Hiroyoshi Miwa

Geographical threshold graphs with small-world and scale-free properties

Many real networks are equipped with short diameters, high clustering, and power-law degree distributions. With preferential attachment and network growth, the model by Barabási and Albert simultaneously reproduces these properties, and geographical versions of growing networks have also been analyzed. However, nongrowing networks with intrinsic vertex weights often explain these features more plausibly, since not all networks are really growing. We propose a geographical nongrowing network model with vertex weights. Edges are assumed to form when a pair of vertices are spatially close and/or have large summed weights. Our model generalizes a variety of models as well as the original nongeographical counterpart, such as the unit disk graph, the Boolean model, and the gravity model, which appear in the contexts of percolation, wire communication, mechanical and solid physics, sociology, economy, and marketing. In appropriate configurations, our model produces small-world networks with power-law degree distributions. We also discuss the relation between geography, power laws in networks, and power laws in general quantities serving as vertex weights.

Distinct Inter-Joint Coordination during Fast Alternate Keystrokes in Pianists with Superior Skill

Musical performance requires motor skills to coordinate the movements of multiple joints in the hand and arm over a wide range of tempi. However, it is unclear whether the coordination of movement across joints would differ for musicians with different skill levels and how inter-joint coordination would vary in relation to music tempo. The present study addresses these issues by examining the kinematics and muscular activity of the hand and arm movements of professional and amateur pianists who strike two keys alternately with the thumb and little finger at various tempi. The professionals produced a smaller flexion velocity at the thumb and little finger and greater elbow pronation and supination velocity than did the amateurs. The experts also showed smaller extension angles at the metacarpo-phalangeal joint of the index and middle fingers, which were not being used to strike the keys. Furthermore, muscular activity in the extrinsic finger muscles was smaller for the experts than for the amateurs. These findings indicate that pianists with superior skill reduce the finger muscle load during keystrokes by taking advantage of differences in proximal joint motion and hand postural configuration. With an increase in tempo, the experts showed larger and smaller increases in elbow velocity and finger muscle co-activation, respectively, compared to the amateurs, highlighting skill level-dependent differences in movement strategies for tempo adjustment. Finally, when striking as fast as possible, individual differences in the striking tempo among players were explained by their elbow velocities but not by their digit velocities. These findings suggest that pianists who are capable of faster keystrokes benefit more from proximal joint motion than do pianists who are not capable of faster keystrokes. The distinct movement strategy for tempo adjustment in pianists with superior skill would therefore ensure a wider range of musical expression.

Analysis of scale-free networks based on a threshold graph with intrinsic vertex weights

Many real networks are complex and have power-law vertex degree distribution, short diameter, and high clustering. We analyze the network model based on thresholding of the summed vertex weights, which belongs to the class of networks proposed by Phys. Rev. Lett. 89, 258702 (2002)]. Power-law degree distributions, particularly with the dynamically stable scaling exponent 2, realistic clustering, and short path lengths are produced for many types of weight distributions. Thresholding mechanisms can underlie a family of real complex networks that is characterized by cooperativeness and the baseline scaling exponent 2. It contrasts with the class of growth models with preferential attachment, which is marked by competitiveness and baseline scaling exponent 3.

Disaster Evacuation Guidance Using Opportunistic Communication: The Potential for Opportunity-Based Service

In recent years, as a practical use of Delay Tolerant Network and Mobile Opportunistic Network, disaster evacuation guidance effective against situations of large-scale urban disasters have been studied. We have proposed a disaster evacuation guidance using opportunistic communication where evacuees gather location information of impassable and congested roads by disaster into their smartphones by themselves, and also share the information with each other by short-range wireless communication between nearby smartphones. Our guidance is designed not only to navigate evacuating crowds to refuges, but also to rapidly aggregate the disaster information. On the other hand, the Great East Japan Earthquake in 2011 taught us a lesson: the only helpful services in disaster situations are services that are daily used by everyone. Inversely services prepared only for disaster situations have never been used in a disaster situation because of lack of maintenance or unawareness by ignorance. To effectively utilise our evacuation guidance, therefore, some service using opportunistic communication should be firstly widespread across the world as an infrastructure and everyone naturally receives much benefit from the service in daily life. In this chapter we consider a possibility of the service, which we call Opportunity-based Service (OBS). We discuss some practical usages not only for disaster situations, but also for daily life, for example, an autonomous human navigation avoiding congestion by crowds. Through reviewing our past works, we try to foresee a possible next-generation information communication technology regarding Big Data, IoT, and pervasive computing on smart environments.

