Variation Of Attenuation Research Articles

Neutron tomography and image registration methods to study local physical deformations and attenuation variations in treated archaeological iron nail samples

This study presents a preliminary examination of the effects of environment changes post-excavation on heavily corroded archaeological Roman iron nails using neutron tomography and image registration techniques. Roman nails were exposed to either a high relative humidity environment, or fast thermal drying as primary experiments to show the power of this imaging technique to monitor and quantify the structural changes of corroded metal artifacts. This research employed a series of pre- and post-treatment tomography acquisitions (time-series) complemented by advanced image registration methods. Based on mutual information (MI) metrics, we performed rigid body and affine image registrations to meticulously account for sample repositioning challenges and variations in imaging parameters. Using non-affine local registration results, in a second step, we detected localized expansion and shrinkage in the samples attributable to imposed environmental changes. Specifically, we observed local shrinkage on the nail that was dried, mostly in their Transformed Medium (TM), the outer layer where corrosion products are cementing soil and sand particles. Conversely, the sample subjected to high relative humidity environment exhibited localized expansion, with varying degrees of change across different regions. This work highlights the efficacy of our registration techniques in accommodating manual removal or loss of extraneous material (loosely adhering soil and TM layers around the nails) post-initial tomography, successfully capturing local structural changes with high precision. Using differential analysis on the accurately registered samples we could also detect and volumetrically quantify the variation in moisture and detect changes in active corrosion sites (ACS) in the sample. These preliminary experiments allowed us to advance and optimize the application of a neutron tomography and image registration workflow for future, more advanced experiments such as humidity fluctuations, corrosion removal through micro-blasting, dechlorination and other stabilization treatments.

Coronary atherosclerotic plaque burden and characterization by spectral computed tomography scan in patients with high lipoprotein a and non-hemodynamically significant stenosis

Abstract Introduction Atherosclerotic coronary disease increases morbidity and mortality worldwide. Lipoprotein A (LpA) has emerged as a cardiovascular risk marker, but little is known of its direct influence in plaque volume and composition. Spectral computed tomography (CT) technology allows to characterize coronary plaques with new promising tools. Purpose To evaluate the association of LpA with the extent and composition of non-significant coronary plaques producing stenosis <50%. Methods We prospectively recruited 109 patients referred for noninvasive CT angiography (November 2023-January 2024) with suspected coronary artery disease. 20 had totally/partially non-calcified, non-significant coronary plaques. Plaques were segmented and volume was measured. Their composition was stablished as calcified (>200 UH), lipidic (<60 UH) and fibrous (60-200 UH). Spectral data-based plaque parameters were analyzed, including radiological attenuation on polyenergetic images (CTPI), on virtual low/high monoenergetic images (CT40KeV and CT140KeV, respectively), variation in attenuation across monoenergetic levels (slope40-140 KeV) and Z-effective value. CT scan images were acquired with a 128 detectors dual-layer spectral scan with prospective-retrospective/synchronization. Intravascular iodine-based contrast was administered. LpA was stablished as high (≥25 mg/dL) or low (<25 mg/dL). Results Mean age was 60 ± 11. Cardiovascular risk factor were equally distributed between groups. We analyzed 33 plaques. Total plaque volume was significantly higher in high LpA patients (125.9 mm3 vs 62.1 mm3). There were no differences in plaque composition by LpA (Table). Additionally, spectral data showed significantly higher plaque attenuation on CT140KeV images in high LpA patients (36.07 vs 21.32 HU; p = 0.05). There were no differences for the rest of spectral parameters. Conclusions Plaque volume was higher in patients with non-significant atherosclerotic disease and high LpA, but these plaques showed similar composition in high and low LpA patients. These patients might, therefore, respond to the same conventional treatment event though there is not specific treatment for high LpA yet. Additionally, spectral CT140KeV images could add more precision differentiating these plaques since radiological attenuation in these reconstructions is higher in patients with high LpA.TableFigure

Temporal variation of S-wave attenuation during the 2009 L'Aquila, Central Italy, seismic sequence

