The Capacitated Clustering Problem (CCP) consists of forming a specified number of clusters or gr... more The Capacitated Clustering Problem (CCP) consists of forming a specified number of clusters or groups from a set of elements in such a way that the sum of the weights of the elements in each cluster is within some capacity limits, and the sum of the benefits between the pairs of elements in the same cluster is maximized. This problem-which has been recently tackled with a GRASP/VNS approach-arises in the context of facility planners at mail processing and distribution. We propose a tabu search and several GRASP variants to find high quality solutions to this NP-hard problem. These variants are based on several neighborhoods, including a new one, in which we implement a one-for-two swapping strategy. We also hybridize both methodologies to achieve improved outcomes. The Maximally Diverse Grouping Problem (MDGP) is a special case of the CCP in which all the elements have a weight of one unit. This problem has been recently studied in the academic context when forming student groups, and we adapt the best method reported in the literature, a tabu search with strategic oscillation (TS_SO), to the CCP. Our empirical study with 50 large instances shows the superiority of the new GRASP with tabu search for the CCP with respect to both the previous GRASP/VNS approach and the adapted TS_SO.
Scatter search is a population-based method that has recently been shown to yield promising outco... more Scatter search is a population-based method that has recently been shown to yield promising outcomes for solving combinatorial and nonlinear optimization problems. Based on formulations originally proposed in the 1960s for combining decision rules and problem constraints, such as the surrogate constraint method, scatter search uses strategies for combining solution vectors that have proved effective in a variety of problem settings. In this paper, we present a scatter search implementation designed to find high quality solutions for the NP-hard linear ordering problem, which has a significant number of applications in practice. The LOP, for example, is equivalent to the so-called triangulation problem for input-output tables in economics. Our implementation goes beyond a simple exercise on applying scatter search, by incorporating innovative mechanisms to combine solutions and to create a balance between quality and diversification in the reference set. We also use a tracking process that generates solution statistics disclosing the nature of combinations and the ranks of antecedent solutions that produced the best final solutions. Our extensive computational experiments with more than 300 instances establishes the effectiveness of our procedure in relation to those previously identified to be best.
In this paper we present ARC a computerized system developed for urban garbage collection. The pa... more In this paper we present ARC a computerized system developed for urban garbage collection. The package is intended to help the planners in the design of efficient collection routes and to facilitate the study and evaluation of alternatives concerning issues such as the type and number of vehicles, frequency of collection and type and location of refuse containers. The final product is a "user friendly" system designed to be used by the planners without outside assistance.
Revista Española de Cardiología (English Edition), 2005
Operative risk stratification scales for use in cardiac surgery have been developed for patients ... more Operative risk stratification scales for use in cardiac surgery have been developed for patients who undergo procedures using extracorporeal circulation. The aims of the present study were to investigate the use of six preoperative risk stratification scales in patients undergoing beating-heart surgery and to identify risk factors for major complications and mortality in our group of patients who underwent revascularization using this approach. Between January 1997 and December 2002, we performed 762 coronary artery bypass operations on the beating heart; 61 patients suffered major complications (8%) and 25 died (3.3%). Risk factors for major complications and death were identified using logistic regression analysis of prospectively collected data. The following risk scores were calculated for each patient: Parsonnet 95, Parsonnet 97, Euroscore, Cleveland, Ontario, and French. Receiver operating characteristic curves were used to compare the ability of each scale to predict mortality and major complications. In our patient group, the preoperative variables associated with increased risk were: need for cardiopulmonary resuscitation, renal dysfunction, peripheral vasculopathy, and the presence of severe left main coronary artery disease, three-vessel disease, or an impaired ejection fraction. Mortality and major complications were best predicted by the Parsonnet 95 and Euroscore scales.
