Journal articles on the topic 'Ghost waves'
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Mackay, Tom G., and Akhlesh Lakhtakia. "Exorcizing ghost waves." Optik 192 (September 2019): 162926. http://dx.doi.org/10.1016/j.ijleo.2019.06.026.
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Robertsson, Johan O. A., Dirk-Jan van Manen, Fredrik Andersson, Lasse Amundsen, and Kurt Eggenberger. "Source deghosting by depth apparition." GEOPHYSICS 82, no. 6 (November 1, 2017): P89—P107. http://dx.doi.org/10.1190/geo2016-0686.1.
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Marine seismic data are distorted by ghosts as waves propagating upward reflect downward from the sea surface. Ghosts appear on the source side and the receiver side. However, whereas the receiver-side ghost problem has been studied in detail, and many different solutions have been proposed and implemented commercially, the source-side ghost problem has remained largely unsolved with few satisfactory solutions available. We have developed a new and simple method to remove sea-surface ghosts that is related to the recently introduced concept of signal apparition. As opposed to the temporal/spatial source signature modulation functions used in the original signal apparition theory, our source deghosting method relies on using sources at different depths but not at the same lateral positions. The new method promises to be particularly suitable for 3D applications on sparse or incomplete acquisition geometries.
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Shapiro, Ilya L., Ana M. Pelinson, and Filipe de O. Salles. "Gravitational waves and perspectives for quantum gravity." Modern Physics Letters A 29, no. 30 (September 28, 2014): 1430034. http://dx.doi.org/10.1142/s0217732314300341.
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Understanding the role of higher derivatives is probably one of the most relevant questions in quantum gravity theory. Already at the semiclassical level, when gravity is a classical background for quantum matter fields, the action of gravity should include fourth derivative terms to provide renormalizability in the vacuum sector. The same situation holds in the quantum theory of metric. At the same time, including the fourth derivative terms means the presence of massive ghosts, which are gauge-independent massive states with negative kinetic energy. At both classical and quantum level such ghosts violate stability and hence the theory becomes inconsistent. Several approaches to solve this contradiction were invented and we are proposing one more, which looks simpler than those what were considered before. We explore the dynamics of the gravitational waves on the background of classical solutions and give certain arguments that massive ghosts produce instability only when they are present as physical particles. At least on the cosmological background one can observe that if the initial frequency of the metric perturbations is much smaller than the mass of the ghost, no instabilities are present.
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Aytun, Katibe. "The footsteps of the receiver ghost in the f-k domain." GEOPHYSICS 64, no. 5 (September 1999): 1618–26. http://dx.doi.org/10.1190/1.1444666.
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Waves traveling upward from subsurface reflective strata continue propagating after they are recorded by receivers as primary reflections. When a sharp velocity discontinuity exists above the receivers, the waves are then reflected back, and are once more recorded by the same receivers but as downgoing waves. This phenomenon is known as the receiver ghost. Based on a thorough study of the f-k response of the receiver ghost in a record, this paper shows that the null frequencies are caused by the time differences between the primary and the ghost arrivals, and that they vary with the angle of incidence. It is further shown that the loci of the null frequencies of each harmonic is a member of a family of hyperbolas with a common pair of asymptotes in the f-k domain.
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Surette, Ray. "A copycat crime meme: Ghost riding the whip." Crime, Media, Culture: An International Journal 16, no. 2 (August 1, 2019): 239–64. http://dx.doi.org/10.1177/1741659019865305.
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A 2006 US copycat crime wave came into being, surged with thousands of crimes committed, and dissipated without substantial news media attention. The development of this early copycat crime meme is traceable to the nature of the crime, “ghost riding the whip,” and the social media and popular music communication channels associated with it. Ghost riding the whip involved traffic violations where drivers exit their cars and dance atop or alongside the moving driverless vehicles. Social media allowed the widespread diffusion of detailed instructions that spread this crime from a single minority community to the middle class within a 3-month period. The study of this copycat crime meme examined four types of data: Google Trends, rap songs, ProQuest news media data, and YouTube videos. The examination of the crime wave suggests how Gabriel Tarde’s 19th-century ideas operate in the contemporary social media era. However, unlike pre-social media-based crime waves that were launched via interpersonal and legacy media communication pathways, for ghost riding, rap songs, YouTube postings, and Google searches spurred its growth. Legacy media were found to be most important during the crime wave’s decline, but not during its diffusion. For this copycat crime meme, social media’s influence flowed in a unique upward and outward pattern and the results raise the research questions as to how social media have changed the dynamics of crime waves and how important legacy media will be in future crime waves.
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Waseer, Waleed Iqbal, Qaisar Abbas Naqvi, and M. Juniad Mughal. "Non-uniform plane waves (ghost waves) in general anisotropic medium." Optics Communications 453 (December 2019): 124334. http://dx.doi.org/10.1016/j.optcom.2019.124334.
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Mohseni, Morteza. "Gravitational waves in ghost free bimetric gravity." Journal of Cosmology and Astroparticle Physics 2012, no. 11 (November 14, 2012): 023. http://dx.doi.org/10.1088/1475-7516/2012/11/023.
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Baranov, Denis. "Seeing a ghost: hybrid waves in anisotropic crystals." Advanced Photonics 1, no. 04 (August 29, 2019): 1. http://dx.doi.org/10.1117/1.ap.1.4.040501.
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Domenico, S. N. "Harnessing the ghost." GEOPHYSICS 55, no. 5 (May 1990): 608–18. http://dx.doi.org/10.1190/1.1442872.
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A previous field experiment demonstrated that the interface between an air‐water mixture of low fractional air volume (say, 0.005) and air‐free water is an effective reflector of acoustic waves, suggesting that acoustic waves in water might be beamed by placing an energy source at the focus of a paraboloidal interface between an air‐water mixture and air‐free water. When this interface is concave downward, wave energy traveling upward and outward from the source at the focus is reflected downward and the surface reflection (ghost) is eliminated. Accordingly, a paraboloid reflector consisting of perforated circular air pipes was constructed and tested with a small water gun at its focus. The structure, suspended from its apex, had a height of 4 ft (1.2 m), a base diameter of 8 ft (2.4 m), and a focus 1 ft (0.3 m) below the apex. The wave field, measured with an air‐bubble stream emanating from the perforated pipes, displays a beam with a nearly constant half‐width of 22 ft (6.7 m) created by the paraboloid reflector. Signal amplitudes directly below the paraboloid on an extension of its axis are as much as 9 dB above, and off‐axis amplitudes are as much as 17 dB below, signal amplitudes for no air‐bubble stream. The source signal’s amplitude spectrum, extending to about 1.5 kHz, is skewed toward higher frequencies by the paraboloid reflector, resulting in a dominant peak frequency of about 1210 Hz. The ghost is not evident. Theoretical wave fields of beamed monofrequency source signals demonstrate that the paraboloid reflector behaves as a high‐cut filter, the band‐pass narrowing as axial distance to the paraboloid decreases and off‐axis distance increases. Axial rates of decrease of the beamed experimental signal with increasing depth, at depths of 20 ft (6.1 m) and greater below the source, compare favorably to those of beamed theoretical continuous sinusoidal signals which are nearly equal at all frequencies within the experimental signal’s frequency band. Additional research is required to determine the complete effect of the paraboloid reflector on water‐gun signal characteristics. The small prototype reflector used in this experiment is not suitable for typical seismic exploration efforts because it produces excessively high‐frequency content. A useful paraboloid reflector may have to be several times the size of this prototype.
