Status of the Red-Listed Plant Species, Smilax wightii A. DC. in Nilgiri Biosphere Reserve, the Western Ghats, India

S. Paulsamy,길봉섭,K.K. Vijayakumar,P. Senthilkumar 한국생태학회 2009 Journal of Ecology and Environment Vol.32 No.4

The rare endemic plant, Smilax wightii, is generally distributed in shola forests at high altitudes in Nilgiri Biosphere Reserve, the Western Ghats, southern India. To determine the ecological status of the species, we surveyed 11 major shola forests in that region. S. wightii has a limited distribution in all sholas (frequency value of <13%). The density of the species is generally around 15/100 m² in the sholas except in Thiashola where it occurred at a density of 40 individuals/100 m². The density of S. wightii was generally greater in the margins of the shoals, while the interior forests contained fewer individuals per unit area. The basal cover occupied by this species ranged between 2246 and 3144 mm²/100 m². The importance value index for S. wightii was >2 in all shoals, which indicates that the species occupies an important position in the lower stratum of shola forests of Nilgiri Biosphere Reserve.

Status of the Red-Listed Plant Species, Smilax wightii A. DC. in Nilgiri Biosphere Reserve, the Western Ghats, India

Paulsamy, S.,Vijayakumar, K.K.,Kil, Bong-Seop,Senthilkumar, P. The Ecological Society of Korea 2009 Journal of Ecology and Environment Vol.32 No.4

The rare endemic plant, Smilax wightii, is generally distributed in shola forests at high altitudes in Nilgiri Biosphere Reserve, the Western Ghats, southern India. To determine the ecological status of the species, we surveyed 11 major shola forests in that region. S. wightii has a limited distribution in all sholas (frequency value of < 13%). The density of the species is generally around $15/100\;m^2$ in the sholas except in Thiashola where it occurred at a density of 40 individuals/$100\;m^2$. The density of S. wightii was generally greater in the margins of the shoals, while the interior forests contained fewer individuals per unit area. The basal cover occupied by this species ranged between 2246 and $3144\;mm^2/100\;m^2$. The importance value index for S. wightii was >2 in all shoals, which indicates that the species occupies an important position in the lower stratum of shola forests of Nilgiri Biosphere Reserve.

Investigations on PD Characteristics of Thermal aged Palm and Corn Oil for Power Transformer Insulation Applications

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.

Flexible and wearable fiber shaped high voltage supercapacitors based on copper hexacyanoferrate and porous carbon coated carbon fiber electrodes

Senthilkumar, S. T.,Kim, J.,Wang, Y.,Huang, H.,Kim, Y. Royal Society of Chemistry 2016 Journal of Materials Chemistry A Vol.4 No.13

<P>In this work, we report the fabrication of a new high voltage hybrid fiber supercapacitor (HFSC) with porous carbon coated carbon fibers (PC@CFs) as the negative electrode and copper hexacyanoferrate coated carbon fibers (CuHCF@CFs) as the positive electrode. Carbon fibers (CFs) were used as both the substrate and the current collector due to their good conductivity, high flexibility, good mechanical strength, and light weight. The as-fabricated HFSC can be cycled reversibly in the range of 0-2 V and exhibits excellent electrochemical performance with a specific capacitance of 19.2 F g(-1) (68.2 mF cm(-2) or 3.1 F cm(-3)) and an energy density of 10.6 W h kg(-1) (180.85 mu Wh cm(-2) or 8.11 mW h cm(-3)), better than those reported in the previous literature. Additionally, the HFSCs have retained their original electrochemical performance even after bending, suggesting good flexibility of the device. The promising results show great potential in developing HFSCs with CuHCF@CFs and PC@CFs electrodes for practical wearable devices.</P>

NUMERICAL SOLUTION FOR ROBOT ARM PROBLEM USING LIMITING FORMULAS OF RK(7,8)

Senthilkumar, S. Korean Society of Computational and Applied Mathem 2008 Journal of applied mathematics & informatics Vol.26 No.3-4

The aim of this article is focused on providing numerical solutions for system of second order robot arm problem using the RK-eight stage seventh order limiting formulas. The parameters governing the arm model of a robot control problem have also been discussed through RK-eight stage seventh order limiting algorithm. The precised solution of the system of equations representing the arm model of a robot has been compared with the corresponding approximate solutions at different time intervals. Results and comparison show the efficiency of the numerical integration algorithm based on the absolute error between the exact and approximate solutions. Based on the numerical results a thorough comparison is carried out between the numerical algorithms.

Sodium-ion hybrid electrolyte battery for sustainable energy storage applications

Senthilkumar, S.T.,Abirami, Mari,Kim, Junsoo,Go, Wooseok,Hwang, Soo Min,Kim, Youngsik Elsevier 2017 Journal of Power Sources Vol.341 No.-

<P><B>Abstract</B></P> <P>Sustainable, safe, and low-cost energy storage systems are essential for large-scale electrical energy storage. Herein, we report a sodium (Na)-ion hybrid electrolyte battery with a replaceable cathode system, which is separated from the Na metal anode by a Na superionic conducting ceramic. By using a fast Na-ion-intercalating nickel hexacyanoferrate (NiHCF) cathode along with an eco-friendly seawater catholyte, we demonstrate good cycling performance with an average discharge voltage of 3.4 V and capacity retention >80% over 100 cycles and >60% over 200 cycle. Remarkably, such high capacity retention is observed for both the initial as well as replaced cathodes. Moreover, a Na-metal-free hybrid electrolyte battery containing hard carbon as the anode exhibits an energy density of ∼146 Wh kg<SUP>−1</SUP> at a current density of 10 mA g<SUP>−1</SUP>, which is comparable to that of lead-acid batteries and much higher than that of conventional aqueous Na-ion batteries. These results pave the way for further advances in sustainable energy storage technology.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A novel sodium-ion hybrid electrolyte battery is fabricated. </LI> <LI> Nickel hexacyanoferrate is prepared via a precipitation method for the cathode. </LI> <LI> Cathode part is an open system which enables a cathode replaceable. </LI> <LI> Seawater used as a low cost and eco-friendly catholyte. </LI> <LI> Both fresh and replaced cathode exhibit excellent electrochemical performances. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Investigations on PD Characteristics of Thermal aged Palm and Corn Oil for Power Transformer Insulation Applications

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.