Operations Research/Computer Science Interfaces Series
... Estadistica e IO, Facultad de Matemdticas, Universitat de Valencia, Dr. Moliner 50, 46100 Bur... more ... Estadistica e IO, Facultad de Matemdticas, Universitat de Valencia, Dr. Moliner 50, 46100 Burjassot, Valencia, Spain, {rafael.marti, Vicente.campos}@uv ... Barnes and Vanston (1981) reported results on three branch and bound algorithms of instances with up 20 jobs and Laguna ...
In this paper we present two new heuristic procedures for the Capacitated Vehicle Routing Problem... more In this paper we present two new heuristic procedures for the Capacitated Vehicle Routing Problem (CVRP). The first one solves the problem from scratch, while the second one uses the information provided by a strong linear relaxation of the original problem. This second algorithm is designed to be used in a branch and cut approach to solve to optimality CVRP
Alrstraeg The Vehicle Routing Problem is a well known, and hard, combinatorial problem, whose pol... more Alrstraeg The Vehicle Routing Problem is a well known, and hard, combinatorial problem, whose polyhedral structure has deserved little attention. In this paper we consider the particular case in which all the demands are equal (since in the general case the associated polytope may be empty). From a known formulation of the problem we obtain the dimension of the corresponding polytope and we study the facetial properties of every inequality in it.
The bandwidth of a matrix { } ij a A = is defined as the maximum absolute difference between i an... more The bandwidth of a matrix { } ij a A = is defined as the maximum absolute difference between i and j for which 0 ≠ ij a. The problem of reducing the bandwidth of a matrix consists of finding a permutation of the rows and columns that keeps the nonzero elements in a band that is as close as possible to the main diagonal of the matrix. This NP-complete problem can also be formulated as a labeling of vertices on a graph, where edges are the nonzero elements of the corresponding symmetrical matrix. Many bandwidth reduction algorithms have been developed since the 1960s and applied to structural engineering, fluid dynamics and network analysis. For the most part, these procedures do not incorporate metaheuristic elements, which is one of the main goals of our current development. Another equally important goal is to design and test a special type of candidate list strategy and a move mechanism to be embedded in a tabu search procedure for the bandwidth reduction problem. This candidate list strategy accelerates the selection of a move in the neighborhood of the current solution in any given iteration. Our extensive experimentation shows that the proposed procedure outperforms the best-known algorithms in terms of solution quality consuming a reasonable computational effort.
In this article we first review previous exact approaches as well as theoretical contributions fo... more In this article we first review previous exact approaches as well as theoretical contributions for the problem of reducing the bandwidth of a matrix. This problem consists of finding a permutation of the rows and columns of a given matrix which keeps the non-zero elements in a band that is as close as possible to the main diagonal. This NP-complete problem can also be formulated as a labeling of vertices on a graph, where edges are the non-zero elements of the corresponding symmetrical matrix. We propose a new branch and bound algorithm and new expressions for known lower bounds for this problem. Empirical results with a collection of previously reported instances indicate that the proposed algorithm compares favourably to previous methods. * Research partially supported by the Ministerio de Educación y Ciencia (ref. TIC2003-C05-01) and by the Agencia Valenciana de Ciencia y Tecnologia (ref. GRUPOS03/189).
In this article we develop a greedy randomized adaptive search procedure (GRASP) for the problem ... more In this article we develop a greedy randomized adaptive search procedure (GRASP) for the problem of reducing the bandwidth of a matrix. This problem consists of finding a permutation of the rows and columns of a given matrix, which keeps the nonzero elements in a band that is as close as possible to the main diagonal. The proposed method may be coupled with a Path Relinking strategy to search for improved outcomes. Empirical results indicate that the proposed GRASP implementation compares favourably to classical heuristics. GRASP with Path Relinking is also found to be competitive with a recently published tabu search algorithm that is considered one of the best currently available for bandwidth minimization.
