ALBERT

Notes: Any set of isotropic layers is equivalent, in the long wavelength limit, to a unique transversely isotropic (TI) layer; to find the elastic moduli of that layer is a solved problem. The converse problem is to find a set of isotropic layers equivalent to a given TI media. Here, explicit necessary and sufficient conditions on the TI stiffness moduli for the existence of an equivalent set of isotropic layers are found by construction of a minimal decomposition consisting of either two or three isotropic constituent layers. When only two constituents are required, their elastic properties are uniquely determined. When three constituents are required, two have the same Poisson's ratio and the same thickness fraction, and even then there is a one-parameter family of satisfactory minimal decompositions. The linear slip model for fractured rock (aligned fractures in an isotropic background) yields a restricted range of transverse isotropy dependent on only four independent parameters. If the ratio of the normal to tangential fracture compliance is small enough, the medium is equivalent to thin isotropic layering and in general its minimal decomposition consists of three constituents.

Notes: Information on the mass and the spatial location of an arbitrary source body can be obtained by performing suitable integrations of 3D gravity and magnetic data along an infinite straight line. No assumptions on the density/magnetization distribution or the shape and location of the source are required.For an oblique borehole, a relationship between the lower limit of the source mass and the distance to the body is obtained. The mass contrast and the magnetic moment of the source can also be estimated.For a vertical borehole, both gravity and vertical magnetic component anomalies have equal areas to the left and right of the depth axis.The particular case of a horizontal gallery not intersecting the body is also studied. If the source is intersected, a lower limit is estimated for the maximum thickness of the body along the gallery. Information on the vertical coordinate of the centre of mass of the source can also be obtained.Numerical tests with synthetic gravity data support the theoretical results.

Notes: Refraction seismics with the shotpoints and the hydrophone cable on the sea-bottom, have become the standard geophysical method for investigating rock quality before constructing offshore tunnels in Norway. In connection with the construction of a sub-sea tunnel by the Norwegian Public Roads Administration, research work was carried out to compare two low-velocity zones, indicated by refraction seismics with other methods. A special resistivity cable for pole-dipole measurements on the sea-floor, with 10 m between the electrodes, was constructed. A 200 m long profile, crossing the two low-velocity zones, was measured with all combinations of electrode distances. The two zones were detected as low-resistivity zones. A special data processing technique to enhance the anomalies is described. Resistivity soundings in a seawater environment to detect fracture zones in the bedrock underneath the bottom sediments, are discussed. It is concluded that severely fractured zones, which may cause difficulties for the tunnel construction, can be detected both with sea-surface and sea-floor arrays using long electrode spacings.

Notes: In order to understand various aspects of radar wave propagation, a survey of electromagnetic wave behaviour relative to the geological characteristics of the formations prospected was undertaken. The sites chosen for the tests were a granite quarry and an underground schist working. By investigating an electrically resistive isotropic site and a conductive anisotropic site, it was demonstrated that non-conventional use of a radar system (antennae raised, various orientations of the transmitter/receiver, etc.) could improve data quality, and could allow information other than reflector depth to be collected (volume scattering intensity, isotropy, etc.). By studying wave propagation velocities, we underlined the difficulties encountered in establishing a velocity versus depth law, despite recourse to seismic data processing, such as NMO corrections. The results of field experiments, complemented by laboratory measurements of dielectric permittivities, clearly showed anisotropy effects: in the case of a path that is perpendicular to the schistosity plane, an electromagnetic wave propagates more slowly and is more attenuated than a wave parallel to the schistosity plane.

Notes: A 2D numerical finite-difference algorithm accounting for surface topography is presented. Higher-order, dispersion-bounded, cost-optimized finite-difference operators are used in the interior of the numerical grid, while non-reflecting absorbing boundary conditions are used along the edges. Transformation from a curved to a rectangular grid achieves the modelling of the surface topography. We use free-surface boundary conditions along the surface. In order to obtain complete modelling of the effects of wave propagation, it is important to account for the surface topography, otherwise near-surface effects, such as scattering, are not modelled adequately. Even if other properties of the medium, for instance randomization, can improve numerical simulations, inclusion of the surface topography makes them more realistic.

Notes: True-amplitude (TA) migration, which is a Kirchhoff-type modified weighted diffraction stack, recovers (possibly) complex angle-dependent reflection coefficients which are important for amplitude-versus-offset (AVO) inversion. The method can be implemented using existing prestack or post-stack Kirchhoff migration and fast Green's function computation programs. Here, it is applied to synthetic single-shot and constant-offset seismic data that include post-critical reflections (complex reflection coefficients) and caustics. Comparisons of the amplitudes of the TA migration image with theoretical reflection coefficients show that the (possibly complex) angle-dependent reflection coefficients are correctly estimated.

Notes: The Fourier pseudospectral method has been widely accepted for seismic forward modelling because of its high accuracy compared to other numerical techniques. Conventionally, the modelling is performed on Cartesian grids. This means that curved interfaces are represented in a ‘staircase fashion‘causing spurious diffractions. It is the aim of this work to eliminate these non-physical diffractions by using curved grids that generally follow the interfaces.A further advantage of using curved grids is that the local grid density can be adjusted according to the velocity of the individual layers, i.e. the overall grid density is not restricted by the lowest velocity in the subsurface. This means that considerable savings in computer storage can be obtained and thus larger computational models can be handled.One of the major problems in using the curved grid approach has been the generation of a suitable grid that fits all the interfaces. However, as a new approach, we adopt techniques originally developed for computational fluid dynamics (CFD) applications. This allows us to put the curved grid technique into a general framework, enabling the grid to follow all interfaces. In principle, a separate grid is generated for each geological layer, patching the grid lines across the interfaces to obtain a globally continuous grid (the so-called multiblock strategy).The curved grid is taken to constitute a generalised curvilinear coordinate system, where each grid line corresponds to a constant value of one of the curvilinear coordinates. That means that the forward modelling equations have to be written in curvilinear coordinates, resulting in additional terms in the equations. However, the subsurface geometry is much simpler in the curvilinear space.The advantages of the curved grid technique are demonstrated for the 2D acoustic wave equation. This includes a verification of the method against an analytic reference solution for wedge diffraction and a comparison with the pseudospectral method on Cartesian grids. The results demonstrate that high accuracies are obtained with few grid points and without extra computational costs as compared with Cartesian methods.

Notes: We describe a least-squares inversion approach to estimating the subsurface resistivity structure from cross-hole or borehole-to-surface electromagnetic data. It is assumed that the resistivity distribution is symmetric about the axis of a borehole and that vertical magnetic dipoles are located on the borehole axis. The receivers are placed either in another borehole or on the earth's surface. The inversion scheme uses the finite-element and smoothness-constrained least-squares methods. The computational effort required to obtain partial derivatives is reduced considerably by using the reciprocity principle. Numerical simulations show that the reconstructions are generally in good agreement with the true structures when the assumption of an axisymmetric earth structure holds. An example involving the breakdown of this assumption, which can be obtained by interchanging the source and receiver boreholes, suggests that the inversion result may also be useful for locating a general 3D anomaly although artifacts are present.

Notes: A crucial point in the processing of 3D seismic data is the migration step, both because of its 3D nature and the computational cost involved. The efficiency and accuracy of 3D migration are determined by the wavefield extrapolation technique employed. Wavefield extrapolation based on second-order differential operators of variable-length is very efficient and accurate at the same time. Compared to migration based on the McClellan transform and operator splitting, the use of variable-length second-order differential operators offers significant advantages. The 3D migration operator has an almost perfect circular symmetry. No positioning errors in the 45° azimuth between the in-line and cross-line directions are evident. The method is, in practice, only limited by spatial aliasing and does not require expensive interpolation of data to reduce numerical artifacts. This reduces the computational cost of 3D one-pass depth migration by a large factor.