Summary We investigate temporal and spatial variations of the spectral decay parameter kappa (κ) before and after the April 6, 2009, L'Aquila earthquake (Mw 6.1), in central Italy. We analyzed foreshocks ten days before and aftershocks occurring ten days and six months after this main event. We select earthquakes with magnitudes Mw ≥ 3.2 registered by the seismic network of central Italy within a radius of 20 km from the epicenter of the L'Aquila mainshock and having hypocenter distances of less than 170 km. We separate near-source, along-path and near-site contributions of κ for each group of events and we detected temporal variations of this S-wave attenuation parameter. We find that ten days before the mainshock κ along the path has the lowest values, probably due to high tectonic stress accumulated, in agreement with previous investigations performed with other techniques, then κ increases during the main event and remains constant during the first ten days of aftershocks. The aftershocks that occurred six months after show an increase in the regional attenuation probably due to the tectonic stress released during the main shock and the earlier aftershocks. From the spatial point of view, ten days before the principal event the foreshocks located to the south show an increase in the near-source attenuation towards the northeast, in the direction of the mainshock. These spatial variations of κ may be related to the presence of crustal fluids near the rupture area, as evidenced by other previous studies. The first ten days of aftershocks that concentrate around the main earthquake have high near-source κ, and those located north of the main rupture have lower values. These observations are consistent with previous investigations that show variations of elastic and anisotropic crustal properties during the L'Aquila earthquake sequence due to dilatancy and fluid diffusion processes within the nucleation zone. We conclude that temporal variations of the spectral decay parameter κ provide important clues for the earthquake cycle in central Italy.

Evaluation of automatic tube current modulation in a CT scanner using a customised homogeneous phantom

Objective.The introduction of automatic tube current modulation (ATCM) has resulted in complex relationships between scanner parameters, patient body habitus, radiation dose, and image quality. ATCM adjusts tube current based on x-ray attenuation variations in the scan region, and overall patient dose depends on a combination of factors. This work aims to develop mathematical models that predict CT radiation dose and image noise in terms of attenuating diameter and all relevant scanner parameters.Approach.A homogenous phantom, equipped with the features to conduct discrete and continuous adaption tests, was developed to model ATCM in a Philips CT scanner. Scanner parameters were varied based on theoretical dose relationships, and a MATLAB script was developed to extract data from DICOM images. R statistical software was employed for data analysis, plotting, and regression modelling.Main Results.Phantom data provided the following insights: Median tube current decreased by 81% as tube potential varied from 80 kVp to 140 kVp. Doubling the DoseRight Index (DRI) from 12 to 24, at 24 cm diameter, produced a 294% increase in mA and a 46% decrease in noise. Mean mA increased by 53% whilst mean noise increased by 5.7% as helical pitch increased from 0.6 to 0.925. Changing rotation time from 0.33s to 0.75s gave a 56% reduction in mean mA and no change in image noise. Increasing detector collimation (n×T) resulted in higher tube currents and lower output image noise values, asnandTwere varied independently. Interpreting these results to apply transformations relevant to each independent variable produced models for tube current and noise with adjusted R-squared values of 0.965 and 0.912, respectively.Significance.The models developed more accurately predict radiation dose and image quality for specific patients and scanner settings. They provide imaging professionals with a practical tool to optimize scan protocols according to patient diameters and clinical objectives.

Exploring the dielectric loss of Martian regolith in the frequency domain using Zhurong radar data

Martian regolith is one of the primary science objectives of Mars exploration missions. The Rover Penetrating Radar carried by Zhurong rover allows for high-resolution subsurface imaging and in-situ measurements of Martian regolith dielectric properties, which are crucial to advance our understanding of Martian geology and hydrological evolution. While earlier studies have derived dielectric constants for the shallow subsurface, further characterization of subsurface materials requires the determination of attenuation properties. In this study, we applied the centroid-frequency shift method to explore the attenuation property of the Martian regolith in the frequency domain. Lateral attenuation variation was analyzed in detail by integrating subsurface radargram and navigation terrain images. The results show that, within a depth of ∼4 m, the attenuation of radar signal for Zhurong subsurface material is equal to a loss tangent of 0.0079, with a standard deviation of 0.001. Based on the loss tangent value, dielectric permittivity and ground characterization, we preclude the possibility that the regolith is predominantly igneous materials. The lateral variation of the attenuation property could likely be attributed to changes in the proportion of duricrusts, which are heterogeneously distributed along the rover traverse. Our findings offer valuable information for understanding the Martian regolith and its evolution, serving as a important reference for future Mars sample return missions.

