bluuebunny/crossref_metadata_2025 huggingface dataset:
Depth-Dependent Transformation of Kaolinite to Dickite In Sandstones of the Norwegian Continental Shelf
Authors: Ehrenberg S. N. , Aagaard P. , Wilson M. J. , Fraser A. R. , Duthie D. M. L.
Published: November 2006

Replacement of kaolinite by dickite has been observed to occur with increasing depth of burial in sandstones from three different basins on the Norwegian continental shelf. In the Garn Formation (Middle Jurassic) of Haltenbanken, samples from 1.4-2-7 km below the sea floor (110°C) contain kaolinite, whereas deeper than 3.2 km (130°C) mainly dickite is present. In the Statfjord Formation (Late Triassic-Early Jurassic) from Gullfaks and Gullfaks Sør Fields, transformation of kaolinite to dickite occurs at ~3.1 km below the sea floor (120°C) From the Stø and Nordmela Formations (Lower to Middle Jurassic) to the Troms Area, kaolin polytypes have been identified in only two shallow and two deep samples, but the results are consistent with the transformation depth determined in two other areas studied. These occurrences are significant because they allow the temperature of the kaolinite/dickite transformation to be established with greater confidence than had been possible previously. Also the observation of this transformation in all three areas so far examined indicates that it may be a general and predictable feature of kaolinbearing sandstones worldwide and therefore a potentially reliable paleogeothermometer. In most cases, the kaolinite occurs as relatively large vermicular crystals, whereas dickite forms more euhedral, blockier crystals. This morphological difference, together with the nature of the structural difference in octahedral occupancy between the kaolinite and dickite, suggests that the transformation occurs by dissolution and reprecipitation, rather then in the solid state.
ESR and IR Evidence for Chromium in Kaolinites
Authors: Mosser C. , Petit S. , Mestdagh M.
Published: November 2006

Evidence obtained from ESR and IR studies is presented for the presence of structural Cr in two natural kaolinites (MILO and GEY) formed in an hydrothermal environment in Sonoma County, California. The XRD patterns show a greater structural disorder for GEY than for MILO, but both have the usual hexagonal shapes as shown by TEM observations. On the basis of EDX analysis of different particles, GEY, on average, appears to be richer in Cr (2.1% Cr203) than MILO (0.6% Cr203). The presence of Fe oxide particles containing some Cr, Ni and V is also indicated by EDX analysis. By FT-IR observation, the octahedral Cr3+position was easily detected by a well resolved spectral feature at 3586 cm-1. The adsorbed Cr3+kaolinite (KMRXCR) presents no band at 3586 cm-1, but two other bands situated at 3527 and 3477 cm-1. The main features of the ESR spectra of these two kaolinites are a set of resonances neargeff4; a broad resonance centred neargeff2 with some modulations; and a set of resonances near gcffl. The broad resonance centred neargeff2 is interpreted as the free iron oxide signal with modulations due to VO2+. The set of resonances neargeff4 is similar to that observed for octahedral Fe3+, but the position is shifted compared to that of octahedral Fe 3+. This set of resonances neargeff4 is, therefore, interpreted as belonging to Cr3+in octahedral position. The resonances atgeff1 are also interpreted as belonging to Cr3-. Comparison with the Cr3+surface-adsorbed ESR signal of a Cr-saturated kaolinite (which is a broad resonance centred neargeff2) strengthens the interpretation of thegeff4 resonances belonging to Cr3+in the octahedral position. The results obtained by the combination of FT-IR and ESR spectroscopics indicate that Cr3+is present in the octahedral position of the MILO and GEY kaolinites.
FT-IR Partial Least-Squares Analysis of Tubular Halloysite in Kaolin Samples from the Mount Hope Kaolin Deposit
Authors: Janik L J. , Keeling J. L.
Published: November 2006

A method of infrared (IR) analysis for quantitative determination of tubular halloysite in mixtures with kaolinite was investigated for drill hole samples collected during an assessment of paper-coating kaolin resources at the Mount Hope Kaolin Deposit, Eyre Peninsula, South Australia. Tubular, dehydrated halloysite from the deposit does not readily intercalate formamide, and the proportion of tubes in <2 μm size-fractions was determined initially from scanning electron micrographs. For samples showing a range of tube contents, a strong correlation between IR spectral response and counts of halloysite tubes was established using partial leastsquares analysis. This provided a rapid technique suitable for routine determination of tubular halloysite in samples from the Mount Hope deposit. Although the universality of the method remains to be tested, it offers an alternative approach to other analytical techniques for assessment of kaolin deposits where the presence of halloysite is suspected.
Development of Interstratification in K-and NH4-Smectite from Jelšový Potok (Slovakia) Treated by Wetting and Drying
Authors: Mikloš D. , Čičel B.
Published: November 2006

