A Young Globular Cluster in the Galaxy NGC 6946

A globular cluster ~15 My old that contains 5x10^5 Msun of stars inside an 11 pc radius has been found in the nearby spiral galaxy NGC 6946, surrounded by clouds of dust and smaller young clusters inside a giant circular bubble 300 pc in radius. At the edge of the bubble is an arc of regularly-spaced clusters that could have been triggered during the bubble's formation. The region is at the end of a spiral arm, suggesting an origin by the asymmetric collapse of spiral arm gas. The globular is one of the nearest examples of a cluster that is similar to the massive old globulars in the Milky Way. We consider the energetics of the bubble and possible formation mechanisms for the globular cluster, including the coalescence of smaller clusters.Comment: 20 pages, 7 figures, accepted for Astrophysical Journal Vol 535, June 1 200

Continuous star cluster formation in the spiral NGC 45

We determined ages for 52 star clusters with masses < 10^6 solar masses in the low surface brightness spiral galaxy NGC 45. Four of these candidates are old globular clusters located in the bulge. The remaining ones span a large age range. The cluster ages suggest a continuous star/cluster formation history without evidence for bursts, consistent with the galaxy being located in a relatively unperturbed environment in the outskirts of the Sculptor group.Comment: 4 pages, 3 figures. To appear in "Island Universes - Structure and Evolution of Disk Galaxies", Terschelling (Netherlands), July 200

The Cosmological Constant in the Quantum Multiverse

Recently, a new framework for describing the multiverse has been proposed which is based on the principles of quantum mechanics. The framework allows for well-defined predictions, both regarding global properties of the universe and outcomes of particular experiments, according to a single probability formula. This provides complete unification of the eternally inflating multiverse and many worlds in quantum mechanics. In this paper we elucidate how cosmological parameters can be calculated in this framework, and study the probability distribution for the value of the cosmological constant. We consider both positive and negative values, and find that the observed value is consistent with the calculated distribution at an order of magnitude level. In particular, in contrast to the case of earlier measure proposals, our framework prefers a positive cosmological constant over a negative one. These results depend only moderately on how we model galaxy formation and life evolution therein.Comment: 18 pages, 4 figures; matches the version published in Phys. Rev.

Farming for ecosystem services: A case study of multifunctional agriculture in Iowa, U.S.A

Agriculture in the United States faces major challenges for the 21st Century; it is at a pivotal stage in terms of integrating societal demands for sustainability and enhanced quality of life from agricultural lands. A growing understanding that farms play key roles in provisioning a wide range of ecosystem services is converging with a surge in public interest in the sustainability of farming and food systems. Farmers in the US Corn Belt are being solicited to manage for an increasingly complex and expanding suite of production and environmental benefits. However, managing landscapes for multiple objectives presents a major challenge and inherently increases management complexity. A critical challenge lies in defining an appropriate set of agriculture and environmental objectives for management across spatial scales. The goal of this research was to analyze the degree to which there is a capacity to manage agricultural landscapes for multiple ecosystem services with existing and emerging agricultural management practices. I addressed this goal by conducting a case study with stakeholders representing agricultural and environmental interests in Iowa, U.S.A., through a mixed methods approach utilizing the Delphi survey technique and in-person interviews with photo elicitation. This thesis presents the case study results regarding the relationship between ecosystem services and agricultural land management; identifies farm scale management practices that are most promising for achieving ecosystem service objectives across scales; and, additionally, presents a portfolio of landscape visualizations depicting scenarios of land management alternatives

Young and intermediate-age massive star clusters

An overview of our current understanding of the formation and evolution of star clusters is given, with main emphasis on high-mass clusters. Clusters form deeply embedded within dense clouds of molecular gas. Left-over gas is cleared within a few million years and, depending on the efficiency of star formation, the clusters may disperse almost immediately or remain gravitationally bound. Current evidence suggests that a few percent of star formation occurs in clusters that remain bound, although it is not yet clear if this fraction is truly universal. Internal two-body relaxation and external shocks will lead to further, gradual dissolution on timescales of up to a few hundred million years for low-mass open clusters in the Milky Way, while the most massive clusters (> 10^5 Msun) have lifetimes comparable to or exceeding the age of the Universe. The low-mass end of the initial cluster mass function is well approximated by a power-law distribution, dN/dM ~ M^{-2}, but there is mounting evidence that quiescent spiral discs form relatively few clusters with masses M > 2 x 10^5 Msun. In starburst galaxies and old globular cluster systems, this limit appears to be higher, at least several x 10^6 Msun. The difference is likely related to the higher gas densities and pressures in starburst galaxies, which allow denser, more massive giant molecular clouds to form. Low-mass clusters may thus trace star formation quite universally, while the more long-lived, massive clusters appear to form preferentially in the context of violent star formation.Comment: 21 pages, 3 figures. To appear as invited review article in a special issue of the Phil. Trans. Royal Soc. A: Ch. 9 "Star clusters as tracers of galactic star-formation histories" (ed. R. de Grijs). Fully peer reviewed. PDFLaTeX, requires rspublic.cls style fil

