Ml Sukhadia University

Udaipur, India

Ml Sukhadia University

Udaipur, India

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Singhal R.K.,University of Rajasthan | Singhal R.K.,Brazilian Center for Research in Physics (CBPF) | Kumari P.,University of Rajasthan | Samariya A.,University of Rajasthan | And 4 more authors.
Applied Physics Letters | Year: 2010

This article reports on reversible manipulation of room temperature ferromagnetism (RTFM) in nondoped bulk CeO2. The magnetization measurements establish that paramagnetic CeO2 is driven to a ferromagnetic state, without change in structure, when vacuum annealed at 600 °C. The Ce ions transform from 4+ to 3+ state, accompanied by evolution of oxygen vacancies (VO) during the RTFM transition, as determined by x-ray photoemission. The F+ centers (the electrons in singly occupied oxygen vacancies) play key role in the exchange mechanism. The transition shows complete reversibility where the RTFM is removed by removing the vacancies through re-heating the vacuum-annealed CeO2 in air. © 2010 American Institute of Physics.


Singhal R.K.,University of Rajasthan | Samariya A.,University of Rajasthan | Kumar S.,Ml Sukhadia University | Xing Y.T.,Brazilian Center for Research in Physics (CBPF) | Saitovitch E.,Brazilian Center for Research in Physics (CBPF)
Materials Letters | Year: 2010

Many dilute magnetic semiconductors, when annealed in hydrogen atmosphere, have been reported to show a giant ferromagnetism. The H-induced lattice defects, mainly the oxygen vacancies, have been suggested to mediate this ferromagnetic coupling. We have also observed huge magnetic induction in paramagnetic Co and Fe-doped ZnO systems, upon hydrogenation; however, the re-heating caused this magnetism to vanish quickly. In the present work, we have furthered these studies on their longevity aspect i.e. the ageing effect. Alarmingly, the magnetic properties of hydrogenated samples stored in dry atmosphere degrade gradually with ageing. On the other hand, the 2% Mn doped ZnO, which depicts only a weak ferromagnetism, and no enhancement in magnetization upon hydrogenation, exhibits no such ageing effect. © 2010 Elsevier B.V. All rights reserved.


Singhal R.K.,University of Rajasthan | Samariya A.,University of Rajasthan | Xing Y.T.,Brazilian Center for Research in Physics (CBPF) | Kumar S.,Ml Sukhadia University | And 4 more authors.
Journal of Alloys and Compounds | Year: 2010

The effect of low level Co doping (5%) on polycrystalline ZnO samples has been investigated to correlate the observed changes in their magnetic state vis à vis changes in their electronic properties. Rietveld refinement of the XRD patterns confirms single phase crystallization of the samples in the wurtzite type lattice, with no evidence of any secondary phases. The as-synthesized Co-doped sample shows a paramagnetic (PM) state, however, when hydrogenated for ∼6 h, it shows a strong ferromagnetic (FM) ordering. The magnetic moment suppressed significantly when hydrogen ions were evaporated by heating and the sample turned completely paramagnetic upon long heating in air. The Co 2p X-ray photoelectron spectroscopy (XPS) results show that the substituted Co ions are in 2+ oxidation state that incorporate at Zn2+ sites and no evidence of metallic Co is observed upon hydrogenation. The XRD refinement results and the O 1s XPS results show clear evidence of oxygen depletion upon hydrogenation, followed by a complete regain upon their long heating in air. A plausible explanation for the observed room temperature ferromagnetism (RTFM) is presented in terms of oxygen vacancies, in the framework of bound magnetic polarons model. Our results evidence that the FM ordering can be switched between "on" and "off" by introducing (upon hydrogenation) or removing (by re-heating), respectively, the oxygen vacancies in the Co-doped ZnO matrix. © 2010 Elsevier B.V. All rights reserved.


Vyas B.M.,Ml Sukhadia University | Sunda S.,Airports Authority of India
Advances in Space Research | Year: 2012

