Volume 33, Issue 1

In this work, the damage in biological soft tissue induced by bubble cavitation is investigated. A typical medical procedure with such damaging side effects is the kidney stone fragmentation by shock-wave lithotripsy. We start with a mesoscopic continuum model that allows the consideration of microstructural information within the macroscopic balance equations. An evolution equation for the temporal development of the bubble distribution function is derived. Furthermore, the constitutive relations of bubble expansion are deduced by means of a spherical shell model. Numerical simulations are presented for a typical soft tissue material and different definitions for a damage parameter are discussed.

The temporal development of arbitrarily distributed voids in a viscoplastic material under different loading regimes is investigated. For this reason, we make use of a mesoscopic continuum model extending the classical space–time domain of continuum mechanics. This extended domain requires a reformulation of the classical balance equations as well as the consideration of additional constitutive quantities. Furthermore, a mesoscopic distribution function is formulated to describe the temporal evolution of different void regimes. Here, we assume a spherical shell model for the porous composites and elaborate all required steps in order to describe load-induced void growth in a metal-like matrix. We conclude with some exemplary results that confirm experimental observations of dynamical fracture.

A comparison is made between two classical methods for the exploitation of the second law of thermodynamics: the Coleman–Noll and the Liu procedure. On the example of a rigid heat conductor with general entropy flux, it is shown that the two procedures are equivalent. This equivalence is demonstrated in the case of a state space including the wanted fields, only, as well as in the case of gradients being relevant for constitutive equations, too. Also, the possible importance of an internal variable or an internal degree of freedom is considered.

The purpose of this paper is to present a local stability analysis of a non-endoreversible heat pump operating at the minimum input power P for given heating load q H to the high-temperature reservoir, in the isothermal couplings of the working fluid with the heat reservoirs T H and T L ( T H > T L ), both having the same heat conductance α and using R to describe internal dissipations of the working fluid. A non-endoreversible heat pump system that is modeled by the differential equation may depend on the numerical values of certain parameters that appear in the equation. From the local stability analysis, we find that a critical point of an almost linear system is a stable node. After a small perturbation, the system state exponentially decays to steady state with either of two relaxation times that are functions of α , R , q H , T H , and the heat capacity C . We can exhibit qualitatively the behavior of solutions of the system by sketching its phase portrait. One eigenvector in a phase portrait is the nonzero constant vector, and the other is a function of α , R , q H , T H , and T L . Finally, we discuss the local stability and energetic properties of the non-endoreversible heat pump.

We describe and discuss the origin of short-term (hours) variations in the concentration of sulfur species (SO 2 , H 2 S, and S 8 0 ) of crater fumaroles discharging at different temperatures (up to 410°C) from five volcanic systems. Sulfur species can be investigated as an independent subsystem within the whole composition characterizing the fumarolic fluids, their chemical behavior being governed by similar laws in volcanic systems. The measured data are time dependent and show regular oscillations whose amplitude is by far larger than the analytical error. The agreement between the theoretical and the measured concentrations of SO 2 , H 2 S, and S 8 0 suggests that the formation of dissipative structures can explain the observed oscillations. Accordingly, the periodicity and the amplitude of the compositional oscillations were found to be in strong relation with the entropy excess of the non-equilibrium systems under investigation. The results of our study suggest that the amplitude and magnitude of short-term natural (self-induced) fluctuations of the sulfur species caused by the presence of the dissipative structures, and their comparison with the compositional variations of other subsystems, should be taken into serious account for geochemical monitoring purposes.