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Journal of Materials science & Technology 2009年第4期25卷 531-534页

作者： G. Giridhar M. rangacharyulu r.v.s.s.n. ravikumar P. sambasiva rao Department of Physics Acharya Nagarjuna University Department of Chemistry Pondicherry University

Electron paramagnetic resonance （EPr） and optical absorption studies were carried out at room temperature on copper doped mixed alkali cadmium phosphate （LinaCdP） glasses to understand the nature and symmetry of dopant. Three samples with varying concentrations of alkali ions have been prepared. The spin Harniltonian parameters obtained from room temperature EPr spectra are： gli=2.437, 9⊥=2.096, A‖=117×10-4 cm-1, A⊥=26×10-4 cm-1 for LinaCdP1, g‖=2.441, g⊥=2.088, A‖=121×10-4 cm-1, A⊥=25×10-4 cm-1 for LinaCdP2and g‖=2.433,g⊥=2.096, A‖=125×10 4cm-1, A⊥=32×10-4cm-1 for LinaCdP3. TheseEPr results indicate that the dopant Cu2＋ ion enters the glass matrix into a tetragonally elongated octahedral site. The bonding parameters evaluated by correlating optical and EPr data suggest that bonding between the central metal ion and ligands is partially covalent. The mixed alkali effect in cadmium phosphate glasses was reported.

关键词： Glasses Electron paramagnetic resonance (EPr) Optical properties

Improved strength and ductility of high alloy containing Al–12Zn–3Mg–2.5Cu alloy by combining non-isothermal step rolling and cold rolling

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International Journal of Minerals,Metallurgy and Materials 2017年第2期24卷 179-185页

作者： v.v.ravikumar s.Kumaran Department of Metallurgical and Materials Engineering National Institute of TechnologyTamil Nadu 620015India

Al-12Zn-3Mg-2.5Cu alloy was prepared using a liquid metallurgy route under the optimized conditions. A sample cut from the ingot was rolled non-isothermally from 400℃ to 100℃ in 100℃ steps, with 15% reduction in thickness; it was then cold rolled isothermally at room temperature for 85% reduction. The cold-rolled alloys were characterized by electron microscopy, hardness test, and tensile test to elucidate their structural evolution and evaluate their mechanical behavior. In the results, the cast alloy consists of a-aluminum and various intermetallic compounds. These compounds are segregated along the grain boundaries, which makes the alloy difficult to roll at room tem- perature. The combined effect of non-isothermal step rolling and cold rolling results in the nano/microsized compounds distributed uniformly in the matrix. The hardness is substantially increased after rolling. This increase in hardness is attributed to the ultra-fine grain size, fine-scale intermetallic compounds, and structural defects （e.g., dislocations, stacking faults, and sub-grains）. The ultimate tensile strength of the rolled alloy is approximately 628 MPa with 7% ductility.

关键词： aluminum zinc magnesium copper alloys non-isothermal cold rolling mechanical properties intermetallic compounds struc-ture defects

A study on the Protective Effect of Cynodon dactylon Leaves Extract in Diabetic rats

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Biomedical and Environmental sciences 2011年第2期24卷 190-199页

作者： Karthik D ravikumar s Department of Biotechnology PRIST University

Objective To investigate the antidiabetic, antioxidant and hypolipidemic efficacy of Cynodon dactylon in diabetic rats. Methods The experimental rats were randomly divided into three groups： Group I： control; Group II： Alloxan diabetic, untreated; and Group III： Alloxan diabetic treated with ethanolic extract of C. dactylon leaves （450 mg/kg bw）. Experimental diabetes was induced by alloxan in a single dose of 150 mg/kg bw. results A significant diminution of fasting blood sugar level was observed and also significant increase in HDL and decrease （P0.05） in cholesterol, triglyceride, LDL and vLDL were observed after 15 days of treatment. The investigation also revealed, the activities of AsT, ALT, ALP, AP, LDH, and CPK （P0.05） were decreased in the extract‐supplemented group. The significant decrease in protein content and sOD, CAT, GPx, and GsH （P0.05） activity and increase in LPO in plasma were found to be ameliorated after treatment. Conclusion Our result supports the fact that administration of extract of C. dactylon leave is able to reduce hyperglycemia and hyperlipidemia risk and also reduced the oxidative stress in diabetic rats.