A K+-saturated and an NH4+ -saturated smectite from Jelgov 37 Potok (Slovakia) was analysed by X-ray diffraction (XRD) after a series of I to 150 wetting and drying (WD) cycles, and the corresponding distribution functions were calculated using the Dyakonov method. From these data the thicknesses and proportions of different layers were determined. Three kinds of layers (A- 1-00 nm, B-1.26 nm and C-1-52 nm) were detected in the original samples. After 15 WD cycles only A and B type layers were identified in the K-smectite, whereas all three varieties were present during the whole WD treatment in the NH4-smectite. After initial changes the mutual proportion of layers seems to be stable. The 1.00 nm layer is the major layer type in the K-smectite and the 1.26 nm layer is the major layer type in the NH4-smectite. The layer thicknesses evolved during the WD experiments. The systematic changes observed for the NH4-smectite were greater than those for the K-smectite.
Iron in Hydrothermal Clays from the Galapagos Spreading Centre Mounds: Consequences for the Clay Transition Mechanism
Authors: Buatier M. D. , Ouyang K. , Sanchez J. P.
Published: November 2006

Glauconite and Fe-smectite, which can be distinguished by their peculiar morphology and stacking sequences, coexist in the Galapagos Spreading Centre hydrothermal mounds. Analytical electron microscopy (AEM) data suggest that Fe is entirely in octahedral sites in Fe-smectite whereas glauconite is K-rich with Fe in tetrahedral and octahedral sites. However, the Mossbauer spectra, recorded at various temperatures for samples containing both smectite and glauconite, were satisfactorily analysed with three overlapping doublets corresponding to Fe in octahedral sites. The contradictory results obtained with the two methods are explained by the presence of small particles of iron oxide intimately associated with glauconite. These particles were detected in Mossbauer spectra obtained at 77 K and 4·2 K and were observed by transmission electron microscopy. Iron oxide is a secondary phase formed by alteration of smectite. These data are in good agreement with the hypothesis that the smectite-glauconite reaction, which occurs at 30 m and low temperature in the Galapagos hydrothermal mounds, is a dissolution-precipitation process, dissolution of Fe-rich smectite being followed by precipitation of glauconite and iron oxides.
Effect of genetic variations in platelet glycoproteins Ibα and VI on the risk for coronary heart disease events in postmenopausal women taking hormone therapy
Authors: Bray Paul F. , Howard Timothy D. , Vittinghoff Eric , Sane David C. , Herrington David M.
Published: November 2006

Millions of women still use postmenopausal hormone therapy (HT). We genotyped 2090 women in Heart and Estrogen/progestin Replacement Study for functional polymorphisms in GP1BA and GP6 and assessed the coronary heart disease (CHD) event rate over 5.8 years of follow-up. In patients receiving placebo, there was an increased CHD death/myocardial infarction (MI)/unstable angina (UA) event rate in carriers of the GP1BA −5C allele (adjusted [adj] P = .006). HT increased the hazard ratio (HR) of CHD events in patients with the GP1BA −5TT genotype by 16% and reduced the HR in patients with the TC+CC genotypes by 46% (adj interaction P < .001). HT reduced the HR in patients with the GP6 13254TT genotype by 17% but increased the HR in patients with the TC+CC genotypes by 35% (adj interaction P < .001). Furthermore, HT increased the HR of CHD events in patients with the GP1BA −5TT plus GP6 13254TC+CC genotypes by 57% and reduced the HR in patients with the GP1BA −5TC+CC plus GP6 13254TT genotypes by 55% (adj interaction P < .001). In postmenopausal women with established CHD, these polymorphisms of platelet genes were predictors of CHD events and significantly modified the effects of HT on CHD risk. It will be important to replicate these findings in other studies.
Characterizing exons 11 and 1 promoters of the mu opioid receptor (Oprm) gene in transgenic mice
Authors: Xu Jin , Xu Mingming , Pan Ying-Xian
Published: November 2006

Background

The complexity of the mouse mu opioid receptor (Oprm) gene was demonstrated by the identification of multiple alternatively spliced variants and promoters. Our previous studies have identified a novel promoter, exon 11 (E11) promoter, in the mouse Oprm gene. The E11 promoter is located ~10 kb upstream of the exon 1 (E1) promoter. The E11 promoter controls the expression of nine splice variants in the mouse Oprm gene. Distinguished from the TATA-less E1 promoter, the E11 promoter resembles a typical TATA-containing eukaryote class II promoter. The aim of this study is to further characterize the E11 and E1 promoters in vivo using a transgenic mouse model.

Results

We constructed a ~20 kb transgenic construct in which a 3.7 kb E11 promoter region and an 8.9 kb E1 promoter region controlled expression of tau/LacZ and tau/GFP reporters, respectively. The construct was used to establish a transgenic mouse line. The expression of the reporter mRNAs, determined by a RT-PCR approach, in the transgenic mice during embryonic development displayed a temporal pattern similar to that of the endogenous promoters. X-gal staining for tau/LacZ reporter and GFP imaging for tau/GFP reporter showed that the transgenic E11 and E1 promoters were widely expressed in various regions of the central nervous system (CNS). The distribution of tau/GFP reporter in the CNS was similar to that of MOR-1-like immunoreactivity using an exon 4-specific antibody. However, differential expression of both promoters was observed in some CNS regions such as the hippocampus and substantia nigra, suggesting that the E11 and E1 promoters were regulated differently in these regions.

