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- 저자 : R.Karthik (검색결과 15 건)
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R. Thanigaiselvan,T. Sree Renga Raja,R.Karthik 대한전기학회 2015 Journal of Electrical Engineering & Technology Vol.10 No.6
Transformer mineral oil which is normally hydrocarbon based is non- biodegradable and pollutes the environment in all aspects. Though vegetable oils are eco-friendly in nature and potentially could be used in transformers as a replacement for the mineral oil, there usage is restricted because of their oxidative instability. The present work focuses on using rapeseed oil and pongamia (pongamia pinnata) oil as effective alternatives for the traditional mineral oil in power transformer. The oxidative stability of the rapeseed oil and pongamia oil is increased by using combinations of the natural and synthetic anti-oxidants as additives. The parameters like breakdown voltage, viscosity, flash point, fire point are measured for the rapeseed oil and pongamia oil with and without the additives as per IEC and ASTM standards. The results shown encouraging changes in the parameter values and ensures the use of the oils as a potential alternative insulation in power transformers.
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R. Karthik,Yu-Shen Hou,Shen-Ming Chen,A. Elangovan,M. Ganesan,P. Muthukrishnan 한국공업화학회 2016 Journal of Industrial and Engineering Chemistry Vol.37 No.-
In the present investigation, we report a facile, reproducible and effortless biological synthesis of silvernanoparticles (Ag-NPs) utilizing Cerasus serrulata (C. serrulata) leaves extract as reducing as well asstabilizing agent. The size of synthesized Ag-NPs was in the range of 15–24 nm when examined withtransmission electron microscopy (TEM) and X-ray diffraction studies. The Ag-NPs obtained using C. serrulata exhibited excellent catalytic activity towards reduction of 4-nitrophenol (4-NPh) to 4-aminophenol in the presence of NaBH4 and demonstrate noteworthy electrochemical performance for 4-NPh reduction. The linear range, detection limit and sensitivity are estimated as 0.09–82.5 mM(r = 0.991), 0.06 mM and 3.0 mA mM 1 cm2 respectively. The Ag-NPs were found to show higherantimicrobial efficiency against Streptococcus mutans and Staphylococcus aureus.
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Delineation of ischemic lesion from brain MRI using attention gated fully convolutional network
R. Karthik,Menaka Radhakrishnan,R. Rajalakshmi,Joel Raymann 대한의용생체공학회 2021 Biomedical Engineering Letters (BMEL) Vol.11 No.1
Precise delineation of the ischemic lesion from unimodal Magnetic Resonance Imaging (MRI) is a challenging task due tothe subtle intensity difference between the lesion and normal tissues. Hence, multispectral MRI modalities are used for characterizingthe properties of brain tissues. Traditional lesion detection methods rely on extracting significant hand-engineeredfeatures to differentiate normal and abnormal brain tissues. But the identification of those discriminating features is quitecomplex, as the degree of differentiation varies according to each modality. This can be addressed well by ConvolutionalNeural Networks (CNN) which supports automatic feature extraction. It is capable of learning the global features from imageseffectively for image classification. But it loses the context of local information among the pixels that need to be retained forsegmentation. Also, it must provide more emphasis on the features of the lesion region for precise reconstruction. The majorcontribution of this work is the integration of attention mechanism with a Fully Convolutional Network (FCN) to segmentischemic lesion. This attention model is applied to learn and concentrate only on salient features of the lesion region bysuppressing the details of other regions. Hence the proposed FCN with attention mechanism was able to segment ischemiclesion of varying size and shape. To study the effectiveness of attention mechanism, various experiments were carried outon ISLES 2015 dataset and a mean dice coefficient of 0.7535 was obtained. Experimental results indicate that there is animprovement of 5% compared to the existing works.
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Thanigaiselvan, R.,Raja, T. Sree Renga,Karthik, R. The Korean Institute of Electrical Engineers 2015 Journal of Electrical Engineering & Technology Vol.10 No.6
Transformer mineral oil which is normally hydrocarbon based is non- biodegradable and pollutes the environment in all aspects. Though vegetable oils are eco-friendly in nature and potentially could be used in transformers as a replacement for the mineral oil, there usage is restricted because of their oxidative instability. The present work focuses on using rapeseed oil and pongamia (pongamia pinnata) oil as effective alternatives for the traditional mineral oil in power transformer. The oxidative stability of the rapeseed oil and pongamia oil is increased by using combinations of the natural and synthetic anti-oxidants as additives. The parameters like breakdown voltage, viscosity, flash point, fire point are measured for the rapeseed oil and pongamia oil with and without the additives as per IEC and ASTM standards. The results shown encouraging changes in the parameter values and ensures the use of the oils as a potential alternative insulation in power transformers.
