Mechanic-elastic properties and radiation attenuation efficiency of TeO2/WO3/K2O composite glass systems for nuclear and medical application.

WO3 effects on neutron and ionizing radiation defending factors of ternary tellurite-based glass blocks with molecular formula 80TeO2 -(20-x)WO3 - xK2O; x = 0-20 mol% (denoted as TKW-glass) has been reported via Phy-X theoretical calculations and Geant4 simulation code. Correlations between shielding factors and kinetics properties of the investigated glasses at different photon energy have been examined. The highest values of mass (MAC) attenuation coefficient were noted at 15 keV of the examined TKW-glass materials with the values of 38.408, 44.388, 49.855, 54.872, 59.492 cm2/g for TKW-0, TKW-5, TKW-10, TKW-15, and TKW-20, respectively. Generally, these values of the TKW-glasses obey the sequence: (TKW-0)MAC< (TKW-5)MAC < (TKW-10)MAC < (TKW-15)MAC < (TKW-20)MAC. The highest mean free path (MFP) values of TKW-glasses were registered at 15 MeV with the values of 6.101, 5.591, 5.097, 4.647, and 4.302 cm for TKW-0, TKW-5, TKW-10, TKW-15, and TKW-20, respectively. The two parameters half value layer (HVL) and MFP follow the pattern: (TKW-0)HVL, MFP > (TKW-5)HVL,MFP > (TKW-10)HVL,MFP > (TKW-15)HVL,MFP > (TKW-20)HVL,MFP. The maximum values of effective atomic number (EAN) took place at gamma energy of 15 keV corresponding to 44.35, 48.86, 52.63, 55.83, and 58.58 for TKW-0, TKW-5, TKW-10, TKW-15, and TKW-20, respectively. The trend of the buildup factors was similar for all of the glass specimens. The fast neutron removal cross-section (ΣR) enhanced as WO3 content increased in the specimens. Thus, the peaked value of ΣR is 0.1059 cm-1 was noted in the TKW-20 sample. Mechanical properties, neutron and γ-rays protection parameters were observed to improve with enhanced WO3 mol% in the TKW-glasses. The current results bear their utilization for neutron and gamma protection purposes.

Fluorinated Langmuir monolayers are more viscous than non-fluorinated monolayers.

The surface shear viscosity of the liquid expanded phase in Langmuir monolayers of fluorinated alcohols differs by orders of magnitude from the corresponding surface shear viscosity of Langmuir monolayers of their non-fluorinated counterparts. The line tension between the liquid expanded and the gaseous phase on the other hand is of similar magnitude for both fluorinated and non-fluorinated surfactants. The difference of fluorinated versus non-fluorinated monolayers is measured by active microrheology and by observing the shape relaxation of distorted liquid expanded domains toward a circular shape. Our microrheology measurements are supported by measurements of the relaxation rates of distortions, which in fluorinated liquid expanded phases are proportional to the deviation of the curvature from the mean curvature, whereas they are proportional to the square of the deviation of the curvature from the mean curvature in non-fluorinated monolayers.

Viral ion channel proteins in model membranes: a comparative study by X-ray reflectivity.

We have investigated the effect of the transmembrane domain of three viral ion channel proteins on the lipid bilayer structure by X-ray reflectivity and scattering from oriented planar bilayers. The proteins show a similar effect on the lipid bilayer structural parameters: an increase in the lipid bilayer hydrophobic core, a decrease in the amplitude of the vertical density profile and a systematic change in the ordering of the acyl chains as a function of protein-to-lipid ratio. These results are discussed in a comparative view.

SARS coronavirus E protein in phospholipid bilayers: an x-ray study.

We investigated the structure of the hydrophobic domain of the severe acute respiratory syndrome E protein in model lipid membranes by x-ray reflectivity and x-ray scattering. In particular, we used x-ray reflectivity to study the location of an iodine-labeled residue within the lipid bilayer. The label imposes spatial constraints on the protein topology. Experimental data taken as a function of protein/lipid ratio P/L and different swelling states support the hairpin conformation of severe acute respiratory syndrome E protein reported previously. Changes in the bilayer thickness and acyl-chain ordering are presented as a function of P/L, and discussed in view of different structural models.

Compactification of a myelin mimetic Langmuir monolayer upon adsorption and unfolding of myelin basic protein.

The surface shear viscosity of a myelin mimetic Langmuir monolayer is investigated upon adsorption of myelin basic protein (MBP). We measure an increase of the surface shear viscosity at picomolar concentrations of the protein, suggesting that the globular conformation of MBP changes upon adsorption at the monolayer. The conformational change enables hydrodynamic interactions of the proteins, with a typical separation of hundreds of nanometers. This unfolding is essential for the compactification of the myelin sheath, serving an enhanced saltatory signal transduction in vertebrates. The viscometry used extends the sensitivity of standard surface viscometers toward lower viscosities.

Nonequilibrium bubbles in a flowing langmuir monolayer.

We investigate the nonequilibrium behavior of two-dimensional gas bubbles in Langmuir monolayers. A cavitation bubble is induced in liquid expanded phase by locally heating a Langmuir monolayer with an IR-laser. At low IR-laser power the cavitation bubble is immersed in quiescent liquid expanded monolayer. At higher IR-laser power thermo capillary flow around the laser-induced cavitation bubble sets in. The thermo capillary flow is caused by a temperature dependence of the gas/liquid line tension. The slope of the line tension with temperature is determined by measuring the thermo capillary flow velocity. Thermodynamically stable satellite bubbles are generated by increasing the surface area of the monolayer. Those satellite bubbles collide with the cavitation bubble. Upon collision the satellite bubbles either coalesce with the cavitation bubble or slide past the cavitation bubble. Moreover we show that the satellite bubbles can also be produced by the emission from the laser-induced cavitation bubbles.

SARS E protein in phospholipid bilayers: an anomalous X-ray reflectivity study.

We report on an anomalous X-ray reflectivity study to locate a labelled residue of a membrane protein with respect to the lipid bilayer. From such experiments, important constraints on the protein or peptide conformation can be derived. Specifically, our aim is to localize an iodine-labelled phenylalanine in the SARS E protein, incorporated in DMPC phospholipid bilayers, which are deposited in the form of thick multilamellar stacks on silicon surfaces. Here, we discuss the experimental aspects and the difficulties associated with the Fourier synthesis analysis that gives the electron density profile of the membranes.

Cavitation of Langmuir monolayers.

Cavitation in liquid expanded and liquid condensed Langmuir monolayers induced by laser heating or microbubble coalescence is studied experimentally using fluorescence and Brewster angle microscopy. The kinetics of hole closure of two-dimensional (2D) gaseous cavitation bubbles exhibits a decelerated dynamics for cavities surrounded by a liquid expanded phase and an accelerated dynamics for cavities in a liquid condensed phase. Most of the cavities in liquid condensed phases possess a nonconvex shape and do not close. The results are compared with theoretical predictions derived for 2D cavitation of liquid monolayers of different surface shear viscosities, and for solid monolayers with diffusive flux of vacancies and interstitials. While part of the theory is in qualitative agreement with the experiment, the experimentally observed hole persistence within the liquid condensed phases and the hole closure within liquid expanded phases remains to be explained. The technique of microbubble coalescence might be particularly useful for the study of the rheological properties of hexatic phases.