DUTCH CONTRIBUTIONS TO THE SIXTH INTERNATIONAL CONGRESS OF SLAVICISTS GRATIS Auteur: none Aantal pagina's: none pagina's Verschijningsdatum: 1968-04-01 Uitgever: Walter De Gruyter EAN: 9783111031439 Taal: nl Link: Download hier Phonological characteristics of the Čakavian dialect of Kali on the island of Ugljan (1994) Van Hove singularities revisited. Beginning with the work of Hirsch and Scalapino the importance of ln 2 - Van Hove singularity in T c - enhancement in La 2 CuO 4 -based compounds was realized, which is nicely reviewed by Rice. However, the theoretical treatment carried out before is incomplete. Two things were apparently not paid due attention to: interplay of particle- particle and particle-hole channels and Umklapp processes. In what follows a two-dimensional weak coupling model of LaCuO 4 will be solved exactly in the ln 2 -approximation. The result in the Hubbard limit one bare charge is that the system is unstable at any sign of interaction. Symmetry breaking moreover is pretty peculiar. Of course, there are separate singlet superconducting pairings in the pp-channel attraction and SDW repulsion and CDW attraction in the ph-channel. In the general model where all 4 charges involved are substantially different, the system might remain metallic. A more realistic approach which takes into account dopping in La-M-Cu-O and interlayer interaction provides at least a qualitative understanding of the experimental picture. Leon Van Hove Léon Van Hove , eminent Belgian theoretical physicist and Research Director General of CERN from , died on 2 September, only eighteen months after a special symposium at CERN marked his 65th birthday and his formal retirement from the Organization to which he had contributed so much. CERN Multimedia. Leon Van Hove chaired the meeting for the last time, the end of the year being also the end of his term as Research Director General. The place was as usual the 6th floor conference room at the Main Building. Léon Van Hove , Le Courrier CERN a grandement bénéficié de sa sagesse et de son jugement et il convenait que nous publiions quelques témoignages que nous avons spécialement demandés pour illustrer ses multiples talents. Nous remercions André Martin qui a bien voulu coordonner ces contributions. Topological map of the Hofstadter butterfly: Fine structure of Chern numbers and Van Hove singularities. Naumis, Gerardo G. The Hofstadter butterfly is a quantum fractal with a highly complex nested set of gaps, where each gap represents a quantum Hall state whose quantized conductivity is characterized by topological invariants known as the Chern numbers. Here we obtain simple rules to determine the Chern numbers at all scales in the butterfly fractal and lay out a very detailed topological map of the butterfly by using a method used to describe quasicrystals: the cut and projection method. Our study reveals the existence of a set of critical points that separates orderly patterns of both positive and negative Cherns that appear as a fine structure in the butterfly. This fine structure can be understood as a small tilting of the projection subspace in the cut and projection method and by using a Chern meeting formula. Finally, we prove that the critical points are identified with the Van Hove singularities that exist at every band center in the butterfly landscape. This book collects the contributions for a meeting in October in Naples under the auspices of the Istituto Italiano per gli Studi Filosofici to commemorate the life and scientific achievements of Leon Van Hove , distinguished theorist and CERN Research Director General from , who died in The articles span Van Hove 's scientific contributions and his involvement in European scientific policy and education. His early scientific work, with contributions to mathematics, statistical mechanics and neutron physics, is covered by A. Messiah and L. Michel, with an appraisal by A. Among Van Hove 's best known research papers is his analysis of neutron scattering data to explore the structure of dense systems and magnetic materials in terms of pair correlation functions. This and its later applications are reviewed by A. Messiah, who also collects some interesting memorabilia from the years they spent together at Princeton, where Van Hove also had a fruitful collaboration with G. Michel undertakes the task of explaining in its full generality the predictions of Van Hove singularities in the phonon dispersion relation for periodic systems. The functional relation between the frequency and wave vector characterizing elastic waves in crystals plays a central role in the explanation of their thermodynamic, acoustic and optical properties. The existence of these singularities was a consequence of applying a beautiful mathematical