Pore-scale simulation of entrapped non-aqueous phase liquid dissolution

We investigated the dissolution of non-aqueous phase liquids (NAPLs) in a three-dimensional random sphere-pack medium using a pore-scale modeling approach to advance fundamental understanding and connect rigorously to microscale processes. Residual NAPL distributions were generated using a morphological approach and the entrapped non-wetting phase was quantitatively characterized by calculating volume, orientation, interfacial area, and shape of isolated NAPL regions. With a detailed aqueous-phase flow field obtained by a multiple-relaxation time lattice Boltzmann approach, we solved the advective–diffusive equation in the pore space using a high-resolution, adaptive-stencil finite-volume scheme and an operator-splitting algorithm. We show good agreement between the mass transfer rates predicted in the computational approach and previously published experimental observations. The pore-scale simulations presented in this work provide the first three-dimensional comparison to the considerable experimental work that has been performed to derive constitutive relations to quantify mass transfer from a residual NAPL to a flowing aqueous phase.     

From bifurcation to failure in a granular material: a DEM analysis

The question of diffuse failure in granular media such as soils is treated by numerical modelling with a discrete element model. Two numerical samples are considered, one dense and the other loose. A criterion based on the sign of the second-order work is applied to the numerical model to detect bifurcation points related to diffuse failure. The notions of loss of controllability and loss of sustainability are taken into account to simulate diffuse failure at bifurcation points detected. Therefore, the failures predicted based on the second-order work criterion are numerically verified.     

基于LOPC的夏季南黄海35°N断面浮游动物水平和垂直分布初探

用集成在移动船载温盐剖面仪(MVP)的激光型浮游生物光学计数仪(LOPC),于2012年7月底在南黄海35°N断面调查浮游动物丰度的水平和垂直分布情况,并对获得高时空分辨率的数据资料进行分析。结果表明,本次调查海域浮游动物的丰度为西高东低,浮游动物分布可能受温度、浮游植物分布、潮致涌升等因素影响,其中温度为最主要因素。该仪器可以作为中国近海浮游生物调查,特别是对浮游动物资源的走航大面调查、垂直分布及其生态学研究的一种有效的手段。     

Fifty years of meteo-glaciological change in Toll Glacier,Bennett Island,De Long Islands,Siberian Arctic

Rapid environmental change has been observed in the De Long Islands, Siberian Arctic, where warming has extensively occurred over the area. To quantitatively evaluate glaciological changes since the 1980s, the climate, mass balance, and the equilibrium line altitude (ELA) of Toll Glacier on Bennett Island were analyzed. Air temperature has increased and solid precipitation has decreased since the 1960s, especially after 2000. The cumulative mass balance of Toll Glacier has had a negative trend since the 1960s and reached approximately −20 m water equivalent (w.e.) in 2000, which is one of the largest changes in the Arctic. These changes are much larger than those in the west Russian Arctic. The warming trend is also correlated with the sea ice distribution in the Siberian Arctic and may lead to feedback effects that cause further Arctic warming.     

北黄海冷水团温度年际变化研究

本文基于1976—2006年国家标准断面(大连—成山头)调查资料,结合ECMWF气温、风速以及辐射等再分析资料,研究了北黄海冷水团的低温中心以及北部锋面的年际变化规律,并对其与气候年际变化信号的关系做了相关性分析以及EOF分析,研究了影响北黄海冷水团的诸多因素。研究结果表明,北黄海冷水团及其北部锋面强度存在明显的年际变化特征,北黄海冷水团中心最低温度具有升温趋势,北部锋面强度具有减弱趋势。分析发现,前冬海温,当地气温,经向风场以及辐射通量都对来年北黄海冷水团的强度存在影响,东亚冬季风的年际变异是影响北黄海冷水团温度年际变化的主要机制,El Nio、La Nia事件成熟期滞后于北黄海冷水团最低温度的相对低值、高值出现,ENSO通过与东亚冬季风的相互作用与北黄海冷水团相联系。     

Structure and mass function of three young open clusters

Using UBVRI CCD data taken from 104-cm Sampurnanand Telescope, ARIES, Nainital, we present the structure, initial mass function and mass segregation of three young age (∼10 Myr) open star clusters: NGC 2129, NGC 1502 and King 12. Based on photometric as well as astrometric criteria, the cluster member stars as well as field stars have been identified. We construct luminosity function which is further used to estimate the mass functions by employing theoretical stellar evolutionary isochrones. The entire cluster region mass function (MF) slopes for NGC 2129, NGC 1502 and King 12 are obtained as −2.55 ± 0.14, −2.73 ± 0.36 and −1.94 ± 0.12 respectively. It is found that changes in the MF slope of King 12 are significantly different compared to NGC 2129 and NGC 1502 from inner region to outer region. The MF slope for King 12 is steeper at larger radii. The dynamical relaxation times for all three clusters are found to be less than age of the clusters. This indicates that all these clusters are dynamically relaxed. We show that for NGC 1502 and King 12, passing off of low mass stars from the inner region of the clusters to the halo occurs during the course of evolution.     

