Numerical simulation of longitudinal settlement of shield tunnel in the coastal city Shanghai

Until now more than 14 subway lines are in operation and some new lines are being built in the coastal city Shanghai. The longitudinal settlement of shield tunnel has significant effect on the safety of the subway operation. In this paper, the deformation of the shield tunnel and the surrounding soil were analyzed by the establishment of a three-dimensional model. The vertical displacements of four paths (Path 1 is on the ground; Path 2 is at the top of the tunnel; Path 3 is in the middle of the tunnel; Path 4 is at the bottom of the tunnel) are affected by the nature of the soil. The horizontal displacement is smaller than the vertical displacement and horizontal displacement of the clay is larger than that of the sand. The distribution of the pore pressure changes with soil properties around the tunnel. The pore pressure of the sand layer is larger than that of the clay layer at the same depth of underlying soil.     

pH值对单环刺螠呼吸排泄的影响

为研究pH值对单环刺螠(Urechis unicinctus)呼吸排泄的影响,采用静水密封法,研究了不同pH值(5、6、7、8、9)对体质量5.65±1.06g单环刺螠耗氧率、排氨率、能量代谢率、O/N值的影响.结果表明,pH值对单环刺螠耗氧率、排氨率、能量代谢率、O/N值均有显著影响(p0.05).单环刺螠耗氧率随pH值的升高而增大,pH值为8时达到最大值,之后随pH值的升高而减小.单环刺螠耗氧率与pH值之间的拟合方程为:OR=-2.977X2+55.188X-176.380,R2=0.937.单环刺螠排氨率的变化与耗氧率相似,在pH值为7时排氨率达到最大值;pH值为9时排氨率最小,与pH值为8的组差异不显著(p0.05).排氨率与pH值之间的拟合方程为:NR=-0.350X2+4.442X-6.822,R2=0.724.单环刺螠能量代谢率、O/N值均随pH值的升高呈先增大后减小的趋势,拟合方程分别为:M=-0.040X2+0.424X-0.044,R2=0.937;A=0.053X2+1.879X-7.470,R2=0.901.pH值为8的环境中,单环刺螠体内蛋白质代谢水平最低,有利于蛋白质的积累.研究表明,单环刺螠在一定pH值范围内可以通过调整生理代谢水平适应水体pH值,其适宜生活在弱碱性水中,生存最适pH值为8.     

Simulation of interactions among multiple debris flows

Adjacent debris flows may interact in many ways: two or more concurrent debris flows may merge; one debris flow can run out over an existing debris flow fan. Such interactions may cause debris flow properties to change in the mixing process as well as more severe adverse effects than those caused by a single debris flow. This paper aims to investigate the interactions among channelized debris flows originated from adjacent catchments. Both concurrent and successive debris flows are considered. If several debris flows originate from different locations concurrently and merge, the volumetric sediment concentration (i.e., the ratio of the volume of solid material to the total volume of debris flow), C _v, is a good index to capture the mixing process of these debris flows. The change in C _v reflects where mixing occurs and the mixing degree. The debris flow properties (e.g., yield stress and dynamic viscosity) evolve in the mixing process and can be captured by the change in C _v. The debris flow with a larger volume dominates the mixing process, and the properties of the mixed debris flow are more similar to those of the larger debris flow. The inundated areas and runout distances of successive debris flows are smaller than those of concurrent debris flows of the same total volume due to the smaller scales of the individual events and blockage by the earlier debris flows. However, the deposit depth in the interacting part of the debris flow fans of successive debris flows can be much larger than that of concurrent debris flows, leading to more destructive cascading hazards (e.g., the formation of debris barrier lakes). The sequence of successive debris flows not only significantly influences the runout characteristics of the debris flows but also substantially affects the cascading hazards.     

Lithofacies paleogeography mapping and reservoir prediction in tight sandstone strata: A case study from central Sichuan Basin,China

