Suresh, Vettoor V; Nandakumaran, V M(World Scientific Publishing Company, 1990)
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Abstract:
Electron-phonon interaction is considered within the framework of the fluctuating
valence of Cu atoms. Anderson's lattice Hamiltonian is suitably modified to take this into
account. Using Green's function technique tbe possible quasiparticle excitations' are
determined. The quantity 2delta k(O)/ kB Tc is calculated for Tc= 40 K. The calculated values
are in good agreement with the experimental results.
Sreekumar, J; Nandakumaran, V M(World Scientific Publishing Company, 1990)
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Abstract:
Large amplitude local density fluctuations in a thin superfluid He film is considered. It is shown that these large amplitude fluctuations travel and behave like "quasi-solitons" under collision, even when the full nonlinearity arising from the Van der Waals potential is taken into account.
Reethamma, Thomas; Nampoori, V P N(Elsevier, 1990)
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Abstract:
Fluorescence of BaS: Sm phosphor has been studied using a pulsed Nitrogen laser (337.1 nm) as the excitation source. The spectrum consists of a broad band in the region 540–660nm superposed by the characteristic Sm3+ lines. Energy level splitting pattern of Sm3+ due to crystal field effects has been calculated and relevent field parameters are evaluated. Analysis shows that Sm3+ takes up Ba2+ substitutional sites.
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.
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.
Aanandan,C K; Mohanan, P; K G Nair(IEEE Journals/ Transactions (USA), 1990)
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Abstract:
A microstrip antenna with large bandwidth is developed
using a parasitic technique . Compared to the available
wide-baud antennas,the proposed antenna structure is very
compact and gives a lessdistorted radiation pattern with frequency .
An impedance bandwidth,eight times that of a conventional patch
antenna of the same size, Isachieved. The concept of coupled microstrip
line model Is extended fortheoretical interpretation of the impedance loci
Sathy, P; Reji, Philip; Nampoori, V P N; Vallabhan, C P G(Elsevier, January 1, 1990)
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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.
Ambika, G; Nandakumaran, V M(Current Science, January 25, 1990)
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Abstract:
We discuss how the presence of frustration brings about
irregular behaviour in a pendulum with nonlinear
dissipation. Here frustration arises owing to
particular choice of the dissipation. A preliminary
numerical analysis is presented which indicates the transition
to chaos at low frequencies of the driving force.
Sathy, P; Reji, Philip; Nampoori, V P N; Vallabhan, C P G(Springer, June , 1990)
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Abstract:
Experimental method for measuring photoacoustic(PA) signals generated by a pulsed laser beam in liquids is described. The pulsed PA technique is found to be a convenient and accurate method for determination of quantum yield in fluorescent dye solutions. Concentration dependence of quantum yield of rhodamine 6G in water is studied using the above method. The results indicate that the quantum yield decreases with increase in concentration in the quenching region in agreement with the existing reports based on radiometric measurements.
This paper discusses the salient features associated with the variation in the BODs
and dissolved oxygen concentration in the Kadinamkulam Kayal based on fortnightly
data from two selected stations from October1987toSeptember1988.The BODs ranged
from 5.76 to 24.39 mg/l in the surface water and from 4.96 to 22.60mg!1 in the bottom
waterat station-l whereas at station-2, it ranged from 0 to 3.74mg/1 in the surface water
and from 0 to 3.40 mg!l in the bottom water. The dissolved oxygen concentration
ranged from 0 to 0.72 mglI in the surface water and from 0 to 0.42 mg!l in the bottom
waterat station-I, At station-2 it ranged from 2.69 to 6.21mg!1 in the surface waterand
from 1.97 to 5.74 mg!1 in the bottom water. The pre-monsoom period showed the
highest BODsof 16.68mg!I while the monsoon period showed the lowest of 0.61 mg!I.
The dissolved oxygen concentration reached its peak during the monsoon period (5.52
mg/I). Long spells of anoxic condition during the post and pre-monsoon periods was
a characteristic feature of the retting zone
Description:
MAHASAGAR
Vol.23, No.2 (December), 1990, pp. 95-101
Ambika, G; Nandakumaran, V M; Babu Joseph,K(World Scientific Publishing Company, 1991)
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Abstract:
We consider a resistively shunted Josephson junction with a resistance that depends inversely on voltage. It is shown that such a junction in the underdamped case can give rise to extremely long-lived metastable states even in the absence of external noise. We investigate numerically this metastable state and its transition to a chaotic state. The junction voltages corresponding to these states are studied.
Jayaraj, M K; Vallabhan, C P G(Thin Solid Films, 1991)
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Abstract:
The dielectric properties of electron beam evaporated Sm2O3 films have been
investigated in the frequency range from 1 kHz to 1 MHz at various temperatures
(300 K-453 K). The dielectric constant is found to depend on film thickness and it
attains a constant value beyond 1000 A. The present electron beam evaporated
Sm2O3 films have a high dielectric constant of 43. The frequency dependence of
and tan teeta at various temperatures is also studied.
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.
The design and development of an L-band printed dipole antenna.
optimized for wide-band applications near first resonance, is reported.
This design has achieved more than 48% impedance bandwidth
(VSWR 2:1), without degrading its overall radiation efficiency
K G Nair; Mohanan, P; Stephen, Rodrigues(Department of Electronics, 1991)
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Abstract:
Design and development of a new feed -horn antenna
with low sidelobe levels is reported . The E-walls of this
antenna are fabricated with low -loss dielectric substrate , periodically
loaded with thin conducting strips . The antenna is found
to be simulating the radiation characteristics of metallic corrugated
horns . This can be an ideal substitute for metallic corrugated
horns with added advantages like light -weight and low
production cost.
Design and development of a new feed -horn antenna
with low sidelobe levels is reported . The E-walls of this
antenna are fabricated with low -loss dielectric substrate ,
periodicallyloaded with thin conducting strips . The antenna
is found to be simulating the radiation characteristics of metallic
Corrugated horns . This can be an ideal substitute for metallic
Corrugated horns with added advantages like light -weight and low
production cost
Ponnachan,P T C; Paulose,C S; Panikkar,K R(Department of Biotechnology, 1991)
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Abstract:
Alloxan induced diabetic animal model was
sed to evaluate the potential antidiabetic effect of
ie aqueous leaf extract of Aegle marmelose. Insuinjection
and oral treatment of Aegle marmelose
of extract to the alloxan induced rats maintained
;e animal weight near to the control rats whereas
,,ere was a significant decrease in weight in alloxan
•duced rats. Insulin injection and oral treatment
the leaf extract reversed the decrease of protein
)ntent in all the organs studied except the pancas.
Glucose level was maintained near to the co-
:rol levels in the insulin injected and leaf extract
Bated alloxan diabetic rats. A significant increased
ucose tolerance was observed in animals orally
ven the leaf extract prior to the experiment. The
suits indicate that there is an increased utilization
glucose in the Aegle marmelose leaf extract treed
rats.
Santhakumari, N C; Vallabhan, C P G(Elsevier, April , 1991)
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Abstract:
dc and ac electrical conductivities, dielectric constant and dielectric loss factor in single crystals of ethylenediammonium dinitrate (EDN) have been measured axiswise as a function of temperature. All the above properties exhibit anomalous variations at 404 K thereby confirming the occurence of a phase transition in EDN at this temperature. Electrical conductivity parameters have been evaluated and possible conduction mechanisms are discussed. The role of protons in electrical trasport phenomenon is established by chemical analysis.
Sasi Kumar, P R; Padmaja, G; Ravi Kumar, A V; Nampoori, V P N; Vallabhan, C P G(Springer, April , 1991)
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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.