Correlations in hexagonal lattice systems : application to carbon nanotubes

We present exact diagonalization studies of two-dimensional electron gas on hexagonal lattice. Using Lanczos method we analyze the influence of the Coulomb correlations on the density of states and spectral functions. Choosing appropriate boundary conditions we simulate the geometry of a single wall carbon nanotube. In particular, integration over the boundary condition in one direction and summation in the other one allows us to perform cluster calculations for a tube-like system with a finite diameter and infinite length

Next-nearest-neighbor hopping in the Falicov-Kimball model

Results of Monte Carlo simulations for the spinless Falicov-Kimball model with the next-nearest-neighbor hopping are presented. We find the critical value of the next-nearest-neighbor hopping integral, below which the low temperature configuration of the localized particles is the same as in the presence of only the nearest-neighbor hopping. Beyond this critical value the localized particles form horizontal or vertical stripes

Thermodynamics of the two-dimensional Falicov-Kimball model: a classical Monte Carlo study

The two-dimensional Falicov-Kimball (FK) model is analyzed using Monte Carlo method. In the case of concentrations of both itinerant and localized particles equal to 0.5 we determine temperature dependence of specific heat, charge density wave susceptibility and density-density correlation function. In the weak interaction regime we find a first order transition to the ordered state and anomalous temperature dependence of the correlation function. We construct the phase diagram of half-filled FK model. Also, the role of next-nearest-neighbor hopping on the phase diagram is analyzed. Lastly, we discuss the density of states and the spectral functions for the mobile particles in weak and strong interaction regime.Comment: 15 pages, RevTe

Dylematy etyczne we współczesnej rachunkowości

Sprawozdawczość finansowa podlega w ostatnich latach nieustającej krytyce. Uważa się, że nie jest ona w stanie sprostać rosnącym potrzebom i wymaganiom inwestorów, którzy nie zadowalają się już suchą informacją z raportów finansowych. Decyzje o lokowaniu kapitału wymagają obecnie danych o charakterze finansowym i niefinansowym, dobrowolnych ujawnień informacji niewymaganych prawem, o znacząco rozszerzonym zakresie, pozwalających na przewidywanie sytuacji finansowej i wyników jednostki w przyszłości. W erze społeczeństwa informacyjnego raport finansowy jednostki gospodarczej stopniowo ewoluuje w kierunku raportowania biznesowego. Inwestorzy potrzebują danych o znacznie większej przejrzystości, zrozumiałych i często wspomaganych informacjami opisowymi. Prezentowana publikacja stanowi głos w dyskusji nad ewolucyjnym charakterem, kształtem, kierunkami rozwoju oraz perspektywami współczesnej rachunkowości.Publikacja finansowana ze środków Rektora Uniwersytetu Łódzkiego

Charge density waves in small metallic and superconducting rings

Experimental results concerning persistent currents in small rings threaded by a magnetic flux do not agree with theoretical predictions, especially for experiments performed in diffusive regime. This suggests important role of disorder in these experiments. In this paper we demonstrate how impurities present in ring modify the persistent current by generating or enhancing charge density waves. The electronic correlations are taken into account for both repulsive as well as attractive electron{electron interaction. The calculations are carried out for one-dimensional rings consisting of up to 12 lattice sites using Lanczos exact diagonalization approach, and for finite-width much larger rings using the Bogolyubov-de Gennes equations

Niszczenie naturalnych odcinków koryt rzecznych na skutek niewłaściwej zabudowy – przykład dolin Czadeczki i Krężelki (Beskid Śląski)

