Improving creep strength of the fine-grained heat-affected zone of novel 9Cr martensitic heat-resistant steel via modified thermo-mechanical treatment

The infamous type Ⅳ failure within the fine-grained heat-affected zone (FGHAZ) in G115 steel weldments seriously threatens the safe operation of ultra-supercritical (USC) power plants.In this work,the traditional thermo-mechanical treatment was modified via the replacement of hot-rolling with cold rolling,i.e.,normalizing,cold rolling,and tempering (NCT),which was developed to improve the creep strength of the FGHAZ in G115 steel weldments.The NCT treatment effectively promoted the dissolution of preformed M_(23)C_(6)particles and relieved the boundary segregation of C and Cr during welding thermal cycling,which accelerated the dispersed reprecipitation of M_(23)C_(6) particles within the fresh reaustenitized grains during post-weld heat treatment.In addition,the precipitation of Cu-rich phases and MX particles was promoted evidently due to the deformation-induced dislocations.As a result,the interacting actions between precipitates,dislocations,and boundaries during creep were reinforced considerably.Following this strategy,the creep rupture life of the FGHAZ in G115 steel weldments can be prolonged by 18.6%,which can further push the application of G115 steel in USC power plants.

Construction of Pd-doped RuO_(2) nanosheets for efficient and stable acidic water oxidation

RuO_(2) has been considered a potential alternative to commercial IrO_(2) for the oxygen evolution reaction(OER)due to its superior intrinsic activity.However,its inherent structure dissolution in acidic environments restricts its commercial applications.In this study,we report a novel Pd-doped ruthenium oxide(Pd–RuO_(2))nanosheet catalyst that exhibits improved activity and stability through a synergistic effect of Pd modulation of Ru electronic structure and the two-dimensional structure.The catalyst exhibits excellent performance,achieving an overpotential of only 204 mVat a current density of 10 mA cm^(-2).Impressively,after undergoing 8000 cycles of cyclic voltammetry testing,the overpotential merely decreased by 5 mV.The PEM electrolyzer with Pd0.08Ru0.92O_(2) as an anode catalyst survived an almost 130 h operation at 200 mA cm^(-2).To elucidate the underlying mechanisms responsible for the enhanced stability,we conducted an X-ray photoelectron spectroscopy(XPS)analysis,which reveals that the electron transfer from Pd to Ru effectively circumvents the over-oxidation of Ru,thus playing a crucial role in enhancing the catalyst's stability.Furthermore,density functional theory(DFT)calculations provide compelling evidence that the introduction of Pd into RuO_(2) effectively modulates electron correlations and facilitates the electron transfer from Pd to Ru,thereby preventing the overoxidation of Ru.Additionally,the application of the two-dimensional structure effectively inhibited the aggregation and growth of nanoparticles,further bolstering the structural integrity of the catalyst.

Research on AC Electronic Load with Energy Recovery Based on Finite Control Set Model Predictive Control

Nowadays,AC electronic loads with energy recovery are widely used in the testing of uninterruptible power supplies and power supply equipment.To tackle the problems of control difficulty,strategy complexity,and poor dynamic performance of AC electronic load with energy recovery of the conventional control strategy,a control strategy of AC electronic load with energy recovery based on Finite Control Set Model Predictive Control(FCSMPC)is developed.To further reduce the computation burden of the FCS-MPC,a simplified FCS-MPC with transforming the predicted variables and using sector to select expected state is proposed.Through simplified model and equivalent approximation analysis,the transfer function of the system is obtained,and the stability and robustness of the system are analyzed.The performance of the simplified FCS-MPC is compared with space vector control(SVPWM)and conventional FCS-MPC.The results show that the FCS-MPC method performs better dynamic response and this advantage is more obvious when simulating high power loads.The simplified FCS-MPC shows similar control performance to conventional FCS-MPC at less computation burden.The control performance of the system also shows better simulation results.

A Predictive Instrument for Sensitive and Expedited Measurement of Ultra-Barrier Permeation

The reliable operation of flexible display devices poses a significant engineering challenge regarding the metrology of high barriers against water vapor.No reliable results have been reported in the range of 10–6 g∙(m^(2)∙d)1,and there is no standard ultra-barrier for calibration.To detect trace amount of water vapor permeation through an ultra-barrier with extremely high sensitivity and a greatly reduced test period,a predictive instrument was developed by integrating permeation models into high-sensitivity mass spectrometry measurement based on dynamic accumulation,detection,and evacuation of the permeant.Detection reliability was ensured by means of calibration using a standard polymer sample.After calibration,the lower detection limit for water vapor permeation is in the range of 10–7 g∙(m^(2)∙d)1,which satisfies the ultra-barrier requirement.Predictive permeation models were developed and evaluated using experimental data so that the steady-state permeation rate can be forecasted from non-steady-state results,thus enabling effective measurement of ultra-barrier permeation within a significantly shorter test period.

