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Rays
Kinds of Rays Terms modified by Rays Selected AbstractsDIAGNOSTIC AND THERAPEUTIC USE OF INFRARED RAYSDIGESTIVE ENDOSCOPY, Issue 2 2000Norichika Narimiya First page of article [source] Out-of-Core and Dynamic Programming for Data Distribution on a Volume Visualization ClusterCOMPUTER GRAPHICS FORUM, Issue 1 2009S. Frank I.3.2 [Computer Graphics]: Distributed/network graphics; C.2.4 [Distributed Systems]: Distributed applications Abstract Ray directed volume-rendering algorithms are well suited for parallel implementation in a distributed cluster environment. For distributed ray casting, the scene must be partitioned between nodes for good load balancing, and a strict view-dependent priority order is required for image composition. In this paper, we define the load balanced network distribution (LBND) problem and map it to the NP-complete precedence constrained job-shop scheduling problem. We introduce a kd-tree solution and a dynamic programming solution. To process a massive data set, either a parallel or an out-of-core approach is required. Parallel preprocessing is performed by render nodes on data, which are allocated using a static data structure. Volumetric data sets often contain a large portion of voxels that will never be rendered, or empty space. Parallel preprocessing fails to take advantage of this. Our slab-projection slice, introduced in this paper, tracks empty space across consecutive slices of data to reduce the amount of data distributed and rendered. It is used to facilitate out-of-core bricking and kd-tree partitioning. Load balancing using each of our approaches is compared with traditional methods using several segmented regions of the Visible Korean data set. [source] Towards virtualized desktop environmentCONCURRENCY AND COMPUTATION: PRACTICE & EXPERIENCE, Issue 4 2010Xiaofei Liao Abstract Virtualization is being widely used now as an emerging trend. Rapid improvements in network bandwidth, ubiquitous security hazards and high total cost of ownership of personal computers have created a growing market for desktop virtualization. Much like server virtualization, virtualizing desktops involves separating the physical location of a client device from its logical interface. But, the performance and usability of some traditional desktop frameworks do not satisfy end-users. Other solutions, including WebOS, which needs to rebuild all daily-used applications into Client/Server mode, cannot be easily accepted by people in a short time. We present LVD, a system that combines the virtualization technology and inexpensive personal computers (PCs) to realize a lightweight virtual desktop system. Comparing to the previous desktop systems, LVD builds an integrated novel desktop environment, which can support the backup, mobility, suspending and resuming of per-user's working environment, and support synchronous using of incompatible applications on different platforms and achieves great saving in power consumption. We have implemented LVD in a cluster with Xen and compared its performance against widely used commercial approaches, including Microsoft RDP, Citrix MetaFrameXP and Sun Ray. Experimental results demonstrate that LVD is effective in performing the functions while imposing little overhead. Copyright © 2009 John Wiley & Sons, Ltd. [source] Stephen G. Ray, Jr., Do No Harm: Social Sin and Christian ResponsibilityCONVERSATIONS IN RELIGION & THEOLOGY, Issue 1 2004Article first published online: 4 MAY 200 Stephen G. Ray, Jr., Do No Harm: Social Sin and Christian Responsibility Reviewed by Peter J. Paris [source] How stupid not to have thought of that: post-copulatory sexual selectionJOURNAL OF ZOOLOGY, Issue 2 2010T. R. Birkhead Abstract Science progresses through ideas or hypotheses; novel ways of viewing the world. If those ideas survive testing, then they are considered ,the truth', or more crucially, truth-for-now, for the essence of science is that if a new idea provides a better explanation of the way the world is, the truth changes. Darwin's idea of evolution by natural selection, published as the Origin in 1859, replaced the earlier truth of physico- or natural-theology introduced by John Ray in 1691. Despite resistance by the church, Darwin's truth gained widespread acceptance, in part due to the efforts of T. H. Huxley, who on reading the Origin said ,How extremely stupid not to have thought of that!' Despite natural selection's enormous explanatory power, there were certain phenomena it apparently could not explain, including female promiscuity. It was only in the 1960s when natural selection was viewed as operating explicitly on individuals (rather than populations or groups), that this changed. Rather than being a cooperative venture between the sexes, sexual reproduction was now viewed in terms of conflicts of interests, and in so doing provided an explanation for female promiscuity (albeit in a male-biased sort of way). Until this point, sexual selection had been concerned exclusively with mate acquisition. With an evolutionary perspective focussing on individuals, it was recognized that sexual selection might continue after insemination, and