基于拓扑子集的势场原子类型的派定

对于除了标准氨基酸、核酸残基以外的一般分子,派定分子中原子的原子类型,确定原子类型在不同分子势场之间的转换,这些工作一般是由人工来完成。本文从分子拓扑学的角度解析了分子势场的原子类型(atom type)定义,以基于分子拓扑子集取代原子类型定义的分子片断为途径,实现势场原子类型的计算机自动派定。该方法易于编程,并能满足用户调整原子类型的意愿。     

A security carving approach for AVI video based on frame size and index

Recovery of fragmented files is an important part of digital forensics. Video files are more likely to be fragmented since their sizes are relatively large that recovering video files without the file system information is meaningful. This paper presents a video recovery technique of a fragmented video file using the frame size information in every frame and the index. Many existing video recovery techniques attempt to recover videos using file system information or header/footer flag. These approaches may fail in the situations which the file system information is unknown or videos are fragmented. The proposed method addresses how to extract AVI file fragments from data images and map all the extracted fragments into original order. Experiments result show that mapping the AVI fragments according to the frame size information in every fragment and index is credible and the non-overwritten part of the fragmented video can be recovered using the method.     

Topological network design: A survey

We consider the problem of topological optimization of communication networks subject to a number of design constraints, such as maximum network diameter, maximum node degree, k-node (link) survivability, and network fault tolerance. The primary design problem can be described as follows: Given a set of network nodes, it is required to find a topology Ψ, selected from all possible topologies, so that the cost of Ψ (measured possibly in terms of the maximum diameter, maximum node degree, etc.) is less than that of any other network topology and such that Ψ satisfies some given design constraints. Fault tolerance is concerned with the ability of the network nodes to communicate in the presence of a set of faulty links and/or nodes. The network design problem considering reliability constraints is NP-hard. We classify the research efforts presented in the literature for solving the topological optimization design problem as hierarchical, enumerative, or iterative techniques. In this paper, we provide a survey of the topological network design techniques under different design constraints. Experimental results obtained by applying a number of algorithms to a set of randomly generated networks are presented and compared.     

Topological operators: a relaxed query processing approach

Relaxation and approximation techniques have been proposed as approaches for improving the quality of query results, in terms of completeness and accuracy, in environments where the user may not be able to specify the query in a complete and exact way, since data are quite heterogeneous or she may not know all the characteristics of data at hand. This problem, mainly addressed for relational and XML data, is nowadays quite relevant also for geo-spatial data, due to their increasing usage in highly critical decisional processes. Among geo-spatial queries, those based on spatial and more precisely topological relations are currently used in an increasing number of applications. As far as we know, no approach has been proposed so far for relaxing queries based on topological predicates when they return an empty or insufficient answer, in order to improve result quality and user satisfaction. In this paper, we consider this problem and we present a general relaxation strategy for, possibly multi-domain, topological selection and join queries. Two specific semantics are also provided: the first applies the minimum amount of relaxation in order to get an acceptable answer; the second relaxes the given query of a certain fixed amount, depending on the considered topological predicate. Index-based processing algorithms, for efficiently executing relaxed queries based on the proposed semantics, are also presented and a specific topological similarity function, to be used for relaxation purposes, is proposed. Experimental results show that the overhead given by query relaxation is acceptable.     

Efficient Implementation Techniques for Topological Predicates on Complex Spatial Objects

