Radhakrishnan, P; V P N Nampoori; Girijavallabhan, C P; Sajan, D George(Physical Review, American Physical Society, 2003)
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Abstract:
In this paper, we report the in-plane and cross-plane measurements of the thermal diffusivity of double
epitaxial layers of n-type GaAs doped with various concentrations of Si and a p-type Be-doped GaAs layer
grown on a GaAs substrate by the molecular beam epitaxial method, using the laser-induced nondestructive
photothermal deflection technique. The thermal diffusivity value is evaluated from the slope of the graph of the
phase of the photothermal deflection signal as a function of pump-probe offset. Analysis of the data shows that
the cross-plane thermal diffusivity is less than that of the in-plane thermal diffusivity. It is also seen that the
doping concentration has a great influence on the thermal diffusivity value. Measurement of p-type Be-doped
samples shows that the nature of the dopant also influences the effective thermal diffusivity value. The results
are interpreted in terms of a phonon-assisted heat transfer mechanism and the various scattering process
involved in the propagation of phonons
Girijavallabhan, C P; Radhakrishnan, P; Nampoori, V P N; Sajan, D George(Physical Review, American Physical Society, October 16, 2003)
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Abstract:
In this paper, we report the in-plane and cross-plane measurements of the thermal diffusivity of double
epitaxial layers of n-type GaAs doped with various concentrations of Si and a p-type Be-doped GaAs layer
grown on a GaAs substrate by the molecular beam epitaxial method, using the laser-induced nondestructive
photothermal deflection technique. The thermal diffusivity value is evaluated from the slope of the graph of the
phase of the photothermal deflection signal as a function of pump-probe offset. Analysis of the data shows that
the cross-plane thermal diffusivity is less than that of the in-plane thermal diffusivity. It is also seen that the
doping concentration has a great influence on the thermal diffusivity value. Measurement of p-type Be-doped
samples shows that the nature of the dopant also influences the effective thermal diffusivity value. The results
are interpreted in terms of a phonon-assisted heat transfer mechanism and the various scattering process
involved in the propagation of phonons.
Nibu, A George; Vallabhan, C P G; Nampoori, V P N; Radhakrishnan, P(Optical Society of America, August , 2002)
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Abstract:
Photothermal beam deflection studies were carried out with GaAs epitaxial double layers grown on semi-insulating GaAs substrates. The impurity densities in thin epitaxial layers were found to influence the effective thermal diffusivity of the entire structure.
George, S D; Radhakrishnan, P; Nampoori, V P N; Vallabhan, C P G(Springer-Verlag, 2003)
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Abstract:
Laser induced transverse photothermal deflection
technique has been employed to determine the thermal parameters
of InP doped with Sn, S and Fe as well as intrinsic
InP. The thermal diffusivity values of these various samples
are evaluated from the slope of the curve plotted between the
phase of photothermal deflection signal and pump-probe offset.
Analysis of the data shows that heat transport and hence
the thermal diffusivity value, is greatly affected by the introduction
of dopant. It is also seen that the direction of heat flow with
respect to the plane of cleavage of semiconductor wafers influences
the thermal diffusivity value. The results are explained in
terms of dominating phonon assisted heat transfer mechanism in semiconductors.
Usha, John; Rajappan Nair, K P(Cochin University of Science & Technology, July , 2006)
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Abstract:
Photothermal effect refers to heating of a sample due to the absorption of
electromagnetic radiation. Photothermal (PT) heat generation which is an example of
energy conversion has in general three kinds of applications. 1. PT material probing
2. PT material processing and 3. PT material destruction. The temperatures involved
increases from 1-. 3. Of the above three, PT material probing is the most important
in making significant contribution to the field of science and technology.
Photothermal material characterization relies on high sensitivity detection techniques
to monitor the effects caused by PT material heating of a sample. Photothermal
method is a powerful high sensitivity non-contact tool used for non-destructive
thermal characterization of materials. The high sensitivity of the photothermal
methods has led to its application for analysis of low absorbance samples. Laser
calorimetry, photothermal radiometry, pyroelectric technique, photoacoustic
technique, photothermal beam deflection technique, etc. come under the broad class
ofphotothermal techniques. However the choice of a suitable technique depends upon
the nature of the sample, purpose of measurement, nature of light source used, etc.