that rather than competing for partners, males compete for fertilizations. Later it was acknowledged that females, through cryptic processes can also influence the outcome of sperm competition. Today, post-copulatory sexual selection provides explanations for many previously bewildering reproductive traits, including the extraordinary diversity in male and female genitalia, the design of spermatozoa and ova, of seminal fluid and of copulation behaviour itself [source] Complex valued Ray,Singer torsion IIMATHEMATISCHE NACHRICHTEN, Issue 10 2010Dan Burghelea Abstract In this paper we extend Witten,Helffer,Sjöstrand theory from selfadjoint Laplacians based on fiber wise Hermitian metrics to nonselfadjoint Laplacians based on fiber wise non-degenerate symmetric bilinear forms. As an application we show that results about the asymptotics of the Ray,Singer torsion of self-adjoint Witten deformation, as well as the strategy proposed by Burghelea,Friedlander,Kappeler to derive the comparison of Ray,Singer and Reidemeister torsion, can be extended to nonself-adjoint Witten deformation. This is then used to conclude the equality of complex analytic and Milnor,Turaev torsion, at least for odd dimensional manifolds, up to sign (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Commentary: Albert Ray, MDPAIN MEDICINE, Issue 2 2004Albert Ray MD No abstract is available for this article. [source] Fixed- versus Variable-domain Interpretations of Tarski's Account of Logical ConsequencePHILOSOPHY COMPASS (ELECTRONIC), Issue 9 2010Paolo Mancosu In this article I describe and evaluate the debate that surrounds the proper interpretation of Tarski's account of logical consequence given in his classic 1936 article ,On the concept of logical consequence'. In the late 1980s Etchemendy argued that the familiar model theoretic account of logical consequence is not to be found in Tarski's original article. Whereas the contemporary account of logical consequence is a variable-domain conception , in that it calls for a reinterpretation of the domain of variation of the quantifiers when evaluating logical consequence ,, no such reinterpretation is found in Tarski's original account, which was rather based on a ,fixed-domain' conception. Etchemendy's claims have sparked a debate on Tarski's conception of logical consequence with important contributions by, among others, Bach, Bays, Corcoran, Gómez-Torrente, Mancosu, Ray, Sagüillo, and Sher. [source] Ethnicity: The New Encyclopedia of Southern Culture by Celeste Ray, EditorTHE JOURNAL OF AMERICAN CULTURE, Issue 4 2007Ray B. Browne No abstract is available for this article. [source] Guest Editorial: The House That Ray BuiltTHE JOURNAL OF POPULAR CULTURE, Issue 2 2010Garyn G. Roberts First page of article [source] FAIRE DE SON HISTOIRE UNE BOUCLE (NOIRE): WAYS OF LOOKING AT TRISTAN TZARAART HISTORY, Issue 1 2009ELIZABETH LEGGE A close examination of pictorial and verbal portraits of Tzara, by both himself and others (Breton, Louis Aragon, Picabia, Germaine Everling, Man Ray, Hans Arp) , as filtered in the art and texts of the dadas and their critics through adaptations of cabbalism, Tao-inflected Africanism, spirit photography and Maurice Barrčs's ponderously mystical nationalism , yields a peculiar portrait of Paris dada, and of Tristan Tzara's ethical role within it. Anti-Semitic slurs against Tzara, used as weapons in dada power politics, while construable as a knowingly disingenuous use of cliché and caricature, raise questions of idiom. Raoul Hausmann's Mechanical Head: the Spirit of Our Time (1919) is analysed as an exemplary approach to dada portraiture, in which constellations of contradictory readymade attributes and associations, including anti-Semitic stereotypes, configure a tragicomic array of received social constructions, revolutionary aspirations, prejudices and ambivalences that constitute individuals as social actors within and outside dada. [source] Equivocal Masculinity: New York Dada in the context of World War IART HISTORY, Issue 2 2002Amelia Jones This essay explores a cluster of works by the group of artists retroactively labelled `New York Dada' in light of the pressures exerted on masculine subjectivity during the WWI period. While the war has, for obvious reasons, been a key reference point for studies of European Dada, it has never been acknowledged (beyond passing references) as a context for the New York group (in particular, for the work of the key figures Man Ray, Francis Picabia and Marcel Duchamp). Failing to attend to the Great War as a crucial historical pressure on the group simply accepts at face value these artists' own desire to escape the war (in the case of Picabia, Duchamp, Jean Crotti and others, by leaving Europe and coming to New York). This essay, in contrast, insists upon attending to the effects of the war environment , with its heated discourses of heroism and patriotic nationalism , on the New York Dada group (which, after all, would not have existed had these artists not left Europe for New York because of the war). Examining the relationship of each of the key NewYork Dada figures to the war, it explores a selection of their works in relation to these