Investigation of the block toppling evolution of a layered model slope by centrifuge test and discrete element modeling

Primary toppling usually occurs in layered rock slopes with large anti-dip angles.In this paper,the block toppling evolution was explored using a large-scale centrifuge system.Each block column in the layered model slope was made of cement mortar.Some artificial cracks perpendicular to the block column were prefabricated.Strain gages,displacement gages,and high-speed camera measurements were employed to monitor the deformation and failure processes of the model slope.The centrifuge test results show that the block toppling evolution can be divided into seven stages,i.e.layer compression,formation of major tensile crack,reverse bending of the block column,closure of major tensile crack,strong bending of the block column,formation of failure zone,and complete failure.Block toppling is characterized by sudden large deformation and occurs in stages.The wedge-shaped cracks in the model incline towards the slope.Experimental observations show that block toppling is mainly caused by bending failure rather than by shear failure.The tensile strength also plays a key factor in the evolution of block toppling.The simulation results from discrete element method(DEM)is in line with the testing results.Tensile stress exists at the backside of rock column during toppling deformation.Stress concentration results in the fragmented rock column and its degree is the most significant at the slope toe.

A modified stochastic model for LS+AR hybrid method and its application in polar motion short-term prediction

Short-term(up to 30 days)predictions of Earth Rotation Parameters(ERPs)such as Polar Motion(PM:PMX and PMY)play an essential role in real-time applications related to high-precision reference frame conversion.Currently,least squares(LS)+auto-regressive(AR)hybrid method is one of the main techniques of PM prediction.Besides,the weighted LS+AR hybrid method performs well for PM short-term prediction.However,the corresponding covariance information of LS fitting residuals deserves further exploration in the AR model.In this study,we have derived a modified stochastic model for the LS+AR hybrid method,namely the weighted LS+weighted AR hybrid method.By using the PM data products of IERS EOP 14 C04,the numerical results indicate that for PM short-term forecasting,the proposed weighted LS+weighted AR hybrid method shows an advantage over both the LS+AR hybrid method and the weighted LS+AR hybrid method.Compared to the mean absolute errors(MAEs)of PMX/PMY sho rt-term prediction of the LS+AR hybrid method and the weighted LS+AR hybrid method,the weighted LS+weighted AR hybrid method shows average improvements of 6.61%/12.08%and 0.24%/11.65%,respectively.Besides,for the slopes of the linear regression lines fitted to the errors of each method,the growth of the prediction error of the proposed method is slower than that of the other two methods.

Simultaneous control of ferromagnetism and ferroelasticity by oxygen octahedral backbone stretching

Coexistence of ferromagnetism and ferroelasticity in a single material is an intriguing phenomenon,but has been rarely found.Here we studied both the ferromagnetism and ferroelasticity in a group of LaCoO3 films with systematically tuned atomic structures.We found that all films exhibit ferroelastic domains with four-fold symmetry and the larger domain size(higher elasticity)is always accompanied by stronger ferromagnetism.We performed synchrotron x-ray diffraction studies to investigate the backbone structure of the CoO6 octahedra,and found that both the ferromagnetism and the elasticity are simultaneously enhanced when the in-plane Co–O–Co bond angles are straightened.Therefore the study demonstrates the inextricable correlation between the ferromagnetism and ferroelasticity mediated through the octahedral backbone structure,which may open up new possibilities to develop multifunctional materials.

Improved LS+MAR hybrid method to UT1-UTC ultra-short-term prediction by using first-order-difference UT1-UTC

Accurate ultra-short-term prediction of the Earth rotation parameters(ERP)holds paramount impor-tance for real-time applications,particularly in reference frame conversion.Among them,diurnal rota-tion(UT1-UTC)which cannot be directly estimated through Global Navigation Satellite System(GNSS)techniques,significantly affects the rapid and ultra-rapid orbit determination of GNsS satellites.Pres-ently,the traditional LS(least squares)+AR(autoregressive)and LS+MAR(multivariate autoregressive)hybrid methods stand as primary approaches for UT1-UTC ultra-short-term predictions(1-10 days).The LS+MAR hybrid method relies on the UT1-UTC and LOD(length of day)series.However,the correlation between LOD and first-order-difference UT1-UTC is stronger than that between LOD and UT1-UTC.In light of this,and with the aid of the first-order-difference UT1-UTC,we propose an enhanced LS+MAR hybrid method to UT1-UTC ultra-short-term prediction.By using the UT1-UTC and LOD data series of the IERS(International Earth Rotation and Reference Systems Service)EOP 14 C04 product,we conducted a thorough analysis and evaluation of the improved method's prediction performance compared to the traditional LS+AR and LS+MAR hybrid methods.According to the numerical results over more than 210 days,they demonstrate that,when considering the correlation information between the LoD and the first-order-difference UT1-UTC,the mean absolute errors(MAEs)of the improved LS+MAR hybrid method range from 21 to 934μs in 1-10 days predictions.In comparison to the traditional LS+AR hybrid method,the MAEs show a reduction of 7-53μs in 1-10 days predictions,with corresponding improvement percentages ranging from 1 to 28%.Similarly,when compared to the traditional LS+MAR hybrid method,the MAEs have a reduction of 5-42μs in 1-10 days predictions,with corresponding improvement percentages ranging from 4-20%.Additionally,when aided by GNSS-derived LOD data series,the MAEs of improved LS+MAR hybrid method experience further reduction.

