University of Chemical Technology and Metallurgy of Sofia
Sofia, Bulgaria

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Hristov J.,University of Chemical Technology and Metallurgy of Sofia
Fundamenta Informaticae | Year: 2017

This paper focuses on an approximate analytical solution of an initial-boundary value problem of spatial-fractional partial differential diffusion equation with RiemannLiouville fractional derivative in space. The spatial correlation of the superdiffusion coefficient as a power-law has been discussed in cases of fast and slow spatial superdiffusion. Approximate closed form solutions in terms of non-linear similarity variable are based on the integral-balance method and series expansion of the assumed parabolic profile with undefined exponent. The law of the spatial and temporal propagation of the solution was the primary issue and discussed in two cases: fast and slow superdiffussion.

Agency: European Commission | Branch: FP7 | Program: BSG-SME | Phase: SME-2011-1 | Award Amount: 1.53M | Year: 2011

The proposed project: Fabric Structures for Solar Power Generation (FabriGen), addresses the need to bring innovative products to the solar energy market to achieve the ambitious European targets for renewable energy generation. The FabriGen project aims to combine organic photovoltaic (OPV) materials with tensile fabrics to enable the construction of solar-power generating fabric structures. These structures could be connected to the grid, or used for distributed power generation, and will enable generators to participate in Feed-In-Tariff schemes that are being offered to promote the uptake of renewable energy technologies. The FabriGen project will research the use of commercial roll-to-roll printing technologies to deposit and pattern state-of-the-art OPV materials and produce large-area PV modules (20cm in research, scaling up to 100cm roll width). Means to integrate the PV fabrication processes with polyester fabric membranes will be developed. A key aspect of the research will be development and integration of barrier and encapsulation layers to provide long-life performance needed for outdoor use. The use of innovative materials to give enhanced UV response and improved resistance to UV degradation will be researched. Compliance testing to EN61646 will be carried out on fabricated PV modules to prepare for microgeneration certification and exploitation in the market.

Agency: European Commission | Branch: FP7 | Program: MC-IAPP | Phase: PEOPLE-2007-3-1-IAPP | Award Amount: 1.81M | Year: 2008

The IMeTI proposal aims to create a programme of applied research for implementation of membrane technology into industry based on experience and knowledge transfer between Academia and Industry. New membranes with improved chemical stability in a wide range of solvents, and better controlled cutoff properties and commercially viable membranes with high selectivity and flux for gas separations will be developed. The overall scientific and technical aim of the IMeTI project is to make important paradigm shifts in organic solvent nanofiltration and high temperature gas separation/purification, using cutting edge technologies based on membranes. The project involves the integration of the invention of new membranes and applications in the University/ Research Institute Partners with the subsequent development of the necessary membrane technology up to processing scale by the SMEs. A key feature of this project will be the interdisciplinary nature of the Partners, and the fact that they bring inter-sectorial competence to the network. We aim to create widely applicable, scalable, high performance process techniques and technologies. The knowledge transfer and training programme involves Early Stage Researchers (ESR), at both university and industrial partners, each of whom gain high quality experience through combination of local and network wide research experience. Experienced Researchers (ER) will provide in depth knowledge, and will assist in mentoring the ESR. Visiting scientists will provide expertise from outside the network. In addition to their individual research, ESR and ER will increase their research capacity and knowledge through attendance of high level research conferences and workshops. IMeTI seeks to contribute to improving the European knowledge supply chain through this industry-academia programme of applied research aimed at developing engineers and scientists who are academically excellent and industrially experienced.

Agency: European Commission | Branch: FP7 | Program: MC-IRSES | Phase: FP7-PEOPLE-2011-IRSES | Award Amount: 250.80K | Year: 2012

The NANEL joint exchange project aims to establish long-lasting research cooperation between Portuguese, Bulgarian, Belgian, Belarusian and Russian scientists in the field of electrochemical synthesis of advanced nanostructured materials. The collaborative consortium joins together a critical mass of the expertise available in the involved groups. The partners bring the complementary experiences and experimental facilities which are essential for effective development and testing of the nanomaterials for to be applied in sensors and photovoltaics. Mutually beneficial transfer of knowledge will be implemented through an intensive exchange program between six partner organizations. The main technical objective of the project is development of novel functional nanomaterials for sensors and solar cell applications on the basis of ordered nanoporous anodic oxides. The main scientific novelty of the project is functionalization of the porous anodic oxides, such as alumina or titania based ones, via electrochemical or electrophoretic ways using non-aqueous electrolytes. Ionic liquids and molten salts will be used as prospective candidates for the electrolytes. The electrochemical synthesis of nanomaterials has several important advantages because of relatively low costs and fine control of the process parameters. The suggested approach will confer creation of new ordered functional nanomaterials via electrochemical routes which are not possible in water-based electrolytes. Use of non-aqueous solution confers significant advantages for specific materials which are not stable in presence of water or can not be electrodeposited because of the relatively narrow electrochemical window of water.

