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Sofia, Bulgaria

Bodurov I.,Plovdiv University | Yovcheva T.,Plovdiv University | Sainov S.,Bulgarian Academy of Science | Sainov S.,Academy Georgi Bonchev str
Colloid and Polymer Science

The present study is focused on the characterization of optical properties of poly (methyl methacrylate) (PMMA) films and the possibilities of modulation and fine tuning of their refractive index by the inclusion of different concentrations of nano-sized titanium dioxide (TiO2) particles (less than 33 nm) and corona poling. The samples are prepared by the "spin coating" method and they are charged in a conventional point-to-plain corona system. The transparent PMMA/TiO2 films exhibit good optical properties in the visible range. An investigation of the film's surface refractive index by two wavelengths laser refractometry utilizing the disappearing diffraction pattern method is carried out. The refractive index increases with increasing the TiO2 content in the nanocomposite films. The corona poling increases the refractive index values for all samples regardless of the polarity and concentration of TiO2 nanoparticles. The results show that the prepared nanocomposite films have a potential application for optical devices. © 2014 Springer-Verlag Berlin Heidelberg. Source

Revalska M.,Agrobioinstitute Bul. Dragan Tzankov | Vassileva V.,Academy Georgi Bonchev str | Goormachtig S.,Ghent University | van Hautegem T.,Ghent University | And 2 more authors.
Current Genomics

Legumes, as protein-rich crops, are widely used for human food, animal feed and vegetable oil production. Over the past decade, two legume species, Medicago truncatula and Lotus japonicus, have been adopted as model legumes for genomics and physiological studies. The tobacco transposable element, Tnt1, is a powerful tool for insertional mutagenesis and gene inactivation in plants. A large collection of Tnt1-tagged lines of M. truncatula cv. Jemalong was generated during the course of the project 'GLIP': Grain Legumes Integrated Project, funded by the European Union (www.eugrainlegumes.org). In the project 'IFCOSMO': Integrated Functional and COmparative genomics Studies on the MOdel Legumes Medicago truncatula and Lotus japonicus, supported by a grant from the Ministry of Education, Youth and Science, Bulgaria, these lines are used for development of functional genomics platform of legumes in Bulgaria. This review presents recent advances in the evaluation of the M. truncatula Tnt1 mutant collection and outlines the steps that are taken in using the Tnt1-tagging for generation of a mutant collection of the second model legume L. japonicus. Both collections will provide a number of legume-specific mutants and serve as a resource for functional and comparative genomics research on legumes. Genomics technologies are expected to advance genetics and breeding of important legume crops (pea, faba bean, alfalfa and clover) in Bulgaria and worldwide. © 2011 Bentham Science Publishers Ltd. Source

Gechev S.M.,Bulgarian Hydrogen Society | Gechev S.M.,Academy Georgi Bonchev str | Iliev H.,Sofia University | Ganev V.,Academy Georgi Bonchev str | Mouhovski J.,Academy Georgi Bonchev str
International Conference on Transparent Optical Networks

The crystal CaF2 and its isotypes SrF2 and BaF2 doped with lanthanide elements, they are investigated for nonlinear optical applications and generation of ultrashort laser pulses. The Yb-doped crystal fluoride matrixes are could be also attractive for ICT, medical interventions, laser materials treatment, etc. The broad near-IR (NIR) luminescence in Yb3+ state (the second telecommunication window) and also their yellow-green and near-UV luminescence of Yb2+ are observed at low temperatures, although for the Yb,Na:CaSrF2 it is clearly observable at normal conditions. The Stokes fluorescence bands between 300 - 400 nm for the Yb,Na:CaSrF2 crystal medium induced from non-parametric processes in UV are narrow, clearly distinguishable and could be applied for novel lasers in UV - VIS range. © 2015 IEEE. Source

Boycheva I.,Agrobioinstitute Blvd. Dragan Tzankov | Vassileva V.,Academy Georgi Bonchev str | Revalska M.,Agrobioinstitute Blvd. Dragan Tzankov | Zehirov G.,Academy Georgi Bonchev str | Iantcheva A.,Agrobioinstitute Blvd. Dragan Tzankov

In eukaryotes, histone acetyltransferases regulate the acetylation of histones and transcription factors, affecting chromatin structural organization, transcriptional regulation, and gene activation. To assess the role of HAC1, a gene encoding for a histone acetyltransferase in Medicago truncatula, stable transgenic lines with modified HAC1 expression in the model plants M. truncatula, Lotus japonicus, and Arabidopsis thaliana were generated by Agrobacterium-mediated transformation and used for functional analyses. Histochemical, transcriptional, flow cytometric, and morphological analyses demonstrated the involvement of HAC1 in plant growth and development, responses to internal stimuli, and cell cycle progression. Expression patterns of a reporter gene encoding beta-glucuronidase (GUS) fused to the HAC1 promoter sequence were associated with young tissues comprised of actively dividing cells in different plant organs. The green fluorescent protein (GFP) signal, driven by the HAC1 promoter, was detected in the nuclei and cytoplasm of root cells. Transgenic lines with HAC1 overexpression and knockdown showed a wide range of phenotypic deviations and developmental abnormalities, which provided lines of evidence for the role of HAC1 in plant development. Synchronization of A. thaliana root tips in a line with HAC1 knockdown showed the involvement of this gene in the acetylation of two core histones during S phase of the plant cell cycle. © 2016 Springer-Verlag Wien Source

Piroeva I.,Academy Georgi Bonchev str | Atanassova-Vladimirova S.,Academy Georgi Bonchev str | Dimowa L.,Bulgarian Academy of Science | Sbirkova H.,Bulgarian Academy of Science | And 3 more authors.
Bulgarian Chemical Communications

This protocol details a rapid preparative procedure enabling the visualization of biological samples like DNA and bacteria by scanning electron microscopy (SEM). This involves the fixation of the samples, followed by subsequent dehydration and the processing for electron microscopy observation. The fixation step is performed by allowing the samples to embed into an agar matrix. The dehydration of the samples ensures that they will not disrupt when processing for SEM observation or in the SEM vacuum camera. The whole process may be achieved for 6-24 hours and has been optimized for the visualization of bacteria, DNA. Samples once processed for SEM can be stored mild vacuum for weeks, allowing sufficient time for image acquisition. © 2013 Bulgarian Academy of Sciences, Union of Chemists in Bulgaria. Source

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