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A Comparative Study on the Self Diffusion of N-Octadecane with Crystal and Amorphous Structure by Molecular Dynamics Simulation
RAO Zhong-Hao, LIU Xin-Jian, ZHANG Rui-Kai, LI Xiang, WEI Chang-Xing, WANG Hao-Dong, LI Yi-Min
Chin. Phys. Lett. 2014, 31 (1):
010501
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DOI: 10.1088/0256-307X/31/1/010501
The straight chain n-alkanes and their mixture, which can be used as phase change materials (PCM) for thermal energy storage, have attracted much attention in recent years. We employ the molecular dynamics (MD) simulation to investigate their thermophysical properties, including self diffusion and melting of n-octadecane with crystal and amorphous structures. Our results show that, although the initial and melted structures of n-octadecane with crystal and amorphous are different, the melting behaviors of n-octadecane judged by the self diffusion behavior are consistent. The MD simulation indicates that both the crystal and amorphous structures are effective for the property investigation of n-octadecane and the simulated conclusion can be used as reference for modeling the alkanes-based PCM system.
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State Transition Induced by Self-Steepening and Self Phase-Modulation
HE Jing-Song, XU Shu-Wei, M. S. Ruderman, R. Erdélyi
Chin. Phys. Lett. 2014, 31 (1):
010502
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DOI: 10.1088/0256-307X/31/1/010502
We present a rational solution for a mixed nonlinear Schr?dinger (MNLS) equation. This solution has two free parameters, a and b, representing the contributions of self-steepening and self phase-modulation (SPM) of an associated physical system, respectively. It describes five soliton states: a paired bright-bright soliton, a single soliton, a paired bright-grey soliton, a paired bright-black soliton, and a rogue wave state. We show that the transition among these five states is induced by self-steepening and SPM through tuning the values of a and b. This is a unique and potentially fundamentally important phenomenon in a physical system described by the MNLS equation.
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Methodological Study on AMS Measurement of U Isotope Ratios in Nanogram U Samples
DONG Ke-Jun, WANG Chen, HE Ming, LIN De-Yu, ZHAO Xing-Hong, LI Li-Li, ZHAO Yong-Gang, DOU Liang, XIE Lin-Bo, WU Shao-Yong, YIN Xin-Yi, WANG Xiang-Gao, SHEN Hong-Tao, YOU Qu-Bo, JIANG Shan
Chin. Phys. Lett. 2014, 31 (1):
010701
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DOI: 10.1088/0256-307X/31/1/010701
The determination of uranium isotopic composition in trace samples is important in different fields. A new measurement method that uses an accelerator mass spectrometry (AMS) technique has been developed for the analysis of uranium isotopic ratios in ultra-trace uranium samples at the China Institute of Atomic Energy. As a result, about 5-nanogram level uranium samples analyzed with AMS is achieved.
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Enhanced Correlation of Electron-Positron Pair in Two and Three Dimensions
TANG Suo, XIE Bai-Song, WANG Hong-Yu, LIU Jie, FU Li-Bin, YU Ming-Young
Chin. Phys. Lett. 2014, 31 (1):
011203
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DOI: 10.1088/0256-307X/31/1/011203
Early time electron-positron correlation in vacuum pair-production in an external field is investigated. The entangled electron and positron wave functions are obtained analytically in the configuration and momentum spaces. It is shown that, relative to that of the one-dimensional theory, two- and three-dimensional calculations yield enhanced spatial correlation and broadened momentum spectra. In fact, at early times the electron and positron almost coincide spatially. The correlation also depends on the direction of the applied field. For the spatial correlation, the transverse correlation is stronger than the longitudinal correlation.
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Three-Body Calculation of the 4He(3H,γ)7Li and 4He(3He,γ)7Be Reactions and Structure of the 7Li and 7Be at Solar Energies
H. Sadeghi, H. Khalili
Chin. Phys. Lett. 2014, 31 (1):
012101
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DOI: 10.1088/0256-307X/31/1/012101
The two 3H+4He and 3He+4He fusion reactions at low energies are usually viewed as an approximate external capture process. We study the 4He(3H,γ)7Li and 4He(3He,γ)7Be reactions in a cluster model, which can take into account two- and three-body electromagnetic currents, using minimal substitution in the explicit momentum dependence of the two- and three-cluster interactions. Our main goal is to explore how the cross section of the low-energy 3H+4He or 3He+4He capture reactions depends on energy. The astrophysical S-factors for these reactions are calculated at very low energies. We construct the conserved realistic Argonne v18 for two nucleons and Urbana IX or Tucson-Melbourne three-cluster interactions, which are considered for calculation. We also calculate the binding energies and the structural properties of 3H+4He or 3He+4He systems. The binding energies are found to be ?37.72 (?36.32) MeV and ?39.35 (?37.43) MeV, with (without) three-body interactions for 7Be and 7Li, in satisfactory agreement with other theoretical results and experimental data, respectively.