Notes: Differences between traveltimes from sonic to seismic frequencies, commonly known as drift, can be attributed to a combination of multiple scattering and absorption. The portion due to scattering can be estimated directly by calculating synthetic seismograms from sonic logs. A simple alternative approach is suggested by the long-wave equivalent averaging formulae for the effective elastic properties of a stack of thin layers, which gives the same traveltime delays as the low-frequency limit of the scattering dispersion. We consider the application of these averaging formulae over a frequency-dependent window with the hope of extending their use to frequencies higher than those allowed by the original validity conditions. However, comparison of the time delay due to window-averaging with the scattering dispersion predicted by the O'Doherty-Anstey formula reveals that it is not possible to specify a form of window that will fit the dispersion across the spectrum for arbitrary log statistics. A window with a width proportional to the wavelength squared matches the behaviour at the low-frequency end of the dispersive range for most logs, and allows an almost exact match of the drift across the entire spectrum for exponential correlation functions.We examine a real log, taken from a hole in nearly plane-layered geology, which displays strong quasi-cyclical variations on one scale as well as more random, smaller-scale fluctuations. The details of its drift behaviour are studied using simple models of the gross features. The form of window which gave a good theoretical fit to the dispersion for an exponential log correlation function can only fit the computed drift at high or low frequencies, confirming that there are at least two significant scale-lengths of fluctuation. A better overall fit is obtained for a window whose width is proportional to the wavelength. The calculated scattering drift is significantly less than that observed from a vertical seismic profile, but the difference cannot be wholly ascribed to absorption. This is because the source frequency of the sonic tool is not appropriate for its resolution (receiver spacing) so that the scattering drift from sonic to seismic frequencies cannot be fully estimated from the layer model derived from the log.

Notes: The analytic signal (AS) is defined as the square root of the sum of the squares of the vertical and the two horizontal derivatives of the total magnetic field ΔT. This paper verifies theoretically that peaks of the AS correlate directly with their magnetic causative bodies and are positioned symmetrically over them, i.e. the main feature of the AS is that it is independent of the inclination of the magnetic field. This avoids the difficulties that are often faced in the conventional process of reduction to pole for ΔT, when the direction of magnetization of the causative bodies is not known. In addition, the AS has characteristics similar to the derivative features of the magnetic field, so that it is very sensitive to edge effects of the causative magnetic bodies. The theoretical derivations are tested by comparison with calculations on models, and, in a field example from Hunan Province, China, the AS is applied successfully to the interpretation of ΔT, whereas the conventional process of reduction to pole fails, due to the reverse magnetization of the causative body.

Notes: An equivalent source procedure is derived for upward continuation of unevenly spaced gravity and magnetic data. The dipole layer is placed on a topographic relief approximated by a polyhedral surface, the stations being the vertices of the triangular faces. The dipoles have linear magnitudes, being directed along the normal vector over each triangle. The unknown values of the dipole magnitudes at each station are obtained by a suitable modification of the usual integral equation considering the discontinuity of the normal vector at each vertex of the dipole surface. Profile data processing is also studied. A numerical test outlines the accuracy and the limitations of the model for the case of a magnetic field significantly perturbed by a rough topographic relief.

Notes: We use a marine seismic dataset to examine the reflections from two gas sands, a lignitic sand and a cineritic bed, by means of their amplitude versus offset (AVO) responses. This offset-dependent signature is related to specific petrophysical and thus elastic situations or to peculiar interference patterns and may help to distinguish the nature of the amplitude anomalies on the stack sections.The prestack analysis is carried out on seismic data which have undergone an accurate true-amplitude processing.It is found that the lignitic-sand reflections exhibit a decreasing AVO while the two-gas sands show markedly increasing AVO trends. Also the reflections from the cineritic layer show increasing amplitudes with offset that may be due either to the petrophysical nature of the cinerites or to thin-layer interference or to both.In order to verify the reliability of the actual AVO responses we develop a detailed model from well data and compute a synthetic CMP seismogram. In order to account for mode conversions and thin-layer effects, the synthetic seismograms are computed using the reflectivity method. The wavelets used in the synthetics are retrieved from actual seismic and borehole data by means of wavelet processing. When finely layered structures are present, the estimation of a reliable wavelet is extremely important to get the correct synthetic AVO response. In particular, the AVO responses of the cineritic layer differ substantially if we make use in the computation of the synthetics of a Ricker wavelet or of a wavelet estimated through wavelet processing.The good match between the observed and modelled data confirms the reliability of the processing sequence and of the final AVO signatures.

Notes: The five-electrode resistivity configuration of Barker, who introduced the concept of offset resistivity measurements, is used in a profiling mode in the search for lateral variations of resistivity down to depths of a few tens of metres. Theoretical computations show that plotting simple pseudosections of offset measurements over faults is sufficient to reveal the fault position. The method is subsequently applied in the field for locating a buried fault in coal measures. Although offset pseudosections are often all that is required, apparent resistivity pseudosections are examined and compared to collations of 1D inversions of the sounding profile data and to computations over 2D models. It is shown that apparent restivity pseudosections may present a rather misleading picture.

Notes: We present a layer-stripping method of migration for irregularly layered media in which first-order velocity discontinuities separate regions of constant or smoothly varying velocity. We use the reverse-time method to migrate seismic data layer by layer, from the surface downwards. As part of the migration of a given layer, the bottom boundary of the layer is defined based on power in the migrated signal, and a seismic section is collected along it. This new section serves as the boundary condition for migration in the next layer. This procedure is repeated for each layer, with the final image formed from the individual layer images. Layer-stripping migration consists of three steps: (1) layer definition, (2) wavefield extrapolation and imaging, and (3) boundary determination. The migration scheme when used with reverse-time extrapolation is similar to datuming with an imaging condition. The reverse-time method uses an explicit fourth-order time, tenth-order space, finite-difference approximation to the scalar wave equation.The advantages of layer-stripping reverse-time migration are: (1) it preserves the benefits of the reverse-time method by handling strong velocity contrasts between layers and steeply dipping structures; (2) it reduces computer memory and saves computation time in high-velocity layers, and (3) it allows interpretational control of the image.Post-stack layer-stripping reverse-time migration is illustrated with a synthetic CMP data example. Prestack migration is illustrated with a synthetic data set and with a marine seismic reflection profile across the Santa Maria Basin and the Hosgri Fault in central California.

Notes: A method of non-invasive NMR in the earth's field has been developed and is now used for groundwater surveys to depths of investigation of 100 m or more.A circular wire loop of diameter 100 m, laid out on the ground, is employed to excite and receive the NMR signal in the earth's field. However, in areas with high electromagnetic noise, the NMR measurements may be inaccurate.To overcome this problem, a noise-reducing figure-of-eight-shaped antenna, consisting of two touching coils each of diameter 50 m, has been utilized.Using this antenna, the NMR signal has been calculated for different depths of water-saturated layers with various inclinations of the geomagnetic field. The model calculations and experimental data have been compared and found to be mutually consistent. The two-coil antenna is shown to be suitable for studies at depths of up to 30–40 m, which is of practical importance for engineering geology.

Notes: A general inversion scheme based on a genetic algorithm is developed to invert seismic observations for anisotropic parameters. The technique is applied to the inversion of shear-wave observations from two azimuthal VSP data sets from the Conoco test site in Oklahoma. Horizontal polarizations and time-delays are inverted for hexagonal and orthorhombic symmetries. The model solutions are consistent with previous studies using trial and error matching of full waveform synthetics. The shear-wave splitting observations suggest the presence of a shear-wave line singularity and are consistent with a dipping fracture system which is known to exist at the test site. Application of the inversion scheme prior to full waveform modelling demonstrates that a considerable saving in time is possible whilst retaining the same degree of accuracy.

Notes: A numerical simulation of electromagnetic propagation through a multilayered medium is performed in order to explain and interpret the signal received from the radar sounding of a temperate glacier. During the winter of 1990, several radar profiles were obtained on the Mont-de-Lans glacier in the French Alps with a ground penetrating radar which uses a phase modulation of the transmitted pulse by coded sequences. The pulse compression is obtained by applying the matched filter to the received signal, which provides a range-resolution of about 8 m in the ice. The profiles recorded on the temperate glacier do not show a single clear reflection from the ice-bedrock interface, but they exhibit widely distributed energy decreasing with depth. This may be due to the inhomogeneous inner structure of the temperate glacier and we use a simple model of a layered medium to compute a simulation of the propagation. Thus, partial reflection at each layer and scattering from a rough basal interface may explain the observed signal. A computer-based technique is used to locate on the data the bottom of the glacier in order to estimate the ice thickness. The results from the different radar profiles are consistent and are a good fit to the thickness which has been determined by other geophysical methods.

Notes: Both approximate and exact formulations for the interaction of an incident elastic wave with a cased borehole are presented. In the approximate method, simple and explicit formulae are derived for the pressure in fluid at low frequencies. In the exact method, elastic potentials in each annulus are represented as a superposition of fundamental solutions to the Helmholtz equations. Continuity of displacements and stresses across layer boundaries are used to determine unknown coefficients. A global matrix algorithm is employed to compute simultaneously these coefficients in individual layers. Calculations show that, in cased boreholes, the borehole effects on downhole seismic measurements are more significant than in open boreholes. A strong resonance occurs in the fluid for SV-wave incidence from a soft formation. This resonance is prominent even at very high frequencies because the tube-wave velocity is raised well above the formation shear velocity by the steel pipe. At a particular angle of incidence of a plane P-wave, the pressure in the fluid is near zero at low frequencies (the cased borehole screening phenomenon). For hard formations and frequencies above 1 kHz, the cased borehole influence on a downhole geophone measurement is significant, especially at grazing incidence. For soft formations, both the pressure in the fluid and the solid displacement on the borehole wall show strong dependence on frequency and angle of incidence, even at low frequencies.

