Jorge Vera - Academia.edu (original) (raw)
Papers by Jorge Vera
... Autor: Rojas Vera, Jorge; Jalilie Elías, Alfredo; Torres Rojas, Luis. Título: Estudio de paci... more ... Autor: Rojas Vera, Jorge; Jalilie Elías, Alfredo; Torres Rojas, Luis. Título: Estudio de pacientes críticamente enfermos con lupus eritematoso sistémico en una unidad de cuidados intensivos / Study of critical patients with systemic lupus erythematosus in intensive care unit. ...
ABSTRACT Definitions are given of basic concepts for describing architectures of systems whose be... more ABSTRACT Definitions are given of basic concepts for describing architectures of systems whose behavior (or executions) can be modelled as a set of events which bear certain causal and timing relationships to one another. These relations between events are partial orderings, and the model of system behavior is called the poset (partially ordered event set) model. We define three fundamental concepts: (i) system component, (ii) architecture, and (iii) refinement mapping between architectures. The concept definitions use elementary mathematics of sets and functions, and are independent of any computer language for architectures. To illustrate the concepts, an executable architecture definition language is described and used to give examples of system components, architectures, and related architectures. A key feature of the language is event pattern which provides the expressive power needed to specify many different kinds of distributed and realtime systems, including systems with asynchronous c...
A conic linear system is a system of the form
This paper deals with two main problems in forest harvesting. The first is that of selecting the ... more This paper deals with two main problems in forest harvesting. The first is that of selecting the locations for the machinery to haul logs from the points where they are felled to the roadside. The second consists in designing the access road network connecting the existing road network with the points where machinery is installed. Their combination induces a very important and difficult problem to solve in forest harvesting. It can be formulated as a combination of two difficult optimization problems: a plant location problem and a fixed charge network flow problem. In this paper, we propose a solution approach based on tabu search. The proposed heuristic includes several enhancements of the basic tabu search framework. The main difficulty lies in evaluating neighboring solutions, which involves decisions related to location of machinery and to road network arcs. Hence, the neighborhood is more complex than in typical applications of metaheuristics. Minimum spanning tree algorithms and Steiner tree heuristics are used to deal with this problem. Numerical results indicate that the heuristic approach is very 2 attractive and leads to better solutions than those provided by state-of-the-art integer programming codes in limited computation times, with solution times significantly smaller. The numerical results do not vary too much when typical parameters such as the tabu tenure are modified, except for the dimension of neighborhood.
METHODS Clinical material. RBC uptake studies. Solutions. Reagents. Preparation of erythrocytes. ... more METHODS Clinical material. RBC uptake studies. Solutions. Reagents. Preparation of erythrocytes. 3OMG uptake. Use of barbiturates. GLUT1 genomic analyses. Statistical analyses. RESULTS Time course of 3OMG influx in the presence and absence ofbarbiturates. Phenobarbital or pentobarbital (10 mmol/L) inhibition of zero-trans3OMG influx. Influence of barbiturate concentration (0‐10 mmol/L) on zero-trans3OMG influx. Kinetic characteristics of pentobarbital inhibition in a patientwith
We study urban traffic equilibrium involving three classes of agents: car users, bus users or pas... more We study urban traffic equilibrium involving three classes of agents: car users, bus users or passengers and bus operators. A partially unregulated transit system is assumed, where bus fares are exogenously determined by municipal or transportation authorities, but bus operators are allowed to choose the routes where they offer service. The paper deals specifically with the bus operators submodel, for
Siam Journal on Optimization, 1996
Mathematics of Operations Research, 2003
Condition numbers based on the "distance to ill-posedness" d have been shown to play a crucial ro... more Condition numbers based on the "distance to ill-posedness" d have been shown to play a crucial role in the theoretical complexity of solving convex optimization models. In this paper, we present two algorithms and corresponding complexity analysis for computing estimates of d for a finite-dimensional convex feasibility problem P d in standard primal form: find x that satisfies
Siam Journal on Optimization, 1999
A convex optimization problem in conic linear form is an optimization problem of the form