theory of M. Morse to physics. Van Hove derived his results by showing that they were inevitable consequences of the global topology of the first Brillouin zone of the periodic lattice. This pioneer work used powerful global analysis techniques to unravel concrete physical properties. For this impressive body of achievement, together with his study of low dimensional phase transitions and non-equilibrium statistical mechanics, he was awarded the prestigious Danny Heinemann Prize of the American Physical Society. Application of Van Hove theory to fast neutron inelastic scattering. The Vane Hove general theory of the double differential scattering cross section has been used to derive the particular expressions of the inelastic fast neutrons scattering kernel and scattering cross section. Since the considered energies of incoming neutrons being less than 10 MeV, it enables to use the Fermi gas model of nucleons. In this case it was easy to derive an analytical expression for the time-dependent correlation function of the nucleus. Further, by using an impulse approximation and a short-collision time approach, it was possible to derive the analytical expression of the scattering kernel and scattering cross section for the fast neutron inelastic scattering. The obtained expressions have been used for Fe nucleus. It has been shown a surprising agreement with the experiments. The main advantage of this theory is in its simplicity for some practical calculations and for some theoretical investigations of nuclear processes. Construction of multi-Regge amplitudes by the Van Hove --Durand method. The Van Hove --Durand method of deriving Regge amplitudes by summing Feynman tree diagrams is extended to the multi-Regge domain. Using previously developed vertex functions for particles of arbitrary spins, single-, double-, and triple-Regge amplitudes incorporating signature are obtained. Criteria necessary to arrive at unique Regge-pole terms are found. It is also shown how external spins can be included. Relation of extended Van Hove singularities to high-temperature superconductivity within strong-coupling theory. Recent angle-resolved photoemission ARPES experiments have indicated that the electronic dispersion in some of the cuprates possesses an extended saddle point near the Fermi level which gives rise to a density of states that diverges like a power law instead of the weaker logarithmic divergence usually considered. We investigate whether this strong singularity can give rise to high transition temperatures by computing the critical temperature T c and isotope effect coefficient α within a strong-coupling Eliashberg theory which accounts for the full energy variation of the density of states. Using band structures extracted from ARPES measurements, we demonstrate that, while the weak-coupling solutions suggest a strong influence of the strength of the Van Hove singularity on T c and α, strong-coupling solutions show less sensitivity to the singularity strength and do not support the hypothesis that band-structure effects alone can account for either the large T c 's or the different T c 's within the copper oxide family. This conclusion is supported when our results are plotted as a function of the physically relevant self-consistent coupling constant, which shows universal behavior at very strong coupling. Role of Van Hove singularities and momentum-space structure in high-temperature superconductivity. There is a great deal of interest in attributing the high critical temperatures of the cuprates to either the proximity of the Fermi level to a Van Hove singularity or to structure of the superconducting pairing potential in momentum space far from the Fermi surface; the latter is particularly important for spin-fluctuation-mediated pairing mechanisms. We examine these ideas by calculating the critical temperature T c for model Einstein-phonon- and spin-fluctuation-mediated superconductors within both the standard, Fermi-surface-restricted Eliashberg theory and the exact Eliashberg theory, which accounts for the full momentum structure of the pairing potential and the energy dependence of the density of states. For our spin fluctuation calculations, we take the dynamical susceptibility to be the pairing potential and examine two models of this susceptibility in the cuprates. We compare and contrast these models with available magnetic neutron-scattering data, since these data provide the most direct constraints on the susceptibility. We also find that the Van Hove singularity enhances T c much less effectively than weak-coupling calculations would suggest. A Van Hove singularity VHS is a singularity in the phonon or electronic density of states of a crystalline solid. When the Fermi energy is close to the VHS, instabilities