A review of linear friction welding of Ni -based superalloys

Ni-based superalloys are one of the most important materials employed in high-temperature applications within the aerospace and nuclear energy industries and in gas turbines due to their excellent corrosion,radiation,fatigue resistance,and high-temperature strength.Linear friction welding(LFW)is a new joining technology with near-net-forming characteristics that can be used for the manu-facture and repair of a wide range of aerospace components.This paper reviews published works on LFW of Ni-based superalloys with the aim of understanding the characteristics of frictional heat generation and extrusion deformation,microstructures,mechanical proper-ties,flash morphology,residual stresses,creep,and fatigue of Ni-based superalloy weldments produced with LFW to enable future optim-um utilization of the LFW process.

Effect of visual perception training on binocular visual function reconstruction in patients after strabismus surgery

AIM:To explore the effect of visual perception learning software training(VPT)on binocular visual function reconstruction in children with intermittent exotropia after strabismus surgery.METHODS:Ninety children with intermittent exotropia admitted to our hospital from June 2018 to December 2018 were included,and randomly divided into VPT and control groups.Children in the control group received basic binocular vision training,while those in the VPT group received VPT after strabismus surgery.Tertiary visual function,visual perception function,Newcastle Control Score(NCS),and ocular position retraction rate were compared at 3 and 12mo after the surgery.RESULTS:At 3 and 12mo after the surgery,the proportion of simultaneous perception,binocular fusion version and binocular stereo vision in the VPT group was conspicuously higher than that in the control group(P<0.05).After the vision training,the binocular visual perception functions of children in both groups were significantly improved compared with that before training(P<0.05).Interestingly,the grating sharpness,texture perception and texture motion perception in the VPT group were dramatically better than control group(P<0.01).The NCS in the VPT group was significantly lower than that in the control group(P<0.05).The ocular position retraction rate in the VPT group was significantly lower than that in the control group at 12mo(8.89%vs 26.67%,P=0.03).CONCLUSION:VPT effectively promotes binocular visual function reconstruction in intermittent exotropia children after strabismus surgery and reduces the strabismus severity and ocular position retraction rate.

Visualization Techniques viaMLBS for Personnel Management in Major Events

Mobile location-based services(MLBS)refer to services around geographic location data.Mobile terminals use wireless communication networks(or satellite positioning systems)to obtain users’geographic location coordinate information based on spatial databases and integrate with other information to provide users with required location-related services.The development of systems based on MLBS has significance and practical value.In this paper a visualization management information system for personnel in major events based on microservices,namely MEPMIS,is designed and implemented by using MLBS.The system consists of a server and a client app,and it has some functions including map search and query,personnel positioning and scheduling,location management,messaging,and location service.Managers of the events can quickly search and locate the staff on the specific area of the map in real-time,and make broadcasting messages to the staff,and manage the staff.The client app is developed on the Android system,by which staff users can send the positions information to the server timely.The client users can search fuzzily near their peers and list their locations,and also call near peers through sending messages or query the history record of staff locations.In the design of the system,several new proposed techniques,including visual annotation method for overlapping locations,correcting trajectory drift algorithm,microservices-based overall system architecture methodology and other new techniques,which are applied to the implementation of the system.Also,HTML5,JQuery,MLBS APIs(Application Program Interfaces)related programming techniques have been used and combined with loading Ajax asynchronously and Json data encapsulation,map marker optimization techniques,that can improve the positioning accuracy and the performance of the system.The developed system with practical functions can enhance the efficiencies of the organization and management of major events.

