bluuebunny/crossref_metadata_2025 huggingface dataset:
Association of Plasma Resistin With Glomerular Filtration Rate and Albuminuria in Hypertensive Adults
Authors: Ellington Allison A. , Malik A. Rauoof , Klee George G. , Turner Stephen T. , Rule Andrew D. , Mosley Thomas H. , Kullo Iftikhar J.
Published: September 2007

Resistin, a recently discovered proinflammatory cytokine, has been variably associated with insulin resistance, inflammation, and renal dysfunction. We investigated the association of plasma resistin with estimated glomerular filtration rate and albuminuria in 1575 hypertensive adults without known coronary heart disease or stroke (857 blacks and 718 non-Hispanic whites). Resistin was measured by a solid phase sandwich immunoassay, estimated glomerular filtration rate was estimated from serum creatinine, and albuminuria was expressed as urine albumin:creatinine ratio. After adjustment for coronary heart disease risk factors (age, sex, body mass index, smoking history, systolic blood pressure, diabetes, and total and high-density lipoprotein cholesterol) and use of renin-angiotensin blockers and statins, higher plasma resistin levels were associated with lower estimated glomerular filtration rate in both ethnic groups (each
P
<0.0001); the association remained significant after further adjustment for a marker of insulin resistance (homeostasis model assessment for insulin resistance) and a marker of inflammation (plasma C-reactive protein) and was seen in subjects with and without diabetes (each
P
<0.0001) in both ethnic groups. Higher plasma resistin levels were associated with a higher urine albumin:creatinine ratio in black subjects with diabetes (
P
<0.0001) and non-Hispanic white subjects with diabetes (
P
=0.032), independent of coronary heart disease risk factors, hypertension medication use, and statin use; the association remained significant after additional adjustment for homeostasis model assessment for insulin resistance and C-reactive protein. In adults with hypertension, higher circulating resistin levels were associated with a lower estimated glomerular filtration rate and with increased urine albumin:creatinine ratio in the presence of concomitant diabetes. This association was independent of coronary heart disease risk factors and markers of insulin resistance and inflammation.
Pulse Pressure Is an Age-Independent Predictor of Stroke Development After Cardiac Surgery
Authors: Benjo Alexandre , Thompson Richard E. , Fine Derek , Hogue Charles W. , Alejo Diane , Kaw Anita , Gerstenblith Gary , Shah Ashish , Berkowitz Dan E. , Nyhan Daniel
Published: September 2007

Chronologic age is a strong predictor of adverse outcomes after cardiac surgery. The variability in age-related cardiovascular changes suggests that age may not be the most accurate predictor of adverse perioperative outcomes. Vascular stiffness has emerged as an important surrogate of vascular aging. In a retrospective review, we investigated the value of vascular stiffness, as assessed by brachial pulse pressure (PP) measurements, in predicting stroke in 703 patients (63.4% men and 36.6% women). Patients were followed for 348±215 days after cardiac surgery. We used a multivariable logistic model and unadjusted and adjusted Cox proportional-hazard models to assess the probability of stroke and the hazards of stroke over time. Stroke patients had a significantly higher PP (81.2 mm Hg versus 64.5 mm Hg;
P
=0.0006). In the logistic regression model, PP was an independent predictor of stroke development (unadjusted odds ratio: 1.35; 95% CI: 1.13 to 1.62, for every 10-mm Hg increase in PP;
P
=0.001). In the unadjusted and adjusted Cox models, PP again predicted stroke (hazard ratio: 1.32; 95% CI: 1.12 to 1.57; hazard ratio: 2.62; 95% CI: 1.49 to 4.60, respectively;
P
=0.001 for both) for every 10 mm Hg increase in PP. Age, gender, and diabetes were not independent predictors of stroke. Ejection fraction was inversely related to stroke in the adjusted model. Kaplan–Meier estimates and corresponding log-rank test indicated that the probability of stroke-free survival function was significantly lower (
P
=0.0067) in patients with PP >72 mm Hg versus <72 mm Hg. This analysis suggests that indices of vascular stiffness could be important predictors of neurologic complications.
On the Clausewitz of the Cold War: Reconsidering the Primacy of Policy in On War
Authors: Echevarria Antulio J.
Published: September 2007

Throughout the Cold War, scholars gave considerable privilege to Clausewitz's observation that war is the “mere continuation of political activity ( Politik) by other means.” It is often referred to in intellectual shorthand as the primacy of policy. This article questions the extent to which emphasis on the primacy of policy has been overstressed, influenced perhaps by the strategic context of the Cold War. Clausewitz's trinitarian concept of war—hostility, chance, political purpose—which appears in what scholars generally agree is On War's only finished chapter, does not portray policy as more dominant than the other tendencies; instead, it presents them as equals, stressing only each one's uniqueness in relation to the others. Reinterpreting policy as equal to the other two aspects of the trinity tends to strengthen the relevance of Clausewitz's overall theory to contemporary wars.
A Comparison of Elementary/K-8 and Middle Schools' Suspension Rates
Authors: Arcia Emily
Published: September 2007

