The classification of phase transitions in first-order and second-order (or continuous) ones is widely used. The nematic-to-isotropic (NI) transition in liquid crystals is a weakly first-order transition, with only small discontinuities in enthalpy and specific volume at the transition which are not always easy to measure. On the other hand, fluctuation effects near the transition, typical for a continuous transition, are present because of the only weakly first-order character. In a recent paper [Phys. Rev. E 69, 022701 (2004)], it was concluded from the static dielectric permittivity in the isotropic phase near the NI transition that less polar mesogens (with little or no pretransitional effects) are characteristic for a first-order NI phase transition, whereas in the case of strongly polar ones (with large pretransitional effects) the NI transition is close to second order. In this paper, we address the question whether it is, indeed, possible to use these fluctuation effects in the isotropic phase to quantify the "strength" of a weakly first-order transition, i.e., how far it is from second order. Therefore, we measured the temperature dependence of the enthalpy near the NI transition of seven liquid crystals with adiabatic scanning calorimetry and compared the measured values of the latent heat with pretransitional effects in the dielectric constant and the specific heat capacity. The compounds used in the comparison are MBBA, 5CB, 8CB, 5NCS, 5CN, 8CHBT, and D7AB. From our analysis we find, contrary to the assertion in the above reference, no correlation between the strength of the NI transition of a given compound and the pretransitional effects observed, neither dielectrically, nor thermally.

The glass transition of pure and diluted honey and the glass transition of the maximally freeze-concentrated solution of honey were investigated by differential scanning calorimetry (DSC). The glass transition temperature, of the pure honey samples accepted as unadulterated varied between -42 and -51 degrees C. Dilution of honey to 90 wt % honey content resulted in a shift of the glass transition temperature by -13 to -20 degrees C. The concentration of the maximally freeze-concentrated honey solutions, as expressed in terms of honey content is approximately 102-103%, i.e., slightly more concentrated in sugars than honey itself. The application of DSC measurements of and in characterization of honey may be considered, but requires systematic study on a number of honeys.

Magnetoresistance measurements have been made on a number of single-crystal samples of the metallic charge-transfer salt P"-(BEDT-TTF}, AuBr"using magnetic fields up to 50 T. The experiments have been carried out for a wide range of orientations of the sample with respect to the magnetic field and for temperatures ranging between 80 mK and 4.2 K. The magnetoresistance exhibits a complex series of Shubnikov -de Haas oscillations, an anisotropic angle dependence, and, below 1 K, hysteresis. Both the hysteresis in the magnetoresistance and frequency mixing effects observed in the Shubnikov -de Haas spectrum can be explained by the effects of Shoenberg magnetic interaction, and this mechanism has been successfully used to model the observed Fourier spectrum of the magnetoresistance. The complex Shubnikov-de Haas frequency spectrum of P"-(BEDT-TTF}zAuBrz is proposed to result from the effects of a spin-density wave on the band structure, which alters the original Fermi surface to produce three two-dimensional carrier pockets. The angle dependence of the Shubnikov-de Haas oscillation amplitudes has been used to deduce the approximate shapes and orientations of these pockets, which are found to be in good qualitative agreement with the proposed model.

We investigated the smectic-A-hexatic-B (SmA-HexB) transition in the liquid-crystal n-hexyl-4'-n-pentyloxybiphenyl-4-carboxilate (650BC) with adiabatic scanning calorimetry. We were able to prove in a direct way that this transition is indeed very weakly first order, as was already suggested in the literature. The latent heat at the transition was determined to be deltaHL = 0.04 +/- 0.02 J/g. Our experiments confirm the high value for the heat capacity critical exponent earlier reported, yielding alpha = 0.64 +/- 0.05.

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