ANTIPLANE SHEAR FIELDS NEAR A CRACK-TIP IN A BRITTLE DAMAGED MATERIAL

In this paper,a simplified brittle damage model is proposed according to the Mazars-Lemaitre damage model for concrete.A closed-form solution for a mode Ⅲ crack is obtained based on the simplified model under small scale damage conditions,which allows for discontinuities of displacement-gradient and tangential stress on the damage boundary.It is pointed out that the discontinuities of field variables near the tip region exist for the brittle damaged material induced by the softening effect of the material.

Multi-dimensional and Multi-threshold Airframe Damage Region Division Method Based on Correlation Optimization

In order to obtain the image of airframe damage region and provide the input data for aircraft intelligent maintenance,a multi-dimensional and multi-threshold airframe damage region division method based on correlation optimization is proposed.On the basis of airframe damage feature analysis,the multi-dimensional feature entropy is defined to realize the full fusion of multiple feature information of the image,and the division method is extended to multi-threshold to refine the damage division and reduce the impact of the damage adjacent region’s morphological changes on the division.Through the correlation parameter optimization algorithm,the problem of low efficiency of multi-dimensional multi-threshold division method is solved.Finally,the proposed method is compared and verified by instances of airframe damage image.The results show that compared with the traditional threshold division method,the damage region divided by the proposed method is complete and accurate,and the boundary is clear and coherent,which can effectively reduce the interference of many factors such as uneven luminance,chromaticity deviation,dirt attachment,image compression,and so on.The correlation optimization algorithm has high efficiency and stable convergence,and can meet the requirements of aircraft intelligent maintenance.

Mitochondrial and nuclear damages and caspase-3 expression in the hippicampal CA3 region of rats with kainic acid induced statuse pilepticus

BACKGROUND: Some scholars believed that the neuronal injury after status epilepticus is apoptosis, the main evidence is the changes of expressions of various apoptosis related genes, such as immediate-early gene, p53 gene and genes of bcl-2 family, etc. But there is still no ultrastructural evidence for apoptosis. OBJECTIVE: To observe the ultrastructural damages of mitochondrion and nucleus and the changes of caspase expression in neurons of hippocampal CA3 region in rats with status epilepticus induced by kainic acid. DESIGN: A randomized controlled study. SETTING: Department of Anesthesiology and Department of Neurology, Qilu Hospital of Shandong University. MATERIALS: Seventy-five adult male Wistar rats of 250-300 g, clean degree, were provided by the experimental animal center of Shandong University. Kainic acid was purchased from Sigma Company (USA); rabbit anti-rat polyclonal antibody caspase-3 from Santa Cruz Company (USA). METHODS: The experiments were carried out in the Department of Anesthesiology, Qilu Hospital of Shandong University from October 2005 to February 2006. ① The 75 rats were randomly divided into experimental group (n =45) and control group (n =30). ② Model establishment, convulsion grading and the judging standards for status epilepticus: Rats in the experimental group were given intraperitoneal injection of kainic acid (10 mg/kg), and those in the control group were injected with saline of the same volume. The time of seizure was recorded and their behavioral manifestations were observed, and the seizure was terminated by intraperitoneal injection of diazepam (10 mg/kg). ③ Observation under electron microscope: At 3, 12 and 24 hours after status epilepticus respectively, bilateral hippocampal tissues were taken out, semithin sections of about 75 nm were prepared after fixation, dehydration and embedding, and then observed under H-800 transmission electron microscope. ④ Immunohistochemical detection: Bilateral hippocampi were removed at 3, 12 and 24 hours after status epilepticus respectively, the fixation, dehydration, transparence, wax immersion and embedding were performed, then serial sections of CA3 region were immunohistochemically determined by the SABC method. Leica QWinV3 image analytical software was applied, then the average number and average gray value of positive cells were calculated. MAIN OUTCOME MEASURES: Results of observation under electron microscope, that of immunohistochemical staining of neurons in hippocampal CA3 region; Comparison of number of caspase-3 positive cells and gray value. RESULTS: All the 75 Wistar rats were involved in the analysis of results. ① Results of observation under electron microscope: At 3 hours after status epilepticus, swelling crista and membranous disintegration were observed under electron microscope. At 24 hours, obvious nuclear changes occurred, and manifested as the side-aggegation of chromatins. ② Results of immunohistochemical detection: In the experimental group, the number of caspase-3 positive cells at 3 hours after status epilepticus had no obvious difference as compared with that in the control group (P > 0.05); At 12 hours, the number and gray value of caspase-3 positive cells in the experimental group were higher than those in the control group (10.49±0.68 vs. 5.33±0.43; 45.57±2.27 vs. 19.79±0.33, P < 0.05), the same results were also observed at 24 hours (37.36±0.57 vs. 5.12±0.47; 115.24±1.22 vs. 18.73±0.42, P < 0.01). CONCLUSION: In the rat models of status epilepticus induced by kainic acid, mitochondrial damage was earlier than the increase of caspase-3 expression and nuclear changes, which suggested that mitochondrion was the key link for the neuronal death after status epilepticus.

