Summary The reliable protection of personal safety and vehicle service security has aroused the rising attention on battery thermal safety issues. This poses ongoing challenges for battery thermal management (BTM) to improve the safety by constantly learning and adopting advanced technologies from thermal management to thermal safety control. On the basis of electrochemical, mechanical, and thermo‐kinetic characteristics of battery behavior evolution under operational conditions of normal and abnormal, BTM with enhanced safety cannot only guarantee the battery operation performance but also improve thermo‐safety behavior with the heat transfer intensifying method. Additionally, via effective measurements to detect and warn the battery behavior evolution characteristics, the combination of emergency cooling, fire extinguishing, and thermal barrier adopted in BTM with enhanced safety can effectively and sufficiently suppress battery thermal overheating and its propagation. As concluded, the synthesized integration of basic BTM and its safety‐enhanced treatment can ensure the optimal working temperature range and prevent thermal overheating from propagation. Thus, the BTM system with enhanced safety has been a promising research priority. This article provides a comprehensive review on BTM with enhanced safety aiming to promote the battery application with high energy density, security, and cyclic stability served for electrification and intelligentization of automobiles. In addition, the summary of relevant research status and key technology is dedicated to improving BTM thermo‐safe design innovation and collaborative optimization, to fit with the sustainable development needs of the long‐term mechanism of energy conservation and green‐energy vehicles marketization.

Abstract-Secret key generation among wireless devices using physical layer information of radio channel has been an attractive alternative for ensuring security in mobile environments. Received signal strength (RSS) based secret key extraction gains much attention due to its easy accessibility in wireless infrastructure. However, the problem of using RSS to generate keys among multiple devices to ensure secure group communication in practice remains open. In this work, we propose a framework for collaborative key generation among multiple wireless devices leveraging RSS. To deal with mobile devices not within each other's communication range, we employ relay nodes to achieve reliable key extraction. To enable secure group communication, two protocols are developed to perform collaborative group key generation via star and chain topologies respectively. We further provide the theoretic analysis on the achievable secrecy rate for both star and chain topologies in the presence of an eavesdropper. Our prototype development using MICAz motes and extensive experiments using fading trend based key extraction demonstrate the feasibility of using RSS for group key generation in both indoor and outdoor environments, and concurrently achieving a lower bit mismatch rate compared to existing studies.

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We present a new approach for predicting stable equilibrium shapes of two-dimensional crystalline islands on flat substrates, as commonly occur through solid-state dewetting of thin films. The new theory is a generalization of the widely used Winterbottom construction (i.e., an extension of the Wulff construction for particles on substrates). This approach is equally applicable to cases where the crystal surface energy is isotropic, weakly anisotropic, strongly anisotropic and "cusped". We demonstrate that, unlike in the classical Winterbottom approach, multiple equilibrium island shapes may be possible when the surface energy is strongly anisotropic. We analyze these shapes through perturbation analysis, by calculating the first and second variations of the total free energy functional with respect to contact locations and island shape. Based on this analysis, we find the necessary conditions for the equilibria to be stable to two-dimensional perturbations and exploit this through a generalization of the Winterbottom construction to identify all possible stable equilibrium shapes. Finally, we propose a dynamical evolution method based on surface diffusion mass transport to determine whether all of the stable equilibrium shapes are dynamically accessible. Applying this approach, we demonstrate that islands with different initial shapes may evolve into different stationary shapes and show that these dynamically-determined stationary states correspond to the predicted stable equilibrium shapes, as obtained from the generalized Winterbottom construction.

A series of MIL-53(Fe) materials were synthesized using a solvothermal method under different temperature and time conditions and were used as catalysts to activate persulfate and degrade Orange G (OG). Influences of the above conditions on the crystal structure and catalytic behavior were investigated. Degradation of OG under different conditions was evaluated, and the possible activation mechanism was speculated. The results indicate that high synthesis temperature (larger than 170 °C) leads to poor crystallinity and low catalytic activity, while MIL-53(Fe) cannot fully develop at low temperature (100 or 120 °C). The extension of synthesis time from 5 h to 3 d can increase the crystallinity of the samples, but weakened the catalytic activity, which was caused by the reduction of BET surface area and the amount of Fe (II)-coordinative unsaturated sites. Among all the samples, MIL-53(Fe)-A possesses the best crystal structure and catalytic activity. In optimal conditions, OG can be totally decolorized after degradation for 90 min, and a removal rate of 74% for COD was attained after 120 min. The initial solution pH had great influence on OG degradation, with the greatest removal in acidic pH environment. ESR spectra showed that sulfate radical (SO4−·), hydroxyl radical (OH·), persulfate radical (S2O8−·), and superoxide radical (O2·) exist in this system under acidic conditions. Furthermore, with the increase of pH, the relative amount of O2· increases while that of OH· and SO4−· decreases, resulting in a reduced oxidizing capacity of the system.

An anisotropic wave in a porous medium is a hot topic in the coastal protection. A fractal derivative model is established, and a variational principle is established for the anisotropic wave traveling. The variational principle reveals an energy conservation law during the traveling process.

Hybrid simulations are carried out to investigate the excitation of oxygen ion cyclotron harmonic waves observed in the inner magnetosphere. The simulations show that these waves can be excited by energetic oxygen ions of a ring-like velocity distribution. The excited waves have properties consistent with observations, but their nearly perpendicular propagation disagrees with the quasi-parallel propagation from the singular value decomposition (SVD) analysis reported earlier. By performing the same SVD analysis on the simulated waves in a three-dimensional simulation, it is demonstrated that the superposition of multiple waves with different azimuthal angles can cause the commonly used SVD analysis of wave propagation to yield incorrectly small wave normal angles. In addition, the results show that the enhanced waves scatter oxygen ions mainly along v ⟂ through cyclotron resonance. The waves may also scatter energetic radiation belt electrons through bounce resonance and transit time scattering, similar to fast magnetosonic waves. Plain Language Summary Waves at multiple harmonics of the oxygen ion cyclotron frequency (known as oxygen ion cyclotron harmonic waves) have been observed in the inner magnetosphere. Their source is still under debate because observations suggest they have quasi-parallel propagation, whereas linear theory reveals unstable modes (of otherwise similar properties) at nearly perpendicular propagation. The present one-dimensional hybrid simulation first demonstrates that the waves can be excited by energetic oxygen ions of a ring-like velocity distribution. More importantly, our three-dimensional simulation shows that the superposition of multiple waves with different azimuthal angles can make the commonly used singular value decomposition method to give false estimate of wave normal angles. Finally, the scattering of ions by the waves excited are examined. The waves can cause efficient transverse heating of the cool background oxygen ions. They might also be capable of scattering the energetic radiation belt electrons through bounce resonance and transit time scattering.