This study was undertaken to examine the suspension percentages among three sixth-grade transition groups: (a) students who attended elementary or K-8 schools in sixth grade and K-8 schools in seventh grade, (b) students who attended elementary or K-8 schools in sixth grade and middle schools in seventh grade, and (c) students who attended middle schools for both sixth and seventh grades. Percentage suspensions were examined by Black and by Latino ethnicity, and by sixth-grade reading achievement. Also, seventh-grade suspension percentages were examined by sixth-grade suspension history. Across race/ ethnicity, achievement, and sixth-grade suspension history, students in middle schools were suspended at substantially higher rates than were students in elementary/K-8 schools. These differences raise concerns about the disciplinary practices used in middle schools and the reasons why these practices are necessary or are deemed appropriate.
Merit and Affirmative Action in Education
Authors: Tierney William G.
Published: September 2007

Throughout the 20th century, one of the central debates pertaining to postsecondary education has been about the concept of merit. Who deserves to go to college? The answer to that question goes to the heart of various policies that have been developed, changed, and debated. Perhaps no other policy has drawn more prominence and criticism than that which has come to be called “affirmative action.” In this article, the author discusses the idea of merit as it relates to affirmative action and postsecondary education. The article first delineates the parameters of what is defined as a “democratic public culture” and then considers the concerns of critics and proponents about affirmative action by exploring the meritocratic assumptions of the concerns. The author concludes by discussing the role that academic institutions might play in advancing the democratic sphere and considers what this role suggests for policies such as affirmative action.
Exploring an English Language Learner's Literacy Learning Opportunities
Authors: Brock Cynthia H.
Published: September 2007

This investigation is an ethnographic case study of the literacy learning opportunities of a fifth-grade Hmong child (pseudonym Deng) who came to the United States from Laos via Thailand at the very end of his third-grade year in school. Deng was one of 25 students in a mainstream urban classroom in the Midwest during his fifth grade in school when this investigation took place. Because Deng had only been in the United States for a little more than a year at the time this investigation began and because English was a relatively new language for him, I was concerned about his opportunities for literacy learning in a classroom where English was the medium of instruction. Deng and I worked collaboratively to explore his literacy learning opportunities in the context of a trade book unit pertaining to the text Maniac Magee.
Further Considerations Concerning the Cohesion-Performance Relation in Military Settings
Authors: Griffith James
Published: September 2007

A recent issue of Armed Forces and Society published an interchange among MacCoun, Wong, Kolditz, and others regarding the relation of cohesion to performance. The discussion was purposefully narrow in its scope, but other literature should be considered to properly frame the larger question of cohesion's function in military settings. Specifically, current and future discussions should acknowledge: (1) the primary function of cohesion as revealed in historical and observational accounts of soldiers in combat; (2) emergent similarities between social support and cohesion, which support the notion that cohesion acts as a moderator rather than a main effect of performance; and (3) findings from a recent meta-analysis that contradict those of Mullen and Cooper. Viewing cohesion's relation to performance as indirect rather than direct has very different and important implications for research, applications, and expected effects of cohesion on group performance.
Penalty Kicks in Soccer
Authors: Coloma Germán
Published: September 2007

This article uses the model proposed by Chiappori, Levitt, and Groseclose to test for mixed-strategy Nash equilibria in a game between a kicker and a goalkeeper in the situation of a penalty kick in soccer. The main contribution of this article is to develop an alternative testing methodology on the basis of the use of a simultaneous-equation regression approach that directly tests the equilibrium conditions. Using the same data as Chiappori et al., the author finds results similar to theirs and also separately analyzes the behavior of different types of players (classified according to which foot they use to kick the ball and to the strategies they choose to mix).
Penalty Shoot-Outs
Authors: Carrillo Juan D.
Published: September 2007

This article proposes a rule to determine the winner of a soccer match, which is different from the traditional penalty shoot-outs at the end of extra time. The author shows that games can be more attractive if penalties are shot before extra time and the outcome counts only if the tie is preserved during extra time. In general, this rule will promote offense by the team that loses the penalty shoot-outs, and it will promote defense by the team that wins the penalty shoot-outs. The author provides conditions on the marginal effect of offensive play in the probabilities of scoring and conceding a goal such that the proposed rule dominates the current one. Last, this study determines a class of functions that satisfies these conditions. More generally, the article shows how the ordering of tasks may affect the incentives to exert and allocate effort.
Evaluating Rent Dissipation in the Spanish Football Industry
Authors: Ascari Guido , Gagnepain Philippe
Published: September 2007

This article proposes to evaluate empirically the consequences of the rent-seeking behavior of football clubs on their costs. The empirical work entails estimating a football wage, result, and demand system with data on clubs competing in the first and second Spanish leagues during the 1996-2003 seasons. The estimation sheds light on wage distortions that differ from 45% to 52% throughout the period considered. This provides an interesting illustration of the financial difficulties faced recently by many European football clubs.
Private Financing and Sports Franchise Values
Authors: Miller Phillip
Published: September 2007

