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An unusual pattern of two bottom simulating reflections (BSRs) has been observed on seismic profiles from the continental margin offshore Western Norway. One of these reflections (BSR1) extends over large areas and has the characteristics of the classical BSR, that is a phase-reversed reflection from the base of the gas-hydrate stability zone. The second BSR (BSR0) occurs at approximately 70 ms two-way travel time beneath BSR1 and is here called a double BSR. The distribution of BSR0 is more local than that of BSR1 and it does not show the phase-reversal relative to the sea floor reflection that is characteristic for a BSR at the gas hydrate-free gas boundary. Results from an industrial borehole, from full waveform inversion of multichannel seismic data, from high-frequency ocean bottom hydrophones, and interpretation of seismic profiles, clearly indicate that BSR1 is reflected from the base of the methane hydrate equilibrium field. Results from full waveform inversion indicate that BSR0 corresponds to a 16–20 m zone where the velocity drops from about 1.8 km/s to a minimum of 1.4 km/s and then increases again. The low velocity of 1.4 km/s suggests the presence of free gas. The results support the hypothesis that BSR0 is a reflection from the base of gas hydrates containing hydrocarbons with a heavier molecular weight in addition to methane gas. Interference of reflections from the top and base of the low-velocity zone associated with BSR0 explain why BSR0 is not phase-reversed.

A sensitivity study of elastic parameters in amplitude-variation-with-slowness (AVS) for small- and large-offset seismic data is presented. In order to handle the non-linearity associated with waveform or amplitude beyond the critical slowness, an inversion algorithm based on Bayes' theory is used. A genetic algorithm was used to obtain the a posteriori probability density (PPD) function. The sensitivity analysis is performed on synthetic data containing P-wave as well as converted S-wave reflections. Four different two-layer models, which represent the typical range of AVS responses associated with the gas-sands normally encountered in exploration, were used to examine how well the elastic parameters can be inverted for different parametrizations by comparing the PPD functions. The sensitivity study results suggest that including wide-angle data in the inversion can greatly enhance the quality of inversion. The converted S-wave reflections can provide valuable extra information that can be used to extract elastic parameters. The results with noisy data demonstrate that the contrast of density and three velocity ratios can be estimated robustly with wide-angle reflection data.

Four compounds, stigmasterol, stigmasterol-β-D-glucopyranoside, luteolin-7-0-glucopyranoside and dotriacontanoic acid isolated from Vernonia cinerea have shown significant antifeedant activity based on percent feeding-deterrence and effective doses (ED50) against two lepidopterous insects, Spodoptera litura and Spilosoma obliqua. © 1998 John Wiley & Sons, Ltd.

Migration velocity analysis, a method for determining long wavelength velocity structure, is a critical step in prestack imaging. Solution of this inverse problem is made difficult by a multimodal objective function; a parameter space often vast in extent; and an evaluation procedure for candidate solutions, involving the calculation of depth-migrated image gathers, that can be prohibitively expensive. Recognizing the global nature of the problem, we employ a genetic algorithm (GA) in the search for the optimum velocity model. In order to describe a model efficiently, regions of smooth variation are identified and sparsely parametrized. Region boundaries are obtained via map migration of events picked on the zero-offset time section. Within a region, which may contain several reflectors, separate components describe long and short wavelength variations, eliminating from the parameter space, models with large velocity fluctuations. Vital to the success of the method is rapid model evaluation, achieved by generating image gathers only in the neighbourhood of specific reflectors. Probability of a model, which we seek to maximize, is derived from the flatness of imaged events. Except for an initial interpretation of the zero-offset time section, our method is automatic in that it requires no picking of residual moveout on migrated gathers. Using an example data set from the North Sea, we show that it is feasible to solve for all velocity parameters in the model simultaneously: the method is global in this respect also.

The essential oil composition of Murraya exotica leaves and flowers from CIMAP Research Farm, Lucknow, were analysed by GC and GC-MS, which resulted in the identification of 56 and 72 constituents, representing 99.8% and 99.2% of the oils, respectively. The leaf oil showed ( £ )-nerolidol (27.8%), α-zingiberene (10.0%), β-caryophyllene (9.7%), (E,E) farnesol (8.9%) and δ-elemene (5.1%) as the major constituents, while the flower oil showed (E,E,E)-α-springene (23.8%), ( £ )-nerolidol (18.7%), (E,E) α-farnesene (13.2%), methyl palmitate (6.8%) and germacrene B (5.9%) as the major constituents.

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.

A field crop of Lippia alba (Mill.) N.E. Br. LAC-2 genotype was raised through stem cuttings at Lucknow. The essential oil yields obtained upon hydrodistillation of leaves harvested between May 1998 and May 1999 varied from 0.6% to 0.8% on fresh weight basis. The GC and GC/MS analyses of the essential oils led to the identification of 15 compounds totalling 85% of the oil: the identified compounds included 4 monoterpene hydrocarbons (2%), 8 oxygenated monoterpenes (82%) and 3 sesquiterpene hydrocarbons (1%). The major constituent of the oil was linalool (65%). Copyright © 2000 John Wiley & Sons, Ltd.

Various extracts/fractions of the whole plant of Convolvulus microphyllus (Convolvulaceae) were bioassayed by the leaf disc method for feeding deterrence using Spilosoma obliqua Walker as a test insect. A new compound, db29-oxodotriacontanol isolated from the chloroform fraction of this plant was proved to be a potent antifeedant constituent under laboratory evaluations, whereas another compound, tetratriacontanoic acid was reported for the first time from this plant. The azadirachtin and crude neem extracts were taken as standard. A new compound (29-oxodotriacontanol) produced 85.74% inhibition at 8000 ppm concentration.