Simplified Distributed Programming with Micro Objects

Developing large-scale distributed applications can be a daunting task. object-based environments have attempted to alleviate problems by providing distributed objects that look like local objects. We advocate that this approach has actually only made matters worse, as the developer needs to be aware of many intricate internal details in order to adequately handle partial failures. The result is an increase of application complexity. We present an alternative in which distribution transparency is lessened in favor of clearer semantics. In particular, we argue that a developer should always be offered the unambiguous semantics of local objects, and that distribution comes from copying those objects to where they are needed. We claim that it is often sufficient to provide only small, immutable objects, along with facilities to group objects into clusters.Comment: In Proceedings FOCLASA 2010, arXiv:1007.499

A numerical approach for modelling thin cracked plates with XFEM

The modelization of bending plates with through the thickness cracks is investigated. We consider the Kirchhoff-Love plate model which is valid for very thin plates. We apply the eXtended Finite Element Method (XFEM) strategy: enrichment of the finite element space with the asymptotic bending and with the discontinuity across the crack. We present two variants and their numerical validations and also a numerical computation of the stress intensity factors

Analysis and Verification of Service Interaction Protocols - A Brief Survey

Modeling and analysis of interactions among services is a crucial issue in Service-Oriented Computing. Composing Web services is a complicated task which requires techniques and tools to verify that the new system will behave correctly. In this paper, we first overview some formal models proposed in the literature to describe services. Second, we give a brief survey of verification techniques that can be used to analyse services and their interaction. Last, we focus on the realizability and conformance of choreographies.Comment: In Proceedings TAV-WEB 2010, arXiv:1009.330

On Negotiation as Concurrency Primitive

We introduce negotiations, a model of concurrency close to Petri nets, with multiparty negotiation as primitive. We study the problems of soundness of negotiations and of, given a negotiation with possibly many steps, computing a summary, i.e., an equivalent one-step negotiation. We provide a complete set of reduction rules for sound, acyclic, weakly deterministic negotiations and show that, for deterministic negotiations, the rules compute the summary in polynomial time

Formalizing Adaptation On-the-Fly

AbstractParadigm models specify coordination of collaborating components via constraint control. Component McPal allows for later addition of new constraints and new control in view of unforeseen adaptation. After addition McPal starts coordinating migration accordingly, adapting the system towards to-be collaboration. Once done, McPal removes obsolete control and constraints. All coordination remains ongoing while migrating on-the-fly, being deflected without any quiescence. Through translation into process algebra, supporting formal analysis is arranged carefully, showing that as-is and to-be processes are proper abstractions of the migrating process. A canonical critical section problem illustrates the approach

Tau Be or not Tau Be? - A Perspective on Service Compatibility and Substitutability

One of the main open research issues in Service Oriented Computing is to propose automated techniques to analyse service interfaces. A first problem, called compatibility, aims at determining whether a set of services (two in this paper) can be composed together and interact with each other as expected. Another related problem is to check the substitutability of one service with another. These problems are especially difficult when behavioural descriptions (i.e., message calls and their ordering) are taken into account in service interfaces. Interfaces should capture as faithfully as possible the service behaviour to make their automated analysis possible while not exhibiting implementation details. In this position paper, we choose Labelled Transition Systems to specify the behavioural part of service interfaces. In particular, we show that internal behaviours (tau transitions) are necessary in these transition systems in order to detect subtle errors that may occur when composing a set of services together. We also show that tau transitions should be handled differently in the compatibility and substitutability problem: the former problem requires to check if the compatibility is preserved every time a tau transition is traversed in one interface, whereas the latter requires a precise analysis of tau branchings in order to make the substitution preserve the properties (e.g., a compatibility notion) which were ensured before replacement.Comment: In Proceedings WCSI 2010, arXiv:1010.233

Ab initio investigation of lattice dynamics of fluoride scheelite LiYF4

We report on the phonon dynamics of LiYF4 obtained by direct method using first principle calculations. The agreement between experimental and calculated modes is satisfactory. An inversion between two Raman active modes is noticed compared to inelastic neutron scattering and Raman measurements. The atomic displacements corresponding to these modes are discussed. Multiple inversions between Raman and infrared active groups are present above 360 cm-1. The total and partial phonon density of state is also calculated and analyzed

American consensus recommendations for gastric scintigraphy: curve fitting with only a few points remains an easy and accurate method to obtain reliable and reproducible gastric emptying estimates.

International audienceBACKGROUND: In 2008, American consensus recommendations for performing gastric emptying (GE) scintigraphy were published. It was recommended that data are acquired only at 0, 1, 2, and 4 h and that the results are expressed as percentages of meal retention. Until now, it was established that the GE time-activity curves should have many points (every 10, 15, or 20 min) to reflect the GE process accurately and to be optimally adjusted by a mathematical model. In this study, we have evaluated the curve fitting using only a few points as proposed by the consensus protocol. MATERIALS AND METHODS: GE scintigraphy tests of 224 patients were retrospectively analyzed. Two curve fittings were done for each patient, either using data acquired every 20 min or using data acquired every hour. A comparison of these two methods was made based on the values of the computed GE parameters. RESULTS: We observed strong correlations between the two methods (r=0.81-0.99, P<0.05). Using the Bland-Altman analysis, more than 95% of the differences were included in the mean difference 95% confidence interval. The mean differences were weak with a relatively small SD and Cohen's k coefficients ranging from 0.84 to 0.93, indicating an excellent agreement between the two methods. CONCLUSION: Our results showed the feasibility and accuracy of curve fitting using only a few points. The curve fitting is easy to perform and allows the computation of reliable and reproducible parameters that reflect the whole GE process

DFT study of pressure induced phase transitions in LiYF4

An investigation of the pressure induced phase transition from the scheelite phase (I41/a, Z=4) to the fergusonite-like phase (I2/a, Z=4)/LaTaO(P21/c, Z=4) of LiYF4 is presented. Employing density functional theory (DFT) within the generalized gradient approximation, the internal degrees of freedom were relaxed for a pressure range of 0 GPa to 20 Gpa. The influence of pressure on the lattice vibration spectrum of the scheelite phase (I41/a, Z=4) was evaluated using the direct approach, i.e. using force constants calculated from atomic displacements. The transition volume is in good agreement with experiment, while the transition pressure is overestimated of 6 GPa. At 20 GPa, a P21/c structure with apentacoordinated lithium cation is found to be the most stable phase. This structure is compatible with a transition driven by a Bg zone-center soft optic mode linked to a soft-acoustic mode along the [11-1] direction as observed for the proper ferroelastic transition of BiVO4

Explicit connection actions in multiparty session types

This work extends asynchronous multiparty session types (MPST) with explicit connection actions to support protocols with op- tional and dynamic participants. The actions by which endpoints are connected and disconnected are a key element of real-world protocols that is not treated in existing MPST works. In addition, the use cases motivating explicit connections often require a more relaxed form of mul- tiparty choice: these extensions do not satisfy the conservative restric- tions used to ensure safety in standard syntactic MPST. Instead, we de- velop a modelling-based approach to validate MPST safety and progress for these enriched protocols. We present a toolchain implementation, for distributed programming based on our extended MPST in Java, and a core formalism, demonstrating the soundness of our approach. We discuss key implementation issues related to the proposed extensions: a practi- cal treatment of choice subtyping for MPST progress, and multiparty correlation of dynamic binary connections