Shared WiFi-Communities – User Generated Infrastructure am Beispiel von FON

Shared WiFi-Communities emerge when users share their private Wireless Fidelity with others and in return get free internet access via community members’ internet connection. Supply of wireless capacity and demand for WLAN usually are coordinated by a central authority therewith users can find specific hosts within the community. Initial players that conduct commercial WiFi-Communities established their position in the market. The international market leader with 170,000 hotspots worldwide is FON. The commercial success of shared WiFi-communities (e.g. FON) depends on the adoption of a special router or modifications of the existing WLAN-infrastructure. More importantly it is essential that users permanently offer broadband capacity to the community. Only then net effects can durably generate enhanced usage benefits. A survey of 268 German FON users reveals that the community shows a high level of cohesion. Users barely vary from the default setting concerning shared bandwidth of the router. Additionally most interviewees offer their WLAN 24 hours a day. Despite the possibility of earning money with the wireless capacity most users do not offer bandwidth with a purely economic ambition. Although the market potential of shared WiFi communities appears tremendous legal obstructions and technical restraints exacerbate penetration.     

Decentralised control of chromatographic simulated moving bed processes based on wave front reconstruction

The behaviour of chromatographic simulated moving bed processes is described by the movement of concentration profiles through a circle of separation columns. A closed-loop control manipulates the profiles in order to meet demands concerning specified product purity and disturbance attenuation. If steep wave fronts of the concentration profiles occur, the controlled variables undergo fast changes in case of a transient of the process. In this case, a reconstruction of the wave fronts is necessary for a successful control.A simple and effective decentralised controller structure is proposed based on cascaded discrete-time PI controllers. On-line product purity measurements and the reconstructed wave fronts are used for control purposes. Two kinds of process models are used: a rigorous model for dynamic simulations, and strongly simplified plant models for the design of the wave front reconstruction and the controller. The latter models are identified based on experimental step tests with the reference plant and numerical simulations. The performance of the control system is evaluated by numerical simulations.     

Disjunctive databases for representing repairs

This paper addresses the problem of representing the set of repairs of a possibly inconsistent database by means of a disjunctive database. Specifically, the class of denial constraints is considered. We show that, given a database and a set of denial constraints, there exists a (unique) disjunctive database, called canonical, which represents the repairs of the database w.r.t. the constraints and is contained in any other disjunctive database with the same set of minimal models. We propose an algorithm for computing the canonical disjunctive database. Finally, we study the size of the canonical disjunctive database in the presence of functional dependencies for both subset-based repairs and cardinality-based repairs.     

A new,flexible and widely applicable software package for the simulation of one-dimensional moisture flow: SoWaM

Most one-dimensional soil moisture flow simulation models have restricted applicability due to (amongst other things): i) insufficient user flexibility; ii) a lack of user friendliness; iii) dependency on scale, temporal and/or spatial, and iv) fixed boundary conditions. Therefore, we developed a simple and highly flexible software package to simulate, visualize and analyze 1-D moisture flow in soils: SoWaM (Soil Water Model). The package has a modular setup and consists of a range of tools to visualize, analyze and compare input data and results. Soil hydraulic properties for each specified soil layer can be defined by either Van Genuchten parameters or cubical splines. Since the model does not impose limits on element size or time interval, it is possible to perform simulations in very high detail, both spatially and temporally. Furthermore, four different criteria for irrigation scheduling have been implemented. The SoWaM package provides an accurate, simple and highly flexible tool to simulate soil moisture flow and to evaluate the effects of various factors on soil water movement, such as timing and amount of irrigation, soil hydraulic properties and soil layering. Results of a case study are presented to illustrate model performance.     

Agent based simulation architecture for evaluating operational policies in transshipping containers

An agent based simulator for evaluating operational policies in the transshipment of containers in a container terminal is described. The simulation tool, called SimPort, is a decentralized approach to simulating managers and entities in a container terminal. Real data from two container terminals are used as input for evaluating eight transshipment policies. The policies concern the sequencing of ships, berth allocation, and stacking rule. They are evaluated with respect to a number of aspects, such as, turn-around time for ships and traveled distance of straddle carriers. The simulation results indicate that a good choice in yard stacking and berthing position policies can lead to faster ship turn-around times. For instance, in the terminal studied the Overall-Time-Shortening policy offers fast turn-around times when combined with a Shortest-Job-First sequencing of arriving ships.     

An investigation of the option space in conceptual building design for advanced building simulation

This article describes research conducted to gather empirical evidence on size, character and content of the option space in building design projects. This option space is the key starting point for the work of any climate engineer using building performance simulation who is supporting the design process. The underlying goal is to strengthen the role of advanced computing in building design, especially in the early conceptual stage, through a better integration of building performance simulation tools augmented with uncertainty analysis and sensitivity analysis. Better integration will need to assist design rather than automate design, allowing a spontaneous, creative and flexible process that acknowledges the expertise of the design team members. This research investigates and contrasts emergent option spaces and their inherent uncertainties in an artificial setting (student design studios) and in real-life scenarios (commercial design project case studies). The findings provide empirical evidence of the high variability of the option space that can be subjected to uncertainty analysis and sensitivity analysis.     

Knowledge assessment-practical example in testing

Knowledge assessment is inseparable part of current e-learning technologies. It can be used for self-assessment of students to give them feedback about their progress in a study or for an intermediate or final grading for tutors. However, knowledge tests are not developed with the adequate care. Author＇s experience in the area of knowledge assessment led to a confidence the ＂unstructured＂ testing is usually used in this process. It means that many of knowledge tests are not designed to reveal the reached level of knowledge. Moreover, testing suites are reviewed very seldom regarding their validity and items correlation. This paper presents experiences gained during the design and implementation of specific software focused on teaching several principles of the Unix-like operating systems. The structure of the specific assignment follows the Bloom＇s taxonomy of educational objectives.     

A cost-effective lexical acquisition process for large-scale thesaurus translation

Thesauri and controlled vocabularies facilitate access to digital collections by explicitly representing the underlying principles of organization. Translation of such resources into multiple languages is an important component for providing multilingual access. However, the specificity of vocabulary terms in most thesauri precludes fully-automatic translation using general-domain lexical resources. In this paper, we present an efficient process for leveraging human translations to construct domain-specific lexical resources. This process is illustrated on a thesaurus of 56,000 concepts used to catalog a large archive of oral histories. We elicited human translations on a small subset of concepts, induced a probabilistic phrase dictionary from these translations, and used the resulting resource to automatically translate the rest of the thesaurus. Two separate evaluations demonstrate the acceptability of the automatic translations and the cost-effectiveness of our approach.

DuD Recht

DuD Recht

DuD Recht