Stanisław Urban

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The Tycho-2 Catalogue presented here is an astro-metric reference catalogue containing positions and proper motions as well as two-colour photometric data for the 2.5 million brightest stars in the sky. The Tycho-2 positions and magnitudes are based on precisely the same observations as the original Tycho Catalogue (hereafter Tycho-1) collected by the star(More)
In this paper, nematic liquid crystalline materials and its mesogenic and physicochemical properties (mainly birefringence, dielectric anisotropy, and viscosity) will be discussed. The influence of number and position of fluorosubstitution on the ability of nematic phase formation in broad temperature range and on the value and sign of dielectric anisotropy(More)
The longitudinal relaxation time tau of a series of alkyl-isothiocyanato-biphenyls (nBT) liquid crystals in the smectic E phase was measured as a function of temperature T and pressure P using dielectric spectroscopy. This relaxation time was found to become essentially constant, independent of T and P, at both the clearing point and the lower temperature(More)
The low frequency relaxation times tau//, which characterize the flip-flop molecular motions in liquid crystalline phases, recently determined in high-pressure experiments for eight liquid crystalline substances, were reanalyzed considering a relation proposed for the glass-forming liquids [C. Dreyfus, Phys. Rev. E 68, 011204 (2003); R. Casalini and C. M.(More)
Pressure-temperature-volume (pVT) measurements were carried out on 2-(4-hexyloxyphenyl)-5-octyl-pyrimidine, a substance exhibiting nematic and smectic A and C polymorphism. Analysis of the longitudinal relaxation times obtained recently for elevated pressures [Czub et al., Z. Naturforsch. A: Phys. Sci. 58, 333 (2003)] was performed for isobaric, isothermal,(More)
Orientational order properties of two fluorinated liquid crystals containing the 1,3,2-dioxaborinane ring have been investigated by means of optical, dielectric, and (13)C and (19)F NMR spectroscopies. The optical birefringence and dielectric anisotropy values determined in the mesomorphic phases were analyzed in terms of well-established theoretical models(More)
In the development of spectroscopy the symmetric top molecule ammonia, NH 3 , has always played an important role f rom an experimental, theoretical and astrophysical point of view, and it continues to do so. It's pyramidal structure leads to the well known inversional transitions in the 1.2 cm wave region, which were the first molecular lines to be(More)
Three liquid crystalline (LC) substances with the cyano-groups attached at the lateral positions to the molecular cores were studied with the aid of dielectric spectroscopy methods. The high frequency relaxation process connected with the molecular reorientations around the long molecular axes was studied in the isotropic, nematic and several smectic(More)
The results of dielectric studies of 6BAP(F) (l-[4-(hexylbicyclo[2,2,2]octyl]-2-(3-fluoro-4-methoxyphenyl)ethane) in the nematic and isotropic phases are presented. The substance has a negative dielectric anisotropy. By applying two experimental techniques, using a network analyzer and time domain spectrometer (TDS), the two main relaxation processes,(More)