Showing papers by "Bulgarian Academy of Sciences published in 2003"

Plant responses to drought and stress tolerance

Abstract: In the natural environment plants are well adapted to minimize damages which only occurs under extreme conditions. In the frame of “physiological window” mild drought induces in plants regulation of water loss and uptake allowing maintenance of their leaf relative water content within the limits where the photosynthetic capacity shows no or little changes. But severe drought induces in plants unfavourable changes leading to inhibition of photosynthesis and growth. The most severe drought stress is desiccation. On the basis of presence or absence of bulk water, the mechanisms of protection are different. While the mechanisms conferring drought tolerance are mainly based on structural stabilization by preferential hydration, desiccation tolerance mechanisms are based on the replacement of water by molecules that form hydrogen bonds. The roles of stomatal and non-stomatal limitation, the behaviour of PS2, specific proteins and Rubisco, lipids and sugars, as well as mechanisms of acclimation and stress tolerance in droughted plants are discussed.

Effect of CeO2 loading on the surface and catalytic behaviors of CeO2-Al2O3-supported Pt catalysts

Abstract: Pt catalysts supported on mixed CeO2-Al2O3 carriers with different CeO2 loading (0.5–10.3 wt.%) were prepared by wetness impregnation method. The catalysts were characterized by SBET, X-ray diffraction (XRD), UV-Vis diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR) and thermogravimetric analysis (TG). It was shown that pretreatment temperature and the concentration of CeO2 in the support influences significantly on the morphology of Pt. XRD showed the formation of nanocrystallites of Pt on the surface of alumina and low-loaded CeO2 (≤6 wt.%) samples at higher temperature of calcination (1073 K). Amorphous Pt was observed in all reduced samples. XPS spectra showed the presence of interaction between Pt and Ce, which leads to easy surface reduction of both, ceria and platinum, as revealed by TPR patterns. The effect of CeO2 loading on the catalytic behavior of supported Pt catalysts in the reaction of CO2 reforming of CH4 was determined. Addition of cerium oxide results in improvement of catalytic performance for the reforming of methane with CO2. Pt catalyst with 1 wt.% of CeO2 exhibited the highest specific activity and stability, due to the increase in the metal–support interface area, caused by the higher Pt dispersion.

FTIR study of low-temperature water-gas shift reaction on gold/ceria catalyst

Abstract: Chemisorption and reactivity of the molecules involved in the water-gas shift (WGS) reaction on gold/ceria catalyst have been studied at 90 and 300 K by FTIR spectroscopy. Forward and reverse WGS reaction at 300 K and up to 573 K have been investigated, too. The FTIR results show that gold causes a strong modification of the surface properties of the support. The nanosized metallic gold particles in close contact with defective ceria play an essential role for the genesis of high catalytic activity in WGS reaction at low temperature and appear to be of crucial importance in explaining the remarkably high stability of this catalytic system. An electronic interaction between small gold metallic nanoparticles and ceria has been evidenced.

Approximate explicit constrained linear model predictive control via orthogonal search tree

Abstract: Solutions to constrained linear model predictive control problems can be precomputed off-line in an explicit form as a piecewise linear state feedback on a polyhedral partition of the state-space, avoiding real-time optimization. We suggest an algorithm that can determine an approximate explicit piecewise linear state feedback by imposing an orthogonal search tree structure on the partition. This leads to a real-time computational complexity that is logarithmic in the number of regions in the partition, and the algorithm yields guarantees on the suboptimality, asymptotic stability and constraint fulfillment.

Structure and redox properties of MnOx/Yttrium-stabilized zirconia (YSZ) catalyst and its used in CO and CH4 oxidation

