Transport mechanism of reverse surface leakage current in AlGaN/GaN high-electron mobility transistor with SiN passivation

The transport mechanism of reverse surface leakage current in the AlGaN/GaN high-electron mobility transistor（HEMT） becomes one of the most important reliability issues with the downscaling of feature size.In this paper,the research results show that the reverse surface leakage current in AlGaN/GaN HEMT with SiN passivation increases with the enhancement of temperature in the range from 298 K to 423 K.Three possible transport mechanisms are proposed and examined to explain the generation of reverse surface leakage current.By comparing the experimental data with the numerical transport models,it is found that neither Fowler-Nordheim tunneling nor Frenkel-Poole emission can describe the transport of reverse surface leakage current.However,good agreement is found between the experimental data and the two-dimensional variable range hopping（2D-VRH） model.Therefore,it is concluded that the reverse surface leakage current is dominated by the electron hopping through the surface states at the barrier layer.Moreover,the activation energy of surface leakage current is extracted,which is around 0.083 eV.Finally,the SiN passivated HEMT with a high Al composition and a thin AlGaN barrier layer is also studied.It is observed that 2D-VRH still dominates the reverse surface leakage current and the activation energy is around 0.10 eV,which demonstrates that the alteration of the AlGaN barrier layer does not affect the transport mechanism of reverse surface leakage current in this paper.

Dynamic leakage mechanism of gas drainage borehole and engineering application

Borehole leakage not only affects the gas drainage effect but also presents considerable risk to human security. For the research on the leakage mechanism of gas drainage borehole, the rheological and visco-elastic-plastic characteristics were considered to establish the mechanical model of coal mass around borehole, which is used to analyze the leakage mechanism and deduce the dynamic leakage model. On the basis of the real coal seam conditions, the variation rules of the stress, leakage ring, and air leakage amount were analyzed through numerical simulation, and the influence factors of air leakage amount were also investigated to provide the theoretical basis for the sealing technology. Results show that the air leakage amount of borehole is inversely proportional to the increase in supporting stress and sealing length, and directly correlated with the increase in borehole radius and softening modulus. Using theoretical analysis, we design a novel active supporting sealing technology that can use grouting material to seal the fractures to reduce the leakage channels and also provide supporting stress to prevent borehole deformation. The engineering test results indicate that the average gas concentration with the novel active supporting sealing technology is increased by 162.12% than that of traditional polyurethane sealing method. Therefore, this technology not only effectively resolves borehole leakage but also significantly improves the gas drainage effect.

The Transport Mechanisms of Reverse Leakage Current in Ultraviolet Light-Emitting Diodes

The transport mechanisms of the reverse leakage current in the UV light-emitting diodes （380nm） are investi- gated by the temperature-dependent current-voltage measurement first. Three possible transport mechanisms, the space-limited-charge conduction, the variable-range hopping and the Poole-Frenkel emission, are proposed to explain the transport process of the reverse leakage current above 295 K, respectively. With the in-depth investigation, the former two transport mechanisms are excluded. It is found that the experimental data agree well with the Poole Frenkel emission model. Furthermore, the activation energies of the traps that cause the reverse leakage current are extracted, which are 0.05eV, 0.09eV, and 0.11 eV, respectively. This indicates that at least three types of trap states are located below the bottom of the conduction band in the depletion region of the UV LEDs.

A Novel Parameter-Optimized Recurrent Attention Network for Pipeline Leakage Detection

