On large minimal blocking sets in PG(2,q)

The size of large minimal blocking sets is bounded by the Bruen–Thas upper bound. The bound is sharp when q is a square. Here the bound is improved if q is a non‐square. On the other hand, we present some constructions of reasonably large minimal blocking sets in planes of non‐prime order. The construction can be regarded as a generalization of Buekenhout's construction of unitals. For example, if q is a cube, then our construction gives minimal blocking sets of size q^4/3 + 1 or q^4/3 + 2. Density results for the spectrum of minimal blocking sets in Galois planes of non‐prime order is also presented. The most attractive case is when q is a square, where we show that there is a minimal blocking set for any size from the interval . © 2004 Wiley Periodicals, Inc. J Combin Designs 13: 25–41, 2005.     

Microwave‐Assisted Direct Esterification of Cyclic Phosphinic Acids

It is known that phosphinic acids do not undergo direct esterification under conventional conditions. However, the reaction may take place on microwave irradiation. 1‐Hydroxy‐3‐phospholene 1‐oxides, 1‐hydroxy‐phospholane 1‐oxides, and a 1‐hydroxy‐1,2,3,4,5,6‐hexahydrophosphinine 1‐oxide were esterified with n‐pentanol, i‐pentanol, n‐octanol, and i‐octanol(2‐ethylhexanol). The phosphinates prepared in 50%–94% yield are all new compounds, and a number of them are useful intermediates.     

Complexation of hydroxamate-based siderophores with cobalt(II/III): growth inhibitory effect of cobalt(III)-desferricoprogen complex on fungi

Solution equilibrium results for Co(II) and Co(III) complexes of two natural hydroxamate-based siderophores, the exocyclic desferricrocin (DFR) and the endocyclic triacetylfusarinine (TAF) are presented. The three hydroxamate chelating functions of TAF were found to complete the octahedral coordination sphere of a Co(II) ion in stepwise processes, but following the coordination of two hydroxamates of DFR practically in one step, the third function, most probably because of sterical reasons, remained uncoordinated. A comparison with corresponding results for the previously studied acyclic desferrioxamine B (DFB) and desferricoprogen (DFC) provided some information about the effects of the molecular framework of siderophores on their cobalt-binding ability. The oxidation of the central metal ion under basic conditions and investigation of the cobalt(III) complexes by cyclic voltammetry were also made. Compared to Fe(III), by several orders of magnitude, higher stability complexes were formed with Co(III). The possibility of any effect of the Co(III)-siderophore complex on microbial Fe(III) uptake was tested by investigation of the antifungal effect of Co(III)-DFC in comparison with that of CoCl₂ on two fungi cultures, Penicillium brevicompactum and Aspergillus fumigatus.     

Photodynamic therapy of nonmelanoma skin cancer with topical hypericum perforatum extract--a pilot study.

Hypericin, the photoactive compound of Hypericum perforatum, is probably the most powerful photosensitizer found in nature. This compound has shown high potency in the photodynamic treatment of tumor cells. However, there is only limited knowledge regarding the photodynamic effect of hypericin on nonmelanoma skin cancer cells. The aim of this prospective study was to investigate the efficacy of photodynamic therapy with topical application of an extract of H. perforatum in actinic keratosis, basal cell carcinoma (BCC) and morbus Bowen (carcinoma in situ). The study was carried out on 34 patients--eight with actinic keratoses (AKs), 21 with BCC and five with Bowen's disease. The extract of H. perforatum was applied on the skin lesions under occlusion and that was followed by irradiation with 75 J cm(-2) of red light 2 h later. The treatment was performed weekly for 6 weeks on average. The percentage of complete clinical response was 50% for AKs, 28% in patients with superficial BCC and 40% in patients with Bowen's disease. There was only a partial remission seen in patients with nodular BCCs. A complete disappearance of tumor cells was found in the histologic preparation of 11% of patients with superficial BCCs and 80% in the patients with Bowen's disease. All patients complained of burning and pain sensations during irradiation. Although the results of this first clinical trial could be regarded as disappointing, there are still possibilities for improvement. Better preparation of the lesions, enhancement of hypericin delivery and other types of light exposure procedures could significantly improve the clinical outcomes of this relatively inexpensive treatment modality.     

