bluuebunny/crossref_metadata_2025_split huggingface dataset:
Blocky regularization schemes for Full‐Waveform Inversion★
Authors: Guitton Antoine 
Published: May 2012

ABSTRACTWith ill‐posed inverse problems such as Full‐Waveform Inversion, regularization schemes are needed to constrain the solution. Whereas many regularization schemes end up smoothing the model, an undesirable effect with FWI where high‐resolution maps are sought, blocky regularization does not: it identifies and preserves strong velocity contrasts leading to step‐like functions. These models might be needed for imaging with wave‐equation based techniques such as Reverse Time Migration or for reservoir characterization. Enforcing blockiness in the model space amounts to enforcing a sparse representation of discontinuities in the model. Sparseness can be obtained using the ℓ1 norm or Cauchy function which are related to long‐tailed probability density functions. Detecting these discontinuities with vertical and horizontal gradient operators helps constraining the model in both directions. Blocky regularization can also help recovering higher wavenumbers that the data used for inversion would allow, thus helping controlling the cost of FWI. While the Cauchy function yields blockier models, both ℓ1 and Cauchy attenuate illumination and inversion artifacts.
Non‐hyperbolic common reflection surface
Authors: Fomel Sergey , Kazinnik Roman 
Published: May 2012

ABSTRACTThe method of common reflection surface (CRS) extends conventional stacking of seismic traces over offset to multidimensional stacking over offset‐midpoint surfaces. We propose a new form of the stacking surface, derived from the analytical solution for reflection traveltime from a hyperbolic reflector. Both analytical comparisons and numerical tests show that the new approximation can be significantly more accurate than the conventional CRS approximation at large offsets or at large midpoint separations while using essentially the same parameters.
Frequency‐space wavefield extrapolation using infinite impulse response digital filters: is it feasible?
Authors: Mousa Wail A. 
Published: May 2012

ABSTRACTThe purpose of this paper is to study the possibility of performing practically stable and efficient frequency‐space (f−x) wavefield extrapolation for the application of seismic imaging and datuming via infinite impulse response (IIR) filters. The model reduction control theory was adopted to design such IIR f−x extrapolation filters. The model reduction theory reduces the order of a given order system which, in this case, involves reducing a finite impulse response (FIR) f−x extrapolation filter system into an IIR f−x extrapolation filter system. This theory relies on decomposing the states of the given filter system into strong and weakly coupled sub‐systems, and then eliminating the weakly coupled states via singular value decomposition of the Hankel and the impulse response Gramian matrices. Simulation results indicate that IIR f−x filters can be obtained, which are stable from an IIR filter design point of view. Simulations also indicate that stable seismic impulse responses and synthetics can be obtained with a reduced system model order and, hence, less computational efforts with respect to the number of complex multiplications and additions per output sample. It is hoped that this study will open new possibilities for researchers to reconsider designing IIR f−x explicit depth extrapolation filters due to their expected computational savings and wavenumber response accuracy, when compared to the FIR f−x explicit depth extrapolation filters.
P‐wave velocity distribution in basalt flows of the Enni Formation in the Faroe Islands from refraction seismic analysis
Authors: Petersen Uni K. , Brown R. James , Andersen Morten S. 
Published: May 2012

ABSTRACTThe main objective of this work is to establish the applicability of shallow surface‐seismic traveltime tomography in basalt‐covered areas. A densely sampled ∼1300‐m long surface seismic profile, acquired as part of the SeiFaBa project in 2003 (Japsen et al. 2006) at Glyvursnes in the Faroe Islands, served as the basis to evaluate the performance of the tomographic method in basalt‐covered areas. The profile is centred at a ∼700‐m deep well. VP, VS and density logs, a zero‐offset VSP, downhole‐geophone recordings and geological mapping in the area provided good means of control.The inversion was performed with facilities of the Wide Angle Reflection/Refraction Profiling program package (Ditmar et al. 1999). We tested many inversion sequences while varying the inversion parameters. Modelled traveltimes were verified by full‐waveform modelling.Typically an inversion sequence consists in several iterations that proceed until a satisfactory solution is reached. However, in the present case with high velocity contrasts in the subsurface we obtained the best result with two iterations: first obtaining a smooth starting model with small traveltime residuals by inverting with a high smoothing constraint and then inverting with the lowest possible smoothing constraint to allow the inversion to have the full benefit of the traveltime residuals.The tomogram gives usable velocity information for the near‐surface geology in the area but fails to reproduce the expected velocity distribution of the layered basalt flows. Based on the analysis of the tomogram and geological mapping in the area, a model was defined that correctly models first arrivals from both surface seismic data and downhole‐geophone data.
Traveltime approximations for inhomogeneous transversely isotropic media with a horizontal symmetry axis
Authors: Alkhalifah Tariq 
Published: May 2012

