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- 저자 : Chakravarti (검색결과 45 건)
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( A. Chakravarty ),( S. N. Chakravarty ) 한국고무학회 2007 고무기술 Vol.8 No.2
Shungit are natural composite materials having unusual structure, consist of uniformly distributed highly dispersed crystalline silicate particles in amorphous carbon matrix. It`s main component is fullerene like Shungit carbon (upto 80%). Studies with Shungit, a non petro based performance carbon filler, in additional quantity to Carbon black in typical automotive tyre carcass, bead & apex and tread compounds as well as replacement of silica filler have been carried out and reported here. Rheological / Rheometric studies, Physico-mechanical properties determination, Dynamic Mechanical analysis & Rubber Process Analyzer studies were carried out with different compounds. Compound mixing was carried out in Brabender Plasticoder. Technological properties of rubber compound with Shungit were considerably improved with respect to Mooney viscosity and time of premature vulcanization start (Scorch Safety). DMA analysis shows lower tan delta value with Shungit containing compound. RPA studies also indicate lower heat development and tan delta. Results indicate that Shungit can replace, fully or partly, Silica in tyre tread compounds containing Carbon black.
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Chakravarti, Ranabir The Asian Association of World Historians 2015 The Asian review of world histories Vol.3 No.1
The paper examines, in the light of current historiography, the recent trends in the application and applicability of the World Historical studies on the Indian Ocean scenario. Calling for the combination of the breadth of the World Historical studies with the analysis of a historical scenario in its specific spatio-temporal context-instead of a synchronic approach-the present study takes a close look at commerce and politics in the western Indian Ocean in the light of an early 14th century Latin Crusade tract, How to Defeat the Saracens by William of Adam (Guillelmus Ade, Tractatus quomodo Sarraceni sunt expugnandi), a Dominican friar. The text offers remarkable insights into the interlocking of the Indian Ocean and the South Asian subcontinent with the Mamluk Sultanate, the Ilkhanid realm and the Crusades. The paper argues for what is now termed as braided and connected histories.
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Chakravarty S.,Sen S. The Korean Society of Rheology 2006 Korea-Australia rheology journal Vol.18 No.2
Of concern in the present theoretical investigation is the study of blood flow and convection-dominated diffusion processes in a model bifurcated artery under stenotic conditions. The geometry of the bifurcated arterial segment having constrictions in both the parent and its daughter arterial lumen frequently appearing in the diseased arteries causing malfunction of the cardiovascular system, is constructed mathematically with the introduction of suitable curvatures at the lateral junction and the flow divider. The streaming blood contained in the bifurcated artery is treated to be Newtonian. The flow dynamical analysis applies the two-dimensional unsteady incompressible nonlinear Wavier-Stokes equations for Newtonian fluid while the mass transport phenomenon is governed by the convection diffusion equation. The motion of the arterial wall and its effect on local fluid mechanics is, however, not ruled out from the present model. The main objective of this study is to demonstrate the effects of constricted flow characteristics and the wall motion on the wall shear stress, the concentration profile and on the mass transfer. The ultimate numerical solutions of the coupled flow and diffusion processes following a radial coordinate transformation are based on an appropriate finite difference technique which attain appreciable stability in both the flow phenomena and the convection-dominated diffusion processes.
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Dynamic response of heat and mass transfer in blood flow through stenosed bifurcated arteries
S. Chakravarty,S. Sen 한국유변학회 2005 Korea-Australia rheology journal Vol.17 No.2
The present study deals with a mathematical model describing the dynamic response of heat and mass transfer in blood flow through bifurcated arteries under stenotic condition. The geometry of the bifurcated arterial segment possessing constrictions in both the parent and the daughter arterial lumen frequently appearing in the diseased arteries causing malfunction of the cardiovascular system, is formulated mathematically with the introduction of the suitable curvatures at the lateral junction and the flow divider. The blood flowing through the artery is treated to be Newtonian. The nonlinear unsteady flow phenomena is governed by the Navier-Stokes equations while those of heat and mass transfer are controlled by the heat conduction and the convection-diffusion equations respectively. All these equations together with the appropriate boundary conditions describing the present biomechanical problem following the radial coordinate transformation are solved numerically by adopting finite difference technique. The respective profiles of the flow field, the temperature and the concentration and their distributions as well are obtained. The influences of the stenosis, the arterial wall motion and the unsteady behaviour of the system in terms of the heat and mass transfer on the blood stream in the entire arterial segment are highlighted through several plots presented at the end of the paper in order to illustrate the applicability of the present model under study.
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U. Chakravarty,P. A. Naik,S. R. Kumbhare,P. D. Gupta 한국광학회 2009 Current Optics and Photonics Vol.13 No.1
An experimental study of energy absorption and x-ray emission from ultrashort laser pulse irradiation of in-situ produced solid clusters has been performed. Silver clusters produced by a 30 mJ, 300 ps laser pulse were irradiated up to an intensity of 3×1017 W/cm2 by a 70 mJ, 45 fs compressed laser pulse from the same Ti:sapphire laser. Absorption of the laser light exceeding 70% was observed, resulting in an x-ray yield (>1 keV) of ~60 μJ/ pulse. This may constitute a much simpler means of intense x-ray generation using ultrashort laser pulses as compared to the irradiation of structured / pre-deposited cluster targets, and it offers higher x-ray conversion efficiency than that from gas clusters and planar solid targets.