Abstract: The complex structure, the redox properties, and the catalytic activity for the MnO x /yttrium-stabilized zirconia (YSZ) catalytic system were explored and reported here The MnO x /YSZ material (10% by wt as MnO 2 ) was characterized by temperature-programmed reduction (TPR), X-ray diffraction (XRD) and FITR spectroscopy of low-temperature CO adsorption The redox properties were explored by exposing the material to H 2 -rich/O 2 -rich environment cycles, at various temperatures (up to 1173 K), followed by material characterization The catalytic activity of the MnO x /YSZ system in CO and CH 4 oxidation (fuel rich/lean) was investigated and correlated with the observed structure and redox properties XRD data indicated that MnO x is well dispersed on the YSZ support, with crystallites below 2–3 nm (close to the XRD detection limit) TPR data show that most of the Mn is present as Mn 3+ and Mn 2+ Low-temperature CO adsorption on MnO x /YSZ shows the formation of Mn 3+ –CO species (2180 cm −1 ) which are easily desorbed by evacuation at 85 K Heating the sample (120 K and up) in CO atmosphere shows the formation of CO 2 and bridged or bidentate carbonates which block the CO adsorption sites At higher temperatures, the CO 3 2− species are mostly converted into HCO 3 − species When CO is adsorbed at 85 K on a sample exposed to a H 2 -rich atmosphere, Mn 2+ –CO species are formed Heating the sample in CO atmosphere (O-rich) leads again to oxidation of CO In this case no CO 2 is formed, but at ∼130 K monodentate carbonates start to emerge Catalytic activity results indicate that the MnO x presence favored the CO oxidation process but had an inhibiting effect on the CH 4 oxidation The kinetic experiments showed that for CO oxidation, the rate is first order in O 2 on MnO x /YSZ catalyst and zero order on the YSZ support

A new method for reconstruction of the vertical electron density distribution in the upper ionosphere and plasmasphere

Abstract: Ground-based ionosphere sounding measurements alone are incapable of reliably modeling the topside electron density distribution above the F layer peak density height. Such information can be derived from Global Positioning System (GPS)-based total electron content (TEC) measurements. A novel technique is presented for retrieving the electron density height profile from three types of measurements: ionosonde (foF2, foE, M3000F2, hmf2), TEC (GPS-based), and O+-H+ ion transition level. The method employs new formulae based on Chapman, sech-squared, and exponential ionosphere profilers to construct a system of equations, the solution of which system provides the unknown ion scale heights, sufficient to construct a unique electron density profile at the site of measurements. All formulae are based on the assumption of diffusive equilibrium with constant scale height for each ion species. The presented technique is most suitable for middle- and high-geomagnetic latitudes and possible applications include: development, evaluation, and improvement of theoretical and empirical ionospheric models, development of similar reconstruction methods utilizing low-earth-orbiting satellite measurements of TEC, operational reconstruction of the electron density on a real-time basis, etc.

Methods for characterization of inorganic and mineral matter in coal: A critical overview

Abstract: The present state of the methods commonly used for inorganic and mineral matter characterization in coal is described and summarized. The application of various separation procedures, macroscopic observations, reflected and transmitted optical microscopy, scanning and transmission electron microscopy, X-ray diffraction, differential thermal and thermogravimetric analyses, Mossbauer spectroscopy, infrared spectroscopy, and chemical analyses are briefly discussed. A short critical overview on the advantages and limitations of the above listed methods as well as some recommendations during their utilization are also presented.

Magnetic response of soils and vegetation to heavy metal pollution--a case study.

Abstract: Fast and cost-effective detection of industrial pollution can significantly promote its ecological, economic, and social assessment. A magnetometric method, used for qualitative determination of anthropogenic contamination, meets these requirements but needs further development in more quantitative terms. It could be used successfully in numerous cases when the heavy metals coexist with strongly magnetic iron oxide particles in the source dust. We present an integrated magnetic and geochemical study that examines the utility of magnetometric techniques for rapid, qualitative detection of metallic pollutants in soils and vegetation. The new aspect of our approach, in comparison with previously published articles on this subject, is the combined investigation (magnetic and geochemical) of both soils and vegetation, thus using an additional medium for employing the magnetometry as a pollution proxy at a site. The study area is a small (approximately 3 km2) region in the suburbs of Sofia (Bulgaria), with the main pollution source being a metallurgical factory. Soil samples have been taken from the topmost 20 cm from private gardens, located at different distances from the factory. Vegetation samples were taken from ryegrass (both leaves and roots) and leaves from two kinds of deciduous trees (maple and acacia). The results show that both vegetation and soils are characterized by enhanced magnetic properties, compared to background material, which is due to the presence of magnetite particles of anthropogenic origin accompanying heavy metal emissions. SEM images and microprobe analyses reveal the presence of a significant amount of particles, containing heavy metals (including iron) in vegetation samples taken close to the main pollution source. Correlation analyses show a statistically significant link (correlation coefficients ranging from 0.6 to 0.7) between magnetic susceptibility and the main heavy metals (Cu, Zn, Pb) in soil samples, indicating that the magnetic susceptibility can provide a proxy method for identifying the relative contribution of industrial pollution in soils and vegetation, that is reliable, inexpensive, and less time-consuming than standard chemical analyses.

