Elastic properties of sodium doped Lithium potassium sulphate, LiK0.9Na0.1SO4, crystal has been studied by
ultrasonic Pulse Echo Overlap [PEO] technique and are reported for the first time. The controversy regarding
the type of crystal found while growth is performed at 35 °C with equimolar fraction of Li2SO4H2O, K2SO4
and Na2SO4 has been resolved by studying the elastic properties. The importance of this crystal is that it
exhibits pyroelectric, ferroelectric and electro optic properties. It is simultaneously ferroelastic and
superionic. The elastic properties of LiK0.9Na0.1SO4 crystal are well studied by measuring ultrasonic velocity
in the crystal in certain specified crystallographic directions and evaluating the elastic stiffness constants,
compliance constants and Poisson’s ratios. The anisotropy in the elastic properties of the crystal are well
explained by the pictorial representation of the surface plots of phase velocity, slowness and linear
compressibility in a-b and a-c planes.
Vimala,George; Jacob, Philip(Department of Electronics, October , 2005)
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Abstract:
The present work is an attempt to probe the elastic properties in some dielectric ceramics, by using ultrasonic pulse echo overlap technique. The base Ba6-xSm8+2xTi18O54 and Ca5Nb2TiO12 are very important dielectrics ceramics used for microwave communication as well as for substrate materials. Ultrasonic is one of the most widely used and powerful techniques to measure elastic properties of solids. The ultrasonic technique is nondestructive in nature and the measurements are relatively straightforward to perform. One unique advantantage of the ultrasonic technique is that both static and dynamic properties can be measured simultaneously. The velocity and attenuation coefficients of the ultrasonic waves propagating through a medium are related to the microscopic structure of the material and they provide valuable information about the structural changes in the system. Among the various ultrasonic techniques, the pulse echo overlap method is the most accurate and precise one. In the present case the decreased elastic properties of Cas-XMg,Nb2TiO12 and Cas-,ZnNb2TiO12 ceramics can be attributed to their mixture phases beyond x = 1. Moreover, the abrupt change in elastic properties observed for x >1 can also be correlated to the structural transformation of the materials from their phase pure form to mixture phases for higher extent of substitution of the concerned material . Ca4(ANb2Ti)012 (A = Mg, Zn) is the strongest compound with the maximum values for elastic properties . This could be due to the possible substitution of Mg/Zn ions with lesser radius [25] than Ca2+ in perovskite B-site of Ca(Cali4Nb2i4Tili4) O3 material to contribute more ordering and symmetry to the system [20]. All other compositions (x > 1) contain mixed-phases and for such mixed-phase samples, the mechanical properties are difficult to explain.
The aim of the study was to investigate the relevance of e—learning in continuing education of
library professionals in the universities in Kerala. /55 part of a survey of library professionals in the
seven major Universities in Kerala to find their continuing education needs, it was found that
majority of the library professionals attend continuing education programmes (CEP) to be trained
in the latest technologies. Internet resources were the preferred mode of information source by
38.9 per cent of the library professionals. The importance of continuing education in developing
the competencies of library professionals is also stressed
Description:
E-Resources and E-Learning:Challenges and Opportunities ,University of Calicut
Santhosh Kumar, G(Cochin University of Science And Technology, June 23, 2010)
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Abstract:
Semantic Web: Software agents on the Semantic Web may use commonly agreed service
language, which enables co-ordination between agents and proactive delivery of learning
materials in the context of actual problems. The vision is that each user has his own
personalized agent that communicates with other agents.
Rajeev, Kumar K; Dr.Sathianandan, K(Cochin University of Science and Technology, June 20, 1989)
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Abstract:
A brief account of the several methods used for the production of thin films is presented in this Chapter. The discussions stress on the important methods used for the fabrication of a-si:H thin films. This review' also reveals ‘that almost all the general methods, like vacuum evaporation, sputtering,
glow discharge and even chemical methods are currently employed for the production of a-Si:H thin films. Each method has its own advantages and disadvantages. However, certain methods are generally preferred. Subsequently a detailed account of the method used here for the preparation of amorphous silicon thin films and their hydrogenation is presented. The metal chamber used for the electrical and dielectric measurements is also described. A brief mention is made-on the electrode
structure, film area and film geometry.
