Research & Development in AYUSH Systems of Medicine in India

Sankaran Madhavan 한국한의학연구원 2006 한국한의학연구원 연구보고서 Vol.- No.-

Chemical composition and larvicidal activity of leaf essential oil from Clausena dentata (Willd) M. Roam. (Rutaceae) against the chikungunya vector, Aedes aegypti Linn. (Diptera: Culicidae)

Sankaran Rajkumar,Arulsamy Jebanesan 한국응용곤충학회 2010 Journal of Asia-Pacific Entomology Vol.13 No.2

Larvicidal activity of essential oil and isolated compounds from Clausena dentata leaves were tested against early fourth instar Aedes aegypti larvae. GC–MS analysis of essential oil revealed the presence of fourteen compounds of which the major compounds were sabinene (21.27%), biofloratriene (19.61%), borneol (18.34%) and β-bisabolol (17.68%). The essential oil of C. dentata exhibited significant larvicidal activity, with 24 h LC50 and LC90 values of 140.2 and 341.6 mg/l, respectively. Larvicidal activities of the four major compounds of essential oil were also tested. The LC50 values of sabinene, biofloratriene, borneol and β-bisabolol were 27.3, 47.4, 43.5 and 33.2 mg/l, respectively. Results of this study show that the leaf essential oil of C. dentata and its four major compounds may be a potent source of natural larvicides.

Self-organized multi-layered graphene-boron-doped diamond hybrid nanowalls for high-performance electron emission devices

Sankaran, Kamatchi Jothiramalingam,Ficek, Mateusz,Kunuku, Srinivasu,Panda, Kalpataru,Yeh, Chien-Jui,Park, Jeong Young,Sawczak, Miroslaw,Michałowski, Paweł Piotr,Leou, Keh-Chyang,Bogdanowicz, Robert,Li The Royal Society of Chemistry 2018 Nanoscale Vol.10 No.3

<P>Carbon nanomaterials such as nanotubes, nanoflakes/nanowalls, and graphene have been used as electron sources due to their superior field electron emission (FEE) characteristics. However, these materials show poor stability and short lifetimes, which prevent their use in practical device applications. The aim of this study was to find an innovative nanomaterial possessing both high robustness and reliable FEE behavior. Herein, a hybrid structure of self-organized multi-layered graphene (MLG)-boron doped diamond (BDD) nanowall materials with superior FEE characteristics was successfully synthesized using a microwave plasma enhanced chemical vapor deposition process. Transmission electron microscopy reveals that the as-prepared carbon clusters have a uniform, dense, and sharp nanowall morphology with sp<SUP>3</SUP> diamond cores encased by an sp<SUP>2</SUP> MLG shell. Detailed nanoscale investigations conducted using peak force-controlled tunneling atomic force microscopy show that each of the core-shell structured carbon cluster fields emits electrons equally well. The MLG-BDD nanowall materials show a low turn-on field of 2.4 V μm<SUP>−1</SUP>, a high emission current density of 4.2 mA cm<SUP>−2</SUP> at an applied field of 4.0 V μm<SUP>−1</SUP>, a large field enhancement factor of 4500, and prominently high lifetime stability (lasting for 700 min), which demonstrate the superiority of these materials over other hybrid nanostructured materials. The potential of these MLG-BDD hybrid nanowall materials in practical device applications was further illustrated by the plasma illumination behavior of a microplasma device with these materials as the cathode, where a low threshold voltage of 330 V (low threshold field of 330 V mm<SUP>−1</SUP>) and long plasma stability of 358 min were demonstrated. The fabrication of these hybrid nanowalls is straight forward and thereby opens up a pathway for the advancement of next-generation cathode materials for high brightness electron emission and microplasma-based display devices.</P>

Response of flame thickness and propagation speed under intense turbulence in spatially developing lean premixed methane–air jet flames

Sankaran, Ramanan,Hawkes, Evatt R.,Yoo, Chun Sang,Chen, Jacqueline H. Elsevier 2015 Combustion and Flame Vol.162 No.9

<P><B>Abstract</B></P> <P>Direct numerical simulations of three-dimensional spatially-developing turbulent Bunsen flames were performed at three different turbulence intensities. The simulations were performed using a reduced methane–air chemical mechanism which was specifically tailored for the lean premixed conditions simulated here. A planar-jet turbulent Bunsen flame configuration was used in which turbulent preheated methane–air mixture at 0.7 equivalence ratio issued through a central jet and was surrounded by a hot laminar coflow of burned products. The turbulence characteristics at the jet inflow were selected such that combustion occured in the thin reaction zones (TRZ) regime. At the lowest turbulence intensity, the conditions fall on the boundary between the TRZ regime and the corrugated flamelet regime, and progressively moved further into the TRZ regime by increasing the turbulent intensity. The data from the three simulations was analyzed to understand the effect of turbulent stirring on the flame structure and thickness. Statistical analysis of the data showed that the thermal preheat layer of the flame was thickened due to the action of turbulence, but the reaction zone was not significantly affected. A global and local analysis of the burning velocity of the flame was performed to compare the different flames. Detailed statistical averages of the flame speed were also obtained to study the spatial dependence of displacement speed and its correlation to strain rate and curvature.</P>

