On climate reconstruction using bivalves: three methods to interpret the chemical signature of a shell

To improve our understanding of the climate process and to assess the human impact on current global warming, past climate reconstruction is essential. The chemical composition of a bivalve shell is strongly coupled to environmental variations and therefore ancient shells are potential climate archives. The nonlinear nature of the relation between environmental condition (e.g. the seawater temperature) and proxy composition makes it hard to predict the former from the latter, however. In this paper we compare the ability of three nonlinear system identification methods to reconstruct the ambient temperature from the chemical composition of a shell. The comparison shows that nonlinear multi-proxy approaches are potentially useful tools for climate reconstructions and that manifold based methods result in smoother and more precise temperature reconstruction.     

A consideration of human immunity-based reinforcement learning with continuous states

Many reinforcement learning methods have been studied on the assumption that a state is discretized and the environment size is predetermined. However, an operating environment may have a continuous state and its size may not be known in advance, e.g., in robot navigation and control. When applying these methods to the environment described above, we may need a large amount of time for learning or failing to learn. In this study, we improve our previous human immunity-based reinforcement learning method so that it will work in continuous state space environments. Since our method selects an action based on the distance between the present state and the memorized action, information about the environment (e.g., environment size) is not required in advance. The validity of our method is demonstrated through simulations for the swingup control of an inverted pendulum.     

A data mining proxy approach for efficient frequent itemset mining

Data mining has attracted a lot of research efforts during the past decade. However, little work has been reported on the efficiency of supporting a large number of users who issue different data mining queries periodically when there are new needs and when data is updated. Our work is motivated by the fact that the pattern-growth method is one of the most efficient methods for frequent pattern mining which constructs an initial tree and mines frequent patterns on top of the tree. In this paper, we present a data mining proxy approach that can reduce the I/O costs to construct an initial tree by utilizing the trees that have already been resident in memory. The tree we construct is the smallest for a given data mining query. In addition, our proxy approach can also reduce CPU cost in mining patterns, because the cost of mining relies on the sizes of trees. The focus of the work is to construct an initial tree efficiently. We propose three tree operations to construct a tree. With a unique coding scheme, we can efficiently project subtrees from on-disk trees or in-memory trees. Our performance study indicated that the data mining proxy significantly reduces the I/O cost to construct trees and CPU cost to mine patterns over the trees constructed.     

开放环境下未知材质的识别技术

针对开放环境下未知物体材质识别的问题,本文提出一种利用欧氏距离区分未知类别和已知类别的物体材质识别方法框架,在该框架下利用支持向量机对物体材质进行识别,分类效果显著。该方法利用距离度量中的欧氏距离与阈值进行比较,距离的均值小于阈值的物体判定为已知类别物体材质,并进行分类;距离大于阈值的物体判定为未知类别物体材质,并利用支持向量机算法进行重新学习识别。本文在慕尼黑工业大学的触觉数据集中的声音数据上进行实验,对比了5种距离度量方法,选择了欧氏距离;与开集稀疏表示分类方法对比,显示出本文提出的方法在声音数据集上具有一定的优势;通过实验选出了合理的阈值,并最终实现了开放环境下识别所有物体材质。实验验证了该框架可以很好地解决开放环境下触觉感知信息的物体材质识别问题。     

Rotation distance is fixed-parameter tractable

Rotation distance between trees measures the number of simple operations it takes to transform one tree into another. There are no known polynomial-time algorithms for computing rotation distance. In the case of ordered rooted trees, we show that the rotation distance between two ordered trees is fixed-parameter tractable, in the parameter, k, the rotation distance. The proof relies on the kernelization of the initial trees to trees with size bounded by 5k.     

Statistical Modeling of the 3D Geometry and Topology of Botanical Trees

We propose a framework for statistical modeling of the 3D geometry and topology of botanical trees. We treat botanical trees as points in a tree‐shape space equipped with a proper metric that captures the geometric and the topological differences between trees. Geodesics in the tree‐shape space correspond to the optimal sequence of deformations, i.e. bending, stretching, and topological changes, which align one tree onto another. In this way, the 3D tree modeling and synthesis problem becomes a problem of exploring the tree‐shape space either in a controlled fashion, using statistical regression, or randomly by sampling from probability distributions fitted to populations in the tree‐shape space. We show how to use this framework for (1) computing statistical summaries, e.g. the mean and modes of variations, of a population of botanical trees, (2) synthesizing random instances of botanical trees from probability distributions fitted to a population of botanical trees, and (3) modeling, interactively, 3D botanical trees using a simple sketching interface. The approach is fast and only requires as input 3D botanical tree models with a known upright orientation.     

