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Journal articles on the topic 'Media and migration'

Author: Grafiati

Published: 4 June 2021

Last updated: 17 February 2022

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1

Vestrum, Robert W., Don C. Lawton, and Ron Schmid. "Imaging structures below dipping TI media." GEOPHYSICS 64, no. 4 (July 1999): 1239–46. http://dx.doi.org/10.1190/1.1444630.

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Seismic anisotropy in dipping shales causes imaging and positioning problems for underlying structures. We developed an anisotropic depth‐migration approach for P-wave seismic data in transversely isotropic (TI) media with a tilted axis of symmetry normal to bedding. We added anisotropic and dip parameters to the depth‐imaging velocity model and used prestack depth‐migrated image gathers in a diagnostic manner to refine the anisotropic velocity model. The apparent position of structures below dipping anisotropic overburden changes considerably between isotropic and anisotropic migrations. The ray‐tracing algorithm used in a 2-D prestack Kirchhoff depth migration was modified to calculate traveltimes in the presence of TI media with a tilted symmetry axis. The resulting anisotropic depth‐migration algorithm was applied to physical‐model seismic data and field seismic data from the Canadian Rocky Mountain Thrust and Fold Belt. The anisotropic depth migrations offer significant improvements in positioning and reflector continuity over those obtained using isotropic algorithms.

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2

Gardels, Nathan. "Migration, Media, Modus Vivendi." New Perspectives Quarterly 18, no. 2 (June 28, 2008): 2–3. http://dx.doi.org/10.1111/0893-7850.00311.

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3

Alkhalifah, Tariq, and Ken Larner. "Migration error in transversely isotropic media." GEOPHYSICS 59, no. 9 (September 1994): 1405–18. http://dx.doi.org/10.1190/1.1443698.

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Most migration algorithms today are based on the assumption that the earth is isotropic, an approximation that is often not valid and thus can lead to position errors on migrated images. Here, we compute curves of such position error as a function of reflector dip for transversely isotropic (TI) media characterized by Thomsen’s anisotropy parameters δ and ε. Depending on whether the migration velocity is derived from stacking velocity or vertical root‐mean‐square (rms) velocity, we find quite contrary sensitivities of the error behavior to the values of δ and ε. Likewise error‐versus‐dip behavior depends in a complicated way on vertical velocity gradient and vertical time, as well as orientation of the symmetry axis. Moreover, error behavior is dependent on just how δ and ε vary with depth. In addition to presenting such error curves, we show migrations of synthetic data that exemplify the mispositioning that results from ignoring anisotropy for P‐wave data. When migration is done using velocities derived from stacking velocity and when medium velocity increases with depth at rates typically encountered in practice, δ alone is sufficient to describe the position error. This is fortunate since the value of δ, unlike ε, can be obtained from combined vertical seismic profile (VSP) and surface seismic data. In contrast, when the migration velocity is obtained from the vertical rms velocity, the position errors depend strongly on ε, suggesting the importance of having an accurate estimate of ε when using an anisotropic migration algorithm.

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4

Yue, Yubo, Paul Sava, Zhongping Qian, Jidong Yang, and Zhen Zou. "Least-squares Gaussian beam migration in elastic media." GEOPHYSICS 84, no. 4 (July 1, 2019): S329—S340. http://dx.doi.org/10.1190/geo2018-0391.1.

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Gaussian beam migration (GBM) is an effective imaging method that has the ability to image multiple arrivals while preserving the advantages of ray-based methods. We have extended this method to linearized least-squares imaging for elastic waves in isotropic media. We have dynamically transformed the multicomponent data to the principal components of different wave modes using the polarization information available in the beam migration process, and then we use Gaussian beams as wavefield propagator to construct the forward modeling and adjoint migration operators. Based on the constructed operators, we formulate a least-squares migration scheme that is iteratively solved using a preconditioned conjugate gradient method. With this method, we can obtain crosstalk-attenuated multiwave images with better subsurface illumination and higher resolution than those of the conventional elastic Gaussian beam migration. This method also allows us to achieve a good balance between computational cost and imaging accuracy, which are both important requirements for iterative least-squares migrations. Numerical tests on two synthetic data sets demonstrate the validity and effectiveness of our proposed method.

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5

Robson, Elsbeth. "Global children, global media: migration, media and childhood." Children's Geographies 8, no. 1 (January 25, 2010): 87–88. http://dx.doi.org/10.1080/14733280903500208.

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6

Zhu, Tianfei, Samuel H. Gray, and Daoliu Wang. "Prestack Gaussian-beam depth migration in anisotropic media." GEOPHYSICS 72, no. 3 (May 2007): S133—S138. http://dx.doi.org/10.1190/1.2711423.