Notes: Seismograms predicted from acoustic or elastic earth models depend very non-linearly on the long wavelength components of velocity. This sensitive dependence demands the use of special variational principles in waveform-based inversion algorithms. The differential semblance variational principle is well-suited to velocity inversion by gradient methods, since its objective function is smooth and convex over a large range of velocity models. An extension of the adjoint state technique yields an accurate estimate of the differential semblance gradient. Non-linear conjugate gradient iteration is quite successful in locating the global differential semblance minimum, which is near the ordinary least-squares global minimum when coherent data noise is small. Several examples, based on the 2D primaries-only acoustic model, illustrate features of the method and its performance.

Notes: Evidence from borehole susceptibility logs and the spectral analysis of aeromagnetic data suggests that the three-dimensional distribution of magnetization within the crust can be described as fractal. This property can be exploited in magnetic interpretation methods which explicitly require statistical information on the spatial variation of magnetization. Specifically, we address the problem of magnetic source depth estimation through downward continuation and gridding aeromagnetic survey data using the method of kriging.When magnetic data are continued downwards the depth at which the power spectrum flattens out (the ‘white’ depth) can be taken to be an estimate of the top of the source distribution. This procedure assumes that individual sources are uncorrelated with each other. Taking into account the correlation of the magnetization using a fractal description leads to a reduction in this depth estimate.Gridding of randomly distributed magnetic measurements using kriging requires an estimate of the covariance of the data. Compared with the assumption of a white (uncorrelated) magnetization distribution, using fractal covariances for kriging produces gridded estimates which more closely reflect the statistics of the underlying magnetization process and produce maps with a justifiable degree of smoothness.

Notes: The superposition integral expressing the field due to a magnetic source body is relatively simple to evaluate in the case of a homogeneous magnetization. In practice this generally requires that any remnant component is uniform and the susceptibility of the body is sufficiently low to permit the assumption of a uniform induced magnetization. Under these conditions the anomalous magnetic field due to a polyhedral body can be represented in an intuitive and physically appealing manner. It is demonstrated that the components of the magnetic field H can be expressed as a simple combination of the potentials due to two elementary source distributions. These are, firstly, a uniform double layer (normally directed dipole moment density) located on the planar polygonal faces of the body and, secondly, a uniform line source located along its edges. In practice both of these potentials (and thus the required magnetic field components) are easily computed. The technique is applicable to polyhedra with arbitrarily shaped faces and the relevant expressions for the magnetic field components are suitable for numerical evaluation everywhere except along the edges of the body where they display a logarithmic singularity.

Notes: Improving the accuracy of NMO corrections and of the corresponding interval velocities entails implementing a better approximation than the formula used since the beginning of seismic processing. The exact equations are not practical as they include many unknowns. The approximate expression has only two unknowns, the reflection time and the rms velocity, but becomes inaccurate for large apertures of the recording system and heterogeneous vertical velocities. Several methods of improving the accuracy have been considered, but the gains do not compensate for the dramatic increase in computing time. Two alternative equations are proposed: the first containing two parameters, the reflection time and the focusing time, is not valid for apertures much greater than is the standard formula, but has a much faster computing time and does not stretch the far traces; the other, containing three parameters, the reflection time, like focusing time and the tuning velocity, retains high frequencies for apertures about twice those allowed by the standard equation. Its computing time can be kept within the same limits. NMO equations, old and new, are designed strictly for horizontal layering, but remain reliable as long as the rays travel through the same layers in both the down and up directions.An equation, similar to Dix's formula, is given to compute the interval velocities. The entire scheme can be automated to produce interval-velocity sections without manual picking.

Notes: The Bjøirnøya West Basin lies between latitudes 73° and 74°, longitudes 16°E and 18°E, contains at least 8 km of sediments deposited from the Late Jurassic, and is of considerable interest for hydrocarbon exploration. The Cenozoic extensional tectonics in the basin can be clearly seen from seismic data with normal faulting and from subsidence curves with rapid subsidence. The extension occurred during the Late Palaeocene with active extension lasting about 6 million years (m.y.) followed by thermal cooling. The tectonic subsidence within the study area shows a three-phase development: phase 1, synrift (58–52 Ma (million years before the present day)), is characterized by rapid subsidence; phase 2, postrift (52–5 Ma), by slow subsidence with occasional uplift; and phase 3 (5–0 Ma), by rapid subsidence. An adaptive finite-element model, with consideration of the radiogenic heat production in the lithosphere, has been used to model the subsidence and heat flow. The modelling of subsidence shows the β-factor distribution varying from 1.9 to 3.5 with an average of 2.4 for the uniform lithospheric extension. The heat-flow modelling predicts a rapid increase of heat flow during the Early Palaeocene. The maximum heat flow at about 52 Ma, which could be as much as 3.0 hfu (10−6 cal/cm2/s), was followed by a decrease in heat flow. A plate-weakening model has been proposed to explain the rapid subsidence for the last 5 m.y. by flexure of the elastic lithosphere which is weakened by a decrease in elastic thickness caused by an increase of the temperature gradient in the lithosphere. The plate-weakening model predicts a heat-flow increase at 5 Ma of up to 2.0 hfu. Our study, using quantitative modelling of the tectonic subsidence, provides a partial (if not a full) understanding of the tectonic development and thermal evolution of the Bjønøya West Basin.

Notes: We present a discrete modelling scheme which solves the elastic wave equation on a grid with vertically varying grid spacings. Spatial derivatives are computed by finite-difference operators on a staggered grid. The time integration is performed by the rapid expansion method. The use of variable grid spacings adds flexibility and improves the efficiency since different spatial sampling intervals can be used in regions with different material properties. In the case of large velocity contrasts, the use of a non-uniform grid avoids spatial oversampling in regions with high velocities. The modelling scheme allows accurate modelling up to a spatial sampling rate of approximately 2.5 gridpoints per shortest wavelength. However, due to the staggering of the material parameters, a smoothing of the material parameters has to be applied at internal interfaces aligned with the numerical grid to avoid amplitude errors and timing inaccuracies. The best results are obtained by smoothing based on slowness averaging. To reduce errors in the implementation of the free-surface boundary condition introduced by the staggering of the stress components, we reduce the grid spacing in the vertical direction in the vicinity of the free surface to approximately 10 gridpoints per shortest wavelength. Using this technique we obtain accurate results for surface waves in transversely isotropic media.

Notes: A method is described to locate secondary faults, which can be difficult to identify on the Bouguer gravity map. The method is based on cross-correlation between the theoretical anomaly due to a vertical step and the second vertical derivative of the Bouguer anomaly. Faults are located from the closed maxima and minima on the cross-correlation contour map calculated for two perpendicular directions. One-dimensional model computations show that the magnitude of the extremum of the cross-correlation is related to the depth to the top of the hanging wall and the throw of the fault. Application of the method to the Bouguer gravity map of the former mouth of the Yellow River in the Shengli Oilfield area near the Bo Hai Sea shows the effectiveness of the method.

Notes: Radio signals from very low frequency (VLF) transmitters distributed world-wide have been used for several decades to study the lateral variations of the electrical conductivity in the upper few hundred metres of the earth's crust. Traditionally, in airborne applications, the total magnetic fields from one or two transmitters are measured to form the basis for construction of maps that primarily show those conductive structures that are parallel or subparallel to the direction to the transmitters. The tensor VLF technique described in this paper makes use of all signals available in a predefined frequency band to construct transfer functions relating the vertical magnetic field and the two horizontal magnetic field components. These transfer functions are uniquely determined for a particular measuring site and contain information about the lateral conductivity variations in all directions. First experiences with real field data, acquired during a test survey in Sweden, show that maps of the so-called peaker, the spatial divergence of the transfer functions, give an image of the conducting structures. Most of the structures can be correlated to small valleys filled with conducting sediments or valleys underlain by conductive fracture zones in the crystalline rocks.