Transportation Research Part B: Methodological, 1993
We study urban traffic equilibrium involving three classes of agents: car users, bus users or pas... more We study urban traffic equilibrium involving three classes of agents: car users, bus users or passengers and bus operators. A partially unregulated transit system is assumed, where bus fares are exogenously determined by municipal or transportation authorities, but bus operators are allowed to choose the routes where they offer service. The paper deals specifically with the bus operators submodel, for
Pediatric Research, 1999
Barbiturates are known to inhibit glucose transport mediated by the facilitative sugar transporte... more Barbiturates are known to inhibit glucose transport mediated by the facilitative sugar transporter GLUTI. We have studied such inhibition in children with GLUT1-deficiency. Zero-trans influx of 14C-labeled 3-O-methyl glucose (3OMG) into erythrocytes of patients (n = 3) was 35% of controls (n = 6). Preincubation with 10 mM phenobarbital or pentobarbital reduced patients' 30MG influx to 17%. In patients and controls, preincubation with barbiturates significantly decreased Vmax in a dose-dependent manner (for pentobarbital, IC50 = 0.84 mM, patient 2). The apparent Km in individuals remained largely unchanged. Three-OMG influx without preincubation resulted in a stronger inhibition at lower barbiturate concentrations. The patients' data are discussed in the light of individual missense mutations (patient 1: R126L and K256V; patient 2: T310I; patient 3: S66F) in the GLUTI gene. In conclusion, in controls and patients with GLUT1-deficiency barbiturates interact with GLUT1, lowering its intrinsic activity. The use of barbiturates in this condition for anesthesia or as anticonvulsants could therefore potentially aggravate the existing glucose transport defect and may put these patients at increased risk.
Mathematical Programming, 1998
In this paper we study the complexity of solving linear programs in finite precision arithmetic. ... more In this paper we study the complexity of solving linear programs in finite precision arithmetic. This is the normal setup in scientific computation, as digital computers work in finite precision. We analyze two aspects of the complexity: one is the number of arithmetic operations required to solve the problem approximately, and the other is the working precision required to carry
European Journal of Operational Research, 2006
This paper describes a strategy for defining priorities for the branching variables in a Branch a... more This paper describes a strategy for defining priorities for the branching variables in a Branch and Bound algorithm. The strategy is based on shape information about the polyhedron over which we are optimizing. This information is related to measures of the integer width, as provided by the so called ''Flatness Theorem''. Our selection rule uses that knowledge to define branching priorities on the variables. Computational results with simulated small to medium size integer problems are presented, as well with multi-knapsack problems. These show savings of about 40% in CPU time, as well as in nodes generated in the search tree, and compare favorably with respect to other standard branching rules.
European Journal of Operational Research, 2007
This paper deals with two main problems in forest harvesting. The first is that of selecting the ... more This paper deals with two main problems in forest harvesting. The first is that of selecting the locations for the machinery to haul logs from the points where they are felled to the roadside. The second consists in designing the access road network connecting the existing road network with the points where machinery is installed. Their combination induces a very important and difficult problem to solve in forest harvesting. It can be formulated as a combination of two difficult optimization problems: a plant location problem and a fixed charge network flow problem. In this paper, we propose a solution approach based on tabu search. The proposed heuristic includes several enhancements of the basic tabu search framework. The main difficulty lies in evaluating neighboring solutions, which involves decisions related to location of machinery and to road network arcs. Hence, the neighborhood is more complex than in typical applications of metaheuristics. Minimum spanning tree algorithms and Steiner tree heuristics are used to deal with this problem. Numerical results indicate that the heuristic approach is very 2 attractive and leads to better solutions than those provided by state-of-the-art integer programming codes in limited computation times, with solution times significantly smaller. The numerical results do not vary too much when typical parameters such as the tabu tenure are modified, except for the dimension of neighborhood.