An annular solar eclipse occurred over the Indian subcontinent during the afternoon hours of January 15, 2010. This event was unique in the sense that solar activity was minimum and the eclipse period coincides with the peak ionization time at the Indian equatorial and low latitudes. The number of GPS receivers situated along the path of solar eclipse were used to investigate the response of total electron content (TEC) under the influence of this solar eclipse. These GPS receivers are part of the Indian Satellite Based Augmentation System (SBAS) named as 'GAGAN' (GPS Aided Geo Augmented Navigation) program. The eight GPS stations located over the wide range of longitudes allows us to differentiate between the various factors induced due to solar eclipse over the equatorial and low latitude ionosphere. The effect of the eclipse was detected in diurnal variations of TEC at all the stations along the eclipse path. The solar eclipse has altered the ionospheric behavior along its path by inducing atmospheric gravity waves, localized counter-electrojet and attenuation of solar radiation intensity. These three factors primarily control the production, loss and transport of plasma over the equatorial and low latitudes. The localized counter-electrojet had inhibited the equatorial ionization anomaly (EIA) in the longitude belt of 72°E-85°E. Thus, there was a negative deviation of the order of 20-40% at the equatorial anomaly stations lying in this 'inhibited EIA region'. The negative deviation of only 10-20% is observed for the stations lying outside the 'inhibited EIA region'. The pre-eclipse effect in the form of early morning enhancement of TEC associated with atmospheric gravity waves was also observed during this solar eclipse. More clear and distinctive spatial and temporal variations of TEC were detected along the individual satellite passes. It is also observed that TEC starts responding to the eclipse after 30 min from start of eclipse and the delay of the maximum TEC deviation from normal trend with respect to the maximum phase of the eclipse was close to one hour in the solar eclipse path. © 2011 COSPAR. Published by Elsevier Ltd. All rights reserved.


Singhal R.K.,University of Rajasthan | Kumar S.,Ml Sukhadia University | Samariya A.,University of Rajasthan | Dhawan M.,University of Rajasthan | And 2 more authors.
Materials Chemistry and Physics | Year: 2012

We report a systematic structural, electronic, and magnetic investigation on occurrence of ferromagnetism and its "switch" action in non-doped bulk ceria (CeO 2). The magnetization measurements establish that the pristine CeO 2 having a paramagnetic ground state can be driven to a ferromagnetic state at room temperature, when hydrogenated at 600 °C. The observed H-induced ferromagnetism is closely related to the oxygen vacancies and the Ce valence state. X-ray photoemission results depict that Ce ions reduce from 4+ to 3+ state along with creation of oxygen vacancies during the ferromagnetic transition. A parallel variation of carrier concentration, revealed by resistance measurements, seems to be a secondary effect of the oxygen vacancies creation. The F + centers, i.e. the electrons in singly occupied oxygen vacancies, seem to play the key role in establishing the ferromagnetism in CeO 2, in the framework of bound magnetic polaron model. The exchange mechanism shows a "switch" action such that one could remove the oxygen vacancies through re-heating the H 2-treated CeO 2 and the ferromagnetism is subsequently vanished. © 2011 Elsevier B.V. All rights reserved.


Dashora A.,University of Mumbai | Patel N.,University of Trento | Kothari D.C.,University of Mumbai | Ahuja B.L.,Ml Sukhadia University | Miotello A.,University of Trento
Solar Energy Materials and Solar Cells | Year: 2014

First principles calculations are performed to study the electronic and optical properties of Cu-doped, N-doped and (Cu+2N)-co-doped anatase TiO 2. Strong hybridization between Cu 3d and N 2p orbitals above the valence band leads to the formation of an isolated intermediate band (IB) deep in the band gap of pure TiO2. The new energetic features, predicted by DFT, have been experimentally confirmed using UV-vis-NIR spectroscopy. In particular, the diffuse reflectance spectrum of the co-doped TiO2 sample shows the presence of two edges which confirm the existence of IB in the band gap. This IB in the band gap of TiO2 is responsible for high visible light absorption through a two-step optical transition between valence and conduction bands via the IB. In mono-doped samples, only a reduction of the band gap is observed which is consistent with the first-principles calculations. X-ray photoelectron spectroscopy of mono- and co-doped TiO2 samples establishes the chemical states of several atomic elements and especially clarifies the key presence of O-vacancies leading to a new position of conduction band minima. The presence of broad IB and the absence of dopant energy levels close to the conduction band minimum in (Cu+2N)-co-doped TiO 2 qualify it to be an efficient material for photovoltaic conversion, photocatalytic water splitting, and photocatalytic degradation of pollutants. © 2014 Elsevier B.V.


Bhatnagar P.,Ml Sukhadia University | Pareek N.,Ml Sukhadia University
Journal of Information Science | Year: 2014

Pseudo relevance feedback-based query expansion is a popular automatic query expansion technique. However, a survey of work done in the area shows that it has a mixed chance of success. This paper captures the limitations of pseudo relevance feedback (PRF)-based query expansion and proposes a method of enhancing its performance by hybridizing corpus-based information, with a genetic fuzzy approach and semantic similarity notion. First the paper suggests use of a genetic fuzzy approach to select an optimal combination of query terms from a pool of terms obtained using PRF-based query expansion. The query terms obtained are further ranked on the basis of semantic similarity with original query terms. The experiments were performed on CISI collection, a benchmark dataset for information retrieval. It was found that the results were better in both terms of recall and precision. The main observation is that the hybridization of various techniques of query expansion in an intelligent way allows us to incorporate the good features of all of them. As this is a preliminary attempt in this direction, there is a large scope for enhancing these techniques. © The Author(s) 2014.


