Attenuation Processes Research Articles

Deep learning-based attenuation for shear-wave leakage from ocean-bottom node data

The high-amplitude shear wave in the z-component of ocean-bottom node (OBN) data challenges conventional seismic data imaging and interpretation. The process of shear-wave attenuation from the z-component data can be regarded as a coherent noise reduction problem. However, conventional noise attenuation methods, such as filtering or matching and subtraction, are time-consuming or have limited accuracy for field data processing. Unlike conventional methods with indirect feature recognition, pretrained neural networks provide end-to-end denoising frameworks by directly predicting and subtracting the shear-wave-free data from the original z-component data. Here, we have developed a deep learning-based method to address the shear-wave leakage problem and adopted a training set generation strategy based on the field data. Denoised z-component data are not needed to train the network. The generation of the training set and the extraction of noise features are based on the data of the x- and p-components. A residual learning strategy is introduced to extract the noise from the field data other than those in the training set. Synthetic examples confirm the excellent performance of our training set generation strategy. Field 4C OBN examples show that our method can attenuate shear-wave noise without harming the signals and, therefore, can be integrated into multicomponent field data processing.

Multi-window spectrum analysis of Búzios oil field PSDM seismic data applied to frequency attenuation study

The intrinsic attenuation is often quantified using the inverse quality factor Q. Methods to estimate Q are mainly based on time domain or frequency domain and sensitive to amplitude and/or frequency band variations. In this sense, noise, signal artifacts or processing steps can alter the amplitude, frequency content and the waveform, what may lead to inaccurate calculations of Q. A way to better understand the frequency band variation in seismic data and verify patterns or problems occurring in the signal frequency band is performing layered or window-by-window spectrum analysis. This work describes a multi-window spectrum analysis method used to better understand the frequency attenuation process as the seismic wave travels through the sediments from the sea bottom down to the reservoir depths in a 3D Kirchhoff Pre-Stack Depth Migrated (PSDM) seismic data from Búzios oil field. To perform the spectral analysis in frequency domain, the PSDM volume was converted to time domain using the same interval velocity volume used to depth-migrate the data. The variation of frequency band as the signal propagates through the sediment package was analyzed dividing the studied crossline sections in 13 layers of 200 ms each, from sea bottom down to the base of pre-salt reservoir formations. The results suggest that most part of higher frequency loss has been occurred in post-salt package. This may be an indication of significant viscoelastic behavior or strong stratigraphic filtering of this interval. Sequentially, higher frequency content is lost slowly from salt top down to the last layer located inside pre-salt formation. Very slight frequency spectrum variation below salt top indicates elastic behavior of the salt formation and underling pre-salt formation in this interval. The spectrum analysis method proposed here has shown to be useful and efficient to identify intervals of different attenuation patterns in seismic data. Additionally, the frequency band study produced by our spectrum analysis can be used to quality-control Q-factor estimation computed by different methods.

Numerical study on fracture control blasting using air–water coupling

Fracture control blasting produces rock fractures in the desired direction, which is significant for the stability of excavation structures in rock engineering. The present study proposes a new method of fracture control blasting using air–water coupling. This method utilizes the difference of explosion stress transfer between air and water, which guides the explosion energy consumption in fracturing rock on water-coupling side, i.e. rock in the excavation zone, and thus the rock in the excavation zone is properly fragmented, and the reserved rock is well protected from damage. Based on the plane strain assumption, the transmission and propagation of explosion stress in the excavation and reserved rock with this method are first theoretically analyzed. Then, fracture control blasting using air–water coupling is numerically studied utilizing the LS-DYNA program. The numerical model is first developed and calibrated in the simulation with the laboratory-scale air-coupling and water-coupling blasting tests. Then, the successive processes of pressure attenuation, fracture evolution and energy consumption under air–water coupling blasting are numerically investigated. Thereafter, the effects of the air–water ratio and decoupling ratio on the performance of fracture control are numerically investigated. The theoretical and numerical results show that good performance of fracture control can be obtained using air–water coupling blasting.

The use of copper isotopes for understanding metal transfer mechanisms within the continuum mine-river-dam (Huelva Region, Spain).

