Journal of Information Processing
Online ISSN : 1882-6652
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Volume 25
Showing 51-100 articles out of 119 articles from the selected issue
• Yuuki Tachioka, Shinji Watanabe, Jonathan Le Roux, John R. Hershey
Type: Regular Papers
Subject area: Speech Processing
Volume 25 (2017) Pages 407-416
Released: June 15, 2017
JOURNALS FREE ACCESS

Reverberant and noisy automatic speech recognition (ASR) using distant stereo microphones is a very challenging, but desirable scenario for home-environment speech applications. This scenario can often provide prior knowledge such as physical information about the sound sources and the environment in advance, which may then be used to reduce the influence of the interference. We propose a method to enhance the binary masking algorithm by using prior distributions of the time difference of arrival. This paper also validates state-of-the-art ASR techniques that include various discriminative training and feature transformation methods. Furthermore, we develop an efficient method to combine discriminative language modeling and minimum Bayes risk decoding in the ASR post-processing stage. We also investigate the effectiveness of this method when used for reverberated and noisy ASR of deep neural networks (DNNs) as well when used in systems that combine multiple DNNs using different features. Experiments on the medium vocabulary sub-task of the second CHiME challenge show that the system submitted to the challenge achieved a 26.86% word error rate (WER), moreover, the DNN system with the discriminative training, speaker adaptation and system combination achieves a 20.40% WER.

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• Toshiyuki Hagiya, Toshiharu Horiuchi, Tomonori Yazaki, Tsuneo Kato, Ta ...
Type: Regular Papers
Subject area: Human-Interface Basics
Volume 25 (2017) Pages 417-425
Released: June 15, 2017
JOURNALS FREE ACCESS

Smartphones offer new opportunities to improve the lives of older adults. Although many older adults are interested in smartphones, most of them face difficulties in self-instruction and need support. Text entry, which is essential for various applications, is one of the most difficult operations to master. Therefore, we propose an assistive typing application that detects input stumbles and provides instructions for typing presented sentences, instead of having human tutors help older adults resolve the input stumbles by themselves. First, we investigated the ways that novice older adults have problems with text entry on smartphones. Next, we confirmed the acceptability of being provided with instructions for text entry by Wizard-of-Oz (WoZ). Then, we constructed an assistive typing application based on the collected data from two user studies. An evaluation with novice older adults (60+) showed that the assistive typing application increased typing speed by 17.2% and reduced input stumble incidence by 59.1% compared with the users' initial performance. Improvement rates were almost the same as those achieved with human tutors.

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• Akimasa Yoshida, Akira Kamiyama, Hiroki Oka
Type: Regular Papers
Subject area: Special Section on Advanced Computing Systems
Volume 25 (2017) Pages 426-437
Released: June 15, 2017
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Thanks to high performance and low power consumption on Android mobile devices such as smartphones and tablet computers, the use of Android platform has been increasing significantly. Android platforms almost consist of ARM-based multicores and most of the applications have been developed in Java language. Recent Android OS introduces the Java runtime environment called ART which enables use of Fork/Join framework. The Fork/Join framework provides the scheduling mechanism with work-stealing and it is mainly used for programs to implement the divide-and-conquer algorithm or the recursive algorithm. However, in the case of ordinary programs, it is difficult to implement a coarse-grain parallel code based on Fork/Join framework considering data-dependency. To cope with such a problem, this paper proposes a coarse-grain parallel code generation scheme using a developed compiler which converts a Java source program with directives into a task-driven parallel code based on Fork/Join framework. In the performance evaluation using four programs from Java Grande Forum Benchmark Suite, the execution on Samsung Galaxy S6 with heterogeneous eight cores could achieve 2.77-5.12 times speedup versus sequential processing and the execution on NVIDIA Shield Tablet with four cores could also achieve 2.34-3.94 times speedup. Consequently, effectiveness of the proposed scheme was confirmed.

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• Fuyumasa Takatsu, Kohei Hiraga, Osamu Tatebe
Type: Regular Papers
Subject area: Special Section on Advanced Computing Systems
Volume 25 (2017) Pages 438-447
Released: June 15, 2017
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The fusion of the research field of high-performance computing (HPC) with that of big data, which has become known as the field of extreme big data, is problematic in that file creation in storage systems such as distributed file systems is not optimized. That is, the large workload leads to simultaneous creations of many files by many processes when creating checkpoints. The need to improve the file creation processes prompted us to design a scale-out distributed file system for post-petascale systems named PPFS. PPFS consists of PPMDS, which is a scale-out distributed metadata server, and PPOSS, which is a scalable distributed storage server for flash storage. The high file creation performance of PPMDS was achieved by using a key-value store for metadata storage and non-blocking distributed transactions to update multiple entries simultaneously. PPOSS depends on PPOST, which is an object storage system that manages the underlying low-level storage, such as Fusion IO ioDrive, a flash device connected through PCI express supporting OpenNVM. The high file creation performance was attained by implementing the PPFS prototype using file creation optimization, termed bulk creation, to reduce the amount of communication between PPMDS and PPOSS. And, to enhance the I/O performance of PPOSS when the client process and PPOSS run on the same node, PPOSS accesses a local storage device directly. The prototype implementation of PPFS with a further file creation optimization called object prefetching achieves 138, 000 Operations Per Second for file creation when using five metadata servers and 128 client processes, thereby exceeding the performance of IndexFS by 2.52 times. With local access optimization, PPOSS reached its limit at a block size of 16KiB, which is an improvement of 1.5 times compared to before optimization. Furthermore, this evaluation indicates that PPFS has a good scalability on file creation and IO performance, that is required for post-petascale systems.

