Showing papers by "Sofia University published in 1998"
TL;DR: In this article, the Raman-active phonons in orthorhombic perovskitelike compounds were studied by measuring Raman spectra in various scattering configurations.
Abstract: The Raman-active phonons in orthorhombic perovskitelike ${\mathrm{YMnO}}_{3}$ and ${\mathrm{LaMnO}}_{3}$ were studied by measuring Raman spectra in various scattering configurations. The experimental Raman line wave numbers and the expected shapes for the phonon modes were compared to those reported for other perovskitelike compounds with the $\mathrm{Pnma}$ structure and to the results of lattice dynamical calculations. The observed Raman lines in the spectra of ${\mathrm{YMnO}}_{3}$ and ${\mathrm{LaMnO}}_{3}$ were assigned to definite atomic motions. The much larger linewidths and strong variation of the Raman spectra with increasing laser power in the case of ${\mathrm{LaMnO}}_{3}$ provide evidence for a structural instability that may result in a phase transition under laser annealing.
519 citations
TL;DR: In this paper, a cubic-type magnetocrystalline anisotropy was found in CoFe 2 O 4 fine powders with particle sizes between 43 A (4.3 ) and 465 A (46.5 ).
246 citations
TL;DR: The low sensitivity of Lactobacillus delbrueckii subsp.
160 citations
TL;DR: Amorphous TiO2 materials, layers and powders, have been produced by different preparation techniques as mentioned in this paper, and the layers have been subjected to electron diffraction and the bulk powders to X-ray diffraction experiments.
Abstract: Amorphous TiO2 materials, layers and powders, have been produced by different preparation techniques. The layers have been subjected to electron diffraction and the bulk powders to X-ray diffraction experiments. Three-dimensional structure models consistent with the experimental structure functions have been constructed by reverse Monte Carlo simulations. Partial distribution functions, interatomic distances and coordination numbers have been extracted from the model atomic configurations. The atomic arrangement in all amorphous TiO2 materials investigated has been found to resemble that occurring in brookite, a crystalline modification of TiO2, and to be well described as an assembly of short, staggered chains of Ti–O octahedra. The crystallization behaviour of amorphous TiO2 materials has also been discussed.
117 citations
TL;DR: The results of this study suggest that joint hypermobility and fibromyalgia are associated, and joint hyperlaxity may play a prominent role in the pathogenesis of pain in Fibromyalgia.
Abstract: Objective. To test the hypothesis that joint hyperlaxity can play some role in the pathogenesis of pain in primary fibromyalgia.
Methods. A total of 66 women with fibromyalgia (according to the 1990 American College of Rheumatology criteria) and 70 women with other rheumatic diseases were examined for joint laxity based on 5 criteria (The Non-Dominant Spanish modification). Individuals meeting 4 or 5 criteria were considered to be hyperlax.
Results. Joint hyperlaxity was detected in 18 (27.3%) of the patients with fibromyalgia and 8 (11.4%) of those with another rheumatic disorder. The statistical analysis revealed significant differences (p < 0.05) between both groups.
Conclusion. The results of this study suggest that joint hypermobility and fibromyalgia are associated. Joint hyperlaxity may play a prominent role in the pathogenesis of pain in fibromyalgia.
101 citations
TL;DR: In this article, the dynamics of micrometer-size polystyrene latex particles confined in thinning foam films was investigated by microscopic interferometric observation, and the behavior of the entrapped particles depends on the mobility of the film surfaces, the particle concentration, hydrophobicity, and rate of film formation.
