Browsing by Author "Maturana, Sergio"

Now showing 1 - 9 of 9
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    A robust optimization approach to wine grape harvesting scheduling
    (ELSEVIER, 2010) Bohle, Carlos; Maturana, Sergio; Vera, Jorge
    Optimization models are increasingly being used in agricultural planning. However, the inherent uncertainties present in agriculture make it difficult. In recent years, robust optimization has emerged as a methodology that allows dealing with uncertainty in optimization models, even when probabilistic knowledge of the phenomenon is incomplete. In this paper, we consider a wine grape harvesting scheduling optimization problem subject to several uncertainties, such as the actual productivity that can be achieved when harvesting. We study how effective robust optimization is solving this problem in practice. We develop alternative robust models and show results for some test problems obtained from actual wine industry problems. (C) 2008 Elsevier B.V. All rights reserved.
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    An optimization approach for scheduling wine grape harvest operations
    (ELSEVIER, 2008) Ferrer, Juan Carlos; Mac Cawley, Alejandro; Maturana, Sergio; Toloza, Sergio; Vera, Jorge
    This article presents a practical tool for optimally scheduling wine grape harvesting operations taking into account both operational costs and grape quality. We solve a mixed-integer linear programming model to support harvest scheduling, labor allocation, and routing decisions. A quality loss function is used to represent wine quality reduction at each vineyard block due to premature or deferred harvest with respect to an optimal date. We present computational results which show that the proposed tool could be used to support grape harvest planning in a large vineyard, at both a tactical and operational level, (C) 2007 Elsevier B.V. All rights reserved.
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    Dynamic biomass growth model for Mytilus chilensis in longline culture systems
    (UNIV VALPARAISO, 2012) Marambio, Jose; Maturana, Sergio; Campos, Bernardita
    A dynamic biomass growth model for the mussel Mytilus chilensis in longline culture systems in proposed. This model determines the biomass by estimating the average weight and the number of mussels per meter of seeded rope, using real data. The average weight is estimated using the von Bertalanffy model modified to incorporate the availability of food in the environment and the reproductive cycle given by the Meat Yield Index, which is the quotient between the meat weight and the total weight. Therefore, the average weight is determined by the availability of food and the biological growth of the species. The model assumes that the number of mussel individuals per meter in the rope is the result of both the species intraspecific competition among M. chilensis individuals and the interspecific competition with individuals of the mytilid Aulacomya atra for the available space in the same seeded rope. The growth rate, the occupied surface and the presence percentage of M. chilensis and A. atra were used to model the competition for the available space. The study was performed at the Rilan basin in the Chiloe Island, southern Chile, during an 18-month period. The results obtained were an R-2 adjusted = 0.98, 0.93, and 0.94 for the variation in size, lineal density and biomass, respectively, which indicate that the proposed dynamic model can be used to predict the biomass over time.
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    Fraud in the health systems of Chile: a detection model
    (PAN AMER HEALTH ORGANIZATION, 2009) Mesa, Francisco R.; Raineri, Andres; Maturana, Sergio; Maria Kaempffer, Ana
    Objectives. To develop a model for detecting cases of organized fraud in Chile based on data from the legal forms for medically authorized leave (formulario legal de licencia medica curativa-MAL) and to establish the relevance of this data to fraud detection.
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    Impact of Using an E-Marketplace in the Construction Supply Process: Lessons from a Case Study
    (ASCE-AMER SOC CIVIL ENGINEERS, 2009) Alarcon, Luis F.; Maturana, Sergio; Schonherr, Ignacio
    The procurement process is critical for construction companies. To improve it, many are resorting to e-marketplaces although they usually do not know exactly how much they can gain by doing so. This paper describes a study that measured the benefits of using an e-marketplace to support the procurement process of a construction company. The study included three marketplaces currently operating in Chile. However, in this paper, we focus on Iconstruye, the most important one. 70 executives and professionals from 25 construction companies randomly selected from the 89 that used this marketplace, were interviewed and asked to fill out a questionnaire. This data was validated using data from Iconstruye and from 33 suppliers. The results show that the adoption of an e-marketplace reduces turnaround time, errors, urgent orders, and irregular purchases. A more reliable procurement process directly contributes to a leaner construction process by reducing upstream variability, procurement cycle times, and the need for large inventories on site. Users also perceive an improvement in certain global indicators when using an e-marketplace.