Conclusion

We have generated a transgenic mouse line to study the E11 and E1 promoters in vivo using tau/LacZ and tau/GFP reporters. The reasonable relevance of the transgenic model was demonstrated by the temporal and spatial expression of the transgenes as compared to those of the endogenous transcripts. We believe that these transgenic mice will provide a useful model for further characterizing the E11 and E1 promoter in vivo under different physiological and pathological circumstances such as chronic opioid treatment and chronic pain models.
The conserved protein kinase-A target motif in synapsin of Drosophilais effectively modified by pre-mRNA editing
Authors: Diegelmann Sören , Nieratschker Vanessa , Werner Ursula , Hoppe Jürgen , Zars Troy , Buchner Erich
Published: November 2006

Background

Synapsins are abundant synaptic vesicle associated phosphoproteins that are involved in the fine regulation of neurotransmitter release. The Drosophila member of this protein family contains three conserved domains (A, C, and E) and is expressed in most or all synaptic terminals. Similar to mouse mutants, synapsin knock-out flies show no obvious structural defects but are disturbed in complex behaviour, notably learning and memory.

Results

We demonstrate that the N-terminal phosphorylation consensus motif RRxS that is conserved in all synapsins investigated so far, is modified in Drosophila by pre-mRNA editing. In mammals this motif represents the target site P1 of protein kinase A (PKA) and calcium/calmodulin dependent protein kinase I/IV. The result of this editing, by which RRFS is modified to RGFS, can be observed in cDNAs of larvae and adults and in both isolated heads and bodies. It is also seen in several newly collected wild-type strains and thus does not represent an adaptation to laboratory culture conditions. A likely editing site complementary sequence is found in a downstream intron indicating that the synapsin pre-mRNA can form a double-stranded RNA structure that is required for editing by the adenosine deaminase acting on RNA (ADAR) enzyme. A deletion in the Drosophila Adar gene generated by transposon remobilization prevents this modification, proving that the ADAR enzyme is responsible for the pre-mRNA editing described here. We also provide evidence for a likely function of synapsin editing in Drosophila. The N-terminal synapsin undeca-peptide containing the genomic motif (RRFS) represents an excellent substrate for in-vitro phosphorylation by bovine PKA while the edited peptide (RGFS) is not significantly phosphorylated. Thus pre-mRNA editing by ADAR could modulate the function of ubiquitously expressed synapsin in a cell-specific manner during development and adulthood.

Conclusion

Similar to several other neuronal proteins of Drosophila, synapsin is modified by ADAR-mediated recoding at the pre-mRNA level. This editing likely reduces or abolishes synapsin phosphorylation by PKA. Since synapsin in Drosophila is required for various forms of behavioural plasticity, it will be fascinating to investigate the effect of this recoding on learning and memory.
Serologic indices of hepatitis B virus infection in military recruits in Greece (2004–2005)
Authors: German Vasilios , Giannakos Georgios , Kopterides Petros , Liaskonis Konstantinos , Falagas Matthew E
Published: November 2006

Background

The prevalence of hepatitis B virus infection in Greece has been decreasing over the last decades. However, recent epidemiological data are lacking.

Methods

We studied 1,840 Army recruits from 05/2004 until 10/2005, and performed serological testing for HBsAg, anti-HBsAg, and anti-HBcAg. We also examined their association with several factors, including age, residential area, socioeconomic class, and educational level.

Results

Mean age (± SD) of the recruits was 20.5 (± 2.1) years. Antibodies to HBV core antigen [anti-HBcAg (+)] were found in 31 (1.68%) of 1,840 participants. Only 6 (0.32%) were HBsAg (+)/anti-HBsAg (-)/anti-HBcAg (+), while 21 (1.14%) were HBsAg (-)/anti-HBsAg (+)/anti-HBcAg (+), and 4 (0.22%) were HBsAg (-)/anti-HBsAg (-)/anti-HBcAg (+). Overall, 1,144 recruits (62.17%) had antibodies against HBsAg [HBsAg (-)/anti-HBsAg (+)/anti-HBcAg (-)]; 665 recruits (36.14%) had undetectable anti-HBsAg levels. Multivariable analysis showed that younger age (OR: 0.87; 95% CI: 0.82–0.92) and advanced educational level (OR: 1.59; 95% CI: 1.32–1.93) were independently associated with serologic evidence suggestive of previous HBV vaccination.

Conclusion

We document a further decline of the prevalence of chronic HBV infection among Greek military recruits, a fact that may support the effectiveness of the ongoing immunization programme.
Cytotoxic drug sensitivity of Epstein-Barr virus transformed lymphoblastoid B-cells
Authors: Markasz Laszlo , Stuber György , Flaberg Emilie , Jernberg Åsa Gustafsson , Eksborg Staffan , Olah Eva , Skribek Henriette , Szekely Laszlo
Published: November 2006

Background

Epstein-Barr virus (EBV) is the causative agent of immunosuppression associated lymphoproliferations such as post-transplant lymphoproliferative disorder (PTLD), AIDS related immunoblastic lymphomas (ARL) and immunoblastic lymphomas in X-linked lymphoproliferative syndrome (XLP). The reported overall mortality for PTLD often exceeds 50%. Reducing the immunosuppression in recipients of solid organ transplants (SOT) or using highly active antiretroviral therapy in AIDS patients leads to complete remission in 23–50% of the PTLD/ARL cases but will not suffice for recipients of bone marrow grafts. An additional therapeutic alternative is the treatment with anti-CD20 antibodies (Rituximab) or EBV-specific cytotoxic T-cells. Chemotherapy is used for the non-responding cases only as the second or third line of treatment. The most frequently used chemotherapy regimens originate from the non-Hodgkin lymphoma protocols and there are no cytotoxic drugs that have been specifically selected against EBV induced lymphoproliferative disorders.