Quality Evaluation of Argan Oil as a Food Product Using Ultrasonic Characterization

Abstract Start This study focuses on evaluating the quality of food-grade argan oil, an essential component of Moroccan cuisine, using experimental ultrasonic characterization. Variations in ultrasonic velocity and attenuation with temperature were exploited as significant parameters for quality control of argan oil. The results reveal an inverse correlation between ultrasonic velocity and temperature, providing a unique model for the studied samples of argan oil. The measurements also show that the acoustic attenuation of argan oil decreases with temperature, while it increases with the volumetric fractions of sunflower oil added to argan oil. The data collected during this experimental study demonstrate that the velocity of the mixture of argan oil and sunflower oil increases with rising temperature. It was observed that both ultrasonic parameters of this mixture are challenging to detect by ultrasound. Ensuring the reproducibility of measurements under the same conditions, reference graphs are established to detect adulteration, especially when considering blends of argan oil with sunflower oil.

Influence of ice properties on wave propagation characteristics in partially frozen soils and rocks: A temperature-dependent rock-physics model

A better understanding of the temperature effects on the propagation characteristics of elastic waves in frozen soils and rocks is imperative for accurately quantifying their freezing degrees. Although the existing rock-physics models based on the three-phase Biot (TPB) theory adeptly interpret observed velocity variation with temperature (VVT) curves, they often lack a comprehensive understanding of the mechanisms underlying attenuation variation with temperature (AVT) curves. In this study, we first extend the TPB theory to incorporate the temperature-dependent properties of ice, such as changes in volumetric fraction, morphology, and viscoelasticity, by integrating the relevant thermodynamic laws. Model parameters related to ice properties and interactions, such as rigidity, shear moduli, density, and friction, are redefined. Then, using a numerical rock-physics modeling approach, we examine influential factors and modes of the wave VVT and AVT responses. Our results indicate that the P- and S-wave velocities increase with source frequency, consolidation degree, and frame-supporting ice content, whereas they decrease with temperature and pore-floating ice content. The P- and S-wave attenuation factors increase with the frame-supporting ice content and decrease with the consolidation degree. Rising temperatures tend to amplify the peak magnitude of the P-wave attenuation factors and shift the central frequency of the S-wave attenuation factors. Finally, within a temperature-controlled laboratory environment, we conduct ultrasonic wave transmission testing on brine-saturated sediment and rock specimens. The results demonstrate that as the temperature increases from −15°C to −3°C, the P- and S-wave velocities decrease, whereas the P-wave attenuation factors decrease and the S-wave attenuation factors initially rise before declining. Our viscoelastic TPB theory outperforms the existing ones in interpreting the S-wave AVT observations. This temperature-dependent rock-physics model holds promise for interpreting the sonic logging data in the time-lapse monitoring of permafrost, glaciers, and Antarctica.

Multi-Scale and Multi-Layer Lattice Transformer for Underwater Image Enhancement

Underwater images are often subject to color deviation and a loss of detail due to the absorption and scattering of light. The challenge of enhancing underwater images is compounded by variations in wavelength and distance attenuation, as well as color deviation that exist across different scales and layers, resulting in different degrees of color deviation, attenuation and blurring. To address these issues, we propose a novel multi-scale and multi-layer lattice transformer (MMLattFormer) to effectively eliminate artifacts and color deviation, prevent over-enhancement, and preserve details across various scales and layers, thereby achieving more accurate and natural results in underwater image enhancement. The proposed MMLattFormer model integrates the advantage of LattFormer to enhance global perception with the advantage of “multi-scale and multi-layer”-configuration to leverages the differences and complementarities between features of various scales and layers to boost local perception. The proposed MMLattFormer model is comprised of multi-scale and multi-layer LattFormers. Each LattFormer primarily encompasses two modules: Multi-head Transposed-attention Residual Network (MTRN) and Gated-attention Residual Network (GRN). The MTRN module enables cross-pixel interaction and pixel-level aggregation in an efficient manner to extract more significant and distinguishable features, whereas the GRN module can effectively suppress under-informed or redundant features and retain only useful information, enabling excellent image restoration exploiting the local and global structures of the images. Moreover, to better capture local details, we introduce depth-wise convolution in these two modules before generating global attention maps and decomposing images into different features to better capture the local context in image features. The qualitative and quantitative results indicate that the proposed method outperforms state-of-the-art approaches in delivering more natural results. This is evident in its superior detail preservation, effective prevention of over-enhancement, and successful removal of artifacts and color deviation on several public datasets.

