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In this work, cultivated Pimenta racemosa from North Indian plains was studied for its leaf volatile composition twice in year at two distinct seasons (spring and autumn) using GC-FID, enantio-GC-FID, GC/MS and 1H-, 13C-NMR and DEPT experiments. Phenylpropanoid was the abundant class of compounds represented by eugenol (72.9%) followed by chavicol (7.7%) whereas myrcene (9.6%) and limonene (3.8%) were identified as the most exclusive terpene constituents in spring collection. The autumn sample was recorded with highest eugenol (92.9%) proportion. Notably, presence of chavicol differentiates this oil from Pimenta dioica. An enantiomeric excess for (S)-(-)-limonene (41.1-45.3%) and (R)-(-)-linalool (86.7-89.9%) was recorded over (R)-(+)-limonene and (S)-(+)-linalool, respectively when separated on 6-tert-butyldimethylsilyl-2,3-diethyl-β-cyclodextrin chiral phase. Moreover, both the monoterpene derivatives occur as enantiomeric mixture in P. racemosa leaf essential oil.

SUMMARY The reliability of information obtained from surface seismic measurements is an important factor to be considered before one attempts to depth migrate or invert seismic data. The uniqueness of the retrieved model can only be achieved if the observed seismic data contain information on all the wavelengths of the Earth structure. In this study we investigated the sensitivity of model parameters obtainable from elastic multi-offset seismic data. We perturbed a background model, which was defined in terms of longitudinal and shear velocities and density, with quasi-sinusoidal perturbations. The reference and perturbed synthetic seismograms were calculated in the intercept time and slowness (τ-p) domain. The seismic waveform misfit between these two synthetic seismograms computed in a least-squares sense was used as a quantitative measure of the sensitivity of model parameters. We found that middle-wavelength variations of model parameters are sensitive to critical-angle seismic data. This was further confirmed by using a 1-D waveform inversion. These results suggest that all wavelengths of model parameters can be retrieved from waveform analysis of seismic reflection/refraction data: the long wavelengths from traveltime data and the short to medium wavelengths from waveform analysis. The non-uniqueness associated with the information gap for middle wavelengths, as previously proposed for seismic reflection data, can therefore be avoided.

Seismic reflection profiles across many continental margins have imaged bottom simulating reflectors (BSRs), which have been interpreted as being formed at the base of a methane hydrate stability field. Such reflectors might arise either from an impedance contrast between high-velocity, partially hydrated sediments and water-saturated sediments or from a contrast with partially gas-saturated sediments. These alternatives may be hard to distinguish by conventional amplitude-versus-offset or waveform modeling approaches. Here we investigate the origin of a high amplitude BSR in the accretionary wedge offshore of western Colombia by seismic waveform inversion. The inversion procedure consists of three steps: firstly, determination of root-mean-square velocities and hence estimates of the interval velocities between major reflectors by a global grid search for maximum normalized energy along elliptical trajectories in the intercept time-slowness domain; secondly, determination of accurate interval velocities between these reflectors by a Monte Carlo search for maximum energy; and thirdly, a waveform fit in the frequency-slowness domain, using differential reflectivity seismograms and a conjugate-gradient optimization algorithm to minimize the sample-by-sample waveform misfit between data and synthetic. At two locations, near a structural high, we find a ∼30-m thick low-velocity zone beneath the BSR, with the properties of a partially gas-saturated zone, while at a third location, where the BSR amplitude is lower, we find no evidence for anomalously low velocities. The preferential development of the BSR in structures that would tend to intercept fluid flow or migrating gas and the presence of free gas beneath the BSR indicate a mechanism of BSR formation in which free methane gas migrates upward into the hydrate stability field or is carried there in advecting pore water.

In a programme to study tribal medicines, particularly for diseases for which the modern medical system has no effective treatment, localities on the Neterhat Plateau and adjoining areas were surveyed. Visits were made in different seasons, four times in two years, and tribal “herbalists” or individuals having medical knowledge of the local flora and living in the area were interviewed. Data on the medicinal uses of 105 plants species were gathered, of which 46 were recorded as new.

