Radiothérapie asservie à la respiration en combinaison avec l'utilisation d'un faisceau sans filtre égalisateur

La radiothérapie stéréotaxique corporelle (SBRT) est une technique couramment employée pour le traitement de tumeurs aux poumons lorsque la chirurgie n’est pas possible ou refusée par le patient. Une complication de l’utilisation de cette méthode provient du mouvement de la tumeur causé par la respiration. Dans ce contexte, la radiothérapie asservie à la respiration (RGRT) peut être bénéfique. Toutefois, la RGRT augmente le temps de traitement en raison de la plus petite proportion de temps pour laquelle le faisceau est actif. En utilisant un faisceau de photons sans filtre égalisateur (FFF), ce problème peut être compensé par le débit de dose plus élevé d’un faisceau FFF. Ce mémoire traite de la faisabilité d’employer la technique de RGRT en combinaison avec l’utilisation un faisceau FFF sur un accélérateur Synergy S (Elekta, Stockholm, Suède) avec une ceinture pneumatique, le Bellows Belt (Philips, Amsterdam, Pays-Bas), comme dispositif de suivi du signal respiratoire. Un Synergy S a été modifié afin de pouvoir livrer un faisceau 6 MV FFF. Des mesures de profils de dose et de rendements en profondeur ont été acquises en cuve à eau pour différentes tailles de champs. Ces mesures ont été utilisées pour créer un modèle du faisceau 6 MV FFF dans le système de planification de traitement Pinnacle3 de Philips. Les mesures ont été comparées au modèle à l’aide de l’analyse gamma avec un critère de 2%, 2 mm. Par la suite, cinq plans SBRT avec thérapie en arc par modulation volumétrique (VMAT) ont été créés avec le modèle 6 MV du Synergy S, avec et sans filtre. Une comparaison des paramètres dosimétriques a été réalisée entre les plans avec et sans filtre pour évaluer la qualité des plans FFF. Les résultats révèlent qu’il est possible de créer des plans SBRT VMAT avec le faisceau 6 MV FFF du Synergy S qui sont cliniquement acceptables (les crières du Radiation Therapy Oncology Group 0618 sont respectés). Aussi, une interface physique de RGRT a été mise au point pour remplir deux fonctions : lire le signal numérique de la ceinture pneumatique Bellows Belt et envoyer une commande d’irradiation binaire au linac. L’activation/désactivation du faisceau du linac se fait par l’entremise d’un relais électromécanique. L’interface comprend un circuit électronique imprimé fait maison qui fonctionne en tandem avec un Raspberry Pi. Un logiciel de RGRT a été développé pour opérer sur le Raspberry Pi. Celui-ci affiche le signal numérique du Bellows Belt et donne l’option de choisir les limites supérieure et inférieure de la fenêtre d’irradiation, de sorte que lorsque le signal de la ceinture se trouve entre ces limites, le faisceau est actif, et inversement lorsque le signal est hors de ces limites. Le logiciel envoie donc une commande d’irradiation au linac de manière automatique en fonction de l’amplitude du signal respiratoire. Finalement, la comparaison entre la livraison d’un traitement standard sans RGRT avec filtre par rapport à un autre plan standard sans RGRT sans filtre démontre que le temps de traitement en mode FFF est réduit en moyenne de 54.1% pour un arc. De la même manière, la comparaison entre la livraison d’un traitement standard sans RGRT avec filtre par rapport à un plan de RGRT (fenêtre d’irradiation de 75%) sans filtre montre que le temps de traitement de RGRT en mode FFF est réduit en moyenne de 27.3% par arc. Toutefois, il n’a pas été possible de livrer des traitements de RGRT avec une fenêtre de moins de 75%. Le linac ne supporte pas une fréquence d’arrêts élevée.

Le blues et le jazz au service de la révolution? : les positions des communistes américains blancs à l’égard de la musique noire et son utilisation à des fins d’agit-prop durant l’entre-deux-guerres (1919-1941)

