Volume 5
Worldwide Scientists
Academician Ivan Petkov Popchev
Academician Vassil Stoyanov Sgurev
Professor Uldis Viesturs
Professor Mikhail Georgiev Matveev
New Books
Bioprocess Engineering
Forthcoming Events
First call for the 20th Anniversary International Symposium "Bioprocess Systems 2007 - BioPS'07"
Modelling and Optimization of Biotechnological Systems
Modelling of Fermentation Processes Based on State Decomposition1-12
Olympia Roeva, Tania Pencheva, Uldis Viesturs, Stoyan Tzonkov
[ +/- abstract ][ full text ]
This paper presents an overview of implementation of state decomposition approach to modelling of Saccharomyces cerevisiae and Escherichia coli cultivation processes. This approach, so-called functional state approach, is an alternative concept which helps in modelling and control of such complex processes like fermentation processes. The concept implementation leads to a process description with simpler and more transparent local models. The functional state approach is originally developed for yeast growth processes. Based on the similarities of main metabolic pathways of yeast and bacteria, the concept of state decomposition could be applied successfully for modelling of Escherichia coli cultivations.
Modelling Chemical Kinetics of Soybean Oil Transesterification Process for Biodiesel Production: An Analysis of Molar Ratio between Alcohol and Soybean Oil Temperature Changes on the Process Conversion Rate13-22
Bruno Wenzel, Maicon Tait, Aparecido Módenes, Alexander Kroumov
[ +/- abstract ][ full text ]
A mathematical model describing chemical kinetics of transesterification of soybean oil for biodiesel production has been developed. The model is based on the reverse mechanism of transesterification reactions and describes dynamics concentration changes of triglycerides, diglycerides, monoglycerides, biodiesel, and glycerol production. Reaction rate constants were written in the Arrhenius form. An analysis of key process variables such as temperature and molar ratio soybean oil- alcohol using response surface analysis was performed to achieve the maximum soybean conversion rate to biodiesel. The predictive power of the developed model was checked for the very wide range of operational conditions and parameters values by fitting different experimental results for homogeneous catalytic and non-catalytic processes published in the literature. A very good correlation between model simulations and experimental data was observed.
Fed-batch Optimization of PHB Synthesis through Mechanistic, Cybernetic and Neural Approaches23-38
Pratap R. Patnaik
[ +/- abstract ][ full text ]
Despite its superiority over chemically synthesized petroleum-based polymers, poly-β-hydroxybutyrate (PHB) has been less successful commercially. A prime reason is the low productivity of microbial processes for PHB. High fermentation efficiency requires good modelling and optimization. Neither classical mechanistic models nor the recent cybernetic models have resulted in sufficiently high yields of PHB. So a neural network description has been proposed here. Relative to the other two approaches, neural optimization doubled the maximum PHB concentration in fed-batch fermentation with Ralstonia eutropha, the most commonly employed organism for PHB production, and it consumed less of the substrates. This advantage and their model-free nature make neural networks an attractive technique to enhance PHB productivity.
A Multiple-objective Optimization of Whey Fermentation in Stirred Tank Bioreactors39-48
Mitko Petrov
[ +/- abstract ][ full text ]
A multiple-objective optimization is applied to find an optimal policy of a fed-batch fermentation process for lactose oxidation from a natural substratum of the strain Kluyveromyces marxianus var. lactis MC5. The optimal policy is consisted of feed flow rate, agitation speed, and gas flow rate. The multiple-objective problem includes: the total price of the biomass production, the second objective functions are the separation cost in downstream processing and the third objective function corresponds to the oxygen mass-transfer in the bioreactor. The multiple-objective optimization are transforming to standard problem for optimization with single-objective function. Local criteria are defined utility function with different weight for single-type vector task. A fuzzy sets method is applied to be solved the maximizing decision problem. A simple combined algorithm guideline to find a satisfactory solution to the general multiple-objective optimization problem. The obtained optimal control results have shown an increase of the process productiveness and a decrease of the residual substrate concentration.
Biomedical Systems
Diagnostic Value of Histological and Microbiological Screening in Etiopathogenesis of Recurrent and Hypertrophic Tonsillitis49-56
Sergejs Isajevs, Aija Zilevica, Jurijs Markovs, Uldis Viesturs, Gundega Knipshe
[ +/- abstract ][ full text ]
Interest in the mechanisms and causes of recurrent tonsillitis is considerable. CD4+CD25+ T-lymphocytes have an important role in the maintenance of immunological tolerance. The aim of our research was to compare the diagnostic value of palatine tonsils histological and microbiological screening in patients with hypertrophic and recurrent tonsillitis. 14 patients with hypertrophic and 10 patients with chronic tonsillitis undergoing tonsillectomy were enrolled in the study. Rapid diagnosis of adenovirus, parainfluenza, influenza A and B, and respiratory syncytial virus infection was made before tonsillectomy by viral antigen detection using the immunofluorescence procedure from tonsils. Herpes simplex and cytomegaloviruses DNA were detected by the polymerase chain reaction. Samples for bacteriological studies were collected using a cotton swab. Immunohistochemical methods were used to evaluate S-100 and TGF-beta1 expression. The obtained results showed that patients with recurrent tonsillitis had less S-100 and TGF-beta1 positive cells in parafollicular regions compared to patients with hypertrophic tonsillitis. In both groups, tonsils were colonized predominantly by gram-positive microorganisms and adenovirus (36% of cases). However, in patients with recurrent tonsillitis, associations of gram-positive, gram-negative bacteria and viruses (40% of cases) were observed. To conclude, recurrent tonsillitis is characterized by the breakdown of the immunological tolerance to oral microflora.