This article examines the impact of receiving a new stadium on team franchise values. The author argues that a new stadium will increase the franchise values of teams regardless of how construction was financed. A team playing in a stadium that it owns will be able to capitalize the value of the stadium in the team's franchise value and will thus have a higher franchise value. Using panel data for Major League Baseball teams from 1990-2002, the author finds that after controlling for team quality and metro area differences, regardless of the financing mechanism, a team playing in a brand new stadium realizes an increase in its franchise value. It is also found that a team playing in its own stadium has a higher franchise value than a team playing in a public stadium. However, the difference in franchise values between playing in a team-owned stadium and playing in a public stadium does not offset the average cost of constructing the stadium. The article thus provides a deeper understanding of the determinants of franchise values and of the motives of sports team owners in their lobbying efforts for public subsidies.
Acknowledgement of Priority
Authors: Cherchye Laurens , Vermeulen Frederic
Published: September 2007

Robust Rankings of Multidimensional Performances: An Application to Tour de France Racing Cyclists

Dr. Knut M. Wittkowski (The Rockefeller University) pointed out that his u-score given in Equation 3 of Wittkowski (2003) and Equation 3 in Wittkowski, Lee, Nussbaum, Chamian, and Krueger (2004) is the same as our net-dominance-metric that aggregates the information provided by our dominance-metric in Equation 2 of Cherchye and Vermeulen (2006). This note is to acknowledge the priority of the work by Wittkowski and his coauthors of which the present authors had unfortunately not been aware.
Telomerase reverse-transcriptase homozygous mutations in autosomal recessive dyskeratosis congenita and Hoyeraal-Hreidarsson syndrome
Authors: Marrone Anna , Walne Amanda , Tamary Hannah , Masunari Yuka , Kirwan Michael , Beswick Richard , Vulliamy Tom , Dokal Inderjeet
Published: September 2007

Dyskeratosis congenita (DC) is a multisystem bone marrow failure syndrome characterized by a triad of mucocutaneous abnormalities and an increased predisposition to malignancy. X-linked DC is due to mutations in DKC1, while heterozygous mutations in TERC (telomerase RNA component) and TERT (telomerase reverse transcriptase) have been found in autosomal dominant DC. Many patients with DC remain uncharacterized, particularly families displaying autosomal recessive (AR) inheritance. We have now identified novel homozygous TERT mutations in 2 unrelated consanguineous families, where the index cases presented with classical DC or the more severe variant, Hoyeraal-Hreidarsson (HH) syndrome. These TERT mutations resulted in reduced telomerase activity and extremely short telomeres. As these mutations are homozygous, these patients are predicted to have significantly reduced telomerase activity in vivo. Interestingly, in contrast to patients with heterozygous TERT mutations or hemizygous DKC1 mutations, these 2 homozygous TERT patients were observed to have higher-than-expected TERC levels compared with controls. Collectively, the findings from this study demonstrate that homozygous TERT mutations, resulting in a pure but severe telomerase deficiency, produce a phenotype of classical AR-DC and its severe variant, the HH syndrome.
Impaired responsiveness to T-cell receptor stimulation and defective negative selection of thymocytes in CCR7-deficient mice
Authors: Davalos-Misslitz Ana C. M. , Worbs Tim , Willenzon Stefanie , Bernhardt Günter , Förster Reinhold
Published: September 2007

The chemokine receptor CCR7 has been implicated in maintenance of thymus morphology and establishment of tolerance to self-antigens. In this study, we provide direct evidence that negative selection of maturing thymocytes is defective in CCR7-deficent mice. Impaired negative selection was observed after TCR/CD3 complex stimulation in vivo as well as in vitro and was prominent in both double-positive and semimature single positive cells (CD4+CD8−CD24high). It is noteworthy that thymocytes of CCR7−/− mice display defective negative selection in response to endogenous superantigens, demonstrating that the defect also occurs under physiological conditions. Disturbed negative selection was correlated with delayed activation kinetics and decreased calcium flux response of CCR7−/− thymocytes after in vitro TCR/CD3 stimulation, suggesting that an impaired response of CCR7−/− thymocytes via TCR-mediated signaling is responsible for defective negative selection in these mice.
Deletion of the dominant autoantigen in NZB mice with autoimmune hemolytic anemia: effects on autoantibody and T-helper responses
Authors: Hall Andrew M. , Ward Frank J. , Shen Chia-Rui , Rowe Cliff , Bowie Laura , Devine Anne , Urbaniak Stanislaw J. , Elson Christopher J. , Barker Robert N.
Published: September 2007

The mechanisms underlying apparently spontaneous autoimmune diseases, such as autoimmune hemolytic anemia (AIHA) in New Zealand Black (NZB) mice, are unknown. Here, we determine the contribution of the dominant red blood cell (RBC) autoantigen, the anion exchanger protein Band 3, to the development of NZB autoimmune responses. The approach was to prevent Band 3 expression in NZB mice by disrupting the AE1 gene. AE1−/− NZB mice produced RBC autoantibodies at the same levels as the wild-type strain, but they differed in recognizing antigens that correspond to glycophorins, rather than Band 3. Splenic T-helper (Th) cells from wild-type NZB mice proliferated strongly against multiple Band 3 peptides, particularly the dominant epitope within aa861-874. This helper response was severely attenuated in AE1−/− animals, leaving only weak proliferation to peptide aa861-874. The results demonstrate that the defect in self-tolerance in NZB AIHA is directed to the RBC type, and is not specific for, or dependent on, Band 3. However, the predisposition to RBC autoimmunity may be focused onto Band 3 by weak Th cell cross-reactivity between the helper dominant epitope and an exogenous antigen. The redundancy of the major autoantigen illustrates the requirement for specific therapy to induce dominant forms of tolerance, such as T-cell regulation.
Postembryonic RNAi in Heterorhabditis bacteriophora: a nematode insect parasite and host for insect pathogenic symbionts
Authors: Ciche Todd A , Sternberg Paul W
Published: September 2007