ABSTRACTTraveltime information is crucial for parameter estimation, especially if the medium is described by a set of anisotropy parameters. We can efficiently estimate these parameters if we are able to relate them analytically to traveltimes, which is generally hard to do in inhomogeneous media. I develop traveltime approximations for transversely isotropic media with a horizontal symmetry axis (HTI) as simplified and even linear functions of the anisotropy parameters. This is accomplished by perturbing the solution of the HTI eikonal equation with respect to the anellipticity parameter, η and the azimuth of the symmetry axis (typically associated with the fracture direction) from a generally inhomogeneous, elliptically anisotropic background medium. Such a perturbation is convenient since the elliptically anisotropic information might be obtained from well velocities in HTI media. Thus, we scan for only η and the symmetry‐axis azimuth. The resulting approximations can provide a reasonably accurate analytical description of the traveltime in a homogenous background compared to other published moveout equations. They also help extend the inhomogenous background isotropic or elliptically anisotropic models to an HTI one with a smoothly variable η and symmetry‐axis azimuth.
How technology drives high‐productivity vibroseis: a historical perspective
Authors: Mougenot Denis , Boucard Daniel 
Published: May 2012

ABSTRACTThe development of high‐productivity seismic recording using the vibroseis method over the last 30 years is treated from a Sercel perspective. The simultaneous use of vibrators has been highly dependent on real‐time field computing capabilities such as those delivered by the correlator‐stackers in the early 1980s. A second step forward in the mid 1980s–early 1990s was related to digital vibrator electronics, which provides efficient management and quality control of fleets of vibrators. However, it was only in the late 1990s with the advent of real‐time satellite positioning (GPS) of these fleets that alternate or simultaneous sweeping was commonly used in production. During the last ten years, thanks to GPS timing, continuous data recording and innovative simultaneous sourcing methodologies, vibroseis has been able to reach unexpected levels of productivity. As a result, the cost per seismic trace has dropped, enabling denser spatial sampling and associated seismic imaging improvement.
The interacting effects of clumped seed dispersal and distance‐ and density‐dependent mortality on seedling recruitment patterns
Authors: Beckman Noelle G. , Neuhauser Claudia , Muller‐Landau Helene C. 
Published: May 2012

Summary1. Seed dispersal and natural enemies both influence spatial patterns of seedlings, which in turn influence future abiotic and biotic interactions, with consequences for plant populations, distributions and diversity. Clumped seed deposition is common, especially for vertebrate‐dispersed seeds, and has the potential to significantly affect interactions with density‐responsive enemies, yet has received relatively little attention.2. We used spatially explicit simulation models to examine how different patterns of seed dispersal and natural enemy attack structure seedling spatial patterns. We simulated clumped seed dispersal by combining a two‐dimensional Student’s T dispersal kernel for expected seed rain with a negative binomial distribution for seed deposition. We based our models for seed mortality on published data reflecting differing life histories of insect seed predators and soil‐borne pathogens. We varied dispersal distance, degree of clumping, type of enemy, enemy dispersal distance and fecundity among simulations.3. Under insect seed predation, seeds escaped predation by dispersing longer distances than insects, resulting in ‘Janzen–Connell’ patterns in which seedling recruitment peaks at intermediate distances. When insects dispersed longer distances than seeds, higher seed densities near the tree satiated insects, resulting in ‘McCanny’ patterns in which seed deposition, survivorship and seedling establishment all decrease with distance from the parent tree. Total seedling establishment was lowest when insects and seeds dispersed similar distances.4. Under pathogen attack, Janzen–Connell patterns predominated except when seedling survival was virtually zero or one everywhere, or in the case where pathogen dispersal distances exceeded seed dispersal distances, producing ‘Hubbell’ patterns in which seed deposition and seedling establishment decrease with distance, though survivorship increases.5. Clumped seed deposition increased the probability of seedling establishment under both insect seed predation and pathogen attack as it led to local satiation of insect seed predators and made it harder for pathogen distributions to track seeds.6. Synthesis. Our modelling study suggests that the relative dispersal distances of seeds and natural enemies are crucial to determining establishment rates and spatial patterns of seedlings. Better characterization of the movement and natural histories of natural enemies is critical to improving our understanding of seedling distributions and plant–enemy interactions.
Differences in triglyceride and cholesterol metabolism and resistance to obesity in male and female vitamin D receptor knockout mice
Authors: Weber K. , Erben R. G. 
Published: May 2012

