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Sofia, Bulgaria

The Bulgarian Academy of science is the National Academy of Bulgaria, established in 1869. The Academy, located in Sofia, is autonomous and has a Society of Academicians, Correspondent Members and Foreign Members. It publishes and circulates different scientific works, encyclopedias, dictionaries and journals, and runs its own publishing house.Stefan Vodenicharov has been president of the BAS since 2012. Its budget in 2009 was 84 million leva, or 42.7 million euro. The Bulgarian Space Agency, part of the BAS, has a budget of 1 million euro. Wikipedia.

Hadjiivanov K.,Bulgarian Academy of Science
Advances in Catalysis | Year: 2014

Surface hydroxyl groups are active centers in many catalytic reactions and can play an important role during catalyst preparation. In this chapter, the application of infrared spectroscopy for identification and characterization of surface OH groups is reviewed. The potential of other techniques is also briefly described. The vibrational signature of various types of hydroxyls is discussed; however, the amount of information that can be gathered from the hydroxyl spectra itself is limited. In contrast, application of probe molecules allows a profound characterization of hydroxyl species. Two scenarios are considered: the formation of H-bonds between hydroxyl groups and probe molecules, and chemical reactions between hydroxyl groups and molecules or ions (such as protonation of basic probe molecules, exchange reactions, redox processes). Means to explore the accessibility and location of hydroxyl groups are introduced. The properties of OD and OH groups are compared, and the application of H/D exchange as a diagnostic reaction is discussed. Finally, the hydroxyl population on materials of practical interest is analyzed. © 2014 Elsevier Inc.

Kantardjiev A.A.,Bulgarian Academy of Science
Nucleic Acids Research | Year: 2012

Quantum.Ligand.Dock (protein-ligand docking with graphic processing unit (GPU) quantum entanglement refinement on a GPU system) is an original modern method for in silico prediction of protein-ligand interactions via high-performance docking code. The main flavour of our approach is a combination of fast search with a special account for overlooked physical interactions. On the one hand, we take care of self-consistency and proton equilibria mutual effects of docking partners. On the other hand, Quantum.Ligand.Dock is the the only docking server offering such a subtle supplement to protein docking algorithms as quantum entanglement contributions. The motivation for development and proposition of the method to the community hinges upon two arguments-the fundamental importance of quantum entanglement contribution in molecular interaction and the realistic possibility to implement it by the availability of supercomputing power. The implementation of sophisticated quantum methods is made possible by parallelization at several bottlenecks on a GPU supercomputer. The high-performance implementation will be of use for large-scale virtual screening projects, structural bioinformatics, systems biology and fundamental research in understanding protein-ligand recognition. The design of the interface is focused on feasibility and ease of use. Protein and ligand molecule structures are supposed to be submitted as atomic coordinate files in PDB format. A customization section is offered for addition of user-specified charges, extra ionogenic groups with intrinsic pKa values or fixed ions. Final predicted complexes are ranked according to obtained scores and provided in PDB format as well as interactive visualization in a molecular viewer. Quantum.Ligand.Dock server can be accessed at html. © 2012 The Author(s).

The bromide minerals solubility in the mixed system (m 1KBr + m 2CaBr 2)(aq) have been investigated at T = 323.15 K by the physico-chemical analysis method. The equilibrium crystallization of KBr(cr), and CaBr 2·4H 2O(cr) has been established. The results from solubility measurements obtained have been combined with experimental equilibrium solubility data available in the literature at T = 298.15 K to construct a chemical model that calculates (solid + liquid) equilibria in the ternary (m 1KBr + m 2CaBr 2)(aq) system. The solubility modelling approach based on fundamental Pitzer specific interaction equations is employed. Temperature extrapolation of the mixed system model provides reasonable mineral solubilities at low (273.15 K) and high temperature (up to 373.15 K). The reference solubility data for (m 1MgBr 2 + m 2CaBr 2)(aq) system, which are available in the literature at T = (273.15, 298.15, and 323.15) K are used to evaluate mixing ion interaction parameters and to develop a model that calculates (solid + liquid) equilibria in this ternary system. The models for both ternary systems give a very good agreement with bromide salts equilibrium solubility data. Limitations of the mixed solution models due to data insufficiencies at high temperature are discussed. The mixed system models presented in this study expand the previously published temperature dependent sodium-potassium-magnesium-bromide model by evaluating potassium-calcium-bromide and magnesium-calcium-bromide mixing solution parameters and by evaluating a chemical potential of double salt 2MgBr 2·CaBr 2·12H 2O(cr), and complete the temperature dependent thermodynamic model of solution behaviour and (solid + liquid) equilibria in quinary system (Na + K + Mg + Ca + Br + H 2O). The results of Pitzer ion interaction model-based thermodynamic studies on binary, and mixed systems within the (Na + K + Mg + Ca + Br + H 2O) system have been summarised. Important thermodynamic characteristics {solubilities (m s), thermodynamic solubility products (as ln K ° sp), standard molar Gibbs free energy of formation (Δ fG ° m), deliquescence relative humidity (DRH)} of the bromide minerals crystallizing from the saturated binary and ternary solutions are given. Model predictions on m s, ln K ° sp, Δ fG ° m, and DRH are compared with those available in the literature. Model calculations are in excellent agreement with the reference experimental data and recommendations. © 2012 Elsevier Ltd. All rights reserved.

Ivanov B.V.,Bulgarian Academy of Science
General Relativity and Gravitation | Year: 2012

A global view is given upon the study of collapsing shear-free perfect fluid spheres with heat flow. We apply a compact formalism, which simplifies the isotropy condition and the condition for conformal flatness. The formulas for the characteristics of the model are straight and tractable. This formalism also presents the simplest possible version of the main junction condition, demonstrated explicitly for conformally flat and geodesic solutions. It gives the right functions to disentangle this condition into well known differential equations like those of Abel, Riccati, Bernoulli and the linear one. It yields an alternative derivation of the general solution with functionally dependent metric components. We bring together the results for static and time-dependent models to describe six generating functions of the general solution to the isotropy equation. Their common features and relations between them are elucidated. A general formula for separable solutions is given, incorporating collapse to a black hole or to a naked singularity. © 2012 Springer Science+Business Media, LLC.

Milchev A.,Bulgarian Academy of Science
Journal of Physics Condensed Matter | Year: 2011

The relaxation, diffusion and translocation dynamics of single linear polymer chains in confinement is briefly reviewed with emphasis on the comparison between theoretical scaling predictions and observations from experiment or, most frequently, from computer simulations. Besides cylindrical, spherical and slit-like constraints, related problems such as the chain dynamics in a random medium and the translocation dynamics through a nanopore are also considered. Another particular kind of confinement is imposed by polymer adsorption on attractive surfaces or selective interfaces - a short overview of single-chain dynamics is also contained in this survey. While both theory and numerical experiments consider predominantly coarse-grained models of self-avoiding linear chain molecules with typically Rouse dynamics, we also note some recent studies which examine the impact of hydrodynamic interactions on polymer dynamics in confinement. In all of the aforementioned cases we focus mainly on the consequences of imposed geometric restrictions on single-chain dynamics and try to check our degree of understanding by assessing the agreement between theoretical predictions and observations. © 2011 IOP Publishing Ltd.

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