Damage Identification under Incomplete Mode Shape Data Using Optimization Technique Based on Generalized Flexibility Matrix

A generalized flexibility–based objective function utilized for structure damage identification is constructed for solving the constrained nonlinear least squares optimized problem. To begin with, the generalized flexibility matrix (GFM) proposed to solve the damage identification problem is recalled and a modal expansion method is introduced. Next, the objective function for iterative optimization process based on the GFM is formulated, and the Trust-Region algorithm is utilized to obtain the solution of the optimization problem for multiple damage cases. And then for computing the objective function gradient, the sensitivity analysis regarding design variables is derived. In addition, due to the spatial incompleteness, the influence of stiffness reduction and incomplete modal measurement data is discussed by means of two numerical examples with several damage cases. Finally, based on the computational results, it is evident that the presented approach provides good validity and reliability for the large and complicated engineering structures.

Automatic recognition of damaged town buildings caused by earthquake using remote sensing information: Taking the 2001 Bhuj, India, earthquake and the 1976 Tangshan, China, earthquake as examples

In the high-resolution images, the undamaged buildings generally show a natural textural feature, while the dam- aged or semi-damaged buildings always exhibit some low-grayscale blocks because of their coarsely damaged sections. If we use a proper threshold to classify the grayscale of image, some independent holes will appear in the damaged regions. By using such statistical information as the number of holes in every region, or the ratio between the area of holes and that of the region, etc, the damaged buildings can be separated from the undamaged, thus automatic detection of damaged buildings can be realized. Based on these characteristics, a new method to auto- matically detect the damage buildings by using regional structure and statistical information of texture is presented in the paper. In order to test its validity, 1-m-resolution iKonos merged image of the 2001 Bhuj earthquake and grayscale aerial photos of the 1976 Tangshan earthquake are selected as two examples to automatically detect the damaged buildings. Satisfied results are obtained.

Extended damage range of(Al0.3Cr0.2Fe0.2Ni0.3)3O4 high entropy oxide films induced by surface irradiation

Irradiation makes structural materials of nuclear reactors degraded and failed.However,the damage process of materials induced by irradiation is not fully elucidated,mostly because the charged particles only bombarded the surface of the materials(within a few microns).In this work,we investigated the effects of surface irradiation on the indirect irradiation region of the(Al0.3Cr0.2Fe0.2Ni0.3)3O4 high entropy oxide(HEO)films in detail by plasma surface interaction.The results show that the damage induced by surface irradiation significantly extends to the indirect irradiation region of HEO film where the helium bubbles,dislocations,phase transformation,and the nickel oxide segregation were observed.

土石坝护坡冻胀破坏水-热-力耦合数值模拟研究

针对寒区土石坝护坡普遍存在的冻胀破坏问题,选取寒区某土石坝工程为研究对象,结合土石坝工程特点,建立考虑水-热-力耦合作用的有限元计算模型。研究护坡在库水位和坝体填土水分迁移作用下冻胀破坏全过程,分析土石坝温度场、水分场和位移场的变化规律,并将位移场有限元计算结果与实测冻胀变形资料进行对比,验证有限元计算结果。研究结果表明:冻胀作用对坝坡影响深度约为2 m,坝坡浅层0~2 m范围的温度变化受外界气温影响较大,坝体内部温度相对坝坡浅层变幅小,且有一定的滞后性;负温使坝坡浅层孔隙水相变成冰,宏观上表现为未冻水体积分数的降低,坝坡浅层土石混合体孔隙水相变、坝体填土内水分向坝坡迁移和冻结峰面向坝体内部移动是护坡冻胀破坏的主要因素;大坝坝坡计算冻胀量为20~30 cm,最大值为36 cm,计算结果与实测冻胀变形资料吻合;护坡冻胀破坏主要由砂砾料垫层、坝体填土等土石混合体冻胀及冰推力共同作用引起。研究结果可为寒区土石坝护坡设计提供参考。

