Random walk modeling of wake dispersion for the exhaust tower of an underground tunnel in urban area

In this paper, some experimental studies on the impact of effluent from an exhaust tower of an underground tunnel with special construction are reported. By measuring the flow field downstream of the tower in NJU meteorological wind tunnel, some flow characteristics in the make area were established. Based on these, an advanced random\|walk dispersion model was set up and applied successfully to the simulation of dispersion in the wake area. The modelling results were in accordance with wind tunnel measurements. The computed maximum of ground surface concentration in the building case was a factor of 3-4 higher than that in the flat case and appeared much closer to the source. The simulation indicated that random walk modelling is an effective and practical tool for the wake stream impact assessment.

TESTING FOR VARYING DISPERSION OF LONGITUDINAL BINOMIAL DATA IN NONLINEAR LOGISTIC MODELS WITH RANDOM EFFECTS

In this paper, it is discussed that two tests for varying dispersion of binomial data in the framework of nonlinear logistic models with random effects, which are widely used in analyzing longitudinal binomial data. One is the individual test and power calculation for varying dispersion through testing the randomness of cluster effects, which is extensions of Dean(1992) and Commenges et al (1994). The second test is the composite test for varying dispersion through simultaneously testing the randomness of cluster effects and the equality of random-effect means. The score test statistics are constructed and expressed in simple, easy to use, matrix formulas. The authors illustrate their test methods using the insecticide data (Giltinan, Capizzi & Malani (1988)).

Dispersion of the Mechanical Parts Performance Indicators Based on the Concept of Random Vector

To solve the precision and reliability problem of various machinery equipments and military vehicles, some military organisations, the industrial sector and the academia at home and abroad begin to pay attention to the statistical distribution of machining dimensions, material properties and service loads, and the system reliability optimization design with constraints and reliability optimization design of various mechanical parts is studied in this way. However, the above researches focus on solving the strength and the life problem, and no studies have been done on the discrete degree and discrete pattern of other performance indicators. The concept of using a random vector to describe the mechanical parts performance indicators is presented; characteristics between the value of the vector variance matrix determinant and the sum of the diagonal covariance matrix in describing the performance indicators of vector dispersion are studied and compared. A clutch diaphragm spring is set as an example, the geometric dimension indicator is described with random vector, and the applicability of using variance matrix determinant and variance matrix trace of geometric dimension vector to describe discrete degree of random vector is studied by using Monte-Carlo simulation method and component discrete degree perturbation method. Also, the effects of different components of diaphragm spring geometric dimension vector on the value of covariance matrix determinant and the sum of covariance matrix diagonal of diaphragm spring performance indicators vector are analyzed. The present study shows that the impacts of the dispersion of diaphragm spring cone angle on every performance dispersion are all ranked first, and far exceed that of other dimension dispersion. So it must be strictly controlled in the production process. The result of the research work provides a reference for the design of diaphragm spring, and also it presents a proper method for researching the performance of other mechanical parts.

The dispersion of surface contaminants by Stokes drift in random waves

Contaminants that are floating on the surface of the ocean are subjected to the action of random waves.In the literature,it has been asserted by researchers that the random wave action will lead to a dispersion mechanism through the induced Stokes drift,and that this dispersion mechanism may have the same order of significance comparable with the others means due to tidal currents and wind.It is investigated whether or not surface floating substances will disperse in the random wave environment due to the induced Stokes drift.An analytical derivation is first performed to obtain the drift velocity under the random waves.From the analysis,it is shown that the drift velocity is a time-independent value that does not possess any fluctuation given a specific wave energy spectrum.Thus,the random wave drift by itself should not have a dispersive effect on the surface floating substances.Experiments were then conducted with small floating objects subjected to P-M spectral waves in a laboratory wave flume,and the experimental results reinforced the conclusion drawn.

Taylor Dispersion of Contaminants by Dual-peak Spectral Random Waves

Recent extensive and important studies have provided detailed information and compelling evidence on how the presence of waves influences the vertical diffusivity/dispersivity in the coastal environment, which can affect various water quality considerations such as the distribution of suspended sediments in the water column as well as the potential of eutrophication. Comparatively, how the presence of waves influences the horizontal diffusivity/dispersivity has received only scant attention in the literature. Our previous works investigated the role played by the Taylor mechanism due to the wave-induced drift profile which leads to the longitudinal dispersion of contaminants in the horizontal direction, under regular sinusoidal waves and random waves with single-peak spectra. Natural waves in the coastal environment, however, often possess dual-peak spectra, comprising both higher frequency wind waves and lower frequency swells. In this study, the Taylor dispersion of contaminants under random waves with dual-peak spectra is examined through analytical derivation and numerical calculations. The effects of various dual-peak spectral parameters on the horizontal dispersion, including the proportion of lower frequency energy, peak frequency ratio and spectral shape parameter, are investigated. The results show that the relative energy distribution between the dual peaks has the most significant effect. Compared with single-peak spectra with equivalent energy, the Taylor dispersion with dual-peak spectra is stronger when the lower frequency is close to the peak frequency of the single-peak spectrum, and weaker with the higher frequency instead. Thus, it can be concluded that with a dual-peak wave spectrum, wind-dominated seas with higher frequency lead to stronger dispersion in the horizontal direction than swell-dominated seas with lower frequency.

