bluuebunny/crossref_metadata_2025_split huggingface dataset:
Frontal and Parietal Components of a Cerebral Network Mediating Voluntary Attention to Novel Events
Authors: Daffner K. R. , Scinto L. F. M. , Weitzman A. M. , Faust R. , Rentz D. M. , Budson A. E. , Holcomb P. J. 
Published: March 2003

Abstract
Despite the important role that attending to novel events plays in human behavior, there is limited information about the neuroanatomical underpinnings of this vital activity. This study investigated the relative contributions of the frontal and posterior parietal lobes to the differential processing of novel and target stimuli under an experimental condition in which subjects actively directed attention to novel events. Event-related potentials were recorded from well-matched frontal patients, parietal patients, and non-brain-injured subjects who controlled their viewing duration (by button press) of line drawings that included a frequent, repetitive background stimulus, an infrequent target stimulus, and infrequent, novel visual stimuli. Subjects also responded to target stimuli by pressing a foot pedal. Damage to the frontal cortex resulted in a much greater disruption of response to novel stimuli than to designated targets. Frontal patients exhibited a widely distributed, profound reduction of the novelty P3 response and a marked diminution of the viewing duration of novel events. In contrast, damage to posterior parietal lobes was associated with a substantial reduction of both target P3 and novelty P3 amplitude; however, there was less disruption of the processing of novel than of target stimuli. We conclude that two nodes of the neuroanatomical network for responding to and processing novelty are the prefrontal and posterior parietal regions, which participate in the voluntary allocation of attention to novel events. Injury to this network is indexed by reduced novelty P3 amplitude, which is tightly associated with diminished attention to novel stimuli. The prefrontal cortex may serve as the central node in determining the allocation of attentional resources to novel events, whereas the posterior parietal lobe may provide the neural substrate for the dynamic process of updating one's internal model of the environment to take into account a novel event.
Vitamin C inhibits FAS-induced apoptosis in monocytes and U937 cells
Authors: Perez-Cruz Isabel , Carcamo Juan M. , Golde David W. 
Published: March 2003

AbstractThe FAS receptor—FAS ligand system is a key apoptotic pathway for cells of the immune system. Ligation of the FAS-receptor (CD95) induces apoptosis by activation of pro—caspase-8 followed by downstream events, including an increase in reactive oxygen species (ROS) and the release of proapoptotic factors from the mitochondria, leading to caspase-3 activation. We investigated the role of vitamin C in FAS-mediated apoptosis and found that intracellular accumulation of pharmacologic concentrations of vitamin C inhibited FAS-induced apoptosis in the monocytic U937 cell line and in fresh human monocytes. Cells were loaded with vitamin C by exposure to dehydroascorbic acid (DHA), thereby circumventing in vitro artifacts associated with the poor transport and pro-oxidant effects of ascorbic acid (AA). Vitamin C inhibition of FAS-mediated apoptosis was associated with reduced activity of caspase-3, -8, and -10, as well as diminished levels of ROS and preservation of mitochondrial membrane integrity. Mechanistic studies indicated that the major effect of vitamin C was inhibition of the activation of caspase-8 with no effect on it enzymatic activity. An independent action of high intracellular concentrations of vitamin C on mitochondrial membrane stabilization was also detected. These studies illuminate the nature of redox-dependent signaling in FAS-induced apoptosis of human monocytes and suggest that vitamin C can modulate the immune system by inhibiting FAS-induced monocyte death. (Blood. 2003;102:336-343)
γδ T cells for immune therapy of patients with lymphoid malignancies
Authors: Wilhelm Martin , Kunzmann Volker , Eckstein Susanne , Reimer Peter , Weissinger Florian , Ruediger Thomas , Tony Hans-Peter 
Published: March 2003

