Acoustic Impedance Research Articles

Quantitative Assessment of the Effect of Instability Levels on Reactive Human Postural Control Using Different Sensory Organization Strategies

Reactive postural control (RPC), essential for maintaining balance during daily activities, relies on a complex sensory system integrating visual, vestibular, and proprioceptive inputs. Deficits in RPC can lead to falls, especially in unpredictable environments where sensory inputs are challenged. Traditional rehabilitation often fails to prepare patients adequately for real-world conditions. This study aims to explore the effects of varying instability levels (ILs) and sensory integration strategies (SIS) on RPC by evaluating balance disturbances without applying additional external force. Twenty-five healthy participants (12 men, 13 women, 24.5 ± 6.1 years) performed balance tasks on Abili® platforms with adjustable ILs (0, 1, 2, 3) while altering sensory strategies (Basic, Visual, Proprioception, Vestibular) using the Modified Clinical Test of Sensory Integration and Balance (mCTSIB). RPC efficiency was measured using the 95th percentile confidence interval for chest movement’s ellipsoid volume and average velocity, analyzed with Wilcoxon signed-rank tests and Cliff’s delta effect size. Results showed significant increases in chest movement velocity and volume, particularly with the Vestibular strategy at higher ILs, with a 7176% increase in chest volume from Basic strategy at 0IL to Vestibular strategy at 3IL. Additionally, removing visual input (Visual and Vestibular strategies) had a greater impact on chest movement than increasing instability levels. These findings underscore the significant role of combined platform instability and reduced sensory input on postural control. This study presents a novel method for challenging balance and suggests that sensory integration with variable instability could be valuable in training and rehabilitation, even for healthy individuals.

High-resolution acoustic-impedance inversion based on a deep-learning-aided representation model of nonstationary seismic data

Building a high-resolution acoustic-impedance (AI) model based on nonstationary seismic data plays a key role in reservoir predictions. However, the common AI inversion methods are faced with two main shortcomings. First, because of the nonstationary feature of seismic data, a multiparameter inverse problem should be considered to not only estimate AI but also to estimate a time-varying wavelet or a quality factor ( Q) model, leading the problem to be more ill posed. Second, the resolution of the estimated AI is limited due to the band-limited nature of nonstationary seismic data. To address these issues, we develop a new nonstationary seismic AI inversion method. Notably, we develop a deep-learning-aided representation model to replace the nonstationary convolution model to solve the forward problem in inversion. Benefiting from multisource information (seismic data and well-log data) and the powerful nonlinear function fitting ability of deep learning, this model can map high-resolution AI to band-limited nonstationary seismic data without requiring a time-varying wavelet or a Q model. A new deep-learning architecture is developed for processing the spatio-temporal seismic data with better accuracy. In addition, total-variation regularization is adopted to enforce a physically reasonable AI model. The results of our 3D synthetic and field data experiments clearly demonstrate that our method has significant advantages over other common methods in building a high-resolution AI model.

Physicochemical characterization of thermally oxidized rapeseed oil: An insight into combining acoustic diagnostic technique and chemometrics

This study aimed to apply an ultrasonic pulse-echo system to characterize thermally oxidized rapeseed oil. After 60 h of heating treatment (165 ± 5°C), the physicochemical (density, viscosity, acid value, iodine value and polar compounds) and acoustic properties (velocity, acoustic impedance, maximum amplitude of the first echo, difference in amplitude, and area under the curve) of rapeseed oil were measured. Support vector machine, random forest (RF), and backpropagation neural network algorithms were used to establish quantitative prediction models for viscosity and polar compounds based on the acoustic properties of rapeseed oil. The results indicated significant correlations between acoustic impedance and viscosity (R=0.70), as well as between acoustic impedance and polar compounds (R=0.79). Heating treatment reduced oil unsaturation and led to the formation of oxidative and polymeric compounds, which in turn increased the velocity and impedance, while decreasing the other three acoustic features. The RF model yielded the best performance in predicting viscosity (R2=0.7944) and polar compounds (R2=0.8385). These findings highlight that ultrasonic technology not only accurately predicts key quality parameters, but also provides a rapid, non-destructive, and cost-effective alternative to traditional methods for characterizing thermally oxidized rapeseed oil.

