Takehiro Furuta

Generalized network Voronoi diagrams: Concepts, computational methods, and applications

In the real world, there are many phenomena that occur on a network or alongside a network; for example, traffic accidents on highways and retail stores along streets in an urbanized area. In the literature, these phenomena are analysed under the assumption that distance is measured with Euclidean distance on a plane. This paper first examines this assumption and shows an empirical finding that Euclidean distance is significantly different from the shortest path distance in an urbanized area if the distance is less than 500 m. This implies that service areas in urbanized areas cannot be well represented by Voronoi diagrams defined on a plane with Euclidean distance, termed generalized planar Voronoi diagrams. To overcome this limitation, second, this paper formulates six types of Voronoi diagrams defined on a network, termed generalized network Voronoi diagrams, whose generators are given by points, sets of points, lines and polygons embedded in a network, and whose distances are given by inward/outward distances, and additively/multiplicatively weighted shortest path distances. Third, in comparison with the generalized planar Voronoi diagrams, the paper empirically shows that the generalized network Voronoi diagrams can more precisely represent the service areas in urbanized areas than the corresponding planar Voronoi diagrams. Fourth, because the computational methods for constructing the generalized planar Voronoi diagrams in the literature cannot be applied to constructing the generalized network Voronoi diagrams, the paper provides newly developed efficient algorithms using the ‘extended’ shortest path trees. Last, the paper develops user‐friendly tools (that are included in SANET, a toolbox for spatial analysis on a network) for executing these computational methods in a GIS environment.

Exact optimal solutions of the minisum facility and transfer points location problems on a network

We consider hierarchical facility location problems on a network called Multiple Location of Transfer Points (MLTP) and Facility and Transfer Points Location Problem (FTPLP), where q facilities and p transfer points are located and each customer goes to one of the facilities directly or via one of the transfer points. In FTPLP, we need to find an optimal location of both the facilities and the transfer points while the location of facilities is given in MLTP. Although good heuristics have been proposed for the minisum MLTP and FTPLP, no exact optimal solution has been tested due to the size of the problems. We show that the minisum MLTP can be formulated as a p-median problem, which leads to obtaining an optimal solution. We also present a new formulation of FTPLP and an enumeration-based approach to solve the problems with a single facility.

Hypercube simulation analysis for a large-scale ambulance service system

A simple yet powerful simulation model for an ambulance service system is devised and applied to a large-scale ambulance system in the Tokyo metropolis. Our simulation can provide useful measures for the location analysis of ambulance stations, which are rarely incorporated in traditional optimal location models, although they are seemingly very important for designing a reliable and efficient emergency system. Comparing simulation output and actual data enables us to investigate the present ambulance system as well as check the validity and limitations of our model. Then we use the model to evaluate solutions to the ambulance station location problem.

New formulation for scheduling problem in multi-hop wireless sensor networks

In this paper, we consider a multi-hop sensor network, where the network topology is a tree, TDMA is employed as medium access control, and all data generated at sensor nodes are delivered to a sink node located on the root of the tree through the network. It is reported that if a transmission schedule that avoids interference between sensor nodes completely can be computed, TDMA is preferable to CSMA/CA in performance. However, solving the scheduling problem for TDMA is difficult, especially, in large-scale multi-hop sensor networks. In this paper, to formulate the scheduling problem for TDMA, we propose min-max model and min-sum model. While the min-max model yields the shortest schedule under the constraints, the min-sum model does not guarantee providing the shortest schedule. Numerical examples show that the min-sum model can provide good schedules in a reasonable CPU time, even when the min-max model fails to compute the shortest schedule in a reasonable CPU time.

An Improved Teaching Behavior Estimation Model from Student Evaluations

Many universities conduct student evaluations. Their purpose is to encourage improvement in teaching. However, the evaluations are merely subjective assessments by students, meaning that instructors cannot necessarily easily relate evaluations to areas for improvement in teaching. To address this issue, we suggest a teaching behavior estimation model that can estimate teaching behaviors from student evaluations of each lesson. In previous research, we built a model on the assumption that teaching behaviors are not correlated with other behaviors and that student evaluation items are uncorrelated to other evaluation items. However, this assumption could not be verified. Our research suggests a new teaching behavior estimation model that represents the correlation between factors of teaching and factors of student evaluations. To analyze this, we conducted canonical correlation between two kinds of factors and obtained correlations. This result shows that it is possible to construct a teaching behavior estimation model based on factors of teaching behavior and factors of student evaluations.

Two Approaches to Cooperative Covering Location Problem and Their Application to Ambulance Deployment

This study proposes two approximation methods to define the coverage probability in ambulance location problems based on the model of cooperative covering proposed by Berman et al. (IEE Trans. 40, 232–245, 2010, [1]) as an extension to classical covering problems. A key ingredient of the model is the estimation of the coverage probability by multiple facilities. We introduce a simple parametric model for the travel time of ambulances and propose two methods to calculate the coverage probability approximately. We report and discuss two solutions obtained from computations using actual data.

Video Bookmarking for Learner Support in Blended Learning: Selection of Appropriate Keywords for Efficient Review of Lecture Video

We investigated a video book marking function, which is expected to be useful for students to efficiently review videotaped lectures. Video book marking allows students to record classroom lectures and mark the start time of specific points in the lecture video. They can later jump directly to bookmarked segments when reviewing the lecture video. It is important that keywords be useful indicators of bookmarked video segment content. In this study, we conducted a questionnaire survey to evaluate five keywords for bookmark labeling. We evaluated the suitability of the keywords based on subjective evaluation and system usage logs. We conclude that the five keywords examined are suitable for efficient video book marking by students during lectures.