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Enhancement of the crystalline perfection of <0 0 1> directed KDP single crystal
P. Rajesh,S. Sreedhar,K. Boopathi,S. Venugopal Rao,P. Ramasamy 한국물리학회 2011 Current Applied Physics Vol.11 No.6
<0 0 1> directed good quality potassium dihydrogen phosphate (KDP) single crystal has been grown by Sankaranarayanan―Ramasamy (SR) method with the vision to improve the crystalline perfection and efficiency. A seed crystal of diameter 25 × 15 × 3 mm^3 was mounted in the ampoule, where the diameter of the ampoule was much bigger than the seed. The size of the crystal grown was 30 × 20 × 60 mm^3. The obtained transparency for the crystal grown by SR method is 93% and by conventional method is 85% in the entire visible region. The HRXRD analysis indicates that the crystalline perfections of the crystals are excellent without having any very internal structural grain boundaries. The obtained FWHM for conventional method grown crystal is 12 arc s and for SR method is 6 arc s. Low dielectric loss indicates that the <0 01> directed crystal contains minimum defects. Higher mechanical stability was observed in SR method grown KDP compared to the other. Laser damage threshold value has been determined using Nd:YAG laser operating at 1064 nm. The optical transmission study and the powder SHG measurement show the suitability of the ingot for nonlinear optical applications.
Venugopal, Pujari,Chandra, T. S. 한국미생물 · 생명공학회 2001 Journal of microbiology and biotechnology Vol.11 No.4
By UV-irradiation of Eremothecium ashbyii DTl, a highly flavinogenic mutant (UV-18-57) and a nonflavinogenic mutant (UV-85) were obtained. The physio-morphological characteristics of these three strains were studied on glucose medium in submerged fermentation. Glucose utilization and mycelial growth occurred in 0-2 days of fermentation. By the third day, the biomass had declined. Extracellular riboflavin excretion was distinct from the second day, reaching a maximum rate by the fourth day. The hyphae of the highly flavinogenic mutant UV-18-57 were broader than DTI, while the nonflavinogenic UV-85 hyphae were very thin. Riboflavin accumulation was high in UV-18-57 (extracellular riboflavin, 825㎍/ml, and intracellular, 490㎍/ml) and caused the mycelia to swell into bulbous forms. Riboflavin accumulation was less in DTI (108㎍/ml extracellular and 24㎍/ml intracellular) and correspondingly its hyphae were thinner than those of UV-18-57 and swollen bulbous mycelia were not prominent. UV-85 was nonflavinogenic and, accordingly, its morphological characteristics included long thin filaments with no intracellular riboflavin accumulation. A large number of greenish fluorescence spores were seen in UV-18-57, whereas DTI had less spores and UV-85 was nonsporulating. Sporulation is correlated with riboflavin production. UV- 18-57 had better mycelial integrity and lysis started only by the seventh day, whereas DTI and UV-85 started to lyze earlier by 4-5 days. By the late stage of fermentation (eighth day), DT1 had a few long, thin filaments indicating some secondary growth, whereas UV-85 showed a compact pellet form of mycelia. Most mycelia of UV-18-57 still appeared intact.
Thangavel, S.,Krishnamoorthy, K.,Kim, S.J.,Venugopal, G. Elsevier Sequoia 2016 JOURNAL OF ALLOYS AND COMPOUNDS Vol.683 No.-
In this study, we demonstrated the facile design of zinc-sulphide decorated reduced graphene-oxide (ZnS-rGO) nanohybrid via microwave method and examined their photocatalytic properties. The physico-chemical properties of the ZnS-rGO were analysed using X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, high resolution scanning electron microscopy, energy dispersive X-ray spectroscopy and laser Raman analyses, respectively. The photocatalytic activity of the prepared ZnS-rGO nanohybrid was examined by the degradation of two model dyes Methylene blue (MB) and Rhodamine-B (RhB). The experimental results suggested that the designed ZnS-rGO nanohybrid possess superior photocatalytic activity with 1.47 and 2.92 fold higher reaction rates for MB and RhB degradation than that of the pure ZnS nanoparticles. A plausible mechanism for the enhanced properties of ZnS-rGO nanohybrid was discussed using photoluminescence spectra. Further, the role of reactive oxygen species on the photocatalytic properties of ZnS-rGO nanohybrid was investigated using appropriate electron and hole scavengers.