SUMMARY Deep seismic-reflection profiles have shown that the lower part of the continental crust often contains many strong, sub-horizontal reflectors. Various suggestions have been made about the origin of such reflections. One explanation, which does not require the invocation of any complex tectonic process, is layering of mafic/ultramafic intrusions of partial melts derived from the upper mantle. We show that the internal layering within large mafic and ultramafic igneous intrusions can form the necessary impedance contrasts with appropriate length scales to produce seismograms similar to those observed from the lower crust, and suggest that such intrusions could be responsible for the character of the observed lower crustal reflections. Such layering could be formed at any stage of crustal formation. This suggestion is consistent with earlier geochemical proposals and does not impose any new constraints on the origin and structure of the continental crust.

Seismic reflection profiles across many continental margins have imaged bottom-simulating reflectors (BSRs) parallel to the seabed; these are often interpreted as the base of a zone in which methane hydrate "ice" is stable. Waveform inversion of seismic reflection data can be used to estimate from seismic data worldwide the velocity structure of a BSR and its thickness. A test of this method at a drill site of the Ocean Drilling Program predicts that sediment pores beneath the BSR contain free methane for approximately 30 meters. The hydrate and underlying gas represent a large global reservoir of methane, which may have economic importance and may influence global climate.

Paget's disease of bone is a rare disorder in India. Patients are usually asymptomatic and incidental radiological investigation invariably clinches the diagnosis. Increased alkaline phosphatase, X-ray, CT scan and scintiscan of bone can be done to confirm the diagnosis. Here we report a case of an 85-yr-old lady who had bilateral hearing loss for last 10 yrs, was admitted incidentally for some other complaints and on investigation diagnosed to have advanced Paget's disease of bone.

Geological sequestration of CO2 is considered to be an important greenhouse gas mitigation technology (Washington et al. 2009). Current public resistance to onshore sequestration sites makes offshore sites an attractive alternative. The Sleipner gas field in the North Sea is such a site and has been the worlds first industrial scale CO2 storage project. An effective CO2 storage requires monitoring and verification over large areas. Time lapse seismic monitoring is an integral tool to do so. Here we use time lapse elastic 2D full wave form inversion (FWI) to monitor CO2 in the Sleipner aquifer reservoir and retrieve the amount of free CO2. Inverted P-wave velocities (Vp) are related to gas saturations using a fluid substitution model employing Gassmann theory assuming patchy saturation. We find that a considerable amount of the injected CO2 could be in dissolved form by 2006 and hence saline aquifers could be a natural reservoir for CO2 storage.

Full waveform inversion is increasing being used in oil industry to quantify P and S-wave velocities of the sub-surface. So far, waveform inversion methods have been either 3D acoustic or 2D elastic. Furthermore, only low frequencies have been used because of the high computation cost. The application of elastic full waveform for 3D reservoir monitoring is still beyond the reach of present day computing technology. Here, we demonstrate the application an injected grid method, where the forward modelling for iterative elastic waveform inversion is performed in a small volume surrounding the reservoir, reducing the cost significant for full waveform. The application of algorithm is demonstrated on Marmousi II data set in a time-lapse mode.

The small, herbaceous species of Phyllanthus, commonly called “Bhumyamalaki” in Sanskrit are widely used medicinal plants, especially for treating jaundice. In Uttar Pradesh, P. amarus Schum. & Thonn., P. fraternus Webster, P. urinaria L. and P. virgatus Forst., grow commonly in the wild. The similarity in appearance and common vernacular names “Bhumyamalaki” or “Bhuianavalah” assigned to these Phyllanthus species create confusion in identifying a particular species. Pharmacognostic studies on the above species of Phyllanthus from Lucknow district (Uttar Pradesh) have been carried out to identify each of them correctly and to avoid confusion and adulteration in commerce.