experiences. Ultimately, I argue that the artists' non-combatant masculinity, compromised in the face of dominant discourses of militarized masculinity, is eerily and disconcertingly echoed by the predominance of shadows, gaps and absences in their visual art works. [source] Shallow Bounding Volume Hierarchies for Fast SIMD Ray Tracing of Incoherent RaysCOMPUTER GRAPHICS FORUM, Issue 4 2008H. Dammertz Abstract Photorealistic image synthesis is a computationally demanding task that relies on ray tracing for the evaluation of integrals. Rendering time is dominated by tracing long paths that are very incoherent by construction. We therefore investigate the use of SIMD instructions to accelerate incoherent rays. SIMD is used in the hierarchy construction, the tree traversal and the leaf intersection. This is achieved by increasing the arity of acceleration structures, which also reduces memory requirements. We show that the resulting hierarchies can be built quickly and are smaller than acceleration structures known so far while at the same time outperforming them for incoherent rays. Our new acceleration structure speeds up ray tracing by a factor of 1.6 to 2.0 compared to a highly optimized bounding interval hierarchy implementation, and 1.3 to 1.6 compared to an efficient kd-tree. At the same time, the memory requirements are reduced by 10,50%. Additionally we show how a caching mechanism in conjunction with this memory efficient hierarchy can be used to speed up shadow rays in a global illumination algorithm without increasing the memory footprint. This optimization decreased the number of traversal steps up to 50%. [source] Comparative morphology of stingray lateral line canal and electrosensory systemsJOURNAL OF MORPHOLOGY, Issue 11 2008Laura K. JordanArticle first published online: 24 JUL 200 Abstract Elasmobranchs (sharks, skates, and rays) possess a variety of sensory systems including the mechanosensory lateral line and electrosensory systems, which are particularly complex with high levels of interspecific variation in batoids (skates and rays). Rays have dorsoventrally compressed, laterally expanded bodies that prevent them from seeing their mouths and more often than not, their prey. This study uses quantitative image analysis techniques to identify, quantify, and compare structural differences that may have functional consequences in the detection capabilities of three Eastern Pacific stingray species. The benthic round stingray, Urobatis halleri, pelagic stingray, Pteroplatytrygon (Dasyatis) violacea, and benthopelagic bat ray, Myliobatis californica, show significant differences in sensory morphology. Ventral lateral line canals correlate with feeding ecology and differ primarily in the proportion of pored and nonpored canals and the degree of branching complexity. Urobatis halleri shows a high proportion of nonpored canals, while P. violacea has an intermediate proportion of pored and nonpored canals with almost no secondary branching of pored canals. In contrast, M. californica has extensive and highly branched pored ventral lateral line canals that extended laterally toward the wing tips on the anterior edge of the pectoral fins. Electrosensory morphology correlates with feeding habitat and prey mobility; benthic feeders U. halleri and M. californica, have greater electrosensory pore numbers and densities than P. violacea. The percentage of the wing surface covered by these sensory systems appears to be inversely related to swimming style. These methods can be applied to a broader range of species to enable further discussion of the relationship of phylogeny, ecology, and morphology, while the results provide testable predictions of detection capabilities. J. Morphol., 2008. © 2008 Wiley-Liss, Inc. [source] GPU-based interactive visualization framework for ultrasound datasetsCOMPUTER ANIMATION AND VIRTUAL WORLDS (PREV: JNL OF VISUALISATION & COMPUTER ANIMATION), Issue 1 2009Sukhyun Lim Abstract Ultrasound imaging is widely used in medical areas. By transmitting ultrasound signals into the human body, their echoed signals can be rendered to represent the shape of internal organs. Although its image quality is inferior to that of CT or MR, ultrasound is widely used for its speed and reasonable cost. Volume rendering techniques provide methods for rendering the 3D volume dataset intuitively. We present a visualization framework for ultrasound datasets that uses programmable graphics hardware. For this, we convert ultrasound coordinates into Cartesian form. In ultrasound datasets, however, since physical storage and representation space is different, we apply different sampling intervals adaptively for each ray. In addition, we exploit multiple filtered datasets in order to reduce noise. By our method, we can determine the adequate filter size without considering the filter size. As a result, our approach enables interactive volume rendering for ultrasound datasets, using a consumer-level PC. Copyright © 2009 John Wiley & Sons, Ltd. [source] Accelerating Ray Tracing using Constrained TetrahedralizationsCOMPUTER GRAPHICS FORUM, Issue 4 2008Ares Lagae Abstract In this paper we introduce the constrained tetrahedralization