Evolution characteristics of Quaternary tectonic stress field in the north and east margin of Qinghai-Xizang plateau

By inversion of fault slip data for Quaternary tectonic stress field and the analysis of crustal deformation after lateTeriary. we explaincd the evolution of crustal dynamic about the north and east margin of Qinghai-Xizang (Tibet)plateau since Miocenc. From middle or late Miocene to early Pleistocene, the tectonic stress field was featured by amaximum principal compression which was coming from the collision of india Plate continued to the boundaryof the plateau. and was basically of reverse faulting type. Since the late period of early Pleistocene, Pleistocene continuedto push northward and the compressional deformation of the plateau interior increased continuously, meanwhile,N W-SE extension appeared on the east side of the plateau. This formed a favorable condition for the interior block offoe plateau to slide towards east and southeast, causing the faults surrounding the plateau to change from thrust tostrike-slip. -The contemporary tectonic stress field was formed from the late period of early Pleistocene and continuedto present. The direction of maximum principal compressional stress rotated clockwise with respect to the previoustectonic stress held. the stress field was mainly of strike-slip type.

Evolution of cumulative Coulomb failure stress in northeastern Qinghai-Xizang (Tibetan) Plateau and its effect on large earthquake occurrence

We simulate accumulative Coulomb failure stress change in a layered Maxwell viscoelastic media in the northeastern Qinghai-Xizang （Tibetan） Plateau since 1920. Lithospheric stress/strain evolution is assumed to be driven by dislocations of large earthquakes （M≥7.0） and secular tectonic loading. The earthquake rupture parameters such as the fault rupture length, width, and slip are either adopted from field investigations or estimated from their statistic relationships with the earthquake magnitudes and seismic moments. Our study shows that among 20 large earthquakes （M≥7.0） investigated, 17 occurred in areas where the Coulomb failure stress change is positive, with a triggering rate of 85%. This study provides essential data for the intermediate to long-term likelihood estimation of large earthquakes in the northeastern Tibetan Plateau.

Effects of Low Temperature Stress on Seedling Growth of Plateau Japonica Rice

[ Objective ] The study aimed to screen rational seedling raising date and seedling raising mode for plateau japonica rice, in order to reduce the effect of low temperature on seedlings. [ Method ] The seedlings of conventional japonica rice Hexi 22-2 and giant embryo No. 1 japonica rice were treated at day tempera- ture 12℃/night temperature 8℃ and day temperature 14 ℃/night temperature 10 ℃, and the indicators including chlorophyll content, soluble sugar content, sol- uble protein content, survival rate, plant height, number of ≥ 1 cm roots, leaf wilting degree and aboveground dry matter weight were determined after treated for 0, 3 and 6 d, respectively. [ Result] Chlorophyll content of seedlings decreased when treated by low temperature for a certain period; with the prolongation of treat- ment time, contents of soluble sugar and soluble protein in some low temperature treatments increased, while plant height, number of ≥ 1 cm roots and aboveground dry matter weight increased slowly, but the growth rate was significantly lower than that at room temperature; with the decrease of temperature and the prolongation of treatment time, leaf wilting degree increased. The comprehensive experimental results showed that with the increasing duration of low temperature, when two japonica rice varieties grew under the same low temperature, seedlings grew more and more slowly, probably because the lower the treatment temperature, the greater the damage on plants. Giant Embryo No. 1 had weaker cold tolerance than Hexi 22-2. [ Conclusion] The study provides a theoretical basis for formula- tion of seedling raising technique of plateau japonica rice.

