Simulation-based Frameworks Research Articles

Mechanized Proofs of Adversarial Complexity and Application to Universal Composability

In this paper we enhance the EasyCrypt proof assistant to reason about computational complexity of adversaries. The key technical tool is a Hoare logic for reasoning about computational complexity (execution time and oracle calls) of adversarial computations. Our Hoare logic is built on top of the module system used by EasyCrypt for modeling adversaries. We prove that our logic is sound w.r.t. the semantics of EasyCrypt programs — we also provide full semantics for the EasyCrypt module system, which was previously lacking. We showcase (for the first time in EasyCrypt and in other computer-aided cryptographic tools) how our approach can express precise relationships between the probability of adversarial success and their execution time. In particular, we can quantify existentially over adversaries in a complexity class, and express general composition statements in simulation-based frameworks. Moreover, such statements can be composed to derive standard concrete security bounds for cryptographic constructions whose security is proved in a modular way. As a main benefit of our approach, we revisit security proofs of some well-known cryptographic constructions and we present a new formalization of Universal Composability (UC).

116 Developing a Framework for the Integration of Skills and Simulation: The 5-Stage Approach

In recent years, there have been many publications providing guidance on simulation-based education and frameworks for development of faculty and delivery of simulation. However, there is not a framework for the integration and delivery of skills and simulation within a pre-registration curriculum. In 2017, Woda The aim of the study was to create a framework that integrates clinical skills and simulation increasing in complexity that can be used for any pre-registration healthcare curriculum. Ability to effectively implement and embed within an existing or new curriculum.We developed a framework using a five-stage approach to scaffold learning. Bringing simulation into the curriculum from the very start with the early introduction of consolidation and simulation allowing for a gradual cognitive load. Our approach builds on technical and non-technical skills alongside an understanding and exposure to simulation, by their final-year students will be debriefing their own teams in simulation and understand the use of simulation debriefing tools. This integration of skills and simulation and move away from ‘task training’ skills teaching aims to create both competence and confidence in students enhancing practice placements and ultimately improving the safety of patients. The approach consists of five stages: (1) online learning; (2) facilitated practical (task training); (3) simulation consolidation (facilitated simulation); (4) simulation days (remote facilitation); (5) clinical practice.The framework is being applied to the 2-year Master's programmes and nursing associate programmes as well as the standard 3-year pre-registration nursing, midwifery, operating department practitioner and paramedic programmes. Skills both technical and non-technical are introduced in years 1 and 2. In year 3, the focus is on knowledge review with a higher expectation of understanding and assimilation into the simulated environments expected. Over the 3 years, facilitation will lessen until students are leading on the simulation delivery and debrief by the end of their course. The same principle is applied to the 2-year programmes. This framework has been applied to all our healthcare courses by mapping the required skills curriculum and using the framework to build the content and set the delivery. The framework has now been adopted by another university.

Nonstationary weather and water extremes: a review of methods for their detection, attribution, and management

Abstract. Hydroclimatic extremes such as intense rainfall, floods, droughts, heatwaves, and wind or storms have devastating effects each year. One of the key challenges for society is understanding how these extremes are evolving and likely to unfold beyond their historical distributions under the influence of multiple drivers such as changes in climate, land cover, and other human factors. Methods for analysing hydroclimatic extremes have advanced considerably in recent decades. Here we provide a review of the drivers, metrics, and methods for the detection, attribution, management, and projection of nonstationary hydroclimatic extremes. We discuss issues and uncertainty associated with these approaches (e.g. arising from insufficient record length, spurious nonstationarities, or incomplete representation of nonstationary sources in modelling frameworks), examine empirical and simulation-based frameworks for analysis of nonstationary extremes, and identify gaps for future research.

Two-level friction damping and its application for passive multi-functional vibration control of high-rise buildings

In recent years, the use of structural elements and/or entire structures with low internal damping are favoured with the increasing trend for unconventional design of structures and infrastructures that combine high functionality and increased aesthetics. One example is the advancement of high-rise buildings, which are built taller, more slender and with more spectacular designs compared to the past. In many of these cases, supplementary damping is included in the structural design by installing distributed passive damping devices, among which the friction damper has become popular due to its relative low cost, high reliability and high efficiency. The conventional friction damper, however, can only mitigate vibrations optimally with respect to a single deformation shape at a single vibration amplitude, which is not enough in cases where additional damping is required to mitigate different magnitudes of the excitation. Thus, the paper scrutinises the performance of the passive two-level friction damper, recently proposed elsewhere, in comparison to the conventional one-level friction damper, and assesses its application for multi-functional vibration control of a high-rise building. Specifically, this paper scrutinises the application and performance of the two-level friction damper in two simulation-based frameworks and ultimately: (i) evaluates and demonstrates the vibration performance of a dynamic system when equipped with this damper type, and (ii) investigates the application of this damper type for mitigation of both wind- and earthquake-induced vibration of a high-rise building. It is found that the optimal performance of the two-level friction damper is covering a larger vibration amplitude range compared to the conventional friction damper, which enabled the two-level friction damper to, in contrast to the conventional friction damper, successfully mitigate both wind- and earthquake-induced vibration in the application example. Based on the findings, it is concluded that the two-level friction damper is able to overcome some of the limitation, application-wise, connected to the amplitude dependence of the one-level friction damper.