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Wang, Linfei, Zhong Wang, Huaishan Liu, Jin Zhang, Lei Xing, and Yanxin Yin. "Hydrate-Bearing Sediment Imaging of Ghost Reflection in Vertical Cable Seismic Data Using Seismic Interferometry." Geofluids 2022 (September 25, 2022): 1–7. http://dx.doi.org/10.1155/2022/3501755.
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Marine vertical cable seismic (VCS) collects seismic waves by hydrophone array vertically suspended in seawater to prospect the offshore geological structure and monitor the reservoir. Due to its irregular source-receiver geometry, the primary imaging has narrow illustration coverage. Here, we proposed a cross-correlation transformation based on ghost wave interferometry. This method can transform the ghost reflections from the vertical cable seismic profile into the virtual surface seismic primaries just like those excited by the source and recorded by marine seismic towed-streamer below sea surface. After processing these virtual primaries with conventional method, we can obtain the ghost reflection imaging section with high resolution which effectively extend the illustration footprints in the subsurface. By application of this transform, virtual primaries are generated from the first-order ghost reflections of the actual VCS data. Then, migration of these virtual primaries provides a high-resolution image of hydrate-bearing sediments.
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Denisov, M. S., and A. A. Egorov. "PROPERTIES OF WAVEFIELD EXTRAPOLATION OPERATORS (ON THE EXAMPLE OF PREDICTION OF GHOST REFLECTIONS)." Russian Journal of geophysical technologies 1, no. 1 (February 1, 2020): 33–59. http://dx.doi.org/10.18303/2619-1563-2019-1-33.
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Seismic deghosting algorithms involve wavefield extrapolation. The operator of such a transformation is integral, and when applied to discrete seismic data, its approximation is used, which corresponds to a method of numerical integration. The paper examines the limits of applicability of the approximation by the method of cells and the method of rectangles. It is shown that when processing 3D seismograms recorded using traditional survey geometries, correct ghost prediction is possible only after interpolation. When processing 2D seismic gathers, it is possible to predict and remove ghost waves for deep and shallow streamers. The streamer shape can be arbitrary. The results of the study and the conclusions made are valid not only for ghost prediction operators, but also for all seismic exploration tasks that involve wavefield extrapolation.
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Szmidt, Kazimierz. "On the SPH Approximations in Modeling Water Waves." Archives of Hydro-Engineering and Environmental Mechanics 60, no. 1-4 (October 1, 2014): 63–86. http://dx.doi.org/10.2478/heem-2013-0009.
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Abstract This paper presents an examination of approximation aspects of the Smoothed Particle Hydrodynamics (SPH) in modeling the water wave phenomenon. Close attention is paid on consistency of the SPH formulation and its relation with a correction technique applied to improve the method accuracy. The considerations are confined to flow fields within finite domains with a free surface and fixed solid boundaries with free slip boundary conditions. In spite of a wide application of the SPH method in fluid mechanics, the appropriate modeling of the boundaries is still not clear. For solid straight line boundaries, a natural way is to use additional (virtual, ghost) particles outside the boundary and take into account mirror reflection of associated field variables. Such a method leads to good results, except for a vicinity of solid horizontal bottoms where, because of the SPH approximations in the description of pressure, a stratification of the fluid material particles may occur. In order to illustrate the last phenomenon, some numerical tests have been made. These numerical experiments show that the solid fluid bottom attracts the material particles and thus, to prevent these particles from penetration into the bottom, a mutual exchange of positions of real and ghost particles has been used in a computation procedure.
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Long, Andrew, Guillaume Cambois, Gregg Parkes, Anders Mattsson, and Terje Lundsten. "A new seismic methodology to significantly improve deeper data character and interpretability on the North West Shelf." APPEA Journal 49, no. 2 (2009): 572. http://dx.doi.org/10.1071/aj08045.
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The sea-surface reflection generates interferences between up- and down-going waves that ultimately limit the bandwidth of marine seismic data. This phenomenon known as ghosting actually occurs twice—on the source side and on the receiver side. Ghost attenuation or elimination to increase the signal bandwidth has been the focus of extensive research. The receiver ghost can be removed using dual-sensor ocean-bottom devices (Barr and Sanders, 1989), a dual-sensor towed streamer (Carlson et al, 2007) or an over/under streamer acquisition (Brink and Svendsen, 1987). The over/under technique can also be used to remove the source ghost (Moldoveanu, 2000) but it requires flip-flop shooting of two sources at two different depths, ultimately halving the survey shot-point density. Alternatively, the source ghost can be attenuated using a beam steering technique originally developed some 60 years ago for dynamite land acquisition (Shock, 1950). The principle is to detonate charges at various depths in a sequence that constructively builds the down-going wave at the expense of the up-going wave. This way the energy of the ghost (the surface-reflected up-going wave) is reduced compared to that of the primary pulse. In this paper we adapt the beam steering approach to airgun arrays in the marine environment.
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Krohn, Christine E., and Thomas J. Murray. "Shallow near-surface effects." GEOPHYSICS 81, no. 5 (September 2016): T221—T231. http://dx.doi.org/10.1190/geo2016-0028.1.
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The top 6 m of the near surface has a surprisingly large effect on the behavior of P- and S-waves. For unconsolidated sediments, the P-wave velocity gradient and attenuation can be quite large. Computer modeling should include these properties to accurately reproduce seismic effects of the near surface. We have used reverse VSP data and computer simulations to demonstrate the following effects for upgoing P-waves. Near the surface, we have observed a large time delay, indicating low velocity ([Formula: see text]), and considerable pulse broadening, indicating high attenuation ([Formula: see text]). Consequently, shallowly buried geophones have greater high-frequency bandwidth compared with surface geophones. In addition, there is a large velocity gradient in the shallow near surface (factor of 10 in 5 m), resulting in the rotation of P-waves to the vertical with progressively smaller amplitudes recorded on horizontal phones. Finally, we have found little indication of a reflection or ghost from the surface, although downgoing reflections have been observed from interfaces within the near surface. In comparison, the following have been observed for upgoing S-waves: There is a small increase in the time delay or pulse broadening near the surface, indicating a smaller velocity gradient and less change in attenuation. In addition, the surface reflection coefficient is nearly one with a prominent surface ghost.
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GOGBERASHVILI, MERAB, and DOUGLAS SINGLETON. "ANTI-DE SITTER ISLAND-UNIVERSES FROM 5D STANDING WAVES." Modern Physics Letters A 25, no. 25 (August 20, 2010): 2131–43. http://dx.doi.org/10.1142/s021773231003358x.
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We construct simple standing wave solutions in a 5D spacetime with a ghost-like scalar field. The nodes of these standing waves are "islands" of 4D anti-de Sitter spacetime. In the case of increasing (decreasing) warp factor, there are a finite (infinite) number of nodes and thus a finite (infinite) number of anti-de Sitter island-universes having different gravitational and cosmological constants. This is similar to the landscape models, which postulate a large number of universes with different parameters.
