wave speed magnitudes were consistently lower in the layered models than in an isolated tendon. For all models, the wave speed-stress relationship was well described by a tensioned beam model after accounting for the added inertia of the adjacent tissues. These results support the premise that externally excited shear waves are measurable in subcutaneous fat and modulate with axial loading in the underlying tendon. The model suggests that adjacent tissues add inertia to the system, which in turn lowers shear wave speeds. This information must be considered when using tensiometry as a clinical or research tool to infer absolute tendon loading. [ABSTRACT FROM AUTHOR]

Shear waves propagating through interfaces where there is a change in stiffness cause reflected waves that can lead to artifacts in shear wave speed (SWS) reconstructions. Two-dimensional (2-D) directional filters are commonly used to reduce in-plane reflected waves; however, SWS artifacts arise from both in- and out-of-imaging-plane reflected waves. Herein, we introduce 3-D shear wave reconstruction methods as an extension of the previous 2-D estimation methods and quantify the reduction in image artifacts through the use of volumetric SWS monitoring and 4-D-directional filters. A Gaussian acoustic radiation force impulse excitation was simulated in phantoms with Young’s modulus ( $E$ ) of 3 kPa and a 5-mm spherical lesion with $E = 6$ , 12, or 18.75 kPa. The 2-D-, 3-D-, and 4-D-directional filters were applied to the displacement profiles to reduce in-and out-of-plane reflected wave artifacts. Contrast-to-noise ratio and SWS bias within the lesion were calculated for each reconstructed SWS image to evaluate the image quality. For 2-D SWS image reconstructions, the 3-D-directional filters showed greater improvements in image quality than the 2-D filters, and the 4-D-directional filters showed marginal improvement over the 3-D filters. Although 4-D-directional filters can further reduce the impact of large magnitude out-of-plane reflection artifacts in SWS images, computational overhead and transducer costs to acquire 3-D data may outweigh the modest improvements in image quality. The 4-D-directional filters have the largest impact in reducing reflection artifacts in 3-D SWS volumes. [ABSTRACT FROM PUBLISHER]

Background: Skin aging is accelerated by extrinsic factors, particularly actinic damage. Over the last decades, both clinical and pathological differences between intrinsic and actinic aging have been characterized. In this work, we aimed at quantifying skin aging by non-invasive in vivo methods. Methods: Young healthy volunteers using indoor tanning facilities and aged people were compared with appropriate controls by measurements of skin elasticity with the Cutometer and the Reviscometer and by semi-quantitative evaluation of the dermal matrix composition by the multiphoton laser tomograph DermaInspect. Results: We found differences between the sun-protected volar forearm and the dorsal side as well as between young and old test persons with all three methods. No significant differences were found between the skin of indoor-tanned test persons and control. Also, gender had no influence on the severity of skin aging. Conclusion: The most consistent results were obtained with the DermaInspect. The considerable inter-individual variation due to the cross-sectional design of the study may have disguised the factual skin damage caused by tanning beds. [ABSTRACT FROM AUTHOR]

Abstract: Magnetic resonance elastography (MRE) is a novel non-invasive approach to determine material stiffness by using a conventional magnetic resonance imaging (MRI) system incorporated with an oscillating motion-sensitizing gradient to detect nodal displacements produced by a shear excitation wave. The effects of material properties, excitation frequency, boundary conditions, and applied tension on shear wavelength measurement must be examined before MRE can become a useful diagnostic tool. We propose finite element (FE) modeling as a robust method to systematically study the effects of these parameters. An axisymmetric FE model was generated with ABAQUS to simulate agarose gel phantoms. The effects of material stiffness, density, and excitation frequency on propagating shear wavelength were examined individually. The effect of the boundary conditions on shear wavelength was also demonstrated. Results of shear wavelength from MRE measurement were compared with the results of FE model, which showed good agreement between the methods. [Copyright &y& Elsevier]

Shear wave rigidity moduli G have been determined using a shear wave propagation technique for sodium montmorillonite suspensions. Measurements were made as a function of time at various values of pH, NaCl concentration ( C) and solids concentration and the data used to estimate G the value of the modulus at t=∞. The dependency of G on pH, C and solids concentration is interpreted in terms of the mode of interaction between particles and the associated volume filling structure. The results suggest that whether a coagulated or dispersive structure develops in these suspensions depends not only on pH and C but also on the degree of delamination of the clay. [ABSTRACT FROM AUTHOR]

• To investigate the posterior eye biomechanics under different intraocular pressures. • High frequency ultrasound elastography. • The relations of posterior eye biomechanics maybe useful for understanding Glaucoma. To quantitatively investigate both optic nerve head (ONH) and peripapillary sclera (PPS) biomechanical properties of porcine eyes through an ultrasonic elastography imaging system in response to both increasing and decreasing intraocular pressure (IOP). The Young's modulus of the ONH and PPS were assessed using our high resolution ultrasonic imaging system which utilized a mechanical shaker to induce shear waves and an off-axis aligned 40 MHz needle transducer to track micron-level displacement along the direction of wave propagation. In this study, imaging on a total of 8 ex vivo porcine eyes preloaded with IOPs from 6 mmHg to 30 mmHg was performed. To have a better understanding of the effect of varying IOP on biomechanics, both increasing and decreasing IOPs were investigated. The increase of the Young's modulus of ONH (92.4 ± 13.9 kPa at 6 mmHg to 224.7 ± 71.1 kPa at 30 mmHg) and PPS (176.8 ± 14.3 kPa at 6 mmHg to 573.5 ± 64.4 kPa at 30 mmHg) following IOP elevation could be observed in the reconstructed Young's modulus of the shear wave elasticity (SWE) imaging while the B-mode structural images remained almost unchanged. In addition, for the same IOP level, both ONH and PPS have a tendency to be stiffer with decreasing IOP as compared to increasing IOP. Our results demonstrate the feasibility of using our ultrasonic elastography system to investigate the stiffness mapping of posterior eye with high resolution in both increasing and decreasing IOPs, making this technique potentially useful for glaucoma. [ABSTRACT FROM AUTHOR]

Grouting of fractured rock mass prior to excavation results in grout-filled discontinuities that govern the deformation characteristics of a site. The influence of joint characteristics on the properties of grouted rocks is important in assessing the effects of grouting on jointed rock mass. However, grouting remains a predominantly empirical practice and the effects of grouting on rock joint behavior and material properties have yet to be accurately assessed. Granular materials, including jointed rocks, typically display nonlinear strain-dependent responses that can be characterized by the shear modulus degradation curve. In this study, the effects of grouting on the strain-dependent shear stiffness of jointed rock mass were investigated at the small-strain (below 10−5) and mid-strain (10−5 to 10−3) ranges using the quasi-static resonant column test and rock mass dynamic test devices. The effects of curing time, axial stress, initial joint roughness, and grouted joint thickness were examined. The results show that (1) grouting of rock joints leads to decreased stress sensitivity and increased small-strain shear stiffness for all tested samples; (2) the grouted rock samples display similar modulus degradation characteristics as the applied grout material; (3) the initial joint roughness determines the stress-dependent behaviors and general stiffness range of the jointed and grouted rocks, but the strain-dependent behaviors are dependent on the properties of the grout material; (4) increased grouted joint thickness results in larger contribution of the grout properties in the overall grouted rock mass. [ABSTRACT FROM AUTHOR]