Sea Surface Temperature-Convection Relationship in Tropical Oceans with Special Emphasis to Intraseasonal Variability of Indian Summer Monsoon

The SST convection relation over tropical ocean and its impact on the South Asian monsoon is the first part of this thesis. Understanding the complicated relation between SST and convection is important for better prediction of the variability of the Indian monsoon in subseasonal, seasonal, interannual, and longer time scales. Improved global data sets from satellite scatterometer observations of SST, precipitation and refined reanalysis of global wind fields have made it possible to do a comprehensive study of the SST convection relation. Interaction of the monsoon and Indian ocean has been discussed. A coupled feedback process between SST and the Active-Break cycle of the Asian summer monsoon is a central theme of the thesis. The relation between SST and convection is very important in the field of numerical modeling of tropical rainfall. It is well known that models generally do very well simulating rainfall in areas of tropical convergence zones but are found unable to do satisfactory simulation in the monsoon areas. Thus in this study we critically examined the different mechanisms of generation of deep convection over these two distinct regions.The study reported in chapter 3 has shown that SST - convection relation over the warm pool regions of Indian and west Pacific oceans (monsoon areas) is in such a way that convection increases with SST in the SST range 26-29 C and for SST higher than 29-30 C convection decreases with increase of SST (it is called Waliser type). It is found that convection is induced in areas with SST gradients in the warm pool areas of Indian and west Pacific oceans. Once deep convection is initiated in the south of the warmest region of warm pool, the deep tropospheric heating by the latent heat released in the convective clouds produces strong low level wind fields (Low level Jet - LLJ) on the equatorward side of the warm pool and both the convection and wind are found to grow through a positive feedback process. Thus SST through its gradient acts only as an initiator of convection. The central region of the warm pool has very small SST gradients and large values of convection are associated with the cyclonic vorticity of the LLJ in the atmospheric boundary layer. The conditionally unstable atmosphere in the tropics is favorable for the production of deep convective clouds.

Studies on the macrobenthic community of Cochin backwaters with special reference to culture of Eriopisa chilkensis (Gammaridae-Amphipoda)

This thesis Entitled studies on the macrobenthic community of cochin backwaters with special reference to culture of eriopisa chilkensis (Gammaridae- amphipoda).Benthic organisms are usually studied for environmental impact assessment, pollution control and resource conservation. The benthic monitoring component has three major objectives: 1) characterize the benthic communities to assess the estuarine health, 2) determine seasonal and spatial variability in benthic communities, and 3) detect changes in the estuarine community through examination of changes in abundances of specific indicator taxa and other standard benthic indices.Cochin backwaters situated at the tip of the northern Vembanad lake is a tropical positive estuarine system. The backwaters of Kerala support as much biological productivity and diversity as tropical rain forest and are responsible for the rich fishery potential of Kerala. Backwaters also act as nursery grounds for commercially important prawns and fishes.The thesis has been subdivided into seven chapters. The first chapter gives a general introduction about the topic and also highlights the scope and purpose of the study. The second chapter covers the methodology adopted for the collection and analysis of water quality parameters, sediment and the macrobenthic fauna.Chapter 3 deals with hydrographic features, sediment characteristics and the spatial variation and abundance of macrobenthic fauna in the Cochin estuary.Chapter 4 explains the impact of organic enrichment on macrobenthic popUlation in the Cochin estuary and includes the comparison of the present data with the earlier work in this region.Chapter 5 deals with seasonal variability in abundance of macrobenthic species in the estuary. The study was conducted from 9 stations during three seasons (pre-monsoon, monsoon and post-monsoon) in 2003.Chapter 6 deals with Life history and Population Dynamics of Eriopisa chilkensis Chilton (Gammaridae-Amphipoda). The life cycle of the gammarid amphipod Eriopisa chilkensis from the Cochin estuary, south west coast of India was studied for the first time under laboratory conditions.

