Variable geometry manned orbital vehicle Patent

Variable geometry manned orbital vehicle having high aerodynamic efficiency over wide speed range and incorporating auxiliary pivotal wing

Structural anomalies, spin transitions and charge disproportionation in LnCoO3

The diamagnetic-paramagnetic and insulator-metal transitions in LnCoO3 perovskites (Ln = La, Y, rare earths) are reinterpreted and modeled as a two-level excitation process. In distinction to previous models, the present approach can be characterized as a LS-HS-IS (low-high-intermediate spin) scenario. The first level is the local excitation of HS Co3+ species in the LS ground state. The second excitation is based on the interatomic electron transfer between the LS/HS pairs, leading finally to a stabilization of the metallic phase based on IS Co3+. The model parameters have been quantified for Ln = La, Pr and Nd samples using the powder neutron diffraction on the thermal expansion of Co-O bonds, that is associated with the two successive spin transitions. The same model is applied to interpret the magnetic susceptibility of LaCoO3 and YCoO3.Comment: 52.Conference on Magnetism and Magnetic Materials, November 2007, Tamp

The vicinal difluoro motif : the synthesis and conformation of erythro- and threo-diastereoisomers of 1,2-difluorodiphenylethanes, 2,3-difluorosuccinic acids and their derivatives

Background: It is well established that vicinal fluorines (RCHF-CHFR) prefer to adopt a gauche rather than an anti conformation when placed along aliphatic chains. This has been particularly recognised for 1,2-difluoroethane and extends to 2,3-difluorobutane and longer alkyl chains. It follows in these latter cases that if erythro and threo vicinal difluorinated stereoisomers are compared, they will adopt different overall conformations if the fluorines prefer to be gauche in each case. This concept is explored in this paper with erythro- and threo- diastereoisomers of 2,3-difluorosuccinates. Results: A synthetic route to 2,3-difluorosuccinates has been developed through erythro- and threo- 1,2-difluoro-1,2-diphenylethane which involved the oxidation of the aryl rings to generate the corresponding 2,3- difluorosuccinic acids. Ester and amide derivatives of the erythro- and threo- 2,3-difluorosuccinic acids were then prepared. The solid and solution state conformation of these compounds was assessed by X-ray crystallography and NMR. Ab initio calculations were also carried out to model the conformation of erythro- and threo- 1,2-difluoro-1,2-diphenylethane as these differed from the 2,3-difluorosuccinates. Conclusion: In general the overall chain conformations of the 2,3-difluorosuccinates diastereoisomers were found to be influenced by the fluorine gauche effect. The study highlights the prospects of utilising the vicinal difluorine motif (RCHF-CHFR) as a tool for influencing the conformation of performance organic molecules and particularly tuning conformation by selecting specific diastereoisomers (erythro or threo).Publisher PDFPeer reviewe