Changes In Attenuation Research Articles

Enhanced response speed of SAW based hydrogen sensor employing a micro-heater

To feature fast hydrogen detection, a new design of surface acoustic wave (SAW) based hydrogen sensor integrated with a micro-heater is proposed in this paper. A 200 MHz delay-line patterned SAW sensing chip coated Pd/Ni alloy hydrogen sensitive film and a micro-heater are prepared on a Y35oX quartz wafer. The hydrogen gas adsorption in Pd/Ni thin-film modulates the SAW propagation, and against the temperature interference, the corresponding changes in acoustic attenuation are collected as the sensor signal. The Micro-heater is designed to catalysis the gas-sensitive effect by regulating the working temperature, and the influence law of heating temperature towards response speed is revealed theoretically, allowing determination of the optimal working temperature. The experimental results verify the theoretical prediction. Fast response (t90 < 2 s), lower power consumption (<1.35 W), and the low detection limit (<15 ppm) are achieved at low working temperature of 75 °C. Furthermore, very low crossed humidity sensitivity and excellent long-term stability are observed.

Comparing two ocean biogeochemical models of Chesapeake Bay with and without the sulfur cycle instead highlights the importance of particle sinking, burial, organic matter, nitrification and light attenuation

A number of models have been developed to simulate hypoxia in the Chesapeake Bay, but these models vary in complexity and in which processes they represent. In this study we implement a previously published biogeochemical code (BioRedoxCNPS) developed for open-ocean waters that includes “cryptic” microbial sulfur cycling within the ChesROMS physical model of the Chesapeake Bay. Sulfur cycling can increase rates of denitrification and anammox in anoxic waters, but the net impacts of such changes on oxygen, nitrate and ammonium are not understood. We compare the results to a physically identical simulation with an estuarine biogeochemical cycling code previously implemented and calibrated in the Bay (ECB). The ECB code neglects sulfur cycling but includes burial of particulate organic matter (POM) and cycling of dissolved organic matter (DOM) and uses different values for many parameters governing phytoplankton growth and particle dynamics. Although the BioRedoxCNPS model produces a better simulation of oxygen and nitrate at a key test site this turns out not to be due to the inclusion of sulfur cycling. Instead, large differences in modeled oxygen and ammonium are largely due to whether or not the biogeochemical codes include cycling of DOM and sedimentary burial of POM. Changes in light attenuation produce large changes in nitrate. Changes in parameters used in both biogeochemical codes (in particular particle sinking velocities) tended to compensate the other differences in model construction. The quantitative impacts of these choices for simulating Chesapeake Bay have not previously been documented in the peer-reviewed literature. Predictions of hydrogen sulfide from our merged model were very sensitive to the choice of parameters and light attenuation. This suggests that observations of hydrogen sulfide could help to constrain these processes in future models.

Immune-Related Thyroiditis in Patients with Advanced Lung Cancer Treated with Immune Checkpoint Inhibitors: Imaging Features and Clinical Implications.

Immune checkpoint inhibitors (ICI) are widely used in advanced nonsmall cell lung cancer (NSCLC) treatment, and the immune-related adverse events involving many organs have been recognized. This article investigated the incidence and imaging characteristics of immune-related thyroiditis in NSCLC patients and correlated the findings with clinical features. A total of 534 NSCLC patients treated with ICI were included. Imaging findings indicative of thyroiditis included changes in morphology and attenuation on restaging chest CT scans and FDG uptake on PET/CT during ICI therapy. Fifty patients (9.4%) had imaging findings indicative of thyroiditis. The median time to onset was 9.5 weeks (range: 0.9-87.4 weeks). The most common finding was diffuse hypoattenuation of the gland (72%), with enlargement in 15 and atrophy in 12 patients. Heterogeneous attenuation of the gland was noted in 12 patients (24%), with enlargement in 7 and atrophy in 1 patient. Two patients (4%) showed increased FDG uptake in the gland on PET/CT without changes in the CT scan. Twenty-two patients who had both clinical and radiologic diagnoses of thyroiditis were more frequently managed with hormone replacement than those with thyroiditis without an imaging abnormality (p < 0.0001). Therefore, awareness of the imaging findings of immune-related thyroiditis may alert clinicians to the presence of clinically relevant thyroiditis.

