Engineering and microstructure properties of contaminated marine sediments solidified by high content of incinerated sewage sludge ash

Management of incinerated sewage sludge ash(ISSA) and dredged contaminated marine sediments(CMSs) is a great challenge for Hong Kong and other coastal cities due to limited landfilling capacity.The present study investigates the use of high content(20% of sediment by mass) of ISSA in combination with cement/lime for solidification/stabilization(S/S) treatment of CMSs to provide a way to reuse the wastes as construction materials.The results showed that ISSA being a porous material was able to absorb a large amount of water rendering a more efficient solidification process of the marine sediment which normally had a very high water content(～80%).The S/S treatment improved the engineering properties of the sediment,but reduced the workability,especially for the lime-treated samples.Lime can be used to replace ordinary Portland cement(OPC) for better heavy metal immobilization and carbon emission reduction.The hardened sediment samples prepared with 10% of lime and 20% of ISSA could attain a strength of 1.6 MPa after 28 d of curing.In addition,leaching tests confirmed that there was no environmental risk induced by these stabilized materials.The formation of hydrated cementitious compounds including calcium silicate hydrate(C-S-H)/calcium aluminate silicate hydrate(C-A-S-H)/hydrocalumite/calcite was mainly responsible for the strength development in the ISSA/lime-treated sediments.     

Flexible electrospun MWCNTs/Ag<Subscript>3</Subscript>PO<Subscript>4</Subscript>/PAN ternary composite fiber membranes with enhanced photocatalytic activity and stability under visible-light irradiation

Semiconductor photocatalysis is a promising technology for removing contaminants from water. Particularly, visible-light photocatalysis has attracted much attention because of its potential to utilize solar energy. However, nano-sized visible-light-driven photocatalysts easily aggregate during water treatment. Besides, it is difficult to recycle them from treated systems. Therefore, it is of great importance to develop visible-light-responsive immobilized photocatalysts with high activity. In this work, MWCNTs/Ag₃PO₄/polyacrylonitrile (PAN) ternary composite fiber membranes (TCFMs) with good photocatalytic performance were fabricated by electrospinning technique combined with in situ Ag₃PO₄ forming reaction. Due to the addition of MWCNTs, the band gap of MWCNTs/Ag₃PO₄/PAN TCFMs became narrower than that of Ag₃PO₄/PAN binary composite fiber membranes (BCFMs), which made MWCNTs/Ag₃PO₄/PAN TCFMs be able to use light at longer wavelengths. Compared with Ag₃PO₄/PAN BCFMs, the as-prepared MWCNTs/Ag₃PO₄/PAN TCFMs showed enhanced photocatalytic activity and stability for degrading rhodamine B (RhB) in batch processing systems, which mainly ascribed to fast electron transfer from Ag₃PO₄ to MWCNTs and the resulting high electron–hole (e^?–h⁺) separation efficiency. Radical trapping experiments revealed that holes (h⁺) and superoxide radicals (^·O₂^?) played primary roles in RhB degradation. In addition, the flexible MWCNTs/Ag₃PO₄/PAN TCFMs also showed potential practical application in the continuous wastewater treatment by a suitable photocatalytic membrane reactor. This work provides a facile approach to prepare flexible supported photocatalytic membrane with visible-light response, high activity and good stability.     

基于梯度转向核的半随机傅里叶域压缩重构算法

针对压缩遥感过程中非严格稀疏和傅里叶域欠采样噪声导致的伪影和混叠现象,本文提出了基于梯度转向核的压缩重构策略（GradSK）。在压缩感知编码过程中提出了半随机傅里叶测量的方式,既保留图像的概要分量,同时保证了K-空间随机欠采样的非连贯性。在压缩感知解码过程中提出了由基于多阶梯度的转向核与有限差分总方差（TV）结合的方法,来解决解码过程中的无约束凸框架问题。实验表明,该方法在解决无噪采样和有噪采样的过程中均有较好性能。     

Thermal Shock Behavior Analysis of Tungsten-Armored Plasma-Facing Components for Future Fusion Reactor

In a fusion reactor, plasma-facing components(PFCs) will suffer severe thermal shock; behavior and performance of PFCs under high heat flux(HHF) loads are of major importance for the long-term stable operation of the reactor. This work investigates the thermo-mechanical behaviors of tungsten armor under high heat loads by the method of finite element modeling and simulating. The temperature distribution and corresponding thermal stress changing rule under different HHF are analyzed and deduced. The Manson–Coffin equation is employed to evaluate the fatigue lifetime(cyclic times of HHF loading) of W-armored first wall under cyclic HHF load. The results are useful for the formulation design and structural optimization of tungsten-armored PFCs for the future demonstration fusion reactor and China fusion experimental thermal reactor.     

