123 research outputs found
Large deviations for local times and intersection local times of fractional Brownian motions and Riemann-Liouville processes
In this paper we prove exact forms of large deviations for local times and
intersection local times of fractional Brownian motions and Riemann-Liouville
processes. We also show that a fractional Brownian motion and the related
Riemann-Liouville process behave like constant multiples of each other with
regard to large deviations for their local and intersection local times. As a
consequence of our large deviation estimates, we derive laws of iterated
logarithm for the corresponding local times. The key points of our methods: (1)
logarithmic superadditivity of a normalized sequence of moments of
exponentially randomized local time of a fractional Brownian motion; (2)
logarithmic subadditivity of a normalized sequence of moments of exponentially
randomized intersection local time of Riemann-Liouville processes; (3)
comparison of local and intersection local times based on embedding of a part
of a fractional Brownian motion into the reproducing kernel Hilbert space of
the Riemann-Liouville process.Comment: To appear in the Annals of Probabilit
Improved HPC method for nonlinear wave tank
The recently developed Harmonic Polynomial Cell (HPC) method has been proved to be a promising choice for solving potential-flow Boundary Value Problem (BVP). In this paper, a flux method is proposed to consistently deal with the Neumann boundary condition of the original HPC method and enhance the accuracy. Moreover, fixed mesh algorithm with free surface immersed is developed to improve the computational efficiency. Finally, a two dimensional (2D) multi-block strategy coupling boundary-fitted mesh and fixed mesh is proposed. It limits the computational costs and preserves the accuracy. A fully nonlinear 2D numerical wave tank is developed using the improved HPC method as a verification. Keywords: Harmonic polynomial cell method, Potential-flow theory, Flux method, Fixed mesh, Multi-block strategy, Nonlinear numerical wave tan
PeSOTIF: a Challenging Visual Dataset for Perception SOTIF Problems in Long-tail Traffic Scenarios
Perception algorithms in autonomous driving systems confront great challenges
in long-tail traffic scenarios, where the problems of Safety of the Intended
Functionality (SOTIF) could be triggered by the algorithm performance
insufficiencies and dynamic operational environment. However, such scenarios
are not systematically included in current open-source datasets, and this paper
fills the gap accordingly. Based on the analysis and enumeration of trigger
conditions, a high-quality diverse dataset is released, including various
long-tail traffic scenarios collected from multiple resources. Considering the
development of probabilistic object detection (POD), this dataset marks trigger
sources that may cause perception SOTIF problems in the scenarios as key
objects. In addition, an evaluation protocol is suggested to verify the
effectiveness of POD algorithms in identifying the key objects via uncertainty.
The dataset never stops expanding, and the first batch of open-source data
includes 1126 frames with an average of 2.27 key objects and 2.47 normal
objects in each frame. To demonstrate how to use this dataset for SOTIF
research, this paper further quantifies the perception SOTIF entropy to confirm
whether a scenario is unknown and unsafe for a perception system. The
experimental results show that the quantified entropy can effectively and
efficiently reflect the failure of the perception algorithm.Comment: 7 pages, 5 figures, 4 tables, submitted to 2023 ICR
Effect of Different Water-Binder Ratios and Fiber Contents on the Fluidity and Mechanical Properties of PVA-ECC Materials
With the development of fiber-reinforced cement composites, the diversity and complexity of application scenarios require enhanced strength and ductility and tough materials in practical engineering. To explore the effects of different water-binder ratios and fiber contents on the fluidity, bending resistance, tensile properties, fracture toughness, and fracture behavior of polyvinyl alcohol (PVA) fiber cement composites, several groups of high ductility test blocks (PVA-engineering cementitious composites (ECC)) with different mixing ratios were designed in this study. Based on the expansion degree, the mechanical experimental data, and the electron microscopy scanning image results, K-value analysis was performed on the strain hardening strength criterion. The effect of the water–binder ratio and the fiber dosing on the PVA-ECC material was determined. Results show that the greater the water-binder ratio is, the better the fluidity of the ECC matrix is. In the same cement system and at the same water-binder ratio, the fluidity of the ECC paste gradually deteriorates with the increase of the fiber content. The water-binder ratio significantly affects the flexural tensile strength of the composite. The flexural and tensile strengths of the PVA-ECC gradually increase as the water-binder ratio decreases, but the ductility gradually decreases. The water-binder ratio of the substrate directly influences the damage behavior of the fibers within the substrate. With the gradual increase of the water-binder ratio, the fiber at the crack interface gradually changes from pull-out morphology to fracture morphology. The strain capacity and the multi-crack cracking performance decrease. To achieve improved working performance in the actual project, the matrix water-binder ratio should be controlled at approximately 0.45, and the PVA fiber dose of 1.7% is optimal. This study can provide a good reference for the optimization of practical engineering components
SOTIF Entropy: Online SOTIF Risk Quantification and Mitigation for Autonomous Driving
Autonomous driving confronts great challenges in complex traffic scenarios,
where the risk of Safety of the Intended Functionality (SOTIF) can be triggered
by the dynamic operational environment and system insufficiencies. The SOTIF
risk is reflected not only intuitively in the collision risk with objects
outside the autonomous vehicles (AVs), but also inherently in the performance
limitation risk of the implemented algorithms themselves. How to minimize the
SOTIF risk for autonomous driving is currently a critical, difficult, and
unresolved issue. Therefore, this paper proposes the "Self-Surveillance and
Self-Adaption System" as a systematic approach to online minimize the SOTIF
risk, which aims to provide a systematic solution for monitoring,
quantification, and mitigation of inherent and external risks. The core of this
system is the risk monitoring of the implemented artificial intelligence
algorithms within the AV. As a demonstration of the Self-Surveillance and
Self-Adaption System, the risk monitoring of the perception algorithm, i.e.,
YOLOv5 is highlighted. Moreover, the inherent perception algorithm risk and
external collision risk are jointly quantified via SOTIF entropy, which is then
propagated downstream to the decision-making module and mitigated. Finally,
several challenging scenarios are demonstrated, and the Hardware-in-the-Loop
experiments are conducted to verify the efficiency and effectiveness of the
system. The results demonstrate that the Self-Surveillance and Self-Adaption
System enables dependable online monitoring, quantification, and mitigation of
SOTIF risk in real-time critical traffic environments.Comment: 16 pages, 10 figures, 2 tables, submitted to IEEE TIT
Nonreciprocal Acoustic Transmission using Lithium Niobate Parity-Time-Symmetric Resonators
Taking advantage of the piezoelectricity of lithium niobate, we achieve nonreciprocal transmission of 10 decibels for a 200-MHz surface acoustic wave using parity-time- symmetric resonators and demonstrate one-way circulation of acoustic waves
Nonreciprocal Acoustic Transmission using Lithium Niobate Parity-Time-Symmetric Resonators
Taking advantage of the piezoelectricity of lithium niobate, we achieve nonreciprocal transmission of 10 decibels for a 200-MHz surface acoustic wave using parity-time- symmetric resonators and demonstrate one-way circulation of acoustic waves
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