multimodality image registration by maximization of mutual information a new approach to the problem of multimodality medical image registration is proposed using a basic concept from information theory mutual information mi or relative entropy as a new matching criterion the method presented in this paper applies mi to measure the statistical dependence or information redundancy between the image intensities of corresponding voxels in both images which is assumed to be maximal if the images are geometrically aligned maximization of mi is a very general and powerful criterion because no assumptions are made regarding the nature of this dependence and no limiting constraints are imposed on the image content of the modalities involved the accuracy of the mi criterion is validated for rigid body registration of computed tomography ct magnetic resonance mr and photon emission tomography pet images by comparison with the stereotactic registration solution while robustness is evaluated with respect to implementation issues such as interpolation and optimization and image content including partial overlap and image degradation our results demonstrate that subvoxel accuracy with respect to the stereotactic reference solution can be achieved completely automatically and without any prior segmentation feature extraction or other preprocessing steps which makes this method very well suited for clinical applications

a complete equational axiomatization for mpa with string iteration we study equational axiomatizations of bisimulation equivalence for the language obtained by extending milner s basic ccs with string iteration string iteration is a variation on the original binary version of the kleene star operation p q obtained by restricting the first argument to be a non empty sequence of atomic actions we show that for every positive integer k bisimulation equivalence over the set of processes in this language with loops of length at most k is finitely axiomatizable provided that the set of actions is finite we also offer an infinite equational theory that completely axiomatizes bisimulation equivalence over the whole language we prove that this result cannot be improved upon by showing that no finite equational axiomatization of bisimulation equivalence over basic ccs with string iteration can exist unless the set of actions is empty

the equivalence in the dcp model abstract the ever increasing complexity of systems stimulates research in the area of processes equivalences in this paper processes are considered as black boxes characterized by their external interactions only and the equivalences are based on this assumption the equivalence relation induced from the partial order defined in johnston s model of discrete communicating processes is studied with the intention of finding its place within the chain of existing equivalences namely trace equivalence testing equivalence bisimulation and observational equivalence unfortunately this model does not compare easily with the others however a modification to the original model consisting in keeping more information within a process identifier namely all of its immediately performable events and explicitly writing deadlocks gives a new equivalence relation j which is finer than the original one and which has the property of being equivalent to bisimulation

transition system specifications with negative premises abstract in this article the general approach to plotkin style operational semantics of groote and vaandrager 1989 is extended to transition system specifications tsss with rules that may contain negative premises two problems arise firstly the rules may be inconsistent and secondly it is not obvious how a tss determines a transition relation we present a general method based on the stratification technique in logic programming to prove consistency of a set of rules and we show how a specific transition relation can be associated with a tss in a natural way then a special format for the rules the ntyft ntyxt format is defined it is shown that for this format three important theorems hold the first theorem says that bisimulation is a congruence if all operators are defined using this format the second theorem states that under certain restrictions a tss in ntyft format can be added conservatively to a tss in pure ntyft ntyxt format finally it is shown that the trace congruence for image finite processes induced by the pure ntyft ntyxt format is precisely bisimulation equivalence

the algebra of timed processes atp the algebra of timed processes atp uses a notion of discrete global time and suggests a conceptual framework for introducing time by extending untimed languages the action vocabularly of atp contains a special element representing the progress of time the algebra has apart from standard operators of process algebras such as prefixing by an action alternative choice and parallel composition a primitive unit delay operator for two arguments processes p and q this operator gives a process which behaves as p before the execution of a time event and behaves as q afterwards it is shown that several d unit delay constructs such as timeouts and watchdogs can be expressed in terms of the unit delay operator and standard process algebra operators a sound and complete axiomatization for bisimulation semantics is studied and two examples illustrating the adequacy of the language for the description of timed systems are given finally we provide a comparison with existing timed process algebras

a logical characterization of observation equivalence brookes and rounds 1983 showed that a finitary formal language regular trace language or reg tl for short which allowed a certain kind of quantification using regular subsets of was not strong enough to distinguish all pairs of observationally inequivalent synchronization trees in the present paper we extend this result to show that there is no class c of subsets of such that c tl can distinguish all pairs of observationally inequivalent synchroni zation trees we then give a characterization of observation equivalence in terms of an infinitary formal language s tl o this language is obtained as an extension of the language s tl singleton trace language of hennessy and milner by the addition of a connective of w conjunctions of formulas of finite hounded depth

unfolding and fixpoint semantics of concurrent constraint logic programs we present a new semantics for a language in the family of concurrent constraint logic languages the semantics can be based on a notion of clause unfolding since the language is closed under this transformation the unfolding semantics is obtained as limit of an infinite unfolding process unfolding is also used to define an immediate consequences operator and therefore a fixpoint semantics in the typical logic programming style the result of both the unfolding and the fixpoint semantics is a set of reactive behaviors which are trees abstractly representing all the possible computations of a program including deadlocks and finite failures the semantics can be made more abstract by defining a suitable notion of equivalence on reactive behaviors in our approach this can be done by reasoning on constraints only thus generalizing the typical behavior of constraint logic programming

compositionality of hennessy milner logic by structural operational semantics this paper presents a method for the decomposition of hml formulas it can be used to decide whether a process algebra term satisfies a hml formula by checking whether subterms satisfy certain formulas obtained by decomposing the original formula the method uses the structural operational semantics of the process algebra the main contribution of this paper is the extension of an earlier decomposition method for the de simone format from the ph d thesis of larsen in 1986 to more general formats

