Variation Of Attenuation Research Articles

Geographical, Seasonal and Diurnal Variations of Acoustic Attenuation, and Sound Speed in the Near‐Surface Martian Atmosphere

AbstractThis work introduces a comprehensive model of sound attenuation and speed on Mars, in light of the recent operation of several microphones on the surface of Mars. The proposed acoustic model calculates the sound speed and attenuation throughout the near‐surface Martian atmosphere based on first‐principles. We evaluate the effects of the seasonal and diurnal cycle of air temperature, pressure and CO2, as well as the concentration of airborne dust on the sound attenuation. The attenuation and speed of sound are most sensitive to the air temperature and, therefore, they vary with the diurnal temperature cycle and to a lesser degree with the seasonal changes in temperature. The speed of sound also varies with the seasonal variations of the concentration of CO2. The main outcome of this work is an acoustic model capable of computing the sound speed and attenuation for any location at the Martian surface at any time of year and any time of day.

Amplitude‐Dependent Energy Dissipation Inferred From Spectral Analyses of Intraslab Earthquakes

AbstractWhile the Earth (rocky planet) can be approximated as an elastic body, it also possesses anelasticity, Q−1, which causes energy dissipation (intrinsic attenuation) during deformation. Rock deformation experiments have demonstrated that Q−1 shows a marked amplitude dependency for strain of >∼10−6, but seismic‐waves‐induced strain is generally much smaller than the threshold value. Therefore, all seismological analyses have assumed amplitude‐independent attenuation. However, theoretical models of dislocation‐induced attenuation have predicted amplitude‐dependent attenuation under high temperatures and pressures equivalent to the crustal and uppermost mantle conditions. This study investigates whether attenuation is actually independent of seismic‐wave amplitudes by a systematic analysis of a large number of spectral amplitudes of co‐located earthquake pairs with different observed amplitudes. We assume the ω2 source and circular crack models to correct for the source parameters of earthquakes. The obtained results suggest that amplitude‐dependent attenuation is required to explain the observations, which contradicts a long‐standing recognition that amplitude‐dependent attenuation is negligible for the propagation of seismic waves. Our model calculation further suggests that Q−1 is proportional to the seismic amplitude, A, whereby Q−1 ∝ A0.1–0.2, which introduces attenuation variations along a given raypath, with significantly enhanced attenuation near the hypocenter. Our result highlights the need to revisit and potentially rethink current models of the physical mechanisms influencing intrinsic attenuation.

Variation of Nonlinearity Parameter and Acoustic Attenuation with Temperature in Few Semiconductors

Variation of Nonlinearity Parameter and Acoustic Attenuation with Temperature in Few Semiconductors

A Source and Ground Motion Study of the Veracruz Earthquakes of 29 October 2009 (Mw5.7) and 4 August 2021 (Mw4.8): Evidence of Strong Azimuthal Variation of Attenuation

We study two moderate earthquakes that occurred offshore the State of Veracruz, in the southwestern Gulf of Mexico, on 29 October 2009 (Mw 5.7) and 4 August 2021 (Mw 4.8). The former was located near the town of Alvarado and latter near the city of Veracruz. The events were well recorded by accelerographs and seismographs at local and regional distances. W-phase regional centroid moment tensor inversion reveals that they had reverse-faulting mechanism, similar to several other earthquakes in the southwestern Gulf of Mexico. Of the seven focal mechanisms now available along the southwestern margin, two are strike slip and the rest are of thrust type, suggesting a heterogeneous stress regime. We take advantage of local and regional recordings produced by these two earthquakes to study the characteristics of the ground motion. Source spectra computed at each station separately (without correcting for the site effect), assuming a reasonable geometrical spreading and Q = 141f 0.63, show remarkably high variability due to difference in path and local site effects. The geometric mean apparent source spectrum (source spectrum including site effects) of both earthquakes may be modeled by an ω2 -Brune source model with a stress drop, Δσ, of 40 MPa. These source spectra, along with the application of stochastic method, yield peak ground acceleration (PGA) and velocity (PGV) as a function of distance in general agreement with the observations. Of greater practical importance is the ground motion at sedimentary sites in the city of Veracruz and at the Laguna Verde Nuclear Power Plant (LVNPP) site, especially from a postulated Mw 6.5 earthquake which is a reasonable scenario event for the region. For the city of Veracruz and LVNPP we estimate site effect with respect to the ω2 -Brune source with Δσ of 2 MPa. There is some support for this Δσ. We apply both stochastic and empirical Green’s functions (EGF) techniques in the estimation of the ground motion. The recording of the 2021 earthquake is taken as the EGF, and Δσ of the EGF and the target event are assumed to be the same and equal to 2 MPa. The predicted PGA and PGV at sedimentary sites in the city of Veracruz and LVNPP above the hypocenter (depth = 20 km) from the postulated Mw 6.5 earthquake are 0.2 g and 10 cm/s and 0.18 g and 3 cm/s, respectively. These results are preliminary as they are based on several assumptions.