Mining areas and in particular those containing massive sulfides have left a heavy environmental legacy with soils and hydrographic networks highly contaminated with metals and metalloids as for example in the Iberian Pyrite Belt (Huelva, Spain). Here, we present new data on copper (Cu) isotopic composition of waters and solids collected along a continuum Mine (Tharsis)-River (Meca)-Lake (Sancho) in the Iberian Pyrite Belt. Our results show that the isotopic signature of pit lakes is spatially variable, but remains stable over the seasons; this signature seems to be controlled by water-rock interaction processes. The data obtained on the Meca River imply a number of attenuation processes such as decrease in the metal concentration by precipitation of secondary minerals. This is accompanied by preferential retention of the heavy isotope (65Cu) with a possibility of living organisms (e.g., algae) participation. The terminal Sancho lake demonstrated constant isotopic signature over the entire depth of the water column despite sizable variations in Cu concentrations, which can be tentatively explained by a superposition of counter-interacting biotic and abiotic processes of Cu fractionation. Overall, the understanding of the isotopic variations along the hydrological continuum is useful for a better understanding of metal element transfer within mining environments and surrounding surface waters.

Numerical Simulation of Plane and Cellular Detonation Wave Suppression in Hydrogen-Air Mixture by Inert Porous Filters

ABSTRACT Calculations of the interaction of plane (one-dimensional) and cellular (two-dimensional) detonation waves in hydrogen-air mixture with inert filters were carried out on the basis of the proposed physical and mathematical models, based on the detailed and reduced kinetics, describing such processes. The realized detonation regimes of attenuation and suppression of detonation were revealed. Comparison of results obtained by detailed and reduced kinetics showed that reduced kinetics gives overestimated detonation velocities compared to the detailed kinetics. But the obtained concentration limits of detonation practically equal to each other for both kinetics models. Comparison of processes of attenuation and suppression of plane and cellular detonation showed that the suppression of cellular detonation is more difficult to achieve compared to a plane detonation wave. Detonation failure criterion that shows that at the increasing the filter particles diameter, it is necessary to increase the volume concentration proportionally in order to successfully suppress detonation both in the case of a plane detonation wave and in the case of cellular detonation, was obtained.

A seasonal transition in biological carbon pump efficiency in the northern Scotia Sea, Southern Ocean

The biological carbon pump (BCP) contributes to the oceanic CO2 sink by transferring particulate organic carbon (POC) into the deep ocean. The magnitude and efficiency of the BCP is likely to vary on timescales of days to seasons, however characterising this variability from shipboard observations is challenging. High resolution, sustained observations of primary production and particle fluxes by autonomous vehicles offer the potential to fill this knowledge gap. Here we present a 4 month, daily, 1 m vertical resolution glider dataset, collected in the high productivity bloom, downstream of South Georgia, Southern Ocean. The dataset reveals substantial temporal variability in primary production, POC flux and attenuation. During the pre-bloom peak phase we find high export efficiency, implying minimal heterotrophic POC consumption, i.e. productivity is decoupled from upper ocean remineralisation processes. As the bloom progresses from its peak through its declining phase, export flux decreases, but transfer efficiency within the upper 100 m of the mesopelagic increases. Conversely, transfer efficiency in the lower mesopelagic decreases in the post-bloom phase, implying that the flux attenuation processes operating in the upper and lower mesopelagic are effectively decoupled. This finding underscores an important limitation of using a single parameter, such as Martin's ‘b’, to characterise POC flux attenuation in a given location or season. Frequent pulses of export flux are observed throughout the deployment, indicating decoupling between primary production and the processes driving export of material from the upper ocean. The mechanisms underlying the observed seasonal changes in BCP magnitude and efficiency are unclear, as temperature and oxygen concentration changed minimally, although the nature of the sinking particles changed substantially as the bloom progressed. Our results highlight the difficulty of capturing temporal variability and episodic flux events with traditional shipboard observations, which affects our conceptual understanding of the BCP. The increasing use of autonomous vehicles to observe particle fluxes will be essential to characterising the temporal variability in magnitude and functioning of the BCP.