Components and Tidal Modulation of the Wave Field in a Semi-enclosed Shallow Bay

The wave fields of coastal bays are comprised of waves generated by far-off storms that enter the bay to combine with waves generated locally by winds inside the bay and regionally outside the bay. In any given location, the resultant wave field varies spatially and temporally, and affects coastal features, such as beaches in estuaries and bays (BEBs). However, wave fields in enclosed bays with tidal shoals are poorly studied, limiting the efficacy of coastal protection and restoration projects in these systems, a critical focus in light of ongoing sea level rise. Here we present observations of the wave field in Tomales Bay, a 20-km-long, narrow, semi-enclosed embayment on the wave-dominated coast of Northern California (USA) with a spring-tide range of 2.5 m. We deployed pressure sensors near several beaches along the linear axis of the bay. Low-frequency waves (4*10^{-2}-2.5*10^{-1} Hz or 4–25-s period) were not observed further than 4 km of the mouth, delineating the “outer bay” region, where remotely generated swell and regionally generated wind waves could dominate. The wave spectrum of the landward “inner bay” was dominated by fetch-limited waves generated within the bay with frequency ge 2.5*10^{-1} Hz. The energy of both ocean waves and locally generated wind waves across all sites were controlled by the tide, but the former by changes in attenuation and the latter likely by modulation of wave generation. Wave energies were low at low tide and high at high tide, but high-frequency wind wave energy was increased during ebb tides while lower-frequency swell energy was reduced during ebb tides, suggesting different mechanisms of tidal influences. Thus, in addition to fluctuations in winds and the presence of ocean waves, tides exert a strong control on the wave energy spectra at coastal features in mesotidal regions. In general, events that may be impactful for BEB morphology are expected to occur when waves due to high winds or high-swell event arrive during high-tide periods. However, no such events were observed during our study and questions remain as to how rarely such events occur across the bay.

Optimization of Scan Delay in Contrast Enhanced Computed Tomography of Pancreas Using Bolus Tracking Category

Introduction: Pancreatic pathologies present a challenge for the medical imaging professionals for detection, classification and staging. Multiphasic multidetector computed tomography provides detailed visualization and definition of deeper and smaller structures and enhancement pattern of tumors during different phases. The objective of this study was to optimize the scan delay time for contrast enhanced computed tomography of pancreas after the use of bolus tracking technique. Materials and methods: Triphasic MDCT of the pancreas was performed on 109 patients after administration of 300-350 mgI/mL contrast medium injected at 3.5 mL/s. Patients were prospectively randomized into three groups with different scanning delays for the three phases (arterial, pancreatic, and venous) after bolus tracking was triggered at 100 HU of aortic contrast enhancement. Mean attenuation values of the abdominal aorta, superior mesenteric artery, pancreatic parenchyma, splenic vein, portal vein, and hepatic parenchyma were measured. Increases in attenuation values after contrast administration were assessed. Results: Mean contrast enhancement in the aorta (change in attenuation, 313–320 HU) and the superior mesenteric artery (change in attenuation, 291–302 HU) approached peak enhancement 4-7 seconds after bolus tracking was triggered. Pancreatic parenchyma became most intensely enhanced (change in attenuation, 107–110 HU) 20-25 seconds after triggering, and then the enhancement gradually decreased. Enhancement of the splenic vein and portal vein peaked at 22 seconds. Liver parenchyma reached 71 HU, 25 seconds after triggering and reached a plateau (change in attenuation, 81-76 HU) at a further scanning delay of 45–50 seconds. Conclusion: Based on the protocol used in this study, the optimum scan delay were 4-7 seconds for arterial phase, 10-22 seconds for pancreatic parenchymal phase and 40-50 seconds for the hepatic parenchymal phase; after bolus tracking triggered at 100 HU in the abdominal aorta.

Metre-scale damage zone characterization usingS-coda waves from active ultrasonic transmission measurements in the STIMTEC project, URL Reiche Zeche, Germany