Accurate detection of pipeline leakage is essential to maintain the safety of pipeline transportation.Recently,deep learning(DL)has emerged as a promising tool for pipeline leakage detection(PLD).However,most existing DL methods have difficulty in achieving good performance in identifying leakage types due to the complex time dynamics of pipeline data.On the other hand,the initial parameter selection in the detection model is generally random,which may lead to unstable recognition performance.For this reason,a hybrid DL framework referred to as parameter-optimized recurrent attention network(PRAN)is presented in this paper to improve the accuracy of PLD.First,a parameter-optimized long short-term memory(LSTM)network is introduced to extract effective and robust features,which exploits a particle swarm optimization(PSO)algorithm with cross-entropy fitness function to search for globally optimal parameters.With this framework,the learning representation capability of the model is improved and the convergence rate is accelerated.Moreover,an anomaly-attention mechanism(AM)is proposed to discover class discriminative information by weighting the hidden states,which contributes to amplifying the normalabnormal distinguishable discrepancy,further improving the accuracy of PLD.After that,the proposed PRAN not only implements the adaptive optimization of network parameters,but also enlarges the contribution of normal-abnormal discrepancy,thereby overcoming the drawbacks of instability and poor generalization.Finally,the experimental results demonstrate the effectiveness and superiority of the proposed PRAN for PLD.

Leakage Prediction Method for Contacting Mechanical Seals with Parallel Faces

Since the beginning of the 20th century, many researches on the sealing characteristic of mechanical seals were carried out broadly and in depth by various methods and some leakage models were built. But due to the lack of the way to characterize the main factors of influence on the leakage, most of the early researches were based on the assumptions that the seal faces topography and the frictional conditions were invariant. In the early built models, the effect of the surface topography change of the seal face on the leakage rate was neglected. Based on the fractal theory, the contact of end faces of the rotary and stationary rings was simplified to be the contact of a rough surface and an ideal rigid smooth surface, and the contact interface＇s cavity size-distribution function as well as the fractal characteristic of the cavity profile curve was discussed. By analyzing the influence of abrasion on the seal face topography and the leakage channel, the time-correlation leakage prediction model of mechanical seals based on the fractal theory was established and the method for predicting the leakage rate of mechanical seals with parallel plane was proposed. The values of the leakage rate predicted theoretically are similar to the measured values of the leakage rate in the model test and in situ test. The experimental results indicate that the leakage rate of mechanical seals is a transient value. The surface topography of the end faces of the seal tings and its change during the frictional wear of mechanical seals can be accurately characterized by the fractal parameters. Under the work conditions of changeless frictional mechanism, the fractal parameters measured or calculated based on the accelerated testing equation can be used to predict the leakage rate of mechanical seal in service. The proposed research provides the basis for determining the leakage state and predicting working life of mechanical seal.

The carbon border adjustment mechanism is inefficient in addressing carbon leakage and results in unfair welfare losses

The European Commission has proposed a Carbon Border Adjustment Mechanism(CBAM)to reduce carbon leakage and create a level playing field for its domestic products and imported goods.Nevertheless,the effectiveness of the proposal remains unclear,especially when it triggers threats of retaliation from trading partners of the European Union.We apply a Computable General Equilibrium model-Global Trade Analysis Project-to assess the economic and environmental impacts of different CBAM schemes.Here we show that the effectiveness of the CBAM to address carbon leakage risks is rather limited,and the CBAM raises concerns over global welfare costs,Correct to Gross Domestic Product(GDP)losses,and violation of equality principles.Trade retaliation leads to multiplied welfare losses,which would mostly be borne by poor countries.Our results question the carbon leakage reduction effect of a unilateral trade policy and suggest that climate change mitigation still needs to be performed within the framework of international cooperation.

Is hand sewing comparable with stapling for anastomotic leakage after esophagectomy? A meta-analysis

AIM:To compare the outcome of hand sewing and stapling for anastomotic leakage after esophagectomy.METHODS:A rigorous study protocol was established according to the recommendations of the Cochrane Collaboration.An electronic database search,hand search,and reference search were used to retrieve all randomized controlled trials that compared hand-sewn and mechanical esophagogastric anastomoses.RESULTS:This study included 15 randomized controlled trials with a total of 2337 patients.The results revealed that there was no significant difference in the incidence of anastomotic leakage between the methods[relative risk(RR)=0.77,95%confidence interval(CI):0.57-1.04;P=0.09],but a subgroup analysis yielded a significant difference for the sutured layer and year of publication(P s<0.05).There was also no significant difference in the incidence of postoperative mortality(RR=1.52,95%CI:0.97-2.40;P=0.07).However,the anastomotic strictures rate was increased in the stapler group compared with the hand-sewn group(RR=1.45,95%CI:1.11-1.91;P<0.01)in the end-to-side subgroup,while the incidence of anastomotic strictures was decreased(RR=0.34,95%CI:0.16-0.76;P<0.01)in the side-to-side subgroup.CONCLUSION:The stapler reduces the anastomotic leakage rate compared with hand sewing.End-to-side stapling increases the risk of anastomotic strictures,but side-to-side stapling decreases the risk.

