On the Polygonal Wear Evolution of Heavy-Haul Locomotive Wheels due to Wheel/Rail Flexibility and Its Mitigation Measures

Wheel polygonal wear can immensely worsen wheel/rail interactions and vibration performances of the train and track,and ultimately,lead to the shortening of service life of railway components.At present,wheel/rail medium-or high-frequency frictional interactions are perceived as an essential reason of the high-order polygonal wear of railway wheels,which are potentially resulted by the flexible deformations of the train/track system or other external excitations.In this work,the effect of wheel/rail flexibility on polygonal wear evolution of heavy-haul locomotive wheels is explored with aid of the long-term wheel polygonal wear evolution simulations,in which different flexible modeling of the heavy-haul wheel/rail coupled system is implemented.Further,the mitigation measures for the polygonal wear of heavy-haul locomotive wheels are discussed.The results point out that the evolution of polygonal wear of heavy-haul locomotive wheels can be veritably simulated with consideration of the flexible effect of both wheelset and rails.Execution of mixed-line operation of heavy-haul trains and application of multicut wheel re-profiling can effectively reduce the development of wheel polygonal wear.This research can provide a deep-going understanding of polygonal wear evolution mechanism of heavy-haul locomotive wheels and its mitigation measures.

Microstructure evolution of a new directionally solidified Ni-based superalloy after long-term aging at 950 ℃ upto 1 000 h

The microstructure evolution of a new directionally solidified（DS） Ni-based superalloy used for gas turbine blades after long-term aging at 950 ℃ was investigated.The results show that the γ ＇ phase becomes more regular in dendritic arm and interdendritic area,while both the mass fraction and the size of γ ＇ phase increase gradually with increasing aging time.During long-term aging,the MC carbide dissolves on the edge to provide the carbon for the formation of M23C6 carbide by the precipitation of Cr at the grain boundary.The rose-shaped γ ＇/γ eutectic partly dissolves into γ matrix and the aging promotes it transform into raft-shape γ ＇.The microstructure is generally stable and no needle-like topologically close-packed phase（TCP） can be found after aging for 1 000 h.

A Long-Term Numerical Model of Morphodynamic Evolution and Its Application to the Modaomen Estuary

Because of the influence of human activities, the evolution of the Modaomen Estuary is no longer a purely natural process. We used a long-term morphodynamic model （PRD-LTMM-10） to study the evolution of the estuary from 1977 to 1988. The model incorporated modules for riprap-siltation promotion and waterway dredging. The model can simulate the morphodynamic evolutionary processes occurring in the Modaomen Estuary during the period of interest. We were able to isolate the long-term influences of various human engineering activities and the roles of natural factors in estuarine evolution. The governance projects had the largest effect on the natural development of the estuary, resulting in larger siltation on the west side. Installation of riprap and reclamation of submerged land resulted in scouring of the main Hengzhou Channel causing deep trough out-shift. Severe siltation narrowed the upper end of the Longshiku Deep Trough.

Noble-Metal-Free Oxygen Evolution Reaction Electrocatalysts Working at High Current Densities over 1000 mA cm^(-2):From Fundamental Understanding to Design Principles

Alkaline water electrolysis provides a promising route for"green hydrogen"generation,where anodic oxygen evolution reaction(OER)plays a crucial role in coupling with cathodic hydrogen evolution reaction.To date,the development of highly active and durable OER catalysts based on earth-abundant elements has drawn wide attention;nevertheless,their performance under high current densities(HCDs≥1000 mA cm^(-2))has been less emphasized.This situation has seriously impeded large-scale electrolysis industrialization.In this review,in order to provide a guideline for designing high-performance OER electrocatalysts,the effects of HCD on catalytic performance involving electron transfer,mass transfer,and physical/chemical stability are summarized.Furthermore,the design principles were pointed out for obtaining efficient and robust OER electrocatalysts in light of recent progress of OER electrocatalysts working above 1000 mA cm^(-2).These include the aspects of developing self-supported catalytic electrodes,enhancing intrinsic activity,enhancing the catalyst-support interaction,engineering surface wettability,and introducing protective layer.Finally,summaries and outlooks in achieving OER at industrially relevant HCDs are proposed.