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Gaussian-beam depth migration is a useful alternative to Kirchhoff and wave-equation migrations. It overcomes the limitations of Kirchhoff migration in imaging multipathing arrivals, while retaining its efficiency and its capability of imaging steep dips with turning waves. Extension of this migration method to anisotropic media has, however, been hampered by the difficulties in traditional kinematic and dynamic ray-tracing systems in inhomogeneous, anisotropic media. Formulated in terms of elastic parameters, the traditional anisotropic ray-tracing systems aredifficult to implement and inefficient for computation, especially for the dynamic ray-tracing system. They may also result inambiguity in specifying elastic parameters for a given medium.To overcome these difficulties, we have reformulated the ray-tracing systems in terms of phase velocity.These reformulated systems are simple and especially useful for general transversely isotropic and weak orthorhombic media, because the phase velocities for these two types of media can be computed with simple analytic expressions. These two types of media also represent the majority of anisotropy observed in sedimentary rocks. Based on these newly developed ray-tracing systems, we have extended prestack Gaussian-beam depth migration to general transversely isotropic media. Test results with synthetic data show that our anisotropic, prestack Gaussian-beam migration is accurate and efficient. It produces images superior to those generated by anisotropic, prestack Kirchhoff migration.

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7

Yue, Yubo, Yujin Liu, Yaonan Li, and Yunyan Shi. "Least-squares Gaussian beam migration in viscoacoustic media." GEOPHYSICS 86, no. 1 (December 16, 2020): S17—S28. http://dx.doi.org/10.1190/geo2020-0129.1.

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Because of amplitude decay and phase dispersion of seismic waves, conventional migrations are insufficient to produce satisfactory images using data observed in highly attenuative geologic environments. We have developed a least-squares Gaussian beam migration method for viscoacoustic data imaging, which can not only compensate for amplitude decay and phase dispersion caused by attenuation, but it can also improve image resolution and amplitude fidelity through linearized least-squares inversion. We represent the viscoacoustic Green’s function by a summation of Gaussian beams, in which an attenuation traveltime is incorporated to simulate or compensate for attenuation effects. Based on the beam representation of the Green’s function, we construct the viscoacoustic Born forward modeling and adjoint migration operators, which can be effectively evaluated by a time-domain approach based on a filter-bank technique. With the constructed operators, we formulate a least-squares migration scheme to iteratively solve for the optimal image. Numerical tests on synthetic and field data sets demonstrate that our method can effectively compensate for the attenuation effects and produce images with higher resolution and more balanced amplitudes than images from acoustic least-squares Gaussian beam migration.

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8

Datts, Mario. "Social Media, Populism, and Migration." Media and Communication 8, no. 4 (October 8, 2020): 73–83. http://dx.doi.org/10.17645/mac.v8i4.3212.

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Several scholars have attributed high hopes to social media regarding their alleged ability to enable a nonhierarchical and freely accessible debate among the citizenship (Loader & Mercea, 2011; Shirky, 2011). Those hopes have culminated in theses such those describing the social web as being a ‘new public sphere’ (Castells, 2009, p. 125) as well as in expectations regarding its revitalizing potential for the ‘Habermas’s public sphere’ (Kruse, Norris, & Flinchum, 2018, p. 62). Yet, these assumptions are not uncontested, particularly in the light of socially mediated populism (Mazzoleni & Bracciale, 2018). Interestingly, research on populism in the social web is still an exception. The same is true for the populist permeation of the social media discourse on migration, as a highly topical issue. This study seeks to elaborate on this research gap by examining to what extent the Twitter debate on the Global Compact for Safe, Orderly, and Regular Migration (GCM) was permeated by populist content. For this purpose, almost 70,000 tweets on the most important Hashtags referring to the GCM that took place in Marrakesh in December 2018 were collected and the 500 widest-reaching tweets analysed in terms of their populist permeation. Against initial expectations, the empirical findings show that populist narratives did not dominate the Twitter debate on migration. However, the empirical results indicate that ordinary citizens play an important role in the creation and dissemination of populist content. It seems that the social web widens the public sphere, including those actors who do not communicate in accordance with the Habermasian conceptualization of it.

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9

Balabanova, Ekaterina, and Ruxandra Trandafoiu. "Media, migration and human rights." Journal of Language and Politics 19, no. 3 (March 24, 2020): 379–90. http://dx.doi.org/10.1075/jlp.20007.bal.

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10

Nossal, Ralph, J. Kiefer, G. H. Weiss, R. Bonner, H. Taitelbaum, and S. Havlin. "Photon migration in layered media." Applied Optics 27, no. 16 (August 15, 1988): 3382. http://dx.doi.org/10.1364/ao.27.003382.

