High capacitance sustainable low‑cost cold plasma exposed activated carbon electrode derived from orange peel waste to eco‑friendly technique

K. A. Vijayalakshmi,K. C. Sowmiya 한국탄소학회 2024 Carbon Letters Vol.34 No.6

Investigations on Z-Source Based Cascaded Five Level Inverter

K. Vijayalakshmi,C. R. Balamurugan 보안공학연구지원센터 2016 International Journal of Signal Processing, Image Vol.9 No.12

The Z source inverter is a novel power conversion topology that can buck and boost the given input voltage. Voltage source inverter (VSI) and current source inverter (CSI) have some common problems. The proposed work eliminates the limitations of both voltage source inverter and current source inverter by replacing multilevel inverter. This paper presents the new inverter topology based on combination of Z Source Inverter (ZSI) and Multi Level Inverter (MLI). The Z source inverter employs a unique impedance network to couple the main circuit to the power source. The basic structure includes one DC voltage source, Z network and multilevel inverter. Thus providing unique features that cannot be provided in both traditional voltage source and current source inverter. The cascaded MLI composed of eight switches to generating five voltage levels. The presence of multilevel inverters provide high output voltages with low harmonics without the use of transformers. The Z source concept can be applied to ac-dc, dc-ac, ac-ac and dc-dc power conversions. This work observes the rms (Root Mean Square) output voltage and presence of THD (Total Harmonic Distortion) in the output waveform by simulating the Z source based multilevel inverter using MATLAB/simulink.

Crystal growth and characterization of an NLO organic crystal: N′-[(Z)-(4-methylphenyl)methylidene]-4-nitrobenzohydrazide

K. Naseema,Vijayalakshmi Rao,K.V. Sujith,Balakrishna Kalluraya 한국물리학회 2010 Current Applied Physics Vol.10 No.4

In this paper, we report the synthesis, growth and characterization of a new organic NLO single crystal of NMPMN (N0-[(Z)-(4-methylphenyl)methylidene]-4-nitrobenzohydrazide), for the first time. The single crystal was grown by slow evaporation method at room temperature. The cell dimensions obtained by single crystal XRD studies reveal that the crystal belongs to triclinic system. It was characterized by different techniques like powder XRD, UV, FTIR, TGA and DSC. The Knoop microhardness test was carried out to measure the mechanical strength of the crystal. Its refractive index was determined by the Brewster’s angle method. The laser damage threshold studies have been carried out for the crystal using a Q-switched Nd:YAG laser of ns pulses at a wavelength of 532 nm. The Kurtz Powder Second Harmonic Generation revealed that the SHG efficiency of the grown crystal is about 50% that of KDP and is found to be phase matchable. The intermolecular O-H···O, O-H···N and C-H···O hydrogen bonds and a π–π stacking interaction between the nitrobenzene and tolyl rings helps to create a delicate balance between the molecular and supramolecular charge transfer processes by creating a noncentrosymmetric structure.

Copper–constantan nanoparticles impregnated PEO + PVP:Li+ blended solid polymer electrolyte films for lithium battery applications

Naveen Kumar, K.,Saijyothi, K.,Vijayalakshmi, L.,Kang, Misook Springer-Verlag 2017 Polymer bulletin Vol.74 No.7

Investigations on the structural, optical and electronic properties of Nd doped ZnO thin films

Subramanian, M,Thakur, P,Gautam, S,Chae, K H,Tanemura, M,Hihara, T,Vijayalakshmi, S,Soga, T,Kim, S S,Asokan, K,Jayavel, R Institute of Physics [etc.] 2009 Journal of Physics. D, Applied Physics Vol.42 No.10

<P>We report the synthesis and characterization of Nd doped ZnO thin films grown on Si (1 0 0) substrates by the spray pyrolysis method. The surface morphology of these thin films was investigated by scanning electron microscopy and shows the presence of randomly distributed structures of nanorods. Grazing angle x-ray diffraction studies confirm that the doped Nd ions occupied Zn sites and these samples exhibited a wurtzite hexagonal-like crystal structure similar to that of the parent compound, ZnO. The micro-photoluminescence measurement shows a decrease in the near band edge position with Nd doping in the ZnO matrix due to the impurity levels. The near-edge x-ray absorption fine structure (NEXAFS) measurements at the O K edge clearly exhibit a pre-edge spectral feature which evolves with Nd doping, suggesting incorporation of more charge carriers in the ZnO system and the presence of strong hybridization between O 2p–Nd 5d orbitals. The Nd M<SUB>5</SUB> edge NEXAFS spectra reveal that the Nd ions are in the trivalent state.</P>

Multivariate Congestion Prediction using Stacked LSTM Autoencoder based Bidirectional LSTM Model