Channels of Czadeczka and Krężelka rivers (Beskidzie Śląski Mts) are at present subjected to regulation because of which these rivers have lost their natural character, partially still preserved. The reasons for the river regulation have been analysed. Using archival maps, the buildings erection time has been analysed on valley floors, in the immediate vicinity of river channels for the period 1790–2012. Next, the distribution of existing buildings has been compared with hydraulic structures in the channels developed in order to regulate the Czadeczka and the Krężelka reaches, such as: concrete and stone embankments reinforcing the channel banks, check dams on channel bottoms. Results indicate a strong correlation between the number of buildings on valley floors in the 20th century and channel regulation. The mechanism of destroying rare, preserved natural river reaches is based on irrational permission allowing construction of buildings in areas threatened by floods and lateral erosion of rivers. Consequently, the inhabitants, in fear of floods and erosion of land or house foundations, seek river regulation that gives them a false sense of security. Natural river reaches are destroyed though efficient protection against floods and lateral erosion is still not provided and the range of possible losses increases even more due to continued building erection

Comprehensive study of the mountainous lake sediments in relation to natural and anthropogenic processes and time (Mały Staw Lake, Poland)

The Sudety Mts. form a chain of mountains in the South of Poland and during the last 200 years were subjected to strong industrial and agricultural pressure. The records of these human-induced changes are stored in natural archives like lake sediments. For the comprehensive study, three sediment cores taken from Mały Staw Lake (Sudety Mts.) were analyzed for the concentration of K, Na, Mn, Fe, Cu, Mg, Zn, Cd, Cr, Ni, Pb and radioactivity of 137Cs and 210Pb. As a result of the studies, the bathymetry map was developed and the sources of solid material supplied to the lake were identified. The geochronology studies of the cores were performed using 210Pb method, to evaluate model of time changes in the sediment. Radioactivity of 210Pbuns (determined indirectly by 210Po) ranged from 1051 ± 64 to 12 ± 8 Bq kg−1. The 137Cs radioactivity was determined directly by gamma spectrometry and varied from525 ± 37Bq kg−1 for top layers to 9.80 ± 5.40 Bq kg−1 for the bottom of the core. Two characteristic peaks of 137Cs radioactivity related to the global fallouts after nuclear weapons testing and the Chernobyl accident were observed and used to confirm210Pb dating method. Chemometrics analysis of the chosen metal’s concentrations combined with sample dating showed distinct imprint of human activity on the studied area

Proton beam irradiation inhibits the migration of melanoma cells

In recent years experimental data have indicated that low-energy proton beam radiation might induce a difference in cellular migration in comparison to photons. We therefore set out to compare the effect of proton beam irradiation and X-rays on the survival and long-term migratory properties of two cell lines: uveal melanoma Mel270 and skin melanoma BLM.Cells treated with either proton beam or X-rays were analyzed for their survival using clonogenic assay and MTT test. Long-term migratory properties were assessed with time-lapse monitoring of individual cell movements, wound test and transpore migration, while the expression of the related proteins was measured with western blot.Exposure to proton beam and X-rays led to similar survival but the quality of the cell colonies was markedly different. More paraclones with a low proliferative activity and fewer highly-proliferative holoclones were found after proton beam irradiation in comparison to X-rays. At 20 or 40 days post-irradiation, migratory capacity was decreased more by proton beam than by X-rays. The beta-1-integrin level was decreased in Mel270 cells after both types of radiation, while vimentin, a marker of EMT, was increased in BLM cells only.We conclude that proton beam irradiation induced long-term inhibition of cellular motility, as well as changes in the level of beta-1 integrin and vimentin. If confirmed, the change in the quality, but not in the number of colonies after proton beam irradiation might favor tumor growth inhibition after fractionated proton therapy

Hofstadter butterfly for a finite correlated system

We investigate a finite two-dimensional system in the presence of external magnetic field. We discuss how the energy spectrum depends on the system size, boundary conditions and Coulomb repulsion. On one hand, using these results we present the field dependence of the transport properties of a nanosystem. In particular, we demonstrate that these properties depend on whether the system consists of even or odd number of sites. On the other hand, on the basis of exact results obtained for a finite system we investigate whether the Hofstadter butterfly is robust against strong electronic correlations. We show that for sufficiently strong Coulomb repulsion the Hubbard gap decreases when the magnetic field increases.Comment: 7 pages, 5 figures, revte