Carbon allocation in Picea jezoensis:Adaptation strategies of a non-treeline species at its upper elevation limit

Understanding the physiological adaptations of non-treeline trees to environmental stress is important to understand future shifts in species composition and distribution of current treeline ecotone.The aim of the present study was to elucidate the mechanisms of the formation of the upper elevation limit of non-treeline tree species,Picea jezoensis,and the carbon allocation strategies of the species on Changbai Mountain.We employed the^(13)C in situ pulse labeling technique to trace the distribution of photosynthetically assimilated carbon in Picea jezoensis at different elevational positions(tree species at its upper elevation limit(TSAUE,1,700 m a.s.l.)under treeline ecotone;tree species at a lower elevation position(TSALE,1,400 m a.s.l.).We analyzed^(13)C and the non-structural carbohydrate(NSC)concentrations in various tissues following labeling.Our findings revealed a significant shift in carbon allocation in TSAUE compared to TSALE.There was a pronounced increase inδ^(13)C allocation to belowground components(roots,soil,soil respiration)in TSAUE compared to TSALE.Furthermore,the C flow rate within the plant-soil-atmosphere system was faster,and the C residence time in the plant was shorter in TSAUE.The trends indicate enhanced C sink activity in belowground tissues in TSAUE,with newly assimilated C being preferentially directed there,suggesting a more conservative C allocation strategy by P.jezoensis at higher elevations under harsher environments.Such a strategy,prioritizing C storage in roots,likely aids in withstanding winter cold stress at the expense of aboveground growth during the growing season,leading to reduced growth of TSAUE compared to TSALE.The results of the present study shed light on the adaptive mechanisms governing the upper elevation limits of non-treeline trees,and enhances our understanding of how non-treeline species might respond to ongoing climate change.

THE APPLICATION OF WEINSTEIN-CHIEN′S METHOD——THE UPPER AND LOWER LIMITS OF FUNDAMENTAL FREQUENCY OF RECTANGULAR PLATES WITH EDGES ARE THE MIXTURE OF SIMPLY SUPPORTED PORTIONS AND CLAMPED PORTIONS

In this paper, the method of relaxed boundary conditions is applied to rectangular plates with edges which are a sort of the mixture of simply supported portions and clamped portions, so that the lower limit of fundamental frequency of such plates is evaluated. A kind of polynomial satisfying the displacement boundary conditions is designed, os that it is enabled to evaluate the upper limit of fundamental frequency by Ritz' method. The practical calculation examples solved by these methods have given satisfactory results. At the end of this paper, it is pointed out that the socalled exact solution of such plates usually evaluated by the force superposition method is essentially a kind of lower limit of solution, if the truncated error of series which occurs in actual calculation is considered.

Different radial growth responses to climate warming by two dominant tree species at their upper altitudinal limit on Changbai Mountain

We analyzed the influence of climate change over the past 50 years on the radial growth of two tree species: Korean pine (Pinus koraiensis) and Yezo spruce (Picea jezoensis), located on Changbai Mountain, Northeast China, using a dendrochronology approach to understand factors that limit the altitude for tree species. Elevated temperatures increased the radial growth of Korean pine and decreased that of Yezo spruce. The positive response of tree growth to hydrothermal conditions was the key reason that the upper limit of elevation of Korean pine followed the temperature fluctuation pattern. Increased temperatures and precipitation and longer growing seasons accelerated Korean pine growth. As the temperature increased, correlations between Korean pine ring-width chronology and precipitation changed from negative to positive. In Yezo spruce, increasing monthly temperatures and inadequate precipitation during the middle and late parts of the growing season led to narrow growth rings, whereas decreasing monthly temperatures and sufficient precipitation during the late growing season promoted growth. Rising temperatures and adequate precipitation increases Korean pine growth, possibly elevating the upper range limit in altitude for this species. In contrast, Yezo spruce growth is negatively affected by warming temperatures and limited precipitation. Under future temperature increases and precipitation fluctuations, the upper limit altitude of Korean pine can reasonably be expected to shift upward and Yezo spruce downward.

Upper-bound limit analysis based on the natural element method

The natural element method （NEM） is a newly- developed numerical method based on Voronoi diagram and Delaunay triangulation of scattered points, which adopts natural neighbour interpolation to construct trial functions in the framework of Galerkin method. Owing to its distinctive advantages, the NEM is used widely in many problems of computational mechanics. Utilizing the NEM, this paper deals with numerical limit analysis of structures made up of perfectly rigid-plastic material. According to kinematic the- orem of plastic limit analysis, a mathematical programming natural element formulation is established for determining the upper bound multiplier of plane problems, and a direct iteration algorithm is proposed accordingly to solve it. In this algorithm, the plastic incompressibility condition is handled by two different treatments, and the nonlinearity and nons- moothness of the goal function are overcome by distinguishing the rigid zones from the plastic zones at each iteration. The procedure implementation of iterative process is quite simple and effective because each iteration is equivalent to solving an associated elastic problem. The obtained limit load multiplier is proved to monotonically converge to the upper bound of true solution. Several benchmark examples are investigated to validate the significant performance of the NEM in the application field of limit analysis.