as a new acceleration structure for ray tracing. A constrained tetrahedralization of a scene is a tetrahedralization that respects the faces of the scene geometry. The closest intersection of a ray with a scene is found by traversing this tetrahedralization along the ray, one tetrahedron at a time. We show that constrained tetrahedralizations are a viable alternative to current acceleration structures, and that they have a number of unique properties that set them apart from other acceleration structures: constrained tetrahedralizations are not hierarchical yet adaptive; the complexity of traversing them is a function of local geometric complexity rather than global geometric complexity; constrained tetrahedralizations support deforming geometry without any effort; and they have the potential to unify several data structures currently used in global illumination. [source] Instant Volumetric Understanding with Order-Independent Volume RenderingCOMPUTER GRAPHICS FORUM, Issue 3 2004Benjamin Mora Rapid, visual understanding of volumetric datasets is a crucial outcome of a good volume rendering application, but few current volume rendering systems deliver this result. Our goal is to reduce the volumetric surfing that is required to understand volumetric features by conveying more information in fewer images. In order to achieve this goal, and in contrast with most current methods which still use optical models and alpha blending, our approach reintroduces the order-independent contribution of every sample along the ray in order to have an equiprobable visualization of all the volume samples. Therefore, we demonstrate how order independent sampling can be suitable for fast volume understanding, show useful extensions to MIP and X-ray like renderings, and, finally, point out the special advantage of using stereo visualization in these models to circumvent the lack of depth cues. Categories and Subject Descriptors: I.3.3 [Computer Graphics]: Picture/Image, Generation, I.3.7 [Computer Graphics]: Three-Dimensional graphics and realism. [source] Ray Tracing Triangular Bézier PatchesCOMPUTER GRAPHICS FORUM, Issue 3 2001S. H. Martin Roth We present a new approach to finding ray,patch intersections with triangular Bernstein,Bézier patches of arbitrary degree. This paper extends and complements on the short presentation17 . Unlike a previous approach which was based on a combination of hierarchical subdivision and a Newton,like iteration scheme21 , this work adapts the concept of Bézier clipping to the triangular domain. The problem of reporting wrong intersections, inherent to the original Bézier clipping algorithm14 , is inves-tigated and opposed to the triangular case. It turns out that reporting wrong hits is very improbable, even close to impossible, in the triangular set,up. A combination of Bézier clipping and a simple hierarchy of nested bounding volumes offers a reliable and accurate solution to the problem of ray tracing triangular Bézier patches. [source] Cell proliferation during blastema formation in the regenerating teleost finDEVELOPMENTAL DYNAMICS, Issue 2 2002Leonor Santos-Ruiz Abstract Epimorphic regeneration in teleost fins occurs through the establishment of a balanced growth state in which a blastema gives rise to all the mesenchymal cells, whereas definite areas of the epidermis proliferate leading to its extension, thus, allowing the enlargement of the whole structure. This type of regeneration involves specific mechanisms that temporally and spatially regulate cell proliferation. To understand how the blastema is formed and how this growth situation is set up, we investigated cell proliferation patterns in the regenerating fin of the goldfish Carassius auratus from the time of amputation to that of blastema formation by using proliferating cell nuclear antigen immunostaining and bromodeoxyuridine labeling. Wound closure and apical epidermal cap formation took place by epidermal migration and re-arrangement, without the contribution of cell proliferation. As soon as the apical cap had formed, the epidermis started to proliferate at its lateral surfaces, in which all layers maintained cycling for the duration of the studied process. The distal epidermal cap, on the contrary, presented very few cycling cells, and its cytoarchitecture was indicative of continuous remodeling due to ray growth. The basal layer of this epidermal cap showed a typical morphology and remained nonproliferative whilst in contact with the proliferating blastema. Proliferation in the mesenchymal compartment of the ray started far from the amputation plane. Subsequently, cycling cells approached that location, until they formed the blastema in contact with the apical epidermal cap. Differences observed between the epidermis and mesenchyma, regarding activation of the cell cycle and the establishment of proliferative patterns, suggest that differential mechanisms regulate cell proliferation in each of these compartments during the initial stages of regeneration. © 2002 Wiley-Liss, Inc. [source] Identifying patterns of diversity of the actinopterygian fulcraACTA ZOOLOGICA, Issue 2009Gloria Arratia Abstract Fin rays, scutes or ridge scales, and fulcra