Pattern Structure of Deterministic Displacement in Random Porous Media with Dispersion Effect

A new model — model of random porous media degradation via several fluid displacing, freezing, and thawing cycles is introduced and investigated in this paper. The fluid transport is based on the deterministic method with dispersion effect. The result shows that the topology and the geometry of the porous media have a strong effect on displacement processes. The cluster size of viscous fingering (VF) pattern in percolation cluster increases with the increase of iteration parameter n. When iteration parameter , VF pattern does not change with n. We find that the displacement fluid forms trapping regions in random porous media with dispersion effect. And the trapping regions will expand with the increasing of the iteration parameter n. When r (throat size) and , the peak value of the distribution increases as n increases, where is the normalized distribution of throat sizes after different displacement-damages but before freezing. The peak value of the distribution reaches a maximum when and , where is the normalized distribution of the size of invaded throat. This result is different from invasion percolation. It is found that the sweep efficiency E increases along with the increasing of iteration parameter n and decreases with the network size L, and E has a minimum as L increases to the maximum size of lattice. The VF pattern in percolation cluster has one frozen zone and one active zone.

TESTING FOR VARYING DISPERSION IN DISCRETE EXPONENTIAL FAMILY NONLINEAR MODELS

It is necessary to test for varying dispersion in generalized nonlinear models.Wei,et al(1998) developed a likelihood ratio test,a score test and their adjustments to test for varying dispersion in continuous exponential family nonlinear models.This type of problem in the framework of general discrete exponential family nonlinear models is discussed.Two types of varying dispersion,which are random coefficients model and random effects model,are proposed,and corresponding score test statistics are constructed and expressed in simple,easy to use,matrix formulas.

Random lasing in dye-doped polymer dispersed liquid crystal film

A dye-doped polymer-dispersed liquid crystal film was designed and fabricated,and random lasing action was studied.A mixture of laser dye,nematic liquid crystal,chiral dopant,and PVA was used to prepare the dye-doped polymer-dispersed liquid crystal film by means of microcapsules.Scanning electron microscopy analysis showed that most liquid crystal droplets in the polymer matrix ranged from 30 μm to 40 μm,the size of the liquid crystal droplets was small.Under frequency doubled 532 nm Nd：YAG laser-pumped optical excitation,a plurality of discrete and sharp random laser radiation peaks could be measured in the range of 575–590 nm.The line-width of the lasing peak was 0.2 nm and the threshold of the random lasing was 9 m J.Under heating,the emission peaks of random lasing disappeared.By detecting the emission light spot energy distribution,the mechanism of radiation was found to be random lasing.The random lasing radiation mechanism was then analyzed and discussed.Experimental results indicated that the size of the liquid crystal droplets is the decisive factor that influences the lasing mechanism.The surface anchor role can be ignored when the size of the liquid crystal droplets in the polymer matrix is small,which is beneficial to form multiple scattering.The transmission path of photons is similar to that in a ring cavity,providing feedback to obtain random lasing output.

Explicit Approximation Solutions and Proof of Convergence of the Space-Time Fractional Advection Dispersion Equations

The space-time fractional advection dispersion equations are linear partial pseudo-differential equations with spatial fractional derivatives in time and in space and are used to model transport at the earth surface. The time fractional order is denoted by β∈ and ?is devoted to the space fractional order. The time fractional advection dispersion equations describe particle motion with memory in time. Space-fractional advection dispersion equations arise when velocity variations are heavy-tailed and describe particle motion that accounts for variation in the flow field over entire system. In this paper, I focus on finding the precise explicit discrete approximate solutions to these models for some values of ?with ?, ?while the Cauchy case as ?and the classical case as ?with ?are studied separately. I compare the numerical results of these models for different values of ?and ?and for some other related changes. The approximate solutions of these models are also discussed as a random walk with or without a memory depending on the value of . Then I prove that the discrete solution in the Fourierlaplace space of theses models converges in distribution to the Fourier-Laplace transform of the corresponding fractional differential equations for all the fractional values of ?and .