G Venugopal,S Ramakrishnan 대한의용생체공학회 2014 Biomedical Engineering Letters (BMEL) Vol.4 No.3
Purpose In this work, an attempt has been made to analyzesurface electromyography (sEMG) signals in dynamiccontractions using bispectrum features. Methods Signals are recorded from the biceps brachii muscleof 50 healthy volunteers during curl exercise. Bispectrumand bicoherence are estimated from the recorded sEMGsignals. Sum and variance of bispectrum and bicoherence arecalculated. Further analysis is carried by dividing the entireduration of the exercise into six zones. Results obtained areverified using the subject’s feedback about first musclediscomfort time. Results Bispectrum is observed with high amplitude peaksat zone where subjects reported first muscle discomfort. Maximum values for sum and variance of bispectrum areobserved in the same zone. Similar patterns are not seen withbicoherence features. In bicoherence sum and bicoherencevariance, distinctive peaks are observed in the zone whentask failure occurs. Conclusions First discomfort zone estimated using bispectrumvariance is found to be in agreement with the subject'sfeedback. It appears that, this method is useful in analyzingprogressive changes associated with muscle mechanics infatigue conditions using non-invasive sEMG recordings.
Corrosion and Nanomechanical Behaviors of 16.3Cr-0.22N-0.43C-1.73Mo Martensitic Stainless Steel
( Rahul Ghosh ),( S. Chenna Krishna ),( A. Venugopal ),( P. Ramesh Narayanan ),( Abhay K. Jha ),( P. Ramkumar ),( P. V. Venkitakrishnan ) 한국부식방식학회(구 한국부식학회) 2016 Corrosion Science and Technology Vol.15 No.6
The effect of nitrogen on the electrochemical corrosion and nanomechanical behaviors of martensitic stainless steel was examined using potentiodynamic polarization and nanoindentation test methods. The results indicate that partial replacement of carbon with nitrogen effectively improved the passivation and pitting corrosion resistance of conventional high-carbon and high- chromium martensitic steels. Post-test observation of the samples after a potentiodynamic test revealed a severe pitting attacks in conventional martensitic steel compared with nitrogen- containing martensitic stainless steel. This was shown to be due to (i) microstructural refinement results in retaining a high-chromium content in the matrix, and (ii) the presence of reversed austenite formed during the tempering process. Since nitrogen addition also resulted in the formation of a Cr<sub>2</sub>N phase as a process of secondary hardening, the hardness of the nitrogen- containing steel is slightly higher than the conventional martensitic stainless steel under tempered conditions, even though the carbon content is lowered. The added nitrogen also improved the wear resistance of the steel as the critical load (Lc2) is less, along with a lower scratch friction coefficient (SFC) when compared to conventional martensitic stainless steel such as AISI 440C.
Thilagavathi Thiyagarajan,Venugopal Deivasigamani,Marnadu Raj,Chandrasekaran Joseph,Thangaraju Dheivasigamani,Baskaran Palanivel,Mohamed S. Hamdy,Mohd. Shkir 한국화학공학회 2021 Korean Journal of Chemical Engineering Vol.38 No.5
Pure tungsten oxide (WO3) nanoparticles (NPs) and WO3/copper tungstate (CuWO4) nanocomposites (NCs) were prepared by varying copper content from (5-20 wt%) via the co-precipitation process. XRD results reveal that the structural parameters of WO3/CuWO4 NCs have been strongly affected via Cu doping. Morphology of synthesized WO3 was noticed to be distinct and particle size was significantly reduced through Cu doping confirmed by employing HRTEM studies. Elemental purity of as synthesized products, elucidated from EDX and XPS analyses, reveals that WO3/CuWO4 nanocomposites contain W, O and Cu elements only. Also, FT-IR spectra and its corresponding assignments indicate the existence of WO3/CuWO4. UV-Visible study shows that WO3/CuWO4 composites have narrow bandgap compared to pure WO3. Photoluminescence spectral peaks intensity of NCs displays a decreasing trend, which supports the enhanced photocatalytic activity. The results clearly show that 20 wt% Cu incorporated WO3 sample exhibits better photocatalytic nature than that of pure WO3 and will be more applicable in purify the water.