En 1936, l’American Music League publiait le recueil de chansons afro-américaines Negro Songs of Protest collectées par le folkloriste communiste Lawrence Gellert. Puis en 1938 et 1939, grâce au financement du mouvement communiste américain, le producteur John Hammond présentait deux concerts intitulés From Spirituals to Swing au Carnegie Hall de New York. En plus de rendre hommage à l’histoire de la musique noire américaine, ces deux concerts défiaient la ségrégation raciale, permettant au Noirs et aux Blancs d’être rassemblés sur une même scène et de s’asseoir ensemble dans l’assistance. Au même moment, la chanteuse jazz Billie Holiday faisait fureur au Café Society, premier club « intégré » de New York et lieu de rassemblement de la gauche radicale, en interprétant soir après soir la chanson ‘’Strange Fruit’’ qui dénonçait l’horreur du lynchage toujours en vigueur dans le Sud des États-Unis. C’était l’époque du Front Populaire, la plus importante période d’influence du mouvement communiste aux États-Unis et, de surcroît, le moment de l’histoire américaine durant lequel la gauche organisée détenait un pouvoir sans précédent sur la culture de masse. Partant d’une discussion sur le potentiel révolutionnaire de la musique noire américaine et cherchant à comprendre le positionnement des mouvements sociaux vis-à-vis la culture, ce mémoire met en lumière le point de vue des communistes américains blancs face à l’émergence et à la popularité grandissante du blues et du jazz noirs aux États-Unis. En fonction des trois principales phases politiques du Parti Communiste américain (CPUSA) – la phase du colorblind class (1919-1928); la phase du nationalisme noir (1928-1935); le Front Populaire (1935-1940) – ce mémoire retrace les changements d’attitude de la vieille gauche envers la culture populaire et suggère que le mouvement communiste américain a tenté d’utiliser le blues et le jazz à des fins d’agit-prop.

A Study on the Engineering Behaviour of Grouted Loose Soils

The constructional activities in the coastal belt of our country often demand deep foundations because of the poor engineering properties and the related problems arising from weak soil at shallow depths.The soil profile in coastal area often consists of very loose sandy soils extending to a depth of 3 to 4 m from the ground level underlain by clayey soils of medium consistency.The very low shearing resistance of the foundation bed causes local as well as punching shear failure.Hence structures built on these soils may suffer from excessive settlements.This type of soil profile is very common in coastal areas of Kerala,especially in Cochin. Further,the high water table and limited depth of the top sandy layer in these areas restrict the depth of foundation thereby further reducing the safe bearing capacity.

Consequence modelling,vulnerability assessment and fuzzy fault tree analysis of hazardous storages in an industrial area

The hazards associated with major accident hazard (MAH) industries are fire, explosion and toxic gas releases. Of these, toxic gas release is the worst as it has the potential to cause extensive fatalities. Qualitative and quantitative hazard analyses are essential for the identitication and quantification of the hazards associated with chemical industries. This research work presents the results of a consequence analysis carried out to assess the damage potential of the hazardous material storages in an industrial area of central Kerala, India. A survey carried out in the major accident hazard (MAH) units in the industrial belt revealed that the major hazardous chemicals stored by the various industrial units are ammonia, chlorine, benzene, naphtha, cyclohexane, cyclohexanone and LPG. The damage potential of the above chemicals is assessed using consequence modelling. Modelling of pool fires for naphtha, cyclohexane, cyclohexanone, benzene and ammonia are carried out using TNO model. Vapor cloud explosion (VCE) modelling of LPG, cyclohexane and benzene are carried out using TNT equivalent model. Boiling liquid expanding vapor explosion (BLEVE) modelling of LPG is also carried out. Dispersion modelling of toxic chemicals like chlorine, ammonia and benzene is carried out using the ALOHA air quality model. Threat zones for different hazardous storages are estimated based on the consequence modelling. The distance covered by the threat zone was found to be maximum for chlorine release from a chlor-alkali industry located in the area. The results of consequence modelling are useful for the estimation of individual risk and societal risk in the above industrial area.Vulnerability assessment is carried out using probit functions for toxic, thermal and pressure loads. Individual and societal risks are also estimated at different locations. Mapping of threat zones due to different incident outcome cases from different MAH industries is done with the help of Are GIS.Fault Tree Analysis (FTA) is an established technique for hazard evaluation. This technique has the advantage of being both qualitative and quantitative, if the probabilities and frequencies of the basic events are known. However it is often difficult to estimate precisely the failure probability of the components due to insufficient data or vague characteristics of the basic event. It has been reported that availability of the failure probability data pertaining to local conditions is surprisingly limited in India. This thesis outlines the generation of failure probability values of the basic events that lead to the release of chlorine from the storage and filling facility of a major chlor-alkali industry located in the area using expert elicitation and proven fuzzy logic. Sensitivity analysis has been done to evaluate the percentage contribution of each basic event that could lead to chlorine release. Two dimensional fuzzy fault tree analysis (TDFFTA) has been proposed for balancing the hesitation factor invo1ved in expert elicitation .

