The slave boson (SB) technique is employed to study the Zeeman spin splitting in a quantum dot. Unlike traditional SB method, each spin is renormalized differently. Two geometries are compared: side connected and embedded. In both cases, it's shown a non linear behavior of the splitting as a function of the magnetic field applied. The results are in line with the latest experiments.

The conductance of a double-dot system in a ring threaded by a magnetic flux is studied. The ring is connected to two leads in such a way that each dot is embedded in one arm of the structure. The currents going through each arm of the ring are determined by the Aharonov-Bohm effect and the dot charging effects. The conductance for different values of the magnetic flux is obtained as a function of the gate potentials applied to the dots, for two situations: when the dot level energies are equal, deltaE = 0, and when they are different but with deltaE smaller than the Coulomb interaction U. The conductance shows quite distinct behavior according to having a finite or zero magnetic flux threading the ring. The system presents S = 1/2 and S = 1 Kondo phenomena for no magnetic flux and is in the S = 1/2 Kondo regime in the case of half a quantum of magnetic flux.

Objective: To compare peer education versus that imparted by health professionals for improving knowledge, risk perception and risky sexual behavior among teenagers attending to family planning clinics of two hospitals in Lima. Material and Methods: Experimental single-blind study carried out at the family planning clinics of Hospital Dos de Mayo and Instituto Materno Perinatal during the year 2000. After signing an informed consent, 206 teenagers considered as being at risk were randomly assigned to one of the two educational interventions and later they were requested to come back at the end of the third month in order to reassess knowledge, attitudes and risky sexual behavior. Sign rank, Mann Whitney and Analysis of Covariance tests were used to compare scores for knowledge, risk perception and sexual behavior after the educational intervention. Results: 89 (84%) out of 106 teenagers assigned to the peer education and 70 (70%) out of 100 teenagers assigned to the education provided by health professionals (p= 0,02). Improvement in the level of knowledge was significantly higher (p= 0,047) in group with peer education compared to the group trained by health professionals; however, significance decreased (p= 0,07) when analysis of covariance was used taking into account the scores for the first interview. Improvements in risk perception and sexual behavior were higher in the group with peer education, but the difference was not statistically significant. Conclusions: Peer education proved to be more effective in improving knowledge and the group undergoing this approach had better follow up rates, so peer education should be promoted as a strategy for decreasing the prevalence of sexually transmitted infections in this population.

Objetivo: Comparar la educación por pares frente a la educación por profesionales de a consultorios de planificación familiar de dos hospitales de Lima, Perú. Material y Métodos: Estudio experimental simple ciego realizado en 1998 en los consultorios de planificación familiar del Hospital Dos de Mayo y el Instituto Materno Perinatal de Lima, Perú. Después del consentimiento, se asignó aleatoriamente a 206 adolescentes consideradas de riesgo a una de las dos intervenciones educativas y luego fueron invitadas a regresar al final del tercer mes para reevaluar sus conocimientos, actitudes y conducta sexual de riesgo. Se usó la prueba de los signos, Mann Whitney y análisis de Covarianza para comparar los puntajes de los cuestionarios de conocimiento, percepción de riesgo y conducta sexual de riesgo después de la intervención educativa. Resultados: 89 (84%) de 106 adolescentes asignadas al grupo de educación por pares y 70 (70%) de las 100 asignadas al grupo de educación por profesionales de la salud (p=0,02) regresaron a la evaluación postintervención. El mejoramiento del nivel de conocimiento fue significativamente mayor (p=0,047) en el grupo de educación por pares que en el grupo capacitado por profesionales de la salud; sin embargo, esta significancia disminuyó (p=0,07) cuando se usó análisis de covarianza para controlar el puntaje obtenido antes de la intervención. El mejoramiento de la percepción y conductas de riesgo fue mayor en el grupo de pares pero esta diferencia no fue significativa. Conclusiones: La educación por pares demostró ser más efectiva en mejorar los conocimientos en las adolescentes y el seguimiento fue mejor en este grupo por lo que debe ser promovida como una estrategia para disminuir la prevalencia de infecciones de transmisión sexual en esta población.