have been traditionally interpreted as modified scales, but their diversity has been almost ignored. Based on results presented here, revised definitions of these elements are provided. At least two patterns of basal fulcra are found in actinopterygians: in Pattern I all or most basal fulcra are paired elements, whereas in Pattern II, a series of unpaired basal fulcra that are bifurcated proximally, and whose forking gradually becomes larger caudad, are followed by a series of paired elements. Basal fulcra are commonly present on unpaired fins of lower actinopterygians, including basal neopterygians. Among living fish they are absent in polypteriforms, Amia and teleosts. Fringing fulcra are always paired. Three patterns of fringing fulcra series are described: the series of fringing fulcra in basal actinopterygians is formed by expanded terminal segments of marginal lepidotrichia (Pattern A). Another series is formed by a combination of slightly expanded or modified terminal segments of rays and independent spiny, small elements (Pattern B). The third series is formed of small, spiny ossified elements positioned along the leading marginal fin ray(s) (Pattern C). Other patterns of basal and fringing fulcra remain to be investigated, along with their phylogenetic implications. [source] Chemical, Mechanical, and Antibacterial Properties of Silver Nanocluster,Silica Composite Coatings Obtained by Sputtering,ADVANCED ENGINEERING MATERIALS, Issue 7 2010Monica Ferraris Abstract Silver nanocluster,silica matrix composite coatings have been deposited by radio frequency (RF) co-sputtering on silica substrates. Field emission scanning electron microscopy and X-ray diffraction spectra of the as deposited and heated samples (150,600,°C) revealed the presence of metal silver nanoclusters, their size depending on the heating treatment. The antibacterial activity of the as deposited and heated samples has been measured in accordance to National Committee for Clinical Laboratory Standards, and it has been demonstrated on samples heated up to 450,°C in contact mode and for samples heated at 600,°C in a liquid environment. Their antibacterial activity was still present after gamma ray and ethylene oxide gas (EtO) sterilization of the samples. Silver leaching tests on the as deposited and heated samples has been measured by graphite furnace atomic absorption spectrometer, revealing an amount ranging from 0.1 to 0.9,µg mm,2, over 28 days. Tape resistance (ASTM D3359-97) and scratch resistance tests have been done on each sample revealing a good adhesion of the coatings on silica. [source] Homozygous deletions within the 11q13 cervical cancer tumor-suppressor locus in radiation-induced, neoplastically transformed human hybrid cellsGENES, CHROMOSOMES AND CANCER, Issue 4 2004Marc S. Mendonca Studies on nontumorigenic and tumorigenic human cell hybrids derived from the fusion of HeLa (a cervical cancer cell line) with GM00077 (a normal skin fibroblast cell line) have demonstrated "functional" tumor-suppressor activity on chromosome 11. It has been shown that several of the neoplastically transformed radiation-induced hybrid cells called GIMs (gamma ray induced mutants), isolated from the nontumorigenic CGL1 cells, have lost one copy of the fibroblast chromosome 11. We hypothesized, therefore, that the remaining copy of the gene might be mutated in the cytogenetically intact copy of fibroblast chromosome 11. Because a cervical cancer tumor suppressor locus has been localized to chromosome band 11q13, we performed deletion-mapping analysis of eight different GIMs using a total of 32 different polymorphic and microsatellite markers on the long arm (q arm) of chromosome 11. Four irradiated, nontumorigenic hybrid cell lines, called CONs, were also analyzed. Allelic deletion was ascertained by the loss of a fibroblast allele in the hybrid cell lines. The analysis confirmed the loss of a fibroblast chromosome 11 in five of the GIMs. Further, homozygous deletion (complete loss) of chromosome band 11q13 band sequences, including that of D11S913, was observed in two of the GIMs. Detailed mapping with genomic sequences localized the homozygous deletion to a 5.7-kb interval between EST AW167735 and EST F05086. Southern blot hybridization using genomic DNA probes from the D11S913 locus confirmed the existence of homozygous deletion in the two GIM cell lines. Additionally, PCR analysis showed a reduction in signal intensity for a marker mapped 31 kb centromeric of D11S913 in four other GIMs. Finally, Northern blot hybridization with the genomic probes revealed the presence of a novel >15-kb transcript in six of the GIMs. These transcripts were not observed in the nontumorigenic hybrid cell lines. Because the chromosome 11q13 band deletions in the tumorigenic hybrid cell lines overlapped with the minimal deletion in cervical cancer, the data suggest that the same gene may be involved in the development of cervical cancer and in radiation-induced carcinogenesis. We propose that a gene localized in proximity to the homozygous deletion is the candidate tumor-suppressor gene. © 2004 Wiley-Liss, Inc. [source] On establishing the accuracy of noise tomography travel-time