structural operational semantics for weak bisimulations in this study we present rule formats for four main notions of bisimulation with silent moves weak bisimulation is a congruence for any process algebra defined by wb cool rules we have similar results for rooted weak bisimulation milner s observational equivalence branching bisimulation and rooted branching bisimulation the theorems stating that say observational equivalence is an appropriate notion of equality for ccs are corollaries of the results of this paper we also give sufficient conditions under which equational axiom systems can be generated from operational rules indeed many equational axiom systems appearing in the literature are instances of this general theory

bisimulation on speed worst case efficiency this paper introduces a novel bi simulation based faster than preorder which relates asynchronous processes where the relative speeds of system components are indeterminate with respect to their worst case timing behavior the study is conducted for a conservative extension of the process algebra ccs called tacs which permits the specification of upper time bounds on action occurrences tacs complements work in plain process algebras which compares asynchronous processes with respect to their functional reactive behavior only and in timed process algebras which focus on analyzing synchronous processes the most unusual contribution is in showing that the proposed faster than preorder coincides with several other preorders two of which consider the absolute times at which actions occur in system runs the paper also develops the semantic theory of tacs by studying congruence properties equational laws and abstractions from internal actions two examples one dealing with mail delivery and one relating two implementations of a simple storage system testify to the practical utility of the new theory

a category of compositional domain models for separable stone spaces in this paper we introduce sfpm a category of sfp domains which provides very satisfactory domain models i e partializations of separable stone spaces 2 stone spaces more specifically sfpm is a subcategory of sfpep closed under direct limits as well as many constructors such as lifting sum product and plotkin powerdomain with the notable exception of the function space constructor sfpm is structurally well behaved in the sense that the functor max which associates to each object of sfpm the stone space of its maximal elements is compositional with respect to the constructors above and continuous a correspondence can be established between these constructors over sfpm and appropriate constructors on stone spaces whereby sfpm domain models of stone spaces defined as solutions of a vast class of recursive equations in sfpm can be obtained simply by solving the corresponding equations in sfpm moreover any continuous function between two 2 stone spaces can be extended to a continuous function between any two sfpm domain models of the original spaces the category sfpm does not include all the sfp s with a 2 stone space of maximal elements csfp s we show that the csfp s can be characterized precisely as suitable retracts of sfpm objects then the results proved for sfpm easily extends to the wider category having csfp s as objects using sfpm we can provide a plethora of partializations of the space of finitary hypersets the hyperuniverse n ann new york acad sci 806 1996 140 these includes the classical ones proposed in abramsky a cook s tour of the finitary non well founded sets unpublished manuscript 1988 inform comput 92 2 1991 161 and mislove et al inform comput 93 1 1991 16 which are also shown to be non isomorphic thus providing a negative answer to a problem raised in mislove et al

a partial ordering semantics for ccs a new operational semantics for pure ccs is proposed that considers the parallel operator as a first class one and permits a description of the calculus in terms of partial orderings the new semantics also for unguarded agents is given in the sos style via the partial ordering derivation relation ccs agents are decomposed into sets of sequential subagents the new derivations relate sets of subagents and describe their actions and the casual dependencies among them the computations obtained by composing partial ordering derivations are observed either as interleaving or partial orderings of events interleavings coincide with milner s many step derivations and linearizations of partial orderings are all and only interleavings abstract semantics are obtained by introducing two relations of observational equivalence and congruence that preserve concurrency these relations are finer than milner s in that they distinguish interleaving of sequential nondeterministic agents from their concurrent execution

on data dependence of exponential stability and stability radii for linear time varying differential algebraic systems abstract this paper is addressed to some questions concerning the exponential stability and its robustness measure for linear time varying differential algebraic systems of index 1 first the bohl exponent theory that is well known for ordinary differential equations is extended to differential algebraic equations then it is investigated that how the bohl exponent and the stability radii with respect to dynamic perturbations for a differential algebraic system depend on the system data the paper can be considered as a continued and complementary part to a recent paper on stability radii for time varying differential algebraic equations n h du v h linh stability radii for linear time varying differential algebraic equations with respect to dynamic perturbations j differential equations 230 2006 579 599

bisimulation can t be traced in the concurrent language ccs two programs are considered the same if they are bisimilar several years and many researchers have demonstrated that the theory of bisimulation is mathematically appealing and useful in practice however bisimulation makes too many distinctions between programs we consider the problem of adding operations to ccs to make bisimulation fully abstract we define the class of gsos operations generalizing the style and technical advantages of ccs operations we characterize gsos congruence in as a bisimulation like relation called ready simulation bisimulation is strictly finer than ready simulation and hence not a congruence for any gsos language

on stability of time varying linear differential algebraic equations we develop a stability theory for time varying linear differential algebraic equations daes well known stability concepts of ordinary differential equations are generalised to daes and characterised lyapunov s direct method is derived as well as the converse of the stability theorems stronger results are achieved for daes which are transferable into standard canonical form in this case the existence of the generalised transition matrix is exploited

intensity based 2 d 3 d registration of cerebral angiograms we propose a new method for aligning three dimensional 3 d magnetic resonance angiography mra with 2 d x ray digital subtraction angiograms dsa our method is developed from our algorithm to register computed tomography volumes to x ray images based on intensity matching of digitally reconstructed radiographs drrs to make the dsa and drr more similar we transform the mra images to images of the vasculature and set to zero the contralateral side of the mra to that imaged with dsa we initialize the search for a match on a user defined circular region of interest we have tested six similarity measures using both unsegmented mra and three segmentation variants of the mra registrations were carried out on images of a physical neuro vascular phantom and images obtained during four neuro vascular interventions the most accurate and robust registrations were obtained using the pattern intensity gradient difference and gradient correlation similarity measures when used in conjunction with the most sophisticated mra segmentations using these measures 95 of the phantom start positions and 82 of the clinical start positions were successfully registered the lowest root mean square reprojection errors were 1 3 mm standard deviation 0 6 for the phantom and 1 5 mm standard deviation 0 9 for the clinical data sets finally we present a novel method for the comparison of similarity measure performance using a technique borrowed from receiver operator characteristic analysis

