1,741 research outputs found
Optimizing deep reinforcement learning policies for deteriorating systems considering ordered action structuring and value of information
No full textInspection and maintenance (I&M) optimization entails many sources of computational complexity, among others, due to high-dimensional decision and state variables in multi-component systems, long planning horizons, stochasticity of objectives and constraints, and inherent uncertainties in measurements and models. This paper studies how the above can be addressed within the context of constrained Partially Observable Markov Decision Processes (POMDPs) and Deep Reinforcement Learning (DRL) in a unified fashion. Special emphasis is paid on how ordered action structuring of I&M actions can be exploited to decompose the respective policy parametrizations in actor-critic DRL schemes, resulting into fully decoupled maintenance and inspection actors. It is shown that the Value of Information (VoI) is naturally utilized in such POMDP control frameworks, as directly associated with the DRL advantage functions that emerge in the gradient computations of the inspection policy parameters. Overall, the presented approach, following the natural flow of engineering decisions, results in new architectural configurations for policy networks, facilitating more efficient training, while alleviating further the dimensionality burdens related to combinatorial definitions of I&M actions. The efficiency of the methodology is demonstrated in numerical experiments of a structural system subject to corrosion, where the optimization problem is formulated to concurrently account for state and model uncertainties as well as long-term probability of failure exceedance constraints. Results showcase that the obtained DRL policies considerably outperform standard decision rules.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Structural Design & Mechanic
Efficient sampling techniques for simulation-based life-cycle structural reliability and seismic fragility assessment
No full textLife-cycle structural reliability assessment and risk analysis of deteriorating systems may involve the modeling of complex time-variant probabilistic processes. Although simulation methods are frequently the only viable tools to solve this kind of problems, they are time-consuming and might be computationally inefficient and unfeasible in practice if small probabilities of failure need to be estimated, particularly for large-scale reliability and risk analysis problems. To mitigate the computational effort of simulation methods in estimating the time-variant failure probability of deteriorating structures, a novel computational approach based on Importance Sampling and clustering-based data reduction techniques is proposed. The computational efficiency of the proposed methodology is demonstrated with practical applications to life-cycle reliability and seismic fragility of reinforced concrete structures exposed to corrosion
CALCULATION OF MOLECULAR PARAMETERS FOR ISOTOPOMERS OF SPECIES OF METHANOL
No full textY.B. Duan and K. Takagi, Phys. Lett. A 207, 203 (1995). M.S. Walsh, Li-Hong Xu, and R.M. Less, J. Mol. Spectrosc. 188. 85(1998); A. Predoi-Cross, Li-Hong, Xu. M.S. Walsh, R.M. Lees, M. Winnerwisser, and H. Lichau, J. Mol. Spectrosc. 188, 94 (1998). Y.B. Duan, L. Wang, I. Mukhopadhyay, and K. Takagi, J. Chem. Phys. 110, 929(1999).Author Institution: Department of Physics, Toyama UniversityTortion-rotational constants have been determined for and isotopomers of the species of methanol with O-16, 17 and 18, using the calculation procedure based on the centrifugal distortion theory for a molecule containing a three-fold symmetric internal These parameters have also been obtained by fitting to observed microwave for in which a correction-free reduced has been used. It is shown that all of the calculated constants are in better agreement with the fitting ones for this molecule than those for the other species of methanol
The effect of dislocation density on the interactions between dislocations and twin boundaries in nanocrystalline materials
No full textThe interactions between dislocations and twinboundaries (TBs) are significantly affected by both intrinsic material properties and extrinsic factors, including stacking fault energy, the energy barriers for dislocation reactions at TBs, twin thickness and applied stress. In this study, dislocation–TB interactions in grains with different dislocationdensities were investigated and we conclude that the dislocationdensity also affects the dislocation–TB interactions. In a twinned grain with a low dislocationdensity, a dislocation may react with a TB to fully or partially penetrate the TB or to be absorbed by the TB via different dislocation reactions. Alternatively, in a twinned grain with a high dislocationdensity, dislocations tangle with each other and are pinned at the TBs, thereby making it unfavourable for further dislocation reactions to mediate dislocation penetration across the TB. This leads to an accumulation of dislocations at the TBs, raising the local strain energy, which, in turn, is released by the activation of secondary twins by partial dislocation emissions from the other side of the T