Medial tibial plateau morphology and stress fracture location:A magnetic resonance imaging study

AIM To determine the location of medial tibial plateau stress fractures and its relationship with tibial plateau morphology using magnetic resonance imaging(MRI).METHODS A retrospective review of patients with a diagnosis of stress fracture of the medial tibial plateau was performed for a 5-year period. Fourteen patients [three female and 11 male, with an average age of 36.4 years(range, 15-50 years)], who underwent knee MRI, were included. The appearance of the tibial plateau stress fracture and the geometry of the tibial plateau were reviewed and measured on MRI.RESULTS Thirteen of 14 stress fractures were linear, and one of them stellated on MRI images. The location of fractures was classified into three types. Three fractures were located anteromedially(AM type), six posteromedially(PM type), and five posteriorly(P type) at the medial tibial plateau. In addition, tibial posterior slope at the medial tibial plateau tended to be larger when the fracture was located more posteriorly on MRI.CONCLUSION We found that MRI showed three different localizations of medial tibial plateau stress fractures, which were associated with tibial posterior slope at the medial tibial plateau.

DYNAMIC SIMULATION OF STRESS AND DISPLACEMENT FIELDS FOR TSINGHAI-TIBET PLATEAU LITHOSPHERE

Tsinghai-Tibet Plateau becomes an important research topic ofglobal tectonics, because of its marvelous thickness and rapiduplifting since Quaternary. By using finite element method, thenumerical simulation is carried out for the movement of structurallithosphere. The deformable elements are employed to simulatestructural zones, and the frictional mechanism is introduced toillustrate the characteristic of a zone with a contact crack surface.The boundary conditions are prescribed by the displacements aroundthe pla- teau.

Physiological responses of artificial moss biocrusts to dehydration-rehydration process and heat stress on the Loess Plateau, China

Ex-situ cultivation of biological soil crusts （biocrusts） is a promising technology to produce materials that can induce the recovery of biocrusts in the field for the purposes of preventing soil erosion and improving hydrological function in degraded ecosystems. However, the ability of artificially cultivated biocrusts to survive under adverse field conditions, including drought and heat stresses, is still relatively unknown. Mosses can bolster biocrust resistance to the stresses （e.g., drought and heat） and the resistance may be introduced prior to field cultivation. In this study, we subjected the well-developed artificial moss biocrusts （dominant species of Didjmodon vinealis （Brid.） Zand.） that we cultivated in the phytotron to a dehydration-rehydration experiment and also a heat stress experiment and measured the activities of protective enzymes （including peroxidase （POD）, superoxide dismutase （SOD）, and catalase （CAT）） and the contents of osmoregulatory substances （including soluble proteins and soluble sugars） and malondialdehyde （MDA, an indicator of oxidative stress） in the stem and leaf fragments of mosses. The results showed that, during the dehydration process, the activities of protective enzymes and the contents of osmoregulatory substances and MDA gradually increased with increasing duration of drought stress （over 13 days）. During the rehydration process, values of these parameters decreased rapidly after 1 d of rehydration. The values then showed a gradual decrease for 5 days, approaching to the control levels. Under heat stress （45℃）, the activities of protective enzymes and the content of soluble proteins increased rapidly within 2 h of heat exposure and then decreased gradually with increasing duration of heat exposure. In contrast, the contents of soluble sugars and MDA always increased gradually with increasing duration of heat exposure. This study indicates that artificial moss biocrusts possess a strong drought resistance and this resistance can be enhanced after a gradual dehydration treatment. This study also indicates that artificial moss biocrusts can only resist short-term heat stress （not long-term heat stress）. These findings suggest that short-term heat stress or prolonged drought stress could be used to elevate the resistance of artificial moss biocrusts to adverse conditions prior to field reintroduction.

Evolution of the Late Cenozoic Tectonic Stress Regime in the Tianshui Basin,Northeast Tibetan Plateau

The Tianshui Basin,located inside the western Qinling orogenic belt and northeastern margin of the Tibetan Plateau （Fig.1）,is a NE-trending Late Cenozoic basin,which documents the neotectonic response of the northeastward growth of Tibetan Plateau.