江南华南茶树高温热害等级指标及分布特征

利用1961—2022年江南和华南茶区510个气象站的日最高气温数据和历史茶树高温热害灾情数据,采用灾情反演和K-Means聚类分析方法,构建并验证江南和华南茶区茶树高温热害等级指标,分析茶树高温热害时空分布特征。结果表明:江南和华南茶区茶树轻度、中度、重度高温热害指标为连续14 d日最高气温的滑动平均值T14≥34.5℃的持续日数分别为1~17 d、18~38 d和超过38 d,验证样本完全符合的准确率为73.9%,基本符合的准确率为91.3%;江南和华南茶区茶树高温热害总次数呈波动变化,分别在1999年和1997年达到最低值,并在2021年达到最高值;华南茶区相对于江南茶区高温热害次数更多,尤其是轻度茶树高温热害,且近62年华南茶区茶树高温热害次数增加趋势显著。

高寒地区早期受冻水泥混凝土力学性能及抗冻耐久性

针对高寒地区新浇筑混凝土易受冻害,导致的路面结构安全隐患和后期服役寿命受限等问题,文中选取西藏地区实际施工材料分别拌制了C30、C40及C45三组水泥混凝土试件,试件在标准养护室养护0,3,7,28 d后移置室外继续养护150 d,研究抗压强度、抗折强度及动弹性模量变化规律,并且对自然养护150 d的试件进行300次冻融循环试验。研究结果表明:当认为标准养护龄期为28 d的混凝土无受冻状态时,标准养护龄期的增加能有效提升混凝土服役初期的抗冻能力,混凝土的受冻率随着养护龄期的增加依次降低;通过掺加粉煤灰和防冻剂,自然养护150 d的混凝土可经受275~300次冻融循环,冻融循环250次后,混凝土内部产生明显的大孔隙及裂隙,试件抗冻指标快速下降;通过建立的冻融损伤度转化公式,可快速对高寒地区不同服役年限的混凝土建筑物进行力学性能预测,进而为运行期建筑物安全性评价提供理论支撑。

两点串联装药爆炸区域增效效果分析

针对串联装药爆炸区域内出现区域增效现象,利用LS-DYNA有限元软件建立了两点装药爆炸的计算模型,针对不同装药间距、不同装药质量条件下两点装药爆炸冲击波的传播过程和相互作用进行了模拟研究,并对数值模拟结果的超压、冲量衰减规律进行了试验验证。分析了两点装药入射冲击波和反射冲击波超压值的相对大小,将冲击波有效作用区内的增效效果区划分成增效明显区、增效过渡区和增效不显区。分析了不同毁伤阈值条件下装药质量、装药间距对冲击波有效作用区区域面积的影响,确定了不同毁伤阈值下的最佳装药间距,得到了装药质量、最佳装药间距与毁伤阈值之间的关系。结果表明:在增效明显区内两点装药爆炸产生的入射波相互作用形成强反射波,强反射波与入射波叠加,超压显著提高,表现为两点装药反射波超压峰值整体高于单点装药入射波的超压峰值;在不同毁伤阈值条件下,随装药间距增加,有效作用区域面积会呈现先增后减的变化趋势,在明确装药质量、毁伤阈值的条件下,存在一个最佳装药间距对应着最大有效作用区域面积;获得了不同毁伤阈值的最佳装药间距工程计算模型,毁伤阈值和最佳装药间距与装药质量立方根的比值呈现多项式函数关系。