Background

Heterorhabditis bacteriophora is applied throughout the world for the biological control of insects and is an animal model to study interspecies interactions, e.g. mutualism, parasitism and vector-borne disease. H. bacteriophora nematodes are mutually associated with the insect pathogen, Photorhabdus luminescens. The developmentally arrested infective juvenile (IJ) stage nematode (vector) specifically transmits Photorhabdus luminescens bacteria (pathogen) in its gut mucosa to the haemocoel of insects (host). The nematode vector and pathogen alone are not known to cause insect disease. RNA interference is an excellent reverse genetic tool to study gene function in C. elegans, and it would be useful in H. bacteriophora to exploit the H. bacteriophora genome project, currently in progress.

Results

Soaking L1 stage H. bacteriophora with seven dsRNAs of genes whose C. elegans orthologs had severe RNAi phenotypes resulted in highly penetrant and obvious developmental and reproductive abnormalities. The efficacy of postembryonic double strand RNA interference (RNAi) was evident by abnormal gonad morphology and sterility of adult H. bacteriophora and C. elegans presumable due to defects in germ cell proliferation and gonad development. The penetrance of RNAi phenotypes in H. bacteriophora was high for five genes (87–100%; Hba-cct-2, Hba-daf-21, Hba-icd-1; Hba-nol-5, and Hba-W01G7.3) and moderate for two genes (usually 30–50%; Hba-rack-1 and Hba-arf-1). RNAi of three additional C. elegans orthologs for which RNAi phenotypes were not previously detected in C. elegans, also did not result in any apparent phenotypes in H. bacteriophora. Specific and severe reduction in transcript levels in RNAi treated L1s was determined by quantitative real-time RT-PCR. These results suggest that postembryonic RNAi by soaking is potent and specific.

Conclusion

Although RNAi is conserved in animals and plants, RNAi using long dsRNA is not. These results demonstrate that RNAi can be used effectively in H. bacteriophora and can be applied for analyses of nematode genes involved in symbiosis and parasitism. It is likely that RNAi will be an important tool for functional genomics utilizing the high quality draft H. bacteriophora genome sequence.
Gene sequence variations of the platelet P2Y12 receptor are associated with coronary artery disease
Authors: Cavallari Ugo , Trabetti Elisabetta , Malerba Giovanni , Biscuola Michele , Girelli Domenico , Olivieri Oliviero , Martinelli Nicola , Angiolillo Dominick J , Corrocher Roberto , Pignatti Pier Franco
Published: September 2007

Background

The platelet P2Y12 receptor plays a key role in platelet activation. The H2 haplotype of the P2Y12 receptor gene (P2RY12) has been found to be associated with maximal aggregation response to adenosine diphosphate (ADP) and with increased risk for peripheral arterial disease. No data are available on its association with coronary artery disease (CAD).

Methods

The H2 haplotype of the P2RY12 was determined in 1378 unrelated patients of both sexes selected according to the presence of significant coronary artery disease (CAD group) or having normal coronary angiogram at cardiac catheterization (CAD-free group). Significant coronary artery disease was angiographically determined, and was defined as a greater than 50% visually estimated luminal diameter stenosis in at least one major epicardial coronary artery.

Results

In the studied population 71.9% had CAD (n = 991) and 28.1% had normal coronary angiogram (n = 387). H2 haplotype carriers were more frequent in the CAD group (p = 0.03, OR = 1.36, 95%CI = 1.02–1.82). The H2 haplotype was significantly associated with CAD in non-smokers (p = 0.007, OR = 1.83 95%CI = 1.17–2.87), but not in smokers. The association remained significant after adjustment for other covariates (age, triglycerides, HDL, hypertension, diabetes) by multivariate logistic regression (p = 0.004, OR = 2.32 95%CI = 1.30–4.15).

Conclusion

Gene sequence variations of the P2Y12 receptor gene are associated with the presence of significant CAD, particularly in non-smoking individuals.
The effects of ProAlgaZyme novel algae infusion on metabolic syndrome and markers of cardiovascular health
Authors: Oben Julius , Enonchong Ebangha , Kuate Dieudonne , Mbanya Dora , Thomas Tiffany C. , Hildreth DeWall J. , Ingolia Thomas D. , Tempesta Michael S.
Published: September 2007

Background

Metabolic Syndrome, or Syndrome X, is characterized by a set of metabolic and lipid imbalances that greatly increases the risk of developing diabetes and cardiovascular disease. The syndrome is highly prevalent in the United States and worldwide, and treatments are in high demand. ProAlgaZyme, a novel and proprietary freshwater algae infusion in purified water, has been the subject of several animal studies and has demonstrated low toxicity even with chronic administration at elevated doses. The infusion has been used historically for the treatment of several inflammatory and immune disorders in humans and is considered well-tolerated. Here, the infusion is evaluated for its effects on the cardiovascular risk factors present in metabolic syndrome in a randomized double-blind placebo-controlled study involving 60 overweight and obese persons, ages 25–60. All participants received four daily oral doses (1 fl oz) of ProAlgaZyme (N = 22) or water placebo (N = 30) for a total of 10 weeks, and were encouraged to maintain their normal levels of physical activity. Blood sampling and anthropometric measurements were taken at the beginning of the study period and after 4, 8 and 10 weeks of treatment. Eight participants did not complete the study.

