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The emission pattern of charged pions has been measured in Au+Au collisions at 1 GeV/nucleon incident energy. In peripheral collisions and at target rapidities, high-energy pions are emitted preferentially towards the target spectator matter. In contrast, low-energy pions are emitted predominantly in the opposite direction. The corresponding azimuthal anisotropy is explained by the interaction of pions with projectile and target spectator matter. This interaction with the spectator matter causes an effective shadowing which varies with time during the reaction. Our observations show that high-energy pions stem from the early stage of the collision whereas low-energy pions freeze out later.

Study Objectives: To determine if the complications associated with skull base fractures are increased when nasotracheal intubation is performed in the field., Design: Retrospective, case-control study over a five-year period., Setting: A helicopter service returning to a Level I trauma center., Type of Participants: All injured patients treated in the field who had either radiographic or clinical evidence of skull base fractures in whom nasotracheal intubation was attempted (38) compared with all patients with skull base fractures in whom nasotracheal intubation was not attempted (48) and a convenience sample of patients without skull base fractures in whom nasotracheal intubation was attempted (45). Patients with obvious midface motion on initial examination were excluded. Complications of skull base fractures were categorized as cerebral spinal fluid leak of longer than 24 hours and/or meningitis, cranial nerve injury, diabetes insipidus, and intracranial placement of the endotracheal tube., Interventions: Blind nasotracheal intubation was performed by experienced flight nurses., Results: There were no patients in whom an endotracheal tube was placed intracranially. There was no significant difference in complication rate between the two groups with skull base fractures (with nasotracheal intubation, 24%; 95% confidence interval, 11% to 40%; without nasotracheal intubation, 25%; 95% confidence interval, 14% to 40%). The group without skull base fracture had none of the complications usually associated with skull base fractures., Conclusion: Patients with skull base fracture have a significant complication rate (25%). The complications associated with skull base fractures are not markedly increased by attempts at nasotracheal intubation in the field.