高海拔严寒地区隧道冻害研究现状及展望

针对高海拔严寒地区隧道冻害问题,结合隧道冻害的相关研究,从冻害类型及原因分析、冻害机制、温度场、处置措施等4个方面的现状进行阐述和分析,对当前研究存在的不足和未来的发展方向进行探讨。主要成果为:1)通过对高海拔严寒地区隧道工程实例进行分析,总结4种冻害类型及4种冻害原因;2)基于含水风化层冻胀理论、整体性围岩冻胀理论、衬砌背后积水冻胀理论、裂隙水冻胀理论等4种冻胀理论,建立多年冻土区以整体性围岩冻胀理论为主、季冻区以裂隙水冻胀理论为主的多理论联合分析的方法;3)温度场研究方法分为现场监测、理论解析、模型试验、数值模拟等4种,其中现场监测是对洞内外温度进行监测,而理论分析、模型试验、数值模拟则是对监测结果进行验证分析;4)冻害处置措施有防排水措施、保温防寒措施、抗冻措施等3种,防冻的关键是将三者相结合进行综合治理;5)指出冻害机制适用性、温度场研究方法现状、处置措施适用性等方面的不足,未来应在高海拔严寒地区建立多种冻胀理论、多种研究方法综合应用的研究体系,并在隧道防排水、保温防寒、抗冻等方面给出处置措施。

断裂破坏区域性泥岩盖层程度研究方法的改进

为了更加准确地研究断裂破坏区域性泥岩盖层程度,基于断裂破坏区域性泥岩盖层机理及程度的影响因素,通过断层岩和区域性泥岩盖层压实成岩程度代替其排替压力,改进了断裂破坏区域性泥岩盖层程度的研究方法,并将改进前后方法分别应用于研究海拉尔盆地贝尔凹陷呼和诺仁构造F1断裂破坏大一下段区域性泥岩盖层程度。结果表明:改进前后方法研究均得到测点9处F1断裂破坏大一下段区域性泥岩盖层程度最大,测点13处最小,其余测点介于二者之间,在测点1~8和12~15处有利于南一段源岩生成油气在大一下段区域性泥岩盖层之下南二段聚集与保存,但测点1~6无油气发现,是由于其构造位置低,油气供给不足,未充满所致,与目前F1断裂处南二段已发现油气分布相吻合。改进前方法研究成果虽与改进后方法研究成果具有相同的变化规律,但其值相对较大,低估了F1断裂破坏大一下段区域性泥岩盖层程度,表明改进后方法研究结果可能更符合地下实际,而且方便易行。

检察环境公益诉讼实践现存问题及其对策——以S省D县检察院为样本

《民事诉讼法》和《行政诉讼法》的出台建立了我国现行的检察环境公益诉讼制度。以S省D县检察院开展的检察环境公益诉讼为出发点,从微观角度分析其在司法实践中存在的证据线索获取困难、诉讼管辖混乱、环境污染造成的损失难以确定、惩罚性赔偿金难以管理等问题。为解决这些问题,更好建设检察环境公益诉讼制度,未来应当加强检察院与行政机关、公民的联动衔接,多途径收集线索;探索建立检察院内部跨区域合作机制,减少在异地管辖、集中管辖背景下程序衔接不畅的问题;引入专业组织和专家辅助人对环境污染定损,并提供相应修复建议;明晰公益诉讼案涉赔偿金的使用和管理制度,由省级以上检察院建立环境损害赔偿基金会。

基于区域特征的图像配准方法

针对毁伤前与毁伤后图像因拍摄时间、角度不同和毁伤导致图像变化剧烈,造成图像无法配准的问题,提出一种基于区域特征的图像配准方法。该方法通过提取建筑物区域的形状特征和空间关系特征,构建建筑物区域的特征描述符,利用特征描述符的相似性完成图像配准。为了使特征描述符具有平移不变性、旋转不变性和尺度不变性,将描述区域与其他区域的中心距离、中心连线与长轴夹角的范围区间均匀分割,利用分割区间的索引构建二元组,通过计算满足二元组对应距离和夹角范围的建筑物区域与描述区域的面积比值作为特征描述符的元素。实验结果表明,与现有方法相比,该方法能完成毁伤前与毁伤后图像的配准,匹配率高,具有较好的鲁棒性。

