RESUMEN
We extend the redundant spacings calibration method for finding piston coefficients affecting the elements of a dilute aperture array so that tilt phase coefficients can also be calculated and corrected without the need for assumptions about the object. The tilt coefficient retrieval method is successfully demonstrated in simulation, and the specifics of correction by image sharpness are discussed, showing that in dilute aperture systems this method does not necessarily produce a unique image.
RESUMEN
The principle of redundant spacings calibration has previously been described for the purpose of calibrating piston phase aberration affecting elements of a dilute aperture array using a system of linear equations in terms of the aperture phases as well as object phase information. Here we develop matrices for the correction of piston phase aberration by use of image sharpness and also by phase retrieval. These are both presented in wavefront sensor formulation in order to draw analogy between the approaches. We then discuss solution ambiguity affecting both methods and describe array design criteria to prevent such ambiguity. The problem of increased image aliasing under image sharpness correction is also highlighted.
RESUMEN
OBJECTIVE: To obtain a better understanding of how stroke events are communicated to 9-1-1 telecommunicators, and how telecommunicators and emergency medical services (EMS) personnel respond to such calls. METHODS: The authors identified 104 patients with a hospital discharge diagnosis of stroke or transient ischemic attack who were transported to hospital by ambulance in two North Carolina counties during 1999 and 2000. Ambulance call reports were abstracted and linked to 9-1-1 call center audiotapes, which were transcribed and verified. RESULTS: Of the 104 calls, 44 were made by medical personnel, 38 by a family member, eight by a bystander or neighbor, five undetermined, and three by other nonmedical personnel. In only six instances (6%) was the call placed by the patient. The most common symptoms reported were altered mental status (40%), trouble walking (32%), impaired speech (27%), and abnormal breathing (27%). Although the word "stroke" was often used (45%), 9-1-1 telecommunicators classified the calls as a stroke in only 31% of cases. However, in the majority of cases (79%), paramedics were dispatched at the highest priority. The median time from dispatch of EMS to patient arrival at the hospital was 41 minutes, approximately half of which was spent at the scene. CONCLUSION: Although typical stroke symptoms are commonly described, calls are often not classified as "strokes" by telecommunicators. Nevertheless, because of the symptoms reported during the calls, the majority of cases are treated as high priority by telecommunicators.