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Bhuyan, Ranjan K.,Thatikonda, Santhosh K.,Dobbidi, Pamu,Renehan, J.M.,Jacob, Mohan V. Techno-Press 2014 Advances in materials research Vol.3 No.2
The microwave dielectric properties of $CeO_2$ nanoparticles (0.5, 1.0 & 1.5wt%) doped $Mg_2TiO_4$ (MTO) ceramics have been investigated at cryogenic temperatures. The XRD patterns of the samples were refined using the full proof program reveal the inverse spinel structure without any secondary phases. The addition of $CeO_2$ nanoparticles lowered the sintering temperature with enhancement in density and grain size as compared to pure MTO ceramics. This is attributed to the higher sintering velocity of the fine particles. Further, the microwave dielectric properties of the MTO ceramics were measured at cryogenic temperatures in the temperature range of 6.5-295 K. It is observed that the loss tangent ($tan{\delta}$) of all the samples increased with temperature. However, the $CeO_2$ nanoparticles doped MTO ceramics manifested lower loss tangents as compared to the pure MTO ceramics. The loss tangents of the pure and MTO ceramics doped with 1.5 wt% of $CeO_2$ nanoparticles measured at 6.5K are found to be $6.6{\times}10^{-5}$ and $5.4{\times}10^{-5}$, respectively. The addition of $CeO_2$ nanoparticles did not cause any changes on the temperature stability of the MTO ceramics at cryogenic temperatures. On the other hand, the temperature coefficient of the permittivity increased with rise in temperature and with the wt% of $CeO_2$ nanoparticles. The obtained lower loss tangent values at cryogenic temperatures can be attributed to the decrease in both intrinsic and extrinsic losses in the MTO ceramics.
G. Lakshmi Vara Prasad,Venkatagurunatham Naidu Kollu,M. Sailaja,S. Radhakrishnan,K. Jagan Mohan,A. Kishore Reddy,G. Rajesh Chandra 한국전기전자재료학회 2024 Transactions on Electrical and Electronic Material Vol.25 No.1
In this paper, we delve into the intriguing realm of Pseudo-morphic High Electron Mobility Transistors (pHEMTs) composed of InAs∕In0.3Al0.7As∕InSb∕In0.3Al0.7As layers, utilizing Silvaco-TCAD for simulation. Our focus centers on the assessment of RF and analog electrical characteristics, with a keen eye on the high-temperature eff ects. The influence of temperature on device performance is meticulously evaluated in comparison to a reference device operating at room temperature. Traditionally, the critical parameters such as threshold voltage ( Vth ), transconductance ( gm ), and Ion∕Ioff ratio have been calculated within the temperature range spanning from 300 K to 700 K. The primary pHEMT device in our study exhibits impressive attributes, featuring a drain current of 950 mA, a threshold voltage of -1.75 V, a high transconductance ( gm ) value of 650 mS/mm, an Ion∕Ioff ratio of 1 × 106 , a transition frequency ( ft ) soaring to 790 GHz, and a maximum frequency ( fmax ) reaching a staggering 1.4 THz. However, as we traverse the temperature spectrum, our findings unveil a compelling narrative. The impact of rising temperature is unequivocal, triggering a cascade of transformations within the device. Notably, as the temperature escalates, we observe a noticeable decrease in current, a reduction in transconductance ( gm ), and a diminishing Ion∕Ioff ratio. To unravel the intricacies of these temperature-induced effects, we introduce the infusion of Machine Learning (ML) into our analysis.
Poly(N-isopropylacrylamide-co-sodium acrylate) hydrogels: Interactions with surfactants
Mohan, Y. M.,Joseph, D. K.,Geckeler, K. E. Wiley Subscription Services, Inc., A Wiley Company 2007 Journal of applied polymer science Vol.103 No.5
<P>Poly(N-isopropylacrylamide-co-sodium acrylate) [poly(NIPAM-co-SA)] hydrogels were modified with three different kind of surfactants (cationic, anionic, and nonionic) to study the effect on the swelling properties. The structural variation of the surfactant-modified hydrogels was investigated in detail. The interaction between the surfactants and the hydrogel varies and strictly depends on the surfactant type. The variation in thermal stability of the modified surfactant hydrogels was investigated and compared with unmodified hydrogel. Further, the hydrogel swelling/diffusion kinetic parameters were investigated and diffusion of water into hydrogel was found to be of the non-Fickian transport mechanism. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3423–3430, 2007</P>
B. Vikram Babu,M. Sushma Reddi,A. Rama Krishna,B. Sathish Mohan,G. Chandana,K. Anjani Devi,B. Sridhar,K. Samatha 한국전기전자재료학회 2022 Transactions on Electrical and Electronic Material Vol.23 No.5
This research article aims at reporting the influence of magnesium by studying the structural, electrical impedance and modulus properties of the Mg substituted Li 4 Ti 5 O 12 . These studies are useful for the electrochemical properties. The XRD reveals that the structure of all the Mg substituted materials belongs to the cubic spinel group having Fd-3m space symmetry. SEM images display the structural, morphological properties with the average size of grains falling in the vicinity of 1 μm. The electrical impedance of Li 4− x Mg x Ti 5 O 12 materials was analyzed at frequencies between 20 Hz and 1 MHz and in the 30–120 °C range of temperature by employing the complex impedance spectroscopy (CIS) method. The modulus formalism is also a suitable tool to understand the dynamical characteristics of electrical transport phenomena. The complex electric modulus spectrum signifi es quantifying the allocation of ion energies or confi gurations in the lattice. Also, it portrays the electrical relaxation of ion-conducting lattices as a feature of materials at a minuscule level. The obtained results of substitution of Mg in Li 4 Ti 5 O 12 anode materials improve the potential applications of conductivity and charge/discharge performance.
