Environmental dispersion in a tidal flow through a depth-dominated wetland

Presented in this paper is a theoretical analysis for longitudinal evolution of mean concentration of an environmental emission into a tidal wetland flow. The velocity distribution of the periodic flow through the wetland is derived, with that for a fully developed steady wetland flow included as a special case. The zero-th, first and the growth of the second order moments of the concentration are rigorously obtained by applying Aris’s method of concentration moments to derive the environmental dispersivity. The necessary time needed for the environmental dispersivity to attain a steady oscillating status is analyzed. The effects of some characteristic parameters, especially one representing the impact of vegetation in the wetland on both velocity profile and environmental dispersivity, and another identifying the effect of flow oscillation on the environmental dispersivity, are illustrated in detail. To reflect the dispersion enhancement by the flow oscillation, a typical example is given to characterize the critical length and duration of the contaminant cloud.     

Flow distribution and environmental dispersivity in a tidal wetland channel of rectangular cross-section

Presented in this paper is a theoretical analysis on flow distribution and environmental dispersivity for a tidal wetland channel of rectangular cross-section. The analytical solution of velocity distribution for the tidal wetland flow is obtained and illustrated with a limiting case covering the known solution for a steady wetland flow. By use of Aris’s method of concentration moments, the environmental dispersivity for a pulsed contaminant emission into the tidal wetland flow is rigorously derived and characterized in terms of dimensionless parameters. The solution is shown to be a generalization of the environmental dispersivity for the corresponding steady wetland flow, taking into account the combined action of periodic oscillation and cross-sectional variation of superficial flow as well as the difference between superficial mass dispersivities in the vertical and lateral directions. For a long time evolution of the contaminant cloud, the environmental dispersivity may approach a stable stage of oscillation with a period equal to the period of the superficial flow. The evolution of environmental dispersivity at the initial stage for the tidal wetland flow is shown not monotonous as it does in the case of the steady wetland flow. It is also found that the period of superficial flow has no impact on the necessary time for the environmental dispersivity to attain the stable stage.     

Cloud concentration statistics and dosage

A new measure of the dilution of contaminant cloud concentration values is introduced. The expected-mass-fraction function is shown to have both experimental and theoretical advantages. There are virtually no measurements of dilution for a contaminant cloud. A cloud in homogeneous turbulence is used as an illustrative example. These calculations can be validated with conventional, fixed-point concentration measurements in a wind tunnel.     

Environmental dispersion in a three-layer wetland flow with free-surface

To further address the characteristic of contaminant transport in wetlands of a multi-layer structure, environmental dispersion of a pulsed contaminant emission into a steady flow is analytically explored in this paper for the typical case of a respectively vegetated or packed three-layer wetland dominated with free-water-surface-effect. The hierarchical structure for the critical length and duration of the contaminant cloud is illustrated for the dispersion of typical contaminant constituents.     

Environmental dispersion in wetland flow

For the typical case of a pulsed contaminant emission into a shallow wetland channel, a theoretical analysis is presented in this paper for the decay of the width-averaged mean concentration under environmental dispersion. The velocity profile of a fully developed steady flow through the wetland channel is obtained with that for the well-known plane Poiseuille flow as a special case. An environmental dispersion model for the mean concentration is devised as an extension of Taylor’s classic analysis on dispersion, and corresponding environmental dispersivity is obtained by Aris’s method of moments and illustrated with an asymptotic time variation with stem dominated, transitional, and width-stem dominated stages. Analytical solution for the longitudinal decay of mean concentration due to environmental dispersion is rigorously derived and characterized with multiple time scales.     

A solution-scheme for the convective-diffusion equation

This paper presents a versatile solution-scheme for the convective-diffusion equation. A small-time, asymptotic, solution for an instantaneous point source of scalar contaminant is expressed as a three-dimensional, Hermite polynomial expansion and manipulated, using superposition, to generate the contaminant concentration field that results at larger times and for arbitrary, continuous or instantaneous, source contaminant distribution. This equation is commonly used to model contaminant dispersion in complex environmental flows so that the considerable degree of generality, flexibility and efficiency of this solution-scheme highly commends it to this application. The off-diagonal terms in the diffusivity tensor and the non-zero gradient of this term and the mean-velocity field are shown to make a significant contribution to the evolution of the contaminant concentration field resulting from the instantaneous release of contaminant from a point source.

