Mixing and Radiative Corrections at LEP I
We present a method for a common treatment of Z ′ exchange, QED corrections, and weak loops in e + e − annihilation. QED corrections are taken into account by convoluting a hard-scattering cross section containing γ, Z, and Z ′ exchange. Weak corrections and ZZ ′ mixing are treated simultaneously by a generalization of weak form factors. Using the properly extended Standard Model program for the Z line shape, ZF I T T ER , we perform and compare two different analyses of the 1990 LEP I data in terms of theories based on the E 6-group and in terms of LR-symmetric models. From the LEP I data alone, the ZZ ′ mixing angle may be limited to |θ M | ≤ 0.01 and the Z ′ mass to M 2 > 118–148 GeV, depending on the model (95% CL).
Physics of precision experiments with Z's
Abstract We review the status of precision tests of the electroweak Standard Model. Radiative corrections play an important role for the interpretation of precision measurements and provide a window for the observation of new physics . Implications of recent results from LEP and hadron colliders are discussed. So far the agreement between experimental data and standard model predictions is almost perfect. In order to establish possible deviations from the Standard Model we have to wait for the next step in accuracy. This will be achieved during this year with about 10 6 Z's per experiment.
Exposure to violence in incarcerated youth from the city of São Paulo.
OBJECTIVE
This study aimed to determine the extent of exposure to community violence among delinquent Brazilian youth in the 12-month period prior to their incarceration and to identify factors associated with this exposure.


METHOD
With an oversampling of girls, a cross-section of youth under 18 years of age from juvenile detention units in the city of São Paulo, Brazil completed a structured interview. Key items related to exposure to violence (witnessed and experienced) were drawn from the Social and Health Assessment questionnaire to cover the 12-month period prior to incarceration.


RESULTS
Participants (n = 325, 89% boys) reported high rates of exposure to violence with largely similar levels for boys and girls. Being threatened with physical harm, being beaten or mugged and/or shot at were the most common forms of violence experienced. After controlling for demographic and family variables, the fact of having peers involved in risk behavior, easy access to guns and previous involvement with the justice system were associated with witnessed violence; whereas having slept on the street was the only variable associated with experienced violence.


CONCLUSION
This group of youth was exposed to high levels of violence and other adverse experiences. Future research should examine the effectiveness of strategies aimed at reducing the exposure to violence of high-risk youth.