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Structural and micro structural studies of PbO-doped SnO_2 sensor for detection of methanol, propanol and acetone

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j.urnal of Natural Gas Chemistry 2011年第2期20卷 179-183页

作者： j. k. srivastava Preeti Pandey V. N. Mishra R. Dwivedi Center for Research in Microelectronics Department of Electronics Engineering Institute of Technology Banaras Hindu University

In the present work.the structural information of PbO-doped SnO2 thick.film sensor has been investigated with X-ray diffractometer （XRD） and scanning electron microscope （SEM）. Initially, SnO2 powder was derived using sol-gel process and was subsequently doped with PbO and ground up to nanosized particles. A suitable gas sensor structure was fabricated on 1′′×1′′ alumina substrate using thick.film technology. The necessary paste for screen printing was also developed. SEM results showed sol-gel derived powder gets more agglomerated in the thick.film form. The sensitivity of the sensor has been investigated at different temperatures （150 ？C？350 ？C） upon exposure to methanol, propanol and acetone, yielding a maximum at 250 ？C for acetone with 1 wt% PbO-doping while at 350 ？C for propanol with 3 wt% PbO-doping of the sensor. The reduction of particle size to nanometers （validated through XRD） leads to a dramatic improvement in sensitivity of sensors for the chosen organic vapors. The results also correlate well with the microstructural properties of the material and the dopant.

关键词： gas sensor nanosized SnO2 Sol-gel thick.film

High-yield synthesis and liquid-exfoliation of two- dimensional belt-lik. hafnium disulphide

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Nano Research 2018年第1期11卷 343-353页

作者： Harneet k.ur Sandeep Yadav Avanish k. srivastava Nidhi Singh Shyama Rath j.rg j. Schneider Om P. Sinha Ritu srivastava National Physical Laboratory Council of Scientific and Industrial Research Dr. K. S. Krishnan Road New Delhi I I O012 India Academy of Scientific and Innovative Research NPL New Delhi 110012 India Technische Universitat Darmstadt Eduard-ZintMnstitut f~r Anorganische und Physikalische Chemie 12 105 117 Alarich-Weiss-Str 12 64287 Darmstadt Germany DepartmentofPhysics andAstrophysics University of Delhi Delhi 110007 India Amity Institute of Nanotechnology Amity University UP Sector 125 Noida Uttar Pradesh 201313 India

Producing environmentally stable monolayers and few-layers of hafnium disulphide （HfS2） with a high yield to reveal its unlock.d electronic and optoelectronic applications is still a challenge. HfS2 is a layered two-dimensional material of group-IV transition metal dichalcogenides. For the first time, we demonstrate a simple and cost-effective method to grow layered belt-lik. nanocrystals of HfS2 with a notably large interlayer spacing followed by their chemical exfoliation. Various microscopic and spectroscopic techniques confirm that these as-grown crystals exfoliate into single or multiple layers in a few minutes using solvent assisted ultrasonification method in N-cyclohexyl-2- pyrrolidone. The exfoliated nanosheets of HfS2 exhibit an indirect bandgap of 1.3 eV with high stability against surface degradation. Furthermore, we demonstrate that these nanosheets hold potential for electronic applications by fabricating a field-effect transistor based on few-layered HfS2, exhibiting a field-effect mobility of 0.95 cm2/（V.s） with a high on/off current modulation ratio of 10,000 in ambient conditions. The method is scalable and has a potential significance for both academic and industrial purposes.

关键词： two-dimensionalmaterials hafnium disulphide nano-crystals liquid-phase exfoliation environment-stabili~ field-effect transistor

Models and form factors for stand volume estimation in natural forest ecosystems: a case study of k.tarniaghat Wildlife Sanctuary (k.WS), Bahraich District, India

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j.urnal of Forestry Research 2013年第2期24卷 217-226页

作者： V. A. j.Adek.nle k. N. Nair A. k. srivastava N. k. Singh Federal University of Technology Dept of Forestry & Wood Technology National Botanical Research Institute (Council for Scientific & Industrial Research) Plant Diversity Systematics & Herbarium Division Rana Pratap Marg Department of Forests Sidhauli Forest Division

In view of the difficulties in stand volume estimation in natural forests, we derived real form factors and models for volume estimation in these types of forest ecosystems, using k.tarniaghat Wildlife Sanctuary as a case study. Tree growth data were obtained for all trees （dbh 〉10 cm） in 4 plots （25 × 25 m） randomly located in each of three strata selected in the forest. The form factor calculated for the stand was 0.42 and a range of 0.42 0.57 was estimated for selected species （density 〉10）. The parameters of model variables were consistent with general growth trends of trees and each was statistically significant. There was no significant difference （p〉0.05） between the observed and predicted volumes for all models and there was very high correlation between observed and predicted volumes. The output of the performance statistics and the logical signs of the regression coefficients of the models demonstrated that they are useful for volume estimation with minimal error. Plotting the biases with respect to considerable regressor variables showed no meaningful and evident trend of bias values along with the independent variables. This showed that the models did not violate regression assumptions and there were no heteroscedacity or multiculnarity problems. We recommend use of the form factors and models in this ecosystem and in similar ones for stand and tree volume estimation.