Sand-rich tight sandstone reservoirs are potential areas for oil and gas exploration. However, the high ratio of sandstone thickness to that of the strata in the formation poses many challenges and uncertainties to traditional lithofacies paleogeography mapping. Therefore, the prediction of reservoir sweet spots has remained problematic in the field of petroleum exploration. This study provides new insight into resolving this problem, based on the analyses of depositional characteristics of a typical modern sand-rich formation in a shallow braided river delta of the central Sichuan Basin, China. The varieties of sand-rich strata in the braided river delta environment include primary braided channels, secondary distributary channels and the distribution of sediments is controlled by the successive superposed strata deposited in paleogeomorphic valleys. The primary distributary channels have stronger hydrodynamic forces with higher proportions of coarse sand deposits than the secondary distributary channels. Therefore, lithofacies paleogeography mapping is controlled by the geomorphology, valley locations, and the migration of channels. We reconstructed the paleogeomorphology and valley systems that existed prior to the deposition of the Xujiahe Formation. Following this, rock-electro identification model for coarse skeletal sand bodies was constructed based on coring data. The results suggest that skeletal sand bodies in primary distributary channels occur mainly in the valleys and low-lying areas, whereas secondary distributary channels and fine deposits generally occur in the highland areas. The thickness distribution of skeletal sand bodies and lithofacies paleogeography map indicate a positive correlation in primary distributary channels and reservoir thickness. A significant correlation exists between different sedimentary facies and petrophysical properties. In addition, the degree of reservoir development in different sedimentary facies indicates that the mapping method reliably predicts the distribution of sweet spots. The application and understanding of the mapping method provide a reference for exploring tight sandstone reservoirs on a regional basis.     

Changes in soil organic carbon and its active fractions in different desertification stages of alpine-cold grassland in the eastern Qinghai–Tibet Plateau

In recent years, the desertification of alpine-cold grasslands has become increasingly serious in the Qinghai–Tibet Plateau in China, but it has not received the same amount of attention as has desertification in (semi)arid areas. Little is thus known about the change in soil organic carbon (SOC) during alpine-cold grassland desertification. To quantify the impacts of desertification on vegetation, SOC and its active fractions in alpine-cold grasslands, areas of light desertified grassland, medium desertified grassland, heavy desertified grassland, serious desertified grassland, and nondesertified grassland were selected as experimental sites in the eastern Qinghai–Tibet Plateau in China. The species number, height and coverage of vegetation were surveyed, and the soil particle fractions, SOC and SOC active fractions (including dissolved organic carbon (DOC), microbial biomass carbon (MBC), and labile organic carbon (LOC) were measured to a depth of 0–100 cm. The results showed that alpine-cold grassland desertification resulted in a significant reduction in vegetation cover, plant biomass, fine soil particles, SOC, DOC, LOC and MBC. The decreases in DOC, LOC and MBC were more rapid and apparent than were those in SOC, and the decrease in MBC was the most obvious among them. The rates of reduction in SOC concentrations accelerated as desertification progressed; most of the SOC was lost in the middle and later desertification stages, with lower losses during early desertification. The results indicate that active SOC fractions, particularly MBC, are more sensitive to desertification and can be used as sensitive indicators of desertification. Efforts to limit desertification and reduce SOC loss in alpine-cold grasslands should focus on early desertification stages and adopt strategies to prevent overgrazing and control the erosion of soil by wind.     

产业内部结构升级对碳排放的影响——基于OECD主要成员国面板数据的实证分析

人类活动所引起的全球变暖已经成为当前世界各国需共同面对的问题。经济结构性特征是受到广泛认可的区域发展阶段替代指标,因而本文分别选用制造业和服务业产业内部结构为基本视角,对其细化信息进行挖掘,并在经济合作与发展组织（OECD）各主要成员国背景下对碳排放随经济发展阶段推进而演化的过程进行计量分析。结果显示：第一,产业内部结构具备更加丰富的区域经济发展阶段信息,能够在普遍意义上提供判别区域经济发展所处时期的良好标准,为处于不同发展阶段的国家进行差异化碳配额权分配提供参考;第二,制造业和服务业内部产业结构升级的阶段性对照结果说明,碳排放峰值时点滞后于工业化的顶峰位置;第三,人为碳排放在经济发展过程中呈现倒U型的固有演化规律,在工业化顶峰前的碳排放逐步增长是为了维持基本经济发展路径的不可抗趋势。因此,发展中国家在工业化顶峰前不承诺排放达峰具有较高合理性,但仍应通过推进产业结构高级化、发展生产性服务业等举措抑制碳排放增速、尽早实现达峰。     