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R. K.Arvind Shriram,S.Chandrasekar,B.Karthik 대한전기학회 2018 Journal of Electrical Engineering & Technology Vol.13 No.2
In recent times, development of nanofluid insulation for power transformers is a hot research topic. Many researchers reported the enhancement in dielectric characteristics of nano modified mineral oils. Considering the drawbacks of petroleum based mineral oil, it is necessary to understand the dielectric characteristics of nanofluids developed with natural ester based oils. Palm oil has better insulation characteristics comparable to mineral oil. However very few research reports is available in the area of nanofluids based on palm oil. Partial discharge (PD) is one of the major sources of insulation performance degradation of transformer oil. It is essential to understand the partial discharge(PD) characteristics by collecting huge data base of PD performance of nano modified palm oil which will increase its confidence level for power transformer application. Knowing these facts, in the present work, certain laboratory experiments have been performed on PD characteristics of nano SiO2 modified palm oil at different electrode configurations. Influence of concentration of nano filler material on the PD characteristics is also studied. Partial discharge inception voltage, Phase resolved partial discharge (PRPD) pattern, PD signal time-frequency domain characteristics, PD signal equivalent timelength-bandwidth mapping, Weibull distribution statistical parameters of PRPD pattern, skewness, repetition rate and phase angle variations are evaluated at different test conditions. From the results of the experiments conducted, we came to understand that PD performance of palm oil is considerably enhanced with the addition of nano-SiO₂ filler at 0.01%wt and 0.05%wt concentration. Significant reduction in PD inception voltage, repetition rate, Weibull shape parameter and PD magnitude are noticed with addition of SiO₂ nanofillers in palm oil. These results will be useful for recommending nano modified palm oil for power transformer applications.
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R. Rajeswari,S. Chandrasekar,B. Karthik 대한전기학회 2019 Journal of Electrical Engineering & Technology Vol.14 No.2
Recent concern towards environmental and fi re safety of transformer operation has led to the development of natural ester based liquid insulation for power transformers. Recent advancements in nano technology confi rm that the nano modifi ed liquid insulation provides superior dielectric and thermal properties. Statistical analysis of the dielectric properties of nano modifi ed liquid dielectrics is very important to qualify them for high voltage insulation applications. In this work, experimental works are carried out to understand the partial discharge (PD), lightning impulse (LI) and breakdown voltage (BDV) characteristics of corn oil fi lled with SiO 2 nano fi llers at diff erent wt% concentration such as 0.01%, 0.05% and 0.1%. Needle/ plane and rod/plane electrode geometry was used for creation of PD source. PD inception voltage, time domain and frequency domain characteristics of PD signals are evaluated. Weibull parameters of Phase Resolved PD pattern are evaluated. LI tests are performed at needle/plane and needle/sphere electrode geometry with standard 1.2/50 μs waveform at both positive and negative polarity. Weibull distribution analysis of LI breakdown voltage values are evaluated at diff erent experimental conditions. BDV tests are carried out at diff erent electrode gap distances such as 1, 2.5, 4 and 5 mm. Scale parameter and shape parameter of Weibull distribution of BDV values are computed. It is mostly observed that addition of nano SiO 2 fi ller at lower wt% concentration in the range of 0.01–0.05% has substantial eff ect in enhancing the PD, LI and BDV characteristics of corn oil. Improvement in PD, LI and BDV characteristics gives confi dent that nano modifi ed corn oil may be considered for outdoor transformer applications.
