Influence of different bell-shaped stenoses on the progression of the disease, atherosclerosis

D. K. Mandal,N. K. Manna,S. Chakrabarti 대한기계학회 2011 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.25 No.8

In the present paper, the effect of symmetrical and asymmetrical bell-shaped stenoses on wall pressure drop, streamline contour, and rise in wall shear stress for the progression of the disease, atherosclerosis has been investigated numerically. The governing equations have been solved by finite volume method. Both steady and pulsatile flow at inlet is considered in our study. It is revealed from the study that the impact of wall pressure and peak wall shear stress on progression of disease are always high for asymmetrical shaped stenosis for both steady and pulsatile flow. The impact of asymmetrical shape on plaque deposition zone is less, if the aggravation changes the shape of stenosis due to change in stricture length only keeping percentage of restriction same. Whereas, the impact of asymmetrical shape on plaque deposition zone will be high, if shape of stenosis changes by increasing both stricture length and percentage of restriction for both steady and pulsatile flow. Impact of pulsatile nature of flow on the aggravation of disease is higher at some timesteps in comparison to steady flow.

NUMERICAL SIMULATIONS OF ADVECTIVE ACCRETION DISKS AROUND BLACK HOLES

CHAKRABARTI SANDIP K.,Ryu D.,MOLTENI D.,SPONHOLZ H.,LANZAFAME G.,EGGUM G. The Korean Astronomical Society 1996 Journal of The Korean Astronomical Society Vol.29 No.suppl1

Molecular chaperones maximize the native state yield on biological times by driving substrates out of equilibrium

Chakrabarti, Shaon,Hyeon, Changbong,Ye, Xiang,Lorimer, George H.,Thirumalai, D. National Academy of Sciences 2017 PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF Vol.114 No.51

<P><B>Significance</B></P><P>Molecular chaperones have evolved to assist the folding of proteins and RNA, thus avoiding the deleterious consequences of misfolding. Thus, it is expected that increasing chaperone concentrations should enhance the yield of native states. While this has been observed in GroEL-mediated protein folding, experiments on <I>Tetrahymena</I> ribozyme folding assisted by CYT-19 surprisingly show the opposite trend. Here, we reconcile these divergent experimental observations by developing a unified theory of chaperone-assisted protein and RNA folding. We show that these ATP-fueled machines drive their substrates out of equilibrium, maximizing the nonequilibrium native yield in a given time rather than the absolute yield or folding rate. The theory predicts that in vivo the number of chaperones is regulated to optimize their functions.</P><P>Molecular chaperones facilitate the folding of proteins and RNA in vivo. Under physiological conditions, the in vitro folding of <I>Tetrahymena</I> ribozyme by the RNA chaperone CYT-19 behaves paradoxically; increasing the chaperone concentration reduces the yield of native ribozymes. In contrast, the protein chaperone GroEL works as expected; the yield of the native substrate increases with chaperone concentration. The discrepant chaperone-assisted ribozyme folding thus contradicts the expectation that it operates as an efficient annealing machine. To resolve this paradox, we propose a minimal stochastic model based on the Iterative Annealing Mechanism (IAM) that offers a unified description of chaperone-mediated folding of both proteins and RNA. Our theory provides a general relation that quantitatively predicts how the yield of native states depends on chaperone concentration. Although the absolute yield of native states decreases in the <I>Tetrahymena</I> ribozyme, the product of the folding rate and the steady-state native yield increases in both cases. By using energy from ATP hydrolysis, both CYT-19 and GroEL drive their substrate concentrations far out of equilibrium, thus maximizing the native yield in a short time. This also holds when the substrate concentration exceeds that of GroEL. Our findings satisfy the expectation that proteins and RNA be folded by chaperones on biologically relevant time scales, even if the final yield is lower than what equilibrium thermodynamics would dictate. The theory predicts that the quantity of chaperones in vivo has evolved to optimize native state production of the folded states of RNA and proteins in a given time.</P>

