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1. Eddy-Current Dynamic Model for Simultaneous Geometrical and Material Parameter Measurements of Magnetic Materials

   https://doi.org/10.1115/DSCC2018-9211  

   Hao, Bingjie; Lee, Kok-Meng; Bai, Kun (September 2018, Proceedings of the ASME 2018 Dynamic Systems and Control Conference)

   This paper presents a distributed current source (DCS) method for modeling the dynamic responses of eddy current density (ECD) induced in electrical conductors and its corresponding magnetic flux density (MFD); both nonmagnetic and weakly magnetized conductors are considered. Unlike conventional numerical methods such as finite element analysis (FEA), the DCS method, which accounts for the eddy-current and magnetization effects by means of equivalent volume and surface current-sources, derives closed-form solutions to the ECD and MFD fields in state-space representation. The model has been experimentally validated and verified by comparing results from FEA simulations with both harmonic and nonharmonic excitations. To gain physical insights to the measured MFD for simultaneous estimating the material/geometrical properties of a conductor, the static and dynamic responses to rectangular pulsed current excitations have been numerically investigated, confirming the feasibility and effectiveness of the measurement methods. 

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2. Analytical Method to Approximate the Impact of Turning on the Macroscopic Fundamental Diagram

   https://doi.org/10.1177/0361198120933274  

   Xu, Guanhao; Yu, Zhengyao; Gayah, Vikash V. (September 2020, Transportation Research Record: Journal of the Transportation Research Board)

   null (Ed.)

   Network macroscopic fundamental diagrams (MFDs) have recently been shown to exist in real-world urban traffic networks. The existence of an MFD facilitates the modeling of urban traffic network dynamics at a regional level, which can be used to identify and refine large-scale network-wide control strategies. To be useful, MFD-based modeling frameworks require an estimate of the functional form of a network’s MFD. Analytical methods have been proposed to estimate a network’s MFD by abstracting the network as a single ring-road or corridor and modeling the flow–density relationship on that simplified element. However, these existing methods cannot account for the impact of turning traffic, as only a single corridor is considered. This paper proposes a method to estimate a network’s MFD when vehicles are allowed to turn into or out of a corridor. A two-ring abstraction is first used to analyze how turning will affect vehicle travel in a more general network, and then the model is further approximated using a single ring-road or corridor. This approximation is useful as it facilitates the application of existing variational theory-based methods (the stochastic method of cuts) to estimate the flow–density relationship on the corridor, while accounting for the stochastic nature of turning. Results of the approximation compared with a more realistic simulation that includes features that cannot be captured using variational theory—such as internal origins and destinations—suggest that this approximation works to estimate a network’s MFD when turning traffic is present. 

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3. LEGOStore: A Linearizable Geo-Distributed Store Combining Replication and Erasure Coding

   https://doi.org/10.14778/3547305.3547323  

   Zare, H.; Cadambe, V.; Urgaonkar, B.; Alfares, N.; Sharma, C.; Merchant, A. (September 2022, Proceedings of the VLDB Endowment)

   We design and implement LEGOStore, an erasure coding (EC) based linearizable data store over geo-distributed public cloud data centers (DCs). For such a data store, the confluence of the following factors opens up opportunities for EC to be latency-competitive with replication: (a) the necessity of communicating with remote DCs to tolerate entire DC failures and implement linearizability; and (b) the emergence of DCs near most large population centers. LEGOStore employs an optimization framework that, for a given object, carefully chooses among replication and EC, as well as among various DC placements to minimize overall costs. To handle workload dynamism, LEGOStore employs a novel agile reconfiguration protocol. Our evaluation using a LEGOStore prototype spanning 9 Google Cloud Platform DCs demonstrates the efficacy of our ideas. We observe cost savings ranging from moderate (5-20%) to significant (60%) over baselines representing the state of the art while meeting tail latency SLOs. Our reconfiguration protocol is able to transition key placements in 3 to 4 inter-DC RTTs (< 1s in our experiments), allowing for agile adaptation to dynamic conditions. 

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4. Nondestructive Evaluation of Additively Manufactured Metal Components with an Eddy Current Technique

   B. Schneider, B; Shoaib, M; Taheri, H; Koester, L; Bigelow, T; Bond, L (January 2018, ASNT 27th Research Symposium Proceedings)

   The ability of Additive Manufacturing (AM) processes to ensure delivery of high quality metal-based components is somewhat limited by insufficient inspection capabilities. The inspection of AM parts presents particular challenges due to the design flexibility that the fabrication method affords. The nondestructive evaluation (NDE) methods employed need to be selected based on the material properties, type of possible defects, and geometry of the parts. Electromagnetic method, in particular Eddy Current (EC), is proposed for the inspections. This evaluation of EC inspection considers surface and near-surface defects in a stainless steel (SS) 17 4 PH additively manufactured sample and a SS 17 4 PH annealed plates manufactured traditionally (reference sample). The surfaces of the samples were polished using 1 micron polishing Alumina grit to achieve a mirror like surface finish. 1.02 mm (0.04”), 0.508 mm (0.02”) and 0.203 mm (0.008”) deep Electronic Discharge Machining (EDM) notches were created on the polished surface of the samples. Lift off and defect responses for both additive and reference samples were obtained using a VMEC-1 commercial instrument and a 500 kHz absolute probe. The inspection results as well as conductivity assessments for the AM sample in terms of the impedance plane signature were compared to response of similar features in the reference sample. Direct measurement of electromagnetic properties of the AM samples is required for precise inspection of the parts. Results show that quantitative comparison of the AM and traditional materials help for the development of EC technology for inspection of additively manufactured metal parts. 

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5. On the impacts of roadway hierarchy on the network Macroscopic Fundamental Diagram

   Xu, Guanhao; Gayah, Vikash V. (January 2021, 100th Annual Meeting of the Transportation Research Board)

   null (Ed.)

   Relationships between average network productivity and accumulation or density aggregated 2 across spatially compact regions of urban networks—so called network Macroscopic Fundamental 3 Diagrams (MFDs)—have recently been shown to exist. Various analytical methods have been put 4 forward to estimate a network’s MFD as a function of network properties, such as average block 5 lengths, signal timings, and traffic flow characteristics on links. However, real street networks are 6 not homogeneous—they generally have a hierarchical structure where some streets (e.g., arterials) 7 promote higher mobility than others (e.g., local roads). This paper provides an analytical method 8 to estimate the MFDs of hierarchical street networks by considering features that are specific to 9 hierarchical network structures. Since the performance of hierarchical networks is driven by how 10 vehicles are routed across the different street types, two routing conditions— user equilibrium and 11 system optimal routing—are considered in the analytical model. The proposed method is first 12 implemented to describe the MFD of a hierarchical one-way limited access linear corridor and 13 then extended to a more realistic hierarchical two-dimensional grid network. For both cases, it is 14 shown that the MFD of a hierarchical network may no longer be unimodal or concave as 15 traditionally assumed in most MFD-based modeling frameworks. These findings are verified using 16 simulations of hierarchical corridors. Finally, the proposed methodology is applied to demonstrate 17 how it can be used to make decisions related to the design of hierarchical street network structures. 

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