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11

Sharma, M. M., and Y. C. Yortsos. "Fines migration in porous media." AIChE Journal 33, no. 10 (October 1987): 1654–62. http://dx.doi.org/10.1002/aic.690331009.

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12

Havlin, S., R. Nossal, B. Trus, and G. H. Weiss. "Photon migration in disordered media." Physical Review A 45, no. 10 (May 1, 1992): 7511–19. http://dx.doi.org/10.1103/physreva.45.7511.

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13

Maeland, E. "Seismic migration in stratified media." IEEE Transactions on Geoscience and Remote Sensing 29, no. 5 (1991): 798–800. http://dx.doi.org/10.1109/36.83998.

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14

Tian, Baoqing, and Jiangjie Zhang. "Migration in orthorhombic media: A prestack time-migration approach." GEOPHYSICS 84, no. 5 (September 1, 2019): C217—C227. http://dx.doi.org/10.1190/geo2018-0552.1.

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High-resolution imaging has become more popular recently in exploration geophysics. Conventionally, geophysicists image the subsurface using the isotropy approximation. When considering the anisotropy effects, one can expect to obtain an imaging profile with higher accuracy than the isotropy approach allows. Orthorhombic anisotropy is considered an ideal approximation in the realistic case. It has been used in the industry for several years. Although being attractive, broad application of orthorhombic anisotropy has many problems to solve. We have developed a novel approach of prestack time migration in the orthorhombic case. The traveltime and amplitude of a wave propagating in orthorhombic media are calculated directly by launching new anisotropic velocity and anisotropic parameters. We validate our methods with synthetic data. We also highlight our methods with model data set and real data. The results found that our methods work well for prestack time migration in orthorhombic media.

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15

GÜÇLÜTEN, Çağrı, and Sedat CERECİ. "MEDIA AT MIGRATION CRIME AND LAW TRIANGLE: MIGRATION CITIES." IEDSR Association 6, no. 11 (February 24, 2021): 319–28. http://dx.doi.org/10.46872/pj.244.

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In this study, based on some striking examples, migration, which is one of the biggest problems of the modern age, and the relationship of crime in expanding cities have been investigated and the impact of immigration on crime, the legal regulations in this context and the media reflections of migration and crime relations, and the legal regulations in the expanding cities via migration have been evaluated. Increasing tension, conflicts, wars, hunger, poverty, economic imbalance, oppression, inequality and unrest based on religion, sects, and culture in the world have increased migration and caused many more problems. The borders that states have determined regarding their sovereign rights over their countries have brought along problems related to the issue of immigration, although they exist throughout history. The severe violations of human rights caused by the torture and deaths experienced during the Second World War caused population mobility all over the world and as a result, the issue of migration has become an important agenda item in our recent history. While international organizations and states try to solve the problems arising from immigration with legal regulations, they cannot keep up with the pace of the problems caused by migration and the increase in crime rates. In this context, the problems faced by immigrants who take their cultural luggage with them to the destination country, especially xenophobia, make the lives of immigrants difficult and at the same time position them in the world of others. From this point of view, cities that grow with migration reach a cosmopolitan structure, if not metropolitan, and transform into places of necessary living, dissatisfaction and chaos. Unemployment, incompatibility, unrest, conflict and problems are experienced to a great extent in overgrown cities. Legal regulations have been insufficient.

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16

Larner, Ken, and Craig Beasley. "Cascaded migrations: Improving the accuracy of finite‐difference migration." GEOPHYSICS 52, no. 5 (May 1987): 618–43. http://dx.doi.org/10.1190/1.1442331.

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The accuracy of time migrations done with finite‐difference schemes deteriorates with increasing reflector dip. Some properties of migration in general, and of finite‐difference approaches in particular, suggest a way of improving the accuracy of finite‐difference schemes for migrating steep dips. First, although data will be undermigrated when too low a velocity is used in migration, a correctly migrated result can be obtained by migrating again, this time with the previously undermigrated result as input. In fact, a sequence of undermigrations will yield the correct result as long as the sum of the squares of the migration velocities used in the different migration stages equals the square of the correct migration velocity. A second property is that the apparent spatial dip of a reflector perceived by the migration process is a function of not only the time dip of the unmigrated reflection, but also the velocity used in the migration. In a sequence of low‐velocity migrations, the apparent spatial dip perceived at each migration stage can be considerably less than the true dip. Thus, because finite‐difference migration is accurate for small spatial dips, the cascaded migrations yield a more accurate result than that of single‐stage migration. Also, because each migration stage is done with low velocity, the depth step can be large; hence, the computational effort need not be. The accuracy of the method is not compromised (in fact, it improves) in media in which velocity increases with depth. Moreover, the cascaded approach suffers no more than other methods of time migration where velocity varies mildly in the lateral direction. In applications of the method to stacked data from the Gulf of Mexico, reflections from near‐vertical flanks of salt domes were migrated with accuracy comparable to that achieved by frequency‐wavenumber domain migration.