asynchronous mappings and asynchronous cellular automata the aim of this paper is the study of asynchronous automata a special kind of automata which encode the independency relation between actions and which enable their concurrent execution these automata introduced by zielonka rairo inform theor appl 21 99 135 1987 constitute a natural extension of finite automata to the case of asynchronous parallelism their behaviour is described by trace languages subsets of partially commutative monoids the main result concerning this class of automata states that they accept exactly all recognizable trace languages in this paper we give new improved constructions of asynchronous automata in the final part of the paper we present a distributed system of messages with bounded time stamps based on asynchronous automata

additive models of probabilistic processes we propose a new model of probabilistic processes in this model a probability is assigned to the action of a prefix and a probability distribution is assigned to the components of a parallel composition in addition the probability of a transition of a probabilistic summation is evaluated as the sum of the probabilities of the same transition of summands multiplied by the probabilities associated to them in the summation the concepts of strong bisimulation degree and weak bisimulation degree are introduced these notions provide us with continuous spectra of strong bisimilarities weak bisimilarities and observation congruences which equate probabilistic processes with different degrees of belief various equational laws of probabilistic processes with respect to these equivalence relations are presented and substitutivities of these equivalence relations under various combinators are established

a unified floquet theory for discrete continuous and hybrid periodic linear systems abstract in this paper we study periodic linear systems on periodic time scales which include not only discrete and continuous dynamical systems but also systems with a mixture of discrete and continuous parts e g hybrid dynamical systems we develop a comprehensive floquet theory including lyapunov transformations and their various stability preserving properties a unified floquet theorem which establishes a canonical floquet decomposition on time scales in terms of the generalized exponential function and use these results to study homogeneous as well as nonhomogeneous periodic problems furthermore we explore the connection between floquet multipliers and floquet exponents via monodromy operators in this general setting and establish a spectral mapping theorem on time scales finally we show this unified floquet theory has the desirable property that stability characteristics of the original system can be determined via placement of an associated but time varying system s poles in the complex plane we include several examples to show the utility of this theory

infinite streams and finite observations in the semantics of uniform concurrency two ways of assigning meaning to a language with uniform concurrency are presented and compared the language has uninterpreted elementary actions from which statements are composed using sequential composition nondeterministic choice parallel composition with communication and recursion the first semantics uses infinite streams in the sense which is a refinement of the linear time semantics of de bakker et al the second semantics uses the finite observations of hoare et al situated in between the divergence and readiness semantics of olderog hoare it is shown that the two models are isomorphic and that this isomorphism induces an equivalence result between the two semantics

time domain analog circuit simulation recent developments of new methods for simulating electric circuits are described emphasis is put on methods that fit existing datastructures for backward differentiation formulae methods these methods can be modified to apply to hierarchically organized datastructures which allows for efficient simulation of large designs of circuits in the electronics industry

two decentralized algorithms for strong interaction fairness for systems with unbounded speed variability abstract we present two randomized algorithms one for message passing and the other for shared memory that with probability 1 schedule multiparty interactions in a strongly fair manner both algorithms improve upon a previous result by joung and smolka proposed in a shared memory model along with a straightforward conversion to the message passing paradigm in the following aspects first processes speeds as well as communication delays need not be bounded by any predetermined constant secondly our algorithms are completely decentralized and the shared memory solution makes use of only single writer variables finally both algorithms are symmetric in the sense that all processes execute the same code and no unique identifier is used to distinguish processes

ccs expressions finite state processes and three problems of equivalence abstract we examine the computational complexity of testing finite state processes for equivalence in milner s calculus of communicating systems ccs the equivalence problems in ccs are presented as refinements of the familiar problem of testing whether two nondeterministic finite automata nfa are equivalent i e accept the same language three notions of equivalence proposed for ccs are investigated namely observational equivalence strong observational equivalence and failure equivalence we show that observational equivalence can be tested in polynomial time as defined in ccs observational equivalence is the limit of a sequence of successively finer equivalence relations k where 1 is nondeterministic finite automaton equivalence we prove that for each fixed k deciding k is pspace complete we show that strong observational equivalence can be decided in polynomial time by reducing it to generalized partitioning a new combinatorial problem of independent interest finally we demonstrate that testing for failure equivalence is pspace complete even for a very restricted type of process

new families of fourier eigenfunctions for steerable filtering a new diadic family of eigenfunctions of the 2 d fourier transform has been discovered specifically new wavelets are derived by steering the elongated hermite gauss filters with respect to rotations thus obtaining a natural generalization of the laguerre gauss harmonics interestingly these functions are also proportional to their 2 d fourier transform their analytical expression is provided in a compact and treatable form by means of a new ad hoc matrix notation in which the cases of even and odd orders of the hermite polynomials are unified moreover these functions can be efficiently implemented by means of a recursive formula that is derived in this paper the proposed filters are applied to the problem of gradient estimation to improve the theoretical canny tradeoff of position accuracy versus noise rejection that occurs in edge detection experimental results show considerable improvements in using the new wavelets over both isotropic gaussian derivatives and other elongated steerable filters more recently introduced finally being the proposed wavelets a set of fourier eigenfunctions they can be of interest in other fields of science such as optics and quantum mechanics

