Transformation of magnetic data to the pole and vertical dip and a related apparent susceptibility transform: exact and approximate approaches

The dipolar character of magnetic data means that there is a high and a low associated with each source. The relative positions and sizes of these highs and lows, varies depending on the magnetic latitude or the inclination of the Earth’s magnetic field. One method for dealing with this complexity is to transform the data to what would collected if the inclination were vertical (as at the magnetic pole); a process that is unstable at low magnetic latitudes. Unfortunately, remanent magnetization adversely impacts the success of this transformation. A second approach is to calculate the analytic-signal amplitude (ASA) of the data, which creates a single positive feature for each source or edge, with the shape being only weakly dependent on the inclination and the presence of remanent magnetization. The ASA anomalies can appear to be relatively broad, so features sometimes merge together on map views of the ASA. A subsequent transformation of the ASA using an appropriate transforming tilt angle can generate a magnetic field of a body that is at the pole and has a vertical dip. The transformation is exact for contacts when calculated from the first-order ASA, but the sign of the transformed data can be incorrect depending on whether you are over one edge or the other edge of a discrete source body. Another, approximate transformation of the zeroth-order ASA does not have this issue and gives good results on synthetic data provided that any noise is handled appropriately. The resulting maps outline the magnetic source bodies and have amplitudes proportional to an apparent magnetic susceptibility. On field data from Black Hill, South Australia, the approximate transformation generates an image that is simple to interpret and enhances some features less obvious on other enhancements of the data.

Selecting an Effective Entropy Estimator for Short Sequences of Bits and Bytes with Maximum Entropy

Entropy makes it possible to measure the uncertainty about an information source from the distribution of its output symbols. It is known that the maximum Shannon’s entropy of a discrete source of information is reached when its symbols follow a Uniform distribution. In cryptography, these sources have great applications since they allow for the highest security standards to be reached. In this work, the most effective estimator is selected to estimate entropy in short samples of bytes and bits with maximum entropy. For this, 18 estimators were compared. Results concerning the comparisons published in the literature between these estimators are discussed. The most suitable estimator is determined experimentally, based on its bias, the mean square error short samples of bytes and bits.

Murchison Widefield Array detection of steep-spectrum, diffuse, non-thermal radio emission within Abell 1127

Diffuse, non-thermal emission in galaxy clusters is increasingly being detected in low-frequency radio surveys and images. We present a new diffuse, steep-spectrum, non-thermal radio source within the cluster Abell 1127 found in survey data from the Murchison Widefield Array (MWA). We perform follow-up observations with the ‘extended’ configuration MWA Phase II with improved resolution to better resolve the source and measure its low-frequency spectral properties. We use archival Very Large Array S-band data to remove the discrete source contribution from the MWA data, and from a power law model fit we find a spectral index of –1.83±0.29 broadly consistent with relic-type sources. The source is revealed by the Giant Metrewave Radio Telescope at 150 MHz to have an elongated morphology, with a projected linear size of 850 kpc as measured in the MWA data. Using Chandra observations, we derive morphological estimators and confirm quantitatively that the cluster is in a disturbed dynamical state, consistent with the majority of phoenices and relics being hosted by merging clusters. We discuss the implications of relying on morphology and low-resolution imaging alone for the classification of such sources and highlight the usefulness of the MHz to GHz radio spectrum in classifying these types of emission. Finally, we discuss the benefits and limitations of using the MWA Phase II in conjunction with other instruments for detailed studies of diffuse, steep-spectrum, non-thermal radio emission within galaxy clusters.

Анализ влияния нелокальности на характеристики ближнего поля слоистой частицы на подложке

The problem of electromagnetic plane wave scattering by a layered nanoparticle with a metal plasmon shell deposited on the surface of a transparent substrate is considered. Using the Discrete Source Method, the influence of spatial nonlocality in a metal layer on the near-field intensity and absorption cross section is investigated. The particle excitation by both a propagating and evanescent wave are considered. It is shown that the substrate has a more significant effect on the optical characteristics of the near field than on the intensity in the far zone. It was found that taking into account the nonlocal effect in the metal leads to a significant decrease in the plasmon resonance amplitude with a small blue shift.

A geomagnetic filter for the Fermi-LAT background

ABSTRACT One of the unsolved questions in γ-ray astronomy is whether the extragalactic γ-ray background is of the discrete-source origin. To respond to this question, one first needs to reduce the data by differentiating charged particles from γ-rays. This procedure is usually performed on the basis of the detector responses. In this paper, we showed that the geomagnetic shielding effect at GeV energies can, to some extent, be used for this purpose for γ-ray telescopes in a low Earth orbit. We illustrated this method by applying it to the Fermi Large Area Telescope data. To partially decompose the charge-filtered background, we examined the contribution from star-forming galaxies by implying a radio/γ-ray connection in consideration of next-generation radio surveys.

On Data-Processing and Majorization Inequalities for f-Divergences with Applications

This paper is focused on the derivation of data-processing and majorization inequalities for f-divergences, and their applications in information theory and statistics. For the accessibility of the material, the main results are first introduced without proofs, followed by exemplifications of the theorems with further related analytical results, interpretations, and information-theoretic applications. One application refers to the performance analysis of list decoding with either fixed or variable list sizes; some earlier bounds on the list decoding error probability are reproduced in a unified way, and new bounds are obtained and exemplified numerically. Another application is related to a study of the quality of approximating a probability mass function, induced by the leaves of a Tunstall tree, by an equiprobable distribution. The compression rates of finite-length Tunstall codes are further analyzed for asserting their closeness to the Shannon entropy of a memoryless and stationary discrete source. Almost all the analysis is relegated to the appendices, which form the major part of this manuscript.