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.

Pyrimidine derivatives as novel acidizing corrosion inhibitors for N80 steel useful for petroleum industry: A combined experimental and theoretical approach

Jiyaul Haque,K.R. Ansari,Vandana Srivastava,M.A. Quraishi,I.B. Obot 한국공업화학회 2017 Journal of Industrial and Engineering Chemistry Vol.49 No.-

The corrosion inhibition performance of two pyrimidine derivatives namely 5-styryl-2,7-dithioxo-2,3,5,6,7,8-hexahydropyrimido[4,5-d] pyrimidin-4(1H) one (PP-1) and 5-(2-hydroxyphenyl)-2,7-dithioxo-2,3,5,6,7,8-hexahydropyrimido[4,5-d]-pyrimidin-4(1H) one (PP-2) on N80 steel corrosion in15% HCl has been studied using gravimetric method, electrochemical impedance spectroscopy (EIS),potentiodynamic polarization, atomic force microscopy (AFM), scanning electron microscopy (SEM), DFT,molecular electrostatic potential and Monte Carlo simulation. The corrosion inhibition efficiencies atoptimum concentration (250 mg/L) are 89.1% (PP-1) and 73.1% (PP-2) respectively at 308 K. The corrosioninhibition efficiency increases with increase in concentration and decreases with temperature. PPsobeyed Langmuir adsorption isotherm. AFM and SEM analyses supported formation of protectivefilm onN80 steel in presence of inhibitors. DFT and Monte Carlo simulation calculations supported experimentalresults.

Determination of Double-K Fracture Parameters of Concrete Using Split-Tension Cube

Shashi Ranjan Pandey,Shailendra Kumar,A. K. L. Srivastava 한국콘크리트학회 2016 International Journal of Concrete Structures and M Vol.10 No.2

This paper presents a revised procedure for computation of double-K fracture parameters of concrete split-tension cube specimen using weight function of the centrally cracked plate of finite strip with a finite width. This is an improvement over the previous work of the authors in which the determination of double-K fracture parameters of concrete for split-tension cube test using weight function of the centrally cracked plate of infinite strip with a finite width was presented. In a recent research, it was pointed out that there are great differences between a finite strip and an infinite strip regarding their weight function and the solution of infinite strip can be utilized in the split-tension specimens when the notch size is very small. In the present work, improved version of LEFM formulas for stress intensity factor, crack mouth opening displacement and crack opening displacement profile presented in the recent research work are incorporated. The results of the double-K fracture parameters obtained using revised procedure and the previous work of the authors is compared. The double-K fracture parameters of split-tension cube specimen are also compared with those obtained for standard three point bend test specimen. The input data required for determining double-K fracture parameters for both the specimen geometries for laboratory size specimens are obtained using well known version of the Fictitious Crack Model.

Modeling of Absorption of NO_2 with Chemical Reaction in a Falling Raindrop

Pareek, Vishnu,Srivastava, Vinod K.,Adesina, Adesoji A. 한국화학공학회 2003 Korean Journal of Chemical Engineering Vol.20 No.2

A model has been proposed for the scavenging of NO_2 in a falling raindrop. After absorption, aqueous NO_2 undergoes a second order reaction to form various ions such as NO^-_2, NO^-_3 and H^+. The model is based on the unsteady state convective diffusion equation which was solved for given boundary conditions by using impicit alternate direction(ADI) method. The circulation of fluid inside and outside the raindrop has been taken into account to realistically describe the flow field in the numerical domain. The model predictions indicate that the pH of a raindrop is a direct function of the drop size and bulk concentration of NO^-_2. The model predicted a pH of about 4.9 for a 100micron raindrop falling through a 20-ppb ambient concentration of NO_2. For the same ambient concentration of NO_2, a 10-micron raindrop would have a pH of about 4.75. The predictions also suggested that for all practical purposes the gas phase resistance may be taken as the rate-controlling step. The predicted values of gas-side mass transfer coefficient compared well with the estimated values using standard mass transfer correlations.