Synthesis and Evaluation of New Type Plant Extraction Corrosion Inhibitor

The use of corrosion inhibitors in the development of oil and gas fields is an important means of effectively preventing metal corrosion, at present, the green growth of the oil and gas industry requires low-toxicity, low-residue, easy-to-post-treatment and other environmentally friendly corrosion inhibitors, however, most industrially used corrosion inhibitors such as mercury salts quaternary ammonium salts, and imidazolines are toxic to some degree. In this paper, a plant extract corrosion inhibitor was synthesized, firstly, the purple sweet potato extract was extracted by ethanol, and then the purple sweet potato extract and alkyl halide such as methane were used to produce the purple sweet potato corrosion inhibitor through condensation extraction and other processes, and the corrosion inhibitory performance of the inhibitor was evaluated by the loss-in-weight method, scanning electron microscopy, polarization curves, and impedance spectroscopy. The results show that there is a certain inhibition effect on N80 steel in the simulated stratum water environment, and the retardation rate can reach 91.38% in the gas phase, and the corrosion product morphology and chemical elements on the surface of N80 steel specimens were characterized by SEM, EDS, and it can be observed that a relatively dense protective film was formed after adding purple sweet potato corrosion inhibitor, and the corrosion inhibition rate can be known according to the weightlessness curve, Tafel curve and impedance curve. The corrosion inhibition rate increases with the increase of corrosion inhibitor concentration.

Indoor tests of sensor-enabled piezoelectric geocable–geogrid composite structure for slope rehabilitation and monitoring

Sensor-enabled piezoelectric geocables were combined with a geogrid to acquire a sensor-enabled piezoelectric geogrid (SPGG) based on the impedance–strain relationship. Tension, pullout, and straight shear tests were conducted on this SPGG configuration. The tension test results indicated that the tensile strain–normalized impedance curves were exponential in form within the first 7 % of strain and the rate of shift in impedance was independent of the tension loading rate. An excellent correspondence between the peak strength and impedance inflection point was observed in the results of the pullout and straight shear tests. Additional validation of the proposed SPGG was conducted through a collapse test of the reinforced soil slope model. The results indicated that the SPGG-obtained strains were similar to actual strain gauge measurements but provided a larger measurement range and that the SPGG was able to sense real-time vibrations during the slope collapse using a voltage analysis, confirming that the proposed SPGG can simultaneously provide soil reinforcement, strain monitoring of reinforcement materials, and vibration sensing. This research is expected to inform the development of a dynamic and static monitoring, large range, and accurate method for monitoring the conditions of reinforced soil over their entire lifecycles.

Study on the Migration Mechanism of Temporary Plugging Agent in Artificial Fractures of Deep Geothermal Reservoirs Based on the Euler-Euler Multiphase Flow Model

The successful use of temporary plugging diverting fracturing technology requires an understanding of the migration and plugging processes of temporary plugging agents into artificial fractures under high temperature settings. In this study, a multiphase flow model for the migration of temporary plugging agents in artificial fractures was developed using the Euler-Euler framework, and numerical simulations were conducted at elevated temperatures. Various factors, including plugging agent injection velocity, concentration, carrying fluid viscosity, wall temperature, and fracture width, were systematically analyzed to assess their impact on the agent’s migration behavior. Detailed analyses, using cloud diagrams of particle volume fraction, velocity, and turbulence intensity, clarified the underlying mechanisms influencing the migration process. The results indicate that as the injection velocity increases, the height of blockages near the wellbore decreases, while the blockage length initially increases before declining. Increasing the concentration of the plugging agent leads to a rise in blockage height and a shift in the front edge toward the injection point. Enhancing the viscosity of the carrying fluid enables the plugging agent to migrate deeper into the fracture, improving deep plugging effectiveness. While changes in wall temperature have limited impact on blockage morphology, temperatures exceeding the critical threshold of 573K significantly intensify particle migration. Moreover, increasing fracture width enhances both the height and length of blockages, with the optimal plugging effect observed when the plugging agent diameter is approximately one-third of the fracture width.

