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Jeyakumar, V.,Kim, S.,Lee, G. M.,Li, G. Springer Science + Business Media 2016 Journal of global optimization Vol.65 No.2
<P>We propose a hierarchy of semidefinite programming (SDP) relaxations for polynomial optimization with sparse patterns over unbounded feasible sets. The convergence of the proposed SDP hierarchy is established for a class of polynomial optimization problems. This is done by employing known sums-of-squares sparsity techniques of Kojima and Muramatsu Comput Optim Appl 42(1):31-41, (2009) and Lasserre SIAM J Optim 17:822-843, (2006) together with a representation theorem for polynomials over unbounded sets obtained recently in Jeyakumar et al. J Optim Theory Appl 163(3):707-718, (2014). We demonstrate that the proposed sparse SDP hierarchy can solve some classes of large scale polynomial optimization problems with unbounded feasible sets using the polynomial optimization solver SparsePOP developed by Waki et al. ACM Trans Math Softw 35:15 (2008).</P>
S. Jeyakumar,K. Marimuthu,T. Ramachandran 대한기계학회 2013 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.27 No.9
The results of mathematical modeling and the experimental investigation on the machinability of aluminium (Al6061) silicon carbide particulate (SiCp) metal matrix composite (MMC) during end milling process is analyzed. The machining was difficult to cut the material because of its hardness and wear resistance due to its abrasive nature of reinforcement element. The influence of machining parameters such as spindle speed, feed rate, depth of cut and nose radius on the cutting force has been investigated. The influence of the length of machining on the tool wear and the machining parameters on the surface finish criteria have been determined through the response surface methodology (RSM) prediction model. The prediction model is also used to determine the combined effect of machining parameters on the cutting force, tool wear and surface roughness. The results of the model were compared with the experimental results and found to be good agreement with them. The results of prediction model help in the selection of process parameters to reduce the cutting force, tool wear and surface roughness, which ensures quality of milling processes.
Terahertz Micro-Strip Patch Antenna Design and Modelling for 6G Mobile Communication
Jeyakumar P.,Anandpushparaj J.,Thanapal P.,Meenatchi S.,Dhamodaran M. 대한전기학회 2023 Journal of Electrical Engineering & Technology Vol.18 No.3
The future mobile communication networks are emerging drastically and research is being pursued all around the world. To match with the increasing demand for high-speed data communication, wide bandwidth and a high gain antenna are required. Therefore, in this work, the frequency above 100 GHz is chosen as it provides high bandwidth and also suitable for short range communication. Initially, we have designed an antenna with carrier frequency of 300 GHz by comparing it with three different patch materials like Copper, Graphene and Gold and the antenna parameters are analysed. The obtained result shows that the graphene patch has a return loss of −27.70 dB, maximum bandwidth of 10.4 GHz and ideal radiation efficiency of 98.38%. Then the link budget evaluation for the target data rate is 100 Gbps at the bandwidth of 30 GHz on 10 m link distance is analyzed for mobile communication. By executing link budget evaluations in terms of code rate, target SNR, path loss and number of antenna elements required are validated. Finally, the proposed link budget is verified for various modulation schemes using MATLAB.
Rathika, R.,Kovendhan, M.,Joseph, D. Paul,Pachaiappan, Rekha,Kumar, A. Sendil,Vijayarangamuthu, K.,Venkateswaran, C.,Asokan, K.,Jeyakumar, S. Johnson Korean Nuclear Society 2020 Nuclear Engineering and Technology Vol.52 No.11
Swift heavy ion (SHI) beam irradiation can generate desirable defects in materials by transferring sufficient energy to the lattice that favours huge possibilities in tailoring of materials. The effect of Ag<sup>15+</sup> ion irradiation with energy 200 MeV on spray deposited V<sub>2</sub>O<sub>5</sub> thin films of thickness 253 nm is studied at various ion doses from 5 × 10<sup>11</sup> to 1 × 10<sup>13</sup> ions/㎠. The XRD results of pristine film confirmed orthorhombic structure of V<sub>2</sub>O<sub>5</sub> and its average crystallite size was found to be 20 nm. The peak at 394 cm<sup>-1</sup> in Raman spectra confirmed O-V-O bonding of V<sub>2</sub>O<sub>5</sub>, whereas 917 cm<sup>-1</sup> arise because of distortion in stoichiometry by a loss of oxygen atoms. Raman peaks vanished completely above the ion fluence of 5 × 10<sup>12</sup> ions/㎠. Optical studies by UV-Vis spectroscopy shows decrement in transmittance with an increase in ion fluence up to 5 × 10<sup>12</sup> ions/㎠. The red shift is observed both in the direct and indirect band gaps until 5 × 10<sup>12</sup> ions/㎠. The surface topography of the pristine film revealed sheath like structure with randomly distributed spherical nano-particles. The roughness of film decreased and the density of spherical nanoparticles increased upon irradiation. Irradiation improved the conductivity significantly for fluence 5 × 10<sup>11</sup> ions/㎠ due to band gap reduction and grain growth.
R. Rathika,M. Kovendhan,D. Paul Joseph,K. Vijayarangamuthu,A. Sendil Kumar,C. Venkateswaran,K. Asokan,S. Johnson Jeyakumar 한국원자력학회 2019 Nuclear Engineering and Technology Vol.51 No.8
Spray deposited Molybdenum trioxide (MoO3) thin film of thickness nearly 379 nm were irradiated with 200 MeV Ag15þ ion beam at different fluences (Ø) of 5 1011,1 1012,5 1012 and 1 1013 ions/cm2. The X-ray diffraction (XRD) pattern of the pristine film confirms orthorhombic structure and the crys-tallinity decreased after irradiation with the fluence of 5 1011 ions/cm2 due to irradiation induced defects and became amorphous at higher fluence. In pristine film, Raman modes at 665, 820, 996 cm1 belong to MoeO stretching, 286 cm1 belong to MoeO bending mode and those below 200 cm1 are associated with lattice modes. Raman peak intensities decreased upon irradiation and vanished completely for the ion fluence of 5 1012 ions/cm2. The percentage of optical transmittance of pristine film was nearly 40%, while for irradiated films it decreased significantly. Red shift was observed for both the direct and indirect band gaps. The pristine film surface had densely packed rod like structures with relatively less porosity. Surface roughness decreased significantly after irradiation. The electrical trans-port properties were also studied for both the pristine and irradiated films by Hall effect. The results are discussed.