Paliwal U.,Ml Sukhadia University | Kothari R.K.,Government College | Joshi K.B.,Ml Sukhadia University
Superlattices and Microstructures | Year: 2012

The electronic, optical and structural properties of Zn xCd 1-xS ySe 1-y quaternary alloys lattice matched to GaAs and InP are studied. The electronic band structure and density of states are computed using empirical pseudopotential method. The disorder effects are included via modified virtual crystal approximation. The bandgap computed from band structures are utilized to evaluate refractive indices, dielectric constants and ionicity factors for the alloys. Among structural properties elastic constants and bulk moduli are computed by combining the EPM with Harrison bond orbital model. All possible semiconductors from the ZnCdSSe system are found to have direct bandgap. The lattice matched alloys have larger band gap and more ionic character than the lattice matched compounds. © 2012 Elsevier Ltd. All rights reserved.


Kachhara R.P.,Ml Sukhadia University | Jodhawat R.L.,Ml Sukhadia University | Bigyapati Devi K.,Ml Sukhadia University
Journal of Earth System Science | Year: 2012

Marine Oligocene sequences in India outcrop only in western part of Kachchh. Earlier researchers have recognized the Oligocene strata under the Nari Series (Nagappa 1959; Chatterji and Mathur 1966). The Nari Series has a type area in Pakistan. It has two subdivisions-the Lower Nari (Lower Oligocene) and the Upper Nari (Upper Oligocene). It seems that there is no valid proof about the age of the Lower Nari due to lack of proper fauna (Eames 1975), and according to Pascoe (1962), the Upper Nari slightly transgress into Aquitanian (Lower Miocene), therefore, one has to be very cautious. Biswas and Raju (1971) reclassified the Oligocene strata of Kachchh and lithostratigraphically clubbed them as the Maniyara Fort Formation with type section along the Bermoti stream. This Formation has four members. The lower three members correspond to the Ramanian Stage (Lower Oligocene, Biswas 1971, 1973) while the uppermost to the Waiorian Stage (Upper Oligocene, Biswas 1965, 1971, 1973). The Ramanian Stage is characterized by large forams especially Nummulites fichteli, Nummulites fichteli intermedius, Lepidocyclina (Eulepidina) dialata and Operculina sp. Several ostracods are also known to occur. Megafauna include bivalves, gastropods, echinoids, corals, mammals and reptiles. Concerning bivalves earlier researchers have recorded a few taxa namely Trisidos semitorta (Lamarck), Cubitostrea angulata (J de C Sowerby), Pecten (Amussiopecten) labadyei d'Archiac and Haime, Periglypta puerpera (Linne') var. aglaurae Brongniart, Ostrea fraasi Mayer Eymer and listed Pecten laevicostatus J de C Sowerby, Callista pseudoumbonella Vredenburg and Clementia papyracea (Gray) from Kachchh as against overall 42 forms from the Nari Series as a whole (Vredenburg 1928). This tempted us to make an attempt to collect bivalve fauna systematically which are occurring prolifically in the Ramanian Stage. In the present work, for this purpose, sections are worked out around Lakhpat (23 °50′N; 68 °47′E), Maniyara Fort (23 °28′05″N; 68 °37′E) Rakhdi Dam (23 °27′26″N; 68 °40′10″E) and Waior (23 °25′05″N; 68 °41′37″E) with a view to highlight the entombed bivalve taxa. Authors have encountered 53 species of which 23 are restricted to the Ramanian Stage. © Indian Academy of Sciences.


Arora J.,Ml Sukhadia University
Biofuels | Year: 2013

The Thar Desert is one of the most populated deserts in the world, with a very high cattle population. The rural population is mainly dependent on fuelwood for cooking, as other sources of energy are either not available or not affordable. The population, cattle and energy requirements generate tremendous pressure on biofuel plants such as Prosopis juliflora, Acacia nilotica, Leptadenia pyrotechnica, Calligonum polygonoides, Calotropis procera and Zizyphus species. Biodiesel production from Jatropha curcas is another renewable energy source, having socioeconomic implications in rural areas with an estimated annual production potential of 200,000 metric tons of seeds in India. Bioenergy resources of the Thar Desert's arid region are presented in this review. This overview presents the biology, biotechnology and current status of various bioenergy resources (plants) of the Thar Desert and some of the future directions for these plants, which will make a profound impact on bioenergy industries as well as the socioeconomic level of the rural population. When the diesel prices will be left to market forces and biodiesel technology will be perfected for 20% blending in 2017, how this scenario will change is also presented. © 2013 Future Science Ltd.

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