SummaryA lean phenotype has been detected in vitamin D receptor (VDR) knockout mice; however, the gender differences in fat metabolism between male and female mice both with age and in response to a high‐fat diet have not been studied before. The objective of our study was to assess changes in body and fat tissue weight, food intake and serum cholesterol and triglyceride in VDR knockout mice from weaning to adulthood and after a challenge of adult animals with a high‐fat diet. Although VDR knockout mice of both sexes consumed more food than wild‐type and heterozygous littermates, their body weight and the weight of fat depots was lower after 6 months on a diet with 5% crude fat content. When adult animals were challenged with a high‐fat diet containing 21% crude fat content for 8 weeks, VDR knockout mice of both sexes had a significantly higher food intake but gained less weight than their wild‐type littermates. Cholesterol levels were higher after 2 days on the high‐fat diet in both sexes, but in the VDR knockout mice, less cholesterol was detected in the serum after 8 weeks. Wild‐type male mice showed signs of fatty liver disease at the end of the experiment, which was not detected in the other groups. In conclusion, lack of the VDR receptor results in reduced fat accumulation with age and when adult mice are fed a high‐fat diet, despite a higher food intake of VDR knockout mice relative to their wild‐type littermates. These effects can be detected in both sexes. Wild‐type male mice react with the highest weight gain and cholesterol levels of all groups and develop fatty liver disease after 8 weeks on a high‐fat diet, while male VDR knockout mice appear to be protected.
A review of oxalate poisoning in domestic animals: tolerance and performance aspects
Authors: Rahman M. M. , Abdullah R. B. , Wan Khadijah W. E. 
Published: May 2012

SummaryPublished data on oxalate poisoning in domestic animals are reviewed, with a focus on tolerance and performance. Oxalic acid is one of a number of anti‐nutrients found in forage. It can bind with dietary calcium (Ca) or magnesium (Mg) to form insoluble Ca or Mg oxalate, which then may lead to low serum Ca or Mg levels as well as to renal failure because of precipitation of these salts in the kidneys. Dietary oxalate plays an important role in the formation of Ca oxalate, and a high dietary intake of Ca may decrease oxalate absorption and its subsequent urinary excretion. Oxalate‐rich plants can be supplemented with other plants as forage for domestic animals, which may help to reduce the overall intake of oxalate‐rich plants. Non‐ruminants appear to be more sensitive to oxalate than ruminants because in the latter, rumen bacteria help to degrade oxalate. If ruminants are slowly exposed to a diet high in oxalate, the population of oxalate‐degrading bacteria in the rumen increases sufficiently to prevent oxalate poisoning. However, if large quantities of oxalate‐rich plants are eaten, the rumen is overwhelmed and unable to metabolize the oxalate and oxalate‐poisoning results. Based on published data, we consider that <2.0% soluble oxalate would be an appropriate level to avoid oxalate poisoning in ruminants, although blood Ca level may decrease. In the case of non‐ruminants, <0.5% soluble oxalate may be acceptable. However, these proposed safe levels of soluble oxalate should be regarded as preliminary. Further studies, especially long‐term studies, are needed to validate and improve the recommended safe levels in animals. This review will encourage further research on the relationships between dietary oxalate, other dietary factors and renal failure in domestic animals.
Alate immigration disrupts soybean aphid suppression by predators
Authors: Costamagna A. C. , McCornack B. P. , Ragsdale D. W. 
Published: May 2012

AbstractNatural enemies suppress many aphid populations, and yet, population outbreaks sometimes occur. The reasons predation fails to suppress such outbreaks are not clearly understood. While manipulating predators to examine their role in soybean aphid population growth, a natural immigration of soybean aphids occurred that enabled us to compare the roles immigration and predation played in population growth. Using predator exclusion cages, we found that predation on the top of the plant accounted for 42.3 ± 11.4% (mean ± SE) reduction in aphid population growth rates. When 90–100% of the canopy was exposed, predation failed to reduce aphid population growth because winged immigrants colonized plants, with an observed 6‐fold increase in alates compared to plants completely covered or exposing only the top nodes (approximately 10% of the total canopy). We conclude that reproduction by immigrants contributed to population growth rates sufficiently to compensate for predation. These results demonstrate that immigration can counteract high levels of predation and lead to aphid population growth rates that could result in outbreak population densities.
Light‐responsive metabolite and transcript levels are maintained following a dark‐adaptation period in leaves of Arabidopsis thaliana
Authors: Florez‐Sarasa Igor , Araújo Wagner L. , Wallström Sabá V. , Rasmusson Allan G. , Fernie Alisdair R. , Ribas‐Carbo Miquel 
Published: May 2012

