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Singh, J.P.,Gautam, S.,Srivastava, R.C.,Asokan, K.,Kanjilal, D.,Chae, K.H. Academic Press 2015 Superlattices and microstructures Vol.86 No.-
Present work investigates the crossover from paramagnetism to superparamagnetism as a function of crystallite size in zinc ferrite nanoparticles using near edge X-ray absorption spectroscopy. Synthesized paramagnetic and superparamagnetic nanoparticles exhibit presence of Fe<SUP>2+</SUP> and Fe<SUP>3+</SUP> ions with dominant concentration of Fe<SUP>3+</SUP> ions. Fe L- and O K-edges spectra of paramagnetic nanoparticles consist of more intense spectral features compared to that of superparamagnetic nanoparticles. This reflects enhanced t<SUB>2g</SUB> and e<SUB>g</SUB> symmetry states of Fe-O hybridized states in paramagnetic nanoparticles induced by increased degree of crystallization.
Avinash Vishwakarma,Sivaiah Bathula,Nagendra S. Chauhan,Ruchi Bhardwaj,Bhasker Gahtori,Avanish K. Srivastava,Ajay Dhar 한국물리학회 2018 Current Applied Physics Vol.18 No.12
SiGe alloy is widely used thermoelectric materials for high temperature thermoelectric generator applications. However, its high thermoelectric performance has been thus far realized only in alloys synthesized employing mechanical alloying techniques, which are time-consuming and employ several materials processing steps. In the current study, for the first time, we report an enhanced thermoelectric figure-of-merit (ZT)∼1.1 at 900 °C in ntype Si80Ge20 nano-alloys, synthesized using a facile and up-scalable methodology consisting of rapid solidification at high optimized cooling rate∼3.4×107 K/s, employing melt spinning followed by spark plasma sintering of the resulting nano-crystalline melt-spun ribbons. This enhancement in ZT>20% over its bulk counterpart, owes its origin to the nano-crystalline microstructure formed at high cooling rates, which results in crystallite size ∼7 nm leading to high density of grain boundaries, which scatter heat-carrying phonons. This abundant scattering resulted in a very low thermal conductivity ∼2.1 Wm−1K−1, which corresponds to ∼50% reduction over its bulk counterpart and is amongst the lowest reported thus far in n-type SiGe alloys. The synthesized samples were characterized using X-ray diffraction, scanning electron microscopy and transmission electron microscopy, based on which the enhancement in their thermoelectric performance has been discussed.
A Linear and Consistent Class of Econometric Estimators in Simultaneous Equations
Srivastava, V.K.,Dwivedi, T.D.,Agnihotri, B.S. The Korean Statistical Society 1979 Journal of the Korean Statistical Society Vol.8 No.2
Striaght-forward application of the ordinary least squares model for estimating the parameters of a simultaneous linear stochastic equations model does not provide consistent estimators due to the fact that the explanatory jointly dependent variables are correlated with the disturbances. The search for consistent estimators during the last three decades has yielded a variety of estimators which can be broadly classified into two groups, namely, limited information and full information. Both the groups fails to uilize the over-identifying restrictions in the structural equations except the one under study while the latter group succeeds; see, e.g. Srivastava(1978) for a brief review and Theil (1961) for a detail description.
Synthesis, magnetic and Mossbauer spectroscopic studies of Cr doped lithium ferrite nanoparticles
Srivastava, M.,Layek, S.,Singh, J.,Das, A.K.,Verma, H.C.,Ojha, A.K.,Kim, N.H.,Lee, J.H. Elsevier Sequoia 2014 JOURNAL OF ALLOYS AND COMPOUNDS Vol.591 No.-
Lithium-based ferrites are promising and potential magnetic materials for microwave applications. They possess a spinel (AB<SUB>2</SUB>O<SUB>4</SUB>) type crystal structure, where the distributions of metal cations over the tetrahedral (A) and octahedral (B) voids play a crucial role for exhibiting different physical properties. Among various parameter of synthesis, pH is an important factor that influences the cation distribution over A and B voids, overall growth of the nanoparticles and different physical properties. In the present work single phase Cr substituted lithium ferrite nanoparticles have been synthesized by the sol-gel method at different pH. The phase identification and crystallite size have been probed by X-ray diffraction studies. The crystallite size changes by 44.2-48.8nm upon varying the pH from 3.5 to 11.5. In order to investigate the cations distribution at A/B sites, Mossbauer spectroscopic measurements were done. The values of magnetic hyperfine field obtained from the Mossbauer data for the A and B sites are ~49.5T and 51T, respectively. Moreover, it is observed that the area ratio of B site to A site increases with increasing the pH. This observation further suggests that the B site is more preferable for Fe<SUP>3+</SUP> cations at higher pH than the A site. The magnetic parameter such as saturation magnetization (M<SUB>s</SUB>), remanent magnetization (M<SUB>r</SUB>), coercive field (H<SUB>C</SUB>) and squareness (S) are determined by vibrating sample magnetometer (VSM) measurements, which show a consistent increase with increasing pH. The reason for the variation in magnetic properties has been explained on the basis of increased Fe<SUP>3+</SUP> cation occupancies at the B site and size effect, which is well supported by Mossbauer spectroscopic and XRD studies.