Evolution of Microstructure and Mechanical Property during Long-Term Aging in Udimet 720Li

Thermal stabilities of microstructure and mechanical property have been investigated on superalloy U720Li, which is of great interest of application for jet engine and land-based turbine disc. The results showed that, the primary and secondary gamma' particles maintain good thermal stability at 650 and 700 degreesC with aging time up to 3000 h, while the tertiary gamma' is apparently dependent on aging temperature and time. The tertiary gamma' particles undergo a procedure of coarsening, dissolution and eventually complete disappearance with the increasing of aging time and temperature. They exhibit unusual high sensibility upon aging temperature, which is attributed to the lattice misfit between the gamma' precipitates and the matrix in the alloy. The grain boundary phase M23C6 remains stable without forming of sigma phase even with aging time up to 3000 h at 700 degreesC. Microhardness decreases apparently with increasing aging time and aging temperature. Theoretical analysis based on dislocation mechanism indicates that the change of microhardness should be attributed to the evolution of the tertiary gamma' during aging.

Review on radiological evolution of COVID-19 pneumonia using computed tomography

BACKGROUND Pneumonia is the main manifestation of coronavirus disease 2019(COVID-19)infection.Chest computed tomography is recommended for the initial evaluation of the disease;this technique can also be helpful to monitor the disease progression and evaluate the therapeutic efficacy.AIM To review the currently available literature regarding the radiological follow-up of COVID-19-related lung alterations using the computed tomography scan,to describe the evidence about the dynamic evolution of COVID-19 pneumonia and verify the potential usefulness of the radiological follow-up.METHODS We used pertinent keywords on PubMed to select relevant studies;the articles we considered were published until October 30,2020.Through this selection,69 studies were identified,and 16 were finally included in the review.RESULTS Summarizing the included works’findings,we identified well-defined stages in the short follow-up time frame.A radiographic deterioration reaching a peak roughly within the first 2 wk;after the peak,an absorption process and repairing signs are observed.At later radiological follow-up,with the limitation of little evidence available,the lesions usually did not recover completely.CONCLUSION Following computed tomography scan evolution over time could help physicians better understand the clinical impact of COVID-19 pneumonia and manage the possible sequelae;a longer follow-up is advisable to verify the complete resolution or the presence of long-term damage.

Scalable graphene foam with ultrahigh conductivity for stabilizing Pt towards efficient hydrogen evolution

For the carbon-based catalyst to be active and stable,especially in harsh electrochemical environments,the key is to decrease the concentration of defects and raise the degree of graphitization of the carbon support.Herein,we develop a highly graphitized graphene foam with multiplicated structure to fabricate self-supporting Pt-based catalysts for efficient and stable hydrogen evolution reaction(HER)performance.Graphene foam(GO-2850)is obtained through an ultra-high temperature treatment at 2850℃,with perfect graphene structure and extremely low defect,ensuring high electrical conductivity and corrosion resistance.Additionally,its multiplicated structure provides an inherently favorable environment for the dispersion of Pt nanoparticles(Pt NPs)and offers abundant channels for electrolyte infiltration during the catalytic process.As a result,the as-prepared Pt/GO-2850 is far active and stable than the Pt NPs supported on commercial carbon paper(Pt/CP)counterpart toward catalyzing HER,exhibiting an outstanding activity and long-term durability(300 h@10 mA·cm^(−2))in acidic/alkaline/seawater electrolytes.This can be attributed to the stronger interaction between the lower-defect GO-2850 substrate and Pt,as evidenced by characterization and theoretical calculations.This work extends further insight into the design self-supporting catalysts of high activity and stability with promising prominent application toward green energy devices.

面向VoNR的语音演进策略分析

随着5G SA网络逐步演进成熟,VoNR已经商用。为更好地提供高品质语音业务,文章以SA组网架构下的EPS Fallback和VoNR两种解决方案为基础,展开两种方案的互操作选择策略、边界策略、路径策略、阶段策略四个方面的分析研究,为各电信运营商在VoNR演进过程中的策略方面和后续的全面开通提供技术借鉴。

Synergistic effect of V and Fe in Ni/Fe/V ternary layered double hydroxides for efficient and durable oxygen evolution reaction

