Interfacial ferromagnetism and exchange bias in CaRuO3/CaMnO3 superlattices.

We have found ferromagnetism in epitaxially grown superlattices of CaRuO(3)/CaMnO(3) that arises in one unit cell at the interface. Scanning transmission electron microscopy and electron energy loss spectroscopy indicate that the difference in magnitude of the Mn valence states between the center of the CaMnO(3) layer and the interface region is consistent with double exchange interaction among the Mn ions at the interface. Polarized neutron reflectivity and the CaMnO(3) thickness dependence of the exchange bias field together indicate that the interfacial ferromagnetism is only limited to one unit cell of CaMnO(3) at each interface. The interfacial moment alternates between the 1 µ(B)/interface Mn ion for even CaMnO(3) layers and the 0.5 µ(B)/interface Mn ion for odd CaMnO(3) layers. This modulation, combined with the exchange bias, suggests the presence of a modulating interlayer coupling between neighboring ferromagnetic interfaces via the antiferromagnetic CaMnO(3) layers.

[Prevalence of HIV antibodies in pregnant women in the Amsterdam HIV reference station research, 1988-1993]. / Prevalentie van HIV-antistoffen bij zwangere vrouwen in het Amsterdamse HIV-peilstationonderzoek, 1988-1993.

Pregnant women were asked to undergo a HIV test in two hospitals, one maternity clinic (n = 12.784; 1988-1993) and one abortion clinic (n = 2089; 1990-1993) in Amsterdam, in order to establish trends in HIV prevalence. Participation rates were 92.4% and 84.4%, respectively. Among pregnant women the overall HIV prevalence was 0.27% (0.04% for pregnant women without a known HIV risk and 2.6% for women with a known HIV risk) and in the abortion clinic the overall HIV prevalence was 0.91%. The HIV prevalence over the years remained fairly constant. In the most recent years a slight rise was noticed in the HIV prevalence in the group pregnant women with a known HIV risk caused by an increase in the number of women from AIDS endemic countries in this group.

The HIV prevalence among pregnant women in the Amsterdam region (1988-1991).

The objective of the study was to monitor the HIV prevalence in the years 1988-1991 among pregnant women in the Amsterdam region, visitors to an abortion clinic and 3 outpatient infertility clinics. All women attending these clinics were asked to participate in the study on a voluntary basis and were tested with informed consent. The women were questioned about risk-bearing behaviour of themselves and their sexual partner(s). In the period 1988-1991, of the 23,827 eligible pregnant women, 22,165 women participated (93.0%). Twenty-seven women were found to be positive for HIV antibodies (0.12%, 95% CI: 0.08%-0.17%), of whom twenty belonged to a known HIV risk group or had a partner who belonged to one of these groups and 7 women had no known HIV risk. Seventeen of the 27 women had a foreign nationality. The annual HIV prevalence among pregnant women was: 1988: 0.28%; 1989: 0.10%; 1990: 0.10%; 1991: 0.11%. In the years 1990 and 1991, of the 1,128 eligible women visiting the abortion clinic 953 (84.5%) were tested. Eleven women were HIV-seropositive (1.15%, 95% CI: 0.6%-2.0%), of whom 9 were from an AIDS endemic region, 1 woman had a partner from this region and 1 woman had no known HIV risk. Four African women had HIV-2 antibodies. At the 3 outpatient infertility clinics 1 woman was found to be HIV-positive (0.13%; 95% CI: 0.02-0.9). She had no other risk than a partner from an AIDS endemic area. In the Amsterdam region there was a steady and low HIV prevalence (0.1%) among pregnant women through the years 1988-1991. The prevalence in the abortion clinic was ten times higher. The program was able to detect possible high risk groups within the population. Migration and travelling can play an important role in the spread of HIV in the general heterosexual population.