Ablation behavior and mechanism of bulk MoAlB ceramic at ∼1670–2550 °C in air plasma flame

In this work, MoAlB samples for plasma exposure test were condensed by spark plasma sintering at 1200 °C for 10 min. Ablation resistance of MoAlB ceramic was investigated in a plasma torch facility for about 30 s at high temperature range of ～1670?2550 °C, which provided a quasi-real hypersonic service environment. The results showed that the linear ablation rate was increased from 0 μm/s at ～1670 °C to 86.4 μm/s at ～2550 °C. At ～1670 °C, the ablated surface of MoAlB ceramic was covered by Al₂O₃ layer, presenting excellent ablation resistance. At ～2220 °C, the macroscopic cracks were induced by thermal stress, which opened up channels for the inward diffusion of oxygen and deteriorated the ablation resistance of the substrate. Above ～2400 °C, the volatile MoO₃ and B₂O₃ and the erosion of viscous oxides by the high shearing force of plasma stream were the main ablation mechanisms.     

Adaptive reversible data hiding for JPEG images with multiple two-dimensional histograms

Joint photographic experts group (JPEG) can provide good quality with small file size but also eliminate extensively the redundancies of images. Therefore, hiding data into JPEG images in terms of maintaining high visual quality at small file sizes has been a great challenge for researchers. In this paper, an adaptive reversible data hiding method for JPEG images containing multiple two-dimensional (2D) histograms is proposed. Adaptability is mainly reflected in three aspects. The first one is to preferentially select sharper histograms for data embedding after $K$ histograms are established by constructing the $k$th ($k\in \{1,2,\dots ,K\}$) histogram using the $k$th non-zero alternating current (AC) coefficient of all the quantized discrete cosine transform blocks. On the other hand, to fully exploit the strong correlation between coefficients of one histogram, the smoothness of each coefficient is estimated by a block smoothness estimator so that a sharply-distributed 2D-histogram is constructed by combining two coefficients with similar smoothness into a pair. The pair corresponding to low complexity is selected priorly for data embedding, leading to high embedding performance while maintaining low file size. Besides, we design multiple embedding strategies to adaptively select the embedding strategy for each 2D histogram. Experimental results demonstrate that the proposed method can achieve higher rate–distortion performance which maintaining lower file storage space, compared with previous studies.     

How to Adapt a Lab-Scale Freeze Dryer for Assessing Dehydrating Curves at Different Heating Conditions

A laboratory-scale freeze dryer was adapted to allow control of the heat supply and on-line monitoring of sample weight during drying under vacuum condition. Several tests were carried out to verify the reliability of the developed system. The system was also tested with 10-mm-thick banana slices, obtaining the fruit drying rate, at different sample holder plate temperatures including 20 and 30°C as well as an unheated plate. The system presented in this work represents a low-cost, flexible, and easy-to-assemble piece of equipment that allows the study and optimization of the freeze drying of foods.     

Photocatalytic oxidation and ozonation of catechol over carbon-black-modified nano-TiO2 thin films supported on Al sheet

The photocatalytic activity of the carbon-black-modified nano-TiO2) (CB-TiO2) thin films was 1.5 times higher than that of TiO2 thin films in degrading Reactive Brilliant Red X-3B. Photocatalytic oxidation and ozonation of catechol over CB-TiO2 thin films supported on Al sheet was investigated. The experiments showed that ozone concentrations had an important effect on TOC removal. The combined photocatalysis with UV irradiation and ozonation (TiO2/UV/O3) process considerably increased TOC removal rate compared to combined photocatalysis with UV irradiation and oxygen oxidation (TiO2/UV/O2) process, ozonation alone (O3) process, combined ozonation and UV irradiation (UV/O3) process. The complete mineralization of catechol followed pseudo-zero-order kinetics dependent upon ozone (oxygen) concentration and indicated catechol concentration did not affect the kinetics during UV/O3 and TiO2/UV/O3 (O2) processes. The kinetic study showed that the rate constants in the complete mineralization of catechol with TiO2/UV/O3 are 1.32-1.80 times higher than that of UV/O3 with the same concentration of ozone. The rate constants are 2.56-5.36 times higher than the maximal rate constants of TiO2/UV/O2 and 4.68-9.8 times higher than the maximal rate constants of TiO2/UV.     