关键词： Cynodon dactylon Ethanolic extract GC‐Ms Alloxan diabetes Antidiabetic Antioxidant Lipid profile Enzyme profile

structural and photoluminescence studies on europium-doped lithium tetraborate(Eu:Li2B4O7)single crystal grown by microtube Czochralski(μT-Cz)technique

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Chinese Physics B 2016年第5期25卷 429-433页

作者： A Kumaresh r Arun Kumar n ravikumar U Madhusoodanan B s Panigrahi K Marimuthu M Anuradha GrD Centre for Materials research PSG College of TechnologyCoimbatoreIndia Department of Physics PSG College of TechnologyCoimbatoreIndia radiation safety Division Indira Gandhi Centre for Atomic ResearchKalpakkamIndia Department of Physics Gandhigram Rural UniversityDindigulIndia PsG Institute of Advanced studies CoimbatoreIndia

rare earth europium（Eu（3＋））-doped lithium tetraborate（Eu：Li_2B_4O_7） crystal is grown from its stoichiometric melt by microtube Czochralski pulling technique（μT-Cz） for the first time. The grown crystals are subjected to powder x-ray diffraction（PXrD） analysis which reveals the tetragonal crystal structure of the crystals. Uv–vis–nIr spectral analysis is carried out to study the optical characteristics of the grown crystals. The crystal is transparent in the entire visible region, and the lower cutoff is observed to be at 304 nm. The existence of BO_3 and BO_4 bonding structure and the molecular associations are analyzed by Fourier transform infrared（FTIr） spectroscopy. The results of excitation and emission-photoluminescence spectra of europium ion incorporated in lithium tetraborate（LTB） single crystal reveal that the observations of peaks at 258,297, and 318 nm in the excitation spectra and peaks at 579, 591, 597, 613, and 651 nm are observed in the emission *** chromaticity coordinates are calculated from the emission spectra, and the emission intensity of the grown crystal is characterized through a CIE 1931（Commission International d＇Eclairage） color chromaticity diagram.

关键词： crystal growth optical material growth from melt photoluminescence study

Antagonistic properties of seagrass associated streptomyces ***-1:A source for anthraquinone rich compound

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Asian Pacific Journal of Tropical Medicine 2012年第11期5卷 887-890页

作者： s.ravikumar M.Gnanadesigan A.saravanan n.Monisha v.Brindha s.Muthumari school of Marine sciences Department of Oceanography and Coastal Area StudiesAlagappa UniversityThondi campusThondi-623 409Ramanathapuram DistrictTamilnaduIndia Department of Microbiology Selvamm Arts and Science CollegeNamakkal-637 003TamilnaduIndia Department of Biotechnology AVS College of Arts and ScienceSalemTamilnaduIndia Department of Biotechnology Thassim Beevi Abdul Kader College for WomenKilakarai-623 517Ramanathapuram DistrictTamilnaduIndia Departemt of Biotechnology Meenakshi Ramasamy Arts and Science CollegeThathanur-621 804Ariyalur DistrictTamilnaduIndia

Objective:To identify the antibacterial potential of seagrass(syringodium isoetifoliutn) associate microbes against bacterial ***:Eumeration of microbial associates were analyzed with leaf and root samples of syringodium *** and MBC were calculated for bacterial pathogens with microbial *** and GC-Ms analysis were calculated for Actinomycetes sp.(Act01) which was the most ***:Of the isolated microbial associates phosphatase producing bacterial isolates were identified as maximum [(26l.78±35.09) CFU×10~4/g]counts in root *** the selected microbial isolates Actinomycete sp(Act01) showed broad spectrum of antibacterial activity against antibiotic resistant and fish bacterial *** analysis of Act01 showed maximum identities(99%) with the streptomyces sp.(GU5500072).The 16s rDnA secondary structure of Act01 showed the free energy values as -366.3 kkal/*** GC-Ms analysis Act01 showed maximum retention value with 23.742 rT and the corresponding chemical class was identified as 1,4-dihydroxy-2-(3- hydroxybutyl)-9,10-anthraquinone 9,***:In conclusion,streptomyces sp. (GU045544.1) from syringodium isoetifolium could be used as potential antibacterial agent.

