On the Application of Mixed Models of Probability and Convex Set for Time-Variant Reliability Analysis

In time-variant reliability problems,there are a lot of uncertain variables from different sources.Therefore,it is important to consider these uncertainties in engineering.In addition,time-variant reliability problems typically involve a complexmultilevel nested optimization problem,which can result in an enormous amount of computation.To this end,this paper studies the time-variant reliability evaluation of structures with stochastic and bounded uncertainties using a mixed probability and convex set model.In this method,the stochastic process of a limit-state function with mixed uncertain parameters is first discretized and then converted into a timeindependent reliability problem.Further,to solve the double nested optimization problem in hybrid reliability calculation,an efficient iterative scheme is designed in standard uncertainty space to determine the most probable point(MPP).The limit state function is linearized at these points,and an innovative random variable is defined to solve the equivalent static reliability analysis model.The effectiveness of the proposed method is verified by two benchmark numerical examples and a practical engineering problem.

水蒸汽浴FeS_(2)高效Fenton降解甲草胺

由于硫化铁在自然环境中的丰富性,其生成活性氧和降解各种有机污染物的类Fenton活性已被广泛研究。然而,由于表面含铁活性位点的暴露有限,它们的类Fenton活性通常不高。在本研究中,以黄铁矿(FeS_(2))为例,基于水蒸汽对FeS_(2)的热处理,开发了一种提高硫化铁矿物Fenton活性的新策略,研究发现经水蒸汽热处理后的FeS_(2)(Heat-FeS_(2))对甲草胺(ACL)的非均相Fenton活性比由水热反应制备的母体FeS_(2)(Fresh-FeS_(2))更高。在初始pH为6.3时,Heat-FeS_(2)-Fenton体系对ACL的降解速率为0.48 min-1,约为Fresh-FeS_(2)-Fentton体系的23倍。电子自旋共振分析和苯甲酸探针实验证实,与Fresh-FeS_(2)-Fenton体系相比,在Heat-FeS_(2)-Fenton体系中产生更多的羟基自由基(·OH)和超氧自由基(·O_(2)^(-))。HeatFeS_(2)的Fenton活性大幅增强主要可归因于含量增加的高活性表面Fe^(2+)/Fe^(3+)组份、较高的Fe^(2+)浸出量和最佳的反应p H条件。扫描电镜,透射电镜,X射线光电子能谱(XPS)和傅里叶变换红外光谱等一系列表征结果表明,热处理可显著促进晶格Fe^(2+)向表面活性Fe^(2+)的转化,同时增强表面SO42-的生成,从而形成高酸性表面。此外,热处理后Fresh-FeS_(2)表面Fe^(2+)在表面总铁中的百分比从13%提高到了Heat-FeS_(2)的29%,而且Heat-FeS_(2)的Fe^(2+)浸出量(0.23 mmol·L-1)也远高于FreshFeS_(2)的Fe^(2+)浸出量(<0.02mmol·L-1)。为了进一步阐明Heat-FeS_(2)材料ACL降解活性增强的机理,我们通过XPS技术监测类Fenton反应前后Heat-FeS_(2)表面Fe和S物种的变化关系。结果表明,H2O_(2)反应后,Fresh-FeS_(2)和Heat-Fee S_(2)中Fe^(2+)和Fe^(3+)的表面含量显著增加,而S_(2)2-物种的表面浓度则相对下降,证实了S_(2)2-物种在Fe^(3+)还原为Fe^(2+)循环中的关键作用。重要的是,本研究不仅加深了对FeS_(2)氧化转化、腐蚀及其对天然环境中有毒有机物转化与降解的认识,而且还提供了一种基于硫化铁矿物的高效Fenton氧化方法。

MXenes/CNTs-based hybrids:Fabrications,mechanisms,and modification strategies for energy and environmental applications