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17

Xu, Sheng, Hervé Chauris, Gilles Lambaré, and Mark Noble. "Common‐angle migration: A strategy for imaging complex media." GEOPHYSICS 66, no. 6 (November 2001): 1877–94. http://dx.doi.org/10.1190/1.1487131.

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Complex velocity models characterized by strong lateral variations are certainly a great motivation, but also a great challenge, for depth imaging. In this context, some unexpected results can occur when using depth imaging algorithms. In general, after a common shot or common offset migration, the resulting depth images are sorted into common‐image gathers (CIG), for further processing such as migration‐based velocity analysis or amplitude‐variation‐with‐offset analysis. In this paper, we show that CIGs calculated by common‐shot or common‐offset migration can be strongly affected by artifacts, even when a correct velocity model is used for the migration. The CIGs are simply not flat, due to unexpected curved events (kinematic artifacts) and strong lateral variations of the amplitude (dynamic artifacts). Kinematic artifacts do not depend on the migration algorithm provided it can take into account lateral variations of the velocity model. This can be observed when migrating the 2‐D Marmousi dataset either with a wave‐equation migration or with a multivalued Kirchhoff migration/inversion. On the contrary, dynamic artifacts are specific to multi‐arrival ray‐based migration/inversion. This approach, which should provide a quantitative estimation of the reflectivity of the model, provides in this context dramatic results. In this paper, we propose an analysis of these artifacts through the study of the ray‐based migration/inversion operator. The artifacts appear when migrating a single‐fold subdata set with multivalued ray fields. They are due to the ambiguous focusing of individual reflected events at different locations in the image. No information is a priori available in the single‐fold data set for selecting the focusing position, while migration of multifold data would provide this information and remove the artifacts by the stack of the CIGs. Analysis of the migration/inversion operator provides a physical condition, the imaging condition, for insuring artifact free CIGs. The specific cases of common‐shot and common‐offset single‐fold gathers are studied. It appears clearly that the imaging condition generally breaks down in complex velocity models for both these configurations. For artifact free CIGs, we propose a novel strategy: compute CIGs versus the diffracting/reflecting angle. Working in the angle domain seems the natural way for unfolding multivalued ray fields, and it can be demonstrated theoretically and practically that common‐angle imaging satisfies the imaging condition in the great majority of cases. Practically, the sorting into angle gathers can not be done a priori over the data set, but is done in the inner depth migration loop. Depth‐migrated images are obtained for each angle range. A canonical example is used for illustrating the theoretical derivations. Finally, an application to the Marmousi model is presented, demonstrating the relevance of the approach.

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18

Bulut., Meryem. "MEDİA, MIGRATION AND CRIME: SYRIAN REFUGIES." International Journal of Advanced Research 5, no. 4 (May 30, 2017): 927–32. http://dx.doi.org/10.21474/ijar01/3897.

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19

Moullagaliev, Narkiz K., and Lyutsiya G. Khismatullina. "Metaphors in Media Discourse on Migration." Journal of History Culture and Art Research 6, no. 5 (November 28, 2017): 131. http://dx.doi.org/10.7596/taksad.v6i5.1242.

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<p>The paper deals with the problems of cognitive linguistic discourse and comparative analysis studies of metaphor as a means of representing migration in mass media. It presents the most productive metaphoric models, shaping the concept of “migration”, that function in printed and electronic media discourses of Great Britain, USA and Russia in 2016-2017. A comparative analysis of metaphorical models representing migration in British, American and Russian media discourses has shown that in media discourses on the migration of 2016-2017, regularly three high-frequency and productive metaphorical models operate: hydronymic, military and morbid. Images of these metaphorical models are united by vectors of anxiety, despair, threats to life and have negative conceptual potential.</p>

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20

Atay, Tülay. "Mediating Migration, Global Media, and Communication." European Journal of Communication 34, no. 6 (November 20, 2019): 698–701. http://dx.doi.org/10.1177/0267323119887566.

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21

Stolic, Tijana. "Media representations of migration and racism." European Journal of Communication 34, no. 6 (November 20, 2019): 691–97. http://dx.doi.org/10.1177/0267323119887838.

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22

GRAY, JOHN, SAMUEL P. HUNTINGTON, JOSEPH CHAMIE, I. K. GUJARAL, RYUTARO HASHIMOTO, REM KOOLHAAS, JOSCHKA FISCHER, et al. "Migration, Media, Modus Vivendi - Spring 2001." New Perspectives Quarterly 25, no. 1 (January 2008): 8–9. http://dx.doi.org/10.1111/j.1540-5842.2008.00928.x.

