Performance comparison of several priority schemes with priority jumps

In this paper, we consider several discrete-time priority queues with priority jumps. In a priority scheduling scheme with priority jumps, real-time and non-real-time packets arrive in separate queues, i.e., the high- and low-priority queue respectively. In order to deal with possibly excessive delays however, non-real-time packets in the low-priority queue can in the course of time jump to the high-priority queue. These packets are then treated in the high-priority queue as if they were real-time packets. Many criteria can be used to decide when packets of the low-priority queue jump to the high-priority queue. Some criteria have already been introduced in the literature, and we first overview this literature. Secondly, we propose and analyse a new priority scheme with priority jumps. Finally, we extensively compare all cited schemes. The schemes all differ in their jumping mechanism, based on a certain jumping criterion, and thus all have a different performance. We show the pros and cons of each jumping scheme.     

Organic nanoparticles suspensions preparation by underwater excimer laser ablation of polycarbonate

Ablation with excimer laser pulses on polycarbonate (PC) film has been performed in ultrapure water. It is demonstrated that it is a new efficient method for organic nanoparticles (ONP) suspensions synthesis. Proof of the formation of ONP is given by analysis of the water phase with AFM and UV-vis spectroscopy. The obtained transmission measurements are approached with the aid of Mie theory to estimate composition of suspensions. Results indicate that the polycarbonate film is partly ablated into nanometric particles with size ranging from 8 up to 180 nm. This is also supported by force atomic microscopy. Confocal Raman microspectroscopy was done directly on water suspensions. Thanks to the optical trapping phenomenon of the nanoparticles, their vibrational Raman spectrum was more easily obtained. Original polycarbonate is lost although some polymeric structures are detected along with graphitic carbon.     

Analysis of a Discrete-Time Queueing System with Timed Vacations

We consider a discrete-time GI-G-1 queueing system with server vacations. Vacations occur whenever the queue becomes empty or whenever a timer expires. When the timer expires one of the following four actions are considered: the server completes transmission of the present packet before leaving for a vacation, the service immediately leaves for a vacation and the interrupted packet's service is either continued, repeated or resampled and repeated after the vacation. Using a probability generating functions approach, we derive various performance measures such as moments of the buffer contents at various time epochs in equilibrium and moments of the packet delay in equilibrium. By means of an example, we then compare the operation modes under consideration.     

Binding energy of transition atoms adsorbed on tungsten

We develop a statistical method to estimate the density of states from the knowledge of its first moments. We apply this method to the calculation of the density of states of an s band in a simple cubic lattice. Then we use it to determine the binding energy of a transition atom adsorbed on tungsten in a LCAO approximation. The binding energies obtained agree with the experimental values, but they do not exhibit the experimental peak which may be due to correlation effects.     

Study of a XVIII century hand-painted Chinese wallpaper by multianalytical non-destructive techniques

In this work, hand-painted wallpaper belonging to a private Portuguese collection was analyzed in order to identify the pigments used. The analyzed artwork was an extraordinary XVIII century Chinese wallpaper that depicts exotic birds and flowers, which was painted with considerable accuracy and expertise. Thorough, in situ, X-ray fluorescence analyses were performed on nearly all the wallpaper. Since the elemental content of several colors was consistent for the four papered walls, strategic micro-samples were taken and analyzed by confocal Raman spectroscopy to further identify the pigments used. Pigments such as yellow ochre, lead white and barium white, vermilion, carmine, azurite and malachite were identified. Optical microscopy was used to analyze the fibers in the paper support, and fibers such as kozo, ramie and hemp or linen were identified.     

Experimental and theoretical study of the multiple scattering of acoustical waves in inhomogeneous media

To describe the propagation of acoustic waves in concrete, we used the results of Waterman for the complex propagation constant in a scattering medium. This makes it possible to calculate the attenuation and phase velocity in the medium concerned. The agreement between theoretical and experimental results being very poor for concrete, we searched for a synthetic medium with a closer correspondence to the theoretical pattern assumed, to determine whether the theory works better for such media. In fact, the synthetic medium gave experimental results in good agreement with the theoretical ones. The results allow us to suggest the use of a more precise treatment suggested by Fikioris and Waterman, which could lead to a better agreement for concrete. However, this extension will be reserved for a later publication.To put an end to the confusion created by misprints in the expressions of certain publications, which have been used as such without correction by some authors, we include here full details of the theory used by us, and give an explanation of our notation.     

Analysis at service completion times of buffers with output interruptions

In an earlier paper [Bruneel, 1983a]we investigated a discrete-time buffer system with infinite waiting room and one single output channel, subjected to stochastic interruptions. For this system, the probability generating function of the number of messages in the buffer at service completion times was derived, under rather general assumptions concerning the arrival process and the server interruption process. However, at a certain point in the analysis, we tacitly introduced an approximation, by neglecting the (statistical) information available on the first customer of a busy period.In the present paper we show that this simplifying assumption is not really necessary in order to keep the problem analytically tractable, and the exact (but rather tedious) derivations are given. As a result, an expression is found for the probability generating function of the buffer contents, which is even less complicated than the one obtained in the previous paper.The results of the two studies are compared and are found to be substantially different from each other for realistic values of the parameters of the system.

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Zusammenfassung In einer früheren Arbeit [Bruneel, 1983a] wurde ein Puffersystem in diskreter Zeit mit einem unbeschränkten Speicherraum und einem zufälligen Unterbrechungen ausgesetzten Ausgabekanal untersucht. Für dieses System wurde die erzeugende Funktion der Anzahl der Aufträge im Puffer zu den Zeitpunkten der Abfertigung eines Auftrags berechnet, wobei recht allgemeine Annahmen über den Ankunftstrom und den Prozeß der Bedienungs-Unterbrechungen zugrundelagen. Dabei wurde auch implizit eine Approximation benutzt, indem (statistische) Information über den ersten Kunden einer Arbeitsperiode nicht berücksichtigt wurde.In der vorliegenden Arbeit wird nun gezeigt, daß mit beträchtlichem Mehraufwand die Analyse auch ohne diese Approximation durchführbar ist.Der resultierende Ausdruck für die erzeugende Funktion des Pufferinhalts ist sogar einfacher. Ein Vergleich zeigt, daß die neuen Ergebnisse bei realistischer Parameterwahl von den früher erzielten beträchtlich abweichen.