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This paper reviews jet noise research conducted at the National Aeronautics and Space Administration (NASA) from the early 1950s to the present day. Research conducted by NASA's predecessor, the National Advisory Committee for Aeronautics (NACA), and during the early years of NASA focused on turbojet noise, where a common approach for reducing jet noise was to limit the jet exit velocity to speeds that provided acceptable noise levels. Suppressors tested during this time resulted in thrust losses that were too severe to be implemented. With the introduction of turbofan engines in the 1960s, NASA shifted research to programs for both subsonic and supersonic aircraft applications with specific noise reduction goals. Subsonic research focused on increasing the bypass ratio of the engine to reduce the jet exit velocity of the core exhaust and adding mixers to the dual exhaust streams. Advances in computational methods improved aerodynamic designs and jet noise prediction tools. Supersonic applications proved to be more troublesome as programs aimed at large commercial transports required higher specific thrust engines. Changing the engine cycle to reduce jet noise was not compatible with mission range and speed requirements. Research for supersonic commercial aircraft remains an area of interest today at NASA.

Background: Information on interlaboratory variation and especially on methodological differences for plasma total homocysteine is lacking., Methods: We studied 14 laboratories that used eight different method types: HPLC with electrochemical detection (HPLC-ED); HPLC with fluorescence detection (HPLC-FD) further subdivided by type of reducing/derivatizing agent; gas chromatography/mass spectrometry (GC/MS); enzyme immunoassay (EIA); and fluorescence polarization immunoassay (FPIA). Three of these laboratories used two methods. The laboratories participated in a 2-day analysis of 46 plasma samples, 4 additional plasma samples with added homocystine, and 3 plasma quality-control (QC) pools. Results were analyzed for imprecision, recovery, and methodological differences., Results: The mean among-laboratory and among-run within-laboratory imprecision (CV) was 9.3% and 5.6% for plasma samples, 8.8% and 4.9% for samples with added homocystine, and 7.6% and 4.2% for the QC pools, respectively. Difference plots showed values systematically higher than GC/MS for HPLC-ED, HPLC-FD using sodium borohydride/monobromobimane (however, for only one laboratory), and EIA, and lower values for HPLC-FD using trialkylphosphine/4-(aminosulfonyl)-7-fluoro-2,1,3-benzoxadiazole. The two HPLC-FD methods using tris(2-carboxyethyl) phosphine/ammonium 7-fluoro-2,1,3-benzoxadiazole-4-sulfonate (SBD-F) or tributyl phosphine/SBD-F, and the FPIA method showed no detectable systematic difference from GC/MS., Conclusions: Among-laboratory variations within one method can exceed among-method variations. Some of the methods tested could be used interchangeably, but there is an urgent need to improve analytical imprecision and to decrease differences among methods.

We describe the use of HPLC with multiwavelength detection to measure retinol, alpha-tocopherol, lutein/zeaxanthin, beta-cryptoxanthin, lycopene, alpha-carotene, trans-beta-carotene, beta-carotene, and the linoleate, oleate, palmitate, and stearate esters of retinol in a single 200-microL serum sample. The method is sensitive enough to detect individual retinyl esters in fasting serum from a nonhyperlipidemic population and requires only 12 min for each sample. Serum concentration ranges and means are reported for retinol, alpha-tocopherol, lutein/zeaxanthin, beta-cryptoxanthin, lycopene, alpha-carotene, trans-beta-carotene, and the sum of the retinyl esters from serum analyses of 3480 participants from several different studies.

Background: Studies in developing countries have shown that children with measles have low serum retinol concentrations and that lower retinol levels are associated with measles-related mortality. Vitamin A therapy has been shown to reduce mortality among African children with acute measles., Objectives: To determine whether serum retinol concentration is low among children with measles in the United States and to determine whether retinol concentration is associated with illness severity., Setting: Pediatric referral hospital and clinic in Milwaukee, WI, during the measles outbreak of 1989-1990., Patients: One hundred fourteen patients < or = 5 years of age evaluated for serologically confirmed measles with serum obtained within 5 days following rash onset., Methods: Serum retinol concentration was determined by high-performance liquid chromatography. Clinical data were collected by hospital record review. A modified Pediatric Risk of Mortality (PRISM) score was used to assess physiologic instability as a measure of illness severity., Results: Retinol concentrations ranged from 0.25 to 1.18 mumol/L (median 0.58 mumol/L); 82 (72%) patients had low retinol concentration (< or = 0.70 mumol/L). Median retinol concentrations were lower among hospitalized patients (0.56 vs 0.70, P = .006) and patients with pneumonia (0.52 vs 0.64, P = .02) but higher among children with otitis media (0.63 vs 0.54, P = .01). Higher modified PRISM scores, reflecting greater physiologic instability, were associated with lower retinol concentration (beta coefficient -.0147, P = .025). In multivariate analysis, higher modified PRISM scores were associated with lower retinol concentration (beta coefficient -.0144, P = .025) even after controlling for hospitalization, presence of complications, race, age, receipt of Aid to Families With Dependent Children, gender, and interval from rash onset until serum was collected., Conclusions: Among these children with measles in an urban United States community, retinol concentrations were depressed, and the degree of depression was associated with illness severity. Vitamin A therapy should be considered for children with measles in the United States who require hospitalization.

