Crossover versus mutation: a comparative analysis of the evolutionary strategy of genetic algorithms applied to combinatorial optimization problems.

Since their first formulation, genetic algorithms (GAs) have been one of the most widely used techniques to solve combinatorial optimization problems. The basic structure of the GAs is known by the scientific community, and thanks to their easy application and good performance, GAs are the focus of a lot of research works annually. Although throughout history there have been many studies analyzing various concepts of GAs, in the literature there are few studies that analyze objectively the influence of using blind crossover operators for combinatorial optimization problems. For this reason, in this paper a deep study on the influence of using them is conducted. The study is based on a comparison of nine techniques applied to four well-known combinatorial optimization problems. Six of the techniques are GAs with different configurations, and the remaining three are evolutionary algorithms that focus exclusively on the mutation process. Finally, to perform a reliable comparison of these results, a statistical study of them is made, performing the normal distribution z-test.

Focusing on the golden ball metaheuristic: an extended study on a wider set of problems.

Nowadays, the development of new metaheuristics for solving optimization problems is a topic of interest in the scientific community. In the literature, a large number of techniques of this kind can be found. Anyway, there are many recently proposed techniques, such as the artificial bee colony and imperialist competitive algorithm. This paper is focused on one recently published technique, the one called Golden Ball (GB). The GB is a multiple-population metaheuristic based on soccer concepts. Although it was designed to solve combinatorial optimization problems, until now, it has only been tested with two simple routing problems: the traveling salesman problem and the capacitated vehicle routing problem. In this paper, the GB is applied to four different combinatorial optimization problems. Two of them are routing problems, which are more complex than the previously used ones: the asymmetric traveling salesman problem and the vehicle routing problem with backhauls. Additionally, one constraint satisfaction problem (the n-queen problem) and one combinatorial design problem (the one-dimensional bin packing problem) have also been used. The outcomes obtained by GB are compared with the ones got by two different genetic algorithms and two distributed genetic algorithms. Additionally, two statistical tests are conducted to compare these results.

[Nocardiosis in patients with human immunodeficiency virus infection in Spain]. / Nocardiosis en enfermos con infección por virus de la inmunodeficiencia humana en España.

BACKGROUND: Nocardia usually infects immunosuppressed patients, particularly with cellular immunity deficiency. Nevertheless, despite severe immunosuppression in patients infected with HIV, nocardiosis is rare among these patients. We report here two cases of nocardiosis in patients with HIV infection and review spanish literature up to 1993, with an analysis of the characteristics of this infection in our country. METHODS AND RESULTS: The two patients consumed drugs parenterally and Nocardia organism were recovered in blood cultures after 48 hours of inoculation in standard culture media. The source of the infection was cutaneous in one patient, over an area of venipuncture, and pulmonary in the other patient. Previously, eleven cases of nocardiosis had been reported in the spanish literature in patients infected with HIV. Eighty-four percent were males, and all of them consumed drugs parenterally and displayed a severe cellular immunodepression; the total CD4 lymphocyte count was lower than 100/mm3 in patients when this finding was available (6/13). At diagnosis only one patient received prophylaxis against other type of infection with antibiotics theoretically effective against Nocardia at diagnosis. The Nocardia species recovered more frequently was asteroides (77%) and the most common location was the skin (54%). Treatments more frequently employed were sulfametoxazole-trimethoprim (45%) and sulfadiazine (36%), with a good response except in those with cerebral involvement. CONCLUSIONS: Nocardiosis in patients with HIV infection is rare in Spain. In contrast with other geographical areas skin involvement was the more common form of infection. Prophylaxis with sulfametoxazole-trimethoprim against other infections could be responsible for a lower than expected incidence among this type of patients.