Nagaon, India
Nagaon, India

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An overview of predominant theoretical models used for predicting the thermal conductivities of dielectric materials is given. The criteria used for different theoretical models are explained. This overview highlights a unified theory based on temperature-dependent thermal-conductivity theories, and a drifting of the equilibrium phonon distribution function due to normal three-phonon scattering processes causes transfer of phonon momentum to (a) the same phonon modes (KK-S model) and (b) across the phonon modes (KK-H model). Estimates of the lattice thermal conductivities of LiF and Mg2Sn for the KK-H model are presented graphically. © 2017, The Korean Physical Society.

Bhuyan P.J.,Nowgong College
Fusion Engineering and Design | Year: 2010

A two dimensional solver is developed for MHD flows with low magnetic Reynolds' number based on the electrostatic potential formulation for the Lorentz forces and current densities which will be used to calculate the MHD pressure drop inside the channels of liquid breeder based Test Blanket Modules (TBMs). The flow geometry is assumed to be rectangular and perpendicular to the flow direction, with flow and electrostatic potential variations along the flow direction neglected. A structured, non-uniform, collocated grid is used in the calculation, where the velocity (u), pressure (p) and electrostatic potential (φ{symbol}) are calculated at the cell centers, whereas the current densities are calculated at the cell faces. Special relaxation techniques are employed in calculating the electrostatic potential for ensuring the divergence-free condition for current density. The code is benchmarked over a square channel for various Hartmann numbers up to 25,000 with and without insulation coatings by (i) comparing the pressure drop with the approximate analytical results found in literature and (ii) comparing the pressure drop with the ones obtained in our previous calculations based on the induction formulation for the electromagnetic part. Finally the code is used to determine the MHD pressure drop in case of LLCB TBM. The code gives similar results as obtained by us in our previous calculations based on the induction formulation. However, the convergence is much faster in case of potential based code. © 2009 Elsevier B.V. All rights reserved.

Majumdar H.C.,B Borooah College | Shyam J.,Nowgong College
Plant Archives | Year: 2013

In the present paper, 20 plant species belonging to 17 families used for treatment of Jaundice in Nalbari District of Assam have been documented. The ethnobotanical information regarding vernacular name, family name, mode of preparation are provided. Different plant parts namely leaf, stem, root, bark, fruits and even whole plants are administered either raw or with some medium. The presence of alkaloids in the plant parts used was tested by using Mayer's reagents, Dragendroff's reagent and Wegner's reagent.

Borthakur L.J.,Nowgong College | Das D.,Tezpur University | Dolui S.K.,Tezpur University
Materials Chemistry and Physics | Year: 2010

Encapsulation of inorganic nano particles (as a core) by polymers (as a shell) is one of the interesting research subjects that lead to the synthesis of nano composite. Some of the preparative methods for the synthesis of nano composite are dispersion, suspension, emulsion and mini-emulsion polymerization techniques. Here core-shell nano composite particles of poly (styrene-co-methyl acrylate) and bentonite (modified with octadecyl amine) were prepared by mini-emulsion polymerization. The mini-emulsions were prepared by dispersing bentonite in the monomers mixture (styrene and methyl acrylate) in the presence of sodium dodecyl benzene sulfate (SDBS) and Span-60 as surfactants and hexadecane as costabilizer using ultra sonication. The stability of both mini-emulsion and the obtained latex depends on premixing procedures, time of ultrasonication, and more importantly on the applied surfactants. The encapsulation of the nano clay was confirmed by FTIR and XRD analysis. The morphology of the nano composite particles was determined by SEM and TEM analysis. TGA analysis of the composite particles shows that they exhibit better thermal stability as compared to the pristine polymer. © 2010 Elsevier B.V. All rights reserved.

Borthakur L.J.,Nowgong College | Konwer S.,Tezpur University | Das R.,Tezpur University | Dolui S.K.,Tezpur University
Journal of Polymer Research | Year: 2011

A series of nearly monodispersed poly(styrene- methyl acrylate) (SMA) copolymer latex particles were coated with polypyrrole having different graphite contents. The composite particles were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), Xray diffraction (XRD) and thermogravimetric analysis (TGA). The d.c. conductivity and the electrochemical behaviour of the particles were studied by using a standard four-probe method and a cyclic voltameter respectively. The dependence of electrical conductivity of the composites on the concentration of graphite in the polypyrrole shell, the methyl acrylate content in SMA copolymer and the temperature was also investigated. The electrical conductivity of the samples can be tuned by varying the graphite content in the polypyrrole shell phase. The d.c. conductivity decreases with increasing methyl acrylate content in the core particles. Electrochemical study (at a scan rate of 50 mV s-1) reveals that the particles are sufficiently stable under redox potential and should find potential applications in various optoelectronic devices. © 2010 Springer Science+Business Media B.V.

Balin Kumar B.,Nowgong College | Prodeep P.,Nowgong College
Research Journal of Chemistry and Environment | Year: 2015

In past few decades ZSM-5 zeolites attracted much attention because of their interesting catalytic properties and great resistance to deactivation. The unique channel structure of ZSM-5 plays crucial roles in restraining side reactions and controlling the product distribution. Since the discovery of ZSM-5 by Argauer and Landolt, many researchers have evaluated a number of ZSM-5 catalysts modified with various transition metal ions. We are reporting herewith the catalytic activity of environmentally benign Ti-exchanged ZSM-5 catalyst for selective acetylation of alcohols using acetic anhydride.

