| Abstract: | The transient interaction between a refraction index grating and light beams during simultaneous writing and thermal fixing of a photorefractive hologram is investigated. With a diffusion- and photovoltaic-dominated carrier transport mechanism and carrier thermal activation (temperature dependent) considered in Fe:LiNbO3 crystal, from the standpoint of field-material coupling, the theoretical thermal fixing time and the space-charge field buildup, spatial distribution, and temperature dependence are given numerically by combining the band transport model with mobile ions with the coupled-wave equation |
| URI: | http://dyuthi.cusat.ac.in/purl/1370 |
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| The steady-stat ... ing in lithium niobate.PDF | (528.9Kb) |
| Abstract: | The thesis entitled “Sterols in Mangrove Sediments of the Cochin Estuary” is an attempt to characterize the sterol content of the mangrove sediments, their dietary status with respect to the natural flora and fauna present, their transfonnations in the sediment and assess contributions, if any to the nursery character of the mangrove eco system. Samplings were done from two sites at Mangalavanam and Vypin. Mangalavanam is a patchy mangrove area in the heart of the city of Cochin and serves as a small bird sanctuary. This is an almost closed system with a single narrow canal linking to the estuary. Vypin, the largest single stretch of mangroves in Kerala, is regularly inundated by a semi diurnal rhythm of Cochin bar mouth. Perhaps, this is the only site in Kerala where one can see mangroves right along the accreting seacoast. However a lot of developmental pressure is threatening the very existence of these mangroves. Post monsoon sediment samples from these areas were used for the present study, as it is the period of maximum faunal growth and activity |
| Description: | School of marine sciences, Cochin University of Science And Technology |
| URI: | http://dyuthi.cusat.ac.in/purl/3428 |
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| Dyuthi-T1397.pdf | (2.032Mb) |
| Abstract: | In case of novel products with short shelf life, sales data was either unavailable or scarcely available. The available methods for the estimation of demand of such products were direct survey methods, collection of opinion or indirect survey methods, comparison with established products and limited market trial. From literature review it was concluded that existing literature for predicting the demand of novel and short life products were scarce. This led to identification of problem namely demand forecast of relatively novel and short life products. Initially conventional methods like naive, exponential smoothing and moving average methods were used to predict the demand. Markov based model was then applied to forecast errors of the conventional methods. This model or algorithm requires only demand data of two consecutive months and hence is suited for demand forecast of novel products.This algorithm was then applied to two novel baked products, one of relatively large quantity and another of relatively small quantity. Naive, exponential smoothing and moving average methods were applied to this data and the forecasts as well as error for all the working days of two consecutive months were estimated. Markov based algorithm was then applied for these errors and the steady state probability was determined for each state of demand. A state of a system is where the system was at a point of time. The demand corresponding to the state with maximum probability was selected and the corresponding profit was estimated. The obtained profits were then compared and the combination with maximum profit was identified and the method is validated by estimating the annual savings that this method will bring to the firm when compared to existing methods in case of products A and BThe suitability of the model was validated by the fact that its implementation on product A and product B fetched more annual savings when compared to existing practice. Return on investment increased for product A and product B when compared to existing methods. Thus it was concluded that a firm can further enhance its profit by implementing this model or algorithm for more number of products. Further the model can be generalized by applying it to more types of novel products with short shelf life. The forecasting of novel and short life products was not much explored in previous research works. This model can act as the benchmark for future researches in forecasting of novel and short life products |
| URI: | http://dyuthi.cusat.ac.in/purl/5161 |
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| Dyuthi-T2195.pdf | (5.865Mb) |
| Abstract: | This thesis Entitled Stochastic modelling and analysis.This thesis is divided into six chapters including this introductory chapter. In second chapter, we consider an (s,S) inventory model with service, reneging of customers and finite shortage of items.In the third chapter, we consider an (s,S) inventoiy system with retrial of customers. Arrival of customers forms a Poisson process with rate. When the inventory level depletes to s due to demands, an order for replenishment is placed.In Chapter 4, we analyze and compare three (s,S) inventory systems with positive service time and retrial of customers. In all these systems, arrivals of customers form a Poisson process and service times are exponentially distributed. In chapter 5, we analyze and compare three production inventory systems with positive service time and retrial of customers. In all these systems, arrivals of customers form a Poisson process and service times are exponentially distributed.In chapter 6, we consider a PH /PH /l inventory model with reneging of customers and finite shortage of items. |
