Predicting the limit pressure capacity of pipe elbows containing single defects

Numerous studies have investigated the weakening effect of corrosion or erosion induced defects on the limit pressure capacity of straight pipes, but few have focused on elbows. In this paper the roles of material and geometric parameters of an elbow with a single defect were studied and formulized by means of a vast nonlinear parametric finite element analysis followed by artificial neural network. Results showed that length, depth and circumferential position of the corroded area have the most effects on the limit pressure capacity. In addition to the primary approach of this paper, an analytical approach was also used by combining some ideas from previous relevant studies to reach to a simple and easy-to-use formula. The predictions of the two methods were compared with each other. This paper presents the first part of two-part study investigating elbows with single defects (part 1) and interacting defects (part 2).     

Fe–Mg diffusion in olivine II: point defect chemistry,change of diffusion mechanisms and a model for calculation of diffusion coefficients in natural olivine

Analysis of existing data and models on point defects in pure (Fe,Mg)-olivine (Phys Chem Miner 10:27–37,1983; Phys Chem Miner 29:680–694, 2002) shows that it is necessary to consider thermodynamic non-ideality of mixing to adequately describe the concentration of point defects over the range of measurement. In spite of different sources of uncertainties, the concentrations of vacancies in octahedral sites in (Fe,Mg)-olivine are on the order of 10⁻⁴ per atomic formula unit at 1,000–1,200 °C according to both the studies. We provide the first explicit plots of vacancy concentrations in olivine as a function of temperature and oxygen fugacity according to the two models. It is found that in contrast to absolute concentrations at ∼1,100 °C and dependence on fO₂, there is considerable uncertainty in our knowledge of temperature dependence of vacancy concentrations. This needs to be considered in discussing the transport properties such as diffusion coefficients. Moreover, these defect models in pure (Fe,Mg)-olivine need to be extended by considering aliovalent impurities such as Al, Cr to describe the behavior of natural olivine. We have developed such a formulation, and used it to analyze the considerable database of diffusion coefficients in olivine from Dohmen et al. (Phys Chem Miner this volume, 2007) (Part - I) and older data in the literature. The analysis documents unequivocally for the first time a change of diffusion mechanism in a silicate mineral—from the transition metal extrinsic (TaMED) to the purely extrinsic (PED) domain, at fO₂ below 10⁻¹⁰  Pa, and consequently, temperatures below 900 °C. The change of diffusion mechanism manifests itself in a change in fO₂ dependence of diffusivity and a slight change in activation energy of diffusion—the activation energy increases at lower temperatures. These are consistent with the predictions of Chakraborty (J Geophys Res 102(B6):12317–12331, 1997). Defect formation enthalpies in the TaMED regime (distinct from intrinsic defect formation) lie between −66 and + 15 kJ/mol and migration energies of octahedral cations in olivine are most likely ∼ 260 kJ/mol, consistent with previous inferences (Phys Chem 207:147–162, 1998). Plots are shown for diffusion at various constant fO₂ as well as along fO₂ buffers, to highlight the difference in behavior between the two. Considering all the diffusion data and constraints from the point defect models, (Fe–Mg) diffusion in olivine along [001] is best described by the Master equations: (1) At oxygen fugacities greater than 10⁻¹⁰ Pa:

氟碳钙铈矿结构中晶体缺陷的高分辨电镜研究

用高分辨电子显微术（ＨＲＥＭ）研究了氟碳钙铈矿（ＢＳ）晶体结构中的无序堆垛和体衍交生现象，结果表明该矿物的衍生多晶体是由钙－铈氟碳酸盐矿物中不同组分的氟碳铈矿（Ｂ）和直氟碳钙铈矿（Ｓ）结构单元层沿ｃ方向无序堆垛而成。高分辨结构象揭示出氟碳钙铈矿衍生多晶体的微结构特征。讨论了氟碳钙铈矿结构中的堆垛层错等晶体缺陷现象。     

中国肺动脉高压诊断与治疗指南(2021版)

目的：探讨双源CT评价成人房间隔缺损（ASD）合并肺动脉高压（PAH）的诊断价值。方法：回顾性分析我院75例成人ASD患者,根据右心导管（RHC）检查术所得肺动脉平均压（mPAP）是否≥25 mmHg分为PAH组（40例）和无PAH组（35例）。所有患者均在术前1周内行DSCT先天性心脏病检查,测量升主动脉直径（AAD）、主肺动脉直径（MPAD）、右肺动脉干直径（RPAD）、左肺动脉干直径（LPAD）、右下肺动脉直径（RLPAD）、双心室短轴最大内径（RVD、LVD）、脊柱室间隔夹角、ASD直径,计算MPAD与AAD比值（rPA）、RVD与LVD比值（RVD/LVD）。采用t检验评价两组患者临床资料、RHC检查指标、CT心血管参数差异;使用ROC曲线确定双源CT对成人ASD合并PAH的诊断效能;使用Pearson等级相关系数分析CT参数与mPAP、PVR的相关性。结果：两组间差异有统计学意义的CT指标有MPAD、RPAD、LPAD、RLPAD、RVD、脊柱室间隔夹角、rPA、RVD/LVD、ASD直径,其中RPAD、LPAD、脊柱室间隔夹角、rPA、RVD/LVD、ASD直径对PAH具有中等强度的诊断效能（AUC均>0.7）;MPAD、rPA、ASD直径与mPAP呈中度正相关,MPAD、rPA、RVD/LVD与PVR呈中度正相关,ASD直径与PVR呈高度正相关。结论：双源CT对成人ASD合并PAH具有一定的诊断价值,可以为临床治疗前综合评估、长期随访与管理提供较好的依据。

