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RISS 인기검색어
- 검색키워드
- 저자 : Chakravarty S. (검색결과 19 건)
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Comparative Analysis of Different Grain Configurations for a Multi-thruster Kinetic Warhead
N. Ananthkrishnan,Hyun Ko,K. Sreesankar,R. Chakravarty,V.S. Renganathan 한국추진공학회 2016 한국추진공학회 학술대회논문집 Vol.2016 No.5
The S-DACS multi-thruster warhead consists of 4 divert and 6 attitude thrusters fed from a common gas generator. Successful S-DACS intercept requires careful selection of the internal ballistics (grain configuration, chamber pressure, etc.), the sensors (seeker range, guidance law, etc.) as well as the external ballistics and sizing (booster diameter, S-DACS release velocity, flight time, maneuverability, etc.). These requirements and constraints are inter-dependent making the S-DACS mission analysis and sizing a difficult task. This work explores the connections between the choice of S-DACS grain configuration and sizing with the chamber pressure as a key parameter. Various parameters and center of gravity/ moment of inertia variations are compared for three different S-DACS grain configurations. Keywords: DACS, grain configuration, mission analysis
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Effect of oxygen partial pressure and annealing on nanocrystalline p-type ZnO:Sb thin films
K. Samanta,A.K. Arora,S. Hussain,S. Chakravarty,R.S. Katiyar 한국물리학회 2012 Current Applied Physics Vol.12 No.5
We have investigated the effect of oxygen partial pressure and annealing on nanocrystalline p-type Sb-doped ZnO thin films, grown by pulsed laser deposition, with hole concentration of 6.5 ×1018/cm3and mobility of 53 cm2/V-s. Uses of higher working pressure or annealing are found to reduce carrier concentration. A strong correlation is observed between carrier concentration and the violet (3.02 eV)emission related to free Zn-vacancy; stronger the violet emission, smaller the carrier concentration. In contrast to earlier suggestion of using higher oxygen pressure for obtaining p-type conductivity, the present results show a deterioration of the quality of film. We have investigated the effect of oxygen partial pressure and annealing on nanocrystalline p-type Sb-doped ZnO thin films, grown by pulsed laser deposition, with hole concentration of 6.5 ×1018/cm3and mobility of 53 cm2/V-s. Uses of higher working pressure or annealing are found to reduce carrier concentration. A strong correlation is observed between carrier concentration and the violet (3.02 eV)emission related to free Zn-vacancy; stronger the violet emission, smaller the carrier concentration. In contrast to earlier suggestion of using higher oxygen pressure for obtaining p-type conductivity, the present results show a deterioration of the quality of film.
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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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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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Theoretical study on the constricted flow phenomena in arteries
S. Sen,S. Chakravarty 한국유변학회 2012 Korea-Australia rheology journal Vol.24 No.4
The present study is dealt with the constricted flow characteristics of blood in arteries by making use of an appropriate mathematical model. The constricted artery experiences the generated wall shear stress due to flow disturbances in the presence of constriction. The disturbed flow in the stenosed arterial segment causes malfunction of the cardiovascular system leading to serious health problems in the form of heart attack and stroke. The flowing blood contained in the stenosed artery is considered to be non-Newtonian while the flow is treated to be two-dimensional. The present pursuit also accounts for the motion of the arterial wall and its effect on local fluid mechanics. The flow analysis applies the time-dependent, two-dimensional incompressible nonlinear Navier-Stokes equations for non-Newtonian fluid representing blood. An extensive quantitative analysis presented at the end of the paper based on large scale numerical computations of the quantities of major physiological significance enables one to estimate the constricted flow characteristics in the arterial system under consideration which deviates significantly from that of normal physiological flow conditions.
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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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Snake venom neutralising factor from the root extract of Emblica officinalis Linn.
S. Sarkhel,A. K. Chakravarty,R. Das,Aparna Gomes,A. Gomes 경희대학교 융합한의과학연구소 2011 Oriental Pharmacy and Experimental Medicine Vol.11 No.1
The folk use of the Indian medicinal plant Emblica officinalis Linn. root extract and its active compound (Pthalate in nature) against snake venom has been established in experimental animal models. From the root extract of Emblica officinalis, a compound was isolated through silica gel column chromatography and the structure was determined by UV, IR, ^1H-NMR, ^(13)C-NMR & EIMS studies. The structure was determined and the active fraction was a pthalate compound, which could neutralize viper and cobra venom induced lethal, hemorrhagic,defibrinogenating, proinflammatory, PLA2, cardiotoxic and neurotoxic activity in experimental animal models. Viper venom induced myotoxicity was antagonized by the compound as shown by the decreased levels of the myotoxicity marker enzymes CPK & LDH. The proinflammatory action of viper venom neutralized by the active compound, showed the involvement of the proinflammatory markers IL-1, IL-6, TNF-α. The present study confirmed the phytomedicinal value of an antisnake venom compound present in the root of Emblica officinalis.
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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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