Improved methodologies for the preparation of highly substituted pyridines

[reaction: see text] Two separate strategies have been developed for the preparation of highly substituted pyridines from 1,2,4-triazines via the inverse-electron-demand Diels-Alder reaction: a microwave-promoted, solvent-free procedure and a tethered imine-enamine (TIE) approach. Both routes avoid the need for a discrete aromatization step and offer significant advantages over the classical methods, giving a wide variety of tri-, tetra-, and penta-substituted pyridines in high, optimized yields.     

Evaluation of two procedures to determine acid and neutral detergent fibers in ruminant feeds of the temperate region of Argentina

The objective of this work was to compare the traditional Van Soest's procedure to analyze neutral detergent fibers (NDF) and acid detergent fibers (ADF) using filtering crucibles (VS) with a semiautomatic method which uses filter bags in an ANKOM Technology Corp. instrument (ANK). Nine ruminant feeds widely used in the temperate region of Argentina were analyzed: soybean meal expeller, alfalfa, pasture silage, ryegrass, corn silage, weeping lovegrass, tall wheatgrass, guinea grass, and barley grass. Four runs were done for each technique and feed. The comparison of ADF and NDF means by the means test for paired samples showed no significant differences between techniques (alpha = 0.01). The variability among runs was greater with the VS method than the ANK, both for NDF, standard deviation (SD) = 0.71 vs 0.39, and for ADF, SD = 0.83 vs 0.56, but the differences were not significant. The linear regressions were VS = 1.43 + 0.95 ANK; R2 = 0.99, and VS = 0.53 + 0.98 ANK; R2 = 0.99 for NDF and ADF, respectively, which indicated a strong linear relationship among the results of both procedures. It was concluded that the ANK procedure gave results comparable to those of the VS method when ruminant feeds from the temperate region of Argentina were analyzed.     

Unprecedented asymmetric induction through configurationally stable lithium N-(alpha-methylbenzyl)phosphinamides. A new entry to enantiomerically pure gamma-aminophosphinic acids and esters

The first examples of configurationally stable N-benzyl-N-phosphinoyl carbanions are described. Their applications to the synthesis of homochiral gamma-aminophosphinic acids and esters via highly enantioselective dearomatising reactions are shown.     

On the use of wavelet filtering and correlation techniques in atmospheric condensed phase spectroscopy

The application of wavelet filtering and analysis in spectroscopy is discussed in relation to the analysis of complex atmospheric spectra, where contributions from condensed phase particles and gas phase molecules are present in the form of broad-band features and narrow lines, respectively. The broad-band contribution can be extracted as the 'smooth signal' component of the wavelet transform, with a large reduction in the size of the corresponding data files. This procedure is applied to an investigation of the H2SO4 aerosol content of a series of atmospheric spectra measured in the ATMOS missions. The sulfate content of the smooth signal is analysed by means of correlation techniques, using a set of laboratory reference spectra of varying sulfuric acid concentration and temperature. Correlation density maps and correlation curves are used to select the most appropriate spectral zones for sulfate analysis and to assess the sulfate aerosol content in the atmosphere subsequent to the eruption of the Mount Pinatubo volcano.     

Ultralow emittance, multi-MeV proton beams from a laser virtual-cathode plasma accelerator

The laminarity of high-current multi-MeV proton beams produced by irradiating thin metallic foils with ultraintense lasers has been measured. For proton energies >10 MeV, the transverse and longitudinal emittance are, respectively, <0.004 mm mrad and <10(-4) eV s, i.e., at least 100-fold and may be as much as 10(4)-fold better than conventional accelerator beams. The fast acceleration being electrostatic from an initially cold surface, only collisions with the accelerating fast electrons appear to limit the beam laminarity. The ion beam source size is measured to be <15 microm (FWHM) for proton energies >10 MeV.     

Adaptive-optics ultrahigh-resolution optical coherence tomography

Merging of ultrahigh-resolution optical coherence tomography (UHR OCT) and adaptive optics (AO), resulting in high axial (3 microm) and improved transverse resolution (5-10 microm) is demonstrated for the first time to our knowledge in in vivo retinal imaging. A compact (300 mm x 300 mm) closed-loop AO system, based on a real-time Hartmann-Shack wave-front sensor operating at 30 Hz and a 37-actuator membrane deformable mirror, is interfaced to an UHR OCT system, based on a commercial OCT instrument, employing a compact Ti:sapphire laser with 130-nm bandwidth. Closed-loop correction of both ocular and system aberrations results in a residual uncorrected wave-front rms of 0.1 microm for a 3.68-mm pupil diameter. When this level of correction is achieved, OCT images are obtained under a static mirror configuration. By use of AO, an improvement of the transverse resolution of two to three times, compared with UHR OCT systems used so far, is obtained. A significant signal-to-noise ratio improvement of up to 9 dB in corrected compared with uncorrected OCT tomograms is also achieved.     

Pulsed laser deposition of magnetic films by ablation of Co- and Fe-based amorphous alloys

Magnetic films were prepared by pulsed laser ablation of amorphous magnetic ribbons (composition Co₆₇Cr₇Fe₄Si₈B₁₄, Fe_73.5Nb₃Cu₁Si_13.5B₉, and Fe₄₀Ni₄₀B₂₀) and permalloy foils (composition Fe_xNi_1-x with x=22,50). Depositions were performed in a vacuum of (2–4)×10^-5 Pa by KrF excimer laser pulses at fluences of between 2 and 7 Jcm². Films were deposited on oxidized silicon wafers, placed 60–80 mm apart from the target. Films were analyzed by SEM, XRD, RBS, and EDS. Ferromagnetic resonance (FMR) spectra were studied at GHz frequencies. From RBS and EDS measurements it follows that the stoichiometry of the targets is preserved in the films to a large extent. The films deposited from amorphous targets remain amorphous. From FMR studies it follows that Fe and Fe-Ni rich films exhibit properties close to those of bulk alloys, having very low magnetization motion damping parameter () of 7.0–7.8×10⁷ rad/s, which are appropriate for fast magnetic sensors. PACS 79.20.Ds; 75.50.Kj; 75.70.-i     

Wide transparency range and high refractive index lead–niobium-germanate glass thin films

Lead–niobium-germanate glass thin films have been produced by pulsed laser deposition in a broad O₂ pressure range (10^-6–10^-1 mbar). The cation composition in the films approaches that of the glass target for a pressure of 10^-2 mbar. The oxygen content is only close to or above that of the glass for a pressure close to 10^-1 mbar, for which a Pb enrichment is also observed. Films grown in vacuum are highly absorbing, whereas transparent films with an absorption edge shifted to the UV with respect to the bulk glass are produced for pressures higher than 10^-2 mbar. The evolution of the optical energy gap and the refractive index of the films with the oxygen pressure is correlated to the changes observed in the film composition and discussed in terms of the features of the deposition process, the role of oxygen in the formation of the glass network and the progressive increase of the oxidation state of the cations as the oxygen pressure is increased. PACS 81.05.Kf; 78.20.Ci; 81.15.Fg