Demonstration of a protein with enhanced resistance to proteinase K in transmissible cytopathic condition elicited by cell-free lysate of free-living ameba Naegleria gruberi

The cell-free lysate of free-living amebae Naegleria gruberi and Naegleria fowleri were reported to elicit cytopathic effect in various cell lines that could be indefinitely transmitted by the culture media. The causative agent showed sensitivity to treatments detrimental to proteins while resisted exposures damaging to nucleic acids. Here we demonstrate that subsequent to exposure to N. gruberi lysate mild digestion with proteinase K reveals the presence of a protein band in HeLa cells absent from control cell lines. Though the small quantity of this protein with enhanced resistance to proteinase K relative to the total protein content of the sample has proved to date insufficient for its purification, we suppose that it is a human cellular protein that assumed altered conformation in a prion-like fashion. The conformational conversion could have been trigerred by an ameba protein in the lysate. In addition, we showed that HeLa cells treated with N. gruberi lysate display elevated cathepsin B activity which is assumed to be a secondary response to the accumulation of the proteinase K-resistant protein. We propose that a number of degenerative sequelae following previous microbial infections in mammals could have a similar pathomechanism. Moreover, epidemiological data strongly suggest that natural prion disease in sheep, goat and cervids may also have an etiology linked to prior infection/colonization with a microbe, as it had already been proposed by one of us.     

Nanophase separation in segmented polyurethane elastomers: Effect of specific interactions on structure and properties

Polyurethanes were prepared from 4,4′-methylenebis (phenyl isocyanate) (MDI), 1,4-butanediol (BD) and poly (tetrahydrofurane) polyether polyol (PTHF). The -OH functional group ratio of polyol/total diol was kept constant at 0.4 in all experiments, while the ratio of the isocianate and hydroxyl groups (NCO/OH) changed between 0.940 and 1.150. Melt polymerization was carried out in an internal mixer. The polymers were characterized with a number of methods including GPC, FTIR, WAXS, DSC, DMA and tensile testing. Changing stoichiometry modifies molecular weight as expected, but the relative concentration of end-groups also changes at the same time. The respective end-groups preferentially associate with each other leading to phase separation. -OH end-groups enter into weaker interactions with each other than urethane and amine groups. The extent of phase separation, as well as the size and properties of the dispersed phase depend on composition. Each property of the polymer is affected differently by molecular weight and phase separation. Melt viscosity depends mostly on the length of the molecules, ultimate tensile properties are influenced also by interactions, while stiffness is determined almost exclusively by phase structure.     

Standard thermodynamic properties of H3PO4(aq) over a wide range of temperatures and pressures

The densities and heat capacities of solutions of phosphoric acid, 0.05 to 1 mol kg-1, were measured using flow vibrating tube densitometry and differential Picker-type calorimetry at temperatures up to 623 K and at pressures up to 28 MPa. The standard molar volumes and heat capacities of molecular H3PO4(aq) were obtained, via the apparent molar properties corrected for partial dissociation, by extrapolation to infinite dilution. The data on standard derivative properties were correlated simultaneously with the dissociation constants of phosphoric acid from the literature using the theoretically founded SOCW model. This made it possible to describe the standard thermodynamic properties, particularly the standard chemical potential, of both molecular and ionized phosphoric acid at temperatures up to at least 623 K and at pressures up to 200 MPa. This representation allows one to easily calculate the first-degree dissociation constant of H3PO4(aq). The performance of the SOCW model was compared with the other approaches for calculating the high-temperature dissociation constant of the phosphoric acid. Using the standard derivative properties, sensitively reflecting the interactions between the solute and the solvent, the high-temperature behavior of H3PO4(aq) is compared with that of other weak acids.     

Influence of particle size on the fracture toughness of a PP-based particulate composite

The main focus of this paper is a numerical investigation of the fracture behavior of a particulate composite (CaCO₃-PP). The composite is modeled as a three-phase continuum and simulated numerically on a microscale by using finite elements. The propagation of a microcrack in a matrix filled with rigid particles covered by an interphase is analyzed. The stress distribution is determined for a variety of particle sizes and material properties of the interphase. The final results, in agreement with experimental data, confirm that the microcrack behavior depends on particle sizes. Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 45, No. 3, pp. 411-418, May-June, 2009.