关键词： Actinomycetes sp. MIC MBC Phylogenetic analysis syringodium isoetifolium

Co-evolution of nuclear rings,bars and the central intensity ratio of their host galaxies

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research in Astronomy and Astrophysics 2020年第2期20卷 15-20页

作者： s.Aswathy C.D.ravikumar Department of Physics University of Calicut

Using a sample of 13 early-type spiral galaxies hosting nuclear rings,we report remarkable correlations between the properties of the nuclear rings and the central intensity ratio(CIr) of their host *** CIr,a function of intensity of light within the central 1.5 and 3 arcsec region,is found to be a vital parameter in galaxy evolution,as it shares strong correlations with many structural and dynamical properties of early-type galaxies,including mass of the central supermassive black hole(sMBH).We use archival HsT images for aperture photometry at the centre of the galaxy image to compute the *** observe that the relative sizes of nuclear rings and ring cluster surface densities strongly correlate with the *** correlations suggest reduced star formation in the centres of galaxies hosting small and dense nuclear *** scenario appears to be a consequence of strong bars as advocated by the significant connection observed between the CIr and bar *** addition,we observe that the CIr is closely related with the integrated properties of the stellar population in the nuclear rings,associating the rings hosting older and less massive star clusters with low values of ***,the CIr can serve as a crucial parameter in unfolding the coupled evolution of bars and rings as it is intimately connected with both their properties.

关键词： galaxies:evolution galaxies:formation galaxies:photometry galaxies:spiral galaxies:starburst

In vitro antiplasmodial activity of methanolic extracts from seaweeds of south West Coast of India

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Asian Pacific Journal of Tropical Medicine 2011年第11期4卷 862-865页

作者： s ravikumar G ramanathan M Gnanadesigan A ramu v vijayakumar school of Marine sciences Department of Oceanography and Coastal Area StudiesAlagappa UniversityThondi CampusThondi - 623 409Ramanathapuram DistrictTamil NaduIndia Department of Microbiology V.H.S.N.College.Virudhunagar DistrictTamil NaduIndia school of Chemistry Department of Inorganic ChemistryMadurai Kamaraj UniversityMadurai DistrictTamil NaduIndia

Objective:To identify the in vitro antiplasmodial activity of seaweed plants against Plasmodium falciparum ***:A total of eight seaweeds were collecled from Kanvakumari district,Tainilnadu,*** in vitro antiplasmodial activity was performed in 96 well plates against Plasmodium falciparum,and preliminary phytochemcial analysis were performed for the ***:Of the selected plants Enteromorpha intestinalis(2.61%) showed maximum percentage of *** minimum concentration of inhibitory(IC_(50)) value was observed with Chaetomorpha antennina[(26.37±4.14)μg/ml.]further,the positive controls such as chloroquine and artemether showed antiplasmodial activities(IC_(50)) with(19.10±5.93) and(6.03±0.21)μg/mL concentrations,*** preliminary phytochemical analysis of the seaweed extracts showed a variety of phytochemical constituents such as carboxylic acids,phenols,protein, resins,steroids and ***:The antiplasmodial activity of the seaweed extract might due to the presence of sugars and phenolic *** the present findings,it is concluded that,the seaweed extract of Chaetomorpha antennina can be further used as a putative antiplasmodial drugs in near future.

关键词： Antiplasmodial activity IC_(50) Phytochemical seaweeds Plasmodium falciparum

Comparative study on Tool Fault Diagnosis Methods Using vibration signals and Cutting Force signals by Machine Learning Technique

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structural Durability & Health Monitoring 2020年第2期14卷 127-145页

作者： suhas s.Aralikatti K.n.ravikumar Hemantha Kumar H.shivananda nayaka v.sugumaran nationalInstitute of Technology Karnataka Mangaluru575025India vellore Institute of Technology University Chennai600127India

The state of cutting tool determines the quality of surface produced on the machined parts.A faulty tool produces poor sur face,inaccurate geometry and non-economic ***,it is necessary to monitor tool condition for *** process to have superior quality and economic *** the pre-sent study,fault classification of single point cutting tool for hard turning has been carried out by employing machine learning *** force and vibration signals were acquired to monitor tool condition during machining.A set of four tooling conditions namely healthy,worn flank,broken insert and extended tool overhang have been considered for the *** machine learning technique was applied to both vibration and cutting force *** wavelet features of the signals have been extracted using discrete wavelet trans formation(DWT).This transformation represents a large dataset into approximation coeffcients which contain the most useful information of the *** features,among features extracted,were selected using J48 decision tree ***-sification of tool conditions was carried out us ing naive Bayes algorithm.A 10 fold cross validation was incorporated to test the validity of classifier.A comparison of performance of classifier was made between cutting force and vibration signal to choose the best signal acquisition method in classifying tool fault conditions using machine learning technique.

