Harilal, S S; Riju C, Issac; Bindhu, C V; Geetha K, Varier; Nampoori, V P N; Vallabhan, C P G(World Scientific Publishing Company, 1995)
[+]
[-]
Abstract:
Pulsed photoacoustic measurements have been carried out in liquid CS2 using 532 nm radiation from a frequency doubled Nd:YAG laser. Variation of signal amplitude with laser fluence clearly indicates the role of multiphoton processes in the generation of photoacoustic effect. It is also shown that four photon induced dissociation and five photon induced ionization are likely processes in CS2 and 532 nm radiation.
Sathy, P; Reji, Philip; Nampoori, V P N; Vallabhan, C P G(Elsevier, January 1, 1990)
[+]
[-]
Abstract:
Two-photon absorption in Rhodamine 6G using the second harmonic of a pulsed Q-switched Nd:YAG laser has been studied by photoacoustic technique. It is observed that there is a competition between one-photon and two-photon absorption processes. At lower concentration the two-photon process is predominant over the one-photon process.
Sasi Kumar, P R; Padmaja, G; Ravi Kumar, A V; Nampoori, V P N; Vallabhan, C P G(Springer, April , 1991)
[+]
[-]
Abstract:
Observation of laser induced two-photon photoemission optogalvanic (TPPOG) effect from tungsten electrode in a discharge cell using 564 nm radiation obtained from a pulsed dye laser is described. The magnitude of the POG signal is studied as a function of laser energy under various discharge parameters. Competition between one-photon and two-photon processes has been observed when nitrogen gas is used in the discharge cell.
The D-eigenvalues of a graph G are the eigenvalues of its distance matrix D, and the
D-energy ED(G) is the sum of the absolute values of its D-eigenvalues. Two graphs are
said to be D-equienergetic if they have the same D-energy. In this note we obtain bounds
for the distance spectral radius and D-energy of graphs of diameter 2. Pairs of equiregular
D-equienergetic graphs of diameter 2, on p = 3t + 1 vertices are also constructed.
Gopalapillai,Indulal; Ivan,Gutman; Vijayakumar,Ambat(Department of Mathematics, August 25, 2007)
[+]
[-]
Abstract:
The D-eigenvalues of a graph G are the eigenvalues of its distance matrix D, and the
D-energy ED(G) is the sum of the absolute values of its D-eigenvalues. Two graphs are
said to be D-equienergetic if they have the same D-energy. In this note we obtain bounds
for the distance spectral radius and D-energy of graphs of diameter 2. Pairs of equiregular
D-equienergetic graphs of diameter 2, on p = 3t + 1 vertices are also constructed.
Pramod, K V; Unnikrishnan, K(Academy Publisher, 2009)
[+]
[-]
Abstract:
A feasible way of implementing a temporal
database is by mapping temporal data model onto a
conventional data model followed by a commercial database
management system. Even though extensions were proposed
to standard SQL for supporting temporal databases, such
proposals have not yet come across standardization
processes. This paper attempts to implement database
operators such as aggregates and universal quantifier for
temporal databases, implemented on top of relational
database systems, using currently available SQL standards.
Hysen, Thomas; Senoy, Thomas; Ramanujan, R V; Anantharaman, M R(Springer, 2008)
[+]
[-]
Abstract:
Activation energy for crystallization (Ec) is a
pertinent parameter that decides the application potential of
many metallic glasses and is proportional to the crystallization
temperature. Higher crystallization temperatures are
desirable for soft magnetic applications, while lower values
for data storage purposes. In this investigation, from the
heating rate dependence of peak crystallization temperature
Tp, the Ec values have been evaluated by three different
methods for metglas 2826 MB (Fe40Ni38B18Mo4) accurately.
The Ec values are correlated with the morphological
changes, and the structural evolution associated with
annealing temperatures is discussed.
Reethamma, Thomas; Nampoori, V P N(Elsevier, December , 1988)
[+]
[-]
Abstract:
Photoluminescence, thermoluminescence and phosphorescence studies of cerium and copper doped BaS phosphors are attempted. Cu+ centres in BaS lattice activate red emission while Ce3+ sensitize the blue emission. Results are explained on the basis of superposition theory involving monomolecular kinetics. In Randall and Wilkins model, the decay and TL studies are found to corelate each other.
this paper, the median and the antimedian of cographs are
discussed. It is shown that if G, and G2 are any two cographs, then there is a
cograph that is both Eulerian and Hamiltonian having Gl as its median and G2
as its antimedian. Moreover, the connected planar and outer planar cographs
are characterized and the median and antimedian graphs of connected, planar
cographs are listed.
