bluuebunny/crossref_metadata_2025 huggingface dataset:
Caring for children with learning disabilities who present problem behaviours: a maternal perspective
Authors: Johnson Robert F. , O'Reilly Michelle , Vostanis Panos
Published: August 2006

The theoretical cognitive model of stress and coping provides a structure to obtain and analyse maternal perceptions of caring for children with learning disabilities who present severe problem behaviours. The Family Fund database identified 18 families who met the sample criteria of children aged five years to 15 years with severe to moderate learning disability presenting severe problem behaviour. Physical aggression was reported to be the primary behavioural problem for 13 of the children. Interviews undertaken with the main carer of the child at their home were taped and transcribed. The data were analysed using grounded theory techniques which identified ‘secondary stressors’ for the parent. These were social isolation, conflict, limitation of lifestyle and self-blame. It is proposed that the amalgamated impact of these can weaken parents' coping resources and, therefore, may prove to be as significant to the negative association with maternal wellbeing as the problem behaviour.
A new modernity?
Authors: O'Connor Justin , Xin Gu
Published: August 2006

This article looks at the arrival of ‘creative industries’ within mainstream policy discourse in China. It attempts to situate this ‘modernising’ discourse within the wider historical conflicts around modernity and modernization in China, suggesting that the progressive function of the ‘creative industries’ discourse frequently claimed by its supporters cannot be taken for granted. The article ends by asking some pointed questions about the immediate future of this agenda in China, with particular reference to the large eastern cities.
From made in China to created in China
Authors: Keane Michael
Published: August 2006

This article provides a macro-perspective on China's repositioning in the global and regional cultural economy, and in doing so questions the structural impact of past practices on future export aspirations. Whereas most accounts of China's media are predicated on top-down control models, the article proposes a media development framework appropriate to China' s aspirations in the first decade of the twenty-first century. The framework is most relevant to those creative content industries in which sunk costs – that is, one-off costs of creative content development – are more than 50 percent of total outlay. Starting from a low base – and constrained by a legacy of state censorship and widespread intellectual property abuse – China aspires to move from ‘made in China’ to ‘created in China’.
Transborder visuality
Authors: Ma Eric Kit-Wai
Published: August 2006

This article examines the interplay between the transborder visual culture of Hong Kong and South China. Transborder visuality refers to the transfer of visual culture from one geographic location to another. It is conceptualized in this project as a crucial nexus of cultural globalization at a time when China is catching up with modernity. By examining the changing patterns of transborder visuality in the case of Hong Kong and South China, the author proposes to make theoretical advances in cultural globalization by applying the concepts of ‘transborder visuality’ and ‘image apparatus’ to better understand the complicated nerves, nodes and social networks that facilitate the production of modern, flexible and sophisticated visual images in the global visual economy.
Nostalgia as content creativity
Authors: Jing Wu
Published: August 2006

A conspicuous trope within contemporary Chinese society, nostalgia is a product of two recent transformations. First, drastic changes in economic and political life have led to anxiety and uncertainty, together with excitement and hope. Second, economic rationalization of the cultural industries has resulted in extensive repackaging and repurposing of existing content in order to reduce cost and secure customer acceptance. This article examines three different modes of nostalgic expression in Chinese cultural industries and argues that they are more about creating competitive imageries of present life than faithfully regenerating an idealized past.
Towards creative da-tong
Authors: Liao Han-Teng
Published: August 2006

This article offers an alternative notion of creative industries. It refocuses the idea of intellectual property as ‘property’ to processes associated with the generation and exploitation of creativity. The article introduces the notion of ‘creative da-tong’, which brings intellectual property reforms now taking place in the West closer to the traditional Chinese idea of ‘Confucian utopia’ ( da-tong). The article also posits a link with xiaokang (‘a well-off or lesser utopia’], which defines official social and economic reform policies in China. In taking into account reformers’ insight into intellectual rights and collaborative production, creative da-tong can assist China in rethinking its conglomeration and privatization agenda, now evident in media and cultural industries. For various strategic reasons, the article further suggests that creative industries, as a policy term, should be differentiated from the established ‘cultural industries’ conglomerates to refer specifically to small and medium enterprises.
The everyday civil war
Authors: De Genova Nicholas
Published: August 2006

In an industrial workplace distinguished by flagrant health and safety violations and a fairly explicit antagonism between the virtually all-male workforce and the plant management, many of the male Mexican/migrant workers' postures of fearlessness and stoic perseverance evinced a sometimes deadly complicity between the compulsions of their masculinity with their own exploitation. While these male workers participated in their own effective subordination to the mandates of their employers, as labor for capital, this article contends that the constitutive role of antagonism and struggle between labor and capital nonetheless defines some of the decisive parameters of everyday life, and thus ought to be central to all critical social inquiry. It becomes crucial then for ethnography in particular to account for the ethnographer's own institutionally mediated social situation and practice. The article therefore examines some of the material and practical conditions of possibility of its own research endeavor, in order to critically and self-reflexively consider the often-agonistic relationship of the ethnographer to the wider politics of workplace ‘training’, managerial surveillance, labor discipline and subordination.
A room with a view
Authors: Engbersen Godfried , van San Marion , Leerkes Arjen
Published: August 2006

