RESUMEN
A widely hypothesized but complex transition from widespread fluvial activity to predominantly aeolian processes is inferred on Mars based on remote sensing data observations of ancient landforms. However, the lack of analysis of in situ martian fluvial deposits hinders our understanding of the flow regime nature and sustainability of the martian fluvial activity and the hunt for ancient life. Studying analogs from arid zones on Earth is fundamental to quantitatively understanding geomorphic processes and climate drivers that might have dominated during early Mars. Here we investigate the formation and preservation of fluvial depositional systems in the eastern Sahara, where the largest arid region on Earth hosts important repositories of past climatic changes. The fluvial systems are composed of well-preserved single-thread sinuous to branching ridges and fan-shaped deposits interpreted as deltas. The systems' configuration and sedimentary content suggest that ephemeral rivers carved these landforms by sequential intermittent episodes of erosion and deposition active for 10-100s years over â¼10,000 years during the late Quaternary. Subsequently, these landforms were sculpted by a marginal role of rainfall and aeolian processes with minimum erosion rates of 1.1 ± 0.2 mm/yr, supplying â¼96 ± 24 × 1010 m3 of disaggregated sediment to adjacent aeolian dunes. Our results imply that similar martian fluvial systems preserving single-thread, short distance source-to-sink courses may have formed due to transient drainage networks active over short durations. Altogether, this study adds to the growing recognition of the complexity of interpreting climate history from orbital images of landforms.
RESUMEN
The incidence and causes of iatrogenic illness in a department of internal medicine were studied prospectively in 1,176 patients admitted from 1 January 1986 to 31 December 1986. A total of 295 patients (25.1%) developed 367 episodes of iatrogenic illness. Phlebitis occurred most frequently (75.2% of all iatrogenic events), followed by drug reactions (10.7%), contusion (4.6%), and urinary tract infections (1.4%). Nineteen patients developed life-threatening events (in 2 it was the cause of death). Etiologic agents included intravenous catheter (79% of all adverse reactions), drugs (9.5%), falls from bed (5.4%), diagnostic procedures (3.3%), and urinary catheterization (1.6%). Risk factors associated with iatrogenic illness were hospital stay longer than 12 days, female sex, poor general medical status on admission, intravenous catheterization, and intravenously administered antibiotics and anticoagulants. We conclude that in our hospital (a) 25% of the inpatient admissions to the general medicine service resulted in iatrogenic illness, (b) most iatrogenic illnesses were not severe (phlebitis), but 2 of 19 patients with life-threatening events died, and (c) the probability of developing iatrogenic illness generally depended on long hospital stay, poor general status at admission, and the use of both intravenous catheters and medication. In our patients, a reduction of hospital stay and a rational limitation of these procedures may diminish the rate of complications.