Topological relationships like overlap, inside, meet, and disjoint uniquely characterize the relative position between objects in space. For a long time, they have been a focus of interdisciplinary research as in artificial intelligence, cognitive science, linguistics, robotics, and spatial reasoning. Especially as predicates, they support the design of suitable query languages for spatial data retrieval and analysis in spatial database systems and geographical information systems. While, to a large extent, conceptual aspects of topological predicates (like their definition and reasoning with them) as well as strategies for avoiding unnecessary or repetitive predicate executions (like predicate migration and spatial index structures) have been emphasized, the development of robust and efficient implementation techniques for them has been largely neglected. Especially the recent design of topological predicates for all combinations of complex spatial data types has resulted in a large increase of their numbers and stressed the importance of their efficient implementation. The goal of this article is to develop correct and efficient implementation techniques of topological predicates for all combinations of complex spatial data types including two-dimensional point, line, and region objects, as they have been specified by different authors and in different commercial and public domain software packages. Our solution consists of two phases. In the exploration phase, for a given scene of two spatial objects, all topological events like intersection and meeting situations are summarized in two precisely defined topological feature vectors (one for each argument object of a topological predicate) whose specifications are characteristic and unique for each combination of spatial data types. These vectors serve as input for the evaluation phase which analyzes the topological events and determines the Boolean result of a topological predicate (predicate verification) or the kind of topological predicate (predicate determination) by a formally defined method called nine-intersection matrix characterization. Besides this general evaluation method, the article presents an optimized method for predicate verification, called matrix thinning, and an optimized method for predicate determination, called minimum cost decision tree. The methods presented in this article are applicable to all known complete collections of mutually exclusive topological predicates that are formally based on the well known nine-intersection model.

Machine fusion to enhance the topology preservation of vector quantization artificial neural networks

Artificial neural networks techniques have been successfully applied in vector quantization (VQ) encoding. The objective of VQ is to statistically preserve the topological relationships existing in a data set and to project the data to a lattice of lower dimensions, for visualization, compression, storage, or transmission purposes. However, one of the major drawbacks in the application of artificial neural networks is the difficulty to properly specify the structure of the lattice that best preserves the topology of the data. To overcome this problem, in this paper we introduce merging algorithms for machine-fusion, boosting-fusion-based and hybrid-fusion ensembles of SOM, NG and GSOM networks. In these ensembles not the output signals of the base learners are combined, but their architectures are properly merged. We empirically show the quality and robustness of the topological representation of our proposed algorithm using both synthetic and real benchmarks datasets.     

分布式空间数据分片与跨边界拓扑连接优化方法

研究分布式空间数据库(distributed spatial database,简称DSDB)中数据按区域分片时的跨边界片段拓扑连接查询问题,并提出相应的优化方法.首先研究了分布式环境下的空间数据的分片与分布,提出了空间数据分片的扩展原则:空间聚集性、空间对象的不分割性、逻辑无缝保持性.然后,将区域分割分片环境下的片段连接分为跨边界和非跨边界两类;同时,将拓扑关系分为两类,重点研究跨边界的两类片段拓扑连接.提出了跨边界空间片段拓扑连接优化的两个定理,并给出了证明.以此为基础,给出了跨边界空间拓扑连接优化规则,包括连接去除规则和连接优化转化规则.最后设计了详细的实验,对自然连接策略、半连接策略以及所提出的连接策略进行效率比较,结果表明,所提出的方法对跨边界连接优化有明显优势.因此,所提出的理论和方法可以用于分布式跨边界拓扑关系查询的优化.     

On optimal design of HDD suspension using topology optimization

 This paper explores the use of topological optimization to systematically design suspensions for hard disk drives (HDD). The design problem is posed as a material distribution problem, which varies spatial thickness of suspensions so as to enhance their dynamic performance. Due to the requirements for specific motion characteristics, suspensions are designed to have higher torsional and lateral frequencies while maintaining an adequate but not too high frequency for transverse bending. The torsional and lateral frequencies are generally higher in order than the transverse frequencies. Due to their non-convex nature, the optimizations of higher-order frequencies were proven to be more difficult than that of the fundamental frequency. To tackle the problem, present work adopted mode-tracking techniques, and attempted two different optimization algorithms to solve the design problem. With reference to the topological results obtained, it is found that the implementation based on sequential quadratic programming (SQP) performed better than that based on optimal criteria (OC). It was also found that the present design method could tremendously improve the dynamic performance of suspensions. Received: 31 December 2001/Accepted: 29 March 2002     

