Longitudinal Propagation Research Articles

Longitudinal elastic wave propagation characteristics of inertant acoustic metamaterials

Longitudinal elastic wave propagation characteristics of acoustic metamaterials with various inerter configurations are investigated using their representative one-dimensional discrete element lattice models. Inerters are dynamic mass-amplifying mechanical elements that are activated by a difference in acceleration across them. They have a small device mass but can provide a relatively large dynamic mass presence depending on accelerations in systems that employ them. The effect of introducing inerters both in local attachments and in the lattice was examined vis-à-vis the propagation characteristics of locally resonant acoustic metamaterials. A simple effective model based on mass, stiffness, or their combined equivalent was used to establish dispersion behavior and quantify attenuation within bandgaps. Depending on inerter configurations in local attachments or in the lattice, both up-shift and down-shift in the bandgap frequency range and their extent are shown to be possible while retaining static mass addition to the host structure to a minimum. Further, frequency-dependent negative and even extreme effective-stiffness regimes are encountered. The feasibility of employing tuned combinations of such mass-delimited inertant configurations to engineer acoustic metamaterials that act as high-pass filters without the use of grounded elements or even as complete longitudinal wave inhibitors is shown. Potential device implications and strategies for practical applications are also discussed.

Effect of deep native defects on ultrasound propagation in TlInS2 layered crystal

We have investigated p-type semiconductor–ferroelectric TlInS2 by means of Photo-Induced Current Transient Spectroscopy (PICTS) technique in the temperature range 77–350K for the detection of native deep defect levels in TlInS2. Five native deep defect levels were detected and their energy levels and capture cross sections were evaluated. Focusing on these data, the influence of these defects on the longitudinal and transverse ultrasound waves propagation as well as the effect of electric field on ultrasound waves were studied at different temperatures. The acoustic properties were investigated by the pulse-echo method. The direct contribution of thermally activated charged defects to the acoustic properties of TlInS2 was demonstrated. The key role of charged native deep level defects in elastic properties of TlInS2 was shown.

PML solution of longitudinal wave propagation in heterogeneous media

This paper describes the development of a model for unbounded heterogeneous domains with radiation damping produced by an unphysical wave absorbing layer. The Perfectly Matched Layer (PML) approach is used along with a displacement-based finite element. The heterogeneous model is validated using the closed-form solution of a benchmark problem: a free rod with two-part modulus subjected to a specified time history. Both elastically supported and unsupported semi-infinite rods with different degrees of inhomogeneity and loading are considered. Numerical results illustrate the effects of inhomogeneity on the response and are compared with those for equivalent homogeneous domains. The effects of characteristic features of the inhomogeneous problem, presence of local maxima and cut-off frequency are determined. A degenerate case of a homogeneous semi-infinite rod on elastic foundations is produced by tending the magnitude of the foundation stiffness to zero. The response of the latter is compared with that of a free rod. The importance of proper selection of the PML parameters to highly accurate and efficient results is demonstrated by example problems.

Sensitivity analysis of pre-stressed concrete sleepers for longitudinal crack prorogation effective factors

Abstract B70 mono-block pre-stressed concrete sleepers are one of the most common sleepers in Iran's railways industry. They have been used in many of the country's railway transition lines. The B70 types of sleepers are classified as pre-stressed concrete beams; therefore the value of pre-stressing force is one of the most important parameters in the field of sleepers' structural designing. Selecting high pre-stressing force due to the fact that it increases the steel bars strength, could increase the possibility of longitudinal cracks formation before service loading, especially if the tensile strength is low. Therefore, pre-stressing force and tensile strength are two important factors for investigating the sensitivity of longitudinal crack formation and propagation in sleepers. Sensitivity analysis has been conducted for tensile strength of concrete and the pre-stressing force in the steel bars, by using finite element method. It could be clearly seen in the results that increasing the tensile strength of concrete, increases the cross section capacity. This increase in the capacity does not have a direct relationship with the increase of the tensile strength. Also the numerical model indicates a linear behavior between different pre-stressing forces and maximum tensile stress around the dowels. Applying higher pre-stressing force values can increase the possibility of longitudinal cracks prior to service loading of the sleepers and also long-term sleepers' service life.