服务核聚变研究领域的集群系统

在核聚变研究领域中,高性能集群的应用十分广泛.一方面需要借助集群进行高性能计算模拟托克马克中粒子的运动状态,另一方面需要存储大量十分珍贵的放电数据以作后续的数据分析.随着位于中国科学技术大学的大型反场箍缩磁约束聚变实验装置“Keda Torus eXperiment”（KTX）的建设取得重要进展,KTX实验室对于高性能计算以及实验数据存储具有高度的需求.因此,部署了一个高性能集群并对存储做出了安全设计.根据IOzone的测试,GPFS文件系统的冗余性机制发挥了作用,数据的读写性能很稳定.     

Residual-stress relaxation mechanism and model description of 5052H32 Al alloy spun ellipsoidal heads during annealing treatment

Marginal-restraint mandrel-free spinning is an advanced technology for manufacturing ellipsoidal heads with large diameter-thickness ratios. Nevertheless, the spinning-induced residual stress, which greatly influences the in-service performance of spun heads, should be removed. In this study, the effects of annealing on the residual-stress relaxation behavior of 5052H32 aluminum alloy spun heads were investigated. It is found that the residual stress first rapidly decreases and then remains steady with the increase in annealing time at the tested annealing temperatures. The relaxation of the residual stress becomes increasingly obvious with the increase in annealing temperature. When the annealing temperature is less than 220℃, there are no obvious changes in grain size. Moreover, the spinning-induced dislocations are consumed by the static recovery behavior, which decreases the residual stress during annealing. When the annealing temperature is approximately 300℃, the broken grains transform into equiaxed grains. In addition, static recrystallization and recovery behaviors occur simultaneously to promote the relaxation of the residual stress. Considering the different stress relaxation mechanisms, a model based on the Zener-Wert-Avrami equation was established to predict the residual-stress relaxation behavior. Finally, the optimized annealing temperature and time were approximately 300℃ and 30 min, respectively.The full text can be downloaded at https://link.springer.com/article/10.1007/s40436-021-00367-w     

Hydraulic conductivity characteristics of carbonated reactive magnesia-treated silt

Carbonation of reactive magnesia (MgO) has recently received increasing attention in the area of soil stabilization and ground improvement. However, as a critical parameter in terms of long-term seepage behavior in the geotechnical analysis, the hydraulic conductivity of carbonated reactive MgO-stabilized silt has not been fully studied. In this context, the effect of water-MgO ratio (ratio of initial water content to MgO content, w₀/c) and carbonation time on hydraulic conductivity (or permeability) characteristics was systematically investigated. Serial microstructural tests including mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC) analyses were applied to elucidate the intrinsic mechanisms. The obtained results indicate that as the initial water-MgO ratio decreases, the void ratio gradually decreases and the reduction of hydraulic conductivity becomes less prominent because of the little presence of flow paths. The hydraulic conductivity of carbonated MgO-admixed silt similar to that of PC-treated silt is mainly governed by the porosity, and its correlation with void ratio is proposed in the article. The variations of permeability with void ratio are consistent with those of the cumulative pore volume from MIP results in general, and the medium pores (3–30 μm) are substantiated to be the primary contributor in controlling the permeability. SEM and DSC analyses reveal that the cementation of soil particles and filling of hydrated magnesium carbonates marginally reduce the voids and permeability. The reasons for changes of permeability behaviors have been confirmed by the pore-size distribution and microstructure characteristics.

     

Efficient NiO/RGO combination for high-cycling-stability supercapacitors by an alkaline hydrothermal strategy

Journal of Applied Electrochemistry - In this paper, NiO/reduced graphene oxide (NiO/RGO) composites were synthesized, and the strong bonding between NiO and RGO stemmed from alkaline hydrothermal...     

一种低码率下的新型码率控制策略

在大多数视频压缩标准中,码率控制方法都是针对中高码率情况而设计的,而在较低码率情况下的工作情况都不够理想。针对这个问题,本文提出了一个较低码率情况下的码率预测模型,并在该模型基础上建立起一种针对较低码率情况的码率控制策略。实验结果证明了这种码率控制策略的有效性。