2,575 research outputs found
A Graphical Approach to Progress for Structured Communication in Web Services
We investigate a graphical representation of session invocation
interdependency in order to prove progress for the pi-calculus with sessions
under the usual session typing discipline. We show that those processes whose
associated dependency graph is acyclic can be brought to reduce. We call such
processes transparent processes. Additionally, we prove that for well-typed
processes where services contain no free names, such acyclicity is preserved by
the reduction semantics.
Our results encompass programs (processes containing neither free nor
restricted session channels) and higher-order sessions (delegation).
Furthermore, we give examples suggesting that transparent processes constitute
a large enough class of processes with progress to have applications in modern
session-based programming languages for web services.Comment: In Proceedings ICE 2010, arXiv:1010.530
Session-based Choreography with Exceptions
AbstractChoreography has recently emerged as a pragmatic and concise way of describing communication-based systems such as web services and financial protocols. Recent studies have investigated the transition from the design stage of a system to its implementation providing an automatic way of mapping a choreograhy into executable code.In this work, we focus on an extension of choreography with a communication-based (interactional) exception mechanism by giving its formal semantics. In particular, we discuss through some examples how interactional exceptions at choreography level can be implemented into end-point code
Execution Models for Choreographies and Cryptoprotocols
A choreography describes a transaction in which several principals interact.
Since choreographies frequently describe business processes affecting
substantial assets, we need a security infrastructure in order to implement
them safely. As part of a line of work devoted to generating cryptoprotocols
from choreographies, we focus here on the execution models suited to the two
levels.
We give a strand-style semantics for choreographies, and propose a special
execution model in which choreography-level messages are faithfully delivered
exactly once. We adapt this model to handle multiparty protocols in which some
participants may be compromised.
At level of cryptoprotocols, we use the standard Dolev-Yao execution model,
with one alteration. Since many implementations use a "nonce cache" to discard
multiply delivered messages, we provide a semantics for at-most-once delivery
A formal model of trust lifecycle management
The rapid development of collaborative environments over the internet has highlighted new concerns over security and trust in such global computing systems. The global computing infrastructure poses an issue of uncertainty about the potential collaborators. Reaching a trusting decision in such environments encompasses both risk and trust assessments. While much work has been done in terms of modelling trust, the investigation of the management of trust lifecycle issues with consideration of both trust and risk is less examined. Our previous work addressed the dynamic aspects of trust lifecycle with a consideration of trust formation, exploitation, and evolution. In this paper we provide an approach for formalizing these aspects. As part of the formalization of the trust lifecycle,we introduce a notion of attraction to model the effect of new pieces of evidence on our opinion. The formalization described in this paper constitutes the basis of ongoing work to investigate the properties of the model
Array of Josephson junctions with a non-sinusoidal current-phase relation as a model of the resistive transition of unconventional superconductors
An array of resistively and capacitively shunted Josephson junctions with
nonsinusoidal current-phase relation is considered for modelling the transition
in high-T superconductors. The emergence of higher harmonics, besides the
simple sinusoid , is expected for dominant \emph{d}-wave
symmetry of the Cooper pairs, random distribution of potential drops, dirty
grains, or nonstationary conditions. We show that additional cosine and sine
terms act respectively by modulating the global resistance and by changing the
Josephson coupling of the mixed superconductive-normal states. First, the
approach is applied to simulate the transition in disordered granular
superconductors with the weak-links characterized by nonsinusoidal
current-phase relation. In granular superconductors, the emergence of
higher-order harmonics affects the slope of the transition. Then, arrays of
intrinsic Josephson junctions, naturally formed by the CuO planes in
cuprates, are considered. The critical temperature suppression, observed at
values of hole doping close to , is investigated. Such suppression,
related to the sign change and modulation of the Josephson coupling across the
array, is quantified in terms of the intensities of the first and second
sinusoids of the current-phase relation. Applications are envisaged for the
design and control of quantum devices based on stacks of intrinsic Josephson
junctions.Comment: Added: comparison with experiments; reference
Liver Transplantation for Hepatitis C and Alcoholic Liver Disease
End-stage liver disease due to hepatitis C (HCV) and cirrhosis from alcohol (ALD) are the commonest indications for
liver transplantation in the western countries. Up to one third of HCV-infected transplant candidates have a history of
significant alcohol intake prior to transplantation. However, there are few data available about the possible interaction between alcohol
and HCV in the post-transplant setting. Patients with both HCV and alcohol are more likely to die on the waiting list than those with
ALD and HCV alone. However, after transplantation, non-risk adjusted graft and patient survival of patients with HCV + ALD are comparable to
those of patients with HCV cirrhosis or ALD cirrhosis alone. In the short and medium term HCV recurrence after transplant in patients with
HCV + ALD cirrhosis does not seem more aggressive than that in patients with HCV cirrhosis alone. A relapse in alcohol consumption in
patients with HCV + ALD cirrhosis does not have a major impact on graft survival. The evidence shows that, as is currently practiced,
HCV + ALD as an appropriate indication for liver transplantation. However, these data are based on retrospective analyses with relatively
short follow-up so the conclusions must be treated with caution
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