Determination of Double-K Fracture Parameters of Concrete Using Split-Tension Cube: A Revised Procedure

Pandey, Shashi Ranjan,Kumar, Shailendra,Srivastava, A.K.L. Korea Concrete Institute 2016 International Journal of Concrete Structures and M Vol.10 No.2

This paper presents a revised procedure for computation of double-K fracture parameters of concrete split-tension cube specimen using weight function of the centrally cracked plate of finite strip with a finite width. This is an improvement over the previous work of the authors in which the determination of double-K fracture parameters of concrete for split-tension cube test using weight function of the centrally cracked plate of infinite strip with a finite width was presented. In a recent research, it was pointed out that there are great differences between a finite strip and an infinite strip regarding their weight function and the solution of infinite strip can be utilized in the split-tension specimens when the notch size is very small. In the present work, improved version of LEFM formulas for stress intensity factor, crack mouth opening displacement and crack opening displacement profile presented in the recent research work are incorporated. The results of the double-K fracture parameters obtained using revised procedure and the previous work of the authors is compared. The double-K fracture parameters of split-tension cube specimen are also compared with those obtained for standard three point bend test specimen. The input data required for determining double-K fracture parameters for both the specimen geometries for laboratory size specimens are obtained using well known version of the Fictitious Crack Model.

A novel SARMA-ANN hybrid model for global solar radiation forecasting

Srivastava, Rachit,Tiwaria, A.N.,Giri, V.K. Techno-Press 2019 Advances in energy research Vol.6 No.2

Global Solar Radiation (GSR) is the key element for performance estimation of any Solar Power Plant (SPP). Its forecasting may help in estimation of power production from a SPP well in advance, and may also render help in optimal use of this power. Seasonal Auto-Regressive Moving Average (SARMA) and Artificial Neural Network (ANN) models are combined in order to develop a hybrid model (SARMA-ANN) conceiving the characteristics of both linear and non-linear prediction models. This developed model has been used for prediction of GSR at Gorakhpur, situated in the northern region of India. The proposed model is beneficial for the univariate forecasting. Along with this model, we have also used Auto-Regressive Moving Average (ARMA), SARMA, ANN based models for 1 - 6 day-ahead forecasting of GSR on hourly basis. It has been found that the proposed model presents least RMSE (Root Mean Square Error) and produces best forecasting results among all the models considered in the present study. As an application, the comparison between the forecasted one and the energy produced by the grid connected PV plant installed on the parking stands of the University shows the superiority of the proposed model.

Multiwavelength Observations of Supersonic Plasma Blob Triggered by Reconnection-Generated Velocity Pulse in AR10808

Srivastava, A. K.,Erdé,lyi, R.,Murawski, K.,Kumar, Pankaj Springer-Verlag 2012 Solar physics Vol.281 No.2

Breakthrough behaviour of NBC canister against carbon tetrachloride: a simulant for chemical warfare agents

Avanish Kumar Srivastava,D. Shah,T.H. Mahato,Beer Singh,A. Saxena,A.K. Verma,S. Shrivastava,A. Roy,S.S. Yadav,A.R. Shrivastava 한국탄소학회 2012 Carbon Letters Vol.13 No.2

A nuclear, biological, chemical (NBC) canister was indigenously developed using active carbon impregnated with ammoniacal salts of copper (II), chromium (VI) and silver (I), and high efficiency particulate aerosol filter media. The NBC canister was evaluated against carbon tetra chloride (CCl4) vapours, which were used as a simulant for persistent chemical warfare agents under dynamic conditions for testing breakthrough times of canisters of gas masks in the National Approval Test of Respirators. The effects of CCl4 concentration, test flow rate, temperature, and relative humidity (RH) on the breakthrough time of the NBC canister against CCl4 vapour were also studied. The impregnated carbon that filled the NBC canister was characterized for surface area and pore volume by N2 adsorption-desorption isotherm at liquid nitrogen temperature. The study clearly indicated that the NBC canister provides adequate protection against CCl4 vapours. The breakthrough time decreased with the increase of the CCl4 concentration and flow rate. The variation in temperature and RH did not significantly affect the breakthrough behaviour of the NBC canister at high vapour concentration of CCl4, whereas the breakthrough time of the NBC canister was reduced by an increase of RH at low CCl4 vapour concentration.

Light-Controlled Self-Assembly of Semiconductor Nanoparticles into Twisted Ribbons

Srivastava, S.,Santos, A.,Critchley, K.,Kim, K.-S.,Podsiadlo, P.,Sun, K.,Lee, J.,Xu, C.,Lilly, G. D.,Glotzer, S. C.,Kotov, N. A. American Association for the Advancement of Scienc 2010 Science Vol.327 No.5971

Non-invasive Methods for Determination of Cellular Growth in Podophyllum hexandrum Suspension Cultures

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.