Vijayalakshmi B,Thanga Ramya S,Ramar K 한국인터넷정보학회 2023 KSII Transactions on Internet and Information Syst Vol.17 No.1

In intelligent transportation systems, traffic management is an important task. The accurate forecasting of traffic characteristics like flow, congestion, and density is still active research because of the non-linear nature and uncertainty of the spatiotemporal data. Inclement weather, such as rain and snow, and other special events such as holidays, accidents, and road closures have a significant impact on driving and the average speed of vehicles on the road, which lowers traffic capacity and causes congestion in a widespread manner. This work designs a model for multivariate short-term traffic congestion prediction using SLSTM_AE-BiLSTM. The proposed design consists of a Bidirectional Long Short Term Memory(BiLSTM) network to predict traffic flow value and a Convolutional Neural network (CNN) model for detecting the congestion status. This model uses spatial static temporal dynamic data. The stacked Long Short Term Memory Autoencoder (SLSTM AE) is used to encode the weather features into a reduced and more informative feature space. BiLSTM model is used to capture the features from the past and present traffic data simultaneously and also to identify the long-term dependencies. It uses the traffic data and encoded weather data to perform the traffic flow prediction. The CNN model is used to predict the recurring congestion status based on the predicted traffic flow value at a particular urban traffic network. In this work, a publicly available Caltrans PEMS dataset with traffic parameters is used. The proposed model generates the congestion prediction with an accuracy rate of 92.74% which is slightly better when compared with other deep learning models for congestion prediction.

Dazzling red emission from TiO2 nanoparticles impregnated co-doped Gd3++Eu3+: PVA polymer nanocomposites for photonic applications

K. Naveen Kumar,R. Padma,L. Vijayalakshmi,강미숙 한국공업화학회 2017 Journal of Industrial and Engineering Chemistry Vol.45 No.-

Red emission was obtained from rare earth doped polymer nanocomposites, namely, composites ofpolyvinyl-alcohol (PVA) co-doped with Gd3+ and Eu3+ and embedded with TiO2 nanoparticles (TiO2NP),under ultraviolet (UV) excitation. We successfully synthesized Eu3+: PVA, Gd3+: PVA, (Gd3+ + Eu3+): PVA,and (Gd3+ + Eu3+ + TiO2NP): PVAfilms by solution casting method. From X-ray diffraction patterns andFourier-transform infrared spectral profiles, the structural details of thefilms and the ion–polymerinteraction mechanism responsible for their formation were systematically analyzed. The thermalstability and decomposition dynamics of the prepared samples were evaluated by thermogravimetry anddifferential thermal analysis. Pertinent optical absorption bands related to Eu3+ and Gd3+ ions in thepolymer composites were observed and assigned to the corresponding electronic transitions. The PVAfilm containing different concentrations of the Eu3+ dopant displayed red emission at 618 nm (5D0!7F2)under UV excitation at 396 nm (7F0!5L6). Upon co-doping with Gd3+ to form the (Gd3+ + Eu3+): PVAfilm,it exhibited red emission that was stronger than that from the singly doped Eu3+: PVAfilm under 270 nmexcitation because of the energy transfer from Gd3+ to Eu3+ ions. After the TiO2 nanoparticles were evenlydispersed in the co-doped (Gd3+ + Eu3+): PVAfilms, the photoluminescence properties were remarkablyenhanced and prominent red emission was observed under 274 nm excitation. The red emission of Eu3+was significantly enhanced through an efficient energy-transfer process from the Gd3+ ions to Eu3+ ionsand from the TiO2 nanoparticles to Eu3+ ions. A possible energy-transfer mechanism was clearlydemonstrated by severalfluorescent methods and lifetime decay dynamics. Based on the above results,these polymer compositefilms are promising candidates for red luminescent photonic devices.

Energy transfer based spectral properties of TiO₂ NPs impregnated co-doped Gd³⁺+Eu³⁺: PVA polymer nanocomposites for luminescent Applications

( K Naveen Kumar ),( L. Vijayalakshmi ),강미숙 한국공업화학회 2016 한국공업화학회 연구논문 초록집 Vol.2016 No.1

We have synthesized Eu³⁺: PVA, Gd³⁺: PVA, Gd³⁺+Eu³⁺: PVA and Gd³⁺+Eu³⁺+ TiO₂ nanoparticles: PVA polymer films by solution casting method. Eu³⁺ doped PVA polymer films displayed a red emission at 618 nm (⁵D₀→⁷F₂) under 396 nm (⁷F₀→⁵L₆) of excitation. Upon co-doping with Gd³⁺ to Eu³⁺: PVA polymer film, it exhibits enriched red emission than singly doped Eu³⁺: PVA under 270 nm of excitation due to energy transfer from Gd³⁺ to Eu³⁺ ions. After dispersion of TiO₂ NPs in the co-doped Gd³⁺+Eu³⁺: PVA polymer films, the PL properties of Eu³⁺ are remarkably enhanced. Red emission of Eu³⁺ is significantly enhanced though an efficient ET process from Gd³⁺ to Eu³⁺ and TiO₂ NPs to Eu³⁺. These polymer nanocomposite films could be suggested as promising candidates for red luminescent photonic devices.