Hristov J.,University of Chemical Technology and Metallurgy of Sofia
Thermal Science | Year: 2010

The fractional (half-time) sub-model of the heat diffusion equation, known as Dirac-like evolution diffusion equation has been solved by the heat-balance integral method and a parabolic profile with unspecified exponent. The fractional heat-balance integral method has been tested with two classic examples: fixed temperature and fixed flux at the boundary. The heat-balance technique allows easily the convolution integral of the fractional half-time derivative to be solved as a convolution of the time-independent approximating function. The fractional sub-model provides an artificial boundary condition at the boundary that closes the set of the equations required to express all parameters of the approximating profile as function of the thermal layer depth. This allows the exponent of the parabolic profile to be defined by a straightforward manner. The elegant solution performed by the fractional heat-balance integral method has been analyzed and the main efforts have been oriented towards the evaluation of fractional (half-time) derivatives by use of approximate profile across the penetration layer.

Vladkova T.G.,University of Chemical Technology and Metallurgy of Sofia
International Journal of Polymer Science | Year: 2010

We present many examples of surface engineered polymeric biomaterials with nanosize modified layers, controlled protein adsorption, and cellular interactions potentially applicable for tissue and/or blood contacting devices, scaffolds for cell culture and tissue engineering, biosensors, biological microchips as well as approaches to their preparation. Copyright © 2010 Todorka G. Vladkova.

Hristov J.,University of Chemical Technology and Metallurgy of Sofia
Thermal Science | Year: 2012

Integral balance solution employing entire domain approximation and the penetration dept concept to the Stokes' first problem of a viscoelastic generalized second grade fluid has been developed. The solution has been performed by a parabolic profile with an unspecified exponent allowing optimization through minimization of the L 2 norm over the domain of the penetration depth. The closedform solution explicitly defines two dimensionless similarity variables ξ = y/(vt) 1/2 and D o = χ 2 = = (p/vt β) 1/2, responsible for the viscous and the elastic responses of the fluid to the step jump at the boundary. The solution was developed with three forms of the governing equation through its 2-D forms (the main solution and example 1) and the dimensionless version showing various sides of the flow field and how the dimensionless groups control it: mainly the effect of the Deborah number. Numerical simulations demonstrating the effect of the various operating parameter and fluid properties on the developed flow filed have been performed.

Miladinova P.,University of Chemical Technology and Metallurgy of Sofia
Polymer Degradation and Stability | Year: 2013

The photostability of eight blue-emitting derivatives of 2-aminoterephthalic acid, three of them containing a stabilizer residue in their molecule in dimethylformamide was investigated. Copolymerisation of methyl methacrylate with four of them, monomer compounds and whitening of methyl methacrylate "in mass" with one of the compounds was accomplished. The copolymers obtained have an intense stable to solvents fluorescence. Photostability of the compounds, thus included in the polymer chain increased. The influence of the luminophores on the photostability of the inherently and whitened "in mass" polymers was established. © 2013 Elsevier Ltd. All rights reserved.

Hristov J.,University of Chemical Technology and Metallurgy of Sofia
European Physical Journal: Special Topics | Year: 2011

The work presents integral solutions of the fractional subdiffusion equation by an integral method, as an alternative approach to the solutions employing hypergeometric functions. The integral solution suggests a preliminary defined profile with unknown coefficients and the concept of penetration (boundary layer). The prescribed profile satisfies the boundary conditions imposed by the boundary layer that allows its coefficients to be expressed through its depth as unique parameter. The integral approach to the fractional subdiffusion equation suggests a replacement of the real distribution function by the approximate profile. The solution was performed with Riemann-Liouville time-fractional derivative since the integral approach avoids the definition of the initial value of the time-derivative required by the Laplace transformed equations and leading to a transition to Caputo derivatives. The method is demonstrated by solutions to two simple fractional subdiffusion equations (Dirichlet problems): 1) Time-Fractional Diffusion Equation, and 2) Time-Fractional Drift Equation, both of them having fundamental solutions expressed through the M-Wright function. The solutions demonstrate some basic issues of the suggested integral approach, among them: a) Choice of the profile, b) Integration problem emerging when the distribution (profile) is replaced by a prescribed one with unknown coefficients; c) Optimization of the profile in view to minimize the average error of approximations; d) Numerical results allowing comparisons to the known solutions expressed to the M-Wright function and error estimations. © 2011 EDP Sciences and Springer.

Hristov J.,University of Chemical Technology and Metallurgy of Sofia
Thermal Science | Year: 2011

The work presents an integral solution of the time-fractional subdiffusion equation as alternative approach to those employing hypergeometric functions. The integral solution suggests a preliminary defined profile with unknown coefficients and the concept of penetration (boundary layer) well known from the heat diffusion and hydrodynamics. The profile satisfies the boundary conditions imposed at the boundary of the boundary layer that allows its coefficients to be expressed through the boundary layer depth as unique parameter describing the profile. The technique is demonstrated by a solution of a time fractional radial equation concerning anomalous diffusion from a central point source in a sphere.

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