Notes: We study the geoelectrical problem of picking out the useful signal from voltage time series, monitored under conditions of a low signal-to-noise ratio and non-stationary noise. Statistical tests performed at different sites show that geoelectrical noise often belongs to the class of non-stationary phenomena with non-Gaussian probability distributions. In such cases, the application of conventional methods of geoelectrical useful signal extraction, based on the stationary white-noise assumption, gives biased estimates. For the on-line processing of geoelectrical recordings, we recommend the use of the periodogram technique combined with the Kolmogorov–Smirnov test, a suitable algorithm of which is described in detail. The suggested procedure allows data acquisition to stop as soon as the useful signal power is estimated with a relative error smaller than a predetermined value. Finally, we compare the suggested procedure with the autoregressive approach. The previously used and simpler periodogram method, applied to the solution of problems of this kind, appears to give better performances than the autoregressive analysis.

Notes: For successful prestack depth migration an accurate velocity model is needed. One method for model updating is based on image gather analysis. In an image gather all reflectors line up horizontally if the correct velocities are used for the depth migration. This is also true for dipping reflectors, as all traces of an image gather belong to the same surface coordinate. The images of the reflector in an image gather curve upwards if the velocity used for the migration is too low, or downwards if the velocity is too high. This deviation can be used for model updating. Curves which depend on depth, offset and a parameter which relates the estimated to the true model are fitted to the image. By calculating the coherence along the deviation curves, this parameter can be estimated and hence an update can be calculated.Formulae are derived for the deviation curves and the update of the velocity depth model for a multilayered model for both shot and common-offset migrated data, with and without gradients. The method is tested on synthetic data with satisfactory results.

Notes: The variation in the density of sediments with depth in a sedimentary basin can be represented by a hyperbolic function. Gravity anomaly expressions for a 2D vertical prism and an asymmetric trapezium with a hyperbolic density distribution are derived in a closed form. These are used in inverting the gravity anomaly of a sedimentary basin with variable density. Firstly, the basin is viewed as a series of prisms juxtaposed with each other. The initial thickness of each prism is obtained from the gravity anomaly at its centre, based on the gravity anomaly of an infinite slab with a hyperbolic density contrast. These thicknesses are improved, based on the differences between the observed and the calculated anomalies. For an improved rate of convergence of the solution, these thicknesses may alternatively be refined using the well-known ridge regression technique. Secondly, the basin is approximated by an asymmetric trapezium and its anomalies are inverted for the parameters of the trapezium using the ridge regression. Since this approximation serves to oversimplify the floor of the basin, it must be used only when the sediment-basement interface has minor undulations. The results of a hypothetical case and two field cases (the San Jacinto Graben, California and the Godavari Graben, southern India) are presented. In both field cases, the interpreted depths are comparable with the real ones, proving the validity of the assumption of a hyperbolic density distribution of the sediments in the two basins considered.

Notes: The polarization direction or 'sign’ of reflected converted P–S waves depends upon the angle of incidence of the incident P-wave. Sign reversal due to reversal of the angle of incidence is often encountered and is an impediment to P–S wave processing and imaging, because when P–S events or P-S migrated images with mixed signs are stacked, destructive interference occurs. We have created and demonstrated a means of correcting for this reversal. To do this, a P-wave angle of incidence is calculated for every point in the image space. This is done by calculating a P–S reflected waveform for every point, by extrapolating the reflected S-wavefield backwards from the receiver line, and then cross-correlating this waveform with the S-wave reflections observed at the receiver line. A multiplier, (sgn α) is assigned to each point in the image space, where α is the angle of incidence of the P-wave.The multiplier was applied to a set of prestack reverse time migration images derived from a cross-borehole physical elastic model data set. The improvement in the stacked image when the sign correction is applied is spectacular. The P-S image quality is comparable to, or better than, stacked migrated P-P images.The method appears to be applicable to all reflection modes and to all recording geometries.

Notes: Fluid permeability in fractured rocks is sensitive to pore-pressure changes. This dependence can have large effects on the flow of fluids through rocks. We define the permeability compliance γ= 1/k(k/δpp)pc, which is the sensitivity of the permeability k to the pore pressure pp at a constant confining pressure pc, and solve the specific problems of constant pressure at the boundary of a half-space, a cylindrical cavity and a spherical cavity. The results show that when the magnitude of permeability compliance is large relative to other compliances, diffusion is masked by a piston-like pressure profile. We expect this phenomenon to occur in highly fractured and compliant rock systems where γ may be large. The pressure profile moves rapidly when fluids are pumped into the rock and very slowly when fluids are pumped out. Consequently, fluid pressure, its history and distribution around injection and production wells may be significantly different from pressures predicted by the linear diffusion equation. The propagation speed of the pressure profile, marked by the point where δpp/δx is a maximum, decreases with time approximately as 〈inlineGraphic alt="inline image" href="urn:x-wiley:00168025:GPR693:GPR_693_mu1" location="equation/GPR_693_mu1.gif"/〉 and the amplitude of the profile also dissipates with time (or distance).The effect of permeability compliance can be important for fluid injection into and withdrawal from reservoirs. For example, excessive drawdown could cause near-wellbore flow suffocation. Also, estimates of the storage capacity of reservoirs may be greatly modified when γ is large. The large near-wellbore pressure gradients caused during withdrawal by large γ can cause sanding and wellbore collapse due to excessive production rates.

Notes: We investigate, from a theoretical point of view, the possibility of performing marine two-level magnetovariational measurements. An apparent resistivity function is denned and calculated after solving the differential equation governing the behaviour of the natural magnetic field variations inside a one-dimensional earth. In order to generalize the problem, a frequency-dependent resistivity is assumed to characterize the layers and the distortions caused by the polarization effects are carefully analysed. The computation of three-layer amplitude and phase diagrams for the apparent resistivity function shows that, in the case of an intermediate polarizable layer, sandwiched between a non-dispersive overburden and substratum, the H-type sequence results are the most affected by the dispersion phenomenon as it occurs in magnetotellurics. Finally we consider the problem of the sensitivity of the method, since, in practice, it requires top and bottom sensors separated by a vertical finite distance. It is found that in the higher-frequency range, due to the strong attenuation of the relative components of the field, the depth of the bottom sensor must be small enough to guarantee detectable signals, well above the full-scale resolution of the acquisition system. Conversely, in the lower-frequency range such a depth must be large enough to allow the difference between the top and bottom signals to be above the same recording sensitivity threshold.

Notes: Based on a Born approximation of a thin sheet integral equation, it is shown that small-scale surficial heterogeneity significantly distorts the electromagnetic field excited by electric dipoles only when either the source or the receiver are located on the heterogeneities. When a surface heterogeneity is beneath the source, the associated distortion of the electromagnetic field is manifest as a change in the effective electric dipole moment. Hence the magnetotelluric transfer functions and impedance relations remain undistorted in this case. When a surface heterogeneity is beneath the receiver, the electric field is severely distorted, but the magnetic field is only slightly distorted. The impedance tensor is therefore strongly distorted, but the tipper vector is almost unaltered. Since the controlled source tipper is a function of 1D earth conductivity, it is proposed that tipper data should be used in the first stage of 1D interpretation. For a 1D earth, the tipper vector must always point towards the source and, in the near-field limit, should have unit length. These two necessary conditions must be met by the measured tipper before it is interpreted one dimensionally.

Notes: A series of model experiments was performed in an ultrasonic laboratory to study the radiation of downhole sources in a variety of formations. Three models were used in the experiments. They were a Lucite model, a Lucite model with a free glass pipe in the centre, and a glass-cased soil model. In addition, a finite-difference modelling technique was used to simulate the wave propagation in these models and the results of the laboratory and numerical experiments are compared. In the Lucite borehole model the waveforms recorded in the experiment agree very well with the finite-difference synthetics. The snapshots of the wavefield from the finite-difference simulation show the radiation pattern of the P- and S-waves in the Lucite formation. These patterns are consistent with the theoretical calculations. In the Lucite model with the free glass pipe, the finite-difference synthetics are also in good agreement with the experimental observations, especially for the conical P-wave arrival. The angle between the wavefront of the conical P-wave and the borehole axis, observed from the snapshot, agrees with the theory. In the cased soil model, the arrival time of the finite-difference synthetics is in good agreement with the laboratory measurements. The relative amplitudes of the P-wave and the Mach wave are not correctly modelled because intrinsic attenuation is not included in the finite-difference calculation. The Mach cone angle from the snapshot agrees with the theoretical prediction. Finally, a finite-difference method was used to simulate Mach-wave propagation in a formation with two horizontal layers. In the case of two slow layers, the Mach-wave generated in the first layer is reflected back from and transmitted through the boundary and another Mach wave is generated at the second layer when the Stoneley wave travels into the second layer. In the case of a formation having one slow and one fast layer, the Mach wave generated in the slow layer is reflected back at the boundary and leaked into the fast layer. There is no Mach wave in the fast layer.