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Broadband Optical Active Waveguides Written by Femtosecond Laser Pulses in Lithium Fluoride
Ismael Chiamenti, Francesca Bonfigli, Anderson S. L. Gomes, Rosa Maria Montereali, Larissa N. da Costa, Hypolito J. Kalinowski
Chin. Phys. Lett. 2014, 31 (1):
014201
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DOI: 10.1088/0256-307X/31/1/014201
Broadband waveguiding through light-emitting strips directly written in a blank lithium fluoride crystal with a femtosecond laser is reported. Light guiding was observed at several optical wavelengths, from blue, 458 nm, to near-infrared, at 1550 nm. Visible photoluminescence spectra of the optically active F2 and F3+ color centers produced by the fs laser writing process were measured. The wavelength-dependent refractive index increase was estimated to be in the order of 10?3–10?4 in the visible and near-infrared spectral intervals, which is consistent with the stable formation of point defects in LiF.
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Mobility Enhancement and Gate-Induced-Drain-Leakage Analysis of Strained-SiGe Channel p-MOSFETs with Higher-κ LaLuO3 Gate Dielectric
YU Wen-Jie, ZHANG Bo, LIU Chang, XUE Zhong-Ying, CHEN Ming, ZHAO Qing-Tai
Chin. Phys. Lett. 2014, 31 (1):
016101
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DOI: 10.1088/0256-307X/31/1/016101
A strained-SiGe p-channel metal-oxide-semiconductor-field-effect transistors (p-MOSFETS) with higher-κ LaLuO3 gate dielectric was fabricated and electrically characterized. The novel higher-κ (κ~30) gate dielectric, LaLuO3, was deposited by molecular-beam deposition and shows good quality for integration into the transistor. The transistor features good output and transfer characteristics. The hole mobility was extracted by the splitting C–V method and a value of 200 cm2/V?s was obtained for strong inversion conditions, which indicates that the hole mobility is well enhanced by SiGe channel and that the LaLuO3 layer does not induce additional significant carrier scattering. Gate induced drain leakage is measured and analyzed by using an analytical model. Band-to-band tunneling efficiencies under high and low fields are found to be different, and the tunneling mechanism is discussed.
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Correlation of Lithium Ionic Diffusion with Nb Concentration in Li7?xLa3Zr2?xNbxO12 Evaluated by an Internal Friction Method
XIA Yu, WANG Xian-Ping, GAO Yun-Xia, HU Jing, ZHUANG Zhong, GUO Li-Jun, FANG Qian-Feng, LIU Chang-Song
Chin. Phys. Lett. 2014, 31 (1):
016201
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DOI: 10.1088/0256-307X/31/1/016201
Solid lithium-ion conductors Li7?xLa3Zr2?xNbxO12 (x=0.25, 0.5, 1, 1.5) with cubic garnet structure are successfully prepared by a solid state reaction method, and the effects of Nb concentration on lithium ion diffusion are investigated by means of internal friction (IF) technique. A prominent relaxation-type IF peak (actually composed of two components) is observed in each Nb doped Li7La3Zr2O12 compound: with apeak PL at lower temperature and a peak PH at higher temperature. The mechanisms of the two components are suggested to be associated with two diffusion processes of lithium ions via vacancies: 48g?48g and 48g?24 d. The relaxational strength of the IF peak gradually decreases, which is accompanied by the activation energy increasing from 0.45 eV to 0.64 eV with the increasing Nb doping level. The corresponding mechanism is ascribed to originate from lattice contraction as well as the lower concentration of diffusion ions induced by the substitution of Zr4+ by Nb5+.
