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Search Results: 1 - 10 of 87979 matches for " Asparouh I. Iliev "
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Changes in Astrocyte Shape Induced by Sublytic Concentrations of the Cholesterol-Dependent Cytolysin Pneumolysin Still Require Pore-Forming Capacity
Christina F?rtsch,Sabrina Hupp,Jiangtao Ma,Timothy J. Mitchell,Elke Maier,Roland Benz,Asparouh I. Iliev
Toxins , 2011, DOI: 10.3390/toxins3010043
Abstract: Streptococcus pneumoniae is a common pathogen that causes various infections, such as sepsis and meningitis. A major pathogenic factor of S. pneumoniae is the cholesterol-dependent cytolysin, pneumolysin. It produces cell lysis at high concentrations and apoptosis at lower concentrations. We have shown that sublytic amounts of pneumolysin induce small GTPase-dependent actin cytoskeleton reorganization and microtubule stabilization in human neuroblastoma cells that are manifested by cell retraction and changes in cell shape. In this study, we utilized a live imaging approach to analyze the role of pneumolysin’s pore-forming capacity in the actin-dependent cell shape changes in primary astrocytes. After the initial challenge with the wild-type toxin, a permeabilized cell population was rapidly established within 20–40 minutes. After the initial rapid permeabilization, the size of the permeabilized population remained unchanged and reached a plateau. Thus, we analyzed the non-permeabilized (non-lytic) population, which demonstrated retraction and shape changes that were inhibited by actin depolymerization. Despite the non-lytic nature of pneumolysin treatment, the toxin’s lytic capacity remained critical for the initiation of cell shape changes. The non-lytic pneumolysin mutants W433F-pneumolysin and delta6-pneumolysin, which bind the cell membrane with affinities similar to that of the wild-type toxin, were not able to induce shape changes. The initiation of cell shape changes and cell retraction by the wild-type toxin were independent of calcium and sodium influx and membrane depolarization, which are known to occur following cellular challenge and suggested to result from the ion channel-like properties of the pneumolysin pores. Excluding the major pore-related phenomena as the initiation mechanism of cell shape changes, the existence of a more complex relationship between the pore-forming capacity of pneumolysin and the actin cytoskeleton reorganization is suggested.
Bacterial Cytolysin during Meningitis Disrupts the Regulation of Glutamate in the Brain, Leading to Synaptic Damage
Carolin Wippel,Jana Maurer,Christina F?rtsch,Sabrina Hupp,Alexandra Bohl,Jiangtao Ma,Timothy J. Mitchell,Stephanie Bunkowski,Wolfgang Brück,Roland Nau,Asparouh I. Iliev
PLOS Pathogens , 2013, DOI: 10.1371/journal.ppat.1003380
Abstract: Streptococcus pneumoniae (pneumococcal) meningitis is a common bacterial infection of the brain. The cholesterol-dependent cytolysin pneumolysin represents a key factor, determining the neuropathogenic potential of the pneumococci. Here, we demonstrate selective synaptic loss within the superficial layers of the frontal neocortex of post-mortem brain samples from individuals with pneumococcal meningitis. A similar effect was observed in mice with pneumococcal meningitis only when the bacteria expressed the pore-forming cholesterol-dependent cytolysin pneumolysin. Exposure of acute mouse brain slices to only pore-competent pneumolysin at disease-relevant, non-lytic concentrations caused permanent dendritic swelling, dendritic spine elimination and synaptic loss. The NMDA glutamate receptor antagonists MK801 and D-AP5 reduced this pathology. Pneumolysin increased glutamate levels within the mouse brain slices. In mouse astrocytes, pneumolysin initiated the release of glutamate in a calcium-dependent manner. We propose that pneumolysin plays a significant synapto- and dendritotoxic role in pneumococcal meningitis by initiating glutamate release from astrocytes, leading to subsequent glutamate-dependent synaptic damage. We outline for the first time the occurrence of synaptic pathology in pneumococcal meningitis and demonstrate that a bacterial cytolysin can dysregulate the control of glutamate in the brain, inducing excitotoxic damage.
Ultra Low-Power Acoustic Detector Applicable in Ambient Assistance Living Systems
Iliev I.
Bioautomation , 2009,
Abstract: Ambient Assisted Living (AAL) includes methods, concepts, systems, devices as well as services, which provide unobtrusive support for daily life based on the context and situation of the assisted person. The technologies applied for AAL are user-centric, i.e. oriented towards the needs and capabilities of the particular user. They are also integrated into the immediate personal environment of the user. As a consequence, the technology is adapting to the user rather than the other way around. The in-house monitoring of elderly or disabled people (hard of hearing, deaf, with limited movement ability), using intelligent sensors is a very desirable service that may potentially increase the user's autonomy and independence while minimizing the risks of living alone. The described ultra low-power acoustic detector allows upgrade of the presented warning systems. It features long-term autonomy and possibility to use it as an element of the wireless personal area network (WPAN).
