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Rajagopal, S.,Prabavathy, S. Techno-Press 2013 Structural Engineering and Mechanics, An Int'l Jou Vol.46 No.6
In the present study, in reinforced concrete structures, beam-column connections are one of the most critical regions in areas with seismic susceptibility. Proper anchorage of reinforcement is vital to enhance the performance of beam-column joints. Congestion of reinforcement and construction difficulties are reported frequently while using conventional reinforcement detailing in beam-column joints of reinforced concrete structures. An effort has been made to study and evaluate the performance of beam-column joints with joint detailing as per ACI-352 (mechanical anchorage), ACI-318 (conventional hooks bent) and IS-456(full anchorage conventional hooks bent) along with confinement as per IS-13920 and without confinement. Apart from finding solutions for these problems, significant improvements in seismic performance, ductility and strength were observed while using mechanical anchorage in combination with X-cross bars for less seismic prone areas and X-cross bar plus hair clip joint reinforcement for higher seismic prone areas. To evaluate the performances of these types of anchorages and joint details, the specimens were assembled into four groups, each group having three specimens have been tested under reversal loading and the results are presented in this paper.
Rajagopal Reddy, V.,Sri Silpa, D.,Yun, H.J.,Choi, C.J. Academic Press 2014 Superlattices and microstructures Vol.71 No.-
The electrical and structural properties of a fabricated W/p-InP Schottky barrier diode (SBD) have been investigated as a function of annealing temperature. The W/p-InP SBD exhibits good rectification behavior. The barrier height (BH) and ideality factor of the W/p-InP SBD are determined to be 0.82eV (I-V)/0.98eV (C-V) and 1.34, respectively. However, the BH is increases to 0.87eV (I-V)/1.08eV (C-V) after annealing at 300<SUP>o</SUP>C. When the SBD is annealed at 400<SUP>o</SUP>C, the BH decreases to 0.74eV (I-V)/0.86eV (C-V) and the ideality factor increases to 1.45. Results indicate that a maximum BH is obtained on the W/p-InP SBD at 300<SUP>o</SUP>C. Norde method is also employed to determine BHs of W/p-InP SBD which are in good agreement with those estimated by the I-V method. Further, Cheung method is used to estimate the series resistance of the W/p-InP SBD, and the consistency is checked using the Norde method. Besides, the energy distribution of interface state density is determined from the forward bias I-V data at different annealing temperatures. Auger electron spectroscopy and X-ray diffraction studies revealed that the formation of W-P interfacial phases at the W/p-InP interface may be the cause for the increase of BH upon annealing at 300<SUP>o</SUP>C. AFM results indicated that the overall surface morphology of the W/p-InP SBD did not change significantly at elevated temperatures.
Rajagopal, Rajesh,Ryu, Kwang-Sun THE KOREAN SOCIETY OF INDUSTRIAL AND ENGINEERING 2018 JOURNAL OF INDUSTRIAL AND ENGINEERING CHEMISTRY -S Vol.60 No.-
<P><B>Abstract</B></P> <P>This paper reports the synthesis of lanthanum oxide/hydroxide nanoparticle (LaNPs)-doped rGO nanosheets. The uniform distribution of LaNPs on the rGO nanosheets was confirmed by FESEM, TEM, and elemental analysis. A dramatic change in electrochemical behavior was observed by adjusting the concentration of LaNPs in rGO (LaG ratio=1:2, 1:1 and 2:1). The LaG 12 showed a better areal capacitance of 889.29Fcm<SUP>−2</SUP> than LaG 11 (428.58Fcm<SUP>−2</SUP>) and LaG 21 (260.72Fcm<SUP>−2</SUP>). Further, improved cycle stability (84% after 1000 cycles) with good impedance behavior confirms LaG 12 is a suitable electrode material for high-performance supercapacitor fabrication.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Rajagopal Reddy, V.,Janardhanam, V.,Won, Jonghan,Choi, Chel-Jong Elsevier 2017 JOURNAL OF COLLOID AND INTERFACE SCIENCE - Vol.499 No.-
<P><B>Abstract</B></P> <P>An Au/Cu<SUB>2</SUB>ZnSnS<SUB>4</SUB> (CZTS)/n-GaN heterojunction (HJ) is fabricated with a CZTS interlayer and probed its chemical states, structural, electrical and frequency-dependent characteristics by XPS, TEM, <I>I</I>-<I>V</I> and <I>C</I>-<I>V</I> measurements. XPS and TEM results confirmed that the CZTS films are formed on the n-GaN surface. The band gap of deposited CZTS film is found to be 1.55eV. The electrical properties of HJ correlated with the Au/n-GaN Schottky junction (SJ). The Au/CZTS/n-GaN HJ reveals a good rectification nature with high barrier height (0.82eV) compared to the Au/n-GaN SJ (0.69eV), which suggests the barrier height is influenced by the CZTS interlayer. The barrier height values assessed by <I>I</I>-<I>V</I>, Cheung’s and Norde functions are closely matched with one other, thus the methods used here are reliable and valid. The extracted interface state density (<I>N<SUB>SS</SUB> </I>) of Au/CZTS/n-GaN HJ is lower compared to the Au/n-GaN SJ that suggests the CZTS interlayer plays an important role in the reduction of <I>N<SUB>SS</SUB> </I>. Moreover, the capacitance-frequency (<I>C</I>-<I>f</I>) and conductance-frequency (<I>G</I>-f) characteristics of SJ and HJ are measured in the range of 1kHz–1MHz, and found that the capacitance and conductance strappingly dependent on frequency. It is found that the <I>N<SUB>SS</SUB> </I> estimated from <I>C</I>-<I>f</I> and <I>G</I>-<I>f</I> characteristics is lower compared to those estimated from <I>I</I>-<I>V</I> characteristics. Analysis confirmed that Poole-Frenkel emission dominates the reverse leakage current in both SJ and HJ, probably related to the structural defects and trap levels in the CZTS interlayer.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Rajagopal Karthikeyan,Kingni Sifeu Takougang,Kom Guillaume Honoré,Pham Viet-Thanh,Karthikeyan Anitha,Jafari Sajad 한국물리학회 2020 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.77 No.2
A chaotic simple jerk system (SJS) that belongs to systems with self-excited and hidden attractors is introduced in this paper. The dynamics of the proposed SJS is analytically and numerically investigated. Interestingly, the influence of the time delay on the proposed chaotic SJS is studied. In addition, the physical existence of self-excited and hidden chaotic attractors found in the proposed SJS and in the time-delayed form of SJSs (TDSJSs) are verified by using Orcard-PSpice software. Finally, chaos synchronization of identical, unidirectional, coupled, proposed chaotic TDSJSs is also reported.
