Universal abundance fluctuations across microbial communities, tropical forests, and urban populations

The growth of complex populations, such as microbial communities, forests, and cities, occurs over vastly different spatial and temporal scales. Although research in different fields has developed detailed, system-specific models to understand each individual system, a unified analysis of different complex populations is lacking; such an analysis could deepen our understanding of each system and facilitate cross-pollination of tools and insights across fields. Here, we analyze time-series data of the human gut microbiome, tropical forest, and urban employment using a shared framework. We demonstrate that a single, three-parameter model of stochastic population dynamics can reproduce the empirical distributions of population abundances and fluctuations in all three data sets. The three parameters characterizing a species measure its mean abundance, deterministic stability, and stochasticity. Our analysis reveals that, despite the vast differences in scale, all three systems occupy a similar region of parameter space when time is measured in generations. In other words, although the fluctuations observed in these systems may appear different, this difference is primarily due to the different observation periods for each system. Further, we show that the distribution of temporal abundance fluctuations is described by just two parameters and derive a two-parameter functional form for abundance fluctuations to improve risk estimation and forecasting

A critical reflection on the use of focus groups as a research method: lessons from trying to hear the voices of NGO beneficiaries in Ghana

The focus group method has been used extensively in social science research in order to gain a deep understanding of participant perceptions of specific topics of interest. However, the method has rarely been used in the social accounting and accountability literature. This paper reviews and critically reflects on the key characteristics of the method drawing on a research project examining NGO (non-governmental organisation) beneficiary perspectives on the accountability processes employed by NGOs in Ghana. It offers insights and future research suggestions that might encourage greater use of the method by social accounting and accountability researchers

Stabilizing the forming process in unipolar resistance switching using an improved compliance current limiter

The high reset current IR in unipolar resistance switching now poses major obstacles to practical applications in memory devices. In particular, the first IR-value after the forming process is so high that the capacitors sometimes do not exhibit reliable unipolar resistance switching. We found that the compliance current Icomp is a critical parameter for reducing IR-values. We therefore introduced an improved, simple, easy to use Icomp-limiter that stabilizes the forming process by drastically decreasing current overflow, in order to precisely control the Icomp- and subsequent IR-values.Comment: 15 pages, 4 figure