Purification and properties of thermostable lipase from a thermophilic Bacillus stearothermophilus MC 7

Abstract: Extracellular thermostable lipase produced by the thermophilic Bacillus stearothermophilus MC 7 was purified to 19.25-fold with 10.2% recovery. The molecular weight of the purified enzyme determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) was shown to be 62 500 Da. The purified enzyme expressed maximum activity at 75-80 OC and its half life was 30min at 70 OC. The K,,, and V,,,,, were calculated to be, respectively, 0.33 mM and 188 pMmin-' mg-' withp-nitrophenyl palmitate @NPP) as a substrate. Enzyme activity was inhibited by divalent ions of heavy metals, thiol and serine inhibitors, whereas calcium ion stimulated its activity. The most advantageous method for immobilization was found to be ionic binding to DEAE Cellulose. The enzyme was able to hydrolyze both soluble and insoluble emulsified substrates and was classified as a lipase, expressing some esterase activity as well. 0 2003 Elsevier Science B.V. All rights reserved.

The role of surface zeta potential and substratum chemistry for regulation of dermal fibroblasts interaction

Abstract: Synthetic materials considered for biohybrid skin or other tissue engineering applications have to support cellular interaction and colonisation of implants. However, despite the number of studies reported in the literature, there is no agreement on the principal factors applicable to modulate the interaction with cells, such as the wettability of biomaterials, their surface potential and chemistry of the surface. Particularly, in this study we were interested on the impact of surface chemistry and net surface (zeta) potential on dermal fibroblasts. To address this question self assembled monolayers of silanes on glass, further derivatized with different functional groups, were used to study the adhesion and proliferation of human skin fibroblasts in response to these factors. The model surfaces were characterized using streaming potential (zeta potential) and water contact angle measurements. All samples were found to be negatively charged at physiological pH (regardless of the different chemistry) increasing (or equal ∼) the magnitude of the negative potential in the following order: hydroxy (OH) OH > EPOXY >SO 3 > COOH > CF 3 functions. The surfaces were found also to be highly wettable, except CF 3 . Interestingly, the best cellular interaction was found on the moderately wettable NH 2 surface representing water contact angle (CA) of 65°, and the worst, on the least wettable CF 3 surface (CA 85°) indicating that not only the surface potential but also the type of functional groups may play an important role. The organisation of α5 and β3 integrins generally followed the same trend of less clustering in focal adhesion plaques when the negative potential increased, except on SO 3 surface, where β3 but not α5 integrins were greatly expressed. Cell growth however, showed a significant decrease on highly charged COOH and SO 3 surfaces, as well as, on non-polar CF 3 functions. The best proliferation response was obtained on surfaces with primary amine groups. The results indicate that the surface (zeta) potential might be a critical parameter for cellular interactions, but also the substratum wettability and the type of functional groups have to be controlled in order to improve the biocompatibility of material surfaces.

Water quality study of the Struma river basin, Bulgaria (1989–1998)

Abstract: The present paper deals with an estimation of the water quality of the Struma river. Long-term trends, seasonal patterns and data set structures are studied by the use of statistical analysis. Nineteen sampling sites along the main river stream and different tributaries were included in the study. The sites are part of the monitoring net of the region of interest. Seventeen chemical indicators of the surface water have been measured in the period 1989–1998 in monthly intervals. It is shown that the water quality is relatively stable throughout the monitoring period, which is indicated by a lack of statistically significant trends for many of the sites and by chemical variables. Several seasonal patterns are observed at the sampling sites and four latent factors are identified as responsible for the data set structure.