Triterpenoids as Biomarkers of Mangrove Organic Matter in Cochin Estuarine System

This thesis entitled triterpenoids as biomarkers of mangrove organic matter in cochin estuarine system.Mangrove forests, known as rainforests of the sea are one of the most important coastal ecosystems in the world in terms of primary production and coastal protection.Estuaries, the important areas of world’s coastal zones link the carbon cycle of the oceans to the continents.Three mangrove ecosystems and three estuarine stations around Cochin region, southwest coast of India were selected for the present study. The thesis is divided into five chapters. Chapter 1 is the Introduction and it deals with the aim and scope of the present study. Chapter 2 is Materials and Methods. This chapter deals with the nature and general geographical features of the study area. It also contains the details of the sampling and analytical methodology.the present study. Chapter 3 is Geochemistry and it includes the seasonal and spatial variations of the geochemical parameters in the surface sediments.Chapter 4 is Biochemical Composition. It covers the biochemical composition of organic matter in the surface sediments to examine the quality and quantity of organic matter.Chapter 5, Triterpenoid Biomarkers in Sediments, characterize the organic matter in the sediments of the mangrove and estuarine ecosystems under study, to assess the possible sources with the help of triterpenoid biomarkers along with other lipid biomarkers.

Withania somnitera and withanolide a mediated restoration of AMPA and NMDA receptor function in pilocarpine induced temporal lobe epilepsy

The onset of spontaneous seizures triggers a cascade of molecular and cellular events that eventually leads to neuronal injury and cognitive decline. The present study investigated the effect of Withania somnifera (WS) root extract and Withanolide A (WA) in restoring behavioural deficit by inhibiting oxidative stress induced alteration in glutamergic neurotransmission. The subdued performance in behavioural tests shows impaired motor coordination and memory. Histopathological investigations revealed significant neuronal loss in hippocampus of epileptic rats indicating glutamate mediated excitotoxicity. The treatment with WS and WA restored behavioural deficit and ameliorated neuronal loss. An altered redox homeostasis leading to oxidative stress is a hallmark of TLE. The antioxidant potential was afflicted in epileptic rats, evident from altered activity of SOD and CAT, down regulation of SOD and GPX expression and enhanced lipid peroxidation. The antioxidant property of WS and WA restored altered antioxidant capacity. Alteration in GDH activity and down regulation of GLAST expression resulted in enhanced glutamate content in the brain regions. The metabolism of glutamate was altered in the form of down regulated GAD expression. The alteration in synthesis, transport and metabolism resulted in further increase of the glutamate concentration at the synapse leading to glutamate mediated excitotoxicity. The decreased NMDA and AMPA receptor binding and down regulated NMDA R1, NMDA 2B and AMPA (GluR2) mRNA expression indicated altered glutamergic receptor function. The treatment with WS and WA reversed altered glutamergic receptor function, synthesis, transport and metabolism. The enhanced levels of second messenger IP3 responsible for Ca2+ mediated toxicity was reversed after treatment with WS and WA. Neurotoxics concentration of glutamate resulted in up regulation of pro apoptotic factors Bax and Caspase 8 and down regulation of anti apoptotic factor Akt resulting in neuronal death. The treatment with WS and WA resulted in activation of Akt and down regulation of Bax and caspase 8 leading to blocking of apoptotic pathway. The treatment with WS and WA resulted in reduced seizure frequency and amelioration of associated alterations suggesting the therapeutic role of Withania somnifera in temporal lobe epilepsy

Reproductive physiology of indian species of the genus perna (family mytilidae)

This thesis deals with the reproductive physiology of the two species of Indian sea mussels, namely the brown mussel perna indica and the green mussel p viridis .The major aspects of the study include ecophysiology of reproduction linking up the animal reproductive cycle of the animals with the ecological conditions of the natural mussel beds, biochemical and histochemical changes associated with reproduction and neurosecretory cycle in synchrony with the reproductive cycle. Some basic studies on gamete morphology and certain aspects of gamete physiology have been taken up. The experimental work deals with the influence of different feeding levels on gamatogenesis and maturation and the effect of ganglia ablation on spawning. The material for the investigation on perna indica were collected from the natural mussel beds at Vizhinjam near Trivandrum and on p.viridic from Elathur, near Calicut. The period of observation extended from October 1981 to December 1982.