INFILTRATION MECHANISM AND QUALITY CONTROL OF CONTACT MATERIALS

The infiltration mechanism, which has great significance for the quality control of electrieal contact material made from W-Cu, W-Ag alloys with high content of tungsten, has been studied. And a directive infiltration technology for improving the product quality and gaining a better economic benefit has been developed.

Deciphering the leakage conduction mechanism of BiFeO_(3)–BaTiO_(3)lead-free piezoelectric ceramics

BiFeO_(3)–BaTiO_(3)(BF–BT)based piezoelectric ceramics are a kind of high-temperature lead-free piezoelectric ceramics with great development prospects due to their high Curie temperature(TC)and excellent electrical properties.However,large leakage current limits their performance improvement and practical applications.In this work,direct current(DC)test,alternating current(AC)impedance,and Hall tests were used to investigate conduction mechanisms of 0.75BiFeO_(3)–0.25BaTiO_(3)ceramics over a wide temperature range.In the range of room temperature(RT)−150℃,ohmic conduction plays a predominant effect,and the main carriers are p-type holes with the activation energy(Ea)of 0.51 eV.When T>200℃,the Ea value calculated from the AC impedance and Hall data is 1.03 eV with oxygen vacancies as a cause of high conductivity.The diffusion behavior of thermally activated oxygen vacancies is affected by crystal symmetry,oxygen vacancy concentration,and distribution,dominating internal conduction mechanism.Deciphering the conduction mechanisms over the three temperature ranges would pave the way for further improving the insulation and electrical properties of BiFeO_(3)–BaTiO_(3)ceramics.

基于混合注意力机制的管道漏磁缺陷分类实验

该文将管道漏磁缺陷分类任务设计成应用型教学实验。该实验使用迁移学习的方法,调用预训练模型ResNet50,并插入主流的注意力机制(SE、CA、ECA、CBAM)进行对比分析。同时,利用Grad-CAM++可解释算法对模型内部的识别逻辑进行可视化,以便帮助学生更好地理解模型。实验结果显示,插入注意力机制的最优模型准确率达99.7%,能够有效识别管道中的正常情况和分类缺陷情况。该实验依托高性能计算机硬件和最新的Pytorch2.0软件包搭建了深度学习平台,有助于培养学生的创新意识和科研能力,也是对多学科交叉融合人才培养模式的探索和实践。

浅埋深综放工作面采空区“三带”分布研究

为研究浅埋深综放工作面采空区“三带”分布规律,在串草圪旦煤矿6101综放工作面采空区埋设束管,对采空区“三带”进行了现场实测。实测结果表明:由于煤层埋深浅、地表起伏大、进风侧存在地表漏风,进风侧采空区“三带”明显滞后于回风侧,进回风两侧氧化带宽度分别为87.8 m和61.4 m。利用FLUENT软件对实测条件下该工作面采空区“三带”进行了数值模拟,模拟结果和现场实测结果基本一致。同时模拟了不漏风条件下该工作面采空区“三带”分布,此时采空区散热带、氧化带范围大幅度减小,进风侧采空区氧化带稍大,而工作面中部和回风侧“三带”分布基本一致。