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    Improving Planning Reliability and Project Performance Using the Reliable Commitment Model
    (2010) Gonzalez, Vicente; Alarcon Cardenas, Luis Fernando; Maturana, Sergio; Mundaca, Fernando; Bustamante, Jose
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    On-site subcontractor evaluation method based on lean principles and partnering practices
    (ASCE-AMER SOC CIVIL ENGINEERS, 2007) Maturana, Sergio; Alarcon, Luis Fernando; Gazmuri, Pedro; Vrsalovic, Mladen
    Subcontracting has greatly increased in the construction industry. It helps shift risk from the main contractor to the subcontractor and promotes specialization. Inadequate subcontracting management, however, may result in an adversarial relationship between main contractors and their subcontractors, uncoordinated on-site execution, and disappointing quality and schedule fulfillment. New subcontractor management methods and tools are being developed and tested as part of a collaborative research project led by the Catholic University Production Management Center with the participation of the Chilean Construction Chamber and several construction companies. The experience gained by testing prototype tools and methods on selected projects enabled us to develop an on-site evaluation method based on lean principles and partnering practices. This method allows main contractors to help subcontractors improve their performance by providing them with periodic feedback. It also supports subcontractor selection based on their previous performance, which helps foster collaborative relationships with those that consistently perform well. The results of the application of the method in two case studies are discussed.
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    Scheduling production for a sawmill: A comparison of a mathematical model versus a heuristic
    (PERGAMON-ELSEVIER SCIENCE LTD, 2010) Maturana, Sergio; Pizani, Enzo; Vera, Jorge
    Sawmill production scheduling is complex. It involves determining which logs to process taking into account the diameter, length, and grade of each log, on one hand, and the finished products that are needed to fulfill the orders, on the other. The cutting pattern determines which products are generated and also the yield, which is how much of the volume of the log ends as finished products. We used two approaches to solve the problem: a mathematical model, which calculates the volume and the schedule of various types of logs, and a heuristic that solves the problem by systematically applying the criteria used by a sawmill programmer in southern Chile. We compare the results of using both approaches under various scenarios in a 6 week planning horizon, with the mathematical model showing a superior performance in almost all instances except two, were both found the optimal solution. The proposed mathematical model can be solved in a relatively short time, which makes it a suitable basis of a practical optimization-based decision support system. (C) 2010 Elsevier Ltd. All rights reserved.
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    Site Management of Work-in-Process Buffers to Enhance Project Performance Using the Reliable Commitment Model: Case Study
    (ASCE-AMER SOC CIVIL ENGINEERS, 2011) Gonzalez, Vicente; Fernando Alarcon, Luis; Maturana, Sergio; Antonio Bustamante, Jose
    Buffers have been commonly used as a production strategy to protect construction processes from the negative impact of variability. Construction practitioners and researchers have proposed several buffering approaches for different production situations and contexts. However, these solutions have been impractical for managing buffers. To overcome this, this study proposes a new site methodology for managing work-in-process (WIP) buffer in repetitive projects, on the basis of the reliable commitment model (RCM). RCM is a decision-making tool based on lean principles, which uses statistical models to develop more reliable work plans at the operational level. RCM helps to manage WIP buffer in work plans by using site information and planning reliability indicators that result in improved project performance, such as labor productivity and process progress. A repetitive building project was used as a case study. The main finding was that labor productivity, process progress, and waiting times improved when using larger WIP buffers than those typically used among crews. This shows the potential of RCM as a practical tool to manage WIP buffer sizes and to promote the use of lean production strategies at the operational level. DOI: 10.1061/(ASCE)CO.1943-7862.0000346. (C) 2011 American Society of Civil Engineers.