Browsing by Author "Wang, Y."
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Item Computing the Gromov-Hausdorff Distance for Metric Trees(Association for Computing Machinery) Agarwal, P. K.; Fox, Kyle J.; Nath, A.; Sidiropoulos, A.; Wang, Y.; Fox, Kyle J.The Gromov-Hausdorff (GH) distance is a natural way to measure distance between two metric spaces. We prove that it is NP-hard to approximate the GH distance better than a factor of 3 for geodesic metrics on a pair of trees. We complement this result by providing a polynomial time O(min{n, rn})-approximation algorithm for computing the GH distance between a pair of metric trees, where r is the ratio of the longest edge length in both trees to the shortest edge length. For metric trees with unit length edges, this yields an O_{√n}-approximation algorithm.1Item Maximisation of the Number of β-View Covered Targets in Visual Sensor Networks(Inderscience Enterprises Ltd., 2019-03-24) Guo, L.; Li, D.; Wang, Y.; Zhang, Z.; Tong, Guangmo; Wu, Weili; Du, Dingzhu; 56851698 (Wu, W); 288884264 (Du, D); Tong, Guangmo; Wu, Weili; Du, DingzhuIn some applications using visual sensor networks (VSNs), the facing directions of targets are bounded. Therefore existing full-view coverage (all the facing directions of a target constitutes a disk) is not necessary. We propose a novel model called β-view coverage model through which only necessary facing directions of a target are effectively viewed. This model uses much fewer cameras than those used by full-view coverage model. Based on β-view coverage model, a new problem called β-view covered target maximisation (BVCTM) problem is proposed to maximise the number of β-view covered targets given some fixed and freely rotatable camera sensors. We prove its NP-hardness and transform it into an Integer Linear Programming problem equivalently. Besides, a (1 - e - 1 )-factor approximate algorithm and a camera-utility based greedy algorithm are given for this problem. Finally, we conduct many experiments and investigate the influence of many parameters on these two algorithms. © 2019 Inderscience Enterprises Ltd.Item New Intrinsic Mechanism on Gum-Like Superelasticity of Multifunctional AlloysLiu, J. -P; Wang, Y. -D; Hao, Y. -L; Wang, Y.; Nie, Z. -H; Wang, D.; Ren, Y.; Lu, Z. -P; Wang, Jinguo; Wang, H.; Hui, X.; Lu, Ning; Kim, Moon J.; Yang, R.Ti-Nb-based Gum Metals exhibit extraordinary superelasticity with ultralow elastic modulus, superior strength and ductility, and a peculiar dislocation-free deformation behavior, most of which challenge existing theories of crystal strength. Additionally, this kind of alloys actually displays even more anomalous mechanical properties, such as the non-linear superelastic behavior, accompanied by a pronounced tension-to-compression asymmetry, and large ductility with a low Poisson's ratio. Two main contradictory arguments exist concerning the deformation mechanisms of those alloys, i.e., formation of reversible nanodisturbance and reversible martensitic transformation. Herein we used the in-situ synchrotron high-energy X-ray scattering technique to reveal the novel intrinsic physical origin of all anomalous mechanical properties of the Ti-24Nb-4Zr-8Sn-0.10O alloy, a typical gum-like metal. Our experiments provide direct evidence on two different kinds of interesting, stress-induced, reversible nanoscale martensitic transitions, i.e., the austenitic regions with B2 structure transform to α" martensite and those with BCC structure transform to ō martensite.Item Odd-Integer Quantum Hall States and Giant Spin Susceptibility in P -Type Few-Layer WSe₂(American Physical Society, 2017-02-10) Xu, S.; Shen, J.; Long, G.; Wu, Z.; Bao, Zhi-qiang; Liu, Cheng-Cheng; Xiao, X.; Han, T.; Lin, J.; Wu, Y.; Lu, H.; Hou, J.; An, L.; Wang, Y.; Cai, Y.; Ho, K. M.; He, Y.; Lortz, R.; Zhang, Fan; Wang, N.; Bao, Zhi-qiang; Liu, Cheng-Cheng; Zhang, FanWe fabricate high-mobility p-type few-layer WSe₂ field-effect transistors and surprisingly observe a series of quantum Hall (QH) states following an unconventional sequence predominated by odd-integer states under a moderate strength magnetic field. By tilting the magnetic field, we discover Landau level crossing effects at ultralow coincident angles, revealing that the Zeeman energy is about 3 times as large as the cyclotron energy near the valence band top at the Γ valley. This result implies the significant roles played by the exchange interactions in p-type few-layer WSe₂, in which itinerant or QH ferromagnetism likely occurs. Evidently, the Γ valley of few-layer WSe₂ offers a unique platform with unusually heavy hole carriers and a substantially enhanced g factor for exploring strongly correlated phenomena.Item Quantum Transport and Band Structure Evolution under High Magnetic Field in Few-Layer Tellurene(American Chemical Society) Qiu, G.; Wang, Y.; Nie, Yifan; Zheng, Yongping; Cho, Kyeongjae; Wu, W.; Ye, P. D.; 0000-0003-4771-3633 (Nie, Y); 0000-0003-2698-7774 (Cho, K); 369148996084659752200 (Cho, K); Nie, Yifan; Zheng, Yongping; Cho, KyeongjaeQuantum Hall effect (QHE) is a macroscopic manifestation of quantized states that only occurs in confined two-dimensional electron gas (2DEG) systems. Experimentally, QHE is hosted in high-mobility 2DEG with large external magnetic field at low temperature. Two-dimensional van der Waals materials, such as graphene and black phosphorus, are considered interesting material systems to study quantum transport because they could unveil unique host material properties due to the easy accessibility of monolayer or few-layer thin films at