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- Khakpour, Narges, et al.
(author)
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Formal modeling of evolving self-adaptive systems
- 2012
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In: Science of Computer Programming. - Amsterdam : Elsevier. - 0167-6423 .- 1872-7964. ; 78:1, s. 3-26
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Journal article (peer-reviewed)abstract
- In this paper, we present a formal model, named PobSAM (Policy-based Self-Adaptive Model), for developing and modeling self-adaptive evolving systems. In this model, policies are used as a mechanism to direct and adapt the behavior of self-adaptive systems. A PobSAM model is a collection of autonomous managers and managed actors. The managed actors are dedicated to the functional behavior while the autonomous managers govern the behavior of managed actors by enforcing suitable policies. A manager has a set of configurations including two types of policies: governing policies and adaptation policies. To adapt the system behavior in response to the changes, the managers switch among different configurations. We employ the combination of an algebraic formalism and an actor-based model to specify this model formally. Managed actors are expressed by an actor model. Managers are modeled as meta-actors whose configurations are described using a multi-sorted algebra called CA. We provide an operational semantics for PobSAM using labeled transition systems. Furthermore, we provide behavioral equivalence of different sorts of CA in terms of splitting bisimulation and prioritized splitting bisimulation. Equivalent managers send the same set of messages to the actors. Using our behavioral equivalence theory, we can prove that the overall behavior of the system is preserved by substituting a manager by an equivalent one.
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- Khakpour, Narges, et al.
(author)
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Notions of Conformance Testing for Cyber-Physical Systems : Overview and Roadmap
- 2015
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In: 26th International Conference on Concurrency Theory. - Wadern : Dagstuhl Publishing. - 9783939897910 ; , s. 18-40
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Conference paper (pop. science, debate, etc.)abstract
- We review and compare three notions of conformance testing for cyber-physical systems. We begin with a review of their underlying semantic models and present conformance-preserving translations between them. We identify the differences in the underlying semantic models and the various design decisions that lead to these substantially different notions of conformance testing. Learning from this exercise, we reflect upon the challenges in designing an “ideal” notion of conformance for cyber-physical systems and sketch a roadmap of future research in this domain.
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- Khakpour, Narges, et al.
(author)
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PobSAM : policy-based managing of actors in self-adaptive systems
- 2010
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In: Proceedings of the 6th International Workshop on Formal Aspects of Component Software (FACS’09, Eindhoven, The Netherlands, November 2-3, 2009). - Amsterdam : Elsevier. ; 263, s. 129-143
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Conference paper (peer-reviewed)
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- Khakpour, Reza, et al.
(author)
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Mechanism of CO2 Electroreduction to Multicarbon Products over Iron Phthalocyanine Single-Atom Catalysts
- 2024
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In: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 128:14, s. 5867-5877
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Journal article (peer-reviewed)abstract
- Carbon dioxide reduction reaction (CO2RR) is a promising method for converting CO2 into value-added products. CO2RR over single-atom catalysts (SACs) is widely known to result in chemical compounds such as carbon monoxide and formic acid that contain only one carbon atom (C1). Indeed, at least two active sites are commonly believed to be required for C–C coupling to synthesize compounds, such as ethanol and propylene (C2+), from CO2. However, experimental evidence suggests that iron phthalocyanine (PcFe), which possesses only a single metal center, can produce a trace amount of C2+ products. To the best of our knowledge, the mechanism by which C2+ products are formed over a SAC such as PcFe is still unknown. Using density functional theory (DFT), we analyzed the mechanism of the CO2RR to C1 and C2+ products over PcFe. Due to the high concentration of bicarbonate at pH 7, CO2RR competes with HCO3– reduction. Our computations indicate that bicarbonate reduction is significantly more favorable. However, the rate of this reaction is influenced by the H3O+ concentration. For the formation of C2+ products, our computations reveal that C–C coupling proceeds through the reaction between in situ-formed CO and PcFe(“0”)–CH2 or PcFe(“-I”)–CH2 intermediates. This reaction step is highly exergonic and requires only low activation energies of 0.44 and 0.24 eV for PcFe(“0”)–CH2 and PcFe(“-I”)–CH2. The DFT results, in line with experimental evidence, suggest that C2+ compounds are produced over PcFe at low potentials whereas CH4 is still the main post-CO product.
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- Singh, Ajeet, et al.
(author)
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Molecular Electrochemical Catalysis of CO-to-Formaldehyde Conversion with a Cobalt Complex
- 2024
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In: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 146:32, s. 22129-22133
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Journal article (peer-reviewed)abstract
- Formox, a highly energy-intensive process, currently serves as the primary source of formaldehyde (HCHO), for which there is a crucial and steadily growing chemical demand. The alternative electrochemical production of HCHO from C1 carbon sources such as CO2 and CO is still in its early stages, with even the few identified cases lacking mechanistic rationalization. In this study, we demonstrate that cobalt phthalocyanine (CoPc) immobilized on multiwalled carbon nanotubes (MW-CNTs) constitutes an excellent electrocatalytic system for producing HCHO with productivity through the direct reduction of CO, the two-electron reduction product of CO2. By carefully adjusting both the pH and the applied potential, we identified conditions that enable the production of HCHO with a partial current density of 0.64 mA cm–2 (17.5% Faradaic efficiency, FE) and a total FE of 61.2% for the liquid products (formaldehyde and methanol). A reduction mechanism is proposed.
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