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Showing papers by "Sofia University published in 1991"


Journal ArticleDOI
TL;DR: A refinement of Kripke modal logic is proposed, and in particular of PDL (propostional dynamic logic) is proposed.
Abstract: We propose a refinement of Kripke modal logic, and in particular of PDL (propostional dynamic logic)

167 citations



Journal ArticleDOI
TL;DR: In this paper, the effect of diffusion of polydisperse micelles on the kinetics of the surface tension is studied theoretically, and it is shown that the surface properties of micellar surfactant solutions depend on which of the relaxation processes of mousellization (fast or slow), has a time constant comparable with the characteristic time of diffusion.

62 citations


Journal ArticleDOI
TL;DR: In this article, a simple and precise method for measurement of contact angles in the range 0° − 180° on solid surfaces is proposed, based on a numerical solution of the Laplace equation for the interfacial profile.

55 citations


Journal ArticleDOI
TL;DR: In this article, the acid-base properties of oxide catalysts were investigated and cyclohexanol conversion was shown to be related to basic sites if at least one proton is released from the organic molecule.
Abstract: Cyclohexanol conversion on oxide catalysts is proposed as a test for the acid-base properties of oxide catalysts. The quantity of cyclohexene formed reflects the existence of Broensted acid sites. The dehydrogenation to cyclohexanone might be related to basic sites if at least one proton is released from the organic molecule. In some cases dehydrogenation to phenol occurred.

54 citations


Journal ArticleDOI
TL;DR: In this article, a notion of completion for quasi-uniform spaces is defined in a categorical manner, and completions for a large class of spaces (called quiet quasi-unsatisfactory spaces) are constructed.

48 citations


Journal ArticleDOI
TL;DR: In this paper, the conditions for the formation of a light bullet pulse, propagating with nearly constant spatial and temporal parameters in a bulk nonlinear medium, are obtained using an induced phase modulation (IPM) configuration.
Abstract: The conditions for the formation of a light bullet pulse, propagating with nearly constant spatial and temporal parameters in a bulk nonlinear medium, are obtained. A pump and probe pulse configuration using an induced phase modulation (IPM) is used. The IPM effect provides a well-controllable spatial and temporal trapping of the probe pulse. The authors derive analytical expressions for the critical parameters of the system, incorporating input power, pulse duration, pump and probe beam radii, medium parameters, etc. The system parameters analyzed are rather general and include varying pump and probe pulse durations and delay. The constant parameters of the light formation are shown to be limited by the walk-off effect. An analytical balance condition is obtained for the spatial and temporal soliton-like formation. >

46 citations


Journal ArticleDOI
TL;DR: In this paper, the thermoelectric properties of GeTe-based materials for the medium temperature range (600 to 900 K) are measured and the best p-type new material is the composition (GeTe)0.4 × 10−3 K−1 at about 700 K.
Abstract: Basic thermoelectric p-type materials for the medium temperature range (600 to 900 K) are GeTe-based materials. Hot-pressed samples of (GeTe)1−x[(Ag2Te)1-y(Sb2Te3)y]x solid solutions with y = 0.6, y = 0.75 are prepared. Their thermoelectric properties (thermoelectric power S, electric conductivity σ and thermal conductivity K) in the temperature range 300 to 750 K are measured. The thermoelectric figure of merit Z = S2σ/K for some compositions in calculated. The best p-type new material is the composition (GeTe)0.8[(Ag2Te)0.4(Sb2Te3)0.6]0.2 with Zmax = 2.4 × 10−3 K−1 at about 700 K. [Russian Text Ignored].

44 citations


Journal ArticleDOI
TL;DR: The podiform chromitites investigated in the course of this study occur in intensely serpentinized dunites and peridotites of unknown age (paleozoic or older) within a metamorphic complex consisting of gneisses, amphibolites and marbles.
Abstract: The podiform chromitites investigated in the course of this study occur in intensely serpentinized dunites and peridotites of unknown age (paleozoic or older) within a metamorphic complex consisting of gneisses, amphibolites and marbles. Concentrations of platinum group elements (PGE) and the distribution of platinum group minerals (PGM) have been investigated in the chromitite occurrences of Dobromirci and Pletene.

40 citations


Journal ArticleDOI
TL;DR: The effect of in vivo administration of ginsenoside Rg1 from Panax ginseng on insulin binding in liver and brain membranes of mice was studied and the increase in insulin binding was related to an increase in the number of insulin receptors rather than to a change in the receptor affinity.
Abstract: The effect of in vivo administration of ginsenoside Rg1 from Panax ginseng on insulin binding in liver and brain membranes of mice was studied. Ginsenoside Rg1 at a dose of 10mg/kg significantly increased [125]insulin binding in both tissues. The increase in insulin binding was related to an increase in the number of insulin receptors rather than to a change in the receptor affinity.