Elastodynamic property closures of elastic waves in polycrystalline materials

In polycrystalline materials like many metals, grainy microstructures significantly influence elastodynamics. Bulk waves scattering at grain boundaries cause attenuation and speed variation in waves. This depends on grain characteristics, including local elasticity and spatial properties. These are modeled statistically to homogenize the microstructure or elastodynamic fields, within bounds. For example, the elasticity of a homogenized medium can't exceed that of individual grains. 'Property closure' is the range within which microstructures yield specific properties like Young's modulus. This presentation introduces property closures for modeling elastic wave properties, specifically attenuation and velocity, in metal alloys. The focus is on the modeling framework and integrating microstructure statistics. An excting prospect of this work is in linking measurable wave properties with other physical quantities dependent on microstructure.

Image classification system for COVID-19 patient X-Ray results using median filter with deep learning method

An image is a representation of an object that is rewritten on a medium with specific values (intensity) and has x and y coordinates. X-ray images are one type of medical image that can be used to detect and study a disease. However, X-ray images can sometimes appear blurry, making interpretation a bit challenging. Furthermore, there is variation in X-ray attenuation between normal tissue and tissue affected by a disease. By using the median filter and implementing deep learning as a method for classifying images based on feature extraction and weights in artificial neural networks. The stages carried out include preprocessing, with training and testing, feature extraction using layers of artificial neural networks that have undergone the filtering process. Then, a custom classifier layer is created to train the classification of COVID and normal classes using data from bottleneck.npy. The results of training and testing yielded an average accuracy of 95%, while the F1 Score evaluation result was 0.9."

Investigation of the dependence of temperature attenuation of the layered bio-tissue

High-intensity focused ultrasound for solid tumor ablation is a noninvasive ultrasound hyperthermia technique wherein ultrasound is transmitted through multiple layers of biological tissues, focusing on the target area. The resulting heat accumulates in the target tissue, leading to irreversible cell death or protein necrosis, achieving tumor ablation. During treatment, the efficiency of acoustic energy converting to heat is closely related to temperature attenuation in the layered tissues. To obtain an accurate prediction of thermal damage, variations in the acoustic parameters should be measured at different temperatures. This study used two methods to induce heating to the tissues: the water heating method (WHM), which involves heat transfer from the outside to the inside, and the ultrasound heating method (UHM), wherein the heat source is located inside the tissue. The finite-amplitude insertion-substitution method was utilized to determine the attenuation coefficients of various bio-tissues such as porcine fat, muscle, and liver as the temperature increased. To mitigate the effects of viscous heating artifacts, the ‘wait then measure’ (WTM) thermometric approach was utilized using wire thermocouples to measure the temperature of the ultrasound-heated tissue. Experimental results demonstrate that the attenuation coefficient of bio-tissues varies with temperature under different heating methods. This study presents the variation in tissue attenuation using WHM at 5 MHz, while tissue categories using UHM are modeled with formulas at a frequency of 2 MHz.

Probing cell metabolism using the two-photon excitation autofluorescence lifetime of tryptophan.

Compared to intensity detection, fluorescence lifetime has the advantage of being unaffected by variations in excitation intensity, fluorophore concentration, or attenuation due to biological absorption and scattering. In this Letter, to the best of our knowledge, we present the use of the two-photon excitation autofluorescence lifetime imaging of tryptophan (TRP) to probe cell metabolism for the first time. Tests of pure chemical samples showed that the fluorescence lifetime of TRP was highly sensitive to changes in molecular conformation and the environment. In in vitro cell experiments, we successfully utilized the fluorescence lifetime of TRP to distinguish tumor cells from healthy cells, track the therapeutic effect of the tumor immunotherapy drug 1-MT for HeLa cells, and monitor cells in response to carbonyl cyanide 3-chlorophenylhydrazone (CCCP)-induced cell apoptosis. These results reveal that the two-photon excitation autofluorescence lifetime of TRP could be a sensitive natural probe of cell metabolism in living cells.

