| 1. |
- Kristan, Matej, et al.
(författare)
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The first visual object tracking segmentation VOTS2023 challenge results
- 2023
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Ingår i: 2023 IEEE/CVF International conference on computer vision workshops (ICCVW). - : Institute of Electrical and Electronics Engineers Inc.. - 9798350307443 - 9798350307450 ; , s. 1788-1810
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Konferensbidrag (refereegranskat)abstract
- The Visual Object Tracking Segmentation VOTS2023 challenge is the eleventh annual tracker benchmarking activity of the VOT initiative. This challenge is the first to merge short-term and long-term as well as single-target and multiple-target tracking with segmentation masks as the only target location specification. A new dataset was created; the ground truth has been withheld to prevent overfitting. New performance measures and evaluation protocols have been created along with a new toolkit and an evaluation server. Results of the presented 47 trackers indicate that modern tracking frameworks are well-suited to deal with convergence of short-term and long-term tracking and that multiple and single target tracking can be considered a single problem. A leaderboard, with participating trackers details, the source code, the datasets, and the evaluation kit are publicly available at the challenge website1
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| 2. |
- Zhang, Zhiqiang, et al.
(författare)
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Numerical Simulation of a Round Determinate Panel Test of Combined Concrete Panel and Welded Wire Mesh
- 2018
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Ingår i: Paper presented at the ISRM International Symposium - 10th Asian Rock Mechanics Symposium, Singapore, October 2018. - : International Society for Rock Mechanics and Rock Engineering / Society for Rock Mechanics and Engineering Geology.
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Konferensbidrag (refereegranskat)abstract
- The sprayed concrete layer, together with external welded wire mesh, has been widely used as an important surface support in underground excavation in civil and mining engineering. Recently, the load carrying capability of combined concrete layer and welded wire mesh was evaluated by a round determinate panel (RDP) test. However, performance assessment by using RDP specimens is hindered by the testing boundary condition and the failure pattern and mechanism of combined concrete layer and welded wire mesh remains unclear. In this paper, the numerical model of the RDP test was set up by means of a FEM code, ABAQUS, and a series of numerical tests were carried out to investigate the failure mechanism and the influence of boundary condition on the performance of the RDP tests. To ensure the constitutive model of concrete embedded in ABAQUS and the material parameters were correctly used, the numerical models were first calibrated by the laboratory results with different concrete panel thickness without using welded wire mesh. After that, the performance of the combined concrete layer and welded wire mesh was examined by using the calibrated concrete model and mesh model and the failure mechanism of the combined specimens was obtained. The results show that the failure pattern matches the laboratory observation rather well and the peak load carrying capacity of the combined concrete layer and welded wire mesh panel is a little higher than that of the concrete only panel but the residual load carrying capacity has been improved. The boundary condition has large effect on the load-displacement curve, which is discussed in detail in the paper. The objective was to develop a numerical methodology which could be used to evaluate the load carrying capacity of combined concrete layer and welded wire mesh and thereby improve the assessment of the performance of shotcrete and welded wire mesh on site.
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| 3. |
- Zhang, Zhi-qiang, et al.
(författare)
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Effect of fault on tunnel stability with different distribution
- 2013
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Ingår i: Global View of Engineering Geology and the Environment. - London : CRC Press, Taylor & Francis Group. - 9781138000780 ; , s. 279-285
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Konferensbidrag (refereegranskat)abstract
- For tunnel engineering, the fault that locates near tunnel always plays an important role on the stability of the surrounding rock mass and the safety of the supporting system. To investigate the influence of the fault on the tunnel stability, systematic numerical experiments are carried out via the FINAL code. Through these numerical experiment results, the displacement and the distribution of the stress in surrounding rock mass are analyzed for these cases of the different locations and dips of fault around tunnel periphery, and the stress in the sprayed concrete layer are analyzed as well. To simulate the characteristics of the fault located in the rock mass, the COJO element, embedded in the FINAL code, is used in all numerical experiments. The quantized results reflecting the rules of the change for the displacement, stress, plastic region in the surrounding rock mass are obtained also in this paper.
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| 4. |
- Botelho, Anneliese H., et al.
(författare)
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Effects of parallel fractures near a free surface on velocity amplification of S-wave
- 2017
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Ingår i: Proceedings of the Ninth International Symposium on Rockbursts and Seismicity in Mines. - Santiago do Chile : University of Chile.
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Konferensbidrag (refereegranskat)abstract
- When rock support is designed in a seismically active underground mine, it is important tochoose the right ejection velocity and calculate corresponding kinetic energy. Field monitoringand back-analyses have shown that ejection velocity of the order of 10 m/s and higher can resultfrom seismic events of moderate magnitude. Such velocities are much higher than those predictedusing peak particle velocity (PPV) obtained from scaling laws. Many researches have reportedthe amplification of particle velocity near excavation surface. Velocity amplification of P-wavetravelling through fractured rock near a free surface was recently studied. The amplification ofseismic waves on the skin of excavation is of interest in case of large seismic events. Seismic eventswith large magnitude are often associated with slip along weaknesses or shear fracturing of intactrock, which according to observations radiate much stronger S-wave as compared to P-wave.In this paper, velocity amplification of S-wave was investigated by modelling the dynamicinteraction between fractured rock and a free surface using a 2D discontinuum-based numericalprogram, UDEC (Universal Distinct Element Code). A 1D model with a fractured zone wasused to represent the fractured rock in this investigation. It is found that the shear stress ratio,wave frequency, fracture stifness, fracture spacing and thickness of fractured zone afect thevelocity amplification, in which the shear stress ratio is the most crucial factor influencing wavetransmission. The results have proved that the interaction of the seismic wave and multiplefractures near the free surface strongly influences the ground motion.
