Harilal, S S; Issac, Riju C; Bindhu, C V; Nampoori, V P N; Vallabhan, C P G(Pramana, September , 1997)
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Abstract:
Time resolved optical emission spectroscopy is employed to study the expansion
dynamics of C2 species in a graphite plasma produced during the Nd : YAG ablation. At low laser
fluences a single peak distribution with low kinetic energy is observed. At higher fluences a twin
peak distribution is found. It has been noted that these double peak time of flight distribution splits
into a triple peak structure at distances >_ 17mm from the target surface. The reason for the
occurrence of multiple peak is due to different formation mechanisms of C2 species
Sunil Kumar, P G; Dr. Nandakumar, C G(Cochin University of Science and Technology, June , 2008)
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Abstract:
Warships are generally sleek, slender with V shaped sections and block
coefficient below 0.5, compared to fuller forms and higher values for commercial
ships. They normally operate in the higher Froude number regime, and the
hydrodynamic design is primarily aimed at achieving higher speeds with the
minimum power. Therefore the structural design and analysis methods are
different from those for commercial ships. Certain design guidelines have been
given in documents like Naval Engineering Standards and one of the new
developments in this regard is the introduction of classification society rules for
the design of warships.The marine environment imposes subjective and objective uncertainties
on ship structure. The uncertainties in loads, material properties etc.,. make
reliable predictions of ship structural response a difficult task. Strength, stiffness
and durability criteria for warship structures can be established by investigations
on elastic analysis, ultimate strength analysis and reliability analysis. For analysis
of complicated warship structures, special means and valid approximations are
required.Preliminary structural design of a frigate size ship has been carried out . A
finite element model of the hold model, representative of the complexities in the
geometric configuration has been created using the finite element software NISA.
Two other models representing the geometry to a limited extent also have been
created —- one with two transverse frames and the attached plating alongwith the
longitudinal members and the other representing the plating and longitudinal
stiffeners between two transverse frames. Linear static analysis of the three models have been carried out and each one with three different boundary
conditions. The structural responses have been checked for deflections and
stresses against the permissible values. The structure has been found adequate
in all the cases. The stresses and deflections predicted by the frame model are
comparable with those of the hold model. But no such comparison has been
realized for the interstiffener plating model with the other two models.Progressive collapse analyses of the models have been conducted for the
three boundary conditions, considering geometric nonlinearity and then
combined geometric and material nonlinearity for the hold and the frame models.
von Mises — lllyushin yield criteria with elastic-perfectly plastic stress-strain curve
has been chosen. ln each case, P-Delta curves have been generated and the
ultimate load causing failure (ultimate load factor) has been identified as a
multiple of the design load specified by NES.Reliability analysis of the hull module under combined geometric and
material nonlinearities have been conducted. The Young's Modulus and the shell
thickness have been chosen as the variables. Randomly generated values have
been used in the analysis. First Order Second Moment has been used to predict
the reliability index and thereafter, the probability of failure. The values have
been compared against standard values published in literature.
Description:
Department of Ship Technology,
Cochin University of Science and Technology
Sreekumar, Krishnapillai; Rajesh Krishnan, G(Eur. J. Org. Chem, August , 2008)
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Abstract:
This paper describes the first use of polystyrene-supported
poly(amidoamine) (PAMAM) dendrimers as heterogeneous
basic organocatalysts for carbon–carbon bond formation.
Polystyrene-supported PAMAM dendrimers of first, second
and third generations have been used as reusable base catalysts
in Knoevenagel condensations of carbonyl compounds
with active methylene compounds. The reactions proceed in short periods of time and with 100% selectivity. This novel
catalyst eliminates the use of aromatic and halogenated solvents,
as well as complex purification processes. The catalysts
can be recycled ten times.
Invertase was immobilized on acid activated montmorillonite via two independent procedures, adsorption and covalent binding. The immobilized enzymes were characterized by XRD, NMR and N2 adsorption measurements and their activity was tested in a fixed bed reactor. XRD revealed that the enzyme was situated on the periphery of the clay and the side chains of different amino acid residues were involved in intercalation with the clay matrix. NMR demonstrated that tetrahedral Al was linked to the enzyme during adsorption and the octahedral Al was involved during covalent binding. Secondary interaction of the enzyme with Al was also observed. N2 adsorption studies showed that covalent binding of enzymes caused pore blockage since the highly polymeric species were located at the pore entrance. The fixed bed reactor proved to be efficient for the immobilized invertase. The optimum pH and pH stability improved upon immobilization. The kinetic parameters calculated also showed an enhanced efficiency of the immobilized systems. They could be used continuously for long period. Covalently bound invertase demonstrated greater operational stability.