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23

Zhu, Tianfei. "Ray‐Kirchhoff migration in inhomogeneous media." GEOPHYSICS 53, no. 6 (June 1988): 760–68. http://dx.doi.org/10.1190/1.1442511.

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A Kirchhoff method that avoids possible singularities on the surface of integration and is more accurate than previous Kirchhoff methods has been developed for seismic migration in laterally inhomogeneous media. It is based on a newly derived integral solution to the acoustic wave equation. This solution indicates that wave fields in an inhomogeneous medium can be expressed as a summation of ray solutions determined by the transport and extended eikonal equations. The extended eikonal equation is, in turn, solved by an asymptotic series. For implementation, a perturbation scheme is developed for solving the ray and transport equations. In addition to computing higher‐order terms of the asymptotic series, this scheme can be used to avoid most of the ray tracing required for wave extrapolation in a medium where vertical variations may be large but lateral variations are small compared to velocity itself. Where an analytic ray solution for the reference velocity used in the perturbation scheme exists, ray‐Kirchhoff migration in such a medium can be carried out without numerical ray tracing.

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24

Run, Peter. "Book Review: Migration and the Media." Media International Australia 146, no. 1 (February 2013): 170. http://dx.doi.org/10.1177/1329878x1314600136.

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25

Mattoscio, Mara, and Megan C. MacDonald. "Introduction: Gender, Migration, and the Media." Feminist Media Studies 18, no. 6 (November 2, 2018): 1117–20. http://dx.doi.org/10.1080/14680777.2018.1532142.

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26

Pink, Brian. "External Migration (April 2002) - Media Release." New Zealand Journal of Geography 113, no. 1 (May 1, 2009): 28. http://dx.doi.org/10.1111/j.0028-8292.2002.tb00827.x.

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27

Georgiou, Myria. "Introduction: gender, migration and the media." Ethnic and Racial Studies 35, no. 5 (May 2012): 791–99. http://dx.doi.org/10.1080/01419870.2011.628041.

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28

Dobrić Basaneže, Katja, and Paulina Ostojić. "Migration Discourse in Croatian News Media." Medijska istraživanja 27, no. 1 (June 18, 2021): 5–27. http://dx.doi.org/10.22572/mi.27.1.1.

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This paper investigates migration discourse in Croatian news media by combining corpus linguistics and critical discourse analysis approach. It first focuses on the phraseological and grammatical context of the terms migrant, imigrant, izbjeglica and azilant, whereupon it investigates the background of such linguistic behaviour. The latter is examined by means of critical discourse analysis, hence, by taking into account the non-linguistic context. This includes the analysis of historical, cultural and political context or sometimes even the relevant case law and standards of protection guaranteed in international humanitarian and human rights law. Results of the study suggest that discrimination does not occur only in the most obvious acts of inhuman treatment, such as pushbacks, but also in the language the media use when reporting on migration process.

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29

Pan, Naide, and William S. French. "Generalized two‐pass three‐dimensional migration for imaging steep dips in vertically inhomogeneous media." GEOPHYSICS 54, no. 5 (May 1989): 544–54. http://dx.doi.org/10.1190/1.1442681.

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Conventional two‐pass 3-D time migration is exactly equivalent to full 3-D time migration in a homogeneous medium. For vertically inhomogeneous media representing typical earth velocities, however, conventional two‐pass 3-D migration fails to correctly image dips beyond about 45 degrees. This failure is the result of an inherent velocity error incurred during the first pass of a two‐pass 3-D migration. For a vertically inhomogeneous medium, the theory of residual migration can be combined with the results for homogeneous media to derive a series of successive two‐pass migration stages which are equivalent to a full 3-D migration. Each stage of this generalized two‐pass 3-D migration is implemented using an appropriate constant migration velocity. In practice, the required number of two‐pass stages can be reduced to a computationally manageable few; and the I/O can be reduced by one‐third to one‐half of that required using a straightforward application of repeated two‐pass migrations. This procedure allows existing 2-D migration programs to be upgraded to steep‐dip 3-D migration programs by use of a simple I/O structure. Any of the basic 2-D migration algorithms can be used, but we have employed a 50-degree finite‐difference algorithm. In addition, generalized two‐pass 3-D migration overcomes the dip limitations of the underlying 2-D finite‐difference migration algorithm for the same reasons that cascaded 2-D migration extends the dip range of 2-D migration algorithms. Synthetic data examples clearly show the success of this method in imaging steep dips in vertically inhomogeneous media.