Effect of Traffic Volume in Real-Time Disaster Evacuation Guidance Using Opportunistic Communications

In case a large-scale disaster hits a big urban area, studies have been undertaken on effective disaster evacuation guidance using mobile phones of evacuees. In our previous work, we proposed a real-time disaster evacuation guidance using opportunistic communications as an application of Delay Tolerant Networking to disaster management. In the guidance, evacuees gather disaster information, such as impassable roads and dangerous areas, on their mobile phones by themselves and share it with each other using opportunistic communications between nearby phones on their evacuation routes to refuge areas. We numerically evaluated the performance of the guidance and showed that the guidance considerably reduces evacuation time. In this evaluation, however, we neglected the effect of traffic volume of evacuees, which might cause serious traffic congestion, inhibiting a smooth evacuation. In this paper, we consider the effect of traffic volume on evacuation time and numerically evaluate the performance again by introducing capacity-constrained nodes on road graphs. We show that the guidance also effectively reduces the evacuation time regardless of the traffic volume.

Distributed Web caching using hash-based query caching method

Distributed Web caching allows multiple clients to quickly access a pool of popular Web pages. Conventional distributed Web caching schemes, e.g., the Internet cache protocol and hash routing, require the sending of many query messages among cache servers and/or impose a large load on the cache servers when they are widely dispersed. To overcome these problems, we propose a hash-based query caching method using both a hash function and a query caching method. This method can find cached objects among several cache servers by using only one query message. Compared to conventional methods, this method reduces cache server overhead, object retrieval latency and loads to the network.

Cluster structures in topology of large-scale social networks revealed by traffic data

Many studies of social networks have recently been published. Interest in topological structures, such as scale-free characteristics, has been particularly strong. In this paper, we focus on the analysis of macro traffic data in a communications network of cellular phone users as a way of investigating large-scale social networks. Behaviors of information exchange between pairs of cellular phone users are reflected in traffic data, which thus reflects interesting features of social networks. We analyze the relationship between the number of customers and the volume of traffic with a view to finding clues about the structure of social networks among the very large set of potential customers. We then demonstrate some interesting features that our analysis reveals: a scale-free topology of human relations, their cluster structures, and behaviors of user-dynamics. In addition, we consider the relationship between traffic volume and the number of customers depending on the situation.

Homesick Lévy Walk and Optimal Forwarding Criterion of Utility-Based Routing under Sequential Encounters

The Internet of Things (IoT) is going to develop integrated and organised networks of all things and beings in the world enabling autonomous computing and information communication for the creation of new values in the future. For such networks by IoT that accept a certain level of communication delay, but that must realise highly-reliable message forwarding, Delay Tolerant Network (DTN) gives a possible solution. Recently, DTN has attracted attention as a future network under challenged network environments where communication delay, disruption, and disconnect frequently occurs. In this chapter, we review some routing protocols for efficient message forwarding in DTN. We also review some mobility models often used for simulating motions of mobile nodes to evaluate the performance of DTN. In this review, we propose our mobility model called Homesick Levy Walk that mimics human mobility patterns of an universal scale-free property of the frequency of human contacts. After this, we also propose our utility-based routing protocol which maximises the expected number of selected relay nodes being likely to encounter a destination node under sequential encounters with nodes. We evaluate the performance of our routing protocol by comparing with some performance measures of some existing routing protocols under the condition that the Homesick Levy Walk is adopted as mobility model. We show that our protocol is comparable to others in arrival rate of messages under a smaller number of message forwarding.We also find that the performance of our protocol is stable up to a few hundred mobile nodes and tends to be scalable with the number of nodes.

Network Design Method Based on Link Protection Taking Account of the Connectivity and Distance Between Sites

High reliability is required in networks, and it is important to build robust networks that are tolerant to network failures. In content delivery services in particular, service interruptions due to disconnection of communication paths between the server and nodes that receive the service must be avoided. Content delivery services use a master server that contains the original content and multiple edge-servers (mirror servers) that hold copies of the content so that communication paths exist between the master server and the edge-servers even in the event of a failure. In addition to the guarantee of network connectivity, large increases in path lengths when changing from the paths used during normal operation to alternative paths in the event of a failure must be avoided from the viewpoint of suppressing degradation of the communication quality and the possibility of congestion. However, building such high-reliability networks involves huge costs. Therefore, it is considered necessary to devise a network design that can realize continuity of communication between the master server and the edge-servers by suppressing sudden increases in path length, even if a failure occurs. In this paper, we formulate a network design problem and show that it is NP-hard. We also design a polynomial-time approximation algorithm for the case where the number of failed links is constant, and we evaluated its performance in various actual network topologies.

CG animation for piano performance

Technologies recreating piano performance in the form of CG animation are eagerly anticipated by people working in various fields, such as content production, music education, etc. Nonetheless, much of the past research has dealt with the mechanical finger movements in piano practice support systems and performance support GUIs, etc. and there has been little research recreating the reality of finger movements. We are promoting research into the analysis and CG expression of realistic and natural piano fingering. This paper describes the following aspects of this research program: (i) measurement of piano fingering using motion capture technology, (ii) generation of a CG animation of fingering using offline/realtime rendering, and (iii) automatic generation of fingering using optimized algorithms. And finally we will introduce examples in which the fingering data created in (i) is used in TV animation.