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Study on the Weld Quality of the Friction Stir Welded Al-6063 Plates Using Square and Pentagonal Profiled Tools
P. Karthikeyan,K. Mahadevan
Journal of Applied Sciences , 2012,
Abstract: Friction stir welding process is used for joining materials such as aluminium, copper, magnesium etc., which are otherwise difficult to weld by the conventional welding processes. In friction stir welding, the tool profile plays a critical role in determining the end properties of the welded joint apart from the other parameters like rotational speed, welding speed and axial load. The aim of the present investigation was to compare the weld quality of the AA6063 plates joined using the square and the pentagonal friction stir welding tool profiles. From the test results it is observed that the square pin tool profile has yielded a good weld bead structure along with superior strength and hardness when compared with the pentagonal tool profile.
Growth, Structural, Optical, Mechanical and Dielectric Characterization of Diammonium Hydrogen Phosphate (DAHP) Single Crystals  [PDF]
P. Selvarajan, N. Joseph John, C.K. Mahadevan
Journal of Minerals and Materials Characterization and Engineering (JMMCE) , 2011, DOI: 10.4236/jmmce.2011.1015108
Abstract: Solubility studies of Diammonium Hydrogen Phosphate(DAHP) in de-ionized water were performed at various temperatures in the range 30-50 °C. Single crystals of DAHP were grown from aqueous solutions by slow evaporation technique. Structural characterization of the grown crystals has been carried out by powder and single crystal X-ray diffraction (XRD) methods. DAHP crystals crystallize in monoclinic structure with the space group P21/c. Second harmonic generation (SHG) for the material of this work was confirmed using Nd: YAG laser. The UV-Visible spectrum show that the grown crystals have wide optical transparency in the entire visible region. The dielectric measurements were made for grown DAHP crystal at the frequencies of 100 Hz and 1 KHz and in the temperature range 30-150 °C. Vickers microhardness value of DAHP crystal is found to increase with increase in load. Value of density of the grown DAHP crystal has been measured and it is well matched with the data of XRD studies.
Relevance Of Human Brain Banking In Neuroscience - A National Facility
Shankar S K,Mahadevan A
Annals of Indian Academy of Neurology , 1999,
Abstract: The lack of animal models for many of the neurodegenerative and psychiatric disorders and the fact that animal models cannot substitute for human tissue led to the establishment of Brain Banks that collect, preserve and provide fresh human tissue for researchers. One such Bank has been set up at the National Institute of Mental Health and Neurosciences funded by Dept. of Biotechnology, Dept. of Science and Technology and ICMR. Brains and tissue fluids (serum and CSF) are collected at autopsy following informed consent from close relatives. One half of the fresh brain from neurodegenerative and psychiatric disorders are frozen at -70′ C while the other half and brains from infective conditions are formalin fixed which can be used for pathomorphological studies. Only fresh frozen tissues that are tested and found negative for HIV and HbsAg are provided for research. The neural tissues as well as tissue fluids that are being supplied by the Brain Bank have supported a number of research projects in diverse fields of neurosciences. Many significant discoveries that have contributed towards understanding pathogenesis of disease, their genetic basis, and evolving prognostic and diagnostic markers for neurologic disease in the CSF have been made possible by the existence of such a facility. The continued functioning of such a facility requires the close co-operation of the clinical neuroscientists, pathologists and the other neuroscientists. Increased awareness and commitment amongst the scientific fraternity is necessary to keep alive the demand and ensure uninterrupted supply of fresh tissue for research. This will help usher in the era of molecular neurobiology with the fond hope that many more of the relentlessly progressive neurodegenerative disorders will eventually find a cause and cure.
Removal of Moisture Content in Paper Machine Using Soft Computing Techniques  [PDF]
M. Senthil Kumar, K. Mahadevan
Circuits and Systems (CS) , 2016, DOI: 10.4236/cs.2016.79220
Abstract: The choice of this investigation is to tune the proportional-integral-derivative (PID) parameters separately for controlling the moisture content in paper industry by using Particle Swarm Optimization (PSO). This paper boon a new algorithm for PID controller tuning based particle swarm optimization. PSO algorithm has recently developed as a very powerful method for real parameter optimization. This new process is proposed to combine both the algorithms to get better optimization values. The proposed algorithm tuned the PID parameters and its performance has been compared with PID algorithm. Compared to PID algorithm technique, dynamic performance requirements such as rise time settling time and peak overshoot optimal values produced by PSO. The plant model represented by the transfer function is obtained by the system identification toolbox.