In this article we combine field observation, interviews, cartographic and police data on nationality and illegality to analyse the social and economic mechanisms explaining the rising presence and social relations of irregular immigrants in the Schilderswijk (disreputable inner district) in the Dutch city of The Hague. Secondly, we pay attention to some unintended consequences of the restrictive policies, such as the rise in subsistence crime among irregular immigrants. Four factors are described that underline the structural nature of irregular migration: (1) the continuing immigration of non-western and East-European immigrants to the Netherlands; (2) a demand for cheap labour in specific (informal) sectors of the post-industrial economy and in remnants of industrial and agricultural sectors; (3) a steady supply of (informal) housing in poor urban districts provided by private (ethnic) households and big landlords; and (4) a demand for potential partners, partly partners who are in a dependent and powerless position.
Syntactic Features of the Syrohexapla of Ezekiel
Authors: Lund Jerome
Published: August 2006

An analysis of syntactic features found in the Syrohexapla of Ezekiel in comparison to the Peshitta, on the one hand, demonstrates diachronic development within the Syriac language, and in comparison to the Greek, on the other hand, proves that the Syrohexapla translation was made for scholarly purposes, not for congregational use.
Directional illumination analysis using beamlet decomposition and propagation
Authors: Wu Ru-Shan , Chen Ling
Published: August 2006

We evaluate directional illumination (DI) and acquisition-aperture efficacy through wave theory-based beamlet decomposition of the wavefield. Beamlet decomposition (wavelet transform along spatial axis) provides localizations in both space and direction of a wavefield. We introduce the image conditions in beamlet domain and local angle domain and then define the local image matrix (LIM). We calculate the DI in the image space for a given source or a group of sources by decomposing Green’s functions into local angle domain at image points. Acquisition-aperture efficacy (AAE) matrix and acquisition dip-response (ADR) vector can be defined to quantify the efficacy of an acquisition configuration for a given subsurface point. As numerical examples, we calculate the DI maps and ADR maps for high- and low-velocity lens models and for the SEG-EAGE 2D salt model. We further investigate the influences of acquisition geometry and overlaying structures on the quality of prestack depth migration image for the subsalt area of the SEG-EAGE model. We find that the ADR maps for different dip angles have good correlation with the image qualities of the corresponding reflectors. DI analysis can be used in the aperture correction for image amplitude in local angle domain for wave theory-based migration methods.
Teleseismic shot-profile migration
Authors: Shragge J. , Artman B. , Wilson C.
Published: August 2006

The shot-profile migration approach of wave-equation migration generates subsurface images using the interferometric principle of crosscorrelating two passive wavefields. These wavefields are typically a source wavefield containing energy from an excited source and a receiver wavefield comprised of scattered-source wavefield energy by the discontinuous earth structure. Shot-profile migration can be recast as a novel way of imaging the earth’s lithosphere using teleseismic wavefield data, where the source wavefield is the directly arriving wavefront and the receiver wavefield is the following wavefield coda. We demonstrate that the shot-profile technique can be tailored to suit teleseismic acquisition geometry and wavefields. Assuming an acoustic framework and 2.5D experimental geometry, we develop procedures that enable kinematic and structural imaging (migration) using both transmission and free-surface reflected passive wavefields. Experiments with synthetic data demonstrate the method’s applicability and illustrate the negative imaging consequence of using inaccurate migration velocity profiles. We apply shot-profile migration to a suite of teleseismic events acquired during the IRIS-PASSCAL CASC-1993 experiment in central Oregon. The imaging results are interpreted to show the Juan de Fuca plate subducting beneath the North American plate. We attribute the observed dissimilarities between these results and other Juan de Fuca subduction- zone images to the combination of different imaging goals and the use of more accurate migration velocity profiles.
Discrimination between phase and amplitude attributes in time-lapse seismic streamer data
Authors: Spetzler Jesper , Kvam Øyvind
Published: August 2006

Time-lapse seismic experiments aim to obtain information about production-related effects in hydrocarbon reservoirs to increase the recovery percentage. However, nonrepeatability problems such as acquisition differences, overburden effects, and noise are often significantly stronger than the imprint of production changes in time-lapse seismic data sets. Consequently, it is very difficult to appraise the changes in petrophysical reservoir parameters over time. We introduce a 4D monitoring approach based on the spectral ratio method. This method produces two time-lapse attributes: the relative change in reflection coefficient and the traveltime shift at reflecting interfaces. These attributes can be used for appraising production-related changes in the subsurface. The approach corrects for time-invariant nonrepeatability effects in the overburden and source-receiver coupling problems in time-lapse surveys. The validity of the method is limited to structurally simple overburden and reservoirs with weak lateral variations. First, we validate the methodology using a synthetic time-lapse seismic experiment. Next, we apply the method to a real time-lapse data set from the Troll West gas province in the North Sea. In the real example, we could not detect movement in the fluid contact of [Formula: see text]. The expected change in amplitude is less than 10%, which is probably below the background noise level for this data set.
CGG method for robust inversion and its application to velocity-stack inversion
Authors: Ji Jun
Published: August 2006

