Showing papers by "Sofia University published in 1984"
TL;DR: In this paper, the diffusion-controlled dissolution of spherical cementite particles in an FeC alloy and an Fe ǫCCr alloy is simulated on a computer.
45 citations
TL;DR: In this article, the thermoelectric properties of polycrystalline samples of GeTe-rich side solid solutions (GeTe)1−x·(AgSbTe2)x, for the compositions x = 0.00, 0.10, 0., 15, 20, and 0.29 are investigated.
Abstract: The thermoelectric properties of polycrystalline samples of GeTe-rich side solid solutions (GeTe)1−x·(AgSbTe2)x, for the compositions x = 0.00, 0.10, 0.15, 0.20, and 0.29 are investigated. The temperature dependences of the Seebeck coefficient and the electrical resistivity and the dependences of the total thermal conductivity at 300 K versus composition are measured. The temperature dependences of the total thermal conductivity and the thermoelectric figure of merit 2 are calculated. The composition with maximum value of 2 is determined as GeTe + 20 mol% AgSbTe2. The reasons for the maximum thermoelectric figure of merit for this composition and for the anomaly changes in the thermoelectric parameters and the sharp increase of Z in the region of phase transitions (OC) are discussed.
Die thermoelektrischen Eigenschaften von polykristallinen Proben der Mischkristalle (GeTe)1−x·(AgSbTe2)x, nahe der VerbindungGeTemit den Zusammensetzungen x = 0,00; 0,10; 0,15; 0,20 und 0,29 werden untersucht. Die Temperaturabhangigkeiten der Thermospannung und des spezifischen elektrischen Widerstandes und die Abhiingigkeiten der thermischen Leitfahigkeit bei 300 K von der Zusammensetzung werden gemessen. Die Temperatura bhangigkeiten der thermischen Leitfahigkeit und des thermischen Wirkungsgrades Z werden berechnet. Die Zusammensetzung mit dem Maximalwert von Z wird bestimmt zu GeTe + 20 Molyo AgSbTe2. Die Ursachen fur den maximalen Wirkungsgrad bei dieser Zusammensetzung und fur das scharfe Anwachsen von Z im Gebiet der Phesenumwandlung (O5h-C53v) fur alle Zusammensetzungen werden diskutiert.
43 citations
TL;DR: Neutron activation analysis has been used to determine the amounts of As, Cd, Cr, Hg, Sb, Se, and Zn in the leaves of Taraxacum offcinale and show that it accumulates these elements, which corresponds to the extent of environmental pollution.
Abstract: Neutron activation analysis has been used to determine the amounts of As, Cd, Cr, Hg, Sb, Se, and Zn in the leaves of Taraxacum offcinale and show that it accumulates these elements. The accumulation corresponds to the extent of environmental pollution. Since Taraxacum officinale is widely distributed it may be successfully used for monitoring metal pollution.
40 citations
TL;DR: The break point observed on fatty acid isotherms corresponds to a transition between two two-dimensional phases, since it is clearly distinct from the collapse as mentioned in this paper. But the transformation from the liquid expanded phase to the liquid condensed phase is slow and relaxations with characteristic times have been observed.
34 citations
TL;DR: In this article, the effect of surface pressure on mixed monolayer composition in the range of surface pressures 0-45 dyn cm−1 is due to processes (1), (2) and (3) occurring.
26 citations
TL;DR: A general review of the group of UU Her-type stars proposed recently as a possible new type of variables is given in this paper, where the available observations (spectra and photometry) reveal them as luminous Population I F-type supergiants of normal composition.
Abstract: A general review of the group of UU Her-type stars proposed recently as a possible new type of variables is given. The available observations (spectra and photometry) reveal them as luminous Population I F-type supergiants of normal composition. This fact contradicts their great distances above the galactic plane. As there is no reason so far to distrust the results from the spectroscopic analyses and photometry, the galactic plane should be excluded as a possible birthplace of the UU Her-stars. In this respect they might probably indicate that recent star formation (though occasional) from already enriched material was possible at high galactic latitudes. Moreover, normal Main-Sequence B-stars seem now also to be found there.
26 citations
TL;DR: In this paper, it was shown that under certain experimental conditions stable wetting and free films of bovine submaxillary mucin (BSM) may be obtained under certain conditions.
22 citations
TL;DR: In this article, the reaction of Glutaconic anhydride with N-substituted benzimidoyl chlorides was investigated aiming at the preparation of α-condensation products.
20 citations
TL;DR: In this paper, it was shown that information about the water temperature and the concentration of the dissolved salts is encoded in the band shape of the O-H stretching region 2800-3800 cm−1.