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• Akitoshi Okumura, Takamichi Hoshino, Susumu Handa, Yugo Nishiyama, Mas ...
Type: Regular Papers
Subject area: Special Section on Consumer Device & System
Volume 25 (2017) Pages 448-458
Released: June 15, 2017
JOURNALS FREE ACCESS

This paper proposes a system of verifying the identity of ticket holders at large-scale events using face recognition, which is called Ticket ID System. Such a system has been required to prevent illegal resale such as ticket scalping. Since illegal resale is a critical problem for popular events in Japan, strict steps are followed for verifying individuals holding tickets at event venues by human visual inspection with ID cards. This task is time consuming for venue attendants. It is also stressful because ticket holders feel uncomfortable when being kept waiting. The problem in verifying ticket holders is how to simultaneously verify identities efficiently and prevent individuals from impersonating others at a large-scale event in which tens of thousands of people participate. Ticket ID system makes it possible to secure the identity of the purchaser and holder of a ticket by using a face-recognition system developed for tablet terminals. Ticket ID System was proven effective for preventing illegal resale by verifying 50, 324 attendees at a large concert of a popular music group. The average accuracy of face recognition was 90%. The average time for identity verification was 7 seconds per person including guidance to ticket holders, which decreased identity-verification time by 30% compared to using only human visual inspection as well as reducing the psychological workload of venue attendants. Survey results obtained from the attendees showed that 94.6% felt it provided more equity in ticket purchasing than methods used before, 83% felt it provided added convenience in verification, and 93.8% felt it would effectively prevent illegal resale.

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• Takahisa Toda, Takeru Inoue
Type: Regular Papers
Subject area: Algorithm Theory
Volume 25 (2017) Pages 459-468
Released: July 15, 2017
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All solutions SAT (AllSAT) is the problem of generating satisfying assignments to a given conjunctive normal form (CNF) and has been a key issue commonly found in several applications of formal verification including model checking. CNF encoding, which translates original problems for AllSAT solvers, spawns many auxiliary variables and, what is worse, obscures functional dependencies over variables. AllSAT solvers consequently have to deal with unnecessarily larger CNFs, although the original problems might be much more tractable in essence. This paper proposes a novel AllSAT solver along with a CNF encoding technique; our solver extracts functional dependencies through the encoding process, and the dependence is effectively utilized to solve the CNF. Our solver is designed based on the OBDD compilation technique, which allows us to efficiently handle intractable CNFs with a number of solutions in dynamic programming manner. Our proposal is very simple but powerful; experiments with real network instances showed that our solver exhibits a great improvement.

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• Xuping Huang, Nobutaka Ono, Akira Nishimura, Isao Echizen
Type: Regular Papers
Subject area: Security Infrastructure
Volume 25 (2017) Pages 469-476
Released: July 15, 2017
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Reversible audio information hiding and sample-scanning methods are proposed for digital audio content to achieve detailed detection and localization of tampered positions in each frame. The method proposed in this study allows detecting multiple tampering and reusing reliable content as well as avoiding false detection which were impossible for other methods to simultaneously achieve. In the proposed method, the original signal is partitioned into fixed-length frames and then transformed into discrete cosine transform (DCT) coefficients by the integer modified DCT (intDCT). Expansion of the DCT coefficients is applied to embed a content-based hash as a payload. The integer DCT algorithm ensures the reversibility of the transform so that the original data and embedded payload can be perfectly restored to enable blind verification of the data integrity. The perceptual evaluation of speech quality (PESQ) with the listening quality objective mean opinion (MOSLQO), the segmental signal to noise ratio (segSNR), and subjective evaluation results show that the proposed algorithm provides good sound quality (MOSLQO and segSNR are respectively 4.41 and 23.31dB on average for a capacity of 8, 000bps). Detection and localization are accurate in terms of correctly localizing tampered frames in case of insertion or deletion.

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• Sho Yokoi, Hiroshi Kajino, Hisashi Kashima
Type: Regular Papers
Subject area: Machine Learning & Data Mining
Volume 25 (2017) Pages 477-485
Released: July 15, 2017
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Link prediction plays an important role in multiple areas of artificial intelligence, including social network analysis and bioinformatics; however, it is often negatively affected by the data sparsity problem. In this paper, we present and validate our hypothesis, i.e., for sparse networks, incidence matrix factorization (IMF) could perform better than adjacency matrix factorization (AMF), the latter used in many previous studies. A key observation supporting our hypothesis here is that IMF models a partially observed graph more accurately than AMF. Unfortunately, a technical challenge we face in validating our hypothesis is that there is not an obvious method for making link prediction using a factorized incidence matrix, unlike the AMF approach. To this end, we developed an optimization-based link prediction method. Then we have conducted thorough experiments using both synthetic and real-world datasets to investigate the relationship between the sparsity of a network and the predictive performance of the aforementioned two factorization approaches. Our experimental results show that IMF performed better than AMF as networks became sparser, which validates our hypothesis.

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• Makoto Fujisawa, Takuya Nakada, Masahiko Mikawa
Type: Regular Papers
Subject area: Image Processing
Volume 25 (2017) Pages 486-493
Released: July 15, 2017
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We propose a fast method of simulating large-scale liquid phenomena by coupling 2D and 3D smoothed particle hydrodynamics (SPH). Our method combines 2D SPH-based shallow water simulation with 3D SPH simulation to effectively treat complex behaviors, such as splashes and breaking waves. To achieve realistic animation, we generate 3D particles from 2D particles by categorizing these particles according to motion and position. One-way interactions between both types of particles are described by the conservation of momentum. We demonstrate the effectiveness of our approach in various graphical scenes.

