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      • KCI등재

        OFDM system with cyclostationary feature detection spectrum sensing

        Arun Kumar,NandhaKumar P. 한국통신학회 2019 ICT Express Vol.5 No.1

        In Orthogonal Frequency Division Multiplexing OFDM, a cyclic prefix (CP) is applied to reduce the intervention between symbols. The CP results in bandwidth wastage, and the solution to this problem leads to the cognitive radio. In the first part of the work, OFDM with CP is presented and integrated with cyclostationary spectrum sensing. Subsequently, OFDM with cyclostationary spectrum sensing without CP is proposed with the function of the filter at the transmitter and receiver being to utilize the bandwidth that is wasted in the CP phase. The Bit Error Rate BER, signal probability detection, false alarm, and error probability are obtained and analyzed.

      • SCISCIESCOPUS

        Au Decorated ZnO hierarchical architectures: Facile synthesis, tunable morphology and enhanced CO detection at room temperature

        Arunkumar, S.,Hou, Tianfeng,Kim, Young-Bae,Choi, Byungchul,Park, Su Han,Jung, Seunghun,Lee, Dong-Weon Elsevier 2017 Sensors and actuators. B Chemical Vol.243 No.-

        <P><B>Abstract</B></P> <P>A highly selective and sensitive gas sensing material was prepared by decorating gold (Au) nanoparticles on zinc oxide <I>(ZnO)</I> nanostructure. First, zinc oxide architectures were synthesised through facile one-pot hydrothermal synthesis route by using zinc acetate as the metal precursors, ethanolamine as the organic Lewis base and water as the reaction medium. The versatile zinc oxide architectures such as (i) nanostars <I>(ZNS)</I>, (ii) marigold flower <I>(ZMF)</I>, (iii) nanorods assembled flower <I>(ZNF)</I> and (iv) nanorods <I>(ZNR)</I> were successfully synthesised by the controlled variation of the reaction medium mole ratio. The crystal structure and morphological evaluation of the as prepared material were investigated in detail by several analytical techniques, and the findings are consistent with each other. The carbon monoxide (CO) sensing ability of the as prepared materials was carried out at different sensing temperature (Ts≤300°C) and at different gas concentration (5–1000 <I>ppm</I>). Gas sensing study clearly shows that the sensor responses are found to be morphology and surface area dependent. Among all the zinc oxide nanostructures, nanostars exhibits excellent sensitivity (S<SUB>R</SUB> ∼31 toward 5 <I>ppm</I>) at the optimized sensing temperature of 275°C. Further, to improve the sensing characteristics and to reduce the operating temperature, different wt% of gold nanopartilces were decorated on the surface of zinc oxide nano-stars by solution impregnation technique. Surface decoration of only 3wt% gold nanoparticles incorporated zinc oxide nanostars exhibits enhanced sensing response (S<SUB>R</SUB> ∼15 toward 50 <I>ppm</I>) at 35°C with an excellent response (Γ<I> <SUB>RES</SUB> </I> ∼8s) and recovery (Γ<I> <SUB>REC</SUB> </I> ∼15s) time. Sensor also posses excellent selectivity toward CO compare to other interfering gases such as methanol, ethanol, acetone and hydrogen.</P>

      • KCI등재

        THE GENERAL SOLUTION AND APPROXIMATIONS OF A DECIC TYPE FUNCTIONAL EQUATION IN VARIOUS NORMED SPACES

        Arunkumar, Mohan,Bodaghi, Abasalt,Rassias, John Michael,Sathya, Elumalai Chungcheong Mathematical Society 2016 충청수학회지 Vol.29 No.2

        In the current work, we define and find the general solution of the decic functional equation g(x + 5y) - 10g(x + 4y) + 45g(x + 3y) - 120g(x + 2y) + 210g(x + y) - 252g(x) + 210g(x - y) - 120g(x - 2y) + 45g(x - 3y) - 10g(x - 4y) + g(x - 5y) = 10!g(y) where 10! = 3628800. We also investigate and establish the generalized Ulam-Hyers stability of this functional equation in Banach spaces, generalized 2-normed spaces and random normed spaces by using direct and fixed point methods.

      • Deposition rate dependent phase/mechanical property evolution in zirconia and ceria-zirconia thin film by EB-PVD technique

        Arunkumar, P.,Aarthi, U.,Sribalaji, M.,Mukherjee, B.,Keshri, Anup Kumar,Tanveer, Waqas Hassan,Cha, Suk-Won,Babu, K. Suresh Elsevier 2018 Journal of alloys and compounds Vol.765 No.-