Design of Ultra-Low Loss Highly Nonlinear Dispersion Flattened Octagonal Photonic Crystal Fibers  [PDF]
G. Dhanu Krishna, G. Prasannan, S. K. Sudheer, V.P. Mahadevan Pillai
Optics and Photonics Journal (OPJ) , 2015, DOI: 10.4236/opj.2015.512032
Abstract: In this study, Octagonal Photonic Crystal Fiber (O-PCF) structures are designed for different air filling fractions with fixed pitch length of 2.2 μm. The light propagating characteristics of PCF structures such as effective refractive index, confinement loss, chromatic dispersion mode effective area and nonlinear coefficient are numerically analyzed. The simulation results show that the fibers have dispersion flattened, ultra-low loss highly nonlinear nature in the wavelength region 1.3 μm to 1.7 μm.
Low-Temperature Spin Dynamics of Doped Manganites: roles of Mn-t2g and eg and O-2p states
Priya Mahadevan,I. V. Solovyev,K. Terakura
Physics , 1999, DOI: 10.1103/PhysRevB.60.11439
Abstract: The low-temperature spin dynamics of doped manganites have been analyzed within a tight-binding model, the parameters of which are estimated by mapping the results of ab initio density functional calculations onto the model. This approach is found to provide a good description of the spin dynamics of the doped manganites, observed earlier within the ab initio calculations. Our analysis not only provides some insight into the roles of the eg and the t2g states but also indicates that the oxygen p states play an important role in the spin dynamics. This may cast doubt on the adaptability of the conventional model Hamiltonian approaches to the analysis of spin dynamics of doped manganites.
Evolution of spectral function in a doped Mott insulator : surface vs. bulk contributions
K. Maiti,Priya Mahadevan,D. D. Sarma
Physics , 1998, DOI: 10.1103/PhysRevLett.80.2885
Abstract: We study the evolution of the spectral function with progressive hole doping in a Mott insulator, $La_{1-x}Ca_xVO_3$ with $x$ = 0.0 - 0.5. The spectral features indicate a bulk-to-surface metal-insulator transition in this system. Doping dependent changes in the bulk electronic structure are shown to be incompatible with existing theoretical predictions. An empirical description based on the single parameter, $U/W$, is shown to describe consistently the spectral evolution.
Spin, charge and orbital ordering in La0.5Sr1.5MnO4
Priya Mahadevan,K. Terakura,D. D. Sarma
Physics , 2001, DOI: 10.1103/PhysRevLett.87.066404
Abstract: We have analyzed the experimental evidence of charge and orbital ordering in La0.5Sr1.5MnO4 using first principles band structure calculations. Our results suggest the presence of two types of Mn sites in the system. One of the Mn sites behaves like an Mn(3+) ion, favoring a Jahn-Teller distortion of the surrounding oxygen atoms, while the distortion around the other is not a simple breathing mode kind. Band structure effects are found to dominate the experimental spectrum for orbital and charge ordering, providing an alternate explanation for the experimentally observed results.
On charge and orbital ordering in La0.5Sr1.5MnO4
Priya Mahadevan,K. Terakura,D. D. Sarma
Physics , 2001, DOI: 10.1103/PhysRevLett.87.066404
Abstract: Using first principle band structure calculations, we critically examine results of resonant x-ray scattering experiments which is believed to directly probe charge and orbital ordering. Considering the specific case of La0.5Sr1.5MnO4, we show that this technique actually probes most directly and sensitively small structural distortions in the system. Such distortions, often difficult to detect with more conventional techniques, invariably accompany and usually cause the orbital and charge orderings. In this sense, this technique is only an indirect probe of such types of ordering. Our results also provide a microscopic explanation of the novel types of charge and orbital ordering realized in this system and other doped manganites.
Investigation on the Change Effected by the Tool Type on the Hardness of Friction Stir Processed AA6063 Aluminium Alloy
D. Peter Pushpanathan,K. Ganesa Balamurugan,K. Mahadevan
Journal of Applied Sciences , 2012,
Abstract: Aluminium alloy 6063 is one of the most popular alloys in the 6000 series which provides good extrudability and surface finish. Various application of this alloy include architectural and building products, electrical components and conduit, pipes for irrigation systems, door and window frames, railings and furniture, etc. However improving its strength by improving the hardness would complement the existing advantages of this alloy. This study was intended to improve the hardness of this alloy by FSP (friction stir processing) technique. The effect of two tool types on the hardness of the friction stir processed surfaces was studied. It was found that the hardness values of the friction stir processed surfaces varied between the tool types. The surfaces processed with both tool types show considerable improvement in the hardness when compared to the hardness of the unprocessed bulk material. Experiments were conducted as per full factorial 23 design of experiment with various process parameter combinations for both tools.
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