Evidence for a solar system-size accretion disk around the massive protostar G192.16-3.82.

Seven-millimeter continuum observations of a massive bipolar outflow source, G192.16-3.82, were made at a milli-arc-second resolution with a capability that links the National Radio Astronomy Observatory's Very Large Array radio interferometer with the Very Long Baseline Array antenna, located in Pie Town, New Mexico. The observations provide evidence for a true accretion disk that is about the size of our solar system and located around a massive star. A model of the radio emission suggests the presence of a binary protostellar system. The primary protostar, G192 S1, at the center of the outflow, with a protostar mass of about 8 to 10 times the solar mass, is surrounded by an accretion disk with a diameter of 130 astronomical units (AU). The mass of the disk is on the order of the protostar mass. The outflow is poorly collimated with a full opening angle of about 40 degrees; there is no indication of a more highly collimated jetlike component. The companion source, G192 S2, is located 80 AU north of the primary source.

Feeding patterns and operant responding by wild and domesticated rats in self-maintenance conditions.

The feeding activity of domesticated and wild rats was studied. The rats obtained all their food by lever pressing in two-lever operant chambers. Concurrent variable interval (VI) and concurrent variable ratio (VR) schedules operated continuously for successive 4-day periods. Feeding occurred as regular, discrete meals, mostly during the night. The schedules did not affect the number or size of meals or the total amount eaten. The interval schedules significantly extended the duration of meals and reduced intermeal intervals. Lever pressing was characterised on concurrent VI schedules by low response rates and frequent alternation and that on concurrent VR schedules by higher response rates confined to one lever. The wild rats ate significantly more than the domesticated rats by increasing the number but not the size of meals, primarily during the night. Feeding behaviour and operant responding are discussed in relation to the effects of domestication and economy of effort in food-seeking. The inhibition caused by handling and food deprivation, which impairs the performance of wild rodents in short sessions is avoided by providing self-maintenance conditions.

Field trials of second-generation anticoagulants against difenacoum-resistant Norway rat populations.

Trials of rodenticidal baits containing 50 p.p.m. difenacoum, 50 p.p.m. bromadiolone or 20 p.p.m. brodifacoum were carried out on farmsteads against populations of Rattus norvegicus containing difenacoum-resistant individuals. Six difenacoum treatments failed in 14--42 days of baiting. Two treatments with bromadiolone succeeded in 23 and 33 days, but four further treatments lasting 35--56 days failed to eradicate the populations. Brodifacoum gave virtually complete control of six populations in 21--73 days and of the ten residual populations left behind by the other two compounds, after baiting for a further 11--85 days. The performance of both bromadiolone and brodifacoum was well below that reported by previous investigators, indicating the possibility of low-grade resistance to these compounds in the difenacoum-resistant strain.