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Pardo, Rosa, Alicia Martínez-González, and Víctor M. Pérez-García. "Nonlinear ghost waves accelerate the progression of high-grade brain tumors." Communications in Nonlinear Science and Numerical Simulation 39 (October 2016): 360–80. http://dx.doi.org/10.1016/j.cnsns.2016.03.014.
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Bogdanos, Charalampos, Salvatore Capozziello, Mariafelicia De Laurentis, and Savvas Nesseris. "Massive, massless and ghost modes of gravitational waves from higher-order gravity." Astroparticle Physics 34, no. 4 (November 2010): 236–44. http://dx.doi.org/10.1016/j.astropartphys.2010.08.001.
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Guo, Peng, Huimin Guan, and George A. McMechan. "Data- and model-domain up/down wave separation for reverse-time migration with free-surface multiples." Geophysical Journal International 223, no. 1 (June 18, 2020): 77–93. http://dx.doi.org/10.1093/gji/ggaa301.
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SUMMARY Seismic data recorded using a marine acquisition geometry contain both upgoing reflections from subsurface structures and downgoing ghost waves reflected back from the free surface. In addition to the ambiguity of propagation directions in the data, using the two-way wave equation for wavefield extrapolation of seismic imaging generates backscattered/turned waves when there are strong velocity contrasts/gradients in the model, which further increases the wavefield complexity. For reverse-time migration (RTM) of free-surface multiples, apart from unwanted crosstalk between inconsistent orders of reflections, image artefacts can also be formed along with the true reflector images from the overlapping of up/downgoing waves in the data and in the extrapolated wavefield. We present a wave-equation-based, hybrid (data- and model-domain) wave separation workflow, with vector seismic data containing pressure- and vertical-component particle velocity from dual-sensor seismic acquisition, for removing image artefacts produced by the mixture of up/downgoing waves. For imaging with free-surface multiples, the wavefield extrapolated from downgoing ghost events (reflected from the free surface) in the recorded data act as an effective source wavefield for one-order-higher free-surface multiples. Therefore, only the downgoing waves in the data should be used as the source wavefield for RTM with multiples; the recorded upgoing waves in the seismograms will be used for extrapolation of the time-reversed receiver wavefield. We use finite-difference (FD) injection for up/down separation in the data domain, to extrapolate the down- and upgoing waves of the common-source gathers for source and receiver wavefield propagation, respectively. The model-domain separation decomposes the extrapolated wavefield into upgoing (backscattered) and downgoing (transmitted) components at each subsurface grid location, to remove false images produced by cross-correlating backscattered waves along unphysical paths. We combine FD injection with the model-domain wavefield separation, for separating the wavefield into up- and downgoing components for the recorded data and for the extrapolated wavefields. Numerical examples using a simple model, and the Sigsbee 2B model, demonstrate that the hybrid up/down separation approach can effectively produce seismic images of free-surface multiples with better resolution and fewer artefacts.
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Si, Nan, Jinwon Park, and Alan J. Brown. "A Direct Ghost Fluid Method for Modeling Explosive Gas and Water Flows." Shock and Vibration 2022 (April 16, 2022): 1–19. http://dx.doi.org/10.1155/2022/1627382.
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This work presents a Direct Ghost Fluid Method (DGFM) as part of a two-fluid numerical framework suitable to model explosive gas and water flows resulting from underwater explosion (UNDEX). Due to the presence of explosive gas and water with shock waves in the modeling domain, classic Eulerian methods with inherent diffusion may not be effective. Numerical diffusion occurs due to nonphysical diffused density at material interfaces, which creates spurious pressure oscillations and significantly degrades the quality of the numerical results. To eliminate or minimize numerical diffusion, sharp interface methods having no mixed elements may be used in multifluid flow computations. The Direct Ghost Fluid Method (DGFM) described in this paper uses direct extrapolation of density (vice pressure) and tangential velocity from real to ghost fluid. The spurious pressure oscillations near the material interface are therefore minimized. One-, two-, and three-dimensional computational fluid dynamics (CFD) solvers that have DGFM as an essential part in their framework to model UNDEX interface conditions are developed, explored, and applied to the simulation of a series of benchmark problems. Excellent agreement is obtained among the simulations, the analytical solutions, and the experiments.
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Broggini, Filippo, Roel Snieder, and Kees Wapenaar. "Data-driven wavefield focusing and imaging with multidimensional deconvolution: Numerical examples for reflection data with internal multiples." GEOPHYSICS 79, no. 3 (May 1, 2014): WA107—WA115. http://dx.doi.org/10.1190/geo2013-0307.1.
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Standard imaging techniques rely on the single scattering assumption. This requires that the recorded data do not include internal multiples, i.e., waves that have bounced multiple times between reflectors before reaching the receivers at the acquisition surface. When multiple reflections are present in the data, standard imaging algorithms incorrectly image them as ghost reflectors. These artifacts can mislead interpreters in locating potential hydrocarbon reservoirs. Recently, we introduced a new approach for retrieving the Green’s function recorded at the acquisition surface due to a virtual source located at depth. We refer to this approach as data-driven wavefield focusing. Additionally, after applying source-receiver reciprocity, this approach allowed us to decompose the Green’s function at a virtual receiver at depth in its downgoing and upgoing components. These wavefields were then used to create a ghost-free image of the medium with either crosscorrelation or multidimensional deconvolution, presenting an advantage over standard prestack migration. We tested the robustness of our approach when an erroneous background velocity model is used to estimate the first-arriving waves, which are a required input for the data-driven wavefield focusing process. We tested the new method with a numerical example based on a modification of the Amoco model.
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Bartolo, Nicola, Purnendu Karmakar, Sabino Matarrese, and Mattia Scomparin. "Cosmic structures and gravitational waves in ghost-free scalar-tensor theories of gravity." Journal of Cosmology and Astroparticle Physics 2018, no. 05 (May 17, 2018): 048. http://dx.doi.org/10.1088/1475-7516/2018/05/048.
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Gandzha, Ivan S., and Vasyl P. Lukomsky. "On water waves with a corner at the crest." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 463, no. 2082 (March 28, 2007): 1597–614. http://dx.doi.org/10.1098/rspa.2007.1840.
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A highly accurate technique for calculating the parameters of the Stokes 120° gravity wave on deep water is proposed. Tanaka's nonlinear transformation of the inverse plane is used to stretch the region near the wave crest for accelerating the convergence of the classical Michell series. Several families of new irregular self-intersecting profiles with a 120° angle at the crest are presented as well. They all degenerate into the Stokes 120° profile as numerical accuracy increases. These solutions seem to represent some kind of the so-called parasitic (or ghost) solutions, which emerge due to discretization of the original continuous problem. Probable physical relevance of such irregular solutions is discussed. The validity of the Stokes theorem about a 120° angle is tested numerically. No solutions with crest angles different from 120° were found. Hence, the Stokes 120° wave seems to be the unique gravity wave with a corner at the crest.
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CAPOZZIELLO, SALVATORE, and MARIAFELICIA DE LAURENTIS. "FURTHER GRAVITATIONAL WAVE MODES FROM HIGHER ORDER GRAVITY." International Journal of Modern Physics: Conference Series 14 (January 2012): 260–69. http://dx.doi.org/10.1142/s2010194512007386.