Stress rise precursor to earthquakes in the Tibetan Plateau

Earthquake prediction thus far has proven to be a very difficult task, but changes in situ stress appear to offer a viable approach for forecasting large earthquakes in Tibet and perhaps other continental regions. High stress anomalies formed along active faults before large earthquakes and disappeared soon after the earthquakes occurred in the Tibetan Plateau. Principle stress increased up to ~2 -?5 times higher than background stress to form high stress anomalies along causative faults before the Ms 8.1 West Kunlun Pass earthquake in November 2001, Ms 8.0 Wenchuan earthquake in May 2008, Ms 6.6 Nimu earthquake in October 2009, Ms 7.1 Yushu earthquake in April 2010 and the Ms 7.0 Lushan earthquake in April 2013. Stress near the epicenters rapidly increased 0.10 - 0.12 MPa over 45 days, ~8 months before the Ms 6.6 Nimu earthquake occurred. The high principle stress anomalies decreased quickly to the normal stress state in ~8 -?12 months after the Ms 8.1 West Kunlun Pass and the Ms 8.0 Wenchuan earthquakes. These high stress anomalies and their demise appear directly related to the immediate stress rise along a fault prior to the earthquakes and the release during the event. Thus, the stress rise appears to be a viable precursor in prediction of large continental earthquakes as in the Tibetan Plateau.

Active Faulting Pattern,Present-day Tectonic Stress Field and Block Kinematics in the East Tibetan Plateau

This paper examines major active faults and the present-day tectonic stress field in the East Tibetan Plateau by integrating available data from published literature and proposes a block kinematics model of the region. It shows that the East Tibetan Plateau is dominated by strike-slip and reverse faulting stress regimes and that the maximum horizontal stress is roughly consistent with the contemporary velocity field, except for the west Qinling range where it parallels the striking of the major strike-slip faults. Active tectonics in the East Tibetan Plateau is characterized by three faulting systems. The left-slip Kunlun-Qinling faulting system combines the east Kunlun fault zone, sinistral oblique reverse faults along the Minshan range and two major NEE-striking faults cutting the west Qinling range, which accommodates eastward motion, at 10--14 mm/a, of the Chuan-Qing block. The left-slip Xianshuihe faulting system accommodated clockwise rotation of the Chuan-Dian block. The Longmenshan thrust faulting system forms the eastern margin of the East Tibetan Plateau and has been propagated to the SW of the Sichuan basin. Crustal shortening across the Longmenshan range seems low （2-4 mm/a） and absorbed only a small part of the eastward motion of the Chuan-Qing block. Most of this eastward motion has been transmitted to South China, which is moving SEE-ward at 7-9 mm/a. It is suggested from geophysical data interpretation that the crust and lithosphere of the East Tibetan Plateau is considerably thickened and theologically layered. The upper crust seems to be decoupled from the lower crust through a decollement zone at a depth of 15-20 kin, which involved the Longmenshan fault belt and propagated eastward to the SW of the Sichuan basin. The Wenchuan earthquake was just formed at the bifurcated point of this decollement system. A rheological boundary should exist beneath the Longmenshan fault belt where the lower crust of the East Tibetan Plateau and the lithospheric mantle of the Yangze block are juxtaposed.

STRESS FIELD ALONG THE REVOLUTION AXIS AND THE FORMATION OF QINGHAI—TIBET PLATEAU

Based on the discovery of the SSW stress field of the Earth and Mars, the authors proposed that each of the celestial bodies in the Solar System possesses a consistent stress field along the revolution axis relative to their own obliquity of the ecliptic ( ε ).This paper describes a deep going study on the control role of the stress field on the formation of the Tibet plateau.1\ Discovery of the stress filed along the revolution axis of the Earth and Mars (1)Discovery of the four tridimensional tectonic systems in the global SSW stress field [1] :In West China, under the action of this stress field, the alternative WNW\|trending belts of fault uplifts and fault depressions intersect the alternative belts of ENE\|trending sinistral and NNW\|trending dextral conjugate shear\|compressive uplifts and depressions,and then combine with the NNE\|trending tensile fault belt, to form the “uplift on uplift" ,the “third\|order overlapped uplift" ,the“depression in depression” ,the “third\|order sunk depression", and also the composite fault uplifts and fault depressions composed of four or more fault groups. They are produced simultaneously and form the rivers, lakes, basins, mountains and plateaus and show the mirror symmetry in section. This tectonic framework can be observed not only in the Qinghai—Tibet plateau but also in all over China and even on the entire Earth. Therefore, the SSW principal compressive stress is the unified global stress field and its model has already been constructed [1] .

