A two-priority fluid flow model : joint steady state distribution of the buffer content processes

We consider a single-server two-class fluid model with a static priority service discipline under which type 1 fluid receives full service priority over type 2 fluid. The two types of fluid are stored in two separate infinite capacity buffers that are emptied at the constant rate of the server. The inputs to the buffers are governed by an external environment process which is taken to be an irreducible finite state continuous time Markov chain. We derive the Laplace-Stieltjes transform of the steady-state joint distribution of the two buffer con-tent processes. The analytic results are illustrated by two simple examples and we display computational results for three larger scale examples.

On modelling the performance and reliability of multimode computer systems

We present an effective technique for the combined performance and reliability analysis of multi-mode computer systems. A reward rate (or a performance level) is associated with each mode of operation. The switching between different modes is characterized by a continuous time Markov chain. Different types of service-interruption interactions (as a result of mode switching) are considered. We consider the execution time of a given job on such a system and derive the distribution of its completion time. A useful dual relationship, between the completion time of a given job and the accumulated reward up to a given time, is noted. We demonstrate the use of our technique by means of a simple example

Discrete-time rewards model-checked

This paper presents a model-checking approach for analyzing discrete-time Markov reward models. For this purpose, the temporal logic probabilistic CTL is extended with reward constraints. This allows to formulate complex measures – involving expected as well as accumulated rewards – in a precise and succinct way. Algorithms to efficiently analyze such formulae are introduced. The approach is illustrated by model-checking a probabilistic cost model of the IPv4 zeroconf protocol for distributed address assignment in ad-hoc networks

A conversion electron Mossbauer spectroscopy study of ion beam mixing at Fe: polyethylene interface

The effects of ion beam induced atomic mixing at the Fe-Polyethylene interface have been investigated by means of conversion electron Mossbauer spectroscopy [CEMS]. It is shown that the as deposited and ion beam mixed composites exhibit distinctly different features. In particular, the ion beam mixed composite shows that presence of Fe2+ state in polyethylene matrix along with the Fe-C austenite like phase

QuantUM: Quantitative Safety Analysis of UML Models

When developing a safety-critical system it is essential to obtain an assessment of different design alternatives. In particular, an early safety assessment of the architectural design of a system is desirable. In spite of the plethora of available formal quantitative analysis methods it is still difficult for software and system architects to integrate these techniques into their every day work. This is mainly due to the lack of methods that can be directly applied to architecture level models, for instance given as UML diagrams. Also, it is necessary that the description methods used do not require a profound knowledge of formal methods. Our approach bridges this gap and improves the integration of quantitative safety analysis methods into the development process. All inputs of the analysis are specified at the level of a UML model. This model is then automatically translated into the analysis model, and the results of the analysis are consequently represented on the level of the UML model. Thus the analysis model and the formal methods used during the analysis are hidden from the user. We illustrate the usefulness of our approach using an industrial strength case study.Comment: In Proceedings QAPL 2011, arXiv:1107.074