ALLUVSIM: A program for event-based stochastic modeling of fluvial depositional systems

This paper presents an algorithm for the construction of event-based fluvial models. The event-based approach may be applied to construct stochastic pseudo-process-based fluvial models for a variety of fluvial styles with conditioning to sparse well data (1–5 wells) and areal and vertical trends. The initial models are generated by placing large-scale features, such as channels and crevasse splays, into the model as geometric objects. These large-scale features are controlled by geometric input parameters provided by the user and are placed into the model to roughly honor well data through a rejection and updating method. Yet, some model to well data mismatch may still occur due to inconsistency in the size and positioning of complicated features relative to the well data. An image processing algorithm is used to post-process realizations to exactly honor all well data. The final, cell-based models, have no data mismatch and contain geologically realistic fluvial features that would be difficult to obtain with other pixel-based methods and precise conditioning that is difficult to obtain with object-based methods.     

Using the Snesim program for multiple-point statistical simulation

Traditionally, there are two mainstream avenues for geostatistical modeling: pixel-based two-point simulation and object-based simulation. Each is good at either data conditioning or reproducing geological shapes, but none is good at both. Multiple-point simulation combines the strengths of these two avenues. As an advanced pixel-based technique, it inherits the flexibility of pixel-based techniques by building the model one pixel at a time, hence data conditioning is easily achieved; it is also capable of reproducing curvilinear geological shapes through borrowing multiple-point statistics from a training image.The snesim code provides such a multiple-point simulation program. A training image is used to represent the prior geological knowledge, which is scanned to obtain the conditioning probability values for the central node belonging to a facies category given any multiple-point conditioning data event. These training probability values are stored in a search tree a prior to simulation. Then in a sequential simulation mode, at each uninformed node, according to its specific conditioning data event a probability value is retrieved from the search tree, and a value is simulated from it.There are many input parameters to the snesim program, the impact of which might not be immediately clear to people who are not familiar with the code. In this paper, we aim at bringing important aspects of this program and providing practical guidelines to using the program. Sensivity analyses are performed on the important input parameters. The results are analyzed and recommendations are provided on how to set these parameters appropriately.     

SimClast: An aggregated forward stratigraphic model of continental shelves

This paper describes a new basin-scale, 2DH model of continental shelves with a focus on generating clastic stratigraphy. The model, SimClast, is capable of simulating fluvial channel network dynamics, plume deposition, wave-induced cross-shore and longshore transport, and large-scale marine circulation. Fluvial channel networks and coastal dynamics are below the resolution of the model discretization and have been parameterized. This subgrid parameterization allows SimClast to maintain a realistic representation of these important sedimentary processes without significantly compromising computational efficiency. Open marine currents and river plume hydrodynamics are represented using a combined potential flow field, which allows SimClast to be used under a wide variety of settings, ranging from single river systems to full basin scale with multiple tributaries and marine currents. The most significant addition to the current suite of dynamic, stratigraphic models is the down and up dip interaction between several sedimentary environments. The explicit linking of the sedimentary environments allows feedback loops to be studied in more detail. Modeling results under time-invariant forcing are consistent with generalized conceptual models of stacking patterns. Yet, internal facies architecture is very complex for both wave- and fluvial-dominated deltas due to the interaction of several competing sedimentary processes.     

A simple algorithm for the mapping of TIN data onto a static grid: Applied to the stratigraphic simulation of river meander deposits

Triangulated irregular networks (TIN) in landscape evolution models have the advantage of representing geologic processes that involve a horizontal component, such as faulting and river meandering, due to their adaptive remeshing capability of moving, adding and deleting nodes. However, the moving node feature is difficult to integrate with the accumulation of a three-dimensional (3D) subsurface stratigraphy, because it requires 3D subsurface interpolation, which results in stratigraphic data loss due to heterogeneity of the subsurface and averaging effects. We present a simple algorithm that maps any changes in the configuration of TIN landscape nodes onto a static grid, facilitating the creation of a fixed stratigraphic record of TIN surface change. The algorithm provides a practical solution not only for the stratigraphic problem, but also for other problems that involve linking of models that use TIN and raster discretization schemes. An example application is presented using the river meandering module incorporated in the CHILD landscape evolution model. Examples are shown of cross-sections, and voxel distributions and geo-archaeological depth–age maps. These illustrate the type of insights that can be obtained from process-based modeling of subsurface fluvial architecture, and highlight potential applications of stratigraphic simulation.     