Methods

As lymphoblastoid cell lines (LCLs) are well established in vitro models for PTLD, we have assessed 17 LCLs for cytotoxic drug sensitivity. After three days of incubation, live and dead cells were differentially stained using fluorescent dyes. The precise numbers of live and dead cells were determined using a custom designed automated laser confocal fluorescent microscope.

Results

Independently of their origin, LCLs showed very similar drug sensitivity patterns against 29 frequently used cytostatic drugs. LCLs were highly sensitive for vincristine, methotrexate, epirubicin and paclitaxel.

Conclusion

Our data shows that the inclusion of epirubicin and paclitaxel into chemotherapy protocols against PTLD may be justified.
T-cell contact-dependent regulation of CC and CXC chemokine production in monocytes through differential involvement of NFκB: implications for rheumatoid arthritis
Authors: Beech Jonathan T , Andreakos Evangelos , Ciesielski Cathleen J , Green Patricia , Foxwell Brian MJ , Brennan Fionula M
Published: November 2006

We and others have reported that rheumatoid arthritis (RA) synovial T cells can activate human monocytes/macrophages in a contact-dependent manner to induce the expression of inflammatory cytokines, including tumour necrosis factor alpha (TNFα). In the present study we demonstrate that RA synovial T cells without further activation can also induce monocyte CC and CXC chemokine production in a contact-dependent manner. The transcription factor NFκB is differentially involved in this process as CXC chemokines but not CC chemokines are inhibited after overexpression of IκBα, the natural inhibitor of NFκB. This effector function of RA synovial T cells is also shared by T cells activated with a cytokine cocktail containing IL-2, IL-6 and TNFα, but not T cells activated by anti-CD3 cross-linking that mimics TCR engagement. This study demonstrates for the first time that RA synovial T cells as well as cytokine-activated T cells are able to induce monocyte chemokine production in a contact-dependent manner and through NFκB-dependent and NFκB-independent mechanisms, in a process influenced by the phosphatidyl-inositol-3-kinase pathway. Moreover, this study provides further evidence that cytokine-activated T cells share aspects of their effector function with RA synovial T cells and that their targeting in the clinic has therapeutic potential.
Methotrexate enhances the anti-inflammatory effect of CF101 via up-regulation of the A3adenosine receptor expression
Authors: Ochaion Avivit , Bar-Yehuda Sara , Cohn Shira , Del Valle Luis , Perez-Liz Georginia , Madi Lea , Barer Faina , Farbstein Motti , Fishman-Furman Sari , Reitblat Tatiana , Reitblat Alexander , Amital Howard , Levi Yair , Molad Yair , Mader Reuven , Tishler Moshe , Langevitz Pnina , Zabutti Alexander , Fishman Pnina
Published: November 2006

Methotrexate (MTX) exerts an anti-inflammatory effect via its metabolite adenosine, which activates adenosine receptors. The A3adenosine receptor (A3AR) was found to be highly expressed in inflammatory tissues and peripheral blood mononuclear cells (PBMCs) of rats with adjuvant-induced arthritis (AIA). CF101 (IB-MECA), an A3AR agonist, was previously found to inhibit the clinical and pathological manifestations of AIA. The aim of the present study was to examine the effect of MTX on A3AR expression level and the efficacy of combined treatment with CF101 and MTX in AIA rats. AIA rats were treated with MTX, CF101, or both agents combined. A3AR mRNA, protein expression and exhibition were tested in paw and PBMC extracts from AIA rats utilizing immunohistochemistry staining, RT-PCR and Western blot analysis. A3AR level was tested in PBMC extracts from patients chronically treated with MTX and healthy individuals. The effect of CF101, MTX and combined treatment on A3AR expression level was also tested in PHA-stimulated PBMCs from healthy individuals and from MTX-treated patients with rheumatoid arthritis (RA). Combined treatment with CF101 and MTX resulted in an additive anti-inflammatory effect in AIA rats. MTX induced A2AAR and A3AR over-expression in paw cells from treated animals. Moreover, increased A3AR expression level was detected in PBMCs from MTX-treated RA patients compared with cells from healthy individuals. MTX also increased the protein expression level of PHA-stimulated PBMCs from healthy individuals. The increase in A3AR level was counteractedin vitroby adenosine deaminase and mimickedin vivoby dipyridamole, demonstrating that receptor over-expression was mediated by adenosine. In conclusion, the data presented here indicate that MTX induces increased A3AR expression and exhibition, thereby potentiating the inhibitory effect of CF101 and supporting combined use of these drugs to treat RA.
Multicentre study on peri- and postoperative central venous oxygen saturation in high-risk surgical patients
Authors:   Collaborative Study Group on Perioperative ScvO2 Monitoring
Published: November 2006

Introduction

Low central venous oxygen saturation (ScvO2) has been associated with increased risk of postoperative complications in high-risk surgery. Whether this association is centre-specific or more generalisable is not known. The aim of this study was to assess the association between peri- and postoperative ScvO2 and outcome in high-risk surgical patients in a multicentre setting.