PRM标量平流方案在GRAPES全球预报系统中的应用

如何更好地模拟水物质的分布,对于数值天气预报效果的改进,特别是对于更好地模拟降水过程,具有重要的意义。半拉格朗日模式中的标量平流计算要求做到高精度、守恒、正定和保形,但GRAPES_GFS (Global-Regional Assimilation and PrEdiction System, Global Forecast System) 中采用的QMSL(Quasi-Monotone Semi-Lagrangian)平流方案在水汽的强梯度、不连续区域计算精度较低,且不能做到严格守恒。本研究借鉴计算流体力学领域的研究进展,将一个基于分段有理函数的物质平流方案PRM(Piecewise Rational Method)引入GRAPES_GFS中,按照通量形式求解水汽方程,并对极区进行了混合等技术处理。通过一系列理想试验对两种平流方案进行了对比,证明了PRM方案精度较高,特别是在水汽梯度大的区域优势明显,频散、耗散误差较小,守恒、保形性也要好于QMSL方案。通过对GRAPES_GFS中批量预报试验效果的检验,验证了PRM方案可以有效地改进模式对水物质分布的模拟,提高了降水的预报效果,对模式综合预报性能的提升也有明显作用。     

Hadley环流强度与中国东部气温的相关分析

利用NCEP / NCAR再分析月平均风场资料和国家气候中心提供的中国160个气象站的月平均气温资料,选用质量流函数计算方法描述平均经圈环流,用环流中心值大小表征其强度,分析1951-2010年Hadley环流强度趋势变化及其与中国东部气温的关系。结果表明：质量流函数能较好地表征平均经圈环流特征,且环流中心值大小能形象地反映环流强度。近60 a来,冬季北半球Hadley环流强度呈线性增强的趋势;夏季南半球Hadley环流强度在20世纪80年代初发生了由减弱趋势转变为显著增强趋势的年代际转折。中国东部大部分地区气温的年代际变化能很好地被Hadley环流强度变化解释,二者呈正相关关系,但显著相关区域随季节变化有所不同。     

Understanding the mobility patterns of Mass Rapid Transit (MRT) passengers amid COVID-19 in Singapore using smart card data

The Mass Rapid Transit (MRT) is one of the major modes of public transportation in Singapore. Understanding the mobility patterns of MRT passengers has implications for improving transportation efficiency. As a city-state with a high population density, Singapore provides a representation of balanced urban dynamics that informs smart urban planning. In this paper, we investigated and visualized (using both static maps and dynamic web map applications) the spatiotemporal characteristics of Singapore's MRT commuting patterns before the COVID-19 pandemic (January 2020) and during the first outbreak (May 2020) and the Omicron wave of the pandemic (February 2022), using MRT smart card data. We also investigated the relationship between the passenger flows of individual MRT stations and the nearby land use types. Our results showed that the spatial patterns of Singapore's MRT commuters match the polycentric urban structure. In addition to central areas, several regional centres were identified as passenger hotspots in multiple time periods. Furthermore, during the outbreak of the pandemic, especially in the period of the ‘circuit breaker’, there was a major decline in MRT passenger flows and a decrease in average MRT commuting distances during weekend/holiday peak hours. Lastly, correlations between passenger flows of MRT stations and the proportion of nearby land use types have been identified.     

Pliocene lahar deposits in the Coastal Cordillera of central Chile: Implications for uplift, avalanche deposits, and porphyry copper systems in the Main Andean Cordillera

Lahar deposits occur within a shallow marine sedimentary succession of the Pliocene La Cueva Formation in the Coastal Cordillera of central Chile (33°40′–34°15′S). Provenance studies of the abundant volcanic material in the lahar deposits suggest that they derive from denudation by mass wasting of Oligocene–Miocene volcanic rocks on the western slopes of the Main Andean Cordillera at the same latitude. Pliocene rock debris deposits preserved in the region of El Teniente (34°S) and scattered along the westernmost part of the Andes of central Chile indicate catastrophic erosive events related to the rapid uplift of the cordilleran block. This rock debris was deposited by avalanches and transformed further downslope into lahars by dilution with stream water. Lahars were channeled along the ancient drainage system that reached a shallow Pliocene sea at the site of the present Coastal Cordillera. The exceedingly rapid exhumation of active porphyry systems during the Early Pliocene in this part of the Andes may have played a role in affecting hydrothermal processes, brecciation, and diatreme formation at the porphyry systems of El Teniente and Río Blanco–Los Bronces.