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Load Scenarios (load + scenario)

Distribution by Scientific Domains

Engineering	75%

Selected Abstracts

Power allocation in the context of dimensioning the air-interface of third generation W-CDMA-based cellular systems

INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 5 2002
P. Demestichas
Abstract The adoption of W-CDMA as an essential component of the air-interface of third-generation cellular systems brings to the foreground the need for new planning methodologies and software tools. In this perspective, this paper addresses planning problems that are important to the dimensioning of W-CDMA-based cellular networks. The problems aim at finding the optimal feasible allocation of transmission power to the sets of uplink and downlink connections that should be supported by the system, so as to cope with a corresponding traffic load scenario. The problems are concisely defined, mathematically formulated and solved by means of two computationally efficient, novel algorithms. The solutions of the problems may be seen as operating points at which the system performance should be driven. Finally, numerical results are presented and concluding remarks are drawn. Copyright © 2002 John Wiley & Sons, Ltd. [source]

The sensitivity of phytoplankton in Loch Leven (U.K.) to changes in nutrient load and water temperature

FRESHWATER BIOLOGY, Issue 1 2008
J. ALEX ELLIOTT
Summary 1. Loch Leven is a shallow, eutrophic lake in Scotland, U.K. It has experienced much change over the 30 years that it has been studied; this has primarily been due to reduced nutrient loads to the lake through active catchment management. Its recovery has been slow and, therefore, we used a phytoplankton community model (PROTECH) to test its sensitivity to changing nutrient loads and water temperature. 2. PROTECH was initialized to simulate the observed phytoplankton community in 1995 and was then repeatedly run through a combination of step-wise changes in water temperature and nutrient load (two treatments were simulated for nutrient load: one changing both nitrate and phosphorus, and one changing just phosphorus). The effect on total chlorophyll- a concentration, cyanobacteria abundance and phytoplankton diversity was examined. 3. Whilst changes in temperature had little effect, variations in the nutrient load produced a range of responses. Increasing only the phosphorus load caused a large increase in Anabaena abundance and total chlorophyll- a concentration. However, the opposite response was recorded when nitrate load was changed as well, with Anabaena increasing its biomass under reduced nutrient load scenarios. 4. The key factor determining the type of response appeared to be nitrogen availability. Anabaena, a nitrogen fixer, could exploit the phosphorus resource of Loch Leven under limiting nitrogen conditions, allowing it to dominate under most of the scenarios tested apart from those supplying extra nitrogen to the lake. The model predictions agree with the observed data, which show that Anabaena continues to dominate the summer phytoplankton bloom in Loch Leven despite the considerable reduction in phosphorus supply from the catchment. This research provides a possible explanation for this. [source]

Improving node behaviour in a QoS control environment by means of load-dependent resource redistributions in LANs,

INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 4 2005
Bernd E. Wolfinger
Abstract An important means to guarantee an acceptable quality of service in networks with real-time communication requirements is the reservation of resources at connection setup time. However, such reserved resources, e.g. transmission bandwidth, may be unused as a consequence of the variations in the actual resource demands. Therefore, a more efficient resource utilization is possible if communicating stations or end-users dynamically hand over some of the free resources temporarily to the other communication partners, e.g. of a ,broadcast network'. This paper concentrates on two fundamental problems of such a demand-based sharing of resources: on the one hand, estimation of the current resource requirement on the basis of load measurements is investigated and, on the other hand, we elaborate efficient algorithms for resource sharing respecting real-time requirements. The algorithms proposed for load estimation and for resource sharing are evaluated analytically with respect to their efficiency for worst-case, average-case and realistic load scenarios. Our approach suggested for resource and traffic management allows one to achieve significantly better utilization of network resources. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Versuche zur Ermüdungsfestigkeit alter Betonstähle

BETON- UND STAHLBETONBAU, Issue 7 2009
Patrick Fehlmann Dipl.
Baustoffe; Bewehrung; Versuche; Brückenbau Abstract Die Frage der Ermüdungssicherheit hat im Zusammenhang mit der Überprüfung bestehender Stahlbetonbauwerke, insbesondere Brücken, an Aktualität gewonnen. Während auf der Einwirkungsseite die Anzahl der Lastwechsel und die Lasten, die die Brücke im Laufe ihres Lebens erfahren hat, von Bedeutung sind, sind es auf der Widerstandsseite die Genauigkeit des Tragwerkmodells und die Materialkennwerte. Mit Letzteren befasst sich dieser Aufsatz. Der wichtigste Parameter auf der Widerstandsseite ist die Ermüdungsfestigkeit des Betonstahls. Mittels Dauerschwingversuchen wurde die Ermüdungsfestigkeit von vier Betonstahlsorten ermittelt. Zwei Sorten stammen von abgebrochenen Brücken aus den 1950er Jahren; zwei weitere sind kürzlich produzierte Sorten von Ring- und Stabmaterial der Betonstahlsorte B 500 B. Das Ziel der Versuche bestand darin, festzustellen, ob das Alter einer Stahlbetonkonstruktion einen Einfluss auf die Ermüdungsfestigkeit des Betonstahls hat. Im Aufsatz werden die Problematik beim Nachweis der Ermüdungssicherheit bestehender Brücken kurz geschildert, die Versuche beschrieben und deren Resultate diskutiert. Fatigue Tests with Old Reinforcing Steels Recently, fatigue safety has become an issue with respect to surveying the condition of existing structures, in particular bridges. While questions considering traffic loads and frequencies dominate the calculations of the appropriate load scenarios, the accuracy of the structural model and material properties play a vital role for the calculation of the resistance. This article deals with the latter. The most important parameter on the resistance side is the fatigue strength of the reinforcement. Therefore, fatigue strength of four brands of reinforcing steel was determined in fatigue tests. Two brands of reinforcement bars could be gathered during demolition work of two bridges which were built in the 1950ies. Another two brands of new reinforcing steel B 500 B, a rod-steel and a steel from the roll, were tested. The aim of the tests was to prove whether age and environment of the built-in reinforcement bars affect their fatigue resistance or not. The article briefly describes the difficulties with verifying the fatigue safety of existing bridges while the main part deals with the experimental work and the discussion of the test results. [source]