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Your search keyword '"McKenna, D.S."' showing total 10 results
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10 results on '"McKenna, D.S."'

2. The potential for ozone depletion in the Arctic polar stratosphere

Author

Brune, W.H., Anderson, J.G., Toohey, D.W., Fahey, D.W., Kawa, S.R., Jones, R.L., McKenna, D.S., and Poole, L.R.

Subjects
Arctic -- Natural history, Research, Natural history, Ozone layer depletion -- Research
Abstract

The nature of the Arctic polar stratosphere is observed to be similar in many respects to that of the Antartic polar stratosphere, where an ozone hole has been identified. Most [...]

Published
1991

3. GHOST - A novel airborne gas chromatograph for in situ measurements of long-lived tracers in the lower stratosphere: method and applications

Author

Bujok, O., Tan, V., Klein, E., Nopper, R., Bauer, R., Engel, A., Gerhards, M.-T., Afchine, A., McKenna, D.S., Schmidt, U., Wienhold, F.G., Fischer, H., and Publica

Subjects
lowermost stratosphere, in-situ gas chromatograph, N2O budget, long-lived tracer, airborne measurement
Abstract

A novel fully-automated airborne gas chromatograph for in situ measurements of long-lived stratospheric tracers has been developed, combining the high selectivity of a mega-bore PLOT capillary column with recently developed sampling and separation techniques. The Gas Chromatograph for the Observation of Stratospheric Tracers (GHOST) has been successfully operated during three STREAM campaigns (Stratosphere Troposphere Experiment by Airborne Measurement) onboard a Cessna Citation II aircraft in two different modes: Either N2O and CF2Cl2 (CFC-12) or CFC-12 and CFCl3 (CFC-d11) have been measured simultaneously, with a time resolution of 2 min for both modes. Under flight conditions the instrument precision for theses species is better than 0.9 %, and the accuracy is better than 2.0 % of the tropospheric values of all measured compounds. The detection limits are below 28 ppb for N2O, 14 ppt for CFC-12, and 8 ppt for CFC-11, respectively, i. e., well below 10 % of the tropospheric values of all measured compounds. Post-mission optimization of the chromatographic separation showed a possible enhancement of the time resolution by up to a factor of 2, associated with a comparable increase in precision and detection limit. As test of actual performance of GHOST results from an in-flight N2O intercomparison with a tunable diode laser absorption spectrometer (TDLAS) are presented. They yield an excellent agreement between both instruments. Furthermore, on the basis of the hitherto most extensive set of upper tropospheric and lower stratospheric data, the relative stratospheric N2O lifetime is re-assessed. When referenced to the WMO reference CFC-11 lifetime of 45 +/- 7 years and N2O lifetime of 91 +/- 15 years is derived, a value substantially smaller than the WMO reference lifetime of 120 years. Moreover, this value implies a stratospheric N2O sink strength of 16.3 +/- 2.7 Tg (N) yr-1 which is 30 % larger than previous estimates.

Published
2001

8. Nasal bone hypoplasia in trisomy 21 at 15-22 weeks' gestation.

Author

Cicero, S., Soneki, J.D., McKenna, D.S., Croom, C.S., Johnson, L., and Nicolaides, K.H.

Subjects
FETUS, NASAL bone, PREGNANCY
Abstract

Objective To investigate the potential value of ultrasound examination of the fetal profile for present/hypoplastic fetal nasal bone at 15-22 weeks' gestation as a marker for trisomy 21. Methods This was an observational ultrasound study in 1046 singleton pregnancies undergoing amniocentesis for fetal karyotyping at 15-22 (median, 17) weeks' gestation. Immediately before amniocentesis the fetal profile was examined to determine if the nasal bone was present or hypoplastic (absent or shorter than 2.5 mm). The incidence of nasal hypoplasia in the trisomy 21 and the chromosomally normal fetuses was determined and the likelihood ratio for trisomy 21 for nasal hypoplasia was calculated. Results All fetuses were successfully examined for the presence of the nasal bone. The nasal bone was hypoplastic in 21/34 (61.8%) fetuses with trisomy 21, in 12/982 (1.2%) chromosomally normal fetuses and in 1/30 (3.3%) fetuses with other chromosomal defects. In 3/21 (14.3%) trisomy 21 fetuses with nasal hypoplasia there were no other abnormal ultrasound findings. In the chromosomally normal group hypoplastic nasal bone was found in 0.5% of Caucasians and in 8.8% of AfroCaribbeans. The likelihood ratio for trisomy 21 for hypoplastic nasal bone was 50.5 (95% C127.1-92.7) and for present nasal bone it was 0.38 (95% CI 0.24-0.56). Conclusion Nasal bone hypoplasia at the 15-22-week scan is associated with a high risk for trisomy 21 and it is a highly sensitive and specific marker for this chromosomal abnormality. [ABSTRACT FROM AUTHOR]

Published
2003
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9. Group B streptococcal infections

Author

McKenna, D.S. and Iams, J.D.

Abstract

Group B streptococcal infection is the most common cause of neonatal sepsis and is responsible for significant neonatal morbidity and mortality. Group B streptococcus is also the causative agent in 50,000 maternal infections per year. Approximately 30% of women have asymptomatic group B streptococcal colonization at some time during pregnancy, but the neonatal attack rate is only about 2 per 1,000 deliveries. Maternal and neonatal risk factors contribute to the rates of vertical transmission and symptomatic neonatal disease. Options that have been investigated for prevention of neonatal group B streptococcal disease include identification of at-risk pregnancies as well as antenatal, intrapartum, and neonatal treatment. The intrapartum treatment of women at risk for vertical transmission of group B streptococcus to their neonates unequivocally has been shown to decrease the rate of neonatal colonization. Practitioners should implement one of two strategies that incorporate intrapartum prophylaxis for prevention of perinatal group B disease.

Published
1998
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