Evidence for faulting and fluid-driven earthquake processes from seismic attenuation variations beneath metropolitan Los Angeles

Seismicity in the Los Angeles metropolitan area has been primarily attributed to the regional stress loading. Below the urban areas, earthquake sequences have occurred over time showing migration off the faults and providing evidence that secondary processes may be involved in their evolution. Combining high-frequency seismic attenuation with other geophysical observations is a powerful tool for understanding which Earth properties distinguish regions with ongoing seismicity. We develop the first high-resolution 3D seismic attenuation models across the region east of downtown Los Angeles using 5,600 three-component seismograms from local earthquakes recorded by a dense seismic array. We present frequency-dependent peak delay and coda-attenuation tomography as proxies for seismic scattering and absorption, respectively. The scattering models show high sensitivity to the seismicity along some of the major faults, such as the Cucamonga fault and the San Jacinto fault zone, while a channel of low scattering in the basement extends from near the San Andreas fault westward. In the vicinity of the Fontana seismic sequence, high absorption, low scattering, and seismicity migration across a fault network suggest fluid-driven processes. Our attenuation and fault network imaging characterize near-fault zones and rock-fluid properties beneath the study area for future improvements in seismic hazard evaluation.

The Complete CEERS Early Universe Galaxy Sample: A Surprisingly Slow Evolution of the Space Density of Bright Galaxies at z ∼ 8.5–14.5

We present a sample of 88 candidate z ∼ 8.5–14.5 galaxies selected from the completed NIRCam imaging from the Cosmic Evolution Early Release Science survey. These data cover ∼90 arcmin2 (10 NIRCam pointings) in six broadband imaging filters and one medium-band imaging filter. With this sample we confirm at higher confidence early JWST conclusions that bright galaxies in this epoch are more abundant than predicted by most theoretical models. We construct the rest-frame ultraviolet luminosity functions at z ∼ 9, 11, and 14 and show that the space density of bright (M UV = −20) galaxies changes only modestly from z ∼ 14 to z ∼ 9, compared to a steeper increase from z ∼ 8 to z ∼ 4. While our candidates are photometrically selected, spectroscopic follow-up has now confirmed 13 of them, with only one significant interloper, implying that the fidelity of this sample is high. Successfully explaining the evidence for a flatter evolution in the number densities of UV-bright z > 10 galaxies may thus require changes to the dominant physical processes regulating star formation. While our results indicate that significant variations of dust attenuation with redshift are unlikely to be the dominant factor at these high redshifts, they are consistent with predictions from models that naturally have enhanced star formation efficiency and/or stochasticity. An evolving stellar initial mass function could also bring model predictions into better agreement with our results. Deep spectroscopic follow-up of a large sample of early galaxies can distinguish between these competing scenarios.

Investigating luminescence-depth profiles from rocks with different lithologies

Understanding of the attenuation of light into a rock surface is fundamental to the successful modelling of the luminescence profile in rock resulting from prolonged daylight exposure. Here, we investigate this light attenuation. Variations in apparent attenuation is first examined using the variation of luminescence signals with depth, modelled in two different ways to obtain attenuation coefficients. These results are compared with direct measurement of optical attenuation for three different rock types (sandstone, basalt, and granite). We conclude that global fitting of different exposure times using a constant but unknown μ gives rise to larger errors than free fitting, where we allow μ to be different for each exposure time. Our results show that because of differences in lithology and distribution of luminescent minerals, the direct measurement of optical attenuation overestimates the attenuation based on luminescence signals.

