Periodic plane-wave least-squares reverse time migration for diffractions

Diffraction imaging is important for high-resolution characterization of small subsurface heterogeneities. However, due to geometry limitations and noise distortion, conventional diffraction imaging methods may produce low-quality images. We have adopted a periodic plane-wave least-squares reverse time migration method for diffractions to improve the image quality of heterogeneities. The method reformulates diffraction imaging as an inverse problem using the Born modeling operator and its adjoint operator derived in the periodic plane-wave domain. The inverse problem is implemented for diffractions separated by a plane-wave destruction filter from the periodic plane-wave sections. Because the plane-wave destruction filter may fail to eliminate hyperbolic reflections and noise, we adopt a hyperbolic misfit function to minimize a weighted residual using an iteratively reweighted least-squares algorithm and thereby reduce residual reflections and noise. Synthetic and field data tests show that the adopted method can significantly improve the image quality of subsalt and deep heterogeneities. Compared with reverse time migration, it produces better images with fewer artifacts, higher resolution, and more balanced amplitude. Therefore, the adopted method can accurately characterize small heterogeneities and provide a reliable input for seismic interpretation in the prediction of hydrocarbon reservoirs.

The weak solvability of the steady problem modelling the flow of a viscous incompressible heat-conductive fluid through the profile cascade

Purpose The paper aims to theoretically study the mathematical model of a steady flow of a heat-conductive incompressible viscous fluid through a spatially periodic plane profile cascade. Design/methodology/approach Reduction of the infinite periodical problem to one period. Leray-Schauder fixed point principle was used. Findings This study proves the existence of a weak solution for arbitrarily large given data (i.e. the inflow velocity and the acting specific body force). Practical implications The author proposed a special boundary condition on the outflow of the domain not only for the velocity and pressure but also for the temperature. Originality/value To the author’s knowledge, the problem has not been studied earlier. More detailed overview is given in the paper in the first part.

THE GINZBURG–LANDAU EQUATION IN THE HEISENBERG GROUP

We consider a functional related with phase transition models in the Heisenberg group framework. We prove that level sets of local minimizers satisfy some density estimates, that is, they behave as "codimension one" sets. We thus deduce a uniform convergence property of these level sets to interfaces with minimal area.These results are then applied in the construction of (quasi)periodic, plane-like minimizers, i.e. minimizers of our functional whose level sets are contained in a spacial slab of universal size in a prescribed direction. As a limiting case, we obtain the existence of hypersurfaces contained in such a slab which minimize the surface area with respect to a given periodic metric.

Efficient Channels of Energy Transfer in High Light Yield LuI3:Ce Scintillator

The extremely high scintillation efficiency of lutetium iodide doped by cerium is explained as a result of several factors controlling the energy transfer from the host matrix to activator, two of which are investigated in the present paper. The first one is the increase of the efficiency of energy transfer from self-trapped excitons to cerium ions in the row LuCl3-LuBr3-LuI3. The STE structure and the efficiency of STE to cerium energy transfer are verified by cluster ab initio calculations. We propose and theoretically validate the possibility of a new channel of energy transfer to excitons and directly to cerium, namely the Auger process when Lu 4f hole relaxes to the valence band hole with simultaneous creation of additional exciton or excitation of cerium. This process should be efficient in LuI3, and inefficient in LuCl3. In order to justify this channel we perform calculations of density of states using a periodic plane-wave density functional approach. The performed estimations theoretically justify the high LuI3:Ce3+ scintillator yield.

Modeling and Design of Materials for Controlled Wave Propagation in Plane Grid Structures

Formulations for the optimal design of plane grids with maximum band gaps are presented. Periodic band-gap structures prevent waves in certain frequency ranges from propagating. Materials or structures with band gaps have many applications, including frequency filters, vibration protection devices and wave guides. Here, a simple model of a periodic plane grid structure is presented and then an optimization problem is formulated where the structure’s band gap above a particular frequency is maximized by the selective addition of non-structural masses. Numerical implementation issues are discussed and examples are presented.