In this paper, we develop a new heuristic procedure for the linear ordering problem (LOP). This N... more In this paper, we develop a new heuristic procedure for the linear ordering problem (LOP). This NP-hard problem has a significant number of applications in practice. The LOP, for example, is equivalent to the so-called triangulation problem for input-output tables in economics. In this paper we concentrate on matrices that arise in the context of this real-world application. The proposed algorithm is based on the tabu search methodology and incorporates strategies for search intensification and diversification. For search intensification, we experiment with path relinking, a strategy proposed several years ago in connection with tabu search, which has been rarely used in actual implementations. Extensive computational experiments with input-output tables show that the proposed procedure outperforms the best heuristics reported in the literature. Furthermore, the experiments also show the merit of achieving a balance between intensification and diversification in the search.
Given a matrix of weights, the Linear Ordering Problem (LOP) consists of finding a permutation of... more Given a matrix of weights, the Linear Ordering Problem (LOP) consists of finding a permutation of the columns and rows in order to maximize the sum of the weights in the upper triangle. This NP-complete problem can also be formulated in terms of graphs, as finding an acyclic tournament with a maximal sum of arc weights in a complete weighted graph. In this paper we first review the previous methods for the LOP and then propose a heuristic algorithm based on the Variable Neighborhood Search (VNS) methodology. The method combines two neighborhoods for an efficient exploration of the search space. We explore different search strategies and propose a hybrid method in which the VNS is coupled with a short term tabu search for improved outcomes. Our extensive experimentation with both real and random instances shows that the proposed procedure competes with the best-known algorithms in terms of solution quality, and has reasonable computing-time requirements.
Scatter search is a population-based method that has recently been shown to yield promising outco... more Scatter search is a population-based method that has recently been shown to yield promising outcomes for solving combinatorial and nonlinear optimization problems. Based on formulations originally proposed in the 1960s for combining decision rules and problem constraints, such as the surrogate constraint method, scatter search uses strategies for combining solution vectors that have proved effective in a variety of problem settings. In this paper, we present a scatter search implementation designed to find high quality solutions for the linear ordering problem. This NP-hard problem has a significant number of applications in practice. The LOP, for example, is equivalent to the so-called triangulation problem for input-output tables in economics. Our implementation goes beyond a simple exercise on applying scatter search, since it incorporates innovative mechanisms to combine solutions and to create a balance between quality and diversification in the reference set. Extensive computational experiments with input-output tables are used to assess the merit of our procedure.
present case. Fujiwara and colleagues [1] reported that the LMCA compression by the dilated pulmo... more present case. Fujiwara and colleagues [1] reported that the LMCA compression by the dilated pulmonary artery associated with ASD disappeared in postoperative coronary angiograms. These results suggest that markedly dilated pulmonary arteries easily compress the LMCA and cause narrowing, which can improve after ASD closure. On the other hand, it is possible that the pulmonary artery dilatation is not promptly improved after ASD closure because of the pulmonary artery vascular remodeling caused by chronic pulmonary artery hypertension, and as a consequence, the degree of LMCA compression may not change. As extrinsic compression of LMCA may cause angina and lead to malignant arrhythmia or sudden death, a precise assessment for LMCA narrowing is very important [7]. Pina and colleagues [8] used a pressure wire to guide the treatment of the compression of the LMCA secondary to pulmonary artery trunk dilatation. In another report, intravascular ultrasonography showed deformation of the LMCA due to extrinsic compression from a markedly dilated main pulmonary artery [6]. They proposed that these devices might be useful for the decision on coronary revascularization. In the present case, although the