Abstract: The investigations of the Raman scattering from water show that information about the water temperature and the concentration of the dissolved salts is encoded in the band shape of the O-H stretching region 2800–3800 cm−1.
20 citations
TL;DR: In this article, an intensive generation of radiation from a discharge-pumped atomic-fluorine gas laser was reported, with a peak power exceeding 330 kW and a total energy of more than 2 mJ, using a NF3∶He (1∶100) gas mixture at total pressure of 500 Torr.
Abstract: An intensive generation of radiation from a discharge-pumped atomic-fluorine gas laser is reported. A peak power exceeding 330 kW and a total energy of more than 2 mJ is obtained for a number of lines in the red, using a NF3∶He (1∶100) gas mixture at total pressure of 500 Torr. The circuitry optimization is described and the conditions for effective operation of the atomic-fluorine laser are discussed. The temporal and the spectral characteristics of the laser emission are also presented.
19 citations
TL;DR: The authors found a nonstatistically significant decrease of the infection rate in the prophylactic group, however, the bacteriologically documented infections and septicemia incidence was significantly higher in the control than in the Prophylaxis group.
Abstract: Thirty-five noninfected patients undergoing induction chemotherapy for acute nonlymphoblastic leukemia (ANLL) were randomized to either receive (19 patients) or not receive (16 control patients) prophylactic granulocyte transfusions (PGT) when their granulocyte count fell below 0.5 X 10(9)/1. Both groups received identical anti-infectious and supportive care except for granulocyte transfusions. The authors found a nonstatistically significant decrease of the infection rate in the prophylactic group. However, the bacteriologically documented infections and septicemia incidence was significantly higher in the control than in the prophylactic group (P less than 0.05). In the control group they observed in 8 of 16 cases life-threatening infections in contrast with only 1 case in the prophylactic group (P less than 0.01). A significant reduction of deaths due to infectious causes in the prophylactic versus control group were also found (P less than 0.05). The authors did not find an increase of pneumonia or pulmonary infiltrates in the patients belonging to prophylactic in comparison to control group.
TL;DR: In this article, a single pass saturable absorber was used to shorten XeCl laser pulses by a factor of more than five of XeC laser pulses with the combined action of both nonlinear absorption and stimulated emission from the dye solution.
TL;DR: In this article, a questionnaire for measuring need for achievement (nAch) was administered to a Bulgarian population consisting of four groups: gifted and talented high-school students, and eminent industrialists, artists etc.
TL;DR: The existence of optimal nodes with preassigned multiplicities is proved for the Hardy spaces Hp (1
Abstract: The existence of optimal nodes with preassigned multiplicities is proved for the Hardy spacesH p (1
TL;DR: In this paper, the general theory of the propagation of electromagnetic TE modes in a layered structure consisting of a homogeneous dielectric layer between two homogeneous optically nonlinear semi-infinite dielectrics is given.
Abstract: The general theory is given of the propagation of electromagnetic TE modes in a layered structure consisting of a homogeneous dielectric layer between two homogeneous optically nonlinear semi-infinite dielectrics. Allowance is made for the nonlinear coefficients of the nonlinear media to be different and a detailed analysis is given, together with the appropriate formulae for the power flow down the guide, as a function of guide wave number, and layer thickness. Detailed consideration is given to the existence conditions for surface waves.
TL;DR: In this paper, the effect of nonlinear changes of the dispersion characteristics of highfrequency azimuthally symmetric surface waves in a plasma column is investigated theoretically, and the effects of (ω + ω) − ω and (ω - ω)-plus ω nonlinear interactions of the third order (in relation to the fundamental wave amplitude) are considered.
Abstract: The effect of the nonlinear changes of the dispersion characteristics of highfrequency azimuthally symmetric surface waves in a plasma column is investigated theoretically. Both (ω + ω) – ω and (ω – ω) + ω nonlinear interactions of the third order (in relation to the fundamental wave amplitude) are considered here. These two types of interactions influence the wave phase velocity and the collisional damping rate in opposite ways. When ω2Pi/v2 1, both interactions are involved; the (ω – ω) + ω interaction associated with the ponderomotive force becomes more important, decreasing the phase velocity and increasing the time damping rate (ωpi and v are ion plasma and electron-neutral collision frequencies, respectively).
TL;DR: In this article, it was shown that the resistivities of thin tin oxide films consisting of SnO2(CaF2) textured along the [100] direction are very high (ϱ > 10 5 Ω cm ).
TL;DR: In this article, a scheme for instrumental neutron activation analysis of ancient and medieval glasses is proposed, where the combination of three irradiations (short time, pile and epithermal) enables the determination of 34 elements.
