The evolution of interfaces for underwater gas jets is the main morphological manifestation of two-phase unstable interaction. The high-speed transient photographic recording and image post-processing methods are used to obtain the interfacial change in a submerged gaseous jet at different stages after its ejection from the Laval nozzle exit. The relationship between the pressure pulsation in the wake flow field and the interfacial change is further analyzed by combining the experimental results with computational results. A theoretical model is employed to address the competition dominant mechanism of interface instability. The results show that the jet interface of a supersonic gas jet gradually changes from one containing wave structures to a transition structure, and finally forms a steady-state conical jet. The fluctuation of the jet interface results in the pulsation of the back-pressure. The dominant mechanism of the interface changes with the development and distribution of the jet, from Kelvin-Helmholtz (K-H) instability beyond the nozzle exit changing to Rayleigh-Taylor (R-T) instability in the downstream.

Polyvinyl alcohol (PVA) hydrogels find applications in various fields, including machinery and tissue engineering, owing to their exceptional mechanical properties. However, the mechanical properties of PVA hydrogels are subject to alteration due to environmental factors such as temperature, affecting their prolonged utilization. To enhance their lifespan, it is crucial to investigate their aging mechanisms. Using physically cross-linked PVA hydrogels, this study involved high-temperature accelerated aging tests at 60 °C for 80 d and their performance was analyzed through macroscopic mechanics, microscopic morphology, and microanalysis tests. The findings revealed three aging stages, namely, a reduction in free water, a reduction in bound water, and the depletion of bound water, corresponding to volume shrinkage, decreased elongation, and a “tough-brittle” transition. The microscopic aging mechanism was influenced by intermolecular chain spacing, intermolecular hydrogen bonds, and the plasticizing effect of water. In particular, the loss of bound water predominantly affected the lifespan of PVA hydrogel structural components. These findings provide a reference for assessing and improving the lifespan of PVA hydrogels.

In this paper, a discrete Boltzmann method (DBM) for plasma kinetics is proposed and further used to investigate the non-equilibrium characteristics in Orszag–Tang (OT) vortex and Richtmyer–Meshkov instability (RMI) problems. The construction of DBM mainly considers two aspects. The first is to build a physical model with sufficient capability to capture underlying physics. The second is to devise schemes for extracting more valuable information from massive data. For the first aspect, the generated model is equivalent to a magnetohydrodynamic model, and a coarse-grained model for extracting the most relevant thermodynamic non-equilibrium (TNE) behaviors including the entropy production rate. For the second aspect, the DBM uses non-conserved kinetic moments of (f−feq) to describe the non-equilibrium states and behaviors of complex systems. It is found that (i) for OT vortex, the entropy production rate and compression difficulty first increase and then decrease with time. (ii) For RMI with interface inversion and re-shock process, the influence of magnetic field on TNE effects shows stages: before the interface inversion, the TNE strength is enhanced by delaying the interface inversion; while after the interface inversion, the TNE strength is significantly reduced. Both the global average TNE strength and entropy production rate contributed by non-organized energy flux can be used as physical criteria to identify whether or not the magnetic field is sufficient to prevent the interface inversion. In general, this paper proposes a generalized physical modeling and analysis scheme that has the potential for investigating the kinetic physics in plasma.

In Autonomous Driving (AD), real-time perception is a critical component responsible for detecting surrounding objects to ensure safe driving. While researchers have extensively explored the integrity of AD perception due to its safety and security implications, the aspect of availability (real-time performance) or latency has received limited attention. Existing works on latency-based attack have focused mainly on object detection, i.e., a component in camera-based AD perception, overlooking the entire camera-based AD perception, which hinders them to achieve effective system-level effects, such as vehicle crashes. In this paper, we propose SlowTrack, a novel framework for generating adversarial attacks to increase the execution time of camera-based AD perception. We propose a novel two-stage attack strategy along with the three new loss function designs. Our evaluation is conducted on four popular camera-based AD perception pipelines, and the results demonstrate that SlowTrack significantly outperforms existing latency-based attacks while maintaining comparable imperceptibility levels. Furthermore, we perform the evaluation on Baidu Apollo, an industry-grade full-stack AD system, and LGSVL, a production-grade AD simulator, with two scenarios to compare the system-level effects of SlowTrack and existing attacks. Our evaluation results show that the system-level effects can be significantly improved, i.e., the vehicle crash rate of SlowTrack is around 95% on average while existing works only have around 30%.