Efficient red-luminescence of CaLa₂ZnO₅ phosphors co-doped by Ce³⁺ and Eu³⁺ ions

Kumar, K. Naveen,Vijayalakshmi, L.,Choi, Jungwook,Kim, Jong Su Elsevier 2019 Journal of alloys and compounds Vol.787 No.-

<P><B>Abstract</B></P> <P>Individually and doubly doped Ce<SUP>3+</SUP>/Eu<SUP>3+</SUP>:CaLa<SUB>2</SUB>ZnO<SUB>5</SUB> (CLZO) phosphors were synthesized by a conventional sol-gel method as highly efficient luminescence-based phosphor materials. X-ray diffraction and field-emission scanning electron microscope were used to analyze the structural and morphological properties. The elements and their ionic states were determined by energy-dispersive spectroscopy and X-ray photoelectron spectroscopy studies, respectively. The assignment of the functional groups was analyzed using Fourier-transform infrared spectral studies. Bright red emission was obtained from Eu<SUP>3+</SUP>-doped CLZO phosphors due to its hypersensitive transition of <SUP>5</SUP>D<SUB>0</SUB>→<SUP>7</SUP>F<SUB>2</SUB> at 626 nm with a royal blue excitation source. By increasing the Eu<SUP>3+</SUP> content, the emission features were rapidly enhanced. Moreover, the red emission related to Eu<SUP>3+</SUP> was further increased by the addition Ce<SUP>3+</SUP> ions as a co-dopant along with Eu<SUP>3+</SUP> in the CLZO matrix due to energy transfer. The energy migration from Ce<SUP>3+</SUP> to Eu<SUP>3+</SUP> is systematically illustrated by several fluorescent approaches, such as photoluminescence analysis, spectral overlap, CIE coordinates, lifetime dynamics, luminescence quantum yields, and color purity. Surprisingly, the CIE coordinates were very close to the NTSC coordinate values. Based on the results, these phosphors could be suitable materials for luminescence-based optoelectronic devices.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Dazzling red emission is obtained from Ce<SUP>3+</SUP>/Eu<SUP>3+</SUP>: CaLa<SUB>2</SUB>ZnO<SUB>5</SUB> phosphors. </LI> <LI> Red emission of Eu<SUP>3+</SUP> was remarkably enhanced by co-doping with Ce<SUP>3+</SUP>. </LI> <LI> Effective sensitization of Ce<SUP>3+</SUP> ions and enhanced quantum yield have been elucidated. </LI> <LI> Energy transfer from Ce<SUP>3+</SUP> to Eu<SUP>3+</SUP> ions by several fluorescence dynamics. </LI> <LI> Meritorious CCT, CIE coordinates and high red color purity have obtained. </LI> </UL> </P>

Optimization of feed and extractant concentration for the liquid–liquid extraction of volatile fatty acids from synthetic solution and landfill leachate

Sameena Begum,Vijayalakshmi Arelli,Gangagni Rao Anupoju,Sridhar S,Suresh K. Bhargava,Nicky Eshtiaghi 한국공업화학회 2020 Journal of Industrial and Engineering Chemistry Vol.90 No.-

Liquid–liquid extraction of volatile fatty acids (VFA) from landfill leachate (LL) as well as syntheticsolution (SS) whose concentration varied from 0.2 to 1 mol/L was investigated. The impact of extractantand feed VFA concentration on extraction efficiency (EE), distribution ratio (KD) and loading ratio (z) withthe help of statistical analysis and process optimization using response surface methodology ispresented. Physical extraction of VFA from SS using seven different diluents was performed to choose thebest diluent. Reactive extraction of VFA was investigated with 10–50% (v/v) trioctylamine (TOA) andtributylphosphate (TBP) as extractants in 1-Octanol. Reactive extraction of VFA results disclosedenhancement of EE due to the synergistic chemical interactions between extractant and diluent. Majorityof the acid extractant complexes formed were 1:1 with TBP while 1:1, 2:1 and 3:1 with TOA as verified byz > 0.5 The optimal extractant concentration for TOA and TBP was found to be 37.8% and 39.09% at a feedconcentration of 0.67 mol/L and 0.81 mol/L for SS respectively to achieve maximum EE of 91% while it was29.3% and 36.2% at 0.2 mol/L for LL to achieve EE of 52% and 57% correspondingly.