Emerging technologies and advanced analyses for non-invasive near-surface site characterization

The in-situ small-strain shear modulus of soil and rock materials is a parameter of paramount importance in geotechnical modeling. It can be derived from non-invasive geophysical surveys, which provide the possibility of testing the subsurface in its natural and undisturbed condition by inferring the velocity of propagation of shear waves. In addition, for soil dynamics and earthquake engineering applications, the small-strain damping ratio plays a relevant role, yet its estimation is still challenging, lacking consolidated approaches for its in-situ evaluation. Recent advancements in instrumentation, such as distributed acoustic sensing (DAS), combined with advanced analysis methodologies for the interpretation of seismic wave propagation (e.g., machine learning and full waveform inversion), open new frontiers in site characterization. This paper presents and compares some advanced applications of measuring 1D and 2D variations in shear wave velocity and attenuation in-situ with reference to a specific case history.

Intrinsic and scattering attenuations of the Sichuan-Yunnan region in China from S coda waves

Seismic attenuation is a fundamental property of the Earth's media. Attenuation structure for the complicated geological structures with strong seismicity in the Sichuan-Yunnan region is poorly studied. In this study, we collected 108,399 waveforms of 11,517 local small earthquakes with magnitudes between 1.5 and 3.5 from January 2014 to September 2021 in the Sichuan-Yunnan region and its adjacent areas. We employed an envelope inversion technique for separating the intrinsic and scattering attenuations of the S coda wave, and obtained the intrinsic and scattering attenuation structures for frequencies between 0.25 and 8.00 Hz. The attenuation structures correlate well with the geological units, and some major faults mark the attenuation variations where historic large earthquakes have occurred. The regional average attenuation shows a negative frequency dependence. The average scattering attenuation has a faster descending rate than the average intrinsic attenuation, and is dominant at low frequencies, while at high frequencies the average intrinsic attenuation is stronger. The lateral variation in the intrinsic attenuation is consistent with the variation in heat flow, the scattering attenuation may be related to the scatter distribution and size. The total attenuation is consistent with the previous studies in this region, and the separate intrinsic and scattering attenuation may be useful in understanding regional tectonics and important in earthquake prevention and disaster reduction.

Time-lapse attenuation variations using distributed acoustic sensing vertical seismic profile data during CO2 injection at CaMI Field Research Station, Alberta, Canada

For seismic monitoring of geologic [Formula: see text] storage, it is useful to measure time-lapse (TL) variations of seismic attenuation. Seismic attenuation directly connects to different petrophysical parameters within the [Formula: see text] storage complex. We have developed an approach to derive smooth time-variant amplitude spectra from seismic signals by using the sparse strongest signal peaks, and then measuring two different attributes (conventional Q factor and its “geometric” counterpart) characterizing the path effects of seismic attenuation from the smooth spectra. This approach is straightforward and does not require sophisticated algorithms or parameterization schemes. We apply this approach to TL distributed acoustic sensing (DAS) vertical seismic profile (VSP) data from the Field Research Station (FRS) [Formula: see text] injection project in southern Alberta, Canada. High-quality stacked reflection records are obtained from the baseline and monitor DAS VSP surveys at the FRS and TL attenuation-attribute differences are derived from these reflection records. TL variations of attenuation are observed within the injection zone at the FRS, which are interpreted as being related to the injected [Formula: see text]. Although there is always a significant trade-off between the accuracy and temporal resolution of the measured attenuation parameters, reliable attenuation measurements around the injection zone are still achieved with an in-use reflection signal of a sufficient length and bandwidth. Attenuation attributes measured from this approach can be an advantageous tool for monitoring the distribution and migration of [Formula: see text] plumes.

A Temperature-Compensated Ku-Band Four-Beam Phased-Array Receiver With Low Attenuation and Relative Phase Variations

A Temperature-Compensated Ku-Band Four-Beam Phased-Array Receiver With Low Attenuation and Relative Phase Variations

A robust optimised multi-material 3D inkjet printed elastic metamaterial

This paper presents and validates a novel elastic metamaterial design, that is optimised for broadband robust vibration control of a structure in the presence of uncertainties, and realised using multi-material additive manufacturing. A novel concept resonator design that allows the resonance frequency to be flexibly tuned via both geometrical and material property modifications is presented and characterised. A unit cell consisting of 12 of these resonators is then proposed. The resonance frequencies and damping ratios of this elastic metamaterial unit cell when attached to a parametrically uncertain example structure are then optimised using a Particle Swarm Optimisation to maximise the mean attenuation in kinetic energy of a structure with parametric uncertainties, based on an analytical model of the system. The performance of the optimised metamaterial is then validated experimentally, and it is shown that the realised metamaterial design is able to achieve a mean of 3.5 dB of broadband attenuation in the presence of uncertainties in the structure. In addition, in the presence of structural uncertainties the robustly optimised design achieves 0.5 dB greater mean attenuation than a design optimised on the nominal structural response alone, and reduced variation in attenuation for different levels of uncertainty.

