High-temperature stability of Mg(Al,Cr)2O4 spinel co-existing with calcium aluminates in air

Cr₂O₃ is a well-known corrosion resistant oxide used in refractory applications. However, it can oxidize into toxic and water-soluble Cr(VI) compounds upon reaction with calcium aluminate cement phases in the presence of oxygen, which subsequently causes disposal problems after use. This study describes the extent to which chromium in the spinel Mg(Al,Cr)₂O₄ phase can be oxidized to Cr(VI) when it reacts with the calcium aluminate cement phases C₁₂A₇, CA, CA₂ and free CaO at 1300 °C in air, using XRD, XPS and leaching tests (TRGS 613 standard) as analytical tools. On reaction with CaO, the Mg(Al,Cr^III)₂O₄ spinel mainly transformed into hauyne (Ca₄Al₆Cr^VIO₁₆) and Ca₅Cr₃O₁₂ which contains both Cr(IV) and Cr(VI). The reaction of C₁₂A₇ and CA with the spinel phase also resulted in the formation of Ca₄Al₆CrO₁₆. Conversely, the reaction of Mg(Al,Cr^III)₂O₄ spinel with CA₂ resulted in the formation of only a trace amount of Cr(VI). Water-soluble Cr(VI) leached in large quantities (>100 mg/L) from samples where the Mg(Al,Cr^III)₂O₄ reacted with either C₁₂A₇ or CA. Almost no Cr(VI) leached from the sample when Mg(Al,Cr^III)₂O₄ reacted with CaO, using the standard TRGS 613 leach test, but a significant amount of Cr(VI) was released into solution when leached with a HCl solution for 12 h. Both Cr(IV) and Cr(VI) present in the Ca₅Cr₃O₁₂ dissolved into acidic solution. Only a small amount of Cr(VI) leached from the sample that resulted when spinel was reacted with CA₂, even after a prolonged HCl leach. Cr(III) in spinel Mg(Al,Cr)₂O₄ is very stable and does not leach in either distilled water or acidic solution.     

A highly active composite electrocatalyst Ni–Fe–P–Nb2O5/NF for overall water splitting

This work demonstrates a facile Nb₂O₅-decorated electrocatalyst to prepare cost-effective Ni–Fe–P–Nb₂O₅/NF and compared HER & OER performance in alkaline media. The prepared electrocatalyst presented an outstanding electrocatalytic performance towards hydrogen evolution reaction, which required a quite low overpotential of 39.05 mV at the current density of ?10 mA cm^?2 in 1 M KOH electrolyte. Moreover, the Ni–Fe–P–Nb₂O₅/NF catalyst also has excellent oxygen evolution efficiency, which needs only 322 mV to reach the current density of 50 mA cm^?2. Furthermore, its electrocatalytic performance towards overall water splitting worked as both cathode and anode achieved a quite low potential of 1.56 V (10 mA cm^?2).     

Rational Designs for Lithium-Sulfur Batteries with Low Electrolyte/Sulfur Ratio

Lithium-sulfur batteries (LSBs) are considered a promising next-generation energy storage device owing to their high theoretical energy density. However, their overall performance is limited by several critical issues such as lithium polysulfide (PS) shuttles, low sulfur utilization, and unstable Li metal anodes. Despite recent huge progress, the electrolyte/sulfur ratio (E/S) used is usually very high (≥20 µL mg⁻¹), which greatly reduces the practical energy density of devices. To push forward LSBs from the lab to the industry, considerable attention is devoted to reducing E/S while ensuring the electrochemical performance. To date, however, few reviews have comprehensively elucidated the possible strategies to achieve that purpose. In this review, recent advances in low E/S cathodes and anodes based on the issues resulting from low E/S and the corresponding solutions are summarized. These will be beneficial for a systematic understanding of the rational design ideas and research trends of low E/S LSBs. In particular, three strategies are proposed for cathodes: preventing PS formation/aggregation to avoid inadequate dissolution, designing multifunctional macroporous networks to address incomplete infiltration, and utilizing an imprison strategy to relieve the adsorption dependence on specific surface area. Finally, the challenges and future prospects for low E/S LSBs are discussed.     

Probing the degenerate pattern growth of {100}<011> orientation in a directionally solidified Al-4.5 wt% Cu alloy

Degenerate pattern is a seemingly disordered morphology but it exhibits the inherently ordered crystal connected with tip-splitting and limited stability which makes it difficult to observe in the metallic system. Here we employ (100)[011] orientated planar-front seeds using directional solidification and reveal the fundamental origins of the degenerate pattern growth in an Al-4.5 wt% Cu alloy. We find that the spacing of the tip-splitting (λ) in the degenerate of the alloys followed a power law, λ∝V^−0.5, and the frequency (f) of the splitting was related to the growth velocity (V) by ƒ∝V^1.5. The dimensionless growth direction (θ/θ₀) increased monotonously and approached 0.6 with faster velocity, attributed to its anisotropy in the interface kinetics. Once growth velocity exceeded a threshold, two types of pattern transitions from degenerate to regular dendrites were proposed. One of them exhibited a random and chaotic mode and the other underwent a rotation in growth direction.     

