bluuebunny/crossref_metadata_2025 huggingface dataset:
Can family planning outreach bridge the urban-rural divide in Zambia?
Authors: White Justin S , Speizer Ilene S
Published: September 2007

Background

Zambia experienced declining aggregate fertility and increasing aggregate contraceptive use from 1990 to 2000. Yet, in rural Zambia, progress in family planning has lagged far behind the advances made in Zambia's urban areas. The contraceptive prevalence rate in Lusaka and other urban areas outstripped the rate in rural Zambia by nearly 25 percentage points (41.2 percent versus 16.6 percent) in 2001. The total fertility rate varied between urban and rural areas by 2.5 children (4.3 versus 6.9 children). This paper considers the urban-rural differentials in Zambia and assesses family planning outreach as a tool to narrow this divide.

Methods

This study uses the Zambia Demographic and Health Survey (DHS) data, collected between 2001 and 2002. Logistic regression techniques were employed to examine factors associated with contraceptive use. The first analysis tested modern contraceptive use versus traditional method use and no use. In addition, separate models were run for samples stratified by type of residence (rural or urban) to determine if different factors were associated with use by residence. A simulation determined the effect of all women receiving at least one household visit from a health worker if all other variables were held constant.

Results

Differences in modern contraceptive use between urban and rural areas persist (OR: 1.56, 95 percent CI: 1.24–1.96) even after adjusting for a number of demographic, socioeconomic, cognitive, and attitudinal factors. Household visits by a community health worker significantly increased the likelihood of modern contraceptive use among rural women (OR: 1.83; 95 percent CI: 1.29–2.58). If all rural women received at least one outreach visit per year, the prevalence rate for modern contraceptive methods would be expected to increase for this group by 5.9 percentage points, a marked increase but less than one-quarter of the total urban-rural differential.

Conclusion

Outreach in the form of health worker visits can improve access to family planning services, but it does not eliminate barriers to access or address continued high-fertility desires in Zambia. Until policymakers consider strategies that address both family planning demand creation and supply of services, progress in Zambia and the rest of sub-Saharan Africa will continue to lag behind the rest of the world.
Spontaneous ventral urethral fistula in a young diabetic man: a case report
Authors: Denzinger Stefan , Wieland Wolf F , Burger Maximilian , Otto Wolfgang
Published: September 2007

We present the first case reported in the medical literature of a patient with a spontaneous ventral urethral fistula accompanied by severe infection due to diabetes mellitus. A 34-year-old man with poor controlled adult-onset diabetes mellitus was admitted to our hospital with a large subcutaneous abscess involving the complete penis, scrotum and perineum. The patient did not report any history of any penile trauma or local infection but has experienced transient swelling of the perineal region following urination. Initial surgical treatment consisted of surgical debridement of necrotic tissue. At this time reconstructive surgery was impossible and a suprapubic cystostomy was performed. After 4 months of suprapubic urinary diversion the urethral fistula resolved and function of external genitalia was reestablished. In a follow-up period of 40 months no recurrence occurred. Spontaneous diabetes-associated ventral urethral fistulas are extremely rare and we are not aware of any other published case report.
Using 3D finite-difference modeling to design wide-azimuth surveys for improved subsalt imaging
Authors: Regone Carl J.
Published: September 2007

Three-dimensional finite-difference modeling studies conducted over subsalt structures in the deepwater Gulf of Mexico confirm the deficiencies of narrow-azimuth towed-streamer surveys and predict significant improvement in image quality with wide-azimuth methods. Finite-difference modeling has provided important design parameters for two separate approaches for wide-azimuth surveys: ocean-bottom receivers distributed in a sparse grid on the ocean floor coupled with a dense grid of source points on the surface, and a wide-azimuth towed-streamer method using multiple seismic vessels in a novel configuration. These two methods complement each other. Ocean-bottom receivers may be used effectively where field development has resulted in many obstacles that might interfere with towed-streamer methods, where the required size of the 3D survey is not too extensive, or where very long offsets are required for all azimuths. Towed-streamer methods are more efficient for large surveys, and key parameters in the wide-azimuth towed-streamer method can be varied to provide a wide range of cost versus data-quality options to make the method suitable for application in scenarios ranging from exploration to field development.
Improved applicability of ray tracing in seismic acquisition, imaging, and interpretation
Authors: Gjøystdal Håvar , Iversen Einar , Lecomte Isabelle , Kaschwich Tina , Drottning Åsmund , Mispel Joachim
Published: September 2007