Intrinsic transfer matrix method and split quaternion formalism for multilayer media

The intrinsic transfer matrix method for 1D longitudinal elastic wave propagation through multilayer media is used to obtain an equivalent split quaternion formalism. Periodic media are analysed in this framework and the presence of a defect is considered. A simple one layer defect and an inversion defect are analysed. A commutative type of split quaternion is identified, which corresponds to defects of the periodic structure that can be placed in any position, the overall acoustic properties of the medium being conserved. Also, a nonperiodic medium composed of such commutative elements has a behaviour independent of the order of elements. Several possible applications in sound wave measurement and processing are outlined. The proposed split quaternion formalism is compact and can make analytical and numerical computations easier.

Analysis of the quench propagation along Nb3Sn Rutherford cables with the THELMA code. Part I: Geometric and thermal models

The paper describes the new lumped thermal model recently implemented in THELMA code for the coupled electromagnetic–thermal analysis of superconducting cables. A new geometrical model is also presented, which describes the Rutherford cables used for the accelerator magnets. A first validation of these models has been given by the analysis of the quench longitudinal propagation velocity in the Nb3Sn prototype coil SMC3, built and tested in the frame of the EUCARD project for the development of high field magnets for LHC machine. This paper shows in detail the models, while their application to the quench propagation analysis is presented in a companion paper.

ATMOSPHERIC CIRCULATION OF HOT JUPITERS: DAYSIDE–NIGHTSIDE TEMPERATURE DIFFERENCES

ABSTRACT The full-phase infrared light curves of low-eccentricity hot Jupiters show a trend of increasing dayside-to-nightside brightness temperature difference with increasing equilibrium temperature. Here, we present a three-dimensional model that explains this relationship, in order to provide insight into the processes that control heat redistribution in tidally locked planetary atmospheres. This three-dimensional model combines predictive analytic theory for the atmospheric circulation and dayside–nightside temperature differences over a range of equilibrium temperatures, atmospheric compositions, and potential frictional drag strengths with numerical solutions of the circulation that verify this analytic theory. The theory shows that the longitudinal propagation of waves mediates dayside–nightside temperature differences in hot Jupiter atmospheres, analogous to the wave adjustment mechanism that regulates the thermal structure in Earth’s tropics. These waves can be damped in hot Jupiter atmospheres by either radiative cooling or potential frictional drag. This frictional drag would likely be caused by Lorentz forces in a partially ionized atmosphere threaded by a background magnetic field, and would increase in strength with increasing temperature. Additionally, the amplitude of radiative heating and cooling increases with increasing temperature, and hence both radiative heating/cooling and frictional drag damp waves more efficiently with increasing equilibrium temperature. Radiative heating and cooling play the largest role in controlling dayside–nightside temperature differences in both our analytic theory and numerical simulations, with frictional drag only being important if it is stronger than the Coriolis force. As a result, dayside–nightside temperature differences in hot Jupiter atmospheres increase with increasing stellar irradiation and decrease with increasing pressure.

Multi-large low-frequency band gaps in a periodic hybrid structure

A hybrid structure composed of a local resonance mass and an external oscillator is proposed in this paper for restraining the elastic longitudinal wave propagation. Theoretical model has been established to investigate the dispersion relation and band gaps of the structure. The results show that the hybrid structure can produce multi-band gaps wider than the multi-resonator acoustic metamaterials. It is much easier for the hybrid structure to yield wide and low band gaps by adjusting the mass and stiffness of the external oscillator. Small series spring constant ratio results in low-frequency band gaps, in which the external oscillator acts as a resonator and replaces the original local resonator to hold the band gaps in low frequency range. Compared with the one-dimensional phononic crystal (PC) lattice, a new band gap emerges in lower frequency range in the hybrid structure because of the added local resonance, which will be a significant assistance in low-frequency vibration and noise reduction. Further, harmonic response analysis using finite element method (FEM) has been performed, and results show that elastic longitudinal waves are efficiently forbidden within the band gaps.

Realization of Complex 3D Phononic Crystals with Wide Complete Acoustic Band Gaps.

Phononic crystals offer unique band structures for acoustic wave propagation. Fabricating intricate threedimensional phononic crystals allows a new class of devices with complex phononic band structures beyond capabilities of two-dimensional designs. We have successfully fabricated novel 3D phononic crystals with 1 mm lattice constant and minimum feature sizes as low as 100 micron using high-resolution stereolithography printing. Here we report the first theoretical calculations and experimental results demonstrating wide complete 3D phononic band gaps not attainable by corresponding 2D structures with the same lattice geometry. Longitudinal and shear wave propagation is suppressed by more than -60 dB in frequency bands as wide as 400 kHz to 1 MHz.

