Haddud,T A; Al-Mansoori,M H; Zamzuri,A K; Shaharudin,S; Abdullah,M K; Mahdi,M A(Microwave and Optical Technology Letters, April 20, 2005)
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Abstract:
In this paper, the generation of a multiwavelength laser
source from a Brillouin -Erbium fiber laser in the long wavelength band
(L-band) region is experimentally demonstrated. The proposed laser
system utilizes a Fabrv-Perot cavity formed by fiber-loop mirrors.
Twenty-four lines of Brillouin-Stokes with line spacings of 10 GHz are
obtained in the L-band region
ABSTRACT: Linseed oil is used in the dual roles of the plasticizer and the fatty
acid component of the activator in nitrile rubber vulcanizates. The study shows
that the substitution can substantially improve the mechanical properties in
addition to other advantages such as increased cure rate, reduced leachability
and reduced compound cost.
The present work undertakes the preparation and physico-chemical characterisation of iron promoted sulphated zirconia
(SZ) with different amounts of iron loading and their application to Friedel-Crafts benzoylation of benzene, toluene and xylene
under different experimental conditions, XRD and laser Raman techniques reveal the stabilisation of the tetragonal phase of
zirconia and the existence of iron in highly dispersed form as Fe203 on the catalyst surface. The surface acidic properties were
determined by ammonia temperature programmed desorption (TPD) and perylene adsorption, The results were supported by
the TGA studies after adsorption of pyridine and 2,6-dimethylpyridine (2,6-DMP), Strong Lewis acid sites on the surface, which
are evident from TPD and perylene adsorption studies. explain the high catalytic activity of the systems towards benzoylation.
The experimental results provide evidence for the truly heterogeneous nature of the reaction. The studies also establish the
resistance to deactivation in the metal incorporated sulphated systems.
Manju, Kurian; Sugunan, S(Indian Journal of Chemistry, October , 2003)
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Abstract:
Iron, aluminium and mixed iron aluminium pillared clays have been prepared by partial hydrolysis method and doped
with IO% Mo, V and Cr. The samples have been characterised by XRD, FTIR and surface area and pore Volume
measurements. The surface acid site distribution has been determined by temperature programmed desorption of ammonia.
Vanadia incorporated systems show maximum acidity. Benzylation of o-xylene has been done as probe reaction to test
catalytic activity. Benzyl chloride is a superior benzylating agent compared to benzyl alcohol in activity and selectivity.
Cent percent selectivity towards monobenzylated product is obtained in all the cases. Fe pillared systems exhibit maximum
activity. The catalytic activities of the systems can be correlated with the amount of strong add sites. The effects of various
reaction variables on the reaction have been studied. Presence of moisture has a diminishing effect on the reaction rate.
Sugunan, S; Nishamol, K(Indian Journal of Chemistry, May , 2002)
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Abstract:
The liquid-phase Friedel-Crafts acylation of toluene using benzoyl chloride as benzoylating agent has heen carried out over Nix, Mn(l-x)Fe2 O4 (x=O, 0.2, 0.4, 0.6, 0.8 and 1.0) type systems under different reaction conditions. It is observed that the systems with high 'x' values are effective for the conversion of BOC and the selective formation of 4-MBP. Selectivity for 4-MBP over MnFe2O4 is more than 90% under the optimized reaction conditions. Sites of moderate acidity is effective in calalyzing the benzoylation reaction.
Malini, K A; Kurian, P; Anantharaman, M R(Elsevier, July , 2003)
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Abstract:
Composite magnetic materials have the unique advantage of property modification for tailoring devices for various
applications. Rubber ferrite composites (RFCs) prepared by incorporating ferrites in rubber matrixes have the advantage of easy
mouldability and flexibility. RFCs containing various loadings of nickel zinc ferrite (NZF) (Ni1 xZnxFe2O4) in a natural rubber
matrix have been prepared. The cure characteristics and the mechanical properties of these composites were evaluated. The
effect of loading on the cure characteristics and tensile properties were also evaluated. It is found that the loading dependence on
the cure time and mechanical properties exhibit an identical pattern.
