Reconstructing Images from Projections Using the Maximum-Entropy Method. Numerical Simulations of Low-Aspect Astrotomography

The reconstruction of images from a small number of projections using the maximum-entropy method (MEM) with the Shannon entropy is considered. MEM provides higher-quality image reconstruction for sources with extended components than the Hogbom CLEAN method, which is also used in low-aspect astrotomography. The quality of image reconstruction for sources with mixed structure containing bright, compact features embedded in a comparatively weak, extended base can be further improved using a difference-mapping method, which requires a generalization of MEM for the reconstruction of sign-variable functions.We draw conclusions based on the results of numerical simulations for a number of model radio sources with various morphologies.Comment: 11 pages, 9 figure

High-visibility multi-photon interference of Hanbury Brown - Twiss type for classical light

Difference-phase (or Hanbury Brown - Twiss type) intensity interference of classical light is considered in higher orders in the intensity. It is shown that, while the visibility of sum-phase (NOON-type) interference for classical sources drops with the order of interference, the visibility of difference-phase interference has opposite behavior. For three-photon and four-photon interference of two coherent sources, the visibility can be as high as 81.8% and 94.4%, respectively. High-visibility three-photon and four-photon interference of space-time and polarization types has been observed in experiment, for both coherent and pseudo-thermal light.Comment: 11 pages, 9 figure

Possibility of local pair existence in optimally doped SmFeAsO(1-x) in pseudogap regime

We report the analysis of pseudogap Delta* derived from resistivity experiments in FeAs-based superconductor SmFeAsO(0.85), having a critical temperature T_c = 55 K. Rather specific dependence Delta*(T) with two representative temperatures followed by a minimum at about 120 K was observed. Below T_s = 147 K, corresponding to the structural transition in SmFeAsO, Delta*(T) decreases linearly down to the temperature T_AFM = 133 K. This last peculiarity can likely be attributed to the antiferromagnetic (AFM) ordering of Fe spins. It is believed that the found behavior can be explained in terms of Machida, Nokura, and Matsubara (MNM) theory developed for the AFM superconductors.Comment: 5 pages, 2 figure

Absence of genetic introgression between Elymus ciliaris and E. pendulinus (Triticeae: Poaceae) as shown by endosperm protein SDS-electrophoresis in connection with hypotheses of E. amurensis origin

The StY-genome group of Elymus species is of special interest, most of its species ranges extending to Russia from southern frontier territories, mainly from China. The ranges of Elymus pendulinus, E. ciliaris and E. amurensis within Russia overlap in the southern part of the Russian Far East only. Elymus ciliaris is considered by Russian taxonomists to be phylogenetically close to E. pendulinus, while hybridization of these species gave rise to the independent species E. amurensis. Moreover, in China, E. amurensis is recognized as a variety of E. ciliaris. Endosperm protein polymorphism was studied by SDS-electrophoresis for the purpose to reveal species specificity in E. pendulinus, E. ciliaris, and E. amurensis from a number of localities in the Primorskii Krai. Accessions of species from places of their joint occurrence were analyzed to detect identical polypeptide components which could have appeared due to genetic introgression. Nevertheless, both electrophoretic images visual analyses and construction the dendrograms of populations with various similarity coefficients revealed a high species specificity of E. ciliaris и E. pendulinus but no signs of introgression in spite of the fact that the two species often grow in common ecotopes and even form sterile hybrids. No indications of the origin of E. amurensis from the highly distinct species E. ciliaris and E. pendulinus were found either.The necessity of biosystematic and experimental methods for confirmation of the origin and taxonomic rank of new and many recognized species in the genus Elymus is shown

TRANSIENT ELECTROMAGNETIC SOUNDING IN 2D, 3D, AND 4D MODES: SEQUENCE OF GEOLOGICAL EXPLORATION ACTIVITIES

From 1980s, electromagnetic prospecting is an integral component of geophysical techniques for oil and gas exploration in many regions of the Russian Federation. Electromagnetic methods are used at all stages of geological exploration, including reconnaissance, discovery, prospecting and appraisal, and economic mining. In oil and gas exploration, the most commonly used technique is the near-field transient electromagnetic sounding (TEM). On the other hand, for each of these stages, specific tasks of electromagnetic prospecting have not been clearly defined yet. Furthermore, there are no standard requirements to the volume of a priori geological and geophysical information, which is sufficient for solving a geological problem. If such information is lacking or insufficient, a geological problem may be incorrectly stated and/or improperly correlated with the current stage of works. Our study aims to define which geological problems should be addressed by electromagnetic survey at the different stages of geological exploration, and to specify the requirements to the availability of a priori geological and geophysical information. We have analyzed the electromagnetic data from the regions of East and West Siberia, which have different geological settings. The main geological problems that can be solved by the seismic and electromagnetic techniques are determined. We propose a set of geophysical survey operations, which is optimal for oil and gas exploration. An effective sequence of electromagnetic prospecting stages is determined, and preliminary and accompanying surveys are specified. The requirements to the availability of a priori information are proposed, and its volume is defined. Geological problems are defined with respect to the corresponding stages of geological exploration. Special attention is given to approaches to the mineral resource estimation and calculation of hydrocarbon reserves, taking into account electromagnetic survey results. It is proposed to use the electromagnetic data at the stage of prospecting and appraisal, which aims to assess the resources of categories Dl and D0, as well as at the exploration stage for estimating the reserves of category C2 in new and explored fields. Approaches to the economic assessment of using electromagnetic surveys as part of the geological exploration are discussed. Our study shows that a correct sequence of electromagnetic prospecting operations at each stage can ensure obtaining an original geological dataset of the given stage and thus providing a proper basis for the next stage of oil-gas field investigation

Invariant description of solutions of hydrodynamic type systems in hodograph space: hydrodynamic surfaces

Hydrodynamic surfaces are solutions of hydrodynamic type systems viewed as non-parametrized submanifolds of the hodograph space. We propose an invariant differential-geometric characterization of hydrodynamic surfaces by expressing the curvature form of the characteristic web in terms of the reciprocal invariants.Comment: 12 page