patient did not have typical angina, electrocardiography revealed negative T waves in precordial and inferior leads. We decided to perform the bypass surgery for LMCA compression as a safety tether, because it was not certain whether the compression would promptly disappear by ASD closure in a short period of time. In fact, although the degree of LMCA narrowing remained unchanged in cardiac MDCT 2 weeks after the operation, the complete resolution of the narrowing was achieved 4 months later. In conclusion, surgical closure of ASD can relieve LMCA narrowing due to extrinsic compression by the enlarged pulmonary artery. Cardiac MDCT is a useful tool to assess etiology of LMCA narrowing as well as to monitor the postoperative course. References 1. Fujiwara K, Naito Y, Higashiue S, et al. Left main coronary trunk compression by dilated main pulmonary artery in atrial septal defect. Report of three cases. J Thorac Cardiovasc Surg 1992;104:449-52. 2. Pac FA, Cagdas DN, Ulas M, Ozatik MA, Pac M. Left main coronary artery and aortic root compression associated with atrial septal defect and pulmonary hypertension. Int J Cardiol 2007;118:e41-3. 3. Kawut SM, Silvestry FE, Ferrari VA, et al. Extrinsic compression of the left main coronary artery by the pulmonary artery in patients with long-standing pulmonary hypertension. Am J Cardiol 1999;83:984-6, A10. 4. Bijl M, Bronzwaer JG, van Rossum AC, Verheugt FW. Angina pectoris due to left main coronary artery compression in Eisenmenger ductus arteriosus. Am Heart J 1993;125:1767-71. 5. Dubois CL, Dymarkowski S, Van Cleemput J. Compression of the left main coronary artery by the pulmonary artery in a patient with the Eisenmenger syndrome. Eur Heart J 2007;28: 1945. 6. Lindsey JB, Brilakis ES, Banerjee S. Acute coronary syndrome due to extrinsic compression of the left main coronary artery in a patient with severe pulmonary hypertension: successful treatment with percutaneous coronary intervention. Cardio
In this paper we explore the influence of adaptive memory in the performance of heuristic methods... more In this paper we explore the influence of adaptive memory in the performance of heuristic methods when solving a hard combinatorial optimization problem. Specifically, we tackle the adaptation of tabu search and scatter search to the bandwidth minimization problem. It consists of finding a permutation of the rows and columns of a given matrix which keeps the non-zero elements in a band that is as close as possible to the main diagonal. This is a classic problem, introduced in the late sixties, that also has a well-known formulation in terms of graphs. Different exact and heuristic approaches have been proposed for the bandwidth problem. Our contribution consists of two new algorithms, one based on the tabu search methodology and the other based on the scatter search framework. We also present a hybrid method combining both for improved outcomes. Extensive computational testing shows the influence of the different elements in heuristic search, such as neighbourhood definition, local search, combination methods and the use of memory. We compare our proposals with the most recent and advanced methods for this problem, concluding that our new methods can compete with them in speed and running time.
Our aim was to evaluate midterm results in patients who underwent mitral valve repair (MVR) for i... more Our aim was to evaluate midterm results in patients who underwent mitral valve repair (MVR) for ischermic mitral regurgitation (IMR) in our most recent experience. From March 2006 to March 2008, 105 patients underwent MVR for IMR. Mean IMR grade was 2.6 ± 1.1, with 46 patients having ≤2/4 and 59 ≥3/4. Five patients (4.8%) died within first month; Two-year freedom from death any cause was 85.5% ± 3.8, freedom from cardiac death was 88.7% ± 3.4. NYHA Class of the survivors was 1.3 ± 0.6, with 3 patients in NYHA Class III. Freedom from death any cause and NYHA Class III-IV was 78.6% ± 4.6. IMR grade decreased from 2.6 ± 1.1 to 0.1 ± 0.3 at the discharge and to 0.5 ± 0.3 after a mean of 7 ± 4 months, with no patient with IMR grade 3/4 or 4/4. MVR for IMR should be performed in patients with moderate-or-more IMR grade or when the MV is excessively dilated, to achieve good midterm results.
Qttestliò - V 7, n.° 3 (setembre 1983) Definiciones. Sea G=(V,E) un grafo ro dirigido, donde V es... more Qttestliò - V 7, n.° 3 (setembre 1983) Definiciones. Sea G=(V,E) un grafo ro dirigido, donde V es un conjunto de n vértices y E es un conjunto de aristas con costes с no negativos asocia e dos. El grado de un vértice es el número de aristas incidentes con él. Un vértice es par ...