Large-scale toppling slope under water level fluctuation of reservoir:A case of Yunnan Province,China

Landslides induced by reservoir inundation are common in Southwest China,negatively influencing hydropower stations.TheWunonglong hydropower station dam was constructed in the upper reaches of the Lancang River,accordingly causing the water level at the Lajinshengu slope to increase by 30 m.A tension crack with a visible depth of 8 m was observed in the upper sector of the Lajinshengu slope after reservoir impoundment for 170 d.In the following days,numerous cracks appeared on the surface of the slope,and the maximum displacement of the slope reached 3.22 m.Then,a large-scale active deformation body within the Lajinshengu slope formed with an area of 2.62×10^(5)m^(2)and a volume of 1.65×10^(7)m^(3).Detailed field investigations,on-site monitoring,and centrifugal model tests were carried out to analyze the surface features,deformation characteristics,and failure mechanism of the Lajinshengu slope.The results show that the slope is an ancient landslide,divided into two parts(i.e.zone A and zone B)by the gully.Zone B is a traction landslide caused by the displacement of zone A.The longterm inundation weakens the soft rock at the slope foot,intensifying the toppling of bedrock and consequently triggering the sliding of the overburden in zone A.The failure mode of the Lajinshengu slope is a typical case of toppling-sliding failure,and the underlying rock toppling drives the overlying sliding.In addition,early identification methods for toppling deformation covered by overburdened soil were proposed based on monitoring data and deformation signs.

Clinical Value of the Quantitative Flow Ratio to Predict Long-term Target Vessel Failure in Patients with In-stent Restenosis after Drug-coated Balloon Angioplasty

Objective The study sought to investigate the clinical predictive value of quantitative flow ratio(QFR)for the long-term target vessel failure(TVF)outcome in patients with in-stent restenosis(ISR)by using drug-coated balloon(DCB)treatment after a long-term follow-up.Methods This was a retrospective study.A total of 186 patients who underwent DCB angioplasty for ISR in two hospitals from March 2014 to September 2019 were enrolled.The QFR of the entire target vessel was measured offline.The primary endpoint was TVF,including target vessel-cardiac death(TV-CD),target vessel-myocardial infarction(TV-MI),and clinically driven-target vessel revascularization(CD-TVR).Results The follow-up time was 3.09±1.53 years,and 50 patients had TVF.The QFR immediately after percutaneous coronary intervention(PCI)was significantly lower in the TVF group than in the no-TVF group.Multivariable Cox regression analysis indicated that the QFR immediately after PCI was an excellent predictor for TVF after the long-term follow-up[hazard ratio(HR):5.15×10−5(6.13×10−8−0.043);P<0.01].Receiver-operating characteristic(ROC)curve analysis demonstrated that the optimal cut-off value of the QFR immediately after PCI for predicting the long-term TVF was 0.925(area under the curve:0.886,95%confidence interval:0.834–0.938;sensitivity:83.40%,specificity:88.00;P<0.01).In addition,QFR≤0.925 post-PCI was strongly correlated with the TVF,including TV-MI and CD-TVR(P<0.01).Conclusion The QFR immediately after PCI showed a high predictive value of TVF after a long-term follow-up in ISR patients who underwent DCB angioplasty.A lower QFR immediately after PCI was associated with a worse TVF outcome.

