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3,493 results on '"Yang, XiaoLong"'

222. Understanding Phonon Scattering by Nano-Precipitates in Potassium-Doped Lead Chalcogenides

Author

Wang, Zhao, Yang, Xiaolong, Feng, Dan, Wu, Haijun, Carrete, Jesus, Zhao, Li-Dong, Li, Chao, Cheng, Shaodong, Peng, Biaolin, Yang, Guang, and He, Jiaqing

Subjects
Condensed Matter - Materials Science
Abstract

We present a comprehensive experimental and theoretical study of phonon scattering by nanoprecipitates in potassium-doped PbTe, PbSe and PbS. We highlight the role of the precipitate size distribution measured by microscopy, whose tuning allows for thermal conductivities lower than the limit achievable with a single size. The correlation between the size distribution and the contributions to thermal conductivity from phonons in different frequency ranges provides a physical basis to the experimentally measured thermal conductivities, and a criterion to estimate the lowest achievable thermal conductivity. The results have clear implications for efficiency enhancements in nanostructured bulk thermoelectrics., Comment: 26 pages, 6 figures

Published
2018
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223. Phonon anharmonic frequency shift induced by four-phonon scattering calculated from first principles

Author

Feng, Tianli, Yang, Xiaolong, and Ruan, Xiulin

Subjects
Condensed Matter - Materials Science
Abstract

Phonon energies at finite temperatures shift away from their harmonic values due to anharmonicity. In this paper, we have realized the rigorous calculation of phonon energy shifts of silicon by three and four-phonon scattering from first principles. The anharmonic fourth-order force constants are calculated by considering up to the fifth nearest neighbors. The results agree reasonably well with available data from inelastic neutron scattering throughout the Brillouin zone. Surprisingly, the frequency shifts of optical phonon modes near the $\Gamma$ point are sensitive to the cutoff radius of the fourth-order force constants, in contrast to the four-phonon scattering rates, which nearly saturate when considering the second nearest neighbors. We have also compared the results with ab initio molecular dynamics simulations and found that the higher order of anharmonicity is important for optical phonons. Our work provides critical insight into the anharmonic phonon frequency shift and will have significant impact on the thermal and optical applications.

Published
2018
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224. Circular-shift Linear Network Codes with Arbitrary Odd Block Lengths

Author

Sun, Qifu Tyler, Tang, Hanqi, Li, Zongpeng, Yang, Xiaolong, and Long, Keping

Subjects
Computer Science - Information Theory
Abstract

Circular-shift linear network coding (LNC) is a class of vector LNC with low encoding and decoding complexities, and with local encoding kernels chosen from cyclic permutation matrices. When $L$ is a prime with primitive root $2$, it was recently shown that a scalar linear solution over GF($2^{L-1}$) induces an $L$-dimensional circular-shift linear solution at rate $(L-1)/L$. In this work, we prove that for arbitrary odd $L$, every scalar linear solution over GF($2^{m_L}$), where $m_L$ refers to the multiplicative order of $2$ modulo $L$, can induce an $L$-dimensional circular-shift linear solution at a certain rate. Based on the generalized connection, we further prove that for such $L$ with $m_L$ beyond a threshold, every multicast network has an $L$-dimensional circular-shift linear solution at rate $\phi(L)/L$, where $\phi(L)$ is the Euler's totient function of $L$. An efficient algorithm for constructing such a solution is designed. Finally, we prove that every multicast network is asymptotically circular-shift linearly solvable.

Published
2018
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