Deep Mechanical Background for the Cenozoic Volcanism in the Tibetan Plateau

The principle prerequisite for the formation of a volcano is the generation of a channel for magma transportation. There is little research on the deep mechanical mechanism for the formation of a magma transportation channel in the Tibetan plateau. Based on the subcrustal mantle convectiongenerated stress field inversed by gravity anomalies, together with its relationship to the Cenozoic volcanism in the plateau, and the mechanism of crustal fracture formation, as well as the numerical results of the evolution of mantle convection beneath the plateau, this paper investigates the deep mechanical mechanism for the formation of a magma transportation channel in the Tibetan plateau. There are two significant extensional convection-generated stress zones beneath the plateau, in which the volcanic rocks in the central and northern parts of the plateau are distributed. The Linzizong volcanism in southern Tibet correlates the upwelling mantle flow prior to the India-Asia collision or during the early stage of the collision. The magnitude of the stress is - 100 MPa, which is the same order of force that causes crustal fractures. The evidence implies that the mantle convection-generated stress is one of the principle causes of crustal fractures, and furthermore, the formation of the magma transportation channel in the Tibetan plateau.

知觉压力对常驻高原军人睡眠质量的影响:职业紧张的调节作用

目的探讨常驻高原军人睡眠质量特点,以及知觉压力、职业紧张等因素对其影响。方法本研究采用横断面研究设计方案。于2023年2月,应用自编的人口学资料调查表、匹兹堡睡眠质量指数量表(Pittsburgh sleep quality index,PSQI)、知觉压力量表(perceived stress scale,PSS-10)、工作内容问卷(job content questionnaire,JCQ),对整群抽取的常驻我国高原某部的3784名高原军人进行测查。结果常驻高原军人PSQI总分为(5.37±2.78)分,PSQI总分及各维度得分均显著高于我国平原常模(P<0.001)。不同年龄、军龄、民族、驻守高原时长、文化程度、家庭结构的常驻高原军人PSQI得分差异具有统计学意义(P<0.001)。低知觉压力组常驻高原军人的PSQI得分显著低于高知觉压力组(t=-12.108,P<0.001)。调节效应分析显示,驻守高原时长、工作自主、工作心理要求、工作环境中的社会支持能调节知觉压力与睡眠质量间的关系(t值分别为8.326、-3.788、-2.145、-6.656,P<0.05),分别解释睡眠质量变异率的14.6%、7.6%、7.0%和7.9%。结论常驻高原军人睡眠质量较差。年龄、军龄、驻守高原时长、民族、家庭结构、文化程度、知觉压力、职业紧张是常驻高原军人睡眠质量的重要影响因素。驻守高原时长、职业紧张能调节常驻高原军人睡眠质量与知觉压力的关系。

米字形填充正方形蜂窝异面平台应力

目的研究冲击速度和结构参数对米字形填充正方形蜂窝异面平台应力的影响规律。方法利用ANSYS/LS-DYNA建立该蜂窝可靠的基于胞元阵列的异面冲击分析有限元模型;基于简化的超折叠单元理论推导该蜂窝的准静态平台应力理论公式,理论值与仿真值相吻合验证理论公式的正确性。对不同壁厚边长比的蜂窝,在不同冲击速度下进行异面冲击仿真分析,利用LS-PrePost软件处理得到相应的接触力-位移曲线,进一步处理得到变形模式和平台应力,并以图表的形式加以展示与分析。结果不同冲击速度下结构参数固定的蜂窝表现出LS、MS和HS等3种不同的异面冲击变形模式,从LS模式转变到MS模式再到HS模式的临界速度分别约为20 m/s和150 m/s;壁厚边长比对变形模式的影响可忽略。结论该蜂窝动态平台应力随冲击速度(或壁厚边长比)的增加而增大,且增长速率不断提高。当其他参数固定时,LS模式和MS模式下该蜂窝的动态平台应力与冲击速度呈二次函数关系,HS模式下动态平台应力与冲击速度的平方呈线性关系;动态平台应力与壁厚边长比呈幂函数关系。基于仿真计算结果,得到了该蜂窝动态平台应力的经验表达式。

