Characteristic Bisimulation for Higher-Order Session Processes

Characterising contextual equivalence is a long-standing issue for higher-order (process) languages. In the setting of a higher-order pi-calculus with sessions, we develop characteristic bisimilarity, a typed bisimilarity which fully characterises contextual equivalence. To our knowledge, ours is the first characterisation of its kind. Using simple values inhabiting (session) types, our approach distinguishes from untyped methods for characterising contextual equivalence in higher-order processes: we show that observing as inputs only a precise finite set of higher-order values suffices to reason about higher-order session processes. We demonstrate how characteristic bisimilarity can be used to justify optimisations in session protocols with mobile code communication

Adaptable processes

We propose the concept of adaptable processes as a way of overcoming the limitations that process calculi have for describing patterns of dynamic process evolution. Such patterns rely on direct ways of controlling the behavior and location of running processes, and so they are at the heart of the adaptation capabilities present in many modern concurrent systems. Adaptable processes have a location and are sensible to actions of dynamic update at runtime; this allows to express a wide range of evolvability patterns for concurrent processes. We introduce a core calculus of adaptable processes and propose two verification problems for them: bounded and eventual adaptation. While the former ensures that the number of consecutive erroneous states that can be traversed during a computation is bound by some given number k, the latter ensures that if the system enters into a state with errors then a state without errors will be eventually reached. We study the (un)decidability of these two problems in several variants of the calculus, which result from considering dynamic and static topologies of adaptable processes as well as different evolvability patterns. Rather than a specification language, our calculus intends to be a basis for investigating the fundamental properties of evolvable processes and for developing richer languages with evolvability capabilities

Internal transitions of negatively charged magnetoexcitons in quantum dots

We report calculations of oscillator strengths for the far infrared absorption of light by the excitonic complexes Xn- (the excess charge, n, ranging from one to four) confined in quantum dots. The magnetic field is varied in an interval which corresponds to ``filling factors'' between 2 and 3/5. Electron-hole interaction effects are seen in the deviations of the peak positions from the Kohn lines, and in the spreading of the oscillator strengths over a few final states. Transition densities are used as an additional tool to characterize the absorption peaks.Comment: Presented as a poster in the Third Stig Lundqvist Conference on Advancing Frontiers of Condensed Matter Physics: Fundamental Interactions and Excitations in Confined Systems, Trieste, August 11 - 1

Estimación de la conductividad eléctrica del tejido humano en la terapia de hipertermia por radiofrecuencia

The use of mathematical models to study complex systems such as physical and biological phenomena allows understanding their behavior, specifically regarding variables and parameters that are difficult to obtain. Additionally, studying optimization techniques has made it possible to approximate the characteristics of these systems by correlating numerical simulations and experimentation. Radiofrequency hyperthermia therapy for cancer treatment is currently under consideration for future medical applications. However, some of its properties are complex to measure, which could prevent their control. This is the case of electrical conductivity, which depends on the induction frequency and the tissue characteristics. In this paper, radiofrequency hyperthermia therapy was simulated via the finite element method. Then, an estimation of the electrical conductivity involved in the treatment was performed using the particle swarm optimization method. The execution time and the difference between the estimated parameter and the exact value were evaluated and compared with those obtained using the Levenberg-Marquardt method. The results indicate a significant agreement between the estimated and exact values in three different cases. The Levenberg-Marquardt method has a difference of 0,1942% and a performance time of 22 minutes, whereas the particle swarm optimization method has a difference of 0,0967% and a performance time of 327 minutes. The latter performs better in terms of parameter value estimation, whereas the former has better computational times. These techniques may help medical doctors to prescribe treatment protocols and may open the possibility of devising control strategies for hyperthermia therapy as a cancer treatment.El uso de modelos matemáticos para el estudio de sistemas complejos como los fenómenos físicos y biológicos permite comprender su comportamiento, específicamente con respecto a variables y parámetros difíciles de obtener. Adicionalmente, el estudio de técnicas de optimización ha permitido aproximar las características de estos sistemas por medio de la correlación de simulaciones numéricas y la experimentación. La terapia de hipertermia por radiofrecuencia para el tratamiento del cáncer está actualmente en consideración para su futura aplicación médica. Sin embargo, algunas de sus propiedades son difíciles de medir, lo cual impediría su control. Este es el caso de la conductividad eléctrica, que depende de la frecuencia de inducción y de las características del tejido. En este artículo se simuló la terapia de hipertermia por radiofrecuencia mediante el método de elementos finitos. Luego se realizó una estimación de la conductividad eléctrica en el tratamiento mediante el método de optimización por enjambres de partículas. Se evaluaron el tiempo de ejecución y la diferencia del valor estimado con respecto al valor exacto, y se compararon sus valores estimados con los obtenidos mediante el método de Levenberg-Marquardt. Los resultados indican una concordancia significativa entre los valores estimados y los exactos en tres casos diferentes. El método de Levenberg-Marquardt tiene una diferencia de 0,1942% y un tiempo de ejecución de 22 minutos, mientras que el método de optimización de enjambres de partículas tiene una diferencia de 0,0967% y un tiempo de ejecución de 327 minutos. Este último tiene un mejor rendimiento en términos de estimación del valor de los parámetros, mientras que el otro tiene un mejor tiempo de ejecución computacional. Estas técnicas podrían ayudar a los médicos a prescribir protocolos de tratamiento y abrir la posibilidad de diseñar estrategias de control para la terapia de hipertermia como tratamiento para el cáncer.Fil: Lopez Perez, Jorge Iván. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Ciencias e Ingeniería de la Computación. Universidad Nacional del Sur. Departamento de Ciencias e Ingeniería de la Computación. Instituto de Ciencias e Ingeniería de la Computación; Argentina. Universidad Santiago de Cali; ColombiaFil: Bermeo Varón, L. A.. Universidad Santiago de Cali; Colombi