Konwer S.,Tezpur University | Barthakur L.J.,Nowgong College | Dolui S.K.,Tezpur University
Journal of Materials Science: Materials in Electronics | Year: 2012

A series of core-shell particles (SMAP/G) having polystyrene-methylacrylate copolymer (styrenemethyl acrylate) as the core and graphite incorporated polyaniline as the shell were prepared by surfactant free mini-emulsion polymerization. Here poly (SMA) copolymer latex particles were first dispersed in water and then coated with polyaniline (PA) by in situ polymerization of aniline in presence of different percentage (0.25, 0.50 and 1.0%) of graphite. The composite particles were characterized by FTIR, XRD and TGA. TEM and SEM analysis confirms the core-shell morphology of the composite particles. DC electrical conductivity values of all the samples were measured by using a standard four-probe method. The effect of temperature and the amount of graphite incorporated into the PA shell on the dc electrical conductivity of the core-shell composites was investigated. The electro chemical behaviour of the core-shell composites was studied by using a cyclic voltammeter. Electro chemical data shows that the core-shell composites are sufficiently stable under redox potential of 50 mV/s to find applications in various electronic devices. © Springer Science+Business Media, LLC 2011.

Borthakur L.J.,Nowgong College | Sharma S.,Tezpur University | Dolui S.K.,Tezpur University
Journal of Materials Science: Materials in Electronics | Year: 2011

The colloidal dispersion of silver nano particles with different concentration (0.5, 1.0 and 1.5%) were synthesized by chemical reduction method using citrate as reducing agent. Colloidal dispersion of Poly (Styrene-co-methylacrylate) (SMA) was synthesized by mini emulsion polymerization technique. The SMA micro particles were used as template for the polymerization of pyrrole in presence of dispersion of silver nano particles by oxidative coupling method. The Ag nano particles and the final core-shell composite particles were characterized by UV-visible, FTIR, SEM, EDX and TEM analysis. The thermal analysis revealed that the SMA-PPy-Ag core-shell particles possesses better thermal stability in comparision with bare PPy-Ag nano composite. The dc conductivity and the electro chemical behaviour of the particles were studied by using a standard four-probe method. The dependence of electrical conductivity of the composites on the concentration of silver in the polypyrrole shell and the methyl acrylate content in SMA copolymer were also investigated The core-shell particles show reversible electrochemical response as revealed by the cyclic voltammetry study. © 2010 Springer Science+Business Media, LLC.

Borthakur L.J.,Nowgong College | Jana T.,Tezpur University | Dolui S.K.,Tezpur University
Journal of Coatings Technology Research | Year: 2010

A series of core-shell polymeric particles with poly(n-butyl acrylate-co-methacrylic acid-co-ethylene glycol dimethylacrylate) as core and poly(styrene-co-methyl methacrylate) as shell were prepared by seeded emulsion polymerization. The role of ethylene glycol dimethylacrylate (EGDMA) is to crosslink the core so as to avoid any probability of gel formation and to bind both the core and the shell phase together. The spherical morphology of the core-shell structure was achieved at 60:40 core to shell ratio. The core-shell morphology was confirmed by SEM and TEM analyses. GPC analysis of the particles reveals that the polymer shows a bimodal mode. The first peak has M w = 382700 and M n = 245200 with polydispersity index of 1.6, and the second peak has M w = 21200 and M n = 14800 with polydispersity index of 1.4. These core-shell latexes were applied as a pigment/binder in emulsion paint and the paint properties like gloss, rock hardness, washability, opacity, etc. were compared with the standard. The results show that these core-shell latexes can provide similar hiding power with 17% reduction of TiO 2 in the paint formulation. © 2010 FSCT and OCCA.

Bhattacharyya N.,Nowgong College | Sarma S.,Gauhati University
Environmental Monitoring and Assessment | Year: 2010

Houttuynia cordata Thunb. is a rhizome-bearing aromatic medicinal herb and is restricted to specialized moist habitats. The plant is collected from natural habitats for local consumption and trade. The status of the species and its variations in physiological performance in different habitats were studied in selected sites of geographically different areas of Brahmaputra valley in eastern India. The surveys were conducted in two different growth stages of the plant during 2005-2007. The sites where the species was encountered were marked and a distribution map was prepared. The frequency and density of the plant was higher in the moist habitats with higher organic carbon (0.85 ± 0.05%). Generally, the density, biomass production and growth had significant (P < 0.05) positive relationship with the soil physicochemical properties (linear curve fit). Soil moisture was the most dependent factor for the plant growth and the optimum growth was recorded at 78 ± 5.6% (r2= 0.9; P0.01). The physiological performance of the plant in all the studied sites were significantly varied (P < 0.05). The growth and development of H. cordata were also different in the flowering and senescence stages. Clay loam soil, average soil pH of 5.9, and 78% soil moisture were the favorable soil characteristics for the better growth of H. cordata and, hence, these data may be considered for conservation of the species. © 2008 Springer Science+Business Media B.V.

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