gsos and finite labelled transition systems recently there has been considerable interest in studying formats of plotkin style inference rules which ensure that the induced labelled transition system semantics have certain properties in this note i shall give a contribution to this line of research by giving a restricted version of bloom istrail and meyer s gsos format bloom et al 1988 bloom 1989 which induces finite labelled transition systems

a compositional protocol verification using relativized bisimulation abstract the purpose of this paper is to illustrate a compositional proof method for communicating systems that is a method in which a property p of a complete system is demonstrated by first decomposing the system then demonstrating properties of the subsystems which are strong enough to entail property p for the complete system in any compositional proof method it is essential that one can abstract away the behavioural aspects of the subsystem which are irrelevant in the context of the complete system our method is an extension of the well established notion of bisimulation it is called relative bisimulation and was developed specifically to allow for such abstractions we illustrate the method in a proof of correctness for a version of the alternating bit protocol

stable families of behavioural equivalences abstract many of the behavioural equivalences studied in the literature see 1 2 3 4 are defined generically on any transition system in particular on their own quotient system it would seem reasonable to expect such an equivalence to be idempotent in this respect in other words to yield the identity the second time we capture this idea in the notion of a stable family of preorders on transition systems and investigate the stability of the equivalences in 1 2 3 4 in addition our approach involves general schemes of definition of equivalences on transition systems which lead to extensions of the hierarchy results of 1

a fully abstract denotational semantics for the calculus of higher order communicating systems abstract in this paper we study the calculus of higher order communicating systems chocs thomsen proc of popl 89 acm 1989 pp 143 154 inform comput 116 1 1995 38 57 in a denotational setting we present a construction of a denotational semantics for chocs which resides in a domain constructed using the standard constructions of separated sum cartesian product the plotkin power domain constructor and recursively defined domains we show under mild restrictions that the denotational semantics and the operational semantics of chocs are fully abstract we have previously proved using bisimulation arguments that processes as first class objects are powerful enough to simulate recursion however the proof is very long and tedious to demonstrate the power of the denotational approach we use it to obtain a very simple proof of the simulation of recursion result

an operational semantics for a calculus for wireless systems in wireless systems the communication mechanism combines features of broadcast synchrony and asynchrony we develop an operational semantics for a calculus of wireless systems we present different reduction semantics and a labelled transition semantics and prove correspondence results between them finally we apply cws to the modelling of the alternating bit protocol and prove a simple correctness result as an example of the kind of properties that can be formalized in this framework a major goal of the semantics is to describe the forms of interference among the activities of processes that are peculiar of wireless systems such interference occurs when a location is simultaneously reached by two transmissions the reduction semantics differ on how information about the active transmissions is managed we use the calculus to describe and analyse a few properties of a version of the alternating bit protocol

the expressive power of implicit specifications abstract in this paper we investigate the expressive power of implicit specifications of concurrent systems that is we consider specifications s specifying a system p not directly but rather in combination with a given environment formally we shall represent the environment as a ccs context of the form a l where a is a process expression and l and are the parallel restriction and renaming operators of ccs respectively we investigate the expressive power of the following three types of implicit specifications a p l b i where is strong bisimulation equivalence and b is a process expression a p l s ii where s is a modal specification and is refinement between modal specifications a generalization of bisimulation equivalence and a p l f iii where f is a formula of hennessy milner logic extended with a maximal recursion construct the paper offers the following two main results when a b and s are recursion free and f is a hennessy milner logic formula the expressive powers of all three types of implicit specifications are the same and equal that of hennessy milner logic when a and s are regular the expressive powers of implicit specifications of type ii and iii are the same and identical to that of hennessy milner logic extended with maximal recursion finally we recall from 21 that the expressive power of implicit specifications does not increase by modelling the environment as other contexts of ccs or other process calculi

generalized om bisimulation history preserving bisimilarity and maximality preserving bisimilarity take full account of the interplay between causality and branching and they are congruences w r t action refinement for suitable classes of petri nets but even for finite safe petri nets they are based on possibly infinite transition systems and it is not obvious how to decide them om bisimulation gives a characterization of history preserving bisimulation for safe nets without internal moves and it allows a decidability result in this paper we generalize om bisimulation and this decidability result to safe nets with internal moves and also treat the case of maximality preserving bisimulation

cpo models for compact gsos languages in this paper we present a general way of giving denotational semantics to a class of languages equipped with an operational semantics that fits the gsos format of bloom istrail and meyer the canonical model used for this purpose will be abramsky s domain of synchronization trees and the denotational semantics automatically generated by our methods will be guaranteed to be fully abstract with respect to the finitely observable part of the bisimulation preorder in the process of establishing the full abstraction result we also obtain several general results on the bisimulation preorder including a complete axiomatization for it and give a novel operational interpretation of gsos languages

full abstraction and recursion the question of extending semantic models for a programming language without recursion to a larger language supporting recursion is of fundamental importance if one wants to develop a modular approach to building models in our previous work 14 we showed how to extend models for a language without recursion to models for a language in which unnested recursion was supported via simultaneous systems of recursive equations in that setting we proved that modest assumptions about the models enabled us to lift adequacy and full abstraction for the models of the base language to analogous results for the models of the extended language in this paper we tackle similar problems for languages with explicit recursion operators starting with a base language l we define what it means for an ordered denotational model for l to be order adequate and strongly order fully abstract with respect to an ordered operational model for l by freely adding identifiers x x and recursion operators x for each x x we obtain an extended language l x in which we single out the sublanguage l c of closed terms we then give general conditions which ensure that an ordered operational model o l o and a related order adequate and strongly order fully abstract denotational model d l d can be extended to an ordered operational model o c l c o and a related ordered denotational model d c l c d which also is order adequate and strongly order fully abstract