Abstract
There is increasing evidence that γδ T cells have potent innate antitumor activity. We described previously that synthetic aminobisphosphonates are potent γδ T cell stimulatory compounds that induce cytokine secretion (ie, interferon γ [IFN-γ]) and cell-mediated cytotoxicity against lymphoma and myeloma cell lines in vitro. To evaluate the antitumor activity of γδ T cells in vivo, we initiated a pilot study of low-dose interleukin 2 (IL-2) in combination with pamidronate in 19 patients with relapsed/refractory low-grade non-Hodgkin lymphoma (NHL) or multiple myeloma (MM). The objectives of this trial were to determine toxicity, the most effective dose for in vivo activation/proliferation of γδ T cells, and antilymphoma efficacy of the combination of pamidronate and IL-2. The first 10 patients (cohort A) who entered the study received 90 mg pamidronate intravenously on day 1 followed by increasing dose levels of continuous 24-hour intravenous (IV) infusions of IL-2 (0.25 to 3 × 106 IU/m2) from day 3 to day 8. Even at the highest IL-2 dose level in vivo, γδ T-cell activation/proliferation and response to treatment were disappointing with only 1 patient achieving stable disease. Therefore, the next 9 patients were selected by positive in vitro proliferation of γδ T cells in response to pamidronate/IL-2 and received a modified treatment schedule (6-hour bolus IV IL-2 infusions from day 1-6). In this patient group (cohort B), significant in vivo activation/proliferation of γδ T cells was observed in 5 patients (55%), and objective responses (PR) were achieved in 3 patients (33%). Only patients with significant in vivo proliferation of γδ T cells responded to treatment, indicating that γδ T cells might contribute to this antilymphoma effect. Overall, administration of pamidronate and low-dose IL-2 was well tolerated. In conclusion, this clinical trial demonstrates, for the first time, that γδ T-cell–mediated immunotherapy is feasible and can induce objective tumor responses. (Blood. 2003;102:200-206)
Kirchhoff scattering series: Insight into the multiple attenuation method
Authors: Ikelle Luc T. , Amundsen Lasse , Gangi Anthony , Wyatt Steven B. 
Published: March 2003

There are two basic integral equations used to represent wavefields in theoretical seismology: the Lippmann‐Schwinger integral equation and the representation theorem. The Born scattering series currently used for attenuating free‐surface multiples has been derived from the Lippmann‐Schwinger integral equation. Similarly, we have used the representation theorem here to derive a Kirchhoff scattering series for attenuating free‐surface multiples in towed‐streamer data.The Kirchhoff series for attenuating free‐surface multiples is, in theory, equivalent to the Born series; most important, like the Born series, it does not require any knowledge of the subsurface. However, it still provides useful insight into the multiple‐attenuation methods because the form of some quantities involved in the Kirchhoff series is different from the form in the Born series. For example, in towed‐streamer seismic data, the Kirchhoff series requires measurements of the vertical derivative of the pressure field in addition to the pressure field itself, whereas the Born series requires only the pressure field and tries to obtain its vertical derivative by multiplying the pressure field in the f‐k domain by the vertical wavenumber (generally known, in the context of multiple attenuation, as the obliquity factor).The existing numerical implementations of the Born scattering multiple attenuation can be easily adapted to the Kirchhoff scattering multiple attenuation. We simply have to replace the computation of the vertical derivative of the pressure field with the recorded one. This is the most important conclusion in this paper for practitioners because they can use the numerically stable implementation of the inverse‐scattering multiple‐attenuation method in the form of a series when the combined measurements of the pressure field and its vertical derivative are available.
Controls on acoustic properties of Upper Jurassic siliciclastic rocks (Boulonnais, northern France)
Authors: Braaksma Hendrik , Kenter Jeroen A. M. , Proust Jean Noel , Dijkmans Vincent , van Hoek Tomas , Mahieux Geoffroy , Drijkoningen Guy G. 
Published: March 2003

More than 200 plugs from outcrop and a nearby borehole in a carbonaceous siliciclastic interval of Late Jurassic (Kimmeridgian to Tithonian) age were quantitatively analyzed for texture, mineralogy, and acoustic properties. Our primary goal was to study the effect of clay (fraction smaller than 8 μm), silt/sand (fraction larger than 8 μm), and carbonate on the acoustic properties. The quantitative nature and volume of the data made it possible to observe four‐dimensional relationships in contoured ternary diagrams. Primary control on the acoustic properties is exerted by porosity, but the trend of this relationship significantly deviates from popular velocity transforms. The contribution of clay, silt/sand, and carbonate particular material and cement explains the remaining variation in acoustic properties. Although no clear linear thresholds are defined, a general trend is that clay and carbonate content have opposite and overlapping effects on acoustic properties, the influence of clay content progressively increases with decreasing carbonate content, and visa versa. With increasing carbonate content, the variation of acoustic velocity at a given porosity value increases to nearly twice of that in the clay‐dominated sediment. Traditional classification boundaries are present but strongly overprinted by this interplay between clay and carbonate.This study may have important implications for porosity and lithofacies prediction from wireline logs in similar mixtures of sediment. In addition, the quantitative character of the textural and mineralogical data may provide a direct link from acoustic properties to the primary depositional system and sequence stratigraphy.
Inherent nonuniqueness in magnetotelluric inversion for 1D anisotropic models
Authors: Yin Changchun 
Published: March 2003