Ray-based seismic modeling methods can be applied at various stages of the exploration and production process. The standard ray method has several advantages, e.g., computational efficiency and the possibility of simulating propagation of elementary waves. As a high-frequency approximation, the method also has a number of limitations, particularly with respect to a lack of amplitude reliability in the presence of rapid changes of the model functions representing elastic parameters and interfaces. Given the objective of improving the applicability of the standard ray method, we present a strategy that does not require specific extension to finite frequencies. Instead, we define each ray-based process as an element of a system that, as a composite process, is able to obtain better results than the ray-based process applied alone. Other elements of the composite process can be finite-difference modeling or numerical solutions for surface and volume integrals, which are basic constituents of Kirchhoff modeling and imaging. We also include among the process elements recently developed techniques for simulating the migration amplitude on a target reflector and in a local volume, e.g., a reservoir zone. The model is decomposed according to its complexity into volume elements, surface elements, or a combination. The composite process consists of a specified interaction between process elements and model elements, which fits well with the philosophy of modern software design. Model elements that will be exposed to ray-tracing algorithms may need appropriate preparation, e.g., smoothing and resampling. We demonstrate specifically, in a tutorial example, that simulating the seismic response from a reflector by ray-based composite processes can yield better results than applying standard ray tracing alone.
Reverse time migration with optimal checkpointing
Authors: Symes William W.
Published: September 2007

Reverse time migration (RTM) requires that fields computed in forward time be accessed in reverse order. Such out-of-order access, to recursively computed fields, requires that some part of the recursion history be stored (checkpointed), with the remainder computed by repeating parts of the forward computation. Optimal checkpointing algorithms choose checkpoints in such a way that the total storage is minimized for a prescribed level of excess computation, or vice versa. Optimal checkpointing dramatically reduces the storage required by RTM, compared to that needed for nonoptimal implementations, at the price of a small increase in computation. This paper describes optimal checkpointing in a form which applies both to RTM and other applications of the adjoint state method, such as construction of velocity updates from prestack wave equation migration.
An approach for 3D multisource, multifrequency CSEM modeling
Authors: Plessix R.-E. , Darnet M. , Mulder W. A.
Published: September 2007

We discuss a practical approach for multisource, multifrequency controlled-source electromagnetic (CSEM) modeling. The approach consists of an efficient iterative multigrid-based solver and an automatic gridding procedure. For a given frequency and a given source location, the automatic gridding procedure ensures that the computational grid is consistent with the discretization of the electromagnetic equations. The conductivity is mapped from the input grid onto the automatically defined computational grid by volume averaging. This mapping changes the conductivity representation. Volume averaging based on the logarithm of the conductivity provides the best result. When the stretching in the computational grid is moderate, we use a multigrid method based on full coarsening. However, when the stretching is more severe, we propose a more robust multigrid method based on semicoarsening. Numerical examples show the usefulness of this approach for survey design and scenario studies over complex heterogeneous structures, when the layered-earth assumption is not satisfactory.
Tensor deconvolution: A method to locate equivalent sources from full tensor gravity data
Authors: Mikhailov Valentin , Pajot Gwendoline , Diament Michel , Price Antony
Published: September 2007

We present a method dedicated to the interpretation of full tensor (gravity) gradiometry (FTG) data called tensor deconvolution. It is especially designed to benefit from the simultaneous use of all the FTG components and of the gravity field. In particular, it uses tensor scalar invariants as a basis for source location. The invariant expressions involve all of the independent components of the tensor. This method is a tensor analog of Euler deconvolution, but has the following advantages compared to the conventional Euler deconvolution method: (1) It provides a solution at every observation point, without the use of a sliding window. (2) It determines the structural index automatically; as a consequence, the structural index follows the variations of the field morphology. (3) It uses all components of the measured full gradient tensor and gravity field, thus reducing errors caused by random noise. It is based on scalar invariants that are by nature insensitive to the orientation of the measuring device. We tested our method on both noise-free and noise-contaminated data. These tests show that tensor solutions cluster in the vicinity of the center of causative bodies, whereas Euler solutions better outline their edges. Hence, these methods should be combined for improved contouring and depth estimation. In addition, we use a clustering method to improve the selection of solutions, which proves advantageous when data are noisy or when signals from close causative bodies interfere.
High-order time discretizations in seismic modeling
Authors: Chen Jing-Bo
Published: September 2007

Seismic modeling plays an important role in explor-ation geophysics. High-order modeling schemes are in demand for practical reasons. In this context, I present three kinds of high-order time discretizations: Lax-Wendroff methods, Nyström methods, and splitting methods. Lax-Wendroff methods are based on the Taylor expansion and the replacement of high-order temporal derivatives by spatial derivatives, Nyström methods are simplified Runge-Kutta algorithms, and splitting methods comprise substeps for one-step computation. Based on these methods, three schemes with third-order and fourth-order accuracy in time and pseudospectral discretizations in space are presented. I also compare their accuracy, stability, and computational complexity, and discuss advantages and shortcomings of these algorithms. Numerical experiments show that the fourth-order Lax-Wendroff scheme is more efficient for short-time simulations while the fourth-order Nyström scheme and the third-order splitting scheme are more efficient for long-term computations.
Aquatic electrical resistivity imaging of shallow-water wetlands
Authors: Mansoor Nasser , Slater Lee
Published: September 2007