EURASIP Journal on Advances in Signal Processing, 2009
Operations Research, 1991
... Autor: Rojas Vera, Jorge; Jalilie Elías, Alfredo; Torres Rojas, Luis. Título: Estudio de paci... more ... Autor: Rojas Vera, Jorge; Jalilie Elías, Alfredo; Torres Rojas, Luis. Título: Estudio de pacientes críticamente enfermos con lupus eritematoso sistémico en una unidad de cuidados intensivos / Study of critical patients with systemic lupus erythematosus in intensive care unit. ...
ABSTRACT Definitions are given of basic concepts for describing architectures of systems whose be... more ABSTRACT Definitions are given of basic concepts for describing architectures of systems whose behavior (or executions) can be modelled as a set of events which bear certain causal and timing relationships to one another. These relations between events are partial orderings, and the model of system behavior is called the poset (partially ordered event set) model. We define three fundamental concepts: (i) system component, (ii) architecture, and (iii) refinement mapping between architectures. The concept definitions use elementary mathematics of sets and functions, and are independent of any computer language for architectures. To illustrate the concepts, an executable architecture definition language is described and used to give examples of system components, architectures, and related architectures. A key feature of the language is event pattern which provides the expressive power needed to specify many different kinds of distributed and realtime systems, including systems with asynchronous c...
A conic linear system is a system of the form
This paper deals with two main problems in forest harvesting. The first is that of selecting the ... more This paper deals with two main problems in forest harvesting. The first is that of selecting the locations for the machinery to haul logs from the points where they are felled to the roadside. The second consists in designing the access road network connecting the existing road network with the points where machinery is installed. Their combination induces a very important and difficult problem to solve in forest harvesting. It can be formulated as a combination of two difficult optimization problems: a plant location problem and a fixed charge network flow problem. In this paper, we propose a solution approach based on tabu search. The proposed heuristic includes several enhancements of the basic tabu search framework. The main difficulty lies in evaluating neighboring solutions, which involves decisions related to location of machinery and to road network arcs. Hence, the neighborhood is more complex than in typical applications of metaheuristics. Minimum spanning tree algorithms and Steiner tree heuristics are used to deal with this problem. Numerical results indicate that the heuristic approach is very 2 attractive and leads to better solutions than those provided by state-of-the-art integer programming codes in limited computation times, with solution times significantly smaller. The numerical results do not vary too much when typical parameters such as the tabu tenure are modified, except for the dimension of neighborhood.
METHODS Clinical material. RBC uptake studies. Solutions. Reagents. Preparation of erythrocytes. ... more METHODS Clinical material. RBC uptake studies. Solutions. Reagents. Preparation of erythrocytes. 3OMG uptake. Use of barbiturates. GLUT1 genomic analyses. Statistical analyses. RESULTS Time course of 3OMG influx in the presence and absence ofbarbiturates. Phenobarbital or pentobarbital (10 mmol/L) inhibition of zero-trans3OMG influx. Influence of barbiturate concentration (0‐10 mmol/L) on zero-trans3OMG influx. Kinetic characteristics of pentobarbital inhibition in a patientwith
We study urban traffic equilibrium involving three classes of agents: car users, bus users or pas... more We study urban traffic equilibrium involving three classes of agents: car users, bus users or passengers and bus operators. A partially unregulated transit system is assumed, where bus fares are exogenously determined by municipal or transportation authorities, but bus operators are allowed to choose the routes where they offer service. The paper deals specifically with the bus operators submodel, for
Siam Journal on Optimization, 1996
Mathematics of Operations Research, 2003
Condition numbers based on the "distance to ill-posedness" d have been shown to play a crucial ro... more Condition numbers based on the "distance to ill-posedness" d have been shown to play a crucial role in the theoretical complexity of solving convex optimization models. In this paper, we present two algorithms and corresponding complexity analysis for computing estimates of d for a finite-dimensional convex feasibility problem P d in standard primal form: find x that satisfies
Siam Journal on Optimization, 1999
A convex optimization problem in conic linear form is an optimization problem of the form