Mechanism of airborne sound absorption through triboelectric effect for noise mitigation

Mitigating broadband noise with passive airborne sound absorbers has been a long-lasting challenge, particularly for low-frequency anthropogenic sounds below kilohertz with long wavelengths, which require bulky materials for effective absorption. Here, we propose a strategy that utilizes local triboelectric effect and in-situ electrical energy dissipation mechanism for airborne sound absorption. This approach involves a fundamentally different mechanism that converts airborne sound into electricity for energy dissipation, in contrast to conventional mechano-thermal energy conversion mechanisms. We establish an equivalent acoustic impedance model to provide theoretical analysis of the underlying sound absorption mechanisms, with a theoretical maximum mechano-electro-thermal coupling efficiency approaching 100% under optimal conditions. We design fibrous triboelectric composite foam materials accordingly and show their substantially boosted acoustic absorption performance experimentally, where the adoption of diverse triboelectric material pairs validates that a larger difference in material charge affinities intensifies the local triboelectric effect and results in higher acoustic absorbing performance.

Physico-chemical Study of Surface Active Ionic Liquid (SAIL) in Aqueous Inulin Solutions: Density and Speed of Sound Measurements

Colloidal formulations of surface active ionic liquid (SAIL) have substantial benefit as efficient carrier mainly for therapeutic/pharmaceutical agents. In this regard, density (ρ) and speed of sound (u) have been employed to evaluate the diverse interactions/association behaviour of greener SAIL tetrabutylammonium dodecylsulphate (TBADS) (0.222 to 2.2 mmol kg-1) in aqueous inulin solutions (0.0, 0.2 and 0.3% w/w) at five different temperatures ranging from 293.15 K to 313.15 K. The volumetric and acoustic parameters viz. isentropic compressibility (κs), apparent molar volume (Vφ) and compressibility (κs,φ), intermolecular free length (Lf), relative association (RA), specific acoustic impedance (Z) and molar sound number ([U]) have been calculated by using density (ρ) and speed of sound (u) values. The existence of hydrophilic/hydrophobic interactions for TBADS in aqueous inulin solution is suggested by the variations in volumetric parameters, which further supported by various calculated acoustic parameters. Thus, the interactional outcomes can offer implications that stabilized inulin in the presence of SAILs and can be utilized for the optimal biotic actions.

Early detection of cardiac dysfunction using shear wave imaging: insights into reduced cardiorespiratory fitness in childhood cancer survivors

Abstract Background Diastolic dysfunction is thought to be the earliest cardiotoxic sequel after cancer therapy among childhood cancer survivors. Despite many survivors do exhibit reduced cardiorespiratory fitness (CRF) potentially due to cardiotoxicity, current echocardiographic parameters fail to detect hidden diastolic dysfunction early after therapy (1). High frame rate (HFR) shear wave imaging (SWI) is a novel tool that could give insights about myocardial stiffness, which is a key determining factor of diastolic function. Purpose We aimed at testing the ability of SWI to detect early alterations in myocardial stiffness among childhood cancer survivors and its relation with the reduced CRF. Methods Fifty childhood cancer survivors (mean 20 ±3 years) who received chemo-and/or- radiotherapy (mean time after treatment: 4 ±3 years) and thirty-two matched healthy volunteers (HV) were recruited. Conventional as well as HFR echocardiographic images (ca. 1200 frames/second) were acquired at rest using a modified commercial echocardiography machine. All participants underwent an incremental, symptom-limited cardiopulmonary exercise test on a treadmill measuring peak oxygen consumption (VO2 peak). HFR data were analysed offline. An anatomical M mode was drawn along the ventricular septum, and tissue Doppler acceleration maps were extracted to measure SW velocities after mitral valve closure (MVC) (Figure 1). Results Among cancer survivors, left ventricular ejection fraction (LVEF) and global longitudinal strain were significantly lower compared to HV (56 % ±4 vs 59 % ±4, and 17.6 % ±1.6 vs 19.1 % ±1.2, respectively; p <0.001). However, both LVEF and GLS were within the normal range and none of them correlated with the peak VO2 (Figure 2A&B). None of the echocardiographic diastolic parameters (e.g. mitral E, E/e’, left atrial volume or TR jet velocity) showed significant difference between both groups (P > 0.05). The mean SW velocities were significantly higher in cancer survivors compared to HV (3.9 ±0.6 m/s vs 3.2 ±0.3 m/s respectively; p <0.001). Interestingly, SW velocities among cancer survivors showed moderate significant negative correlation with the VO2 peak (r= -0.590, p <0.001) indicating increasing myocardial stiffness as the cardiorespiratory fitness declined (Figure 2C). Conclusions Our data indicate that myocardial stiffness in cancer survivors is significantly increased. We hypothesize that this increased stiffness may at least in part explain the significantly reduced cardiorespiratory fitness in this population. Echocardiographic shear wave elastography appears as a promising non-invasive tool for early detection of diastolic dysfunction in follow-up of childhood cancer survivors.Figure 1.Figure 2.