This study uses aquatic electrical resistivity imaging (ERI) to predict spatial and temporal patterns of pore-fluid conductivity in wetland soils of a shallow-water wetland. The technique involves floating electrodes from a paddleboat. Resistivity measurements for the study were obtained six times over a four-month period, covering a [Formula: see text] grid. Three-dimensional inversion is used in the study to determine the conductivity distribution of the subsurface, using the smoothness-constrained least-squares optimization method. Surface water depth and conductivity were entered as known information in the 3D inversion and measurement error (for constraining the inversion) estimated from tie points. Pore-fluid conductivity was constrained using (1) surface conduction measurements obtained from laboratory experiments on soils extracted from the wetland and (2) a correction for temporal and spatial temperature variations using direct surface water temperature measurements. The study demonstrates that aquatic ERI is an ideal method for determining the resistivity structure of wetland sediments covered by a shallow surface water layer. In the field example presented here, changes in pore-water conductivity estimated from inverted models suggest that contamination migrates from marginal landfills into the wetland soils during rainfall.
Optimal blended spectral-element operators for acoustic wave modeling
Authors: Seriani Géza , Oliveira Saulo P.
Published: September 2007

Spectral-element methods, based on high-order polynomials, are among the most commonly used techniques for computing accurate simulations of wave propagation phenomena in complex media. However, to retain computational efficiency, very high order polynomials cannot be used and errors such as numerical dispersion and numerical anisotropy cannot be totally avoided. In the present work, we devise an approach for reducing such errors by considering modified discrete wave operators. We analyze consistent and lumped operators together with blended operators (weighted averages of consistent and lumped operators). Furthermore, using the operator-blending approach and a novel dispersion analysis method, we develop optimal spectral-element operators that have increased numerical accuracy, without resorting to very high order operators. The new operators are faster and computationally more efficient than consistent operators. Our approach is based on the tensor product decomposition of the element matrices into 1D factors. We apply standard lumping to the factor associated with the 1D mass matrix. A simplified numerical dispersion analysis of arbitrary order and spatial dimension provides a practical criterion for weighting consistent and lumped matrices. The approach is general and is valid for solving both the time-dependent and the stationary (Helmholtz) wave equations.
Multiple cracks in VTI rocks: Effective properties and fracture characterization
Authors: Grechka Vladimir
Published: September 2007

The existing fracture-characterization techniques are based on assuming the unfractured host rock either to be isotropic or the magnitudes of both the background and crack-induced anisotropies to be small. I relax both assumptions and examine the effective media caused by fractures with realistic (not small) crack densities in a strongly anisotropic, primarily transversely isotropic (TI) host rock. The analysis of penny-shaped cracks in the noninteraction approximation (NIA) reveals the dependence of their excess fracture compliance tensors on the orientation of the background symmetry axis. As a result of this dependence, the excess fracture compliance tensor generally becomes rotationally noninvariant even when the cracks are circular. One of the consequences of this complication (compared to the background isotropy) is a reduction of symmetry from TI to monoclinic resulting from the presence of a single oriented fracture set. Verti–cal dry cracks in a vertically transversely isotropic (VTI) host constitute an important exception to this general rule.The effective symmetry for this arrangement is approximately orthorhombic (or orthotropic) even in the presence of multiple fracture sets that have arbitrary azimuths. I perform finite-element simulations on the so-called digital rocks to verify both the proximity of effective symmetry to orthotropy and the accuracy of the NIA up to the crack density of 0.15. Multiple sets of dry vertical cracks in a VTI host not only result in nearly orthorhombic effective symmetry but also their cumulative influence is equivalent to that of just two orthogonal (or principal) fracture sets. The possibility of replacing multiple fracture sets with two orthogonal ones paves the way for their characterization. The inverse problem of estimating the parameters of two orthogonal crack systems in a VTI background from the effective elasticity, however, is known to be nonunique. I suggest overcoming its ambiguity by combining 3D, wide-azimuth, multicomponent seismic data with sonic logs.
Waveform tomography at a groundwater contamination site: Surface reflection data
Authors: Gao Fuchun , Levander Alan , Pratt R. Gerhard , Zelt Colin A. , Fradelizio Gian-Luigi
Published: September 2007

We have applied acoustic-waveform tomography to 45 2D seismic profiles to image the 3D geometry of a buried paleochannel at a groundwater-contamination site at Hill Air Force Base in Utah. The paleochannel, which is incised into an alluvium-covered clay aquitard, acts as a trap for dense nonaqueous-phase liquids (DNAPLs) that contaminate the shallowest groundwater system in the study area. The 2D profiles were extracted from a 3D surface reflection data set. First-arrival traveltime tomography provided initial velocity models for the waveform tomography. We inverted for six frequency components in the band [Formula: see text] of the direct and refracted waves to produce 45 2D velocity models. The flanks and bottom of a channel with a maximum depth of about [Formula: see text] were well modeled in most of the 45 parallel 2D slices, which allowed us to construct a 3D image of the channel by combining and interpolating between the 45 image slices. The 3D model of the channel will be useful for siting extraction wells within the site remediation program. The alluvium that fills the channel showed marked vertical and lateral velocity heterogeneity. Traveltime tomography and waveform tomography can be complementary approaches. Used together, they can provide high-resolution images of complicated shallow structures.
Finite-difference modeling of wave propagation on microscale: A snapshot of the work in progress
Authors: Saenger Erik H. , Ciz Radim , Krüger Oliver S. , Schmalholz Stefan M. , Gurevich Boris , Shapiro Serge A.
Published: September 2007