Joint Resource Allocation and Admission Control in Sliced Fog Radio Access Networks

Network slicing based fog radio access network(F-RAN) has emerged as a promising architecture to support various novel applications in 5 G-and-beyond wireless networks. However, the co-existence of multiple network slices in F-RANs may lead to significant performance degradation due to the resource competitions among different network slices. In this paper, the downlink F-RANs with a hotspot slice and an Internet of Things(Io T) slice are considered, in which the user equipments(UEs) of different slices share the same spectrum. A novel joint resource allocation and admission control scheme is developed to maximize the number of UEs in the hotspot slice that can be supported with desired quality-of-service, while satisfying the interference constraint of the UEs in the Io T slice. Specifically, the admission control and beamforming vector optimization are performed in the hotspot slice to maximize the number of admitted UEs, while the joint sub-channel and power allocation is performed in the Io T slice to maximize the capability of the UEs in the Io T slice tolerating the interference from the hotspot slice. Numerical results show that our proposed scheme can effectively boost the number of UEs in the hotspot slice compared to the existing baselines.

Wear behavior of Zn-38Al-3.5Cu-1.2Mg/SiC_(p) composite under different stabilization treatments

A Zn-38Al-3.5Cu-1.2Mg composite reinforced with nano-SiC_(p) was fabricated via stirring-assisted ultrasonic vibration.To improve the abrasive resistance of the Zn-38Al-3.5Cu-1.2Mg/SiC_(p) composite,several stabilization treatments with distinct solid solutions and aging temperatures were designed.The results indicated that the optimal stabilization treatment for the Zn-38Al-3.5Cu-1.2Mg/SiC_(p) composite comprised solution treatment at 380℃for 6 h and aging at 170℃for 48 h.The stabilization treatment led to the formation of dispersive and homogeneous nano-SiC_(p).During the friction wear condition,the nano-SiC_(p) limited the microstructure evolution from the hardα(Al,Zn)phase to the softβ(Al,Zn)phase.Moreover,the increased amount of nano-SiC_(p) improved the grain dimension and contributed to the composite abrasive resistance.Furthermore,the stabilization treatment suppressed the crack initiation and propagation in the friction wear process,thereby improving the abrasive resistance of the Zn-38Al-3.5Cu-1.2Mg/SiC_(p) composite.

Blockchain-based fog radio access networks:Architecture,key technologies,and challenges

Fog Radio Access Network(F-RAN)has been regarded as a promising solution to the alleviation of the ever-increasing traffic burden on current and future wireless networks,for it shifts the caching and computing resources from remote cloud to the network edge.However,it makes wireless networks more vulnerable to security attacks as well.To resolve this issue,in this article,we propose a secure yet trustless Blockchain-based F-RAN(BF-RAN),which allows a massive number of trustless devices to form a large-scale trusted cooperative network by leveraging the key features of blockchain,such as decentralization,tamper-proof,and traceability.The architecture of BF-RAN is first presented.Then,the key technologies,including access control,dynamic resource management,and network deployment are discussed.Finally,challenges and open problems in the BF-RAN are identified.

大尺度类周期阵列结构快速电磁仿真方法

类周期结构具有独特的电磁波调控特性,在天线、雷达探测、目标隐身等领域具有重要研究价值,而针对大尺度类周期阵列的高效精确电磁仿真一直是电磁计算领域的重难点问题.本文从类周期阵列几何相似性出发,提出了一种具有函数复用机制的并行综合函数法(parallel synthetic basis functions method, p-SBFM),首次实现并验证了p-SBFM在多构型类周期阵列分析中的有效性.相比传统电磁数值算法, p-SBFM在大尺度类周期阵列分析中,能够在一定程度上克服精度、效率、内存消耗三方面指标难以兼顾的难题,为类周期结构的工程应用提供理论分析和仿真手段.