Results

ProAlgaZyme brought about statistically significant (p < 0.001) reductions in the following: weight, body fat, total cholesterol, LDL-cholesterol, triglycerides, C-reactive protein and fasting blood glucose levels, accompanied by a significant (p < 0.001) increase in HDL-cholesterol levels over the 10-week study period. The infusion was well-tolerated and no side effects were noted.

Conclusion

ProAlgaZyme (4 fl oz daily) consumption resulted in significant reductions in weight and blood glucose levels, while significantly improving serum lipid profiles and reducing markers of inflammation, thus improving cardiovascular risk factors in overweight and obese subjects over a course of 10 weeks with an absence of adverse side effects.

Trial Registration

US ClinicalTrials.gov NCT00489333
Primary colorectal small cell carcinoma: A clinicopathological and immunohistochemical study of 10 cases
Authors: El Demellawy Dina , Khalifa Mahmoud A , Ismiil Nadia , Wong Shun , Ghorab Zeina
Published: September 2007

Colorectal small cell carcinoma (SmCC) is a rare tumor with an aggressive course. The aim of this study is to summarize our experience with this tumor and to highlight its immunohistochemical profile. Ten cases of colorectal SmCC were identified in our files and a panel of immunostains was performed. Follow up was available for the average of 3 years, during which 7 patients died and 3 were alive with disease. All cases were positive for LMWK, CK 19 and pancytokeratin but were negative for TTF-1 and CA 125. EGFR was positive in 7 cases. TTF-1 negative staining may be valuable in differentiating it from its pulmonary counterpart. CDX2, mCEA, CD56, synaptophysin, NSE and chromogranin can help differentiate it from non-endocrine poorly differentiated adenocarcinoma. The expression of EGFR in a subset of patients has not been reported earlier and has to be evaluated in larger series to assess its role in the planning of targeted biologic therapy.
Cross-species cluster co-conservation: a new method for generating protein interaction networks
Authors: Karimpour-Fard Anis , Detweiler Corrella S , Erickson Kimberly D , Hunter Lawrence , Gill Ryan T
Published: September 2007

Co-conservation (phylogenetic profiles) is a well-established method for predicting functional relationships between proteins. Several publicly available databases use this method and additional clustering strategies to develop networks of protein interactions (cluster co-conservation (CCC)). CCC has previously been limited to interactions within a single target species. We have extended CCC to develop protein interaction networks based on co-conservation between protein pairs across multiple species, cross-species cluster co-conservation.
Accelerated wound healing in leukocyte-specific, protein 1-deficient mouse is associated with increased infiltration of leukocytes and fibrocytes
Authors: Wang JianFei , Jiao Haiyan , Stewart Tara L , Lyons Megan V H , Shankowsky Heather A , Scott Paul G , Tredget Edward E
Published: September 2007

Wound healing is a complex process involving the integrated actions of numerous cell types, soluble mediators, and ECM. Recently, a newly identified cell type, the fibrocyte, has been reported to contribute to wound healing and fibrotic conditions such as hypertrophic scarring. We previously established leukocyte-specific protein 1 (LSP1) as a marker for fibrocytes. LSP1 is an F-actin binding protein and substrate of p38 mitogen-activated protein kinase and protein kinase C, and has been reported to be important in leukocyte chemotaxis. We examine the biological roles of LSP1 in skin wound healing using Lsp1−/− null mice. These animals showed accelerated healing of full-thickness skin wounds, with increased re-epithelialization rates, collagen synthesis, and angiogenesis. Healing wounds in Lsp1−/− mice had higher densities of neutrophiles, macrophages, and fibrocytes. Along with increased leukocyte infiltration, levels of macrophage-derived chemokine expression, TGF-β1, and VEGF were all up-regulated. These results demonstrate that the absence of LSP1 promotes healing of skin wounds. The primary mechanism seems to be an increase in leukocyte infiltration, leading to locally elevated synthesis and release of chemokines and growth factors. Further analysis of Lsp1−/− mice may suggest ways to improve wound healing and/or treat fibrotic conditions of skin and other tissue.
Modeling the impact of wide-azimuth acquisition on subsalt imaging
Authors: VerWest Bruce J. , Lin Dechun
Published: September 2007