This paper investigates the inherent nonuniqueness in the inversion of magnetotelluric (MT) measurements over an earth with a layered anisotropic resistivity distribution. This kind of nonuniqueness arises from the fact that even accurate and complete data contain insufficient information to uniquely resolve the earth parameters. For a very simple anisotropic case, where all layers in the earth have at least one horizontal principal axis in common coinciding with the x‐ or y‐axis of the Cartesian coordinate system, the resolvable parameters or parameter combinations from MT surface observations are identified by analyzing the structure of the conductivity tensor of the earth and the differential equations the electromagnetic (EM) fields satify. It is found that for a layered anisotropic earth model, several parameters can be uniquely resolved from the MT inversion while others are nonresolvable. However, particular combinations of the nonresolvable parameters can be uniquely resolved. These theoretical findings on the parameter resolvability of MT anisotropic inversion are further verified by a number of numerical experiments using synthetic data and a nonlinear parameter estimation technique. For this purpose, I parameterize the resistivity tensor assigned to each layer of the earth with three principal resistivities and three Euler angles, and then use the three Euler angles, the logarithms of three principal resistivities, and the logarithmic thickness as inverse parameters. This guarantees that the layer thickness is positive and the resistivity tensor is positive‐definite, while at the same time the inverse parameters may span the whole real axis. Numerical inversion results for different anisotropic models also reveal the fact that the resolvable parameters and parameter combinations are invariant with respect to the starting model. This means that for different starting models, the inversion results for some earth parameters might be individually quite different; however, particular combinations of these parameters remain unchanged.
Gravimagnetic anomaly formulas for polyhedra of spatially linear media
Authors: Holstein Horst 
Published: March 2003

Formulas for the gravity potential, field, and field gradient tensor are derived for a polyhedral target body of a spatially linear density medium. The formulas also define the magnetic potential and field in the case of a medium of spatially linear magnetization. This work generalizes existing solutions for the gravity field of a polyhedral target of linearly varying density. The formulas are analyzed for singularities and for numerical error growth. Error growth with increasing target distance is found to be higher than in the corresponding uniform polyhedral case. Examination of the error sources reveals that some error reduction is possible. On this basis, new algorithms of improved error control over existing algorithms are proposed for the linear medium. Computational results confirm the expected improvement.
Application of artificial intelligence for Euler solutions clustering
Authors: Mikhailov Valentine , Galdeano Armand , Diament Michel , Gvishiani Alexei , Agayan Sergei , Bogoutdinov Shamil′ , Graeva Elena , Sailhac Pascal 
Published: March 2003

Results of Euler deconvolution strongly depend on the selection of viable solutions. Synthetic calculations using multiple causative sources show that Euler solutions cluster in the vicinity of causative bodies even when they do not group densely about the perimeter of the bodies. We have developed a clustering technique to serve as a tool for selecting appropriate solutions.The clustering technique uses a methodology based on artificial intelligence, and it was originally designed to classify large data sets. It is based on a geometrical approach to study object concentration in a finite metric space of any dimension. The method uses a formal definition of cluster and includes free parameters that search for clusters of given properties.Tests on synthetic and real data showed that the clustering technique successfully outlines causative bodies more accurately than other methods used to discriminate Euler solutions. In complex field cases, such as the magnetic field in the Gulf of Saint Malo region (Brittany, France), the method provides dense clusters, which more clearly outline possible causative sources. In particular, it allows one to trace offshore the main inland tectonic structures and to study their interrelationships in the Gulf of Saint Malo.The clusters provide solutions associated with particular bodies, or parts of bodies, allowing the analysis of different clusters of Euler solutions separately. This may allow computation of average parameters for individual causative bodies. Those measurements of the anomalous field that yield clusters also form dense clusters themselves. Application of this clustering technique thus outlines areas where the influence of different causative sources is more prominent. This allows one to focus on these areas for more detailed study, using different window sizes, structural indices, etc.
Traveltime and conversion‐point computations and parameter estimation in layered, anisotropic media by τ‐ptransform
Authors: van der Baan Mirko , Kendall J.‐Michael 
Published: March 2003

Anisotropy influences many aspects of seismic wave propagation and, therefore, has implications for conventional processing schemes. It also holds information about the nature of the medium. To estimate anisotropy, we need both forward modeling and inversion tools. Forward modeling in anisotropic media is generally done by ray tracing. We present a new and fast method using the τ‐p transform to calculate exact reflection‐moveout curves in stratified, laterally homogeneous, anisotropic media for all pure‐mode and converted phases which requires no conventional ray tracing. Moreover, we obtain the common conversion points for both P‐SV and P‐SH converted waves. Results are exact for arbitrary strength of anisotropy in both HTI and VTI media (transverse isotropy with a horizontal or vertical symmetry axis, respectively).Since inversion for anisotropic parameters is a highly nonunique problem, we also develop expressions describing the phase velocities that require only a reduced number of parameters for both types of anisotropy. Nevertheless, resulting predictions for traveltimes and conversion points are generally more accurate than those obtained using the conventional Taylor‐series expansions. In addition, the reduced‐parameter expressions are also able to handle kinks or cusps in the SV traveltime curves for either VTI or HTI symmetry.
Focusing in dip and AVA compensation on scattering‐angle/azimuth common image gathers
Authors: Brandsberg‐Dahl Sverre , de Hoop Maarten V. , Ursin Bjorn 
Published: March 2003