Effect of negative remodeling of the side branch ostium on the efficacy of a two-stent strategy for distal left main bifurcation lesions:an intravascular ultrasound study

OBJECTIVES To investigate whether negative remodeling(NR) detected by intravascular ultrasound(IVUS) of the side branch ostium(SBO) would affect in-stent neointimal hyperplasia(NIH) at the one-year follow-up and the clinical outcome of target lesion failure(TLF) at the long-term follow-up for patients with left main bifurcation(LMb) lesions treated with a two-stent strategy.METHODS A total of 328 patients with de novo true complex LMb lesions who underwent a 2-stent strategy of percutaneous coronary intervention(PCI) treatment guided by IVUS were enrolled in this study. We divided the study into two phases. Of all the patients, 48 patients who had complete IVUS detection pre-and post-PCI and at the 1-year follow-up were enrolled in phase Ⅰ analysis, which aimed to analyze the correlation between NR and in-stent NIH at SBO at the 1-year follow-up. If the correlation was confirmed, the cutoff value of the remodeling index(RI) for predicting NIH ≥ 50% was analyzed next. The phase Ⅱ analysis focused on the incidence of TLF as the primary endpoint at the 1-to 5-year follow-up for all 328 patients by grouping based on the cutoff value of RI.RESULTS In phase I: according to the results of a binary logistic regression analysis and receiver operating characteristic(ROC) analysis, the RI cutoff value predicting percent NIH ≥ 50% was 0.85 based on the ROC curve analysis, with a sensitivity of 85.7%, a specificity of 88.3%, and an AUC of 0.893(0.778, 1.000), P = 0.002. In phase Ⅱ: the TLR rate(35.8% vs. 5.3%, P < 0.0001)was significantly higher in the several NR(s NR, defined as RI ≤ 0.85) group than in the non-s NR group.CONCLUSION The NR of LCx O is associated with more in-stent NIH post-PCI for distal LMb lesions with a 2-stent strategy,and NR with RI ≤ 0.85 is linked to percent NIH area ≥ 50% at the 1-year follow-up and more TLF at the 5-year follow-up.

Mechanical responses of underground carriageway structures due to construction of metro tunnels beneath the existing structure:A case study

To understand the mechanical response pattern of the existing structure and ground due to the construction of metro tunnels underneath,the finite difference method is adopted to study the torsional deformation and stress variation of the existing structure and the effect of underground carriageway structures on the surface subsidence.The curves of the maximum differential subsidence,torsion angle,and distortion of the cross-section of the existing structure show two peaks in succession during traversing of two metro tunnels beneath it.The torsion angle of the existing structure changes when the two tunnels traverse beneath it in opposite directions.The first traversing of the shield tunnel mainly induces the magnitude variation in torsional deformation of the existing structure,but the second traversing of the subsurface tunnel may cause a dynamic change in the magnitude and form of torsional deformation in the existing structure.The shielding effect can reduce the surface subsidence caused by metro tunnel excavation to a certain extent,and the development trend of subsidence becomes slower as the excavation continues.

高校工科专业课程思政的实践探索与策略研究——以“流体力学与液压传动”课程为例

在深入分析工科专业课程思政建设存在问题的基础上,以沈阳建筑大学机械学院“流体力学与液压传动”课程为例,按照教育部《课程思政实施纲要》的要求,依据工科专业课程特点,提出“三结合、两融入、一联动”的课程思政实施原则,并构建“三师联动、网课融合”的协同育人模式,力求潜移默化地实现对学生的价值引领,以达到寓价值塑造于知识传授和能力培养之中的目的。

基于激光诱导击穿光谱的果木炭燃烧对空气成分影响的研究

果木炭是一种常见的燃料,其燃烧过程中产生的气体和烟尘气溶胶会影响环境空气质量并损害人体健康,因此对果木炭燃烧过程中空气成分进行检测与分析具有重要意义。采用激光诱导击穿光谱(LIBS)技术对果木炭燃烧时的空气、烟尘气溶胶进行检测,同时检测果木炭及其燃烧灰烬作为辅助分析。对四种样品的谱线进行标定,发现果木炭燃烧时空气中碳浓度增大,生成的气溶胶中含有Ca、Mg、K、Si等元素。果木炭和灰烬的元素组成较为相似,均含有C、Fe、Mg、Ca、Sr、K、Na和Ba等元素,果木炭光谱中C、H元素谱线强度均高于灰烬。此外,结合机器学习算法对有无果木炭燃烧时的空气进行区分,选取C、CN分子特征谱线所在的波段作为聚类分析的原始特征。主成分分析(PCA)结果表明在有无果木炭燃烧两种条件下的空气能被较好地区分,证明LIBS结合PCA技术能有效地识别果木炭的燃烧并检测果木炭燃烧造成的空气污染。进一步利用LIBS结合机器学习算法对果木炭及其燃烧灰烬进行区分,发现区分效果良好,为果木炭燃烧后的回收利用提供了参考。