Motion Sensor Noise Attenuation Using Deep Learning

A method is proposed to attenuate both instrumental and environmental noise from motion sensor records in multisensor streamer acquisition. The main elements are two convolutional neural network models. The first model attenuates vertical narrow band high amplitude noise mainly generated by the instruments attached to the streamers. The second model attenuates widespread background noise mainly associated with environmental conditions. To reduce the risk of possible signal loss an addback flow in the curvelet domain is used. The motivation for the work presented here was to develop a fully automated noise attenuation method that eliminates the need for time-consuming and subjective user parameter testing. The method has been validated using seismic data from different parts of the world and shown to consistently produce superior results to other state-of-the-art noise attenuation processes.

Microbial indicators along a metallic contamination gradient in tropical coastal sediments.

The structure and diversity of microbial community inhabiting coastal sediments reflect the exposition to contaminants. Aiming to assess the changes in the microbiota from Sepetiba Bay (SB, Brazil) sediments, correlations between the 16S rRNA gene data (V4-V5 region), metal contamination factors (CF), and the ecological risk classification provided by the Quality Ratio (QR) index were considered. The results show that microbial diversity differs significantly between the less (SB external sector) and the most (SB internal sector) polluted sectors. Also, differences in the microbial community structure regarding the ecological risk classifications validated the QR index as a reliable tool to report the SB chronic contamination. Microbial indicator genera resistant to metals (Desulfatiglans, SEEP-SRB1, Spirochaeta 2, among others) presented mainly anaerobic metabolisms. These genera are related to the sulfate reducing and methanogenic metabolisms probably participating in the natural attenuation processes but also associated with greenhouse gas emissions. In contrast, microbial indicator genera sensitive to metals (Rubripirellula, Blastopirellula, Aquibacter, among others) presented mainly aerobic metabolisms. It is suggested that future works should investigate the metabolic functions to evaluate the influence of metallic contaminants on microbial community inhabiting SB sediment.

Untargeted metabolomic analysis to explore the impact of soil amendments in a non-conventional wastewater treatment

As non-conventional wastewater treatment, vegetation filters make the most of the natural attenuation processes that occur in soil to remove contaminants, while providing several environmental benefits. However, this practice may introduce contaminants of emerging concern (CECs) and their transformation products (TPs) into the environment. A potential improvement to the system was tested using column experiments containing soil (S) and soil amended with woodchips (SW) or biochar (SB) irrigated with synthetic wastewater that included 11 selected CECs. This study evaluated: i) known CECs attenuation and ii) unknown metabolites formation. Known CECs attenuation was assessed by total mass balance by considering both water and soil media. An untargeted metabolomic strategy was developed to assess the formation of unknown metabolites and to identify them in water samples. The results indicated that SB enhanced CECs attenuation and led to the formation of fewer metabolites. Sorption and biodegradation processes were favored by the bigger surface area of particles in SB column, especially for compounds with negative charges. Incorporating woodchips into soil shortened retention times in the column, which reduced attenuation phenomena and resulted in the formation of significantly more metabolites. Incomplete biodegradation reactions, fostered by shorter retention times in SW column could mainly explain these results.

Presence of pharmaceuticals and bacterial resistance genes in river epilithic biofilms exposed to intense agricultural and urban pressure

The continuous discharge of pharmaceutical compounds into the aquatic environment has raised concerns over the contamination of water resources. Urban activities and intensive animal breeding are important sources of contamination. The accumulation of antibiotics may lead to the transfer or alternatively maintain the presence of resistance genes in natural microbial communities existing in epilithic biofilms. The objective of this study was to evaluate the pharmaceutical contamination levels and the presence of resistance genes in biofilms from a South Brazilian watershed. The Guaporé watershed exhibits a high diversity of land use, including agricultural and urban areas with differing levels of anthropogenic pressure. Seventeen sites along the Guaporé watershed were monitored. Biofilm samples were collected in two seasons (winter and summer), and the pharmaceutical concentration and quantity of resistance genes were analyzed. All monitored sites were contaminated with pharmaceuticals. Agricultural activities contribute through transferring pharmaceuticals derived from the application of animal waste to agricultural fields. The most contaminated site (pharmaceuticals and bacterial resistance genes) was located in an urban area exposed to high pressure. Decreases in the contamination of biofilms were also observed, exemplifying processes of natural attenuation in the watershed. The quality of the biofilms sampled throughout the watershed served as a useful tool to understand and monitor environmental pollution.