measurements in a realistic mediumGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2009Victor C. Tsai SUMMARY It has previously been shown that the Green's function between two receivers can be retrieved by cross-correlating time series of noise recorded at the two receivers. This property has been derived assuming that the energy in normal modes is uncorrelated and perfectly equipartitioned, or that the distribution of noise sources is uniform in space and the waves measured satisfy a high frequency approximation. Although a number of authors have successfully extracted travel-time information from seismic surface-wave noise, the reason for this success of noise tomography remains unclear since the assumptions inherent in previous derivations do not hold for dispersive surface waves on the Earth. Here, we present a simple ray-theory derivation that facilitates an understanding of how cross correlations of seismic noise can be used to make direct travel-time measurements, even if the conditions assumed by previous derivations do not hold. Our new framework allows us to verify that cross-correlation measurements of isotropic surface-wave noise give results in accord with ray-theory expectations, but that if noise sources have an anisotropic distribution or if the velocity structure is non-uniform then significant differences can sometimes exist. We quantify the degree to which the sensitivity kernel is different from the geometric ray and find, for example, that the kernel width is period-dependent and that the kernel generally has non-zero sensitivity away from the geometric ray, even within our ray theoretical framework. These differences lead to usually small (but sometimes large) biases in models of seismic-wave speed and we show how our theoretical framework can be used to calculate the appropriate corrections. Even when these corrections are small, calculating the errors within a theoretical framework would alleviate fears traditional seismologists may have regarding the robustness of seismic noise tomography. [source] Traveltime approximation for a reflected wave in a homogeneous anisotropic elastic layerGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2002M. Zillmer Summary An approximation to the traveltime field is calculated for an elastic wave that propagates in a homogeneous anisotropic layer and is reflected at a plane boundary. The traveltime is approximated by a Taylor series expansion with the third derivative of the traveltime being taken into account. The coefficients of the series refer to the seismic ray, which is locally the fastest ray. Simple formulae are obtained for orthorhombic media in the crystal coordinate system, which relate the traveltimes of the reflected waves to the elastic constants of the medium. A numerical example is presented for wave propagation in orthorhombic olivine, which is a constituent of the Earth's mantle. A second example is given by an isotropic host rock with a set of parallel cracks, which is an important model for wave propagation in the Earth's crust. The elastic parameters can be determined by measuring the reflection times as a function of source,receiver offset. The approximate traveltime,distance curves are compared with traveltimes obtained from seismic ray tracing. [source] A Maslov-propagator seismogram for weakly anisotropic mediaGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2002Georg Rümpker Summary We introduce a formalism to calculate shear-wave seismograms for weakly-anisotropic and inhomogeneous media. The method is based on the combination of the forward-propagator method, which accounts for shear-wave interaction along a single reference ray, and the Maslov ray-summation, which incorporates amplitude and phase information from neighbouring rays to account for waveform and diffraction effects at caustics and in shadow regions. The approach is based on the assumption that the multiply split shear waves, on the way to a given receiver, travel along a common ray path that can by obtained from ray tracing in an isotropic reference medium (i.e. the common-ray approximation). The forward propagator and the Maslov amplitude are expressed with respect to radial and transverse coordinates (perpendicular to the ray propagation direction) that are defined uniquely by the initial conditions. Local polarizations and slownesses of the fast and slow shear-waves in the direction of propagation are obtained from the eikonal equation. The Maslov-propagator phase is given by the average shear-wave traveltime along the reference ray. Phase advances and delays of individual shear wave components are accounted for by the propagator. The geometrical-spreading information required for the Maslov integration is supplied by dynamic ray tracing in the isotropic reference medium. In the high-frequency limit effective phase functions are defined to assess the validity of the Maslov propagator phase information. For a homogeneous isotropic reference medium, we find good agreement with exact Maslov phase functions for anisotropic perturbations of up to 20 per cent. As a numerical application we consider effects of inhomogeneous anisotropy in a shear-wave cross-hole survey. The variations of the transversely-isotropic medium require 2-D slowness integrals. The method can handle discontinuities of the fast polarization along the ray path and also for neighbouring rays which is important for the slowness integration. Smooth transitions between isotropic and anisotropic regions along the ray path can be accounted for without the need to switch between numerical formulations. [source] Wavefront healing: a banana,doughnut perspectiveGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2001S.