Methods

Three large European university hospitals (two in Finland, one in Switzerland) participated. In 60 patients with intra-abdominal surgery lasting more than 90 minutes, the presence of at least two of Shoemaker's criteria, and ASA (American Society of Anesthesiologists) class greater than 2, ScvO2 was determined preoperatively and at two hour intervals during the operation until 12 hours postoperatively. Hospital length of stay (LOS) mortality, and predefined postoperative complications were recorded.

Results

The age of the patients was 72 ± 10 years (mean ± standard deviation), and simplified acute physiology score (SAPS II) was 32 ± 12. Hospital LOS was 10.5 (8 to 14) days, and 28-day hospital mortality was 10.0%. Preoperative ScvO2 decreased from 77% ± 10% to 70% ± 11% (p < 0.001) immediately after surgery and remained unchanged 12 hours later. A total of 67 postoperative complications were recorded in 32 patients. After multivariate analysis, mean ScvO2 value (odds ratio [OR] 1.23 [95% confidence interval (CI) 1.01 to 1.50], p = 0.037), hospital LOS (OR 0.75 [95% CI 0.59 to 0.94], p = 0.012), and SAPS II (OR 0.90 [95% CI 0.82 to 0.99], p = 0.029) were independently associated with postoperative complications. The optimal value of mean ScvO2 to discriminate between patients who did or did not develop complications was 73% (sensitivity 72%, specificity 61%).

Conclusion

Low ScvO2 perioperatively is related to increased risk of postoperative complications in high-risk surgery. This warrants trials with goal-directed therapy using ScvO2 as a target in high-risk surgery patients.
Multicomponent VSP imaging of tight-gas sands
Authors: O’Brien John , Harris Ron
Published: November 2006

Low-porosity Bossier and Cotton Valley sands of the East Texas Basin, U. S., have only a small acoustic impedance contrast with the encasing shales but a greater relative contrast in shear-wave impedance. Vertical seismic profile (VSP) data acquired with both a near-offset and far-offset P-wave source clearly demonstrate the P-P reflectivity and P-S mode conversions within the Bossier section. We designate conventional P-wave reflectivity as P-P, shear-wave reflectivity as S-S, and P-wave/shear-wave mode conversion data as P-S. While Bossier P-P reflectivity is low, it appears to be adequate for mapping thick sandbodies such as the York Sandstone, the main exploration target in this area. However, P-P reflectivity is even lower and is inadequate for imaging the overlying Cotton Valley Sands. In contrast, the far-offset VSP data acquired with a P-wave source demonstrate a high level of P-S-mode conversion, which is used to image this interval with definition that is not provided by P-P reflectivity. This provides strong support for the use of P-S-mode conversion imaging for seismic characterization of tight sand reservoirs. Near-offset shear-wave VSP data acquired with a shearwave source show low S/N ratio and limited bandwidth for the downgoing waveform because of the depth of the target; shear-wave energy appears to have a more limited range of propagation than P-waves. Such effects may also have a strong negative impact on multicomponent imaging of these sands using surface seismic techniques. Multicomponent 3D VSP imaging provides a superior solution by placing the geophones closer to the subsurface zone of interest.
Various-scale electromagnetic investigations of high-salinity zones in a coastal plain
Authors: Mitsuhata Yuji , Uchida Toshihiro , Matsuo Koichi , Marui Atsunao , Kusunose Kinichirou
Published: November 2006

Three different-scale electromagnetic (EM) measurements have been performed in the Kujukuri coastal plain, southeast Japan, to investigate the distribution of saline groundwater. The three techniques were audio-frequency magnetotelluric (AMT), transient electromagnetic (TEM), and small loop-loop EM measurements. The resistivity sections estimated from these data sets reveal three independent resistivity distributions extending to different depths. The AMT method reveals a regional-scale resistivity distribution across the plain to a maximum depth of approximately [Formula: see text] and the existence of deep conductive zones, which are inferred to be associated with fossil seawater trapped in a Pleistocene formation. The TEM results show a medium-scale resistivity distribution to depths of approximately [Formula: see text], in which two shallow conductive zones are recognized. It is concluded that these features are caused by present seawater intrusion and high-salinity salt-marsh deposits formed during sporadic marine regressions. The small loop-loop EM method provided a shallow resistivity profile that highlights the conductive salt-marsh deposits and resistive sandy ridges. Although these resistivity sections correspond to different depth ranges, the overlapping portions of the sections are very consistent with one another. These EM methods are useful in detecting and interpreting important resistivity features. Taking the geologic evolution of the coastal plains into consideration is crucial when interpreting resistivity profiles such as these, and our results suggest that the presence of fossil seawater is an important factor controlling resistivity at a variety of depths.
Imaging complex structure in shallow seismic-reflection data using prestack depth migration
Authors: Bradford John H. , Liberty Lee M. , Lyle Mitch W. , Clement William P. , Hess Scott
Published: November 2006

