DSpace Angular :: Browsing by Author "Marianov, V"

Browsing by Author "Marianov, V"

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A procedure for the strategic planning of locations, capacities and districting of jails: application to Chile
(PALGRAVE PUBLISHERS LTD, 2005) Marianov, V; Fresard, F
Using the Chilean jail system as a case study, we present a model for finding the location of a number of new jails, as well as the size and districting of new and existing jails, so that the cost of the system is minimized. We propose a minimum regret procedure for choosing a good solution, given that several future scenarios are possible. The jail capacities range from a few tens to 2000 inmates. The population is composed of pre-trial detainees, people under trial and sentenced offenders. Each one of these categories has different requirements, in terms of the site of their confinement. Inmates stay in the system for periods that go from a few days to life sentences. Some overcrowding is allowed, but penalized by the model. Several scenarios of future population are used for finding a solution for the Chilean system, where there are some 33 000 inmates.
Allocating servers to facilities, when demand is elastic to travel and waiting times
(EDP SCIENCES S A, 2005) Marianov, V; Rios, M; Barros, FJ
Public inoculation centers are examples of facilities providing service to customers whose demand is elastic to travel and waiting time. That is, people will not travel too far, or stay in line for too long to obtain the service. The goal, when planning such services, is to maximize the demand they attract, by locating centers and staffing them so as to reduce customers' travel time and time spent in queue. In the case of inoculation centers, the goal is to maximize the people that travel to the centers and stay in line until inoculated. We propose a procedure for the allocation of multiple servers to centers, so that this goal is achieved. An integer programming model is formulated. Since demand is elastic, a supply-demand equilibrium equation must be explicitly included in the optimization model, which then becomes nonlinear. As there are no exact procedures to solve such problems, we propose a heuristic procedure, based on Heuristic Concentration, which finds a good solution to this problem. Numerical examples are presented.
Anticoverage models for obnoxious material transportation
(PION LTD, 2002) Marianov, V; ReVelle, C; Shih, S
We present models for the design of routes for transportation of loads that might become hazardous or obnoxious to the population living along these routes. We take into consideration the fact that the values of the properties that are close to the roads used for the transportation may decrease as a consequence of this activity. As opposed to the traditional approach, of minimizing the population along the routes, we propose to include a compensation cost as a direct cost of choosing the routes. This compensation could include, for instance, a reduction in property tax rates. Two formulations are presented, covering different patterns of effects on property values. As an example of application of the models, we provide some computational experience.
Beyond Nintendo: design and assessment of educational video games for first and second grade students
(PERGAMON-ELSEVIER SCIENCE LTD, 2003) Rosas, R; Nussbaum, M; Cumsille, P; Marianov, V; Correa, M; Flores, P; Grau, V; Lagos, F; Lopez, X; Lopez, V; Rodriguez, P; Salinas, M
The main objective of this study was to evaluate the effects of the introduction of educational videogames into the classroom, on, learning, motivation, and classroom dynamics. These effects were studied using a sample of 1274 students from economically disadvantaged schools in Chile. The videogames were specifically designed to address the educational goals of the first and second years of school, for basic mathematics and reading comprehension. The sample was divided into experimental groups (EG), internal control groups (IC) and external control groups (EC). Students in the EG groups, used the experimental video games during an average of 30 h over a 3-month period. They were evaluated on their acquisition of reading comprehension, spelling, and mathematical skills, and on their motivation to use video games. Teachers' expectations of change due to the use of video games, their technological transfer, and handling of classroom dynamics, were assessed through ad hoc tests and classroom observations. The results show significant differences between the EG and IC groups in relation to the EC group in Math, Reading Comprehension and Spelling, but no significant differences in these aspects were found between the EG and the IC groups. Teacher reports and classroom observations confirm an improvement in motivation to learn, and a positive technological transfer of the experimental tool. Although further studies regarding the effects of learning through videogame use are imperative, positive effects on motivation and classroom dynamics, indicate that the introduction of educational video games can be a useful tool in promoting learning within the classroom. (C) 2002 Elsevier Science Ltd. All rights reserved.