Common image gathers (CIGs) in the offset and surface azimuth domain are used extensively in migration velocity analysis and amplitude variation with offset (AVO) studies. If the geology is complex and the ray field becomes multipathed, the quality of the CIGs deteriorates. To overcome these problems, the CIGs are generated as a function of scattering angle and azimuth at the image point. The CIGs are generated using an algorithm based on the inverse generalized Radon transform (GRT), stacking only over migration dip angles. Including only dips in the vicinity of the geological dip, or focusing in dip, suppresses artifacts in and results in improved signal‐to‐noise ratio on the CIGs. Migration velocity analysis can be based upon the differential semblance criterion. The analysis~is~then carried out by minimizing a functional of the derivative of the CIGs with respect to horizontal coordinates (offset/azimuth or scattering‐angle/azimuth), but AVO/amplitude variation with angle (AVA) effects will degrade the performance of the velocity analysis. We overcome this problem by computing an inverse GRT modified to compensate for AVA effects. The resulting CIGs can be used for velocity analysis based upon differential semblance, while they can be stacked to produce improved images. The algorithms are developed for inhomogeneous anisotropic elastic media, but they have so far only been tested on imaging‐inversion of PP and PS reflected waves in an isotropic elastic medium. This was done on two synthetic datasets generated by finite‐difference modeling and ocean‐bottom seismic (OBS) data from the Valhall field. We show that by performing the imaging of the real OBS data in the angle domain, it is possible to construct a well‐focused PP image of the Valhall reservoir directly beneath the “gas cloud” in the overburden.
Least‐squares wave‐equation migration for AVP/AVA inversion
Authors: Kühl Henning , Sacchi Mauricio D. 
Published: March 2003

We present an acoustic migration/inversion algorithm that uses extended double‐square‐root wave‐equation migration and modeling operators to minimize a constrained least‐squares data misfit function (least‐squares migration). We employ an imaging principle that allows for the extraction of ray‐parameter‐domain common image gathers (CIGs) from the propagated seismic wavefield. The CIGs exhibit amplitude variations as a function of half‐offset ray parameter (AVP) closely related to the amplitude variation with reflection angle (AVA). Our least‐squares wave‐equation migration/inversion is constrained by a smoothing regularization along the ray parameter. This approach is based on the idea that rapid amplitude changes or discontinuities along the ray parameter axis result from noise, incomplete wavefield sampling, and numerical operator artifacts. These discontinuities should therefore be penalized in the inversion.The performance of the proposed algorithm is examined with two synthetic examples. In the first case, we generated acoustic finite difference data for a horizontally layered model. The AVP functions based on the migrated/inverted ray parameter CIGs were converted to AVA plots. The AVA plots were then compared to the true acoustic AVA of the reflectors. The constrained least‐squares inversion compares favorably with the conventional migration, especially when incompleteness compromises the data. In the second example, we use the Marmousi data set to test the algorithm in complex media. The result shows that least‐squares migration can mitigate kinematic artifacts in the ray‐parameter domain CIGs effectively.
Crooked‐line 2D seismic reflection imaging in crystalline terrains: Part 1, data processing
Authors: Nedimović Mladen R. , West Gordon F. 
Published: March 2003

For cost and access reasons, most of the seismic reflection data collected in crystalline terrains have been acquired by 2D crooked‐line profiling. When the survey geometry is significantly irregular and the geologic structures have cross‐profile dip, several standard 2D imaging procedures severely underperform. As a result, reflection signal is poorly aligned across individual common midpoint (CMP) gathers, and much is lost during the CMP stack. To improve imaging, either the methods used to align signal before stack need to be modified or more tolerant methods of combining trace signals than the standard CMP stack need to be applied. Because a high‐fold 2D crooked‐line profile is really a 3D survey of a swath of terrain around the processing line, better signal alignment before CMP stacking may be achieved by revisiting the traveltime equation and including the cross‐dip terms into the moveout calculations. Therefore, in addition to the correction of NMO and in‐line dip moveout (DMO), we also locally compute and subsequently remove cross‐dip moveout (CDMO). This requires a procedure for estimating the amount of cross‐dip associated with each local reflection event. Stacking after the successful removal of the CDMO yields what we call an optimum cross‐dip stack—a seismic section that is significantly more complete and informative than the standard stack. Alternatively, amplitude stacking appears to be more robust to residual time anomalies. When little or no cross‐dip information can be extracted from the 2D crooked‐line data, we use it as a last resort to obtain a section that contains more structural information than the standard stack.