寒区隧道内气温分布特征及影响因素

受严寒气候影响,寒冷地区的隧道工程普遍面临不同程度的衬砌挂冰、冻融损伤甚至开裂、路面结冰、排水系统冻结失效等一系列冻害问题,给隧道工程的建设和运营带来了极大的挑战。负温环境是隧道冻害产生的必要条件,掌握隧道内气温沿进深方向的分布是寒区隧道冻害研究和工程防治措施采取的基础和前提。然而,不同寒区隧道工程的隧址区环境气象、工程结构和交通情况等因素各不相同,导致不同隧道内气温的分布特征存在显著差异。因此,准确地预测和获取寒区隧道内气温纵向分布仍是亟待解决的问题。为得到寒区隧道内气温分布特征及其影响因素,本文采用文献调研和数据统计与分析的方法,收集整理了我国52座寒区隧道内气温的现场监测数据以及相关影响因素数据。依据寒区隧道内气温分布特征,将其划分为对称型、非对称型和贯通型三类,并对各类型寒区隧道的长度和埋深情况进行了统计分析。在此基础上,探讨了隧址区气温和隧道围岩地热以及洞内通风对隧道内气温分布的影响机制,之后针对引起隧道内空气流动的自然风、工程建设、机械通风和交通情况四类因素进行了分析,并指出各类因素的主次影响顺序。研究表明,当隧道两端洞口自然环境要素基本相同且两端洞口高差不大时,隧道内气温往往呈对称型分布;当隧道内存在较大纵坡坡度或受洞外盛行风向影响时,隧道内气温多呈非对称型分布;而当隧道长度较短、埋深小且盛行单向风时,隧道内气温分布常为贯通型。隧址区(隧道进出口)环境气温对隧道内气温分布起决定性作用,隧道埋深状况决定了地热作用从而对洞内气温产生重要影响。通风是影响隧道内气温的关键因素,其中自然风、工程中纵坡设计因素分别为进出口高差较小、长度较短的隧道和进出口高差较大、长度较长的隧道内气温分布的主导因素,工程附属结构、机械通风、交通情况为相对次要因素。本研究工作可为寒区隧道冻害问题研究和保温设防设计以及运营维护提供参考。

寒区铁路隧道防寒抗冻关键技术研究与展望

寒区铁路隧道冻害问题不仅威胁到隧道结构的稳定,同时给铁路安全运营带来巨大的安全隐患,其一直是寒区隧道工程的难点和研究热点,工程界迫切需要可靠、高效的防寒抗冻工程技术措施。首先,调研了我国寒区铁路隧道的建设及运营情况,总结分析了常见的隧道冻害现象,包括衬砌开裂掉块、拱顶挂冰、道床积冰、排水系统冻结等。然后,针对当前寒区隧道缺乏隧道温度场时空分布预测方法、隧道冻害机制和演化规律不清晰、防寒抗冻设计方法与治理技术不成熟这3个技术难点,对已取得的研究成果进行总结和讨论,相关成果如下:1)研发了寒区隧道室内试验系统,结合大量的温度场相关实测数据,探明了温度场时空分布规律,建立了温度场预测方法;2)研发了渗流试验设备,揭示了冻害产生的链发式机制,查明了排水系统冻结规律与冻融响应机制;3)建立了寒区铁路隧道抗冻防寒设计标准,形成了隧道冻害综合防控体系。最后,展望了我国寒区铁路隧道防寒抗冻研究在防寒保温材料、主动保温系统、温度场规律预测等方面进一步深化研究的方向。

基于群组决策的寒区隧道冻害风险评价研究

研究目的:为客观有效评估隧道冻害程度,基于群组决策和三角模糊数法构建寒区隧道冻害风险评价模型。首先,采用更有利于专家表达的三角模糊数建立判断矩阵,利用相容度指标确定专家判断水平,从而赋予相应权重;其次,综合考虑引起寒区隧道冻害的温度、水文、围岩条件和工程措施等因素,形成二级评价指标,通过三角模糊数群组决策模型确定各指标权重;再次,将二级评价指标分为10个定量指标和6个定性指标,定量指标按梯形分布建立隶属度函数,定性指标由专家按百分制打分,再按梯形分布函数确定各等级隶属度;最后,通过模糊综合评价方法计算确定隧道冻害等级,并提供相应的预防措施。研究结论:(1)选取温度、水文、围岩条件和工程措施4个一级指标、16个二级指标,设置4个冻害等级,构建了基于三角模糊数的群组决策寒区隧道冻害风险综合评价体系;(2)本文提出的冻害风险评价模型应用于杀虎口隧道,风险等级评价结果与隧道实际冻害一致,验证了模型的合理性;(3)本文模型更加客观全面,可为隧道冻害风险提供安全预警和防控建议。

