Spatio-temporal evolution and topographic gradient effect of land use and ecosystem service value in the Lhasa River Basin

The Lhasa River Basin forms an essential human settlement area in the southern part of the Qinghai-Tibet Plateau.This study employed ecosystem service value(ESV)evaluation model,terrain gradient grading,and Geodetector to analyze land use and ESV in the Lhasa River Basin from 1985 to 2020.The findings reveal that:(1)From 1985 to 2020,grassland was the dominant land use.There was a trend of grassland reduction and the expansion of other land types.(2)ESV has increased over the research period(with a total increase of 0.84%),with higher values in the southeast and lower values in the northwest.Grassland contributed the most to ESV,and climate regulation and hydrological regulation were the ecosystem services that contribute the most to ESV.(3)Natural factors like NDVI and altitude,as well as economic factors like population density and distance from roads,influenced the spatial differentiation of ESV,the explanatory power of NDVI reached up to 0.47.The interaction between factors had a greater impact than individual factors.These research results can provide theoretical support for national spatial planning and ecological environment protection in the Lhasa River Basin and other similar areas.

Spatiotemporal evolution of ecosystem service value and topographic gradient effect in the Da-Xiao Liangshan Mountains in Sichuan Province,China

The Da-Xiao Liangshan mountains are critical ecological function areas and essential ecological barriers in the upper reaches of the Yangtze River in China.This study selected a total of six periods of land use land cover(LULC)data from 1995 to 2020,to estimate the ecosystem service value(ESV)and analyzed its spatiotemporal evolution and topographic gradient divergence.The results showed that:(1)The ESV increased by 1.1 billion yuan,with an increase rate of 1.47%from 1995 to 2020.Two time periods,2005–2010 and 2015–2020,showed more significant increases than other periods.(2)The elevation and slope of mountainous areas determine the type of land use and further influence the spatial pattern of ESV.(3)Although woodland and grassland are the main land use types of the study area(more than 90%),the hydrological regulation function of the water area partially compensated for the impact of the encroachment of the built-up area on the ESV of grassland.(4)The spatial distribution of ESVs showed an inverted V-shaped characteristic as the topographic gradient increased,with the dominant position being the 5th topographic gradient zone.Finally,this study provided relevant recommendations for ecosystem protection and optimization.The findings of this study clarified the influence of topographical factors on the spatial differentiation of ESV and provided novel insights into ecosystem protection.

MODE Ⅰ CRACK TIP FIELD WITH STRAIN GRADIENT EFFECTS

A plane strain mode 1 crack tip field with strain gradient effects is investigated.A new strain gradient theory is used.An elastic-power law hardening strain gradient material is considered and two hardening laws,i.e.a separation law and an integration law are used respectively.As for the material with the separation law hardening,the angular distributions of stresses are consistent with the HRR field,which differs from the stress results;the angular distributions of couple stresses are the same as the couple stress results.For the material with the integration law hardening,the stress field and the couple stress field can not exist simultaneously,which is the same as the conclusion,but for the stress dominated field,the an- gular distributions of stresses are consistent with the HRR field;for the couple stress dominated field,the an- gular distributions of couple stresses are consistent with those in Ref.However,the increase in stresses is not observed in strain gradient plasticity because the present theory is based on the rotation gradient of the deformation only,while the crack tip field of mode 1 is dominated by the tension gradient,which will be shown in another paper.

