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This paper presents an approach to modelling population density as a function of space and time, both of which are treated over a continuous domain. An equilibrium (or alternatively, an optimal) distribution of urban population density is specified exogenously. The rate of change of the actual population density is then considered to be a function of the deviations between the actual and the equilibrium (or optimal) density distributions, over time. This adjustment process is interpreted as being realized by internal migration, immigration/emigration, and/or natural growth. A formal specification of the models results in integral—differential equations. A solution procedure that uses double Laplace transforms and partial Laplace transforms with respect to space and time is outlined. Properties relating to the limiting distributions are discussed. An example that makes use of exponential functions is presented; and procedures for computing explicit, and possibly heuristic, solutions are noted.

The entropy-maximizing formalism used in urban and regional modelling has typically been applied within a static or equilibrium context. This paper presents a dynamic entropy model of the distribution of population over time. It is initially assumed that a Markov chain adequately represents the residential relocation process. The strategy then involves maximizing the entropy of a Markov chain, subject to suitable constraints, so as to generate least-biased estimates of the Markovian parameters. If a stationary process is assumed, these in turn allow the projection of the probability distribution vector of population densities over successive, equal, time intervals.

Biological markers used to assess the effects of environmental pollution have attracted considerable attention from regulatory agencies and are currently under evaluation at a number of research facilities throughout the world. However promising a biomarker-based biomonitoring approach may be, the development of this concept is complicated by a range of technical issues. This book provides a conceptional framework for research and application of biomarkers. International experts on biomonitoring have formulated a unified strategy for the development and validation of biomarkers in assessing environmental health as well as appropriate protocols for their implementation and interpretation in a biological monitoring program

The characterization of multiplicity of high-mass stars is of fundamental importance to understand their evolution, the diversity of observed core-collapse supernovae and the formation of gravitational wave progenitor systems. Despite that, until recently, one of the final phases of massive star evolution – the cool supergiant phase – has received comparatively little attention. In this study, we aim to explore the multiplicity among the cool supergiant (CSG) population in the Large and Small Magellanic Clouds (LMC and SMC, respectively). To do this we compile extensive archival radial velocity (RV) measurements for over 1000 CSGs from the LMC and SMC, spanning a baseline of over 40 yr. By statistically correcting the RV measurements of each stellar catalogue to the Gaia DR2 reference frame we are able to effectively compare these diverse observations. We identify 45 CSGs where RV variations cannot be explained through intrinsic variability, and are hence considered binary systems. We obtain a minimum binary fraction of 15±4 per cent for the SMC and of 14±5 per cent for the LMC, restricting our sample to objects with at least 6 and 5 observational epochs, respectively. Combining these results, we determine a minimum binary fraction of 15±3 per cent for CSGs. These results are in good agreement with previous results which apply a correction to account for observational biases. These results add strength to the hypothesis that the binary fraction of CSGs is significantly lower than their main-sequence counterparts. Going forward, we stress the need for long-baseline multi-epoch spectroscopic surveys to cover the full parameter space of CSG binary systems. ; The authors acknowledge support from the Spanish Government Ministerio de Ciencia e Innovación through grants PGC-2018-091 3741-B-C22 and SEV 2015-0548, and from the Canarian Agency for Research, Innovation and Information Society (ACIISI), of the Canary Islands Government, and the European Regional Development Fund (ERDF), under grant with reference ...

This article presents the attitudinal response of rural villagers in Papua New Guinea to mobile telephony, based on a threshold study made during the early stages of its adoption. The research indicates that the introduction of mobile telecommunications has generally been viewed positively, with mobile phones affording social interaction with loved ones. Nonetheless, negative concerns have been strongly felt, notably financial costs and anxiety about mobile phones aiding in the coordination of extramarital liaisons and criminal activities. The communities investigated previously had scant access to modern communication technologies, some still using traditional means such as wooden slit drums, known locally as garamuts. The expansion of mobile network coverage has introduced into communal village life the capability to communicate dyadically and privately at a distance. Investigation into the adoption of mobile phones thus promotes understanding about traditional means of communication and notions of public and private interactions.