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Effect of nano-and micron-sized K0.5Na0.5NbO3 fillers on the dielectric and piezoelectric properties of PVDF composites

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Journal of Advanced Ceramics 2016年第4期5卷 92-页

作者： bharathi PONrAJ rajasekhar bHIMIrEDDI K.b.r.varma Materials research Centre Indian Institute of Science Bangalore-560012 India

Polymer nanocrystal composites were fabricated by embedding polyvinylidene fluoride (PVDF) with K0.5Na0.5NbO3 (KNN) nanocrystallites of different volume fraction using the hot-pressing *** comparison,PVDF-KNN microcrystal composites of the same compositions were also fabricated which facilitated the studies of the crystallite size (wide range) effect on the dielectric and piezoelectric *** structural,morphological,dielectric,and piezoelectric properties of these nano and micro crystal composites were *** incorporation of KNN fillers in PVDF at both nanometer and micron scales above 10 vol％ resulted in the formation of polar β-form of *** room temperature dielectric constant as high as 3273 at 100 Hz was obtained for the PVDF comprising 40 vol％ KNN nanocrystallites due to dipole-dipole interactions (as the presence of β-PVDF is prominent),whereas it was only 236 for the PVDF containing the same amount (40 vol％) of micron-sized crystallites of KNN at the same *** theoretical models were employed to predict the dielectric constants of the PVDF-KNN nano and micro crystal *** PVDF comprising 70 vol％ micron-sized crystallites of KNN exhibited a d33 value of 35 pC/N,while the nanocrystal composites of PVDF-KNN did not exhibit any piezoelectric response perhaps due to the unrelieved internal stress within each grain,besides the fact that they have less domain walls.

关键词： polyvinylidene fluoride (PVDF) K0.5Na0.5NbO3 (KNN) composites β-PVDF nanocrystallites

Water and nutrient recovery from urine:A lead up trail using nano-structured In_(2)S_(3)photo electrodes

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Chinese Physics b 2021年第5期30卷 531-535页

作者： r Jayakrishnan T r Sreerev Adith varma Department of Physics University of KeralaThiruvananthapuramKerala 695581India Photovoltaic research Laboratory Christian College Chenagnnur 689122India

Developments of economic systems are critical for bio-regenerative life support systems in manned space *** this work we report on the feasibility of using two direct sunlight powered processes sequentially for the recovery of water and nutrients from *** work presents experimental evidence on nutrient and water recovery achieved using the proto-type designed and *** report the design and testing of a solar still which would serve on the nutrient recovery *** cooled condensate from the solar still is fed into a solar powered electrolysis unit where nano-structured indium sulphide(In_(2)S_(3))thin films coated over fluorine doped tin oxide(SnO_(2):F)substrate serve as one of the working *** electrolysis takes place in the absence of an electrolyte which manifests as a technical achievement of our *** results show that the COD level in the recycled water is very *** In_(2)S_(3)photo-electrodes are stable without any physical damage after the process.

关键词： semiconductors water quality thin film structure and morphology electrolysis

Numerical modeling of a tunnel in jointed rocks subjected to seismic loading

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Underground Space 2019年第2期4卷 133-146页

作者： Malavika varma V.b.Maji A.boominathan Department of Civil Engineering Indian Institute of Technology MadrasChennaiIndia

The studies on the performance of tunnels under static loads are reported extensively in the literature but their performances under dynamic loads are *** present study highlights some of the important aspects of jointed rock tunnels during seismic *** literature review provides a shake table experimental study of a jointed rock tunnel.A Universal Distinct Element Code(UDEC)model is developed from this shake table *** model tunnel is subjected to a scaled input motion of the 1985 Mexico *** numerical results are validated systematically with the findings of the shake table ***,the developed numerical model is used to perform parametric studies to understand the effect of in-situ stress,joint angles,joint stiffness,and joint friction angle on the deformation and stability of the tunnel under the same earthquake input *** is observed that some joint angle combinations form a wedge that yields excessive deformation and subsequently a complete *** exponential decrease in deformation occurred in the tunnel as the joint stiffness *** is found that the shallow tunnels are more susceptible to damage under the action of earthquake loads.