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It is shown that linearizing higher order theories of gravity, further gravitational massive modes emerge. Besides massless spin-2, also spin-0 and spin-2 massive and ghost fields have to be considered. We investigate the possible detectability of such additional modes on the stochastic cosmic background of gravitational waves by ground-based and space interferometric detectors and calculate the detectable energy density of the spectrum. In conclusion, these massive modes could be of interest for direct detection by the forthcoming LISA experiment.
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Schuster, Gerard T., Fred Followill, Lewis J. Katz, Jianhua Yu, and Zhaojun Liu. "Autocorrelogram migration: Theory." GEOPHYSICS 68, no. 5 (September 2003): 1685–94. http://dx.doi.org/10.1190/1.1620642.
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We present the equations for migrating inverse‐vertical‐seismic‐profile‐while‐drilling and common‐midpoint autocorrelograms. These equations partly generalize the 1D autocorrelation imaging methods of Katz and Claerbout to 2D and 3D media, and also provide a formal mathematical procedure for imaging the reflectivity distribution from autocorrelograms. The imaging conditions are designed to migrate specific events in the autocorrelograms, either the direct‐primary correlations or the direct‐ghost correlations. Here, direct stands for direct wave, primary stands for primary reflections, and ghost denotes free‐surface ghost reflections. The main advantage in migrating autocorrelograms is that the source wavelet does not need to be known, which is the case for seismic data generated by a rotating drill bit or for vibroseis data with a corrupted pilot signal. Another advantage is that the source and receiver static problems are mitigated by autocorrelation migration. Two limitations are that autocorrelation of traces amplifies coherent noise such as surface waves, and produces undesirable coherent noise denoted as “virtual multiples.” Similar to “physical multiples,” such noise can, in principle, be partially suppressed by filtering and stacking of migration images obtained from many different shot gathers. Results with both synthetic and field data validate this conjecture, and show that autocorrelogram migration can be a viable alternative to standard migration when the source signal is not adequately known or there are severe static problems.
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Osen, Are, Lasse Amundsen, and Arne Reitan. "Removal of water‐layer multiples from multicomponent sea‐bottom data." GEOPHYSICS 64, no. 3 (May 1999): 838–51. http://dx.doi.org/10.1190/1.1444594.
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A method for suppressing water‐layer multiples in multicomponent sea‐floor measurements is presented. The multiple suppression technique utilizes the concept of wavefield separation into upgoing and downgoing modes just below the sea floor for eliminating the sea‐floor ghost, the sea‐surface ghost, and the accompanying water‐layer reverberations. The theory applies to each of the recorded components: pressure, vertical velocity, and horizontal velocities. The fundamental physical principle for the multiple suppression technique rests on identifying these multiples as downgoing waves just below the sea floor, while the primaries of interest arriving from the subsurface are upgoing waves. White presented this realization for the pressure component three decades ago; hence, the theory for the velocity field is an extension of the theory. In this paper, the theory is derived for an experiment with a marine source in the water layer above a locally flat, elastic sea floor with known elastic parameters. The method is otherwise multidimensional and operates on a shot‐to‐shot basis; hence, it is computationally fast. Aside from this, we show that this demultiple method removes the strongest multiples in sea‐floor data without knowledge of the source wavelet. Synthetic and real data examples are provided to illustrate the application of the algorithms to the pressure, in‐line velocity, and vertical velocity components. The numerical tests show that strong multiples have been attenuated on the pressure and the velocity recordings, producing promising results.
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Hussain, Fiaz, Ghulam Shabbir, Shabeela Malik, and Muhammad Ramzan. "Conformal vector fields for some vacuum classes of pp-waves space-times in ghost free infinite derivative gravity." International Journal of Geometric Methods in Modern Physics 18, no. 07 (March 18, 2021): 2150109. http://dx.doi.org/10.1142/s0219887821501097.
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The aim of this paper is to find conformal vector fields (CVFs) for some vacuum classes of the pp-waves space-times in the ghost free infinite derivative gravity (IDG). In order to find the CVFs of the above-mentioned space-times in the IDG, first, we deduce various classes of solutions by employing a classification procedure that in turn leads towards 10 cases. By reviewing each case thoroughly by direct integration technique, we find that there exists only one case for which the space-time admits proper CVFs whereas in rest of the cases, the space-time either becomes flat or it admits homothetic vector fields (HVFs) or Killing vector fields (KVFs). The overall dimension of CVFs for the pp-waves space-times in the IDG has turned out to be one, two, seven or fifteen.
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Tsai, Yuan-Shiang, and Der-Chang Lo. "A Ghost-Cell Immersed Boundary Method for Wave–Structure Interaction Using a Two-Phase Flow Model." Water 12, no. 12 (November 29, 2020): 3346. http://dx.doi.org/10.3390/w12123346.
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The air-water two-phase flow model is developed to study the transformation of monochromatic waves passing over the submerged structure. The level set method is employed to describe the motion of the interface while the effect of the immersed object on the fluid is resolved using the ghost-cell immersed boundary method. The computational domain integrated with the air-water and fluid-solid phases allows the use of uniform Cartesian grids. The model simulates the wave generation, wave decomposition over a submerged trapezoidal breakwater, and the formation of the vortices as well as the drag and lift forces caused by the surface waves over three different configurations of the submerged structures. The numerical results show the capability of the present model to accurately track the deformation of the free surface. In addition, the variation of the drag and lift forces depend on the wavelength and wave induced vortices around the submerged object. Hence, the study observes that the triangular structure experiences the relatively small wave force.
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Sanfirov, I. A., A. I. Babkin, and A. G. Yaroslavtsev. "Prospects for studies into transversal waves in salt rock mines." Mining informational and analytical bulletin, no. 7 (June 20, 2020): 45–63. http://dx.doi.org/10.25018/0236-1493-2020-7-0-45-63.
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The article discusses a disputable method proposed by some researchers (Zhukov, Prigara, 2019) for underground seismics with seismic images of transversal waves reflected from opposite sides. The conclusions on the behavior of the transversal waves in excitation of oscillations in underground excavations contradict to the numerous research findings obtained by different scientists in different seismic conditions. The reason for such contradictions lies in the erroneous idea of uniformity of rock mass enclosing underground openings. This idea neglects the actual conditions of excitation and recording of elastic waves, the great influence of the openings and the altered adjacent rock mass, as well as the velocity thin-layering. The validity of the method suggested for separation of oppositely directed wave fields recorded in the uniform space-and-time domain of a seismogram is evaluated. Artificiality of the wave fields in the upper and lower half-spaces due to admixture of ghost signals discordant to the geoseismic profile is demonstrated. Finally, the structure of the seismic cross-sections obtained by the suggested method contradicts both objective estimates of resolving power and the common geological understanding of the tectonic structure of a mineral deposit.
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Chen, Jun, and Yun-Xian Liu. "Theoretical study of ghost imaging with cold atomic waves under the condition of partial coherence." Journal of Physics: Conference Series 568, no. 1 (December 8, 2014): 012002. http://dx.doi.org/10.1088/1742-6596/568/1/012002.
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Sen, Malcolm. "Risk and Refuge: Contemplating Precarity in Irish Fiction." Irish University Review 49, no. 1 (May 2019): 13–31. http://dx.doi.org/10.3366/iur.2019.0376.
