| 1. |
- Bera, Sudarsan, et al.
(författare)
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Thermodynamics and Microphysics Relation During CAIPEEX-I
- 2019
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Ingår i: Pure and Applied Geophysics. - : Springer Science and Business Media LLC. - 0033-4553 .- 1420-9136. ; 176:1, s. 371-388
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Tidskriftsartikel (refereegranskat)abstract
- Influence of the environmental thermodynamics on the microphysics of deep cumulus clouds over different parts of India is studied using in situ airborne observations from the Cloud Aerosol Interaction and Precipitation Enhancement EXperiment (CAIPEEX) during 2009. This study provides an understanding of the thermodynamics–microphysics relation over the Indian summer-monsoon region. Relatively stronger updraft and turbulence are noted in the pre-monsoon cloud base layers compared to that of the monsoon clouds. It is illustrated from the in situ observations as well as from a microphysical parcel model that the vertical variation of cloud droplet number concentration (CDNC) has a well-defined peak at a certain height above the cloud base. This elevated CDNC peak is found to be connected with the cloud parcel buoyancy and cumulative convective available potential energy (cCAPE). Higher parcel buoyancy above the cloud base of dry pre-monsoon clouds is associated with stronger in-cloud updraft velocity, higher supersaturation and higher droplet number concentration (in addition to aerosol effect). Higher adiabatic fraction and lower entrainment rate are observed in polluted clouds where boundary layer moisture is low, compared to clean clouds. Relative dispersion of droplet size distribution is found to vary concurrently with air mass characteristics and aerosol number concentration observed over different locations during the experiment. Aerosol–precipitation relationships are also investigated from the observation. Maximum reflectivity and rain rates showed a direct link with boundary layer water vapor content rather than with subcloud aerosol number concentration.
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| 2. |
- Jayakumar, O. D., et al.
(författare)
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1D Morphology Stabilization and Enhanced Magnetic Properties of Co : ZnO Nanostructures on Codoping with Li: A Template-Free Synthesis
- 2009
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Ingår i: Crystal Growth & Design. - : American Chemical Society (ACS). - 1528-7483 .- 1528-7505. ; 9:10, s. 4450-4455
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Tidskriftsartikel (refereegranskat)abstract
- ID natiostructures of Zn1-xCoxO (x = 0, 0.03 and 0.05) and Co and Li codoped ZnO (Zn0.85Li0.10Co0.05O) were prepared by a soft chemical method. We report a very interesting observation of morphological control and transformation of ZnO nanorods to spherical particles induced by Co substitution. It is also remarkable to note that the morphology completely reverts back to rod shape by Li incorporation. In addition to this unusual observation, the Li incorporation enhances the room-temperature ferromagnetic (RTFM) properties. These experimental observations are well-supported by theory work as well. These results are significant, as the I D RTFM will have implications in spintronic devices.
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| 3. |
- Jayakumar, O. D., et al.
(författare)
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Tunable Ferromagnetism accompanied by Morphology Control in Li-doped Zn0.97Ni0.03O
- 2010
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 114:41, s. 17428-17433
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Tidskriftsartikel (refereegranskat)abstract
- We report morphological and ferromagnetic property control in ZnO nanorod structures by an optimum doping of Ni and Li. Nanostructures of Zn0.97-xNi0.03LixO (x = 0, 0.03, 0.05, 0.08, and 0.10) are prepared by a solvothermal method. High aspect ratio (5-15) ZnO nanorods transform to particles (with 1-3 aspect ratio) influenced by 3 at. % Ni substitution in ZnO (Zn0.97Ni0.03O). It is remarkable to note that the Zn1.97Ni0.03O particles completely retain the nanorod shape with significantly increased aspect ratio (15-30) when 3 at.c/a Li ions are codoped in (Zn0.99Li0.03Ni0.30O). Li substitution tits enhances ferromagnetism with largest magnetization (0.8 emu.g(-1)) observed for Zn0.94Li0.03Ni0.03O. For Li concentration >3 at.%, the aspect ratio as well as the magnetization decreased considerably. These experimental observations are explained by first-principles modeling. At low Li-on-Zn acceptor concentrations, the total magnetization is increased by lower Ni d-state populations, whereas at higher Li concentrations the population of ZnO host states decreases the ferromagnetism by induced magnetic moments on the oxygens. We discuss the significant implications of these results on the nanorods structures of room temperature ferromagnetic materials, which are expected to play pivotal role in developing spintronic devices.
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| 4. |
- Persson, Clas, et al.
(författare)
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Morphology and Magnetic Coupling in ZnO:Co and ZnO:Ni Co-Doped with Li
- 2011
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Ingår i: Acta Physica Polonica. A. - 0587-4246 .- 1898-794X. ; 119:2, s. 95-98
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Tidskriftsartikel (refereegranskat)abstract
- Zn0.95Co0.05O and Zn0.97Ni0.03O nanorods, prepared by a solvothermal method, show intriguing morphology and magnetic properties when co-doped with Li. At low and moderate Li incorporation (below 10 and 3 at.% Li in the Co- and Ni-doped samples, respectively) the rod aspect ratio is increased and room temperature ferromagnetic properties are enhanced, whereas the ferromagnetic coupling in Zn0.97Ni0.03O is decreased for Li concentrations > 3 at.%. First-principles theoretical analyses demonstrate that Li co-doping has primarily two effect 3 in bulk Zn1-xMxO (with M = Co or Ni). First, the Li-on-Zn acceptors increase the local magnetic moment by depopulating the M 3d minority spin-states. The magnetic coupling is Ruderman-Kittel-Kasuya-Yosida-like both without and with Li co-doping. Second, Li-on-Zn prefer to be close to the M atoms to compensate the M-O bonds and to locally depopulate the 3d states, and this will help forming high aspect nanostructures. The observed room temperature ferromagnetism in Li co-doped Zn1-xMxO nanorods can therefore be explained by the better rod morphology in combination with ionizing the magnetic M atoms.
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