A rockfall is a typical dynamic problem of a discontinuous block system originating from a dangerous rock mass and always presents serious geo-hazards along highway slopes in mountainous areas. This ...study aims to investigate the failure mechanisms and movement characteristics of rockfalls through a three-dimensional discontinuous deformation analysis (3D DDA) method and attempts to comprehensively examine the complicated kinematic process of rockfall disasters. In terms of the initial failure and post-movement characteristics (i.e., motion trajectory and kinetic energy) of a rockfall, the effectiveness of 3D DDA is verified by comparing its results with those of laboratory experiments. Taking the K4580 typical high-steep slope undergoing rockfalls along the G318 national highway in Tibet as an example, the initiation and failure of a single boulder and a large-scale rock mass at the source area were simulated by 3D DDA. Then, the movement characteristics of the boulder and massive collapsing rocks along the slopes of different geometrical characteristics, i.e., the slopes before the landslide and after the shallow and deep landslides, were studied. The results show that the 3D DDA has significant advantages in analysing the failure mechanisms of slope rockfalls and can satisfactorily simulate the spatial movement (e.g., lateral deviation and deflection) of blocks by considering the 3D geometry of the slopes and blocks. The 3D DDA numerical simulation can predict the movement range, deposition position, and affected area of rockfall disasters, which can provide a basis for formulating disaster prevention countermeasures in actual projects.
Toppling is a representative failure mode of discontinuity-controlled rock slopes. As a discrete numerical method, discontinuous deformation analysis (DDA) is well-suited for simulating the movement ...process, contact transformation, and large displacement and deformation of rock block systems, which are formed in jointed rock masses. In the present study, a three-dimensional (3D) DDA method was conducted to study the toppling failure mechanisms of rock slopes by introducing the global contact theory. Considering dynamic equilibrium conditions, the analyses of toppling slopes were performed and the corresponding formulations were derived. The algebraic and mechanical computation of the global contact theory was illustrated and implemented into the 3D DDA method. An experimental apparatus for studying the toppling process of blocks was developed and a series of laboratory experiments were carried out for different block distributions under different conditions. By comparing with the results of the analytical methods and laboratory experiments, the accuracy of the 3D DDA method was verified. Numerical examples, including a classical toppling slope, an ideal mountain slope, and a real toppling case were analyzed to further research the toppling failure mechanisms. The results revealed that the 3D DDA method can effectively predict slope instability and simulate the failure process of toppling slopes. The results of the dynamics-based formulations, experiments and 3D DDA enrich the instability conditions of slope-toppling. Moreover, the general phenomena and laws of the toppling failure were presented.
Rockfall is a common geological disaster in rock slope projects. An understanding of the motion processes and characteristics of the rock blocks originating from a rockfall is of profound importance ...for comprehending the mechanism(s) of rockfall disasters. In this study, a field experimental system comprising binocular stereovision was developed for examining rockfalls, and a series of experiments on rockfall motion characteristics were performed on slopes near an abandoned section of the G318 national highway in Tibet, China. The indices of motion characteristics such as the lateral displacement, staying position, jumping height, and kinetic energy evolution of the blocks under different work conditions (e.g. different masses, shapes, falling heights, falling angles, and different geometrical characteristics in the slopes) were investigated by combining experiments with a three-dimensional discontinuous deformation analysis (3D DDA) method. The results show that the field experimental system has high accuracy in monitoring the block movement processes. The 3D DDA results agree well with those from the experiments, and the evolutions of the motion characteristics of the rockfall under different conditions are quantitatively obtained. Furthermore, the results provide insight into the laws of rockfall movements and dynamic impact processes, and lay a foundation for the design of rockfall protection measures and engineering approaches for disaster prevention and mitigation.
The right bank slope of the Dagangshan hydropower station has undergone large deformation during excavation, which may continue to increase and cause slope instability and failure, threatening dam ...construction and safe operation. This study analysed the deformation and instability of this discontinuity-controlled rock slope by three-dimensional discontinuous deformation analysis (3D-DDA). A microseismic monitoring technique was adopted to capture the spatial and temporal distributions of microseismic events. The unknown geological discontinuities and the potential slip surface inside the slope were determined. By combining monitoring data with the geological information, the 3D-DDA model was established to analyse the 3D deformation characteristics of the slope. In addition, the slope deformation and failure under various conditions, such as over excavations, as well as various joint penetrations, joint dip directions, and friction angles were further investigated. It was found that the simulation of the critical sliding state of blocks by 3D-DDA is effective after improvement of the critical sliding model of joint contact between blocks, and the computational results showed good agreement with monitoring results. Slope deformation is caused by the accumulation of micro-crack damage in deep rock masses, and it is closely related to its internal and external conditions. Furthermore, the failure modes and mechanisms of the slope with 3D topography are presented, which may be helpful for the design of a slope reinforcement scheme.