In the present study, we have synthesized copper/copper‐oxide nanoparticles by laser ablation of copper metal in aqueous solution of sodium dodecyl sulfate. The focused output of 1064 nm wavelength of pulsed Nd:YAG laser is used for ablation. The synthesized nanoparticles are characterized by UV‐visible absorption, X‐ray diffraction, transmission electron microscopy and Raman spectroscopy techniques. The synthesis of copper/copper oxide nanoparticles are confirmed by XRD and Raman studies. The possible mechanism of nanoparticle formation is also discussed.

Cadmium oxide nanoparticles are synthesized by pulsed laser ablation of cadmium metal in double distilled water, which are found stable for 24 hours. The sample is characterized by using UV‐VIS absorption, scanning electron microscopy, thermo gravimetric analysis, differential thermal analysis, X‐ray diffraction and fourier transform infrared techniques. XRD pattern shows that as synthesized nanopowder has maximum amount of the Cadmium hydroxide rather than its oxide, which converts into Cadmium oxide after annealing at 350° C.

Laser ablation of nickel nanoparticles suspended in double deionized water has been studied using Nd:YAG laser (355 nm) with energy 30 mJ/pulse. Produced nanoparticles are analyzed by UV‐visible absorption spectroscopy at certain interval (0, 20, 40, 60 minute). The particles are characterized by Transmission Electron Microscopy (TEM), and X‐ray Diffraction (XRD). TEM image shows that particles have crystal like structure and these particles are in the range of 20 nm to 50 nm.

An improved extraction procedure resulted into a six-fold yield of bioactive fraction than the usual extraction method with a high per cent of feeding deterrence against 3rd instar larvae of Spilarctia obliqua and Spodoptera litura. The effective concentration (EC 50 ) of PH-2 was 4321 and 4155 ppm against the two insects. No loss in feeding deterrency was recorded when the bioactive ether fraction, PH-2 was exposed to sunlight for 6 h.

Since the 1980’s a significant amount of research in the field of full waveform has been conducted, and we are now at the stage where more accurate descriptions of the subsurface are being sought in addition to the elastic parameters. Elasticity accounts for materials that have a capacity to store mechanical energy with no dissipation of energy. A more accurate description of real earth media takes into account the time-dependent nature of previous stress states. In other words, the material possess a characteristic referred to as a memory effect (Robertsson et al. 1994).

Surface enhanced Raman scattering based optical sensing (SERS‐OS) is one of the most powerful techniques for the sensitive and selective detection of low concentration analytes. Mostly, metallic nanoparticles, such as Ag, Au and Cu, are used as substrate materials in this technique. Present work is concerned with the possibility of utilization of colloidal zinc nanoparticles, produced by pulsed laser ablation method, as substrate material in SERS‐OS.

We present a new method for traveltime tomography. In this method, the traveltime between source and receiver is described by an analytical function, which consists of a series expansion of geometrical coordinates of the source and receiver locations. As the traveltime is derived from the eikonal equation, the analytical function must also satisfy the eikonal equation. This condition imposes a strong constraint on its uniqueness. The coefficients of the series expansion are estimated by minimizing the misfit between the observed and the analytical time function in a least-square sense. Once the coefficients of the series expansion are known, the eikonal equation, which also turns out to be in the form of a series expansion, provides the velocity in the medium. Thus there are two analytical functions, one defining the traveltime and the other defining the slowness, and they can be used for prestack depth migration and velocity model definition. The method can easily be extended to incorporate reflection data and has potential for solving 3-dimensional seismic reflection and global seismology inverse problems.