MODE Ⅰ AND MODE Ⅱ CRACK TIP ASYMPTOTIC FIELDS WITH STRAIN GRADIENT EFFECTS

The strain gradient effect becomes significant when the size of frac- ture process zone around a crack tip is comparable to the intrinsic material length l, typically of the order of microns. Using the new strain gradient deformation theory given by Chen and Wang, the asymptotic fields near a crack tip in an elastic-plastic material with strain gradient effects are investigated. It is established that the dom- inant strain field is irrotational. For mode Ⅰ plane stress crack tip asymptotic field, the stress asymptotic field and the couple stress asymptotic field can not exist si- multaneously. In the stress dominated asymptotic field, the angular distributions of stresses are consistent with the classical plane stress HRR field; In the couple stress dominated asymptotic field, the angular distributions of couple stresses are consistent with that obtained by Huang et al. For mode Ⅱ plane stress and plane strain crack tip asymptotic fields, only the stress-dominated asymptotic fields exist. The couple stress asymptotic field is less singular than the stress asymptotic fields. The stress asymptotic fields are the same as mode Ⅱ plane stress and plane strain HRR fields, respectively. The increase in stresses is not observed in strain gradient plasticity for mode Ⅰ and mode Ⅱ, because the present theory is based only on the rotational gradi- ent of deformation and the crack tip asymptotic fields are irrotational and dominated by the stretching gradient.

A Study of Retention Time Gradient Effect of Gradientally Loaded Columns

In this work, the 'retention time gradient effect' of gradient GC columns is intensively studied to establish some equations and formulas for structure calculation of chromatographic columns. In addition, the relevant computer programs are designed.

Effect of gravity gradient in weak equivalence principle test

A high accuracy test of the weak equivalence principle（WEP） is of great scientific significance no matter whether its result is positive. We analyze the gravity gradient effect which is a main systematic error source in the test of WEP.The result shows that the uncompensated gravity gradient effect from the coupling term of the dominated gravity gradient multipole moment component q_（21） and the relative multipole field component Q_（21） contributes to an uncertainty of 1×10^（-11） on the E otv os parameter. We make a Q_（21） compensation to reduce the effect by about 20 times, and the limit of the test precision due to this coupling is improved to a level of a part in 10^（13）.

pH Overpotential for Unveiling the pH Gradient Effect of H^(+)/OH^(−)Transport in Electrode Reaction Kinetics

The pH gradient caused by H^(+)/OH^(−)transport on an electrode surface is the key factor determining reaction performance,but its detailed impact on the electrode reaction kinetics has yet to be clarified.Here,the pH gradient effect was determined by developing electrode reaction equations,considering the overpotential assigned to the pH gradient called pH overpotential.The pH gradient effect was revealed to involve two aspects:(1)the Nernst pH overpotential,accounting for the common Nernst relationship with pH,and(2)the pH-dependent function of the electron-transfer coefficient(α_(pH)).Both parts were verified experimentally using oxygen reduction reaction and hydrogen evolution reaction,obviously,with differentα_(pH) functions.Detailedα_(pH) function effect was clarified based on numerical calculations of the electrode reaction equations.We found that the effect could be assessed suitably by an apparent constant(α_(app))and a nonlinear fitting method proposed forα_(app) value estimation.The results of this study provide the kinetic fundamentals of electrode reactions involving H^(+)/OH^(−)and contribute to the understanding and assessment of their performance with the H^(+)/OH^(−)transport effect.

Linear Strain-Gradient Effect on the Energy Bandgap in Bent CdS Nanowires

尽管在半导体的可能的非同类的紧张效果被调查了因为在一半上世纪和紧张坡度能每在灵活 nanostructures 的测微计是超过 1% ，我们仍然缺乏他们对精力乐队的影响的理解。这里，我们进行紧张坡度的系统的阴极射线发光光谱学研究在在低温度的有弹性地弄弯的 CdS nanowires 的导致的激子精力移动，并且发现在弄弯的 nanowires 的激子精力红移动与紧张坡度成正比，格子失真的一个索引。密度功能的计算在弄弯的 nanostructures 显示出乐队差距减小的一样的趋势并且揭示内在的机制。半导体的乐队差距上的重要线性紧张坡度效果应该在在 nanoelectronics 调节光电子的性质的方法上打开新灯。

Effects of Transverse Temperature Gradient on the Rotor Velocity in an Ultrasonic Motor

As a result of the nonlinear effect, acoustic streaming has been widely used for increasing the transport coefficient or driving a rotor, for example, in resonant cavities and non-contact ultrasonic motors. It has been demonstrated by experiments that a temperature gradient transverse to the wave propagating direction can significantly increase the velocity of the streaming flows in resonant cavities. To check whether the transverse temperature gradient can also increase the working velocity of acoustic streaming-driven motors, we investigate this issue by numerically solving the hydrodynamic equations. It is found that the velocity of the rotor only weakly depends on the transverse temperature gradient, e.g., even with a temperature difference of 40℃ between the rotor and the stator, the velocity increases only -8.8%.