Accuracy of Volumetric Bone Mineral Density Measurement in Weight Bearing, Cone Beam Computed Tomography

Background: Weight bearing computed tomography (WBCT) utilizes cone beam CT technology to provide assessments of lower limb joint structures while they are functionally loaded. Grey-scale values indicative of X-ray attenuation that are output from cone beam CT are challenging to calibrate, and their use for bone mineral density (BMD) measurement remains debatable. To determine whether WBCT can be reliably used for cortical and trabecular BMD assessment, we sought to establish the accuracy of BMD measurements at the knee using modern WBCT by comparing them to measurements from conventional CT.Methods: A hydroxyapatite phantom with three inserts of varying densities was used to systematically quantify signal uniformity and BMD accuracy across the acquisition volume. We evaluated BMD in vivo (n = 5, female) using synchronous and asynchronous calibration techniques in WBCT and CT. To account for variation in attenuation along the height (z-axis) of acquisition volumes, we tested a height-dependent calibration approach for both WBCT and CT images.Results: Phantom BMD measurement error in WBCT was as high as 15.3% and consistently larger than CT (up to 5.6%). Phantom BMD measures made under synchronous conditions in WBCT improved measurement accuracy by up to 3% but introduced more variability in measured BMD. We found strong correlations (R = 0.96) as well as wide limits of agreement (-324 mgHA/cm3 to 183 mgHA/cm3) from Bland-Altman analysis between WBCT and CT measures in vivo that were not improved by height-dependent calibration.Conclusion: Whilst BMD accuracy from WBCT was found to be dependent on apparent density, accuracy was independent of the calibration technique (synchronous or asynchronous) and the location of the measurement site within the field of view. Overall, we found strong correlations between BMD measures from WBCT and CT and in vivo measures to be more accurate in trabecular bone regions. Importantly, WBCT can be used to distinguish between anatomically relevant differences in BMD, however future work is necessary to determine the repeatability and sensitivity of BMD measures in WBCT.

Experimental Observation of a New Attenuation Mechanism in hcp‐Metals That May Operate in the Earth's Inner Core

AbstractSeismic observations show the Earth's inner core has significant and unexplained variation in seismic attenuation with position, depth and direction. Interpreting these observations is difficult without knowledge of the visco‐ or anelastic dissipation processes active in iron under inner core conditions. Here, a previously unconsidered attenuation mechanism is observed in zinc, a low pressure analog of hcp‐iron, during small strain sinusoidal deformation experiments. The experiments were performed in a deformation‐DIA combined with X‐radiography, at seismic frequencies (∼0.003–0.1 Hz), high pressure and temperatures up to ∼80% of melting temperature. Significant dissipation (0.077 ≤ Q−1(ω) ≤ 0.488) is observed along with frequency dependent softening of zinc's Young's modulus and an extremely small activation energy for creep (⩽7 kJ mol−1). In addition, during sinusoidal deformation the original microstructure is replaced by one with a reduced dislocation density and small, uniform, grain size. This combination of behavior collectively reflects a mode of deformation called “internal stress superplasticity”; this deformation mechanism is unique to anisotropic materials and activated by cyclic loading generating large internal stresses. Here we observe a new form of internal stress superplasticity, which we name as “elastic strain mismatch superplasticity.” In it the large stresses are caused by the compressional anisotropy. If this mechanism is also active in hcp‐iron and the Earth's inner‐core it will be a contributor to inner‐core observed seismic attenuation and constrain the maximum inner‐core grain‐size to ≲10 km.

Revealing crack initiation and extension of brittle rock via time-lapse acoustic attenuation: Insights from active ultrasonic experiments

