Radhakrishnan, P; V P N Nampoori; Girijavallabhan, C P; Thomas Lee, S; Jose, Gin; Unnikrishnan, N V(Journal of Optics A: Pure and Applied Optics, July 12, 2001)
[+]
[-]
Abstract:
The fabrication and characterization of a fibre optic pH sensor based on
evanescent wave absorption is presented. The unclad portion of a
multi-mode optical fibre is coated with a pH sensitive dye, which is
immobilized by the sol–gel route. The sensitivity of the device has been
found to increase when multiple sol–gel coatings are used as the sensing
region. The dynamic range and the temporal response of the sensor are
investigated for two different dyes, namely bromocresol purple and
bromocresol green. The performance of the device is evaluated in terms of
the results obtained during actual measurements
Girijavallabhan, C P; Radhakrishnan, P; V P N Nampoori; Thomas Lee, S; Jose, Gin; Unnikrishnan, N V(Journal of Optics A : Pure and Applied Optics, July 12, 2001)
[+]
[-]
Abstract:
The fabrication and characterization of a fibre optic pH sensor based on
evanescent wave absorption is presented. The unclad portion of a
multi-mode optical fibre is coated with a pH sensitive dye, which is
immobilized by the sol–gel route. The sensitivity of the device has been
found to increase when multiple sol–gel coatings are used as the sensing
region. The dynamic range and the temporal response of the sensor are
investigated for two different dyes, namely bromocresol purple and
bromocresol green. The performance of the device is evaluated in terms of
the results obtained during actual measurements
V P N Nampoori; Radhakrishnan, P; Girijavallabhan, C P; Thomas Lee, S; Jose, Gin; Unnikrishnan, N V(Journal of Optics A: Pure and Applied Optics, July 12, 2001)
[+]
[-]
Abstract:
The fabrication and characterization of a fibre optic pH sensor based on
evanescent wave absorption is presented. The unclad portion of a
multi-mode optical fibre is coated with a pH sensitive dye, which is
immobilized by the sol–gel route. The sensitivity of the device has been
found to increase when multiple sol–gel coatings are used as the sensing
region. The dynamic range and the temporal response of the sensor are
investigated for two different dyes, namely bromocresol purple and
bromocresol green. The performance of the device is evaluated in terms of
the results obtained during actual measurements.
The 2,4,6-triphenylthiapyrylium ion has been obtained imprisoned inside the supercages of the tridirectional,
large pore zeolites Y and beta via ship-in-a-bottle synthesis from chalcone and acetophenone in the presence of
hydrogen sulfide. The resulting solids are efficient and robust photocatalysts that are able to degrade phenol and
aniline in water with a higher efficiency than the P-25 TiO2 standard. Preliminary tests have shown that these
encapsulated dye materials are also efficient photocatalysts for the oxidative degradation of malodorous sulfurcontaining
molecules.
Abraham, Thomas N; George, K E(Taylor & Francis, 2007)
[+]
[-]
Abstract:
Short fiber reinforced thermoplastics have generated much
interest these days since fibrous materials tend to increase both
mechanical and thermal properties, such as tensile strength, flexural
strength, flexural modulus, heat deflection temperature, creep
resistance, and some times impact strength of thermoplastics. If
the matrix and reinforcement are both based on polymers the composite
are recyclable. The rheological behavior of recyclable composites
based on nylon fiber reinforced polypropylene (PP) is reported
in this paper. The rheological behavior was evaluated both using a
capillary rheometer and a torque rheometer. The study showed that
the composite became pseudoplastic with fiber content and hence
fiber addition did not affect processing adversely at higher shear
rates. The torque rheometer data resembled that obtained from
the capillary rheometer. The energy of mixing and activation energy
of mixing also did not show much variation from that of PP alone.