The present investigations are done on polymer thin films employing photothermal
beam deflection technique, for the successful determination of their thermal
diffusivity. Here the sample is excited by a He-Ne laser (A = 6328...\ ) which acts as
the pump beam. Due to the refractive index gradient established in the sample surface
and in the adjacent coupling medium, another optical beam called probe beam (diode
laser, A= 6500A ) when passed through this region experiences a deflection and is
detected using a position sensitive detector and its output is fed to a lock-in amplifier
from which the amplitude and phase of the deflection can be directly obtained. The
amplitude and phase of the signal is suitably analysed for determining the thermal
diffusivity.The production of polymer thin film samples has gained considerable
attention for the past few years. Plasma polymerization is an inexpensive tool for
fabricating organic thin films. It refers to formation of polymeric materials under the
influence of plasma, which is generated by some kind of electric discharge. Here
plasma of the monomer vapour is generated by employing radio frequency (MHz)
techniques. Plasma polymerization technique results in homogeneous, highly
adhesive, thermally stable, pinhole free, dielectric, highly branched and cross-linked
polymer films. The possible linkage in the formation of the polymers is suggested by
comparing the FTIR spectra of the monomer and the polymer.Near IR overtone investigations on some organic molecules using local mode
model are also done. Higher vibrational overtones often provide spectral
simplification and greater resolution of peaks corresponding to nonequivalent X-H
bonds where X is typically C, N or O. Vibrational overtone spectroscopy of
molecules containing X-H oscillators is now a well established tool for molecular
investigations. Conformational and steric differences between bonds and structural
inequivalence ofCH bonds (methyl, aryl, acetylenic, etc.) are resolvable in the higher
overtone spectra. The local mode model in which the X-H oscillators are considered
to be loosely coupled anharmonic oscillators has been widely used for the
interpretation of overtone spectra. If we are exciting a single local oscillator from the
vibrational ground state to the vibrational state v, then the transition energy of the
local mode overtone is given by .:lE a......v = A v + B v2
• A plot of .:lE / v versus v will
yield A, the local mode frequency as the intercept and B, the local mode diagonal
anharmonicity as the slope. Here A - B gives the mechanical frequency XI of the
oscillator and B = X2 is the anharmonicity of the bond. The local mode parameters XI
and X2 vary for non-equivalent X-H bonds and are sensitive to the inter and intra
molecular environment of the X-H oscillator.
Description:
Department of Physics,
Cochin University of Science and Technology
Suma, C.S; Dr. Manoj, N.(Cochin University of Science and Technology, June 14, 2016)
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Abstract:
The thesis entitled “Photovoltaic and nonlinear optical studies of a few Donor-π-Acceptor molecules with s-triazine core” embodies the results of the investigations carried out to study unsymmetrically substituted s-Triazine cored starburst donor – acceptor systems with a bipodal acceptor/anchoring group design. The thesis opens with a review on the application of organic donor-acceptor systems in photovoltaics with special emphasis on applications in dye sensitised solar cells. The review also briefly discusses the application of such systems in the development of nonlinear optical materials.The unique structure of s-triazine do not permit direct coupling between the donor and acceptor moieties and this has been used as an effective tool for tuning HOMO and LUMO energy levels of such donor acceptor molecules. The effect of nature of the -bridge and the acceptor groups on the photovoltaic properties was studied and the results are presented in chapters 2, 3 and 4. Among the three types of -bridges studied, thiophene served as the best in terms of improving absorption spectral properties. Thiophene bridged dyes (DTT-CYA, DTT-RHA, DTT-BA and DTT-TBA) showed better coverage of the solar spectrum. Photovoltaic properties of these dyes were studied by constructing sandwhich model dye sensitized solar cells with nanocryasalline thin film of TiO2 on FTO coated with the respective dye as the photoanode, I-/I3- and Br-/Br3- as the redox couple/electrolyte and a platinized FTO as the cathode. The cell parameters and the photoconversion efficiency calculated show that the thiophene bridged dyes when used with Br-/Br3- as the redox couple/electrolyte have the optimal performance
Nampoori, V P N; Radhakrishnan, P; Girijavallabhan, C P; Kumar, G A; Thomas, J; Unnikrishnan, N V; George, N(Journal of Materials Science ,Kluwer Academic Publishers, 2000)
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Abstract:
Physical and optical properties of various free base and metallic phthalocyanine (Pc) doped
glass matrix are reported for the first time. Absorption spectral measurements of H2Pc,
MnPc, NiPc, CoPc, CuPc, MoOPc, ZnPc and FePc doped borate glass matrix have been
made in the 200–1100 nm region and the spectra obtained are analyzed in the 2.1–6.2 eV
region to obtain the optical band gap (Eg) and the width of the band tail (Et). Other
important optical and physical parameters viz. refractive index (n), molar extinction
coefficient ("), density (½), glass transition temperature (Tg), molecular concentration (N ),
polaron radius (rp), intermolecular separation (R), molar refractivity (Rm) are also reported.
