Rapid computation of far-field statistics for random obstacle scattering

In this article, we consider the numerical approximation of far-field statistics for acoustic scattering problems in the case of random obstacles. In particular, we consider the computation of the expected far-field pattern and the expected scattered wave away from the scatterer as well as the computation of the corresponding variances. To that end, we introduce an artificial interface, which almost surely contains all realizations of the random scatterer. At this interface, we directly approximate the second order statistics, i.e., the expectation and the variance, of the Cauchy data by means of boundary integral equations. From these quantities, we are able to rapidly evaluate statistics of the scattered wave everywhere in the exterior domain, including the expectation and the variance of the far-field. By employing a low-rank approximation of the Cauchy data's two-point correlation function, we drastically reduce the cost of the computation of the scattered wave's variance. Numerical results are provided in order to demonstrate the feasibility of the proposed approach

Optical Emission Lines and the X-Ray Properties of Type 1 Seyfert Galaxies

In this contribution we report on the study of the optical emission lines and X-ray spectra of a sample of Type 1 AGNs, collected at the Sloan Digital Sky Survey database and observed by the XMM Newton satellite. Exploiting the different instruments carried onboard XMM, we identify the spectral components of the soft and hard energy bands (in the range from 0.3 keV up to 10 keV). The properties of the X-ray continuum and of the Fe Kalpha line feature are investigated in relation to the optical broad emission line profiles and intensity ratios. The resulting picture of emission, absorption and reflection processes is interpreted by means of a BLR structural model that was developed on the basis of independent optical and radio observations.Comment: 6 pages, 3 figures, Proceedings of the VIII Serbian Conference on Spectral Line Shapes in Astrophysics, accepted for publication on Baltic Astronomy. Corrected typos in V

Proton therapy Monte Carlo SRNA-VOX code

The most powerful feature of the Monte Carlo method is the possibility of simulating all individual particle interactions in three dimensions and performing numerical experiments with a preset error. These facts were the motivation behind the development of a general-purpose Monte Carlo SRNA program for proton transport simulation in technical systems described by standard geometrical forms (plane, sphere, cone, cylinder, cube). Some of the possible applications of the SRNA program are: (a) a general code for proton transport modeling, (b) design of accelerator-driven systems, (c) simulation of proton scattering and degrading shapes and composition, (d) research on proton detectors; and (e) radiation protection at accelerator installations. This wide range of possible applications of the program demands the development of various versions of SRNA-VOX codes for proton transport modeling in voxelized geometries and has, finally, resulted in the ISTAR package for the calculation of deposited energy distribution in patients on the basis of CT data in radiotherapy. All of the said codes are capable of using 3-D proton sources with an arbitrary energy spectrum in an interval of 100 keV to 250 MeV

Revealing the nature of central emission nebulae in the dwarf galaxy NGC 185

In this paper we present new optical observations of the galaxy NGC 185 intended to reveal the status of supernova remnants (SNRs) in this dwarf companion of the Andromeda galaxy. Previously, it was reported that this galaxy hosts one SNR. Our deep photometric study with the 2m telescope at Rozhen National Astronomical Observatory using narrow-band H$\alpha$ and [SII] filters revealed complex structure of the interstellar medium in the center of the galaxy. To confirm the classification and to study the kinematics of the detected nebulae, we carried out spectroscopic observations using the SCORPIO multi-mode spectrograph at the 6m telescope at the Special Astrophysical Observatory of the Russian Academy of Science, both in low- and high-resolution modes. We also searched the archival X-ray and radio data for counterparts of the candidate SNRs identified by our optical observations. Our observations imply the presence of one more SNR, one possible HII region previously cataloged as part of an SNR, and the presence of an additional source of shock ionization in one low-brightness PN. We detected enhanced [SII]/H_alpha and [NII]/H_alpha line ratios, as well as relatively high (up to 90 km s$^{-1}$) expansion velocities of the two observed nebulae, motivating their classification as SNRs (with diameters of 45 pc and 50 pc), confirmed by both photometric and spectral observations. The estimated electron density of emission nebulae is 30 - 200 cm$^{-3}$. Archival XMM-Newton observations indicate the presence of an extended, low-brightness, soft source in projection of one of the optical SNRs, whereas the archival VLA radio image shows weak, unresolved emission in the center of NGC 185.Comment: 15 pages, 14 figures, accepted for publication in A&

RXJ 0921+4529: a binary quasar or gravitational lens?

