基于时间衰减和密度的任意簇数据流聚类

数据挖掘的一个重要分支是数据流聚类技术。基于K均值算法的基础提出了CluTA算法。该算法在处理用K均值方法分类得到的结果时考虑时间衰减因素和相似簇的合并,达到用户对时间的要求并实现了任意形状簇聚类。理论分析和实验结果都表明算法具有可行性。     

Managing megaprojects: a focused approach

In mid 1990, we began work on software for the Boeing 777 aircraft, a project that would involve 30 suppliers and require 9 million person hours to complete. The various systems in the 777, most of which are digitally controlled, required that we develop, test, and certify about 2.5 million lines of new software, mostly as Ada code, and incorporate about 1.6 million lines of commercial off the shelf software to deliver the 777 for commercial use. The entire process had to be sufficiently mature to support the first flight of this fly by wire aircraft by June 1994 and to ensure its certification for passenger flights by June 1995. Delivering the Boeing 777 on schedule-with 95 percent of the initially promised functionality-was simply a matter of specifying the requirements early, creating a plan and resource allocation supported by experience, then monitoring and enforcing performance to schedule. To do this, we used around 70 people to monitor the project, along with hundreds of software engineers drawn from both Boeing and the suppliers, who were sharing their progress monitoring and reporting with Boeing. The 777 software development met the majority of its goals, with only about 120,000 lines of nonessential functionality deferred at initial delivery. To achieve this success, we relied upon four key tactics which are outlined     

Techniques for increasing the stream capacity of a high-performancemultimedia server

High-performance servers and high-speed networks will form the backbone of the infrastructure required for distributed multimedia information systems. A server for an interactive distributed multimedia system may require thousands of gigabytes of storage space and a high I/O bandwidth. In order to maximize the system utilization, and thus minimize the cost, it is essential that the load be balanced among each of the server's components, viz. the disks, the interconnection network and the scheduler. Many algorithms for maximizing retrieval capacity from the storage system have been proposed in the literature. This paper presents techniques for improving the server capacity by assigning media requests to the nodes of a server so as to balance the load on the interconnection network and the scheduling nodes. Five policies for request assignment-round-robin (RR), minimum link allocation (MLA), minimum contention allocation (MCA), weighted minimum link allocation (WMLA) and weighted minimum contention allocation (WMCA)-are developed. The performance of these policies on a server model developed by the authors (1995) is presented. We also consider the issue of file replication, and develop two schemes for storing the replicas: the parent group-based round-robin placement (PGBRRP) scheme, and the group-wide round-robin placement (GWRRP) scheme. The performance of the request assignment policies in the presence of file replication is presented     

Security analysis of a new stream cipher

From 1st February of 2004, Europe launches the ECRYPT project, which collects lots of stream ciphers from all over the world. These new stream ciphers are unlike the tradi- tional stream ciphers that use LFSRs as basic building blocks; instead they use mo…     

On the behaviour of a stressed cotton canopy in a direct air stream

Reflectance variations of a stressed cotton canopy were conducted in the presence of a fan-generated air stream to investigate the effects of air movement and the resulting temperature changes on remotely-sensed data. The initial drop in reflectance after application of the air stream was found to be greatest in the morning because leaf turgor was at a maximum, enabling leaves on the windward side of the canopy to assume surprisingly stable vertical positions. This transient configuration in the morning was responsible for greater stem displacement (relative to that of the afternoon), because the leaf area normal to the air stream was maximized, thus increasing the capacity of the canopy to trap light. By afternoon, a reduction in leaf turgor was responsible for less stem displacement and consequently a reduction in light-trapping capability. However, reflectance oscillations were greater because the leaves had become sufficiently limp to flutter at the edges and about the petioles exposing both adaxial and abaxial surfaces to the incident light. The optical and thermal radiometric manifestations of this behaviour were modelled using the damped harmonic oscillator approximation by considering the canopy as a transducer for converting a mechanical response to an optical response. These relationships were combined with temperature information to derive a simple relationship for the relative entropy per radian employing thematic mapper bands 3 and 4. For a constant temperature situation the relative entropy was found to be nearly linear for both bands.     

Dynamic hierarchical triangulation of a clustered data stream

This paper presents a novel approach to handle large amounts of geometric data. A data stream clustering is used to reduce the amount of data and build a hierarchy of clusters. The data stream concept allows for the processing of very large data sets. The cluster hierarchy is then used in a dynamic triangulation to create a multiresolution model. It allows for the interactive selection of a different level of detail in various parts of the data.A method for removal multiple points from Delaunay triangulation is proposed. It is significantly faster than the traditional approach. The clustering and the triangulation are supplemented by an elliptical metric to handle data with anisotropic properties.Compared to the closest competitive method by Isenburg et al., the presented algorithm requires only a single pass over the data and offers a high flexibility. These advantages culminate in a long running time. The method was tested on several large digital elevation maps. The clustering phase can take up to a few hours. Once the cluster hierarchy is built, the terrains can be efficiently manipulated in real time.     