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• Hideyuki Kawabata
Type: Regular Papers
Subject area: Special Section on Programming
Volume 25 (2017) Pages 494-504
Released: July 15, 2017
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Exact Real Arithmetic on Fast Binary Cauchy Sequences (FBCSs) provides us a simple and fairly fast way to obtain numerical results of arbitrary precision. The arithmetic on FBCSs can be implemented concisely in a lazy functional language with unlimited-length integer arithmetic, such that each FBCS is represented by a function that generates approximated values with respect to requested precisions. However, application of the arithmetic on FBCSs to programs such as matrix computations, that usually involve large amount of references to common subexpressions, requires care to avoid the blowup of the amount of computation caused by the fact that approximated values are not shared among multiple references. Although simple memoization might alleviate the situation, the effect would be limited since required precisions for subexpressions tend to be various. In this paper, we present an extended design of the arithmetic on FBCSs that enables the memoization based on quantized precision, that is expected to enlarge the reuse rate and reduce the amount of computation without sacrificing the properties of the arithmetic to be exact arithmetic. Numerical experiments by using our prototype libraries in Haskell demonstrated that our approach possesses the potential to outperform existing implementations by orders of magnitude in speed and memory consumption.

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• Jun-Li Lu, Makoto P. Kato, Takehiro Yamamoto, Katsumi Tanaka
Type: Regular Papers
Subject area: Special Section on Databases
Volume 25 (2017) Pages 505-513
Released: July 15, 2017
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We address the problem of event identification on microblogs with special attention to implicit reference cases in which events are not referred to by event's information. Most studies identify events referred to by event's information, while there are many implicitly referred events by microblogs, which are difficult to identify for short text such as microblogs. We therefore tackled implicit reference cases by analyzing links from microblogs. The links are able to connect opinions or feeling to their referred events. The analysis of links is particularly important for certain types of implicit references. In addition, we predict reference type of a microblog for accurately ranking referred events. The experimental results suggest that our method was effective for implicit references and predicting reference type was essential for identifying implicitly or explicitly referred events together.

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• Hiro Ito
Type: Special Issue of Discrete and Computational Geometry, Graphs, and Games
Volume 25 (2017) Pages 514
Released: August 15, 2017
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• Erik D. Demaine, Martin L. Demaine, Sarah Eisenstat, Adam Hesterberg, ...
Type: Special Issue of Discrete and Computational Geometry, Graphs, and Games
Subject area: Invited papers
Volume 25 (2017) Pages 515-527
Released: August 15, 2017
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We consider variations on the classic video game Tetris where pieces are k-ominoes instead of the usual tetrominoes (k=4), as popularized by the video games ntris and Pentris. We prove that it is NP-complete to survive or clear a given initial board with a given sequence of pieces for each k ≥ 5, complementing the previous NP-completeness result for k=4. More surprisingly, we show that board clearing is NP-complete for k=3; and if pieces may not be rotated, then clearing is NP-complete for k=2 and survival is NP-complete for k=3. All of these problems can be solved in polynomial time for k=1.

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• Jin Akiyama, Sin Hitotumatu, Motonaga Ishii, Akihiro Matsuura, Ikuro S ...
Type: Special Issue of Discrete and Computational Geometry, Graphs, and Games
Subject area: Invited papers
Volume 25 (2017) Pages 528-536
Released: August 15, 2017
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In this paper, an n-dimensional polytope is called Wythoffian if it is derived by the Wythoff construction from an n-dimensional regular polytope whose finite reflection group belongs to An, Bn, Cn, F4, G2, H3, H4 or I2(p). Based on combinatorial and topological arguments, we give a matrix-form recursive algorithm that calculates the number of k-faces (k =0, 1,..., n) of all the Wythoffian-n-polytopes using Schläfli-Wythoff symbols. The correctness of the algorithm is reconfirmed by the method of exhaustion using a computer.

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Type: Special Issue of Discrete and Computational Geometry, Graphs, and Games
Subject area: Geometry
Volume 25 (2017) Pages 537-541
Released: August 15, 2017
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Let Π be a convex decomposition of a set P of n ≥ 3 points in general position in the plane. If Π consists of more than one polygon, then either Π contains a deletable edge or Π contains a contractible edge.

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• Bernardo M. Ábrego, Kory Dondzila, Silvia Fernández-Merchant, Evgeniya ...
Type: Special Issue of Discrete and Computational Geometry, Graphs, and Games
Subject area: Geometry
Volume 25 (2017) Pages 542-550
Released: August 15, 2017
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We bound the rectilinear local crossing number of the complete bipartite graph Km, n for every m and n, and completely determine its value when min(m, n) ≤ 4 .

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• Atsushi Kaneko, Mikio Kano, Mamoru Watanabe
Type: Special Issue of Discrete and Computational Geometry, Graphs, and Games
Subject area: Geometry
Volume 25 (2017) Pages 551-553
Released: August 15, 2017
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Assume that 2a red points, 2b blue points and 2c green points lie on a line, and they are bisected into a left part I and a right part J by a point so that each of them contains a+b+c points. Then we show that there exist a point set XI and a point set YJ such that both X and Y consist of consecutive points, |X|=|Y|, and each of I-X+Y and J-Y+X contains exactly a red points, b blue points and c green points. Moreover we extend this result to multi-colored point sets.