基于随机本构模型的HTPB推进剂装药结构完整性评估

针对HTPB推进剂力学性能的分散性问题,引入用对数正态概率密度函数描述的随机参数,构建随机本构模型,开展了基于随机本构模型的发动机药柱在点火增压工况下的结构完整性分析。结果表明:通过随机本构模型预测的5组应力应变曲线与试验的5组应力应变曲线重合度较高,试验曲线全部落在95%的概率区间之内,随机本构模型可以较好地反映推进剂材料的分散性;药柱的力学响应与随机参数有关,最大Von Mises应力、最大Von Mises应变、最大位移、最大损伤指数及安全系数均与随机参数呈近似线性关系;基于试验曲线拟合的本构模型和基于概率区间预测的随机本构模型获得的药柱力学响应误差不超过1%,基于概率区间预测的随机本构模型可以准确预测点火增压载荷下的药柱力学响应。

扫描电镜/能谱法对粉底液的检测分类研究

为建立一种将扫描电镜/能谱法与多元统计学结合检测粉底液物证的方法。对收集到的50个粉底液样本进行前处理,利用扫描电镜/能谱仪对样本进行分析测试,将50个样本大致分成2大类;结合K-Means聚类对实验数据进行处理,将2大类样本细化分为4类;最后利用随机森林算法搭建分类模型,40个样本作为训练集,10个样本作为测试集,测试集的预测正确率达到86.6%,预测效果良好,可实现样本分类自动化。此方法操作简单,可实现无损检材、分类效果良好,可直接用于公安机关侦查破案,在法庭科学领域有广阔的应用前景。

Realization of a source-device-independent quantum random number generator secured by nonlocal dispersion cancellation

Quantum random number generators(QRNGs)can provide genuine randomness by exploiting the intrinsic probabilistic nature of quantum mechanics,which play important roles in many applications.However,the true randomness acquisition could be subjected to attacks from untrusted devices involved or their deviations from the theoretical modeling in real-life implementation.We propose and experimentally demonstrate a source-device-independent QRNG,which enables one to access true random bits with an untrusted source device.The random bits are generated by measuring the arrival time of either photon of the time–energy entangled photon pairs produced from spontaneous parametric downconversion,where the entanglement is testified through the observation of nonlocal dispersion cancellation.In experiment,we extract a generation rate of 4 Mbps by a modified entropic uncertainty relation,which can be improved to gigabits per second by using advanced single-photon detectors.Our approach provides a promising candidate for QRNGs with no characterization or error-prone source devices in practice.

三维背景噪声数值模拟及频散曲线验证

近年来,以人类生产活动产生的振动和天然振动作为震源的背景噪声成像技术逐渐成为研究热点。无论是基于已知模型对背景噪声成像方法以及频散曲线提取方法的有效性进行验证,还是对背景噪声数据采集方式进行参数优化,均需通过波场数值模拟手段获取所需的背景噪声理论合成数据。三维数值模拟是背景噪声成像中的一项重要研究内容。针对背景噪声在时间域和空间域上具有随机性的特点,将随机震源引入三维瑞雷波波场有限差分数值模拟,实现背景噪声数据的有效计算,将模拟得到的噪声记录用基于Aki公式的两道法提取频散曲线并与理论频散曲线对比,以验证噪声模拟的可行性和有效性。理论模型测试结果表明:当震源参数处于合理范围时,合成背景噪声数据频散曲线与理论频散曲线拟合效果良好;同时三维模拟数据提取的频散曲线比二维模拟数据提取精度更高。

裂隙介质中Pu迁移的连续时间随机游走模拟

为更准确地模拟核素的非菲克迁移行为并寻求一种更合理的建模方法,根据一维裂隙岩柱中Pu(钚)迁移试验资料,利用基于不同联合概率密度的连续时间随机游走(CTRW)模型和传统对流-弥散方程(ADE)对Pu迁移的穿透曲线(BTC)进行了过程模拟,对比分析了ADE模型、CTRW-TPL模型、CTRW-TPLA模型和CTRW-ETA模型的拟合程度及适用性,进而选择出最优的模型对不同胶体浓度下Pu在裂隙介质中的迁移进行模拟研究.结果表明,相较于传统ADE模型,参数拟合后考虑吸附作用的CTRW-TPL模型能有效地描述非菲克迁移行为特征,CTRW-ETA拟合过程更易实现,但能为迁移行为的刻画提供的信息较少.研究还发现胶体的存在显著提高了Pu在裂隙介质中的迁移性,但胶体浓度超过某个临界值后,随着浓度升高Pu的迁移性反而减弱,在CTRW理论框架中,该过程表现为表征广义运移速度和弥散系数的参数值先增大后减小,而介质对溶质颗粒的平均吸附率先减小后增大.