基于CsPbBr_(3)纳米片的低阈值上转换等离子体激光器

上转换激光器为新一代高度集成的非线性光电应用提供了一个强大的平台,解决了现代光子集成电路不断发展对小型化、低损耗和高质量非线性光源的诉求.然而,对于具有反斯托克斯过程的上转换激光器,减小尺寸和阈值是其不可避免的巨大挑战.本文报道了一种基于CsPbBr_(3)纳米片的室温上转换等离子体纳米激光器,该激光器在较宽的尺寸范围内表现出显著的阈值降低,同时依旧保持着较高的品质因子.更激动人心的是,本文成功制造了厚度低至70 nm的小型化上转换等离子体激光器,突破光学衍射极限到深亚波长范围.同时,本文利用仿真模拟描述了双光子激发光场的分布情况,揭示了等离子体辅助激光发射并降低阈值的过程.此外,SiO_(2)绝缘层厚度依赖实验证明了双光子激发光约束强度和珀塞尔效应的可调谐特性,这为实现等离子体器件性能的有效调控提供了有效方案.本文展示了高效和低阈值的上转换等离子体纳米激光器,为片上非线性光源的发展奠定了夯实的基础.

Air to fuel:Direct capture of CO_(2)from air and in-situ solar-driven conversion into syngas via Ni_(x)/NaA nanomaterials

Ever-increasing CO_(2)emissions and atmospheric concentration mainly due to the burning of traditional fossil fuels have caused severe global warming and climate change problems.Inspired by nature’s carbon cycle,we propose a novel dual functional catalyst-sorbent to tackle energy and environmental problems simultaneously via direct capture of CO_(2)from air and in-situ solar-driven conversion into clean fuels.Economically and operationally advantageous,the planned coupling reaction can be carried out in a single reactor without the requirement for an extra trapping device.The great CO_(2)capture and conversion performance in an integrated step is shown by the CO_(2)capacity of up to 0.38 mmol·g^(−1)for adsorption from 500 ppm CO_(2)at 25℃and the CO_(2)conversion rate of up to 95%.Importantly,the catalyst-sorbent is constituted of a nonprecious metal Ni catalyst and an inexpensive commercially available CO_(2)sorbent,viz,zeolite NaA.Furthermore,this designed dual functional material also exhibits outstanding stability performance.This work offers a novel pathway of capturing CO_(2)in the air at room temperature and converting it by CH4 into fuel,contributing to the new era of carbon neutrality.

建构巴蜀核科普联盟——以专业、专注、专精拉近核与公众的距离

为进一步“整体•协同”川渝地区核科普声量,持续提升中国核工业品牌价值、增强科研品牌向心力,2024年5月29日,“科普•共创品牌•未来”四川省核学会核科普与公众沟通专业分会成立大会暨首届“巴蜀核声”核工业品牌传播文化沙龙在四川成都隆重举行。本次活动由中国核工业集团有限公司、四川省核学会指导,中国核动力研究设计院承办。

Formation mechanism and control methods of acicular ferrite in HSLA steels:A review

High strength low alloy（HSLA） steels have been widely used in pipelines,power plant components,civil structures and so on,due to their outstanding mechanical properties as high strength and toughness,and excellent weldability.Multi-phase microstructures containing acicular ferrite or acicular ferrite dominated phase have been proved to possess good comprehensive properties in HSLA steels.This paper mainly focuses on the formation mechanisms and control methods of acicular ferrite in HSLA steels.Effect of austenitizing conditions,continuous cooling rate,and isothermal quenching time and temperature on acicular ferrite transformation was reviewed.Furthermore,the modified process to control the formation of multi-phase microstructures containing acicular ferrite,as intercritical heat treatments,step quenching treatments and thermo-mechanical controlled processing,was summarized.The favorable combination of mechanical properties can be achieved by these modified treatments.

Controlled synthesis of high-quality W-Y2O3 composite powder precursor by ascertaining the synthesis mechanism behind the wet chemical method