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• Kazuki Matsubara, Chie Nara
Type: Special Issue of Discrete and Computational Geometry, Graphs, and Games
Subject area: Geometry
Volume 25 (2017) Pages 554-558
Released: August 15, 2017
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It was proved that any orthogonal polyhedron is continuously flattened by using a property of a rhombus. We investigated the method precisely, and found that there are infinitely many ways to flatten such polyhedra. We prove that the infimum of the area of moving creases is zero for α-trapezoidal polyhedra, which is a generalization of semi-orthogonal polyhedra. Also we prove that, for any integer n, there exists a continuous flattening motion whose area of moving creases is arbitrarily small for any n-gonal pyramid with a circumscribed base and a top vertex being just above the incenter of the base. As a by-product we provide a continuous flattening motion whose area of moving creases is arbitrarily small for more general types of polyhedra.

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• Kostantinos Georgiou, Evangelos Kranakis, Alexandra Steau
Type: Special Issue of Discrete and Computational Geometry, Graphs, and Games
Subject area: Geometry
Volume 25 (2017) Pages 559-571
Released: August 15, 2017
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We study a new problem concerning search in the plane involving a robot and an immobile treasure, initially placed at distance 1 from each other. The length β of an arc (a fence) which is placed within the perimeter of the disk centered at the initial position of the robot, as well as the promise that the treasure is outside the fence, is given as part of the input. The goal is to devise movement trajectories so that the robot locates the treasure in minimum time. Notably, although the presence of the fence limits searching uncertainty, the location of the fence is unknown, and the worst case analysis is determined adversarially. Nevertheless, the robot has the ability to make cross-cuts by moving in the interior of the disk. In particular, the robot can attempt a number of chord-jump moves if it happens to be within the fence or if an endpoint of the fence is discovered. The optimal solution to our question can be obtained as a solution to a complicated optimization problem, which involves trigonometric functions, and trigonometric equations that do not admit closed form solutions. For the 1-Jump Algorithm, we fully describe the optimal trajectory, and provide an analysis of the associated cost as a function of β. Our analysis indicates that the optimal k-Jump Algorithm requires that the robot has enough memory and computation power to compute the optimal chord-jumps. Motivated by this, we give an abstract performance analysis for every k-Jump Algorithm. Subsequently, we present a highly efficient Halving Heuristic k-Jump Algorithm that can effectively approximate the optimal k-Jump Algorithm, with very limited memory and computation requirements. Further, we explore randomized algorithms and analyze their expected worst-case performance.

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• Yusuke Yokosuka, Keiko Imai
Type: Special Issue of Discrete and Computational Geometry, Graphs, and Games
Subject area: Geometry
Volume 25 (2017) Pages 572-579
Released: August 15, 2017
JOURNALS FREE ACCESS

Map labeling is the problem of placing labels at corresponding graphical features on a map. There are two main optimization problems: the label number maximization problem and the label size maximization problem. In general, both problems are NP-hard for static maps. Recently, the widespread use of several applications, such as personal mapping systems, has increased the importance of dynamic maps and the label number maximization problem for dynamic cases has been studied. In this paper, we consider the label size maximization problem for points on rotating maps. Our model is as follows. For each label, an anchor point is chosen inside the label or on its boundary. Each label is placed such that the anchor point coincides with the corresponding point on the map. Furthermore, while the map fully rotates from 0 to 2π, the labels are placed horizontally according to the angle of the map. Our problem consists of finding the maximum scale factor for the labels such that the labels do not intersect, and determining the placing of the anchor points. We describe an O(n log n)-time and O(n)-space algorithm for the case where each anchor point is inside the label. Moreover, if the anchor points are on the boundaries, we also present an O(n log n)-time and O(n)-space exact and approximation algorithms for several label shapes.

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• Hugo A. Akitaya, Erik D. Demaine, Jason S. Ku
Type: Special Issue of Discrete and Computational Geometry, Graphs, and Games
Subject area: Origami
Volume 25 (2017) Pages 580-589
Released: August 15, 2017
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Simple folding (folding along one line at a time) is a practical form of origami used in manufacturing such as sheet metal bending. We prove strong NP-completeness of deciding whether a crease pattern can be simply folded, both for orthogonal paper with assigned orthogonal creases and for square paper with assigned or unassigned creases at multiples of 45°. These results settle a long standing open problem, where weak NP-hardness was established for a subset of the models considered here, leaving open the possibility of pseudopolynomial-time algorithms. We also formalize and generalize the previously proposed simple folding models, and introduce new infinite simple-fold models motivated by practical manufacturing. In the infinite models, we extend our strong NP-hardness results, as well as polynomial-time algorithms for rectangular paper with assigned or unassigned orthogonal creases (map folding). These results motivate why rectangular maps have orthogonal but not diagonal creases.

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• Yasuhiko Asao, Erik D. Demaine, Martin L. Demaine, Hideaki Hosaka, Aki ...
Type: Special Issue of Discrete and Computational Geometry, Graphs, and Games
Subject area: Origami
Volume 25 (2017) Pages 590-600
Released: August 15, 2017
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We show how to fold a piece of paper and punch one hole so as to produce any desired pattern of holes. Given n points on a piece of paper (finite polygon or infinite plane), we give algorithms to fold the paper flat so that those n points and no other points of paper map to a common location, so that punching one hole and unfolding produces exactly the desired pattern of holes. Furthermore, we can forbid creases from passing through the points (allowing noncircular hole punches). Our solutions use relatively few creases (in some cases, polynomially many), and can be expressed as a linear sequence of folding steps of complexity O(1)—a generalization of simple folds which we introduce.

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• Erik D. Demaine, Jason S. Ku
Type: Special Issue of Discrete and Computational Geometry, Graphs, and Games
Subject area: Origami
Volume 25 (2017) Pages 601-609
Released: August 15, 2017
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Isometries always exists to fold a paper to match a non-expansive folding of its boundary. However, there is little known about designing crease patterns that satisfy multiple constraints at the same time. In this paper, we analyze crease patterns that can fold to multiple prescribed folded boundaries, as well as flat-foldable states, such that every crease in the crease pattern is finitely folded in each folding. Additionally, we show how to layout simpler units in a grid to approximate triangulated surfaces.

