Search

Cyclohexene esterification–hydrogenation for the efficient production of cyclohexanol will be commercialized for the first time. Cu/MgO/Al2O3 catalysts with layered double hydroxides as precursors were developed, and the effect of altering the reduction temperature on the catalytic activity was explored. Fresh and spent Cu/MgO/Al2O3 catalysts exhibited excellent catalytic performance after thermal treatment during the hydrogenation of cyclohexyl acetate to cyclohexanol. STEM images showed that the Cu particles grew slightly, without obvious aggregation. Based on the results of XAES and in situ FTIR of the adsorbed CO method, optimal performance (conversion rate of 99.59% with 98.94% selectivity) was achieved, which was attributed to the synergistic effect on the surface-active Cu0 and Cu+ sites with Cu0/(Cu0 + Cu+) of around 0.70, and the ratios could be maintained at temperatures of 513–553 K. The morphology of Cu/MgO/Al2O3 catalysts was well preserved during the hydrogenation of cyclohexyl acetate, indicating potential industrial applications. The well-dispersed Cu/MgO/Al2O3 catalyst with a stable microstructure possesses an adjustable valence state and thermal stability during the hydrogenation of cyclohexyl acetate, giving it industrial application prospects. [ABSTRACT FROM AUTHOR]

Stable all‐inorganic CsPbX3 perovskite nanocrystals (PNCs) with high optical yield can be used in combination with graphene as photon sensors with high responsivity (up to 106 A W−1) in the VIS‐UV range. The performance of these perovskite/graphene field effect transistors (FET) is mediated by charge transfer processes at the perovskite – graphene interface. Here, the effects of high electric (up to 3000 kV cm−1) and magnetic (up to 60 T) fields applied perpendicular to the graphene plane on the charge transfer are reported. The authors demonstrate electric‐ and magnetic‐field dependent charge transfer and a slow (>100 s) charge dynamics. Magneto‐transport experiments in constant (≈0.005 T s−1) and pulsed (≈1000 T s−1) magnetic fields reveal pronounced hysteresis effects in the transfer characteristics of the FET. A magnetic time is used to explain and model differences in device behavior under fast (pulsed) and slowly (continuous) changing magnetic fields. The understanding of the dynamics of the charge transfer in perovskite/graphene heterostructures developed here is relevant for exploitation of these hybrid systems in electronics and optoelectronics, including ultrasensitive photon detectors and FETs for metrology. [ABSTRACT FROM AUTHOR]

Self‐assembly of nanocrystals into controlled structures while uncompromising their properties is one of the key steps in optoelectronic device fabrication. Herein, zigzag CsPbBr3 perovskite nanocrystals are demonstrated with a precise number of components with nanocube morphology, these can be successfully obtained through a dipole‐induced self‐assembly process. The addition of a trace amount of deionized water facilitates the transfer from CsPbBr3 nanocubes to intermediates of CsPb2Br5 and Cs3In2Br9, which then fastly release reaction monomers leading to further homogenous nucleation of CsPbBr3 nanocubes, followed by the formation of zigzag CsPbBr3 nanocrystals through a dipole‐induced self‐assembly process. Dipole moment along <110> axis is found to be the driving force for the assembly of nanocubes into zigzag nanocrystals. The zigzag CsPbBr3 nanocrystals exhibit desirable optical properties comparable to their nanocube counterparts and offer advantages for amplified spontaneous emission and lasing applications with low pump thresholds of 3.1 and 6.02 µJ cm−2, respectively. This study not only develops a strategy for producing highly controlled zigzag perovskite nanocrystals and provides insights on the dipole‐induced self‐assembly mechanisms, but also opens an avenue for their application in lasing. [ABSTRACT FROM AUTHOR]

Quasi‐2D Ruddlesden‐Popper perovskites receive tremendous attention for application in light‐emitting diodes (LEDs). However, the role of organic ammonium spacers on perovskite film has not been fully‐understood. Herein, a spacer cation assisted perovskite nucleation and growth strategy, where guanidinium (GA+) spacer is introduced into the perovskite precursor and at the interface between the hole transport layer (HTL) and the perovskite, to achieve dense and uniform perovskite films with enhanced optical and electrical performance is developed. A thin GABr interface pre‐formed on HTL provides more nucleation sites for perovskite crystal; while the added GA+ in perovskite reduces the crystallization rate due to strong hydrogen bonding interacts with intermediates, which promotes the growth of enhanced‐quality quasi‐2D perovskite films. The ionized ammonium group (NH3+) of GA+ also favors formation of polydisperse domain distribution, and amine or imine (NH2 or NH) group interact with perovskite defects through coordination bonding. The spacer cation assisted nucleation and growth strategy is advantageous for producing efficient and high‐luminance perovskite LEDs, with a peak external quantum efficiency of over 20% and a luminance up to 100 000 cd m−2. This work can inform and underpin future development of high‐performance perovskite LEDs with concurrent high efficiency and brightness. [ABSTRACT FROM AUTHOR]

