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RISS 인기검색어
- 검색키워드
- 저자 : Biswajit Choudhury (검색결과 4 건)
- 무료
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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.
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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.
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Bird community of Rajiv Gandhi Orang National Park, Assam
Biswajit Chakdar,Hilloljyoti Singha,Manabendra Ray Choudhury 국립중앙과학관 2019 Journal of Asia-Pacific Biodiversity Vol.12 No.4
A total of 284 species of birds have been recorded in Rajiv Gandhi Orang National Park during fieldsurveys carried out in 2013-2016 and records from previous observers. This includes five Critically Endangered(Baer’s pochard Aythya baeri, Bengal florican Houbaropsis bengalensis, Red-headed vultureSarcogyps calvus, White-rumped vulture Gyps bengalensis, and Slender-billed vulture Gyps tenuirostris),five Endangered (Greater adjutant Leptoptilos dubius, Egyptian vulture Neophron percnopterus, Steppeeagle Aquila nipalensis, Pallas’s fish eagle Haliaeetus leucoryphus, and Long-tailed grass babbler Laticillacinerascens), 10 Vulnerable (Common pochard Aythya ferina, Lesser adjutant Leptoptilos javanicus, Woollynecked stork Ciconia episcopus, Indian spotted eagle Clanga hastata, Greater spotted eagle Clanga clanga,Finn’s weaver Ploceus megarhynchus, Bristled grassbird Chaetornis striata, Marsh babbler Pellorneumpalustre, Swamp francolin Francolinus gularis, and Slender-billed babbler Chatarrhaea longirostris), and 17Near Threatened birds. Siltation of wetlands, proliferation of Bombax ceiba, and invasive alien plantspecies are the major threats to the avifauna of the park.
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Conservation status of some endangered mammals in Barak Valley, Northeast India
Nazimur Rahman Talukdar,Biswajit Singh,Parthankar Choudhury 국립중앙과학관 2018 Journal of Asia-Pacific Biodiversity Vol.11 No.2
From the ancient time, the Northeast part of India is rich in biodiversity because of its diverse topographic, climatic features. Different varieties of mammalian, avian, and herpetofauna are endemic to this region. Unfortunately, life of this diverse flora and fauna is in jeopardy due to serious anthropogenic pressure. Once a large number of globally important species sustained in the Barak Valley. However, with the increasing population and subsequent demand on natural resources and developing activities, many of the species are no more found in the valley. If the conservation action is not initiated, the remaining species will also vanish with time. This article highlights the distribution and conservation problems of four endangered species in the Barak Valley of Assam, India and recommended conservation tactics.
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