Digital rock methodology combines modern microscopic imaging with advanced numerical simulations of the physical properties of rocks. Modeling of elastic-wave propagation directly from rock microstructure is integral to this technology. We survey recent development of the rotated staggered grid (RSG) finite-difference (FD) method for pore-scale simulation of elastic wave propagation in digital rock samples, including the dynamic elastic properties of rocks saturated with a viscous fluid. Examination of the accuracy of this algorithm on models with known analytical solutions provide an additional accuracy condition for numerical modeling on the microscale. We use both the elastic and viscoelastic versions of the RSG algorithm to study gas hydrates and to simulate propagation of Biot’s slow wave. We applyRSG method ology to examine the effect of gas hydrate distributions in the pore space of a rock. We compare resulting P-wave velocities with experimentally measured data, as a basis for building an effective-medium model for rocks containing gas hydrates. We then perform numerical simulations of Biot’s slow wave in a realistic 3D digital rock model, fully saturated with a nonviscous fluid (corresponding to the high-frequency limit of poroelasticity), and placed inside a bulk fluid. The model clearly demonstrates Biot’s slow curve when the interface is open between the slab and bulk fluid. We demonstrate slow wave propagation in a porous medium saturated with a viscous fluid by analyzing an idealized 2D porous medium represented alternating solid and viscous fluid layers. Comparison of simulation results with the exact solution for this layered system shows good agreement over a broad frequency range.
Numerical investigation of implementation of air-earth boundary by acoustic-elastic boundary approach
Authors: Xu Yixian , Xia Jianghai , Miller Richard D.
Published: September 2007

The need for incorporating the traction-free condition at the air-earth boundary for finite-difference modeling of seismic wave propagation has been discussed widely. A new implementation has been developed for simulating elastic wave propagation in which the free-surface condition is replaced by an explicit acoustic-elastic boundary. Detailed comparisons of seismograms with different implementations for the air-earth boundary were undertaken using the (2,2) (the finite-difference operators are second order in time and space) and the (2,6) (second order in time and sixth order in space) standard staggered-grid (SSG) schemes. Methods used in these comparisons to define the air-earth boundary included the stress image method (SIM), the heterogeneous approach, the scheme of modifying material properties based on transversely isotropic medium approach, the acoustic-elastic boundary approach, and an analytical approach. The method proposed achieves the same or higher accuracy of modeled body waves relative to the SIM. Rayleigh waves calculated using the explicit acoustic-elastic boundary approach differ slightly from those calculated using the SIM. Numerical results indicate that when using the (2,2) SSG scheme for SIM and our new method, a spatial step of 16 points per minimum wavelength is sufficient to achieve 90% accuracy; 32 points per minimum wavelength achieves 95% accuracy in modeled Rayleigh waves. When using the (2,6) SSG scheme for the two methods, a spatial step of eight points per minimum wavelength achieves 95% accuracy in modeled Rayleigh waves. Our proposed method is physically reasonable and, based on dispersive analysis of simulated seismographs from a layered half-space model, is highly accurate. As a bonus, our proposed method is easy to program and slightly faster than the SIM.
Effective attenuation anisotropy of thin-layered media
Authors: Zhu Yaping , Tsvankin Ilya , Vasconcelos Ivan
Published: September 2007

One of the well-known factors responsible for the anisotropy of seismic attenuation is interbedding of thin attenuative layers with different properties. Here, we apply Backus averaging to obtain the complex stiffness matrix of an effective medium formed by an arbitrary number of anisotropic, attenuative constituents. Unless the intrinsic attenuation is uncommonly strong, the effective velocity function is controlled by the real-valued stiffnesses (i.e., independent of attenuation) and can be determined from the known equations for purely elastic media. Attenuation analysis is more complicated because the attenuation parameters are influenced by the coupling between the real and imaginary parts of the stiffness matrix. The main focus of this work is on effective transversely isotropic models with a vertical symmetry axis (VTI) that include isotropic and VTI constituents. Assuming that the stiffness contrasts, as well as the intrinsic velocity and attenuation anisotropy, are weak, we develop explicit first-order (linear) and second-order (quadratic) approximations for the attenuation-anisotropy parameters [Formula: see text], [Formula: see text], and [Formula: see text]. Whereas the first-order approximation for each parameter isgiven sim-ply by the volume-weighted average of its interval values, the second-order terms include coupling between various factors related to both heterogeneity and intrinsic anisotropy. Interestingly, the effective attenuation for P- and SV-waves is anisotropic even for a medium composed of isotropic layers with identical attenuation, provided there is a velocity variation among the constituent layers. Contrasts in the intrinsic attenuation, however, do not create attenuation anisotropy, unless they are accompanied by velocity contrasts. Extensive numerical testing shows that the second-order approximation for [Formula: see text], [Formula: see text], and [Formula: see text] is close to the exact solution for most plausible subsurface models. The accuracy of the first-order approximation depends on the magnitude of the quadratic terms, which is largely governed by the strength of the velocity (rather than attenuation) anisotropy and velocity contrasts. The effective attenuation parameters for multiconstituent VTI models vary within a wider range than do the velocity parameters, with almost equal probability of positive and negative values. If some of the constituents are azimuthally anisotropic with misaligned vertical symmetry planes, the effective velocity and attenuation functions may have different principal azimuthal directions or even different symmetries.
Study of riverine deposits using electromagnetic methods at a low induction number
Authors: Sambuelli Luigi , Leggieri Salvatore , Calzoni Corrado , Porporato Chiara
Published: September 2007