Appraisal and mathematical properties of fragility analysis methods
No full textFragility analysis aims to compute the probabilities of a system exceeding certain damage conditions given different levels of hazard intensity. Fragility analysis is therefore a key process of performance-based earthquake engineering, with a number of approaches developed and widely recognized, including Incremental Dynamic Analysis (IDA), Multiple Stripe Analysis (MSA), and cloud analysis. Additionally, extended fragility analysis has recently been shown to possess important attributes of mathematical consistency and extensibility. This work provides a critical review of the different fragility methods by explaining the underlying probabilistic models and assumptions, as well as their connections to the extended fragility method. It is proven that IDA-based fragility curves provide an upper bound of the actual fragility, and cloud analysis manifests suboptimality issues arising from its underlying assumptions. MSA is identified to be a probit-linked Bernoulli regression model, similar to the one proposed by Shinozuka and coworkers. The latter, in turn, is shown to be a limiting subcase of the generalized linear model framework introduced within the extended fragility analysis. The paper first presents a simple case of one intensity measure and two damage condition states, and the discussion is subsequently extended to more general cases of multiple intensity measures and damage states. The discussed attributes are demonstrated in several numerical applications. Overall, this work aims to provide new insights on fragility methods, enabling efficient, accurate, and consistent estimations of structural performance, as well as promoting new research directions in earthquake engineering and other related fields.Structural Design & Mechanic
Information leak in Liu et al.’s quantum private comparison and a new protocol
No full textIn a recent paper [W. Liu, Y.B. Wang, Z.T. Jiang, Opt. Commun. 284, 3160 (2011)], a quantum private comparison (QPC) protocol based on W states was presented. Compared to the previous QPCs, the protocol is promising for that it can prevent the comparison result from revealing to the third party. However, this study point out that a flaw of information leak is existent in the protocol. And a new QPC which can avoid the flaw and has higher efficiency is proposed in this paper
Some molecule-based materials low dimension nanostructures
No full textMolecule based materials nanoarchitectures have been employed as important nanoscale building blocks for advanced materials and smart miniature devices to fulfill the increasing needs of high materials usage efficiency. Different dimension molecule based materials based nanoarchitectures, especially low dimension nanostructures, attract significant attention due to its fascinating controlled structure and functionality-easy tailoring with excellent semi-conductive properties and stability. In this report, we discuss the some molecule based materials self-assembled oriented functional nanoarchitectures by coordinated inducing. The molecular material building blocks, aggregate structures and their properties in optical, electrical and photoelectrical properties were shown.
REFERENCES
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Elemental redistribution in a nanocrystalline Ni–Fe alloy induced by high-pressure torsion
No full textAn electrochemically deposited nanocrystalline supersaturated face-centred-cubic Ni–21 at.% Fe alloy with an initial average grain size of ?21 nm was processed using high-pressure torsion (HPT) that resulted in grain growth via grain rotation and coalescence to an average grain size of ?53 nm. Atom probe tomography investigations revealed that the supersaturated Ni–Fe solid solution was stable under HPT and that C and S atoms, which are the major impurities in the material and segregated to the grain boundaries (GBs) of the as-deposited material, migrated from disappearing GBs to the remaining GBs during HPT. We propose that the elemental redistribution was facilitated by GB diffusion and the motion of a large volume of HPT-induced defects at the GB regions during the grain growth process. This elemental redistribution process is different from other HPT-induced elemental redistribution processes reported in the literatur
Strain hardening and softening in a nanocrystalline Ni–Fe alloy induced by severe plastic deformation
No full textThe strain response of an electrochemically deposited nanocrystalline Ni–20 wt.% Fe alloy processed by high-pressure torsion (HPT) was investigated by monitoring changes in hardness. Strain hardening was observed in the very early stage of HPT, followed by strain softening before the onset of a second strain hardening stage. Structural investigations revealed that the two hardening stages were associated with an increase in dislocation density, whereas the strain softening stage was accompanied by a reduction in the dislocation and twin densities, thereby demonstrating the main dependence of hardness on the dislocation density in this material. Grain growth occurred during HPT and its role in the hardness evolution is also discusse
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