The modified conjugate gradient (CG) method, called the conjugate guided gradient (CGG) method, is a robust iterative inversion method producing a parsimonious model estimation. The CG method for solving least-squares (LS) (i.e., [Formula: see text]-norm minimization) problems is modified to solve for different norms or different minimization criteria by guiding the gradient vector appropriately during iteration steps. Guiding is achieved by iteratively reweighting either the residual vector or the gradient vector during iteration steps like the iteratively reweighted least-squares IRLS method does. Robustness is achieved by weighting the residual vector and parsimonious model estimation is obtained by weighting the gradient vector. Unlike the IRLS method, however, the CGG method doesn’t change the corresponding forward operator of the problem and is implemented in a linear inversion template. Therefore, the CGG method requires less computation than the IRLS method. Since the solution in the CGG method is found in a least-squares sense along the gradient direction guided by the weights, this solution can be interpreted as the LS solution located in the guided gradient direction. Guiding the gradient gives us more flexibility in the choice of weighting parameters than the IRLS method. I applied the CGG method to velocity-stack inversion, and the results show that the CGG method gives a far more robust and parsimonious model estimation than the standard [Formula: see text]-norm solution, with results comparable to the [Formula: see text]-norm IRLS solution.
Integrated estimation of interval-attenuation profiles
Authors: Rickett James
Published: August 2006

Quantitative estimates of seismic attenuation are useful for a variety of applications, ranging from seismic-acquisition design, to seismic processing, amplitude analysis, and reservoir characterization. I frame the estimation of interval attenuation from a set of seismic wavelets as a linear inversion of their log-amplitude spectra. The initial spectrum at the first depth location and a set of depth-varying amplitude scalers are estimated simultaneously with an effective-attenuation [Formula: see text] profile. The algorithm can be regarded as a tomographic extension of the spectral-ratio method that uses all the information available in the amplitude spectra, appropriately weighted so that estimates are not biased by noise. Constraints can be applied to ensure the [Formula: see text] values vary smoothly, and solving for log [Formula: see text] rather than [Formula: see text] ensures only positive attenuation values. Tests on synthetic and field data illustrate the trade-off between vertical resolution and sensitivity to noise. A covariance study indicates that improvements in interval-attenuation estimates over the traditional spectral-ratio method come from systematic-noise handling and the explicit constraints on [Formula: see text], rather than the fact that the inversion ties the log-spectral data together with a single estimate of the spectrum at the first depth location.
Green’s functions extraction and surface-wave tomography from microseisms in southern California
Authors: Gerstoft Peter , Sabra Karim G. , Roux Philippe , Kuperman W. A. , Fehler Michael C.
Published: August 2006

We use crosscorrelations of seismic noise data from 151 stations in southern California to extract the group velocities of surface waves between the station pairs for the purpose of determining the surface-wave velocity structure. We developed an automated procedure for estimating the Green’s functions and subsequent tomographic inversion from the 11,325 station pairs based on the characteristics of the noise field. We eliminate specific events by a procedure that does not introduce any spurious spectral distortion in the band of interest, 0.05–[Formula: see text]. Further, we only used the emerging arrival structure above a threshold signal-to-noise ratio. The result is that mostly station pairs with their axes oriented toward the sea are used, consistent with the noise having a microseism origin. Finally, it is the time derivative of the correlation function that is actually related to the Green’s function. The emergence of the time-domain Green’s function is proportional to the square root of the recording time and inversely proportional to the square root of the distance between stations. The tomographic inversion yields a surface-wave velocity map that compares favorably with more conventional and elaborate experimental procedures.
Early arrival waveform tomography on near-surface refraction data
Authors: Sheng Jianming , Leeds Alan , Buddensiek Maike , Schuster Gerard T.
Published: August 2006