Multistep Relaxations in a Spin-Crossover Lattice with Defect: A Spatiotemporal Study of the Domain Propagation

We study the spatio-temporal formation and spreading of the low-spin state (LS) during the thermal spin transition and the cooperative relaxation of the photo-induced metastable high spin (HS) state at low temperature, in the presence of a structural defect. The model is made of a two-dimensional rectangular-shaped lattice with discrete spins coupled by springs. The investigations are performed for a perfect lattice and a lattice with a hole (simulating the defect) with a fixed size. We found that the presence of the defect affects the thermal equilibrium by reducing the size of the thermal hysteresis at the transition, although the transition temperature remains unchanged. The study of the low-temperature relaxation of the defect-free lattice from HS to LS state indicated the existence of three different regimes of the growth process: (i) a first regime of growth from one corner of the rectangle along the width, then followed by (ii) a second regime of longitudinal propagation at almost constant velocity, and (iii) a third rapid regime when the system feels the surface or the border of the crystal. When a hole is injected inside the lattice, it results in (i) the deformation of the HS/LS interface’s shape when it approaches the defect position; and (ii) the slowing down of its propagation velocity. These results, which are in good agreement with available experimental data, are discussed in terms of elastic energy stored in the system during the relaxation process.

Modeling of ultrasonic nonlinearities for dislocation evolution in plastically deformed materials: Simulation and experimental validation

A nonlinear constitutive relationship was established to investigate nonlinear behaviors of ultrasonic wave propagation in plastically damaged media based on analyses of mixed dislocation evolution. Finite element simulations of longitudinal wave propagation in plastically deformed martensite stainless steel were performed based on the proposed nonlinear constitutive relationship, in which the contribution of mixed dislocation to acoustic nonlinearity was considered. The simulated results were validated by experimental measurements of plastically deformed 30Cr2Ni4MoV martensite stainless steels. Simulated and experimental results both reveal a monotonically increasing tendency of the normalized acoustic nonlinearity parameter as a function of plastic strain. Microscopic studies revealed that the changes of the acoustic nonlinearity are mainly attributed to dislocation evolutions, such as dislocation density, dislocation length, and the type and fraction of dislocations during plastic loading.

Influence of Skull Anisotropic Mechanical Properties in Low-Intensity Focused Ultrasound

Low-intensity focused ultrasound (LIFU) is a new noninvasive brain stimulation technique where ultrasound is applied with low frequency and intensity to focus at a target region within the brain in order to exhibit or inhibit neuronal activity. In applying LIFU to the human brain, the skull is the main barrier due to its well-known high anisotropic mechanical properties which will affect the ultrasound focusing thereby affecting the neuromodulation or brain stimulation. This study aims at investigating the influence of the anisotropic mechanical properties of the skull on ultrasound propagation and focusing in LIFU. In this study, we used 2D finite element (FE) head models incorporating the isotropic and anisotropic properties of the skull. Three kinds of stresses were examined and shown within the skull: namely the normal stress in the direction of wave propagation ([Formula: see text]-stress), normal stress in the transverse direction to the wave propagation ([Formula: see text]-stress), and shear stress. Our analysis show that although most of the pressure that reaches to the brain is due to the longitudinal wave propagation through the skull, the stress in the transverse direction to the wave propagation direction ([Formula: see text]-stress) has the main influence on the pressure profile inside the brain. The results also show that the anisotropic properties of the skull broaden the focal size about 19% and 13% in the longitudinal and transverse directions, respectively more than the case of considering the isotropic properties in the realistic 2D FE head model. The results indicate the importance of considering the anisotropic properties of the skull in practicing LIFU to achieve accurate targeting within the brain.

Collective scattering of an incident monochromatic circularly polarized wave in an unmagnetized non-equilibrium plasma

Collective scattering of an incident monochromatic circularly polarized electromagnetic wave in an unmagnetized non-equilibrium plasma is investigated. The wave equation of the scattered waves are numerically solved by giving wave spectra of the incident electromagnetic wave and a variety of longitudinal fluctuations of a plasma. In addition to the well known symmetric ion and electron features of frequency spectrum in an equilibrium plasma, some asymmetries are found in a frequency spectrum when anisotropic longitudinal wave propagation or the effect of the presence of a beam mode are taken into account.

