Multi--Pressure Polytropes as Models for the Structure and Stability of Molecular Clouds. I. Theory

Molecular clouds are supported by thermal pressure, magnetic pressure, and turbulent pressure. Each of these can be modeled with a polytropic equation of state, so that overall the total pressure is the sum of the individual components. We model the turbulent pressure as being due to a superposition of Alfven waves. The theory of polytropes is generalized to allow for the flow of entropy in response to a perturbation, as expected for the entropy associated with wave pressure. The equation of state of molecular clouds is "soft", so that the properties of the clouds are generally governed by the conditions at the surface. In general, the polytropes are not isentropic, and this permits large density and pressure drops to occur between the center and the edge of the polytropes, as is observed.Comment: Submitted to ApJ with 10 figure

Much Ado About Nothing: Several Large-Area Surveys for Radio Pulsars From Arecibo

We report surveyed regions and flux limits for several large-area surveys at 430 MHz for radio pulsars using the 305 m reflector at Arecibo, Puerto Rico. The surveys used integration times between 8 and 67 s and covered a total area of ~515 square degrees. No previously undiscovered pulsars were detected in these regions, although all previously known pulsars were detected. The nondetection of new pulsars places constraints on the population of low-luminosity pulsars and must be taken into account in estimates of the local density of millisecond pulsars