Volume 26, Issue 2

Experimental results on the evolution of patterns in surface-tension driven Bénard convection are reported. Experiments were performed in a hexagonal container with an aspect ratio Г = 65 for different distances (ε) to convection threshold and two Prandtl numbers ( Pr 1 = 440 and Pr 2 = 880). Regular hexagonal patterns are initially imposed that are then allowed to relax. A stability diagram of the spatial modes, the variation of the stable modes band and the selected mean wavenumber were established as functions of ε and Pr . For the mean wavenumber, an increase followed by a decrease, is observed for Pr 1 ; and an opposite behavior is observed for Pr 2 . The bandwidth of stable modes broadens with ε, the broadening being larger for Pr 2 than for Pr 1 . Using the phenomenological model of Swift-Hohenberg, developed for roll patterns and adapted to hexagonal patterns, a potential function is defined, which allows the study of the time evolution of such arrays. This function is minimized during the transition of the structure from the initial to the steady (asymptotic) state. The various wavenumber selection mechanisms are considered: bulk contribution (wavenumber disparity, cell row bending), topological defects and sidewalls. The total potential is mainly influenced by the wavenumber variation and by defects. Owing to the special geometry of the container, sidewall and bulk effects related to the local wave vector divergence (due to the disalignment and the bending of the cell rows), play a less important role, at least in such medium size containers. From the experiment, it follows that the model is valid up to an ε of about 9 for both Pr . Beyond that limit, the potential fluctuates probably due to the spatiotemporal mobility of the structure and the nucleation of defects, whose number increases with increasing ε.

Photon correlation spectroscopy has been used as a method to determine the size of the particles of a polymer colloid. This experimental study provides information about the morphology of the external polymer chains formed during the particles synthesis process. The results can be explained on basis on the “hairy layer” model. According to this model the polymer chains extend to the solution in a length depending upon the pH of the liquid phase.

A thermodynamic description of the Peltier heat at the aluminum and the oxygen electrode in the system NaF–AlF 3 –Al 2 O 3 is given. The thermoelectric power in melts with molar ratios n NaF / n AlF3 from 3.0 to 1.0, saturated with alumina are measured. Seebeck coefficients for molten fluoride electrolytes saturated with alumina, electrolytes that are relevant for aluminum electrowinning electrolysis cells, are reported. The results allow determinations of Peltier heats of aluminum, oxygen and carbon electrodes in NaF–AlF 3 electrolytes saturated with alumina. For molar ratios of n NaF / n AlF3 between 2.6 and 1.2, there is a Peltier heating of the aluminum cathode. This heating is in the same order of magnitude as the electrolyte Joule heat, when the current density is 0.7 A cm −2 . For molar ratio n NaF / n AlF3 equal to 1.0 the Peltier effect at the aluminum electrode approaches zero. From theoretical considerations we expect a drop also for molar ratio 3.0. For the anode we report a Peltier cooling that is larger than the heat produced by the anodic overvoltage, in melts with NaF/AlF 3 molar ratio between 2.6 and 1.2 saturated with alumina.

In this paper we analyze elastic and anelastic deformations of a continuous system with non-Euclidean structure. The focus of this study is the intrinsic material metric, gαβ , for the measurement of distances between material particles in the reference configuration. The main results of the theory of deformation are reformulated taking into account the non-Euclidean structure. The consequences of the second law of thermodynamics have been investigated both for thermoelastic and viscoanelastic solids.

Thermodynamic stability of materials is investigated in the presence of internal variables. The possibility of phase boundaries in nonequilibrium solid materials is considered which suggests the concept of phase breaking similar to the phase transitions in case of fluid and gaseous systems. Two particular models of damage mechanics are proposed and investigated in more detail as illustrative examples. Both models are direct thermodynamic generalizations of well known damage mechanical models considering general loading conditions. According to these thermodynamic suggestions a new failure criterion is suggested for microcracked materials and compared with experiments and other criteria.

Progressing biological evolution is discussed in the framework of nonequilibrium thermodynamics. It is connected with an increase of the mass specific standard metabolism given by coefficient a in the allometric relation (1) between oxygen consumption rate and body mass of an animal. Three “heat barriers” are found in the course of such a bioenergetic evolution. The first heat barrier concerns an animal's overheating during active movement and is overcome by the development of thermoregulation and the appearance of homeothermic animals. A second barrier arises when the coefficient a reaches values connected with lethal body temperatures. The transition across this second heat barrier occurs as result of reasonable activities and the appearance of civilization. The third heat barrier will arise during the further development of human civilization, connected with a highly increased energy production and a fatal warming of the Earth atmosphere. The manner to overcome this barrier will probably depend on the assimilation of space and the establishment of energy consuming industries outside the Earth. The bioenergetic evolution discussed in this paper does not exclude other trends of evolution, e.g. increase of size, and does not mean to be the only aspect of biological evolution.