Photoacoustic thermal characterization of Al2O3–Ag ceramic nanocomposites

Laser-induced nondestructive photoacoustic (PA) technique has been employed to determine the thermal diffusivity of nanometal (Ag) dispersed ceramic alumina matrix sintered at different temperatures. The thermal diffusivity values are evaluated by knowing the transition frequency from the amplitude spectrum of PA signal using the one-dimensional heat flow model of Rosencwaig and Gersho. Analysis of the data shows that heat transport and hence the thermal diffusivity value is greatly affected by the influence of incorporation of foreign atom. It is also seen that sintering temperature affects the thermal diffusivity value in a substantial manner. The results are interpreted in terms of variation in porosity and carrier-assisted heat transport mechanism in nanometal dispersed ceramics.

Realisation of a Target Classifier For Noise Sources in the Ocean

This thesis addresses one of the emerging topics in Sonar Signal Processing.,viz.the implementation of a target classifier for the noise sources in the ocean, as the operator assisted classification turns out to be tedious,laborious and time consuming.In the work reported in this thesis,various judiciously chosen components of the feature vector are used for realizing the newly proposed Hierarchical Target Trimming Model.The performance of the proposed classifier has been compared with the Euclidean distance and Fuzzy K-Nearest Neighbour Model classifiers and is found to have better success rates.The procedures for generating the Target Feature Record or the Feature vector from the spectral,cepstral and bispectral features have also been suggested.The Feature vector ,so generated from the noise data waveform is compared with the feature vectors available in the knowledge base and the most matching pattern is identified,for the purpose of target classification.In an attempt to improve the success rate of the Feature Vector based classifier,the proposed system has been augmented with the HMM based Classifier.Institutions where both the classifier decisions disagree,a contention resolving mechanism built around the DUET algorithm has been suggested.

A Beacon based Localization System for Autonomous Mobile Robots and its Applications in Traffic and Transport Control

ACCURATE sensing of vehicle position and attitude is still a very challenging problem in many mobile robot applications. The mobile robot vehicle applications must have some means of estimating where they are and in which direction they are heading. Many existing indoor positioning systems are limited in workspace and robustness because they require clear lines-of-sight or do not provide absolute, driftfree measurements.The research work presented in this dissertation provides a new approach to position and attitude sensing system designed specifically to meet the challenges of operation in a realistic, cluttered indoor environment, such as that of an office building, hospital, industrial or warehouse. This is accomplished by an innovative assembly of infrared LED source that restricts the spreading of the light intensity distribution confined to a sheet of light and is encoded with localization and traffic information. This Digital Infrared Sheet of Light Beacon (DISLiB) developed for mobile robot is a high resolution absolute localization system which is simple, fast, accurate and robust, without much of computational burden or significant processing. Most of the available beacon's performance in corridors and narrow passages are not satisfactory, whereas the performance of DISLiB is very encouraging in such situations. This research overcomes most of the inherent limitations of existing systems.The work further examines the odometric localization errors caused by over count readings of an optical encoder based odometric system in a mobile robot due to wheel-slippage and terrain irregularities. A simple and efficient method is investigated and realized using an FPGA for reducing the errors. The detection and correction is based on redundant encoder measurements. The method suggested relies on the fact that the wheel slippage or terrain irregularities cause more count readings from the encoder than what corresponds to the actual distance travelled by the vehicle.The application of encoded Digital Infrared Sheet of Light Beacon (DISLiB) system can be extended to intelligent control of the public transportation system. The system is capable of receiving traffic status input through a GSM (Global System Mobile) modem. The vehicles have infrared receivers and processors capable of decoding the information, and generating the audio and video messages to assist the driver. The thesis further examines the usefulness of the technique to assist the movement of differently-able (blind) persons in indoor or outdoor premises of his residence.The work addressed in this thesis suggests a new way forward in the development of autonomous robotics and guidance systems. However, this work can be easily extended to many other challenging domains, as well.

