天然气的扩散模型及扩散量的计算方法

盖层的存在是天然气成藏和保存的必要条件之一,而浓度封闭又是盖层的一种重要的封闭机理。在前人工作的基础上,研究了浓度封闭的机理,进一步系统建立了天然气扩散的地质和数学模型,并给出了模型的初始化条件,对天然气扩散量的计算方法作了讨论。     

大地电磁测深曲线平滑尺度

在大地电磁测深中由于噪声干扰常使得观测的信号发生畸变,严重地影响了信号的分析,因此如何有效地对噪声干扰进行滤波及怎样选择滤波时间尺度是当前数据处理中的难点。利用各向异性扩散(Anisotropic Diffusion,AD)及扩散平衡(Diffusion Balance,DB)方法在噪声压制与信号特征的保护及形态特征的恢复上达到了合理的平衡。模拟与实测数据显示:利用AD与DB可使平滑后的信号与原始信号达到高精度的逼近,信噪比从14.19 dB提高到69.25 dB;扩散平衡时间与噪声强度密切相关,噪声强度越高达到扩散平衡的时间越长;有效地压制了实测信号中的“飞点”干扰,恢复了信号的基本形态。     

Lagrangian and Eulerian estimates of circulation in the lee of Kapiti Island,New Zealand

Lagrangian drifters, moored acoustic Doppler current meters and hydrographic observations are combined with wind observations to describe the mean and variable nature of flow around Kapiti Island, New Zealand. Thirteen day-long deployments of up to six Lagrangian drifters show the mean flow is to the southwest, with evidence of stronger flows in the channel separating the island from the mainland, and an island wake in the lee of the island. Vortices in this island wake may be tidally driven. Scaling considerations suggest the flow is strong enough that tidal-generated vortices are shed on each tidal cycle. Both the drifters and mooring data suggest that the d’Urville Current around Kapiti Island has a significant wind-driven component. During north-westerlies, the drifters tend to hug the coast, and south-eastwards flows in the Rauoterangi Channel are accelerated. We suggest the observed correlation is the local expression of a South Taranaki basin scale response to the winds.     

Simultaneously simulate vertical and horizontal expansions of a future urban landscape: a case study in Wuhan,Central China

While there are extensive studies of urban 2D forms, research on the varying geometric features and spatial distribution patterns of urban 3D spaces is comparatively rare. In this paper, we propose a coupled model, known as BPANN-CBRSortCA, which is based on a back propagation artificial neural network (BPANN) and case-based reasoning technology with sort cellular automaton (CBRSortCA) to simulate future urban building heights and their spatial distribution. BPANN–CBRSortCA uses BPANN to predict the vertical extrusion of building heights and uses CBRSortCA to simulate horizontal urban expansion. The BPANN–CBRSortCA model is innovative because of its capabilities to simultaneously project urban growth in the vertical and horizontal dimensions. The proposed model also overcomes the limitations of the traditional cellular automata models that cannot simulate ‘diffused’ urban expansion. This research used Wuhan City as a case study to simulate vertical and horizontal urban expansion from 2015 to 2025. The results showed the following: (1) in the next 10 years, new build-up will mainly appear along the edge of Hongshan and Hanyang Districts or will occupy bare land in the form of ‘filling’ and (2) the tallest buildings will be mainly located to the south of East Lake in Hongshan District and on undeveloped land within the city. These simulation results can provide a reference for future urban planning.     

On the scavenging of SO2 by cloud and raindrops: I. A theoretical study of SO2 absorption and desorption for water drops in air

An extention of our previous theory for trace gas absorption into freely-falling cloud and raindrops is presented. This theory describes the convective diffusion of a trace gas through air and into a water drop with internal circulation, the drop falling at its terminal velocity. Using flow fields for the circulating water inside and for the moving air outside the drop, obtained by numerical solutions to the Navier—Stokes equation of motion, we numerically solved the convective diffusion equation to determine the uptake of SO₂ by water drops of various sizes, time exposure to the gas phase, and concentration of SO₂ in the gas phase. It was found that for drops of radius larger than 1 mm and relatively low gas concentrations (10 ppb (v)), resistance to gas diffusion lies mainly in the gas phase; while for drops of radius less than 500 m and gas concentrations larger than those found in the atmosphere (1% (v)), the resistance to diffusion lies primarily in the liquid phase. With drop sizes and gas concentrations between these limits, the rate of SO₂ uptake is controlled by a coupled resistance to diffusion inside and outside the drop. In addition to our general model, a simplified version was formulated which allows considerable savings in computer time for evaluation and improved ease of handling without significant loss of accuracy. A comparison between our simplified model and that of Barrie (1978) shows that the boundary-layer approach of Barrie may be a useful alternate approach to estimating trace gas absorption by water drops, provided appropriate values are chosen for the thickness of the boundary layers involved.     