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30

Akbar, Faruq E., Mrinal K. Sen, and Paul L. Stoffa. "Prestack plane‐wave Kirchhoff migration in laterally varying media." GEOPHYSICS 61, no. 4 (July 1996): 1068–79. http://dx.doi.org/10.1190/1.1444028.

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Conventional Kirchhoff migration methods are applied to seismograms in the offset‐time (x − t) domain. We describe the theory, numerical details, and examples of a prestack depth migration method in the plane‐wave domain that is valid in laterally inhomogeneous media. The theory is based on a Kirchhoff‐Helmholtz formulation of the wavefield and uses plane‐wave‐transformed shot gathers for migration. We use geometric ray theory for the source wavefield continuation operator and a plane‐wave expansion of the receiver wavefield in the integrand of the Kirchhoff‐Helmholtz integral. The source and receiver plane‐wave traveltimes are computed at each grid point in the subsurface using a finite‐difference approximation of the eikonal equation with appropriate initial and boundary conditions. We developed an efficient technique to compute imaging time by a combination of these two times. The technique allows us to design algorithms for migrating shot gather or constant ray‐parameter sections efficiently. We evaluate the efficiency and accuracy of the algorithm with three sets of synthetic data examples with varying degrees of complexity. We also compare the performance of the parallel algorithms using Parallel Virtual Machine (PVM). Migration of a marine data set results in excellent images of a mud volcano and the top of an accretionary prism of an active continental margin on the Nicoya Peninsula of Costa Rica.

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31

Jacobsen, Christine M. "Communicating Irregular Migration." American Behavioral Scientist 59, no. 7 (February 27, 2015): 886–97. http://dx.doi.org/10.1177/0002764215573260.

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This essay addresses the question of how irregular migration is framed in Western media from the location of the migration researcher. What challenges and dilemmas do media frames and practices of framing create for researchers’ participation in communicating research about irregular migration to the public? The essay is written in dialogue with topics raised by the articles in the special issue and seeks to supplement, and at times interrogate, its scrutiny of how irregular migration is covered in the news and received by the audience.

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32

Amazonas, Daniela, Rafael Aleixo, Jörg Schleicher, and Jessé C. Costa. "Anisotropic complex Padé hybrid finite-difference depth migration." GEOPHYSICS 75, no. 2 (March 2010): S51—S59. http://dx.doi.org/10.1190/1.3337317.

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Standard real-valued finite-difference (FD) and Fourier finite-difference (FFD) migrations cannot handle evanescent waves correctly, which can lead to numerical instabilities in the presence of strong velocity variations. A possible solution to these problems is the complex Padé approximation, which avoids problems with evanescent waves by rotating the branch cut of the complex square root. We have applied this approximation to the acoustic wave equation for vertical transversely isotropic media to derive more stable FD and hybrid FD/FFD migrations for such media. Our analysis of the dispersion relation of the new method indicates that it should provide more stable migration results with fewer artifacts and higher accuracy at steep dips. Our studies lead to the conclusion that the rotation angle of the branch cut that should yield the most stable image is 60° for FD migration, as confirmed by numerical impulse responses and work with synthetic data.

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33

Alkhalifah, Tariq. "Gaussian beam depth migration for anisotropic media." GEOPHYSICS 60, no. 5 (September 1995): 1474–84. http://dx.doi.org/10.1190/1.1443881.

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Gaussian beam migration (GBM), as it is implemented today, efficiently handles isotropic inhomogeneous media. The approach is based on the solution of the wave equation in ray‐centered coordinates. Here, I extend the method to work for 2-D migration in generally anisotropic inhomogeneous media. Extension of the Gaussian‐beam method from isotropic to anisotropic media involves modification of the kinematics and dynamics in the required ray tracing. While the accuracy of the paraxial expansion for anisotropic media is comparable to that for isotropic media, ray tracing in anisotropic media is much slower than that in isotropic media. However, because ray tracing is just a small portion of the computation in GBM, the increased computational effort in general anisotropic GBM is typically only about 40%. Application of this method to synthetic examples shows successful migration in inhomogeneous, transversely isotropic media for reflector dips up to and beyond 90°. Further applications to synthetic data of layered anisotropic media show the importance of applying the proper smoothing to the velocity field used in the migration. Also, tests with synthetic data show that the quality of anisotropic migration of steep events in a medium with velocity increasing with depth is much more sensitive to the Thomsen anisotropy parameter ε than to the parameter δ. Thus, a good estimate of ε is needed to apply anisotropic migration with confidence.

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34

Twigt, Mirjam, and Dafni Mangalousi. "Editorial: Connecting (Forced) Migration and Media Studies." for(e)dialogue 2, no. 1 (June 29, 2018): 1–11. http://dx.doi.org/10.29311/for(e)dialogue.v2i1.2803.