Automatic seizure onset detection plays an important role in epilepsy diagnosis. In this paper, a novel seizure onset detection method is proposed by combining empirical mode decomposition (EMD) of ...long-term scalp electroencephalogram (EEG) with common spatial pattern (CSP). First, wavelet transform (WT) and EMD are employed on EEG recordings respectively for filtering pre-processing and time-frequency decomposition. Then CSP is applied to reduce the dimension of multi-channel time-frequency representation, and the variance is extracted as the only feature. Afterwards, a support vector machine (SVM) group consisting of ten SVMs is served as a robust classifier. Finally, the post-processing is adopted to acquire a higher recognition rate and reduce the false detection rate. The results obtained from CHB-MIT database of 977 h scalp EEG recordings reveal that the proposed system can achieve a segment-based sensitivity of 97.34% with a specificity of 97.50% and an event-based sensitivity of 98.47% with a false detection rate of 0.63/h. This proposed detection system was also validated on a clinical scalp EEG database from the Second Hospital of Shandong University, and the system yielded a sensitivity of 93.67% and a specificity of 96.06%. At the event-based level, a sensitivity of 99.39% and a false detection rate of 0.64/h were obtained. Furthermore, this work showed that the CSP spatial filter was helpful to identify EEG channels involved in seizure onsets. These satisfactory results indicate that the proposed system may provide a reference for seizure onset detection in clinical applications.
Recently, deep learning approaches, especially convolutional neural networks (CNNs), have attracted extensive attention in iris recognition. Though CNN-based approaches realize automatic feature ...extraction and achieve outstanding performance, they usually require more training samples and higher computational complexity than the classic methods. This work focuses on training a novel condensed 2-channel (2-ch) CNN with few training samples for efficient and accurate iris identification and verification. A multi-branch CNN with three well-designed online augmentation schemes and radial attention layers is first proposed as a high-performance basic iris classifier. Then, both branch pruning and channel pruning are achieved by analyzing the weight distribution of the model. Finally, fast finetuning is optionally applied, which can significantly improve the performance of the pruned CNN while alleviating the computational burden. In addition, we further investigate the encoding ability of 2-ch CNN and propose an efficient iris recognition scheme suitable for large database application scenarios. Moreover, the gradient-based analysis results indicate that the proposed algorithm is robust to various image contaminations. We comprehensively evaluated our algorithm on three publicly available iris databases for which the results proved satisfactory for real-time iris recognition.
Epilepsy is a chronic neurological disease associated with abnormal neuronal activity in the brain. Seizure detection algorithms are essential in reducing the workload of medical staff reviewing ...electroencephalogram (EEG) records. In this work, we propose a novel automatic epileptic EEG detection method based on Stockwell transform and Transformer. First, the S-transform is applied to the original EEG segments, acquiring accurate time-frequency representations. Subsequently, the obtained time-frequency matrices are grouped into different EEG rhythm blocks and compressed as vectors in these EEG sub-bands. After that, these feature vectors are fed into the Transformer network for feature selection and classification. Moreover, a series of post-processing methods were introduced to enhance the efficiency of the system. When evaluating the public CHB-MIT database, the proposed algorithm achieved an accuracy of 96.15%, a sensitivity of 96.11%, a specificity of 96.38%, a precision of 96.33%, and an area under the curve (AUC) of 0.98 in segment-based experiments, along with a sensitivity of 96.57%, a false detection rate of 0.38/h, and a delay of 20.62 s in event-based experiments. These outstanding results demonstrate the feasibility of implementing this seizure detection method in future clinical applications.
