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928 results on '"LEE, D. T."'

1. Topology of Coronal Magnetic Fields: Extending the Magnetic Skeleton Using Null-like Points

Author

Lee, D. T. and Brown, D. S.

Subjects
Astrophysics - Solar and Stellar Astrophysics
Abstract

Many phenomena in the Sun's atmosphere are magnetic in nature and study of the atmospheric magnetic field plays an important part in understanding these phenomena. Tools to study solar magnetic fields include magnetic topology and features such as magnetic null points, separatrix surfaces, and separators. The theory of these has most robustly been developed under magnetic charge topology, where the sources of the magnetic field are taken to be discrete, but observed magnetic fields are continuously distributed, and reconstructions and numerical simulations typically use continuously distributed magnetic boundary conditions. This article investigates the pitfalls in using continuous source descriptions, particularly when null points on the $z=0$ plane are obscured by the continuous flux distribution through, e.g., the overlap of non-point sources. The idea of null-like points on the boundary is introduced where the parallel requirement on the field $B_{\parallel}=0$ is retained but the requirement on the perpendicular component is relaxed, i.e., $B_{\perp}\ne0$. These allow the definition of separatrix-like surfaces which are shown (through use of a squashing factor) to be a class of quasi-separatrix layer, and separator-like lines which retain the x-line structure of separators. Examples are given that demonstrate that the use of null-like points can reinstate topological features that are eliminated in the transition from discrete to continuous sources, and that their inclusion in more involved cases can enhance understanding of the magnetic structure and even change the resulting conclusions. While the examples in this article use the potential approximation, the definition of null-like points is more general and may be employed in other cases such as force-free field extrapolations and MHD simulations., Comment: 21 pages, 11 figures, Accepted for publication in SolPhys

Published
2020
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2. O(f) Bi-Approximation for Capacitated Covering with Hard Capacities

Author

Kao, Mong-Jen, Tu, Hai-Lun, and Lee, D. T.

Subjects
Computer Science - Discrete Mathematics
Abstract

We consider capacitated vertex cover with hard capacity constraints (VC-HC) on hypergraphs. In this problem we are given a hypergraph $G=(V,E)$ with a maximum edge size $f$. Each edge is associated with a demand and each vertex is associated with a weight (cost), a capacity, and an available multiplicity. The objective is to find a minimum-weight vertex multiset such that the demands of the edges can be covered by the capacities of the vertices and the multiplicity of each vertex does not exceed its available multiplicity. In this paper we present an $O(f)$ bi-approximation for VC-HC that gives a trade-off on the number of augmented multiplicity and the cost of the resulting cover. In particular, we show that, by augmenting the available multiplicity by a factor of $k \ge 2$, a~cover with a cost ratio of $\Big(1+\frac{1}{k-1}\Big)(f-1)$ to the optimal cover for the original instance can be obtained. This improves over a previous result, which has a cost ratio of $f^2$ via augmenting the available multiplicity by a factor of $f$.

Published
2016

3. The $(1|1)_R$-Centroid Problem on the Plane

Author

Yu, Hung-I, Lin, Tien-Ching, and Lee, D. T.

Subjects
Computer Science - Computational Geometry, Computer Science - Data Structures and Algorithms, I.3.5, F.2.2
Abstract

In 1982, Drezner proposed the (1|1)-centroid problem on the plane, in which two players, called the leader and the follower, open facilities to provide service to customers in a competitive manner. The leader opens the first facility, and then the follower opens the second. Each customer will patronize the facility closest to him (ties broken in favor of the leader's one), thereby decides the market share of the two players. The goal is to find the best position for the leader's facility so that his market share is maximized. The best algorithm for this problem is an $O(n^2 \log n)$-time parametric search approach, which searches over the space of possible market share values. In the same paper, Drezner also proposed a general version of (1|1)-centroid problem by introducing a minimal distance constraint $R$, such that the follower's facility is not allowed to be located within a distance $R$ from the leader's. He proposed an $O(n^5 \log n)$-time algorithm for this general version by identifying $O(n^4)$ points as the candidates of the optimal solution and checking the market share for each of them. In this paper, we develop a new parametric search approach searching over the $O(n^4)$ candidate points, and present an $O(n^2 \log n)$-time algorithm for the general version, thereby close the $O(n^3)$ gap between the two bounds., Comment: 27 pages, 6 figures. A preliminary version of this paper has been submitted to ISAAC 2016

