José Luis Pérez de la Cruz

Multiobjective A * search with consistent heuristics

The article describes and analyzes NAMOA*, an algorithm for multiobjective heuristic graph search problems. The algorithm is presented as an extension of A*, an admissible scalar shortest path algorithm. Under consistent heuristics A* is known to improve its efficiency with more informed heuristics, and to be optimal over the class of admissible algorithms in terms of the set of expanded nodes and the number of node expansions. Equivalent beneficial properties are shown to prevail in the new algorithm.

Effect of DT-TX 30, a combined thromboxane synthase inhibitor and thromboxane receptor antagonist, on retinal vascularity in experimental diabetes mellitus.

Combined thromboxane synthase inhibitors and thromboxane receptors antagonists have been shown to have a beneficial effect on different models of thrombosis in vivo. We studied the action of one of these compounds (DT-TX 30) compared with dazoxiben (a thromboxane synthase inhibitor) on retinal vascularity in streptozotocin-diabetic rats. Ten nondiabetic animals were treated with isotonic saline, 30 (10 animals per group) were given 0.4, 4, and 8 mg kg(-1) per day of DT-TX 30 (p.o.) and 30 (10 animals per group) were given 10, 50, and 100 mg kg(-1) per day of dazoxiben (p.o.) over a 90-day study period. DT-TX 30 caused a dose-dependent decrease of platelet aggregation and thromboxane B2 synthesis. There was an increase of 9, 65, and 166% in the synthesis of prostacyclin after treatment with 0.4, 4, and 8 mg kg(-1) per day, respectively. Retinal vascularity increased in 51, 72, and 182% of animals in response to the three doses used. Synthesis of prostacyclin and the degree of retinal vascularity showed a linear correlation (r2=0.6528,p<0.00001). Dazoxiben, at doses that inhibited thromboxane synthesis as much as DT-TX 30, increased prostacyclin production and retinal vascularity with less potency than DT-TX 30. In conclusion, the antagonism of thromboxane receptors may be an important additional effect to the inhibition of thromboxane synthase in the prevention of ischemic retinal lesions in experimental diabetes.

TAPLI: An adaptive web-based learning environment for Linear Programming

In this paper we present TAPLI, an adaptive web-based learning environment for Linear Programming. TAPLI is in fact a set of adaptive tools offered in a web-based learning environment: a) an adaptive hypermedia component, that is responsible of presenting the learning contents; b) a testing component, based on the SIETTE system (that implements Computerized Adaptive Tests using Item Response Theory as inference machine to estimate the student’s knowledge level); and c) a drill-and-practice component, which generates exercises adapted to the student’s knowledge level, and which coaches students while solving the problems posed by the system, offering guidance, support, help and feedback. The estimation of the student’s knowledge level made by SIETTE is used by TAPLI as a basis to provide adaptation at all stages of the learning process: while learning the contents, while making tests, when being proposed an exercise and while solving it. Additionally the system provides an open student model that allows to inspect in detail the state of his/her knowledge at any time and to change the learning goals at any moment during the interaction with the system.

Multiobjective shortest path problems with lexicographic goal-based preferences

Multiobjective shortest path problems are computationally harder than single objective ones. In particular, execution time is an important limiting factor in exact multiobjective search algorithms. This paper explores the possibility of improving search performance in those cases where the interesting portion of the Pareto front can be initially bounded. We introduce a new exact label-setting algorithm that returns the subset of Pareto optimal paths that satisfy a set of lexicographic goals, or the subset that minimizes deviation from goals if these cannot be fully satisfied. Formal proofs on the correctness of the algorithm are provided. We also show that the algorithm always explores a subset of the labels explored by a full Pareto search. The algorithm is evaluated over a set of problems with three objectives, showing a performance improvement of up to several orders of magnitude as goals become more restrictive.

An elementary fuzzy programming language

In this paper, we define a fuzzy imperative programming language (called L), powerful enough to express crisp and fuzzy algorithms. Its small instruction set is designed to enhance readability, and it is proved before that the class of functions that can be programmed in L is equivalent to the class of functions computed by a W-Turing machine and to the W-recursive functions. The language is defined by means of an attribute grammar, and we present some examples of programs and their execution. A compiler has been built for the language, whose features are briefly described.

An empirical comparison of some multiobjective graph search algorithms

This paper compares empirically the performance in time and space of two multiobjective graph search algorithms, MOA* and NAMOA*. Previous theoretical work has shown that NAMOA* is never worse than MOA*. Now, a statistical analysis is presented on the relative performance of both algorithms in space and time over sets of randomly generated problems.

The Role of Multicriteria Problem Solving in Design

The paper analyses the application of multicriteria problem solving methods to design in the light of KLDE 0, a Knowledge Level theory of design. The pros and cons of three usual multicriteria decision rules applied to the resolution of incompleteness, inconsistency, imprecision, and ambiguity is discussed with the aid of a simple example.

A case of pathology in multiobjective heuristic search

This article considers the performance of the MOA* multiobjective search algorithm with heuristic information. It is shown that in certain cases blind search can be more efficient than perfectly informed search, in terms of both node and label expansions. A class of simple graph search problems is defined for which the number of nodes grows linearly with problem size and the number of nondominated labels grows quadratically. It is proved that for these problems the number of node expansions performed by blind MOA* grows linearly with problem size, while the number of such expansions performed with a perfectly informed heuristic grows quadratically. It is also proved that the number of label expansions grows quadratically in the blind case and cubically in the informed case.

Heuristic multiobjective search for hazmat transportation problems

This paper describes the application of multiobjective heuristic search algorithms to the problem of hazardous material (hazmat) transportation. The selection of optimal routes inherently involves the consideration of multiple conflicting objectives. These include the minimization of risk (e.g. the exposure of the population to hazardous substances in case of accident), transportation cost, time, or distance. Multiobjective analysis is an important tool in hazmat transportation decision making. This paper evaluates the application of multiobjective heuristic search techniques to hazmat route planning. The efficiency of existing algorithms is known to depend on factors like the number of objectives and their correlations. The use of an informed multiobjective heuristic function is shown to significantly improve efficiency in problems with two and three objectives. Test problems are defined over random graphs and over a real road map.

Preoperative levosimendan. A new way for organoprotection.

Preoperative use of levosimendan in cardiac surgery patients is one of the most attractive therapeutic alternatives in subjects with left or right ventricular dysfunction. Our review explores the pharmacological bases and clinical evidence for the use of levosimendan, with the intention of making a series of recommendations regarding its use in preoperative optimization prior to cardiac surgery. We carried out a survey of 102 Spanish anesthesiologists in order to shed light on the grey areas regarding the use of this drug prior to surgery. Our findings suggest that levosimendan is recommended for patients with severe left or right ventricular dysfunction, moderate left ventricular dysfunction in which Intra-aortic Balloon Counterpulsation (IABC) is necessary and severe pulmonary hypertension. Administration of levosimendan prior to surgical cardiac intervention without an initial bolus reduces the likelihood of complications.