Quantifying the influence of rainfall,vegetation and animals on soil erosion and hillslope connectivity in the monsoonal tropics of northern Australia

Erosion of soil by water is facilitated by both diffusive and fluvial processes. Here we examine three different soil redistribution processes operating at very different spatial and temporal scales in the monsoonal tropics of northern Australia. The first process, rainsplash, operates across the entire catchment. This process, while subject to annual and seasonal variations in rainfall amount and intensity, can be considered a constant forcing and redistributes on average 9 t ha⁻¹ year⁻¹ (range −0.9 to 19 t ha⁻¹ year⁻¹). The second process, bioturbation, where in this study soil is disturbed by feral pigs (wild boar), occurs in selected areas throughout each year. Pigs exhume 3 to 36.0 t ha⁻¹ year⁻¹ (average ~11 t ha⁻¹ year⁻¹). The effect of this disturbance may last for many years afterwards. The third process is the disturbance of the soil surface by tree throw and creation of pit–mound topography (also a form of bioturbation), together with the resultant placement of the tree superstructure (above ground biomass) on the ground, which may form debris dams. Tree throw at the scale examined here is likely to occur only once every 50–100 years, with the influence of this single event lasting for at least 10 years post event. Tree throw in a single event exhumed ~5 t ha⁻¹ (1.1–9.5 t ha⁻¹) of soil. In contrast to rainsplash, pig disturbance and tree throw events are largely point-based phenomena. Field observation suggests that it takes many years for the disturbance from both pigs and tree throw to be removed. We find here that in terms of relative soil redistribution, rainsplash has the largest influence, with any erosional disturbance by pigs and tree throw being within the variability of rainsplash. However, the disruption of surface flow by the pig digs and tree throw disrupts sedimentological and hydrological connectivity.     

橄榄岩中尖晶石化学成分分带的机理及其地质意义

橄榄岩中尖晶石的化学成分分带显示，在由温度降低引起的亚固相平衡过程中，与橄榄石及斜方辉石相邻的尖晶石边缘贫Mg和Al、富Fe和Cr，而与单斜辉石相邻的尖晶石边线相反。尖晶石的Fe和Mg分带为其他矿物的粒间Fe－Mg离子扩散所致；尖晶石中的Cr和Al分带则是尖晶石晶体内部Cr－Al离子的交互扩散所致。本文从热力学理论角度说明了尖晶石晶体内部的Cr－Al交互扩散受其Fe－Mg分带的控制；从热力学计算证明了尖晶石内Al必须从富Fe处向富Mg处扩散，解释了尖晶石中Mg和Al及Fe和Cr分带的一致性。     

Simulating the spatial diffusion of memes on social media networks

This article reports the findings from simulating the spatial diffusion processes of memes over social media networks by using the approach of agent-based modeling. Different from other studies, this article examines how space and distance affect the diffusion of memes. Simulations were carried out to emulate and to allow assessment of the different levels of efficiency that memes spread spatially and temporally. Analyzed network structures include random networks and preferential attachment networks. Simulated spatial processes for meme diffusion include independent cascade models and linear threshold models. Both simulated and real-world social networks were used in the analysis. Findings indicate that the numbers of information sources and opinion leaders affect the processes of meme diffusion. In addition, geography is still important in the processes of spatial diffusion of memes over social media networks.     

Metamorphic evolution,partial melting and rapid exhumation above an ancient flat slab: insights from the San Emigdio Schist,southern California

The San Emigdio and related Pelona, Orocopia, Rand and Sierra de Salinas schists of southern California were underplated beneath the southern Sierra Nevada batholith and adjacent southern California batholith along a shallow segment of the subducting Farallon plate in Late Cretaceous to early Tertiary time. These subduction accretion assemblages represent a regional, deeply exhumed, shallowly dipping domain from an ancient slab segmentation system and record the complete life cycle of the segmentation process from initial flattening and compression to final extensional collapse. An important unresolved question regarding shallow subduction zones concerns how the thermal structure evolves during the slab flattening process. New field relationships, thermobarometry, thermodynamic modelling and garnet diffusion modelling are presented that speak to this issue and elucidate the tectonics of underplating and exhumation of the San Emigdio Schist. We document an upsection increase in peak temperature (i.e. inverted metamorphism), from 590 to 700 °C, peak pressures ranging from 8.5 to 11.1 kbar, limited partial melting, microstructural evidence for large seismic events, rapid cooling (825–380 °C Myr^?1) from peak conditions and an ‘out and back’P–T path. While inverted metamorphism is a characteristic feature of southern California schists, the presence of partial melt and high temperatures (>650 °C) are restricted to exposures with maximum depositional ages between 80 and 90 Ma. Progressive cooling and tectonic underplating beneath an initially hot upper plate following the onset of shallow subduction provide a working hypothesis explaining high temperatures and partial melting in San Emigdio and Sierra de Salinas schists, inverted metamorphism in the schist as a whole, and the observed P–T trajectory calculated from the San Emigdio body. Lower temperatures in Pelona, Orocopia and Rand schists are likewise explained in the context of this overarching model. These results are consistent with an inferred tectonic evolution from shallow subduction beneath the then recently active Late Cretaceous arc to exhumation by rapid trench‐directed channelized extrusion in the subducted schist.