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.
In general Indian summer monsoon rainfall did not show any significant trend in all Indian summer monsoon rainfall series, however, it was reported that the ISMR is subjected to spatial trends. This paper made an attempt to bring out long term trends of different intensity classes of summer monsoon rainfall in different regions of Indian subcontinent. The long term trend of seasonal and monthly rainfall were also made using the India Meteorological Department gridded daily rainfall data with a spatial resolution of 1° × 1° latitude-longitude grid for the period from 1st January, 1901 to 31st December, 2003. The summer monsoon rainfall shows an increasing trend in southeast, northwest and northeast regions, whereas decreasing trend in the central and west coastal regions. In monthly scale, July rainfall shows decreasing trend over west coastal and central Indian regions and significant increasing trend over northeast region at 0.1% significant level. During the month August, decreasing trend is observed in the west coastal stations at 10% significant level. In most of the stations, mean daily rainfall shows an increasing trend for low and very high intense rainfall. For the moderate rainfall, the trend is different for different regions. In the central and southern regions the trend of moderate and moderately high classes show increasing trend. And for the high and very high intensity classes, the trend is decreasing significantly. In the northeastern regions, above 10 mm/day rainfall shows significantly increasing trend with 0.1% significant level.
Girijavallabhan, C P; Radhakrishnan, P; Nampoori, V P N; 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
Anantharaman, M R; van den Oetelaar, L C A; Helwegen, J H J M; Brongersma, H H; Ross, J R H; Seshan, K; Smits, R H H(Academic Press, July 20, 1995)
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Abstract:
A series of vanadium-niobium oxide catalysts in which the
vanadia content varies between 0.3 and 18mol%was prepared
by coprecipitation. These catalysts were characterized by X-ray
diffraction (XRD), X-ray photoelectron spectroscopy (XPS),
low-energy ion scattering (LEIS), and by catalytic testing in
the oxidative dehydrogenation reaction of propane. The results
of the surface analysis by XPS and LEIS are compared. It is
concluded that the active site on the catalyst surface contains
2.0 ± 0.3 vanadium atoms on average. This can be understood
byassuming the existenceof two or three different sites:isolated
vanadium atoms, pairs of vanadium atoms, or ensembles of
three vanadium atoms. At higher vanadium concentration more
vanadium clusters with a higher activity are at the surface.LEIS
revealed that as the vanadium concentration in the catalyst
increases, vanadium replaces niobium at the surface. At vanadium
concentrations above 8 mol%, new phases such as P-(Nb,
V)20S which are less active because vanadium is present in
isolated sites are formed, while the vanadium surface concentration
shows a slight decrease
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.
Anantharaman, M R; Saravanan, S; Venkitachalam, S; Joseph, Mathai C(IOP Publishing Ltd and Deutsche Physikalische Gesellschaft, June 17, 2004)
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Abstract:
Thermally stable materials with low dielectric constant (k < 3.9)
are being hotly pursued. They are essential as interlayer dielectrics/intermetal
dielectrics in integrated circuit technology, which reduces parasitic capacitance
and decreases the RC time constant. Most of the currently employed materials
are based on silicon. Low k films based on organic polymers are supposed to
be a viable alternative as they are easily processable and can be synthesized
with simpler techniques. It is known that the employment of ac/rf plasma
polymerization yields good quality organic thin films, which are homogenous,
pinhole free and thermally stable. These polymer thin films are potential
candidates for fabricating Schottky devices, storage batteries, LEDs, sensors,
super capacitors and for EMI shielding. Recently, great efforts have been made in
finding alternative methods to prepare low dielectric constant thin films in place
of silicon-based materials. Polyaniline thin films were prepared by employing
an rf plasma polymerization technique. Capacitance, dielectric loss, dielectric
constant and ac conductivity were evaluated in the frequency range 100 Hz–
1 MHz. Capacitance and dielectric loss decrease with increase of frequency and
increase with increase of temperature. This type of behaviour was found to be in
good agreement with an existing model. The ac conductivity was calculated from
the observed dielectric constant and is explained based on the Austin–Mott model
for hopping conduction. These films exhibit low dielectric constant values, which
are stable over a wide range of frequencies and are probable candidates for low k
applications.
Sijikumar,S; Dr.Mohan Kumar, K(Department of Atmospheric Sciences, 2003)
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Abstract:
The main objective of the of present study are to study the intraseasonal variability of LLJ and its relation with convective heating of the atmosphere, to establish whether LLJ splits into two branches over the Arabian sea as widely believed, the role of horizonatal wind shear of LLJ in the episodes of intense rainfall events observed over the west coast of India, to perform atmospheric modeling work to test whether small (meso) scale vortices form during intense rainfall events along the west coast; and to study the relation between LLJ and monsoon depression genesis. The results of a study on the evolution of Low Level Jetstream (LLJ) prior to the formation of monsoon depressions are presented. A synoptic model of the temporal evolution of monsoon depression has been produced. There is a systematic temporal evolution of the field of deep convection strength and position of the LLJ axis leading to the genesis of monsoon depression. One of the significant outcomes of the present thesis is that the LLJ plays an important role in the intraseasonal and the interannual variability of Indian monsoon activity. Convection and rainfall are dependent mainly on the cyclonic vorticity in the boundary layer associated with LLJ. Monsoon depression genesis and the episodes of very heavy rainfall along the west coast of India are closely related to the cyclonic shear of the LLJ in the boundary layer and the associated deep convection. Case studies by a mesoscale numerical model (MM5) have shown that the heavy rainfall episodes along the west coast of India are associated with generation of mesoscale cyclonic vortices in the boundary layer.
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.
Anantharaman, M R; Malini, K A; Ajay, Gupta(Springer, June 14, 2004)
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Abstract:
Nanocomposites with magnetic components possessing nanometric dimensions, lying in the range
1–10 nm, are found to be exhibiting superior physical properties with respect to their coarser sized counterparts.
Magnetic nanocomposites based on gamma iron oxide embedded in a polymer matrix have been prepared
and characterized. The behaviour of these samples at low temperatures have been studied using Mössbauer
spectroscopy. Mössbauer studies indicate that the composites consist of very fine particles of g-Fe2O3 of which
some amount exists in the superparamagnetic phase. The cycling of the preparative conditions were found to
increase the amount of g-Fe2O3 in the matrix
Description:
Bull. Mater. Sci., Vol. 27, No. 4, August 2004, pp. 361–366
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.
Lethakumary,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