Band 31, Heft 2

Biochemical networks usually possess information that expresses the degree of organization and integration of the system. A function, I ( X : Y ) N , called mutual information of integration, allows one to define, on a quantitative basis, three dierent types of organization and integration of these systems. If I ( X : Y ) N = 0, the network is devoid of any collective property and does not possess any information. If, alternatively, I ( X : Y ) N > 0, the system is integrated, i.e., it behaves as a coherent whole but possesses few collective properties. Last, if I ( X : Y ) N < 0, the system is emergent, or complex, and possesses many collective properties. Reduction of the properties of a network to the properties of its component subnetworks is possible only in the first case considered above. Emergence of both information and collective properties in a protein network can appear as a consequence of a competition between two ligands for the same sites of a protein, or as a consequence of conformation changes of the proteins. One can easily derive the expression of the mutual information of integration of a network in steady state provided that a condition, called generalized microscopic reversibility, applies. This condition implies that the transition states of substrate release and catalysis stabilize the same conformation of the enzyme involved in these two processes. Departure from generalized microscopic reversibility, and from thermodynamic equilibrium, results in a change of the value of the mutual information of integration of the system.

A genuine variational principle developed by Gyarmati in the field of thermodynamics of irreversible processes unifying the theoretical requirements of technical, environmental, and biological sciences is employed to study the effects of uniform suction and injection in the heat transfer and boundary layer flow with power function main stream velocity and surface temperature variations, over a wedge. The velocity and temperature distributions inside the boundary layer are considered as simple polynomial functions and the variational principle is formulated. The Euler–Lagrange equations are reduced to simple polynomial equations in terms of boundary layer thicknesses. The values of skin friction and heat transfer are calculated for any given values of Prandtl number Pr , wedge angle parameter m , wall temperature exponent n , and suction/injection parameter H . The obtained analytic results are compared with known numerical solutions and the comparison establishes the fact that the accuracy is remarkable.

In this work we analyze the stability of a non-endoreversible Curzon–Ahlborn engine, taking into account the engine's implicit time delays. When comparing the system's dynamic stability with its thermodynamic properties (efficiency and power output), we find that the temperature ratio τ = T 2 / T 1 ( T 1 > T 2 being the temperatures of the external heat reservoirs) represents a trade-off between stability and energetic properties. This result is in agreement with previous studies of the endoreversible Curzon–Ahlborn engine. The only dierence is that, in the non-endoreversible case, τ can only increase up to R (with R < 1, a parameter measuring the degree of internal irreversibilities), while in the endoreversible case it can grow up to one. Finally, we demonstrate that the total time delay does not destabilize the system steady-state, regardless of its length, and thus it does not seem to play a role in the dynamic-thermodynamic property trade-off.

The thermal instability of a viscoelastic (Kuvshiniski-type) fluid in a porous medium is considered. Following linearized stability theory and normal mode analysis, the dispersion relation is obtained. For stationary convection, the medium permeability is found to have a destabilizing effect and a Kuvshiniski viscoelastic fluid behaves like a Newtonian fluid. The principle of exchange of stabilities is found to be satisfied. The thermal instability of a rotating Kuvshiniski viscoelastic fluid in a porous medium is also studied. For stationary convection, it is found that rotation has a stabilizing effect, whereas the medium permeability has both stabilizing and destabilizing effects. The uniform rotation introduces oscillatory modes in the system that were non-existent in its absence.