An analytical packet/flow-level modelling approach for wireless LANs with Quality-of-Service support

We present an analytical packet/flow-level modelling approach for the performance analysis of IEEE 802.11e WLAN, where we explicitly take into account QoS differentiation mechanisms based on minimum contention window size values and Arbitration InterFrame Space (AIFS) values, as included in the Enhanced Distributed Channel Access (EDCA) protocol of the 802.11e standard. We first enhance the packet-level approach previously used for best-effort WLANs to include traffic classes with different QoS requirements. The packet-level model approach yields service weights that discriminate among traffic classes. From these observations, the packet/flow-level model for 802.11e is the \textit{generalized} discriminatory processor-sharing (GDPS) queueing model where the state-dependent system capacity is distributed among active traffic classes according to state-dependent priority weights. Extensive simulations show that the discriminatory processor-sharing model closely represents the flow behavior of 802.11e

Molecular diagnosis and genotyping of Clostridium difficile

Clostridium difficile was first discovered in 1935, but it was not until 1977 that this bacterium was found to be associated with pseudomembranous colitis. The disease was considered to be caused by the production of two C. difficile toxins, toxins A and B (TcdA and TcdB). TcdA was shown to exhibit enterotoxic effects on the intestine, whereas TcdB was shown to be more cytotoxic. Strains of C. difficile that do not produce these toxins are known to be non-toxinogenic and therefore non-pathogenic. However, outbreaks and more severe infections due to strains producing only TcdB have been described. To diagnose C. difficile -associated disease, a method with a high sensitivity and specificity is necessary. This thesis describes the application of methods based on the molecular detection of the pathogen in comparison with conventional microbiological methods. After isolation of the pathogen, the epidemiology of C. difficile -associated disease can be studied using molecular typing methods on the isolates. These typing methods need to be highly discriminatory, depending on the epidemiological data to be studied, and methods need to be stable en reproducible, with the possibility to exchange data between different laboratories all over the world.UBL - phd migration 201

An analytical model for CDMA downlink rate optimization taking into account uplink coverage restriction

This paper models and analyzes downlink and uplink power assignment in Code Division Multiple Access (CDMA) mobile networks. By discretizing the area into small segments, the power requirements are characterized via a matrix representation that separates user and system characteristics. We obtain a closed-form analytical expression of the so-called Perron-Frobenius eigenvalue of that matrix, which provides a quick assessment of the feasibility of the power assignment for each distribution of calls over the segments. Our results allow for a fast evaluation of outage and blocking probabilities. The result also enables a quick evaluation of feasibility that may be used for capacity allocation. Our combined downlink and uplink feasibility model is applied to determine maximal system throughput in terms of downlink rates. \u

Throughputs in processor sharing models for integrated stream and elastic traffic

We present an analytical study of throughput measures in processor sharing queueing systems with randomly varying service rates, modelling a communication link in an integrated services network carrying prioritised stream traffic and elastic traffic. A number of distinct throughput measures for the elastic traffic are defined and analysed. In particular, the differences between the various throughput measures and the impact of the elastic call size distribution are investigated. It is concluded that the call-average throughput, which is most relevant from the user point of view but typically hard to analyse, is very well approximated by the newly proposed so-called expected instantaneous throughput, which can easily be obtained from the system's steady state distribution. \u

Informatie-infrastructuur als basis voor de herinrichting van bedrijfsprocessen : resultaten van een praktijkstudie

Veel organisaties hebben moeite om hun informatievoorziening adequaat toe te snijden op de markt van de jaren negentig. In organisaties met een turbulente omgeving blijken hulpmiddelen als informatiebeleids- en -planningtechnieken slechts zeer beperkt bruikbaar om de snel groter wordende mogelijkheden van informatietechnologie (IT) effectief te benutten. In dit artikel wordt een benaderingswijze beschreven voor de toepassing van IT in organisaties, waarin de begrippen informatie-infrastructuur en Business Process Redesign (BPR) centraal staan. Het artikel laat eerst zien op welke wijze een informatie-infrastructuur een ankerpunt en referentiekader kan zijn voor BPR. Vervolgens wordt verslag gedaan van een toetsing van de benaderingswijze bij het bedrijf Stork Brabant B.