Constraining the active tectonic deformation of Andaman-Nicobar Arc in the background of December 26,2004 Great Sumatra-Andaman Earthquake

The Andaman-Nicobar Islands in the Bay of Bengal lies in a zone where the Indian plate subducts beneath the Burmese microplate, and therefore forms a belt of frequent earthquakes. Few efforts, not withstanding the available historical and instrumental data were not effectively used before the Mw 9.3 Sumatra-Andaman earthquake to draw any inference on the spatial and temporal distribution of large subduction zone earthquakes in this region. An attempt to constrain the active crustal deformation of the Andaman-Nicobar arc in the background of the December 26, 2004 Great Sumatra-Andaman megathrust earthquake is made here, thereby presenting a unique data set representing the pre-seismic convergence and co-seismic displacement.Understanding the mechanisms of the subduction zone earthquakes is both challenging sCientifically and important for assessing the related earthquake hazards. In many subduction zones, thrust earthquakes may have characteristic patterns in space and time. However, the mechanism of mega events still remains largely unresolved.Large subduction zone earthquakes are usually associated with high amplitude co-seismic deformation above the plate boundary megathrust and the elastic relaxation of the fore-arc. These are expressed as vertical changes in land level with the up-dip part of the rupture surface uplifted and the areas above the down-dip edge subsided. One of the most characteristic pattern associated with the inter-seismic era is that the deformation is in an opposite sense that of co-seismic period.This work was started in 2002 to understand the tectonic deformation along the Andaman-Nicobar arc using seismological, geological and geodetic data. The occurrence of the 2004 megathrust earthquake gave a new dimension to this study, by providing an opportunity to examine the co-seismic deformation associated with the greatest earthquake to have occurred since the advent of Global Positioning System (GPS) and broadband seismometry. The major objectives of this study are to assess the pre-seismic stress regimes, to determine the pre-seismic convergence rate, to analyze and interpret the pattern of co-seismic displacement and slip on various segments and to look out for any possible recurrence interval for megathrust event occurrence for Andaman-Nicobar subduction zone. This thesis is arranged in six chapters with further subdivisions dealing all the above aspects.

Impacts of Climate variability on Agriculture in Kerala

The study revealed that southwest monsoon rainfall in Kerala has been declining while increasing in post monsoon season. The annual rainfall exhibits a cyclic trend of 40-60 years, with a significant decline in recent decades. The intensity of climatological droughts was increasing across the State of Kerala through it falls under heavy rainfall zone due to unimodal rainfall pattern. The moisture index across the State of Kerala was moving from B4 to B3 humid, indicating that the State was moving from wetness to dryness within the humid climate.The study confirms that a warming Kerala is real as maximum, minimum and mean temperatures and temperature ranges are increasing. The rate of increase in maximum temperature was high (1.46°C) across the high ranges, followed by the coastal belt (1.09°C) of Kerala while the rate of increase was relatively marginal (0.25°C) across the midlands. The rate of increase in temperature across the high ranges is probably high because of deforestation. It indicates that the highranges and coastal belts in Kerala are vulnerable to global warming and climate change when compared to midlands.Interestingly, the trend in annual rainfall is increasing at Pampadumpara (Idukki), while declining at Ambalavayal across the highranges. In the case of maximum temperature, it was showing increasing trend at Pampadumpara while declining trend at Ambalavayal. In the case of minimum temperature it is declining at Pampadumpara while increasing in Ambalavalal.The paddy productivity in Kerala during kharif / virippu is unlikely to decline due to increasing temperature on the basis of long term climate change, but likely to decline to a considerable extent due to prolonged monsoon season, followed by unusual summer rains as noticed in 2007-08 and 2010-11.All the plantation crops under study are vulnerable to climate variability such as floods and droughts rather than long term changes in temperature and rainfall.

Development of Free Space Method for Material Characterisation and GPR Study & A Case Study on Biological Samples

