Dynamical Functions of a 1D Correlated Quantum Liquid

We extend to initial ground states with zero spin density m = 0 the expressions provided by the pseudofermion dynamical theory (PDT) for the finite-energy one- and two-electron spectral-weight distributions of a one-dimensional (1D) correlated metal with on-site particle-particle repulsion. The spectral-function expressions derived in this paper were used in recent successful and detailed theoretical studies of the finite-energy singular features in photoemission of the organic compound tetrathiafulvalene-tetracyanoquinodimethane (TTF-TCNQ) metallic phase. Our studies take into account spectral contributions from types of microscopic processes that do not occur for finite values of the spin density. Expressions for the spectral functions in the vicinity of the singular border lines which also appear in the TTF- TCNQ spectral-weight distribution are derived. In addition, the PDT expressions are generalized for electronic densities in the vicinity of half filling. Further details on the processes involved in the applications to TTF-TCNQ are reported. Our results are useful for the further understanding of the unusual spectral properties observed in low-dimensional organic metals and also provide expressions for the one- and two-atom spectral functions of a correlated quantum system of ultracold fermionic atoms in a 1D optical lattice with on-site two-atom repulsion

Scattering mechanisms and spectral properties of the one-dimensional Hubbard model

It is found that the finite-energy spectral properties of the one-dimensional Hubbard model are controlled by the scattering of charged $\eta$-spin-zero $2\nu$-holon composite objects, spin-zero $2\nu$-spinon composite objects, and charged $\eta$-spin-less and spin-less objects, rather than by the scattering of independent $\eta$-spin 1/2 holons and spin 1/2 spinons. Here $\nu =1,2,...$. The corresponding $S$ matrix is calculated and its relation to the spectral properties is clarified.Comment: 8 pages, no figure

Környezetszennyező komponensek eltávolítása műanyaghulladékok pirolízistermékéből = Elimination of polluting components from pyrolysis oils of plastics wastes

A pályázat céljának megfelelően műanyaghulladékokból nyert pirolízisolajokat módosítottunk szilárd fázisú katalizátorok segítségével a nitrogén- és a halogéntartalom csökkentése érdekében. Megállapítottuk, hogy az Y és ß zeolitok többnyire megváltoztatják a polimerek hőbomlástermék vegyületeit, magát a hőbomlás reakcióját azonban kevéssé befolyásolják. Gyengén savas zeolit katalizátorágyon a pirolízistermék molekulák heteroatomot (nitrogént és oxigént) tartalmazó csoportjai leszakadnak, így a pirolizátum nitrogéntartalma a gázfázisba kerül, míg a szénhidrogén szegmensek egy- és kétgyűrűs aromás szénhidrogén vegyületekké alakulnak. A nátrium-zeolit kisebb molekulákra tördeli, és gyűrűbe zárja a hőbomlás termékeit, de nem bontja a szén-nitrogén kötéseket; így ez a katalizátor alig csökkenti a pirolízisolaj nitrogéntartalmát. A foszfortartalmú gyengén savas szervetlen égésgátlók jelentős hatással vannak a polimerek hőbomlási folyamataira és azok termékeire, azonban a pirolízisolaj nitrogéntartalmát nem befolyásolják. A nátriumionos Y és ß zeolitok általában alkalmasak a klór- és brómtartalmú pirolízisolajok halogéntartalmának mérséklésére, de halogénmentesítő aktivitásuk jelentősen eltérő a különböző típusú szerves klór- és brómvegyületek esetében. Tanulmányoztuk a deaktiválódott zeolitok regenerálhatóságát is. A katalitikus aktivitás elvesztését okozó szenes lerakódás minősége eltérőnek bizonyult a protonos és a nátriumion tartalmú zeolitoknál. | In accordance with the goals of the project pyrolysis oils of plastics waste have been converted over solid catalysts in order to decrease their nitrogen and halogen content. Our observations showed that the thermal decomposition reactions of polymers are hardly altered, but their products are mostly modified by Y and ß zeolite. The heteroatom (N and O) containing groups of the pyrolysis product molecules are cleaved over zeolites of weak acidity, thus the nitrogen content of the pyrolysate is moved to the gas phase, while the hydrocarbon parts are converted to aromatic hydrocarbons of one and two rings. Over sodium-zeolites the pyrolysis product molecules are either split at C-C bonds or cyclised. But the C-N bonds are not cleaved, so the nitrogen content of the pyrolysis oil has hardly decreased over these zeolites. The inorganic phosphor containing flame retardants of weak acidity proved to influence the thermal decomposition process of the polymers, however, the nitrogen content of the pyrolysis oil has not been changed by them. Our experiments revealed that Na-Y and Na-ß zeolite can be applied for dehalogenating pyrolysis oils of chlorine and bromine containing polymers, nevertheless their catalytic activity considerably differ for various types of organic chloro-and bromo-compounds. The regeneration of the deactivated zeolites has been also studied. The quality of the deposited coke proved to be different on the surface of protonated and sodium forms of zeolite

Phase diagram and magnetic collective excitations of the Hubbard model in graphene sheets and layers