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• Zachary Abel, Brad Ballinger, Erik D. Demaine, Martin L. Demaine, Jeff ...
Type: Special Issue of Discrete and Computational Geometry, Graphs, and Games
Subject area: Origami
Volume 25 (2017) Pages 610-615
Released: August 15, 2017
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In this paper, we introduce the notion of “rep-cube”: a net of a cube that can be divided into multiple polygons, each of which can be folded into a cube. This notion is inspired by the notion of polyomino and rep-tile; both are introduced by Solomon W. Golomb, and well investigated in the recreational mathematics society. We prove that there are infinitely many distinct rep-cubes. We also extend this notion to doubly covered squares and regular tetrahedra.

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• Julián Fresán-Figueroa, Eduardo Rivera-Campo
Type: Special Issue of Discrete and Computational Geometry, Graphs, and Games
Subject area: Graphs
Volume 25 (2017) Pages 616-620
Released: August 15, 2017
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A 2-switch on a simple graph G consists of deleting two edges {u, v} and {x, y} of G and adding the edges {u, x} and {v, y}, provided the resulting graph is a simple graph. It is well known that if two graphs G and H have the same set of vertices and the same degree sequence, then H can be obtained from G by a finite sequence of 2-switches. While the 2-switch transformation preserves the degree sequence other conditions like connectivity may be lost. We study the restricted case where 2-switches are applied to trees to obtain trees.

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• Liang Zhao
Type: Special Issue of Discrete and Computational Geometry, Graphs, and Games
Subject area: Graphs
Volume 25 (2017) Pages 621-626
Released: August 15, 2017
JOURNALS FREE ACCESS

Let G=(V, E) be an undirected graph with a set V of nodes and a set E of edges, |V|=n. A node v is said to distance-k dominatea node w if w is reachable from v by a path consisting of at most k edges. A set DV is said a distance-k dominating setif every node can be distance-k dominated by some vD. The size of a minimum distance-k dominating set, denoted by γk(G), is called the distance-k domination number of G. The value γk(n) is defined by γk(n) = max{γk(G) : G has n nodes}. This paper considers γk(n) for maximal outerplanar graphs. There is a conjecture γk(n) = max{⌊ n/(2k+1)⌋, 1}, which was proved for k=1, 2. This paper gives a unified and simpler proof for k=1, 2, 3. In fact, a stronger result is shown that for all n > 2k and r = n mod (2k+1) ≤ 6, there exist at least 2k+1-r distinct distance-k dominating sets of size at most ⌊ n/(2k+1)⌋, which can be found in linear time.

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• Sergey Bereg, Hiro Ito
Type: Special Issue of Discrete and Computational Geometry, Graphs, and Games
Subject area: Graphs
Volume 25 (2017) Pages 627-633
Released: August 15, 2017
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Let G and H be two graphs with the same vertex set V. It is well known that a graph G can be transformed into a graph H by a sequence of 2-switches if and only if every vertex of V has the same degree in both G and H. We study the problem of finding the minimum number of 2-switches for transforming G into H.

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Type: Special Issue of Discrete and Computational Geometry, Graphs, and Games
Subject area: Graphs
Volume 25 (2017) Pages 634-638
Released: August 15, 2017
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The metric dimension of a connected graph G is the minimum number of vertices in a subset W of V(G) such that all other vertices are uniquely determined by its vector distance to the vertices in W. In this paper, we consider a connected graph G where every vertex of G has relatively same probability to resolve some distinct vertices in G, namely a (μ, σ)-regular graph. We give tight lower and upper bounds on the metric dimension of a connected (μ, σ)-regular graphs of order n ≥ 2 where 1 ≤ µn-1 and σ=n-1.

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• Norhazwani Md Yunos, Aleksandar Shurbevski, Hiroshi Nagamochi
Type: Special Issue of Discrete and Computational Geometry, Graphs, and Games
Subject area: Graphs
Volume 25 (2017) Pages 639-654
Released: August 15, 2017
JOURNALS FREE ACCESS

The Traveling Salesman Problem (TSP) is one of the most well-known NP-hard optimization problems. Following a recent trend of research which focuses on developing algorithms for special types of TSP instances, namely graphs of limited degree, in an attempt to reduce a part of the time and space complexity, we present a polynomial-space branching algorithm for the TSP in an n-vertex graph with degree at most 5, and show that it has a running time of O*(2.3500n), which improves the previous best known time bound of O*(2.4723n) given by the authors (the 12th International Symposium on Operations Research and Its Application (ISORA 2015), pp.45-58, 2015). While the base of the exponent in the running time bound of our algorithm is greater than 2, it still outperforms Gurevich and Shelah's O*(4n nlog n) polynomial-space exact algorithm for the TSP in general graphs (SIAM Journal of Computation, Vol.16, No.3, pp.486-502, 1987). In the analysis of the running time, we use the measure-and-conquer method, and we develop a set of branching rules which foster the analysis of the running time.

