In this paper a new car-following model with consideration of time-delayed velocity difference is proposed to investigate the effect of time-delayed velocity on traffic flow via bifurcation analysis. ...Based on this model, the linear stability analysis is carried out and the corresponding stability condition is obtained. Then the Hopf bifurcation analysis is performed in term of theoretical analysis and numerical simulation. The result shows that there exist Hopf bifurcation critical points and the position of the critical points is found to be located on the boundary of the instability region. Finally, the influence of the delay time and sensitivity of velocity difference on Hopf bifurcation is discussed, respectively.
•A new car-following model with consideration of time-delayed velocity difference (TDVD) is proposed to investigate the influence of time-delayed velocity on traffic flow via bifurcation analysis. The stability condition is obtained by linear analysis.•We conduct the Hopf bifurcation analysis for TDVD model via theoretical analysis and numerical computation. The results show that there exist Hopf bifurcation critical points and the occurrence of Hopf bifurcation causes the loss of stability in TDVD model to generate traffic jams.•Finally, the influence of the delay time and sensitivity of velocity difference on the Hopf bifurcation is discussed, respectively.
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•A new hindered settling velocity model for activated sludge is proposed.•This model is related to fractal dimension and other flocs characteristics.•It describes the settling ...velocity after a fragmentation-flocculation process.•The model reproduces the abrupt decrease of final hindered settling velocity.•The fractal dimension explains the structure of flocs formed from primary flocs.
The modelling of the activated sludge hindered settling velocity as a function of the flocs characteristics and the incorporation of these models to the secondary settling tanks simulation is a hardly studied subject. Commonly used empirical models cannot describe the changes in the settling velocity caused by changes in the flocs characteristics. In this paper, a model for the hindered settling velocity as a function of the fractal dimension and other flocs characteristics is proposed. The model was used to describe the settling velocity after a flocculation process originated by activated sludge fragmentation. The model reproduces the observed abrupt decrease of hindered settling velocity in a small range of suspended solids concentration. It also enables to relate the flocs characteristics and the settling velocity to the fragmentation and sludge aggregation mechanisms.
In this paper, a new car-following model is proposed with the consideration of the incorporating timid and aggressive behaviors on single lane. The linear stability condition with the incorporating ...timid and aggressive behaviors term is obtained. Numerical simulation indicates that the new car-following model can estimate proper delay time of car motion and kinematic wave speed at jam density by considering the incorporating the timid and aggressive behaviors. The results also show that the aggressive behavior can improve traffic flow while the timid behavior deteriorates traffic stability, which means that the aggressive behavior is better than timid behavior since the aggressive driver makes rapid response to the variation of the velocity of the leading car. Snapshot of the velocities also shows that the new model can approach approximation to a wide moving jam.
•A new car-following model is presented by incorporating the timid and aggressive driving behaviors.•The traffic timid and aggressive driving behaviors have been studied on the stability of traffic flow.•The starting process is investigated with the difference of the timid and aggressive effects.•The numerical results show that more aggressive driving behaviors can improve the stability of traffic flow than timid driving behaviors.
Three-dimensional physics-based numerical simulations (3D-PBS) of the seismic response of the Santiago Basin, Chile, were performed considering a large-scale velocity model and shallow crustal ...earthquake scenarios, associated with the west-verging thrust San Ramón Fault. Numerical results show that competent gravelly soils in the center of the basin respond with low seismic amplification and shorter durations of strong ground motions, unlike less competent fine-grained soils in the northern area. A significant increase in the seismic intensities is observed in the vicinity of rock outcrops, attributable to the generation of surface waves. Seismic amplification factors were calculated with respect to a reference site on gravel and their values show high levels of amplification in the vicinity of the seismic source, and on soils with low shear wave velocities (Vs) and long fundamental vibration periods. On the other hand, empirical ground motion models (GMM) were used to estimate amplification factors for peak ground accelerations and spectral accelerations at various periods. Results from GMMs and 3D-PBS were compared, showing similarities in the attenuation pattern on stiff soils, but differences in soils with low Vs. Moreover, 3D-PBS captured site effects associated with the local geomorphology, unlike GMMs.