E014 CO2 Thin Beds Imaging Using Full Waveform Inversion–Applications to Synthetic and Real Time–Lapse Data A. Gosselet* (Institut de Physique du Globe de Paris (IPGP)) & S.C. Singh (Institut de Physique du Globe de Paris) SUMMARY Global warming attributed to the greenhouse gas effect has generated growing interest in geological sequestration of CO2 over the past decade. Seismic monitoring is a key process in the strategy to reduce atmospheric CO2 emissions from a security standpoint and for sequestration optimization itself. Application of time domain full wave form inversion is proposed to estimate subsurface elastic properties using time-lapse data. The method

C031 Elastic Full Waveform Inversion of Multi- Component OBC Seismic Data – Application to Alba Field UK Central North Sea T.J. Sears* (University of Cambridge) S.C. Singh (Institut de Physique du Globe de Paris) & P.J. Barton (University of Cambridge) SUMMARY Elastic full waveform inversion of multi-component ocean-bottom cable seismic data has previously been applied to a range of synthetic examples in both one- and two-dimensions demonstrating the ability to quantify both P- and S-wave velocities in depth. Here results from application to a real dataset from the Alba Field UK Central North Sea are presented. Data were inverted in

The research vessel RV Maurice Ewing was recently 'retired' ( http://tinyurl.com/ejjz3 ), but data from an earlier voyage have been used to prepare remarkable seismic reflection images of the Mohorovicic discontinuity or Moho, the boundary between the Earth's crust and the mantle. Three-dimensional images from the 9° N overlapping spreading centre at the East Pacific Rise, suggest that the Moho is formed just beneath the ridge axis at zero-age. These images throw new light on the evolution of ocean spreading centres and the formation of the lower crust. The determination of melt distribution in the crust and the nature of the crust–mantle boundary (the ‘Moho’) is fundamental to the understanding of crustal accretion processes at oceanic spreading centres. Upper-crustal magma chambers have been imaged beneath fast- and intermediate-spreading centres1,2,3,4 but it has been difficult to image structures beneath these magma sills. Using three-dimensional seismic reflection images, here we report the presence of Moho reflections beneath a crustal magma chamber at the 9° 03′ N overlapping spreading centre, East Pacific Rise. Our observations highlight the formation of the Moho at zero-aged crust. Over a distance of less than 7 km along the ridge crest, a rapid increase in two-way travel time of seismic waves between the magma chamber and Moho reflections is observed, which we suggest is due to a melt anomaly in the lower crust. The amplitude versus offset variation of reflections from the magma chamber shows a coincident region of higher melt fraction overlying this anomalous region, supporting the conclusion of additional melt at depth.

Elastic full waveform inversion of seismic reflection data is an alternative to conventional stack based processing. Both travel-time and amplitude information within shot domain data are used to invert for the sub-surface velocity, from a starting model containing the long wavelength features. Although full waveform inversion is computationally intense, the ability to invert for both P- and S-wave velocity, in a data driven manner, makes the computational burden worthwhile. Building on previous developments in waveform inversion, such as the benefit of wide-aperture data, we consider multi-component ocean-bottom cable seismic data. Synthetic examples show that it is possible to invert for and to quantify both P- and S-wave velocity. Example synthetic work is presented, followed by a summary of work in progress on real data. Inversion for the shallow sub-seabed region is of particular interest. Successful inversion for the shallow region may be used to help solve shear-wave static problems observed in OBC data. This idea is explored in a synthetic example, and acts as an objective for real data application, with results to be presented.

Processing of wide-angle seismic data in the tau-p domain provides advantages over the conventional processing in the time-offset domain. A continuous moveout analysis is applied to a long-offset marine dataset from the Faeroe-Shetland Basin, in order to exploit wide-angle arrivals for imaging the sub-basalt structure. Continuous analysis is performed via the animation of a number of constant moveout stacks (CMS). Each stack is obtained via the application of a fourth-order non-elliptical moveout correction to all of the CMP gathers of the profile, already transformed into and pre-processed within the tau-p domain. A non-stretch stack can be obtained as an `abstract' of a CMS volume after picking the optimal strip of each stack.