绒囊暂堵液堵漏机理研究

绒囊流体因其具有较好堵漏性能,广泛应用于钻完井、修井等石油工程勘探开发各个阶段。明确绒囊流体堵漏的微观机理可以更好的指导现场堵漏。室内测定了绒囊内绒囊的粒径分布、封堵岩心的孔喉分布及封堵压力,利用微观实验装置观测其基质孔隙内的充填暂堵过程,最后结合理论分析明确绒囊流体微观堵漏机理。结果表明,体系内绒囊的粒径分布0~350 μm,岩心孔喉的粒径分布0.7~15 μm,同一绒囊流体封堵4种岩心封堵压5.42~17.65 MPa且随着渗透率的减小而增大,绒囊通过聚集、变形可对基质孔喉、微裂缝进行全面封堵。根据拉普拉斯定理结合室内实验结果可知,绒囊流体堵漏的微观机理为:岩心内的绒囊流体在流动过程中压缩变形产生了附加阻力,大量的附加阻力相互叠加产生了封堵压力,阻止了井漏的发生。

欧盟碳边境调节机制的探析及其对中国的影响和应对

欧盟碳边境调节机制(CBAM)本质上是一种新型的技术性贸易壁垒,是欧盟针对部分进口商品的碳排放向企业征收税费,该法案的实施有助于欧盟恢复经济并抢占全球气候治理的话语权及“碳排放”权的定价权,防止欧盟内部企业向排放成本更低的国家进行转移,从而避免“碳泄露”。文章阐述了CBAM出台的背景、进展及意义,对CBAM实施可能对我国相关产业产生不同程度影响进行分析,建议应紧抓挑战和机遇,构建企业欧盟碳关税信息披露相关技术指南,推进可再生能源和碳交易市场机制建设。

AlGaN/GaN HEMT器件高温栅偏置应力后栅极泄漏电流机制分析

AlGaN/GaN高电子迁移率晶体管(HEMT)的栅特性会受到温度应力和电应力的影响.在高温栅偏置(HTGB)应力下,器件的栅特性会发生退化,如栅极泄漏电流增大.为了研究退化机理,分析了AlGaN/GaN HEMT在栅电压为-2 V时,250℃高温应力作用后的栅极泄漏电流机制.随着HTGB时间的增加,栅极泄漏电流持续增大,受到应力器件在室温下静置后栅极泄漏电流密度恢复约20%.结果表明,在正向偏置范围内,栅极泄漏电流是由热电子发射(TE)引起的.在反向偏置范围内,普尔-弗伦克尔(PF)发射在小电压范围内占主导地位.阈值电压附近的范围由势垒层中的陷阱辅助隧穿(TAT)引起;在大电压范围内,福勒-诺德海姆(FN)隧穿导致栅极发生泄漏.

基于Newmark-β法的非接触式机械密封轴向振动研究

振动对非接触式机械密封性能有着重要影响,如导致碰撞和泄漏。构建包括静环-液膜-动环-弹性元件的密封系统模型,探讨自由衰减振动、自激振动和地震极端振动3种激励下,密封系统静环、动环和弹性元件的位移以及密封系统泄漏和碰撞的情况。研究表明:在不受外界激励的情况下,在自由衰减振动下密封系统轴向稳定性和密封性能良好;密封系统在受到简谐振动激振力形式的自激振动干扰后,系统位移量明显增大,会显著影响密封性能;叠加一定地震烈度的随机平稳地震动影响下,弹性元件位移量大幅增加,密封失效。振动对非接触式机械密封性能的影响显著,应确保密封端面间液膜厚度稳定且足够小,以维持密封系统的长周期运转。

BiFeO_(3)/BaTiO_(3)铁电超晶格的电学性能研究

采用脉冲激光沉积技术在(001)取向SrTiO_(3)(STO)单晶衬底上生长了BiFeO_(3)/BaTiO_(3)(BFO/BTO)超晶格,研究了超晶格的微结构、铁电性能以及电输运机制。研究表明,BFO/BTO薄膜在STO衬底上外延生长。在薄膜层总厚度相同的条件下,相对于BTO及BFO单层薄膜,BFO/BTO超晶格表现出了更好的铁电性与更低的漏电流,且漏电流随着周期数的增多而减小。空间电荷限制电流(SCLC)是超晶格主导的电输运机制。超晶格中的人工界面对提升其铁电与漏电性能起着重要的作用。