Broadcasting in All-Output-Port Meshes of Trees with Distance-Insensitive Switching

Meshes of trees are hybrids of meshes and trees with outstanding properties, namely small degree and diameter and large bisection width. Moreover, they are known to be area universal, i.e., they can simulate any network with the same wire area with only a polylogarithmic slowdown. Meshes of trees are known to outperform meshes in execution of algorithms with local communication patterns, e.g., sorting, for which distance-sensitive switching, such as store-and-forward, suffices. Nowadays, parallel machines use distance-insensitive, e.g., wormhole, switching. A challenging problem is to design optimal or efficient algorithms for one-to-all broadcast in all-output-port networks with distance-insensitive switching, since the lower bound on the number of rounds, log_Δ+1N, where Δ is the node degree, is very strict. This problem has been solved for tori and hypercubes quite recently. In this paper, we present nearly optimal algorithms for one-to-all broadcast in both square and rectangular 2-D meshes of trees and cube 3-D meshes of trees. The algorithms need at most one round more than the trivial lower bound. We also show requirements for deadlock-free execution of the algorithms. Meshes of trees are not node-symmetric, they are not even regular. This paper shows that, in contrast to meshes, the irregularity is not an obstacle for designing efficient schemes for such an intensive communication pattern, as the all-output-port broadcast.     

基于Hamming范数的XML流相关性估测算法

在数据库理论中,如何在较小的空间条件下快速地比较不同的XML(extensible markup language)流的差异性是一个基本问题.在这一问题的研究中,人们提出了树编辑距离等测度来描述XML文本的差异性.提出了一种基于Hamming范数的l₀测度——即XML树的不同子树的个数,并以此来刻画XML文本的相关性.在数据流模型下,给出了基于空间有界伪随机数发生器、稳态分布于哈希函数的l₀测度的概率算法.理论上的时空复杂性分析、正确性证明与实验模拟结果表明,这一概率算法对问题的输入提供了一个理想的近似.     

Spatial downscaling of TRMM 3B43 precipitation considering spatial heterogeneity

The availability of accurate precipitation data with high spatial resolution is deemed necessary for many types of hydrological, meteorological, and environmental applications. The Tropical Rainfall Measuring Mission (TRMM) data sets can provide effective precipitation information, but at coarse resolution (0.25°), so it is very important to improve their resolution. There is a strong relationship between precipitation and other environment variables (e.g. vegetation and topography). The existing precipitation-downscaling methods attempt to describe this relationship by using a uniform empirical model. However, in the real world, the relationship is disturbed due to the influence of certain factors such as soil type, hydrological conditions, and human activities. In this study, a new downscaling method considering this spatial heterogeneity was proposed to downscale version 7 of the TRMM 3B43 precipitation product, which assumes that the relationship varies spatially but is the same in a local region. At a spatial resolution of 0.25°, the spatially varying relationship among TRMM, normalized difference vegetation index (NDVI), and digital elevation model (DEM) is explored by using a local regression analysis approach known as geographically weighted regression (GWR), but this relationship is the same in a pixel of 0.25° × 0.25°. The derived relationship is used to construct the precipitation downscaling model, which then produces 1 km downscaled precipitation data. The existing and proposed downscaling methods were both tested in North China for 2008–2011. The accuracy of the downscaled precipitation was validated by comparing it with observed precipitation data from 49 meteorological stations located in the study area. The results show that GWR is more suitable to capture the relationship among TRMM, DEM, and NDVI (minimum R² = 0.93). Compared with the existing downscaling method, the proposed method, which consistently showed increased R² (e.g. from 0.80 to 0.82 in 2011) and reduced RMSE (e.g. from 125.4 mm to 91 mm in 2011) in all four years, can more accurately produce downscaled precipitation data.     

A constrained edit distance algorithm between semi-ordered trees

In this paper, we propose a formal definition of a new class of trees called semi-ordered trees and a polynomial dynamic programming algorithm to compute a constrained edit distance between such trees. The core of the method relies on a similar approach to compare unordered [Kaizhong Zhang, A constrained edit distance between unordered labeled trees, Algorithmica 15 (1996) 205–222] and ordered trees [Kaizhong Zhang, Algorithms for the constrained editing distance between ordered labeled trees and related problems, Pattern Recognition 28 (3) (1995) 463–474]. The method is currently applied to evaluate the similarity between architectures of apple trees [Vincent Segura, Aida Ouangraoua, Pascal Ferraro, Evelyne Costes, Comparison of tree architecture using tree edit distances: Application to two-year-old apple tree, Euphytica 161 (2007) 155–164].     

