Fluctuation spectrum of fluid membranes coupled to an elastic meshwork: jump of the effective surface tension at the mesh size

We identify a class of composite membranes: fluid bilayers coupled to an elastic meshwork that are such that the meshwork's energy is a function F(el)[A(xi)] not of the real microscopic membrane area A, but of a smoothed membrane's area A(xi), which corresponds to the area of the membrane coarse grained at the mesh size xi. We show that the meshwork modifies the membrane tension sigma both below and above the scale xi, inducing a steep crossover of amplitude deltasigma=dF(el)/dA(xi). The predictions of our model account for the fluctuation spectrum of red blood cell membranes coupled to their cytoskeleton. Our results indicate that the cytoskeleton might be under extensional stress, which would provide a means to regulate available membrane areas. We also predict an observable tension jump for membranes decorated with polymer "brushes."     

Different strategies for obtaining high opacity films of MFC with TiO2 pigments

The present study examines the production and characterization of opaque solid films made with microfibrillated cellulose (MFC) suspension and titanium dioxide (TiO₂) nanoparticles. Three different strategies were investigated: a blend of (1) MFC and TiO₂ (2) a premix in which TiO₂ particles are used to favor the fibrillation step of MFC and (3) a sol–gel strategy in which TiO₂ particles were directly generated onto the surface of MFC. The different process parameters have been optimized both for the production of MFC and the sol–gel reaction. Gel suspensions containing different ratios of TiO₂ were morphologically and chemically characterized. In order to characterize the size and the nature of the particles, diffraction laser scattering, atomic force microscopy were used while the thermo gravimetric analysis and X-ray diffraction were used to investigate the degradation of MFC for all the three strategies. To highlight the level of dispersion of TiO₂ within the MFC network, scanning electron microscopy in BSE mode has been employed. Finally, the transparence and the mechanical properties of solid films were measured by UV spectrophotometry and tensile tests, respectively. Very good TiO₂ dispersion and high opacity MFC films have been achieved with a very low amount of TiO₂. Thus, the best strategy that takes into account the easiest process for making the hybrids and leading to the high level of opacity with the lowest ratio of TiO₂ is the premix strategy.     

Modèle électromagnétique d'objet dissimulé

We model propagation of electromagnetic waves in a medium, which is inhomogeneous with a rough layer, and which hides an object. We first get an effective medium, and then we solve the problem by integral equations.     

Size and sequence and the volume change of protein folding

The application of hydrostatic pressure generally leads to protein unfolding, implying, in accordance with Le Chatelier's principle, that the unfolded state has a smaller molar volume than the folded state. However, the origin of the volume change upon unfolding, ΔV(u), has yet to be determined. We have examined systematically the effects of protein size and sequence on the value of ΔV(u) using as a model system a series of deletion variants of the ankyrin repeat domain of the Notch receptor. The results provide strong evidence in support of the notion that the major contributing factor to pressure effects on proteins is their imperfect internal packing in the folded state. These packing defects appear to be specifically localized in the 3D structure, in contrast to the uniformly distributed effects of temperature and denaturants that depend upon hydration of exposed surface area upon unfolding. Given its local nature, the extent to which pressure globally affects protein structure can inform on the degree of cooperativity and long-range coupling intrinsic to the folded state. We also show that the energetics of the protein's conformations can significantly modulate their volumetric properties, providing further insight into protein stability.     

Spectres de Vibration de l'Acide Furanne 2,3-Dicarboxylique et de ses Sels de Potassium en Solution Aqueuse

Raman and infrared spectra of furan 2,3-dicarboxylic acid and of its potassium salts in aqueous solution have been investigated in the range 100–4000 cm⁻¹. An assignment of the bands is given on the basis of C_s symmetry. The polarization of the Raman lines shows that the furan ring is planar. The carboxylate groups of the neutral ion are orthogonal. The intramolecular hydrogen bond existing in the crystalline acid and potasium hydrogen salt is sufficiently strong to be maintained in aqueous solution and the resulting chelate rings are in the furan plane.     

Discrimination of C NMR signals in solid material with liquid-like behavior presenting residual dipolar proton–proton homonuclear interactions: application on seeds

In this communication, we propose, a modified spin echo fourier transform (SEFT) experiment run under magic angle spinning (MAS) to obtain structural informations of the liquid-like domains inside complex organic materials. It includes a proton-proton dipolar decoupling such as BLEW12 or Lee-Goldburg sequence just after the 180 degrees 13C refocusing pulse and short echo delays are used in order to overcome T(2) relaxation. This very easy implemented sequence allows a clear discrimination among fast relaxing 13C signals between those with a pure liquid-like behavior and those presenting residual proton-proton dipolar coupling. The interests of the sequence, combined with other classical NMR experiments, are illustrated on whole vegetable seeds that represent an example of a complex material.     

Connected functional working spaces: a framework for the teaching and learning of functions at upper secondary level

ZDM – Mathematics Education - This paper aims at contributing to remedy the narrow treatment of functions at upper secondary level. Assuming that students make sense of functions by working...     

N-Functionalised heterocyclic dicarbene complexes of silver: Synthesis and structural studies

A range of new diimidazolium salts, held together by an alkyl unit and bearing alcohol pendant arms on their nitrogen, was synthesized. A short modular reaction pathway leads to the N-heterocyclic carbene (NHC) precursors, differing by the flexibility of the bridge, the steric bulk of substituents in α-position of the OH groups and the anions. Treatment of diimidazolium salts with Ag₂O yields Ag^I(carbene)₂ complexes. The related trimethylene-bridged bis-NHC silver complexes 6 and 7 were crystallised with di-tosylate and di-hexafluorophosphate anions, respectively. Their X-ray structures revealed dimeric species, involving two ligands with different arrangements around the Ag cations, leading to crossed and parallel conformations.