•Two scenarios of Mw 6.0 earthquakes generated at the San Ramon Fault were evaluated.•3D physics-based numerical simulations (3D-PBS) consider a large-scale Vs model.•Amplification patterns from 3D-PBS tend to agree with results from ground motion models.•Differences in predictions are detected in sites prone to develop surface waves.•Fine-grained soils away from the fault scarp amplify and extend the ground motion.
In this paper, the delayed-feedback control method for car-following model is proposed with the combination of V2V communication. The stability condition is obtained with the consideration of the ...control signals by applying control method. Numerical simulation indicates that the control signals can alleviate traffic jam successfully, which is in accordance with analytical results. In a conclusion, the performance of traffic flow is improved with delayed-feedback control method under V2V communication situation for car-following theory.
•A delayed-feedback control is proposed for car-following model.•Linear stability condition is deduced from linear stability analysis with control theory.•Numerical simulations validate the positive stability when traffic jams sudden appear.
The collision-free velocity model is a microscopic pedestrian model, which despite its simplicity, reproduces fairly well several self-organization phenomena in pedestrian dynamics. The model ...consists of two components: a direction sub-model that combines individual desired moving direction and neighbor’s influence to imitate the process of navigating in a two-dimensional space, and an intrinsically collision-free speed sub-model which controls the speed of the agents with respect to the distance to their neighbors.
In this paper we generalize the collision-free velocity model by introducing the influence of walls and extending the distance calculations to velocity-based ellipses. Besides, we introduce enhancements to the direction sub-module that smooth the direction changes of pedestrians in the simulation; a shortcoming that was not visible in the original model due to the symmetry of the circular shapes. Moreover, the introduced improvements mitigate backward movements, leading to a more realistic distribution of pedestrians especially in bottleneck scenarios.
We study by simulation the effects of the pedestrian’s shape by comparing the fundamental diagram in narrow and wide corridors. Furthermore, we validate our generalized approach by investigating the flow through bottlenecks with varying exit’s widths.
•Completing the collision-free velocity model by introducing the influence of walls.•Using velocity-based ellipses to represent pedestrians projection on plane.•Eliminating unrealistic backward movement of agents during simulation.•Mitigating unnatural shaking of agents during simulation.
The structure and dynamics of the upper mantle control tectonics, seismicity, magmatism, and the development of mineral deposits. Seismic tomography maps spatial variations in seismic velocity and ...offers essential information on the variations of temperature in the mantle, the thickness and mechanical strength of the lithosphere, and the convection patterns below it. Thanks to the growth in the station coverage, tomographic models of Asia reveal increasingly detailed structures, in particular in its best-sampled parts. Here, we present a new waveform tomography model, ASIA2024, constrained by massive global and regional datasets. The data coverage used to construct ASIA2024 is maximised across the hemisphere centred at Asia. In China, in particular, dense national network data enhances the sampling. Our waveform tomography extracts structural information from surface waves and from S and multiple S body waves. The effects of errors are suppressed by statistical and targeted outlier analyses and the removal of the least mutually consistent data. Extensive comparisons of contemporary tomographic models reveal both consensus features and differences between models and demonstrate relative advantages of different approaches and data types. ASIA2024 advances the resolution of the imaging compared to the state of the art at the scale of the continent. A prominent high-velocity anomaly at lithospheric depths shows the Indian cratonic lithosphere underthrusting and subducting beneath Tibet. In the transition zone below the plateau, a fragmented high-velocity anomaly indicates lithospheric remnants, probably from different phases of subduction. The lithosphere beneath most diamondiferous kimberlites—originally emplaced on thick cratonic lithosphere—is observed to be still thick at present. Relatively low velocities at kimberlite locations are indicative of craton-lithosphere thinning and are detected beneath northwestern Siberian Craton (Siberian Traps) and most of the Indian Shield (Deccan Traps and surroundings), with the exception of the intact cratonic lithosphere beneath northeastern Dharwar Craton. This suggests that the mantle plumes responsible for the traps have eroded the deep cratonic lithosphere. Thin lithosphere and recent basaltic volcanism are observed in eastern Sino-Korean and Yangtze Cratons, with subduction, stretching, and rifting likely to have weakened and modified their cratonic roots. Cenozoic basalts are found exclusively where the lithosphere is observed to be thin. Beneath the Hainan volcanic region, a low-velocity anomaly is observed throughout the upper mantle, consistent with the previously proposed Hainan Plume feeding the magmatism. The shape of the anomaly indicates a complex morphology of the upwelling. Low-velocity anomalies in the mantle transition zone beneath the Hangai Dome and southern Siberian Craton are consistent with hot upwelling(s) and horizontal asthenospheric flow feeding the dispersed basaltic volcanism. Sediment-hosted metal deposits tend to be located near contrasts in the thickness of the lithosphere, including craton boundaries and other substantial heterogeneities. Intraplate seismicity is controlled by plate-boundary stresses and lateral variations of the lithospheric thickness and strength. Areas with relatively thin lithosphere across Asia tend to localise deformation and seismicity. The Gujarat seismic zone in India is collocated with an area of warm, thin lithosphere. This suggests a relationship between the occurrence of devastating earthquakes there and deformation in the mechanically weak part of the plate.
