Santhakumari, N C; Vallabhan, C P G(Elsevier, May , 1992)
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Abstract:
D.C. and a.c. electrical conductivities, dielectric constant and dielectric loss factor in single crystals of ethylenediammonium sulphate, (H3NCH2CH2NH3)(SO4), have been measured axiswise as a function of temperature. Anomalous variations in all the above properties at 480 K indicate the occurrence of a phase transition in the above material at this temperature. The existence of such a phase transition is also confirmed by DSC measurements. Electrical conductivity results are analysed and the activation energies of conduction at different temperature regions have been evaluated from the logσ vs 103T−1 plot. Possible mechanisms for the electrical conduction process are discussed, the available results being in favour of a proton transport model.
Joseph, P M; Dr.Saseendran Pillai, P R(Cochin University of Science & Technology, May , 1992)
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Abstract:
Systems which employ underwater acoustic energy
for observation or communication are called sonar systems. The active and passive sonars are the two
types of systems used for the detection and localisation
of targets in underwater. Active sonar involves the
transmission of an acoustic signal which, when reflected
from a target, provides the sonar receiver with a basis
for the detection and estimation. Passive sonar bases
its detection and estimation on sounds which emanate
from the target itself--Machinery noise, flow noise,
transmission from its own active sonar etc.Electroacoustic transducers are used in sonar
systems for the transmission and detection of acoustic
energy. The transducer which is used for the transmission
of acoustic energy is called projector and the
one used for reception is called hydrophone. Since a
single transducer is not sufficient enough for long
range and directional transmission, a properly distributed
array of transducers are to be used [9-11].The need and requirement for spatial processing
to generate the most favourable directivity patterns for
transducer systems used in underwater applications have
already been analysed by several investigators [12-21].The desired directivity pattern can be either generated
by the use of suitable focussing techniques or by an
array of non-directional sensor elements, whose arrangements,
spacing and the mode of excitation provide the
required radiation pattern or by the combination of
these.While computing
that
the directivity pattern, it is
assumed strength of the elements are
unaffected by
the
the
source
acoustic pressure at each source.
However, in closely packed a r r a y s , the acoustic interaction
effects experienced among the elements will
modify the behaviour of individual elements and in turn
will reduce the acoust ic source leve 1 wi t h respect to
the maximum t heoret i cal va 1ue a s well as degrade the
beam pa t tern. Th i s ef fect shou 1d be reduced in systems
that are intended to generate high acoustic power output
and unperturbed beam patterns [2,22-31].The work herein presented includes an approach
for designing efficient and well behaved underwater
transd~cer arrays, taking into account the acoustic
interaction effect experienced among the closely packed
multielement arrays.Architectural modifications
reducing the interaction effect
different radiating apertures.
Description:
Department of Electronics, Cochin University
of Science and Technology.
Rajasree, K; Ravikumar, A V; Radhakrishnan, P; Nampoori, V P N; Vallabhan, C P G(Springer, April , 1992)
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Abstract:
Photothermal deflection technique was used for determining the laser damage threshold of polymer samples of teflon (PTFE) and nylon. The experiment was conducted using a Q-switched Nd-YAG laser operating at its fundamental wavelength (1-06μm, pulse width 10 nS FWHM) as irradiation source and a He-Ne laser as the probe beam, along with a position sensitive detector. The damage threshold values determined by photothermal deflection method were in good agreement with those determined by other methods.
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.
The morphological and biochemical response of calli and seedlings of different
rice cultivars were compared under acid saline conditions. Calli of
both tolerant and sensitive varieties showed severe stress symptoms like
browning and necrosis, but the onset of stress symptoms was delayed in
Pokkali. Seedlings of Pokkali showed minimal stress symptoms in lower
salinities, and curling and senescence of older leaves in higher salinities
although plants revived on amelioration of stress. Seedlings of the other
varieties showed severe stress symptoms even at low salinities and plant
death at higher salinities. Salt stress induced accumulation of the putative
osmoprotectant proline in calli and seedlings of all varieties. Proline accumulation
was higher in sensitive varieties than in Pokkali. These results
indicate that proline accumulation is not directly correlated with salt
tolerance in rice.
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.
The self adhesion behaviour of thermoplastic polyurethane (TPU) in itself and its
composite with short Kevlar fibre with respect to contact time, temperature, pressure, and fibre
loading has been studied. The adhesion strength showed two linear increments of different slopes
with respect to the square root of time: with temperature and pressure of contact, the adhesion
strength was improved. The maximum strength was obtained with 20 phr of short fibre in only one of
the mating substrates in the peel test sample. The duration for wetting and diffusion was shifted to
longer time intervals with fibres loaded in both the substrates.
Sunil K Narayanankutty(John Wiley & Sons,Inc, 1992)
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Abstract:
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.