Notes: Geophysical surveys and chemical analyses on cores were carried out in three Ontario peatlands, from which we have gained a better understanding of the peat properties that control the geophysical responses. The electrical conductivity depends linearly on the concentration of total dissolved solids in the peat pore waters and the pore waters in turn bear the ionic signatures of the underlying mineral sediments. The ionic concentration, and thus the electrical conductivity, increase linearly from the surface to basement. The average bulk electrical conductivity of peatlands at Ellice Marsh, near Stratford, and at Wally Creek Area Forest Drainage Project, near Cochrane, are of the order of 25 mS/m. The Mer Bleue peatland, near Ottawa, has extremely high electrical conductivity, reaching levels of up to 380 mS/m near the base of the peat. The Mer Bleue peatland water has correspondingly high values of total dissolved solids, which originate from the underlying Champlain Sea glaciomarine clays. The dielectric permittivity in peats is largely controlled by the bulk water content. Ground penetrating radar can detect changes in water content greater than 3%, occurring within a depth interval less than 15 cm. The principal peatland interfaces detected are the near-surface aerobic to anaerobic transition and the peat to mineral basement contact. The potential for the successful detection of the basement contact using the radar can be predicted using the radar instrument specifications, estimates of the peatland depth, and either the bulk peat or the peat pore water electrical conductivities. Predicted depths of penetration of up to 10 m for Ellice Marsh and Wally Creek exceed the observed depths of 1 to 2 m. At Mer Bleue, on the other hand, we observe that, as predicted, a 100 MHz signal will penetrate to the base of a 2 m thick peat but a 200 MHz signal will not.

Notes: The investigation of water in salt-rock formations is of particular relevance to underground nuclear waste repositories. In the Asse salt-mine (Germany) a study into the relationship of in situ resistivity to water content has been made. Measurements were carried out in older rock-salt using an electrode array in boreholes, an electrode profile in a drift and small resistivity sensors in and around a drift seal. Further measurements were made on moist zones in a contact area of younger rock-salt and carnallitite and also in older rock-salt with anhydrite bands using electrode profiles in the drifts. The resistivities range from 102Ωm to 106Ωm. Corresponding probes have water contents from 0.01% to 1.3%. A definite relationship between resistivity and water content is revealed which can be described by Archie's law using a cementation factor m of 1.9. Porosities are between 0.08% and 1.4% and the saturations vary considerably. An explicit influence of saturation on resistivity cannot be discovered using the present data. The results enable us to estimate the in situ water content and the order of the in situ porosity using resistivity surveys at different scales. This increases significantly the safety of a nuclear repository site.

Notes: Minimization of seismic residuals does not guarantee uniqueness of the model, and this implies ambiguities in the inversion. Amplitude vs. offset (AVO) inversion does not lead to a unique solution of single elastic interface parameters unless converted and S-wave or critical angle reflections are available. Given the ambiguity of AVO inversion, this paper discusses the interaction between AVO and velocity estimation. The number of independent parameters necessary to describe an isolated reflection with AVO behaviour and residual velocity error is determined. Statistical analysis allows the establishment of an approximate equivalence of the effects of AVO and slight velocity variations; this equivalence cannot be solved without geological a priori information (kinematic equivalence). The data are then decomposed into compound events (i.e. sequences of N interfaces that follow each other at a fixed time lag). The decomposition is obtained by extrapolating the results of the analysis from narrowband to wideband data. Compound events decomposition demonstrates that AVO inversion is ambiguous, not only in the physical parameter space (P- and S-wave velocities, and density) but also kinematically. As an example of compound event decomposition, a medium is derived. This medium is geologically implausible but is kinematically equivalent.

Notes: Knowledge of the declination and inclination of the total and induced magnetization vectors is normally required for the interpretation and analysis of magnetic anomalies. A new method of estimating the direction of the total magnetization vector of magnetized rocks from magnetic anomalies is proposed. The unknown declination and inclination (D*T and I*T) can be found by applying a reduction-to-the-pole operator to the measured anomalies for different couples of total magnetization direction parameters (DT and IT) and by observing the variation of the anomaly minimum as a function of both DT and I*T.and D*T are estimated using the maximum of this function. Comparing our method to previous methods, one advantage is that our estimates are not zero-level dependent; furthermore, the method allows inclinations to be well estimated, with the same accuracy as declinations; finally declinations are not underestimated. Our method is applied to a real case and meaningful results are obtained; it is shown that the feasibility of the method is improved by removing the low-frequency components.

Notes: An efficient algorithm is presented to compute the Hankel transform. The algorithm yields simultaneously all the required weights for a given order of the Bessel function using the fast Fourier transform. An additional shift is introduced to the filter abscissa besides Koefoed's shift to give a better filter performance.

Notes: The stacking velocity best characterizes the normal moveout curves in a common-mid-point gather, while the migration velocity characterizes the diffraction curves in a zero-offset section as well as in a common-midpoint gather. For horizontally layered media, the two velocity types coincide due to the conformance of the normal and the image ray. In the case of dipping subsurface structures, stacking velocities depend on the dip of the reflector and relate to normal rays, but with a dip-dependent lateral smear of the reflection point. After dip-moveout correction, the stacking velocities are reduced while the reflection-point smear vanishes, focusing the rays on the common reflection points. For homogeneous media the dip-moveout correction is independent of the actual velocity and can be applied as a dip-moveout correction to multiple offset before velocity analysis.Migration to multiple offset is a prestack, time-migration technique, which presents data sets which mimic high-fold, bin-centre adjusted, common-midpoint gathers. This method is independent of velocity and can migrate any 2D or 3D data set with arbitrary acquisition geometry. The gathers generated can be analysed for normal-moveout velocities using traditional methods such as the interpretation of multivelocity-function stacks. These stacks, however, are equivalent to multi-velocity-function time migrations and the derived velocities are migration velocities.

Notes: A new definition of apparent resistivity for the presentation of magnetotelluric sounding data is proposed. The new definition is based on the frequency-normalized impedance function. Both the existing and proposed definitions of apparent resistivity are analysed theoretically and are compared using model curves computed for a 1D earth model. Apparent resistivity curves computed using the proposed definition are a better approximation to the true resistivity values of the subsurface layers. In addition, the layers are more noticeable on the apparent resistivity curves, which is an advantage, especially for the ascending and descending type of apparent resistivity curve.

Notes: A gravimetric survey, covering a site 200 m square, was carried out in order to locate karstic cavities. After eliminating the regional trend using a polynomial fit, the residual is modelled by least-squares prediction. Correlated signals for several wavelengths are detected. The inversion of these anomalies is performed by a global 3D adjustment using spherical bodies as models. The adjustment is repeated in order to obtain a stable configuration. The results show the probable presence of a system of cavities and galleries. Data collected from boreholes and the subsequent appearance of sink-holes are consistent with the results.

Notes: We have measured the velocities and attenuations of compressional and shear waves in 29 water-saturated samples of sandstones and shales at a confining pressure of 60 MPa and at frequencies of about 0.85 MHz. The measurements were made using a pulse echo method in which the samples (diameter 5 cm, length 1.5 cm to 2.5 cm) were placed between perspex buffer rods inside a high-pressure cell. The velocity of each seismic wave was determined from the traveltime difference of equivalent phase points (corrected for diffraction effects) of the signals reflected from the top and from the base of each sample. Attenuation was determined in a similar way by comparison of the diffraction corrected amplitudes of the signals. The attenuation data are presented as ‘quality factors’: Qp and Qs for compressional and shear waves respectively. The results show that Qs is strongly correlated with Vs, that Qp is weakly correlated with Vp, and that Qp is strongly correlated with Qs. Qp is strongly dependent on the volume percentage of the assemblage of intra-pore minerals, whether they are clays or carbonates. It is concluded that the attenuation mechanism is due to the local fluid flow arising from the differential dilation of the solid rock frame and the intra-pore mineral assemblage, which is a result of their very different elastic moduli.

Notes: An attempt to resolve non-uniqueness in the interpretation of transient electromagnetic (TEM) sounding data using measured data alone is made. It is shown in the various examples studied that sufficiently early time measurements can be the determining factor in reducing the ambiguity caused by model equivalence. The early delay times thus play a dual role in transient soundings: they are responsible for resolving shallow structures and they may eliminate the ambiguity in the interpretation of geoelectric parameters of deeper targets. This is illustrated by the results of a follow-up TEM survey at the Dead Sea coast of Israel where the use of supplementary early time measurements allowed non-uniqueness in the determination of the depth to fresh/saline groundwater interface to be resolved.