Performance characteristics of p-i-n hetero-junction organic photovoltaic cell with CuPc:F₄-TCNQ hole transport layer

Senthilkumar, N.,Park, S.,Kang, H.S.,Park, D.W.,Choe, Y. Korean Society of Industrial and Engineering Chemi 2011 Journal of industrial and engineering chemistry Vol.17 No.4

We have investigated the effect of strong p-type organic semiconductor F<SUB>4</SUB>-TCNQ-doped CuPc hole transport layer on the performance of p-i-n hetero-junction photovoltaic device from ITO/PEDOT:PSS/CuPc:F<SUB>4</SUB>-TCNQ (5wt%)/CuPc:C60 (blending ratio 1:1)/C60/BCP/LiF/Al, fabricated via vacuum deposition process and have evaluated the J-V characteristics such as short circuit current (J<SUB>sc</SUB>), open circuit voltage (V<SUB>oc</SUB>), fill factor (FF) and energy conversion efficiency (η<SUB>e</SUB>) of the device. By doping of F<SUB>4</SUB>-TCNQ into CuPc hole transport layer, absorption intensities in absorption spectra were increased, which supports that uniform dispersion of organic molecules in the hole transport layer with lowered value of surface roughness can be obtained. Eventually, current injection was enhanced through the layer, which comparatively improves the performance of the photovoltaic cell with energy conversion efficiency of 0.50% in this study.

Seawater battery performance enhancement enabled by a defect/edge-rich, oxygen self-doped porous carbon electrocatalyst

Senthilkumar, S. T.,Park, Sung O.,Kim, Junsoo,Hwang, Soo Min,Kwak, Sang Kyu,Kim, Youngsik Royal Society of Chemistry 2017 Journal of Materials Chemistry A Vol.5 No.27

<P>Low-cost oxygen evolution/reduction reaction (OER/ORR) catalysts are critically important for energy conversion/storage systems. Here, a porous carbon (PC) catalyst is prepared as a low-cost catalyst from grapefruit peel biowaste using a facile hydrothermal carbonization combined with a chemical activation process. When examined as an OER/ORR catalyst in seawater, the PC exhibits an unexpected, highly efficient catalytic activity. From density functional theory (DFT) calculations, we found that sp<SUP>3</SUP>-bonded carbon atoms, zigzag edges with or without -COOH and -OH, and armchair edges with -O- are responsible for its superior OER/ORR activity. The suitability of the PC as a catalyst is tested in the half-cell of a Na/seawater battery, which exhibits a decreased voltage gap of ∼0.47 V between charge and discharge voltage curves. This value is even lower than those of Pt/C (∼0.68 V), IrO2(∼0.66 V) and MnO2(∼0.73). Also, a full cell of the metal-free seawater battery is assembled using hard carbon and PC as an anode and a catalyst, respectively. The full cell shows a lower voltage gap (∼0.65 V) with the voltage efficiency of ∼83-84% and excellent cycle life over 100 cycles. Our results confirm PC derived from grapefruit peels as an alternative to expensive Pt/C and IrO2catalysts for the OER/ORR activities in seawater batteries.</P>

Potentiostatic activation of as-made graphene electrodes for high-rate performance in supercapacitors

Senthilkumar, K.,Jeong, S.,Lah, M.S.,Sohn, K.S.,Pyo, M. Elsevier Sequoia 2016 Journal of Power Sources Vol. No.

A thermally expanded graphene oxide (EGO) electrode is electrochemically activated to simultaneously introduce electrolyte-accessible mesopores and oxygen functional groups. The former is produced via O<SUB>2</SUB> evolution and the latter is incorporated by the intermediate hydroxyl radicals generated during the potentiostatic oxidation of H<SUB>2</SUB>O in 1 M H<SUB>2</SUB>SO<SUB>4</SUB> at 1.2 V (vs. Ag/AgCl). When applied as a supercapacitor, the potentiostatically treated EGO (EGO-PS) shows significant enhancement in an electric-double layer (EDL) process with a noticeable Faradaic reaction and delivers high capacitance at fast charge/discharge (C/D) rates (334 F g<SUP>-1</SUP> at 0.1 A g<SUP>-1</SUP> and 230 F g<SUP>-1</SUP> at 50 A g<SUP>-1</SUP>). In contrast to EGO-PS, EGO that is oxidized potentiodynamically (EGO-PD) shows negligible enhancement in EDL currents. EGO that is subjected to successive potential pulses also shows behaviors similar to EGO-PD, which indicates the importance of hydroxyl radical accumulation via a potentiostatic method for simultaneous functionalization and microstructural control of graphenes. The potentiostatic post-treatment presented here is a convenient post-treatment strategy that could be used to readily increase capacitance and simultaneously improve the high-rate performance of carbon-based electrodes.