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Effect of Mg/Co on the properties of CdS thin films deposited by spray pyrolysis technique
R. Murugesan,S. Sivakumar,K. Karthik,P. Anandan,M. Haris 한국물리학회 2019 Current Applied Physics Vol.19 No.10
Mg, Co doped and (Mg, Co) co-doped CdS thin films were prepared using chemical spray pyrolysis method. It is observed from the X-ray diffraction study that the deposited film exhibit cubic phase of CdS with preferred orientation along the (111) plane and incorporation of Mg and Co has been confirmed form energy dispersive analysis and XPS analysis as well. The doped and codoped CdS thin films exhibit 1LO and 2LO vibrations as confirmed by Raman spectrum. The core level XPS spectra ensures the incorporation of doping elements precisely. The morphological variations due to the incorporation of Co and Mg in CdS thin films have been observed by FE-SEM. The particle sizes and crystalline nature have been revealed from HRTEM images and corresponding SAED patterns. The co-doped CdS thin films show a significant shift blue in absorption spectrum. Improved magnetic properties have been observed for the co-doped CdS thin films
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Strontium in Al–Si–Mg Alloy: A Review
M. R. Sai Ganesh,Nikhil Reghunath,M. J.Levin,Adarsh Prasad,Sanapala Doondi,Karthik V. Shankar 대한금속·재료학회 2022 METALS AND MATERIALS International Vol.28 No.1
The present article reviews the development of cast aluminium alloy with highlights on improvement in the morphological,mechanical, tribological, and ageing properties of Sr modifed Al–Si and Al–Si–Mg alloys. Aluminium and its alloys fndapplication in the automobile and aviation industries. The main objective of utilizing aluminium alloys for structural application, manufacturing of pistons and engine block for automobile industries is its lightweight and low density. However, thelow hardness of these alloys results in a high wear rate. The main factor that afects the properties of aluminium alloys isits microstructure, morphological behaviour, size of the grain and phase distribution. The morphological modifcation forthese alloys is done through diferent processing techniques like casting, heat treatment, solutionising, and alloying elementaddition which augments the mechanical, corrosion, and tribological behaviour of these alloys. Of the alloying elementadditions Sr has proved to a very efective modifer for the alloy, and hence the method of modifcation was studied in detail. The unwanted efects especially porosity, being one of the main factors for failure of components, were investigated andmethods to reduce it according to many researchers were included. Reinforcing the aluminium matrix with ceramic particlesand surface modifcation also enhances the properties of aluminium alloys. The current article reviews the recent techniquesto augment the microstructure, value of hardness, tensile properties, tribological properties, and corrosion behaviour of castAl–Si and Al–Si–Mg alloys by the addition of strontium. Moreover, this review also focuses on the future scope of thesealuminium alloys for structural application in automobile and lightweight industries.
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B. Karthik,R. Veerababu,D. V. V. Satyanarayana 대한금속·재료학회 2016 METALS AND MATERIALS International Vol.22 No.3
Effect of aging and oxidation on strain hardening behaviour of a nickel-free high nitrogen austenitic stainless steel has been investigated using room temperature tensile tests and TEM. The alloy in both oxidised and unoxidised conditions exhibits a transition in flow behaviour that can be described best by the Ludwigson flow relationship as evident from the lowest values of the sum of residual squares, χ 2 , of the fit. The transition in macroscopic flow behaviour with strain has been correlated to change in deformation mechanism from planar slip in the low strain regime (LSR) to deformation twinning and slip in the high strain regime (HSR) in solution treated (ST) condition of the alloy. However, the LSR of the alloy aged for longer times (>100 h) is characterized by the formation of dislocation tangles, while the HSR is marked by the formation of well-defined finer dislocation cell structure. This difference in deformation sub-structures in low and high strain regimes between ST and long term aged samples has been correlated to the change in stacking fault energy due to the precipitation of Cr2N and σ-phases. Further, the alloy in ST condition exhibits the highest strain hardening rate, which then progressively decreases with aging time.
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Reddy, K.R.,Karthik, K.V.,Prasad, S.B.B.,Soni, S.K.,Jeong, H.M.,Raghu, A.V. Pergamon Press 2016 Polyhedron Vol.120 No.-
<P>An organo-inorganic photocatalytic nanocomposite material based on conjugated polymer, polyaniline (PANI) with titanium dioxide (TiO2) nanoparticles has been developed by performing in situ chemical oxidative polymerization of aniline with ammonium persulfate (APS) oxidant in the presence of hydrothermally synthesized TiO2 nanoparticles. The structural and morphological properties of TiO2/PANI nanocomposites were analyzed by transmission electron microscopy (TEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR), respectively. The TEM results of the TiO2/PANI nanocomposites showed that TiO2 nanoparticles of 5-10 nm of sizes are dispersed in the PANI matrix. FT-IR spectra show that the TiO2/PANI nanocomposites are almost identical to the structure of PANI alone. The photocatalytic activities of the nanocomposites were evaluated by the photocatalytic degradation of Rhodamine B (RhB), Methylene Blue (MB) and phenol in the presence of UV-light irradiation. The composite catalysts exhibited higher photocatalytic activity for the degradation of organic pollutants than unmodified TiO2 nanoparticles, which is due to sensitizing effect of PANI. (C) 2016 Published by Elsevier Ltd.</P>
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