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This Special Issue on (Forced) Migration and Media is the result of two workshops organised at the University of Leicester: a workshop on (Forced) Migration and Media-research that took place on the 13th of June 2016 and a Community Impact event that was organised on the 18th of July, 2016. These workshops were a response to the topical interest for refugees’ access to digital technology and the dehumanizing language used in, especially but not limited to British, media regarding migrants and/or refugees (Berry, Garcia-Blanco, & Moore, 2015). (Forced) was purposefully bracketed as the label ‘refugee’ has its own difficulties. The differentiation between economic and forced migrants for instance negates that reasons behind migration are often multi-causal and multi-layered. It reinforces thinking in dichotomies that homogenizes and tends to negate in-between complexities, as is often appropriated as a governing tool to victimize, exclude and curtail the rights of human beings (Crawley & Skleparis, 2017; Lindley, 2010; Zetter, 2007). In this editorial, we reflect upon the main outcomes of the workshop we and other PhD-colleagues organised on the 13th of June, 2016, and connect them to the articles within this Special Issue.

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MOTOSHIMA, Takayuki, and Junya INOUE. "ANALYSIS OF CONTAMINANT MIGRATION IN HETEROGENEOUS MEDIA." Journal of applied mechanics 7 (2004): 451–59. http://dx.doi.org/10.2208/journalam.7.451.

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Rothenberger, Liane, Ahmed Elmezeny, and Jeffrey Wimmer. "Mediating Media Usage in Times of Migration." MedienPädagogik: Zeitschrift für Theorie und Praxis der Medienbildung 35, Media literacy (October 19, 2019): 55–73. http://dx.doi.org/10.21240/mpaed/35/2019.10.19.x.

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The use and regulation of mobile media devices of children and adolescents in refugee families is largely unexplored. Our qualitative approach utilizes in-depth guided interviews with parents and children in Arabic speaking refugee families in Germany. All interviewed families have resided in Germany from one to four years. The sample consists of both couples and single parents, while most children are in their final year of kindergarten, in primary school, or secondary school. The study explores the selection and usage of mobile media devices and content in their social context, such as the use of social media platforms and apps at home and for school. Our research highlights changes in mobile media usage after the interviewees’ arrival in Germany due to the different socio-cultural environment and a changed media agency. The amount of change greatly depends on the age of the children, for example, the younger they were when arriving in Germany, the less likely they are to use mobile media to stay in touch with their former friends. Additionally, most children and adolescents tend to consume German media content more often than Arabic content. In the rare cases they do consume Arabic media content, it is in the presence of their parents, who state that they do so to bring their children closer to their roots.

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Chinju, Hirofumi, Shinya Nagasaki, Satoru Tanaka, Tadao Tanaka, and Susumu Muraoka. "Filtration in Colloid Migration through Porous Media." Journal of Nuclear Fuel Cycle and Environment 5, no. 1 (1998): 59–66. http://dx.doi.org/10.3327/jnuce.5.1_59.

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Tenner, Stefan. "GAST:ARBAJTERSKI R:ADIO – Migration and media in Serbia." Telematics and Informatics 27, no. 2 (May 2010): 177–81. http://dx.doi.org/10.1016/j.tele.2009.06.003.

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Righi, Alessandra. "Assessing migration through social media: a review." Mathematical Population Studies 26, no. 2 (March 11, 2019): 80–91. http://dx.doi.org/10.1080/08898480.2019.1565271.

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Shiramizu, Shigehiko. "Global Migration, Ethnic Media and Ethnic Identity." Asian and Pacific Migration Journal 9, no. 3 (September 2000): 273–85. http://dx.doi.org/10.1177/011719680000900303.

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Lorenz, M. R., V. J. Novotny, and V. R. Deline. "Lubricant migration in particulate magnetic recording media." IEEE Transactions on Magnetics 27, no. 6 (November 1991): 5088–90. http://dx.doi.org/10.1109/20.278749.

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Almenara-Niebla, Silvia. "The Sage Handbook of media and migration." Information, Communication & Society 23, no. 10 (June 10, 2020): 1549–51. http://dx.doi.org/10.1080/1369118x.2020.1778057.

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Komito, Lee. "Social media and migration: Virtual community 2.0." Journal of the American Society for Information Science and Technology 62, no. 6 (March 22, 2011): 1075–86. http://dx.doi.org/10.1002/asi.21517.

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Patterson, Jeffrey. "The SAGE Handbook of media and migration." Critical Studies in Media Communication 37, no. 3 (April 24, 2020): 275–77. http://dx.doi.org/10.1080/15295036.2020.1755096.

