Abelian networks II. Halting on all inputs

Abelian networks are systems of communicating automata satisfying a local commutativity condition. We show that a finite irreducible abelian network halts on all inputs if and only if all eigenvalues of its production matrix lie in the open unit disk.Comment: Supersedes sections 5 and 6 of arXiv:1309.3445v1. To appear in Selecta Mathematic

Abelian networks III. The critical group

The critical group of an abelian network is a finite abelian group that governs the behavior of the network on large inputs. It generalizes the sandpile group of a graph. We show that the critical group of an irreducible abelian network acts freely and transitively on recurrent states of the network. We exhibit the critical group as a quotient of a free abelian group by a subgroup containing the image of the Laplacian, with equality in the case that the network is rectangular. We generalize Dhar's burning algorithm to abelian networks, and estimate the running time of an abelian network on an arbitrary input up to a constant additive error.Comment: supersedes sections 7 and 8 of arXiv:1309.3445v1. To appear in the Journal of Algebraic Combinatoric

International City/County Management Association 1999 Revenue Estimation Survey Revisited

In 1899 the National Municipal League declared that it was the duty of the Mayor to submit to the Council the annual budget of current expenses of the city, for almost as long, the budgeting process has been researched (Hou, 2006). Researching budgets is important and needed but comparatively little attention has been paid to revenue forecasts or to those responsible for the generation of revenue forecasts. Professional public administrators responsible for generating revenue forecasts have largely been overlooked in research. Judging by the lack of scholarly material available in academic journals, it appears the political process in which budget forecasts are created is of primary concern to researchers. In 1999 the International City/County Management Association (ICMA) fielded the Revenue Estimation survey. This study revealed, although forecasters have been educated in the fields of public administration and business administration, they overwhelmingly rely on less sophisticated forecasting models comprised of naïve and incremental technical approaches when building revenue forecasts (Bahl et al., 1984; Jung & Kang, 2007; Pinkowski, 2004; Reddick, 2004; Sun, 2005; Zorn, 1982). Compounding this issue of using less sophisticated forecast models, city governments have become increasingly reliant on less stable and less predictable revenue sources(Bland, 2009). In 2009, after the beginning of the most recent recession, media outlets began reporting stories highlighting economic troubles at all levels of government. Local governments in particular have not been immune to the financial stresses of the last six years (Bland, 2009). The evident lack of scholarly material focused on forecasters and the increased need for more sophisticated forecast models provides a research opportunity that may lead to increased forecast accuracy. This project may also have a positive impact on the financial well-being of governments facing increased revenue uncertainty. Given this lack of scholarly research, permission was granted by ICMA to re-field the 1999 Revenue Estimation survey. Re-fielding the survey in 2011 will provide a complementary dataset to the original 1999 dataset from which comparative analyses can be made. The purpose of this research project is to determine if revenue forecasting competencies of city employees became more sophisticated between 1999 and 2011

The Effect of Formation Redshifts on the Cluster Mass-Temperature Relation

I employ an ensemble of hydrodynamical simulations and the XSPEC MEKAL emission model to reproduce observable spectral and flux-weighted temperatures for 24 clusters. Each cluster is imaged at 16 points in its history, which allows the investigation of evolutionary effects on the mass-temperature relation. In the zero redshift scaling relations, I find no evidence for a relationship between cluster temperature and formation epoch for those clusters which acquired 75% of their final mass since a redshift of 0.6. This result holds for both observable and intrinsic intracluster medium temperatures, and implies that halo formation epochs are not an important variable in analysis of observable cluster temperature functions.Comment: 6 pages, 3 postscript figures, submitted to MNRAS Letter

Effect of Jump Direction and External Load on Single-Legged Jump-Landing Biomechanics

International Journal of Exercise Science 13(1): 234-248, 2020. External load may increase an individual’s risk of non-contact anterior cruciate ligament (ACL) injury during single-legged jump-landing (SLJL).This study evaluated the effects of jump direction and external load on hip and knee joint motion and time to stabilization (TTS) during SLJL. Seventeen active males (n = 8) and females (22.2 ± 3.0 y, 1.75 ± 0.08 m, 73.4 ± 12.0 kg) participated in this randomized, crossover designed study. Single-legged jump-landings performed in two conditions, including without external load (BW) and with a torso-worn weight vest equal to 10% of the participant’s body weight (BW+10%), from backward, forward, medial, and lateral SLJL directions. Two-way repeated measures ANOVA did not identify any significant interactions (P \u3e .01, η2: \u3c .001 - .037), but some main effects for condition with small effect sizes were identified (P \u3c .01,η2: .009 - .039). Several main effects for SLJL direction were identified with larger effect sizes (P \u3c .01, η2: .010 - .574). This suggests SLJL direction may challenge different components of SLJL biomechanics, and that recreationally active, college-aged individuals may possess effective compensatory mechanisms that can mitigate the effect of BW+10%