调频连续波激光多路并行相干精密长度测量方法

面向航空航天等大型复杂机电系统,长度测量的需求从单独的一维位移测量发展到多目标、灵活便于拓展的多路并行测量。调频连续波激光雷达长度测量技术具备抗干扰、精度高、无合作等优势。本文基于调频连续波激光雷达技术开展多路并行相干精密长度测量方法研究,针对传统长度测量系统存在光纤色散、辅助路光纤漂移导致长度测量精度降低问题,提出一种含有氰化氢气体吸收池的三光路马赫-曾德尔干涉测量系统,在此基础上,基于光开关结构实现精密长度多路并行测量。通过精密导轨长度测量实验结果表明,提出的方法在3.6 m长度范围内标准差不超过25μm,实现了四路并行长度测量。与商用激光干涉仪测量结果比较,多路测量结果的绝对误差不超过30μm。

宇航总体单位商业航天发展战略探究

以商业航天为主要业务的众多民营企业,以及按照市场化运营的国有企业的迅速崛起,对宇航总体单位的发展战略带来诸多外部环境要素变化。文章梳理了我国商业航天发展历程及产业布局现状,分析了商业航天背景下宇航总体单位面临的机遇与挑战,提出了未来发展战略调整建议,为宇航总体单位兼顾重大工程国家能力与商业航天市场,实现可持续发展,更好的服务于航天强国建设提供了思考方向。

新能源电源控制故障响应对交流线路距离保护影响分析

大规模风电、光伏新能源经交流送出系统中,送出线路发生故障后,新能源电源控制的故障响应严重影响交流线路距离保护的动作性能。该文分析了新能源电源典型控制策略对故障后电源等值阻抗及系统功角的影响,故障后电源等值阻抗和系统功角显著增大。进一步研究了不同类型距离保护的动作性能。针对测距式距离保护,揭示了线路正向区外或反向区外发生经过渡电阻故障时保护误动、线路正向区内故障时保护拒动机理。针对比相式距离保护,揭示了正序极化电压相位受控偏移导致线路区内相间短路故障时保护拒动、区外反向故障时保护误动机理。利用实时数字仿真平台(real time digital simulation system,RTDS)建立了仿真模型,利用仿真结果和现场实际误动数据验证了理论分析的正确性,为大规模新能源送出线路故障分析和后备保护配置提供了理论依据。

Analysis of mechanical strengths of extreme line casing joint considering geometric, material, and contact nonlinearities

To address the challenges associated with difficult casing running,limited annular space,and poor cementing quality in the completion of ultra-deep wells,the extreme line casing offers an effective solution over conventional casings.However,due to its smaller size,the joint strength of extreme line casing is reduced,which may cause failure when running in the hole.To address this issue,this study focuses on the CST-ZTΦ139.7 mm×7.72 mm extreme line casing and employs the elastic-plastic mechanics to establish a comprehensive analysis of the casing joint,taking into account the influence of geometric and material nonlinearities.A finite element model is developed to analyze the forces and deformations of the extreme line casing joint under axial tension and external collapse load.The model investigates the stress distribution of each thread tooth subjected to various tensile forces and external pressures.Additionally,the tensile strength and crushing strength of the extreme line casing joint are determined through both analytical and experimental approaches.The findings reveal that,under axial tensile load,the bearing surface of each thread tooth experiences uneven stress,with relatively high equivalent stress at the root of each thread tooth.The end thread teeth are valuable spots for failure.It is observed that the critical fracture axial load of thread decreases linearly with the increase of thread tooth sequence.Under external pressure,the circumferential stress is highest at the small end of the external thread,leading to yield deformation.The tensile strength of the joint obtained from the finite element model exhibits a relative error of less than 7%compared to the analytical and experimental values,proving the reliability of the finite element model.The tensile strength of the joint is 3091.9 k N.Moreover,in terms of anti-collapse capability,the joints demonstrate higher resistance to collapse compared to the casing body,which is consistent with the test results where the pipe body experiences collapse and failure while the joints remain intact during the experiment.The failure load of the casing body under external collapse pressure is 87.4 MPa.The present study provides a basic understanding of the mechanical strengths of extreme line casing joint.

Dynamic propagation velocity of a positive streamer in a 3 m air gap under lightning impulse voltage

Streamers represent an important stage in the initiation of gap discharge. In this work, we used an eight-frame intensified charge-coupled device camera to capture the streamer development process when a lightning impulse voltage of 95%–100% U50% was applied in a 3 m rod–plate gap and the streamer velocity was analyzed. Analysis of the observations shows that streamer velocity can be defined by three stages: rapid velocity decline(stage 1), rapid velocity rise(stage 2)and slow velocity decline(stage 3). The effects of electrode shape, applied voltage and gap breakdown or withstanding on streamer velocity were analyzed. The electrode with a larger radius of curvature will result in a higher initial velocity, and a higher voltage amplitude will cause the streamer to propagate faster at stage 3. Gap withstanding or breakdown has no obvious effect on streamer velocity. In addition, the experimental results are compared with previous results and the statistical characteristics of the primary streamer discharge are discussed.