on the final sequence of a finitary set functor a standard construction of the final coalgebra of an endofunctor involves defining a chain of iterates starting at the final object of the underlying category and successively applying the functor in this paper we show that for a finitary set functor this construction always yields a final coalgebra in 2 steps

proof systems for satisfiability in hennessy milner logic with recursion abstract an extension of hennessy milner logic with recursion is presented a recursively specified formula will have two standard interpretations a minimal one and a maximal one minimal interpretations of formulas are useful for expressing liveness properties of processes whereas maximal interpretations are useful for expressing safety properties we present sound and complete proof systems for both interpretations for when a process satisfies a possibly recursive formula the rules of the proof systems consist of an introduction rule for each possible structure of a formula and are intended to extend the work of stirling and winskel moreover the proof systems may be presented directly in prolog to yield a decision procedure for verifying when a finite state process satisfies a specification given as a possibly recursive formula

criteria for the trivial solution of differential algebraic equations with small nonlinearities to be asymptotically stable differential algebraic equations consisting of a constant coefficient linear part and a small nonlinearity are considered conditions that enable linearizations to work well are discussed in particular for index 2 differential algebraic equations there results a kind of perron theorem that sounds as clear as its classical model

a complete axiomatization of finite state acsr processes a real time process algebra called acsr has been developed to facilitate the specification and analysis of real time systems acsr supports synchronous timed actions and asynchronous instantaneous events timed actions are used to represent the usage of resources and to model the passage of time events are used to capture synchronization between processes to be able to specify real time systems accurately acsr supports a notion of priority that can be used to arbitrate among timed actions competing for the use of resources and among events that are ready for synchronization in addition to operators common to process algebra acsr includes the scope operator which can be used to model timeouts and interrupts equivalence between acsr terms is based on the notion of strong bisimulation this paper briefly describes the syntax and semantics of acsr and then presents a set of algebraic laws that can be used to prove equivalence of acsr processes the contribution of this paper is the soundness and completeness proofs of this set of laws the completeness proof is for finite state acsr processes which are defined to be processes without free variables under parallel operator or scope operator

non regular iterators in process algebra we consider three forms of non regular iteration in process algebra the push down operation de5ned by x y x x y x y y the nesting operation de5ned by x y x x y x y and the back and forth operation de5ned by xy x xy y y in the process algebraic framework acp with abstraction and one of orwe provide de5nitions of the following standard processes stack context free process bag and queue these de5nitions apply to all standard behavioural equivalences we only use x x whereis the silent step moreover these results yield the expressive power to express computable processes modulo rooted branching bisimulation equivalence and hence support the equational founding of process algebra standard processes can be represented as terms c 2001 elsevier science b v all rights reserved

deciding bisimulation equivalences for a class of non finite state programs traditionally many automatic program verification techniques have been applicable only to finite state programs in this paper we extend some of these techniques to a class of infinite state programs that in addition to having a finite state control component may read store and write but not perform any other computations on data such programs are data independent in the sense that their behavior does not depend on the actual data values supplied we consider the problems of deciding strong equivalence and observation equivalence defined by bisimulations as in ccs between such programs these equivalences have major applications in verification of communication protocols we present reductions of these problems to the problem of deciding strong equivalence and observation equivalence between finite state programs for which polynomial time algorithms exist the equivalence problems on data independent programs are shown to be np hard in the size of the programs

petri nets event structures and domains part i abstract the general aim of this paper is to find a theory of concurrency combining the approaches of petri and scott and others in part i we introduce our formalisms to connect the abstract ideas of events and domains of information we show how casual nets induce certain kinds of domains where the information points are certain sets of events this allows translations between the languages of net theory and domain theory following the idea that events of causal nets are occurrences we generalise causal nets to occurrence nets by adding forwards conflict just as infinite flow charts unfold finite ones so transition nets can be unfolded into occurrence nets next we extend the above connections between nets and domains to these new nets event structures which are intermediate between nets and domains play an important part in all our work finally as an example of how concepts translate from one formalism to the other we show how petri s notion of confusion ties up with kahn and plotkin s concrete domains in part ii we shall continue the job of connecting up notions within net theory and the theory of domains in particular we shall examine the idea of states of computations

the category theoretic solution of recursive domain equations recursive specifications of domains plays a crucial role in denotational semantics as developed by scott and strachey and their followers the purpose of the present paper is to set up a categorical framework in which the known techniques for solving these equations find a natural place the idea is to follow the well known analogy between partial orders and categories generalizing from least fixed points of continuous functions over cpos to initial ones of continuous functors over omega categories to apply these general ideas we introduce wand s bf o categories where the morphism sets have a partial order structure and which include almost all the categories occurring in semantics the idea is to find solutions in a derived category of embeddings and we give order theoretic conditions which are easy to verify and which imply the needed categorical ones the main tool is a very general form of the limit colimit coincidence remarked by scott in the concluding section we outline how compatibilit

on the semantics of markov automata markov automata describe systems in terms of events which may be nondeterministic may occur probabilistically or may be subject to time delays we define a novel notion of weak bisimulation for such systems and prove that this provides both a sound and complete proof methodology for a natural extensional behavioural equivalence between such systems a generalisation of reduction barbed congruence the well known touchstone equivalence for a large variety of process description languages

