Constraints on the176Lu cosmochronometer

In an endeavour to resolve reported discrepancies in the value of the branching ratio of¹⁷⁶Lu at astrophysical energies, a new determineation of the¹⁷⁵Lu (nγ)^176mLu capture cross section has been measured as 958 ± 58 mb. This gives a value of the branching ratio of 0.21 ±0.05. This result indicates that some reequilibration of the ground and isomeric states of¹⁷⁶Lu occurs in stellar environments undergoing s-process nucleosynthesis, and confirms that¹⁷⁶Lu is not a reliable cosmochronometer. However the very existence of¹⁷⁶Lu in the solar system implies that the ground state of¹⁷⁶Lu was not completely depopulated, and provides the possibility of using this nuclide as a sensitive thermometer for stellar processes.     

基于众源轨迹数据的人造地表覆盖增量信息提取

目前,我国已研制出2000年、2010年两期30m分辨率全球地表覆盖数据集。为了保持该数据集的现势性,需要及时发现全球地表覆盖增量信息并更新相应数据。采用遥感影像、测绘数据提取全球地表覆盖变化信息的传统方式,存在费用高,不及时等问题。近年来众源地理数据迅猛发展,特别是由于众源轨迹数据具有免费共享、可靠性强与准实时等优点被广泛应用在交通道路信息提取的应用中。经分析我们发现轨迹数据与人造地表覆盖之间存在一定的对应关系,因此,本文研究提出了一种采用众源轨迹提取人造地表覆盖增量信息的方法。该方法首先对原始轨迹数据进行预处理,然后将轨迹数据栅格化,再依据轨迹点栅格覆盖比率进行人造地表覆盖数据粗提取并去除微小孔洞及独立栅格单元,最后将其与全球人造地表覆盖数据作栅格运算提取人造地表覆盖增量信息,并用纽约市实际轨迹数据验证了该方法的可行性。     

2.4m望远镜曝光时间计算器的设计和实现

望远镜的曝光时间计算器对于远程观测以及不熟悉整个观测系统的观测人员尤为重要,因为它可以帮助观测者制定合理的观测计划。设计并实现了高美古2.4m望远镜系统的曝光时间计算器(exposuretimecalculator,ETC),它可以根据望远镜及其终端设备的参数,通过计算给出待测天体曝光时间的参考值。这为观测者了解现有条件下极限观测能力,设置曝光时间或者是给定星等和曝光时间计算信噪比提供了依据。将ETC计算结果与实际测光标准星的数据进行了比较,结果表明ETC对测光标准星的计算结果是可靠的。     

明渠规则断面流量测量方法研究

针时现有明渠流量测量方法的不足,提出一种规则断面明渠流量的自动测量方法-流速-水位法.首先基于断面流速分布经验公式,给出流速-水位法测量明渠断面流量的基本原理、计算公式及测量步骤;然后应用该法对某实际灌区的两个典型断面进行流量测量,并与流速-面积法的实测结果作对比,两者符合的较好,说明本文所提出的流速-水位法是准确可行的.实例应用成果表明,所提出的流速-水位法可用于规则断面明渠流量的自动测量.     

桩-土间剪切应力的传递探讨

对不同情况下桩-土间剪切应力进行了初步的理论分析,并基于ADINA有限元程序,对不同情况下的桩-土间剪切应力进行了计算对比分析。结果表明,同种土体和桩体条件下,各种模式达到极限状态时桩-土间剪切应力不同,堆载作用下负摩擦力值最大,抗拔桩负摩阻力值最小,桩顶受压桩、托桩的摩阻力值介于其间;桩材泊松比在0.15～0.35范围内时,桩侧摩阻力随泊松比的增大而增大。所得结论有助于进一步认识桩-土相互作用规律以及桩-土荷载传递机制。     

振动频率对饱和黏性土动力特性的影响

在回顾加荷频率对土样动力特性影响的研究基础上,采用某土石坝心墙防渗黏性土饱和试样,通过动三轴试验,研究了振动频率f对土样动力特性的影响。动强度试验结果表明：当 0.1～4 Hz时,动强度随f的升高而增大,但f继续升高后,动强度却有下降趋势。当 0.1～1.0 Hz时,频率愈高动孔压比愈大;当 1.0～6.0 Hz时,总的趋势为频率愈高,动孔压比愈小。表明频率较高时,动孔隙水压力来不及上升和扩散。较高频率f持续作用下,试样有吸水现象并伴随动孔压的下降。动模量阻尼试验结果是：f愈低,试样动变形开展愈充分;f愈高,动模量和阻尼比愈大。     

Modeling the sediment yield from landslides in the Shihmen Reservoir watershed,Taiwan

