Determining what sets of trees can be the clique trees of a chordal graph

Chordal graphs have characteristic tree representations, the clique trees. The problems of finding one or enumerating them have already been solved in a satisfactory way. In this paper, the following related problem is studied: given a family T of trees, all having the same vertex set V, determine whether there exists a chordal graph whose set of clique trees equals T. For that purpose, we undertake a study of the structural properties, some already known and some new, of the clique trees of a chordal graph and the characteristics of the sets that induce subtrees of every clique tree. Some necessary and sufficient conditions and examples of how they can be applied are found, eventually establishing that a positive or negative answer to the problem can be obtained in polynomial time. If affirmative, a graph whose set of clique trees equals T is also obtained. Finally, all the chordal graphs with set of clique trees equal to T are characterized.Fil: de Caria, Pablo Jesús. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Departamento de Matemáticas; ArgentinaFil: Gutierrez, Marisa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Departamento de Matemáticas; Argentin

The Effects of Privatization on Firms and on Social Welfare: The Chilean Case

Chile led the Latin American pack in launching its far-reaching privatization program, but the question of whether the process has made firms more profitable remains. Also unclear is whether society as a whole is better off because of privatization. This paper looks at the performance of several industries to gauge the effects of privatization on Chilean firms and social welfare. The authors’ research, which is both broad and deep, yields some surprising findings. For example, contrary to commonly-held perceptions of bloated state-run bureaucracies, the authors find that the employment ranks of regulated entities actually swelled after their ownership switched to private hands. The paper evaluates a wide range of aspects of the privatization process, from highway tolls to private pension fund returns to school vouchers, and concludes with some concrete recommendations for future improvements.

A quasi-experimental evaluation of parents as sexual health educators resulting in delayed sexual initiation and increased access to condoms.

OBJECTIVE: To evaluate the effectiveness of an educational intervention for parents of first year high school students in the State of Morelos, Mexico, whose aim was to impact adolescents' sexual behavior, knowledge and access to contraception. MATERIAL AND METHODS: Quasi-experimental prospective study with eleven control and eleven intervention schools using self-administered questionnaires for parents and adolescents pre- and post-intervention. Parent-child dyads in the control and intervention schools were matched according to parents' propensity score; the average treatment effect (ATE) was estimated for adolescent's outcome variables. RESULTS: At follow-up, we found significant differences for adolescents in the intervention schools: 6.8% delayed initiation of sexual intercourse, 14.4% had correct knowledge about emergency contraception (EC), and 164% reported having received condoms from their parents, when comparing with students in control schools. CONCLUSIONS: Our results suggest that parent-focused interventions could be an innovative and effective strategy to promote adolescents sexual health

HIV prevention in Mexican schools: prospective randomised evaluation of intervention.

OBJECTIVE: To assess effects on condom use and other sexual behaviour of an HIV prevention programme at school that promotes the use of condoms with and without emergency contraception. DESIGN: Cluster randomised controlled trial. SETTING: 40 public high schools in the state of Morelos, Mexico. PARTICIPANTS: 10 954 first year high school students. INTERVENTION: Schools were randomised to one of three arms: an HIV prevention course that promoted condom use, the same course with emergency contraception as back-up, or the existing sex education course. Self administered anonymous questionnaires were completed at baseline, four months, and 16 months. Students at intervention schools received a 30 hour course (over 15 weeks) on HIV prevention and life skills, designed in accordance with guidelines of the joint United Nations programme on HIV/AIDS. Two extra hours of education on emergency contraception were given to students in the condom promotion with contraception arm. MAIN OUTCOME MEASURES: Primary outcome measure was reported condom use. Other outcomes were reported sexual activity; knowledge and attitudes about HIV and emergency contraception; and attitudes and confidence about condom use. RESULTS: Intervention did not affect reported condom use. Knowledge of HIV improved in both intervention arms and knowledge of emergency contraception improved in the condom promotion with contraception arm. Reported sexual behaviour was similar in the intervention arms and the control group. CONCLUSION: A rigorously designed, implemented, and evaluated HIV education course based in public high schools did not reduce risk behaviour, so such courses need to be redesigned and evaluated. Addition of emergency contraception did not decrease reported condom use or increase risky sexual behaviour but did increase reported use of emergency contraception

Educación y modernidad. Entre la utopía y la burocracia

Sin resume

On minimal vertex separators of dually chordal graphs: properties and characterizations

Many works related to dually chordal graphs, their cliques and neighborhoods were published by Brandstädt et al. (1998) [1] and Gutierrez (1996) [6]. We will undertake a similar study by considering minimal vertex separators and their properties instead. We find a necessary and sufficient condition for every minimal vertex separator to be contained in the closed neighborhood of a vertex and two major characterizations of dually chordal graphs are proved. The first states that a graph is dually chordal if and only if it possesses a spanning tree such that every minimal vertex separator induces a subtree. The second says that a graph is dually chordal if and only if the family of minimal vertex separators is Helly, its intersection graph is chordal and each of its members induces a connected subgraph. We also found adaptations for them, requiring just O(|E(G)|) minimal vertex separators if they are conveniently chosen. We obtain at the end a proof of a known characterization of the class of hereditary dually chordal graphs that relies on the properties of minimal vertex separators.Fil: de Caria, Pablo Jesús. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Departamento de Matemáticas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; ArgentinaFil: Gutierrez, Marisa. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Departamento de Matemáticas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentin

Optimal design of a carbon dioxide separation process with market uncertainty and waste reduction

The aim of this work is to optimize the conceptual design of an amine-based carbon dioxide (CO2) separation process for Enhanced Oil Recovery (EOR). A systematic approach is applied to predict the economic profitability of the system while reducing the environmental impacts. Firstly, we model the process with UniSim and determine the governing degrees of freedom (DoF) through a sensitivity analysis. Then, we proceed with the formulation of the economic problem, where the employment of econometric models allows us to predict the highest dynamic economic potential (DEP). In the second part, we apply the Waste Reduction (WAR) algorithm to quantify the environmental risks of the studied process. This method is based on the minimization of the potential environmental indicator (PEI) by using the generalization of the Waste Reduction algorithm. Results show that the CO2 separation plant is promising in terms of economic revenues. However, the PEI value indicates that the higher the profitability, the larger the environmental risk. The optimal value of the DEP corresponds to 0.0274 kmol/h and 60 ◦C, with a plant capacity according to the mole flow rate of the produced acid gas. In addition, the highest environmental risk is observed at the upper bounds of the DoF.Fil: Gutierrez, Juan Pablo. Universidad Nacional de Salta. Facultad de Ingeniería; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Investigaciones para la Industria Química. Universidad Nacional de Salta. Facultad de Ingeniería. Instituto de Investigaciones para la Industria Química; ArgentinaFil: Erdmann, Eleonora. Universidad Nacional de Salta. Facultad de Ingeniería; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Investigaciones para la Industria Química. Universidad Nacional de Salta. Facultad de Ingeniería. Instituto de Investigaciones para la Industria Química; ArgentinaFil: Manca, Davide. Politecnico di Milano; Itali