robust gradient based 3 d 2 d registration of ct and mr to x ray images one of the most important technical challenges in image guided intervention is to obtain a precise transformation between the intrainterventional patient s anatomy and corresponding preinterventional 3 d image on which the intervention was planned this goal can be achieved by acquiring intrainterventional 2 d images and matching them to the preinterventional 3 d image via 3 d 2 d image registration a novel 3 d 2 d registration method is proposed in this paper the method is based on robustly matching 3 d preinterventional image gradients and coarsely reconstructed 3 d gradients from the intrainterventional 2 d images to improve the robustness of finding the correspondences between the two sets of gradients hypothetical correspondences are searched for along normals to anatomical structures in 3 d images while the final correspondences are established in an iterative process combining the robust random sample consensus algorithm ransac and a special gradient matching criterion function the proposed method was evaluated using the publicly available standardized evaluation methodology for 3 d 2 d registration consisting of 3 d rotational x ray computed tomography magnetic resonance mr and 2 d x ray images of two spine segments and standardized evaluation criteria in this way the proposed method could be objectively compared to the intensity gradient and reconstruction based registration methods the obtained results indicate that the proposed method performs favorably both in terms of registration accuracy and robustness the method is especially superior when just a few x ray images and when mr preinterventional images are used for registration which are important advantages for many clinical applications

about fair asynchrony abstract this paper examines the joint influence of fairness and asynchrony on the semantic modelling of a c c s like language fairness is the guarantee for every agent engaged in a computation to communicate with the other asynchronous agents if such communications are infinitely often possible programs are compared according to an implementation preorder which reflects the inclusion of observable properties whenever for every context c and for every program r no computation of r experimenting upon c p allows to recognize p versus q p is considered less than q a fully abstract model of the preorder is constructed in a domain of infinitary language preferred here to classical algebraic domains the restriction to bounded parallelism is analysed in that simplified framework the model turns effective and moreover decidable

a process algebra for timed systems a standard process algebra is extended by a new action which is meant to denote idling until the next clock cycle a semantic theory based on testing is developed for the new language this is characterised in terms of barbs a variety of ready traces and also characterised as the initial theory generated by a set of equations

determinancy observation equivalence trace equivalence abstract if an experiment s is conducted on a parallel process p then in general different processes may result from the experiment due to the nondeterministic behaviour of p in the notation of milner 1980 p p for different p process p is called determinate if the resulting processes are all equivalent i e if p p and p p then p and p are equivalent this means that although p behaves nondeterministically this cannot be detected by an observer of p let denote observation equivalence used in ccs milner 1980 let f denote the much weaker failure equivalence used for csp hoare et al 1981 brookes 1983 and let t denote the still weaker trace equivalence we show that the three corresponding notions of determinancy are the same and that for determinate processes f and t are the same determinacy is preserved under and f but not under t

a context dependent equivalence between processes abstract in recent years several equivalences between nondeterministic and concurrent processes have been proposed in order to capture different notions of the extensional behaviour of a process usually the equivalences are congruences with respect to the process constructing operations in order to support hierarchic development of systems with the purpose of achieving more flexible hierarchic development methods we suggest parametrizing the equivalences with information about contexts we carry out the suggestion in full for the bisimulation equivalence which we parameterize with a special type of context information called environments as a main theorem we offer a useful characterization of the information ordering on environments also a modal characterization of the parameterized bisimulation equivalence is presented

distributed bisimulations a new equivalence between concurrent processes is proposed it generalizes the well known bisimulation equivalence to take into account the distributed nature of processes the result is a noninterleaving semantic theory concurrent processes are differentiated from processes that are non deterministic but sequential the new equivalence together with its observational version is investigated for a subset of the language ccs and various algebraic characterizations are obtained

continuation method for computing certain singular points for index 1 differential algebraic equations we will use the arclength continuation method to compute certain singular points for index 1 daes backward difference method will be employed to descretize the problem we will show that the resulting numerical iterative matrix is nonsingular in the presence of the singularity some numerical examples will be given to show the efficiency of the resulting augmented system

bisimulation of automata abstract we view ccs terms as defining nondeterministic automata an algebraic representation of automata is given and categories of automata and simulations between them are defined the crucial feature is the consideration of only the pure simulations which carry the pure actual determined states of the domain automation to the pure states of the codomain automaton the pure epimorphisms between the automata partition the category into bisimulation equivalence classes there is a unique canonical representative for each bisimulation equivalence class these results hold for weak bisimulation and hence for strong bisimulation essentially the same results are obtained with regard to rooted bisimulation equivalence classes of automata with start states

stability of periodic solutions of index 2 differential algebraic systems this paper deals with periodic index 2 differential algebraic equations and the question whether a periodic solution is stable in the sense of lyapunov as the main result a stability criterion is proved this criterion is formulated in terms of the original data so that it may be used in practical computations

non well founded sets modeled as ideal fixed points abstract motivated by ideas from the study of abstract data types we show how to interpret non well founded sets as fixed points of continuous transformations of an initial continuous algebra we conisder a preordered structure closely related to the set hf of well founded hereditarily finite sets by taking its ideal completion we obtain an initial continuous algebra in which we are able to solve all of the usual systems of equations that characterize hereditarily finite non well founded sets in this way we are able to obtain a structure which is isomorphic to hf 1 the non well founded analog of hf