The thesis mainly focuses on material characterization in different environments: freely available samples taken in planar fonn, biological samples available in small quantities and buried objects.Free space method, finds many applications in the fields of industry, medicine and communication. As it is a non-contact method, it can be employed for monitoring the electrical properties of materials moving through a conveyor belt in real time. Also, measurement on such systems at high temperature is possible. NID theory can be applied to the characterization of thin films. Dielectric properties of thin films deposited on any dielectric substrate can be determined. ln chemical industry, the stages of a chemical reaction can be monitored online. Online monitoring will be more efficient as it saves time and avoids risk of sample collection.Dielectric contrast is one of the main factors, which decides the detectability of a system. lt could be noted that the two dielectric objects of same dielectric constant 3.2 (s, of plastic mine) placed in a medium of dielectric constant 2.56 (er of sand) could even be detected employing the time domain analysis of the reflected signal. This type of detection finds strategic importance as it provides solution to the problem of clearance of non-metallic mines. The demining of these mines using the conventional techniques had been proved futile. The studies on the detection of voids and leakage in pipes find many applications.The determined electrical properties of tissues can be used for numerical modeling of cells, microwave imaging, SAR test etc. All these techniques need the accurate determination of dielectric constant. ln the modem world, the use of cellular and other wireless communication systems is booming up. At the same time people are concemed about the hazardous effects of microwaves on living cells. The effect is usually studied on human phantom models. The construction of the models requires the knowledge of the dielectric parameters of the various body tissues. lt is in this context that the present study gains significance. The case study on biological samples shows that the properties of normal and infected body tissues are different. Even though the change in the dielectric properties of infected samples from that of normal one may not be a clear evidence of an ailment, it is an indication of some disorder.ln medical field, the free space method may be adapted for imaging the biological samples. This method can also be used in wireless technology. Evaluation of electrical properties and attenuation of obstacles in the path of RF waves can be done using free waves. An intelligent system for controlling the power output or frequency depending on the feed back values of the attenuation may be developed.The simulation employed in GPR can be extended for the exploration of the effects due to the factors such as the different proportion of water content in the soil, the level and roughness of the soil etc on the reflected signal. This may find applications in geological explorations. ln the detection of mines, a state-of-the art technique for scanning and imaging an active mine field can be developed using GPR. The probing antenna can be attached to a robotic arm capable of three degrees of rotation and the whole detecting system can be housed in a military vehicle. In industry, a system based on the GPR principle can be developed for monitoring liquid or gas through a pipe, as pipe with and without the sample gives different reflection responses. lt may also be implemented for the online monitoring of different stages of extraction and purification of crude petroleum in a plant.Since biological samples show fluctuation in the dielectric nature with time and other physiological conditions, more investigation in this direction should be done. The infected cells at various stages of advancement and the normal cells should be analysed. The results from these comparative studies can be utilized for the detection of the onset of such diseases. Studying the properties of infected tissues at different stages, the threshold of detectability of infected cells can be determined.

Geodynamics of the Andaman - Sumatra - Java Trench - Arc System Based on Gravity and Seismotectonic Study

This work aims to study the variation in subduction zone geometry along and across the arc and the fault pattern within the subducting plate. Depth of penetration as well as the dip of the Benioff zone varies considerably along the arc which corresponds to the curvature of the fold- thrust belt which varies from concave to convex in different sectors of the arc. The entire arc is divided into 27 segments and depth sections thus prepared are utilized to investigate the average dip of the Benioff zone in the different parts of the entire arc, penetration depth of the subducting lithosphere, the subduction zone geometry underlying the trench, the arctrench gap, etc.The study also describes how different seismogenic sources are identified in the region, estimation of moment release rate and deformation pattern. The region is divided into broad seismogenic belts. Based on these previous studies and seismicity Pattern, we identified several broad distinct seismogenic belts/sources. These are l) the Outer arc region consisting of Andaman-Nicobar islands 2) the back-arc Andaman Sea 3)The Sumatran fault zone(SFZ)4)Java onshore region termed as Jave Fault Zone(JFZ)5)Sumatran fore arc silver plate consisting of Mentawai fault(MFZ)6) The offshore java fore arc region 7)The Sunda Strait region.As the Seismicity is variable,it is difficult to demarcate individual seismogenic sources.Hence, we employed a moving window method having a window length of 3—4° and with 50% overlapping starting from one end to the other. We succeeded in defining 4 sources each in the Andaman fore arc and Back arc region, 9 such sources (moving windows) in the Sumatran Fault zone (SFZ), 9 sources in the offshore SFZ region and 7 sources in the offshore Java region. Because of the low seismicity along JFZ, it is separated into three seismogenic sources namely West Java, Central Java and East Java. The Sunda strait is considered as a single seismogenic source.The deformation rates for each of the seismogenic zones have been computed. A detailed error analysis of velocity tensors using Monte—Carlo simulation method has been carried out in order to obtain uncertainties. The eigen values and the respective eigen vectors of the velocity tensor are computed to analyze the actual deformation pattem for different zones. The results obtained have been discussed in the light of regional tectonics, and their implications in terms of geodynamics have been enumerated.ln the light of recent major earthquakes (26th December 2004 and 28th March 2005 events) and the ongoing seismic activity, we have recalculated the variation in the crustal deformation rates prior and after these earthquakes in Andaman—Sumatra region including the data up to 2005 and the significant results has been presented.ln this chapter, the down going lithosphere along the subduction zone is modeled using the free air gravity data by taking into consideration the thickness of the crustal layer, the thickness of the subducting slab, sediment thickness, presence of volcanism, the proximity of the continental crust etc. Here a systematic and detailed gravity interpretation constrained by seismicity and seismic data in the Andaman arc and the Andaman Sea region in order to delineate the crustal structure and density heterogeneities a Io nagnd across the arc and its correlation with the seismogenic behaviour is presented.