The Capacitated Clustering Problem (CCP) consists of forming a specified number of clusters or gr... more The Capacitated Clustering Problem (CCP) consists of forming a specified number of clusters or groups from a set of elements in such a way that the sum of the weights of the elements in each cluster is within some capacity limits, and the sum of the benefits between the pairs of elements in the same cluster is maximized. This problem-which has been recently tackled with a GRASP/VNS approach-arises in the context of facility planners at mail processing and distribution. We propose a tabu search and several GRASP variants to find high quality solutions to this NP-hard problem. These variants are based on several neighborhoods, including a new one, in which we implement a one-for-two swapping strategy. We also hybridize both methodologies to achieve improved outcomes. The Maximally Diverse Grouping Problem (MDGP) is a special case of the CCP in which all the elements have a weight of one unit. This problem has been recently studied in the academic context when forming student groups, and we adapt the best method reported in the literature, a tabu search with strategic oscillation (TS_SO), to the CCP. Our empirical study with 50 large instances shows the superiority of the new GRASP with tabu search for the CCP with respect to both the previous GRASP/VNS approach and the adapted TS_SO.
Scatter search is a population-based method that has recently been shown to yield promising outco... more Scatter search is a population-based method that has recently been shown to yield promising outcomes for solving combinatorial and nonlinear optimization problems. Based on formulations originally proposed in the 1960s for combining decision rules and problem constraints, such as the surrogate constraint method, scatter search uses strategies for combining solution vectors that have proved effective in a variety of problem settings. In this paper, we present a scatter search implementation designed to find high quality solutions for the NP-hard linear ordering problem, which has a significant number of applications in practice. The LOP, for example, is equivalent to the so-called triangulation problem for input-output tables in economics. Our implementation goes beyond a simple exercise on applying scatter search, by incorporating innovative mechanisms to combine solutions and to create a balance between quality and diversification in the reference set. We also use a tracking process that generates solution statistics disclosing the nature of combinations and the ranks of antecedent solutions that produced the best final solutions. Our extensive computational experiments with more than 300 instances establishes the effectiveness of our procedure in relation to those previously identified to be best.
In this paper we present ARC a computerized system developed for urban garbage collection. The pa... more In this paper we present ARC a computerized system developed for urban garbage collection. The package is intended to help the planners in the design of efficient collection routes and to facilitate the study and evaluation of alternatives concerning issues such as the type and number of vehicles, frequency of collection and type and location of refuse containers. The final product is a "user friendly" system designed to be used by the planners without outside assistance.
Revista Española de Cardiología (English Edition), 2005
Operative risk stratification scales for use in cardiac surgery have been developed for patients ... more Operative risk stratification scales for use in cardiac surgery have been developed for patients who undergo procedures using extracorporeal circulation. The aims of the present study were to investigate the use of six preoperative risk stratification scales in patients undergoing beating-heart surgery and to identify risk factors for major complications and mortality in our group of patients who underwent revascularization using this approach. Between January 1997 and December 2002, we performed 762 coronary artery bypass operations on the beating heart; 61 patients suffered major complications (8%) and 25 died (3.3%). Risk factors for major complications and death were identified using logistic regression analysis of prospectively collected data. The following risk scores were calculated for each patient: Parsonnet 95, Parsonnet 97, Euroscore, Cleveland, Ontario, and French. Receiver operating characteristic curves were used to compare the ability of each scale to predict mortality and major complications. In our patient group, the preoperative variables associated with increased risk were: need for cardiopulmonary resuscitation, renal dysfunction, peripheral vasculopathy, and the presence of severe left main coronary artery disease, three-vessel disease, or an impaired ejection fraction. Mortality and major complications were best predicted by the Parsonnet 95 and Euroscore scales.