Abstract: A scheme for instrumental neutron activation analysis of ancient and medieval glasses is proposed. The combination of three irradiations (short time, pile and epithermal) enables the determination of 34 elements. The accuracy of the method is evaluated by analyzing two glass standard reference materials. Results from the analysis of three glasses from different times are presented.
TL;DR: In this article, the first observation of excimer laser action in the near ir region in Na 2 b 3 ∑ + g (v' = 0) a x 3 ∆ + u bound -free transition centered at 830 nm was reported.
TL;DR: In this article, the 13C NMR spectra of isocoumarin, N-methyl-1(2H)-isoquinolinone and 14 of their 3-and/or 4-substituted derivatives were measured and assigned with the aid of various spectral techniques.
Abstract: The 13C NMR spectra of isocoumarin, N-methyl-1(2H)-isoquinolinone and 14 of their 3- and/or 4-substituted derivatives were measured and assigned with the aid of various spectral techniques. The values of the one-bond and some of the long-range 13C-13C-1H coupling constants are reported. The effect of substitution on the 13C chemical shifts is discussed.
TL;DR: In this paper, the IR spectra of 1-hexene, 1-heptene, cyclohexenes, n-propanol and tert-butanol, adsorbed on H-ZSM-5 zeolite, evacuated at 675 K, revealed a band at 1520 cm −1 after contacting with the Zeolite at 373 J. The second assumption was confirmed by the subsequent disappearance of the zeolitic OH bands.
TL;DR: In this article, a new type of angular bond coordinates are introduced and the number of intensity parameters reduced, and further advances in theoretical approach were presented. And the authors defined the bond polar parameters as derivatives of the total molecular dipole moment with respect to linear and angular coordinates associated with individual bond vibrational distortions, and obtained via transformation of the experimental dipole moments derivatives.
TL;DR: In this paper, a study of the screening effect of the laser induced microplasma and the possibility of improving the limit of detection, the concentration sensitivity and reproducibility in laser microspectral analysis is presented.
TL;DR: In this article, the influence of the structural phase transition on the electronic structure of Pb1−xGexTe near the band gap is investigated theoretically and it is shown that the absolute minimum of the conduction band and the absolute maximum of the valence band are shifted in the (111) plane of the Brillouin zone.
Abstract: The influence of the structural phase transition on the electronic structure of Pb1−xGexTe near the band gap is investigated theoretically. It is shown that the absolute minimum of the conduction band and the absolute maximum of the valence band are shifted in the (111) plane of the Brillouin zone. The surfaces of constant energy develop from toroidal-shaped ones near the band edge to a figure of revolution obtained from two intersecting ellipses for the usual carrier concentration of 1017 cm−3.
[Russian Text Ignored]
TL;DR: In this paper, the influence of multiple intramolecular hydrogen bonds on the tautomeric equilibrium of 1,3-diketones by means of NMR-spectroscopy was analyzed.
TL;DR: In this paper, the time dependence of resonantly scattered radiation is studied and it is shown that the reported discrepancy between theory and experiment is due to nonresonant scattering of recoilless radiation which has not been taken into account in the earlier studies.
TL;DR: In this paper, a Spectrophotometric method for determination of aminoglycoside antibiotics tobramycin, apramymycin and kanamycin in formulations has been developed.
Abstract: A Spectrophotometric method for determination of the aminoglycoside antibiotics tobramycin, apramycin and kanamycin in formulations has been developed. The method is based on the formation in slightly acidic medium of an ion-pair between the protonated antibiotic and the anionic form of Bromothymol Blue. The ionpair is extracted with chloroform and the absorbance measured at 430 nm. Beer's law is followed in the range 1−5×10−3M.
TL;DR: The effects observed are explained well by the orientations of the whole purple membrane fragments, and the faster process detected in the electric light scattering decay curve could be attributed to changes in the form and/or the volume of purple membrane aggregates.
TL;DR: In this article, the conditions for the quantitative extraction of metal chelates and their composition and optical characteristics have been determined as well as their spectral properties and their molar absorptivities.
Abstract: Sensitive extraction-spectrophotometric procedures are described for the complexes of Cu(II), Zn(II), Cd(II) and Hg(II) with 5-Br-PADAP using chloroform as solvent. Optimal conditions have been established for the quantitative extraction of the metal chelates and their composition and optical characteristics have been determined as well. The conditional extraction constants amount logKex′=10, the molar absorptivities of the complexes being 105 l·mole−1·cm−1. Job's method and equilibrium shift method indicate the molar ratios M∶5-Br-PADAP=1∶2.