We conducted electromagnetic (EM) profiles along the Po River in Turin, Italy. The aim of this activity was to verify the applicability of low-induction-number EM multifrequency soundings carried out from a boat in riverine surveys and to determine whether this technique, which is cheaper than air-carried surveys, could be used effectively to define the typology of sediments and to estimate the stratigraphy below a riverbed. We used a GEM-2 handheld broadband EM sensor operating with six frequencies to survey the investigated area. Ground-penetrating radar (GPR), a conductivity meter, and a time-domain reflectometer were used to estimate the bathymetry and to measure the EM properties of the water. A global positioning system, working in real-time kinematic mode, tracked the route of the boat with centimetric accuracy. We analyzed the induction number, the depth of investigation (DOI), and the sensitivity of our experimental setup by forward modeling — varying the water depth, frequency, and bottom-sediment resistivity. The simulations optimized the choice of the frequencies that could be used reliably for the interpretation. The [Formula: see text] signal had a DOI in the Po River water [Formula: see text] of [Formula: see text] and provided sediment resistivities higher than [Formula: see text]. We applied a bathymetric correction to the conductivity data using the water depths obtained from the GPR data. We plotted a map of the river bottom resistivity and compared this map to the results of a direct sediment sampling campaign. The resistivity values [Formula: see text] were compatible with the saturated gravel and pebbles in a sandy matrix, which resulted from direct sampling and with the known geology.
An unsplit convolutional perfectly matched layer improved at grazing incidence for the seismic wave equation
Authors: Komatitsch Dimitri , Martin Roland
Published: September 2007

The perfectly matched layer (PML) absorbing boundary condition has proven to be very efficient from a numerical point of view for the elastic wave equation to absorb both body waves with nongrazing incidence and surface waves. However, at grazing incidence the classical discrete PML method suffers from large spurious reflections that make it less efficient for instance in the case of very thin mesh slices, in the case of sources located close to the edge of the mesh, and/or in the case of receivers located at very large offset. We demonstrate how to improve the PML at grazing incidence for the differential seismic wave equation based on an unsplit convolution technique. The improved PML has a cost that is similar in terms of memory storage to that of the classical PML. We illustrate the efficiency of this improved convolutional PML based on numerical benchmarks using a finite-difference method on a thin mesh slice for an isotropic material and show that results are significantly improved compared with the classical PML technique. We also show that, as the classical PML, the convolutional technique is intrinsically unstable in the case of some anisotropic materials.
Attenuation of specular and diffracted 2D multiples in image space
Authors: Alvarez Gabriel , Biondi Biondo , Guitton Antoine
Published: September 2007

In complex areas, the attenuation of specular and diffracted multiples in image space is an attractive alternative to surface-related multiple elimination (SRME) and to data space Radon filtering. We present the equations that map, via wave-equation migration, 2D diffracted and specular water-bottom multiples from data space to image space. We show the equations for both subsurface-offset-domain common-image-gathers (SODCIGs) and angle-domain common-image-gathers (ADCIGs). We demonstrate that when migrated with sediment velocities, the over-migrated multiples map to predictable regions in both SODCIGs and ADCIGs. Specular multiples focus similarly to primaries, whereas diffracted multiples do not. In particular, the apex of the residual moveout curve of diffracted multiples in ADCIGs is not located at the zero aperture angle. We use our equation of the residual moveout of the multiples in ADCIGs to design an apex-shifted Radon transform that maps the 2D ADCIGs into a 3D model space cube whose dimensions are depth, curvature, and apex-shift distance. Well-corrected primaries map to or near the zero-curvature plane and specularly reflected multiples map to or near the zero apex-shift plane. Diffracted multiples map elsewhere in the cube according to their curvature and apex-shift distance. Thus, specularly reflected as well as diffracted multiples can be attenuated simultaneously. We show the application of our apex-shifted Radon transform to a 2D seismic line from the Gulf of Mexico. Diffracted multiples originate at the edges of the salt body and we show that we can successfully attenuate them, along with the specular multiples, in the image Radon domain.
Modeling and inversion of magnetic and VLF-EM data with an application to basement fractures: A case study from Raigarh, India
Authors: Ramesh Babu V. , Ram Subhash , Sundararajan N.
Published: September 2007

We present modeling of magnetic and very low frequency electromagnetic (VLF-EM) data to map the spatial distribution of basement fractures where uranium is reported in Sambalpur granitoids in the Raigarh district, Chhattisgarh, India. Radioactivity in the basement fractures is attributed to brannerite, [Formula: see text] complex, and uranium adsorbed on ferruginous matter. The amplitude of the 3D analytical signal of the observed magnetic data indicates the trend of fracture zones. Further, the application of Euler 3D deconvolution to magnetic data provides the spatial locations and depth of the source. Fraser-filtered VLF-EM data and current density pseudosections indicate the presence of shallow and deep conductive zones along the fractures. Modeling of VLF-EM data yields the subsurface resistivity distribution of the order of less than 100 ohm-m of the fractures. The interpreted results of both magnetic and VLF-EM data agree well with the geologic section obtained from drilling.
Probabilistic seismic inversion based on rock-physics models
Authors: Spikes Kyle , Mukerji Tapan , Dvorkin Jack , Mavko Gary
Published: September 2007