Irrevocable-choice algorithms for sampling from a stream

The problem of sampling from data streams has attracted significant interest in the last decade. Whichever sampling criteria is considered (uniform sample, maximally diverse sample, etc.), the challenges stem from the relatively small amount of memory available in the face of unbounded streams. In this work we consider an interesting extension of this problem, the framework of which is stimulated by recent improvements in sensing technologies and robotics. In some situations it is not only possible to digitally sense some aspects of the world, but to physically capture a tangible aspect of that world. Currently deployed examples include devices that can capture water/air samples, and devices that capture individual insects or fish. Such devices create an interesting twist on the stream sampling problem, because in most cases, the decision to take a physical sample is irrevocable. In this work we show how to generalize diversification sampling strategies to the irrevocable-choice setting, demonstrating our ideas on several real world domains.     

Effects of planar inlet plenums on the hydrodynamically developing flows in rectangular microchannels of complementary aspect ratios

The effects of planar inlet plenum geometry on the developing flow fields in two rectangular microchannels of reciprocal aspect ratios (H/W ∼2.75 and ∼0.40) were investigated for Re _D =  1–100 using micro particle image velocimetry (μPIV). These two microchannels were made by a precision sawing and silicon microfabrication techniques. Both the velocity profiles and centerline velocity developments were clearly resolved and extracted along the axial distance from μPIV results. The entrance lengths were found from the centerline velocities using a decaying exponential fitting function where the centerline velocity reaches 99% of the fully developed centerline velocity. The proposed fitting function showed excellent agreement with the experimental results. The planar plenum was shown to cause an upstream predevelopment resulting in the significant reductions in the entrance lengths. Two entrance length correlations were proposed in the forms of Atkinson et al.’s (AIChE J 15:548–553, 1969) and Chen’s (J Fluids Eng 95:153–158, 1973) correlations. The proposed entrance length correlations showed that acquired constant portion and slope of the entrance lengths showed 23–27 and 70–81% reductions for H/W =  2.75 while the entrance length correlation for H/W =  0.40 showed 69–73% increase and 41–63% decrease in the constant portion and slope, respectively.     

Multirobot systems: a classification focused on coordination

Multirobot systems (MRS) are, nowadays, an important research area within robotics and artificial intelligence and a growing number of systems have recently been presented in the literature. Since application domains and tasks that are faced by MRS are of increasing complexity, the ability of the robots to cooperate can be regarded as a fundamental feature. In this paper, we present a survey of the recent work in the area by specifically examining the forms of cooperation and coordination realized in the MRS. In particular, we propose a new taxonomy for classification of the approaches to coordination in MRS and we describe some systems, which we consider representative in our taxonomy. We finally discuss the outcomes of our analysis and try to highlight future trends of the research on MRS.     

An analysis of the relation between stream channel sinuosity and stream channel gradient

Existing literature lends credence to the idea that channel sinuosity and channel gradient are independent morphologic elements responding to characteristics of the water and sediment regime of a stream. At the same time, sinuosity and gradient are viewed as closely related variables, since sinuosity is often defined as a ratio of valley gradient to channel gradient over a stream reach. These conceptions of the sinuosity variable are essentially contradictory if viewed from the standpoint of process, since in the latter case, water and sediment characteristics have no direct bearing on the determination of sinuosity, but only the potential of indirect influence operating through the channel gradient. This paper presents an empirical analysis aimed at evaluating the validity of these two conceptions of the sinuosity variable. The results of the analysis strongly support the gradient ratio concept and suggest that the traditional sinuosity variable is not reasonably viewed as an independent element of stream channel morphology, since it is essentially determined by the same process as that which determines the channel gradient. Thus, channel sinuosity is insignificantly influenced by the direct effects of water and sediment discharge. Certain indirect effects of these factors do exist, however, given the role of channel gradient in the determination of sinuosity. A summary of these results is given in the form of a two-equation recursive model.     

Evaluating shape correspondence for statistical shape analysis: a benchmark study

This paper introduces a new benchmark study to evaluate the performance of landmark-based shape correspondence used for statistical shape analysis. Different from previous shape-correspondence evaluation methods, the proposed benchmark first generates a large set of synthetic shape instances by randomly sampling a given statistical shape model that defines a ground-truth shape space. We then run a test shape-correspondence algorithm on these synthetic shape instances to identify a set of corresponded landmarks. According to the identified corresponded landmarks, we construct a new statistical shape model, which defines a new shape space. We finally compare this new shape space against the ground-truth shape space to determine the performance of the test shape-correspondence algorithm. In this paper, we introduce three new performance measures that are landmark independent to quantify the difference between the ground-truth and the newly derived shape spaces. By introducing a ground-truth shape space that is defined by a statistical shape model and three new landmark-independent performance measures, we believe the proposed benchmark allows for a more objective evaluation of shape correspondence than previous methods. In this paper, we focus on developing the proposed benchmark for $2$D shape correspondence. However it can be easily extended to $3$D cases.     