叱石成書:書籍史與宋代石學

宋代學者在石學的表達和呈現形式上有過諸多思考和嘗試,其實踐的最終結果,就是形成了以《集古錄》和《隸釋》馬代表的兩種不同的研究範式。這兩個範式的出現,也與書籍制度和椎拓技術的變化息息相關。

重型板状类工件三维质心检测方法

提出一种针对特大、特重板状类工件三维质心位置测量新方法。假想四个过质心的切面去切工件,四个切面与工件表面相交得到四条交线、两个交点;通过在工件上建立合适测量坐标系和基准面,测量两个交点坐标位置即得到质心坐标位置。对该方法测量误差源进行分析,验证误差满足测量要求。将该方法应用于实际产品中,结果表明该方法可实施性好。

核电管道弯曲半径检测方法研究

核电管道弯曲半径的检测属于大直径小圆弧测量范畴,针对管道弯曲直径较大、弯管外缘形状不规则而难以对半径准确测量问题,提出新的检测思路。该文使用激光跟踪仪采集管道表面三维点数据,结合SA测量分析软件模拟管道三维特征量,计算实际弯曲角度,建立评价基准面即管道中分面,在中分面上截取弯曲段内外圆弧轮廓点数据,依据图纸理论半径并兼顾管道实际弯曲角度,CAD辅助作图,统一圆弧唯一中心,精确界定圆弧轮廓边界,计算截取点到中心距离,更为合理的评价弯曲半径值,保证弯曲半径的测量评价不脱离管道整体结构尺寸链。该文方法与标准数模比对法的测量结果偏差为0.43 mm,满足相对公差±10 mm的要求,得到更为准确的检测结果。

新能源经柔直送出场景下功角变化导致比相式距离保护不正确动作机制分析

新能源电源经柔性直流输电线路接入交流系统已经成为电力系统中的典型场景。以基于模块化多电平换流器的柔性直流(modular multilevel converter-high voltage direct current,MMC-HVDC)受端交流线路配置的正序电压为极化电压的比相式距离保护为研究对象,结合受端换流器的控制策略,分析了新能源经柔性高压直送出系统中柔直受端交流线路发生短路故障场景下该保护的适应性:在发生相间金属性短路故障情况下,距离保护存在区内短路拒动以及反向区外短路误动的风险。为探究保护不正确动作机制,首先在电压平面上分析了参量变化对距离保护动作行为的影响,揭示了距离保护内在的系统功角与短路容量约束,推导了距离保护正确动作的功角边界。通过将柔直侧系统进行合理等值,受端交流线路发生相间金属性短路故障后,受端换流器控制策略使得系统等值功角增大,距离保护特性位于动作边界,存在拒动/误动风险。利用RTDS建立了风电经柔直送出系统的仿真模型,分析了受端交流线路故障后系统的等值功角特征,验证了距离保护的不正确动作特性。