-H. Hung SUMMARY Wavefront healing is a ubiquitous diffraction phenomenon that affects cross-correlation traveltime measurements, whenever the scale of the 3-D variations in wave speed is comparable to the characteristic wavelength of the waves. We conduct a theoretical and numerical analysis of this finite-frequency phenomenon, using a 3-D pseudospectral code to compute and measure synthetic pressure-response waveforms and ,ground truth' cross-correlation traveltimes at various distances behind a smooth, spherical anomaly in an otherwise homogeneous acoustic medium. Wavefront healing is ignored in traveltime tomographic inversions based upon linearized geometrical ray theory, in as much as it is strictly an infinite-frequency approximation. In contrast, a 3-D banana,doughnut Fréchet kernel does account for wavefront healing because it is cored by a tubular region of negligible traveltime sensitivity along the source,receiver geometrical ray. The cross-path width of the 3-D kernel varies as the square root of the wavelength , times the source,receiver distance L, so that as a wave propagates, an anomaly at a fixed location finds itself increasingly able to ,hide' within the growing doughnut ,hole'. The results of our numerical investigations indicate that banana,doughnut traveltime predictions are generally in excellent agreement with measured ground truth traveltimes over a wide range of propagation distances and anomaly dimensions and magnitudes. Linearized ray theory is, on the other hand, only valid for large 3-D anomalies that are smooth on the kernel width scale ,(, L). In detail, there is an asymmetry in the wavefront healing behaviour behind a fast and slow anomaly that cannot be adequately modelled by any theory that posits a linear relationship between the measured traveltime shift and the wave-speed perturbation. [source] Paraxial ray methods for anisotropic inhomogeneous mediaGEOPHYSICAL PROSPECTING, Issue 1 2007Tijmen Jan Moser ABSTRACT A new formalism of surface-to-surface paraxial matrices allows a very general and flexible formulation of the paraxial ray theory, equally valid in anisotropic and isotropic inhomogeneous layered media. The formalism is based on conventional dynamic ray tracing in Cartesian coordinates along a reference ray. At any user-selected pair of points of the reference ray, a pair of surfaces may be defined. These surfaces may be arbitrarily curved and oriented, and may represent structural interfaces, data recording surfaces, or merely formal surfaces. A newly obtained factorization of the interface propagator matrix allows to transform the conventional 6 × 6 propagator matrix in Cartesian coordinates into a 6 × 6 surface-to-surface paraxial matrix. This matrix defines the transformation of paraxial ray quantities from one surface to another. The redundant non-eikonal and ray-tangent solutions of the dynamic ray-tracing system in Cartesian coordinates can be easily eliminated from the 6 × 6 surface-to-surface paraxial matrix, and it can be reduced to 4 × 4 form. Both the 6 × 6 and 4 × 4 surface-to-surface paraxial matrices satisfy useful properties, particularly the symplecticity. In their 4 × 4 reduced form, they can be used to solve important boundary-value problems of a four-parametric system of paraxial rays, connecting the two surfaces, similarly as the well-known surface-to-surface matrices in isotropic media in ray-centred coordinates. Applications of such boundary-value problems include the two-point eikonal, relative geometrical spreading, Fresnel zones, the design of migration operators, and more. [source] Traveltime computation by wavefront-orientated ray tracingGEOPHYSICAL PROSPECTING, Issue 1 2005Radu Coman ABSTRACT For multivalued traveltime computation on dense grids, we propose a wavefront-orientated ray-tracing (WRT) technique. At the source, we start with a few rays which are propagated stepwise through a smooth two-dimensional (2D) velocity model. The ray field is examined at wavefronts and a new ray might be inserted between two adjacent rays if one of the following criteria is satisfied: (1) the distance between the two rays is larger than a predefined threshold; (2) the difference in wavefront curvature between the rays is larger than a predefined threshold; (3) the adjacent rays intersect. The last two criteria may lead to oversampling by rays in caustic regions. To avoid this oversampling, we do not insert a ray if the distance between adjacent rays is smaller than a predefined threshold. We insert the new ray by tracing it from the source. This approach leads to an improved accuracy compared with the insertion of a new ray by interpolation, which