New simulation-based frameworks for multi-objective reliability-based design optimization of structures

• Two new simulation-based frameworks are presented for MORBDO problems. • Only one simulation run is needed during entire multi-objective optimization process. • The Pareto optimal set is enhanced by iterative local search of the proposed NSWSM. • WSM evaluates reliability of design candidates to conduct NSGA-II to true Pareto-set. • New simulations are suitable for complex problems with discrete and continuous variables. In the present study, two new simulation-based frameworks are proposed for multi-objective reliability-based design optimization (MORBDO). The first is based on hybrid non-dominated sorting weighted simulation method (NSWSM) in conjunction with iterative local searches that is efficient for continuous MORBDO problems. According to NSWSM, uniform samples are generated within the design space and, then, the set of feasible samples are separated. Thereafter, the non-dominated sorting operator is employed to extract the approximated Pareto front. The iterative local sample generation is then performed in order to enhance the accuracy, diversity, and increase the extent of non-dominated solutions. In the second framework, a pseudo-double loop algorithm is presented based on hybrid weighted simulation method (WSM) and the Non-dominated Sorting Genetic Algorithm II (NSGA-II) that is efficient for problems including both discrete and continuous variables. According to hybrid WSM-NSGA-II, proper non-dominated solutions are produced in each generation of NSGA-II and, subsequently, WSM evaluates the reliability level of each candidate solution until the algorithm converges to the true Pareto solutions. The valuable characteristic of presented approaches is that only one simulation run is required for WSM during entire optimization process, even if solutions for different levels of reliability be desired. Illustrative examples indicate that NSWSM with the proposed local search strategy is more efficient for small dimension continuous problems. However, WSM-NSGA-II outperforms NSWSM in terms of solutions quality and computational efficiency, specifically for discrete MORBDOs. Employing global optimizer in WSM-NSGA-II provided more accurate results with lower samples than NSWSM.

Probabilistic Termination and Composability of Cryptographic Protocols

When analyzing the round complexity of multi-party protocols, one often overlooks the fact that underlying resources, such as a broadcast channel, can by themselves be expensive to implement. For example, it is well known that it is impossible to implement a broadcast channel by a (deterministic) protocol in a sublinear (in the number of corrupted parties) number of rounds. The seminal works of Rabin and Ben-Or from the early 1980s demonstrated that limitations as the above can be overcome by using randomization and allowing parties to terminate at different rounds, igniting the study of protocols over point-to-point channels with probabilistic termination and expected constant round complexity. However, absent a rigorous simulation-based definition, the suggested protocols are proven secure in a property-based manner or via ad hoc simulation-based frameworks, therefore guaranteeing limited, if any, composability. In this work, we put forth the first simulation-based treatment of multi-party cryptographic protocols with probabilistic termination. We define secure multi-party computation (MPC) with probabilistic termination in the UC framework and prove a universal composition theorem for probabilistic termination protocols. Our theorem allows to compile a protocol using deterministic termination hybrids into a protocol that uses expected constant round protocols for emulating these hybrids, preserving the expected round complexity of the calling protocol. We showcase our definitions and compiler by providing the first composable protocols (with simulation-based security proofs) for the following primitives, relying on point-to-point channels: (1) expected constant round perfect Byzantine agreement, (2) expected constant round perfect parallel broadcast, and (3) perfectly secure MPC with round complexity independent of the number of parties.

A Modular Decision-centric Approach for Reusable Design Processes

The reusability of design processes modeled in existing Product Lifecycle Management (PLM) and Computer Aided Engineering (CAE) frameworks has been limited to the level of flow charts or activity-based diagrams that serve as planning and organizational aids. Current simulation-based design frameworks provide limited support for reuse of design processes at a level where design processes are networks of computational operations, specifically the capabilities to reuse (a) design processes for different products, and (b) collaborative design strategies. In this article, we address these limitations by providing a modeling approach for simulation-based design processes so that they can be archived in a generic modular fashion and reused for collaborative design of different products. The proposed approach is based on four foundations: (a) modeling design processes as hierarchical systems, (b) separation of declarative and procedural information, (c) modeling design processes as decision-centric activities, and (d) modeling interactions between decision makers using game theoretic protocols. These four fundamentals of the approach are instantiated in the form of generic computational templates for products, processes, decisions, and pertinent interfaces. The approach is illustrated using a proof of concept implementation in ModelCenter. The implementation is validated by showing the reusability of design processes for two different products, a spring and a pressure vessel, in individual and collaborative design scenarios. The approach has potential for supporting reusability of broader PLM processes.