填充式肋板蜂窝结构异面冲击响应

为改善蜂窝结构异面的力学性能,在传统六边形蜂窝的基础上引入了肋板结构,耦合成一种新型填充式肋板蜂窝结构。利用显式动力学有限元方法研究了填充式肋板蜂窝的异面在不同冲击速度和冲击角度作用下的冲击响应特性和能量吸收能力。结果表明:填充式肋板蜂窝的变形模式受到冲击速度和冲击角度的影响;填充肋板与外部胞壁之间存在耦合增强效应,可使蜂窝的力学性能增强,能量吸收能力提高15.08%;冲击端和固定端的平台应力均随着冲击角度的增大而减小;动态承载性能随着冲击角度的增大而减小。相对密度会影响填充肋板与外部胞壁之间的耦合效应以及填充式肋板蜂窝结构的能量吸收能力。

新型星形负泊松比抗冲击结构设计与入水冲击

针对跨介质飞行器入水过程中受到较大冲击载荷的问题,提出一种基于工程需求的负泊松比抗冲击结构拓扑优化设计方法,通过将弹性模量和泊松比引入拓扑优化设计的目标函数,得到满足抗冲击性能需求的负泊松比星形-四边形蜂窝(Star-quadrangular Honeycomb,SQH)结构。在建立SQH结构理论分析模型的基础上,推导冲击载荷下的平台应力解析公式,并通过数值模拟仿真进行校验。通过与星形-圆环蜂窝(Star-circle Honeycomb,SCH)等多种负泊松比结构的比吸能进行对比,得到SQH结构在低速、中速、高速冲击下的比吸能分别高于SCH结构28.74%、45.2%、7.03%。通过流固耦合仿真分析,对所设计的SQH夹层结构进行入水冲击降载研究,进一步讨论SQH夹层结构主要尺寸参数对入水冲击特性的影响。研究结果表明,在尺寸允许范围内,SQH单元倾角和单元壁厚的增大均使得结构产生的加速度峰值减小,动能转化为结构的变形能也减小,验证了用于工程需求的负泊松比结构拓扑优化设计的有效性。

基于FSR嵌入的智能泡沫在气动夹爪的应用

如何控制工业夹爪对易损物体的夹持力是一件具有挑战的任务,通常是利用有着力传感器的电动夹爪进行反馈控制,但这种方法昂贵且额外增加了夹爪的复杂程度。基于直书写3D打印,设计了一种内嵌力敏电阻器(FSR)的智能硅橡胶泡沫,安装在气动夹爪的指尖,不仅能监测夹持状态,还能在气压超过阈值后一定范围内,保持夹持力的恒定,以保护物体。实验结果表明:智能泡沫在4~12 N的工作范围内,误差不超过1.5N。当气压在450~560kPa范围内,能维持夹持力约14.6N。

内嵌负泊松比型耦合蜂窝结构的共面冲击响应

为提升蜂窝结构共面的力学性能,引入了内凹负泊松比结构,并将其内嵌到传统六边形蜂窝共面孔隙内,复合成一种新型内嵌负泊松比型耦合蜂窝结构。利用显式动力学有限元方法研究了内嵌负泊松比型耦合蜂窝结构的共面在不同冲击速度作用下的冲击响应特性和能量吸收能力。结果表明:耦合蜂窝结构的变形模式受到冲击速度和耦合角的影响;耦合蜂窝结构冲击端和固定端的名义应力-名义应变曲线与其变形模式和耦合角有关,且耦合角越大,名义应力水平越低;耦合蜂窝结构的平台应力和比吸能均随着耦合角的增大而减小,在高速冲击时,其平台应力降低2%~9%,比吸能降低7%~20%;相对密度影响耦合蜂窝结构的平台应力和能量吸收能力。