关键词： natural forest tree volume Estimation biodiversity tree height forest inventory

Environmental Exposure to Lead as a Risk.for Prostate Cancer

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Biomedical and Environmental Sciences 2002年第4期15卷 298-305页

作者： M．k.j.SIDDIQUI S．srivastava 等 IndustialToxicologyReserachCentre PostBoxNo.80.M.G.Marg.Lucknow226－001India Dr RMLAvadhUniversityFaizabad－224001India

Obj.ctive To evaluate the possible role of environmental exposure to lead as a risk.factor for prostate pathology in patients suffering from prostate cancer (PCA) and benign prostate hyperplasia (BPH). Methods Blood lead (BPb) level was determined in PCA and BPH cases using a graphite furnace Atomic Absorption Spectrophotometer and compared with those in a control group living in the similar socioeconomic environment. Results BPb was significantly higher in PCA and BPH cases than in normals (Pj.sting for age as a possible confounders. However, positive association between blood lead and TEARS was relatively higher in PCA patients (r=0.77, Pk.factor for prostate cancer and/or benign prostate hyperplasia possibly through generation of reactive oxygen species and/or reducing the level of zinc which acts as a cellular growth protector.

关键词： Benign prostate hyperplasia Prostate cancer Blood lead Atomic Absorption Spectrophotometer

Advent of clean and green technology for preparation of low-cholesterol dairy cream powder:supercritical fluid extraction process

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Food Quality and Safety 2018年第4期2卷 205-211页

作者： Mousumi Ghosh Chitra j. Shubhangi srivastava Hari Niwas Mishra Agricultural and Food Engineering Department Indian Institute of Technology KharagpurNalanda roadKharagpurWest Mednipore721302India

Obj.ctives:Due to health issues related to cholesterol and the emphasis on manufacture of low cholesterol food products,the research was undertak.n for the extraction of cholesterol from cream powder using supercritical fluid extraction(SCFE)*** and Methods:Face centered composite design(FCCD)was used to design the experiments with three independent variables viz.,extraction temperature(40˚C-75˚C),extraction pressure(100-250 bar)and dynamic time(2.5-3.5 h)tak.ng two responses(cholesterol and fat content).The standardized flow rate and static time were 5 L/min(expanded CO_(2) gas)and 30 min,*** surface methodology was used for optimizing the process ***:It was found that higher operating pressure,low extraction temperature and moderate amount of dynamic time facilitated the removal of *** optimized process conditions of 75˚C,204 bar and 3.5 h dynamic time yielded 39%reduction in cholesterol content and 10.6%reduction in total fat content of the cream ***:Thus,a low cholesterol cream powder was developed with health benefits for people suffering from cardiovascular diseases.

关键词： cholesterol supercritical fluid extraction HPLC face-centred composite design response surface methodology

Evaluation of Inhibitory Effect of the Plant Phyllanthus amarus Against Dermatophytic Fungi Microsporum gypseum

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Biomedical and Environmental Sciences 2004年第3期17卷 359-365页

作者： ANURAG AGRAWAL SHALINI srivastava j.N.srivastava M.M.SRIVASAVA Department of Chemistry Faculty of Science Dayalbagh Educational Institute Deemed University Agra-282 005 IndiaDepartment of Chemistry Faculty of Science Dayalbagh Educational Institute Deemed University Agra-282 005 IndiaDepartment of Botany Faculty of Science Dayalbagh Educational Institute Deemed University Agra-282 005 IndiaDepartment of Chemistry Faculty of Science Dayalbagh Educational Institute Deemed University Agra-282 005 India

Obj.ctive The antifungal activity of various solvent extracts (such as ether, chloroform, ethyl acetate and ethyl alcohol) of the plant Phyllanthus amarus against dermatophytic fungi Microsporum gypseum was observed. Method Antifungal bioassay in terms of reduction in weight, colony diameter and sporulation of the target fungal colony was carried out using Broth Dilution method. Results Root part of the plant, extracted in various organic solvents did not show any noticeable antifungal activity. The percentage inhibition observed in different solvent extracts of aerial part was found as reduction in weight: chloroform [50.3%], ethyl acetate [27.7%] and ethyl alcohol [12.1%], reduction in colony diameter: chloroform [53.4%], ethyl acetate [31.4%] and ethyl alcohol [15.0%] and reduction in sporulation: maximum inhibition in chloroform extract, at test concentration of 4000 ppm at incubation period of 8 days. Conclusion Chloroform fraction of the aerial part of the plant P. amarus shows significant inhibitory effect against dermatophytic fungi M. gypseum and requires chemical characterization for its bioactive principle.