On the Linear-Cost Subtree-Transfer Distance between Phylogenetic Trees

Different phylogenetic trees for the same group of species are often produced either by procedures that use diverse optimality criteria [16] or from different genes [12] in the study of molecular evolution. Comparing these trees to find their similarities and dissimilarities (i.e., distance ) is thus an important issue in computational molecular biology. Several distance metrics including the nearest neighbor interchange (nni) distance and the subtree-transfer distance have been proposed and extensively studied in the literature. This article considers a natural extension of the subtree-transfer distance, called the linear-cost subtree-transfer distance, and studies the complexity and efficient approximation algorithms for this distance as well as its relationship to the nni distance. The linear-cost subtree-transfer model seems more suitable than the (unit-cost) subtree-transfer model in some applications. The following is a list of our results: 1. The linear-cost subtree-transfer distance is in fact identical to the nni distance on unweighted phylogenies. 2. There is an algorithm to compute an optimal linear-cost subtree-transfer sequence between unweighted phylogenies in O(n ⋅ 2 ^O(d) ) time, where d denotes the linear-cost subtree-transfer distance. Such an algorithm is useful when d is small. 3. Computing the linear-cost subtree-transfer distance between two weighted phylogenetic trees is NP-hard, provided we allow multiple leaves of a tree to share the same label (i.e., the trees are not necessarily uniquely labeled). 4. There is an efficient approximation algorithm for computing the linear-cost subtree-transfer distance between weighted phylogenies with performance ratio 2 . Received May 8, 1997; revised February 20, 1998.     

Magnetohydrodynamics of accretion disks

Accretion disks in close binary systems originate when mass overflow occurs from the primary star onto the compact star. When the compact star is a neutron star or a black hole the inner parts of the thin disk extend to the Alfvén radius respectively a few times the Schwarzchild radius. In the Keplerian rotating highly turbulent inner parts of the accretion disk magnetic fields are strongly amplified and expelled from the disk thus leading to the formation of a magnetically structured accretion disk corona, sandwiching the disk to which it is electrodynamically coupled. The magnetic energy supplied to the corona is radiated by inverse Compton scattering of soft X-ray photons produced in the disk by the viscous heating of the accreting matter. This may explain why certain X-ray sources show a very large fluctuating hard X-ray component. The interaction of the inner parts of an accretion disk with the magnetosphere around a neutron star leads to channeled accretion onto the magnetic poles, resulting in the phenomenon of X-ray pulsars with the associated spin variations due to angular momentum transfer. The interaction of disk coronal structures with the relatively weak magnetic fields of old fast spinning neutron stars lead to a new form of interaction around the so called beat frequency that can be used as a model for quasiperiodic oscillations in low-mass X-ray binaries.     

An Edit Distance between Quotiented Trees

Abstract. In this paper we propose a dynamic programming algorithm to compare two quotiented trees using a constrained edit distance. A quotiented tree is a tree defined with an additional equivalent relation on vertices and such that the quotient graph is also a tree. The core of the method relies on an adaptation of an algorithm recently proposed by Zhang for comparing unordered rooted trees. This method is currently being used in plant architecture modelling to quantify different types of variability between plants represented by quotiented trees.     

Metadata-driven optimal transcoding in a multimedia proxy

An adaptive multimedia proxy is presented which provides (1) caching, (2) filtering, and (3) media gateway functionalities. The proxy can perform media adaptation on its own, either relying on layered coding or using transcoding mainly in the decompressed domain. A cost model is presented which incorporates user requirements, terminal capabilities, and video variations in one formula. Based on this model, the proxy acts as a general broker of different user requirements and of different video variations. This is a first step towards What You Need is What You Get (WYNIWYG) video services, which deliver videos to users in exactly the quality they need and are willing to pay for. The MPEG-7 and MPEG-21 standards enable this in an interoperable way. A detailed evaluation based on a series of simulation runs is provided.     

