Universal scaling in the power-law size distribution of pelagic fish schools is established. The power-law exponent of size distributions is extracted through the data collapse. The distribution depends on the school size only through the ratio of the size to the expected size of the schools an arbitrary individual engages in. This expected size is linear in the ratio of the spatial population ...

We investigated the capacity of internal border control to limit influenza spread in an emergent pandemic in the context of Australia, a country with a low-population density and geopolitical boundaries that may facilitate restrictions. Mathematical models were used to study the time delay between epidemics in 2 population centers when travel restrictions were imposed. The models demonstrated t...

Many of Africa’s poor live in low-rainfall areas where relatively large investments may be needed to increase agricultural productivity. This paper uses the results from an assessment of expected returns to research on soil fertility management at the Kenya Agricultural Research Institute to explore the extent to which such investments can be justified on efficiency and equity grounds. While re...

BACKGROUND There are few studies on age and sex-specific asthma prevalence in the age range 1-6 years. The purpose of this report was to estimate age and sex specific asthma prevalence in preschool children and to analyse the influence of possible demographic and geographic determinants. METHODS All 70 allergen avoidance day-care centres and 140 matched ordinary day-care centres across Sweden...

A common technique of measuring population density of microorganisms grown in liquid media is to withdraw a sample of the suspension and measure its apparent optical density with a spectrophotometer. The device we describe is capable of continually and automatically monitoring the population density of microorganisms grown in suspension.

The SIR-model is a basic epidemic model that classifies a population into three subgroups: susceptible S, infected I and removed R. This model does not take into consideration the spatial distribution of each subgroup, but considers the total number of individuals belonging to each subgroup. There are many variants of the SIR-model. For studying the spatial distribution, stochastic processes ha...

BACKGROUND This study aims to investigate whether mothers' perceived neighbourhood environment is associated with outdoor playtime of 2- to 3.5-year-old children. METHODS Cross-sectional analyses were conducted using data from the Healthy Beginnings Trial (HBT). Data on children's outdoor playtime and mothers' perceived neighbourhood environment were collected through face-to-face interviews ...

The risk of becoming a West Nile virus case in New York State, excluding New York City, was evaluated for persons whose town of residence was proximal to spatial clusters of dead American crows (Corvus brachyrhynchos). Weekly clusters were delineated for June-October 2002 by using both the binomial spatial scan statistic and kernel density smoothing. The relative risk of a human case was estima...

I give a review of catalogues of galaxies, clusters of galaxies and superclusters – sources of information to study the large-scale structure of the Universe. Thereafter I shall discuss the power spectrum of density perturbations, and the correlation function – principal description functions which characterize the large-scale structure. I shall pay special attention to the geometric interpreta...

This laboratory exercise investigates the influence of population density on offspring number and size in burying beetles. Students test the theoretical predictions that brood size declines and offspring size increases when competition over resources becomes stronger with increasing population density. Students design the experiment, collect and analyze the data, and discuss the results in the ...