Uncovering the Electron‐Phonon Interplay and Dynamical Energy‐Dissipation Mechanisms of Hot Carriers in Hybrid Lead Halide Perovskites

The discovery of slow hot carrier cooling in hybrid organic–inorganic lead halide perovskites (HOIPs) has provided exciting prospects for efficient solar cells that can overcome the Shockley–Queisser limit. Questions still loom over how electron‐phonon interactions differ from traditional polar semiconductors. Herein, the electron‐phonon coupling (EPC) strength of common perovskite films (MAPbBr3, MAPbI3, CsPbI3, and FAPbBr3) is obtained using transient absorption spectroscopy by analyzing the hot carrier cooling thermodynamics via a simplified two‐temperature model. Density function theory calculations are numerically performed at relevant electron‐temperatures to confirm experiments. Further, the variation of carrier‐temperature over a large range of carrier‐densities in HOIPs is analyzed, and an “S‐shaped” dependence of the initial carrier‐temperature to carrier‐density is reported. The phenomenon is attributed to the dominance of the large polaron screening and the destabilization effect which causes an increasing‐decreasing fluctuation in temperature at low excitation powers ; and a hot‐phonon bottleneck which effectively increases the carrier temperature at higher carrier‐densities. The turning point in the relationship is indicative of the critical Mott density related to the nonmetal‐metal transition. The EPC analysis provides a novel perspective to quantify the energy transfer in HOIPs, electron‐lattice subsystem, and the complicated screening‐bottleneck interplay is comprehensively described, resolving the existing experimental contradictions

Numerical Simulation of Water and Mud Inrush Processes in Mountain Tunnels Using Coupled Lattice Boltzmann/Discrete Element Methods

Investigating the mechanism of sudden water inrush and mudflow in mountain tunnels is crucial for implementing preventive measures. Tunnel excavation through a fault or fractured zone can easily trigger sudden water inrush or mudflow. In this paper, the coupled lattice Boltzmann method (LBM) and discrete element method (DEM) were employed to reproduce the process of water and mud inrush in mountain tunnels. The failure of tunnel mud burst and water inrush involves a fluid–solid coupling process. A two-dimensional Boltzmann method for fluids and DEM for particles were utilized, with the coupled LBM-DEM boundary adopting the immersed moving boundary method. For simulating the water inrush process, a numerical model was established to replicate the flow of water particles within karst pipelines, featuring dimensions of 7 cm length, 4 cm width, and consisting of 100 particles. Particles are transported through water flow to the outlet of karst pipelines under hydraulic gradient loading. When the hydraulic gradient exceeds 6, the Darcy velocity gradually tends to be constant. As for simulating the mud inrush process, a numerical model was developed with dimensions of 5 cm length and 4 cm height, incorporating 720 randomly generated particles. The results demonstrated the successful reproduction of the evolution process encompassing three consecutive stages of tunnel mud-burst failure: initiation, acceleration, and stabilization. The occurrence of mud inrush disasters is attributed to combined action involving disaster-causing geotechnical materials, groundwater pressure, and tunnel excavation

Transmission of Normal P-Waves across a Single Joint Based on g‐λ Model

This paper investigates the wave transmission and reflection of an elastic P-wave at a single joint for normal incidence. First, considering a coupled joint (correction parameter λ, 0<λ<1), a normal deformation constitutive model of the joint (g‐λ model) under static or quasi-static loading is introduced and then extended to dynamic loading. The nonlinearity of the joint stress-deformation curve increases with increasing λ. Second, the interaction between the P-wave and the joint is investigated by using the method of characteristics and the displacement discontinuity method to deduce the differential expression of the transmitted wave’s particle velocity. The approximate analytical expressions of the transmission and reflection coefficients are obtained according to the Lemaitre equivalent strain assumption. Third, parametric studies are conducted to evaluate the effects of λ on transmission characteristics for a normally incident P-wave at a single joint. The results show that the particle velocity of the transmitted wave depends on λ. When λ takes the limit values 0 and 1, the transmitted wave’s particle velocities are then consistent with the conclusions of the classical exponential model and the Barton–Bandis model. In addition, the transmission and reflection coefficients are discussed with respect to λ and also to the ratio of the joint closure to the maximum allowable joint closure

Theoretical Study on Radial Distribution Laws of Rock Mass Damage Factors under Decoupled Charge Blasting

In this paper, the radial distribution laws of damage factors under decoupled charge blasting are studied for the optimization design of blasting parameters. Through defining the critical radial decoupling coefficient, the damage zone around the borehole is partitioned and the characteristics are described. Based on the damage factor defined by Taylor’s effective elastic modulus, the formulas of the radial distribution laws of damage factors are derived by the attenuation law of stress wave and the theory of thick-walled cylinder, respectively, which are then superposed to obtain the formula under the combined action of explosion stress wave and quasistatic gas. Experimental verification indicates that the theoretical values, which have a good correlation with the test data and are of high accuracy, can characterize the radial distribution laws of damage factors and estimate the damage range. When a radial decoupling coefficient is less than the critical value, the attenuation rate of damage factors firstly increases and then decreases with the increase of distance, and a serious damage zone is caused. Conversely, it decreases gradually, and the serious damage zone is not caused. Therefore, on the premise of stable detonation, it is necessary to apply an appropriate radial decoupling coefficient which is larger than the critical value to smooth or presplit blasting

New Application: A Hand Air Writing System Based on Radar Dual View Sequential Feature Fusion Idea

