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This article reviews rarefied gas flow computations based on nonlinear model Boltzmann equations using deterministic high-order gas-kinetic unified algorithms (GKUA) in phase space. The nonlinear Boltzmann model equations considered include the BGK model, the Shakhov model, the Ellipsoidal Statistical model and the Morse model. Several high-order gas-kinetic unified algorithms, which combine the discrete velocity ordinate method in velocity space and the compact high-order finite-difference schemes in physical space, are developed. The parallel strategies implemented with the accompanying algorithms are of equal importance. Accurate computations of rarefied gas flow problems using various kinetic models over wide ranges of Mach numbers 1.2–20 and Knudsen numbers 0.0001–5 are reported. The effects of different high resolution schemes on the flow resolution under the same discrete velocity ordinate method are studied. A conservative discrete velocity ordinate method to ensure the kinetic compatibility condition is also implemented. The present algorithms are tested for the one-dimensional unsteady shock-tube problems with various Knudsen numbers, the steady normal shock wave structures for different Mach numbers, the two-dimensional flows past a circular cylinder and a NACA 0012 airfoil to verify the present methodology and to simulate gas transport phenomena covering various flow regimes. Illustrations of large scale parallel computations of three-dimensional hypersonic rarefied flows over the reusable sphere–cone satellite and the re-entry spacecraft using almost the largest computer systems available in China are also reported. The present computed results are compared with the theoretical prediction from gas dynamics, related DSMC results, slip N–S solutions and experimental data, and good agreement can be found. The numerical experience indicates that although the direct model Boltzmann equation solver in phase space can be computationally expensive, nevertheless, the present GKUAs for kinetic model Boltzmann equations in conjunction with current available high-performance parallel computer power can provide a vital engineering tool for analyzing rarefied gas flows covering the whole range of flow regimes in aerospace engineering applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • Atom-planting method introduces three Ga species in MWW zeolite. • Ga-OH is more active for ethane dehydrogenation and tandem RWGS reaction. • Pt-Ga bimetallic catalyst is active for RWGS reaction in tandem with the EDH. Ga-loaded MWW zeolite catalysts with MWW topology was synthesized by atom-planting through dehydrochlorination of deborated ERB-1 and hydroxyl groups in GaCl 3 , and further loaded with Pt by ion exchange method for ethane direct dehydrogenation (EDH) and CO 2 oxidative dehydrogenation (CO 2 -ODH) of ethane. The atom-planting introduced GaCl 3 generated zeolite framework Si(OH)Ga, extra-framework Ga-OH species and Ga 2 O 3 in synthesized catalysts. And the extra-framework Ga-OH species showed higher ethane dehydrogenation activity compared with the Ga 2 O 3 species, while the Brönsted acid sites of framework Si(OH)Ga species could further convert the pruduced ethylene to aromatics. The Ga-OH species prepared by atom-planting generate [GaH]2+ and [GaH 2 ]+ during CO 2 -ODH reaction, which have better ability to activate CO 2 and has good activity for reverse water gas shift reaction as tandem reaction to promote the ethane dehydrogenation. The electron transfer between Pt and Ga 2 O 3 made the Pt-Ga bimetallic catalyst show good dehydrogenation activity and stability in the EDH and CO 2 -ODH reactions. [ABSTRACT FROM AUTHOR]

Abstract In Wi-Fi fingerprinting localization systems, good positioning accuracy requires accurate fingerprint databases; however, the collection of accurate is a labor intensive work. Therefore, the collection, calibration and maintenance of fingerprints in Wi-Fi positioning have always been hot research topics. In this paper, a parameterized fingerprint optimization system is proposed to obtain an accurate fingerprint database. The pairs of RSS (received signal strength) and corresponding position are collected through path survey several times, which makes the collection process more efficient but brings more noise. The wall-induced wireless signal propagation theory taking floor plans into account is used to model the APs through the least squares. The predicted values from theory are combined with survey values for de-noising in fingerprint database. An experiment performed at indoor environment shows that compared with the original fingerprints, the positioning accuracy of the optimized fingerprints is improved by 0.6 m on average from many tests. [ABSTRACT FROM AUTHOR]

Highlights • Mixing augmentation mechanisms of three devices were analyzed and compared. • Streamwise vorticity induced by additional vorticity is the main reason for mixing enhancement. • Stagnation pressure loss induced by the pulsed jet is small. • Air jet enhances mixing and reduces the hydrogen distribution on the bottom. • Ramp has a highly remarkable improvement on mixing efficiency and penetration depth. Abstract Numerical investigation of some mixing enhancement strategies based on the traditional transverse injection technique proposed in recent years was carried out by means of the three-dimensional Reynolds-average Navier–Stokes (RANS) equations coupled with the two equation k-ω shear stress transport (SST) turbulence model. The numerical approaches employed in the current study were validated against the available two- and three-dimensional data in the open literature, and they can be used with confidence to achieve a better understanding of mixing augmentation mechanisms in transverse injection flow fields with various mixing enhancement strategies, namely the pulsed jet, the air jet and the ramp. Results obtained in this study provide important insight into complex flow phenomena. Various fundamental mechanisms dictating the intricate flow characteristics for the transverse injection flow field with various mixing enhancement strategies, including the circulation, vertical structures, velocity vectors and shock wave systems, have been analyzed systematically. The performance parameters of the transverse injection flow fields, such as the mixing length, the fuel penetration depth and the stagnation pressure loss have been compared. Different mixing enhancement strategies have their advantages and disadvantages, and the combination of various mixing enhancement strategies may be a promising injection strategy for better mixing performance of the transverse injection flow field. A stronger streamwise vorticity is the main reason for the mixing enhancement. However, the mixing length and the stagnation pressure loss of the transverse injection flow field show opposite trends from each other with a variance in the intensity of streamwise vorticity. [ABSTRACT FROM AUTHOR]