The mixed evacuation problem

A dynamic network introduced by Ford and Fulkerson is a directed graph with capacities and transit times on its arcs. The quickest transshipment problem is one of the most fundamental problems in dynamic networks. In this problem, we are given sources and sinks. Then the goal of this problem is to find a minimum time limit such that we can send the right amount of flow from sources to sinks. In this paper, we introduce a variant of this problem called the mixed evacuation problem. This problem models an emergent situation in which people can evacuate on foot or by car. The goal is to organize such a mixed evacuation so that an efficient evacuation can be achieved. In this paper, we study this problem from the theoretical and practical viewpoints. In the first part, we prove the polynomial-time solvability of this problem in the case where the number of sources and sinks is not large, and also prove the polynomial-time solvability and computational hardness of its variants with integer constraints. In the second part, we apply our model to the case study of Minabe town in Wakayama prefecture, Japan.     

The roles of supply network centralities in firm performance and the moderating effects of reputation and export-orientation

Abstract

This study explores how supply network degree, closeness, and betweenness centralities affect firm performance, and the moderating effects of organizational reputation (measured by PageRank centrality) and export-orientation. The supply chain relationship empirical data are drawn from manufacturing and manufacturing service companies in Hong Kong, China. Social network analysis and moderated regression analysis were adopted to test the hypotheses for a sample of 814 focal firms with 3086 supply chain ties. The results indicate that in-degree and closeness centralities improve firm performance. Reputation is found to positively moderate the relationship between closeness and sales performance, but negatively moderates the relationship between betweenness and sales performance. Export-orientation has no effect on relationships. This study contributes to the literature by providing additional empirical evidence on the role of supply network position in firm performance. It also introduces PageRank centrality as a new measure of organizational reputation in a supply network.     

Online graph exploration algorithms for cycles and trees by multiple searchers

This paper deals with online graph exploration problems by multiple searchers. The information on the graph is given online. As the exploration proceeds, searchers gain more information on the graph. Assuming an appropriate communication model among searchers, searchers can share the information about the environment. Thus, a searcher must decide which vertex to visit next based on the partial information on the graph gained so far by searchers. We assume that all searchers initially start the exploration at the origin vertex, and the goal is that each vertex is visited by at least one searcher and all searchers finally return to the origin vertex. The objective is to minimize the time when the goal is achieved. We study the case of cycles and trees. For the former, we give an optimal online exploration algorithm in terms of competitive ratio, and for the latter, we also give an online exploration algorithm which is optimal among greedy algorithms.     

Preoperative sexual status of Japanese localized prostate cancer patients: comparison of sexual activity and EPIC scores

Objective: This study aimed to evaluate the relationship between sexual activity and sexual function using questionnaires distributed to middle-aged Japanese patients with localized prostate cancer.

Methods: A total of 145 patients who underwent radical prostatectomy were enrolled in the survey reported on herein. Sexual activity and sexual function were investigated via the Expanded Prostate Cancer Index Composite (EPIC) and an original self-reported questionnaire.

Results: Of participants, 24.1% and 20.7% had sexual activity within a month period as investigated via the EPIC and original questionnaire, respectively. However, 29.7% of all those who reported sexual activity rate reported “about once every 2?months to a year,” as shown in the original questionnaire. Regarding sexual function as addressed through EPIC, no results within that questionnaire’s measure of sexual function showed significant differences among patients with a rate of actual sexual activity.

Conclusions: The present survey showed that more than quarter of preoperative middle-aged Japanese prostate cancer patients surveyed had actual sexual activity, though not within the preceding 4?weeks. To precisely evaluate sexual function of middle-aged Japanese patients, it is necessary to consider actual sexual activity.