A Univariate Analysis of Risk Factors for Diabetic Nephropathy57-67
Anthony Shannon, Yee Hung Choy
[ +/- abstract ][ full text ]
This paper uses actual data from 267 patients with non-insulin-dependent (Type 2) diabetes mellitus in order to see how the various risk factors can affect the progression of diabetic nephropathy. Examination of each independent variable individually can only provide a preliminary idea of how important each variable is by itself. The relative importance of all the variables has to be examined simultaneously by multivariate methods. The approach succeeds in identifying preliminary risk factors such as smoking for males, although the females had higher fasting blood glucose at diagnosis. Not surprisingly, hypertension is common among patients of both sexes and it has an association with proteinuria in female patients in the sample.
Adaptive Phase Aberration Correction in Multi-Element Synthetic Aperture Imaging Systems68-77
Vera Behar
[ +/- abstract ][ full text ]
The problem of phase aberration correction in Multi-element Synthetic Aperture Focusing (MSAF) imaging systems is considered in this paper. In the MSAF imaging, the phase distortions caused by tissue inhomogenities can be adaptively estimated and compensated in two successive stages of signal processing – partial beamforming (low-resolution image) and synthetic aperture formation (high-resolution image). In this paper, two methods that can be used for phase correction at the stage of high-resolution image formation are studied – a Full Common Spatial Frequency (FCSF) technique and a Partial Common Spatial Frequency (PCSF) technique. The two techniques are based on the estimate of the cross-correlation function between low-resolution images, which is used for evaluation of phase aberration errors when forming a final high-resolution image. The effectiveness of each technique for phase aberration correction is determined by the improvement factor, which is defined as difference in dynamic range between the corrected image and the distorted one.
Qualitative Modelling of Quasi-homogeneous Effects in ERK and STAT Interaction Dynamics78-89
Nikola Georgiev, Valko Petrov, Elena Nikolova, Georgi Georgiev
[ +/- abstract ][ full text ]
On the basis of qualitative analysis of author’s model published in previous paper, the stability and temporal behaviour of quasi-homogeneous distributions of ERK-protein concentrations are analyzed in terms of corresponding reaction-diffusion problem. The stable quasi-homogeneous distributions are treated as a dynamical basis of pathway compartmentalization. It is also shown, that a crowding effect exists in the form of loss of pathway stability. An experimentally verifiable issue for possible existence of protein scaffolding mechanism is derived on the basis of its qualitative correspondence with the pattern formation and molecular crowding effects inherent to the considered model. Moreover, it is demonstrated, that the predicted ERK and STAT pathway instability can be interpreted as traveling wave propagation of molecular concentration drop and jump from the nucleus membrane to the cell one and vice versa.
Review of Quantitative Structure – Activity Relationships for Acute Mammalian Toxicity90-105
Ivanka Tsakovska, Iglika Lessigiarska, Tatiana Netzeva, Ilza Pajeva, Andrew Worth
[ +/- abstract ][ full text ]
This paper reviews Quantitative Structure-Activity Relationship (QSAR) models for acute mammalian toxicity published in the last decade. A number of QSAR models based on cytotoxicity data from mammalian cell lines are also included because of their possible use as a surrogate system for predicting acute toxicity to mammals. On the basis of the review, the following conclusions can be made: i) a relatively small number of models for in vivo toxicity are published in the literature. This is due to the nature of the endpoint – acute systemic toxicity is usually related to whole body phenomena and therefore is very complex. The complexity of the mechanisms involved leads to difficulties in the QSAR modelling; ii) most QSAR models identify hydrophobicity as a parameter of high importance for the modelled toxicity. In addition, many models indicate the role of the electronic and steric effects; iii) most of the literature-based models are restricted to single chemical classes. Models based on more heterogeneous data sets are those incorporated in expert systems. In general, the QSAR models for mammalian toxicity identified in this review are considered useful for investigating the mechanisms of toxicity of defined chemical classes. However, for predictive purposes in the regulatory assessment of chemicals most of the models require additional information to satisfy internationally agreed validation principles. In addition, the development of new models covering larger chemical domains would be useful for the regulatory assessment of chemicals.
Monolithic Controlled Delivery Systems: Part II. Basic Mathematical Models106-117
Rumiana Blagoeva, Assen Nedev
[ +/- abstract ][ full text ]
The article presents a brief but comprehensive review of the large variety of mathematical models of drug controlled release from polymeric monoliths in the last 25 years. The models are considered systematically, from the first simple empirical models up to the most comprehensive theoretical ones taking into account the main release mechanisms (diffusion, swelling, dissolution or erosion) simultaneously. Their advantages and limitations are briefly discussed and some applications are outlined. The present review shows the choice of appropriate mathematical model for a particular controlled system design mainly depends on the desired predictive ability and accuracy of the model. This aspect is connected with the necessity the main factors influencing the concrete release kinetics, especially the basic controlling mechanisms, to be identified in advance.

© 2006, BAS, Institute of Biophysics and Biomedical Engineering