Showing papers by "Sofia University published in 1996"
TL;DR: In this article, the electrophoretic mobility of oil droplets, dispersed without any surfactant in the aqueous phase, was measured and the results showed that the oil droplet are negatively charged and the magnitude of their ζ-potential strongly depends on pH and the ionic strength of the aiquous phase.
Abstract: The electrophoretic mobility of oil droplets, dispersed without any surfactant in the aqueous phase, was measured. Four different oils were studied: xylene, dodecane, hexadecane, and perfluoromethyldecalin. Special precautions were undertaken to avoid artifacts caused by the presence of surfactant impurities. The results show that the oil droplets are negatively charged and the magnitude of their ζ-potential strongly depends on pH and the ionic strength of the aqueous phase. The electrophoretic mobility is almost independent of the type of specific nonpolar oil. Series of experiments were performed to check different hypotheses about the origin of the spontaneous charging of the oil−water interfaces. The results lead to the conclusion that hydroxyl ions, released by the dissociation−association equilibrium of the water molecules, adsorb at the oil−water interface. The specific adsorption energy was estimated to be 25kT per ion (kT is the thermal energy). The molecular origin and the implications of this ...
736 citations
TL;DR: In this article, the authors present experimental and theoretical results on high-harmonic generation in noble gases using an 805 nm, 25 fs, titanium-doped sapphire laser.
Abstract: We present experimental and theoretical results on high-harmonic generation in noble gases using an 805 nm, 25 fs, titanium-doped sapphire laser. The harmonic energies observed are unexpectedly high when compared with experimental and theoretical results to date for longer excitation pulses. We observe that the efficiency of harmonic production is highest for shorter pulses. Furthermore, the wavelength of the harmonics can be tuned by adjusting the sign of the chirp of the excitation pulse, demonstrating a tunable, ultrashort-pulse, $l25\mathrm{fs}$ soft-x-ray source.
291 citations
TL;DR: It is concluded that nematodes offer excellent perspectives to assess effects of pollutants at the community level and suggest that the nematode community was also affected indirectly by copper and pH via other components of the soil food web.
Abstract: Four copper (0, 250, 500, and 750 kg Cu · haa−1) and pH (4.0, 4.7, 5.4, and 6.1 in 1 M KCl) treatments were applied to an arable agroecosystem. Effects on the nematode community were assessed after 10 years of exposure under field conditions. Both copper and pH had major influences on nematodes. The effect of copper was generally enhanced with decreasing soil pH. The lowest copper application rate which had a significant negative effect on the total number of nematodes was 250 kg. ha−1 at pH 4.0, which is equivalent to a copper concentration of 0.32 mg.L−1 in 0.01 M calcium chloride (Cu-CaCl2). Species composition and the abundance of trophic groups were more sensitive than the total number of nematodes. Combinations of high copper and low pH significantly reduced the number of bacterial-feeding nematodes, whereas the number of hyphal-feeding nematodes increased. Omnivorous and predacious nematodes showed the most sensitive response, becoming extinct when Cu-CaCl2 was 0.8 to 1.4 mg.L−1. Plant-feeding nematodes showed the largest differences in abundance and appeared to reflect the effects of copper and pH on primary production. The results suggest that the nematode community was also affected indirectly by copper and pH via other components of the soil food web. It is concluded that nematodes offer excellent perspectives to assess effects of pollutants at the community level.
202 citations
TL;DR: In this article, the kinematic information contained in these gneisses shows that shear-deformation occurred during development of a nappe complex, characterized by south to southwestward (foreland directed) piling-up and is associated with both coeval and subsequent extension.
Abstract: Mylonitic gneisses of the Bulgarian and Greek Rhodope were deformed under medium pressure-type metamorphism. The kinematic information contained in these gneisses shows that shear-deformation occurred during development of a nappe complex. Lithologies and metamorphic histories allow a lower (footwall) and an upper (hanging wall) terrane to be distinguished that define a crustal-scale duplex. As oceanic crust is involved, collision between two continental units with subsequent crustal thickening is inferred. The blocks would be Moesia to the north, and the Lower-Rhodope promontory to the south, which collided in the Mesozoic to early Cenozoic. The nappe complex is characterized by south to southwestward (foreland directed) piling-up and is associated with both coeval and subsequent extension. The late extension is associated with the establishment of a high temperature-low pressure metamorphic gradient and plutonism that predates, but makes a transition to, the lithospheric extension of the Aegean Arc.