电磁导航支气管镜在肺外周病变中诊断价值及安全性的meta分析

背景与目的 肺癌的发病率与死亡率一直位居恶性肿瘤前列。随着肺癌检测技术的进步与检测率的提高,检测技术对肺外周病变(peripheral pulmonary lesions, PPLs)的诊断准确率一直存在争议。本研究旨在系统评价电磁导航支气管镜(electromagnetic navigation bronchoscopy, ENB)在诊断PPLs中的诊断价值及安全性。方法 系统检索万方数据知识服务平台、中国知网、Embase、PubMed、Cochrane Library、Web of Science关于ENB对PPLs诊断率的相关文献,应用Stata 16.0、RevMan 5.4与Meta-Disc 1.4软件进行meta分析。结果 共有54篇文献、合计55项研究被纳入数据分析。ENB在PPLs诊断中的合并灵敏度、特异度、阳性似然比、阴性似然比和诊断比值比分别为0.77(95%CI:0.73-0.81)、0.97(95%CI:0.93-0.99)、24.27(95%CI:10.21-57.67)、0.23(95%CI:0.19-0.28)和104.19(95%CI:41.85-259.37)。受试者工作特征曲线下面积为0.90(95%CI:0.87-0.92)。亚组分析与meta回归显示研究的异质性来源于研究类型、辅助定位技术、样本量、病变大小和麻醉类型。辅助定位技术和全身麻醉方式的使用提高了ENB在PPLs中的诊断效果。ENB操作相关的不良反应和并发症发生率较低。结论 ENB在PPLs诊断中具有良好的准确性与安全性。

蒽环类药物治疗乳腺癌患者左右心室心肌纵向力学的变化

目的探讨三维超声心动图(3DE)及斑点追踪成像技术(STI)评估蒽环类药物对乳腺癌患者心功能影响的价值。方法对2020年7月-2021年11月首诊并术前接受蒽环类化疗的乳腺癌患者38例进行前瞻性研究,对术前乳腺癌患者化疗前、第2次化疗后24 h内、第4次化疗后24 h内、化疗周期结束后进行超声心动图检查,对超声心动图常规参数、3DE及STI获得心功能的各参数进行比较。采用Pearson相关性分析心功能各参数与药物剂量的相关性。结果LVGLS、RVGLS及RVFWLSap与蒽环类药物累积剂量呈负相关性。与化疗前比较,蒽环类药物化疗后各周期LVEF、3D-LVEF、3D-RVEF、LVGLS、RVGLS、RVFWLSbas、RVFWLSmid、RVFWLSap各参数均有减低,其中化疗周期结束后LVEF、3D-LVEF、3D-RVEF、LVGLS、RVFWLSmid、RVFWLSap的差异性具有统计学意义(P<0.05),3D-LVEF出现显著性差异早于LVEF,RVFWLS各节段比RVGLS较早出现显著性差异性。结论乳腺癌患者接受蒽环类化疗后可造成心肌功能损害,3DE及STI可早期为临床提供关于蒽环类化疗药致乳腺癌患者心功能损害的有利证据。

Dissolution and reprecipitation of 14H-LPSO structure accompanied by dynamic recrystallization in hot-extruded Mg_(89)Y_(4)Zn_(2)Li_(5) alloy

We investigate the variation induced in long-period stacking ordered(LPSO)structures,dynamic recrystallization(DRX),and mechanical performance of hot-extruded Mg89Y4Zn2Li5 alloys fabricated at different extrusion speeds(Ve=0.4,0.8,1.0,1.2 mm/s)and die angles(α=30°,60°,90°)under 400℃,the dissolution and reprecipitation of 14H LPSO structure accompanied by DRX process are then clarified in detail.Upon all extrusion conditions,the block 18R LPSO structures elongate in the extrusion direction,while the lamellar 14H LPSO structures dissolve under the deformation strain.In addition,due to discontinuous and continuous DRX mechanisms,all hot-extruded alloys have a full DRX microstructure consisting of equiaxed recrystallized grains,but the DRX grain size reduces when both extrusion speed and die angle decrease.Note that,in the interior of DRX grains,thin LPSO lamellae mixing 14H,18R and 24R structures nucleate and dynamically precipitate due to the dissolution of the original lamellar 14H LPSO structures.Furthermore,the hot-extruded Mg_(89)Y_(4)Zn_(2)Li_(5)alloy becomes stronger as decreasing of the extrusion speed and die angle,whereas the ductility remains nearly constant.Finally,the hotextruded Mg_(89)Y_(4)Zn_(2)Li_(5)alloy achieves an excellent strength-ductility balance at a relatively low extrusion speed(0.4 mm/s)and small die angle(30°)mainly due to the elongated 18R LPSO structure,fine and full DRX microstructure,thin mixed LPSO precipitates in the DRX grains,twins and dislocations.

