Browsing by Author "Wu, Tao"

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    A NDIR Mid-Infrared Methane Sensor with a Compact Pentahedron Gas-Cell
    (MDPI, 2020) Ye, Weilin; Tu, Zihan; Xiao, Xupeng; Simeone, Alessandro; Yan, Jingwen; Wu, Tao; Wu, Fupei; Zheng, Chuantao; Tittel, Frank K.
    In order to improve the performance of the large divergence angle mid-infrared source in gas sensing, this paper aims at developing a methane (CH4) sensor with non-dispersive infrared (NDIR) technology using a compact pentahedron gas-cell. A paraboloid concentrator, two biconvex lenses and five planar mirrors were used to set up the pentahedron structure. The gas cell is endowed with a 170 mm optical path length with a volume of 19.8 mL. The mathematical model of the cross-section and the three-dimension spiral structure of the pentahedron gas-cell were established. The gas-cell was integrated with a mid-infrared light source and a detector as the optical part of the sensor. Concerning the electrical part, a STM32F429 was employed as a microcontroller to generate the driving signal for the IR source, and the signal from the detector was sampled by an analog-to-digital converter. A static volumetric method was employed for the experimental setup, and 20 different concentration CH4 samples were prepared to study the sensor’s evaluation, which revealed a 1σ detection limit of 2.96 parts-per-million (ppm) with a 43 s averaging time.
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    Smoothing vs. buffering for end-to-end QoS: Fundamental issues and comparison
    (2000) Wu, Tao; Knightly, Edward W.
    Smoothing traffic flows at the network edge to reduce their burstiness has been shown to have significant benefits for video-on-demand systems and deterministic services. In this thesis, we investigate the relative abilities of smoothing and buffering to improve a network's admissible region for end-to-end delay-bounded statistical services. In single multiplexer systems, we show that buffering outperforms smoothing for any end-to-end delay bound and loss probability. We find that this behavior is due not only to statistical buffer sharing, but also to heterogeneity of the traffic flows' time scales. In multi-node scenarios, key issues for buffering and smoothing are user QoS requirements, traffic characteristics, and route length. For example, we find that as the number of hops traversed increases, the advantages of buffering diminish due to node-to-node buffer partitioning; and while smoothing is asymptotically superior, we find that in practice, the "critical route length" required to realize a smoothing gain is so large that buffering results in larger admissible regions, even in many multi-node scenarios.