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• Mohd Shahrizan bin Othman, Aleksandar Shurbevski, Yoshiyuki Karuno, Hi ...
Type: Special Issue of Discrete and Computational Geometry, Graphs, and Games
Subject area: Graphs
Volume 25 (2017) Pages 655-666
Released: August 15, 2017
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We examine a routing problem that arises when an unmanned aerial vehicle (UAV), or drone, is used in the last-stretch of parcel delivery to end customers. In the scenario that we study, a delivery truck is dispatched carrying a shipment of parcels to be delivered to customers. While the truck is following a predetermined route, a drone is charged with making the last-stretch delivery of a parcel from the truck to a customer's doorstep. Given a set of customers to be served and a set of rendezvous points where the drone can meet with the truck to pick up a parcel, we ask what the quickest way is of delivering all parcels to the end customers. We model this problem as a problem of finding a special type of a path in a graph of a special structure, and show that the graph problem is NP-hard even when all edge weights are restricted to be 1 or 2. Furthermore, we identify a special instance type that can be solved optimally in polynomial time. Finally, we propose a polynomial-time approximation algorithm for the graph problem in metric graphs, and show that its approximation ratio is bounded above by 2 in restricted metric graphs.

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• Etsuji Tomita, Sora Matsuzaki, Atsuki Nagao, Hiro Ito, Mitsuo Wakatsuk ...
Type: Special Issue of Discrete and Computational Geometry, Graphs, and Games
Subject area: Graphs
Volume 25 (2017) Pages 667-677
Released: August 15, 2017
JOURNALS FREE ACCESS

We present further improvements to a branch-and-bound maximum-clique-finding algorithm MCS (WALCOM 2010, LNCS 5942, pp.191-203) that was shown to be fast. First, we employ a variant of an efficient approximation algorithm KLS for finding a maximum clique. Second, we make use of appropriate sorting of vertices only near the root of the search tree. Third, we employ a lightened approximate coloring mainly near the leaves of the search tree. A new algorithm obtained from MCS with the above improvements is named k5_MCT. It is shown that k5_MCT is much faster than MCS by extensive computational experiments. In particular, k5_MCT is shown to be faster than MCS for gen400_p0.9_75, gen400_p0.9_65 and gen400_p0.9_55 by over 81,000, 39,000 and 19,000 times, respectively.

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• Koki Suetsugu
Type: Special Issue of Discrete and Computational Geometry, Graphs, and Games
Subject area: Games and Puzzles
Volume 25 (2017) Pages 678-681
Released: August 15, 2017
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Achievement games are usually played and studied for polynominos which are commonly called animals, and it is known whether each animal is a winner or a loser, except for one animal called Snaky. In this paper, we study achievement games for unconnected shapes which we call creatures. We mostly discuss them on a one-dimensional board, because they exhibit interesting behavior even in this simple setting. We determined whether a creature is a winner or a loser for those composed of no more than three stones. Furthermore, we proved there is an arbitrary large paving winner.

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• Jeffrey Bosboom, Erik D. Demaine, Martin L. Demaine, Adam Hesterberg, ...
Type: Special Issue of Discrete and Computational Geometry, Graphs, and Games
Subject area: Games and Puzzles
Volume 25 (2017) Pages 682-694
Released: August 15, 2017
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We prove the computational intractability of rotating and placing n square tiles into a 1 × n array such that adjacent tiles are compatible — either equal edge colors, as in edge-matching puzzles, or matching tab/pocket shapes, as in jigsaw puzzles. Beyond basic NP-hardness, we prove that it is NP-hard even to approximately maximize the number of placed tiles (allowing blanks), while satisfying the compatibility constraint between nonblank tiles, within a factor of 0.9999999702 (On the other hand, there is an easy 1/2-approximation). This is the first (correct) proof of inapproximability for edge-matching and jigsaw puzzles. Along the way, we prove NP-hardness of distinguishing, for a directed graph on n nodes, between having a Hamiltonian path (length n-1) and having at most 0.999999284(n-1) edges that form a vertex-disjoint union of paths. We use this gap hardness and gap-preserving reductions to establish similar gap hardness for 1 × n jigsaw and edge-matching puzzles.

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• Akira Suzuki, Masashi Kiyomi, Yota Otachi, Kei Uchizawa, Takeaki Uno
Type: Special Issue of Discrete and Computational Geometry, Graphs, and Games
Subject area: Games and Puzzles
Volume 25 (2017) Pages 695-707
Released: August 15, 2017
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Hitori is a popular “pencil-and-paper” puzzle defined as follows. In n-hitori, we are given an n × n rectangular grid in which each square is labeled with a positive integer, and the goal is to paint a subset of the squares so that the following three rules are satisfied: Rule 1) No row or column has a repeated unpainted label; Rule 2) Painted squares are never (horizontally or vertically) adjacent; Rule 3) The unpainted squares are all connected (via horizontal and vertical connections). The grid is called an instance of n-hitori if it has a unique solution. In this paper, we introduce hitori number and maximum hitori numberwhich are defined as follows: For every integer n, hitori number h(n) is the minimum number of different integers used in an instance where the minimum is taken over all the instances of n-hitori. For every integer n, maximum hitori number $\bar{h}(n)$ is the maximum number of different integers used in an instance where the maximum is taken over all the instances of n-hitori. We then prove that ⌈(2n-1)/3⌉ ≤ h(n) ≤ 2⌈n/3⌉+1 for n ≥ 2 and ⌈(4n2-4n+11)/5⌉ ≤ $\bar{h}(n)$ ≤ (4n2+2n-2)/5 for n ≥ 3.

