Parameterized Verification of Graph Transformation Systems with Whole Neighbourhood Operations

We introduce a new class of graph transformation systems in which rewrite rules can be guarded by universally quantified conditions on the neighbourhood of nodes. These conditions are defined via special graph patterns which may be transformed by the rule as well. For the new class for graph rewrite rules, we provide a symbolic procedure working on minimal representations of upward closed sets of configurations. We prove correctness and effectiveness of the procedure by a categorical presentation of rewrite rules as well as the involved order, and using results for well-structured transition systems. We apply the resulting procedure to the analysis of the Distributed Dining Philosophers protocol on an arbitrary network structure.Comment: Extended version of a submittion accepted at RP'14 Worksho

On computing fixpoints in well-structured regular model checking, with applications to lossy channel systems

We prove a general finite convergence theorem for "upward-guarded" fixpoint expressions over a well-quasi-ordered set. This has immediate applications in regular model checking of well-structured systems, where a main issue is the eventual convergence of fixpoint computations. In particular, we are able to directly obtain several new decidability results on lossy channel systems.Comment: 16 page

The Parametric Ordinal-Recursive Complexity of Post Embedding Problems

Post Embedding Problems are a family of decision problems based on the interaction of a rational relation with the subword embedding ordering, and are used in the literature to prove non multiply-recursive complexity lower bounds. We refine the construction of Chambart and Schnoebelen (LICS 2008) and prove parametric lower bounds depending on the size of the alphabet.Comment: 16 + vii page

Reachability of Communicating Timed Processes

We study the reachability problem for communicating timed processes, both in discrete and dense time. Our model comprises automata with local timing constraints communicating over unbounded FIFO channels. Each automaton can only access its set of local clocks; all clocks evolve at the same rate. Our main contribution is a complete characterization of decidable and undecidable communication topologies, for both discrete and dense time. We also obtain complexity results, by showing that communicating timed processes are at least as hard as Petri nets; in the discrete time, we also show equivalence with Petri nets. Our results follow from mutual topology-preserving reductions between timed automata and (untimed) counter automata.Comment: Extended versio

An evaluation of orbital exenteration at st John eye hospital

A dissertation submitted to the Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, in fulfillment of the requirements for the degree of Master of Medicine in OphthalmologyOrbital exenteration is a surgical procedure used in the management of advanced malignant disease. It is used to treat both invasive and recurrent orbital tumours. This disfiguring surgical procedure involves removal of orbital contents, including the periorbita, eyelids and sometimes varying amounts of the surrounding peri-orbital skin. Studies from developing countries have shown that Squamous Cell Carcinoma (SCC) is the predominant indication for orbital exenteration. The high prevalence of conjunctival SCC in Sub-Saharan African has a strong link to ultraviolet radiation, Human Immunodeficiency Virus infection (HIV) and Human Papilloma Virus (HPV) infection. As the burden of disease increases, it becomes crucial for clinicians in Africa and other developing countries to understand how these Tumours’ behave, and how HIV potentially impacts on the disease. Such an evaluation may potentially benefit current management strategies. Furthermore, the need to effectively and appropriately manage such a neoplastic burden in a developing world setting with limited resources is of fundamental importance. This study reports an experience of orbital exenteration at this institution. OBJECTIVES: Firstly to describe all orbital tumours exenterated at St. John Eye Hospital over a four year period in terms of histopathology, tumour behaviour and completeness of excision. Secondly to determine if a link to HIV infection exists. DESIGN AND METHOD: A retrospective analysis of electronic records from the National Health Laboratory System (NHLS) was conducted on all the patients who underwent an orbital exenteration at St. John Eye Hospital from the 1st of July 2008 to 30th of June 2012 RESULTS: The total number of patients who underwent an orbital exenteration in the stated time period was 84. Twenty eight patients were excluded from the study and the final sample size was therefore 56. The average age of presentation was 42 and the overall female to male ratio was 1:1.07. Four patients underwent a lid sparing procedure while the remaining 52 patients had a total exenteration. The tissue of origin was conjunctival in 75% of cases. The most frequent presenting complaint and indication for surgery was an invasive conjunctival tumour in 56% of patients, followed by a gross orbital tumour in 27% of patients. Squamous cell carcinoma of the conjunctiva was the most frequently diagnosed tumour. Out of 56 specimens, 51(91.06%) were of the squamous cell type, 1.79% High Grade Squamous Dysplasia, 3.57% Leiomyosarcoma, 1.79% Metastatic Breast Adenocarcinoma and 1.79% Spindle Cell Melanoma. Histological grading of all specimens showed 69.64% of these tumours were moderately differentiated, 21.43% poorly differentiated and 8.93% were unknown. The distribution of the tumour staging in the sample group, according to the TNM Classification was as follows, 51.79%- Stage 4, 19.64% -Stage 3, 10.71%-Stage 2, 1.79% Stage 1, 1.79% Stage Tumour In Situ and 14.28% unknown. Regarding completeness of excision, 53.57% of tumours had positive tumour margins and 42.86% showed complete excision with clear margins, 3.57% were unknown. Only 28(50%) patients had a HIV result on electronic record. CD4 counts were available for 23 out of the 28 patients.MT201

Nesting parameters of Turtle Doves Streptopelia turtur arenicola breeding in Bahrain.