交互的极线几何建模方法

讨论了一种基于图像的交互式几何建模方法，该方法利用手动方式标定模型的平行线、特征点，得到照相机参数，进而计算出模型的几何信息，并从图像中提取纹理，提出一种最优纹理选取算法，以确保拼接纹理的合理性，该算法主要应用于构造形状规则的模型，不需要知识照相机的内外参数，简便实用，实验结果表明，该方法在一定的场合下可以满足重建要求，重建出的三维模型具有照片真实感，并且能够实时漫游。     

改进约束三角网在沉积相带图中的应用研究

针对在沉积相带追踪中,常规三角剖分算法构造的三角网无法自动解决河道砂体跨井排不连通问题,提出了一种相带边界线自动识别方法。该方法的关键步骤是采用逐点插入法先生成无约束三角网;再根据河道砂体连通情况插入虚拟井,并通过该虚拟井建立跨井排井的连通线,将这两条线作为约束边插入第一步生成的三角网中,将三角网部分重构,形成最终约束三角网,对该三角网进行相带边界追踪。系统前端采用。 NET网页框架和Applet网页嵌入技术,核心绘图功能采用Java 2D绘图技术,效果良好。     

A CAD System for Color Design of a Car

We have developed a color CAD system which enables a color designer to evaluate and create body colors of a car on a graphic display and put this system into practical use. The system has three features; generating realistic images comparable to photography to satisfy the car designer's needs, through close analysis of the physical phenomena taking place in the real environment, reproducing the desired colors very accurately on a CRT monitor, through analysis of the CRT colorimetric characteristics of reproducing the specified colors in response to the input signals, and utilizing a parallel computer to generate realistic images at a high speed and to control colors through interactive operation. Application of the CAD system reported here to the field of color design made it possible to fully evaluate and create body colors by means of computer graphics, replacing the conventional method which requires the painting of clay models or prototype cars.     

A simple algorithm for checking compatibility among discrete conditional distributions

A distribution is said to be conditionally specified when only its conditional distributions are known or available. The very first issue is always compatibility: does there exist a joint distribution capable of reproducing all of the conditional distributions? We review five methods-mostly for two or three variables-published since 2002, and we conclude that these methods are either mathematically too involved and/or are too difficult (and in many cases impossible) to generalize to a high dimension. The purpose of this paper is to propose a general algorithm that can efficiently verify compatibility in a straightforward fashion. Our method is intuitively simple and general enough to deal with any full-conditional specifications. Furthermore, we illustrate the phenomenon that two theoretically equivalent conditional models can be different in terms of compatibilities, or can result in different joint distributions. The implications of this phenomenon are also discussed.     

基于单幅图像的真实感人体动画合成

由于单幅图像缺失三维信息以及完整的纹理信息,基于单幅图像的真实感三维人体动画合成极具挑战性。针对单幅图像三维信息缺失问题,提出了一种基于SMPL参数模型的三维人体几何重建方法。该方法以单幅图像为输入,先根据输入图像人体轮廓信息变形标准的SMPL参数模型分别生成与目标轮廓一致的正反面的三维几何模型,然后利用基于B样条插值的网格拼接融合算法拼接正反面三维几何,最后为了恢复正确的手部几何,利用基于B样条插值的网格拼接融合算法,将重建后的模型上错误的手部几何用标准SMPL参数模型上正确的手部几何替换。同时,针对单幅图像中纹理缺失的问题,提出了一个称为FBN（front to back network）的对抗生成网络,用于恢复被遮挡的人体背面纹理。实验结果表明,该方法生成的具有完整纹理的人体几何能够由3D运动数据驱动运动,生成具有高度真实感的三维人体动画。     