| Description: | Department of Mathematics, Cochin University of Science and Technology |
| URI: | http://dyuthi.cusat.ac.in/purl/3067 |
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| Dyuthi-T1041.pdf | (2.021Mb) |
| Description: | Department of Statistics, Cochin University of Science and Technology |
| URI: | http://dyuthi.cusat.ac.in/purl/2366 |
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| Dyuthi-T0638.pdf | (768.2Kb) |
| Abstract: | This thesis analyses certain problems in Inventories and Queues. There are many situations in real-life where we encounter models as described in this thesis. It analyses in depth various models which can be applied to production, storag¢, telephone traffic, road traffic, economics, business administration, serving of customers, operations of particle counters and others. Certain models described here is not a complete representation of the true situation in all its complexity, but a simplified version amenable to analysis. While discussing the models, we show how a dependence structure can be suitably introduced in some problems of Inventories and Queues. Continuous review, single commodity inventory systems with Markov dependence structure introduced in the demand quantities, replenishment quantities and reordering levels are considered separately. Lead time is assumed to be zero in these models. An inventory model involving random lead time is also considered (Chapter-4). Further finite capacity single server queueing systems with single/bulk arrival, single/bulk services are also discussed. In some models the server is assumed to go on vacation (Chapters 7 and 8). In chapters 5 and 6 a sort of dependence is introduced in the service pattern in some queuing models. |
| Description: | Department of mathematics & statistics, Cochin University of Science And Technology |
| URI: | http://dyuthi.cusat.ac.in/purl/3451 |
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| Dyuthi-T1409.pdf | (4.187Mb) |
| Abstract: | The objective of this thesis is to study the time dependent behaviour of some complex queueing and inventory models. It contains a detailed analysis of the basic stochastic processes underlying these models. In the theory of queues, analysis of time dependent behaviour is an area.very little developed compared to steady state theory. Tine dependence seems certainly worth studying from an application point of view but unfortunately, the analytic difficulties are considerable. Glosod form solutions are complicated even for such simple models as M/M /1. Outside M/>M/1, time dependent solutions have been found only in special cases and involve most often double transforms which provide very little insight into the behaviour of the queueing systems themselves. In inventory theory also There is not much results available giving the time dependent solution of the system size probabilities. Our emphasis is on explicit results free from all types of transforms and the method used may be of special interest to a wide variety of problems having regenerative structure. |
| Description: | Department of mathematics, Cochin University of Science And Technology |
| URI: | http://dyuthi.cusat.ac.in/purl/3336 |
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| Dyuthi-T1300.pdf | (3.599Mb) |
| Abstract: | Nano magnetic oxides are promising candidates for high density magnetic storage and other applications. Nonspherical mesoscopic iron oxide particles are also candidate materials for studying the shape, size and strain induced modifications of various physical properties viz. optical, magnetic and structural. Spherical and nonspherical iron oxides having an aspect ratio, ~2, are synthesized by employing starch and ethylene glycol and starch and water, respectively by a novel technique. Their optical, structural, thermal and magnetic properties are evaluated. A red shift of 0⋅24 eV is observed in the case of nonspherical particles when compared to spherical ones. The red shift is attributed to strain induced changes in internal pressure inside the elongated iron oxide particles. Pressure induced effects are due to the increased overlap of wave functions. Magnetic measurements reveal that particles are superparamagnetic. The marked increase in coercivity in the case of elongated particles is a clear evidence for shape induced anisotropy. The decreased specific saturation magnetization of the samples is explained on the basis of weight percentage of starch, a nonmagnetic component and is verified by TGA and FTIR studies. This technique can be modified for tailoring the aspect ratio and these particles are promising candidates for drug delivery and contrast enhancement agents in magnetic resonance imaging |
| Description: | Bull. Mater. Sci., Vol. 31, No. 5, October 2008, pp. 759–766 |
| URI: | http://dyuthi.cusat.ac.in/purl/4387 |
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| Strain induced ... edby a novel technique.pdf | (1.595Mb) |
