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Effect of Temperature on Grain Size in AA6063 Aluminum Alloy Subjected to Repetitive Corrugation and Straightening

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Acta Metallurgica Sinica(English Letters) 2019年第7期32卷 835-844页

作者： N. Thangapandian S. Balasivanandha Prabu k. A. padmanabhan Department of Mechanical Engineering St. Joseph's Institute of Technology Chennai 600119 India Department of Mechanical Engineering College of Engineering Guindy Anna University. Chennai 600025 India

The influence of processing temperature on grain size reduction in AA 6063 aluminum alloy subjected to repetitive corrugation and straightening (RCS) is investigated in this work. The aluminum alloy was processed by RCS at different temperatures (room temperature, 100 ℃, 200 ℃ and 300 ℃) till the maximum number of passes possible before failure and the mechanical properties such as tensile strength and hardness were measured. The grain size and their misorientation of grains of the processed samples were analyzed using the electron backscattered diffraction. The results indicated that the transformation of low-angle grain boundaries to high-angle grain boundaries and dislocation tangles were highly dependent on the strain imparted, which could be controlled by selecting the proper processing temperature. As a result, the mechanical properties are affected. In particular, the room temperature tensile strength and hardness values of the processed material decrease with increasing processing temperature.

关键词： Repetitive corrugation and straightening Strain Grain size reduction/refinement EBSD Strength Hardness

Performance assessment of prefabricated vertical drains in mitigating soil reliquefaction subjected to repeated seismic events using shaking table experiments

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Frontiers of Structural and Civil Engineering 2024年第3期18卷 411-427页

作者： Gowtham padmanabhan Ganesh kumar SHANMUGAM Department of Earthquake Engineering Indian Institute of Technology RoorkeeUttarakhand 247667India Geotechnical Engineering Division CSIR-Central Building Research Institute Academy of Scientific and Innovative Research(AcSIR)Uttarakhand 247667India

The use of prefabricated vertical drains(PVD)in liquefiable deposits is gaining attention due to enhanced ***,investigations on PVD in mitigating re-liquefaction during repeated shaking events are not *** study performed a series of shaking table experiments on untreated and PVD-treated specimens prepared with 40%and 60%relative *** sinusoidal loading was applied with an incremental peak acceleration of 0.1g,0.2g,0.3g,and 0.4g,at 5 Hz shaking frequency with 40 s *** performance of treated ground was evaluated based on the generation and dissipation of excess pore water pressure(EPWP),induced sand densification,subsidence,and cyclic stress *** addition,the strain accumulated in fresh and exhumed PVD was investigated using geotextile tensile testing apparatus aided with digital image *** evidence of pore pressure was reported up to 0.2g peak acceleration for 40%and 60%relative density *** continuous occurrence of soil densification and drainage medium restrained and delayed the generation of EPWP and expedited the dissipation *** study demonstrates PVD can mitigate re-liquefaction,without suffering from deterioration,when subjected to medium to high intense repeated shaking events.

关键词： prefabricated vertical drains drainage re-liquefaction shaking table digital image correlation

Experimental studies on liquefaction and reliquefaction potential of saturated ground subjected to repeated incremental acceleration loading with varying shaking duration

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Earthquake Engineering and Engineering Vibration 2023年第4期22卷 909-920页

作者： Gowtham padmanabhan Ganesh kumar Shanmugam Department of Earthquake Engineering Indian Institute of Technology RoorkeeRoorkeeUttarakhand 247667India Geotechnical Engineering Division CSIR-Central Building Research InstituteAcademy of Scientific and Innovative Research(AcSIR)RoorkeeUttarakhand 247667India

Past research has focused on the factors that influence liquefaction under normal shaking ***,studies on parameters that influence the reliquefaction potential of saturated deposits during repeated shaking events are *** this study,an attempt has been made to examine the influence of acceleration amplitude and shaking duration on liquefaction and reliquefaction potential under repeated shaking conditions is conducted.1-g uni-axial shaking table experiments were performed on saturated ground prepared with 40%and 60%relative *** prepared ground was subjected to alternate longer and shorter shaking durations(40 and 20 s)of repeated incremental 0.1 g,0.2 g,0.3 g and 0.4 g acceleration loading,*** variation in density,excess pore water pressure(EPWP),cyclic resistance ratio(CRR)and surface settlement were *** results showed that due to repeated incremental shaking events,reliquefaction was observed on the prepared *** longer shaking duration,the post-liquefied soil showed density improvement with improved soil ***,the application of shorter duration loading followed by longer shaking reduced the beneficial effect of density improvement by disturbing the densified *** to this,the ground was found to be more susceptible to reliquefaction in the subsequent incremental longer shaking event.

