Charge screening in valence band of solids and in the Fermi sea. Origin of weak-boson masses

Summary An attempt is made to explain the masses of Z and W^± bosons by means of a screening mechanism analogous to charge screening in metals. It considers the effect of the electroweak force on the distribution of negativekinetic-energy neutrinos, which fills the whole universe (neutrino Fermi sea). The large weak-boson masses appear to be a direct consequence of the vanishing neutrino mass.     

Stereoselective hydrogenation of methylcyclohex-2-ene-1,4-diols used in the synthesis of ampelomins and deoxy-carbasugars

Stereoselective hydrogenation of methylcyclohex-2-ene-1,4-diols used as important intermediates for the preparation of ampelomins and deoxy-carbasugars was studied. These olefins were obtained in few steps from a chiral cis-diol resulting from microbial oxidation of toluene. Although the stereoselective hydrogenation of this type of substrates is difficult, high yields were obtained for heterogeneous hydrogenation using Adam’s catalyst, where steric hindrance controlled the stereochemical outcome of the process. On the other hand, for homogeneous hydrogenation of similar olefins using Crabtree’s catalyst, coordination with the allylic alcohols allowed for a controlled hydrogen addition from the more hindered face. In this manner two protocols for the hydrogenation of these types of substrates resulting in complementary stereoselectivities are described.     

A re-examination of fermi's hyperfine contact interaction

Summary The hyperfine coupling between spin of electrons ins states and nuclear spin is generally represented by a contact Hamiltonian in which a δ(r) factor appears. Utilizing relativistic equations and considering pointlike nuclei, we show that the δ(r) factor must be replaced by a steeply decreasing radial function of half-maximum width δr=5.8·10⁻¹⁴Z cm. For hydrogen, the correction with respect to the contact Hamiltonian turns out to be small, but for high-Z nuclei this correction acquires substantial importance. For iron 1s states, it rises up to 9.6%.     

On the instability of ionospheric plasma originated by charge separations in the troposphere. The «UFO» phenomenon mechanism

Summary The troposphere is the seat of powerful processes which originate separation of electric charges. Thunder clouds give rise to a huge vertical separation of charges. But also known is a different electrification mechanism activated by wind, which allows for horizontal separation of charges. In favourable conditions, when charges are displaced at long distances, image charges appear in the ionspheric plasma and an upward electric field is originated which makes the ionosphere boundary unstable. If this occurs, recombination of displaced charges involves ionosphere conductivity and gives rise to a downward electron stream ejected from the bottom of the ionosphere. It may produce a peculiar airglow phenomenon, which consists of the emission of light in a narrow region lying at stratospheric or mesospheric altitudes. This outcome of the electrification process just mentioned shows a close connection with a special class of ?UFO? sightings, that is, those referred to by J. Hynek as ?nocturnal light? and which consist of bright specks of light moving in the night sky.     

On the radioluminescent emission of BaF2

Summary The luminescence of barium fluoride excited by X-rays has been recordedvs. wavelength. The spectrum shows two components due to recombination of excitons bound to Frenkel defects and to luminescent centres also active in the thermoluminescent process. The results are interpreted by means of a model based on the Prener and Williams recombination scheme.     

Antiferromagnetism in double-layered perowskitic oxides SrLa2Fe2O7 and BaLa2Fe2O7

Il Nuovo Cimento D - Two double-layered perowskitic compounds have been investigated by XRD analysis and Mössbauer spectroscopy. The experimental data allow the conclusion that magnetization...     

Stereoselective synthesis of 3-oxygenated-cis-dialkyl-2,5-substituted tetrahydrofurans from cyclohexadienediols

The 3-oxygenated-cis-dialkyl-2,5-substituted tetrahydrofuran system, present in several natural products, was prepared with good selectivity by acidic cyclization of 5-alkene-1,2,4-triol derivatives. The starting alkenol was obtained in few steps from a chiral cis-diol resulting from microbial oxidation of bromobenzene. The study of the cyclization allowed the rationalization of all experimental results by assuming a complete ionization at the allylic position and a model close to the one proposed by Labelle for homoallylic induction in five-membered ring closures.     

A study of lattice defects in alkali fluorides by thermoluminescence experiments

Summary Lattice defects in KF, NaF and LiF are investigated by recording the thermoluminescent emission of X-irradiated samplesvs. temperature and wavelength. Experimental results show the presence of cation vacancies and interstitials in KF and NaF and of F⁽⁻⁾ vacancies and interstitials in NaF and LiF. In NaF, the ionization energy of V_F centres is found to be 6.4 eV, that of H centres 5.6 eV.     

A Mössbauer study of the silica-like structures of FePO4 and (Al0.67Fe0.33)PO4

Summary Samples of FePO₄ and (Al_0.67Fe_0.33)PO₄ have been investigated by M?ssbauer spectroscopy. The data obtained on quadruple splittings are in agreement with neutron scattering and XRD data on (Al, Fe)O₄ tetrahedra structures.