Padmaja, G; Ravi Kumar, A V; Vidyalal, V; Radhakrishnan, P; Nampoori, V P N; Vallabhan, C P G(Springer, June , 1991)
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Abstract:
The spectroscopic analysis of the emission from the plasma produced by irradiating a highT c superconducting GdBa2Cu3O7 target with a high power Nd:YAG laser beam shows the existence of the bands from different oxides in addition to the lines from neutrals and ions of the constituent elements. The spectral emissions by oxide species in laser-induced plasma show considerable time delays as compared to those from neutral and ionic species. Recombination processes taking place during the cooling of the hot plasma, rather than the plasma expansion velocities, have been found to be responsible for the observed time delays in this case. The decays of emission intensities from various species are found to be non-exponential.
Rani, Joseph(Huthig & Wepf Verlag, Basel, June 5, 1991)
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Abstract:
Antioxidants were attached to hydroxy-terminated liquid natural rubber by modified
Friedel-Crafts alkylation reaction using anhydrous zinc chloride as catalyst. The rubber
bound antioxidants were found to be less volatile and less extractable compared to
conventional antioxidants. The bound antioxidants were tried both in latex compounds
and dry rubber compounds. The vulcanizates showed improved ageing resistance
compared to vulcanizates based on conventional antioxidants.
Sunil,K Narayanankutty(Elsevier Science Publishers Ltd., August 29, 1991)
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Abstract:
The thermal degradation of short kevlar fibre-thermoplastic polyurethane
(TPU) composites has been studied by Thermogravimetric Analysis (TGA)
and Differential Scanning Calorimetry (DSC). TGA showed that the thermal
degradation of TPU takes place in two steps with peak maxima (T1max and
T2ma,) at 383°C and 448°C, respectively. In the presence of 10-40 phr of short
kevlar fibres, T1_ and T2max were shifted to lower temperatures. The
temperature of onset of degradation was increased from 245 to 255°C at 40
parts per hundred rubber (phr) fibre loading. Kinetic studies showed that the
degradation of TPU and kevlar-TPU composite follows first-order reaction
kinetics. The DSC study showed that there is an improvement in thermal
stability of TPU in the presence of 20 phr of short kevlar fibres.
Amritkar, R E; Gade, P M; Gangal, A D; Nandakumaran, V M(The American Physical Society, September , 1991)
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Abstract:
We consider the stability properties of spatial and temporal periodic orbits of one-dimensional coupled-map lattices. The stability matrices for them are of the block-circulant form. This helps us to reduce the problem of stability of spatially periodic orbits to the smaller orbits corresponding to the building blocks of spatial periodicity, enabling us to obtain the conditions for stability in terms of those for smaller orbits.
Thomas, Baby; Sathianandan, K; Nampoori, V P N; Vallabhan, C P G; Ramachandran, T(American Institute of Physics, September , 1991)
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Abstract:
A high power Nz laser of the double-Blumlein type having a modified gas flow system,
electrode configuration, and discharge geometry with minimum inductance is described. By
incorporating a triggere’d-pressurized spark gap switch, arc-free operation was achieved
for a wide E/P range. The device gives a peak power in excess 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 dependence of output power on parameters such as operating pressure, voltage,
and repetition rate are discussed.
Sangster,A J(Microwave and Optical Technology Letters, September , 1991)
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Abstract:
A new microstrip antenna element is described which exhibits polarization
agility. This is achieved by employing a T-slot radiator
which is driven by the edge fields of a balanced microstrip line. The
balanced line can support two propagating modes. namely. an even
mode and an odd mode, and be switching between these modes. the
orthogonal arms of the T-slot radiator are separately excited thus
forming orthogonally polarized radiated fields. A nucrostrip patch
antenna, which displays polarization agility using the sane mechanism,
is also described
Ravi Kumar, A V; Padmaja, G; Radhakrishnan, P; Nampoori, V P N; Vallabhan, C P G(Springer, October , 1991)
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Abstract:
The acoustic signals generated in solids due to interaction with pulsed laser beam is used to determine the ablation threshold of bulk polymer samples of teflon (polytetrafluoroethylene) and nylon under the irradiation from a Q-switched Nd:YAG laser at 1.06µm wavelength. A suitably designed piezoelectric transducer is employed for the detection of photoacoustic (PA) signals generated in this process. It has been observed that an abrupt increase in the amplitude of the PA signal occurs at the ablation threshold. Also there exist distinct values for the threshold corresponding to different mechanisms operative in producing damages like surface morphology, bond breaking and melting processes at different laser energy densities.
Mohanan, P; K G Nair; Stephen, Rodrigues(Department of Electronics, November , 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.
Sunil,K Narayanankutty(Gordon and Breach Science Publishers, December 10, 1991)
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Abstract:
Tear and wear properties of short kevlar fiber, thermoplastic polcurethane (TPU) composite with
respect to fiber loading-and fiber onentation has been studied and the fracture surfaces were examined
under scanning electron microscope (SEM). Tear strength first decreased up to 20 phr fiber loading
and then gradually increased with increasing fiber loading. Anisotropy in tear strength was evident
beyond a fiber loading of 20 phr. Tear fracture surface of unfilled TPU showed sinusoidal folding
characteristics of high strength matrix. At low fiber loading the tear failure was mainly due to fibermatrix failure whereas at higher fiber loading the failure occurred by fiber breakage. Abrasion loss
shows a continuous rise with increasing fiber loading, the loss in the transverse orientation of fibers
being higher than that in the longitudinal orientation. The abraded surface showed lone cracks and
ridges parallel to the direction of abrasion indicating an abrasive wear mechanism. In the presence of
fber the abrasion loss was mainly due to fiber low.
