Showing papers by "Romanian Academy published in 1999"

Recent directions of world hydrogen production

Abstract: Hydrogen can be produced on a large scale through economically favorable raw materials and processes. Utilization of water as an exhaustible supply of hydrogen is well known. This is very much an area open to research, so that traditional methods can be considered, as well as non-traditional approaches. This paper examines the present status and looks at different approaches for technological advances. The paper reports on some of the new developments in the progress of the recent directions of world hydrogen production, with emphasis on photolytical hydrogen processes. The aim of this article is to inform the reader of new research on hydrogen production.

Identification and function of neonatal Fc receptor in mammary gland of lactating mice.

Abstract: In addition to its proposed function in regulating serum IgG levels, the MHC class I-related neonatal Fc receptor (FcRn) is known to play a role in IgG transfer across rodent yolk sac and neonatal intestine. In contrast to humans, for which transplacental transfer of IgG appears to be the only mechanism of maternal IgG delivery, the transmission of IgG in mice occurs both antenatally (yolk sac) and neonatally (transport from mother's milk across intestinal epithelial cells). In the current study, a possible role for FcRn in regulating IgG transfer into milk has been investigated. FcRn has been shown to be present in functional form in the mammary gland of lactating mice, and is localized to the epithelial cells of the acini. Analysis of the transfer of Fc fragments and IgG which have different affinities for FcRn indicate that, unexpectedly, these proteins are transferred in inverse correlation with their binding affinity for FcRn. Thus, in the lactating mammary gland FcRn appears to play a role in recycling IgG in a mode that may have relevance to FcRn trafficking during the maintenance of constant serum IgG levels.

A statistical analysis of n- and o-glycan linkage conformations from crystallographic data

Abstract: We have generated a database of 639 glycosidic linkage structures by an exhaustive survey of the available crystallographic data for isolated oligosaccharides, glycoproteins, and glycan-binding proteins. For isolated oligosaccharides there is relatively little crystallographic data available. A much larger number of glycoprotein and glycan-binding protein structures have now been solved in which two or more linked monosaccharides can be resolved. In the majority of these cases, only a few residues can be seen. Using the 639 glycosidic linkage structures, we have identified one or more distinct conformers for all the linkages. The O5-C1-O-C(x)' torsion angles for all these distinct conformers appear to be determined chiefly by the exo-anomeric effect. The Manalpha1-6Man linkage appears to be less restrained than the others, showing a wide degree of dispersion outside the ranges of the defined conformers. The identification of distinct conformers for glyco-sidic linkages allows "average" glycan structures to be modeled and also allows the easy identification of distorted glycosidic linkages. Such an analysis shows that the interactions between IgG Fc and its own N-linked glycan result in severe distortion of the terminal Galbeta1-4GlcNAc linkage only, indicating the strong interactions that must be present between the Gal residue and the protein surface. The applicability of this crystallographic based analysis to glycan structures in solution is discussed. This database of linkagestructures should be a very useful reference tool in three-dimensional structure determinations.

Asymptotic H/sub /spl infin// control of singularly perturbed systems with parametric uncertainties

Abstract: This paper deals with the problem of control of singularly perturbed linear continuous-time systems. The authors' attention is focused on the design of a composite linear controller based on the slow and fast problems such that both stability and a prescribed H/sub /spl infin// performance for the full-order system are achieved. The asymptotic behavior of the composite controller is studied, which is independent of the singular perturbation /spl epsiv/ when /spl epsiv/ is sufficiently small. Furthermore, the problem of robust control for the above system with parameter uncertainty is also investigated.

Seismic Images of a Solar Flare

Abstract: We have used helioseismic holography to render seismic images of the solar flare of 1996 July 9, whose helioseismic signature was recently reported by Kosovichev & Zharkova. We computed time series of "egression power maps" in 2 mHz bands centered at 3.5 and 6 mHz. These images suggest an oblong acoustic source associated with the flare some 18 Mm in the north-south direction and approximately 15 Mm in the east-west direction. The considerable preponderance of the flare acoustic power emanates in the 3.5 mHz band. However, because the ambient noise in the 6 mHz band is much lower and the diffraction limit for 6 mHz waves is much finer, the flare is rendered far more clearly in the 6 mHz band. The 6 mHz flare signature lags the 3.5 mHz by approximately 4 minutes.

DNA Computing Based on Splicing: The Existence of Universal Computers

Abstract: We prove that splicingsystems with finite components and certain controls on their work are computationallycomplete (they can simulate any Turing Machine); moreover, there are universalsplicingsystems (systems with all components fixed which can simulate any given splicing system, when an encoding of the particular system is added—as a program—to the universal system).

