[en] Organic thin films of poly(3-hexylthiophene) (P3HT) and the fullerene derivative [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) mixed in 1:1 mass ratio were deposited by spin coating from a chlorobenzene solution. The substrates used were glass and Si wafers. The films were produced for future application in organic solar cells. After the deposition procedure, the P3HT:PCBM films were annealed in argon atmosphere at different temperatures or were kept in the solvent vapour for 10 min in order to stabilize the coatings. The films were characterized by Fourier Transform Infrared Spectroscopy (FTIR), optical transmission and reflection spectroscopy, Raman spectroscopy and photoluminescence (PL) measurements. The highest absorption coefficient and best crystallization of the films was obtained upon thermal annealing at 140^oC and treatment in solvent vapour. Annealing at temperatures above 140⁰C gradually destroyed the crystalline order, and annealing at 160^oC led to the amorphization of the P3HT in the film. For the purpose of charge separation the best post-deposition treatment appeared to be 60^oC, as demonstrated by the PL measurements. In this case, the best interpenetration of the two constituents of the bulk heterojunction was most probably achieved

[en] Parameter estimation and high-speed small targets detection in randomly arriving impulse interference environment is a challenging task in radar systems design. Conventional radar detection architectures like spectral discrimination and non-coherent integration have been considered and used but with limited success. In this paper an improved target detection architecture, making use of Hough velocity estimation technique is presented. The algorithm is based on a Track-Before-Detect (TBD) processing method, which allows for the previously collected data to be used in the target detection process and parameter estimation. The presented technique has a lot of advantages compared to traditional ones. The presented results can be successfully applied for radar target parameter estimation as well as in the existing communication network receivers making use of pulse signals. Key words: signal processing, Hough transform, target detection and velocity estimation

[en] The aim of the present paper is to study virtual steady-state vibrations in the neighbourhood of resonance conditions of a rotor with six degrees of freedom in linear homogeneous elasto-viscous field. Unstable frequencies zones are determined by “limited” power of an electric motor with linear characteristic and only one time-constant. Bogoliubov–Mitropolsky’s asymptotical method is applied in the neighbourhood of single basic resonance by small difference between natural and driving frequencies. The influence of the motor’s time-constant is analyzed on the value of unstable frequency’s zones by quasi steady-state increasing/decreasing frequencies (jump phenomenon). By special condition increasing of the driving frequency in growing rate could be seen right after resonance due to transfer from “small” angular coordinates to main rotation. Experimental result is applied

[en] This work presents the research of Faraday Effect in the energetic field around the fundamental absorption edge of the pure and doped with cobalt and nickel ions magnesium sulfite hexahydrate (MgSO_3.6H_2O). The width of the crystal band gap and the type of interband transitions are determined, based on the spectra of the Faraday rotation. These data match the results of the calculated electronic band structure of MgSO_3.6H_2O. Exchange interaction between the free charge carriers and the d-ions of cobalt and nickel is observed, which shows that the crystal doped with cobalt should possess ions in charged state Co_2"+ Key words: magnesium sulfite hexahydrate MgSO_3.6H_2O, width of the band gap, interband transitions, Faraday rotation, exchange interaction

[en] The HEU to LEU conversion of the IRT–Sofia research reactor of the Institute for Nuclear Research and Nuclear Energy of the Bulgarian Academy of Sciences was jointly studied with the Argonne National Laboratory as a part of the RERTR Programme. The main purpose of the collaboration consisted in accomplishment of safety analyses and preparation of documents used for regulatory approval tasks solution. The main steps and results which are fundamental for the preparation of IRT–Sofia Safety Analyses Report including Operating Limits and Conditions are presented in this paper. The documents prepared by INRNE in accordance with the European nuclear safety requirements and IAEA recommendations were submitted for approval to the Bulgarian Nuclear Regulatory Agency at the end of 2010. Key words: research reactor, safety analyses report, Nuclear Regulatory Agency

[en] The extreme solar activity in early September 2017 at minimum of solar cycle 24 is analysed. The beginning of the intensive solar-terrestrial disturbances was the Active Region AR2673, which produced four powerful eruptions class X, including the strongest flare X9.3 of Solar Cycle 24 on September 6, 2017, after which began G4 – Severe geomagnetic storm on 07÷08.09.2017 with Ap = 106, and also the second strongest flare of Solar Cycle 24 on September 10, 2017, which generated instantly the ground level enhancement of cosmic rays or Ground Level Event No 72 (GLE72). The three space regions of impact are investigated and analysed in the present paper: 1) Sun – photosphere and solar corona; 2) Interplanetary space with solar wind and its basic parameters – velocity V , density or concentration N , temperature T p and intensity of the magnetic field B ; 3) Earth and its magnetosphere. Calculations of the solar wind parameters from measurements by SOHO and DSCOVR space probes in the point of Lagrange are made: the kinetic (dynamic) energy density Ek , thermal energy density E t and magnetic energy density Em during the investigated period September 2–15, 2017. We found two interesting phenomena in the investigated period: 1) tunnel effect in the Earth’s environment, and 2) specific distribution of the solar wind energy density during and after the CME. It is likely that both kinetic and magnetic energies can be used as predictors of strong geomagnetic storms. Key words: solar activity, flares, coronal mass ejection (CME), G4 – Severe geomagnetic storm, solar energetic particles (SEPs), ground-level enhancement (GLE), space weather

