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Fractal Structure of C-S-H and Tobermorite Phases

100%
Janik J., Kurdowski W., Podsiadły R., Samseth J.
Acta Physica Polonica A
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2001
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vol. 100
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issue 4
529-537
EN
The C-S-H I phase is the main component of the cement paste, which is a near-amorphous, highly porous gel. Due to high porosity of the sample in this phase we can observe a fractal nature of the volume pores distribution, similar to that observed for silica aerogels. The C-S-H I phase is thermodynamically unstable and crystallize to a tobermorite phase, forming crystal aggregates on the surface of the amorphous paste. The mixture of these two phases, formed in this way, have irregular volume and surface structures, both of which may exhibit the fractal nature. To study the fractal nature of the matter the small angle neutron scattering method is frequently used. We present here the results of small angle neutron scattering studies supported by the X-ray diffraction and scanning electron microscope observations of several samples with the common molar C/S ratio equal to 1. Some of the samples were autoclaved during various time periods to accelerate transformation of the C-S-H I phase to tobermorite. We observed the fractal properties of the volume structure of all samples under study. Moreover, we observed also the fractal behaviors of the surfaces of the samples which were autoclaved.
2
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Studies of Fractal Aspects of Cement

100%
Janik J., Kurdowski W., Podsiadły R., Samseth J.
Acta Physica Polonica A
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1996
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vol. 90
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issue 6
1179-1184
EN
Small angle neutron scattering can be used to reveal the fractal nature of matter. The problems of fractal aspects of the structure of cement are related to those of fractal aspects of silica aerogels. Natural cement, when mixed with water, transforms after a series of chemical reactions (in a large part) into an amorphous phase called C-S-H. It is believed that the cationic sublattice composed of CaO_{6} octahedrons constitutes the C-S-H structural basis, to which the SiO_{4} tetrahedral chains are attached. It is a layer structure in which the cation sublattice determines the way of SiO_{4} condensation. It is natural to expect that in this way one may obtain a really amorphous substance, since some tetrahedrons may be lacking, which leads to defects. We present here the results of a small angle neutron scattering and X-ray diffraction study of several samples with the pure C-S-H phase for which during the process of chemical synthesis various ratios of molar contents of CaO and SiO_{2} were used (various C/S ratios). We obtained a gradual change of fractal characteristics with the change of C/S ratio.
3
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Correlation Induced Optimization of Wave Functions: the Hubbard Chain

100%
Spałek J., Podsiadły R., Wójcik W.
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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.
4
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Fast Stochastic Reorientations in Nematic PAA and PAP

88%
Podsiadły R., Mayer J., Janik J. A., Krawczyk J., Stanek T.
Acta Physica Polonica A
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1997
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vol. 91
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issue 3
513-518
EN
Incoherent quasielastic neutron scattering spectra were measured for nematic para-azoxyanisole (PAA) and para-azoxyphenetole (PAP) with the energy resolution of ca. 30 μ eV, at Dubna IBR-2 reactor. Data processing contained a careful background subtraction and the multiple scattering correction. The corrected spectra were subjected to a reorientational model fitting procedure. For PAA, a model of two convoluted reorientations - that of benzene rings coupled with the terminals and that of the whole molecule around the long molecular axis - gave a fairly good description of the quasielastic neutron scattering spectrum. For PAP, introducing a third motion - interconformational jumps in the ethoxy terminals - in addition to motions suggested for PAA, gave a good agreement with the measured quasielastic neutron scattering spectrum.
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