Geometry of 3D MAT and its application to moulding surfaces

This paper investigates the differential geometry of 3D MAT (medial axis transform) using the moving frame and differential form. After constructing the mapping relation and moving frames around both the MA (medial axis) point and the associated boundary points, various curves are defined to serve as carriers for the study. Based on analysis of the infinitesimal translation and rotation of the moving frames, the relations of distance differentials, rotation vectors and differential invariants are derived. Furthermore, a special case in the 3D MAT, the normal form, is defined for the moulding surfaces, where the 3D problem can be converted into a 2D one.     

以用户为中心的可见光通信协作传输中训练资源分配算法

以用户为中心的可见光通信协作传输是近年来出现的新架构,这导致虚拟小区之间出现重叠。为避免导频污染问题,每个虚拟小区中的光接入点(AP)或者虚拟小区中选择相同AP的用户发送的训练序列应该是正交的。针对可见光通信中以用户为中心的协作网络,研究训练资源的正交分配问题,提出了一种新的导频分配算法,联合导频分配和用户选择问题,以期最大限度地增加虚拟小区内可被接入的用户数。分析和仿真结果表明,该导频分配方案可以有效改善导频污染问题,提高训练资源利用率,并且相比已有的导频分配方案,性能有所改进。     

Ultrasmall rhodium nanoclusters anchored on nitrogen-doped carbon nanotubes with embedded nickel nanoparticles as magnetically recyclable catalysts for efficient ammonia-borane hydrolysis

Facile yet efficient synthesis of high-performance nanocatalysts for hydrogen evolution from ammonia-borane (AB) hydrolysis is paramount. Here, we reported a novel hybrid nanocatalyst comprised of Rh nanoclusters (1.56 nm in diameters) anchored on nitrogen (N)-doped carbon nanotubes with embedded Ni nanoparticles (Ni@NCNTs), which was fabricated through adsorption of Rh ions on Ni@NCNTs. The achieved hybrid of Rh/Ni@NCNTs displayed excellent catalytic property (Turnover frequency: 959 min⁻¹) toward AB hydrolysis, higher than many prior developed Rh-based catalysts. Note that this hybrid could be reused for at least nine runs with complete AB conversion to hydrogen. Rh nanoclusters with small size exhibiting high atom utilization and the synergetic effect between Ni and Rh are responsible for the excellent catalytic property of Rh/Ni@NCNTs toward AB hydrolysis. This work highlights the importance of utilization of magnetically recyclable Ni@NCNTs as support and synergetic component for efficient hydrolysis of AB.     

Reducing treatment zone diameter in orthokeratology and its effect on peripheral ocular refraction

PurposeTo determine whether orthokeratology (OK) induced treatment zone (TZ) diameter can be reduced by altering OK lens design, and if so the impact of modifying TZ diameter on relative peripheral refraction (RPR).Methods16 subjects (mean age 23.4 ± 1.5 years; 8 female) completed the study. Standard (Control) OK lens design (PJ, Capricornia, Australia) or a modified version (Test) where the back optic zone diameter was reduced, and back optic zone asphericity and intermediate lens curves were altered, were worn overnight only for 7-nights in a randomised double masked order, with a minimum 1-week wash out (no lens wear) between lens designs. Full correction of refractive error was targeted. Refraction; best corrected visual acuity (BCVA); RPR (Shin-Nippon NVision-k 5001) along the horizontal and vertical meridians; and corneal topography (Medmont E300) were measured before starting lens wear and in the morning after lens removal after the seventh night of lens wear for both lens designs. TZ diameter and decentration was calculated from corneal topography.ResultsAfter 7-nights of wear both lens designs created -2.00D refraction effect with no significant difference in refractive effect or change to BCVA between the designs. The Test design created a significantly smaller horizontal (4.78 ± 0.37 vs 5.70 ± 0.37 mm, p < 0.001) and vertical (5.09 ± 0.51 vs 5.92 ± 0.51 mm p < 0.001) TZ diameter. The TZ was decentered inferior temporal with no significant difference between designs. There was no significant difference between the lens designs in RPR along the horizontal and vertical meridians at any measurement period.ConclusionsOK induced TZ diameter can be reliably reduced by altering OK lens design without detrimentally effecting lens centration or refractive effect. Reducing TZ diameter did not alter RPR, though measurement artifacts could be responsible for masking an effect. Longitudinal studies are needed to assess whether smaller TZ OK lens designs increase efficacy for slowing progression of myopia.     

移动网络中的独立式安全管理系统

本文提出一种适用于移动网络的安全管理系统,由于访问网络能够独立地对漫游用户进行认证,所以称该系统为独立式安全管理(ISM).基于ISM设计一种漫游用户的认证协议,通过对协议的比较分析可以看出,相对于其它安全管理系统,ISM的突出优点是安全责任划分清晰、认证效率高.