Rajagopal, Rajesh,Ryu, Kwang-Sun Pergamon Press 2018 Electrochimica Acta Vol. No.
<P><B>Abstract</B></P> <P>Nanostructured MnO<SUB>2</SUB> was synthesized using a facile hydrothermal technique with potassium permanganate as a precursor. Rare earth elements, lanthanum and cerium, were used to control the porosity of the MnO<SUB>2</SUB> nanostructures. Nanorod-, nanoflower-, nanoneedle-, and nanoneedles/nanopetal-shaped MnO<SUB>2</SUB> nanostructures were synthesized by changing the concentration of the rare earth elements. The as-synthesized MnO<SUB>2</SUB> nanorods, La – MnO<SUB>2</SUB> nanoneedles, Ce – MnO<SUB>2</SUB> nanoflowers, and La/Ce – MnO<SUB>2</SUB> nanoneedles/nanopetals were examined using a range of physico chemical characterization techniques. Scanning electron microscopy and transmission electron microscopy – energy dispersive X-ray spectroscopy confirmed the morphology of the MnO<SUB>2</SUB> nanostructures and the elemental distribution. The porous natures of the synthesized MnO<SUB>2</SUB> nanostructures were analyzed by nitrogen adsorption technique. The electrochemical behavior of the MnO<SUB>2</SUB> nanostructures was examined by cyclic voltammetry, charge – discharge and electrochemical impedance spectroscopy tests. The La/Ce – MnO<SUB>2</SUB> nanoneedles/nanopetals electrode exhibited a high specific capacitance of 825 F g<SUP>−1</SUP> at an applied current density of 10 A g<SUP>−1</SUP>. The La/Ce – MnO<SUB>2</SUB> nanoneedles/nanopetals were also mixed with 5, 10, 15 and 20 wt% of rGO nanosheets to enhance the electrochemical behavior. The 20 rGO@La/Ce – MnO<SUB>2</SUB> sample showed extraordinary electrochemical behavior; the calculated specific capacitance was 1165 F g<SUP>−1</SUP> at an applied current density of 10 A g<SUP>−1</SUP>. A 20 rGO@La/Ce – MnO<SUB>2</SUB> and activated carbon asymmetric supercapacitor coin cell device exhibited ∼93% capacitance retention after 1000 cycles. These results highlight the potential of 20 rGO@La/Ce – MnO<SUB>2</SUB> as an electrode material for supercapacitor applications.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Manganese oxide nanostructures were synthesized by hydrothermal process. </LI> <LI> Lanthanum and cerium used to control the porosity of manganese oxide. </LI> <LI> La/Ce mixed MnO<SUB>2</SUB> nanoneedles/nanopetals showing good electrochemical behavior. </LI> <LI> rGO mixed La/Ce – MnO<SUB>2</SUB> was prepared to improve the storage capacity. </LI> <LI> 20rGO@ La/Ce – MnO<SUB>2</SUB> electrode exhibited high specific capacitance of 1165 F g<SUP>−1</SUP>. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Rajagopal, S.,Prabavathy, S.,Kang, Thomas H.K. 테크노프레스 2014 Earthquakes and structures Vol.7 No.5
This paper studies the response of seismic behavior of reinforced concrete exterior beam-column joints under reversal loading with different anchorages and joint core details. The joint core was detailed without much confinement (group-I) and/or with proposed X-cross bars in the core (group-II). The beam longitudinal reinforcement's anchorages were designed as per ACI 352 (headed bars), ACI 318 (conventional $90^{\circ}$ bent hooks) and IS 456 ($90^{\circ}$ bent hooks with extended tails). The nonlinear finite element analysis response of the beam-column joints was studied, along with initial and progressive cracks up to failure. The experimental and analytical results were compared and presented in this paper to make more scientific conclusions.