Wide-azimuth towed streamer (WATS) acquisition improves the subsalt seismic image by suppressing multiples, improves the results of 3D surface-related-multiple elimination (SRME) processing, and provides more uniform seismic illumination of subsalt targets. A simple model shows that the additional suppression of multiples in the case of WATS acquisition is the result of a natural weighting of the traces going into the stack due to the areal nature of the acquisition. This simple model also shows that the extent of the additional multiple suppression is strongly dependent on the acquisition effort. A sparse acquisition effort will result in little additional multiple suppression. The use of 3D SRME processing is shown to be more accurate in predicting multiples, given input data with multiple azimuths, compared to making similar predictions from narrow-azimuth data. Three-dimensional SRME has the potential to reduce the residual multiples to the same extent as WATS acquisition with a higher acquisition effort. A complex model demonstrates that WATS acquisition does reduce the multiple-generated noise in subsalt images, but 3D SRME processing further reduces the residual multiple noise. The use of 3D SRME may reduce the multiples more than that achieved by increasing the cable half-aperture in the WATS acquisition effort. Finally, ray trace modeling is used to investigate the effect of WATS acquisition on subsurface illumination for subsalt imaging. We show that narrow-azimuth acquisition produces irregularities in subsalt illumination perpendicular to the acquisition direction which are a potential cause of migration noise. WATS acquisition results in higher and more uniform subsalt illumination and, hence, improves the subsalt image by reducing subsalt migration noise.
Application of the nearly perfectly matched layer in acoustic wave modeling
Authors: Hu Wenyi , Abubakar Aria , Habashy Tarek M.
Published: September 2007

In this work, we successfully applied an alternative formulation of the perfectly matched layer (PML), the so-called nearly PML (NPML), to acoustic wave propagation modeling. The NPML formulation shows great advantages over the standard complex stretched coordinate PML. The NPML formulation deviates from the standard PML through an inexact variable change, but this fact only affects the wave behavior in the NPML layer, which is outside the region of interest. The equivalence of the wave-absorbing performance between these two PML formulations (the standard complex stretched coordinate PML formulation and the NPML formulation) in 3D Cartesian coordinates for acoustic wave propagation modeling is proved mathematically in this work. In time-domain methods, the advantages of the NPML over the standard PML were explained by both the analytical analysis and the numerical simulations in terms of implementation simplicity and computational efficiency. The computation time saving is up to 17% for the 2D example used in this work. For 3D problems, this computational saving is more significant. After theoretically analyzing the numerical reflections from the NPML and the standard PML, we concluded that these two PML formulations have exactly the same performance, even after spatial discretization. This conclusion is validated by numerical experiment. Finally, we tested the NPML in the Marmousi velocity model and found its wave-absorbing rate is high enough, even for this realistic structure.
A Helmholtz iterative solver for 3D seismic-imaging problems
Authors: Plessix R.-E.
Published: September 2007

A preconditioned iterative solver for the 3D frequency-domain wave equation applied to seismic problems is evaluated. The preconditioner corresponds to an approximate inverse of a heavily damped wave equation deduced from the (undamped) wave equation. The approximate inverse is computed with one multigrid cycle. Numerical results show that the method is robust and that the number of iterations increases roughly linearly with frequency when the grid spacing is adapted to keep a constant number of discretization points per wavelength. To evaluate the relevance of this iterative solver, the number of floating-point operations required for two imaging problems are roughly evaluated. This rough estimate indicates that the time-domain migration approach is more than one order of magnitude faster. The full-wave-form tomography, based on a least-squares formulation and a scale separation approach, has the same complexity in both domains.
3D wave-equation interferometric migration of VSP free-surface multiples
Authors: He Ruiqing , Hornby Brian , Schuster Gerard
Published: September 2007

Interferometric migration of free-surface multiples in vertical-seismic-profile (VSP) data has two significant advantages over standard VSP imaging: (1) a significantly larger imaging area compared to migrating VSP primaries and (2) less sensitivity to velocity-estimation and static errors than other methods for migration of multiples. In this paper, we present a 3D wave-equation interferometric migration method that efficiently images VSP free-surface multiples. Synthetic and field data results confirm that a reflectivity image volume, comparable in size to a 3D surface seismic survey around the well, can be computed economically. The reflectivity image volume has less fold density and lower signal-to-noise ratio than that obtained by a conventional 3D surface seismic survey because of the relatively weak energy of multiples and the limited number of geophones in the well. However, the efficiency of this method for migrating VSP multiples suggests that it might sometimes be a useful tool for 4D seismic monitoring where reflectivity images can be computed quickly for each time-lapse survey.
Velocity model building by semblance maximization of modulated-shot gathers
Authors: Soubaras Robert , Gratacos Bruno
Published: September 2007

In recent years, wave-equation migration has greatly enhanced imaging in complex velocity models. However, velocity model building is still dependent on ray-theory approximations. We propose a full wave-equation methodology for velocity model building based on the nonlinear inversion of a semblance criterion with respect to the velocity field. A newly described type of migration, called the modulated-shot migration, is used to obtain the necessary gathers, which are indexed in surface angle. The semblance of these gathers, after spatial averaging, is used as the cost function. This methodology is shown to successfully image the Marmousi model and the subsalt part of the Sigsbee model, especially in terms of focusing, which is as good as with the true model, but also in terms of depthing which is enhanced compared with the initial model. Realistic constraints are used in terms of minimum frequency, maximum offset, and crudeness of the starting model. A key point in the success of this methodology is the multiscale approach wherein the iterations are started on a coarse scale, and ended at a finer scale.
Approximate ray tracing for qP-waves in inhomogeneous layered media with weak structural anisotropy
Authors: Dehghan Kaveh , Farra Véronique , Nicolétis Laurence
Published: September 2007