多学科协同育人:高校工科专业课程思政建设实践探讨——以“机械设计基础”课程为例

以普通高等工科类院校专业基础课“机械设计基础”为例,分析课程思政建设面临的主要问题,提出“一中心、三统筹、五推进”的课程思政建设思路及多学科协同育人教学模式,从强化现代教育理念、优化人才培养方案、创新师资队伍建设、丰富课堂教学形式和完善课程考核方式等方面探讨课程思政建设的具体措施,并结合教学实例阐述多学科协同育人的实施过程和成效。

基于Citespace的课程思政研究发展态势分析

以CNKI数据库中1759篇课程思政相关文献为研究对象,基于文献计量方法和可视化工具,对课程思政领域的研究成果进行信息挖掘。研究发现:①发文量的波动表明课程思政研究具有一定的政策导向性特点。

Brain-derived neurotrophic factor, sex hormones and cognitive decline in male patients with schizophrenia receiving continuous antipsychotic therapy

BACKGROUND There are systematic differences in clinical features between women and men with schizophrenia(SCZ).The regulation of sex hormones may play a potential role in abnormal neurodevelopment in SCZ.Brain-derived neurotrophic factor(BDNF)and sex hormones have complex interacting actions that contribute to the etiology of SCZ.AIM To investigate the influence of BDNF and sex hormones on cognition and clinical symptomatology in chronic antipsychotic-treated male SCZ patients.METHODS The serum levels of follicle-stimulating hormone,luteinizing hormone(LH),estradiol(E2),progesterone,testosterone(T),prolactin(PRL)and BDNF were compared between chronic antipsychotic-treated male(CATM)patients with SCZ(n=120)and healthy controls(n=120).The Positive and Negative Syndrome Scale was used to quantify SCZ symptoms,while neuropsychological tests were used to assess cognition.Neuropsychological tests,such as the Digit Cancellation Test(DCT),Semantic Verbal Fluency(SVF),Spatial Span Test(SS),Paced Auditory Serial Addition Test(PASAT),Trail Making Task(TMT-A),and Block Design Test(BDT),were used to assess executive functions(BDT),attention(DCT,TMT-A),memory(SS,PASAT),and verbal proficiency(SVF).RESULTS Although E2 levels were significantly lower in the patient group compared to the healthy controls,T,PRL,and LH levels were all significantly higher.Additionally,the analysis revealed that across the entire sample,there were positive correlations between E2 Levels and BDNF levels as well as BDNF levels and the digital cancellation time.In CATM patients with SCZ,a significant correlation between the negative symptoms score and PRL levels was observed.CONCLUSION Sex hormones and BDNF levels may also be linked to cognitive function in patients with chronic SCZ.

特高压GIL故障定位超声衰减特性及试验研究

苏通气体绝缘金属封闭输电线路(gas-insulated transmissionline,GIL)综合管廊工程单相GIL长度接近5.8 km,在运行过程中一旦发生内部击穿将会对电网安全运行造成极大隐患,超声波原理故障定位方法可以快速和准确查找故障位置以便开展检修更换,难点在于超声波在特高压GIL上传输衰减特性及传感器的布置方法,其决定了故障定位的精度。为达到苏通工程故障定位到GIL气室的要求,研究了超声波在特高压GIL中衰减特性,开展了特高压GIL故障模拟试验和真型故障定位试验,获得了超声波经过特高压GIL直线单元、气隔盆子和伸缩节的衰减规律,得到了苏通工程GIL单个气室直线单元传感器布置方法,并对后续研究工作提供了一定建议。研究结果表明,超声波经GIL直线单元36 m传播后衰减约60%,经气隔盆子和伸缩节衰减约70%和89%,苏通工程单个气室布置2~3个超声波传感器即可达到故障定位到气室的精度要求。

特高压GIL壳体温升测试分析及工程运维措施建议

GIL壳体温升是反映GIL运行情况的重要指标,国家标准规定运行中的GIL壳体温度不能超过70℃。为验证实际带电环境中特高压GIL温升是否满足要求,本研究结合苏通工程特高压GIL的研制和带电考核情况,开展了实际环境条件下特高压GIL壳体温升带电测试,获得了严酷环境条件下GIL壳体最高温度及壳体温升长期随环境温度变化的规律,对比分析了型式试验和带电测试条件下温升差异的原因,提出了苏通工程GIL运维建议措施。研究结果表明,GIL壳体最高温度为65.58℃(环境温度36.15℃),苏通工程南北引接站安装区域部分GIL单元考虑反光材料应用可以减少太阳辐射引起的热量吸收作用,保障GIL安全可靠运行。