枪托结构对射击精度影响分析

为研究立姿无依托抵肩射击最优的枪托结构对射击精度的影响,提出一种射击精度的仿真与实验对比分析方案。在人枪系统动力学模型基础上,以枪托抵肩面倾斜角度、枪托刚度为设计优化变量,通过协同仿真获取膛口跳角、内弹道随机散布对比曲线;将立靶散布R50的仿真计算结果与试验结果作对比,结果基本一致,误差小于15%。结果表明:采取6°软枪托时,射弹散布有明显的优化,该方案对优化人枪系统中枪械结构和人机工效设计具有指导作用。

A THREE-DIMENSIONAL RANDOM DISPERSION MODEL WITHIN SURFACE LAYER

Taking advantage of the relation of lateral Lagrangian time scale T_(LY) with the stability and height, we establish a three-dimensional random dispersion model and simulate the dispersing process of a ground source within the surface layer. The results calculated show that under the condition of stable stratifica- tion our model is obviously better improved than those obtained by assuming T_(LY) to be constant, while under unstable condition, not much improved.

Validation of Pore-Scale Simulations of Hydrodynamic Dispersion in Random Sphere Packings

We employ the lattice Boltzmann method and random walk particle tracking to simulate the time evolution of hydrodynamic dispersion in bulk,random,monodisperse,hard-sphere packings with bed porosities(interparticle void volume fractions)between the random-close and the random-loose packing limit.Using JodreyTory and Monte Carlo-based algorithms and a systematic variation of the packing protocols we generate a portfolio of packings,whose microstructures differ in their degree of heterogeneity(DoH).Because the DoH quantifies the heterogeneity of the void space distribution in a packing,the asymptotic longitudinal dispersion coefficient calculated for the packings increases with the packings’DoH.We investigate the influence of packing length(up to 150 d_(p),where d_(p) is the sphere diameter)and grid resolution(up to 90 nodes per d_(p))on the simulated hydrodynamic dispersion coefficient,and demonstrate that the chosen packing dimensions of 10 d_(p)×10 d_(p)×70 d_(p) and the employed grid resolution of 60 nodes per d_(p) are sufficient to observe asymptotic behavior of the dispersion coefficient and to minimize finite size effects.Asymptotic values of the dispersion coefficients calculated for the generated packings are compared with simulated as well as experimental data from the literature and yield good to excellent agreement.

多孔介质渗流随机模型

将随机模拟方法应用于多孔介质中的物质传输过程,对不同孔隙通道联结率下的弥散规律进行了分析.模 拟中发现:在渗流阈值附近,存在反常弥散和优势通道现象,纵向弥散系数也比通常欧几里德空间大得多;流体在多 孔介质中的弥散受结构影响很大.

黑河流域水资源动态变化及其趋势的灰色Markov链预测

根据有关水文气象台站的观测数据,对黑河流域水资源时空分布特征及变化规律进行了分析,并基于GM(1,1)模型和Markov链原理,提出了一个用于黑河流域的水资源变化趋势预测的灰色离散随机过程模型。结果表明,从1944年有观测记录以来的近60a时间里,以黑河干流为代表的黑河流域天然径流经历了几个长度不等的丰水段与枯水段,而目前正处于1996年开始第5个丰水段的下降段的最低点或自2000年开始的第6个枯水段的起始点。未来几年里,黑河流域天然水资源的变化总体上将呈现一种偏枯或平水偏枯的状态,但径流偏枯的幅度将不会很大。

揉散法治疗急性乳腺炎初期的随机对照临床研究

背景:急性乳腺炎是乳腺的急性感染性疾病,大量抗生素治疗往往不能取得很好疗效,应积极寻找安全有效的非药物疗法。目的:验证揉散法治疗急性乳腺炎初期的临床疗效。设计、场所、对象和干预措施:采用多中心随机对照试验,将198例来自上海中医药大学附属岳阳中西医结合医院和龙华医院以及上海市杨浦区妇幼保健院的急性乳腺炎初期患者随机分为治疗组和对照组各99例。治疗组施以推拿揉散手法,对照组口服头孢拉定,均治疗5 d。主要结局指标:观察乳腺局部肿块大小、症状体征积分等效应指标和不良反应。结果:治疗组总有效率为95.92%(94/98),对照组总有效率为80%(76/95),两组总有效率比较,差异有统计学意义(P<0.05);两组治疗前后肿块大小与症状体征积分差值比较,差异均有统计学意义(P<0.05)。结论:揉散法治疗急性乳腺炎初期疗效确切,具有安全性和可重复性。