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Financial speculation and capitalist accumulation leave spatial and temporal traces. When the waves of the global financial collapse reached Ireland and culminated in the extreme measure of the comprehensive state guarantee, the receding excesses of the Celtic Tiger revealed a landscape that was gentrified and alienating. The spectrality of the ghost estates of Ireland became a synecdochal signifier of Ireland's ignominious fall from the podium of neoliberal grace and the focus of both popular lament and critical intervention. This essay provides a deferred assessment of the uncanniness of dwelling in post-Celtic Tiger Ireland by concentrating on the socioecological fallout of ruins and the longterm casualties of land speculation: that is, transformations of landscape into real estate, and of place into property. Reading Ireland's ghost estates as ‘imperial formations’ that ‘register the ongoing quality of processes of decimation, displacement, and reclamation’ – to use Ann Laura Stoler's term – the essay brings to the fore questions of dwelling and homeliness that suggest more protracted imperial processes which ‘saturate the subsoil of people's lives and persist, sometimes subjacently, over a longer durée’. To demonstrate these arguments the essay will analyse works by Kevin Barry, Sara Baume, and Claire Keegan.
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Aristodemo, Francesco, Domenico Davide Meringolo, and Paolo Veltri. "A MULTI-NODE APPROACH TO SIMULATE THIN COASTAL STRUCTURES IN THE SPH CONTEXT." Coastal Engineering Proceedings, no. 35 (June 23, 2017): 1. http://dx.doi.org/10.9753/icce.v35.structures.1.
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We propose an improvement in modeling solid boundary
conditions for 2D weakly-compressible Smoothed Particle Hydrodynamics (SPH) simulations for cases in
which the thickness of the body is small compared to the desired
particle size and the fluid surrounds the body from more than one
side. Specifically, the fixed ghost particles technique developed by
Marrone et al. (2011), based on interpolation nodes located within the
fluid domain, is here extended to a multi-node approach. The fluid
domain is thus divided into various sub-areas and an interpolation
node for the considered solid particle is associated to every
sub-area. Consequently, the solid particles present an array of
values interpolated at different sub-areas for the same physical
quantity. When a fluid particle located in a specific region
interacts with a multi-node fixed ghost particle, the last assumes
the field values interpolated in the reference area through the
associated node. The present modeling allows to adopt a coarser
spatial resolution to model the same physical problem, resulting in
a reduction of the computational cost.
The proposed solid boundary treatment is applied to horizontal decks and perforated
wall-caisson breakwaters subjected to regular waves. In this
context, an automatic hybrid diffusive formulation is introduced in order to prevent shock
waves during water impacts and preserve the hydrostatic pressure.
The formulation is obtained by defining a variable parameter
detecting the occurrence of relevant density gradients induced by
fluid impacts, resulting in an automatic switch between the two
formulations.
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Tratt, David M., John A. Hackwell, Bonnie L. Valant-Spaight, Richard L. Walterscheid, Lynette J. Gelinas, James H. Hecht, Charles M. Swenson, et al. "GHOST: A Satellite Mission Concept for Persistent Monitoring of Stratospheric Gravity Waves Induced by Severe Storms." Bulletin of the American Meteorological Society 99, no. 9 (September 2018): 1813–28. http://dx.doi.org/10.1175/bams-d-17-0064.1.
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AbstractThe prediction of tropical cyclone rapid intensification is one of the most pressing unsolved problems in hurricane forecasting. The signatures of gravity waves launched by strong convective updrafts are often clearly seen in airglow and carbon dioxide thermal emission spectra under favorable atmospheric conditions. By continuously monitoring the Atlantic hurricane belt from the main development region to the vulnerable sections of the continental United States at high cadence, it will be possible to investigate the utility of storm-induced gravity wave observations for the diagnosis of impending storm intensification. Such a capability would also enable significant improvements in our ability to characterize the 3D transient behavior of upper-atmospheric gravity waves and point the way to future observing strategies that could mitigate the risk to human life caused by severe storms. This paper describes a new mission concept involving a midinfrared imager hosted aboard a geostationary satellite positioned at approximately 80°W longitude. The sensor’s 3-km pixel size ensures that the gravity wave horizontal structure is adequately resolved, while a 30-s refresh rate enables improved definition of the dynamic intensification process. In this way the transient development of gravity wave perturbations caused by both convective and cyclonic storms may be discerned in near–real time.
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KOBAYASHI, Kazumichi, Yoshinori JINBO, and Hiroyuki TAKAHIRA. "Application of Multigrid Ghost Fluid Method to the Interaction of Shock Waves with Bubbles in Liquids." TRANSACTIONS OF THE JAPAN SOCIETY OF MECHANICAL ENGINEERS Series B 77, no. 773 (2011): 20–32. http://dx.doi.org/10.1299/kikaib.77.20.
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Jia, Xiyu, Shushan Wang, Jie Xu, Jingxiao Zhang, Yuan Gao, and Feng Ma. "Nonlinear characteristics and corrections of near-field underwater explosion shock waves." Physics of Fluids 34, no. 4 (April 2022): 046108. http://dx.doi.org/10.1063/5.0087939.
Full textAbstract:
The shock wave characteristics within the near-field are one of the most challenging aspects of understanding an underwater explosion. The latest numerical and experimental techniques were utilized to investigate the near-field pressure distribution and decay features after a shock disturbance. The governing equations in the numerical simulation were discretized with a fifth-order weighted essentially non-oscillatory scheme in space and a third-order Runge–Kutta scheme in time, and multi-medium interactions were defined and resolved via the modified ghost fluid method. The test system consisted of a synchronized high-speed framing camera and polyvinylidene fluoride (PVDF) sensors. Three identical spherical composition B charges were examined under the same test conditions, and the raw data from the high-speed camera were processed with edge detection and circle fitting techniques. The comparison showed that the high-speed camera image data, the PVDF signals, and the numerical computation results were highly consistent with each other. Higher-order correction terms were added to the pressure peak distribution model and the pressure decay model as nonlinear corrections based on further comprehensive and insightful analysis of the verified results. The corrected models not only fit with the near-field data but had better accuracy under the far-field condition as well.
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Dobson, Eleanor. "GODS AND GHOST-LIGHT: ANCIENT EGYPT, ELECTRICITY, AND X-RAYS." Victorian Literature and Culture 45, no. 1 (February 13, 2017): 119–35. http://dx.doi.org/10.1017/s1060150316000462.
Full textAbstract:
In 1892 the celebrated physicistand chemist William Crookes commented on the existence of “an almost infinite range of ethereal vibrations or electrical rays,” which he believed could revolutionize telegraphic communications (174). A few years later, and aided by Crookes's experiments with vacuums, the German physicist Wilhelm Röntgen successfully produced X-rays, a hitherto unrecorded form of electromagnetic radiation, which he tantalizingly described as “a new kind of invisible light” (Röntgen 413; Warner 256). Crookes was quick to speculate as to “the possibility of links between roentgen rays and the cerebral ganglia,” that an undiscovered organ in the brain might be “capable of transmitting and receiving . . . electrical rays” (Lyons 105; Crookes 176). X-rays, he thought, might prove a psychic counterpart to higher wavelength radio waves, allowing the transmission of messages telepathically rather than telegraphically, and even communication with the world of the spirits (Lyons 105). Crookes theorized that the parapsychological was intimately entwined with the findings of contemporary physics, occupying different zones of the same electromagnetic spectrum. An ardent Spiritualist, he believed that the ether, the “impalpable, invisible entity, by which all space is supposed to be filled” and which contained countless “channels of communication” also sustained “ghost-light . . . invisible to the naked eye” and acted as a medium that allowed “ethereal bodies to rise up” (Crookes 174; Warner 253–56). In other words, the matter through which light and electrical signals passed was envisaged as the same substance which allowed the spirits to fluctuate between visible and invisible forms. These links between the electromagnetic field and the occult, endorsed by Crookes and certain other members of his circles such as the Society for Psychical Research, anticipated turn-of-the-century associations between electricity, radiation and ancient Egypt which, through its reputation as the birthplace of magic, was central to Victorian conceptions of the supernatural.
