Schmidt‐hammer exposure‐age dating (SHD) of snow‐avalanche impact ramparts in southern Norway: approaches,results and implications for landform age,dynamics and development

Schmidt‐hammer exposure‐age dating (SHD) was applied to the problem of dating the diachronous surfaces of five distal river‐bank boulder ramparts deposited by snow avalanches plunging into the Jostedøla and Sprongdøla rivers in the Jostedalsbreen region of southern Norway. Approaches to local high‐precision linear age calibration, which controlled in different ways for boulder roundness, were developed. The mean age (SHD_mean) and the maximum age (SHD_max) of surface boulders were estimated for whole ramparts, crests and distal fringes. Interpretation was further assisted by reference to R‐value distributions. SHD_mean ages (with 95% confidence intervals) ranged from 520 ± 270 years to 5375 ± 965 years, whereas SHD_max ages (expected to be exceeded by <5% of surface boulders) ranged from 675 to 9065 years. SHD ages from the Jostedøla ramparts tended to be older than those associated with the Sprongdøla, rampart crests were younger than the respective distal fringes, and use of relatively rounded boulders yielded more consistent SHD ages than angular boulders. The SHD_mean ages indicate differences in recent levels of snow‐avalanche activity between ramparts and provide insights into rampart dynamics as boulders are deposited on rampart crests and, in smaller numbers, on the distal fringes. SHD_max ages provide minimum age estimates of rampart age (i.e. the time elapsed since the ramparts began to form) and suggest that at least some of the ramparts have been developing since the early Holocene. Copyright © 2015 John Wiley & Sons, Ltd.     

Theory and experimental study for sliding isolators with variable curvature

Because a conventional isolation system with constant isolation frequency is usually a long‐period dynamic system, its seismic response is likely to be amplified in earthquakes with strong long‐period wave components, such as near‐fault ground motions. Seismic isolators with variable mechanical properties may provide a promising solution to alleviate this problem. To this end, in this work sliding isolators with variable curvature (SIVC) were studied experimentally. An SIVC isolator is similar to a friction pendulum system (FPS) isolator, except that its sliding surface has variable curvature rather being spherical. As a result, the SIVC's isolation stiffness that is proportional to the curvature becomes a function of the isolator displacement. By appropriately designing the geometry of the sliding surface, the SIVC is able to possess favorable hysteretic behavior. In order to prove the applicability of the SIVC concept, several prototype SIVC isolators, whose sliding surfaces are defined by a sixth‐order polynomial function, were fabricated and tested in this study. A cyclic element test on the prototype SIVC isolators and a shaking table test on an SIVC isolated steel frame were all conducted. The results of both tests have verified that the prototype SIVC isolators do indeed have the hysteretic property of variable stiffness as prescribed by the derived formulas in this study. Moreover, it is also demonstrated that the proposed SIVC is able to effectively reduce the isolator drift in a near‐fault earthquake with strong long‐period components, as compared with that of an FPS system with the same friction coefficient. Copyright © 2011 John Wiley & Sons, Ltd.     

长岛震群震源谱参数反演和震源参数特征

采用高频截止(High-Cut)震源模型,以均方根误差最小原则稳健地求解震源谱参数,并由此推算震源尺度和静态应力降。实际应用显示,该模型的理论谱对观测谱有很好的拟合,可明显改善拐角频率识别准确度。计算了长岛震群内71次M_L≥2.5地震事件的震源参数,结果表明：(1)拐角频率处于2～10 Hz范围,与震级大小存在一定的相关性,截止频率范围处于10～30 Hz之间,与地震大小的相关性不明显;(2)地震矩M₀分布在10¹²～10¹⁴ N·m,与震级M_L存在正相关关系：logM₀=0.977M_L+10.186;M_L与矩震级M_W之间的关系为：M_W=0.651M_L+0.766;(3)根据相对应力降时域演化发现,自2017年3月3日M_L4.5地震之后应力快速释放,应力降水平在均值附近波动,而且多数M_L≥3.5地震发生于...     

A Review of Studies Dealing with Tree Rings and Rockfall Activity: The Role of Dendrogeomorphology in Natural Hazard Research

Over the last few years, rockfall research has increasingly focused on hazard assessment and risk analysis. Input data on past rockfall activity were gathered from historical archives and lichenometric studies or were obtained through frequency–volume statistics. However, historical records are generally scarce, and lichenometry may only yield data with relatively low resolutions. On forested slopes, in contrast, tree-ring analyses may help, generally providing annual data on past rockfall activity over long periods. It is the purpose of the present literature review to survey the current state of investigations dealing with tree-ring sequences and rockfall activity, with emphasis on the extent to which dendrogeomorphology may contribute to rockfall research. Firstly, a brief introduction describes how dendrogeomorphological methods can contribute to natural hazard research. Secondly, an account is provided of the output of dendrogeomorphological studies investigating frequencies, volumes or spatial distributions of past rockfall activity. The current and potential strengths of dendrogeomorphology are then presented before, finally, the weaknesses of tree rings as natural archives of past rockfall activity are discussed and promising directions for further studies outlined.     

