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121.
The National Land Cover Database (NLCD) 2001 Alaska land cover classification is the first 30-m resolution land cover product available covering the entire state of Alaska. The accuracy assessment of the NLCD 2001 Alaska land cover classification employed a geographically stratified three-stage sampling design to select the reference sample of pixels. Reference land cover class labels were determined via fixed wing aircraft, as the high resolution imagery used for determining the reference land cover classification in the conterminous U.S. was not available for most of Alaska. Overall thematic accuracy for the Alaska NLCD was 76.2% (s.e. 2.8%) at Level II (12 classes evaluated) and 83.9% (s.e. 2.1%) at Level I (6 classes evaluated) when agreement was defined as a match between the map class and either the primary or alternate reference class label. When agreement was defined as a match between the map class and primary reference label only, overall accuracy was 59.4% at Level II and 69.3% at Level I. The majority of classification errors occurred at Level I of the classification hierarchy (i.e., misclassifications were generally to a different Level I class, not to a Level II class within the same Level I class). Classification accuracy was higher for more abundant land cover classes and for pixels located in the interior of homogeneous land cover patches. 相似文献
122.
Urban growth modeling of Kathmandu metropolitan region, Nepal 总被引:6,自引:0,他引:6
The complexity of urban system requires integrated tools and techniques to understand the spatial process of urban development and project the future scenarios. This research aims to simulate urban growth patterns in Kathmandu metropolitan region in Nepal. The region, surrounded by complex mountainous terrain, has very limited land resources for new developments. As similar to many cities of the developing world, it has been facing rapid population growth and daunting environmental problems. Three time series land use maps in a fine-scale (30 m resolution), derived from satellite remote sensing, for the last three decades of the 20th century were used to clarify the spatial process of urbanization. Based on the historical experiences of the land use transitions, we adopted weight of evidence method integrated in cellular automata framework for predicting the future spatial patterns of urban growth. We extrapolated urban development patterns to 2010 and 2020 under the current scenario across the metropolitan region. Depending on local characteristics and land cover transition rates, this model produced noticeable spatial pattern of changes in the region. Based on the extrapolated spatial patterns, the urban development in the Kathmandu valley will continue through both in-filling in existing urban areas and outward rapid expansion toward the east and south directions. Overall development will be greatly affected by the existing urban space, transportation network, and topographic complexity. 相似文献
123.
A certifying algorithm for a problem is an algorithm that provides a certificate with each answer that it produces. The certificate is an evidence that can be used to authenticate the correctness of the answer. A Hamiltonian cycle in a graph is a simple cycle in which each vertex of the graph appears exactly once. The Hamiltonian cycle problem is to determine whether or not a graph contains a Hamiltonian cycle. The best result for the Hamiltonian cycle problem on circular-arc graphs is an O(n2logn)-time algorithm, where n is the number of vertices of the input graph. In fact, the O(n2logn)-time algorithm can be modified as a certifying algorithm although it was published before the term certifying algorithms appeared in the literature. However, whether there exists an algorithm whose time complexity is better than O(n2logn) for solving the Hamiltonian cycle problem on circular-arc graphs has been opened for two decades. In this paper, we present an O(Δn)-time certifying algorithm to solve this problem, where Δ represents the maximum degree of the input graph. The certificates provided by our algorithm can be authenticated in O(n) time. 相似文献
124.
We consider the following problem: Given a finite set of straight line segments in the plane, find a set of points of minimum size, so that every segment contains at least one point in the set. This problem can be interpreted as looking for a minimum number of locations of policemen, guards, cameras or other sensors, that can observe a network of streets, corridors, tunnels, tubes, etc. We show that the problem is strongly NP-complete even for a set of segments with a cubic graph structure, but in P for tree structures. 相似文献
125.
We compare the fixed parameter complexity of various variants of coloring problems (including List Coloring, Precoloring Extension, Equitable Coloring, L(p,1)-Labeling and Channel Assignment) when parameterized by treewidth and by vertex cover number. In most (but not all) cases we conclude that parametrization by the vertex cover number provides a significant drop in the complexity of the problems. 相似文献
126.
127.
逻辑函数的无冗余覆盖选择问题 总被引:1,自引:1,他引:0
王波 《计算机应用与软件》2000,17(10):19-24,38
逻辑函数的最小化算法可分为两大步骤:产生本源蕴涵项和在这些蕴涵项中选择一个最小覆盖。人说后者比前者更加困难,这的确是事实。我们这里提出一个无冗余和选择一个最小覆盖的算法。给定函数f的一个本源覆盖G,首先将G分为三个子集:实质本源项子集E,完全冗余项子集R和相对冗余项子集P。然后在P中选择一个子集P^*,使P^*∪E为f的一个近似最小覆盖。很明显,后一项任务比前者要复杂得多。所以,我们的讨论侧重于后 相似文献
128.
张艳 《数码设计:surface》2008,(1):46-48
文章分析了插图在流行音乐CD封套设计中广泛应用的原因,对CD封套设计中的插图三个显著特点:时尚性、形式多元化、视觉艺术化进行了重点分析与讨论,证实插图在流行音乐CD封套设计中的优势所在,阐释了其美学价值和商业价值。 相似文献
129.
Determining order relationship between events of a distributed computation is a fundamental problem in distributed systems
which has applications in many areas including debugging, visualization, checkpointing and recovery. Fidge/Mattern’s vector-clock
mechanism captures the order relationship using a vector of size N in a system consisting of N processes. As a result, it incurs message and space overhead of N integers. Many distributed applications use synchronous messages for communication. It is therefore natural to ask whether it is possible to reduce the timestamping overhead for such applications.
In this paper, we present a new approach for timestamping messages and events of a synchronously ordered computation, that is, when processes communicate using synchronous messages. Our approach depends on decomposing edges in the communication
topology into mutually disjoint edge groups such that each edge group either forms a star or a triangle. We show that, to accurately capture the order relationship between
synchronous messages, it is sufficient to use one component per edge group in the vector instead of one component per process.
Timestamps for events are only slightly bigger than timestamps for messages. Many common communication topologies such as
ring, grid and hypercube can be decomposed into edge groups, resulting in almost 50% improvement in both space and communication overheads. We prove that the problem of
computing an optimal edge decomposition of a communication topology is NP-complete in general. We also present a heuristic
algorithm for computing an edge decomposition whose size is within a factor of two of the optimal. We prove that, in the worst
case, it is not possible to timestamp messages of a synchronously ordered computation using a vector containing fewer than
components when N ≥ 2. Finally, we show that messages in a synchronously ordered computation can always be timestamped in an offline manner
using a vector of size at most .
An earlier version of this paper appeared in 2002 Proceedings of the IEEE International Conference on Distributed Computing
Systems (ICDCS).
The author V. K. Garg was supported in part by the NSF Grants ECS-9907213, CCR-9988225, an Engineering Foundation Fellowship.
This work was done while the author C. Skawratananond was a Ph.D. student at the University of Texas at Austin. 相似文献
130.
在装酸槽车上采用了“双锥平衡密封盖”,解决了汽车运输过程及贮罐贮存中酸雾对环境的污染问题,并实现了装卸过程中的压力自控,从而简化了操作,减少了浪费,取得了良好社会经济效益。 相似文献