Hydrated clusters of organic molecules generated by IR OPO resonant desorption of frozen aqueous solutions

Long series of hydrated clusters of organic molecules (formaldehyde, methanol, ethanol and tryptophan) have been generated by infrared optical parametric oscillator (OPO) resonant desorption of frozen aqueous solutions. Using a comparative approach, we derived some general trends from cluster size and velocity distribution measurements. In the biologically interesting case of tryptophan amino acid, our technique yields a much longer (and complete) series of hydrated clusters than that obtained previously using a combined laser desorption/pulsed jet expansion technique [L.C. Snoek, R.T. Kroemer, J.P. Simons: Phys. Chem. Chem. Phys. 4, 2130 (2002)]. PACS 79.20.La; 36.40.-c; 82.80.Ms     

Electronic and ionic conductivities and point defects in ytterbium sesquioxide at high temperature

From the study of complex impedance diagrams applied to a symmetric cell Pt-Yb₂O₃-Pt, the authors have shown the mixed character of electrical conduction within the ytterbium sesquioxide. The measurements were performed at thermodynamic equilibrium in the temperature range from 1423 to 1623 K and the partial pressure of oxygen range from 10^?12 to 1 atm. The variations of ionic and electronic conductivity as a function of P_O2, were interpreted in terms of point defects e′, ?, V?_Yb and Yb_{$\text{I}\text{?}$}, in the general case of a Frenkel disorder. The relative contributions and the activation energies of conduction of these different defects were determined.     

No pre-critical enhancement observed in C(π, γ)N(g.s.) at q 2mπ

The cross section and angular distribution for the reaction ¹³C(π⁺, γ)¹³N(g.s.) have been measured from 37 to 85° in the laboratory, at a pion energy of 115.5 MeV. The observed cross section ranges from 320 to 660 nb/sr. These results do not show the large magnitude and wide-angle peaking expected if pre-critical effects due to nascent pion condensation were present. In addition, the observed cross section is less than one-half of the predictions of available theoretical calculations which do not include the pre-critical effect. Data on the reaction ¹H(π⁻, γ)n at T_π = 116.6 MeV were also obtained for calibration purposes. These data agree with expectations based on knowledge of the inverse reaction and previous measurements.     

Validation of Registration Techniques Applied to XRD Signals for Stress Evaluations in Titanium Alloys

To estimate stresses near specimen surfaces, X-ray diffraction (XRD) is applied to titanium alloys. Some of these alloys are difficult to study since they are composed of various phases of different proportions, shapes and scales. For millimetric probed volumes, such multi-phase microstructures induce shallow and noisy diffraction signals. Two peak registration techniques are introduced and validated thanks to tensile tests performed on two titanium alloy samples.     

Fluorescent Dynamic Covalent Polymers for DNA Complexation and Templated Assembly

Dynamic covalent polymers (DCPs) offer opportunities as adaptive materials of particular interest for targeting, sensing and delivery of biological molecules. In this view, combining cationic units and fluorescent units along DCP chains is attractive for achieving optical probes for the recognition and delivery of nucleic acids. Here, we report on the design of acylhydrazone-based DCPs combining cationic arginine units with π-conjugated fluorescent moieties based on thiophene-ethynyl-fluorene cores. Two types of fluorescent building blocks bearing neutral or cationic side groups on the fluorene moiety are considered in order to assess the role of the number of cationic units on complexation with DNA. The (chir)optical properties of the building blocks, the DCPs, and their complexes with several types of DNA are explored, providing details on the formation of supramolecular complexes and on their stability in aqueous solutions. The DNA-templated formation of DCPs is demonstrated, which provides new perspectives on the assembly of fluorescent DCP based on the nucleic acid structure.