Biomedical subjects
RJ Johnson
Publications and source records attributed to RJ Johnson.
Direct observation of heterogeneous chemistry in the atmosphere
The heterogeneous replacement of chloride by nitrate in individual sea-salt particles was monitored continuously over time in the troposphere with the use of aerosol time-of-flight mass spectrometry. Modeling calculations show that the observed chloride displacement process is consistent with a heterogeneous chemical reaction between sea-salt particles and gas-phase nitric acid, leading to sodium nitrate production in the particle phase accompanied by liberation of gaseous HCl from the particles. Such single-particle measurements, combined with a single-particle model, make it possible to monitor and explain heterogeneous gas/particle chemistry as it occurs in the atmosphere.
The Dislocated Knee.
Knee dislocation, although relatively rare, may be the result of high-or low-velocity injuries. Well established is the need for urgent diagnosis and treatment to avoid vascular complications and amputation. The initial evaluation should include objective assessment of arterial circulation by means of Doppler pressure measurements; the finding of any asymmetric pressure warrants an arteriogram. Late arterial occlusion may occur, which mandates careful serial reexamination in all patients, including those with initially symmetric pressure. Injury to the peroneal nerve is also common, and the recovery of neurologic function is unpredictable. An operative approach for the young and otherwise healthy patient is outlined. In the absence of definitive clinical studies, the timing and extent of the repair/reconstruction and the optimum rehabilitation still remain uncertain. Therefore, individual patient management must be dictated by circumstances such as instability, swelling, activity level, and the risk of postoperative joint stiffness.