As an emerging preparation technology,wet chemical method has been employed widely to produce lots of alloy materials such as W and Mo based alloys,owing to its unique technical advantages.Ascertaining the synthesis mechanism behind wet chemical method is indispensable for controlled synthesis of highquality W-Y2 O3 composite powder precursor.The co-deposition mechanism of yttrium and tungsten component behind the wet chemical method of preparing yttrium-doped tungsten composite nanopowder was investigated systematically in this work.A series of co-deposited composite powders fabricated under different acidity conditions were used as research targets for investigating the effect of surface composition and structure on co-deposition efficiency.It was found that white tungstic acid has more W-OH bonds and much higher co-deposition efficiency with Y^3+ions than yellow tungstic acid.It is illustrated that the coordination reaction between W-OH bonds on tungstic acid particles and Y^3+ions brings the co-deposition of yttrium and tungsten component into being.Through displacing H^+ions in W-OH bonds,Y^3+ions can be adsorbed on the surface of or incorporated into tungstic acid particles in form of ligand.Consequently,to control and regulate Y2 O3 content in powder precursor accurately,H^+ion concentration in wet chemical reaction should be in range of 0.55-2.82 mol L^-1 to obtain white tungstic acid.Besides,H^+ion concentration also has prominent effect on the grain size and morphology of reduced powder precursor.The optimal value should be around 1.58 mol L^-1,which can lead to minimum W grain size(about 17 nm) without bimodal structure.The chemical mechanism proposed in this work could produce great sense to preparation of high-quality precursor for sintering high-performance Y2 O3 dispersion strengthened W based alloys.Our work may also shed light on the approach to exploit analogous synthesis mechanism in other alloy systems.

Microstructures and mechanical properties of friction stir welds on 9% Cr reduced activation ferritic/martensitic steel

In this study,the microstructures and mechanical properties of 9%Cr reduced activation ferritic/martensitic（RAFM） steel friction stir welded joints were investigated.When a W-Re tool is used,the recommended welding parameters are 300 rpm rotational speed,60 mm/min welding speed and10 kn axial force.In stir zone（SZ）,austenite dynamic recrystallization induced by plastic deformation and the high cooling rates lead to an obvious refinement of prior austenite grains and martensite laths.The microstructure in SZ contains lath martensite with high dislocation density,a lot of nano-sized MX and M3C phase particles,but almost no M23C6 precipitates.In thermal mechanically affect zone（TMAZ）and heat affect zone（HAZ）,refinement of prior austenite and martensitic laths and partial dissolution of M（23）C6 precipitates are obtained at relatively low rotational speed.However,with the increase of heat input,coarsening of martensitic laths,prior austenite grains,and complete dissolution of M23C6 precipitates are achieved.Impact toughness of SZ at-20℃ is slightly lower than that of base material（BM）,and exhibits a decreasing trend with the increase of rotational speed.

Tailoring the secondary phases and mechanical properties of ODS steel by heat treatment

The oxide dispersion strengthened(ODS) steel with the nominal composition of Fe–14 Cr–2 W–0.3 Ti–0.2 V–0.07 Ta–0.3 Y2O3(wt%) was fabricated by mechanical alloying and hot isostatic pressing(HIP). In order to optimize the relative volume fraction of secondary phases, the as-HIPed ODS steel was annealed at 800°C, 1000°C, 1200°C for 5 h, respectively. The microstructures and different secondary phases of the as-HIPed and annealed ODS samples were identified by scanning electron microscopy(SEM), transmission electron microscopy(TEM), and X-ray diffraction(XRD). The tensile properties of all the ODS steels at room temperature were also investigated. The results indicate that annealing is an effective way to control the microstructure and the integral secondary phases. The annealing process promotes the dissolution of M23C6 particles, thus promoting the precipitation of TiC.No obvious coarsening of Y2Ti2O7 nanoparticles can be observed during annealing. The tensile results indicate that the annealed ODS sample with the optimized secondary phases and high density possesses the best mechanical properties.

Variation of activation energy determined by a modified Arrhenius approach:Roles of dynamic recrystallization on the hot deformation of Ni-based superalloy

The hot deformation behaviors of Ni18 Cr9 Co9 Fe5 Nb3 Mo superalloy were explored in the formation temperature range free ofγ’phase with various strain rates applied.The hot deformation behaviors are initially modeled with Arrhenius equation which gives an average activation energy of 581.1 kJ mol^(-1).A modified Arrhenius approach,including the updated Zener-Hollomon parameter is proposed to consider the change of activation ene rgy under different deformation conditions which turns out a relatively accurate computation for activation energy of hot deformation,i.e.,the standard variance for modified model calculated in the covered deformation condition is just 35.4%of that for Arrhenius equation.The modified model also proposes a map for activation ene rgy which ranges from 571.5-589.0 kJ mol^(-1)for various deformation conditions.Microstructural features of the representative superalloy specimens were characterized by electron backscattered diffraction(EBSD)techniques in order to clarify the influence of activation energy on the microstructural formation.It is found that the Ni-based superalloy samples with higher activation energy are promoted by the degree of dynamic recrystallization which suggests that the rise in activation energy gives either a better recrystallization rate or finer grains.

