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Pietzsch A.,Helmholtz Center Berlin | Nisar J.,Pakistan Atomic Energy Commission PAEC | Jamstorp E.,Paul Scherrer Institute | Grasjo J.,Uppsala University | And 3 more authors.
Journal of Electron Spectroscopy and Related Phenomena | Year: 2015

By combining X-ray absorption spectroscopy and first principles calculations we have determined the electronic structure of synthetic and natural kaolinite as a model system for engineered and natural clay materials. We have analyzed defect states in the band gap and find that both natural and synthetic kaolinite contain defects where oxygen replaces hydrogen in one of the Al (0 0 1)-hydroxyl groups of the kaolinite clay sheets. The band gap of both synthetic and natural kaolinite is found to decrease by about 3.2 eV as this defect is formed. © 2015 Elsevier B.V. All rights reserved. Source

Akhtar N.,Pakistan Institute of Nuclear Science and Technology | Akhtar N.,Pakistan Institute of Engineering and Applied Sciences | Mahmood S.,Pakistan Institute of Nuclear Science and Technology | Mahmood S.,Pakistan Institute of Engineering and Applied Sciences | And 2 more authors.
Plasma Physics and Controlled Fusion | Year: 2014

The modulational instability and envelope solitons of ion acoustic waves in an unmagnetized nonthermal electron-positron-ion (epi) plasma are investigated. The ions are taken to be dynamic and warm while electrons and positrons are assumed to be inertialess and hot which follow the kappa (or Generalized Lorentzian) distribution. The Krylov-Bogoliubov-Mitropolsky method is used to derive the nonlinear Schrödinger equation for nonlinear amplitude modulation of ion acoustic waves in nonthermal epi plasmas with warm ions. The dispersive and nonlinear coefficients are obtained for ion acoustic waves in nonthermal epi plasmas which depend on spectral indices of kappa distributed electrons and positrons, ion temperature and positron density. The modulationally stable and unstable regions are studied for a wide range of wave numbers and it is found that the finite ion temperature, positron density and spectral indices of kappa distributed electrons and positrons play a significant role in the formation of bright and dark envelope solitons in nonthermal epi plasmas with adiabatically heated ions. Our findings are applicable to explain some aspects of nonlinear propagation of envelope solitons in astrophysical plasma situations such as neutron stars or pulsars where nonthermal epi plasmas with warm ions can exist (Arons J 2009 Astrophys. Space Sci. Library 357 373, Blasi P and Amato E 2011 Astrophys. Space Sci. Proc. pp 623-41, Asif and Saeed 2011 Plasma Phys. Control. Fusion 53 095006). © 2014 IOP Publishing Ltd. Source

Rafique J.,Harbin Institute of Technology | Yu J.,Harbin Institute of Technology | Zha X.,Harbin Institute of Technology | Rafique K.,Pakistan Atomic Energy Commission PAEC
Bulletin of Materials Science | Year: 2010

Ultra thin and aligned carbon nanofibres (CNFs) have been fabricated by heat treatment from aligned polyacrylonitrile (PAN) nanofibre precursors prepared by electrospinning. The alignment of the precursor nanofibres was achieved by using a modified electrospinning set up developed recently, where a tip collector was used to collect and align the nanofibres. The average diameter of the aligned CNFs is about 80 nm. The stabilization and carbonization behaviour were studied mainly based on the randomly oriented PAN nanofibres. The effects of stabilization and carbonization temperatures, temperature-increasing rates, and with and without substrates on the morphology and structure of the CNFs were investigated. Fourier transform infrared spectroscopy, scanning electron microscopy, X-ray diffraction, transmission electron microscopy and Raman spectroscopy were used to characterize the structure of the CNFs and thermogravimetric/ differential temperature analysis was used to evaluate the thermal behaviour of PAN nanofibres. © Indian Academy of Sciences. Source

Wang B.,KTH Royal Institute of Technology | Kanhere P.D.,Nanyang Technological University | Chen Z.,Nanyang Technological University | Nisar J.,Pakistan Atomic Energy Commission PAEC | And 4 more authors.
Journal of Physical Chemistry C | Year: 2013

In this paper, we have employed DFT and HSE06 methods to study the doping effects on the NaTaO3 photocatalyst. N, S, C, and P monodoping and N-N, C-S, P-P, and N-P codoping have been studied. The redopants' formation energies have been calculated, and we find S monodoping is energetically more favorable than any other elemental doping. The mechanism of anion doping on the electronic properties of NaTaO3 is discussed. We find the band gap reduces significantly if we dope with anionic elements whose p orbital energy is higher than the O 2p orbitals. N and S can shift the valence band edge upward without losing the ability to split water into H2 and O2. Double-hole-mediated codoping can decrease the band gap significantly. On the basis of our calculations, codoping with N-N, C-S, and P-P could absorb visible light. However, they can only decompose water into H2 when the valence band edge is above the water oxidation level. © 2013 American Chemical Society. Source

Arif A.,National Institute for Biotechnology and Genetic Engineering NIBGE | Zafar Y.,Pakistan Atomic Energy Commission PAEC | Arif M.,National Institute for Biotechnology and Genetic Engineering NIBGE | Blumwald E.,University of California at Davis
Molecular Biotechnology | Year: 2013

An increasing volume of evidence indicating the mechanisms of drought tolerance of AVP1-overexpressing transgenic plants has been reported. In the present study, we are reporting the experiments conducted for the drought tolerance of AVP1 overexpressing plants and WT tobacco plants in three water regimes named as "fully watered," "less-watered," and "desiccated". Results suggest that AVP1 plants exhibited greater vigor and drought tolerance in quantitative terms i.e., increase in size and weight of shoots and capsules. AVP1 plants produced more seeds than WT across all three water regimes. The less-watered regime was found to produce the greatest contrast. AVP1 overexpression enhanced solute accumulation in vacuoles resulting in an increase in water retention and turgor of the cell. The ultrastructure study of AVP1 overexpressing cells and WT leaf cells revealed that AVP1 plants displayed more turgid and hyperosmotic cells than WT. Moreover, guard cells in the AVP1 plants exhibited thick cell walls, few vacuoles, and deep and close stomata, whereas WT plants showed larger vacuoles and relatively open stomata aperture with no significant difference in size and number of the cells per unit area. © 2012 Springer Science+Business Media, LLC. Source

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