The role of oxygen vacancies and their location in the magnetic properties of Ce(1-x)Cu(x)O(2-δ) nanorods.

Ceria (CeO2) is a promising dilute magnetic semiconductor. Several studies report that the intrinsic and extrinsic structural defects are responsible for room temperature ferromagnetism in undoped and transition metal doped CeO2 nanostructures; however, the nature of the kind of defect necessary to promote and stabilize the ferromagnetism in such a system is still a matter of debate. In the work presented here, nanorods from the system Ce1-xCuxO2-δ with x = 0, 0.01, 0.03, 0.05 and 0.10, with the more stable {111} surface exposed were synthesized by a microwave-assisted hydrothermal method. A very careful structure characterization confirms that the Cu in the samples assumes a majority 2+ oxidation state, occupying the Ce (Ce(4+) and Ce(3+)) sites with no secondary phases up to x = 0.05. The inclusion of the Cu(2+) in the CeO2 structure leads to the introduction of oxygen vacancies in a density proportional to the Cu(2+) content. It is supposed that the spatial distribution of the oxygen vacancies follows the Cu(2+) distribution by means of the formation of a defect complex consisting of Cu(2+) ion and an oxygen vacancy. Superconducting quantum interference device magnetometry demonstrated a diamagnetic behavior for the undoped sample and a typical paramagnetic Curie-Weiss behavior with antiferromagnetic interactions between the Cu(2+) ions for the single phase doped samples. We suggest that the presence of oxygen vacancies is not a sufficient condition to mediate ferromagnetism in the CeO2 system, and only oxygen vacancies in the surface of nanostructures would lead to such a long range magnetic order.

Sleep time and cardiovascular risk factors in adolescents: the HELENA (Healthy Lifestyle in Europe by Nutrition in Adolescence) study.

OBJECTIVE: We aimed to examine the association between adolescents' sleep time and a cardiometabolic risk score. A second aim was to examine associations between sleep time and individual cardiometabolic risk factors. METHODS: Adolescents (N=699; ages, 12.5-17.5 years) participating in the HELENA (Healthy Lifestyle in Europe by Nutrition in Adolescence) study were examined. Sleep time was reported by a questionnaire. Physical activity (PA) was assessed by accelerometry (n=497). Cardiometabolic risk factors measurements included insulin resistance, blood pressure, adiposity markers, cardiorespiratory fitness, and blood lipids. A cardiovascular disease risk score was computed. Associations were examined by a multilevel regression analysis (linear for individual risk factors and Poisson for the clustered risk score). RESULTS: For school days no association was found between sleep time and cardiometabolic risk factors. At weekend days, the prevalence ratio (PR) of having a clustered risk score increased by 15% for each additional hour of sleep controlling for age, sex, and socioeconomic status (SES); however, the prevalence disappeared when adjusting for PA. CONCLUSIONS: In European adolescents sleep time is not associated with cardiometabolic risk factors when important confounders are considered. Future research about sleep cardiovascular risk factors should register other sleep dimensions (sleep patterns or disturbances) to provide a better insight in this scientific field.

HIV and infections of similar transmission patterns in a drug injectors community of Santos, Brazil.

To study the prevalence of HIV and infections with related transmission patterns, we interviewed and obtained blood samples from 220 injecting drug users (IDUs), sampled by snowballing, from the city of Santos in the state of São Paulo, Brazil, where the estimated number of IDUs (10,000) comprises approximately 2% of the entire population. Seroprevalence of HIV, hepatitis B and C, syphilis, and HTLV (1 and 2) was assessed and compared with that in 197 blood donors from the same city, matched for age and gender. Risk behavior related to HIV was assessed by a standard questionnaire applied to the IDU sample. Univariate and multivariate analyses of the risk factors were performed. Seroprevalences found were 62% for HIV, 75% for HCV, 75% for HBV, 34% for syphilis, and 25% for HTLV (1 and 2) among IDUs, which compare with 0.0%, 2%, 23%, 12%, and 1% for blood donors, respectively. The risk for parenterally transmitted infections in this IDU community was higher than that for sexually transmitted infections (odds ratio for syphilis, 3.57; hepatitis B, 10.0; and hepatitis C, 100). The results of the mutivariate risk analysis showed that daily rate of ID use >5 times/day (OR = 6.73), not changing behavior to avoid AIDS (OR= 3.28), ID use >15 days/month (OR = 2.72), and ID use in the last 2 months (OR = 2.23) were the risk behaviors significantly associated with HIV infection.

The basic reproduction ratio of HIV among intravenous drug users.

A new approach for the estimation of the Basic Reproduction Ratio R0 for HIV among intravenous drug users (IVDU) is proposed. This approach is based in an adaptation of the models proposed by Ross and Macdonald for vector-borne infections. A straightforward adaptation of Macdonald's model is presented first: biological vectors are replaced by needles and syringes and we consider a homogeneous population of IVDUs; next we present a modified model where several heterogeneities are considered. Some of those heterogeneities are due to intrinsic differences between needles and syringes and biological vectors; others, such as those related to movements of individuals between communities, should apply to both biological vectors and injection apparatuses. An example of the calculations of R0 for a real IVDUs community is presented.