a semantic theory for value passing processes based on the late approach a general class of languages for value passing calculi based on the late semantic approach is defined and a concrete instantiation of the general syntax is given this is a modification of the standard ccs according to the late approach three kinds of semantics are given for this language first a plotkin style operational semantics by means of an applicative labelled transition system is introduced this is a modification of the standard labelled transition system that caters for value passing according to the late approach as an abstraction late bisimulation preorder is given then a general class of denotational models for the late semantics is defined a denotational model for the concrete language is given as an instantiation of the general class two equationally based proof systems are defined the first one which is value finitary i e only reasons about a finite number of values at each time is shown to be sound and complete with respect to this model the second proof system a value infinitary one is shown to be sound with respect to the model whereas the completeness is proven later the operational and the denotational semantics are compared and it is shown that the bisimulation preorder is finer than the preorder induced by the denotational model we also show that in general the bisimulation preorder is strictly included in the model induced preorder finally a value finitary version of the bisimulation preorder is defined and the full abstractness of the denotational model with respect to it is shown it is also shown that for ccsl the bisimulation preorder coincides with the preorder induced by the model from this we can conclude that if we allow for parameterized recursion in our language we may express processes which coincide in any algebraic domain but are distinguished by the bisimulation this shows that if we extend ccsl in this way we obtain a strictly more expressive language

how floquet theory applies to index 1 differential algebraic equations local stability of periodic solutions is established by means of a floquet theory for index 1 differential algebraic equations linear differential algebraic equations with periodic coefficients are considered in detail and a natural notion of the monodromy matrix is obtained that generalizes the well known theory for regular ordinary differential equations

bisimulation and action refinement abstract for event structures with silent moves we consider several types of bisimulation that incorporate true concurrency to a varying degree and show how each can be lifted in a uniform way to a congruence with respect to action refinement we prove that we have constructed the coarsest congruences that respect interleaving pomset and history preserving bisimulation

semantics for finite delay abstract we produce a fully abstract model for a notion of process equivalence taking into account issues of fairness called by milner fair bisimilarity the model uses aczel s anti foundation axiom and it is constructed along the lines of the anti founded model for sccs given by aczel we revisit aczel s semantics for sccs where we prove a unique fixpoint theorem under the assumption of guarded recursion then we consider milner s extension of sccs to include a finite delay operator e working with fair bisimilarity we construct a fully abstract model which is also fully abstract for fortification we discuss the solution of recursive equations in the model the paper is concluded with an investigation of the algebraic theory of fair bisimilarity

recovering the position and orientation of free form objects from image contours using 3d distance maps the accurate matching of 3d anatomical surfaces with sensory data such as 2d x ray projections is a basic problem in computer and robot assisted surgery in model based vision this problem can be formulated as the estimation of the spatial pose position and orientation of a 3d smooth object from 2d video images the authors present a new method for determining the rigid body transformation that describes this match the authors method performs a least squares minimization of the energy necessary to bring the set of the camera contour projection lines tangent to the surface to correctly deal with projection lines that penetrate the surface the authors consider the minimum signed distance to the surface along each line i e distances inside the object are negative to quickly and accurately compute distances to the surface the authors introduce a precomputed distance map represented using an octree spline whose resolution increases near the surface this octree structure allows the authors to quickly find the minimum distance along each line using best first search experimental results for 3d surface to 2d projection matching are presented for both simulated and real data the combination of the authors problem formulation in 3d their computation of line to surface distances with the octree spline distance map and their simple minimization technique based on the levenberg marquardt algorithm results in a method that solves the 3d 2d matching problem for arbitrary smooth shapes accurately and quickly

floquet theorem for linear implicit nonautonomous difference systems the aim of this paper is to develop the floquet theory for linear implicit difference systems lids it is proved that any index 1 lids can be transformed into its kronecker normal form then the floquet theorem on the representation of the fundamental matrix of index 1 periodic lids has been established as an immediate consequence the lyapunov reduction theorem is proved some applications of the obtained results are discussed

on meije and sccs infinite sum operators vs non guarded definitions une des principales differences actuellement entre meije et sccs se trouve dans les limites que le calcul precedent etablit a l interieur de sa syntaxe sur la creation de choix de comportement inifini a chaque point du processus

bisimulation through probabilistic testing abstract we propose a language for testing concurrent processes and examine its strength in terms of the processes that are distinguished by a test by using probabilistic transition systems as the underlying semantic model we show how a testing algorithm can distinguish with a probability arbitrarily close to one between processes that are not bisimulation equivalent we also show a similar result in a slightly stronger form for a new process relation called 2 3 bisimulation which lies strictly between that of simulation and bisimulation finally the ultimately strength of the testing language is shown to identify a new process relation called probabilistic bisimulation which is strictly stronger than bisimulation

petr nets algebras morphisms and compositionality abstract it is shown how a category of petri nets can be viewed as a subcategory of two sorted algebras over multisets this casts petri nets in a familiar framework and provides a useful idea of morphism on nets different from the conventional definition the morphisms here respect the behaviour of nets the categorical constructions which result provide a useful way to synthesise nets and reason about nets in terms of their components for example various forms of parallel composition of petri nets arise naturally from the product in the category this abstract setting makes plain a useful functor from the category of petri nets to a category of spaces of invariants and provides insight into the generalisations of the basic definition of petri nets for instance the coloured and higher level nets of kurt jensen arise through a simple modification of the sorts of the algebras underlying nets further it provides a smooth formal relation with other models of concurrency such as milner s calculus of communicating systems ccs and hoare s communicating sequential processes csp though this is only indicated in this paper