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GUMRUKCUOGLU, A. E., C. LIN, and S. MUKOHYAMA. "SELF-ACCELERATING UNIVERSE IN NONLINEAR MASSIVE GRAVITY." Modern Physics Letters A 28, no. 03 (January 23, 2013): 1340016. http://dx.doi.org/10.1142/s0217732313400166.
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We discuss the self-accelerating universe solutions in the framework of the potentially ghost-free, nonlinear massive gravity theory recently proposed by de Rham–Gabadadze–Tolley. The theory allows general Friedmann–Robertson–Walker solutions with negative curvature. The contribution of the mass terms at the background level is an effective cosmological constant term depending on the parameters of the theory. We also discuss the cosmological perturbations in these backgrounds, as well as similar solutions of the extended versions of the theory; the actions of the scalar and vector degrees do not undergo a modification with respect to general relativity, while the two polarizations of gravity waves acquire a time-dependent effective mass term. This may lead to a modification of the stochastic gravitational wave spectrum.
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BINI, DONATO, SALVATORE CAPOZZIELLO, and GIAMPIERO ESPOSITO. "GRAVITATIONAL WAVES ABOUT CURVED BACKGROUNDS: A CONSISTENCY ANALYSIS IN DE SITTER SPACETIME." International Journal of Geometric Methods in Modern Physics 05, no. 07 (November 2008): 1069–83. http://dx.doi.org/10.1142/s0219887808003211.
Full textAbstract:
Gravitational waves are considered as metric perturbations about a curved background metric, rather than the flat Minkowski metric since several situations of physical interest can be discussed by this generalization. In this case, when the de Donder gauge is imposed, its preservation under infinitesimal spacetime diffeomorphisms is guaranteed if and only if the associated covector is ruled by a second-order hyperbolic operator which is the classical counterpart of the ghost operator in quantum gravity. In such a wave equation, the Ricci term has opposite sign with respect to the wave equation for Maxwell theory in the Lorenz gauge. We are, nevertheless, able to relate the solutions of the two problems, and the algorithm is applied to the case when the curved background geometry is the de Sitter spacetime. Such vector wave equations are studied in two different ways: (i) an integral representation, (ii) through a solution by factorization of the hyperbolic equation. The latter method is extended to the wave equation of metric perturbations in the de Sitter spacetime. This approach is a step towards a general discussion of gravitational waves in the de Sitter spacetime and might assume relevance in cosmology in order to study the stochastic background emerging from inflation.
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Chen, Songtao, Weiwen Zhao, and Decheng Wan. "On the scattering of focused wave by a finite surface-piercing circular cylinder: A numerical investigation." Physics of Fluids 34, no. 3 (March 2022): 035132. http://dx.doi.org/10.1063/5.0086826.
Full textAbstract:
For nonlinear wave–structure interactions, the high-frequency scattered waves can be identified within the drag-inertia regime, especially in steep incident waves where viscous effects are not negligible. According to previous studies, this unexpected phenomenon is highly associated with the local flow field, posing challenges to the existing harmonic-based diffraction solutions (mostly up to second-order). To overcome these shortcomings in potential flows, we establish a high-fidelity numerical wave tank to solve this two-phase free surface flow in the open source computational fluid dynamics framework OpenFOAM. We implement the ghost fluid method to eliminate the spurious velocities, mostly reported in two-phase volume of fluid solvers, in the vicinity of the free surface and preserve a sharp air–water interface. A modified generating–absorbing boundary condition is employed to achieve high computational efficiency without passive relaxation zones. Good agreement with experimental data demonstrates the reliability and accuracy of the present numerical wave tank in extreme wave conditions. On this basis, this paper numerically investigates the wave scattering of the focused wave by a finite surface-piercing circular cylinder, with emphasis on the flow mechanism. Three types of high-frequency scattered waves are identified in the near field, namely, Type-1, Type-2, and Type-1* waves. The typical mechanisms of each type are analyzed in depth with detailed flow field data, which confirms and complements the observations from previous experiments. More importantly, the primary vortical structures involved in scattering are extracted by the Liutex vortex identification method. The behaviors of these vortical structures could characterize the evolution of the high-frequency scattered waves and provide new insights into this strongly nonlinear phenomenon. An overall schematic of the wave scattering evolution in this complex condition is summarized for a straightforward understanding.
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Galbreath, Kurt E., Heather M. Toman, Chenhong Li, and Eric P. Hoberg. "When parasites persist: tapeworms survive host extinction and reveal waves of dispersal across Beringia." Proceedings of the Royal Society B: Biological Sciences 287, no. 1941 (December 23, 2020): 20201825. http://dx.doi.org/10.1098/rspb.2020.1825.
Full textAbstract:
Investigations of intercontinental dispersal between Asia and North America reveal complex patterns of geographic expansion, retraction and isolation, yet historical reconstructions are largely limited by the depth of the record that is retained in patterns of extant diversity. Parasites offer a tool for recovering deep historical insights about the biosphere, improving the resolution of past community-level interactions. We explored biogeographic hypotheses regarding the history of dispersal across Beringia, the region intermittently linking Asia and North America, through large-scale multi-locus phylogenetic analyses of the genus Schizorchis , an assemblage of host-specific cestodes in pikas (Lagomorpha: Ochotonidae). Our genetic data support palaeontological evidence for two separate geographic expansions into North America by Ochotona in the late Tertiary, a history that genomic evidence from extant pikas does not record. Pikas descending from the first colonization of Miocene age persisted into the Pliocene, subsequently coming into contact with a second wave of Nearctic colonists from Eurasia before going extinct. Spatial and temporal overlap of historically independent pika populations provided a window for host colonization, allowing persistence of an early parasite lineage in the contemporary fauna following the extinction of its ancestral hosts. Empirical evidence for ancient ‘ghost assemblages' of hosts and parasites demonstrates how complex mosaic faunas are assembled in the biosphere through episodes of faunal mixing encompassing parasite lineages across deep and shallow time.
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Gao, Si, and Tiegang Liu. "1D Exact Elastic-Perfectly Plastic Solid Riemann Solver and Its Multi-Material Application." Advances in Applied Mathematics and Mechanics 9, no. 3 (January 17, 2017): 621–50. http://dx.doi.org/10.4208/aamm.2015.m1340.
Full textAbstract:
AbstractThe equation of state (EOS) plays a crucial role in hyperbolic conservation laws for the compressible fluid. Whereas, the solid constitutive model with elastic-plastic phase transition makes the analysis of the solid Riemann problem more difficult. In this paper, one-dimensional elastic-perfectly plastic solid Riemann problem is investigated and its exact Riemann solver is proposed. Different from previous works treating the elastic and plastic phases integrally, we resolve the elastic wave and plastic wave separately to understand the complicate nonlinear waves within the solid and then assemble them together to construct the exact Riemann solver for the elastic-perfectly plastic solid. After that, the exact solid Riemann solver is associated with the fluid Riemann solver to decouple the fluid-solid multi-material interaction. Numerical tests, including gas-solid, water-solid high-speed impact problems are simulated by utilizing the modified ghost fluid method (MGFM).
