177 research outputs found
Modeling Basic Aspects of Cyber-Physical Systems
Designing novel cyber-physical systems entails significant, costly physical
experimentation. Simulation tools can enable the virtualization of experiments.
Unfortunately, current tools have shortcomings that limit their utility for
virtual experimentation. Language research can be especially helpful in
addressing many of these problems. As a first step in this direction, we
consider the question of determining what language features are needed to model
cyber-physical systems. Using a series of elementary examples of cyber-physical
systems, we reflect on the extent to which a small, experimental
domain-specific formalism called Acumen suffices for this purpose.Comment: Presented at DSLRob 2012 (arXiv:cs/1302.5082
Pre-deployment Analysis of Smart Contracts -- A Survey
Smart contracts are programs that execute transactions involving independent
parties and cryptocurrencies. As programs, smart contracts are susceptible to a
wide range of errors and vulnerabilities. Such vulnerabilities can result in
significant losses. Furthermore, by design, smart contract transactions are
irreversible. This creates a need for methods to ensure the correctness and
security of contracts pre-deployment. Recently there has been substantial
research into such methods. The sheer volume of this research makes
articulating state-of-the-art a substantial undertaking. To address this
challenge, we present a systematic review of the literature. A key feature of
our presentation is to factor out the relationship between vulnerabilities and
methods through properties. Specifically, we enumerate and classify smart
contract vulnerabilities and methods by the properties they address. The
methods considered include static analysis as well as dynamic analysis methods
and machine learning algorithms that analyze smart contracts before deployment.
Several patterns about the strengths of different methods emerge through this
classification process
Cyber-Physical Systems: A Model-Based Approach
In this concise yet comprehensive Open Access textbook, future inventors are introduced to the key concepts of Cyber-Physical Systems (CPS). Using modeling as a way to develop deeper understanding of the computational and physical components of these systems, one can express new designs in a way that facilitates their simulation, visualization, and analysis. Concepts are introduced in a cross-disciplinary way. Leveraging hybrid (continuous/discrete) systems as a unifying framework and Acumen as a modeling environment, the book bridges the conceptual gap in modeling skills needed for physical systems on the one hand and computational systems on the other. In doing so, the book gives the reader the modeling and design skills they need to build smart, IT-enabled products. Starting with a look at various examples and characteristics of Cyber-Physical Systems, the book progresses to explain how the area brings together several previously distinct ones such as Embedded Systems, Control Theory, and Mechatronics. Featuring a simulation-based project that focuses on a robotics problem (how to design a robot that can play ping-pong) as a useful example of a CPS domain, Cyber-Physical Systems: A Model-Based Approach demonstrates the intimate coupling between cyber and physical components, and how designing robots reveals several non-trivial control problems, significant embedded and real-time computation requirements, and a need to consider issues of communication and preconceptions
Metoprolol versus low-dose sotalol for prevention of high-risk post coronary artery bypass grafting atrial fibrillation
Background: The optimal therapeutic strategy for high-risk postoperative atrial fibrillation (POAF) remains less well defined. Our objectives were to investigate the efficacy of prophylactic metoprolol versus low-dose sotalol regimens to prevent high-risk atrial fibrillation (AF) following coronary artery bypass surgery (CABG).
Methods: We assigned 113 consecutive patients referred for CABG to either metoprolol or low-dose sotalol regimen. The primary end-point was the frequency of POAF during the 6-week follow-up.
Results: Out of 113 patients enrolled, 52.2% % received metoprolol (n= 59) while 44.8% received sotalol (n= 54). The frequency of POAF at follow-up was significantly higher among the metoprolol group (59.3 % versus 50 %; P=0.017). The predictors of POAF were: age > 60 years (OR: 1.86 (1.01-4.41); P= 0.03), EF (OR: 2 (1.05-3.83); P= 0.02), and sotalol was protective against POAF (OR= 0.49%; (95% CI=0.25 -0.97); P=0.02). The length of hospital stay was significantly higher in the metoprolol group (7.5±1.3 % versus 6.1±1.2 days; P<0.001).