OBC technology provides information on both pressure and 3 components particle velocity recorded at the seafloor level, allowing complementary PP and PS imaging. In the following paper, we describe a new elastic decomposition scheme in the tau-p domain that separates upgoing-downgoing P and S wavefields and eliminates all water layer related multiples. We introduce frequency dependant operators to calibrate the geophones and to characterize the P wave reflection coefficient at the seafloor. The process does not require any a priori knowledge of seafloor parameters. We start by describing theoretical aspects for complete decomposition. Then, we detail a multi-step procedure for estimating the shear wave velocity at the seafloor, for extracting the upgoing S wavefield and finally for removing peg-leg arrivals. We show successful tests on a real dataset. The results suggest promising avenues for further processing.

Low frequencies (below 10 Hz) are less attenuated and less scattered than high frequencies while penetrating through highly heterogeneous basalt layers. Therefore imaging of the deep targets using wide-angle seismic data (e.g. subbasalt imaging) requires exploitation of a narrow band of the lower end of the spectrum. Spectral whitening is employed to enhance the resolution in the stacked section by intensifying the low-frequency component of each small segment of traces. Spectral whitening in the tau-p domain may be used for tackling the spectral effects introduced by directional propagation. A stacked section of a wide-angle data set from the Faeroe-Shetland Basin shows that a higher resolution image of the deep sub-basalt structure of the area may be achieved when low frequencies are exploited. ©2006 Society of Exploration Geophysicists

P068 Full waveform inversion of multi-component OBC seismic data Abstract 1 Advances in computer technology have made full waveform inversion a more realistic and achievable process. In addition to overcoming the computational challenges involved the inverse problem itself has been helped through different techniques. The use of long-offset data and preliminary inversion of lower frequencies are seen to mitigate problems of nonlinearity. Medium wavelength features thought missing from near offset reflection data may then be resolved and convergence to a unique solution is made possible. However while the inversion of compressional (P) -wave velocity from marine streamer data is more

A16 DATA-DRIVEN P-S SEPARATION IN OBC DATA EDME P. 1 SOUDANI M.T.A. 2 3 BOELLE J.L. 2 SINGH S.C 1 . Abstract 1 OBC technology provides information on both pressure and particle velocity recorded at the seafloor level allowing complementary PP and PS imaging. In the following paper we describe a new elastic decomposition scheme that separates upgoing-downgoing P and S wavefields in the��-p domain. We introduce frequency dependant operators to calibrate the geophones so that the process does not require any a priori knowledge of seafloor parameters. We start by describing theoretical aspects for complete decomposition. Then we detail

We present a three-dimensional upper crustal model of the 9degrees03'N overlapping spreading center (OSC) on the East Pacific Rise that assists in understanding the relationship between melt sills and upper crustal structure at a ridge discontinuity with enhanced melt supply at crustal levels. Our P wave velocity model obtained from tomographic inversion of similar to 70,000 crustal first arrival travel times suggests that the geometry of extrusive emplacement are significantly different beneath the overlapping spreading limbs. Extrusive volcanic rocks above the western melt sill are inferred to be thin ( similar to 250 m). More extensive accumulation of extrusives is inferred to the west than to the east of the western melt sill. The extrusive layer inferred above the eastern melt sill thickens from similar to 350 ( at the neovolcanic axis) to 550 m ( to the west of the melt sill). Volcanic construction is likely to be significant in the formation of ridge crest morphology at the OSC, particularly at the tip of the eastern limb. On the basis of our interpretation of the velocity model, we propose that enhanced magma supply at crustal levels at the OSC may provide an effective mechanism for the migration of ridge discontinuities. This "dynamic magma supply model'' may explain the commonly observed nonsteady migration pattern of ridge discontinuities by attributing this to the temporal fluctuations in melt availability to the overlapping spreading limbs

Overlapping spreading centers (OSCs) play a key role in models of magma distribution at fast spreading ridges. To investigate the relationship between ridge-axis discontinuities and magma supply, we conducted a three-dimensional seismic reflection and tomography experiment at the 9°03′N OSC along the East Pacific Rise. Tomographic analysis imaged a broad mid-crustal low velocity zone (LVZ) beneath parts of the overlapper and the associated overlap basin, demonstrating that it is magmatically robust. The complementary datasets reveal a complex storage and tapping of melt: the LVZ and melt sill at either end of the overlap basin are not simply centered beneath the rise crest but are skewed inwards. The subsequent focussing of the LVZ and sill beneath the axis of the eastern limb appears to be due to melt migration toward the tip. The OSC western limb is less magmatically robust and may be in the process of dying.