高原工况压气机叶轮振动失效特征分析

针对高原工况下离心压气机叶轮振动失效问题,以某增压发动机压气机叶轮为研究对象建立仿真模型,使用非定常计算流体动力学方法分析高原共振工况下叶轮受到的气流激励时域与频域特征,并基于单向流固耦合,使用瞬态动力学与谐响应方法研究气流激励作用下叶轮共振响应特征,得出高原工况叶轮振动失效原因。结果表明,高原工况叶轮在4阶气流激励作用下发生共振,激励主要来源于叶片与蜗舌间的动静干涉作用,叶顶间隙泄漏流增大了吸力面20%弦长位置的压力波动。气流激励下叶轮共振导致叶片前缘振动应力升高,振动应力幅值达101.5 MPa,与实际叶片振动失效情况一致。

驻高原人员心理应激状况调查

目的 探讨驻高原人员心理应激状况。方法 选取2022年1月~12月赴高原执行任务的96名人员为研究对象,设为研究组。运用军事群体心理应激预警检测工具(ATQMGS)进行调查,比较研究组人员与常模ATQMGS得分情况,分析研究组人员不同职级、不同文化程度及在不同海拔高度时ATQMGS得分差异。结果 研究组人员应对方式、工作积极性、自我效能、社会支持因子及附加项目29得分低于常模,附加项目30、31、32得分高于常模(P<0.05或0.01)。研究组初级人员控制感因子得分低于中级人员,应对方式、工作积极性、控制感因子得分低于干部人员,社会支持因子得分高于干部人员(P<0.05或0.01);研究组中级人员社会支持因子得分高于干部人员(P<0.05)。研究组初中文化程度人员应对方式、自我效能、控制感因子得分及附加项目31得分低于高中文化程度人员,领导支持、应对方式、自我效能、控制感、社会支持因子得分及附加项目31得分低于大专及以上文化程度人员(P<0.05或0.01);研究组高中文化程度人员控制感因子得分低于大专及以上文化程度人员(P<0.05)。研究组高海拔人员应对方式、控制感因子得分高于超高海拔人员,附加项目32得分低于超高海拔人员(P<0.05或0.01)。结论 职级低、文化程度低、海拔高的驻高原人员容易发生不良心理应激反应,对此类人群应该进行针对性心理指导,维护心理健康。

2001-2020年黄土高原植被生长季干旱的时空分布

基于MODIS实际蒸散量(ET)和潜在蒸散量(PET)反演作物缺水指数(CWSI),研究黄土高原生长季干旱时空变化特征,并用CWSI和植被归一化指数(NDVI)进行偏相关分析以探究生长季内最干旱月份对NDVI的影响。结果表明:1)黄土高原生长季CWSI多年平均值为0.777,处于中度干旱状态,空间分布表现为东南部较轻,西北部较严重的特征,且高程在1200~1700 m区域内的干旱程度最高;2)2001-2020年多年生长季CWSI整体呈显著下降趋势,其中2001年干旱程度最高,2018年干旱程度最低;在整个生长季内,黄土高原在4月的干旱程度最高;8月的干旱程度最低。具体表现为:4-10月,干旱等级从重旱过渡到中旱和轻旱,又从轻旱演变成中旱;3)从植被类型角度分析,荒漠、草原的分布区域属于重旱;草甸、栽培植被、灌丛的分布区域属于中旱;针叶林、阔叶林的分布区域属于轻旱,且不同植被类型在植被生长季的CWSI均呈波动下降趋势。研究结果可为黄土高原地区的生态预警和旱灾预估提供科学依据。