We report the new spectroscopic observations of the gravitational lens RXJ 021+4529 with the multi-mode focal reducer SCORPIO of the SAO RAS 6-m telescope. The new spectral observations were compared with the previously observed spectra of components A and B of RXJ 0921+4529, i.e. the same components observed in different epochs. We found a significant difference in the spectrum between the components that cannot be explained with microlensing and/or spectral variation. We conclude that RXJ 0921+4529 is a binary quasar system, where redshifts of quasars A and B are 1.6535 +/- 0.0005 and 1.6625 +/- 0.0015, respectively.Comment: 6 pages, 5 figures, accepted for publication in The Astrophysical Journal Letter

Distributed Consensus Control of DFIGs with Storage for Wind Farm Power Output Regulation

Today the state-of-the-art (SoA) wind generators (WGs) are the double-fed induction (DFIGs) with integrated storage devices. In the future, these WGs are expected to be one of the largest producers of renewable energy worldwide. In this paper, we propose a distributed control methodology for solving the problem of coordinating and controlling a group of SoA WGs to attain fast wind farm (WF) power output regulation with each storage device providing the same amount of power, i.e with equal sharing among the storage devices. Our proposed methodology introduces a consensus protocol for coordinating the grid-side converters (GSCs), whose dynamical equations constitute their closed-loop dynamics, and a particular closed-loop form for the interfacing capacitor dynamics. We establish stability of these closed-loop dynamics by leveraging singular perturbation and Lyapunov theories, proving that with these closed-loop dynamics DFIGs accomplish their assigned control objectives. Finally, we analytically construct a distributed and a Control Lyapunov Function (CLF) -based control law for the GSC and the DCDC converter respectively, which jointly lead to the desired closed-loop dynamics. We demonstrate the effectiveness of our methodology through simulations on the IEEE 24-bus reliability test system (RTS)

Detailed Analysis of Balmer Lines in a Sloan Digital Sky Survey Sample of 90 Broad Line Active Galactic Nuclei

In order to contribute to the general effort aiming at the improvement of our knowledge about the physical conditions within the Broad Line Region (BLR) of Active Galactic Nuclei (AGN), here we present the results achieved by our analysis of the spectral properties of a sample of 90 broad line emitting sources, collected at the Sloan Digital Sky Survey (SDSS) database. By focusing our attention mainly onto the Balmer series of hydrogen emission lines, which is the dominant feature in the optical wavelength range of many BLR spectra, we extracted several flux and profile measurements, which we related to other source properties, such as optical continuum luminosities, inferred black hole masses, and accretion rates. Using the Boltzmann Plot method to investigate the Balmer line flux ratios as a function of the line profiles, we found that broader line emitting AGN typically have larger H_alpha / H_beta and smaller H_gamma / H_beta and H_delta / H_beta line ratios. With the help of some recent investigations, we model the structure of the BLR and we study the influence of the accretion process on the properties of the BLR plasma.Comment: 14 pages, 11 figures, fixes the wrong names of 4 objects; published on Ap

Copper production in Majdanpek in sixties and seventies of the 16th century

In this paper the practice of mine Majdanpek during sixties and seventies of the XVI century has been investigated with an accent on copper production. The attention has been also given to various subjects from considering copper treatment and use to forbidden activities connected to copper illegal production and trade with Persia

The line parameters and ratios as the physical probe of the line emitting regions in AGN

Here we discuss the physical conditions in the emission line regions (ELR) of active galactic nuclei (AGN), with the special emphasize on the unresolved problems, e.g. the stratification of the Broad Line Region (BLR) or the failure of the photoionization to explain the strong observed optical Fe II emission. We use here different line fluxes in order to probe the properties of the ELR, such as the hydrogen Balmer lines (Ha to He), the helium lines from two subsequent ionization levels (He II 4686 and He I 5876) and the strongest Fe II lines in the wavelength interval 4400-5400 \AA. We found that the hydrogen Balmer and helium lines can be used for the estimates of the physical parameters of the BLR, and we show that the Fe II emission is mostly emitted from an intermediate line region (ILR), that is located further away from the central continuum source than the BLR.Comment: 8 pages, 9 figures, 2 tables, New Astronomy Reviews (Proceeding of 7th SCSLSA), in pres