Diabetic gastroparesis alters the biomagnetic signature of the gastric slow wave.

Gastroparesis is characterized by delayed gastric emptying without mechanical obstruction, but remains difficult to diagnose and distinguish from other gastrointestinal (GI) disorders. Gastroparesis affects the gastric slow wave, but non-invasive assessment has been limited to the electrogastrogram (EGG), which reliably characterizes temporal dynamics but does not provide spatial information. We measured gastric slow wave parameters from the EGG and magnetogastrogram (MGG) in patients with gastroparesis and in healthy controls. In addition to dominant frequency (DF) and percentage power distribution (PPD), we measured the propagation velocity from MGG spatiotemporal patterns and the percentage of slow wave coupling (%SWC) from EGG. No significant difference in DF was found between patients and controls. Gastroparesis patients had lower percentages of normogastric frequencies (60 ± 6% vs 78 ± 4%, p < 0.05), and higher brady (9 ± 2% vs 2 ± 1%, p < 0.05) and tachygastric (31 ± 2% vs 19 ± 1%, p < 0.05) frequency content postprandial, indicative of uncoupling. Propagation patterns were substantially different in patients and longitudinal propagation velocity was retrograde at 4.3 ± 2.9 mm/s vs anterograde at 7.4 ± 1.0 mm/s for controls (p < 0.01). No difference was found in %SWC from EGG. Gastric slow wave parameters obtained from MGG recordings distinguish gastroparesis patients from controls. Assessment of slow wave propagation may prove critical to characterization of underlying disease processes. Future studies should determine pathologic indicators from MGG associated with other functional gastric disorders, and whether multichannel EGG with appropriate signal processing also reveals pathology.

Monitoring of setting time of self-consolidating concrete using ultrasonic wave propagation method and other tools

Concrete setting behaviour and strength development strongly influence the scheduling of construction operations such as surfacing, trowelling, jointing, saw-cutting and formwork removal. The aim of this study was to investigate technologies available to monitor the changing properties of a fresh mixture, particularly for use with self-consolidating concrete (SCC). In order to evaluate test methods to monitor the setting and stiffening behaviour of conventional concrete and SCC, mixtures were made with different aggregate types and sizes and different cementitious materials. A number of techniques were used to monitor setting time, stiffening and formwork pressure of SCC mixtures. These included longitudinal (P-wave) ultrasonic wave propagation, penetrometer-based setting time, semi-adiabatic calorimetry and formwork pressure. Tests were conducted on a large matrix of SCC mixes designed for bridge construction applications. The results revealed that the P-wave test and calorimetric measurements can be used to monitor the stiffening and setting of SCC mixtures.

On the Origin and Handling of the Force Oscillation Phenomenon in Tensile Impact Testing of Polymer Materials

Stress respectively force oscillation in mechanical testing is a phenomenon that can be monitored independent of material, stress state and test setup. This study looks at the phenomenon of force oscillation in tensile impact testing on viscoelastic materials and its dependency on longitudinal stress wave propagation. In addition to the extensive research on stress wave propagation and the force oscillation phenomenon, published within the last decades, the Society of Automotive Engineering (SAE) also gives valuable recommendations regarding tensile impact testing on polymer materials. Existing limitations to tensile impact testing reported earlier can be overcome using the approach outlined in this paper. Furthermore, we give an analysis to stress wave propagation in tensile impact testing and its correlation to force oscillations: We find that (1) longitudinal stress wave propagation in tensile specimens cannot be considered to be the origin of the force oscillation phenomenon - even more so it can be neglected, (2) specimens in tensile impact testing are exposed to a nearly oscillation free loading which is presented for haul-off velocities of up to 10 m/s and (3) it is not possible to achieve force equilibrium in the load train conducting tensile impact tests. In addition, we present an approach to measure a nearly oscillation free force signal in tensile impact testing on polymer materials up to 10 m/s. For this purpose a modification of a standard dumbbell specimen is introduced. Measurements presented in this paper are conducted using state of the art 3D high-speed deformation measurement technology based on Digital Image Correlation (DIC).