Emerging two-dimensional(2D)layered metal carbide and nitride materials,commonly termed MXenes,are increasingly recognized for their applications across diverse fields such as energy,environment,and catalysis.In the past few years,MXenes/carbon nanotubes(CNTs)-based hybrids have attracted extensive attention as an important catalyst in energy and environmental fields,due to their superior multifunctions and mechanical stability.This review aims to address the fabrication strategies,the identification of the enhancement mechanisms,and recent progress regarding the design and modification of MXenes/CNTs-based hybrids.A myriad of fabrication techniques have been systematically summarized,including mechanical mixing,spray drying,three-dimensional(3D)printing,self-assembly/in-situ growth,freeze drying,templating,hydrothermal methods,chemical vapor deposition(CVD),and rolling.Importantly,the identification of the enhancement mechanisms was thoroughly discussed from the two dimensions of theoretical simulations and in-situ analysis.Moreover,the recent advancements in profound applications of MXenes/CNTs-based hybrids have also been carefully revealed,including energy storage devices,sensors,water purification systems,and microwave absorption.We also underscore anticipated challenges related to their fabrication,structure,underlying mechanisms,modification approaches,and emergent applications.Consequently,this review offers insights into prospective directions and the future trajectory for these promising hybrids.It is expected that this review can inspire new ideas or provide new research methods for future studies.

New method for controlling minimum length scales of real and void phase materials in topology optimization

Minimum length scale control on real and void material phases in topology optimization is an important topic of research with direct implications on numerical stability and solution manufacturability.And it also is a challenge area of research due to serious conflicts of both the solid and the void phase element densities in phase mixing domains of the topologies obtained by existing methods.Moreover,there is few work dealing with controlling distinct minimum feature length scales of real and void phase materials used in topology designs.A new method for solving the minimum length scale controlling problem of real and void material phases,is proposed.Firstly,we introduce two sets of coordinating design variable filters for these two material phases,and two distinct smooth Heaviside projection functions to destroy the serious conflicts in the existing methods(e.g.Guest Comput Methods Appl Mech Eng 199(14):123-135,2009).Then,by introducing an adaptive weighted 2-norm aggregation constraint function,we construct a coordinating topology optimization model to ensure distinct minimum length scale controls of real and void phase materials for the minimum compliance problem.By adopting a varied volume constraint limit scheme,this coordinating topology optimization model is transferred into a series of coordinating topology optimization sub-models so that the structural topology configuration can stably and smoothly changes during an optimization process.The structural topology optimization sub-models are solved by the method of moving asymptotes(MMA).Then,the proposed method is extended to the compliant mechanism design problem.Numerical examples are given to demonstrate that the proposed method is effective and can obtain a good 0/1 distribution final topology.

Porous 3D carbon-based materials:An emerging platform for efficient hydrogen production

Due to their unique properties and uninterrupted breakthrough in a myriad of clean energy-related applications,carbon-based materials have received great interest.However,the low selectivity and poor conductivity are two primary difficulties of traditional carbon-based materials(zero-dimensional(0D)/one-dimensional(1D)/two-dimensional(2D)),enerating inefficient hydrogen production and impeding the future commercialization of carbon-based materials.To improve hydrogen production,attempts are made to enlarge the surface area of porous three-dimensional(3D)carbon-based materials,achieve uniform interconnected porous channels,and enhance their stability,especially under extreme conditions.In this review,the structural advantages and performance improvements of porous carbon nanotubes(CNTs),g-C_(3)N_(4),covalent organic frameworks(COFs),metal-organic frameworks(MOFs),MXenes,and biomass-derived carbon-based materials are firstly summarized,followed by discussing the mechanisms involved and assessing the performance of the main hydrogen production methods.These include,for example,photo/electrocatalytic hydrogen production,release from methanolysis of sodium borohydride,methane decomposition,and pyrolysis-gasification.The role that the active sites of porous carbon-based materials play in promoting charge transport,and enhancing electrical conductivity and stability,in a hydrogen production process is discussed.The current challenges and future directions are also discussed to provide guidelines for the development of next-generation high-efficiency hydrogen 3D porous carbon-based materials prospected.