Observation of two-photon induced photoemission optogalvanic effect

Observation of laser induced two-photon photoemission optogalvanic (TPPOG) effect from tungsten electrode in a discharge cell using 564 nm radiation obtained from a pulsed dye laser is described. The magnitude of the POG signal is studied as a function of laser energy under various discharge parameters. Competition between one-photon and two-photon processes has been observed when nitrogen gas is used in the discharge cell.

Existence of multiple attractors and the nature of bifurcations in a discontinuous logistic map

We present the analytical investigations on a logistic map with a discontinuity at the centre. An explanation for the bifurcation phenomenon in discontinuous systems is presented. We establish that whenever the elements of an n-cycle (n > 1) approach the discontinuities of the nth iterate of the map, a bifurcation other than the usual period-doubling one takes place. The periods of the cycles decrease in an arithmetic progression, as the control parameter is varied. The system also shows the presence of multiple attractors. Our results are verified by numerical experiments as well.

Scaling relations in the Lyapunov exponents of one dimensional maps

We establish numerically the validity of Huberman-Rudnick scaling relation for Lyapunov exponents during the period doubling route to chaos in one dimensional maps. We extend our studies to the context of a combination map. where the scaling index is found to be different.

The photoemission optogalvanic effect in a Ne-Nd hollow cathode

Laser-induced photoelectric and photoemission optogalvanic effects in a Ne-Nd hollow cathode discharge have been studied using a continuous wave laser source. The potential barrier for photoinduced electron emission from the cathode decreases as the applied voltage is increased. Owing to secondary electron emission in the plasma, the photocurrent is greater than that without discharge. The multiplication of secondary electrons and the quantum efficiency are also investigated.

Subcritical Hopf bifurcation in Ne-Nd hollow cathode discharge

We report the experimental observation of subcritical Hopf bifurcation and the existence of non-oscillating “windows” in the dynamics of a Ne-Nd hollow cathode discharge current as the control parameter.

Studies on the fracture behaviour of polymer blends with special reference to PP/HDPE and PS/HIPS blends

Investigations on the fracture behaviour of polymer blends is the topic of this thesis. The blends selected are PP/HDPE and PS/HIPS. PP/HDPE blend is chosen due to its commercial importance and PS/HIPS blend is selected to study the transition from brittle fracture to ductile fracture.PP/HDPE blends were prepared at different compositions by melt blending at 180°C and fracture failure process was investigated by conducting notch sensitivity test and tensile test at different strain rates. The effects of two types of modifiers (particulate and elastomer) on the fracture behaviour and notch sensitivity of PP/HDPE blends were studied. The modifiers used are calcium carbonate, a hard particulate filler commonly used in plastics and Ethylene Propylene Diene Monomer (EPDM). They were added in 2%, 4% and 6% by weight of the blends.The study shows that the mechanical properties of PP/HDPE blends can be optimized by selecting proper blend compositions. The selected modifiers are found to alter and improve the fracture behaviour and notch sensitivity of the blends. Particulate fillers like calcium carbonate can be used for making the mechanical behaviour more stable at the various blend compositions. The resistance to notch sensitivity of the blends is found to be marginally lower in the presence of calcium carbonate. The elastomeric modifier EPDM produces a better stability of the mechanical behaviour. A low concentration of EPDM is sufficient to effect such a change. EPDM significantly improves the resistance to notch sensitivity of the blends. The study shows that judicious selection of modifiers can improve the fracture behaviour and notch sensitivity of PP/HDPE blends and help these materials to be used for critical applications.For investigating the transition in fracture behaviour and failure modes, PS/HIPS blends were selected. The blends were prepared by melt mixing followed by injection moulding to prepare the specimens for conducting tensile, impact and flexure tests. These tests were used to simulate the various conditions which promote failure.The tensile behaviour of unnotched and notched PS/HIPS blend samples were evaluated at slow speeds. Tensile strengths and moduli were found to increase at the higher testing speed for all the blend combinations whereas maximum strain at break was found to decrease. For a particular speed of testing, the tensile strength and modulus show only a very slight decrease as HIPS content is increased up to about 40%. However, there is a drastic decrease on increasing the HIPS content thereafter.The maximum strain at break shows only a very slight change up to about 40% HIPS content and thereafter shows a remarkable increase. The notched specimens also follow a comparable trend even though the notch sensitivity is seen high for PS rich blends containing up to 40% HIPS. The notch sensitivity marginally decreases with increase in HIPS content. At the same time, it is found to increase with the increase in strain rate. It is observed that blends containing more than 40% HIPS fail in ductile mode.The impact characteristics of PSIHIPS blends studied were impact strength, the energy absorbed by the test specimen and impact toughness. Remarkable increase in impact strength is observed as HIPS content in the blend exceeds 40%. The energy absorbed by the test specimens and the impact toughness also show a comparable trend.Flexural testing which helps to characterize the load bearing capacity was conducted on PS/HIPS blend samples at the two different testing speeds of 5mmlmin and 10 mm/min. The flexural strength increases with increase in testing speed for all the blend compositions. At both the speeds, remarkable reduction in flexural strength is observed as HIPS content in the blend exceeds 40%. The flexural strain and flexural energy absorbed by the specimens are found to increase with increase in HIPS content. At both the testing speeds, brittle fracture is observed for PS rich blends whereas HIPS rich blends show ductile mode of failure.Photoelastic investigations were conducted on PS/HIPS blend samples to analyze their failure modes. A plane polariscope with a broad source of light was utilized for the study. The coloured isochromatic fringes formed indicate the presence of residual stress concentration in the blend samples. The coverage made by the fringes on the test specimens varies with the blend composition and it shows a reducing trend with the increase in HIPS content. This indicates that the presence of residual stress is a contributing factor leading to brittle fracture in PS rich blends and this tendency gradually falls with increase in HIPS content and leads to their ductile mode of failure.