An innovative decentralized strategy for I-AUVs cooperative manipulation tasks

In the last years, a challenging field of autonomous robotics is represented by cooperative mobile manipulation carried out in different environments (aerial, terrestrial and underwater environment). As regards cooperative manipulation of Intervention-Autonomous Underwater Vehicles (I-AUVs), this application is characterized by a more complex environment of work, compared to the terrestrial or aerial ones, both due to different technological problems, e.g. localization and communication in underwater environment. However, the use of Autonomous Underwater Vehicle (AUV) and I-AUV will necessarily grow up in the future exploration of the sea. Particularly, cooperative I-AUVs represent the natural evolution of single centralized I-AUV because they may be used in various underwater assembly tasks, such as complex underwater structure construction and maintenance (e.g. underwater pipeline and cable transportation can be carried out by multiple cooperative I-AUVs). Furthermore, underwater search and rescue tasks could be more efficient and effective if multiple I-AUVs were used.In this paper, the authors propose an innovative decentralized approach for cooperative mobile manipulation of I-AUVs. This decentralized strategy is based on a different use of potential field method; in particular, a multi-layer control structure is developed to in parallel manage the coordination of the swarm, the guidance and navigation of the I-AUVs and the manipulation task. The main advantage of the potential field method is that less information is necessary: navigation and control problems are reduced to the evaluation of the distance vector among the vehicles, object and obstacles. Moreover, because of the technological problems caused by the underwater environment, the reduction of the transmitted data is one of the keypoints of this architecture. In MATLAB^®-Simulink^®, the authors have simulated a transportation task of a partially known object along a reference trajectory in an unknown environment, where some obstacles are placed. The task is performed by an I-AUV swarm composed of four vehicles, each one provided of a 7 Degrees Of Freedom (DOFs) robotic arm.     

指定验证人的(t,n)门限代理签名方案

将指定验证人概念引入门限代理签名,提出了一个指定验证人的(t,n)门限代理签名方案.该方案不仅实现了门限代理签名,而且还能实现只有指定验证人一起才能验证门限代理签名的特性.在普通的门限代理签名方案中,任何人都能验证门限代理签名的有效性.然而,在某些情况下,只希望指定的验证人一起才能验证门限代理签名.这在实际中是需要的,如电子商务中的电子投标等.另外,该方案还具有在原始签名人需要时,收回某个代理签名人代理权的特性.     

Polynomial-Time Algorithms for Minimum-Time Broadcast in Trees

Abstract. This paper addresses the minimum-time broadcast problem under several modes of the line model, i.e., when long-distance calls can be placed along paths in the network. It is well known that the minimum-time broadcast problem can be solved in polynomial time under the single-port edge-disjoint paths mode. However, it is equally well known that either relaxing the model to the all-port edge-disjoint paths mode, or constraining the model to the single-port vertex-disjoint paths mode, leads to NP-complete problems; and exact solutions have been derived for specific topologies only (e.g., hypercubes or tori). In this paper we present polynomial-time algorithms for minimum-time broadcast in trees. These algorithms are obtained by application of an original technique called the merging method , which can be applied in a larger context, for instance, to solve the multicast problem or to address the restricted regimen. The merging method requires solving the minimal contention-free matrix problem whose solution presents some interest on its own.     

A Phase‐Based Approach for Animating Images Using Video Examples

We present a novel approach for animating static images that contain objects that move in a subtle, stochastic fashion (e.g. rippling water, swaying trees, or flickering candles). To do this, our algorithm leverages example videos of similar objects, supplied by the user. Unlike previous approaches which estimate motion fields in the example video to transfer motion into the image, a process which is brittle and produces artefacts, we propose an Eulerian phase‐based approach which uses the phase information from the sample video to animate the static image. As is well known, phase variations in a signal relate naturally to the displacement of the signal via the Fourier Shift Theorem. To enable local and spatially varying motion analysis, we analyse phase changes in a complex steerable pyramid of the example video. These phase changes are then transferred to the corresponding spatial sub‐bands of the input image to animate it. We demonstrate that this simple, phase‐based approach for transferring small motion is more effective at animating still images than methods which rely on optical flow.     

Computing the Quartet Distance between Evolutionary Trees in Time O( n log n)

Evolutionary trees describing the relationship for a set of species are central in evolutionary biology, and quantifying differences between evolutionary trees is therefore an important task. The quartet distance is a distance measure between trees previously proposed by Estabrook, McMorris, and Meacham. The quartet distance between two unrooted evolutionary trees is the number of quartet topology differences between the two trees, where a quartet topology is the topological subtree induced by four species. In this paper we present an algorithm for computing the quartet distance between two unrooted evolutionary trees of n species, where all internal nodes have degree three, in time O(n log n. The previous best algorithm for the problem uses time O(n ²).     

Computing the Quartet Distance between Evolutionary Trees in Time O ( n log n )

Evolutionary trees describing the relationship for a set of species are central in evolutionary biology, and quantifying differences between evolutionary trees is therefore an important task. The quartet distance is a distance measure between trees previously proposed by Estabrook, McMorris, and Meacham. The quartet distance between two unrooted evolutionary trees is the number of quartet topology differences between the two trees, where a quartet topology is the topological subtree induced by four species. In this paper we present an algorithm for computing the quartet distance between two unrooted evolutionary trees of n species, where all internal nodes have degree three, in time O(n log n. The previous best algorithm for the problem uses time O(n ²).