SUMMARYStudies of controlled hydraulic stimulation experiments with active and passive seismic monitoring conducted in Underground Research Laboratories (URLs) benefit from specific knowledge of hydraulic parameters, close by microseismic monitoring revealing structural details of the rock mass, and detailed evolution of seismicity in response to injection operations. Microseismic monitoring is commonly used to characterize a stimulated reservoir volume, for example, in terms of damage evolution of the rock mass. Since seismic attenuation is affected by damage of the rock volume, active seismic sources covering sizes from the centimetre to decimetre scale may help us to investigate space–time varying attenuation properties in a reservoir. This may allow us to monitor damage evolution of the stimulated rock volume in more detail, also since active seismic sources produce stronger signals leading to a broader frequency range that can be analysed compared to passive seismic signals. Within the STIMTEC project in the URL Reiche Zeche (URL-RZ) in Freiberg (Germany), more than 300 active Ultrasonic Transmission (UT) measurements were performed before and after hydraulic stimulations in two boreholes in the targeted rock volume, an anisotropic metamorphic gneiss. The signal-frequency content ranges between 1 and 60 kHz. Assuming scattering attenuation to dominate over intrinsic attenuation, we here apply the single isotropic scattering model. S-coda waves of 88 spatially representative UT measurements are used to estimate the coda quality factor (QC). We obtain stable QC estimates for centre frequencies of octave-width frequency bands between 3 and 21 kHz. We group neighbouring UT measurements to stabilize the observations and form eight UT groups in total, covering different depth intervals in three boreholes and four different time periods to investigate scattering attenuation changes in a spatiotemporal manner. Our final mean QC ($\overline {{Q}_C} $) estimates show characteristic frequency-dependence as observed at the field scale in geological reservoirs. We find temporal variations of QC are strongly connected to hydraulic stimulation, and these variations are more significant than those resolved from velocity changes. $\overline {{Q}_C} $ estimates at frequencies above 15 kHz indicate healing of injection-induced small-scale fractures during a two-months post-stimulation phase. Larger fractures, mostly sampled by lower frequencies (&amp;lt;15 kHz), seem to be more persistent with time (over 15 months). We observe spatial differences of $\overline {{Q}_C} $ values near the mine galleries (driftway and vein drift) and relate these observations to different extents and characteristics of the galleries’ excavation damage zones. Our results further support previous assumptions based on borehole televiewer logs and mapped structures of an existing fault with larger damage zone that crosses the stimulated rock volume NW-SE between the galleries. We conclude that the coda analysis of active UT measurements complements established imaging methods used during experiments in URLs. In particular, coda analysis is a powerful tool for the detection of damage zones and for monitoring local fracture networks with immediate application for imaging georeservoirs considered for exploitation or underground storage of gases and liquids.

Effect of Barometric Pressure Fluctuations on Gas Transport over Soil Surfaces

Molar diffusion mechanism is generally considered to be the main physical process of gas transport at the soil–atmosphere interface. However, the advection mechanism in porous medium can considerably affect soil gas transport. Barometric pressure fluctuations caused by pressure pumps is one of the main factors that affects the advection mechanism. Most of the existing studies are overly focused on the construction of complex mathematical models and cannot exclude other environmental factors from interfering. In the present study, a simple attenuation form of barometric fluctuations was explored as a “minimum unit” of pressure wave in laboratory. A pressure attenuation model (PAM) was developed to verify the relationship between pressure difference and gas emission from soil surface by measuring the change in pressure attenuation. The effect of pressure fluctuations on soil surface gas fluxes was then quantified based on the calculated fluxes. In addition, the relationship between the physical properties of the soil medium and the change in pressure was also analyzed. The results show that fluctuations in air pressure can cause a change in soil CO2 fluxes by an order of magnitude (change of 1 Pa can result in approximately 100% change in flux for sandy loam). The sensitivity of different soil medium to pressure differences was positively correlated with soil gas permeability, which is the main physical property of soil that influences the response of gas to pressure fluctuations. These results provide important prerequisites for quantifying more complex pressure fluctuations in a future study.

Research on the Propagation of Acoustic Signal and Attenuation Change Law of Gas Pipeline Double-Point Leakage

In order to better model the acoustic signal propagation and attenuation of pipeline leaks, a laboratory gas pipeline leak detection platform taking air as the experimental medium is hereby adopted to investigate the law of hole spacing on acoustic signal propagation and attenuation at different pressures for double-point leaks. The results show that in the case of a fixed pressure, the amplitude of the three hole spacing in the propagation along the pipe decreases gradually, while that near the leak point decreases the most, with a maximum difference being up to 90%, after which the difference gap between the amplitude is gradually narrowed; different hole spacing has little effect on the RMS voltage along the downstream of the double-point leak pipe but exercises a greater effect on the RMS voltage propagation between the double-point leak; the attenuation coefficient of the leak signal decreases generally with the distance, which generally becomes smaller with the increasing distance and that along the downstream of the pipeline and near the leakage point decreases the most in the case of the double-point leakage, with a decrease rate reaching close to 50%. Then, the decrease rate becomes smaller gradually and reaches close to 20%, while that of the attenuation coefficient of the two distances between the three sensors is relatively close for the double-point leakage, with the first section close to 50% to 60% and the second section close to 60% to 80%. Under the condition where the pressure is different and the hole spacing remains the same, the acoustic signal increases with the increasing pressure when the attenuation coefficient decreases.

