Results 1 - 10 of 2098
Results 1 - 10 of 2098. Search took: 0.026 seconds
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[en] Due to heating period of samples during examinations of the sintering kinetics of materials it is, in principle, impossible to maintain isothermal conditions of the process, especially in the initial periods of time, when the most important changes in rates and degrees of sintering are taking place. For this reason, it is always vague whether the observed laws of changes in the density degree are determined by the sintering mechanism or by the heating rate of samples. The examination of the sintering kinetics in non-isothermal conditions is methodically more correct when the change in density degree and in temperature of samples is controlled. The method of analysis of the kinetics data on sintering, which is proposed, is based on this: if under some other identical conditions, the densification degree depends on the heating rate very essentially, then the rate of this process does not depend on the heating rate, because during the infinitely little interval of time dtau the process may be taken as isothermal at any rate of heating (dT/dtau). On the example of sintering Naf in nonisothermal conditions was shown the way how the calculate kinetic parameters of the sintering process, as well as to constract isothermal density curves by means of it. It was established that, in this way, the examination of the sintering kinetics in nonisothermal conditions is distinguished, apart from some insignificant difficulties, by a greater reliability of the results
[en] In commenting on a paper by Moharil (J. Phys. D.: 14:1677 (1981)) the claim made in that paper that the proposed method of analysing thermoluminescent isothermal decay curves for general order kinetics is more accurate than other methods since it is not dependent on the trap depth, is disputed. In a reply the original author maintains that his claim is not that the experimental accuracy of the suggested method is an improvement but that the advantage lies in not using trap depth values. (U.K.)
[en] Athermic analyses for the kinetic study of the reactions in the solid state are preferred because they consume much less experimental work time than the isothermal tests, and lead to more accurate calculations of the energies of activation of reactions that have occurred. In the present work are required conditions where you can apply the equation of speed of an athermal reaction in a low alloy in solid steel. From records of steel (AISI 1050) dilatometric triples were calculated kinetics (E, Ko, n) that characterize the reactions that occurred during the tempering of samples using different methods of iso conversion, one of which is a new modification of the method of Friedman. Also, has shown that during the formation of carbide Epsilon in the first stage of the tempering has occurred a saturation of sites, which validates the use of some methods. Finally, the orders of the reactions occurred during tempering of steel studied treatment are calculated.
[en] The normalization condition of the 3- and 4-particle distribution functions is used to integrate the closure relations that generalize the well-known Ornstein-Zernike (OZ) integral for the compressibility and the two-particle correlation. In a similar way to the two-body OZ relation, the 3- and 4-particle closure integrals are written in terms of the compressibility and its derivatives, allowing their immediate evaluation. These explicit expressions are useful in the perturbation theory of fluids and in testing approximations for the 3- and 4-particle correlations, such as Kirkwood's superposition approximation. As an illustration, these closure integrals are evaluated for the hard-sphere system. (Author)
[en] We derive a fundamental relationship between the mean and the variability of isometric force. The relationship arises from an optimal collection of active motor units such that the force variability assumes a minimum (optimal isometric force). The relationship is shown to be independent of the explicit motor unit properties and of the dynamical features of isometric force production. A constant coefficient of variation in the asymptotic regime and a nonequilibrium fluctuation-dissipation theorem for optimal isometric force are predicted
[en] The paper considers the velocity of ionization waves in a non-isothermal plasma. The results obtained are confirmed by experimental data. (author)
[ru]Rassmatrivaetsja vopros o skorosti ionizacionnyh voln v neizotermicheskoj plazme. Poluchennaja zavisimost' dlja skorosti ionizacionnyh voln podtverzhdaetsja jeksperimental'nymi dannymi. (author)
[en] Highlights: • MHD shock waves turn unstable through emergence of complex-conjugate mode pair. • Critical manifolds are computed across which the stability change occurs. • For slow shocks, the transition occurs also in the so-called parallel regime. • Numerical method tracks invariant subspaces and preserves analyticity. This note studies classical magnetohydrodynamic shock waves in an inviscid fluidic plasma that is assumed to be a perfect conductor of heat as well as of electricity. For this mathematically prototypical material, it identifies, mainly numerically, two critical manifolds in parameter space, across which slow resp. fast MHD shock waves undergo emergence of a complex conjugate pair of unstable transverse modes. For slow shocks, this emergence occurs in a particularly interesting way already in the parallel case, in which it happens at the spectral value and the critical manifold possesses a simple explicit algebraic representation. Results of refined numerical treatment show that within the set of non-parallel slow shocks the unstable mode pair emerges from two generically different spectral values . For fast shocks, the critical manifold does not intersect the parallel regime and the emergence within the set of non-parallel fast shocks again starts from two generically different spectral values.
[en] The properties are examined of a system of dipoles which can be randomly in one of two states, which are called slow or fast according to the rate at which the (dipoles in them change their orientation, and in one of two orientations. There is a local interaction between the dipoles such that the rotation of a dipole has fixed probabilities of changing the state of its neighboring dipoles frm slow to fast or vice versa. The isothermal relaxation of the system was studied mainly in a mean field approximation, and also by computer simulations. The results show that the non-exponential decay of the system's response function is associated with the fact that initially the decay is due mainly to the depolarization of the dipoles in fast states, while the later stages are associated mainly with the transfer of polarized dipoles from slow to fast states and their subsequent depolarization. This could be a quite general mechanism for non-exponential dielectric relaxation. A comparison between the relaxation of systems for which the populations of the two types of state was and was not initially in equilibrium shows that a time dependent transition rate is not a very useful concept
[en] We present an improved experimental procedure of separating a composite thermoluminescence glow curve into its components. Careful monitoring of the isothermal cleaning process using the initial rise method ensures the complete thermal removal of TL peaks. Digital subtraction of two experimental TL glow curves yields individual experimental TL glow peaks. Several standard methods (initial rise and whole glow curve) are used to obtain the energy values and frequency factors of the traps. The method has been used successfully to analyze the well-known composite TL glow curve of the dosimetric material LiF (TLD-100). The limitations of the method are illustrated by analyzing the highly complex TL glow curve of a UV irradiated synthetic calcite consisting of at least 6 TL peaks. Although the method works best for TL glow curves described by first order kinetics, it should also be applicable to more general kinetics