6,654 research outputs found
Technical approaches for measurement of human errors
Human error is a significant contributing factor in a very high proportion of civil transport, general aviation, and rotorcraft accidents. The technical details of a variety of proven approaches for the measurement of human errors in the context of the national airspace system are presented. Unobtrusive measurements suitable for cockpit operations and procedures in part of full mission simulation are emphasized. Procedure, system performance, and human operator centered measurements are discussed as they apply to the manual control, communication, supervisory, and monitoring tasks which are relevant to aviation operations
Elasticity and Petri nets
Digital electronic systems typically use synchronous clocks and primarily assume fixed duration of their operations to simplify the design process. Time elastic systems can be constructed either by replacing the clock with communication handshakes (asynchronous version) or by augmenting the clock with a synchronous version of a handshake (synchronous version). Time elastic systems can tolerate static and dynamic changes in delays (asynchronous case) or latencies (synchronous case) of operations that can be used for modularity, ease of reuse and better power-delay trade-off. This paper describes methods for the modeling, performance analysis and optimization of elastic systems using Marked Graphs and their extensions capable of describing behavior with early evaluation. The paper uses synchronous elastic systems (aka latency-tolerant systems) for illustrating the use of Petri nets, however, most of the methods can be applied without changes (except changing the delay model associated with events of the system) to asynchronous elastic systems.Peer ReviewedPostprint (author's final draft
Causality and the Modeling of the Measurement Process in Quantum Theory
In this paper we provide a general account of the causal models which attempt
to provide a solution to the famous measurement problem of Quantum Mechanics
(QM). We will argue that --leaving aside instrumentalism which restricts the
physical meaning of QM to the algorithmic prediction of measurement outcomes--
the many interpretations which can be found in the literature can be
distinguished through the way they model the measurement process, either in
terms of the efficient cause or in terms of the final cause. We will discuss
and analyze why both, 'final cause' and 'efficient cause' models, face severe
difficulties to solve the measurement problem. In contradistinction to these
schemes we will present a new model based on the immanent cause which, we will
argue, provides an intuitive understanding of the measurement process in QM
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The tarantula toxin GxTx detains K+ channel gating charges in their resting conformation.
Allosteric ligands modulate protein activity by altering the energy landscape of conformational space in ligand-protein complexes. Here we investigate how ligand binding to a K+ channel's voltage sensor allosterically modulates opening of its K+-conductive pore. The tarantula venom peptide guangxitoxin-1E (GxTx) binds to the voltage sensors of the rat voltage-gated K+ (Kv) channel Kv2.1 and acts as a partial inverse agonist. When bound to GxTx, Kv2.1 activates more slowly, deactivates more rapidly, and requires more positive voltage to reach the same K+-conductance as the unbound channel. Further, activation kinetics are more sigmoidal, indicating that multiple conformational changes coupled to opening are modulated. Single-channel current amplitudes reveal that each channel opens to full conductance when GxTx is bound. Inhibition of Kv2.1 channels by GxTx results from decreased open probability due to increased occurrence of long-lived closed states; the time constant of the final pore opening step itself is not impacted by GxTx. When intracellular potential is less than 0 mV, GxTx traps the gating charges on Kv2.1's voltage sensors in their most intracellular position. Gating charges translocate at positive voltages, however, indicating that GxTx stabilizes the most intracellular conformation of the voltage sensors (their resting conformation). Kinetic modeling suggests a modulatory mechanism: GxTx reduces the probability of voltage sensors activating, giving the pore opening step less frequent opportunities to occur. This mechanism results in K+-conductance activation kinetics that are voltage-dependent, even if pore opening (the rate-limiting step) has no inherent voltage dependence. We conclude that GxTx stabilizes voltage sensors in a resting conformation, and inhibits K+ currents by limiting opportunities for the channel pore to open, but has little, if any, direct effect on the microscopic kinetics of pore opening. The impact of GxTx on channel gating suggests that Kv2.1's pore opening step does not involve movement of its voltage sensors
Immanent Powers versus Causal Powers (Propensities, Latencies and Dispositions) in Quantum Mechanics
In this paper we compare two different notions of 'power', both of which
attempt to provide a realist understanding of quantum mechanics grounded on the
potential mode of existence. For this propose we will begin by introducing two
different notions of potentiality present already within Aristotelian
metaphysics, namely, irrational potentiality and rational potentiality. After
discussing the role played by potentiality within classical and quantum
mechanics, we will address the notion of causal power which is directly related
to irrational potentiality and has been adopted by many interpretations of QM.
We will then present the notion of immanent power which relates to rational
potentiality and argue that this new concept presents important advantages
regarding the possibilities it provides for understanding in a novel manner the
theory of quanta. We end our paper with a comparison between both notions of
'power', stressing some radical differences between them.Comment: Forthcoming in: Probing the Meaning and Structure of Quantum
Mechanics, D. Aerts, M.L. Dalla Chiara, C. de Ronde and D. Krause (Eds.),
World Scientific, Singapore. arXiv admin note: text overlap with
arXiv:1310.453
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