关键词： Tunnel Jointed rocks Seismic loading UDEC

Structural and electrical characterization of bi2VO5.5 / bi4Ti3O12 bilayer thin films deposited by pulsed laser ablation technique

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Natural Science 2010年第10期2卷 1073-1078页

作者： Neelam Kumari Saluru baba Krupanidhi kalidhindi balakrishna raju varma 不详

The pulsed laser ablation technique has been employed to fabricate bilayer thin films con-sisting of layered structure ferroelectric bismuth vanadate (bi2VO5.5) and bismuth titanate (bi4Ti3O12) on platinized silicon substrate. The phase formation of these films was confirmed by X-ray diffraction (XrD) studies and the crystallites in these bilayers were randomly oriented as indicated by diffraction pattern consisting of the peaks corresponding to both the materials. The homogeneous distribution of grains (~300 nm) in these films was confirmed by atomic force microscopy. The cross-sectional scanning electron microscopy indicated the thickness of these films to be around 350 nm. The film exhi-bited P-E hysteresis loops with Pr ~ 11 ?C/cm2 and Ec ~ 115 kV/cm at room temperature. The dielectric constant of the bilayer was ~ 225 at 100 kHz which was higher than that of homogeneous bi2VO5.5 film.

关键词： Thin Films Ferroelectric Dielectric Laser ablation

Unmanned aerial vehicle (UAV)-assisted pesticide application for pest and disease prevention and control in rice

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International Journal of Agricultural and biological Engineering 2024年第5期17卷 88-95页

作者： Sreenath ragiman Kiran babu Talluri varma NrG Vidya Sagar b Department of Plant Pathology College of AgricultureRajendranagarProfessor Jayashankar Telangana State Agricultural UniversityHyderabad 500030India Institute of rice research ARIProfessor Jayashankar Telangana State Agricultural UniversityHyderabad 500030India

Unmanned Aerial Vehicles (UAVs) have emerged as innovative tools in agriculture, revolutionizing crop protection practices and the use of pesticide combinations to aid the management of insect pests and diseases in a single application. This research delves into assessing the efficacy of drone-based pesticide spraying utilizing combinations of pesticides to combat insect pests and diseases in rice cultivation. In kharif 2022, the physically compatible combination of insecticides (chlorantraniliprole 18.5% SC and tetraniliprole 200 SC) with fungicides (picoxystrobin 7.5%+tricyclazole 22.5% SC and tebuconazole 50%+trifloxystrobin 25% WG) were administered via drones and compared with conventional Taiwan sprayer. The results indicated that tebuconazole+trifloxystrobin, when applied via drones, exhibited the highest control efficacy against the brown spot, sheath blight, and sheath rot (47.8%, 77.4%, and 75.2% respectively). Moreover, combination treatment, i.e., tetraniliprole+(tebuconazole+trifloxystrobin), applied using a drone, achieved the most effective control (78.1%) against grain discoloration. Additionally, drone-based tetraniliprole application showed effectiveness against stem borer and whorl maggot (efficacy rates of 49.1%, 66.6%, and 60.7% for dead hearts, white ear, and whorl maggot, respectively). Overall, the pesticide combination treatment, i.e., tetraniliprole+(tebuconazole+trifloxystrobin), showed higher control efficacy against all the insect pests and diseases and recorded the highest grain yield of 7995 kg/hm2 with an incremental cost-benefit ratio (ICbr) of (1:5.63) when sprayed with a drone. Overall, this study underscores the potential of drone-assisted pesticide application in effectively managing multiple insect pests and diseases in rice, offering superior precision, efficacy, efficiency, and yield.

关键词： bio-efficacy drone spraying drone-based pest management precision agriculture pesticide combinations

Cryptic species composition and genetic diversity within bemisia tabaci complex in soybean in India revealed by mtCOI DNA sequence

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Journal of Integrative Agriculture 2015年第9期14卷 1786-1795页

作者： Prasanna H C Kanakala S Archana K Jyothsna P varma r K Malathi V G Division of Vegetable Improvement Indian Institute of Vegetable Research Advanced Centre for Plant Virology Division of Plant PathologyIndian Agricultural Research Institute Department of Plant Pathology Jawaharlal Nehru Krishi Vishwavidyalaya

bemisia tabaci is a cryptic species complex, causing signiifcant loss on many agricultural y important crops worldwide. Knowledge on species composition and diversity within b. tabaci complex is critical for evolving sustainable pest management strategies. Here we investigate the whitelfy species complex in soybean in major soybean growing states of India. The mitochondrial cytochrome oxidase gene subunit-1 (mtCOI) based phylogenetic relationships established using bayesian methods indicated the existence of three cryptic species namely Asia I, Asia II 1, and Asia II 7. Al the haplotypes detected in the study could be assigned to these three cryptic species fol owing the species demarcation criteria of 3.5%divergence threshold. Of these, Asia II 1 was found to be predominant with wide spread distribution across the surveyed regions from cool temperate zones to hot and humid tropical plains. On the contrary, cryptic species Asia II 7 showed localized distribu-tion. The Asia II 1 exhibited the highest haplotype diversity and Asia I showed high level of nucleotide diversity. There was a signiifcantly high genetic differentiation among these three cryptic species. The MEAM 1, a dreadful invasive species was not detected in the specimens tested in the current study. The diversity and distribution of three cryptic species is discussed in the light of current knowledge on distribution of whitelfy species in India and yel ow mosaic disease observed during sampling survey.