We develop a waveform-tomography method for estimating the velocity distribution that minimizes the waveform misfit between the predicted and observed early arrivals in space-time seismograms. By fitting the waveforms of early arrivals, early arrival waveform tomography (EWT) naturally takes into account more general wave-propagation effects compared to the high-frequency method of traveltime tomography, meaning that EWT can estimate a wider range of slowness wavenumbers. Another benefit of EWT is more reliable convergence compared to full-waveform tomography, because an early-arrival misfit function contains fewer local minima. Synthetic test results verify that the waveform tomogram is much more accurate than the traveltime tomogram and that this algorithm has good convergence properties. For marine data from the Gulf of Mexico, the statics problem caused by shallow, gassy muds was attacked by using EWT to obtain a more accurate velocity model. Using the waveform tomogram to correct for statics, the stacked section was significantly improved compared to using the normal move-out (NMO) velocity, and moderately improved compared to using the traveltime tomogram. Inverting high-resolution land data from Mapleton, Utah, showed an EWT velocity tomogram that was more consistent with the ground truth (trench log) than the traveltime tomogram. Our results suggest that EWT can provide supplemental, shorter-wavelength information compared to the traveltime tomogram for both shallow and moderately deep seismic data.
Diffuse fields in ultrasonics and seismology
Authors: Weaver Richard L. , Lobkis Oleg I.
Published: August 2006

We review the history of diffuse ultrasonic waves in solids with emphasis on recent developments in field-field correlations and their identification with Green’s function. The basic principles appear to be well understood now, and the identity between these two waveforms has been proven under a variety of assumed conditions that guarantee a diffuse field. Promise for practical passive imaging is good; nevertheless, measurements sometimes fail to fully agree with theory. We ascribe this in some cases to incomplete convergence — insufficient amounts of data have been processed. In other cases, it is probably because of a lack of perfect diffuseness; ambient nonmultiply scattered fields are often not equipartitioned and imperfectly diffuse.
Vector imaging of converted wave data in laterally uniform media with VTI anisotropy
Authors: Jing Charlie , Dickens Thomas A. , Winbow Graham A.
Published: August 2006

A vector imaging method has been developed for PS-converted waves in laterally homogeneous vertically transverse isotropic (VTI) media. It decomposes the converted-wave data into two upgoing quasi-shear waves ([Formula: see text] and [Formula: see text]) within the prestack migration algorithm according to subsurface image and surface receiver locations. Because the decomposition is performed as part of the migration, it is consistent with the dip and polarization of the seismic events, unlike traditional algorithms that use premigration rotations. Two shear-wave images with potentially enhanced resolution are formed simultaneously from the vector migration. The effects of VTI anisotropy on PS-converted wave imaging and the capability of the PS vector imaging algorithm to provide enhanced images are illustrated using a point-scatterer model.
Robust estimates of 3D reflector dip and azimuth
Authors: Marfurt Kurt J.
Published: August 2006

Much of seismic stratigraphy is based on the morphology of seismic textures. The identification of reflector terminations and subtle changes in dip and azimuth allows us to infer coherent progradational and transgressive packages as well as more chaotic slumps, fans, and braided-stream complexes; infill of karsted terrains; gas seeps; and, of course, faults and angular unconformities. A major difficulty in estimating reflector dip and azimuth arises at discrete lateral and vertical discontinuities across which reflector dip and azimuth change. The smearing across these boundaries produced by traditional dip and azimuth estimations is avoided by using temporally and spatially shifted multiple windows that contain each analysis point. This more robust estimation of dip and azimuth leads to increased resolution of well-established algorithms such as coherence, coherent amplitude gradients, and structurally oriented filtering. More promising still is the analysis of high-resolution dip and azimuth through volumetric estimates of reflector curvature and angular unconformities. This new technique is demonstrated using two land data volumes, one from the Louisiana salt province and the other from the fractured Fort Worth basin.
Accuracy of heterogeneous staggered-grid finite-difference modeling of Rayleigh waves
Authors: Bohlen Thomas , Saenger Erik H.
Published: August 2006

Heterogeneous finite-difference (FD) modeling assumes that the boundary conditions of the elastic wavefield between material discontinuities are implicitly fulfilled by the distribution of the elastic parameters on the numerical grid. It is widely applied to weak elastic contrasts between geologic formations inside the earth. We test the accuracy at the free surface of the earth. The accuracy for modeling Rayleigh waves using the conventional standard staggered-grid (SSG) and the rotated staggered grid (RSG) is investigated. The accuracy tests reveal that one cannot rely on conventional numerical dispersion discretization criteria. A higher sampling is necessary to obtain acceptable accuracy. In the case of planar free surfaces aligned with the grid, 15 to 30 grid points per minimum wavelength of the Rayleigh wave are required. The widely used explicit boundary condition, the so-called image method, produces similar accuracy and requires approximately half the sampling of the wavefield compared to heterogeneous free-surface modeling. For a free-surface not aligned with the grid (surface topography), the error increases significantly and varies with the dip angle of the interface. For an irregular interface, the RSG scheme is more accurate than the SSG scheme. The RSG scheme, however, requires 60 grid points per minimum wavelength to achieve good accuracy for all dip angles. The high computation requirements for 3D simulations on such fine grids limit the application of heterogenous modeling in the presence of complex surface topography.
Cone-based electrical resistivity tomography
Authors: Pidlisecky Adam , Knight Rosemary , Haber Eldad
Published: August 2006

