Variation of Avrami parameter during non-isothermal surface crystallization of glass powders with different sizes

The influence of grain size on the surface crystallization kinetics is investigated by non-isothermal Differential Thermal Analysis and Scanning Electron Microscopy. For this purpose, different powder fractions of a model glass forming diopside via surface crystallization and crystallization induced porosity, are used. The activation energy of crystallization, E_C, is determined from Kissinger plot, and the Avrami parameter, m, is estimated by both Ozawa and of Augis–Bennett methods. The values of E_C decrease from 530 to 300 kJ/mol when grain size increases. Simultaneously, the m value drops from 2.5 to 1.3. This result contradicts to the widespread fallacy that the reaction order should be equal to one in the case of surface crystallization. During the initial stage of surface crystallization three dimensional growth takes place, a fact confirmed by the SEM investigations. Later on, one dimensional growth inwards the grain is observed, leading to the reaction order changes from 3 to 1.     

Relative isomer abundance of fullerenes and carbon nanotubes correlates with kinetic stability

A methodology to evaluate the kinetic stability of carbon nanostructures is presented based on the assumption of the independent and random nature of thermal vibrations. The kinetic stability is directly correlated to the cleavage probability for the weakest bond of a given nanostructure. The application of the presented method to fullerenes and carbon nanotubes yields clear correlation to their experimentally observed relative isomer abundances. The general and simple formulation of the method ensures its applicability to other nanostructures for which formation is controlled by kinetic factors.     

Electronic Correlations,Electronic and Vibrational Spectroscopy,and Dynamic Properties of С60 and С70 Fullerenes and their Condensed Phases

Russian Physics Journal - The article provides a critical analysis of the key spectroscopic data on the study of the structure and properties of various molecular solids and phases based on C60 and...     

Complete intersection dimension

A new homological invariant is introduced for a finite module over a commutative noetherian ring: its CI-dimension. In the local case, sharp quantitative and structural data are obtained for modules of finite CI-dimension, providing the first class of modules of (possibly) infinite projective dimension with a rich structure theory of free resolutions. The first author was partly supported by NSF Grant No. DMS-9102951.     

Frictional Oscillations Under the Action of Almost Periodic Excitation

Frictional oscillations under the action of almost periodic force are studied. The modulation equations are derived by the multiple scales method to study bifurcations behavior. Heteroclinic Melnikov function is constructed to obtain the region of chaotic solutions of these equations. Bifurcations of almost periodic orbits are studied by Van der Pol transformation and averaging procedure.     

Bifurcation Analysis of a Vibropercussion System by the Method of Amplitude Surfaces

An amplitude surface is introduced to analyze the bifurcation behavior of a system upon change in two characteristic parameters. A bifurcation analysis of a vibropercussion system with changing force amplitude and frequency is performed as an example of using amplitude surfaces. Bifurcations of codimension two are revealed.     

Regions of chaotic oscillations of discrete mechanical systems with piecewise-linear elastic characteristics

Kharkov Polytechnic Institute, Ukraine. Translated from Prikladnaya Mekhanika, Vol. 30, No. 5, pp. 81–88, 1994.