Data-assimilated time-lapse visco-acoustic full-waveform inversion: Theory and application for injected CO2 plume monitoring

Continuous seismic monitoring for quantifying CO2 plume migration and detection of any potential leakages in the subsurface is essential for the security of long-term anthropogenic carbon dioxide geologic storage. Traditional time-lapse full-waveform inversion (TLFWI) methods aim to map the CO2 distribution by estimating seismic velocity changes, but recent studies find that CO2-induced attenuation is an important complement to seismic velocity for tracking the CO2 plumes and even quantifying the CO2 saturation. We have developed a novel data-assimilated TLFWI method to construct high-resolution time-lapse velocity and attenuation changes from dense time-lapse monitoring data. This method consists of two theoretical developments: visco-acoustic full-waveform inversion (QFWI) and multiparameter hierarchical matrix-powered extended Kalman filter (mHiEKF). The method is capable of (1) posing temporal constraints to retrieve time-lapse information from dense monitoring data by using mHiEKF, (2) accurately recovering high-spatial-resolution velocity and attenuation perturbations using first-order equation system-based QFWI, and (3) providing the model uncertainty by estimating their model standard deviation. With numerical examples, we first find the effectiveness of the new QFWI on estimating accurate velocity and attenuation models simultaneously. Then, a CO2 leakage case and a realistic Frio-II CO2 monitoring case are presented to find the advantages and applicability of our data-assimilated QFWI method for estimating time-lapse changes using dense time-lapse monitoring surveys. By assimilating time-lapse seismic monitoring data over time, our data-assimilated QFWI method can improve the resolution of velocity and attenuation changes and decrease their model uncertainties.

An X-Band High-Accuracy GaAs Multifunction Chip With Amplitude and Phase Control

This paper presents a high-accuracy multifunction chip (MFC) with amplitude and phase control in X-band. The MFC is designed with a common leg structure and incorporates a 6-bit attenuator (ATT), a 6-bit phase shifter (PS), two gain compensation amplifiers (GCAs), three single pole double throw switches (SPDTs), and fourteen logic control circuits. The interstage matching networks (IMNs) are inserted to compensate for the insertion phase and attenuation changes from the design due to the mismatches occurring when cascading the separately designed PS and ATT blocks. The receive and transmit modes switching is achieved by using four SPDTs. In addition, the resistance feedback is used in GCAs to compensate for passive losses and provide gain to the MFC. The proposed MFC is fabricated in 0.15- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> GaAs pseudomorphic high-electron-mobility transistor (pHEMT) process. In the range of 8–11 GHz, the measured maximum root-mean-square (RMS) amplitude error of the MFC is less than 0.28 dB, and the maximum RMS phase error is less than 3.3°. Moreover, the MFC is achieved with a size of 4.3 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times2.85$ </tex-math></inline-formula> mm. Excellent performance and compact size make the MFC great potential in spaceborne phased array applications.

Quantitative Assessment and Comparative Analysis of Longitudinal Lung CT Scans of Chest-Irradiated Nonhuman Primates.

Computed tomography (CT) imaging has been used to diagnose radiation-induced lung injury for decades. However, histogram-based quantitative tools have rarely been applied to assess lung abnormality due to radiation-induced lung injury (RILI). Here, we used first-order summary statistics to derive and assess threshold measures extracted from whole lung histograms of CT radiodensity in rhesus macaques. For the present study, CT scans of animals exposed to 10 Gy of whole thorax irradiation were utilized from a previous study spanning 2-9 months postirradiation. These animals were grouped into survivors and non-survivors based on their clinical and experimental endpoints. We quantified the change in lung attenuation after irradiation relative to baseline using three density parameters; average lung density (ALD), percent change in hyper-dense lung volume (PCHV), hyperdense volume as a percent of total volume (PCHV/TV) at 2-month intervals and compared each parameter between the two irradiated groups (non-survivors and survivors). We also correlated our results with histological findings. All the three indices (ALD, PCHV, PCHV/TV) obtained from density histograms showed a significant increase in lung injury in non-survivors relative to survivors, with PCHV relatively more sensitive to detect early RILI changes. We observed a significant positive correlation between histologic pneumonitis scores and each of the three CT measurements, indicating that CT density is useful as a surrogate for histologic disease severity in RILI. CT-based three density parameters, ALD, PCHV, PCHV/TV, may serve as surrogates for likely histopathology patterns in future studies of RILI disease progression.

