Francisco J. López

The impact of price decreases on telephone and cell phone diffusion

The diffusion process (the degree of penetration within a region) of telephones and cell phones has proceeded rapidly in most regions, but the factors influencing diffusion rates are still unknown. Using data from six regions (which varied in terms of economic wealth, stage of diffusion, technological and social infrastructures, and institutional policies), and two different technologies (telephone and cell phone) we showed that price-adjusted diffusion models had better explanatory power than pure diffusion models, validating Gurbaxani and Mendelsons model. We found that the impact of price decreases was positive and significant in all regions and for both technologies. Additionally the study showed that the impact of price decreases was stronger for less wealthy regions and for nations with higher developed social infrastructure (as measured by educational level) and greater political stability (as measured by Mauros composite index) after controlling for GDP. We also found that, in general, the price effect was stronger for telephones (an older technology) than for cell phones.

Minimizing the normalized sum of square for workload deviations on m parallel processors

In many organizations, it is desirable to distribute workload as equally as possible among a group of employees or machines. This paper proposes a performance measure, that we call the Normalized Sum of Square for Workload Deviations (NSSWD), and studies the problem of how to schedule a set of n jobs on m parallel identical processors in order to minimize the NSSWD. The NSSWD criterion is relevant where uniformity of wear to machines or of workload to employees is desirable. An algorithm, called Workload Balancing (WB), is proposed for solving this problem. Moreover, we perform a simulation experiment to evaluate WB against several well-known heuristics in the literature. Lastly, we discuss the computational results obtained from the simulation experiment.

Measuring e-Commerce Technology Enabled Business Value: An Exploratory Research

While a plethora of anecdotal evidence exists, there is little empirical evidence on the value-creating potential of e-commerce technologies. The present research investigates whether firms using e-commerce technologies are successful in generating business value and, if so, what e-commerce drivers determine success and how to best use these drivers. This work shows how diffusion theory can be used to analyze the wide-spread utilization of e-commerce technologies and how they create business value. It presents an exploratory model of e-commerce business value grounded in information technology (IT) business value and productivity literature. We use a sample from more than 550 company executives, identified as innovative and successful users of IT.

Parallel machine scheduling problems considering regular measures of performance and machine cost

This research considers a broad range of scheduling problems in the parallel machines environment. Schedules are evaluated according to two independent components of the objective function: (1) machine cost consisting of a fixed cost and a variable cost; and (2) a regular measure of performance. This study is only one of a few that take the selection of machines among those available as a decision variable. For machine cost with concave functions, we derive the general characteristics of optimal solutions with respect to decisions on the number of machines to use and the way to load the machines. Our analysis is not restricted to the machine cost criterion, but may be extended to other measures with concave functions. Furthermore, we provide a Pareto efficient perspective in understanding the tradeoff between machine cost and any regular measure of performance.

Supplier allocation and safety stock determination based on supplier reliability

Supplier selection and allocation of demand across suppliers has become a critical activity for organisations. Safety stocks are necessary to protect against shortages caused by supplier delivery failures and to achieve reasonable customer service levels. We present a new supplier selection model that determines safety stocks based on the supplier delivery reliability. The model includes procurement costs, supplier management costs, inventory carrying costs, and loss costs due to missed deliveries. An example is provided, followed by a sensitivity analysis that illustrates how the model can be used to analyse different sourcing strategies under various cost parameters.

Minimizing total weighted flowtime subject to minimum makespan on two identical parallel machines

We study the problem of scheduling n jobs on two identical parallel processors or machines where an optimal schedule is defined as one with the shortest total weighted flowtime (i.e., the sum of the weighted completion time of all jobs), among the set of schedules with minimum makespan (i.e., the completion time of the last job finished). We present a two phase non-linear Integer Programming formulation for its solution, admittedly not to be practical or useful in most cases, but theoretically interesting since it models the problem. Thus, as an alternative, we propose an optimization algorithm, for small problems, and a heuristic, for large problems, to find optimal or near optimal solutions. Furthermore, we perform a computational study to evaluate and compare the effectiveness of the two proposed methods.

Adding and removing an attribute in a DEA model: theory and processing

We present a theoretical and computational study of the impact of inserting a new attribute and removing an old attribute in a data envelopment analysis (DEA) model. Our objective is to obviate a portion of the computational effort needed to process such model changes by studying how the efficient/inefficient status of decision-making units (DMUs) is affected. Reducing computational efforts is important since DEA is known to be computationally intensive, especially in large-scale applications. We present a comprehensive theoretical study of the impact of attribute insertion and removal in DEA models, which includes sufficient conditions for identifying efficient DMUs when an attribute is added and inefficient DMUs when an attribute is removed. We also introduce a new procedure, HyperClimb, specially designed to quickly identify some of the new efficient DMUs, without involving LPs, when the model changes with the addition of an attribute. We report on results from computational tests designed to assess this procedures effectiveness.

An Algorithm to Find the Lineality Space of the Positive Hull of a Set of Vectors

The positive hull of a finite set of vectors,

Algorithms to determine the edges of a convex hull from its vertices

{\cal V}

A BACKWARD APPROACH LPC-BASED CONSTRUCTIVE HEURISTIC

, in d-dimensional space may or may not contain a lineality space