Attitude determination is fundamental for spacecraft missions in aerospace engineering. Kalman filter (KF) is the optimal estimator in least square sense and, using the symmetry properties of matrix Lie groups system, the invariant Kalman filter (IKF) has been developed to boost the filtering performance for attitude estimation. However, due to presence of frequent and severer maneuvers, the Lie groups attitude dynamics is usually corrupted by significant biases and heavy-tailed outliers, which usually leads to decreased precision of IKF. For attitude estimation problem troubled by biased and heavy-tailed process noise, this work proposes a new invariant Kalman filter (VBAIKF) by constructing the hierarchical Gaussian system model: the probability density function of prior estimate state is first described using the student's t distribution, while the unknown scale covariance matrix and degrees of freedom (dof) of the employed student's t distribution are defined as the inverse Wishart distribution (IWD) and Gamma distribution. In VBAIKF, the Lie groups rotation matrix of spacecraft, the biased mean, the parameters of dof and scale covariance matrix are online estimated together by variational Bayesian fixed-point iterations. The simulation results with Lie groups attitude estimation system further verify the superior filtering adaptability and precision of proposed approach VBAIKF than other methods for attitude determination with biased mean and heavy-tailed process noise. [ABSTRACT FROM AUTHOR]

For some flight missions, such as autonomous landing on mobile platforms, the demands on indicators such as target-tracking accuracy and so on are relatively high. To achieve this, a guidance system with excellent precision is necessary. An asymmetric tracking differentiator based on a tracking differentiator is proposed to establish the guidance system. On the basis of the proposed asymmetric tracking differentiator, an altitudinal and horizontal helicopter guidance system structure is designed. In this paper, a guidance law is designed in order to meet the accuracy and precision requirements in the autonomous landing and transition process. Apart from that, a plane-motion-guidance law is also designed to realize static and dynamic point tracking, linear route tracking and circular route tracking to improve the trajectory smoothness and accuracy. Finally, simulations of the autonomous landing process on moving platforms, including three stages, namely approaching, tracking and landing, are completed. The application effects and precision of the autonomous landing guidance algorithm under different wave heights and period conditions are analyzed through the obtained simulation curves. [ABSTRACT FROM AUTHOR]

Quantum dots (QDs) of formamidinium lead triiodide (FAPbI3) perovskite hold great potential, outperforming their inorganic counterparts in terms of phase stability and carrier lifetime, for high‐performance solar cells. However, the highly dynamic nature of FAPbI3 QDs, which mainly originates from the proton exchange between oleic acid and oleylamine (OAm) surface ligands, is a key hurdle that impedes the fabrication of high‐efficiency solar cells. To tackle such an issue, here, protonated‐OAm in situ to strengthen the ligand binding at the surface of FAPbI3 QDs, which can effectively suppress the defect formation during QD synthesis and purification processes is selectively introduced. In addition, by forming a halide‐rich surface environment, the ligand density in a broader range for FAPbI3 QDs without compromising their structural integrity, which significantly improves their optoelectronic properties can be modulated. As a result, the power conversion efficiency of FAPbI3 QD solar cells (QDSCs) is enhanced from 7.4% to 13.8%, a record for FAPbI3 QDSCs. Furthermore, the suppressed proton exchange and reduced surface defects in FAPbI3 QDs also enhance the stability of QDSCs, which retain 80% of the initial efficiency upon exposure to ambient air for 3000 hours. [ABSTRACT FROM AUTHOR]

This work studies the ${H}_{\infty }$ -based minimal energy control with a preset convergence rate (PCR) problem for a class of disturbed linear time-invariant continuous-time systems with matched external disturbance. This problem aims to design an optimal controller so that the energy of the control input satisfies a predetermined requirement. Moreover, the closed-loop system asymptotic stability with PCR is ensured simultaneously. To deal with this problem, a modified game algebraic Riccati equation (MGARE) is proposed, which is different from the game algebraic Riccati equation in the traditional ${H}_{\infty } $ control problem due to the state cost being lost. Therefore, a unique positive-definite solution of the MGARE is theoretically analyzed with its existing conditions. In addition, based on this formulation, a novel approach is proposed to solve the actuator magnitude saturation problem with the system dynamics being exactly known. To relax the requirement of the knowledge of system dynamics, a model-free policy iteration approach is proposed to compute the solution of this problem. Finally, the effectiveness of the proposed approaches is verified through two simulation examples. [ABSTRACT FROM AUTHOR]

Quasi-two-dimensional (quasi-2D) perov- skites possess the preponderances of large exciton binding energy and quantum confinement effects compared with three-dimensional (3D) perovskites. The unique properties of quasi-2D perovskite have attracted extensive attention in the field of optoelectronic devices, especially in the light emitting diode (LED) direction. However, the adverse effects between the perovskite emission layer and the popularly used hole transport layer (HTL) Poly(3,4-ethylenedioxythiophene):poly (styrene sulfonate) (PEDOT:PSS) have degrade the device performance, such as large energy level barrier and exciton quenching. Here we demonstrated high performance of LED with enhanced brightness and efficiency by modifying the PEDOT:PSS with NdBr3, which not only decreases exciton quenching, but also decreases HOMO level of the PEDOT:PSS, thereby improving the charge balance. The final performance of the perovskite light-emitting diode (PeLED) device was obtained with a maximum luminance of 18684 cd m−2, a maximum current efficiency (CE) of 48.4 cd A−1 and an external quantum efficiency (EQE) of up to 15.5% when using NdBr3 modified PEDOT:PSS. [ABSTRACT FROM AUTHOR]