Nature of the Green Luminescent Center in Zinc Oxide

We apply a number of complementary characterization techniques including electron paramagnetic resonance, optical absorption, and photoluminescence spectroscopies to characterize a wide range of different ZnO phosphor powders. We generally observe a good correlation between the 510-nm green emission intensity and the density of paramagnetic isolated oxygen vacancies. In addition, both quantities are found to peak at a free-carrier concentration ne, of about 1.4 × 1018 cm-3. We also find that the green emission intensity can be strongly influenced by free-carrier depletion at the particle surface, especially for small particles and/or low doping. Our data suggest that the green PL in ZnO phosphors is due to the recombination of electrons in singly occupied oxygen vacancies with photoexcited holes in the valence band.

Direct Observation of Mobile Protons in SiO2 Thin Films: Potential Application in a Novel Memory Device

In this work we show that annealing of silicon/silicon‐dioxide/silicon structures in forming gas (N2:H2; 95:5) above 500°C leads to spontaneous incorporation of mobile H+ ions in the buried SiO2 layer. We demonstrate that, unlike the alkali ions feared as killer contaminants in the early days, the space charge distribution of these mobile protons within the buried oxide layer can be very well controlled and easily rearranged with relatively high speed at room temperature. The hysteresis in the flat band voltage shift provides a unique vehicle to study proton kinetics in silicon dioxide thin films. It is further shown how this effect has great potential as the basis for a reliable nonvolatile FET memory device that is expected to be competitive with state‐of‐the‐art Si‐based memory technologies. The power of this novel device is its simplicity; it requires few processing steps, all of which are standard in Si integrated‐circuit fabrication.

Associations between ethnicity and self-reported hallucinations in a population sample of young adults in The Netherlands

BACKGROUND

Psychotic disorders are more common in people from ethnic minorities. If psychosis exists as a continuous phenotype, ethnic disparities in psychotic disorder will be accompanied by similar ethnic disparities in the rate of psychotic symptoms. This study examined ethnic disparities in self-reported hallucinations in a population sample of young adults. MethodA cross-sectional population survey (n=2258) was carried out in the south-west Netherlands. Seven ethnic groups were delineated: Dutch natives, Turks, Moroccans, Surinamese/Antilleans, Indonesians, other non-Western immigrants (mostly from Africa or Asia) and Western immigrants (mostly from Western Europe). Self-reported auditory and visual hallucinations were assessed with the Adult Self-Report (ASR). Indicators of social adversity included social difficulties and a significant drop in financial resources.

RESULTS

Compared to Dutch natives, Turkish females [odds ratio (OR) 13.48, 95% confidence interval (CI) 5.97-30.42], Moroccan males (OR 8.36, 95% CI 3.29-21.22), Surinamese/Antilleans (OR 2.19, 95% CI 1.05-4.58), Indonesians (OR 4.15, 95% CI 1.69-10.19) and other non-Western immigrants (OR 3.57, 95% CI 1.62-7.85) were more likely to report hallucinations, whereas Western immigrants, Turkish males and Moroccan females did not differ from their Dutch counterparts. When adjusting for social adversity, the ORs for self-reported hallucinations among the non-Western immigrant groups showed considerable reductions of 28% to 52%.

CONCLUSIONS

In a general population sample, several non-Western immigrant groups reported hallucinations more often than Dutch natives, which is consistent with the higher incidence of psychotic disorders in most of these groups. The associations between ethnicity and hallucinations diminished after adjustment for social adversity, which supports the view that adverse social experiences contribute to the higher rate of psychosis among migrants.

In vitro expanded cells contributing to rapid severe combined immunodeficient repopulation activity are CD34+38-33+90+45RA-

Expansion of hematopoietic stem cells could be used clinically to shorten the prolonged aplastic phase after umbilical cord blood (UCB) transplantation. In this report, we investigated rapid severe combined immunodeficient (SCID) repopulating activity (rSRA) 2 weeks after transplantation of CD34(+) UCB cells cultured with serum on MS5 stromal cells and in serum- and stroma-free cultures. Various subpopulations obtained after culture were studied for rSRA. CD34(+) expansion cultures resulted in vast expansion of CD45(+) and CD34(+) cells. Independent of the culture method, only the CD34(+)33(+)38(-) fraction of the cultured cells contained rSRA. Subsequently, we subfractionated the CD34(+)38(-) fraction using stem cell markers CD45RA and CD90. In vitro differentiation cultures showed CD34(+) expansion in both CD45RA(-) and CD90(+) cultures, whereas little increase in CD34(+) cells was observed in both CD45RA(+) and CD90(-) cultures. By four-color flow cytometry, we could demonstrate that CD34(+)38(-)45RA(-) and CD34(+)38(-)90(+) cell populations were largely overlapping. Both populations were able to reconstitute SCID/nonobese diabetic mice at 2 weeks, indicating that these cells contained rSRA activity. In contrast, CD34(+)38(-)45RA(+) or CD34(+)38(-)90(-) cells contributed only marginally to rSRA. Similar results were obtained when cells were injected intrafemorally, suggesting that the lack of reconstitution was not due to homing defects. In conclusion, we show that after in vitro expansion, rSRA is mediated by CD34(+)38(-)90(+)45RA(-) cells. All other cell fractions have limited reconstitutive potential, mainly because the cells have lost stem cell activity rather than because of homing defects. These findings can be used clinically to assess the rSRA of cultured stem cells.

Viable CD34+ stem cell content of a cord blood graft: which measurement performed before transplantation is most representative?

BACKGROUND

Patient survival in allogeneic cord blood transplantation is critically dependent on total nucleated cell (TNC) count or total CD34+ cell count per kg of body weight. Theoretically, viable CD34+ cell measurement at the time of infusion should give a better indication of the suitability of a certain transplant. The relation between measurements on different samples and viable CD34+ cell count on the graft itself was analyzed.

STUDY DESIGN AND METHODS

Viable CD34+ cells were measured with a no-wash, single-platform technique with 7-aminoactinomycin D. Analysis was performed before freezing on the cord blood, after freezing and thawing on the cord blood unit itself, and on various samples.

RESULTS

Cord blood volume correlated poorly with viable CD34+ cell content (r=0.24) as did initial TNC count and WBC count (r=0.57 and r=0.48, respectively). In contrast, viable CD34 cell content determined before freezing correlated well with viable CD34 cell content of the graft (r=0.91) but was on average 25 percent higher than after freezing and thawing. The best correlations with the CD34+ cell content of the cord blood unit were obtained with CD34 cell measurements on a separate cryovial (r=0.95). These CD34 cell measurements on frozen samples were found to be very reproducible (r=0.96).

CONCLUSION

Viable CD34 cell count of the graft is both accurate and precise when measured on a separate sample frozen together with the cord blood unit. This measurement can be performed by the transplant center to exclude between-laboratory variability.