A study was carried out to find out the effects of prior physical activity, sports participation and prior military training on the incidence of stress fractures among Gentlemen Cadets (GC's) undergoing military training at Indian Military Academy (IMA). One thousand and fourteen GC's were followed up for a period of 12 weeks. Thirty-seven GC's developed stress fractures during the study period. The incidence of stress fractures was significantly higher in GC's without any prior military training (p=0.0009). They were compared with 100 healthy controls drawn from the study population to study the influence of the other mentioned factors. There was no significant association between prior physical activity and stress fractures (OR=0.74, 95% CL=0.26 to 2.05, p=0.688). There was also no significant relationship between sports participation and stress fractures (OR=0.79. 95% CCL=0.35 to 1.81, p=0.684).

An improved extraction procedure resulted into a six-fold yield of bioactive fraction than the usual extraction method with a high per cent of feeding deterrence against 3rd instar larvae of Spilarctia obliqua and Spodoptera litura. The effective concentration (EC50) of PH-2 was 4321 and 4155 ppm against the two insects. No loss in feeding deterrency was recorded when the bioactive ether fraction, PH-2 was exposed to sunlight for 6 h.

Long offset marine seismic data for commercial exploration of sedimentary basins has recently been acquired in several areas of hydrocarbon interest. The extra information provided by these longer offsets can significantly improve the inferred velocity model describing the survey region. However to handle the diversity of information contained within such datasets there is a need to develop a more complete approach than is presently undertaken. Therefore, the current practice of modelling the traveltimes of the main events is extended by waveform fitting of the data through explicit full wavefield modelling. The wavefield inversion scheme we implement uses a finite difference solution to the elastic wave equation in the time distance domain and is therefore capable of extrapolating wavefields through arbitrary complex 2D models.

Summary We propose a new strategy for traveltime tomography and analysis of real data, by using a semi-automated traveltime picking procedure. The manual aspect is limited to the selection of a few starting points for the automatic picking of key events, which is carried out on a single common offset or common shot sections, and to the choice of a threshold parameter for the reliability of the picks. From parameters optimized while picking, estimation may be made of local amplitude, phase and signal-to-noise ratio of arrivals; event slopes and curvatures can also be extracted. This procedure has been specifically developed to support subsequent application of inversion methods to long offset data and has been demonstrated to be robust and accurate after application to real seismic data. Other useful applications are for deletion and reconstruction of events and for multiple removal.

1. SUMMARY We describe a hybrid optimization method of inversion which combines a local method with a genetic algorithm, and apply it to determine the anisotropic parameters from multi-component seismic waveform data. In the inversion we use a fitness function which measures the agreement between the synthetic and observed data. The synthetic seismograms from a point source in horizontally stratified anisotropic media are calculated using the reflectivity technique. In the initial stage of this hybrid optimization method, the global space-sampling properties of the genetic algorithm are used to direct the search to the region close in the global solution. This solution i s further improved using a local search method. The numerical experiments presented in this paper illustrate the feasibility of the approach.

In prestack migration or imaging processing, estimation of a background velocity structure is a critical step. There are two main approaches to estimate seismic velocity using reflection traveltimes: one approach is traveltime tomography and the other is inversion using the coherency measure semblance.

