Browsing by Author "Chang, Ching-Hao"

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A scalable and accurate distributed traffic generator with Fourier transformed distribution over multiple commodity platforms
(2019-10-15)
Chang, Ching-Hao
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Lin, Ying-Dar
;
Lai, Yu-Kuen
;
Lai, Yuan-Cheng
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資訊工程學系
The rapid growth of high-speed computer networks poses a challenge in the design of testing and verification equipment. The hardware-based packet generators that are often used in the verification process are accurate but costly. Software-based packet generators, on the other hand, are relatively low-cost but have a limited performance with low accuracy. This paper proposes a Fourier-based profile decomposition and formulation methodology for a distributed packet generating system, featuring good horizontal scalability and high accuracy. Different from traditional software-based packet generators, this proposed system extracts the traffic components from a specific traffic distribution applying Fourier transformation to generate traffic components. These traffic components are distributed to one or more worker nodes for packet generation, and thus achieving higher aggregated traffic rate in any given distribution. The system design is based on the Data Plane Development Kits (DPDK) framework to maximize the traffic generation performance. The accuracy and performance of the proposed system scale according to the number of worker nodes used. Currently, with multiple CPU cores and five workers, the proposed system can generate aggregated traffic of more than 40 Gbps in a Poisson distribution.
Internet of Underwater Things: Challenges and Routing Protocols
(2018-01-01)
Liou, En-Cheng
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Kao, Chien-Chi
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Chang, Ching-Hao
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Lin, Yi-Shan
;
Huang, Chun-Ju
The Internet of Underwater Things (IoUT) is a novel class of Internet of Things (IoT) that enables practical applications toward developing smart cities. Underwater Wireless Sensor Network (UWSN) shows great potential for the future but also poses new challenges for IoUT. In addition, routing protocol will play a major role in handling how to forward data among the substantial number of"things". In this paper, we call attention to the challenges for IoUT, provide an exhaustive investigation of cutting-edge routing protocol and find the connection between the challenges and routing protocols for IoUT.
Topological Hall Effect in Single Thick SrRuO3 Layers Induced by Defect Engineering
(1970-01-01)
Wang, Changan
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Chang, Ching-Hao
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Herklotz, Andreas
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Chen, Chao
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Ganss, Fabian
The topological Hall effect (THE) has been discovered in ultrathin SrRuO3 (SRO) films, where the interface between the SRO layer and another oxide layer breaks the inversion symmetry resulting in the appearance of THE. Thus, THE only occurs in ultrathin SRO films of several unit cells. In addition to employing a heterostructure, the inversion symmetry can be broken intrinsically in bulk SRO by introducing defects. In this study, THE is observed in 60-nm-thick SRO films, in which defects and lattice distortions are introduced by helium ion irradiation. The irradiated SRO films exhibit a pronounced THE in a wide temperature range from 5 to 80 K. These observations can be attributed to the emergence of Dzyaloshinskii-Moriya interaction as a result of artificial inversion symmetry breaking associated with the lattice defect engineering. The creation and control of the THE in oxide single layers can be realized by ex situ film processing. Therefore, this work provides new insights into the THE and illustrates a promising strategy to design novel spintronic devices.
Tunable disorder and localization in the rare-earth nickelates
(2019-05-02)
Wang, Changan
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Chang, Ching-Hao
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Huang, Angus
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Wang, Pei-Chun
;
Wu, Ping-Chun
We demonstrate that transport in metallic rare-earth nickelates can be engineered by directly tuning the electronic mean free path. Using irradiation as a tool to induce disorder, we drive this system from a metallic phase into an Anderson insulator. This proceeds via an intermediate regime which shows a thermal crossover from insulating to metallic behavior. We argue that this phase falls within the paradigm of weak localization in three dimensions. We develop a theoretical model for the temperature dependence of resistivity which shows good agreement with our data. The three-dimensional weak localization picture is supported by magnetoconductivity, which scales as similar to B-2 up to several tesla. Interestingly, our data indicate that this phase lies in the Mott-Ioffe-Regel regime with the mean free path approaching the lattice constant. Upon further increasing disorder, the charge carriers are localized, leading to insulating behavior at all temperatures. Our results show that irradiation provides a "clean" tuning knob for the mean free path, without altering other system parameters. This suggests promising directions for studies of Anderson localization.