Transportation Research Part B: Methodological, 1993
We study urban traffic equilibrium involving three classes of agents: car users, bus users or pas... more We study urban traffic equilibrium involving three classes of agents: car users, bus users or passengers and bus operators. A partially unregulated transit system is assumed, where bus fares are exogenously determined by municipal or transportation authorities, but bus operators are allowed to choose the routes where they offer service. The paper deals specifically with the bus operators submodel, for
Pediatric Research, 1999
Barbiturates are known to inhibit glucose transport mediated by the facilitative sugar transporte... more Barbiturates are known to inhibit glucose transport mediated by the facilitative sugar transporter GLUTI. We have studied such inhibition in children with GLUT1-deficiency. Zero-trans influx of 14C-labeled 3-O-methyl glucose (3OMG) into erythrocytes of patients (n = 3) was 35% of controls (n = 6). Preincubation with 10 mM phenobarbital or pentobarbital reduced patients' 30MG influx to 17%. In patients and controls, preincubation with barbiturates significantly decreased Vmax in a dose-dependent manner (for pentobarbital, IC50 = 0.84 mM, patient 2). The apparent Km in individuals remained largely unchanged. Three-OMG influx without preincubation resulted in a stronger inhibition at lower barbiturate concentrations. The patients' data are discussed in the light of individual missense mutations (patient 1: R126L and K256V; patient 2: T310I; patient 3: S66F) in the GLUTI gene. In conclusion, in controls and patients with GLUT1-deficiency barbiturates interact with GLUT1, lowering its intrinsic activity. The use of barbiturates in this condition for anesthesia or as anticonvulsants could therefore potentially aggravate the existing glucose transport defect and may put these patients at increased risk.
Mathematical Programming, 1998
In this paper we study the complexity of solving linear programs in finite precision arithmetic. ... more In this paper we study the complexity of solving linear programs in finite precision arithmetic. This is the normal setup in scientific computation, as digital computers work in finite precision. We analyze two aspects of the complexity: one is the number of arithmetic operations required to solve the problem approximately, and the other is the working precision required to carry
European Journal of Operational Research, 2006
This paper describes a strategy for defining priorities for the branching variables in a Branch a... more This paper describes a strategy for defining priorities for the branching variables in a Branch and Bound algorithm. The strategy is based on shape information about the polyhedron over which we are optimizing. This information is related to measures of the integer width, as provided by the so called ''Flatness Theorem''. Our selection rule uses that knowledge to define branching priorities on the variables. Computational results with simulated small to medium size integer problems are presented, as well with multi-knapsack problems. These show savings of about 40% in CPU time, as well as in nodes generated in the search tree, and compare favorably with respect to other standard branching rules.
European Journal of Operational Research, 2007
This paper deals with two main problems in forest harvesting. The first is that of selecting the ... more This paper deals with two main problems in forest harvesting. The first is that of selecting the locations for the machinery to haul logs from the points where they are felled to the roadside. The second consists in designing the access road network connecting the existing road network with the points where machinery is installed. Their combination induces a very important and difficult problem to solve in forest harvesting. It can be formulated as a combination of two difficult optimization problems: a plant location problem and a fixed charge network flow problem. In this paper, we propose a solution approach based on tabu search. The proposed heuristic includes several enhancements of the basic tabu search framework. The main difficulty lies in evaluating neighboring solutions, which involves decisions related to location of machinery and to road network arcs. Hence, the neighborhood is more complex than in typical applications of metaheuristics. Minimum spanning tree algorithms and Steiner tree heuristics are used to deal with this problem. Numerical results indicate that the heuristic approach is very 2 attractive and leads to better solutions than those provided by state-of-the-art integer programming codes in limited computation times, with solution times significantly smaller. The numerical results do not vary too much when typical parameters such as the tabu tenure are modified, except for the dimension of neighborhood.
EURASIP Journal on Advances in Signal Processing, 2009
Operations Research, 1991