Determining the 3D spatial distribution of subsurface properties is a challenging, but critical, part of managing the cleanup of contaminated sites. We have developed a minimally invasive technology that can provide information about the 3D distribution of electrical conductivity. The technique, cone-based electrical resistivity tomography (C-bert), integrates resistivity tomography with cone-penetration testing. Permanent current electrodes are emplaced in the subsurface and used to inject current into the subsurface region of interest. The resultant potential fields are measured using a surface reference electrode and an electrode mounted on a cone penetrometer. The standard suite of cone penetration measurements, including high-resolution resistivity logs, are also obtained and are an integral part of the C-bert method. C-bert data are inverted using an inexact Gauss-Newton algorithm to produce a 3D electrical conductivity map. A majorchallenge with the inversion is the large local perturbation around the measurement location, due to the highly conductive cone. As the cone is small with respect to the total model space, explicit modeling of the cone is cost prohibitive. We have developed a rapid method for solving the forward model which uses iteratively determined boundary conditions (IDBC). This allows us to generate a computationally feasible, preinversion correction for the cone perturbation. We assessed C-bert by performing a field test to image the conductivity structure of the Kidd 2 site near Vancouver, British Columbia. A total of nine permanent current electrodes were emplaced and five C-bert data sets were obtained, resulting in 6516 data points. These data were inverted to obtain a 3D conductivity image of the subsurface. Furthermore, we demonstrated, using a synthetic experiment, that C-bert can yield high quality electrical conductivity images in challenging field situations. We conclude that C-bert is a promising new imaging technique.
Target-oriented wave-equation inversion
Authors: Valenciano Alejandro A. , Biondi Biondo , Guitton Antoine
Published: August 2006

A target-oriented strategy can be applied to estimate a wave-equation least-squares inverse (LSI) image. By explicitly computing the wave-equation Hessian, the LSI image is obtained as the solution of a nonstationary least-squares inverse filtering problem. The rows of the Hessian are the nonstationary filters containing information about the acquisition geometry, the velocity model, and the band-limited characteristics of the seismic data. By exploiting the sparsity and the structure of the Hessian matrix, a large number of iterations, necessary to achieve convergence, can be computed cheaply. The results on a structurally complex model show the improvements of the LSI image versus the migrated image.
Time-reversal acoustics in complex environments
Authors: Fink Mathias
Published: August 2006

Time-reversal mirrors (TRMs) refocus an incident acoustic field to the position of the original source regardless of the complexity of the propagation medium. TRMs have now been implemented in a variety of physical scenarios from megahertz ultrasonics with aperture sizes of the order of centimeters to ocean acoustics at hundreds to thousands of hertz with aperture sizes of the order of hundreds of meters. Common to this broad range of scales is a remarkable robustness — exemplified by observations at all scales — that the more complex the medium between the probe source and the TRM, the sharper the focus. The relationship between the medium complexity and the size of the focal spot is studied in this paper. This relationship is certainly the most exciting property of TRM compared to standard focusing devices. A TRM acts as an antenna that uses complex environments to appear wider than it is, resulting in a broadband pulse with a refocusing quality that does not depend on the TRM aperture. In this paper, we investigate both the role of the time-reversal window duration and the bandwidth of the time-reversed signals for various media (waveguide, closed cavity, random medium).
Imaging of multiple reflections
Authors: Berkhout A. J. , Verschuur D. J.
Published: August 2006

Current multiple-removal algorithms in seismic processing use either differential moveout or predictability. If the differential moveout between primaries and multiples is small, prediction is the only option available. In the last decade, multidimensional prediction-error filtering by weighted convolution, such as surface-related multiple elimination (SRME), have proved to be very successful in practice. So far, multiples have been considered as noise and have been discarded after the removal process. In this paper, we argue that multiple reflections contain a wealth of information that can be used in seismic processing to improve the resolution of reservoir images beyond current capability. In the near future, one may expect that the so-called weighted-crosscorrelation (WCC) concept may offer an attractive alternative in approaching the multiple problem. WCC creates an option to avoid the adaptive subtraction process as applied in prediction-error algorithms. Moreover, it allows the transformation of multiples into primaries. The latter means that seismic imaging with primaries and multiples (nonlinear process) can be implemented by a sequence of linear processes, including the transformation of multiples into primaries and the imaging of primaries.
The virtual source method: Theory and case study
Authors: Bakulin Andrey , Calvert Rodney
Published: August 2006

We present a way to image through complex overburden. The method uses surface shots with downhole receivers placed below the most complex part of the troublesome overburden. No knowledge of the velocity model between shots and receivers is required. The method uses time-reversal logic to create a new downward-continued data set with virtual sources (VS's) at the geophone locations. Time reversal focuses energy that passes through the overburden into useful primary energy for the VS. In contrast to physical acoustics, our time reversal is done on a computer, utilizing conventional acquisition with surface shots and downhole geophones.

