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Pawan Kumar,Rakesh Kumar Dwivedi,Pawan Kumar,Ravikant Prasad,Praveen Kumar Siwach,Hari Krishna Singh 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.58 No.1
Thin films of La_(0.80)Sr_(0.20)Mn_(1−x)Cu_xO_3 with x = 0.00, 0.04, 0.08, 0.10, 0.15, and 0.20 were deposited on single-crystal LaAlO_3 (100) (LAO) substrates at 250 ± 10 ℃ by using a nebulized spray pyrolysis technique. Structural, surface, and transport characterizations were done by X-ray diffraction (XRD), atomic force microscopy (AFM) and the standard four probe technique, respectively. XRD patterns revealed the formation of single-phase polycrystalline films with a rhombohedral crystal structure. Cu substitution resulted in a uniform decrease in the metal insulator transition (T_(IM)) temperature up to x = 0.10, followed by a drastic decrease in T_(IM) for x = 0.15. Finally, the metal-insulator transition vanished for higher Cu concentrations (x = 0.20) in the observed temperature range. The variation in T_(IM) with the amount of added Cu is explained on the basis of the double exchange mechanism. Cu substitution has been found to perturb the Mn^(3+)-O-Mn^(4+) network and has a strong influence on T_(IM). The variation in resistivity maxima with temperature for different Cu concentrations showed a systematic trend up to x ∼ 0.10. We also explored the electrical conduction at T > T_(IM) in the framework of small polaron hopping in the adiabatic limit. The activation energy showed a strong dependence on the Cu concentration. The maximum magneto-resistance (MR) up to 10%, was observed for x = 0.15 at low temperatures.
Anomalous Weak Ferromagnetism in Electron-doped Nd_(1−x)Sr_xMnO_3 (0.50 ≤ x ≤ 0.62) Thin Films
Pawan Kumar,Ravikant Prasad,Hari Krishna Singh,Rakesh Kumar Dwivedi,Avanish Kumar Srivastava,Mangala Prasad Singh 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.4
In the present work we demonstrate that an anomalous weak ferromagnetism occurs in the composition range 0.50 ≤ x ≤ 0.62 in nanostructured thin films of Nd_(1−x)Sr_xMnO_3 (NSMO). Nanocrystalline thin films of overdoped manganite Nd_(1−x)Sr_xMnO_3 (<I>x</I> ∼ 0.50, 0.55, 0.60 and 0.62) on single crystal LaAlO_3 (001) substrates are grown by nebulized chemical spray pyrolysis technique. These single phase films possess average crystallite size ∼15 nm and the width of the grain boundaries is ∼1 - 2 nm. In the composition range 0.50 ≤ x ≤ 0.62, the ground state of NSMO is A-type antiferromagnetic (AFM) metallic. However, in the present films a broad paramagnetic (PM) to ferromagnetic (FM) transition is observed in all the compositions at T_C ∼ 226 K for x = 0.50 and 235 K for rest of the samples. All the films show a well-defined M-H hysteresis loop at 5 K. The coercivity (H_C) of these films is much larger than those having composition range 0.35 < x < 0.45. For x = 0.50 (0.62) film H_C = -1210 (-1484) Oe and +1162 (+1476) Oe. The asymmetry in coercivity suggests the presence of weak exchange bias effect in these films. It is observed that the FM ground state in these films have smaller magnetic moment per Mn atom than the expected full moment using the rigid model, we term this as a weak ferromagnetic (WFM) state arising due to the destabilization of the AFM ordering. We propose a possible scenario based on the combined effect of spin reorganization and enhanced orbital disordering in nanosized manganites, to explain the observed anomalous weak ferromagnetism in the A-type AFM spin ordered regime.
