Canalización mediática ("agenda-setting") y elecciones en Estados Unidos.

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Periodismo y nuevas tecnologías: Perfiles de los periodistas del siglo XXI.

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Anisotropic Optical Properties of Heavy-Rare-Earth Single Crystals

The optical absorptivities of oriented single crystals of hcp Gd, Tb, Dy, Ho, Er, Tm, and Lu were measured at 4.2 K between 0.2 and 4.4 eV. Polarized radiation was used to reveal the optical anisotropy. Systematic movement of structures in the absorptivity and optical conductivity was observed as a result of trends within sp and d bands. Low-energy structures were related to effects of s−f exchange interaction, but were more complicated than previously thought

Absorptivity of Single-Crystal Yttrium at 4.2 K

Measurements of the absorptivity of single crystals of Y were made between 0.15 and 4.4 eV at 4.2 K. Polarized radiation was used with the electric vector parallel or perpendicular to the c^ axis of the crystal. The observed structures in the absorptivity were interpreted on the basis of band calculations for Sc, Re, and Gd and qualitative agreement was found between the band structures and the observed spectra

Optical properties of Ti, Zr, and Hf from 0.15 to 30 eV

The absorptivity or reflectivity of polycrystalline samples of Ti, Zr, and Hf was measured from 0.15 to ∼30 eV. The data were Kramers-Kronig analyzed to determine the dielectric functions. Between ∼0.2 and ∼7 eV, each metal showed five structures in the absorptivity and ε2. These were interpreted as interband transitions within the d bands. The ε2 spectra had minima near 7 eV similar to that observed in the bcc transition metals. Additional structures at higher energy could be related to transitions involving highlying bands and the core levels. The electron-energy-loss functions were calculated and discussed in terms of volume and surface plasmons. These metals, like the other transition metals studied, exhibited two volume and two surface plasmons

Optical properties of crystalline tungsten

The optical properties of W are presented between 0.15 and 33 eV. The optical absorptivity or reflectivity was measured at near-normal incidence, and the data were Kramers-Kronig analyzed to determine the dielectric functions. Drude parameters were determined at low energy and were used to separate interband and intraband contributions to ε2. Structures in ε2 were apparent at 0.42, 0.97, 1.82, 2.35, 3.42, 5.25, 8.8, 11.3, 16.5, 22.5, and 31.5 eV. These features were discussed in terms of recent calculations of Christensen and Feuerbacher and by analogy to other transtion metals studied. The loss functions were shown to have three volume plasmons (25.3, 15.2, and 10.0 eV) and three surface plasmons (20.8, 14.8, and 9.7 eV). Structure near 31.5 eV was interpreted as due to NVII core transitions

Optical investigation of the electronic structure of bulk Rh and Ir

Optical-reflectivity data are presented for Rh and Ir for a photon energy range between 0.2 and 40 eV. Strong interband structures are observed in the calculated dielectric functions and optical conductivities, and these are discussed in terms of recent energy-band calculations. The dielectric functions are used to calculate the electron-energy-loss functions. Both metals are shown to possess the characteristic double pair of surface and volume plasmons, though the higher-energy pair is strongly distorted by interband absorption occurring near ℏωp

Optical properties of V, Ta, and Mo from 0.1 to 35 eV

The absorptivity or reflectivity of crystals of V, Ta, and Mo was measured from 0.1 to 35 eV. The data were Kramers-Kronig analyzed to determine the dielectric functions. The inadequacy of a simple Drude model to describe absorption at low energy is discussed. Structure in the dielectric functions is discussed in terms of direct interband transitions which extend to about 18 eV. Features below 6 eV are attributed to transitions near Σ, G, and perhaps along P(D)N for V, Ta, and Mo, with additional transitions in Mo from the Δ portion of the Brillouin zone. High-lying energy bands are identified as giving rise to high-energy structure in the dielectric functions. Results obtained previously for Nb are reviewed and compared. The electron-energy-loss functions were calculated and are discussed in terms of volume and surface plasmons. These metals all exhibit two volume and two surface plasmons

Photoemission studies of the γ−α phase transition in Ce: Changes in 4f character

Photoemission studies of the γ−α phase transition in cerium show changes in two 4f-related features in the valence band (0.3 and 2 eV below EF) and broadening of the multiplet structure in the region of the 4d−4f transitions. We show that the observed features can be explained by increased hybridization of the 4f wave function upon entering the α phase

Canalización mediática ("agenda-setting") y elecciones en Estados Unidos.

Sin resume