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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 technique. For 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 properties. The structural, morphological, dielectric, and piezoelectric properties of these nano and micro crystal composites were investigated. The incorporation of kNN fillers in PVDF at both nanometer and micron scales above 10 vol% resulted in the formation of polar β-form of PVDF. The 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 frequency. Various theoretical models were employed to predict the dielectric constants of the PVDF–kNN nano and micro crystal composites. The 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) k 0.5 Na 0.5 NbO 3 (kNN) composites β -PVDF nanocrystallites

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

Thermo-diffusion impact on immiscible flow characteristics of convectively heated vertical two-layered baffle saturated porous channels in a suspension of nanoparticles:an analytical study

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Applied Mathematics and Mechanics(English Edition) 2023年第2期44卷 307-324页

作者： S.P.V.ANANTH b.N.HANUMAGOWDA S.V.k.varma C.S.k.rAJU I.kHAN P.rANA Department of Mathematics School of Applied SciencesREVA UniversityBangalore 560064India Department of Mathematics GITAM School of ScienceGITAM UniversityBangalore 562163India Department of Mathematics College of Science Al-ZulfiMajmaah UniversityAl-Majmaah 11952Saudi Arabia School of Mathematical Sciences College of Science and TechnologyWenzhou-Kean UniversityWenzhou 325060Zhejiang ProvinceChina

The heat and mass transfer of two immiscible fluids in an inclined channel with thermal diffusion,vicious,and Darcy dissipation is *** first region consists of a clear fluid,and the second one is filled with a nanofluid saturated with a porous *** behaviors of Cu-H_(2)O,In-H_(2)O,and Au-H_(2)O nanofluids are *** transport properties are assumed to be *** coupled non-linear equations of the flow model are transformed into the dimensionless form,and the solutions for the velocity,temperature,and concentration are obtained by the regular perturbation *** are carried out on the flow characteristics for various values of the material *** results show that the velocity and temperature of the fluids enhance with the thermal Grashof number,solutal Grashof number,and brinkman number while decrease with the porosity parameter and solid volume fraction.

关键词： viscous fluid nanofluid heat and mass transfer thermal diffusion

Analytical analysis of inclined three-layered composite channel with cobalt ferrite nanoparticles and Hall current in Darcy medium

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Propulsion and Power research 2023年第4期12卷 523-538页

作者： P.V.Ananth Subray b.N.Hanumagowda C.S.k.raju S.V.k.varma Prakash Jagdish Se-Jin Yook Nehad Ali Shah Department of Mathematics School of Applied SciencesREVA UniversityBengaluruKarnatakaIndia School of Mechanical Engineering Hanyang University222 Wangsimni-roSeongdong-guSeoul 04763Republic of Korea Department of Mechanical Engineering Science Faculty of Engineering&The Built EnvironmentUniversity of JohannesburgSouth Africa Department of Mechanical Engineering Sejong UniversitySeoul 05006Republic of Korea

The present study explores the influence of electromagnetic effects on the flow of a nanofluid in a saturated permeable medium,confined between a clear viscous fluid in an inclined *** nanofluid consists of cobalt ferrite nanoparticles dispersed in ethylene *** governing equations are derived considering Darcy's law for the permeable medium and Tiwari's model for fluids containing nano-sized ***,radiation and dissipation effects are incorporated into the energy *** equations are transformed into dimensionless form and solved analytically using the perturbation *** results are analyzed through graphs and tables for different material *** findings reveal that higher electric and magnetic strengths have a significant impact on the fluid velocity at the interface of the two fluids,resulting in reduced shear both at the clear fluid surface and the interface between *** highlights the crucial role played by electric and magnetic strengths in modifying flow ***,combining electric and magnetic strengths with nanofluids can be utilized to achieve desired qualities in multi-fluid flow and enhance heat transfer characteristics.