We present approximate equations for qP-wave ray tracing and paraxial ray tracing in inhomogeneous layered weakly transversely isotropic (TI) media. Inside layers, the symmetry axis direction of the TI medium is allowed to vary continuously. Approximate equations are based on perturbation theory in which deviations of anisotropy from isotropy are considered to be first-order quantities. For qP-waves propagating in a TI medium, the approximate ray-tracing and paraxial ray-tracing equations depend on three parameters and two angles defining the direction of the symmetry axis. We also present the boundary conditions at interfaces for first-order rays and paraxial rays and compute reflection/transmission coefficients to the first order. All the quantities required for evaluation of the Green’s function are calculated to the first order, except the traveltime that is calculated to the second order. The accuracy of the presented algorithm is verified on simple models with respect to exact ray-tracing results. For anisotropy of about [Formula: see text], considered in the examples presented, the relative errors in traveltime and amplitude are less than [Formula: see text] and [Formula: see text], respectively. We then consider media where the symmetry axis is conformable with the structure, named structural transverse isotropy (STI). The method is applied to simple STI models and to a realistic overthrust model, showing significant differences with vertical transverse isotropy (VTI) models not only for traveltimes, but also for amplitudes.
Integrated gravity and seismic interpretation in the Norman Range, Northwest Territories, Canada
Authors: Lawton Donald C. , Isaac J. Helen
Published: September 2007

We integrate the interpretation of gravity data acquired across the Norman Range near Norman Wells, Northwest Territories, Canada, with geologic mapping and the processing and interpretation of a 2D reflection seismic line. Our purpose is to determine which of two contrasting structural models of deformation is supported by both gravity and seismic data. Interpretation of the gravity data implies that the more likely structural model is that of thin-skinned deformation with a low-angle thrust fault having a décollement within Upper Cambrian evaporites. We use this structural model to guide the development of a velocity model for prestack depth migration of the seismic line. Interpretation of the processed seismic line supports the thin-skinned deformation model.
Seismic modeling of gas chimneys
Authors: Arntsen Børge , Wensaas Lars , Løseth Helge , Hermanrud Christian
Published: September 2007

We propose a simple acoustic model explaining the main features of gas chimneys. The main elements of the model consist of gas diffusing from a connected fracture network and into the surrounding shale creating an inhomogeneous gas saturation. The gas saturation results in an inhomogeneous fluctuating compressional velocity field that distorts seismic waves. We model the fracture network by a random-walk process constrained by maximum fracture length and angle of the fracture with respect to the vertical. The gas saturation is computed from a simple analytical solution of the diffusion equation, and pressure-wave velocities are locally obtained assuming that mixing of shale and gas occurs on a scale much smaller than seismic wavelengths. Synthetic seismic sections are then computed using the resulting inhomogeneous velocity model and shown to give rise to similar deterioration in data quality as that found in data from real gas chimneys. Also, synthetic common-midpoint (CMP) gathers show the same distorted and attenuated traveltime curves as those obtained from a real data set. The model shows clearly that the features of gas chimneys change with geological time (a model parameter in our approach), the deterioration of seismic waves being smallest just after the creation of the gas chimney. It seems likely that at least some of the features of gas chimneys can be explained by a simple elastic model in combination with gas diffusion from a fracture network.
Dynamic permeability of porous rocks and its seismic signatures
Authors: Müller Tobias M. , Lambert Gracjan , Gurevich Boris
Published: September 2007

In inhomogeneous porous media, the mechanism of wave-induced fluid flow causes significant attenuation and dispersion of seismic waves. In connection with this phenomenon, we study the impact of spatial permeability fluctuations on the dynamic behavior of porous materials. This heterogeneous permeability distribution further complicates the ongoing efforts to extract flow permeability from seismic data. Based on the method of statistical smoothing applied to Biot’s equations of poroelasticity, we derive models for the dynamic-equivalent permeability in 1D and 3D randomly inhomogeneous media. The low-frequency limit of this permeability corresponds to the flow permeability governing fluid flow in porous media. We incorporate the dynamic-equivalent permeability model into the expressions for attenuation and dispersion of P-waves, also obtained by the method of smoothing. The resulting attenuation and dispersion model is confirmed by numerical computations in randomly layered poroelastic structures. The results suggest that the effect of wave-induced fluid flow can be observed in a broader frequency range than previously thought. The peak attenuation shifts along the frequency axis depending on the strength of the permeability fluctuations. We conclude that estimation of flow permeability from seismic attenuation is only possible if permeability fluctuations are properly accounted for.
Analysis and application of coal-seam seismic waves for detecting abandoned mines
Authors: Yancey Daniel J. , Imhof Matthias G. , Feddock John E. , Gresham Tod
Published: September 2007

