Note on the cardinality of some sets of clones

All minimal clones containing a three-element grupoid have been determined in [3]. In this paper we solve the problem of the cardinality of the set of clones which contain some of these clones

Dynamic Role Authorization in Multiparty Conversations

Protocol specifications often identify the roles involved in communications. In multiparty protocols that involve task delegation it is often useful to consider settings in which different sites may act on behalf of a single role. It is then crucial to control the roles that the different parties are authorized to represent, including the case in which role authorizations are determined only at runtime. Building on previous work on conversation types with flexible role assignment, here we report initial results on a typed framework for the analysis of multiparty communications with dynamic role authorization and delegation. In the underlying process model, communication prefixes are annotated with role authorizations and authorizations can be passed around. We extend the conversation type system so as to statically distinguish processes that never incur in authorization errors. The proposed static discipline guarantees that processes are always authorized to communicate on behalf of an intended role, also covering the case in which authorizations are dynamically passed around in messages.Comment: In Proceedings BEAT 2014, arXiv:1408.556

A Typed Model for Dynamic Authorizations

Security requirements in distributed software systems are inherently dynamic. In the case of authorization policies, resources are meant to be accessed only by authorized parties, but the authorization to access a resource may be dynamically granted/yielded. We describe ongoing work on a model for specifying communication and dynamic authorization handling. We build upon the pi-calculus so as to enrich communication-based systems with authorization specification and delegation; here authorizations regard channel usage and delegation refers to the act of yielding an authorization to another party. Our model includes: (i) a novel scoping construct for authorization, which allows to specify authorization boundaries, and (ii) communication primitives for authorizations, which allow to pass around authorizations to act on a given channel. An authorization error may consist in, e.g., performing an action along a name which is not under an appropriate authorization scope. We introduce a typing discipline that ensures that processes never reduce to authorization errors, even when authorizations are dynamically delegated.Comment: In Proceedings PLACES 2015, arXiv:1602.0325

Efficient compensation handling via subjective updates

Programming abstractions for compensation handling and dynamic update are crucial in specifying reliable interacting systems, such as Collective Adaptive Systems (CAS). Compensations and updates both specify how a system reacts in response to exceptional events. Prior work showed that different semantics for compensation handling can be encoded into a calculus of adaptable processes with objective updates, in which a process is reconfigured by its context. This paper goes further by considering subjective updates, in which, intuitively, a process reconfigures itself. A calculus of adaptable processes with subjective update its introduced, and its expressivity is assessed by encoding two semantics for compensation handling. The resulting encodings are more efficient than those using objective updates: they require less computational steps

On primitives for compensation handling as adaptable processes

Mechanisms for compensation handling and dynamic update are increasingly relevant in the specification of reliable communicating systems. Compensations and updates are intuitively similar: both specify how the behavior of a concurrent system changes at runtime in response to an exceptional event. However, calculi for concurrency with compensations and updates are technically quite different. We compare calculi for concurrency with compensation handling and dynamic update from the standpoint of their relative expressiveness. We develop two encodings of a process calculus with compensation handling into a calculus of adaptable processes. These encodings differ in the target language considered: the first considers adaptable processes with subjective updates in which, intuitively, a process reconfigures itself; the second considers objective updates in which a process is reconfigured by a process in its context. Our main discovery is that subjective updates are more efficient than objective ones in encoding primitives

Cytotoxicity of amorphous calcium phosphate multifunctional composite coatings on titanium obtained by in situ anodization/anaphoretic deposition

The cytotoxicity of amorphous calcium phosphate (ACP) and chitosan lactate (ChOL) multifunctional and hybrid composite coatings on MRC-5 human lung fibroblast cell line was elucidated. ACP/TiO2 and ACP/TiO2/ /ChOL were deposited onto Ti by a novel in situ anodization/anaphoretic process at constant voltage. Cytotoxicity tests showed that there was no significant decrease in the survival of healthy MRC-5 cells exposed to composite samples without chitosan lactate, while there was an increase in the number of viable cells in the sample containing ChOL. These findings show that there was improved cell proliferation, differentiation and cell viability in the ChOL-containing sample, which makes ACP/TiO2/ChOL coating a good candidate for applications in medicine and stomatology