Metal Surface Treatment Effects on Screen Printed Silicon Solar Cells

Chakrabarty K.,Mangalaraj D.,Kim K. H.,Dhungel S. K.,Park J. H.,Singh S. N. The Korean Institute of Electrical and Electronic 2003 Transactions on Electrical and Electronic Material Vol.4 No.4

High series resistance due to the presence of glass frit is one of the major problems for screen printed silicon solar cells. Cells having electrical parameters below the prescribed values are usually rejected during solar module fabrication. Therefore, it is highly desirable to improve the electrical parameters of the silicon solar cells and thereby to increase the overall production yield. It was observed that, the performance of low quality mono-crystalline silicon solar cells made by standard screen printing technology could be improved remarkably by novel surface treatment. We have chemically treated the surface using sodium hydroxide (NaOH) and silver nitrate ($AgNO_3$) solutions. NaOH treatment helps to reduce the series resistance by decreasing the presence of excess glass frit on the top silver grid contact. The $AgNO_3$ treatment is used to reduce the series resistance comes from the deposition of silver on the grids by filling the holes present (if any) within the grid pattern.

Positron annihilation spectroscopy of polyacrylonitrile-based carbon fibers embedded with multi-wall carbon nanotubes

Chakrabarti, K.,Nambissan, P.M.G.,Mukherjee, C.D.,Bardhan, K.K.,Kim, C.,Yang, K.S. Elsevier 2006 Carbon Vol.44 No.5

<P><B>Abstract</B></P><P>Polyacrylonitrile (PAN)-based carbon fibers, embedded with multi-wall carbon nanotubes (MWCNT) in different concentrations, have been prepared by an electrospinning technique and investigated using scanning electron microscopy, Raman, and positron annihilation spectroscopy. An analysis of the positron lifetime and Doppler broadened spectral line shape has been made. Positron lifetime spectra for all the samples give best fit for three distinct lifetime components. Raman data has been used to estimate the sp<SUP>2</SUP> mole fraction in the fiber. It is found that the gradual changes incorporated in the fiber due to the addition of MWCNTs are reflected as well defined changes in the positron lifetime and the <I>S</I> parameter of the Doppler broadened spectral line. Annihilation parameters are discussed from the point of view of formation of distinct positron trapping sites in the form of vacancy type defects at the interfaces of MWCNTs and the PAN matrix, and their variations in concentration due to different amount of MWCNTs added.</P>

Application of RAPD markers for characterization of ${\gamma}$-ray-induced rose mutants and assessment of genetic diversity

Chakrabarty, D.,Datta, S.K. The Korean Society of Plant Biotechnology 2010 Plant biotechnology reports Vol.4 No.3

Six parent and their 12 gamma ray-induced somatic flower colour mutants of garden rose were characterized to discriminate the mutants from their respective parents and understanding the genetic diversity using Random amplification of polymorphic DNA (RAPD) markers. Out of 20 primers screened, 14 primers yielded completely identical fragments patterns. The other 7 primers gave highly polymorphic banding patterns among the radiomutants. All the cultivars were identified by using only 7 primers. Moreover, individual mutants were also distinguished by unique RAPD marker bands. Based on the presence or absence of the 48 polymorphic bands, the genetic variations within and among the 18 cultivars were measured. Genetic distance between all 18 cultivars varied from 0.40 to 0.91, as revealed by Jaccard's coefficient matrix. A dendrogram was constructed based on the similarity matrix using the Neighbor Joining Tree method showed three main clusters. The present RAPD analysis can be used not only for estimating genetic diversity present in gamma ray-induced mutants but also for correct identification of mutant/new varieties for their legal protection under plant variety rights.

