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[en] A new set of expressions has been derived for the determination of the activation energy E of a thermoluminescence (TL) peak. Unlike those previously existing in the literature, the present expressions take into account the variation of the symmetry factor μg(x) with um=(E/kTm) where x is the fractional intensity, k the Boltzmann constant and Tm the peak temperature and prior knowledge of the order of kinetics b is not required. The applicability of the present expressions have been tested using both numerically generated and experimental thermoluminescence peaks. (author)
[en] The purpose of this short communication is to demonstrate that the compensation effect is not general for the individual material but appears in the comparison of the pre-exponential factors and activation energies among various materials. (orig./MM)
[en] Highlights: ► The microstructure evolution of cold-rolled Zr 702 during annealing was studied. ► The recrystallization kinetics of cold rolled Zr 702 was determined. ► The JMAK exponent increased with increasing temperature and rolling reduction. ► The activation energy for recrystallization of cold-rolled sheets was obtained. -- Abstract: Using the hardness test, we determined the recrystallization kinetics of cold-rolled Zr 702. The rate of the recrystallization process increased with increasing annealing temperature and rolling reduction. The Johnson–Mehl–Avrami–Kolmogorov (JMAK) exponent obtained was less than 1, which also increased with increasing annealing temperature and rolling reduction. The activation energies for the recrystallization of the 38.9% and 71.0% cold-rolled sheets were 232 kJ/mol and 251 kJ/mol, respectively
[en] The effect of γ-quanta on the electrical conductivity of GaS layered single crystal, pure and alloyed with 0.1at % Yb and Sm has been studied at a temperature range of 100-300K. It has been established that the electrical conductivity of crystals decreases due to the formation of acceptor- and donor-type levels corresponding to 1.56 and 0.16 eV activation energy as a result of insertion of the dopant atom Yb into the GaS matrix. Although the inclusion of the dopant atom Sm partially reduces the conductivity of the GaS crystal (∼0.24 eV) at 100–300K, its conductivity is of a metallic character at 100-190K and it is semiconductor in the high-temperature regions
[en] A new approach to study of gas-solid exchange processes is offered and tested. It is known, that under gas environment storage at certain temperature T with pressure p there are two competitive processes - sorption and desorption. The methodics for activation energies of sorption and desorption definition by thermodesorption experiments and without any suppositions on parameters value a (reaction order) and Ks0 (sorption constant) are presented
[en] It has been investigated the interrelationship between the changes occurred in IR spectra of initial and gamma irradiated composite samples obtained on the basis of Si nanoparticles with copolymer P(VDF-TrFE) of polyvinylidene fluoride with tetraftoretilen and electrical properties It is shown that, optical properties of P(VDF-TeFE)/nano-Si composites change depending on the amount of filler and irradiation dose and there is a one-valued relationship between this change and electrical properties of composites. Based on the analysis of IR spectra obtained before and after gamma radiation of P (VDFTeFE)/nano-Si composites, we can say that the crystallization rate of the system is increasing as a result of interaction of the active centers formed on the matrix after radiation with the surface of Si nanoparticles on the interphase boundary. The optical properties of P (VDF-TeFE)/nano-Si composites obtained based on the P (VDF-TeFE) polymer change depending on the amount of filler and the radiation dose, and there is a one-valued relationship between this change and the electrical properties of the composites.
[en] The potential energy surfaces for the formation of cytosine (Cyt) and a protonated cytosine (CytH+) from reactions of urea with cyanoacetylene (CA), cyanoacetaldehyde (CAA), or their protonated ions, CAAH+ and CAH+ with or without H2O, have been determined from quantum chemical calculation using the CBS-QB3 method. The overall activation energies of the formation of Cyt or CytH+ from urea + CA, urea + CAA and, urea + CAH+ are 127, 211, and 31 kJ mol−1, respectively, which are too high for the thermal reactions to occur in the interstellar medium (ISM). The barrierless reaction pathways have been proposed for the formation of CytH+ from urea + CAH++ H2O and urea + CAAH+. A kinetic analysis shows that the synthesis of Cyt through the formation of CytH+ from urea, CAH+, and H2O would be possible in the ISM.
[en] Certain experimental results on diffusion of carbon in beryllium are considered and D0 and Q parameters of this process are shown to be linked by D0=Aexp(B/Q) dependence (compensative effect). Values of diffusion activation entropy calculated using this dependence constitute 15-20 R. These values are too high to be explained on the ground of elastic model. There is a number of process peculiarities, in particular, high value of activation energy and low level of carbon diffusion mobility in beryllium. Practically all difficulties may be overcome in case one can assume that carbon diffuses in form of mixed pairs of atoms one of which occupies interstitial position, while the other-substitution one
[en] Kappa (κ) carrageenan gels prepared with various carrageenan concentrations in pure water were completely dried and then swelled in water vapor. Steady state fluorescence measurements were performed using a spectrometer equipped with temperature controller. Pyranine was embedded in κ-carrageenan gels as a fluorescence probe during gel preparation. The fluorescence intensity, I, increased exponentially as swelling time is increased for all gel samples. The increase in I was modelled using Li-Tanaka equation from which swelling time constants, τc and cooperative diffusion coefficients, Dc were determined. It was observed that Dc increased as the swelling temperature was increased. On the other hand at each temperature, it was seen that Dc decreased as kappa carrageenan concentration was increased. Activation energies for swelling were obtained and found to be 57.4, 58.3 and 62.73kJ mol-1 for the gels with increasing amount of κ-carrageenan content
[en] Helium atoms in nickel at elevated temperatures exist primarily in substitutional sites, from which they may diffuse by a vacancy, dissociative, or exchange mechanism. The diffusion rates for these processes are calculated using the Embedded Atom Method. The dissociative mechanism is found to be dominant for all temperatures, provided that the vacancy concentration is not far above equilibrium. The activation energies involved in the different mechanisms are found to agree with activation energies derived from previous helium release experiments. (orig.)