The radial velocities and physical parameters of HD 553
R. Duemmler,I. Kh. Iliev,L. Iliev
Physics , 2002, DOI: 10.1051/0004-6361:20021316
Abstract: HD 553 was discovered as an eclipsing binary by Hipparcos. Here, we present the first radial velocity curve for this system. It is found that HD 553 is a double-lined spectroscopic binary. Despite the large luminosity difference, the two components of the system are of very simmilar mass. The primary, a K0-giant, fills a large fraction of its Roche-lobe. The secondary is, despite its very similar mass, still a late-type dwarf. The radial velocity curve allows to constrain several stellar and system parameters.
Generalization of Ehrlich-Kjurkchiev method for multiple roots of algebraic equations
Anton I. Iliev
Mathematics , 2001,
Abstract: In this paper a new method which is a generalization of the Ehrlich-Kjurkchiev method is developed. The method allows to find simultaneously all roots of the algebraic equation in the case when the roots are supposed to be multiple with known multiplicities. The offered generalization does not demand calculation of derivatives of order higher than first simultaneously keeping quaternary rate of convergence which makes this method suitable for application from the practical point of view.
A Generalization of Obreshkoff-Ehrlich Method for Multiple Roots of Polynomial Equations
A. I. Iliev
Mathematics , 2001,
Abstract: In this paper we develop a new method which is a generalization of the Obreshkoff -Ehrlich method for the cases of algebraic, trigonometric and exponential polynomials. This method has a cubic rate of convergence. It is efficient from the computational point of view and can be used for simultaneous finding all roots if the roots have known multiplicities. This new method in spite of the arbitrariness of multiplicities is of the same complexity as the methods for simultaneous finding all roots of simple roots. We do not use divided differences with multiple knots and this fact does not lead to calculation of derivatives of the given polynomial of higher order, but only of first ones.
A Generalization of Obreshkoff-Ehrlich Method for Multiple Roots of Algebraic, Trigonometric and Exponential Equations
A. I. Iliev
Mathematics , 2001,
Abstract: In this paper methods for simultaneous finding all roots of generalized polynomials are developed. These methods are related to the case when the roots are multiple. They possess cubic rate of convergence and they are as labour-consuming as the known methods related to the case of polynomials with simple roots only.
Abundance analysis of Am binaries and search for tidally driven abundance anomalies - III. HD116657, HD138213, HD155375, HD159560, HD196544 and HD204188
I. Stateva,I. Kh. Iliev,J. Budaj
Physics , 2011, DOI: 10.1111/j.1365-2966.2011.20108.x
Abstract: We continue here the systematic abundance analysis of a sample of Am binaries in order to search for possible abundance anomalies driven by tidal interaction in these binary systems. New CCD observations in two spectral regions (6400-6500, 6660-6760 AA) of HD116657, HD138213, HD155375, HD159560, HD196544 and HD204188 were obtained. Synthetic spectrum analysis was carried out and basic stellar properties, effective temperatures, gravities, projected rotational velocities, masses, ages and abundances of several elements were determined. We conclude that all six stars are Am stars. These stars were put into the context of other Am binaries with 10 < Porb < 200 days and their abundance anomalies discussed in the context of possible tidal effects. There is clear anti-correlation of the Am peculiarities with v sin i. However, there seems to be also a correlation with the eccentricity and may be with the orbital period. The dependence on the temperature, age, mass, and microturbulence was studied as well. The projected rotational velocities obtained by us were compared to those of Royer et al. (2002) and Abt & Morrell (1995).
Search for the 3He isotope in the atmospheres of HgMn stars
I. Stateva,T. Ryabchikova,I. Iliev
Physics , 1998,
Abstract: We carried out a detailed analysis of the helium lines at 4921, 5876 and 6678 A in the spectra of the HgMn stars HD 58661, HD 172044, HD 185330 and HD 186122. For the first of these lines, the isotopic shift reaches +0.33 A for pure 3He, while for the last one, the maximum shift is +0.50 A. The 5876 line does not show any significant isotopic shift and is chosen for comparison. No trace of 3He was found in the atmosphere of HD 172044, while its presence was confirmed in HD 185330. This isotope is clearly present in the atmosphere of HD 58661. The results obtained for HD 186122 were ambiguous, 3He being apparently present in the 4921 line but not in the 6678 line, possibly because the latter is very weak.
Shell signs in the hydrogen-line spectrum of some lambda Bootis-type stars
I. Kh. Iliev,I. S. Barzova
Physics , 1998,
Abstract: The hydrogen-line spectrum of eight lambda Boo type stars is studied. The observed H_delta and H_gamma profiles are compared with Kurucz's theoretical profiles. The existence of weak emission-like details in the cores of five lambda Boo stars is demonstrated. The Inglis-Teller formula is used to calculate the electron densities. It is found that electron densities in the atmospheres of stars with peculiar H-line profiles are twice lower than in stars with normal profiles. The conclusion is made that stars with peculiar profiles exhibit some of the characteristics usually observed in stars with extended atmospheres.
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