| Abstract: | The dynamics and associated stability analysis of tidal inlets situated on the southwest coast of India, namely Andhakaranazhi (90 45 J OO JJN and 760 17 J 29 JJ E) and the other at Cochin harbour inlet (90 58 1 04 J1N and 760 14 1 50 1J E) have beenconducted. A detailed study on the inlet regime of Cochin barmouth (permanent in nature) was attempted so as to elucidate information on: (a) channel characteristics (b) tidal hydraulics and (c) stability of the inlet. In this connection, a naturally occurring seasonal sandbar formation at Andhakaranazhi, near Sherthallay, about 20 km south of Cochin inlet, was also chosen as a site ofstudy brought out conclusively the dynamical study. The aspects of ( 1) tidal influx/out flux (2) channel morphology (3) sedimentation regime and (4) stability and factors related to stability of these locations. The above aspects are supported by suitable mathematical formulations to describe the associated coastal processes, wherever applicable |
| Description: | School of marine science, Department of Physical Oceanography, Cochin University of Science and Technology |
| URI: | http://dyuthi.cusat.ac.in/purl/3353 |
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| Dyuthi-T1330.pdf | (9.928Mb) |
| Abstract: | The theory of deterministic chaos is used to study the three rings A, B, and C of Saturn and the French and Cassini divisions in between them. The data set comprises Voyager photopolarimeter measurements. The existence of spatially distributed strange attractors is shown, implying that the system is open, dissipative, nonequilibrium, and non-Markovian in character. |
| URI: | http://dyuthi.cusat.ac.in/purl/2630 |
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| Dyuthi-P0189.pdf | (894.3Kb) |
| URI: | http://dyuthi.cusat.ac.in/purl/5177 |
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| Dyuthi-T2212.pdf | (5.042Mb) |
| URI: | http://dyuthi.cusat.ac.in/purl/5594 |
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| Dyuthi T-2635.pdf | (4.488Mb) |
| URI: | http://dyuthi.cusat.ac.in/purl/5092 |
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| Dyuthi-T 2158.pdf | (4.571Mb) |
| URI: | http://dyuthi.cusat.ac.in/purl/5072 |
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| Dyuthi- T 2136.pdf | (10.82Mb) |
| URI: | http://dyuthi.cusat.ac.in/purl/5128 |
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| Dyuthi-T 2193.pdf | (9.503Mb) |
| Abstract: | Electromagnetic tomography has been applied to problems in nondestructive evolution, ground-penetrating radar, synthetic aperture radar, target identification, electrical well logging, medical imaging etc. The problem of electromagnetic tomography involves the estimation of cross sectional distribution dielectric permittivity, conductivity etc based on measurement of the scattered fields. The inverse scattering problem of electromagnetic imaging is highly non linear and ill posed, and is liable to get trapped in local minima. The iterative solution techniques employed for computing the inverse scattering problem of electromagnetic imaging are highly computation intensive. Thus the solution to electromagnetic imaging problem is beset with convergence and computational issues. The attempt of this thesis is to develop methods suitable for improving the convergence and reduce the total computations for tomographic imaging of two dimensional dielectric cylinders illuminated by TM polarized waves, where the scattering problem is defmed using scalar equations. A multi resolution frequency hopping approach was proposed as opposed to the conventional frequency hopping approach employed to image large inhomogeneous scatterers. The strategy was tested on both synthetic and experimental data and gave results that were better localized and also accelerated the iterative procedure employed for the imaging. A Degree of Symmetry formulation was introduced to locate the scatterer in the investigation domain when the scatterer cross section was circular. The investigation domain could thus be reduced which reduced the degrees of freedom of the inverse scattering process. Thus the entire measured scattered data was available for the optimization of fewer numbers of pixels. This resulted in better and more robust reconstructions of the scatterer cross sectional profile. The Degree of Symmetry formulation could also be applied to the practical problem of limited angle tomography, as in the case of a buried pipeline, where the ill posedness is much larger. The formulation was also tested using experimental data generated from an experimental setup that was designed. The experimental results confirmed the practical applicability of the formulation. |
| Description: | Department of Electronics, Cochin University of Science and Technology |
| URI: | http://dyuthi.cusat.ac.in/purl/2546 |
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| Dyuthi-T0690.pdf | (8.779Mb) |
| Abstract: | The aim of the present study is to understand the biennial scale stratosphere-troposphere interactions over India, and synoptic to interannual timescale meridional stratosphere-troposhere exchanges caused by upper tropospheric/lower stratospheric longwaves using NCEP/NCAR reanalysis data and satellite measured total ozone data. The biennial timescale interaction between lower stratosphere and troposphere over Thumba is analysed using high-resolution radiosonde data. The results suggest that TBO and QBO are two different phenomena with nearly biennial periodicity. Interannual timescale meridional stratosphere-troposphere exchanges caused by the newly documented Asia Pacific Wave (APW) were analysed using ozone as tracer of atmospheric motion. Synoptic timescale meridional stratosphere-troposhere exchanges caused by subtropical upper tropospheric long waves over Asia were studied using global total ozone measurements from TOMS. This research work can be extended to study the influence of decadal scale epochal nature in Indian summer monsoon activity on the APW generated total ozone anomalies around the globe and the trend estimates in total ozone |