Abstract: The dynamics of micrometer-size polystyrene latex particles confined in thinning foam films was investigated by microscopic interferometric observation. The behavior of the entrapped particles depends on the mobility of the film surfaces, the particle concentration, hydrophobicity, and rate of film formation. When the films were stabilized by sodium dodecyl sulfate, no entrapment of particles between the surfaces was possible. When protein was used as a stabilizer, a limited number of particles were caught inside the film area due to the decreased mobility of the interfaces. In this case, extraordinary long-ranged (>100 μm) capillary attraction leads to two-dimensional (2D) particle aggregation. A major change occurs when the microspheres are partially hydrophobized by the presence of cationic surfactant. After the foam films are opened and closed a few times, a layer of particles simultaneously adsorbed to the two interfaces is formed, which sterically inhibits any further film opening and thinning. The ...
100 citations
TL;DR: In this article, a membrane consisting of Aliquat 336 chloride immobilized in polyvinyl chloride (PVC) is described, which extracts gold(III) selectively from hydrochloric acid solutions in the presence of a 500-fold higher concentration of copper(II).
93 citations
TL;DR: An explicit upper bound for the number of zeros of the integral of degree n polynomials f, g, on the open interval for which the cubic curve contains an oval was derived in this article.
Abstract: An explicit upper bound is derived for the number of the zeros of the integral of degree n polynomials f, g, on the open interval for which the cubic curve contains an oval. The proof exploits the properties of the Picard-Fuchs system satisfied by the four basic integrals , i,j=0,1, generating the module of complete Abelian integrals I(h) (over the ring of polynomials in h).
92 citations
TL;DR: In this paper, a theoretical study of the catalytic activation of hydrogen peroxide on titanium silicalites is presented, showing that the interaction between peroxide and solvent molecules is weak.
86 citations
TL;DR: In this paper, a new wind stress data set, based on ship observations, is prepared, which uses additional data and more accurate parameterization of the boundary layer physics, compared to the existing wind stress estimates, and the intercomparison between forcing data sets is focused on the heat flux and freshwater flux at the sea surface.
77 citations
TL;DR: A Method for flexible instructional module development is presented which aims at assisting the educational designers in the development of flexible instructional modules, ie, modules, which are easily adaptable to different learner's needs, allow learNER's choices and different delivery platforms, including distance delivery.
Abstract: The paper deals with the problem of designing flexible learning and instruction. Flexibility is considered both from the learner's and the designer's perspective. The potential of telematics in the design, development and implementation of flexible and distance learning is discussed. A Method for flexible instructional modules development is presented which aims at assisting the educational designers in the development of flexible instructional modules, ie, modules, which are easily adaptable to different learner's needs, allow learner's choices and different delivery platforms, including distance delivery. Examples of Method applications and current development of a software system to facilitate the Method's implementation are reported.
TL;DR: Danov et al. as mentioned in this paper derived a system of partial differential equations describing the evolution of long-wave disturbances in the presence of surfactant and evaporation and applied it to a two-layered liquid film attached to a heated solid substrate.
TL;DR: The model of micelle growth, extended in this way, compared well with the experimental data and provides a quantitative description of the micelle size and charge as functions of the surfactant.
Abstract: To interpret quantitatively experimental data for the growth of rodlike anionic surfactant micelles in the presence of Al3+ ions, we undertook experimental and theoretical investigations. We determ...
TL;DR: In situ reinforced binary and ternary polymer/polymer composites are obtained by the melt blending of poly(ethylene terephthalate) (PET), polyamide-6 (PA-6), and polyamide -66 as discussed by the authors in an extruder in the presence of a catalyst, followed by drawing of the extrudate and annealing of drawn blends.
