Effects of gemini surfactants on egg phosphatidylcholine bilayers in the fluid lamellar phase

The influence of 1,4-butanediamonium-N,N'-dialkyl-N,N,N',N'-tetramethyl dibromides (CmA, m = 7-16 is the number of alkyl carbons) on the egg yolk phosphatidylcholine (EYPC) bilayer thickness and lipid surface area at the bilayer-aqueous phase interface is studied using X-ray diffraction on fluid lamellar CmA + EYPC + H2O phases as a function of CmA:EYPC and H2O:EYPC molar ratios and the alkyl chain length m. At the constant CmA:EYPC = 0.4 and H2O:EYPC = 18 molar ratios, the CmA induced bilayer thickness decrease shows a minimum and the lipid surface area increase a maximum at the alkyl chain length m = 9. The obtained results are discussed in the context of a structural perturbation model of the cut-off effect in biological potencies of surfactants which occurs when increasing the alkyl substituent chain length above the critical value.     

Pancyclicity of Strong Products of Graphs

We prove that the strong product of graphs G₁××G_n is pancyclic, in particular hamiltonian, for nc for any cln(25/12)+1/640.75 whenever all G_i are connected graphs with the maximum degree at most .This research was supported by KONTAKT ME 337 as a part of REU programme and in part by GACR 201/99/0242The author acknowledges partial support by NSF grant DMS-9900969 and by Institute for Theoretical Computer ScienceThe author acknowledges partial support by Institute for Theoretical Computer ScienceInstitute for Theoretical Computer Science is supported by Ministry of Education of Czech Republic as project LN00A056Final version received: August 6, 2003     

Synthesis and characterization of (octaaryltetraazaporphyrinato)indium(III) complexes for optical limiting

The preparation of (octaaryltetraazaporphyrinato)indium(III) chlorides [aryl = phenyl (5a), p-tert-butylphenyl (6a), p-(trifluoromethyl)phenyl (7a), m-(trifluoromethyl)phenyl (8a)] and their reactions with aryl Grignard reagents XMgBr to give 5b-8b [X = p-(trifluoromethyl)phenyl] and 5c (R = 3,5-difluorophenyl) are described. The characterization of all compounds by UV-vis, FT-IR, and (1)H and (13)C NMR spectroscopy was performed. The hypsochromic shift of all bands in the absorption spectra of complexes 5a-8a is observed in the sequence 6a < 5a < 7a approximately 8a. This is associated with the increasing electron-withdrawing character of the aryl substituents in the periphery of the tetraazaporphyrin macrocycle. Compounds 8a,b are very good soluble in organic solvents with 8a exhibiting the higher photochemical stability among the various synthesized species. The optical limiting (OL) properties of the complexes have been studied and correlated with the structure of the (tetraazaporphyrinato)indium(III) complexes and the electronic nature of the different substituents. In particular, the OL effect at 532 nm increases on going from the series of compounds 5 to the series 8.     

Rheological studies of concentrated guar gum

Polymers and surfactants are essential ingredients of the printing paste. Polysaccharides are used commercially to thicken, suspend or stabilise aqueous systems. Also they are used to produce gels and to act as flocculates, binders, lubricants, to serve as modifiers of film properties, and have a function as adjusters of rheological parameters. Surfactants, on the other hand, perform numerous functions acting as dispersants, wetting agents, emulsifiers and antifoaming agents. The rheological properties of polysaccharide thickeners (guar gums with different substitution levels and different producers) at different concentrations and temperatures and, second, the effects produced by the addition of nonionic surfactants (polyoxyethylene stearyl alcohols with different numbers of EO groups) have been studied under linear and nonlinear shear conditions. Experimental data have been correlated with the different models: flow curves with the Cross, Carreau and Meter-Bird model, and mechanical spectra with the generalized Maxwell model and Friedrich-Braun model. The surface tensions of aqueous systems containing polysaccharide and/or surfactants have been determined over extended concentration ranges in order to detect the CMC conditions and to provide a better understanding about the polysaccharide-surfactant interactions.     

On the polynomial-space completeness of intuitionistic propositional logic

We present an alternative, purely semantical and relatively simple, proof of the Statman's result that both intuitionistic propositional logic and its implicational fragment are PSPACE-complete.This paper was supported by grant 401/01/0218 of the Grant Agency of the Czech Republic. % Mathematics Subject Classification (2000):     

Threshold strangeness production in pp interactions

During the actual lectures, features of the COSY-Jülich accelerator were presented, followed by a short summary of ongoing experiments at the COoler SYnchrotron COSY using internal as well as external beams in the range of 45 MeV to 2.5 GeV. Here the research of the COSY-11 collaboration is presented. This °⁰ facility studies the hidden and open strangeness production observing the ν and η′ as well the K⁺Y and K⁺K^? production in the proton—proton interactions at the respective thresholds.