Thomas Lee, S; Dinesh Kumar, S; Suresh Kumar, P; Radhakrishnan, P; Vallabhan, C P G; Nampoori, V P N(Elsevier, 2003)
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Abstract:
We propose and demonstrate a new technique for evanescent wave chemical sensing by writing long period gratings in a bare multimode plastic clad silica fiber. The sensing length of the present sensor is only 10 mm, but is as sensitive as a conventional unclad evanescent wave sensor having about 100 mm sensing length. The minimum measurable concentration of the sensor reported here is 10 nmol/l and the operating range is more than 4 orders of magnitude. Moreover, the detection is carried out in two independent detection configurations viz., bright field detection scheme that detects the core-mode power and dark field detection scheme that detects the cladding mode power. The use of such a double detection scheme definitely enhances the reliability and accuracy of the results. Furthermore, the cladding of the present fiber need not be removed as done in conventional evanescent wave fiber sensors.
V P N Nampoori; Radhakrishnan, P; Girijavallabhan, C P; Geetha, K; Rajesh, M(Journal of Optics A: Pure and Applied Optics, Institute of Physics Publishing, February 24, 2004)
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Abstract:
We report the position dependent tuning of fluorescence emission from
rhodamine 6G doped polymethylmethacrylate film waveguide using a side
illumination technique. The transmitted fluorescence as a function of the
distance from the point of illumination is measured by translating the
waveguide horizontally across a monochromatic light source. This technique
has been utilized to characterize the optical loss in dye doped waveguides.
We observe that the optical loss coefficients for shorter and longer distances
of propagation through the dye doped waveguide are different. At longer
distance of propagation a decrease in optical loss coefficient is observed
Radhakrishnan, P; V P N Nampoori; Girijavallabhan, C P; Geetha, K; Rajesh, M(Journal of Optics A: Pure and Applied Optics, Institute of Physics Publishing, February 24, 2004)
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Abstract:
We report the position dependent tuning of fluorescence emission from
rhodamine 6G doped polymethylmethacrylate film waveguide using a side
illumination technique. The transmitted fluorescence as a function of the
distance from the point of illumination is measured by translating the
waveguide horizontally across a monochromatic light source. This technique
has been utilized to characterize the optical loss in dye doped waveguides.
We observe that the optical loss coefficients for shorter and longer distances
of propagation through the dye doped waveguide are different. At longer
distance of propagation a decrease in optical loss coefficient is observed
Girijavallabhan, C P; Radhakrishnan, P; V P N Nampoori; Geetha, K; Rajesh, M(Journal of Optics A: Pure and Applied Optics, Institute of Physics Publishing, February 24, 2004)
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Abstract:
We report the position dependent tuning of fluorescence emission from
rhodamine 6G doped polymethylmethacrylate film waveguide using a side
illumination technique. The transmitted fluorescence as a function of the
distance from the point of illumination is measured by translating the
waveguide horizontally across a monochromatic light source. This technique
has been utilized to characterize the optical loss in dye doped waveguides.
We observe that the optical loss coefficients for shorter and longer distances
of propagation through the dye doped waveguide are different. At longer
distance of propagation a decrease in optical loss coefficient is observed
Anupam,Chandran R; Thomaskutty,Mathew; Aanandan,C K; Mohanan,P; Vasudevan,K(Microwave and Optical Technology Letters, February 5, 2004)
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Abstract:
A novel technique for backscattering reduction for both TE
and TM polarisation, employing a metallo-dielectric structure based on
Sierpinski carpet fractal geometry, is reported. A reduction in backscattered
power of --30 dB is obtained for normal incidence in the X-band for the
structure using the third iterated stage of the fractal geometry
Thomas, Baby; Ramachandran, T; Radhakrishnan, P; Nampoori, V P N; Vallabhan, C P G(IOP Publishing, 1991)
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Abstract:
A low inductance, triggered spark gap switch suitable for a high-current fast discharge system has been developed. The details of the design and fabrication of this pressurized spark gap, which uses only commonly available materials are described. A transverse discharge Blumlein-driven N2 laser incorporating this device gives a peak output power of 700 kW with a FWHM of 3 ns and an efficiency of 0.51%, which is remarkably high for a pulsed nitrogen laser system.
Moosad, K P B; Abdul Rasheed, T M; Nampoori, V P N; Sathianandan, K(Optical Society of America, 1990)
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Abstract:
Low power optical phase conjugation in polyvinyl alcohol
films embedded with saturable dyes is reported. Phase
conjugate reflectivity achieved is higher than that obtained
in the case of similar gelatin films.