With this approach, we can image below extremely complex (realistic) overburden — in fact, the more complex the better. We recast the data to those with sources where we actually know and can control the waveform that has a downward-radiation pattern that may also be controlled, and is reproducible for 4D even if the near-surface changes or the shooting geometry is altered slightly.

To illustrate the method, we apply the VS technique to a synthetic, elastic example with extreme heterogeneity, where conventional approaches fail to image the data. A 4D field-data example shows that the VS method (VSM) enables sensitive reservoir monitoring below a complex, time-variant near surface that is not achievable with surface 4D seismic or conventional 4D vertical seismic profiling (VSP).
Residual stereotomographic inversion
Authors: Neckludov Dmitry , Baina Reda , Landa Evgeny
Published: August 2006

Depth migration requires highly accurate knowledge of the subsurface velocity field. Different traveltime tomographic methods are used for this purpose. Stereotomography is a tomographic method that uses local dip estimates in addition to traveltimes for velocity model estimation. We present a new methodology for velocity model updating. It combines poststack stereotomography and residual moveout velocity inversion. The former is used for initial model construction and the latter for updating the velocity model. Residual inversion is a kind of stereotomographic inversion applied to common reflection point (CRP) gathers after model-based moveout correction. Velocity analysis can be made more efficient by preselecting the traces that contribute to a series of CRP gathers and using only these traces for inversion. The algorithm is defined in a two-step procedure. First, ray tracing from the reflection point for nonzero reflection offsets defines the source and receiver locations of the data traces in the CRS gather. Then these traces are moveout corrected according to the calculated traveltimes and residual moveout is estimated. The interval velocity model is updated by fitting the velocity that minimizes estimated residuals. Application of the proposed technique demonstrates its robustness and reliability for fast and automatic velocity model estimation.
Stoneley-wave speed modeling in general anisotropic formations
Authors: Chi Shihong , Tang Xiaoming
Published: August 2006

For determining anisotropy using acoustic logging data, Stoneley waves are the only wave modes that are sensitive to formation properties transverse to the borehole axis. We derive Stoneley-wave speeds in deviated and horizontal wells penetrating anisotropic formations. We first apply the elastic theory of an anisotropic body to find the radial displacement of a borehole cross section under uniform pressure. We then derive the effective formation modulus based on quasistatic analysis. Finally, we derive a two-dimensional analytical solution for low-frequency Stoneley-wave speed in a horizontal well penetrating a transversely isotropic formation with a vertical symmetry axis. For deviated wells, we derive a 3D analytical solution that is also valid for general anisotropic formations. Our analytic solutions agree with the finite-difference modeling results and are particularly suited for strongly anisotropic formations. With increasing well deviation the sensitivity of Stoneley-wave speed to horizontal shear-wave velocity decreases and the sensitivity to vertical shear-wave velocity increases.
Permeability prediction from MICP and NMR data using an electrokinetic approach
Authors: Glover P. W. , Zadjali I. I. , Frew K. A.
Published: August 2006

The accurate modeling of oil, gas, and water reservoirs depends fundamentally upon access to reliable rock permeabilities that cannot be obtained directly from downhole logs. Instead, a range of empirical models are usually employed. We propose a new model that has been derived analytically from electrokinetic theory and is equally valid for all lithologies. The predictions of the new model and four other common models (Kozeny-Carman, Berg, Swanson, and van Baaren) have been compared using measurements carried out on fused and unfused glass bead packs as well as on 91 rock samples representing 11 lithologies and three coring directions. The new model provides the best predictions for the glass bead packs as well for all the lithologies. The crux of the new model is to have a good knowledge of the relevant mean grain diameter, for example, from MICP data. Hence, we have also predicted the permeabilities of 21 North Sea well cores using all five models and five different measures of relevant grain size. These data show that the best predictions are provided by the use of the new model with the geometric mean grain size. We have also applied the new model to the prediction of permeability from NMR data of a [Formula: see text] thick sand-shale succession in the North Sea by inverting the [Formula: see text] spectrum to provide a value for the geometric mean grain size. The new model shows a good match to all 348 core measurements from the succession, performing better than the SDR, Timur-Coates, HSCM, and Kozeny-Carman predictions.
Factors facilitating or limiting the use of AVO for coal-bed methane
Authors: Peng Suping , Chen Huajing , Yang Ruizhao , Gao Yunfeng , Chen Xinping
Published: August 2006