关键词： 1g–shaking table reliquefaction acceleration amplitude shaking duration relative density

Emergent perspective of gravity and dark energy

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Research in Astronomy and Astrophysics 2012年第8期12卷 891-916页

作者： T.padmanabhan IUCAA Pune University CampusGaneshkhind

There is sufficient amount of internal evidence in the nature of gravitational theories to indicate that gravity is an emergent phenomenon like, e.g, elasticity. Such an emergent nature is most apparent in the structure of gravitational dynamics. It is, however, possible to go beyond the field equations and study the space itseff as emer- gent in a well-defined manner in （and possibly only in） the context of cosmology. In the first part of this review, I describe various pieces of evidence which show that gravitational field equations are emergent. In the second part, I describe a novel way of studying cosmology in which I interpret the expansion of the universe as equivalent to the emergence of space itself. In such an approach, the dynamics evolves towards a state of holographic equipartition, characterized by an equality in the number of bulk and surface degrees of freedom in a region bounded by the Hubble radius. This prin- ciple correctly reproduces the standard evolution of a Friedmann universe. Further, （a） it demands the existence of an early inflationary phase as well as late time accelera- tion for its successful implementation and （b） allows us to link the value of late time cosmological constant to the e-folding factor during inflation.

关键词： cosmology: theory -- cosmology: cosmological parameters -- emergentgravity -- holographic principle

Evaluation of influence of cold atmospheric pressure argon plasma operating parameters on degradation of aqueous solution of Reactive Blue 198(RB-198)

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Plasma Science and Technology 2020年第5期22卷 114-125页

作者： k NAVANEETHA PANDIYARAJ D VASU P V A padmanabhan M PICHUMANI R R DESHMUkH V kANDAVELU Research Division of Plasma Processing(RDPP) Department of PhysicsSri Shakthi Institute of Engineering and TechnologyChinniyam Palayam(post)Coimbatore-641062India Department of Nanoscience and Technology Sri Ramakrishna Engineering CollegeCoimbatore-641022India Department of Physics Institute of Chemical TechnologyMatungaMumbai 400019India Department of Chemistry Sri Shakthi Institute of Engineering and TechnologyL&T bypassChinniyam Palayam(post)Coimbatore-641062India

The intention of this work is to remove Reactive Blue 198(RB-198)dye components from simulated water solution using cold atmospheric pressure argon plasma *** solutions of RB-198 dye were treated as a function of various operating parameters such as applied potential,reaction time and distance between the plasma jet and surface of the *** efficiency of the degradation of RB-198 molecules was explored by means of UV-Vis *** reactive species involved during the treatment process were examined by optical emission spectra(OES).The present hydroxyl radicals(OH·radical)and hydrogen peroxide(H2O2)in the plasma-treated aqueous dye solutions were investigated using various spectroscopic *** other parameters such as total organic carbon(TOC),conductivity and p H were also *** toxicity of plasma-treated RB-198 solution was finally studied by diffusion bacterial analysis and by tracking seed germination *** results show that a higher degradation percentage of99.27%was acquired for the RB-198 treated at higher reaction time and applied potential,and shorter distance between the plasma jet and water *** may be due to the formation of various reactive oxygen(OH·radical,atomic oxygen(O)and H2O2)and nitrogen species(nitric oxide(NO)radicals and N2 second positive system(N2 SPS))during the processes as confirmed by OES analysis and other spectroscopy ***(17.7%-81.8%)and pH(7.5-3.4)values of the plasma-treated RB-198 decreased significantly with respect to various operation parameters,which indicates the decomposition of RB-198 molecules in the aqueous ***,the conductivity of plasma-treated RB-198 aqueous solutions was found to have increased linearly during the plasma treatment due to the formation of various ionic species in aqueous *** toxicity analysis clearly exhibits the non-toxic behavior of plasma-treated RB-198 aqueous solution towards the bacterial growth and germination of see

关键词： RB-198 degradation non-toxicity cold atmospheric pressure plasma jet

Effect of process parameters on springback behaviour during air bending of electrogalvanised steel sheet

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Journal of Zhejiang University-Science A(Applied Physics & Engineering) 2011年第3期12卷 183-189页

作者： Durairaj VASUDEVAN Rajumani SRINIVASAN Palani padmanabhan Department of Mechanical Engineering PSNA College of Engineering and Technology Department of Mechanical Engineering RVS College of Engineering and Technology Bharath Niketan Engineering College

This work aims to study the springback behaviour of electrogalvanised (EG) steel sheets during the air bending *** have been conducted to analyse the influence of various parameters such as coating thickness,orientation of the sheet,punch radius,die radius,die opening,punch velocity,and punch travel on springback *** is established that the springback increases with increasing coating thickness,punch radius,punch travel,die radius,die opening,and punch *** 90° orientation exhibits higher springback than 0° orientation.