Zinc salts of ethyl, isopropyl, and butyl xanthates are prepared
in the laboratory, and the effect of these xanthates with zinc diethyl
dithiocarbamate (ZDC) on the vulcanization of HAF-filled nitrile butadiene
rubber (NBR) compounds has been studied at different temperatures. The cure
times of these compounds have been compared with that of NBR compounds
containing TMTD/MBTS. The rubber compounds with the three xanthate
accelerators and ZDC are cured at various temperatures from 60 to 150°C.
The sheets are molded and properties such as tensile strength, tear strength,
cross-link density, elongation at break, compression set, abrasion resistance,
flex resistance, etc. have been evaluated. The properties show that zinc salt
of the xanthate/ZDC accelerator system has a positive synergistic effect on the
cure rate and mechanical properties of NBR compounds.
Jayaraj, M K; Vallabhan, C P G(IOP Publishing, 1990)
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Abstract:
AC thin film electroluminescent devices of MIS and MISIM have been fabricated with a novel dielectric layer of Eu2O3 as an insulator. The threshold voltage for light emission is found to depend strongly on the frequency of excitation source in these devices. These devices are fabricated with an active layer of ZnS:Mn and a novel dielectric layer of Eu2O3 as an insulator. The observed frequency dependence of brightness-voltage characteristics has been explained on the basis of the loss characteristic of the insulator layer. Changes in the threshold voltage and brightness with variation in emitting or insulating film thickness have been investigated in metal-insulator-semiconductor (MIS) structures. It has been found that the decrease in brightness occurring with decreasing ZnS layer thickness can be compensated by an increase in brightness obtained by reducing the insulator thickness. The optimal condition for low threshold voltage and higher stability has been shown to occur when the active layer to insulator thickness ratio lies between one and two.
Lethakumari,B; Sreedevi,Menon K; Aanandan,C K; Vasudevan,K; Mohanan,P(Microwave and Optical Technology Letters, July 20, 2004)
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Abstract:
This paper presents the outcome of the experimental studies
performed on L-strip fed compact rectangular microstrip antenna.
The effect of the feed parameters upon the characteristics of the antenna
is studied in detail. The antenna offers an impedance bandwidth of
nearly 20% and is suitable for broadband applications
Sreedevi,Menon K; Lethakumary,B; Bijumon,P V; Sebastian,M T; Mohanan,P(Microwave and Optical Technology Letters, May 5, 2005)
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Abstract:
In this paper, the advantages of using L-shaped microviij)
feed to e.tcite a rectangular dielectric resonator cuuenna (DRA) by elemanagnetic
coupling are presented. This feeding technique enhances the
hardsvidth and gain of the antenna without affecting its size. The experimental
re srdts are validated using Fidelity software based on the finitedifference
tine-domain (FDTD) method
Jayaraj, M K(Electrochemical Society, December 17, 2007)
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Abstract:
Highly transparent, luminescent and biocompatible ZnO quantum dots were prepared in water, methanol, and ethanol using
liquid-phase pulsed laser ablation technique without using any surfactant. Transmission electron microscopy analysis confirmed
the formation of good crystalline ZnO quantum dots with a uniform size distribution of 7 nm. The emission wavelength could be
varied by varying the native defect chemistry of ZnO quantum dots and the laser fluence. Highly luminescent nontoxic ZnO
quantum dots have exciting application potential as florescent probes in biomedical applications.
V P N Nampoori; Litty, Irimpan; Bindu, Krishnan; Radhakrishnan, P(Elsevier Journal of Colloid and Interface Science, April 29, 2008)
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Abstract:
In this article we present the spectral and nonlinear optical properties of ZnO–TiO2 nanocomposites prepared
by colloidal chemical synthesis. Emission peaks of ZnO–TiO2 nanocomposites change from 340 nm
to 385 nm almost in proportion to changes in Eg. The nanocomposites show self-defocusing nonlinearity
and good nonlinear absorption behaviour. The nonlinear refractive index and the nonlinear absorption
increase with increasing TiO2 volume fraction at 532 nm and can be attributed to the enhancement of
exciton oscillator strength. ZnO–TiO2 is a potential nanocomposite material for the tunable light emission
and for the development of nonlinear optical devices with a relatively small limiting threshold