Improvement of Mechanical and Acoustic Characteristics of Halloysite Nanotube-Reinforced Polyurethane Elastomer Composites and Their Applications

Polyurethane incorporated with nanofillers such as carbon nanotubes, basalt fibers, and clay nanoparticles has presented remarkable potential for improving the performance of the polymeric composites. In this study, the halloysite nanofiller-reinforced polyurethane elastomer composites were prepared via the semi-prepolymer method. The impact of different halloysites (halloysite nanotubes and halloysite nanoplates) in polyurethane composites was investigated. Scanning electron microscopy, X-ray diffraction, infrared spectroscopy, electronic universal tensile testing, and acoustic impedance tube testing were employed to characterize the morphology, composition, phase separation, mechanical properties, and sound insulation of the samples. The composite fabricated with 0.5 wt% of halloysite nanotubes introduced during quasi-prepolymer preparation exhibited the highest tensile strength (22.92 ± 0.84 MPa) and elongation at break (576.67 ± 17.99%) among all the prepared samples. Also, the incorporation of 2 wt% halloysite nanotubes into the polyurethane matrix resulted in the most significant overall improvements, particularly in terms of tensile strength (~44%), elongation at break (~40%), and sound insulation (~25%) within the low-frequency range of 50 to 1600 Hz. The attainment of these impressive mechanical and acoustic characteristics could be attributed to the unique lumen structure of the halloysite nanotubes, good dispersion of the halloysites in the polyurethane, and the interfacial bonding between the matrix and halloysite fillers.

Entropy generation in radiative motion of tangent hyperbolic nanofluid in the presence of gyrotactic microorganisms and activation energy

In this work, entropy generation is optimized through the application of the second law of thermodynamics. The slip mechanisms, Brownian diffusions, and thermophoresis are elaborated using the tangent hyperbolic nanomaterial model. Magnetohydrodynamic (MHD) fluid is taken into consideration. To characterize the impact of activation energy, a unique model involving the binary chemical reaction is deployed. The effects of mixed convection that is nonlinear in nature, bioconvection, and Joule effect are all taken into consideration. The key partial differential equations (PDEs) are reduced into ordinary differential equations (ODEs) by utilizing appropriate similarity transformations and then solved numerically with the help of a built-in ‘bvp4c’ technique of MATLAB software. Varied flow parameters’ impacts on the nanoparticle volume concentration, entropy number, microorganism concentration, temperature, and velocity fields are analyzed using graphs. Various flow variables are taken into consideration to calculate the total rate of entropy generation. The obtained results show that concentration irreversibility, Joule effect irreversibility, viscous dissipation, and heat irreversibility all influence the entropy. The numerical outcomes were observed by fixing the physical parameters as 0.1<α<4.0, 0.1<M<1.2, 0.1<Nr<2.2, 0.1<Le<2.2, 0.1<Nb<0.4, 0.1<Nt<1.0, 2.0<⁡Pr⁡<5.0, and 0.1<Lb<2.0, as well as their impact on the momentum, thermal, concentration, and microorganism density profiles. From results, an increasing estimate of the variable representing chemical reaction indicates a decline in the concentration. The higher the chemical reaction variable, Hartmann number, and Weissenberg number, the higher the entropy number, while the Bejan number has a contrary behavior. Subsequently, all the outcomes are plotted in graphs and discussed in detail, when subjected to the involving physical quantities.