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Zusammenfassung Die vorliegende Arbeit gibt eine vielseitig brauchbare Lösungsmethode für die konvektive Diffusionsgleichung. Die für kurze Zeiten gültige asymptotische Lösung für eine plötzlich wirkende Punktquelle der diffundierenden Skalargröße wird als dreidimensionale Entwicklung in Hermite'schen Polynomen dargestellt. Dies wird benützt um das Feld für größere Zeiten darzustellen, für beliebige, kontinuierliche oder diskontinuierliche Quellverteilungen. Diese Gleichung wird allgemein benützt als Modell für Dispersion von Schadstoffen in komplizierten Strömungen bei natürlichen Umgebungsverhältnissen; die Allgemeingültigkeit, Anpassungsfähigkeit und Wirksamkeit der Lösung machen die Methode für diese Anwendungen besonders geeignet. Es wird gezeigt, daß die Nichtdiagonalterme des Diffusionstensors sowie die nichtverschwindenden Gradienten dieses Termes und der mittleren Geschwindigkeit wesentliche Beiträge zur Entwicklung des Feldes leisten, die von der Punktquelle erzeugt wurde.

     

Multi-stage stochastic programming models for provisioning cloud computing resources

We focus on the resource provisioning problem of a cloud consumer from an Infrastructure-as-a-Service type of cloud. The cloud provider offers two deployment options, which can be mixed and matched as appropriate. Cloud instances may be reserved for a fixed time period in advance at a smaller usage cost per hour but require a full commitment and payment for the entire contract duration. In contrast, on-demand instances reflect a pay-as-you-go policy at a premium. The trade-off between these two options is rooted in the inherent uncertainty in demand and price and makes it attractive to complement a base reserved capacity with on-demand capacity to hedge against the spikes in demand. This paper provides several novel multi-stage stochastic programming formulations to enable a cloud consumer to handle the cloud resource provisioning problem at a tactical level. We first formulate the cloud resource provisioning problem as a risk-neutral multi-stage stochastic program, which serves as the base model for further modeling variants. In our second set of models, we also incorporate a certain concept of system reliability. In particular, chance constraints integrated into the base formulation require a minimum service level met from reserved capacity, provide more visibility into the future available capacity, and smooth out expensive on-demand usage by hedging against possible demand fluctuations. An extensive computational study demonstrates the value of the proposed models by discussing computational performance, gleaning practical managerial insights from the analysis of the solutions of the proposed models, and quantifying the value of the stochastic solutions.     

Advection-Diffusion in Reversing and Oscillating Flows: 1. The Effect of a Single Reversal

Motivated by the need to understand effluent dispersion in shallowtidal waters, a two-dimensional analysis of advection and diffusionin a reversing flow has been carried out. The flow speed varieslinearly with time, passing through zero at time t=0. A pointsource discharges contaminant into this flow at a steady rate,so that water which is close to the source around the time offlow reversal will become highly contaminated. Thus a peak inthe contaminant concentration field will appear, moving downstreamafter the reversal at a speed close to that of the flow. Thisconcentration peak has certain characteristics similar to acloud of contaminant from an instantaneous discharge at t=0.The solution of the advection-diffusion equation is in the formof an integral of concentration fields due to instantaneousreleases of contaminant at all previous times. At large timesafter the flow reversal, asymptotic analysis yields good approximationsto this integral. The use of Laplace's method is equivalentto ignoring longitudinal diffusion (the boundary-layer approximation);however, the expansion obtained in this way is not uniformlyvalid near the concentration peak, indicating that longitudinaldiffusion plays an important role in the development of thispeak. Uniformly valid expansions are obtained for the concentrationaround the peak, and also around the source where the boundary-layerapproximation always breaks down. Numerical integration hasalso been carried out, the results being used to produce contourplots of concentration for various times either side of theflow reversal.     