Microstructure evolution and mechanical properties of linear friction welded S31042 heat-resistant steel

S31042 heat-resistant steel was joined by linear friction welding （LFW） in this study. The microstructure and the mechanical properties of the LFWed joint were investigated by optical microscopy, scanning electronic microscopy, transmission electron microscopy, hardness test and tensile test. A defect-free joint was achieved by using LFW under reasonable welding parameters. The dynamic recrystallization of austenitic grains and the dispersed precipitation of NbCrN particles resulting from the high stress and high temperature in welding, would lead to a improvement of mechanical property of the welded joint. With increasing the distance flom the weld zone to the parent metal, the austenitic grain size gradually increases from -1 μm to - 150 μm, and the microhardness decreases from 301 HV to 225 HV. The tensile strength （about 731 MPa） of the welded joint is comparable to that of the S31042 in the solution-treated state.

Refined microstructure and enhanced mechanical properties in Mo-Y_(2)O_(3)alloys prepared by freeze-drying method and subsequent low temperature sintering

The ultrafine Mo-Y_(2)O_(3)composite powders were successfully synthesized by innovative freeze-drying method.Consequently,the freeze-dried Mo-Y_(2)O_(3)composite powders with high sintering activities possess an average grain size of 54 nm.After low temperature sintering at 1600°C,the Mo-Y_(2)O_(3)alloys maintaining a high density(99.6%)have the finest grain size(620 nm)comparing with available literature about oxide dispersion strengthened molybdenum alloy(ODS-Mo).The oxide particles remain their small size(mainly<50 nm)within Mo grains and at Mo grain boundaries.Furthermore,the Y_(5)MO_(2)O_(12)particles were firstly observed within Mo matrix,and its formation can absorb nearby oxygen impurities,which involves the purification of Mo matrix.The mechanical properties show that Mo-Y_(2)O_(3)alloy possess a high hardness of 487±28 HV_(0.2),a high yield strength of 902 MPa,a high compressive strength of1110 MPa,respectively.Our work suggests that freeze-drying and subsequent low temperature sintering can shed light on the preparation of ultrafine ODS-Mo alloys with high performance.

Effect of Image Noise on the Classification of Skin Lesions Using Deep Convolutional Neural Networks

Skin lesions are in a category of disease that is both common in humans and a major cause of death.The classification accuracy of skin lesions is a crucial determinant of the success rate of curing lethal diseases.Deep Convolutional Neural Networks(CNNs)are now the most prevalent computer algorithms for the purpose of disease classification.As with all algorithms,CNNs are sensitive to noise from imaging devices,which often contaminates the quality of the images that are fed into them.In this paper,a deep CNN(Inception-v3)is used to study the effect of image noise on the classification of skin lesions.Gaussian noise,impulse noise,and noise made up of a compound of the two are added to an image dataset,namely the Dermofit Image Library from the University of Edinburgh.Evaluations,based on t-distributed Stochastic Neighbor Embedding(t-SNE)visualization,Receiver Operating Characteristic(ROC)analysis,and saliency maps,demonstrate the reliability of the Inception-v3 deep CNN in classifying noisy skin lesion images.

Exploring associations between streetscape factors and crime behaviors using Google Street View images

Understanding the influencing mechanism of the urban streetscape on crime is fairly important to crime prevention and urban management.Recently,the development of deep learning technology and big data of street view images,makes it possible to quantitatively explore the relationship between streetscape and crime.This study computed eight streetscape indexes of the street built environment using Google Street View images firstly.Then,the association between the eight indexes and recorded crime events was revealed with a poisson regression model and a geographically weighted poisson regression model.An experiment was conducted in downtown and uptown Manhattan,New York.Global regression results show that the influences of Motorization Index on crimes are significant and positive,while the effects of the Light View Index and Green View Index on crimes depend heavily on the socioeconomic factors.From a local perspective,the Pedestrian Space Index,Green View Index,Light View Index and Motorization Index have a significant spatial influence on crimes,while the same visual streetscape factors have different effects on different streets due to the combination differences of socioeconomic,cultural and streetscape elements.The key streetscape elements of a given street that affect a specific criminal activity can be identified according to the strength of the association.The results provide both theoretical and practical implications for crime theories and crime prevention efforts.