193 citations
TL;DR: The calculated values of the intercellular CO 2 concentration, CO 2 -compensation point and the maximal carboxylating efficiency of ribulose-l,5-bisphosphate car boxylase support the suggestion that biochemical factors are involved in the response of photosynthesis to SA.
193 citations
TL;DR: In this article, fine CoFe 2 O 4 particles with average size of 50 A have been produced by coprecipitation from Fe(II and Co(II) solutions followed by a low-temperature calcination.
105 citations
TL;DR: In this paper, a method for determination of the three-phase contact angle at the surface of a micrometer-sized particle (latex sphere, oil droplet, or biological cell) is described.
Abstract: A novel method for determination of the three-phase contact angle at the surface of a micrometer-sized particle (latex sphere, oil droplet, or biological cell) is described. The particle is entrapped within a liquid filmofequilibriumthicknesssmallerthantheparticlediameter. Thusaliquidmeniscus(alayerofuneven thickness) is formed around the particle. When observed in reflected monochromatic light, this meniscus appearsasaninterferencepatternofconcentricbrightanddarkfringes. Fromtheradiioftheinterference fringes, one can restore the meniscus shape by using the solution of the Laplace equation of capillarity. In this way the three-phase contact angle of the particle and the capillary pressure can be determined. We demonstrate the applicability of our method to latex spheres from several batch samples (between 1 and 7 Im in diameter) and to oil droplets, stabilized by adsorbed protein layer. The numerical procedures used for contact angle determination are described, and illustrative results are presented and discussed.
93 citations
TL;DR: It is observed that the harmonic spectrum of argon taken with laser pulses contains harmonics up to 20 orders higher than for 100 fs laser pulses with the intensity, and it is shown that this increase in harmonics is because the atom survives to intensities.
Abstract: High-harmonic generation using ultrashort laser pulses with pulse durations 25 to 200 fs is s theoretically and experimentally. We observe that the harmonic spectrum of argon taken with laser pulses contains harmonics up to 20 orders higher than for 100 fs laser pulses with the intensity. We show that this increase in harmonics is because the atom survives to highe intensities, due in part to the nonadiabatic response of the atomic dipole to the fast rise time pulse. [S0031-9007(96)01018-6]
92 citations
TL;DR: In this article, the authors show that drawing results in the formation of a highly oriented fibrillar structure of PET which is preserved even after annealing above the melting point of polyamide 6 (PA 6).
89 citations
TL;DR: In this article, the authors demonstrate that the hydration repulsion between smooth charged surfaces can be attributed to the interplay of two effects which are not taken into account in the conventional DLVO theory.
87 citations
TL;DR: In this paper, the Zamolodchikov brothers proposed exact three-point correlation functions for N = 1 supersymmetric Liouville theory, which describe the reflection amplitudes.
TL;DR: In this article, the authors present methods for obtaining new solutions to the bispectral problem by giving its abstract algebraic version suitable for generalizations, which are illustrated by new classes of Bispectral operators.
TL;DR: In this paper, a polymerized complex technique was used to prepare high-purity La 2 Ti 2 O 7 and Nd 2 Ti O 7 using a mixture of mixed solutions of citric acid, ethylene glycol, and mixed-metal chelate complexes.
TL;DR: In this article, the authors measured particle−particle and particle−wall capillary interactions as a function of the separation distance, based on counterbalancing the moment of a couple of forces acting between two pairs of particles by the torsion moment of thin platinum wire.