Notes: Flow of fluids in many hydrocarbon reservoirs and aquifers is enhanced by the presence of cracks and fractures. These cracks could be detected by their effects on propagation of compressional and shear waves through the reservoir: several theories, including Hudson's, claim to predict the seismic effects of cracks. Although Hudson's theory has already been used to calculate crack densities from seismic surveys, the predictions of the theory have not yet been tested experimentally on rocks containing a known crack distribution. This paper describes an experimental verification of the theory. The rock used, Carrara marble, was chosen for its uniformity and low porosity, so that the effect of cracks would not be obscured by other influences. Cracks were induced by loading of laboratory specimens. Velocities of compressional and shear waves were measured by ultrasound at 0.85 MHz in dry and water-saturated specimens at high and low effective pressures. The cracks were then counted in polished sections of the specimens. In ‘dry’ specimens with both dry and saturated cracks, Hudson's theory overpredicted observed crack densities by a constant amount that is attributed to the observed value being systematically underestimated. The theory made poor predictions for fully saturated specimens. Shear-wave splitting, caused by anisotropy due to both crystal and crack alignment, was observed. Cracks were seen to follow grain boundaries rather than the direction of maximum compression due to loading. The results demonstrate that Hudson's theory may be used in some cases to determine crack and fracture densities from compressional- and shear-wave velocity data.

Notes: The paper by Slob and Ziolkowski (1993) is apparently a comment on my paper (Szaraniec 1984) on odd-depth structure. In fact the basic understanding of a seismogram is in question. The fundamental equation for an odd-depth model and its subsequent deconvolution is correct with no additional geological constraints. This is the essence of my reply which is contained in the following points.〈list xml:id="l1" style="custom"〉1The discussion by Slob and Ziolkowski suffers from incoherence. On page 142 the Goupillaud (1961) paper is quoted:“… we must use a sampling rate at least double that… minimum interval…”. In the following analysis of such a postulated model Slob and Ziolkowski say that “… two constants are used in the model: Δt as sampling rate and 2Δt as two-way traveltime”. By reversing the Goupillaud postulation all the subsequent criticism becomes unreliable for the real Goupillaud postulation as well as the odd-depth model.2Slob and Ziolkowski take into consideration what they call the total impulse response. This is over and above the demands of the fundamental property of an odd-depth model.Following a similar approach I take truncated data in the form of a source function, S(z), convolved with a synthetic seismogram (earth impulse response), R̃(z), the free surface being included. The problem of data modelling is a crucial one and will be discussed in more detail below. By my reasoning, however, the function 〈displayedItem type="mathematics" xml:id="mu1" numbered="no"〉〈mediaResource alt="image" href="urn:x-wiley:00168025:GPR81:GPR_81_mu1"/〉 may be considered as a mathematical construction introduced purely to work out the fundamental property. In this connection there is no question of this construction having a physical meaning.It is implicit that in terms of system theory, K(z) stands for what is known as input impedance.3Our understandings of data are divergent but Slob and Ziolkowski state erroneously that:“Szaraniec (1984) gives (21) as the total impulse response…”. This point was not made.This inappropriate statement is repeated and echoed throughout the paper making the discussion by Slob and Ziolkowski, as well as the corrections proposed in their Appendix A, ineffective.Thus, my equation (2) is quoted in the form 〈displayedItem type="mathematics" xml:id="mu2" numbered="no"〉〈mediaResource alt="image" href="urn:x-wiley:00168025:GPR81:GPR_81_mu2"/〉which is in terms of the reflection response Gsc and holds true at least in mathematical terms. No wonder that “this identity is not valid for the total impulse response” (sic), which is denoted as G(z). None the less a substitution of G for Gsc is made in Appendix A, equation (A3). The equation numbers in my paper and in Appendix A are irrelevant, but (A3) is substituted for (32) (both numbers of equations from the authors’ paper). Afterwards, the mathematical incorrectness of the resulting equation is proved (which was already evident) and the final result (A16) is quite obviously different from my equation (2). However, the substitution in question is not my invention.4With regard to the problem of data modelling, I consider a bi-directional ID seismic source located just below the earth's surface. The downgoing unit impulse response is accompanied by a reflected upgoing unit impulse and the earth response is now doubled. The total impulse response for this model is thus given by 〈displayedItem type="mathematics" xml:id="mu3" numbered="no"〉〈mediaResource alt="image" href="urn:x-wiley:00168025:GPR81:GPR_81_mu3"/〉where (—r0) =— 1 stands for the surface reflection coefficient in an upward direction. Thus〈displayedItem type="mathematics" xml:id="mu4" numbered="no"〉〈mediaResource alt="image" href="urn:x-wiley:00168025:GPR81:GPR_81_mu4"/〉 that is to say, the total response to a unit excitation is identical with the input impedance as it must be in system theory.The one-directional 1D seismic source model is in question. There must be a reaction to every action. When only the downgoing unit impulse of energy is considered, what about the compensation?5In more realistic modelling, an early part of a total seismogram is unknown (absent) and the seismogram is seen in segments or through the windows. That is why in the usual approach, especially in dynamic deconvolution problems, synthetic data in the presence of the free surface are considered as an equivalent of the global reflection coefficient. It is implicit that model arises from a truncated total seismogram represented as a source function convolved with a truncated global reflection coefficient.Validation or invalidation of the truncation procedure for a numerically specified model may be attempted in the frame of the odd-depth assumption. My equations (22) and (23) have been designed for investigating the absence or presence of truncated energy.The odd-depth formalism allows the possibility of reconstructing an earlier part of a seismogram (Szaraniec 1984), that is to say, a numerical recovery of unknown moments which are unlikely designed by Slob and Ziolkowski for the data.

Notes: Summary Organosolv lignin was used as organic filler for polypropylene (PP) and poly(ethene-co-vinylacetate) (EVA) containing 13wt-% vinylacetate. As a function of the lignin content, which was varied between 0 and 30wt-%, mechanical properties such as Young's modulus, yield stress, fracture stress, and elongation at break of the thermoplastic lignin-based compounds were measured. Both lignin-filled thermoplastics exhibit pronounced matrix reinforcement with increasing lignin content. Due to better interfacial adhesion between lignin and EVA, 30wt-% lignin addition to EVA doubles Young's modulus without sacrificing high elongation at break.

Notes: Summary 4-Vinylphthalic anhydride can be prepared from phthalic acid via bromination and subsequent olefination (Heck-reaction). Homo- and copolymerization with styrene was accomplished using AIBN as initiator. The copolymer compositions were determined by infrared-spectroscopy. The copolymerization parameters are rs=0,15 and rVPA=3,09, the corresponding Q, e values of 4-vinylphthalic anhydride are estimated as Q=3,34 and e=0.09. Despite the fact that the molecular weights were rather low as a consequence of the reaction contions, the glass transition temperatures rise with increasing VPA content. The homopolymer has a glass transition temperature in the order of 226°C.

Notes: Summary Immiscible melt mixed blends of a crystallisable polyolefin (isotactic polypropylene, PP) and atactic polystyrene (PS) were prepared in a wide composition range. It was found that when PP is the major component in the blend its crystallisation behaviour is not affected by blending it with PS. However if PP is the minor component, it will be dispersed in the immiscible PS matrix, hence the nucleation mechanism changes from predominantly heterogeneous to predominantly homogeneous as long as the size of the dispersed PP droplets is below a critical value (of the order of 1–2 μm).

Notes: Summary New types of epoxy compounds containing biphenyl and azophenyl groups were synthesized. Model glycidyl ethers with one epoxy group were prepared to study the first reaction steps during the curing process. Diglycidyl ethers with or without a hexamethylene spacer were made to obtain epoxy networks. The structures of some intermediates and of the epoxy compounds synthesized were confirmed by Proton and Carbon-13 NMR spectroscopy.

Notes: Summary A novel initiator, i.e. trimethylsilylmethyllithium has been successfully used for the ring opening polymerization of cyclosiloxanes, in toluene or in the bulk, in the presence of the cryptand [211] or DMSO. Suitable conditions have been found in which monomodal distributions of molecular weights are observed for homopolymers of 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane (V4) as well as for copolymers of V4 with D3 or D4.

Notes: Summary Methylalumoxane (MAO)-activated rac-[1,2-bis(η5-(9-fluorenyl))-1-phenylethane]zirconium dichloride (1) was used for propene polymerization at 30, 50, and 70°C and constant monomer concentration. The polypropene products are isotactic with stereoregularities depending on the polymerization temperature. The pentad distributions follow “enantiomorphic site statistics”, indicating stereocontrol being conducted by the chiral catalyst site.