Rani, Joseph; Jayamma,Francis; George,K E(Pergamon Press Ltd, December 18, 1991)
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Abstract:
The effects of modifying blends of poly(vinyl chloride) (PVC) with linear low density
polyethylene (LLDPE) by means of acrylic acid, maleic anhydride, phenolic resins and p-phenylene
diamine were investigated. Modification by acrylic acid and maleic anhydride in the presence of dicumyl
peroxide was found to be the most useful procedure for improving the mechanical behaviour and adhesion
properties of the blend. The improvement was found to be due mainly to the grafting of the carboxylic
acid to the polymer chains; grafting was found to be more effective in LLDPE/PVC blends than in pure
LLDPE.
Suresh, Vettoor V; Nandakumaran, V M(Physica C,Elsevier Science, 1992)
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Abstract:
The density of states and the low temperature specific heat of higb-Tc superconductors are calculated in a functional integral formalism using the slave boson technique. The manybody calculation in a saddle point approximation shows that the Iow energy
sector is dominated by 3 single band. The calculated values of density of states are in good agreement with experimental results.
Reji, Philip; Sathy, P; Nampoori, V P N; Jacob, Philip; Vallabhan, C P G(IOP, 1992)
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Abstract:
Two-photon absorption in methanol solutions of Rhodamine 6G is investigated by photoacoustics using the second harmonic of a pulsed Nd:YAG laser. Competition between one-photon and two-photon processes is observed, depending critically on the sample concentration and input light flux.
Radhakrishnan, P; Nampoori, V P N; Vallabhan, C P G(Indian Journal of Physics, 1992)
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Abstract:
A simple fiber optic concentration sensor based on the coupling of light f rom one
fiber to another through a solution is discussed. The operational characteristics of the sensor are
illustrated by taking the solutions of potassium permanganate and fast green dye as samples.The extrinsic type sensor described here shows linearity at lower concentrations.
The effect of an external flaw on the tensile strength of short kevlar fiber-thermoplastic
composites has been studied with respect to fiber content, fiber orientation,
location of the external flaw, and the temperature of test. The composites showed
a three-step reduction in tensile strength with increasing flaw size. The critical flaw-length
region was shifted to higher flaw-size levels with increasing fiber content. With increasing
temperature, the critical flaw length was increased in the case of unfilled TPU, whereas it
remained more or less constant in the case of short kevlar fiber-filled-TPU composite.
Thomas, Baby; Nampoori, V P N(Solid State Communications, 1992)
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Abstract:
A method of preparation of strontium sulphide phosphors doped
with europium is given. Nitrogen laser excited fluorescence emission
spectra of these phosphors in the visible region are recorded. A band
with line structure in the region 350-430 nm and a new broad band at
460 nm are observed. The splitting pattern for the 6p levels of Eu 2+ are
given.
Somatic embryos were induced from scutellar callus of immature zygotic embryos of T aestivum cv.
Chinese Spring. Observations on precociously germinating somatic embryos revealed that: (i) In the initial
stages the coleoptile is split, exposes the shoot apex and forms a green trichomatous leafy structure.
In the germinating zygotic embryo, the coleoptile is tubular, (ii) Unlike what has been inferred earlier the
leafy structure is the coleoptile and not the scutellum, (iii) Bipolarity of the embryoid is established later
when root develops at the basal end.
Hunagund,P V; Jose,K A; Mohanan, P; Nair, K G(Indian Journal of Radio & Space Physics, February , 1992)
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Abstract:
Results of exhaustive study of the effect of metallic flanges on H-plane radiation characteristics of V-slot
waveguide antenna are presented . It has been established that the beam can be sharpened or broadened by
varying the flange angle . The adjustment of the flange angle and flange width would further improve the
radiation pattern , yielding optimum efficiency from the flanged system
The effect of various processing parameters, such as nip gap, friction ratio
and roll temperature, on the tensile properties of short Kevlar aramid
fibre-thermoplastic polyurethane composite has been investigated and the tensile
and tear fracture surfaces have been characterised using a scanning electron microscope.
A nip gap of 0.45 mm, a friction ratio of 1.15 and a roll temperature of 62°C
was found to give optimum mechanical properties. Scanning electron microscopy
study revealed a higher extent of fibre orientation in the milling direction in the
above condition.
Plants were regenerated from callus induced from leaf disc explants of a tomato F, hybrid heterozygous
for three marker loci (a), without anthocyanin (aw), and hairless (hl). Regenerants
were studied for somaclonal variation at the phenotypic level by scoring for variation in the marker loci,
and at the DNA level by probing geomic DNA blots with a chlorophyll a/b binding protein (Cab-3C)
cDNA sequence. While no variation was observed at the phenotypic level in over 950 somaclones studied,
DNA polymorphism for the Cab locus could be detected in two out of 17 somaclones tested. Tissue
culture induced variation at the phenotypic level for specific loci is very low (less than 0.001 for a, awor
hl) but DNA sequence changes are induced at much greater frequency (- 0.1 for a multicopy gene family
such as Cab).