1,721,290 research outputs found
Produzione di pioni neutri in collisioni tra ioni pesanti con Ossigeno sedici a Elab/A=38 Mev
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Effects of electronic correlation on x-ray absorption and dichroic spectra at L-2,(3) edge
No full textWe present a new theoretical approach to describe x-ray absorption and magnetic circular dichroism spectra in the presence of electron-electron correlation. Our approach provides an unified picture to include correlations in both charged and neutral excitations, namely in direct/inversion photoemission where electrons are removed/added, and photoabsorption where electrons are promoted from core levels to empty states. We apply this approach to the prototypical case of the L-2,(3) edge of 3d transition metals and we show that the inclusion of many-body effects in the core level excitations is essential to reproduce, together with satellite structures in core level photoemission, the observed asymmetric lineshapes in x-ray absorption and dichroic spectra
Selected papers from the 4th workshop on European Collaboration for Higher Education and Research in Nuclear Engineering & Radiological Protection
No full textThe fourth workshop on European Collaboration for Higher Education and Research in Nuclear Engineering & Radiological Protection was held in Favignana (Sicily), May 26-28th 2008. Participants came from 7 countries presenting 30 papers, 19 of which have been collected as selected works to appear in the present special issue. As the name implies, the meeting was part of an ongoing series, representing a yearly occasion for the CHERNE network of European Universities to meet and exchange their most recent achievements in nuclear research, and develop continuously new ways of scientific collaboration.
The meeting was organised jointly by the Universities of Bologna, Catania and Messina, under the auspices and high patronage of the Regione Sicilia, the regional Government of Sicily, and in particular of the regional Superintendence for Culture and Education.
The workshop was not limited to a specific topic, but rather comprised all applications of nuclear technologies, and papers were presented on nuclear power generation systems, nuclear physics and detection, nuclear medical applications, radioisotope technologies, all representing the front end of nuclear research at the respective Institutions. The participation of non-University Institutions with scientific interest in nuclear sciences was very welcome, and scientists from ENEA (the Italian nuclear research centre) and from INFN (the Italian National Institute for Nuclear Physics) attended and presented some of their current nuclear research
First principles study of the normal state electronic properties of the Bi-2212 cuprate superconductor
No full textWe present detailed first-principles calculations of the normal state electronic properties of the Bi2Sr2CaCu2O8 (Bi-2212) high T-C superconductor by means of the linearized augmented plane wave (LAPW) method within the framework of density functional theory (DFT). We describe the crystal structure by the body-centered tetragonal (BCT) cell with space group I4/mmm and optimize its volume, c/a ratio and atomic positions by total energy and atomic-force minimization. The optimization of the cell leads to small but visible changes in the topology of the Fermi surface, rounding the shape of the CuO2 barrels, and moving both the BiO bands, responsible for the pockets near the (M) over bar point, below the Fermi level. We have then studied the influence of the large distortions in the BiO plane observed in nature by means of an root2 x root2 orthorhombic cell (with Bbmb space group). Differently to what has been observed in the literature for the Bi-2201 compound, we find that for Bi-2212 the orthorhombic distortion does not induce relevant changes to the binding energies of the BiO bands, conserving their metallic character. (C) 2003 Elsevier B.V. All rights reserved
First-principles calculation of x-ray dichroic spectra within the full-potential linearized augmented planewave method: An implementation into the Wien2k code
No full textX-ray absorption and its dependence on the polarization of light is a powerful tool to investigate the orbital and spin moments of magnetic materials and their orientation relative to crystalline axes. Here, we present a program for the calculation of dichroic spectra from first principles. We have implemented the calculation of X-ray absorption spectra for left and right circularly polarized light into the Wien2k code. In this package, spin-density functional theory is applied in an all-electron scheme that allows to describe both core and valence electrons on the same footing. The matrix elements, which define the dependence of the photo-absorption cross-section on the polarization of light and on the sample magnetization, are computed within the dipole approximation. Results are presented for the L2,3 and M4,5 egdes of CeFe2 and compared to experiments
Decoherence induced by hyperfine interactions with nuclearspins in antiferromagnetic molecular rings
No full textDecoherence induced by hyperfine interactions with nuclearspins in antiferromagnetic molecular ringsMolecular magnets are effective few-level spin systems that allow for the observation of coherent dynamics. Electronic coherence is mainly limited by hyperfine interactions with nuclear spins. Here, we theoretically investigate the resulting inhomogeneous broadening and electron-nuclear entanglement: They take place on the nanosecond and microsecond time scales, respectively. Our microscopic description allows us to clarify the role played by the different chemical elements. The effect of spin echo and the dependence of decoherence on the magnetic field are also estimated. © 2008 The American Physical Society
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