The role of acoustic plasmons in the recently discovered high Tc superconductors
is discussed. It is shown that the exchange of acoustic plasmons together with the
usual phonon exchange between electrons can give rise to a Tc - 100 K.
Nibu A, George; Vallabhan, C P G; Nampoori, V P N; George, A K; Radhakrishnan, P(Society of Photo-Optical Instrumentation Engineers, 2001)
[+]
[-]
Abstract:
We report the use of an open photoacoustic cell configuration
for the evaluation of thermal effusivity of liquid crystals. Initially, the
method is calibrated using water and glycerol as transparent liquid
samples, and the role of thermal conductivity of these liquids on the
photoacoustic signal amplitude is discussed. To demonstrate the application
of the present method for the evaluation of thermal effusivity of
liquid crystals, we have used certain multicomponent nematic liquid crystal
mixtures, namely BL001, BL002, BL032, and BL035. Each of these
liquid crystal mixtures contains four to nine components and are primarily
based on the cyanobiphenyl structure. The measured values of thermal
effusivity of BL001 and BL002 were found to be almost the same, but
differ from those of BL032 and BL035, which implies a difference in
composition of the latter two from the former two mixtures.
Kumar, G A; Thomas, J; George, N; Kumar, B A; Radhakrishnan, P; Nampoori, V P N; Vallabhan, C P G(Society of Glass Technology, 2000)
[+]
[-]
Abstract:
Optical absorption studies of free base and rare earth incorporated phthalocyanine doped borate glass matrix are reported for the first lime. The absorption spectra recorded in the UV- VIS region show two well defined absorption bands of phthalocyanine (Pc) molecule, namely the Soret band (B) and the Q band. The Q band always shows its characteristic splitting in all the doped glass matrices and the intensities of these components are found to vary from one Pc to another. Some of the important optical parameters, namely optical absorption coefficient (a), molar extinction coefficient (ε), absorption cross section (σa), oscillator strength (f), electric dipole strength (q2), absorption half bandwidth (Δλ) of the principal optical transitions have also been evaluated. Moreover, the spectral dependence of refractive index (n) and thereby the optical dielectric constant (ε) on wavelength yielded values of carrier concentration to effective mass ratio (N/m*) of the phthalocyanine molecule in the present glassy systems. Optical band gap (Eg) and width of the band tail (Et) are computed and their variations among the prepared samples are also discussed.
Jayaraj, M K(Electrochemical Society, February 18, 2008)
[+]
[-]
Abstract:
The optical and carrier transport properties of amorphous transparent zinc indium tin oxide (ZITO)(a-ZITO) thin films and the
characteristics of the thin-film transistors TFTs were examined as a function of chemical composition. The as-deposited films
were very conductive and showed clear free carrier absorption FCA . The analysis of the FCA gave the effective mass value of
0.53 me and a momentum relaxation time of 3.9 fs for an a-ZITO film with Zn:In:Sn = 0.35:0.35:0.3. TFTs with the as-deposited
channels did not show current modulation due to the high carrier density in the channels. Thermal annealing at 300°C decreased
the carrier density and TFTs fabricated with the annealed channels operated with positive threshold voltages VT when Zn
contents were 25 atom % or larger. VT shifted to larger negative values, and subthreshold voltage swing increased with decreasing
the Zn content, while large on–off current ratios 107–108 were kept for all the Zn contents. The field effect mobilities ranged
from 12.4 to 3.4 cm2 V−1 s−1 for the TFTs with Zn contents varying from 5 to 48 atom %. The role of Zn content is also
discussed in relation to the carrier transport properties and amorphous structures.
Jayaraj, M K(American Vacuum Society, January 8, 2008)
[+]
[-]
Abstract:
Structural, electronic, and optical properties of amorphous and transparent zinc tin oxide films
deposited on glass substrates by pulsed laser deposition (PLD) were examined for two chemical
compositions of Zn:Sn=1:1 and 2:1 as a function of oxygen partial pressure PO2 used for the film
deposition and annealing temperature. Different from a previous report on sputter-deposited films
Chiang et al., Appl. Phys. Lett. 86, 013503 2005 , the PLD-deposited films crystallized at a lower
temperature 450 °C to give crystalline ZnO and SnO2 phases. The optical band gaps Tauc gaps
were 2.80−2.85 eV and almost independent of oxygen PO2
, which are smaller than those of the
corresponding crystals 3.35−3.89 eV . Films deposited at low PO2
showed significant subgap
absorptions, which were reduced by postthermal annealing. Hall mobility showed steep increases
when carrier concentration exceeded threshold values and the threshold value depended on the film
chemical composition. The films deposited at low PO2
2 Pa had low carrier concentrations. It is
thought that the low PO2
produced high-density oxygen deficiencies and generated electrons, but
these electrons were trapped in localized states, which would be observed as the subgap absorptions.