CHARACTERIZATION OF A FLUVIAL DELTAIC SALT-INFLUENCED SYSTEM FOR CO2 STORAGE USING SEISMIC POST-STACK INVERSION AND SELF-ORGANIZING MAPS IN THE UPPER MIOCENE, ONSHORE LOUISIANA

Basins that have historically been explored for hydrocarbons are now seen through a new perspective for carbon capture and storage. Legacy hydrocarbon reservoirs may now have the potential to become carbon storage targets. The Miocene Sandstone in south Louisiana is a stratigraphic interval that contains favorable zones for carbon storage, and seismic interpretation is a critical tool for characterizing these sands and estimating the amount of possible carbon storage. New workflows leveraging machine learning and seismic inversion can be applied to legacy fields to generate a new estimate for pore space and carbon storage capacity. The study area contains a 3D seismic survey covering 310 mi2 (803 km2) and 16 wells. Using these data, the workflow leverages self-organized maps (SOM) to identify zones of interest both laterally and vertically for carbon storage. SOM provides an uplift in resolution for interpretation compared to single attributes. A model-based acoustic impedance inversion produces porosity information that is used in tandem with SOM outputs. The acoustic impedance results strongly correlate to porosity within the target sands, and the SOM and porosity maps delineate specific sand lobes for potential storage. Wellbore data within the sand lobe align with SOM and inversion results and show rock quality with 26% average porosity and 90 feet gross thickness. The research highlights a project sized target within the middle Miocene containing 10.3 Megatons of estimated CO2 storage. Using SOM and inversion maps in tandem is an effective way for screening an area for carbon storage targets.

The relationship of hemorheological blood values and blood velocity of microcirculatory bloodstream in rats` skin vessels

Non-invasive study of blood rheology is relevant, but quite complex issue. When systemic blood viscosity and hematocrit levels deviate, blood flow indicators in different parts of microvasculature change. Purpose of the study – research of blood flow characteristics in skin microcirculatory bloodstream of rats obtained by high-frequency ultrasound Dopplerography (HFUD) with given changes in rheological blood indicators. The studies were carried out on pubescent male Wistar rats. 3 experimental groups were formed. Group 1 (n = 21) “Hemodilution” – viscosity 1.99 ± 0.02 mPa*s, hematocrit 31.48 ± 0.31%. Group 2 (n = 32) “Reference values” – animals with unchanged blood levels – viscosity 2.84 ± 0.03 mPa*s, hematocrit 41.60 ± 0.3%. Group 3 (n = 32) “Erythrocytosis” – viscosity 3.95 ± 0.04 mPa*s, hematocrit 54.56 ± 0.23%. Dynamic blood viscosity in vitro studies were carried out on oscillatory viscometer. In order to evaluate hematocrit level heparinized whole blood was centrifuged in glass capillaries using; hematocrit values were assessed taking into account sedimentation of formed elements column using a hematocrit reader card. Blood flow in skin microcirculatory bloodstream of rats` left thigh area was estimated by HFUD method using Minimax-Doppler-K hardware and software system, with ultrasound transducer (frequency 20 MHz). Statistical analysis showed the models are correct. Blood indicators of the animals in three experimental groups differed statistically and significantly in terms of blood viscosity and hematocrit. Discriminant analysis was used to determine the relations between rheological blood parameters and characteristics of blood velocity in microcirculatory bloodstream which made it possible to identify the most significant characteristics of blood flow that tend to change depending on altered blood composition. These include: mean systolic velocity Vas (p 0.01), mean velocity Vam (p 0.001), mean volume velocity Qam (p 0.001), vascular resistance index RI (p 0.01) and the percentage of blood cells moving in low-speed H' (p = 0.03). The reliability of selected characteristics was checked with one-way analysis of variance; and their significance in determining membership in “Hemodilution”, “Reference values” or “Erythrocytosis” groups according to HFUD data was confirmed. Based on this analysis classification functions were generated for non-invasive dynamic blood viscosity determination according to ultrasound Dopplerography data.