Hyperledger Fabric:Evaluating Endorsement Policy Strategies in Supply Chains

Hyperledger Fabric is a permissioned blockchain solution, in which network participation is controlled by predefined rules. This makes it an attractive platform for enterprise settings. In Fabric, endorsement policies are used to specify the peers that must confirm a transaction before it can be considered as valid and appended to the ledger. This work examines various implications of Fabric's endorsement policy component, for which different endorsement policy strategies (and subsequent trade-offs) are evaluated by modeling two real-world supply chain case studies. This work discusses how vulnerable endorsement policies can lead to admitting inauthentic data on the ledger. To address this issue, several approaches are proposed to balance integrity with limited disclosure of confidential information, with or without hosting a network peer directly. Furthermore, the concept of multi-tenancy in blockchain networks is introduced as a way of reducing the technological barrier in technology adoption

Reversible Session-Based Concurrency in Haskell

A reversible semantics enables to undo computation steps. Reversing message-passing, concurrent programs is a challenging and delicate task; one typically aims at causally consistent reversible semantics. Prior work has addressed this challenge in the context of a process model of multiparty protocols (or choreographies). In this paper, we describe a Haskell implementation of this reversible operational seman- tics. We exploit algebraic data types to faithfully represent three core ingredients: a process calculus, multiparty session types, and forward and backward reduction semantics. Our implementation bears witness to the convenience of pure functional programming for implementing reversible languages

Tuning the ionic character of sodium dodecyl sulphate via counter-ion binding: an experimental and computational study

Solutions of surfactants exhibit remarkable features, such as a tunable amphiphilic character, which can further be varied for ionic surfactants through variations in their Coulombic interactions. These properties are very useful in many industrial applications such as in extraction, purification, and formulation processes, as detergents, wetting agents, or emulsifiers. Rather unexpectedly, the addition of tetrabutylammonium chloride ([N4,4,4,4]Cl) to solutions of the ionic surfactant of sodium dodecyl sulphate (SDS) results in the appearance of a phase transition above the lower critical solution temperature (LCST), a property usually associated with non-ionic surfactants. The aim of this study is to provide a detailed nanoscopic scenario on the interaction between SDS micelles and [N4,4,4,4]Cl moieties to better understand the nature of the LCST cloud point and how to confer it to a given ionic surfactant system. A coarse-grained molecular dynamics (CG-MD) computational framework, under the latest MARTINI 3.0 force field, was developed and validated using available literature data. The impact of [N4,4,4,4]Cl concentration in the phase of SDS micellar aqueous solutions was then characterized and compared using experimental results. Specifically, dynamic light scattering (DLS) measurements and small-angle X-ray scattering (SAXS) profiles were obtained at different [N4,4,4,4]+/[DS]- molar ratios (from 0.0 to 1.0) and compared with the CG-MD results. A good agreement between computer simulations and experimental findings was obtained, reinforcing the suitability of GC-MD to simulate complex phase behaviors. When the [N4,4,4,4]+/[DS]- molar ratio is 0.5, the system yielded clusters of enclosed small [DS]- aggregates. Thus, the CG-MD simulations showed the formation of mixed [DS]- and [N4,4,4,4]+ aggregates with [N4,4,4,4]+ cations acting as a bridge between small [DS]- micelles. The CG-MD simulation framework developed in this work captured the role of [N4,4,4,4]+ in the micellar phase transition whilst improving the results obtained with preceding computer models for which the limitations on capturing SDS and [N4,4,4,4]Cl mixtures in aqueous solutions are also shown in detail.publishe

Centaurus A as a source of extragalactic cosmic rays with arrival energies well beyond the GZK cutoff

The ultra--high energy cosmic rays recently detected by several air shower experiments could have an extragalactic origin. In this case, the nearest active galaxy Centaurus A might be the source of the most energetic particles ever detected on Earth. We have used recent radio observations in order to estimate the arrival energy of the protons accelerated by strong shock fronts in the outer parts of this southern radio source. We expect detections corresponding to particles with energies up to $\sim 2.2 \times 10^{21}$ eV and an arrival direction of ($l \approx 310^{\circ}$, $b \approx 20^{\circ}$) in galactic coordinates. The future Southern Hemisphere Pierre Auger Observatory might provide a decisive test for extragalactic models of the origin of the ultra--high energy cosmic rays.Comment: Some remarks by the referee added, to appear in Astroparticle Physic