the 2D quantum limit. For the first time, we report direct observation of QHE in a novel low-dimensional material system, tellurene. High-quality 2D tellurene thin films were acquired from recently reported hydrothermal method with high hole mobility of nearly 3000 cm2/(V s) at low temperatures, which allows the observation of well-developed Shubnikov-de Haas (SdH) oscillations and QHE. A four-fold degeneracy of Landau levels in SdH oscillations and QHE was revealed. Quantum oscillations were investigated under different gate biases, tilted magnetic fields, and various temperatures, and the results manifest the inherent information on the electronic structure of Te. Anomalies in both temperature-dependent oscillation amplitudes and transport characteristics were observed that are ascribed to the interplay between the Zeeman effect and spin-orbit coupling, as depicted by the density functional theory calculations. ©2018 American Chemical Society.Item Robust Resource Allocation for MISO Cognitive Radio Networks under Two Practical Non-Linear Energy Harvesting Models(Institute of Electrical and Electronics Engineers Inc.) Zhang, X.; Wang, Y.; Zhou, F.; Al-Dhahir, Naofal; Deng, X.; 113149196515374792028 (Al-Dhahir, N); Al-Dhahir, NaofalTo achieve a good tradeoff between the consumed power and the harvested power, a robust resource optimization problem is studied in a multiple-input single-output cognitive radio network with simultaneous wireless information and power transfer under imperfect channel state information. Unlike most of the existing works that assume an ideal linear energy harvesting (EH) model, we assume two practical non-linear EH models. In order to solve the resulting challenging non-convex problem, we propose an algorithm based on successive convex approximation and prove that a rank-one solution is obtained in each iteration of the proposed algorithm. Our simulation results quantify the effect of the sensitivity threshold of the EH circuit on the harvested power. ©2018 IEEEItem The Band Structure Change of Hf₀.₅Zr₀.₅O₂/Ge System upon Post Deposition Annealing(Elsevier B.V., 2019-05-25) Feng, Z.; Peng, Y.; Liu, H.; Sun, Y.; Wang, Y.; Meng, M.; Liu, H.; Wang, J.; Wu, R.; Wang, Xinglu; Cho, Kyeongjae; Han, G.; Dong, H.; 0000-0003-2698-7774 (Cho, K); 369148996084659752200 (Cho, K); Wang, Xinglu; Cho, KyeongjaeHafnium zirconium oxide films have been utilized in negative capacitance (NC) field-effect transistors (FETs). The band alignment of semiconductor and HfZrOₓ film is critical to obtain high device performance. The band alignment of Hf₀.₅Zr₀.₅O₂/SiOₓ/Ge system before and after post deposition annealing at 500 °C is studied via angle resolved X-ray photoelectron spectroscopy, synchrotron radiation photoemission spectroscopy and UV–Visible spectroscopy. The band gap of Hf₀.₅Zr₀.₅O₂ is seen narrowed 0.27 ± 0.05 eV, and the valence band offset between Hf₀.₅Zr₀.₅O₂ and Ge decreases 0.25 eV ± 0.05 eV after PDA at 500 °C. Therefore, the conduction band offset is nearly unchanged. This work gives insights into the interface physics about Hf₀.₅Zr₀.₅O₂/SiOₓ and is valuable for Ge-based NC pFETs. ©2019 Elsevier B.V.Item The Ion/Electron Temperature Characteristics of Polar Cap Classical and Hot Patches and their Influence on Ion Upflow(Blackwell Publishing Ltd) Ma, Y. -Z; Zhang, Q. -H; Xing, Z. -Y; Heelis, Roderick A.; Oksavik, K.; Wang, Y.; 0000-0002-5543-5357 (Heelis, RA); Heelis, Roderick A.The term of “polar cap hot patch” is a newly identified high-density plasma irregularity at high latitudes, which is associated with high electron temperature and particle precipitation, while a classical polar cap patch has lower electron temperature. To investigate characteristics of hot patches versus classical patches, five years of in situ database of plasma observations from the DMSP satellites was analyzed. For the first time, we show how the ion/electron temperature ratio (or temperature difference) can be used to distinguish between classical and hot patches. For classical patches (Ti/Te > 0.8 or Te Ti + 600 K), the vertical ion flux is generally upward. The highest upflow occurrence was found near the polar cap boundary, associated with hot patches, particle precipitation, strong convection speed, and localized field-aligned currents. This result shows that the polar cap hot patches may play a very important role in solar wind-magnetosphere-ionosphere coupling processes. ©2018. American Geophysical Union. All Rights Reserved.Item Tiers in One-Sided Matching Markets: Theory and Experimental InvestigationWang, Y.; Haruvy, Ernan; 205185198 (Haruvy, E)The design of a matching market may affect behavior in prematch stages. In some settings, forward-looking agents might purchase low-priced properties with the intention of trading up. From a design standpoint, such behavior is undesirable. We investigate a tiered structure as a potential solution. Using a model that endogenizes prematch acquisition decisions, we show that tiers promote exchange while protecting the primary market. In the laboratory, we find that both firm revenue and total social surplus are improved by tiered matching, and the amount of improvement depends on the exchange mechanism the firm uses. We focus on two popular mechanisms-deposit first and request first. We find that subjects are less likely to take advantage of the match under tier-free deposit first mechanism, possibly because of risk aversion. Thus, a tiered approach is more critical under the request first mechanism. We confirm that risk aversion partly explains deviations from theory.