Molecular interaction studies of Gamma-aminobutyric acid (GABA) in an aqueous medium at various temperatures: A comprehensive analysis using volumetric, thermoacoustic and DFT methods

The interaction of Gamma-aminobutyric acid (GABA) in an aqueous medium at various concentrations (0.101–1.086) mol·kg−1 as a function of temperature is being studied using volumetric, viscosity and acoustic analysis. The calculation of apparent molar volume (VΦ), partial molar volume (V∅o), apparent molar isentropic compression (Kϕ) and partial molar isentropic compression (Kϕ0) of GABA in an aqueous medium has been done by measuring the densities and speed of the sound in the temperature range of 298.15–323.15 K. The thermo-acoustic parameters like adiabatic compressibility (βs), acoustic impedance (Z), intermolecular free length (Lf), relative association (RA), relaxation time (τ), internal pressure (πi), enthalpy (ΔH), Gibbs free energy (ΔG), and change in entropy (ΔS) are also computed. The strength of the hydrogen bond interaction of GABA in an aqueous medium and its dipole moment are calculated using single-point energy calculations. These calculations employ IEFPCM and PCM solvation models using DFT/B3LYP and MP2 methods with the 6-311G++ (d, p) basis set. The outcomes are interpreted in terms of hydrogen bond interactions that exist in the mixture.

Homotopic dynamic solution of hydrodynamic nonlinear natural convection containing superhydrophobicity and isothermally heated parallel plate with hybrid nanoparticles

Abstract The purpose of this work is to investigate the effect of thermal radiation on convective heat transfer for an electrically conducting hybrid nanofluid moving perpendicularly through a microchannel with parallel plates heated under isothermal conditions, while subjected to a transverse magnetic field. In this case, one surface exhibited a superhydrophobic slip and temperature jump, whereas the others did not. The objective of the study was to determine the impacts of thermal radiation, heat generation, and magnetism on the volume flow rate, velocity, and bulk temperature when either surface is heated by a constant wall temperature. Our findings reveal that the radiation parameter significantly influences both the Nusselt number and skin friction differently depending on the surface conditions, while also reducing flow rate and bulk temperature. The heat generation parameter similarly affects these variables but varies with the type of surface being heated. Additionally, both the velocity and temperature profiles increase with the porosity parameter and heat generation coefficient, regardless of the heated surface. Statistical analysis confirms the significance of magnetic and heat generation parameters in determining skin friction and the Nusselt number, and streamlines and isotherms illustrating the effects of thermal radiation and magnetism on two different hybrid nanofluids when heated on nonslip and superhydrophobic surfaces were provided. These insights provide valuable information for the design and maintenance of mini- and microdevices in the fields of nanoscience and nanotechnology.

Experimental demonstration of a liquid piston Stirling engine with a wet regenerator

In this study, a liquid piston Stirling engine with a water-absorbing wick to keep the regenerator wet (LPSE(wet)) was designed and built. The feasibility of operating the LPSE (wet) at lower temperatures to increase power output compared with that of a liquid piston Stirling engine with a dry regenerator (LPSE (dry)) was experimentally verified. First, the critical temperatures of LPSE (wet) and LPSE (dry) were measured. The experimental results revealed that LPSE (dry) operated at 100 °C, whereas LPSE (wet) operated at 65 °C. Thus, in this study, LPSE (wet) can be operated at a critical temperature 35 °C lower than that of LPSE (dry). The LPSE (wet) could be operated continuously for 900 min, demonstrating the effectiveness of the water-absorbing wick mechanism for long-duration operation. Next, the specific acoustic impedance distribution, the phase difference between the pressure and the cross-sectional mean velocity distribution, and the acoustic power distribution inside the device were measured for LPSE (dry) and LPSE (wet) during each operation. The results confirmed that both LPSE (dry) and LPSE (wet) realized a traveling wave field in which the phase difference between the pressure and cross-sectional mean velocity was close to zero and the specific acoustic impedance more than 30 times the characteristic impedance of a sound wave propagating in free space, which are required to obtain high thermal efficiency, near the regenerator position. The ratio of acoustic power before and after the regenerator was 1.18 (at a hot end temperature of 130 °C) for LPSE (dry) and 1.54 (at a hot end temperature of 90 °C) for LPSE (wet). Under the same conditions, the acoustic power of LPSE (wet) was 10 times or above that of LPSE (dry). These results confirmed that LPSE (wet) designed in this study could operate at lower temperatures and exhibit higher-power output than LPSE(dry).