Operations Research/Computer Science Interfaces Series
... Estadistica e IO, Facultad de Matemdticas, Universitat de Valencia, Dr. Moliner 50, 46100 Bur... more ... Estadistica e IO, Facultad de Matemdticas, Universitat de Valencia, Dr. Moliner 50, 46100 Burjassot, Valencia, Spain, {rafael.marti, Vicente.campos}@uv ... Barnes and Vanston (1981) reported results on three branch and bound algorithms of instances with up 20 jobs and Laguna ...
In this paper we present two new heuristic procedures for the Capacitated Vehicle Routing Problem... more In this paper we present two new heuristic procedures for the Capacitated Vehicle Routing Problem (CVRP). The first one solves the problem from scratch, while the second one uses the information provided by a strong linear relaxation of the original problem. This second algorithm is designed to be used in a branch and cut approach to solve to optimality CVRP
Alrstraeg The Vehicle Routing Problem is a well known, and hard, combinatorial problem, whose pol... more Alrstraeg The Vehicle Routing Problem is a well known, and hard, combinatorial problem, whose polyhedral structure has deserved little attention. In this paper we consider the particular case in which all the demands are equal (since in the general case the associated polytope may be empty). From a known formulation of the problem we obtain the dimension of the corresponding polytope and we study the facetial properties of every inequality in it.
The bandwidth of a matrix { } ij a A = is defined as the maximum absolute difference between i an... more The bandwidth of a matrix { } ij a A = is defined as the maximum absolute difference between i and j for which 0 ≠ ij a. The problem of reducing the bandwidth of a matrix consists of finding a permutation of the rows and columns that keeps the nonzero elements in a band that is as close as possible to the main diagonal of the matrix. This NP-complete problem can also be formulated as a labeling of vertices on a graph, where edges are the nonzero elements of the corresponding symmetrical matrix. Many bandwidth reduction algorithms have been developed since the 1960s and applied to structural engineering, fluid dynamics and network analysis. For the most part, these procedures do not incorporate metaheuristic elements, which is one of the main goals of our current development. Another equally important goal is to design and test a special type of candidate list strategy and a move mechanism to be embedded in a tabu search procedure for the bandwidth reduction problem. This candidate list strategy accelerates the selection of a move in the neighborhood of the current solution in any given iteration. Our extensive experimentation shows that the proposed procedure outperforms the best-known algorithms in terms of solution quality consuming a reasonable computational effort.
In this article we first review previous exact approaches as well as theoretical contributions fo... more In this article we first review previous exact approaches as well as theoretical contributions for the problem of reducing the bandwidth of a matrix. This problem consists of finding a permutation of the rows and columns of a given matrix which keeps the non-zero elements in a band that is as close as possible to the main diagonal. This NP-complete problem can also be formulated as a labeling of vertices on a graph, where edges are the non-zero elements of the corresponding symmetrical matrix. We propose a new branch and bound algorithm and new expressions for known lower bounds for this problem. Empirical results with a collection of previously reported instances indicate that the proposed algorithm compares favourably to previous methods. * Research partially supported by the Ministerio de Educación y Ciencia (ref. TIC2003-C05-01) and by the Agencia Valenciana de Ciencia y Tecnologia (ref. GRUPOS03/189).
In this article we develop a greedy randomized adaptive search procedure (GRASP) for the problem ... more In this article we develop a greedy randomized adaptive search procedure (GRASP) for the problem of reducing the bandwidth of a matrix. This problem consists of finding a permutation of the rows and columns of a given matrix, which keeps the nonzero elements in a band that is as close as possible to the main diagonal. The proposed method may be coupled with a Path Relinking strategy to search for improved outcomes. Empirical results indicate that the proposed GRASP implementation compares favourably to classical heuristics. GRASP with Path Relinking is also found to be competitive with a recently published tabu search algorithm that is considered one of the best currently available for bandwidth minimization.