洪水频率分析的次序统计量

系统阐述了洪水频率分析涉及的洪水次序统计量和广义次序统计量及其抽样分布,并通过数学实验和统计试验两种途径研究了洪水次序统计量、频率次序统计量和重现期次序统计量抽样分布的统计特征及其关系。研究得到的次序统计量和广义次序统计量抽样分布的期望值和中值关系为系统分析和评价适线法奠定了理论基础。     

吉林晚古生代榆木川基性岩的地球化学特征及其岩石成因

位于兴蒙造山带张广才岭块体的榆木川辉绿玢岩,K—AT年龄测定表明其形成年龄为262～264Ma,主微量元素研究表明,辉绿玢岩SiO2含量为47.02％～52.60％,贫K2O（0.13％～0.47％）,Na2O〉K2O,属于低钾拉斑系列,稀土分布模式属于轻稀土略亏损的平坦型,微量元素原始地幔标准化图解中大离子亲石元素（Rh、Ba、Sr）较为富集,但不存在高场强元素（Nb、Ta）的亏损,同位素组成显示Sr同位素初始比值在0.704958～0.705631之间,εNd（t）值（72～81）较高且变化较小,表明其来源于亏损地幔的部分熔融且成岩过程中未受到地壳物质的混染。基性岩形成于造山后的伸展拉张背景,并结合前人的研究成果,认为晚古生代（约270Ma）兴蒙造山带已经进入晚期,此时加厚的岩石圈由于重力不稳定发生拆沉减薄作用,导致软流圈的大量上涌和岩石圈拉张,从而引起先存亏损岩石圈地幔的部分熔融,最后侵入地壳深部形成研究区辉绿玢岩。     

超声回弹综合法检测单一构件混凝土强度推定值的保证率分析

在实际工程检测数据的基础上,利用M on te C arlo试验对单一构件混凝土强度推定值的保证率问题进行了分析。30片梁板实测数据分析结果表明:将构件各测区混凝土强度换算值的最小值作为该构件的混凝土强度推定值的保证率范围为79.0%~94.2%,小于《超声回弹综合法检测混凝土强度技术规程》(CECS 02:88)规定的95%保证率要求,因此,对结构性能鉴定而言该混凝土强度推定值是偏于不安全的,应引起试验检测人员的充分重视。     

Assessing the Measurement Consistency Between the Jason-2/AMR and SARAL/AltiKa/DFMR Microwave Radiometers Using Simultaneous Nadir Observations

SARAL/AltiKa has a Dual Frequency Microwave Radiometer (DFMR), and Jason-2 has an Advanced Microwave Radiometer (AMR). Both microwave radiometer sensors include a 23.8 GHz primary water sensing channel. The measurement consistencies between DFMR and AMR are important for establishing a consistent altimetry data set between SARAL/AltiKa and Jason-2 in order to accurately assess sea level rise in a long-term time series. This study investigates the measurement consistency in the 23.8 GHz channel between DFMR and AMR at the Simultaneous Nadir Overpasses (SNO's) between the two satellites and also at coldest ocean brightness temperature locations. Preliminary results show that while both instruments show no significant trends over the one year since the launch of SARAL, a consistent relative bias of 2.88 K (DFMR higher than AMR) with a standard deviation of 0.98 K is observed. The relative bias at the lowest brightness temperature from the SNO method (-3.82 K) is consistent with that calculated from coldest ocean method (-3.74 K). The relative bias exhibits strong latitude (and scene temperature) dependency, changing from -3.82 K at high latitudes to -0.92 K near the equator. There also exists an asymmetry between the northern and southern hemisphere. The relative bias increases toward the lower end of brightness temperature.     

基于多体分析的浅水FPSO和水下软钢臂系泊系统运动特性研究

基于多体动力分析方法进行FPSO和水下软钢臂系泊系统的运动特性研究。相较于非线性弹簧模拟软钢臂系泊系统或者其他近似模拟方法,多体分析方法可以充分考虑系泊系统具体结构形式及其动力项对FPSO运动性能的影响,更好的预报系统运动响应和系泊力。本文将FPSO和水下钢臂结构模拟成2个具有6自由度的独立结构,两者用系泊链组进行连接。基于三维势流理论应用汇源分布法,首先在频域内进行FPSO的水动力参数分析,进而在时域内对系统进行耦合动力分析。本文重点讨论系泊系统黏性力和二阶波浪力对系统响应的影响,计算结果发现系泊系统黏性力对系泊力有一定影响,而在浅水条件下二阶波浪力的计算对准确预报系统运动及系泊力非常重要。     

不同固有频率比条件下圆柱双自由度涡激振动特性的数值研究

采用RANS方法,结合SST k-ω湍流模型,对不同顺流向与横顺流向固有频率的比值(即固有频率比,fnx/fny)条件下低质量比圆柱体的双自由度涡激振动进行了二维数值模拟。圆柱体的质量比为2.6,雷诺数范围为2 500~18 750,相应的约化速度范围为2~15,包括了经典试验中出现的整个锁定范围。通过研究发现,固有频率比是影响振动特性的重要参数,随着固有频率比的增加,响应幅值逐渐降低且向更高的约化速度偏移;在低约化速度范围内,固有频率比对顺流向和横流向振动之间的相位差以及升力频率有较大影响,从而得到各种不同偏向的8字形轨迹;最后对不同固有频率比条件下的尾涡模式进行了讨论,给出了对应不同约化速度时的尾涡模式。