M. Kovendhan,D. Paul Joseph,P. Manimuthu,A. Sendilkumar,S.N. Karthick,S. Sambasivam,K. Vijayarangamuthu,김희제,최병춘,K. Asokan,C. Venkateswaran,R. Mohan 한국물리학회 2015 Current Applied Physics Vol.15 No.5
Lithium (Li) (0-5 wt%) doped V2O5 thin films were spray deposited at 450 ℃ onto ITO substrates. Structural analysis using X-ray diffraction and Raman spectroscopy revealed orthorhombic phase of the films. In addition to the V2O5 phase, presence of VO2 peaks due to high deposition temperature is also evident from structural and optical characterization. The non-stoichiometric nature of the films due to loss of the terminal O atom was confirmed from Raman spectroscopy. The direct band gap, indirect bandgap, and phonon energies were also calculated from optical studies. Different charge states of vanadium ions present in the film were identified from X-ray photoelectron spectroscopy study. Results from cyclic voltammetry experiments reflected significant differences between the undoped and Li doped V2O5 samples. Transport properties by Hall-effect measured at room temperature indicated significant increase in conductivity, carrier concentration and mobility of V2O5 thin films on doping with Li. A Dye Sensitized Solar Cell (DSSC) was fabricated using mobility enhanced 5 wt% Li doped V2O5 film as photoanode and its efficiency was found to be 2.7%. A simple electrochromic cell is fabricated using undoped V2O5 thin film to demonstrate the colour change.
M. Mohan,K. Panduranga Vittal 대한전기학회 2019 Journal of Electrical Engineering & Technology Vol.14 No.1
Multi-terminal VSC-based HVDC transmission system is the recent interest for grid integration of large-scale offshore wind farms. Protection of multi-terminal voltage source converters (VSC)-based HVDC transmission systems against DC faults is challenging. This paper presents a single-ended protection scheme for DC faults in a three-terminal VSC-HVDC transmission system. The under-voltage criterion is used to distinguish the DC faults from the transient and normal conditions. The rate of change of DC voltage and current as well as the variation of transient energy is used to discriminate the internal faults from the external faults. The DC fault current has very high value within a few milliseconds during the transient phases such as the capacitor discharging and diode freewheeling stages. Therefore, current limiting reactors are introduced in series with the DC circuit breaker to maintain the DC fault current within the breaker capacity. The single-ended protection scheme is tested with the three-terminal VSC-HVDC transmission system with current limiting reactors for various DC fault conditions. The DC fault data is generated from PSCAD/EMTDC simulation and the protection scheme is tested in MATLAB environment. Test results show that the proposed protection scheme gives reliable protection for the DC faults in a three-terminal VSC-HVDC transmission system.
K. Narayan,S. Varadharajaperumal,G. Mohan Rao,M. Manoj Varma,T. Srinivas 한국물리학회 2013 Current Applied Physics Vol.13 No.1
In this paper we present the effect of thickness variation of hole injection and hole blocking layers on the performance of fluorescent green organic light emitting diodes (OLEDs). A number of OLED devices have been fabricated with combinations of hole injecting and hole blocking layers of varying thicknesses. Even though hole blocking and hole injection layers have opposite functions, yet there is a particular combination of their thicknesses when they function in conjunction and luminous efficiency and power efficiency are maximized. The optimum thickness of CuPc (Copper(II) phthalocyanine) layer, used as hole injection layer and BCP (2,9 dimethyl-4,7-diphenyl-1,10-phenanthroline) used as hole blocking layer were found to be 18 nm and 10 nm respectively. It is with this delicate adjustment of thicknesses, charge balancing is achieved and luminous efficiency and power efficiency were optimized. The maximum luminous efficiency of 3.82 cd/A at a current density of 24.45 mA/cm2 and maximum power efficiency of 2.61 lm/W at a current density of 5.3 mA/cm2 were achieved. We obtained luminance of 5993 cd/m2 when current density was 140 mA/cm2. The EL spectra was obtained for the LEDs and found that it has a peaking at 524 nm of wavelength.
M. Mohan,K. Panduranga Vittal 대한전기학회 2019 Journal of Electrical Engineering & Technology Vol.14 No.1
Voltage source converters (VSC)-based high voltage direct current (HVDC) link is an economical option for the long distance bulk power transmission, and it can be used to interconnect the offshore wind farms with an AC grid. Due to the penetration of VSC-HVDC system into the AC grid, the performance of the distance relay gets affected when a transmission line close to the point of common coupling (PCC) subjected to power system disturbances. In such condition, the PCC voltage is increased due to the VSC-HVDC control action, that causes the Zone-2 fault can be seen as a Zone-3 fault. As a result, the miscoordination of Zone-2 protection can occur in the distance relays. This paper presents both the analytical and simulation studies carried out on a VSC-HVDC system influence on the distance relay performance under fault conditions using PSCAD/EMTDC. Simulation results show that the presence of VSC-HVDC system greatly affects the performance of the Zone-2 and Zone-3 relay in an AC transmission line. Besides, the maloperation of the Zone-2 and Zone-3 relay is mitigated by varying the AC voltage reference input of the decoupled d-q controller of VSC-HVDC. Also, the effect of fault resistance on Zone-1 ground relay performance is analyzed.