Search results for "Operations Research"

Técnicas exactas y heurísticas en el diseño automático de redes de planificación de proyectos

1993

Entry-Item-Quantity-ABC Analysis-Based Multitype Cigarette Fast Sorting System

2012

Published version of an article in the journal: Mathematical Problems in Engineering. Also available from the publisher at: http://dx.doi.org/10.1155/2012/847591 Open access Numerous items, small order, and frequent delivery are the characteristics of many distribution centers. Such characteristics generally increase the operating costs of the distribution center. To remedy this problem, this study employs the Entry-Item-Quantity (EIQ) method to identify the characteristic of the cigarette distribution center and further analyzes the importance degree of customers and the frequently ordered products by means of EQ/EN/IQ-B/IK statistic charts. Based on these analyses as well as the total rep…

A heuristic algorithm for project scheduling with splitting allowed

1996

In this article, we analyze the precedence diagramming method, the only published algorithm for time-only project scheduling with activity splitting allowed. The criteria used in this method (forward and backward pass computations) for deciding when an activity has to be interrupted are shown to be invalid in some situations. We look into the causes of these failures and propose new formulae that always provide feasible solutions. The new algorithm has been tested on 240 randomly generated problems ranging up to 600 activities and 7,200 precedence relationships, resulting in an average deviation from optima of less than 1 percent.

Contingent claim valuation in a market with different interest rates

1995

The problem of contingent claim valuation in a market with a higher interest rate for borrowing than for lending is discussed. We give results which cover especially the European call and put options. The method used is based on transforming the problem to suitable auxiliary markets with only one interest rate for borrowing and lending and is adapted from a paper of Cvitanic and Karatzas (1992) where the authors study constrained portfolio problems.

Value preserving portfolio strategies and the minimal martingale measure

1998

We consider some relations between the minimal martingale measure and the value preserving martingale measure in a continuous-time securities market. Under the assumption of continuous share prices we show that under a structure condition both these martingale measures exist and indeed coincide. This however does not mean that the corresponding concepts of value preserving portfolio strategies and (local) risk minimisation in the area of option hedging in incomplete markets are identical.

Adaptive memory programing for the robust capacitated international sourcing problem

2008

The International Sourcing Problem consists of selecting a subset from an available set of potential suppliers internationally located. The selected suppliers must meet the demand for items from a set of plants, which are also located worldwide. Since the costs are affected by macroeconomic conditions in the countries where the supplier and the plant are located, the formulation considers the uncertainty associated with changes in these conditions. We formulate the robust capacitated international sourcing problem by means of a scenario-optimization approach. When dealing with uncertainty, one of the most common approaches in the literature is to formulate the problem via a set of possible …

Testing the validity of the International Atomic Energy Agency (IAEA) safety culture model

2012

This paper takes the first steps to empirically validate the widely used model of safety culture of the International Atomic Energy Agency (IAEA), composed of five dimensions, further specified by 37 attributes. To do so, three independent and complementary studies are presented. First, 290 students serve to collect evidence about the face validity of the model. Second, 48 experts in organizational behavior judge its content validity. And third, 468 workers in a Spanish nuclear power plant help to reveal how closely the theoretical five-dimensional model can be replicated. Our findings suggest that several attributes of the model may not be related to their corresponding dimensions. Accordi…

Estimated radiation exposure of German commercial airline cabin crew in the years 1960-2003 modeled using dose registry data for 2004-2015.

2016

Exposure to ionizing radiation of cosmic origin is an occupational risk factor in commercial aircrew. In a historic cohort of 26,774 German aircrew, radiation exposure was previously estimated only for cockpit crew using a job-exposure matrix (JEM). Here, a new method for retrospectively estimating cabin crew dose is developed. The German Federal Radiation Registry (SSR) documents individual monthly effective doses for all aircrew. SSR-provided doses on 12,941 aircrew from 2004 to 2015 were used to model cabin crew dose as a function of age, sex, job category, solar activity, and male pilots' dose; the mean annual effective dose was 2.25 mSv (range 0.01–6.39 mSv). In addition to an inverse …

Adaptation to life after surgical removal of the bladder—an application of graphical Markov models for analysing longitudinal data

2004

Graphical Markov models have been developed particularly for the analysis of observational data. They allow the control of various background variables when analysing theoretically relevant associations. This paper demonstrates the application and some advantages of graphical Markov models in comparison to conventional statistical analyses. The aim of the study was to identify patients at risk for developing decreased health-related quality of life (QoL) after cystectomy and to explore the influence of coping on QoL in this situation. Therefore, the method was applied to analyse the data of a prospective study, in which 81 patients with bladder cancer were interviewed pre-operatively and in…

From heart-rate data to training quantification: a comparison of 3 methods of training-intensity analysis.

2014

Purpose:The authors directly compared 3 frequently used methods of heart-rate-based training-intensity-distribution (TID) quantification in a large sample of training sessions performed by elite endurance athletes.Methods:Twenty-nine elite cross-country skiers (16 male, 13 female; 25 ± 4 y; 70 ± 11 kg; 76 ± 7 mL · min−1 · kg−1 VO2max) conducted 570 training sessions during a ~14-d altitude-training camp. Three analysis methods were used: time in zone (TIZ), session goal (SG), and a hybrid session-goal/time-in-zone (SG/TIZ) approach. The proportion of training in zone 1, zone 2, and zone 3 was quantified using total training time or frequency of sessions, and simple conversion factors across…