Notes: Summary A satisfactory synthesis route to a new monomer, the 3-chloro-4-nitrostyrene (3-CNS) is described. The results of free radical polymerisation experiments (limit of conversion, global kinetics) are reported by comparison with those of the isomer 4-chloro-3-nitrostyrene (4-CNS). They show the great influence of the nitro group position which markedly increases the reactivity of 3-CNS.

Notes: Summary Poly(β-hydroxy nonanoate)-polystyrene graft copolymers were prepared by the reaction of active polystyrene containing peroxide group with poly(β-hydroxy nonanoate) at 80°C. Graft copolymers with a wide graft composition range depending on the amount of active polystyrene in the original mixture were produced and separated from the grafting product by fractional precipitation. NMR and IR spectra of the graft copolymers were containing the characteristic bands of the corresponding blocks. DSC curves of the graft copolymers had a large endotherm between 50 and 110°C.

Notes: Summary The isothermal crystallization kinetics of the isotactic content of three poly(1-hexadecene) samples with different tacticity has been studied by real-time small-angle X-ray scattering using synchrotron radiation. The process was analyzed in terms of the Avrami equation. The value of the Avrami exponent was found to be approximately 1, suggesting instantaneous nucleation followed by rod-like growth. The results are compared with those previously obtained by differential scanning calorimetry.

Notes: Summary In the present work we report the results of the polymerization of styrene using diphenylzinc-butanone, Ph2Zn-MeCOEt. Our results indicate that these systems induce the polymerization of styrene reaching a larger conversion when the molar ratio MeCOEt/Ph2Zn=1,0. According to size exclusion chromatography, SEC, studies of the polystyrene obtained using the Ph2Zn-MeCOEt showed unimodal curves and have molecular weight distribution narrower than those obtained using the Ph2Zn-H2O system, suggesting a more simple reaction system.

Notes: Summary Fast atom bombardment mass spectrometry (FAB-MS) has been used to identify oligomers with different end groups obtained by the carbonate interchange reaction of bisphenol-A with dimethyl carbonate and the partial methanolysis of poly(bisphenol-A carbonate)s. Based on the FAB-MS data, a reaction pathway for the formation of compounds in the synthesized oligomers is proposed.

Notes: Abstract A series of semi-interpenetrating polymer networks (semi-IPN's) based on different compositions of an acyclic polyethylene terephthalate oligomer and unsaturated polyester resin (UP) were prepared. The oligomer was dissolved in the resin containing styrene crosslinker. Later this mixture was crosslinked at room temperature using methyl ethyl ketone peroxide catalyst and cobalt naphtanate as promoter. The tensile strength of the IPN's decreases as the concentration of oligomer increases, whereas, elongation to break increases. A characterization of the oligomer used is also presented.

Notes: Summary The impact properties of 1:1 polyolefin-polystyrene blends compatibilised with a series of hydrogenated styrene-butadiene block copolymers of various structures have been studied with a view to establishing a structure-property realationship. The most effective compatibiliser in this context appears to be a low molecular weight triblock (Kraton G1652). Addition of only 5% Kraton G1652 affords a ca. three-fold improvement in the impact strength for a 1:1 PP/PS blend over the uncompatibilised blend and leads to near HIPS impact strength for a 1:1 LDPE/PS blend. This compatibiliser is as effective as a high molecular weight tapered diblock and appears to be substantially more effective than either low molecular weight diblocks or a higher molecular weight triblock.

Notes: Summary In the copolymerizations of 1-chloro-1-octyne (ClOc) and 1-chloro-2-phenylacetylene (ClPA) with norbornene (NBE) by MoCl5-n-Bu4Sn in toluene at-20°C, both comonomers were consumed simultaneously. The GPC curves of the copolymerization products were unimodal and identical irrespective of the RI and UV (290 nm) detectors. The13C NMR spectra of the products exhibited the presence of cross-propagating sequences. From these results, it is concluded that the copolymerization products are copolymers and not mixtures of homopolymers. The monomer reactivity ratios were: rClOc=0.69, rNBE=6.4; rClPA=1.0, rNBE=3.1. The more electron-donating the ring substituent of CiPA, the more reactive the ClPA in copolymerization with NBE.

Notes: Summary Polymerization of 1-phenyl-2-(p-phenoxyphenyl)acetylene (p-PhODPA), 1-phenyl-2-(p-methoxyphenyl)acetylene, and 1-phenyl-2-(p-n-butoxyphenyl)acetylene was examined. These monomers polymerized with TaCl5-n-Bu4Sn to give methanol-insoluble polymers in over 60% yields. Poly(p-PhODPA) was a yellow solid completely soluble in toluene, CHCl3, etc., and its weight-average molecular weight was about 1.0x106 or higher. This polymer was thermally very stable (the onset temperature of weight loss in TGA in air was 420 °C). Its oxygen permeability coefficient (P o 2) was 37 barrers (P o 2/P n 2 2.2) and similar to that of natural rubber. In contrast, the other two polymers did not completely dissolve in any organic solvent, and their thermal stability was lower.

Notes: Summary Chelating polymers obtained by copolymerization of methacryl-oylmalodiethylester (MMDEt) with styrene, methylmethacrylate (MMA), N-vinylpyrrolidone (VPD) and N,N-dimethylacrylamide (DMAM) as well as the homopolymer of methacryloylmalodiethylester (MMDEt) have been investigated. Watersoluble chelating polymers derived from copolymerization with DMAM offer not only the possibility of a very fast removal of metal ions from aqueous solution, but are also insoluble after complexing certain metal ions and can therefore be separated by filtration. As additional investigations on the model acetyloylmalodiethylester (AMDEt) show, preferably hard metal ions such as Mg2+, Ca2+, Al3+ and Cu2+ with an ionic radius up to 1 Å are chelated by the enolic form of the β-ketodiester. The number of ligands for a metal ion corresponds to its valence.

Notes: Summary The 300 MHz 1H-NMR spectrum of free radical initiated poly(3-bromostyrene) is similar to the 1H-NMR spectra of certain poly(vinyl heterocycles) and can be interpreted in a like manner. The 13C-NMR is typical of spectra for meta-substituted polystyrenes, with some of the carbon resonances showing a sensitivity to polymer stereochemistry. The spectra indicate that poly(3-bromostyrene) synthesized by free radical initiation is an atactic polymer.

Notes: Summary Thermal molecular motion of a series of comb-shaped polymers with heptadecafluorodecyl side chains (CF 8C2-) has been studied based on dynamic viscoelastic measurement. The main chain of comb-shaped polymers was poly(fumarate), poly(methacrylate), and poly(acrylate). Poly(fluoroalkylfumarate) with heptadecafluorodecyl group, P(CF 8C2-iPF) was amorphous polymer, whereas poly(acrylate) and poly(methacrylate) with CF 8C2-, P(CF 8C2-Acr) and P(CF 8C2-MAcr) showed mesomorphic behavior. The pervaporation behavior of water/organic mixtures through amorphous polymer, P(CF 8C2-iPF), and mesomorphic one, P(CF 8C2-Acr), were investigated. The distinct increase in permselectivity has been observed at the mesomorphic transition of P(CF 8C2-Acr).

Notes: Sammary New donor-acceptor substituted diarylacetylene hyperpolarizable chromophores bearing an amino group as donor and a methylsulfonyl group as acceptor at each extremities of an azatolane conjugated path have been designed to get a good nonlinearity-transparency trade-off, and synthesized. Corresponding methacrylate esters have been obtained then submitted to free radical polymerization, leading to novel side-chain nonlinear optical polymers and copolymers.

Notes: Summary An attempt is made to extend the model of Leibler for the emulsifying activity and interfacial properties of A-b-B diblock copolymers in incompatible blends of the homopolymers A and B-which are identical with the respective copolymer components- to enthalpically interacting C-b-D diblock copolymers, the block C being thermodynamically compatible with A and D with B. Due to the attractive enthalpic interaction the A/C-b-D/B compatibilized blends are promising for optimum phase adhesion (bold types for thermodynamically compatible partners). Thus, the extended model for a plane interfacial layer includes the enthalpic interaction of the compatible polymer pairs beside the entropic effects. The approach starts with the equillibrium supposition, not taking into consideration enthalpy driven migration effects of the block copolymer from the bulk to the interface, The model confirms a dominant role of the enthalpic interaction between blocks of the diblock copolymer and the respective homopolymers to the compatibilization of incompatible blend components. It is applicable also for blends compatibilized with block copolymers of unfavourable repulsive type interaction, A/C-b-D/B, and for blend systems with mixed type interactions, e. g. A/C-b-B/B or A/C-b-D/B.

Notes: Summary Poly(2-thienyl vinyl ketone) was synthesized via free radical initiation and its 300 H-NMR and 75.5 MHz 13C-NMR spectra were recorded and analyzed. The analysis showed that poly(2-thienyl vinyl ketone) is an atactic polymer.