        <P><B>Abstract</B></P> <P>Pure zirconia (ZrO<SUB>2</SUB>) and ceria (16 mol%) stabilized zirconia (CeSZr) thin films were prepared by electron beam physical vapor deposition with varying deposition rates (1, 4 and 8 Å/s) in order to correlate the phase changes to the mechanical property. X-ray diffraction and Raman spectra results indicate the presence of mixed monoclinic and tetragonal phases in ZrO<SUB>2</SUB> film, but tetragonal phase dominated at lower deposition rate. However, irrespective of the deposition rate, cerium addition to ZrO<SUB>2</SUB> resulted in complete stabilization of tetragonal phase. Depending on the presence of dual (ZrO<SUB>2</SUB>) or single (CeSZr) phase, either surface cracks or well-connected grain structure was observed in SEM, respectively. Thus, CeSZr film showed a four-fold increase in hardness in comparison to ZrO<SUB>2</SUB>, which can be attributed to the complete stabilization of tetragonal phase that hinders the crack propagation along the grain. Plastic deformation of CeSZr film was found to be 1.80 × 10<SUP>−2</SUP> GPa, which is about ∼55% higher as compared to pure ZrO<SUB>2</SUB> film (8.04 × 10<SUP>−3</SUP> GPa). Thus, the development of CeSZr coating may lead to better surface protection of many components.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Zirconia and ceria (16 mol%) stabilized zirconia (CeSZr) films deposited by EB-PVD. </LI> <LI> ZrO2 thin film showed mixed tetragonal and cubic structure. </LI> <LI> CeSZr thin film formed with single phase tetragonal structure. </LI> <LI> CeSZr film exhibited a four-fold increase in hardness in comparison to ZrO2 film. </LI> <LI> Deposition rate and chemistry influence the mechanical property of films. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

      • Improved electrochemical reversibility of over-lithiated layered Li<sub>2</sub>RuO<sub>3</sub> cathodes: Understanding aliovalent Co<sup>3+</sup> substitution with excess lithium

        Arunkumar, Paulraj,Jeong, Woo Jin,Won, Seob,Im, Won Bin Elsevier 2016 Journal of Power Sources Vol.324 No.-

        <P><B>Abstract</B></P> <P>Over-lithiated layered Li<SUB>2+<I>x</I> </SUB>Ru<SUB>1−x</SUB>Co<SUB> <I>x</I> </SUB>O<SUB>3</SUB> (<I>x</I> = 0, 0.1, 0.2, and 0.5) cathodes were synthesized through a solid-state reaction, which exhibits a superlattice structure. We investigated the effects of aliovalent Co<SUP>3+</SUP> doping with excess lithium on the structural and electrochemical properties of layered Li<SUB>2</SUB>RuO<SUB>3</SUB> cathodes. X-ray diffraction suggests the formation of a solid-solution where Co<SUP>3+</SUP> occupies the Ru<SUP>4+</SUP> sites in the transition metal layer while maintaining the layered Li<SUB>2</SUB>RuO<SUB>3</SUB> structure. The electrochemical results indicate an enhanced electrochemical lithium reversibility of the cathodes at high C-rates (1C) than the pristine Li<SUB>2</SUB>RuO<SUB>3</SUB>. In particular, the high-performance Li<SUB>2.1</SUB>Ru<SUB>0.9</SUB>Co<SUB>0.1</SUB>O<SUB>3</SUB> cathode delivered an initial capacity of 250 mAh g<SUP>−1</SUP> with an enhanced Li<SUP>+</SUP> extraction of 0.66 mol (52% capacity retention) after 100 cycles at 1C compared to the 0.28 mol of Li<SUP>+</SUP> extraction (21% capacity retention) associated with the pristine Li<SUB>2</SUB>RuO<SUB>3</SUB>. Low content of Co<SUP>3+</SUP> could realize an enhanced reversible Li<SUP>+</SUP> extraction that originated from the improved reversible anionic redox chemistry, cation ordering with superlattice structure, and facile charge transfer process. The role of Co<SUP>3+</SUP> content on the lithium reversibility of over-lithiated layered cathodes, containing excess lithium were investigated.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Cycling performance of Li<SUB>2.1</SUB>Ru<SUB>0.9</SUB>Co<SUB>0.1</SUB>O<SUB>3</SUB> is dramatically improved at high C-rate. </LI> <LI> Low Co<SUP>3+</SUP> content is sufficient to achieve high Li reversibility. </LI> <LI> High reversible Li extraction (52%) of Li<SUB>2.1</SUB>Ru<SUB>0.9</SUB>Co<SUB>0.1</SUB>O<SUB>3</SUB> at 1C after 100 cycle. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

      • Versatile Ca<sub>4</sub>F<sub>2</sub>Si<sub>2</sub>O<sub>7</sub> Host from Defect-Induced Host Emission to White-Light-Emitting Ce<sup>3+</sup>-Doped Ca<sub>4</sub>F<sub>2</sub>Si<sub>2</sub>O<sub>7</sub> Phosphor for Near-UV Solid-State Lighting

        Arunkumar, Paulraj,Kim, Yoon Hwa,Im, Won Bin American Chemical Society 2016 The Journal of Physical Chemistry Part C Vol.120 No.8