关键词： Three-layered flow Inclined composite channel Electromagnetic field Nanofluid Porous region

Spectral narratives of microstructural restyling and their controls on hydrocarbon generation potential from coal

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International Journal of Coal Science & Technology 2023年第3期10卷 167-189页

作者： Tushar Adsul Santanu Ghosh Anwita Ojha Sudip bhattacharyya Atul kumar varma Coal Geology and Organic Petrology Laboratory Department of Applied GeologyIndian Institute of Technology(Indian School of Mines)DhanbadJharkhand 826004India Department of Geology Mizoram UniversityAizawlMizoram 796004India Specialized Coal Petrography Laboratory Natural Energy ResourcesMission II-BGeological Survey of IndiaDK-6Sector-IlSalt Lake CityKolkataWest Bengal 700091India

The low to medium-rank Tertiary coals from Meghalaya,India,are explored for the first time for their comprehensive micro-structural characterization using the FTIr and raman ***,results from these coals are compared with the Permian medium and high-rank coals to understand the microstructural restyling during coalification and its controls on hydrocarbon *** coal samples are grouped based on the mean random vitrinite reflectance values to record the transformations in spectral attributes with increasing coal *** aliphatic carbon and the apparent aromaticity respond sharply to the first coalification jump(r:0.50%)during low to medium-rank transition and anchizonal metamorphism of the high-rank ***,the raman band intensity ratio changes during the first coalification jump but remains invari-able in the medium-rank coals and turns subtle again during the onset of pregraphitization in high-rank coals,revealing a polynomial trend with the coal *** rock-Eval hydrogen index and genetic potential also decline sharply at the first coalification ***,an attempt to comprehend the coal microstructural controls on the hydrocarbon poten-tial reveals that the Tertiary coals comprise highly reactive aliphatic functionalities in the type I-S kerogen,along with the low paleotemperature(74.59-112.28℃)may signify their potential to generate early-mature ***,the presence of type II-II admixed kerogen,a lesser abundance of reactive moieties,and overall moderate paleotemperature(91.93-142.52℃)of the Permian medium-rank coals may imply their mixed hydrocarbon ***,anchizonal metamorphism,polycondensed aromatic microstructure,and high values of paleotemperature(~334.25 to~366.79℃)of the high-rank coals indicate a negligible potential of producing any hydrocarbons.

关键词： Early mature oil generation Meghalaya high-sulfur coal Type II-S kerogen Microstructural ordering Coalification jump Hydrocarbon generation potential

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

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

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

Influence of coke structure on coke quality using image analysis method

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International Journal of Coal Science & Technology 2018年第4期5卷 473-485页

作者： b.Ghosh b.k.Sahoo b.Chakrabortv k.k.Manjhi S.k.Das J.N.Sahu Atul k.varma research & Development Centre for Iron and Steel Steel Authority of India Limited (SAIL)RanchiJharkhand 834002India Institute of Chenlical Technology Faculty of ChemistryUniversity of Stuttgart70550 StuttgartGermany Coal Geology and Organic Petrology Laboratory Department of Applied GeologyIITIndian School of Mines (ISM)Dhanbad 826004India South Ural State University 76Lenin Aven.ChelyabinskRussia 454080

The quality of coke affects the performance of the blast furnace, factors affecting coke quality include coal properties, coal charge granulometry and carbonization conditions. The coke properties in elude the size analysis, cold strength (Micum Indices-M4(). MI0) and hot strength (Coke reactivity Index-CrI, Coke Strength after reaction-CSr) properties and structural properties such as coke structure and texture. Structural properties comprise the porosity, pore-cell wall thickness and pore sizes, while textures consist of the carbon forms in the coke. In present work, advanced method such as image analysis method was used to interpret coke microstructure. Conventional methods such as determination of coke porosity by measurement of real and apparent density and mercury porosimetry have a number of limitations. Coke size, magnification, number of image frames captured, process of pellet preparations and coke properties such as M4(), M|0, CrI and CSr (low, medium and high values) were taken as variables for experimental purposes. The coke structure parameters such as porosity, length, perimeter, breadth, roundness, pore-wall thickness and pore size distribution of the pores were determined by image analysis method. This method provided average porosity in addition to pore-wall thickness and pore-size distribution. The pore wall thickness measuremenl by image analysis method provided significant correlations with M40, CrI and CSr values. This explained the usability of image analysis for coke structure measurement.

关键词： Image analysis Coke structure Porosity Micro structure roundness Pore wall thickness