Sheeba, M; Rajesh, M; Mathew, S; Nampoori, V P N; Vallabhan, C P G; Radhakrishnan, P(Optical Society of America, April , 2008)
[+]
[-]
Abstract:
Two-photon excited (TPE) side illumination fluorescence studies in a Rh6G-RhB dye mixture doped polymer optical fiber (POF) and the effect of energy transfer on the attenuation coefficient is reported. The dye doped POF is pumped sideways using 800 nm, 70 fs laser pulses from a Ti:sapphire laser, and the TPE fluorescence emission is collected from the end of the fiber for different propagation distances. The fluorescence intensity of RhB doped POF is enhanced in the presence of Rh6G as a result of energy transfer from Rh6G to RhB. Because of the reabsorption and reemission process in dye molecules, an effective energy transfer is observed from the shorter wavelength part of the fluorescence spectrum to the longer wavelength part as the propagation distance is increased in dye doped POF. An energy transfer coefficient is found to be higher at shorter propagation distances compared to longer distances. A TPE fluorescence signal is used to characterize the optical attenuation coefficient in dye doped POF. The attenuation coefficient decreases at longer propagation distances due to the reabsorption and reemission process taking place within the dye doped fiber as the propagation distance is increased.
Rani, Joseph(OPA (Overseas Publishers Association), December 3, 1996)
[+]
[-]
Abstract:
Filled and gum compounds of Isobutylene-Isoprene rubber were extruded through a
laboratory extruder at various feeding rates, different temperatures and revolutions per
minute. The extruded compounds were vulcanized up to their optimum cure times and
the mechanical properties of the vulcanizates were determined. The properties suggest
that there is a particular feeding rate in the starved fed region, which results in maximum
mechanical properties. The study shows that running the extruder at a slightly
starved condition is an attractive means of improving the physical properties.
Indic, P; Pratap, R; Nampoori, V P N; Pradhan, N(International Journal of Neuroscience, 1999)
[+]
[-]
Abstract:
We propose to show in this paper, that the time series obtained from biological systems such as human brain are invariably nonstationary because of different time scales involved in the dynamical process. This makes the invariant parameters time dependent. We made a global analysis of the EEG data obtained from the eight locations on the skull space and studied simultaneously the dynamical characteristics from various parts of the brain. We have proved that the dynamical parameters are sensitive to the time scales and hence in the study of brain one must identify all relevant time scales involved in the process to get an insight in the working of brain.
Reactive extrusion is an attractive means of polymer processing since the shaping
and reaction take place in a single operation. In this paper we report the silane
grafting of polyethylenes in a single screw extruder. The optimum conditions for
silane grafting, viz. temperature, shear rate, silane and DCP concentrations, were
determined on a torque rheometer and then actual extrusion was performed
using these conditions. The study shows that an optimum low level of grafting/
crosslinking can be introduced into polyethylene during its extrusion for better
mechanical behavior and=or thermal stability without affecting the processability.
Biju,Kumar; Raveendranath,U; Mohanan,P; Mathew,K T; Hajian,M; Ligthart,L P(Microwave and Optical Technology Letters, July 20, 2000)
[+]
[-]
Abstract:
A simple and efficient method for determining the complex
permittivity of dielectric materials from both reflected and transmitted signals is presented. It is also novel because the technique is implemented using two pyramidal horns without any focusing mechanisms. The dielectric constant of a noninteractive and distributive (NID) mixture of dielectrics is also determined
Wilson, K J; Vallabhan, C P G(IOP Publishing, 1989)
[+]
[-]
Abstract:
A simple and inexpensive linear magnetic field sweep generating system suitable for magnetic resonance experiments is described. The circuit, utilising a modified IC bootstrap configuration, generates field sweep over a wide range of sweep durations with excellent sweep linearity.
Vermeeren,G; Rogier,H; Olyslager,F; Zutter De,D(IEE Electronics letters,UK, September 13, 2001)
[+]
[-]
Abstract:
A single-feed rectangular-ring microstrip antenna is proposed for
indoor communication under the Bluetooth protocol. The
dimensions of the antenna together with the location of the feed
point are optimized through field simulations in order to cover the
Bluetooth bandwidth and to avoid linear polarization. The
performance and the efficiency of the antenna are illustrated in a
real indoor environment
Santhi, A; Vinu V, Namboodiri; Radhakrishnan, P; Nampoori, V P N(American Institute of Physics, 2006)
[+]
[-]
Abstract:
The authors apply the theory of photothermal lens formation and also that of pure optical nonlinearity to account for the phase modulation in a beam as it traverses a nonlinear medium. It is used to simultaneously determine the nonlinear optical refraction and the thermo-optic coefficient. They demonstrate this technique using some metal phthalocyanines dissolved in dimethyl sulfoxide, irradiated by a Q-switched Nd:YAG laser with 10 Hz repetition rate and a pulse width of 8 ns. The mechanism for reverse saturable absorption in these materials is also discussed.