Prestack depth migration (PSDM) analysis has the potential to significantly improve the accuracy of both shallow seismic reflection images and the measured velocity distributions. In a study designed to image faults in the Alvord Basin, Oregon, at depths from [Formula: see text], PSDM produced a detailed reflection image over the full target depth range. In contrast, poststack time migration produced significant migration artifacts in the upper [Formula: see text] that obscured reflection events and limited the structural interpretation in the shallow section. Additionally, an abrupt increase from [Formula: see text] to [Formula: see text] in the PSDM velocity model constrained the interpretation of the transition from sedimentary basin fill to basement volcanic rocks. PSDM analysis revealed a complex extensional history with at least two distinct phases of basin growth and a midbasin basement high that forms the division between two major basin compartments.
Local linear coherent noise attenuation based on local polynomial approximation
Authors: Lu Wenkai , Zhang Wenpo , Liu Dongqi
Published: November 2006

We propose a new technique for the attenuation of locally coherent noise. We assume that the moveout of the noise is locally linear and approximate its amplitude variations with offset using piecewise (local) polynomial models. Thus, our method consists of three steps: detection of the noise (locally linear coherent noise, LLCN), amplitude estimation by a local polynomial approximation (LPA), and subtraction of the estimated coherent noise from the original data. Applying the proposed method to synthetic data and to a field data set shows that the LPA filter has good ability to model LLCN and is insensitive to the filter parameters. Comparisons of the results obtained by our method with those from the traditional frequency-wavenumber filter and the localized 2D filter in the Fourier projection domain (FPF) show that the new method outperforms both traditional methods in situations with complex coherent noise.
Amplitude analysis of isotropic P-wave reflections
Authors: van der Baan Mirko , Smit Dirk
Published: November 2006

The analysis of amplitude variation with offset (AVO) of seismic reflections is a very popular tool for detecting gas sands. It is assumed in AVO, however, that plane-wave reflection coefficients can be used directly to analyze amplitudes measured in the time-offset domain. This is not true for near-critical angles of reflection. Plane-wave reflection coefficients incorporate the contribution of the head wave. A plane-wave decomposition such as a proper [Formula: see text] transform must be applied to the seismic data for accurate analysis of reflection coefficients near critical angles. Amplitudes after plane-wave decomposition are related directly to the plane-wave reflection coefficients; geometric-spreading corrections are no longer required, and polarization effects of P-P reflections recorded on the [Formula: see text]-component are also removed. Conventional, linearized expressions for the isotropic P-P-wave reflection coefficient depend on contrasts in three parameters, and they require background information about average P-wave/S-wave velocity ratios. We derive a new reduced-parameter expression that depends only on two free parameters without loss of accuracy. No extra prior parameter information is needed either. The reduction in free parameters is achieved by explicitly incorporating P-wave moveout information. A new AVO strategy is developed that requires moveout analysis of three reflections: the target horizon, the reflections directly above and below the target horizon, and the amplitudes of the target horizon. The new AVO expression can be used in the time-offset domain for precritical arrivals and in the [Formula: see text] domain for precritical and critical reflections.
Radial profiling of the three formation shear moduli and its application to well completions
Authors: Sinha Bikash K. , Vissapragada Badarinadh , Renlie Lasse , Tysse Sveinung
Published: November 2006

Near-wellbore alteration in shear stiffnesses in the three orthogonal planes can be described in terms of radial variations of the three shear moduli or slownesses. The three shear moduli are different in formations exhibiting orthorhombic or lower degree of symmetry, as is the case in deviated wellbores in triaxially stressed formations. These shear moduli are affected by factors such as overbalanced drilling, borehole stress concentrations, shale swelling, near-wellbore mechanical damage, and supercharging of permeable formations. The two vertical shear moduli [Formula: see text] and [Formula: see text] in an anisotropic formation with a vertical [Formula: see text]-axis are obtained from crossed-dipole sonic data, whereas the horizontal shear modulus [Formula: see text] is estimated from borehole Stoneley data. The effective shear modulus [Formula: see text] is smaller than the vertical shear moduli [Formula: see text] or [Formula: see text] in a poroelastic formation exhibiting high horizontal fluid mobility. Consequently, analyses of radial profiling of the three shear moduli in a reasonably uniform lithology interval yield useful correlations, with mobility impaired by an increased amount of clay or by near-wellbore damage in a shaley sand reservoir interval in a North Sea vertical well. Radial profiling results help to identify suitable depths for fluid sampling and to complete a well for optimum production.
Fixed-source and fixed-receiver walkaway seismic noise tests: A field comparison
Authors: Vincent Paul D. , Tsoflias Georgios P. , Steeples Don W. , Sloan Steve D.
Published: November 2006

Seismologists and geophysical literature often use the term “walkaway” to describe any survey used to analyze wavetrains based on source-to-receiver offset. A distinction should be made between receiver-group moveout (fixed-source walkaway) and source moveout (fixed-receiver walkaway) when multiple channels simultaneously record signal from multiple independent geophones. Three data sets are presented that illustrate this distinction: one collected in an area where a fixed-receiver walkaway survey recorded similar data and was more time efficient than a fixed-source walkaway survey, and two others collected in an area where dipping reflectors and laterally varying velocities caused the fixed-receiver walkaway data to be significantly different than the fixed-source walkaway data. The results show that, while still useful, clarity in recorded data is lost when fixed-receiver walkaway surveys are substituted for fixed-source walkaway surveys in areas with uneven surface topography, dipping interfaces, or laterally varying velocities. This is because walkaway seismograms are displayed by source-to-receiver offset, whereas neighboring traces do not correspond necessarily with neighboring raypaths or reflection points.
Time-shift imaging condition in seismic migration
Authors: Sava Paul , Fomel Sergey
Published: November 2006