Predicting brittle rock failure is essential for rock mechanics research and early disaster alerts in deep rock engineering. Successful prediction relies on identifying crack initiation and extension. However, currently, there is no universally accepted method for accurately identifying and tracking crack evolution to predict brittle failure of the surrounding rock. In this study, the propagation parameters of transmission ultrasonic waves were used to characterize crack behaviors at the laboratory scale. The differential acoustic attenuation term was proposed by modifying the spectral ratio method to evaluate the dissipation capability of the corresponding medium to the transmitted ultrasonic waves. In addition to acoustic attenuation, velocity and amplitude attenuation were introduced to characterize the damage evolution during brittle failure. The indicators were analyzed by conducting a uniaxial compression test on a sandstone sample with a single flaw. During compression, active ultrasonic surveys were conducted to attain the propagation parameters. The two-dimensional digital image correlation method was simultaneously applied to capture the full-field strain on the front surface of the sample. The shear and tensile strain profiles indicated that the shear damage initially accumulated at the tips of the flaw, causing a reduction in the velocity and amplitude of the transmitted ultrasonic waves. The acoustic attenuation indicator in the flaw-tip regions increased before the shear strain began. As the damage developed further, the acoustic attenuation increased overall, with numerous local fluctuations in the flaw-tip regions due to stress rearrangement and damage development, while the velocity and amplitude remained consistently low. In contrast, intact regions that were far away from the tips of the flaw exhibited different characteristics. The velocity and amplitude variations were more staged, while the acoustic attenuation changed gradually. The results indicated that the variations in the propagation parameters exhibited specific patterns before the damage was initiated, offering a potential for predicting crack initiation. The variations in the acoustic attenuation, velocity, and amplitude attenuation allow for tracking the crack propagation.

An ultrasound approach to characterize mixtures of vegetable oils with the same type of dominant chemical compositions

The non-destructive characterization of ultrasonic properties in mixtures of vegetable oils with similar dominant chemical compositions is becoming increasingly important for various applications. The combination of ultrasonic wave reflection as an experimental method and the partial least squares statistical method has been employed to establish reference graphs and models for detecting adulterated oils. This experimental study focuses precisely on measuring the attenuation and ultrasonic velocity of mixtures of organic argan oil with volumetric fractions of sesame oil, peanut oil or argan oil extracted from kernels depulped by goats. The measurements exhibit distinct behaviors manifested by electrical signals for the mixture obtained after the addition of each volumetric fraction, reflecting the capability of the adopted method to detect this difference. A notable decrease in ultrasonic velocity is observed in the mixtures as the quantity of added oil increases, with a maximum variation of 11 m/s for the argan/peanut oil mixture. Conversely, The attenuation of ultrasonic waves increases proportionally with the added volumetric fractions, with the argan/peanut oil mixture exhibiting an attenuation variation range of 3.57 Np/m. Prediction models for the added volumetric fractions to organic argan oil based on attenuation and ultrasonic velocity, showed a weak correlation between the predicted quantity of added oil and the actual quantity added to organic argan oil, with determination coefficients (r2) not exceeding 65%. The weak correlation is due to the similar chemical compositions of the oils. These results underscore the value of ultrasonic-statistical analysis for authenticating and ensuring the quality of vegetable oils. However, the limitations highlight the need to refine models for better accuracy. This method can verify oil authenticity in the food industry, ensuring consumer protection and quality standards. Additionally, it offers a quick and simple alternative to traditional methods, reducing costs and improving efficiency in quality control processes.

Pulse-echo ultrasound attenuation tomography

Objective. We present the first fully two-dimensional attenuation imaging technique developed for pulse-echo ultrasound systems. Unlike state-of-the-art techniques, which use line-by-line acquisitions, our method uses steered emissions to constrain attenuation values at each location with multiple crossing wave paths, essential to resolve the spatial variations of this tissue property. Approach. At every location, we compute normalized cross-correlations between the beamformed images that are obtained from emissions at different steering angles. We demonstrate that their log-amplitudes provide the changes between attenuation-induced amplitude losses undergone by the different incident waves. This allows us to formulate a linear tomographic problem, which we efficiently solve via a Tikhonov-regularized least-squares approach. Main results. The performance of our tomography technique is first validated in numerical examples and then experimentally demonstrated in custom-made tissue-mimicking phantoms with inclusions of varying size, echogenicity, and attenuation. We show that this technique is particularly good at resolving lateral variations in tissue attenuation and remains accurate in media with varying echogenicity. Significance. Based on a similar principle, this method can be easily combined with computed ultrasound tomography in echo mode for speed-of-sound imaging, paving the way towards a multi-modal ultrasound tomography framework characterizing multiple acoustic tissue properties simultaneously.