Effect of gradient magnetic field on physiochemistry functions of rice seedlings

Rice varieties Handao 2,Zhongbai 4,Han-jingzi,and Akihikari were treated with gradi-ent magnetic fileld to study the effect of gradi-ent field on rice.The magnetic field was madeup of 12 plots magnetic plates arranged in eachother south and north pole.The magneticstrength was 0-40 mT.Each four varieties wasput under the magnetic plate 15 cm away,andwent through the magnetic field with the speedof 20 cm/s.The same varieties without thetreatment were used as CK.Both of the seedswere soaked in water for 48 h in room temper-ature,and then sprouted on the porcelain platewith absorbed water paper.When the

ANALYSIS OF SIZE EFFECT,SHEAR DEFORMATION AND DILATION IN DIRECT SHEAR TEST BASED ON GRADIENT- DEPENDENT PLASTICITY

The paper concerns the issue of size law,localized deformation and dilation or compaction due to shear localization. It is assumed that the shear localization initiates at the peak shear stress in the form of single shear band,and based on gradient-dependent plasticity,an analytical solution on size effect or snap-back is obtained. The results show that the post peak response becomes steeper and even exhibits snap-back with increasing of length. For small specimen,the relative shear displacement when specimen failure occurs is lower than that of larger specimen and the shear stress-relative displacement curve becomes steeper. The theoretical solution on non-uniformity of strains in shear band is obtained and evolution of the relative shear displacement is represented. By resorting to the linear relation between local plastic shear strain and local plastic volumetric strain,the dilation and compaction within shear band are analyzed. Relation between apparent shear strain and apparent normal strain and relation between shear displacement and vertical displacement are established.

THE CURATIVE EFFECT OF HIGH EFFICIENCY HEMODIALYSIS AND THE GRADIENT CHANGE OF PLASMA OSMOTIC PRESSURE(Report of 27 Cases)

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考虑应力梯度效应的金属微梁屈服模型研究

一系列微加载测试结果表明,金属微梁的弯曲强度会随着材料外部几何特征尺寸的减小而显著升高,呈现出明显的尺寸相关性.基于位错塞积模型,探讨了纯金属单晶微梁的初始屈服应力,并提出了描述其尺寸相关性行为的关键内禀特征长度.通过综合分析现有的微梁弯曲实验及其离散位错动力学数值模拟结果,并考虑到位错-自由表面交互作用的影响,提出了一种仅涉及位错源的位错塞积构型.在此构型下,对线性应力梯度作用下的位错塞积行为进行了连续性分析,并建立了一个由位错源主导的应力梯度屈服模型.该模型有效地解释了微梁初始屈服应力的尺寸相关性,并与实验结果一致.研究结果表明,针对外部几何特征尺寸在数微米及以下的纯金属单晶微梁,位错塞积行为是其尺寸相关性行为的主导机制,而且刻画这种行为需要两个内禀特征长度参数,即位错源长度和位错塞积长度.为解释非均匀加载条件下微尺度晶体材料屈服应力的尺寸相关性行为,特别是纯金属单晶微梁,提供了新的视角.

