Analysis and efficient simulation of queueing models of telecommunications systems

In modern packet-switched telecommunication systems, information (such as email, sound, pictures) is transported in the form of small packets (or cells) of data through a network of links and routers. The Quality of Service provided by such a network can suffer from phenomena such as loss of packets (due to buffer overflow) and excessive delays. These aspects of the system are adequately described by queueing models, so the study of such models is of great relevance for designing systems such that they provide the required QoS. This thesis contributes methods for the efficient estimation of several loss probabilities in various queueing models of communications systems. The focus is on rare-event simulation using importance sampling, but some analytical, asymptotic and numerical results are also provided

The Petrov type of the five-dimensional Myers-Perry metric

We point out that the Myers-Perry metric in five dimensions is algebraically special. It has Petrov type \underline{22}, which is the Petrov type of the five-dimensional Schwarzschild metric.Comment: 4 pages, 1 figur

Analysis of State-Independent Importance-Sampling Measures for the Two-Node Tandem Queue

We investigate the simulation of overflow of the total population of a Markovian two-node tandem queue model during a busy cycle, using importance sampling with a state-independent change of measure. We show that the only such change of measure that may possibly result in asymptotically efficient simulation for large overflow levels is exchanging the arrival rate with the smallest service rate. For this change of measure, we classify the model's parameter space into regions of asymptotic efficiency, exponential growth of the relative error, and infinite variance, using both analytical and numerical techniques

A 5-MHz 11-bit delay-based self-oscillating ΣΔ modulator in 0.025 mm2

In this paper a self-oscillating Sigma Delta modulator is presented. By introducing this self-oscillation in the system, the loop filter operates at a speed significantly lower than dictated by the clock frequency. This allows for a simple and power efficient design of the opamps used in the loop filter. The self-oscillation is induced here by introducing a controlled delay in the feedback loop of the modulator. A second order CMOS prototype was constructed in a 0.18 um technology. A clock frequency of 850MHz generates a self-oscillation mode at 106.25 MHz. The modulator achieves a dynamic range (DR) of 66 dB for a signal bandwidth of 5 MHz. The power consumption is only 6mW and the chip area of the modulator core is 0.025mm^2

Polydactyly of the foot

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Eulogizing Realism : Documentary Chronotopes in Nineteenth-Century Prose Fiction

In this contribution we try to probe the generic chronotope of realism, which, judging from its astonishing productivity in the nineteenth century and the profound impact it has had on literary evolution and theory ever since, can be designated nothing less than a hallmark in the general history of narrative. Although we are primarily concerned with the description of the principles of construction underlying the realistic, “documentary”, chronotope, we would also like to touch upon some of its rather evident, but still somewhat under-discussed similarities with the genre of historiography. For, despite an abundance of what could be called “touches of realism” in a plethora of literary texts and genres (both narrative and poetic) since the very beginnings of literary history itself, the direct germs of realism as it developed into a particular narrative genre or generic chronotope during the nineteenth century may well be situated in “prescientific” historiographical works such as those of Gibbon or Michelet