A site-specific rock-physics transform from porosity, mineralogy, and pore fluid to elastic-wave velocities is used to invert seismic amplitude data for clay content, total porosity, and saturation. The implementation is Bayesian and produces probabilistic values of the reservoir properties from seismic measurements and well data. This method focuses on an exploration setting where minimal data exist. Two key assumptions reduce the problem and keep the prior information as noncommittal as possible. First, a prior interpretation of the seismic data is required that provides a geobody on which to perform the inversion. Second, the reservoir thickness is assumed to be constant, as are the rock properties within the reservoir. The prior distributions of the reservoir properties are assumed to be uncorrelated and independent, although this is not an essential assumption. Central to theinversion is the generation of a complete set of earth models derived from the prior distribution. A site-specific rock-physics model translates these properties (clay content, porosity, and saturation) into the elastic domain. A complete set of forward seismic models accompanies the earth models, and these seismic models are compared to the real data on a trace-by-trace basis. The reservoir properties corresponding to the seismic models that match the real data within predefined errors are used to construct the posterior. This method was tested on well and seismic data from offshore western South Africa. Initial results at calibration and test wells indicate an overprediction of porosity and uncertain predictions of clay content and saturation. This is a result of the constant-thickness assumption. However, a highly negative correlation between porosity and thickness is predicted, which manifests the success of this method.
Application of a new 2D time-domain full-waveform inversion scheme to crosshole radar data
Authors: Ernst Jacques R. , Green Alan G. , Maurer Hansruedi , Holliger Klaus
Published: September 2007

Crosshole radar tomography is a useful tool in diverse investigations in geology, hydrogeology, and engineering. Conventional tomograms provided by standard ray-based techniques have limited resolution, primarily because only a fraction of the information contained in the radar data (i.e., the first-arrival times and maximum first-cycle amplitudes) is included in the inversion. To increase the resolution of radar tomograms, we have developed a versatile full-waveform inversion scheme that is based on a finite-difference time-domain solution of Maxwell’s equations. This scheme largely accounts for the 3D nature of radar-wave propagation and includes an efficient method for extracting the source wavelet from the radar data. After demonstrating the potential of the new scheme on two realistic synthetic data sets, we apply it to two crosshole field data sets acquired in very different geologic/hydrogeologic environments. These are the first applications of full-waveform tomography to observed crosshole radar data. The resolution of all full-waveform tomograms is shown to be markedly superior to that of the associated ray tomograms. Small subsurface features a fraction of the dominant radar wavelength and boundaries between distinct geological/hydrological units are sharply imaged in the full-waveform tomograms.
Interferometric surface-wave isolation and removal
Authors: Halliday David F. , Curtis Andrew , Robertsson Johan O. A. , van Manen Dirk-Jan
Published: September 2007

The removal of surface waves (ground roll) from land seismic data is critical in seismic processing because these waves tend to mask informative body-wave arrivals. Removal becomes difficult when surface waves are scattered, and data quality is often impaired. We apply a method of seismic interferometry, using both sources and receivers at the surface, to estimate the surface-wave component of the Green’s function between any two points. These estimates are subtracted adaptively from seismic survey data, providing a new method of ground-roll removal that is not limited to nonscattering regions.
Cross-property relations between electrical conductivity and the seismic velocity of rocks
Authors: Carcione José M. , Ursin Bjørn , Nordskag Janniche I.
Published: September 2007

Cross-property relations are useful when some rock properties can be measured more easily than other properties. Relations between electrical conductivity and seismic velocity, stiffness moduli, and density can be obtained by expressing the porosity in terms of those properties. There are many possible ways to combine the constitutive equations to obtain a relation, each one representing a given type of rock. The relations depend on the assumptions to obtain the constitutive equations. In the electromagnetic case, the equations involve Archie’s law and its modifications for a conducting frame, the Hashin-Shtrikman (HS) bounds, and the self-similar and complex refraction-index method (CRIM) models. In the elastic case, the stress-strain relations are mainly based on the time-average equation, the HS bounds, and the Gassmann equation. Also, expressions for dry rocks and for anisotropic media, using Backus averaging, are analyzed. The relations are applied to a shale saturated with brine (overburden) and to a sandstone saturated with oil (reservoir). Tests with sections of a North Sea well log show that the best fit is given by the relation between the Gassmann velocity and the CRIM, self-similar, and Archie models for the conductivity.
Vector-migration of standard copolarized 3D GPR data
Authors: Streich Rita , van der Kruk Jan , Green Alan G.
Published: September 2007