Passive Q-Switching of a Yb:LuVO_4 Laser with Cr^(4+):YAG:Approaching the Intrinsic Upper Limit of Repetition Rate

We demonstrate a diode pumped Yb：LuVO4 laser that can be passively Q-switched by a Cr^（4＋）：YAG saturable absorber having an initial transmission as high as 99.3%.A maximum pulsed output power of 2.35 W is generated at a repetition rate of 285.7 kHz,approaching or very near the intrinsic upper limit imposed by the recovery time of the Cr^（4＋）：YAG saturable absorber,and the resulting pulse energy,duration and peak power are,respectively,8.2μJ,39.2ns and 0.209kW.

Force analysis of pile foundation in rock slope based on upper-bound theorem of limit

Based on the characteristic that the potential sliding surfaces of rock slope are commonly in the shape of either line or fold line,analysis thought of conventional pile foundation in the flat ground under complex load condition was applied and the upper-bound theorem of limit analysis was used to compute thrust of rock layers with all possible distribution shapes. The interaction of slope and pile was considered design load in terms of slope thrust,and the finite difference method was derived to calculate inner-force and displacement of bridge pile foundation in rock slope under complex load condition. The result of example shows that the distribution model of slope thrust has certain impact on displacement and inner-force of bridge pile foundation. The maximum displacement growth rate reaches 54% and the maximum moment and shear growth rates reach only 15% and 20%,respectively,but the trends of inner-force and displacement of bridge pile foundation are basically the same as those of the conventional pile foundation in the flat ground. When the piles bear the same level lateral thrust,the distribution shapes of slope thrust have different influence on inner-force of pile foundation,especially the rectangle distribution,and the triangle thrust has the smallest displacement and inner-force of pile foundation.

Upper bound limit analysis of roof collapse in shallow tunnels with arbitrary cross sections under condition of seepage force

The analytical solutions for predicting the exact shape of collapse mechanisms in shallow tunnels with arbitrary excavation profiles were obtained by virtue of the upper bound theorem of limit analysis and variation principle according to Hoek-Brown failure criterion. The seepage force was included in the upper bound limit analysis, and it was computed from the gradient of excess pore pressure distribution. The seepage was regarded as a work rate of external force. The numerical results of roof collapse in square and circular tunnels with different rock parameters were derived and discussed, which proves to be valid in comparison with the previous work. The influences of different parameters on the shape of collapsing blocks were also discussed.

Combined influence of nonlinearity and dilation on slope stability evaluated by upper-bound limit analysis

The combined influence of nonlinearity and dilation on slope stability was evaluated using the upper-bound limit analysis theorem.The mechanism of slope collapse was analyzed by dividing it into arbitrary discrete soil blocks with the nonlinear Mohr–Coulomb failure criterion and nonassociated flow rule.The multipoint tangent(multi-tangent) technique was used to analyze the slope stability by linearizing the nonlinear failure criterion.A general expression for the slope safety factor was derived based on the virtual work principle and the strength reduction technique,and the global slope safety factor can be obtained by the optimization method of nonlinear sequential quadratic programming.The results show better agreement with previous research result when the nonlinear failure criterion reduces to a linear failure criterion or the non-associated flow rule reduces to an associated flow rule,which demonstrates the rationality of the presented method.Slope safety factors calculated by the multi-tangent inclined-slices technique were smaller than those obtained by the traditional single-tangent inclined-slices technique.The results show that the multi-tangent inclined-slices technique is a safe and effective method of slope stability limit analysis.The combined effect of nonlinearity and dilation on slope stability was analyzed,and the parameter analysis indicates that nonlinearity and dilation have significant influence on the result of slope stability analysis.

New Upper Limit ofγ-Rays Emitted by Tritium Nucleus

Using a strong tritium source and a low background HPGe spectrometer a new upper limit of γ-rays emitted by tritium nucleus,less than 3.4X10^(-13),is obtained.

Upper Bound Limit Analysis of Anisotropic Soils

In this paper,a novel discretization method inσ-τspace is developed to calculate the upper bound limit loads and failure modes of anisotropic Mohr-Coulomb materials.To achieve this objective,the Mohr-Coulomb yield criterion is linearized inσ-τspace,which allows for upper bound solution of soils whose cohesion and friction coefficient varying with direction.The finite element upper limit analysis formulation using the modified anisotropic yield criterion is then developed.Several examples are given to illustrate the capability and effectiveness of the proposed numerical procedure for computing rigorous upper bounds for anisotropic soils.