3D-printed polarization-independent low-cost flexible frequency selective surface based dual-band microwave absorber

Abstract A 3D-printed polarization-independent low-cost lightweight and flexible frequency selective surface based dual-band microwave absorber is presented in this paper. Two concentric square loops fabricated at different heights using 3D printing technology are responsible for exhibiting dual-band responses at 3.32 GHz (S-band) and 5.46 GHz (C-band) with more than 97% absorptivities. The corresponding full widths at half maximum bandwidths are observed as 230 MHz (3.21–3.44 GHz) and 450 MHz (5.27–5.72 GHz). The proposed topology is polarization-insensitive owing to the four-fold symmetry. The absorption phenomenon is explained with the analysis of current distributions at the surface and impedance curves at the frequencies of resonance. Further, the performance has been evaluated for both planar and curved surfaces with different angles of curvature, and the good agreement between the measured and simulated responses confirms the flexible behavior of the proposed structure.

Geological inference of channel and polka-dot seismic anomalies in Yeongil bay, Pohang

The Engineering Ocean Seismic 3D system, which enables ultra-high-resolution seismic surveys on a smaller survey scale, was deployed in Yeongil Bay, Pohang, South Korea. The region is renowned for abundant shallow gas deposits and faults. Based on acoustic impedance contrast and abnormal behavior observations, two seismic anomalies termed channel and polka-dot anomalies have been identified in the seismic volume. Seismic attribute analysis based on the signal amplitude and structural characteristics reveals that these anomalies correspond to shallow biogenic gas deposits. Structural interpretation of the seismic volume revealed that the contractional deformation resulting from post-Miocene neotectonics has resulted in uplift and reverse faulting in the Pohang region, contributing to the formation of anomalies. The channel anomalies correspond to gas-saturated tidal channels that formed during eustatic sea-level changes in the post-Last Glacial Maximum period. The polka-dot anomalies are located in topographic lows and are overlain by neotectonic sediment. The different behaviors of these anomalies in a seismic volume can be attributed to the different thicknesses of overburden overlying each of the anomalies.

Dynamic control of elastic wave transmission by a digital metalayer

Piezoelectric materials with shunt circuits have aroused much research interest due to flexible parameter adjustment. However, shunted piezoelectric elements are difficult to respond to the dynamic changes in the whole system due to the absence of autonomous control ability, which constrains their practical applications. Here, we propose a digital metalayer to control the wave energy transmission across different materials in real time. This digital metalayer comprises a stack of multiple piezoelectric lead zirconate titanate (PZT) disks connected with shunt capacitance circuits (SCCs). The external digital control system adjusts the effective acoustic impedance of the PZT disks through digital potentiometers and microprogrammed control unit, thereby enabling digital manipulation of wave transmission. Utilization of optimized SCCs further enhances adjustment accuracy, supporting both negative and positive capacitance values. The experiments demonstrate that this digital metalayer exhibits remarkable performance in controlling wave transmission. Moreover, the distinct variations in transmitted amplitudes, precisely controlled by the digital metalayer, are harnessed as binary signals for information transmission. An image of letters is encoded into a series of amplitude-modulated waves by the digital metalayer and clearly transmitted. The proposed digital metalayer shows great promise for applications in intelligent impedance matching and the real-time modulation systems.

Estimates of natural frequencies for nuclear vibration, and an assessment of the feasibility of selective ultrasound ablation of cancer cells

Selective ablation of cancer cells by ultrasound would be transformative for cancer therapy, but has not yet been possible. A key challenge is that cancerous and non-cancerous cells typically have similar acoustic impedance and are thus indistinguishable as materials in their responses to ultrasound. However, in certain cancers, cytoskeletal and nuclear lamin structures differ between healthy and malignant cells, opening the possibility of exploiting structural differences that manifest as different vibrational responses. To assess the possibility that the nuclei of certain cancerous cells might vibrate at different frequencies, we measured sizes and effective indentation moduli of a range of cancerous and non-cancerous cells from several cell lines and regions of the brain, and estimated the natural frequencies for nuclear vibration. Results suggest a potential difference in natural frequency for nuclear vibration between certain cancerous and non-cancerous cells, on the order of tens of kHz. This gap is potentially sufficient for selective ablation and motivates future experimentation on these specific cell types.