Abstract: Particle−particle and particle−wall capillary interactions were measured as a function of the separation distance. The “particles” were vertical thin glass cylinders and/or small glass spheres, protruding from an air/liquid interface. The particles attract each other due to the overlapping of the menisci formed around each of them. The force of interaction is detected by a sensitive torsion microbalance. It is based on counterbalancing the moment of a couple of forces, acting between two pairs of particles, by the torsion moment of a thin platinum wire. By varying the wire diameter, we accessed forces differing by several orders of magnitude, from about 5 dyn at small separation between the particles down to 0.001 dyn at large separation. The smallest force was measured with two cylinders of diameters about 300 μm. For two spheres (diameters 1.2 mm) we obtained difference in the forces corresponding to different heights of protrusion from the liquid surface. For interacting sphere and glass cylinder the f...
TL;DR: In this paper, a mechanistic explanation for the stereoselectivity of salicylaldehydes with phosphonoacetates was given, giving the coumarin-3-phosphonates and 1,2-benzoxaphosphorine-3 carboxylates.
TL;DR: It is found that space-time focusing of the pulse within the laser crystal imposes a limitation on the pulse duration as a function of the crystal length, so good compensation of the net group-velocity dispersion of the cavity is not sufficient for successful sub-10-fs operation of the laser.
Abstract: We present results of a three-dimensional model of a Kerr-lens mode-locked titanium-doped sapphire laser in the sub-10-fs regime of operation. We find that space–time focusing of the pulse within the laser crystal imposes a limitation on the pulse duration as a function of the crystal length. Thus good compensation of the net group-velocity dispersion of the cavity is not sufficient for successful sub-10-fs operation of the laser. The dependence of the pulse duration on the intracavity dispersion is also presented, which demonstrates that pulses as short as 6 fs can be generated directly from the laser.
TL;DR: In this paper, a new model of mixed surfactant systems has been developed, which includes two parameters only connected directly with the Gibbs free energy of the aggregates, which can be determined using both the aggregation equilibrium constant values or the phase composition data.
Abstract: A new model of mixed surfactant systems have been developed in the work presented. It includes two parameters only connected directly with the Gibbs free energy of the surfactant aggregation. They can be determined using both the aggregation equilibrium constant values or the phase composition data. It has been shown also the relation between these new parameters and the same of the regular solution approximation and the alternative models. The possibility to describe the available experimental information about the micelle composition as a function of the singly dispersed surfactant mixture composition better than by the other models has been shown also.
TL;DR: In this paper, the adsorption of heavy metal cations on two CeO2 samples, (C-1, 209 m2 g−1, prepared by hydrolysis of Ce(NH4)2(NO3)6, and C-2, 123 m2g−1), synthesized by HNO3 and EDTA, has been investigated and conditions for quantitative and reproducible elution and subsequent atomic absorption spectrometry are established.
01 Feb 1996
TL;DR: In this paper, Backlund-Darboux transformations on maximal algebras of commuting ordinary differential operators are defined and the action of these transformations on related objects: wave functions, tau-functions, and spectral algesbras.
Abstract: We define Backlund-Darboux transformations in Sato's Grassman- nian. They can be regarded as Darboux transformations on maximal algebras of commuting ordinary differential operators. We describe the action of these transformations on related objects: wave functions, tau-functions and spectral algebras.
TL;DR: In this article, the properties of the possible solitary electromagnetic waves, propagating in two-dimensional SIS Josephson junction without dissipative losses are investigated on the basis of the local theory of the junction.
Abstract: The properties of the possible solitary electromagnetic waves, propagating in two-dimensional SIS Josephson junction without dissipative losses are investigated on the basis of the local theory of the junction. A classification of the waves in the junction with respect to the Swihart velocity is made. It is shown that allowed and forbidden areas for the wave numbers, wave frequency and wave amplitude exist. The cut-off frequency for the solitary waves which velocity is greater than the Swihart velocity can be smaller than the Josephson plasma frequency and moreover these waves can propagate only in a junction that is large in the direction perpendicular to the propagation direction. On the contrary the solitary waves which velocity is smaller than the Swihart velocity request junction size in the above direction to be smaller than a critical one. The investigated two-dimensional solitary waves can be connected with one or two quanta of the magnetic flux.