Metal Surface Treatment Effects on Screen Printed Silicon Solar Cells

K.Chakrabarty,D.Mangalaraj,김경해,S.K.Dhungel,J.H.Park,이준신,S.N.Singh 한국전기전자재료학회 2003 Transactions on Electrical and Electronic Material Vol.4 No.4

High series resistance due to the presence of glass frit is one of the major problems for screen printed silicon solar cells. Cells having electrical parameters below the prescribed values are usually rejected during solar module fabrication. Therefore, it is highly desirable to improve the electrical parameters of the silicon solar cells and thereby to increase the overall production yield. It was observed that, the performance of low quality mono-crystalline silicon solar cells made by standard screen printing technology could be improved remarkably by novel surface treatment. We have chemically treated the surface using sodium hydroxide (NaOH) and silver nitrate (AgNO3) solutions. NaOH treatment helps to reduce the series resistance by decreasing the presence of excess glass frit on the top silver grid contact. The AgNO3 treatment is used to reduce the series resistance comes from the deposition of silver on the grids by filling the holes present (if any) within the grid pattern.

A proposed organic Schottky barrier photodetector for application in the visible region

A.D.D. Dwivedi,Arun Kumar Singh,Rajiv Prakash,P. Chakrabarti 한국물리학회 2010 Current Applied Physics Vol.10 No.3

The fabrication and characterization of an organic photodetector (OPD) in the form of ITO coated glass/polycarbazole (PCz)/Al Schottky contact is reported. The device has been fabricated in our laboratory for the first time using the polymer synthesized by us. The device has been subsequently characterized in respect of electrical and optical properties in order to explore its potential for possible use as a detector in the visible region at 650 nm. It is observed that the detector exhibits a reasonably high value of peak detectivity (~6 × 106 cm Hz1/2W-1) near zero bias voltage at V = 0.2 V.

New Instabilities in Accretion Flows onto Black Holes

MOLTENI D.,FAUCI F.,GERARDI G.,BISIKALO D.,KUZNETSOV O.,ACHARYA K.,CHAKRABARTI S. The Korean Astronomical Society 2001 Journal of The Korean Astronomical Society Vol.34 No.4

The accretion disks are usually supposed symmetric to reflection on the Z=0 plane. Asymmetries in the flow are be ver-y small in the vicinity of the compact accretor. However their existence can have a important role in the case of subkeplerian accretion flows onto black holes. These flows lead to strong heating and even to the formation of shocks close to the centrifugal barrier. Large asymmetries are due to the development of the KH instability triggered by the small turbulences at the layer separating the incoming flow from the out coming shocked flow. The consequence of this phenomenon is the production of asymmetric outflows of matter and quasi periodic oscillations of the inner disk regions up and down the Z=0 plane.

Improvement of Commercial Silicon Solar Cells with N⁺-P-N⁺ Structure using Halogenic Oxide Passivation

K. Chakrabarty,D. Mangalaraj,Kim, Kyung-Hae,Park, J.H.,J. Yi The Korean Institute of Electrical and Electronic 2003 Transactions on Electrical and Electronic Material Vol.4 No.6

This paper describes the effect of halogenic gettering during oxide passivation of commercial solar cell with the $N^{+}$-P-$N^{+}$ structure. In order to study the effect of halogenic gettering on $N^{+}$-P-$N^{+}$ structure mono-crystalline silicon solar cell, we performed conventional POCl$_3$ diffusion for emitter formation and oxide passivation in the presence of HCl vapors. The $N^{+}$-P-$N^{+}$ structure based silicon solar cells were found to have higher short circuit current and minority carrier lifetime. Their performance was also found to be superior than the conventional $N^{+}$-P-$N^{+}$ structure based mono-crystalline silicon solar cell. The cell parameters of the $n^{+}$-p-$p^{+}$ and $n^{+}$-p-$n^{+}$ structure based cells, passivated by HCl assisted oxidation were measured. The improvement in $I_{sc}$ was attributed to the effect of the increased diffusion length of minority carriers, which came from the halogenic gettering effect during the growth of passivating oxide. The presence of chlorine caused gettering of the cells by removing the heavy metals, if any. The other advantage of the presence of chlorine was the removal of the diffusion induced (in oxygen environment) stacking faults and line defects from the surfaces of the silicon wafers. All these effects caused the improvement of the minority carrier lifetime, which in-turn helped to improve the quality of the solar cells.