Inverse Limit of Spaces of Upper Semicontinuous Functions

Given a compact Hausdorff space X, U(X) denotes the compact Hausdorff space of all the upper semicontinuous functions from X to the unit interval with the dual lim inf topology. Then U is an endofunctor on compact Hausdorff space. It is proved in this note that this functor preserves inverse limits.

THE INTEGRAL AS A FUNCTION OF THE UPPER LIMIT AND AN ANALYTICAL SOLUTION TO PLANE STRAIN DRAWING AND EXTRUSION

A kinematically admissible velocity field which is different from Avitzur's is established in Cartesian Coordinates. An upper-bound analytical solution to strip drawing andextrusion is obtained by using the integral as a function of the upper limit in this paper.

考虑水力效应的裂缝边坡稳定性非线性能耗分析

现有考虑水力效应的裂缝边坡稳定性分析大多基于线性破坏准则,而岩土体破坏往往呈现非线性特征,因此开展水力效应影响下的裂缝边坡稳定性非线性极限上限分析具有重要意义。基于极限分析上限定理及强度折减技术,结合“外切线法”非线性破坏准则,构建坡顶含竖直裂缝的边坡对数螺旋线破坏模式,根据虚功原理推导出裂缝边坡安全系数解析式,通过MATLAB优化计算,结合边坡工程实例探讨了典型因素对裂缝边坡稳定性、临界裂缝及滑动面位置的影响规律。研究结果表明:随着地下水位h的持续上升,边坡安全系数不断降低,临界裂缝深度逐渐增大且临界裂缝位置逐渐向坡顶缘偏移;非线性系数m明显影响边坡的稳定性,边坡安全系数随着非线性系数的增大显著减小,采用线性破坏准则会高估地下水位变化对边坡稳定性的影响;随着非线性系数的增大,临界裂缝深度随之增大,临界裂缝位置距离坡顶缘越来越远,滑坡体体积逐渐增大;裂缝与坡顶缘距离l m随着非线性系数m的增大而增大(当m增大0.2时,l m增大约1 m),且随着裂缝与坡顶缘距离的增大,边坡安全系数无明显变化,临界裂缝深度先逐渐减小后趋于稳定。

大截面矩形顶管施工对既有管线影响研究

顶管施工会扰动邻近建筑物,危及工程安全。该文以苏州市城北路综合管廊元和塘段顶管工程为背景,通过ABAQUS有限元分析软件建立三维模型,研究顶管下穿地下管线施工对管周土及既有管线影响,并基于极限分析方法探讨了管线失稳模式。结果表明:大直径矩形顶管顶进方向的影响范围约为2倍顶管宽度,两侧的影响范围约为1倍顶管宽度,地下管线到顶管轴线的水平距离为0.5倍~1倍顶管宽度时,应注意管线受到的水平方向附加荷载是否会导致管线破坏;管线与顶管相对位置对管线破坏影响较为显著,越靠近顶管的管线破坏越严重,滑移线由顶管两侧经由管线向地面发展,破坏部位由管线顶部两侧延伸至底部;除受与顶管相对位置影响外,管线破坏模式还受矩形顶管形状影响,管线顶部及靠近顶管顶角区域破坏风险最大。

开洞刚性墙后土体破坏模式运动单元上限分析

超载作用下开洞地下刚性连续墙后土体稳定性问题具有广泛的工程应用背景。考虑墙体矩形开洞宽度足够大,且刚性墙与土体完全光滑接触等条件,参考构造刚性多块体上限法思路,预设墙后土体极简破坏机构并转化为初始三角网格,提出交替循环式新增节点、单元缩减、对角互换及成层加密等网格更新措施,同步开展基于刚体平动运动单元上限方法的刚性墙后土体破坏分析,通过多层级非线性规划运算获得高精度临界超载系数σ_(s)/c上限解,界定墙后土体滑移线网破坏模式及其定量范围与扩展边界。进一步依前述流程计算获得多参数影响下的临界超载系数σ_(s)/c上限解图表,结果表明:1)刚性墙后土体典型破坏特征表现为土体上方和开洞处的整体下沉刚性区域,开洞前方核心区域以密集滑移线网区隔的刚性滑块群,以及外围主要滑动面;2)临界超载系数σ_(s)/c随土体内摩擦角ϕ增大而增大,且后续增幅显著增加;3)σ_(s)/c随开洞深度比C/D的增大呈现出近似线性增大的趋势;4)相较于ϕ和C/D,土体重度参数γD/c的变化对于σ_(s)/c的影响不甚明显,σ_(s)/c随γD/c增大呈现近似线性减小的趋势;5)σ_(s)/c受剪胀角参数ψ/ϕ的影响与ϕ的增大程度密切相关。本研究结果可为开洞地下刚性连续墙后土体失稳破坏模式定量分析、破坏机理研究及工程措施制定等工作提供有力的数据支持。