To investigate nutritional status and heterosexual human immunodeficiency virus (HIV) transmission, we performed a nested case-control study of sexually active, adult women in Kigali, Rwanda. Forty-five women who seroconverted during the 24-month study period were compared to 74 women who remained seronegative throughout the study. Seroconvertors and nonseroconvertors did not differ in preseroconversion serum levels of vitamin A, carotenoids, vitamin E, selenium, albumin, ferritin, or cholesterol. Weight loss, however, was a significant predictor of eventual HIV seroconversion. Subsequent seroconvertors lost an average of 1.5 kg during the first 6 months of the study compared with a 1.0-kg gain (p = 0.001) for nonconvertors. Nine of 27 (33%) seroconvertors, compared with one of 44 (2%) controls, lost at least 5 kg in the 6-month period beginning 1 year before their seroconversion (odds ratio, 21.5, 95% confidence interval 4.1-112). The association between weight loss and seroconversion was independent of other potential risk factors such as socioeconomic status, pregnancy, and genital ulcer disease. In addition to these findings for measured weight loss during follow-up, reported weight loss before enrollment was also a risk factor for subsequent seroconversion. Additional studies of heterosexual HIV transmission are needed to determine whether or not weight loss is causally related to susceptibility for HIV infection.

Recent studies show that vitamin A levels decrease during measles and that vitamin A therapy can improve measles outcome in children in the developing world. Vitamin A levels of children with measles have not been studied in developed countries. We therefore measured vitamin A levels in 89 children with measles younger than 2 years and in a reference group in New York City, NY. Vitamin A levels in children with measles ranged from 0.42 to 3.0 mumol/L; 20 (22%) were low. Children with low levels were more likely to have fever at a temperature of 40 degrees C or higher (68% vs 44%), to have fever for 7 days or more (54% vs 23%), and to be hospitalized (55% vs 30%). Children with low vitamin A levels had lower measles-specific antibody levels. No child in the reference group had a low vitamin A level. Our data show that many children younger than 2 years in New York City have low vitamin A levels when ill with measles, and that such children seem to have lower measles-specific antibody levels and increased morbidity. Clinicians may wish to consider vitamin A therapy for children younger than 2 years with severe measles. Additional studies of vitamin A in measles and other infectious diseases, and in vaccine efficacy trials, should be done.

A standard nuclear medicine computer system was modified to accept video input and utilized to perform digital intravenous and intra-arterial angiography, substration of CT images and enhance ultrasound images as well as to read video and magnetic tape. This system provides greater versatility and adaptability than presently conceptualized and produced digital systems and deserves further evaluation as a multipurpose imaging device.

Erythrocyte protoporphyrin (EP) has been used for more than 30 years as an indicator of lead intoxication, iron deficiency, and porphyrias. Recently, numerous analytical problems associated with various EP methods have been reported, including a lack of consensus among investigators regarding the best calibration material or analytical procedure. We investigated commercially available protoporphyrin IX (PPIX) standard materials and measured the millimolar absorptivity (m epsilon) of these materials, focusing on variables affecting the determination of their absorptivities. Among the five forms of PPIX available, PPIX dimethyl ester, when hydrolyzed to PPIX free acid, gave the most consistent and reproducible results. This work confirmed our earlier observations, made on more than 600 separate occasions during 12 years, that the m epsilon of PPIX free acid in 1.5 mol/L HCl at the Soret maximum is 297 +/- 1.3 L.mmol-1.cm-1, 19% higher than the arbitrary value of 241 L.mmol-1.cm-1 generally accepted by most investigators but based on unpublished data. We propose that the m epsilon of 297 L.mmol-1.cm-1 for PPIX be adopted and that PPIX dimethyl ester be used for the calibration of acid-extraction methods. A detailed protocol for the preparation and verification of PPIX from the dimethyl ester is available upon request.