The Turtle Dove Streptopelia turtur arenicola (E Hartert, 1894) breeds from Morocco east to Tripoli, and from Iraq and Iran east through Afghanistan, Turkestan and Khirgiz steppes to northwest China (del Hoyo et al 1997). Within the Arabian peninsula it has been recorded breeding in Kuwait, Saudi Arabia, United Arab Emirates, Oman and Yemen in addition to Bahrain. It has not been recorded breeding in Qatar though suitable habitat exists there (Jennings 2010). Turtle Doves are widespread and common migrants throughout Arabia. They are thought to spend the winter in the Sahel and Ethiopia, returning north March–May to breed. Post breeding movements occur July–October and there is no evidence of wintering in Arabia (del Hoyo et al 1997, Beaman \u26 Madge 1998, Jennings 2010). The earliest record of breeding in Bahrain dates back to 1969, with additional records from 1982, 1985 and 1993 (Nightingale \u26 Hill 1993). The largest estimate was of 30 nests in Al Areen wildlife park in July 1985 (Nightingale \u26 Hill 1993). The colony monitored in the current study is immediately south of Al Areen wildlife park, in a group of mature desert broom Leptadenia pyrotechnica bushes, and may be the only Turtle Dove colony in Bahrain. Anecdotal evidence suggests that this breeding colony has been present annually for several decades at least, though recent evidence of birds breeding within the park was not available. The aims of the study were to gather information on the breeding parameters of this Turtle Dove colony, to estimate colony size and to conduct ringing of the chicks in the hope of getting recoveries to elucidate movement patterns of these Bahrain birds

Zero-Reachability in Probabilistic Multi-Counter Automata

We study the qualitative and quantitative zero-reachability problem in probabilistic multi-counter systems. We identify the undecidable variants of the problems, and then we concentrate on the remaining two cases. In the first case, when we are interested in the probability of all runs that visit zero in some counter, we show that the qualitative zero-reachability is decidable in time which is polynomial in the size of a given pMC and doubly exponential in the number of counters. Further, we show that the probability of all zero-reaching runs can be effectively approximated up to an arbitrarily small given error epsilon > 0 in time which is polynomial in log(epsilon), exponential in the size of a given pMC, and doubly exponential in the number of counters. In the second case, we are interested in the probability of all runs that visit zero in some counter different from the last counter. Here we show that the qualitative zero-reachability is decidable and SquareRootSum-hard, and the probability of all zero-reaching runs can be effectively approximated up to an arbitrarily small given error epsilon > 0 (these result applies to pMC satisfying a suitable technical condition that can be verified in polynomial time). The proof techniques invented in the second case allow to construct counterexamples for some classical results about ergodicity in stochastic Petri nets.Comment: 20 page

Parameterized Model-Checking for Timed-Systems with Conjunctive Guards (Extended Version)

In this work we extend the Emerson and Kahlon's cutoff theorems for process skeletons with conjunctive guards to Parameterized Networks of Timed Automata, i.e. systems obtained by an \emph{apriori} unknown number of Timed Automata instantiated from a finite set $U_1, \dots, U_n$ of Timed Automata templates. In this way we aim at giving a tool to universally verify software systems where an unknown number of software components (i.e. processes) interact with continuous time temporal constraints. It is often the case, indeed, that distributed algorithms show an heterogeneous nature, combining dynamic aspects with real-time aspects. In the paper we will also show how to model check a protocol that uses special variables storing identifiers of the participating processes (i.e. PIDs) in Timed Automata with conjunctive guards. This is non-trivial, since solutions to the parameterized verification problem often relies on the processes to be symmetric, i.e. indistinguishable. On the other side, many popular distributed algorithms make use of PIDs and thus cannot directly apply those solutions

Forward Analysis and Model Checking for Trace Bounded WSTS

We investigate a subclass of well-structured transition systems (WSTS), the bounded---in the sense of Ginsburg and Spanier (Trans. AMS 1964)---complete deterministic ones, which we claim provide an adequate basis for the study of forward analyses as developed by Finkel and Goubault-Larrecq (Logic. Meth. Comput. Sci. 2012). Indeed, we prove that, unlike other conditions considered previously for the termination of forward analysis, boundedness is decidable. Boundedness turns out to be a valuable restriction for WSTS verification, as we show that it further allows to decide all $\omega$-regular properties on the set of infinite traces of the system