考虑底部塑性区的深埋隧洞围岩压力上限解

基于极限分析理论,提出一种适用于软弱围岩的深埋隧道围岩压力的计算方法。考虑隧道底部塑性变形区的影响,构建纺锤形的破坏模型。基于该破坏模型构建围岩速度场,引入侧压系数λ_(1)和底压系数λ_(2),推导围岩压力的理论计算公式。根据计算公式进行编程优化计算,分析不同非线性系数m下,侧压系数λ_(1)、底压系数λ_(2)对围岩压力的影响。研究结果表明:随着内摩擦角减小,“纺锤”上下两端塑性区不断向外延伸;非线性系数m对围岩压力有显著影响,当非线性系数一致时,提高侧压系数λ_(1)可以降低拱顶和隧道底部压力,提高底压系数λ_(2)可以降低拱顶和边墙压力;在岩土体非线性特征明显的地区,计算深埋隧洞围岩压力时应考虑底部塑性区。

震后趋势判定技术系统CAAFs震后余震预测效果评价

自2019年正式运行以来,震后趋势判定技术系统CAAFs为震后应急与趋势研判及时提供数据和技术支撑。本文梳理总结CAAFs系统持续4.5年产出的数据,从全国和不同地区两个方面评价系统产出的震后余震预测结果,得到以下三点认识:①震级上限预测(发生某震级以上地震的可能性不大)的正确率大多为90%及以上,显著优于震级区间预测(存在发生同等大小地震的可能或存在发生某震级左右地震的可能),各分区预测情况差异不大;②震级区间预测震级普遍比地震实况偏高,实际7日内发生的最大余震震级与预测震级的差值(震级偏差)落入[-0.5,0.5]区间的地震比例约为44%,落入[-1,1]区间的地震比例约为69%,越靠近[-0.5,0.5]区间,地震的比例越高;③震级区间预测中,各分区有一定差异,西南地区优于西北、华南和华北东北三个地区,总的来看4~5级地震预测情况不如其他震级区间,可能与该震级区间内地震的最大余震震级变化范围较大有关。

考虑基质吸力影响的非饱和路堤三维稳定性上限分析

采用极限上限分析定理构建了路堤失稳的三维旋转破坏机构,继而根据Bishop非饱和土抗剪强度理论,考虑非饱路堤内部基质吸力的空间分布及其随地下水位的变化,建立了路堤破坏土体外力功率与内部能量耗散功率的能量守恒方程,并利用遗传算法编写了非饱和路堤最小上限解的高效搜索算法。通过将非饱和土路堤基底破坏模式退化为边坡破坏模式,并与现有非饱和土边坡稳定性计算结果对比,验证了所提上限解的正确性和遗传搜寻算法的准确性。进一步地,对路堤三维稳定性的关键影响因素展开了系统分析,研究了路堤填土孔径分布、基质吸力、进气值倒数、路堤倾角以及有效内摩擦角等因素对路堤三维稳定性的影响规律。研究表明,非饱和土质路堤的稳定性不仅取决于路堤填土性质,而且依赖于影响土体吸力大小与分布的填土孔径参数和进气值等因素。地下水位升降引起的基质吸力变化对路堤稳定性存在显著影响。研究结果为路堤稳定性精细化分析提供了重要的理论依据。

一个新的涉及一个多重可变上限函数和一个部分和的半离散Hilbert型不等式

应用权函数的方法,Euler-Maclaurin求和公式,Abel部分求和公式及实分析技巧,求出了一个新的涉及一个多重可变上限函数和一个部分和的半离散Hilbert型不等式.作为应用,考虑了特殊参数下不等式中最佳常数因子联系多参数的等价条件及一些特殊不等式.

海啸作用下滨水挡土墙抗震滑动稳定性上限分析

针对沿海地区滨水挡土墙在海啸和地震联合作用下易发生被动破坏的问题,结合极限分析上限法和拟静力法确定地震荷载,研究了海啸作用下滨水挡土墙的抗震滑动稳定性。通过建立墙体滑动与破坏区土楔体整体滑动的墙-土系统及速度容许场,推导出水平地震加速度系数(kh)的表达式。分析了海啸、海平面与地下水高度及墙-地和墙-土摩擦角对地震屈服加速度系数的影响。结果表明,控制地下水位在适当高度并增大墙-土摩擦角可以有效提高滨水挡土墙的抗震滑动稳定性。与经典极限平衡理论相比,该方法考虑了土体的塑性流动及挡土墙的位移模式,且无需计算地震被动土压力的值。