Published
2016

4. The Multi-service Location Problems

Author

Yu, Hung-I, Kao, Mong-Jen, Lee, D. T., Barbosa, Simone Diniz Junqueira, Editorial Board Member, Filipe, Joaquim, Editorial Board Member, Ghosh, Ashish, Editorial Board Member, Kotenko, Igor, Editorial Board Member, Yuan, Junsong, Editorial Board Member, Zhou, Lizhu, Editorial Board Member, Chang, Chuan-Yu, editor, Lin, Chien-Chou, editor, and Lin, Horng-Horng, editor

Published
2019
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5. An O(f) Bi-approximation for Weighted Capacitated Covering with Hard Capacity

Author

Tu, Hai-Lun, Kao, Mong-Jen, Lee, D. T., Barbosa, Simone Diniz Junqueira, Editorial Board Member, Filipe, Joaquim, Editorial Board Member, Ghosh, Ashish, Editorial Board Member, Kotenko, Igor, Editorial Board Member, Yuan, Junsong, Editorial Board Member, Zhou, Lizhu, Editorial Board Member, Chang, Chuan-Yu, editor, Lin, Chien-Chou, editor, and Lin, Horng-Horng, editor

Published
2019
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6. Optimal Time-Convex Hull under the Lp Metrics

Author

Dai, Bang-Sin, Kao, Mong-Jen, and Lee, D. T.

Subjects
Computer Science - Computational Geometry
Abstract

We consider the problem of computing the time-convex hull of a point set under the general $L_p$ metric in the presence of a straight-line highway in the plane. The traveling speed along the highway is assumed to be faster than that off the highway, and the shortest time-path between a distant pair may involve traveling along the highway. The time-convex hull ${TCH}(P)$ of a point set $P$ is the smallest set containing both $P$ and \emph{all} shortest time-paths between any two points in ${TCH}(P)$. In this paper we give an algorithm that computes the time-convex hull under the $L_p$ metric in optimal $O(n\log n)$ time for a given set of $n$ points and a real number $p$ with $1\le p \le \infty$.

Published
2013

7. Online Power-Managing Strategy with Hard Real-Time Guarantees

Author

Chen, Jian-Jia, Kao, Mong-Jen, Lee, D. T., Rutter, Ignaz, and Wagner, Dorothea

Subjects
Computer Science - Data Structures and Algorithms
Abstract

We consider the problem of online dynamic power management that provides hard real-time guarantees. In this problem, each of the given jobs is associated with an arrival time, a deadline, and an execution time, and the objective is to decide a schedule of the jobs as well as a sequence of state transitions on the processors so as to minimize the total energy consumption. In this paper, we examine the problem complexity and provide online strategies to achieve energy-efficiency. First, we show that the competitive factor of any online algorithm for this problem is at least 2.06. Then we present an online algorithm which gives a 4-competitive schedule. When the execution times of the jobs are unit, we show that the competitive factor improves to 3.59. At the end, the algorithm is generalized to allow a trade-off between the number of processors we use and the energy-efficiency of the resulting schedule.

Published
2013

8. Higher Order City Voronoi Diagrams

Author

Gemsa, Andreas, Lee, D. T., Liu, Chih-Hung, and Wagner, Dorothea

Subjects
Computer Science - Computational Geometry
Abstract

We investigate higher-order Voronoi diagrams in the city metric. This metric is induced by quickest paths in the L1 metric in the presence of an accelerating transportation network of axis-parallel line segments. For the structural complexity of kth-order city Voronoi diagrams of n point sites, we show an upper bound of O(k(n - k) + kc) and a lower bound of {\Omega}(n + kc), where c is the complexity of the transportation network. This is quite different from the bound O(k(n - k)) in the Euclidean metric. For the special case where k = n - 1 the complexity in the Euclidean metric is O(n), while that in the city metric is {\Theta}(nc). Furthermore, we develop an O(k^2(n + c) log n)-time iterative algorithm to compute the kth-order city Voronoi diagram and an O(nc log^2(n + c) log n)-time divide-and-conquer algorithm to compute the farthest-site city Voronoi diagram., Comment: 15 pages, extended version of paper to appear in Proc. 13th Scandinavian Symposium and Workshops on Algorithm Theory (SWAT'12), Helsinki, Finland, 2012

Published
2012

9. Capacitated Domination: Constant Factor Approximation for Planar Graphs

Author

Kao, Mong-Jen and Lee, D. T.