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Deiterding, Ralf. "High-Resolution Numerical Simulation and Analysis of Mach Reflection Structures in Detonation Waves in Low-Pressure H2–O2–Ar Mixtures: A Summary of Results Obtained with the Adaptive Mesh Refinement Framework AMROC." Journal of Combustion 2011 (2011): 1–18. http://dx.doi.org/10.1155/2011/738969.
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Numerical simulation can be key to the understanding of the multidimensional nature of transient detonation waves. However, the accurate approximation of realistic detonations is demanding as a wide range of scales needs to be resolved. This paper describes a successful solution strategy that utilizes logically rectangular dynamically adaptive meshes. The hydrodynamic transport scheme and the treatment of the nonequilibrium reaction terms are sketched. A ghost fluid approach is integrated into the method to allow for embedded geometrically complex boundaries. Large-scale parallel simulations of unstable detonation structures of Chapman-Jouguet detonations in low-pressure hydrogen-oxygen-argon mixtures demonstrate the efficiency of the described techniques in practice. In particular, computations of regular cellular structures in two and three space dimensions and their development under transient conditions, that is, under diffraction and for propagation through bends are presented. Some of the observed patterns are classified by shock polar analysis, and a diagram of the transition boundaries between possible Mach reflection structures is constructed.
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Okafor, Chukwuemeka, and JohnMary K. Ani. "The National Youth Service Corps Programme and Growing Security Threat in Nigeria." Africa’s Public Service Delivery and Performance Review 2, no. 2 (June 1, 2014): 149. http://dx.doi.org/10.4102/apsdpr.v2i2.56.
Full textAbstract:
The National Youth Service Corps (NYSC) was established in 1973 after the Nigerian civil war to involve Nigerian university graduates below the age of thirty in nation building. Gradually, the scheme was opened-up for polytechnic graduates. The article presents the objectives and deployment policy of the programme. It shows that the early phase of the programme recorded the problems of corruption, ghost corps members, accommodation, language barriers as well as hostile culture. However, the contemporary Nigerian society has been overtaken by the destructive wind of insecurity. The article reveals that the various waves of political violence in the country, including Boko Haram terrorism, hostage crises, and geographical threats have turned into a collection of overwhelming menace to the programme, thereby leading to massive agitation for itabrogation. The article recommends for multiple series of reforms in order to protect the lives of many Nigerian graduates that are building the nation through this admirable development programme.
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Si, Nan, and Alan Brown. "A Framework of Runge–Kutta, Discontinuous Galerkin, Level Set and Direct Ghost Fluid Methods for the Multi-Dimensional Simulation of Underwater Explosions." Fluids 7, no. 1 (December 29, 2021): 13. http://dx.doi.org/10.3390/fluids7010013.
Full textAbstract:
This work describes the development of a hybrid framework of Runge–Kutta (RK), discontinuous Galerkin (DG), level set (LS) and direct ghost fluid (DGFM) methods for the simulation of near-field and early-time underwater explosions (UNDEX) in early-stage ship design. UNDEX problems provide a series of challenging issues to be solved. The multi-dimensional, multi-phase, compressible and inviscid fluid-governing equations must be solved numerically. The shock front in the solution field must be captured accurately while maintaining the total variation diminishing (TVD) properties. The interface between the explosive gas and water must be tracked without letting the numerical diffusion across the material interface lead to spurious pressure oscillations and thus the failure of the simulation. The non-reflecting boundary condition (NRBC) must effectively absorb the wave and prevent it from reflecting back into the fluid. Furthermore, the CFD solver must have the capability of dealing with fluid–structure interactions (FSI) where both the fluid and structural domains respond with significant deformation. These issues necessitate a hybrid model. In-house CFD solvers (UNDEXVT) are developed to test the applicability of this framework. In this development, code verification and validation are performed. Different methods of implementing non-reflecting boundary conditions (NRBCs) are compared. The simulation results of single and multi-dimensional cases that possess near-field and early-time UNDEX features—such as shock and rarefaction waves in the fluid, the explosion bubble, and the variation of its radius over time—are presented. Continuing research on two-way coupled FSI with large deformation is introduced, and together with a more complete description of the direct ghost fluid method (DGFM) in this framework will be described in subsequent papers.
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Wu, C. H., O. M. Faltinsen, and B. F. Chen. "Time-Independent Finite Difference and Ghost Cell Method to Study Sloshing Liquid in 2D and 3D Tanks with Internal Structures." Communications in Computational Physics 13, no. 3 (March 2013): 780–800. http://dx.doi.org/10.4208/cicp.261011.020212s.
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AbstractA finite difference scheme with ghost cell technique is used to study viscous fluid sloshing in 2D and 3D tanks with internal structures. The Navier-Stokes equations in a moving coordinate system are derived and they are mapped onto a time-independent and stretched domain. The staggered grid is used and the revised SIMPLEC iteration algorithm is performed. The developed numerical model is rigorously validated by extensive comparisons with reported analytical, numerical and experimental results. The present numerical results were also validated through an experiment setup with a tank excited by an inclined horizontal excitation or a tank mounted by a vertical baffle. The method is then applied to a number of problems including sloshing fluid in a 2D tank with a bottom-mounted baffle and in a 3D tank with a vertical plate. The phenomena of diagonal sloshing waves affected by a vertical plate are investigated in detail in this work. The effects of internal structures on the resonant frequency of a tank with liquid are discussed and the present developed numerical method can successfully analyze the sloshing phenomenon in 2D or 3D tanks with internal structures.
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Florea, Bogdan Mihai. "Bandit: Here to Haunt You! On Why I Became an Émigré Theatre Maker." Art History & Criticism 15, no. 1 (December 1, 2019): 131–44. http://dx.doi.org/10.2478/mik-2019-0010.
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Summary The article employs concepts of time lag, inspired by Ernst Bloch, and ghost and haunting, borrowed from Jacques Derrida. It also draws on Svetlana Boym’s and Vilém Flusser’s vision of the émigré and on Dominick LaCapra’s and Slavoj Žižek’s interpretations of trauma. The analysis is also informed by Karen Jürs-Munby’s and Cathy Caruth’s views on trauma and its representation in theatre. This critical apparatus is put into motion in the particular context of BANDIT: a theatre project developed in the UK by two Romanian émigré theatre-makers. The main focus is on exposing links between the references to trauma contained in the theatre piece BANDIT and the makers’ self-imposed artistic exile in the UK. The article seeks to answer the following question: what has pushed us, the makers of BANDIT, to leave our native country and what is our (new) role (as artists) in the country of emigration? The discussion is carried out within the wider context of the vast waves of Romanian emigration to Western Europe (after the fall of the Iron Curtain). The article critiques the troublesome relation of the contemporary Romanian society to its Communist past and the apparent inability and/or unwillingness to deal with the repressed/traumatic memories of that past. Analysis of BANDIT as performance of lingering trauma also references the historical Percentages agreement between Stalin and Churchill—the informal agreement that established spheres of influence in Europe at the end of the Second World War. Identifying the Iron Curtain as the epicentre of traumatic memory for Eastern Europeans, the discussion about BANDIT also makes a reference to Communist crimes against political prisoners committed in Romanian prisons in 1951–1952, put in parallel with the toxic EU referendum campaign in the UK in 2016. Underpinned by Derrida’s thinking, the article explains how the Romanian émigré-artist (as a paragon of the Romanian / Eastern European émigré in general) has to fashion herself into a ghost that haunts the adoptive culture, using artistic exile as a platform for processing the traumatic memories of an unresolved past.
