| 2071. |
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| 2072. |
- Lu, P. F., et al.
(författare)
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Structural properties and energetics of GaAs nanowires
- 2013
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Ingår i: Physica E: Low-Dimensional Systems and Nanostructures. - : Elsevier BV. - 1386-9477. ; 52, s. 34-39
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Tidskriftsartikel (refereegranskat)abstract
- Using the first-principles density functional theory, we have investigated the geometric structure and electronic properties of GaAs nanowires. Compared with bulk GaAs, wurtzite nanowires are found to be more stable over zinc-blende nanowires. A revised cohesive energy is provided based on the influence of different kinds of surface dangling bonds. Our calculation indicates that GaAs nanowires display bistability namely both zinc-blende and wurtzite nanowire will form around 90 A diameters. Furthermore, most GaAs nanowires are found to be semiconducting except for the zinc-blende nanowires. In zinc-blende nanowires it is mainly due to the twofold coordinated atoms associated with the surface state will decrease the band gap. Upon H passivation, these nanowires become semiconducting and the trend of the band gap decreases with the diameter increases.
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| 2073. |
- Lu, P. F., et al.
(författare)
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Vanadium doping on magnetic properties of H-passivated ZnO nanowires
- 2014
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Ingår i: Journal of Materials Science. - : Springer Science and Business Media LLC. - 0022-2461 .- 1573-4803. ; 49:8, s. 3177-3182
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Tidskriftsartikel (refereegranskat)abstract
- A comprehensive theoretical investigation on the electronic and magnetic properties of V-doped and H-passivated ZnO nanowires (NWs) was performed using spin-polarized density functional theory. The magnetic couplings of six configurations of V-doped ZnO NWs are studied in detail and stable ferromagnetism (FM) ordering is found in certain configurations. The FM mechanism originated from the strong hybridization of V 3d and O 2p around the Fermi level. Our results show that the uniaxial strain is an effective method to tune the magnetic properties of this material system. Room temperature ferromagnetism in these V-doped ZnO NWs indicates that these materials have a promising application in nanoscale spintronics.
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| 2074. |
- Lu, San, et al.
(författare)
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Magnetotail reconnection onset caused by electron kinetics with a strong external driver
- 2020
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Ingår i: Nature Communications. - : Springer Nature. - 2041-1723. ; 11:1
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Tidskriftsartikel (refereegranskat)abstract
- Magnetotail reconnection plays a crucial role in explosive energy conversion in geospace. Because of the lack of in-situ spacecraft observations, the onset mechanism of magnetotail reconnection, however, has been controversial for decades. The key question is whether magnetotail reconnection is externally driven to occur first on electron scales or spontaneously arising from an unstable configuration on ion scales. Here, we show, using spacecraft observations and particle-in-cell (PIC) simulations, that magnetotail reconnection starts from electron reconnection in the presence of a strong external driver. Our PIC simulations show that this electron reconnection then develops into ion reconnection. These results provide direct evidence for magnetotail reconnection onset caused by electron kinetics with a strong external driver.
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| 2075. |
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| 2076. |
- Lu, Z., et al.
(författare)
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26.8 m 350 GHz wireless transmission of beyond 100 Gbit/s supported by THz photonics
- 2019
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Ingår i: Asia Communications and Photonics Conference, ACP. - : OSA - The Optical Society.
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Konferensbidrag (refereegranskat)abstract
- A THz photonic wireless communication system with a record transmission of 100.8 Gbit/s over 26.8 m distance operating at 350 GHz is experimentally demonstrated without any THz amplifications. The probabilistic shaped 16-QAM-OFDM and advanced nonlinear digital signal processing routine are employed. Asia Communications and Photonics Conference (ACP).
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| 2077. |
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| 2078. |
- Lundberg, Hans, et al.
(författare)
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New laboratory lifetime measurements of U II for the uranium cosmochronometer
- 2001
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Ingår i: Astronomy & Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 372:3, s. 50-52
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Tidskriftsartikel (refereegranskat)abstract
- We present new measurements of radiative lifetimes for six energy levelsof singly ionized uranium, U II, using laser-induced fluorescencetechnique. One of the levels,5f36d7p6M13/2 at 26191 cm-1,decays by a transition at 3859.6 Å. This line has recently beenobserved in the spectrum of the metal-poor star CS1082-001, the firstdetection of uranium outside the solar system. The lambda 3859 line canbe used as the presently most accurate cosmochronometer (Cayrel et al.cite{Cayrel}). Our value of the lifetime of the6M13/2 level is 18.6+/-0.7 ns, and it confirms thef-value used in the Nature article by Cayrel et al. (cite{Cayrel}),which is based on an experimental lifetime of 20+/-5 ns (Chen &Borzileri cite{Chen}). The new measurement also removes the doubt aboutthe choice between that value and other f-values in the literature,differing by a factor of 3. Adopting the same branching fraction as Chen& Borzileri (cite{Chen}) for the 3859.6 Å line, we derive agf-value of 0.68, which is 8% higher than the value used by Cayrel etal. (cite{Cayrel}). Of significance for the chronometer is also thereduced uncertainty of the radiative lifetime, 4% compared to 25%, andconsequently of the f-value, which should decrease the uncertainty inthe determination of the stellar age considerably.
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| 2079. |
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| 2080. |
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