Very-Long-Baseline Radio Interferometry: The Mark III System for Geodesy, Astrometry, and Aperture Synthesis.

The Mark III very-long-baseline interferometry (VLBI) system allows recording and later processing of up to 112 megabits per second from each radio telescope of an interferometer array. For astrometric and geodetic measurements, signals from two radio-frequency bands (2.2 to 2.3 and 8.2 to 8.6 gigahertz) are sampled and recorded simultaneously at all antenna sites. From these dual-band recordings the relative group delays of signals arriving at each pair of sites can be corrected for the contributions due to the ionosphere. For many radio sources for which the signals are sufficiently intense, these group delays can be determined with uncertainties under 50 picoseconds. Relative positions of widely separated antennas and celestial coordinates of radio sources have been determined from such measurements with 1 standard deviation uncertainties of about 5 centimeters and 3 milliseconds of arc, respectively. Sample results are given for the lengths of baselines between three antennas in the United States and three in Europe as well as for the arc lengths between the positions of six extragalactic radio sources. There is no significant evidence of change in any of these quantities. For mapping the brightness distribution of such compact radio sources, signals of a given polarization, or of pairs of orthogonal polarizations, can be recorded in up to 28 contiguous bands each nearly 2 megahertz wide. The ability to record large bandwidths and to link together many large radio telescopes allows detection and study of compact sources with flux densities under 1 millijansky.

Epidemiologic features of head injury in a predominantly rural population.

The characteristics of occurrence of head trauma were studied in north central Virginia. In 1978, 735 cases of head trauma were identified with documented head injuries occurring within the defined service area, and with a minimum overnight hospital stay. Overall occurrence was 208/100,000 population. The highest occurrence was found in the 15-19 age group (407/100,000). Nonwhites showed higher rates than whites. Motor vehicle crashes were the most frequent mechanism of injury (55% of patients) followed by falls (20%), and interpersonal violence (11%). Short-term time trends reveal unique daily, weekly, and seasonal patterns for motor vehicle crashes, falls, and interpersonal violence. Selected prevention strategies are discussed. The use of passive restraints in motor vehicles is recommended as one important means of reducing the occurrence and severity of head injuries.

The nurse practitioner: role, physician utilization, patient acceptance.

A comprehensive study of nurse practitioners was undertaken by the University of Virginia Schools of Medicine and Nursing in the summer of 1974 to evaluate nurse practitioner training programs of the University of Virginia and to determine the effectiveness and responsibilities of nurse practitioners in various practice settings. Data on nurse practitioners in a number of locations in Virginia and in the Philadelphia metropolitan area were collected and analyzed to determine the way in which the nurse practitioners' time was allocated among various duties and to evaluate nurse practitioner performance by physicians and patients. Nurse practitioners performed a wide variety of clinical and nonclinical tasks. Most physicians were satisfied with the practitioner's performance, although there was some inconsistency between physicians and nurse practitioners regarding actual duties performed. A high percentage of physicians stated they would hire a nurse practitioner to replace one who left their employ. Physicians' reasons for hiring a nurse practitioner, as well as their previous contact with such personnel, were examined. Regarding patient attitudes toward nurse practitioners, data indicated that patients were satisfied with nurse practitioners and felt comfortable being treated by them.