Sound attenuation in two-dimensional glasses at finite temperatures.

The thermal conductivity of glasses exhibits an unusual temperature dependence compared to their crystalline counterparts. Sound attenuation due to disorder in glasses was proposed to be important in rationalizing this special behavior. Simulation studies suggest that in the harmonic approximation, the sound attenuation follows Rayleigh scattering scaling at small wave vector in both two-dimensional (2D) and 3D glasses. The influence of the anharmonicity on sound attenuation has very recently been investigated numerically, but only in 3D glasses. Hence, it remains unknown in simulations how sound attenuation changes with the wave vector in 2D glasses when the anharmonicity comes into play. Here, we address this issue by performing computer simulations in low-temperature 2D glasses over a large range of glass stabilities. We find that the way the anharmonicity affects sound attenuation in 2D glasses is the same as that in 3D, thus revealing that numerically the influence of the anharmonicity on sound attenuation does not rely on the spatial dimension.

Thymic cyst: Is attenuation artifactually increased on contrast-enhanced CT?

Thymic cysts are often misinterpreted as thymomas or lymph nodes, then leading to unnecessary thymectomy. The purpose of this study was to investigate how the adjacent large vessels artifactually affected attenuation values of thymic cysts on contrast-enhanced CT (CE-CT). In this retrospective study, a total of 84 patients were included with pathological diagnosis of thymic cysts and preoperative CE-CT. Quantitative measurements of the size, CT attenuation of thymic cysts and CT attenuation of adjacent large vessels were performed on preoperative CE-CT. According to the absolute change in attenuation of the cysts between contrast-enhanced and nonenhanced CT, the patients were classified into the groups of artifactual hyper-density, unchanged density, and artifactual hypo-density. CT characteristics were compared between the three groups. Furthermore, multivariable logistic regression analysis was performed to determine the independent factors for artifactual hyper-density. The group of artifactual hyper-density had smaller short diameter of the cysts, higher postcontrast attenuation values and lower nonenhanced attenuation values of the adjacent large vessel. Furthermore, the multivariable logistic analysis showed that artifactual hyper-density of thymic cysts was negatively associated with nonenhanced attenuation of adjacent large vessel, and positively associated with postcontrast attenuation of adjacent large vessel and postcontrast attenuation of cysts. Most cases with >20 HU nonenhanced CT attenuation in surgically resected cases. Artifactual hyper-density─pseudo-enhancement phenomenon of thymic cysts was more apparent in higher increasing attenuation of adjacent large vessels on CE-CT. A well understanding of this phenomenon can help reduce preoperative misdiagnosis and unnecessary thymectomy.

Role of neodymium substitution on the structural, magnetic and microwave absorbing properties of nickel ferrites

The neodymium substituted nickel ferrites with a nominal composition of NiNdxFe(2-x)O4 (with x = 0.00; 0.01; 0.03; 0.05; 0.06; 0.08 and 0.10) were successfully synthesized by milling technique. The NiO, Nd2O3 and Fe2O3 powders were used as raw materials and were prepared in a mole ratio. The characterization of the samples was done by X-ray diffraction (XRD), Fourier-Transform Infrared Spectroscopy (FTIR), scanning electron microscopy (SEM), vibrating sample magnetometer (VSM) and vector network analyzer (VNA). In this study, the PXRD showed and verified that all Nd3+ ion successfully substituted the NiFe2O4 samples with a single cubic spinel phase. Infrared spectra showed two strong absorption bands in the frequency range of 405–420 cm−1 and 595–610 cm−1, which were respectively attributed to tetrahedral and octahedral sites of the spinel ferrites. The SEM revealed homogenous morphology on all NiNdxFe(2-x)O4 but still not uniform powders. The particle size of the powder ranged from 150 to 700 nm. The magnetic properties of all of the samples showed a ferrimagnetic behavior. The Ms value was decreased when the Hc increased with increases in the Nd3+ substitution value. The ability to absorb the microwave measured by VNA shows the enhancement of the microwave attenuation where the Nd3+ substitution increased. The microwave attenuation changes increased from 91.25% to 98.32%. It can be seen that the composition of x at 0.05 promises to be new material for microwave absorption.