Carbonitride MXene Ti_(3)CN(OH)_(x)@MoS_(2)hybrids as efficient electrocatalyst for enhanced hydrogen evolution

Renewable energy powered electrocatalytic water splitting is a promising strategy for hydrogen generation,and the design and development of high-efficiency and earth-abundant electrocatalysts for hydrogen evolution reaction(HER)are highly desirable.Herein,MoS2 nanoflowers decorated two-dimensional carbonitride-based MXene Ti3CN(OH)x hybrids have been constructed by etching and post-hydrothermal methods.The electrochemical performance of the as-obtained Ti_(3)CN(OH)_(x)@MoS_(2)hybrids having a quasi core-shell structure is fascinating:An overpotential of 120 mV and a Tafel slope of 64 mV∙dec^(−1)can be delivered at a current density of 10 mA∙cm^(−2).And after 3,000 cyclic voltammetry cycles,it can be seen that there is no apparent attenuation.Both the experimental results and density functional theory(DFT)calculations indicate that the synergetic effects between Ti_(3)CN(OH)x and MoS_(2)are responsible for the robust electrochemical HER performance.The electrons of-OH group in Ti_(3)CN(OH)x are transferred to MoS_(2),making the adsorption energy of the composite for H almost vanish.The metallic Ti_(3)CN(OH)x is also beneficial to the fast charge transfer kinetics.The construction of MXene-based hybrids with optimal electronic structure and unique morphology tailored to the applications can be further used in other promising energy storage and conversion devices.

三维MXenes异质结及其应用

MXenes因其独特的表面化学性质、可调的金属组份、良好的亲水性和较高的载流子浓度,近年来被广泛应用于诸多研究领域.与其他二维材料类似,MXenes可与其他材料进行复合构建异质结,形成MXenes基三维多孔材料,从而显著增强其反应活性,提升其相关性能.尤其是这些三维多孔MXenes材料所具有的三维结构和明确的孔径,可显著提高电化学过程中各种离子和电子的传输速率,因此在电化学能量存储、传感、催化和环境领域应用前景广阔.在这篇综述中,作者以MXenes/碳、MXenes/无机物和MXenes/聚合物这三种主要的MXenes基异质结为研究对象,系统地总结了近年来三维多孔MXenes基异质结的构建方法的研究进展.同时,深入探讨了三维多孔MXenes基异质结在光催化、环境监测和电化学储能中的应用进展.最后,详细归纳了三维多孔MXenes基异质结的孔隙形成机制、性质和应用之间的关系,并提出了作者独到的见解.本综述可为三维多孔MXenes基异质结在高性能材料和器件中的设计、制造和应用等方面提供指导.

Damage mechanism and evaluation model of compressor impeller remanufacturing blanks:A review

The theoretical and technological achievements in the damage mechanism and evaluation model obtained through the national basic research program“Key Fundamental Scientific Problems on Mechanical Equipment Remanufacturing”are reviewed in this work.Large centrifugal compressor impeller blanks were used as the study object.The materials of the blanks were FV520B and KMN.The mechanism and evaluation model of ultra-high cycle fatigue,erosion wear,and corrosion damage were studied via theoretical calculation,finite element simulation,and experimentation.For ultra-high cycle fatigue damage,the characteristics of ultra-high cycle fatigue of the impeller material were clarified,and prediction models of ultra-high cycle fatigue strength were established.A residual life evaluation technique based on the“b-HV-N”(where b was the nonlinear parameter,HV was the Vickers hardness,and N was the fatigue life)double criterion method was proposed.For erosion wear,the flow field of gas-solid two-phase flow inside the impeller was simulated,and the erosion wear law was clarified.Two models for erosion rate and erosion depth calculation were established.For corrosion damage,the electrochemical and stress corrosion behaviors of the impeller material and welded joints in H2S/CO2 environment were investigated.KISCC(critical stress intensity factor)and da/dt(crack growth rate,where a is the total crack length and t is time)varied with H2S concentration and temperature,and their variation laws were revealed.Through this research,the key scientific problems of the damage behavior and mechanism of remanufacturing objects in the multi-strength field and cross-scale were solved.The findings provide theoretical and evaluation model support for the analysis and evaluation of large centrifugal compressor impellers before remanufacturing.

From imines to amides via NHC-mediated oxidation

The unprecedented NHC-mediated oxidation of imines to amides is described.This protocol features broad substrate scope and allows rapid assembly of amides in good to high yields.Notably,this process includes not only the umpolung of imines,but also the discovery of NHC-bound 1,2-dioxetane intermediates.