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- 저자 : M. R. Praveen Kumar (검색결과 5 건)
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Sreekanth, T.V.M.,Basivi, Praveen Kumar,Nagajyothi, P.C.,Dillip, G.R.,Shim, J.,Ko, T.J.,Yoo, K. Elsevier 2018 Journal of chromatography Vol.1580 No.-
<P><B>Abstract</B></P> <P>Melamine and thiourea-derived graphitic carbon nitrides (M-GCN/T-GCN) were synthesized and characterized. The surface properties were investigated using inverse gas chromatography (IGC) and compared. Net retention volumes of M-GCN and T-GCN were measured with <I>n</I>-alkanes (C<SUB>5</SUB>–C<SUB>10</SUB>) and polar probes. The London dispersive surface free energies ( γ s d ), calculated using Schultz and Dorris–Gray methods, decreased linearly with increasing temperature. The specific components of the enthalpy and entropy of adsorption for the polar probes were obtained using the Schultz, Dong, and Sawyer–Brookman methods. The Gutmann’s Lewis acid–base parameters, <I>K<SUB>a</SUB> </I> and <I>K<SUB>b</SUB> </I>, were determined using the surface free energy ( Δ G a S ) via these methods. The surface character ‘<I>S’</I> values (<I>K<SUB>b</SUB> </I>/<I>K<SUB>a</SUB> </I>) of M-GCN and T-GCN using the respective methods are 4.04, 3.78, and 5.08 and 4.11, 5.27, and 2.86. Hence, the surfaces contain more basic than acidic sites and could interact strongly with acidic media. Thus, IGC elucidates the surface charges of the GCN matrix resulting from surface chemical modification.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Graphitic carbon nitride was synthesized using two precursors, melamine and thiourea. </LI> <LI> Physicochemical properties were confirmed by XRD, XPS and BET. </LI> <LI> Inverse gas chromatography was employed to understand surface free energy of GCN. </LI> <LI> The London dispersive parameters were determined by Schultz/Dorris–Gray methods. </LI> <LI> The Lewis acid–base parameters, showing the more basic character of GCN. </LI> </UL> </P>
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On-Chip Spiral Inductors and On-Chip Spiral Transistors for Accurate Numerical Modeling
M. Dhamodaran,R. Praveen Kumar,S. Jegadeesan 한국자기학회 2018 Journal of Magnetics Vol.23 No.1
This paper presents a new model for designing on-chip spiral inductor and on-chip spiral transistors. For this, the coupling between on-chip inductors and transistors has been implemented. The electromagnetic coupling between the inductors and the transistors and the mutual inductance are modeled by presenting the magnetic vector potential to study the coupling effect. It changes the surface integral of the magnetic field into the loop integral of the magnetic vector potential to calculate the coupling. In this method, the partial mutual inductance idea to compute the mutual inductance between two conductor sections instead of conductor loops can be developed. The inductance classification is applied to an on-chip environment to characterize interconnects and integrated inductors. The investigative model is reconsidered to incorporate the semiconductor substrate losses and the skin effect. The numerical solutions of the investigative model are also presented. To simulate the proposed model ADS Momentum software is used.
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An Integrated Training Aid System using Personalized Exercise Prescription
Jang S. J.,Park S. R.,Jang Y. G.,Oh Y. K.,Kwak H. M.,Diwakar Praveen Kumar,Park S. H.,Yoon Y. R. The Korean Society of Medical and Biological Engin 2005 의공학회지 Vol.26 No.5
Continuously motivating people to exercise regularly is more important than finding a way out of barriers such as lack of time, cost of equipment, lack of nearby facilities, and poor weather. Our proposed system presents practicable methods of motivation through a diverse exercise aid system. The Health Improvement and Management System (all-in-one system which saves space and maintenance costs) measures and evaluates a diverse body shape analysis and physical fitness test and directs users to automated personalized exercise prescription which is prescribed by the expert system of three types of exercise templates: aerobics, anaerobics, and leisure sports. Automated personalized exercise prescriptions are built into XML based documents because the data needs to be in the form of flexible, expansible, and convertible structures in order to process various exercise templates, BIOFIT, a digital exercise trainer, monitors and provides feedback on the physiological parameters while users are working out in the gymnasium. If these parameters do not range within the prescribed target zone, the device will alarm users to control the exercise and make the exercise trainer adjust systemically the proper exercise level. Numeric health information such as the report of the physical fitness test and the exercise prescription makes people stay interested in exercising. In addition, this service can be delivered through the Internet.
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Design and Analysis of Thermoacoustic Refrigerators Using Air as Working Substance
B. G. PRASHANTHA,S. SEETHARAMU,G. S. V. L. NARASIMHAM,M. R. Praveen Kumar 대한설비공학회 2019 International Journal Of Air-Conditioning and Refr Vol.27 No.1
In this paper, the design of 50 W thermoacoustic refrigerators operating with air as working substance at 10 bar pressure and 3% drive ratio for a temperature difference of 28 K is described. The design strategies discussed in this paper help in design and development of low cost thermoacoustic coolers compared to helium as the working substance. The design and optimization of spiral stack and heat exchangers, and the promising 0.2λ and 0.15λ resonator design with taper and divergent section with hemispherical end are discussed. The surface area, volume, length and power density of the hemispherical end design with air as working substance is found better compared to the published 10 and 50 W coolers using helium as the working substance. The theoretical design results are validated using DeltaEC software simulation results. The DeltaEC predicts 51.4% improvement in COP (1.273) at the cold heat exchanger temperature of −2.7∘C with air as working substance for the 50W 0.15λTDH resonator design compared to the published 50W 0.25λTDH resonator design with helium as working substance.
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B. G. PRASHANTHA,S. SEETHARAMU,G. S. V. L. NARASIMHAM,M. R. Praveen Kumar 대한설비공학회 2019 International Journal Of Air-Conditioning and Refr Vol.27 No.2
This paper deals with the design of thermoacoustic refrigerators using linear thermoacoustic theory. The refrigerator components are designed at 3% drive ratio by considering the practical limitations of providing sufficient spacing for attaching the loudspeaker to the resonator tube and accommodating instrumentation. The effects of spiral stack spacing in terms of thermal penetration depth on the theoretical performance of refrigerator using helium and air as working substances are discussed. The quarter-wavelength resonator designs with taper and divergent section terminated with hemispherical end are optimized with helium and air for better performance. Theoretical results are validated with DeltaEC software results and are in agreement with each other. Helium shows better performance compared to air but lacks power density. The DeltaEC predicts COP 0.514 at the cold heat exchanger temperature of −30∘C with helium compared to air (COP 0.616 at8.8∘C) for the 50 W cooling power 100 mm diameter quarter-wavelength resonator designs.
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