关键词： Fault diagnosis of cutting tool naive Bayes classifer,decision tree technique

Long term optical variability of bright X-ray point sources in elliptical galaxies

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research in Astronomy and Astrophysics 2014年第10期14卷 1251-1263页

作者： v.Jithesh ranjeev Misra P.shalima K.Jeena C.D.ravikumar B.r.s.Babu Department of Physics University of CalicutMalappuram-673635India Inter-University Centre for Astronomy and Astrophysics Post Bag 4GaneshkhindPune-411007India Department of Physics Providence Women's CollegeMalaparambaCalicut-673009India Department of Physics Sultan Qaboos UniversityMuscatOman

We present long term optical variability studies of bright X-ray sources in four nearby elliptical galaxies with the Chandra Advanced CCD Imaging spectrometer array （ACIs-s） and observations from the Hubble space Telescope （HsT） Advanced Camera for surveys. Out of the 46 bright （X-ray counts 〉 60） sources that are in the common field of view of the Chandra and HsT observations, 34 of them have potential optical counterparts, while the rest of them are optically dark. After taking into account systematic errors, estimated using optical sources in the field as a reference, we find that four of the X-ray sources （three in nGC 1399 and one in nGC 1427） have variable optical counterparts at a high level of significance. The X-ray luminosities of these sources are ～10^38 erg s^-1 and are also variable on similar time scales. The optical variability implies that the optical emission is asso- ciated with the X-ray source itself rather than being the integrated light from a host globular cluster. For one source, the change in optical magnitude is 〉 0.3, which is one of the highest reported for this class of X-ray sources and this suggests that the optical variability is induced by the X-ray activity. However, the optically variable sources in nGC 1399 have been reported to have blue colors （g - z 〉 1）. All four sources have been detected in the infrared （Ir） by spitzer as point sources, and their ratios of 5.8 to 3.6 μm flux are 〉 0.63, indicating that their Ir spectra are like those of Active Galactic nuclei （AGns）. While spectroscopic confirmation is required, it is likely that all four sources are background AGns. We find none of the X-ray sources having opticalfir colors different from AGns to be optically variable.

关键词： (Galaxy ) globular clusters general -- galaxies photometry -- X-rays galaxies

Influence of heat treatment on the machinability and corrosion behavior of AZ91 Mg alloy

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Journal of Magnesium and Alloys 2018年第1期6卷 52-58页

作者： swetha Chowdary v ravikumar Dumpala Anand Kumar s Kondaiah vv ratna sunil B Department of Mechanical Engineering Rajiv Gandhi University of Knowledge Technologies(AP-IIIT)Nuzvid521202India Department of Mechanical Engineering Visvesvaraya National Institute of TechnologyNagpurMaharashtra 440010India Department of Mechanical Engineering Dayananda Sagar UniversityBengaluru560068India Department of Mechanical Engineering Tirumala Engineering CollegeNarasaraopetAndhra Pradesh 522601India

In the present study,AZ91 Mg alloy was heat treated at 410℃ for 6,12 and 24 h to investigate the influence of heat treatment on machinability and corrosion *** effect of soaking time on the amount and distribution of Mg 17 Al 12(β-phase)was analyzed under the optical *** measurements demonstrated the increased hardness with increased heat treatment soaking time,which can be attributed to the solid solution *** influence of super saturatedα-grains on reducing the cutting force(F z)with respect to increased cutting speed was observed as *** corrosion behavior of the heat treated specimens was studied by conducting electrochemical ***,corrosion rate of heat treated samples was observed as increased compared with the base *** the results,it is evident that the machinability of AZ91 Mg alloy can be improved by producing super saturatedα-grains through heat treatment but at the cost of losing corrosion resistance.

关键词： AZ91 Mg alloy solid solution Turning Corrosion Machinability