The derivation of ground-penetrating radar (GPR) images in which the amplitudes of reflections and diffractions are consistent with subsurface electromagnetic property contrasts requires migration algorithms that correctly account for the antenna radiation patterns and the vectorial character of electromagnetic wavefields. Most existing vector-migration techniques are based on far-field approximations of Green’s functions, which are inappropriate for the majority of GPR applications. We have recently developed a method for rapidly computing practically exact-field Green’s functions in a multicomponent vector migration scheme. A significant disadvantage of this scheme is the extra effort needed to record, process, and migrate at least two components of GPR data. By making straightforward modifications to the multi-component algorithm, we derive an equivalent exact-field sin-gle-component vector-migration scheme that can be applied to most standard GPR data acquired using a single copolarized antenna pair. Our new formulation is valid for polarization-independent features (e.g., most point scatterers, spheres, and planar objects), but not for polarization-dependent ones (e.g., most underground public utilities). A variety of tests demonstrates the stability of the exact-field single-component operators. Applications of the new scheme to synthetic and field-recorded GPR data containing dipping planar reflections produce images that are virtually identical to the corresponding multicomponent vector-migrated images and are almost invariant to the relative orientations of antennas and reflectors. The new single-component vector-migration scheme is appropriate for migrating the majority of GPR data acquired by researchers and practitioners.
Heat Shock Proteins and Autoimmunity in Patients with Carotid Atherosclerosis
Authors: RIGANÒ RACHELE , PROFUMO ELISABETTA , BUTTARI BRIGITTA , TAGLIANI ANGELA , PETRONE LINDA , D'AMATI GIULIA , IPPOLITI FLORA , CAPOANO RAFFAELE , FUMAGALLI LORENZO , SALVATI BRUNO , BUSINARO RITA
Published: September 2007

Abstract:  Studies aimed at elucidating the pathogenetic mechanisms underlying the initiation and progression of human atherosclerosis have emphasized the central role of inflammatory and immune cells. Atherosclerotic plaques are infiltrated by activated macrophages, T and B lymphocytes, plasma cells, and mast cells, releasing inflammatory molecules, which amplify the severity of the disease. Endothelial cells subjected to various stress conditions express increased amounts of heat shock proteins (HSPs), some of the most successfully conserved proteins throughout evolution. Many experimental observations reviewed in this article draw attention to several HSPs targeted by a specific cellular and humoral immune response in patients with atherosclerotic disease. The review also reports preliminary data obtained by our group on the possible role of HSP90 as a candidate autoantigen in carotid atherosclerosis. Our study deals with the presence of specific antibodies and T cells directed against HSP90 in patients with carotid atherosclerotic plaques. In 60% of these subjects' sera but in none of the sera from healthy controls immunoblotting (IB) detected the presence of specific antibodies. Moreover, 20% of peripheral blood mononuclear cells (PBMC) samples from patients but none from healthy subjects proliferated in response to human purified HSP90. In vitro experiments showed an upregulation of HSP90 expression in endothelial cells exposed to oxidative stress by treatment with H2O2 and greater release of soluble HSP90 in culture supernatants from H2O2‐treated cells than from untreated cells.
Free Hemoglobin
Authors: BUTTARI BRIGITTA , PROFUMO ELISABETTA , PETRONE LINDA , PIETRAFORTE DONATELLA , SIRACUSANO ALESSANDRA , MARGUTTI PAOLA , DELUNARDO FEDERICA , ORTONA ELENA , MINETTI MAURIZIO , SALVATI BRUNO , RIGANÒ RACHELE
Published: September 2007

Abstract:  Atherosclerosis is a chronic inflammatory multifactorial disease in which immune responses are key pathogenetic factors. T cell–mediated immunity contributes to the initiation and progression of atherosclerotic disease, but the nature of antigens responsible for immune cell activation is still not completely elucidated. Convincing evidence supports a determinant role of autoimmune responses to self‐structures in shaping the progression of the disease. Autoimmune responses may be directed against altered self‐structures, such as oxidized low‐density lipoproteins (LDL). Oxidative stress, increasingly reported in patients with atherosclerosis, is the major event causing protein structural modification, thus inducing the appearance of neo/cryptic epitopes on the molecule. Intraplaque hemorrhage, a common event in advanced lesions, causes the deposition of large amounts of hemoglobin (Hb). The pro‐oxidative intraplaque microenvironment may induce structural changes in extra‐erythrocytic free Hb, thus generating novel/cryptic autoantigenic epitopes. We demonstrated that an oxidized Hb preparation enriched in hemichromes expands IFN‐γ‐secreting T lymphocytes in patients with advanced carotid atherosclerosis and enhances the phenotypical and functional maturation of human monocyte‐derived dendritic cells induced by lipopolysaccharide (LPS). Overall, our findings suggest that oxidized forms of Hb could act as a dangerous signal for the immune system, thus contributing to the inflammatory process that takes place within the atherosclerotic plaque.
Lupus Anticoagulant Activity as a Thrombosis Risk Factor in Lung Adenocarcinoma Patients
Authors: DE MEIS ERNESTO , PINHEIRO VERA R. , LOURES MARIA APARECIDA L. , KOTOUC MARIA MERCEDES , ZAMBONI MAURO M. , GUEDES MARIA TEREZA S. , BARROS AILCE S. , CASTILHO ILDA AKEMI M. , LEVY ROGER A.
Published: September 2007

