LEIR lattice

The Low Energy Ion Ring (LEIR) is a low energy ion cooling and accumulation ring and serves to compress long ion pulses from Linac3 into high density bunches suitable for LHC ion operation. Issues of the LEIR lattice are to fulfil all constraints with a small number of quadrupoles and compensations of perturbations due to an electron cooler and gradients seen by the beam in the bending magnets during the ramp. Furthermore, experimental investigations via orbit response measurements will be reported

Study of the volume and spin collapse in orthoferrite LuFeO_3 using LDA+U

Rare earth (R) orthoferrites RFeO_3 exhibit large volume transitions associated with a spin collapse. We present here ab initio calculations on LuFeO_3. We show that taking into account the strong correlation among the Fe-3d electrons is necessary. Indeed, with the LDA+U method in the Projector Augmented Wave (PAW), we are able to describe the isostructural phase transition at 50 GPa, as well as a volume discontinuity of 6.0% at the transition and the considerable reduction of the magnetic moment on the Fe ions. We further investigate the effect of the variation of U and J and find a linear dependence of the transition pressure on these parameters. We give an interpretation for the non-intuitive effect of J. This emphasizes the need for a correct determination of these parameters especially when the LDA+U is applied to systems (e.g in geophysical investigations) where the transition pressure is a priori unknown

Таблиці ходу росту модальних вільхових деревостанів Лівобережного Лісостепу України

Intensive forest management requires studying the growth and productivity of forest stands for solving various management tasks. The peculiarities of the growth of black alder stands were studied by many foresters. However, for modeling estimated features of alder stands the growth tables by M. Davydov for Forest-steppe and Polissya are most widely used. Consequently, it is necessary to develop a regional system for modeling the growth of coppice alder stands for the conditions of the Left Bank Forest-steppe. The data on 84 sample plots, located in different parts of the study area were processed in our study, on 15 of them model trees were selected. After processing the data of sample plots and model trees, in order to identify the patterns of distribution of estimated features of alder stands and to determine the homogeneity of experimental data, their statistical analysis was carried out, which confirms the hypothesis that the studied base of empirical data sufficiently describes the black alder stands and is suitable for simulation of taxation dynamics indicators. During the research, statistical and analytical methods in combination were used. The heights dynamics were calculated based on the data of the analytical approach, and all other parameters were defined using regression dependences on the statistical material of the sample plots and the Forest Fund database. The model of the growth of alder stands in the region of study was constructed in terms of height, diameter, density of stocking, and form factor. Based on the results of the average height modeling, a dynamic productivity scale corresponding to one type of growth has been created. Based on the received models of the basic estimated features, the table of the growth of the modal coppice alder stands of the Left Bank Forest-steppe of Ukraine for the prevailing productivity classes is compiled. The developed norms, although consistent with the general regularities of the growth of alder stands, however, better describe the growth dynamics in the regional aspect. This confirms the necessity of creation regional tables for the black alder stands of the Left-Bank Forest-steppe of Ukraine.Проаналізовано літературні джерела з проблематики дослідження ходу росту насаджень вільхи чорної вегетативного походження в Україні та за її межами. Розглянуто передумови моделювання таксаційних показників вільхових деревостанів Лівобережного Лісостепу України. З метою виявлення закономірностей розподілу таксаційних показників вільхових деревостанів і визначення однорідності дослідних даних пробних площ і модельних дерев проведено їхній статистичний аналіз. Його результати підтверджують гіпотезу, що досліджувана база емпіричних даних достатньо повно описує насадження вільхи чорної і придатна для моделювання динаміки таксаційних показників. Побудовано моделі росту вільшанику регіону дослідження за висотою, діаметром, абсолютною повнотою та видовим числом. За результатами моделювання середньої висоти створено динамічну бонітетну шкалу, що відповідає одному типу росту. Керуючись отриманими моделями основних таксаційних показників, складено таблиці ходу росту модальних вільхових деревостанів вегетативного походження Лівобережного Лісостепу України для переважаючих класів бонітету. Порівняння отриманих нормативів з існуючими таблицями ходу росту вільхи чорної свідчить про наявність спільних закономірностей росту вільхових деревостанів. Водночас значуща різниця динаміки росту вільшанику окремих регіонів підтверджує необхідність складання регіональних таблиць ходу росту безпосередньо для Лівобережного Лісостепу України

Anomalous magnetic response of the spin-one-half Falicov-Kimball model

The infinite-dimensional spin one-half Falicov-Kimball model in an external magnetic field is solved exactly. We calculate the magnetic susceptibility in zero field, and the magnetization as a function of the field strength. The model shows an anomalous magnetic response from thermally excited local moments that disappear as the temperature is lowered. We describe possible real materials that may exhibit this kind of anomalous behavior.Comment: 17 pages, 6 encapsulated postscript figures (included), submitted to Phys. Rev.

The Dynamical Cluster Approximation: Non-Local Dynamics of Correlated Electron Systems

We recently introduced the dynamical cluster approximation(DCA), a new technique that includes short-ranged dynamical correlations in addition to the local dynamics of the dynamical mean field approximation while preserving causality. The technique is based on an iterative self-consistency scheme on a finite size periodic cluster. The dynamical mean field approximation (exact result) is obtained by taking the cluster to a single site (the thermodynamic limit). Here, we provide details of our method, explicitly show that it is causal, systematic, $\Phi$-derivable, and that it becomes conserving as the cluster size increases. We demonstrate the DCA by applying it to a Quantum Monte Carlo and Exact Enumeration study of the two-dimensional Falicov-Kimball model. The resulting spectral functions preserve causality, and the spectra and the CDW transition temperature converge quickly and systematically to the thermodynamic limit as the cluster size increases.Comment: 19 pages, 13 postscript figures, revte

Charge-transfer metal-insulator transitions in the spin-one-half Falicov-Kimball model

The spin-one-half Falicov-Kimball model is solved exactly on an infinite-coordination-number Bethe lattice in the thermodynamic limit. This model is a paradigm for a charge-transfer metal-insulator transition where the occupancy of localized and delocalized electronic orbitals rapidly changes at the metal-insulator transition (rather than the character of the electronic states changing from insulating to metallic as in a Mott-Hubbard transition). The exact solution displays both continuous and discontinuous (first-order) transitions.Comment: 22 pages including 4 figures(eps), RevTe

Material-Specific Investigations of Correlated Electron Systems

We present the results of numerical studies for selected materials with strongly correlated electrons using a combination of the local-density approximation and dynamical mean-field theory (DMFT). For the solution of the DMFT equations a continuous-time quantum Monte-Carlo algorithm was employed. All simulations were performed on the supercomputer HLRB II at the Leibniz Rechenzentrum in Munich. Specifically we have analyzed the pressure induced metal-insulator transitions in Fe2O3 and NiS2, the charge susceptibility of the fluctuating-valence elemental metal Yb, and the spectral properties of a covalent band-insulator model which includes local electronic correlations.Comment: 14 pages, 7 figures, to appear in "High Performance Computing in Science and Engineering, Garching 2009" (Springer