Vision-based sparse topological mapping

Most of the existing appearance-based topological mapping algorithms produce dense topological maps in which each image stands as a node in the topological graph. Sparser maps can be built by representing groups of visually similar images of a sequence as nodes of a topological graph. In this paper, we present a sparse/hierarchical topological mapping framework which uses Image Sequence Partitioning (ISP) to group visually similar images of a sequence as nodes which are then connected on the occurrence of loop closures to form a topological graph. An indexing data structure called Hierarchical Inverted File (HIF) is proposed to store the sparse maps so as to perform loop closure at the two different resolutions of the map namely the node level and image level. TFIDF weighting is combined with spatial and frequency constraints on the detected features for improved loop closure robustness. Our approach is compared with two other existing sparse mapping approaches which use ISP. Sparsity, efficiency and accuracy of the resulting maps are evaluated and compared to that of the other two techniques on publicly available outdoor omni-directional image sequences.     

Algorithms for Extracting Correct Critical Points and Constructing Topological Graphs from Discrete Geographical Elevation Data

Researchers in the fields of computer graphics and geographical information systems (GISs) have extensively studied the methods of extracting terrain features such as peaks, pits, passes, ridges, and ravines from discrete elevation data. The existing techniques, however, do not guarantee the topological integrity of the extracted features because of their heuristic operations, which results in spurious features. Furthermore, there have been no algorithms for constructing topological graphs such as the surface network and the Reeb graph from the extracted peaks, pits, and passes. This paper presents new algorithms for extracting features and constructing the topological graphs using the features. Our algorithms enable us to extract correct terrain features; i.e., our method extracts the critical points that satisfy the Euler formula, which represents the topological invariant of smooth surfaces. This paper also provides an algorithm that converts the surface network to the Reeb graph for representing contour changes with respect to the height. The discrete elevation data used in this paper is a set of sample points on a terrain surface. Examples are presented to show that the algorithms also appeal to our visual cognition.     

VTUTIN: a full screen gel management editor

Large DNA sequences are now routinely sequenced by the cloning of randomly generated fragments into single-stranded DNA phage vectors (the 'shotgun' method). Various programs exist for computerized assembly of such fragments, including the phases of data entry, homology searching and gel-management/editing. Many gel-management editors are rudimentary in nature, using either line-editing techniques or using unnatural displays or command systems. Others are available only on restricted types of computer system. The program VTUTIN makes full screen editing along the lines of modern text editors available for the complex data type of sets of sequence gels and their consensus. Not only are the data displayed on the VDU screen in a natural manner, but VTUTIN has also been written to model the command system of a well-established text editor (PDP-11 KED or VAX/VMS EDT) to simplify editor use and learning. VTUTIN has been written in Pascal in a modular form so that wide-spread portability is facilitated. VTUTIN is currently implemented to work on VT-100 type terminals although the modularity of the code should allow straightforward conversion for other terminal types and should also permit simple alteration to model any other text editor.     

Image and Pattern Analysis of 1650 B.C. Wall Paintings and Reconstruction

In this paper, a color image segmentation method and a pattern analysis are presented, in connection with the extraordinary 1650 B.C. wall paintings found in the Greek island of Thera. These wall paintings are usually reconstructed from thousands of fragments widely scattered in the excavated site. The fragments' depiction manifests inhomogeneous color decay, cracks, added extraneous material, etc. The proposed color image segmentation method takes into account the decay problems and offers a very good approximation of the initial fragment depiction as the artist drew it in the late Bronze Age. The algorithm performs essentially better than other standard segmentation schemes as extensive qualitative tests indicate. Moreover, it offers clear-cut color regions and region borders for each fragment depiction. The whole approach is based on classifying the pixels into a number of regions where each region is described by a normal distribution, followed by fragment-decay reduction and edge refining. Extensive pattern analysis to the obtained region borders leads to the conclusion that 3650 years ago, the artist most probably used advanced geometrical methods in order to construct handcrafted ldquoFrench curvesrdquo (stencils or templates) and use them to draw certain figures. On the basis of the aforementioned results, specific pattern matching techniques are employed for the reconstruction of wall paintings, depicting spirals, from their constituent fragments.     