Radhakrishnan, P; Nampoori, V P N; Girijavallabhan, C P; Kumar, G A; Thomas, J; Unnikrishnan, N V; George, N(Journal of Materials Science ,Kluwer Academic Publishers, 2000)
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Abstract:
Physical and optical properties of various free base and metallic phthalocyanine (Pc) doped
glass matrix are reported for the first time. Absorption spectral measurements of H2Pc,
MnPc, NiPc, CoPc, CuPc, MoOPc, ZnPc and FePc doped borate glass matrix have been
made in the 200–1100 nm region and the spectra obtained are analyzed in the 2.1–6.2 eV
region to obtain the optical band gap (Eg) and the width of the band tail (Et). Other
important optical and physical parameters viz. refractive index (n), molar extinction
coefficient ("), density (½), glass transition temperature (Tg), molecular concentration (N ),
polaron radius (rp), intermolecular separation (R), molar refractivity (Rm) are also reported.
Girijavallabhan, C P; Radhakrishnan, P; V P N Nampoori; Kumar, G A; Thomas, J; Unnikrishnan, N V; George, N(Journal of Materials Science ,Kluwer Academic Publishers, 2000)
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Abstract:
Physical and optical properties of various free base and metallic phthalocyanine (Pc) doped
glass matrix are reported for the first time. Absorption spectral measurements of H2Pc,
MnPc, NiPc, CoPc, CuPc, MoOPc, ZnPc and FePc doped borate glass matrix have been
made in the 200–1100 nm region and the spectra obtained are analyzed in the 2.1–6.2 eV
region to obtain the optical band gap (Eg) and the width of the band tail (Et). Other
important optical and physical parameters viz. refractive index (n), molar extinction
coefficient ("), density (½), glass transition temperature (Tg), molecular concentration (N ),
polaron radius (rp), intermolecular separation (R), molar refractivity (Rm) are also reported
Narayana Pillai, V; Dr.Murthy, A V S(Cochin University of Science And Technology, 1982)
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Abstract:
The present study is aimed at observing the variations, in
space and time, of see of the important hydrographic parameters such
as sea water temperature, salinity and Resolved oxygen within the
coastal waters along the south-west coast of Indiametween Ratnagiri
(17°OO*N,73°20'E) and cape comorin ( 8°10'N,77°30*E). Specific data
relating to the process of upwelling and sinking was collected mainly
to evaluate the extent and intensity of the vertical mixing processes
active in the area under study. The study also attempted possible correlations between the observed parameters and the occurrence and migrations of some of the major pelagic fishery resources such as sardine,mackerel and anchovy in the area under study
Description:
School of marine sciences, Cochin University of Science And Technology
Reshmi, R; Dr.Sugunan, S(Cochin University of Science and Technology, September , 2009)
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Abstract:
Biotechnology is currently considered as a useful altemative to conventional process technology in industrial and catalytic fields. The increasing awareness of the need to create green and sustainable production processes in all fields of chemistry has stimulated materials scientists to search for innovative catalysts supports. lmmobilization of enzymes in inorganic matrices is very useful in practical applications due to the preserved stability and catalytic activity of the immobilized enzymes under extreme conditions. Nanostructured inorganic, organic or hybrid organic-inorganic nanocomposites present paramount advantages to facilitate integration and miniaturization of the devices (nanotechnologies), thus affording a direct connection between the inorganic, organic and biological worlds. These properties, combined with good chemical stability, make them competent candidates for designed biocatalysts, protein-separation devices, drug delivery systems, and biosensors Aluininosilicate clays and layered double hydroxides, displaying, respectively, cation and anion exchange properties, were found to be attractive materials for immobilization because of their hydrophilic, swelling and porosity properties, as well as their mechanical and