In this paper, we develop a new heuristic procedure for the linear ordering problem (LOP). This N... more In this paper, we develop a new heuristic procedure for the linear ordering problem (LOP). This NP-hard problem has a significant number of applications in practice. The LOP, for example, is equivalent to the so-called triangulation problem for input-output tables in economics. In this paper we concentrate on matrices that arise in the context of this real-world application. The proposed algorithm is based on the tabu search methodology and incorporates strategies for search intensification and diversification. For search intensification, we experiment with path relinking, a strategy proposed several years ago in connection with tabu search, which has been rarely used in actual implementations. Extensive computational experiments with input-output tables show that the proposed procedure outperforms the best heuristics reported in the literature. Furthermore, the experiments also show the merit of achieving a balance between intensification and diversification in the search.
Given a matrix of weights, the Linear Ordering Problem (LOP) consists of finding a permutation of... more Given a matrix of weights, the Linear Ordering Problem (LOP) consists of finding a permutation of the columns and rows in order to maximize the sum of the weights in the upper triangle. This NP-complete problem can also be formulated in terms of graphs, as finding an acyclic tournament with a maximal sum of arc weights in a complete weighted graph. In this paper we first review the previous methods for the LOP and then propose a heuristic algorithm based on the Variable Neighborhood Search (VNS) methodology. The method combines two neighborhoods for an efficient exploration of the search space. We explore different search strategies and propose a hybrid method in which the VNS is coupled with a short term tabu search for improved outcomes. Our extensive experimentation with both real and random instances shows that the proposed procedure competes with the best-known algorithms in terms of solution quality, and has reasonable computing-time requirements.
Scatter search is a population-based method that has recently been shown to yield promising outco... more Scatter search is a population-based method that has recently been shown to yield promising outcomes for solving combinatorial and nonlinear optimization problems. Based on formulations originally proposed in the 1960s for combining decision rules and problem constraints, such as the surrogate constraint method, scatter search uses strategies for combining solution vectors that have proved effective in a variety of problem settings. In this paper, we present a scatter search implementation designed to find high quality solutions for the linear ordering problem. This NP-hard problem has a significant number of applications in practice. The LOP, for example, is equivalent to the so-called triangulation problem for input-output tables in economics. Our implementation goes beyond a simple exercise on applying scatter search, since it incorporates innovative mechanisms to combine solutions and to create a balance between quality and diversification in the reference set. Extensive computational experiments with input-output tables are used to assess the merit of our procedure.
present case. Fujiwara and colleagues [1] reported that the LMCA compression by the dilated pulmo... more present case. Fujiwara and colleagues [1] reported that the LMCA compression by the dilated pulmonary artery associated with ASD disappeared in postoperative coronary angiograms. These results suggest that markedly dilated pulmonary arteries easily compress the LMCA and cause narrowing, which can improve after ASD closure. On the other hand, it is possible that the pulmonary artery dilatation is not promptly improved after ASD closure because of the pulmonary artery vascular remodeling caused by chronic pulmonary artery hypertension, and as a consequence, the degree of LMCA compression may not change. As extrinsic compression of LMCA may cause angina and lead to malignant arrhythmia or sudden death, a precise assessment for LMCA narrowing is very important [7]. Pina and colleagues [8] used a pressure wire to guide the treatment of the compression of the LMCA secondary to pulmonary artery trunk dilatation. In another report, intravascular ultrasonography showed deformation of the LMCA due to extrinsic compression from a markedly dilated main pulmonary artery [6]. They proposed that these devices might be useful for the decision on coronary revascularization. In the present case, although the patient did not have typical