Subjects
Computer Science - Data Structures and Algorithms
Abstract

We consider the capacitated domination problem, which models a service-requirement assigning scenario and which is also a generalization of the dominating set problem. In this problem, we are given a graph with three parameters defined on the vertex set, which are cost, capacity, and demand. The objective of this problem is to compute a demand assignment of least cost, such that the demand of each vertex is fully-assigned to some of its closed neighbours without exceeding the amount of capacity they provide. In this paper, we provide the first constant factor approximation for this problem on planar graphs, based on a new perspective on the hierarchical structure of outer-planar graphs. We believe that this new perspective and technique can be applied to other capacitated covering problems to help tackle vertices of large degrees.

Published
2011

13. Optimal Time-Convex Hull under the L p Metrics

Author

Dai, Bang-Sin, Kao, Mong-Jen, Lee, D. T., Hutchison, David, editor, Kanade, Takeo, editor, Kittler, Josef, editor, Kleinberg, Jon M., editor, Mattern, Friedemann, editor, Mitchell, John C., editor, Naor, Moni, editor, Nierstrasz, Oscar, editor, Pandu Rangan, C., editor, Steffen, Bernhard, editor, Sudan, Madhu, editor, Terzopoulos, Demetri, editor, Tygar, Doug, editor, Vardi, Moshe Y., editor, Weikum, Gerhard, editor, Dehne, Frank, editor, Solis-Oba, Roberto, editor, and Sack, Jörg-Rüdiger, editor

Published
2013
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14. Finding Maximum Sum Segments in Sequences with Uncertainty

Author

Yu, Hung-I, Lin, Tien-Ching, Lee, D. T., Hutchison, David, Series editor, Kanade, Takeo, Series editor, Kittler, Josef, Series editor, Kleinberg, Jon M., Series editor, Mattern, Friedemann, Series editor, Mitchell, John C., Series editor, Naor, Moni, Series editor, Nierstrasz, Oscar, Series editor, Pandu Rangan, C., Series editor, Steffen, Bernhard, Series editor, Sudan, Madhu, Series editor, Terzopoulos, Demetri, Series editor, Tygar, Doug, Series editor, Vardi, Moshe Y., Series editor, Weikum, Gerhard, Series editor, Asano, Takao, editor, Nakano, Shin-ichi, editor, Okamoto, Yoshio, editor, and Watanabe, Osamu, editor

Published
2011
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15. An Output-Sensitive Approach for the L 1/L ∞ k-Nearest-Neighbor Voronoi Diagram

Author

Liu, Chih-Hung, Papadopoulou, Evanthia, Lee, D. T., Hutchison, David, Series editor, Kanade, Takeo, Series editor, Kittler, Josef, Series editor, Kleinberg, Jon M., Series editor, Mattern, Friedemann, Series editor, Mitchell, John C., Series editor, Naor, Moni, Series editor, Nierstrasz, Oscar, Series editor, Pandu Rangan, C., Series editor, Steffen, Bernhard, Series editor, Sudan, Madhu, Series editor, Terzopoulos, Demetri, Series editor, Tygar, Doug, Series editor, Vardi, Moshe Y., Series editor, Weikum, Gerhard, Series editor, Demetrescu, Camil, editor, and Halldórsson, Magnús M., editor

Published
2011
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16. The Density Maximization Problem in Graphs