Systematic characterization of sediment microbial community structure and function associated with anaerobic microbial degradation of PBDEs in coastal wetland

As the widely used flame retardant, polybrominated diphenyl ethers (PBDEs) have been ubiquitously detected in wetland sediments. Microbial degradation is the importantly natural attenuation process for PBDEs in sediments. In this study, the microbial degradation of PBDEs and inherent alternation of microbial communities were explored in anaerobic sediments from coastal wetland, North China. BDE-47 and BDE-153 could be degraded by the indigenous microbes, with biodegradation following pseudo-first-order kinetic. In sediments, the major genera for BDE-47 and BDE-153 degradation were Paeisporosarcina and Gp7, respectively, in single exposure. However, Marinobacter was dominant genera in the combined exposure to BDE-47 and BDE-153, and competition against Marinobacter existed between BDE-47 and BDE-153 degradation. Analysis of bacterial metabolic function indicated that membrane transport, amino acid and carbohydrate metabolism were included in degradation. This study provides the systematic characterization of the sediment microbial community structure and function associated anaerobic microbial degradation of PBDEs in coastal wetland.

Rapid Near-Field Attenuation of Ground Motion from Shallow Induced Earthquakes, Case Study: Preston New Road, United Kingdom

Abstract Ground motions from shallow induced earthquakes and tectonic seismicity were investigated in this study by directly modeling the seismic attenuation quality factor (Q) using spectral fitting and coda envelope decay methods. We use data from the Preston New Road (PNR) shale gas induced seismicity sequences near Blackpool, United Kingdom, in 2018 and 2019, in addition to regional tectonic events in the United Kingdom. Our results show that the local Q obtained from the induced seismic sequences at PNR, attributed to shallower layers in the crust, leads to a rapid rate of near-field decay (sudden loss in amplitude of earthquake signal over a short distances), with significantly stronger attenuation than observed for regional events. We furthermore find that estimates of Q are nonunique to a given record, differing both with the method and the analysis windows used, particularly at high frequency. These differences can be attributed to the different modeling methodologies (e.g., different assumptions) or to fundamental differences in physical attenuation processes within the seismic wavefield itself, which traverses multiple ray paths and comprises various phases. Our results indicate that to model ground motions for shallow earthquakes, it is important to consider the composite Q along a specific path rather than an average regional Q. To this extent, a depth-dependent attenuation model is considered crucial to bridge the gap between shallow induced earthquakes and tectonic seismicity.

Multi-port DC circuit breaker based on dual capacitor current limiting and energy sink

The coupling relationship between the removal of the fault current and the dissipation of the residual energy of the fault line during the fault isolation process of the multi-port capacitive current-limiting DC circuit breaker prolongs the breaking time of the fault to a certain extent. In order to solve the above problems, this paper proposes a multi-port DC circuit breaker based on dual-capacitor current limiting and energy sinking on the premise of decoupling the fault current attenuation and removal process and the fault line residual energy discharge process. Further reduce the fault breaking time and equipment withstand voltage requirements of the DC circuit breaker. Firstly, the topology and working principle of the proposed circuit breaker are analyzed, and then the parameters in the topology are designed. Then a simulation model is built in the PSCAD/EMTDC simulation platform to verify the fault breaking performance and breaking time. The effect of decoupling the fault current clearing process and the fault line residual energy discharge process on the effectiveness of shortening the fault breaking time is verified.