MaterialVis: Material visualization tool using direct volume and surface rendering techniques

Visualization of the materials is an indispensable part of their structural analysis. We developed a visualization tool for amorphous as well as crystalline structures, called MaterialVis. Unlike the existing tools, MaterialVis represents material structures as a volume and a surface manifold, in addition to plain atomic coordinates. Both amorphous and crystalline structures exhibit topological features as well as various defects. MaterialVis provides a wide range of functionality to visualize such topological structures and crystal defects interactively. Direct volume rendering techniques are used to visualize the volumetric features of materials, such as crystal defects, which are responsible for the distinct fingerprints of a specific sample. In addition, the tool provides surface visualization to extract hidden topological features within the material. Together with the rich set of parameters and options to control the visualization, MaterialVis allows users to visualize various aspects of materials very efficiently as generated by modern analytical techniques such as the Atom Probe Tomography.     

Genetic approaches for topological active nets optimization

The topological active nets (TANs) model is a deformable model used for image segmentation. It integrates features of region-based and edge-based segmentation techniques so it is able to fit the contours of the objects and model their inner topology. Also, topological changes in its structure allow the detection of concave and convex contours, holes, and several objects in the scene. Since the model deformation is based on the minimization of an energy functional, the adjustment depends on the minimization algorithm. This paper presents two evolutionary approaches to the energy minimization problem in the TAN model. The first proposal is a genetic algorithm with ad hoc operators whereas the second approach is a hybrid model that combines genetic and greedy algorithms. Both evolutionary approaches improve the accuracy of the segmentation even though only the hybrid model allows topological changes in the model structure.     

Spatial learning for navigation in dynamic environments

This article describes techniques that have been developed for spatial learning in dynamic environments and a mobile robot system, ELDEN, that integrates these techniques for exploration and navigation. In this research, we introduce the concept of adaptive place networks, incrementally-constructed spatial representations that incorporate variable-confidence links to model uncertainty about topological adjacency. These networks guide the robot's navigation while constantly adapting to any topological changes that are encountered. ELDEN integrates these networks with a reactive controller that is robust to transient changes in the environment and a relocalization system that uses evidence grids to recalibrate dead reckoning.     

Applying bifocal displays to topological maps

Presentation techniques for topological networks can be broadly classified as distortion‐oriented and nondistortion‐oriented. Although there has been a growing interest in applying various distortion‐oriented techniques, the application of an earlier example, the bifocal display, has so far been underexploited. This article describes a number of human‐computer interface techniques potentially relevant to the presentation and navigation of topological networks associated with transport systems, and describes a preliminary experimental study of a number of techniques for presenting the London Underground map as part of a real‐time information system for travelers.     

Bridging proper orthogonal decomposition methods and augmented Newton–Krylov algorithms: An adaptive model order reduction for highly nonlinear mechanical problems

This article describes a bridge between POD-based model order reduction techniques and the classical Newton/Krylov solvers. This bridge is used to derive an efficient algorithm to correct, “on-the-fly”, the reduced order modelling of highly nonlinear problems undergoing strong topological changes. Damage initiation problems tackled via a corrected hyperreduction method are used as an example. It is shown that the relevancy of reduced order model can be significantly improved with reasonable additional costs when using this algorithm, even when strong topological changes are involved.     

区间值度量空间的紧性和仿紧性

给出了区间值度量空间的概念,根据一般拓扑学中紧性的相关定义及其等价条件,证明了由区间值度量诱导的拓扑具有的紧性及其一系列等价关系,讨论了该诱导的拓扑空间具有仿紧性。