关键词： Phyllanthus amarus Antifungal activity Microsporum gypseum Sk.n infections

Enhanced dielectric and optical properties of nanoscale barium hexaferrites for optoelectronics and high frequency application

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Chinese Physics B 2018年第12期27卷 517-525页

作者： j.Mohammed A B Suleiman Tchouank.Tek.u Carol T H Y Hafeez j.oti Sharma Pradip k.Maj. Sachin Godara k.mar A k.srivastava Department of Physics School of Chemical Engineering and Physical Sciences Lovely Professional University Department of Physics Faculty of Science Federal University Dutse SRM Research Institute SRM University Department of Polymer and Processing Engineering Indian Institute of Technology Roorkee Department of Chemistry Guru Nanak Dev University

M-type barium hexaferrites with chemical composition Ba1-xDyxFe12-yCryO19(x = 0.0, 0.1, 0.2, and y =0.0, 0.4, 0.5) were synthesized via sol–gel auto-combustion method. The samples were pre-sintered at 400℃ for 3 h and sintered at 950℃ for 5 h. The changes in the structural, dielectric, and optical properties were studied after the substitution of Dy3+and Cr3+ions. X-ray diffraction(XRD) analysis confirms the formation of single phase hexaferrites with the absence of secondary phase. FTIR analysis gives an idea of the formation of hexaferrites with the appearance of two peak. at 438 cm-1and 589 cm-1. The field emission scanning electron micrographs(FESEM) show a combination of crystallites with large shapes close to hexagonal platelet-lik. shape and others with rice or rod-lik. shapes, whereas EDX and elemental analysis confirm the stoichiometry of prepared samples. The calculated band gap from UV-vis NIR spectroscopy spectra was found to decreases with increase in Dy3+–Cr3+substitution. The dielectric properties were explained on the basis of Maxwell–Wagner model. Enhancement of dielectric constant at higher frequencies was observed in all the samples. Low dielectric loss is also observed in all the samples and Cole–Cole plot shows that grain boundary resistance(Rgb) contribute most to the dielectric properties. The prepared samples exhibit properties that could be useful for optoelectronics and high frequency application.

关键词： Maxwell–Wagner model dielectric constant Cole–Cole plot optical band-gap

Radiation Losses in the Microwave X Band in Al-Cr Substituted Y-Type Hexaferrites

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Chinese Physics Letters 2017年第4期34卷 35-38页

作者： D.Basandrai R.k.Bedi A.Dhami j.Sharma S.B.Narang k.Pubby A.k.srivastava Research Scholar Department of Physics I. K. Gujral Punjab Technical University Jalandhar India Department of Physics Lovely Professional University Phagwara India principal Satyam Institute of Engineering & Technology Amritsar India Department of Electronic Technology Guru Nanak Dev University Amritsar India

We present a study on radiation losses in the microwave X band in Al-Cr substituted Y-type hexaferrites, namely Ba2Mg2Alx/2Crx/2Fe12-xO22 （x = 0, 0.5 and 1.0）. The study is performed by means of a vector network.analyzer, Fourier transform infrared spectroscopy, a vibrating sample magnetometer and x-ray powder diffraction. Ba2Mg2Fe12O22 hexaferrite shows radiation loss of -37.25dB （99.999% loss） at frequency 9.81 GHz, which can be attributed to its high value of saturation magnetization, i.e., 22.08emu/g. Moreover, we obtain that magnetic properties have strong influence on the radiation losses.

关键词： Ba Al Radiation Losses in the Microwave X Band in Al-Cr Substituted Y-Type Hexaferrites Cr

Effect of the orientation of non-spherical metal nanoparticle with respect to light polarization on its transient optical response

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Nanotechnology and Precision Engineering 2023年第2期6卷 41-47页

作者： Asha Singh Himanshu srivastava Rama Chari j.j.yabalan Nano Science Laboratory Materials Science SectionRaja Ramanna Centre for Advanced TechnologyIndore 452013India Lithography and Microscopy Laboratory Synchrotrons Utilization SectionRaja Ramanna Centre for Advanced TechnologyIndore 452013India

Nanoparticles with non-spherical shapes are now being widely used for various photonic *** observe experimentally that the magnitude as well as the time dependence of the transient absorption of a colloid of silver nanoplatelets depends on the relative polarization of the pump and probe *** have been a few reports about the dependence of the transient signal magnitude on polarization,but little information is available on its temporal *** a theoretical model,we show that this observed behavior arises from the fact that the energy absorption by a non-spherical nanoparticle depends on,among other factors,the nanoparticle orientation with respect to the pump and probe polarization *** is essential to consider this when estimating nanoparticle characteristics such as carrier thermalization time,carrier–phonon scattering time,and complex polarizability from transient absorption measurements.

关键词： Ultrafast dynamics Metal Nanoparticles Transient Absorption Polarization dependence