High-performance and stable electrocatalysts are vital for the oxygen evolution reaction(OER).Herein,via a one-pot hydrothermal method,Ni/Fe/V ternary layered double hydroxides(NiFeV-LDH)derived from Ni foam are fabricated to work as highly active and durable electrocatalysts for OER.By changing the feeding ratio of Fe and V salts,the prepared ternary hydroxides were optimized.At an Fe:V ratio of 0.5:0.5,NiFeV-LDH exhibits outstanding OER activity superior to that of the binary hydroxides,requiring overpotentials of 269 and 274 mV at 50 mA·cm^(−2)in the linear sweep voltammetry and sampled current voltammetry measurements,respectively.Importantly,NiFeV-LDH shows extraordinary long-term stability(≥75 h)at an extremely high current density of 200 mA·cm^(−2).In contrast,the binary hydroxides present quick decay at 200 mA·cm^(−2)or even reduced current densities(150 and 100 mA·cm^(−2)).The outstanding OER performance of NiFeV-LDH benefits from the synergistic effect of V and Fe while doping the third metal into bimetallic hydroxide layers:(a)Fe plays a crucial role as the active site;(b)electron-withdrawing V stabilizes the high valence state of Fe,thus accelerating the OER process;(c)V further offers great stabilization for the formed intermediate of FeOOH,thus achieving superior durability.

Analytical long-term evolution and perturbation compensation models for BeiDou MEO satellites

The current paper establishes the analytical models of the long-term evolution and perturbation compensation strategy for Medium Earth Orbits（MEO）shallow-resonant navigation constellation,with application to the Chinese Bei Dou Navigation Satellite System（BDS）.The long-term perturbation model for the relative motion is developed based on the Hamiltonian model,and the long-term evolution law is analyzed.The relationship between the control boundary of the constellation and the offset of the orbital elements is analyzed,and a general analytical method for calculating the offset of the orbit elements is proposed.The analytical model is further improved when the luni-solar perturbations are included.The long-term evolutions of the BDS MEO constellation within 10 years are illustrated,and the effectiveness of the proposed analytical perturbation compensation calculation approach is compared with the traditional numerical results.We found the fundamental reason for the nonlinear variations of the relative longitude of ascending node and the mean argument of latitude is the long-periodic variations of the orbital inclination due to the luni-solar perturbations.The proposed analytical approach can avoid the numerical iterations,and reveal the essential relationship between the orbital element offsets and the secular drifts of the constellation configuration.Moreover,there is no need for maintaining the BDS MEO constellation within 10 years while using the perturbation compensation method.

Microstructural evolution and its influence on the impact toughness of GH984G alloy during long-term thermal exposure

The microstructure evolution and its effect on the impact toughness of a new Ni-Fe based alloy GH984 G,used in 700℃ ultra-super critical coal-fired power plant,were investigated during thermal exposure at 650℃-750℃ for up to 10,000 h.The results show that the impact toughness at room tempe rature drops rapidly at the early stage during thermal exposure at 700℃ and then has no significant change even if after exposure for 10,000 h.The significant decline of the impact toughness is attributed to the coarsening of M_(23)C_(6) carbides at grain boundaries,which weakens the grain boundary strength and leads to the aging-induced grain boundary embrittlement.The M_(23)C_(6) carbides have almost no change with further thermal exposure and the impact toughness also remains stable.Additionally,the impact toughness rises with the increase of thermal exposure temperature.The size of γ' after thermal exposure at 750℃ for10,000 h is much bigger than that at 650℃ and 700℃ for 10,000 h.There fore,the intragranular strength decreases significantly due to the transformation of the interaction between γ' and dislocation from stro ngly coupled dislocation shearing to Orowan bowing.More plastic deformation occurs within grains after thermal exposure at 750℃ for 10,000 h,which increases the impact toughness.

A Survey on Channel Measurements and Models for Underground MIMO Communication Systems

The high reliability of the communication system is critical in metro and mining applications for personal safety,channel optimization,and improving operational performance.This paper surveys the progress of wireless communication systems in underground environments such as tunnels and mines from 1920 to 2022,including the evolution of primitive technology,advancements in channel modelling,and realization of various wireless propagation channels.In addition,the existing and advanced channel modeling strategies,which include the evolution of different technologies and their applications;mathematical,analytical,and experimental techniques for radio propagation;and significance of the radiation characteristics,antenna placement,and physical environment of multiple-input multiple-output(MIMO)communication systems,are analyzed.The given study introduces leaky coaxial cable(LCX)and distributed antenna system(DAS)designs for improving narrowband and wideband channel capacity.The paper concludes by figuring out open research areas for the future technologies.