We discuss the magnetic phases of the Hubbard model for the honeycomb lattice both in two and three spatial dimensions. A ground state phase diagram is obtained depending on the interaction strength U and electronic density n. We find a first order phase transition between ferromagnetic regions where the spin is maximally polarized (Nagaoka ferromagnetism) and regions with smaller magnetization (weak ferromagnetism). When taking into account the possibility of spiral states, we find that the lowest critical U is obtained for an ordering momentum different from zero. The evolution of the ordering momentum with doping is discussed. The magnetic excitations (spin waves) in the antiferromagnetic insulating phase are calculated from the random-phase-approximation for the spin susceptibility. We also compute the spin fluctuation correction to the mean field magnetization by virtual emission/absorpion of spin waves. In the large $U$ limit, the renormalized magnetization agrees qualitatively with the Holstein-Primakoff theory of the Heisenberg antiferromagnet, although the latter approach produces a larger renormalization

The TTF finite-energy spectral features in photoemission of TTF-TCNQ: The Hubbard-chain description

A dynamical theory which accounts for all microscopic one-electron processes is used to study the spectral function of the 1D Hubbard model for the whole $(k, \omega)$-plane, beyond previous studies which focused on the weight distribution in the vicinity of the singular branch lines only. While our predictions agree with those of the latter studies concerning the tetracyanoquinodimethane (TCNQ) related singular features in photoemission of the organic compound tetrathiafulvalene-tetracyanoquinodimethane (TTF-TCNQ) metallic phase, the generalized theory also leads to quantitative agreement concerning the tetrathiafulvalene (TTF) related finite-energy spectral features, which are found to correspond to a value of the on-site repulsion $U$ larger than for TCNQ. Our study reveals the microscopic mechanisms behind the unusual spectral features of TTF-TCNQ and provides a good overall description of those features for the whole $(k, \omega)$-plane.Comment: To appear in Journal of Physics: Condensed Matte

Thermal decomposition of black locust and wheat straw under torrefaction

In this work the torrefaction of two typical Hungarian biomass materials, wheat straw and black locust wood was studied. Three different torrefaction temperatures were applied: 225, 250 and 300°C with one hour isothermal period. The untreated and torrefied biomass materials were characterized by thermogravimetric analysis (TGA) and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) techniques. The alkali ion contents of the samples were determined by ICP-OES technique. It was found that the thermal treatment at 225°C for 1 hour modifies the thermal decomposition mechanism of the cellulose content of the sample, indicating chemical changes in the cellulose structure. At 250°C the hemicellulose content of the analyzed biomass materials partially decomposes. Furthermore, the most labile lignin groups (terminal CH2OH) also start to decompose. At 300°C torrefaction temperature the major part of hemicellulose and cellulose decomposes. The degree of the cellulose decomposition highly correlates with the alkali ion content of the samples

Catalytic pyrolysis of mixtures modeling municipal waste

In this work the temperatures of the thermal decomposition of model waste mixtures were determined with and without catalysts under slow heating conditions applying thermogravimetry-mass spectrometry (TG/MS) technique. The catalytic effect of HZSM-5 and Ni-Mo catalysts were tested on the thermal stability of model waste mixtures. Significantly decreased thermal decomposition temperature (by about 200°C) was observed in case of plastic mixture in the presence of 10 % HZSM-5 catalyst. The catalytic effect of HZSM-5 catalyst was hindered when the domestic waste model mixtures contained biomass components as well. The effect of cellulose and lignin on the catalytic activity of HZSM-5 catalyst was tested and significant poisoning effect was observed in both cases. The presence of 50% cellulose or 10% lignin in the waste mixture completely deactivates the HZSM-5 catalyst

Electron-electron interaction effects on the photophysics of metallic single-walled carbon nanotubes

Single-walled carbon nanotubes are strongly correlated systems with large Coulomb repulsion between two electrons occupying the same $p_z$ orbital. Within a molecular Hamiltonian appropriate for correlated $\pi$-electron systems, we show that optical excitations polarized parallel to the nanotube axes in the so-called metallic single-walled carbon nanotubes are to excitons. Our calculated absolute exciton energies in twelve different metallic single-walled carbon nanotubes, with diameters in the range 0.8 - 1.4 nm, are in nearly quantitative agreement with experimental results. We have also calculated the absorption spectrum for the (21,21) single-walled carbon nanotube in the E$_{22}$ region. Our calculated spectrum gives an excellent fit to the experimental absorption spectrum. In all cases our calculated exciton binding energies are only slightly smaller than those of semiconducting nanotubes with comparable diameters, in contradiction to results obtained within the {\it ab initio} approach, which predicts much smaller binding energies. We ascribe this difference to the difficulty of determining the behavior of systems with strong on-site Coulomb interactions within theories based on the density functional approach. As in the semiconducting nanotubes we predict in the metallic nanotubes a two-photon exciton above the lowest longitudinally polarized exciton that can be detected by ultrafast pump-probe spectroscopy. We also predict a subgap absorption polarized perpendicular to the nanotube axes below the lowest longitudinal exciton, blueshifted from the exact midgap by electron-electron interactions