Abstract:  There is a high incidence of thrombosis in cancer patients. Retrospective studies indicate that lupus anticoagulant (LA) antibodies can be a thrombosis risk factor in cancer. In 77 patients with different forms of cancer LA and thrombosis incidence were retrospectively evaluated. In a prospective study, with 42 lung adenocarcinoma patients, we measured plasma LA, fibrinogen, factor VIII (FVIII), and thrombosis incidence. A high frequency of LA and thrombosis were observed in both studies. In isolation LA, increased levels of FVIII and fibrinogen could not be considered good markers for the development of thrombosis.
Chronic Inflammatory Autoimmune Disorders and Atherosclerosis
Authors: ABOU‐RAYA S. , ABOU‐RAYA A. , NAIM A. , ABUELKHEIR H.
Published: September 2007

Abstract:  Rheumatoid arthritis (RA), periodontal disease (PD), and coronary artery disease (CAD) are common chronic inflammatory diseases. RA is associated with accelerated vascular risk resulting in an increased prevalence of CAD with attendant early mortality and excess morbidity. RA and PD have a common pathobiology. Accordingly, the aim of this study was to evaluate the association between RA, PD, and CAD and the influence of systemic inflammatory factors. A total of 100 active RA patients of which 50 had established CAD and 50 had no CAD were assessed for PD. All subjects underwent a clinical, cardiac, dental, laboratory, and radiological evaluation. Blood samples were obtained and the level of high‐sensitivity C‐reactive protein (hs‐CRP), total white blood counts (WBC), erythrocyte sedimentation rate (ESR), fibrinogen and tumor necrosis alpha (TNF‐α), total cholesterol (TC), and high‐density lipoprotein (HDL) were assayed. The findings of this study demonstrated an association between RA, PD, and CAD. The RA patients with CAD had significantly more PD than RA patients without CAD, P < 0.001. The inflammatory markers hs‐CRP, ESR, WBC, fibrinogen, and TNF‐α were raised in all patients but were significantly higher in RA patients with CAD who also had PD, that is, in those with more inflammatory disease burden. HDL levels were lower in RA patients with CAD when compared to RA patients without CAD, P < 0.005. Evidence from this study shows an association between RA, PD, CAD, and systemic levels of the inflammatory mediators. The implication is that inflammation may be the central link between the chronic inflammatory autoimmune disorders and atherosclerosis.
Autoantibodies in Autism Spectrum Disorders (ASD)
Authors: WILLS SHARIFIA , CABANLIT MARICEL , BENNETT JEFF , ASHWOOD PAUL , AMARAL DAVID , VAN DE WATER JUDY
Published: September 2007

Abstract:  Autism spectrum disorders (ASD) are a heterogeneous group of neurodevelopmental disorders defined behaviorally by abnormalities in social, verbal, and nonverbal communication. The etiologies of ASD are unknown, likely to be the result of a variety of numerous genetic, neurological, environmental, and immunological interactions that lead to a general behavioral phenotype defined as ASD. This review will focus on the various immune system anomalies, in particular, autoantibodies, which have been reported in subjects with ASD. In addition, we will discuss recent studies performed by our group concerning the presence of autoantibodies directed against neural antigens, which are observed in patients with ASD.
Autoantibodies against Glial Antigens in Paraneoplastic Neurological Diseases
Authors: TSCHERNATSCH M. , GROSS O. , KNEIFEL N. , KRASENBRINK I. , GERRIETS T. , KAPS M. , BLAES F.
Published: September 2007

Abstract:  Paraneoplastic neurological syndromes are clinically heterogeneous manifestations of cancer, but are not caused by the tumor or its metastases. Because autoantibodies reacting with tumor and nervous system tissue have been described, an autoimmune pathogenesis is suspected. Most autoantibodies are directed against neuronal proteins. Here, we describe the impact of antiglial autoantibodies in paraneoplastic neurological syndromes. Anti‐CRMP5 and antiglial nuclear antibody both can be associated with different paraneoplastic neurological syndromes and tumors.
Hearing Loss as the Presenting Feature of Systemic Vasculitis
Authors: LIDAR MERAV , CARMEL ELDAR , KRONENBERG YONA , LANGEVITZ PNINA
Published: September 2007

Abstract:  Hearing loss, both sensorineural and conductive, is a well‐recognized manifestation of systemic vasculitis, yet has only infrequently been described as its initial presentation. We describe three cases in which hearing loss preceded the diagnosis of systemic vasculitis by a period of a few weeks to more than 6 months. While steroid therapy was initiated immediately in one of the cases, comprehensive immunosuppressive therapy was given only after additional manifestations compatible with vasculitis appeared, allowing for a diagnosis of Wegener's granulomatosis in two of the cases and undifferentiated vasculitis, in the third. Hearing improved in all patients, albeit, residual dysfunction remained. Prompt referral for a complete rheumatologic workup in cases of unexplained hearing loss would allow for a timely diagnosis of a collagen vascular disease and facilitate early initiation of systemic therapy, possibly yielding better audiological results.