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| 5. |
- Botelho, Anneliese H., et al.
(författare)
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Velocity amplification of obliquely incident s-wave through fractures near free-surface
- 2019
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Ingår i: Rock Mechanics for Natural Resources and Infrastructure Development - Full Papers. - : Taylor & Francis. ; , s. 1487-1494
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Konferensbidrag (refereegranskat)abstract
- The rockfall risk due to mining-induced seismicity reduces by installing appropriate rock support to absorb the kinetic energy from a seismic event, which is calculated by assuming the mass of ejected rock and its ejection velocity. Estimation of ejection velocity is normally based on scaling laws that do not consider the effect of the excavation free-surface and existing fractures near the excavation free-surface. Field monitoring studies have shown that the peak particle velocity on the free-surface can be much larger than the velocity in deep solid rock. The interaction between the fractures and the free-surface under incident S-wave is investigated by using a two-dimensional UDEC model with fractured zone characterized as one, two, three and four sets of parallel fractures with varied intersecting angles. The results show that wave amplification factor varies according to the incident wave angle, the number of fracture sets and fracture spacing.
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| 6. |
- Eitzenberger, Andreas, et al.
(författare)
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Numerical simulation of train-induced vibrations in rock masses
- 2012
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Ingår i: Harmonising rock engineering and the environment. - Leiden : CRC Press/Balkema. - 9780415804448 ; , s. 1189-1194
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Konferensbidrag (refereegranskat)abstract
- The vibrations generated by a moving train in a tunnel will radiate into the surrounding ground which, in densely populated areas, will reach nearby buildings and its residents. Analyses are commonly made where the aim is to estimate the ground-borne noise and vibrations levels that may occur in nearby buildings. A common assumption is to treat the rock mass as an isotropic, homogeneous, and linear elastic material. Thus, the influence of discontinuities on the propagation of waves is not considered in the analyses. Within this study, numerical simulations were performed to study the propagation of low-frequency waves through a rock mass near a tunnel. A single period sinusoidal wave was applied as dynamic source on the floor of the tunnel. Observation points were located on the ground surface and around the tunnel. The influence on wave propagation from overburden, position of a discontinuity in relation to the tunnel, and normal and shear stiffness of the discontinuity, was studied by using the Universal Distinct Element Code (UDEC). The results show that increasing overburden reduces the vibration levels on the ground surface. Furthermore, the influence of the normal and shear stiffness of discontinuities depends on where the horizontal discontinuity is positioned in relation to the tunnel. If the horizontal discontinuity is positioned above the dynamic source (e.g. above tunnel or in the tunnel wall) the vibration levels on the ground surface will be reduced but if the horizontal discontinuity is located below the dynamic source (e.g. below the tunnel) the vibration levels on the ground surface will be enhanced. In our analyses, discontinuities only have an impact on the wave propagation if the normal and shear stiffness of is ≤10 GPa/m.
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| 7. |
- Gao, Yipeng, et al.
(författare)
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Research on the Security of Visual Reasoning CAPTCHA
- 2021
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Ingår i: PROCEEDINGS OF THE 30TH USENIX SECURITY SYMPOSIUM. - : USENIX ASSOC. - 9781939133243 ; , s. 3291-3308
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Konferensbidrag (refereegranskat)abstract
- CAPTCHA is an effective mechanism for protecting computers from malicious bots. With the development of deep learning techniques, current mainstream text-based CAPTCHAs have been proven to be insecure. Therefore, a major effort has been directed toward developing image-based CAPTCHAs, and image-based visual reasoning is emerging as a new direction of such development. Recently, Tencent deployed the Visual Turing Test (VTT) CAPTCHA. This appears to have been the first application of a visual reasoning scheme. Subsequently, other CAPTCHA service providers (Geetest, NetEase, Dingxiang, etc.) have proposed their own visual reasoning schemes to defend against bots. It is, therefore, natural to ask a fundamental question: are visual reasoning CAPTCHAs as secure as their designers expect? This paper presents the first attempt to solve visual reasoning CAPTCHAs. We implemented a holistic attack and a modular attack, which achieved overall success rates of 67.3% and 88.0% on VTT CAPTCHA, respectively. The results show that visual reasoning CAPTCHAs are not as secure as anticipated; this latest effort to use novel, hard AI problems for CAPTCHAs has not yet succeeded. Based on the lessons we learned from our attacks, we also offer some guidelines for designing visual CAPTCHAs with better security.
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| 8. |
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| 9. |
- Li, Angui, et al.
(författare)
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Ventilation and environmental control of underground spaces : a short review
- 2019
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Ingår i: E3S Web of Conferences. - : EDP Sciences.
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Konferensbidrag (refereegranskat)abstract
- More and more underground spaces were used in 21st century because of rapid urbanization, traffic problems, etc. Underground city, metro, tunnel, mine, industrial and agriculture engineering, civil air defence engineering need large underground spaces. Underground spaces with different thermal, ventilation and lighting environments may cause comfort, health and safety problems. Concrete problems include excessive humidity, heat transfer specialty, excessive CO caused by blockage in long distance traffic tunnels, difficulty in smoke exhaust and evacuation during fire, harmful microorganism, radioactivity pollutants, psychological problems, and so forth. Air quality control technologies for underground spaces, including ventilation technology, dehumidification technology, natural energy utilization technology, smoke extraction technology and ventilation resistance reduction technology, will be reviewed. Ventilation for smoke-proof/evacuation and ventilation will also be reviewed.
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| 10. |
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