University of Potsdam

About: University of Potsdam is a education organization based out in Potsdam, Germany. It is known for research contribution in the topics: Population & Computer science. The organization has 9629 authors who have published 26740 publications receiving 759745 citations. The organization is also known as: Universität Potsdam.

Forecasting species ranges by statistical estimation of ecological niches and spatial population dynamics

Abstract: Aim The study and prediction of species–environment relationships is currently mainly based on species distribution models. These purely correlative models neglect spatial population dynamics and assume that species distributions are in equilibrium with their environment. This causes biased estimates of species niches and handicaps forecasts of range dynamics under environmental change. Here we aim to develop an approach that statistically estimates process-based models of range dynamics from data on species distributions and permits a more comprehensive quantification of forecast uncertainties. Innovation We present an approach for the statistical estimation of process-based dynamic range models (DRMs) that integrate Hutchinson's niche concept with spatial population dynamics. In a hierarchical Bayesian framework the environmental response of demographic rates, local population dynamics and dispersal are estimated conditional upon each other while accounting for various sources of uncertainty. The method thus: (1) jointly infers species niches and spatiotemporal population dynamics from occurrence and abundance data, and (2) provides fully probabilistic forecasts of future range dynamics under environmental change. In a simulation study, we investigate the performance of DRMs for a variety of scenarios that differ in both ecological dynamics and the data used for model estimation. Main conclusions Our results demonstrate the importance of considering dynamic aspects in the collection and analysis of biodiversity data. In combination with informative data, the presented framework has the potential to markedly improve the quantification of ecological niches, the process-based understanding of range dynamics and the forecasting of species responses to environmental change. It thereby strengthens links between biogeography, population biology and theoretical and applied ecology.

Model-driven development with the jABC

Abstract: We present the jABC, a framework for model driven application development based on Lightweight Process Coordination. With jABC, users (product developers and system/software designers) easily develop services and applications by composing reusable building-blocks into hierarchical (flow-) graph structures that are executable models of the application. This process is supported by an extensible set of plugins providing additional functionalities, so that the jABC models can be animated, analyzed, simulated, verified, executed and compiled. This way of handling the collaborative design of complex software systems has proven to be effective and adequate for the cooperation of non-programmers and technical people, and it is now being rolled out in the operative practice.

Efficient Polymer Solar Cells Based on M3EH−PPV

Abstract: We report on polymer blend solar cells with an external quantum efficiency of more than 30% and a high overall energy conversion efficiency (ECE) under white light illumination (100 mW/cm2) of up to 1.7% using a blend of M3EH−PPV (poly[2,5-dimethoxy-1,4-phenylene-1,2-ethenylene-2-methoxy-5-(2-ethylhexyloxy)−(1,4-phenylene-1,2-ethenylene)]) and CN−ether−PPV (poly[oxa-1,4-phenylene-1,2-(1-cyano)ethenylene-2,5-dioctyloxy-1,4-phenylene-1,2-(2-cyano)ethenylene-1,4-phenylene]). We attribute these high efficiencies to the formation of a vertically composition graded structure during spin coating. Photoluminescence measurements performed on the blend layers indicated the formation of exciplexes between both types of polymers, which we propose to be one factor preventing even higher efficiencies.

Dynamics and manipulation of entanglement in coupled harmonic systems with many degrees of freedom

Abstract: We study the entanglement dynamics of a system consisting of a large number of coupled harmonic oscillators in various configurations and for different types of nearest-neighbour interactions. For a one-dimensional chain, we provide compact analytical solutions and approximations to the dynamical evolution of the entanglement between spatially separated oscillators. Key properties such as the speed of entanglement propagation, the maximum amount of transferred entanglement and the efficiency for the entanglement transfer are computed. For harmonic oscillators coupled by springs, corresponding to a phonon model, we observe a non-monotonic transfer efficiency in the initially prepared amount of entanglement, i.e. an intermediate amount of initial entanglement is transferred with the highest efficiency. In contrast, within the framework of the rotating- wave approximation (as appropriate, e.g. in quantum optical settings) one finds a monotonic behaviour. We also study geometrical configurations that are analogous to quantum optical devices (such as beamsplitters and interferometers) and observe characteristic differences when initially thermal or squeezed states are entering these devices. We show that these devices may be switched on and off by changing the properties of an individual oscillator. They may therefore be used as building blocks of large fixed and pre-fabricated but programmable structures in which quantum information is manipulated through propagation. We discuss briefly possible experimental realizations of systems of interacting harmonic oscillators in which these effects may be confirmed experimentally.

CSR Communication Intensity in Chinese and Indian Multinational Companies

Abstract: Manuscript Type: Empirical Research Question/Issue: Why do firms in China, which has a higher level of economic development, communicate less CSR than firms in India? We use a model that includes country-, industry-, and firm-level factors to predict CSR communications intensity, a proxy for CSR activities. Research Findings/Insights: Using data on 68 of the largest multinational companies in China and India, our study shows that Indian firms communicate more CSR primarily due to a more rule-based, as opposed to relation-based, governance environment. Firms in the manufacturing industry tend to communicate more CSR. Firm-level characteristics such as size, duality of CEO and board chairperson, and percentage of external members on the board also have a significant influence on CSR communications. Theoretical/Academic Implications: The main theoretical contribution of our study is to bring a three-level perspective, relying not only on firm- and industry-specific factors, but also on the governance environment, to the study of firms’ CSR behavior. We show that the national governance environment dominates the national income level in affecting CSR communications intensity. We demonstrate that the macro institutional environment in a country strongly affects firm CSR behavior. Our findings suggest that CSR should be studied by considering multilevel antecedents. Practitioner/Policy Implications: Our study suggests that in order to improve the CSR of firms, policy makers in India and China must first try to improve public governance at the national level. Executives doing business with Chinese and Indian companies need to better understand the contrasting governance and their effects on the CSR practices in each country. For the international community and those concerned about product safety and other social issues related to China and India, our findings suggest that improvement will not be immediate since the governance environment changes relatively slowly.