1,492,702 research outputs found
Focused Light Field Camera based on Solid Immersion Microlens Arrays with Large f-number
No full textEmpty Squares in Arbitrary Orientation Among Points
No full textThis paper studies empty squares in arbitrary orientation among a set P of n points in the plane. We prove that the number of empty squares with four contact pairs is between Ω(n) and O(n²), and that these bounds are tight, provided P is in a certain general position. A contact pair of a square is a pair of a point p ∈ P and a side of the square with p ∈ . The upper bound O(n²) also applies to the number of empty squares with four contact points, while we construct a point set among which there is no square of four contact points. We then present an algorithm that maintains a combinatorial structure of the L_∞ Voronoi diagram of P, while the axes of the plane continuously rotate by 90 degrees, and simultaneously reports all empty squares with four contact pairs among P in an output-sensitive way within O(slog n) time and O(n) space, where s denotes the number of reported squares. Several new algorithmic results are also obtained: a largest empty square among P and a square annulus of minimum width or minimum area that encloses P over all orientations can be computed in worst-case O(n² log n) time
L_1 Geodesic Farthest Neighbors in a Simple Polygon and Related Problems
No full textIn this paper, we investigate the L_1 geodesic farthest neighbors in a simple polygon P, and address several fundamental problems related to farthest neighbors. Given a subset S subseteq P, an L_1 geodesic farthest neighbor of p in P from S is one that maximizes the length of L_1 shortest path from p in P. Our list of problems include: computing the diameter, radius, center, farthest-neighbor Voronoi diagram, and two-center of S under the L_1 geodesic distance. We show that all these problems can be solved in linear or near-linear time based on our new observations on farthest neighbors and extreme points. Among them, the key observation shows that there are at most four extreme points of any compact subset S subseteq P with respect to the L_1 geodesic distance after removing redundancy
Intra-operative MRI with MR detectable endoscope using tunable lens filled with MR contrast agent
No full textDuring brain surgery, location of lesions can change in real-time due to leakage of cerebrospinal fluid. Therefore, navigating an MR-Endoscope probe with real-time intraoperative MRI is important in clinical application. However, conventional tracking system attached to the endoscope probe induces severe artifacts and is expensive and bulky. In this study, we propose a technique for navigating the endoscope probe without additional tracking system through segmentation of signals from tunable lens filled with gadolinium contrast agents. We also demonstrated tunable liquid-filled lens endoscope for intraoperative MRI. The proposed system/approach would be a good alternative as a tracking system for intraoperative MRI
Minimum-Width Double-Strip and Parallelogram Annulus
No full textIn this paper, we study the problem of computing a minimum-width double-strip or parallelogram annulus that encloses a given set of n points in the plane. A double-strip is a closed region in the plane whose boundary consists of four parallel lines and a parallelogram annulus is a closed region between two edge-parallel parallelograms. We present several first algorithms for these problems. Among them are O(n^2) and O(n^3 log n)-time algorithms that compute a minimum-width double-strip and parallelogram annulus, respectively, when their orientations can be freely chosen
Best and worst-case coverage problems for arbitrary paths in wireless sensor networks
No full textThe best-case and the worst-case coverage were proposed originally for a single source and destination pair in a sensor network. In this paper, we propose a new coverage measure of the sensor network considering arbitrary paths. Surprisingly, this new measure captures both the best-case and the worst-case coverage of the sensor network simultaneously, enabling us to evaluate the given network in a global viewpoint. Accordingly, we pose the evaluation and the deployment problems; the former is to evaluate the new coverage measure of a given sensor network, and the latter is to find an optimal placement of k additional sensor nodes to improve the coverage for a given positive integer k. We present several algorithms solving the problems that are either centralized or localized with theoretical proofs and simulation results, showing that our algorithms are efficient and easy to implement in practice while the quality of outputs is guaranteed by formal proofs. Our algorithms are based on an interesting relation between our new coverage measure and a certain quantity of a point set, called the bottleneck, which has been relatively well studied in other disciplines. In doing so, we prove that a maximal support path can always be found in the minimum spanning tree; this is another contribution of ours.This research was supported by Ministry of Culture,
Sports and Tourism(MCST) and Korea Culture Content
Agency(KOCCA) in the Culture Technology(CT) Research
& Development Program 2009. Work by S.W. Bae
was supported by the Contents Convergence Software Research
Center funded by the GRRC Program of Gyeonggi
Province, South Korea
NO removal by reducing agents and additives in the selective non-catalytic reduction (SNCR) process
No full textThe effect of the additives on the selective non-catalytic reduction (SNCR) reaction has been determined in a three-stage laboratory scale reactor. The optimum reaction temperature is lowered and the reaction temperature window is widened with increasing concentrations of the gas additives (CO, CH4). The optimum reaction temperature is lowered and the maximum NO removal efficiency decreases with increasing the concentration of alcohol additives (CH3OH, C2H5OH). The addition of phenol lowers the optimum reaction temperature about 100-150 degrees C similar to that of the toluene addition. The volatile organic compounds (VOCs: C6H5OH, C7H8) can be utilized in-the SNCR process to enhance NO reduction and removed at the same time. A previously proposed simple kinetic model can successfully apply the NO reduction by NH3 and the present additives. (c) 2006 Elsevier Ltd. All rights reserved.Ministry of Commerce, Industry and Energy, Kore
Experimental excitation and characterization of cladding modes in photonic crystal fiber
No full textWe extend the previous theoretical study on the effect of outer silica cladding to the analysis on real field profiles in a practical PCF. Clear field profiles for the first higher-order cladding modes are presented and discussed. The observed mode fields are reproduced by numerical calculations, and it turns out that they correspond to LP(16) mode groups. Optical properties of the observed modes such as lobe direction and polarization are also investigated. The results of this study will be useful in the design of the PCF-based optical devices utilizing cladding mode coupling. (C) 2010 Optical Society of AmericaThis work was partially supported by a Korea Research Foundation Grant funded by the
Korean Government (KRF-2008-313-C00350)
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