Fast, exact CMB power spectrum estimation for a certain class of observational strategies

We describe a class of observational strategies for probing the anisotropies in the cosmic microwave background (CMB) where the instrument scans on rings which can be combined into an n-torus, the {\em ring torus}. This class has the remarkable property that it allows exact maximum likelihood power spectrum estimation in of order $N^2$ operations (if the size of the data set is $N$) under circumstances which would previously have made this analysis intractable: correlated receiver noise, arbitrary asymmetric beam shapes and far side lobes, non-uniform distribution of integration time on the sky and partial sky coverage. This ease of computation gives us an important theoretical tool for understanding the impact of instrumental effects on CMB observables and hence for the design and analysis of the CMB observations of the future. There are members of this class which closely approximate the MAP and Planck satellite missions. We present a numerical example where we apply our ring torus methods to a simulated data set from a CMB mission covering a 20 degree patch on the sky to compute the maximum likelihood estimate of the power spectrum $C_\ell$ with unprecedented efficiency.Comment: RevTeX, 14 pages, 5 figures. A full resolution version of Figure 1 and additional materials are at http://feynman.princeton.edu/~bwandelt/RT

Heterotrophic respiration in disturbed forests : a review with examples from North America

Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 116 (2011): G00K04, doi:10.1029/2010JG001495.Heterotrophic respiration (RH) is a major process releasing carbon to the atmosphere and is essential to understanding carbon dynamics in terrestrial ecosystems. Here we review what is known about this flux as related to forest disturbance using examples from North America. The global RH flux from soils has been estimated at 53–57 Pg C yr−1, but this does not include contributions from other sources (i.e., dead wood, heart-rots). Disturbance-related inputs likely account for 20–50% of all RH losses in forests, and disturbances lead to a reorganization of ecosystem carbon pools that influences how RH changes over succession. Multiple controls on RH related to climate, the material being decomposed, and the decomposers involved have been identified, but how each potentially interacts with disturbance remains an open question. An emerging paradigm of carbon dynamics suggests the possibility of multiple periods of carbon sinks and sources following disturbance; a large contributing factor is the possibility that postdisturbance RH does not always follow the monotonic decline assumed in the classic theory. Without a better understanding and modeling of RH and its controlling factors, it will be difficult to estimate, forecast, understand, and manage carbon balances of regions in which disturbance frequency and severity are changing. Meeting this challenge will require (1) improved field data on processes and stores, (2) an improved understanding of the physiological and environmental controls of RH, and (3) a more formal analysis of how model structure influences the RH responses that can be predicted.Support was provided by the U.S. Geologic Survey and the Kaye and Ward Richardson Endowment

Herbivores shape woody plant communities in theKruger National Park: lessons from three long-termexclosures

The role of grazers in determining vegetation community compositions and structuring plant communities is well recognised in grassy systems. The role of browsers in affecting savanna woody plant communities is less clear. We used three long-term exclosures in the Kruger National Park to determine the effect of browsers on species compositions and population structures of woody communities. Species assemblages, plant traits relating to browsing and soil nutrients were compared inside and outside of the exclosures. Our results showed that browsers directly impact plant species distributions, densities and population structures by actively selecting for species with traits which make them desirable to browsers. Species with high leaf nitrogen, low total phenolic content and low acid detergent lignin appeared to be favoured by herbivores and therefore tend to be rare outside of the exclosures. This study also suggested that browsers have important indirect effects on savanna functioning, as the reduction of woody cover can result in less litter of lower quality, which in turn can result in lower soil fertility. However, the magnitude of browser effects appeared to depend on inherent soil fertility and climate. CONSERVATION IMPLICATIONS: Browsers were shown to have significant impacts on plant communities. They have noticeable effects on local species diversity and population structure, as well as soil nutrients. These impacts are shown to be related to the underlying geology and climate. The effects of browsers on woody communities were shown to be greater in low rainfall, fertile areas compared to high rainfall, infertile soils