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Oxygen vacancy and dopant concentration dependent magnetic properties of Mn doped TiO2 nanoparticle
Biswajit Choudhury,Amarjyoti Choudhury 한국물리학회 2013 Current Applied Physics Vol.13 No.6
Mn doped TiO2 nanoparticles are synthesized by solegel method. Incorporation of Mn shifts the diffraction peak of TiO2 to lower angle. The position and width of the Raman peak and photoluminescence intensity of the doped nanoparticles varies with oxygen vacancy and Mn doping level. The electron spin resonance spectra of the Mn doped TiO2 show peaks at g ¼ 1.99 and 4.39, characteristic of Mn2þ state. Reduction in the emission intensity, on Mn doping, is owing to the increase of nonradiative oxygen vacancy centers. Mn doped TiO2, with 2% Mn, shows ferromagnetic ordering at low applied field. Paramagnetic contribution increases as Mn loading increases to 4% and 6%. Temperature dependent magnetic measurement shows a small kink in the ZFC curve at about 40 K, characteristic of Mn3O4. The ferromagnetic ordering is possibly due to the interaction of the neighboring Mn2þ ions via oxygen vacancy (Fþ center). Increase in Mn concentration increases the fraction of Mn3O4 phase and thereby increases the paramagnetic ordering.
Biswajit Choudhury,Amarjyoti Choudhury 한국물리학회 2013 Current Applied Physics Vol.13 No.1
Doping of Nd distorts the lattice structure of CeO2, increases the lattice strain and expands the lattice. Oxygen vacancies and other ceria related defects contribute to the lattice strain. Shifting and broadening of the F2g Raman peak of doped sample, compared to pure CeO2, is indicative of local structure distortion on doping. Dopant induced enhancement of oxygen vacancies, in the CeO2 lattice, is further confirmed by the generation of a new Raman peak at 543 cm1 that is otherwise absent in the pure one. UVevis spectroscopy gives an understanding of the different types of fef electronic transition of Nd in the crystalline environment of CeO2. Effective band gap of CeO2 reduces upto Nd concentration of 2.5%. The band gap, however, increases at 4% of Nd due to BursteineMoss shift. Photoluminescence intensity of pure CeO2 decreases with Nd concentration owing to the increase in the number of non radiative oxygen vacancies. These vacancies act as luminescence quencher and reduce the emission intensity. Photoluminescence excitation spectra confirm the presence of these oxygen vacancies in the CeO2 nanocrystallites.
WEAK INEQUALITIES WITH CONTROL FUNCTIONS AND FIXED POINT RESULTS
Choudhury, Binayak S. The Korean Society for Computational and Applied M 2010 Journal of applied mathematics & informatics Vol.28 No.3
In recent times control functions have been used in several problems of metric fixed point theory. Also weak inequalities have been considered in a number of works on fixed points in metric spaces. Here we have incorporated a control function in certain weak inequalities. We have established two fixed point theorems for mapping satisfying such inequalities. Our results are supported by examples.
Choudhuri, C.,Young-Han Kim,Mitra, U. IEEE 2013 IEEE transactions on information theory Vol.59 No.6
<P>The problem of state communication over a discrete memoryless channel with discrete memoryless state is studied when the state information is available strictly causally at the encoder. It is shown that block Markov encoding, in which the encoder communicates a description of the state sequence in the previous block by incorporating side information about the state sequence at the decoder, yields the minimum state estimation error. When the same channel is used to send additional independent information at the expense of a higher channel state estimation error, the optimal tradeoff between the rate of the independent information and the state estimation error is characterized via the capacity-distortion function. It is shown that any optimal tradeoff pair can be achieved via rate-splitting. These coding theorems are then extended optimally to the case of causal channel state information at the encoder using the Shannon strategy.</P>
Short and long distance contributions to B→K<sup>∗</sup>γγ
Choudhury, S.R.,Cornell, A.S.,Mahajan, Namit Elsevier 2004 Physics letters: B Vol.580 No.3
<P><B>Abstract</B></P><P>We study the decay of the neutral <I>B</I> meson to K<sup>∗</sup>γγ within the framework of the Standard Model, including long distance contributions.</P>