Two in-seam reflection surveys and one transmission survey were acquired at an abandoned underground mine near Hurley, Virginia, to demonstrate the feasibility of detecting abandoned-mine voids utilizing coal-seam seismic waves. Standard, commonly available tools for seismic reflection processing were used. The mine was detected and located by using trapped coal-seam seismic waves observed in both the transmission and reflection data. Detecting the void, however, was not good enough to replace drilling entirely. We conclude that in-seam seismic methods can be used for detection; but if a potential void is detected, focused drilling should be applied for accurate mapping and to circumvent potentially hazardous areas.
Leaky mode: A mechanism of horizontal seismic attenuation in a gas-hydrate-bearing sediment
Authors: Zanoth Sebastian R. , Saenger Erik H. , Krüger Oliver S. , Shapiro Serge A.
Published: September 2007

The leaky mode is a possible attenuation mechanism of seismic waves propagating along lamination in gas-hydrate-bearing sediment layers. This horizontal propagation attenuation mechanism occurs when a high-velocity layer is embedded in a low-velocity zone. This is a typical situation for gas hydrate occurrences. To quantify this attenuation mechanism, a 2D digital rock model based on the crosswell data of the Mallik 2002 Gas Hydrate Production Research Well Program is used. For simplicity, our elastic simulations exclude attenuation mechanisms like scattering loss or intrinsic absorption. We demonstrate that the leaky mode is a significant horizontal attenuation mechanism that cannot be neglected. The effective attenuation of gas-hydrate-bearing sediments is a combination of intrinsic and scattering attenuation by small-scale heterogeneties and the leaky mode.
Wave reflection at an anelastic transversely isotropic ocean bottom
Authors: Sidler Rolf , Carcione José M.
Published: September 2007

We study the reflection of waves at the ocean bottom, which is modeled as a plane interface separating a viscoacoustic medium (water) and a viscoelastic transversely isotropic solid whose axis of rotational symmetry is perpendicular to the bottom. We compute the plane-wave reflection coefficient (including the phenomenon known as the Rayleigh window) both numerically — by amplitude variation with offset (AVO) analysis of synthetic seismograms generated using a domain decomposition method and analytically. A first simulation considers the water-steel interface, for which experimental data is available. Then, we consider soft sediments and stiff crustal rocks for various values of the anellipticity parameter [Formula: see text]. The domain-decomposition technique relies on one grid for the fluid and another grid for the solid and uses Fourier and Chebyshev differential operators. The ane-lastic and anisotropic stress-strain relation is described by the Zener model. Special attention is given to modeling the boundary conditions at the ocean bottom. For this purpose, we further develop the technique for wave propagation at fluid/anelastic-anisotropic-solid interfaces. AVO slowness-frequency-domain analysis is used to compute the reflection coefficient and phase angle from the synthetic seismograms. This allows us to verify the domain-decomposition algorithm, which is shown to model with high accuracy the Rayleigh window for varying [Formula: see text]. The comparison also verifies the calculation of the analytical plane-wave reflection coefficient because a wrong choice of the sign of the vertical slowness of the reflected wave may cause nonphysical discontinuities in the coefficient. Moreover, the pseudospectral modeling code allows a general material variability and a complete and accurate characterization of the seismic response of an anisotropic ocean bottom.
Generalization of von Neumann analysis for a model of two discrete half-spaces: The acoustic case
Authors: Haney Matthew M.
Published: September 2007

Evaluating the performance of finite-difference algorithms typically uses a technique known as von Neumann analysis. For a given algorithm, application of the technique yields both a dispersion relation valid for the discrete time-space grid and a mathematical condition for stability. In practice, a major shortcoming of conventional von Neumann analysis is that it can be applied only to an idealized numerical model — that of an infinite, homogeneous whole space. Experience has shown that numerical instabilities often arise in finite-difference simulations of wave propagation at interfaces with strong material contrasts. These interface instabilities occur even though the conventional von Neumann stability criterion may be satisfied at each point of the numerical model. To address this issue, I generalize von Neumann analysis for a model of two half-spaces. I perform the analysis for the case of acoustic wave propagation using a standard staggered-grid finite-difference numerical scheme. By deriving expressions for the discrete reflection and transmission coefficients, I study under what conditions the discrete reflection and transmission coefficients become unbounded. I find that instabilities encountered in numerical modeling near interfaces with strong material contrasts are linked to these cases and develop a modified stability criterion that takes into account the resulting instabilities. I test and verify the stability criterion by executing a finite-difference algorithm under conditions predicted to be stable and unstable.
General representations for wavefield modeling and inversion in geophysics
Authors: Wapenaar Kees
Published: September 2007

Acoustic, electromagnetic, elastodynamic, poroelastic, and electroseismic waves are all governed by a unified matrix-vector wave equation. The matrices in this equation obey the same symmetry properties for each of these wave phenomena. This implies that the wave vectors for each of these phenomena obey the same reciprocity theorems. By substituting Green’s matrices in these reciprocity theorems, unified wavefield representations are obtained. Analogous to the well-known acoustic wavefield representations, these unified representations find applications in geophysical modeling, migration, inversion, multiple elimination, and interferometry.