Phase Transition Of First Kind Research Articles

PHASE TRANSITIONS IN THE DEBRIS FLOW GEOSYSTEMS

The evolution of a geosystem can be described as a continuous process. Stages of geosystems evolution: the formation of a massif of loose rocks in a site, its transformation to potential massifs due to diagenesis and morphogenesis, the occurrence and movement of a debris flow, unloading of large-block and then – fine-dispersed material and the passage of a debris-flow. Each stage of the geosystem evolution can be described as a transition from one subsystem level to another and the change of states of the system – as phase transitions of first kind. Physical processes occurring within the system cause it. The most important transition is from a solid state (potential debris-flows massif-conditionally homogeneous solid having an internal structure) to a and mudflow (quasi-liquid state). The transition of a potential massif to another phase state is due not only to external factors (the inflow of free water into the site), but also internal: the mineralogical composition of rocks of the potential massif (the content of hydrophilic minerals). The most important parameter that determines both the connectivity of the soils of the potential massif and the conditions of its transition to the liquid phase are the electric forces at the contacts between the elements of the mineral skeleton (soil particles). Electrical forces provide a connection between the ground particles. The liquid component of the mudflow is traditionally described as a debris-flow suspension, but a coherent and mudflow is not a suspension. A suspension is a dispersed system consisting of a solid dispersed phase and a liquid dispersion medium in which the solid is uniformly distributed as minute particles in a liquid substance in suspension. Such a medium is not able to carry over long distances block-boulder material having a higher density than the suspension. Nevertheless, a coherent and mudflow is a conditionally single-phase system in which water is predominantly in a molecular bound state. The physical analogue of a coherent and mudflow is a colloidal system, since in a connected village fine-earth particles are distributed in a continuous dispersion medium and do not precipitate. This circumstance is key in the physical modeling of connected debris-flows and mudflows.

Cosmological aspects of a unified dark energy and dust dark matter model

Recently, a model of modified gravity plus single scalar field was proposed, in which the scalar couples both to the standard Riemannian volume form given by the square root of the determinant of the Riemannian metric, as well as to another non-Riemannian volume form given in terms of an auxiliary maximal rank antisymmetric tensor gauge field. This model provides an exact unified description of both dark energy (via dynamically generated cosmological constant) and dark matter (as a “dust” fluid due to a hidden nonlinear Noether symmetry). In this paper, we test the model against Supernovae type Ia experimental data and investigate the future Universe evolution which follows from it. Our results show that this model has very interesting features allowing various scenarios of Universe evolution and in the same time perfectly fits contemporary observational data. It can describe exponentially expanding or finite expanding Universe and moreover, a Universe with phase transition of first kind. The phase transition occurs to a new, emerging at some time ground state with lower energy density, which affects significantly the Universe evolution.

Influence of the intrinsic thermistor effect in VO2 coplanar switching devices

Experimental investigations of the temperature dependence of the electrical conductivity σ(T) of VO2 thin films in coplanar switching devices have shown a thermistor-like behaviour of σ(T) below the critical temperature T = Tc. At Tc the VO2 material undergoes a structural phase transition of first kind which is connected with a sharp jump in the σ(T)-curve reaching a constant value σ2 for T ≧ Tc. Approximating the measured σ(T)-curve by σ1 = σo exp [– ΔE/kBT] for T < Tc (thermistor effect) and σ2 = const for T ≧ Tc the hitherto neglected influence of the thermistor effect on the static and dynamic switching behaviour of a coplanar. VO2 switching device is calculated numerically in dependence on relevant model parameters. Especially, the ambient temperature To is varied and an optimal value of To has been obtained where a minimal time of a switching cycle appears for a fixed parameter constellation.