Stable and Unstable Circular Strings in Inflationary Universes

It was shown by Garriga and Vilenkin that the circular shape of nucleated cosmic strings, of zero loop-energy in de Sitter space, is stable in the sense that the ratio of the mean fluctuation amplitude to the loop radius is constant. This result can be generalized to all expanding strings (of non-zero loop-energy) in de Sitter space. In other curved spacetimes the situation, however, may be different. In this paper we develop a general formalism treating fluctuations around circular strings embedded in arbitrary spatially flat FRW spacetimes. As examples we consider Minkowski space, de Sitter space and power law expanding universes. In the special case of power law inflation we find that in certain cases the fluctuations grow much slower that the radius of the underlying unperturbed circular string. The inflation of the universe thus tends to wash out the fluctuations and to stabilize these strings.Comment: 15 pages Latex, NORDITA 94/14-

Report of the Iowa educational butter contest

At the beginning of the year 1903 an educational butter contest was instituted by the Dairy Department, at Ames, Iowa. The co-operation of the State Dairy Commissioner, H. R. Wright, was secured throughout the test. Each exhibitor sent a thirty pound tub of butter to Ames every other month, thus making six exhibits during the year. The butter was scored at Ames by Prof. G. L. McKay, and P. H. Kiefier, Assistant State Commissioner, acted as expert. As soon as the butter was scored a sample for chemical analysis was taken from each tub. The butter was then sent to New York to be re-scored by Mr. W. H. Healy. The average of the two scores at Ames and New York constituted the real basis upon which the final decision was rendered

The moisture content of butter and methods of controlling it

Much American butter has in the past been criticised by commercial judges on account of containing too much moisture (leaky butter, as butter judges term it), when, in reality, it showed by chemical analysis only a low percentage of water. This is undoubtedly due to improper incorporation of the moisture, as much butter, apparently dry, contains a high moisture content. It is also a well known fact that the amount of butter which is being made from a given amount of fat varies a great deal at the different creameries. Some makers are able to produce only 110 pounds of butter from 100 pounds of fat, while some other makers are able to produce 120 pounds of butter of equal commercial quality from the same amount of fat; that is, some are able to get an overrun of only about ten per cent, while some others obtain an overrun of about 20 per cent

Constraining star cluster disruption mechanisms

Star clusters are found in all sorts of environments and their formation and evolution is inextricably linked to the star formation process. Their eventual destruction can result from a number of factors at different times, but the process can be investigated as a whole through the study of the cluster age distribution. Observations of populous cluster samples reveal a distribution following a power law of index approximately -1. In this work we use M33 as a test case to examine the age distribution of an archetypal cluster population and show that it is in fact the evolving shape of the mass detection limit that defines this trend. That is to say, any magnitude-limited sample will appear to follow a dN/dt=1/t, while cutting the sample according to mass gives rise to a composite structure, perhaps implying a dependence of the cluster disruption process on mass. In the context of this framework, we examine different models of cluster disruption from both theoretical and observational standpoints.Comment: To appear in the proceedings of IAU Symposium 266: "Star Clusters: Basic Galactic Building Blocks Throughout Time And Space", eds. R. de Grijs and J. Lepin

Structural Refinement for the Modal nu-Calculus

We introduce a new notion of structural refinement, a sound abstraction of logical implication, for the modal nu-calculus. Using new translations between the modal nu-calculus and disjunctive modal transition systems, we show that these two specification formalisms are structurally equivalent. Using our translations, we also transfer the structural operations of composition and quotient from disjunctive modal transition systems to the modal nu-calculus. This shows that the modal nu-calculus supports composition and decomposition of specifications.Comment: Accepted at ICTAC 201