Modification of spectral characteristics and optogalvanic response in neon hollow cathode under laser excitation

The changes in emission characteristics of a neon hollow cathode discharge by resonant laser excitation of 1s 5→2p 2 and 1s 5→2p 4 transition have been studied by simultaneously monitoring the optogalvanic effect and the laser induced fluorescence. It has been observed that resonant excitation causes substantial variation in the relative intensities of lines in the emission spectrum of neon discharge.

High resolution optogalvanic study in nitrogen discharge

Doppler limited high resolution spectrum in the wavelength region 17224 to 17236 cm−1 of the first positive system (B 3Π g −A 3Σ u + ) of the N2 molecule is recorded by optogalvanic spectroscopic technique using a single mode ring dye laser. It is observed that the intensity and line width of the rotational line increase with the discharge current. Dependence of the collision broadening coefficient on the current was also evaluated.

Excitation and Emission Characteristics of Pretreated SrS:Mn:Ce Phosphors

Excitation and emission spectra of SrS : Mn : Ce phosphors have been studied in detail at various Mn and Ce concentrations. In order to study the effect of external pressure on phosphors, the samples were pretreated under various pressures. Four bands around 470 nm, 530 nm, 310 nm and 620 nm were observed, when the samples were excited with 265 nm radiation. The effect of pressure is to reduce the fluorescence ability of the phosphors, and the luminescence vanishes above O· 1 ton m-2 pressure. The fluorescence ability, however, can be regained on retiring the sample. The emission mechanism has been attributed to two luminescentcenters in the forbidden gap. An appreciable amount of photocurrent has also been observed for the sample.

House Building and Personal Finance-A Study of Salaried Employees in Kerala

School of Management Studies,Cochin University of Science and Technology

Samakaleen Kavitha Mein Paaristhitik Vimarsh : Ek Adhyayan

Department of Hindi, Cochin University of Science and Technology

Studies on underwater propagation development of programmable arrays

The thesis presented here includes the designing of underwater transducer arrays, taking into account the ‘interaction effects’ [30] among the closely packed radiators. Methods of minimizing the ‘interaction effects‘ by modifying the radiating aperture, are investigated. The need for this study arises as it is one of the important peculiar limitations that stands in the way of achieving maximum range of transmission of acoustic signals. Application of the modified array format for the generation of narrow beam low frequency sound waves, through nonlinear interactions, is discussed. Other techniques that can be advantageously exploited in array synthesis are also investigated