Determination of the long wavelength, or background, velocity structure is a critical step in prestack imaging. We have developed an efficient procedure for the solution of this non-linear inverse problem using a genetic algorithm (GA). In our approach velocities are described by splines; velocity values at spline nodes are the parameters in the inversion. We distinguish between primary nodes, affecting very long wavelength variation, and secondary nodes, describing more rapid change. The GA evolves a population of trial solutions, seeking out the globally fittest velocity model. Key to the method is the evaluation of fitness, which is carried out in three steps: (1) map migration of zero-offset traveltimes through the trial velocity model to identify the approximation locations of primary reflectors; (2) prestack Kirchhoff depth migration to generate image gathers in narrow depth windows centered on the predicted reflector locations; (3) calculation of horizontal semblance within the image gathers. For the correct velocity model, reflection events appear flat in each of the gathers; thus, by calculating horizontal semblance we obtain a measure of fitness for the GA. Since the migration is performed over a narrow depth range in the neighborhood of a given reflector, rays need only be traced from a small number of depth points for each gather; additional ray information can be efficiently obtained using paraxial approximations.

In this paper, we present a new approach for travel-time tomography in which ray tracing is not required. Analytical expressions for the travel-time between any two points and the slowness in a 2D inhomogeneous medium are obtained by minimizing the difference between the analytical travel-time function and observed travel-times. The analytical functions satisfy the Eikonal equation everywhere in the medium, and hence provide a unique solution for the slowness. The computation of travel-times using the analytical function can be much faster than that using ray tracing for pre-stack migration. Furthermore, the computation can be carried out during the migration which will avoid storing of the travel-time field and increase the efficiency of pre-stack migration.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Usual tomography methods require ray tracing to numerically compote the traveltime in order to estimate, at each iteration of the inversion, the error between the data, i.e. the recorded times, and the computed times out of the current velocity model. Furthermore pre-stack migration also requires intensive traveltime computation to calculate the Green's function, which constitutes a time consuming step for both roversion and migration processes.

According to ray theory, the traveltime T(R,S) between any source S and receiver R is related to the slowness distribution ŋ at any point X by the integral: T(R,S) = ∫ г(ŋ) ŋ(X)dl, where г(ŋ) is the ray path which yields the minimum traveltime and dl is the arc length. Because the ray path г(ŋ) depends upon the actual slowness ŋ, the inverse problem consisting of recovering the slowness distribution from the traveltime T(R,S) is non linear. A common approach is to linearize the traveltime with respect to a known slowness and iteratively update the current estimate. This requires ray tracing to compute the traveltime misfit.

Seismic reflection profiles across many continent al margins have imaged "bottom simulating reflectors" (BSRs), which are interpreted as marking the base of a methane hydrate stability field. BSRs often have very high amplitude and can be continuous for many kilometres, so they provide an ideal target for a waveform inversion scheme. Knowledge of the detailed velocity structure in the vicinity of the BSR allows us to determine whether it is underlain by a free gas zone, and estimate the thickness of such a zone where present.

An efficient simulation has been developed to analyze the dynamics and control of spacecraft comprised of multiple flexible articulating bodies. The implementation employs a typical Order-(N) multibody dynamics approach coupled with a state-of-the-art symbolic equation optimization algorithm. The relationship among computational time, system topology, number of the bodies and number of modes per body is empirically determined. For practical application in a CHAIN topology, the computational time is proportional to NB e S 5 , where NB is the number of bodies, and NM is the number of modes per body. Applied to the analysis of Space Station Freedom (SSF), which has a TREE topology, the order of the method is demonstrated to be proportional to N M ~ , where 1.4 < A < 2.0.

Deep seismic reflection profiles show that the lower part of the continental crust often contains many strong sub-horizontal reflections. These reflections are interpreted as a sequence of finely layered structuren. To confirm or invalidate this interpretation, we can use a seismic waveform inversion to estimate the reflectivity in the lower crust. However, it is very difficult to invert for the whole data set, partly because of large computation time in modelling and partly because the reflected energy in the upper crost dominates the misfit function.