混凝土连续组合小箱梁桥温度效应有限元分析

以亚沟枢纽互通G匝道桥作为依托工程,采用有限元数值分析方法对混凝土小箱梁桥在各国规范规定的温度梯度模式下进行仿真模拟,研究混凝土小箱梁桥在不同温度梯度模式作用下顶板、腹板和底板温度效应的分布规律,得出各国规范对于桥梁温度梯度模式方面规定的差异性。研究结果表明:在不同的温度梯度模式下,混凝土小箱梁桥的顶板、腹板和底板产生的正截面法向温度效应差异较大;沿梁长方向,边跨各截面产生的温度应力波动幅度较大,而中跨各截面产生的温度应力趋于相同;各国规范规定的竖向温度梯度荷载对混凝土小箱梁桥作用后产生的温度效应曲线之间存在规律性。可对类似混凝土连续组合小箱梁桥温度效应的计算提供参考。

土地利用与城市轨道交通客流的非线性关系

城市轨道交通站点影响范围内土地利用对客流影响具有时空分异特征且存在类型差异,为针对性探讨不同站点两者的复杂非线性关系,提出一种基于土地利用空间分布规律、对站点实际影响范围进行差异化识别的方法;并通过分时段多尺度地理加权回归,获取能够表征土地利用对客流影响时空变化特征的站点聚类指标,采用K-means++算法将研究区域内的站点划分为4类;进而基于改进的梯度提升决策树模型分类定量探讨不同类别下土地利用与轨道交通客流的复杂非线性关系。研究表明:通过捕捉不同站点土地利用与客流的时空分异特征对站点进行分类识别,可有效提升两者非线性关系模型的解释度。根据模型输出结果,发现不同类别站点影响轨道交通客流的关键土地利用要素不同,第1类中关键变量为相对重要性分别为61.35%和30.08%的公交站点数量和慢行密度;第4类的情况类似但相对数值有所变化,公交站点数量的相对重要性由61.35%下降至30.31%;建筑密度在第2类中以66.57%的相对重要度占据最大比例;但在第3类中仅占5.59%。此外,不同类别站点影响范围内土地利用与轨道交通客流的关系存在较为显著且各异的阈值效应。研究表明,对于不同类别站点的用地开发应各有侧重,且应结合实际将土地利用设计指标控制在相应的合理范围内。研究为差异化的站点周边土地利用开发策略的制定提供了理论支持和量化指导。

基于实测数据的高海拔大日温差地区拱上组合梁桥-无砟轨道体系温度场研究

温度作用是影响桥梁-轨道结构服役性能的重要因素之一。为探究高海拔大日温差地区拱上组合梁桥-无砟轨道体系的温度场变化规律,基于某拟建铁路上承式大跨拱桥桥址处的环境温度持续监测数据与卫星反演得到的太阳辐射数据,建立了考虑太阳辐射阴影遮挡效应的拱上组合梁桥-无砟轨道体系温度场模型,重点分析日温度变化规律和竖向温差分布规律,获得了考虑实测气温和太阳辐射逐时变化的全年日温度场;采用广义帕累托分布对竖向温差样本进行了极值分布估计,确定不同超越概率的竖向温差代表值,提出多折线形式的竖向温度梯度模式。研究结果表明,梯度相较于平原地区更为显著,无砟轨道的遮挡效应使得温度梯度分布上移,钢梁外侧腹板在冬季产生局部梯度作用;基于实测数据的温差极值估计方法考虑了环境温度和太阳辐射对结构温度场的随机影响,可为特殊地区桥梁设计阶段温度作用的计算提供参考。

地温梯度在塔里木盆地古生界热演化研究中的应用

塔里木盆地古生界烃源岩热史研究,特别是对超深古老烃源岩热演化认识存在较大争议,热演化阶段评价方法一直是困扰烃源岩热史研究的关键问题。调研结果表明,塔里木盆地寒武系古地温梯度变化在2.95~3.6℃/hm之间,按照生烃温度门槛值65℃计算,分别需要上覆地层厚度2203~1806 m,相差397 m,即2.58℃,温度差值较小。因此认为,塔里木盆地寒武系古地温梯度变化较小,可以忽略每期地温梯度取值上的差别,厚度可能是决定温度的主要因素;地层沉积与残留厚度可比较准确地获得,误差主要取决于剥蚀厚度的恢复。通过可靠获取的地层厚度、古地温梯度和剥蚀厚度等参数,以及烃源岩生烃图版,对塔里木盆地寒武系玉尔吐斯组烃源岩热演化阶段进行了评价;界定了关键期环满加尔坳陷的有效烃源岩及其分布,对玉尔吐斯组有效烃源岩及其规模生烃能力进行了预测和划分,并预测和划分了晚期成藏的有利区域。不同阶段有效烃源岩及其规模生烃量是每期成藏富集的关键,利用该方法避免了成熟度判识缺少可靠温标的问题,为塔里木盆地深层—特深层石油勘探和开发以及晚期成藏有利区的选择提供了重要的科学依据。

