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  • 1
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    Portable microwave frequency dissemination in free space and implications on ground-to-satellite synchronization (2015)
    American Institute of Physics (AIP)
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    Publication Date: 2015-05-19
    Description: Frequency dissemination and synchronization in free space play an important role in global navigation satellite system, radio astronomy, and synthetic aperture radar. In this paper, we demonstrated a portable radio frequency dissemination scheme via free space using microwave antennas. The setup has a good environment adaptability and high dissemination stability. The frequency signal was disseminated at different distances ranging from 10 to 640 m with a fixed 10 Hz locking bandwidth, and the scaling law of dissemination stability on distance and averaging time was discussed. The preliminary extrapolation shows that the dissemination stability may reach 1 × 10 −12 /s in ground-to-satellite synchronization, which far exceeds all present methods, and is worthy for further study.
    Print ISSN: 0034-6748
    Electronic ISSN: 1089-7623
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Published by American Institute of Physics (AIP)
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  • 2
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    Magnetization reversal and coercivity of Fe3Se4 nanowire arrays (2015)
    American Institute of Physics (AIP)
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    Publication Date: 2015-02-14
    Description: The microstructure and magnetic properties of Fe 3 Se 4 nanowire (NW) arrays in anodic aluminum oxide (AAO) porous membrane are studied. Cross-sectional SEM and plane-view TEM images show that the mean wire diameter ( d w ) and the center-to-center spacing ( D ) of Fe 3 Se 4 nanowires are about 220 nm and 330 nm, respectively. The field-cooled magnetization dependent on the temperature indicates a Curie temperature around 334 K for the Fe 3 Se 4 nanowires. The coercivities of Fe 3 Se 4 nanowires at 10 K, obtained from the in-plane and out-of-plane hysteresis loops, are as high as 22.4 kOe and 23.3 kOe, which can be understood from the magnetocrystalline anisotropy and the magnetization reversal process.
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 3
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    Communication: Non-monotonic evolution of dynamical heterogeneity in unfreezing process of metallic glasses (2015)
    American Institute of Physics (AIP)
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    Publication Date: 2015-07-30
    Description: The relaxation dynamics in unfreezing process of metallic glasses is investigated by the activation-relaxation technique. A non-monotonic dynamical microstructural heterogeneities evolution with temperature is discovered, which confirms and supplies more features to flow units concept of glasses. A flow unit perspective is proposed to microscopically describe this non-monotonic evolution of the dynamical heterogeneities as well as its relationship with the deformation mode development of metallic glasses.
    Print ISSN: 0021-9606
    Electronic ISSN: 1089-7690
    Topics: Chemistry and Pharmacology , Physics
    Published by American Institute of Physics (AIP)
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  • 4
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    Abnormal magnetic ordering and ferromagnetism in perovskite ScMnO3 film (2015)
    American Institute of Physics (AIP)
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    Publication Date: 2015-06-13
    Description: Bulk multiferroic ScMnO 3 is the stable hexagonal phase, and it is very difficult to prepare its perovskite orthorhombic phase even under high pressure. We fabricated the orthorhombic ScMnO 3 thin film by pulsed laser deposition through suitable substrate LaAlO 3 and found that nano-scale twin-like domains are naturally formed in the thin film. Magnetic properties of the orthorhombic ScMnO 3 thin films show that, besides normal antiferromagnetic ordering at 47 K, an anomalous magnetic transition occurs at 27 K for 60 nm film and at 36 K for 150 nm film only along the c-axis, which is absent in the ab-plane. Moreover, the second magnetic transition for both films is suppressed when the applied field increases from 1 kOe to 10 kOe. In addition, the ferromagnetism shows up in both films at 10 K, and saturation magnetization increases dramatically in 60 nm film compared with 150 nm film. We propose that the second magnetic transition might be more of lattice strain effect and also related to magnetism-induced ferroelectric polarization in orthorhombic RMnO 3 thin films and low-temperature ferromagnetic properties in our films originate from the nano-scale twin-like domain structure.
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 5
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    Oxygen vacancy formation, crystal structures, and magnetic properties of three SrMnO3−δ films (2016)
    American Institute of Physics (AIP)
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    Publication Date: 2016-08-05
    Description: The crystal structures and magnetic properties of the 40 nm brownmillerite SrMnO 2.5 film, perovskite SrMnO 3-δ film, and mixed-phase film have been systematically investigated. The features of the oxygen vacancy ordering superstructure in the brownmillerite SrMnO 2.5 film are observed from HRSTEM as follows: the dark stripes with a periodicity of four (110) planes of the cubic perovskite appearing at an angle of 45° with the substrate-film interface and extra reflection spots in fast Fourier transformation patterns along the (001) plane. When annealing the brownmillerite SrMnO 2.5 film under higher oxygen pressure, the top portion undergoes structure transition into perovskite SrMnO 3-δ as seen in the mixed-phase film consisting of the perovskite SrMnO 3-δ phase dominating at the top part and the brownmillerite SrMnO 2.5 phase dominating at the bottom part. The magnetic properties and Mn valences of the brownmillerite SrMnO 2.5 film indicate that this film, similar to the bulk, is antiferromagnetic with T N at 375 K. However, the strained tetragonal perovskite SrMnO 3-δ film exhibits ferromagnetic behavior with Curie temperature at 75 K and a saturation magnetization of 2.5μ B /Mn at 2 K. Moreover, the top perovskite SrMnO 3-δ phase of the mixed-phase film also exhibits ferromagnetic behavior evidenced by the existence of the exchange bias. We propose that the ferromagnetic properties in both the perovskite SrMnO 3-δ film and the top perovskite SrMnO 3-δ phase in the mixed-phase film originate from Mn 3+ –Mn 4+ double exchange coupling. However, the formation of Mn 3+ differs for the two samples in that it is caused by oxygen vacancies in the former and the distribution of oxygen content across the film during annealing in the latter.