基于移动激光扫描的地铁隧道渗漏水定位及快速检测方法

渗漏水是地铁隧道最主要的病害之一,也会导致其他结构病害,开展地铁隧道渗漏水病害检测方法研究具有重要意义。本文聚焦于地铁隧道渗漏水问题,提出了一种基于移动激光扫描点云数据的渗漏水定位及检测方法。首先,结合移动激光扫描检测方法,开展了隧道精确定位方法研究。然后,对YOLOv7模型进行了改进,引入了ConvNeXt网络和CBAM模块以使模型更好地捕获多尺度、多抽象级别的特征,增强对渗漏水关键特征的关注;使用GIoU Loss损失函数,使模型能够更好地处理不完整渗漏水框;预测时使用Soft-NMS加权平均的方法,保留更多的边界框,从而提高检测精度。结合在重庆地铁获取的激光扫描数据构建的盾构法和矿山法隧道渗漏水数据集,验证了本文方法的高效性和稳健性。消融试验表明,本文方法相较于基线模型在不同数据集上均取得了显著的性能提升,在盾构法数据集中,准确率P提升了8.1%,召回率R提升了4%;在矿山法数据集中,准确率P提升了8.6%,召回率R提升了6.8%。同时,与主流目标检测算法,如Faster RCNN(Swin)、Faster RCNN(ConvNeXt)、YOLOv8对比,本文方法在精度和速度方面都表现出优势。最后,本文展示了部分隧道渗漏水的定位与检测结果,以验证本文方法的实用性。

面向间隙变化的三螺杆泵流场动力学特性仿真

文中为模拟三螺杆泵在运行时的磨损所造成的间隙变化,建立了间隙变化的三螺杆泵流场有限元模型,对流场网格进行了无关性验证,利用Fluent软件对流场进行仿真,实现对不同间隙下三螺杆泵的动力学仿真分析,得到了不同间隙下泵内流体压力场分布与速度矢量分布结果。研究结果表明,不同类型的间隙对流场压力分布有不同的影响区间;不同类型间隙的流场发生泄露回流的区域分布不同;其中齿间间隙对流场压降作用最明显,法向间隙对流场出口流量的影响最明显。

LW25-252型断路器气动阀体密封圈检修(检验)方法

某220 kV站内进口设备LW25-252型断路器为单台供气式气动机构,内部气动阀由于存在运行时间较长,密封圈老化导致出现气动阀频繁漏气。文章通过研究该站LW25-252型断路器中VA133、VA134型气动阀,经过对气动阀的拆接、工作原理分析以及各部位密封垫作用,确定阀体内活塞杆密封圈为气动阀漏气根源,根据阀体活塞杆结构研制专用工具供拆解、组装阀体,并进一步模拟集中供气模式设计气动阀体检测平台,对修后气动阀进行自测自检,实现对该厂家VA133、VA134型气动阀自拆自修自检,降低对外部厂家援助依赖。

控制棒驱动机构楔形迷宫密封组件设计与密封性能研究

控制棒驱动机构(CRDM)与压力容器管座之间通常采用焊接连接,针对堆芯换料导致的拆卸不便以及二次焊接时密封性能变差等问题,对控制棒驱动机构的连接形式进行了研究,提出了一种便于维修和利于拆卸的楔形迷宫密封结构。首先,引入了迷宫密封的设计理念,加入了楔形密封结构,采用钢制压力容器的设计标准,计算了工况下控制棒驱动机构所需的最小壁厚和热压载荷耦合作用下的临界屈服温度;然后,应用有限元方法模拟了C形环工作状态,研究了金属C形环的回弹特性及密封面状态;最后,针对楔形迷宫密封组件开展了泄漏率试验和热循环试验。研究结果表明:工况下的最小壁厚为10 mm,临界屈服温度为72.5℃;C形环尺寸越大,最大线比压值越小,密封面的贴合程度越高;楔形迷宫密封组件的泄露率小于1.0×10-6 Pa·m 3/s,能够满足多次拆卸工况下的密封要求。