107 research outputs found

    Effect of Bridge-Pier Differential Settlement on the Dynamic Response of a High-Speed Railway Train-Track-Bridge System

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    A model based on the theory of train-track-bridge coupling dynamics is built in the article to investigate how high-speed railway bridge pier differential settlement can affect various railway performance-related criteria. The performance of the model compares favorably with that of a 3D finite element model and train-track-bridge numerical model. The analysis of the study demonstrates that all the dynamic response for a span of 24 m is slightly larger than that for a span of 32 m. The wheel unloading rate increases with pier differential settlement for all of the calculation conditions considered, and its maximum value of 0.695 is well below the allowable limit. Meanwhile, the vertical acceleration increases with pier differential settlement and train speed, respectively, and the values for a pier differential settlement of 10 mm and speed of 350 km/h exceed the maximum allowable limit stipulated in the Chinese standards. On this basis, a speed limit for the exceeding pier differential settlement is determined for comfort consideration. Fasteners that had an initial tensile force due to pier differential settlement experience both compressive and tensile forces as the train passes through and are likely to have a lower service life than those which solely experience compressive forces

    Enhanced Photodetection in Graphene-Integrated Photonic Crystal Cavity

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    We demonstrate the controlled enhancement of photoresponsivity in a graphene photodetector by coupling to slow light modes in a long photonic crystal linear defect cavity. Near the Brillouin zone (BZ) boundary, spectral coupling of multiple cavity modes results in broad-band photocurrent enhancement from 1530 nm to 1540 nm. Away from the BZ boundary, individual cavity resonances enhance the photocurrent eight-fold in narrow resonant peaks. Optimization of the photocurrent via critical coupling of the incident field with the graphene-cavity system is discussed. The enhanced photocurrent demonstrates the feasibility of a wavelength-scale graphene photodetector for efficient photodetection with high spectral selectivity and broadband response

    The Optimal Patent Portfolio of The Technology Standards Alliances in Innovation Competition

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    Unlike the dominant theories based on the rigid assumption that “technology standards must contain only essential patents”, this paper discusses the standard alliances that are engaged in their cumulative innovation. Its focus is particularly on a more realistic setting that a standard alliance should contain both the essential and the non-essential patents. We use the essential-patent’s ratio, which denotes the percentage of the essential patents in the total patents in a standard, as the cumulative innovation model’s core variable. The mathematical analysis illustrates that the essential-patent’s ratio performs an important role in the arguments’ standards. There is an optimal portfolio that maximizes the alliances’ efficiency in an innovation competition. It implies that the social welfare effects depend on the dynamic trade-off between the long-term technical gap caused by the technological upgrades’ missing opportunities and the short-term welfare losses that consumers may suffer. The patents’ and antitrust laws should tolerate a certain number of non-essential patents being contained by the technology standards
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