38,596 research outputs found
Representation Theorems for Petri Nets
No full textThis paper retraces, collects, summarises, and mildly extends the contributions of the authors --- both together and individually --- on the theme of representing the space of computations of Petri nets in its mathematical essence
Models of Computation: A Tribute to Ugo Montanari’s Vision
No full textUgo’s research activity in the area of Models of Computation (MoC, for short) has been prominent, influential and broadly scoped. In this introductory contribution we would like to recall some of the influential MoC models put forward by Ugo which cut across the three approaches
On the Algebraic Structure of Petri Nets
No full textThis paper retraces, collects, and summarises the contributions of the author --- both individually and in collaboration with others --- on the theme of algebraic, compositional approaches to the semantics of Petri nets
Role-based access control for a distributed calculus
No full textRole-based access control (RBAC) is increasingly attracting attention because it reduces the complexity and cost of security administration by interposing the notion of role in the assignment of permissions to users. In this paper, we present a formal framework relying on an extension of the -calculus to study the behaviour of concurrent systems in a RBAC scenario. We define a type system ensuring that the specified policy is respected during computations, and a behavioural equivalence to equate systems. We then consider a more sophisticated feature that can be easily integrated in our framework, i.e., the possibility of automatically adding role activations and deactivations to processes to be run under a given policy (whenever possible). Finally, we show how the framework can be easily extended to express significant extensions of the core RBAC model, such as roles hierarchies or constraints determining the acceptability of the system components
An Approach to the Category of Net Computations
No full textWe introduce the notion of strongly concatenable process as a refinement of concatenable processes [DMM89] which can be expressed axiomatically via a functor from the category of Petri nets to an appropriate category of symmetric strict monoidal categories, in the precise sense that, for each net , the strongly concatenable processes of are isomorphic to the arrows of . In addition, we identify a coreflection right adjoint to and characterize its replete image, thus yielding an axiomatization of the category of net computations
A Distributed Calculus for Role-Based Access Control
No full textRole-based access control (RBAC) is increasingly attracting attention because it reduces the complexity and cost of security administration by interposing the notion of role in the assignment of permissions to users. In this paper, we present a formal framework relying on an extension of the π calculus to study the behavior of concurrent systems in a RBAC scenario. We define a type system ensuring that the specified policy is respected during computations, and a bisimulation to equate systems. The theory is then applied to three meaningful examples, namely finding the ‘minimal’ policy to run a given system, refining a system to be run under a given policy (whenever possible), and minimizing the number of users in a given system without changing the overall behavior
A Dependently Typed Ambient Calculus
No full textThe Ambient calculus is a successful model of distributed, mobile computation, and has been the vehicle of new ideas for resource access control. Mobility types have been used to enforce elementary access control policies, expressed indirectly via classification of ambients in groups by means of ‘group types.’ The paper presents a theory of dependent types for the Ambient calculus which allows greater flexibility, while keeping the complexity away from the programmer into the type system
On the Category of Petri Net Computations
No full textWe introduce the notion of strongly concatenable process as a refinement of concatenable processes [DMM89] which can be expressed axiomatically via a functor from the category of Petri nets to an appropriate category of symmetric strict monoidal categories, in the precise sense that, for each net , the strongly concatenable processes of are isomorphic to the arrows of . In addition, we identify a coreflection right adjoint to and characterize its replete image, thus yielding an axiomatization of the category of net computations
Synthesis of Tetrahydrofurans via Chemoselective Addition of organolithium and Grignard Reagents to γ-Chloroketones in Deep Eutectic Solvents and Water
No full textAmong saturated oxygen heterocycles, substituted tetrahydrofuran derivatives are important structural components of several natural compounds.1 Synthesis and functionalization of 2,2- disubstituted tetrahydrofurans, in particular are generally based on Williamson’s intramolecular cyclization of γ-chloroalcohols as a result of reaction with different organometallic compounds. Volatile organic solvents generally used in laboratories or in industrial processes may cause environmental problems, because their accumulation in the atmosphere, thereby contributing to ozone depletion and smog in urban areas. Thus, to further assess the potential impact of more ecofriendly solvents in organolithium chemistry, we turned our attention to the so-called Deep Eutectic Solvents (DESs)2, which were introduced by Abbott and co-workers in 2003.3 DESs are formed by mixing a hydrogen-bond donor (e.g., urea) and a hydrogen-bond acceptor (e.g., the quaternary ammonium salt choline chloride), two solid starting materials with higher melting points than the eutectic mixture.
Very recent independent contribution from Hevia4 and our group5 have shown that the reactions of simple or functionalized organolithiums can be nicely performed in DESs at room temperature and under air competitively with protonolysis. In this communication, the formation of 2,2-disubstituted tetrahydrofuran derivated through the direct addition of organolithium and Grignard reagents to 4- cholobutyrophenone, chosen as model substrate, in both DESs and water. Different eutectic mixture and different organometallic’s concentrations influence on the yields of the final products. The influence of different eutectic mixtures and of the concentration of the employed organometallic species on the yield of the final products will be tackled as well.
References:
1. (a) Wolfe, J. P.; Hay, M. B. Tetrahedron 2007, 63, 261; (b) Lorente, A.; Lamariano-Merketegi, J.; Albericio, F.;
Alvarez, M. Chem. Rev. 2013, 113, 4567;
2. Francisco, M.; van den Bruinhorst, A.; Kroon, M. C. Angew. Chem. Int. Ed. 2013, 52, 3074;
3. A. P. Abbott, G. Copper, D. L. Davies, R. K. Rasheed, V. Tambyrajah Chem. Commun. 2003, 70;
4. Hevia, Angew. Chem, Int. Ed., 2014, 53, 5969-5973;
5. Mallardo, V.; Rizzi, R.; Sassone, F.; Mansueto, R.; Perna, F. M.; Salomone, A.; Capriati. V., Chem Comm. 2014, 50,
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Algebraic theories for contextual pre-nets
No full textThe algebraic models of computation for contextual nets that have been proposed in the literature either rely on a non-free monoid of objects, or introduce too many fictitious behaviors that must be somewhat filtered out. In this paper, we exploit partial membership equational logic to define a suitable theory of models, where the meaningful concurrent computations can be selected by means of membership predicates
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