Seismic imaging based on single-scattering approximation is in the analysis of the match between the source and receiver wavefields at every image location. Wavefields at depth are functions of space and time and are reconstructed from surface data either by integral methods (Kirchhoff migration) or by differential methods (reverse-time or wavefield extrapolation migration). Different methods can be used to analyze wavefield matching, of which crosscorrelation is a popular option. Implementation of a simple imaging condition requires time crosscorrelation of source and receiver wavefields, followed by extraction of the zero time lag. A generalized imaging condition operates by crosscorrelation in both space and time, followed by image extraction at zero time lag. Images at different spatial crosscorrelation lags are indicators of imaging accuracy and are also used for image-angle decomposition. In this paper, we introduce an alternative prestack imaging condition in which we preserve multiple lags of the time crosscorrelation. Prestack images are described as functions of time shifts as opposed to space shifts between source and receiver wavefields. This imaging condition is applicable to migration by Kirchhoff, wavefield extrapolation, or reverse-time techniques. The transformation allows construction of common-image gathers presented as functions of either time shift or reflection angle at every location in space. Inaccurate migration velocity is revealed by angle-domain common-image gathers with nonflat events. Computational experiments using a synthetic data set from a complex salt model demonstrate the main features of the method.
3D surface-related multiple elimination using parabolic sparse inversion
Authors: Hokstad Ketil , Sollie Roger
Published: November 2006

The basic theory of surface-related multiple elimination (SRME) can be formulated easily for 3D seismic data. However, because standard 3D seismic acquisition geometries violate the requirements of the method, the practical implementation for 3D seismic data is far from trivial. A major problem is to perform the crossline-summation step of 3D SRME, which becomes aliased because of the large separation between receiver cables and between source lines. A solution to this problem, based on hyperbolic sparse inversion, has been presented previously. This method is an alternative to extensive interpolation and extrapolation of data. The hyperbolic sparse inversion is formulated in the time domain and leads to few, but large, systems of equations. In this paper, we propose an alternative formulation using parabolic sparse inversion based on an efficient weighted minimum-norm solution that can be computed in the angular frequency domain. The main advantage of the new method is numerical efficiency because solving many small systems of equations often is faster than solving a few big ones. The method is demonstrated on 3D synthetic and real data with reflected and diffracted multiples. Numerical results show that the proposed method gives improved results compared to 2D SRME. For typical seismic acquisition geometries, the numerical cost running on 50 processors is [Formula: see text] per output trace. This makes production-scale processing of 3D seismic data feasible on current Linux clusters.
Estimation of velocity and attenuation coefficient maps from crosswell seismic data
Authors: Plessix René-Edouard
Published: November 2006

Using a classic traveltime tomography and an attenuation tomography based on the centroid frequency shift method, velocity and attenuation coefficient tomograms are computed from two crosswell seismic data. Because of the limited frequency band of the data and the difficulties of picking the first transmitted events, velocity and attenuation coefficients are assumed independent of frequency during the processing, meaning that the attenuation linearly increases with frequency. This reduces the possibility of using a theoretical model to interpret the results. Moreover, attenuation results include both scattering and viscous attenuation. Nevertheless, the attenuation coefficient tomograms confirm some of the features seen in the velocity tomograms: The sand zones show a higher attenuation, although the shale zones and the seals of the reservoirs show a lower attenuation. With a Kramers-Kronig relation for the dispersion formula based on frequency-independent attenuation coefficient, the smooth part of the measured sonic velocity could be approximated from the seismic velocity and attenuation coefficient.
Automatic inversion of magnetic anomalies from two height levels using finite-difference similarity transforms
Authors: Stavrev Petar , Gerovska Daniela , Araúzo-Bravo Marcos J.
Published: November 2006

We solve the inverse magnetic problem for the depth and shape of simple sources in the presence of a regional field and truly random noise. We do not use noise-generating derivatives nor are we forced to solve complex systems of equations. Our inverse operator applies a new geometric type of field transform, the finite-difference similarity transform (FDST), that is based on a postulated degree of homogeneity in the potential field. Magnetic data from two height levels are required for the calculation of the FDSTs. The FDSTs are generated for an assumed central point of similarity (CPS) and a trial value (index) for the coefficient of similarity, and they are sensitive to the distance between the source and the CPS and to the agreement between the index and the degree of homogeneity in the data. When the CPS converges to a singular point in the potential field, say, the center or the topedge of the source, and when the trial index converges on the degree of homogeneity present in the data, the FDST drops in amplitude and its plot approaches a straight line, thereby signaling an interpretation for the source position and type. All inverse operations are fully automated and applicable to the interpretation of large data sets. The necessary data for the second level can be obtained by actual measurement or, alternatively, by deriving them from the data at the first level by an upward, analytical continuation. Upward continuation suppresses high-wavenumber random noise and thus contributes to a stable inversion. Model tests show that a suitable height for the second level is less than the expected depth of the source below the first level, while a suitable window length is about twice that depth. Examples show that the proposed inversion is effective on both model and field data. Note that this approach can be extended to the inversion of any component or derivative of the 2D or 3D magnetic or gravity fields from simple sources.
Adaptive finite-element modeling using unstructured grids: The 2D magnetotelluric example
Authors: Key Kerry , Weiss Chester
Published: November 2006