Description:
Division of Thin Film, Department
of Physics, Cochin University of Science and Technology
Jayaraj, M K(Institute of Materials Engineering Australasia Ltd, 2005)
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Abstract:
ZnGa2O4 spinel is a promising new UV transparent electronic conductor. Enhancing the electrical conductivity of this
potential oxide phosphor can make it a promising transparent conducting oxide. In this paper, we have investigated the
effects of processing and doping on the conductivity of semiconducting ZnGa2O4, particularly thin films. Crystalline
zinc gallate thin films have been deposited on fused quartz substrates employing the pulsed laser deposition (PLD)
technique at room temperature for an oxygen partial pressure of 0.1 Pa (0.001mbar). The films were found to be UV
transparent, the band gap of which shifted to 4.75eV on hydrogen annealing. The band gap of the oxygen stoichiometric
bulk powder samples (4.55eV) determined from diffuse reflection spectrum (DRS) shifted to 4.81eV on reduction in a
hydrogen atmosphere. The electrical conductivity improved when Sn was incorporated into the ZnGa2O4 spinel. The
conductivity of ZnGa2O4:Sn thin films was further improved on reduction.
Navil Kumar, R; Dr.Girijavallabhan,C P(Cochin University Of Science And Technology, June 28, 1989)
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Abstract:
In the present thesis a series of exhaustive
investigations have been carried out on a number of crystalline
samples with special reference tx> the jphase transitions
exhibited by them. These include single crystals
of pure, doped or deuterated specimens of certain ammonium
containing crystals viz., (NH )34H(SO4)2, (NH4)2HPO4,
(NH4)2Cr2O7 znui NH4H2PO4. ac/dc electrical conductivity,
dielectric constant, ionic thermocurrent as wwifil as photoacoustic
measurements have been carried out on most of
them over a wide range of temperature. In addition investigations
have been carried out in pure and doped single
crystals of NaClO3 and NaNO3 using ionic thermocurrent
measurements and these are presented here. Special attention
has been paid to reveal the mechanism of electrical conduction
in various phases of "these crystals and to evaluate
the different parameters involved in the conduction as well
as phase transition process.
The thesis contains ten chapters ‘
Description:
Department of Physics, Cochin
University of Science and Technology
Heterojunction diodes of n-type ZnO/p-type silicon (100) were fabricated by
12 pulsed laser deposition of ZnO films on p-Si substrates in oxygen ambient at
13 different pressures. These heterojunctions were found to be rectifying with a
14 maximum forward-to-reverse current ratio of about 1,000 in the applied
15 voltage range of -5 V to +5 V. The turn-on voltage of the heterojunctions was
16 found to depend on the ambient oxygen pressure during the growth of the ZnO
17 film. The current density–voltage characteristics and the variation of the
18 series resistance of the n-ZnO/p-Si heterojunctions were found to be in line
19 with the Anderson model and Burstein-Moss (BM) shift.
Syamaprasad, U; Vallabhan, C P G(Elsevier, May , 1981)
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Abstract:
Anomalous variations of d.c. electrical conductivity with temperature are observed in ammonium sulphate single crystals, suggesting a possible phase transition at 150°C. Measurements of thermally stimulated current also support these results. The mechanism of electrical conduction is explained on the basis of studies made on doped and quenched crystals.
Navil Kumar, R; Vallabhan, C P G(IOP Publishing, 1989)
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Abstract:
DC and AC electrical conductivity measurements in single crystals of diammonium hydrogen phosphate along the c axis show anomalous variations at 174, 246 and 416 K. The low-frequency dielectric constant also exhibits peaks exactly at these temperatures with a thermal hysteresis of 13 degrees C for the peak at 416 K. These specific features of the electrical properties are in agreement with earlier NMR second-moment data and can be identified with three distinct phase transitions that occur in the crystal. The electrical conductivity values have been found to increase linearly with impurity concentration in specimens doped with a specific amount of SO42- ions. The mechanisms of the phase transition and of the electrical conduction process are discussed in detail.
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.
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.
Syamaprasad, U; Dr.Girijavallabhan,C P(Cochin University of Science And Technology, December , 1981)
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Abstract:
The thesis aims to present the results of the
experimental investigations on the electrical properties like
electrical conductivity, dielectric constant and ionic thermo~
currents in certain ammonium containing ferroelectric crystals
viz. LiNH4SO4, (NH4)2SO4 and (NH4)5H(SO4)2. Special attention
has been paid in revealing the mechanisms of electrical conduction
in the various phases of these crystals and those asso~
ciated with the different phase transitions occurring in them,
by making studies on doped, quenched and deuterated crystals.