2023年4月28—29日冻害对陇东苹果花期的影响分析

本研究以2023年4月28—29日陇东地区发生的苹果严重冻害事件为案例,旨在通过分析气象数据和苹果发育期资料,探讨不同品种和种植地域的苹果对低温冻害的敏感性及其影响因素。研究选取了庆城、合水、西峰、宁县、正宁、镇原、平凉等地区的国家级气象站1971—2023年的气温观测资料及1994—2023年西峰农业气象试验站的苹果发育期资料,采用统计学方法分析了不同品种、不同种植地域最低温度、低温持续时间与苹果花蕊受冻级别的相关性。结果表明,冻害对陇东苹果早熟品种嘎啦系、蜜脆、粉红女士,晚熟品种瑞阳、瑞雪、瑞香红等影响较小;对中熟品种富士系影响较大;苹果种植地域山地、平原较川地、塬畔严重;陇东苹果由于气候变暖原因花期提前,当温度降低到-2℃以下时,冻害程度会随着温度的降低和持续时间的增加而加重。在苹果花期,低温是影响冻害的主导因素,而最低温度和低温持续时间则是决定冻害程度的关键指标。如果温度持续低于苹果花期的耐受极限,那么冻害的发生和严重程度将随着低温的持续时间延长而增加,并通过实际灾情验证。本研究的结论对于优化苹果种植策略、改良品种选择、提高果业产值及振兴乡村经济具有重要意义。

广西双季早稻高温热害精细化风险评估与区划研究

基于灾害风险分析原理,利用广西89个国家级气象站1970─2020年气象观测数据和广西各主产市(县)早稻种植面积、产量资料,以及相关地理信息数据等,从灾害致灾因子危险性、承灾体暴露度、承灾体脆弱性以及防灾减灾能力等方面筛选风险评估指标,采用灾害风险指数法、层次分析法等技术方法构建了广西双季早稻高温热害的风险评估模型,并利用GIS技术对广西早稻高温热害进行了风险评估分析和精细化风险区划。结果表明:广西早稻高温热害的综合风险高值区主要位于左江河谷、右江河谷区域和桂中盆地等;低风险区主要分布在桂西北和桂北山区。本研究结果可为广西早稻生产趋利避害、优化布局、防灾减灾提供决策参考。

高地震烈度寒区钢-混凝土组合梁桥抗震韧性评价

综合考虑桥梁系统灾变全过程,提出了一种适用于高地震烈度寒区的钢-混凝土组合梁桥抗震韧性评价方法。基于现有统计数据,综合考虑桩基沉降损伤、疲劳损伤以及冻融损伤,建立了高地震烈度寒区钢-混凝土组合梁桥震前功能损失函数;将地震易损性分析与桥梁抗震韧性评价相结合,建立了桥梁系统震后恢复函数;提出了震前临界维修加固年限和临时保通状态。结果表明:在高地震烈度冻土区的钢-混凝土组合梁桥系统的临界维修加固年限随地震动峰值加速度的增大而减小,当地震动峰值加速度分别为0.10g、0.15g、0.20g、0.30g时,桥梁系统的临界维修加固年限预计分别为27年、24年、19年、8年;当桥位在Ⅸ度及以上设防区时,必须在桥梁方案设计中考虑增设减隔震装置;桥梁系统的恢复时间随地震动峰值加速度的增大而增大,韧性指标随地震动峰值加速度的增大而减小;桥梁在运营20年后发生地震作用时,地震动峰值加速度为0.10g和0.15g的地震动预计不会影响桥梁通行,地震动峰值加速度为0.20g~0.40g的地震动需要进行维修加固实现临时保通,预计恢复时间为1~42天,韧性指标为0.647~0.578,恢复至临时保通状态的韧性指标最大值为0.650。