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Rismani Yazdi, Saeed, Reza Nosrati, Corey A. Stevens, David Vogel, and Carlos Escobedo. "Migration of magnetotactic bacteria in porous media." Biomicrofluidics 12, no. 1 (January 2018): 011101. http://dx.doi.org/10.1063/1.5024508.

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Wenzel, F. "Frequency‐wavenumber migration in laterally heterogeneous media." GEOPHYSICS 56, no. 10 (October 1991): 1671–73. http://dx.doi.org/10.1190/1.1442977.

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In a recent paper, Stoffa et al. (1990) presented a split‐step Fourier migration method. It takes laterally varying migration velocities into account by splitting the reference slowness into an average slowness, constant within the migration interval, and a perturbation term which accounts for the lateral variations. The method works accurately only if the lateral slowness variations are smooth and angles of propagation are near‐vertical. The restriction to steep propagation angles stems from the fact that the wavefield is accurately propagated with respect to the reference slowness but a five‐degree approximation is used to accommodate the lateral variations. This note presents a theory that avoids the five‐degree assumption and thus generalizes the split‐step algorithm.

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Dong, Zhengxin, and George A. McMechan. "3-D prestack migration in anisotropic media." GEOPHYSICS 58, no. 1 (January 1993): 79–90. http://dx.doi.org/10.1190/1.1443353.

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A three‐dimensional (3-D) prestack reverse‐time migration algorithm for common‐source P‐wave data from anisotropic media is developed and illustrated by application to synthetic data. Both extrapolation of the data and computation of the excitation‐time imaging condition are implemented using a second‐order finite‐ difference solution of the 3-D anisotropic scalar‐wave equation. Poorly focused, distorted images are obtained if data from anisotropic media are migrated using isotropic extrapolation; well focused, clear images are obtained using anisotropic extrapolation. A priori estimation of the 3-D anisotropic velocity distribution is required. Zones of anomalous, directionally dependent reflectivity associated with anisotropic fracture zones are detectable in both the 3-D common‐ source data and the corresponding migrated images.

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Chan, Brenda Kin Ying. "Leaving China: Media, Migration and Transnational Imagination." Journal of Chinese Overseas 1, no. 1 (2005): 130–33. http://dx.doi.org/10.1163/179325405788639337.

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Sarkar, Debashish, and Ilya Tsvankin. "Migration velocity analysis in factorized VTI media." GEOPHYSICS 69, no. 3 (May 2004): 708–18. http://dx.doi.org/10.1190/1.1759457.

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One of the main challenges in anisotropic velocity analysis and imaging is simultaneous estimation of velocity gradients and anisotropic parameters from reflection data. Approximating the subsurface by a factorized VTI (transversely isotropic with a vertical symmetry axis) medium provides a convenient way of building vertically and laterally heterogeneous anisotropic models for prestack depthmigration. The algorithm for P‐wave migration velocity analysis (MVA) introduced here is designed for models composed of factorized VTI layers or blocks with constant vertical and lateral gradients in the vertical velocity VP0. The anisotropic MVA method is implemented as an iterative two‐step procedure that includes prestack depth migration (imaging step) followed by an update of the medium parameters (velocity‐analysis step). The residual moveout of the migrated events, which is minimized during the parameter updates, is described by a nonhyperbolic equation whose coefficients are determined by 2D semblance scanning. For piecewise‐factorized VTI media without significant dips in the overburden, the residual moveout of P‐wave events in image gathers is governed by four effective quantities in each block: (1) the normal‐moveout velocity Vnmo at a certain point within the block, (2) the vertical velocity gradient kz, (3) the combination kx[Formula: see text] of the lateral velocity gradient kx and the anisotropic parameter δ, and (4) the anellipticity parameter η. We show that all four parameters can be estimated from the residual moveout for at least two reflectors within a block sufficiently separated in depth. Inversion for the parameter η also requires using either long‐spread data (with the maximum offset‐to‐depth ratio no less than two) from horizontal interfaces or reflections from dipping interfaces. To find the depth scale of the section and build a model for prestack depth migration using the MVA results, the vertical velocity VP0 needs to be specified for at least a single point in each block. When no borehole information about VP0 is available, a well‐focused image can often be obtained by assuming that the vertical‐velocity field is continuous across layer boundaries. A synthetic test for a three‐layer model with a syncline structure confirms the accuracy of our MVA algorithm in estimating the interval parameters Vnmo, kz, kx, and η and illustrates the influence of errors in the vertical velocity on the image quality.

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Wang, Feng, Jiangchuan Liu, Minghua Chen, and Haiyang Wang. "Migration Towards Cloud-Assisted Live Media Streaming." IEEE/ACM Transactions on Networking 24, no. 1 (February 2016): 272–82. http://dx.doi.org/10.1109/tnet.2014.2362541.

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