Hydrodynamic focusing with a microlithographic manifold: controlling the vertical position of a focused sample

A microfluidic manifold has been designed, fabricated, and tested that hydrodynamically focuses a sample into the center of a microchannel and provides control over the vertical position of the sample via the flow-rates of the focusing fluids. To characterize the focusing action, a mixing experiment was performed in which the sample fluid and focusing fluid contained different fluorescent dyes. By sweeping the ratio of the rate of the top focusing fluid to the rate of the bottom focusing fluid, the sample was positioned first near the top of the microchannel and then translated downward in steps to the bottom of the microchannel. Images were obtained with confocal microscopy, and the presumptive concentration distributions were computed using multiphysics software. The simulations were shown by direct visual comparison with the experimental images to accurately predict the distributions of fluids in our device. In order to quantitatively compare the two data sets, the images and simulations were analyzed using a simple center-of-mass measurement, and according to this measurement, the simulations accurately predicted the vertical position the focused sample.     

MPEG节目流到传输流的转化

MPEG系统流部分规定了视频文件的两种不同形式，分别用于不同的用途。在视频点播的软件开发中，为了提高视频流的传输质量，需要从节目流到传输流进行转化，介绍了MPEG节目流和传输流的语法结构，实现了从节目流到传输流的转化。     

Improving the performance of focused web crawlers

This work addresses issues related to the design and implementation of focused crawlers. Several variants of state-of-the-art crawlers relying on web page content and link information for estimating the relevance of web pages to a given topic are proposed. Particular emphasis is given to crawlers capable of learning not only the content of relevant pages (as classic crawlers do) but also paths leading to relevant pages. A novel learning crawler inspired by a previously proposed Hidden Markov Model (HMM) crawler is described as well. The crawlers have been implemented using the same baseline implementation (only the priority assignment function differs in each crawler) providing an unbiased evaluation framework for a comparative analysis of their performance. All crawlers achieve their maximum performance when a combination of web page content and (link) anchor text is used for assigning download priorities to web pages. Furthermore, the new HMM crawler improved the performance of the original HMM crawler and also outperforms classic focused crawlers in searching for specialized topics.     

Estimating the Parameters of a Tapered Pareto Distribution

Automation and Remote Control - The article deals with the problem of estimating the parameters of a tapered Pareto distribution. Using the moment method, we obtain new estimates depending on an...     

CellJoin: a parallel stream join operator for the cell processor

Low-latency and high-throughput processing are key requirements of data stream management systems (DSMSs). Hence, multi-core processors that provide high aggregate processing capacity are ideal matches for executing costly DSMS operators. The recently developed Cell processor is a good example of a heterogeneous multi-core architecture and provides a powerful platform for executing data stream operators with high-performance. On the down side, exploiting the full potential of a multi-core processor like Cell is often challenging, mainly due to the heterogeneous nature of the processing elements, the software managed local memory at the co-processor side, and the unconventional programming model in general. In this paper, we study the problem of scalable execution of windowed stream join operators on multi-core processors, and specifically on the Cell processor. By examining various aspects of join execution flow, we determine the right set of techniques to apply in order to minimize the sequential segments and maximize parallelism. Concretely, we show that basic windows coupled with low-overhead pointer-shifting techniques can be used to achieve efficient join window partitioning, column-oriented join window organization can be used to minimize scattered data transfers, delay-optimized double buffering can be used for effective pipelining, rate-aware batching can be used to balance join throughput and tuple delay, and finally single-instruction multiple-data (SIMD) optimized operator code can be used to exploit data parallelism. Our experimental results show that, following the design guidelines and implementation techniques outlined in this paper, windowed stream joins can achieve high scalability (linear in the number of co-processors) by making efficient use of the extensive hardware parallelism provided by the Cell processor (reaching data processing rates of ≈13 GB/s) and significantly surpass the performance obtained form conventional high-end processors (supporting a combined input stream rate of 2,000 tuples/s using 15 min windows and without dropping any tuples, resulting in ≈8.3 times higher output rate compared to an SSE implementation on dual 3.2 GHz Intel Xeon).     

Analysing a stream authentication protocol using model checking

In this paper, we consider how one can analyse a stream authentication protocol using model checking techniques. In particular, we will be focusing on the Timed Efficient Stream Loss-tolerant Authentication Protocol, TESLA. This protocol differs from the standard class of authentication protocols previously analysed using model checking techniques in the following interesting way: an unbounded stream of messages is broadcast by a sender, making use of an unbounded stream of keys; the authentication of the n-th message in the stream is achieved on receipt of the n+1-th message. We show that, despite the infinite nature of the protocol, it is possible to build a finite model that correctly captures its behaviour.     

Study of a simulated stream machine for dataflow computation

In this paper, a stream-based dataflow architecture is proposed, and its simulation model, which has helped to evaluate the effectiveness of the proposed architectural concept, is discussed. The machine integrates the conventional Von Neumann type of control flow subsystem with a dataflow processing element of token storage type. The control flow unit tackles the dynamic nature of the stream structure including input/output whereas the dataflow unit does the computation part in an applicative style. A pipelined version of the stream machine is also discussed. The effectiveness of the machine is studied by running a few example programs in the simulated machine. The machine is expected to be useful in real time signal processing applications.