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Trapping Behavior of He in Ti Revisited by ab initio Calculations
WAN Chu-Bin, ZHOU Xiao-Song, LI Shi-Na, ZHANG Hui-Jun, LIANG Jian-Hua, PENG Shu-Ming, JU Xin
Chin. Phys. Lett. 2014, 31 (1):
017102
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DOI: 10.1088/0256-307X/31/1/017102
We report a detailed ab initio study of the trapping behavior of interstitial helium atoms (IHAs) in hcp Ti. The tetrahedral interstitial site for one He is confirmed to be the most stable IHA configuration, but the most favorable interstitial site comprises two adjacent octahedral sites for two helium atoms. The octahedral IHA can trap another IHA regardless of the site where it is initially located, whereas the tetrahedral IHA cannot. Hybridization among the different states is responsible for the stable order, which has significant implications for He clustering and bubble nucleation that can affect material performance in future fusion reactors. These results provide the basis for the development of improved atomistic models.
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Direct Observation of High-Temperature Superconductivity in One-Unit-Cell FeSe Films
ZHANG Wen-Hao, SUN Yi, ZHANG Jin-Song, LI Fang-Sen, GUO Ming-Hua, ZHAO Yan-Fei, ZHANG Hui-Min, PENG Jun-Ping, XING Ying, WANG Hui-Chao, FUJITA Takeshi, HIRATA Akihiko, LI Zhi, DING Hao, TANG Chen-Jia, WANG Meng, WANG Qing-Yan, HE Ke, JI Shuai-Hua, CHEN Xi, WANG Jun-Feng, XIA Zheng-Cai, LI Liang, WANG Ya-Yu, WANG Jian, WANG Li-Li, CHEN Ming-Wei, XUE Qi-Kun, MA Xu-Cun
Chin. Phys. Lett. 2014, 31 (1):
017401
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DOI: 10.1088/0256-307X/31/1/017401
We prepared one-unit-cell (1-UC) thick FeSe films on insulating SrTiO3 substrates with non-superconducting FeTe protection layers by molecular beam epitaxy for ex situ studies. By direct transport and magnetic measurements, we provide definitive evidence for high temperature superconductivity in the 1-UC FeSe films with an onset TC above 40 K and an extremely large critical current density JC∼1.7×106 A/cm2 at 2 K, which are much higher than TC∼8 K and JC∼104 A/cm2 for bulk FeSe, respectively. Our work may pave the way to enhancing and tailoring superconductivity by interface engineering.
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Strain Induced Metastable Phase and Phase Revolution in PbTiO3-CoFe2O4 Nanocomposite Film
HU Chuan-Sheng, LUO Zhen-Lin, SUN Xia, PAN Guo-Qiang, HE Qing, WEN Wen, ZHOU Xing-Tai, Ichiro Takeuchi, GAO Chen
Chin. Phys. Lett. 2014, 31 (1):
017701
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DOI: 10.1088/0256-307X/31/1/017701
An inter-component epitaxial strain-induced PbTiO3 metastable phase is observed in a PbTiO3-CoFe2O4 epitaxial composite film, corresponding to the dielectric anomaly reported previously. High-resolution synchrotron radiation X-ray diffraction and first principles calculation demonstrate the coexistence of different PbTiO3 phases, even a possible morphotropic phase boundary in the film, elucidating the underlying microscopic mechanism of the formation of PbTiO3 metastable phase. This sheds light on the design and manipulation of electromechanical properties of epitaxial films, through the strain engineering.
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Near-Field Enhancement and Absorption Properties of Metal-Dielectric-Metal Microcavities in the Mid-Infrared Range
HENG Hang, YANG Li, YE Yong-Hong
Chin. Phys. Lett. 2014, 31 (1):
018101
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DOI: 10.1088/0256-307X/31/1/018101
An important property of optical metamaterials is the ability to concentrate light into extremely tiny volumes, so as to enhance their interaction with quantum objects. In this work, we numerically study the near-field enhancement and absorption properties inside the cylindrical microcavities formed by a Au-GaAs-Au sandwiched structure. At normal incidence, the obtained reflection spectra show that the resonance wavelength of microcavities operates in the range of 5–5.8 μm. We also calculate the contrast C (C=1?Rmin), which can be increased to 97% by optimizing the structure's geometry parameters. Moreover, we demonstrate that the multilayer structure with sub-wavelength electromagnetic confinement allows 103–104-fold enhancement of the electromagnetic energy density inside the cavities, which contains the most energy of the incident electromagnetic radiation and has a higher quality factor Q, indicating a narrower linewidth for surface enhanced molecular absorption spectroscopy and the tracking of characteristic molecular vibrational modes in the mid-infrared region. The structure is insensitive to the polarization of the incident wave due to the symmetry of the cylindrical microcavities. The unique properties of the metal-dielectric-metal metamaterials will have potential applications in new plasmonic detectors, bio-sensing and solar cells, etc.
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47 articles
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