In recent years, non-contact human&ndash;computer interactions have aroused much attention. In this paper, we mainly propose a dual view observation system based on the frontal and side millimeter-wave radars (MWR) to collect echo data of the Air writing digits &ldquo;0~9&rdquo;, simultaneously. Additionally, we also propose a novel distance approximation method to make the trajectory reconstruction more efficient. To exploit these characteristics of spatial-temporal adjacency in handwriting digits, we propose a novel clustering algorithm, named the constrained density-based spatial clustering of application with noise (CDBSCAN), to remove background noise or clutter. Moreover, we also design a robust gesture segmentation method by using twice-difference and high&ndash;low thresholds. In our trials and comparisons, based on the trajectories formulated by echo data series of time&ndash;distance and time&ndash;velocity of dual views, we present a lightweight-based convolution neural network (CNN) to realize these digits recognition. Experiment results show that our system has a relatively high recognition accuracy, which would provide a feasible application for future human&ndash;computer interaction scenarios

Surface-mediated selective photocatalytic aerobic oxidation reactions on TiO2 nanofibres

N-doped TiO2 nanofibres were observed to possess lower aerobic oxidation activity than undoped TiO2 nanofibres in the selective photocatalytic aerobic oxidation of enzylamine and 4-methoxybenzyl alcohol. This was attributed to the reduction free energy of O2 adsorption in the vicinity of nitrogen dopant sites, as indicated by density functional theory (DFT) calculations when three-coordinated oxygen atoms are substituted by nitrogen atoms. It was found that the activity recovered following a controlled calcination of the N-doped NFs in air. The dependence of the conversion of benzylamine and 4-methoxybenzyl alcohol on the intensity of light irradiation confirmed that these reactions were driven by light. Action spectra showed that the two oxidation reactions are responsive to light from the UV region through to the visible light irradiation range. The extended light absorption wavelength range in these systems compared to pure TiO2 materials was found to result from the formation of surface complex species following adsorption of reactants onto the catalysts' surface, evidenced by the in situ IR experiment. Both catalytic and in situ IR results reveal that benzaldehyde is the intermediate in the aerobic oxidation of benzylamine to N-benzylidenebenzylamine process

New Application: A Hand Air Writing System Based on Radar Dual View Sequential Feature Fusion Idea

In recent years, non-contact human–computer interactions have aroused much attention. In this paper, we mainly propose a dual view observation system based on the frontal and side millimeter-wave radars (MWR) to collect echo data of the Air writing digits “0~9”, simultaneously. Additionally, we also propose a novel distance approximation method to make the trajectory reconstruction more efficient. To exploit these characteristics of spatial-temporal adjacency in handwriting digits, we propose a novel clustering algorithm, named the constrained density-based spatial clustering of application with noise (CDBSCAN), to remove background noise or clutter. Moreover, we also design a robust gesture segmentation method by using twice-difference and high–low thresholds. In our trials and comparisons, based on the trajectories formulated by echo data series of time–distance and time–velocity of dual views, we present a lightweight-based convolution neural network (CNN) to realize these digits recognition. Experiment results show that our system has a relatively high recognition accuracy, which would provide a feasible application for future human–computer interaction scenarios

Modified alumina nanofiber membranes for protein separation

Large-scale purification/separation of bio-substances is a key technology required for rapid production of biological substances in bioengineering. Membrane filtration is a new separation process and has potential to be used for concentration (removal of solvent), desalting (removal of low molecular weight compounds), clarification (removal of particles), and fractionation (protein-protein separation). In this study, we developed an efficient membrane for protein separation based on ceramic nanofibers. Alumina nanofibers were prepared on a porous support and formed large flow passages. The radical changes in membrane structure provided new ceramic membranes with a large porosity (more than 70%) due to the replacement of bulk particles with fine fibers as building components. The pore size had an average of 11 nm and pure water flux was approximately 360 L•h-1•m-2•bar-1. Further surface modification with a self-assembled monolayer of (3-aminopropyl) triethoxysilane enhanced the membrane filtration properties. Characterization with SEM, FTIR, contact angle, and proteins separation tests indicated that the fibril layers uniformly spread on the surface of the porous support. Moreover, the membrane surface was changed from hydrophilic to hydrophobic after silane groups were grafted. It demonstrated that the silane-grafted alumina fiber membrane can reject 100% BSA protein and 92% cellulase protein. It was also able to retain 75% trypsin protein while maintaining a permeation flux of 48 L•h-1•m-2•bar-1

Online Adaptive Model Identification and State of Charge Estimation for Vehicle-Level Battery Packs

Accurate state of charge (SOC) estimation of traction batteries plays a crucial role in energy and safety management for electric vehicles. Existing studies focus primarily on cell battery SOC estimation. However, numerical instability and divergence problems might occur for a large-size lithium-ion battery pack consisting of many cells. This paper proposes a high-performance online model identification and SOC estimation method based on an adaptive square root unscented Kalman filter (ASRUKF) and an improved forgetting factor recursive least squares (IFFRLS) for vehicle-level traction battery packs. The model parameters are identified online through the IFFRLS, where the conventional method might encounter numerical stability problems. By updating the square root of the covariance matrix, the divergence problem in the traditional unscented Kalman filter is solved in the ASRUKF algorithm, where the positive semi-definiteness of the covariance matrix is guaranteed. Combined with the adaptive noise covariance matched filtering algorithm and real-time compensation of system error, the proposed method solves the problem of ever-degrading estimation accuracy in the presence of time-varying noise with unknown statistical characteristics. Using a 66.2-kWh vehicle battery pack, we experimentally verified that the proposed algorithm could achieve high estimation accuracy with guaranteed numerical stability. The maximum error of SOC estimation can be bounded by 1%, and the root-mean-square error is as low as 0.47% under real-world vehicle operating conditions