长皮膏治疗下肢静脉性溃疡的临床疗效评价

目的评价中药长皮膏治疗下肢静脉性溃疡的疗效。方法采用随机对照方法,将60例下肢静脉性溃疡患者分成两组,治疗组(n=30)采用长皮膏外敷,对照组(n=30)采用洗必泰油纱布外敷。通过创面愈合率、疼痛指数、创面形态、中医症候评分对两组患者下肢静脉性溃疡的疗效进行评价。结果治疗组的创面愈合率、疼痛指数、创面形态、中医症候评分及治疗后总评分均优于对照组,且具有统计学差异(P<0.05)。结论中药长皮膏外用治疗下肢静脉性溃疡有显著的临床疗效。

煤矿管道安装机器人机械臂机液联合仿真研究

针对煤矿管道安装机器人机械臂管道下放工作阶段的大臂、中臂和小臂液压缸爬行问题,利用AMESim和Simcenter 3D软件建立机液联合仿真模型,依据设定的仿真工况,利用仿真分析平衡回路液压缸产生爬行现象的原因。对平衡回路进行改进,改进后验证结果表明:合理选配各臂平衡阀先导阻尼直径、调压弹簧刚度和先导比可使抓管机械臂管道下放工作阶段基本消除爬行现象,进行较为平稳的工作。

特高压GIL伸缩节温度分布的测量与分析

温升特性是特高压GIL结构设计的重要一环,型式试验发现特高压GIL伸缩节的温度要明显高于其他单元位置,且呈现各方向、各部位温升不一致的情形,在阳光辐射条件下可能会超过标准要求,为保证苏通GIL综合管廊GIL安全可靠运行,开展了特高压GIL伸缩节温度分布的测量,对比分析了型式试验和现场运行条件下温升差异和分布不一致的原因,找到了伸缩节发热最高部位点,提出了相应运维措施建议,防止伸缩节局部温度超过标准要求,结果表明在苏通工程投运后能够对GIL安全可靠运行提供一定帮助。

食管癌微创McKeown术后胸腔胃和纵隔胃的形成对心肺并发症的影响

目的:探讨食管癌患者经微创McKeown术后胸腔胃和纵隔胃的形成对心肺并发症的影响及其机制。方法:采用回顾性队列研究方法,选取2017年12月至2020年9月郑州大学第一附属医院行微创McKeown手术的697例食管癌患者,根据术后复查胸部CT的影像资料,分为胸腔胃(管状胃部分或全部位于胸腔内)和纵隔胃(管状胃位于后纵隔食管床内)两组。通过对比分析两组的一般临床特征、手术相关变量及术后心肺并发症的发病率,探讨行微创McKeown术后两种管状胃位置的形成机制及其与心肺并发症的关系。结果:对比两组手术变量,纵隔胃组的胃切除面积方面大于胸腔胃组[(65.7±38.2)cm2 vs.(55.0±31.7)cm2,P<0.001],管状胃宽度[(3.3±0.7)cm vs.(4.1±1.1)cm,P<0.001]和胃胸比(管状胃宽度和胸腔宽度的比值)[(0.30±0.1)vs.(0.39±0.1),P<0.001]均为纵隔胃组小于胸腔胃组。对比两组术后并发症,肺不张(36.0%vs. 54.2%,P<0.001)、胸腔积液(40.7%vs. 53.8%,P=0.001)和心血管并发症(16.0%vs. 22.3%,P=0.042)的发病率纵隔胃组较胸腔胃组低,而气胸、皮下积气、呼吸衰竭、吻合口瘘及吻合口狭窄的发病率和一般临床特征两组间差异无统计学意义(P>0.05)。结论:行食管癌微创McKeown手术时,纵隔胃的形成可以降低肺不张、胸腔积液和心血管并发症的发病率,胃切除面积与两种管状胃的形成有关,当胃切除面积较大时更易形成纵隔胃。

大斑啄木鸟啄击运动观测及运动机理分析

目的研究啄木鸟的啄击运动机理,探究啄木鸟啄击树干时运动和力学特性.方法利用MATLAB将高速摄像机拍摄的啄木鸟啄击运动视频片段分解成图像序列,观测啄木鸟啄击运动并分析运动参数;根据啄木鸟啄击运动特点和骨骼系统特点建立啄木鸟连杆模型,并对啄木鸟啄击进行力学分析.结果啄木鸟最大啄击速度为4.056 m/s、冲击加速度为8112 m/s^2、啄击时胸椎和尾椎所受最大力矩分别为2.3 N·m和3 N·m.结论啄木鸟在产生大冲击时身体稳定且关节承受力矩较小,可将啄木鸟啄击运动机理应用在破碎锤的仿生设计中可使机构受力状态更加合理,从而降低材料性能要求,有利于降低成本延长使用寿命.