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1
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Application of fibre-optic flame monitoring systems to diagnostics of combustion process in power boilers

100%
Wójcik W.
|
2008
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vol. 56
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issue 2
2
Content available remote

Strongly Correlated Electrons in a Magnetic Field: Fermi Liquid versus Spin Liquid

64%
Spałek J., Wójcik W.
Acta Physica Polonica A
|
1994
|
vol. 85
|
issue 2
357-361
EN
We compare the Fermi liquid (FL) and statistical spin liquid (SSL) representations of the electronic properties for strongly correlated systems. In particular, we discuss the entropy, as well as the magnetization as a function of band filling, temperature and magnetic field. These properties are quite different in the two (FL, SSL) states. Antiferromagnetic state disappears for a small number of holes in the doped Mott insulator.
3
Content available remote

RKKY Mechanism of Spin Interaction of Localized Protons in Neutron Stars

64%
Kutschera M., Wójcik W.
Acta Physica Polonica A
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1997
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vol. 92
|
issue 2
375-377
EN
We study the spin coupling of protons which are localized in dense neutron star matter. The effective spin interaction of neighbouring protons is induced by the direct spin interaction of protons with the background neutrons. The exchange integral of the effective proton-proton spin interaction is calculated. The interaction is ferromagnetic in a wide range of neutron star matter parameters.
4
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Non-Fermi Liquid Behavior of Correlated Fermions in Applied Field

51%
Korbel P., Spałek J., Wójcik W.
Acta Physica Polonica A
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1997
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vol. 92
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issue 2
323-326
EN
We have determined an instability of the Fermi-liquid state of almost localized fermions in an applied magnetic field. It is proposed that a transition to a strongly correlated fermions (statistical-spin-liquid) state takes place at that point. The resultant magnetization curve and the field dependence of the specific heat are calculated and compared with those for CeRu_{2}Si_{2}.
5
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Lieb-Wu Solution, Gutzwiller-Wave-Function, and Gutzwiller-Ansatz Approximations with Adjustable Single-Particle Wave Function for the Hubbard Chain

51%
Kurzyk J., Spałek J., Wójcik W.
Acta Physica Polonica A
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2007
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vol. 111
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issue 4
603-618
EN
The optimized single-particle wave functions contained in the parameters of the Hubbard model (t and U) were determined for an infinite atomic chain. In effect, the electronic properties of the chain as a function of interatomic distance R were obtained and compared for the Lieb-Wu exact solution, the Gutzwiller-wave-function approximation, and the Gutzwiller-ansatz case. The ground state energy and other characteristics for the infinite chain were also compared with those obtained earlier for a nanoscopic chain within the exact diagonalization combined with an ab initio adjustment of the single-particle wave functions in the correlated state (exact diagonalization combined with an ab initio method). For the sake of completeness, we briefly characterize also each of the solutions. Our approach completes the Lieb-Wu solution, as it provides the system electronic properties evolution as a function of physically controlable parameter - the interatomic distance.
6
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Optimized Wannier Functions for Hubbard Chain

51%
Kurzyk J., Wójcik W., Spałek J.
Acta Physica Polonica A
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2009
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vol. 115
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issue 1
114-116
EN
One-dimensional atomic chain with a variable-range hopping is described within the extended Hubbard model. The Gutzwiller-ansatz approximation is used to determine the optimized single-particle (Wannier) wave functions in the correlated state. Hopping integral up to the third neighbors is taken into account and the results are compared with those for the infinite hopping range. Ground state energy of the system is compared with that making use of the rigorous Lieb-Wu solution with the optimized wave functions. The evolution of the properties as a function of interatomic distance is discussed.
7
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Influence of the electrolyte concentration on interaction between silica particles

51%
Wójcik W., Jańczuk B., Ogonowski R.
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2008
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vol. 63
17-30
EN
The destruction time of the sediment column structure was measured for different fractions of silica particles in NaCl and CaCl2 solutions whose concentrations were varied from 0.25 M to 2.0 M. A linear relationship between the reciprocal of the destruction time of the silica sediment column structure and average diameter of the silica fraction, the density and work of cohesion of the solutions was found. The determined values of the particle diameter, the cohesion work and density of the solution calculated from these linear dependences for the time equal to infinity (1/t = 0) were named critical. Using the above critical parameters the detachment force of one particle from another was calculated. For the system whose components had critical values the detachment force was found to be equal to the attachment force resulting from the interfacial interaction. On the basis of our earlier study and Derjaguin's approximation the radius of the contact plane and the attachment force between two silica particles were calculated. The detachment force decreased with increasing salt concentration, but the attachment force was nearly constant. It was found that for a given salt concentration the relationship of the reciprocal of the destruction time as a function of the difference between the detachment and attachment forces was also linear. It appeared that for the silica column structure having critical parameters the values of the difference between the detachment and attachment forces were negative. This means that in the calculation of the attachment force between silica particles in the studied solutions an additional interaction should be taken into account.
8
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Correlated Fermions Close to Mott Localization: Deviations from Landau Fermi-Liquid Picture

51%
Spałek J., Wójcik W., Korbel P.
Acta Physica Polonica A
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1997
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vol. 92
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issue 2
277-280
EN
We summarize the main novel features of almost localized fermions in the presence of au applied magnetic field: (i) the spin dependence of their effective mass, which leads to quantum beats in the de Haas-van Alphen effect and (ii) the presence of a nonlinear molecular field and related metamagnetic behavior.
9
Content available remote

Correlation Induced Optimization of Wave Functions: the Hubbard Chain

51%
Spałek J., Podsiadły R., Wójcik W.
|
EN
We determine the explicit form of the single-particle Wannier functions {w_{i}(r)} appearing in the parameters of quantum models. The method is illustrated on the example of the Hubbard chain, for which we derive the renormalized wave equation starting from a variational principle and by treating the system ground state energy as a functional of {w_{i}(r)} and their derivatives. In this manner, the optimized basis is obtained only after the electronic correlations have been included in the rigorous Lieb-Wu solution. The results for the ground state energy and the size of the renormalized s-type orbitals, both as a function of interatomic distance, are calculated explicitly.
10
Content available remote

Correlated Electron Systems of Different Dimensionalities

51%
Kurzyk J., Wójcik W., Spałek J.
Acta Physica Polonica A
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2008
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vol. 114
|
issue 1
175-178
EN
The optimized single-particle wave functions contained in the parameters of the Hubbard model (hopping integral t and intraatomic interaction U) are determined explicitly in the correlated state for electronic systems of various symmetries and dimensions: Hubbard chain, square and triangular lattices, and the three cubic lattices: SC, BCC, and FCC. In effect, the electronic properties of these structures as a function of the interatomic distance R are obtained. In most cases, the model parameters do not scale linearly with the lattice constant. Also, the atomic part of the total ground state energy changes with the U/t ratio and therefore should be (and is) included in the analysis. The solutions of dimensions D>1 are analyzed by utilizing the approximate Gutzwiller treatment.
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