Taylor dispersion in a packed tube

Presented in this paper is a theoretical analysis for longitudinal scalar spread of mean concentration under a fully developed flow in a tube packed with porous media. A general form of momentum equation for superficial flow in porous media is introduced as a combination of the Navier–Stokes equation and Darcy’s law plus a superficial dispersion term due to phase discontinuity between the fluid flow and solid frame. The analytical solution presented for the fully developed superficial flow includes that for the Poiseulle flow in an evacuated tube as a limiting case. As an extension of Taylor’s classical work on dispersion of soluble matter in solvent flowing slowly through an evacuated tube, a one-dimensional dispersion equation valid for overall environmental assessment of contaminant is rigorously derived by cross-sectionally averaging the superficial mass equation and introducing a closure relation for a new unknown out of the averaging procedure, and corresponding Taylor dispersivity determined is shown to be a generalization of Taylor’s well-known result for the Poiseulle flow.     

Persistence Terrace for Topological Inference of Point Cloud Data

Topological data analysis (TDA) is a rapidly developing collection of methods for studying the shape of point cloud and other data types. One popular approach, designed to be robust to noise and outliers, is to first use a smoothing function to convert the point cloud into a manifold and then apply persistent homology to a Morse filtration. A significant challenge is that this smoothing process involves the choice of a parameter and persistent homology is highly sensitive to that choice; moreover, important scale information is lost. We propose a novel topological summary plot, called a persistence terrace, that incorporates a wide range of smoothing parameters and is robust, multi-scale, and parameter-free. This plot allows one to isolate distinct topological signals that may have merged for any fixed value of the smoothing parameter, and it also allows one to infer the size and point density of the topological features. We illustrate our method in some simple settings where noise is a serious issue for existing frameworks and then we apply it to a real dataset by counting muscle fibers in a cross-sectional image. Supplementary material for this article is available online.     

Galerkin-based multi-scale time integration for nonlinear structural dynamics

This paper deals with a GALERKIN-based multi-scale time integration of a viscoelastic rope model. Using HAMILTON's dynamical formulation, NEWTON's equation of motion as a second-order partial differential equation is transformed into two coupled first order partial differential equations in time. The considered finite viscoelastic deformations are described by means of a deformation-like internal variable determined by a first order ordinary differential equation in time. The corresponding multi-scale time-integration is based on a PETROV-GALERKIN approximation of all time evolution equations, leading to a new family of time stepping schemes with different accuracy orders in the state variables. The resulting nonlinear algebraic time evolution equations are solved by a multi-level NEWTON-RAPHSON method. Realizing this transient numerical simulation, we also demonstrates a parallelized solution of the viscous evolution equation in CUDA©. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Control Parametrization and Finite Element Method for Controlling Multi-species Reactive Transport in an Underground Channel

In this paper, a cleaning program involving effluent discharge of several species in a one-dimensional underground channel is considered. Due to environmental health requirements, the outlet concentration of each species at any time during the entire cleaning activities has to be kept at a certain low level in order to offset the deteriorating effect of contaminant destruction. Thus, a computational scheme using combined control parametrization and finite element method is used to develop a cleaning program to meet the above environmental health requirements. Numerical examples have been used to illustrate the efficiency of our method.     

Coupled consolidation and contaminant transport model for simulating migration of contaminants through the sediment and a cap

Capping contaminated sediments in waterways is an alternate remediation technique to dredging and is typically much cheaper than dredging. When cap material is placed on top of contaminated sediment, it has both a short-term and long-term hydraulic impact on the underlying sediment. A numerical model of consolidation, based on a nonlinear finite strain theory for a consolidating fine-grained sediment bed was developed. The nonlinear equation of consolidation was solved in a material (or reduced) coordinate using an explicit finite difference numerical scheme. An one-dimensional advection–diffusion equation with sorption and decay was solved on a convective coordinate using a finite volume total variation diminishing (TVD) scheme for the contaminant concentration within the consolidating sediment. The contaminant transport model was coupled with the consolidation model. The time and space varying porosities, permeabilities, and advective velocities computed by the consolidation model were linked to the transport model at the same time level. A number of benchmark tests that are relevant to the consolidation of a fine-grained sediment were designed and tested. The relative contribution of consolidation-induced transient advective velocities on the migration of a contaminant during consolidation was also investigated. The coupled model performance was validated by simulating the transport of hazardous chemicals under consolidation in a confined aquatic disposal (CAD) site in the Lower Duwamish Waterway, Seattle.     