Finding locations for public service centres that compete with private centres: Effects of congestion
(SPRINGER, 2004) Marianov, V; Rios, M; Taborga, P
We propose a locational model for public service centres when they compete with private centres. Customers may be captured by the centre offering shorter distance or lower waiting times. Both types of centres provide paid services to high-income customers, and public centres also provide subsidised services to low-income customers. Equilibrium must be found in public centres between low-income population coverage and high-income population capture. We analyse the effects of waiting times on the design of the public service and apply the model to data for Santiago, Chile.
Hierarchical location-allocation models for congested systems
(ELSEVIER SCIENCE BV, 2001) Marianov, V; Serra, D
In this paper we address the issue of locating hierarchical facilities in the presence of congestion. Two hierarchical models are presented, where lower level servers attend requests first, and then, some of the served customers are referred to higher level servers. In the first model, the objective is to find the minimum number of servers and their locations that will cover a given region with a distance or time standard. The second model is cast as a maximal covering location (MCL) formulation. A heuristic procedure is then presented together with computational experience. Finally, some extensions of these models that address other types of spatial configurations are offered. (C) 2001 Elsevier Science B.V. All rights reserved.
Linear, non-approximated models for optimal routing in hazardous environments
(STOCKTON PRESS, 1998) Marianov, V; ReVelle, C
A linear optimisation model is presented for the routing of vehicles through hazardous environments or for routing vehicles carrying hazardous materials. The model seeks to find the route with the minimum cost and the minimum probability of accident. As opposed to previously published models, the formulation is linear and no approximations are needed, even in the case of high risk. Several forms of considering risk are presented, as well as a simple method of solution in polynomial time. An example is shown and solved.
Location models for airline hubs behaving as M/D/c queues
(PERGAMON-ELSEVIER SCIENCE LTD, 2003) Marianov, V; Serra, D
Models are presented for the optimal location of hubs in airline networks, which take into consideration the congestion effects. Hubs, which are typically the most congested airports, are modeled as M/D/c queuing systems. A formula is derived for the probability of a number of customers in the system, which is later used to propose a capacity constraint. This constraint limits the probability of more than b airplanes in queue, to be smaller than or equal to a given value. Due to the computational complexity of the formulation, the model is solved using a heuristic based on tabu search. Computational experience is presented together with an example using a data set available in the literature.
Location of hubs in a competitive environment
(ELSEVIER SCIENCE BV, 1999) Marianov, V; Serra, D; ReVelle, C
We offer a formulation that locates hubs on a network in a competitive environment; that is, customer capture is sought, which happens whenever the location of a new hub results in a reduction of the current cost (time, distance) needed by the traffic that goes from the specified origin to the specified destination. The formulation presented here reduces the number of variables and constraints as compared to existing covering models. This model is suited for both air passenger and cargo transportation. In this model, each origin-destination flow can go through either one or two hubs, and each demand point can be assigned to more than a hub, depending on the different destinations of its traffic. Links ("spokes") have no capacity limit. Computational experience is provided. (C) 1999 Elsevier Science B.V. AU rights reserved.
Location-allocation of multiple-server service centers with constrained queues or waiting times
(KLUWER ACADEMIC PUBL, 2002) Marianov, V; Serra, D
Recently, the authors have formulated new models for the location of congested facilities, so to maximize population covered by service with short queues or waiting time. In this paper, we present an extension of these models, which seeks to cover all population and includes server allocation to the facilities. This new model is intended for the design of service networks, including health and EMS services, banking or distributed ticket-selling services. As opposed to the previous Maximal Covering model, the model presented here is a Set Covering formulation, which locates the least number of facilities and allocates the minimum number of servers (clerks, tellers, machines) to them, so to minimize queuing effects. For a better understanding, a first model is presented, in which the number of servers allocated to each facility is fixed. We then formulate a Location Set Covering model with a variable (optimal) number of servers per service center (or facility). A new heuristic, with good performance on a 55-node network, is developed and tested.