Conclusion: Prophylactic low-dose sotalol could be superior to metoprolol for the prophylaxis of POAF in high-risk patients. However, Larger prospective multicenter randomized trials are needed to confirm our findings
Cyber-Physical Systems: A Model-Based Approach
In this concise yet comprehensive Open Access textbook, future inventors are introduced to the key concepts of Cyber-Physical Systems (CPS). Using modeling as a way to develop deeper understanding of the computational and physical components of these systems, one can express new designs in a way that facilitates their simulation, visualization, and analysis. Concepts are introduced in a cross-disciplinary way. Leveraging hybrid (continuous/discrete) systems as a unifying framework and Acumen as a modeling environment, the book bridges the conceptual gap in modeling skills needed for physical systems on the one hand and computational systems on the other. In doing so, the book gives the reader the modeling and design skills they need to build smart, IT-enabled products. Starting with a look at various examples and characteristics of Cyber-Physical Systems, the book progresses to explain how the area brings together several previously distinct ones such as Embedded Systems, Control Theory, and Mechatronics. Featuring a simulation-based project that focuses on a robotics problem (how to design a robot that can play ping-pong) as a useful example of a CPS domain, Cyber-Physical Systems: A Model-Based Approach demonstrates the intimate coupling between cyber and physical components, and how designing robots reveals several non-trivial control problems, significant embedded and real-time computation requirements, and a need to consider issues of communication and preconceptions
A Semantic Account of Rigorous Simulation
Hybrid systems are a powerful formalism for modeling cyber-physical systems. Reachability analysis is a general method for checking safety properties, especially in the presence of uncertainty and non-determinism. Rigorous simulation is a convenient tool for reachability analysis of hybrid systems. However, to serve as proof tool, a rigorous simulator must be correct wrt a clearly defined notion of reachability,which captures what is intuitively eachable in finite time. As a step towards addressing this challenge, this paper presents a rigorous simulator in the form of an operational semantics and a specification in the form of a denotational semantics. We show that, under certain conditions about the representation of enclosures, the rigorous simulator is correct. We also show that finding a representation satisfying these assumptions is non-trivial
Enclosing the behavior of a hybrid system up to and beyond a Zeno point
Even simple hybrid systems like the classic bouncing ball can exhibit Zeno behaviors. The existence of this type of behavior has so far forced simulators to either ignore some events or risk looping indefinitely. This in turn forces modelers to either insert ad hoc restrictions to circumvent Zeno behavior or to abandon hybrid modeling. To address this problem, we take a fresh look at event detection and localization. A key insight that emerges from this investigation is that an enclosure for a given time interval can be valid independently of the occurrence of a given event. Such an event can then even occur an unbounded number of times, thus making it possible to handle certain types of Zeno behavior
Sound over-approximation of probabilities
Safety analysis of high confidence systems requires guaranteed bounds on the probabilities of events of interest. Establishing the correctness of algorithms that aim to compute such bounds is challenging. We address this problem in three steps. First, we use monadic transition systems (MTS) in the category of sets as a framework for modeling discrete time systems. MTS can capture different types of system behaviors, but we focus on a combination of non-deterministic and probabilistic behaviors that often arises when modeling complex systems. Second, we use the category of posets and monotonic maps as a setting to define and compare approximations. In particular, for the MTS of interest, we consider approximations of their configurations based on complete lattices. Third, by restricting to finite lattices, we obtain algorithms that compute over-approximations, i.e., bounds from above within some partial order of approximants, of the system configuration after n steps. Interestingly, finite lattices of “interval probabilities” may fail to accurately approximate configurations that are both non-deterministic and probabilistic, even for deterministic (and continuous) system dynamics. However, better choices of finite lattices are available
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