Tiered Tagging and Combined Language Models Classifiers

Abstract: We address the problem of morpho-syntactic disambiguation of arbitrary texts in a highly inflectional natural language. We use a large tagset (615 tags), EAGLES and MULTEXT compliant [5]. The large tagset is internally mapped onto a reduced one (82 tags), serving statistical disambiguation, and a text disambiguated in terms of this tagset is subsequently subject to a recovery process of all the information left out from the large tagset. This two step process is called tiered tagging. To further improve the tagging accuracy we use a combined language models classifier, a procedure that interpolates the results of tagging the same text with several register-specific language models.

Precise Asymptotics in Spitzer's Law of Large Numbers

Abstract: Let X, X1, X2,... be a sequence of i.i.d. random variables such that EX=0, assume the distribution of X is attracted to a stable distribution with exponent α<1, and set Sn=X1+ ··· +Xn. We prove that $$\sum\limits_{n{\text{ }} \geqslant {\text{ }}1} {{\text{ }}\frac{{\text{1}}}{{\text{n}}}{\text{ }}} P(|S_n | \geqslant \varepsilon n){\text{ }} \sim {\text{ }}\frac{\alpha }{{\alpha - 1}}{\text{ }}( - \log \varepsilon {\text{) as }}\varepsilon \searrow {\text{0}}$$

Biodegradation and bioconversion of cellulose wastes using bacterial and fungal cells immobilized in radiopolymerized hydrogels

Abstract: Annually, great amounts of cellulose wastes, which could be measured in many billions of tons, are produced worldwide as residues from agricultural activities and industrial food processing. Consequently, the use of microorganisms in order to remove, reduce or ameliorate these potential polluting materials is a real environmental challenge, which could be solved by a focused research concerning efficient methods applied in biological degradation processes. In this respect, the scope of this chapter is to present the state of the art concerning the biodegradation of redundant cellulose wastes from agriculture and food processing by continuous enzymatic activities of immobilized bacterial and fungal cells as improved biotechnological tools and, also, to report on our recent research concerning cellulose wastes biocomposting to produce natural organic fertilizers and, respectively, cellulose bioconversion into useful products, such as: ‘single-cell protein’ (SCP) or ‘protein-rich feed’ (PRF). In addition, there are shown some new methods to immobilize microorganisms on polymeric hydrogels such as: poly-acrylamide (PAA), collagen-poly-acrylamide (CPAA), elastin-poly-acrylamide (EPAA), gelatin-poly-acrylamide (GPAA), and poly-hydroxy-ethyl-methacrylate (PHEMA), which were achieved by gamma polymerization techniques. Unlike many other biodegradation processes, these methods were performed to preserve the whole viability of fungal and bacterial cells during long term bioprocesses and their efficiency of metabolic activities. The immobilization methods of viable microorganisms were achieved by cellular adherence mechanisms inside hydrogels used as immobilization matrices which control cellular growth by: reticulation size, porosity degree, hydration rate in different colloidal solutions, organic and inorganic compounds, etc. The preparative procedures applied to immobilize bacterial and fungal viable cells in or on radiopolymerized hydrogels and, also, their use in cellulose wastes biodegradation are discussed in detail. In all such performed experiments were used pure cell cultures of the following cellulolytic microorganisms: Bacillus subtilis and Bacillus licheniformis from bacteria, and Pleurotus ostreatus, Pleurotus florida, and Trichoderma viride from fungi. These species of microorganisms were isolated from natural habitats, then purified by microbiological methods, and finally, tested for their cellulolytic potential. The cellulose biodegradation, induced especially by fungal cultures, used as immobilized cells in continuous systems, was investigated by enzymatic assays and the bioconversion into protein-rich biomass was determined by mycelial protein content, during such long time processes. The specific changes in cellular development of immobilized bacterial and fungal cells in PAA hydrogels emphasize the importance of physical structure and chemical properties of such polymeric matrices used for efficient preservation of their metabolic activity, especially to perform in situ environmental applications involving cellulose biodegradation by using immobilized microorganisms as long-term viable biocatalysts.

Stabilization of Linear Systems

Abstract: The general problem of stabilization of linear systems consists of designing a controller that uses information on a measurable output in order to influence the behavior of the state considered as a deviation from a desired equilibrium.

Protein specific N-glycosylation of tyrosinase and tyrosinase-related protein-1 in B16 mouse melanoma cells.