一种基于神经网络的沉积相识别方法

将人工神经网络(ANN)模式识别技术应用于对测井曲线进行单井划相,加快了划相速度,大大提高了工作效率.根据某地区的河流微相特征标志,给出了一种基于神经网络的沉积相识别方法.神经网络采用带有动量项和自适应学习率的反向传播算法(BP)进行训练.     

Direct numerical study of hypersonic flow about a swept parabolic body

Direct numerical simulations (DNS) of hypersonic flow about a swept parabolic body have been performed to study the global stability of flow in the leading-edge region of a swept blunt body. Previous stability investigations have been based on local models but have not fully succeeded in reproducing the established experimental findings. The current flow configuration represents a more realistic model and is thus expected to resolve some of the remaining questions. However, novel approaches like DNS-based global stability theory are necessary for such flow models and are employed in this study. As a result, boundary-layer modes have been identified by different but complementary techniques as the dominant instability mechanism. The DNS starting with small-amplitude white noise provide further evidence for the presence of non-modal effects which may be important in the subcritical regime. From a methodological point of view, the potential for quantitative flow analysis by combining numerical simulations with advanced iterative techniques represents a promising direction for investigating the governing physical processes of complex flows.     

Feature preserving Delaunay mesh generation from 3D multi-material images

Generating realistic geometric models from 3D segmented images is an important task in many biomedical applications. Segmented 3D images impose particular challenges for meshing algorithms because they contain multi-material junctions forming features such as surface patches, edges and corners. The resulting meshes should preserve these features to ensure the visual quality and the mechanical soundness of the models. We present a feature preserving Delaunay refinement algorithm which can be used to generate high-quality tetrahedral meshes from segmented images. The idea is to explicitly sample corners and edges from the input image and to constrain the Delaunay refinement algorithm to preserve these features in addition to the surface patches. Our experimental results on segmented medical images have shown that, within a few seconds, the algorithm outputs a tetrahedral mesh in which each material is represented as a consistent submesh without gaps and overlaps. The optimization property of the Delaunay triangulation makes these meshes suitable for the purpose of realistic visualization or finite element simulations.     

A compound class of Weibull and power series distributions

In this paper we introduce the Weibull power series (WPS) class of distributions which is obtained by compounding Weibull and power series distributions, where the compounding procedure follows same way that was previously carried out by Adamidis and Loukas (1998). This new class of distributions has as a particular case the two-parameter exponential power series (EPS) class of distributions (Chahkandi and Ganjali, 2009), which contains several lifetime models such as: exponential geometric (Adamidis and Loukas, 1998), exponential Poisson (Kus, 2007) and exponential logarithmic (Tahmasbi and Rezaei, 2008) distributions. The hazard function of our class can be increasing, decreasing and upside down bathtub shaped, among others, while the hazard function of an EPS distribution is only decreasing. We obtain several properties of the WPS distributions such as moments, order statistics, estimation by maximum likelihood and inference for a large sample. Furthermore, the EM algorithm is also used to determine the maximum likelihood estimates of the parameters and we discuss maximum entropy characterizations under suitable constraints. Special distributions are studied in some detail. Applications to two real data sets are given to show the flexibility and potentiality of the new class of distributions.     

Sentence level topic models for associated topics extraction

In LDA model, independence assumptions in the Dirichlet distribution of the topic proportions lead to the inability to model the connections between topics. Some researchers have attempted to break them and thus obtained more powerful topic models. Following this strategy, by using an association matrix to measure the association between latent topics, we develop an associated topic model (ATM), in which consecutive sentences are considered important and the topic assignments for words are jointly determined by the association matrix and the sentence level topic distributions, instead of the document-specific topic distributions only. This approach gives a more realistic modeling of latent topic connections where the presence of a topic may be connected with the presence of another. We derive a collapsed Gibbs sampling algorithm for inference and parameter estimation for the ATM. The experimental results demonstrate that the ATM gives a more practical interpretation and is capable of learning more associated topics.