Economic Valuation of Coastal Wetlands: A Study of Cochin Back waters in Kerala

The major objective of this chapter was to estimate the indirect benefits provided by the Cochin wetlands to direct, indirect and non-user populations.This chapter gives the details of the Contingent valuation survey that was executed in the study area. Section one described the actual survey and its execution. Section two undertook a detailed discussion of the methodological issues involved in the survey. Section three contained some discussion on the study.This analysis has demonstrated the feasibility of extending the use of contingent valuation methods to local populations in developing countries like India. Certain issues emerge from these applications. Income is strongly related to willingness to pay in these surveys, yet income levels are often low.Secondly, education is not a factor that influences willingness to pay in the coastal belt very much. Rather, relation of individual occupation to any wetland based activity very much influenced their willingness to pay. The study revealed that people very much valued the indirect function performed by wetlands, in fact as much as they valued the direct benefits provided by the system. There still exist differences of opinions among experts when undertaking such valuation studies. However, in the absence of a better technique for valuing environmental services that have no markets, this is definitely a first step

Studies on polymer blends with special reference to NBR/PVC and CR/PVC blends

The study is undertaken on PVC blends because of their all-round importance-One of the most prominent needs of PVC in application end-use is permanent plasticizationlo. Butadiene-acrylonitrile rubber (NBR) has been utilized as permanent plasticizer for PVC since the 1940s for wire and cable insulation, food contact, and pondliners used for oil containment23'24. Also plasticized PVC has been added to vulcanizable nitrile rubber, to yield improved ozone, thermal ageing, and chemical resistance resulting in applications including fuel hose covers, gaskets, conveyor belt covers, and printing roll covers. This blend is miscible in the range of 23 to 45 per cent acrylonitrile content in the butadiene-acrylqnitrile copolymerzs. The first phase of the study was directed towards modification blends. These blends, in addition to the polymers, require a host of additives like curatives for the NBR phase and stabilizers for the PVC phase26of the existing PVC blends, especially NBR/PVC. The second phase of the study was directed towards the development of novel PVC based blends. Chloroprene rubber (polychloroprene) (CR) is structurally similar to PVC and hence is likely to form successful blends with PVC32.

Effect of industrial pollution on the benthic communities of a tropical estuary

Cochin backwaters, a tropical barbuilt estuary is well known for its prawn, molluscan and demersal fisheries. Also it formed the dumping area for sewage,235 retting of husks and discharge of effluents from industries located on either side of it. As a result the fishery is being gradually dwindled year after year due to the lowering of the water quality. The effect of industrial polution on the benthic community of this tropical estuary was worked out. An area extending over 21 km from the mouth of the estuary to upstream of industrial belt was selected. Temporal and spatial variations of 16 environmental parameters at 9 stations along the area were monitored monthly during 1981. Benthic fauna of these 9 stations consisted of amphipods , polychaetes, isopods, tanaidaceans, molluscs and other crustaceans (Decapods, Acetes, Alpheids, Balanus, insect larvae, chironomid larvae, cumacea and some fresh water forms ). Apart from these, sea anemone, flat worms, nematodes, sipunculoids, echinoderms and fishes were also encountered. 75 species belonging to 31 faunal groups were identified. Of these 31 groups, amphipods, polychaedes, isopods, tanaidaceans and molluscs were numerically abundant. Rest of the 26 groups (including 13 riverine forms) were found less significant due to their rare occurrence/low numerical abundance. Polychaetes and molluscs were the only major groups present at all the stations.