| URI: | http://dyuthi.cusat.ac.in/purl/27 |
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| Dyuthi-T0084.pdf | (6.411Mb) |
| URI: | http://dyuthi.cusat.ac.in/purl/5409 |
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| 01_title.pdf | (214.9Kb) |
| 02_certificate.pdf | (5.425Kb) |
| 03_declaration.pdf | (5.281Kb) |
| 04_preface.pdf | (376.6Kb) |
| 05_contents.pdf | (495.1Kb) |
| 06_chapter 1.pdf | (710.4Kb) |
| 07_chapter 2.pdf | (668.0Kb) |
| 08_chapter 3.pdf | (223.2Kb) |
| 09_chapter 4.pdf | (229.3Kb) |
| 10_chapter 5.pdf | (223.0Kb) |
| 11_chapter 6.pdf | (324.7Kb) |
| 12_chapter 7.pdf | (437.1Kb) |
| 13_references.pdf | (742.9Kb) |
| Abstract: | Glass fiber reinforced polymer (GFRP) rebars have been identified as an alternate construction material for reinforcing concrete during the last decade primarily due to its strength and durability related characteristics. These materials have strength higher than steel, but exhibit linear stress–strain response up to failure. Furthermore, the modulus of elasticity of GFRP is significantly lower than that of steel. This reduced stiffness often controls the design of the GFRP reinforced concrete elements. In the present investigation, GFRP reinforced beams designed based on limit state principles have been examined to understand their strength and serviceability performance. A block type rotation failure was observed for GFRP reinforced beams, while flexural failure was observed in geometrically similar control beams reinforced with steel rebars. An analytical model has been proposed for strength assessment accounting for the failure pattern observed for GFRP reinforced beams. The serviceability criteria for design of GFRP reinforced beams appear to be governed by maximum crack width. An empirical model has been proposed for predicting the maximum width of the cracks. Deflection of these GFRP rebar reinforced beams has been predicted using an earlier model available in the literature. The results predicted by the analytical model compare well with the experimental data |
| Description: | Construction and Building Materials 21 (2007) 1709–1719 |
| URI: | http://dyuthi.cusat.ac.in/purl/4539 |
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| Strength and se ... h GFRP bars in flexure.pdf | (372.3Kb) |
| Abstract: | Hat Stiffened Plates are used in composite ships and are gaining popularity in metallic ship construction due to its high strength-to-weight ratio. Light weight structures will result in greater payload, higher speeds, reduced fuel consumption and environmental emissions. Numerical Investigations have been carried out using the commercial Finite Element software ANSYS 12 to substantiate the high strength-to-weight ratio of Hat Stiffened Plates over other open section stiffeners which are commonly used in ship building. Analysis of stiffened plate has always been a matter of concern for the structural engineers since it has been rather difficult to quantify the actual load sharing between stiffeners and plating. Finite Element Method has been accepted as an efficient tool for the analysis of stiffened plated structure. Best results using the Finite Element Method for the analysis of thin plated structures are obtained when both the stiffeners and the plate are modeled using thin plate elements having six degrees of freedom per node. However, one serious problem encountered with this design and analysis process is that the generation of the finite element models for a complex configuration is time consuming and laborious. In order to overcome these difficulties two different methods viz., Orthotropic Plate Model and Superelement for Hat Stiffened Plate have been suggested in the present work. In the Orthotropic Plate Model geometric orthotropy is converted to material orthotropy i.e., the stiffeners are smeared and they vanish from the field of analysis and the structure can be analysed using any commercial Finite Element software which has orthotropic elements in its element library. The Orthotropic Plate Model developed has predicted deflection, stress and linear buckling load with sufficiently good accuracy in the case of all four edges simply supported boundary condition. Whereas, in the case of two edges fixed and other two edges simply supported boundary condition even though the stress has been predicted with good accuracy there has been large variation in the deflection predicted. This variation in the deflection predicted is because, for the Orthotropic Plate Model the rigidity is uniform throughout the plate whereas in the actual Hat Stiffened Plate the rigidity along the line of attachment of the stiffeners to the plate is large as compared to the unsupported portion of the plate. The Superelement technique is a method of treating a portion of the structure as if it were a single element even though it is made up of many individual elements. The Superelement has predicted the deflection and in-plane stress of Hat Stiffened Plate with sufficiently good accuracy for different boundary conditions. Formulation of Superelement for composite Hat Stiffened Plate has also been presented in the thesis. The capability of Orthotropic Plate Model and Superelement to handle typical boundary conditions and characteristic loads in a ship structure has been demonstrated through numerical investigations. |
| Description: | Study about Hat Stiffened Plate |
| URI: | http://dyuthi.cusat.ac.in/purl/5038 |
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| Dyuthi-T2103 .pdf | (2.669Mb) |
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