Abstract: A method for quantitatively evaluating and using multiple geophysical datasets and external constraints for performing velocity model building through simultaneous Joint Inversion and finalized at the improvement of seismic depth images in particularly difficult geology and hydrocarbon high-risk exploration areas is disclosed, which involved the development of techniques: to derive an iterative depth-domain seismic imaging workflow which allows for the simultaneous use of seismic post-migration Common Image Gather residuals together with first arrival (First Break) residuals in conjunction with gravity data and magnetotelluric data; to include in the iterative Joint Inversion workflow the setup of external a-priori constraints as well as of external constraints weighted by probability functions; to include in the iterative Joint Inversion workflow the probabilistic evaluation of the relationships among geophysical parameters that are distinguished into analytical, empirical and structural (i.e.

Abstract: Methods and apparatus are provided for generating velocity models for pre-stack depth migration (“PSDM”). Seismic, gravity and electromagnetic joint inversion input data are generated based on observed seismic, gravity and electromagnetic data (e.g., magnetotelluric and/or controlled source electromagnetic), and velocity, density and resistivity models. A joint inversion is performed to produce a multiparametric model that is a function of velocity, density and resistivity parameter distributions. The separate parameter distributions are extracted from the multiparametric model, and the extracted velocity model is used to perform a PSDM. A migration velocity analysis is performed on PSDM output to generate seismic image residuals. If the seismic image residuals meet predetermined quality objectives, the extracted velocity model is output as the final velocity model for PSDM.

Abstract: Block copolymer of the structure A-B, wherein: ##STR1## A is a polylactamic block of recurring units: t,0010 WHEREIN PM is a linear polymethylene chain having from 3 to 13 carbon atoms,B is a polyoxymethylene block of recurring units [CH.sub.2 O]. The block copolymer contains at least 2 wt.% of block B and at least 0.05 wt.% of block A.The block copolymer can be used as technopolymer when rich in block B, or in the field of yarns and molded products when rich in block A.

Abstract: Polyoxymethylene is prepared by feeding anhydrous formaldehyde into a reaction medium containing a liquid organic diluent non-solvent for the polyoxymethylene and non-reactive towards the other constituents of the reaction medium, and containing in a dispersed form a polymer A carrying a terminal ionic couple on its macromolecular chain, said polymer A being a polylactamic block of recurring units ##STR1## wherein PM is a linear polymethylene chain having from 3 to 13 carbon atoms, and being present in a proportion of from 0.001 to 0.1% by weight with respect to the polyoxymethylene.

Abstract: Polyformaldehyde is prepared by feeding anhydrous formaldehyde to a reaction medium containing a liquid organic diluent non-solvent for the polyformaldehyde and non-reactive towards the other constituents of the reaction medium, and containing in a dispersed form a copolymer A-B, whereinA is a polylactonic block of recurring units ##EQU1## B is a polylactamic block of recurring units ##EQU2## wherein PM.sub.1 and PM.sub.2 are linear polymethylene chains having from 2 to 13 and 3 to 13 carbon atoms, respectively.

Abstract: A novel block copolymer HO--D--A--B--D--H, whereinA is a polylactonic block of recurring units ##EQU1## B is a polylactamic block of recurring units ##EQU2## C is a polyoxymethylene block of recurring units--CH.sub.2 O--is prepared by catalytic polymerization of at least one lactone ##EQU3## with at least one lactam ##EQU4## wherein: PM.sub.1 and PM.sub.2 are polymethylene linear chains having from 2 to 13 and 3 to 13 carbon atoms, respectively, and being either non-substituted or having at least one hydrogen atom replaced by an alkyl, aryl, alkylaryl or cycloalkyl radical, and reaction of the resulting A-B copolymer with monomeric formaldehyde.The block copolymer HO--D--A--B--D--H having a preponderant percentage in blocks A, B or D, respectively, behaves as a polylactone, polylactam or polyformaldehyde, respectively, having improved properties.