Dr.P Radhakrishnan
http://dyuthi.cusat.ac.in:8080/xmlui/handle/purl/688
2024-02-07T21:21:53ZComparative Performance of Two Fiber Optic Ammonia Sensors Employing Different Sensing Materials
http://dyuthi.cusat.ac.in:8080/xmlui/handle/purl/2042
Comparative Performance of Two Fiber Optic Ammonia Sensors Employing Different Sensing Materials
Jinesh, Mathew; Mahesh, V V; Radhakrishnan, P
The design and fabrication of fiber based ammonia sensors employing Bromothymol blue
and Chitosan as sensing elements are presented in this paper. In the presence of ammonia gas the
absorption of Bromothymol blue changes while in the case of Chitosan the refractive index changes
which in turn modulates the intensity of light propagating through a fiber.
2008-08-01T00:00:00ZUse of photoacoustic effect for the detection of phase transitions in liquid crystal mixtures
http://dyuthi.cusat.ac.in:8080/xmlui/handle/purl/1838
Use of photoacoustic effect for the detection of phase transitions in liquid crystal mixtures
Radhakrishnan, P; V P N Nampoori; Girijavallabhan, C P; Nibu, A George; George, A K
We report on a laser induced photoacoustic study of the nematic-to-isotropic
transition in certain commercial nematic liquid crystal mixtures, namely BL001, BL002,
BL032 and BL035. A simple analysis of the experimental data using the
Rosencwaig–Gersho theory shows that the heat capacities of all these compounds exhibit a
sharp peak as the temperature of the sample is varied across the transition region. Also,
substantial differences in the photoacoustic signal amplitudes in nematic and isotropic phases
have been noticed for all the mixtures. The increased light scattering property of the nematic
phase may be the reason for the enhanced photoacoustic signal amplitude in this phase
2000-10-13T00:00:00ZUse of an open photoacoustic cell for the thermal characterisation of liquid crystals
http://dyuthi.cusat.ac.in:8080/xmlui/handle/purl/1835
Use of an open photoacoustic cell for the thermal characterisation of liquid crystals
Radhakrishnan, P; Nampoori, V P N; Girijavallabhan, C P; Nibu, A George; George, A K
In this paper, we describe the use of an open cell
photoacoustic configuration for the evaluation of the thermal
effusivity of liquid crystals. The feasibility, precision and reliability
of the method are initially established by measuring
the thermal effusivities of water and glycerol, for which the
effusivity values are known accurately. In order to demonstrate
the use of the present method in the thermal characterization
of liquid crystals, we have measured the thermal
effusivity values in various mesophases of 4-cyano-4 -
octyloxybiphenyl (8OCB) and 4-cyano-4 -heptyloxybiphenyl
(7OCB) liquid crystals using a variable temperature open
photoacoustic cell. A comparison of the measured values for
the two liquid crystals shows that the thermal effusivities of
7OCB in the nematic and isotropic phases are slightly less
than those of 8OCB in the corresponding phases
2001-07-18T00:00:00ZThermal characterization of intrinsic and extrinsic InP using photoacoustic technique
http://dyuthi.cusat.ac.in:8080/xmlui/handle/purl/1832
Thermal characterization of intrinsic and extrinsic InP using photoacoustic technique
Radhakrishnan, P; V P N Nampoori; Girijavallabhan, C P; Sajan, D George
An open photoacoustic cell operating in the low range of chopping
frequency has been employed to evaluate the thermal diffusivity values of
intrinsic InP and InP doped with S, Sn and Fe. The experimental set-up is
calibrated by the evaluation of thermal diffusivity value of pure Si and
GaAs. The present investigation shows that doped samples show a reduced
value for thermal diffusivity compared to intrinsic sample. From the
analysis of data it is also seen that nature of dopant clearly influences the
thermal diffusivity value of semiconductors. The results are explained in
terms of phonon assisted heat transfer mechanism in semiconductors
2003-04-02T00:00:00Z