Biochemical and molecular studies of cadmium resistance and metal biosorption in bacterial species isolated from cochin environment

Cochin, commercial capital of Kerala, located on the west-coast of South India has a large number of chemical and sea food industries. Earlier studies in the past indicated that these industries contribute to heavy metal pollution, particularly mercury, copper, and cadmium, in Cochin backwater. Hence, in the present study, it was desired to isolate cadmium resistant bacteria from effluent discharged by chemical industry with a view to develop an ideal bioremediation process for safe discharge of industrial effluent in to the nearby aquatic environment. Effluent from three industries, located in the industrial belt of Cochin, were collected from the discharge point and cadmium resistant bacteria were screened using standard microbiological techniques

Assessment of Water Quality along the Coastal Areas of Kerala: A Study of the Tsunami Impact on Groundwater

Everywhere, on the coastal belt it is proved without doubt that the pristine ground water quality was severely deteriorated after the 26 December 2004 Indian Ocean Tsunami. But how far is more relevant, as it is decided by the so-called pre-tsunamic situation of the region. In water quality studies it is this reference finger print which earmarks regional ground water chemistry based on which the monthly variability could rationally be interpreted. This Ph D thesis comprises the testing and evaluation of the facts: whether there is any significant difference in the water quality parameters under study between stations and between months in Tsunami Affected Dug Wells (TADW). Whether the selected water quality parameters vary significantly from BIS and WHO standards. Whether the water quality index (WQI) differ significantly between Tsunami Affected Dug Wells (TADW) and Bore Wells (BW). Whether there is any significant difference in the water quality parameters during December 2005 and December 2008. Is there any significant change in the Water Quality Parameters before 2001 and after tsunami (2005) in TADW.

POST-MONSOON SEA SURFACE TEMPERATURE AND CONVECTION ANOMALIES OVER INDIAN AND PACIFIC OCEANS

We have studied sea surface temperature (SST) anomalies over the Indian and Pacific Oceans (domain 25 °S to 25°N and 40 °E to 160 °W) during the three seasons following the Indian summer monsoon for wet monsoons and also for dry monsoons accompanied or not by El Ni˜no. A dry monsoon is followed by positive SST anomalies in the longitude belt 40 to 120 °E, negative anomalies in 120 to 160 °E and again positive anomalies east of 160 °E. In dry monsoons accompanied by El Ni˜no the anomalies have the same sign, but are much stronger. Wet monsoons have weak anomalies of opposite sign in all three of the longitude belts. Thus El Ni˜no and a dry monsoon have the same types of association with the Indian and Pacific Ocean SSTs. In the sector 40 to 120 °E SST anomalies first appear over the western part of the Indian Ocean (June to September) followed by the same sign of anomalies over its eastern part and China Sea (October to March). By March after a dry monsoon or El Ni˜no the Indian Ocean between 10 °N and 10 °S has a spatially large warm SST anomaly. Anomalies in deep convection tend to follow the SST anomalies, with warm SST anomalies producing positive convection anomalies around the seasonal location of the intertropical convergence zone

Characteristic Study of the Boundary Layer Parameters over the Arabian Sea and the Bay of Bengal Using the QuikSCAT Dataset

The marine atmospheric boundary layer (MABL) plays a vital role in the transport of momentum and heat from the surface of the ocean into the atmosphere. A detailed study on the MABL characteristics was carried out using high-resolution surface-wind data as measured by the QuikSCAT (Quick scatterometer) satellite. Spatial variations in the surface wind, frictional velocity, roughness parameter and drag coe±cient for the di®erent seasons were studied. The surface wind was strong during the southwest monsoon season due to the modulation induced by the Low Level Jetstream. The drag coe±cient was larger during this season, due to the strong winds and was lower during the winter months. The spatial variations in the frictional velocity over the seas was small during the post-monsoon season (»0.2 m s¡1). The maximum spatial variation in the frictional velocity was found over the south Arabian Sea (0.3 to 0.5 m s¡1) during the southwest monsoon period, followed by the pre-monsoon over the Bay of Bengal (0.1 to 0.25 m s¡1). The mean wind-stress curl during the winter was positive over the equatorial region, with a maximum value of 1.5£10¡7 N m¡3, but on either side of the equatorial belt, a negative wind-stress curl dominated. The area average of the frictional velocity and drag coe±cient over the Arabian Sea and Bay of Bengal were also studied. The values of frictional velocity shows a variability that is similar to the intraseasonal oscillation (ISO) and this was con¯rmed via wavelet analysis. In the case of the drag coe±cient, the prominent oscillations were ISO and quasi-biweekly mode (QBM). The interrelationship between the drag coe±cient and the frictional velocity with wind speed in both the Arabian Sea and the Bay of Bengal was also studied.