the power of the future perfect in program logics the expressiveness of branching time tense temporal logics whose eventually operators are relativised to general paths into the future is investigated these logics are interpreted in models obtained by generalising the usual notion of transition system to allow infinite transitions it is shown that the presence of formulae expressing the future perfect enables one to prove that the expressiveness of the logic can be characterised by a notion of bisimulation on the generalised transition systems the future perfect is obtained by adding a past tense operator to the language finally the power of various tense languages from the literature are investigated in this framework

towards categorical models for fairness fully abstract presheaf semantics of sccs with finite delay we present a presheaf model for the observation of infinite as well as finite computations we give a concrete representation of the presheaf model as a category of generalised synchronisation trees and show that it is coreflective in a category of generalised transition systems which are a special case of the general transition systems of hennessy and stirling this can be viewed as a first step towards representing fairness in categorical models for concurrency the open map bisimulation is shown to coincide with extended bisimulation of hennessy and stirling which is essentially fair ctl bisimulation we give a denotational semantics of milner s sccs with finite delay in the presheaf model which differs from previous semantics by giving the meanings of recursion by final coalgebras and meanings of finite delay by initial algebras of the process equations for delay finally we formulate milner s operational semantics of sccs with finite delay in terms of generalised transition systems and prove that the presheaf semantics is fully abstract with respect to extended bisimulation

a compositional m calculus proof system for statecharts processes abstract in this paper we propose a quite general process language called which can be suitably instantiated to model the synchronous language statecharts the main novelty of the language is an operator of process refinement for representing statecharts hierarchy moreover we define a compositional proof system for checking calculus properties of processes such a proof system is sound in general and it is complete for finite state processes including the one corresponding to statecharts

calculi for synchrony and asynchrony abstract a calculus for distributed computation is studied based upon four combinators a central idea is an abelian group of actions which models the interfaces between components of a distributed computing agent using a notion of bisimulation congruence relations are defined over computing agents and thence an algebraic theory is derived the calculus models both synchronous and asynchronous computation in particular it is shown that the author s calculus of communicating systems 1980 which is an asynchronous model is derivable from the calculus presented here

bohl exponent for time varying linear differential algebraic equations we study stability of linear time varying differential algebraic equations daes the bohl exponent is introduced and finiteness of the bohl exponent is characterised the equivalence of exponential stability and a negative bohl exponent is shown and shift properties are derived we also show that the bohl exponent is invariant under the set of bohl transformations for the class of daes which possess a transition matrix introduced in this article the bohl exponent is exploited to characterise boundedness of solutions of a cauchy problem and robustness of exponential stability

branching time and abstraction in bisimulation semantics in comparative concurrency semantics one usually distinguishes between linear time and branching time semantic equivalences milner s notion of observatin equivalence is often mentioned as the standard example of a branching time equivalence in this paper we investigate whether observation equivalence really does respect the branching structure of processes and find that in the presence of the unobservable action of ccs this is not the case therefore the notion of branching bisimulation equivalence is introduced which strongly preserves the branching structure of processes in the sense that it preserves computations together with the potentials in all intermediate states that are passed through even if silent moves are involved on closed ccs terms branching bisimulation congruence can be completely axiomatized by the single axion scheme a y z y a y z where a ranges over all actions and the usual loaws for strong congruence we also establish that for sequential processes observation equivalence is not preserved under refinement of actions whereas branching bisimulation is for a large class of processes it turns out that branching bisimulation and observation equivalence are the same as far as we know all protocols that have been verified in the setting of observation equivalence happen to fit in this class and hence are also valid in the stronger setting of branching bisimulation equivalence

algebraic calculi of processes and net expressions abstract it is shown that the meije algebra of processes can be expressed in a flow algebra the algebra of net expressions we then use this fact to derive a normal form for the calculus

a synchronous π calculus the sl synchronous programming model is a relaxation of the esterel synchronous model where the reaction to the absence of a signal within an instant can only happen at the next instant in previous work we have revisited the sl synchronous programming model in particular we have discussed an alternative design of the model introduced a cps translation to a tail recursive form and proposed a notion of bisimulation equivalence in the present work we extend the tail recursive model with first order data types obtaining a non deterministic synchronous model whose complexity is comparable to the one of the calculus we show that our approach to bisimulation equivalence can cope with this extension and in particular that labelled bisimulation can be characterised as a contextual bisimulation

on the stability behaviour of systems obtained by index reduction index reduction may destabilize the asymptotic stability of stationary solutions we analyze in some detail how index reduction via an artificial lagrangian multiplier as well as the baumgarte method behaves

a proof theoretic characterization of observational equivalence abstract hennessy and milner have shown that observational equivalence can be characterized by a modal language we show here that a subset of this language without an explicit negation operator also characterizes it using this subset we offer sound and complete modal proof systems for simple nondeterministic languages of processes in the case where observational equivalence is not a congruence we show that the observational congruence can also be characterized modally using this new language we again offer a sound and complete proof system we briefly comment upon proof systems for extensions of the nondeterministic process languages

structure of concurrency abstract noninterleaving models of concurrency assume that behavioural properties of systems can be adequately modelled in terms of causal partial orders we claim that the structure of concurrency is richer with causality being only one of the invariants generated by a set of closely related executions or observations the model we propose supports three levels of abstraction the observation level invariant level and system level and we will proceed from the bottom observation level to the top system level this is in contrast to the way other models for concurrency are introduced as they essentially support two levels of abstraction the system level and behavioural level which includes both observations and invariants with the direction of development going from the system to behavioural level in this paper we first discuss the notion of an observation of a concurrent behaviour in particular we investigate the role played by interval partial orders we then introduce a general framework for dealing with invariants generated by sets of closely related observations this leads to the formulation of the notion of a concurrent history whose structural properties are subsequently studied