Hsieh,Gui-Bin; Chen,Ming-Huang; Wong,Kin-Lu Wong(IEE Electronics letters,UK, June 21, 2001)
[+]
[-]
Abstract:
A novel technique for obtaining dual-hand circular polarization
(CP) radiation of a single-feed circular microstrip antenna in
proposed and demonstrated. By embedding two pain of arc shaped
slots of proper lengths close to the boundary of a circular
patch, and protruding one of the arc-shaped slots with a narrow
slit, the circular microstrip antenna can perform dual-hand CP
radiation using a single probe feed. Details of the antenna design
Binoy,G S; Aanandan,C K; Mohanan,P; Vasudevan,K(Microwave and Optical Technology Letters, June 20, 2000)
[+]
[-]
Abstract:
A novel dual frequency dual-polarized square microstrip
patch antenna embedded with a slot is presented. The proposed
antenna offers tunability of the frequency ratio between the two
frequencies by adjusting the slot dimensions. This configuration
also provides a size reduction up to -51 and 35% for the two modes
as compared to a square micro strip patch antenna
The quantum yields of singlet oxygen production and
lifetimes at the gas–solid interface in silica gel material
are determined. Different photosensitizers (PS) are encapsulated
in parallelepipedic xerogel monoliths (PS-SG). PS were chosen according
to their known photooxidation properties: 9,10-dicyanoanthracene
(DCA), 9,10-anthraquinone (ANT), and a benzophenone
derivative, 4-benzoyl benzoic acid (4BB). These experiments
are mainly based on time-resolved 1O2 phosphorescence detection,
and the obtained FD and tD values are compared with
those of a reference sensitizer for production, 1H-phenalen-1-
one (PN), included in the same xerogel. The trend between their
ability to oxidize organic pollutants in the gas phase and their efficiency
for production is investigated through photooxidation
experiments of a test pollutant dimethylsulfide (DMS). The
FD value is high for DCA-SG relative to the PN reference, whereas
it is slightly lower for 4BB-SG and for ANT-SG. FD is related to
the production of sulfoxide and sulfone as the main oxidation
products for DMS photosensitized oxidation. Additional mechanisms,
leading to C!S bond cleaveage, appear to mainly occur
for the less efficient singlet oxygen sensitizers 4BB-SG and ANTSG.
Litty, Irimpan; Nampoori, V P N; Radhakrishnan, P; Bindu, Krishnan; Deepthy, A(American Institute of Physics, 2008)
[+]
[-]
Abstract:
We have investigated the third-order nonlinearity in ZnO nanocolloids with particle sizes in the range 6-18 nm by the z-scan technique. The third-order optical susceptibility χ(3) increases with increasing particle size (R) within the range of our investigations. In the weak confinement regime, an R2 dependence of χ(3) is obtained for ZnO nanocolloids. The optical limiting response is also studied against particle size.
Litty, Irimpan; Nampoori, V P N; Radhakrishnan, P; Deepthy, A; Bindu, Krishnan(American Institute of Physics, 2007)
[+]
[-]
Abstract:
In this article we present size dependent spectroscopic observations of nanocolloids of ZnO. ZnO is reported to show two emission bands, an ultraviolet (UV) emission band and another in the green region. Apart from the known band gap 380 nm and impurity 530 nm emissions, we have found some peculiar features in the fluorescence spectra that are consistent with the nanoparticle size distribution. Results show that additional emissions at 420 and 490 nm are developed with particle size. The origin of the visible band emission is discussed. The mechanism of the luminescence suggests that UV luminescence of ZnO colloid is related to the transition from conduction band edge to valence band, and visible luminescence is caused by the transition from deep donor level to valence band due to oxygen vacancies and by the transition from conduction band to deep acceptor level due to impurities and defect states. A correlation analysis between the particle size and spectroscopic observations is also discussed.
Binoy,G S; Aanandan,C K; Mohanan,P; Vasudevan,K(Microwave Engineering Group,Department of Electronics, January 5, 2002)
[+]
[-]
Abstract:
A novel dual frequency design of a square microstrip antenna coaxially
fed along the diagonal with a chip capacitor mounted at the bottom of
the stub is introduced. This design provides enhanced area reduction and
good cross-polarization levels. The antenna design can be used as a compact
antenna system where limited size is a major requirement. The details of the
antenna design and experimental results are presented