Torrential floods and town and country planning in Serbia

Torrential floods are the most frequent natural catastrophic events in Serbia, causing the loss of human lives and huge material damage, both in urban and rural areas. The analysis of the intra-annual distribution of maximal discharges aided in noticing that torrential floods have a seasonal character. The erosion and torrent control works (ETCWs) in Serbia began at the end of the 19th century. Effective protection from torrential floods encompasses biotechnical works on the slopes in the watershed and technical works on the torrent beds, within a precisely defined administrative and spatial framework in order to achieve maximal safety for people and their property. Cooperation to overcome the conflicts between the sectors of the water resources management, forestry, agriculture, energetics, environmental protection and local economic development groups is indispensable at the following levels: policy, spatial planning, practice, investments and education. The lowest and most effective level is through the Plans for Announcement of Erosive Regions (PAERs) and the Plans for Protection from Torrential Floods (PPTFs), with Hazard Zones (HZs) and Threatened Areas (TAs) mapping on the basis of the hydrologic, hydraulic and spatial analysis of the factors that are important for the formation of torrential floods. Solutions defined through PAERs and PPTFs have to be integrated into Spatial Plans at local and regional levels

Spin evolution of neutron stars

In this paper we review the basics of magneto-rotational properties of neutron stars focusing on spin-up/spin-down behavior at different evolutionary stages. The main goal is to provide equations for the spin frequency changes in various regimes (radio pulsar, propeller, accretor, etc.). Since presently spin behavior of neutron stars at all stages remains a subject of many uncertainties, we review different suggestions made over the years in the literature.Comment: 44 pages, accepted for publication in Galaxies (2024), special issue 'The 10th Anniversary of Galaxies: The Astrophysics of Neutron Stars', Eds. R. Mignani, M. Razzano, S. Popo

Two Active States of the Narrow-Line Gamma-Ray-Loud AGN GB 1310 + 487

Context. Previously unremarkable, the extragalactic radio source GB1310 487 showed gamma-ray flare on 2009 November 18, reaching a daily flux of approximately 10(exp -6) photons cm(exp -2) s(exp -1) at energies E greater than 100MeV and became one of the brightest GeV sources for about two weeks. Its optical spectrum shows strong forbidden-line emission while lacking broad permitted lines, which is not typical for a blazar. Instead, the spectrum resembles those of narrow emission-line galaxies. Aims. We investigate changes in the object's radio-to-GeV spectral energy distribution (SED) during and after the prominent gamma-ray flare with the aim of determining the nature of the object and of constraining the origin of the variable high-energy emission. Methods. The data collected by the Fermi and AGILE satellites at gamma-ray energies; Swift at X-ray and ultraviolet (UV); the Kanata, NOT, and Keck telescopes at optical; OAGH and WISE at infrared (IR); and IRAM30m, OVRO 40m, Effelsberg 100m, RATAN-600, and VLBA at radio are analyzed together to trace the SED evolution on timescales of months. Results. The gamma-ray radio-loud narrow-line active galactic nucleus (AGN) is located at redshift z = 0.638. It shines through an unrelated foreground galaxy at z = 0.500. The AGN light is probably amplified by gravitational lensing. The AGN SED shows a two-humped structure typical of blazars and gamma-ray-loud narrow-line Seyfert 1 galaxies, with the high-energy (inverse-Compton) emission dominating by more than an order of magnitude over the low-energy (synchrotron) emission during gamma-ray flares. The difference between the two SED humps is smaller during the low-activity state. Fermi observations reveal a strong correlation between the gamma-ray flux and spectral index, with the hardest spectrum observed during the brightest gamma-ray state. The gamma-ray flares occurred before and during a slow rising trend in the radio, but no direct association between gamma-ray and radio flares could be established. Conclusions. If the gamma-ray flux is a mixture of synchrotron self-Compton (SSC) and external Compton (EC) emission, the observed GeV spectral variability may result from varying relative contributions of these two emission components. This explanation fits the observed changes in the overall IR to gamma-ray SED

Effect of Annealing Treatment on the Optical Properties of Silicon Nitride Waveguides

