The kinetics of thermal anomalies at the phase transitions in the tetraethylammonium zinc tetrachloride
crystal [N(C2H5)4]2ZnCl4
has been studied by the differential scanning calorimetry method
over a wide range of rate of temperature change, from 1 to
100 K min−1. The crystal is known to undergo structural phase transitions of first order at
which the nucleus of the final phase characterized by a symmetry different to that
of the initial phase appears and develops. The classical Johnson–Mehl–Avrami
model cannot be applied to describe the two phase transitions taking place in the
non-isothermal process. Making use of the isothermal process taking place below
T1C, the intermediate phase has been shown to be metastable; the energy of the process is
Ea = 146 ± 7 kJ mol−1, while the
Avrami exponent n = 2.3 ± 0.2.
The dynamics of segmental motions in semicrystalline poly(vinylidene fluoride) has been studied by means of dielectric and mechanical spectroscopies and nuclear magnetic resonance method. The relaxation data, obtained from different techniques, over a wide temperature and frequency range, have been analyzed in terms of main-chain segmental motion, described by phenomenological Havriliak-Negami function. The results indicate that the correlations between local conformational transitions in the amorphous phase are intermediate. Good agreement between the experimental and calculated data offers a contribution to the understanding of molecular dynamics in the glassy state of the polymer.
The histological structure directly influences the biomechanical properties of venous wall with rSV showing least compliance and cSV the greatest compliance.
The increased use of allograft tissue for musculoskeletal repair has brought more focus to the safety of allogenic tissue and the efficacy of various sterilization techniques. The currently available literature contains few examples of studies on long-lasting strains of bones but no example for irradiated bones. In this study the bovine femurs from a 2-year-old animal were machine cut and irradiated with the doses of 10, 15, 25, 35, 45 and 50 kGy. The dynamic mechanical analysis was performed at 1 Hz at the room temperature in a 3-point bending configuration for 2880 minutes. The final values of E' and E″ were dose independent but they were reached at different periods. For this reason, so called "critical point" was introduced for the further analysis. All the examined sample groups were characterized by statistically significant lower values of the critical point in comparison with the control samples (p<0.05) but the biggest differences were observed between the control samples and the samples irradiated with the doses of 10, 15 and 25 kGy. Current results and literature review suggest that the dose of 35 kGy is the optimal dose for ionizing radiation sterilization.
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