Sugunan, S; Ampili, S; Bindhu, Jacob; Rani, Varghese(Indian Journal of Chemistry, February , 1996)
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Abstract:
The surface acidity and basicity of ternary oxides of
La, Ce and AI have been determined using a set of
Hammett indicators. The data have been correlated
with the catalytic activity of these oxides towards the
liquid phase reduction of cycIohexanone in 2-propanol.
Louis, Godfrey; Philip, J(The American Physical Society, 1996)
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Abstract:
A detailed ultrasonic study of the elastic properties of lithium ammonium sulfate ~LiNH4SO4! or LAS has
been carried out below room temperature. The elastic constants of LAS at room temperature are reported. The
discrepancy present in earlier elastic constant data associated with the different choice of axes for this orthorhombic
system are clarified. The results of the temperature variation study down to 220 K confirm the
ferroelastic phase transition at 285 K and establish a thermal hysteresis of about 2.5 K between the cooling and
heating cycles. Results of the investigation on the suspected weak phase transition at 256 K suggest that this
transition occurs at 242 K on cooling and at 256 K on heating, thus having a thermal hysteresis of about 14 K.
However, since the observed elastic anomaly for this transition is very small, the nature of this transition still
remains unclear
Bindhu, C V; Harilal, S S; Riju C, Issac; Nampoori, V P N; Vallabhan, C P G(World Scientific Puhlishing Company, 1996)
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Abstract:
Pulsed photoacoustic technique which is found to be a very convenient and accurate method, is used for the determination of absolute fluorescence quantum yield of laser dye rhodamine B. Concentration and power dependence of quantum yield of rhodamine B in methanol for excitation at 532 nm is reported here. Results show that a rapid decrease in quantum yield as the concentration is increased and finally it reaches the limit corresponding to fluorescence quenching.
Lovely, M R; Radhakrishnan, P; Nampoori, V P N; Vallabhan, C P G(Indian Journal of Pure and Applied Physics, January , 1996)
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Abstract:
The design and development of an evanescent wave sensor to determine the etching rate of the core of an optical fibre is discussed in this paper. The working of the device is based on the principle of propagation and loss of the evanescent wave in the cladding region of the fibre. The fraction of light intensity creeping out of the core of an uncladded fibre is a function of the core radius. As this radius decreases, the evanescent wave coupling to the medium surrounding the core enhances. This results in a decrease of the transmitted light intensity through the fibre. This technique is useful to design and fabricate optical fibres with different core geometries.
Harilal, S S; Riju C, Issac; Bindhu, C V; Nampoori, V P N; Vallabhan, C P G(World Scientific Publishing Company, 1996)
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Abstract:
Laser ablation processes in liquid benzene, toluene and carbon disulphide have been investigated by pulsed photoacoustic technique using 532 nm radiation from a frequency doubled Q-switched Nd:YAG laser. The nature of variation of photoacoustic signal amplitude with laser energy clearly indicates that different phenomena are involved in the generation of photoacoustic effect and these are discussed in detail. Our results suggest multiphoton induced photofragmentation as the most plausible interaction process occurring during laser ablation in these liquids.
Saratchandran, P P; Nandakumaran, V M; Ambika, G(Springer, November , 1996)
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Abstract:
By introducing a periodic perturbation in the control parameter of the logistic map we have investigated the period locking properties of the map. The map then gets locked onto the periodicity of the perturbation for a wide range of values of the parameter and hence can lead to a control of the chaotic regime. This parametrically perturbed map exhibits many other interesting features like the presence of bubble structures, repeated reappearance of periodic cycles beyond the chaotic regime, dependence of the escape parameter on the seed value and also on the initial phase of the perturbation etc.
Ajithprasad, K C; Nampoori, V P N; Vallabhan, C P G(Elsevier, 1996)
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Abstract:
Photoemission optogalvanaic (POG) effect has been observed by irradiating copper target electrode, in a nitrogen discharge cell using 1.06 μm and frequency doubled 532 nm Nd:YAG laser pulse. Measurement of the nature of the variation of POG signal strength with 532 nm laser fluence confirms the two photon induced photoelectric emission from copper. However, using 1.06 μm laser pulses thermally assisted photoemission is observed.
Harilal, S S; Issac, Riju C; Bindhu, C V; Nampoori, V P N; Vallabhan, C P G(American Institute of Physics, September 15, 1996)
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Abstract:
Laser ablation of graphite has been carried out using 1.06mm radiation from a Q-switched Nd:YAG
laser and the time of flight distribution of molecular C2 present in the resultant plasma is
investigated in terms of distance from the target as well as laser fluences employing time resolved
spectroscopic technique. At low laser fluences the intensities of the emission lines from C2 exhibit
only single peak structure while beyond a threshold laser fluence, emission from C2 shows a twin
peak distribution in time. The occurrence of the faster velocity component at higher laser fluences
is explained as due to species generated from recombination processes while the delayed peak is
attributed to dissociation of higher carbon clusters resulting in the generation of C2 molecule.
Analysis of measured data provides a fairly complete picture of the evolution and dynamics of
C2 species in the laser induced plasma from graphite.
Bindhu, C V; Harilal, S S; Geetha K, Varier; Issac, Riju C; Nampoori, V P N; Vallabhan, C P G(IOP, 1996)
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Abstract:
The dual-beam thermal lens technique has been found to be very
effective for the measurement of fluorescence quantum yields of dye solutions. The
concentration-dependence of the quantum yield of rhodamine B in methanol is
studied here using this technique. The observed results are in line with the
conclusion that the reduction in the quantum yield in the quenching region is
essentially due to the non-radiative relaxation of the absorbed energy. The thermal
lens has been found to become abberated above 40 mW of pump laser power.
This low value for the upper limit of pump power is due to the fact that the medium
is a resonantly absorbing one.
Vidyalal, V; Rajasree, K; Vallabhan, C P G(World Scientific Publishing Company, 1996)
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Abstract:
A simple experimental set-up is described to measure the electromagnetic shielding property of high Tc superconducting samples. Measurements were performed using HTSC materials in the form of laser ablated thin films, powders and sintered pellets. Samples used were Gd-123 in pure and doped form as well as a few Bi-based superconducting ceramics. For comparison, similar measurements were carried out on metals like aluminium, copper and μ metal. Very effective shielding was observed for HTSC materials compared to the conventional materials mentioned above. However it also depended on the sample types and poor shielding was observed for powdered HTSC material in comparison to thin films prepared by laser ablation.