北京大学陆面过程模式PKULM(Peking University Land Model)介绍及检验

陆面过程模式是气候模式和天气模式的核心组成部分之一.在土壤—植被—大气耦合模式(Soil-PlantAtmosphere Model,SPAM)的基础上,发展了新一代北京大学陆面过程模式PKULM(Peking University Land Model).本文首先介绍了PKULM的辐射传输、湍流输送、光合作用、土壤水热输送等过程的参数化方案;采用隐式迭代计算框架,发展并应用了一个快速的线性方程组求解算法,提高了模式计算稳定性;提出并使用了二分搜索算法计算气孔阻抗,避免了CLM(Community Land Model)等使用的迭代方法在干旱区不稳定的情况,提高了模式的适用性;采用水势为基础的土壤水分扩散方程,使模式能够模拟土壤饱和区的水分输送过程,为进一步与水文过程模式耦合奠定了基础;还发展了一个地表积水与径流过程的机理模型,提高了模式对地表水分平衡过程的模拟能力;最后,使用"中国西北干旱区陆—气相互作用观测试验"平凉站的资料对模式进行了检验并与NOAH(National Center for Environmental Prediction,Oregon State University,Air Force,and Hydrology Lab model)陆面过程模式的模拟结果进行了比较,结果表明PKULM能够较好地模拟西北半干旱区农田下垫面地气交换过程.     

2.5D direct‐current resistivity forward modelling and inversion by finite‐element–infinite‐element coupled method

To reduce the numerical errors arising from the improper enforcement of the artificial boundary conditions on the distant surface that encloses the underground part of the subsurface, we present a finite‐element–infinite‐element coupled method to significantly reduce the computation time and memory cost in the 2.5D direct‐current resistivity inversion. We first present the boundary value problem of the secondary potential. Then, a new type of infinite element is analysed and applied to replace the conventionally used mixed boundary condition on the distant boundary. In the internal domain, a standard finite‐element method is used to derive the final system of linear equations. With a novel shape function for infinite elements at the subsurface boundary, the final system matrix is sparse, symmetric, and independent of source electrodes. Through lower upper decomposition, the multi‐pole potentials can be swiftly obtained by simple back‐substitutions. We embed the newly developed forward solution to the inversion procedure. To compute the sensitivity matrix, we adopt the efficient adjoint equation approach to further reduce the computation cost. Finally, several synthetic examples are tested to show the efficiency of inversion.     

青藏高原东南缘基于背景噪声的Rayleigh面波方位各向异性研究

青藏高原东南缘地区是现今地壳形变和地震活动最强烈的地区之一,也是研究青藏高原现今变形机制和构造演化规律的重要区域.本研究使用云南区域地震台网的55个宽频带地震台站连续地震背景噪声数据,采用双台站互相关方法获得Rayleigh(瑞利)面波经验格林函数,提取相速度频散曲线,反演得到云南地区周期5~34s范围内方位各向异性分布图像.反演结果揭示:短周期(5~12s)Rayleigh面波快波优势方向与区域断裂走向有很好的一致性,快波方向随着断裂走向的变化而变化.周期16~26s快波优势方向与反映上地壳特性的5~12s图像总体图像相似,但细节略有不同.其中,滇中块体内易门断裂和滇中块体内东侧的普渡河断裂附近,各向异性快波方向从NS向NW方向旋转;易门断裂以西呈NW向.这反映了青藏高原物质东流和川滇块体受到青藏块体的南东向挤压作用.周期30~34s范围的各向异性,滇缅泰块体和印支块体,快波优势方向为NS和NNW向;而在滇中块体内部,各向异性快波方向呈顺时针旋转变化,可能与青藏高原物质向东逃逸有关.本文还开展了与体波各向异性的对比分析,通过与近震S波分裂、Pms转换波分裂和远震SKS、PKS和SKKS(以后简称为XKS)分裂的对比研究,发现随着周期的增大,得到的快波优势方向与XKS剪切波快波偏振方向趋向一致,与地壳快剪切波偏振方向呈一定夹角.本研究认为,青藏高原东南缘地区壳幔各向异性具有不同的特征和形成机制.     

中国房间空气调节器行业节能减排潜力分析

2012年,中国房间空气调节器（空调器）保有量约为3.57亿台,依据抽样调查数据计算得到保有量装机容量,采用各省市夏季平均温度估算超过26℃的时间作为运行时间计算得出年电力消耗约3.28×1011 kW?h,折合碳排放约为318 Mt CO₂当量。由于空调器国内需求量将进一步增长,预计到2030年保有量将达到当前的4～5倍。在电力结构不变情景下,空调器总体能效提高1倍,2030年空调器电力消耗产生的温室气体排放约为603 Mt CO₂当量。假设空调器总体能效提高1倍、高能效产品消费比例进一步提高并伴随中国能源结构调整,如水电、核电、太阳能等低碳能源比例不断提高,在满足中国空调器需求的前提下,2030年中国空调器电力消耗产生的温室气体排放可以争取控制在当前的水平。