[en] A new method was developed for the total reflection X-ray fluorescence (TXRF) determination of rhenium in molybdenum concentrates using gallium as internal standard. The samples were analyzed as slurries in Triton™ X-114. The experimental parameters, such as sample pretreatment and deposition, as well as slurry concentration, were optimized and matrix effects were investigated. Comparison with an independent method as well as the certified reference material CGL-202 were used for method validation. The method was applied to the determination of rhenium in a molybdenum concentrate from the “Elatsite-med” industrial plant located in Mirkovo, Bulgaria. The results obtained confirmed the suitability of TXRF for the fast and easy determination of rhenium in molybdenum concentrates. Key words: rhenium, molybdenum sulfide, TXRF analysis, gallium internal standard, slurry sampling

[en] The CMS (Compact Muon Solenoid) experiment is a general purpose detector, located at the CERN Large Hadron Collider (LHC). It has a muon spectrometer equipped with a redundant system composed of three different detector technologies – Resistive Plate Chambers (RPCs) and Drift Tubes (DTs) in the barrel and RPC and Cathode Strip Chambers (CSCs) in the endcap region. All three are used for muon reconstruction and triggering. The RPC detector system consists of a total of 1056 double-gap chambers, covering the pseudo-rapidity region up to |η| ≤1.6. Here we present the Resistive Plate Chambers performance results for the period of 2015 and 2016 with pp collisions at 13 TeV. The stability of the RPC performance is reported in terms of efficiency, cluster size and rate distributions. Key words: Resistive Plate Chambers, muon spectrometers

[en] Recent reports evidence a number of new radiopharmaceuticals for diagnostic and theragnostic purposes. However, they have been only biologically characterized using biodistribution studies. A more detailed information concerning their pharmacokinetic parameters is desirable for radiopharmaceutical’s complete characterization. However, easy-to-use tools to assist researchers in the assessment of the radiopharmacokinetic parameters are not available in nuclear medicine so far. In this article we present a developed five-compartmental mathematical model and a dedicated software CoKiMo, designed to calculate the radiopharmaceuticals’ pharmacokinetic parameters. CoKiMo software can be used to obtain the time-activity curves of the five main organs such as blood pool distribution, kidney, liver, and other two organs of interest from the biodistribution data. The curves are obtained by interpolation of organ activity values, measured separately at different moments of time, and then can be integrated to calculate the radiopharmaceutical’s biological half-life ( T _1/2) and mean residence time. The transfer rate constants in the organs are obtained as a solution of a number of linear differential equations, described by the model. The data obtained by the program provide information about the organ’s uptake and clearance useful in the characterization of the radiopharmaceuticals. Key words: multi-compartmental model, radiopharmacokinetics, biodistribution

[en] Giant cell tumour of bone (GCTB) is considered to be a histologically benign osseous tumour, which tends to exhibit local invasion and tendency for formation of pulmonary metastases. It has a high rate of recurrence and may undergo malignant transformation. The tumour is composed of three types of cells: osteoclast-like multinucleated giant cells, spindle-shaped stromal cells of mesenchymal origin and cells of the monocyte-macrophage lineage. Giant and stromal cells are responsible for the production and release of matrix metalloproteinases (MMP-s), which accelerate the breakdown of the extracellular matrix (ECM) and have a key role in local tumour invasion, as well as distant metastasis. The biological behaviour of GCTB can be assessed by radiographic appearance on the basis of Campanacci’s classification, which classifies the tumour into 3 grades depending on the radiographic signs of local invasion. The aim of the present study was to establish whether a correlation exists between the radiographic appearance of GCTB grades 1 and 3 according to Campanacci’s classification and the expression of MMP‑9. We studied clinical material from 8 patients and conducted an immunohistochemical analysis of the MMP‑9 expression. A positive reaction was observed predominantly in stromal cells and was more intensive in lesions with aggressive radiographic appearance as compared to those with latent behaviour. The established correlation between MMP-9 expression by tumour cells and biological behaviour, assessed on the basis of radiographic appearance, may further support the role of MMP‑9 as a prognostic marker for possible aggressive behaviour and tendency for metastatic spread. Key words: giant cell tumour of bone, matrix metalloproteinase‑9, radiography, correlation