Author

Kao, Mong-Jen, Katz, Bastian, Krug, Marcus, Lee, D. T., Rutter, Ignaz, Wagner, Dorothea, Hutchison, David, Series editor, Kanade, Takeo, Series editor, Kittler, Josef, Series editor, Kleinberg, Jon M., Series editor, Mattern, Friedemann, Series editor, Mitchell, John C., Series editor, Naor, Moni, Series editor, Nierstrasz, Oscar, Series editor, Pandu Rangan, C., Series editor, Steffen, Bernhard, Series editor, Sudan, Madhu, Series editor, Terzopoulos, Demetri, Series editor, Tygar, Doug, Series editor, Vardi, Moshe Y., Series editor, Weikum, Gerhard, Series editor, Fu, Bin, editor, and Du, Ding-Zhu, editor

Published
2011
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17. Spanning Ratio and Maximum Detour of Rectilinear Paths in the L 1 Plane

Author

Grüne, Ansgar, Lin, Tien-Ching, Yu, Teng-Kai, Klein, Rolf, Langetepe, Elmar, Lee, D. T., Poon, Sheung-Hung, Hutchison, David, Series editor, Kanade, Takeo, Series editor, Kittler, Josef, Series editor, Kleinberg, Jon M., Series editor, Mattern, Friedemann, Series editor, Mitchell, John C., Series editor, Naor, Moni, Series editor, Nierstrasz, Oscar, Series editor, Pandu Rangan, C., Series editor, Steffen, Bernhard, Series editor, Sudan, Madhu, Series editor, Terzopoulos, Demetri, Series editor, Tygar, Doug, Series editor, Vardi, Moshe Y., Series editor, Weikum, Gerhard, Series editor, Cheong, Otfried, editor, Chwa, Kyung-Yong, editor, and Park, Kunsoo, editor

Published
2010
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18. Broadcasting in Heterogeneous Tree Networks

Author

Su, Yu-Hsuan, Lin, Ching-Chi, Lee, D. T., Hutchison, David, editor, Kanade, Takeo, editor, Kittler, Josef, editor, Kleinberg, Jon M., editor, Mattern, Friedemann, editor, Mitchell, John C., editor, Naor, Moni, editor, Nierstrasz, Oscar, editor, Pandu Rangan, C., editor, Steffen, Bernhard, editor, Sudan, Madhu, editor, Terzopoulos, Demetri, editor, Tygar, Doug, editor, Vardi, Moshe Y., editor, Weikum, Gerhard, editor, Thai, My T., editor, and Sahni, Sartaj, editor

Published
2010
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19. Scene Location Guide by Image-Based Retrieval

Author

Jhuo, I-Hong, Chen, Tsuhan, Lee, D. T., Hutchison, David, editor, Kanade, Takeo, editor, Kittler, Josef, editor, Kleinberg, Jon M., editor, Mattern, Friedemann, editor, Mitchell, John C., editor, Naor, Moni, editor, Nierstrasz, Oscar, editor, Pandu Rangan, C., editor, Steffen, Bernhard, editor, Sudan, Madhu, editor, Terzopoulos, Demetri, editor, Tygar, Doug, editor, Vardi, Moshe Y., editor, Weikum, Gerhard, editor, Boll, Susanne, editor, Tian, Qi, editor, Zhang, Lei, editor, Zhang, Zili, editor, and Chen, Yi-Ping Phoebe, editor

Published
2010
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20. Geometric Minimum Diameter Minimum Cost Spanning Tree Problem

Author

Seo, Dae Young, Lee, D. T., Lin, Tien-Ching, Hutchison, David, editor, Kanade, Takeo, editor, Kittler, Josef, editor, Kleinberg, Jon M., editor, Mattern, Friedemann, editor, Mitchell, John C., editor, Naor, Moni, editor, Nierstrasz, Oscar, editor, Pandu Rangan, C., editor, Steffen, Bernhard, editor, Sudan, Madhu, editor, Terzopoulos, Demetri, editor, Tygar, Doug, editor, Vardi, Moshe Y., editor, Weikum, Gerhard, editor, Dong, Yingfei, editor, Du, Ding-Zhu, editor, and Ibarra, Oscar, editor

Published
2009
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21. Optimal Randomized Algorithm for the Density Selection Problem