     

利用路由器自适应限流防御分布拒绝服务攻击

提出一种自适应路由器限流算法防御分布拒绝服务攻击的机制.该算法的关键是由被攻击者要求经挑选的相距k跳(hop)的上游路由器对目的为被攻击者的数据流进行限流,从而将被攻击者的服务支援在各数据流之间达到一种类最大-最小公平的流量分配.还在一个实际的因特网拓扑上针对攻击数据流和合法数据流的不同分布和流量模型考察了算法的效果.结果表明这种以服务器为中心的路由器限流是对抗分布拒绝服务攻击的一种很有前途的方法.     

图像驱动的三维模型外观细节增强

随着计算机游戏与电影视觉特效的普及应用,仅通过纹理贴图已不能满足用户需求。然而,为三维模型制作视觉真实的表面外观,即在包含几何细节变化(如金属腐蚀、石料风化、木质裂纹等)同时辅之以与几何变化合理匹配的材质颜色却是一件困难且耗时的工作。文章提出了一种能够从单幅图像中提取物体的外观细节(材质与几何信息)并增强至三维模型表面的方法。该方法是一种新型的几何约束的非刚性2D-3D融合配准算法,可以通过将配准后的模型提供的几何信息作为先验知识实现更好的本征图像分解结果。利用图像中同步分解出的互相关的多尺度几何信息与材质纹理信息组成的非参数外观模型,文中提出了一种法向量约束的几何变形算法将外观纹理恢复到代理模型上。通过上述步骤,文章提出的方法能够帮助建模师制作具有多尺度外观细节的三维模型。     

Three-dimensional human shape inference from silhouettes: reconstruction and validation

Silhouettes are robust image features that provide considerable evidence about the three-dimensional (3D) shape of a human body. The information they provide is, however, incomplete and prior knowledge has to be integrated to reconstruction algorithms in order to obtain realistic body models. This paper presents a method that integrates both geometric and statistical priors to reconstruct the shape of a subject assuming a standardized posture from a frontal and a lateral silhouette. The method is comprised of three successive steps. First, a non-linear function that connects the silhouette appearances and the body shapes is learnt and used to create a first approximation. Then, the body shape is deformed globally along the principal directions of the population (obtained by performing principal component analysis over 359 subjects) to follow the contours of the silhouettes. Finally, the body shape is deformed locally to ensure it fits the input silhouettes as well as possible. Experimental results showed a mean absolute 3D error of 8 mm with ideal silhouettes extraction. Furthermore, experiments on body measurements (circumferences or distances between two points on the body) resulted in a mean error of 11 mm.     

基于Sentinel-2的闪电河流域农作物分类研究

以内蒙古闪电河流域为研究区,基于Sentinel2光学遥感影像结合随机森林和支持向量机算法,采用3种方案:基于像元的分类方法、面向对象的分类方法及改进的基于像元分类与面向对象分割相结合的集成方法,对研究区内的农作物进行精细提取.结果表明:①基于随机森林采用基于像元的方法进行分类,所有地类的总体精度为97.8％,Kapp...     

Topologically correct reconstruction of tortuous contour forests

Motivated by the need for correct and robust 3D models of neuronal processes, we present a method for reconstruction of spatially realistic and topologically correct models from planar cross sections of multiple objects. Previous work in 3D reconstruction from serial contours has focused on reconstructing one object at a time, potentially producing inter-object intersections between slices. We have developed a robust algorithm that removes these intersections using a geometric approach. Our method not only removes intersections but can guarantee a given minimum separation distance between objects. This paper describes the algorithm for geometric adjustment, proves correctness, and presents several results of our high-fidelity modeling.