Summary
The effect of previous light conditions on metabolite and transcript levels was investigated in leaves of Arabidopsis thaliana during illumination and after light‐enhanced dark respiration (LEDR), when dark respiration was measured.
Primary carbon metabolites and the expression of light‐responsive respiratory genes were determined in A. thaliana leaves before and after 30 min of darkness following different light conditions. In addition, metabolite levels were determined in the middle of the night and the in vivo activities of cytochrome and alternative respiratory pathways were determined by oxygen isotope fractionation.
A large number of metabolites were increased in leaves of plants growing in or transiently exposed to higher light intensities. Transcript levels of respiratory genes were also increased after high light treatment. For the majority of the light‐induced metabolites and transcripts, the levels were maintained after 30 min of darkness, where higher and persistent respiratory activities were also observed. The levels of many metabolites were lower at night than after 30 min of darkness imposed in the day, but respiratory activities remained similar.
The results obtained suggest that ‘dark’ respiration measurements, as usually performed, are probably made under conditions in which the overall status of metabolites is strongly influenced by the previous light conditions.
Patterns of Coping with Partner Violence: Experiences of Refugee Women in Jordan
Authors: Al‐Modallal Hanan 
Published: May 2012

AbstractObjectiveThe relationship between intimate partner violence (IPV) and women's use of negative and positive coping strategies was investigated.Design and SampleFor this cross‐sectional study, a convenience sample of 300 refugee women was recruited from health care centers in three cities in Jordan. Logistic regression adjusted to women's demographic characteristics was used.ResultsThe study's results revealed that, compared to non victims, victimized women showed a lower tendency to receive psychological support from the family (adjusted OR = 0.53, 95% CI = 0.29–0.96), to smoke (adjusted OR = 0.28, 95% CI = 0.09–0.82), to use tranquilizers (adjusted OR = 0.014, 95% CI = 0.00‐0.86), to think of suicide (adjusted OR = 0.04, 95% CI = 0.009–0.15), and to attempt suicidal actions (adjusted OR = 0.02, 95% CI = 0.002–0.19).ConclusionsThe study indicated that women's lack of use of negative coping strategies (smoking, use of tranquilizers, suicidal thoughts, and suicidal actions) was promising. However, the lack of use of positive coping strategies (disclosure of abuse, psychological support from friends, and help from family/friends) was somewhat concerning. The role of health care professionals may be helpful in this context. Counseling and support to IPV victims via effective listening, nonjudgmental discussions, and provision of information can be offered by health professionals as part of the treatment in health care centers.
Changes in problem‐based and routine‐based healthcare attendance: a comparison of three national dental health surveys
Authors: Geyer Siegfried , Micheelis Wolfgang 
Published: May 2012

AbstractBackgroundHealthcare utilization either may be guided by a preventive orientation leading to regular visits to the doctor, or it may be triggered by impaired health. Using data from three German national surveys, we wanted to examine whether the effects of income on the utilization of dental health services increased over time owing to the considerable decrease in insurance coverage over the years and the increase in higher out‐of‐pocket costs from patients.MethodsData from three national dental health surveys (1989, 1997 and 2005) were used. The data of all respondents aged between 35 and 44 years were available, and the number of caries‐free and unrestored healthy teeth was used as outcome.ResultsOver the years, the proportion of routine attenders increased considerably, and the dental health measure used indicates the improvement. The least educated respondents and those with the lowest income profited less than other groups. In spite of higher copayments, the effects of income on the utilization of dental care did not increase over time. Regarding the results of education, a significant effect was only found in the study from 2005. No clear differences between routine‐ and problem‐oriented attenders emerged with respect to the dental health measure chosen.ConclusionsMaterial conditions and education had effects on utilization behaviour. Contrary to expectation, increasing copayments did not yield higher effects of income on healthcare utilization.
XMM–Newton EPIC and OM observation of Nova Centauri 1986 (V842 Cen)
Authors: Luna G. J. M. , Diaz M. P. , Brickhouse N. S. , Moraes M. 
Published: May 2012

ABSTRACT
We report the results from the temporal and spectral analysis of an XMM–Newton observation of Nova Centauri 1986 (V842 Cen). We detect a period at 3.51 ± 0.4 h in the EPIC data and at 4.0 ± 0.8 h in the Optical Monitor (OM) data. The X-ray spectrum is consistent with the emission from an absorbed thin thermal plasma with a temperature distribution given by an isobaric cooling flow. The maximum temperature of the cooling flow model is keV. Such a high temperature can be reached in a shocked region and, given the periodicity detected, most likely arises in a magnetically channelled accretion flow characteristic of intermediate polars. The pulsed fraction of the 3.51-h modulation decreases with energy as observed in the X-ray light curves of magnetic cataclysmic variables, possibly due either to occultation of the accretion column by the white dwarf body or phase-dependent to absorption. We do not find the 57-s white dwarf spin period, with a pulse amplitude of 4 mmag, reported by Woudt et al. in either the OM data, which are sensitive to pulse amplitudes ≳0.03 mag, or the EPIC data, sensitive to pulse fractions p≳ 14 ± 2 per cent.