36 citations


Journal ArticleDOI
TL;DR: In this paper, the diazotization at elevated temperature of the weakly basic heterocyclic amine 2-amino-6-methoxybenzothiazole, which is used in the production of basic dyes was investigated.

Book ChapterDOI
01 Jan 1991
TL;DR: In this paper, all possible subsequences of positive integers for which the suitably centered and normalized total gain S nk in n k Petersburg games has an asymptotic distribution as k → ∞, and identify the corresponding set of Hmiting distributions.
Abstract: We determine all possible subsequences \(\left\{ {n_k } \right\}_{k = 1}^\infty\)of the positive integers for which the suitably centered and normalized total gain S nk in n k Petersburg games has an asymptotic distribution as k → ∞, and identify the corresponding set of Hmiting distributions. We also solve all the companion problems for lightly, moderately, and heavily trimmed versions of the sum S nk and for the respective sums of extreme values in S nk .

Journal ArticleDOI
TL;DR: In this paper, an explanation based on the Stoner-wohlfarth model was proposed for thermal activation in a disordered system of BaFe 12 O 19 particles, which accounts for the Hopkinson effect.

Journal ArticleDOI
TL;DR: For the first time to the authors' knowledge, a frequency-domain description of the passive mode-locking process is presented, which provides complete information for the amplitude and phase evolution of the individual modes.
Abstract: We present a computer simulation of the mode-locking process in a pulsed Nd:YAG laser with a nonlinear mirror based on second-harmonic generation For the first time to our knowledge, a frequency-domain description of the passive mode-locking process is presented, which provides complete information for the amplitude and phase evolution of the individual modes The mode locking is described as being due to the interaction of the longitudinal modes in the nonlinear mirror through second-harmonic and sum- and difference-frequency generation

Journal ArticleDOI
TL;DR: In this paper, the surface pressure/area dependence on pH in spread and adsorption layers of bovine serum albumin (BSA), β-lactoglobulin A and ovalbumin was investigated using the Wilhelmy method.

Journal ArticleDOI
TL;DR: In this paper, a deformable droplet model was proposed to explain the abnormally low measured values of the second virial and diffusion coefficients as well as the dimer formation in microemulsions.

Journal ArticleDOI
TL;DR: In this paper, the authors analyzed the contribution of the following kinetic processes to the hysteresis loop: Marangoni effect, bulk-to-surface diffusion-controlled interchange of molecules and film formation from liposomes.

Journal ArticleDOI
TL;DR: In this paper, the possibilities of the two methods have been compared for the analysis of a large number of vegetable reference materials and the results showed that nine common elements are common for both methods (Ca, Cd, Co, Cu, Fe, Mg, Mn, Na, Zn) out of all determined elements (28 by INAA and 11 by AAS).
Abstract: INAA and flame AAS have been used for the analysis of a large number of vegetable reference materials. Out of all determined elements (28 by INAA and 11 by AAS) nine are common for both methods (Ca, Cd, Co, Cu, Fe, Mg, Mn, Na, Zn) and for these the possibilities of the two methods have been compared.

Journal ArticleDOI
TL;DR: Zhelyazkov et al. as mentioned in this paper studied the influence of a metal enclosure on the electromagnetic wave characteristics and on the structure of a plasma column sustained by the wave itself, and obtained axial profiles of the dimensionless electron number density, wave power, wave number, and wave electric field components.
Abstract: In this paper, we have studied the influence of a metal enclosure on the electromagnetic wave characteristics and on the structure of a plasma column sustained by the wave itself. The present work is an extension of a theoretical model of a plasma column produced by a traveling azimuthally-symmetric electromagnetic surface wave (Zhelyazkov, I. and Benova, E., J. Appl. Phys. 66, 1641 (1989)). The axial profiles of the dimensionless electron number density, wave power, wave number, and wave electric field components have been obtained as a function of an additional parameter η - R1/R taking into account the presence of a metal enclosure near the discharge tube (R being the plasma column radius, R1 the metal tube radius). These results are applied to particular experimental setups.

Journal ArticleDOI
TL;DR: In this article, a theoretical model of a plasma column sustained by an electromagnetic surface wave in the dipolar (m = 1) mode for two different gas-discharge regimes: free-fall/diffusion and recombination respectively, is presented.
Abstract: This paper presents a theoretical model of a plasma column sustained by an electromagnetic surface wave in the dipolar ( m =1) mode for two different gas-discharge regimes: free-fall/diffusion and recombination respectively. The dispersion characteristics of the wave and the axial profiles of the plasma density, wave power, wavenumber and wave-field components for a given regime are specified by one numerical parameter σ = ωR/C , where ω is the angular wave frequency, R the plasma radius and c the speed of light, irrespective of the gas nature and pressure. It is established that there exists a ‘critical’ value of this parameter, σ cr = 0·3726, below which a plasma is not likely to be sustained. A comparison between the axial structures of plasma columns sustained by electromagnetic waves in the dipolar and azimuthally symmetric modes is made. The model is in agreement with the available experimental results.