Evaluation of a wheel-based seismic acquisition system for a planetary rover

Prior to using in-situ planetary resources, efficient mapping of geochemical and physical characteristics of the near surface will be required. As part of an integrated geophysical instrument suite on exploration and prospecting vehicles, we investigated the suitability of seismic piezo-sensors rigidly mounted on the interior of a generic rover wheel. Factors that can compromise proper data acquisition for this system include the natural mechanical resonance of the wheel and wheel-to-ground coupling. We characterized the natural resonance frequency bands of a generic wheel with an electromagnetic shaker. We also collected seismic shot gathers for subsequent seismic surface-wave analysis using a wheel in both a dry, laboratory sand tank (1.8 × 1.8 × 0.6 m) and in frozen loess soils within the United States Army Corps of Engineers Permafrost Tunnel in Alaska. For our wheel, self-weighted coupling to the ground was found to be adequate, although suitable wheelbase dimensions can constrain field acquisition geometries. In unconsolidated sediments, represented by medium sand (0.25–0.5 mm), wheel resonance of 1 kHz does not affect the fundamental mode used in shear-wave-velocity-to-depth inversion. When analyzed, shot-gather data collected from both wheel-mounted sensors and sand-planted sensors, in loose dry sand, effectively captured similar fundamental surface-wave modes. This is evident in frequency-versus-phase velocity dispersion images. Because narrow frequency bands of wheel resonance exhibit a high signal-to-noise ratio, they also readily detect lateral attenuation changes. Thus, wheel resonance can also be used to capture soil attenuation changes, including those produced when pore H2O ice acts to cement the regolith or loose-grained soils.

Noninvasive tracking of solidification using ultrasound

Noninvasive tracking of solidification is typically done by monitoring the sample’s surface temperature. This approach is error-prone and not always appropriate for complex geometries and often does not provide complete information on the sample’s transitioning phases. This feasibility study investigates using ultrasonic waves to noninvasively track solidification in wax. Ultrasonic sensors are used in through-transmission mode to monitor the response over the solidification period. The difference in speed of sound between the wax’s liquid and solid phase allows for the solid fraction of the sample to be calculated over the solidification period and the time of complete solidification to be identified. Changes in attenuation during solidification are consistent across experiments. These changes are likely to provide additional information about the cast once they are fully understood. Temperature probes are used to verify the results obtained from the ultrasonic data. The ultimate goal of the project is to use a metal sample and connect information from the ultrasonic signal to the material properties and grain structure of the cast using noninvasive ultrasound technology.

Prevalence of lung atelectasis in sedated dogs examined with computed tomography

BackgroundComputed tomography (CT) scanning of the lung is known to be a valuable tool when investigating lung pathology of the dog. During CT-scan the dog needs to be immobilized and general anesthesia has historically been considered as gold standard although being a more expensive and time-consuming alternative to sedation. Today, modern high speed multidetector CT-scanners offer new possibilities for sedation as an alternative. Both anesthesia and sedation can cause lung atelectasis, and this can be problematic when reading the CT-images since it potentially can masque or mimic lung pathology leading to misdiagnosis. The objective of this prospective analytic study was to investigate the prevalence of lung atelectasis and changes in lung attenuation over time in dogs that receive intravenous sedation and positioned in sternal recumbency.Results20 dogs without known lung pathology underwent three consecutive CT-scans of the lung; the first scan was initiated as soon as the dog was sufficiently sedated, the second scan approximately 5 min after the first one and the last scan after the dog’s orthopaedic scan was completed. The dogs received intravenous sedation in a combination of dexmedetomidine and butorphanol and were kept positioned in a strict sternal recumbency during sedation and exam. Each lung lobe was individually examined in an axial plane and measurements of dorsal, ventral, and mean lung attenuation were made. Atelectasis or areas with poorly aerated lung tissue were not detected as all parts of the lobes were normally aerated at all three scans. A statistically significant increase in lung attenuation between the first and the second scan (P = 0.03) and between the first and the third scan (P = 0.0004) was seen in the ventral part of the lobes.ConclusionsThis study indicates that CT-examination of the lungs can be performed on sedated dogs that are kept in a sternal recumbency without development of atelectasis. It also suggests that there is an early correlation between time and increase in lung attenuation.

