Design of Business Media - An Integrated Model of Electronic Commerce

Information and communication technology (ICT) enables and demands entirely new ways of doing business. Two of the challenges nowadays are (1) to find new business models for Electronic Commerce and (2) to establish platforms with comprehensive integrated services for Electronic Commerce. The forthcoming challenge is (3) to design platforms accessible both for (software) agents as well as for humans

Constructing New Media

Media are explored to envision, to design, and to implement platforms for knowledge management within communities. They actively shape, support and develop the community being resident on a medium. We study Intranets as media for knowledge management and provide an agent-oriented model for Intranets. We argue that organization and logical space of a community have to be reconstructed on the medium and that new knowledge and organizational structures can evolve by using the medium. We distinguish as counterparts the organizational structure and the knowledge being represented on the platform and the organizational structure and the knowledge of the community resident on the medium. We propose a media dialog and a media spiral between those counterparts as processes of shaping a community by a medium and of developing and implementing new knowledge and new organizational structures within a community on a medium

Convective Turbulent Dust Emission: Process, parameterization, and relevance in the Earth system

Convective turbulence generates localized and intermittent surface shear stress and can effectively entrain dust into the atmosphere. This mechanism is referred to as "Convective Turbulent Dust Emission" (CTDE) and is considered as the most important form of direct aerodynamic dust entrainment. CTDE occurs predominantly at weak mean wind conditions, when the buoyancy production of atmospheric turbulence is most pronounced. CTDE is a stochastic process and does not need to involve the saltation of sand-sized grains. This process is so far not included in dust emission schemes and therefore the significance of CTDE for the global dust budget and its impacts on the Earth system remain largely unknown. Here we develop a new parameterization scheme of CTDE. We couple the scheme to the WRF (Weather Research and Forecasting) model in LES (Large-Eddy Simulation) and regional mode with chemistry (WRF/Chem) and investigate the process and its significance for local and regional scale dust emissions. In the parameterization scheme for regional application, the stochastic nature of the process is considered by describing the aerodynamic lifting forces and inter-particle cohesive forces as probability density functions (pdfs). The lifting force was first described as joint pdf of turbulent horizontal and vertical wind velocities. We then determined the lifting force using a new similarity theory for instantaneous momentum flux, obtained from the LES results. The inter-particle cohesive force was described as lognormal distribution with semi-empirical distribution moments. Correction methods for roughness element and moisture effects were suggested. The CTDE scheme was calibrated and validated against field observations recorded in the Horqin Sandy Land area in China and during the Japan-Australia Dust Experiment (JADE) in Australia. The roughness correction is preliminary and could not be tested due to a lack of data for evaluation. Only fractional cover was therefore accounted for in the model simulations. Coupled to the regional model WRF/Chem, the calibrated dust emission scheme was used to assess the long-term regional contribution of CTDE to the overall dust budget for Australia. We showed that a persistent background dust concentration can be generated by CTDE. By comparison with model estimates of global dust emissions, we found that during the study year, the Australian CTDE comprised about 6-17% relative to the yearly global dust emissions. It even exceeded the global model estimates for annual Australian dust emissions, arguably due to favorable conditions in the study year compared to the climatological mean, underrepresentation of regional characteristics, and corresponding underestimation of Australian dust emissions in the global models. Additionally, the disuse of a comprehensive drag partition scheme in our model potentially led to CTDE overestimation. On the local scale, CTDE was observed as being about twice as frequent as saltation bombardment and aggregates disintegration (SADE) and produced more than 80% of dust emissions compared to that of SADE. Our results suggest that CTDE may be a significant driver of soil nutrient redistribution and air quality at the local scale while contributing to the global impacts of dust on radiation interactions and biogeochemical cycles

Field observations of the variability of dust emission, its size-spectrum and mineralogy

