Monetary Rules and Stock Market Value

We examine the wealth effects of two widely-advocated monetary rules. An inflation rule offers lower dividend volatility than a money growth rule, but the latter can provide higher expected dividends. Thus, the real value of the stock market is higher under the inflation rule if and only if the market's intertemporal elasticity of substitution is sufficiently low

Radioactive Probes of the Supernova-Contaminated Solar Nebula: Evidence that the Sun was Born in a Cluster

We construct a simple model for radioisotopic enrichment of the protosolar nebula by injection from a nearby supernova, based on the inverse square law for ejecta dispersion. We find that the presolar radioisotopes abundances (i.e., in solar masses) demand a nearby supernova: its distance can be no larger than 66 times the size of the protosolar nebula, at a 90% confidence level, assuming 1 solar mass of protosolar material. The relevant size of the nebula depends on its state of evolution at the time of radioactivity injection. In one scenario, a collection of low-mass stars, including our sun, formed in a group or cluster with an intermediate- to high-mass star that ended its life as a supernova while our sun was still a protostar, a starless core, or perhaps a diffuse cloud. Using recent observations of protostars to estimate the size of the protosolar nebula constrains the distance of the supernova at 0.02 to 1.6 pc. The supernova distance limit is consistent with the scales of low-mass stars formation around one or more massive stars, but it is closer than expected were the sun formed in an isolated, solitary state. Consequently, if any presolar radioactivities originated via supernova injection, we must conclude that our sun was a member of such a group or cluster that has since dispersed, and thus that solar system formation should be understood in this context. In addition, we show that the timescale from explosion to the creation of small bodies was on the order of 1.8 Myr (formal 90% confidence range of 0 to 2.2 Myr), and thus the temporal choreography from supernova ejecta to meteorites is important. Finally, we can not distinguish between progenitor masses from 15 to 25 solar masses in the nucleosynthesis models; however, the 20 solar mass model is somewhat preferred.Comment: ApJ accepted, 19 pages, 3 figure

Caenorhabditis elegans predation on Bacillus anthracis: Decontamination of spore contaminated soil with germinants and nematodes

Remediation of Bacillus anthracis-contaminated soil is challenging and approaches to reduce overall spore levels in environmentally contaminated soil or after intentional release of the infectious disease agent in a safe, low-cost manner are needed. B. anthracis spores are highly resistant to biocides, but once germinated they become susceptible to traditional biocides or potentially even natural predators such as nematodes in the soil environment. Here, we describe a two-step approach to reducing B. anthracis spore load in soil during laboratory trials, whereby germinants and Caenorhabditis elegans nematodes are applied concurrently. While the application of germinants reduced B. anthracis spore load by up to four logs depending on soil type, the addition of nematodes achieved a further log reduction in spore count. These laboratory based results suggest that the combined use of nematodes and germinants could represent a promising approach for the remediation of B. anthracis spore contaminated soil

The Cool ISM in Elliptical Galaxies. I. A Survey of Molecular Gas

We present preliminary results from a survey of CO emission from members of a volume-limited sample of non-cluster elliptical galaxies. Our intent is to compare the gas properties of these ellipticals to a sample of lenticulars selected using similar criteria. The data, although still sparse, suggest that the cool gas in ellipticals shows the same puzzling upper mass cutoff found in the lenticular galaxies. We find, however, significantly lower detection rates and possibly much lower H2/HI mass ratios in the ellipticals. The detection rate is higher among the lower-mass galaxies, as has been found previously. This seems puzzling given that the deeper potential wells of the larger galaxies ought to make gas retention easier, but perhaps that effect is overwhelmed by feedback from the central suppermassive black hole. As we have observed ~40 percent of our sample, the conclusions are necessarily tentative at this time.Comment: Accepted for publication in the Astrophysical Journa

The Life and Death of Dense Molecular Clumps in the Large Magellanic Cloud

We report the results of a high spatial (parsec) resolution HCO+ (J = 1-0) and HCN (J = 1-0) emission survey toward the giant molecular clouds of the star formation regions N105, N113, N159, and N44 in the Large Magellanic Cloud. The HCO+ and HCN observations at 89.2 and 88.6 GHz, respectively, were conducted in the compact configuration of the Australia Telescope Compact Array. The emission is imaged into individual clumps with masses between 10^2 and 10^4 solar masses and radii of <1 pc to ~2 pc. Many of the clumps are coincident with indicators of current massive star formation, indicating that many of the clumps are associated with deeply-embedded forming stars and star clusters. We find that massive YSO-bearing clumps tend to be larger (>1 pc), more massive (M > 10^3 solar masses), and have higher surface densities (~1 g cm^-2), while clumps without signs of star formation are smaller (<1 pc), less massive (M < 10^3 solar masses), and have lower surface densities (~0.1 g cm^-2). The dearth of massive (M >10^3 solar masses) clumps not bearing massive YSOs suggests the onset of star formation occurs rapidly once the clump has attained physical properties favorable to massive star formation. Using a large sample of LMC massive YSO mid-IR spectra, we estimate that ~2/3 of the massive YSOs for which there are Spitzer mid-IR spectra are no longer located in molecular clumps; we estimate that these young stars/clusters have destroyed their natal clumps on a time scale of at least 3 x 10^{5}$ yrs.Comment: Accepted to ApJ 3-19-201