《广韵》从“甫”得声的语音关系研究

文章以《广韵》中从“甫”得声的谐声字为主要材料,结合上古和中古的声韵地位分析,总结该谐声系列从上古到中古的语音演变情况,并运用比较法和材料分析法,揭示该谐声系列的语音演变及发展规律,为深入进行谐声系统的语音演变研究提供可资参考的材料。

Evolution of γ’ Particles in Ni-Based Superalloy Weld Joint and Its Effect on Impact Toughness During Long-Term Thermal Exposure

Effects of long-term thermal exposure on γ’ particles evolution and impact toughness in the weld joint of Nimonic 263(N263)superalloy were deeply studied at 750℃.Results showed that the precipitates in the weld metal were mainly composed of fine γ’ particles,bulky MC carbides,and small M23C6 carbides.With the thermal exposure time increasing from o to 3000 h,γ’ particles in the weld metal grew up from 19.7 nm to 90.1 nm at an extremely slow rate.After being exposed for 1000 h,γ’ particles coarsened and some of them transformed into acicular η phase.At the same time,MC carbides decomposed to form η phase and γ’ particles.This dynamic transition ensured the slight reduction in impact toughness of the weld metal after the thermal exposure,which indicated the stable serving performance of N263 weld joint.

江西赣方言古全浊声母今读新论

通过对江西赣方言古全浊声母的今读情况的考察发现,江西赣方言古全浊声母今读有多种发展模式,这种状态的形成是江西早期土著方言与北方移民语言相互作用以及后来赣方言自身发展的结果。

固定通信网络向IMS网络演进的方案探讨

在通信网络向全IP化驱动下,话音业务网适用全IP化运营和业务发展而向IMS(IP多媒体子系统)网络演进。通过对IMS技术特征分析,提出IMS网络承接固网话音通信业务和满足视频通信业务需求的部署以及固网网络演进方案。

汉语方言上声的全次浊分调现象

文章利用"汉语方言地图集数据库"和其他公开发表的材料,对汉语方言中全浊上与次浊上声调相分的现象进行考察,整理描写这种音变现象的类型,指出上声全次浊分调是一种官话型的音变,在方言地图上以"漏斗式"的演变模式向东南方言扩散,东南方言在完成上声全次浊分调的过程中,有数种不同的演变类型。

中国联通5G无线网演进策略研究

从5G适用场景出发,通过业务发展、网络覆盖、部署时间、投资成本及竞争需要等多维度进行分析,提出适合中国联通的5G业务发展、5G无线网络部署、CU-DU分离及5G语音解决策略及演进建议,同时面向5G网络演进提出现阶段无线网应对的措施。

基于机器学习分析VoLTE视频通话质量的研究及应用

针对目前评估VoLTE视频通话质量的方法的缺点,提出了一种基于机器学习和网络指标参数的VoLTE视频通话质量评估方法。首先,采集解码核心网的网络参数指标数据,并进行预处理;然后,选取用于VoLTE视频通话质量评估的关键特征,并通过对比选取合适的机器学习算法,构建VoLTE视频质量评估的评估模型,从而实现不依赖于测试环境和原始视频的VoLTE视频通话质量实时评估。通过对从XDR(用户话单)数据中提取的特征指标数据进行预处理研究,解决了特征指标的标准化问题,便于指标特征输入评估模型;通过特征工程选出评估VoLTE视频通话的关键特征,减少特征维数,从而降低了算法的复杂度;同时采用先进的机器学习技术保证和提升算法的评估准确性。

面向5G Advanced网络的话音业务演进研究

伴随着移动通信网络技术的代际更替,话音业务技术也在同步演进。对运营商话音技术演进路线进行了总结,在对4G VoLTE及5G VoNR话音解决方案进行分析的基础上,提出了5G Advanced网络架构下的话音解决方案——VoNR+,并对VoNR+业务需求、关键技术以及未来发展方向进行了探讨。