Efficient implementation of an explicit partitioned shear and longitudinal wave propagation algorithm

Efficient implementation of an explicit partitioned shear and longitudinal wave propagation algorithm

Divergent Longitudinal Propagation ofWhiteMatter Degradation inLogopenicand Semantic Variants ofPrimary Progressive Aphasia.

Clinico-pathological distinction of primary progressive aphasia (PPA) can be challenging at clinic presentation. In particular, cross-sectional neuroimaging signatures across the logopenic (lvPPA) and semantic (svPPA) variants are difficult to establish, with longitudinal profiles showing greater divergence. Assess longitudinal propagation of white matter degradation in lvPPA and svPPA to determine disease progression over time, and whether this reflects distinct underlying pathology. A cohort of 27 patients with dementia (12 lvPPA; 15 svPPA) and 12 healthy controls were assessed at baseline and 1-year follow-up on the Addenbrooke's Cognitive Examination-Revised and Sydney Language Battery. Diffusion weighted images were collected at both time-points and analyzed for longitudinal white matter change using DTI-TK and TBSS. LvPPA patients showed a significant decline in naming and repetition, over 1 year, while svPPA patients declined in naming and comprehension. Longitudinal imaging revealed widespread bilateral degradation of white matter tracts in lvPPA over a 1-year period with early involvement of the left posterior inferior longitudinal fasciculus (ILF). SvPPA demonstrated focal left lateralized white matter degradation involving the uncinate fasciculus (UF) and anterior ILF, propagating to the right UF with disease progression. LvPPA and svPPA cohorts showed distinct longitudinal cognitive and white matter profiles. We propose differences in multi-centric and focal white matter dysfunction in lvPPA and svPPA, respectively, reflect underlying pathological differences. The clinical relevance of white matter degradation and mechanisms underlying disease propagation are discussed.

Frequency domain simulations for the determination of liner effects on longitudinal wave propagation

Frequency domain simulations for the determination of liner effects on longitudinal wave propagation

Abstract 13447: An Injectable Conductive Polymer Hydrogel Improves Electrical Conduction Velocity in the Injured Heart

Introduction: Scar formation after a myocardial infarction (MI) delays electrical impulse propagation, inducing dysynchronous cardiac activation and uncoordinated contraction. We generated an injectable biocompatible conductive polymer that not only stabilized the infarct region, but also facilitated electrical signal propagation across the scar tissue to enhance synchronous ventricular contraction. Methods/Results: Oxidative polymerization was employed to conjugate polypyrrole (PPY) to chitosan (CHI) and hydrogels were created by glutaraldehyde crosslinking. Biomaterials with 4 different PPY:CHI ratios (CHI, 3PPY:10CHI, 3 PPY:100 CHI, 3 PPY:1000CHI ) were generated. Electrical conductivity was measured by two-probe cyclic voltammetry. The 3PPY:10CHI ratio had significantly greater conductivity than the other concentrations (2.37х10-4±6.25х10-5S/cm, n=6, P&lt;0.05). Improved electrical propagation was demonstrated when neonatal rat cardiomyocytes cultured on 3PPY:10CHI had significantly higher Ca2+ transient propagation velocity (by optical mapping with a fluo-4/AM indicator) than those cultured on other concentrations (17.25±2.23cm/s, n=15, P&lt;0.05). Thus, 3PPY:10CHI was employed for in vivo studies employing a cryoinjury model (with a uniform scar size). Saline, CHI, and 3PPY:10CHI were injected into Sprague-Dawley rat hearts 1 week after injury. The sequence of cardiac electrical activation was visualized using an optical mapping system 1 month post-injection. Saline (57.7±2.5cm/s, n=4)- and CHI (47.1±3.5cm/s, n=3)-injected hearts showed disrupted propagation patterns and significantly reduced conduction velocity, while 3PPY:10CHI (74.3±4.7cm/s, n=5)-treated hearts had higher conduction velocities that were similar to healthy controls (81.3±0.59cm/s, n=3). Conclusion: A polypyrrole-conjugated chitosan hydrogel supported cell attachment and improved electrical conductivity in vitro. The 3PPY:10CHI biomaterial enhanced Ca2+ transient propagation in cultured cardiomyocytes and intra-myocardial injection of the material improved longitudinal electrical impulse propagation across the scar. This new biomaterial may be a new potential therapy to synchronize cardiac contraction.