Author

Lin, Tien-Ching, Lee, D. T., Hutchison, David, editor, Kanade, Takeo, editor, Kittler, Josef, editor, Kleinberg, Jon M., editor, Mattern, Friedemann, editor, Mitchell, John C., editor, Naor, Moni, editor, Nierstrasz, Oscar, editor, Pandu Rangan, C., editor, Steffen, Bernhard, editor, Sudan, Madhu, editor, Terzopoulos, Demetri, editor, Tygar, Doug, editor, Vardi, Moshe Y., editor, Weikum, Gerhard, editor, Dong, Yingfei, editor, Du, Ding-Zhu, editor, and Ibarra, Oscar, editor

Published
2009
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22. Introduction

Author

Lee, D. T., Shieh, S. P., Tygar, J. D., Lee, D. T., editor, Shieh, S. P., editor, and Tygar, J. D., editor

Published
2005
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23. Maximizing the Number of Independent Labels in the Plane

Author

Yu, Kuen-Lin, Liao, Chung-Shou, Lee, D. T., Hutchison, David, editor, Kanade, Takeo, editor, Kittler, Josef, editor, Kleinberg, Jon M., editor, Mattern, Friedemann, editor, Mitchell, John C., editor, Naor, Moni, editor, Nierstrasz, Oscar, editor, Pandu Rangan, C., editor, Steffen, Bernhard, editor, Sudan, Madhu, editor, Terzopoulos, Demetri, editor, Tygar, Doug, editor, Vardi, Moshe Y., editor, Weikum, Gerhard, editor, Preparata, Franco P., editor, and Fang, Qizhi, editor

Published
2007
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24. Efficient Algorithms for the Sum Selection Problem and K Maximum Sums Problem

Author

Lin, Tien-Ching, Lee, D. T., Hutchison, David, editor, Kanade, Takeo, editor, Kittler, Josef, editor, Kleinberg, Jon M., editor, Mattern, Friedemann, editor, Mitchell, John C., editor, Naor, Moni, editor, Nierstrasz, Oscar, editor, Pandu Rangan, C., editor, Steffen, Bernhard, editor, Sudan, Madhu, editor, Terzopoulos, Demetri, editor, Tygar, Dough, editor, Vardi, Moshe Y., editor, Weikum, Gerhard, editor, and Asano, Tetsuo, editor

Published
2006
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25. Priority-Based Genetic Local Search and Its Application to the Traveling Salesman Problem

Author

Wei, Jyh-Da, Lee, D. T., Hutchison, David, editor, Kanade, Takeo, editor, Kittler, Josef, editor, Kleinberg, Jon M., editor, Mattern, Friedemann, editor, Mitchell, John C., editor, Naor, Moni, editor, Nierstrasz, Oscar, editor, Pandu Rangan, C., editor, Steffen, Bernhard, editor, Sudan, Madhu, editor, Terzopoulos, Demetri, editor, Tygar, Dough, editor, Vardi, Moshe Y., editor, Weikum, Gerhard, editor, Wang, Tzai-Der, editor, Li, Xiaodong, editor, Chen, Shu-Heng, editor, Wang, Xufa, editor, Abbass, Hussein, editor, Iba, Hitoshi, editor, Chen, Guo-Liang, editor, and Yao, Xin, editor

Published
2006
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26. Randomized Algorithm for the Sum Selection Problem

Author

Lin, Tien-Ching, Lee, D. T., Hutchison, David, editor, Kanade, Takeo, editor, Kittler, Josef, editor, Kleinberg, Jon M., editor, Mattern, Friedemann, editor, Mitchell, John C., editor, Naor, Moni, editor, Nierstrasz, Oscar, editor, Pandu Rangan, C., editor, Steffen, Bernhard, editor, Sudan, Madhu, editor, Terzopoulos, Demetri, editor, Tygar, Dough, editor, Vardi, Moshe Y., editor, Weikum, Gerhard, editor, Deng, Xiaotie, editor, and Du, Ding-Zhu, editor

Published
2005
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35. Restricted track assignment with applications

Author

Sarrafzadeh, Majid, Lee, D. T., Goos, Gerhard, editor, Hartmanis, Juris, editor, Ibaraki, Toshihide, editor, Inagaki, Yasuyoshi, editor, Iwama, Kazuo, editor, Nishizeki, Takao, editor, and Yamashita, Masafumi, editor

Published
1992
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