Dynamic softening of vortex lines in YBa2Cu3O7−δ single crystals

Transport measurements in the mixed state of oxygen-deficient YBa₂Cu₃O_7−δ single crystals using the flux transformer configuration show that the flux liquid changes with increasing anisotropy from strongly correlated to uncorrelated in the field direction. For intermediate coupling, the current inducing loss of vortex correlation has a maximum near the irreversibility temperature. Thus, an effective softening of vortex lines with decreasing temperature is detected. We propose a simple model that accounts for this behavior by including the effects of the pinning potential on the dynamics of vortices.     

A simple route to syn α-Amino-β-Hydroxy esters by C-2 regioselective opening of a, β-Epoxy esters with metal halides

α,β-Epoxy esters are opened by NaX (X = I, Br) in a regio and stereoselective fashion to β-hydroxy-α-halo esters, which represent suitable precursors of syn α-amino-β-hydroxy esters and β-hydroxy esters.     

One-pot direct conversion of 2,3-epoxy alcohols into enantiomerically pure 4-hydroxy-4,5-dihydroisoxazole 2-oxides

[structure: see text]. A new methodology for the one-pot direct conversion of 2,3-epoxy alcohols into enantiomerically pure 4-hydroxy-4,5-dihydroisoxazole 2-oxides 1 has been found. The reaction works at room temperature and can be run at the 5-10 g scale. The mixture of 4,5-cis and 4,5-trans isomers obtained can be separated as such or as the bis-TDS ethers. A preliminary example of reductive cleavage of 1 to the corresponding amino polyol is also reported.     

Ab initio simulations of homoepitaxial SiC growth

We present first-principle calculations on the initial stages of SiC homoepitaxial growth on the beta-SiC(111)-(sqrt[3]xsqrt[3]) surface. We show that the nonstoichiometric reconstruction plays a relevant role in favoring the attainment of high-quality films. The motivation is twofold: On one hand, we find that the reconstruction controls the kinetics of adatom incorporation; on the other hand, we observe that the energy gain upon surface stability can induce the reorganization of the deposited material into a crystalline structure, thus revealing that a surface-driven mechanism is able to stabilize defect-free layer deposition on Si-rich surfaces.     

CeCl(3) x 7H(2)O-NaI catalyzed hydrooxacyclization of unsaturated 3-hydroxy esters

[reaction: see text] Cerium(III) chloride heptahydrate and sodium iodide in boiling acetonitrile promote cyclization of 3-hydroxyalkenoic acids esters giving 5-substituted tetrahydrofuranacetic acid esters and 6-substituted tetrahydropyranacetic acid esters in fair to good yield and with complete retention of the absolute configuration of the starting 3-hydroxy ester.     

A new, simple, and mild azidolysis of vinylepoxides

A new, simple, and mild regio-and stereocontrolled azidolysis of vinylepoxides with TMSN₃/BF₃ system is reported. The method appears of general value and works very well particularly in the presence of electron-poor olefins, regardless of the size of substituents on the heterocyclic ring.     

Preparation of new 2‐amino‐ and 2,3‐diamino‐pyridine trifluoroacetyl enamine derivatives and their application to the synthesis of trifluoromethyl‐containing 3H‐pyrido[2,3‐b][1,4] diazepinols

The synthesis of a novel series of the intermediates N²(N³)‐[1‐alkyl(aryl/heteroaryl)‐3‐oxo‐4,4,4‐trifluoroalk‐1‐en‐1‐yl]‐2‐aminopyridines [F₃CC(O)CH?CR¹(2? NH?C₅H₃N)] and 2,3‐diaminopyridines [F₃CC(O)CH?CR¹(2‐NH₂‐3‐NH? C₅H₃N)], where R¹ = H, Me, C₆H₅, 4‐FC₆H₄, 4‐CIC₆H₄, 4‐BrC₆H₄, 4‐CH₃C₆H₄, 4‐OCH₃C₆H₄, 4,4′‐biphenyl, 1‐naphthyl, 2‐thienyl, 2‐furyl, is reported. The corresponding series of 2‐aryl(heteroaryl)‐4‐trifluoromethyl‐3H‐pyrido[2,3‐b][1,4]diazepin‐4‐ols obtained from intramolecular cyclization reaction of the respective trifluoroacetyl enamines or from the direct cyclocondensation reaction of 4‐methoxy‐1,1,1‐trifluoroalk‐3‐en‐2‐ones with 2,3‐diaminopyridine, under mild conditions, is also reported.     

Single-walled carbon nanotubes produced by cw CO2-laser ablation: study of parameters important for their formation

The production of single-walled carbon nanotubes (SWNTs) using the cw CO₂-laser ablation technique is reported. Different metals and metal concentrations in the carbon targets as well as different buffer gases and gas pressures have been used in order to study their influence on the formation of SWNTs. It is shown that the conditions near the evaporation zone, i.e. especially the local temperature environment induced by the laser radiation as well as the used metals play a key role in the formation process of SWNTs. Employing a very simple experimental setup the cw CO₂-laser ablation technique easily provides the environment favorable for the growth of high quality SWNT material under a wide range of experimental conditions.