Lateral Variations in Teleseismic Attenuation of the Conterminous U.S. and New Insights Derived From Its Relationship to Mantle Seismic Velocity

AbstractMuch of our knowledge of the North American lithosphere comes from imaging seismic velocities. Additional constraints on the subsurface can be gained by studying seismic attenuation, which has different sensitivity to physical properties. We produce a model of lateral variations in attenuation across the conterminous U.S. by analyzing data recorded by the EarthScope Transportable Array. We divide the study area into 12 overlapping tiles and differential attenuation is measured in each tile independently; and twice for four of the tiles. Measurements are combined into a smooth map using a set of linear inversions. Comparing results for adjacent tiles and for repeated tiles shows that the imaged features are robust. The final map shows generally higher attenuation west of the Rocky Mountain Front than east of it, with significant small length scale variations superimposed on that broad pattern. In general, there is a strong anticorrelation between differential attenuation and shear wave velocities at depths of 80–250 km. However, a given change in velocity may correspond to a large or small change in attenuation, depending on the area; suggesting that different physical mechanisms are operating. In the western and south‐central U.S., as well as the Appalachians, velocity variations are large compared to attenuation changes, while the opposite is true in the north‐central and southeastern U.S. Calculations with the Very Broadband Rheology calculator show that these results are consistent with the main source of heterogeneity being temperature and melt fraction in the former regions and grain size variability in the latter ones.

Free-layer damping influence on the evanescent wave in a strip containing periodic acoustic black holes

This work demonstrates the transformation of wave motions in a periodic two-dimensional (2D) ABH structure with one-dimensional (1D) lattice subject to the damping dissipation. The free-layer damping (FLD) treatment is employed to achieve the damping dissipation. Numerical results, alongside analyses based on the local dispersion relation model, expose the effect of dissipation on bandgap (BG), which is always accompanied by the ABH-featured local resonance. Analyses show that the dissipative periodic ABH strip enables comparable attenuation intensity as that in its corresponding non-dissipation periodic ABH strip due to fact that the periodic ABH strip has two types of BG: (i) one shows infinite group velocity and constant lattice phase; (ii) another is accompanied by the discontinuous dispersion curves for the same flexural wave. The minimal attenuation inside these two BGs is less affected by the dissipation level. The discontinuity phenomenon inside the BG is attributed to the coupling between different flexural wave evanescent modes. As a result, the reduction of minimal attenuation inside the BG is less sensitive to the dissipation level. This attenuation variation subject to the damping dissipation inside the BG is distinguished from the weakened attenuation in traditional local resonance BG, in which there always exists a phase jump by π/a. Along with the ABH-enhanced dissipation, the dissipative periodic ABH strip enables broadband attenuation by inducing wide complex waves, while obtaining considerable attenuation intensity.

Double distance dependence in high-frequency ground motion along the plate boundary in Northern Chile

In subduction zones, the forearc crust transitions from a highly fractured wedge near the trench to a less fractured basement near the volcanic arc. Here we study the role of wedge integrity on the frequency content of strong ground motion produced by subduction earthquakes in Northern Chile. Our data includes aftershocks from the 2014 Mw 8.1 Iquique earthquake and intermediate-depth seismicity, including the 2005 Mw 7.6 Tarapacá earthquake. We focus on the S-wave spectral decay parameter κ obtained from strong ground motion in the frequency band 2−40Hz, paying particular attention to how κ varies with hypocentral distance. We report two distinct trends of κ versus hypocentral distance. One trend applies to events near the trench, where we observe a rapid increase of κ with hypocentral distance. Another trend applies to events near the bottom of the megathrust and greater depths, where we observe a relatively slow increase of κ with hypocentral distance. We interpret this difference as resulting from a heterogeneous tectonic structure with lateral variations in anelastic attenuation (i.e., attenuation seems stronger in the fractured wedge near the trench). Our results improve our understanding of the role of high-frequency ground motion in seismic hazard analysis near the Chilean coastline. In addition, our results stress the need for a better characterization of anelastic attenuation in the Chilean subduction zone, specially close to the highly fractured wedge near the trench.