angina, electrocardiography revealed negative T waves in precordial and inferior leads. We decided to perform the bypass surgery for LMCA compression as a safety tether, because it was not certain whether the compression would promptly disappear by ASD closure in a short period of time. In fact, although the degree of LMCA narrowing remained unchanged in cardiac MDCT 2 weeks after the operation, the complete resolution of the narrowing was achieved 4 months later. In conclusion, surgical closure of ASD can relieve LMCA narrowing due to extrinsic compression by the enlarged pulmonary artery. Cardiac MDCT is a useful tool to assess etiology of LMCA narrowing as well as to monitor the postoperative course. References 1. Fujiwara K, Naito Y, Higashiue S, et al. Left main coronary trunk compression by dilated main pulmonary artery in atrial septal defect. Report of three cases. J Thorac Cardiovasc Surg 1992;104:449-52. 2. Pac FA, Cagdas DN, Ulas M, Ozatik MA, Pac M. Left main coronary artery and aortic root compression associated with atrial septal defect and pulmonary hypertension. Int J Cardiol 2007;118:e41-3. 3. Kawut SM, Silvestry FE, Ferrari VA, et al. Extrinsic compression of the left main coronary artery by the pulmonary artery in patients with long-standing pulmonary hypertension. Am J Cardiol 1999;83:984-6, A10. 4. Bijl M, Bronzwaer JG, van Rossum AC, Verheugt FW. Angina pectoris due to left main coronary artery compression in Eisenmenger ductus arteriosus. Am Heart J 1993;125:1767-71. 5. Dubois CL, Dymarkowski S, Van Cleemput J. Compression of the left main coronary artery by the pulmonary artery in a patient with the Eisenmenger syndrome. Eur Heart J 2007;28: 1945. 6. Lindsey JB, Brilakis ES, Banerjee S. Acute coronary syndrome due to extrinsic compression of the left main coronary artery in a patient with severe pulmonary hypertension: successful treatment with percutaneous coronary intervention. Cardio
In this paper we explore the influence of adaptive memory in the performance of heuristic methods... more In this paper we explore the influence of adaptive memory in the performance of heuristic methods when solving a hard combinatorial optimization problem. Specifically, we tackle the adaptation of tabu search and scatter search to the bandwidth minimization problem. It consists of finding a permutation of the rows and columns of a given matrix which keeps the non-zero elements in a band that is as close as possible to the main diagonal. This is a classic problem, introduced in the late sixties, that also has a well-known formulation in terms of graphs. Different exact and heuristic approaches have been proposed for the bandwidth problem. Our contribution consists of two new algorithms, one based on the tabu search methodology and the other based on the scatter search framework. We also present a hybrid method combining both for improved outcomes. Extensive computational testing shows the influence of the different elements in heuristic search, such as neighbourhood definition, local search, combination methods and the use of memory. We compare our proposals with the most recent and advanced methods for this problem, concluding that our new methods can compete with them in speed and running time.
Our aim was to evaluate midterm results in patients who underwent mitral valve repair (MVR) for i... more Our aim was to evaluate midterm results in patients who underwent mitral valve repair (MVR) for ischermic mitral regurgitation (IMR) in our most recent experience. From March 2006 to March 2008, 105 patients underwent MVR for IMR. Mean IMR grade was 2.6 ± 1.1, with 46 patients having ≤2/4 and 59 ≥3/4. Five patients (4.8%) died within first month; Two-year freedom from death any cause was 85.5% ± 3.8, freedom from cardiac death was 88.7% ± 3.4. NYHA Class of the survivors was 1.3 ± 0.6, with 3 patients in NYHA Class III. Freedom from death any cause and NYHA Class III-IV was 78.6% ± 4.6. IMR grade decreased from 2.6 ± 1.1 to 0.1 ± 0.3 at the discharge and to 0.5 ± 0.3 after a mean of 7 ± 4 months, with no patient with IMR grade 3/4 or 4/4. MVR for IMR should be performed in patients with moderate-or-more IMR grade or when the MV is excessively dilated, to achieve good midterm results.
Qttestliò - V 7, n.° 3 (setembre 1983) Definiciones. Sea G=(V,E) un grafo ro dirigido, donde V es... more Qttestliò - V 7, n.° 3 (setembre 1983) Definiciones. Sea G=(V,E) un grafo ro dirigido, donde V es un conjunto de n vértices y E es un conjunto de aristas con costes с no negativos asocia e dos. El grado de un vértice es el número de aristas incidentes con él. Un vértice es par ...
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Papers by Vicente Campos