Stability of metal-rich very massive stars

We revisit the stability of very massive nonrotating main-sequence stars at solar metallicity, with the goal of understanding whether radial pulsations set a physical upper limit to stellar mass. Models of up to 938 solar masses are constructed with the Mesa code, and their linear stability in the fundamental mode, assumed to be the most dangerous, is analysed with a fully nonadiabatic method. Models above 100 MSun have extended tenuous atmospheres ("shelves") that affect the stability of the fundamental. Even when positive, this growth rate is small, in agreement with previous results. We argue that small growth rates lead to saturation at small amplitudes that are not dangerous to the star. A mechanism for saturation is demonstrated involving nonlinear parametric coupling to short-wavelength g modes and the damping of the latter by radiative diffusion. The shelves are subject to much more rapidly growing strange modes. This also agrees with previous results but is extended here to higher masses. The strange modes probably saturate via shocks rather than mode coupling but have very small amplitudes in the core, where almost all of the stellar mass resides. Although our stellar models are hydrostatic, the structure of their outer parts suggests that optically thick winds, driven by some combination of radiation pressure, transsonic convection, and strange modes, are more likely than pulsation in the fundamental mode to limit the main-sequence lifetime.Comment: 14 pages, 8 figures, 1 appendix; this version to be published in MNRA

The structure of US local governments is often a poor predictor of local economic growth.

In the US metropolitan areas can be organized in different ways, with some areas having more or fewer local governments, with competing schools of thought over which structure leads to greater economic growth. In new research which examines over 300 US metropolitan areas, Christopher Goodman finds that the structure of local governments can be important, but it is often specific to certain regions and can be easily overshadowed by the underlying economic characteristics of metropolitan areas

Florida is dissolving the Reedy Creek Improvement District, home of Disney World. What happens next is anyone’s guess.

Following criticism from the Disney company over a controversial education bill, last week Florida’s Governor, Ron DeSantis signed legislation which would dissolve the Reedy Creek Improvement District, the location of the company’s Disney World Resort. Chris Goodman explains the history of the special district, how it has functioned, and the uncertainty around what may happen next

Meteorological satellite products support for project COHMEX

The first year effort focussed on real-time support and satellite data collection during the field phase of COHMEX. Work efforts following the field phase of COHMEX concentrated on post-processing of the real-time data sets, and generation of enhanced, research-quality satellite data sets for selected COHMEX core days. These satellite-derived data sets will augment the special COHMEX conventional data base with high horizontal and temporal resolution information. The data sets will be examined for their usefulness in delineating important elements in the meteorological environment leading to convective activity. In addition, a limited research effort was conducted using the Cooperative Institute for Meteorological Satellite Studies (CIMSS) 4-d data assimilation system in conjunction with evaluating VISSR Atmospheric Sounder (VAS) and His-resolution Interferometer Sounder (HIS) data. The need to address the characteristics of the data types, and the problems they introduce into 4-d assimilation procedures is evident. The HIS instrument was flown aboard an ER-2 aircraft on several occasions during COHMEX. One of the flights was chosen for further study. Processed VAS soundings and COHMEX radiosonde data were also collected for this day. The case study included an evaluation of the HIS and VAS data and an impact study of the data on the assimilation system analysis

Consequentialism, Climate Harm and Individual Obligations

Does the decision to relax by taking a drive rather than by taking a walk cause harm? In particular, do the additional carbon emissions caused by such a decision make anyone worse off? Recently several philosophers have argued that the answer is no, and on this basis have gone on to claim that act-consequentialism cannot provide a moral reason for individuals to voluntarily reduce their emissions. The reasoning typically consists of two steps. First, the effect of individual emissions on the weather is miniscule: the planet’s meteorological system is so large, and the size of individual emissions so tiny, that whatever impact an individual emission has on the weather must be vanishingly small. Second, vanishingly small impacts aren’t morally relevant because no one could possibly tell the difference between such an impact occurring and it not occurring. In this paper, we show why both steps are mistaken, and hence why act-consequentialism implies that each of us has an individual obligation to do what we can to stop damaging the climate, including by refraining from, or perhaps by purchasing offsets against, our own individual luxury carbon emissions

Speed of sound in disordered Bose-Einstein condensates

Disorder modifies the sound-wave excitation spectrum of Bose-Einstein condensates. We consider the classical hydrodynamic limit, where the disorder correlation length is much longer than the condensate healing length. By perturbation theory, we compute the phonon lifetime and correction to the speed of sound. This correction is found to be negative in all dimensions, with universal asymptotics for smooth correlations. Considering in detail optical speckle potentials, we find a quite rich intermediate structure. This has consequences for the average density of states, particularly in one dimension, where we find a "boson dip" next to a sharp "boson peak" as function of frequency. In one dimension, our prediction is verified in detail by a numerical integration of the Gross-Pitaevskii equation.Comment: final, extended version with 2 new figure

An Incremental Iterated Response Model of Pragmatics

Recent Iterated Response (IR) models of pragmatics conceptualize language use as a recursive process in which agents reason about each other to increase communicative efficiency. These models are generally defined over complete utterances. However, there is substantial evidence that pragmatic reasoning takes place incrementally during production and comprehension. We address this with an incremental IR model. We compare the incremental and global versions using computational simulations, and we assess the incremental model against existing experimental data and in the TUNA corpus for referring expression generation, showing that the model can capture phenomena out of reach of global versions