TL;DR: Phosphorus retention is known to be an important factor in the development of secondary hyperparathyroidism, and new work has demonstrated that a high extracellular phosphorus concentration directly stimulates parathyroid hormone secretion and synthesis.
Abstract: Hyperparathyroidism is a common finding in patients with renal failure. Phosphorus retention is known to be an important factor in the development of secondary hyperparathyroidism. Exciting new work has demonstrated that a high extracellular phosphorus concentration directly stimulates parathyroid hormone secretion and synthesis. Dietary phosphorus also modulates parathyroid function indirectly by decreasing calcitriol production, and it interferes with the calcaemic response to parathyroid hormone. The information available suggests that the control exerted by phosphorus is critical, via indirect and direct actions, in preventing the development of secondary hyperparathyroidism.
TL;DR: In this paper, the role of hydrophobic protein SPC on the structure and dilatational rheological properties of the model monolayers of alveolar surfactant was investigated, using a developed Rheological approach and atomic force microscopy (AFM) imaging.
TL;DR: In this paper, the inverse fluidization is used to solve the problem when the biofilm microorganisms multiply and increase in thickness, and the maximum biofilm thickness at which no diffusional limitation is observed is shown.
Abstract: The inverse fluidization is a new multiphase gas-liquid or gas-liquid-solid system. The first studies of two phase (liquid-solid) inverse fluidization were originally published independently by Shimodaira et al. [6], Nikolov et al. [5] and Fan et al. [2]. The main difference between the classic and inverse fluidization is that the solid particle density in the inverse fluidized bed is less than the density of the continuous fluid and therefore the bed is fluidized by a downflow of the fluid. Schematic illustration of both classic and inverse fluidized beds is shown in Figure 1. One of the most important recent applications of fluidized beds is in the field of bioreactor engineering. It is well known that almost all types of microorganisms spontaneously attach themselves to any inert solid surface in contact with the liquid growth media. The microorganisms use exopolysaccharide {open_quotes}bridges{close_quotes} to attach themselves to the solid support and to each other. This structure of microorganisms and exopolysaccharides is known as biofilm. The fluidized bed bioreactors are used primarily for processes in which the fluidized particles are used as an inert solid support. There is a problem when the biofilm microorganisms multiply and the biofilm thickness increase. This limits diffusion ofmore » oxygen and/or the organic substrate to the deeper layers of the biofilm. Starvation of the microorganisms at the base of the biofilm causes pieces of the biofilm to detach (Figure 2) and leads to ineffective bioreactor operation. The maximal biofilm thickness at which no diffusional limitation is observed (phase 3 in Figure 2), is usually around 100 {mu}m. Therefore, to operate the bioreactor efficiently, the biofilm thickness should be approximately 100 {mu}m. The use of inverse fluidization can solve this problem. 6 refs., 10 figs.« less
TL;DR: A change in the kinetic behaviour is observed, due to the 'melting' of the hydrophobic tails in the lipid aggregates, which may have various consequences of biological and pharmacological importance.
Posted Content•
TL;DR: In this article, the authors define B\"acklund-Darboux transformations in Sato's Grassmannian and describe the action of these transformations on related objects: wave functions, tau-functions and spectral algebras.
Abstract: We define B\"acklund--Darboux transformations in Sato's Grassmannian. They can be regarded as Darboux transformations on maximal algebras of commuting ordinary differential operators. We describe the action of these transformations on related objects: wave functions, tau-functions and spectral algebras.
This paper is the second of a series of papers (hep-th/9510211, q-alg/9602011, q-alg/9602012) on the bispectral problem.
15 Oct 1996
TL;DR: In this article, a theoretical approach to the kinetics of adsorption on the expanding interface of a micellar surfactant solution is proposed, where nonlinear partial differential equations of mass transfer of the micelles and monomers are reduced to ordinary differential equations, which are solved numerically along with the nonlinearized adaption isotherm as a boundary condition.
