Chiral and herringbone symmetry breaking in water-surface monolayers

We report the observation from monolayers of eicosanoic acid in the L′2 phase of three distinct out-of-plane first-order diffraction peaks, indicating molecular tilt in a nonsymmetry direction and hence the absence of mirror symmetry. At lower pressures the molecules tilt in the direction of their nearest neighbors. In this region we find a structural transition, which we tentatively identify as the rotator-herringbone transition L2d−L2h

Small Scale Variants of the AES

Abstract. In this paper we define small scale variants of the AES. These variants inherit the design features of the AES and provide a suitable framework for comparing different cryptanalytic methods. In particular, we provide some preliminary results and insights when using off-theshelf computational algebra techniques to solve the systems of equations arising from these small scale variants.

Polymorphism and hydration of zopiclone : Determination of crystal structures, and thermodynamic studies as a function of temperature and water vapor pressure

Racemic Zopiclone crystallises as a dihydrate (DH) or as a conglomerate (A). Upon heating, DH dehydrates to an anhydrous racemate (B) which transforms into the 1:l mixture of enantiomers (A). It can be inferred from crystallographic and thermodynamic data that the anhydrous racemate is metastable with respect to the 1:l mixture of enantiomers (A) whatever the water vapour pressure and the temperature. Thus, the B → A transition appears to occur monotropically

Crystalline Self-Aggregation and a Pressure Driven Solid-Solid Phase Transition in a Fluorinated Langmuir Monolayer

Monolayers of PFA, a fluorinated surfactant, on water were studied using synchrotron X-ray grazing incidence diffraction (GID) and reflectivity measurements (XR). The uncompressed monolayer is found to self-assemble into crystalline domains giving a strong GID peak. Upon compression and decompression a surface pressure driven solid-solid phase transition takes place. A hexagonal lattice with vertical molecules at high pressure undergoes a distortion due to a rigid molecular tilt as the pressure is decreased. Bragg rod scans provide conclusive evidence for a tilt of about 20° at 10 mN/m and show the tilt to be towards nearest neighbours. The uncompressed monolayer has a molecular tilt of about 25°

Tetramorphism of fananserine : p, T diagram and stability hierarchy from crystal structure determinations and thermodynamic studies

The structures of four crystalline phases of fananserine have been solved and their melting properties determined. The p-T diagram for this tetramorphism has been constructed by combining these data. Three out of the four solids are associated with stable p-Tdomains. Two of them have a low-pressure enantiotropic character in narrow p-T domains. The fourth one is intrinsically metastable. The stability ranking agrees with that inferred from solubility measurements at room temperature