Hydrothermal synthesis and spark plasma sintering of NaY zeolite as solid-state matrices for cesium-137 immobilization

Hydrothermal synthesis of NaY-type zeolite was carried out and the effect of temperature on the phase composition, crystal structure, textural characteristics, particle size and morphology, as well as sorption properties to Cs⁺ ions was studied. Solid-state matrices based on NaY zeolite the Faujasite structure containing 26.1 wt% cesium were obtained by spark plasma sintering (SPS) with high values of compressive strength (to 132.9 MPa) and Vickers microhardness to HV~ 698, Fracture toughness (K_1c) ~ 1.26 MPa m^1/2. The kinetics of ceramic matrices consolidation, phase composition and morphology using dilatometric studies, XRD, and SEM were studied. The thermogravimetric analysis shown the high thermal stability of the obtained samples up to 1300 °C. The high hydrolytic stability of CsAlSiO₄ ceramic was proven (leaching rate of 2.33 ×10^?8 g·cm^?2·day^?1 and cesium diffusion coefficient De 1.41 ×10^?13), which exceeds the requirements of GOST R 50926–96 and ISO 6961:1982 for solid-state matrices.     

Exploring Hf-Ta-O precipitation upon ablation of Hf-Ta-Si-C coating on C/C composites

To improve the ablation resistance of C/C composites, a Hf-Ta-Si-C coating was fabricated by chemical vapor co-deposition. The ablation resistances of Hf-Si-C and Hf-Ta-Si-C coatings were characterized comparatively. After introducing Ta, the ablation resistance, smoothness and integrity of the ablated coating improved. Hf-Si-O and Hf-Ta-Si-O glass wires were observed. To investigate the reaction processes of the two types of glass wires, TEM observation was carried out and coupled to molecular dynamics simulations. These illustrated that Hf and Ta atoms tend gather together at high temperature. To investigate the effect of Hf-Ta-O precipitation on the ablation behavior, supplementary experiments were carried out on bulk ceramics with the same target composition, confirming that precipitation reaction could accelerated the formation of a smooth and intact oxide layer, playing a positive role in protecting C/C composites.     

The electrification accelerator: Understanding the implications of autonomous vehicles for electric utilities

The intersection of autonomous vehicles, ride sharing and transportation electrification could have significant implications for electric utilities. This paper analyses how the development of shared autonomous electric vehicles may make electrified transportation more likely and why this may lead to a more rapid than expected shift in the current transportation paradigm. We also discuss how these trends may affect utilities and suggest what they can do to prepare for the transition.     

获各琦铜矿铜Ⅱ矿体选矿捕收剂方案探索

针对获各琦铜矿铜Ⅱ矿体赋存特点为沉积变质矿床,具有层位控矿及岩性控矿的特点,铜矿体赋存在石英岩中,并由多条矿体组成,存在较大的选矿难度。笔者通过不同药剂制度下进行了选矿指标必选,获得了较优的选矿指标,可提高Cu回收率3%-5%。     

Ablation behavior of ZrB2–SiC protective coating for carbon/carbon composites

Ablation behavior of ZrB₂–SiC protective coating for carbon/carbon composites during oxyacetylene flame test at 2500 °C was investigated by analyzing the microstructure differentiation caused by the increasing intensity of ablation from the border to the center of the surface. After ablation, a continuous SiO₂ scale, a porous SiO₂ layer inlaid with fine ZrO₂ nuclei, and a continuous ZrO₂ scale respectively emerged in the border region, the transitional region, and the center region. In order to investigate the ablation microstructure in the initial stage, the sub-layer microstructure was characterized and found to be mainly formed by coral-like structures of ZrO₂, which showed huge difference with the continuous structure of ZrO₂ on the surface layer. A kinetic model concerning the thickness change induced by volatilization and oxidation during ablation was built to explain the different growth mechanisms of the continuous ZrO₂ scale and the coral-like ZrO₂ structure.