基于三维经食管超声心动图数据的左心耳3D打印模型的准确性研究

目的应用三维经食管超声心动图(3D-TEE)数据重建并打印心房颤动患者左心耳3D模型,分析其准确性。方法选取行3D-TEE及心脏增强CT检查的心房颤动患者20例,对其3D-TEE左心耳数据进行后处理,使用软质类橡胶材料打印3D实体模型,测量左心耳模型的开口长径、开口短径、深度并评估解剖分型,将其与3D-TEE、CT测量结果进行比较及一致性分析。结果3D模型与3D-TEE测量左心耳开口长径、开口短径、深度比较差异均无统计学意义;3D模型与3D-TEE测量左心耳开口长径、开口短径、深度的ICC分别为0.97、0.98、0.98。3D模型、3D-TEE测量左心耳开口长径、开口短径、深度均小于CT,差异均有统计学意义(均P<0.05);3D模型与CT测量左心耳开口长径、短径、深度的ICC分别为0.91、0.90、0.90,3D-TEE与CT测量左心耳开口长径、开口短径、深度的ICC分别为0.91、0.88、0.90。3D模型与CT在评估左心耳形态、分叶方面比较差异均无统计学意义;两种技术评估左心耳形态、分叶的一致性均很高(Kappa=0.86、0.91,均P<0.05)。3D-TEE与CT在评估左心耳形态、分叶方面比较差异均无统计学意义;两种技术评估左心耳形态的一致性较高(Kappa=0.71,P<0.05),评估左心耳分叶的一致性很高(Kappa=0.81,P<0.05)。结论基于3D-TEE数据的3D打印模型可准确还原心房颤动患者左心耳各径线数据;与3D-TEE相比,3D模型在评估左心耳形态及分叶方面与CT重建一致性更高。

视网膜血管床面积在糖尿病视网膜病变中的应用研究进展

视网膜血管床面积(RVBA)是在超广角荧光素血管造影(UWFA)图像中分割出的视网膜血管的面积总和,是一个以平方毫米为单位的绝对值,客观性较强。RVBA主要受视网膜血管直径和长度的影响,其增加或减少取决于局部缺血和血管生成之间的“竞争”,可以提示视网膜血管形态上的细微改变。作为研究视网膜血管性疾病的新指标,与既往常用的缺血指数(ISI)、无灌注区面积(NPA)等相比,RVBA可能具有更高的稳定性和准确性。目前,RVBA主要被用于评估糖尿病视网膜病变(DR)的病程进展和疗效预后。与正常眼相比,DR眼的视网膜总RVBA更大;在抗血管内皮生长因子(VEGF)治疗后DR眼的视网膜总RVBA下降。这些发现为研究DR中的微血管病变提供了有利支持。本文就RVBA在DR中的应用作一综述,为RVBA在视网膜静脉阻塞(RVO)等其它视网膜血管性疾病中的临床研究提供参考。

Exploring the regulatory mechanism of tRNA-derived fragments 36 in acute pancreatitis based on small RNA sequencing and experiments

