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Epoxy dielectrics with high through-plane thermal conductivity (λ) hold great promise for applications in the thermal management of advanced power electronics. Intensive attempts have been made to improve the λ of epoxy by filling with boron nitride nanosheets (BNNSs). However, it remains a great challenge to achieve a satisfactory increased λ by a small amount of BNNS loading. Herein, we reported a new strategy to prepare epoxy dielectrics with internal three-dimensional phonon transport channels by vacuum freeze-drying and vacuum impregnation. Aramid nanofibers (ANFs) and BNNSs were used for the collaborative construction of a vertical interconnected thermal framework. The resultant ANF-BNNS/epoxy achieved a high through-plane λ of 0.87 W m−1 K−1 at only 1.43 vol. % BNNS, which is ∼17.1% higher than that of the BNNS/epoxy counterpart with even 18.34 vol. % randomly distributed BNNS. The increasing efficiency of λ of epoxy by ANF-BNNS is tenfold more than that of the conventional blending methods. In addition, the ANF-BNNS/epoxy composite also exhibits a low dielectric constant and low dielectric loss. The findings of this study offer an inspired venue to develop high-performance thermally conductive epoxy dielectrics with a minimal BNNS loading. [ABSTRACT FROM AUTHOR]

Background: Physical activity (PA) exerts an important influence on glycemic control in type 2 diabetes (T2D) patients. Alterations in body composition in patients with T2D may be involved in the overall pathophysiologic process, but PAs and alterations in body composition have been poorly studied. Methods: A total of 615 patients with T2D were selected by convenient sampling. The patients were investigated with the International Physical Activity Questionnaire (IPAQ-S). Moreover, biochemical indices were collected, and the progression of the body composition of the subjects was determined via dual-energy X-ray absorptiometry (DXA). The variables included lumbar bone mineral density (LSBMD), femoral neck bone mineral density (FNBMD), hip bone mineral density (HBMD), whole-body bone mineral density (TBMD), limb skeletal muscle mass index (ASMI), whole-body fat percentage (B-FAT) and trunk fat percentage (T-FAT). Moreover, the levels of physical activity (high level of physical activity [H-PA], medium level of physical activity [M-PA] and low level of physical activity [L-PA]) were divided into three groups to analyze the changes in patient body composition with changes in physical activity level. Results: One-way analysis of variance showed that β-CTX, TP1NP, HbA1c, B-FAT and T-FAT increased significantly (p< 0.05), while 25(OH)D, LSBMD, FNBMD, HBMD, TBMD and ASMI decreased significantly (p< 0.001) with the decrease of physical activity. However, there was no significant difference in serum lipids between lnHOMA-ir and lnHOMA-β (p 0.05). Multiple linear regression model was established to gradually adjust for clinical confounding factors. It was found that physical activity level was independently positively correlated with LSBMD, FNBMD, HBMD, TBMD, and ASMI, and was independently negatively correlated with B-FAT and T-FAT in patients with type 2 diabetes. Conclusion: A lack of physical activity is an independent risk factor for decreased bone mineral density, decreased skeletal muscle content and increased fat content in patients with T2D. [ABSTRACT FROM AUTHOR]

The relationship between the size distribution of inclusions and the total oxygen in steel was studied by following the inclusions' size and number of the samples at different locations. The content of macro-inclusions in liquid steel could be estimated accurately by the fluctuation of total oxygen in the same sample,which quantified the cleanliness evaluation index. The number of inclusions per unit volume decreased exponentially with the increase in sizes. Also,the distribution uniformity of inclusions in steel worsened as the size increased. Thus,micro-inclusions with the size below 10 μm occupied above 95% of total inclusions in the liquid steel,which showed a good relationship between the measured value of total oxygen and the integration oxygen in micro-inclusions.Total oxygen could represent the uniform distribution level of inclusions in steel; good uniform of inclusions in steel meant small fluctuation. Macro-inclusions could result in the fluctuation of total oxygen. Large fluctuation of total oxygen reflected a high amount of macro-inclusions in steel.

