Browsing by Author "Li, C."
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Item Chemically Modified Graphene Films with Tunable Negative Poisson’s Ratios(Nature Publishing Group, 2019-06-04) Wen, Y.; Gao, E.; Hu, Zhenxing; Xu, Tingge; Lu, Hongbing; Xu, Z.; Li, C.; Hu, Zhenxing; Xu, Tingge; Lu, HongbingGraphene-derived macroscopic assemblies feature hierarchical nano- and microstructures that provide numerous routes for surface and interfacial functionalization achieving unconventional material properties. We report that the microstructural hierarchy of pristine chemically modified graphene films, featuring wrinkles, delamination of close-packed laminates, their ordered and disordered stacks, renders remarkable negative Poisson’s ratios ranging from −0.25 to −0.55. The mechanism proposed is validated by the experimental characterization and theoretical analysis. Based on the understanding of microstructural origins, pre-strech is applied to endow chemically modified graphene films with controlled negative Poisson’s ratios. Modulating the wavy textures of the inter-connected network of close-packed laminates in the chemically modified graphene films also yields finely-tuned negative Poisson’s ratios. These findings offer the key insights into rational design of films constructed from two-dimensional materials with negative Poisson’s ratios and mechanomutable performance. © 2019, The Author(s).Item Decoupling the Influence of Surface Structure and Intrinsic Wettability on Boiling Heat Transfer(American Institute of Physics Inc.) Dai, Xianming (Simon); Wang, P.; Yang, F.; Li, X.; Li, C.; 0000-0001-5050-2867 (Dai, X); 308247739 (Dai, X; Dai, Xianming (Simon)Surface structure and intrinsic wettability are both important for boiling heat transfer. While superhydrophilic micro, nano, and hierarchical surfaces are widely used for boiling enhancement, in which the surface structure and intrinsic wettability usually couple together. This study aims to decouple their influences on boiling heat transfer. Copper meshes are utilized as the microporous structures, and conformal superhydrophilic films of TiO₂ are deposited by atomic layer deposition (ALD). Although ALD coatings for boiling have been done on flat surfaces, this study separates the influence of surface structure from that of intrinsic wettability on a three-dimensional microporous surface. By comparing two and four layer meshes, we show that the surface structure has no obvious influence on the critical heat flux (CHF), but can significantly enhance the heat transfer coefficient (HTC). The intrinsic superhydrophilicity dramatically increases the CHF due to the fast rewetting of dryout regions. Our conclusion is that fast rewetting is critical to increase the CHF, while large surface areas are vital to enhance the HTC. © 2018 Author(s).Item High Thermal Conductivity in Isotopically Enriched Cubic Boron Phosphide(WILEY-VCH Verlag GmbH & Co.) Zheng, Q.; Li, S.; Li, C.; Lv, Y.; Liu, X.; Huang, P. Y.; Broido, D. A.; Lv, Bing; Cahill, D. G.; Li, S.; Liu, X.; Lv, BingZinc blende boron arsenide (BAs), boron phosphide (BP), and boron nitride (BN) have attracted significant interest in recent years due to their high thermal conductivity (Λ) predicted by first-principles calculations. This research reports the study of the temperature dependence of Λ (120 K < T < 600 K) for natural isotope-abundance BP and isotopically enriched 11BP crystals grown from modified flux reactions. Time-domain thermoreflectance is used to measure Λ of sub-millimeter-sized crystals. At room temperature, Λ for BP and 11BP is 490 and 540 W m−1 K−1, respectively, surpassing the values of conventional high Λ materials such as Ag, Cu, BeO, and SiC. The Λ of BP is smaller than only cubic BN, diamond, graphite, and BAs among single-phase materials. The measured Λ for BP and 11BP is in good agreement with the first-principles calculations above 250 K. The quality of the crystals is verified by Raman spectroscopy, X-ray diffraction, and scanning transmission electron microscopy. By combining the first-principles calculations and Raman measurements, a previously misinterpreted Raman mode is reassigned. Thus, BP is a promising material not only for heat spreader applications in high-power microelectronic devices but also as an electronic material for use in harsh environments. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, WeinheimItem Low-Complexity Generalized Spatial Modulation Schemes Using Codebook-Assisted MIMO Detectors(Institute of Electrical and Electronics Engineers Inc.) Chen, Y.; Cheng, W.; Li, C.; Haas, Zygmunt J.; 68658964 (Haas, ZJ); Haas, Zygmunt J.Generalized spatial modulation (GSM) is an attractive transmission technique for multiple-input multiple-output (MIMO) systems because of its spectral efficiency and energy efficiency. The maximum likelihood (ML) detector provides the optimal performance for GSM signal detection, but also leads to a high level of detection complexity. In this paper, both hard-decision and soft-decision detectors, which are based on a low-complexity codebook-assisted tree-search algorithm, are investigated. In addition, outer low-density parity-check (LDPC) codes are designed such that the concatenated schemes are able to provide error performances which are very close to those of the schemes using conventional detectors, but with a much lower level of computational complexity.