There are similarities and differences in employing amplitude variation with offset (AVO) to explore for gas-sand reservoirs, as opposed to coal-bed methane (CBM) reservoirs. The main similarity is that large Poisson’s ratio contrasts, resulting in AVO gradient anomalies, are expected for both kinds of reservoirs. The main difference is that cleating and fracturing raise the Poisson’s ratio of a coal seam as it improves its reservoir potential for CBM, while gas always lowers the Poisson’s ratio of a sandstone reservoir. The top of gas sands usually has a negative AVO gradient, leading to a class one, two, or three anomaly depending on the impedance contrast with the overlying caprock. On the other hand, the top of a CBM reservoir has a positive AVO gradient, leading to a class four anomaly. Three environmental factors may limit the usage of AVO for CBM reservoirs: the smaller contrast in Poisson’s ratio between a CBM reservoir and its surrounding rock, variations in the caprock of a specific CBM reservoir, and the fact that CBM is not always free to collect at structurally high points in the reservoir. However, other factors work in favor of using AVO. The strikingly high reflection amplitude of coal improves signal/noise ratio and hence the reliability of AVO measurements. The relatively simple characteristics of AVO anomalies make them easy to interpret. Because faults are known to improve the quality of CBM reservoirs, faults accompanied by AVO anomalies would be especially convincing. A 3D-AVO example offered in this paper shows that AVO might be helpful to delineate methane-rich sweet spots within coal seams.
Split-step Fourier migration of GPR data in lossy media
Authors: Sena Armando R. , Stoffa Paul L. , Sen Mrinal K.
Published: August 2006

Migration of ground-penetrating radar (GPR) data traditionally has been implemented assuming uniform, nonconductive, and nondispersive media. However, in many real applications, the effects of heterogeneities, conductivity, or dispersion can be important, so it is necessary to consider these effects to image the data correctly. We implement the split-step Fourier technique for migration of GPR data in 2D media transverse-electric (TE) or transverse-magnetic (TM) propagation modes and demonstrate how it takes into account, naturally and efficiently, the effects of dispersion, attenuation, and heterogeneities. Compensation for attenuation during migration implies applying a gain that can make the numerical algorithm unstable. We introduce a homogeneous plane-wave approximation that gives greater stability to the migration technique, allowing a stable and satisfactory migration of the GPR data up to depths equivalent to three times the skin depth computed at the dominant frequency of the radar signal. Multiple slowness references of split-step migration for lossy media are introduced and compared with the single-reference slowness technique. Finally, we propose two limited gain modifications of the migration algorithm and study their usefulness when highly lossy zones are in the media.
Microtubule dynamics in the budding yeast mating pathway
Authors: Molk Jeffrey N. , Bloom Kerry
Published: August 2006

In order for haploid gametes to fuse during fertilization, microtubules (MTs) must generate forces that are sufficient to move the nuclei together. Nuclear movements during fertilization rely on microtubule-associated proteins (MAPs), many of which have been characterized extensively during mitosis. A useful model system to study MT-dependent forces before nuclear fusion, or karyogamy, is the mating pathway of budding yeast. Dynamic MTs are guided to the mating projection (shmoo tip) when plus-end-binding proteins interact with polarized actin microfilaments. If two shmoo tips are in proximity they may fuse, dissolving the MT-cortical interactions. Subsequently, oppositely oriented MT plus ends interact and draw the nuclei together. The plus-end-binding proteins in the yeast mating pathway are conserved in metazoan cells and may play a role in higher eukaryotic fertilizaton. Thus, understanding the mechanism of plus end orientation and karyogamy in budding yeast will reveal mechanisms of MT-dependent force generation conserved throughout evolution.
Covalent Fixation of the Cyclic Tetramer of a Metallo-porphyrin Based on Self-complementary Quadruple Hydrogen Bonding
Authors: Ohkawa Haruki , Takayama Akihiro , Nakajima Satoshi , Nishide Hiroyuki
Published: August 2006

The stability of quadruple hydrogen bonding in the cyclic tetramer of a metallo-porphyrin before and after a covalent fixation was investigated. According to competition and energy-transfer experiments, the exchange reaction between the cyclic tetramers of the metallo-porphyrin was fully suppressed by the covalent fixation. This spontaneous cyclization–covalent fixation strategy based on olefin metathesis can open the way to the use of cyclic assemblies in a solid phase.
Cycloaddition Reactions of Transition Metal-containing Benzopyrylium and Related Zwitterionic Intermediates
Authors: Kusama Hiroyuki , Iwasawa Nobuharu
Published: August 2006

Recent advances in generation and cycloaddition reactions of transition metal-containing benzopyrylium and related zwitterionic intermediates from o-alkynylphenylcarbonyl or imine derivatives are summarized focussing on the difference of the two reaction pathways, that is, [3 + 2] and [4 + 2] cycloaddition reactions.
Trade, FDI, and the Organization of Firms
Authors: Helpman Elhanan
Published: August 2006

New developments in the world economy have triggered research designed to better understand the changes in trade and investment patterns, and the reorganization of production across national borders. Although traditional trade theory has much to offer in explaining parts of this puzzle, other parts required new approaches. Particularly acute has been the need to model alternative forms of involvement of business firms in foreign activities because organizational change has been central in the transformation of the world economy. This paper reviews the literature that has emerged from these efforts. The theoretical refinements have focused on the individual firm, studying its choices in response to its own characteristics, the nature of the industry in which it operates, and the opportunities afforded by foreign trade and investment. Important among these choices are organizational features, such as sourcing strategies. But the theory has gone beyond the individual firm, studying the implications of firm behavior for the structure of industries. It provides new explanations for trade structure and patterns of foreign direct investment, both within and across industries, and has identified new sources of comparative advantage.
Base Station Location and Service Assignments in W–CDMA Networks
Authors: Kalvenes Joakim , Kennington Jeffery , Olinick Eli
Published: August 2006