Ultralow-carbon steel is an important material for automobile production. Titanium is usually added in this steel grade to form a precipitant and improve the deep drawing property of the steel. However, due to the deoxidation capacity of Ti, Ti addition will directly generate Ti-bearing oxide inclusions instead of the precipitant. To reduce the amount of Ti-bearing oxide inclusions, samples were collected during the RH refining based on the basic oxygen furnace-Ruhrstahl-Heraeus reactor-continuous casting (BOF-RH-CC) ultralow-carbon steel production process, and the oxygen content and inclusion characterization after Al addition and Ti addition were analyzed. The thermodynamics calculation software FactSage was adopted to calculate the Fe-Al-Ti-O inclusion stability phase diagram. The results show that the Al2O3 inclusion usually acts as the nucleation point of the Ti-bearing oxide inclusion, which wraps the Al2O3 inclusion to form the Al-Ti-O complex inclusion. To avoid the generation of the Ti-bearing oxide inclusions, the mass fraction of dissolved Al in the molten steel should be greater than 0.01% when the Ti mass fraction is 0.1%. Furthermore, the generation and growth behavior of the Ti-bearing oxide inclusion were also studied. Based on the calculation of the growth rate and the comparison of the adhesion work of the Al2O3 inclusion and the Ti2O3 inclusion, it is concluded that the growth rate of Ti2O3 inclusion is greater than that of Al2O3 inclusion, and it is more difficult for Ti2O3 inclusions to collide with each other and to be removed at 1600℃. Therefore, the generation of Ti-bearing oxide inclusions should be strictly controlled to improve the removal rate of oxide inclusions in ultralow-carbon steels.

The gas-liquid two-phase flow in the up leg of the Ruhrstahl-Hereaeus (RH) unit is one of the main momentum sources of the whole device, and it affects the flow state of the molten steel in the ladle. A physical model of 300 t RH in 1:6 ratio was set up to simulate the bubble behavior process and to measure the change of the RH circulation flow in the up leg and in the vacuum chamber. The gas-liquid fraction and the movement velocity of bubbles were measured to assess the residence time of the bubbles in the vacuum chamber. In addition, the formation of the bubbles at different values of the RH circulation flow and liquid-level height in the vacuum chamber were recorded by a high-speed camera. One of the main factors influencing the bubble formation is the increase of the lifting gas flow in the vacuum chamber. With the increase of blowing gas, the large independent bubbles undergo multiple collisions, break into small bubbles, and finally small and large irregular-sized bubbles coexist. When the liquid height is>80 mm, the residence time of the bubbles in the vacuum chamber achieves a stable value and cannot be further affected by the increase of the liquid-level height in the vacuum chamber. At a lifting gas flow of 3000 L·min-1, a weak decreasing trend of the residence time of bubbles is observed, and the bubbles start polymerizing in the vacuum chamber. In conclusion, for the 300 t RH physical model, the liquid height in the vacuum chamber is recommended to be 80 mm, whereas the lifting gas flow should be set at 3500 L·min-1. After these optimization steps, the decarburization time decreases from 21.4 to 17.5 min.

This study established a two-dimensional mathematical model of solidification and heat transfer for a bloom with a 310 mm×360 mm cross-section using ANSYS software, which was verified by nail-shooting experiments in the narrow side of the bloom and surface temperature testing. The effect of the casting process parameters, such as superheat, casting speed, and secondary cooling intensity, on the solid fraction in the strand centerline and the solidified shell was investigated. Moreover, the optimum casting speed and the optimum solid fraction in the core of the partially solidified strand throughthe soft reduction zone were determined by the model considering the hot ductility of the high-carbon wear-resistant ball steel BU. Plant trials of BU with different casting speeds were performed to validate the theoretical model and analyze the effect of the casting speed on the segregation and shrinkage cavity of BU on a 310 mm×360 mm bloom caster equipped with final electromagnetic stirring (F-EMS) combined with mechanical soft reduction (reduction amount with 17 mm). The results show that the inner defects (e. g., center segregation, V-segregation, and shrinkage cavity) significantly improve when the casting speed is adjusted to meet the required soft reduction zone as a matter of priority; otherwise, the casting speed is only adjusted to preferentially satisfy the required F-EMS stirring region. The inner quality does not show any obvious improvement. Except for the internal cracks and the negative center segregation caused by the improper distribution of the reduction amount, the inner defects (e. g., macro segregation and shrinkage cavity) significantly improve with a casting speed of 0.52 m·min-1 and a solid fraction in the strand centerline ranging from 0.30 and 0.75 in the soft reduction zone.