Broadband multi-wavelength properties of M87 during the 2017 Event Horizon Telescope campaign

High Energy AstrophysicsInstrumentatio

Observation of a sudden cessation of a very-high-energy gamma-ray flare in PKS 1510-089 with H.E.S.S. and MAGIC in May 2016

The flat spectrum radio quasar (FSRQ) PKS 1510-089 is known for its complex multiwavelength behavior, and is one of only a few FSRQs detected at very high energy (VHE, E >100 GeV) -rays. VHE -ray observations with H.E.S.S. and MAGIC during late May and early June 2016 resulted in the detection of an unprecedented flare, which reveals for the first time VHE -ray intranight variability in this source. While a common variability timescale of 1.5 hr is found, there is a significant deviation near the end of the flare with a timescale of ∼ 20 min marking the cessation of the event. The peak flux is nearly two orders of magnitude above the low-level emission. For the first time, curvature is detected in the VHE -ray spectrum of PKS 1510-089, which is fully explained through absorption by the extragalactic background light. Optical R-band observations with ATOM reveal a counterpart of the -ray flare, even though the detailed flux evolution differs from the VHE lightcurve. Interestingly, a steep flux decrease is observed at the same time as the cessation of the VHE flare. In the high energy (HE, E >100 MeV) -ray band only a moderate flux increase is observed with Fermi-LAT, while the HE -ray spectrum significantly hardens up to a photon index of 1.6. A search for broad-line region (BLR) absorption features in the -ray spectrum indicates that the emission region is located outside of the BLR. Radio VLBI observations reveal a fast moving knot interacting with a standing jet feature around the time of the flare. As the standing feature is located ∼ 50 pc from the black hole, the emission region of the flare may have been located at a significant distance from the black hole. If this correlation is indeed true, VHE rays have been produced far down the jet where turbulent plasma crosses a standing shock.Accepted manuscrip

Mutual influence of additives of Ca and Si on properties of Cr-doped YAG ceramics

Cr-doped yttrium aluminum garnet ceramics with different concentration of additives Ca and Si were synthesized by vacuum reaction sintering. It was established that simultaneous doping with Ca and Si effects crucially on morphology and optical ceramics properties. Average grain size of such ceramics can reach to 1.08±0.06 μm that is much more less against the ceramics without Ca dopant. The optical properties of the ceramics deteriorate significantly with increase of Ca concentration. The degree of Cr4+ transformation to Cr3+ under air annealing is not well due to competition between Cr⁴⁺ and Si⁴⁺ ions to be charge compensated by Ca²⁺. Sintering aid SiO₂, which used in widespread ceramic technology to produce the high optical quality ceramics based on YAG, cannot be applied to produce the Cr⁴⁺-doped YAG ceramics with Ca as a charge compensator

Influence of Ca and Mg doping on the microstructure and optical properties of YAG ceramics

Ceramics of yttrium aluminum garnet doped with Ca or Mg are produced by solid state reaction under vacuum sintering. The influence of CaO and MgO additives themselves on microstructure and optical properties of YAG ceramics is investigated. Ceramics of Mg-doped YAG is transparent while ceramics of Ca-doped YAG is fully opaque due to high concentration of residual porosity into later. Changing concentration of Ca affects significantly on the grain growth, the average grain size increase with increasing of Ca concentration. Changing concentration of Mg from 0.05 to 0.5 at.% doesn't influence on grain size of the ceramics. It is proposed that liquid appears on the grain boundaries of the ceramics due to CaO additive. This liquid causes increasing the diffusion of components through the grain boundaries that speed up the grain growth and traps the pores while no such liquid exists for MgO additive. This difference is determined by the different ways of interaction of CaO and MgO with the basic YAG components Al₂O₃ and Y₂O₃. It is determined that the Mg concentration ranges in vicinity of 0.15 at.% Mg to produce Mg:YAG ceramics of higher transparency

Optical, thermal, strength properties and SHG efficiency of KDP single crystals doped with N,N'-dimethyl urea

Pure single crystals of potassium dihydrophosphate (KDP) and the ones doped with N,N′-dimethylurea (NN′DU) were grown by the temperature reduction method onto a point seed. The dopant concentration in the mother liquor was 0.15 and 0.45 wt. %. The study of the transmission spectra of KDP:NN′DU crystals, as well as the change in their strength properties (mechanical and laser strength) and thermal properties (differential thermal and thermogravimetric analyses) in the growth sectors {101} and {100} confirms the occurrence of NN′DU molecules in both growth sector. It was shown that doping of the crystals with NN′DU molecules led to an increase in the efficiency of second harmonic generation by two times in the sector {100} of KDP:NN′DU crystals as compared with pure KDP

The European mistletoe ( Viscum album

The hemiparasitic European mistletoe, Viscum album L. (Viscaceae), displays a rapid and remarkable expansion into natural and urban ecosystems in Ukraine. The monitoring and management of this quickly spreading species is becoming increasingly difficult as new plant species become hosts. Unlike other local mistletoe species, the European mistletoe has a broad distribution and thus requires a countrywide pest status assessment for control. This review outlines the major taxonomic and evolutionary issues pertinent to V. album with an emphasis on the characters used to distinguish its five currently recognized subspecies. The review also provides an updated distribution map and host range for the three V. album subspecies in Ukraine [V. album subsp. album, V. album subsp. abietis (Wiesb.) Janch., and V. album subsp. austriacum (Wiesb.) Vollm.], addressing the current knowledge of their biology and ecology. A significant portion of the paper is devoted to the diversity of organisms associated with V. album, including herbivores, endophytes, and parasites, drawing particular attention to major pollination and dispersal vectors, as well as potential biocontrol agents for this mistletoe species.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author