Abstract 17083: Aortic Luminal Contrast Attenuation Varies With Dissection Morphology and is Associated With Need For Intervention

Introduction: Prognostication after acute Type B aortic dissection (aTBAD) may be limited when relying upon static computed tomographic angiography (CTA) images to evaluate a dynamic process. We performed an exploratory study to characterize variations in luminal contrast attenuation on CTA, as a surrogate for blood flow in dissection, and to determine whether the resulting parameters held prognostic value. Methods: Retrospective, single-institution data for patients with aTBAD were gathered from 1999-2020. Patients with prior dissection repairs were excluded. Dissection morphology was classified by the SVS/STS scheme and location/number of fenestrations. Hounsfield unit ratios (HUR) comparing lumina, phases, and aortic zone were calculated. Aortic growth, false lumen thrombosis, and need for intervention were evaluated with univariable logistic regression. Results: After exclusions, 85 patients were identified (mean age 61.9 years, 69.4% male). SVS/STS B 3,10 (20%) and B 3,5 (12.9%) predominated (Figure). Most fenestrations were in Zone 4/5 (56.5%) and associated with more equilibrated HUR (0.93) compared to dissections without fenestration (0.70, p = 0.04). Fenestration zone was not associated with HUR ( p = 0.59). Intervention occurred in 65.9%, most often for aneurysmal degeneration (43.8%), followed by visceral/limb ischemia (32.6%). Growth occurred in 28.2%. Increased arterial false-to-true HUR was strongly associated with eventual need for intervention (OR 25.3 [95% CI 4.15-188.4], p = 0.001) while increased delayed-to-arterial false lumen HUR was associated with decreased intervention (OR 0.49 [95% CI 0.25-0.89], p = 0.02). Conclusion: In patients with aTBAD, calculated permutations of HUR across lumina and between CTA phases may give insight into blood flow dynamics, which in turn likely impact need for intervention. Future prospective studies of time-resolved CTA are likely to hold significant prognostic value and alter management.

Power allocation algorithm for capacity maximization in 5G MIMO systems

The multiple input - multiple output (MIMO) systems have sparked a lot of research interest because of their ability to increase the system capacity without using much bandwidth. The High-Speed Train (HST) communication system's capacity was calculated by assuming that the SNR is unaffected by variations in attenuation and channel losses. Here, considering this optimization problem, a power allocation algorithm using the Water-Filling technique is proposed for the MIMO system with known Channel Side Information (CSI) at the transmitter and receiver. The presented algorithm may be efficiently optimized for improving channel capacity to achieve spectral efficiency (SE).

Screening the B- and T-cell epitope map of TP0136 and exploring their effect in a Treponema pallidum rabbit model

The systemic immune response, including B- and T-cell reactions, plays a corresponding role in syphilis infections. The TP0136 protein is a target of the immune response in infected hosts and may mediate the immune response. Here, we developed a method that combining reverse vaccine approach with Pepscan/T-cell proliferation to screen and identify three B-cell and two T-cell epitopes of TP0136, and explore the role of the B- and T-cell epitopes in immunized-infected animals. The results showed that immunized with B-cell epitopes not only had no protective effect but also aggravated the syphilitic lesion development. While immunized with T-cell epitopes of TP0136 could induce a strong Th1-cellular immunity response, which could attenuate syphilitic lesion development to a certain extent. The variation in exacerbation or attenuation of skin lesions, induced by distinct B- and T-cell epitopes of Tp0136, within the host's defense against syphilis warrants in-depth exploration.

Investigation of the influence of macrozones in titanium alloys on the propagation and scattering of ultrasound

The presence of macrozones (or micro-textured regions) in Ti-6Al-4V (Ti-64) was shown to be a potential cause to the onset of cold dwell fatigue which reduces fatigue life significantly. Past research has demonstrated the potential of using ultrasonic testing for macrozone characterization, with the variation of ultrasound attenuation, backscatter and velocity in the presence of macrozones. However, due to the complexity of the microstructure, some physical phenomena that were observed are still not well understood. In this study, we propose the use of finite-element polycrystalline models to provide us with a means to systematically study the wave-macrozone interaction. Through this investigation performed using two-dimensional models, we are able to identify important correlations between macrozone characteristics (size, shape and texture) and ultrasound responses (attenuation, backscatter and velocity). The observed behaviours are then validated experimentally, and we also highlight how this understanding can potentially aid with the characterization of macrozones in Ti-64 samples.