Characteristics of dynamic shear modulus and damping ratio and the structural formula of EPS particles lightweight soil

Dynamic triaxial tests of lightweight soil were conducted to explore the dynamic characteristics of expanded polystyrene (EPS) particle lightweight soil under traffic load. The effects of different mixed ratios, confining pressure, frequency on the backbone curves, dynamic shear modulus, and damping ratio characteristics of lightweight soil were investigated. The maximum dynamic shear modulus formula and maximum damping ratio formula of lightweight soil were established. The results indicated that backbone curves of lightweight soil had typical nonlinear and strain-hardening characteristics. With an increase in dynamic shear strain, the dynamic shear modulus curves appeared as inverse “S-shaped”. The dynamic shear modulus in the initial stage varied under different confining pressures. For γd＞10−4, the attenuation rate of the dynamic shear modulus increased with an increase in the dynamic shear strain, and for γd＞10−2, the relationship curve between the dynamic shear modulus and dynamic shear strain coincided gradually, and the attenuation process then stabilized. Owing to the special structure of lightweight soil, the damping ratio curves were “Bell-shaped” and “S-shaped.” Both the confining pressure and compressive yield stress determined the change trends of the damping ratio curves of the lightweight soil. The specimens were in an over-consolidated state and the mixed soil was in the state of shear dilatancy under dynamic loads when the confining pressure was less than the compressive yield stress, resulting in “Bell-shaped” damping ratio curve. The specimens were in the normal consolidated state and the mixed soil was in the state of shear shrinkage under dynamic loads when the confining pressure was greater than the compressive yield stress, resulting in “S-shaped” damping ratio curves. The calculation methods of the relative structural degree k and generalized void ratio e' of lightweight soil were defined to express the structural damage laws of lightweight soil having different mixed ratios under complex stress conditions using a unified formula. Based on Hardin's empirical formulas, the maximum dynamic shear modulus and maximum damping ratio formulas of lightweight soil were established by introducing the relative structural degree k and generalized void ratio e'. The formulas can quantitatively describe the dynamic responses of the special structure of lightweight soil under complex stress conditions.

Impact of green finance on renewable energy development: A spatiotemporal consistency perspective

The accurate understanding and grasping of green finance's role and effect process would help improve the accuracy of policies and, thereby, the development of renewable energy in China. Based on a newly built structural break modified SPDM (Spatial Panel Dobbin Model), this study explores the spatiotemporal consistency effects of green finance on renewable energy development and their geographical attenuation process. Several results could be obtained: (1) green finance plays an improving role in developing renewable energy in terms of both local and neighboring regions; (2) the effect objective areas of green finance are transferred from local regions to neighboring regions progressively as green finance grows in China, since the effect degree become weaker in local regions but stronger in neighboring regions; (3) the outflow phenomenon of green finance's effect on renewable energy development is stopped and reversed to siphon effect by the public health crisis that happened in 2019; (4) for green finance's spillover effects on renewable energy development, there are apparent geographic attenuation boundaries in areas near 700 km and impacting dense regions in areas near 350 km.

Mesocosm experiment to determine the contribution of adsorption, biodegradation, hydrolysis and photodegradation in the attenuation of antibiotics at the water sediment interface

To understand the fate of antibiotics in the aquatic environment, we need to evaluate to which extent the following processes contribute to the overall antibiotic attenuation: adsorption to river sediment, biodegradation, hydrolysis and photodegradation. A laboratory scale mesocosm experiment was conducted in 10 L reactors filled with river sediment and water. The reactors were spiked with four classes of antibiotics (fluoroquinolones, macrolides, sulfonamides, tetracyclines), as well as clindamycin and trimethoprim. The experimental-set-up was designed to study the attenuation processes in parallel in one mesocosm experiment, hence also considering synergetic effects. Our results showed that antibiotics belonging to the same class exhibited similar behavior. Adsorption was the main attenuation process for the fluoroquinolones and tetracyclines (44.4 to 80.0 %). For the sulfonamides, biodegradation was the most frequent process (50.2 to 65.1 %). Hydrolysis appeared to be significant only for tetracyclines (12.6 to 41.8 %). Photodegradation through visible light played a minor role for most of the antibiotics – fluoroquinolones, sulfonamides, and trimethoprim (0.7 to 24.7 %). The macrolides were the only class of antibiotics not affected by the studied processes and they persisted in the water phase. Based on our results, we propose to class the antibiotics in three groups according to their persistence in the water phase. Fluoroquinolones and tetracyclines were non-persistent (half-lives shorter than 11 d). Chlorotetracycline, sulfapyridine and trimethoprim showed a moderate persistence (half-lives between 12 and 35 d). Due to half-lives longer than 36 d sulfonamides and clindamycin were classified as persistent.