Landslides generate enormous volumes of sediment in mountainous watersheds; however, quantifying the downstream transport of landslide‐derived sediment remains a challenge. Landslide erosion and sediment delivery to the Shihmen Reservoir watershed in Taiwan was estimated using empirical landslide frequency–area and volume–area relationships, empirical landslide runout models, and the Hydrological Simulation Program‐ FORTRAN (HSPF). Landslide erosion rates ranged from 0.4 mm yr^‐1 to 2.2 mm yr^‐1 during the period 1986–2003, but increased to 7.9 mm yr^‐1 following Typhoon Aere in 2004. The percentage of landslide sediment delivered to streams decreased from 78% during the period 1986–1997 to 55% in 2004. Although the delivery ratio was lower, the volume of landslide sediment delivered to streams was 2.81 × 10⁶ Mg yr^‐1 in 1986–1997 and 8.60 × 10⁶ Mg yr^‐1 in 2004. Model simulations indicate that only a small proportion of the landslide material was delivered downstream. An average of 13% of the landslide material delivered to rivers was moved downstream during the period 1986–1997. In 2004, the period including Typhoon Aere, the annual fluvial sediment yield accounted for approximately 23% of the landslide material delivered to streams. In general, the transfer of sediment in the fluvial system in the Shihmen Reservoir watershed is dominantly transport limited. The imbalance between sediment supply and transport capacity has resulted in a considerable quantity of landslide material remaining in the upper‐stream regions of the watershed. Copyright © 2012 John Wiley & Sons, Ltd.     

新疆巴楚和塔什库尔干地震台下方地壳结构研究

Using the teleseismic waveform data recorded by the seismic station Bachu( hereafter referred to as station BCH) i n the Tarim Basin and the seismic station Taxkorgan(h ereafter referred to as station TAG) i n the west Kunlun Mountains for years,we applied the receiver function H-κ stacking method to study the crustal structure beneath stations BCH and TAG. The results showed that there are obvious differences in the crustal thickness beneath stations BCH and TAG,and the regional crustal thickness and terrain have a very good corresponding relationship. There are high crustal average V P/ V S values beneath the two stations. The crustal thickness is 44 km,and the crustal average wave velocity ratio is 1. 849 beneath station BCH. There is a sharp discontinuity in the middle of the crust beneath station BCH at a depth of 21 km. There is a low average P wave velocity and low V P/ V S from the surface to the discontinuity beneath station BCH.The depth of the discontinuity is consistent with the lower interface of the focal depth from accurate location in the Jiashi earthquake source area adjacent to station BCH; and may be the crustal brittle-ductile conversion boundary. The crustal thickness is 69 km,and the crustal average wave velocity ratio is 1. 847 beneath station TAG,a thicker crust and high V P/ V S may indicate that materials in the lower crustal are prone to plastic flow,which is responsible for the thickening of the crust.     

Effects of riverbed incision on the hydrology of the Vietnamese Mekong Delta

The hydrogeomorphology of the Vietnamese Mekong Delta (VMD) has been significantly altered by natural and anthropogenic drivers. In this study, the spatiotemporal changes of the flow regime were examined by analysing the long-term daily, monthly, annual and extreme discharges and water levels from 1980 to 2018, supported by further investigation of the long-term annual sediment load (from the 1960s to 2015), river bathymetric data (in 1998, 2014 and 2017) and daily salinity concentration (from the 1990s to 2015) using various statistical methods and a coupled numerical model. Then, the effects of riverbed incision on the hydrology were investigated. The results show that the dry season discharge (i.e., in March–June) of the Tien River increased by up to 23% from the predam period (1980–1992) to the postdam period (1993–2018) but that the dry season water level at My Thuan decreased by up to −46%. The annual mean and monthly water levels in June at Tan Chau and in January and June–October at My Thuan in the Tien River decreased statistically, even though the respective discharges increased significantly. These decreased water levels instead of the increased discharges were attributed to the accelerated riverbed incision upstream from My Thuan, which increased by more than three times, from a mean rate of −0.16 m/year (−16.7 Mm³/year) in 1998–2014 to −0.5 m/year (−52.5 Mm³/year) in 2014–2017. This accelerated riverbed incision was likely caused by the reduction in the sediment load of the VMD (from 166.7 Mt/year in the predam period to 57.6 Mt/year in the postdam period) and increase in sand mining (from 3.9 Mm³ in 2012 to 13.43 Mm³ in 2018). Collectively, the decreased dry season water level in the Tien River is likely one of the main causes of the enhanced salinity intrusion.     

唐山M 4.8地震地磁谐波振幅比变化

针对2012年5月28日河北唐山M 4.8地震,采用地磁谐波振幅比方法,分析昌黎、静海、红山及承德地磁台2007年1月至2015年12月地磁观测数据,结果显示：各台站10 min周期的计算结果波动性明显,其他周期形态较为一致;距震中最近的昌黎地磁台Y_ZHx（NS）测向的10-40 min周期地磁谐波在下降至极低值后,开始转折时发生地震,而Y_ZHy（EW）测向未出现明显转折现象;位于河北平原地震带中部的静海地磁台对此次地震反应显著,2个测向在震前均出现下降-转折-上升的变化特征。通过对比位于不同地区的4个地磁台站地磁谐波振幅比变化,发现受大范围整体构造应力场作用的影响,计算结果具有相似的趋势性变化特征,具体到局部地区或断裂带内部,各台站之间显示出一定差异。