Notes: Summary Poly(2-fluoro-1,4-phenylenevinylene), PFPV, and its copolymers have been synthesized via water soluble precursor route and their electrical and optical propreties were measured. It seems that electron-withdrawing fluorine substituent on phenylene ring increases the band-gap of PFPV and it affects electrical and optical properties. The conductivity values of FeCl3-doped drawn polymer films ranged from 10-1 to 101 Scm-1 depending on their composition, and were 10 times larger than those of undrawn ones. The χ(3) value for undrawn PFPV, using THG technique at 1907nm fundamental wavelength, was 4.76x10-12 esu.

Notes: Summary A simple method for using differential scanning calorimeters to determine the crystallinity of syndiotactic polystyrene has been developed. Its validity was confirmed by use of infrared and x-ray analysis, as well as comparison to data from the literature. This method will be used to determine the effect of nucleating agents, shear stress, and temperature on the crystallization kinetics of syndiotactic polystyrene.

Notes: Summary Polyether-modified fullerenes have been prepared under mild conditions by reacting C60 or C70 in toluene with a precursor poly(oxyethylene) or poly(oxypropylene) polymer possessing amino end-groups. In the early stages of the interaction, soluble products are formed. Later, cross-linking proceeds between the polyfunctional fullerenes and the bifunctional polyethers. The non-crosslinked fullerene derivatives are soluble both in toluene and water; by evaporation of toluene, very adhesive films are formed.

Notes: Summary Poly(sodium alkyl 2-hydroxy-3-methacryloyloxypropyl phosphate)s as polysoap induced the radical polymerization of methyl methacrylate and styrene in the absence of an added radical initiator in water at 80°C. The polysoap having a C14 alkyl group showed the highest activity of all tested groups. The generalized initiation mechanism of the spontaneous polymerization in which the micellar aggregation state participates is discussed.

Notes: Summary Racemic ((3S,4R)-(3R,4S))-3-methyl-4-benzyloxycarbonyl-2-oxetanone has been prepared by a simple and reproductible method starting from a racemic mixture of threo-((2S,3S)-(2R,3R))-3-methylaspartic acid as chiral precursor. This α, β substituted β-lactone has been polymerized anionically, using tetraethylammonium benzoate as initiator, to yield high molecular weight and amorphous racemic threo-poly(β-benzyl-3-methylmalate). The catalytic cleavage of protecting benzyl ester groups has been conducted in different solvents and racemic threo-poly(β-3-methylmalic acid) has been obtained in N-methylpyrrolidone at room temperature. Racemic threo-poly(β-3-methylmalic acid-co-benzyl-β-3-methylmalate) has been prepared by heterogeneous H2/Pd charchoal catalyzed partial hydrogenolysis of the polymer precursor. Solubility of these different materials has been considered. Hydrolysis of threo-poly(β-3-methylmalic acid) has conducted to racemic threo-3-methylmalic acid. High resolution 13C NMR and selective INEPT NMR have been used for resonances assignment of polymers and copolymers. This new poly(β-hydroxy acid) type polyester expands the family of poly(β-malic acid) derivatives by opening the route for tailor making functional polystereoisomers with two stereogenic centers in the main chain and with the presence of an hydrophobic alkyl group and an hydrophilic carboxylic acid group in the macromolecule.

Notes: Summary The dependence of intensity of surface enhanced Raman scattering on the concentration of poly (4-vinyl pyridine) solutions was investigated. The spectral quality and the Raman scattering intensities of the enhanced spectra of poly (4-vinyl pyridine) adsorbed on nitric acid-roughened silver foil were inversely proportional to the concentration when it changed from semi-dilute to very dilute. The band intensity-concentration plot displays a turning point corresponding to the critical concentration for coil shrinkage. The observed phenomena are in accordance with Qian's proposal for the existence of C s for coil shrinkage in dilute solution.

Notes: Summary The unconventional liquid chromatography of polymers under limiting conditions of their solubility was applied to poly(methyl methacrylate)s differing in their tacticity. The polymers were dissolved in thermodynamically good solvents and injected into an appropriate size exclusion chromatographic (SEC) column flushed with matched, moderately strong nonsolvents. The set of (limiting) conditions was found under which less soluble syndiotactic poly(methyl, methacrylate) moved along the column together with the zone of its initial solvent while better soluble isotactic poly(methyl methacrylate) was eluted according to the SEC mechanism. This indicates the potential of liquid chromatography under limiting conditions to characterize the tacticity of poly(methyl methacrylate)s.

Notes: Summary Dynamic mechanical properties of poly(dimethylphenyl methacrylátes) were studied considering the different positions of the methyl groups on the phenyl ring. In all cases a clear α relaxation can be observed which is associated to the polymer glass transition temperature (Tg). Nevertheless, at lower temperatures, viscoelastic activity is negligible. A correlation between the steric hindrance due to the methyl groups and the temperature at which the relaxation is detected, was established.

Notes: Summary Dielectric permittivity and loss have been measured over the frequency range 10-2 Hz-10 kHz between 100 K and 350 K for samples of 50/50 mixtures of each of two hyperbranched polyesters, one five-generation hydroxy functional (5G-OH) and one threegeneration alkyl-terminated polymer (3G), with dielectrically inactive linear polyethylene. The thermal transitions of the hyperbranched polymers were studied with differential scanning calorimetry. Three relaxation transitions were found in 5G-OH: α, the glass-rubber transition and two subglass processes denoted β and γ showing Arrhenius temperature dependence both with an activation energy of 96±2kJ mol-1. The low temperature process could be assigned to motions of the terminal hydroxyl groups whereas β is due to reorientation of the ester groups. Sample 3G showed only a glass transition and one subglass process being assigned to reorientation of the ester groups. The high activation energy (202 kJ mol-1) of this process indicates that the ester groups are highly constrained in this polymer.

Notes: Summary The chemistry of poly(methyl methacrylate) subjected to 193-nm radiation, emitted by an argon-fluorine excimer laser, was studied by X-ray photoelectron spectroscopy. From the O/C atomic ratios measured at two different sampling depths, it is concluded that the role of depolymerization in the laser ablation process may be less important than previously suggested.

Notes: Summary Poly(vinyl butyral) (PVB)was found to precipitate from a clear plasticizer solution as it was cooled and this unique temperature (TP) (UCST) was noted. Poly(vinyl chloride) (PVC) did not precipitate and in this case the temperature at which it went into solution (TS) was noted. A quantity, referred to previously as the miscibility parameter (MP), is an excellent relative quantitative indicator of the miscibility of poly(vinyl butyral) and poly(vinyl chloride) with plasticizers as demonstrated from a correlation of MP with TP and Ts. Each polymer-plasticizer system is unique. A plot of MP vs. TP or TS for several polymer-plasticizer systems allows additional plasticizers to be evaluated for their plasticizing ability from calculated MP's without resorting to additional experimental measurements. The absolute level of MP acceptability is dictated by the application. For PVB, a copolymer which precipitates from a plasticizer/solvent, the interaction parameter chi(χ) is chi critical ( $$\chi _{cr} $$ ) at the TP of PVB in plasticizer. Since TP approximates the Θ temperature in the limit of molecular weight, the temperature of precipitation or Θ temperature, the solvent volume VS, and the $$\chi _{cr} $$ , define the theoretical MPcr as given by $$\frac{{(\chi _{cr} - 0.35)RT}}{{V_S }}$$ . All MPcr s were≈0.3 which represents the critical MP above which phase separation occurs. The low molecular weight plasticizers were estimated to drastically increase MPcr to about 1 for acceptable application compatibility and this value compares favorably with (PVB) acceptability for a wide range of plasticizer-PVB combinations based on a plasticizer DP of about 20.

Notes: Summary Frictional forces are very sensitive to the interface structure and the chemical and atomic structure of surfaces. It has been shown in the late 80′s (1) that lateral forces due to friction can be measured by atomic force microscopy (AFM) in the contact mode (2,3). This involves measurements which evoke vertical deflection of the AFM probe and observation of lateral forces which twist the AFM force sensor. A simultaneous detection of vertical deflection and twisting of the microcantilever can be done by using a four-sectored positional sensitive photodetector which measures the change in the deflection of a laser light reflected off the top of the microcantilever. The newest generation of SPM (Scanning Probe Microscope) equipment allows for simultaneous AFM and Lateral Force Microscopy (LFM) scans. There is ample evidence in the literature that contact-mode AFM can be used not only to investigate polymer morphology (4,5), but also to study polymer architecture from a true molecular perspective (6).