The rheological properties parameters of paddy soil affect the interaction between the tillage tools and soil, thus influencing the operation quality and power consumption. In order to study the ...effects of tillage methods and moisture content on the rheological properties parameters of paddy soil in the middle and lower reaches of the Yangtze River, uniaxial compression creep tests of paddy soils with four moisture contents under no tillage (moisture contents: 26.71%, 24.52%, 23.26%, 21.28%) and plough tillage (moisture contents: 26.77%, 25.55%, 23.40%, 20.56%) were carried out using a TMS-PRO texture analyzer. The creep properties curves obtained from the tests, and the rheological constitutive equation of paddy soil under compression was established by Burgers viscoelastic model. Respectively, the quantitative change rules of creep properties of paddy soil with different moisture contents under different tillage methods and the correlation between these parameters were explored. The results showed that the moisture content under the three-year plough tillage and no tillage methods had significant influence on the rheological properties parameters of paddy soil (P < 0.05). The instantaneous elastic modulus, delay elastic modulus, and viscosity coefficient of the two paddy soils (no tillage and plough tillage soils) decreased with the increase of moisture content. However, the variation rules of relaxation time and delay viscosity coefficient with moisture content differed between these two paddy soils. Specifically, the strain rate of the two paddy soils decreased as moisture content decreased, where the total strain combines elastic strain, viscous strain, and viscoelastic strain. The initial strain rate and steady strain rate of the plough tillage paddy soils were lower than that of the no tillage paddy soils. The established creep model equation could be used to obtain viscoelastic rheological parameters of paddy soil in a wide range. The fitting equations between rheological parameters and moisture content were introduced into Burgers model, and the coupling equations between creep deformation and moisture content and time were derived, which could be used to predict the creep properties and deformation behavior of paddy soil in a certain range of no tillage and ploughed field. Overall, this study has a certain theoretical significance for the development and improvement of paddy soil rheology theory, and can also provide theoretical basis and technical support for the research of agricultural machinery design optimization, field water, soil conservation, soil tillage and compaction related simulation analysis in the middle and lower reaches of the Yangtze River.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
As a frequent occurring geomorphological process characterized by high energy and mobility, the rockfall movement is the basis of the disaster prediction and mitigation. In this study, the kinematic ...evolution behaviors of rockfalls are investigated using three-dimensional discontinuous deformation analysis (3D DDA) based on block kinematics. A series of field experiments are designed by orthogonal experimental method to study the block movement considering the influence of the slope angle, the characteristics of the block itself and the initial falling conditions. Selecting the combination of factors that have the most significant influence on the block movement, the 3D DDA numerical model is established and the effectiveness of 3D DDA is verified by comparing the displacement and kinetic energy evolutions obtained by experiments. Then, the 3D DDA is applied to simulate the rockfalls of Wangxia slope in Chongqing, and the kinematic evolutions of the entire rockfall processes are further studied by analyzing the rock mass instability and the movement trajectory and kinetic energy evolutions of blocks. The experimental results show that slope angle has the greatest influence on block kinematics, followed by block mass, falling height, block shape and falling angle. In the practical slope analysis, the rockfall processes consist of sliding failure, oblique projectile movement, flying over or colliding with the highway, and flying away from the slope, showing 3D movement characteristics due to lateral translation and rotation. The rockfall kinematic evolutions induce slope disasters to the highway, and pose a threat to shipping in Yangtze River channel. The 3D DDA method can quantitatively analyze the failure of dangerous rock masses and the kinematic evolutions of rockfalls after instability, which is helpful to provide revealing insights into the rockfall disaster processes and mechanisms.
Ultrahigh N-doped porous carbon graphene nanosheets (NPC@GNS) with two-dimensional (2D) multilayer sandwich framework are elaborately designed from ZIF-8 nanoparticles in situ grown on graphene oxide ...(GO) with 2-methyimidazole and polyvinyl pyrrolidone added as nitrogen precursor through a facile one-step fast pyrolysis and explored in lithium-ion batteries (LIBs). As the process-enhanced anode material, the NPC@GNS provide a high capacity of 906.6 mAh g−1 after 100 cycles at 0.5 A g−1, and an average capacity of 378.2 mAh g−1 after an extremely long cycling durability over 1000 cycles at 5 A g−1. It is worth noting that the superior electrochemical performance of the NPC@GNS electrode as the anode for LIBs confirms the reliability of the sufficient “point and plane” 2D sandwich framework, and a portion of the micropores and a large number of preferred mesoporous channels help to facilitate rapid charge transfer, which indicates that NPC@GNS is a vibrant material that plays a key role in contributing to the application in future energy storage.
•A simple nitrogen-doped sandwich structure was synthesized in situ.•The preferred mesoporous structure benefits the diffusion of ions and transportation of electrons.•The composite showed excellent cycle stability, rate performance and high specific capacity.
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