Global Attracting Equilibria for Coupled Systems with Ceiling Density Dependence

In this paper, we present a system of two difference equations modeling the dynamics of a coupled population with two patches. Each patch can house only a limited number of individuals (called a carrying capacity) because resources like food and breeding sites are limited in each patch. We assume that the population in each patch is governed by a linear model until reaching a carrying capacity in each patch, resulting in map which is nonlinear and not sublinear. We analyze the global attractors of this model

Spatio-temporal variation in childhood growth in Nigeria: a comparison of aggregation and interpolation

The mean height-for-age Z-score (HAZ) of children under five is an important indicator of the health status of a population. HAZ values are frequently aggregated and reported at the national level, potentially obscuring important within-country variation. We evaluated aggregation and interpolation methods to provide sub-national estimates over space and time, using survey data from Nigeria in 1990, 2003, 2008, and 2013. We aggregated HAZ values by region and by state, and interpolated the values spatially and spatio-temporally using thin plate splines. The results were evaluated with cross-validation using the root mean squared error (RMSE) as a measure of goodness of fit. Mean HAZ values increased from 1990 to 2013, but values rose more sharply in southern Nigeria than in the North. All methods performed better than assuming a constant national average. The state-level aggregation, and the spatial and spatio-temporal interpolations had similar RMSE values, but the interpolation methods showed more detailed spatial variation. Spatio-temporal interpolation produced good results in all conditions, including in years with sparse sampling and when extrapolating to years for which there were no observations

Global Attracting Equilibria for Coupled Systems with Ceiling Density Dependence

In this paper, we present a system of two difference equations modeling the dynamics of a coupled population with two patches. Each patch can house only a limited number of individuals (called a carrying capacity) because resources like food and breeding sites are limited in each patch. We assume that the population in each patch is governed by a linear model until reaching a carrying capacity in each patch, resulting in map which is nonlinear and not sublinear. We analyze the global attractors of this model

Niches of three sympatric montane ground-dwelling squirrels: Relative importance of climate, topography, and landcover.

Species with different ecological niches will likely exhibit distinct responses to a changing environment. Differences in the magnitude of niche specialization may also indicate which species may be more vulnerable to environmental change, as many life-history characteristics are known to affect climate change vulnerability. We characterized the niche space of three sympatric high-elevation ground-dwelling squirrels, yellow-bellied marmot (Marmota flaviventer), Belding's ground squirrel (Urocitellus beldingi), and golden-mantled ground squirrel (Callospermophilus lateralis), in the alpine and upper subalpine regions of the Sierra Nevada in California. We used 5879 observations of individual squirrels, collected from 4 years (2009-2012) of transect survey data, to quantify which ecogeographical variable types (climate, topography, or landcover) were most important in defining the niche of each species. We conducted Ecological Niche Factor Analysis to quantify the niche and generate indices of "marginality" (magnitude of selection) and "specialization" (narrowness of niche space). All three species demonstrated differential use of niche space when compared to the available niche space. Moreover, the relative importance of the variables shaping the niche differed among these species. For example, the presence of meadows was important in defining the niche for U. beldingi and M. flaviventer, but the presence of conifers was important to C. lateralis. Precipitation was important in defining the niche for all three species, positively so for U. beldingi, and negatively for the other two species. The niche breadth of these three species was also positively associated with geographic range size. Mammals in high-elevation mountain systems often are perceived as vulnerable to climate shifts, but our results underscore the importance of also including non-climate-based factors in defining the niche. The overall magnitude of niche selection for all three species was driven by a combination of topographic, climatic, and landcover factors; thus, efforts to forecast areas where these species can persist in the future need to evaluate from more than just a climatic perspective

Measurement of the ZZ production cross section and search for anomalous couplings in 2l2l' final states in pp collisions at sqrt(s)=7 TeV

Submitted to the Journal of High Energy Physics ; see paper for full list of authorsA measurement is presented of the ZZ production cross section in the ZZ to 2l 2l' decay mode with l = e, mu and l' = e, mu, tau in proton-proton collisions at sqrt(s) = 7 TeV with the CMS experiment at the LHC. Results are based on data corresponding to an integrated luminosity of 5.0 inverse femtobarns. The measured cross section sigma(pp to ZZ) = 6.24 [+0.86/-0.80] (stat.) [+0.41/-0.32] (syst.) +/- 0.14 (lumi.) pb is consistent with the standard model predictions. The following limits on ZZZ and ZZ gamma anomalous trilinear gauge couplings are set at 95% confidence level: -0.011 f[4;Z] < 0.012, -0.012 < f[5;Z] < 0.012, -0.013 < f[4;gamma] < 0.015, and -0.014 < f[5,gamma] < 0.014

Problems in measuring the cash recovery rate and measurement error in estimates of the firm IRR

This paper considers the impact on estimates of the IRR derived from the cash recovery rate approach to the estimation of economic performance of an inability to observe the conceptually defined CRR from accounting data. In particular, it considers a typical proxy used in empirical applications of the CRR approach and asks the question — under what circumstances will this proxy fail to measure the true CRR? Two circumstances are identified. First, the empirical CRR will not measure the true CRR when advertising and research expenditures exist which should be treated as part of the composite investment (and, hence, as investment expenditures) but are expensed in the accounting records -referred to as the capitalize/expense case. Second, the empirical CRR will not measure the true CRR when the composite investment is made up of projects with different lives — referred to as the retirement case. For these two cases, relationships are developed between the proxy and the true CRR. From these relationships the impact of errors in measuring the CRR on estimates of the IRR are deduced. Analytically, it is demonstrated that, in the capitalize/expense case, the inability to measure the CRR produces measurement error in the IRR estimate that is monotonically and negatively related to the rate of investment growth. Further, as the proportion of expensed investment expenditures increases, measurement error increases if the investment growth rate is less than the IRR and decreases if the investment growth rate is greater than the IRR. In the retirement case, it is identified analytically that measurement error also will be monotonically and negatively related to the investment growth rate. This is the case even though the analyst is able to specify the basic relationship between investment outflows and subsequent cash inflows (the inability to spec ify this basic relationship is a problem considered in many papers on the CRR approach). Numerical examples suggest that these effects are not insignificant in size a priori.