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NIKI, Kazuhiro, Yoshinori JINBO, and Hiroyuki TAKAHIRA. "The Two-Dimensional Direct Numerical Simulations of the Propagation of Pressure Waves in Gas-Liquid Two-Phase Flows with the Ghost Fluid Method." JAPANESE JOURNAL OF MULTIPHASE FLOW 25, no. 5 (2012): 459–67. http://dx.doi.org/10.3811/jjmf.25.459.
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de Rham, Claudia, Sebastian Garcia-Saenz, Lavinia Heisenberg, and Victor Pozsgay. "Cosmology of Extended Proca-Nuevo." Journal of Cosmology and Astroparticle Physics 2022, no. 03 (March 1, 2022): 053. http://dx.doi.org/10.1088/1475-7516/2022/03/053.
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Abstract Proca-Nuevo is a non-linear theory of a massive spin-1 field which enjoys a non-linearly realized constraint that distinguishes it among other generalized vector models. We show that the theory may be extended by the addition of operators of the Generalized Proca class without spoiling the primary constraint that is necessary for consistency, allowing to interpolate between Generalized Proca operators and Proca-Nuevo ones. The constraint is maintained on flat spacetime and on any fixed curved background. Upon mixing extended Proca-Nuevo dynamically with gravity, we show that the constraint gets broken in a Planck scale suppressed way. We further prove that the theory may be covariantized in models that allow for consistent and ghost-free cosmological solutions. We study the models in the presence of perfect fluid matter, and show that they describe the correct number of dynamical variables and derive their dispersion relations and stability criteria. We also exhibit, in a specific set-up, explicit hot Big Bang solutions featuring a late-time self-accelerating epoch, and which are such that all the stability and subluminality conditions are satisfied and where gravitational waves behave precisely as in General Relativity.
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Porębska, Anna, Krzysztof Barnaś, Bartosz Dendura, Olga Kania, Marta Łukasik, Aleksandra Rogulska, Ernestyna Szpakowska-Loranc, and Miłosz Zieliński. "Lockdown in a disneyfied city: Kraków Old Town and the first wave of the Covid-19 pandemic." URBAN DESIGN International 26, no. 4 (October 4, 2021): 315–31. http://dx.doi.org/10.1057/s41289-021-00175-5.
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AbstractThis paper presents the geography of the historic central district of Kraków, Poland before, during and after the first wave of the 2020 pandemic. It describes how the disneyfied main part of the UNESCO heritage site of universal values turned into a ghost town as functional changes were turning into physical ones amid restrictions. From the results of pre-pandemic processes (that, as we argue, turned the city into its disneyfied version), to the lockdown (that later revealed itself to be but the first one in a row), to the post-lockdown recovery, these changes are presented in modified figure-ground diagrams with accessibility being defined by both tangible and intangible properties. The results are set against the background of the city’s current policies regarding economic recovery, mobility and accessibility to urban green areas. As an attempt to address the present vulnerability of the once resilient historic city centres—of which Kraków Old Town is a luminous example—this paper tends to be a voice in the debate on the post-2020 planning and the strategies we will need to face the subsequent waves of this, or other, pandemics as well as consequences of climate change.
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Petersson, N. Anders, and Björn Sjögreen. "Super-Grid Modeling of the Elastic Wave Equation in Semi-Bounded Domains." Communications in Computational Physics 16, no. 4 (October 2014): 913–55. http://dx.doi.org/10.4208/cicp.290113.220514a.
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AbstractWe develop a super-grid modeling technique for solving the elastic wave equation in semi-bounded two- and three-dimensional spatial domains. In this method, waves are slowed down and dissipated in sponge layers near the far-field boundaries. Mathematically, this is equivalent to a coordinate mapping that transforms a very large physical domain to a significantly smaller computational domain, where the elastic wave equation is solved numerically on a regular grid. To damp out waves that become poorly resolved because of the coordinate mapping, a high order artificial dissipation operator is added in layers near the boundaries of the computational domain. We prove by energy estimates that the super-grid modeling leads to a stable numerical method with decreasing energy, which is valid for heterogeneous material properties and a free surface boundary condition on one side of the domain. Our spatial discretization is based on a fourth order accurate finite difference method, which satisfies the principle of summation by parts. We show that the discrete energy estimate holds also when a centered finite difference stencil is combined with homogeneous Dirichlet conditions at several ghost points outside of the far-field boundaries. Therefore, the coefficients in the finite difference stencils need only be boundary modified near the free surface. This allows for improved computational efficiency and significant simplifications of the implementation of the proposed method in multi-dimensional domains. Numerical experiments in three space dimensions show that the modeling error from truncating the domain can be made very small by choosing a sufficiently wide super-grid damping layer. The numerical accuracy is first evaluated against analytical solutions of Lamb’s problem, where fourth order accuracy is observed with a sixth order artificial dissipation. We then use successive grid refinements to study the numerical accuracy in the more complicated motion due to a point moment tensor source in a regularized layered material.
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Pedrol de Freitas, Giovana, Heitor Francischini, Frederico Tapajós de Souza Tâmega, Paula Spotorno-Oliveira, and Paula Dentzien-Dias. "On ex situ Ophiomorpha and other burrow fragments from the Rio Grande do Sul Coastal Plain, Brazil: paleobiological and taphonomic remarks." Journal of Paleontology 94, no. 6 (May 27, 2020): 1148–64. http://dx.doi.org/10.1017/jpa.2020.29.
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AbstractThe Rio Grande do Sul Coastal Plain (southern Brazil) is composed of extensive marine and continental deposits related to at least four lagoon-barrier systems of Pleistocene−Holocene age. Part of these deposits is currently submerged and passing through erosion processes by waves. Vertebrate and invertebrate body and trace fossils are constantly exhumed from these deposits and redeposited on the modern beach face. Among them, a total of 253 fragments of crustacean burrows were collected for this study. Two ichnospecies of Ophiomorpha Lundgren, 1891 were recognized (O. nodosa Lundgren, 1891 and O. puerilis Gibert et al., 2006), but most of the materials can only be assigned to the ‘SOT’ group (Spongeliomorpha de Saporta, 1887, Ophiomorpha, and Thalassinoides Ehrenberg, 1944), mainly because of the lack of a pelleted lining. The absence of pellets and, as a consequence, the ichnotaxonomy of these specimens, is related to taphonomical processes (exhumation, reworking, and transportation) that acted during formation of the ex situ assemblage. The paleoenvironmental dynamics and a taphonomical model are presented to demonstrate how these processes affected the trace fossils since their construction, through exhumation until deposition. Neoichnological observations led us to infer larger producers in comparison to the extant ghost shrimp Sergio mirim (Rodrigues, 1971).