thermal stability.The aim of this study is the replacement of inorganic catalysts by immobilized lipases to obtain purer and healthier products.Mesocellular silica foams were synthesized by oil-in-water microemulsion templating route and were functionalized with silane and glutaraldehyde. " The experimental results from IR spectroscopy and elemental analysis demonstrated the presence of immobilized lipase and also functionalisation with silane and glutaraldehyde on the supports.The present work is a comprehensive study on enzymatic synthesis of butyl isobutyrate through esterification reaction using lipase immobilized onto mesocellular siliceous foams and montmorillonite K-10 via adsorption and covalent binding. Moreover, the irnrnobil-ization does not modify the nature of the kinetic mechanism proposed which is of the Bi-Bi Ping—Pong type with inhibition by n-butanol. The immobilized biocatalyst can be commercially exploited for the synthesis of other short chain flavor esters.
Mesocellular silica foams (MCF) were synthesized by microemusion templating method via two different routes (hydrothermal and room temperature). and were functionalized with silane and glutaraldehyde. Candida rugosa lipase was adsorbed onto MCF silica and clay using heptane as the coupling medium for reactions in non-aqueous media. I From XRD results, a slight broadening and lowering of d spacing values after immobilization and modification was observed in the case of MCF 160 and MCF35 but there was no change in the d-spacing in the case of K-10 which showed that the enzymes are adsorbed only on the external surface. This was further confirmed from the nitrogen adsorption measurements
Description:
Department of Applied Chemistry, Cochin University of Science and Technology
Jeena,Augustine; Dr.Sarita,Bhat G(Cochin University of Science and Technology, July 19, 2012)
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Abstract:
This thesis entitled Physicochemical and molecular characterization of bacteriophages ΦSP-1and ΦSP-3, specific for pathogenic Salmonella and evaluation of their potential as biocontrol agent . Salmonella were screened using standard methodologies from various environmental samples including chicken caecum. Salmonella strains, which were previously isolated and stocked in the lab, were also included in this study as host, for screening Salmonella specific lytic phages. The Salmonella strain in this study designated as S49 which helped in phage propagation by acting as host bacteria was identified as Salmonella enterica subsp. enterica by 16S rRNA gene analysis and serotyping .
A total of three Salmonella specific phage named as ΦSP-1, ΦSP-2 and ΦSP-3 were isolated from chicken intestine samples via an enrichment protocol employing the double agar overlay method. ΦSP-1 and ΦSP-3 showing consistent lytic nature were selected for further study and were purified by repeated plating after picking of single isolated plaques from the lawns of Salmonella S49 plates. Both the phages produced small, clear plaques indicating their lytic nature. ΦSP-1 and ΦSP-3 were concentrated employing PEG-NaCl precipitation method before further characterization.
The focus of present study was to isolate, characterize and verify the efficacy of lytic bacteriophages against the robust pathogen Salmonella, capable of surviving under various hostile conditions. Two phages, ΦSP-1 and ΦSP-3, belonging to two families, Podovoridae and Siphoviridae were isolated.
Description:
Department of Biotechnology, Cochin University of Science and Technology
Santhosh Kumar, G(Cochin University of Science And Technology, September 29, 2013)
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Abstract:
Science is search for the laws of underlying phenomena of the nature. Engineering
constructs the nature as we wish. Interestingly the huge engineering infrastructure like world
wide web has grown in such a complex structure such that we need to see the fundamental
science behind the structure and behaviour of these networks. This talk covers the science
behind the complex networks like web, biological, social etc. The talk aim to discuss the
basic theories that govern the static as well as the dynamics of such interesting networks