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Berkovitch A.,Geomage | Deev K.,Geomage | Landa E.,OPERA
First Break | Year: 2011

MultiFocusing technology can dramatically improve the quality of seismic imaging especially in cases of low fold data, poor signal-to-noise ratio and sparse 3D acquisition. MF technology, based on multiparameter analysis of the wavefield and summation along predicted time surfaces, has been applied to enhance time imaging sections by dramatically increasing the fold of coherent summation of seismic signals. One of the main limitations of the zero-offset MF method is a quasi-hyperbolic approximation for actual travel-time surfaces. COMF traveltime formulas provide an adequate representation of arrival times for arbitrary offset and source-receiver configuration. The COMF correction formula is remarkably accurate even for strong curved reflectors. The correlation procedure is repeated for each imaging point, for each offset and for each time sample. It is important to note that the described procedure can be applied locally within a small vicinity of each seismic trace and does not require global full offset approximation. Source

Silvestrov I.,Russian Academy of Sciences | Baina R.,OPERA | Landa E.,Tel Aviv University
Geophysical Prospecting | Year: 2016

We propose a method for imaging small-scale diffraction objects in complex environments in which Kirchhoff-based approaches may fail. The proposed method is based on a separation between the specular reflection and diffraction components of the total wavefield in the migrated surface angle domain. Reverse-time migration was utilized to produce the common image gathers. This approach provides stable and robust results in cases of complex velocity models. The separation is based on the fact that, in surface angle common image gathers, reflection events are focused at positions that correspond to the apparent dip angle of the reflectors, whereas diffracted events are distributed over a wide range of angles. The high-resolution radon-based procedure is used to efficiently separate the reflection and diffraction wavefields. In this study, we consider poststack diffraction imaging. The advantages of working in the poststack domain are its numerical efficiency and the reduced computational time. The numerical results show that the proposed method is able to image diffraction objects in complex environments. The application of the method to a real seismic dataset illustrates the capability of the approach to extract diffractions. © 2015 European Association of Geoscientists & Engineers. Source

Fomel S.,University of Texas at Austin | Landa E.,OPERA
Journal of Applied Geophysics | Year: 2014

Structural information in seismic images is uncertain. The main cause of this uncertainty is uncertainty in velocity estimation. We adopt the technique of velocity continuation for estimating velocity uncertainties and corresponding structural uncertainties in time-migrated images. Data experiments indicate that structural uncertainties can be significant even when both structure and velocity variations are mild. © 2013 The Authors. Source

Landa E.,OPERA
Hart's E and P | Year: 2011

Multifocusing (MF) technology, based on multiparameter stacking, has been applied to enhance time imaging sections by dramatically increasing the fold of coherent summation of seismic signals. Implementation of the MF method is technically challenging because it requires defining three moveout parameters in the 2-D case and eight in the 3-D case, as opposed to a single parameter. MF technology was applied to low-fold and low-quality data from northwestern Russia. The MF method not only provides coherent stacking of seismic data with arbitrary source-receiver distribution to create high-quality time images, but it also has the potential to compute enhanced prestack seismic traces. The number and location of traces in the produced supergathers can be different from the input locations, and the resulting traces can be regular with increased signal-to-noise ratio due to partial coherent summation. The method is robust in the presence of non-coherent noise. Source

Faenzi E.,Novartis | Zedda L.,Novartis | Bardelli M.,Novartis | Spensieri F.,Novartis | And 16 more authors.
Vaccine | Year: 2012

Protective antibody responses to a single dose of 2009 pandemic vaccines have been observed in the majority of healthy subjects aged more than 3 years. These findings suggest that immune memory lymphocytes primed by previous exposure to seasonal influenza antigens are recruited in the response to A/H1N1 pandemic vaccines and allow rapid seroconversion. However, a clear dissection of the immune memory components favoring a fast response to pandemic vaccination is still lacking. Here we report the results from a clinical study where antibody, CD4+ T cell, plasmablast and memory B cell responses to one dose of an MF59-adjuvanted A/H1N1 pandemic vaccine were analyzed in healthy adults. While confirming the rapid appearance of antibodies neutralizing the A/H1N1 pandemic virus, we show here that the response is dominated by IgG-switched antibodies already in the first week after vaccination. In addition, we found that vaccination induces the rapid expansion of pre-existing CD4+ T cells and IgG-memory B lymphocytes cross-reactive to seasonal and pandemic A/H1N1 antigens. These data shed light on the different components of the immune response to the 2009 H1N1 pandemic influenza vaccination and may have implications in the design of vaccination strategies against future influenza pandemics. © 2012 Elsevier Ltd. Source

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