Abstract: A theoretical approach to the kinetics of adsorption on the expanding interface of a micellar surfactant solution is proposed. The nonlinear partial differential equations of mass transfer of the micelles and monomers are reduced to ordinary differential equations, which are solved numerically along with the nonlinearized adsorption isotherm as a boundary condition. Being more general, this theoretical approach is consistent also with the special case of small deviations from equilibrium widely used in the kinetics of micellization. The theory is applied further to fit the experimental data for dynamic surface tension of micellar solutions of sodium dodecyl sulfate and sodium polyoxyethylene-2 sulfate measured by the maximum bubble pressure (MBP) method. The expansion of the bubble surface is accounted for by using the experimental dependence of the bubble size on time. The calculated effective rate constant of micelle decay for sodium dodecyl sulfate turns out to be sensitive to the mechanism of the micelle's disintegration. This provides a possibility for one to determine the rate constants of the fast and slow processes in the relaxation kinetics of micellization by using a relatively simple experimental technique for dynamic surface tension measurement like the MBP method.
TL;DR: Comparisons between the desorption rates of the β- CD/lipolytic product complexes and the enzymatic hydrolysis rates of long chain PC, in the presence of β-CD in the aqueous subphase, showed that the rate limiting step is neither the formation of theβ-CD/lipolipase A 2 product complexes nor their Desorption into the water subphase but the hydrolyses of the PC monomolecular films by PLA 2.
Journal Article•
TL;DR: The results show that in vivo gamma-IFN inhibits apoptosis of B cells from B-CLL patients and the inhibitory effect of gamma-ifN on apoptosis correlates directly with the severity of the disease and this is likely explained by a marked upregulation of Gamma-IFn receptors in cells from patients in the high-risk group.
Abstract: Apoptosis was evaluated in B cells from 41 patients with B-CLL and 20 healthy aged-matched controls. B cells were cultured with and without gamma-IFN and other cytokines; apoptosis was quantified at regular intervals throughout a 5-day culture period. According to Rai's criteria, 17 patients were classified as good risk, 16 as intermediate and eight as high risk. In vitro, purified B cells from B-CLL patients were evaluated for apoptosis. Maximal apoptosis (44.12%) was observed at day 5 in cells from patients with poor prognosis. The addition of gamma-IFN to the culture media prevented apoptosis in a dose-dependent manner. Maximal inhibition of apoptosis was achieved with 100 IU/ml of gamma-IFN. The degree of inhibition of apoptosis by gamma-IFN was greater in cells from the high-risk group patients than in those from the intermediate and good prognosis group (P < 0.0001). The expression of gamma-IFN receptors in B-CLL cells was evaluated using a MnAb against the extracellular domain of gamma-IFN receptor. After 4 days in culture with gamma-IFN, only cells from the intermediate- and high-risk groups showed an increase in the density of gamma-IFN receptors (P < 0.001). gamma-IFN was not detected in the sera of our study patients. However gamma-IFN was detectable in the media from both normal B cells and B-CLL cells in culture; there was no difference in the amount of gamma-IFN released by cells from the three groups of patients studied. Our results show that in vivo gamma-IFN inhibits apoptosis of B cells from B-CLL patients. The inhibitory effect of gamma-IFN on apoptosis correlates directly with the severity of the disease and this is likely explained by a marked upregulation of gamma-IFN receptors in cells from patients in the high-risk group.
TL;DR: In this article, the effect of the surfactants nonylphenol polyethylene glycol (D1), dinaphthylmethane-4,4′-disulphonic acid (D2), and polyethylenes glycol with molecular weight 400 (D3) on cadmium-zinc dust cementation kinetics as well as on the Cadmium deposit structure was investigated.
TL;DR: In this paper, second-order subdifferentials of Clarke's type of C1,1 functions are defined in Banach spaces with separable duals and their properties are proved.
Abstract: We present second-order subdifferentials of Clarke's type of C1,1 functions, defined in Banach spaces with separable duals One of them is an extension of the generalized Hessian matrix of such functions in ℝn, considered by J B H-Urruty, J J Strodiot and V H Nguyen Various properties of these subdifferentials are proved Second-order optimality conditions (necessary, sufficient) for constrained minimization problems with C1,1 data are obtained