FEM based Virtual Prototyping and Design of Third Harmonic Excitation System for Low Voltage Brushless Alternators

Salient pole brushless alternators coupled to IC engines are extensively used as stand-by power supply units for meeting in- dustrial power demands. Design of such generators demands high power to weight ratio, high e ciency and low cost per KVA out- put. Moreover, the performance characteristics of such machines like voltage regulation and short circuit ratio (SCR) are critical when these machines are put into parallel operation and alterna- tors for critical applications like defence and aerospace demand very low harmonic content in the output voltage. While designing such alternators, accurate prediction of machine characteristics, including total harmonic distortion (THD) is essential to mini- mize development cost and time. Total harmonic distortion in the output voltage of alternators should be as low as possible especially when powering very sophis- ticated and critical applications. The output voltage waveform of a practical AC generator is replica of the space distribution of the ux density in the air gap and several factors such as shape of the rotor pole face, core saturation, slotting and style of coil disposition make the realization of a sinusoidal air gap ux wave impossible. These ux harmonics introduce undesirable e ects on the alternator performance like high neutral current due to triplen harmonics, voltage distortion, noise, vibration, excessive heating and also extra losses resulting in poor e ciency, which in turn necessitate de-rating of the machine especially when connected to non-linear loads. As an important control unit of brushless alternator, the excitation system and its dynamic performance has a direct impact on alternator's stability and reliability. The thesis explores design and implementation of an excitation i system utilizing third harmonic ux in the air gap of brushless al- ternators, using an additional auxiliary winding, wound for 1=3rd pole pitch, embedded into the stator slots and electrically iso- lated from the main winding. In the third harmonic excitation system, the combined e ect of two auxiliary windings, one with 2=3rd pitch and another third harmonic winding with 1=3rd pitch, are used to ensure good voltage regulation without an electronic automatic voltage regulator (AVR) and also reduces the total harmonic content in the output voltage, cost e ectively. The design of the third harmonic winding by analytic methods demands accurate calculation of third harmonic ux density in the air gap of the machine. However, precise estimation of the amplitude of third harmonic ux in the air gap of a machine by conventional design procedures is di cult due to complex geome- try of the machine and non-linear characteristics of the magnetic materials. As such, prediction of the eld parameters by conven- tional design methods is unreliable and hence virtual prototyping of the machine is done to enable accurate design of the third har- monic excitation system. In the design and development cycle of electrical machines, it is recognized that the use of analytical and experimental methods followed by expensive and in exible prototyping is time consum- ing and no longer cost e ective. Due to advancements in com- putational capabilities over recent years, nite element method (FEM) based virtual prototyping has become an attractive al- ternative to well established semi-analytical and empirical design methods as well as to the still popular trial and error approach followed by the costly and time consuming prototyping. Hence, by virtually prototyping the alternator using FEM, the important performance characteristics of the machine are predicted. Design of third harmonic excitation system is done with the help of results obtained from virtual prototype of the machine. Third harmonic excitation (THE) system is implemented in a 45 KVA ii experimental machine and experiments are conducted to validate the simulation results. Simulation and experimental results show that by utilizing third harmonic ux in the air gap of the ma- chine for excitation purposes during loaded conditions, triplen harmonic content in the output phase voltage is signi cantly re- duced. The prototype machine with third harmonic excitation system designed and developed based on FEM analysis proved to be economical due to its simplicity and has the added advan- tage of reduced harmonics in the output phase voltage.