        <P>White-light-emitting Ca4-xF2Si2O7:xCe(3+) phosphor and violet-light emitting oxyfluoride Ca4F2Si2O7 host were synthesized by solid-state reaction. Ca4-xF2Si2O7:xCe(3+) has strong absorption in the near-UV region (370 nm) and shows a broad emission in the range of 390-600 nm centered at 475 nm. Under 315 rim excitation, a narrow blue emission was observed. The Ca4F2Si2O7 host synthesized under the same reduction conditions exhibited-violet emission due to the formation of anion-deficient nonstoichiorrietric Ca4F2-delta Si2O7+delta/2, species. The broad emission of Ca4F2Si2O7:xCe(3+) phosphor is attributed to Ce3+ occupying two crystallographic calcium sites available in the host. A white LED device was fabricated using Ca4F2Si2O7:Ce3+ without any additive phosphor, displaying excellent CIE chromaticity (0.29, 0.35) close to white emission with a color rendering index of 97. These exceptional optical properties of Ca4F2Si2O7:Ce3+ suggest the promising application of the single activator phosphor that could produce white light under near-UV-based LEDs.</P>

      • KCI등재

        Measurement of liquid film thickness in air - water two phase flows in conventional and mini channels using image processing

        Arunkumar Seshadri,Swetha Mahadevan,Venkatesan Muniyandi 한국화학공학회 2015 Korean Journal of Chemical Engineering Vol.32 No.5

        The measurement and study of liquid films in the case of two phase flows is significant in many heat transfer and mass transfer applications, such as chemical process industries, micro reactors, coating processes and in boilers. The focus of the present study was to measure and characterize the thickness of the liquid films for various two phase flow regimes in conventional and in mini channels using a non-intrusive technique. Experiments were performed on tubes of diameters 0.6, 1.5, 2.6 and 3.4mm. The superficial velocities of gas and liquid are in the range of 0.01-50 and 0.01-3m/s, respectively. The flow patterns were recorded with a high speed camera. A method to determine the two phase flow velocity using image registration has been discussed. Morphological processing and gray scale analysis were used to determine the liquid film thickness and characterize the flow regimes. The flow patterns identified are bubbly, dispersed bubbly, slug, slug-annular, wavy-annular, stratified, and annular. The flow regimes were validated with flow maps available in the literature. The liquid film thickness was identified by distance transform technique in image processing. The magnitude of film thickness varied with liquid and gas flow velocities. The film thickness was represented in terms of capillary number. The variation in film thickness along the length of the flow regime has been discussed. A relation between the liquid film thicknesses measured using the non-intrusive image processing technique and capillary number for the conventional and mini tubes is proposed based on the analysis. It is concluded from the proposed correlation that the variation in liquid film thickness is different for conventional and mini channels because of the effect of inertial dominance in conventional channels and viscous dominance in mini channels.

      • SCOPUSKCI등재

        A NEW TYPE OF THE ADDITIVE FUNCTIONAL EQUATIONS ON INTUITIONISTIC FUZZY NORMED SPACES

        Arunkumar, Mohan,Bodaghi, Abasalt,Namachivayam, Thirumal,Sathya, Elumalai Korean Mathematical Society 2017 대한수학회논문집 Vol.32 No.4

        In this paper, we introduce a new type of additive functional equations and establish the generalized Ulam-Hyers stability for it in intuitionistic fuzzy normed space by using direct and fixed point methods.

      • Hydrophobic Organic Skin as a Protective Shield for Moisture-Sensitive Phosphor-Based Optoelectronic Devices

        Arunkumar, Paulraj,Kim, Yoon Hwa,Kim, Ha Jun,Unithrattil, Sanjith,Im, Won Bin American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.8

        <P>A moisture-stable, red-emitting fluoride phosphor with an organic hydrophobic skin is reported. A simple strategy was employed to form a metal-free, organic, passivating skin using oleic acid (OA) as a hydrophobic encapsulant via solvothermal treatment. Unlike other phosphor coatings that suffer from initial efficiency loss, the OA-passivated K2SiF6:Mn4+ (KSF-OA) phosphor exhibited the unique property of stable emission efficiency. Control of thickness and a highly transparent passivating layer helped to retain the emission efficiency of the material after encapsulation. A moisture-stable KSF-OA phosphor could be synthesized because of the exceptionally hydrophobic nature of OA and the formation of hydrogen bonds (F...H) resulting from the strong interactions between the fluorine in KSF and hydrogen in OA. The KSF-OA phosphor exhibited excellent moisture stability and maintained 85% of its emission intensity even after 450 h at high temperature (85 degrees C) and humidity (85%). As a proof-of-concept, this strategy was used for another moisture-sensitive SrSi2O2N2:Eu2+ phosphor which showed enhanced moisture stability, retaining 85% of emission intensity after 500 h under the same conditions. White light-emitting were fabricated using surface-passivated KSF and Y3Al5O12:Ce3+ which exhibited excellent color rendering index of 86, under blue LED excitation.</P>

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