Biofiltration of hydrogen sulfide: Trends and challenges
Vikrant, Kumar,Kailasa, Suresh Kumar,Tsang, Daniel C.W.,Lee, Sang Soo,Kumar, Pawan,Giri, Balendu Shekhar,Singh, Ram Sharan,Kim, Ki-Hyun Elsevier 2018 JOURNAL OF CLEANER PRODUCTION Vol.187 No.-
<P><B>Abstract</B></P> <P>Expansion of modern industry coupled with a lack of effective treatment systems has resulted in excessive release of toxic and odorous pollutants such as hydrogen sulfide (H<SUB>2</SUB>S). Development of treatment measures is therefore necessary to protect ecosystems and human health. This paper explores recent advances in H<SUB>2</SUB>S treatment technologies. Particular focus is placed on innovative and recent advances in biofiltration, especially for wastewater treatment facilities and biogas generation (e.g., use of innovative packing media for better performance and reduced pressure drop, eliminating sulfate accumulation, and development of modeling techniques). The review also identifies current challenges and future prospects (e.g., fluctuations in methane and carbon dioxide concentrations during biogas upgradation, optimizing anoxic H<SUB>2</SUB>S biofiltration, and understanding the effects of operating conditions on biofilter performance) for improving biofiltration by highlighting research gaps in related fields.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Hydrogen sulfide (H<SUB>2</SUB>S) is a water-soluble gas with the characteristic malodor. </LI> <LI> In this review, we briefly discussed the physicochemical properties and sources of H<SUB>2</SUB>S. </LI> <LI> We dealt biological approaches for the removal of H<SUB>2</SUB>S. </LI> <LI> The challenges and prospects related to these treatment methods are also described. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Fuzzy system reliability using intuitionistic fuzzy Weibull lifetime distribution
Kumar, Pawan,Singh, S.B. The Korean Reliability Society 2015 International Journal of Reliability and Applicati Vol.16 No.1
Present study investigates the fuzzy reliability of some systems using intuitionistic fuzzy Weibull lifetime distribution, in which the lifetime parameters are assumed to be fuzzy parameter due to uncertainty and inaccuracy of data. Expressions for fuzzy reliability, fuzzy mean time to failure, fuzzy hazard function and their ${\alpha}$-cut have been discussed when systems follow intuitionistic fuzzy Weibull lifetime distribution. A numerical example is also taken to illustrate the methodology to calculate the fuzzy reliability characteristics of systems.
Fuzzy system reliability using intuitionistic fuzzy Weibull lifetime distribution
Pawan Kumar,S. B. Singh 한국신뢰성학회 2015 International Journal of Reliability and Applicati Vol.16 No.1
Present study investigates the fuzzy reliability of some systems using intuitionistic fuzzy Weibull lifetime distribution, in which the lifetime parameters are assumed to be fuzzy parameter due to uncertainty and inaccuracy of data. Expressions for fuzzy reliability, fuzzy mean time to failure, fuzzy hazard function and their α-cut have been discussed when systems follow intuitionistic fuzzy Weibull lifetime distribution. A numerical example is also taken to illustrate the methodology to calculate the fuzzy reliability characteristics of systems.
Variants of compatible mappings in fuzzy metric spaces
Pawan Kumar,Balbir Singh,Z. K. Ansari 원광대학교 기초자연과학연구소 2018 ANNALS OF FUZZY MATHEMATICS AND INFORMATICS Vol.15 No.2
In this paper, we introduce the notions of compatible mappings of type(R), type (K) and type (E) in Fuzzy metric spaces and prove some common fixed point theorems for these mappings.In fact, we call these maps as variants of compatible mappings.
A bridged ruthenium dimer (Ru–Ru) for photoreduction of CO2 under visible light irradiation
Anurag Kumar,Pawan Kumar,Aathira M.S.,Dharmendra Pratap Singh,Babita Behera,Suman L. Jain 한국공업화학회 2018 Journal of Industrial and Engineering Chemistry Vol.61 No.-
A bridged binuclear complex consisting of two ruthenium units (Ru–Ru) connected through a bridging ligand was synthesized, in which one unit serves as a photosensitizer, while another unit works as a catalyst. The synthesized Ru–Ru photocatalyst was tested for photoreduction of CO2 to give CO and HCOOH under visible light irradiation in the presence of triethanolamine as a sacrificial donor. The yield of CO and HCOOH was found to be 54 ppm and 28 ppm respectively after 12 h of irradiation. Due to the binding of photosensitizer and catalyst units in a single molecule via bridging ligand provides faster and efficient electron transfer from sensitizer to catalyst unit which resulted in the higher activity and better product yields.