Tuning the Electronic and Magnetic Properties of Phosphorene by Vacancies and Adatoms
Srivastava, Pooja,Hembram, K. P. S. S.,Mizuseki, Hiroshi,Lee, Kwang-Ryeol,Han, Sang Soo,Kim, Seungchul American Chemical Society 2015 The Journal of Physical Chemistry Part C Vol.119 No.12
<P>We report a density functional theory (DFT) study regarding the effects of atomic defects, such as vacancies and adatom adsorption, on the electronic and magnetic properties of phosphorene (a two-dimensional monolayer of black phosphorus). A monovacancy in the phosphorene creates an in-gap state in the band gap of pristine phosphorene and induces a magnetic moment, even though pristine phosphorene is nonmagnetic. In contrast, both planar and staggered divacancies do not change the magnetic properties of phosphorene, although a staggered divacancy creates states in the gap. Our DFT calculations also show that adsorption of nonmetallic elements (C, N, and O) and transition metal elements (Fe, Co, and Ni) can change the magnetic properties of phosphorene with or without vacancies. For example, the nonmagnetic pristine phosphorene becomes magnetic after the adsorption of N, Fe, or Co adatoms, and the magnetic phosphorene with a monovacancy becomes nonmagnetic after the adsorption of C, N, or Co atoms. We also demonstrate that for O- or Fe-adsorbed monovacancy structure the electronic and magnetic properties are tunable via the control of charge on the phosphorene system. These results provide insight for achieving metal-free magnetism and a tunable band gap for various electronic and spintronic devices based on phosphorene.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2015/jpccck.2015.119.issue-12/jp5110938/production/images/medium/jp-2014-110938_0008.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jp5110938'>ACS Electronic Supporting Info</A></P>
Srivastava, S.N.L.,Sharma, K. Asian Australasian Association of Animal Productio 1998 Animal Bioscience Vol.11 No.4
In a feeding trial, Jamunapari male kids (18) of about 4 months age were equally divided into two groups of nine animals each. Goats in the experimental group were fed sun-dried pelleted Leucaena leucocephala leaves and those in the control group were offered a conventional diet without Leucaena leaves as per Kearl (1982) recommendations for a period of 6 months. Daily dry matter intake DMI/100 kg BW was $3.13{\pm}0.04kg$ in the Leucaena group and $3.30{\pm}0.05kg$ in the control. There were significant (p < 0.01) differences in the apparent digestibilities of DM, OM, CP, EE, CF and NFE being lower in the Leucaena group. Contents of digestible crude protein (DCP) and total digestible nutrients (TDN) were 11.40 and 52.20%, respectively, in the Leucaena group and 14.04 and 66.10%, respectively in the control. The nitrogen in the Leucaena group was not well utilized as compared to the control, though kids were in positive nitrogen balance in both the groups. The average daily weight gain of kids on pelleted Leucaena was $29.95{\pm}2.60g$ as against $42.09{\pm}3.24g$ observed in the control. The mean DMI/kg LW gain was significantly (p < 0.01) higher in the Leucaena group ($14.70{\pm}0.78kg$) as compared to the control ($11.55{\pm}0.46kg$). The Hb, BUN, SGOT and SGPT concentrations were statistically similar in both the groups. Histopathological examination of thyroid gland of goats sacrificed at the end of experiment did not reveal any signs of colloidal goitre associated with mimosine toxicity. No significant pathological alterations were observed in vital organs irrespective of dietary treatment. Sundried, pelleted Leucaena foliage appears to be a promising potential feed for growing goats without any significant deleterious effect.
A. K. Srivastava,Saurabh Chattopadhyay,V. S. Bisaria,T. Scheper 한국생물공학회 2002 Biotechnology and Bioprocess Engineering Vol.7 No.6
Culture conductivity and on-line NADH fluorescence were used to measure celulargrowth in plant cel suspension cultures of Podophyllum hexandrum. An inverse corelation between dry cel weight and medium conductivity was observed during shake flask cultivation. A linear relationship between dry cel weight and culture NADH fluorescence was obtained during the exponential phase of batch cultivation in a bioreactor under the pH stat (pH 6) conditions. It was observed that conductivity measurement were suitable for biomass characterisation under highly done for pH control the conductivity measurement could not be applied. On the other hand the NADH fluorescence measurement allowed online-in situ biomass monitoring of rather heterogenous plant cel suspension cultures in bioreactor even under the most desirable pH stat conditions.
Ashok K. Srivastava,Gunjan Prakash,C. J. S. K. Emmannuel 한국생물공학회 2005 Biotechnology and Bioprocess Engineering Vol.10 No.3
Seeds of neem were collected from different parts of India and analyzed for their azadirachtin content by High Performance Liquid Chromatography (HPLC). In order to assess the effects of genotypic and geographical variation on azadirachtin content in cell cultures, callus development was attempted in the seeds containing high and low concentration of azadirachtin. The concentration of azadirachtin in callus cultures was significantly affected by the explant source. Seed kernels with higher azadirachtin content produced higher azadirachtin content in callus cultures and lower azadirachtin content was seen in callus cultures produced from seed kernels with low azadirachtin content. The protocol for development of elite stock culture of Azadirachta indica was established with the objective of selecting a high azadirachtin-producing cell line. The highest azadirachtin-producing cell line was selected and the effects of different media and illumination conditions on growth and azadirachtin production were studied in shake flask suspension culture. Detailed batch growth kinetics was also established. These studies provided elite starter culture and associated protocols for cultivation of A. indica plant cell culture in the bioreactor.