Similar effects were observed for 600 °C crystallized films and their resistivities were increased by
formation of subgap states due to the reducing high-temperature condition. High carrier
concentrations and large mobilities were obtained in an intermediate PO2
region for the as-deposited films.
Highly conductive and transparent thin films of amorphous zinc indium tin oxide are prepared at room temperature by co-sputtering of zinc
10 oxide and indium tin oxide. Cationic contents in the films are varied by adjusting the power to the sputtering targets. Optical transmission study of
11 films showed an average transmission greater than 85% across the visible region. Maximum conductivity of 6×102 S cm−1 is obtained for Zn/In/
12 Sn atomic ratio 0.4/0.4/0.2 in the film. Hall mobility strongly depends on carrier concentration and maximum mobility obtained is 18 cm2 V−1 s−1
13 at a carrier concentration of 2.1×1020 cm−3. Optical band gap of films varied from 3.44 eV to 3 eV with the increase of zinc content in the film
14 while the refractive index of the films at 600 nm is about 2.0.
Optical emission spectroscopic studies were carried out on the plasma produced by ablation of zinc
oxide target using the third harmonic 355 nm of Q-switched Nd:YAG laser, in vacuum and at three
different ambient gas oxygen pressures. The spatial variations of electron density Ne and electron
temperature Te were studied up to a distance of 20 mm from the target surface. The kinematics of
the emitted particles and the expansion of the plume edge are discussed. The optimum conditions
favorable for the formation of high quality zinc oxide thin films are thereby suggested.
V P N Nampoori; Girijavallabhan, C P; Harilal, S S; Riju, C Issac; Bindhu, C V(Journal of Physics D : Applied Physics, January 24, 1997)
[+]
[-]
Abstract:
Optical emission studies of C2 molecules in plasma obtained by Nd:YAG
laser ablation of graphite in a helium atmosphere are reported for irradiances in the
range (1–9:2/ x 1010 W cm−2. The characteristics of the spectral emission intensity
from the C2 (Swan band) species have been investigated as functions of the
distance from the target, ambient pressure and laser irradiance. Estimates of
vibrational temperatures of C2 species under various irradiance conditions are
made. Results of measurements performed under different ambient helium gas
pressures are also discussed.
Girijavallabhan, C P; V P N Nampoori; Harilal, S S; Riju, C Issac; Bindhu C V(Journal of Physics D : Applied Physics, January 24, 1997)
[+]
[-]
Abstract:
Optical emission studies of C2 molecules in plasma obtained by Nd:YAG
laser ablation of graphite in a helium atmosphere are reported for irradiances in the
range (1–9:2/ x 1010 W cm−2. The characteristics of the spectral emission intensity
from the C2 (Swan band) species have been investigated as functions of the
distance from the target, ambient pressure and laser irradiance. Estimates of
vibrational temperatures of C2 species under various irradiance conditions are
made. Results of measurements performed under different ambient helium gas
pressures are also discussed.
Deepa, Jose; Shelly John, M; Radhakrishnan, P; Nampoori, V P N; Vallabhan, C P G(Elsevier, July 18, 1998)
[+]
[-]
Abstract:
A novel fibre optic sensor for the in situ measurement of the rate of deposition of thin films has been developed. Evanescent wave in the uncladded portion of a multimode fibre is utilised for this sensor development. In the present paper we demonstrate how this sensor is useful for the monitoring of the deposition rate of polypyrrole thin films, deposited by an AC plasma polymerisation method. This technique is simple, accurate and highly sensitive compared with existing techniques.
Harilal, S S; Bindhu, C V; Nampoori, V P N; Vallabhan, C P G(American Institute of Physics, 1999)
[+]
[-]
Abstract:
Optical limiting and thermo-optic properties of C60 in toluene are studied using 532 nm, 9 ns pulses from a frequency-doubled Nd:YAG laser. Optical limiting studies in these fullerene molecules lead to the conclusion that reverse saturable absorption is the major mechanism for limiting properties in these molecules. Thermal lensing measurements are also performed in fullerene solutions. The quadratic dependence of thermal lens signal on incident energy confirms that enhanced optical absorption by the sample via excited triplet state absorption may play a leading role in the limiting property.