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 6
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    Structural signatures evidenced in dynamic crossover phenomena in metallic glass-forming liquids (2016)
    American Institute of Physics (AIP)
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    Publication Date: 2016-05-27
    Description: Molecular dynamics simulations were performed to investigate dynamic evolution in metallic glass-forming liquids during quenching from high temperature above melting point down to supercooled region. Two crossover temperatures T A and T S ( T A  〉  T S ) are identified, and their physical meanings are clarified. T A and T S are found to be not only the sign of dynamic crossover phenomena but also the manifestation of two key structure correlation lengths ξ s . As temperature decreases below T A , ξ s goes beyond the nearest-neighbor distance, resulting in the Arrhenius-to-non-Arrhenius transition of structural relaxation time and the failure of Stokes-Einstein (SE) relation. As T S is traversed, the increase rate of ξ s reaches the maximum, leading to the simultaneous appearance of dynamical heterogeneity and fractional SE relation. It is further found that structure correlation increases much faster than dynamic correlation, playing a role of structural precursor for dynamic evolution in liquids. Thus, a structural link is established for deeper understanding dynamic crossover phenomena.
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 7
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    Revealing flow behaviors of metallic glass based on activation of flow units (2016)
    American Institute of Physics (AIP)
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    Publication Date: 2016-05-27
    Description: Atomic level flow plays a critical role in the mechanical behavior of metallic glass (MG) while the connection between the flow and the heterogeneous microstructure of the glass remains unclear. We describe the heterogeneity of MGs as the elastic matrix with “inclusions” of nano-scale liquid-like flow units, and the plastic flow behavior of MGs is considered to be accommodated by the flow units. We show that the model can explain the various deformation behaviors, the transformation from inhomogeneous deformation to homogeneous flow upon strain rate or temperature, and the deformation map in MGs, which might provide insights into the flow mechanisms in glasses and inspiration for improving the plasticity of MGs.
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
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  • 8
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    Effect of dynamical heterogeneity on heat capacity at glass transition in typical silicate glasses (2015)
    American Institute of Physics (AIP)
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    Publication Date: 2015-12-30
    Description: The heat capacity jump ΔC p at glass transition and the dynamical heterogeneity are two of the most important features of glass forming liquids. In order to reveal the intrinsic relationship between the two properties, a model glass system (Na 2 O) x (SiO 2 ) 1−x (x = 0.2–0.35) was studied by the systematic measurements of the ΔC p and the mechanical relaxation in the supercooled liquid region. A linear increase in ΔC p with increasing content of Na 2 O was found, indicating direct contributions of the locally fast dynamics around Na 2 O to ΔC p . This positive correlation between the locally heterogeneous dynamics and ΔC p was further confirmed by the dynamical heterogeneity analyses. Our results might be helpful for understanding the nature of glass transition.
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
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  • 9
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    Evolution of structural and dynamic heterogeneities during elastic to plastic transition in metallic glass (2015)
    American Institute of Physics (AIP)
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    Publication Date: 2015-10-22
    Description: We investigate the evolution of microscopically localized flow under a constant applied strain in apparent elastic region of a prototypical metallic glass (MG). The distribution and evolution of energy barriers and relaxation time spectra of the activated flow units in MG with time are obtained via activation-relaxation method. The results show that the unstable nano-scale liquid-like regions acting as flow units in the glass can be activated by external stress, and their evolution with time shows a crossover from localized activation to cascade as the proportion of the flow units reaches a critical percolation value. The flow unit evolution leads to a mechanical elastic-to-plastic transition or macroscopic plastic flow. A plausible diagram involved in time, stress, and temperature is established to understand the deformations and the flow mechanisms of MGs and could provide insights on the intriguing dilemmas of glassy nature, the flow units, and their correlations with the deformation behaviors in MGs.
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
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  • 10
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    Revealing localized plastic flow in apparent elastic region before yielding in metallic glasses (2015)
    American Institute of Physics (AIP)
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    Publication Date: 2015-12-24
    Description: The microscopically localized flow before yielding in metallic glass (MG) is hard to be detected using conventional mechanical tests due to its extremely slow process with a long time scale and lack of structural information. We present a stress relaxation approach to circumvent the experimental problem and to reveal the evolution of the flow before yielding in MG by detecting the evolution of structural heterogeneity and activation energy barrier spectra of flow units. We report on explicit correlations among dynamical heterogeneities, nanoscale flow units, and yielding, revealing a transition from the microscopically flow to macroscopic yielding in MG.
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
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