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S. Chakravarty,S. Sen 한국유변학회 2006 Korea-Australia rheology journal Vol.18 No.2
Of concern in the present theoretical investigation is the study of blood flow and convection-dominated diffusion processes in a model bifurcated artery under stenotic conditions. The geometry of the bifurcated arterial segment having constrictions in both the parent and its daughter arterial lumen frequently appearing in the diseased arteries causing malfunction of the cardiovascular system, is constructed mathematically with the introduction of suitable curvatures at the lateral junction and the flow divider. The streaming blood contained in the bifurcated artery is treated to be Newtonian. The flow dynamical analysis applies the two-dimensional unsteady incompressible nonlinear Navier-Stokes equations for Newtonian fluid while the mass transport phenomenon is governed by the convection diffusion equation. The motion of the arterial wall and its effect on local fluid mechanics is, however, not ruled out from the present model. The main objective of this study is to demonstrate the effects of constricted flow characteristics and the wall motion on the wall shear stress, the concentration profile and on the mass transfer. The ultimate numerical solutions of the coupled flow and diffusion processes following a radial coordinate transformation are based on an appropriate finite difference technique which attain appreciable stability in both the flow phenomena and the convection-dominated diffusion processes.
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Propulsion System Modeling and Control of a Warhead with Multi-thruster Configuration
Rajtilok Chakravarty,Nachiket Wadwankar,N. Ananthkrishnan,V.S. Renganathan,Hyun Ko,Ji-Hyung Lee 한국추진공학회 2013 한국추진공학회 학술대회논문집 Vol.2013 No.12
A novel internal pressure controller is developed for a Kinetic Energy Interceptor (KEI) equipped with a multi-thruster configuration. To that end, first the propulsion system model for solid fuel with a tubular grain burning configuration is detailed. Subsequently the internal pressure control logic design and implementation is laid out and a closed loop simulation is successfully demonstrated where varying chamber pressure is demanded and met by the controller by varying the thruster throat areas appropriately.
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Nath Deena,Chakravarty Sujay,Deshpade U.P.,Arasu A.V. Thanikai,Baskaran R.,Shekar N.V. Chandra 한국물리학회 2022 Current Applied Physics Vol.34 No.-
In this work for the first time, we are reporting the unusual observation of the Kondo effect with the coexistence of room temperature ferromagnetism in AlN/Al/AlN trilayer thin film. The grown film shows resistivity minimum at a temperature of ~48K, which shifts to the lower temperature on the application of magnetic fields. After considering various possibilities for an upturn in resistivity, we found that the Kondo scattering is responsible for upturn at low temperature. The simultaneous presence of ferromagnetism and Kondo scattering is explained by spatial variation of nitrogen vacancy defects from the film surface to the Al sandwich layer. Furthermore, magneto-transport properties of the film measured at different temperature exhibits both negative and positive components described by localized magnetic moment model for the spin scattering of carriers and two-band model, respectively. This work provides insight into the novel co-existence of ferromagnetism and Kondo effect in crystalline AlN.
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Physiological flow of shear-thinning viscoelastic fluid past an irregular arterial constriction
Sarifuddin,Santabrata Chakravarty,Prashanta Kumar Mandal 한국유변학회 2013 Korea-Australia rheology journal Vol.25 No.3
The present investigation deals with the effect of the shape of a stenosis on the flow characteristics of blood, having shear-thinning viscoelastic rheological properties by using a suitable mathematical model. Keeping the relevance of the physiological situation, the mathematical model is developed by treating blood as a non-Newtonian shear-thinning viscoelastic fluid characterised by unsteady Oldroyd-3-constant model through an axisymmetric irregular arterial stenosis obtained from casting of a mildly stenosed artery (cf. Back et al., 1984). Comparison with the well-known cosine-shaped stenosis, in order to estimate the effect of surface roughness on the flow characteristics of blood, has however not been ruled out from the present study. Numerical illustrations are presented for a physiological flow, as well as for an equivalent simple pulsatile flow with equal stroke volume to that of the physiological flow, and the differences in their flow behaviour are recorded and discussed. The Marker and Cell method is developed in cylindrical co-ordinate system in order to tackle the highly nonlinear governing equations of motion. The effects of the quantities of significance such as Reynolds number, Deborah number, blood viscoelasticity and flow pulsatility, as well on the velocity components, pressure drop, wall shear stress and patterns of streamlines are quantitatively investigated graphically. Comparison of the results reveals that although the behaviour of two different pulses are similar at the same instant of time, there exist some important deviations in the flow pattern, pressure drop and wall shear stress as well. The present results also predict that the excess pressure drop across the cosine stenosis compared with the irregular one is consistent with several existing results in the literature which substantiate sufficiently to validate the applicability of the model under consideration.
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