关键词： whitefly mitochondrial cytochrome oxidase gene subunit-1 AsiaⅠ AsiaⅡ 1 AsiaⅡ 7 begomovirus and yellow mosaic disease

Effect of TeO_(2) addition on the dielectric properties of CaCu_(3)Ti_(4)O_(12) ceramics derived from the oxalate precursor route

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Journal of Advanced Dielectrics 2013年第4期3卷 26-33页

作者： P.Thomas K.b.r.varma Dielectric Materials Division Central Power Research Institute Bangalore 560080India Materials research Centre Indian Institute of Science Bangalore 560012India

CaCu_(3)Ti_(4)O_(12)(CCTO)ceramics which has perovskite structure gained considerable attention due to its giant *** it has high tan(0.1 at 1 kHz)at room temperature,which needs to be minimized to the level of practical ***,TeO_(2) which is a good glass former has been deliberately added to CCTO nanoceramic(derived from the oxalate precursor route)to explore the possibility of reducing the dielectric loss while maintaining the high *** structural,morphological and dielectric properties of the pure CCTO and TeO_(2) added ceramics were studied using X-ray diffraction,Scanning Electron Microscope along with Energy Dispersive X-ray Analysis(EDX),spectroscopy and Impedance *** the 2.0 wt.%TeO_(2) added ceramics,there is a remarkable difference in the microstructural features as compared to that of pure CCTO *** sample exhibited permittivity values as high as 7387 at 10 KHz and low dielectric loss value of 0.037 at 10 kHz,which can be exploited for the high frequency capacitors application.

关键词： Dielectric TeO_(2) CaCu_(3)Ti_(4)O_(12) ceramic

STrUCTUrAL AND DIELECTrIC PrOPErTIES OF GLASSES IN THE SYSTEM TeO_(2)-CaCu_(3)Ti_(4)O_(12)

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Journal of Advanced Dielectrics 2012年第4期2卷 47-54页

作者： P.THOMAS K.b.r.varma Dielectric Materials Division Central Power research Institute Bangalore 560080India Materials research Centre Indian Institute of Science Bangalore 560012India

The glasses in the system(100-x)TeO_(2)-xCaCu_(3)Ti_(4)O_(12),(x=0.25 mol.%to 3 mol.%)were *** color varied from olive green to brown as the CaCu_(3)Ti_(4)O_(12)(CCTO)content increased in TeO_(2) *** X-ray powder diffraction and differential scanning calorimetric analyses that were carried out on the as-quenched samples confirmed their amorphous and glassy nature *** dielectric constant and loss in the 100Hz1MHz frequency range were monitored as a function of temperature(50-400℃).The dielectric constant(ε′_(τ))and the loss(D)increased as the CCTO content increased in TeO_(2) at all the frequencies and temperatures under ***,the ε′_(τ) and D were found to be frequency-independent in the 50-200℃ temperature *** value obtained for the loss at 1MHz was 0.0019 which was typical of low loss materials,and exhibited near constant loss(NCL)in the 100Hz-1MHz frequency *** electrical relaxation was rationalized using the electric modulus *** glasses may be of considerable interest as substrates for high frequency circuit elements in conventional semiconductor industries owing to their high thermal stability.

关键词： Dielectric TeO_(2) CaCu_(3)Ti_(4)O_(12) glass

Static and cyclic oxidation of Nb-Cr-V-W-Ta high entropy alloy in air from 600 to 1400℃

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Journal of Materials Science & Technology 2020年第3期38卷 189-196页

作者： S.K.varma Francelia Sanchez Sabastian Moncayo C.V.ramana Department Metallurgical Materials and Biomaterials EngineeringThe University of Texas at El PasoEl PasoTX79968-0520USA Center for Advanced Materials research(CMr) The University of Texas at El PasoEl PasoTX79968-0520USA

An oxidation resistance study has been made on Nb-Cr-V-W-Ta high entropy alloy in a range of temperature from 600 to 1400℃in *** oxidation study has been performed for either(a)12 or 24 h of heating time or(b)3 or 10℃/min heating rates to the desired oxidation *** oxidation study conducted for three and a half days has been conducted at 600,700,and 800℃using 12 h of heating *** alloy can withstand the cyclic oxidation process with only a reasonable loss of *** identification of oxides indicates crystals of W and Ta oxides in cylindrical form while Nb and Cr oxides show a nodular or granular morphology at both 1000 and 1200℃while and additional of oxide of V in whisker forms at 1200℃.

关键词： High entropy alloys Nb-Cr-V-W-Ta Microstructures Oxidation