Optically-induced charge storage in self-assembled InAs quantum dots

We present results on spectrally resolved photo-resistance studies of optically-induced charge storage effects in self-organized InAs quantum dots (QDs). The stored charge can be detected and erased electrically. The investigated structure designed for electron or hole storage in the QDs consists of a modulation doped two-dimensional channel which was grown on top of a layer of InAs QDs, separated by an asymmetric tunnel barrier. Our results show that optical QD charging with spectral resolution provides information on the charging dynamics and on the quantity and spectral dependence of stored charges in the QDs. This is a novel technique by which QD excitation spectra can be studied. Spectrally resolved storage effect measurements on electrons as well as on holes allowed to investigate thermal redistribution of carriers in the quantum dot layer. It was found that only at low temperatures carriers can be stored selectively over long time scales in the InAs QDs. The charge storage effect is observable for several hours at temperatures up to 170 K, for several seconds up to 250 K due to an increase in thermal emission of stored charges.     

Unternehmensweite Anwendungs-integration — Zentrale Anreizsetzung zur Realisierung von Netzwerkeffekten bei dezentralen Entscheidungsstrukturen

This article deals with several issues arising from decentralized decision making in the field of enterprise application integration. At present many enterprises cannot establish the optimal middleware solution due to differing local interests. To solve this problem, the article focuses on centralized coordination using incentives to realise network effects and develops an optimisation-algorithm, determining the payoff-minimal incentives paid by a central architecture unit. The developed algorithm uses the segment-, application-, interface-and cost structures — based on documented information — as input. Finally, a case study conducted in the financial services industry illustrates both the developed algorithm and the corresponding results.     

Spatial statistics of carbon nanotube polymer composites

Dispersion, distribution, and alignment of carbon nanotubes (CNT) in polycarbonate (PC) composites are quantified by means of statistical analysis of transmission electron microscopy (TEM) images. The analysed images originate from samples with 0.875 and 2 wt% CNT, processed by compression and injection moulding, respectively. The composites exhibit different microstructures with different electrical properties, depending on the processing parameters. By means of stereological approaches for projections of three dimensional fibre systems the CNT contents within the TEM samples are estimated. The tendency of CNT clustering as well as characteristic distances between the CNT and CNT clusters are quantified by evaluation of morphological functions. Furthermore, a correlation function is introduced to obtain a quantitative measure of CNT clustering within the isotropic compression moulded samples. For the injection moulded samples the correlation function is used to derive local orientation factors. The results underline that clustering of CNT can enhance and alignment of tubes can reduce electrical conductivity.     

The perfectly matched layer as lateral boundary infinite-difference transmission-line analysis

Using a perfectly matched layer (PML) as lateral boundary in waveguide analysis introduces artificial modes and other unexpected effects. This paper presents results of a finite-difference frequency-domain approach and an analytical investigation of the PML's capability to simulate the lateral open space, including an accuracy estimation. A criterion how to detect the desired modes out of the mode spectrum is also given. The findings are verified for a coplanar waveguide radiating into the substrate     

Compartmental residence time estimation in batch granulators using a colourimetric image analysis algorithm and Discrete Element Modelling

In this paper we present an experimental technique and a novel colourimetric image analysis algorithm to economically evaluate particle residence times within regions of batch granulators for use in compartmental population balance models. Residence times are extracted using a simple mixing model in conjunction with colourimetric data. The technique is applied to the mixing of wet coloured granules (binary and ternary systems) in a laboratory scale mixer. The resulting particle concentration evolutions were in qualitative agreement with those from the mixing model. It was seen that the algorithm was most stable in the case of the binary colour experiments. Lastly, simulations using the Discrete Element Method (DEM) were also performed to further validate the assumptions made in the analysis of the experimental results. Particle concentrations from the simulations showed the same trends as the experiment and highlighted the importance of particle size distributions on the DEM residence times.     

Combining clinical departments and wards in maximum-care hospitals

OR Spectrum - Sharing bed capacity across clinical departments improves bed availability via pooling effects. This means in effect that fewer beds are required to satisfy a given service level when...     

Network Externalities and Compatibility Among Standards: A Replicator Dynamics and Simulation Analysis

The importance of network externalities for the development of technology and industry structure has been recognized in evolutionary economic for a long time. However, network externalities are no isolated phenomena. They are based on competing standards in a comprehensive network of technology lines that are based on one another and remain to various degrees interoperable or compatible. As some evidence from the ICT sector inparticular shows, compatibility and tying or bundling of standards may be employed as strategic tools. The present paper investigates the economic role of tied standards for the dynamics of competition between standards. A replicator model operating on an aggregated level is complemented by an agent-based simulation with explicit representation of the network structure among users. A variety of effects are studied, including the role of initial usage share, manipulation of compatibility, expansion of vendors into other segments, as well as the network structure and central or peripheral positioning of agents. The agent-based model contrasts a complete network and a regular ring network with asymmetric network structures derived from Barabàsi and Albert’s preferential attachment mechanism and triadic closure.