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• Takashi Horiyama, Takashi Iizuka, Masashi Kiyomi, Yoshio Okamoto, Ryuh ...
Type: Special Issue of Discrete and Computational Geometry, Graphs, and Games
Subject area: Games and Puzzles
Volume 25 (2017) Pages 708-715
Released: August 15, 2017
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We study a combinatorial game named “sankaku-tori” in Japanese, which means “triangle-taking” in English. It is an old pencil-and-paper game for two players played in Western Japan. The game is played on points on the plane in general position. In each turn, a player adds a line segment to join two points, and the game ends when a triangulation of the point set is completed. The player who completes more triangles than the other wins. In this paper, we formalize this game and investigate three restricted variants of this game. We first investigate a solitaire variant; for a given set of points and line segments with two integers t and k, the problem asks if you can obtain t triangles after k moves. We show that this variant is NP-complete in general. The second variant is the standard two player version, but the points are in convex position. In this case, the first player has a nontrivial winning strategy. The last variant is a natural extension of the second one; we have the points in convex position but one point inside. Then, it turns out that the first player has no winning strategy.

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Type: Special Issue of Discrete and Computational Geometry, Graphs, and Games
Subject area: Games and Puzzles
Volume 25 (2017) Pages 716-723
Released: August 15, 2017
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Sliding maze puzzles like Ricochet Robots and Atomix are puzzles in which solvers must maneuver agents around a grid board subject to the constraint that whenever an agent moves in some direction, it must move as far as possible in that direction. In general, finding an optimal solution to these puzzles is known to be PSPACE-complete. This paper further shows that these puzzles are W[SAT]-hard with respect to the number of robots in the puzzle instance (and therefore unlikely to be Fixed Parameter Tractable).

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• Akihiro Uejima, Hiroaki Suzuki, Atsuki Okada
Type: Special Issue of Discrete and Computational Geometry, Graphs, and Games
Subject area: Games and Puzzles
Volume 25 (2017) Pages 724-729
Released: August 15, 2017
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Pipe Link, which is a pencil-and-paper puzzle introduced by Japanese puzzle publisher Nikoli, is played on a rectangular grid of squares. We studied the computational complexity of Pipe Link, and this paper shows that the problem to decide if a given instance of Pipe Link has a solution is NP-complete by a reduction from the Hamiltonian circuit problem for a given planar graph with a degree of at most 3. Our reduction is carefully designed so that we can also prove ASP-completeness of the another-solution-problem.

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• Kazuya Haraguchi, Ryoya Tanaka
Type: Special Issue of Discrete and Computational Geometry, Graphs, and Games
Subject area: Games and Puzzles
Volume 25 (2017) Pages 730-734
Released: August 15, 2017
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The Building puzzle (a.k.a., the Skyscraper) is a Latin square completion-type puzzle like Sudoku, KenKen and Futoshiki. Recently, Iwamoto and Matsui showed the NP-completeness of the decision problem version of this puzzle, which asks whether a given instance has a solution or not. We provide a stronger result in the present paper; it is still NP-complete to decide whether we can complete a single line of the grid (i.e., a 1 × n or an n × 1 subgrid) without violating the rule.

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• Mikhail Bouniaev, Nikolai Dolbilin
Type: Special Issue of Discrete and Computational Geometry, Graphs, and Games
Subject area: Combinatorics, Codingd theory, and Auctions
Volume 25 (2017) Pages 735-740
Released: August 15, 2017
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The concept of t-bonded sets was briefly introduced by the second author in 1976 under the name of d-connected sets, though it has not received due consideration. This concept is a generalization of the concept of Delone (r, R)-systems. In light of the developments in the local theory for crystals that occurred since 1976 and demands in chemistry and crystallography, we believe the local theory for t-bonded sets deserves to be developed to describe materials whose atomic structures is multi-regular “microporous” point set. For a better description of such “microporous” structures it is worthwhile to take into consideration a parameter that represents atomic bonds within the matter. The overarching goal of this paper is to prove that analogous local conditions that guarantee that a Delone set is a regular (or multi-regular) system also guarantee that a t-bonded set is a regular (or multi-regular) t-bonded system.

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• Ko Sakai, Yutaka Sato
Type: Special Issue of Discrete and Computational Geometry, Graphs, and Games
Subject area: Combinatorics, Codingd theory, and Auctions
Volume 25 (2017) Pages 741-744
Released: August 15, 2017
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In this paper we propose a new construction method of Gray maps for groups. In a earlier paper, we succeeded the Type 1 construction for all groups of order 16 and confirmed that we can construct Type 2 maps for several groups of order 16, but failed to construct such maps for other groups. Therefore, in this paper we try to apply the new construction method to them.

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• Hiroyuki Umeda, Takao Asano
Type: Special Issue of Discrete and Computational Geometry, Graphs, and Games
Subject area: Combinatorics, Codingd theory, and Auctions
Volume 25 (2017) Pages 745-754
Released: August 15, 2017
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We discuss Nash equilibria in combinatorial auctions with item bidding. Specifically, we give a characterization for the existence of a Nash equilibrium in such a combinatorial auction when valuations by two bidders satisfy symmetric and subadditive properties. Based on this characterization, we can obtain an algorithm for deciding whether a Nash equilibrium exists in such a combinatorial auction.

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• Hiroki Takakura
Type: Special Issue of Applications and the Internet in Conjunction with　Main Topics of COMPSAC 2016
Volume 25 (2017) Pages 755
Released: August 15, 2017
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• Guolei Yang, Ying Cai
Type: Special Issue of Applications and the Internet in Conjunction with　Main Topics of COMPSAC 2016
Subject area: Invited Papers
Volume 25 (2017) Pages 756-765
Released: August 15, 2017
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Anonymous location data may be correlated with restricted spaces like home and office for subject identification. This creates significant privacy risks to users when they disclose their location to applications like location-based services. In this paper, we address this problem with a novel approach named restricted space cloaking. This scheme cloaks a user's location only when the location is inside a restricted space. When in non-restricted spaces, the location is reported as is. We show that this cloaking strategy is capable of full location privacy protection: given a restricted space, the adversary does not know when its owner was there; given a non-restricted location, the adversary does not know who has ever visited there. Such protection is not available from the existing cloaking techniques. In addition to full location privacy protection, the proposed strategy makes it possible for users to cloak their locations without disclosing accurate locations to either a trusted anonymizer or other users. We discuss the implementation challenges and present corresponding solutions. The performance of the proposed solutions is evaluated through simulation.

