Formal verification of a leader election protocol in process algebra

AbstractIn 1982 Dolev, et al. [10] presented an O(nlogn) unidirectional distributed algorithm for the circular extrema-finding (or leader-election) problem. At the same time Peterson came up with a nearly identical solution. In this paper, we bring the correctness of this algorithm to a completely formal level. This relatively small protocol, which can be described on half a page, requires a rather involved proof for guaranteeing that it behaves well in all possible circumstances. To our knowledge, this is one of the more advanced case-studies in formal verification based on process algebra

Finite driving rate and anisotropy effects in landslide modeling

In order to characterize landslide frequency-size distributions and individuate hazard scenarios and their possible precursors, we investigate a cellular automaton where the effects of a finite driving rate and the anisotropy are taken into account. The model is able to reproduce observed features of landslide events, such as power-law distributions, as experimentally reported. We analyze the key role of the driving rate and show that, as it is increased, a crossover from power-law to non power-law behaviors occurs. Finally, a systematic investigation of the model on varying its anisotropy factors is performed and the full diagram of its dynamical behaviors is presented.Comment: 8 pages, 9 figure

GT2004-53082 ALL-ELECTRIC ACTUATOR FOR MID-SIZE GAS TURBINES

ABSTRACT A number of actuators are available for mid-size industrial gas turbine engines in the marketplace today. These designs utilize pneumatic, hydraulic, electro-pneumatic, electrohydraulic, and all-electric actuation technologies. The electrohydraulic has been the most common mid-size industrial gas turbine actuation technology over the last 20 years. This paper focuses on a new all-electric actuator technology developed specifically for mid-size gas turbines using an integrally mounted controller. This paper discusses the significant technical challenges to integrally mounting allelectric actuator motor controller

Ice-lens formation and geometrical supercooling in soils and other colloidal materials

We present a new, physically-intuitive model of ice-lens formation and growth during the freezing of soils and other dense, particulate suspensions. Motivated by experimental evidence, we consider the growth of an ice-filled crack in a freezing soil. At low temperatures, ice in the crack exerts large pressures on the crack walls that will eventually cause the crack to split open. We show that the crack will then propagate across the soil to form a new lens. The process is controlled by two factors: the cohesion of the soil, and the geometrical supercooling of the water in the soil; a new concept introduced to measure the energy available to form a new ice lens. When the supercooling exceeds a critical amount (proportional to the cohesive strength of the soil) a new ice lens forms. This condition for ice-lens formation and growth does not appeal to any ad hoc, empirical assumptions, and explains how periodic ice lenses can form with or without the presence of a frozen fringe. The proposed mechanism is in good agreement with experiments, in particular explaining ice-lens pattern formation, and surges in heave rate associated with the growth of new lenses. Importantly for systems with no frozen fringe, ice-lens formation and frost heave can be predicted given only the unfrozen properties of the soil. We use our theory to estimate ice-lens growth temperatures obtaining quantitative agreement with the limited experimental data that is currently available. Finally we suggest experiments that might be performed in order to verify this theory in more detail. The theory is generalizable to complex natural-soil scenarios, and should therefore be useful in the prediction of macroscopic frost heave rates.Comment: Submitted to PR

PTEN and DNA-PK determine sensitivity and recovery in response to WEE1 inhibition in human breast cancer

Inhibition of WEE1 kinase by AZD1775 has shown promising results in clinical cancer trials, but markers predicting AZD1775 response are lacking. Here we analysed AZD1775 response in a panel of human breast cancer (BC) cell lines by global proteome/transcriptome profiling and identified two groups of basal-like BC (BLBCs): ‘PTEN low’ BLBCs were highly sensitive to AZD1775 and failed to recover following removal of AZD1775, while ‘PTEN high’ BLBCs recovered. AZD1775 induced phosphorylation of DNA-PK, protecting cells from replication-associated DNA damage and promoting cellular recovery. Deletion of DNA-PK or PTEN, or inhibition of DNA-PK sensitized recovering BLBCs to AZD1775 by abrogating replication arrest, allowing replication despite DNA damage. This was linked to reduced CHK1 activation, increased cyclin E levels and apoptosis. In conclusion, we identified PTEN and DNA-PK as essential regulators of replication checkpoint arrest in response to AZD1775 and defined PTEN as a promising biomarker for efficient WEE1 cancer therapy

Task shifting and integration of HIV care into primary care in South Africa: The development and content of the streamlining tasks and roles to expand treatment and care for HIV (STRETCH) intervention

Background: Task shifting and the integration of human immunodeficiency virus (HIV) care into primary care services have been identified as possible strategies for improving access to antiretroviral treatment (ART). This paper describes the development and content of an intervention involving these two strategies, as part of the Streamlining Tasks and Roles to Expand Treatment and Care for HIV (STRETCH) pragmatic randomised controlled trial. Methods: Developing the intervention: The intervention was developed following discussions with senior management, clinicians, and clinic staff. These discussions revealed that the establishment of separate antiretroviral treatment services for HIV had resulted in problems in accessing care due to the large number of patients at ART clinics. The intervention developed therefore combined the shifting from doctors to nurses of prescriptions of antiretrovirals (ARVs) for uncomplicated patients and the stepwise integration of HIV care into primary care services. Results: Components of the intervention: The intervention consisted of regulatory changes, training, and guidelines to support nurse ART prescription, local management teams, an implementation toolkit, and a flexible, phased introduction. Nurse supervisors were equipped to train intervention clinic nurses in ART prescription using outreach education and an integrated primary care guideline. Management teams were set up and a STRETCH coordinator was appointed to oversee the implementation process. Discussion: Three important processes were used in developing and implementing this intervention: active participation of clinic staff and local and provincial management, educational outreach to train nurses in intervention sites, and an external facilitator to support all stages of the intervention rollout

Weaving Concurrency in eXecutable Domain-Specific Modeling Languages

International audienceThe emergence of modern concurrent systems (e.g., Cyber-Physical Systems or the Internet of Things) and highly-parallel platforms (e.g., many-core, GPGPU pipelines, and distributed platforms) calls for Domain-Specific Modeling Languages (DSMLs) where concurrency is of paramount importance. Such DSMLs are intended to propose constructs with rich concurrency semantics, which allow system designers to precisely define and analyze system behaviors. However , specifying and implementing the execution semantics of such DSMLs can be a difficult, costly and error-prone task. Most of the time the concurrency model remains implicit and ad-hoc, embedded in the underlying execution environment. The lack of an explicit concurrency model prevents: the precise definition, the variation and the complete understanding of the semantics of the DSML, the effective usage of concurrency-aware analysis techniques, and the exploitation of the concurrency model during the system refinement (e.g., during its allocation on a specific platform). In this paper, we introduce a concurrent executable metamodeling approach, which supports a modular definition of the execution semantics , including the concurrency model, the semantic rules, and a well-defined and expressive communication protocol between them. Our approach comes with a dedicated metalanguage to specify the communication protocol, and with an execution environment to simulate executable models. We illustrate and validate our approach with an implementation of fUML, and discuss the modularity and applicability of our approach

Distributed Consensus, Revisited

We provide a novel model to formalize a well-known algorithm, by Chandra and Toueg, that solves Consensus among asynchronous distributed processes in the presence of a particular class of failure detectors (Diamond S or, equivalently, Omega), under the hypothesis that only a minority of processes may crash. The model is defined as a global transition system that is unambigously generated by local transition rules. The model is syntax-free in that it does not refer to any form of programming language or pseudo code. We use our model to formally prove that the algorithm is correct