Atmospheric mineral dust consists of tiny mineral particles that are produced by the wind erosion of arid and semi-arid surfaces of the Earth, and it is one of the most important aerosols in terms of mass in the global atmosphere [1]. The physical and chemical properties of dust, that is, its particle size distribution (PSD), mineralogical composition, shape and mixing state determine its impact on the Earth’s system. Dust mineralogy in particular has been identified by the Intergovernmental Panel on Climate Change (IPCC) as a key uncertainty in the overall contribution of aerosols to radiative forcing [2] and many studies over recent years have shown its potential importance [3,4]. Despite this, Earth System models typically assume dust aerosols to have a globally uniform composition, neglecting the known local and regional variations in the mineralogical composition of the sources [5,6] and therefore, preventing further understanding of the role of dust in the Earth system. However, this simplification is justified by the current incomplete understanding of the physical processes at emission, the lack of coincident measurements of individual mineral PSDs for emitted dust and the parent soil, the fundamental disagreements among existing dust emission schemes on multiple aspects, the limited global knowledge of soil mineral content and the insufficient knowledge of the mixing state of the minerals. The ERC Consolidator Grant called FRAGMENT (FRontiers in dust minerAloGical coMposition and its Effects upoN climaTe) aims to address these limitations and to better understand and constrain the global mineralogical composition of dust along with its effects upon climate. This ambitious and multidisciplinary project combines theory, field measurements, laboratory analyses, remote spectroscopy and modelling

Sensitivity of aeolian modelling to soil particle size data

The simulation of size-dependent sand transport and dust emission requires particle size distributions (PSDs) of parent soil as input data. However, soil PSDs are difficult to measure and different sample pre-treatment and measurement techniques can give different results which may significantly affect the model estimates of sand/dust fluxes. In large-scale (regional to global) dust models (e.g. GCMs), soils are usually classified according to their hydraulic properties and this classification is not necessarily consistent with soil classifications based on PSD. Over the Australian continent, 29 soil samples have been collected and their PSDs analyzed at high resolution (256 size classes) by Coulter Multisizer.It is found that samples for a given USDA soil texture class (e.g. loam), can have profoundly different PSDs. This suggests that a new soil type classification dedicated for wind-erosion modeling is needed; which reflects the natural particle and aggregate size condition of soils. In this study, we use a wind erosion model to test how uncertainties in PSDs affect the model performance. The range of uncertainties in sand and dust fluxes arising from particle-size uncertainties is quantified

Formalisierung und Architektur von Medien und ihren Gemeinschaften

Zusammenfassung: "Medienmodell und Medienreferenzmodell werden als Modelle für Plattformen für Gemeinschaften von natürlichen und künstlichen Agenten eingeführt. Diese Modelle werden mit Logik, Rewrite Logic, Labelled Deductive Systems und Modaler Logik formalisiert. Aus dieser Formalisierung wird eine generische Architektur für Medien entwickelt. Anhand der Beispiele eines Online-Buchladens, eines Online Marktes und der Analyse von Gemeinschaften werden Modelle, Modellierung und Architektur motiviert und konkretisiert.

Relevance of convective turbulent dust emission (CTDE) in the Earth system

Convective turbulence generates localized and intermittent surface shear stress and can effectively entrain dust into the atmosphere. This mechanism is referred to as 'Convective Turbulent Dust Emission' (CTDE) and is considered as the most important form of direct aerodynamic dust entrainment. CTDE occurs predominantly at weak mean wind conditions, when the buoyancy production of atmospheric turbulence is most pronounced. CTDE is a stochastic process and does not need to involve the saltation of sand-sized grains. An improved parameterization for CTDE is presented, which represents both aerodynamic lifting and inter-particle cohesive forces as probability distributions. The dust emission scheme therefore accounts for the stochastic nature of CTDE. The scheme was evaluated against field data recorded in the Horqin Sandy Land area in China and during the Japan-Australia Dust Experiment (JADE) in Australia. Coupled to the regional model WRF/Chem, the calibrated dust emission scheme was used to assess the long-term regional contribution of CTDE to the overall dust budget for Australia. We show that a persistent background dust concentration can be generated by CTDE. The modeled dust concentrations were compared to PM10 measurements monitored by the DustWatch Australia network. An estimate on the relevance of CTDE compared to saltation bombardment at the local and regional scales is given and implications for climate are highlighted