Abstract: Tyrosinase and tyrosinase-related protein-1 (TRP-1) are two melanogenic enzymes that regulate melanin biosynthesis. Both are glycoproteins and belong to the TRP-1 gene family. They share a significant level of sequence similarity in several regions, including the catalytic domain and the potential N-glycosylation sites. We have recently shown that inhibition of the early steps of N-glycan processing in B16F1 cells dramatically affects tyrosinase activity and melanin synthesis. We present here results on N-glycan processing of TRP-1 and tyrosinase and compare the maturation process and activity of both glycoproteins in the presence of inhibitors of the endoplasmic reticulum stages of N-glycosylation. N-glycan analysis reveals that each of these two glycoproteins contains a mixture of high-mannose and sialylated complex N-glycans. However, in contrast to TRP-1, tyrosinase presents a homogeneous high-mannose glycoform, also. In the presence of alpha-glucosidases inhibitors, the maturation of tyrosinase N-glycans is completely inhibited, whereas TRP-1 is still able to acquire some complex glycans, indicating that endomannosidase acts preferentially on the later glycoprotein. In addition, the dopa-oxidase activity of tyrosinase is totally abolished, whereas for TRP-1 it is only partially affected. The results suggest that despite their structural similarity, tyrosinase is more sensitive than TRP-1 to perturbations of early N-glycan processing, in terms of maturation and catalytical activity.

On the base locus of the generalized theta divisor

Abstract: In response to a question of Beauville, we give a new class of examples of base points for the linear system ¦Θ¦on the moduli space SUX(r) of semistable rank r vector bundles of trivial determinant on a curve X and we prove that for sufficiently large r the base locus is positive dimensional.

On Synchronization in P Systems

Abstract: The P systems were recently introduced as distributed parallel computing models of a biochemical type. Multisets of objects are placed in a hierarchical structure of membranes and they evolve according to given rules, which are applied in a synchronous manner: at each step, all objects which can evolve, from all membranes, must evolve. We consider here the case when this restriction is removed. As expected, unsynchronized systems (even using catalysts) are weaker than the synchronized ones, providing that no priority relation among rules is considered. The power of P systems is not diminished when a priority is used and, moreover, the catalysts can change their states, among two possible states for each catalyst.

The Hamburg/SAO Survey for Emission–Line Galaxies - I. A First List of 70 Galaxies

Abstract: We present rst results 1 of the Hamburg/SAO Survey for Emission-Line Galaxies (HSS therein, SAO { Special Astrophysical Observatory, Russia) which is based on the digitized objective-prism photoplates database of the Hamburg Quasar Survey (HQS). The main goal of this survey is the search for emission-line galaxies (ELG) in order to create a new deep sample of blue compact galax- ies (BCG) in a large sky area. Another important goal of this work is to search for new extremely low-metallicity galaxies. We present the rst results of spectroscopy ob- tained with the 2.2 m telescope at the German-Spanish Observatory at Calar Alto, and with the 6 m telescope at the Russian Special Astrophysical Observatory. The primary ELG candidate selection criteria applied were a blue continuum (near 4000 A) and the presence of emission lines close to 5000 A recognized on digitized prism spectra of galaxies with magnitudes in the range B =1 6 : 0 19: m 5. The spectroscopy resulted in the de- tection or/and quantitative spectral classication of 74 emission-line objects. Of them 55 are newly discovered, and 19 were already known as galaxies before. 11 of the latter have redshifts and are known ELGs. For most of the known galaxies emission line ratios were measured for the rst time and an improved classication is pre- sented. 47 objects are classied as BCGs, one as Sy2 galaxy, six as possible LINERs, and four as new QSOs.

Thermal Degradation of Polyvinyl Chloride

Abstract: The thermal degradation of a sort of polyvinyl chloride was investigated. Complex processes for polyvinyl chloride degradation were evidenced. The kinetic analysis of dehydrochlorination and of subsequent processes was carried out. A change of mechanism was detected when dehydrochlorination goes to completion. The values of non-isothermal kinetic parameters determined by various methods are in a satisfactory agreement. The obtained results allowed some clarifications concerning the thermal degradation steps.

Studies on the Non-Isothermal Decomposition of H3PMo12O40·xH2O and H4PVMo11O40·yH2O

Abstract: This paper reports a comparative study of the non-isothermal decompositions of the heteropolyacids HPM and HPVM, with structures consisting of Keggin units (KUs). Non-isothermal analysis at low heating rates demonstrated the existence of 4 crystal hydrate species, depending on the temperature. The stability domains of the anhydrous forms of HPM and HPVM were found to be 150–380°C, respectively. Processing of the TG curves obtained at different heating rates by the Ozawa method revealed that the decomposition of anhydrous HPM takes place according to a unitary mechanism, whilst for anhydrous HPVM two mechanisms are observed. Thus, the first part of the constitution water is lost simultaneously with the departure of vanadium from the KU as VO2+, while the second part is lost at higher temperatures as in the case HPM.