关键词： Springback Electrogalvanised (EG) steel Air bending

Study of pressure surge during priming phase of start transient in an initially unprimed pump-fed liquid rocket engine

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Propulsion and Power Research 2022年第3期11卷 353-375页

作者： Debanjan Das P.padmanabhan Systems Reliability Group ISRO Propulsion ComplexIndian Space Research OrganisationTirunelveli(Mahendragiri)Tamil Nadu627133India

In this paper, transient phenomenon during start up process of a pump fed liquidrocket engine is investigated through numerical simulation. The engine studied in this workis designed such that engine systems are not wetted with propellant until the engine is com-manded to start. This is achieved by positioning the valves for propellant admission at the inter-face of test stand/flight stage and the engine. To evaluate engine performance during starttransient for such systems, unsteady flow simulation was conducted using Method of Charac-teristics and equations for priming. The same has been reported in this work. The results indi-cated a brief period of abrupt pressure rise at pump upstream after opening of the propellantadmission valves, during the process of priming of engine systems at valve *** peak pressure obtained was significantly higher than the propellant tank pressure as wellas the steady state pump suction pressure. The transitory pressure rise was found to occurdue to flow resistance at impeller inlet caused by formation of a forced vortex for orientingthe flow through impeller blades during off design transient regime. The maximum pressureat pump upstream, as computed from start transient simulation, was used as a design inputfor pump inlet feed lines. The engine was realized and subsequently qualified in a ground test facility. Hot test data obtained for pressure and flow rate during transient regime were found tobe in good agreement with the simulation results.

关键词： Method of Characteristics Priming analysis Liquid rocket engines Start transient Off design pump losses

Incorporation of silica into the goethite structure: a microscopic and spectroscopic study

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Acta Geochimica 2018年第6期37卷 911-921页

作者： Abdullah Musa Ali Eswaran padmanabhan Hassan Baioumy Department of Geosciences Faculty of Geosciences and Petroleum Engineering Universiti Teknologi PETRONAS(UTP)

Quartz and iron(hydr)oxide are reactive surface phases that are often associated with one another in soils and sediments. Despite the several studies on the coating of quartz with iron oxides, the reactivity of dissolved species(Si) leached from quartz with iron(hydr)oxides has received limited attention. In this study, goethite synthesized on quartz substrates were characterized using field emission scanning electron microscopy, X-ray diffraction(XRD), transmission electron microscopy, and Fouriertransform infrared(FT-IR) spectroscopy. The SEM characterization revealed that bundles of thin parallel aligned goethite rods were formed at p H [ 10, while large pseudohexagonal crystals of twinned goethite needles were synthesized at p H B 10 after dehydration and hydration in the alkaline media. TEM analysis showed expanded and distorted lattice spacing of the crystal structure of iron(hydr)oxide due to silica incorporation. The characterization showed that silica increased the crystallite size of the goethite and transformed its acicular texture to a larger,twinned needle structure. FT-IR and XRD analyses revealed band shifts in crystal bonds as well as new bond formations, which indicate the presence of changes in the chemical environment of Fe–O and Si–O bonds. Thus, the presence of sorbed silicates modifies the crystal and lattice structure of goethite.

关键词： Quartz Goethite Twinned goethite Microscopic characterization(FESEM and TEM) FT-IR spectroscopy

Construction of Ag_(2)CO_(3)/BiOBr/CdS ternary composite photocatalyst with improved visible-light photocatalytic activity on tetracycline molecule degradation

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Journal of Environmental Sciences 2023年第3期125卷 47-60页

作者： kaliyappan Perumal Shajahan Shanavas Tansir Ahamad Annamalai karthigeyan padmanabhan Murugakoothan Material Research and Development Laboratory Postgraduate and Research Department of PhysicsPachaiyappa’s CollegeChennai 600030India Nano and Hybrid Materials Laboratory Department of PhysicsPeriyar UniversitySalem 636001India Department of Chemistry College of ScienceKing Saud UniversityRiyadh 11451Saudi Arabia Department of Physics and Nanotechnology Faculty of Engineering and TechnologySRM Institute of Science and TechnologyKattankulathurKanchipuram 603203India

Photocatalytic degradation was considered as a best strategy for the removal of antibiotic drug pollutants from *** photocatalyst of ABC (Ag_(2)CO_(3)/BiOBr/CdS) composite synthesized by hydrothermal and precipitation *** ABC composite used to investigate the degradation activity of tetracycline (TC) under visible light *** physicochemical characterization methods (*** electron microscopy (SEM),transmission electron microscopy (TEM),high resolution-transmission electron microscopy (HR-TEM),ultraviolet visible spectroscopy (UV),photoluminescence (PL) and time resolved photoluminescence (TRPL) clearly indicate that the composite has been construct successfully that enhances the widened visible light absorption,induces charge transfer and separation efficiency of electron–hole *** photocatalytic activity of all samples was examined through photodegradation of tetracycline in aqueous *** photocatalytic degradation rate of ABC catalyst could eliminate 98.79% of TC in 70 min,which is about 1.5 times that of Ag_(2)CO_(3),1.28 times that of BiOBr and 1.1 times that of BC catalyst,*** role of operation parameters like,TC concentration,catalyst dosage and initial pH on TC degradation activity were *** experiment was demonstrated that·OH and O_(2)·-were played a key role during the photocatalysis process that was evidently proved in electron paramagnetic resonance (EPR) *** addition,the catalyst showed good activity perceived in reusability and stability test due to the synergistic effect between its *** mechanism of degradation of TC in ABC composite was proposed based on the detailed *** current study will give an efficient and recyclable photocatalyst for antibiotic aqueous pollutant removal.

关键词： Ag_(2)CO_(3)/BiOBr/CdS Photocatalyst Tetracycline Degradation Stability