Efficient Noise Reduction Method Using Iterative Median Filter for Digital Images

Sakthidasan Sankaran,Velmurugan Nagarajan 대한전자공학회 2015 ITC-CSCC :International Technical Conference on Ci Vol.2015 No.6

Random valued desire noise reduction is one of the most important processes to enhance the quality of digital images. In this paper, we propose an efficient restoration method for the deduction of random-valued impulse noise. On the way to achieve the goal of better rebuilding, we employ a decision-treebased impulse noise detector to identify the corrupted pixels, and an edge-preserving sort out to rebuild the concentration values of corrupted pixels. To improve the quality of the digital images, a median based adaptive concept is used in reduction of random valued impulse noise. The results show that the proposed technique can achieve enhanced performances in terms of both quantitative estimate and image eminence than the prior methods. Furthermore, the performance can be enhanced by iterative median filter methods. For performance analysis the PSNR (dB) value resultant to original and reconstructed image is compared and edge preservation will be proved with edge detection methods.

Effect of air chambers on the compression wave propagating along a high-speed railway tunnel

Rohit Sankaran Iyer,DONG HYEON KIM,김희동 대한기계학회 2023 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.37 No.2

An array of air chambers embedded on the tunnel track is numerically investigated for different configurations. The air chambers act as an in-tunnel countermeasure to alleviate non-linear steepening of compression waves during propagation process thereby mitigating emission of high amplitude micro-pressure waves (MPWs) from the exit portal. The air chambers are designed to entrap the incoming flow and induce damping behavior so as to reduce wave steepening in tunnels. Initially, qualititative comparisons are made between Helmholtz resonator and damping type air chambers. Thereafter, the quantitative assessment of the compression wave properties are checked in detail. From results, over damped air chamber shows 60 % reduction in peak over pressure for weak compression wave whereas the Helmholtz resonator and critically damped shows 35 % and 22 %, respectively. Similarly, due to the presence of over damped air chamber, 17 % reduction in maximum pressure gradient is noticed while critically damped shows close to 10 % reduction.

Prediction of entry compression waves induced by a high-speed train entering tunnel

Rohit Sankaran Iyer,김동현,김희동 대한기계학회 2018 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.32 No.11

Tunnel wave produced by an entering high-speed train has always been one of the most prominent problems in the field of aeroacoustics. These waves are formed at the entrance of the tunnel and propagate ahead of the train at the local speed of sound. The formation process of the first of the successive compression wave at the entrance decides the nature and intensity of the subsequent waves. Thus, to visualize and understand the formation process; a numerical study has been conducted using commercial computational fluid dynamics (CFD) solver FLUENT 17.1. The dynamic mesh update techniques have been implemented to update the stationary domains as the train moves inside it. Pressure inside the tunnel is measured at distinct points to study the changes in the intensity of the compression wave. The flow physics has been comprehended using pressure plots and contours.

Overreaction around DJIA Milestone Events : Evidence from an Intraday Analysis

Harikumar Sankaran,Jayashree Harikumar,Violeta Diaz People&Global Business Association 2014 Global Business and Finance Review Vol.19 No.2

We extend prior research by examining investor trading in individual stocks around a market level psychological anchor. We use intraday trade and quote data to examine trading in Dow component stocks around the time DJIA first crossed a millenary milestone. Prior evidence uses monthly returns and documents momentum trading around Dow 52-week high and historical highs. In spite of nine out of eleven millenary milestones in our sample that are simultaneously a Dow 52-week high and a historical high, we find that the pattern of order imbalance, spreads, and returns around milestone crossing indicates an overreaction and not momentum trading.

Missile Defenses and Strategic Stability in Asia: Evidence from Simulations

Jaganath Sankaran 동아시아연구원 2020 Journal of East Asian Studies Vol.20 No.3

The contention over the quantity and quality of regional missile defenses forward-deployed by the United States in the Asia-Pacific region animates much of the US–China disagreement about strategic stability. The Chinese argue that the deployed assets exceed reasonable defensive requirements and suggest that if these missile-defense deployments continue, they will be forced to increase the size of their nuclear arsenal. In disagreement, the United States claims that regional missile defenses are defensive by design, limited in scope, and necessary to defeat a North Korean missile campaign. In this article, a series of simulation experiments were developed to empirically test these opposing arguments over missile defenses and strategic stability. The simulations indicate that current deployments are necessary for defense and proportional to the threat. The analysis also argues that current deployments do not possess the ability to alter the US–China strategic nuclear balance significantly. The article concludes with a discussion of other subjective aspects of national security that may explain Chinese concerns and explore possible ways to reassure China.

Study on the Compression Waves Propagating along a Railway Tunnel with Multiple Branch Shafts

Rohit Sankaran Iyer,김동현,김태호,김희동 대한기계학회 2023 대한기계학회 춘추학술대회 Vol.2023 No.5