Journal ArticleDOI
TL;DR: In this article, the nonlinear behavior of surface waves propagating along a plasma column is investigated, including measurements of the dispersion of the waves and the evolution of the wave envelope and wave spectrum when the waves are excited with an amplitude modulated signal.
Abstract: The nonlinear behaviour of surface waves propagating along a plasma column is investigated. The experiments include (i) measurements of the nonlinear dispersion of the waves and (ii) observation of the evolution of the shape of the wave envelope and of the wave spectrum when the waves are excited with an amplitude-modulated signal

Journal ArticleDOI
TL;DR: A second-harmonic nonlinear mirror formed by a LiIO(3) frequency doubler and a dichroic output mirror is employed to mode lock the 1.34-microm transition of a pulsed Nd:YAlO( 3) laser.
Abstract: A second-harmonic nonlinear mirror formed by a LiIO3 frequency doubler and a dichroic output mirror is employed to mode lock the 1.34-μm transition of a pulsed Nd:YAlO3 laser. Pulses of 15-ps duration are reliably generated simultaneously at 1.34 and 0.67 μm.

Journal ArticleDOI
TL;DR: In this paper, the action of 2-phenyl-benzothiazoles (BT) as photo-sensitizers of the photo-degradation of poly(vinyl chloride) (PVC) is studied.

Journal ArticleDOI
TL;DR: A very large nuptial flight of the ant Leptothorax acervorum is described at an open hilltop site in Britain, where the mating behaviour of these ants involved not only a large mating swarm but also sexual/calling behaviour by the females.
Abstract: We describe in detail a very large nuptial flight of the antLeptothorax acervorum at an open hilltop site in Britain. The mating behaviour of these ants involved not only a large mating swarm but also sexual/calling behaviour by the females. The females left the flight to land on vertical objects, where they took up a characteristic calling posture, in which females of closely related species are known to release pheromones that are sexually attractive to males. ThatLeptothorax acervorum has a complex mating behaviour involving both large nuptial flights and sexual calling has important consequences for the interpretation of the evolution of polygyny in this species and social parasitism in its close relatives.


Journal ArticleDOI
TL;DR: In this paper, a significant shortening of the output pulse duration in an actively mode-locked laser was observed when one of the laser mirror was replaced with a nonlinear mirror, based on second harmonic generation.

Journal ArticleDOI
TL;DR: In this article, the authors derived the magnitude and the sign of the interfacial bending moment of the droplets in fluid dispersal systems on the basis of a thermodynamic approach, and showed that the total bending moment can be expressed as a superposition of contributions connected with the different components in the system.

Journal ArticleDOI
TL;DR: The reaction of α-chloroimines with homophthalic anhydrides leads to the formation of the isoguinoline ring system incorporated in furo[3,4-c]isoquinolinediones 8 - 10, resp. 13a-(chloromethyl)-8H-dibenzo[a,g]-quinolizine-8-one-13-carboxylic acids 12.

Book ChapterDOI
01 Jan 1991
TL;DR: In this paper, it was established experimentally that at a given temperature, the boundaries between the stripes are moving downwards with constant velocities, and colored circular spots, of lesser thickness than the surrounding film, are moving upwards in the lower stripes and, eventually, fuse with the corresponding colored stripe.
Abstract: Vertical, macroscopic thinning films formed from micellar solutions or latex suspensions exhibit a series of parallel, colored horizontal stripes of different thickness and, with time, of gradually increasing width. Such a step-wise profile can be explained by the existence of an ordered structure of spherical colloidal particles inside the film. It was established experimentally that, at a given temperature, the boundaries between the stripes are moving downwards with constant velocities. In addition, it was observed that colored circular spots, of lesser thickness than the surrounding film, are moving upwards in the lower stripes and, eventually, fuse with the corresponding colored stripe. The motion of the circular spots in a vertical stratifying film was used to determine the viscous properties of the ordered structure inside the film. It was found that the effective dynamic viscosity of the colloid crystal-like structure inside the film was about 100 times larger than the viscosity of the pure solvent.

Journal ArticleDOI
TL;DR: The experimentally obtained apparent values of the Michaelis-Menten constant, the maximum reaction rate, and the energy of activation lead to the conclusion that the keratin containing substrates are not so easily digested as those containing collagen.
Abstract: The reactivity of partially purified alkaline protease fromBacillus subtilis, to keratin and collagen containing substances has been investigated. The experimentally obtained apparent values of the Michaelis-Menten constant (Km), the maximum reaction rate (Kmax, and the energy of activation (Ea), lead to the conclusion that: 1. The keratin containing substrates are not so easily digested as those containing collagen. 2. The kinetics of the reaction with time has been investigated.