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The echelon usage control of helicopters is one of the most import job in the aviation equipment support,the overall efficiency of helicopter can be maximized by arranging the echelon usage. Aiming at the difficulty and lack of evaluation index in the echelon usage control, two methods of the echelon usage control are introduced, the way of echelon optimization control technology is mainly expatiated, the influences of different parameters in the echelon usage control are deduced and analyzed, and three evaluation indexes of echelon usage control are presented. Finally, a case study is carried out by using the method of echelon optimization technology, the results indicate that the sum of minimum time and maximum time of annual mission is a constant, the parameter selection method deduced in the paper is correct, and the evaluation indexes proposed are reasonable, and the research direction of the next step is clarified.

Supercritical fluids exist widely in nature and have enduringly attracted scientific and industrial interest. In power systems like liquid rocket engines, fluids undergo the trans-critical process transferred from the subcritical state to the supercritical state, and the phase change process exhibits different features distinguished from subcritical evaporation. In this work, we conducted a series of molecular dynamics studies on the behavior of methanol (MeOH), n-heptane (C7), and binary C7/MeOH droplets under supercritical nitrogen environments. The emphasis is on clarifying the transient characteristics and physical origins of the trans-critical evolution of droplets. During the trans-critical process, droplets are found to experience an unstable period without a spherical shape, where the droplet diameter no longer decreases, violating the traditional d2-law rule. The occurrence of nonspherical droplets is related to the microstructural behavior of trans-critical droplets. Two types of microscopic structures within the droplet are identified: large-scale thermally induced clusters for long-chain C7 and hydrogen-bond connected network-like structures for MeOH, which contains hydroxyl (–OH) groups. Based on these findings, the mechanism behind the evolution of trans-critical droplets is illustrated. Finally, we determine the boundary of ambient conditions in the form of dimensionless expressions T r − 1 = a (p r − 1) − b , which dictate whether droplets can maintain a spherical shape during the trans-critical process. [ABSTRACT FROM AUTHOR]

Benzene (C6H6) and 1,3-cyclopentadiene (c-C5H6) are critical intermediate species in the combustion of fossil fuel and the formation of polycyclic aromatic hydrocarbons (PAHs). This study investigates the underlying mechanisms of pyrolysis and oxidation of C6H6 and c-C5H6 in the presence of O2, NO and NO2, respectively, under combustion conditions via ReaxFF molecular dynamics simulations. The size growth in the pyrolysis system is accompanied by an amorphous nature as well as an increase in the C/H ratio. In the oxidation sytems, NO2 is the most effective in the oxidation of both C6H6 and c-C5H6, followed by NO and O2. In the presence of NOx, O and N radicals generated in the high-temperature decomposition reactions of NO and NO2 are actively involved in the addition and H-abstraction reactions of C6H6 and c-C5H6. Remarkably, the decomposition of NO2 dramatically increases the number of O radicals in the system, which significantly accelerates the ring-opening of C6H6 and c-C5H6 by O-addition and forms linear-C6H6O and C5H6O species, respectively. Afterwards, the formation of –CH2– by H-transfer plays an essential role in the decomposition of linear–C6H6O and –C5H6O. Reaction pathways of O and N radicals with C6H6 and c-C5H6 are reported in detail. The O and N-addition of C6H6 facilitate the decomposition to resonance-stabilized cyclopentadienyl radicals after the restructuring of the C–C bond. [ABSTRACT FROM AUTHOR]

This letter proposes a novel four-dimensional multiprobe anechoic chamber (4D-MPAC) method for emulating time-domain nonstationary channel models of over-the-air testing. The proposed method adds time dimension to the 3D-MPAC system, so that the channel model with spatial parameters changing over time can be emulated. In addition, 4-D power angular spectrum similarity percentage (4D-PSP) as a figure of merit to evaluate the accuracy of the channel reconstruction is proposed for the first time. Based on the 4D-PSP, genetic algorithm is designed to reduce the number of active probes and testing cost. Furthermore, a dynamic motion scenario in a street is modeled by ray tracing simulation, where the time-domain nonstationary channel model is reconstructed by the proposed method with a small number of probes. [ABSTRACT FROM AUTHOR]

Benzene (C 6 H 6 ) and 1,3-cyclopentadiene (c-C 5 H 6 ) are critical intermediate species in the combustion of fossil fuel and the formation of polycyclic aromatic hydrocarbons (PAHs). This study investigates the underlying mechanisms of pyrolysis and oxidation of C 6 H 6 and c-C 5 H 6 in the presence of O 2 , NO and NO 2 , respectively, under combustion conditions via ReaxFF molecular dynamics simulations. The size growth in the pyrolysis system is accompanied by an amorphous nature as well as an increase in the C/H ratio. In the oxidation sytems, NO 2 is the most effective in the oxidation of both C 6 H 6 and c-C 5 H 6 , followed by NO and O 2 . In the presence of NO x , O and N radicals generated in the high-temperature decomposition reactions of NO and NO 2 are actively involved in the addition and H-abstraction reactions of C 6 H 6 and c-C 5 H 6 . Remarkably, the decomposition of NO 2 dramatically increases the number of O radicals in the system, which significantly accelerates the ring-opening of C 6 H 6 and c-C 5 H 6 by O-addition and forms linear-C 6 H 6 O and C 5 H 6 O species, respectively. Afterwards, the formation of -CH 2 - by H-transfer plays an essential role in the decomposition of linear-C 6 H 6 O and -C 5 H 6 O. Reaction pathways of O and N radicals with C 6 H 6 and c-C 5 H 6 are reported in detail. The O and N-addition of C 6 H 6 facilitate the decomposition to resonance-stabilized cyclopentadienyl radicals after the restructuring of the C-C bond.