Introduction. Silicon nitride is a highly promising material for fabrication of photonic integrated circuits (PICs). Plasma-enhanced chemical vapor deposition is a prospective method for large-scale industrial production of silicon nitride-based PICs. The disadvantage of this method, which limits its practical application, consists in high insertion losses in the telecommunication frequency band due to absorption on the Si–H and N–H bonds remaining from the film growth process. Thermal annealing is the most common method for breaking these bonds and reducing losses. Therefore, investigation of the impact of annealing on the optical properties of photonic integrated waveguides is an important research task.Aim. To investigate the effect of annealing treatment on the optical properties of PICs based on the silicon nitride films with different thicknesses obtained by plasma-enhanced chemical vapor deposition.Materials and methods. The work investigates the effect of annealing treatment on the optical properties of PICs based on the silicon nitride films with thicknesses of 200, 400 and 700 nm. To that end, the transmission characteristics of a set of test elements were measured using a high-definition component analyzer in the frequency range of 185…196 THz.Results. Frequency dependencies of loss and coupling coefficients, as well as the group index before and after annealing were extracted from the measured transmission characteristics of the test elements. It was found that waveguides on a 200-nm-thick film exhibited higher losses in comparison with the waveguides on thicker films. The waveguides with cross sections of 900 × 400 and 900 × 700 nm2 demonstrate the losses below 5 dB in the frequency range of 185…190 THz. A rapid increase in losses due to absorption on the N–H bonds was observed at the frequencies above 190 THz. The work shows that thermal annealing reduces insertion losses across the frequency range from 185 to 196 THz. The adequacy of extracted optical parameters is confirmed by comparing theoretical and experimental transmission characteristics of the ring resonator.Conclusion. The obtained results demonstrate that silicon nitride waveguides fabricated by the method of plasma-enhanced chemical vapor deposition require the stage of thermal annealing. Vacuum annealing at 600 °C for 30 min reduces insertion losses in the waveguides with cross sections of 900 × 400 and 900 × 700 nm2 down to 4 dB/cm in the frequency band from 185 to 196 THz

Spectroscopy of Optical Counterparts of Ultraluminous X-ray Sources

Here we present the results of panoramic and long-slit observations of eight ULX nebular counterparts held with the 6m SAO telescope. In two ULXNe we detected for the first time signatures of high excitation ([OIII]5007 / H\beta > 5). Two of the ULXs were identified with young (T ~ 5-10 Myr) massive star clusters. Four of the eight ULX Nebulae (ULXNe) show bright high-excitation lines. This requires existence of luminous (~ 10^{38} .. 10^{40} erg/s) UV/EUV sources coinciding with the X-ray sources. Other 4 ULXNe require shock excitation of the gas with shock velocities of 20-100km/s. However, all the studied ULXN spectra show signatures of shock excitation, but even those ULXNe where the shocks are prevailing show presence of a hard ionizing source with the luminosity at least ~10^{38} erg/s. Most likely shock waves, X-ray and EUV ionization act simultaneously in all the ULXNe, but they may be roughly separated in two groups, shock-dominated and photoionization-dominated ULXNe. The ULXs have to produce strong winds and/or jets powering their nebulae with \~10^{39} erg/s. Both the wind/jet activity and the EUV source needed are consistent with the suggestion that ULXs are high-mass X-ray binaries with the supercritical accretion disks of the SS433 type.Comment: submitted to Astrophysical Bulletin (Bull. Special Astrophys. Obs.

Electrical, Thermal and Optical Diagnostics of an Atmospheric Plasma Jet System

Plasma diagnostics of atmospheric plasmas is a key tool in helping to understand processing performance issues. This paper presents an electrical, optical and thermographic imaging study of the PlasmaStream atmospheric plasma jet system. The system was found to exhibit three operating modes; one constricted/localized plasma and two extended volume plasmas. At low power and helium flows the plasma is localized at the electrodes and has the electrical properties of a corona/filamentary discharge with electrical chaotic temporal structure. With increasing discharge power and helium flow the plasma expands into the volume of the tube, becoming regular and homogeneous in appearance. Emission spectra show evidence of atomic oxygen, nitric oxide and the hydroxyl radical production. Plasma activated gas temperature deduced from the rotational temperature of nitrogen molecules was found to be of order of 400 K: whereas thermographic imaging of the quartz tube yielded surface temperatures between 319 and 347 K.<br/

Spin Evolution of Neutron Stars

In this paper we review the basics of magneto-rotational properties of neutron stars focusing on spin-up/spin-down behavior at different evolutionary stages. The main goal is to provide equations for the spin frequency changes in various regimes (radio pulsar, propeller, accretor, etc.). Since presently the spin behavior of neutron stars at all stages remains a subject of many uncertainties, we review different suggestions made over the years in the literature