Louchka Popova-Zeugmann

Bio: Louchka Popova-Zeugmann is an academic researcher from Humboldt University of Berlin. The author has contributed to research in topics: Petri net & Stochastic Petri net. The author has an hindex of 10, co-authored 33 publications receiving 496 citations. Previous affiliations of Louchka Popova-Zeugmann include Humboldt State University.

On Time Petri Nets.

Abstract: In this chapter we study Time Petri nets: After the introduction of this kind of time-dependent Petri net, we will discuss variations of the rules defining the possible state changes. We then show how to reduce the state space of an arbitrary Time Petri net to a discrete one and use this to study the dynamic behavior of these time-dependent Petri nets under both qualitative and quantitative aspects.

Time and Petri Nets

Abstract: At first glance the concepts of time and of Petri nets are quite contrary: while time determines the occurrences of events in a system, classic Petri nets consider their causal relationships and they represent events as concurrent systems. But if we take a closer look at how time and causality are intertwined we realize that there are many possible ways in which time and Petri nets interact. This book takes a closer look at three time-dependent Petri nets: Time Petri nets, Timed Petri nets, and Petri nets with time windows. The author first explains classic Petri nets and their fundamental properties. Then the pivotal contribution of the book is the introduction of different algorithms that allow us to analyze time-dependent Petri nets. For Time Petri nets, the author presents an algorithm that proves the behavioral equivalence of a net where time is designed once with real and once with natural numbers, so we can reduce the state space and consider the integer states exclusively. For Timed Petri nets, the author introduces two time-dependent state equations, providing a sufficient condition for the non-reachability of states, and she also defines a local transformation for converting these nets into Time Petri nets. Finally, she shows that Petri nets with time-windows have the ability to realize every transition sequence fired in the net omitting time restrictions. These classes of time-dependent Petri nets show that time alone does not change the power of a Petri net, in fact time may or may not be used to force firing. For Time Petri nets and Timed Petri nets we can say that they are Turing-powerful, and thus more powerful than classic Petri nets, because there is a compulsion to fire at some point in time. By contrast, Petri nets with time-windows have no compulsion to fire, their expressiveness power is less than that of Turing-machines. This book derives from advanced lectures, and the text is supported throughout withexamples and exercises. It issuitable for graduate courses in computer science, mathematics, engineering, and related disciplines, and as a reference for researchers.

Time Petri Nets for Modelling and Analysis of Biochemical Networks

Abstract: Biochemical networks are modelled at different abstraction levels. Basically, qualitative and quantitative models can be distinguished, which are typically treated as separate ones. In this paper, we bridge the gap between qualitative and quantitative models and apply time Petri nets for modelling and analysis of molecular biological systems. We demonstrate how to develop quantitative models of biochemical networks in a systematic manner, starting from the underlying qualitative ones. For this purpose we exploit the well-established structural Petri net analysis technique of transition invariants, which may be interpreted as a characterisation of the system?s steady state behaviour. For the analysis of the derived quantitative model, given as time Petri net, we present structural techniques to decide the time-dependent realisability of a transition sequence and to calculate its shortest and longest time length. All steps of the demonstrated approach consider systems of integer linear inequalities. The crucial point is the total avoidance of any state space construction. Therefore, the presented technology may be applied also to infinite systems, i.e. unbounded Petri nets.

Time Petri Nets

Abstract: In this chapter we study Time Petri nets: After the introduction of this kind of time-dependent Petri net, we will discuss variations of the rules defining the possible state changes. We then show how to reduce the state space of an arbitrary Time Petri net to a discrete one and use this to study the dynamic behavior of these time-dependent Petri nets under both qualitative and quantitative aspects.

Worst-case Analysis of Concurrent Systems with Duration Interval Petri Nets

Abstract: This paper deals with computing the minimal and maximal execution durations in a given concurrent control system in order to support dependability engineering by assuring the meeting of prescribed deadlines. For that purpose, a new type of time-dependent Petri nets - the Duration Interval Petri net - is introduced, and a dedicated reachability graph is defined in a discrete way. Using this reachability graph, shortest and largest time paths between two arbitrary states of the control system, and by this way minimal and maximal execution times, can be computed.

Comparing the Expressiveness of Timed Automata and Timed Extensions of Petri Nets

Abstract: Time dependant models have been intensively studied for many reasons, among others because of their applications in software verification and due to the development of embedded platforms where reliability and safety depend to a large extent on the time features. Many of the time dependant models were suggested as real-time extensions of several well-known untimed models. The most studied formalisms include Networks of Timed Automata which extend the model of communicating finite-state machines with a finite number of real-valued clocks, and timed extensions of Petri nets where the added time constructs include e.g. time intervals that are assigned to the transitions (Time Petri Nets) or to the arcs (Timed-Arc Petri Nets). In this paper, we shall semi-formally introduce these models, discuss their strengths and weaknesses, and provide an overview of the known results about the relationships among the models.

Computational modelling of the receptor-tyrosine-kinase-activated MAPK pathway

Abstract: The MAPK (mitogen-activated protein kinase) pathway is one of the most important and intensively studied signalling pathways It is at the heart of a molecular-signalling network that governs the growth, proliferation, differentiation and survival of many, if not all, cell types It is de-regulated in various diseases, ranging from cancer to immunological, inflammatory and degenerative syndromes, and thus represents an important drug target Over recent years, the computational or mathematical modelling of biological systems has become increasingly valuable, and there is now a wide variety of mathematical models of the MAPK pathway which have led to some novel insights and predictions as to how this system functions In the present review we give an overview of the processes involved in modelling a biological system using the popular approach of ordinary differential equations Focusing on the MAPK pathway, we introduce the features and functions of the pathway itself before comparing the available models and describing what new biological insights they have led to

Childhood maltreatment and inflammatory markers: a systematic review.

Abstract: OBJECTIVE: Childhood maltreatment (CM) has been associated with several diseases in adult life, including diabetes, obesity and mental disorders. Inflammatory conditions have been postulated as possible mediators of this relationship. The aim was to conduct a systematic review regarding the association between CM and inflammatory markers in adulthood. METHOD: A literature search of the PubMed, ISI, EMBASE and PsychINFO databases was conducted. The key terms used were as follows: 'Child Maltreatment', 'Childhood Trauma', 'Early Life Stress', 'Psychological Stress', 'Emotional Stress', 'Child Abuse' and 'Child Neglect'. They were cross-referenced separately with the terms: 'C-reactive Protein (CRP)', 'Tumor Necrosis Factor', 'Cytokine', 'Interleukin', 'Inflammatory' and 'Inflammation'. RESULTS: Twenty articles remained in the review after exclusion criteria were applied. Studies showed that a history of CM was associated with increased levels of CRP, fibrinogen and proinflammatory cytokines. Increased levels of circulating CRP in individuals with a history of CM were the most robust finding among the studies. Data about anti-inflammatory mediators are still few and inconsistent. CONCLUSION: Childhood maltreatment is associated with a chronic inflammatory state independent of clinical comorbidities. However, studies are heterogeneous regarding CM assessment and definition. Important methodological improvements are needed to better understand the potential impact of CM on inflammatory response. Language: en