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- 저자 : B. Karthik (검색결과 13 건)
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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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Senthilkumar, S.,Karthik, B.,Chandrasekar, S. The Korean Institute of Electrical Engineers 2014 Journal of Electrical Engineering & Technology Vol.9 No.5
Partial discharge (PD) detection plays a major role in the life time assessment of liquid insulation in power transformers. Many research works are being carried out to replace conventional mineral oil insulation in transformers by vegetable oils. It is necessary to understand the PD characteristics of vegetable oils before recommending them as an alternate for mineral oil. In this paper, the breakdown strength and PD characteristics of palm and corn oil were investigated in both unaged and thermally aged conditions. Laboratory experiments were performed as per IEC test procedures. PD signals were measured using wide band detection system. Phase resolved PD pattern of vegetable oils and mineral oil were compared. Effect of increase in voltage stress on the PD pattern of palm and corn oil were studied. Time and frequency domain analysis of PD pulses at needle-plane electrode configuration was carried out. Statistical analysis of PD pattern i.e. skewness and shape parameter variations with respect to applied thermal stress were also carried out. From the results, it is observed that palm and corn oils have better breakdown strength and PD characteristics even under long-term thermal stress and hence they can be used for power transformer applications.
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S.Senthilkumar,B.Karthik,S.Chandrasekar 대한전기학회 2014 Journal of Electrical Engineering & Technology Vol.9 No.5
Partial discharge (PD) detection plays a major role in the life time assessment of liquid insulation in power transformers. Many research works are being carried out to replace conventional mineral oil insulation in transformers by vegetable oils. It is necessary to understand the PD characteristics of vegetable oils before recommending them as an alternate for mineral oil. In this paper, the breakdown strength and PD characteristics of palm and corn oil were investigated in both unaged and thermally aged conditions. Laboratory experiments were performed as per IEC test procedures. PD signals were measured using wide band detection system. Phase resolved PD pattern of vegetable oils and mineral oil were compared. Effect of increase in voltage stress on the PD pattern of palm and corn oil were studied. Time and frequency domain analysis of PD pulses at needle-plane electrode configuration was carried out. Statistical analysis of PD pattern i.e. skewness and shape parameter variations with respect to applied thermal stress were also carried out. From the results, it is observed that palm and corn oils have better breakdown strength and PD characteristics even under long-term thermal stress and hence they can be used for power transformer applications.
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Augustine Amalraj,Karthik Varma,Joby Jacob,Chandradhara Divya,Ajaikumar B. Kunnumakkara,Sidney J. Stohs,Sreeraj Gopi 한국식품영양과학회 2017 Journal of medicinal food Vol.20 No.10
Rheumatoid arthritis (RA) is an autoimmune, chronic systemic inflammatory disorder. The long-term use of currently available drugs for the treatment of RA has many potential side effects. Natural phytonutrients may serve as alternative strategies for the safe and effective treatment of RA, and curcuminoids have been used in Ayurvedic medicine for the treatment of inflammatory conditions for centuries. In this study, a novel, highly bioavailable form of curcumin in a completely natural turmeric matrix was evaluated for its ability to improve the clinical symptoms of RA. A randomized, double-blind, placebo-controlled, three-arm, parallel-group study was conducted to evaluate the comparative efficacy of two different doses of curcumin with that of a placebo in active RA patients. Twelve patients in each group received placebo, 250 or 500 mg of the curcumin product twice daily for 90 days. The responses of the patients were assessed using the American College of Rheumatology (ACR) response, visual analog scale (VAS), C-reactive protein (CRP), Disease Activity Score 28 (DAS28), erythrocyte sedimentation rate (ESR), and rheumatoid factor (RF) values. RA patients who received the curcumin product at both low and high doses reported statistically significant changes in their clinical symptoms at the end of the study. These observations were confirmed by significant changes in ESR, CPR, and RF values in patients receiving the study product compared to baseline and placebo. The results indicate that this novel curcumin in a turmeric matrix acts as an analgesic and anti-inflammatory agent for the management of RA at a dose as low as 250 mg twice daily as evidenced by significant improvement in the ESR, CRP, VAS, RF, DAS28, and ACR responses compared to placebo. Both doses of the study product were well tolerated and without side effects.
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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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Amritha P. P.,Karthik Gadabanahalli,Venkatraman Bhat,Kishore Kumar B. N. 한국간담췌외과학회 2021 Annals of hepato-biliary-pancreatic surgery Vol.25 No.1
Estimation of quantity and rate of bleeding is of great value in the management of patients with acute GI bleed. Endoscopy and multiphase contrast enhanced computed tomography (MCECT) are the presently employed two important methods for this purpose. Still there is a lacuna in the methods of precise estimation of amount of bleed, which at the moment are somewhat unreliable and subjectively evaluated. We present the value of dynamic contrast-enhanced CT examination in quantitatively estimating the amount of extravasated blood with the help of three illustrative clinical examples. Technique CT examination, the methodology for assessment of quantity of bleed is presented and the discussion of existing literature regarding the estimation methods is presented.
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Narayanan, V. Jayaprakash,Karthik, B.,Chandrasekar, S. The Korean Institute of Electrical Engineers 2014 Journal of Electrical Engineering & Technology Vol.9 No.4
Flashover of power transmission line insulators is a major threat to the reliable operation of power system. This paper deals with the flashover prediction of polymeric insulators used in power transmission line applications using the novel condition monitoring technique developed by PD signal time-frequency map and neural network technique. Laboratory experiments on polymeric insulators were carried out as per IEC 60507 under AC voltage, at different humidity and contamination levels using NaCl as a contaminant. Partial discharge signals were acquired using advanced ultra wide band detection system. Salient features from the Time-Frequency map and PRPD pattern at different pollution levels were extracted. The flashover prediction of polymeric insulators was automated using artificial neural network (ANN) with back propagation algorithm (BPA). From the results, it can be speculated that PD signal feature extraction along with back propagation classification is a well suited technique to predict flashover of polymeric insulators.
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V. Jayaprakash Narayanan,B. Karthik,S. Chandrasekar 대한전기학회 2014 Journal of Electrical Engineering & Technology Vol.9 No.4
Flashover of power transmission line insulators is a major threat to the reliable operation of power system. This paper deals with the flashover prediction of polymeric insulators used in power transmission line applications using the novel condition monitoring technique developed by PD signal time-frequency map and neural network technique. Laboratory experiments on polymeric insulators were carried out as per IEC 60507 under AC voltage, at different humidity and contamination levels using NaCl as a contaminant. Partial discharge signals were acquired using advanced ultra wide band detection system. Salient features from the Time-Frequency map and PRPD pattern at different pollution levels were extracted. The flashover prediction of polymeric insulators was automated using artificial neural network (ANN) with back propagation algorithm (BPA). From the results, it can be speculated that PD signal feature extraction along with back propagation classification is a well suited technique to predict flashover of polymeric insulators.
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Arvind Shriram, R.K.,Chandrasekar, S.,Karthik, B. The Korean Institute of Electrical Engineers 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 $SiO_2$ 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 $nano-SiO_2$ 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 $SiO_2$ nanofillers in palm oil. These results will be useful for recommending nano modified palm oil for power transformer applications.
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