is the method usually applied in wavefront construction. The traveltimes computed along the rays are used for the estimation of traveltimes on a rectangular grid. This estimation is carried out within a region bounded by adjacent wavefronts and rays. As for the insertion criterion, we consider the wavefront curvature and extrapolate the traveltimes, up to the second order, from the intersection points between rays and wavefronts to a gridpoint. The extrapolated values are weighted with respect to the distances to wavefronts and rays. Because dynamic ray tracing is not applied, we approximate the wavefront curvature at a given point using the slowness vector at this point and an adjacent point on the same wavefront. The efficiency of the WRT technique is strongly dependent on the input parameters which control the wavefront and ray densities. On the basis of traveltimes computed in a smoothed Marmousi model, we analyse these dependences and suggest some rules for a correct choice of input parameters. With suitable input parameters, the WRT technique allows an accurate traveltime computation using a small number of rays and wavefronts. [source] Histology of the fetal prune belly syndrome with reference to the efficacy of prenatal decompressionINTERNATIONAL JOURNAL OF UROLOGY, Issue 5 2000Kenji Shimada Abstract Background: Deficient abdominal musculature, complex abnormalities of urinary tracts and bilateral abdominal cryptorchidism represent the basic characteristics of prune belly syndrome (PBS). Although prenatal diagnosis of PBS is rarely made, because of the wide variety of ultrasonographic images, reported cases have gradually increased. Once a fetus suspected of having PBS is found, it is sometimes difficult for the pediatric urologists to decide how to treat them. The histology of the kidney and urinary tracts in fetuses with PBS was reviewed in order to give suggestions on the management of prenatal cases. Methods: Autopsy records of nine fetuses (5 males, 2 females and 2 undetermined) with characteristically distended and deficient abdominal wall were reviewed. Gestational age (GA) at detection ranged from 12 to 25 weeks and at delivery from 13 to 32 weeks. Results: Renal histology in two fetuses showed earlier than normal disappearance of cortical nephrogenic zone replaced by cortical cysts and dysplastic structures. The nephrogenic zone was retained in five fetuses which were younger than GA 20 weeks. While the number of glomeruli along the medullary ray was normal for the age in three fetuses younger than GA 20 weeks, it was decreased in all others. Bladder histology was variable showing both increased musculature and defective or dysplastic muscles. There was a tendency for connective tissues in the bladder wall to increase in proportion to GA, The ureter revealed scarcity of muscle bundles among dense connective tissue. The urethra was atretic in eight fetuses. Conclusion: The clinical implication from the renal histology is that decompression of the urinary tract should be done before GA 20 weeks. However, the early fetal treatment appears to have no effect on the urodynamics in this disorder with deficient musculature. [source] Calculation of the instrumental function in X-ray powder diffractionJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3 2006A. D. Zuev A new method for calculating the total instrumental function of a conventional Bragg,Brentano diffractometer has been developed. The method is based on an exact analytical solution, derived from diffraction optics, for the contribution of each incident ray to the intensity registered by a detector of limited size. Because an incident ray is determined by two points (one is related to the source of the X-rays and the other to the sample) the effects of the coupling of specific instrumental functions, for example, equatorial and axial divergence instrumental functions, are treated together automatically. The intensity at any arbitrary point of the total instrumental profile is calculated by integrating the intensities over two simple rectangular regions: possible point positions on the source and possible point positions on the sample. The effects of Soller slits, a monochromator and sample absorption can also be taken into account. The main difference between the proposed method and the convolutive approach (in which the line profile is synthesized by convolving the specific instrumental functions) lies in the fact that the former provides an exact solution for the total instrumental function (exact solutions for specific instrumental functions can be obtained as special cases), whereas the latter is based on the approximations for the specific instrumental functions, and their coupling effects after the convolution are unknown. Unlike the ray-tracing method, in the proposed method the diffracted rays contributing to the registered intensity are considered as combined (part of the diffracted cone) and, correspondingly, the contribution to the instrumental line profile is obtained analytically for this part of the diffracted cone and not for a diffracted unit ray as in ray-tracing simulations. [source] | ||||||||||||||||||||||||||||||||||||||||||||||||||||