The report on the observation of two new phase transitions in
(NH4) S O2 and of a similar one in ( NH4 ) H (2SO4 ) are included. The relaxation mechanisms of the impurity-vacancy complexes and the space charge phenomena in pure and doped crystals of LiNH4SO4 and (NH4)2SO4 and the observation of a new type of ionic thermo-current viz. Protonic Thermo-Current (PTC) in these crystals are also presented here.
Description:
Department of Physics, Cochin University of Science and Technology
Abraham,P K; Dr.Sathianandan, K(Cochin University of Science and Technology, July , 1989)
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Abstract:
This thesis Entitled Electrical switching studies on the thin flims of polyfuran and polyacrylonitrile prepared by plasma polymerisation and vacuum evaporated amorphous silicon.A general introduction to the switching and allied phenomena is presented. Subsequently, developments of switching in thin films are described. The Mott transition is qualitatively presented. The working of a switching transitor is outlined and compared to the switching observed in thin films. Characteristic parameters of switching such as threshold voltage, time response to a, voltage pulse, and delay time are described. The various switching configurations commonly used are discussed. The mechanisms used to explain the switching behaviour like thermal, electrothermal and purely electronic are reviewed. Finally the scope, feasibility and the importance of polymer thin films in switching are highlighted.
Description:
Department of Physics, Division of Thin Film, Cochin University of Science and Tecnology
Dipyrromethene-Cu(II) derivatives possessing two dodecane alkyl chains have been used for the modification of gold
electrodes. Electroactive host molecules have been incorporated into a lipophilic dodecanethiol SAM deposited onto
gold electrodes through hydrophobic and van der Waals interactions (embedment technique). The presence of
dipyrromethene-Cu(II) redox centers on the electrode surface was proved by cyclic voltammetry and Osteryoung
square-wave voltammetry. The Au electrodes incorporating redox active Cu(II)-dipyrromethene SAMs were used for
the direct voltammetric determination of paracetamol in human plasma.
Girish Kumar,K; Joseph, Renjini(Taylor & Francis, June 1, 2009)
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Abstract:
A metalloporphyrin incorporated carbon paste sensor has been developed
for the determination of metronidazole benzoate (MTZB). Zn(II) complex
of 5,10,15,20-tetrakis (3-methoxy-4-hydroxy phenyl) porphyrin (TMHPP) was
used as the active material. The MTZB gave a well-defined reduction peak at
- 0.713V in 0.1 mol l -1 phosphate buffer solution of pH around 7. Compared
with bare carbon paste electrode (CPE), the TMHPP Zn(II) modified electrode
significantly enhanced the reduction peak current of MTZB as well as lowered
its reduction potential. Under optimum conditions the reduction peak current
was proportional to MTZB concentration over the range 1×10-3 mol1-1 to 1×10-5mol1-1. The detection limit was found to be 4.36×10-6mol1-1
. This
sensor has been successfully applied for the determination of MTZB in pharmaceutical
formulations and urine samples.
Girish Kumar,K; Thomas, D; Joseph, R; Issac, S; Lonappan, L(The Institution of Engineering and Technology, October 10, 2011)
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Abstract:
A differential pulse voltammetric sensor for the determination of tamsulosin hydrochloride (TAM) using multiwalled carbon nanotubes
(MWNTs)–Nafion-modified glassy carbon electrode (GCE) has been developed. MWNTs were dispersed in water with the help of Nafion
and were used to modify the surface of GCE via solvent evaporation. At MWNT-modified electrode, TAM gave a well-defined oxidation
peak at a potential of 1084 mV in 0.1 M acetate buffer solution of pH 5. Compared to the bare electrode, the peak current of TAM
showed a marked increase and the peak potential showed a negative deviation. The determination conditions, such as the amount of
MWNT–Nafion suspension, pH of the supporting electrolyte and scan rate, were optimised. Under optimum conditions, the oxidation
peak current was proportional to the concentration of TAM in the range 1 × 1023 M–3 × 1027 M with a detection limit of
9.8 × 1028 M. The developed sensor showed good stability, selectivity and was successfully used for the determination of TAM in pharmaceutical
formulations and urine samples