Numerical study of instability mechanism in the air-core vortex formation process

Air-core vortices are a ubiquitous phenomenon in the intakes of hydropower stations. Due to the transient and instability of two-phase vorticial flow, the prediction of air-core vortex formation is challenging, and understanding of the instability mechanism remains elusive. In this study, the large eddy simulation (LES) method and a coupled level-set and volume-of-fluid (CLSVOF) method are performed to study air-core vortex formation in a benchmark reservoir with a horizontal intake pipe. The process of air-core vortex formation can be classified into an inception stage, an instability stage, and a stability stage. In the instability stage, the surface vortex repeatedly goes through the process of inception, enhancement, attenuation, and extinction. The movement of the counterrotating secondary vortices and water surface level fluctuation plays a negative role in air-core vortex formation. The additional motion generated by the counterrotating pair drives the pair to the back wall. The main vortex undergoes attenuation due to the stretching/tilting effects induced by the secondary vortex. Water level fluctuations briefly increase the submergence depth, which in turn reduces the vertical velocity gradient and vertical vorticity, destabilizing the vortex. The perturbation of the air-core vortex by water level fluctuations is present only at the beginning of the instability stage.

CG-DRR：digital reconstructed radiograph generation algorithm based on Cycle-GAN

CG-DRR：digital reconstructed radiograph generation algorithm based on Cycle-GAN

Laboratory Analysis on the Performance of 5G NSA Communication in a Suburban Scenario

The propagation of information by electromagnetic waves suffers different types of interference, according to the characteristics of the environment. The 5G system relies on adaptive modulation and coding techniques to better suit the channel and maximize effective data exchange between the user equipment and the network. Practical studies on the behaviour of the system under different environmental conditions, subject to attenuation processes such as fading, are important to understand and improve the 5G efficiency. This work has analysed the effect of the MCS (Modulation and Coding Scheme) variation on throughput for channel degraded by the multipath fading effect in a mobile communication. The analysis was carried out showing that the decision algorithms in terms of MCS switching to maintain adequate data rates according to the requirement (QoS) is an important factor. Considering both 64 QAM and 256 QAM, the throughput degradation effect was more evident in higher-order modulations due to the higher probability of bit error in the symbol constellation. This study can be a key for understanding and developing robust MCS switcher for 5G and beyond communications.

Application of N-Doped Carbon–Silicon Oxycarbide Based on POSS Synthesis in Lithium-Ion Batteries

Si/C materials have attracted much attention as anode materials for lithium-ion batteries. Here, nitrogen-doped silica carbon composites with a carbon-coated structure were synthesized using poly(1-vinylimidazole) in the presence of octavinyl-silsesquioxane followed by annealing and magnesium thermal reduction processes of the polymer precursor (PPVIm). Benefiting from the moderate Si–O–C bonds, the prepared NSiOC possesses a high first discharge capacity of 1862.3 mAh·g–1 at 0.2 A·g–1 and an initial Coulombic efficiency of 70.0% at 30 °C. When the temperature rises to 60 °C, the first discharge and charge specific capacities of the synthesized anode material at 0.2 A·g–1 increase to 2103.0 and 1528.7 mAh·g–1 with an ultralong lifespan of more than 1000 cycles. Moreover, the results show that the degradation of performance during the initial phase of cycles can be ascribed to the formation of an SEI layer and insufficient electrolyte penetration. The battery maintains a steady state (nearly 600 consecutive cycles) for a long time afterward as the activation of the anode material increases, attributed to the low expansion coefficient originating from the porous structure of the carbon capping layer and silicon oxide. In addition, the electrochemical attenuation process of the electrode material with a unique inorganic silica skeleton and exceptional electrochemical performance was also investigated for the assistance of future design in high-performance electrode materials.