多源煤基固废充填体固结与承载性能的温度效应研究

为研究煤基固废膏体充填体在煤矿深部高地温环境下的固结承载性能,采用单轴压缩和声发射试验,测试不同养护温度(20、35、50℃)和龄期(3、7、14、28 d)影响下膏体充填体强度与破坏特征;通过SEM测定充填胶结体微观形貌和矿物组成,从微观角度揭示养护温度对水化反应的影响规律。研究结果表明:伴随养护温度的升高,其对水化反应的影响逐渐从促进转变为抑制,28 d抗压强度在养护温度为35℃时达到最大值;声发射事件主要发生在压密和破坏阶段,养护温度提高促使声发射活动提前活跃,充填体破坏形态逐渐由延性破坏转变为脆性破坏;由于热损伤作用,高温养护加快了充填体早期水化反应速率,而对养护后期充填体内C-S-H和孔隙结构造成破坏,对其长期强度的增加产生不利影响。

基于渐近均匀化的梯度加筋板结构优化设计

梯度加筋板结构以其优异性能广泛应用于航空航天、汽车和交通等领域。针对梯度板的渐变结构导致均匀化及两尺度优化设计计算量过大及效率过低的问题,本文采用机器学习方法搭建以微结构变形参数为输入、等效刚度系数为输出的人工神经网络,实现等效刚度的高效预测。在优化过程中,本文引入表征单胞变形的单元设计变量,实现梯度板局部变形的显式控制,并引入映射函数节点设计变量,保证优化过程中单胞的局部变形与映射函数一致,方便两尺度优化结果解耦。数值算例验证了本文方法的有效性和正确性。

环鄱阳湖城市群“三生”用地转型的生态环境效应及其地形梯度分析

[目的]准确评估“三生”用地转型对生态环境质量的影响,可为国土空间优化和区域高质量发展提供科学依据。[方法]基于环鄱阳湖城市群2000年、2010年、2020年的土地利用数据,使用土地转移矩阵、生态环境质量指数、地形分布指数等方法,分析了“三生”用地转型过程、生态环境效应及其梯度分异特征。[结果](1) 2000—2020年环鄱阳湖城市群生活用地大幅增长(1 063.45 km^(2)),生态用地持续减少(997.41 km^(2)),生产用地总体上保持稳定,主要的用地转型模式为城镇生活用地和工矿生产用地对农业生产用地和林地生态用地的侵占。(2)时序变化上,2000—2010年,随着工矿生产用地和城乡生活用地的扩张,生态环境质量指数由1.428下降至1.424;2010—2020年,伴随着生态用地的恢复以及城镇生活用地和工矿生产用地内部格局的不断优化,生态环境质量指数由1.424升至1.447。(3)空间分布上,整体上呈现“东西高、中部低”的空间分布格局,形成了以南昌大都市圈为中心的中部生态环境质量低值区和以宜春市、景德镇市、上饶市为中心的东西部生态环境质量高值区。(4)随着地形梯度的上升,低质量区的分布指数下降,高等级质量区逐渐呈优势分布;2000—2020年,低质量区趋向于向高地形梯度转移,较高质量区和高质量区的下移趋势明显。[结论]20年间研究区的生态环境质量整体向好,空间分布差异较大。土地利用转型导致了用地属性及其空间格局的双重变化,建议在布局各类用地时,既要注重对生产、生活用地的“总量控制”,又要保证生态用地的完整性和连通性。