Phylogenetic relationships of Echinostoma Rudolphi, 1809 (Digenea: Echinostomatidae) and related genera re-assessed via DNA and morphological analyses.

Abstract: In order to investigate the relationships within the Echinostomatidae two data sets of gene sequences were analysed. The first consisted of all previously published ND1 sequences (20) together with 17 new sequences. The latter represented six species from the cosmopolitan genera Echinostoma, Echinoparyphium, Hypoderaeum and Isthmiophora. The second data-set of ITS sequences again included all previously published sequences (12) and three new sequences from species of Echinostoma, Echinoparyphium and Isthmiophora. All new isolates, as well as voucher material from five previously sequenced isolates, were identified on the basis of morphological characters. The phylogenetic trees inferred from the ND1 data set helped to clarify the generic affiliation of all isolates and confirmed the morphological identifications. The only exception was Echinoparyphium aconiatum, whose current position in the genus Echinoparyphium was not supported by the sequence data. Although the ITS data provided insufficient resolution for an unequivocal solution to the relationships within the genus Echinostoma, it supported the identification of Echinoparyphium ellisi and the distinct species status of three isolates of Echinostoma revolutum as predicted from the ND1 data.

Precision neutrino oscillation physics with an intermediate baseline reactor neutrino experiment

Abstract: We discuss the physics potential of intermediate $L\ensuremath{\sim}20--30\mathrm{km}$ baseline experiments at reactor facilities. Assuming that the solar neutrino oscillation parameters $\ensuremath{\Delta}{m}_{\ensuremath{\bigodot}}^{2}$ and ${\ensuremath{\theta}}_{\ensuremath{\bigodot}}$ lie in the high LMA solution region, we show that such an intermediate baseline reactor experiment can determine both $\ensuremath{\Delta}{m}_{\ensuremath{\bigodot}}^{2}$ and ${\ensuremath{\theta}}_{\ensuremath{\bigodot}}$ with a remarkably high precision. We perform also a detailed study of the sensitivity of the indicated experiment to $\ensuremath{\Delta}{m}_{\mathrm{atm}}^{2},$ which drives the dominant atmospheric ${\ensuremath{ u}}_{\ensuremath{\mu}}$ $({\overline{\ensuremath{ u}}}_{\ensuremath{\mu}})$ oscillations, and to \ensuremath{\theta}---the neutrino mixing angle limited by the data from the CHOOZ and Palo Verde experiments. Irrespective of the actual values of $\ensuremath{\Delta}{m}_{\ensuremath{\bigodot}}^{2},$ we find that this experiment can improve the bounds on ${\mathrm{sin}}^{2}\ensuremath{\theta},$ and, if the value of ${\mathrm{sin}}^{2}\ensuremath{\theta}$ is large enough, ${\mathrm{sin}}^{2}\ensuremath{\theta}\ensuremath{\gtrsim}0.02,$ the energy resolution of the detector is sufficiently good and if the statistics is relatively high, it can determine with extremely high precision the value of $\ensuremath{\Delta}{m}_{\mathrm{atm}}^{2}.$ We also explore the potential of the intermediate baseline reactor neutrino experiment for determining the type of the neutrino mass spectrum, which can be with normal or inverted hierarchy, assuming $\ensuremath{\Delta}{m}_{\ensuremath{\bigodot}}^{2}$ to lie in the high LMA solution region. We show that the conditions under which the type of neutrino mass hierarchy can be determined are quite challenging, but are within the reach of the experiment under discussion.

Diamond-type lipid cubic phase with large water channels.

Abstract: This paper describes a diamond cubic phase with large water channels and determines the temperature dependence of the bilayer thickness in the cubic monoolein/octylglucoside/water system based on time-resolved synchrotron X-ray diffraction data. The X-ray diffraction study established a diamond-type lipid cubic phase with large water channels (Dlarge), which has not been previously reported. It is a distinct phase, different from the diamond cubic phase with normal water channels (Dnormal). The larger channels might allow an enhanced entrapment efficiency of biomolecules in lipid cubic phases. The X-ray diffraction patterns recorded during a thermal scan showed a cubic−cubic structural transition from Dlarge to Dnormal. The obtained cubic phases displayed much larger lattice spacings as compared to those of pure monoolein at full hydration.