RESUMEN
Chemical, paleontological, and mineralogical analyses of a 7.5-meter core from the middle of Lake Valencia, Venezuela, have provided information on the paleoclimatic history of this low-elevation, low-latitude site for the last 13,000 years. The data show that dry climates existed in this region from 13,000 years before present (B.P.) until about 10,000 years B.P. The Lake Valencia Basin was occupied by intermittent saline marshes at that time. About 10,000 years B.P., a permanent lake of fluctuating salinity formed and arboreal plant communities replaced the earlier dominant xeric herbaceous vegetation and marsh plants. By 8500 years B.P., Lake Valencia reached moderate to low salinities and discharged water; the modern vegetation became established at that time. After 8500 years B.P., the lake twice ceased discharging as a result of reduced watershed moisture. The second of these drying episodes is still in progress and has been aggravated by human activities in the watershed.
RESUMEN
The technic and safety aspects of the radiographic evaluation of neonates with RDS are discussed. A study of radiographs taken in an intensive care nursery revealed that densitometric measurements are helpful in distinguishing changes in lung aeration from changes in radiographic quality. The radiation exposure to neonates was 5.1 (SD 2.3) mR per film and 44.9 (SD 39.7) MR per neonate. Limited chromosomal studies revealed no detectable abnormalities. The radiation exposure to the staff was minimal. The low-radiation exposure to the staff and neonates is the result of careful attention to radiation hygiene.