Kailasnath, M; Sreejaya, T S; Rajesh, Kumar; Vallabhan, C P G; Nampoori, V P N; Radhakrishnan, P(Elsevier, 2008)
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Abstract:
Preparation of an appropriate optical-fiber preform is vital for the fabrication of graded-index polymer optical fibers (GIPOF), which are considered to be a good choice for providing inexpensive high bandwidth data links, for local area networks and telecommunication applications. Recent development of the interfacial gel polymerization technique has caused a dramatic reduction in the total attenuation in GIPOF, and this is one of the potential methods to prepare fiber preforms for the fabrication of dye-doped polymer-fiber amplifiers. In this paper, the preparation of a dye-doped graded-index poly(methyl methacrylate) (PMMA) rod by the interfacial gel polymerization method using a PMMA tube is reported. An organic compound of high-refractive index, viz., diphenyl phthalate (DPP), was used to obtain a graded-index distribution, and Rhodamine B (Rh B), was used to dope the PMMA rod. The refractive index profile of the rod was measured using an interferometric technique and the index exponent was estimated. The single pass gain of the rod was measured at a pump wavelength of 532 nm. The extent of doping of the Rh B in the preform was studied by axially exciting a thin slice of the rod with white light and measuring the spatial variation of the fluorescence intensity across the sample.
Sudha Kartha, C; Ramachandran, T; Nampoori, V P N; Sathianandan, K(Solid State Communications, 1986)
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Abstract:
Variations in the decay times of the characteristic green emissions at 522.7, 551.3, 549.6, 547.6, 542.2, 540.2, 535.9 and 533.5nm from
CaF2 :H03+ with concentration are studied at RT and LNT. A pulsed N2
laser beam of power density 1.5 MW cm-2 is used for the excitation.
Temperature dependent concentration quenching of the decay times are
observed for all the emission bands. But an increase in the decay time due
to the reabsorption process is also observed for a few of the above bands.
Sudha Kartha, C; Ramachandran, T; Nampoori, V P N; Sathianandan, K(Elsevier, 1986)
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Abstract:
Variations in the decay times of the characteristic green emissions at 522.7, 551.3, 549.6, 547.6, 542.2, 540.2, 535.9 and 533.5 nm from CaF2:Ho3+ with concentration are studied at RT and LNT. A pulsed N2 laser beam of power density 1.5 MW cm-2 is used for the excitation. Temperature dependent concentration quenching of the decay times are observed for all the emission bands. But an increase in the decay time due to the reabsorption process is also observed for a few of the above bands.
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.
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.
Nisha,N R; Singh,A D(Department of Marine Geology and Geophysics,Faculty of Marine Sciences, 2002)
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Abstract:
In the present investigation, an attempt is made to study late Quaternary foraminiferal and pteropod records of the shelf of northern Kerala and to evaluate their potentiality in paleocenographic and paleoclimatic reconstruction. The study gives details of sediment cores, general characteristics of foraminifera and pteropod species recorded from the examined samples and their systematic classification, spatial distribution of Recent foraminifera and pteropods and their response to varying bathymetry, nature of substrate, organic matter content in sediment and hydrography across the shelf. An attempt is also made to establish an integrated chronostratigraphy for the examined core sections. An effort is also made to identify microfaunal criteria useful in biostratigraphic division in shallow marine core sections. An attempt is made to infer various factors responsible for the change in microfaunal assemblage. Reconstruction of sea level changes during the last 36,000 years was attempted based on the pteropod record. The study reveals a bathymetric control on benthic/planktic (BF/PF) foraminiferal and pteropods/planktic foraminiferal (Pt/PF) abundance ratio. Bathymetric distribution pattern of BF/PF ratio is opposite to the (Pt/PF) ratio with decreasing trend of former from the shore across the shelf. Quantitative benthic foraminiferal record in the surficial sediments reveals a positive correlation between the diversity and bathymetry. R-mode cluster analysis performed on 30n significant Recent benthic foraminiferal, determines three major assemblage.
Chandran,A R; Mathew,T; Aanandan,C K; Mohanan,P; Vasudevan,K(Department of Electronics, September , 2004)
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Abstract:
Electromagnetic scattering behaviour of a superstrate loaded metallo–
dielectric structure based on Sierpinski carpet fractal geometry is
reported. The results indicate that the frequency at which backscattering
is minimum can be tuned by varying the thickness of the superstrate.
A reduction in backscattered power of 44 dB is obtained
simultaneously for both TE and TM polarisations of the incident field.
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.