Abstract: In situ reinforced binary and ternary polymer/polymer composites are obtained by the melt blending of poly(ethylene terephthalate) (PET), polyamide-6 (PA-6), and polyamide-66 (PA-66) in an extruder in the presence of a catalyst, followed by drawing of the extrudate and annealing of the drawn blends. The blends were studied by DSC, X-ray, SEM, and mechanical testing. After drawing, all the components were found to be oriented, forming microfibrils with diameters of about 1–2 μm. The chemical nature of the homopolymers affects the blends' morphologies; while the PA-66/PA-6 blend is homogeneous, phase separation is established in the case of PET/PA-6. The decrease in the enthalpy of melting of the blend components as well as the depression of their peaks of crystallization from the melt, compared to pure homopolymers, are indications that block copolymers have been formed via interchange reactions during the blending process. On the one hand, these copolymers improve the compatibility of the homopolymers, and on the other hand, they alter the chemical composition of the blends. After thermal treatment at 245°C, i.e., above the Tm of PA-6, the latter undergoes some disorientation, while PET and PA-66 retain their microfibrillar shape, and in this way, a compositelike structure is created. The presence of chemical bonds between the separate phases via copolymers favors the cocrystallization of PA-66 and PA-6 as well as the cooperative crystallization of PET, PA-6, and PA-66, both modes fostering improved compatibility (adhesion) of the blend components. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67: 723–737, 1998
TL;DR: In this article, the experimental data for the growth of rod-like surfactant micelles in the presence of a 2:1 electrolyte (CaCl2) do not comply with the available theory, which was originally developed for a 1: 1 electrolyte.
TL;DR: In this article, a linear relation between the energy of hydrogen-bond formation, ΔE, and the H−F stretching frequency shift, ΔνH-F, was obtained for the systems studied.
Abstract: Ab initio molecular-orbital calculations at the HF/6-31G(d,p) level were used to investigate the hydrogen bonding between open-chain aliphatic carbonyl compounds and hydrogen fluoride. The carbonyl compounds studied are H2CO, HCOOH, HCOSH, HCOOCH3, HCONH2, HCONO2, HCOCN, HCOF, HCOCl, HCOCH3, HCOCF3, CH3COOH, CH3COSH, CH3COOCH3, CH3CONH2, CH3CONO2, CH3COCN, CH3COF, CH3COCl, CH3COCH3, and CH3COCF3. Geometry optimization and vibrational-frequency and infrared-intensity calculations at the optimized geometry were performed for isolated and hydrogen-bonded systems. The estimated energies of hydrogen-bond formation were corrected for zero-point vibrational energy and basis-set superposition error. In agreement with expectations a linear relation (R = 0.994) between the energy of hydrogen-bond formation, ΔE, and the H−F stretching frequency shift, ΔνH-F, was obtained for the systems studied. A linear dependency was also found between ΔE and the change of H−F bond length, ΔrH-F (R = 0.994). Effective bond charges...
TL;DR: In this article, a negative answer to the questions raised by D.Blair-S.Ianus and A.Gray, respectively, of whether a compact almost Kahler manifold with Hermitian Ricci tensors belongs to the class AH2 is Kahler is given.
Abstract: We present a study of natural almost Hermitian structures on twistor spaces of quaternionic Kahler manifolds. This is used to supply (4n + 2)-dimensional examples (n > 1) of symplec tic non-Kahler manifolds. Studying their curvature properties we give a negative answer to the questions raised by D.Blair-S.Ianus and A.Gray, respectively, of whether a compact almost Kahler manifold with Hermitian Ricci tensor or whose curvature tensor belongs to the class AH2 is Kahler.
TL;DR: Endoscopic sphincterotomy resolves biliary obstruction and postoperative fistulae in most patients with hepatic hydatid cysts that have ruptured into the biliary tract, although in some cases, a biliary prosthesis may be required.
TL;DR: In this article, the validity of a higher order factorial structure of a Bulgarian version of the Beck Depression Inventory (BDI) for non-clinical adolescents was tested using a cross validation of three independent samples (n1 = 227, n2 = 172, n3 = 292).
Abstract: The purpose of the present study was to test for the validity of a higher order factorial structure of a Bulgarian version of the Beck Depression Inventory (BDI) for non clinical adolescents. In a cross validation of three independent samples (n1 = 227; n2 = 172; n3 = 292), and based on the analysis of covariance structures within the framework of a confirmatory factor analytic model, findings yielded exceptionally strong support for the hypothesized second-order three-factor structure. These findings add to a growing cross-cultural agglomerate of construct validity data related to the factorial structure of the BDI. Results are expected to be of substantial interest to both researchers and clinicians whose concerns focus on depression as it bears on this population.