Spatial variation of body wave attenuation in Garhwal-Kumaun Himalaya region, India

We have investigated the spatial variation of body wave attenuation in Garhwal-Kumaun Himalaya region from the datasets of 465 well located earthquakes, recorded at 52 broadband stations between 2017 and 2020. The body wave attenuation parameters QP and QS were estimated at each station by applying the extended coda normalization method for five different central frequencies ranging from 1.5 to 18 Hz. Strong frequency-dependent body wave attenuation was observed at each station over the whole region. Also, we found a significant variation of QP and QS from north to south which is consistent with geotectonic diversity beneath the study region. We have also made separate estimations of frequency-dependent relations for Garhwal and Kumaun Himalaya region in order to investigate the lateral variation in attenuation characteristics, and obtained the frequency-dependent relations as follows: QP=30±3f1.05±0.05, QS=143±20f0.88±0.07 for the Garhwal Himalaya region and QP=31±1f1.09±0.02, QS=121±11f1.00±0.04 for the Kuamun Himalaya region. Obtained Q values indicate strong body wave attenuation for both the region with no significant lateral variation. It may suggest the presence of crustal level folding, faulting, aqueous fluids, and metamorphic fluids below both the regions. Also, the ratios of QS/QP are high (>1) for the entire analyzed frequency range, suggesting a significant level of heterogeneity and tectonic complexities in the crust of the study region.

Beamforming for Sensing: Hybrid Beamforming based on Transmitter-Receiver Collaboration for Millimeter-Wave Sensing

Previous mmWave sensing solutions assumed good signal quality. Ensuring an unblocked or strengthened LoS path is challenging. Therefore, finding an NLoS path is crucial to enhancing perceived signal quality. This paper proposes Trebsen, a Transmitter-REceiver collaboration-based Beamforming scheme SENsing using commercial mmWave radars. Specifically, we define the hybrid beamforming problem as an optimization challenge involving beamforming angle search based on transmitter-receiver collaboration. We derive a comprehensive expression for parameter optimization by modeling the signal attenuation variations resulting from the propagation path. To comprehensively assess the perception signal quality, we design a novel metric perceived signal-to-interference-plus-noise ratio (PSINR), combining the carrier signal and baseband signal to quantify the fine-grained sensing motion signal quality. Considering the high time cost of traversing or randomly searching methods, we employ a search method based on deep reinforcement learning to quickly explore optimal beamforming angles at both transmitter and receiver. We implement Trebsen and evaluate its performance in a fine-grained sensing application (i.e., heartbeat). Experimental results show that Trebsen significantly enhances heartbeat sensing performance in blocked or misaligned LoS scenes. Comparing non-beamforming, Trebsen demonstrates a reduction of 23.6% in HR error and 27.47% in IBI error. Moreover, comparing random search, Trebsen exhibits a 90% increase in search speed.

Application of Dual-target Computed Tomography for Material Decomposition of Low-Z Materials

The extension of conventional computed tomography known as spectral computed tomography involves utilizing the variations in X-ray attenuation, driven by spectral and material dependencies. This technique enables the virtual decomposition of scanned objects, revealing their elemental constituents. The resultant images provide quantitative information, such as material concentration within the scanned volume. Enhancements in results are achievable through methods that capitalize on the strong correlation among decomposed images, effectively minimizing noise and artifacts. The Rigaku nano3DX submicron tomograph uses a dual-target source, which allows the generation of two distinct X-ray spectra through different target materials. This configuration holds promise for high-resolution applications in spectral tomography, particularly for low-Z materials, where it offers high contrast in the acquired images. The potential of this setup in the context of spectral computed tomography is explored in this contribution, delving into its applications for materials characterized by low atomic numbers.

Seasonal Variation of Total Attenuation between Airborne Platform and Earth Station in South-West Region, Nigeria

The seasonal variation of total attenuation in the southwest region of Nigeria has been computed using eight (8) years dataset at Ku- and Ka-band of the transmitted power of the radar, transmitted antenna gain and the received antenna gain of the satellite retrieved from the archived of the GPM. The results obtained fluctuates between the seasons at Ku- and Ka-band. From the results obtained at Ku-and Ka-band, the results from analysis showed that the peak total attenuation was recorded between the early (MAM) and late wet (JJA) season when the intensity of rainfall is maximum in the South-West region. As a result, the effect on the airborne-earth station link will be severe which may further lead to signal outage. However, the state where the highest total attenuation was consistent is Lagos state. These seasons and Lagos state must be taking into consideration by engineers and radiowave propagation group when planning and sitting radiowave propagation in the study area.