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• Hiroyuki Sato
Type: Special Issue of Applications and the Internet in Conjunction with　Main Topics of COMPSAC 2016
Subject area: Invited Papers
Volume 25 (2017) Pages 766-774
Released: August 15, 2017
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These days, ICT service environments have dramatically changed in their complexity. Accordingly, related business logics for business processes such as provisioning, resource limit, conditional authorization and delegation have grown in its complexity. In this paper, we generalize the idea of access tokens of OAuth, and propose “authorization by documents.” In our model, a user submits a document as evidence of privilege claim, and a server verifies the document to prove the appropriateness of the user's privilege. A document can be complicated, reflecting some business flow in an institution. If the process and result of business flow are expressed by using documents, the evidence as documents can reflect arbitrarily complex business flow. For this purpose, we formalize documents, and define document tree logic (DTL) as a variant of CTL* to express the policies associated with documents. Typical business processes including request and approval, delegation, and approval by document circular are expressed in DTL, and verified by using documents as evidence.

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• Kazuyuki Shudo, Takashi Yaguchi
Type: Special Issue of Applications and the Internet in Conjunction with Main Topics of COMPSAC 2016
Subject area: Parallel and Distributed Processing Technology
Volume 25 (2017) Pages 775-782
Released: August 15, 2017
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There have been proposed protocols to achieve causal consistency with a distributed data store that does not make safety guarantees. Such protocols work with an unmodified data store if it is implemented as middleware or a shim layer while it can be implemented inside a data store. But the middleware approach has required modifications to applications. Applications have to explicitly specify data dependency to be managed. Our Letting-It-Be protocol to the contrary, handles all implicit dependency naturally resulting from data accesses even though it is implemented as middleware. Our protocol does not require any modifications to either data stores or applications. It works with them as they are. It trades performance for the merit to some extent. Throughput declines from a data store alone were 21% in the best case and 78% in the worst case without multi-level management of dependency graph, which is a performance optimization technique.

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• Hiroshi Yamamoto, Tomoya Ohiwa, Katsuyuki Yamazaki
Type: Special Issue of Applications and the Internet in Conjunction with　Main Topics of COMPSAC 2016
Subject area: Network Architecture
Volume 25 (2017) Pages 783-787
Released: August 15, 2017
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A new support system is proposed for monitoring and advising elderly people. The proposed system uses a single microcomputer with various sensors to collect data in a room of the house where the elderly is living alone. It detects a gradual change of activity of the elderly by extracting general pattern of the activity from the measurement data (especially, time series data of sound strength) of the sensors. When the activity patterm markedly changes from the general model, notifications and advice are sent to not only the elderly but also their family with the aim of maintaining the good physical condition of the elderly and encouraging them to perform health-aware activities. As a first step of the study, the feasibility of behavior estimation from the collected sound data was evaluated. The evaluation results clarified that the measured sound data can be used to estimate the behavior of elderly people.

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• Hiroyuki Sato, Yasuo Okabe, Motonori Nakamura
Type: Special Issue of Applications and the Internet in Conjunction with　Main Topics of COMPSAC 2016
Subject area: Network Services
Volume 25 (2017) Pages 788-795
Released: August 15, 2017
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The concept and design of access federations have been widely accepted and their world-wide deployment is in progress. In an access federation, control of user information (personal identification information) is a key issue in its operation in terms of privacy. Pseudonym is proposed and implemented as a solution to this problem. We consider the case where the requirement of privacy protection by using pseudonyms and that of user identification for service providing conflict with each other. In this paper, we propose a “counting server” for the identification of different pseudonyms or social identities. SPs can use this identification information to provide special services such as student discount and limit of use. We also show an implementation of this scheme on Shibboleth/SAML platforms. Related protocols are designed, another SAML engine is provided on SP, and a counting server is provided. Furthermore, we analyze this scheme, and prove the security properties.

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• Eiichi Hayakawa
Type: Special Issue of Embedded Systems Engineering
Volume 25 (2017) Pages 796
Released: August 15, 2017
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• Tasuku Ishigooka, Habib Saissi, Thorsten Piper, Stefan Winter, Neeraj ...
Type: Special Issue of Embedded Systems Engineering
Subject area: Formal Methods
Volume 25 (2017) Pages 797-810
Released: August 15, 2017
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The application of cyber-physical systems (CPSs) in safety-critical application domain requires rigorous verification of their functional correctness and safety-relevant properties. We propose a practical verification process which enables to conduct safety verification of safety critical CPSs. The verification process consists of (a) a system model construction method, which generates a system model by combining software described in C and plant model code reused from model-based development, (b) a model transformation method, which transforms the plant models including differential algebraic equations (DAE) to approximate models without DAE to reduce verification complexity induced by DAE solver execution, (c) a model simplification framework, which enables the simplification of bond-graph plant models using domain-knowledge-based replacement of complex model components for further verification overhead reductions, and (d) a formal verification based on symbolic execution. We implemented the proposed methods and framework, and successfully applied the proposed verification process for safety verification of automotive brake control systems. The results of the study demonstrate that the verification detects a complex failure condition in a real-world brake control system from the generated system model and that the automated model transformations of the CPS models yield significant verification complexity reductions without impairing the ability to detect unsafe behavior.

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