Existing numerical modeling techniques commonly used for electromagnetic (EM) exploration are bound by the limitations of approximating complex structures using a rectangular grid. A more flexible tool is the adaptive finite-element (FE) method using unstructured grids. Composed of irregular triangles, an unstructured grid can readily conform to complicated structural boundaries. To ensure numerical accuracy, adaptive refinement using an a posteriori error estimator is performed iteratively to refine the grid where solution accuracy is insufficient. Two recently developed asymptotically exact a posteriori error estimators are based on a superconvergent gradient recovery operator. The first relies solely on the normed difference between the recovered gradients and the piecewise constant FE gradients and is effective for lowering the global error in the FE solution. For many problems, an accurate solution is required only in a few discreteregions and a more efficient error estimator is possible by considering the local influence of errors from coarse elements elsewhere in the grid. The second error estimator accomplishes this by using weights determined from the solution to an appropriate dual problem to modify the first error estimator. Application of these methods for 2D magnetotelluric (MT) modeling reveals, as expected, that the dual weighted error estimator is far more efficient in achieving accurate MT responses. Refining about 15% of elements per iteration gives the fastest convergence rate. For a given refined grid, the solution error at higher frequencies varies in proportion to the skin depth, requiring refinement about every two decades of frequency. The transverse electric (TE) and transverse magnetic (TM) modes exhibit different field behavior, and refinement should consider the effects of both. An example resistivity model of seafloor bathymetry underlain by complex salt intrusions and dipping and faulted sedimentary layers illustrates the benefits of this new technique.
Some characteristics of the electromagnetic field from radio transmitters in Europe
Authors: Pedersen Laust B. , Bastani Mehrdad , Dynesius Lars
Published: November 2006

The radiomagnetotelluric (RMT) method utilizes man-made signals generated by distant transmitters or by dedicated local transmitters. Man-made electromagnetic (EM) signals in the [Formula: see text] frequency band come mainly from two sources: (1) distant radio transmitters operating in the [Formula: see text] band and (2) nearby or distant industrial sources emitting either transients or higher harmonics of [Formula: see text]. The natural or background EM signals form a kind of noise floor. In Europe for the [Formula: see text] band, there generally are sufficient transmitters available to estimate the EM transfer functions completely, i.e., the full impedance tensor and the tipper vector. We show examples of the variability of power spectra and azimuthal distributions of transmitters from sites in Sweden, Hungary, The Netherlands, and Spain. We also show that the estimated transfer functions are stable as a function of time; even under typical noisy conditions, simple stacking of spectra in narrow frequency bands provides good-quality estimates of transfer functions.
Geophysical surveys of earthquake-induced liquefaction deposits in the New Madrid seismic zone
Authors: Wolf Lorraine W. , Tuttle Martitia P. , Browning Sharon , Park Stephanie
Published: November 2006

We explore the effectiveness and limitations of electrical and electromagnetic methods in imaging buried, earthquake-induced liquefaction deposits. Geophysical surveys conducted at liquefaction sites in the New Madrid seismic zone (NMSZ) in the central United States demonstrate that these subsurface-imaging techniques can be useful tools in paleoseismology. Paleoseismological studies of liquefaction features provide one of the few means for estimating recurrence intervals of large earthquakes in the NMSZ, a region with widespread evidence of strong ground shaking but short instrumental record. Noninvasive geophysical methods minimize ground disturbance during these studies, an attribute of particular importance when the studies are conducted at federally protected archaeological sites. Surveys such as those described here can be used to locate buried liquefaction deposits and to site trenches for detailed geologic studies.
Optimizing decision threshold and weighting parameter for UXO discrimination
Authors: Huang Haoping , SanFilipo Bill , Won I. J.
Published: November 2006

Establishing a decision threshold to separate unexploded ordnance (UXO) from clutter is a critical task in UXO discrimination procedures. It is, however, a difficult task because the decision threshold depends on many parameters such as local geology, distribution of UXO and clutter, and cultural and environmental noise at a given UXO cleanup site. Some discrimination algorithms also use site-dependent weighting factors. In practice, one determines these parameters empirically from calibration experiments. To facilitate this task, we introduce a simple function called the degree of discrimination, constructed from calibration plots at a UXO cleanup site. First, we compute the degree of discrimination for a representative set of thresholds and weighting factors using ground truth data from the calibration site. Then, we find the optimum decision threshold and weighting factors associated with the best degree of discrimination. Finally, we use these optimal parameters for the UXO site cleanup. We have conducted two experiments using the broadband electromagnetic (EM) sensor with a concentric coil configuration. Our experiments show that 92% of UXO is declared and 74% of clutter is rejected using our optimized threshold and weights. A blind test shows that optimizing the threshold and weights increases the degree of discrimination from 0 to 0.15. Our tests also show that the detection scheme with a collective threshold for all UXO types is easier to use and yields better discrimination than the scheme based on individual thresholds for each UXO type.