Designing a wideband code division multiple access (W–CDMA) network is a complicated task requiring the selection of sites for radio towers, analysis of customer demand, and assurance of service quality in terms of signal-to-interference ratio requirements. This investigation presents a net-revenue maximization model that can help a network planner with the selection of tower sites and the calculation of service capacity. The integer programming model takes as input a set of candidate tower locations with corresponding costs, a number of customer locations with corresponding demand for traffic, and the revenue potential for each unit of capacity allocated to each demand point. Based on these data, the model can be used to determine the selection of radio towers and the service capacity of the resulting radio network. The basic model is a large integer program and requires a special algorithm for practical solution. Our algorithm uses a priority branching scheme, an optimization-gap tolerance between 1% and 10%, and two sets of global valid inequalities that tighten the upper bounds obtained from the linear programming relaxation. The algorithm has been implemented in software for the AMPL/CPLEX system and an empirical investigation has been conducted. Using over 300 problem instances with up to 40 towers and 250 service locations, various combinations of algorithm settings have been evaluated. Using the recommended setting results in a design tool that generally runs in under 20 minutes on a 667 MHz AlphaStation.
Performance Loss Bounds for Approximate Value Iteration with State Aggregation
Authors: Van Roy Benjamin
Published: August 2006

We consider approximate value iteration with a parameterized approximator in which the state space is partitioned and the optimal cost-to-go function over each partition is approximated by a constant. We establish performance loss bounds for policies derived from approximations associated with fixed points. These bounds identify benefits to using invariant distributions of appropriate policies as projection weights. Such projection weighting relates to what is done by temporal-difference learning. Our analysis also leads to the first performance loss bound for approximate value iteration with an average-cost objective.
Poisson Disorder Problem with Exponential Penalty for Delay
Authors: Bayraktar Erhan , Dayanik Savas
Published: August 2006

We solve the Poisson disorder problem when the delay is penalized exponentially. Our objective is to detect as quickly as possible the unobservable time of the change (or disorder) in the intensity of a Poisson process. The disorder time delimits two different regimes in which one employs distinct strategies (e.g., investment, advertising, manufacturing). We seek a stopping rule that minimizes the frequency of false alarms and an exponential (unlike previous formulations, which use a linear) cost function of the detection delay. In the financial applications, the exponential penalty is a more apt measure for the delay cost because of the compounding of the investment growth. The Poisson disorder problem with a linear delay cost was studied by Peskir and Shiryaev [2002. Solving the Poisson Disorder Problem. Advances in Finance and Stochastics. Springer, Berlin, Germany, 295–312], which is a limiting case of ours.
Lipschitz Continuity of the Optimal Value via Bounds on the Optimal Set in Linear Semi-Infinite Optimization
Authors: Cánovas María J. , López Marco A. , Parra Juan , Toledo F. Javier
Published: August 2006

We consider the parametric space of all the linear semi-infinite programming problems with constraint systems having the same index set. Under a certain regularity condition, the so-called well-posedness with respect to the solvability, it is known from Cánovas et al. [2] that the optimal value function is Lipschitz continuous around the nominal problem π. In this paper we obtain an explicit Lipschitz constant for such a function in a certain neighborhood of π. We emphasize the fact that both the constant and the size of the neighborhood are exclusively expressed in terms of the nominal problem data, and that they involve the distances to primal and to dual inconsistency. Moreover, a uniform bound for the optimal set is provided. This bound constitutes a key ingredient to derive the Lipschitz constant for the optimal value function.
Models and Algorithms for Stochastic Online Scheduling
Authors: Megow Nicole , Uetz Marc , Vredeveld Tjark
Published: August 2006

We consider a model for scheduling under uncertainty. In this model, we combine the main characteristics of online and stochastic scheduling in a simple and natural way. Job processing times are assumed to be stochastic, but in contrast to traditional stochastic scheduling models, we assume that jobs arrive online, and there is no knowledge about the jobs that will arrive in the future. The model incorporates both stochastic scheduling and online scheduling as a special case. The particular setting we consider is nonpreemptive parallel machine scheduling, with the objective to minimize the total weighted completion times of jobs. We analyze simple, combinatorial online scheduling policies for that model, and derive performance guarantees that match performance guarantees previously known for stochastic and online parallel machine scheduling, respectively. For processing times that follow new better than used in expectation (NBUE) distributions, we improve upon previously best-known performance bounds from stochastic scheduling, even though we consider a more general setting.