BACKGROUND Acute pancreatitis(AP)is a disease featuring acute inflammation of the pancreas and histological destruction of acinar cells.Approximately 20%of AP patients progress to moderately severe or severe pancreatitis,with a case fatality rate of up to 30%.However,a single indicator that can serve as the gold standard for prognostic prediction has not been discovered.Therefore,gaining deeper insights into the underlying mechanism of AP progression and the evolution of the disease and exploring effective biomarkers are important for early diagnosis,progression evaluation,and precise treatment of AP.AIM To determine the regulatory mechanisms of tRNA-derived fragments(tRFs)in AP based on small RNA sequencing and experiments.METHODS Small RNA sequencing and functional enrichment analyses were performed to identify key tRFs and the potential mechanisms in AP.Reverse transcription quantitative polymerase chain reaction(RT-qPCR)was conducted to determine tRF expression.AP cell and mouse models were created to investigate the role of tRF36 in AP progression.Lipase,amylase,and cytokine levels were assayed to examine AP progression.Ferritin expression,reactive oxygen species,malondialdehyde,and ferric ion levels were assayed to evaluate cellular ferroptosis.RNA pull down assays and methylated RNA immunoprecipitation were performed to explore the molecular mechanisms.RESULTS RT-qPCR results showed that tRF36 was significantly upregulated in the serum of AP patients,compared to healthy controls.Functional enrichment analysis indicated that target genes of tRF36 were involved in ferroptosisrelated pathways,including the Hippo signaling pathway and ion transport.Moreover,the occurrence of pancreatic cell ferroptosis was detected in AP cells and mouse models.The results of interference experiments and AP cell models suggested that tRF-36 could promote AP progression through the regulation of ferroptosis.Furthermore,ferroptosis gene microarray,database prediction,and immunoprecipitation suggested that tRF-36 accelerated the progression of AP by recruiting insulin-like growth factor 2 mRNA binding protein 3(IGF2BP3)to the p53 mRNA m6A modification site by binding to IGF2BP3,which enhanced p53 mRNA stability and promoted the ferroptosis of pancreatic follicle cells.CONCLUSION In conclusion,regulation of nuclear pre-mRNA domain-containing protein 1B promoted AP development by regulating the ferroptosis of pancreatic cells,thereby acting as a prospective therapeutic target for AP.In addition,this study provided a basis for understanding the regulatory mechanisms of tRFs in AP.

Atomic-scale engineering of advanced catalytic and energy materials via atomic layer deposition for eco-friendly vehicles

Zero-emission eco-friendly vehicles with partly or fully electric powertrains have exhibited rapidly increased demand for reducing the emissions of air pollutants and improving the energy efficiency. Advanced catalytic and energy materials are essential as the significant portions in the key technologies of eco-friendly vehicles, such as the exhaust emission control system,power lithium ion battery and hydrogen fuel cell. Precise synthesis and surface modification of the functional materials and electrodes are required to satisfy the efficient surface and interface catalysis, as well as rapid electron/ion transport. Atomic layer deposition(ALD), an atomic and close-to-atomic scale manufacturing method, shows unique characteristics of precise thickness control, uniformity and conformality for film deposition, which has emerged as an important technique to design and engineer advanced catalytic and energy materials. This review has summarized recent process of ALD on the controllable preparation and modification of metal and oxide catalysts, as well as lithium ion battery and fuel cell electrodes. The enhanced catalytic and electrochemical performances are discussed with the unique nanostructures prepared by ALD. Recent works on ALD reactors for mass production are highlighted. The challenges involved in the research and development of ALD on the future practical applications are presented, including precursor and deposition process investigation, practical device performance evaluation, large-scale and efficient production, etc.

Assessment of Lubrication Property and Machining Performance of Nanofluid Composite Electrostatic Spraying(NCES)Using Different Types of Vegetable Oils as Base Fluids of External Fluid

The current study of minimum quantity lubrication(MQL)concentrates on its performance improvement.By contrast with nanofluid MQL and electrostatic atomization(EA),the proposed nanofluid composite electrostatic spraying(NCES)can enhance the performance of MQL more comprehensively.However,it is largely influenced by the base fluid of external fluid.In this paper,the lubrication property and machining performance of NCES with different types of vegetable oils(castor,palm,soybean,rapeseed,and LB2000 oil)as the base fluids of external fluid were compared and evaluated by friction and milling tests under different flow ratios of external and internal fluids.The spraying current and electrowetting angle were tested to analyze the influence of vegetable oil type as the base fluid of external fluid on NCES performances.The friction test results show that relative to NCES with other vegetable oils as the base fluids of external fluid,NCES with LB2000 as the base fluid of external fluid reduced the friction coefficient and wear loss by 9.4%-27.7%and 7.6%-26.5%,respectively.The milling test results display that the milling force and milling temperature for NCES with LB2000 as the base fluid of external fluid were 1.4%-13.2%and 3.6%-11.2%lower than those for NCES with other vegetable oils as the base fluids of external fluid,respectively.When LB2000/multi-walled carbon nanotube(MWCNT)water-based nanofluid was used as the external/internal fluid and the flow ratio of external and internal fluids was 2:1,NCES showed the best milling performance.This study provides theoretical and technical support for the selection of the base fluid of NCES external fluid.