Crustal permeability changes inferred from seismic attenuation: Impacts on multi-mainshock sequences

We use amplitude ratios from narrowband-filtered earthquake seismograms to measure variations of seismic attenuation over time, providing unique insights into the dynamic state of stress in the Earth’s crust at depth. Our dataset from earthquakes of the 2016–2017 Central Apennines sequence allows us to obtain high-resolution time histories of seismic attenuation (frequency band: 0.5–30 Hz) characterized by strong earthquake dilatation-induced fluctuations at seismogenic depths, caused by the cumulative elastic stress drop after the sequence, as well as damage-induced ones at shallow depths caused by energetic surface waves. Cumulative stress drop causes negative dilatation, reduced permeability, and seismic attenuation, whereas strong-motion surface waves produce an increase in crack density, and so in permeability and seismic attenuation. In the aftermath of the main shocks of the sequence, we show that theM≥ 3.5 earthquake occurrence vs. time and distance is consistent with fluid diffusion: diffusion signatures are associated with changes in seismic attenuation during the first days of the Amatrice, Visso-Norcia, and Capitignano sub-sequences. We hypothesize that coseismic permeability changes create fluid diffusion pathways that are at least partly responsible for triggering multi-mainshock seismic sequences. Here we show that anelastic seismic attenuation fluctuates coherently with our hypothesis.

Study of Acoustic Attenuation Trends in Permendur 49 Magnetostrictive Material

The mechanical properties of ferromagnetic materials change when the magnetization level of these materials changes. This phenomenon occurs due to magnetostriction. The change in direction of the magnetic domains is the reason for magnetostriction. In this paper, we hypothesize that the amount of acoustic attenuation in ferromagnetic materials depends on their magnetization level. To prove this hypothesis, a numerical approach is employed and the results compared to previous results in the literature. Permendur, an iron-cobalt alloy that exhibits a large magnetostriction effect, is used for the simulation. The results of the numerical study show that ultrasonic reflection and transmission coefficients in Permendur change in response to changes in the external magnetic field. A comparison between these numerical results and experimental results in the literature allows us to determine the changes in acoustic attenuation due to the magnetic field. The results show that there is an increasing trend at first, and then a decreasing trend, between acoustic absorption attenuation and increasing external magnetic field. This approach would be useful in ultrasonic testing of ferromagnetic materials when the reflected echoes are not detectable due to attenuation.The mechanical properties of ferromagnetic materials change when the magnetization level of these materials changes. This phenomenon occurs due to magnetostriction. The change in direction of the magnetic domains is the reason for magnetostriction. In this paper, we hypothesize that the amount of acoustic attenuation in ferromagnetic materials depends on their magnetization level. To prove this hypothesis, a numerical approach is employed and the results compared to previous results in the literature. Permendur, an iron-cobalt alloy that exhibits a large magnetostriction effect, is used for the simulation. The results of the numerical study show that ultrasonic reflection and transmission coefficients in Permendur change in response to changes in the external magnetic field. A comparison between these numerical results and experimental results in the literature allows us to determine the changes in acoustic attenuation due to the magnetic field. The results show that there is an increasing trend at first, and then a decreasing trend, between acoustic absorption attenuation and increasing external magnetic field. This approach would be useful in ultrasonic testing of ferromagnetic materials when the reflected echoes are not detectable due to attenuation.

Study of Acoustic Attenuation Trends in Permendur 49 Magnetostrictive Material

The mechanical properties of ferromagnetic materials change when the magnetization level of these materials changes. This phenomenon occurs due to magnetostriction. The change in direction of the magnetic domains is the reason for magnetostriction. In this paper, we hypothesize that the amount of acoustic attenuation in ferromagnetic materials depends on their magnetization level. To prove this hypothesis, a numerical approach is employed and the results compared to previous results in the literature. Permendur, an iron-cobalt alloy that exhibits a large magnetostriction effect, is used for the simulation. The results of the numerical study show that ultrasonic reflection and transmission coefficients in Permendur change in response to changes in the external magnetic field. A comparison between these numerical results and experimental results in the literature allows us to determine the changes in acoustic attenuation due to the magnetic field. The results show that there is an increasing trend at first, and then a decreasing trend, between acoustic absorption attenuation and increasing external magnetic field. This approach would be useful in ultrasonic testing of ferromagnetic materials when the reflected echoes are not detectable due to attenuation.