Multiple path routing algorithm for IP networks
(ELSEVIER SCIENCE BV, 2005) Rios, M; Marianov, V; Avagliano, A
Internet routing protocols, such as Open Shortest Path First (OSPF), compute a shortest path tree from each node to other nodes in the network, using link-state information. Such protocols do not consider the queueing situation at a given node. An alternate path of higher cost may be more convenient to use than the optimum path when a long queue is present at the node. This paper proposes a new Multiple Path Routing Algorithm (MPRA), which uses dynamic shortest path tree mechanisms, load balancing among alternative paths to destination, and path feasibility analysis to avoid network loops. A better-cost model is also introduced. Computer simulations show that MPRA measured parameters (throughput, packet delay, etc.) improve over OSPF by amounts close to 30% for unbalanced networks, and close to 20% for balanced networks. (c) 2004 Elsevier B.V. All rights reserved.
Optimal location of public health centres which provide free and paid services
(NATURE PUBLISHING GROUP, 2001) Marianov, V; Taborga, P
A model and a heuristic are presented for finding the most effective location of public health centres providing non-vital services in competition with existing private health centres. While private centres provide only services to customers who can pay for them, public centres provide both paid services to affluent customers, and subsidised services to customers belonging to low-income groups (a hierarchical structure). While low-income customers are assigned to fixed public centres, high-income customers can choose which centre to patronise. To find the solution of this problem, the equilibrium between maximum coverage of low-income population (within a pre-specified distance), and an adequate capture of high-income population must be found. Thus, in the public service, the revenues obtained from paid services are used to partly cover the costs of the subsidised services, and the number of centres that can be located depends on how many high-income clients can be captured. Capture of a high-income client happens when a public centre is located closer to the client than any of the existing private centres. Computational experience with optimal, as well as special heuristic, methods for solving this problem is described.
Probabilistic, maximal covering location-allocation models for congested systems
(BLACKWELL PUBLISHERS, 1998) Marianov, V; Serra, D
When dealing with the design of service networks, such as health and emergency medical services, banking or distributed ticket-selling services, the location of service centers has a strong influence on the congestion at each of them, and, consequently, on the quality of service. In this paper, several probabilistic maximal covering location-allocation models with constrained waiting time for queue length are presented to consider service congestion. The first model considers the location of a given number of single-server centers such that the maximum population is served within a standard distance, and nobody stands in line for longer than a given time or with more than a predetermined number of other users. Several maximal coverage models are then formulated with one or more servers per service center. A new heuristic is developed to solve the models and tested in a 30-node network.
Survivable capacitated network design problem: new formulation and Lagrangean relaxation
(PALGRAVE MACMILLAN LTD, 2000) Rios, M; Marianov, V; Gutierrez, M
This work is focused on the analysis of the survivable capacitated network design problem. This problem can be stated as follows: Given a supply network with point-to-point traffic demands, specific survivability requirements, a set of available capacity ranges and their corresponding discrete costs for each are, find minimum cost capacity expansions such that these demands can be met even if a network component fails. Solving this problem consists of selecting the links and their capacity, as well as the routings for each demand in every failure situation. This type of problem can be shown to be NP-hard. A new linear mixed-integer mathematical programming formulation is presented. An effective solution procedure based on Lagrangean relaxation is developed. Comparison heuristics and improvement heuristics are also described. Computational results using these procedures on different sizes of randomly generated networks are reported.
Trading off species protection and timber production in forests managed for multiple objectives
(SAGE PUBLICATIONS LTD, 2004) Marianov, V; Snyder, S; ReVelle, C
We address a multiobjective forest-management problem that maximizes harvested timber volume and maximizes the protection of species through the selection of protected habitat reserves. As opposed to reserving parcels of the forest for general habitat purposes, as most published works do, the model we present, and its several variants, concentrate on the preservation status of each one of the species living in the forest under study. Thus, all of the formulations we propose trade off harvested timber volume against the weighted number of preserved species. Each formulation represents a different management policy. Casting the models in a static setting allows us to analyze the effect of several management policies through computational experience with different forest-stucture-species relationships.

Browsing by Author "Marianov, V"

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