Using Spatial Analysis to Study the Values of Variable Rate Technology and Information

We present a review of the last few years' literature on the economic feasibility of variable rate technology in agriculture. Much of the research on this topic has involved the estimation of site-specific yield response functions. Data used for such estimations most often inherently lend themselves to spatial analysis. We discuss the different types of spatial analyses that may be appropriate in estimating various types yield response functions. Then, we present a taxonomy for the discussion of the economics of precision agriculture technology and information. We argue that precision agriculture technology and information must be studied together since they are by nature economic complements. We contend that longer-term, multi-location agronomic experiments are needed for the estimation of ex ante optimal variable input rates and the expected profitability of variable rate technology and information gathering. We use our taxonomy to review the literature and its results with consistency and rigor.precision agriculture, spatial econometrics, variable rate technology, Research and Development/Tech Change/Emerging Technologies, C31, O33, Q16,

Cold Dark Matter Substructure and Galactic Disks

We perform a set of high-resolution, dissipationless N-body simulations to investigate the influence of cold dark matter (CDM) substructure on the dynamical evolution of thin galactic disks. Our method combines cosmological simulations of galaxy-sized CDM halos to derive the properties of substructure populations and controlled numerical experiments of consecutive subhalo impacts onto initially-thin, fully-formed disk galaxies. We demonstrate that close encounters between massive subhalos and galactic disks since z~1 should be common occurrences in LCDM models. In contrast, extremely few satellites in present-day CDM halos are likely to have a significant impact on the disk structure. One typical host halo merger history is used to seed controlled N-body experiments of subhalo-disk encounters. As a result of these accretion events, the disk thickens considerably at all radii with the disk scale height increasing in excess of a factor of 2 in the solar neighborhood. We show that interactions with the subhalo population produce a wealth of distinctive morphological signatures in the disk stars including: conspicuous flares; bars; low-lived, ring-like features in the outskirts; and low-density, filamentary structures above the disk plane. We compare a resulting dynamically-cold, ring-like feature in our simulations to the Monoceros ring stellar structure in the MW. The comparison shows quantitative agreement in both spatial distribution and kinematics, suggesting that such observed complex stellar components may arise naturally as disk stars are excited by encounters with subhalos. These findings highlight the significant role of CDM substructure in setting the structure of disk galaxies and driving galaxy evolution.Comment: 10 pages, 4 figures. To appear in the proceedings of the IAU Symposium No. 254 "The Galaxy Disk in Cosmological Context", Copenhagen 9-13 June 2008, Denmark, (Eds.) J. Andersen, J. Bland-Hawthorn & B. Nordstrom, Cambridge University Pres

Shapes of dark matter halos

I present an analysis of the density shapes of dark matter halos in LCDM and LWDM cosmologies. The main results are derived from a statistical sample of galaxy-mass halos drawn from a high resolution LCDM N-body simulation. Halo shapes show significant trends with mass and redshift: low-mass halos are rounder than high mass halos, and, for a fixed mass, halos are rounder at low z. Contrary to previous expectations, which were based on cluster-mass halos and non-COBE normalized simulations, LCDM galaxy-mass halos at z=0 are not strongly flattened, with short to long axis ratios of s = 0.70 +/- 0.17. I go on to study how the shapes of individual halos change when going from a LCDM simulation to a simulation with a warm dark matter power spectrum (LWDM). Four halos were compared, and, on average, the WDM halos are more spherical than their CDM counterparts (s =0.77 compared to s = 0.71). A larger sample of objects will be needed to test whether the trend is significant.Comment: 5 pages, 2 figures, to appear in proceedings of the May 2001 Yale workshop "The Shapes of Galaxies and their Halos