Dependence Estimation Over a Finite Bivariate Failure Time Region

This articleconcerns nonparametric estimation of association between bivariatefailure times. In the presence of independent right censoring,the support for failure time variates may be restricted and measuresof dependence over a finite failure time region may be of particularinterest. To this end, the reciprocal cross ratio function, weightedby the bivariate failure time density, is proposed as a summarymeasure of dependence over a failure time region. This `relativerisk' estimator is shown to be consistent and asymptoticallynormally distributed, with consistent bootstrap variance estimator.A finite-region version of Kendall's tau, which is suitable forcensored failure time data, is also proposed, and correspondingasymptotic distribution theory is noted. The accuracy of theseasymptotic approximations is studied in simulations and an illustrationis provided.     

Adoption of the mobile Internet: An empirical study of multimedia message service (MMS)

Multimedia message service (MMS) provides more multimedia communication with entertainment effects than current text-based short message service (SMS). While many reports indicate that the mobile Internet market will be huge, little is known about whether people will accept MMS. This study applies innovation diffusion theory to examine the factors that influence the adoption of MMS. The proposed model was empirically evaluated by using survey data collected from 207 users concerning their perceptions of MMS. The findings indicate that perceptions of use were different over innovation diffusion stages. Specifically, there was a significant difference between potential adopters and users. The results may provide further insights into MMS marketing strategies.     

MARKET VENTURES, MORAL LOGICS, AND AMBIGUITY: Crafting a New Organizational Form in Post-Socialist China

How do institutional entrepreneurs craft new organizational forms under unstable conditions, especially when all of the relevant organizational models have serious liabilities in terms of legitimacy? Previous literature argues that emergent organizational models must adopt existing organizational elements in order to solve three problems: (1) gaining access to resources, (2) exploiting previous competencies, and (3) demonstrating legitimacy to salient audiences. Yet, these three distinct needs often require very different organizational elements associated with diverse, contradictory moral logics. This article, which examines the case of for‐profit ventures started by Chinese state organizations in the 1990s, reveals one strategy that entrepreneurs can use to solve this problem—to deliberately increase ambiguity about the organization's central characteristics and its underlying moral logic. This strategy makes it possible for new organizations to solve the problems of resources, competency, and legitimacy by simultaneously adopting (and adapting) contradictory organizational elements.     

Maximum-likelihood estimates and likelihood-ratio criteria for multivariate elliptically contoured distributions

For a class of multivariate elliptically contoured distributions the maximum-likelihood estimators of the mean vector and covariance matrix are found under certain conditions. Likelihood-ratio criteria are obtained for a class of null hypotheses. These have the same form as in the normal case.     

Ethnicity-of-Interviewer Effects Among Mexican-Americans and Anglos

A general interpersonal deference explanation for ethnicity-of-interviewereffects is tested with a random survey of Anglos and Mexican-Americansusing Anglo and Hispanic interviewers and questions relatedto Mexican-American culture. The theory was most clearly supportedamong Anglo respondents. The mixed support found among Mexican-Americanssuggests that deference is strongest when questions deal withthe culture represented by the interviewer, not the respondent.     

Two Variations of the Minimum Steiner Problem

Given a set S of starting vertices and a set T of terminating vertices in a graph G = (V,E) with non-negative weights on edges, the minimum Steiner network problem is to find a subgraph of G with the minimum total edge weight. In such a subgraph, we require that for each vertex s S and t T, there is a path from s to a terminating vertex as well as a path from a starting vertex to t. This problem can easily be proven NP-hard. For solving the minimum Steiner network problem, we first present an algorithm that runs in time and space that both are polynomial in n with constant degrees, but exponential in |S|+|T|, where n is the number of vertices in G. Then we present an algorithm that uses space that is quadratic in n and runs in time that is polynomial in n with a degree O(max {max {|S|,|T|}–2,min {|S|,|T|}–1}). In spite of this degree, we prove that the number of Steiner vertices in our solution can be as large as |S|+|T|–2. Our algorithm can enumerate all possible optimal solutions. The input graph G can either be undirected or directed acyclic. We also give a linear time algorithm for the special case when min {|S|,|T|} = 1 and max {|S|,|T|} = 2.The minimum union paths problem is similar to the minimum Steiner network problem except that we are given a set H of hitting vertices in G in addition to the sets of starting and terminating vertices. We want to find a subgraph of G with the minimum total edge weight such that the conditions required by the minimum Steiner network problem are satisfied as well as the condition that every hitting vertex is on a path from a starting vertex to a terminating vertex. Furthermore, G must be directed acyclic. For solving the minimum union paths problem, we also present algorithms that have a time and space tradeoff similar to algorithms for the minimum Steiner network problem. We also give a linear time algorithm for the special case when |S| = 1, |T| = 1 and |H| = 2.An extended abstract of part of this paper appears in Hsu et al. (1996).Supported in part by the National Science Foundation under Grants CCR-9309743 and INT-9207212, and by the Office of Naval Research under Grant No. N00014-93-1-0272.Supported in part by the National Science Council, Taiwan, ROC, under Grant No. NSC-83-0408-E-001-021.     

Scheduling Truck Arrivals at an Air Cargo Terminal

We consider the scheduling of truck arrivals at an air cargo terminal. By coordinating arrivals of cargo delivery trucks with outbound flight departure schedules, some of the shipments can be transferred directly to the departing flights, while others will be stored at the terminal's storage facility and incur extra handling and storage costs. The objective is to obtain a feasible schedule so as to minimize the total cost of operations. We formulate the problem as a time‐indexed integer program and show that, even with limited number of unloading docks at the terminal, the problem is non‐trivial (NP‐hard in the strong sense). Our solution method includes an exact solution procedure to determine an optimal unloading sequence for the shipments carried by each truck, together with a Lagrangian relaxation‐based heuristic for assigning trucks to truck docks and determining truck arrival times. We conducted computational experiments to test the performance of our solution method. Computational results show that our method can generate near‐optimal solutions efficiently. Our simulation results indicate that the scheduling approach proposed in this paper has the potential to generate significant cost savings over a first‐come, first‐served approach currently used at the air cargo terminal that we observed.     

A Generalization of Geometric Brownian Motion with Applications

Although geometric Brownian motion has a great variety of applications, it can not cover all the random phenomena. The purpose of this article is to propose a model that generalizes geometric Brownian motion. We present some interesting applications of this model in financial engineering and statistical inferences for the unknown parameters.