TL;DR: In this article, the stability and the lifetime of foams are governed by the M, in all experiments, and the effect of bivalent forces and short-range hydration repulsion is related to two major effects influencing the an important role of foam films.
TL;DR: In this paper, the authors used least square linear regression (LQR) to determine the 10 years (1984-1993) trends in precipitation chemistry and deposition for all major ions.
TL;DR: The results imply that the presence of vegetation influences the ecotoxicological effect of pollutants, and the risk assessment of pollutants could increase its realism by the inclusion of the response of communities of soil organisms in the absence of plants.
TL;DR: In this article, the natural skew-symmetric curvature operator has pointwise constant eigenvalues and a local classification (up to isometry) of such manifolds in dimension 4 is given.
Abstract: We study manifolds where the natural skew-symmetric curvature operator has pointwise constant eigenvalues. We give a local classification (up to isometry) of such manifolds in dimension 4. In dimension 3, we describe such manifolds up to a classification of three - dimensional Riemannian manifolds with principal Ricci curvatures r1 = r2 = 0, r3- arbitrary. We give examples of such manifolds in all dimensions which do not have constant sectional curvature; these manifolds are not pointwise Osserman manifolds in general.
TL;DR: Danov et al. as discussed by the authors performed a linear analysis of the stability of a two-layered liquid film which is evaporating upon a horizontal solid substrate, and the resulting system of ordinary dierential equations describes the evolution of small long-wave disturbances of the film shape and the surfactant distribution during the film evaporation.
TL;DR: In this paper, the p + p → π+ + + + d reaction close to threshold was measured employing a magnetic spectrograph with track reconstruction, a very thin liquid hydrogen target and an accelerated proton beam with high phase space density.
TL;DR: In this paper, it was shown that any q-KdV solution leads to a solution of the q-approximation of the 1-Toda lattice equations.
TL;DR: In this article, a 3D interdisciplinary model has been used to test the sensitivity of the Black Sea's ecosystem to physical processes using the GHER primitive equation model, which is forced by climatological monthly mean fields of temperature, salinity and wind stress at the air-sea interface; the river discharges of the Danube, Dnestr and Dnepr are taken into account.
TL;DR: By condensation of quaternary heterocyclic compounds with 4-chloroquinolinium salts in the presence of basic agents, such as triethylamine, 10 monomethine cyanine dyes with one or two positive charges have been synthesized as mentioned in this paper.
TL;DR: A novel antibacterial substance produced by a strain isolated from Bulgarian yellow cheese, identified by molecular typing to belong to the species Lactobacillus delbrueckii, which is a rare producer of bacteriocins, was characterized.
Abstract: A novel antibacterial substance produced by a strain isolated from Bulgarian yellow cheese was characterized. The producer strain was identified by molecular typing to belong to the species Lactobacillus delbrueckii, which is a rare producer of bacteriocins. The inhibitory agent was heat stable and active against lactic acid bacteria species and several food-borne pathogens : Listeria monocytogenes, Staphylococcus aureus, Enterococcus faecalis, Escherichia coli, Yersinia enterocolitica and Y. pseudotuberculosis. Its sensitivity to amylolitic enzymes and lipase suggested that a lipid and carbohydrate moiety could be important for the activity. The amino acid content of the purified bacteriocin was estimated to 29 amino acids. The bacteriocin was shown to be small (3·6–6 kDa) by three different methods : HPLC gel-filtration, SDS-PAGE and amino acid contents.
TL;DR: Two new flavone glycosides, luteolin and chrysoeriol 7-(6″-β- d -apiofuranosyl )-β -glucopyranodides have been isolated from the aerial parts of Phlomis nissolii.