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•Seismic tomography maps the structure of Asia's upper mantle in increasing detail.•Our new waveform tomography model, ASIA2024, advances the resolution of the imaging.•Mantle lithosphere exerts primary controls on tectonics, seismicity and magmatism.•Lithospheric thickness and plate boundary stresses control intraplate seismicity.•Evolution of continental lithosphere is evidenced by mantle structure and volcanism.
In this study, we built a high‐resolution 3D S‐wave velocity model of the South China Sea (SCS) and adjacent areas by the joint inversion of surface wave dispersions retrieved from ambient noise and ...earthquake data. We first measured Rayleigh wave phase velocity dispersions from the waveforms recorded by 94 broadband seismic stations. Subsequently, we used a generalized least squares inversion scheme with spatially varying resolution to perform 2D tomographic inversion at different periods. Lastly, we performed 1D inversion at different grid points and obtained the 3D S‐wave velocity model in the depth range of 15–250 km. Our model reveals a prominent high velocity (high‐V) anomaly beneath the SCS basin and shows that the lithosphere beneath the SCS basin is about 70–80 km thick. We observe a prominent low velocity (low‐V) anomaly in the asthenosphere beneath the SCS basin, and we interpret this as evidence for the ongoing partial melting of the asthenosphere. An obvious high‐V anomaly is also revealed beneath the Khorat Plateau (KP) in the depth range of 80–150 km, suggesting that the KP has a cold and thick lithosphere and has suffered limited destruction in the Cenozoic era. In the northern part of Kalimantan Island (KI), a prominent low‐V anomaly is shown in the upper 60 km of the lithosphere revealing the upwelling of the asthenosphere. Our findings shed lights on the tectonic evolution of the SCS and adjacent areas.
Key Points
A high‐resolution 3D S‐wave velocity model is built in the South China Sea and adjacent areas
There is a prominent high velocity anomaly beneath the South China Sea Basin and the lithosphere thickness is about 70–80 km
The obvious low velocity anomaly beneath the northern Kalimantan Island may indicate the upwelling of the asthenosphere
In this paper, a new anticipation optimal velocity model (AOVM) is proposed by considering anticipation effect on the basis of the full velocity difference model (FVDM) for car-following theory on ...single lane. The linear stability condition is derived from linear stability analysis. Starting and braking process is investigated for the car motion under a traffic signal, which shows that the results accord with empirical traffic values. Especially AOVM can avoid the disadvantage of the unrealistically high deceleration appearing in FVDM. Furthermore, numerical simulation shows that AOVM might avoid the disadvantage of negative velocity and headway that occur at small sensitivity coefficients in the FVDM since the anticipation effect is taken into account in AOVM, which means that collision disappears with the consideration of an appropriate anticipation parameter.
•A new anticipation optimal velocity car-following model is proposed.•The anticipation effects on the stability of traffic flow have been explored.•The starting and braking process were carried out through simulation.•The anticipation effects of the optimal velocity can avoid the disadvantage of negative velocity.
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