     

罗江县水库土坝汶川大地震震害调查与分析

5·12汶川8.0级大地震对德阳市罗江县的水库造成了不同程度的破坏,经济损失严重,若水库出现渍坝现象,将会带来更大的损失。对罗江县19座高危以上险情水库的土坝震害进行了调查研究.发现典型的震害现象包括裂缝、渗漏、防浪墙损坏以及泄水建筑物和附属设施的损毁等。根据水库土坝的震前病害调查资料可以看出：水库土坝在地震前多是带病运行,严重影响地震时水库运行的因素主要有土料或填筑质量差、坝基问题、坝体结构设计不当、蚁害、观测设施不全等。依据震后水库土坝的破坏形态,分析了水库大坝的震前病害对大坝震害现象的影响。为今后水库土坝的抗震设计提供基础性的资料。     

基于XGBoost算法的电网二次设备缺陷分类研究

电网二次设备缺陷严重程度的精确判断可为设备的运行和维护提供重要依据.针对电网二次设备缺陷数据特征量多、人为判断难度大、易出错等问题,提出基于XGBoost（eXtreme Gradient Boosting）的二次设备缺陷分类方法,提高二次设备缺陷分类的准确率.首先,对二次设备历史缺陷数据进行去异常值、编码等一系列预处理工作,并筛选出与设备缺陷相关性高的特征建立特征指标集;然后,利用历史缺陷数据对XGBoost模型进行训练和参数寻优;最后,用训练好的分类模型实现二次设备缺陷的准确分类.本文采用某电厂二次设备缺陷数据对所提算法进行算例分析,并与传统分类器（决策树、逻辑回归等）进行比较,结果表明XGBoost可以实现对二次设备缺陷程度的精确判断,进而可以很好地辅助检修人员进行设备的维护与管理.     

激光干涉测距三维秩亏网的拟稳平差

激光跟踪仪采用激光干涉测距原理,其测距精度远远高于测角精度。利用激光跟踪仪的高精度激光干涉测距值,构成空间三维激光干涉测边网,可以消除测角误差对空间点位的影响,大幅度提高三维点坐标精度。由于激光干涉测距三维网存在数亏问题,且整网控制点的稳定性不同,因此采用秩亏自由网平差模型,分别以测站点和定向点为拟稳点对测量数据进行平差解算。平差结果表明,在拟稳点选择合理的情况下,空间点三维坐标平差值反算的距离与测量距离的差值优于±10μm;点位误差可以优于±20μm。     

裂纹缺陷体积百分数与CT数的关系分析

本文利用混合体的线性衰减系数的线性表示,推导出材料受力环境下,不含杂质时,微裂纹群的出现所带来的密度相对变化量与CT数相对变化量之间的关系式。进一步分析得到了裂纹缺陷体积百分数相对变化量与CT数相对变化量之间的关系式。含单杂质时,得到了裂纹缺陷体积百分数相对变化量与CT数相对变化量的关系式,并且把结论进一步推广到多杂质情形。为后期利用CT进行材料疲劳寿命分析奠定了理论基础。     

非对称局部壁厚减薄海底管道的屈曲分析

在深海环境中,海底管线不仅承受较高外压,还会因为海水及运输介质的常年侵蚀而形成腐蚀缺陷,而腐蚀缺陷往往会导致管道的外压承载力下降。基于壳体稳定性理论,建立了含有非对称局部壁厚减薄管道在外压作用下的屈曲压力理论公式。公式具有广泛的适用性,当内、外局部壁厚减薄深度相等时,可用于计算含有对称局部壁厚减薄管道屈曲压力,而当内部或外部缺陷深度为零时,便可用于计算只含外部或者内部腐蚀缺陷的管道屈曲压力。通过有限元分析验证了该公式的正确性,结果表明公式可以准确预测不同缺陷位置及尺寸时管道的屈曲压力。详细研究了局部壁厚减薄缺陷位置、长度和深度等参数对屈曲压力的影响。研究表明,局部腐蚀对管道的屈曲压力产生重要影响,尤其当腐蚀角度和深度较大时,在腐蚀形成初期就会造成管道的承载力急剧下降,并且管道的屈曲压力与缺陷的径向位置有关,腐蚀缺陷位于管道外侧时的屈曲压力明显大于其位于管道内侧时的屈曲压力。     

Mechanisms of OH defect incorporation in naturally occurring,hydrothermally formed diopside and jadeite

The IR spectrum of an alpine, hydrothermally formed diopside containing 17 wt ppm H₂O consists of three main OH absorption bands centred at 3647, 3464 and 3359 cm⁻¹. Jadeite from a Californian vein occurrence is characterised by bands at 3616 and 3557 cm⁻¹ and contains about 197 wt ppm H₂O. Based on the pleochroic scheme of the OH absorption bands in diopside, OH defect incorporation models are derived on the basis of fully occupied cation sites and under the assumption of M1 and M2 site vacancies; OH defects replacing O2 oxygen atoms are most common. The less pronounced OH pleochroism and the broad band absorption pattern of jadeite indicate a high degree of OH defect disordering. The pleochroic scheme of the main absorption bands at 3616 and 3557 cm⁻¹ implies partial replacement of O2 oxygen atoms by OH dipoles pointing to vacant Si sites. Under the assumption of M1 and M2 site vacancies, O1–H and O2–H defects are also derivable. OH incorporation modes assuming Si-vacancies should be considered for jadeite-rich clinopyroxenes formed in deep crust and upper mantle regions.