面向不确定需求租户集的云服务智能匹配模型

为了解决云计算环境下由海量租户集和资源集间的不确定性因素引起的高质量云服务获取困难的问题,提出了一种描述动态异构租户集不确定性需求的方法.在此基础上,构建属性权重完全未知情况下的云服务智能匹配模型,排除了租户提交权值造成的偏差.神经网络以属性区间计算的相离度作为输入,服务满意度为输出来动态模拟租户集的不确定需求,运用萤火虫算法求解模型获取最优服务组合.最后,实例验证了神经网络的可靠性以及算法的有效性.实验结果表明,模型能有效获取高质量的云服务组合,优于传统的匹配方法.     

污染物在非饱和带内运移的流固耦合数学模型及其渐近解

污染物在非饱和带中运移过程是多组分多相渗流问题.在考虑气相的存在对水相影响的前提下,基于流固耦合力学理论,建立了污染物在非饱和带内运移的流固耦合数学模型.对该强非线性数学模型采用摄动法及积分变换法进行拟解析求解,得出了解析表达式.对非饱和带内的孔隙压力分布、孔隙水流速以及污染物的浓度在耦合与非耦合气相条件下的分布规律进行解析计算.对该渐近解与Faust模型的计算结果进行了对比分析,结果表明:该模型解与Faust解基本吻合,且气相作用以及介质的变形对溶质的输运过程产生较大的影响,从而验证了解析表达式的正确性和实用性.这为定量化预报预测污染物在非饱和带中迁移转化和实验室确定压力-饱和度-渗透率三者之间的关系提供了可靠的理论依据.     

空间分数阶电报方程的格子Boltzmann方法

应用格子Boltzmann方法（LBM）对Riemann Liouville空间分数阶电报方程进行了数值模拟研究.首先,将分数阶算子中的积分项进行离散化处理,并进行了收敛阶分析.然后,构建了带修正函数项的一维三速度(D1Q3)的LBM演化模型.利用Chapman Enskog多尺度技术和Taylor展开技术,推导出各平衡态分布函数和修正函数的具体表达式,准确地从所建的演化模型恢复出宏观方程.最后,数值计算结果表明该模型是稳定、有效的.     

国内云计算研究进展可视化分析

以CNKI收录的2007-2012年间5212篇云计算文献为研究对象,采用文献计量、社会网络分析法,从文献的年代、来源期刊及基金资助分布,作者及其合作、研究机构及其合作,研究热点及其演进等方面可视化分析了国内云计算研究进展.     

Some aspects in practical estimation of groundwater contaminant concentrations

Spatial distribution of groundwater contaminant concentration has special characteristics such as approximate symmetric profile, for example, in the transversal direction to groundwater flow direction, a certain ratio in directional propagation distances, etc. To obtain a geophysically appropriate semivariogram which is a key factor in estimation of groundwater contaminant concentration at desired locations, these special characteristics should be considered. Specifically, the concepts of symmetry and ratio are considered in this paper. By applying these two concepts, significant improvement of semivariograms, estimation variances, and final estimation results compared with the ones by conventional approaches which usually do not account for symmetry and ratio are shown using field experimental data.     

基于中医健康云的健康养老服务平台设计与应用

中医健康云能将中医的特色化、标准化与大数据、人工智能应用完美融合。本文基于中医健康云技术和老龄群体对养老服务的迫切需求,对中医健康云服务平台和架构设计进行建设性研究,同时分析中医健康云平台的关键技术所在,进而提出中医健康云在健康养老服务中的应用设计。以期利用互联网与大数据,融合传统中医智慧,对老龄群体的健康进行动态跟踪与实时咨询,为老年群体提供及时、有效和针对性的健康养老服务。